Hong Kong, China
Hong Kong, China

City University of Hong Kong is a public research university located in Kowloon Tong, Hong Kong. It was founded in 1984 as City Polytechnic of Hong Kong and became a fully accredited university in 1994. CityU offers over 50 bachelor's degree programmes through its constituent colleges and schools. Postgraduate degree programmes are offered by the Chow Yei Ching School of Graduate Studies. Wikipedia.


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A novel class of heterodinuclear PtRu complexes are provided, and the methods for preparing the complexes are described. The inhibitory activities of the heterodinuclear PtRu complexes against cancer/tumor cell growth, including cancer/tumor cells having a resistance to cisplatin, are further demonstrated.


A method for matching one or more buyers with one or more sellers to facilitate trade in a marketplace provided by a service provider includes the steps of receiving a bid to sell mobile data from one or more sellers, receiving a bid to buy mobile data from one or more buyers, matching at least a portion of the bid of the one or more buyers with at least a portion of the bid of the one or more sellers based on: a revenue maximization function to maximize the service providers revenue based on a relationship between administration revenue and bid revenue, facilitating a transfer of the mobile data from the one or more seller to the one or more buyer, following the matching of the one or more buyers with the one or more sellers, through the service provider.


Patent
City University of Hong Kong | Date: 2015-07-27

Transistors can be used for a variety of electronic-based applications. Therefore, transistor efficiency and performance is of importance. An apparatus is presented herein to increase the locking range of transistors by leveraging cross-coupled injection transistors in conjunction with symmetry injection transistors. The transistor efficiency can also be increase by reducing a parasitic capacitance associated with the components of the transistor.


There is provided a compound for use as material in cathode of a battery. The compound has i) at least sodium or ii) sodium and lithium as a first ingredient, copper as a second ingredient, at least a first transition metal in a third ingredient (M) selected from a group including manganese, nickel, iron, copper, zinc, chromium, vanadium, titanium, molybdenum and tungsten, niobium; and oxygen as a fourth ingredient; and wherein the compound has a chemical formula of Na_(y)Cu_(x)M_(1-x)O_(2), or Li_(a)Na_(b)Cu_(x)M_(i-x)O_(2).


Patent
City University of Hong Kong | Date: 2015-09-09

A system and method for an electrochemical detector includes a plurality of receptors disposed on a semiconductor layer, wherein the plurality of receptors are arranged to interact with a target substance so as to alter an electrical characteristic of the semiconductor layer.


Patent
City University of Hong Kong | Date: 2016-11-10

The present invention is concerned with a method of rapid identification of a mammalian species origin or mammalian species origins of a sample.


Cryptographic techniques for encrypting images, and decrypting and reconstructing images, are provided to facilitate preventing unauthorized access to images. A holographic cryptographic component (HCC) generates complex holograms of multi-dimensional source images of a multi-dimensional object scene. The HCC generates phase holograms, based on the complex holograms, using a stochastic hologram generation process, and encrypts the phase holograms to generate encrypted holograms based on a random phase mask, which can be the private encryption key. At the decoding end, an HCC overlays a conjugate phase mask on the encrypted holograms to decrypt them, wherein the decrypted holograms are illuminated with a coherent light source to generate holographic images that reconstruct the source images. The source images are only reconstructed properly if the correct phase mask is used. If HCC applies the encryption process repetitively to the same source image, HCC can generate a different encrypted hologram in each run.


Patent
City University of Hong Kong | Date: 2015-08-31

Fast processing of information represented in digital holograms is provided to facilitate generating a hologram for displaying three-dimensional (3-D) holographic images representative of a 3-D object scene on a display device. A holographic generator component (HGC) can receive or generate visual images, comprising depth and parallax information, of a 3-D object scene. A hologram processor component can apply a first non-uniform transform to a visual image to generate a first signal, and can apply a second transform to the first signal to generate a second signal that corresponds to a hologram that represents the 3-D object scene. The hologram can be illuminated with a light beam to facilitate generating a holographic image(s) that can be a reconstructed image that reconstructs the 3-D object scene. A display component can display the holographic image(s) for viewing by an observer.


Patent
City University of Hong Kong | Date: 2015-08-20

A repairable electrical component includes one or more electrodes and a pliable casing, the one or more electrodes positioned within the pliable casing, wherein the repairable electrical component is configured to self-repair if the repairable electrical component or any part of the repairable component is partially damaged. A method of forming a repairable electrical component includes forming one or more electrodes, the electrodes comprising a core, an intermediate layer of ferromagnetic material and a pyrrole based material defining an outer layer, the outer layer encapsulating the core and ferromagnetic layer, positioning the one or more electrodes within an electrolyte, providing a casing to enclose the one or more electrodes and the electrolyte, the casing formed from a polyurethane material.


Patent
City University of Hong Kong | Date: 2015-08-03

An antenna includes a dielectric resonator coupled to a ground plane provided on a substrate having a slot structure on the ground plane; and a monopole substantially surrounded by the dielectric resonator; wherein, when the monopole, the dielectric resonator and the slot structure are excited with an electrical signal, the combination of the monopole, the dielectric resonator and the slot structure is arranged to radiate an electromagnetic signal associated with the electrical signal in a substantially unidirectional manner.


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
City University of Hong Kong | Date: 2015-09-30

An antenna for use in a communication system with a number of plates connected to a ground plane, where when the number of plates are excited by at least two electrical signals, the number of plates are arranged to radiate at least two electromagnetic signals each having an independent resonant frequency.


Patent
City University of Hong Kong | Date: 2016-05-26

A multistable structure including local portions arranged to undergo processing by at least one of the physical treatment and chemical treatment so as to form localized stimulations of the treated portions; wherein the treated portions are arranged to interact with the untreated portion of the structure to form a prescribed residual stress distribution associated with the treated portions and the untreated portion of the structure, the prescribed residual stress distribution being arranged to provide at least one alternative stable configuration to the structure.


Patent
City University of Hong Kong | Date: 2015-08-28

The systems and methods disclosed herein, in one aspect thereof, can encrypt and decrypt messages using a multivariate extended Clipped Hopfield neural network that uses a Diffie-Hellman like key exchange algorithm. The proposed cryptosystem comprises three stages that are involved in the communication. A first stage, where parameters are initialized and private keys are generated, a second stage where various base matrix pairs and threshold vectors are synchronized between the sender and the recipient, and a third stage, where encryption/decryption is performed.


Patent
City University of Hong Kong | Date: 2015-09-02

A system and method of an electronic apparatus for use in a communication system includes a switching module arranged to combine a plurality of input signals received by a plurality of input ports in connection with the switching module to define a combined input signal having a plurality of frequency components; and a loading module arranged to receive the combined input signal from the switching module and to individually separate each of the plurality of frequency components of the combined input signal by processing the combined input signal with a plurality of resonating networks, each arranged to resonate at a resonance frequency associated with each of the plurality of frequency components of the combined input signals.


Patent
City University of Hong Kong | Date: 2015-10-28

A single-ended signal can be converted to a differential signal or reverse. A printed circuit board component can comprise a bottom metal layer and a top metal layer, wherein the bottom metal layer is connected to the top metal layer by an array of metal posts, and wherein the array of metal posts is arranged to form a substrate integrated waveguide network configured to transmit a set of electromagnetic waves corresponding to a single-ended signal represented according to a bandwidth. Furthermore, in an aspect, the device can comprise a coaxial to waveguide adaptor component comprising a coaxial cable port portion and a waveguide port portion, wherein the waveguide port portion guides the set of electromagnetic waves to the substrate integrated waveguide network.


He J.,City University of Hong Kong | He J.,Guangdong University of Technology | Zeller M.,Youngstown State University | Hunter A.D.,Youngstown State University | Xu Z.,City University of Hong Kong
Journal of the American Chemical Society | Year: 2012

We describe a white emitting coordination network solid that can be conveniently applied as a thin film onto a commercial UV-LED lamp for practical white lighting applications. The solid state material was discovered in an exercise of exploring molecular building blocks equipped with secondary groups for fine-tuning the structures and properties of coordination nets. Specifically, CH 3SCH 2CH 2S- and (S)-CH 3(OH)CHCH 2S- (2-hydroxylpropyl) were each attached as secondary groups to the 2,5- positions of 1,4-benzenedicarboxylic acid (bdc), and the resultant molecules (L1 and L2, respectively) were crystallized with Pb(II) into the topologically similar 3D nets of PbL1 and PbL2, both consisting of interlinked Pb-carboxyl chains. While the CH 3S- groups in PbL1 are not bonded to the Pb(II) centers, the hydroxy groups in PbL2 participate in coordinating to Pb(II) and thus modify the bonding features around the Pb(II), but only to a slight and subtle degree (e.g., Pb-O distances 2.941-3.116 Å). Interestingly, the subtle change in structure significantly impacts the properties, i.e., while the photoluminescence of PbL1 is yellowish green, PbL2 features bright white emission. Also, the homochiral side group in PbL2 imparts significant second harmonic generation, in spite of its seemingly weak association with the main framework (the NLO-phore). In a broad perspective, this work showcases the idea of secondary group participation (SGP) in the construction of coordination networks, an idea that parallels that of hemilabile ligands in organometallics and points to an effective strategy in developing advanced functions in solid state framework materials. © 2011 American Chemical Society.


Li D.M.,City University of Hong Kong | Liew K.M.,City University of Hong Kong | Cheng Y.,Shanghai University
Computer Methods in Applied Mechanics and Engineering | Year: 2014

This paper presents the formulation and numerical implementation of the improved complex variable element-free Galerkin (ICVEFG) method for two-dimensional large deformation problems of elastoplasticity in total Lagrangian description. The ICVEFG method is a novel element free Galerkin (EFG) method based on the improved complex variable moving least-squares (ICVMLS) approximation. The ICVMLS approximation has all the advantages inherited from the complex variable moving least-squares (CVMLS) approximation. The function J in the ICVMLS approximation has an explicit physical meaning, compared with the former. The Galerkin weak form is employed to obtain the equations system and the penalty method is used to apply essential boundary conditions. Several numerical examples presented show that the ICVEFG method has greater precision and efficiency compared to the EFG and CVEFG methods. © 2013 Elsevier B.V.


Liu H.-L.,Guangdong University of Technology | Gu F.,Guangdong University of Technology | Zhang Q.,City University of Hong Kong | Zhang Q.,University of Essex
IEEE Transactions on Evolutionary Computation | Year: 2014

This letter suggests an approach for decomposing a multiobjective optimization problem (MOP) into a set of simple multiobjective optimization subproblems. Using this approach, it proposes MOEA/D-M2M, a new version of multiobjective optimization evolutionary algorithm-based decomposition. This proposed algorithm solves these subproblems in a collaborative way. Each subproblem has its own population and receives computational effort at each generation. In such a way, population diversity can be maintained, which is critical for solving some MOPs. Experimental studies have been conducted to compare MOEA/D-M2M with classic MOEA/D and NSGA-II. This letter argues that population diversity is more important than convergence in multiobjective evolutionary algorithms for dealing with some MOPs. It also explains why MOEA/D-M2M performs better. © 2013 IEEE.


Chen Z.,Shanghai University | Chen Z.,City University of Hong Kong | Pan D.,Shanghai University | Li Z.,Shanghai University | And 5 more authors.
Chemical Reviews | Year: 2014

The key scientific issues in the application and development of semiconductor micro/nanodevices and optoelectronics components have driven scientists to investigate in depth the design, preparation, micro/nanostructure, and performance of semiconductor materials. Semiconductor oxides are fundamental to the development of smart and functional materials, devices, and systems. These oxide materials have two unique structural features: mixed cation valences and an adjustable oxygen deficiency, which are the bases for creating and tuning many novel material properties, from chemical to physical. Special attention has been focused on tin oxide during the past few decades and this material is now established as one of the most promising materials for producing numerous novel functional properties due to its excellent chemical and physical properties.


Djordjevich A.,City University of Hong Kong
International Journal of Heat and Mass Transfer | Year: 2012

One-dimensional advection-diffusion equation with variable coefficients in semi-infinite media is solved using explicit finite difference method for three dispersion problems: (i) solute dispersion along steady flow through inhomogeneous medium, (ii) temporally dependent solute dispersion along uniform flow through homogeneous medium, and (iii) solute dispersion along temporally dependent unsteady flow through inhomogeneous medium. The continuous point source of uniform nature is considered at the origin of the medium. Results are compared to analytical solutions reported in the literature and good agreement was found. We have shown that explicit finite difference method is effective and accurate for solving advection-diffusion equation with variable coefficients in semi-infinite media, which is especially important when arbitrary initial and boundary conditions are required. © 2012 Elsevier Ltd. All rights reserved.


Chung W.,City University of Hong Kong
Applied Energy | Year: 2011

Energy end-use for all sectors (commercial, residential, transport, industrial) in Hong Kong shows that the residential share increased from 14.2% in 1990 to 18.1% in 2007, such share increase has prompted the authors to analyze the issue. The Divisia decomposition analysis is used to evaluate the respective contributions of changes in (1) the number of households, (2) share of different types of residential households, (3) efficiency gains, and (4) climate condition to the energy use increase. The analysis reveals that the major contributor was the increase of the number of households, and the second major contributor was the intensity effect. As expected, the segment of the private housing (apartments) was becoming less energy efficient. In addition, it is interesting to note that the energy end-use per household in the segment of government rental subsidized housing (apartments) was decreasing. The decrease of the household income in this segment may be one of the reasons while statistics showing that the number of low-income household was increasing and leaning towards the lowest income classes. On the other hand, it is believed that people tend to consume more energy to obtain a quality life characterized with comfortable living with the growth of economy and improvement of living standard. However, Hong Kong becomes a counterexample since 2004. Therefore, changing the residents' behavior may not be an effective tactic for reducing energy consumption. © 2011 Elsevier Ltd.


Zhang Z.,University of Science and Technology Beijing | Long K.,University of Science and Technology Beijing | Wang J.,City University of Hong Kong | Dressler F.,University of Innsbruck
IEEE Communications Surveys and Tutorials | Year: 2014

Inspired by swarm intelligence observed in social species, the artificial self-organized networking (SON) systems are expected to exhibit some intelligent features (e.g., flexibility, robustness, decentralized control, and self-evolution, etc.) that may have made social species so successful in the biosphere. Self-organized networks with swarm intelligence as one possible solution have attracted a lot of attention from both academia and industry. In this paper, we survey different aspects of bio-inspired mechanisms and examine various algorithms that have been applied to artificial SON systems. The existing well-known bio-inspired algorithms such as pulse-coupled oscillators (PCO)-based synchronization, ant-and/or bee-inspired cooperation and division of labor, immune systems inspired network security and Ant Colony Optimization (ACO)-based multipath routing have been surveyed and compared. The main contributions of this survey include 1) providing principles and optimization approaches of variant bio-inspired algorithms, 2) surveying and comparing critical SON issues from the perspective of physical-layer, Media Access Control (MAC)-layer and network-layer operations, and 3) discussing advantages, drawbacks, and further design challenges of variant algorithms, and then identifying their new directions and applications. In consideration of the development trends of communications networks (e.g., large-scale, heterogeneity, spectrum scarcity, etc.), some open research issues, including SON designing tradeoffs, Self-X capabilities in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)/LTE-Advanced systems, cognitive machine-to-machine (M2M) self-optimization, cross-layer design, resource scheduling, and power control, etc., are also discussed in this survey. © 2014 IEEE.


Yu W.,City University of Hong Kong | Chen G.,City University of Hong Kong | Cao M.,University of Groningen | Kurths J.,Humboldt University of Berlin
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2010

This paper considers a second-order consensus problem for multiagent systems with nonlinear dynamics and directed topologies where each agent is governed by both position and velocity consensus terms with a time-varying asymptotic velocity. To describe the system's ability for reaching consensus, a new concept about the generalized algebraic connectivity is defined for strongly connected networks and then extended to the strongly connected components of the directed network containing a spanning tree. Some sufficient conditions are derived for reaching second-order consensus in multiagent systems with nonlinear dynamics based on algebraic graph theory, matrix theory, and Lyapunov control approach. Finally, simulation examples are given to verify the theoretical analysis. © 2006 IEEE.


Wen G.,Peking University | Duan Z.,Peking University | Yu W.,Nanjing Southeast University | Chen G.,City University of Hong Kong
International Journal of Robust and Nonlinear Control | Year: 2013

This paper is concerned with the problem of consensus in directed networks of multiple agents with intrinsic nonlinear dynamics and sampled-data information. A new protocol is induced from a class of continuous-time linear consensus protocols by implementing data-sampling technique and a zero-order hold circuit. On the basis of a delayed-input approach, the sampled-data multi-agent system is converted to an equivalent nonlinear system with a time-varying delay. Theoretical analysis on this time-delayed system shows that consensus with asymptotic time-varying velocities in a strongly connected network can be achieved over some suitable sampled-data intervals. A multi-step procedure is further presented to estimate the upper bound of the maximal allowable sampling intervals. The results are then extended to a network topology with a directed spanning tree. For the case of the topology without a directed spanning tree, it is shown that the new protocol can still guarantee the system to achieve consensus by appropriately informing a fraction of agents. Finally, some numerical simulations are presented to demonstrate the effectiveness of the theoretical results and the dependence of the upper bound of maximal allowable sampling interval on the coupling strength. Copyright © 2012 John Wiley & Sons, Ltd.


Wei K.-K.,City University of Hong Kong | Teo H.-H.,National University of Singapore | Chan H.C.,National University of Singapore | Tan B.C.Y.,National University of Singapore
Information Systems Research | Year: 2011

The digital divide has loomed as a public policy issue for over a decade. Yet, a theoretical account for the effects of the digital divide is currently lacking. This study examines three levels of the digital divide. The digital access divide (the first-level digital divide) is the inequality of access to information technology (IT) in homes and schools. The digital capability divide (the second-level digital divide) is the inequality of the capability to exploit IT arising from the first-level digital divide and other contextual factors. The digital outcome divide (the third-level digital divide) is the inequality of outcomes (e.g., learning and productivity) of exploiting IT arising from the second-level digital divide and other contextual factors. Drawing on social cognitive theory and computer self-efficacy literature, we developed a model to show how the digital access divide affects the digital capability divide and the digital outcome divide among students. The digital access divide focuses on computer ownership and usage in homes and schools. The digital capability divide and the digital outcome divide focus on computer self-efficacy and learning outcomes, respectively. This model was tested using data collected from over 4,000 students in Singapore. The results generate insights into the relationships among the three levels of the digital divide and provide a theoretical account for the effects of the digital divide. While school computing environments help to increase computer self-efficacy for all students, these factors do not eliminate knowledge the gap between students with and without home computers. Implications for theory and practice are discussed. © 2011 INFORMS.


Majchrzak A.,University of Southern California | Majchrzak A.,Ramon Llull University | Wagner C.,City University of Hong Kong | Yates D.,U.S. Air force
MIS Quarterly: Management Information Systems | Year: 2013

In this study, we explore the Wiki affordance of enabling shaping behavior within organizational intranets supported by Wikis. Shaping is the continuous revision of one's own and others' contributions to a Wiki. Shaping promotes knowledge reuse through improved knowledge integration. Recognizing and clarifying the role of shaping allows us to theorize new ways in which knowledge resources affect knowledge reuse. We examine the role of three knowledge resources of a Wiki contributor: knowledge depth, knowledge breadth, and assessment of the level of development of the Wiki community's transactive memory system. We offer preliminary evidence based on a sample of experienced organizational Wiki users that the three different knowledge resources have differential effects on shaping, that these effects differ from the effects on the more common user behavior of simply adding domain knowledge to a Wiki, and that shaping and adding each independently affect contributors' perceptions that their knowledge in the Wiki has been reused for organizational improvement. By empirically distinguishing between the different knowledge antecedents and consequences of shaping and adding, we derive implications for theory and research on knowledge integration and reuse.


Natarajan K.,City University of Hong Kong | Teo C.P.,National University of Singapore | Zheng Z.,National University of Singapore
Operations Research | Year: 2011

In this paper, we analyze mixed 0-1 linear programs under objective uncertainty. The mean vector and the second-moment matrix of the nonnegative objective coefficients are assumed to be known, but the exact form of the distribution is unknown. Our main result shows that computing a tight upper bound on the expected value of a mixed 0-1 linear program in maximization form with random objective is a completely positive program. This naturally leads to semidefinite programming relaxations that are solvable in polynomial time but provide weaker bounds. The result can be extended to deal with uncertainty in the moments and more complicated objective functions. Examples from order statistics and project networks highlight the applications of the model. Our belief is that the model will open an interesting direction for future research in discrete and linear optimization under uncertainty. © 2011 INFORMS.


Kankanhalli A.,National University of Singapore | Lee O.-K.,University of Massachusetts Boston | Lim K.H.,City University of Hong Kong
Information and Management | Year: 2011

Organizations are implementing electronic repository systems to facilitate knowledge reuse but with varying degrees of success. There is a lack of understanding of how individual and technical factors interact in determining knowledge reuse and the performance benefits that could be derived from electronic knowledge repositories. We proposed a model to explain the impact of user motivation and the user's perception of the value of the available knowledge repository on knowledge reuse and the individual's performance benefits through using the system. Through a field survey, we found that perceived knowledge repository capability and intrinsic motivation positively affected knowledge reuse, which in turn impacted the benefits derived from using the system. We also found that perceived knowledge repository capability moderated the relationship between extrinsic reward and knowledge reuse. © 2011 Elsevier B.V. All rights reserved.


Yu W.,Nanjing Southeast University | Yu W.,RMIT University | Chen G.,City University of Hong Kong | Cao M.,University of Groningen
IEEE Transactions on Automatic Control | Year: 2011

This technical note studies the consensus problem for cooperative agents with nonlinear dynamics in a directed network. Both local and global consensus are defined and investigated. Techniques for studying the synchronization in such complex networks are exploited to establish various sufficient conditions for reaching consensus. The local consensus problem is first studied via a combination of the tools of complex analysis, local consensus manifold approach, and Lyapunov methods. A generalized algebraic connectivity is then proposed to study the global consensus problem in strongly connected networks and also in a broad class of networks containing spanning trees, for which ideas from algebraic graph theory, matrix theory, and Lyapunov methods are utilized. © 2006 IEEE.


Chen N.,National University of Singapore | Tsui K.L.,City University of Hong Kong
IIE Transactions (Institute of Industrial Engineers) | Year: 2013

Condition monitoring is an important prognostic tool to determine the current operation status of a system/device and to estimate the distribution of the remaining useful life. This article proposes a two-phase model to characterize the degradation process of rotational bearings. A Bayesian framework is used to integrate historical data with up-to-date in situ observations of new working units to improve the degradation modeling and prediction. A new approach is developed to compute the distribution of the remaining useful life based on the degradation signals, which is more accurate compared with methods reported in the literature. Finally, extensive numerical results demonstrate that the proposed framework is effective and efficient. © 2013 Taylor & Francis Group, LLC.


Yu W.,City University of Hong Kong | Yu W.,Nanjing Southeast University | Chen G.,City University of Hong Kong | Cao M.,University of Groningen
Automatica | Year: 2010

This paper studies some necessary and sufficient conditions for second-order consensus in multi-agent dynamical systems. First, basic theoretical analysis is carried out for the case where for each agent the second-order dynamics are governed by the position and velocity terms and the asymptotic velocity is constant. A necessary and sufficient condition is given to ensure second-order consensus and it is found that both the real and imaginary parts of the eigenvalues of the Laplacian matrix of the corresponding network play key roles in reaching consensus. Based on this result, a second-order consensus algorithm is derived for the multi-agent system facing communication delays. A necessary and sufficient condition is provided, which shows that consensus can be achieved in a multi-agent system whose network topology contains a directed spanning tree if and only if the time delay is less than a critical value. Finally, simulation examples are given to verify the theoretical analysis. © 2010 Elsevier Ltd. All rights reserved.


Chen X.,University of Electronic Science and Technology of China | Hao G.,City University of Hong Kong | Li L.,Old Dominion University
International Journal of Production Economics | Year: 2014

We investigate a one-period two-echelon supply chain composed of a risk-neutral supplier that produces short life-cycle products and a loss-averse retailer that orders from the supplier via option contracts and sells to end-users with stochastic demand in the selling season. When a single retail season begins, the retailer can obtain goods by purchasing and exercising call options. We derive the loss-averse retailer's optimal ordering policy and the risk-neutral supplier's optimal production policy under these conditions. In addition, we find that the loss-averse retailer may order less than, equal to, or more than the risk-neutral retailer. Further, we show that the loss-averse retailer's optimal order quantity may increase in retail price and decrease in option price and exercise price, which is different from the case of a risk-neutral retailer. Finally, we study coordination of the supply chain and show that there always exists a Pareto contract as compared to the non-coordinating contracts. © 2013 Elsevier B.V.


Mei J.,Harbin Institute of Technology | Ren W.,University of California at Riverside | Chen J.,City University of Hong Kong | Ma G.,Harbin Institute of Technology
Automatica | Year: 2013

In this paper, we study the distributed coordination problem for multiple Lagrangian systems in the presence of parametric uncertainties under a directed graph without using neighbors' velocity information in the absence of communication. We consider two cases, namely, the distributed containment control problem with multiple stationary leaders and the leaderless synchronization problem. In both cases, distributed adaptive control algorithms without using neighbors' velocity information are proposed. The control gains in the algorithms are varying with distributed updating laws. Furthermore, necessary and sufficient conditions on the directed graph are presented, respectively, such that all followers converge to the stationary convex hull spanned by the stationary leaders asymptotically in the containment control problem and the systems synchronize asymptotically in the leaderless synchronization problem. Finally, simulation examples are provided to show the effectiveness of the proposed control algorithms. © 2013 Elsevier Ltd. All rights reserved.


Wen G.,Peking University | Duan Z.,Peking University | Yu W.,Nanjing Southeast University | Chen G.,City University of Hong Kong
International Journal of Robust and Nonlinear Control | Year: 2012

The problem of second-order consensus is investigated in this paper for a class of multi-agent systems with a fixed directed topology and communication constraints where each agent is assumed to share information only with its neighbors on some disconnected time intervals. A novel consensus protocol designed based on synchronous intermittent local information feedback is proposed to coordinate the states of agents to converge to second-order consensus under a fixed strongly connected topology, which is then extended to the case where the communication topology contains a directed spanning tree. By using tools from algebraic graph theory and Lyapunov control approach, it is proved that second-order consensus can be reached if the general algebraic connectivity of the communication topology is larger than a threshold value and the mobile agents communicate with their neighbors frequently enough as the network evolves. Finally, a numerical example is simulated to verify the theoretical analysis. Copyright © 2011 John Wiley & Sons, Ltd.


Cao Y.,Air Force Research Lab | Yu W.,Nanjing Southeast University | Yu W.,RMIT University | Ren W.,University of California at Riverside | Chen G.,City University of Hong Kong
IEEE Transactions on Industrial Informatics | Year: 2013

This paper reviews some main results and progress in distributed multi-agent coordination, focusing on papers published in major control systems and robotics journals since 2006. Distributed coordination of multiple vehicles, including unmanned aerial vehicles, unmanned ground vehicles, and unmanned underwater vehicles, has been a very active research subject studied extensively by the systems and control community. The recent results in this area are categorized into several directions, such as consensus, formation control, optimization, and estimation. After the review, a short discussion section is included to summarize the existing research and to propose several promising research directions along with some open problems that are deemed important for further investigations. © 2005-2012 IEEE.


Sun H.,City University of Hong Kong | Chen G.Y.J.,National University of Singapore | Yao S.Q.,National University of Singapore
Chemistry and Biology | Year: 2013

Proteins are fundamental components of all living systems and critical drivers of biological functions. The large-scale study of proteins, their structures and functions, is defined as proteomics. This systems-wide analysis leads to a more comprehensive view of the intricate signaling transduction pathways that proteins engage in and improves the overall understanding of the complex processes supporting the living systems. Over the last two decades, the development of high-throughput analytical tools, such as microarray technologies, capable of rapidly analyzing thousands of protein-functioning and protein-interacting events, has fueled the growth of this important field. Herein, we review the most recent advancements in microarray technologies, with a special focus on peptide microarray, small molecule microarray, and protein microarray. These technologies have become prominent players in proteomics and have made significant changes to the landscape of life science and biomedical research. We will elaborate on their performance, advantages, challenges, and future directions. © 2013 Elsevier Ltd.


Peng K.-Q.,Beijing Normal University | Lee S.-T.,City University of Hong Kong
Advanced Materials | Year: 2011

Semiconductor nanowires are attracting intense interest as a promising material for solar energy conversion for the new-generation photovoltaic (PV) technology. In particular, silicon nanowires (SiNWs) are under active investigation for PV applications because they offer novel approaches for solar-to-electric energy conversion leading to high-efficiency devices via simple manufacturing. This article reviews the recent developments in the utilization of SiNWs for PV applications, the relationship between SiNW-based PV device structure and performance, and the challenges to obtaining high-performance cost-effective solar cells. Silicon nanowires (SiNWs) are attracting intense interest as a promising material for solar energy conversion for the new-generation photovoltaic (PV) technology. This article reviews recent developments in the utilization of SiNWs for PV applications, the relationship between SiNW-based PV device structure and performance, and the challenges to obtaining high-performance cost-effective solar cells. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Jia X.,City University of Hong Kong | Zhou Y.,Zhejiang Normal University
Nonlinear Analysis: Real World Applications | Year: 2014

Recently, Pokorný and Zhou proved that if â€- u3â€-L∞(0,T;L103(ℝ 3))a1 or â€-xu3â€- L∞(0,T;L3019(ℝ3)a1, then the weak solution u of the 3D Navier-Stokes equations is regular on ℝ 3×(0,T]. In this paper we remove the smallness assumptions by using a new approach which may be of independent interest and further application. © 2011 Elsevier Ltd. All rights reserved.


Zeng S.X.,Shanghai JiaoTong University | Xie X.M.,Shanghai University | Tam C.M.,City University of Hong Kong
Technovation | Year: 2010

The complexity of innovation processes led to a tremendous growth in the use of external networks by small- and medium-sized enterprises (SMEs). Based on a survey to 137 Chinese manufacturing SMEs, this paper empirically explores the relationships between different cooperation networks and innovation performance of SME using the technique of structural equation modeling (SEM). The study finds that there are significant positive relationships between inter-firm cooperation, cooperation with intermediary institutions, cooperation with research organizations and innovation performance of SMEs, of which inter-firm cooperation has the most significant positive impact on the innovation performance of SMEs. Surprisingly, the result reveals that the linkage and cooperation with government agencies do not demonstrate any significant impact on the innovation performance of SMEs. In addition, these findings confirm that the vertical and horizontal cooperation with customers, suppliers and other firms plays a more distinct role in the innovation process of SMEs than horizontal cooperation with research institutions, universities or colleges, and government agencies. © 2009 Elsevier Ltd. All rights reserved.


Wang X.-H.,University of Electronic Science and Technology of China | Xue Q.,City University of Hong Kong | Choi W.-W.,University of Macau
IEEE Microwave and Wireless Components Letters | Year: 2010

In this letter, double-sided parallel-strip line (DSPSL) has been used to build a novel differential filter with ultra- wideband (UWB) response. Swap structures, based on DSPSL, are employed in the design to realize 180° phase shift. So the swap structures can realize the conversion between differential- and common-mode. Utilizing the characteristic, the input common- mode signals will be cancelled at the center of the filter, while the input differential-mode signals can propagate in the proposed filter. The proposed new differential filter was calculated in analytical method, and was simulated by the full-wave electromagnetic simulator, and was validated by the measurement. The last results show they have a good in-band and out-band performance. With fractional bandwidth of 110% centered at 3 GHz, the differential-mode signals can propagate with UWB frequency response, while the common-mode signals are suppressed below -20 dB in the whole frequency band. © 2010 IEEE.


Yamakawa Y.,Babson College | Yang H.,City University of Hong Kong | Lin Z.,University of Texas at Dallas
Research Policy | Year: 2011

How does the nature of firms' alliance portfolio in terms of exploration versus exploitation affect performance? Building on prior research grounded in the resource-based view and the relational perspective, we expand firms' boundary to include their inter-firm relationships and their immediate environment, and develop an extended resource-based framework centering on the concept of fit. Specifically, we propose that whether the exploration versus exploitation orientation of an alliance portfolio may benefit firm performance depends on how such an orientation fits the firm's internal organizational characteristics, strategic orientations, and the industry environment. Data from five U.S. industries over eight years largely support our thesis. Overall, our study calls for a holistic approach to consider the importance of organizational, strategic, and environmental fit in understanding the performance implications of alliance-formation choices. © 2010 Elsevier B.V. All rights reserved.


Grant
Agency: Cordis | Branch: FP7 | Program: CP | Phase: ICT-2009.1.1 | Award Amount: 7.45M | Year: 2010

The availability of position information plays an increasing role in wireless communications networks already today and will be an integral part of future systems. They inherently can offer the ability for stand-alone positioning especially in situations where conventional satellite based positioning systems such as GPS fail (e.g., indoor). In this framework, positioning information is an important enabler either for location and context-aware services or even to improve the communications system itself.The WHERE2 project is a successor of the WHERE project and addresses the combination of positioning and communications in order to exploit synergies and to enhance the efficiency of future wireless communications systems. The key objective of WHERE2 is to assess the fundamental synergies between the two worlds of heterogeneous cooperative positioning and communications in the real world under realistic constraints. The estimation of the position of mobile terminals (MTs) is the main goal in WHERE2. The positioning algorithms combine measurements from heterogeneous infrastructure and complement them by cooperative measurements between MTs, additional information from inertial sensors, and context information. Based on the performance of the geo-aided positioning strategies (in the sense of accuracy, complexity, overhead of signalling, reliability of the provided information, etc.) the impact on coordinated, cooperative, and cognitive networks is assessed. This is done under realistic scenarios and system parameters following on-going standardization processes. A joint and integrated demonstration using multiple hardware platforms provides a verification of the performance of dedicated cooperative algorithms.All the tasks in WHERE2 are covered by different work packages, which are in close interaction to ensure an integral research of cooperative positioning and communications.


Grant
Agency: Cordis | Branch: FP7 | Program: CP | Phase: ICT-2007.1.1 | Award Amount: 5.55M | Year: 2008

To increase ubiquitous and mobile network access and data rates, scientific and technological development is more and more focussing on the integration of radio access networks (RANs). For an efficient usage of RANs, knowledge of the position of mobile terminals (MTs) is valuable information in order to allocate resources or predict the allocation within a heterogeneous RAN infrastructure.\nThe main objective of WHERE is to combine wireless communications and navigation for the benefit of the ubiquitous access for a future mobile radio system. The impact will be manifold, such as real time localization knowledge in B3G/4G systems that allow them to increase efficiency. Satellite navigation systems will be supplemented with techniques that improve accuracy and availability of position information.\nThe WHERE project addresses the combination of positioning and communication in order to exploit synergies and to improve the efficiency of future wireless communication systems.\nThus, the estimation of the position of MTs based on different RANs is the main goal in WHERE. Positioning algorithms and algorithms for combining several positioning measurements allow to estimate the position of MTs. Appropriate definitions of scenarios and system parameters together with channel propagation measurements and derived models will allow to assess the performance of RAN based positioning. Based on the performance of RAN positioning, location based strategies and protocols will be developed in order to optimise as well as to cross-optimise different OSI layers of communication systems and RAT selection policies. Performance assessment of the algorithms is provided by theoretical studies and simulations. Hardware signal processing will provide a verification of the performance of dedicated algorithms under realistic conditions. \nAll the tasks are covered by different work packages, which are in close interaction to ensure an integral research of positioning and communications.


Grant
Agency: Cordis | Branch: H2020 | Program: RIA | Phase: WASTE-7-2015 | Award Amount: 7.82M | Year: 2016

NoAW : No Agro-Waste. Innovative approaches to turn agricultural waste into ecological and economic assets. Driven by a near zero-waste society requirement, the goal of NoAW project is to generate innovative efficient approaches to convert growing agricultural waste issues into eco-efficient bio-based products opportunities with direct benefits for both environment, economy and EU consumer. To achieve this goal, the NoAW concept relies on developing holistic life cycle thinking able to support environmentally responsible R&D innovations on agro-waste conversion at different TRLs, in the light of regional and seasonal specificities, not forgetting risks emerging from circular management of agro-wastes (e.g. contaminants accumulation). By involving all agriculture chain stakeholders in a territorial perspective, the project will: (1) develop innovative eco-design and hybrid assessment tools of circular agro-waste management strategies and address related gap of knowledge and data via extensive exchange through the Knowledge exchange Stakeholders Platform, (2) develop breakthrough knowledge on agro-waste molecular complexity and heterogeneity in order to upgrade the most widespread mature conversion technology (anaerobic digestion) and to synergistically eco-design robust cascading processes to fully convert agro-waste into a set of high added value bio-energy, bio-fertilizers and bio-chemicals and building blocks, able to substitute a significant range of non-renewable equivalents, with favourable air, water and soil impacts and (3) get insights of the complexity of potentially new, cross-sectors, business clusters in order to fast track NoAW strategies toward the field and develop new business concepts and stakeholders platform for cross-chain valorisation of agro-waste on a territorial and seasonal basis.


Li Z.,Beijing Institute of Technology | Duan Z.,Peking University | Chen G.,City University of Hong Kong
Automatica | Year: 2011

This paper addresses the distributed H2 and H∞ control problems for multi-agent systems with linear or linearized dynamics. An undirected multigraph with loops is used to represent the communication topology of a multi-agent network. A distributed controller is designed, based on the relative states of neighboring agents and a subset of absolute states of the networked agents. The notions of H∞ and H2 performance regions are introduced and analyzed, respectively. A necessary and sufficient condition for the existence of a controller yielding an unbounded H∞ performance region is derived. A multi-step procedure for suboptimal H∞ controller synthesis is presented. It is also shown that the H∞ performance limit of the network under the distributed controller is equal to the minimal H∞ norm of a single agent achieved by using the state feedback controller. It is finally shown that, contrarily to the H∞ case, the H2 performance limit scales with the number of agents in the network. © 2011 Elsevier Ltd. All rights reserved.


Wang F.,Institute of Materials Research and Engineering of Singapore | Wang F.,City University of Hong Kong | Deng R.,City University of Hong Kong | Liu X.,Institute of Materials Research and Engineering of Singapore | And 2 more authors.
Nature Protocols | Year: 2014

Sodium gadolinium fluoride (NaGdF4) is an ideal host material for the incorporation of luminescent lanthanide ions because of its high photochemical stability, low vibrational energy and its ability to mediate energy exchanges between the lanthanide dopants. This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission. These nanoparticles can then be used as luminescent probes in biological samples, in 3D displays, in solar energy conversion and in photodynamic therapy. The NaGdF4 nanoparticles are grown through co-precipitation in a binary solvent mixture of oleic acid and 1-octadecene. Doping by lanthanides with controlled compositions and concentrations can be achieved concomitantly with particle growth. The lanthanide-doped NaGdF4 nanoparticles then serve as seed crystals for subsequent epitaxial growth of shell layers comprising different lanthanide dopants. The entire procedure for the preparation and isolation of the core-shell nanoparticles comprising two epitaxial shell layers requires ∼15 h for completion. © 2014 Nature America, Inc. All rights reserved.


News Article | March 1, 2017
Site: www.PR.com

Over 7,500 global students whittled down to just 96 for two-day event in Shenzhen Shenzhen, China, March 01, 2017 --( Each had undertaken a gruelling selection process to test their knowledge of IP and IT subjects, to be eligible for the trip. Huawei, known for its mobile phones, hosted 32 China teams, including six overseas teams, from across the globe at the inaugural event (25-26 February) at its Shenzhen HQ, including teams from Pakistan, South Africa, Australia, Russia, and Western Europe. They undertook an eight-hour practical challenge that thoroughly tests their knowledge of routers, switching, security, WLAN, plus cloud, storage and Big Data. The students are members of the Huawei ICT Academy, a worldwide not-for-profit programme that encourages the next generation of ICT professionals for a better connected world. Of the 150m people across the globe who work in ICT industries, just under 3m are estimated to work in professional or certified roles (1). Lintuo Wu, Huawei ICT Academy director, said: “The pan-global growth in internet start-ups suggests ICT talent is thriving, however, the opposite is the case. Businesses, particularly those in smaller countries, struggle to find people with the right ICT skills to deal with security, the cloud and data storage. “Training the next generation of IT professionals to understand how to handle the staggeringly large amounts of information we produce is a significant challenge. The Huawei ICT Academy hopes to influence the upskilling of the global ICT workforce through educational opportunities, to create a better ICT talent ecosystem.” Pallavi Malhotra, Huawei ICT Academy manager, said: “More and more university students, and those wanting to embark on an ICT career realise they need the full suite of academic knowledge and practical know-how to enter the current ICT workplace. Huawei ICT Academy qualifications provide the foundations, from routers or switching, to cloud computing, or security, to help students find those roles. We can also provide a career path for ICT professionals right up to certification, to enable them to aim for middle to senior level positions.” References: (1) “GIC 2020 Skills Assessment” published 2015 by IPPP, International Professional Practice Partnership About Huawei ICT Academy The Huawei ICT Academy is part of a number of Huawei outreach programmes to enrich life and improve efficiency around the world. Huawei works with over 200 global colleges and universities, including the University of Reading in the UK, University of Sydney in Australia, University of Alicante in Spain, National University of Computer & Emerging Sciences (FAST-NU) in Pakistan, and University of São Paulo in Brazil City University of Hong Kong, and has trained over 200,000 students up to 2016. To date, Huawei has provided cloud services to over 2,500 customers in the government and public utility, telecom, energy, and finance sectors across 108 countries and regions, deploying more than 1.4 million virtual machines. It has also built 660 data centers worldwide, including 255 cloud data centers. Its ICT solutions, products, and services are used in more than 170 countries and regions, serving over one-third of the world's population. With more than 170,000 employees, Huawei is committed to enabling the future information society, and building a better connected world. Shenzhen, China, March 01, 2017 --( PR.com )-- The best ICT students from across the globe flew to China this week to pit their brains against each other in a challenge that highlights the skills needed for a connected world.Each had undertaken a gruelling selection process to test their knowledge of IP and IT subjects, to be eligible for the trip.Huawei, known for its mobile phones, hosted 32 China teams, including six overseas teams, from across the globe at the inaugural event (25-26 February) at its Shenzhen HQ, including teams from Pakistan, South Africa, Australia, Russia, and Western Europe.They undertook an eight-hour practical challenge that thoroughly tests their knowledge of routers, switching, security, WLAN, plus cloud, storage and Big Data.The students are members of the Huawei ICT Academy, a worldwide not-for-profit programme that encourages the next generation of ICT professionals for a better connected world.Of the 150m people across the globe who work in ICT industries, just under 3m are estimated to work in professional or certified roles (1).Lintuo Wu, Huawei ICT Academy director, said: “The pan-global growth in internet start-ups suggests ICT talent is thriving, however, the opposite is the case. Businesses, particularly those in smaller countries, struggle to find people with the right ICT skills to deal with security, the cloud and data storage.“Training the next generation of IT professionals to understand how to handle the staggeringly large amounts of information we produce is a significant challenge. The Huawei ICT Academy hopes to influence the upskilling of the global ICT workforce through educational opportunities, to create a better ICT talent ecosystem.”Pallavi Malhotra, Huawei ICT Academy manager, said: “More and more university students, and those wanting to embark on an ICT career realise they need the full suite of academic knowledge and practical know-how to enter the current ICT workplace. Huawei ICT Academy qualifications provide the foundations, from routers or switching, to cloud computing, or security, to help students find those roles. We can also provide a career path for ICT professionals right up to certification, to enable them to aim for middle to senior level positions.”References:(1) “GIC 2020 Skills Assessment” published 2015 by IPPP, International Professional Practice PartnershipAbout Huawei ICT AcademyThe Huawei ICT Academy is part of a number of Huawei outreach programmes to enrich life and improve efficiency around the world.Huawei works with over 200 global colleges and universities, including the University of Reading in the UK, University of Sydney in Australia, University of Alicante in Spain, National University of Computer & Emerging Sciences (FAST-NU) in Pakistan, and University of São Paulo in Brazil City University of Hong Kong, and has trained over 200,000 students up to 2016.To date, Huawei has provided cloud services to over 2,500 customers in the government and public utility, telecom, energy, and finance sectors across 108 countries and regions, deploying more than 1.4 million virtual machines. It has also built 660 data centers worldwide, including 255 cloud data centers.Its ICT solutions, products, and services are used in more than 170 countries and regions, serving over one-third of the world's population. With more than 170,000 employees, Huawei is committed to enabling the future information society, and building a better connected world. Click here to view the list of recent Press Releases from Huawei ICT Academy


LAHORE, PAKISTAN, March 02, 2017 /24-7PressRelease/ -- Six ICT students from Pakistan who beat over 2,000 of their countrymen for a place at a global ICT challenge will fly to China this week to highlight the skills needed for a connected world. The students were selected as part of a Government-sponsored initiative that saw around 2,300 entrants from more than 30 universities tested during two gruelling rounds of competition. Six were eventually chosen from a shortlist of 50 during the second test event in Lahore in November. Huawei, known for its mobile phones, will host 32 China teams including six overseas teams, from across the globe at the inaugural event at its Shenzhen HQ, including representatives from Western Europe, South Africa, Australia, and Russia. Over 7,500 students entered the competition worldwide. The Pakistan delegation comprising two teams, will undertake an eight-hour practical challenge that thoroughly tests their knowledge of routers, switching, security, WLAN, plus cloud, storage, and Big Data. The top three teams will be announced at the end, along with six of the best mentors. The students are members of the Huawei ICT Academy, a worldwide not-for-profit programme that encourages the next generation of ICT professionals for a better connected world. The development of ICT skills in Pakistan is hampered by poor electricity supply to rural schools. Just 31% have access, compared with 53% in urban areas(1). Lintuo Wu, Huawei ICT Academy director, said: "The high number of entrants for this competition underlines the thirst in Pakistan to develop ICT knowledge and skills among University students. The Huawei ICT Academy hopes to influence the upskilling of Pakistan's ICT workforce through educational opportunities and the creation of a better ICT talent ecosystem." Pallavi Malhotra, Huawei ICT Academy manager, said: "More and more university students, and those wanting to embark on an ICT career realise they need the full suite of academic knowledge and practical know-how to enter the current ICT workplace. Huawei ICT Academy qualifications provide the foundations, from routers or switching, to cloud computing, or security, to help students find those roles. We can also provide a career path for ICT professionals right up to certification, to enable them to aim for middle to senior level positions." References 1. "Information and Communication Technology (ICT) in Education in Asia" April 2014, by UNESCO, United Nations Educational, Scientific and Cultural Organization About Huawei ICT Academy The Huawei ICT Academy is part of a number of Huawei outreach programmes to enrich life and improve efficiency around the world. Huawei works with over 200 global colleges and universities, including the University of Reading in the UK, University of Sydney in Australia, University of Alicante in Spain, National University of Computer & Emerging Sciences (FAST-NU) in Pakistan, and University of São Paulo in Brazil City University of Hong Kong, and has trained more than 200,000 students up to 2016. To date, Huawei has provided cloud services to over 2,500 customers in the government and public utility, telecom, energy, and finance sectors across 108 countries and regions, deploying more than 1.4 million virtual machines. It has also built 660 data centers worldwide, including 255 cloud data centers. Its ICT solutions, products, and services are used in more than 170 countries and regions, serving over one-third of the world's population. With more than 170,000 employees, Huawei is committed to enabling the future information society, and building a better connected world.


Grant
Agency: Cordis | Branch: H2020 | Program: RIA | Phase: INT-04-2015 | Award Amount: 3.72M | Year: 2016

This Project aims to address an increasingly pressing global challenge: How to achieve the EUs development goals and the UNs Sustainable Development Goals, while meeting the global target of staying within two degrees global warming and avoid transgressing other planetary boundaries. EU policies must align with sustainable development goals (Article 11 TFEU). The impacts of climate change and global loss of natural habitat undermine the progress achieved by pursuing the Millennium Development Goals and threaten the realisation of EU development policy goals. Our focus is the role of EUs public and private market actors. They have a high level of interaction with actors in emerging and developing economies, and are therefore crucial to achieving the EUs development goals. However, science does not yet cater for insights in how the regulatory environment influences their decision-making, nor in how we can stimulate them to make development-friendly, environmentally and socially sustainable decisions. Comprehensive, ground-breaking research is necessary into the regulatory complexity in which EU private and public market actors operate, in particular concerning their interactions with private and public actors in developing countries. Our Consortium, leading experts in law, economics, and applied environmental and social science, is able to analyse this regulatory complexity in a transdisciplinary and comprehensive perspective, both on an overarching level and in depth, in the form of specific product life-cycles: ready-made garments and mobile phones. We bring significant new evidence-based insights into the factors that enable or hinder coherence in EU development policy; we will advance the understanding of how development concerns can be successfully integrated in non-development policies and regulations concerning market actors; and we provide tools for improved PCD impact assessment as well as for better corporate sustainability assessment.


News Article | February 28, 2017
Site: en.prnasia.com

HONG KONG, Feb. 28, 2017 /PRNewswire/ -- HKBN Ltd. ("HKBN" or the "Group"; SEHK stock code: 1310) announced today that with effect from 1 March 2017, Ni Quiaque Lai ("NiQ") will be named Chief Operating Officer ("COO"). Formerly the Group's Chief Talent & Financial Officer ("CT&FO"), NiQ, in this expanded new role, will lead the Group's sales and marketing operations for the residential market whilst he retains executive oversight of his previous CT&FO responsibilities in finance, legal as well as Talent engagement. NiQ's appointment leverages a multifunctional perspective to consolidate greater synergy between HKBN's various teams to drive sustainable growth for the Group's business and operations. Whilst NiQ will retain executive oversight in the respective areas of finance, Talent engagement and legal, Andrew Wong, Financial Controller, CY Chan, Associate Director -- Talent Management & Organization Development and Co-Owner, and Amy Tam, Head of Legal & Company Secretary and Co-Owner, will step up to take on more operational management responsibilities in their respective areas. As COO, NiQ will report directly to CEO and Co-Owner William Yeung. William Yeung said, "NiQ's strong leadership and deep understanding across many different aspects of our business means he is well positioned to unify our strengths and steer HKBN's growth via improved strategic thinking, efficiency and agility among teams." The Group also announces that its Chief Marketing Officer, Selina Chong, has decided to step down from her role with effect from 19 March 2017 to focus on new opportunities beyond HKBN. In her five years with the Group, Selina successfully strengthened the HKBN brand, making it a highly compelling choice for broadband, mobile, and OTT services as well as enterprise solutions. The Group thanks Selina for her tremendous contributions and wishes her all the best in her future endeavours. HKBN Ltd. (SEHK Stock Code: 1310, together with its subsidiaries, the "Group") is an investment holding company. The Group is Hong Kong's largest provider of residential high speed fibre broadband (symmetrical 100Mbps to 1,000Mbps) services by number of subscriptions, and a fast growing enterprise solutions provider. The Group offers a full range of telecommunications solutions for both the residential and enterprise markets, encompassing broadband and Wi-Fi network services, cloud solutions, data connectivity, data facilities, system integration, mobile services, entertainment and voice communications. HKBN owns an extensive fibre network in Hong Kong, which covers over 2.2 million residential homes passed, representing approximately 81% of Hong Kong's total residential units, and 2,300 commercial buildings. HKBN embraces "Make our Hong Kong a Better Place to Live" as its core purpose, and takes great pride in developing its Talents into a competitive advantage. The Group is managed by about 340 Co-Owners who have invested their own savings to buy HKBN shares, representing the majority of supervisory and management level Talents in the Group. NiQ Lai, Chief Operating Officer and Co-Owner, joined 2004. NiQ has over 24 years of experience in telecom, research and finance industries. Prior to joining the Group, NiQ was Director and Head of Asia Telecom Research at Credit Suisse. In 2016, NiQ was chosen Best CFO in Hong Kong in the FinanceAsia Survey. As one of the pioneers shaping HKBN's unique Talent culture into a competitive advantage, he was named a Champion of Human Resources by The Hong Kong HRM Awards in 2009. In his youth, NiQ aspired to be a professional tennis player but a lack of sporting talent diverted him into the corporate track instead. NiQ holds a Bachelor of Commerce Degree from the University of Western Australia, and an Executive Master of Business Administration Degree from Kellogg-HKUST, Hong Kong. NiQ is a Fellow member of the Hong Kong Institute of Certified Public Accountants and CPA Australia. Andrew Wong, Financial Controller, joined 2006. Andrew joined the Group as Manager in 2006 and is now responsible for overall finance functions. During his 10 years with the Group, Andrew has been a key team member responsible for different capital projects such as the management buyout in 2012, the initial public offering in 2015, acquisition of New World Telecom in 2016 and several major refinancing projects between 2013 and 2016. Prior to joining HKBN, Andrew spent five years with KPMG in Hong Kong specializing in the telecommunications industry. He holds a Bachelor's Degree in Accounting and Law from the University of Manchester in the UK and an Executive Master of Business Administration Degree from the Chinese University of Hong Kong. He is also a member of the Hong Kong Institute of Certified Public Accountants. CY Chan, Associate Director -- Talent Management & Organization Development and Co-Owner, joined 2011. CY oversees HKBN's Talent management, organization development and performance improvement strategy and initiatives. He has over 15 years of experience in organizational change, HR and business development. As a business consultant and HR practitioner across different industries, CY has worked for Wilson Learning China, Dun & Bradstreet and Hutchison Global Communications, and was involved in large sized consultancy projects like partnership projects for MTR Corporation, raising commercial awareness of NGOs for the Social Welfare Department and leadership development programmes for over 60 organizations across the South China region. Believing that success starts with a clear purpose, he enjoys sharing his experience and hopes that he can be a catalyst for the career and life success of others. CY holds a Master of Science Degree in Strategic HRM from Hong Kong Baptist University and a Master of Social Science Degree in Applied Psychology from City University of Hong Kong. Amy Tam, Head of Legal & Company Secretary and Co-Owner, joined 2015. With over 20 years of experience in the legal field, Amy oversees the legal and regulatory aspects of the Group. Prior to joining HKBN, she worked in both private practice and as a Senior Legal Advisor for MTR Corporation Limited. Amy was admitted as a solicitor and practicing lawyer of Hong Kong by the High Court of Hong Kong in July 1991 and has been a member of the Law Society of Hong Kong since July 1991. In 1992, she was also admitted as a solicitor of the Supreme Court of England and Wales. Amy's expertise covers general commercial work, property management, compliance and corporate governance, China business and general litigation. She believes that by committing to a high standard of corporate governance practices, the integrity of the Group's operations is safeguarded and stakeholder trust is also maintained.


Home > Press > NTU scientists invent bubble technology which can shoot drugs deep into tumors: Using ultrasound, drug particles can be directed to a specific area Abstract: Scientists at Nanyang Technological University (NTU Singapore) have invented a new way to deliver cancer drugs deep into tumour cells. The NTU scientists create micro-sized gas bubbles coated with cancer drug particles and iron oxide nanoparticles, and then use magnets to direct these bubbles to gather around a specific tumour. Ultrasound is then used to vibrate the microbubbles, providing the energy to direct the drug particles into a targeted area. This innovative technique was developed by a multidisciplinary team of scientists, led by Asst Prof Xu Chenjie from the School of Chemical and Biomedical Engineering and Assoc Prof Claus-Dieter Ohl from the School of Physical and Mathematical Sciences. NTU's microbubbles were successfully tested in mice and the study has been published by the Nature Publishing Group in Asia Materials, the top journal for materials sciences in the Asia-Pacific region. Overcoming limitations of chemotherapy Asst Prof Xu, who is also a researcher at the NTU-Northwestern Institute for Nanomedicine, said their new method may solve some of the most pressing problems faced in chemotherapy used to treat cancer. The main issue is that current chemotherapy drugs are largely non-targeted. The drug particles flow in the bloodstream, damaging both healthy and cancerous cells. Typically, these drugs are flushed away quickly in organs such as the lungs and liver, limiting their effectiveness. The remaining drugs are also unable to penetrate deep into the core of the tumour, leaving some cancer cells alive, which could lead to a resurgence in tumour growth. "The first unique characteristic of our microbubbles is that they are magnetic. After injecting them into the bloodstream, we are able to gather them around the tumour using magnets and ensure that they don't kill the healthy cells," explains Asst Prof Xu, who has been working on cancer diagnosis and drug delivery systems since 2004. "More importantly, our invention is the first of its kind that allows drug particles to be directed deep into a tumour in a few milliseconds. They can penetrate a depth of 50 cell layers or more - which is about 200 micrometres, twice the width of a human hair. This helps to ensure that the drugs can reach the cancer cells on the surface and also inside the core of the tumour." Clinical Associate Professor Chia Sing Joo, a Senior Consultant at the Tan Tock Seng Hospital's Endoscopy Centre and the Urology & Continence Clinic, was one of the consultants for this study. A trained robotic surgeon experienced in the treatment of prostate, bladder and kidney cancer, Assoc Prof Chia said, "For anticancer drugs to achieve their best effectiveness, they need to penetrate into the tumour efficiently in order to reach the cystoplasm of all the cancer cells that are being targeted without affecting the normal cells. "Currently, these can be achieved by means of a direct injection into the tumour or by administering a large dosage of anticancer drugs, which can be painful, expensive, impractical and might have various side effects." The specialist in Uro-oncology added that if NTU's technology proves to be viable, clinicians might be able to localise and concentrate the anticancer drugs around a tumour, and introduce the drugs deep into tumour tissues in just a few seconds using a clinical ultrasound system. "If successful, I envisage it can be a good alternative treatment in the future, one which is low cost and yet effective for the treatment of cancers involving solid tumours, as it might minimise the side effects of drugs." New drug delivery system The motivation for this research project is to find alternative solutions for drug delivery systems that are non-invasive and safe. Ultrasound uses soundwaves with frequencies higher than those heard by the human ear. It is commonly used for medical imaging such as to get diagnostic images. Magnets, which can draw and attract the microbubbles, are already in use in diagnostic machines such the Magnetic Resonance Imaging (MRI). "We are looking at developing novel drug carriers - essentially better ways of delivering drugs with minimum side effects," explained Prof Ohl, an expert in biophysics who had published previous studies involving drug delivery systems and bubble dynamics. "Most prototype drug delivery systems on the market face three main challenges before they can be commercially successful: they have to be non-invasive, patient-friendly and yet cost-effective. "Using the theory of microbubbles and how their surface vibrates under ultrasound, we were able to come up with our solution that addresses these three challenges." Interdisciplinary team This study, which took two and a half years, involved a 12-man international interdisciplinary team consisting of NTU scientists as well as scientists from City University of Hong Kong and Tel Aviv University in Israel. Two NTU undergraduates doing their Final Year Project and one student in Summer Research Internship Programme (NTU) were also part of the team. Moving forward, the team will be adopting this new drug delivery system in studies on lung and liver cancer using animal models, and eventually clinical studies. They estimate that it will take another eight to ten years before it reaches human clinical trials. About Nanyang Technological University A research-intensive public university, Nanyang Technological University, Singapore (NTU Singapore) has 33,500 undergraduate and postgraduate students in the colleges of Engineering, Business, Science, Humanities, Arts, & Social Sciences, and its Interdisciplinary Graduate School. It has a new medical school, the Lee Kong Chian School of Medicine, set up jointly with Imperial College London. NTU is also home to world-class autonomous institutes - the National Institute of Education, S Rajaratnam School of International Studies, Earth Observatory of Singapore, and Singapore Centre for Environmental Life Sciences Engineering - and various leading research centres such as the Nanyang Environment & Water Research Institute (NEWRI), Energy Research Institute @ NTU and the Institute on Asian Consumer Insight (ACI). Ranked 13th in the world, NTU has also been ranked the world's top young university for the last two years running. The University's main campus has been named one of the Top 15 Most Beautiful in the World. NTU also has a campus in Novena, Singapore's medical district. 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.


Xu C.,Zhengzhou University of Light Industry | Arancon R.A.D.,University of Cordoba, Spain | Arancon R.A.D.,City University of Hong Kong | Labidi J.,University of the Basque Country | Luque R.,University of Cordoba, Spain
Chemical Society Reviews | Year: 2014

Research on lignin deconstruction has recently become the center of interest for scientists and companies worldwide, racing towards harvesting fossil-fuel like aromatic compounds which are so durably put together by plants as products of millions of years of evolution. The natural complexity and high stability of lignin bonds (also as an evolutionary adaptation by plants) makes lignin depolymerization a highly challenging task. Several efforts have been directed towards a more profound understanding of the structure and composition of lignin in order to devise pathways to break down the biopolymer into useful compounds. The present contribution aims to provide an overview of key advances in the field of lignin depolymerisation. Protocols and technologies will be discussed as well as critically evaluated in terms of possibilities and potential for further industrial implementation. © the Partner Organisations 2014.


Cai S.,Carleton University | Jun M.,New Mexico State University | Yang Z.,City University of Hong Kong
Journal of Operations Management | Year: 2010

This study investigates the effects of Chinese companies' institutional environment on the development of trust and information integration between buyers and suppliers. Three aspects of China's institutional environment are salient: legal protection, government support, and the importance of guanxi (interpersonal relationships). This study uses structural equation modeling to analyze data collected from 398 Chinese manufacturing companies. Government support and importance of guanxi significantly affect trust, which subsequently influences two elements of information integration, namely, information sharing and collaborative planning. Furthermore, the importance of guanxi has a direct, positive impact on information sharing, and government support has a direct, positive effect on both information sharing and collaborative planning. © 2009 Elsevier B.V.


Kim J.-S.,City University of Hong Kong | Jain S.,University of Maine, United States
Environmental Research Letters | Year: 2011

Typhoons originating in the west Pacific are major contributors to climate-related risk over the Korean peninsula. The current perspective regarding improved characterization of climatic risk and the projected increases in the intensity, frequency, duration, and power dissipation of typhoons during the 21st century in the western North Pacific region motivated a reappraisal of historical trends in precipitation. In this study, trends in the magnitude and frequency of seasonal precipitation in the five major river basins in Korea are analyzed on the basis of a separation analysis, with recognition of moisture sources (typhoon and non-typhoon). Over the 1966-2007 period, typhoons accounted for 21-26% of seasonal precipitation, with the largest values in the Nakdong River Basin. Typhoon-related precipitation events have increased significantly over portions of Han, Nakdong, and Geum River Basins. Alongside broad patterns toward increases in the magnitude and frequency of precipitation, distinct patterns of trends in the upper and lower quartiles (corresponding to changes in extreme events) are evident. A trend typology - spatially resolved characterization of the combination of shifts in the upper and lower tails of the precipitation distribution - shows that a number of sub-basins have undergone significant changes in one or both of the tails of the precipitation distribution. This broader characterization of trends illuminates the relative role of causal climatic factors and an identification of 'hot spots' likely to experience high exposure to typhoon-related climatic extremes in the future. © 2011 IOP Publishing Ltd.


The P.-L.,Multimedia University | Sun H.,City University of Hong Kong
Industrial Management and Data Systems | Year: 2012

Purpose - There are very few studies on the impact of job attitude on knowledge sharing. The purpose of this paper is to examine the effects of job involvement, job satisfaction, organisational commitment, and organisational citizenship behaviour (OCB) on employees' knowledge sharing behaviour. Design/methodology/approach - This research is based on a survey of 116 Information Systems personnel in Malaysia. Structural equation modelling is used to test the hypothesis. Findings - The results show that job involvement, job satisfaction and OCB are independent and positively related to employees' knowledge sharing behaviour. However, organisational commitment has a negative relationship with knowledge sharing behaviour. It is found that OCB is not a significant mediator between job involvement, job satisfaction organisational commitment and knowledge sharing behaviour. Research limitations/implications - It is widely reported that knowledge workers may not be willing to share with others since they can always argue that it is not their job to share. Therefore, knowledge sharing can be regarded as an extra job. OCB is an extra-role behaviour which is especially relevant to research on knowledge sharing. Theories and research methods in OCB may be used in future research on knowledge sharing. Practical implications - Given the importance of knowledge sharing in today's competitive business world, this study provides a broader understanding of different dimensions of job attitudes in relation to employees' knowledge sharing behaviours. Our findings suggest that organisational administrators and managers should look into ways of improving the levels of job satisfaction, job involvement, and OCB in order to facilitate knowledge sharing behaviour. Originality/value - This study makes two distinct additions to the organisational behaviour and knowledge sharing literature. First, job attitudes appear to be significantly related to knowledge sharing behaviour, addressing a research gap in the literature of knowledge sharing and employee attitudes. Second, this study reveals that OCB directly affects knowledge sharing but it does not mediate employees' job attitudes to promote knowledge sharing behaviours. © Emerald Group Publishing Limited.


Zhu W.,Chongqing University of Posts and Telecommunications | Zhu W.,New York University | Jiang Z.-P.,New York University | Feng G.,City University of Hong Kong | Feng G.,Abdulaziz University
Automatica | Year: 2014

In this paper, the event-based consensus problem of general linear multi-agent systems is considered. Two sufficient conditions with or without continuous communication between neighboring agents are presented to guarantee the consensus. The advantage of the event-based strategy is the significant decrease of the number of controller updates for cooperative tasks of multi-agent systems involving embedded microprocessors with limited on-board resources. The controller updates of each agent are driven by properly defined events, which depend on the measurement error, the states of its neighboring agents and an arbitrarily small threshold. It is shown that the controller updates for each agent only trigger at its own event time instants. A simulation example is presented to illustrate the theoretical results. © 2013 Elsevier Ltd. All rights reserved.


Karmee S.K.,City University of Hong Kong | Karmee S.K.,North West University South Africa
Renewable and Sustainable Energy Reviews | Year: 2016

Depletion of fossil fuels, environmental damage due to pollution and energy security have intensified research on alternative liquid biofuels. A major portion of municipal solid waste is food waste. Huge quantities of food waste is generated worldwide and currently its disposal is becoming a challenge. Food waste contain carbohydrates, lipids, phosphates, vitamins and amino acids. Carbohydrate, lipid and carbon containing materials present in food waste can be converted to bioethanol, biodiesel and biooil. Lipid extracted from food waste is converted to biodiesel in 95-97% yield. On the other hand, 92-96% bioethanol obtained by fermentation of food waste. Along this line, pyrolysis of food waste can be performed to obtain biooil and biochar. In this paper, technical feasibility, prospects and policies for liquid biofuel preparation from food waste was evaluated. Also, limitations of using food waste as a resource for biofuel production is discussed. © 2015 Elsevier Ltd. Allrightsreserved.


Wang Q.,Beihang University | Chen G.,City University of Hong Kong | Perc M.,University of Maribor
PLoS ONE | Year: 2011

This paper investigates the dependence of synchronization transitions of bursting oscillations on the information transmission delay over scale-free neuronal networks with attractive and repulsive coupling. It is shown that for both types of coupling, the delay always plays a subtle role in either promoting or impairing synchronization. In particular, depending on the inherent oscillation period of individual neurons, regions of irregular and regular propagating excitatory fronts appear intermittently as the delay increases. These delay-induced synchronization transitions are manifested as wellexpressed minima in the measure for spatiotemporal synchrony. For attractive coupling, the minima appear at every integer multiple of the average oscillation period, while for the repulsive coupling, they appear at every odd multiple of the half of the average oscillation period. The obtained results are robust to the variations of the dynamics of individual neurons, the system size, and the neuronal firing type. Hence, they can be used to characterize attractively or repulsively coupled scalefree neuronal networks with delays. © 2011 Wang et al.


Huang X.,Shanghai JiaoTong University | Zhi C.,City University of Hong Kong | Jiang P.,Shanghai JiaoTong University | Golberg D.,Japan International Center for Materials Nanoarchitectonics | And 2 more authors.
Advanced Functional Materials | Year: 2013

Dielectric polymer composites with high thermal conductivity are very promising for microelectronic packaging and thermal management application in new energy systems such as solar cells and light emitting diodes (LEDs). However, a well-known paradox is that conventional composites with high thermal conductivity usually suffer from the high dielectric constant and high dielectric loss, while on the other hand, composite materials with excellent dielectric properties usually possess low thermal conductivity. In this work, an ideal dielectric thermally conductive epoxy nanocomposite is successfully fabricated using polyhedral oligosilsesquioxane (POSS) functionalized boron nitride nanotubes (BNNTs) as fillers. The nanocomposites with 30 wt% fraction of POSS modified BNNTs exhibit much lower dielectric constant, dielectric loss tangent, and coefficient of thermal expansion in comparison with the pure epoxy resin. As an example, below 100 Hz, the dielectric loss of the nanocomposites with 20 and 30 wt% BNNTs is reduced by one order of magnitude in comparison with the pure epoxy resin. Moreover, the nanocomposites show a dramatic thermal conductivity enhancement of 1360% in comparison with the pristine epoxy resin at a BNNT loading fraction of 30 wt%. The merits of the designed composites are suggested to originate from the excellent intrinsic properties of embedded BNNTs, effective surface modification by POSS molecules, and carefully developed composite preparation methods. An ideal, dielectric, thermally conductive epoxy nanocomposite is successfully fabricated using polyhedral oligosilsesquioxane (POSS) functionalized boron nitride nanotubes (BNNTs) as fillers. Compared with the pure epoxy resin, the nanocomposites with POSS modified BNNTs not only exhibit much lower dielectric constant and dielectric loss tangent but also have high thermal conductivity and a low coefficient of thermal expansion Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Yang Q.,City University of Hong Kong | Ahuja N.,University of Illinois at Urbana - Champaign
IEEE Transactions on Image Processing | Year: 2012

In this paper, we propose a simple but effective image transform, called the epipolar distance transform, for matching low-texture regions. It converts image intensity values to a relative location inside a planar segment along the epipolar line, such that pixels in the low-texture regions become distinguishable. We theoretically prove that the transform is affine invariant, thus the transformed images can be directly used for stereo matching. Any existing stereo algorithms can be directly used with the transformed images to improve reconstruction accuracy for low-texture regions. Results on real indoor and outdoor images demonstrate the effectiveness of the proposed transform for matching low-texture regions, keypoint detection, and description for low-texture scenes. Our experimental results on Middlebury images also demonstrate the robustness of our transform for highly textured scenes. The proposed transform has a great advantage, its low computational complexity. It was tested on a MacBook Air laptop computer with a 1.8 GHz Core i7 processor, with a speed of about 9 frames per second for a video graphics array-sized image. © 2012 IEEE.


Wang Z.,Hong Kong Baptist University | Wang L.,City University of Hong Kong | Perc M.,University of Maribor
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

Traditionally, the evolution of cooperation has been studied on single, isolated networks. Yet a player, especially in human societies, will typically be a member of many different networks, and those networks will play different roles in the evolutionary process. Multilayer networks are therefore rapidly gaining on popularity as the more apt description of a networked society. With this motivation, we here consider two-layer scale-free networks with all possible combinations of degree mixing, wherein one network layer is used for the accumulation of payoffs and the other is used for strategy updating. We find that breaking the symmetry through assortative mixing in one layer and/or disassortative mixing in the other layer, as well as preserving the symmetry by means of assortative mixing in both layers, impedes the evolution of cooperation. We use degree-dependent distributions of strategies and cluster-size analysis to explain these results, which highlight the importance of hubs and the preservation of symmetry between multilayer networks for the successful resolution of social dilemmas. © 2014 American Physical Society.


Huang X.,Shanghai JiaoTong University | Zhi C.,City University of Hong Kong | Jiang P.,Shanghai JiaoTong University
Journal of Physical Chemistry C | Year: 2012

Utilizing synergetic effects of different fillers is an important strategy to design and develop high-performance nanocomposites. However, owing to the well-known problems such as dispersion, solution viscosity control, and so on, synergetic enhancement effects are usually offset by the defects induced by fillers in highly loaded nanocomposites. In this work, remarkable synergetic efficiency was realized in graphene nanoplatelet (GNP) and multiwalled carbon nanotube (CNT) highly loaded epoxy composites through a well-designed fabrication method. Dramatic thermal conductivity enhancement was observed in the epoxy composites with 10-50 vol% nanocarbon filler due to synergetic effects. For example, the composite with 20 vol% CNTs and 20 vol% GNPs possess a thermal conductivity up to 6.31 W/mK. This is even much higher than that of the composites with individual 50 vol % CNTs or 50 vol% GNPs. A maximum thermal conductivity 7.30 W/mK was obtained, which is 38-fold of that of the pure epoxy resin. Thermal transport channels in the composites were thoroughly analyzed, and the mechanism of high synergetic effects achieved in thermal conductivity enhancement was discussed from the viewpoints of intrinsic properties, dispersion, contact, and matrix interaction of the fillers. © 2012 American Chemical Society.


Hirata A.,Tohoku University | Fujita T.,Tohoku University | Wen Y.R.,Tohoku University | Schneibel J.H.,City University of Hong Kong | And 3 more authors.
Nature Materials | Year: 2011

Oxide-dispersion-strengthened steels are the most promising structural materials for next-generation nuclear energy systems because of their excellent resistance to both irradiation damage and high-temperature creep. Although it has been known for a decade that the extraordinary mechanical properties of oxide-dispersion-strengthened steels originate from highly stabilized oxide nanoclusters with a size smaller than 5nm, the structure of these nanoclusters has not been clarified and remains as one of the most important scientific issues in nuclear materials research. Here we report the atomic-scale characterization of the oxide nanoclusters using state-of-the-art Cs-corrected transmission electron microscopy. This study provides compelling evidence that the nanoclusters have a defective NaCl structure with a high lattice coherency with the bcc steel matrix. Plenty of point defects as well as strong structural affinity of nanoclusters with the steel matrix seem to be the most important reasons for the unusual stability of the clusters at high temperatures and in intensive neutron irradiation fields. © 2011 Macmillan Publishers Limited. All rights reserved.


Li X.,Shanghai JiaoTong University | Tian P.,Shanghai JiaoTong University | Leung S.C.H.,City University of Hong Kong
International Journal of Production Economics | Year: 2010

This paper studies a version of stochastic vehicle routing problems, in which travel and service times are stochastic, and a time window constraint is associated with each customer. This problem is originally formulated as a chance constrained programming model and a stochastic programming model with recourse in terms of different optimization criteria. To efficiently solve these two models, a heuristic based on tabu search, which takes into account the stochastic nature of this problem, is then proposed. Finally, some testing instances with different properties are established to investigate the algorithmic performance, and the computational results are then reported. © 2010 Elsevier B.V. All rights reserved.


Doan X.V.,University of Warwick | Natarajan K.,City University of Hong Kong
Operations Research | Year: 2012

Given a combinatorial optimization problem with an arbitrary partition of the set of random objective coefficients, we evaluate the tightest-possible bound on the expected optimal value for joint distributions consistent with the given multivariate marginals of the subsets in the partition. For univariate marginals, this bound was first proposed by Meilijson and Nadas [Meilijson, I., A. Nadas. 1979. Convex majorization with an application to the length of critical path. J. Appl. Probab. 16(3) 671-677]. We generalize the bound to nonoverlapping multivariate marginals using multiple-choice integer programming. New instances of polynomial-time computable bounds are identified for discrete distributions. For the problem of selecting up to M items out of a set of N items of maximum total weight, the multivariate marginal bound is shown to be computable in polynomial time, when the size of each subset in the partition is O(logN). For an activity-on-arc PERT network, the partition is naturally defined by subsets of incoming arcs into nodes. The multivariate marginal bound on expected project duration is shown to be computable in time polynomial in the maximum number of scenarios for any subset and the size of the network. As an application, a polynomial-time solvable two-stage stochastic program for project crashing is identified. An important feature of the bound developed in this paper is that it is exactly achievable by a joint distribution, unlike many of the existing bounds. © 2012 INFORMS.


Su H.,Huazhong University of Science and Technology | Chen G.,City University of Hong Kong | Wang X.,Shanghai JiaoTong University | Lin Z.,University of Virginia
Automatica | Year: 2011

We investigate second-order consensus of multiple nonlinear dynamical mobile agents with a virtual leader in a dynamic proximity network. We assume that only a small fraction of agents in the group have access to the information about the position and velocity of the virtual leader through, for example, certain pre-designed communication mechanism such as wireless broadcasting or sensing. To avoid fragmentation, we propose a connectivity-preserving second-order consensus algorithm. Under the assumption that the initial network is connected, we introduce local adaptation strategies for both the weights on the velocity navigational feedback and the velocity coupling strengths that enable all agents to synchronize with the virtual leader even when only one agent is informed, without requiring any knowledge of the agent dynamics. We finally provide some convincing simulation results to illustrate the theoretical results. © 2010 Elsevier Ltd. All rights reserved.


Li H.-X.,City University of Hong Kong | Qi C.,Shanghai JiaoTong University
Journal of Process Control | Year: 2010

Many industrial processes belong to distributed parameter systems (DPS) that have strong spatial-temporal dynamics. Modeling of DPS is difficult but essential to simulation, control and optimization. The first-principle modeling for known DPS often leads to the partial differential equation (PDE). Because it is an infinite-dimensional system, the model reduction (MR) is very necessary for real implementation. The model reduction often works with selection of basis functions (BF). Combination of different BF and MR results in different approaches. For unknown DPS, system identification is usually used to figure out unknown structure and parameters. Using various methods, different approaches are developed. Finally, a novel kernel-based approach is proposed for the complex DPS. This paper provides a brief review of different DPS modeling methods and categorizes them from the view of time-space separation. © 2010 Elsevier Ltd.


News Article | February 15, 2017
Site: www.eurekalert.org

Global climate change is affecting our planet and mankind; climate science is thus instrumental in informing policy makers about its dangers, and in suggesting emission limits. Science also shows that staying within limits, while meeting the aspirations of a growing global population requires fundamental changes in energy conversion and storage. The majority of low-carbon technology innovation observed in the last decades, such as the 85% cost reduction in photovoltaic cell production since 2000, was driven by largely uncoordinated national policies. These included research incentives in Japan and the U.S., feed-in tariffs in Germany, and tax breaks in the U.S. During the AAAS 2017 Annual Meeting in Boston, Tobias Schmidt, ETH Zurich - The Swiss Federal Institute of Technology in Zurich, Switzerland, Jessika Trancik, Massachusetts Institute of Technology, Cambridge, U.S.A., and Masaru Yarime, City University of Hong Kong, will review the successes and failures of policies for low-carbon technology innovation and show how characteristics of both the technologies and the policy instruments themselves helped and, in some ways, hindered technological progress. In addition, they will demonstrate how research by the innovative science community can inform policy decisions in the future to accelerate low-carbon innovation and affect the livelihood of our planet in the long-term, despite limited resources. Wind and solar energy installations have grown rapidly in recent decades as their costs have fallen. It remains unclear; however, whether these trends will continue, allowing the technologies to measurably contribute to climate change mitigation. Jessika Trancik, Associate Professor of Energy Studies at the Massachusetts Institute of Technology (MIT) in Cambridge, USA, uses the case example of photovoltaic technology to uncover the key determinants of innovation from the formulation of policy to the design of technologies. She explains the feedback of emission reduction and the practical lessons that emerge for engineers and policy makers alike. Recent empirical studies demonstrate that innovation patterns and technological learning can differ strongly between energy technologies. Fostering low-carbon innovation may thus require technology-specific policy interventions. Tobias Schmidt, Assistant Professor of Energy Politics at ETH Zurich, Switzerland compares photovoltaics (PV), wind and lithium-ion battery storage technologies in relation to the locus of innovation in the industry value chain, learning feedback, and type of innovation. He relates his observations to technology architecture and production processes deriving implications for other energy technologies. Based on these analyses, Schmidt makes recommendations for the design of policy portfolios to accelerate innovation in clean energy. Masaru Yarime, Associate Professor at the School of Energy and Environment, City University in Hong Kong presents case studies from Japan and the U.S. on how low-carbon energy technologies can be implemented within the larger systems of smart cities. Their implementation calls for the promotion and integration of a variety of innovations in the electronic, housing, automotive, and infrastructure sectors. This requires collaboration and coordination with relevant stakeholders in academia, industry, government, and civil society. Yarime examines smart city projects with policy implications for platform creation, technological development, and end-user engagement. Meet us at AAAS 2017 "Accelerating Low-Carbon Innovation through Policy" Saturday, February 18th, 2017 8:00 - 9:30 AM Room 311, Hynes Convention Centre Boston, USA


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 S.K.,Nanjing Southeast University | Wang J.,Nanjing Southeast University | Chan K.S.,City University of Hong Kong
New Journal of Physics | Year: 2014

Silicene is a 2D topological insulator due to its fairly large spin-orbital interaction and features a buckled lattice structure that allows one to control the effective mass of Dirac electrons by a perpendicular electric field. We propose the use of a spatially alternative electric field to generate multiple topologically-protected interface states (TIS) in the bulk silicene. It is shown that when the valley-dependent electron mass (defining the Chern number of an insulating bulk silicene) changes its sign or discontinues due to spatial variation of the electric field, multiple TIS appear in the insulating bulk silicene. The TIS come from the K and valleys and sustain dissipationless valley or spin-valley-dependent currents, which are immune to both the valley-conservation and spin-observation scattering. It is also found that the coupling among TIS due to spatial electron tunneling excites the TIS, and whether there is an excitation gap or not depends on the even or odd TIS number. Our findings may shed light on manufacturing topological electron devices. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


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.


Koutinas A.A.,Agricultural University of Athens | Vlysidis A.,Agricultural University of Athens | Pleissner D.,City University of Hong Kong | Kopsahelis N.,Agricultural University of Athens | And 5 more authors.
Chemical Society Reviews | Year: 2014

The transition from a fossil fuel-based economy to a bio-based economy necessitates the exploitation of synergies, scientific innovations and breakthroughs, and step changes in the infrastructure of chemical industry. Sustainable production of chemicals and biopolymers should be dependent entirely on renewable carbon. White biotechnology could provide the necessary tools for the evolution of microbial bioconversion into a key unit operation in future biorefineries. Waste and by-product streams from existing industrial sectors (e.g., food industry, pulp and paper industry, biodiesel and bioethanol production) could be used as renewable resources for both biorefinery development and production of nutrient-complete fermentation feedstocks. This review focuses on the potential of utilizing waste and by-product streams from current industrial activities for the production of chemicals and biopolymers via microbial bioconversion. The first part of this review presents the current status and prospects on fermentative production of important platform chemicals (i.e., selected C2-C6 metabolic products and single cell oil) and biopolymers (i.e., polyhydroxyalkanoates and bacterial cellulose). In the second part, the qualitative and quantitative characteristics of waste and by-product streams from existing industrial sectors are presented. In the third part, the techno-economic aspects of bioconversion processes are critically reviewed. Four case studies showing the potential of case-specific waste and by-product streams for the production of succinic acid and polyhydroxyalkanoates are presented. It is evident that fermentative production of chemicals and biopolymers via refining of waste and by-product streams is a highly important research area with significant prospects for industrial applications. This journal is © the Partner Organisations 2014.


Wang Q.,Beihang University | Chen G.,City University of Hong Kong
Chaos | Year: 2011

We study the dependence of synchronization transitions in scale-free networks of bursting neurons with hybrid synapses on the information transmission delay and the probability of inhibitory synapses. It is shown that, irrespective of the probability of inhibitory synapses, the delay always plays a subtle role during synchronization transition of the scale-free neuronal networks. In particular, regions of irregular and regular propagating excitatory fronts appear intermittently as the delay increases. These delay-induced synchronization transitions are manifested as well-expressed minima in the measure for spatiotemporal synchrony. In addition, it is found that, for smaller and larger probability of inhibitory synapses, intermittent synchronization transition is relatively profound, while for the moderate probability of inhibitory synapses, synchronization transition seems less profound. More interestingly, it is found that as the probability of inhibitory synapses is large, regions of synchronization are upscattering. © 2011 American Institute of Physics.


Qian Y.,Shanxi University | Liang J.,Shanxi University | Wu W.-Z.Z.,Zhejiang Ocean University | Dang C.,City University of Hong Kong
IEEE Transactions on Fuzzy Systems | Year: 2011

Zadehs seminal work in theory of fuzzy-information granulation in human reasoning is inspired by the ways in which humans granulate information and reason with it. This has led to an interesting research topic: granular computing (GrC). Although many excellent research contributions have been made, there remains an important issue to be addressed: What is the essence of measuring a fuzzy-information granularity of a fuzzy-granular structure? What is needed to answer this question is an axiomatic constraint with a partial-order relation that is defined in terms of the size of each fuzzy-information granule from a fuzzy-binary granular structure. This viewpoint is demonstrated for fuzzy-binary granular structure, which is called the binary GrC model by Lin. We study this viewpoint from from five aspects in this study, which are fuzzy BINARY-granular-structure operators, partial-order relations, measures for fuzzy-information granularity, an axiomatic approach to fuzzy-information granularity, and fuzzy-information entropies. © 2010 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.


Wang J.-W.,Beihang University | Wu H.-N.,Beihang University | Li H.-X.,City University of Hong Kong
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2012

In this paper, a distributed fuzzy control design based on Proportional-spatial Derivative (P-sD) is proposed for the exponential stabilization of a class of nonlinear spatially distributed systems described by parabolic partial differential equations (PDEs). Initially, a Takagi-Sugeno (T-S) fuzzy parabolic PDE model is proposed to accurately represent the nonlinear parabolic PDE system. Then, based on the T-S fuzzy PDE model, a novel distributed fuzzy P-sD state feedback controller is developed by combining the PDE theory and the Lyapunov technique, such that the closed-loop PDE system is exponentially stable with a given decay rate. The sufficient condition on the existence of an exponentially stabilizing fuzzy controller is given in terms of a set of spatial differential linear matrix inequalities (SDLMIs). A recursive algorithm based on the finite-difference approximation and the linear matrix inequality (LMI) techniques is also provided to solve these SDLMIs. Finally, the developed design methodology is successfully applied to the feedback control of the Fitz-Hugh-Nagumo equation. © 2012 IEEE.


Wu H.-N.,Beihang University | Wang J.-W.,Beihang University | Li H.-X.,City University of Hong Kong
IEEE Transactions on Fuzzy Systems | Year: 2012

This paper deals with the exponential stabilization problem for a class of nonlinear spatially distributed processes that are modeled by semilinear parabolic partial differential equations (PDEs), for which a finite number of actuators are used. A fuzzy control design methodology is developed for these systems by combining the PDE theory and the Takagi-Sugeno (T-S) fuzzy-model-based control technique. Initially, a T-S fuzzy parabolic PDE model is proposed to accurately represent a semilinear parabolic PDE system. Then, based on the T-S fuzzy model, a Lyapunov technique is used to design a continuous fuzzy state feedback controller such that the closed-loop PDE system is exponentially stable with a given decay rate. The stabilization condition is presented in terms of a set of spatial differential linear matrix inequalities (SDLMIs). Furthermore, a recursive algorithm is presented to solve the SDLMIs via the existing linear matrix inequality optimization techniques. Finally, numerical simulations on the temperature profile control of a catalytic rod are given to verify the effectiveness of the proposed design method. © 2012 IEEE.


Liu Y.,City University of Hong Kong | Moevius L.,Rudolf Peierls Center for Theoretical Physics | Xu X.,Hong Kong University of Science and Technology | Qian T.,Hong Kong University of Science and Technology | And 2 more authors.
Nature Physics | Year: 2014

Engineering surfaces that promote rapid drop detachment1,2 is of importance to a wide range of applications including anti-icing3-5, dropwise condensation6 and self-cleaning7-9. Here we show how superhydrophobic surfaces patterned with lattices of submillimetre-scale posts decorated with nanotextures can generate a counter-intuitive bouncing regime: drops spread on impact and then leave the surface in a flattened, pancake shape without retracting. This allows a fourfold reduction in contact time compared with conventional complete rebound1,10-13. We demonstrate that the pancake bouncing results from the rectification of capillary energy stored in the penetrated liquid into upward motion adequate to lift the drop. Moreover, the timescales for lateral drop spreading over the surface and for vertical motion must be comparable. In particular, by designing surfaces with tapered micro/nanotextures that behave as harmonic springs, the timescales become independent of the impact velocity, allowing the occurrence of pancake bouncing and rapid drop detachment over a wide range of impact velocities. © 2014 Macmillan Publishers Limited. All rights reserved.


Fung A.L.-C.,City University of Hong Kong | Raine A.,University of Pennsylvania
Journal of Personality Disorders | Year: 2012

There has been no prior research on peer victimization and child or adolescent schizotypal personality. This study tests the hypothesis that increased peer victimization is associated with increased schizotypal personality. Schizotypy was assessed using the SPQ-C (Schizotypal Personality Questionnaire-Child) in 3,508 male and female schoolchildren aged 8 to 16 years. All forms of peer victimization (physical, verbal, social manipulation, attack on property) were associated with schizotypal personality in both males and females across all age groups. Signifcant victimization more than doubled schizotypy scores. It is hypothesized that peer victimization may predispose to paranoid ideation, social anxiety, and lack of close friends, and consequently heightened schizotypal personality. © 2012 The Guilford Press.


Chen Z.,Hong Kong University of Science and Technology | Wang B.,City University of Hong Kong | Wang Z.,Hong Kong University of Science and Technology | Zhu G.,City University of Hong Kong | Sun J.,Hong Kong University of Science and Technology
Angewandte Chemie - International Edition | Year: 2013

Starting from three achiral compounds, the title reaction provides rapid access to a variety of molecules that contain indoline, tetrahydroquinoline, and tetrahydroisoquinoline moieties (see scheme). The process features the efficient formation of multiple new bonds and chiral centers, excellent stereoselectivity, oxetane desymmetrization, and easy product purification through filtration. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Liu G.,City University of Hong Kong | Hong L.J.,Hong Kong University of Science and Technology
Operations Research | Year: 2011

The Greeks are the derivatives (also known as sensitivities) of the option prices with respect to market parameters. They play an important role in financial risk management. Among many Monte Carlo methods of estimating the Greeks, the classical pathwise method requires only the pathwise information that is directly observable from simulation and is generally easier to implement than many other methods. However, the classical pathwise method is generally not applicable to the Greeks of options with discontinuous payoffs and the second-order Greeks. In this paper, we generalize the classical pathwise method to allow discontinuity in the payoffs. We show how to apply the new pathwise method to the first- and second-order Greeks and propose kernel estimators that require little analytical efforts and are very easy to implement. The numerical results show that our estimators work well for practical problems. © 2011 INFORMS.


Raine A.,University of Pennsylvania | Fung A.L.-C.,City University of Hong Kong | Lam B.Y.H.,City University of Hong Kong
Schizophrenia Bulletin | Year: 2011

While persuasive evidence has accumulated over the past 15 years documenting an association between schizophrenia and violence, there are 3 unresolved issues. First, does a downward extension of this relationship exist at the nonclinical level with respect to schizotypal personality and aggression in children? Second, is aggression more associated with impulsive reactive aggression or with more planned proactive aggression. Third and importantly, does peer victimization mediate the relationship between schizotypy and aggression? A further aim of this cross-sectional study was to examine the utility of a new child self-report measure of schizotypal personality. These issues were examined in a sample of 3804 schoolchildren assessed on schizotypy using the Schizotypal Personality Questionnaire-Child (SPQ-C), reactive-proactive aggression, and peer victimization. A confirmatory factor analysis confirmed the 3-factor structure (cognitive-perceptual, interpersonal, and disorganized) of the SPQ-C. Schizotypy was positively associated with total aggression and reactive aggression but not with proactive aggression. Peer victimization was found to significantly mediate the schizotypy-aggression relationship, accounting for 58.9% of the association. Results are broadly consistent with the hypothesis that schizotypal features elicit victimization from other children, which in turn predisposes to reactive retaliatory aggression. Findings are to the authors' knowledge the first to document any mediator of the schizotypy-aggression relationship and have potential treatment implications for violence reduction in schizophrenia-spectrum disorders. This study also provides initial evidence for the factorial and discriminant validity of a brief and simple measure of schizotypal personality in children as young as 8 years. © 2011 The Author.


Wang J.-W.,Beihang University | Wu H.-N.,Beihang University | Li H.-X.,City University of Hong Kong
IEEE Transactions on Fuzzy Systems | Year: 2011

This paper considers the problem of fuzzy control design for a class of nonlinear distributed parameter systems that is described by first-order hyperbolic partial differential equations (PDEs), where the control actuators are continuously distributed in space. The goal of this paper is to develop a fuzzy state-feedback control design methodology for these systems by employing a combination of PDE theory and concepts from TakagiSugeno (TS) fuzzy control. First, the TS fuzzy hyperbolic PDE model is proposed to accurately represent the nonlinear first-order hyperbolic PDE system. Subsequently, based on the TS fuzzy-PDE model, a Lyapunov technique is used to analyze the closed-loop exponential stability with a given decay rate. Then, a fuzzy state-feedback control design procedure is developed in terms of a set of spatial differential linear matrix inequalities (SDLMIs) from the resulting stability conditions. Furthermore, utilizing the finite-difference approximation method (with a backward difference for the spatial derivative), a recursive algorithm is presented to solve the SDLMIs via the existing LMI optimization techniques. Finally, the developed design methodology is successfully applied to the control of a nonisothermal plug-flow reactor. © 2011 IEEE.


Afzal S.,Monash University | Daoud W.A.,City University of Hong Kong | Langford S.J.,Monash University
ACS Applied Materials and Interfaces | Year: 2013

Thin films of meso-tetra(4-carboxyphenyl)porphyrinato copper(II) (CuTCPP) in conjunction with anatase TiO2 have been formed on cotton fabric. Their self-cleaning properties have been investigated by conducting photocatalytic degradation of methylene blue, coffee and wine stains under visible-light irradiation. CuTCPP/TiO2-coated cotton fabrics showed superior self-cleaning performance when compared to bare TiO2-coated cotton. Furthermore, CuTCPP/TiO2-coated fabrics showed significant photostability under visible-light as compared to free base TCPP/TiO 2-coated fabrics. The fabrics were characterized by FESEM, XRD and UV-vis spectroscopy. An insight into the mechanistic aspects of the CuTCPP/TiO2 photocatalysis is also discussed. Visible-light driven self-cleaning cotton based on copper(II) porphyrin/TiO2 catalyst exhibits significant potential in terms of stability and reproducibility for self-cleaning applications. © 2013 American Chemical Society.


Zhang Q.,City University of Hong Kong | Zhang K.,City University of Hong Kong | Xu D.,City University of Hong Kong | Yang G.,China Academy of Engineering Physics | And 4 more authors.
Progress in Materials Science | Year: 2014

Nanoscale metal oxide materials have been attracting much attention because of their unique size- and dimensionality-dependent physical and chemical properties as well as promising applications as key components in micro/nanoscale devices. Cupric oxide (CuO) nanostructures are of particular interest because of their interesting properties and promising applications in batteries, supercapacitors, solar cells, gas sensors, bio sensors, nanofluid, catalysis, photodetectors, energetic materials, field emissions, superhydrophobic surfaces, and removal of arsenic and organic pollutants from waste water. This article presents a comprehensive review of recent synthetic methods along with associated synthesis mechanisms, characterization, fundamental properties, and promising applications of CuO nanostructures. The review begins with a description of the most common synthetic strategies, characterization, and associated synthesis mechanisms of CuO nanostructures. Then, it introduces the fundamental properties of CuO nanostructures, and the potential of these nanostructures as building blocks for future micro/nanoscale devices is discussed. Recent developments in the applications of various CuO nanostructures are also reviewed. Finally, several perspectives in terms of future research on CuO nanostructures are highlighted. © 2013 Elsevier Ltd. All rights reserved.


Chiu L.,Nanjing Southeast University | Xue Q.,City University of Hong Kong
IEEE Transactions on Microwave Theory and Techniques | Year: 2010

This paper presents a new class of wideband 90 ° hybrid coupler with an arbitrary coupling level. The physical size of the proposed coupler is close to that of a conventional two-section branch-line coupler, but it has an additional phase inverter. The impedance bandwidth of the proposed coupler is close to that of a four-section branch-line coupler. The proposed coupler is a backward-wave coupler with a port assignment different from that of a conventional branch-line coupler. The design formulas of the proposed coupler are proved based on its even- and odd-mode half structures. We demonstrated three couplers at the center frequency of 2 GHz with different design parameters. © 2006 IEEE.


Zhou L.,Nantong University | Ho D.W.C.,City University of Hong Kong | Zhai G.,Shibaura Institute of Technology
Automatica | Year: 2013

This paper addresses the stability analysis problem for switched linear continuous-time singular systems. First, based on the equivalent dynamics decomposition form, a refined description for state jumps of the switched singular system is presented, which indicates that overall state jumps are resulted by two sequential state jumps. Second, sufficient conditions for exponential stability of the switched singular system with stable subsystems are presented. It is shown that the stability property of the system is completely determined by the switched reduced-order dynamic subsystem and the switching law induced state jumps. Then, a sufficient stability condition for the switched singular system with both stable and unstable subsystems is obtained. Finally, numerical examples are presented to illustrate the effectiveness of the proposed approach. © 2013 Elsevier Ltd. All rights reserved.


Wu H.-N.,Beihang University | Wang J.-W.,Beihang University | Li H.-X.,City University of Hong Kong | Li H.-X.,Central South University
Automatica | Year: 2012

This paper investigates the problem of designing a distributed H∞ fuzzy controller with constraint for a class of nonlinear spatially distributed processes modeled by first-order hyperbolic partial differential equations (PDEs). The purpose of this paper is to design a distributed fuzzy state feedback controller such that the closed-loop PDE system is exponentially stable with a prescribed H∞ performance of disturbance attenuation, while the control constraint is respected. Initially, a TakagiSugeno (TS) hyperbolic PDE model is proposed to accurately represent the nonlinear PDE system. Then, based on the TS fuzzy PDE model, a distributed H∞ fuzzy controller design with constraint is developed in terms of a set of coupled differential/algebraic linear matrix inequalities (D/ALMIs) in space. Furthermore, a suboptimal distributed H∞ fuzzy controller with constraint is proposed to minimize the level of attenuation. The finite difference method in space and the existing linear matrix inequality (LMI) optimization techniques are employed to approximately solve the suboptimal fuzzy control design problem. Finally, the proposed design method is applied to the distributed control of a nonlinear system described by two coupled first-order hyperbolic PDEs to illustrate its effectiveness. © 2012 Elsevier Ltd. All rights reserved.


Lu J.,Nanjing Southeast University | Lu J.,City University of Hong Kong | Ho D.W.C.,City University of Hong Kong
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2010

The globally exponential synchronization problem for general dynamical networks is considered in this paper. One quantity will be distilled from the coupling matrix to characterize the synchronizability of the corresponding dynamical networks. The calculation of such a quantity is very convenient even for large-scale networks. The network topology is assumed to be directed and weakly connected, which implies that the coupling configuration matrix can be asymmetric, weighted, or reducible. This assumption is more consistent with the realistic network in practice than the constraint of symmetry and irreducibility. By using the Lyapunov functional method and the Kronecker product techniques, some criteria are obtained to guarantee the globally exponential synchronization of general dynamical networks. In addition, numerical examples, including small-world and scale-free networks, are given to demonstrate the theoretical results. It will be shown that our criteria are available for large-scale dynamical networks. © 2006 IEEE.


Wang J.-W.,Beihang University | Wu H.-N.,Beihang University | Li H.-X.,City University of Hong Kong
Automatica | Year: 2012

This paper is concerned with the problem of robustly stochastically exponential stability and stabilization for a class of distributed parameter systems described by uncertain linear first-order hyperbolic partial differential equations (FOHPDEs) with Markov jumping parameters, for which the manipulated input is distributed in space. Based on an integral-type stochastic Lyapunov functional (ISLF), the sufficient condition of robustly stochastically exponential stability with a given decay rate is first derived in terms of spatial differential linear matrix inequalities (SDLMIs). Then, an SDLMI approach to the design of robust stabilizing controllers via state feedback is developed from the resulting stability condition. Furthermore, using the finite difference method and the standard linear matrix inequality (LMI) optimization techniques, recursive LMI algorithms for solving the SDLMIs in the analysis and synthesis are provided. Finally, a simulation example is given to demonstrate the effectiveness of the developed design method. © 2012 Elsevier Ltd. All rights reserved.


Fan J.,Nanjing Southeast University | Chu P.K.,City University of Hong Kong
Small | Year: 2010

The synthesis, properties, and biological applications of group IV nanoparticles including silicon, diamond, silicon carbide, and germanium are summarized. They have superior innate biocompatibility, robust fluorescence with high quantum yield and without photobleaching or even without blinking, as well as unique mechanical, chemical, and physical properties that make them very promising novel toolkits for bioimaging and drug delivery.


Wang Z.,Hong Kong University of Science and Technology | Ai F.,City University of Hong Kong | Zhao W.,Hong Kong University of Science and Technology | Zhu G.,City University of Hong Kong | And 2 more authors.
Journal of the American Chemical Society | Year: 2015

A new organocatalytic transfer hydrogenation strategy for the asymmetric synthesis of 1,1-diarylethanes is described. Under mild conditions, a range of 1,1-diarylethanes substituted with an o-hydroxyphenyl or indole unit could be obtained with excellent efficiency and enantioselectivity. We also extended the protocol to an unprecedented asymmetric hydroarylation of 1,1-diarylalkenes with indoles for the synthesis of a range of highly enantioenriched 1,1,1-triarylethanes bearing acyclic all-carbon quaternary stereocenters. These diaryl- and triarylethanes exhibit impressive cytotoxicity against a number of human cancer cell lines. Preliminary mechanistic studies combined with DFT calculations provided important insight into the reaction mechanism. © 2014 American Chemical Society.


Lu J.,Nanjing Southeast University | Lu J.,City University of Hong Kong | Ho D.W.C.,City University of Hong Kong | Cao J.,Nanjing Southeast University
Automatica | Year: 2010

This paper focuses on the problem of globally exponential synchronization of impulsive dynamical networks. Two types of impulses are considered: synchronizing impulses and desynchronizing impulses. In previous literature, all of the results are devoted to investigating these two kinds of impulses separately. Thus a natural question arises: Is there any unified synchronization criterion which is simultaneously effective for synchronizing impulses and desynchronizing impulses? In this paper, a unified synchronization criterion is derived for directed impulsive dynamical networks by proposing a concept named "average impulsive interval". The derived criterion is theoretically and numerically proved to be less conservative than existing results. Numerical examples including scale-free and small-world structures are given to show that our results are applicable to large-scale networks. © 2010 Elsevier Ltd. All rights reserved.


Brown E.S.,University of California at Los Angeles | Chan T.F.,Hong Kong University of Science and Technology | Bresson X.,City University of Hong Kong
International Journal of Computer Vision | Year: 2012

The active contours without edges model of Chan and Vese (IEEE Transactions on Image Processing 10(2):266-277, 2001) is a popular method for computing the segmentation of an image into two phases, based on the piecewise constant Mumford-Shah model. The minimization problem is non-convex even when the optimal region constants are known a priori. In (SIAM Journal of Applied Mathematics 66(5):1632-1648, 2006), Chan, Esedolu, and Nikolova provided a method to compute global minimizers by showing that solutions could be obtained from a convex relaxation. In this paper, we propose a convex relaxation approach to solve the case in which both the segmentation and the optimal constants are unknown for two phases and multiple phases. In other words, we propose a convex relaxation of the popular K-means algorithm. Our approach is based on the vector-valued relaxation technique developed by Goldstein et al. (UCLA CAM Report 09-77, 2009) and Brown et al. (UCLA CAM Report 10-43, 2010). The idea is to consider the optimal constants as functions subject to a constraint on their gradient. Although the proposed relaxation technique is not guaranteed to find exact global minimizers of the original problem, our experiments show that our method computes tight approximations of the optimal solutions. Particularly, we provide numerical examples in which our method finds better solutions than the method proposed by Chan et al. (SIAM Journal of Applied Mathematics 66(5):1632-1648, 2006), whose quality of solutions depends on the choice of the initial condition. © 2011 Springer Science+Business Media, LLC.


Leung K.W.,City University of Hong Kong | Lim E.H.,University Tunku Abdul Rahman | Fang X.S.,City University of Hong Kong
Proceedings of the IEEE | Year: 2012

This paper explains the basic characteristics of dielectric resonator antennas (DRAs), with emphasis on the effect of the form factor on their resonance (operating) frequencies. It is followed by discussions on their recent developments in higher order mode, circularly polarized, dual function, and transparent designs over the last few years. The idea of using glass DRAs as decoration antennas is proposed and demonstrated for the first time. © 2012 IEEE.


Li L.,City University of Hong Kong | Ho D.W.C.,City University of Hong Kong | Lu J.,Nanjing Southeast University
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2013

In this paper, we study the consensus problem of multi-agent networks subject to communication constrains. Undirected and weighted network is considered here. Two types of communication constrains are discussed in this paper: i) each agent can only exchange quantized data with its neighbors and ii) each agent can only obtain the delayed information from its neighbors. The main contribution of this paper is to provide a precise mathematical treatment for the continuous multi-agent network with quantization and time delay. The existence of a global solution to the resulting system is firstly proved in the Filippov sense and then we prove that the solution converges to a practical consensus set asymptotically. Here, practicalconsensus means that the final consensus values are bounded within an interval, but not a value. Further, an explicit relationship among time delay, quantization parameter and the practical consensus set are theoretically presented. Numerical examples are finally given to demonstrate the effectiveness of the obtained theoretical results. © 2013 IEEE.


Song Z.,City University of Hong Kong | Dai H.-H.,City University of Hong Kong | Sun Q.-P.,Hong Kong University of Science and Technology
International Journal of Plasticity | Year: 2013

In this paper, we study the stress-induced isothermal phase transitions of a shape memory alloy wire, with a focus on homogeneous or piecewise homogeneous deformations. Based on the constitutive model in the literature with the specific Helmholz free energy and rate of mechanical dissipation, the three-dimensional model is formulated. Identifying the characteristic axial strain as the small parameter, we arrive at the asymptotic one-dimensional equation which involves the stress, the axial strain and the phase state variable. By considering the evolution law of the phase state variable, the stress-strain relations corresponding to austenite, martensite and phase transition (phase mixture) regions are obtained. Although we take the dissipation into consideration, we find that each of the pure loading and unloading processes is equivalent to the Ericksen's bar problem with three branches in the stress-strain curve. As a result, we successfully deduce the analytical formulas for the nucleation stresses and propagation stresses. The analytical results reveal explicitly how such important quantities depend on the material constants and the temperature. We also demonstrate that they capture a number of features observed in experiments. As an important application, we show that these formulas can be used for calibration of the material constants (such as the difference of the thermal free energies of two phases) by comparing with the measured nominal stress-strain curves. Three examples are also provided. © 2012 Elsevier Ltd. All rights reserved.


Lazar M.A.,Monash University | Daoud W.A.,Monash University | Daoud W.A.,City University of Hong Kong
RSC Advances | Year: 2013

Nanocrystalline titanium dioxide (NTO) mediated photocatalysis is a powerful tool for the total mineralization of a wide range of organic compounds caused by the in situ generation of hydroxyl radicals upon ultraviolet/visible light irradiation. NTO is well known for its non-selective catalysis, especially in aqueous media. However, making NTO into a selective photocatalyst enables selective degradation of compounds as well as selective formation of valuable organic products. Both selective degradation and selective formation using NTO are based on the same principles of photocatalysis. Selectivity in degradation is achieved in the attraction, adsorption, and mineralization stages of photocatalysis whereas desorption of the oxygenated products, moderate crystallinity of NTO and doping are responsible for selective formation. Recent reports on NTO selective photocatalysis are reviewed in this article according to the chemistry used to achieve selectivity. This journal is © The Royal Society of Chemistry 2013.


News Article | April 18, 2016
Site: www.cemag.us

Scientists at Nanyang Technological University (NTU) have invented a new way to deliver cancer drugs deep into tumor cells. The NTU scientists create micro-sized gas bubbles coated with cancer drug particles and iron oxide nanoparticles, and then use magnets to direct these bubbles to gather around a specific tumor. Ultrasound is then used to vibrate the microbubbles, providing the energy to direct the drug particles into a targeted area. This innovative technique was developed by a multidisciplinary team of scientists, led by Assistant Professor Xu Chenjie from the School of Chemical and Biomedical Engineering and Associate Professor Claus-Dieter Ohl from the School of Physical and Mathematical Sciences. NTU’s microbubbles were successfully tested in mice and the study has been published by the Nature Publishing Group in Asia Materials, the top journal for materials sciences in the Asia-Pacific region. Xu, who is also a researcher at the NTU-Northwestern Institute for Nanomedicine, says their new method may solve some of the most pressing problems faced in chemotherapy used to treat cancer. The main issue is that current chemotherapy drugs are largely non-targeted. The drug particles flow in the bloodstream, damaging both healthy and cancerous cells. Typically, these drugs are flushed away quickly in organs such as the lungs and liver, limiting their effectiveness. The remaining drugs are also unable to penetrate deep into the core of the tumor, leaving some cancer cells alive, which could lead to a resurgence in tumor growth. “The first unique characteristic of our microbubbles is that they are magnetic. After injecting them into the bloodstream, we are able to gather them around the tumor using magnets and ensure that they don’t kill the healthy cells,” explains Xu, who has been working on cancer diagnosis and drug delivery systems since 2004. “More importantly, our invention is the first of its kind that allows drug particles to be directed deep into a tumor in a few milliseconds. They can penetrate a depth of 50 cell layers or more — which is about 200 micrometers, twice the width of a human hair. This helps to ensure that the drugs can reach the cancer cells on the surface and also inside the core of the tumor.” Clinical Associate Professor Chia Sing Joo, a Senior Consultant at the Tan Tock Seng Hospital’s Endoscopy Centre and the Urology & Continence Clinic, was one of the consultants for this study. A trained robotic surgeon experienced in the treatment of prostate, bladder and kidney cancer, Chia says, “For anticancer drugs to achieve their best effectiveness, they need to penetrate into the tumor efficiently in order to reach the cystoplasm of all the cancer cells that are being targeted without affecting the normal cells. “Currently, these can be achieved by means of a direct injection into the tumor or by administering a large dosage of anticancer drugs, which can be painful, expensive, impractical and might have various side effects.” The specialist in Uro-oncology added that if NTU’s technology proves to be viable, clinicians might be able to localize and concentrate the anticancer drugs around a tumor, and introduce the drugs deep into tumor tissues in just a few seconds using a clinical ultrasound system. “If successful, I envisage it can be a good alternative treatment in the future, one which is low cost and yet effective for the treatment of cancers involving solid tumors, as it might minimize the side effects of drugs.” The motivation for this research project is to find alternative solutions for drug delivery systems that are non-invasive and safe. Ultrasound uses soundwaves with frequencies higher than those heard by the human ear. It is commonly used for medical imaging such as to get diagnostic images. Magnets, which can draw and attract the microbubbles, are already in use in diagnostic machines such the Magnetic Resonance Imaging (MRI). “We are looking at developing novel drug carriers — essentially better ways of delivering drugs with minimum side effects,” explains Ohl, an expert in biophysics who had published previous studies involving drug delivery systems and bubble dynamics. “Most prototype drug delivery systems on the market face three main challenges before they can be commercially successful: they have to be non-invasive, patient-friendly and yet cost-effective. “Using the theory of microbubbles and how their surface vibrates under ultrasound, we were able to come up with our solution that addresses these three challenges.” This study, which took two and a half years, involved a 12-man international interdisciplinary team consisting of NTU scientists as well as scientists from City University of Hong Kong and Technion-Israel Institute of Technology (Technion). Two NTU undergraduates doing their Final Year Project and one student in Summer Research Internship Program (NTU) were also part of the team. Moving forward, the team will be adopting this new drug delivery system in studies on lung and liver cancer using animal models, and eventually clinical studies. They estimate that it will take another eight to 10 years before it reaches human clinical trials. Source: Nanyang Technological University


News Article | April 19, 2016
Site: www.biosciencetechnology.com

Scientists at Nanyang Technological University (NTU Singapore) have invented a new way to deliver cancer drugs deep into tumor cells. The NTU scientists create micro-sized gas bubbles coated with cancer drug particles and iron oxide nanoparticles, and then use magnets to direct these bubbles to gather around a specific tumor. Ultrasound is then used to vibrate the microbubbles, providing the energy to direct the drug particles into a targeted area. This innovative technique was developed by a multidisciplinary team of scientists, led by Asst Prof Xu Chenjie from the School of Chemical and Biomedical Engineering and Assoc Prof Claus-Dieter Ohl from the School of Physical and Mathematical Sciences. NTU's microbubbles were successfully tested in mice and the study has been published by the Nature Publishing Group in Asia Materials, the top journal for materials sciences in the Asia-Pacific region. Asst Prof Xu, who is also a researcher at the NTU-Northwestern Institute for Nanomedicine, said their new method may solve some of the most pressing problems faced in chemotherapy used to treat cancer. The main issue is that current chemotherapy drugs are largely non-targeted. The drug particles flow in the bloodstream, damaging both healthy and cancerous cells. Typically, these drugs are flushed away quickly in organs such as the lungs and liver, limiting their effectiveness. The remaining drugs are also unable to penetrate deep into the core of the tumor, leaving some cancer cells alive, which could lead to a resurgence in tumor growth. "The first unique characteristic of our microbubbles is that they are magnetic. After injecting them into the bloodstream, we are able to gather them around the tumour using magnets and ensure that they don't kill the healthy cells," explains Asst Prof Xu, who has been working on cancer diagnosis and drug delivery systems since 2004. "More importantly, our invention is the first of its kind that allows drug particles to be directed deep into a tumor in a few milliseconds. They can penetrate a depth of 50 cell layers or more - which is about 200 micrometres, twice the width of a human hair. This helps to ensure that the drugs can reach the cancer cells on the surface and also inside the core of the tumour." Clinical Associate Professor Chia Sing Joo, a Senior Consultant at the Tan Tock Seng Hospital's Endoscopy Centre and the Urology & Continence Clinic, was one of the consultants for this study. A trained robotic surgeon experienced in the treatment of prostate, bladder and kidney cancer, Assoc Prof Chia said, "For anticancer drugs to achieve their best effectiveness, they need to penetrate into the tumor efficiently in order to reach the cystoplasm of all the cancer cells that are being targeted without affecting the normal cells. "Currently, these can be achieved by means of a direct injection into the tumor or by administering a large dosage of anticancer drugs, which can be painful, expensive, impractical and might have various side effects." The specialist in Uro-oncology added that if NTU's technology proves to be viable, clinicians might be able to localize and concentrate the anticancer drugs around a tumor, and introduce the drugs deep into tumor tissues in just a few seconds using a clinical ultrasound system. "If successful, I envisage it can be a good alternative treatment in the future, one which is low cost and yet effective for the treatment of cancers involving solid tumors, as it might minimize the side effects of drugs." The motivation for this research project is to find alternative solutions for drug delivery systems that are non-invasive and safe. Ultrasound uses soundwaves with frequencies higher than those heard by the human ear. It is commonly used for medical imaging such as to get diagnostic images. Magnets, which can draw and attract the microbubbles, are already in use in diagnostic machines such the Magnetic Resonance Imaging (MRI). "We are looking at developing novel drug carriers - essentially better ways of delivering drugs with minimum side effects," explained Prof Ohl, an expert in biophysics who had published previous studies involving drug delivery systems and bubble dynamics. "Most prototype drug delivery systems on the market face three main challenges before they can be commercially successful: they have to be non-invasive, patient-friendly and yet cost-effective. "Using the theory of microbubbles and how their surface vibrates under ultrasound, we were able to come up with our solution that addresses these three challenges." This study, which took two and a half years, involved a 12-man international interdisciplinary team consisting of NTU scientists as well as scientists from City University of Hong Kong and Tel Aviv University in Israel. Two NTU undergraduates doing their Final Year Project and one student in Summer Research Internship Programme (NTU) were also part of the team. Moving forward, the team will be adopting this new drug delivery system in studies on lung and liver cancer using animal models, and eventually clinical studies. They estimate that it will take another eight to ten years before it reaches human clinical trials.


What you have just observed is an example of the Leidenfrost effect, named for Johann Gottlob Leidenfrost, an 18th-century German physician and scientist. The phenomenon occurs when a liquid, upon approaching an object that is much hotter than the liquid's boiling point, produces a vapor which insulates the liquid from the surface of the object. This repulsive force, say scientists, has two consequences. It prevents droplets of the liquid from making physical contact with the surface, causing them instead to hover over the surface. And it causes the droplets to boil off more slowly than they would on a surface with a lower temperature that is still above the liquid's boiling point. Researchers in Hong Kong and at Lehigh University recently demonstrated that it is possible to exploit the Leidenfrost effect to control the direction and destination of liquid droplets on a surface and thus to cool it more efficiently. They achieved this by lithographically patterning a surface with microscale features that convert excess surface tension into a kinetic energy that propels droplets to "hot spots" on the surface. The discovery, say Zuankai Wang of the City University of Hong Kong and Manoj Chaudhury of Lehigh, has the potential to improve technologies that involve microfluidics, heat transfer, heat exchange, micro-heat exchange, water management and thermal management. "Many applications, such as power plant reactors, require the management and control of the movement of water droplets at very high temperatures," says Wang, an associate professor of mechanical and biomedical engineering at City University. "Typically, the cooling of extremely hot surfaces has been accomplished with spray cooling. You spray a lot of water droplets onto a surface and as they boil, they take away the heat. "At a high temperature, however, this doesn't work because the Leidenfrost effect prevents the droplets from making sufficient contact with the surface to cool it. Thus it takes too long to cool a surface by boiling off water." Wang, Chaudhury and their colleagues reported their results today (Feb. 1) in Nature Physics, a journal of Nature magazine, in an article titled "Directional transport of high-temperature Janus droplets mediated by structural topography." The article's lead author is Jing Li, a Ph.D. candidate in the department of mechanical and biomedical engineering at City University. Scientists in the last 20 years have learned to control the movement of liquid droplets on a solid surface by breaking the wetting symmetry that results from the impact of a droplet on a surface. They have accomplished this by harnessing gradients of surface energy and by utilizing light, temperature, electric force and mechanical vibration. Chaudhury, the Franklin J. Howes Jr. Distinguished Professor of Chemical and Biomolecular Engineering at Lehigh, for example, has published articles with his students in Science and Langmuir describing their successful efforts to direct the movement of water droplets on surfaces. But scientists have not yet achieved this control on surfaces heated to Leidenfrost temperatures and above, or on surfaces with extremely hot local spots. Two years ago, Wang came up with the idea of creating topographical contrasts on a silicon wafer by etching the wafer surface with micropillars and arranging the pillars in zones that vary according to the density of the pillars and the contact angle of the pillars with the surface. "The Leidenfrost Effect has been extensively studied for drag reduction, while the presence of the undesired vapor layer also prevents efficient heat transfer," says Wang. "Thus, we came up with the idea of creating an asymmetric surface to control droplet motion at high temperatures." In their Nature Physics article, the researchers reported that their experiments, which were conducted in Hong Kong, showed that "judicious control of the structural topography and operating temperature range of the solid substrate" served to break the wetting symmetry of droplets. The group also reported a "new physical phenomenon in which two concurrent wetting states—Leidenfrost and contact-boiling—can be designed in a single droplet [heated] above its boiling point." The droplet, the researchers wrote in Nature Physics, "exhibits a contrasting (or Janus) thermal state with a lower contact angle in the boiling region, but a higher angle in the Leidenfrost region." This contrast generates "a gradient of curvature, and thus a gradient of Laplace pressure." "As the [droplet's] viscous dissipation is minimal," the researchers wrote, "the resulting excess surface energy of the droplet is converted to kinetic energy, naturally causing it to dislodge from the surface and take flight into the air. The droplet eventually gets deposited in the contact-boiling region." The researchers liken this phenomenon to the action of a slingshot and note that something similar occurs with a filamentous mushroom called Basidiomycota. Each spore of the fungus is part hydrophobic, with a shape like a thin film, and part hydrophilic, with a shape like a sphere. When the two regions make contact, they coalesce, and the tension between hydrophobic and hydrophilic regions creates a force that carries the entire spore into the air. "This is a chemical effect that nature produces," says Shuhuai Yao, an associate professor of mechanical and aerospace engineering at the Hong Kong University of Science and Technology. "At the point of coalescence, there is an asymmetry but the desire for symmetry causes a transitory state and generates a force that propels the spore." The contrasting topographies of the micropillars on Wang's silicon wafer create a similar phenomenon. At a high temperature, as one part of the droplet is boiling and one is non-boiling, an asymmetry is created. But as with the Basidiomycota, the natural tendency toward symmetry creates the slingshot effect that propels the droplet. There is, however, a critical difference between the two phenomena, the researchers say. While nature makes no effort to guide a spore but instead merely to release it, a droplet on a bio-inspired surface can be targeted to a specific place and made to land on a hot spot and boil off. More information: Jing Li et al. Directional transport of high-temperature Janus droplets mediated by structural topography, Nature Physics (2016). DOI: 10.1038/NPHYS3643


Lee S.K.,Korea Institute of Energy Research | Mogi G.,Tokyo University of Technology | Hui K.S.,City University of Hong Kong
Renewable and Sustainable Energy Reviews | Year: 2013

The Low Carbon, Green Growth was declared as Korean national agenda in 2008. Korea has been enhancing the green growth for the sustainable economic development and fostering energy. To improve Korean national energy security and promote the Low Carbon, Green Growth, we established a long term strategic energy technology roadmap. In this paper, five criteria, such as economical impact, commercial potential, inner capacity, technical spin-off, and development cost, were used to assess the strategic energy technologies against high oil prices. We developed the integrated two-stage multi-criteria decision making (MCDM) approach which was used to evaluate the relative weights of criteria and measures the relative efficiency of energy technologies against high oil prices. On the first stage, the fuzzy analytic hierarchy process, reflecting the vagueness of human thought with interval values instead of crisp numbers, allocated the relative weights of criteria effectively instead of the AHP approach. On the second stage, the data envelopment analysis approach measured the relative efficiency of energy technologies against high oil prices with economic viewpoints. The relative efficiency score of energy technologies against high oil prices can be the fundamental decision making data which help decision markers to effectively allocate the limited R&D resources. © 2013 Elsevier Ltd.


Leung S.C.H.,City University of Hong Kong | Zhang D.,Xiamen University
Expert Systems with Applications | Year: 2011

In this paper, an orthogonal strip packing problem with rotation of items and without the guillotine packing constraint is considered. A fast heuristic algorithm for the large-scale problems is presented. This heuristic algorithm is mainly based on heuristic strategies inspired by the wall-building rule of bricklayers in daily life. The heuristics is simple and the setting of parameter is not required. Each layer is initialized with either a single item or a bunch of equal-width items. The remaining part of the layer is filled by a bottom-left strategy preferring items which eliminate corners of the current layout. Items can also be placed across several layers. Then, the evaluation rule, which is based on the fitness value for different rectangles to a given position, is able to select an appropriate rectangle to pack. The computational results on a broad range of benchmark problems show that the fast layer-based heuristic algorithm can compete with other latest heuristics and meta-heuristics from the literature in terms of both solution quality and computational time. The fast layer-based heuristic algorithm can compete with the latest published algorithms. In particular, it performs better for large-scale problem instances. © 2010 Elsevier Ltd. All rights reserved.


Cai D.W.H.,California Institute of Technology | Quek T.Q.S.,Institute for Infocomm Research | Tan C.W.,City University of Hong Kong
IEEE Transactions on Signal Processing | Year: 2011

This paper studies the max-min weighted signal-to-interference-plus-noise ratio (SINR) problem in the multiple- input-multiple-output (MIMO) downlink, where multiple users are weighted according to priority and are subject to a weighted-sum-power constraint. First, we study the multiple-input-single-output (MISO) and single-input-multiple- output (SIMO) problems using nonlinear Perron-Frobenius theory. As a by-product, we solve the open problem of convergence for a previously proposed MISO algorithm by Wiesel, Eldar, and Shamai in 2006. Furthermore, we unify our analysis with respect to the previous alternate optimization algorithm proposed by Tan, Chiang, and Srikant in 2009, by showing that our MISO result can, in fact, be derived from their algorithm. Next, we combine our MISO and SIMO results into an algorithm for the MIMO problem. We show that our proposed algorithm is optimal when the channels are rank-one, or when the network is operating in the low signal-to-noise ratio (SNR) region. Finally, we prove the parametric continuity of the MIMO problem in the power constraint, and we use this insight to propose a heuristic initialization strategy for improving the performance of our (generally) suboptimal MIMO algorithm. The proposed initialization strategy exhibits improved performance over random initialization. © 2011 IEEE.


Du K.,Xiamen University | Du K.,City University of Hong Kong
Journal of Computational Physics | Year: 2011

We consider electromagnetic scattering from two-dimensional (2D) overfilled cavities embedded in an infinite ground plane. The unbounded computational domain is truncated to a bounded one by using a transparent boundary condition (TBC) proposed on a semi-ellipse. For overfilled rectangular cavities with homogeneous media, another TBC is introduced on the cavity apertures, which produces a smaller computational domain. The existence and uniqueness of the solutions of the variational formulations for the transverse magnetic and transverse electric polarizations are established. In the exterior domain, the 2D scattering problem is solved in the elliptic coordinate system using the Mathieu functions. In the interior domain, the problem is solved by a finite element method. Numerical experiments show the efficiency and accuracy of the new boundary conditions. © 2011 Elsevier Inc.


Kuo W.,City University of Hong Kong | Zhu X.,University of Tennessee at Knoxville
IEEE Transactions on Reliability | Year: 2012

Many importance measures have been proposed with respect to the diverse considerations of system performance, reflecting different probabilistic interpretations and potential applications. This paper studies importance measures in reliability, including their definitions, probabilistic interpretations, properties, computations, and comparability. It categorizes importance measures into the structure, reliability, and lifetime types based on the knowledge for determining them. It covers importance measures of individual components, and ones of pairs and groups of components. It also investigates importance measures in consecutive-k-out-of-n systems. © 2012 IEEE.


Kuo W.,City University of Hong Kong | Zhu X.,University of Tennessee at Knoxville
IEEE Transactions on Reliability | Year: 2012

To identify the critical components or sets of components in a system, various importance measures have been proposed with different probabilistic perspectives and applications. Many of these importance measures are actually related to each other in some ways. This paper summarizes the importance measures in reliability, and presents relations and comparisons among them, focusing on their interrelations to the B-importance, the dominant relations among them, the dual relations, their performances in typical systems, and their computations. The early versions of the importance measures are for binary coherent systems, while the recent research is not limited to this type of system. This paper investigates the extensions of importance measures in noncoherent systems, multistate systems, continuum systems, and repairable systems. © 2012 IEEE.


Zhou G.,Tsinghua University | Chung W.,City University of Hong Kong | Zhang X.,Tsinghua University
Energy | Year: 2013

Undesirable output-oriented Data Envelopment Analysis (DEA) models with different return of scales are used to study the CO2 (Carbon dioxide) emissions performance of the transport sector throughout China's 30 administrative regions. Empirical results show that the number of efficient regions has decreased since 2004, hitting the lowest record in 2006, and improving slightly afterwards. The overall average performance rating reached its peak in 2004 and continuously decreased until it hit its lowest record in 2006. Although it slightly increased in 2007, performance rating has decreased since 2008. This pattern is consistent with the policy guidance of the transport sector in the 11th Five-Year Plan (2006-2010). In general, Eastern China performed better than Central and Western by adjusting undesirable output (CO2). However, Central performed better than Eastern and Western by adjusting both CO2 emissions and desirable outputs. It may be because that transport infrastructure facilities are heavily concentrated in Eastern and spatial clusters. The clusters are like stair steps decreasing from the higher Eastern to Central then to the lower Western. This indicates that the development of transport infrastructure go hand in hand in China. Hence, Eastern may not have too much improvement room by adjusting desirable outputs. © 2012 Elsevier Ltd.


Yao M.Z.,City University of Hong Kong | Zhong Z.-J.,Sun Yat Sen University
Computers in Human Behavior | Year: 2014

This study aims to examine the causal priority in the observed empirical relationships between Internet addiction and other psychological problems. A cross-lagged panel survey of 361 college students in Hong Kong was conducted. Results show that excessive and unhealthy Internet use would increase feelings of loneliness over time. Although depression had a moderate and positive bivariate relationship with Internet addiction at each time point, such a relationship was not significant in the cross-lagged analyses. This study also found that online social contacts with friends and family were not an effective alternative for offline social interactions in reducing feelings of loneliness. Furthermore, while an increase in face-to-face contacts could help to reduce symptoms of Internet addiction, this effect may be neutralized by the increase in online social contacts as a result of excessive Internet use. Taken as a whole, findings from the study show a worrisome vicious cycle between loneliness and Internet addiction. © 2013 Elsevier Ltd. All rights reserved.


Bao S.P.,City University of Hong Kong | Liang G.D.,Sun Yat Sen University | Tjong S.C.,City University of Hong Kong
Carbon | Year: 2011

Poly(vinylidene fluoride) (PVDF)/carbon nanofiber (CNF) composites with filler content ranging from 0.047 to 4.7 vol.% were prepared with non-solvent precipitation followed by melt compression. The morphology and electrical conductivity of the composites before and after mechanical stretching were examined. The results showed that CNFs were dispersed homogeneously in the PVDF matrix and a low electrical percolation threshold of 0.90 vol.% CNFs was obtained. Mechanical stretching led to a sharp decrease in the electrical conductivity of a composite containing 0.94 vol.% CNF. This was caused by the destruction of a conducting network structure when the fillers aligned along the stretching direction. This did not happen when the filler content was increased to 1.88 vol.%. The percolating composites displayed a positive temperature coefficient (PTC) effect with the effect being larger in stretched composites. This can be attributed to the presence of PVDF β-phase in stretched composites as revealed by X-ray diffraction and Fourier transform infrared spectroscopy. © 2010 Elsevier Ltd. All rights reserved.


Huang Y.,University of California at San Diego | Tan C.W.,Qualcomm | Rao B.D.,City University of Hong Kong
IEEE Transactions on Wireless Communications | Year: 2013

This paper studies joint beamforming and power control in a coordinated multicell downlink system that serves multiple users per cell to maximize the minimum weighted signal-to-interference-plus-noise ratio. The optimal solution and distributed algorithm with geometrically fast convergence rate are derived by employing the nonlinear Perron-Frobenius theory and the multicell network duality. The iterative algorithm, though operating in a distributed manner, still requires instantaneous power update within the coordinated cluster through the backhaul. The backhaul information exchange and message passing may become prohibitive with increasing number of transmit antennas and increasing number of users. In order to derive asymptotically optimal solution, random matrix theory is leveraged to design a distributed algorithm that only requires statistical information. The advantage of our approach is that there is no instantaneous power update through backhaul. Moreover, by using nonlinear Perron-Frobenius theory and random matrix theory, an effective primal network and an effective dual network are proposed to characterize and interpret the asymptotic solution. © 2002-2012 IEEE.


Ye G.,City University of Hong Kong | Ye G.,Guangdong Ocean University
Nonlinear Dynamics | Year: 2014

A block-based image encryption algorithm using wave function and chaotic system is presented. A random sequence generated by the chaotic system is used to find the source point in the wave and produces a diffusion matrix for modular operation. In the encryption process, the keystream is dependent on both the plain-image and the secret key. It changes in each encryption round. Theoretical analyses and simulation results show the high security of the proposed method, including the large key space, fairly uniform histogram, zero correlation between neighbouring pixels, resistance to differential attacks, and high efficiency. Therefore, our algorithm is a practical scheme for digital image encryption. © 2013 Springer Science+Business Media Dordrecht.


Ye G.,Guangdong Ocean University | Ye G.,City University of Hong Kong | Wong K.-W.,Guangdong Ocean University
Nonlinear Dynamics | Year: 2012

An efficient image encryption algorithm using the generalized Arnold map is proposed. The algorithm is composed of two stages, i.e., permutation and diffusion. First, a total circular function, rather than the traditional periodic position permutation, is used in the permutation stage. It can substantially reduce the correlation between adjacent pixels. Then, in the stage of diffusion, double diffusion functions, i.e., positive and opposite module, are utilized with a novel generation of the keystream. As the keystream depends on the processed image, the proposed method can resist known- and chosen-plaintext attacks. Experimental results and theoretical analysis indicate the effectiveness of our method. An extension of the proposed algorithm to other chaotic systems is also discussed. © Springer Science+Business Media B.V. 2012.


Zheng S.Y.,Sun Yat Sen University | Chan W.S.,City University of Hong Kong
IEEE Transactions on Industrial Electronics | Year: 2014

For the first time, a differential phase shifter with harmonic suppression is proposed. Not only does the proposed structure provide a constant differential phase shift over a wide bandwidth, but it also has good harmonic rejection. Compared to the existing coupled-line phase shifters, the proposed stub-loaded transmission line configurations show good performance, with simplicity in both design and fabrication. Design formulas for the structure are derived using an analytical technique. Optimal design parameters for typical differential phase shifts which are independent of substrate used and operating frequency are provided to allow for a quick design procedure. To illustrate the principles, a broadband 45$\circ phase shifter with harmonic suppression is designed, fabricated, and measured. It achieved excellent performance with small insertion loss, small phase deviation within the desired bandwidth, and good out-of-band rejection. © 1982-2012 IEEE.


He Y.,Xiamen University | Wang S.,CAS Academy of Mathematics and Systems Science | Lai K.K.,City University of Hong Kong
Energy Economics | Year: 2010

This paper empirically investigates the cointegrating relationship between crude oil prices and global economic activity. The Kilian economic index is used as an indicator of global economic activity. Based on a supply-demand framework and the cointegration theory, we find that real futures prices of crude oil are cointegrated with the Kilian economic index and a trade weighted US dollar index, and crude oil prices are influenced significantly by fluctuations in the Kilian economic index through both long-run equilibrium conditions and short-run impacts. We also develop an empirically stable, data-coherent and single-equation error-correction model (ECM) which has sensible economic properties. Empirical results based on the ECM show that the adjustment implied by a permanent change in the Kilian economic index is a relatively drawn-out process. © 2009 Elsevier B.V.


Xu S.-X.,Sun Yat Sen University | Dai D.,City University of Hong Kong | Zhao Y.-Q.,Sun Yat Sen University
Communications in Mathematical Physics | Year: 2014

In this paper, we study the singularly perturbed Laguerre unitary ensemble(formula presentet.)>with(formula presentet.) and t >  0. Due to the effect of t/x for varying t, the eigenvalue correlation kernel has a new limit instead of the usual Bessel kernel at the hard edge 0. This limiting kernel involves ψ-functions associated with a special solution to a new third-order nonlinear differential equation, which is then shown to be equivalent to a particular Painlevé III equation. The transition of this limiting kernel to the Bessel and Airy kernels is also studied when the parameter t changes in a finite interval (0, d]. Our approach is based on Deift–Zhou nonlinear steepest descent method for Riemann–Hilbert problems. © 2014, Springer-Verlag Berlin Heidelberg.


He H.-D.,Shanghai Maritime University | Lu W.-Z.,City University of Hong Kong
Building and Environment | Year: 2012

An investigation of historical database of environmental pollutants (RSP, NO, NO2, NOx, Ozone, SO2, NO/NO2 and NO2/NOx) and meteorological parameters at selected air monitoring stations in Hong Kong, is reported in this paper. Multiple regression and principal component analysis are employed to predict ozone levels from data of pollutants and meteorological variables. The results indicated that the performance of logarithmic transformation of ozone values is better than original data; based on this transformation, the variable NO2/NOx explained 75% of variation of the ozone level at Sha Tin and 83% at Kwun Tong. The ozone level increased exponentially with increase of NO2/NOx but the critical point was judged to be 0.5. In addition, due to close relationships between these studied variables, influence of meteorological variables on ozone concentration was confirmed being incorporated in pollutant variables and could not be segregated in the regression model. The results showed that meteorological variables account for 31% and 34% of ozone variation at Sha Tin and Kwun Tong, respectively. The cloud amount was observed as the most important factor at both stations. Data of Sha Tin and Kwun Tong were compared to ascertain the effect of geographical location on ozone variation. It seems that ozone level depended more heavily on variations in pollutants and meteorological variables. It can be deduced that Kwun Tong located near Victoria harbor and surrounded by hilly terrain of Kowloon and Hong Kong Island is in a disadvantageous position in terms of ozone dispersion, which results in relatively high ozone concentration. © 2011 Elsevier Ltd.


Hong-di H.,Shanghai Maritime University | Wei-Zhen L.,City University of Hong Kong
Stochastic Environmental Research and Risk Assessment | Year: 2012

A detailed study on particulate matter from vehicle emission was carried out at roadsides in Hong Kong downtown area. The study aims to explore the variations of particulate matter at roadsides in morning and afternoon. Data of concentrations of different size groups of particulate matter were collected and analyzed. It was found that the particulate levels generally vary periodically with traffic signal changes. During the green traffic light period, concentrations of the particulate matter increase to peak point and then diffuse to a relatively stable level in the red traffic light period. Such stable level is regarded as background level, to which pedestrians are exposed when they walk-by and cross the zebra zones. To analyze and further explore the collected data, a statistical distribution model, i. e., goodness-of-fit test, was employed. It was noticed that the lognormal distribution best fits the particulate matter data in both morning and afternoon. In addition, the non-parametric test was also used to assess the differences between morning and afternoon data. The results show that both data sets statistically differ from each other at 5% significance level. It can be deduced that the change of traffic volume, humidity and wind speed between morning and afternoon may cause this difference. © 2011 Springer-Verlag.


Leung S.C.H.,City University of Hong Kong | Lin Y.,Xiamen University | Zhang D.,Xiamen University
Computers and Operations Research | Year: 2012

This paper presents an extended local search algorithm (ELS) for the irregular strip packing problem. It adopts two neighborhoods, swapping two given polygons in a placement and placing one polygon into a new position. The local search algorithm is used to minimize the overlap on the basis of the neighborhoods mentioned above and the unconstrained nonlinear programming model is adopted to further minimize the overlap during the search process. Moreover, the tabu search algorithm is used to avoid local minima, and a compact algorithm is presented to improve the result. The results of standard test instances indicate that when compared with other existing algorithms, the presented algorithm does not only show some signs of competitive power but also updates several best known results. © 2011 Elsevier Ltd. All rights reserved.


News Article | November 13, 2015
Site: www.rdmag.com

Researchers from RMIT Univ. in Melbourne have helped crack the code to ultra-secure telecommunications of the future in an international research project that could also expedite the advent of quantum computing. A team co-led by RMIT MicroNano Research Facility Director Professor David Moss has added a new twist to create photon pairs that fit on a tiny computer chip. The breakthrough, published in Nature Communications, heralds the next-generation of integrated quantum optical technology, being compatible with current technology and secure communications. The team pioneered a new approach based on a micro-ring resonator - a tiny optical cavity - in which energy conservation constraints can be exploited to suppress classical effects while amplifying quantum processes. They used laser beams at different wavelengths and then had to overcome the risk of the two pump beams being able to destroy the photons' fragile quantum state. "One of the properties of light exploited within quantum optics is 'photon polarization', which is essentially the direction in which the electric field associated with the photon oscillates,'' Moss said. "Processes used to generate single photons or photon pairs on a chip allow the generation of photons with the same polarization as the laser beam, forcing us to find a way to directly mix, or cross-polarize, the photons via a nonlinear optical process on a chip for the first time.'' Moss worked with Professor Roberto Morandotti at the INRS-EMT in Canada and researchers from the University of Sussex and Herriot Watt University, City University of Hong Kong, and the Xi'an Institute in Chin, on the research. "While a similar suppression of classical effects has been observed in gas vapours and complex micro-structured fibres, this is the first time it has been reported on a chip, opening a route for building scalable integrated devices that exploit the mixing of polarization on a single photon level,'' he said. "It also has the advantage that the fabrication process of the chip is compatible with that currently used for electronic chips which not only allows the exploitation of the huge global infrastructure of CMOS foundries, but will ultimately offer the potential to integrate electronic devices on the same chip. "Both of these are fundamental requirements for the ultimate widespread adoption of optical quantum technologies.''


News Article | April 29, 2016
Site: phys.org

The new material is designed to help healthy cells "win the race" to a medical implant, beating off competition from bacterial cells and thus reducing the likelihood of the implant being rejected by the body. The failure rate of certain medical implants is high – around 40% for hip implants – due to the formation of thin films of microorganisms on an implant when it is first inserted into the body. This prevents healthy cells from attaching and results in the body eventually rejecting the implant, potentially leading to serious medical complications for patients. Reporting their findings in the IOP Publishing journal Biomedical Materials, a team of researchers from the Agency for Science, Technology and Research in Singapore, Nanyang Technological University and City University of Hong Kong produced a material that not only repelled bacteria but also attracted healthy cells. The base of the material was made of multiple layers of water-soluble macromolecules called polyelectrolytes, onto which specific bonding molecules, called ligands, were attached. The team tested various concentrations of different ligands. They found that a naturally occurring protein building block called RGD was effective at inhibiting the attachment of bacterial cells and attracting healthy cells when it was attached to multilayers of certain polyelectrolytes. It surpassed collagen in this regard. "The method we developed helped the host cells win the so-called 'race-for-surface' battle, forming a confluent layer on the implant surface which protects it from possible bacterial adhesion and colonisation," explains the lead author, Vincent Chan of Nanyang Technological University. Medical implants currently incorporate antibacterial silver coatings. "However, the total amount of silver used must be very carefully controlled because high concentrations could kill mammalian cells and become toxic to the human body," says Professor Chan. By comparison, "the bio-selective coatings we've created do not have this problem, as the materials used are non-toxic and the environmentally sustainable preparation process uses water as a solvent." "At the moment this is just a proof-of-concept study, so there is still a long way to go before the coating can be used on implants in a clinical setting," he adds. "In future studies we hope to improve the long-term stability of the coating." Explore further: New optimized coatings for implants reduce risk of infection


News Article | November 17, 2015
Site: www.scientificcomputing.com

Researchers have added a new twist to create photon pairs that fit on a tiny computer chip. The breakthrough heralds the next-generation of integrated quantum optical technology, being compatible with current technology and secure communications. The research team pioneered a new approach based on a micro-ring resonator — a tiny optical cavity — in which energy conservation constraints can be exploited to suppress classical effects while amplifying quantum processes. The team, co-led by RMIT MicroNano Research Facility Director Professor David Moss, used laser beams at different wavelengths and then had to overcome the risk of the two pump beams being able to destroy the photons’ fragile quantum state. “One of the properties of light exploited within quantum optics is ‘photon polarization,’ which is essentially the direction in which the electric field associated with the photon oscillates,’’ Moss said. “Processes used to generate single photons or photon pairs on a chip allow the generation of photons with the same polarization as the laser beam, forcing us to find a way to directly mix, or cross-polarize, the photons via a nonlinear optical process on a chip for the first time.’’ Moss worked with Professor Roberto Morandotti at the INRS-EMT in Canada and researchers from the University of Sussex and Herriot Watt University, City University of Hong Kong, and the Xi’an Institute in Chin, on the research. “While a similar suppression of classical effects has been observed in gas vapors and complex micro-structured fibers, this is the first time it has been reported on a chip, opening a route for building scalable integrated devices that exploit the mixing of polarization on a single photon level,’’ he said. “It also has the advantage that the fabrication process of the chip is compatible with that currently used for electronic chips, which not only allows the exploitation of the huge global infrastructure of CMOS foundries, but will ultimately offer the potential to integrate electronic devices on the same chip. “Both of these are fundamental requirements for the ultimate widespread adoption of optical quantum technologies.’’ The research was published in Nature Communications.


News Article | November 16, 2015
Site: www.nanotech-now.com

Home > Press > Photons on a chip set new paths for secure communications Abstract: Researchers from RMIT University in Melbourne have helped crack the code to ultra-secure telecommunications of the future in an international research project that could also expedite the advent of quantum computing. A team co-led by RMIT MicroNano Research Facility Director Professor David Moss has added a new twist to create photon pairs that fit on a tiny computer chip. The breakthrough, published in Nature Communications, heralds the next-generation of integrated quantum optical technology, being compatible with current technology and secure communications. The team pioneered a new approach based on a micro-ring resonator - a tiny optical cavity - in which energy conservation constraints can be exploited to suppress classical effects while amplifying quantum processes. They used laser beams at different wavelengths and then had to overcome the risk of the two pump beams being able to destroy the photons' fragile quantum state. "One of the properties of light exploited within quantum optics is 'photon polarization', which is essentially the direction in which the electric field associated with the photon oscillates,'' Moss said. "Processes used to generate single photons or photon pairs on a chip allow the generation of photons with the same polarization as the laser beam, forcing us to find a way to directly mix, or cross-polarize, the photons via a nonlinear optical process on a chip for the first time.'' Moss worked with Professor Roberto Morandotti at the INRS-EMT in Canada and researchers from the University of Sussex and Herriot Watt University, City University of Hong Kong, and the Xi'an Institute in Chin, on the research. "While a similar suppression of classical effects has been observed in gas vapours and complex micro-structured fibres, this is the first time it has been reported on a chip, opening a route for building scalable integrated devices that exploit the mixing of polarization on a single photon level,'' he said. "It also has the advantage that the fabrication process of the chip is compatible with that currently used for electronic chips which not only allows the exploitation of the huge global infrastructure of CMOS foundries, but will ultimately offer the potential to integrate electronic devices on the same chip. "Both of these are fundamental requirements for the ultimate widespread adoption of optical quantum technologies.'' 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.


Liu F.,City University of Hong Kong | Liang Z.,City University of Hong Kong | Li J.,University of Birmingham
Physical Review Letters | Year: 2013

We introduce a field transformation method for wave manipulation based on completely reciprocal and passive materials. While coordinate transformations in transformation optics (TO) change the size and shape of an object, field transformations give us direct control on the impedance and polarization signature of an object. Using our approach, a new type of perfect conductor can be realized to completely convert between transverse electric and transverse magnetic polarizations at any incidence angles and a perfect magnetic conductor of arbitrary shape can be mimicked by using anisotropic materials. The approach can be further combined with TO to enhance existing TO devices. For example, a dielectric cylinder can become completely transparent for both polarizations using bianisotropic materials. © 2013 American Physical Society.


Torabi M.,City University of Hong Kong | Aziz A.,Gonzaga University
International Communications in Heat and Mass Transfer | Year: 2012

This paper analytically investigates the thermal performance of convective-radiative T-shape fin with simultaneous variation of thermal conductivity, heat transfer coefficient and surface emissivity with temperature. Unlike some other fin studies, the sink temperatures for convection and radiation are assumed to be non-zero. This model is a more realistic representation of fins in actual engineering practice. The collection of graphs provided should facilitate design and performance evaluation of T-shaped fins. © 2012 Elsevier Ltd.


Torabi M.,City University of Hong Kong | Aziz A.,Gonzaga University
International Communications in Heat and Mass Transfer | Year: 2012

This article investigates entropy generation in an asymmetrically cooled hollow cylinder with temperature dependent thermal conductivity and internal heat generation. The inside surface of the cylinder is cooled by convection on its inside surface while the outside surface experiences simultaneous convective-radiative cooling. The thermal conductivity of the cylinder as well as the internal heat generation within the cylinder are linear functions of temperature, introducing two nonlinearities in the one-dimensional steady state heat conduction equation. A third nonlinearity arises due to radiative heat loss from the outside surface of the cylinder. The nonlinear system is solved analytically using the differential transformation method (DTM) to obtain the temperature distribution which is then used to compute local and total entropy generation rates in the cylinder. The accuracy of DTM is verified by comparing its predictions with the analytical solution for the case of constant thermal conductivity and constant internal heat generation. The local and total entropy generations depend on six dimensionless parameters: heat generation parameter Q, thermal conductivity parameter β, conduction-convection parameters Nc 1 and Nc 2, conduction-radiation parameter Nr, convection sink temperature δ and radiation sink temperature ζ. © 2012 Elsevier Ltd.


Kang M.,City University of Hong Kong | Liu F.,City University of Hong Kong | Li J.,University of Birmingham
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We show that metamaterials can be used as a testing ground to investigate spontaneous symmetry breaking associated with non-Hermitian quantum systems. By exploring the interplay between near-field dipolar coupling and material absorption or gain, we demonstrate various spontaneous breaking processes of the PT symmetry for a series of effective Hamiltonians associated with the scattering matrix. By tuning the coupling parameter, coherent perfect absorption, laser action, and gain-induced complete reflection (π reflector) by using an ultrathin metamaterial can be obtained. Moreover, an ideal PT symmetry can be established effectively in a passive system by exploring the balance between scattering and absorption loss using metamaterials. © 2013 American Physical Society.


Wu L.,Harbin Institute of Technology | Ho D.W.C.,City University of Hong Kong
Automatica | Year: 2010

This paper is concerned with the sliding mode control (SMC) of nonlinear singular stochastic systems with Markovian switching. An integral sliding surface function is designed, and the resulting sliding mode dynamics is a full-order Markovian jump singular stochastic system. By introducing some specified matrices, a new sufficient condition is proposed in terms of strict linear matrix inequality (LMI), which guarantees the stochastic stability of the sliding mode dynamics. Then, a SMC law is synthesized for reaching motion. Moreover, when there exists an external disturbance, the ℒ2 disturbance attenuation performance is analyzed for the sliding mode dynamics. Some related sufficient conditions are also established. © 2010 Elsevier Ltd. All rights reserved.


Torabi M.,City University of Hong Kong | Aziz A.,Gonzaga University | Zhang K.,City University of Hong Kong
Energy | Year: 2013

This paper establishes the performance characteristics of convective-radiative longitudinal fins of rectangular, trapezoidal and concave parabolic profiles with simultaneous variation of thermal conductivity, heat transfer coefficient and surface emissivity with temperature. The convection and radiation sink temperatures were assumed to be non-zero. The calculations are carried out using the differential transformation method (DTM). The accuracy of the DTM is confirmed by comparing its predictions with the results from an analytical solution and a well-tested numerical procedure. A new idea of volume adjusted fin heat transfer rate, fin effectiveness, and fin efficiency is introduced to compare the performances of trapezoidal and concave parabolic fins with the rectangular fin. Results presented illustrate the effects of thermal conductivity parameter, emissivity parameter, convection-conduction parameter, radiation-conduction parameter, and dimensionless convection and radiation sink temperatures on the performance of fins. © 2013 Elsevier Ltd.


Qiu J.,Harbin Institute of Technology | Feng G.,City University of Hong Kong | Feng G.,Nanjing University of Science and Technology | Gao H.,Harbin Institute of Technology
IEEE Transactions on Fuzzy Systems | Year: 2012

This paper is concerned with the problem of robust ${\mathscr H}infty output feedback control for a class of continuous-time Takagi-Sugeno (T-S) fuzzy affine dynamic systems using quantized measurements. The objective is to design a suitable observer-based dynamic output feedback controller that guarantees the global stability of the resulting closed-loop fuzzy system with a prescribed ${\mathscr H}\infty disturbance attenuation level. Based on common/piecewise quadratic Lyapunov functions combined with S-procedure and some matrix inequality convexification techniques, some new results are developed to the controller synthesis for the underlying continuous-time T-S fuzzy affine systems with unmeasurable premise variables. All the solutions to the problem are formulated in the form of linear matrix inequalities (LMIs). Finally, two simulation examples are provided to illustrate the advantages of the proposed approaches. © 1993-2012 IEEE.


Chen H.,Harbin Institute of Technology | Sun D.,City University of Hong Kong
IEEE Transactions on Robotics | Year: 2012

Significant demand for both accuracy and productivity in batch manipulation of microparticles highlights the need to develop an automatic arraying approach to placing groups of particles into a predefined array with right pairs. This paper presents our latest effort to achieve this objective using integrated robotics and holographic optical tweezers technologies, where holographic optical tweezers function as special robot end-effectors to manipulate the microparticles. Based on the physical dynamics of trapping, a potential-field-based controller is developed to drive every pair of particles to the assigned array, while preventing collisions between particles. The significance of the proposed controller lies in the capability of driving two groups of particles into a common array in right pair and controlling the interdistances between the particles in pairs. Experiments are performed to demonstrate the effectiveness of the proposed approach. © 2012 IEEE.


Liu F.,University of Birmingham | Liu F.,City University of Hong Kong | Li J.,City University of Hong Kong
Physical Review Letters | Year: 2015

By considering gauge transformations on the macroscopic Maxwell's equations, a two-dimensional gauge field, with its pseudomagnetic field in the real space, is identified as tilted anisotropy in the constitutive parameters. We show that the optical spin Hall effect with broadband response and one-way edge states become possible simply by using anisotropic media. The proposed gauge field also allows us to obtain unidirectional propagation for a particular pseudospin based on the Aharonov-Bohm effect. Our approach will be useful in spoof magneto-optics with arbitrary magnetic fields mimicked by metamaterials with subwavelength unit cells. It also serves as a generic way to design polarization-dependent devices. © 2015 American Physical Society.


Huang L.,Harbin Institute of Technology | So H.C.,City University of Hong Kong
IEEE Transactions on Signal Processing | Year: 2013

Numerous methodologies have been investigated for source enumeration in sample-starving environments. For those having their root in the framework of random matrix theory, the involved distribution of the sample eigenvalues is required. Instead of relying on the eigenvalue distribution, this work devises a linear shrinkage based minimum description length (LS-MDL) criterion by utilizing the identity covariance matrix structure of noise subspace components. With linear shrinkage and Gaussian assumption of the observations, an accurate estimator for the covariance matrix of the noise subspace components is derived. The eigenvalues obtained from the estimator turn out to be a linear function of the corresponding sample eigenvalues, enabling the LS-MDL criterion to accurately detect the source number without incurring significantly additional computational load. Furthermore, the strong consistency of the LS-MDL criterion for m,n\ura{} ∞ and m/n\ura{} c in (0,∞) is proved, where m and n are the antenna number and snapshot number, respectively. Simulation results are included for illustrating the effectiveness of the proposed criterion. © 1991-2012 IEEE.


Aziz A.,Gonzaga University | Torabi M.,City University of Hong Kong | Zhang K.,City University of Hong Kong
Energy Conversion and Management | Year: 2013

This paper studies a radial fin of uniform thickness with convective heating at the base and convective-radiative cooling at the tip. The fin is assumed to experience uniform internal heat generation. The exposed surfaces of the fin lose heat by simultaneous convection and radiation to the surroundings. Two types of fin materials are investigated: homogeneous material and functionally graded material (FGM). For the homogeneous material, the thermal conductivity is assumed to be a linear function of temperature, while for the FGM fin the thermal conductivity is modeled as a linear function of the dimensionless radial coordinate. The analysis is conducted using the differential transformation method (DTM). The accuracy of DTM is verified by comparing the results for the simplified versions of the present model with an exact analytical solution derived here. Once the accuracy of DTM is authenticated, the method is used to generate results for the general problem formulated here. These results illustrate the effects of various dimensionless parameters on the thermal performance of homogeneous material fins and FGM fins. © 2013 Elsevier B.V. All rights reserved.


Zeng W.-J.,City University of Hong Kong | So H.C.,City University of Hong Kong | Huang L.,Harbin Institute of Technology
IEEE Transactions on Signal Processing | Year: 2013

A family of algorithms, named ℓ p-MUSIC, for direction-of-arrival (DOA) estimation in impulsive noise is proposed. The ℓ p-MUSIC estimator adopts the ℓ p-norm (1leq p< 2) of the residual fitting error matrix as the objective function for subspace decomposition, rather than the Frobenius norm that is used in the conventional MUSIC method. Although the matrix ℓ p -norm minimization based subspace decomposition will lead to a nonconvex optimization problem, two iterative algorithms are designed for achieving efficient solutions. The first algorithm is the iteratively reweighted singular value decomposition (IR-SVD), where the SVD of a reweighted data matrix is performed in each iteration. The second algorithm solves the nonconvex matrix ℓ p-norm minimization by alternating convex optimization. Two complex-valued Newton's methods with optimal step size in each iteration are devised to solve the resulting convex problem. The convergence of the iterative procedure is also proved. Numerical results verify that the ℓ p-MUSIC methodology outperforms the standard MUSIC scheme and several existing outlier-resistant DOA estimation approaches in terms of resolution capability and estimation accuracy. © 1991-2012 IEEE.


Safa A.,City University of Hong Kong | Nair G.B.,Indian National Institute of Cholera and Enteric Diseases | Kong R.Y.C.,City University of Hong Kong
Trends in Microbiology | Year: 2010

Vibrio cholerae typically contains a prophage that carries the genes encoding the cholera toxin, which is responsible for the major clinical symptoms of the disease. In recent years, new pathogenic variants of V. cholerae have emerged and spread throughout many Asian and African countries. These variants display a mixture of phenotypic and genotypic traits from the two main biotypes (known as 'classical' and 'El Tor'), suggesting that they are genetic hybrids. Classical and El Tor biotypes have been the most epidemiologically successful cholera strains during the past century, and it is believed that the new variants (which we call here 'atypical El Tor') are likely to develop successfully in a manner similar to these biotypes. Here, we describe recent advances in our understanding of the epidemiology and evolution of the atypical El Tor strains. © 2009 Elsevier Ltd. All rights reserved.


Luk K.-M.,City University of Hong Kong | Wu B.,City University of Hong Kong | Wu B.,Broadradio Technologies Ltd.
Proceedings of the IEEE | Year: 2012

In this paper, stringent requirements imposed on the design of base station antennas for mobile communications are summarized. Conventional techniques for implementing base station antennas are reviewed. The complementary antenna concept of combining an electric dipole with a magnetic dipole is reconsidered. Recently, this kind of antenna has been commonly called a "Huygen's source". The purpose is to develop wideband unidirectional antennas with stable frequency characteristics and low back radiation. Based on this concept, the magnetoelectric dipole was invented by integrating an electric dipole with an L-probe fed shorted quarter-wave patch antenna. A number of magnetoelectric dipoles with different radiation patterns and different polarizations have been developed in recent years. An overview of the characteristics of this new class of complementary antennas is presented. Major design challenges are explained. Finally, a new magnetoelectric dipole that is low in profile and robust in structure is presented. The magnetic dipole part of this antenna is realized by a triangular-shaped loop antenna. The antenna is inherently direct current (dc) grounded, which satisfies the requirement for outdoor applications. © 2012 IEEE.


Qiu J.,Harbin Institute of Technology | Feng G.,City University of Hong Kong | Feng G.,Nanjing University of Science and Technology | Gao H.,Harbin Institute of Technology
IEEE Transactions on Fuzzy Systems | Year: 2013

This paper investigates the problem of robust H∞ output feedback control for a class of continuous-time Takagi-Sugeno (T-S) fuzzy affine dynamic systems with parametric uncertainties and input constraints. The objective is to design a suitable constrained piecewise affine static output feedback controller, guaranteeing the asymptotic stability of the resulting closed-loop fuzzy control system with a prescribed H∞ disturbance attenuation level. Based on a smooth piecewise quadratic Lyapunov function combined with S-procedure and some matrix inequality convexification techniques, some new results are developed for static output feedback controller synthesis of the underlying continuous-time T-S fuzzy affine systems. It is shown that the controller gains can be obtained by solving a set of linear matrix inequalities (LMIs). Finally, three examples are provided to illustrate the effectiveness of the proposed methods. © 1993-2012 IEEE.


Qiu J.,Harbin Institute of Technology | Feng G.,City University of Hong Kong | Feng G.,Nanjing University of Science and Technology | Gao H.,Harbin Institute of Technology
IEEE Transactions on Fuzzy Systems | Year: 2011

This paper investigates the problem of robust ℋ∞ output-feedback control for a class of networked nonlinear systems with multiple packet dropouts. The nonlinear plant is represented by Takagi-Sugeno (T-S) fuzzy affine dynamic models with norm-bounded uncertainties, and stochastic variables that satisfy the Bernoulli random binary distribution are adopted to characterize the data-missing phenomenon. The objective is to design an admissible output-feedback controller that guarantees the stochastic stability of the resulting closed-loop system with a prescribed ℋ∞ disturbance attenuation level. It is assumed that the plant premise variables, which are often the state variables or their functions, are not measurable so that the controller implementation with state-space partition may not be synchronous with the state trajectories of the plant. Based on a piecewise quadratic Lyapunov function combined with an S-procedure and some matrix inequality convexifying techniques, two different approaches to robust output-feedback controller design are developed for the underlying T-S fuzzy affine systems with unreliable communication links. The solutions to the problem are formulated in the form of linear matrix inequalities (LMIs). Finally, simulation examples are provided to illustrate the effectiveness of the proposed approaches. © 2011 IEEE.


Wu L.,Harbin Institute of Technology | Ho D.W.C.,City University of Hong Kong | Li C.W.,City University of Hong Kong
Systems and Control Letters | Year: 2011

This paper is concerned with the sliding mode control (SMC) of a continuous-time switched stochastic system. A sufficient condition for the existence of reduced-order sliding mode dynamics is derived and an explicit parametrization of the desired sliding surface is also given. Then, a sliding mode controller is then synthesized for reaching motion. Moreover, the observer-based SMC problem is also investigated. Some sufficient conditions are established for the existence and the solvability of the desired observer and the observer-based sliding mode controller is synthesized. Finally, numerical examples are provided to illustrate the effectiveness of the proposed theory. © 2011 Elsevier B.V. All rights reserved.


Weng Q.,Japan International Center for Materials Nanoarchitectonics | Weng Q.,University of Tsukuba | Wang X.,Japan International Center for Materials Nanoarchitectonics | Zhi C.,City University of Hong Kong | And 3 more authors.
ACS Nano | Year: 2013

Layered boron nitrides (BNs) are usually viewed as excellent protective coatings and reinforcing materials due to their chemical inertness and high mechanical strength. However, the attention paid to their potential applications in gas sorption, especially in case of hydrogen, has obviously been insufficient. Herein, a novel BN material (i.e., porous microbelts), with the highest specific surface area ever reported for any BN system, up to 1488 m 2 g-1, is obtained through one-step template-free reaction of a boron acid-melamine precursor with ammonia. Comprehensive high-resolution transmission electron microscopy, X-ray diffraction, and Raman characterizations all confirm that the obtained BN phase is partially disordered, shows an enlarged average spacing between adjacent (0002) layers (d0002 = 0.38 nm, compared to normal 0.33 nm for a bulk layered BN), and belongs to an intermediate state between hexagonal (h-BN) and amorphous (a-BN) phases. By changing the synthesis temperatures, the textures of obtained porous microbelts are adjustable. H2 sorption evaluations demonstrate that the materials exhibit high and reversible H2 uptake from 1.6 to 2.3 wt % at 77 K and at a relatively low pressure of 1 MPa. © 2013 American Chemical Society.


Chen Y.,City University of Hong Kong | Xue W.,Nanjing University | Yang J.,Rutgers University
Operations Research | Year: 2013

We consider a stochastic inventory control problem in which a buyer makes procurement decisions while facing periodic random demand and two supply sources, namely, a long-term contract supplier and a spot market. The contract between the buyer and the supplier partially shields the latter from the vicissitudes of the spot market, in that the price paid by the buyer to the supplier is only partially linked to the spot price at the moment. After fulfilling the minimum-order commitment with the supplier, the buyer has the full freedom to source from both the supplier and the market. Procurement from the spot market also incurs a fixed setup cost. We show that an optimal policy consists of three different policy forms, with the realization of each depending on the buyer's inventory level and the prevalent spot price. Certain conditions are identified under which monotone trends exist between policy parameters and the current spot price. © 2013 INFORMS.


Qian C.,Harbin Institute of Technology | Huang L.,Harbin Institute of Technology | So H.C.,City University of Hong Kong
Signal Processing | Year: 2014

A low-complexity ESPRIT algorithm for direction-of-arrival (DOA) estimation is devised in this work. Unlike the conventional subspace based methods, the proposed scheme only needs to calculate two sub-matrices of the sample covariance matrix, that is, R11â̂̂CK× K and R21â̂̂C(M-K)×K, avoiding its complete computation. Here, M is the number of sensors of the array, K satisfies P≤K≤min(M,N) with P being the number of source signals and N being the number of snapshots. Meanwhile, a Nyström-based approach is utilized to correctly compute the signal subspace which only requires O( MK2) flops. Thus, the proposed method has the advantage of computational attractiveness, particularly when Kâ ¡M. Furthermore, we derive the asymptotic variances of the estimated DOAs. Numerical results are included to demonstrate the effectiveness of the developed DOA estimator. © 2013 Elsevier B.V.


Chen S.,Zhejiang University of Science and Technology | Li Y.F.,City University of Hong Kong
IEEE Transactions on Industrial Informatics | Year: 2013

3-D Vision is now a common sensing method frequently used in industrial applications. With the convenience of an uncalibrated system, 3-D reconstruction by a self-calibration technique is possible, but always incomplete or unreliable. This paper presents a novel method to analyze the blur distribution in an image and find the optimal focusing distance so that additional constraints can be used to generate absolute measurement of the models. With the assumption of a Gaussian distribution model of the point spread function, this paper applies two theorems to efficiently compute the defocusing extent on stripe edges. Because the blurring diameter implies the distance from the sensor to the surface, we can upgrade the 3-D map obtained from self-calibration with the known scaling factor. Through theoretical and experimental analysis, we find that not only the technology is feasible, but also both the accuracy and the efficiency are satisfactory. © 2005-2012 IEEE.


News Article | August 22, 2016
Site: www.spie.org

A microsphere superlens is used to convert evanescent waves into propagating waves and provide an imaging efficiency that is 40 times higher than for atomic force microscopy. In general, existing microscopy methods can be separated into three categories, namely, optical microscopy, electron microscopy, and scanning probe microscopy (SPM). Optical microscopy provides a non-invasive, high-speed, relatively low-cost, and environmentally compatible technique for the observation of objects down to the sub-microscale. The imaging resolution of optical microscopy, however, is confined to about half of the illuminating wavelength (in the lateral dimensions), and is several times worse in the axial dimension because of the diffraction limit. Alternative, high-resolution microscopy methods in which the diffraction limit can be overcome are therefore required. In recent work, super-resolution fluorescence microscopes have been successfully advanced to nanoscale resolutions in life science studies.1–3 With these microscopes, however, there is a loss of structural information that restricts their potential applications in semiconductor wafer inspection, the exploration of nanoscale materials/structures, and the non-invasive study of dynamic processes.4, 5 Furthermore, there are few microscopy methods (except for SPM) with which super-resolution imaging can be achieved in all three dimensions, without the use of fluorescent dyes. Indeed, there are also some limitations that prevent the application of SPM in more research fields. Such limitations of SPM include the invasiveness (because of scanning tips), poor time efficiency, and tip (broadening) effects. In other studies, efforts have been made to overcome the lateral diffraction limit of microscopy techniques in a more convenient way. It has been demonstrated that dielectrics with micro- or wavelength-scale spherical structures can be used to realize sub-diffraction-limited resolution (from about 200–50nm).6, 7 Observations of sub-cellular structures8 and 75nm adenoviruses9 have also been successfully demonstrated with microsphere superlenses. When these lenses are combined with a scanning laser confocal microscope, they can be used to resolve structures with feature sizes of about 25nm.10 In our previous work, we showed that a microsphere superlens can be used to enhance the resolution—to the nanoscale—of a microendoscopy approach that was based on a graded-index lens.12 In our more recent work, we have demonstrated a new 3D super-resolution microscopy technique. This method—known as near-field assisted white-light interferometry (NFWLI)—is illustrated in Figure 1. For this approach, we take advantage of the topography acquisition capability of white-light interferometry and the lateral near-field imaging principles of the microsphere superlens.11 Figure 1. Schematic illustration of the near-field assisted white-light interferometry (NFWLI) technique. (a) The NFWLI system is constructed by integrating a microsphere superlens into a Linnik white-light interferometer. The system consists of an analyzer (A), quarter-waveplate (Q), beam splitter (BS), polarizing beam splitter (PBS), polarizer (P), Köhler illumination (KI), mirror (M), piezoelectric ceramic scanner (PZT), and two objectives (O1 and O2). (b) Image frames are recorded during PZT linear scanning along the light path, as indicated by the red arrow. (c) Analyses of the recorded interference images are used to construct the 3D morphology of the measured objects. (d) The final constructed (super-resolution) 3D morphology. Schematic illustration of the near-field assisted white-light interferometry (NFWLI) technique. (a) The NFWLI system is constructed by integrating a microsphere superlens into a Linnik white-light interferometer. The system consists of an analyzer (A), quarter-waveplate (Q), beam splitter (BS), polarizing beam splitter (PBS), polarizer (P), Köhler illumination (KI), mirror (M), piezoelectric ceramic scanner (PZT), and two objectives (O1 and O2). (b) Image frames are recorded during PZT linear scanning along the light path, as indicated by the red arrow. (c) Analyses of the recorded interference images are used to construct the 3D morphology of the measured objects. (d) The final constructed (super-resolution) 3D morphology. 11 In most situations, the vertical information for a sample cannot be constructed directly by analyzing interference images of evanescent waves (because of the lack of phase information along the vertical direction). In our NFWLI technique, however, we use a microsphere superlens to convert the evanescent waves into propagating waves. We also reconstruct the phase information along the vertical direction from the evanescent waves. By analyzing the recorded images that are generated by the interference of the converted propagating waves and the reference light beams, we can construct the morphology of a sample (with sub-diffraction-limited resolution) in all three dimensions. We have tested our NFWLI method by observing structures within central processing unit chips. These chips have lateral dimensions of about 50nm and a vertical dimension of about 10nm. We conducted these observations (see Figure 2) without the use of fluorescent dyes and within 25s, i.e., 40 times faster than for atomic force microscope (AFM) measurements. We find—see Figure 2(d–f)—that the profiles we obtained with our NFWLI technique are consistent, and that they are similar to those we obtained via AFM scanning. Our results also demonstrate that the NFWLI method can operate well in both air and in water. Figure 2. Examples of using NFWLI for the inspection of semiconductor chips. Observations are made of (a) 90nm features, (b) an array of nanodots, and (c) 65nm structures. Scanning electron microscope images (i), virtual images generated with a microsphere superlens (ii), atomic force microscope (AFM) scanning images (iii), and the 3D morphology constructed by NFWLI (iv) are shown in each case. (d–f) Comparisons of the cross sections—marked by the blue and red lines in (a–c)—obtained via AFM scanning and NFWLI. Examples of using NFWLI for the inspection of semiconductor chips. Observations are made of (a) 90nm features, (b) an array of nanodots, and (c) 65nm structures. Scanning electron microscope images (i), virtual images generated with a microsphere superlens (ii), atomic force microscope (AFM) scanning images (iii), and the 3D morphology constructed by NFWLI (iv) are shown in each case. (d–f) Comparisons of the cross sections—marked by the blue and red lines in (a–c)—obtained via AFM scanning and NFWLI. 11 In summary, we have developed a new technique—near-field assisted white-light interferometry—that provides significant advantages over standard scanning probe microscopy for 3D nanoscale morphology profiling. For example, our NFWLI approach has a much improved time efficiency for large-area nanoscale morphology acquisition (i.e., with a field of view that is on the order of micrometers). In addition, our method is non-invasive because the microsphere superlens does not need to be in direct contact with the samples, and it produces reduced repeatability errors (i.e., it does not require scanning probe tips that may wear out during repeated scans and thus cause surface profiling errors). We believe that NFWLI therefore has great potential as a practical 3D super-resolution microscopy method for label-free, high-speed, non-invasive, and environmentally compatible imaging. Indeed, all these properties should facilitate 3D nanoscale imaging of integrated circuit devices, nanomaterials, and biological entities (e.g., cell membranes, viruses, or biomolecules) in the future. The observable area of NFWLI, however, is currently confined by the microsphere's field of view, and we are therefore currently exploring several effective methods to overcome this limitation. Department of Mechanical and Biomedical Engineering City University of Hong Kong Department of Mechanical and Biomedical EngineeringCity University of Hong Kong 1. R. Schmidt, C. A. Wurm, S. Jakobs, J. Engelhardt, A. Egner, S. W. Hell, Spherical nanosized focal spot unravels the interior of cells, Nat. Methods 5, p. 539-544, 2008. 2. M. G. L. Gustafsson, L. Shao, P. M. Carlton, C. J. R. Wang, I. N. Golubovskaya, W. Z. Cande, D. A. Agard, J. W. Sedat, Three-dimensional resolution doubling in wide-field fluorescence microscopy by structured illumination, Biophys. J. 94, p. 4957-4970, 2008. 6. J. Y. Lee, B. H. Hong, W. Y. Kim, S. K. Min, Y. Kim, M. V. Jouravlev, R. Bose, et al., Near-field focusing and magnification through self-assembled nanoscale spherical lenses, Nature 460, p. 498-501, 2009. 10. Y. Yan, L. Li, C. Feng, W. Guo, S. Lee, M. Hong, Microsphere-coupled scanning laser confocal nanoscope for sub-diffraction-limited imaging at 25nm lateral resolution in the visible spectrum, ACS Nano 8, p. 1809-1816, 2014.


Wu J.,Hong Kong Baptist University | Chan R.K.Y.,Hong Kong Baptist University | Chan R.K.Y.,City University of Hong Kong
Optics Express | Year: 2013

We report a fast fluorescence imaging flow cytometer for phytoplankton analysis that can achieve a volume flow rate up to 1ml/min. The instrument shows a high immunity to motion blur in image captured with a lateral resolution of 0.75 0.06 ?m for a wide size range ~1 ?m to ~200 ?m. This is made possible by suppressing the out-of-focus light using thin light sheet illumination and image deconvolution, and by precluding the motion-blur with a unique flow configuration. Preliminary results from untreated coastal water samples show the technique has high potential as a practical field instrument for monitoring phytoplankton abundance and species composition. ©2013 Optical Society of America.


Wu J.,Hong Kong Baptist University | Li J.,Hong Kong Baptist University | Chan R.K.Y.,Hong Kong Baptist University | Chan R.K.Y.,City University of Hong Kong
Optics Express | Year: 2013

This paper reports a light sheet fluorescence imaging flow cytometer for 3D sectioning of phytoplankton. The instrument developed has the inherent advantages of high cell counting throughput and high spatial resolution information derived from flow cytometry and light sheet microscopy. The throughput of the instrument is quantified by the sample volume flow rate of 0.5 μl/min with a spatial resolution as achieved by light sheet microscopy. Preliminary results from 3D morphology of the internal chlorophyll-a structure of two dinoflagellates species show promising application potentials of the method for phytoplankton taxonomy of selected species and species groups. © 2013 Optical Society of America.


Hao X.,Tongji University | Hao X.,Inner Mongolia University of Science and Technology | Zhai J.,Tongji University | Kong L.B.,Nanyang Technological University | Xu Z.,City University of Hong Kong
Progress in Materials Science | Year: 2014

Lead zirconate (PbZrO3 or PZ)-based antiferroelectric (AFE) materials, as a group of important electronic materials, have attracted increasing attention for their potential applications in high energy storage capacitors, micro-actuators, pyroelectric security sensors, cooling devices, and pulsed power generators and so on, because of their novel external electric field-induced phase switching behavior between AFE state and ferroelectric (FE) state. The performances of AFE materials are strongly dependent on the phase transformation process, which are mainly determined by the constitutions and the external field. For AFE thin/thick films, the electrical properties are also strongly dependent on their thickness, crystal orientation and the characteristics of electrode materials. Accordingly, various strategies have been employed to tailor the phase transformation behavior of AFE materials in order to improve their performances. Due to their relatively poor electrical strength (low breakdown fields), most PZ-based orthorhombic AFE ceramics are broken down before a critical switching field can be applied. As a consequence, the electric-field-induced transition between AFE and FE phase of only those AFE bulk ceramics, with compositions within tetragonal region near the AFE/FE morphotropic phase boundary (MPB), can be realized experimentally at room temperature. AFE materials with such compositions include (Pb,A)ZrO3 (A = Ba, Sr), (Pb1-3/2xLa x)(Zr1-yTiy)O 3 (PLZT x/(1-y)/y), (Pb0.97La0.02)(Zr,Sn,Ti) O3 (PLZST) and Pb0.99(Zr,Sn,Ti)0.98Nb 0.02O3 (PNZST). As compared to bulk ceramics, AFE thin and thick films always display better electric-field endurance ability. Consequently, room temperature electric-field-induced AFE-FE phase transition could be observed in the AFE thin/thick films with orthorhombic structures. Moreover, AFE films are more easily integrated with silicon technologies. Therefore, AFE thin/thick films have been a subject of numerous researches. This review serves to summarize the recent progress of PZ-based AFE materials, focusing on the external field (electric field, hydrostatic pressure and temperature) dependences of the AFE-FE phase transition, with a specific attention to the performances of AFE films for various potential applications, such as high energy storage, electric field induced strains, pyroelectric effect and electrocaloric effect. © 2014 Elsevier Ltd. All rights reserved.


Ji S.,Georgia State University | Li Y.,Georgia State University | Jia X.,City University of Hong Kong
Proceedings - IEEE INFOCOM | Year: 2011

Data collection is an important operation of wireless sensor networks (WSNs). The performance of data collection can be measured by its achievable network capacity. Most existing works focus on the capacity of unicast, multicast or snapshot data collection in single-radio single-channel wireless networks, and no dedicated works consider the continuous data collection capacity for WSNs in detail under the protocol interference model. In this paper, we first propose a multi-path scheduling algorithm for the snapshot data collection in single-radio multi-channel WSNs and prove that its achievable network capacity is at least W/3.63/Hρ2 +o(p), which is a tighter lower bound compared with the previously best result in [5] which is W/8p 2, where W is the bandwidth over a channel, H is the number of the available orthogonal channels, ρis the ratio of the interference radius over the transmission radius of a sensor and o(p) is a linear equation of ρ. For the continuous data collection problem, although the authors in [5] claim that data collection can be pipelined with existing works, we find that such an idea cannot actually improve network capacity. We explain the reason for this and propose a novel continuous data collection method for dual-radio multi-channel WSNs. This method significantly speeds up the data collection process, and achieves a capacity of nW/12M(3.63/H ρ2+0(p) when δe ≤ 12, or nW/Mδe(3.63/H ρ2+0(p) when δe > 12, where n is the number of sensors, M is a constant valueandusually M < n, and δe is the maximum number of leaf nodes having a same parent node in the routing tree (i.e. data collection tree). The simulation results also indicate that the proposed algorithms significantly improve network capacity compared with the existing works. © 2011 IEEE.


Cheung C.M.K.,Hong Kong Baptist University | Lee M.K.O.,City University of Hong Kong
Decision Support Systems | Year: 2010

Online social networks (Facebook, MySpace, LinkedIn and the like) have become truly significant new phenomena in human communication and interaction patterns and may have a profound impact in the way people communicate and connect with each other. In this study, the decision to use an online social network is conceptualized as intentional social action and the relative impact of the three modes of social influence processes (compliance, internalization, and identification) on intentional social action to use (collective intention) is examined. An empirical study of Facebook users (n = 389) found that collective intention to use a social networking site is determined by both subjective norm and social identity. Further, social identity is found to be a second-order latent construct comprised of cognitive, evaluative, and affective (first-order) components. Implications for research and practice are discussed. © 2009 Elsevier B.V. All rights reserved.


Jin X.,City University of Hong Kong | Zhao M.,City University of Hong Kong | Chow T.W.S.,City University of Hong Kong | Pecht M.,City University of Hong Kong | Pecht M.,University of Maryland University College
IEEE Transactions on Industrial Electronics | Year: 2014

Bearings are critical components in induction motors and brushless direct current motors. Bearing failure is the most common failure mode in these motors. By implementing health monitoring and fault diagnosis of bearings, unscheduled maintenance and economic losses caused by bearing failures can be avoided. This paper introduces trace ratio linear discriminant analysis (TR-LDA) to deal with high-dimensional non-Gaussian fault data for dimension reduction and fault classification. Motor bearing data with single-point faults and generalized-roughness faults are used to validate the effectiveness of the proposed method for fault diagnosis. Comparisons with other conventional methods, such as principal component analysis, local preserving projection, canonical correction analysis, maximum margin criterion, LDA, and marginal Fisher analysis, show the superiority of TR-LDA in fault diagnosis. © 2013 IEEE.


Xing Y.,City University of Hong Kong | He W.,University of Maryland University College | Pecht M.,University of Maryland University College | Tsui K.L.,City University of Hong Kong
Applied Energy | Year: 2014

Ambient temperature is a significant factor that influences the accuracy of battery SOC estimation, which is critical for remaining driving range prediction of electric vehicles (EVs) and optimal charge/discharge control of batteries. A widely used method to estimate SOC is based on an online inference of open-circuit voltage (OCV). However, the fact that the OCV-SOC is dependent on ambient temperature can result in errors in battery SOC estimation. To address this problem, this paper presents an SOC estimation approach based on a temperature-based model incorporated with an OCV-SOC-temperature table. The unscented Kalman filtering (UKF) was applied to tune the model parameters at each sampling step to cope with various uncertainties arising from the operation environment, cell-to-cell variation, and modeling inaccuracy. Two dynamic tests, the dynamic stress test (DST) and the federal urban driving schedule (FUDS), were used to test batteries at different temperatures. Then, DST was used to identify the model parameters while FUDS was used to validate the performance of the SOC estimation. The estimation was made covering the major working range from 25% to 85% SOC. The results indicated that our method can provide accurate SOC estimation with smaller root mean squared errors than the method that does not take into account ambient temperature. Thus, our approach is effective and accurate when battery operates at different ambient temperatures. Since the developed method takes into account the temperature factor as well as the complexity of the model, it could be effectively applied in battery management systems for EVs. © 2013 Elsevier Ltd.


Zhang W.-A.,City University of Hong Kong | Zhang W.-A.,Zhejiang University of Technology | Feng G.,City University of Hong Kong | Yu L.,Zhejiang University of Technology
Automatica | Year: 2012

This paper presents a distributed fusion estimation method for estimating states of a dynamical process observed by wireless sensor networks (WSNs) with random packet losses. It is assumed that the dynamical process is not changing too rapidly, and a multi-rate scheme by which the sensors estimate states at a faster time scale and exchange information with neighbors at a slower time scale is proposed to reduce communication costs. The estimation is performed by taking into account the random packet losses in two stages. At the first stage, every sensor in the WSN collects measurements from its neighbors to generate a local estimate, then local estimates in the neighbors are further collected at the second stage to form a fused estimate to improve estimation performance and reduce disagreements among local estimates at different sensors. Local optimal linear estimators are designed by using the orthogonal projection principle, and the fusion estimators are designed by using a fusion rule weighted by matrices in the linear minimum variance sense. Simulations of a target tracking system are given to show that the time scale of information exchange among sensors can be slower while still maintaining satisfactory estimation performance by using the developed estimation method. © 2012 Elsevier Ltd. All rights reserved.


Zhang W.-A.,Zhejiang University of Technology | Zhang W.-A.,City University of Hong Kong | Yu L.,Zhejiang University of Technology | Feng G.,City University of Hong Kong
Automatica | Year: 2011

This paper is concerned with the optimal linear estimation problem for discrete time-varying networked systems with communication constraints. The communication constraint considered is that only one network node is allowed to gain access to a shared communication channel, then the various network nodes of the networked systems are scheduled to transmit data according to a specified media access control protocol, and a remote estimator performs the estimation task with only partially available measurements. The channel accessing processes of those network nodes are modeled by Bernoulli processes, and optimal linear filters are designed by using the orthogonal projection principle and the innovation analysis approach. It is shown that the optimal estimation performances critically depend on the channel accessing probabilities of the network nodes and the packet loss probability, and the optimal filters can be obtained by solving recursive Lyapunov and Riccati equations. An illustrative example is finally given to show the effectiveness of the proposed filters. © 2011 Elsevier Ltd. All rights reserved.


Liu Z.-W.,Huazhong University of Science and Technology | Guan Z.-H.,Huazhong University of Science and Technology | Shen X.,University of Waterloo | Feng G.,City University of Hong Kong
IEEE Transactions on Automatic Control | Year: 2012

In this technical note, an impulsive consensus algorithm is proposed for second-order continuous-time multi-agent networks with switching topology. The communication among agents occurs at sampling instants based on position only measurements. By using the property of stochastic matrices and algebraic graph theory, some sufficient conditions are obtained to ensure the consensus of the controlled multi-agent network if the communication graph has a spanning tree jointly. A numerical example is given to illustrate the effectiveness of the proposed algorithm. © 2012 IEEE.


Vasan A.S.S.,University of Maryland University College | Long B.,University of Electronic Science and Technology of China | Pecht M.,University of Maryland University College | Pecht M.,City University of Hong Kong
IEEE Transactions on Industrial Electronics | Year: 2013

Analog circuits play a vital role in ensuring the availability of industrial systems. Unexpected circuit failures in such systems during field operation can have severe implications. To address this concern, we developed a method for detecting faulty circuit condition, isolating fault locations, and predicting the remaining useful performance of analog circuits. Through the successive refinement of the circuit's response to a sweep signal, features are extracted for fault diagnosis. The fault diagnostics problem is posed and solved as a pattern recognition problem using kernel methods. From the extracted features, a fault indicator (FI) is developed for failure prognosis. Furthermore, an empirical model is developed based on the degradation trend exhibited by the FI. A particle filtering approach is used for model adaptation and RUP estimation. This method is completely automated and has the merit of implementation simplicity. Case studies on two analog filter circuits demonstrating this method are presented. © 1982-2012 IEEE.


Cheung C.M.K.,Hong Kong Baptist University | Lee M.K.O.,City University of Hong Kong
Decision Support Systems | Year: 2012

The advance of the Internet facilitates consumers to share and exchange consumption-related advice through online consumer reviews. This relatively new form of word-of-mouth communication, electronic word-of-mouth (eWOM) communication, has only recently received significant managerial and academic attention. Many academic studies have looked at the effectiveness of positive eWOM communication, examining the process by which eWOM influences consumer purchasing decisions. eWOM behavior is primarily explained from the individual rational perspective that emphasizes a cost and benefit analysis. However, we felt there was a need for an extensive study that examines consumers' motives for eWOM. In this paper, we focus on the factors that drive consumers to spread positive eWOM in online consumer-opinion platforms. Building on the social psychology literature, we identified a number of key motives of consumers' eWOM intention and developed an associated model. We empirically tested the research model with a sample of 203 members of a consumer review community, OpenRice.com. The model explains 69% of the variance, with reputation, sense of belonging and enjoyment of helping other consumers significantly related to consumers' eWOM intention. The results of this study provide important implications for research and practice. © 2012 Elsevier B.V. All rights reserved.


Sutanto J.,ETH Zurich | Palme E.,Newscron Ltd. | Tan C.-H.,City University of Hong Kong | Phang C.W.,Fudan University
MIS Quarterly: Management Information Systems | Year: 2013

Privacy has been an enduring concern associated with commercial information technology (IT) applications, in particular regarding the issue of personalization. IT-enabled personalization, while potentially making the user computing experience more gratifying, often relies heavily on the user's personal information to deliver individualized services, which raises the user's privacy concerns. We term the tension between personalization and privacy, which follows from marketers exploiting consumers' data to offer personalized product information, the personalization-privacy paradox. To better understand this paradox, we build on the theoretical lenses of uses and gratification theory and information boundary theory to conceptualize the extent to which privacy impacts the process and content gratifications derived from personalization, and how an IT solution can be designed to alleviate privacy concerns. 1 Set in the context of personalized advertising applications for smartphones, we propose and prototype an IT solution, referred to as a personalized, privacy-safe application, that retains users' information locally on their smartphones while still providing them with personalized product messages. We validated this solution through a field experiment by benchmarking it against two more conventional applications: a base non-personalized application that broadcasts non-personalized product information to users, and a personalized, non-privacy safe application that transmits user information to a central marketer's server. The results show that (com-pared to the non-personalized application), while personalized, privacy-safe or not increased application usage (reflecting process gratification), it was only when it was privacy-safe that users saved product messages (reflecting content gratification) more frequently. Follow-up surveys corroborated these nuanced findings and further revealed the users' psychological states, which explained our field experiment results. We found that saving advertisements for content gratification led to a perceived intrusion of information boundary that made users reluctant to do so. Overall our proposed IT solution, which delivers a personalized service but avoids transmitting users' personal information to third parties, reduces users' perceptions that their information boundaries are being intruded upon, thus mitigating the personalization-privacy paradox and increasing both process and content gratification.


Liu Z.-Q.,City University of Hong Kong | Liu Y.-K.,Hebei University
Soft Computing | Year: 2010

This paper proposes an axiomatic framework from which we develop the theory of type-2 (T2) fuzziness, called fuzzy possibility theory. First, we introduce the concept of a fuzzy possibility measure in a fuzzy possibility space (FPS). The fuzzy possibility measure takes on regular fuzzy variable (RFV) values, so it generalizes the scalar possibility measure in the literature. One of the interesting consequences of the FPS is that it leads to a new definition of T2 fuzzy set on the Euclidean space Rm which we call T2 fuzzy vector, as a map to the space instead of on the space. More precisely, we define a T2 fuzzy vector as a measurable map from an FPS to the space Rm of real vectors. In the current development, we are suggesting that T2 fuzzy vector is a more appropriate definition for a T2 fuzzy set on Rm In the literature, a T2 fuzzy set is usually defined via its T2 membership function, whereas in this paper, we obtain the T2 possibility distribution function as the transformation of a fuzzy possibility measure from a universe to the space Rm via T2 fuzzy vector. Second, we develop the product fuzzy possibility theory. In this part, we give a general extension theorem about product fuzzy possibility measure from a class of measurable atom-rectangles to a product ample field, and discuss the relationship between a T2 fuzzy vector and T2 fuzzy variables. We also prove two useful theorems about the existence of an FPS and a T2 fuzzy vector based on the information from a finite number of RFV-valued maps. The two results provide the possible interpretations for the concepts of the FPS and the T2 fuzzy vector, and thus reinforce the credibility of the approach developed in this paper. Finally, we deal with the arithmetic of T2 fuzzy variables in fuzzy possibility theory. We divide our discussion into two cases according to whether T2 fuzzy variables are defined on single FPS or on different FPSs, and obtain two theorems about T2 fuzzy arithmetic. © Springer-Verlag 2009.


Chen S.,Zhejiang University of Technology | Li Y.,City University of Hong Kong | Kwok N.M.,University of New South Wales
International Journal of Robotics Research | Year: 2011

In this paper we provide a broad survey of developments in active vision in robotic applications over the last 15 years. With increasing demand for robotic automation, research in this area has received much attention. Among the many factors that can be attributed to a high-performance robotic system, the planned sensing or acquisition of perceptions on the operating environment is a crucial component. The aim of sensor planning is to determine the pose and settings of vision sensors for undertaking a vision-based task that usually requires obtaining multiple views of the object to be manipulated. Planning for robot vision is a complex problem for an active system due to its sensing uncertainty and environmental uncertainty. This paper describes such problems arising from many applications, e.g. object recognition and modeling, site reconstruction and inspection, surveillance, tracking and search, as well as robotic manipulation and assembly, localization and mapping, navigation and exploration. A bundle of solutions and methods have been proposed to solve these problems in the past. They are summarized in this review while enabling readers to easily refer solution methods for practical applications. Representative contributions, their evaluations, analyses, and future research trends are also addressed in an abstract level. © SAGE Publications 2011.


Fonseca J.,Joseph Fourier University | O'Sullivan C.,Imperial College London | Coop M.R.,City University of Hong Kong | Lee P.D.,University of Manchester
Geotechnique | Year: 2013

Over the past 50 years, experimental studies have repeatedly demonstrated that the mechanical behaviour of sand is sensitive to the material fabric, that is, the arrangement of the grains. Up until now there have been relatively few attempts to describe this fabric quantitatively. Much of our understanding of the link between the particle movements and interactions and the macro-scale response of granular materials, including sand, comes from discrete-element modelling and experiments on 'analogue' sands with simple, idealised shapes. This paper investigates methods of quantifying the directional fabric of a real sand and its evolution under loading. Statistical analyses of the distribution of fabric directional data in terms of particle, contact normal, branch vector and void orientations were carried out at different stages of shearing deformation. The data show that the initial particle orientation fabric that develops during the deposition of the material tends to persist during shearing, while in the post-peak regime the contact normals seem to be reoriented along the direction of the major principal stress. Different patterns were observed within the shear band, as both the particles and the contact normal vectors appeared to rotate along the shear plane. © 2013 Thomas Telford Ltd.


Chen S.Y.,Zhejiang University of Technology | Li Y.F.,City University of Hong Kong
IEEE Sensors Journal | Year: 2011

Estimation of the blurring effect is very important for many imaging systems. This letter reports an idea to efficiently and robustly compute the blurring parameter on certain stripe edges. Two formulas are found to determine the degree of imaging blur only by calculating the area sizes under the corresponding profile curves, without the need for deconvolution or transformation over the image. The method can be applied to many applications such as vision sensing of scene depth. A 3-D vision system is taken as an implementation instance. © 2010 IEEE.


Halawa E.,Charles Darwin University | GhaffarianHoseini A.,University of Malaya | Hin Wa Li D.,City University of Hong Kong
Renewable Energy | Year: 2014

In regions where solar energy is abundant, solar energy can play a vital role in attaining energy sustainability. Sizing solar energy systems requires the availability of solar radiation data on horizontal surface which can then be used to calculate solar radiation intensity on any tilted surface using appropriate conversion factors or formula. In many parts of the world, especially in developing countries, such data is not readily available. Many researchers have found that monthly average daily value of global solar radiation on horizontal surface can be estimated when meteorological parameters such as duration of sunshine, number of rainy days, relative humidity, etc. are available. Many empirical correlations have been developed based on this approach. The development of such a correlation has been made possible through the availability of solar and other meteorological data required for their validation. This paper presents a review on the existing empirical correlations and critically looks at the practicality of such correlations. This raises the question on the appropriateness of the past and present approaches adopted by researchers in this field. The paper also discusses various related aspects and proposes new directions for future research. © 2014 Elsevier Ltd.


Cheung C.M.K.,Hong Kong Baptist University | Thadani D.R.,City University of Hong Kong
Decision Support Systems | Year: 2012

The notion of electronic word-of-mouth (eWOM) communication has received considerable attention in both business and academic communities. Numerous studies have been conducted to examine the effectiveness of eWOM communication. The scope of published studies on the impact of eWOM communication is large and fragmented and little effort has been made to integrate the findings of prior studies and evaluate the status of the research in this area. In this study, we conducted a systematic review of eWOM research. Building upon our literature analysis, we used the social communication framework to summarize and classify prior eWOM studies. We further identified key factors related to the major elements of the social communication literature and built an integrative framework explaining the impact of eWOM communication on consumer behavior. We believe that the framework will provide an important foundation for future eWOM research work. © 2012 Elsevier B.V. All rights reserved.


Yao T.,City University of Hong Kong | Ngo C.-W.,City University of Hong Kong | Mei T.,Microsoft
IEEE Transactions on Image Processing | Year: 2013

Search reranking is regarded as a common way to boost retrieval precision. The problem nevertheless is not trivial especially when there are multiple features or modalities to be considered for search, which often happens in image and video retrieval. This paper proposes a new reranking algorithm, named circular reranking, that reinforces the mutual exchange of information across multiple modalities for improving search performance, following the philosophy that strong performing modality could learn from weaker ones, while weak modality does benefit from interacting with stronger ones. Technically, circular reranking conducts multiple runs of random walks through exchanging the ranking scores among different features in a cyclic manner. Unlike the existing techniques, the reranking procedure encourages interaction among modalities to seek a consensus that are useful for reranking. In this paper, we study several properties of circular reranking, including how and which order of information propagation should be configured to fully exploit the potential of modalities for reranking. Encouraging results are reported for both image and video retrieval on Microsoft Research Asia Multimedia image dataset and TREC Video Retrieval Evaluation 2007-2008 datasets, respectively. © 1992-2012 IEEE.


Chow C.-F.,The Hong Kong Institute of Education | Lam M.H.W.,City University of Hong Kong | Wong W.-Y.,Hong Kong Baptist University
Analytical Chemistry | Year: 2013

The detection of neutral biogenic amines plays a crucial role in food safety. Three new heterobimetallic Ru(II)-Ln(III) donor-acceptor complexes, KPrRu, KNdRu, and KSmRu, K{[Ru(II)(tBubpy)(CN) 4]2-Ln(III)(H2O)4} (where tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine), have been synthesized and characterized. Their photophysical and X-ray crystallographic data were reported in this study. These complexes were found to be selective for biogenic amine vapors, such as histamine, putrescine, and spermidine, with a detection limit down to the ppb level. The sensitivities of these complexes to the amines were recorded as ∼log K = 3.6-5.0. Submicron rods of the complexes, with a nanoscale diameter and microscale length, were obtained through a simple precipitation process. Free-standing polymeric films with different degrees of porosity were fabricated by blending the submicron rods with polystyrene polymer. The polymer with the highest level of porosity exhibited the strongest luminescence enhancement after amine exposure. Real time monitoring of gaseous biogenic amines was applied to real fish samples (Atlantic mackerel) by studying the spectrofluorimetric responses of the Ru(II)-Ln(III) blended polymer film. © 2013 American Chemical Society.


Wang D.,City University of Hong Kong | Miao Q.,University of Electronic Science and Technology of China | Pecht M.,University of Maryland University College
Journal of Power Sources | Year: 2013

Lithium-ion batteries are widely used as power sources in commercial products, such as laptops, electric vehicles (EVs) and unmanned aerial vehicles (UAVs). In order to ensure a continuous power supply, the functionality and reliability of lithium-ion batteries have received considerable attention. In this paper, a battery capacity prognostic method is developed to estimate the remaining useful life of lithium-ion batteries. This capacity prognostic method consists of a relevance vector machine and a conditional three-parameter capacity degradation model. The relevance vector machine is used to derive the relevance vectors that can be used to find the representative training vectors containing the cycles of the relevance vectors and the predictive values at the cycles of the relevance vectors. The conditional three-parameter capacity degradation model is developed to fit the predictive values at the cycles of the relevance vectors. Extrapolation of the conditional three-parameter capacity degradation model to a failure threshold is used to estimate the remaining useful life of lithium-ion batteries. Three instance studies were conducted to validate the developed method. The results show that the developed method is able to predict the future health condition of lithium-ion batteries. © 2013 Elsevier B.V. All rights reserved.


Cheung C.M.K.,Hong Kong Baptist University | Chiu P.-Y.,Hong Kong Baptist University | Lee M.K.O.,City University of Hong Kong
Computers in Human Behavior | Year: 2011

The growth and popularity of online social networks has created a new world of collaboration and communication. More than a billion individuals around the world are connected and networked together to create, collaborate, and contribute their knowledge and wisdom. Despite the importance of online social networks, there is relatively little theory-driven empirical research available to address this new type of communication and interaction phenomena. In this paper, we explored the factors that drive students to use online social networks (e.g., Facebook). Specifically, we conceptualized the use of online social networks as intentional social action and we examined the relative impact of social influence, social presence, and the five key values from the uses and gratification paradigm on We-Intention to use online social networks. An empirical study of Facebook users (n = 182) revealed that We-Intention to use online social networks is strongly determined by social presence. Among the five values, social related factors had the most significant impact on the intention to use. Implications for research and practice are discussed. © 2010 Elsevier Ltd. All rights reserved.


Siu Y.-F.,The Hong Kong Institute of Education | Chan S.,Hong Kong Baptist University | Wong K.-M.,City University of Hong Kong | Wong W.-S.,The Hong Kong Institute of Education
Pain Medicine (United States) | Year: 2012

Purpose. The comorbidity of chronic pain and sleep disturbances has received increasing research attention in Western clinical pediatric populations; yet, little is known about its sociodemographic and psychological correlates in non-Western community pediatric populations. This study aimed to examine the prevalence of comorbid chronic pain and sleep disturbances and its associated factors in a community sample of Chinese adolescents. Methods. A total of 1,518 adolescents aged from 11 to 19 years participated in this school-based study. Apart from sociodemographic background, participants were assessed on chronic pain, sleep disturbances, depression, perceived stress, and social support. Prevalence of co-occurrence of chronic pain and sleep disturbances was determined. Participants with single symptom were compared with those with symptom co-occurrence on pain characteristics and sleep patterns. Multiple regression model evaluated factors associated with symptom comorbidity. Results. While the prevalence of chronic pain and sleep disturbances was 11.4% and 25.6%, respectively, the overall prevalence of comorbid chronic pain and sleep disturbances was 19.1% (95% confidence interval: 16.9, 21.4). Fully adjusted stepwise regression analysis identified being female, more depressive symptoms, and higher perceived stress to be significantly associated with comorbid symptoms. Adolescents with both symptoms reported significantly more pain sites, higher worst pain, and higher pain-associated interference than those reported chronic pain only. Participants with comorbid symptoms also had poor subjective sleep quality, greater sleep disturbances, and more daytime dysfunction than those reported sleep disturbances only. Conclusions. Our data offered preliminary evidence that comorbid chronic pain and sleep disturbances occurred among about one-fifth in the present sample of Chinese community adolescents. Future studies should examine whether the two symptoms interact with each other in affecting the physical, mental, and cognitive development of adolescents. © 2012 Wiley Periodicals, Inc.


Chen S.,Zhejiang University of Technology | Zhang J.,University of Hamburg | Li Y.,City University of Hong Kong
IEEE Transactions on Industrial Informatics | Year: 2012

Background subtraction is important for detecting moving objects in videos. Currently, there are many approaches to performing background subtraction. However, they usually neglect the fact that the background images consist of different objects whose conditions may change frequently. In this paper, a novel hierarchical background model is proposed based on segmented background images. It first segments the background images into several regions by the mean-shift algorithm. Then, a hierarchical model, which consists of the region models and pixel models, is created. The region model is a kind of approximate Gaussian mixture model extracted from the histogram of a specific region. The pixel model is based on the cooccurrence of image variations described by histograms of oriented gradients of pixels in each region. Benefiting from the background segmentation, the region models and pixel models corresponding to different regions can be set to different parameters. The pixel descriptors are calculated only from neighboring pixels belonging to the same object. The experimental results are carried out with a video database to demonstrate the effectiveness, which is applied to both static and dynamic scenes by comparing it with some well-known background subtraction methods. © 2006 IEEE.


News Article | November 9, 2016
Site: www.cemag.us

A new type of sensor has the potential to replace sniffer dogs when it comes to detecting explosives such as TNT. This week, researchers from a number of institutions including TU Delft are publishing an article about this subject in the American Chemical Society's journal Nano Letters. “For the first time ever, we have used molecules with a lantern-type cage structure to fabricate sensitive nanosensors that can detect explosive substances such as TNT,” says researcher Louis de Smet (affiliated with TU Delft and Wageningen University). “These cage structures have a capacity of about 1 cubic nanometer, which precisely accommodates a single TNT molecule.” Researchers from TU Delft, the University of Twente, Philips Research, the City University of Hong Kong, and the University of Melbourne have chemically bound an ultrathin layer of these specially developed cages to the surface of a sensor chip containing a few dozen sensitive nanosensors. A single cage is not sufficient for detection purposes. “Porous molecules are used quite often to capture ambient molecules,” explains De Smet. “In the case of relatively small molecules, as with explosives, the challenge is to ensure that the cage structure is not only the right size but that it also has the right anchor points so that the molecule can click into place – thus rendering it detectable. For this work, we therefore use layers consisting of so-called MOP molecules (Metal-Organic Polyhedra). Through variation with a large number of geometric and electronic properties of these complex cage molecules, we are able to capture the ‘explosive’ molecules we are looking for. And the presence of such a molecule also causes the electrical conductance of the underlying silicon nanowires to change in a very characteristic way. We can measure this and thus confirm that we have actually found TNT molecules from an explosive.” “Eventually, we may be able to use this type of sensor to detect explosives – in a war situation, for example, or when facing a terrorist threat,” says De Smet. “Currently, very different, qualitative methods are mainly used for this, involving chemical reactions causing color changes, for instance, or the deployment of sniffer dogs. The great thing about our method is that you can not only detect whether there are traces of TNT but you can also determine the amount.” Cao, PhD candidate at TU Delft and Zhu, postdoctoral researcher at the University of Twente initiated this work and performed the experiments, while Shang did the computational work. Klootwijk, Sudhölter, Huskens and De Smet supervised the project.


News Article | February 15, 2017
Site: phys.org

Adaptive Solar Facade. Credit: Chair for Architecture and Building Systems, Institute of Technology in Architecture, ETH Zurich Global climate change is affecting our planet and mankind; climate science is thus instrumental in informing policy makers about its dangers, and in suggesting emission limits. Science also shows that staying within limits, while meeting the aspirations of a growing global population requires fundamental changes in energy conversion and storage. The majority of low-carbon technology innovation observed in the last decades, such as the 85% cost reduction in photovoltaic cell production since 2000, was driven by largely uncoordinated national policies. These included research incentives in Japan and the U.S., feed-in tariffs in Germany, and tax breaks in the U.S. During the AAAS 2017 Annual Meeting in Boston, Tobias Schmidt, ETH Zurich - The Swiss Federal Institute of Technology in Zurich, Switzerland, Jessika Trancik, Massachusetts Institute of Technology, Cambridge, U.S.A., and Masaru Yarime, City University of Hong Kong, will review the successes and failures of policies for low-carbon technology innovation and show how characteristics of both the technologies and the policy instruments themselves helped and, in some ways, hindered technological progress. In addition, they will demonstrate how research by the innovative science community can inform policy decisions in the future to accelerate low-carbon innovation and affect the livelihood of our planet in the long-term, despite limited resources. Wind and solar energy installations have grown rapidly in recent decades as their costs have fallen. It remains unclear; however, whether these trends will continue, allowing the technologies to measurably contribute to climate change mitigation. Jessika Trancik, Associate Professor of Energy Studies at the Massachusetts Institute of Technology (MIT) in Cambridge, USA, uses the case example of photovoltaic technology to uncover the key determinants of innovation from the formulation of policy to the design of technologies. She explains the feedback of emission reduction and the practical lessons that emerge for engineers and policy makers alike. Considering Different Types of Learning in Low-Carbon Innovation Policy Recent empirical studies demonstrate that innovation patterns and technological learning can differ strongly between energy technologies. Fostering low-carbon innovation may thus require technology-specific policy interventions. Tobias Schmidt, Assistant Professor of Energy Politics at ETH Zurich, Switzerland compares photovoltaics (PV), wind and lithium-ion battery storage technologies in relation to the locus of innovation in the industry value chain, learning feedback, and type of innovation. He relates his observations to technology architecture and production processes deriving implications for other energy technologies. Based on these analyses, Schmidt makes recommendations for the design of policy portfolios to accelerate innovation in clean energy. Masaru Yarime, Associate Professor at the School of Energy and Environment, City University in Hong Kong presents case studies from Japan and the U.S. on how low-carbon energy technologies can be implemented within the larger systems of smart cities. Their implementation calls for the promotion and integration of a variety of innovations in the electronic, housing, automotive, and infrastructure sectors. This requires collaboration and coordination with relevant stakeholders in academia, industry, government, and civil society. Yarime examines smart city projects with policy implications for platform creation, technological development, and end-user engagement. Explore further: Fiscal incentives may help reduce carbon emissions in developing countries


Wu W.,Wuhan University | Wu W.,City University of Hong Kong | Jiang C.,Wuhan University | Roy V.A.L.,City University of Hong Kong
Nanoscale | Year: 2015

Photocatalytic degradation of toxic organic pollutants is a challenging tasks in ecological and environmental protection. Recent research shows that the magnetic iron oxide-semiconductor composite photocatalytic system can effectively break through the bottleneck of single-component semiconductor oxides with low activity under visible light and the challenging recycling of the photocatalyst from the final products. With high reactivity in visible light, magnetic iron oxide-semiconductors can be exploited as an important magnetic recovery photocatalyst (MRP) with a bright future. On this regard, various composite structures, the charge-transfer mechanism and outstanding properties of magnetic iron oxide-semiconductor composite nanomaterials are sketched. The latest synthesis methods and recent progress in the photocatalytic applications of magnetic iron oxide-semiconductor composite nanomaterials are reviewed. The problems and challenges still need to be resolved and development strategies are discussed. This journal is © The Royal Society of Chemistry.


Tan C.W.,City University of Hong Kong | Friedland S.,University of Illinois at Chicago | Low S.H.,California Institute of Technology
IEEE Journal on Selected Areas in Communications | Year: 2011

Spectrum management is used to improve performance in multiuser communication system, e.g., cognitive radio or femtocell networks, where multiuser interference can lead to data rate degradation. We study the nonconvex NP-hard problem of maximizing a weighted sum rate in a multiuser Gaussian interference channel by power control subject to affine power constraints. By exploiting the fact that this problem can be restated as an optimization problem with constraints that are spectral radii of specially crafted nonnegative matrices, we derive necessary and sufficient optimality conditions and propose a global optimization algorithm based on the outer approximation method. Central to our techniques is the use of nonnegative matrix theory, e.g., nonnegative matrix inequalities and the Perron-Frobenius theorem. We also study an inner approximation method and a relaxation method that give insights to special cases. Our techniques and algorithm can be extended to a multiple carrier system model, e.g., OFDM system or receivers with interference suppression capability. © 2006 IEEE.


Tan C.W.,City University of Hong Kong | Chiang M.,Princeton University | Srikant R.,Urbana University
IEEE Transactions on Signal Processing | Year: 2011

Maximizing the minimum weighted signal-to-interference-and-noise ratio (SINR), minimizing the weighted sum mean-square error (MSE) and maximizing the weighted sum rate in a multiuser downlink system are three important performance objectives in nonconvex joint transceiver and power optimization, where all the users have a total power constraint. We show that, through connections with the nonlinear Perron-Frobenius theory, jointly optimizing power and beamformers in the max-min weighted SINR problem can be solved optimally in a distributed fashion. Then, connecting these three performance objectives through the arithmetic-geometric mean inequality and nonnegative matrix theory, we solve the weighted sum MSE minimization and the weighted sum rate maximization in the weak interference regimes using fast algorithms. In the general case, we first establish optimality conditions to the weighted sum MSE minimization and the weighted sum rate maximization problems and provide their further connection to the max-min weighted SINR problem. We then propose a distributed weighted proportional SINR algorithm that leverages our fast max-min weighted SINR algorithm to solve for local optimal solution of the two nonconvex problems, and give conditions under which global optimality is achieved. Numerical results are provided to complement the analysis. © 2011 IEEE.


Tan C.W.,City University of Hong Kong | Chiang M.,Princeton University | Srikant R.,Urbana University
IEEE/ACM Transactions on Networking | Year: 2013

In this paper, we consider a wireless network where interference is treated as noise, and we study the nonconvex problem of sum rate maximization by power control. We focus on finding approximately optimal solutions that can be efficiently computed to this NP-hard problem by studying the solutions to two related problems, the sum rate maximization using a signal-to-interference-plus- noise ratio (ssr SINR ) approximation and the max-min weighted ssr SINR optimization. We show that these two problems are intimately connected, can be solved efficiently by algorithms with fast convergence and minimal parameter configuration, and can yield high-quality approximately optimal solutions to sum rate maximization in the low interference regime. As an application of these results, we analyze the connection-level stability of cross-layer utility maximization in the wireless network, where users arrive and depart randomly and are subject to congestion control, and the queue service rates at all the links are determined by the sum rate maximization problem. In particular, we determine the stability region when all the links solve the max-min weighted ssr SINR problem, using instantaneous queue sizes as weights. © 1993-2012 IEEE.


Cao Z.,Wuhan University | Wang Y.,City University of Hong Kong
Structural Safety | Year: 2014

The inherent spatial variability of soils is one of the major sources of uncertainties in soil properties, and it can be characterized explicitly using random field theory. In the context of random fields, the spatial correlation between the values of a soil property concerned at different locations is represented by its correlation structure (i.e., correlation functions). How to select a proper correlation function for a particular site has been a challenging task, particularly when only a limited number of project-specific test results are obtained during geotechnical site characterization. This paper develops a Bayesian model comparison approach for selection of the most probable correlation function among a pool of candidates (e.g., single exponential correlation function, binary noise correlation function, second-order Markov correlation function, and squared exponential correlation function) for a particular site using project-specific test results and site information available prior to the project (i.e., prior knowledge, such as engineering experience and judgments). Equations are derived for the proposed Bayesian model comparison approach, in which the inherent spatial variability is modeled explicitly using random field theory. Then, the proposed method is illustrated and validated through simulated cone penetration test (CPT) data and four sets of real CPT data obtained from the sand site of the US National Geotechnical Experimentation Sites (NGES) at Texas A&M University. In addition, sensitivity studies are performed to explore the effects of prior knowledge, the measurement resolution (i.e., sampling interval), and data quantity (i.e., sampling depth) on selection of the most probable correlation function for soil properties. It is found that the proposed approach properly selects the most probable correlation function and is applicable for general choices of prior knowledge. The performance of the method is improved as the measurement resolution improves and the data quantity increases. © 2013 Elsevier Ltd.


Cai D.W.H.,California Institute of Technology | Quek T.Q.S.,Singapore University of Technology and Design | Tan C.W.,City University of Hong Kong | Low S.H.,California Institute of Technology
IEEE Transactions on Signal Processing | Year: 2012

This paper considers the max-min weighted signal-to-interference-plus-noise ratio (SINR) problem subject to multiple weighted-sum power constraints, where the weights can represent relative power costs of serving different users. First, we study the power control problem. We apply nonlinear Perron-Frobenius theory to derive closed-form expressions for the optimal value and solution and an iterative algorithm which converges geometrically fast to the optimal solution. Then, we use the structure of the closed-form solution to show that the problem can be decoupled into subproblems each involving only one power constraint. Next, we study the multiple-input-single-output (MISO) transmit beamforming and power control problem. We use uplink-downlink duality to show that this problem can be decoupled into subproblems each involving only one power constraint. We apply this decoupling result to derive an iterative subgradient projection algorithm for the problem. © 1991-2012 IEEE.


Sorooshyari S.,Bell LaboratoriesAlcatel Lucent | Tan C.W.,City University of Hong Kong | Chiang M.,Princeton University
IEEE/ACM Transactions on Networking | Year: 2012

The deployment of cognitive radio networks enables efficient spectrum sharing and opportunistic spectrum access. It also presents new challenges to the classical problem of interference management in wireless networks. This paper develops an axiomatic framework for power allocation in cognitive radio networks based on four goals: QoS protection to primary users, opportunism to secondary users, admissibility to secondary users, and autonomous operation by individual users. Two additional goals, licensing and versatility, which are desirable rather than essential, are also presented. A general class of Duo Priority Class Power Control (DPCPC) policies that satisfy such goals is introduced. Through theoretical analysis and simulation, it is shown that a specific interference-aware power-control algorithm reaches such goals. © 2012 IEEE.


Chen L.,Chinese University of Hong Kong | He S.,City University of Hong Kong | Zhang S.,University of Minnesota
Operations Research | Year: 2011

In this paper we develop tight bounds on the expected values of several risk measures that are of interest to us. This work is motivated by the robust optimization models arising from portfolio selection problems. Indeed, the whole paper is centered around robust portfolio models and solutions. The basic setting is to find a portfolio that maximizes (respectively, minimizes) the expected utility (respectively, disutility) values in the midst of infinitely many possible ambiguous distributions of the investment returns fitting the given mean and variance estimations. First, we show that the single-stage portfolio selection problem within this framework, whenever the disutility function is in the form of lower partial moments (LPM), or conditional value-at-risk (CVaR), or value-at-risk (VaR), can be solved analytically. The results lead to the solutions for single-stage robust portfolio selection models. Furthermore, the results also lead to a multistage adjustable robust optimization (ARO) solution when the disutility function is the second-order LPM. Exploring beyond the confines of convex optimization, we also consider the so-called S-shaped value function, which plays a key role in the prospect theory of Kahneman and Tversky. The nonrobust version of the problem is shown to be NP-hard in general. However, we present an efficient procedure for solving the robust counterpart of the same portfolio selection problem. In this particular case, the consideration of the robustness actually helps to reduce the computational complexity. Finally, we consider the situation whereby we have some additional information about the chance that a quadratic function of the random distribution reaches a certain threshold. That information helps to further reduce the ambiguity in the robust model. We show that the robust optimization problem in that case can be solved by means of semidefinite programming (SDP), if no more than two additional chance inequalities are to be incorporated. © 2011 INFORMS.


Sun Y.,Wuhan University | Fang Y.,City University of Hong Kong | Lim K.H.,City University of Hong Kong
Decision Support Systems | Year: 2012

This study aims to address two research gaps in prior studies on knowledge sharing in virtual communities (VCs). First, prior studies have focused on knowledge sharing VCs with no explicit reward system, but VCs sharing knowledge based on a competition-based reward system (e.g., transactional VCs) have not been explored. Second, prior related studies have concentrated on the determinants of initial participation in sharing knowledge rather than sustained participation despite there being important distinctions between these two stages of participation behavior. In this study, we focus on understanding sustained participation in knowledge sharing in transactional VCs by drawing on expectancy-value theory and a social learning process. Considering that a social learning process is involved in maintaining sustained participation, we propose that task complexity and self-efficacy - two social learning factors - moderate the relationship between motivation and sustained participation. A field survey with 205 subjects in a transactional virtual community was conducted to test the research model. According to the findings, extrinsic and intrinsic motivations significantly influence sustained participation intention. A negative interaction effect between extrinsic motivation and task complexity, as well as positive interaction effect between intrinsic motivation and self-efficacy, was also observed. A non-linear interaction effect between intrinsic motivation and task complexity was also found. Study implications and future research directions are also discussed. © 2012 Elsevier B.V. All rights reserved.


Leung P.C.M.,City University of Hong Kong | Leung P.C.M.,MTR Corporation | Lee E.W.M.,City University of Hong Kong
Applied Energy | Year: 2013

According to the records of Hong Kong rail operator, MTR Corporation, the weekly electrical consumption of each railway station ranges from 18. MWh to 230. MWh. Since the electrical consumption of stations is a major factor in the planning of infrastructure, a good prediction of the electrical consumption will greatly assist in the design of the station infrastructure. This study develops an intelligent approach to predict the energy consumption of railway stations. Multi-layered Perceptron (MLP) is adopted to mimic the non-linear correlation between energy consumption, the spatial design of the station, meteorological factors and also the usage of the 19 stations selected. Coefficient of correlation is obtained between the MLP predicted results and the actual collected data to evaluate the performance of the prediction. We apply statistical approach to assess the performance of the developed MLP model. It shows that minimum coefficient of correlation is 0.96 with a 95% confidence level which is considered sufficient for engineering application. This approach is also adopted to predict the profile of the weekly electrical consumption of a selected station. The predicted profile reasonably agrees with that of the actual consumption. This study develops a useful tool to estimate the electrical power consumption of new MTR stations. © 2012 Elsevier Ltd.


Au S.-K.,City University of Hong Kong | To P.,Arup
Journal of Structural Engineering (United States) | Year: 2012

This paper presents work on validating the dynamic wind load predicted by a wind tunnel model with the values identified from full-scale field vibration data of a super-tall building in Hong Kong. Dynamic wind load in this work refers to the power spectral density (PSD) of the modal force near the natural frequency of a particular mode of the building, in the context of random vibration with stationary loading and response. This quantity reflects the turbulence characteristics integrated over the building body and is of importance in wind engineering design. This study presents a method to predict the modal PSD of wind load of the first two translational modes of a tall building. The method combines wind tunnel test information and mean wind data available in the free field; the latter taken to be at the Waglan Island station maintained by the Hong Kong Observatory. On the full-scale side, although the modal PSD is not directly observable, it is identified from field vibration data measured at the building top during strong wind events. A Bayesian modal identification method is used for determining the most probable value and the uncertainty of the modal parameters including the natural frequency, damping ratio, and the modal PSD. A number of recent strong wind events are analyzed. Reasonable agreement is observed between the wind tunnel model predictions and the values identified from field data. Factors that can potentially lead to discrepancy are discussed. As the same random vibration modeling consistent with conventional wind engineering design has been used in the wind tunnel prediction model and field identification model, the results are directly transferable among these three disciplines. © 2012 American Society of Civil Engineers.


Cao Z.,Wuhan University | Cao Z.,City University of Hong Kong | Wang Y.,City University of Hong Kong
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014

This paper develops Bayesian approaches for facilitating the determination of characteristic (or nominal) values of geomaterial properties in geotechnical analysis and design when extensive testing cannot be performed, which is the case for a majority of geotechnical projects, particularly those of a small or medium size. These Bayesian approaches aim to characterize probabilistically the undrained shear strength, Su, of clay using a limited amount of liquidity index (LI) test data, and to provide a logical route to determine the characteristic values for analysis and design, particularly those using probability-based design codes. The proposed approaches include (1) a Bayesian model comparison approach that selects the most appropriate likelihood model, a key element in the Bayesian framework, using a limited number of LI data obtained from a specific project site, and (2) a Bayesian equivalent sample approach that uses the selected likelihood model, integrates the sound engineering judgment/local experience with the project-specific LI data, and transforms the integrated knowledge into a large number of equivalent samples using Markov chain Monte Carlo simulation. Conventional statistical analysis of the equivalent samples is subsequently performed to determine characteristic values of the Su profile. The proposed approaches use engineering judgment/local experience in a quantifiable and transparent manner and effectively tackle the difficulty of generating meaningful statistics and probability distributions of soil properties from a usually limited number of test data obtained during geotechnical site investigation. © 2014 American Society of Civil Engineers.


Kusiak A.,University of Iowa | Zhang Z.,City University of Hong Kong | Verma A.,State University of New York at Buffalo
Energy | Year: 2013

Recent developments in wind energy research including wind speed prediction, wind turbine control, operations of hybrid power systems, as well as condition monitoring and fault detection are surveyed. Approaches based on statistics, physics, and data mining for wind speed prediction at different time scales are reviewed. Comparative analysis of prediction results reported in the literature is presented. Studies of classical and intelligent control of wind turbines involving different objectives and strategies are reported. Models for planning operations of different hybrid power systems including wind generation for various objectives are addressed. Methodologies for condition monitoring and fault detection are discussed. Future research directions in wind energy are proposed. © 2013 Elsevier Ltd.


Yang L.,Xi'an University of Architecture and Technology | Yan H.,Xi'an University of Architecture and Technology | Yan H.,Henan Polytechnic University | Lam J.C.,City University of Hong Kong
Applied Energy | Year: 2014

Buildings account for about 40% of the global energy consumption and contribute over 30% of the CO2 emissions. A large proportion of this energy is used for thermal comfort in buildings. This paper reviews thermal comfort research work and discusses the implications for building energy efficiency. Predicted mean vote works well in air-conditioned spaces but not naturally ventilated buildings, whereas adaptive models tend to have a broader comfort temperature ranges. Higher indoor temperatures in summertime conditions would lead to less prevalence of cooling systems as well as less cooling requirements. Raising summer set point temperature has good energy saving potential, in that it can be applied to both new and existing buildings. Further research and development work conducive to a better understanding of thermal comfort and energy conservation in buildings have been identified and discussed. These include (i) social-economic and cultural studies in general and post-occupancy evaluation of the built environment and the corresponding energy use in particular, and (ii) consideration of future climate scenarios in the analysis of co- and tri-generation schemes for HVAC applications, fuel mix and the associated energy planning/distribution systems in response to the expected changes in heating and cooling requirements due to climate change. © 2013 Elsevier Ltd.


Provided are an artificial atom of a metamaterial by coiling up space, a metamaterial including the artificial element, and a device including the metamaterial. The artificial atom of the metamaterial by coiling up space includes a first coiling unit that coils up a first space and a second coiling unit that coils up a second space and that is connected with the first coiling unit.


Provided are an artificial atom of a metamaterial by coiling up space, a metamaterial including the artificial element, and a device including the metamaterial. The artificial atom of the metamaterial by coiling up space includes a first coiling unit that coils up a first space and a second coiling unit that coils up a second space and that is connected with the first coiling unit.


Cheung L.Y.G.,Arup | O'Sullivan C.,Imperial College London | Coop M.R.,City University of Hong Kong
International Journal of Rock Mechanics and Mining Sciences | Year: 2013

The Discrete Element Method was used to model the behaviour of two natural sandstones that are commonly used as analogues for oil reservoir sandstones. With a relatively large number of parameters needed to define the model and few micro-scale data on which to base them, a parametric study was first carried out to identify how each parameter affects the overall macroscopic behaviour. This study highlighted the importance of the load share between the particle contacts and the bonds. The model for the more strongly cemented sandstone was calibrated against the response observed at a single stress level and predictions at other stress levels were then found to be good. A second, more weakly cemented, sandstone was also modelled. It was found that while this sandstone had a very much lower cement content by weight, only minor modifications were needed to the bond strengths and the proportion of bonded contacts compared to the more strongly bonded material. This may be because of the failure to model the natural fabric of the sandstones. In general the post-peak regime was not modelled well, nor was the volumetric response, the latter as a result of the failure to achieve the in-situ porosities in the model. © 2013 .


Semenov A.A.,RAS Institute for Nuclear Research | Woo C.H.,City University of Hong Kong
Acta Materialia | Year: 2012

The application of phase-field modeling to void formation and growth under irradiation is analyzed. Here our focus is on the energy of the diffuse interfaces of the void system, which is customarily modeled by a Ginzburg-type gradient energy term with a parameterized coefficient. To correctly emulate the kinetics of void formation, the corresponding free-energy change is calibrated against the classical nucleation model, where the void-matrix boundary is well defined. We find that the gradient-energy coefficient may be conveniently treated as a constant independent of void size, even for voids down almost to the atomic size. We also find that the diffuse void interface in phase-field simulation has to be treated on an ultrafine spatial scale to reproduce the void energetic characteristics and growth behavior derived from the sharp boundary approach. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


News Article | September 27, 2016
Site: www.materialstoday.com

Materials Today is delighted to announce the launch of two new journals: Materials Today Chemistry and Materials Today Energy. These journals represent the latest addition to Elsevier’s Materials Today family; a growing collection of daughter titles, and an extended family of over 100 publications in materials sciences and related fields. Now open for submissions, Materials Today Chemistry and Materials Today Energy are multi-disciplinary journals focused on two of the largest and most exciting areas of materials science, and will publish high quality original research articles, short communications and reviews. The journals offer rapid review with expert advice, and maximum visibility of published articles via ScienceDirect and MaterialsToday.com. Leading the new energy focused title is Editor-in-Chief Professor Chun-Sing Lee from the City University of Hong Kong. "Our quality of living is closely related to how we can harvest, convert and store energy in an efficient, safe and clean manner. Although great progress in energy-related technologies has been achieved, more work is urgently needed; all of these technologies are closely related to the development of new materials” commented Prof Lee. “With extensive and increasing international research on advanced materials for energy applications, the editorial team expects to see high demand and rapid growth of Materials Today Energy over the next few years.” Meanwhile, Professor Xian-Zheng Zhang from Wuhan University China is at the helm of Materials Today Chemistry, as the Editor-in-Chief. Materials chemistry is one of the fastest developing areas of science, covering the application of chemistry-based techniques to the study of materials. Prof Zhang described his excitement at being involved in the new title; “I am delighted to be leading one of the two newest Materials Today journals. Materials Today Chemistry will provide researchers with a new forum for the discussion of ground breaking results in materials chemistry and related disciplines, and is expected to become one of the leading publications in the field." Alongside the extended family of journals, the new publications join Applied Materials Today, as well as the flagship Materials Today title, which is also undergoing some exciting changes - in addition to the dedicated proceedings journal Materials Today: Proceedings, and sound science publication Materials Today Communications. Materials Today Chemistry and Materials Today Energy are now open for the submission of high quality original research articles, short communications and reviews. For more information on the Materials Today family visit www.materialstoday.com/about.


Wang Y.-M.,Fuzhou University | Chin K.-S.,City University of Hong Kong
Information Sciences | Year: 2011

Eigenvector method (EM) is a well-known approach to deriving priorities from pairwise comparison matrices in the analytic hierarchy process (AHP), which requires the solution of a set of nonlinear eigenvalue equations. This paper proposes an approximate solution approach to the EM to facilitate its computation. We refer to the approach as a linear programming approximation to the EM, or LPAEM for short. As the name implies, the LPAEM simplifies the nonlinear eigenvalue equations as a linear programming for solution. It produces true weights for perfectly consistent pairwise comparison matrices. Numerical examples are examined to show the validity and effectiveness of the proposed LPAEM and its significant advantages over a recently developed linear programming method entitled LP-GW-AHP in rank preservation. © 2011 Elsevier Inc. All rights reserved.


Zhong W.,City University of Hong Kong | Lee C.K.,Hong Kong Polytechnic University | Ron Hui S.Y.,University of Hong Kong | Ron Hui S.Y.,Imperial College London
IEEE Transactions on Industrial Electronics | Year: 2013

In this paper, we present a brief overview of historical developments of wireless power and an analysis on the use of Tesla's resonators in domino forms for wireless power transfer. Relay resonators are spaced between the transmitter and receiver coils with the objectives of maximizing energy efficiency and increasing the overall transmission distance between the power source and the load. Analytical expressions for the optimal load and maximum efficiency at resonance frequency are derived. These equations are verified with practical measurements obtained from both coaxial and noncoaxial domino resonator systems. To avoid the use of high operating frequency for wireless power transfer in previous related research, the technique presented here can be used at submegahertz operation so as to minimize the power loss in both the power supply and the output stage. We demonstrated both theoretically and practically that unequal spacing for the coaxial straight domino systems has better efficiency performance than the equal-spacing method. Also, the flexibility of using resonators in various domino forms is demonstrated. © 2012 IEEE.


Cheung R.,University of South Australia | Vogel D.,City University of Hong Kong
Computers and Education | Year: 2013

Collaborative technologies support group work in project-based environments. In this study, we enhance the technology acceptance model to explain the factors that influence the acceptance of Google Applications for collaborative learning. The enhanced model was empirically evaluated using survey data collected from 136 students enrolled in a full-time degree program that used Google Applications to support project work. According to the research results, determinants of the technology acceptance model are the major factors influencing the adoption of the technology. In addition, the subjective norm represented by peers is found to significantly moderate the relationship between attitude and intention toward the technology. However, our results do not show a significant effect of subjective norms represented by instructors and mass media on students' intentions to use the technology. The ability to share information in the collaborative learning environment is found to influence intention and behavior toward the Google Applications platform. © 2012 Elsevier Ltd. All rights reserved.


Lo Yuk-Ping C.,University of Hong Kong | Thomas N.,City University of Hong Kong
Health Policy and Planning | Year: 2010

In the closing decade of the 20th century the myriad challenges posed by infectious disease in a globalized environment began to be re-conceptualized as threats to national and human security. The most widely applied model for identifying and responding to such threats is securitization theory, as proposed by the Copenhagen School. Although its analytical framework is generally accepted, its utility remains contested; especially in non-European and non-state settings. The papers in this special edition have several aims: (1) to analyse ways by which Asian states and international organizations have identified health challenges as security threats, (2) to draw upon the securitization model as a way of understanding the full extent to which these states and international organizations have responded to the health threat, and (3) to identify areas where the theory might be strengthened so as to provide greater analytical clarity in areas of health security. This paper acts as a broad introduction to a set of papers on 'Unhealthy governance' and explores some of the key findings from the subsequent papers. © The Author 2010; all rights reserved.


Wang Y.-M.,Fuzhou University | Chin K.-S.,City University of Hong Kong
Expert Systems with Applications | Year: 2011

Performance assessment often has to be conducted under uncertainty. This paper proposes a "fuzzy expected value approach" for data envelopment analysis (DEA) in which fuzzy inputs and fuzzy outputs are first weighted, respectively, and their expected values then used to measure the optimistic and pessimistic efficiencies of decision making units (DMUs) in fuzzy environments. The two efficiencies are finally geometrically averaged for the purposes of ranking and identifying the best performing DMU. The proposed fuzzy expected value approach and its resultant models are illustrated with three numerical examples, including the selection of a flexible manufacturing system (FMS). © 2011 Elsevier Ltd. All rights reserved.


Wang Y.-M.,Fuzhou University | Chin K.-S.,City University of Hong Kong
Information Sciences | Year: 2011

Quality function deployment (QFD) is a planning tool used in new product development and quality management. It aims at achieving maximum customer satisfaction by listening to the voice of customers. To implement QFD, customer requirements (CRs) should be identified and assessed first. The current paper proposes a linear goal programming (LGP) approach to assess the relative importance weights of CRs. The LGP approach enables customers to express their preferences on the relative importance weights of CRs in their preferred or familiar formats, which may differ from one customer to another but have no need to be transformed into the same format, thus avoiding information loss or distortion. A numerical example is tested with the LGP approach to demonstrate its validity, effectiveness and potential applications in QFD practice. © 2011 Elsevier Inc. All rights reserved.


La Grange A.,City University of Hong Kong | Pretorius F.,University of Hong Kong
Urban Studies | Year: 2016

The specificity of Hong Kong’s gentrification trajectory reflects its urban morphology, political institutions, and social and economic structure. While continuously renewing itself economically, much of the city’s inner urban area building stock is old and functionally obsolete, whilst nevertheless providing affordable, well-located housing for lower-income and disadvantaged groups and small-scale commercial clusters. Constrained redevelopment is not the result of economic decline but rather of formidable frictions that make land assembly and vacant possession of buildings difficult. Hong Kong’s executive-led, quasi democratic government articulates with the public ownership of land and its management through the leasehold system, and leads inner-city redevelopment through the Urban Renewal Authority (URA) supported by various institutional and statutory arrangements. (Re)development is favoured because it generates significant state revenue from physical and economic intensification of sites. Although gentrification is not an agenda of the URA, it is a significant outcome of its redevelopment activities. © 2014, © Urban Studies Journal Limited 2014.


Tao X.,City University of Hong Kong | Hui S.Y.R.,University of Hong Kong | Hui S.Y.R.,Imperial College London
IEEE Transactions on Industrial Electronics | Year: 2012

This paper presents a dynamic photoelectrothermal theory for light-emitting diode (LED) systems. In addition to photometric, electrical, and thermal aspects, this theory incorporates the time domain into the generalized equations. A dynamic model for a general LED system is developed for system analysis. This theory highlights the fact that the luminous output of an LED system will decrease with time from the initial operation to the steady state due to the rising temperature of the heat sink and the LED devices. The essential thermal time constants involved in the LED systems are explained. The time factor is critical in understanding how much the luminous output will decrease with time and is essential to the optimal designs of the LED systems that are operated continuously (e.g., general lighting) or momentarily (e.g., traffic lights). Experiments on several LED systems at different time frames have been conducted, and the practical measurements confirm the validity of this theory. © 2011 IEEE.


Chui W.H.,University of Hong Kong | Chan H.C.,City University of Hong Kong
Child Abuse and Neglect | Year: 2013

Objective: Macau is a Special Administrative Region (SAR) of China with over 95% of the population is of Chinese descent. Research on school bullying using Macanese samples is virtually nonexistent. Thus, this study is among the first to sample this population by exploring the association between bullying perpetration and victimization, and the level of self-control among a group of school-aged Macanese adolescents. Methods: A total of 365 participants, aged between 10 and 17 years, from two male-only schools (a boarding and a non-boarding schools) in Macau are surveyed. The Illinois Bully Scale (Espelage & Holt, 2001) and Self-Control Scale (Grasmick, Tittle, Bursik, & Arneklev, 1993) are used to measure the participants bullying behaviors and self-control level, respectively. Results: Overall finding indicates that bullying perpetration is negatively associated with the participants' level of self-control. Conclusion: These findings provide further support for the importance of self-control in bullying perpetration. Implications of the findings are offered by way to increase the youngsters' level of self-control in order to reduce their propensity to engage in bullying perpetration at school. © 2012 Elsevier Ltd.


Wong W.S.,City University of Hong Kong | Fielding R.,University of Hong Kong
Journal of Pain | Year: 2011

Western studies document the prevalence of chronic pain in the general adult population to be between 2 and 55%. Knowing the prevalence of chronic pain among Chinese populations provides important comparative perspective: To determine the prevalence of chronic pain in the general population of Hong Kong; evaluate the relationship of chronic pain with sociodemographic and lifestyle factors; and describe the pain characteristics among chronic pain sufferers. A total of 5,001 adults aged ≥18 years (response rate 58%) drawn from the general population of Hong Kong completed the Chronic Pain Grade (CPG) questionnaire, providing information on chronic pain and sociodemographic status using telephone interviews. Overall 34.9% reported pain lasting more than 3 months (chronic pain), having an average of 1.5 pain sites; 35.2% experienced multiple pain sites, most commonly of the legs, back, and head with leg and back being rated as the most significant pain areas among those with multiple pain problems. The CPG criteria classified 21.5% of those with chronic pain symptoms as Grade III or above. Fully adjusted stepwise regression analyses identified being female, older age, divorced/separated, having part-time employment, existing long-term health problems, higher HADS Anxiety scores, poor QoL (mental health component), and low self-perceived health to be significantly associated with chronic pain. Perspective: Our data evidenced that chronic pain is common in the general population of Hong Kong, and the prevalence is highest among women and middle-aged adults. © 2011 by the American Pain Society.


Wang Y.-M.,Fuzhou University | Chin K.-S.,City University of Hong Kong
Expert Systems with Applications | Year: 2010

Two-stage data envelopment analysis (DEA) has been researched by a number of authors. In a recent paper by Kao and Hwang (2008), the overall efficiency of two-stage process was defined as the product of the efficiencies of two individual stages. In a more recent paper by Chen, Cook, Li, and Zhu (2009), the overall efficiency of two-stage process was modeled as a weighted sum of the efficiencies of two individual stages. This paper looks into further two-stage DEA and proposes some alternative DEA models for two-stage process to show that (i) the overall efficiency of two-stage process can also be modeled as a weighted harmonic mean of the efficiencies of two individual stages; (ii) the two-stage DEA model of Kao and Hwang (2008) can be easily extended to variable returns to scale (VRS) assumption; and (iii) the additive efficiency decomposition model of Chen et al. (2009) can be generalized to taking into account the relative importance weights of two individual stages. Numerical illustrations are provided to show the potential applications of the proposed new DEA models. © 2010 Elsevier Ltd. All rights reserved.


Tam H.-y.,City University of Hong Kong | Cheng H.,Beijing Institute of Technology
Journal of Materials Processing Technology | Year: 2010

Uniformity of removal affects the finishing, and in some cases, the form accuracy of the polished surface. Tool paths are required for the automation of surface polishing. How the tool path may affect the removal of material in polishing is investigated in this paper. An analysis of how removal at a location due to polishing along adjacent path lines is presented. Four tool paths reportedly used in polishing are covered: scanning, bi-scanning, Hilbert and Peano paths. Removal in the inner surface as well as near the edges of surfaces is examined through simulations and analysis. The results show that, for the same path pitch, the peak-to-valley height (hpv) in the inner part of the removal map is the same for scanning, bi-scanning and Peano, while the texture of the removal maps can be quite different. The hpv values of Hilbert are more than double those of Peano, although both are fractal paths. Removal near the edges is particularly severe for scanning-type tool paths. The ratio of the edge peak height to the inner peak height is about 1.6 on average for scanning. The uniformity of removal further deteriorates as the ellipticity of the tool contact increases. When the contact direction is closely aligned with the path line direction, that ratio goes up to about 2.9 for contact ellipticity of 2. Polishing experiments have also been conducted. Both experiments and simulations point to the presence of edge effects in scanning paths and its absence in Peano paths. It is further proposed that, for more uniform removal of material: (1) changes in the tool path direction should be well distributed and (2) the direction of the path lines should be well balanced over the entire surface. Crown Copyright © 2010.


Gain A.K.,University of New South Wales | Chan Y.C.,City University of Hong Kong
Microelectronics Reliability | Year: 2014

Nano-sized, nonreacting, noncoarsening ZrO2 ceramic particles reinforced Sn-Ag-Cu composite solders were prepared by mechanically dispersing nano-particles into Sn-Ag-Cu solder and investigated their microstructure, kinetic analysis and mechanical properties i.e., shear strength, hardness and high temperature/mechanical damping characteristics. From microstructures evaluation, it was clear that composite solders containing ZrO2 ceramic nano-particles significantly impact on the formation of intermetallic compounds (IMCs) at their interfaces as well as refined microstructure in the solder ball regions. The growth behavior of IMCs layer at the interfaces in composite solders was lower than that of plain Sn-Ag-Cu solders. Moreover, after long time aging, some microcracks were clearly observed at the interface due to the formation of excessive IMC layer and softening nature of plain Sn-Ag-Cu solder joints. Mechanical properties i.e., shear strength, hardness and high temperature/mechanical damping characteristics were successfully investigated. The experimental results showed that composite solder joints exhibited higher hardness and shear strength as compared to the plain Sn-Ag-Cu solder joints. In addition, composite solder containing ZrO2 nano-particles exhibited lower damping capacity as compared with plain Sn-Ag-Cu solder due to fine microstructure and uniformly distributed ZrO2 nano-particles which increase the dislocation density. © 2014 Elsevier Ltd. All rights reserved.


Wang H.,University of Hong Kong | Leung D.Y.C.,University of Hong Kong | Leung M.K.H.,City University of Hong Kong
Applied Energy | Year: 2012

The aluminum energy conversion processes have been characterized to be carbon-free and sustainable. However, their applications are restrained by aluminum production capacity as aluminum is never found as a free metal on the earth. This study gives an assessment of typical aluminum-based energy processes in terms of overall energy efficiency and cost. Moreover, characteristics associated with different processes are identified. Results in this study indicate the route from which aluminum is produced can be a key factor in determining the efficiency and costs. Besides, the aluminum-air battery provides a more energy-efficient manner for the conversion of energy stored in primary aluminum and recovered aluminum from products compared to aluminum-based hydrogen production, whereas the aluminum-based hydrogen production gives a more energy-efficient way of utilizing energy stored in secondary aluminum or even scrap aluminum. © 2011 Elsevier Ltd.


Wong W.S.,City University of Hong Kong | Fielding R.,University of Hong Kong
Journal of Sleep Research | Year: 2011

Prevalence estimates of insomnia in western general populations are well documented, but population-based epidemiological data on insomnia in Chinese adults are scarce. The aims of the present study were to determine the prevalence of insomnia in the general population of Hong Kong, compare components of sleep disturbances and lifestyle factors stratified by sex, and identify risk factors for insomnia. Using a population-based cross-sectional design, a total of 5001 Chinese adults aged ≥18years completed a telephone interview on the Pittsburgh Sleep Quality Index (PSQI), Hospital Anxiety and Depression Scale (HADS) and measures of quality of life (QoL) indexed by Medical Outcomes Study 12-item Short-Form Health Survey (SF12), lifestyle and sociodemographic details. Insomnia was defined by a PSQI global score >5. The resultant weighted prevalence of insomnia was 39.4%, equivalent to 2.2 million affected adults in Hong Kong. Women reported significantly poorer component and global sleep quality (all P<0.05). Fully adjusted stepwise regression analyses identified non-full-time employment status, existing long-term health problems, alcohol consumption four to seven times per week, higher HADS scores, poor mental health component of QoL and low self-perceived health were associated significantly with insomnia (all P<0.05). Our results suggest that insomnia is highly prevalent among Hong Kong Chinese adults and is associated with frequent use of alcohol, poor mental health and QoL. © 2010 European Sleep Research Society.


Wang H.J.,University of Delaware | Zhao J.L.,City University of Hong Kong
Decision Support Systems | Year: 2011

In a globalized economic environment with volatile business requirements, continuous process improvement needs to be done regularly in various organizations. However, maintaining the consistency of workflow models under frequent changes is a significant challenge in the management of corporate information services. Unfortunately, few formal approaches are found in the literature for managing workflow changes systematically. In this paper, we propose an analytical framework for workflow change management through formal modeling of workflow constraints, leading to an approach called Constraint-centric Workflow Change Analytics (CWCA). A core component of CWCA is the formal definition and analysis of workflow change anomalies. We operationalize CWCA by developing a change anomaly detection algorithm and validate it in the context of procurement management. A prototype system based on an open-source rule engine is presented to provide a proof-of-concept implementation of CWCA. © 2011 Elsevier B.V. All rights reserved.


Xi Z.,University of New South Wales | Feng G.,City University of Hong Kong | Hesketh T.,University of New South Wales
IEEE Transactions on Fuzzy Systems | Year: 2011

This paper addresses piecewise sliding-mode control for Takagi-Sugeno (T-S) fuzzy models. A novel sliding-mode control (SMC) design approach is developed which is based on individual sliding surface in each local region of the T-S fuzzy systems. Conditions of existence of sliding mode in the associated region are given. The chattering effect around region boundaries is analyzed, and prevention of such chattering is discussed. Two illustrative examples are finally given to illustrate the effectiveness and performance of the proposed controller. © 2006 IEEE.


Gunawan C.,University of New South Wales | Teoh W.Y.,City University of Hong Kong | Marquis C.P.,University of New South Wales | Amal R.,University of New South Wales
ACS Nano | Year: 2011

The work investigates the source of toxicity of copper oxide nanoparticles (CuO NPs) with respect to its leaching characteristic and speciation. Complexation-mediated leaching of CuO NPs by amino acids was identified as the source of toxicity toward Escherichia coli, the model microorganism used in the current study. The leached copper-peptide complex induces a multiple-fold increase in intracellular reactive oxygen species generation and reduces the fractions of viable cells, resulting in the overall inhibition of biomass growth. The cytotoxicity of the complex leachate is however different from that of equivalent soluble copper salts (nitrates and sulfates). A pH-dependent copper speciation during the addition of copper salts gives rise to uncoordinated copper ions, which in turn result in greater toxicity and cell lysis, the latter of which was not observed for CuO NPs even at comparable pH. Since leaching did not occur with micrometer-sized CuO, no cytotoxicty effect was observed, thus highlighting the prominence of materials toxicity at the nanoscale. © 2011 American Chemical Society.


Xi Z.,University of New South Wales | Feng G.,City University of Hong Kong | Hesketh T.,University of New South Wales
IEEE Transactions on Fuzzy Systems | Year: 2011

This paper addresses the issue of piecewise integral sliding-mode control (ISMC) for the TakagiSugeno (TS) fuzzy systems. ISMC is chosen to stabilize the TS fuzzy system because of its superior capability in treating uncertainties. Individual integral sliding surfaces are designed in different operating regions of the TS fuzzy system. Conditions on the existence of the sliding mode in the associated region are given. The chattering phenomenon around region boundaries is analyzed, and the prevention of such chattering is discussed. An illustrative example is finally given to show the efficiency of the proposed method. © 2006 IEEE.


Teoh W.Y.,City University of Hong Kong | Scott J.A.,University of New South Wales | Amal R.,University of New South Wales
Journal of Physical Chemistry Letters | Year: 2012

The field of heterogeneous photocatalysis has expanded rapidly in the last four decades, having undergone various evolutionary phases related to energy and the environment. The two most significant applications of photocatalysis are geared toward solar water splitting and the purification of air and water. Notably, the interdisciplinary nature of the field has increased significantly, incorporating semiconductor physics, surface sciences, photo and physical chemistry, materials science, and chemical engineering. Whereas this forms the basis on which the field continues to grow, adequate bridging of multidisciplinary knowledge remains essential. By recalling some of the classical fundamentals of photocatalysis, this Perspective provides contemporary views on heterogeneous photochemical conversion, encompassing charge transport characteristics, radical chemistry and organic degradation mechanisms, photocatalyst design, and photoreactor engineering. © 2012 American Chemical Society.


Yuen A.N.Y.,University of Hong Kong | Ho S.M.Y.,City University of Hong Kong | Chan C.K.Y.,University of Hong Kong
Psycho-Oncology | Year: 2014

Objective This study aimed to examine the effects of dispositional hope on psychopathology as well as self-perceived positive change in childhood cancer survivors through the potential mediation of cancer-related ruminations. Methods A cross-sectional design was used, and a group of childhood cancer survivors (N = 89; mean age = 23.2 years; age range = 17.2-31.3 years) were studied. Dispositional hope level was measured by the Hope Scale; positive and negative cancer-related ruminations were assessed by the Chinese Cancer-related Rumination Scale; depression symptoms were measured by Beck Depression Inventory; and anxiety symptoms were measured by Beck Anxiety Inventory. Positive adjustment outcome of posttraumatic growth (PTG) was assessed by the Chinese Post-traumatic Growth Inventory. Multiple regressions were used to analyze the relationship between dispositional hope and the outcome variables of PTG, anxiety and depression and the potential mediators of positive and negative cancer-related rumination. Results Dispositional hope was positively related to PTG, and the correlation was specifically mediated by positive cancer-related rumination. Dispositional hope also correlated with lower levels of depression and anxiety, specifically mediated by negative cancer-related rumination. Conclusion The present finding supported hope as a significant positive factor for childhood cancer survivors, which was associated with PTG and better psychological adjustment. The findings may inform development of therapeutic intervention programs aimed at increasing childhood cancer patients' hope levels, which may be correlated with more positive cancer-related thoughts and better adjustment. The present study, which examined survivors diagnosed at young age, may enrich existing studies on the effect of onset age and adjustment outcomes. Copyright © 2013 John Wiley & Sons, Ltd.


Zhong W.X.,City University of Hong Kong | Lee C.K.,University of Hong Kong | Hui S.Y.R.,University of Hong Kong | Hui S.Y.R.,Imperial College London
IEEE Transactions on Power Electronics | Year: 2012

In this paper, a general analysis on wireless power domino-resonator systems with noncoaxial axes is presented. The mathematical formulation established can in principle be used to analyze wireless resonator systems with various domino forms. In this study, it is used to analyze and evaluate wireless domino-resonator systems with circular structures because such structures have more than one main power flow paths and have not been analyzed previously. Based on the superposition method, individual power flow paths are analyzed and then their interactions are emerged and explained with vector diagrams. Unlike the resonator pair used by Tesla, it is demonstrated that optimization of the domino systems can be achieved under "nonresonance frequency" operation and optimal load conditions. The shift of the optimal frequency from the resonance frequency is due to the multiple power flow paths. The theoretical results have been favorably verified with practical measurements obtained from two circular systems. © 2012 IEEE.


Lee C.K.,University of Hong Kong | Zhong W.X.,City University of Hong Kong | Hui S.Y.R.,University of Hong Kong | Hui S.Y.R.,Imperial College London
IEEE Transactions on Power Electronics | Year: 2012

In this paper, the effects of the magnetic coupling of nonadjacent resonators on the optimal frequency of wireless power transfer are addressed. A power analysis has been carried out to identify the adjacent and nonadjacent power flow components. It is found that such cross-coupling effects of nonadjacent resonators would cause the maximum efficiency operation to slightly shift away from the resonance frequency of the resonators. Theoretical reasons for such phenomena are provided and experimentally confirmed with practical measurements in a wireless power transfer system comprising several magnetically coupled resonators arranged in a straight domino form. © 2011 IEEE.


Chung C.Y.-S.,University of Hong Kong | Li S.P.-Y.,City University of Hong Kong | Louie M.-W.,City University of Hong Kong | Lo K.K.-W.,City University of Hong Kong | Yam V.W.-W.,University of Hong Kong
Chemical Science | Year: 2013

Water-soluble alkynylplatinum(ii) terpyridine complexes, [Pt{tpy(C 6H4CH2NMe3-4)-4′}(C≡C- Ar)](OTf)2 [Ar = C6H3-(OH)2-3,5 (1), C6H4OH-4 (2), C6H3-(OMe) 2-3,5 (3)], have been synthesized and characterized. The photophysical and electrochemical properties of the complexes have been studied. Complex 1 has been found to undergo aggregation at low pHs, leading to metal-metal and/or π-π interactions and the emergence of a triplet metal-metal-to-ligand charge transfer (3MMLCT) emission in the near-infrared (NIR) region, the intensity of which has been enhanced 1350-fold over that at physiological pH. Such 'switchable' NIR emission of complex 1 was employed in cell-imaging experiments. The pH response of the 3MMLCT emission of complex 1 in cellular compartments has been studied using experiments with fixed Madin-Darby canine kidney (MDCK) cells, while live cell-imaging experiments revealed that complex 1 could function as a NIR luminescent probe for the tracking of the location of acidic organelles such as lysosomes. © 2013 The Royal Society of Chemistry.


Wang Y.-M.,Fuzhou University | Chin K.-S.,City University of Hong Kong
International Journal of Production Economics | Year: 2010

Cross-efficiency evaluation is an effective method for ranking decision-making units (DMUs) in data envelopment analysis (DEA) and can be performed with different formulations (aggressive or benevolent), secondary goals, and models. This paper proposes some new alternative models for DEA cross-efficiency evaluation to provide more methodological options for the decision maker (DM) to choose from. The proposed new alternative models are illustrated with two numerical examples. The results are believed to be more realistic than those obtained by the alternative secondary goals suggested by Liang et al. [Liang, L., Wu, J., Cook, W.D. and Zhu, J., 2008a. Alternative secondary goals in DEA cross-efficiency evaluation. International Journal of Production Economics 113 (2), 10251030]. © 2010 Elsevier B.V.All rights reserved.


Zhao L.,PLA Fourth Military Medical University | Liu L.,PLA Fourth Military Medical University | Wu Z.,PLA Fourth Military Medical University | Zhang Y.,PLA Fourth Military Medical University | Chu P.K.,City University of Hong Kong
Biomaterials | Year: 2012

Micro/nanotopographical modification of biomaterials constitutes a promising approach to direct stem cell osteogenic differentiation to promote osseointegration. In this work, titania nanotubes (NTs) 25 and 80nm in size with the acid-etched Ti topography (AcidTi) and hierarchical hybrid micropitted/nanotubular topographies (Micro/5VNT and Micro/20VNT) are produced to mimic the structure of the natural bone extracellular matrix (ECM). The effects on bone mesenchymal stem cell (MSC) osteogenic differentiation are studied systematically by various microscopic and biological characterization techniques. Cell adhesion is assayed by nucleus fluorescence staining and cell proliferation is studied by CCK-8 assay and fl{ligature}ow cytometry. Osteogenic differentiation is assayed by alkaline phosphatase (ALP) expression, collagen secretion, matrix mineralization, and quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis on the osteogenesis related gene expression. All the topographies are observed to induce MSC osteogenic differentiation in the absence of osteogenic supplements. The nanotube surfaces significantly promote cell attachment and spread, collagen secretion and ECM mineralization, as well as osteogenesis-related gene expression. Among them, Micro/20VNT shows the best ability to simultaneously promote MSC proliferation and osteogenic differentiation. Our results unambiguously demonstrate their excellent ability to support MSC proliferation and induce MSC osteogenic differentiation, especially those with the micropitted topography. © 2011 Elsevier Ltd.


Wang Y.-M.,Fuzhou University | Chin K.-S.,City University of Hong Kong
Computers and Mathematics with Applications | Year: 2011

Fuzzy quality function deployment (QFD) has been extensively used for translating customer requirements (CRs) into product design requirements (DRs) in fuzzy environments. Existing approaches, however, for rating technical importance of DRs in fuzzy environments are found problematic, either incorrect or inappropriate. This paper investigates how the technical importance of DRs can be correctly rated in fuzzy environments. A pair of nonlinear programming models and two equivalent pairs of linear programming models are developed, respectively, to rate the technical importance of DRs. The developed models are examined and illustrated with two numerical examples. © 2011 Elsevier Ltd. All rights reserved.


Wang Y.-M.,Fuzhou University | Chin K.-S.,City University of Hong Kong
International Journal of Approximate Reasoning | Year: 2011

Fuzzy analytic hierarchy process (AHP) proves to be a very useful methodology for multiple criteria decision-making in fuzzy environments, which has found substantial applications in recent years. The vast majority of the applications use a crisp point estimate method such as the extent analysis or the fuzzy preference programming (FPP) based nonlinear method for fuzzy AHP priority derivation. The extent analysis has been revealed to be invalid and the weights derived by this method do not represent the relative importance of decision criteria or alternatives. The FPP-based nonlinear priority method also turns out to be subject to significant drawbacks, one of which is that it may produce multiple, even conflict priority vectors for a fuzzy pairwise comparison matrix, leading to entirely different conclusions. To address these drawbacks and provide a valid yet practical priority method for fuzzy AHP, this paper proposes a logarithmic fuzzy preference programming (LFPP) based methodology for fuzzy AHP priority derivation, which formulates the priorities of a fuzzy pairwise comparison matrix as a logarithmic nonlinear programming and derives crisp priorities from fuzzy pairwise comparison matrices. Numerical examples are tested to show the advantages of the proposed methodology and its potential applications in fuzzy AHP decision-making. © 2010 Elsevier Inc. All rights reserved.


Chui W.H.,University of Hong Kong | Chan H.C.,City University of Hong Kong
Criminal Behaviour and Mental Health | Year: 2013

Background Little research has been conducted with Hong Kong juvenile probationers. Aims The goals of this study are to examine the psychological characteristics of 14- to 20-year-old male probationers and to test their relationship with broad types of offending - violent and nonviolent. Methods Participants were drawn from the only transitional housing facility for juvenile probationers aged 14-20 years. Offence types and numbers were rated from self-report. Various schedules were rated at interview with consenting young men to describe them in terms of eight psychological characteristics: self-esteem, life satisfaction, social bonding, positive affect, negative affect, impulsivity, pro-criminal attitude and self-perceived life problems. Results A total of 113 young men completed the assessment, 90% of those eligible. The average psychological profile of these young men was fairly typical for their communities. Pro-criminal attitudes, however, correlated with both main types of offending, whereas main affective state was differently associated. Predominantly, negative affect was associated with violent offending and predominantly positive affect with nonviolent offending. Conclusions Participants in this study generally reported higher levels of positive psychological well-being than in previous nondelinquent Chinese samples. Implications for practice and future research A case-control study comparing such offenders with nondelinquents is required to clarify these findings. A longitudinal design is now indicated to test the direction of relationships between psychological indicators and offending. These steps would be useful precursors to a service evaluation of probation hostels for young offenders. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.


Song K.,University of Electronic Science and Technology of China | Mo Y.,University of Electronic Science and Technology of China | Xue Q.,City University of Hong Kong | Fan Y.,University of Electronic Science and Technology of China
IEEE Transactions on Industrial Electronics | Year: 2014

Two new wideband four-way out-of-phase slotline power dividers are proposed in this paper. The half-wavelength slotlines are employed to construct the presented compact power dividers. Based on the proposed power-dividing circuit, a four-way power divider is implemented with compact size and simple structure. To obtain high isolation among the four output ports and good output impedance matching, another four-way out-of-phase slotline power divider with improved isolation performance is designed by introducing an air-bridge resistor and two slotlines with isolation resistors. The simulated and measured results of the proposed power dividers demonstrate reasonable performance of impedance matching, insertion loss, amplitude balancing, and isolation among the output ports. © 1982-2012 IEEE.


Wang W.-Q.,University of Electronic Science and Technology of China | Wang W.-Q.,City University of Hong Kong | So H.C.,City University of Hong Kong
IEEE Transactions on Signal Processing | Year: 2014

Different from conventional phased-array, which provides only angle-dependent beampattern, frequency diverse array (FDA) employs a small frequency increment across the antenna elements and results in a range-angle-dependent beampattern. This beampattern offers a potential to localize the targets in two dimensions in terms of slant ranges and azimuth angles. However, it is difficult to obtain the target location information from a standard FDA radar due to the couplings in range and angle responses. In this paper, we propose a transmit subaperturing scheme on the FDA radar for range and angle estimation of targets. The essence is to divide the FDA elements into multiple subarrays and optimize the transmit beamspace matrix with the use of convex optimization. We also discuss several practical issues for designing the FDA radar system parameters. Since the subarrays offer decoupled range and angle responses, the targets can be located using the beamspace-based multiple signal classification algorithm. The range and angle estimation performance is evaluated by comparing with the Cramér-Rao lower bound. © 1991-2012 IEEE.


Yang K.,Soochow University of China | Zhang S.,Soochow University of China | Zhang G.,Beijing University of Chemical Technology | Sun X.,Beijing University of Chemical Technology | And 2 more authors.
Nano Letters | Year: 2010

Although biomedical applications of carbon nanotubes have been intensively studied in recent years, its sister, graphene, has been rarely explored in biomedicine. In this work, for the first time we study the in vivo behaviors of nanographene sheets (NGS) with polyethylene glycol (PEG) coating by a fluorescent labeling method. In vivo fluorescence imaging reveals surprisingly high tumor uptake of NGS in several xenograft tumor mouse models. Distinctive from PEGylated carbon nanotubes, PEGylated NGS shows several interesting in vivo behaviors including highly efficient tumor passive targeting and relatively low retention in reticuloendothelial systems. We then utilize the strong optical absorbance of NGS in the near-infrared (NIR) region for in vivo photothermal therapy, achieving ultraefficient tumor ablation after intravenous administration of NGS and low-power NIR laser irradiation on the tumor. Furthermore, no obvious side effect of PEGylated NGS is noted for the injected mice by histology, blood chemistry, and complete blood panel analysis in our pilot toxicity study. Although a lot more efforts are required to further understand the in vivo behaviors and the long-term toxicology of this new type of nanomaterials, our work is the first success of using carbon nanomaterials for efficient in vivo photothermal therapy by intravenous administration and suggests the great promise of graphene in biomedical applications, such as cancer treatment. © 2010 American Chemical Society.


Prasarnphanich P.,Chulalongkorn University | Wagner C.,City University of Hong Kong
IEEE Transactions on Industrial Electronics | Year: 2011

This paper investigates the sustainability of a type of digital ecosystem, namely, knowledge-sharing communities built on the wiki model. Sustainability is hypothesized to result from the participation of contributors with varying levels of resources and interests. The differences in resources and interests, according to the critical-mass theory, enable such communities to overcome typical start-up and growth problems. This paper describes a preliminary empirical test of the critical-mass theory in this context, with Wikipedia as a test case that demonstrates sustainability as well as resource and interest heterogeneity, based on a survey of 78 Wikipedians. The characteristic patterns of success exhibited in Wikipedia are expected to inform the management of other wiki-based information assets. © 2009 IEEE.


Duan L.,Singapore University of Technology and Design | Huang J.,Chinese University of Hong Kong | Shou B.,City University of Hong Kong
IEEE Transactions on Mobile Computing | Year: 2012

This paper presents a comprehensive analytical study of two competitive secondary operators' investment (i.e., spectrum leasing) and pricing strategies, taking into account operators' heterogeneity in leasing costs and users' heterogeneity in transmission power and channel conditions. We model the interactions between operators and users as a three-stage dynamic game, where operators simultaneously make spectrum leasing decisions in Stage I, and pricing decisions in Stage II, and then users make purchase decisions in Stage III. Using backward induction, we are able to completely characterize the dynamic game's equilibria. We show that both operators' investment and pricing equilibrium decisions process interesting threshold properties. For example, when the two operators' leasing costs are close, both operators will lease positive spectrum. Otherwise, one operator will choose not to lease and the other operator becomes the monopolist. For pricing, a positive pure strategy equilibrium exists only when the total spectrum investment of both operators is less than a threshold. Moreover, two operators always choose the same equilibrium price despite their heterogeneity in leasing costs. Each user fairly achieves the same service quality in terms of signal-to-noise ratio (SNR) at the equilibrium, and the obtained predictable payoff is linear in its transmission power and channel gain. We also compare the duopoly equilibrium with the coordinated case where two operators cooperate to maximize their total profit. We show that the maximum loss of total profit due to operators' competition is no larger than 25 percent. The users, however, always benefit from operators' competition in terms of their payoffs. We show that most of these insights are robust in the general SNR regime. © 2012 IEEE.


Zhang H.,City University of Hong Kong | Lewis F.L.,University of Texas at Arlington | Qu Z.,University of Central Florida
IEEE Transactions on Industrial Electronics | Year: 2012

This paper presents three design techniques for cooperative control of multiagent systems on directed graphs, namely, Lyapunov design, neural adaptive design, and linear quadratic regulator (LQR)-based optimal design. Using a carefully constructed Lyapunov equation for digraphs, it is shown that many results of cooperative control on undirected graphs or balanced digraphs can be extended to strongly connected digraphs. Neural adaptive control technique is adopted to solve the cooperative tracking problems of networked nonlinear systems with unknown dynamics and disturbances. Results for both first-order and high-order nonlinear systems are given. Two examples, i.e., cooperative tracking control of coupled Lagrangian systems and modified FitzHugh-Nagumo models, justify the feasibility of the proposed neural adaptive control technique. For cooperative tracking control of the general linear systems, which include integrator dynamics as special cases, it is shown that the control gain design can be decoupled from the topology of the graphs, by using the LQR-based optimal control technique. Moreover, the synchronization region is unbounded, which is a desired property of the controller. The proposed optimal control method is applied to cooperative tracking control of two-mass-spring systems, which are well-known models for vibration in many mechanical systems. © 2012 IEEE.


Dou F.F.,University of Electronic Science and Technology of China | Hon Y.C.,City University of Hong Kong
Engineering Analysis with Boundary Elements | Year: 2014

Based on kernel-based approximation technique, we devise in this paper an efficient and accurate numerical scheme for solving a backward problem of time-fractional diffusion equation (BTFDE). The kernels used in the approximation are the fundamental solutions of the time-fractional diffusion equation which can be expressed in terms of the M-Wright functions. To stably and accurately solve the resultant highly ill-conditioned system of equations, we successfully combine the standard Tikhonov regularization technique and the L-curve method to obtain an optimal choice of the regularization parameter and the location of source points. Several 1D and 2D numerical examples are constructed to demonstrate the superior accuracy and efficiency of the proposed method for solving both the classical backward heat conduction problem (BHCP) and the BTFDE. © 2013 Elsevier Ltd. All rights reserved.


Zhang H.,University of Electronic Science and Technology of China | Zhong H.,University of Electronic Science and Technology of China | Dang C.,City University of Hong Kong
IEEE Transactions on Fuzzy Systems | Year: 2012

This paper is concerned with the problem of delay-dependent H∞ filter design for a class of discrete-time nonlinear interconnected system with time-varying delays via the Takagi-Sugeno (T-S) fuzzy model. The T-S fuzzy model consists of N time-delay T-S fuzzy subsystems, and a decentralized H∞ filter is designed for each subsystem. Based on the delay-dependent piecewise Lyapunov-Krasovskii functional (DDPLKF) and with an improved free-weighting matrix technique, the delay-dependent stability and a prescribed H∞ performance index are guaranteed for the overall filtering error system. A sufficient condition for the existence of such a filter is established by using linear matrix inequalities (LMIs) that are numerically feasible. Two numerical examples are given to demonstrate the effectiveness and advantage of the proposed approach. © 2012 IEEE.


Zhang J.,Beijing University of Chemical Technology | Feng G.,City University of Hong Kong
Automatica | Year: 2014

This paper concerns the problem of event-driven observer-based output feedback control of linear systems. Contrary to normal sampled-data control systems, where the controller is updated periodically, in event-driven systems, it is updated only when an "event" happens, and a typical event is defined as some error signals exceeding a given threshold. Both continuous- and discrete-time event detector cases are considered. It is shown that even with the significantly reduced sampling frequency, the global uniform ultimate boundedness of the event-driven closed-loop systems can also be guaranteed. A numerical example is finally used to illustrate the effectiveness and advantages of the proposed approaches. © 2014 Elsevier Ltd. All rights reserved.


Dou F.F.,University of Electronic Science and Technology of China | Hon Y.C.,City University of Hong Kong
Engineering Analysis with Boundary Elements | Year: 2012

We investigate in this paper a Cauchy problem for the time-fractional diffusion equation (TFDE). Based on the idea of kernel-based approximation, we construct an efficient numerical scheme for obtaining the solution of a Cauchy problem of TFDE. The use of M-Wright functions as the kernel functions for the approximation space allows us to express the solution in terms of M-Wright functions, whose numerical evaluation can be accurately achieved by applying the inverse Laplace transform technique. To handle the ill-posedness of the resultant coefficient matrix due to the noisy Cauchy data, we adapt the standard Tikhonov regularization technique with the L-curve method for obtaining the optimal regularization parameter to give a stable numerical reconstruction of the solution. Numerical results indicate the efficiency and effectiveness of the proposed scheme. © 2012 Elsevier Ltd. All rights reserved.


He Y.,Soochow University of China | Fan C.,CAS Shanghai Institute of Applied Physics | Lee S.-T.,Soochow University of China | Lee S.-T.,City University of Hong Kong
Nano Today | Year: 2010

There has been rapidly increasing interest in design and synthesis of siliconbased nanostructured materials for bioapplications. In this review, we focus on recent research progress in design, synthesis and bioapplications of two silicon-based nanostructures, zero-dimensional silicon quantum dots and one-dimensional silicon nanowires. These two low-dimensional silicon nanomaterials have found important applications in ultrasensitive biomolecular detection and fluorescent cellular imaging. We further highlight major challenges and promises in this area. © 2010 Elsevier Ltd.


Duan L.,Singapore University of Technology and Design | Huang J.,Chinese University of Hong Kong | Shou B.,City University of Hong Kong
IEEE Transactions on Mobile Computing | Year: 2013

Femtocells can effectively resolve the poor connectivity issue of indoor cellular users. This paper investigates the economic incentive for a cellular operator to add femtocell service on top of its existing macrocell service. We model the interactions between a cellular operator and users as a Stackelberg game: The operator first determines spectrum allocations and pricings of femtocell and macrocell services, and then heterogeneous users choose between the two services and the amount of resource to request. In the ideal case where the femtocell service has the same full spatial coverage as the macrocell service, we show that the operator will choose to provide femtocell service only, as this leads to a better user quality of service and a higher operator profit. However, if we impose the constraint that no users' payoffs decrease after introducing the femtocell service, then the operator will always continue providing the macrocell service (with or without the femtocell service). Furthermore, we study the impact of operational cost, limited coverage, and spatial reuse on femtocell service provision. As the operational cost increases, fewer users are served by femtocell service and the operator's profit decreases. When the femtocell service has limited spatial coverage, the operator always provides the macrocell service beside the femtocell service. However, when the coverage is high or the total resource is low, the operator will set the prices such that all users who can access femtocell will choose to use the femtocell service only. Finally, spatial reuse of spectrum will increase the efficiency of femtocell services and gives the operator more incentives to allocate spectrum to femtocells. © 2002-2012 IEEE.


Song K.,University of Electronic Science and Technology of China | Xue Q.,City University of Hong Kong
IEEE Transactions on Industrial Electronics | Year: 2013

A novel ultrawideband (UWB) ring-cavity multiple-way parallel power divider is presented in this paper. The approximated equivalent-circuit model of the power-dividing unit is presented to analyze its structural parameters and electrical performance. The overall circuit model of the proposed power divider is also given. To verify its potential to accommodate large numbers of power-dividing ports, a UWB 32-way ring-cavity power divider is developed with reasonable agreement between the simulated and measured results. The measured return loss is greater than 10 dB over the entire UWB and also greater than 15 dB from 4.2 to 9.2 GHz. The average insertion loss, amplitude imbalance, phase imbalance, and group delay are around 15.4 dB (including the 15-dB power-dividing insertion loss), ±0.7 dB, ±5° , and 0.85 ns, respectively, across the UWB. In addition, the isolations between the output ports are greater than 10 dB over the UWB except for those between the adjacent output ports. © 1982-2012 IEEE.


Hu J.,University of Electronic Science and Technology of China | Feng G.,City University of Hong Kong
Asian Journal of Control | Year: 2011

This paper presents a study of a tracking control problem for a multiagent system with an active leader and quantized communication constraints. We first design a discrete-time distributed estimator-based tracking control for each follower-agent and analyze the tracking convergence with the help of the Riccati equation and common Lyapunov function when the communication channel is perfect and the interconnection topology is time-varying. Then a stochastic quantization strategy is applied to model the information communication in the agent coordination and the corresponding solution to the tracking control problem is also given. Finally, a numerical example is given to illustrate the tracking control algorithm. © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.


Lim C.W.,City University of Hong Kong | Xu X.S.,Dalian University of Technology
Applied Mechanics Reviews | Year: 2010

Many of the early works on symplectic elasticity were published in Chinese and as a result, the early works have been unavailable and unknown to researchers worldwide. It is the main objective of this paper to highlight the contributions of researchers from this part of the world and to disseminate the technical knowledge and innovation of the symplectic approach in analytic elasticity and applied engineering mechanics. This paper begins with the history and background of the symplectic approach in theoretical physics and classical mechanics and subsequently discusses the many numerical and analytical works and papers in symplectic elasticity. This paper ends with a brief introduction of the symplectic methodology. A total of more than 150 technical papers since the middle of 1980s have been collected and discussed according to various criteria. In general, the symplectic elasticity approach is a new concept and solution methodology in elasticity and applied mechanics based on the Hamiltonian principle with Legendre's transformation. The superiority of this symplectic approach with respect to the classical approach is at least threefold: (i) it alters the classical practice and solution technique using the semi-inverse approach with trial functions such as those of Navier, Ĺvy, and Timoshenko; (ii) it consolidates the many seemingly scattered and unrelated solutions of rigid body movement and elastic deformation by mapping with a series of zero and nonzero eigenvalues and their associated eigenvectors; and (iii) the Saint-Venant problems for plane elasticity and elastic cylinders can be described in a new system of equations and solved. A unique feature of this method is that bending of plate becomes an eigenvalue problem and vibration becomes a multiple eigenvalue problem. © 2010 American Society of Mechanical Engineers.


Hu J.,University of Electronic Science and Technology of China | Feng G.,City University of Hong Kong
Automatica | Year: 2010

In this paper, a distributed tracking control scheme with distributed estimators has been developed for a leader-follower multi-agent system with measurement noises and directed interconnection topology. It is supposed that each follower can only measure the relative positions of its neighbors in a noisy environment, including the relative position of the second-order active leader. A neighbor-based tracking protocol together with distributed estimators is designed based on a novel velocity decomposition technique. It is shown that the closed loop tracking control system is stochastically stable in mean square and the estimation errors converge to zero in mean square as well. A simulation example is finally given to illustrate the performance of the proposed control scheme. © 2010 Elsevier Ltd. All rights reserved.


Zuo Z.,Tianjin University | Zuo Z.,City University of Hong Kong | Ho D.W.C.,City University of Hong Kong | Wang Y.,Tianjin University
Automatica | Year: 2010

In this paper, the problem of robust fault tolerant control for a class of singular systems subject to both time-varying state-dependent nonlinear perturbation and actuator saturation is investigated. A sufficient condition for the existence of a fixed-gain controller is first proposed which guarantees the regularity, impulse-free and stability of the closed-loop system under all possible faults. An optimization problem with LMI constraints is formulated to determine the largest contractively invariant ellipsoid. An adaptive fault tolerant controller is then developed to compensate for the failure effects on the system by estimating the fault and updating the design parameter matrices online. Both of these two controllers are in the form of a saturation avoidance feedback with the advantage of relatively small actuator capacities compared with the high gain counterpart. An example is included to illustrate the proposed procedures and their effectiveness. © 2010 Elsevier Ltd. All rights reserved.


Zhu P.,Hunan University | Zhang L.W.,Shanghai Ocean University | Liew K.M.,City University of Hong Kong
Composite Structures | Year: 2014

A meshless local Petrov-Galerkin approach based on the moving Kriging interpolation technique is developed for geometrically nonlinear thermoelastic analysis of functionally graded plates in thermal environments (prescribed a temperature gradient or heat flux). The Kriging interpolation method makes the constructed shape functions possess Kronecker delta function property and thus special techniques for enforcing essential boundary conditions are avoided. In the thermal analysis, the dependency of thermal conductivity of functionally graded materials on temperature is involved, which gives rise to a nonlinear partial differential heat conduction equation. The nonlinear formulation of large deflection of the functionally graded plates is based on the first-order shear deformation plate theory in the von Kármán sense by taking small strains and moderate rotations into account. The incremental form of nonlinear equations is obtained by Taylor series expansion and the tangent stiffness matrix is explicitly developed in two different ways within the framework of the local meshless method. The nonlinear solutions are computed using the Newton-Raphson iteration method. Parametric and convergence studies are conducted to examine the stability of the proposed method and then several selected numerical examples are presented to demonstrate the accuracy and effectiveness of the method for nonlinear bending problems of functionally graded plates in thermal environments. © 2013 Elsevier Ltd.


Zhang L.W.,Shanghai Ocean University | Zhu P.,Hunan University | Liew K.M.,City University of Hong Kong
Composite Structures | Year: 2014

The mechanical and thermal buckling behaviors of ceramic-metal functionally grade plates (FGPs) were studied by using a local Kriging meshless method. The local meshless method was developed based on the local Petrov-Galerkin weak-form formulation combined with shape functions having the Kronecker delta function property, constructed by the Kriging interpolation. The cubic spline function of high continuity was used as the weight function to simplify the local weak form of governing equations with the integration on the internal boundaries vanishing. The transverse shear strains of FGPs were incorporated by employing the first-order shear deformation plate theory and plate material properties were assumed to change exponentially along the thickness direction. Convergence and comparison studies examined the stability and accuracy of the presented method. Two types of FGMs, Al/Al2O3 and Ti-6Al-4V/Aluminum oxide, were chosen for mechanical and thermal buckling analyses. The influences of volume fraction exponent, boundary condition, length-to-thickness ratio and loading type on the buckling behaviors of FGPs were discussed. © 2013 Elsevier Ltd.

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