Hong Kong, China

The Hong Kong University of Science and Technology is a public research university in Clear Water Bay Peninsula, Hong Kong. Established in 1991, it is one of the territory's youngest statutory universities.The University currently consists of four disciplinary schools, which offer degrees in Business, Engineering, Science and Social Science & Humanities, alongside Interdisciplinary Programs Office, which provides cross-disciplinary programs, and Fok Ying Tung Graduate School/Fok Ying Tung Research Institute, which aims at technology transfer and commercialization. HKUST has been continuously viewed as one of the top three higher education institutions in Hong Kong. Wikipedia.


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Patent
Hong Kong University of Science, Technology and Hadasit Medical Research Services And Development Ltd. | Date: 2016-11-25

The present invention provides compositions and methods for treating, preventing, and inhibiting viral replication, viral infections and viral diseases and disorders, comprising the use of artemisinin derivatives having anti-viral activity.


Patent
Hong Kong University of Science and Technology | Date: 2016-08-19

The present subject matter is directed to water disinfection by pulsed electric field (PEF) systems. The present subject matter relates to a pulsed electric field assembly with a separator that separates and disinfects the microorganisms in drinking water. The present subject matter relates to an anti-corrosion electrode, particularly an electrode having a zeolite coating layer serving as a protector, a process for the preparation a zeolite coating on a conducting electrode substrate, and application of the zeolite coated electrode on water electrolysis and PEF systems.


Patent
City University of Hong Kong, Hong Kong University of Science and Technology | Date: 2015-08-26

Group aware command based arrangement is provided. An alignment command can be received, an undirected graph comprising a group of graph nodes connected by graph edges can be constructed, wherein the group of graph nodes represent a group of selected display elements, and the undirected graph can be partitioned as a function of identifying a severable graph edge of the graph edges that connects a pair of graph nodes included in the group of graph nodes to form a first collection of graph nodes and a second collection of graph nodes.


Patent
Hong Kong University of Science and Technology | Date: 2015-05-15

Techniques are provided for forming a gallium nitride flip-chip light-emitting diode. In an aspect, a device is provided that includes a gallium nitride layer, a passivation layer, a set of first conductive layers, and a second conductive layer. The gallium nitride layer is formed on a substrate that includes a first plurality of recesses associated with a first structure and a second plurality of recesses associated with a second structure, where the first plurality of recesses and the second plurality of recesses are associated with a first conductive material. The set of first conductive layers is formed on the passivation layer and corresponds to the first conductive material. The second conductive layer is formed on the passivation layer and corresponds to a second conductive material.


Tong Y.,Beihang University | She J.,Hong Kong University of Science and Technology | Ding B.,Microsoft | Chen L.,Hong Kong University of Science and Technology | And 2 more authors.
Proceedings of the VLDB Endowment | Year: 2016

Recently, with the development of mobile Internet and smartphones, the online minimum bipartite matching in real time spatial data (OMBM) problem becomes popular. Specifically, given a set of service providers with specific locations and a set of users who dynamically appear one by one, the OMBM problem is to find a maximum-cardinality matching with minimum total distance following that once a user appears, s/he must be immediately matched to an unmatched service provider, which cannot be revoked, before subsequent users arrive. To address this problem, existing studies mainly focus on analyzing the worst-case competitive ratios of the proposed online algorithms, but study on the performance of the algorithms in practice is absent. In this paper, we present a comprehensive experimental comparison of the representative algorithms of the OMBM problem. Particularly, we observe a surprising result that the simple and efficient greedy algorithm, which has been considered as the worst due to its exponential worst-case competitive ratio, is significantly more effective than other algorithms. We investigate the results and further show that the competitive ratio of the worst case of the greedy algorithm is actually just a constant, 3.195, in the average-case analysis. We try to clarify a 25-year misunderstanding towards the greedy algorithm and justify that the greedy algorithm is not bad at all. Finally, we provide a uniform implementation for all the algorithms of the OMBM problem and clarify their strengths and weaknesses, which can guide practitioners to select appropriate algorithms for various scenarios. © 2016 VLDB Endowment 21508097/16/08.


Shi T.,Hong Kong University of Science and Technology | Leung C.K.Y.,Hong Kong University of Science and Technology
Computers and Structures | Year: 2017

Strain hardening cementitious composite (SHCC) are materials exhibiting high deformation capacity and excellent crack control. In applications where SHCC is employed to enhance durability, information on the crack width and spacing under loading is important. In conventional finite element analysis, the material is commonly modeled as a continuum with tri-linear tensile behavior, which cannot capture the crack pattern. Here an efficient discrete model for SHCC is proposed to address such an issue, with the use of continuum element for matrix damage/cracking, truss element for fiber bridging effect and interface element for matrix-fiber interaction. Appropriate constitutive laws are assumed for these elements and the parameters are calibrated from direct tensile test. The validity of the model is shown by analyzing a tensile specimen and the realistic multiple cracking process of SHCC is captured. Through a systematic parametric study, the effects of important model parameters on the tensile behavior of the composites are assessed. The proposed model is further improved to accurately reproduce the evolution of crack pattern, including average and maximum crack width, crack density and crack width distribution. Efficient and accurate, the model can be used for analysis of SHCC members under bending, restrained shrinkage or subject to reflective cracking. © 2017 Elsevier Ltd


Ding C.,Hong Kong University of Science and Technology
Designs, Codes, and Cryptography | Year: 2017

It has been known for a long time that t-designs can be employed to construct both linear and nonlinear codes and that the codewords of a fixed weight in a code may hold a t-design. While a lot of progress in the direction of constructing codes from t-designs has been made, only a small amount of work on the construction of t-designs from codes has been done. The objective of this paper is to construct infinite families of 2-designs and 3-designs from a type of binary linear codes with five weights. The total number of 2-designs and 3-designs obtained in this paper are exponential in any odd m and the block size of the designs varies in a huge range. © 2017 Springer Science+Business Media New York


Chen M.,Hong Kong University of Science and Technology | Sun J.,Hong Kong University of Science and Technology
Angewandte Chemie - International Edition | Year: 2017

Catalytic asymmetric N-alkylation of indoles and carbazoles represents a family of important but underdeveloped reactions. Herein, we describe a new organocatalytic strategy in which in situ generated aza-para-quinone methides are employed as the alkylating reagent. With the proper choice of a chiral phosphoric acid and an N-protective group, the intermolecular C−N bond formation with various indole and carbazole nucleophiles proceeded efficiently under mild conditions with excellent enantioselectivity and functional-group compatibility. Control experiments and kinetic studies provided important insight into the reaction mechanism. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim


Tromp R.M.,Leiden University | Altman M.S.,Hong Kong University of Science and Technology
Ultramicroscopy | Year: 2017

Accurately measuring defocus in cathode lens instruments (Low Energy Electron Microscopy - LEEM, and Photo Electron Emission Microscopy - PEEM) is a pre-requisite for quantitative image analysis using Fourier Optics (FO) or Contrast Transfer Function (CTF) image simulations. In particular, one must establish a quantitative relation between lens excitation and image defocus. One way to accomplish this is the Real-Space Microspot LEED method, making use of the accurately known angles of diffracted electron beams, and the defocus-dependent shifts of their corresponding real-space images. However, this only works if a sufficiently large number of diffracted beams is available for the sample under investigation. An alternative is to shift the sample along the optical axis by a known distance, and measure the change in objective lens excitation required to re-focus the image. We analytically derive the relation between sample shift and defocus, and apply our results to the measurement and analysis of achromats in an aberration-corrected LEEM instrument. © 2017.


Ma X.,Hong Kong University of Science and Technology | Cao N.,Tongji University
Proceedings of the ACM Conference on Computer Supported Cooperative Work, CSCW | Year: 2017

Danmaku is an emerging socio-digital media paradigm that puts anonymous, asynchronous user-generated scrolling comments on videos. (How) can danmaku afford the illusion and realization of social interactions, if at all possible given its interactional incoherence nature? To answer this question, we collect Chinese danmaku users' reflection on their motivations to use this social service and explore the actual practices that meet the needs. According to a preliminary danmaku usage survey, users consider it as an information seeking and emotion venting channel. Through archival analysis of real-world data, we find that danmaku commentaries are relatively short, video-centric, saturated with emotions, and similar in syntactic and semantic features. Users have developed a set of mechanisms adapted to the medium, to leverage such textbased messages to foster interpersonal and hyperpersonal communication for sharing of facts, thoughts, and feelings. © 2017 ACM.


Cao X.-R.,Shanghai JiaoTong University | Cao X.-R.,Hong Kong University of Science and Technology
IEEE Transactions on Automatic Control | Year: 2017

The stochastic calculus of non-smooth functions indicates that for a continuous semi-martingale X(t), the changes of a function h[X(t)] at its semi-smooth point (both right-and left-hand side derivatives exist) X(t) = x in [t,t + dt] is at the scale of the local time of X(t), with a mean of the order \sqrt{dt} in the case of Ito processes. We introduce the relative time which evolves at the scale of local time when the semi-martingale is at a semi-smooth point of h(x). The change of h[X(t)] in [t,t + dt] can be precisely measured in the scale of relative time, while this change is wrongly ignored with regular time scale dt. The optimal control problem is well defined with the regular time replaced by the relative time; however, dynamic programming does not seem work well for this problem. We apply the direct-comparison-based optimization approach to the control problem formulated in relative time and derive the generalized Hamilton-Jacobi-Bellman (HJB) equations, which consist of two parts, the classical HJB equation for smooth points, and some additional relations for semi-smooth points. Under some bounded conditions, the optimal value function is the (classical) solution to the generalized HJB equations, and viscosity solution is not needed. In addition, we show that the singular control problem can be formulated and solved in the same framework with the relative time. © 1963-2012 IEEE.


Guan X.,Hubei University of Economics | Chen Y.-J.,Hong Kong University of Science and Technology
Production and Operations Management | Year: 2017

This study investigates the interactions between a manufacturer's information acquisition and quality disclosure strategies in a supply chain setting in which the manufacturer privately knows his product quality but is uncertain about consumer preferences. We argue that the manufacturer should treat his information acquisition and quality disclosure decisions as an integrated process because these decisions can significantly influence a retailer's rational inferences about product quality and can have conflicting effects on his own profitability. Although information acquisition helps a manufacturer subsequently craft better pricing and quality disclosure strategies, it also leaks certain product information to the retailer, thus helping the retailer better estimate product quality. Therefore, in equilibrium, a manufacturer may choose not to acquire any consumer information, even when such acquisition is costless. Moreover, we find that this adverse effect of acquisition is highly dependent on the cost of disclosure and consumers’ preference differentiation. Increased consumer preference differentiation may have a non-monotonic relationship with the manufacturer's profit, and information acquisition can become detrimental to the manufacturer once the disclosure cost is sufficiently high. © 2016 Production and Operations Management Society


Cheng L.,Hong Kong University of Science and Technology | Ki W.-H.,Hong Kong University of Science and Technology
Digest of Technical Papers - IEEE International Solid-State Circuits Conference | Year: 2017

Fast load-transient responses are crucial for DC-DC converters to cope with the demands of modern highly integrated system-on-chip (SoC) designs. Various techniques have been proposed to improve transient responses by enhancing the speed of the controller, and/or by increasing the slew rate of the inductor current (SRL), as shown in Fig. 10.6.1. To enhance the speed of the controller, a capacitor-current-sensor (CCS) calibration technique with load-transient optimization (LTO) is proposed for current-mode control in [1], and zero-delay synchronized (ZDS) and quasi-current-mode hysteretic control are proposed in [2] and [3], respectively. Although these converters may achieve near-optimal transient responses (only limited by SRL), the circuit complexity is greatly increased. To increase SRL, multiphase topologies have been widely used [1], [2,4]. For an N-phase converter, SRL can be effectively increased by N times, at the expense of using N bulky inductors that increase both volume and cost. Hybrid schemes that comprise the parallel operation of the DC-DC converter and a linear regulator can improve the responses by injecting additional charging current (Ich) without adding extra inductors. In [5], activating and deactivating the hybrid scheme is accomplished by monitoring the output voltage Vo within the steady-state window [Vo-ΔVo, Vo]. However, a large ΔVo is needed for good noise immunity, and the slow SRL also requires a high Ich that increases loss during the transients. © 2017 IEEE.


Gao Y.,Hong Kong University of Science and Technology | Li L.,Hong Kong University of Science and Technology | Mok P.K.T.,Hong Kong University of Science and Technology
Digest of Technical Papers - IEEE International Solid-State Circuits Conference | Year: 2017

Light-emitting diodes (LEDs) are becoming the dominant lighting source over their conventional counterparts. Besides the benefits of high efficiency and long lifetime, LEDs also show great potential for high-speed data transmission because of their wide bandwidth (BW). In addition to offering general lighting, the light output can be modulated with fast-switched LEDs to achieve visible light communication (VLC). Though over 100Mb/s data-rate has been demonstrated with white LEDs in the laboratory, the high-frequency modulation is hardly supported by commonly used dimmable drivers with switching converters to regulate LED current. In these drivers, the changing slope of LED current is limited by both low loop BW and large inductors and capacitors [1]. The linear multiple-string LED drivers [2], free of inductors and big capacitors, theoretically can provide higher turn on/off speed. However, the light output of these drivers usually varies significantly at the double-line-frequency, which not only is considered as a harmful optical flicker, but also greatly affects the effectiveness of data transmission. The linear driver in [3] regulates the product of LED current and LED voltage to mitigate the optical variation, but a multiplier has to be added in the regulation loop, resulting in limited BW. © 2017 IEEE.


Yang F.,Hong Kong University of Science and Technology | Mok P.K.T.,Hong Kong University of Science and Technology
Digest of Technical Papers - IEEE International Solid-State Circuits Conference | Year: 2017

Ultra-low-voltage operation is highly demanded in a system that adopts the DVFS scheme, e.g., a portable device that sustains days-long standby with a tiny battery. Such a system usually embeds modules that have specific minimum supply voltages. Point-of-load low-dropout regulators (LDOs) are used to power these modules as per the required applications, from a global supply rail Vdd. The global Vdd is noisy and can be varied within a wide range, which adds to the difficulty of designing LDOs in such applications. © 2017 IEEE.


Shi L.,Hong Kong University of Science and Technology | Zhao T.,Hong Kong University of Science and Technology
Journal of Materials Chemistry A | Year: 2017

Two-dimensional inorganic materials, such as exfoliated graphene, have been under much research attention as of late, for their high surface-to-mass ratio and unique physical and chemical properties. Many of these properties are highly sought after in Li/Na-based batteries. In this paper, we review recent advances in inorganic 2D materials and summarize their applications as: (i) the electrode materials or additives for Li/Na-ion batteries; (ii) the scaffold or interfacial layer for lithium-metal anodes; (iii) the cathode for Li/Na-O2 batteries; and (iv) the anchoring material for lithium polysulfides for Li-S batteries. The challenges of employing 2D materials in these Li/Na-based batteries to improve performance are discussed and possible solutions are proposed. © The Royal Society of Chemistry.


Wang Q.-H.,Singapore Management University | Hui K.-L.,Hong Kong University of Science and Technology
Information Systems Research | Year: 2017

We study the strategic benefits of mergers and acquisitions (M&As) when competing information technology vendors sell different generations of the same product with different quality. We assume the newproduct arrives unexpectedly when an installed base of the old product exists. We show that the combination of consumers' purchase history and heterogeneity leads to new demand complexity that gives rise to innovative product strategies.We find that shelving the old product is an important motivation for M&A. The acquirer may exercise static or intertemporal price discrimination depending on whether it can exercise upgrade pricing. M&A may speed up or slow down new product consumption, and it can lead to delayed new product introduction in some markets. However, it always increases the acquirer's profit and can sometimes help maximize social welfare. We discuss relevant managerial and policy implications. © 2017 INFORMS.


Zhang H.,Hong Kong University of Science and Technology | Lin F.,Hong Kong University of Science and Technology
Artificial Intelligence | Year: 2017

We consider a simple language for writing causal action theories, and postulate several properties for the state transition models of these theories. We then consider some possible embeddings of these causal action theories in some other action formalisms, and their implementations in logic programs with answer set semantics. In particular, we propose to consider what we call permissible translations from these causal action theories to logic programs. We identify two sets of properties, and prove that for each set, there is only one permissible translation, under strong equivalence, that can satisfy all properties in the set. We also show that these two sets of conditions are minimal in that removing any condition from each of them will result in multiple permissible mappings. Furthermore, as it turns out, for one set, the unique permissible translation is essentially the same as Balduccini and Gelfond's translation from Gelfond and Lifschitz's action language B to logic programs. For the other, it is essentially the same as Lifschitz and Turner's translation from the action language C to logic programs. This work provides a new perspective on understanding, evaluating and comparing action languages by using sets of properties instead of examples. The results in this paper provide a characterization of two representative action languages B and C in terms of permissible mappings from our causal action theories to logic programs. It will be interesting to see if other action languages can be similarly characterized, and whether new action formalisms can be defined using different sets of properties. © 2017 Elsevier B.V.


Shum K.L.,Hong Kong University of Science and Technology
Renewable and Sustainable Energy Reviews | Year: 2017

This paper analyzes major categories of renewable policy instruments in light of the framework of Transition Management. We leveraged the concept of levelized cost of electricity (LCOE) to unify the discussion of these instruments by elaborating the differing effects such instruments have on the formation of the socio-technological regime. Regimes are sets of grammer. logics and contexts which enable and constrain the interaction of actors associated with a physical technology. We compare these instruments by assuming the normative organization objective of a regime to be that of enhancing the cost-effectiveness of respective instruments. In other words, the socio-technological regime is to be organized and optimized to improve the LCOE of the energy technology. Our main contribution is to propose the rationalization of the regime objective and the implications to regime management and development strategy. This in turn would facilitate a much needed synthesis of normative and evolutionary deliberation in the framework of Transition Management. © 2017 Elsevier Ltd


Tang B.Z.,Hong Kong University of Science and Technology
20th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2016 | Year: 2016

Traditional Π-conjugated fluorophores are prone to aggregate with light emission quenching which is known as aggregation-caused quenching (ACQ). We have observed an opposite phenomenon termed "aggregation-induced emission" (AIE) and identified the restriction of intramolecular rotation (RIR) as the main reason for the AIE effect. The miniature AIE Dots mentioned here include bare AIE dots that spontaneously aggregated in biological systems, AIE dots prepared by encapsulation and AIE dye labelled polymer dots or silica NPs (Fig.1).1 It has been found that the AIE dots show superior features to conventional organic dyes and QDs, such as large absorptivity, high brightness, excellent biocompatibility, free of random blinking, and strong photobleaching resistance.1, 2a, b, c These merits have enabled the use of AIEgens in fluorescent imaging at the subcellular, cellular and tissue levels in a noninvasive and high contrast manner.


Arya S.,Hong Kong University of Science and Technology | Da Fonseca G.D.,University of Auvergne | Mounty D.M.,University of Maryland University College
Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms | Year: 2017

In the polytope membership problem, a convex polytope K in Rd is given, and the objective is to preprocess K into a data structure so that, given a query point q 2 Rd, it is possible to determine efficiently whether q 2 K. We consider this problem in an approximate setting and assume that d is a constant. Given an approximation parameter > 0, the query can be answered either way if the distance from q to K's boundary is at most " times K's diameter. Previous solutions to the problem were on the form of a space-time trade o, where logarithmic query time demands O(1="d1) storage, whereas storage O(1=(d1)=2) admits roughly O(1="(d1)=8) query time. In this paper, we present a data structure that achieves logarithmic query time with storage of only O(1=(d1)=2), which matches the worst-case lower bound on the complexity of any approximating polytope. Our data structure is based on a new technique, a hierarchy of ellipsoids defined as approximations to Macbeath regions. As an application, we obtain major improvements to approximate Euclidean nearest neighbor searching. Notably, the storage needed to answer approximate nearest neighbor queries for a set of n points in O(log n " ) time is reduced to O(n=d=2). This halves the exponent in the "-dependency of the existing space bound of roughly O(n="d), which has stood for 15 years (Har- Peled, 2001). Copyright © by SIAM.


Song S.,Tsinghua University | Chen L.,Hong Kong University of Science and Technology
ACM Transactions on Database Systems | Year: 2017

A recent article [Vincent et al. 2015] concerns the correctness of several results in reasoning about differential dependencies (DDs), originally reported in Song and Chen [2011]. The major concern by Vincent et al. [2015] roots from assuming a type of infeasible differential functions in the given DDs for consistency and implication analysis, which are not allowed in Song and Chen [2011]. A differential function is said to be infeasible if there is no tuple pair with values that can satisfy the specified distance constraints. For example, [price(〈2, 〉4)] requires the difference of two price values to be 〈 2 and 〉 4 at the same time, which is clearly impossible. Although DDs involving infeasible differential functions may be syntactically interesting, they are semantically meaningless and would neither be specified by domain experts nor discovered from data. For these reasons, infeasible differential functions are not considered [Song and Chen 2011] and the results in Song and Chen [2011] are correct, in contrast to what is claimed in Vincent et al. [2015]. © 2017 ACM.


Lu C.,Hong Kong University of Science and Technology | Leung C.K.Y.,Hong Kong University of Science and Technology
Construction and Building Materials | Year: 2017

Fiber dispersion, especially the variation of fiber content among different sections of a member, is a major factor that influences the mechanical properties of fiber composites. In this study which focuses on Strain Hardening Cementitious Composites (SHCC), a numerical approach is proposed to compute the bridging laws in various sections of a specimen with varying content of randomly distributed fibers. Through the analysis, the weakest plane which governs the ultimate strength and saturated crack spacing is determined. This weakest plane is then investigated for members of different sizes, and a size effect is revealed. © 2017 Elsevier Ltd


Chang D.C.,Hong Kong University of Science and Technology
European Physical Journal Plus | Year: 2017

According to the Special Theory of Relativity, there should be no resting frame in our universe. Such an assumption, however, could be in conflict with the Standard Model of cosmology today, which regards the vacuum not as an empty space. Thus, there is a strong need to experimentally test whether there is a resting frame in our universe or not. We propose that this can be done by precisely measuring the masses of two charged particles moving in opposite directions. If all inertial frames are equivalent, there should be no detectable mass difference between these two particles. If there is a resting frame in the universe, one will observe a mass difference that is dependent on the orientation of the laboratory frame. The detailed experimental setup is discussed in this paper. © 2017, The Author(s).


News Article | May 1, 2017
Site: www.eurekalert.org

By measuring this emerging vital sign, system could help monitor and diagnose health issues like cognitive decline and cardiac disease We've long known that breathing, blood pressure, body temperature and pulse provide an important window into the complexities of human health. But a growing body of research suggests that another vital sign - how fast you walk - could be a better predictor of health issues like cognitive decline, falls, and even certain cardiac or pulmonary diseases. Unfortunately, it's hard to accurately monitor walking speed in a way that's both continuous and unobtrusive. Professor Dina Katabi's group at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) have been working on the problem, and believe that the answer is to go wireless. In a new paper, the team presents "WiGait," a device that can measure the walking speed of multiple people with 95 to 99 percent accuracy using wireless signals. The system is an update of a device that Katabi's team presented to President Obama in 2015. The size of a small painting, the device can be placed on the wall of a person's house. It builds on Katabi's previous work that analyzes wireless signals reflected off people's bodies to measure a range of behaviors, from breathing and falling to specific emotions. (The signals emit roughly 100 times less radiation than a standard cellphone.) "By using in-home sensors, we can see trends in how walking speed changes over longer periods of time," says lead author and PhD student Chen-Yu Hsu. "This can provide insight into whether someone should adjust their health regimens, whether that's doing physical therapy or altering their medications." WiGait is also 85 to 99 percent accurate at measuring a person's stride length, which could allow researchers to better understand conditions like Parkinson's disease that are characterized by reduced step size. Hsu and Katabi developed WiGait in collaboration with CSAIL PhD student Zachary Kabelac and master's student Rumen Hristov, alongside undergraduate Yuchen Liu from the Hong Kong University of Science and Technology, and assistant professor Christine Liu from the Boston University School of Medicine. The team will present their paper in May at ACM's CHI Conference on Human Factors in Computing Systems in Colorado. Today walking speed is measured by physical therapists or clinicians using a stopwatch. Wearables like FitBit can only roughly estimate your speed based on your step count; GPS-enabled smartphones are similarly inaccurate and can't work indoors; and cameras are intrusive and can only monitor one room at a time. The only method that's comparably accurate is VICON motion-tracking, which isn't widely available enough to be practical for monitoring day-to-day health changes. Meanwhile, WiGait measures walking speed with a high level of granularity, without requiring that the person wear or carry a sensor. It does so by analyzing the surrounding wireless signals and their reflections off a person's body. Also, the team's algorithm can distinguish walking from other movements, such as cleaning the kitchen or brushing one's teeth. According to Katabi, the device could help reveal a wealth of important health information, particularly for the elderly: a change in walking speed, for example, could mean an injury or that the person is at an increased risk of falling. "Many avoidable hospitalizations are related to issues like falls, congestive heart disease, or chronic obstructive pulmonary disease which have all been shown to be correlated to gait speed," Katabi says. "Reducing the number of hospitalizations, even by a small amount, could vastly improve healthcare costs." The team developed WiGait to be more privacy-minded than cameras, showing you as nothing more than a moving dot on a screen. In the future they hope to train it on people with walking impairments like Parkinson's, Alzheimer's or MS, to help physicians accurately track disease progression and adjust medications. "The true novelty of this device is that it can map major metrics of health and behavior without any active engagement from the user, which is especially helpful for the cognitively impaired," says Ipsit Vahia, a geriatric clinician at McLean Hospital and Harvard Medical School who was not involved in the research. "Gait speed is a proxy indicator of many clinically important conditions, and down the line this could extend to measuring sleep patterns, respiratory rates, and other vital human behaviors."


GF Securities and HKUST Entrepreneurship Center Successfully Hosted a Joint Public Lecture during the "One Million Dollar Entrepreneurship Competition" GF Securities Co., Ltd. ("GF Securities" or "the Company"; HKSE: 1776; SZSE: 000776) and Hong Kong University of Science and Technology Entrepreneurship Center ("HKUST Entrepreneurship Center", and the Hong Kong University of Science and Technology, "HKUST") jointly held a public lecture yesterday on campus, aiming to promote the "HKUST One Million Dollar Entrepreneurship Competition", and attracted numerous students and start-up-ers. Since 2011, the "One Million Dollar Entrepreneurship Competition" ("he Competition") has been held for six consecutive years, with divisions extending to Beijing, Guangzhou, Shenzhen, and Macau. Being the Platinum sponsor of the Hong Kong Division, GF Securities has fully participated and supported the event. In recent years, start-ups have sprung up all over the country. "The 7th HKUST Million Dollar International Entrepreneurship Competition" has attracted nearly 100 entries in Hong Kong division only, with total over 900 teams in all five divisions. As the Platinum sponsor, GF Securities, drawing from its professional expertise, gave a public lecture named "Startup Exit Strategy and a Brief Introduction to the Securities Market in China" for college students in Hong Kong. This will give young entrepreneurs a better understanding of capital markets and help equip them to manage successful start-ups. The public lecture was presented by Ms. Wang Chumei, Senior Vice President of GF Securities' Investment Banking Division. She made comparisons between the listing process in Hong Kong and China, capital withdrawal strategies for start-up companies and the mergers and acquisitions (M&A) process. The lecture helped college students gain a better business prospective, and enabled them to plan better for future start-ups. The lecture was successful and met with enthusiastic responses. Ms. Wang stayed after the lecture to answer all of the questions and enquiries raised by students. GF Securities is one of the first full-service investment banks in China. The Company was successfully listed on the main boards of the Shenzhen Stock Exchange and the Hong Kong Stock Exchange, in 2010 and 2015, respectively. It is fully licensed to provide comprehensive coverage across: investment banking, wealth management, trading and institutional client services, and investment management. Balanced development of each business line has helped GF Securities to achieve top rankings throughout capital markets in China. The Company is devoted to serving high quality SMEs and high net-worth clients throughout Asia. The investment banking division has a large reserve of SME clients which have become leading enterprises across various industries. GF Securities possesses valuable experience and professional expertise in singling out value creating start-ups for cultivation. Furthermore, the Company's holdings include GF Xinde Investment Management Corporation Limited, GF Qianhe investment Corporation Limited and GF Holdings (Hong Kong) Corporation Limited etc. These subsidiaries are experienced at navigating capital markets and focus on equity investment through SMEs. Being a major sponsor of the competition, jointly with HKUST, GF Securities, will provide invaluable knowledge for students, and help the youth to achieve their aspirations. Placing a lot of emphasis on "corporate citizenship", GF Securities, while seizing opportunities for continual development, has strictly adhered to promoting public welfare as they grow. In 2011, GF Securities Co., Ltd., GF Fund Management Co., Ltd., GF Futures Co., Ltd. and GF Xinde Investment Management Co., Ltd. jointly set up the "GF Securities Social Charity Foundation" ("the Foundation") which includes various social responsibility initiatives, of which the micro-entrepreneurship program is an essential part. From 2015 to 2016, the Foundation organized various activities, such as "Micro-entrepreneurial Action for College Students" and "Seeking Entrepreneurial Heroes" in China. The Foundation has contributed a total of RMB8 million in support of entrepreneurial endeavors. Mr. Lin Zhihai, President of GF Securities and Chairman of GF Securities Social Charity Foundation, said, "In recent years, business connections between Hong Kong and the Mainland have been increasingly closer. Meanwhile, the capital market in Hong Kong enjoys a high degree of internationalization, and attracts many investors and entrepreneurs worldwide every year, providing a good platform for start-ups. GF Securities, as a provider of comprehensive capital market services focuses on serving China's high-quality SMEs and affluent individuals, is willing to actively encourage the youth in Hong Kong to start businesses and cultivate outstanding entrepreneurs. In 2017, GF Securities will continue to implement the unity of social and economic benefits. While striving to create value for shareholders and customers, the Company will actively participate in social charity events, and increase efforts to alleviate poverty. GF Securities goal is to be an internationally competitive investment bank with a widely recognized global brand. ". About GF Securities Co. Ltd Established in 1991, GF Securities is one of the first, full-service investment banks in China. The Company was successfully listed on the main boards of the Shenzhen stock Exchange (Stock code: 000776.SZ), and the Hong Kong Stock Exchange (Stock code: 1776.HK), in 2010 and 2015, respectively. Relying on excellent business performance, risk management and quality services, the company achieves sustained and steady development, and is one of the most influential securities companies in China. The Company possesses industry-leading innovation capabilities and has built a diversified business portfolio serving various corporations, individuals, institutional investors, financial institutions and governments. As of December 31, 2016, the Company operates 264 brokerage branches, providing extensive national coverage to 31 provinces, cities, and autonomous regions throughout China. For two consecutive years in 2015 and 2016, GF Securities ranked second on "Hurun's Top Brands List" amongst Chinese securities companies. The Company is actively committed to social responsibility and caring, focusing on education and poverty through "GF Securities Social Charity Foundation", and as a result has enjoyed a strong reputation and an influential brand. L.R. Capital Announced its Pre-IPO Investment of RMB500 Million in Xinte Energy, a Subsidiary of TBEA


News Article | May 1, 2017
Site: phys.org

Unfortunately, it's hard to accurately monitor walking speed in a way that's both continuous and unobtrusive. Professor Dina Katabi's group at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) have been working on the problem, and believe that the answer is to go wireless. In a new paper, the team presents "WiGait," a device that can measure the walking speed of multiple people with 95 to 99 percent accuracy using wireless signals. The system is an update of a device that Katabi's team presented to President Obama in 2015. The size of a small painting, the device can be placed on the wall of a person's house. It builds on Katabi's previous work that analyzes wireless signals reflected off people's bodies to measure a range of behaviors, from breathing and falling to specific emotions. (The signals emit roughly 100 times less radiation than a standard cellphone.) "By using in-home sensors, we can see trends in how walking speed changes over longer periods of time," says lead author and PhD student Chen-Yu Hsu. "This can provide insight into whether someone should adjust their health regimens, whether that's doing physical therapy or altering their medications." WiGait is also 85 to 99 percent accurate at measuring a person's stride length, which could allow researchers to better understand conditions like Parkinson's disease that are characterized by reduced step size. Hsu and Katabi developed WiGait in collaboration with CSAIL PhD student Zachary Kabelac and master's student Rumen Hristov, alongside undergraduate Yuchen Liu from the Hong Kong University of Science and Technology, and assistant professor Christine Liu from the Boston University School of Medicine. The team will present their paper in May at ACM's CHI Conference on Human Factors in Computing Systems in Colorado. Today walking speed is measured by physical therapists or clinicians using a stopwatch. Wearables like FitBit can only roughly estimate your speed based on your step count; GPS-enabled smartphones are similarly inaccurate and can't work indoors; and cameras are intrusive and can only monitor one room at a time. The only method that's comparably accurate is VICON motion-tracking, which isn't widely available enough to be practical for monitoring day-to-day health changes. Meanwhile, WiGait measures walking speed with a high level of granularity, without requiring that the person wear or carry a sensor. It does so by analyzing the surrounding wireless signals and their reflections off a person's body. Also, the team's algorithm can distinguish walking from other movements, such as cleaning the kitchen or brushing one's teeth. According to Katabi, the device could help reveal a wealth of important health information, particularly for the elderly: a change in walking speed, for example, could mean an injury or that the person is at an increased risk of falling. "Many avoidable hospitalizations are related to issues like falls, congestive heart disease, or chronic obstructive pulmonary disease which have all been shown to be correlated to gait speed," Katabi says. "Reducing the number of hospitalizations, even by a small amount, could vastly improve healthcare costs." The team developed WiGait to be more privacy-minded than cameras, showing you as nothing more than a moving dot on a screen. In the future they hope to train it on people with walking impairments like Parkinson's, Alzheimer's or MS, to help physicians accurately track disease progression and adjust medications. "The true novelty of this device is that it can map major metrics of health and behavior without any active engagement from the user, which is especially helpful for the cognitively impaired," says Ipsit Vahia, a geriatric clinician at McLean Hospital and Harvard Medical School who was not involved in the research. "Gait speed is a proxy indicator of many clinically important conditions, and down the line this could extend to measuring sleep patterns, respiratory rates, and other vital human behaviors." Explore further: X-ray vision? New technology making it a reality for $300 More information: Paper: "Extracting Gait Velocity and Stride Length from Surrounding Radio Signals" people.csail.mit.edu/cyhsu/papers/wigait_chi17.pdf


Quantum entanglement, one of the most intriguing features of multi-particle quantum system, has become a fundamental building block in both quantum information processing and quantum computation. If two particles are entangled, no matter how far away they are separated, quantum mechanics predicts that measurement of one particle leads to instantaneous wave-function collapse of the other particle. Such "spooky action at a distance" seems contradictory to our common belief and, in 1935, Einstein attempted to use entanglement to criticize quantum mechanics -- that the quantum description of physical reality is incomplete. Einstein believed that no information could travel faster than light, and suggested that there might be some local hidden variable theories that could explain the world in a deterministic way, if and only if they obey realism and locality. In 1964, J. S. Bell showed that the debate can be experimentally resolved by testing an inequality; by measuring correlations between entangled parties, the result calculated from local hidden variable theories should be constrained by the Bell inequality, which on the other hand can be violated in the prediction of quantum mechanics. Making use of a specifically-developed slow light technique to reduce the velocity of light dramatically, researchers at the Hong Kong University of Science and Technology implemented a Bell Test and were able to generate frequency-bin entangled narrowband biphotons from spontaneous four-wave mixing (SFWM) in cold atoms with a double-path configuration, where the phase difference between the two spatial paths can be controlled independently and nonlocally. Their findings were published in the journal Optica on April 15, 2017 (doi: 10.1364/OPTICA.4.000388). "We tested the CHSH Bell inequality and registered |?|=2.52±0.48|S|=2.52±0.48, which violates the Bell inequality |?|?2," said Shengwang Du, professor of Physics at HKUST and the leader of the research team. "We have unambiguously demonstrated the generation of frequency-bin entangled narrowband (about 1 MHz) biphotons, which can efficiently interact with stationary atomic quantum nodes in an atom-photon quantum network. Because of their narrow bandwidth, these biphotons can be stored and retrieved from a quantum memory with high efficiency." "Our result, for the first time, tests the Bell inequality in a nonlocal temporal correlation of frequency-bin entangled narrowband biphotons with time-resolved detection," said Xianxin Guo, a co-author of the paper. "This will have applications in quantum information processing involving time-frequency entanglement." The study revealed the temporal details that agree well with theory calculation based on quantum mechanics, and implies the possibility of encoding and decoding qubit information in the time domain. "Our narrowband frequency-bin entangled biphoton source in this work can be ideally implemented to produce pure heralded single photons in a two-color qubit state with a tunable phase, making use of entanglement, linear optics, and time-resolved detection," said Guo.


Quantum entanglement, one of the most intriguing features of multi-particle quantum systems, has become a fundamental building block in both quantum information processing and quantum computation. If two particles are entangled, no matter how far away they are separated, quantum mechanics predicts that measurement of one particle leads to instantaneous wave-function collapse of the other particle. Such "spooky action at a distance" is non-intuitive, and in 1935, Einstein attempted to use entanglement to criticize quantum mechanics to suggest that the quantum description of physical reality is incomplete. Einstein believed that no information could travel faster than light, and suggested that there might be some local hidden variable theories that could explain the world in a deterministic way, if and only if they obey realism and locality. In 1964, J. S. Bell showed that the debate can be experimentally resolved by testing an inequality; by measuring correlations between entangled parties, the result calculated from local hidden variable theories should be constrained by the Bell inequality, which, on the other hand, can be violated in the predictions of quantum mechanics. By reducing the velocity of light dramatically, researchers at the Hong Kong University of Science and Technology implemented a Bell Test and were able to generate frequency-bin entangled narrowband biphotons from spontaneous four-wave mixing (SFWM) in cold atoms with a double-path configuration, where the phase difference between the two spatial paths can be controlled independently and nonlocally. Their findings were published in the journal Optica on April 15, 2017. "We tested the CHSH Bell inequality and registered |S|=2.52±0.48|S|=2.52±0.48, which violates the Bell inequality |S|≤2," said Shengwang Du, professor of Physics at HKUST and the leader of the research team. "We have unambiguously demonstrated the generation of frequency-bin entangled narrowband (about 1 MHz) biphotons, which can efficiently interact with stationary atomic quantum nodes in an atom-photon quantum network. Because of their narrow bandwidth, these biphotons can be stored and retrieved from a quantum memory with high efficiency." "Our result, for the first time, tests the Bell inequality in a nonlocal temporal correlation of frequency-bin entangled narrowband biphotons with time-resolved detection," said Xianxin Guo, a co-author of the paper. "This will have applications in quantum information processing involving time-frequency entanglement." The study revealed temporal details that agree well with theory calculations based on quantum mechanics, and implies the possibility of encoding and decoding qubit information in the time domain. "Our narrowband frequency-bin entangled biphoton source in this work can be ideally implemented to produce pure heralded single photons in a two-color qubit state with a tunable phase, making use of entanglement, linear optics, and time-resolved detection," said Guo. More information: Xianxin Guo et al, Testing the Bell inequality on frequency-bin entangled photon pairs using time-resolved detection, Optica (2017). DOI: 10.1364/OPTICA.4.000388


News Article | April 20, 2017
Site: phys.org

This energy, predicted seven decades ago by the Dutch scientist Hendrik Casimir, arises from quantum effects and can be seen experimentally by placing two opposing plates very close to each other in a vacuum. At close range, the plates repel each other, which could be useful to certain technologies. Until recently, however, harnessing this "Casimir force" to do anything useful seemed impossible. A new silicon chip built by researchers at Hong Kong University of Science and Technology and Princeton University is a step toward harnessing the Casimir force. Using a clever assembly of micron-sized shapes etched into the plates, the researchers demonstrated that the plates repel as they are brought close together. Constructing this device entirely out of a single silicon chip could open the way to using the Casimir force for practical applications such as keeping tiny machine parts from sticking to each other. The work was published in the February issue of the journal Nature Photonics. "This is among the first experimental verifications of the Casimir effect on a silicon chip," said Alejandro Rodriguez, an assistant professor of electrical engineering at Princeton University, who provided theoretical calculations for the device, which was built by a team led by Ho Bun Chan at Hong Kong University of Science and Technology. "And it also allows you to make measurements of forces in very nontrivial structures like these that cause repulsion. It is a double-whammy." The silicon structure looks like two plates lined with teeth that face each other across a tiny gap which is only about 100 nanometers wide. (A human hair is 60,000-80,000 nanometers wide.) As the two plates are pushed closer together, the Casimir force comes into play and pushes them apart. This repulsive effect happens without any input of energy and to all appearances, in a vacuum. These characteristics led this energy to be called "zero-point energy." They also fueled earlier claims that the Casimir force could not exist because its existence would imply some sort of perpetual motion, which would be impossible according to the laws of physics. The force, which has since been experimentally confirmed to exist, arises from the normal quantum fluctuations of the few atoms that persist in the chasm despite the evacuation of all the air. The team demonstrated that it is possible to build a device in silicon to control the Casimir force. "Our paper shows that it is possible to control the Casimir force using structures of complex, tailor-made shapes," said Ho Bun Chan, senior author on the paper and a scientist at the Hong Kong University of Science and Technology. His team drew on earlier work by Rodriguez published in 2008 that proposed shapes that would be expected to yield a Casimir force that could both attract and repel. "This paper is the experimental realization using a structure inspired by Rodriguez's design," Chan said. Rodriguez and his team at Princeton developed techniques that allowed the researchers to compute interactions between two parallel plates as they approach each other. With these tools, they were then able to explore what would happen if more complex geometries were used. This led to some of the first predictions of a repulsive Casimir force in 2008. The Rodriguez group used nanophotonic techniques, which involved measuring how light would interact with the structures, to get at the complex equations of how the force arises from the interaction of two plates. The silicon device included a small mechanical spring that the researchers used to measure the force between the two plates, and to verify that the quantum force can be repulsive. The roughly T-shaped silicon teeth are what allow the repulsive force to form. The repulsion comes from how different parts of the surface interact with the opposite surface. "We tried to think about what kind of shapes Chan's group would have to fabricate to lead to a significant repulsive force, so we did some background studies and calculations to make sure they would see enough non-monotonicity as to be measurable," Rodriguez said. Going forward, the researchers plan to explore other configurations that may give rise to even larger repulsive forces and more well-defined repulsion at larger separations. Explore further: Raising the prospects for quantum levitation More information: L. Tang et al. Measurement of non-monotonic Casimir forces between silicon nanostructures, Nature Photonics (2017). DOI: 10.1038/nphoton.2016.254


Yuan Y.,National University of Singapore | Kwok R.T.K.,Hong Kong University of Science and Technology | Tang B.Z.,Hong Kong University of Science and Technology | Tang B.Z.,South China University of Technology | And 2 more authors.
Journal of the American Chemical Society | Year: 2014

Targeted drug delivery to tumor cells with minimized side effects and real-time in situ monitoring of drug efficacy is highly desirable for personalized medicine. In this work, we report the synthesis and biological evaluation of a chemotherapeutic Pt(IV) prodrug whose two axial positions are functionalized with a cyclic arginine-glycine-aspartic acid (cRGD) tripeptide for targeting integrin αvβ3 overexpressed cancer cells and an apoptosis sensor which is composed of tetraphenylsilole (TPS) fluorophore with aggregation-induced emission (AIE) characteristics and a caspase-3 enzyme specific Asp-Glu-Val-Asp (DEVD) peptide. The targeted Pt(IV) prodrug can selectively bind to αvβ3 integrin overexpressed cancer cells to facilitate cellular uptake. In addition, the Pt(IV) prodrug can be reduced to active Pt(II) drug in cells and release the apoptosis sensor TPS-DEVD simultaneously. The reduced Pt(II) drug can induce the cell apoptosis and activate caspase-3 enzyme to cleave the DEVD peptide sequence. Due to free rotation of the phenylene rings, TPS-DEVD is nonemissive in aqueous media. The specific cleavage of DEVD by caspase-3 generates the hydrophobic TPS residue, which tends to aggregate, resulting in restriction of intramolecular rotations of the phenyl rings and ultimately leading to fluorescence enhancement. Such noninvasive and real-time imaging of drug-induced apoptosis in situ can be used as an indicator for early evaluation of the therapeutic responses of a specific anticancer drug. © 2014 American Chemical Society.


Shi H.,National University of Singapore | Liu J.,Hong Kong University of Science and Technology | Geng J.,National University of Singapore | Tang B.Z.,Hong Kong University of Science and Technology | And 3 more authors.
Journal of the American Chemical Society | Year: 2012

Specific bioprobes with fluorescence turn-on response are highly desirable for high contrast biosensing and imaging. In this work, we developed a new generation bioprobe by integrating tetraphenylsilole, a fluorogenic unit with aggregation-induced emission (AIE) characteristic, with cyclic arginine-glycine-aspartic acid tripeptide (cRGD), a targeting ligand to integrin α vβ 3 receptor. Emission of the AIE probe is switched on upon its specific binding to integrin α vβ 3, which allows quantitative detection of integrin α vβ 3 in solution and real-time imaging of the binding process between cRGD and integrin α vβ 3 on cell membrane. The probe can be used for tracking integrin α vβ 3 and for identifying integrin α vβ 3-positive cancer cells. © 2012 American Chemical Society.


Kou S.,National University of Singapore | Peng X.,Hong Kong University of Science and Technology
Operations Research | Year: 2016

This paper attempts to provide a decision-theoretic foundation for the measurement of economic tail risk, which is not only closely related to utility theory but also relevant to statistical model uncertainty. The main result is that the only risk measures that satisfy a set of economic axioms for the Choquet expected utility and the statistical property of general elicitability (i.e., there exists an objective function such that minimizing the expected objective function yields the risk measure) are the mean functional and value-at-risk (VaR), in particular the median shortfall, which is the median of tail loss distribution and is also the VaR at a higher confidence level. We also discuss various approaches of backtesting and their relations to elicitability and co-elicitability; in particular, we show that the co-elicitability of VaR and expected shortfall does not lead to a reliable backtesting method for expected shortfall and there have been only indirect backtesting methods for expected shortfall. Furthermore, we extend the result to address model uncertainty by incorporating multiple scenarios. As an application, we argue that median shortfall is a better alternative than expected shortfall for setting capital requirements in Basel Accords. © 2016 INFORMS.


Tan P.,National University of Singapore | Quan L.,Hong Kong University of Science and Technology | Zickler T.,Harvard University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2011

Different materials reflect light in different ways, and this reflectance interacts with shape, lighting, and viewpoint to determine an object's image. Common materials exhibit diverse reflectance effects, and this is a significant source of difficulty for image analysis. One strategy for dealing with this diversity is to build computational tools that exploit reflectance symmetries, such as reciprocity and isotropy, that are exhibited by broad classes of materials. By building tools that exploit these symmetries, one can create vision systems that are more likely to succeed in real-world, non-Lambertian environments. In this paper, we develop a framework for representing and exploiting reflectance symmetries. We analyze the conditions for distinct surface points to have local view and lighting conditions that are equivalent under these symmetries, and we represent these conditions in terms of the geometric structure they induce on the Gaussian sphere and its abstraction, the projective plane. We also study the behavior of these structures under perturbations of surface shape and explore applications to both calibrated and uncalibrated photometric stereo. © 2011 IEEE.


Chen S.,University of Adelaide | Xing W.,China University of Petroleum - East China | Duan J.,University of Adelaide | Hu X.,Hong Kong University of Science and Technology | Qiao S.Z.,University of Adelaide
Journal of Materials Chemistry A | Year: 2013

The fast growing interest in portable electronic devices and electric vehicles has stimulated extensive research in high performance energy storage devices, such as supercapacitors. Nanostructured electrodes can achieve high electrochemical performances in supercapacitors owing to their high surface atom ratio, tuneable texture and unique size-dependent properties that can afford effective electrolyte diffusion and improved charge transportation and storage during charging-discharging. This review reports on the recent progress in designing and fabricating different kinds of nanostructured electrodes, including electrical double layer based electrodes such as porous carbons and graphene, and Faradic reaction based electrodes such as metal oxides/hydroxides and conductive polymers. Furthermore, the review also summarizes the advances of hybrid electrodes, which store charges by both mechanisms, such as porous carbons-metal oxides/hydroxides, porous carbons-conductive polymers, graphene-metal oxides/hydroxides, and graphene-conductive polymers. Finally, we provide some perspectives as to the future directions of this intriguing field. © 2013 The Royal Society of Chemistry.


Li X.S.,Hong Kong University of Science and Technology | Dafalias Y.F.,University of California at Davis | Dafalias Y.F.,National Technical University of Athens
Journal of Engineering Mechanics | Year: 2012

An Anisotropic Critical State Theory (ACST) for granular media is presented, which accounts for the role of anisotropic fabric at critical state. It enhances the requirements of critical values for the stress and void ratio of the classical Critical State Theory (CST) by an additional requirement of critical value for an appropriate measure of fabric-anisotropy. A fabric tensor and its evolution toward a critical value, norm-wise and direction-wise, is introduced motivated by micromechanical and experimental studies. On the basis of a scalar-valued fabric-anisotropy variable relating the evolving fabric tensor to the loading direction, a dilatancy state line is defined in the void ratio-pressure plane which determines a dilatancy state parameter ζ that characterizes the contracting or dilating trends of the current state. When the fabric-anisotropy variable reaches its critical state value, the dilatancy state line becomes identical to the critical state line and the ζ identical to the well-known state parameter ψ An immediate corollary is the uniqueness of the critical state line, for which a thermodynamic proof is provided on the basis of the Gibbs condition. Static liquefaction is obtained when ζ = o with the stress ratio reaching its critical value but not the void ratio and the fabric. Simulations of anisotropic material response by a triaxial model are used to illustrate the effectiveness of the novel ACST. © 2012 American Society of Civil Engineers.


Ding D.,National University of Singapore | Li K.,Institute of Materials Research and Engineering of Singapore | Liu B.,National University of Singapore | Liu B.,Institute of Materials Research and Engineering of Singapore | And 3 more authors.
Accounts of Chemical Research | Year: 2013

Fluorescent bioprobes are powerful tools for analytical sensing and optical imaging, which allow direct visualization of biological analytes at the molecular level and offer useful insights into complex biological structures and processes. The sensing and imaging sensitivity of a bioprobe is determined by the brightness and contrast of its fluorescence before and after analyte binding. Emission from a fluorophore is often quenched at high concentration or in aggregate state, which is notoriously known as concentration quenching or aggregation-caused quenching (ACQ). The ACQ effect limits the label-to-analyte ratio and forces researchers to use very dilute solutions of fluorophores. It compels many probes to operate in a fluorescence "turn-off" mode with a narrow scope of practical applications.The unique aggregation-induced emission (AIE) process offers a straightforward solution to the ACQ problem. Typical AIE fluorogens are characterized by their propeller-shaped rotorlike structures, which undergo low-frequency torsional motions as isolated molecules and emit very weakly in solutions. Their aggregates show strong fluorescence mainly due to the restriction of their intramolecular rotations in the aggregate state. This fascinating attribute of AIE fluorogens provides a new platform for the development of fluorescence light-up molecules and photostable nanoaggregates for specific analyte detection and imaging.In this Account, we review our recent AIE work to highlight the utility of AIE effect in the development of new fluorescent bioprobes, which allows the use of highly concentrated fluorogens for biosensing and imaging. The simple design and fluorescence turn-on feature of the molecular AIE bioprobes offer direct visualization of specific analytes and biological processes in aqueous media with higher sensitivity and better accuracy than traditional fluorescence turn-off probes. The AIE dot-based bioprobes with different formulations and surface functionalities show advanced features over quantum dots and small molecule dyes, such as large absorptivity, high luminosity, excellent biocompatibility, free of random blinking, and strong photobleaching resistance. These features enable cancer cell detection, long term cell tracing, and tumor imaging in a noninvasive and high contrast manner. Recent research has significantly expanded the scope of biological applications of AIE fluorogens and offers new strategies to fluorescent bioprobe design. We anticipate that future development on AIE bioprobes will combine one- or multiphoton fluorescence with other modalities (e.g., magnetic resonance imaging) or functionalities (e.g. therapy) to fully demonstrate their potential as a new generation of theranostic reagent. In parallel, the advances in molecular biology will provide more specific bioreceptors, which will enable the development of next generation AIE bioprobes with high selectivity and sensitivity for molecular sensing and imaging. © 2013 American Chemical Society.


Chen K.,Hong Kong University of Science and Technology | Tong X.,Beijing Normal University
Biometrika | Year: 2010

A maximum likelihood method with spline smoothing is proposed for linear transformation models with varying coefficients. The estimation and inference procedures are computationally easy. Under some regularity conditions, the estimators are proved to be consistent and asymptotically normal. A simulation study using the Stanford transplant data is presented to show that the proposed method performs well with a finite sample and is easy to use in practice. © 2010 Biometrika Trust.


Mukhopadhyay A.,Hong Kong University of Science and Technology | Yeung C.W.M.,National University of Singapore
Journal of Marketing Research | Year: 2010

This research studies the effect of consumers' lay theories of selfcontrol on their choices of products for young children. The authors find that people who hold the implicit assumption that self-control is a small resource that can be increased over time ("limited-malleable theorists") are more likely to engage in behaviors that may benefit children's selfcontrol. In contrast, people who believe either that self-control is a large resource ("unlimited theorists") or that it cannot increase over time ("fixed theorists") are less likely to engage in such behaviors. Field experiments conducted with parents demonstrate that limited-malleable theorists take their children less frequently to fast-food restaurants, give their children unhealthful snacks less often, and prefer educational to entertaining television programs for them. Similar patterns are observed when nonparent adults make gift choices for children or while babysitting. The authors obtain these effects with lay theories both measured and manipulated and after they control for demographic and psychological characteristics, including own self-control. These results contribute to the literature on self-control, parenting, and consumer socialization. © 2010, American Marketing Association.


Ma Y.,University of California at Riverside | Liu A.,Hong Kong University of Science and Technology | Hua Y.,University of California at Riverside
IEEE Transactions on Signal Processing | Year: 2014

We present optimization algorithms for source and relay power allocations in a multicarrier relay system with direct link, where the source power is allowed to transmit in both phases in a two-phase relay scheme. We show that there is a significant benefit to the system capacity by allowing the source power to be distributed over both phases. Specifically, we consider the joint optimization of source and relay power to minimize a general cost function. The joint optimization problem is non-convex and the complexity of finding the optimal solution is extremely high. Using the alternating optimization (AO) method, the joint problem is decomposed into a convex source power allocation problem and a non-convex relay power allocation problem. By exploiting the specific structure of the problem, we present efficient algorithms that yield the exact optimal solutions for both source and (non-convex) relay power allocation problems. Then we show that the overall AO algorithm converges to a stationary point of the joint problem. Moreover, the proposed AO algorithm is asymptotically optimal for large relay transmit power or large source-relay channel gain. Finally, simulations show that the proposed AO algorithm achieves significant gain over various baselines. © 2013 IEEE.


Liu Y.-J.,Tsinghua National Laboratory for Information Sciences and Technology | Chen Z.,Hong Kong University of Science and Technology | Tang K.,Hong Kong University of Science and Technology
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2011

In the research of computer vision and machine perception, 3D objects are usually represented by 2-manifold triangular meshes M. In this paper, we present practical and efficient algorithms to construct iso-contours, bisectors, and Voronoi diagrams of point sites on M, based on an exact geodesic metric. Compared to euclidean metric spaces, the Voronoi diagrams on M exhibit many special properties that fail all of the existing euclidean Voronoi algorithms. To provide practical algorithms for constructing geodesic-metric-based Voronoi diagrams on M, this paper studies the analytic structure of iso-contours, bisectors, and Voronoi diagrams on M. After a necessary preprocessing of model M, practical algorithms are proposed for quickly obtaining full information about iso - contours, bisectors, and Voronoi diagrams on M. The complexity of the construction algorithms is also analyzed. Finally, three interesting applicationssurface sampling and reconstruction, 3D skeleton extraction, and point pattern analysisare presented that show the potential power of the proposed algorithms in pattern analysis. © 2011 IEEE.


Ma E.,University of California at Riverside | Ma E.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2015

It is shown that in extensions of the standard model of quarks and leptons where the additive lepton number L is broken by two units, so that Z2 lepton parity, i.e., (-1)L which is either even or odd, remains exactly conserved, there is the possibility of stable dark matter without additional symmetry. This applies to many existing simple models of Majorana neutrino mass with dark matter, including some radiative models. Several well-known examples are discussed. This new insight leads to the construction of a radiative type II seesaw model of neutrino mass with dark matter where the dominant decay of the doubly charged Higgs boson ξ++ is into W+W+ instead of the expected li+lj+ lepton pairs for the well-known tree-level model. © 2015 American Physical Society. © 2015 American Physical Society.


Ma E.,University of California at Riverside | Ma E.,Hong Kong University of Science and Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

I propose a model of radiative charged-lepton and neutrino masses with A4 symmetry. The soft breaking of A4 to Z3 lepton triality is accomplished by dimension-three terms. The breaking of Z3 by dimension-two terms allows cobimaximal neutrino mixing (θ13≠0, θ23=π/4, δCP=±π/2) to be realized with only very small finite calculable deviations from the residual Z3 lepton triality. This construction solves a long-standing technical problem inherent in renormalizable A4 models since their inception. © 2016 The Author.


Mei J.,Hong Kong University of Science and Technology | Hong Y.,Hong Kong University of Science and Technology | Hong Y.,China Institute of Technology | Lam J.W.Y.,Hong Kong University of Science and Technology | And 6 more authors.
Advanced Materials | Year: 2014

"United we stand, divided we fall."-Aesop.Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Ma E.,University of California at Riverside | Ma E.,Hong Kong University of Science and Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

In all scalar extensions of the standard model of particle interactions, the one Higgs boson responsible for electroweak symmetry breaking always mixes with other neutral scalars at tree level unless a symmetry prevents it. An unexplored important option is that the mixing may be radiative, and thus guaranteed to be small. Two first such examples are discussed. One is based on the soft breaking of the discrete symmetry Z3. The other starts with the non-Abelian discrete symmetry A4 which is then softly broken to Z3, and results in the emergence of an interesting dark-matter candidate together with a light mediator for the dark matter to have its own long-range interaction. © 2016 The Author.


Zhao W.,Hong Kong University of Science and Technology | Sun J.,Hong Kong University of Science and Technology
Journal of the American Chemical Society | Year: 2013

We have developed an efficient method for medium and large ring lactone synthesis by a conceptually different ring-expansion strategy. The design of an unprecedented ring conjunction mode of oxetene, combined with the appropriate choice of a Lewis acid promoter and an additive, constitutes the key components of the new process. Enabled by this new approach, the reaction does not require high dilution or slow addition. © 2013 American Chemical Society.


Mei J.,China Institute of Technology | Mei J.,Hong Kong University of Science and Technology | Leung N.L.C.,China Institute of Technology | Leung N.L.C.,Hong Kong University of Science and Technology | And 7 more authors.
Chemical Reviews | Year: 2015

Aggregation-induced emission (AIE) is another photophysical phenomenon associated with chromophore aggregation. The concept of AIE has been introduced by a group of researchers in 2001. In the AIE process, non-emissive luminogens are induced to emit by the aggregate formation. The luminogens exhibiting AIE attributes are termed AIEgens, by analogue with the term of 'mesogens' for the molecules showing mesomorphism under suitable conditions.


Chen Y.,Imperial College London | Chen Y.,University of Macau | McKay M.R.,Hong Kong University of Science and Technology
IEEE Transactions on Information Theory | Year: 2012

In this paper, we compute two important information-theoretic quantities which arise in the application of multiple-input multiple-output (MIMO) antenna wireless communication systems: the distribution of the mutual information of multiantenna Gaussian channels, and the Gallager random coding upper bound on the error probability achievable by finite-length channel codes. We show that the mathematical problem underpinning both quantities is the computation of certain Hankel determinants generated by deformed versions of classical weight functions. For single-user MIMO systems, it is a deformed Laguerre weight; for multiuser MIMO systems, it is a deformed Jacobi weight. We apply two different methods to characterize each of these Hankel determinants. First, we employ the ladder operators of the corresponding monic orthogonal polynomials to give an exact characterization of the Hankel determinants in terms of Painlevé differential equations. This turns out to be a Painlevé V for the single-user MIMO scenario and a Painlevé VI for the multiuser scenario. We then introduce Coulomb fluid linear statistics methods to derive closed-form approximations for the MIMO mutual information distribution and the error probability which, although formally valid for large matrix dimensions, are shown to give accurate results even when the matrix dimensions are small. Focusing on the single-user mutual information distribution, we then employ the exact Painlevé V representation with the help of the Coulomb fluid linear statistics approximation to yield deeper insights into the scaling behavior in terms of the number of antennas and signal-to-noise ratio (SNR). Among other things, these results allow us to study the asymptotic Gaussianity of the distribution as the number of antennas increase, and to investigate when and why such approximations break down as the SNR increases. Based on the Painlevé, we also derive recursive formulas for explicitly computing in closed form any desired number of correction terms to the asymptotic mean and variance, as well as closed-form asymptotic expressions for any desired number of higher order cumulants. Using these cumulants, we propose new closed-form approximations to the mutual information distribution which are shown to be very accurate, not only in the bulk but also in the tail region of interest for the outage probability. © 2012 IEEE.


Li S.,Columbia University | McKay M.R.,Hong Kong University of Science and Technology | Chen Y.,University of Macau
IEEE Transactions on Information Theory | Year: 2013

This paper builds upon our recent work which computed the moment generating function of the multiple-input multiple-output mutual information exactly in terms of a Painlevé V differential equation. By exploiting this key analytical tool, we provide an in-depth characterization of the mutual information distribution for sufficiently large (but finite) antenna numbers. In particular, we derive systematic closed-form expansions for the high-order cumulants. These results yield considerable new insight, such as providing a technical explanation as to why the well-known Gaussian approximation is quite robust to large signal-to-noise ratio for the case of unequal antenna arrays, while it deviates strongly for equal antenna arrays. In addition, by drawing upon our high-order cumulant expansions, we employ the Edgeworth expansion technique to propose a refined Gaussian approximation which is shown to give a very accurate closed-form characterization of the mutual information distribution, both around the mean and for moderate deviations into the tails (where the Gaussian approximation fails remarkably). For stronger deviations where the Edgeworth expansion becomes unwieldy, we employ the saddle point method and asymptotic integration tools to establish new analytical characterizations which are shown to be very simple and accurate. Based on these results, we also recover key well-established properties of the tail distribution, including the diversity-multiplexing-tradeoff. © 1963-2012 IEEE.


Liang J.,National University of Singapore | Tang B.Z.,Hong Kong University of Science and Technology | Tang B.Z.,South China University of Technology | Liu B.,National University of Singapore | Liu B.,Institute of Materials Research and Engineering ASTAR
Chemical Society Reviews | Year: 2015

Driven by the high demand for sensitive and specific tools for optical sensing and imaging, bioprobes with various working mechanisms and advanced functionalities are flourishing at an incredible speed. Conventional fluorescent probes suffer from the notorious effect of aggregation-caused quenching that imposes limitation on their labelling efficiency or concentration to achieve desired sensitivity. The recently emerged fluorogens with an aggregation-induced emission (AIE) feature offer a timely remedy to tackle the challenge. Utilizing the unique properties of AIE fluorogens (AIEgens), specific light-up probes have been constructed through functionalization with recognition elements, showing advantages such as low background interference, a high signal to noise ratio and superior photostability with activatable therapeutic effects. In this tutorial review, we summarize the recent progress in the development of specific AIEgen-based light-up bioprobes. Through illustration of their operation mechanisms and application examples, we hope to provide guidelines for the design of more advanced AIE sensing and imaging platforms with high selectivity, great sensitivity and wide adaptability to a broad range of biomedical applications. This journal is © The Royal Society of Chemistry.


Patent
National University of Singapore, Hong Kong University of Science and Technology | Date: 2013-05-24

The development of a series of fluorescent materials including heterocycle-functionalized luminogens with aggregation-induced/enhanced emission (AIE/AEE), long wavelength emission, and high solid state fluorescence quantum efficiency is contemplated. The described fluorescent materials are promising candidates in selective luminescence-based chemosensor for Hg^(2+) or ATP, fluorescent staining for mitochondria in living cells with high photostability, stimuli-responsive luminescent materials, and materials for optical waveguides. In addition, these heterocycle-functionalized luminogens are particularly useful as fluorescent labels for biopolymers such as peptides, antibodies, or nucleic acids, making them useful as AIE-active biocompatible probes for clinical cancer imaging and diagnostics.


The development of fluorescent bioprobes comprising organic fluorescent compounds that exhibit aggregation induced emission (AIE) properties, methods of producing the same, and their practical applications for in vitro and in vivo bioimaging.


Grant
Agency: European Commission | Branch: FP7 | Program: CSA-SA | Phase: SST-2007-6.0-01;SST-2007-6.0-02 | Award Amount: 506.34K | Year: 2008

Contributing to the European Research Area in surface transport to strengthen the competitiveness of the European surface transport sector. This will be achieved by using the excellent EURNEX competence to provide research excellence capabilities to European Small and Medium Size Enterprises (SMEs). Furthermore the cooperation with research excellencies from non EU countries will stimulate research that is of mutual interest and strengthen the European as well as non European research excellencies. EURNEX, the European Rail Research Network of Excellence, started on 01 January 2004 and has been granted for 4 years with 6 Mio within the 6th Framework Programme of EC. It involves 66 research institutes from 20 European countries and the associations of industry and operators UNIFE, UIC and UITP. More than 80 % of the members cover not only the rail research domain but surface transport. EURNEX supports the aims of the EC to see an interoperable and harmonised European rail system contributing to co-modality and a strong internationally competitive European railway industry by integrating the fragmented research, sharing knowledge and coordinating current research. The main benefits for the integration of non EU researchers in EURNEX are the scientific exchange on an international level, the training of junior scientists and researchers using the EURNEX assets, the identification of research areas that are of mutual interest, and the solving of problems in the international railway sector with European know how. The main benefits, that SMEs contributing as associated partners in EURNEX can gain, are an overview of the state of the art of the surface transport sector as a whole as well as specific topics, an insight in current research trends, an evaluation of their individual know how (respecting sensitive information), and an access to excellent research capabilities and test facilities.


Patent
National University of Singapore, Hong Kong University of Science and Technology | Date: 2015-01-27

The present invention is drawn toward luminogens and chemical compositions comprising a target recognition motif, a hydrophilic moiety, a linking moiety, and at least one luminogen. Additionally presented are methods of: assessing the conversion of a prodrug into its active form, assessing the therapeutic efficacy of a prodrug, detecting glutathione in a biological sample, detecting alkaline phosphatase in a sample, and conducting fluorescence imaging or magnetic resonance imaging with the use of luminogen-containing compositions.


Grant
Agency: European Commission | Branch: FP7 | Program: CSA | Phase: ICT-2007.1.3 | Award Amount: 533.71K | Year: 2008

Standardisation, and associated regulations, in respect of RFID is of critical importance in realising open systems applications of global significance, such as supply chain traceability and logistics. Of parallel significance is the numbering and identification coding required facilitating global systems applications. While much of the emphasis of European attentions to RFID focuses upon electronic product code (EPC) and associated EPC-compliant data carriers it has to be recognised that other numbering systems exist and are being promoted for global applications. The ubiquitous identification (UID) system being promoted widely within the Asia-Pacific regions of the world. There is a need to resolve the global numbering requirements and the means whereby these numbers can be freely issued, managed and maintained. The European emphasis upon EPC also extends to a disproportionate attention to EPCglobal designated standards in contrast to ISO/IEC standards and promotion of the Internet of Things as an aspirational objective for RFID and alignment with the European research framework in respect of ubiquitous computing and networks. Again there is a need to identify and consider the components that distinguish a global framework for RFID regulation, standardisation and developments with respect to RFID. A support action programme is proposed in which this broader framework can be recognised and used as a basis for providing a more incisive reference platform for European usage of RFID and a more informative foundation for European regulatory decisions. The team assembled for the support action benefits from involvement in two UK Government funded Global Watch missions on RFID, one to the USA and one to Japan. It also includes experts on ISO/IEC standardisation and regulatory issues.


News Article | March 4, 2016
Site: www.nature.com

At Biopolis, a sprawling research complex in Singapore, Chi Ching Goh leans over an anaesthetized mouse lying on the table in front of her, and carefully injects it with a bright yellow solution. She then gently positions the mouse's ear underneath a microscope, and flips a switch to bathe the ear in ultraviolet light. Seen through the microscope's eyepiece, the illumination makes the blood underneath the skin glow green, tracing the delicate vessels that carry the solution through the creature's body. Ultimately, Goh, a PhD candidate at the National University of Singapore, hopes that the method will help her to find blood vessels that are leaking owing to inflammation, perhaps helping to detect malaria or predict strokes. Crucial to her technique are the virus-sized particles that give the solution its colour. Just a few tens of nanometres across, they are among a growing array of 'nanolights' that researchers are tailoring to specific types of fluorescence: the ability to absorb light at one wavelength and re-emit it at another. Many naturally occurring compounds can do this, from jellyfish proteins to some rare-earth compounds. But nanolights tend to be much more stable, versatile and easier to prepare — which makes them attractive for users in both industry and academia. The best-established examples are quantum dots: tiny flecks of semiconductor that are prized for their beautiful, crisp colours. Now, however, other types of nanolight are on the rise. Some have a rare ability to absorb lots of low-energy photons and combine the energy into a handful of high-energy photons — a trick that opens up opportunities such as producing multiple colours at once. Others are made from polymers or small organic molecules. These are less toxic than quantum dots and often outshine them — much to the amazement of chemists, who are used to carbon-based compounds simply degrading in the presence of ultraviolet light. “I was kind of surprised to find that we can make organic particles much brighter than inorganic particles,” says Bin Liu, a chemical engineer at the National University of Singapore and the designer of the fluorescent nanoparticles that Goh is using. Nanolights have already begun to find application in areas ranging from flat-screen displays to biochemical tests. And researchers are working towards even more ambitious uses in fields such as solar energy, DNA mapping, motion sensing and even surgery. “The research is certainly fast-paced,” says Daniel Chiu, who studies fluorescent nanoparticles at the University of Washington in Seattle. It is also increasingly wide ranging, adds Paul Alivisatos, a chemist at the University of California, Berkeley, and a co-founder of the first quantum-dot technology companies. “It's so much fun now.” The nanolight era began with the discovery of quantum dots in 1981. Russian physicists were growing tiny crystals of the semiconductor cuprous chloride in silicate glass and observed that the colour of the glass depended on the size of the particles1. The crystals were so small that quantum effects were kicking in and they were behaving somewhat like atoms: they could absorb or emit light only as specific colours, with the exact frequencies depending on the size or shape of the particles (see 'Bridge the gap'). The quantum dots were bright and beautiful, says Yin Thai Chan, who studies them at the National University of Singapore, but “there were no obvious applications”. By the early 2000s, however, the pure colours had begun to attract television manufacturers, as well as biomedical researchers, who saw their potential for labelling specific proteins and DNA segments. “Everything is good about quantum dots,” says Liu — except for one thing: their toxicity. The best-performing dots contain cadmium, which can poison cells. This limits their usefulness in biology and in applications such as household electronics, because some countries do not allow use of the element in such devices. To some extent, this problem can be overcome by replacing cadmium with zinc or indium, which are considerably less toxic, or by wrapping cadmium-based quantum dots in polymers that are biocompatible. But the toxicity is still a drawback for researchers who are pursuing ambitious applications such as fluoresence-guided surgery, in which nanoparticles are injected into a tumour, for instance, to make it glow and help surgeons to remove all traces of it. Partly in response to this challenge, researchers have begun to develop nanoparticles from materials that fluoresce naturally. Because the light-emitting properties of these nanolights come from their composition rather than their size or shape, they are easier to make with specific colours. “Practically, this is useful because of the difficulties to synthesize everything in the same size,” says Chiu. It also frees up nanolight researchers to explore alternative materials, such as semiconducting polymers. Studied for their potential in electronics since the 1950s, these polymers consist of simple compounds linked into a long chain in which electrons are free to move, but only at certain energies determined by the chain's composition. Light is emitted when electrons are kicked up to higher energy levels by some outside source, such as ultraviolet light, then fall back down to lower levels. The polymers can also be decorated with side groups to give them specific properties — for example, targeting them to cancer cells, or helping them to dissolve in water. And when chains are aggregated into polymer nanoparticles, or 'P-dots', they can be as much as 30 times brighter than a quantum dot of comparable size2. Semiconducting polymers do tend to be less stable than the inorganic semiconductors used in quantum dots. But because they are based on carbon, and contain no metals, they are much more likely to be biocompatible. P-dots have been used to stain and image cells, and also as sensors to detect oxygen, enzymes or metal ions such as copper. In 2013, for example, Chiu and his collaborators reported that a P-dot bound to a terbium ion can detect biomolecules produced by bacterial spores3. Under an ultraviolet lamp, the P-dots glow dark blue and the terbium ions emit a faint neon green colour. But when passing biomolecules attach themselves to terbium, the ions' light strengthens to a bright green. The P-dots' light remains unchanged, so it serves as an internal standard. Unfortunately, P-dots also have a fundamental problem: the polymer molecules are packed together so closely that they can be affected by 'quenching' — a phenomenon in which most of the energy coming from the original light source is quickly dissipated and fails to trigger fluorescence. Quenching has a huge impact on efficiency, says Yang-Hsiang Chan, a chemist at National Sun Yat-Sen University in Kaohsiung, Taiwan. One way to tackle it is to add bulky groups onto the polymer backbone to prevent the polymers from getting too close to each other. But this can be self-defeating: the resulting nanoparticles tend to be too fat to get into cells, say, or too dim to be useful. “It is very hard to get the right balance,” says Chan, who is working to solve the problem by designing new polymers. A more fundamental solution was pioneered in 2001, when Ben Zhong Tang at the Hong Kong University of Science and Technology in Clear Water Bay found that a class of small organic molecules would fluoresce only when they aggregate together4. These molecules are shaped like propellers or pinwheels, and they fluoresce when packed because they can no longer move and waste their energy. Instead, they release their energy as light — a phenomenon Tang has named aggregation-induced emission (AIE). He called the molecules AIE-gens. Over the next few years, Tang and his students changed the side groups and introduced elements such as nitrogen or oxygen, and AIE-gens can now glow in the entire spectrum of colours from ultraviolet to near-infrared. “My students quickly made a lot,” says Tang. “We can change the colour at will.” In 2011, Tang met Liu through a collaboration at the Institute of Materials Research and Engineering in Singapore, part of the government-backed Agency for Science, Technology and Research (A∗STAR). At that time, AIE-gens were performing well, except that they could not dissolve in water, which made them difficult to use in biological applications. Liu was an expert in making things water-soluble, so Tang gave her some of his best AIE-gens to work with. Liu solved the problem by experimenting with polymers that are oil-loving on one end and water-loving on the other. The AIE-gens crowd within the polymer's oil-loving ends, and its water-loving ends point outwards to form a protective shell, resulting in a water-soluble capsule with a dense core full of AIE-gens. Liu designed a protective shell for the resulting nanoparticles, called AIE-dots, such that it could be decorated with various chemical groups that are tailored to specific applications. The shell can easily accommodate a wide variety of AIE-gens, says Liu, “so that we can screen a lot of molecules very quickly to find out which one is the best.” AIE-dots have been used to stain various tissues, from blood vessels to cancer cells to intracellular organelles such as mitochondria. Last year, Liu, Tang and their colleagues reported an AIE-dot that could be useful in a type of light-activated treatment known as photodynamic therapy5. It carries two molecules on its surface: one to get the dot into a cancer cell, and another to make it stick to the mitochondria. Once excited by an external light source, the AIE-dot produces red light that generates oxygen radicals near the mitochondria and kills the cancer cells. The best AIE-dots can be 40 times brighter than quantum dots6. “With AIE, high density in constrained space produces high brightness,” says Guangxue Feng, a research assistant in Liu's lab. That is particularly useful for applications such as visualization of tissues or long-term tracking of cancer cells, which halve the number of nanoparticles per cell every time they divide. But the brightness comes at a cost: AIE-dots produce a much broader, more-muted spectrum than the pure, brilliant colours of quantum dots. But that hasn't kept Liu from starting LuminiCell, a spin-off company in Singapore that produces AIE-dots in three colours and three sizes for research such as Goh's at A∗STAR. Tang is also trying to start a company; both he and Liu are now hoping to gain approval from the US Food and Drug Administration to test AIE-dots for human use in applications such as fluorescence-guided surgery. Another thing that limits the biological use of nanolights is that most of them absorb ultraviolet or visible light, which can penetrate only a few millimetres into tissue. Longer-wavelength near-infrared radiation can penetrate up to three centimetres — a much better depth for uses such as releasing drugs. But infrared light does not have enough energy to break the bonds that hold drugs on the nanoparticle, so many researchers are turning to a process called upconversion. This involves making material that can absorb multiple low-energy infrared photons, accumulate the energy and then re-emit it as higher-energy ultraviolet or visible photons. The group of heavy-metal elements known as lanthanides are particularly good at this trick. In 2011, Xiaogang Liu at the National University of Singapore reported that his laboratory had created a particularly versatile type of nanoparticle7 with a Russian doll-like structure. It consists of a series of concentric shells that each contains a different combination of lanthanides. The energy from infrared light is absorbed by the core, then migrates outwards layer by layer, snowballing from lanthanide to lanthanide before finally emerging as high-energy light near the surface. The 15 lanthanides can be combined in numerous different ways to produce nanoparticles that emit in all colours, sometimes even several at once. In one demonstration, a student in Liu's lab shone an infrared laser through a series of beakers containing clear solutions of the nanoparticles: glowing lines of purple and green light appeared in the beakers where the infrared beam passed through. Liu thinks that these upconversion nanoparticles have tremendous potential in photovoltaics, where they could help to capture near-infrared light, which makes up almost half of the Sun's radiation. This is a long way from being practical, however: the brightest available nanoparticles convert just 10% of the light they absorb. Liu's group is working to build a library of these nanoparticles — no small task considering the number of lanthanides — to systematically study their properties and work on making them brighter. Last December, Marta Cerruti, a biomaterials scientist at McGill University in Montreal, Canada, reported a proof-of-concept system in which a lanthanide-containing nanoparticle is coated with a gel that contains a 'drug' — for testing purposes, a compact, stable protein8. After absorbing near-infrared light, the nanoparticle emits infrared, visible and ultraviolet light simultaneously. The infrared emission allows the researchers to track the nanoparticle's location, and the ultraviolet light cleaves the protein's bond to the gel and releases it — or at least, it has in the laboratory. Cerruti's group is now planning tests in animals. At the end of the day, quantum dots are still the nanolights to beat. “They are the de facto standard,” says Chan. “A lot of the fundamental phenomena concerning light emission are established in quantum dots and it shapes the way others explain what they see.” Quantum dots are also still a research frontier. For example, they are getting a boost from relatively new semiconducting materials such as the perovskites. Unlike conventional semiconductors, which have a fixed ratio of elements, perovskites can have variable ratios, so researchers can tailor the dots' emission by varying their composition as well as their size. “They have two degrees of freedom for tunability,” says Edward Sargent, a materials engineer at the University of Toronto, Canada. Last year, Sargent reported a hybrid material in which quantum dots are held within a perovskite9, yielding the kind of high brightness and good electron mobility that manufacturers might like for use in flat-screen displays. Other researchers are hoping to combine the best properties of each component by pursuing hybrid nanolights. Bin Liu, for example, is trying to blend AIE-dots with quantum dots to produce narrow emissions. And semiconducting polymers paired with AIE-dots can produce much brighter particles than either alone10. Another grand challenge for nanolights is to create versions that emit infrared wavelengths efficiently. That would open up applications in motion sensing, from tiny detectors that tell the screen to turn off when a mobile phone is lifted to the ear to sophisticated devices for self-driving cars and home monitoring for elderly people. “There's so much more we could do,” says Sargent.


University of Texas at Dallas physicists have published new findings examining the electrical properties of materials that could be harnessed for next-generation transistors and electronics. Dr. Fan Zhang, assistant professor of physics, and senior physics student Armin Khamoshi recently published their research on transition metal dichalcogenides, or TMDs, in the journal Nature Communications. Zhang is a co-corresponding author, and Khamoshi is a co-lead author of the paper, which also includes collaborating scientists at Hong Kong University of Science and Technology. In recent years, scientists and engineers have become interested in TMDs in part because they are superior in many ways to graphene, a one-atom thick, two-dimensional sheet of carbon atoms arranged in a lattice. Since it was first isolated in 2004, graphene has been investigated for its potential to replace conventional semiconductors in transistors, shrinking them even further in size. Graphene is an exceptional conductor, a material in which electrons move easily, with high mobility. "It was thought that graphene could be used in transistors, but in transistors, you need to be able to switch the electric current on and off," Zhang said. "With graphene, however, the current cannot be easily switched off." In their search for alternatives, scientists and engineers have turned to TMDs, which also can be made into thin, two-dimensional sheets, or monolayers, just a few molecules thick. "TMDs have something graphene does not have -- an energy gap that allows the flow of electrons to be controlled, for the current to be switched on and off," Khamoshi said. "This gap makes TMDs ideal for use in transistors. TMDs are also very good absorbers of circularly polarized light, so they could be used in detectors. For these reasons, these materials have become a very popular topic of research." One of the challenges is to optimize and increase electron mobility in TMD materials, a key factor if they are to be developed for use in transistors, Khamoshi said. In their most recent project, Zhang and Khamoshi provided the theoretical work to guide the Hong Kong group on the layer-by-layer construction of a TMD device and on the use of magnetic fields to study how electrons travel through the device. Each monolayer of TMD is three molecules thick, and the layers were sandwiched between two sheets of boron nitride molecules. The behavior of electrons controls the behavior of these materials," Zhang said. "We want to make use of highly mobile electrons, but it is very challenging. Our collaborators in Hong Kong made significant progress in that direction by devising a way to significantly increase electron mobility." The team discovered that how electrons behave in the TMDs depends on whether an even or odd number of TMD layers were used. "This layer-dependent behavior is a very surprising finding," Zhang said. "It doesn't matter how many layers you have, but rather, whether there are an odd or even number of layers." Because the TMD materials operate on the scale of individual atoms and electrons, the researchers incorporated quantum physics into their theories and observations. Unlike classical physics, which describes the behavior of large-scale objects that we can see and touch, quantum physics governs the realm of very small particles, including electrons. On the size scale of everyday electrical devices, electrons flowing through wires behave like a stream of particles. In the quantum world, however, electrons behave like waves, and the electrical transverse conductance of the two-dimensional material in the presence of a magnetic field is no longer like a stream -- it changes in discrete steps, Zhang said. The phenomenon is called quantum Hall conductance. "Quantum Hall conductance might change one step by one step, or two steps by two steps, and so on," he said. "We found that if we used an even number of TMD layers in our device, there was a 12-step quantum conductance. If we applied a strong enough magnetic field to it, it would change by six steps at a time." Using an odd number of layers combined with a low magnetic field also resulted in a 6-step quantum Hall conductance in the TMDs, but under stronger magnetic fields, it became a 3-step by 3-step phenomenon. "The type of quantum Hall conductance we predicted and observed in our TMD devices has never been found in any other material," Zhang said. "These results not only decipher the intrinsic properties of TMD materials, but also demonstrate that we achieved high electron mobility in the devices. This gives us hope that we can one day use TMDs for transistors." The research was supported in part by the National Science Foundation, UT Dallas Research Enhancement Funds and UT Dallas Undergraduate Research Scholar Awards.


News Article | January 25, 2016
Site: phys.org

New research suggests that oscillating heavy particles generated "clocks" in the primordial universe that could be used to determine what produced the initial conditions that gave rise to the universe. Credit: Yi Wang and Xingang Chen How did the universe begin? And what came before the Big Bang? Cosmologists have asked these questions ever since discovering that our universe is expanding. The answers aren't easy to determine. The beginning of the cosmos is cloaked and hidden from the view of our most powerful telescopes. Yet observations we make today can give clues to the universe's origin. New research suggests a novel way of probing the beginning of space and time to determine which of the competing theories is correct. The most widely accepted theoretical scenario for the beginning of the universe is inflation, which predicts that the universe expanded at an exponential rate in the first fleeting fraction of a second. However a number of alternative scenarios have been suggested, some predicting a Big Crunch preceding the Big Bang. The trick is to find measurements that can distinguish between these scenarios. One promising source of information about the universe's beginning is the cosmic microwave background (CMB) - the remnant glow of the Big Bang that pervades all of space. This glow appears smooth and uniform at first, but upon closer inspection varies by small amounts. Those variations come from quantum fluctuations present at the birth of the universe that have been stretched as the universe expanded. The conventional approach to distinguish different scenarios searches for possible traces of gravitational waves, generated during the primordial universe, in the CMB. "Here we are proposing a new approach that could allow us to directly reveal the evolutionary history of the primordial universe from astrophysical signals. This history is unique to each scenario," says coauthor Xingang Chen of the Harvard-Smithsonian Center for Astrophysics (CfA) and the University of Texas at Dallas. While previous experimental and theoretical studies give clues to spatial variations in the primordial universe, they lack the key element of time. Without a ticking clock to measure the passage of time, the evolutionary history of the primordial universe can't be determined unambiguously. "Imagine you took the frames of a movie and stacked them all randomly on top of each other. If those frames aren't labeled with a time, you can't put them in order. Did the primordial universe crunch or bang? If you don't know whether the movie is running forward or in reverse, you can't tell the difference," explains Chen. This new research suggests that such "clocks" exist, and can be used to measure the passage of time at the universe's birth. These clocks take the form of heavy particles, which are an expected product of the "theory of everything" that will unite quantum mechanics and general relativity. They are named the "primordial standard clocks." Subatomic heavy particles will behave like a pendulum, oscillating back and forth in a universal and standard way. They can even do so quantum-mechanically without being pushed initially. Those oscillations or quantum wiggles would act as clock ticks, and add time labels to the stack of movie frames in our analogy. "Ticks of these primordial standard clocks would create corresponding wiggles in measurements of the cosmic microwave background, whose pattern is unique for each scenario," says coauthor Yi Wang of The Hong Kong University of Science and Technology. However, current data isn't accurate enough to spot such small variations. Ongoing experiments should greatly improve the situation. Projects like CfA's BICEP3 and Keck Array, and many other related experiments worldwide, will gather exquisitely precise CMB data at the same time as they are searching for gravitational waves. If the wiggles from the primordial standard clocks are strong enough, experiments should find them in the next decade. Supporting evidence could come from other lines of investigation, like maps of the large-scale structure of the universe including galaxies and cosmic hydrogen. And since the primordial standard clocks would be a component of the "theory of everything," finding them would also provide evidence for physics beyond the Standard Model at an energy scale inaccessible to colliders on the ground. This research is detailed in a paper by Xingang Chen and Mohammad Hossein Namjoo (CfA/UT Dallas) and Yi Wang (The Hong Kong University of Science and Technology). It has been accepted for publication in the Journal of Cosmology and Astroparticle Physics and is available online.


HONG KONG, Nov. 22, 2016 /PRNewswire/ -- Hong Kong Science and Technology Parks Corporation ("HKSTP") today staged a ground-breaking ceremony to mark the official beginning of the Hong Kong Science Park Expansion Programme. The expansion will see the addition of two purpose-built R&D-fit office buildings that will provide extra capacity to sustain the vibrant growth of the innovation and technology ("I&T") ecosystem in Hong Kong. The ground-breaking ceremony was officiated by the Hon C Y Leung, GBM, GBS, JP, the Chief Executive of the Hong Kong Special Administrative Region; the Hon Nicholas W. YANG, JP, the Secretary for Innovation and Technology; and the Hon Mrs Fanny Law, GBS, JP, HKSTP Chairperson. HKSTP received support from the HKSAR Government for the HK$4.4 billion expansion programme earlier this year. Under the programme, two buildings of 14 and 15 storeys will be built on a 1.18 hectare site west of Science Park Phase 3. The new towers are expected to provide an additional around 74,000 sqm or 22% more office space when completed in 2020. The Government's continuous investment in I&T infrastructure signifies a strong commitment to providing a favourable environment for a vibrant I&T ecosystem, which will benefit the society as a whole, with the industry in particular, in the long run. HKSTP's Chairperson the Hon Fanny Law, GBS, JP, said, "Today's groundbreaking ceremony marks the commencement of a new phase of development of the Science Park which is a testimony of the HKSAR government's commitment to the promotion of innovation and technology in Hong Kong. I am most grateful to the Government's unwavering support and the funding approval from the Legislative Council for Science Park's Expansion." "Thanks to our professional teams in HKSTP, we have an excellent track record of completing projects within budget and on time, and delivering high quality. The recently completed Phase 3 has achieved over 10% savings and won 10 prestigious building awards. I am sure my colleagues will keep up this record in the expansion programme," said Mrs Law. "Earlier this year, we celebrated the 15th anniversary of HKSTP. Given the encouraging progress over the past two years, I believe, if we continue on this path with the time-honored Hong Kong spirit and efficiency, and with all stakeholders working together in concert, Hong Kong would rank among the top 10 global start-up ecosystems, and be widely recognised as an innovation hub in Asia in future," added Mrs Law. HKSTP Chief Executive Officer Albert Wong said: "HKSTP's goal is to double the size of the start-up community in the Park and attract more leading overseas technology corporations to our ecosystem in the coming few years. Even as we are beginning the expansion of the Park's infrastructure, we already have many strategic initiatives in place to ensure our value-added services exceed the needs of all our stakeholders. We welcome local and international innovators to leverage the initiatives and facilities already in place at Science Park to ramp up their R&D work, and we endeavour to provide more of such tailor-designed support measures to fuel the growth of our ecosystem as our facilities expand." Ongoing development keeps Science Park in tune with evolving needs The Science Park, having completed its three-phase development on the 22 hectare site this year as planned, currently provides a total of 330,000 sqm office area in 21 office blocks. The three-phase development, spanning 15 years as per the original plan, enables Science Park to contribute significant economic benefits to Hong Kong annually through empowering the vibrant growth of the I&T sector. Catering to the growing needs of different forms of space to innovate, to inspire and be inspired through interacting with other creative minds in the ecosystem, HKSTP has introduced thematic collaborative work spaces within the Park such as the Robotics Garage and the Open Data Studio. Such developments show that Science Park will continue to be an organic being that will keep evolving in tune with the needs of the I&T ecosystem. The international achievements of the Science Park community also reflect the ongoing success of HKSTP's efforts -- Science Park incubatees and graduates have accumulatively registered 907 IPs and obtained a total of about HK$1,650 million in angel funding and venture capital investment, and they have received 436 local and international awards and recognitions as at the end of October 2016. Comprising Science Park, InnoCentre and Industrial Estates, Hong Kong Science & Technology Parks Corporation (HKSTP) is a statutory body dedicated to building a vibrant innovation and technology ecosystem to connect stakeholders, nurture technology talents, facilitate collaboration, and catalyse innovations to deliver social and economic benefits to Hong Kong and the region. Established in May 2001, HKSTP has been driving the development of Hong Kong into a regional hub for innovation and growth in several focused clusters including Electronics, Information & Communications Technology, Green Technology, Biomedical Technology, Materials and Precision Engineering. We enable science and technology companies to nurture ideas, innovate and grow, supported by our R&D facilities, infrastructure, and market-led laboratories and technical centres with professional support services. We also offer value added services and comprehensive incubation programmes for technology start-ups to accelerate their growth. Technology businesses benefit from our specialised services and infrastructure at Science Park for applied research and product development; enterprises can find creative design support at InnoCentre; while skill-intensive businesses are served by our three industrial estates at Tai Po, Tseung Kwan O and Yuen Long. More information about HKSTP is available at www.hkstp.org.


News Article | December 6, 2016
Site: www.nanotech-now.com

Home > Press > Physicists decipher electronic properties of materials in work that may change transistors Abstract: University of Texas at Dallas physicists have published new findings examining the electrical properties of materials that could be harnessed for next-generation transistors and electronics. Dr. Fan Zhang, assistant professor of physics, and senior physics student Armin Khamoshi recently published their research on transition metal dichalcogenides, or TMDs, in the journal Nature Communications. Zhang is a co-corresponding author, and Khamoshi is a co-lead author of the paper, which also includes collaborating scientists at Hong Kong University of Science and Technology. In recent years, scientists and engineers have become interested in TMDs in part because they are superior in many ways to graphene, a one-atom thick, two-dimensional sheet of carbon atoms arranged in a lattice. Since it was first isolated in 2004, graphene has been investigated for its potential to replace conventional semiconductors in transistors, shrinking them even further in size. Graphene is an exceptional conductor, a material in which electrons move easily, with high mobility. "It was thought that graphene could be used in transistors, but in transistors, you need to be able to switch the electric current on and off," Zhang said. "With graphene, however, the current cannot be easily switched off." Beyond Graphene In their search for alternatives, scientists and engineers have turned to TMDs, which also can be made into thin, two-dimensional sheets, or monolayers, just a few molecules thick. "TMDs have something graphene does not have -- an energy gap that allows the flow of electrons to be controlled, for the current to be switched on and off," Khamoshi said. "This gap makes TMDs ideal for use in transistors. TMDs are also very good absorbers of circularly polarized light, so they could be used in detectors. For these reasons, these materials have become a very popular topic of research." One of the challenges is to optimize and increase electron mobility in TMD materials, a key factor if they are to be developed for use in transistors, Khamoshi said. In their most recent project, Zhang and Khamoshi provided the theoretical work to guide the Hong Kong group on the layer-by-layer construction of a TMD device and on the use of magnetic fields to study how electrons travel through the device. Each monolayer of TMD is three molecules thick, and the layers were sandwiched between two sheets of boron nitride molecules. The behavior of electrons controls the behavior of these materials," Zhang said. "We want to make use of highly mobile electrons, but it is very challenging. Our collaborators in Hong Kong made significant progress in that direction by devising a way to significantly increase electron mobility." The team discovered that how electrons behave in the TMDs depends on whether an even or odd number of TMD layers were used. "This layer-dependent behavior is a very surprising finding," Zhang said. "It doesn't matter how many layers you have, but rather, whether there are an odd or even number of layers." Electron Physics Because the TMD materials operate on the scale of individual atoms and electrons, the researchers incorporated quantum physics into their theories and observations. Unlike classical physics, which describes the behavior of large-scale objects that we can see and touch, quantum physics governs the realm of very small particles, including electrons. On the size scale of everyday electrical devices, electrons flowing through wires behave like a stream of particles. In the quantum world, however, electrons behave like waves, and the electrical transverse conductance of the two-dimensional material in the presence of a magnetic field is no longer like a stream -- it changes in discrete steps, Zhang said. The phenomenon is called quantum Hall conductance. "Quantum Hall conductance might change one step by one step, or two steps by two steps, and so on," he said. "We found that if we used an even number of TMD layers in our device, there was a 12-step quantum conductance. If we applied a strong enough magnetic field to it, it would change by six steps at a time." Using an odd number of layers combined with a low magnetic field also resulted in a 6-step quantum Hall conductance in the TMDs, but under stronger magnetic fields, it became a 3-step by 3-step phenomenon. "The type of quantum Hall conductance we predicted and observed in our TMD devices has never been found in any other material," Zhang said. "These results not only decipher the intrinsic properties of TMD materials, but also demonstrate that we achieved high electron mobility in the devices. This gives us hope that we can one day use TMDs for transistors." ### The research was supported in part by the National Science Foundation, UT Dallas Research Enhancement Funds and UT Dallas Undergraduate Research Scholar Awards. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Tong Y.,Hong Kong University of Science and Technology | Chen L.,Hong Kong University of Science and Technology | Ding B.,University of Illinois at Urbana - Champaign
Proceedings - International Conference on Data Engineering | Year: 2012

In recent years, many new applications, such as sensor network monitoring and moving object search, show a growing amount of importance of uncertain data management and mining. In this paper, we study the problem of discovering threshold-based frequent closed item sets over probabilistic data. Frequent item set mining over probabilistic database has attracted much attention recently. However, existing solutions may lead an exponential number of results due to the downward closure property over probabilistic data. Moreover, it is hard to directly extend the successful experiences from mining exact data to a probabilistic environment due to the inherent uncertainty of data. Thus, in order to obtain a reasonable result set with small size, we study discovering frequent closed item sets over probabilistic data. We prove that even a sub-problem of this problem, computing the frequent closed probability of an item set, is #P-Hard. Therefore, we develop an efficient mining algorithm based on depth-first search strategy to obtain all probabilistic frequent closed item sets. To reduce the search space and avoid redundant computation, we further design several probabilistic pruning and bounding techniques. Finally, we verify the effectiveness and efficiency of the proposed methods through extensive experiments. © 2012 IEEE.


Hu R.,HKUST Shenzhen Research Institute | Hu R.,Hong Kong University of Science and Technology | Leung N.L.C.,Hong Kong University of Science and Technology | Tang B.Z.,HKUST Shenzhen Research Institute | And 2 more authors.
Chemical Society Reviews | Year: 2014

Macromolecules with aggregation-induced emission (AIE) attributes are a class of luminescent materials that display enhanced emission when they are aggregated. They have attracted much attention because of their good solubility, processability, high emission efficiency in the aggregated states, etc. A large variety of AIE macromolecules have been developed, showing exponential growth of research interest in this field. This review summarizes the design principles and recent synthetic advancements, topological structures, as well as the frontiers of functionalities and potential applications of AIE macromolecules, especially fluorescence sensing, biological applications and optoelectronic applications, with an emphasis on the recent progress. New luminogenic systems without conventional chromophores displaying aggregated state emission are discussed. The highly dense clusters of heteroatoms with lone pair electrons in these systems may serve as the chromophore and are cited as "heterodox clusters". It is expected that the mechanistic insights into the AIE phenomena, based on the restriction of intramolecular motions and structure rigidification, can guide the future design of AIE materials with fascinating structures and functionalities. © 2014 The Royal Society of Chemistry.


Hu B.,Hong Kong University of Science and Technology | Hu B.,HKUST Shenzhen Research Institute | Wang X.R.,Hong Kong University of Science and Technology | Wang X.R.,HKUST Shenzhen Research Institute
Physical Review Letters | Year: 2013

The stability of the well-known Walker propagating domain wall (DW) solution of the Landau-Lifshitz-Gilbert equation is analytically investigated. Surprisingly, a propagating DW is always dressed with spin waves so that the Walker rigid-body propagating DW mode does not occur in reality. In the low field region only stern spin waves are emitted while both stern and bow waves are generated under high fields. In a high enough field, but below the Walker breakdown field, the Walker solution could be convective or absolute unstable if the transverse magnetic anisotropy is larger than a critical value, corresponding to a significant modification of the DW profile and DW propagating speed. © 2013 American Physical Society.


Kleeberg C.,TU Braunschweig | Cheung M.S.,Hong Kong University of Science and Technology | Lin Z.,Hong Kong University of Science and Technology | Marder T.B.,Durham University
Journal of the American Chemical Society | Year: 2011

Reaction of [(IPr)Cu-OtBu] (1) with pinB-SiMe 2Ph (2) leads to the Cu-silyl complex [(IPr)Cu-SiMe 2Ph] (3). Insertion of CO 2 into the Cu-Si bond of 3 is followed by transformation of the resulting silanecarboxy complex [(IPr)Cu-O 2CSiMe 2Ph] (4) to the silanolate complex [(IPr)Cu-OSiMe 2Ph] (5) via extrusion of CO. As 5 reacts readily with 2 to regenerate 3, a catalytic CO 2 reduction to CO is feasible. The individual steps were studied by in situ 13C NMR spectroscopy of a series of stoichiometric reactions. Complexes 3, 4, and 5 were isolated and fully characterized, including single-crystal X-ray diffraction studies. Interestingly, the catalytic reduction of CO 2 using silylborane 2 as a stoichiometric reducing agent leads not only to CO and pinB-O-SiMe 2Ph but also to PhMe 2Si-CO 2-SiMe 2Ph as an additional reduction product. © 2011 American Chemical Society.


Gao L.,Shanghai JiaoTong University | Wang X.,Shanghai JiaoTong University | Xu Y.,Shanghai JiaoTong University | Zhang Q.,Hong Kong University of Science and Technology
IEEE Journal on Selected Areas in Communications | Year: 2011

Cognitive radio is a promising paradigm to achieve efficient utilization of spectrum resource by allowing the unlicensed users (i.e., secondary users, SUs) to access the licensed spectrum. Market-driven spectrum trading is an efficient way to achieve dynamic spectrum accessing/sharing. In this paper, we consider the problem of spectrum trading with single primary spectrum owner (or primary user, PO) selling his idle spectrum to multiple SUs. We model the trading process as a monopoly market, in which the PO acts as monopolist who sets the qualities and prices for the spectrum he sells, and the SUs act as consumers who choose the spectrum with appropriate quality and price for purchasing. We design a monopolist-dominated quality-price contract, which is offered by the PO and contains a set of quality-price combinations each intended for a consumer type. A contract is feasible if it is incentive compatible (IC) and individually rational (IR) for each SU to purchase the spectrum with the quality-price intended for his type. We propose the necessary and sufficient conditions for the contract to be feasible. We further derive the optimal contract, which is feasible and maximizes the utility of the PO, for both discrete-consumer-type model and continuous-consumer-type model. Moreover, we analyze the social surplus, i.e., the aggregate utility of both PO and SUs, and we find that, depending on the distribution of consumer types, the social surplus under the optimal contract may be less than or close to the maximum social surplus. © 2006 IEEE.


Zhang H.,Shandong University | Song X.,Shandong Normal University | Song X.,Shandong Provincial Key Laboratory for Novel Distributed Computer Software Technology | Shi L.,Hong Kong University of Science and Technology
IEEE Transactions on Automatic Control | Year: 2012

We consider remote state estimation over a packet-dropping network. A new suboptimal filter is derived by minimizing the mean squared estimation error. The estimator is designed by solving one deterministic Riccati equation. Convergence of the estimation error covariance and mean square stability of the estimator are proved under standard assumptions. It is shown that the new estimator has smaller error covariance and has wider applications when compared with the linear minimum mean squared error estimator. One of the key techniques adopted in this technical note is the introduction of the innovation sequence for the multiplicative noise systems. © 2012 IEEE.


Lu X.,Fudan University | Ba S.,University of Connecticut | Huang L.,Fudan University | Feng Y.,Hong Kong University of Science and Technology
Information Systems Research | Year: 2013

The value of promotional marketing and word-of-mouth (WOM) is well recognized, but few studies have compared the effects of these two types of information in online settings. This research examines the effect of marketing efforts and online WOM on product sales by measuring the effects of online coupons, sponsored keyword search, and online reviews. It aims to understand the relationship between firms' promotional marketing and WOM in the context of a third party review platform. Using a three-year panel data set from one of the biggest restaurant review websites in China, the study finds that both online promotional marketing and reviews have a significant impact on product sales, which suggests promotional marketing on third party review platforms is still an effective marketing tool. This research further explores the interaction effects between WOM and promotional marketing when these two types of information coexist. The results demonstrate a substitute relationship between the WOM volume and coupon offerings, but a complementary relationship between WOM volume and keyword advertising. © 2013 Informs.


Long Y.-Z.,Qingdao University | Yu M.,Hong Kong University of Science and Technology | Sun B.,Qingdao University | Gu C.-Z.,CAS Institute of Physics | Fan Z.,Hong Kong University of Science and Technology
Chemical Society Reviews | Year: 2012

Semiconducting inorganic nanowires (NWs), nanotubes and nanofibers have been extensively explored in recent years as potential building blocks for nanoscale electronics, optoelectronics, chemical/biological/optical sensing, and energy harvesting, storage and conversion, etc. Besides the top-down approaches such as conventional lithography technologies, nanowires are commonly grown by the bottom-up approaches such as solution growth, template-guided synthesis, and vapor-liquid-solid process at a relatively low cost. Superior performance has been demonstrated using nanowires devices. However, most of the nanowire devices are limited to the demonstration of single devices, an initial step toward nanoelectronic circuits, not adequate for production on a large scale at low cost. Controlled and uniform assembly of nanowires with high scalability is still one of the major bottleneck challenges towards the materials and device integration for electronics. In this review, we aim to present recent progress toward nanowire device assembly technologies, including flow-assisted alignment, Langmuir-Blodgett assembly, bubble-blown technique, electric/magnetic- field-directed assembly, contact/roll printing, planar growth, bridging method, and electrospinning, etc. And their applications in high-performance, flexible electronics, sensors, photovoltaics, bioelectronic interfaces and nano-resonators are also presented. © The Royal Society of Chemistry 2012.


Wu J.,Hong Kong University of Science and Technology | Jia Q.-S.,Tsinghua University | Johansson K.H.,KTH Royal Institute of Technology | Shi L.,Hong Kong University of Science and Technology
IEEE Transactions on Automatic Control | Year: 2013

We consider sensor data scheduling for remote state estimation. Due to constrained communication energy and bandwidth, a sensor needs to decide whether it should send the measurement to a remote estimator for further processing. We propose an event-based sensor data scheduler for linear systems and derive the corresponding minimum squared error estimator. By selecting an appropriate event-triggering threshold, we illustrate how to achieve a desired balance between the sensor-to-estimator communication rate and the estimation quality. Simulation examples are provided to demonstrate the theory. © 1963-2012 IEEE.


Wu P.Y.,ViXS Systems | Tsui S.Y.S.,Fujitsu Limited | Mok P.K.T.,Hong Kong University of Science and Technology
IEEE Journal of Solid-State Circuits | Year: 2010

Monolithic PWM voltage-mode buck converters with a novel Pseudo-Type III (PT3) compensation are presented. The proposed compensation maintains the fast load transient response of the conventional Type III compensator; while the Type III compensator response is synthesized by adding a high-gain low-frequency path (via error amplifier) with a moderate-gain high-frequency path (via bandpass filter) at the inputs of PWM comparator. As such, smaller passive components and low-power active circuits can be used to generate two zeros required in a Type III compensator. Constant Gm/C biasing technique can also be adopted by PT3 to reduce the process variation of passive components, which is not possible in a conventional Type III design. Two prototype chips are fabricated in a 0.35-μm CMOS process with constant G m/C biasing technique being applied to one of the designs. Measurement result shows that converter output is settled within 7 μs for a load current step of 500 mA. Peak efficiency of 97% is obtained at 360 mW output power, and high efficiency of 86% is measured for output power as low as 60 mW. The area and power consumption of proposed compensator is reduced by > 75% in both designs, compared to an equivalent conventional Type III compensator.© 2006 IEEE.


Peng Y.,Hong Kong University of Science and Technology | Wang F.,Hong Kong University of Science and Technology | Wang Z.,Hong Kong University of Science and Technology | Alsayed A.M.,Solvay Group | And 4 more authors.
Nature Materials | Year: 2015

The microscopic kinetics of ubiquitous solid-solid phase transitions remain poorly understood. Here, by using single-particle-resolution video microscopy of colloidal films of diameter-tunable microspheres, we show that transitions between square and triangular lattices occur via a two-step diffusive nucleation pathway involving liquid nuclei. The nucleation pathway is favoured over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases. We also observed that nucleation precursors are particle-swapping loops rather than newly generated structural defects, and that coherent and incoherent facets of the evolving nuclei exhibit different energies and growth rates that can markedly alter the nucleation kinetics. Our findings suggest that an intermediate liquid should exist in the nucleation processes of solid-solid transitions of most metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid-solid transition theory.


Atzeni I.,Polytechnic University of Catalonia | Ordonez L.G.,Polytechnic University of Catalonia | Scutari G.,State University of New York at Buffalo | Palomar D.P.,Hong Kong University of Science and Technology | Fonollosa J.R.,Polytechnic University of Catalonia
IEEE Transactions on Smart Grid | Year: 2013

Demand-side management, together with the integration of distributed energy generation and storage, are considered increasingly essential elements for implementing the smart grid concept and balancing massive energy production from renewable sources. We focus on a smart grid in which the demand-side comprises traditional users as well as users owning some kind of distributed energy sources and/or energy storage devices. By means of a day-ahead optimization process regulated by an independent central unit, the latter users intend to reduce their monetary energy expense by producing or storing energy rather than just purchasing their energy needs from the grid. In this paper, we formulate the resulting grid optimization problem as a noncooperative game and analyze the existence of optimal strategies. Furthermore, we present a distributed algorithm to be run on the users' smart meters, which provides the optimal production and/or storage strategies, while preserving the privacy of the users and minimizing the required signaling with the central unit. Finally, the proposed day-ahead optimization is tested in a realistic situation. © 2010-2012 IEEE.


HONG KONG, Dec. 21, 2016 /PRNewswire/ -- Hong Kong Science and Technology Parks Corporation ("HKSTP") and Guangzhou Institutes of Biomedicine and Health ("GIBH") cohosted the second Hong Kong and Guangzhou International Conference on Stem Cell & Regenerative Medicine on December 16. During this high-profile event which was attended by HKSAR Chief Executive The Hon CY Leung and a number of major government officials, the Chinese Academy of Science ("CAS"), a research and development authority in Mainland China, announced the setting up of the Guangzhou Hong Kong Stem Cell and Regenerative Medicine Research Centre at Hong Kong Science Park ("HKSP"), under the auspices of its subsidiary GIBH. Remarking on this significant initiative, The Hon. Fanny Law, GBS, JP, Chairperson of HKSTP, said: "We see opportunities for Hong Kong to evolve into a cell therapy centre, capitalising on Hong Kong's world-class medical system, and credible clinical trial centres with data accepted by FDA, EMA as well as CFDA, which is unique to Hong Kong." "Our ambition is to grow an industry in advanced therapy medicinal products, leveraging on the complementary strengths of Hong Kong, Guangzhou and Shenzhen, to form a leading 'Cell Therapy Valley' where the latest technologies are being developed, tested and implemented for the benefit of ethnic Chinese patients who suffer from existing incurable diseases," Mrs Law said. Prof Bai Chunli, President of CAS, said that the proposed research centre "will create the environment for stakeholders to make connections, share information and tap into each other's academic resources for the benefits of the world", and the centre has the potential to mature into a platform that will "strengthen existing partnerships, maximise innovation capacities and reinforce strategic co-operations of the science and technology communities between China and Hong Kong". GIBH is yet another world-renowned biomedicine research authority to set up its base in HKSP, after Karolinska Institutet, which opened the Hong Kong node of its dedicated regenerative medicine facility, the Ming Wai Lau Centre for Reparative Medicine, at HKSP in October 2016. HKSP is also home to 14 other stem cell and cell therapy companies from around the world. At the conference, expert speakers shared their latest research discoveries and insights in stem cell therapy for liver fibrosis, cell therapy for diabetes, and epigenetic fingerprinting and tissue engineering that facilitate pre-clinical drug discovery for Alzheimer's disease, reaffirming stem cell therapy holds great promise in curing debilitating diseases such as Parkinson's, Alzheimer's, spinal cord injury, diabetes and stroke and presenting great potentials for researchers in the field. As HKSTP is stepping up its effort to develop HKSP and Hong Kong as the ideal R&D base and hub for stem cell research and regenerative medicine, Mrs Law pointed out at the conference that a set of clear regulatory guidelines that facilitates clinical translation of advanced cell therapies while safeguarding the interests of patients is fundamental for realising this vision. World stem cell experts from the US, the UK, Mainland China, Europe and Australia attending the Stem Cell Conference joined Hong Kong colleagues in a pre-event round-table discussion to recommend the way forward for the regulatory environment in Hong Kong, referencing the regulatory structures in other countries. Group convenor Prof Marc Turner, who is the Medical Director of Scottish National Blood Transfusion Service, reported at the conference that the group suggested a single stream of legislation covering supply of starting materials, manufacture, administration and follow up. "Since Hong Kong has a relatively clear space, our advice would be to join up tissue and cell legislation with cellular therapy and advanced therapy legislation all in one piece, to be consistent. That would be the most coherent way to do it, therefore in the longer term it will be the most efficient," he said. HKSTP Chief Executive Officer Mr Albert Wong said: "HKSTP has established a strong rapport with the global biomedical community. This is apparent in the sterling speaker lineup of our Stem Cell Conference. Stem cell R&D is a key pillar for supporting healthy ageing, which is one of the key priorities of HKSTP. We will redouble efforts in building the cell therapy ecosystem in Science Park and help the community excel and develop, so that we can ride on the global momentum of stem cell R&D to move forward in the advanced therapy value chain, as Hong Kong endeavours to develop an appropriate regulatory environment for this field." Comprising Science Park, InnoCentre and Industrial Estates, Hong Kong Science & Technology Parks Corporation (HKSTP) is a statutory body dedicated to building a vibrant innovation and technology ecosystem to connect stakeholders, nurture technology talents, facilitate collaboration, and catalyse innovations to deliver social and economic benefits to Hong Kong and the region. Established in May 2001, HKSTP has been driving the development of Hong Kong into a regional hub for innovation and growth in several focused clusters including Electronics, Information & Communications Technology, Green Technology, Biomedical Technology, Materials and Precision Engineering. We enable science and technology companies to nurture ideas, innovate and grow, supported by our R&D facilities, infrastructure, and market-led laboratories and technical centres with professional support services. We also offer value added services and comprehensive incubation programmes for technology start-ups to accelerate their growth. Technology businesses benefit from our specialised services and infrastructure at Science Park for applied research and product development; enterprises can find creative design support at InnoCentre; while skill-intensive businesses are served by our three industrial estates at Tai Po, Tseung Kwan O and Yuen Long. More information about HKSTP is available at www.hkstp.org.


News Article | November 11, 2016
Site: www.acnnewswire.com

Exploring New Business Opportunities Under the Belt and Road A Hong Kong business delegation visited the Iranian capital Tehran this week to explore new business opportunities arising from the Belt and Road Initiative. It is the city's first official delegation since the United Nations lifted sanctions against Iran in January this year. Financial Secretary of the Hong Kong Special Administrative Region (HKSAR) John Tsang led more than 30 business leaders from finance, information and communications technology, infrastructure and real estate services and logistics sectors to Iran from 7 to 10 November. The delegation was jointly organised by the HKSAR Government and the Hong Kong Trade Development Council (HKTDC). Among them were Vice Chairman and Chief Executive of Bank of China (Hong Kong) Limited Yue Yi, Executive Director of China State Construction International Holdings Limited Danny Hung, Chairman of Airport Authority Hong Kong Jack So and the President of the Hong Kong University of Science and Technology Professor Tony Chan. Forum promotes business ties Speaking to more than 300 Iranian business leaders at the Iran-Hong Kong Business Cooperation Forum, HKTDC Executive Director Margaret Fong noted that Iran is a key player in China's Belt and Road Initiative. "Iran gives us a vivid example of the Belt and Road Initiative in action, including the rail link between Tehran and Yiwu in China's Zhejiang province. A new Silk Road Railway is also planned from Urumqi to Tehran." She added that Hong Kong is part of the Initiative, "providing professional and financial services that are crucial to integrating business along the routes of the Silk Road Economic Belt and the Maritime Silk Road." Ms Fong called on the business community in Iran to join the next Belt and Road Summit in Hong Kong on 11 September 2017 to explore more opportunities with their Hong Kong counterparts. Other speakers at the Forum included Financial Secretary Mr Tsang, Iran's Minister of Economic Affairs and Finances HE Mr Tayyebnia Ali, Director of Foreign Investment Department of Organisation for Investment Economic & Technical Assistance of Iran (OIETAI) Jamali Ahmad, President of Iran Chamber of Commerce and Industries (ICCI) Asadollah Asgaroladi and President of Iran Chamber of Commerce, Industries and Mines Association (ICCIMA) Gholamhossein Shafei. Hong Kong- Iran trade links Iran is Hong Kong's sixth-largest export market in the Middle East. In the first nine months of 2016, Hong Kong's exports to Iran stood at US$107 million, representing a 16.6 per cent year-on-year increase. Major products include telecommunication equipment and parts, civil engineering and contractors' plant and equipment, miscellaneous chemical products, electrical apparatus for electrical circuits as well as measuring, checking, analysing & controlling instruments & apparatus. Photo Download: http://bit.ly/2g2fEeI To view press releases in Chinese, please visit http://mediaroom.hktdc.com/tc About HKTDC Established in 1966, the Hong Kong Trade Development Council (HKTDC) is a statutory body dedicated to creating opportunities for Hong Kong's businesses. With more than 40 offices globally, including 13 on the Chinese mainland, the HKTDC promotes Hong Kong as a platform for doing business with China, Asia and the world. With 50 years of experience, the HKTDC organises international exhibitions, conferences and business missions to provide companies, particularly SMEs, with business opportunities on the mainland and in international markets, while providing information via trade publications, research reports and digital channels including the media room. For more information, please visit: www.hktdc.com/aboutus. Follow us on Google+, Twitter @hktdc, LinkedIn. Google+: https://plus.google.com/+hktdc Twitter: http://www.twitter.com/hktdc LinkedIn: http://www.linkedin.com/company/hong-kong-trade-development-council Contact:


Xiao J.,Hong Kong University of Science and Technology | Yang S.,Hong Kong University of Science and Technology
Journal of Materials Chemistry | Year: 2012

A bio-inspired approach has enabled the first synthesis of Co xNi 1-xO (0 ≤ x < 1) nanorods on reduced graphene oxide (RGO) sheets. The key is the crystallization process from amorphous precursors in a disordered and hydrated state being able to take compositions arbitrarily different from that of the known stable mixed oxide NiCo 2O 4. This success has permitted further screening of the compositions for electrochemical capacitors. Co xNi 1-xO/RGO nanocomposite electrodes achieve a peak specific capacitance when the Co/Ni molar ratio is close to 1. For example, Co 0.45Ni 0.55O/RGO nanocomposite electrode has exhibited a specific capacitance up to 823.0 F g -1 (based on the total active materials mass) and 909.4 F g -1 (based on the oxide mass) at 1 A g -1, which are among the highest for Co/Ni oxides. Also revealed was their superior cycling stability compared to the Co 3O 4/RGO and NiO/RGO nanocomposites, with a surprising increase of the specific capacity in the initial 100 cycles before flattening out. In addition, testing of (Co 0.45Ni 0.55O/RGO)//RGO asymmetric cells yielded an energy density up to 35.3 Wh kg -1 at a cell voltage of 1.5 V, much higher than those of the symmetric cells (Co 0.45Ni 0.55O/RGO)//(Co 0.45Ni 0.55O/RGO) (20.2 Wh kg -1) and RGO//RGO (4.5 Wh kg -1). Even at a high power density of 3614.0 W kg -1, the asymmetric cell could still maintain an energy density of 28.0 Wh kg -1. There was only a <4% loss of the initial specific capacitance after 1000 cycles of charge/discharge at 2 A g -1. © 2012 The Royal Society of Chemistry.


Gan J.,Hong Kong University of Science and Technology | Ho H.S.,Hong Kong University of Science and Technology | Liang L.,Hong Kong University of Science and Technology
Journal of Physical Oceanography | Year: 2013

This study reveals the dynamics behind the intensified, downslope, cross-isobath transport over a widened shelf (narrowing downwave) in the northeastern South China Sea (NSCS) during a downwelling event. Utilizing a three-dimensional numerical model over an idealized NSCS shelf, this study identified the forcing process and derived an analytical understanding of the invoked dynamics for the intensified downslope crossisobath transport. This study found that the transport was formed by an amplified geostrophic transport because of an increased positive along-isobath pressure gradient force (PGF), PY and by an enhanced bottom Ekman transport due to converging flow over the widened shelf. Based on the depth-integrated vorticity dynamics, PY was linked with net frictional stress curl in the water column and the curl was primarily associated with the shear vorticity field induced by downwelling jet. The increased positive vorticity seaside of the jet provided positive PY for the downslope geostrophic transport. The cross-isobath PGF, PX which was geostrophically formed and shaped by the spatially asymmetric isobaths of the widened shelf, determined the intensities of the jet and thus the associated shear vorticity that quantified the respective bottom friction transport and PY for the intensified cross-isobath transport. It was found that the downslope transport over the widened shelf was strengthened in a stratified flow by the linked intensifications of barotropic PX or the concurrent downwelling jet, shear vorticity field, PY and bottom friction because of an increase of volume flux upstream of the widened shelf. © 2013 American Meteorological Society.


Lin F.,Hong Kong University of Science and Technology | Zhou Y.,University of Western Sydney
Artificial Intelligence | Year: 2011

We first embed Pearce's equilibrium logic and Ferraris's propositional general logic programs in Lin and Shoham's logic of GK, a nonmonotonic modal logic that has been shown to include as special cases both Reiter's default logic in the propositional case and Moore's autoepistemic logic. From this embedding, we obtain a mapping from Ferraris's propositional general logic programs to circumscription, and show that this mapping can be used to check the strong equivalence between two propositional logic programs in classical logic. We also show that Ferraris's propositional general logic programs can be extended to the first-order case, and our mapping from Ferraris's propositional general logic programs to circumscription can be extended to the first-order case as well to provide a semantics for these first-order general logic programs. © 2010 Elsevier B.V. All rights reserved.


Lau A.S.M.,Hong Kong University of Science and Technology
Journal of Medical Internet Research | Year: 2011

Background: Web 2.0 provides a platform or a set of tools such as blogs, wikis, really simple syndication (RSS), podcasts, tags, social bookmarks, and social networking software for knowledge sharing, learning, social interaction, and the production of collective intelligence in a virtual environment. Web 2.0 is also becoming increasingly popular in e-learning and e-social communities. Objectives: The objectives were to investigate how Web 2.0 tools can be applied for knowledge sharing, learning, social interaction, and the production of collective intelligence in the nursing domain and to investigate what behavioral perceptions are involved in the adoption of Web 2.0 tools by nurses. Methods: The decomposed technology acceptance model was applied to construct the research model on which the hypotheses were based. A questionnaire was developed based on the model and data from nurses (n = 388) were collected from late January 2009 until April 30, 2009. Pearson's correlation analysis and t tests were used for data analysis. Results: Intention toward using Web 2.0 tools was positively correlated with usage behavior (r = .60, P < .05). Behavioral intention was positively correlated with attitude (r = .72, P < .05), perceived behavioral control (r = .58, P < .05), and subjective norm (r = .45, P < .05). In their decomposed constructs, perceived usefulness (r = .7, P < .05), relative advantage (r = .64, P < .05), and compatibility (r = .60,P < .05) were positively correlated with attitude, but perceived ease of use was not significantly correlated (r = .004, P < .05) with it. Peer (r = .47, P < .05), senior management (r = .24,P < .05), and hospital (r = .45, P < .05) influences had positive correlations with subjective norm. Resource (r= .41,P< .05) and technological (r= .69,P< .05) conditions were positively correlated with perceived behavioral control. Conclusions: The identified behavioral perceptions may further health policy makers' understanding of nurses' concerns regarding and barriers to the adoption of Web 2.0 tools and enable them to better plan the strategy of implementation of Web 2.0 tools for knowledge sharing, learning, social interaction, and the production of collective intelligence. © Adela S.M. Lau.


Xie F.X.,University of Hong Kong | Zhang D.,University of Hong Kong | Su H.,Hong Kong University of Science and Technology | Ren X.,University of Hong Kong | And 3 more authors.
ACS Nano | Year: 2015

Solar cells incorporating lead halide-based perovskite absorbers can exhibit impressive power conversion efficiencies (PCEs), recently surpassing 15%. Despite rapid developments, achieving precise control over the morphologies of the perovskite films (minimizing pore formation) and enhanced stability and reproducibility of the devices remain challenging, both of which are necessary for further advancements. Here we demonstrate vacuum-assisted thermal annealing as an effective means for controlling the composition and morphology of the CH3NH3PbI3 films formed from the precursors of PbCl2 and CH3NH3I. We identify the critical role played by the byproduct of CH3NH3Cl on the formation and the photovoltaic performance of the perovskite film. By completely removing the byproduct through our vacuum-assisted thermal annealing approach, we are able to produce pure, pore-free planar CH3NH3PbI3 films with high PCE reaching 14.5% in solar cell device. Importantly, the removal of CH3NH3Cl significantly improves the device stability and reproducibility with a standard deviation of only 0.92% in PCE as well as strongly reducing the photocurrent hysteresis. © 2014 American Chemical Society.


Li J.,Hong Kong University of Science and Technology
IEEE Transactions on Engineering Management | Year: 2010

A learning perspective was applied to examining when multinational corporations select universities rather than local firms as partners in international RD alliances. Data were collected on 327 international RD alliances established over the 1995 - 2001 period in China, an emerging economy where intellectual property rights protection is still far from adequate, over the 19952001 period. The effects of factors such as the international investors host country RD experience and the ventures research objectives on the selection of universities or research institutes as local partners for RD alliances were analyzed. Analysis using logistic regression models suggests that the contribution of local universities and research institutes to such RD collaborations is likely to be high when foreign investors have had abundant prior RD experience in the host country and when the alliance has been established primarily for research rather than development purposes. The implications for theory, practice, and policymaking are discussed. © 2009 IEEE.


Lau A.K.W.,Hong Kong University of Science and Technology | Tang E.,Hong Kong Polytechnic University | Yam R.C.M.,City University of Hong Kong
Journal of Product Innovation Management | Year: 2010

While the beneficial impacts of supplier and customer integration are generally acknowledged, very few empirical research studies have examined how an organization can achieve better product performance through product innovation enhanced by such integration. This paper thus examines the impact of key supplier and customer integration processes (i.e., information sharing and product codevelopment with supplier and customer, respectively) on product innovation as well as their impact on product performance. It contributes to existing literature by asking how such integration activities affect product innovation and performance in both direct and indirect ways. After surveying 251 manufacturers in Hong Kong, this study tested the relationships among information sharing, product codevelopment, product innovativeness, and performance with three control variables (i.e., company size, type of industry, and market certainty). Structural equation modeling with correlation and t-tests was used to test the hypothesized research model. The findings indicate a direct, positive relationship between supplier and customer integration and product performance. In particular, this study verifies that sharing information with suppliers and product codevelopment with customers directly improves product performance. In addition, this study empirically examines the indirect effects of supplier and customer integration processes on product performance, mediated by innovation. This has seldom been attempted in previous research. The empirical findings show that product codevelopment with suppliers improves performance, mediated by innovation. However, the sampled firms cannot improve their product innovation by sharing information with their current customers and suppliers as well as codeveloping new products with the customers. If the adoption of supplier and customer integration is not cost free, the findings of this study may suggest firms work on particular supplier and customer integration processes (i.e., product codevelopment with suppliers) to improve their product innovation. The study also suggests that companies codevelop new products only with new customers and lead users instead of current ones for product innovation. For managers, this study has demonstrated that both information sharing and product codevelopment affect performance directly and indirectly. Managers should put more emphasis on these key processes, especially when linked with product innovation. Managers should consider involving their suppliers and customers in the early stages of design. Information sharing with suppliers is also important in product development. As suggested by this study, extensive effort on supplier and customer integration should be made to directly augment current product performance and product innovation at the same time. © 2010 Product Development & Management Association.


Hou Y.,Hong Kong University of Science and Technology | Yu M.,Hong Kong University of Science and Technology | Chen X.,City University of Hong Kong | Wang Z.,City University of Hong Kong | Yao S.,Hong Kong University of Science and Technology
ACS Nano | Year: 2015

Vapor condensation plays a key role in a wide range of industrial applications including power generation, thermal management, water harvesting and desalination. Fast droplet nucleation and efficient droplet departure as well as low interfacial thermal resistance are important factors that determine the thermal performances of condensation; however, these properties have conflicting requirements on the structural roughness and surface chemistry of the condensing surface or condensation modes (e.g., filmwise vs dropwise). Despite intensive efforts over the past few decades, almost all studies have focused on the dropwise condensation enabled by superhydrophobic surfaces. In this work, we report the development of a bioinspired hybrid surface with high wetting contrast that allows for seamless integration of filmwise and dropwise condensation modes. We show that the synergistic cooperation in the observed recurrent condensation modes leads to improvements in all aspects of heat transfer properties including droplet nucleation density, growth rate, and self-removal, as well as overall heat transfer coefficient. Moreover, we propose an analytical model to optimize the surface morphological features for dramatic heat transfer enhancement. © 2014 American Chemical Society.


Wang Q.,Hong Kong University of Science and Technology | Du X.,Northwest Normal University
IEEE Transactions on Information Theory | Year: 2010

Binary sequences with optimal autocorrelation are needed in many applications. Two constructions of binary sequences with optimal autocorrelation of period N ≡ 0 (mod 4) are investigated. The two constructions are powerful and generic in the sense that many classes of binary sequences with optimal autocorrelation could be obtained from binary sequences with ideal autocorrelation. General results on the minimal polynomials of these binary sequences are derived. Based on the results, both the linear complexities and the minimal polynomials are determined. © 2006 IEEE.


Leung S.,Hong Kong University of Science and Technology | Qian J.,Michigan State University
Journal of Computational Physics | Year: 2010

We propose the backward phase flow method to implement the Fourier-Bros-Iagolnitzer (FBI)-transform-based Eulerian Gaussian beam method for solving the Schrödinger equation in the semi-classical regime. The idea of Eulerian Gaussian beams has been first proposed in [12]. In this paper we aim at two crucial computational issues of the Eulerian Gaussian beam method: how to carry out long-time beam propagation and how to compute beam ingredients rapidly in phase space. By virtue of the FBI transform, we address the first issue by introducing the reinitialization strategy into the Eulerian Gaussian beam framework. Essentially we reinitialize beam propagation by applying the FBI transform to wavefields at intermediate time steps when the beams become too wide. To address the second issue, inspired by the original phase flow method, we propose the backward phase flow method which allows us to compute beam ingredients rapidly. Numerical examples demonstrate the efficiency and accuracy of the proposed algorithms. © 2010 Elsevier Inc.


Cai H.,Hong Kong University of Science and Technology | Poon A.W.,Hong Kong University of Science and Technology
Optics Letters | Year: 2010

We demonstrate optical manipulation and transport of 1 μm sized polystyrene particles on silicon nitride microringresonator-based add-drop devices in an integrated optofluidic chip. By tuning the input laser wavelength and upon certain resonance quality factors, we observe microparticles (i) transported to the throughput port, (ii) routed to the microring and trapped in round trips, and (iii) transported to the drop port. We investigate the microparticle velocity at various laser wavelengths and in various spatial regions of the devices with different resonance quality factors. Such a device can act as a particle add-drop filter for "particle circuits" in lab-on-a-chip applications. © 2010 Optical Society of America.


Leung K.W.-T.,Hong Kong University of Science and Technology | Lee D.L.,Hong Kong University of Science and Technology
IEEE Transactions on Knowledge and Data Engineering | Year: 2010

User profiling is a fundamental component of any personalization applications. Most existing user profiling strategies are based on objects that users are interested in (i.e., positive preferences), but not the objects that users dislike (i.e., negative preferences). In this paper, we focus on search engine personalization and develop several concept-based user profiling methods that are based on both positive and negative preferences. We evaluate the proposed methods against our previously proposed personalized query clustering method. Experimental results show that profiles which capture and utilize both of the user's positive and negative preferences perform the best. An important result from the experiments is that profiles with negative preferences can increase the separation between similar and dissimilar queries. The separation provides a clear threshold for an agglomerative clustering algorithm to terminate and improve the overall quality of the resulting query clusters. © 2010 IEEE.


Lian X.,Hong Kong University of Science and Technology | Chen L.,Hong Kong University of Science and Technology
Proceedings of the VLDB Endowment | Year: 2010

Set similarity join has played an important role in many real-world applications such as data cleaning, near duplication detection, data integration, and so on. In these applications, set data often contain noises and are thus uncertain and imprecise. In this paper, we model such probabilistic set data on two uncertainty levels, that is, set and element levels. Based on them, we investigate the problem of probabilistic set similarity join (PS 2J) over two probabilistic set databases, under the possible worlds semantics. To efficiently process the PS 2J operator, we first reduce our problem by condensing the possible worlds, and then propose effective pruning techniques, including Jaccard distance pruning, probability upper bound pruning, and aggregate pruning, which can filter out false alarms of probabilistic set pairs, with the help of indexes and our designed synopses. We demonstrate through extensive experiments the PS 2J processing performance on both real and synthetic data. © 2010 VLDB Endowment.


Ding C.,Hong Kong University of Science and Technology | Yang Y.,Southwest Jiaotong University | Tang X.,Southwest Jiaotong University
IEEE Transactions on Information Theory | Year: 2010

In communication systems, frequency hopping spread spectrum and direct sequence spread spectrum are two main spread coding technologies. Frequency hopping sequences are used in FH-CDMA systems. In this paper, an earlier idea of constructing optimal sets of frequency hopping sequences is further investigated. New optimal parameters of sets of frequency hopping sequences are obtained with subcodes of the ReedSolomon codes. Optimal sets of frequency hopping sequences are constructed with a class of irreducible cyclic codes. As a byproduct, the weight distribution of a subclass of irreducible cyclic codes is determined. © 2006 IEEE.


Li W.-J.,Hong Kong University of Science and Technology | Yeung D.Y.,Hong Kong University of Science and Technology
IEEE Transactions on Knowledge and Data Engineering | Year: 2010

In multiple-instance learning (MIL), an individual example is called an instance and a bag contains a single or multiple instances. The class labels available in the training set are associated with bags rather than instances. A bag is labeled positive if at least one of its instances is positive; otherwise, the bag is labeled negative. Since a positive bag may contain some negative instances in addition to one or more positive instances, the true labels for the instances in a positive bag may or may not be the same as the corresponding bag label and, consequently, the instance labels are inherently ambiguous. In this paper, we propose a very efficient and robust MIL method, called Multiple-Instance Learning via Disambiguation (MILD), for general MIL problems. First, we propose a novel disambiguation method to identify the true positive instances in the positive bags. Second, we propose two feature representation schemes, one for instance-level classification and the other for bag-level classification, to convert the MIL problem into a standard single-instance learning (SIL) problem that can be solved by well-known SIL algorithms, such as support vector machine. Third, an inductive semi-supervised learning method is proposed for MIL. We evaluate our methods extensively on several challenging MIL applications to demonstrate their promising efficiency, robustness, and accuracy. © 2006 IEEE.


He Z.,Hong Kong University of Science and Technology | Chung A.C.S.,Hong Kong University of Science and Technology
International Journal of Computer Vision | Year: 2010

Extracting reliable image edge information is crucial for active contour models as well as vascular segmentation in magnetic resonance angiography (MRA). However, conventional edge detection techniques, such as gradient-based methods and wavelet-based methods, are incapable of returning reliable detection responses from low contrast edges in the images. In this paper, we propose a novel edge detection method by combining B-spline wavelet magnitude with standard deviation inside local region. It is proved theoretically and demonstrated experimentally in this paper that the new edge detection method, namely BWLSD, is able to give consistent and reliable strengths for edges with different image contrasts. Moreover, the relationship between the size of local region with non-zero wavelet magnitudes and the scale of wavelet function is established. This relationship indicates that if the scale of the adopted wavelet function is s, then the size of a local region, from which the standard deviation is estimated, should be 2s-1. The proposed edge detection technique is embedded in FLUX, namely, BWLSD-FLUX, for vascular segmentation in MRA image volumes. Experimental results on clinical images show that, as compared with the conventional FLUX, BWLSD-FLUX can achieve better segmentations of vasculatures in MRA images under same initial conditions. © 2009 Springer Science+Business Media, LLC.


Zheng Y.,Hong Kong University of Science and Technology | Tai C.-L.,Hong Kong University of Science and Technology
Computer Graphics Forum | Year: 2010

We present a new intuitive UI, which we call cross-boundary brushes, for interactive mesh decomposition. The user roughly draws one or more strokes across a desired cut and our system automatically returns a best cut running through all the strokes. By the different natures of part components (i.e., semantic parts) and patch components (i.e., flatter surface patches) in general models, we design two corresponding brushes: part-brush and patch-brush. These two types of brushes share a common user interface, enabling easy switch between them. The part-brush executes a cut along an isoline of a harmonic field driven by the user-specified strokes. We show that the inherent smoothness of the harmonic field together with a carefully designed isoline selection scheme lead to segmentation results that are insensitive to noise, pose, tessellation and variation in user's strokes. Our patch-brush uses a novel facet-based surface metric that alleviates sensitivity to noise and fine details common in region-growing algorithms. Extensive experimental results demonstrate that our cutting tools can produce user-desired segmentations for a wide variety of models even with single strokes. We also show that our tools outperform the state-of-art interactive segmentation tools in terms of ease of use and segmentation quality. © 2010 The Eurographics Association and Blackwell Publishing Ltd.


Ding C.,Hong Kong University of Science and Technology | Tang X.,Southwest Jiaotong University
IEEE Transactions on Information Theory | Year: 2010

Binary sequences with low correlation have applications in communication systems and cryptography. Though binary sequences with optimal autocorrelation were constructed in the literature, no pair of binary sequences with optimal autocorrelation are known to have also best possible cross correlation. In this paper, new bounds on the cross correlation of binary sequences with optimal autocorrelation are derived, and pairs of binary sequences having optimal autocorrelation and meeting some of these bounds are presented. These new bounds are better than the Sarwate bounds on the cross correlation of binary sequences with optimal autocorrelation. © 2006 IEEE.


Lee K.A.W.,Hong Kong University of Science and Technology
Advances in Experimental Medicine and Biology | Year: 2012

Interactions between Intrinsically Disordered Protein Regions (IDRs) and their targets commonly exhibit localised contacts via target-induced disorder to order transitions. Other more complex IDR target interactions have been termed "fuzzy" because the IDR does not form a well-defined induced structure. In some remarkable cases of fuzziness IDR function is apparently sequence independent and conferred by amino acid composition. Such cases have been referred to as "random fuzziness" but the molecular features involved are poorly characterised. The transcriptional activation domain (EAD) of oncogenic Ewing's Sarcoma Fusion Proteins (EFPs) is an ≈280 residue IDR with a biased composition restricted to Ala, Gly, Gln, Pro, Ser, Thr and Tyr. Multiple aromatic side chains (exclusively from Try residues) and the particular EAD composition are crucial for molecular recognition but there appears to be no other major geometrically constrained requirement. Computational analysis of the EAD using PONDR (Molecular Kinetics, Inc. http://www.pondr. com) complements the functional data and shows, accordingly, that propensity for structural order within the EAD is conferred by Tyr residues. To conclude, molecular recognition by the EAD is extraordinarily malleable and involves multiple aromatic contacts facilitated by a flexible peptide backbone and, most likely, a limited number of weaker contributions from amenable side chains. I propose to refer to this mode of fuzzy recognition as "polyaromatic", noting that it shares some fundamental features with the "polyelectrostatic" (phosphorylation-dependent) interaction of the Sic1 Cdk inhibitor and Cdc4.-I will also speculate on more detailed models for molecular recognition by the EAD and their relationship to native (non-oncogenic) EAD function. © 2012 Landes Bioscience and Springer Science+Business Media.


Zhang K.,Lawrence Berkeley National Laboratory | Kwok J.T.,Hong Kong University of Science and Technology
IEEE Transactions on Neural Networks | Year: 2010

The finite mixture model is widely used in various statistical learning problems. However, the model obtained may contain a large number of components, making it inefficient in practical applications. In this paper, we propose to simplify the mixture model by minimizing an upper bound of the approximation error between the original and the simplified model, under the use of the L 2 distance measure. This is achieved by first grouping similar components together and then performing local fitting through function approximation. The simplified model obtained can then be used as a replacement of the original model to speed up various algorithms involving mixture models during training (e.g., Bayesian filtering, belief propagation) and testing [e.g., kernel density estimation, support vector machine (SVM) testing]. Encouraging results are observed in the experiments on density estimation, clustering-based image segmentation, and simplification of SVM decision functions. © 2006 IEEE.


Lin T.,Hong Kong University of Science and Technology | Shang X.S.,East China University of Science and Technology | Adisoejoso J.,Hong Kong University of Science and Technology | Liu P.N.,East China University of Science and Technology | Lin N.,Hong Kong University of Science and Technology
Journal of the American Chemical Society | Year: 2013

On-surface polymerization represents a novel bottom-up approach for producing macromolecular structures. To date, however, most of the structures formed using this method exhibit a broad size distribution and are disorderly adsorbed on the surface. Here we demonstrate a strategy of using metal-directed template to control the on-surface polymerization process. We chose a bifunctional compound which contains pyridyl and bromine end groups as the precursor. Linear template afforded by pyridyl-Cu-pyridyl coordination effectively promoted Ullmann coupling of the monomers on a Au(111) surface. Taking advantage of efficient topochemical enhancement owing to the conformation flexibility of the Cu-pyridyl bonds, macromolecular porphyrin structures that exhibit a narrow size distribution were synthesized. We used scanning tunneling microscopy and kinetic Monte Carlo simulation to gain insights into the metal-directed polymerization at the single molecule level. The results reveal that the polymerization process profited from the rich chemistry of Cu which catalyzed the C-C bond formation, controlled the size of the macromolecular products, and organized the macromolecules in a highly ordered manner on the surface. © 2013 American Chemical Society.


Qiu Y.,Hong Kong University of Science and Technology | Zhang X.,Hong Kong University of Science and Technology | Yang S.,Hong Kong University of Science and Technology
Physical Chemistry Chemical Physics | Year: 2011

Thermal nitridation of reduced graphene oxide sheets yields highly conductive (∼1000-3000 S m-1) N-doped graphene sheets, as a result of the restoration of the graphene network by the formation of C-N bonded groups and N-doping. Even without carbon additives, supercapacitors made of the N-doped graphene electrodes can deliver remarkable energy and power when operated at higher voltages, in the range of 0-4 V. © the Owner Societies 2011.


Pan L.,Hong Kong University of Science and Technology | Zhang M.,Hong Kong University of Science and Technology
Physiology | Year: 2012

Usher syndrome 1 (USH1) is the most common and severe form of hereditary loss of hearing and vision. Genetic, physiological, and cell biological studies, together with recent structural investigations, have not only uncovered the physiological functions of the five USH1 proteins but also provided mechanistic explanations for the hearing and visual deficiencies in humans caused by USH1 mutations. This review focuses on the structural basis of the USH1 protein complex organization. © 2012 Int. Union Physiol. Sci./Am. Physiol. Soc.


Liu L.,Hong Kong University of Science and Technology | Wong R.C.-W.,Hong Kong University of Science and Technology
Proceedings of the ACM SIGMOD International Conference on Management of Data | Year: 2011

Finding shortest paths is a fundamental operator in spatial databases. Recently, terrain datasets have attracted a lot of attention from both industry and academia. There are some interesting issues to be studied in terrain datasets which cannot be found in a traditional two-dimensional space. In this paper, we study one of the issues called a slope constraint which exists in terrain datasets. In this paper, we propose a problem of finding shortest paths with the slope constraint. Then, we show that this new problem is more general than the traditional problem of finding shortest paths without considering the slope constraint. Since finding shortest paths with the slope constraint is costly, we propose a new framework called surface simplification so that we can compute shortest paths with the slope constraint efficiently. Under this framework, the surface is "simplified" such that the complexity of finding shortest paths on this simplified surface is lower. We conducted experiments to show that the surface simplification is very efficient and effective not only for the new problem with the slope constraint but also the traditional problem without the slope constraint. © 2011 ACM.


Lian X.,Hong Kong University of Science and Technology | Chen L.,Hong Kong University of Science and Technology
Proceedings of the ACM SIGMOD International Conference on Management of Data | Year: 2011

In this paper, we tackle the problem of efficiently answering queries on probabilistic RDF data graphs. Specifically, we model RDF data by probabilistic graphs, and an RDF query is equivalent to a search over subgraphs of probabilistic graphs that have high probabilities to match with a given query graph. To efficiently processqueries on probabilistic RDF graphs, we propose effective pruning mechanisms, structural and probabilistic pruning. For the structural pruning, we carefully design synopses for vertex/edge labels by considering their distributions and other structural information, in order to improve the pruning power. For the probabilistic pruning, we derive a cost model to guide the pre-computation of probability upper bounds such that the query cost is expected to be low. We construct an index structure that integrates synopses/statistics for structural and robabilistic pruning, and propose an efficient approach to answer queries on probabilistic RDF graph data. The efficiency of our solutions has been verified through extensive experiments. © 2011 ACM.


Li Y.S.,Hong Kong University of Science and Technology | Zhao T.S.,Hong Kong University of Science and Technology
International Journal of Hydrogen Energy | Year: 2012

A new cathode architecture for anion-exchange membrane fuel cells (AEMFCs) is proposed and fabricated by direct deposition of palladium (Pd) particles onto the surface of the micro-porous layer (MPL) that is interfaced with a backing layer. The MPL is composed of carbon nanotubes while the backing layer is made of a carbon paper. The sputter-deposited electrode with a worm-like shape not only extends the electrochemical active surface area, but also facilitates the oxygen transport. This new cathode, albeit with a Pd loading as low as 0.035 mg cm-2, enables the peak power density of an AEM direct ethanol fuel cell to be as high as 88 mW cm-2 (at 60 °C), which is even higher than that using a conventional cathode with a 15-times higher Pd loading. The significance of the present work lies in the fact that the new sputter-deposited electrode is more suitable for fuel-electrolyte-fed fuel cells than the conventional electrode designed for proton-exchange membrane fuel cells (PEMFCs). © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Lei T.,Hong Kong University of Science and Technology | Poon A.W.,Hong Kong University of Science and Technology
Optics Express | Year: 2011

We model and analyze coupled-resonator optical waveguide (CROW) based refractive index (RI) sensors using pixelized spatial detection. Our modeled cascaded Fabry-Perot (FP) CROWs reveal that the intra-band states mode-field distributions vary upon effective RI change at a single wavelength. The spatial Fourier transform of the CROW mode-field distributions, with each cavity field intensity integrated as a pixel, shows spatial frequency peak shift, which constitutes the basis of such a spatial domain sensor. The spatial domain sensing performance depends on the cavity number, the cavity length and the inter-cavity coupling. Our modeled 21-element CROW sensor attains a detection limit of 10-4 refractive index unit (RIU) with a sensing dynamic range of 10-3 RIU. Detailed analysis of the spatial frequency harmonic peak amplitude variation further suggests an improved detection limit. Finite-difference time-domain (FDTD) simulations of an 11-element microring CROW device shows sensitivity consistent with the FP modeling. © 2011 Optical Society of America.


Li Y.S.,Hong Kong University of Science and Technology | Zhao T.S.,Hong Kong University of Science and Technology
International Journal of Hydrogen Energy | Year: 2012

It has recently been demonstrated that anion-exchange membrane direct ethanol fuel cells (AEM DEFCs) can yield a high power density. The operating stability and durability of this type of fuel cell is, however, a concern. In this work, we report the durability test of an AEM DEFC that is composed of a Pd/C anode, an A201 membrane, and a Fe-Co cathode and show that the major voltage loss occurs in the initial discharge stage, but the loss becomes smaller and more stable with the discharge time. It is also found that the irreversible degradation rate of the fuel cell is around 0.02 mV h-1, which is similar to the degradation rate of conventional acid direct methanol fuel cells (DMFCs). The experimental results also reveal that the performance loss of the AEM DEFC is mainly attributed to the anode degradation, while the performance of the cathode and the membrane remains relatively stable. The TEM results indicate that the particle size of the anode catalyst increases from 2.3 to 3.5 nm after the long-term discharge, which reduces the electrochemical active surface area and hence causes a decrease in the anode performance. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Xu Q.,Hong Kong University of Science and Technology | Zhao T.S.,Hong Kong University of Science and Technology
Progress in Energy and Combustion Science | Year: 2015

The flow battery is a promising technology for large-scale storage of intermittent power generated from solar and wind farms owing to its unique advantages such as location independence, scalability and versatility. The widespread commercialization of flow batteries, thus far, is still hindered by certain technical barriers. Removal of these barriers requires a fundamental understanding of the complex electrochemical and transport behaviors of flow batteries. Mathematical modeling and simulation serve important roles in the exploration of these complex phenomena and to the prediction as well as improvement of the cell performance of different system designs. In this review, a comprehensive study is performed to review and summarize state-of-the-art flow batteries and to provide an outlook on the future and potential of flow battery modeling. The review begins with a description of the physical and chemical processes of common flow batteries, followed by the detailed discussion of the governing equations for transports of mass, momentum, heat and charge as well as the electrochemical reactions for porous-medium models. The determination of key transport properties for the porous-medium models and their effects on modeling results are also analyzed. In addition, lattice Boltzmann method, molecular dynamics and density function simulations as well as stack-level network models for flow batteries are reviewed. Finally, the issues facing the future of flow battery modeling are addressed. © 2015 Elsevier Ltd. All rights reserved.


Wong A.S.L.,Hong Kong University of Science and Technology | Lee R.H.K.,Hong Kong University of Science and Technology | Cheung A.Y.,Hong Kong University of Science and Technology | Yeung P.K.,University of Hong Kong | And 3 more authors.
Nature Cell Biology | Year: 2011

Cyclin-dependent kinase 5 (Cdk5) is a serine/threonine kinase that is increasingly implicated in various neurodegenerative diseases. Deregulated Cdk5 activity has been associated with neuronal death, but the underlying mechanisms are not well understood. Here we report an unexpected role for Cdk5 in the regulation of induced autophagy in neurons. We have identified endophilin B1 (EndoB1) as a Cdk5 substrate, and show that Cdk5-mediated phosphorylation of EndoB1 is required for autophagy induction in starved neurons. Furthermore, phosphorylation of EndoB1 facilitates EndoB1 dimerization and recruitment of UVRAG (UV radiation resistance-associated gene). More importantly, Cdk5-mediated phosphorylation of EndoB1 is essential for autophagy induction and neuronal loss in models of Parkinson's disease. Our findings not only establish Cdk5 as a critical regulator of autophagy induction, but also reveal a role for Cdk5 and EndoB1 in the pathophysiology of Parkinson's disease through modulating autophagy.


Wang J.,Zhejiang University | Mei J.,Zhejiang University | Hu R.,Hong Kong University of Science and Technology | Sun J.Z.,Zhejiang University | And 3 more authors.
Journal of the American Chemical Society | Year: 2012

It has been difficult to decipher the mechanistic issue whether E/Z isomerization is involved in the aggregation-induced emission (AIE) process of a tetraphenylethene (TPE) derivative, due to the difficulty in the synthesis of its pure E and Z conformers. In this work, pure stereoisomers of a TPE derivative named 1,2-bis{4-[1-(6-phenoxyhexyl)-4-(1,2,3-triazol)yl]phenyl}-1,2- diphenylethene (BPHTATPE) are successfully synthesized. Both isomers show remarkable AIE effect (α AIE ≥ 322) and high fluorescence quantum yield in the solid state (φ F 100%). The conformers readily undergo E/Z isomerization upon exposure to a powerful UV light and treatment at a high temperature (>200 °C). Such conformational change, however, is not observed under normal fluorescence spectrum measurement conditions, excluding the involvement of the E/Z isomerization in the AIE process of the TPE-based luminogen. The molecules of (E)-BPHTATPE self-organize into ordered one-dimensional nanostructures such as microfibers and nanorods that show obvious optical waveguide effect. BPHTATPE shows rich chromic effects, including mechano-, piezo-, thermo-, vapo-, and chronochromisms. Its emission peak is bathochromically shifted by simple grinding and pressurization and the spectral change is reversed by fuming with a polar solvent, heating at a high temperature, or storing at room temperature for some time. The multiple chromic processes are all associated with changes in the modes of molecular packing. © 2012 American Chemical Society.


Leung C.W.T.,Hong Kong University of Science and Technology | Hong Y.,Hong Kong University of Science and Technology | Chen S.,Hong Kong University of Science and Technology | Zhao E.,Hong Kong University of Science and Technology | And 3 more authors.
Journal of the American Chemical Society | Year: 2013

Tracking the dynamics of mitochondrial morphology has attracted much research interest because of its involvement in early stage apoptosis and degenerative conditions. To follow this process, highly specific and photostable fluorescent probes are in demand. Commercially available mitochondria trackers, however, suffer from poor photostability. To overcome this limitation, we have designed and synthesized a fluorescent agent, tetraphenylethene- triphenylphosphonium (TPE-TPP), for mitochondrial imaging. Inherent from the mitochondrial-targeting ability of TPP groups and the aggregation-induced emission (AIE) characteristics of the TPE core, TPE-TPP possesses high specificity to mitochondria, superior photostability, and appreciable tolerance to environmental change, allowing imaging and tracking of the mitochondrial morphological changes in a long period of time. © 2012 American Chemical Society.


Cai H.,Hong Kong University of Science and Technology | Poon A.W.,Hong Kong University of Science and Technology
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2012

We study optical trapping of microparticles on an optofluidic chip using silicon nitride waveguide junctions and tapered-waveguide junctions. We demonstrate the trapping of single 1 μm-sized polystyrene particles using the evanescent field of waveguide junctions connecting a submicrometer-sized input-waveguide and a micrometer-sized output-waveguide. Particle trapping is localized in the vicinity of the junction. We also demonstrate trapping of one and two 1μm-sized polystyrene particles using tapered-waveguide junctions connecting a submicrometer-sized singlemode input-waveguide and a micrometer-sized multimode output-waveguide. Particle trapping occurs near the taper output end, the taper center and the taper input end, depending on the taper aspect ratio. © 2012 The Royal Society of Chemistry.


Leung E.M.K.,Hong Kong University of Science and Technology | Chan W.,Hong Kong University of Science and Technology
Chemical Research in Toxicology | Year: 2015

Prolonged exposure to aristolochic acid (AA) contaminated slimming drugs and food is believed to be associated with the development of endemic nephropathy in Belgian women and in farmers living alongside the Danube River. Decades of research has revealed the pathophysiology of carcinogenesis of AA, and the molecular mechanisms underlying renal interstitial fibrosis remain unclear. We hypothesized that RNA modification may have contributed to the observed toxicity of AA. Thus, a highly sensitive and selective ultra-high performance liquid chromatography-coupled tandem mass spectrometric method was developed to quantify RNA-AA adducts in target and nontarget organs of AA-dosed rats. The results revealed, for the first time, that AA forms RNA adducts in vitro and in vivo. Comparative studies on DNA revealed that RNA is modified by AA at frequencies approximately 6-fold higher than that of DNA in both kidney and liver tissue in AA-dosed rats. Results also demonstrated that guanosine is modified by AA at frequencies significantly higher than that of adenosine, 2-deoxyadenosine, and 2-deoxyguanosine in both organs of the AA-dosed. This finding suggests that guanosine is a major target for AA and that guanosine adducts of AA might be critical lesions in the pathophysiology of AA-induced toxicity. It is anticipated that the results of our study may open up a new area of investigating the nephrotoxicity and/or carcinogenicity by quantifying RNA adducts using the UPLC-MS/MS technique of high sensitivity and selectivity. © 2015 American Chemical Society.


Xie H.,Hong Kong University of Science and Technology | Xie H.,Zhejiang GongShang University | Lin Z.,Hong Kong University of Science and Technology
Organometallics | Year: 2014

The detailed reaction mechanisms of the C=O hydrosilylation of isocyanate and the C=S bond cleavage of isothiocyanate mediated by the neutral ruthenium silylene hydride complex Cp(CO)(H)Ru=Si(H){C(SiMe3)3} have been investigated with the aid of density functional theory calculations. Through the investigation, the difference in reactivity between isocyanate and isothiocyanate toward the ruthenium silylene hydride complex has been examined and discussed. The different bond strengths and π-accepting abilities of C=O and C=S and the different degrees of affinity of O and S toward the Si center in the silylene ligand contribute to the different reactivities of the isocyanate and isothiocyanate substrates observed experimentally. © 2014 American Chemical Society.


Liu X.-J.,Hong Kong University of Science and Technology | Wong C.L.,Hong Kong University of Science and Technology | Law K.T.,Hong Kong University of Science and Technology
Physical Review X | Year: 2014

The study of non-Abelian Majorana zero modes advances our understanding of the fundamental physics in quantum matter and pushes the potential applications of such exotic states to topological quantum computation. It has been shown that in two-dimensional (2D) and 1D chiral superconductors, the isolated Majorana fermions obey non-Abelian statistics. However, Majorana modes in a Z2 time-reversal-invariant (TRI) topological superconductor come in pairs due to Kramers's theorem. Therefore, braiding operations in TRI superconductors always exchange two pairs of Majoranas. In this work, we show interestingly that, due to the protection of time-reversal symmetry, non-Abelian statistics can be obtained in 1D TRI topological superconductors and may have advantages in applications to topological quantum computation. Furthermore, we unveil an intriguing phenomenon in the Josephson effect, that the periodicity of Josephson currents depends on the fermion parity of the superconducting state. This effect provides direct measurements of the topological qubit states in such 1D TRI superconductors.


Liang T.,Hong Kong University of Science and Technology | Ye W.,Hong Kong University of Science and Technology
Communications in Computational Physics | Year: 2014

Aiming at simulating micro gas flows with accurate boundary conditions, an efficient hybrid algorithmis developed by combining themolecular dynamics (MD) method with the direct simulationMonte Carlo (DSMC)method. The efficiency comes from the fact that theMD method is applied only within the gas-wall interaction layer, characterized by the cut-off distance of the gas-solid interaction potential, to resolve accurately the gas-wall interaction process, while the DSMC method is employed in the remaining portion of the flow field to efficiently simulate rarefied gas transport outside the gas-wall interaction layer. A unique feature about the present scheme is that the coupling between the two methods is realized by matching the molecular velocity distribution function at the DSMC/MD interface, hence there is no need for one-toone mapping between a MD gas molecule and a DSMC simulation particle. Further improvement in efficiency is achieved by taking advantage of gas rarefaction inside the gas-wall interaction layer and by employing the "smart-wall model" proposed by Barisik et al. The developed hybrid algorithm is validated on two classical benchmarks namely 1-D Fourier thermal problem and Couette shear flow problem. Both the accuracy and efficiency of the hybrid algorithm are discussed. As an application, the hybrid algorithm is employed to simulate thermal transpiration coefficient in the free-molecule regime for a system with atomically smooth surface. Result is utilized to validate the coefficients calculated from the pure DSMC simulation with Maxwell and Cercignani-Lampis gas-wall interaction models. ©c 2014 Global-Science Press.


Xiao M.,Hong Kong University of Science and Technology | Zhang Z.Q.,Hong Kong University of Science and Technology | Chan C.T.,Hong Kong University of Science and Technology
Physical Review X | Year: 2014

Surface impedance is an important concept in classical wave systems such as photonic crystals (PCs). For example, the condition of an interface state formation in the interfacial region of two different one-dimensional PCs is simply ZSL + ZSR = 0, where ZSL(ZSR)is the surface impedance of the semiinfinite PC on the left-hand (right-hand) side of the interface. Here, we also show a rigorous relation between the surface impedance of a one-dimensional PC and its bulk properties through the geometrical (Zak) phases of the bulk bands, which can be used to determine the existence or nonexistence of interface states at the interface of the two PCs in a particular band gap. Our results hold for any PCs with inversion symmetry, independent of the frequency of the gap and the symmetry point where the gap lies in the Brillouin zone. Our results provide new insights into the relationship between surface scattering properties, the bulk band properties, and the formation of interface states, which in turn can enable the design of systems with interface states in a rational manner.


Wang R.,Hong Kong University of Science and Technology | Wang W.-X.,Hong Kong University of Science and Technology
Environmental Science and Technology | Year: 2010

We explored the roles of mercury speciation on the bioaccumulation (both aqueous and dietary uptake and elimination) of inorganic mercury (Hg[II]) and methylmercury (MeHg) in tilapia (Oreochromis niloticus) by controlling the mercury binding to inorganic and organic ligands. For the aqueous uptake, we showed that the uptake rates of Hg(II) were significantly higher at 0 psu compared with those at 10 psu and 28 psu. Based on the mercury-Cl complexes distribution, we found a positive relationship between the Hg(II) aqueous uptake rate and the abundance of neutral HgCl2. Such relationship was further confirmed by the uptake experiments conducted over a lower salinity range (0-6 psu), suggesting that HgCl2 0 was the predominant species taken up by tilapia. In the presence of dissolved organic carbon (DOC) from different sources (Suwannee River and natural local waters), mercury uptake rates all decreased dramatically over a wide range of salinity, especially for Hg(II), indicating the overwhelming influence of DOC as opposed to the single effect of salinity. Using the mercury-Cl-DOC model, we demonstrated for the first time that the inhibition of DOC was dependent on the Cl-, which was less significant at middle salinity level for both mercury forms. In contrast to the complex influence of water conditions on dissolved uptake, we found no significant influence of acclimated salinity on the dietary assimilation and elimination of both mercury species in tilapia. Our results demonstrated the importance of speciation in understanding the mercury bioaccumulation in various natural systems and its broad biogeochemical cycling. © 2010 American Chemical Society.


Liu X.-J.,Hong Kong University of Science and Technology | Law K.T.,Hong Kong University of Science and Technology | Ng T.K.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2014

A Majorana zero bound mode exists in the vortex core of a chiral p+ip superconductor or superfluid, which can be driven from an s-wave pairing state by two-dimensional spin-orbit coupling. We propose here a novel scheme based on realistic cold atom platforms to generate two-dimensional spin-orbit interactions in a blue-detuned square optical lattice, and predict both the quantum anomalous Hall effect and chiral topological superfluid phase in the experimentally accessible parameter regimes. This work may open a new direction with experimental feasibility to observe non-Abelian topological orders in cold atom systems. © 2014 American Physical Society.


He J.J.,Hong Kong University of Science and Technology | Ng T.K.,Hong Kong University of Science and Technology | Lee P.A.,Massachusetts Institute of Technology | Law K.T.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2014

In this work, we find that Majorana fermions induce selective equal spin Andreev reflections (SESARs), in which incoming electrons with certain spin polarization in the lead are reflected as counterpropagating holes with the same spin. The spin polarization direction of the electrons of this Andreev reflected channel is selected by the Majorana fermions. Moreover, electrons with opposite spin polarization are always reflected as electrons with unchanged spin. As a result, the charge current in the lead is spin polarized. Therefore, a topological superconductor which supports Majorana fermions can be used as a novel device to create fully spin-polarized currents in paramagnetic leads. We point out that SESARs can also be used to detect Majorana fermions in topological superconductors. © 2014 American Physical Society.


Yuan N.F.Q.,Hong Kong University of Science and Technology | Mak K.F.,Cornell University | Law K.T.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2014

Molybdenum disulphide (MoS2) has attracted much interest in recent years due to its potential applications in a new generation of electronic devices. Recently, it was shown that thin films of MoS2 can become superconducting with a highest Tc of 10 K when the material is heavily gated to the conducting regime. In this work, using the group theoretical approach, we determine the possible pairing symmetries of heavily gated MoS2. Depending on the electron-electron interactions and Rashba spin-orbit coupling, the material can support an exotic spin-singlet p+ip-wavelike, an exotic spin-triplet s-wavelike, and a conventional spin-triplet p-wave pairing phase. Importantly, the exotic spin-singlet p+ip-wave phase is a topological superconducting phase that breaks time-reversal symmetry spontaneously and possesses nonzero Chern numbers where the Chern number determines the number of branches of chiral Majorana edge states. © 2014 American Physical Society.


Cheung T.H.,Stanford University | Cheung T.H.,Hong Kong University of Science and Technology | Rando T.A.,Stanford University | Rando T.A.,Neurology Service and Rehabilitation Research
Nature Reviews Molecular Cell Biology | Year: 2013

Subsets of mammalian adult stem cells reside in the quiescent state for prolonged periods of time. This state, which is reversible, has long been viewed as dormant and with minimal basal activity. Recent advances in adult stem cell isolation have provided insights into the epigenetic, transcriptional and post-transcriptional control of quiescence and suggest that quiescence is an actively maintained state in which signalling pathways are involved in maintaining a poised state that allows rapid activation. Deciphering the molecular mechanisms regulating adult stem cell quiescence will increase our understanding of tissue regeneration mechanisms and how they are dysregulated in pathological conditions and in ageing. © 2013 Macmillan Publishers Limited. All rights reserved.


Liao S.,Hong Kong University of Science and Technology | Chung A.C.S.,Hong Kong University of Science and Technology
IEEE Transactions on Medical Imaging | Year: 2010

A new feature based nonrigid image registration method for magnetic resonance (MR) brain images is presented in this paper. Each image voxel is represented by a rotation invariant feature vector, which is computed by passing the input image volumes through a new bank of symmetric alpha stable $(S\alpha S)$ filters. There are three main contributions presented in this paper. First, this work is motivated by the fact that the frequency spectrums of the brain MR images often exhibit non-Gaussian heavy-tail behavior which cannot be satisfactorily modeled by the conventional Gabor filters. To this end, we propose the use of $S\alpha S$ filters to model such behavior and show that the Gabor filter is a special case of the $S\alpha S$ filter. Second, the maximum response orientation (MRO) selection criterion is designed to extract rotation invariant features for registration tasks. The MRO selection criterion also significantly reduces the number of dimensions of feature vectors and therefore lowers the computation time. Third, in case the segmentations of the input image volumes are available, the Fisher's separation criterion (FSC) is introduced such that the discriminating power of different feature types can be directly compared with each other before performing the registration process. Using FSC, weights can also be assigned automatically to different voxels in the brain MR images. The weight of each voxel determined by FSC reflects how distinctive and salient the voxel is. Using the most distinctive and salient voxels at the initial stage to drive the registration can reduce the risk of being trapped in the local optimum during image registration process. The larger the weight, the more important the voxel. With the extracted feature vectors and the associated weights, the proposed method registers the source and the target images in a hierarchical multiresolution manner. The proposed method has been intensively evaluated on both simulated and real 3-D datasets obtained from BrainWeb and Internet Brain Segmentation Repository (IBSR), respectively, and compared with HAMMER, an extended version of HAMMER based on local histograms (LHF), FFD, Demons, and the Gabor filter based registration method. It is shown that the proposed method achieves the highest registration accuracy among the five widely used image registration methods. © 2006 IEEE.


Huang J.,Los Alamos National Laboratory | Liu T.,Hong Kong University of Science and Technology | Wang L.-T.,University of Chicago | Yu F.,Fermi National Accelerator Laboratory
Physical Review Letters | Year: 2014

We reveal a set of novel decay topologies for the 125 GeV Higgs boson in supersymmetry which are initiated by its decay into a pair of neutralinos, and discuss their collider search strategies. This category of exotic Higgs decays is characterized by the collider signature: visible objects+ET, with ET dominantly arising from escaping dark matter particles. Their benchmark arises naturally in the Peccei-Quinn symmetry limit of the minimal supersymmetric standard model singlet extensions, which is typified by the coexistence of three light particles: singletlike scalar h1 and pseudoscalar a1, and singlinolike neutralino χ1, all with masses of 10GeV, and the generic suppression of the exotic decays of the 125 GeV Higgs boson h2h1h1, a1a1 and χ1χ1, however. As an illustration, we study the decay topology: h2χ1χ2, where the binolike χ2 decays to h1χ1 or a1χ1, and h1/a1ff̄, with ff̄=+-, bb̄. In the dimuon case (mh1/a11GeV), a statistical sensitivity of S/B>6 can be achieved easily at the 8 TeV LHC, assuming (ppWh2)/(ppWhSM)Br(h2+-χ1χ1)=0.1. In the bb̄ case (mh1/a145GeV), 600fb1 data at the 14 TeV LHC can lead to a statistical sensitivity of S/B>5, assuming (ppZh2)/(ppZhSM) Br(h2bb̄χ1χ1)=0.5. These exotic decays open a new avenue for exploring new physics couplings with the 125 GeV Higgs boson at colliders. © 2014 American Physical Society.


Man K.L.,Hong Kong University of Science and Technology | Tringides M.C.,Iowa State University | Loy M.M.T.,Hong Kong University of Science and Technology | Altman M.S.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2013

Mass transport in the Pb wetting layer on the Si(111) surface is investigated by observing nonequilibrium coverage profile evolution with low energy electron microscopy and microlow energy electron diffraction. Equilibration of an initial coverage step profile occurs by the exchange of mass between oppositely directed steep coverage gradients that each move with unperturbed shape. The bifurcation of the initial profile, the shape of the profile between the two moving edges, and the time dependence of equilibration are all at odds with expectations for classical diffusion behavior. These observations signal a very unusual coverage dependence of diffusion or may even reveal an exceptional collective superdiffusive mechanism. © 2013 American Physical Society.


Yeung K.L.,Hong Kong University of Science and Technology | Han W.,Hong Kong University of Science and Technology
Catalysis Today | Year: 2014

This review article surveys the use of zeolites and mesoporous materials in fuel cell device and, operations. Zeolites are increasingly used to modify and improve the fuel cell membrane to address the, problems of fuel crossover and membrane stability. Mesoporous carbons and carbon aerogels with, their large surface area, high porosity and good interconnectivity are considered ideal material for electrodes and electrocatalysts. Zeolites and mesoporous materials are also employed as template to create nano-, micro- and macro-scale structures for new electrocatalysts. Furthermore, zeolites are used as catalyst, adsorbent and membrane in fuel processing from hydrogen production to purification. © 2013 Published by Elsevier B.V.


Nasiry J.,Hong Kong University of Science and Technology | Popescu I.,Decision science Area
Operations Research | Year: 2011

We study the dynamic pricing implications of a new, behaviorally motivated reference price mechanism based on the peak-end memory mode. This model suggests that consumers anchor on a reference price that is a weighted average of the lowest and most recent prices. Loss-averse consumers are more sensitive to perceived losses than gains relative to this reference price. We find that a range of constant pricing policies is optimal for the corresponding dynamic pricing problem. This range is wider the more consumers anchor on lowest prices, and it persists when buyers are loss neutral, in contrast with previous literature. In a transient regime, the optimal pricing policy is monotone and converges to a steady-state price, which is lower the more extreme and salient the low-price anchor is. Our results suggest that behavioral regularities, such as peak-end anchoring and loss aversion, limit the benefits of varying prices, and caution that the adverse effects of deep discounts on the firm's optimal prices and profits might be more enduring than previous models predict. © 2011 INFORMS.


Ruan L.,Hong Kong University of Science and Technology | Ruan L.,Massachusetts Institute of Technology | Lau V.K.N.,Hong Kong University of Science and Technology | Win M.Z.,Massachusetts Institute of Technology
IEEE Transactions on Signal Processing | Year: 2013

Interference alignment (IA) has attracted great attention in the last few years for its breakthrough performance in interference networks. However, despite the numerous works dedicated to IA, the feasibility conditions of IA remains unclear for most network topologies. The IA feasibility analysis is challenging as the IA constraints are sets of high-degree polynomials, for which no systematic tool to analyze the solvability conditions exists. In this work, by developing a new mathematical framework that maps the solvability of sets of polynomial equations to the linear independence of their first-order terms, we propose a sufficient condition that applies to MIMO interference networks with general configurations. We have further proved that this sufficient condition coincides with the necessary conditions under a wide range of configurations. These results further consolidate the theoretical basis of IA. © 1991-2012 IEEE.


Rao X.,Hong Kong University of Science and Technology | Ruan L.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2013

Interference alignment is degree of freedom optimal on $K$- user MIMO interference channels and many previous works have studied the transceiver designs. However, these works predominantly focus on networks with perfect channel state information at the transmitters and symmetrical interference topology. In this paper, we consider a limited feedback system with heterogeneous path loss and spatial correlations and investigate how the dynamics of the interference topology can be exploited to improve the feedback efficiency. We propose a novel spatial codebook design and perform dynamic quantization via bit allocations to adapt to the asymmetry of the interference topology. We bound the system throughput under the proposed dynamic scheme in terms of the transmit SNR, feedback bits, and the interference topology parameters. It is shown that when the number of feedback bits scales with SNR as Cslog SNR+ O(1), the sum degrees of freedom of the network are preserved. Moreover, the value of scaling coefficient Cs can be significantly reduced in networks with asymmetric interference topology. © 1991-2012 IEEE.


Wang W.-X.,Hong Kong University of Science and Technology | Guan R.,Hong Kong University of Science and Technology
Environmental Toxicology and Chemistry | Year: 2010

We examined the subcellular partitioning of zinc (Zn) in Daphnia magna both under acute and chronic exposures. In the acute Zn toxicity tests, the daphnids were exposed to different Zn concentrations for 48 h or to one lethal concentration (1,000 μg/L) for different durations (time to death for up to 47 h). Significant mortality of daphnids was observed when the newly accumulated Zn concentration reached a threshold level of approximately 40μg/g wet weight (or 320 μg/g dry wt), approximately 3.5 times higher than the background tissue concentration (92 μg/g dry wt). Chronic exposure (14 d) to Zn resulted in nonobservable effect on survivorship and growth at newly accumulated tissue concentration of over 40μg/g wet weight. With increasing Zn acute exposure, more Zn was partitioned into the cellular debris fraction, indicating that this fraction was presumably the first targeted site of binding for Zn upon entering the animals. The importance of other subcellular fractions either decreased accordingly or remained comparable. We found that the metal-sensitive fraction (Zn distribution in the organelles and heat-denatured proteins) did not predict the acute Zn toxicity in Daphnia. During chronic exposure, however, no major change of the subcellular partitioning of Zn with increasing Zn exposure was documented. Zinc was mainly found in the organelles and heat-stable protein fractions during chronic exposure, suggesting that any subcellular repartitioning occurred primarily during acute exposure. Metallothioneins were induced upon chronic Zn exposure, but its induction evidently lagged behind the Zn accumulation. Our present study showed that the subcellular fractionation approach could not be readily used to predict the acute and chronic toxicities of Zn in Daphnia. A tissue-based Zn accumulation approach with a threshold Zn tissue concentration was better in predicting acute Zn toxicity. © 2010 SETAC.


Xu K.,Hong Kong University of Science and Technology | Huang J.-C.,National Taiwan Ocean University
Journal of Computational Physics | Year: 2010

With discretized particle velocity space, a multiscale unified gas-kinetic scheme for entire Knudsen number flows is constructed based on the BGK model. The current scheme couples closely the update of macroscopic conservative variables with the update of microscopic gas distribution function within a time step. In comparison with many existing kinetic schemes for the Boltzmann equation, the current method has no difficulty to get accurate Navier-Stokes (NS) solutions in the continuum flow regime with a time step being much larger than the particle collision time. At the same time, the rarefied flow solution, even in the free molecule limit, can be captured accurately. The unified scheme is an extension of the gas-kinetic BGK-NS scheme from the continuum flow to the rarefied regime with the discretization of particle velocity space. The success of the method is due to the un-splitting treatment of the particle transport and collision in the evaluation of local solution of the gas distribution function. For these methods which use operator splitting technique to solve the transport and collision separately, it is usually required that the time step is less than the particle collision time. This constraint basically makes these methods useless in the continuum flow regime, especially in the high Reynolds number flow simulations. Theoretically, once the physical process of particle transport and collision is modeled statistically by the kinetic Boltzmann equation, the transport and collision become continuous operators in space and time, and their numerical discretization should be done consistently. Due to its multiscale nature of the unified scheme, in the update of macroscopic flow variables, the corresponding heat flux can be modified according to any realistic Prandtl number. Subsequently, this modification effects the equilibrium state in the next time level and the update of microscopic distribution function. Therefore, instead of modifying the collision term of the BGK model, such as ES-BGK and BGK-Shakhov, the unified scheme can achieve the same goal on the numerical level directly. Many numerical tests will be used to validate the unified method. © 2010 Elsevier Inc.


Wang W.,Hong Kong University of Science and Technology | Zhang Q.,Hong Kong University of Science and Technology
Proceedings - IEEE INFOCOM | Year: 2014

The proliferation of sensor-equipped smartphones has enabled an increasing number of context-aware applications that provide personalized services based on users' contexts. However, most of these applications aggressively collect users sensing data without providing clear statements on the usage and disclosure strategies of such sensitive information, which raises severe privacy concerns and leads to some initial investigation on privacy preservation mechanisms design. While most prior studies have assumed static adversary models, we investigate the context dynamics and call attention to the existence of intelligent adversaries. In this paper, we first identify the context privacy problem with consideration of the context dynamics and malicious adversaries with capabilities of adjusting their attacking strategies, and then formulate the interactive competition between users and adversaries as a zero-sum stochastic game. In addition, we propose an efficient minimax learning algorithm to obtain the optimal defense strategy. Our evaluations on real smartphone context traces of 94 users validate the proposed algorithm. © 2014 IEEE.


Dong H.,Hong Kong University of Science and Technology | Lo I.M.C.,Hong Kong University of Science and Technology
Water Research | Year: 2013

To enhance colloidal stability of nano zero-valent iron (NZVI) used for groundwater remediation, the surfaces of such NZVI can be modified via coating with organic stabilizers. These surface stabilizers can electrostatically, sterically, or electrosterically stabilize NZVI suspensions in water, but their efficacy is affected by the presence of humic acid (HA) in groundwater. In this study, the effect of HA on the colloidal stability of NZVI coated with three types of stabilizers (i.e., polyacrylic acid (PAA), Tween-20 and starch) was evaluated. Differing stability behaviors were observed for different surface-modified NZVIs (SM-NZVI) in the presence of HA. Fluorescence spectroscopic analysis probed the possible interactions at the SM-NZVI-HA interface, providing a better understanding of the effect of HA on SM-NZVI stability. The adsorption of HA on the surface of PAA-modified NZVI via complexation with NZVI (rather than the PAA stabilizer) enhanced the electrosteric repulsion effect, increasing the stability of the particles. However, for NZVI modified with Tween-20 or starch, HA could interact with the surface stabilizer and apparently play a " bridge" role among the particles, which might induce aggregation of the particles. Therefore, the stability behavior of NZVI modified with Tween-20 or starch might have resulted from the combined effect of " bridging" and " electrosteric" exerted by HA. © 2012 Elsevier Ltd.


Pan Y.,Hong Kong University of Science and Technology | Zhang X.,Hong Kong University of Science and Technology
Water Research | Year: 2013

Total organic iodine (TOI) is a collective parameter and a toxicity indicator for all the iodinated disinfection byproducts in a water sample. The currently used TOI measurement method involves adsorption of organic iodine onto activated carbon, pyrolysis of adsorbed organic iodine to hydrogen iodide, absorption of hydrogen iodide into a solution, and off-line separation/detection of iodide in the absorption solution using ion chromatography coupled with conductivity detection. In this study, a new approach with ultra performance liquid chromatography/electrospray ionization-mass spectrometry (UPLC/ESI-MS) detection by setting selected ion recording of m/. z 127 in the negative ion mode (instead of ion chromatography-conductivity detection) was developed for off-line iodide separation/detection in the TOI measurement. An obstacle with the new approach was found to be a series of adducts (with the same m/. z value as iodide) formed in the mobile phase and at the ESI-MS sample cone, which were effectively eliminated by acidifying the absorption solution with formic acid and optimizing the instrumental parameters. By comparing the calibration curves of seven aliphatic and aromatic iodine-containing standard compounds, iodoacetic acid was determined to be an appropriate calibration standard for the TOI measurement. This new approach was found to be more sensitive, accurate and rapid. The quantitation limit of TOI was 5 μg/L as I for a 40 mL water sample or 2.5 μg/L as I for an 80 mL water sample. TOI recoveries were 94-103% for seven iodine-containing compounds and 91-108% for two wastewater and six tap water samples. The run duration for analyzing iodide in the absorption solution was only 4 min. With the new approach, TOI concentrations in various types of water samples were successfully analyzed and compared. This approach provides a sensitive tool for investigating the formation and control of iodinated DBPs in disinfected drinking water and wastewater. © 2012 Elsevier Ltd.


Herrup K.,Hong Kong University of Science and Technology | Herrup K.,Rutgers University
Current Opinion in Cell Biology | Year: 2013

The process of cell division is highly complex. The DNA of the genome must be accurately replicated and segregated into two precisely equal portions; the cytoskeleton must be actively rearranged; and the cellular motor forces that allow the separation of the replicated chromosomes and the splitting of the mother cell into two daughters must be kept under strict spatial and temporal regulation. Not surprisingly for a process of this complexity, there is a wide range of proteins whose location and activity must be accurately controlled to ensure both efficiency and precision. Although the demands placed on these cell cycle proteins are high, once cells such as neurons differentiate they enter a long non-mitotic phase where evolution has conspired to repurpose many of these proteins, leading them to assume new and often unrelated cellular tasks. In neurons there is a wide range of non-cycling functions for these 'cell cycle' proteins and this review covers some of the best-known examples. There is little apparent logic to the second use, but the sheer number of examples suggests that there must be a significant evolutionary advantage to this repurposing strategy. © 2013 Elsevier Ltd.


Ye F.,Hong Kong University of Science and Technology | Zhang M.,Hong Kong University of Science and Technology
Biochemical Journal | Year: 2013

PDZ domains are highly abundant protein Cprotein interaction modules and are often found in multidomain scaffold proteins. PDZ-domain-containing scaffold proteins regulate multiple biological processes, including trafficking and clustering receptors and ion channels at defined membrane regions, organizing and targeting signalling complexes at specific cellular compartments, interfacing cytoskeletal structures with membranes, and maintaining various cellular structures. PDZ domains, each with90-amino-acid residues folding into a highly similar structure, are best known to bind to short C-terminal tail peptides of their target proteins. A series of recent studies have revealed that, in addition to the canonical target-binding mode, many PDZ Ctarget interactions involve amino acid residues beyond the regular PDZ domain fold, which we refer to as extensions. Such extension sequences often form an integral structural and functional unit with the attached PDZ domain, which is defined as a PDZ supramodule. Correspondingly, PDZdomain- binding sequences from target proteins are frequently found to require extension sequences beyond canonical short Cterminal tail peptides. Formation of PDZ supramodules not only affords necessary binding specificities and affinities demanded by physiological functions of PDZ domain targets, but also provides regulatory switches to be built in the PDZ Ctarget interactions. At the 20th anniversary of the discovery of PDZ domain proteins, we try to summarize structural features and target-binding properties of such PDZ supramodules emerging from studies in recent years. © 2013 The Author(s).


Zheng Z.,Hong Kong University of Science and Technology | Han Y.,Hong Kong University of Science and Technology
Journal of Chemical Physics | Year: 2010

We studied the self-diffusion of colloidal ellipsoids in a monolayer near a flat wall by video microscopy. The image processing algorithm can track the positions and orientations of ellipsoids with subpixel resolution. The translational and rotational diffusions were measured in both the laboratory frame and the body frame along the long and short axes. The long-time and short-time diffusion coefficients of translational and rotational motions were measured as functions of the particle concentration. We observed the nondiffusive crossover region in the intermediate time regime due to the caging of neighboring particles. Both the beginning and the ending times of the intermediate regime exhibit power-law dependence on concentration. The long-time and short-time diffusion anisotropies change nonmonotonically with concentration and reach minima in the semidilute regime because the motions along long axes are caged at lower concentrations than the motions along short axes. The time derivatives of mean-square displacements change linearly with the inverse of time in the intermediate time regimes at various particle densities. This indicates that their relaxation functions decay as 1/t which provides new challenges in theory. The effects of coupling between rotational and translational Brownian motions were demonstrated and the two time scales corresponding to anisotropic particle shape and anisotropic neighboring environment were measured. © 2010 American Institute of Physics.


Liu X.-J.,Massachusetts Institute of Technology | Liu X.-J.,Hong Kong University of Science and Technology | Law K.T.,Hong Kong University of Science and Technology | Ng T.K.,Hong Kong University of Science and Technology | Lee P.A.,Massachusetts Institute of Technology
Physical Review Letters | Year: 2013

Chern insulators are band insulators which exhibit a gap in the bulk and gapless excitations in the edge. Detection of Chern insulators is a serious challenge in cold atoms since the Hall transport measurements are technically unrealistic for neutral atoms. By establishing a natural correspondence between the time-reversal invariant topological insulator and the quantum anomalous Hall system, we show for a class of Chern insulators that the topology can be determined by only measuring Bloch eigenstates at highly symmetric points of the Brillouin zone. Furthermore, we introduce two experimental schemes, including the spin-resolved Bloch oscillation, to carry out the measurement. These schemes are highly feasible under realistic experimental conditions. Our results may provide a powerful tool to detect topological phases in cold atoms. © 2013 American Physical Society.


Ciucci F.,Hong Kong University of Science and Technology
Electrochimica Acta | Year: 2013

In this article several computational tools related to parameter identification and optimal experimental design (OED) in electrochemical impedance spectroscopy (EIS) are introduced. Weighted and iteratively reweighted least squares are revisited and are coupled to an optimization procedure, which aims at increasing the confidence on the estimated parameters and/or at shortening the experimental time without compromising the accuracy of the estimates. A sequential algorithm allowing real-time implementation of OED is also developed. A fuel cell electrode system model is used to test and validate the methods developed.


Xu J.B.,Hong Kong University of Science and Technology | Zhao T.S.,Hong Kong University of Science and Technology
RSC Advances | Year: 2013

The design of electrodes for polymer electrolyte membrane fuel cells (PEMFCs) is a delicate balance of electrochemical and mass transport issues. High performance fuel cell electrode materials require nanoarchitectures with established nanoscopic reaction zones and efficient molecular transport of gas- or liquid-phase reactants and products to and from the electrochemical reaction zones. Mesoporous carbon (MC), with uniquely combined electrochemical and mass transport characteristics is an ideal electrode material for polymer electrolyte membrane fuel cells as its mesoscopic structures not only enables electrocatlysts to be highly dispersed, but also offers ideal pore morphologies that facilitate mass transport. Recently, a wide variety of applications of MCs in PEMFCs have been exploited. This article provides a review of these past efforts with an attempt to gain a better understanding of the role of MCs in PEMFCs. The contribution of MCs in the gas diffusion layer is addressed first and their roles in the catalyst layer are then discussed. The advantages and disadvantages, the acting mechanism to promote electrochemical and mass transport characteristics, and the strategies to improve present electrode materials are discussed. This journal is © The Royal Society of Chemistry.


Zhao C.-M.,Hong Kong University of Science and Technology | Wang W.-X.,Hong Kong University of Science and Technology
Environmental Science and Technology | Year: 2010

Silver nanoparticles (AgNP) are widely used as antibacterial products, and there are increasing concerns for their potential environmental risks in aquatic ecosystems. The biokinetics of AgNP in aquatic organisms has not yet been determined. In the present study, we employed a radiotracer methodology to quantify the biokinetics of AgNP in a freshwater cladoceran Daphnia magna, including the uptake from water, dietary assimilation, and elimination of AgNP. We found that the uptake of AgNP was concentration dependent and governed by two phases. The uptake rate constant (ku) was 0.060 L/g/h at low AgNP concentrations (2, 10, and 40 μg/L), which was 4.3 times lower than that of the Ag free ion. At a higher AgNP concentration (160 and 500 μg/L), the uptake rate increased disproportionately, likely as a result of direct ingestion of these nanoparticles by the daphnids. When the AgNP were associated with the algal food, their dietary assimilation efficiency (AE) was in the range of 22-45%, which was much higher than the dietary assimilation of Ag quantified under the same food conditions. The efflux rate constants of AgNP in daphnids were also much lower than those of the Ag, again suggesting the difficulty of eliminating AgNP by the daphnids. Water excretion was the main elimination route for both AgNP and Ag, but a higher percentage of AgNP was lost through fecal production. Finally, we used a kinetic equation to compare the importance of aqueous and dietary uptake of AgNP using the quantified kinetic parameters. The biokinetic model showed that more than 70% of AgNP accumulated in the daphnids was through ingestion of algae, highlighting the importance of AgNP transport along the food chain. Our present study showed the unique characteristic of AgNP biokinetics and suggested that more attention should be paid to the dietborne AgNP toxicity in aquatic ecosystems. © 2010 American Chemical Society.


Shi C.,Hong Kong University of Science and Technology | Jia G.,Hong Kong University of Science and Technology
Coordination Chemistry Reviews | Year: 2013

There has been much interest in the chemistry of rhenium carbyne complexes, complexes with a rhenium-carbon triple bond. A number of rhenium carbyne complexes have been obtained from various synthetic routes. A variety of interesting chemical properties of rhenium carbyne complexes have also been reported. This review summarizes the work related to the synthesis and reactivity of mononuclear rhenium carbyne complexes. © 2012 Elsevier B.V.


Chen S.,Hong Kong University of Science and Technology | Kwok H.S.,Hong Kong University of Science and Technology
Optics Express | Year: 2010

Light extraction from organic light-emitting diodes (OLEDs) by scattering the light is one of the effective methods for large-area lighting applications. In this paper, we present a very simple and cost-effective method to rough the substrates and hence to scatter the light. By simply sand-blasting the edges and back-side surface of the glass substrates, a 20% improvement of forward efficiency has been demonstrated. Moreover, due to scattering effect, a constant color over all viewing angles and uniform light pattern with Lambertian distribution has been obtained. This simple and cost-effective method may be suitable for mass production of large-area OLEDs for lighting applications. ©2009 Optical Society of America.


Yobas L.,Hong Kong University of Science and Technology
Journal of Micromechanics and Microengineering | Year: 2013

Among the electrophysiology techniques, the voltage clamp and its subsequent scaling to smaller mammalian cells, the so-called patch clamp, led to fundamental discoveries in the last century, revealing the ionic mechanisms and the role of single-ion channels in the generation and propagation of action potentials through excitable membranes (e.g. nerves and muscles). Since then, these techniques have gained a reputation as the gold standard of studying cellular ion channels owing to their high accuracy and rich information content via direct measurements under a controlled membrane potential. However, their delicate and skill-laden procedure has put a serious constrain on the throughput and their immediate utilization in the discovery of new cures targeting ion channels until researchers discovered 'lab-on-a-chip' as a viable platform for the automation of these techniques into a reliable high-throughput screening functional assay on ion channels. This review examines the innovative 'lab-on-a-chip' microtechnologies demonstrated towards this target over a period of slightly more than a decade. The technologies are categorically reviewed according to their considerations for design, fabrication, as well as microfluidic integration from a performance perspective with reference to their ability to secure G Ω seals (gigaseals) on cells, the norm broadly accepted among electrophysiologists for quality recordings that reflect ion-channel activity with high fidelity. © 2013 IOP Publishing Ltd.


Zheng Z.,Hong Kong University of Science and Technology | Wang F.,Hong Kong University of Science and Technology | Han Y.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2011

We observed a two-step glass transition in monolayers of colloidal ellipsoids by video microscopy. The glass transition in the rotational degree of freedom was at a lower density than that in the translational degree of freedom. Between the two transitions, ellipsoids formed an orientational glass. Approaching the respective glass transitions, the rotational and translational fastest-moving particles in the supercooled liquid moved cooperatively and formed clusters with power-law size distributions. The mean cluster sizes diverge in power law as they approach the glass transitions. The clusters of translational and rotational fastest-moving ellipsoids formed mainly within pseudonematic domains and around the domain boundaries, respectively. © 2011 American Physical Society.


Liu A.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2013

Consider media streaming in MIMO interference networks whereby multiple base stations (BS) simultaneously deliver media to their associated users using fixed data rates. The performance is fundamentally limited by the cross-link interference. We propose a cache-induced opportunistic cooperative MIMO (CoMP) for interference mitigation. By caching a portion of the media files, the BSs opportunistically employ CoMP to transform the cross-link interference into spatial multiplexing gain. We study a mixed-timescale optimization of MIMO precoding and cache control to minimize the transmit power under the rate constraint. The cache control is to create more CoMP opportunities and is adaptive to the long-term popularity of the media files. The precoding is to guarantee the rate requirement and is adaptive to the channel state information and cache state at the BSs. The joint stochastic optimization problem is decomposed into a short-term precoding and a long-term cache control problem. We propose a precoding algorithm which converges to a stationary point of the short-term problem. Based on this, we exploit the hidden convexity of the long-term problem and propose a low complexity and robust solution using stochastic subgradient. The solution has significant gains over various baselines and does not require explicit knowledge of the media popularity. © 2013 IEEE.


Feng W.-Z.,Hong Kong University of Science and Technology | Nath P.,Northeastern University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Analysis of contributions from vectorlike leptonic supermultiplets to the Higgs diphoton decay rate and to the Higgs boson mass is given. Corrections arising from the exchange of the new leptons and their superpartners as well as their mirrors are computed analytically and numerically. We also study the correlation between the enhanced Higgs diphoton rate and the Higgs mass corrections. Specifically, we find two branches in the numerical analysis: on the lower branch the diphoton rate enhancement is flat, while on the upper branch it has a strong correlation with the Higgs mass enhancement. It is seen that a factor of 1.4-1.8 enhancement of the Higgs diphoton rate on the upper branch can be achieved, and a 4-10 GeV positive correction to the Higgs mass can also be obtained simultaneously. The effect of this extra contribution to the Higgs mass is to release the constraint on weak-scale supersymmetry, allowing its scale to be lower than in the theory without extra contributions. The vectorlike supermultiplets also have collider implications which could be testable at the LHC and at the ILC. © 2013 American Physical Society.


Wang S.,Hong Kong University of Science and Technology | Wang W.,Hong Kong University of Science and Technology | Lin N.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2011

We study single conjugated polyphenylene oligomers consisting of 3n (2≤n≤12) phenyl units by means of cryogenic scanning tunneling microscopy and spectroscopy. The spatially resolved local densities of states reveal a progressive development of a continuous conduction band out of discrete molecular orbitals as the length of the oligomers increases. The experimental results are satisfactorily described by tight-binding calculations which gave a conduction band bandwidth of 4.5±0.2eV and a band gap of 3.1±0.2eV for an infinitely long polymer. We observed two types of defects, known as conformational torsional angle misfit and metasite kink. Tight-binding as well as density-functional theory model calculations confirm that both types of defects effectively destroy the delocalization. © 2011 American Physical Society.


Wang Q.,Hong Kong University of Science and Technology
IEEE Transactions on Information Theory | Year: 2010

Frequency hopping (FH) is one of the basic spread coding technologies in spread spectrum communications. FH sequences are needed in FH code-division multiple access (CDMA) systems. For the anti-jamming purpose, FH sequences are required to have a large linear span. A few optimal sets of FH sequences are available in the literature. However, their sequences have very small linear spans. It is known that an optimal set of FH sequences could be transformed to another optimal set of FH sequences with large linear spans by a power permutation, if the power is chosen properly [see C. Ding and J. Yin, IEEE Trans. Inf. Theory, vol. IT-54, pp. 3741-3745, 2008]. The objective of this paper is to investigate this idea of C. Ding and J. Yin further, and determine the linear span of the FH sequences in the optimal sets obtained by applying a power permutation to some existing optimal sets of FH sequences. © 2006 IEEE.


Yang Z.,Hong Kong University of Science and Technology | Liu Y.,Hong Kong University of Science and Technology
IEEE Transactions on Parallel and Distributed Systems | Year: 2010

The proliferation of wireless and mobile devices has fostered the demand for context-aware applications, in which location is one of the most significant contexts. Multilateration, as a basic building block of localization, however, has not yet overcome the challenges of 1) poor ranging measurements; 2) dynamic and noisy environments; and 3) fluctuations in wireless communications. Hence, multilateration-based approaches often suffer from poor accuracy and can hardly be employed in practical applications. In this study, we propose Quality of Trilateration (QoT) that quantifies the geometric relationship of objects and ranging noises. Based on QoT, we design a confidence-based iterative localization scheme, in which nodes dynamically select trilaterations with the highest quality for location computation. To validate this design, a prototype network based on wireless sensor motes is deployed and the results show that QoT well represents trilateration accuracy, and the proposed scheme significantly improves localization accuracy. © 2010 IEEE.


Lian X.,Hong Kong University of Science and Technology | Chen L.,Hong Kong University of Science and Technology
ACM Transactions on Database Systems | Year: 2010

Reverse skyline queries over uncertain databases have many important applications such as sensor data monitoring and business planning. Due to the wide existence of uncertainty in many real-world data, answering reverse skyline queries accurately and efficiently over uncertain data has become increasingly important. In this article, we formalize the probabilistic reverse skyline query over uncertain data, in both monochromatic and bichromatic cases, and propose effective pruning methods, namely spatial pruning and probabilistic pruning, to reduce the search space of the reverse skyline query processing. Moreover, efficient query procedures have been presented seamlessly integrating the proposed pruning methods. Furthermore, a novel query type, namely Probabilistic Reverse Furthest Skyline (PRFS) query, is proposed and tackled under the larger, the better dominance semantics of skyline. Variants of probabilistic reverse skyline have been proposed and tackled, including those that return objects with top-k highest probabilities and that retrieve top-k reverse skylines. Extensive experiments demonstrated the efficiency and effectiveness of our approaches with various experimental settings. © 2010 ACM.


Li M.,Hong Kong University of Science and Technology | Liu Y.,Hong Kong University of Science and Technology
IEEE Transactions on Knowledge and Data Engineering | Year: 2010

Contour mapping is a crucial part of many wireless sensor network applications. Many efforts have been made to avoid collecting data from all the sensors in the network and producing maps at the sink, which is proven to be inefficient. The existing approaches (often aggregation based), however, suffer from heavy transmission traffic and incur large computational overheads on each sensor node. We propose Iso-Map, an energy-efficient protocol for contour mapping, which builds contour maps based solely on the reports collected from intelligently selected isoline nodes in wireless sensor networks. Iso-Map achieves high-quality contour mapping while significantly reducing the generated traffic from O(n) to O(\sqrt n), where n is the total number of sensor nodes in the field. The pernode computation overhead is also restrained as a constant. We conduct comprehensive trace-driven simulations to verify this protocol, and demonstrate that Iso-Map outperforms the previous approaches in the sense that it produces contour maps of high fidelity with significantly reduced energy cost. © 2006 IEEE.


Wang Q.,Hong Kong University of Science and Technology
IEEE Transactions on Information Theory | Year: 2010

Binary sequences with good autocorrelation are needed in many applications. A construction of binary sequences with three-level autocorrelation was recently presented. This construction is generic and powerful in the sense that many classes of binary sequences with three-level autocorrelation could be obtained from any difference set with Singer parameters. The objective of this paper is to determine both the linear complexity and the minimal polynomial of two classes of binary sequences, i.e., the class based on the Singer difference set, and the class based on the GMW difference set. © 2006 IEEE.


Tang X.,Southwest Jiaotong University | Ding C.,Hong Kong University of Science and Technology
IEEE Transactions on Information Theory | Year: 2010

Sequences with optimal autocorrelation property are needed in certain communication systems and cryptography. In this paper, a construction of balanced quaternary sequences with period N ≡ 2 (mod 4) and optimal autocorrelation value and a construction of almost balanced binary sequences with period N ≡ 0 (mod 4) and optimal autocorrelation value are presented. Both constructions are a generalization of earlier ones. © 2006 IEEE.


Yang M.,Hong Kong University of Science and Technology | Ma G.,Hong Kong University of Science and Technology | Yang Z.,Hong Kong University of Science and Technology | Sheng P.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2013

We present a structurally and conceptually simple acoustic double negative metamaterial comprising two coupled membranes. Owing to its symmetry, the system can generate both monopolar and dipolar resonances that are separately tunable, thereby making broadband double negativity possible. A homogenization scheme is implemented that enables the exact characterization of our metamaterial by the effective mass density and bulk modulus even beyond the usual long-wavelength regime, with the measured displacement fields on the sample's surfaces as inputs. Double negativity is achieved in the frequency range of 520-830 Hz. Transmission and reflection predictions using effective parameters are shown to agree remarkably well with the experiment. © 2013 American Physical Society.


Li Y.,CAS Shanghai Institutes for Biological Sciences | Du X.-F.,CAS Shanghai Institutes for Biological Sciences | Liu C.-S.,CAS Shanghai Institutes for Biological Sciences | Wen Z.-L.,Hong Kong University of Science and Technology | Du J.-L.,CAS Shanghai Institutes for Biological Sciences
Developmental Cell | Year: 2012

Microglia are the primary immune cells in the brain. Under physiological conditions, they typically stay in a "resting" state, with ramified processes continuously extending to and retracting from surrounding neural tissues. Whether and how such highly dynamic resting microglia functionally interact with surrounding neurons are still unclear. Using in vivo time-lapse imaging of both microglial morphology and neuronal activity in the optic tectum of larval zebrafish, we found that neuronal activity steers resting microglial processes and facilitates their contact with highly active neurons. This process requires the activation of pannexin-1 hemichannels on neurons. Reciprocally, such resting microglia-neuron contact reduces both spontaneous and visually evoked activities of contacted neurons. Our findings reveal an instructive role for neuronal activity in resting microglial motility and suggest the function for microglia in homeostatic regulation of neuronal activity in the healthy brain. Little is known about the role of resting microglia in the healthy brain. Looking in vivo in zebrafish, Li et al. uncover reciprocal regulation between neurons and resting microglia in which neuronal activity provokes the formation of microglial contacts that, in turn, downregulate the activity of contacted neurons. © 2012 Elsevier Inc.


Ruan L.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2010

In this paper, we consider a cognitive multi-hop relay secondary user (SU) system sharing the spectrum with some primary users (PU). The transmit power as well as the hop selection of the cognitive relays can be dynamically adapted according to the local (and causal) knowledge of the instantaneous channel state information (CSI) in the multi-hop SU system. We shall determine a low complexity, decentralized algorithm to maximize the average end-to-end throughput of the SU system with dynamic spatial reuse. The problem is challenging due to the decentralized requirement as well as the causality constraint on the knowledge of CSI. Furthermore, the problem belongs to the class of stochastic Network Utility Maximization (NUM) problems which is quite challenging. We exploit the time-scale difference between the PU activity and the CSI fluctuations and decompose the problem into a master problem and subproblems. We derive an asymptotically optimal low complexity solution using divide-and-conquer and illustrate that significant performance gain can be obtained through dynamic hop selection and power control. The worst case complexity and memory requirement of the proposed algorithm is O(M 2) and O(M 3) respectively, where M is the number of SUs. © 2010 IEEE.


Zhou X.,Australian National University | McKay M.R.,Hong Kong University of Science and Technology
IEEE Transactions on Vehicular Technology | Year: 2010

We consider the problem of secure communication with multiantenna transmission in fading channels. The transmitter simultaneously transmits an information-bearing signal to the intended receiver and artificial noise to the eavesdroppers. We obtain an analytical closed-form expression of an achievable secrecy rate and use it as the objective function to optimize the transmit power allocation between the information signal and the artificial noise. Our analytical and numerical results show that equal power allocation is a simple yet near-optimal strategy for the case of noncolluding eavesdroppers. When the number of colluding eavesdroppers increases, more power should be used to generate the artificial noise. We also provide an upper bound on the SNR, above which, the achievable secrecy rate is positive and shows that the bound is tight at low SNR. Furthermore, we consider the impact of imperfect channel state information (CSI) at both the transmitter and the receiver and find that it is wise to create more artificial noise to confuse the eavesdroppers than to increase the signal strength for the intended receiver if the CSI is not accurately obtained. © 2006 IEEE.


Chen S.,South University of Science and Technology of China | Kwok H.-S.,Hong Kong University of Science and Technology
Israel Journal of Chemistry | Year: 2014

Light outcoupling from organic light-emitting diodes (OLEDs) is essential for developing energy-saving displays and efficient lighting sources. Nanocrystallized organic thin films exhibiting scattering features have been considered as effective light extractors for OLEDs. This paper reviews recent advancements in nanocrystallized thin films and their applications in OLEDs. Due to the advantages of easy preparation and OLED compatibility, nanocrystallized organic thin films can integrate with OLEDs as external or internal light extractors easily. Significant light enhancement has been achieved. The fabrication methods and mechanisms of light enhancement are discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Cui Y.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2010

In this paper, we consider the distributive queue-aware power and subband allocation design for a delay-optimal OFDMA uplink system with one base station, K users and NF independent subbands. Each mobile has an uplink queue with heterogeneous packet arrivals and delay requirements. We model the problem as an infinite horizon average reward Markov decision problem (MDP) where the control actions are functions of the instantaneous channel state information (CSI) as well as the joint queue state information (QSI). To address the distributive requirement and the issue of exponential memory requirement and computational complexity, we approximate the subband allocation Q-factor by the sum of the per-user subband allocation Q-factor and derive a distributive online stochastic learning algorithm to estimate the per-user Q-factor and the Lagrange multipliers (LM) simultaneously and determine the control actions using an auction mechanism. We show that under the proposed auction mechanism, the distributive online learning converges almost surely (with probability 1). For illustration, we apply the proposed distributive stochastic learning framework to an application example with exponential packet size distribution. We show that the delay-optimal power control has the multilevel water-filling structure where the CSI determines the instantaneous power allocation and the QSI determines the water-level. The proposed algorithm has linear signaling overhead and computational complexity OKNF, which is desirable from an implementation perspective. © 2006 IEEE.


Hu L.,Sun Yat Sen University | You F.,Sun Yat Sen University | Yu T.,Hong Kong University of Science and Technology
Materials and Design | Year: 2014

Based on the cells' collapse mechanisms revealed from the numerical simulations, analytical models are established to deduce the crushing strength of the honeycombs along the y-direction with wide range of impact velocity, which express crushing strength as a function of the impact velocity, the cell size, the cell-wall angle, and the mechanical properties of the base material. The analytical predictions are in good agreement with the numerical simulation results. The optimal cell-wall angle of the honeycomb is analytically obtained as about 45°, which provides a theoretical confirmation on the finding from the numerical simulations. Moreover, a dynamic sensitivity index is proposed to quantitatively evaluate the sensitivity of the honeycombs' crushing strength to the impact velocity, which is expressed as a function of the cell-wall angle and the honeycomb's relative density. It is shown that the dynamic sensitivity of the honeycomb is reversely proportional to the honeycomb's relative density, while the crushing strength of the honeycomb with β = 45° is the least sensitive to the impact velocity. © 2013 Elsevier Ltd.


Chen H.,Hong Kong University of Science and Technology | Poon A.W.,Hong Kong University of Science and Technology
Applied Physics Letters | Year: 2010

We demonstrate two-photon absorption (TPA) photocurrent in p-i-n diode embedded silicon microdisk resonators. Our experiments reveal TPA photocurrent spectra with peaks corresponding to the microdisk resonance modes. The photocurrents at resonance wavelengths exceed those at off-resonance wavelengths by up to three orders of magnitude. We study the microdisk photocurrent spectra with various p-i-n diode intrinsic region widths in the microdisk rim. We report TPA photovoltaic effect with maximum power generation efficiency of ∼0.3%. © 2010 American Institute of Physics.


Ning X.,Beijing Jiaotong University | Tsung F.,Hong Kong University of Science and Technology
IIE Transactions (Institute of Industrial Engineers) | Year: 2012

Statistical Process Control (SPC) techniques are useful tools for detecting changes in process variables. The structure of process variables has become increasingly complex as a result of increasingly complex technologies. The number of variables is usually large and categorical variables may appear alongside continuous variables. Such observations are considered to be high-dimensional and mixed-type observations. Conventional SPC techniques may lose their accuracy and efficiency in detecting changes in a process with high-dimensional and mixed-type observations. This article presents a density-based SPC approach, which is derived from a Local Outlier Factor (LOF) scheme, as a solution to this problem. The parameters in an LOF scheme are investigated and a procedure to design a corresponding control chart is presented. The good performance of the proposed control scheme is demonstrated via numerical simulation. © 2012 Copyright Taylor and Francis Group, LLC.


Zhang T.-Y.,Hong Kong University of Science and Technology | Ren H.,Hong Kong University of Science and Technology
Acta Materialia | Year: 2013

Taking advantage of both the Gibbs and McLean adsorption isotherms, we develop a Gibbs-approach-based adsorption isotherm for grain boundary (GB) segregation in nanograined (ng) polycrystals. An excess GB thickness is introduced to describe the excess of GB atomic volume in comparison with the atomic volume in lattice. The GB bulk modulus is determined with the excess GB thickness and a universal function. The newly developed adsorption isotherm is able to analyze simultaneously stresses, concentrations and their coupling behaviors in grains and GBs. Numerical calculations and plots are conducted to illustrate the theoretical analysis. The results show that the apparent solute concentration could be greatly enhanced in ng materials, due to a large grain boundary volume fraction and a considerable increase in the lattice concentration that is, in turn, boosted by the concentration-induced stresses. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Mollon G.,CNRS Contacts and Structural Mechanics Laboratory | Zhao J.,Hong Kong University of Science and Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2014

The inability of simulating the grain shapes of granular media accurately has been an outstanding issue preventing particle-based methods such as discrete element method from providing meaningful information for relevant scientific and engineering applications. In this study we propose a novel statistical method to generate virtual 3D particles with realistically complex yet controllable shapes and further pack them effectively for use in discrete-element modelling of granular materials. We combine the theory of random fields for spherical topology with a Fourier-shape-descriptor based method for the particle generation, and develop rigorous solutions to resolve the mathematical difficulties arising from the linking of the two. The generated particles are then packed within a prescribed container by a cell-filling algorithm based on Constrained Voronoi Tessellation. We employ two examples to demonstrate the excellent control and flexibility that the proposed method can offer in reproducing such key characteristics as shape descriptors (aspect ratio, roundness, sphericity, presence of facets, etc.), size distribution and solid fraction. The study provides a general and robust framework on effective characterization and packing of granular particles with complex shapes for discrete modelling of granular media. © 2014 Elsevier B.V.


DeJong M.J.,University of Cambridge | Dimitrakopoulos E.G.,Hong Kong University of Science and Technology
Earthquake Engineering and Structural Dynamics | Year: 2014

Predicting the rocking response of structures to ground motion is important for assessment of existing structures, which may be vulnerable to uplift and overturning, as well as for designs which employ rocking as a means of seismic isolation. However, the majority of studies utilize a single rocking block to characterize rocking motion. In this paper, a methodology is proposed to derive equivalence between the single rocking block and various rocking mechanisms, yielding a set of fundamental rocking parameters. Specific structures that have exact dynamic equivalence with a single rocking block, are first reviewed. Subsequently, approximate equivalence between single and multiple block mechanisms is achieved through local linearization of the relevant equations of motion. The approximation error associated with linearization is quantified for three essential mechanisms, providing a measure of the confidence with which the proposed methodology can be applied. © 2014 John Wiley & Sons, Ltd.


Dimitrakopoulos E.G.,Hong Kong University of Science and Technology | DeJong M.J.,University of Cambridge
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2012

In this paper, the dynamic response of the rocking block subjected to base excitation is revisited. The goal is to offer new closed-form solutions and original similarity laws that shed light on the fundamental aspects of the rocking block. The focus is on the transient dynamics of the rocking block under finite-duration excitations. An alternative way to describe the response of the rocking block, informative of the behaviour of rocking structures under excitations of different intensity, is offered. In the process, limitations of standard dimensional analysis, related to the orientations of the involved physical quantities, are revealed. The proposed dimensionless and orientationless groups condense the response and offer a lucid depiction of the rocking phenomenon. When expressed in the appropriate dimensionless- orientationless groups, the rocking response becomes perfectly self-similar for slender blocks (within the small rotations range) and practically self-similar for non-slender blocks (larger rotations). Using this formulation, the nonlinear and non-smooth rocking response to pulse-type ground motion can be directly determined, and need only be scaled by the intensity and frequency of the excitation. © 2012 The Royal Society.


Lu Q.,Hong Kong University of Science and Technology
Nature Structural and Molecular Biology | Year: 2014

Class I myosins can sense cellular mechanical forces and function as tension-sensitive anchors or transporters. How mechanical load is transduced from the membrane-binding tail to the force-generating head in myosin-1 is unknown. Here we determined the crystal structure of the entire tail of mouse myosin-1c in complex with apocalmodulin, showing that myosin-1c adopts a stable monomer conformation suited for force transduction. The lever-arm helix and the C-terminal extended PH domain of the motor are coupled by a stable post-IQ domain bound to calmodulin in a highly unusual mode. Ca2+ binding to calmodulin induces major conformational changes in both IQ motifs and the post-IQ domain and increases flexibility of the myosin-1c tail. Our study provides a structural blueprint for the neck and tail domains of myosin-1 and expands the target binding modes of the master Ca2+-signal regulator calmodulin. © 2014 Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.


Tso C.Y.,Hong Kong University of Science and Technology | Chao C.Y.H.,Hong Kong University of Science and Technology
International Journal of Refrigeration | Year: 2012

Composite adsorbents were synthesized from activated carbon, silica-gel and CaCl 2. The optimized condition for adsorption cooling systems was obtained when raw activated carbon was impregnated by soaking in 10 wt.% sodium silicate solution for 48 h and then in 30 wt.% CaCl 2 solution for 48 h. A 0.805 kg kg -1 of difference in equilibrium water uptake between 25 °C and 115 °C was recorded at atmospheric pressure. Besides, an adsorption rate test unit was built to study the adsorption isotherms and adsorption rates in which 0.23 kg kg -1 of adsorption capacity was recorded at 27 °C and a water vapor pressure of 900 Pa. The ideal coefficient of performance (COP) and the average specific cooling power (SCP) for an adsorption cooling system using the composite adsorbent were estimated to be 0.70 and 378 W kg -1 respectively. The results demonstrated that the composite adsorbents can be a good candidate for low temperature heat-driven adsorption cooling and dehumidification systems. © 2012 Elsevier Ltd and IIR. All rights reserved.


Zheng Y.,Microsoft | Capra L.,University College London | Wolfson O.,University of Illinois at Chicago | Yang H.,Hong Kong University of Science and Technology
ACM Transactions on Intelligent Systems and Technology | Year: 2014

Urbanization's rapid progress has modernized many people's lives but also engendered big issues, such as traffic congestion, energy consumption, and pollution. Urban computing aims to tackle these issues by using the data that has been generated in cities (e.g., traffic flow, human mobility, and geographical data). Urban computing connects urban sensing, data management, data analytics, and service providing into a recurrent process for an unobtrusive and continuous improvement of people's lives, city operation systems, and the environment. Urban computing is an interdisciplinary field where computer sciences meet conventional city-related fields, like transportation, civil engineering, environment, economy, ecology, and sociology in the context of urban spaces. This article first introduces the concept of urban computing, discussing its general framework and key challenges from the perspective of computer sciences. Second, we classify the applications of urban computing into seven categories, consisting of urban planning, transportation, the environment, energy, social, economy, and public safety and security, presenting representative scenarios in each category. Third, we summarize the typical technologies that are needed in urban computing into four folds, which are about urban sensing, urban data management, knowledge fusion across heterogeneous data, and urban data visualization. Finally, we give an outlook on the future of urban computing, suggesting a few research topics that are somehow missing in the community. © 2014 ACM 2157-6904/2014/09-ART38 $15.00.


Ng C.W.W.,Hong Kong University of Science and Technology | Xu J.,Hong Kong University of Science and Technology
Canadian Geotechnical Journal | Year: 2012

Although the small-strain shear modulus of saturated soils is known to be significantly affected by stress history, consisting of the overconsolidation ratio (OCR) and recent stress history, the effects of suction history on the small-strain shear modulus of unsaturated soils have rarely been reported. In this study, the effects of suction history, which refers to current suction ratio (CSR) and recent suction history, on both the very-small-strain shear modulus (G 0) and shear modulus reduction curve of an unsaturated soil, are investigated by carrying out constant net mean stress compression triaxial tests with bender elements and local strain measurements. In addition, the effect of suction magnitude on G0 and the shear modulus reduction curve is also investigated. At a given suction, G 0, elastic threshold strain (ε e), and the rate of shear modulus reduction all increase with CSR. On the other hand, the effect of recent suction history on G0 is not significant. The effect of direction of recent suction path (θ) on the shear modulus reduction curve is not distinct. However, the magnitude of recent suction path (l) affects the shear modulus reduction curve significantly when θ = -90°.


Gao Z.,Hong Kong University of Science and Technology | Zhao J.,Hong Kong University of Science and Technology
Computers and Geotechnics | Year: 2012

Artificially cemented sand has been widely used in practical applications relevant to soil improvement and liquefaction mitigation. It has also been frequently used in laboratory tests to simulate the cementation and bonding formed in naturally structured sand. Known to be difficult to characterize, the behavior of artificially cemented sand is typically affected by its internal structure consisting of both bonding and fabric. In this study, a novel constitutive model is proposed to describe the effect of bonding and fabric anisotropy on the behavior of artificially cemented sand. We choose the triaxial tensile strength as a macroscopic representation of the inter-particle bonding, and a fabric tensor to characterize the fabric in sand. The yield function adopted in the model is an extension of a recently developed anisotropic failure criterion, with the frictional parameter therein being replaced by a proper hardening parameter. A de-bonding law is proposed by assuming the de-bonding process is driven by the development of plastic deformation. The soil fabric is kept constant in the study to account for inherent anisotropy. Relevant model parameters can be conveniently calibrated by conventional laboratory tests. The model is employed to predict the behavior of cemented Ottawa sand and multiple-sieving-pluviated Toyoura sand, and the predictions compare well with the experimental data. © 2011 Elsevier Ltd.


Dai H.,Central University of Finance and Economics | Tseng M.M.,Hong Kong University of Science and Technology
International Journal of Production Economics | Year: 2012

Mismatch of inventory information between the reality and what is on the record of information systems has been generally accepted as inventory inaccuracy. Its financial impacts go beyond the cost of direct inventory loss at each stage of the supply chain. The discrepancy also results in increasing holding and shortage cost because information distortion propagates along the supply chain. With the growing emphasis on responsiveness and cost of inventory, inventory inaccuracy has become a critical hurdle to achieve high performance supply chains. The emergence of RFID technology offers a possible solution to alleviate the growing cost of inventory inaccuracy. However, differs from tangible justification based on shrinkage reduction, adoption of RFID technology has to be justified with improvement in intangible information flow. The objective of this paper is to present a systematic approach with analytical models to quantify the extent of saving from timely information as well as reduction in information distortion and its amplification. With the increasing dynamic and complexity of global supply chain, this paper may shed some new light on framing the discussion of investing in RFID technology. © 2012 Elsevier B.V. All rights reserved.


Zhan C.,Hong Kong University of Science and Technology | Ki W.-H.,Hong Kong University of Science and Technology
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2012

This paper presents an output-capacitor-free adaptively biased low-dropout regulator with subthreshold undershoot-reduction (ABSTUR LDR) for SoC power management applications. Techniques of adaptive biasing (AB) and Miller compensation with Q-reduction are employed to achieve low-voltage high-precision regulation with extended loop bandwidth while maintaining low quiescent current and high current efficiency. The pass transistor is designed to work in the linear region at heavy load to save silicon area, and a symmetrically matched current-voltage mirror is used to implement the AB scheme with accurate current sensing for the full load range. The dedicated STUR circuit, which is low-voltage compatible and consumes very low current in the steady state, is inserted to momentarily but exponentially increase the gate discharging current of the pass transistor when the LDR output has a large undershoot due to a large step up of the load current. Undershoot voltage is hence dramatically reduced. Stability of the ABSTUR LDR is thoroughly analyzed and tradeoffs between the undershoot-reduction strength and the light load stability are discussed. Features of the proposed ABSTUR LDR are experimentally verified by a prototype fabricated in a standard 0.35-μm CMOS process. © 2004-2012 IEEE.


Dangkulwanich M.,Howard Hughes Medical Institute | Ishibashi T.,Howard Hughes Medical Institute | Ishibashi T.,Hong Kong University of Science and Technology | Bintu L.,Howard Hughes Medical Institute | And 3 more authors.
Chemical Reviews | Year: 2014

A review of the various aspects of transcription that have been addressed using methods of single-molecule detection and manipulation is studied. Whereas single-subunit viral polymerases such as T7 and SP6 RNAP can start transcription at a promoter region without additional cofactors, multi subunit bacterial and eukaryotic RNA polymerase (RNAPs) require transcription factors that aid the enzyme to recognize and bind to the promoter. Through the combination of single molecule manipulation and single-molecule fluorescence methods in the same experiment, it should be possible to follow, the internal dynamics of the polymerase or the binding of a regulatory factor and simultaneously monitor the mechanical variables of position, force, and torque. The result of these efforts will be a multidimensional picture of transcription that will provide crucial information about the relative timing of various molecular events and therefore reveal their causal connection.


Leung Shingyu S.,Hong Kong University of Science and Technology
Journal of Computational Physics | Year: 2011

We propose efficient Eulerian methods for approximating the finite-time Lyapunov exponent (FTLE). The idea is to compute the related flow map using the Level Set Method and the Liouville equation. There are several advantages of the proposed approach. Unlike the usual Lagrangian-type computations, the resulting method requires the velocity field defined only at discrete locations. No interpolation of the velocity field is needed. Also, the method automatically stops a particle trajectory in the case when the ray hits the boundary of the computational domain. The computational complexity of the algorithm is O(Δx -(d+1)) with d the dimension of the physical space. Since there are the same number of mesh points in the x-t space, the computational complexity of the proposed Eulerian approach is optimal in the sense that each grid point is visited for only O(1) time. We also extend the algorithm to compute the FTLE on a co-dimension one manifold. The resulting algorithm does not require computation on any local coordinate system and is simple to implement even for an evolving manifold. © 2011 Elsevier Inc.


Pan K.,Hong Kong University of Science and Technology | Wang W.-X.,Hong Kong University of Science and Technology
Environmental Pollution | Year: 2011

Differences in the accumulation of mercury (Hg) in five species of marine bivalves, including scallops Chlamys nobilis, clams Ruditapes philippinarum, oysters Saccostrea cucullata, green mussels Perna viridis, and black mussels Septifer virgatus, were investigated. The bivalves displayed different patterns of Hg accumulation in terms of the body concentrations of methylmercury (MeHg) and total Hg (THg), as well as the ratio of MeHg to THg. Parameters of the biodynamics of the accumulation of Hg(II) and MeHg could reflect the species-dependent Hg concentrations in the bivalves. With the exception of black mussels, we found a significant relationship between the efflux rates of Hg(II) and the THg concentrations in the bivalves. The interspecific variations in the MeHg to THg ratio were largely controlled by the relative difference between the elimination rates of Hg(II) and MeHg. Stable isotope (δ 13C) analysis indicated that the five bivalve species had contrasting feeding niches, which may also affect the Hg accumulation. © 2010 Published by Elsevier Ltd.


Wu Y.,Hong Kong University of Science and Technology | Wang W.-X.,Hong Kong University of Science and Technology
Environmental Pollution | Year: 2011

We examined the accumulation, subcellular distribution, and toxicity of Hg(II) and MeHg in three marine phytoplankton (the diatom Thalassiosira pseudonana, the green alga Chlorella autotrophica, and the flagellate Isochrysis galbana). For MeHg, the inter-species toxic difference could be best interpreted by the total cellular or intracellular accumulation. For Hg(II), both I. galbana and T. pseudonana exhibited similar sensitivity, but they each accumulated a different level of Hg(II). A higher percentage of Hg(II) was bound to the cellular debris fraction in T. pseudonana than in I. galbana, implying that the cellular debris may play an important role in Hg(II) detoxification. Furthermore, heat-stable proteins were a major binding pool for MeHg, while the cellular debris was an important binding pool for Hg(II). Elucidating the different subcellular fates of Hg(II) and MeHg may help us understand their toxicity in marine phytoplankton at the bottom of aquatic food chains. © 2010 Published by Elsevier Ltd.


Hou D.,Hong Kong University of Science and Technology | Ma H.,Hong Kong University of Science and Technology | Zhu Y.,Henan Polytechnic University | Li Z.,Hong Kong University of Science and Technology
Acta Materialia | Year: 2014

Calcium silicate hydrate (C-S-H) is the most important hydration product of cement-based materials. In the nanostructure of C-S-H, structural water molecules are distributed in the interlayer region and determine the mechanical performance of C-S-H gel. In this study, C-S-H gels with different water contents expressed as the water/Ca ratio are characterized in the light of molecular dynamics. In order to study the influence of the water molecules, the structures of 12 C-S-H gel samples with water/Ca ratios from 0 to 0.95 are investigated. It is found that the penetration of water molecules transforms the C-S-H gel from an amorphous to a layered structure by silicate depolymerization as the water content gradually increases. The structures are then tested for mechanical properties by simulated uniaxial tension and compression. The mechanical tests associated with structural analysis reveal that the structural water molecules can greatly weaken the stiffness and the cohesive force by replacing the ionic-covalent bond with unstable H-bond connections. By studying the tensile failure mechanism of C-S-H gels at different humidity levels, the disconnecting role of the structural water molecules is comprehensively interpreted. Because the interlayer water molecules prevent reconstruction of the bonds between the Caw and the silicate chains, the plasticity of the C-S-H gels is reduced significantly in the change from a dry state to a saturated state. In addition, the compressive strength of a C-S-H gel in the saturated state is much larger than the tensile strength. This provides molecular evidence for the tensile weakness of cement paste. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Mak M.S.H.,Hong Kong University of Science and Technology | Lo I.M.C.,Hong Kong University of Science and Technology
Chemosphere | Year: 2011

This study investigated the removal kinetics and mechanisms of Cr(VI) and As(V) by Fe(0) in the presence of fulvic acid (FA) and humic acid (HA) by means of batch experiments. The focus was on the involvements of FA and HA in redox reactions, metal complexation, and iron corrosion product aggregation in the removal of Cr(VI) and As(V) removal by Fe(0). Synthetic groundwater was used as the background electrolyte to simulate typical groundwater. The results showed faster Cr(VI) removal in the presence of HA compared to FA. Fluorescence spectroscopy revealed that no redox reaction occurred in the FA and HA. The results of the speciation modeling indicate that the free Fe(II) concentration was higher in the presence of HA, resulting in a higher removal rate of Cr(VI). However, the removal of As(V) was inhibited in the HA solution. Speciation modeling showed that the concentration of dissolved metal-natural organic matter (metal-NOM) complexes significantly affected the aggregation of the iron corrosion products which in turn affected the removal of As(V). The aggregation was found to be induced by gel-bridging of metal-NOM with the iron corrosion products. The effects of metal-NOM on the aggregation of the iron corrosion products were further confirmed by TEM studies. Larger sizes of iron corrosion products were formed in the FA solution compared to HA solution. This study can shed light on understanding the relationships between the properties of NOM (especially the content of metal-binding sites) and the removal of Cr(VI) and As(V) by Fe(0). © 2011 Elsevier Ltd.


Chang H.,Tohoku University | Chang H.,Huazhong University of Science and Technology | Wu H.,Tohoku University | Wu H.,Hong Kong University of Science and Technology
Energy and Environmental Science | Year: 2013

Graphene, a two-dimensional carbon sheet with one atom thickness and one of the thinnest materials in universe, has inspired huge interest in physics, materials science, chemistry and biology. However, pure graphene sheets are limited for many applications despite their excellent characteristics and scientists face challenges to induce more and controlled functionality. Therefore graphene nanocomposites or hybrids are attracting increasing efforts for real applications in energy and environmental areas by introducing controlled functional building blocks to graphene. In this Review, we first give a brief introduction of graphene's unique physical and chemical properties followed by various preparation and functionalization methods for graphene nanocomposites in the second section. We focus on recent energy-related progress of graphene nanocomposites in solar energy conversion (e.g., photovoltaic and photoelectrochemical devices, artificial photosynthesis) and electrochemical energy devices (e.g., lithium ion battery, supercapacitor, fuel cell) in the third section. We then review the advances in environmental applications of functionalized graphene nanocomposites for the detection and removal of heavy metal ions, organic pollutants, gas and bacteria in the fourth section. Finally a conclusion and perspective is given to discuss the remaining challenges for graphene nanocomposites in energy and environmental science. © 2013 The Royal Society of Chemistry.


Cheung Z.H.,Hong Kong University of Science and Technology | Ip N.Y.,Hong Kong University of Science and Technology
Trends in Cell Biology | Year: 2012

Since the identification of cyclin-dependent kinase-5 (Cdk5) as a tau kinase and member of the Cdk family almost 20 years ago, deregulation of Cdk5 activity has been linked to an array of neurodegenerative diseases. As knowledge on the etiopathological mechanisms of these diseases evolved through the years, Cdk5 has also been implicated in additional cellular events that are affected under these pathological conditions. From the role of Cdk5 in the regulation of synaptic functions to its involvement in autophagy deregulation, significant insights have been obtained regarding the role of Cdk5 as a key regulator of neurodegeneration. Here, we summarize recent findings on the involvement of Cdk5 in the pathophysiological mechanisms underlying various neurodegenerative diseases. © 2011 Elsevier Ltd.


Ni R.,Hong Kong University of Science and Technology | Chau Y.,Hong Kong University of Science and Technology
Journal of the American Chemical Society | Year: 2014

A synthetic mimic of viral structure has been constructed by the synergistic co-assembly of a 16-amino acid peptide and plasmid DNA. The rational design of this short peptide, including segments for binding DNA and forming β-sheet, is inspired by viral capsid protein. The resulting nanostructures, which we term nanococoons, appear as ellipsoids of virus-like dimension (65 × 47 nm) and display repeating stripes of ∼4 nm wide. We propose that the co-assembly process involves DNA as a template to assist the organization of peptide strands by electrostatic interaction, while the bilayer β-sheets and their lateral association stabilize the peptide "capsid" and organize the DNA within. The hierarchy affords an extremely stable structure, protecting peptide and DNA against enzymatic digestion. It opens a new and facile avenue to fabricate viral alternatives with diverse functions. © 2014 American Chemical Society.


Liu X.-J.,University of Maryland University College | Liu X.-J.,Hong Kong University of Science and Technology | Liu Z.-X.,Tsinghua University | Liu Z.-X.,Massachusetts Institute of Technology | Cheng M.,University of Maryland University College
Physical Review Letters | Year: 2013

We propose to observe and manipulate topological edge spins in a one-dimensional optical lattice based on currently available experimental platforms. Coupling the atomic spin states to a laser-induced periodic Zeeman field, the lattice system can be driven into a symmetry protected topological (SPT) phase, which belongs to the chiral unitary (AIII) class protected by particle number conservation and chiral symmetries. In the free-fermion case the SPT phase is classified by a Z invariant which reduces to Z4 with interactions. The zero edge modes of the SPT phase are spin polarized, with left and right edge spins polarized to opposite directions and forming a topological spin qubit (TSQ). We demonstrate a novel scheme to manipulate the zero modes and realize single spin control in an optical lattice. The manipulation of TSQs has potential applications to quantum computation. © 2013 American Physical Society.


Xuan F.,Hong Kong University of Science and Technology | Hsing I.-M.,Hong Kong University of Science and Technology
Journal of the American Chemical Society | Year: 2014

We present a nonlinear hybridization chain reaction (HCR) system in which a trigger DNA initiates self-sustained assembly of quenched double-stranded substrates into fluorescent dendritic nanostructures. During the process, an increasing number of originally sequestered trigger sequences labeled with fluorescent reporters are freed up from quenched substrates, leading to chain-branching growth of the assembled DNA dendrimers and an exponential increase in the fluorescence intensity. The triggered assembly behavior was examined by PAGE analysis, and the morphologies of the grown dendrimers were verified by AFM imaging. The exponential kinetics of the fluorescence accumulation was also confirmed by time-dependent fluorescence spectroscopy. This method adopts a simple sequence design strategy, the concept of which could be adapted to program assembly systems with higher-order growth kinetics. © 2014 American Chemical Society.


Zheng X.,Anhui University of Science and Technology | Yan Y.,Anhui University of Science and Technology | Yan Y.,Hong Kong University of Science and Technology | Di Ventra M.,University of California at San Diego
Physical Review Letters | Year: 2013

We investigate the real-time current response of strongly correlated quantum dot systems under sinusoidal driving voltages. By means of an accurate hierarchical equations of motion approach, we demonstrate the presence of prominent memory effects induced by the Kondo resonance on the real-time current response. These memory effects appear as distinctive hysteresis line shapes and self-crossing features in the dynamic current-voltage characteristics, with concomitant excitation of odd-number overtones. They emerge as a cooperative effect of quantum coherence - due to inductive behavior - and electron correlations - due to the Kondo resonance. We also show the suppression of memory effects and the transition to classical behavior as a function of temperature. All these phenomena can be observed in experiments and may lead to novel quantum memory applications. © 2013 American Physical Society.


Weng L.-T.,Hong Kong University of Science and Technology
Applied Catalysis A: General | Year: 2014

This paper provides a critical review on the applications of time-of-flight secondary ion mass spectrometry (ToF-SIMS) in heterogeneous catalysis, with a particular emphasis on the examples published during the last decade. The covered areas include supported metal oxide catalysts, supported metal catalysts, electrocatalysts for oxygen-reduction reaction and organometallic clusters as precursors for the preparation of heterogeneous catalysts. The molecular specificity and surface sensitivity of ToF-SIMS have been shown to be extremely useful in the surface characterization of heterogeneous catalysts, in particular in the areas of assessing the formation of new compounds or interactions between different components (e.g. active phase-active phase or active phase-support), providing more precision on the structure of surface species, monitoring the different steps of catalyst preparation and/or activation, etc. In some cases, ToF-SIMS is able to provide unique molecular information that is unattainable with other conventional techniques and thus give a more precise characterization of the heterogeneous catalysts. Finally, the advantages and limitations of ToF-SIMS with respect to other more conventional techniques such as XPS are also discussed. © 2013 Elsevier B.V.


Lin F.,Hong Kong University of Science and Technology
Artificial Intelligence | Year: 2016

We consider the problem of representing and reasoning about computer programs, and propose a translation from a core procedural iterative programming language to first-order logic with quantification over the domain of natural numbers that includes the usual successor function and the "less than" linear order, essentially a first-order logic with a discrete linear order. Unlike Hoare's logic, our approach does not rely on loop invariants. Unlike the typical temporal logic specification of a program, our translation does not require a transition system model of the program, and is compositional on the structures of the program. Some non-trivial examples are given to show the effectiveness of our translation for proving properties of programs. © 2016 Elsevier B.V.


Ahadi A.,Hong Kong University of Science and Technology | Sun Q.,Hong Kong University of Science and Technology
Applied Physics Letters | Year: 2013

Stress hysteresis (H) and temperature dependence of phase transition stress (d σ / d T) are the two signatures of first-order phase transition in shape memory alloys. We studied the effects of grain size on these two properties in polycrystalline superelastic NiTi with the average grain size from 10 nm to 1500 nm. We identified a critical grain size (∼60 nm) below which both H and d σ / d T rapidly decrease, leading to vanishing hysteresis and breakdown of Clausius-Clapeyron equation. The physics behind such grain size effects are the dominance of interfacial energy in the energetics of the polycrystal and the lack of two-phase coexistence at nano-scales. © 2013 AIP Publishing LLC.


Wang W.,Hong Kong University of Science and Technology | Shi X.,City University of Hong Kong | Wang S.,Hong Kong University of Science and Technology | Van Hove M.A.,City University of Hong Kong | Lin N.,Hong Kong University of Science and Technology
Journal of the American Chemical Society | Year: 2011

We have studied the organometallic intermediate of a surface-supported Ullmann coupling reaction from 4, 4″-dibromo-p-terphenyl to poly(para-phenylene) by scanning tunneling microscopy/spectroscopy and density functional theory calculations. Our study reveals at a single-molecular level that the intermediate consists of biradical terphenyl (ph)3 units that are connected by single Cu atoms through C-Cu-C bridges. Upon further increasing the temperature, the neighboring biradical (ph)3 units are coupled by C-C bonds forming poly(para-phenylene) oligomers while the Cu atoms are released. © 2011 American Chemical Society.


Zheng Q.,Hong Kong University of Science and Technology | Zheng Q.,University of Shanghai for Science and Technology | Zheng Q.,Leibniz Institute of Polymer Research | Li Z.,Hong Kong University of Science and Technology | And 2 more authors.
Progress in Materials Science | Year: 2014

The exciting features in almost all modern portable and house-hold electronics are driven by optoelectronics that extensively use transparent conductive films (TCFs) in components, such as touch screens, liquid crystal displays, organic photovoltaic cells and organic light-emitting diodes. Because of its excellent electrical conductivity, optical transparency and mechanical properties, graphene has been considered an ideal material to replace the existing, expensive indium tin oxide (ITO) as TCFs. Graphene oxide (GO) in the form of colloidal suspension is not only scalable for high volume production at low costs, but also compatible with emerging technologies based on flexible substrates. This paper reviews the current state-of-the-art developments and future prospects of TCFs synthesized using GO suspension. In addition, several established approaches are introduced, which have been proven effective in improving the optoelectrical performance of GO-based TCFs. They include chemical doping treatments, use of large size GO sheets, and hybrids with other nanostructured materials, such as carbon nanotubes (CNTs), metal nanowires (NWs) or nanogrids. © 2014 Elsevier Ltd. All rights reserved.


Ng C.W.W.,Hong Kong University of Science and Technology | Lu H.,Hong Kong University of Science and Technology
Canadian Geotechnical Journal | Year: 2014

Any tunnelling process inevitably induces changes in stress in the ground and may adversely affect nearby pile foundations. The interaction between tunnelling and an existing pile has been investigated by researchers and a certain amount of fundamental understanding has been gained. However, the effects of different tunnel excavation sequences on an adjacent pile remain to be understood. In this paper, a series of three-dimensional centrifuge model tests and numerical back-analyses were carried out to investigate the effects of construction sequence of twin tunnels on an existing pile in dry sand. Two tunnelling sequences were investigated: (i) a sequence involving tunnelling near the pile toe followed by tunnelling near the mid-depth of the pile shaft (i.e., test TS); (ii) sequence involving tunnelling near the mid-depth of the pile shaft followed by tunnelling near the pile toe (i.e., test ST). The measured cumulative pile settlement was about 33% larger for tunnelling sequence ST than for tunnelling sequence TS. Due to different tunnelling sequences, the apparent losses of pile capacity were 40% and 29% for sequences ST and TS, respectively. Although the computed reductions in normal stress acting on the pile induced by twin tunnelling were almost the same in tests TS and ST, tunnelling near the pile toe induced a larger decrease in the end-bearing and shaft resistances at the lower part of the pile in test ST than in test TS. In contrast to the measured pile head settlements, different tunnelling sequences had a limited effect on measured ground surface settlements and additional bending moments in the pile.


Chen H.X.,Hong Kong University of Science and Technology | Zhang L.M.,Hong Kong University of Science and Technology
Engineering Geology | Year: 2014

Rainfall-induced slope failures are one of the most frequent hazards on hilly terrains. This paper proposes a physically-based distributed cell model to predict regional rainfall-induced shallow slope failures in two-layer soils under realistic rainfall conditions. The model consists of four components; namely, a digital terrain model, a spatial rainfall distribution model, an infiltration analysis model, and a slope stability and reliability evaluation model. The digital terrain is discretized into a grid of numerous cells first, with the properties of the soils in each cell assigned. Universal kriging is then adopted to interpolate the spatial rainfall distribution. Afterwards, the infiltration analysis model is used to analyze the infiltration process in two-layer soils under realistic rainfall conditions. The slope stability and reliability evaluation model is finally adopted to assess the regional slope stability and reliability. The distributed cell model is applied to evaluate the spatial and temporal response of a 164.5km2 area to rainfall near the epicenter of the 2008 Wenchuan earthquake zone. Comparison between the predicted and observed slope failures triggered by the 13 August 2010 storm shows that this model is capable of predicting the locations of rainfall-induced slope failures reasonably well. The model is intended for use as a module in a real-time warning system for rainfall-induced slope failures. © 2014 Elsevier B.V.


Du W.,Hong Kong University of Science and Technology | Wang G.,Hong Kong University of Science and Technology
Earthquake Engineering and Structural Dynamics | Year: 2014

SUMMARY: Earthquake-induced slope displacement is an important parameter for safety evaluation and earthquake design of slope systems. Traditional probabilistic seismic hazard analysis usually focuses on evaluating slope displacement at a particular location, and it is not suitable for spatially distributed slopes over a large region. This study proposes a computationally efficient framework for fully probabilistic seismic displacement analysis of spatially distributed slope systems using spatially correlated vector intensity measures (IMs). First, a spatial cross-correlation model for three key ground motion IMs, that is, peak ground acceleration (PGA), Arias intensity, and peak ground velocity, is developed using 2686 ground motion recordings from 11 recent earthquakes. To reduce the computational cost, Monte Carlo simulation and data reduction techniques are utilized to generate spatially correlated random fields for the vector IMs. The slope displacement hazards over the region are further quantified using empirical predictive equations. Finally, an illustrative example is presented to highlight the importance of the spatial correlation and the advantage of using spatially correlated vector IMs in seismic hazard analysis of spatially distributed slopes. © 2013 John Wiley & Sons, Ltd.


Zhao H.F.,Hong Kong University of Science and Technology | Zhang L.M.,Hong Kong University of Science and Technology
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014

It is well known that saturated silt and fine sand are susceptible to instability during undrained shearing. Coarse granular soils may also be unstable during undrained shearing or during rainfall infiltration starting at an unsaturated state. This paper investigates the instability of three saturated and unsaturated granular soils with different fines contents (f 550, 32, and 10%). Isotropic consolidation tests and mercury intrusion porosimetry tests were first conducted to investigate the instability of the microstructures of these granular soils. Then drained and undrained triaxial tests were conducted to investigate the instability behavior under the saturated condition. Subsequently, wetting tests under the constant shear stress condition were carried out on unsaturated specimens to investigate the instability of the same soils during water infiltration. The instability in the microstructures is in accordance with the compressibility of the soils. The instability during undrained shearing under saturated conditions is described using relations between the state parameter and the peak shear strength or slope of the instability line of the soil. The instability of an unsaturated soil along a wetting path depends on the stress ratio and net confining pressure. Using the equivalent mean effective stress concept, a unified instability line is defined for both saturated and unsaturated soils. © 2014 American Society of Civil Engineers.


Liu C.,Hong Kong University of Science and Technology | Li Z.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2010

In this Letter, we propose a composite nanochannel system, where half of the channel is of low surface energy, while the other half has a relatively high surface energy. Molecular dynamics simulations show that fluids in such channels can be continuously driven by a symmetric temperature gradient. In the low surface energy part, the fluid moves from high to low temperature, while the fluid migrates from low to high temperature in the high surface energy part. The mechanisms that govern the flow are explained and the conditions required to guarantee the flow and the possible applications are discussed. © 2010 The American Physical Society.


Shao M.,Hong Kong University of Science and Technology
Journal of Power Sources | Year: 2014

The direct observation of the microstructural evolution and state-of-charge (SOC) distribution in active materials is crucial to understand the lithiation/delithiation mechanisms during electrochemical cycling of lithium-ion batteries (LIBs). Owing to their high spatial resolutions and capability to map chemical states by combining other spectroscopic techniques, microscopic techniques including X-ray fluorescence (XRF) microscopy, Raman microscopy, transmission X-ray microscopy (TXM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) play significant roles in real time monitoring the dynamic changes in the LIB electrodes and materials. This paper reviews the recent progress of using in situ microscopic techniques to study LIB materials, including Si-, Sn-, Ge-, C- and metal oxides-based anode materials, and layered oxysulfide, metal fluorides, LiCoO2, LiNi 0.8Co0.15Al0.05O2, LiMn 2O4, LiFePO4 cathode materials. © 2014 Elsevier B.V. All rights reserved.


Wong C.L.M.,Hong Kong University of Science and Technology | Law K.T.,Hong Kong University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In this work, we show that a quasi-one-dimensional dx2-y2-wave superconductor with Rashba spin-orbit coupling is a DIII class, time-reversal invariant, topological superconductor (TS), which supports a Majorana Kramers Doublet (MKD) at each end of the TS. A MKD is a pair of Majorana end states (MESs) protected by time-reversal symmetry (TRS). An external magnetic field breaks TRS and drives the system from DIII to D class in which case a single MES appears at each end of the TS. We show that a MKD induces resonant Andreev reflection with zero-bias conductance peak of 4e2/h. Experimental realizations of the proposed model are discussed. © 2012 American Physical Society.


Ciucci F.,Hong Kong University of Science and Technology | Lai W.,Michigan State University
Electrochimica Acta | Year: 2012

In this paper the electrochemical impedance response of phase transition materials is investigated within the Cahn-Hilliard framework. The application of regular perturbation techniques allows the determination of analytical expressions for stable perturbations around constant initial condition. If the initial condition corresponds to a steady state configuration with coexistence of two phases on the sample, then approximate analytical expressions can be found by suitable modification of the boundary conditions. In particular, the impedance response of a particle being synchronously charged/discharged on both sides (reflective conditions), featuring two phases and a phase transition region, is equivalent to the impedance response of a particle of smaller size allowing current go through (absorbing conditions). © 2012 Elsevier Ltd. All rights reserved.


Zhu J.,Hong Kong University of Science and Technology | Zhu J.,CAS Shanghai Institutes for Biological Sciences | Shang Y.,Hong Kong University of Science and Technology | Zhang M.,Hong Kong University of Science and Technology
Nature Reviews Neuroscience | Year: 2016

Membrane-associated guanylate kinases (MAGUKs) are a family of scaffold proteins that are highly enriched in synapses and are responsible for organizing the numerous protein complexes required for synaptic development and plasticity. Mutations in genes encoding MAGUKs and their interacting proteins can cause a broad spectrum of human psychiatric disorders. Here, we review MAGUK-mediated synaptic protein complex formation and regulation by focusing on findings from recent biochemical and structural investigations. These mechanistic-based studies show that the formation of MAGUK-organized complexes is often directly regulated by protein phosphorylation, suggesting a close connection between neuronal activity and the assembly of dynamic protein complexes in synapses. © 2016 Macmillan Publishers Limited. All rights reserved.


Chan C.,Hong Kong University of Science and Technology | Ng T.-K.,Hong Kong University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We study in this paper time-reversal δ-impurity scattering effects in the bulk of topological insulators (TI) in two and three dimensions. Specifically we consider how impurity scattering strength is affected by the bulk band structure of topological insulators. An interesting band inversion effect associated with the change of the system from ordinary to topological insulator is pointed out. Experimental consequences of our findings are discussed. © 2012 American Physical Society.


Muppala J.K.,Hong Kong University of Science and Technology
Proceedings - 2011 Workshop on Embedded Systems Education, WESE 2011 | Year: 2011

Does smartphone application development provide an opportunity to explore various aspects of embedded software? This question is the primary motivator behind the ideas explored in this paper. We cannot deny the ubiquitous nature of smartphones. Leveraging on this already available "platform" to convey embedded software concepts to Computer Science (CS) students seems an exciting opportunity. Traditionally CS have often shied away from the field of embedded systems owing to their perception of this area as "hardware" oriented, not without reason. We explore the Android platform as a means of advancing embedded software concepts to CS students. Copyright 2010 ACM.


Yu Z.-G.,Hong Kong University of Science and Technology | Wang W.-X.,Hong Kong University of Science and Technology
Water Research | Year: 2013

With the rapid increase of carbon nanotube (CNT) applications, there are considerable concerns of their inevitable releases into the aquatic environments. CNTs may interact with and further influence the fate and transport of other pollutants such as toxic metals. In the present study, non-covalent and nontoxic dispersant polyvinyl pyrrolidone (PVP) was used to provide a relatively stable test solution for CNTs. The dissolved uptake rate constant (ku) and the dietary assimilation efficiency (AE) of cadmium (Cd) and zinc (Zn) were then quantified in a freshwater zooplankton Daphnia magna in the presence of different CNTs (without functionalized - single-walled nanotubes-SWNTs, multi-walled nanotubes-MWNTs, and with functionalized - F-SWNTs, F-MWNTs, containing oxygen functional groups at the defect sites of CNTs) concentrations. We demonstrated that different CNTs exposures led to distinctive metal accumulation patterns. Non-functionalized CNTs significantly decreased the metal uptake rate from the dissolved phase, possibly because of their effects on the physiological activity of animals. In contrast, the F-CNTs (F-SWNTs and F-MWNTs) adsorbed the metals and increased the metal accumulation in daphnids in a concentration-dependent manner, due to the ingestion of F-CNTs associated metals. The AEs of metals in D. magna were elevated by CNTs physical blocking of the animal guts. Our present study showed that CNTs could serve as a new pathway for metal accumulation. This raised a new environmental problem of CNTs since they may induce the accumulation of toxic metals from the dietary exposure. © 2013 Elsevier Ltd.


Liu Y.,Hong Kong University of Science and Technology | Poon A.W.,Hong Kong University of Science and Technology
Optics Express | Year: 2010

An optothermal tweezer was developed with a single-beam laser at 1550 nm for manipulation of colloidal microparticles. Strong absorption in water can thermally induce a localized flow, which exerts a Stokes' drag on the particles that complements the gradient force. Long-range capturing of 6 μm polystyrene particles over ∼ 176 μm was observed with a tweezing power of ∼ 7 mW. Transportation and levitation,targeted deposition and selective levitation of particles were explored to experimentally demonstrate the versatility of the optothermal tweezer as a multipurpose particle manipulation tool. © 2010 Optical Society of America.


Yao H.,Hong Kong University of Science and Technology | Ren J.,Hong Kong University of Science and Technology | Tong R.,Hong Kong University of Science and Technology
Chemical Communications | Year: 2013

A short and flexible [3+2+1] synthetic strategy was developed for the synthesis of substituted tetrahydropyran-4-ones, featuring [3+2]-cycloaddition of α,β-unsaturated nitrile oxides and alkenes and oxa-Michael cyclization in a 6-endo-trig fashion. The efficiency of this synthetic strategy was further demonstrated by the concise total synthesis of (±)-diospongin A in 8 steps with 20.2% yield. This journal is © The Royal Society of Chemistry.


Yu M.,Hong Kong University of Science and Technology | Long Y.-Z.,Qingdao University | Sun B.,Qingdao University | Fan Z.,Hong Kong University of Science and Technology
Nanoscale | Year: 2012

As the demand for renewable energy resource is growing rapidly worldwide, a variety of energy materials and technologies are being developed. In this review, we aim to summarize recent developments in the state-of-the-art research on energy harvesting technologies such as thin-film Si or Ge, CdTe, GaAs, organic, hybrid, and dye-sensitized solar cells (DSSCs) utilizing one-dimensional (1D) nanomaterials, mainly semiconductor nanowires, nanocones, nanotubes and nanofibers, which are prepared by vapor-liquid-solid method, colloidal lithography, template-guided growth, or electrospinning. Moreover, the future challenges (such as efficiency improvement and natural resource limitations) and prospects of nanostructured solar cells are proposed. © 2012 The Royal Society of Chemistry.


Radke A.M.,Hong Kong University of Science and Technology | Tseng M.M.,Hong Kong University of Science and Technology
CIRP Annals - Manufacturing Technology | Year: 2012

Engineering-to-order has steadily increased shares of total production. By its own nature, the order specific products often come without pre-defined bills-of-materials which undermines the starting point of prevailing inventory planning methods. Manufacturers often have to confront with difficult, if not impossible, choices for meeting the highly responsive service level without investing in costly inventory, particularly for long lead time items. In this paper, a novel inventory planning approach is presented. Based on predetermined inventory budget, customer responsiveness can be optimized by considering risks associated with supply chain uncertainty, component commonality, substitution possibility, market intelligence, and other salient factors. © 2012 CIRP.


Zhang Q.,Princeton University | Austin R.H.,Princeton University | Austin R.H.,Hong Kong University of Science and Technology
Annual Review of Condensed Matter Physics | Year: 2012

It is a common mistake to view cancer as a single disease with a single possible cure which we have just not found yet. In reality cancer takes on many forms that share a common symptom: uncontrolled cell growth and successful invasion of cancer colonies to remote regions of the body. The key reason why we may never be able to defeat cancer may lie in the extreme heterogeneity of the population of the cells in a tumor: there is no one magic bullet. We will try in this review to show how the developing field of the physics of biological heterogeneity can help us understand and quantify the emergent heterogeneity that makes cancer such a fundamental puzzle. Copyright © 2012 by Annual Reviews. All rights reserved.


Zhao W.,Hong Kong University of Science and Technology | Wang Z.,Hong Kong University of Science and Technology | Sun J.,Hong Kong University of Science and Technology
Angewandte Chemie - International Edition | Year: 2012

That's about the size of it: The title molecules react with siloxy alkynes in the presence of a Brønsted acid to deliver medium-sized lactones through a [6+2] cyclization (see scheme; TIPS=triisopropylsilyl). This process is the first intermolecular synthesis of such lactones and involves a sequence of several selective ring-opening/ring-closing events. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zhao Y.-M.,Hong Kong University of Science and Technology | Cheung M.S.,Hong Kong University of Science and Technology | Lin Z.,Hong Kong University of Science and Technology | Sun J.,Hong Kong University of Science and Technology
Angewandte Chemie - International Edition | Year: 2012

NHC meets F: NHC-bound enolates undergo a catalytic asymmetric fluorination reaction to β,γ-unsaturated α-fluoroesters, which are obtained with good efficiency and stereoselectivity (see scheme, NFSI=N- fluorobenzenesulfonimide). The strategy overcomes possible challenges, such as fluorination in the γ position and difluorination. Experimental evidence combined with DFT calculations provides insight into the reaction mechanism. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


McKay M.R.,Hong Kong University of Science and Technology | Collings I.B.,CSIRO | Tulino A.M.,Alcatel - Lucent
IEEE Transactions on Information Theory | Year: 2010

This paper investigates the achievable sum rate of multiple-input multiple-output (MIMO) wireless systems employing linear minimum mean-squared error (MMSE) receivers. We present a new analytic framework which exploits an interesting connection between the achievable sum rate with MMSE receivers and the ergodic mutual information achieved with optimal receivers. This simple but powerful result enables the vast prior literature on ergodic MIMO mutual information to be directly applied to the analysis of MMSE receivers. The framework is particularized to various Rayleigh and Rician channel scenarios to yield new exact closed-form expressions for the achievable sum rate, as well as simplified expressions in the asymptotic regimes of high and low signal-to-noise ratios (SNRs). These expressions lead to the discovery of key insights into the performance of MIMO MMSE receivers under practical channel conditions. © 2009 IEEE.


Gao Y.,Hong Kong University of Science and Technology | Wang Y.H.,Hong Kong University of Science and Technology
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014

This paper reports K0 of dry sand in response to different loading conditions and under secondary compression. The experiments were carried out using an oedometer and tactile pressure sensors were used to measure the horizontal stress for K0 calculations. During loading, K0 remains a constant as the vertical stress σ'v increases. The corresponding discrete element method (DEM) simulations reproduced this experimental finding and suggest that the force transmission pattern is similar and the contact forces among particles are proportionally increased in both the horizontal and vertical directions to give a constant K0 as σ'v increases. K0 increases as the overconsolidation ratio (OCR) increases during unloading because of the locked-in horizontal stress. Reloading makes the sample less sensitive to OCR and thus the sample behaves as if it were in a normally consolidated state where K0 is a constant. Experimental results and DEM simulations demonstrate that the horizontal stress σ'h and K0 continue to increase during secondary compression on the loading path. Secondary compression is initiated by creep at particle contacts and exhibits similar responses like primary creep. The subsequent loading after secondary compression can gradually bring K0 back to its initial value. During secondary compression on the unloading path, however, K0 continues to decrease according to the DEM simulation results. The creep process tends to relax the locked-in horizontal stress and the sample expands in the vertical direction. Therefore, σ'h and K0 gradually decreases. © 2014 American Society of Civil Engineers.


Zhao Z.,Hangzhou Normal University | Lam J.W.Y.,Hong Kong University of Science and Technology | Tang B.Z.,Hong Kong University of Science and Technology
Journal of Materials Chemistry | Year: 2012

Luminescent materials with efficient solid-state emissions are important for the advancement of optoelectronics. Recently, a new class of propeller-like luminogenic molecules with aggregation-induced emission (AIE) characteristics has drawn increasing research interest. Among them, tetraphenylethene (TPE) is an archetypal luminogen with a simple molecule structure but shows a splendid AIE effect. Utilizing TPE as a building block, an effective strategy to create efficient solid-state emitters is developed. In this feature article, we review mainly our recent work on the construction of luminogenic materials from TPE and present their applications in organic light-emitting diodes. The applicability of the synthetic strategy and the utility of the resulting materials are demonstrated. © The Royal Society of Chemistry 2012.


Man K.L.,Hong Kong University of Science and Technology | Altman M.S.,Hong Kong University of Science and Technology
Journal of Physics Condensed Matter | Year: 2012

Low energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) are two powerful techniques for the investigation of surfaces, thin films and surface supported nanostructures. In this review, we examine the contributions of these microscopy techniques to our understanding of graphene in recent years. These contributions have been made in studies of graphene on various metal and SiC surfaces and free-standing graphene. We discuss how the real-time imaging capability of LEEM facilitates a deeper understanding of the mechanisms of dynamic processes, such as growth and intercalation. Numerous examples also demonstrate how imaging and the various available complementary measurement capabilities, such as selected area or micro low energy electron diffraction (μLEED) and micro angle resolved photoelectron spectroscopy (μARPES), allow the investigation of local properties in spatially inhomogeneous graphene samples. © 2012 IOP Publishing Ltd.


Han Y.,Hong Kong University of Science and Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The six-vertex model is mapped to three-dimensional sphere stacks and different boundary conditions corresponding to different containers. The shape of the container provides a qualitative visualization of the boundary effect. Based on the sphere-stacking picture, we map the phase spaces of the six-vertex models to discrete networks. A node in the network represents a state of the system, and an edge between two nodes represents a zero-energy spin flip, which corresponds to adding or removing a sphere. The network analysis shows that the phase spaces of systems with different boundary conditions share some common features. We derived a few formulas for the number and the sizes of the disconnected phase-space subnetworks under the periodic boundary conditions. The sphere stacking provides new challenges in combinatorics and may cast light on some two-dimensional models. © 2010 The American Physical Society.


Kuang Q.,Hong Kong University of Science and Technology | Kuang Q.,Xiamen University | Yang S.,Hong Kong University of Science and Technology
ACS Applied Materials and Interfaces | Year: 2013

Porous nanostructures of semiconductors are well-known for their ability to enhance the photocatalytic activity thanks to the large specific surface area and abundant active sites for the reactions, interfacial transport, and high utilization of light arising from multireflections in the pores. In this paper, we have successfully fabricated a special porous SrTiO3 three-dimensional (3D) architecture through a facile hydrothermal reaction at 150 C, using layered protonated titanate hierarchical spheres (LTHSs) of submicrometer size as a precursor template. The SrTiO3 architecture is characterized by the 3D assembly of hundreds of highly oriented nanocubes of 60-80 nm by the partial sharing of (100) faces, thereby displaying porous but single-crystal-like features reminiscent of mesocrystals. Our experimental results have shown the key roles played by the template effect akin to that in topotactic transformation in crystallography and Ostwald-ripening-assisted oriented attachment in the formation of such nanocube assemblies. Compared to the solid SrTiO3 photocatalysts previously synthesized by high-temperature solid-state methods, the as-synthesized porous SrTiO 3 nanocube assemblies have relatively large specific surface areas (up to 20.83 m2·g-1), and thus they have exhibited enhanced photocatalytic activity in hydrogen evolution from water splitting. Expectantly, our synthetic strategy using LTHSs as the precursor template may be extended to the fabrication of other titanate photocatalysts with similar porous hierarchical structures by taking advantage of the diversity of the perovskite-type titanate. © 2013 American Chemical Society.


Ji R.,CAS Institute of Semiconductors | Xu J.,Hong Kong University of Science and Technology | Yang L.,CAS Institute of Semiconductors
IEEE Photonics Technology Letters | Year: 2013

We demonstrate a five-port optical router that is suitable for large-scale photonic networks-on-chip. The optical router is designed to passively route the optical signal travelling in one direction and actively route the optical signal making a turn. In the case that an XY dimension-order routing is used, the passive routing feature guarantees that the maximum power consumption to route the data through the network is a constant that is independent of the network size. The fabricated device has an efficient footprint of ∼ 460× 1000μ m2. The routing functionality of the device is verified by using a 12.5-Gbit/s optical signal. The capability of multiwavlength routing for the optical router is also explored and discussed. © 1989-2012 IEEE.


Zhu X.,Tianjin University | Chen Z.,Hong Kong University of Science and Technology | Tang C.,Tianjin University
Optics Letters | Year: 2013

In optical metrology, state of the art algorithms for background and noise removal of fringe patterns are based on space-frequency analysis. In this Letter, an approach based on variational image decomposition is proposed to remove background and noise from a fringe pattern simultaneously. In the proposed method, a fringe image is directly decomposed into three components: a first one containing background, a second one fringes, and a third one noise, which are described in different function spaces and are solved by minimization of the functional. A simple technical process involved in the minimization algorithm improves the convergence performance. The proposed approach is verified with the simulated and experimental fringe patterns. © 2013 Optical Society of America.


Huang H.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2011

In this paper, we consider a Partial Interference Alignment and Interference Detection (PIAID) design for K-user quasi-static MIMO interference channels with discrete constellation inputs. Each transmitter has M antennas and transmits L independent data streams to the desired receiver with N receive antennas. We focus on the case where not all K-1 interfering transmitters can be aligned at every receiver. As a result, there will be residual interference at each receiver that cannot be aligned. Each receiver detects and cancels the residual interference based on the constellation map. However, there is a window of unfavorable interference profile at the receiver for Interference Detection (ID). In this paper, we propose a low complexity Partial Interference Alignment scheme in which we dynamically select the user set for IA so as to create a favorable interference profile for ID at each receiver. We first derive the average symbol error rate (SER) by taking into account of the non-Guassian residual interference due to discrete constellation. Using graph theory, we then devise a low complexity user set selection algorithm for the PIAID scheme, which minimizes the asymptotically tight bound for the average end-to-end SER performance. Moreover, we substantially simplify interference detection at the receiver using Semi-Definite Relaxation (SDR) techniques. It is shown that the SER performance of the proposed PIAID scheme has significant gain compared with various conventional baseline solutions. © 2011 IEEE.


Liu J.,Hong Kong University of Science and Technology | Potter A.C.,Massachusetts Institute of Technology | Law K.T.,Hong Kong University of Science and Technology | Lee P.A.,Massachusetts Institute of Technology
Physical Review Letters | Year: 2012

One of the simplest proposed experimental probes of a Majorana bound state is a quantized (2e2/h) value of zero-bias tunneling conductance. When temperature is somewhat larger than the intrinsic width of the Majorana peak, conductance is no longer quantized, but a zero-bias peak can remain. Such a nonquantized zero-bias peak has been recently reported for semiconducting nanowires with proximity induced superconductivity. In this Letter we analyze the relation of the zero-bias peak to the presence of Majorana end states, by simulating the tunneling conductance for multiband wires with realistic amounts of disorder. We show that this system generically exhibits a (nonquantized) zero-bias peak even when the wire is topologically trivial and does not possess Majorana end states. We make comparisons to recent experiments, and discuss the necessary requirements for confirming the existence of a Majorana state. © 2012 American Physical Society.


Lau A.K.W.,Hong Kong University of Science and Technology
Industrial Management and Data Systems | Year: 2011

Purpose - Recent studies have found inconsistent findings on the impact of supplier and customer involvement on new product development. This study thus aims to explore what contextual factors affect supplier and customer involvement altogether and how such involvement affects new product performance. Design/methodology/approach - The study used structural equation modelling to analyze empirical survey data from 251 manufacturers in Hong Kong. Findings - The study found that modular design, product innovation, and internal coordination are positively correlated with the supplier and customer involvement. Such involvement and product innovation lead to better new product performance. Research limitations/implications - The study is limited to the use of cross-sectional data and a single key informant approach, and the industry structure of the sampled industries. Practical implications - The study examines the contextual factors of supplier and customer involvement and how such involvement relates to new product development with new empirical evidence. The study not only provides new empirical evidence to support the importance of supply chain management in product development, but also extends existing literature to identify new contextual factors for such involvement. Originality/value - The study re-examines generalized beliefs about supplier and customer involvement in new product development, and extends prior studies of the contextual dimensions of product modularity, product innovativeness, and internal coordination on such involvement in an empirical way. © 2011 Emerald Group Publishing Limited. All rights reserved.


Chen J.,Fudan University | Ng J.,Hong Kong University of Science and Technology | Lin Z.,Fudan University | Chan C.T.,Hong Kong University of Science and Technology
Nature Photonics | Year: 2011

A photon carries Łk of momentum, so it may be anticipated that light will 'push' on any object standing in its path by means of the scattering force1-3. In the absence of an intensity gradient, using a light beam to pull a particle backwards is counter-intuitive. Here, we show that it is possible to realize a backward scattering force that pulls a particle all the way towards the source without an equilibrium point. The underlining physics is the maximization of forward scattering via interference of the radiation multipoles. We show explicitly that the necessary condition to realize a negative (pulling) optical force is the simultaneous excitation of multipoles in the particle, and if the projection of the total photon momentum along the propagation direction is small, an attractive optical force is possible. This possibility adds 'pulling' as an additional degree of freedom to optical micromanipulation. © 2011 Macmillan Publishers Limited. All rights reserved.


Zhang Y.,Hong Kong University of Science and Technology | Yeung D.-Y.,Hong Kong University of Science and Technology
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2010

Automatic age estimation from facial images has aroused research interests in recent years due to its promising potential for some computer vision applications. Among the methods proposed to date, personalized age estimation methods generally outperform global age estimation methods by learning a separate age estimator for each person in the training data set. However, since typical age databases only contain very limited training data for each person, training a separate age estimator using only training data for that person runs a high risk of overfitting the data and hence the prediction performance is limited. In this paper, we propose a novel approach to age estimation by formulating the problem as a multi-task learning problem. Based on a variant of the Gaussian process (GP) called warped Gaussian process (WGP), we propose a multi-task extension called multi-task warped Gaussian process (MTWGP). Age estimation is formulated as a multi-task regression problem in which each learning task refers to estimation of the age function for each person. While MTWGP models common features shared by different tasks (persons), it also allows task-specific (person-specific) features to be learned automatically. Moreover, unlike previous age estimation methods which need to specify the form of the regression functions or determine many parameters in the functions using inefficient methods such as cross validation, the form of the regression functions in MTWGP is implicitly defined by the kernel function and all its model parameters can be learned from data automatically. We have conducted experiments on two publicly available age databases, FG-NET and MORPH. The experimental results are very promising in showing that MTWGP compares favorably with state-of-the-art age estimation methods. ©2010 IEEE.


Tan C.,Hong Kong University of Science and Technology | Wang W.-X.,Hong Kong University of Science and Technology
Environmental Pollution | Year: 2014

Titanium dioxide (TiO2) nanoparticles are widely used in water treatments, yet their influences on other contaminants in the water are not well studied. In this study, the aqueous uptake, assimilation efficiency, and toxicity of two ionic metals (cadmium-Cd, and zinc-Zn) in a freshwater zooplankton, Daphnia magna, were investigated following 2 days pre-exposure to nano-TiO2. Pre-exposure to 1 mg/L nano-TiO2 resulted in a significant increase in Cd and Zn uptake from the dissolved phase. After the nano-TiO2 in the guts were cleared, the uptake rates immediately recovered to the normal levels. Concurrent measurements of reactive oxygen species (ROS) and metallothioneins (MTs) suggested that the increased metal uptake was mainly due to the increased number of binding sites provided by nano-TiO2 presented in the guts. Consistently, pre-exposure to nano-TiO2 increased the toxicity of aqueous Cd and Zn due to enhanced uptake. Our study provides the evidence that nano-TiO2 in the guts of animals could increase the uptake and toxicity of other contaminants. © 2013 Elsevier Ltd. All rights reserved.


Yu H.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2011

Rank-constrained optimization problems have received an increasing intensity of interest recently, because many optimization problems in communications and signal processing applications can be cast into a rank-constrained optimization problem. However, due to the nonconvex nature of rank constraints, a systematic solution to general rank-constrained problems has remained open for a long time. In this paper, we focus on a rank-constrained optimization problem with a Schur-convex/concave objective function and multiple trace/log-determinant constraints. We first derive a structural result on the optimal solution of the rank-constrained problem using majorization theory. Based on the solution structure, we transform the rank-constrained problem into an equivalent problem with a unitary constraint. After that, we derive an iterative projected steepest descent algorithm which converges to a local optimal solution. Furthermore, we shall show that under some special cases, we can derive a closed-form global optimal solution. The numerical results show the superior performance of our proposed technique over the baseline schemes. © 1991-2012 IEEE.


Wu Y.,Hong Kong University of Science and Technology | Tsang D.H.K.,Hong Kong University of Science and Technology
IEEE Communications Letters | Year: 2011

We study energy-efficient spectrum sensing and transmission for Cognitive Radio (CR) which jointly determines its sensing and transmission durations. Our results quantify the impact of different power consumption components (i.e., sensing, transmission, and idling) on SU's optimal sensing and transmission durations. Our results also show that with a limited power capacity, SU has to strike a balance in energy consumption between sensing and transmission via appropriate idling. © 2006 IEEE.


Xu J.,University of Texas at Austin | Zhang J.,Hong Kong University of Science and Technology | Andrews J.G.,University of Texas at Austin
IEEE Transactions on Wireless Communications | Year: 2011

The Wyner model has been widely used to model and analyze cellular networks due to its simplicity and analytical tractability. Its key aspects include fixed user locations and the deterministic and homogeneous interference intensity. While clearly a significant simplification of a real cellular system, which has random user locations and interference levels that vary by several orders of magnitude over a cell, a common presumption by theorists is that the Wyner model nevertheless captures the essential aspects of cellular interactions. But is this true? To answer this question, we compare the Wyner model to a model that includes random user locations and fading. We consider both uplink and downlink transmissions and both outage-based and average-based metrics. For the uplink, for both metrics, we conclude that the Wyner model is in fact quite accurate for systems with a sufficient number of simultaneous users, e.g., a CDMA system. Conversely, it is broadly inaccurate otherwise. Turning to the downlink, the Wyner model becomes inaccurate even for systems with a large number of simultaneous users. In addition, we derive an approximation for the main parameter in the Wyner model the interference intensity term, which depends on the path loss exponent. © 2006 IEEE.


Xuan Y.,Hong Kong University of Science and Technology | Lea C.-T.,Hong Kong University of Science and Technology
IEEE/ACM Transactions on Networking | Year: 2011

It is well known that without admission control, network congestion is bound to occur. However, to implement admission control is difficult in IP-based networks, which are constructed out of the end-to-end principle, and semantics of most major signaling protocols can only be interpreted at the edge of the network. Even if routers can perform admission control internally, the path computation and the state updating activities required for setting up and tearing down each flow will overwhelm the network. A new QoS architecture, called a nonblocking network, has been proposed recently, and it requires no internal admission control and can still offer hard QoS guarantees. In this architecture, as long as each edge node admits not more than a specified amount of traffic, the network will never experience link congestion. For multicast networks, the main problem with this approach is low throughput. Conventional tree-based multicast routing algorithms lead to a throughput so low that the nonblocking concept is rendered impractical. In this paper, we show how network coding can solve this problem. We demonstrate that a nonblocking unicast network and a multicast network share the same optimal paths, and that a nonblocking multicast network with network coding can admit the same amount of traffic as a nonblocking unicast network. The above conclusions apply to explicit-routing (MPLS-like) and shortest-path routing (IP-like) networks. © 2010 IEEE.


Wu Y.,Hong Kong University of Science and Technology | Zhang T.,Hong Kong University of Science and Technology | Tsang D.H.K.,Hong Kong University of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2011

In this work we study joint pricing and power allocation for Dynamic Spectrum Access (DSA) networks with Stackelberg game. In our model, Primary User (PU) is the game leader and jointly determines its power allocation (to guarantee its QoS requirement) and the interference price charged to Secondary User (SU) (to reap revenue). Meanwhile, SU is the game follower and determines its power demand in response to PU's decisions. We quantify PU's and SU's benefit from the channel sharing model by deriving the Stackelberg equilibrium. Our results show that PU's equilibrium profit is asymptotically upper bounded with its marginal power cost and rate requirement. A distributed algorithm is proposed to find the equilibrium. We also propose an incentive-compatible mechanism for PU and SU to keep the social welfare optimum cooperatively. We extend our Stackelberg game to the multiple SUs scenario, where the interference among SUs results in a noncooperative power demand subgame. We propose a low-complexity heuristic algorithm for PU to maximize its profit. Our results show that PU can benefit by selecting multiple SUs to share its channel if SUs' mutual interference is limited. © 2011 IEEE.


Zhao W.,Hong Kong University of Science and Technology | Hsing I.-M.,Hong Kong University of Science and Technology
Chemical Communications | Year: 2010

We report here a method to manipulate the amount of thiolated DNA attached per gold nanoparticle from a few to tens of strands in less than an hour, which involves the tuning of the respective amount of salt and time of addition of thiolated oligo(ethylene glycol) during mononucleotide-mediated conjugation process. © 2010 The Royal Society of Chemistry.


Xuan L.-J.,Hong Kong University of Science and Technology | Xu K.,Hong Kong University of Science and Technology
Journal of Computational Physics | Year: 2013

Up to an arbitrary order of the Chapman-Enskog expansion of the kinetic Bhatnagar-Gross-Krook (BGK) equation, a corresponding analytic solution can be obtained. Based on such a compact exact solution, a new gas-kinetic scheme is constructed for the compressible Navier-Stokes equations. Instead of using a discontinuous initial condition in the gas-kinetic BGK-NS method Xu [K. Xu, A gas-kinetic BGK scheme for the Navier-Stokes equations, and its connection with artificial dissipation and Godunov method, J. Comput. Phys. 171 (2001) 289-335.], the new scheme starts with a continuous initial flow distribution at a cell interface which is obtained through an upwind-biased WENO reconstruction, and uses the time accurate solution for the flux evaluation. The new kinetic scheme not only preserves favorable properties of the existing BGK-NS method, such as stability, high resolution, and good performance in capturing discontinuity, but also achieves a very high efficiency, which is even more efficient than the same order well-defined classical finite difference scheme based on the macroscopic governing equations directly. The stability, accuracy, and efficiency of the new scheme are evaluated quantitatively through numerical tests. The new scheme captures sharp discontinuity without post-shock oscillation, and has high accuracy in resolving viscous solution. Due to the use of time-accurate analytical solution, the overall performance of the new scheme is superior in comparison with the finite difference or finite volume schemes which start from the same initial reconstruction and use the numerical Runge-Kutta methods for time accuracy. © 2012 Elsevier Inc.


Amini A.,Hong Kong University of Science and Technology | Yan W.,Monash University | Sun Q.,Hong Kong University of Science and Technology
Applied Physics Letters | Year: 2011

We conducted the measurement of the hardness-depth relationship of NiTi shape memory alloy with a sharp Berkovich indenter. Different from most ductile metals, NiTi reacts to the mechanical load of indentation through phase transition underneath the indentation tip. We found that the hardness decreases rapidly with the increase of the indentation depth and eventually approaches a constant. To understand the depth dependency, we performed energy analysis involving the bulk and the interface energies of the transformation zone. We derived the hardness-depth relationship which well explains the experimental results. The finding is useful in hardness measurement of materials involving solid-state phase transitions. © 2011 American Institute of Physics.


Zhang S.,Huawei | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2011

In this paper, we consider the problem of multi-relay selection for multi-stream cooperative MIMO systems with M relay nodes. Traditionally, relay selection approaches are primarily focused on selecting one relay node to improve the transmission reliability given a single-antenna destination node. As such, in the cooperative phase whereby both the source and the selected relay nodes transmit to the destination node, it is only feasible to exploit cooperative spatial diversity (for example by means of distributed space time coding). For wireless systems with a multi-antenna destination node, in the cooperative phase it is possible to opportunistically transmit multiple data streams to the destination node by utilizing multiple relay nodes. Therefore, we propose a low overhead multi-relay selection protocol to support multi-stream cooperative communications. In addition, we derive the asymptotic performance results at high SNR for the proposed scheme and discuss the diversity- multiplexing tradeoff as well as the throughput-reliability tradeoff. From these results, we show that the proposed multi-stream cooperative communication scheme achieves lower outage probability compared to existing baseline schemes. © 2011 IEEE.


He S.,Hong Kong University of Science and Technology | Chan S.-H.G.,Hong Kong University of Science and Technology
IEEE Communications Surveys and Tutorials | Year: 2016

The growing commercial interest in indoor location-based services (ILBS) has spurred recent development of many indoor positioning techniques. Due to the absence of global positioning system (GPS) signal, many other signals have been proposed for indoor usage. Among them, Wi-Fi (802.11) emerges as a promising one due to the pervasive deployment of wireless LANs (WLANs). In particular, Wi-Fi fingerprinting has been attracting much attention recently because it does not require line-of-sight measurement of access points (APs) and achieves high applicability in complex indoor environment. This survey overviews recent advances on two major areas of Wi-Fi fingerprint localization: advanced localization techniques and efficient system deployment. Regarding advanced techniques to localize users, we present how to make use of temporal or spatial signal patterns, user collaboration, and motion sensors. Regarding efficient system deployment, we discuss recent advances on reducing offline labor-intensive survey, adapting to fingerprint changes, calibrating heterogeneous devices for signal collection, and achieving energy efficiency for smartphones. We study and compare the approaches through our deployment experiences, and discuss some future directions. © 1998-2012 IEEE.


Lin P.,Hong Kong Polytechnic University | Luo X.,Hong Kong University of Science and Technology | Hsing I.-M.,Hong Kong University of Science and Technology | Yan F.,Hong Kong Polytechnic University
Advanced Materials | Year: 2011

Organic electrochemical transistors are integrated in flexible microfluidic systems. A novel label-free DNA sensor is developed based on the devices with single-stranded DNA probes immobilized on gate electrodes. These devices successfully detect complementary DNA targets at low concentrations using a pulse-enhanced hybridization technique in microfluidic channels. Organic electrochemical transistors are excellent candidates for flexible, highly sensitive, and low-cost biosensors. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Jin S.,Nanjing Southeast University | McKay M.R.,Hong Kong University of Science and Technology | Zhong C.,Queen's University of Belfast | Wong K.-K.,University College London
IEEE Transactions on Information Theory | Year: 2010

This paper presents an analytical characterization of the ergodic capacity of amplify-and-forward (AF) MIMO dual-hop relay channels, assuming that the channel state information is available at the destination terminal only. In contrast to prior results, our expressions apply for arbitrary numbers of antennas and arbitrary relay configurations. We derive an expression for the exact ergodic capacity, simplified closed-form expressions for the high SNR regime, and tight closed-form upper and lower bounds. These results are made possible by employing recent tools from finite-dimensional random matrix theory, which are used to derive new closed-form expressions for various statistical properties of the equivalent AF MIMO dual-hop relay channel, such as the distribution of an unordered eigenvalue and certain random determinant properties. Based on the analytical capacity expressions, we investigate the impact of the system and channel characteristics, such as the antenna configuration and the relay power gain. We also demonstrate a number of interesting relationships between the dual-hop AF MIMO relay channel and conventional point-to-point MIMO channels in various asymptotic regimes. © 2010 IEEE.


Marxer M.,Hong Kong University of Science and Technology | Ma H.T.,Hong Kong University of Science and Technology | Man W.Y.,Hong Kong University of Science and Technology | Poon R.Y.C.,Hong Kong University of Science and Technology
Oncogene | Year: 2014

A number of small-molecule inhibitors of Aurora kinases have been developed and are undergoing clinical trials for anti-cancer therapies. Different Aurora kinases, however, behave as very different targets: while inhibition of Aurora A (AURKA) induces a delay in mitotic exit, inhibition of Aurora B (AURKB) triggers mitotic slippage. Furthermore, while it is evident that p53 is regulated by Aurora kinase-dependent phosphorylation, how p53 may in turn regulate Aurora kinases remains mysterious. To address these issues, isogenic p53-containing and -negative cells were exposed to classic inhibitors that target both AURKA and AURKB (Alisertib and ZM447439), as well as to new generation of inhibitors that target AURKA (MK-5108), AURKB (Barasertib) individually. The fate of individual cells was then tracked with time-lapse microscopy. Remarkably, loss of p53, either by gene disruption or small interfering RNA-mediated depletion, sensitized cells to inhibition of both AURKA and AURKB, promoting mitotic arrest and slippage respectively. As the p53-dependent post-mitotic checkpoint is also important for preventing genome reduplication after mitotic slippage, these studies indicate that the loss of p53 in cancer cells represents a major opportunity for anti-cancer drugs targeting the Aurora kinases. © 2014 Macmillan Publishers Limited.


Ho E.S.L.,University of Edinburgh | Komura T.,University of Edinburgh | Tai C.-L.,Hong Kong University of Science and Technology
ACM Transactions on Graphics | Year: 2010

This paper presents a new method for editing and retargeting motions that involve close interactions between body parts of single or multiple articulated characters, such as dancing, wrestling, and sword fighting, or between characters and a restricted environment, such as getting into a car. In such motions, the implicit spatial relationships between body parts/objects are important for capturing the scene semantics. We introduce a simple structure called an interaction mesh to represent such spatial relationships. By minimizing the local deformation of the interaction meshes of animation frames, such relationships are preserved during motion editing while reducing the number of inappropriate interpenetrations. The interaction mesh representation is general and applicable to various kinds of close interactions. It also works well for interactions involving contacts and tangles as well as those without any contacts. The method is computationally efficient, allowing real-time character control. We demonstrate its effectiveness and versatility in synthesizing a wide variety of motions with close interactions. © 2010 ACM.


Hu Y.,Hong Kong University of Science and Technology | Lam H.,Hong Kong University of Science and Technology
Journal of Proteome Research | Year: 2013

The identification of phosphorylated proteins remains a challenge in proteomics, partially due to the difficulty in assigning tandem mass (MS/MS) spectra to their originating peptide sequences with correct phosphosite localization. Because of its advantages in efficiency and sensitivity, spectral library searching is a promising alternative to conventional sequence database searching. Our work aims to construct the largest collision-induced dissociation (CID) MS/MS spectral libraries of phosphorylated peptides in human (Homo sapiens) and four model organisms (Saccharomyces cerevisiae, Drosophila melanogaster, Caenorhabditis elegans, and Mus musculus) to date, to facilitate phosphorylated peptide identification by spectral library searching. We employed state-of-the-art search methods to published data and applied two recently published phosphorylation site localization tools (PhosphoRS and PTMProphet) to ascertain the phosphorylation sites. To further increase the coverage of this library, we predicted "semi-empirical" spectra for peptides containing known phosphorylation sites from the corresponding template unphosphorylated peptide spectra. The performance of the spectral libraries built were evaluated and found to be superior to conventional database searching in terms of sensitivity. Updated spectral libraries of phosphorylated peptides are made freely available for use with the spectral search engine SpectraST. The work flow being developed will be used to continuously update the libraries when new data become available. © 2013 American Chemical Society.


Ng C.Y.,Hong Kong University of Science and Technology
Applied Soft Computing Journal | Year: 2016

With the growing general awareness of the need to protect the environment as well as the increasingly stringent regulatory requirements imposed by various national and cross-national bodies, manufacturers have to minimise the environmental impacts of their products. Environmental considerations have therefore become a new key criterion for evaluating design alternatives during the product development stage. To facilitate non-Life Cycle Assessment (LCA) experts, such as most product designers, in evaluating the design alternatives in terms of environmental friendliness, this paper introduces a decision-making mechanism that combines the multiple criteria decision making (MCDM) approaches with LCA methodology. This evidential reasoning-based approach is a fast-track and objective tool which ranks the available design alternatives according to their potential environmental impacts. The environmental impacts of design alternatives assessed by the LCA are used for the weight elicitation processes of the proposed approach. A case application is conducted to illustrate the use of the proposed method to evaluate the environmental performances of design alternatives. © 2016 Elsevier B.V. All rights reserved.


Feng J.,Zhejiang University of Technology | Qin Z.,Zhejiang University of Technology | Yao S.,Hong Kong University of Science and Technology
Langmuir | Year: 2012

The coalescence-induced condensate drop motion on some superhydrophobic surfaces (SHSs) has attracted increasing attention because of its potential applications in sustained dropwise condensation, water collection, anti-icing, and anticorrosion. However, an investigation of the mechanism of such self-propelled motion including the factors for designing such SHSs is still limited. In this article, we fabricated a series of superhydrophobic copper surfaces with nanoribbon structures using wet chemical oxidation followed by fluorization treatment. We then systematically studied the influence of surface roughness and the chemical properties of as-prepared surfaces on the spontaneous motion of condensate drops. We quantified the "frequency" of the condensate drop motion based on microscopic sequential images and showed that the trend of this frequency varied with the nanoribbon structure and extent of fluorination. More obvious spontaneous condensate drop motion was observed on surfaces with a higher extent of fluorization and nanostructures possessing sufficiently narrow spacing and higher perpendicularity. We attribute this enhanced drop mobility to the stable Cassie state of condensate drops in the dynamic dropwise condensation process that is determined by the nanoscale morphology and local surface energy. © 2012 American Chemical Society.


He C.,Hong Kong University of Science and Technology | Hu X.,Hong Kong University of Science and Technology
Adsorption | Year: 2012

A novel ordered mesoporous carbon containing basic nitrogen functional groups was synthesized by ammonia-tailoring at a temperature of 1173 K and was applied for reactive dye adsorption. The basic nitrogencontaining functional groups incorporated into the carbon surface could enhance the dispersive interactions between the carbon and dye molecules due to the electron-donating effect as well as the electrostatic interactions between the carbon surface and the anions of the dyes. It was found tha this novel functionalized ordered mesoporous carbon could increase the adsorption capacity of reactive red 2 at 298 K by around 40 % and 100 % as compared with the unmodified carbon and a commercial activated carbon, respectively. The Freundlich isotherm showed better correlation with the experimental adsorption data of ammonia-tailored samples than the Langmuir isotherm due to the increased surface heterogeneity induced by the nitrogen-containing functional groups. Adsorption of reactive red 2 was an endothermic process as the adsorption capacity increased with increasing temperature. Low desorption efficiency revealed that the adsorption of reactive red 2 on the modified CMK-3 was extremely favorable, tending to be weakly reversible. © Springer Science+Business Media, LLC 2012.


Wang J.,Hong Kong University of Science and Technology | Wang W.-X.,Hong Kong University of Science and Technology
Environmental Toxicology and Chemistry | Year: 2014

With increasing use of silver nanoparticles (AgNPs), concerns about their potential deleterious effects on aquatic ecosystems have increased. Most previous studies have focused on the toxicity of AgNPs while their bioavailability has been seldom investigated. The present study examined the effects of salinity on the aggregation kinetics as well as the bioavailability of commercial 80-nm citrate-coated AgNPs (c-AgNPs) in the presence or absence of a nonionic surfactant (Tween 20) to marine medaka (Oryzias melastigma). In addition, the uptake of soluble Ag was quantified for comparison and for deducting the uptake of soluble Ag during AgNP exposure by applying a biokinetic model. The authors found that the addition of Tween 20 immediately slowed down the process of aggregation of AgNPs, and an elevated amount of Tween 20 (20μM) kept AgNPs well dispersed, even in the 30-psu salinity medium. Uptake rate constants (ku) of AgNPs were less than half the soluble Ag at low salinities (1 psu and 5 psu), while limited bioavailability of c-AgNPs was observed at high salinities (15 psu and 30 psu). However, the Tween 20-stabilized AgNPs (t-AgNPs) were accumulated by medaka at comparable rates as the soluble Ag, indicating the importance of dispersion for bioavailability of AgNPs in a highly ionic environment. The present study provided the first insight of the bioavailability of AgNPs to fish in a high-ionic environment. More studies are needed to gain a full understanding of bioavailability of AgNPs in marine environments. Environ Toxicol Chem 2014;33:632-640. © 2013 SETAC.


McFerran B.,University of Michigan | Mukhopadhyay A.,Hong Kong University of Science and Technology
Psychological Science | Year: 2013

Obesity is a major public health problem, but despite much research into its causes, scientists have largely neglected to examine laypeople's personal beliefs about it. Such naive beliefs are important because they guide actual goal-directed behaviors. In a series of studies across five countries on three continents, we found that people mainly believed either that obesity is caused by a lack of exercise or that it is caused by a poor diet. Moreover, laypeople who indicted a lack of exercise were more likely to actually be overweight than were those who implicated a poor diet. This effect held even after controlling for several known correlates of body mass index (BMI), thereby explaining previously unexplained variance. We also experimentally demonstrated the mechanism underlying this effect: People who implicated insufficient exercise tended to consume more food than did those who indicted a poor diet. These results suggest that obesity has an important, pervasive, and hitherto overlooked psychological antecedent. © The Author(s) 2013.


Flowerdew L.,Hong Kong University of Science and Technology
ReCALL | Year: 2012

This paper illustrates how a freely available online corpus has been exploited in a module on teaching business letters covering the following four speech acts (functions) commonly found in business letters: invitations, requests, complaints and refusals. It is proposed that different strategies are required for teaching potentially non-face-threatening (invitations, requests) and face-threatening (complaints, refusals) speech acts. The hands-on pedagogic activities follow the 'guided inductive approach' advocated by Johansson (2009) and draw on practices and strategies covered in the literature on using corpora in language learning and teaching, viz. the need for 'pedagogic mediation', and the 'noticing' hypothesis from second language acquisition studies. © 2012 European Association for Computer Assisted Language Learning.


Wu R.,University of Science and Technology of China | Sin J.K.O.,Hong Kong University of Science and Technology
IEEE Transactions on Power Electronics | Year: 2012

In this paper, high-efficiency silicon-embedded coreless coupled inductors are demonstrated for power supply on chip applications. The embedded coupled inductors have two interleaved thick inductor coils embedded in the bottom layer of the Si substrate and four copper vias formed in the top substrate layer. The embedded coupled inductors can be stacked underneath the active circuitry for compact on-chip integration, while small resistances can be achieved with the thick embedded coils, which lead to high efficiency. As a demonstration, embedded coupled inductors with a small area of 0.5mm 2 were designed and fabricated according to the on-chip dc-dc converter with the highest reported efficiency. The fabricated embedded coupled inductors show a much higher efficiency of 93% compared to the 84% efficiency of the originally used on-substrate coupled inductors, allowing the total converter loss to be reduced by 38% and the converter efficiency to be improved from 78% to 85%. © 2012 IEEE.


Rao X.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2014

To fully utilize the spatial multiplexing gains or array gains of massive MIMO, the channel state information must be obtained at the transmitter side (CSIT). However, conventional CSIT estimation approaches are not suitable for FDD massive MIMO systems because of the overwhelming training and feedback overhead. In this paper, we consider multi-user massive MIMO systems and deploy the compressive sensing (CS) technique to reduce the training as well as the feedback overhead in the CSIT estimation. The multi-user massive MIMO systems exhibits a hidden joint sparsity structure in the user channel matrices due to the shared local scatterers in the physical propagation environment. As such, instead of naively applying the conventional CS to the CSIT estimation, we propose a distributed compressive CSIT estimation scheme so that the compressed measurements are observed at the users locally, while the CSIT recovery is performed at the base station jointly. A joint orthogonal matching pursuit recovery algorithm is proposed to perform the CSIT recovery, with the capability of exploiting the hidden joint sparsity in the user channel matrices. We analyze the obtained CSIT quality in terms of the normalized mean absolute error, and through the closed-form expressions, we obtain simple insights into how the joint channel sparsity can be exploited to improve the CSIT recovery performance. © 2014 IEEE.


Zhang F.,Hong Kong University of Science and Technology | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2014

In this paper, we consider delay-optimal power control for an energy harvesting wireless system with finite energy storage. The wireless system is powered solely by a renewable energy source with bursty data arrivals, and is characterized by a data queue and an energy queue. We consider a delay-optimal power control problem and formulate an infinite horizon average cost Markov decision process (MDP). To deal with the curse of dimensionality, we introduce a virtual continuous time system and derive closed-form approximate priority functions for the discrete time MDP at various operating regimes. Based on the approximation, we obtain an online power control solution which is adaptive to the channel state information as well as the data and energy queue state information. The derived power control solution has a multi-level water-filling structure, where the water level is determined jointly by the data and energy queue lengths. In the simulations, we show that the proposed scheme has significant performance gain compared with various baselines. © 2014 IEEE.


Hong L.J.,Hong Kong University of Science and Technology | Liu G.,City University of Hong Kong
Operations Research | Year: 2010

A probability is the expectation of an indicator function. However, the standard pathwise sensitivity estimation approach, which interchanges the differentiation and expectation, cannot be directly applied because the indicator function is discontinuous.In this paper, we design a pathwise sensitivity estimator for probability functions based on a result of Hong [Hong, L. J. 2009. Estimating quantile sensitivities. Oper. Res. 57(1) 118-130]. We show that the estimator is consistent and follows a central limit theorem for simulation outputs from both terminating and steady-state simulations, and the optimal rate of convergence of the estimator is n?2/5 where n is the sample size. We further demonstrate how to use importance sampling to accelerate the rate of convergence of the estimator to n?1/2, which is the typical rate of convergence for statistical estimation. We illustrate the performances of our estimators and compare them to other well-known estimators through several examples. © 2010 INFORMS.


Shi Y.,Hong Kong University of Science and Technology | Zhang J.,Hong Kong University of Science and Technology | Letaief K.B.,Hong Kong University of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2014

A cloud radio access network (Cloud-RAN) is a network architecture that holds the promise of meeting the explosive growth of mobile data traffic. In this architecture, all the baseband signal processing is shifted to a single baseband unit (BBU) pool, which enables efficient resource allocation and interference management. Meanwhile, conventional powerful base stations can be replaced by low-cost low-power remote radio heads (RRHs), producing a green and low-cost infrastructure. However, as all the RRHs need to be connected to the BBU pool through optical transport links, the transport network power consumption becomes significant. In this paper, we propose a new framework to design a green Cloud-RAN, which is formulated as a joint RRH selection and power minimization beamforming problem. To efficiently solve this problem, we first propose a greedy selection algorithm, which is shown to provide near-optimal performance. To further reduce the complexity, a novel group sparse beamforming method is proposed by inducing the group-sparsity of beamformers using the weighted ℓ1/ℓ2-norm minimization, where the group sparsity pattern indicates those RRHs that can be switched off. Simulation results will show that the proposed algorithms significantly reduce the network power consumption and demonstrate the importance of considering the transport link power consumption. © 2014 IEEE.


Tu L.,Hong Kong University of Science and Technology | Chen L.,Hong Kong University of Science and Technology | Banfield D.K.,Hong Kong University of Science and Technology
Traffic | Year: 2012

Vps74p, a member of the GOLPH3 protein family, binds directly to coatomer and the cytoplasmic tails of a subset of Golgi-resident glycosyltransferases to mediate their Golgi retention. We identify a cluster of arginine residues at the N-terminal end of GOLPH3 proteins that are necessary and sufficient to mediate coatomer binding. While loss of coatomer binding renders Vps74p non-functional for glycosyltransferase retention, the Golgi membrane-binding capabilities of the mutant protein are not significantly reduced. We establish that the oligomerization status and phosphatidylinositol-4-phosphate-binding properties of Vps74p largely account for the membrane-binding capacity of the protein and identify an Arf1p-Vps74p interaction as a potential contributing factor in Vps74p Golgi membrane association. © 2012 John Wiley & Sons A/S.


Xu K.,Hong Kong University of Science and Technology
Acta Mechanica Sinica/Lixue Xuebao | Year: 2015

Abstract: All fluid dynamic equations are valid under their modeling scales, such as the particle mean free path and mean collision time scale of the Boltzmann equation and the hydrodynamic scale of the Navier–Stokes (NS) equations. The current computational fluid dynamics (CFD) focuses on the numerical solution of partial differential equations (PDEs), and its aim is to get the accurate solution of these governing equations. Under such a CFD practice, it is hard to develop a unified scheme that covers flow physics from kinetic to hydrodynamic scales continuously because there is no such governing equation which could make a smooth transition from the Boltzmann to the NS modeling. The study of fluid dynamics needs to go beyond the traditional numerical partial differential equations. The emerging engineering applications, such as air-vehicle design for near-space flight and flow and heat transfer in micro-devices, do require further expansion of the concept of gas dynamics to a larger domain of physical reality, rather than the traditional distinguishable governing equations. At the current stage, the non-equilibrium flow physics has not yet been well explored or clearly understood due to the lack of appropriate tools. Unfortunately, under the current numerical PDE approach, it is hard to develop such a meaningful tool due to the absence of valid PDEs. In order to construct multiscale and multiphysics simulation methods similar to the modeling process of constructing the Boltzmann or the NS governing equations, the development of a numerical algorithm should be based on the first principle of physical modeling. In this paper, instead of following the traditional numerical PDE path, we introduce direct modeling as a principle for CFD algorithm development. Since all computations are conducted in a discretized space with limited cell resolution, the flow physics to be modeled has to be done in the mesh size and time step scales. Here, the CFD is more or less a direct construction of discrete numerical evolution equations, where the mesh size and time step will play dynamic roles in the modeling process. With the variation of the ratio between mesh size and local particle mean free path, the scheme will capture flow physics from the kinetic particle transport and collision to the hydrodynamic wave propagation. Based on the direct modeling, a continuous dynamics of flow motion will be captured in the unified gas-kinetic scheme. This scheme can be faithfully used to study the unexplored non-equilibrium flow physics in the transition regime. Graphical Abstract: The most successful governing equations for gas dynamics are the Navier-Stokes (NS) equations in the hydrodynamic scale and the Boltzmann equation in the kinetic scale. Between these two limiting scales, there is no well-accepted equations for non-equilibrium flow description. As shown in Fig.2, the kinetic equation identifies particle transport and collision, and the hydrodynamic ones capture wave propagation. The direct modeling for computational fluid dynamics is to construct a continuous spectrum of governing equation in all scales from kinetic to hydrodynamic scales. [Figure not available: see fulltext.] © 2015, The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg.


Huang K.,University of Hong Kong | Lau V.K.N.,Hong Kong University of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2014

Microwave power transfer (MPT) delivers energy wirelessly from stations called power beacons (PBs) to mobile devices by microwave radiation. This provides mobiles practically infinite battery lives and eliminates the need of power cords and chargers. To enable MPT for mobile recharging, this paper proposes a new network architecture that overlays an uplink cellular network with randomly deployed PBs for powering mobiles, called a hybrid network. The deployment of the hybrid network under an outage constraint on data links is investigated based on a stochastic-geometry model where single-antenna base stations (BSs) and PBs form independent homogeneous Poisson point processes (PPPs) with densities λ-b and λ-p, respectively, and single-antenna mobiles are uniformly distributed in Voronoi cells generated by BSs. In this model, mobiles and PBs fix their transmission power at p and q, respectively; a PB either radiates isotropically, called isotropic MPT, or directs energy towards target mobiles by beamforming, called directed MPT. The model is used to derive the tradeoffs between the network parameters (p, λ-b, q, λ-p) under the outage constraint. First, consider the deployment of the cellular network. It is proved that the outage constraint is satisfied so long as the product pλ-b^\frac{alpha}{2} is above a given threshold where α is the path-loss exponent. Next, consider the deployment of the hybrid network assuming infinite energy storage at mobiles. It is shown that for isotropic MPT, the product qλ-p λ-b^\frac{alpha}{2} has to be above a given threshold so that PBs are sufficiently dense; for directed MPT, z-mqλ-p λ-b^\frac{alpha}{2} with z-m denoting the array gain should exceed a different threshold to ensure short distances between PBs and their target mobiles. Furthermore, similar results are derived for the case of mobiles having small energy storage. © 2002-2012 IEEE.


Li C.,Hong Kong University of Science and Technology | Zhang J.,Hong Kong University of Science and Technology | Letaief K.B.,Hong Kong University of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2014

Small cell networks have recently been proposed as an important evolution path for the next-generation cellular networks. However, with more and more irregularly deployed base stations (BSs), it is becoming increasingly difficult to quantify the achievable network throughput or energy efficiency. In this paper, we develop an analytical framework for downlink performance evaluation of small cell networks, based on a random spatial network model, where BSs and users are modeled as two independent spatial Poisson point processes. A new simple expression of the outage probability is derived, which is analytically tractable and is especially useful with multi-antenna transmissions. This new result is then applied to evaluate the network throughput and energy efficiency. It is analytically shown that deploying more BSs can always increase the network throughput, but the throughput will scale with the BS density first linearly, then logarithmically, and finally converge to a constant. On the other hand, increasing the number of BS antennas can decrease the outage probability exponentially, thus can always increase the network throughput. However, increasing the BS density or the number of transmit antennas will first increase and then decrease the energy efficiency if the non-transmission power or the circuit power consumption is less than certain thresholds, and the optimal BS density and the optimal number of BS antennas can be found. Otherwise, the energy efficiency will always decrease. Simulation results shall demonstrate that our conclusions based on the random network model are general and also hold in a regular grid-based model. © 2002-2012 IEEE.


Zhou K.,Hong Kong University of Science and Technology | Cai L.,Hong Kong University of Science and Technology
IEEE/ASME Transactions on Mechatronics | Year: 2014

Resistance spot welding (RSW) is one of the most commonly used methods in the manufacturing process for joining sheet metal together. This paper deals with the constant current control for RSW, which is the most common control strategy in actual applications. Since the process of RSW is nonlinear and time-varying, conventional control schemes do not yield satisfactory performance. To cope with this problem, a new control method is proposed in this paper. By solving the governing equation of the equivalent circuit of the RSW electrical system at each control cycle at its local coordinate frame, a nonlinear relationship between input and output variables is obtained. The relationship can be used to estimate an approximate value of the trigger time of the silicon-controlled rectifier for the next control cycle based on the information of the previous control cycle. In order to compensate the estimation error and improve the performance of the closed-loop system, a proportional-derivative (PD) controller is employed. Because the proposed controller regulates trigger time error instead of output current error, the parameters of the PD controller are easy to determine. The effectiveness of the proposed controller was verified through experiments under different conditions. Experimental results showed that the performance of the proposed controller was much better than that of a well-tuned proportional-integral-derivative controller. © 2013 IEEE.


Liu M.,ETH Zurich | Liu M.,Hong Kong University of Science and Technology | Siegwart R.,ETH Zurich
IEEE Transactions on Robotics | Year: 2014

Scene recognition problems for mobile robots have been extensively studied. This is important for tasks such as visual topological mapping. Usually, sophisticated key-point-based descriptors are used, which can be computationally expensive. In this paper, we describe a lightweight novel scene recognition method using an adaptive descriptor, which is based on color features and geometric information that are extracted from an uncalibrated omnidirectional camera. The proposed method enables a mobile robot to perform online registration of new scenes onto a topological representation automatically and solve the localization problem to topological regions simultaneously, all in real time. We adopt a Dirichlet process mixture model (DPMM) to describe the online inference process. It is based on an approximation of conditional probabilities of the new measurements given incrementally estimated reference models. It enables online inference speeds of up to 50 Hz for a normal CPU. We compare it with state-of-the-art key-point descriptors and show the advantage of the proposed algorithm in terms of performance and computational efficiency. A real-world experiment is carried out with a mobile robot equipped with an omnidirectional camera. Finally, we show the results on extended datasets. © 2013 IEEE.


Huang Y.,Hong Kong Baptist University | Palomar D.P.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2014

Quadratically constrained quadratic programming (QCQP) with double-sided constraints has plenty of applications in signal processing as have been addressed in recent years. QCQP problems are hard to solve, in general, and they are typically approached by solving a semidefinite programming (SDP) relaxation followed by a postprocessing procedure. Existing postprocessing schemes include Gaussian randomization to generate an approximate solution, rank reduction procedure (the so-called purification), and some specific rank-one matrix decomposition techniques to yield a globally optimal solution. In this paper, we propose several randomized postprocessing methods to output not an approximate solution but a globally optimal solution for some solvable instances of the double-sided QCQP (i.e., instances with a small number of constraints). We illustrate their applicability in robust receive beamforming, radar optimal code design, and broadcast beamforming for multiuser communications. As a byproduct, we derive an alternative (shorter) proof for the Sturm-Zhang rank-one matrix decomposition theorem. © 2014 IEEE.


Wang W.,Hong Kong University of Science and Technology | Zhang Q.,Hong Kong University of Science and Technology
IEEE Wireless Communications | Year: 2014

As the demands for mobile phone access to the data services are expanding, advantages in cellular services can be gained by offering enhanced user experience through cost-effective broadband mobile. By reducing the distance between base stations and end users, femtocells provide higher data rates and better indoor coverage. The small size of a femtocell also improves spectrum reuse, which contributes to higher spectrum efficiency. As femtocells are usually unplanned, efficient operation and maintenance are required to maximize the benefits of femtocell access. As one of the fundamental functionalities in network maintenance, a selfhealing mechanism aims to autonomously alleviate the impact of coverage or capacity loss induced by cell outage. Existing studies on the self-healing problem have focused on macrocell networks, while none of them has systematically investigated the problem in the context of femtocells networks. In this article we argue that the distinct features of the two-tier macro-femto system require dedicated architectures for self-healing femtocell networks. We present three different architectures, and further investigate their advantages and limitations. Then we call attention to the local cooperative architecture, which, with proper design, satisfies the practical requirements imposed by the salient features of femtocell networks. We further verify the benefits of the local cooperative architecture by proposing a self-healing scheme for femtocell networks. © 2014 IEEE.


Ng J.,Hong Kong University of Science and Technology | Lin Z.,Hong Kong University of Science and Technology | Lin Z.,Fudan University | Chan C.T.,Hong Kong University of Science and Technology
Physical Review Letters | Year: 2010

We propose a theory to explain optical trapping by optical vortices (OVs), which are emerging as important tools to trap mesoscopic particles. The common perception is that the trapping is solely due to the gradient force and that it may be characterized by three real force constants. However, we show that the OV trap can exhibit complex force constants, implying that the trapping must be stabilized by ambient damping. At different damping levels, particles exhibit remarkably different dynamics, such as stable trapping and periodic and aperiodic orbital motions. © 2010 The American Physical Society.


Xu R.,Hong Kong University of Science and Technology | Liu B.,Hong Kong University of Science and Technology | Yuan J.,Hong Kong University of Science and Technology
IEEE Journal of Solid-State Circuits | Year: 2012

High-speed CMOS imaging sensors (CIS) normally have low sensitivity because of the large integration capacitance. They also have high noise because pixel circuits cannot implement correlated double sampling (CDS) to remove the pixel reset noise. For applications, such as micro-computed tomography (micro-CT), this is a major limitation. In this work, we developed a technique to achieve high sensitivity and low noise for high-speed CIS. To maximize the sensitivity, we designed a new capacitive transimpedance amplifier (CTIA) pixel with a tiny metal-oxide-metal capacitor. The pixel circuit also implements CDS. As a result, the temporal noise is greatly reduced, and the sensitivity improves dramatically. To compensate the mismatch of small integration capacitors across the pixel array, an on-chip calibration scheme with in-pixel circuits is developed. Fully differential column circuits are designed to suppress the power supply injection in the large array of high-speed column circuits. A successive-approximation analog-to-digital (SAR ADC) is designed to achieve 10-bit resolution and to fit in the 15-μm column pitch. For testing modes, column circuits are configured into a two-step ADC to provide 13-bit dynamic range. The 256 × 256 CIS design is fabricated in a 0.18-μm CMOS process. The imager samples up to 1500 fps. The pixel integration capacitor is 0.7 fF, which enables 68.5 · s sensitivity under the white illumination. The CIS temporal noise is 13.6 -. This sensitivity and noise performances are much better than previous high-speed CIS benchmark designs. Running at 1500 fps, the CIS can capture recognizable images with illumination down to 1 lux. The on-chip calibration suppresses the fixed-pattern noise lower than 0.52%. The prototype chip consumes 390 mW of power. © 2012 IEEE.


Xu R.,Hong Kong University of Science and Technology | Liu B.,Qualcomm | Yuan J.,Hong Kong University of Science and Technology
IEEE Journal of Solid-State Circuits | Year: 2012

Array sensors require a high-performance analog-to-digital converter (ADC) array with small area and low power. Successive-approximation register (SAR) ADC has good potential for ADC array due to its simple analog circuits. However, SAR ADCs with 10-b resolution and higher normally need a large capacitor array due to the stringent matching requirement. The large capacitor array also limits the ADC dynamic performance. The capacitor mismatch has been compensated by analog calibration techniques. In this work, a novel digital calibration method is developed for SAR ADC based on dithering. With dithering, weights of most significant bit (MSB) capacitors can be measured accurately so that very small capacitors can be used in the SAR ADC due to the relaxed matching requirement. A modified bit-cycling procedure is developed to avoid the code gaps caused by capacitor dithering. This calibration technique requires no analog calibration overhead and simple digital decoders. The technique is implemented in an ADC array design including 256 SAR ADCs for a high-speed CMOS imaging sensor in a 0.18-μm CMOS process. The 10-b SAR ADC is designed with the minimum capacitor array size in the process. A single SAR ADC only occupies 15μm×710μ m. Sampling at 768 kS/s, peak DNL and peak INL of the original ADCs averaged across the array are 0.82 least significant bit (LSB) and 3.85 LSB, respectively. For a signal close to the Nyquist frequency, original ADCs have 7.96-b average ENOB. After calibration with dithering, ADCs have 0.55-LSB peak DNL and 0.77-LSB peak INL averaged across the array. The average ENOB improves to 9.83 b. Compared with the benchmark 10-b SAR ADCs, this design is the most area-efficient design. In this work, the calibration decoders are implemented off-chip. With a sample-and-hold amplifier, the calibration method can run in the background. © 2012 IEEE.


Ho E.N.Y.,Hong Kong University of Science and Technology | Mok P.K.T.,Hong Kong University of Science and Technology
IEEE Transactions on Circuits and Systems II: Express Briefs | Year: 2012

A low-dropout regulator for on-chip application with a power-supply rejection (PSR) boosting filter circuit for enhancing supply noise rejection at middle-to-high frequency over a wide loading range is presented in this brief. The idea has been analytically modeled and experimentally verified with a standard 0.13- μm CMOS process. The on-chip compensation capacitance is 1 pF. For the PSR filter design, the total on-chip capacitance is 20 pF. From the experimental results, the implemented regulator can operate with supply voltage of 1.2 V with nominal dropout voltage of 0.2 V at maximum load of 50 mA and I Q of 37.32 μA. © 2012 IEEE.


Zheng S.,Hong Kong University of Science and Technology | Luong H.C.,Hong Kong University of Science and Technology
IEEE Journal of Solid-State Circuits | Year: 2013

This paper presents a 65 nm CMOS digital polar transmitter with on-chip power amplifier (PA) for WCDMA and WLAN application. The proposed architecture is composed of a digital interpolation filter for up-sampling of the input amplitude-control word (ACW), a 9-bit switched-capacitor array for the digital polar modulation (DPM), and a 6-bit PA array to achieve the output power range for the target applications. A linearization technique is implemented by adaptively changing the PA bias voltage according to the RF envelope. To generate this bias voltage, the RF envelope of the PA input is extracted by a digital-to-analog converter (DAC) with the ACW signals as its input. A scaled replica of the PA, which only needs to operate at the Amplitude Modulation (AM) frequency, is employed to sense the RF envelope and to regulate the PA bias voltage with an analog feedback loop to minimize the distortion in the AM path. Even without amplitude pre-distortion, the transmitter system measures RMS-EVM of 2.83% and 4.07% for WCDMA and WLAN 54-Mb/s 64-QAM OFDM respectively while providing a peak output power of 20.4 dBm with PAE 32.3%. © 1966-2012 IEEE.


Yin J.,Hong Kong University of Science and Technology | Luong H.C.,Hong Kong University of Science and Technology
IEEE Journal of Solid-State Circuits | Year: 2013

This paper presents a magnetically tuned (MT) multimode VCO featuring an ultrawide frequency tuning range. A switched-triple-shielded transformer is proposed to change the magnetic coupling coefficient between the primary and secondary coils in the transformer tank to greatly increase the frequency tuning range of the dual-band VCO to cover the whole E-band continuously. Fabricated in a 65-nm CMOS process, the MT-VCO measures a frequency tuning range of 41.1% from 57.5 to 90.1 GHz while consuming 7 to 9 mA at 1.2-V supply with chip area of 0.03 mm2. The measured phase noises at 10-MHz offset from carrier frequencies of 58, 72.2, 80.5, and 90.1 GHz, are -107.4, -111.8, -107.8, and -105.1 dBc/Hz, respectively, which correspond to FOMT between - 184.2 and - 192.2 dBc/Hz. © 1966-2012 IEEE.


Du K.-L.,Concordia University at Montréal | Mow W.H.,Hong Kong University of Science and Technology
IEEE Transactions on Vehicular Technology | Year: 2010

Cognitive radio (CR) technology is a promising way to improve the bandwidth efficiency of underutilized radio spectra. For practical CR systems with limited a priori knowledge of the primary users' signal characteristics, spectrum sensing is mainly based on energy detection and cyclostationary feature detection. Energy detection is simple and practical but becomes ineffective at a low signal-to-interference-and-noise ratio (SINR). Conventional cyclostationary feature detection based on cyclic spectrum estimation can robustly detect weak signals from primary users by only exploiting the cyclostationarity property of communication signals. However, the high implementation complexity it requires limits its widespread usage. In the literature, the use of smart-antenna technology is suggested to track the locations of the primary users and apply transmit beamforming to avoid spatial interference with their signals. The objective of this paper is to establish adaptive cyclostationary (receive) beamforming as an effective spectrum-sensing method with affordable complexity for multiple-antenna cognitive radio. Specifically, we introduce a new spectrum-sensing method that exploits a recently proposed beamforming algorithm, called the adaptive cross-self-coherent-restoral (ACS) algorithm. The complexity of the resultant algorithm is higher than that of the energy detector but is at least an order of magnitude smaller than that of the previous cyclostationary feature detectors, such as the Fourier spectrum cyclic density analysis method and its multitaper-Loève version. Their performances for spectrum sensing are empirically evaluated and compared in detail in an example. © 2006 IEEE.


Huang C.,Hong Kong University of Science and Technology | Mok P.K.T.,Hong Kong University of Science and Technology
IEEE Journal of Solid-State Circuits | Year: 2013

In today's fully-integrated converters, the integrated LC components dominate the chip-area and have become the major limitation of reducing the cost and increasing the current density. This paper presents a 100 MHz four-phase fully-integrated buck converter with standard package bondwire inductors and a flying capacitor (C rmFLY) topology for chip-area reduction, occupying 1.25 mm2 effective area in 0.13-μm CMOS technology. A four-phase operation is introduced for chip-area reduction with the cost penalty minimized by utilizing standard package bondwire inductance as power inductors. Meanwhile, an extra more than 40% chip-area saving is achieved by the simple but effective CrmFLY topology to take advantage of the parasitic bondwire inductance at the input for ripple attenuation. A maximum output current of 1.2 A is obtained by the four-phase operation, while only 3.73 nF overall integrated capacitors are required. Also, with the chip-area hungry integrated spiral metal inductors eliminated, the current density is significantly increased. 0.96 A/mm2; current density and 82.4% efficiency is obtained with 1.2 V to 0.9 V voltage conversion without using any off-chip inductors or advanced processes. The reliability is also verified by measurement with various bondwire inductances and configurations. © 1966-2012 IEEE.


Wang R.,Huawei | Lau V.K.N.,Hong Kong University of Science and Technology | Cui Y.,Hong Kong University of Science and Technology
IEEE Journal on Selected Topics in Signal Processing | Year: 2011

In this paper, we consider a two-hop relay-assisted cognitive downlink Orthogonal frequency-division multiple access (OFDMA) system (named as secondary system) dynamically accessing a spectrum licensed to a primary network, thereby improving the efficiency of spectrum usage. A cluster-based relay-assisted architecture is proposed for the secondary system, where relay stations are employed for minimizing the interference to the users in the primary network and achieving fairness for cell-edge users in the secondary system. Based on this architecture, an asymptotically optimal solution is derived for jointly controlling data rates, transmission power, and subchannel allocation to optimize the average weighted sum goodput where the proportional fair scheduling (PFS) is included as a special case. This solution supports decentralized implementation, requires small communication overhead, and is robust against imperfect channel state information at the transmitter (CSIT) and imperfect sensing measurement. The proposed solution achieves significant throughput gain and better user-fairness compared with the existing designs. Finally, we derive a simple and asymptotically optimal scheduling solution as well as the associated closed-form performance under the proportional fair scheduling for a large number of users. The system throughput is shown to be O(N(1-q p)(1-q p N)ln ln K c), where K c is the number of users in one cluster, N is the number of subchannels, and q p is the active probability of primary users. © 2011 IEEE.


Bian L.,CAS Institute of Theoretical Physics | Liu T.,Hong Kong University of Science and Technology | Shu J.,CAS Institute of Theoretical Physics
Physical Review Letters | Year: 2015

We present a class of cancellation conditions for suppressing the total contributions of Barr-Zee diagrams to the electron electric dipole moment (eEDM). Such a cancellation is of particular significance after the new eEDM upper limit was released by the ACME Collaboration, which strongly constrains the allowed magnitude of CP violation in Higgs couplings and hence the feasibility of electroweak baryogenesis (EWBG). Explicitly, if both the CP-odd Higgs-photon-photon (Z boson) and the CP-odd Higgs-electron-positron couplings are turned on, a cancellation may occur either between the contributions of a CP-mixing Higgs boson, with the other Higgs bosons being decoupled, or between the contributions of CP-even and CP-odd Higgs bosons. With a cancellation, large CP violation in the Higgs sector is still allowed, yielding successful EWBG. The reopened parameter regions would be probed by future neutron, mercury EDM measurements, and direct measurements of Higgs CP properties at the Large Hadron Collider Run II and future colliders. © 2015 American Physical Society. © 2015 American Physical Society.


Lai A.C.H.,Center for Environmental Sensing and Modelling | Lee J.H.W.,Hong Kong University of Science and Technology
Journal of Fluid Mechanics | Year: 2012

An array of closely spaced round buoyant jets interact dynamically due to the pressure field induced by jet entrainment. Mutual jet attraction can result in a significant change in jet trajectories. Jet merging also leads to overlapping of the passive scalar fields associated with the individual jets, resulting in mixing characteristics that are drastically different from those of an independent free jet. A general semi-analytical model for the dynamic interaction of multiple buoyant jets in stagnant ambient conditions is proposed. The external irrotational flow field induced by the buoyant jets is computed by a distribution of point sinks with strength equal to the entrainment per unit length along the unknown jet trajectories and accounting for boundary effects. The buoyant jet trajectories are then determined by an iterative solution of an integral buoyant jet model by tracking the changes in the external entrainment flow and dynamic pressure fields. The velocity and concentration fields of the jet group are obtained by momentum or kinetic energy superposition for merged jets and plumes, respectively. The modelling approach is supported by numerical solution of the Reynolds-averaged Navier-Stokes equations. The model shows that jet merging and mixing can be significantly affected by jet interactions. Model predictions of the multiple jet trajectories, merging height, as well as the centreline velocity and concentration of the buoyant jet group are in good agreement with experimental data for: (i) a clustered momentum jet group; (ii) a turbulent plume pair; and (iii) a rosette buoyant jet group. Dynamic interactions between a jet group are shown to decrease with the addition of an ambient cross-flow. © 2012 Cambridge University Press.


Matthaiou M.,Chalmers University of Technology | Zhong C.,Zhejiang University | McKay M.R.,Hong Kong University of Science and Technology | Ratnarajah T.,University of Edinburgh
IEEE Journal on Selected Areas in Communications | Year: 2013

The performance of single-cell distributed multiple-input multiple-output (D-MIMO) systems is not only affected by small-scale Rayleigh fading but also from large-scale fading and path-loss. In this paper, we elaborate on the sum rate of D-MIMO systems employing linear zero-forcing receivers, accounting for both large and small-scale fading effects, as well as spatial correlation at the transmit side. In particular, we consider the classical lognormal model and propose closed-form upper and lower bounds on the achievable sum rate. Using these bounds as a starting point, we pursue a "large-system" analysis and provide asymptotic expressions when the number of antennas at the base station (BS) grow large, and when the number of antennas at both ends grow large with a fixed and finite ratio. A detailed characterization in the asymptotically high and low signal to noise ratio regimes is also provided. An interesting observation from our results is that in order to maximize the sum rate, the RPs should be placed at unequal distances to the BS when they experience the same level of shadowing. The resulting closed-form expressions are compared with the corresponding results on MIMO optimal receivers. © 1983-2012 IEEE.


Liu F.,Hong Kong University of Science and Technology | Huang X.,Hong Kong University of Science and Technology | Chan C.T.,Hong Kong University of Science and Technology
Applied Physics Letters | Year: 2012

We show that two-dimensional acoustic crystals (ACs) can be designed to exhibit Dirac cone dispersion at k → = 0. Effective medium theory finds that some of these ACs can have effectively zero reciprocal of bulk modulus 1/ eff and zero mass density eff, and thus zero refractive indices at the Dirac point. Numerical simulations are used to demonstrate various phenomena associated with the zero spatial phase change inside such materials. © 2012 American Institute of Physics.


An L.,Hong Kong University of Science and Technology | Zhao T.S.,Hong Kong University of Science and Technology
Energy and Environmental Science | Year: 2011

A barrier that limits the performance of anion exchange membrane (AEM) direct ethanol fuel cells (DEFCs) is that state-of-the-art AEMs do not allow the fuel cell to operate at high temperatures (< 60°C). Here we describe an alkaline DEFC that employs a cation exchange membrane (CEM) and show that this type of CEM-DEFC can stably discharge with a high power density at an operating temperature as high as 90°C. © 2011 The Royal Society of Chemistry.


Wang W.,Hong Kong University of Science and Technology | Chau Y.,Hong Kong University of Science and Technology
Chemistry of Materials | Year: 2012

We recently reported a two-component self-assembling system, where the core of nanoparticles (NPs) was first assembled by a simple triskelion Fmoc-conjugate (FTAEA) and then stabilized by an oligopeptide, Fmoc-FY. Here we showed that the two-component NPs were stable upon heating, incubation, and dilution. We expanded the oligopeptides suitable for stabilization and therefore allowed peptides to serve the dual role of stabilization and functionalization. Twelve molecules were systematically designed and tested to define the design criteria of oligopeptide stabilizers, which are summarized as follows: 1) carrying Fmoc headgroup to match with the aromatic groups on the NP core, 2) restricting the first amino acid to those with self-interacting side chains, and 3) the net charge of the hydrophilic oligopeptide sequence being negative. To validate these criteria, we designed two bioactive peptides, Fmoc-FC and Fmoc-FRGD, which were demonstrated to be capable of stabilizing FTAEA NPs. The bioactivity of the peptide was illustrated with Nile red-loaded Fmoc-FRGD stabilized NPs of around 70 nm in diameters. These NPs were differentially internalized by MDA-MB-435 human cancer cells compared to NPs stabilized with the scrambled sequence, Fmoc-FRDG. Our results here showed that the stepwise aromatic-driven self-assembly provided a facile and versatile approach to construct functionalized and bioactive NPs, which are expected to find applications in drug delivery and bioimaging. © 2011 American Chemical Society.


Rowell C.,Hong Kong University of Science and Technology | Lam E.Y.,University of Hong Kong
IEEE Transactions on Antennas and Propagation | Year: 2012

The performance characteristics of the capacitive slot, or a slot placed between the feed and ground connections, in a planar inverted-F antenna (PIFA) are comprehensively analyzed. The PIFA capacitive slot behavior is measured inside a two antenna system within a mobile phone where the first antenna is a multiple band PIFA and the second antenna is a higher frequency band PIFA directly overlapping with the first antenna higher frequency band. The dual band PIFA in this paper is designed to be resonant in the quad-band GSM+3G/4G, and the second PIFA is resonant in the 3G/4G frequency bands. The capacitive slot has three types of behaviors: affect the matching of existing frequency resonances, induce another frequency resonance, and improve the isolation between the two antennas. Together with optimal antenna ground and feed placement, the capacitive slot can act as a notched bandstop filter to decrease the S 21 mutual coupling between the two antennas by over 20 dB and decrease the envelope correlation by almost one order of magnitude. © 1963-2012 IEEE.


Wang J.,Hong Kong University of Science and Technology | Scutari G.,State University of New York at Buffalo | Palomar D.P.,Hong Kong University of Science and Technology
IEEE Transactions on Signal Processing | Year: 2011

Cognitive radio (CR) systems improve the spectral efficiency by allowing the coexistence in harmony of primary users (PUs), the legacy users, with secondary users (SUs). This coexistence is built on the premises that no SU can generate interference higher than some prescribed limits against PUs. The system design based on perfect channel state information (CSI) can easily end up violating the interference limits in a realistic situation where CSI may be imperfect. In this paper, we propose a robust design of CR systems, composed of multiple PUs and multiple noncooperative SUs, in either single-input single-output (SISO) frequency-selective channels or more general multiple-input multiple-output (MIMO) channels. We formulate the design of the SU network as a noncooperative game, where the SUs compete with each other over the resources made available by the PUs, by maximizing their own information rates subject to the transmit power and robust interference constraints. Following the philosophy of the worst-case robustness, we take explicitly into account the imperfectness of SU-to-PU CSI by adopting proper interference constraints that are robust with respect to the worst channel errors. Relying on the variational inequality theory, we study the existence and uniqueness properties of the Nash equilibria of the resulting robust games, and devise totally asynchronous and distributed algorithms along with their convergency properties. We also propose efficient numerical methods, based on decomposition techniques, to compute the robust transmit strategy for each SU. © 2010 IEEE.


Ma H.,Hong Kong University of Science and Technology | Li Z.,Hong Kong University of Science and Technology
Computers and Concrete | Year: 2013

In this study, the pore structure of Portland cement paste is experimentally characterized by MIP (mercury intrusion porosimetry) and nitrogen adsorption, and simulated by a newly developed status-oriented computer model. Cement pastes with w/c=0.3, 0.4 and 0.5 at ages from 1 day to 120 days are comprehensively investigated. It is found that MIP cannot generate valid pore size distribution curves for cement paste. Nevertheless, nitrogen adsorption can give much more realistic pore size distribution curves of small capillary pores, and these curves follow the same distribution mode. While, large capillary pores can be effectively characterized by the newly developed computer model, and the validity of this model has been proved by BSE imaging plus image analysis. Based on the experimental findings and numerical simulation, a hypothesis is proposed to explain the formation mechanism of the capillary pore system, and the realistic representation of the pore structure of hydrated cement paste is established.