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Nanyang Technological University is a young, research-intensive university in Singapore. It is one of the largest public universities in Singapore.NTU was inaugurated in 1991, originally as an English-medium technical and teaching college occupying the grounds of the former Nanyang University, a Chinese-medium university which had been consolidated into the National University of Singapore in 1980. Over the years, NTU has grown to become a full-fledged research university, and currently provides a high-quality global education to close to 33,000 undergraduate and postgraduate students. The student body includes top scholars and international olympiad medallists from the region and beyond. Hailing from more than 70 countries, the university's 4000-strong teaching and research staff also bring dynamic international perspectives and years of solid industry experience.In recent years, various college and university rankings have placed NTU amongst the top universities in Asia and beyond. In the 2014 QS World University Rankings, NTU is ranked 39th globally , and is placed 1st in the world among young universities according to the 2014 QS Top 50 Under 50. NTU's College of Engineering is also ranked 9th in the world according to the latest 2014 QS World University Rankings by Faculty. In the 2014 Times Higher Education World University Rankings, NTU is ranked at 61st globally . NTU's business school, Nanyang Business School, was rated 64th in the world by the Economist Intelligence Unit in 2013. Wikipedia.

Chen C.-M.,Nanyang Technological University
Energy Economics | Year: 2013

The paper reexamines non-additive environmental efficiency models with weakly-disposable undesirable outputs appeared in the literature of energy economics. These efficiency models are used in numerous studies published in this journal and other energy-related outlets. Recent studies, however, have found key limitations of the weak-disposability assumption in its application to environmental efficiency analysis. It is found that efficiency scores obtained from non-additive efficiency models can be non-monotonic in pollution quantities under the weak-disposability assumption - which is against common intuition and the principle of environmental economics. In this paper, I present taxonomy of efficiency models found in the energy economics literature and illustrate the above limitations and discuss implications of monotonicity from a practical viewpoint. Finally, I review the formulations for a variable returns-to-scale technology with weakly-disposable undesirable outputs, which has been misused in a number of papers in the energy economics literature. An application to evaluating the energy efficiencies of 23 European Union states is presented to illustrate the problem. © 2013 Elsevier B.V.

Wu J.,Nanyang Technological University | Rehg J.M.,Georgia Institute of Technology
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2011

CENsus TRansform hISTogram (CENTRIST), a new visual descriptor for recognizing topological places or scene categories, is introduced in this paper. We show that place and scene recognition, especially for indoor environments, require its visual descriptor to possess properties that are different from other vision domains (e.g., object recognition). CENTRIST satisfies these properties and suits the place and scene recognition task. It is a holistic representation and has strong generalizability for category recognition. CENTRIST mainly encodes the structural properties within an image and suppresses detailed textural information. Our experiments demonstrate that CENTRIST outperforms the current state of the art in several place and scene recognition data sets, compared with other descriptors such as SIFT and Gist. Besides, it is easy to implement and evaluates extremely fast. © 2011 IEEE.

Sun L.,Shenyang Jianzhu University | Huang W.M.,Nanyang Technological University
Soft Matter | Year: 2010

As recently demonstrated, after programming, thermo-responsive shape memory polymers can exhibit the multi-shape memory effect (SME) upon heating. In addition, it is confirmed that the temperature corresponding to the maximum recovery stress in constrained recovery is roughly the temperature at which pre-deformation is conducted, a phenomenon known as the temperature memory effect (TME). In this paper, we propose a framework to investigate the underlying mechanisms behind both effects and provide the conditions for the TME. According to this framework, we can achieve fully controllable shape recovery following a very complicated sequence in a continuous manner. © 2011 The Royal Society of Chemistry.

Kline K.A.,Nanyang Technological University | Bowdish D.M.E.,McMaster University
Current Opinion in Microbiology | Year: 2016

The global population is rapidly aging. Currently, 566 million people are ≥65 years old worldwide, with estimates of nearly 1.5 billion by 2050, particularly in developing countries. Infections constitute a third of mortality in people ≥65 years old. Moreover, lengthening life spans correlate with increased time in hospitals or long-term care facilities and exposure to drug-resistant pathogens. Indeed, the risk of nosocomial infections increases with age, independent of duration spent in healthcare facilities. In this review, we summarize our understanding of how the aging immune system relates to bacterial infections. We highlight the most prevalent infections affecting aging populations including pneumonia, urinary tract infections, and wound infections and make recommendations for future research into infection in aging populations. © 2015 Elsevier Ltd.

Muller F.,University of Birmingham | Tora L.,French Institute of Health and Medical Research | Tora L.,Nanyang Technological University
Biochimica et Biophysica Acta - Gene Regulatory Mechanisms | Year: 2014

One of the key events in eukaryotic gene regulation and consequent transcription is the assembly of general transcription factors and RNA polymerase II into a functional pre-initiation complex at core promoters. An emerging view of complexity arising from a variety of promoter associated DNA motifs, their binding factors and recent discoveries in characterising promoter associated chromatin properties brings an old question back into the limelight: how is a promoter defined? In addition to position-dependent DNA sequence motifs, accumulating evidence suggests that several parallel acting mechanisms are involved in orchestrating a pattern marked by the state of chromatin and general transcription factor binding in preparation for defining transcription start sites. In this review we attempt to summarise these promoter features and discuss the available evidence pointing at their interactions in defining transcription initiation in developmental contexts. This article is part of a Special Issue entitled: Chromatin and epigenetic regulation of animal development. © 2013 Elsevier B.V.

Bhattacharjya S.,Nanyang Technological University
Current Topics in Medicinal Chemistry | Year: 2016

Antimicrobial peptides (AMPs) establish the first line of host defense mechanism against invading microorganisms including bacteria, viruses, fungi and parasites. In recent years, emergence and spread of antibiotic resistance bacterial pathogens have dawn considerable interest in investigations of AMPs. The ability of AMPs to exert lethality against multiple drug-resistant (MDR) bacteria has incited promising avenues for antibiotic development. As a mode of action, most AMPs perturb the membrane organization of bacterial cells. The outer membrane lipopolysaccharide (LPS) of Gramnegative bacteria establishes a superior permeability barrier, in contrast to the peptidoglycan layer of Gram-positive bacteria. Due to LPS barrier, development of antibiotics for drug resistant Gram- negative bacteria are more complicated, with only fewer compounds in the pipeline. Recent studies have demonstrated that LPS actively regulate mode of action of AMPs on the lethality of Gram-negative bacteria. LPS, also known as endotoxin, is the primary agent for septic shock syndromes in intensive care unit killing over 120,000 people in the USA. Currently, anti-sepsis therapies are greatly lacking. Therefore, LPS has been considered as a target for the development of antimicrobial and antisepsis drugs. In recent and past few years, 3-D structures and interactions of a number of AMPs have been determined in complex with LPS micelles. These studies have generated molecular insights towards mode of action and synergistic activity of AMPs in the outer membrane. In this review, atomic resolution structures and interactions of potent AMPs with LPS are discussed providing novel insights of their mode of action. © 2016 Bentham Science Publishers.

Shvets E.,MRC LMB | Ludwig A.,Nanyang Technological University | Nichols B.J.,MRC LMB
Current Opinion in Cell Biology | Year: 2014

Recent data from the study of the cell biology of caveolae have provided insights both into how these flask-shaped invaginations of the plasma membrane are formed and how they may function in different contexts. This review discusses experiments that analyse the composition and ultrastructural distribution of protein complexes responsible for generating caveolae, that suggest functions for caveolae in response to mechanical stress or damage to the plasma membrane, that show that caveolae may have an important role during the signalling events for regulation of metabolism, and that imply that caveolae can act as endocytic vesicles at the plasma membrane. We also highlight unexpected roles for caveolar proteins in regulating circadian rhythms and new insights into the way in which caveolae may be involved in fatty acid uptake in the intestine. Current outstanding questions in the field are emphasised. © 2014 Elsevier Ltd.

Kakarala R.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2011

Ranking data is a type of data obtained in some elections, in customer surveys, as well as from web search results. Such data may be considered as a type of signal defined on the group of permutations of n objects, denoted S n. There exists a Fourier transform for Sn obtained from group representation theory, which is well known in the mathematics literature. However, previous work has not approached the transform from a signal processing perspective: in particular, there is no discussion of what constitutes magnitude and phase, nor any analysis of what phase information might tell us beyond a well-known connection to group translation. This paper explores the properties of the phase spectrum of ranking data; in particular, a novel contribution is the formulation of the bispectrum for ranking data, which may be used for studying phase linearity. Analysis of two well-known ranking data sets shows that they are surprisingly well fit by linear phase approximations. © 2010 IEEE.

Tsai F.S.,Nanyang Technological University
Expert Systems with Applications | Year: 2011

Exploratory data analysis often relies heavily on visual methods because of the power of the human eye to detect structures. For large, multidimensional data sets which cannot be easily visualized, the number of dimensions of the data can be reduced by applying dimensionality reduction techniques. This paper reviews current linear and nonlinear dimensionality reduction techniques in the context of data visualization. The dimensionality reduction techniques were used in our case study of business blogs. The superior techniques were able to discriminate the various categories of blogs quite accurately. To our knowledge, this is the first study using dimensionality reduction techniques for visualization of blogs. In summary, we have applied dimensionality reduction for visualization of real-world blog data, with potential applications in the ever-growing digital realm of social media. © 2010 Elsevier Ltd. All rights reserved.

Tsai F.S.,Nanyang Technological University
Expert Systems with Applications | Year: 2011

The proliferation of advanced, online, three-dimensional mapping programs provides Web users with detailed aerial and satellite maps, high-powered graphics and animation, and customization capabilities. This mapping revolution can transform the landscape of the Web into a geographic Web, where information can be organized geographically, so that users can understand information in the proper context. In this paper, we describe a geographic information retrieval system that is able to search for location-specific information in Singapore-based Web sites. The user is able to view their search locations on a satellite map instead of the two-dimensional maps currently used in street directories. The Web-based search engine is able to search for locations based on area names, building names, and groups of landmark types, business names, and business categories. Furthermore, the user is also able to use their current coordinates as a parameter so that the search engine is able to return results in order of the distance from the user's current location. © 2010 Elsevier Ltd. All rights reserved.

Leong D.T.,National University of Singapore | Ng K.W.,Nanyang Technological University
Advanced Drug Delivery Reviews | Year: 2014

For decades, 2D cell culture format on plastic has been the main workhorse in cancer research. Though many important understandings of cancer cell biology were derived using this platform, it is not a fair representation of the in vivo scenario. In this review, both established and new 3D cell culture systems are discussed with specific references to anti-cancer drug and nanomedicine applications. 3D culture systems exploit more realistic spatial, biochemical and cellular heterogeneity parameters to bridge the experimental gap between in vivo and in vitro settings when studying the performance and efficacy of novel nanomedicine strategies to manage cancer. However, the complexities associated with 3D culture systems also necessitate greater technical expertise in handling and characterizing in order to arrive at meaningful experimental conclusions. Finally, we have also provided future perspectives where cutting edge 3D culture technologies may be combined with under-explored technologies to build better in vitro cancer platforms. © 2014 Elsevier B.V.

Das S.,Jadavpur University | Suganthan P.N.,Nanyang Technological University
IEEE Transactions on Evolutionary Computation | Year: 2011

Differential evolution (DE) is arguably one of the most powerful stochastic real-parameter optimization algorithms in current use. DE operates through similar computational steps as employed by a standard evolutionary algorithm (EA). However, unlike traditional EAs, the DE-variants perturb the current-generation population members with the scaled differences of randomly selected and distinct population members. Therefore, no separate probability distribution has to be used for generating the offspring. Since its inception in 1995, DE has drawn the attention of many researchers all over the world resulting in a lot of variants of the basic algorithm with improved performance. This paper presents a detailed review of the basic concepts of DE and a survey of its major variants, its application to multiobjective, constrained, large scale, and uncertain optimization problems, and the theoretical studies conducted on DE so far. Also, it provides an overview of the significant engineering applications that have benefited from the powerful nature of DE. © 2010 IEEE.

Adams D.H.,Nanyang Technological University | Adams D.H.,National Taiwan University
Physical Review Letters | Year: 2010

A way to identify the would-be zero modes of staggered lattice fermions away from the continuum limit is presented. Our approach also identifies the chiralities of these modes, and their index is seen to be determined by gauge field topology in accordance with the index theorem. The key idea is to consider the spectral flow of a certain Hermitian version of the staggered Dirac operator. The staggered fermion index thus obtained can be used as a new way to assign the topological charge of lattice gauge fields. In a numerical study in U(1) backgrounds in two dimensions it is found to perform as well as the Wilson index while being computationally more efficient. It can also be expressed as the index of an overlap Dirac operator with a new staggered fermion kernel. © 2010 The American Physical Society.

Zhu X.-L.,Zhengzhou University of Light Industry | Wang Y.,Nanyang Technological University
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2011

This paper studies the problem of stabilization for sampled-data neural-network-based control systems with an optimal guaranteed cost. Unlike previous works, the resulting closed-loop system with variable uncertain sampling cannot simply be regarded as an ordinary continuous-time system with a fast-varying delay in the state. By defining a novel piecewise Lyapunov functional and using a convex combination technique, the characteristic of sampled-data systems is captured. A new delay-dependent stabilization criterion is established in terms of linear matrix inequalities such that the maximal sampling interval and the minimal guaranteed cost control performance can be obtained. It is shown that the newly proposed approach can lead to less conservative and less complex results than the existing ones. Application examples are given to illustrate the effectiveness and the benefits of the proposed method. © 2010 IEEE.

Zhou Y.,Nanyang Technological University
Journal of Medical Imaging and Health Informatics | Year: 2013

Ultrasound is a popular imaging modality for its safety and low cost. Its role in the diagnosis of breast cancer is discussed, and its performance is then compared to those of mammography (gold standard) and MRI. Besides conventional B-mode and color or power Doppler ultrasound images, latest development of acoustic radiation force impulse (ARFI) and supersonic shear imaging and their application in breast diagnosis are introduced. © 2013 American Scientific Publishers.

Kong A.W.-K.,Nanyang Technological University
IEEE Transactions on Image Processing | Year: 2013

IrisCode, developed by Daugman, in 1993, is the most influential iris recognition algorithm. A thorough understanding of IrisCode is essential, because over 100 million persons have been enrolled by this algorithm and many biometric personal identification and template protection methods have been developed based on IrisCode. This paper indicates that a template produced by IrisCode or its variants is a convex polyhedral cone in a hyperspace. Its central ray, being a rough representation of the original biometric signal, can be computed by a simple algorithm, which can often be implemented in one Matlab command line. The central ray is an expected ray and also an optimal ray of an objective function on a group of distributions. This algorithm is derived from geometric properties of a convex polyhedral cone but does not rely on any prior knowledge (e.g., iris images). The experimental results show that biometric templates, including iris and palmprint templates, produced by different recognition methods can be matched through the central rays in their convex polyhedral cones and that templates protected by a method extended from IrisCode can be broken into. These experimental results indicate that, without a thorough security analysis, convex polyhedral cone templates cannot be assumed secure. Additionally, the simplicity of the algorithm implies that even junior hackers without knowledge of advanced image processing and biometric databases can still break into protected templates and reveal relationships among templates produced by different recognition methods. © 2012 IEEE.

Liang Z.-X.,Nanyang Technological University
Natural Product Reports | Year: 2015

Covering: up to the end of 2014 The cyclic dinucleotide c-di-GMP has emerged in the last decade as a prevalent intracellular messenger that orchestrates the transition between the motile and sessile lifestyles of many bacterial species. The motile-to-sessile transition is often associated with the formation of extracellular matrix-encased biofilm, an organized community of bacterial cells that often contributes to antibiotic resistance and host-pathogen interaction. It is increasingly clear that c-di-GMP controls motility, biofilm formation and bacterial pathogenicity partially through regulating the production of exopolysaccharides (EPS) and small-molecule secondary metabolites. This review summarizes our current understanding of the regulation of EPS biosynthesis by c-di-GMP in a diversity of bacterial species and highlights the emerging role of c-di-GMP in the biosynthesis of small-molecule secondary metabolites. This journal is © The Royal Society of Chemistry.

Pumera M.,Nanyang Technological University
ACS Nano | Year: 2014

While the electrochemistry of redox-active ions or molecules has been studied for decades, the electrochemistry of individual nanoparticles remains largely unexplored. In this issue of ACS Nano, Stuart et al. report the direct electrochemical detection of impacting carbon C60 nanoparticles in a non-aqueous solution. This study opens up the possibility of detecting and counting various redox-active inorganic, organic, and carbon-based nanoparticles, one by one, in colloids and suspensions by a simple and highly sensitive technique. The method developed by Stuart et al. enables the determination of the type, size, and concentration of the nanoparticles. One can foresee a wide scope of potential applications, ranging from the environmental monitoring of nanoparticles to the detection of self-propelled autonomous nano- and micromachines. © 2014 American Chemical Society.

Shi L.,Hong Kong University of Science and Technology | Xie L.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2012

We consider sensor power scheduling for estimating the state of a general high-order Gauss-Markov system. A sensor decides whether to use a high or low transmission power to communicate its local state estimate or raw measurement data with a remote estimator over a packet-dropping network. We construct the optimal sensor power schedule which minimizes the expected terminal estimation error covariance at the remote estimator under the constraint that the high transmission power can only be used m < T + 1 times, given the time-horizon from k = 0 to k = T. We also discuss how to extend the result to cases involving multiple power levels scheduling. Simulation examples are the provided to demonstrate the results. © 1991-2012 IEEE.

Rotgans J.I.,Nanyang Technological University
Advances in Health Sciences Education | Year: 2012

The present study aimed at providing an overview of the most common themes of research into medical education. Changes in frequency of occurrence of these themes over time and differences between US and European journals were studied. The most productive institutions and researchers in the field were examined. A content analysis was carried out on 10,168 abstracts extracted from the six most influential journals in medical education published since 1988. Twenty-nine major themes were identified, of which student assessment, clinical and communication skills, clinical clerkships, and problem-based learning were the most prominent ones. Some of these themes, such as multiple-choice examinations or computer-assisted instruction seemed to have had their day, whereas other topics, such as the study of clinical clerkships, clinical reasoning, and scholarship in education were on their way up. Medical education research turned out to be a thoroughly international affair to which both US and European research centers contribute. The medical education literature shows an overwhelming emphasis on the preparation of medical students for professional practice. Moreover, the emphasis is very much on the individual student; most research seems to have been conducted with a psychological perspective in mind. It is argued that medical education research would profit from broadening its scope, including sociological, economical, ecological, and system perspectives. These perspectives might bring answers to new questions relevant to the quality of medical education. It is suggested that medical education is in need of moving beyond the conventional effectiveness-driven research approach to a more theory- and discovery-driven approach. © 2011 Springer Science+Business Media B.V.

Tsai F.S.,Nanyang Technological University
Expert Systems with Applications | Year: 2011

Blog mining addresses the problem of mining information from blog data. Although mining blogs may share many similarities to Web and text documents, existing techniques need to be reevaluated and adapted for the multidimensional representation of blog data, which exhibit dimensions not present in traditional documents, such as tags. Blog tags are semantic annotations in blogs which can be valuable sources of additional labels for the myriad of blog documents. In this paper, we present a tag-topic model for blog mining, which is based on the Author-Topic model and Latent Dirichlet Allocation. The tag-topic model determines the most likely tags and words for a given topic in a collection of blog posts. The model has been successfully implemented and evaluated on real-world blog data. © 2010 Elsevier Ltd. All rights reserved.

Lin W.,Nanyang Technological University | Jay Kuo C.-C.,University of Southern California
Journal of Visual Communication and Image Representation | Year: 2011

Visual quality evaluation has numerous uses in practice, and also plays a central role in shaping many visual processing algorithms and systems, as well as their implementation, optimization and testing. In this paper, we give a systematic, comprehensive and up-to-date review of perceptual visual quality metrics (PVQMs) to predict picture quality according to human perception. Several frequently used computational modules (building blocks of PVQMs) are discussed. These include signal decomposition, just-noticeable distortion, visual attention, and common feature and artifact detection. Afterwards, different types of existing PVQMs are presented, and further discussion is given toward feature pooling, viewing condition, computer-generated signal and visual attention. Six often-used image metrics (namely SSIM, VSNR, IFC, VIF, MSVD and PSNR) are also compared with seven public image databases (totally 3832 test images). We highlight the most significant research work for each topic and provide the links to the extensive relevant literature. © 2011 Elsevier Inc. All rights reserved.

Huang G.-B.,Nanyang Technological University
Cognitive Computation | Year: 2015

The emergent machine learning technique—extreme learning machines (ELMs)—has become a hot area of research over the past years, which is attributed to the growing research activities and significant contributions made by numerous researchers around the world. Recently, it has come to our attention that a number of misplaced notions and misunderstandings are being dissipated on the relationships between ELM and some earlier works. This paper wishes to clarify that (1) ELM theories manage to address the open problem which has puzzled the neural networks, machine learning and neuroscience communities for 60 years: whether hidden nodes/neurons need to be tuned in learning, and proved that in contrast to the common knowledge and conventional neural network learning tenets, hidden nodes/neurons do not need to be iteratively tuned in wide types of neural networks and learning models (Fourier series, biological learning, etc.). Unlike ELM theories, none of those earlier works provides theoretical foundations on feedforward neural networks with random hidden nodes; (2) ELM is proposed for both generalized single-hidden-layer feedforward network and multi-hidden-layer feedforward networks (including biological neural networks); (3) homogeneous architecture-based ELM is proposed for feature learning, clustering, regression and (binary/multi-class) classification. (4) Compared to ELM, SVM and LS-SVM tend to provide suboptimal solutions, and SVM and LS-SVM do not consider feature representations in hidden layers of multi-hidden-layer feedforward networks either. © 2015, Springer Science+Business Media New York.

Cambria E.,Nanyang Technological University | White B.,SLAC
IEEE Computational Intelligence Magazine | Year: 2014

Natural language processing (NLP) is a theory-motivated range of computational techniques for the automatic analysis and representation of human language. NLP research has evolved from the era of punch cards and batch processing (in which the analysis of a sentence could take up to 7 minutes) to the era of Google and the likes of it (in which millions of webpages can be processed in less than a second). This review paper draws on recent developments in NLP research to look at the past, present, and future of NLP technology in a new light. Borrowing the paradigm of 'jumping curves' from the field of business management and marketing prediction, this survey article reinterprets the evolution of NLP research as the intersection of three overlapping curves-namely Syntactics, Semantics, and Pragmatics Curves- which will eventually lead NLP research to evolve into natural language understanding.

Li B.,Wuhan University | Hoi S.C.H.,Nanyang Technological University
ACM Computing Surveys | Year: 2014

Online portfolio selection is a fundamental problem in computational finance, which has been extensively studied across several research communities, including finance, statistics, artificial intelligence, machine learning, and data mining. This article aims to provide a comprehensive survey and a structural understanding of online portfolio selection techniques published in the literature. From an onlinemachine learning perspective, we first formulate online portfolio selection as a sequential decision problem, and then we survey a variety of state-of-the-art approaches, which are grouped into several major categories, including benchmarks, Follow-the-Winner approaches, Follow-the-Loser approaches, Pattern-Matching-based approaches, and Meta-Learning Algorithms. In addition to the problem formulation and related algorithms, we also discuss the relationship of these algorithms with the capital growth theory so as to better understand the similarities and differences of their underlying trading ideas. This article aims to provide a timely and comprehensive survey for both machine learning and data mining researchers in academia and quantitative portfolio managers in the financial industry to help them understand the state of the art and facilitate their research and practical applications. We also discuss some open issues and evaluate some emerging new trends for future research. © 2014 ACM.

Koh C.L.,Nanyang Technological University
Sensors (Basel, Switzerland) | Year: 2013

Quorum sensing is a system of stimuli and responses in relation to bacterial cell population density that regulates gene expression, including virulence determinants. Consequently, quorum sensing has been an attractive target for the development of novel anti-infective measures that do not rely on the use of antibiotics. Anti-quorum sensing has been a promising strategy to combat bacterial infections as it is unlikely to develop multidrug resistant pathogens since it does not impose any selection pressure. A number of anti-quorum sensing approaches have been documented and plant-based natural products have been extensively studied in this context. Plant matter is one of the major sources of chemicals in use today in various industries, ranging from the pharmaceutical, cosmetic, and food biotechnology to the textile industries. Just like animals and humans, plants are constantly exposed to bacterial infections, it is therefore logical to expect that plants have developed sophisticated of chemical mechanisms to combat pathogens. In this review, we have surveyed the various types of plant-based natural products that exhibit anti-quorum sensing properties and their anti-quorum sensing mechanisms.

Medronho B.,University of Algarve | Lindman B.,Lund University | Lindman B.,Nanyang Technological University
Current Opinion in Colloid and Interface Science | Year: 2014

Cellulose is a polymer so widely abundant and versatile that we can find it almost everywhere in many different forms and applications. Cellulose dissolution is a key aspect of many processes; the present treatise reviews the main achievements in the dissolution area. In particular, the main solvents used and underlying mechanisms are discussed. As is described, cellulose solvents are of highly different nature giving great challenges in the understanding and analyzing the subtle balance between different interactions. Recent work has much emphasized the role of cellulose charge and the concomitant ion entropy effects, as well as hydrophobic interactions. © 2013 Elsevier Ltd.

Zhang Q.,Nanyang Technological University
Nature Photonics | Year: 2016

The radiation pressure of light has been widely used to cool trapped atoms or the mechanical vibrational modes of optomechanical systems. Recently, by using the electrostrictive forces of light, spontaneous Brillouin cooling and stimulated Brillouin excitation of acoustic modes of the whispering-gallery-type resonator have been demonstrated. The laser cooling of specific lattice vibrations in solids (that is, phonons) proposed by Dykman in the late 1970s, however, still remains sparsely investigated. Here, we demonstrate the first strong spontaneous Raman cooling and heating of a longitudinal optical phonon (LOP) with a 6.23 THz frequency in polar semiconductor zinc telluride nanobelts. We use the exciton to resonate and assist photoelastic Raman scattering from the LOPs caused by a strong exciton–LOP coupling. By detuning the laser pump to a lower (higher) energy-resolved sideband to make a spontaneous scattering photon resonate with an exciton at an anti-Stokes (Stokes) frequency, the dipole oscillation of the LOPs is photoelastically attenuated (enhanced) to a colder (hotter) state. © 2016 Nature Publishing Group

We present a simple solution surface dip coating method for fabricating transparent and conductive carbon nanotube/polyvinyl butyral (CNT/PVB) composite films. This fabrication process is simple to scale production and requires only ethanol and water as solvents, which is green and environment friendly.

Li S.,Nanjing University of Posts and Telecommunications | Huo F.,Nanyang Technological University
Small | Year: 2014

Hybrid crystals containing encapsulated functional species exhibit promising novel physical and chemical properties. The realization of many properties critically depends on the selection of suitable functional species for incorporation, the rational control of the crystallinity of the host materials, and the manipulation of the distribution of the encapsulated species; only a few hybrid crystals achieve this. Here, a novel synthetic method enables the encapsulation of functional species within crystalline metal-organic frameworks (MOFs). Various kinds of single-crystalline MOFs with incorporated particles are presented. The encapsulated particles can be distributed in a controllable manner, and the hybrid crystals are applied to the heterogeneous catalysis of the reduction of nitroarenes. These findings suggest a general approach for the construction of MOF materials with potential applications; by combining species and MOFs with suitable functionalities, new properties - not possible by other means - may arise. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Patra J.C.,Nanyang Technological University
IEEE Transactions on Energy Conversion | Year: 2011

Design and development process of solar cells can be greatly enhanced by using accurate models that can predict their behavior accurately. Recently, there has been a surge in research efforts in multijunction (MJ) solar cells to improve the conversion efficiency. Modeling of MJ solar cells poses greater challenges because their characteristics depend on the complex photovoltaic phenomena and properties of the materials used. Currently, several commercial complex device modeling software packages, e.g., ATLAS, are available. But these software packages have limitations in predicting the behavior of MJ solar cells because of several assumptions made on the physical properties and complex interactions. Artificial neural networks have the ability to effectively model any nonlinear system with complex mapping between its input and output spaces. In this paper, we proposed a novel Chebyshev neural network (ChNN) to model a dual-junction (DJ) GaInP/GaAs solar cell. Using the ChNN, we have modeled the tunnel junction characteristics and developed models to predict the external quantum efficiency, and I-V characteristics both at one sun and at dark levels. We have shown that the ChNN-based models perform better than the commercial software, ATLAS, in predicting the DJ solar cell characteristics. © 2010 IEEE.

Neuzil P.,Institute of Microelectronics, Singapore | Wong C.C.,Institute of Microelectronics, Singapore | Wong C.C.,Nanyang Technological University | Reboud J.,Institute of Microelectronics, Singapore
Nano Letters | Year: 2010

Herein we demonstrate giant piezoresistance in silicon nanowires (NWs) by the modulation of an electric field-induced with an external electrical bias. Positive bias for a p-type device (negative for an n-type) partially depleted the NWs forming a pinch-off region, which resembled a funnel through which the electrical current squeezed. This region determined the total current flowing through the NWs. In this report, we combined the electrical biasing with the application of mechanical stress, which impacts the charge carriers' concentration, to achieve an electrically controlled giant piezoresistance in nanowires. This phenomenon was used to create a stress-gated field-effect transistor, exhibiting a maximum gauge factor of 5000, 2 orders of magnitude increase over bulk value. Giant piezoresistance can be tailored to create highly sensitive mechanical sensors operating in a discrete mode such as nanoelectromechanical switches. © 2010 American Chemical Society.

Liu D.,IBM | Zhang Y.P.,Nanyang Technological University
Proceedings of the IEEE | Year: 2012

This paper discusses the integration of array antennas in chip packages for highly integrated 60-GHz radios. First, we evaluate fixed-beam array antennas, showing that most of them suffer from feed network complexity and require sophisticated process techniques to achieve enhanced performance. We describe the grid array antenna and show that is a good choice for fixed-beam array antenna applications due to its easy feed network design and manufacture. Then, we examine switched-beam array antennas using the Rotman lens or Butter matrix, illustrating that they allow scanning only in one plane and some miss a link even in the boresight direction. Nevertheless, a switched-beam array antenna uses a conceptually simple switch circuit to select the best signal path and may be a cost-effective approach to implementing steerable antennas in the 60-GHz band. Finally, we describe adaptive beam or phased array antennas and highlight the challenges and practical realizations of phased array antennas in both ceramic and organic chip packages for single-chip 60-GHz radios. © 2012 IEEE.

Zheng W.-T.,Jilin University | Sun C.Q.,Nanyang Technological University | Sun C.Q.,Xiangtan University
Energy and Environmental Science | Year: 2011

As a new class of materials, carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) have been continuing fascinating the community with properties that can be seen from neither bulk graphite nor diamond. Although the physics and chemistry of these carbon allotropes have been intensively investigated from various perspectives, the laws governing the fascinations and their interdependence remain as yet undetermined. From the perspectives of bond and nonbond formation, dissociation, relaxation, vibration, and the associated energetics and dynamics of charge repopulation, polarization, densification, and localization, this article aims to show that the broken-bond-induced local bond contraction and bond strength gain, quantum entrapment and densification of charge and energy, polarization of the unpaired edge dangling σ-bond electrons, and the formation of the pseudo-π-bond between the dangling σ-bond electrons along the edges are responsible for the anomalies. Theoretical reproduction of the experimentally observed elastic modulus enhancement, melting point depression, layer-number, strain, pressure and temperature induced Raman shift, C 1s core-level positive shift, work function reduction, band gap expansion, edge and defect selective generation of the Dirac-Fermi polarons and the associated magnetism consistently confirmed that the shorter and stronger bonds between undercoordinated carbon atoms modulate locally the atomic cohesive energy, the Hamiltonian, and hence the detectable bulk properties. The polarization of the unpaired dangling σ-bond electrons by the densely, deeply, and locally entrapped core and bonding electrons generates the massless, magnetic and mobile Dirac-Fermi polarons at sites surrounding vacancies and zigzag-GNR edges. The pseudo-π-bond formation between the nearest dangling σ-bond electrons along the armchair-GNR and the reconstructed zigzag-GNR edges discriminates them from the zigzag-GNR edges or vacancies in the electronic and magnetic properties. Consistency between predictions and observations confirmed that the C-C bond contracts by up to 30% with a 152% bond strength gain at the edges with respect to those in the bulk diamond. © 2011 The Royal Society of Chemistry.

Wang J.,Chinese University of Hong Kong | Cheng J.,Nanyang Technological University
Proceedings of the VLDB Endowment | Year: 2012

The k-truss is a type of cohesive subgraphs proposed recently for the study of networks. While the problem of computing most co-hesive subgraphs is NP-hard, there exists a polynomial time al-gorithm for computing k-truss. Compared with k-core which is also efficient to compute, k-truss represents the " core" of a k-core that keeps the key information of, while filtering out less impor-tant information from, the k-core. However, existing algorithms for computing k-truss are inefficient for handling today's massive networks. We first improve the existing in-memory algorithm for computing k-truss in networks of moderate size. Then, we propose two I/O-efficient algorithms to handle massive networks that can-not fit in main memory. Our experiments on real datasets verify the efficiency of our algorithms and the value of k-truss. © 2012 VLDB Endowment.

Chian K.S.,Nanyang Technological University | Leong M.F.,Institute Of Bioengineering And Nanotechnology, Singapore | Kono K.,National University of Singapore | Kono K.,Fukushima Medical University
The Lancet Oncology | Year: 2015

Removal of malignant tissue in patients with oesophageal cancer and replacement with autologous grafts from the stomach and colon can lead to problems. The need to reduce stenosis and anastomotic leakage after oesophagectomy is a high priority. Developments in tissue-engineering methods and cell-sheet technology have improved scaffold materials for oesophageal repair. Despite the many successful animal studies, few tissue-engineering approaches have progressed to clinical trials. In this Review, we discuss the status of oesophagus reconstruction after surgery. In particular, we highlight two clinical trials that used decellularised constructs and epithelial cell sheets to replace excised tissues after endoscopic submucosal dissection or mucosal resection procedures. Results from the trials showed that both decellularised grafts and epithelial-cell sheets prevented stenosis. By contrast, animal studies have shown that the use of tissue-engineered constructs after oesophagectomy remains a challenge. © 2015 Elsevier Ltd.

Tan S.-M.,Nanyang Technological University
Bioscience Reports | Year: 2012

Leucocytes are highly motile cells. Their ability to migrate into tissues and organs is dependent on cell adhesion molecules. The integrins are a family of heterodimeric transmembrane cell adhesion molecules that are also signalling receptors. They are involved in many biological processes, including the development of metazoans, immunity, haemostasis, wound healing and cell survival, proliferation and differentiation. The leucocyte-restricted β2 integrins comprise four members, namely αLβ2, αMβ2, αXβ2 and αDβ2, which are required for a functional immune system. In this paper, the structure, functional regulation and signalling properties of these integrins are reviewed.

Zhang B.,University of South Carolina | Zhou K.,University of Canterbury | Wang D.,Nanyang Technological University
IEEE Transactions on Industrial Electronics | Year: 2014

In this paper, a multirate repetitive control (RC) scheme is developed and applied to constant-voltage constant-frequency pulsewidth modulation converter systems. In this scheme, the converter has a fast sampling rate, while the repetitive controller has a reduced sampling rate. The learning is based on the downsampled input and error signals in previous periods. The multirate RC synthesis method, as well as its convergence and stability conditions, is discussed in detail. Systematic experiments are also carried out to illustrate the effectiveness of multirate RC. Experimental results show that, with a well-designed multirate RC, the total harmonic distortion can be very low. This approach can reduce the computation delay caused by the plug-in RC in each switching control period and will enhance the system stability. Consequently, the switching control frequency of the converter can be increased to compensate the control performance loss. This approach is suitable for design of cost-effective and flexible converter control systems. © 1982-2012 IEEE.

Hines L.,Carnegie Mellon University | Campolo D.,Nanyang Technological University | Sitti M.,Carnegie Mellon University
IEEE Transactions on Robotics | Year: 2014

This study presents the design of a novel minimalist liftoff-capable flapping-wing microaerial vehicle. Two wings are each directly driven by a geared pager motor by utilizing an elastic element for energy recovery, resulting in a maximum lift-to-weight ratio of 1.4 at 10 Hz for the 2.7 g system. Separate directly driven wings allow the system to both resonate and control individual wing flapping angle, reducing necessary power consumption, as well as allowing the production of roll and pitch body torques. With a series of varied prototypes, system performance is examined with change in wing offset from center of rotation and elastic element stiffness. Prototype liftoff is demonstrated with open loop driving a tethered prototype without guide wires. A dynamic model of the system is adapted and compared with the prototype experimental results for later use in prototype optimization. © 2013 IEEE.

Pumera M.,Nanyang Technological University
Materials Today | Year: 2011

Biosensing is paramount for improving the quality of human life. Biosensors and biosensing protocols are able to detect a wide range of compounds, sensitively and selectively, with applications in security, health care for point-of-care analyses of diseases, and environmental safety. Here, we describe biosensors and biosensing systems employing graphene. Graphene is a zero-gap semiconductor material, which is electroactive and transparent. Because of its interesting properties, graphene has found its way into a wide variety of biosensing schemes. It has been used as a transducer in bio-field-effect transistors, electrochemical biosensors, impedance biosensors, electrochemiluminescence, and fluorescence biosensors, as well as biomolecular labels. In our review, we describe the application of graphene for enzymatic biosensing, DNA sensing, and immunosensing. We compare different techniques and present our views on the future development of the field. © 2011 Elsevier Ltd.

Do K.D.,Nanyang Technological University
Asian Journal of Control | Year: 2012

This paper presents a design of cooperative controllers that force a group of N mobile agents with an elliptic shape and limited sensing ranges to perform a desired formation and that guarantee no collisions between any agents in the group. The desired formation can be stabilized at feasible reference trajectories with bounded time derivatives. The formation control design is based on explicit algebraic separation conditions between ellipses, root conditions of cubic polynomials, the Lyapunov direct method, and smooth or p-times differentiable step functions. These functions are incorporated into novel potential functions to solve the collision avoidance problem without the need for switchings despite the agents' limited sensing ranges. © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.

Mukherjee S.,Nanyang Technological University
American Journal of Sports Medicine | Year: 2012

Background: Head and face injuries in field hockey are a concern. However, published data on injuries in field hockey are minimal, with apparently no reports on head and face injuries in elite youth hockey players during major international tournaments. Purpose: To provide a descriptive account of head and face injuries in elite youth male field hockey players during the Men's Junior World Cup 2009. Study Design: Descriptive epidemiological study. Methods: A total of 324 players were observed during 58 matches in the tournament. The injury reporting system was based on that used in team sports during international tournaments. All the head and face injury documentation was done by direct on-location observation by a trained sports medicine physician followed by confirmation from the team doctors or physical the rapists. Results: A total of 24 head and face injuries were documented. The overall injury frequency rate was 16 per 1000 match hours and 19 per 1000 player matches. There were 92% of injuries that were of contact type, with the head being the most common site and contusion being the most common type of injury. The incidence of injuries was higher during the second half and during the medal/ranking phase of the tournament. Conclusion: The risk of head and face injuries is high in elite youth players with a potential of both short- and long-term player time loss in international tournaments. Rigorous enforcement of rules prohibiting body contact can significantly reduce the chances of head and face injuries in elite youth field hockey players. In addition, player education on the injury risks and safe practices at the developmental stages is desirable to prevent injuries and prolong sporting careers. © 2012 American Orthopaedic Society for Sports Medicine.

Chan C.Y.,Nanyang Technological University
IET Power Electronics | Year: 2012

The development of non-linear controllers for a tri-state boost converter in the presence of an unknown load is addressed. In contrast to the conventional boost converter, the tri-state boost converter has two control inputs and does not have a right-half-plane zero. The controllers are designed using the average model of the tri-state boost converter to vary both the 'boost' and 'capacitor-charging' intervals using the average model of the tri-state boost converter to achieve fast response and a small inductor current. Experimental results to illustrate the features of the controllers are provided. © 2011 The Institution of Engineering and Technology.

Low Y.M.,Nanyang Technological University
Structural Safety | Year: 2012

The fatigue life of a structure is inherently random when the loading is irregular. There is a vast body of literature on the analysis of the mean fatigue damage, but very few studies have been devoted to the variance. This paper presents an improved method for analyzing the variance of the damage for any narrowband Gaussian process. The field of application is not confined to the linear oscillator, unlike approaches in previous studies. The method is simple to apply; it involves a single summation for arbitrary processes, and closed form solutions are available for special cases (linear oscillator and bandpass process). The effectiveness of the method is demonstrated through case studies encompassing a variety of systems, including a realistic spectrum commonly seen in offshore engineering. Using rainflow counting of simulated time domain stresses as a benchmark, the proposed method is shown to yield a highly precise prediction of the variance. Moreover, it is significantly more accurate than an existing method for the linear oscillator system. © 2011 Elsevier Ltd.

Wu Y.I.,Nanyang Technological University | Wong K.T.,Hong Kong Polytechnic University
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

A new scheme is herein proposed to localize an acoustic source. This new method blends the received signal strength indication (RSSI) approach of geolocation, and the acoustic vector-sensor (AVS) (a.k.a., vector-hydrophone) based direction-finding (DF). Unlike customary RSSI-based source-localization, this proposed approach needs only two (not three or more) passive anchor-nodes: 1) one pressure-sensor, and 2) one physically compact triad of three (collocating, but orthogonally oriented) acoustic velocity-sensors. The latter can estimate the direction-of-arrival (DOA) of an emitter, regardless of that emitters arbitrary/unknown center-frequency, bandwidth, spectrum, and near-field/far-field location. This triads DOA estimates can be distributed processed, locally, apart from the pressure-sensors measured power, to estimate the emitters radial distance. This proposed algorithm is noniterative, requires no initial estimate, is closed form, and can accommodate any prior known propagation-loss exponent. © 2006 IEEE.

Areepattamannil S.,Nanyang Technological University
Journal of General Psychology | Year: 2014

This study examined the relationships between academic motivation - intrinsic motivation, extrinsic motivation, amotivation - and mathematics achievement among 363 Indian adolescents in India and 355 Indian immigrant adolescents in Canada. Results of hierarchical multiple regression analyses showed that intrinsic motivation, extrinsic motivation, and amotivation were not statistically significantly related to mathematics achievement among Indian adolescents in India. In contrast, both intrinsic motivation and extrinsic motivation were statistically significantly related to mathematics achievement among Indian immigrant adolescents in Canada. While intrinsic motivation was a statistically significant positive predictor of mathematics achievement among Indian immigrant adolescents in Canada, extrinsic motivation was a statistically significant negative predictor of mathematics achievement among Indian immigrant adolescents in Canada. Amotivation was not statistically significantly related to mathematics achievement among Indian immigrant adolescents in Canada. Implications of the findings for pedagogy and practice are discussed. © 2014 2014 Taylor & Francis Group, LLC.

Zhao D.,Nanyang Technological University
AIAA Journal | Year: 2012

To suppress combustion instabilities, Helmholtz resonators are typically used as acoustic dampers to dissipate acoustic waves. However, they tend to be effective over a narrow-frequency bandwidth. Furthermore, the space available for applying such resonators is limited. To effectively use the space and to reduce the transmission of acoustic waves, aparallel-coupled Helmholtz resonator network, with two resonators connected via athin compliant membrane, was designed and experimentally tested. It was found that the compliant membrane motion gave rise to the production of additional transmission loss peaks at nonresonant frequencies of the resonators. A numerical model was then developed to simulate the experiments. Green's function approach was used to determine the membrane motion, which was associated with the rate of resonators cavities volume change. Good agreement between the numerical and experimental results was observed. To damp frequency-varying noise, the membrane vibration was actively tuned by implementing a trust-region Newton conjugate-gradient method. Transmission loss was found to increase to approximately 25 dB over a broad frequency range. Finally, experimental tests of other resonator network configurations were conducted, which included blocking one of the resonator necks or removing the diaphragm. Copyright © 2011 by Dan Zhao.

Zhou K.,Nanyang Technological University
Acta Mechanica | Year: 2012

This paper develops a semi-analytic model for periodically structured composites, of which each period contains an arbitrary distribution of particles/fibers or inhomogeneities in a three-dimensional space. The inhomogeneities can be of arbitrary shape and have multiple phases. The model is developed using the Equivalent Inclusion Method in conjunction with a fast Fourier Transform algorithm and the Conjugate Gradient Method. The interactions among inhomogeneities within one computational period are fully taken into account. An accurate knowledge of the stress field of the composite is obtained by setting the computational period to contain one or more structural periods of the composite. The effective moduli of the composite are calculated from average stresses and elastic strains. The model is used to analyze the stress field and effective moduli of anisotropic composites that have cubic symmetry. It shows that the bulk and shear moduli predicted by the present model are well located within the Hashin-Shtrikman bounds. The study also shows that the stress field of the composite can be significantly affected by the distribution of inhomogeneities even though the effective moduli are not affected much. © Springer-Verlag 2011.

Jiang H.,East China University of Science and Technology | Ma J.,Nanyang Technological University | Li C.,East China University of Science and Technology
Journal of Materials Chemistry | Year: 2012

We demonstrated the facile loading of ultrafine and loosened K-birnessite MnO 2 floccules on the surface of polyaniline (PANI) nanofibers by simply soaking the polyaniline nanofibers in a KMnO 4 aqueous solution for electrochemical energy storage applications. The as-prepared PANI-MnO 2 coaxial nanofibers with optimal composition, when applied as an electrode, exhibited a high specific capacitance (383 F g -1 at 0.5 A g -1) with good rate and cycling stability in 1 M Na 2SO 4 aqueous solution. Such intriguing electrochemical performance is mainly attributed to the synergistic effects of the combined pseudo-capacitive contributions from the core and shell. The present findings promoted the development of advanced electrode materials, exhibiting huge potential for supercapacitors. © The Royal Society of Chemistry 2012.

Rajendran A.,Nanyang Technological University
Journal of Chromatography A | Year: 2012

Preparative supercritical fluid chromatography (prep-SFC) is an important separation process in the chromatographers toolbox. Owing to the unique properties of the mobile phase, which is predominantly CO 2, the behavior of SFC is markedly different from high performance liquid chromatography (HPLC). This review article focuses on the scale-up of preparative chromatography. The basics of SFC, with particular focus on highlighting the key differences between SFC and HPLC, are introduced. Then, a framework for rational design of prep-SFC is proposed. This framework is based on obtaining basic system parameters from analytical scale equipment, i.e., with very small amount of material, and performing design and optimization in silico to evaluate process performance and to identify operating conditions for scale-up. The tools required to obtain the input parameters such as adsorption isotherms are discussed and the development of the design and optimization framework is elaborated. Examples from the literature which use this approach for successful scale-up are provided. Finally the design of multi-column SFC systems is discussed. © 2012 Elsevier B.V.

Muthaiah S.,Nanyang Technological University | Hong S.H.,Seoul National University
Advanced Synthesis and Catalysis | Year: 2012

An efficient, operatively simple, acceptorless, and base-free dehydrogenation of secondary alcohols and nitrogen-containing heterocyclic compounds was achieved by using readily available ruthenium hydride complexes as precatalysts. The complex RuH 2(CO)(PPh 3) 3 (1) and Shvo's complex (2) showed excellent activities for the dehydrogenation of secondary alcohols and nitrogen containing heterocycles. In addition to complexes 1 and 2, the complex RuH 2(PPh 3) 4 (3) also showed moderate to excellent activity for the acceptorless dehydrogenation of nitrogen-containing heterocyclic compounds. Kinetic studies on the oxidation reaction of 1-phenylethanol using complex 1 were carried out in the presence and the absence of external triphenylphosphine (PPh 3). External addition of PPh 3 had a negative influence on the rate of the reaction, which suggested that dissociation of PPh 3 occurred during the course of the reaction. Hydrogen was evolved from the oxidation reaction of 1-phenylethanol by using 1 mol% of 1 (88%) and 2 (92%), which demonstrated the possible usage of the catalytic systems in hydrogen generation. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ang R.P.,Nanyang Technological University
Child psychiatry and human development | Year: 2012

This study examined the criterion validity of the Child Behavior Checklist (CBCL) and Teacher's Report Form (TRF) problem scales and items in demographically-matched Singapore samples of referred and non-referred children (840 in each sample for the CBCL and 447 in each sample for the TRF). Internal consistency estimates for both the CBCL and TRF scales were good. Almost all CBCL and TRF problem scales and items significantly discriminated between referred and non-referred children, with referred children scoring higher, as expected. The largest referral status effects were on attention problems scales and their associated items, with the TRF having larger effects than the CBCL. Effect sizes for demographic variables such as age, gender, ethnicity and SES were much smaller than effect sizes for referral status, across both the CBCL and TRF forms and at both the scale and item levels. These findings suggest that teachers can be effective partners in identifying children who need mental health services and those who do not.

Yoshikai N.,Nanyang Technological University
Bulletin of the Chemical Society of Japan | Year: 2014

This account provides an overview of cobalt-catalyzed C-H bond functionalization reactions that have been developed in our group since 2009, including hydroarylation of alkynes and alkenes, C-H/electrophile coupling, and addition of arylzinc reagents to alkynes involving 1,4-cobalt migration. © 2014 The Chemical Society of Japan.

Oggier F.,Nanyang Technological University | Hassibi B.,California Institute of Technology
IEEE Transactions on Information Theory | Year: 2011

We consider the MIMO wiretap channel, that is a MIMO broadcast channel where the transmitter sends some confidential information to one user which is a legitimate receiver, while the other user is an eavesdropper. Perfect secrecy is achieved when the transmitter and the legitimate receiver can communicate at some positive rate, while insuring that the eavesdropper gets zero bits of information. In this paper, we compute the perfect secrecy capacity of the multiple antenna MIMO broadcast channel, where the number of antennas is arbitrary for both the transmitter and the two receivers. Our technique involves a careful study of a Sato-like upper bound via the solution of a certain algebraic Riccati equation. © 2011 IEEE.

Koh J.H.L.,Nanyang Technological University
Computers in Human Behavior | Year: 2011

The computer self-efficacy of teachers contributes positively to their technology integration self-efficacy. Many studies have examined instructional strategies that foster computer self-efficacy but not their corresponding impact on teachers' technology integration self-efficacy. This study investigated the instructional strategies used for pre-service teacher computer skills instruction and their corresponding impact on teacher computer self-efficacy and technology integration self-efficacy. Using a multiple case-study approach, video recordings were made of the class sessions of three participating instructors throughout a semester. Content analysis of these video recordings found the instructors using three approaches of computer skills instruction: Extensive behavioral modeling, targeted behavioral modeling, and independent problem-solving. Analysis of pre and post-study student survey responses also found that the three instructional approaches raised their perceived computer self-efficacy. However, the effect sizes were largest when the independent problem-solving approach was used. This approach was also found to have had better motivational effects on students than the extensive behavioral modeling approach. On the other hand, computer skills instruction increased students' technology integration self-efficacy only when instructors modeled teaching-related examples and provided students with multiple mastery experiences of technology integration practices. The applications of the three computer skills instructional approaches for teacher education are discussed. © 2011 Elsevier Ltd. All rights reserved.

Morris M.W.,Columbia University | Chiu C.-Y.,Nanyang Technological University | Liu Z.,Columbia University
Annual Review of Psychology | Year: 2015

We review limitations of the traditional paradigm for cultural research and propose an alternative framework, polyculturalism. Polyculturalism assumes that individuals' relationships to cultures are not categorical but rather are partial and plural; it also assumes that cultural traditions are not independent, sui generis lineages but rather are interacting systems. Individuals take influences from multiple cultures and thereby become conduits through which cultures can affect each other. Past literatures on the influence of multiple cultural identities and cultural knowledge legacies can be better understood within a polyculturalist rubric. Likewise, the concept elucidates how cultures are changed by contact with other cultures, enabling richer psychological theories of intercultural influence. Different scientific paradigms about culture imply different ideologies and policies; polyculturalism's implied policy of interculturalism provides a valuable complement to the traditional policy frames of multiculturalism and colorblindness. © 2015 by Annual Reviews. All rights reserved.

Chong Y.D.,Nanyang Technological University | Stone A.D.,Yale University
Physical Review Letters | Year: 2012

A formula for the laser linewidth of arbitrary cavities in the multimode nonlinear regime is derived from a scattering analysis of the solutions to semiclassical laser theory. The theory generalizes previous treatments of the effects of gain and openness described by the Petermann factor. The linewidth is expressed using quantities based on the nonlinear scattering matrix, which can be computed from steady-state ab initio laser theory; unlike previous treatments, no passive cavity or phenomenological parameters are involved. We find that low cavity quality factor, combined with significant dielectric dispersion, can cause substantial deviations from the Shawlow-Townes-Petermann theory. © 2012 American Physical Society.

Hao Y.,Shanghai JiaoTong University | Asundi A.,Nanyang Technological University
Optics Letters | Year: 2013

Digital holography (DH) is a 3D measurement technique with a theoretical axial resolution of better than 1-2 nm. However, practically, the axial resolution has been quoted to be in the range 10-20 nm. One possible reason is that the axial measurement error is much larger so that the theoretical axial resolution cannot be achieved. Until now the axial measurement errors of the DH system have not been thoroughly discussed. In this Letter, the impact of CCD chip size on the axial measurement error is investigated through both simulation and experiment. The results show that a larger CCD size reduces the axial measurement error and improves the measurement accuracy of edges. © 2013 Optical Society of America.

Gumert M.D.,Nanyang Technological University | Malaivijitnond S.,Chulalongkorn University
American Journal of Physical Anthropology | Year: 2012

Long-tailed macaques (Macaca fascicularis) feed opportunistically in many habitats. The Burmese subspecies (M. f. aurea) inhabits coastal areas in southwestern Thailand and Myanmar, and some of their populations have adapted lithic customs for processing encased foods in intertidal habitats. We investigated the diet of such macaques in Laemson National Park, Thailand, and identified the variety of foods they processed with stones. We conducted 36 shore surveys to study tool sites following feeding activity, during which we counted the minimum number of individual (MNI) food items found at each site. We identified 47 food species (43 animals and four plants), from 37 genera. We counted 1,991 food items during surveys. Nearly all were mollusks (n = 1,924), with the small remainder primarily consisting of crustaceans and nuts. The two most common foods, rock oysters (Saccostrea cucullata; n = 1,062) and nerite snails (Nerita spp.; n = 538), composed 80.2% of our sample. Four prey species comprised 83.2% of the sample (MNI = 1,656), S. cucullata (n = 1,062), Nerita chamaeleon (n = 419), Thais bitubercularis (n = 95), and Monodonta labio (n = 80). Macaques selected a wide variety of foods. However, they heavily concentrated on those that were abundant, easy to access, and sufficiently sized. The Burmese long-tailed macaque stone-processed diet, which focuses on intertidal marine prey, differs from Sapajus and Pan, who use stones primarily for encased nuts and fruits. In terms of diversity of foods exploited, coastal stone-based predation by macaques resembles the diet of coastal-foraging humans (Homo sapiens sapiens). Copyright © 2012 Wiley Periodicals, Inc.

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.

Luyt B.,Nanyang Technological University
Journal of the American Society for Information Science and Technology | Year: 2012

Wikipedia is frequently viewed as an inclusive medium. But inclusivity within this online encyclopedia is not a simple matter of just allowing anyone to contribute. In its quest for legitimacy as an encyclopedia, Wikipedia relies on outsiders to judge claims championed by rival editors. In choosing these experts, Wikipedians define the boundaries of acceptable comment on any given subject. Inclusivity then becomes a matter of how the boundaries of expertise are drawn. In this article I examine the nature of these boundaries and the implications they have for inclusivity and credibility as revealed through the talk pages produced and sources used by a particular subset of Wikipedia's creators-those involved in writing articles on the topic of Philippine history. © 2012 ASIS&T.

Yao Y.,Nanyang Technological University
Journal of tissue engineering and regenerative medicine | Year: 2010

In recent years, transforming growth factor-β3 (TGFβ3) has interested more and more researchers with its competence in engineered histogenesis. In the present study we employed recombinant adenoviral vectors to deliver the constitutively active TGFβ3 gene to human dermal fibroblasts, which could maintain the continuous secretion of TGFβ3 from the cells. The expression of type I collagen in the Ad-TGFβ3 group increased significantly in comparison with other three groups: Neg (cells without treatment of the adenovirus), Ad-null (cells with treatment of the adenovirus, without the inserted gene) and Ad-shRNA (cells with treatment of the adenovirus encoding shRNA specific for type I collagen). Additionally, we demonstrated that TGFβ3 enhanced the expression of Smad4 while inhibiting that of MMP-9, thus promoting the collagen transcription via the Smad signal transduction pathway and restraining collagen degradation by MMP-9, which contributed to the increasing type I collagen expression level. As type I collagen mediates cell-material interactions by providing anchorage, the viability of encapsulated fibroblasts in Ad-TGFβ3 group was significantly higher than that in other three groups. Accordingly, this approach forms an effective way to improve the compatibility of non-adhesive hydrogels containing anchorage-dependent cells. Copyright © 2010 John Wiley & Sons, Ltd.

Jiang H.,East China University of Science and Technology | Ma J.,Nanyang Technological University | Li C.,East China University of Science and Technology
Chemical Communications | Year: 2012

We demonstrate a simple and scalable strategy for synthesizing hierarchical porous NiCo 2O 4 nanowires which exhibit a high specific capacitance of 743 F g -1 at 1 A g -1 with excellent rate performance (78.6% capacity retention at 40 A g -1) and cycling stability (only 6.2% loss after 3000 cycles). © 2012 The Royal Society of Chemistry.

Li Z.,Peking University | Ren W.,University of California at Riverside | Liu X.,Beijing Institute of Technology | Xie L.,Nanyang Technological University
Automatica | Year: 2013

This paper considers the distributed consensus problem of multi-agent systems with general continuous-time linear dynamics for both the cases without and with a leader whose control input might be nonzero and time varying. For the case without a leader, based on the relative output information of neighboring agents, two types of distributed adaptive dynamic consensus protocols are proposed, namely, the edge-based adaptive protocol which assigns a time-varying coupling weight to each edge in the communication graph and the node-based adaptive protocol which uses a time-varying coupling weight for each node. These two adaptive protocols are designed to ensure that consensus is reached in a fully distributed fashion for all undirected connected communication graphs. It is shown that the edge-based adaptive consensus protocol is applicable to arbitrary switching connected graphs. For the case where there exists a leader whose control input is possibly nonzero and bounded, a distributed continuous adaptive protocol is designed to guarantee the ultimate boundedness of the consensus error with respect to any communication graph which contains a directed spanning tree with the leader as the root and whose subgraph associated with the followers is undirected, requiring neither global information of the communication graph nor the upper bound of the leader's control input. A distributed discontinuous protocol is also discussed as a special case. Simulation examples are finally given to illustrate the theoretical results. © 2013 Published by Elsevier Ltd.

Zhang Y.P.,Nanyang Technological University
IEEE Transactions on Antennas and Propagation | Year: 2011

This paper studies the electrical separation and fundamental resonance of differentially-driven microstrip antennas with dual-probe feeds on both electrically thick substrate of high permittivity and electrically thin substrate of low permittivity. The electrical separation is defined as the ratio of the distance ξ of the dual-probe feeds to the free-space wavelength λo. It is found that the occurrence of resonance of the fundamental mode is related with the electrical separation of the dual-probe feeds. When the electrical separation ξ/λo ≥ ψ is satisfied, the resonance occurs. Otherwise, the resonance does not occur. It is shown that the empirical factor ψ is smaller for the electrically thicker substrate of higher permittivity than that for electrically thinner substrate of low permittivity and is smaller for the circular patch than that for the rectangular patch. To validate the relationship of the occurrence of fundamental resonance with the electrical separation, several differentially-driven microstrip antennas were fabricated on the electrically thin substrate of the low permittivity and measured. It is observed that the simulated and measured results are in acceptable agreement for these differentially-driven microstrip antennas. Thus, the electrical separation condition derived in this paper should be very useful in guiding the design of differentially-driven microstrip antennas. © 2006 IEEE.

Pollitz F.F.,U.S. Geological Survey | Burgmann R.,University of California at Berkeley | Banerjee P.,Nanyang Technological University
Geophysical Research Letters | Year: 2011

The three-dimensional crustal displacement field as sampled by GPS is used to determine the coseismic slip of the 2011 M9.0 Tohoku Earthquake. We employ a spherically layered Earth structure and use a combination of onland GPS, out to ∼4000 km from the rupture, and offshore GPS, which samples the high-slip region on the interplate boundary along the Japan trench. Inversion of the displacement field for dip slip, assuming an interplate boundary of variable dip and striking 195°, yields a compact slip maximum of about 33 m located 200 km east of Sendai. The geodetic moment is 4.06 × 1022 N m, corresponding to Mw = 9.0. The area of maximum slip is concentrated at a depth of about 10 km, is updip of the rupture areas of the M ≈ 7 Miyagi-oki earthquakes of 1933, 1936, 1937, and 1978, and roughly coincides with the rupture area of the M7.1 1981 Miyagi-oki earthquake. The overlap of the 2011 slip area with several preceding ruptures suggests that the same asperities may rupture repeatedly with M ≈ 7 events within several decades of one another. Copyright 2011 by the American Geophysical Union.

Klauck H.,Nanyang Technological University
Proceedings of the Annual IEEE Conference on Computational Complexity | Year: 2011

We show several results related to interactive proof modes of communication complexity. First we show lower bounds for the QMA-communication complexity of the functions Inner Product and Disjointness. We describe a general method to prove lower bounds for QMA-communication complexity, and show how one can 'transfer' hardness under an analogous measure in the query complexity model to the communication model using Sherstov's pattern matrix method. Combining a result by Vereshchagin and the pattern matrix method we find a partial function with AM-communication complexity O(log n), PP-communication complexity Ω(n1/3), and QMA-communication complexity Ω(n 1/6). Hence in the world of communication complexity noninteractive quantum proof systems are not able to efficiently simulate conondeterminism or interaction. These results imply that the related questions in Turing machine complexity theory cannot be resolved by 'algebrizing' techniques. Finally we show that in MA-protocols there is an exponential gap between one-way protocols and two-way protocols for a partial function (this refers to the interaction between Alice and Bob). This is in contrast to nondeterministic, AM-, and QMA-protocols, where one-way communication is essentially optimal. © 2011 IEEE.

Seow K.T.,Nanyang Technological University
IEEE Transactions on Control Systems Technology | Year: 2014

An organizational control architecture for supervising a class of multilevel hierarchical discrete-event systems is proposed in this paper. The architecture can be built on the basis of a standard scalable hierarchical design method, formalizing a common design practice of structuring the control of a discrete-event organization bottom-up into a consistent multiworld control hierarchy. It is shown that, under some mild condition of fairness, a multilevel recursive control law exists that is optimal and nonblocking. This law governs the hierarchy top-down as a dynamic programming recursion, over which an organizational control algorithm is obtained that computes the control decisions partially online and in linear time. It is explained and illustrated how the approach reduces the complexity of off-line control synthesis and increases the online transparency of control operations. © 2013 IEEE.

Wang Q.,Nanyang Technological University
Computers and Education | Year: 2010

The ability to work collaboratively is highly valued in today's workplace. However, collaboration does not often naturally happen in a group. Certain strategies must be applied to coordinate individual efforts and monitor the learning process so that effective collaboration can take place. 34 groups from 4 PGDE (Post Graduate Diploma in Education) classes at NIE (National Institute of Education) in Singapore participated in this study. Each group of four members used an online shared workspace to collaborate. Results showed that about half groups actively used the workspaces to share resources, negotiate ideas, and coordinate their collaboration. On the other hand, using the workspaces helped the teacher to easily track and monitor the collaborative learning process, as the workspaces documented what group members did and how they gradually completed the assignment. The students were also required to write weekly progress reports. Results showed that writing progress reports helped group members to reflect on what they had done and also provided additional information for the teacher to confirm their individual contributions. Issues involved in coordinating and monitoring the collaborative learning process are discussed. © 2010 Elsevier Ltd. All rights reserved.

Lee C.S.,Nanyang Technological University
Computers in Human Behavior | Year: 2010

Affordances of information communication technology (ICT) are often thought to influence communicators' usage of a communication technology. This is not surprising since ICTs vary on different dimensions; some ICTs may impose constraints while others afford certain resources. Despite the widespread usage of ICTs in the workplace, we are still not clear about how affordances of ICTs support communicators during ICT-supported interaction. This exploratory study aims to understand the relationship between affordances of ICTs and perceived communication failures (i.e. low, moderate, high). Data for this research was collected from a leading global IT consulting company. We found strong association between affordances of ICT and perceived communication failures. In particular, we found that textual and audio affordances were used to manage high perceived communication failures. Additionally, we were able to identify the core and tangential affordances of ICTs that were useful to help organization communicators enhance their communication competence and reduce potential communication failures. © 2009 Elsevier Ltd. All rights reserved.

The current work demonstrates that native α-cyclodextrin, anchored onto sub-2 μm silica particles via "click" reactions and packed into a 5 cm column, was found to be effective for the resolution of 11 pairs of dansyl-DL-amino acids (DAAs) using ultra-high performance liquid chromatography (UHPLC). All DAAs were completely or partially separated on the column and the resolution achieved for 7 pairs of DAAs was significantly greater than 1.5. It was found that the buffer type exerted a profound impact on the separation. The effects of analyte substituents adjacent to the chiral center of analytes as well as operation conditions with respect to the separation efficiency were discussed. Five racemic compounds with single or double rings also got resolved on this short α-CD column to some extent.

The catalytic reaction of myo-inositol oxygenase, a nonheme diiron enzyme, is initiated by the binding of an O2 molecule to the ferrous center of a mixed-valence Fe(II)Fe(III) intermediate. This generates a (superoxo)Fe(III)Fe(III) reactive species that abstracts a hydrogen atom from the myo-inositol substrate. To understand the effects of protein environment and intracluster dispersion on this O2-binding process, we undertook a combined ONIOM(B3LYP:AMBER) and energy decomposition analysis. The interaction energy between the active site and the thousands of atoms present in the protein environment was decomposed into electrostatic, van der Waals (vdW) and polarization terms. These terms were further decomposed into contributions from individual amino acid residues. The dispersion effect, which is not adequately accounted for by the B3LYP method, was estimated in an empirical manner. The results show that the electrostatic, vdW, and polarization effects slightly enhance the O2 binding process. The dispersion effect enhances O 2 binding more significantly than these effects. Despite these stabilizing effects, the entropy effect disfavors O2 binding, making the process almost thermoneutral. © 2011 American Chemical Society.

Cheng N.-S.,Nanyang Technological University
Powder Technology | Year: 2011

The wall effect on the pressure drop in packed beds could be considered by modifying the Ergun equation based on the concept of hydraulic radius. However, the prediction of the two constants involved in the modified Ergun equation, if using the correlations available in the literature, could differ significantly from one another, and all correlations are not applicable for very low bed-to-particle diameter ratios. In this study, a capillary-type model is proposed to be composed of a bundle of capillary tubes subject to a series of local energy losses, the latter being simulated in terms of sphere drag. The formulas derived provide a good description of variations in the two constants for bed-to-particle diameter ratios ranging from 1.1 to 50.5. © 2011 Elsevier B.V.

Seker U.O.,Nanyang Technological University
Nanoscale | Year: 2013

Utilization of light is crucial for the life cycle of many organisms. Also, many organisms can create light by utilizing chemical energy emerged from biochemical reactions. Being the most important structural units of the organisms, proteins play a vital role in the formation of light in the form of bioluminescence. Such photoproteins have been isolated and identified for a long time; the exact mechanism of their bioluminescence is well established. Here we show a biomimetic approach to build a photoprotein based excitonic nanoassembly model system using colloidal quantum dots (QDs) for a new bioluminescent couple to be utilized in biotechnological and photonic applications. We concentrated on the formation mechanism of nanohybrids using a kinetic and thermodynamic approach. Finally we propose a biosensing scheme with an ON/OFF switch using the QD-GFP hybrid. The QD-GFP hybrid system promises strong exciton-exciton coupling between the protein and the quantum dot at a high efficiency level, possessing enhanced capabilities of light harvesting, which may bring new technological opportunities to mimic biophotonic events.

Song J.,Nanyang Technological University | Guo F.,Shanghai JiaoTong University
Thin-Walled Structures | Year: 2013

The collapse of thin-walled tubes under axial and oblique loading is frequently encountered in real crash events. The windowing and multi-cell methods are effective in improving tubes' energy absorbing performance. In this paper, a comparative study on the performance of windowed and multi-cell square tubes of the same weight under axial and oblique loading is conducted numerically. The results show that the multi-cell tube can achieve higher mean crushing force than the windowed tube but the windowed tube has lower initial peak force. The effectiveness of both methods reduces as the load angle increases. Moreover, the multi-cell and windowed tubes may have worse performance than the conventional tube if the former two collapse in global bending and the later in axial mode. © 2013 Elsevier Ltd.

Park S.Y.,Institute for Infocomm Research | Yu Y.J.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2012

Mixed-scaling-rotation (MSR) coordinate rotation digital computer (CORDIC) is an attractive approach to synthesizing complex rotators. This paper presents the fixed-point error analysis and parameter selections of MSR-CORDIC with applications to the fast Fourier transform (FFT). First, the fixed-point mean squared error of the MSR-CORDIC is analyzed by considering both the angle approximation error and signal round-off error incurred in the finite precision arithmetic. The signal to quantization noise ratio (SQNR) of the output of the FFT synthesized using MSR-CORDIC is thereafter estimated. Based on these analyses, two different parameter selection algorithms of MSR-CORDIC are proposed for general and dedicated MSR-CORDIC structures. The proposed algorithms minimize the number of adders and word-length when the SQNR of the FFT output is constrained. Design examples show that the FFT designed by the proposed method exhibits a lower hardware complexity than existing methods. © 1991-2012 IEEE.

Kemao Q.,Nanyang Technological University
Optics and Lasers in Engineering | Year: 2015

The applications of windowed Fourier fringe analysis in the past decade are reviewed. Because fringe patterns from different optical measurement systems are similar, the reviewed applications are classified according to the functions of the windowed Fourier transform being used in fringe pattern analysis: denosing exponential phase fields, demodulating carrier fringe patterns, getting phase derivatives, and utilizing local properties. From these applications, the windowed Fourier transform is shown to be effective and versatile for fringe pattern analysis. © 2014 Elsevier Ltd.

You K.-Y.,Tsinghua University | Xie L.-H.,Nanyang Technological University
Zidonghua Xuebao/Acta Automatica Sinica | Year: 2013

With the rapid development of sensing, information processing, and communication technologies, the research in the emerging area of networked control systems (NCS) has attracted considerable attention in the research community. The purpose of this survey is to provide a review of state-of-the-art of such research. We particularly discuss various network conditions required for different control purposes, such as the minimum rate coding for stabilizability of linear systems in the presence of time-varying channel capacity, the critical packet loss rate for the stability of the Kalman filter with intermittent observations, network topology for coordination of networked multi-agent systems, as well as event-driven sampling for energy and communication efficiency. The common goal of discussion on these topics is to reveal the effect of the communication network on the operation of the networked systems. Copyright © 2013 Acta Automatica Sinica. All rights reserved.

Zhao D.,Nanyang Technological University
Combustion and Flame | Year: 2012

Combustion instabilities in a Rijke tube could be triggered by the transient growth of flow disturbances, which is associated with its non-normality. In this work, a Rijke tube with three different temperature configurations resulting from a laminar premixed flame are considered to investigate its non-normality and the resulting transient growth of flow disturbances in triggering combustion instabilities. For this, a general thermoacoustic model of a Rijke tube is developed. Unsteady heat release from the flame is assumed to be caused by its surface variations, which results from the fluctuations of the oncoming flow velocity. Coupling the flame model with a Galerkin series expansion of the acoustic waves present enables the time evolution of flow disturbances to be calculated, thus providing a platform on which to gain insights on the Rijke tube stability behaviors. Both eigenmodes orthogonality analysis and transient growth analysis of flow disturbances are performed by linearizing the flame model and recasting it into the classical time-lag . N-τ formulation. It is shown from both analyses that Rijke tube is a non-normal thermoacoustic system and its non-normality depends strongly on the temperature configurations and the flame position. Furthermore, the most 'dangerous' position at which the flame is more susceptible to combustion instabilities are predicted by real-time calculating the maximum transient growth rate of acoustical energy. © 2012 The Combustion Institute.

Zhang Y.,Nanyang Technological University
Advances in Structural Engineering | Year: 2015

The safety of offshore structures is highly dependent on the marine environment, where the latter could result damages to the structures through the deterioration process. A realistic analysis of the offshore structural performance with marine deteriorations is a challenging task. The traditional probabilistic model is sometimes too biased and could lead to undesirable results since the available information regarding the corrosion process is usually quite imprecise and uncertain. In this paper, the robustness assessment of offshore structures with consideration of corrosion effect is investigated through the fuzzy concept. The fuzzy model is introduced to quantify the thickness reduction associated with the corrosion process. The uncertainty regarding the time varying effect of the ultimate strength is analyzed in the computation to reflect the structural deterioration process. The concept of entropy is used to measure the degree of uncertainties in the input and output of a structural model in the robustness assessment. In order to demonstrate this innovation, this paper selects several similar structural models and compares their performances for the same level of damage imprecision. The results are also compared to the traditional probabilistic assessment methods and the experimental models in the literature. The advantage of applying this concept is shown in the results for comparing the performances of different structural systems with various intensities of imprecision in the input parameter. The comparison also demonstrates different cases while the corrosion process is extended to longer period.

Lee K.,Singapore National Institute of Education | Bull R.,Singapore National Institute of Education | Ho R.M.H.,Nanyang Technological University
Child Development | Year: 2013

Although early studies of executive functioning in children supported Miyake et al.'s (2000) three-factor model, more recent findings supported a variety of undifferentiated or two-factor structures. Using a cohort-sequential design, this study examined whether there were age-related differences in the structure of executive functioning among 6- to 15-year-olds (N = 688). Children were tested annually on tasks designed to measure updating and working memory, inhibition, and switch efficiency. There was substantial task-based variation in developmental patterns on the various tasks. Confirmatory factor analyses and tests for longitudinal factorial invariance showed that data from the 5- to 13-year-olds conformed to a two-factor structure. For the 15-year-olds, a well-separated three-factor structure was found. © 2013 Society for Research in Child Development, Inc.

Lee C.B.,Nanyang Technological University
Computers and Education | Year: 2010

This study examines the interactions between problem solving and conceptual change in an elementary science class where students build system dynamic models as a form of problem representations. Through mostly qualitative findings, we illustrate the interplay of three emerging intervening conditions (epistemological belief, structural knowledge and domain knowledge), the choice of learning strategy and the learning outcomes through a theoretical model. © 2010 Elsevier Ltd. All rights reserved.

He B.,Nanyang Technological University | Yu J.X.,Chinese University of Hong Kong
Proceedings of the VLDB Endowment | Year: 2011

OLTP (On-Line Transaction Processing) is an important business system sector in various traditional and emerg-ing online services. Due to the increasing number of users, OLTP systems require high throughput for executing tens of thousands of transactions in a short time period. En-couraged by the recent success of GPGPU (General-Purpose computation on Graphics Processors), we propose GPUTx, an OLTP engine performing high-throughput transaction executions on the GPU for in-memory databases. Com-pared with existing GPGPU studies usually optimizing a single task, transaction executions require handling many small tasks concurrently. Specifically, we propose the bulk execution model to group multiple transactions into a bulk and to execute the bulk on the GPU as a single task. The transactions within the bulk are executed concurrently on the GPU. We study three basic execution strategies (one with locks and the other two lock-free), and optimize them with the GPU features including the hardware support of atomic operations, the massive thread parallelism and the SPMD (Single Program Multiple Data) execution. We eval-uate GPUTx on a recent NVIDIA GPU in comparison with its counterpart on a quad-core CPU. Our experimental re-sults show that optimizations on GPUTx significantly im-prove the throughput, and the optimized GPUTx achieves 4-10 times higher throughput than its CPU-based counter-part on public transaction processing benchmarks. © 2011 VLDB Endowment.

Kai L.,Shanghai University | Kemao Q.,Nanyang Technological University
Optics Express | Year: 2013

A generalized regularized phase tracker (GRPT) for demodulation of a single fringe pattern was recently proposed. It is very successful for many fringe patterns. However, the GRPT has poor performance in the area where the fringe pattern is sparse. An improved GRPT (iGRPT) with two novel improvements is proposed to overcome the problem. First, the fixed window used in the GRPT is replaced by a spatially adaptive window. Second, a background regularization term and a modulation regularization term are incorporated in the cost function. With these two improvements, the proposed iGRPT can successfully demodulate sparse fringes and thus improves the demodulation capability of the GRPT. Simulation and experimental results are presented to verify the performance of the iGRPT. ©2013 Optical Society of America.

Vyas A.,Nanyang Technological University
Journal of Experimental Biology | Year: 2013

Typically, female rats demonstrate clear mate choice. Mate preference is driven by the evolutionary need to choose males with heritable parasite resistance and to prevent the transmission of contagious diseases during mating. Thus, females detect and avoid parasitized males. Over evolutionary time scales, parasite-free males plausibly evolve to advertise their status. This arrangement between males and females is obviously detrimental to parasites, especially for sexually transmitted parasites. Yet Toxoplasma gondii, a sexually transmitted parasite, gets around this obstacle by manipulating mate choice of uninfected females. Males infected with this parasite become more attractive to uninfected females. The ability of T. gondii to not only advantageously alter the behavior and physiology of its host but also secondarily alter the behavior of uninfected females presents a striking example of the 'extended phenotype' of parasites. Toxoplasma gondii also abolishes the innate fear response of rats to cat odor; this likely increases parasite transmission through the trophic route. It is plausible that these two manipulations are not two distinct phenotypes, but are rather part of a single pattern built around testosterone-mediated interplay between mate choice, parasitism and predation. © 2013 Published by The Company of Biologists Ltd.

Song Q.,Nanyang Technological University
IEEE Transactions on Neural Networks | Year: 2010

An Elman network (EN) can be viewed as a feedforward (FF) neural network with an additional set of inputs from the context layer (feedback from the hidden layer). Therefore, instead of the offline backpropagation-through-time (BPTT) algorithm, a standard online (real-time) backpropagation (BP) algorithm, usually called Elman BP (EBP), can be applied for EN training for discrete-time sequence predictions. However, the standard BP training algorithm is not the most suitable for ENs. A low learning rate can improve the training of ENs but can also result in very slow convergence speeds and poor generalization performance, whereas a high learning rate can lead to unstable training in terms of weight divergence. Therefore, an optimal or suboptimal tradeoff between training speed and weight convergence with good generalization capability is desired for ENs. This paper develops a robust extended EBP (eEBP) training algorithm for ENs with a new adaptive dead zone scheme based on eEBP training concepts. The adaptive learning rate and adaptive dead zone optimize the training of ENs for each individual output and improve the generalization performance of the eEBP training. In particular, for the proposed eEBP training algorithm, convergence of the ENs' weights with the adaptive dead zone estimates is proven in the sense of Lyapunov functions. Computer simulations are carried out to demonstrate the improved performance of eEBP for discrete-time sequence predictions. © 2010 IEEE.

The introduction of information and communication technologies (ICT) such as mobile phones to basic health service providers in rural areas can help bridge lacunae in their work environment, resulting from under-capacitated resources, constrained access to information and delayed interventions. The midwife mobile phone project was implemented in 15 health centres in Aceh Besar, Indonesia involving 223 midwives. The study group (121 participants) used project cell phones to transmit health statistics to a central database, contact coordinators and peers for health advice and information, and communicate with doctors and patients.The ICT for healthcare development model (Author, Lwin, Ang, Lin, & Santoso, 2008) was used a heuristic to determine project effectiveness. Findings from the project indicate that the mobile phone has proven to be an effective and efficient device for facilitating smoother communication, and allowing speedier emergency response. The system also aids in gathering and disseminating health-related information to midwives, who in turn convey this knowledge to the patient community. The Technology-Community-Management model (Author & Zhao, 2009; Lee & Author, 2008) was used as a conceptual framework for probing the design of ICT for development projects. In particular, infrastructural, economic, technological, and socio-cultural barriers were examined to highlight the tension between a top-down hierarchical model of technology diffusion versus a more participatory bottom-up approach. © 2010 International Communication Association.

You K.,Tsinghua University | Xie L.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2013

This paper is concerned with the design of transmission scheduler and estimator for linear discrete-time stochastic systems to reduce the number of measurements to be transmitted from sensor to estimator. To this purpose, both controllable and uncontrollable scheduling schemes are considered, respectively. A controllable scheduler is designed as a deterministic function of system measurements, and sequentially decides the transmission of each element of a measurement vector to the estimator. We derive an approximate minimum mean square error (MMSE) estimator. On the other hand, an uncontrollable scheduler means that the transmission of the measurement vector is driven by a random process which is independent of system evolution. The MMSE estimator under this scheduler is cast as the Kalman filtering with intermittent observations. Some stability conditions are established for both the estimators. Finally, illustrative examples are included to validate the theoretical results. © 1991-2012 IEEE.

Song Q.,Nanyang Technological University
IEEE Transactions on Neural Networks | Year: 2011

In this paper, we propose a robust initialization of a Jordan network with a recurrent constrained learning (RIJNRCL) algorithm for multilayered recurrent neural networks (RNNs). This novel algorithm is based on the constrained learning concept of the Jordan network with a recurrent sensitivity and weight convergence analysis, which is used to obtain a tradeoff between the training and testing errors. In addition to using classical techniques for the adaptive learning rate and the adaptive dead zone, RIJNRCL employs a recurrent constrained parameter matrix to switch off excessive contributions from the hidden layer neurons based on weight convergence and stability conditions of the multilayered RNNs. It is well known that a good response from the hidden layer neurons and proper initialization play a dominant role in avoiding local minima in multilayered RNNs. The new RIJNRCL algorithm solves the twin problems of weight initialization and selection of the hidden layer neurons via a novel recurrent sensitivity ratio analysis. We provide the detailed steps for using RIJNRCL in a few benchmark time-series prediction problems and show that the proposed algorithm achieves superior generalization performance. © 2006 IEEE.

Zhou Y.,Nanyang Technological University
Gastroenterology Research and Practice | Year: 2014

Pancreatic cancer is under high mortality but has few effective treatment modalities. High-intensity focused ultrasound (HIFU) is becoming an emerging approach of noninvasively ablating solid tumor in clinics. A variety of solid tumors have been tried on thousands of patients in the last fifteen years with great success. The principle, mechanism, and clinical outcome of HIFU were introduced first. All 3022 clinical cases of HIFU treatment for the advanced pancreatic cancer alone or in combination with chemotherapy or radiotherapy in 241 published papers were reviewed and summarized for its efficacy, pain relief, clinical benefit rate, survival, Karnofsky performance scale (KPS) score, changes in tumor size, occurrence of echogenicity, serum level, diagnostic assessment of outcome, and associated complications. Immune response induced by HIFU ablation may become an effective way of cancer treatment. Comments for a better outcome and current challenges of HIFU technology are also covered. © 2014 Yufeng Zhou.

Skote M.,Nanyang Technological University
Journal of Fluid Mechanics | Year: 2013

Direct numerical simulations have been performed to study the drag reduction resulting from spatial oscillations of a segment of the wall under a turbulent boundary layer. The oscillating motion is imposed by utilizing a streamwise modulated spanwise wall forcing. The results are compared with earlier simulations using temporal oscillations with an identical segment and forcing amplitudes, and with a frequency related to the wavelength through a convective velocity. Two different oscillation amplitudes with equal oscillation wavelength have been used, which allows for a direct comparison between a relatively weak and strong forcing of the flow. The weaker forcing results in 25 % drag reduction while the stronger forcing, with twice the amplitude, yields 41 % drag reduction. Comparison with the temporal cases reveals drastically improved energy savings for the spatial oscillation technique, in accordance with earlier channel flow investigations. The streamwise variation of spanwise shear is shown to follow the analytical solution to the laminar Navier-Stokes equations derived under the assumption of constant friction velocity. Furthermore, the spanwise velocity profiles at various phases are compared with the analytical solution, and show very good agreement. The downstream development of the spatial Stokes layer thickness is theoretically estimated to be ∼x1/15, in general agreement with the simulation data. The spatial variation of the spanwise Reynolds stress is investigated and compared with the variation in time for the temporal wall forcing cases. The controversy regarding a zero or non-zero production of spanwise Reynolds stress in the temporal case is elucidated. In addition, comparison with the spatial case reveals that a second production term originating from the downstream variation of the spanwise wall velocity has a negative contribution to the production, and hence relates to the larger drag reduction in the case of spatial forcing. © 2013 Cambridge University Press.

Gan T.H.,DSO National Laboratories | Tan E.L.,Nanyang Technological University
IEEE Transactions on Antennas and Propagation | Year: 2013

An unconditionally stable fundamental locally one-dimensional (LOD) finite-difference time-domain (FDTD) method with second-order temporal accuracy and complying divergence (CD) (denoted as LOD2-CD-FDTD) is presented for three-dimensional (3-D) Maxwell's equations. While the conventional LOD-FDTD method does not have complying divergence, the LOD2-CD-FDTD method has complying divergence in a manner analogous to the conventional explicit FDTD method. The update procedures for a family of LOD-FDTD methods that employ similar splitting matrix operators are presented. By extending the previous concept of achieving second-order temporal accuracy for the LOD2-FDTD method via implicit output processing, we hereby propose novel, explicit output processing that not only retains second-order temporal accuracy, but also complying divergence for the LOD2-CD-FDTD method. The current source implementation for the LOD2-CD-FDTD method involves source-incorporation in only the first procedure. To further enhance efficiency, the LOD2-CD-FDTD method is formulated into the fundamental LOD2-CD-FDTD method with efficient matrix-operator-free right-hand sides. Subsequently, detailed implementation for the fundamental LOD2-CD-FDTD method is presented. Analytical proof is provided to ascertain the second-order temporal accuracy of the LOD2-CD-FDTD method. Numerical results and examples are also presented to validate the divergence-complying property of the LOD2-CD-FDTD method. © 1963-2012 IEEE.

Cai S.-M.,Nanyang Technological University | Gong Y.,South University of Science and Technology of China
IEEE Transactions on Signal Processing | Year: 2013

In this paper, we consider cognitive beamforming for multiple secondary data streams subject to individual signal-to-noise ratio (SNR) requirements for each secondary data stream. In such a cognitive radio system, the secondary user is permitted to use the spectrum allocated to the primary user as long as the caused interference at the primary receiver is tolerable. With both secondary SNR constraint and primary interference power constraint, we aim to minimize the secondary transmit power consumption. By exploiting the individual SNR requirements, we formulate this cognitive beamforming problem as an optimization problem on the Stiefel manifold. Both zero forcing beamforming (ZFB) and nonzero forcing beamforming (NFB) are considered. For the ZFB case, we derive a closed-form beamforming solution. For the NFB case, we prove that the strong duality holds for the nonconvex primal problem and thus the optimal solution can be easily obtained by solving the dual problem. Finally, numerical results are presented to illustrate the performance of the proposed cognitive beamforming solutions. © 1991-2012 IEEE.

Xiong C.,Nanyang Technological University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We apply the Callan-Harvey anomaly-inflow mechanism to the study of QCD (chromoelectric) flux tubes, quark (pair) creation, and the chiral magnetic effect, using new variables from the Cho-Faddeev-Niemi decomposition of the gauge potential. A phenomenological description of chromoelectric flux tubes is obtained by studying a gauged Nambu-Jona-Lasinio effective Lagrangian, derived from the original QCD Lagrangian. At the quantum level, quark condensates in the QCD vacuum may form a vortexlike structure in a chromoelectric flux tube. Quark zero modes trapped in the vortex are chiral and lead to a two-dimensional gauge anomaly. To cancel it, an effective Chern-Simons coupling is needed and, hence, a topological charge density term naturally appears. © 2013 American Physical Society.

Wu K.,Nanyang Technological University
International Journal of Production Research | Year: 2014

Queueing theory is commonly used to evaluate the performance of production systems. Due to the complexity of practical production lines, choosing correct queueing models under the existence of interruptions can be intricate, but is critical to the evaluation of system performance. This paper gives a review of research in this area, proposes a systematic way to classify different types of interruptions in manufacturing systems and suggests proper queueing models for each category. The operational definition of service time is given and the decomposition properties for the run-based state-induced and time-based preemptive events are explained. The corresponding G/G/1 approximate models are proposed. © 2013 Taylor and Francis.

Roca X.,Nanyang Technological University | Krainer A.R.,Cold Spring Harbor Laboratory | Eperon I.C.,University of Leicester
Genes and Development | Year: 2013

Splice site selection is fundamental to pre-mRNA splicing and the expansion of genomic coding potential. 5′ Splice sites (5′ss) are the critical elements at the 5′ end of introns and are extremely diverse, as thousands of different sequences act as bona fide 5′ss in the human transcriptome. Most 5′ss are recognized by base-pairing with the 5′ end of the U1 small nuclear RNA (snRNA). Here we review the history of research on 5′ss selection, highlighting the difficulties of establishing how basepairing strength determines splicing outcomes. We also discuss recent work demonstrating that U1 snRNA:5′ss helices can accommodate noncanonical registers such as bulged duplexes. In addition, we describe the mechanisms by which other snRNAs, regulatory proteins, splicing enhancers, and the relative positions of alternative 5′ss contribute to selection. Moreover, we discuss mechanisms by which the recognition of numerous candidate 5′ss might lead to selection of a single 5′ss and propose that protein complexes propagate along the exon, thereby changing its physical behavior so as to affect 5′ss selection. © 2013 by Cold Spring Harbor Laboratory Press.

Chiba S.,Nanyang Technological University
Chemistry Letters | Year: 2012

This Highlight Review describes a Cu-Rh bimetallic redox relay catalytic system that enables efficient synthesis of highly substituted isoquinolines and their derivatives from readily available aryl ketoximes or α-arylvinyl azides with internal alkynes via C-H bond functionalization. A preliminary mechanistic investigation revealed that both the Cu and Rh catalysts are prerequisites to achieve the present process, and play their particular roles with synergistic cooperation during the multistep sequence. © 2012 The Chemical Society of Japan.

Zhao D.,Nanyang Technological University | Reyhanoglu M.,Embry - Riddle Aeronautical University
Journal of Sound and Vibration | Year: 2014

Transient growth of acoustic disturbances could trigger thermoacoustic instability in a combustion system with non-orthogonal eigenmodes, even with stable eigenvalues. In this work, feedback control of transient growth of flow perturbations in a Rijke-type combustion system is considered. For this, a generalized thermoacoustic model with distributed monopole-like actuators is developed. The model is formulated in state-space to gain insights on the interaction between various eigenmodes and the dynamic response of the system to the actuators. Three critical parameters are identified: (1) the mode number, (2) the number of actuators, and (3) the locations of the actuators. It is shown that in general the number of the actuators K is related to the mode number N as K=N2. For simplicity in illustrating the main results of the paper, two different thermoacoustic systems are considered: system (a) with one mode and system (b) that involves two modes. The actuator location effect is studied in system (a) and it is found that the actuator location plays an important role in determining the control effort. In addition, sensitivity analysis of pressure- and velocity-related control parameters is conducted. In system (b), when the actuators are turned off (i.e., open-loop configuration), it is observed that acoustic energy transfers from the high frequency mode to the lower frequency mode. After some time, the energy is transferred back. Moreover, the high frequency oscillation grows into nonlinear limit cycle with the low frequency oscillation amplified. As a linear-quadratic regulator (LQR) is implemented to tune the actuators, both systems become asymptotically stable. However, the LQR controller fails in eliminating the transient growth, which may potentially trigger thermoacoustic instability. In order to achieve strict dissipativity (i.e., unity maximum transient growth), a transient growth controller is systematically designed and tested in both systems. Comparison is then made between the performance of the LQR controller and that of the transient growth controller. It is found in both systems that the transient growth controller achieves both exponential decay of the flow disturbance energy and unity maximum transient growth. © 2014 Elsevier Ltd.

Zhang J.,Nanyang Technological University | Hong S.H.,Seoul National University
Organic Letters | Year: 2012

Direct N-acylation of lactams, oxazolidinones, and imidazolidinones was achieved with aldehydes by Shvo's catalyst without using any other stoichiometric reagent. The N-acylations with α,β-unsaturated aldehydes were achieved with excellent yields. © 2012 American Chemical Society.

Pumera M.,Nanyang Technological University
Electrochemistry Communications | Year: 2013

The electrochemical behaviors of single-, few- and multi-layer graphene, graphene oxides, reduced graphene oxides, CVD graphene and three-dimensional graphene are discussed and critically evaluated, providing an up-to-date summary on the progress of the field. © 2013 Elsevier B.V.

Chhowalla M.,Rutgers University | Shin H.S.,Ulsan National Institute of Science and Technology | Eda G.,National University of Singapore | Li L.-J.,Academia Sinica, Taiwan | And 2 more authors.
Nature Chemistry | Year: 2013

Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs-obtained either through exfoliation of bulk materials or bottom-up syntheses-are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors. © 2013 Macmillan Publishers Limited. All rights reserved.

Hasan M.,University of Manitoba | Hossain E.,University of Manitoba | Niyato D.,Nanyang Technological University
IEEE Communications Magazine | Year: 2013

Machine-to-machine communication, a promising technology for the smart city concept, enables ubiquitous connectivity between one or more autonomous devices without or with minimal human interaction. M2M communication is the key technology to support data transfer among sensors and actuators to facilitate various smart city applications (e.g., smart metering, surveillance and security, infrastructure management, city automation, and eHealth). To support massive numbers of machine type communication (MTC) devices, one of the challenging issues is to provide an efficient way for multiple access in the network and to minimize network overload. In this article, we review the M2M communication techniques in Long Term Evolution- Advanced cellular networks and outline the major research issues. Also, we review the different random access overload control mechanisms to avoid congestion caused by random channel access of MTC devices. To this end, we propose a reinforcement learning-based eNB selection algorithm that allows the MTC devices to choose the eNBs (or base stations) to transmit packets in a self-organizing fashion. © 2013 IEEE.

Su R.,Nanyang Technological University | Woeginger G.,TU Eindhoven
Automatica | Year: 2011

In performance evaluation or supervisory control, we often encounter problems of determining the maximum or minimum string execution time for a finite language when estimating the worst-case or best-case performance. It has been shown in the literature that the time complexity for computing the maximum string execution time for a finite language is polynomial with respect to the size of an automaton recognizer of that language and the dimension of the corresponding resource matrices. In this paper we provide a more efficient algorithm to compute such maximum string execution time. Then we show that it is NP-complete to determine the minimum string execution time. © 2011 Elsevier Ltd. All rights reserved.

Zhou Y.,Nanyang Technological University
Ultrasonics | Year: 2013

High intensity focused ultrasound (HIFU) is emerging as an effective oncology treatment modality according to the clinical experience in the last decade. The temperature at the focus can reach over 65 °C within seconds, denaturing cellular proteins and resulting in coagulative necrosis. HIFU parameters are usually kept the same for each treatment spot in tumor ablation. Because of the thermal diffusion from nearby spots, the lesion size will gradually increase as the HIFU therapy progresses, which leads to insufficient treatment of initial spots and over exposure of later ones. From the viewpoint of the physician, uniform lesions with the least energy exposure and the least energy are preferred in tumor ablation. In this study, an algorithm was developed to determine the number of HIFU pulses delivered to each spot in order to generate uniform lesions that fill the region-of-interest completely. The exposure energies required using different scanning pathways (raster scanning, spiral scanning from the center to the outside, and spiral scanning from the outside to the center), spot spacing (1 mm, 2 mm, 4 mm, and 6 mm) and motion time (from 0 s to 400 s) were compared with each other. It is found that spiral scanning from the outside to the center with spot spacing of 2 mm and motion time less than 10 s needs the least numbers of pulses or HIFU energy in uniform lesion production with the minimal temperature elevation. In addition, the effects of thermal properties of tissue (i.e., specific heat capacity, convective heat transfer coefficient, and thermal conductivity) on HIFU ablation were investigated in order to determine the HIFU treatment planning for various targets. Uniform lesion production in the transparent gel phantom and ex vivo bovine liver samples using the proposed algorithm proved effective and accord with the simulation for different scanning pathways by an extracorporeal clinical HIFU system. Therefore, dynamically adjusting ultrasound exposure energy can improve the efficacy and safety of HIFU ablation, and the treatment planning depends on the scanning protocol and thermal properties of the target. © 2012 Elsevier B.V. All rights reserved.

Mitchell W.,Agency for Science, Technology and Research Singapore | Mitchell W.,Nanyang Technological University
Current Opinion in Chemical Biology | Year: 2011

DNA sequencing has uncovered microbial secondary metabolic potential that never surfaced in fermentation based screens. Deep and cheap sequencing of a genus such as Streptomyces can rapidly expose hundreds of metabolic genes and operons. Meanwhile, synthetic biologists, in their quest to engineer advanced biofuels, are mastering metabolic engineering. Natural products, a reliable source of new therapeutic leads for many years, have fallen into disfavor with drug discoverers partly because these molecules are rarely available as pure compounds and sourcing is often problematic. The convergence of next generation sequencing and synthetic biology, along with less spectacular progress in analytic technologies such as mass spectroscopy, opens the door to the creation of large, reliable libraries of pure natural products for drug discovery. © 2011 Elsevier Ltd.

Jackman J.A.,Nanyang Technological University
Biointerphases | Year: 2012

As one of the most important interfaces in cellular systems, biological membranes have essential functions in many activities such as cellular protection and signaling. Beyond their direct functions, they also serve as scaffolds to support the association of proteins involved in structural support, adhesion, and transport. Unfortunately, biological processes sometimes malfunction and require therapeutic intervention. For those processes which occur within or upon membranes, it is oftentimes difficult to study the mechanism in a biologically relevant, membranous environment. Therefore, the identification of direct therapeutic targets is challenging. In order to overcome this barrier, engineering strategies offer a new approach to interrogate biological activities at membrane interfaces by analyzing them through the principles of the interfacial sciences. Since membranes are complex biological interfaces, the development of simplified model systems which mimic important properties of membranes can enable fundamental characterization of interaction parameters for such processes. We have selected the hepatitis C virus (HCV) as a model viral pathogen to demonstrate how model membrane platforms can aid antiviral drug discovery and development. Responsible for generating the genomic diversity that makes treating HCV infection so difficult, viral replication represents an ideal step in the virus life cycle for therapeutic intervention. To target HCV genome replication, the interaction of viral proteins with model membrane platforms has served as a useful strategy for target identification and characterization. In this review article, we demonstrate how engineering approaches have led to the discovery of a new functional activity encoded within the HCV nonstructural 5A protein. Specifically, its N-terminal amphipathic, α-helix (AH) can rupture lipid vesicles in a size-dependent manner. While this activity has a number of exciting biotechnology and biomedical applications, arguably the most promising one is in antiviral medicine. Based on the similarities between lipid vesicles and the lipid envelopes of virus particles, experimental findings from model membrane platforms led to the prediction that a range of medically important viruses might be susceptible to rupturing treatment with synthetic AH peptide. This hypothesis was tested and validated by molecular virology studies. Broad-spectrum antiviral activity of the AH peptide has been identified against HCV, HIV, herpes simplex virus, and dengue virus, and many more deadly pathogens. As a result, the AH peptide is the first in class of broad-spectrum, lipid envelope-rupturing antiviral agents, and has entered the drug pipeline. In summary, engineering strategies break down complex biological systems into simplified biomimetic models that recapitulate the most important parameters. This approach is particularly advantageous for membrane-associated biological processes because model membrane platforms provide more direct characterization of target interactions than is possible with other methods. Consequently, model membrane platforms hold great promise for solving important biomedical problems and speeding up the translation of biological knowledge into clinical applications.

Wong T.K.S.,Nanyang Technological University
Materials | Year: 2012

The time dependent dielectric breakdown phenomenon in copper low-k damascene interconnects for ultra large-scale integration is reviewed. The loss of insulation between neighboring interconnects represents an emerging back end-of-the-line reliability issue that is not fully understood. After describing the main dielectric leakage mechanisms in low-k materials (Poole-Frenkel and Schottky emission), the major dielectric reliability models that had appeared in the literature are discussed, namely: the Lloyd model, 1/E model, thermochemical E model, E1/2 models, E2 model and the Haase model. These models can be broadly categorized into those that consider only intrinsic breakdown (Lloyd, 1/E, E and Haase) and those that take into account copper migration in low-k materials (E1/2, E2). For each model, the physical assumptions and the proposed breakdown mechanism will be discussed, together with the quantitative relationship predicting the time to breakdown and supporting experimental data. Experimental attempts on validation of dielectric reliability models using data obtained from low field stressing are briefly discussed. The phenomenon of soft breakdown, which often precedes hard breakdown in porous ultra low-k materials, is highlighted for future research.© 2012 by the authors.

Yu N.,Harvard University | Wang Q.,Nanyang Technological University | Capasso F.,Harvard University
Laser and Photonics Reviews | Year: 2012

This paper reviews beam engineering of mid-infrared and terahertz quantum cascade lasers (QCLs), based on two approaches: designer plasmonic structures and deformed microcavities. The plasmonic structures couple laser emission into surface waves and control the laser wavefront in the near-field, thereby greatly increasing beam collimation or introducing new functionalities to QCLs. The plasmonic designs overall preserve laser performance in terms of operating temperature and power output. The deformed microcavity QCLs operate primarily on whispering-gallery modes, which have much higher quality factors than other modes, leading to lower threshold current densities. Cavity deformations are carefully controlled to greatly enhance directionality and output power. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhao D.,Nanyang Technological University
Energy Conversion and Management | Year: 2013

In this work, a convection-driven Rijke-Zhao thermo-acoustic-piezo system is designed and experimentally tested to demonstrate its potential for harvesting thermal energy. For this, a nonlinear theoretical model is developed to simulate the energy conversion process, i.e. heat-to-sound-to-electricity in the present system. Unlike the conventional conduction-driven thermoacoustic converters, our present system involves no heat exchangers and stacks. As a heat source is placed in a Rijke-Zhao tube with two bifurcating daughter branches, self-sustained thermoacoustic oscillations are generated. The resulting acoustic fields in the bifurcating branches are dramatically different. One branch is associated with 'hot' oscillations. However the other is with 'cold' oscillations at ambient temperature, which enable a piezoelectric generator being implemented to the end of the branch. In order to measure the acoustic fields in the bifurcating branches, two arrays of thermocouples and microphones are used. The maximum sound pressure level is around 139 dB. The output electric power and acoustical energy conversion efficiency are measured and compared with that from a similar but a conduction-driven thermo-acoustic-piezo system. It is found that 60% more power is generated. And the energy conversion efficiency is increased by 105%. These experimental results confirm that the developed Rijke-Zhao thermo-acoustic-piezo system is an invaluable tool in designing a simple, low-cost, energy-efficient thermoacoustic system. © 2012 Elsevier Ltd. All rights reserved.

Yang E.-H.,Nanyang Technological University | Li V.C.,University of Michigan
Cement and Concrete Research | Year: 2012

This paper presents results of deliberate tailoring of engineered cementitious composites (ECC) for impact resistance. Microstructure control involving fiber, matrix and fiber/matrix interface was based on steady-state dynamic crack growth analyses accounting for rate dependence of composite phases. Uniaxial tensile stress-strain curves of the resulting impact resistant ECC were experimentally determined for strain rates ranging from 10 - 5 s - 1 to 10 - 1 s - 1. Low speed drop weight tower test on ECC panels and beams was also conducted. Damage characteristics, load and energy dissipation capacities, and response to repeated impacts, were studied. © 2012 Elsevier Ltd. All rights reserved.

Li G.,Data Storage Institute Singapore | Wen C.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2012

In this paper, we consider the parametric version of Wiener systems where both the linear and nonlinear parts are identified with clipped observations in the presence of internal and external noises. Also the static functions are allowed noninvertible. We propose a classification based support vector machine (SVM) and formulate the identification problem as a convex optimization. The solution to the optimization problem converges to the true parameters of the linear system if it is an finite-impulse-resposne (FIR) system, even though clipping reduces a great deal of information about the system characteristics. In identifying a Wiener system with a stable infinite-impulse-response (IIR) system, an FIR system is used to approximate it and the problem is converted to identifying the FIR system together with solving a set of nonlinear equations. This leads to biased estimates of parameters in the IIR system while the bias can be controlled by choosing the order of the approximated FIR system. © 2012 IEEE.

Kapur M.,Nanyang Technological University
Cognitive Science | Year: 2014

When learning a new math concept, should learners be first taught the concept and its associated procedures and then solve problems, or solve problems first even if it leads to failure and then be taught the concept and the procedures? Two randomized-controlled studies found that both methods lead to high levels of procedural knowledge. However, students who engaged in problem solving before being taught demonstrated significantly greater conceptual understanding and ability to transfer to novel problems than those who were taught first. The second study further showed that when given an opportunity to learn from the failed problem-solving attempts of their peers, students outperformed those who were taught first, but not those who engaged in problem solving first. Process findings showed that the number of student-generated solutions significantly predicted learning outcomes. These results challenge the conventional practice of direct instruction to teach new math concepts and procedures, and propose the possibility of learning from one's own failed problem-solving attempts or those of others before receiving instruction as alternatives for better math learning. © 2014 Cognitive Science Society, Inc.

Cheng N.-S.,Nanyang Technological University
Water Resources Research | Year: 2011

Roughness length scale is important in the evaluation of resistance caused by submerged vegetation in open channel flows. By transforming the concept of hydraulic radius, a representative roughness height is proposed in this study for quantifying effect of submerged vegetation on flow resistance in the surface layer. The proposed roughness height is characterized by its proportionality to both stem diameter and vegetation concentration and performs better than other length scales in collapsing resistance data collected under a wide range of vegetation conditions. An approach is then developed for estimate of the average flow velocity and thus resistance coefficients for both cases of rigid and flexible vegetation. Comparisons are also made between the present study and other four formulas available in the literature. This study also shows that all the formulas, if simplified for some simple conditions, can be unified in a general form. Copyright 2011 by the American Geophysical Union.

Zhao L.,Nanyang Technological University
BMC bioinformatics | Year: 2012

Prediction of B-cell epitopes from antigens is useful to understand the immune basis of antibody-antigen recognition, and is helpful in vaccine design and drug development. Tremendous efforts have been devoted to this long-studied problem, however, existing methods have at least two common limitations. One is that they only favor prediction of those epitopes with protrusive conformations, but show poor performance in dealing with planar epitopes. The other limit is that they predict all of the antigenic residues of an antigen as belonging to one single epitope even when multiple non-overlapping epitopes of an antigen exist. In this paper, we propose to divide an antigen surface graph into subgraphs by using a Markov Clustering algorithm, and then we construct a classifier to distinguish these subgraphs as epitope or non-epitope subgraphs. This classifier is then taken to predict epitopes for a test antigen. On a big data set comprising 92 antigen-antibody PDB complexes, our method significantly outperforms the state-of-the-art epitope prediction methods, achieving 24.7% higher averaged f-score than the best existing models. In particular, our method can successfully identify those epitopes with a non-planarity which is too small to be addressed by the other models. Our method can also detect multiple epitopes whenever they exist. Various protrusive and planar patches at the surface of antigens can be distinguishable by using graphical models combined with unsupervised clustering and supervised learning ideas. The difficult problem of identifying multiple epitopes from an antigen can be made easied by using our subgraph approach. The outstanding residue combinations found in the supervised learning will be useful for us to form new hypothesis in future studies.

Pumera M.,Nanyang Technological University
Current Drug Metabolism | Year: 2012

Nanomaterials and nanotechnology is in forefront of materials research. Minimal attention is given to the potential participation of these materials in cell metabolism. Here we review recent efforts to understanding how carbon nanomaterials participate on cell metabolism. First, the introduction to the materials science of graphene, carbon nanotubes and metallic nanoparticles is give. Second, different mechanisms of participation of these materials on the cell metabolism are discussed and elucidated. © 2012 Bentham Science Publishers.

Koh J.B.Y.,Nanyang Technological University
Microfluidics and Nanofluidics | Year: 2015

In this review article, we seek to provide a link between our understanding of the spermatozoa on the physical aspects and applications involving assisted reproduction, so that future research in this field can be better poised for improving current procedures. A brief discussion is included regarding the difference in the fluid mechanics of a Newtonian and viscoelastic fluid medium. A review is then done on the current microfluidic sorting techniques applicable to spermatozoa, which includes the albumin gradient separation, fluorescence activated flow cytometry, electrophoresis, dielectrophoresis, countercurrent distribution, movement of motile sperms, accumulation at walls, and optical trapping. Common preparation methods for spermatozoa used in assisted reproduction are also introduced. A number of other general particle manipulation methods which could potentially be incorporated for sperm sorting are also discussed. © 2014, Springer-Verlag Berlin Heidelberg.

Grayman J.H.,Nanyang Technological University
Social Science and Medicine | Year: 2014

After more than 20 years of sporadic separatist insurgency, the Free Aceh Movement and the Indonesian government signed an internationally brokered peace agreement in August 2005, just eight months after the Indian Ocean tsunami devastated Aceh's coastal communities. This article presents a medical humanitarian case study based on ethnographic data I collected while working for a large aid agency in post-conflict Aceh from 2005 to 2007. In December 2005, the agency faced the first test of its medical and negotiation capacities to provide psychiatric care to a recently amnestied political prisoner whose erratic behavior upon returning home led to his re-arrest and detention at a district police station. I juxtapose two methodological approaches-an ethnographic content analysis of the agency's email archive and field-based participant-observation-to recount contrasting narrative versions of the event. I use this contrast to illustrate and critique the immediacy of the humanitarian imperative that characterizes the industry. Immediacy is explored as both an urgent moral impulse to assist in a crisis and a form of mediation that seemingly projects neutral and transparent transmission of content. I argue that the sense of immediacy afforded by email enacts and amplifies the humanitarian imperative at the cost of abstracting elite humanitarian actors out of local and moral context. As a result, the management and mediation of this psychiatric case by email produced a bureaucratic model of care that failed to account for complex conditions of chronic political and medical instability on the ground. © 2014 Elsevier Ltd.

Chen T.,Nanyang Technological University
Chemical Engineering Research and Design | Year: 2010

The primary objective of this note is to reduce the false alarms in multivariate statistical process control (MSPC). The issue of false alarms is inherent within MSPC as a result of the definition of control limits. It has been observed that under normal operating conditions, the occurrence of " out-of-control" data, i.e. false alarms, conforms to a Bernoulli distribution. Therefore, this issue can be formally addressed by developing a Binomial distribution for the number of " out-of-control" data points within a given time window, and a second-level control limit can be established to reduce the false alarms. This statistical approach is further extended to consider the combination of multiple control charts. The proposed methodology is demonstrated through its application to the monitoring of a benchmark simulated chemical process, and it is observed to effectively reduce the false alarms whilst retaining the capability of detecting process faults. © 2009 The Institution of Chemical Engineers.

Cao J.,Hangzhou Dianzi University | Lin Z.,Nanyang Technological University
Information Sciences | Year: 2014

This paper proposes the Bayesian approach to signal detection in compressed sensing (CS) using compressed measurements directly. A general expression of the probability of error is obtained where the prior probabilities of hypotheses could be equal or unequal and the additive noise is assumed to be uncorrelated Gaussian noise with possibly unequal variances. Upper and lower bounds of the probability of error are also derived using the restricted isometry property (RIP) constant and then the more computationally feasible mutual coherence of a given sampling matrix in CS. When the difference between the prior probabilities is sufficiently small and the signal to noise ratio is relatively large, an approximate but simpler expression of the probability of error is obtained. Furthermore, a new bound of the probability of error is derived in terms of a piecewise function. Numerical simulations are also provided to illustrate the new theoretical results. © 2014 Elsevier Inc. All rights reserved.

Gumert M.D.,Nanyang Technological University | Malaivijitnond S.,Chulalongkorn University
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2013

Tool selection can affect the success of a tool-based feeding task, and thus toolusing animals should select appropriate tools when processing foods.We performed a field experiment on Piak Nam Yai Island in Laem Son National Park, Thailand, to test whether Burmese long-tailed macaques (Macaca fascicularis aurea) selected stone tools according to food type. We baited the island's shores with stone sets ('tool tests') in an effort to attract macaques to use stones presented in a quasi-experimental design. Tool tests were placed at 344 locations for 126 days over a 2 year period, with each set containing four stones of different mass (categories: X, 40-60 g; S, 90-100 g; M, 150-200 g; and L, 400-1000 g). Tool tests were checked when we could access them. The number of times each tool test was checked varied (1-32), for a total of 1950 checks. We also studied 375 non-experimental stone tools that were found at naturally occurring tool-use sites. Our data were not collected by direct observation, but by inspecting stones after use. We found an association between stone mass and food type. In the tool tests, we found S-stones were chosen most often for attached oysters, and L-stones were chosen most often for unattached foods. L-stones were almost always chosen for larger unattached foods (greater than 3 cm length), while for smaller unattached foods (less than or equal to 3 cm length) selection was less skewed to L-stones and more evenly distributed between the M- and L-stone categories. In the non-experimental study, we found that mass varied significantly across five food categories (range: 16-5166 g). We reveal more detail on macaque stone tool mass than previous studies, showing that macaques select differing stone masses across a variety of tool-processed foods. Our study is the first step in investigating the behavioural and cognitive mechanisms that macaques are using during tool selection. © 2013 The Author(s) Published by the Royal Society. All rights reserved.

Thai V.V.,Nanyang Technological University
International Journal of Logistics Research and Applications | Year: 2013

There has been very little research done in logistics service on how its quality is defined and attributed. In this paper, we aim to explore the definition of the concept of quality in logistics service and its associated dimensions by constructing a conceptual model and test it empirically. A survey was conducted in Singapore with 2333 logistics service providers and customers from Singapore Logistics Association and Singapore's National Shipper Council. A total of 171 questionnaires including 86 from logistics service providers and 85 customers were returned. After the process of exploratory factor analysis followed by confirmatory factor analysis, we found that the revised model of five factors and 20 items of logistics service quality (LSQ) is valid and reliable to measure the quality of logistics service. It was also indicated from the study that the quality of customer focus is deemed the most critical to enhance the perceived LSQ. © 2013 Copyright Taylor and Francis Group, LLC.

Pumera M.,Nanyang Technological University
Energy and Environmental Science | Year: 2011

There is enormous interest in the use of graphene-based materials for energy storage. This article discusses the progress that has been accomplished in the development of chemical, electrochemical, and electrical energy storage systems using graphene. We summarize the theoretical and experimental work on graphene-based hydrogen storage systems, lithium batteries, and supercapacitors. Even though the research on the use of graphene for energy storage began very recently, the explosive growth of the research conducted in this area makes this minireview timely. © 2011 The Royal Society of Chemistry.

Dong F.M.,Nanyang Technological University
Journal of Combinatorial Theory. Series B | Year: 2015

For any integer k≥0, let ξk be the supremum in (1, 2] such that the flow polynomial F(G, λ) has no real roots in (1, ξk) for all graphs G with at most k vertices of degrees larger than 3. We prove that ξk can be determined by considering a finite set of graphs and show that ξk=2 for k≤2, ξ3=1.430⋯ , ξ4=1.361⋯ and ξ5=1.317⋯. © 2014 Elsevier Inc.

Wong L.-H.,Nanyang Technological University
Educational Technology and Society | Year: 2013

As part of a learner's learning ecology, the informal, out-of-school settings offer virtually boundless opportunities to advance one's learning. This paper reports on "Move, Idioms!", a design for Mobile-Assisted Language Learning experience that accentuates learners' habit of mind and skills in making meaning with their daily encounters, and associating those with the language knowledge learned in formal learning settings. The students used smartphones on a 1:1, 24x7 basis to capture photos in real-life contexts as artifacts related to Chinese idioms, made sentences with the idioms, and then posted them onto a wiki space for peer reviews. In this paper, we focus on investigating students' cognitive processes and patterns in artifact creations in informal settings. Our analysis and interpretation of such student activities is framed by the notion of Learner-Generated Context (LGC) (Luckin, 2008), a reconceptualization of 'learning contexts' that implies greater learner autonomy. Through two case studies, we gained better understanding in the impact of LGC and how it is crystallized in seamless learning processes with the interplay of physical settings, parental involvements and the mediation of mobile technology. © International Forum of Educational Technology & Society (IFETS).

Ho J.,Nanyang Technological University
Marine Policy | Year: 2010

Although a 'blue' Arctic Ocean is predicted in the summertime to occur from the middle of this century, current rates of warming indicate an earlier realization. Also, routes along the coast of Siberia will be navigable much earlier. However, before the Arctic routes can reliably be used on a large scale for transit by shipping along its passages, more investments are required on infrastructure and the provision of marine services to ensure the safe and secure transit of shipping with minimal environmental impact. © 2009 Elsevier Ltd. All rights reserved.

Kong A.W.K.,Nanyang Technological University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2015

IrisCode has been used to gather iris data for 430 million people. Because of the huge impact of IrisCode, it is vital that it is completely understood. This paper first studies the relationship between bit probabilities and a mean of iris images (The mean of iris images is defined as the average of independent iris images.) and then uses the Chi-square statistic, the correlation coefficient and a resampling algorithm to detect statistical dependence between bits. The results show that the statistical dependence forms a graph with a sparse and structural adjacency matrix. A comparison of this graph with a graph whose edges are defined by the inner product of the Gabor filters that produce IrisCodes shows that partial statistical dependence is induced by the filters and propagates through the graph. Using this statistical information, the security risk associated with two patented template protection schemes that have been deployed in commercial systems for producing application-specific IrisCodes is analyzed. To retain high identification speed, they use the same key to lock all IrisCodes in a database. The belief has been that if the key is not compromised, the IrisCodes are secure. This study shows that even without the key, application-specific IrisCodes can be unlocked and that the key can be obtained through the statistical dependence detected. © 1979-2012 IEEE.

Zhang J.,University of Southampton | MacDonald K.F.,University of Southampton | Zheludev N.I.,University of Southampton | Zheludev N.I.,Nanyang Technological University
Light: Science and Applications | Year: 2013

We introduce a dielectric photonic metamaterial presenting a giant nonlinear optical response driven by resonant optomechanical forces. Being inherently free of Joule losses, it exhibits optical bistability at intensity levels of less than 0.2mWμm-2 and, furthermore, manifests nonlinear asymmetric transmission with a forward : backward optical extinction ratio of more than 30 dB. © 2013 CIOMP. All rights reserved.

Lu H.,Harbin Institute of Technology | Min Huang W.,Nanyang Technological University
Applied Physics Letters | Year: 2013

The present work studies the synergistic effect of self-assembled carboxylic acid-functionalized carbon nanotube (CNT) and carbon fiber on the electrical property and electro-activated recovery behavior of shape memory polymer (SMP) nanocomposites. The combination of CNT and carbon fiber results in improved electrical conductivity in the SMP nanocomposites. Carboxylic acid-functionalized CNTs are grafted onto the carbon fibers and then self-assembled by deposition to significantly enhance the reliability of the bonding between carbon fiber and SMP via van der Waals and covalent crosslink. Furthermore, the self-assembled carboxylic acid-functionalized CNTs and carbon fibers enable the SMP nanocomposites for Joule heating triggered shape recovery. © 2013 AIP Publishing LLC.

Quistgaard E.M.,Karolinska Institutet | Low C.,Karolinska Institutet | Moberg P.,Karolinska Institutet | Tresaugues L.,Karolinska Institutet | And 2 more authors.
Nature Structural and Molecular Biology | Year: 2013

Here we present two structures of the major facilitator (MFS) xylose transporter XylE from Escherichia coli in inward open and partially occluded inward open conformations. These structures provide key information about the transport cycle of XylE and the closely related human GLUT transporters. This is, to our knowledge, the first MFS transporter structure determined in more than one conformational state, which may establish XylE as an important MFS model protein. © 2013 Nature America, Inc. All rights reserved.

Adav S.S.,Nanyang Technological University
Molecular & cellular proteomics : MCP | Year: 2012

Trichoderma reesei is a mesophilic, filamentous fungus, and it is a major industrial source of cellulases, but its lignocellulolytic protein expressions on lignocellulosic biomass are poorly explored at present. The extracellular proteins secreted by T. reesei QM6a wild-type and hypercellulolytic mutant Rut C30 grown on natural lignocellulosic biomasses were explored using a quantitative proteomic approach with 8-plex high throughput isobaric tags for relative and absolute quantification (iTRAQ) and analyzed by liquid chromatography tandem mass spectrometry. We quantified 230 extracellular proteins, including cellulases, hemicellulases, lignin-degrading enzymes, proteases, protein-translocating transporter, and hypothetical proteins. Quantitative iTRAQ results suggested that the expressions and regulations of these lignocellulolytic proteins in the secretome of T. reesei wild-type and mutant Rut C30 were dependent on both nature and complexity of different lignocellulosic carbon sources. Therefore, we discuss here the essential lignocellulolytic proteins for designing an enzyme mixture for optimal lignocellulosic biomass hydrolysis.

Low Y.M.,Nanyang Technological University
Probabilistic Engineering Mechanics | Year: 2010

This paper presents a method for calculating the fatigue damage from a stochastic bimodal process, in which the high frequency (HF) and low frequency (LF) components are narrowband Gaussian processes. Rainflow cycle counting identifies the following: small but numerous cycles, and large but fewer ones. In existing methods, the small-cycle amplitudes are assumed to be identical to that of the HF cycles, whereas the large-cycle amplitudes are approximated as the sum of the HF and LF amplitudes. The novelty of the present approach lies in the recognition and incorporation of two effects, which concern the reduction of the small-cycle amplitudes caused by the LF process, and the offset between the HF and LF peaks. Parametric studies are conducted, investigating a wide range of parameters. Using time domain simulation as a benchmark, the present method is found to provide a vast improvement over existing methods, with a root-mean-square error of ∼1%. © 2009 Elsevier Ltd. All rights reserved.

Wilder-Smith A.,Nanyang Technological University | Macary P.,National University of Singapore
Current Infectious Disease Reports | Year: 2014

Because of the increasing incidence, geographic expansion and economic burden of dengue transmission, dengue poses major challenges to policy makers. A vaccine against dengue is urgently needed, but vaccine development has been hampered by the lack of an appropriate animal model, poor understanding of correlates of successful human immunity, the fear of immune enhancement, and viral interference in tetravalent combinations. The most suitable target epitopes for vaccines, as well as the role of nonstructural proteins remain elusive. The chimeric yellow fever bonebased live attenuated dengue vaccine is furthest in development, but initial efficacy results have been disappointing. Lessons learnt from this failure will affect the design of future trials, and increase the urgency to identify the best epitope and immune correlates. Dengue vaccine introduction will not be the only strategy to combat dengue, but needs to be “packaged” with novel vector control approaches, with community-based interventions to reduce the number of breeding sites, and reducing the case fatality rate by improving case management. © The Author(s) 2014.

Carmi A.Y.,Nanyang Technological University
Digital Signal Processing: A Review Journal | Year: 2013

In the first part of this work, a novel Kalman filtering-based method is introduced for estimating the coefficients of sparse, or more broadly, compressible autoregressive models using fewer observations than normally required. By virtue of its (unscented) Kalman filter mechanism, the derived method essentially addresses the main difficulties attributed to the underlying estimation problem. In particular, it facilitates sequential processing of observations and is shown to attain a good recovery performance, particularly under substantial deviations from ideal conditions, those which are assumed to hold true by the theory of compressive sensing. In the remaining part of this paper we derive a few information-theoretic bounds pertaining to the problem at hand. The obtained bounds establish the relation between the complexity of the autoregressive process and the attainable estimation accuracy through the use of a novel measure of complexity. This measure is used in this work as a substitute to the generally incomputable restricted isometric property. © 2012 Elsevier Inc.

Cao J.,Nanyang Technological University
Journal of the Franklin Institute | Year: 2013

This paper considers the problem of time delay-dependent exponential stability criteria for the time-delay linear system. Utilizing the linear inequality matrices (LMIs) and slack matrices, a novel criterion based on the Lyapunov-Krasovskii methodology is derived for the exponential stability of the time-delay system. Based on the criteria condition we concluded that the upper bound of the exponential decay rate for the time-delay system can be easily calculated. In addition, an improved sufficient condition for the robust exponential stability of uncertain time-delay system is also proposed. Numerical examples are provided to show the effectiveness of our results. Comparisons between the results derived by our criteria and the one given in Liu (2004) [1], Mondie and Kharitonov (2005) [2], and Xu et al. (2006) [3] show that our methods are less conservative in general. Furthermore, numerical results also show that our criteria can guarantee larger exponential decay rates than the ones derived by Liu (2004) [1] and Mondie and Kharitonov (2005) [2] in all time delay points we have tested and in some of time delay points obtained by Xu et al. (2006) [3]. © 2013 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.

Goh K.H.,Nanyang Technological University | Bockstedt J.C.,University of Arizona
Information Systems Research | Year: 2013

Applying behavioral economic theories, we hypothesize that consumers have sticky reference prices for individual information goods, but their perceived value for customizable bundle offers can be significantly influenced by the framing of a multipart pricing scheme. The potential impacts of these framing effects are measurable changes in consumer behavior and sales outcomes. We conducted a series of behavioral experiments and a large-scale natural field experiment involving actual purchases of customized information good bundles to confirm and analyze the hypothesized effects. The results demonstrate a consumer's willingness to purchase a customized bundle of information goods, the size of the resulting bundling, and the consumer's perceptions of the transaction are each significantly influenced by the design of the multipart pricing scheme. These results hold even when the final price and size of a customized bundle are the same across differing schemes. We discuss the potential tradeoffs in economic outcomes that result from price framing (e.g., likelihood of sale versus size of purchased bundles) and the implications for information good retailers. © 2013 INFORMS.

Wu Y.I.,Nanyang Technological University
The Journal of the Acoustical Society of America | Year: 2012

Herein investigated are computationally simple microphone-array beamformers that are independent of the frequency-spectra of all signals, all interference, and all noises. These beamformers allow the listener to tune the desired azimuth-elevation "look direction." No prior information is needed of the interference. These beamformers deploy a physically compact triad of three collocated but orthogonally oriented velocity sensors. These proposed schemes' efficacy is verified by a jury test, using simulated data constructed with Mandarin Chinese (a.k.a. Putonghua) speech samples. For example, a desired speech signal, originally at a very adverse signal-to-interference-and-noise power ratio (SINR) of -30 dB, may be processed to become fully intelligible to the jury.

Haque M.H.,Nanyang Technological University
IEEE Transactions on Energy Conversion | Year: 2010

A simple method for analyzing the steady-state performance of a self-excited induction generator with P-Q load model is described in this letter. First, the basic operating equations of the generator are derived from its equivalent circuit, and then solved using a numerical-based routine. The proposed method is then tested on a 1.5-kW induction generator and the simulation results obtained are compared with the corresponding experimental values. © 2009 IEEE.

Kraut R.,Nanyang Technological University
Journal of Neurochemistry | Year: 2011

The last 10 years have seen a rebirth of interest in lipid biology in the fields of Drosophila development and neurobiology, and sphingolipids have emerged as controlling many processes that have not previously been studied from the viewpoint of lipid biochemistry. Mutations in sphingolipid regulatory enzymes have been pinpointed as affecting cell survival and growth in tissues ranging from muscle to retina. Specification of cell types are also influenced by sphingolipid regulatory pathways, as genetic interactions of glycosphingolipid biosynthetic enzymes with many well-known signaling receptors such as Notch and epidermal growth factor receptor reveal. Furthermore, studies in flies are now uncovering unexpected roles of sphingolipids in controlling lipid storage and response to nutrient availability. The sophisticated genetics of Drosophila is particularly well suited to uncover the roles of sphingolipid regulatory enzymes in development and metabolism, especially in light of conserved pathways that are present in both flies and mammals. The challenges that remain in the field of sphingolipid biology in Drosophila are to combine traditional developmental genetics with more analytical biochemical and biophysical methods, to quantify and localize the responses of these lipids to genetic and metabolic perturbations. © 2011 International Society for Neurochemistry.

Chong E.K.M.,Nanyang Technological University
Computers and Education | Year: 2010

For the net-generation students learning in a Web 2.0 world, research is often equated with Googling and approached with a mindset accustomed to cut-and-paste practices. Recognizing educators' concern over such students' learning dispositions on the one hand, and the educational affordances of blogging on the other, this study examines the use of blogging to initiate students into academic research at the tertiary level. It focuses on the experiences of three students from a third-year music class working on their research paper with blog-based supervision provided by the teacher. The course, in a hybrid fashion, combined face-to-face lectures and tutorials with blog sharing and discussion. The students' individually-owned blogs were specifically used as their research diaries in which they logged in their work in progress, they then received input from both the teacher and fellow students. Based on the researcher's self-evaluation of the teaching-supervising process, an analysis of the students' blog discourse, and students' survey feedback, this article offers useful insights and suggestions for educators interested in either using or researching on blogging as a means to develop students' research skills and understanding. © 2010 Elsevier Ltd. All rights reserved.

Grimsdale A.C.,Nanyang Technological University
Current Organic Chemistry | Year: 2010

Phenylene-based polymers are a widely studied class of blue-emitting materials for use in polymer light-emitting diodes intended for display applications. This review looks at the various types of such polymers that have been synthesised and the problems that have arisen in obtaining stable and efficient blue emission from them. The emission colour from phenylene-based polymers can be ntrolled by linking some or all of the phenylene units with short carbon or nitrogen bridges, and it has been found that by varying the amount and type of bridges pure blue emission can be obtained. Both aggregation of chains, and the formation of emissive defects cause instability of the emission colour and it is shown that this can be surmounted by appropriate choice of substituents and synthetic routes. In particular the formation of defects is promoted by hydrogens on the bridgeheads, and polymers with aryl substituents at the bridgeheads have been found to much more stable than those with alkyl substituents. High device efficiency can be obtained by incorporation of appropriate charge transporting substituents, which also may help with reducing problems with colour stability. It is shown that by correct design of the polymer structure and appropriate synthetic strategy it is possible to obtain efficient, stable, pure blue emission from phenylene- based polymers. © 2010 Bentham Science Publishers Ltd.

Tan S.,Pennsylvania State University | Davey C.A.,Nanyang Technological University
Current Opinion in Structural Biology | Year: 2011

Chromatin plays a fundamental role in eukaryotic genomic regulation, and the increasing awareness of the importance of epigenetic processes in human health and disease emphasizes the need for understanding the structure and function of the nucleosome. Recent advances in chromatin structural studies, including the first structures of nucleosomes containing the Widom 601 sequence and the structure of a chromatin protein-nucleosome assembly, have provided new insight into stretching of nucleosomal DNA, nucleosome positioning, binding of metal ions, drugs and therapeutic candidates to nucleosomes, and nucleosome recognition by nuclear proteins. These discoveries ensure promising future prospects for unravelling structural attributes of chromatin. © 2010 Elsevier Ltd.

Guruswami V.,Carnegie Mellon University | Xing C.,Nanyang Technological University
Proceedings of the Annual ACM Symposium on Theory of Computing | Year: 2013

We consider Reed-Solomon (RS) codes whose evaluation points belong to a subfield, and give a linear-algebraic list decoding algorithm that can correct a fraction of errors approaching the code distance, while pinning down the candidate messages to a well-structured affine space of dimension a constant factor smaller than the code dimension. By pre-coding the message polynomials into a subspace-evasive set, we get a Monte Carlo construction of a subcode of Reed-Solomon codes that can be list decoded from a fraction (1 - R - ε) of errors in polynomial time (for any fixed ε > 0) with a list size of O(1=ε). Our methods extend to algebraic-geometric (AG) codes, leading to a similar claim over constant-sized alphabets. This matches parameters of recent results based on folded variants of RS and AG codes. Further, the underlying algebraic idea also extends nicely to Gabidulin's construction of rank-metric codes based on linearized polynomials. This gives the first construction of positive rate rank-metric codes list decodable beyond half the distance, and in fact gives codes of rate R list decodable up to the optimal (1 - R - ε) fraction of rank errors. We introduce a new notion called subspace designs as another way to pre-code messages and prune the subspace of candidate solutions. Using these, we also get a deterministic construction of a polynomial time list decodable subcode of RS codes. By using a cascade of several subspace designs, we extend our approach to AG codes, which gives the first deterministic construction of an algebraic code family of rate R with efficient list decoding from 1-R-ε fraction of errors over an alphabet of constant size (that depends only on ε). The list size bound is almost a constant (governed by log (block length)), and the code can be constructed in quasi-polynomial time. Copyright 2013 ACM.

Unger T.,University College Dublin | Markin N.,Nanyang Technological University
IEEE Transactions on Information Theory | Year: 2011

In the context of space-time block codes (STBCs), the theory of generalized quaternion and biquaternion algebras (i.e., tensor products of two quaternion algebras) over arbitrary base fields is presented, as well as quadratic form theoretic criteria to check if such algebras are division algebras. For base fields relevant to STBCs, these criteria are exploited, via Springer's theorem, to construct several explicit infinite families of (bi-)quaternion division algebras. These are used to obtain new 2 × 2 and 4 × 4 STBCs. © 2011 IEEE.

Phan V.-T.,Nanyang Technological University | Lee H.-H.,University of Ulsan
IEEE Transactions on Industry Applications | Year: 2012

In this paper, the control of a stand-alone doubly fed induction generator (DFIG)-based wind power conversion system with unbalanced and nonlinear loads is investigated. Under these load conditions, the quality of stator voltage and current waveforms of the DFIG is strongly affected due to the negative and distorted components, reducing the performance of other normal loads connected to the DFIG. To tackle this problem, the control strategy is comprehensively developed in both rotor-side converter (RSC) and load-side converter (LSC) of the DFIG. The LSC is used as an active power filter to compensate for unbalanced and distorted stator currents whereas the RSC is developed to fully eliminate unbalanced and harmonic voltages at the point of common coupling. The proposed compensation method is based on current controllers in either the RSC or the LSC, which employ a proportional integral plus a resonant controller. These current controllers are controlled in the positive synchronous reference frame so that the rotor current and stator current are directly regulated without decomposing sequential components. Analytical issues on how to eliminate unbalanced and distorted components in the stator voltage and current are also described in this paper. To verify the effectiveness of the proposed control strategy, experimental results with 2.2-kW DFIG topology are presented and discussed in the paper. © 2006 IEEE.

Rawat R.S.,Nanyang Technological University
IEEE Transactions on Plasma Science | Year: 2013

Low-temperature (< 10 eV) plasmas with densities varying over a very wide range from 1013m-3 at the lower end to as high as 1023m-3 have firmly established themselves as one of the most efficient and versatile tools to create and process materials at nanoscale. The dense plasma focus (DPF) device, which is a noncylindrical Z-pinch facility that compresses the plasma to very high energy densities, offers a complex mix of high energy ions of the filling gas species, immensely hot and dense decaying plasma, fast-moving ionization wave front, and a strong shockwave that provides a unique plasma and a physical/chemical environment that is completely unheard of in any other conventional plasma-based deposition or processing facility. This review aims to highlight the novel features offered by pulsed high-energy-density pinch plasmas from a DPF, having temperatures and densities a few orders of magnitudes higher than conventional low-temperature plasmas, in the processing and the synthesis of materials at nanoscale. The nanoscale fabrication using the DPF device is elaborated and discussed in two broad categories: 1) top-down nanoscale fabrication by processing of bulk or thin-film target materials that are placed downstream the anode axis by the energetic transient flux of energetic ions, the hot decaying plasma, the fast ionization wave front, and the shock front; and 2) bottom-up nanoscale fabrication by deposition of nanostructured thin films of metals and/or their nitrides, carbides, and oxides by ablating the metal fitted on to the anode top under suitable reactive or inert background plasma. © 1973-2012 IEEE.

Kuryavyi V.,Sloan Kettering Cancer Center | Phan A.T.,Nanyang Technological University | Patel D.J.,Sloan Kettering Cancer Center
Nucleic Acids Research | Year: 2010

Previous studies have demonstrated that nuclease hypersensitivity regions of several proto-oncogenic DNA promoters, situated upstream of transcription start sites, contain guanine-rich tracts that form intramolecular G-quadruplexes stabilized by stacked G•G•G•G tetrads in monovalent cation solution. The human c-kit oncogenic promoter, an important target in the treatment of gastrointestinal tumors, contains two such stretches of guanine-rich tracts, designated c-kit1 and c-kit2. Our previous nuclear magnetic resonance (NMR)-based studies reported on the novel G-quadruplex scaffold of the c-kit1 promoter in K+-containing solution, where we showed for the first time that even an isolated guanine was involved in G-tetrad formation. These NMR-based studies are now extended to the c-kit2 promoter, which adopts two distinct all-parallel-stranded conformations in slow exchange, one of which forms a monomeric G-quadruplex (form-I) in 20 mM K+-containing solution and the other a novel dimeric G-quadruplex (form-II) in 100 mM K+-containing solution. The c-kit2 promoter dimeric form-II G-quadruplex adopts an unprecedented all-parallel-stranded topology where individual c-kit2 promoter strands span a pair of three-G-tetrad-layer-containing all-parallel-stranded G-quadruplexes aligned in a 3′ to 5′-end orientation, with stacking continuity between G-quadruplexes mediated by a sandwiched A•A non-canonical pair. We propose that strand exchange during recombination events within guanine-rich segments, could potentially be mediated by a synapsis intermediate involving an intergenic parallel-stranded dimeric G-quadruplex. © The Author(s) 2010. Published by Oxford University Press.

Powdthavee N.,Nanyang Technological University | van den Berg B.,University of York
Journal of Health Economics | Year: 2011

Many recent writings in health policy have proposed that health be valued directly and in monetary terms using the new well-being valuation method. Yet there is no clear consensus on what the best measure of individual's experience may be for the evaluation process. To shed light on this issue, monetary values for a number of health problems are compared across different well-being measures within the same UK data set. We find that, whilst there is strong internal consistency of health impacts within each well-being measure, hugely different monetary valuations are obtained for the same health problem across different well-being measures. Our results, although should only viewed as illustrative, call for economists to rethink about which measure of well-being or experienced utility to be used in the well-being valuation method, should the approach ever be implemented in real policy contexts. © 2011 Elsevier B.V.

Qin X.S.,Nanyang Technological University
Stochastic Environmental Research and Risk Assessment | Year: 2012

A fuzzy parameterized probabilistic analysis (FPPA) method was developed in this study to assess risks associated with environmental pollution-control problems. FPPA integrated environmental transport modeling, fuzzy transformation, probabilistic risk assessment, fuzzy risk quantification into a general risk assessment framework, and was capable of handling uncertainties expressed as fuzzy-parameterized stochastic distributions. The proposed method was applied to two environmental pollution problems, with one being about the point-source pollution in a river system with uncertain water quality parameters and the other being concerned with groundwater contaminant plume from waste landfill site with poorly known contaminant physical properties. The study results indicated that the complex uncertain features had significant impacts on modeling and risk-assessment outputs; the degree of impacts of modeling parameters were highly dependent on the level of imprecision of these parameters. The results also implied that FPPA was capable of addressing vagueness or imprecision associated with probabilistic risk evaluation, and help generate risk outputs that could be elucidated under different possibilistic levels. The proposed method could be used by environmental managers to evaluate trade-offs involving risks and costs, as well as identify management solutions that sufficiently hedge against dual uncertainties. © 2011 Springer-Verlag.

Luyt B.,Nanyang Technological University
Journal of the American Society for Information Science and Technology | Year: 2011

Given their ease of use and capability for interactivity, new media are seen as having the potential to make visible previously marginalized voices. The online presence of the writing of history is increasing, and this potential would be a welcome development for the field as it would create a much richer set of easily available historical perspectives. However, this article suggests that the achievement of this promise is fraught with difficulty and that a more likely outcome is a mapping of the status quo in historical representation onto the new media. To illustrate this, I present an analysis of the Wikipedia accounts of Singaporean and Philippine history. For Singapore, alternative historical visions are not as developed as those for the Philippines, and this is reflected in the nature of the respective Wikipedia accounts. I suggest that a possible means to achieve something more of the promise of digital media for history is for information professionals to take a keener interest in Wikipedia, with an eye to helping include accounts of documented historical perspectives that are ignored by mainstream historiographical traditions. © 2011 ASIS&T.

Sin S.-C.J.,Nanyang Technological University
Journal of the American Society for Information Science and Technology | Year: 2011

International collaborative papers are increasingly common in journals of many disciplines. These types of papers are often cited more frequently. To identify the coauthorship trends within Library and Information Science (LIS), this study analyzed 7,489 papers published in six leading publications (ARIST, IP&M, JAMIA, JASIST, MISQ, and Scientometrics) over the last three decades. Logistic regression tested the relationships between citations received and seven factors: authorship type, author's subregion, country income level, publication year, number of authors, document type, and journal title. The main authorship type since 1995 was national collaboration. It was also the dominant type for all publications studied except ARIST, and for all regions except Africa. For citation counts, the logistic regression analysis found all seven factors were significant. Papers that included international collaboration, Northern European authors, and authors in high-income nations had higher odds of being cited more. Papers from East Asia, Southeast Asia, and Southern Europe had lower odds than North American papers. As discussed in the bibliometric literature, Merton's Matthew Effect sheds light on the differential citation counts based on the authors' subregion. This researcher proposes geographies of invisible colleagues and a geographic scope effect to further investigate the relationships between author geographic affiliation and citation impact. © 2011 ASIS&T.

Tan L.T.,Nanyang Technological University
Journal of Applied Phycology | Year: 2010

A plethora of structurally novel bioactive secondary metabolites have been reported from the prokaryotic filamentous marine cyanobacteria in the past few decades. In addition to the production of harmful toxins, these marine blue-green algae are emerging as an important source of anticancer drugs. The majority of these potent biomolecules, including the dolastatins, curacin A, hectochlorin, the apratoxins, and the lyngbyabellins, belongs to the mixed polyketide-polypeptide structural class. Furthermore, a high proportion of these natural products target eukaryotic cytoskeleton, such as tubulin and actin microfilaments, making them an attractive source of potential anticancer drugs. In recent years, a number of potent marine cyanobacteria have also been reported to modulate cell death and apoptosis in cancer cells as well as target enzymes such as histone deacetylase. A number of marine cyanobacterial compounds have also served as structural templates for the generation of new drug leads, further attesting to the importance of these marine microbes as an important source of new pharmaceuticals. This review serves to highlight the chemistry and biology of selected anticancer marine cyanobacterial natural products exhibiting significant biological activities in the nanomolar or submicromolar range, and their discussion will be based on the different modes of action. © 2010 Springer Science+Business Media B.V.

Shalabney A.,Ben - Gurion University of the Negev | Abdulhalim I.,Ben - Gurion University of the Negev | Abdulhalim I.,Nanyang Technological University
Optics Letters | Year: 2012

We show that adding a thin dielectric layer with high refractive index on top of the metallic layer in surface plasmon resonance sensors in the Kretschmann-Raether configuration in the spectral mode causes a redshift of the resonance wavelength, narrowing of the resonance dip, and an enhancement to the spectral sensitivity. Surprisingly, together with the sensitivity enhancement, the dip becomes much narrower and the figure of merit is considerably improved, particularly in the IR range. © 2012 Optical Society of America.

Kai L.,Shanghai University | Kemao Q.,Nanyang Technological University
Optics Express | Year: 2011

An algorithm for dynamic phase retrieval in temporal speckle pattern interferometry using least squares method and windowed Fourier filtering is proposed. The least squares method is used to evaluate the phase change between two speckle patterns provided that the phase of either one speckle pattern has been estimated. The windowed Fourier filtering is used to eliminate the noise in the phase change. Based on these two techniques, the proposed algorithm determines the phase of the initial speckle pattern by phase shifting method at first, then the phase of the rest speckle patterns are retrieved by sequentially evaluating the phase changes between every two consecutive speckle patterns. The algorithm solves the problem of speckle decorrelation by refreshing the reference image frame by frame, and also avoids the problem of error accumulation during the reference image refreshing process by the windowed Fourier filtering. Two experimental results are presented to demonstrate the effectiveness and robustness of the proposed algorithm. © 2011 Optical Society of America.

Tay W.P.,Nanyang Technological University
IEEE Transactions on Information Theory | Year: 2012

We consider the decentralized binary hypothesis testing problem in networks with feedback, where some or all of the sensors have access to compressed summaries of other sensors' observations. We study certain two-message feedback architectures, in which every sensor sends two messages to a fusion center, with the second message based on full or partial knowledge of the first messages of the other sensors. We also study one-message feedback architectures, in which each sensor sends one message to a fusion center, with a group of sensors having full or partial knowledge of the messages from the sensors not in that group. Under either a Neyman-Pearson or a Bayesian formulation, we show that the asymptotically optimal (in the limit of a large number of sensors) detection performance (as quantified by error exponents) does not benefit from the feedback messages, if the fusion center remembers all sensor messages. However, feedback can improve the Bayesian detection performance in the one-message feedback architecture if the fusion center has limited memory; for that case, we determine the corresponding optimal error exponents. © 1963-2012 IEEE.

Zhao D.,Nanyang Technological University
Applied Mechanics and Materials | Year: 2012

Self excited combustion oscillations are caused by a coupling between acoustic waves and unsteady heat release. A premixed laminar flame in a Rijke tube, anchored to a metal gauze, is considered in this work. The flame response to flow disturbances is investigated by developing a nonlinear kinematic model based on the classical G -equation, with the assumption of a time-invariant laminar flame speed. Unsteady heat release from the flame is assumed to be caused by its surface variations, which results from the fluctuations of the oncoming flow velocity. The flame is acoustically compact, and its presence causes the mean temperature undergoing a jump, whose effect on the dynamics of the thermo-acoustic system is discussed. Coupling the flame model with a Galerkin series expansion of the acoustic waves present enables the time evolution of the flow disturbances to be calculated. It was found that the model can predict the mode shape and the frequencies of the excited combustion oscillations very well. Moreover, the fundamental mode is found to be the easiest one to be triggered among all acoustic modes. To gain insight about the mode selection and triggering, further numerical investigation is conducted by linearizing the flame model and recasting into the popular n ττ formulation. © (2012) Trans Tech Publications, Switzerland.

Joshi S.C.,Nanyang Technological University
Materials | Year: 2011

Sol-gel transformations in HPMC (hydroxypropyl methylcellulose) are being increasingly studied because of their role in bio-related applications. The thermo-reversible behavior of HPMC is particularly affected by its properties and concentration in solvent media, nature of additives, and the thermal environment it is exposed to. This article contains investigations on the effects of salt additives in Hofmeister series on the HPMC gelation. Various findings regarding gelation with salt ions as well as with the ionic and non-ionic surfactants are presented. The gel formation in physiological salt fluids such as simulated gastric and intestine fluids is also examined with the interest in oral drug delivery systems. The processes of swelling, dissolution and dispersion of HPMC tablets in simulated bio-fluids are explored and the release of a drug from the tablet affected by such processes is studied. Explanations are provided based on the chemical structure and the molecular binding/association of HPMC in a media. The test results at the body or near-body temperature conditions helped in understanding the progress of the gelation process within the human body environment. The detailed interpretation of various molecule level interactions unfolded the sol-gel mechanisms and the influence of a few other factors. The obtained test data and the established mathematical models are expected to serve as a guide in customizing applications of HPMC hydrogels.© 2011 by the authors.

Feng T.,Nanyang Technological University
Journal of Combinatorial Theory. Series A | Year: 2011

Let p be a prime larger than 3 and congruent to 3 modulo 4, and let G be the non-abelian group of order p 3 and exponent p. We study the structure of a putative difference set with parameters (p 3,p 3-1/ 2,p 3-3/ 4) in G which is fixed by a certain element of order p in Aut(G). We then give a construction of skew Hadamard difference set in the group G for each prime p>3 that is congruent to 3 modulo 4. This is the first infinite family of non-abelian skew Hadamard difference sets. Finally, we show that the symmetric designs derived from these new difference sets are not isomorphic to the Paley designs. © 2009 Elsevier Inc.

Privault N.,Nanyang Technological University
Electronic Journal of Combinatorics | Year: 2011

We introduce a family of polynomials that generalizes the Bell polynomials, in connection with the combinatorics of the central moments of the Poisson distri- bution. We show that these polynomials are dual of the Charlier polynomials by the Stirling transform, and we study the resulting combinatorial identities for the number of partitions of a set into subsets of size at least 2.

Lee J.-M.,Nanyang Technological University
Fluid Phase Equilibria | Year: 2012

Nine ionic liquids containing pyridinium, pyrrolidinium and piperidinium cations with anion bis(trifluoromethylsulfonyl)imide were synthesized to investigate the ability of ionic liquids to extract silver, palladium, or gold metal ions from water at room temperature. Results are reported for distribution coefficients and extraction percentages with these ionic liquids. Ionic liquids containing a disulfide group or a nitrile group exhibit good extraction properties for silver or palladium ions. Gold ions were efficiently and selectively extracted with these functionalized ionic liquids. The influence of the mass ratio of water to ionic liquid on distribution coefficient or extraction percentage for aqueous gold ions was evaluated. © 2012 Elsevier B.V.

Wu M.S.,Nanyang Technological University | Kirchner H.O.K.,Leibniz Institute for New Materials
Journal of the Mechanics and Physics of Solids | Year: 2010

A second-order nonlinear elastic model is developed for biogels, whereby the elastic constants are estimated from the free energy densities for polymer networks and polymer-water mixtures. For typical values of the constants, important physical insights are revealed: a biogel stiffens under tension, contracts longitudinally under torsion (inverse Poynting effect), and experiences a negative normal stress under simple shear. This approach of extracting nonlinear elastic constants works for any constitutive law, and has the advantage of exploring physical phenomena without recourse to computationally intensive simulations. © 2009 Elsevier Ltd. All rights reserved.

Directed activation: Cationic CpCoIII (Cp=1,2,3,4,5-pentamethylcyclopentadienyl) complexes, either well-defined or in situ-generated, promote catalytic functionalization of arene C-H bonds with a variety of electrophilic reaction partners by directed C-H activation. These complexes not only emulate known reaction patterns of CpRhIII analogues, but also exhibit remarkable catalytic activity or unique reactivity. DG=Directing group. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lee J.-M.,Nanyang Technological University
Chemical Engineering Journal | Year: 2011

Experimental studies were made in the range 298-338. K for four synthesized piperidinium ionic liquids containing an alkyl chain on the cation 1-methyl-1-propylpiperidinium, 1-methyl-1-butylpiperidinium, and 1-methyl-1-octylpiperidinium with anion bis(trifluoromethylnsulfonyl)imide or bis(pentafluoroethysulfonyl)imide, and for three newly synthesized piperidinium ionic liquids containing a functional group on the cation 1-methyl-1-(3-cyano-1-propyl)piperidinium, 1-methyl-1-(pent-4-en-1-yl)piperidinium, or 1-methyl-1-[4,5-bis(methylthio)-1-penthyl]piperidinium with anion bis(trifluoromethylsulfonyl)imide. The influence of alkyl-chain length and the influence of a functional group on the cation on polarity and on three Kamlet-Taft parameters were investigated. The Kamlet-Taft parameters obtained are hydrogen-bond acidity α, hydrogen-bond basicity β, and dipolarity/polarizability π*. © 2011 Elsevier B.V.

Pal M.,Nanyang Technological University
PloS one | Year: 2011

The nuclear hormone receptor PPARβ/δ is integral to efficient wound re-epithelialization and implicated in epidermal maturation. However, the mechanism underlying the latter process of epidermal differentiation remains unclear. We showed that ligand-activated PPARβ/δ indirectly stimulated keratinocyte differentiation, requiring de novo gene transcription and protein translation. Using organotypic skin cultures constructed from PPARβ/δ- and angiopoietin-like 4 (ANGPTL4)-knockdown human keratinocytes, we showed that the expression of ANGPTL4, a PPARβ/δ target gene, is essential for the receptor mediated epidermal differentiation. The pro-differentiation effect of PPARβ/δ agonist GW501516 was also abolished when keratinocytes were co-treated with PPARβ/δ antagonist GSK0660 and similarly in organotypic skin culture incubated with blocking ANGPTL4 monoclonal antibody targeted against the C-terminal fibrinogen-like domain. Our focused real-time PCR gene expression analysis comparing the skin biopsies from wildtype and ANGPTL4-knockout mice confirmed a consistent down-regulation of numerous genes involved in epidermal differentiation and proliferation in the ANGPTL4-knockout skin. We further showed that the deficiency of ANGPTL4 in human keratinocytes and mice skin have diminished expression of various protein kinase C isotypes and phosphorylated transcriptional factor activator protein-1, which are well-established for their roles in keratinocyte differentiation. Chromatin immunoprecipitation confirmed that ANGPTL4 stimulated the activation and binding of JUNB and c-JUN to the promoter region of human involucrin and transglutaminase type 1 genes, respectively. Taken together, we showed that PPARβ/δ regulates epidermal maturation via ANGPTL4-mediated signalling pathway.

Wong L.-H.,Nanyang Technological University
Technology, Pedagogy and Education | Year: 2013

The proliferation of mobile technology has opened up or enhanced opportunities for more personalised, self-directed learning experiences beyond the four walls of classrooms. This paper reports an attempt to rise above the past five years' studies on one-to-one mobile seamless learning by foregrounding the notions of facilitated and self-directed seamless learning to distinguish between externally and self-initiated learning activities. The paper argues that in order to nurture genuine self-directed seamless learners, practitioners ought to develop and enact systematic and cyclic facilitated seamless learning processes to enculturate the students. A domain-independent facilitated seamless learning (FSL) process framework is proposed to guide the design of a new seamless learning environment as well as to analyse existing designs. To demonstrate the versatility of the framework, two case studies are presented - one pertaining to the domain of the Chinese language and another to science learning. Through post-study reflections on the underpinning concepts on seamless learning and empirical findings, the author proposes additional guidelines for more effective applications of the framework. It is hoped that the guidelines can serve to inform the design of mobile seamless learning environments in future. © 2013 Copyright Association for Information Technology in Teacher Education.

Zhou Y.,Nanyang Technological University
Journal of Endourology | Year: 2012

Purpose: A new method was devised to suppress the bubble cavitation in the lithotripter focal zone to reduce the propensity of shockwave-induced renal injury. Materials and Methods: An edge extender was designed and fabricated to fit on the outside of the ellipsoidal reflector of an electrohydraulic lithotripter to disturb the generation of diffraction wave at the aperture, but with little effect on the acoustic field inside the reflector. Results: Although the peak negative pressures at the lithotripter focus using the edge extender at 20 kV were similar to that of the original configuration (-11.1±0.9 vs -10.6±0.7 MPa), the duration of the tensile wave was shortened significantly (3.2±0.54 vs 5.83±0.56 μs, P<0.01). There is no difference, however, in both the amplitude and duration of the compressive shockwaves between these two configurations as well as the -6 dB beam width in the focal plane. The significant suppression effect of bubble cavitation was confirmed by the measured bubble collapse time using passive cavitation detection. At the lithotripter focus, while only about 30 shocks were needed to rupture a blood vessel phantom using the original HM-3 reflector at 20 kV, no damage could be produced after 300 shocks using the edge extender. Meanwhile, the original HM-3 lithotripter at 20 kV can achieve a stone comminution efficiency of 50.4±2.0% on plaster-of-Paris stone phantom after 200 shocks, which is comparable to that of using the edge extender (46.8±4.1%, P=0.005). Conclusions: Modifying the diffraction wave at the lithotripter aperture can suppress the shockwave-induced bubble cavitation with significant reduced damage potential on the vessel phantom but satisfactory stone comminution ability. © Copyright 2012, Mary Ann Liebert, Inc.

Song J.,Nanyang Technological University
International Journal of Impact Engineering | Year: 2013

Tubular structures under oblique loading may collapse in axial or bending mode when the load angle is smaller or larger than certain critical value, and the bending mode has much lower energy absorption. In the present study, windowed square tubes subject to oblique impact were numerically studied, with variables being load angle, width and height of window and impact velocity. Next, a new design method was proposed which can effectively increase the tube's critical load angle without compromising its energy absorbing capacity. The method therefore has great potential in industrial applications where large load angles are expected. © 2012 Elsevier Ltd. All rights reserved.

Pumera M.,Nanyang Technological University
Chemistry - An Asian Journal | Year: 2011

Research on nanotoxicity is of extremely high scientific, social, and economic value. As nanomaterial-based products enter the market, there is an urgent need for related research in order to prevent dramatic consequences of any health-oriented issues caused by nanotechnology-driven products. The results of research on nanotoxicity have profound significance because the design of nanomaterials used in industry and consumer products should be based on the outcome of such research. The research has multi-billion dollar significance for industry and an even greater value for consumers and health care. Such research could prevent an enormous burden in terms of the cost of care for chronic health problems of the entire population caused by the widespread use of untested nanomaterials. The tremendous progress of nanotechnology has not been accompanied by sufficient studies of nanomaterial toxicity even though they possess unique, completely new properties. Thus, their toxicity can neither be extrapolated from the toxicity of bulk materials nor from the toxicity of their constituents in ionic form. This Focus Review discusses the current state of nanotoxicity research and nanotoxicology from the point of view of molecular science. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rajendran S.,Nanyang Technological University
Computer Methods in Applied Mechanics and Engineering | Year: 2010

Three sufficient conditions are proposed for an iso-parametric finite element formulation to be immune to mesh-distortion effects, even for extremely distorted element geometries for which the Jacobian geometric mapping goes negative! Illustrative element formulations are presented to test the sufficiency of the proposed conditions. Numerical results confirm that the illustrative elements are indeed capable of giving mesh-distortion immune solution for extreme mesh distortions. This has been possible partly because the stiffness integral is free of the Jacobian term in the new formulation. © 2009 Elsevier B.V.

Webster R.D.,Nanyang Technological University
Chemical Record | Year: 2012

A review summarizing the voltammetric literature of the liposoluble vitamins A, D, E and K in organic solvents containing supporting electrolyte is presented. Electrochemical studies that were performed by attaching the vitamins to electrode surfaces and performing voltammetric scans in aqueous solutions are also summarized. Vitamins A (retinol and retinal) and D (cholecaliferol and ergocalciferol) undergo chemically irreversible voltammetric oxidation processes in organic solvents to form complicated or unknown compounds that cannot be electrochemically converted back to the starting materials. In contrast to vitamins A and D, vitamins E and K undergo chemically reversible electron-transfer processes that are often coupled to proton-transfer reactions. Vitamin E (a phenol) is voltammetrically oxidized in aprotic organic solvents in a -2e -/-H + process to form a diamagnetic cation, which is unusually long-lived compared to the analogous cations produced during the oxidation of other phenols. In an aqueous environment, vitamin E is electrochemically oxidized to the hydroquinone in a chemically irreversible -2e - process. In low moisture content aprotic solvents, vitamin K (a quinone) is reduced in two one-electron chemically reversible steps to form first a radical anion (semiquinone, at E 1) and then at more negative potentials a dianion is formed (at E 2). The dianion is especially prone to strong hydrogen-bonding interactions with trace water present in the organic solvents, resulting in a shift in the formal reduction potential of E 2 to more positive potentials as more water is added to the solvent. Copyright © 2012 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Maher K.,TUM CREATE | Yazami R.,Nanyang Technological University
Journal of Power Sources | Year: 2014

Lithium ion batteries (LiB) are cycled under a galvanostatic regime (∼C/2-rate) between 2.75 V and 4.2 V for up to 1000 cycles. After each completed 100 cycles, the discharge capacity, capacity loss, average discharge potential were determined under the same C/2 rate. Then cells undergo an additional charge and discharge cycle at C/6 rate followed by a thermodynamics measurements test. This enables open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) data to be assessed. It is found that with increasing cycle number, the entropy and enthalpy profiles show more significant changes than those observed in the discharge and the OCP curves especially at particular SOC and OCP values. These differences are attributed to the higher sensitivity of entropy and enthalpy state functions to changes in the crystal structure of the graphite anode and the lithiated cobalt oxide (LCO) induced by cycle aging compared to the free energy ΔG (OCP) alone. The thermodynamics data are supported by post-mortem X-ray diffractometry (XRD) and Raman scattering (RS) analyses on the electrode materials. The results show important LCO crystal structure degradation, whereas, surprisingly, the graphite anode remains almost unaffected by heavy cycling, if not improved. © 2013 Elsevier B.V. All rights reserved.

Schluter J.U.,Nanyang Technological University
Journal of Aircraft | Year: 2010

A study was conducted to demonstrate lift enhancement at low Reynolds number using self-activated movable flaps. Measurements were performed to test the water tunnel setup and compare the current measurements with experimental data. The data were compared with measurements performed by a team of researchers on airfoils at similar Reynolds numbers. The airfoil model for the measurements was manufactured out of aluminum, using computer-numerically controlled cutting and polished to reduce the roughness. Three different airfoils were investigated under the study, including the NACA0012, SD8020, and NACA4412. Carbon fiber material with a total weight of about 5 g was used for the fabrication of the flap. The flaps were attached on both sides of the airfoil to assure the symmetry of the airfoils for the symmetric airfoils NACA0012 and SD8020. The measurements revealed that the use of the flaps improved the stall behavior significantly.

Skoric M.M.,Nanyang Technological University
Journal of Broadcasting and Electronic Media | Year: 2013

This research examines the implications of social media use for political engagement among young people in Singapore. The project included a qualitative analysis of a student protest, followed by a national survey of young Singaporeans. The findings suggest that social media use is positively related to traditional political participation, while also providing evidence of the continued importance of traditional media for political engagement. More specifically, we find that the attention paid to news in traditional media is a more important predictor of both traditional and online participation than the generic use of Facebook. © 2013 Copyright Taylor and Francis Group, LLC.

Klauck H.,Nanyang Technological University
Proceedings of the Annual ACM Symposium on Theory of Computing | Year: 2010

A strong direct product theorem states that if we want to compute k independent instances of a function, using less than k times the resources needed for one instance, then the overall success probability will be exponentially small in k. We establish such a theorem for the randomized communication complexity of the Disjointness problem, i.e., with communication const·kn the success probability of solving k instances of size n can only be exponentially small in k. This solves an open problem of [KSW07, LSS08]. We also show that this bound even holds for AM-communication protocols with limited ambiguity. The main result implies a new lower bound for Disjointness in a restricted 3-player NOF protocol, and optimal communication-space tradeoffs for Boolean matrix product. Our main result follows from a solution to the dual of a linear programming problem, whose feasibility comes from a so-called Intersection Sampling Lemma that generalizes a result by Razborov [Raz92]. Copyright 2010 ACM.

Lian H.,Nanyang Technological University
Pattern Recognition Letters | Year: 2012

In this short note, we demonstrate the use of principal components analysis (PCA) for one-class support vector machine (one-class SVM) as a dimension reduction tool. However, unlike almost all other usage of PCA which extracts the eigenvectors associated with top eigenvalues as the projection directions, here it is the eigenvectors associated with small eigenvalues that are of interests, and in particular the null of the eigenspace, since the null space in fact characterizes the common features of the training samples. Image retrieval examples are used to illustrate the effectiveness of dimension reduction. © 2012 Elsevier B.V. All rights reserved.

Wu J.,Nanyang Technological University
IEEE Transactions on Image Processing | Year: 2012

Histograms are used in almost every aspect of image processing and computer vision, from visual descriptors to image representations. Histogram intersection kernel (HIK) and support vector machine (SVM) classifiers are shown to be very effective in dealing with histograms. This paper presents contributions concerning HIK SVM for image classification. First, we propose intersection coordinate descent (ICD), a deterministic and scalable HIK SVM solver. ICD is much faster than, and has similar accuracies to, general purpose SVM solvers and other fast HIK SVM training methods. We also extend ICD to the efficient training of a broader family of kernels. Second, we show an important empirical observation that ICD is not sensitive to the C parameter in SVM, and we provide some theoretical analyses to explain this observation. ICD achieves high accuracies in many problems, using its default parameters. This is an attractive property for practitioners, because many image processing tasks are too large to choose SVM parameters using cross-validation. © 2012 IEEE.

Sin S.C.J.,Nanyang Technological University
Library and Information Science Research | Year: 2012

Information behavior (IB) and public library usage studies seldom simultaneously analyze individual-level characteristics and community-level information service factors. Thus, it is uncertain whether changes in community-level factors, such as an increase in public library funding and service level, make a difference in an individual's library usage after differences in personal characteristics are accounted for. Applying the person-in-environment (PIE) framework designed to integrate individual agency and sociostructural factors in IB research, this study used structural equation modeling (SEM) to test the factors influencing a student's frequency of public library usage for schoolwork, leisure, and Internet access. It mapped and merged a nationally representative survey of 13,000 U.S. 12th graders with census tract data and public library statistics. The SEM findings indicate that school information environment, frequency of school library use, race/ethnicity, and home computer availability were among the top three factors affecting public library usage for schoolwork, leisure, and Internet access. More importantly, library service levels had a positive impact on students' library usage in terms of frequency of use. Specifically, even after personal differences such as each student's socioeconomic status and achievement motivation were controlled for, higher service levels in the student's neighborhood public library contributed to more frequent library usage. The findings pinpoint the benefits for individual-level IB study to incorporate etic measures of community-level factors. The findings also suggest that continuous effort to fund high levels of public library services-particularly in disadvantaged areas-is worthwhile. Such efforts should be encouraged. © 2012 Elsevier Inc.

Lu L.,Nanyang Technological University | Hong W.,Drive.SG | Hong W.,Xiamen University
Seminars in Cell and Developmental Biology | Year: 2014

The retrograde trafficking from endosomes to the trans-Golgi network (TGN) is one of the major endocytic pathways to divert proteins and lipids away from lysosomal degradation. Retrograde transported cargos enter the TGN via two itineraries from either the early endosome/recycling endosome or the late endosome and involve various machinery components such as retromer, sorting nexins, clathrin, small GTPases, tethering factors and SNAREs. Recently, the pathway has been recognized for its role in signal transduction, physiology and pathogenesis of human diseases. © 2014 Elsevier Ltd.

Cheng N.-S.,Nanyang Technological University
Journal of Hydraulic Engineering | Year: 2013

The emergent vegetation in open-channel flows is usually simulated using arrays of circular cylinders in laboratory experiments. Analysis of recent experimental data reveals that for a given Reynolds number, the drag coefficient of a cylinder in a dense array is larger than that of an isolated cylinder. A new approach is applied to parameterize the drag coefficient and Reynolds number for flows through arrays of emergent cylinders. The approach is developed based on the concept of pseudofluid, for which an analogy is made between the cylinderinduced drag in an open-channel flow and that induced by the cylinder settling in a stationary fluid. With the proposed parameterization, the experimental database is successfully reorganized in such a way that a generalized drag coefficient is related to a generalized Reynolds number by one single curve, which is valid for a wide range of solid fractions and Reynolds numbers. However, it should be mentioned that only rigid circular stems are considered in this study and their induced drag is assumed to be dominant in comparison with the channel bed resistance. © 2013 American Society of Civil Engineers.

Sin S.C.J.,Nanyang Technological University | Kim K.-S.,University of Wisconsin - Madison
Library and Information Science Research | Year: 2013

Sojourns to other countries, such as for studying abroad, are increasingly common. However, adjusting to life in a different country can be stressful and require significant effort. Sojourners need to not only maintain and expand their social networks, but they also continuously seek information about their new environment. While international students are a sizable group, their daily information behavior is not well understood. This study posits that social networking sites (SNS), such as Facebook, may play an important role in international students' everyday life information seeking (ELIS). Using descriptive statistics, ANOVA, and structural equation modeling (SEM), the study analyzed international students' everyday life information needs, their usage of SNS for ELIS, and the relationships among demographics, personality traits, SNS usage, and perceived usefulness of the acquired everyday life information. Findings indicate that a majority of the respondents frequently used SNS for ELIS. Younger students, undergraduates, and extroverts were more likely to use SNS for ELIS, while no gender difference was found. Notably, among the nine user characteristics and behavior factors, SNS usage emerged as the only positive predictor of perceived usefulness of acquired information in meeting daily needs. This indicates that SNS serve as a valuable channel for purposeful everyday life information seeking. Beyond its social support value, the ELIS value of SNS is a fruitful area for future research. © 2013 Elsevier Inc.

Jiang Y.,Nanyang Technological University | Park C.-M.,Ulsan National Institute of Science and Technology
Chemical Science | Year: 2014

We have developed a dual reaction manifold that enables the selective synthesis of both pyridines and pyrroles from the common substrates α-diazo oxime ethers. The strong propensity of 1,3-dienyl nitrenes for 4π-electrocyclization to give pyrroles could be diverted to 6π-electrocyclization via a 1,6-hydride shift or prototropic isomerization, leading to the exclusive formation of pyridines by employing metal nitrene complexes derived from α-diazo oxime ethers under Rh(ii) catalysis. Furthermore, an orthogonal catalytic system has been identified that promotes the selective formation of 1H-pyrroles from the same substrates by redirecting the reactivity of vinyl 2H-azirine intermediates. This journal is © the Partner Organisations 2014.

Straub D.,Georgia State University | Ang S.,Nanyang Technological University
MIS Quarterly: Management Information Systems | Year: 2011

A divorce between IS academicians and those in practice is premature. First, researchers have produced evidence that the topics attacked by scholars are what practice needs and wants to know about. Second, there is no credible evidence that knowledge transfer is not taking place. The first gap relates to the topics or themes that researchers tackle and their alignment with what practitioners deem to be central to their needs. The second alleged gap relates to whether research conducted by academics is made accessible to and is actually used by practitioners. One of the ways scholars have studied topic relevance is through the analysis of different types or classes of journals so it is important that we develop this idea next as a basis for our later reasoning. There is additional recent scientific evidence of the usefulness of topics in the IS academic press.

Son H.,Nanyang Technological University | Lee K.-M.,Georgia Institute of Technology
IEEE Transactions on Industrial Electronics | Year: 2010

This paper presents a control system design for a particular form of variable-reluctance spherical motors, referred to here as a spherical wheel motor (SWM). The method decoupling the spin from the inclination offers a means to control, in open loop (OL), the inclination of a continuously rotating shaft. Specifically, the OL controller presented in this paper combines a multispeed switching control law for controlling the spin motion and a dynamic model-based control law for regulating the rotor inclination of an SWM. The concept feasibility of the OL-controlled SWM (consisting of permanent magnets in a rotor and electromagnets in a stator) has been experimentally demonstrated. The experimental study not only demonstrates the design procedure but also provides intuitive insights into the effects of key operation parameters on the SWM dynamics. The results presented here will serve as a basis for developing feedback controllers for increasing accuracy and robustness for disturbance rejection. © 2010 IEEE.

Wong C.H.,Nanyang Technological University
Computational Materials Science | Year: 2010

The elastic properties of imperfect armchair and zig-zag single-walled carbon nanotubes under axial tension are studied by molecular dynamics simulations. Vacancy defects of different sizes and at different locations are reconstructed into carbon nanotubes and their elastic properties such as the Young's modulus, tensile strength and tensile failure strain are obtained and compared with their perfectly structured counterparts. Simulation results indicate that the elastic properties are more sensitive to the location than to the size of the vacancy defects. Young's modulus, tensile strength and tensile failure strain of a carbon nanotube suffer significant degradation when the vacancy defects are located along the traverse direction. The diameter effects of the carbon nanotubes are also reported in this work. © 2010 Elsevier B.V. All rights reserved.

Subiantoro A.,TUM CREATE | Ooi K.T.,Nanyang Technological University
International Journal of Refrigeration | Year: 2013

Expanders have been shown to improve the energy efficiencies of refrigeration systems. The current technology is also adequate to manufacture and integrate expanders to practical air-conditioners. In this paper, an economic analysis of the installation of expanders on to existing vapor compression cooling systems, particularly medium scale air-conditioners, is presented. Various refrigerants, including the established and the newly proposed varieties, are considered. From the investigations, it was found that when the expander efficiency is 50%, the payback periods of most conventional systems are below 3 years in high temperature countries with high electricity tariffs and are above 5 years in other countries. Expanders are especially attractive for the transcritical CO2 and the R404A systems. The payback periods are shorter for systems with highly efficient expanders, high cooling loads, high ambient temperatures and for low refrigerating temperature applications. © 2013 Elsevier Ltd and IIR. All rights reserved.

Foth B.J.,Nanyang Technological University
Molecular & cellular proteomics : MCP | Year: 2011

Studies of the Plasmodium falciparum transcriptome have shown that the tightly controlled progression of the parasite through the intra-erythrocytic developmental cycle (IDC) is accompanied by a continuous gene expression cascade in which most expressed genes exhibit a single transcriptional peak. Because the biochemical and cellular functions of most genes are mediated by the encoded proteins, understanding the relationship between mRNA and protein levels is crucial for inferring biological activity from transcriptional gene expression data. Although studies on other organisms show that <50% of protein abundance variation may be attributable to corresponding mRNA levels, the situation in Plasmodium is further complicated by the dynamic nature of the cyclic gene expression cascade. In this study, we simultaneously determined mRNA and protein abundance profiles for P. falciparum parasites during the IDC at 2-hour resolution based on oligonucleotide microarrays and two-dimensional differential gel electrophoresis protein gels. We find that most proteins are represented by more than one isoform, presumably because of post-translational modifications. Like transcripts, most proteins exhibit cyclic abundance profiles with one peak during the IDC, whereas the presence of functionally related proteins is highly correlated. In contrast, the abundance of most parasite proteins peaks significantly later (median 11 h) than the corresponding transcripts and often decreases slowly in the second half of the IDC. Computational modeling indicates that the considerable and varied incongruence between transcript and protein abundance may largely be caused by the dynamics of translation and protein degradation. Furthermore, we present cyclic abundance profiles also for parasite-associated human proteins and confirm the presence of five human proteins with a potential role in antioxidant defense within the parasites. Together, our data provide fundamental insights into transcript-protein relationships in P. falciparum that are important for the correct interpretation of transcriptional data and that may facilitate the improvement and development of malaria diagnostics and drug therapy.

Henderson J.C.,Nanyang Technological University
International Journal of Tourism Research | Year: 2011

Religion and tourism share a close relationship in which the former motivates travel and is a source of assorted visitor attractions. Pilgrimage is one expression of the ties between the two and the paper identifies key pilgrimage tourism issues pertaining to demand and provision that are discussed within the context of the contemporary hajj. The hajj by Muslims to the cities they deem holy in Saudi Arabia is a distinctive illustration that involves the mass movement of pilgrims every year. Numbers are strictly controlled, but set to rise as the government pursues a policy of expanding space at certain holy sites and encouraging an increase in the supply of accommodation and other amenities as well as enhancing supporting infrastructure. Some projects are very ambitious, leading to questions about whether the pace of development is sustainable. The purpose of the study is to improve understanding of the uniqueness and significance of the hajj phenomenon and illuminate the challenges of managing large-scale religious tourism events in the changing world of the twenty-first century. © 2010 John Wiley & Sons, Ltd.

Pumera M.,Nanyang Technological University
Journal of Materials Chemistry C | Year: 2014

Graphene exhibits zero band gap, very small electrical resistivity, fast heat dissipation, and fast heterogeneous electron transfer properties. These features, coupled with affordable preparation cost and high surface area, predetermine graphene materials for application in electronic and electrochemical devices. Doping graphene with electron-withdrawing or -donating heteroatoms leads to tailoring of graphene electronic and electrochemical properties. Here, we discuss doping of graphene-based materials with main group heteroatoms (s and p blocks). We will also discuss the application of such doped graphenes in electronic, sensing, and energy storage/generation devices. This journal is © the Partner Organisations 2014.

Yu J.,Georgia Institute of Technology | Zhou X.,Nanyang Technological University
IEEE Communications Magazine | Year: 2010

We review and summarize several 100G per channel high-capacity transmission systems enabled by advanced technologies such as multilevel modulation format, new low-loss and large effective area fiber, hybrid EDFA/Raman amplification, and digital coherent detection technologies. We show that high-speed QPSK, 8PSK, 8QAM, and 16QAM can all be generated using commercially available optical modulators using only binary electrical drive signals through novel synthesis methods, and that all of these modulation formats can be detected using digital coherent detection. We also show our latest research results on 400 Gb/s and 1 Tb/s per channel by using orthogonal DWDM transmission technologies. © 2010 IEEE.

Liu N.,Singapore General Hospital | Wang H.,Nanyang Technological University
IEEE Signal Processing Letters | Year: 2010

Extreme learning machine (ELM) was proposed as a new class of learning algorithm for single-hidden layer feedforward neural network (SLFN). To achieve good generalization performance, ELM minimizes training error on the entire training data set, therefore it might suffer from overfitting as the learning model will approximate all training samples well. In this letter, an ensemble based ELM (EN-ELM) algorithm is proposed where ensemble learning and cross-validation are embedded into the training phase so as to alleviate the overtraining problem and enhance the predictive stability. Experimental results on several benchmark databases demonstrate that EN-ELM is robust and efficient for classification. © 2006 IEEE.

Zhou M.,Anhui University of Science and Technology | Lou X.W.,Nanyang Technological University | Xie Y.,Anhui University of Science and Technology
Nano Today | Year: 2013

In view of the worldwide energy challenge in the 21st century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. The performance of advanced PEC devices is fundamentally related to the semiconductor photoelectrode design at the nanoscale. Among various architectures, two-dimensional (2D) nanosheets with thickness generally below 100 nm hold great promise for highly efficient PEC water splitting. Hence, this article mainly provides a comprehensive review of current research efforts that focus on the scientific and technological possibilities of using 2D nanosheets to fabricate efficient photoelectrodes for PEC water splitting, followed by a concise overview of the state-of-the-art progress of 2D nanosheets, where we also present a discussion of how to overcome the challenges that have prevented realizing the full potential of 2D nanosheets. Particular attention is paid on two major approaches. One is to align nanosheets directly on the substrate to maximize the morphological advantages of 2D nanosheets. The other is to further reduce the thickness of common 2D nanosheets to single or a few atomic layers aiming at regulating the intrinsic physical and chemical properties for PEC water splitting. Both of the approaches have led to excellent improvements on PEC performance and greatly broaden the knowledge about where and how the existing semiconductor materials can be used in solar energy-related applications. It is hence envisioned that 2D nanosheets can offer wide opportunities and perspectives on the directions toward high-efficiency solar energy conversion. © 2013 Elsevier Ltd.

Liang Z.-X.,Nanyang Technological University
Natural Product Reports | Year: 2010

The review highlights the recent progress on the elucidation of the biosynthetic mechanism of enediyne natural products. A large body of knowledge has been gathered from the genetic, biochemical and structural studies since the sequencing of the first two enediyne gene clusters in 2002. Primary attention is devoted to the novel pathways and enzymes in the biosynthesis of the enediyne warhead as well as the peripheral moieties. © The Royal Society of Chemistry 2010.

This study examined pre-service teachers' self-reported intention to use technology. One hundred fifty-seven participants completed a survey questionnaire measuring their responses to six constructs from a research model that integrated the Technology Acceptance Model (TAM) and Theory of Planned Behavior (TPB). Structural equation modeling was used as the main technique for data analysis. This study contributes to the growing interest among researchers in using models to explain users' intention to use technology. The results of this study showed that the TAM constructs were significant in explaining pre-service teachers' intention to use technology. However, the core constructs of the TPB, subjective norm and perceived behavioral control (represented by facilitating conditions in this study) required further examination. Overall, this study indicated that attitude toward computer use had the largest effect on the intention to use technology. © 2012 Copyright Taylor and Francis Group, LLC.

Kong A.W.K.,Nanyang Technological University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2012

IrisCode is an iris recognition algorithm developed in 1993 and continuously improved by Daugman. Understanding IrisCode's properties is extremely important because over 60 million people have been mathematically enrolled by the algorithm. In this paper, IrisCode is proved to be a compression algorithm, which is to say its templates are compressed iris images. In our experiments, the compression ratio of these images is 1:655. An algorithm is designed to perform this decompression by exploiting a graph composed of the bit pairs in IrisCode, prior knowledge from iris image databases, and the theoretical results. To remove artifacts, two postprocessing techniques that carry out optimization in the Fourier domain are developed. Decompressed iris images obtained from two public iris image databases are evaluated by visual comparison, two objective image quality assessment metrics, and eight iris recognition methods. The experimental results show that the decompressed iris images retain iris texture that their quality is roughly equivalent to a JPEG quality factor of 10 and that the iris recognition methods can match the original images with the decompressed images. This paper also discusses the impacts of these theoretical and experimental findings on privacy and security. © 2012 IEEE.

Pumera M.,Nanyang Technological University
Nanoscale | Year: 2010

In the past few years, we have witnessed rapid developments in the realization of the old nanotechnology dream, autonomous nanosubmarines. These nanomachines are self-powered, taking energy from their environment by electrocatalytic conversion of chemicals present in the solution, self-propelled by flux of the electrons within the submarine and the hydronium ions on the surface of the nanosub, powering it in the direction opposite to that of the flux of the hydronium. These nanosubmarines are responsive to external fields, able to follow complex magnetic patterns, navigate themselves in complex microfluidic channels, follow chemical gradients, carry cargo, and communicate with each other. This minireview focuses on a discussion of the fundamentals of the electrophoretic mechanism underlying the propulsion of this sort of nanosub, as well as a demonstration of the proof-of-concept capabilities of nanosubmarines. © 2010 The Royal Society of Chemistry.

Chen C.-M.,Nanyang Technological University | Delmas M.A.,University of California at Los Angeles
Operations Research | Year: 2012

Growing social concerns over the environmental externalities associated with business activities are pushing firms to identify activities that create economic value with less environmental impact and to become more eco-efficient. Over the past two decades, researchers have increasingly used frontier efficiency models to evaluate productive efficiency in the presence of undesirable outputs, such as greenhouse gas emissions or toxic emissions. In this paper, we identify critical flaws in existing frontier models and show that these models can identify eco-inefficient firms as eco-efficient. We develop a new eco-inefficiency frontier model that rectifies these problems. Our model calculates an eco-inefficiency score for each firm and improvements in outputs necessary to attain eco-efficiency. We demonstrate through a Monte Carlo experiment that our eco-inefficiency model provides a more reliable measurement of corporate eco-inefficiency than the existing frontier models. We also extend the single-output Cobb-Douglas production function to multiple desirable and undesirable outputs. This extension allows for greater flexibility in the simulation analysis of frontier models. © 2012 INFORMS.

Pumera M.,Nanyang Technological University
Chemical Society Reviews | Year: 2010

Graphene-based nanomaterials are in the forefront of chemical research. This tutorial review provides an introduction to their electrochemistry, its fundamentals and applications. Selected examples of applications in energy storage and sensing are presented. The synthetic methods for preparing graphenes as well as their materials chemistry are thoroughly discussed, as they have a profound influence on the electronic and electrochemical behavior of graphene-related nanomaterials. Inherent electrochemistry and spectroelectrochemistry of graphene nanomaterials is discussed thoroughly. Important application in sensing and energy storage areas are highlighted. © 2010 The Royal Society of Chemistry.

Modi K.,University of Oxford | Modi K.,National University of Singapore | Brodutch A.,Macquarie University | Brodutch A.,University of Waterloo | And 5 more authors.
Reviews of Modern Physics | Year: 2012

One of the best signatures of nonclassicality in a quantum system is the existence of correlations that have no classical counterpart. Different methods for quantifying the quantum and classical parts of correlations are among the more actively studied topics of quantum-information theory over the past decade. Entanglement is the most prominent of these correlations, but in many cases unentangled states exhibit nonclassical behavior too. Thus distinguishing quantum correlations other than entanglement provides a better division between the quantum and classical worlds, especially when considering mixed states. Here different notions of classical and quantum correlations quantified by quantum discord and other related measures are reviewed. In the first half, the mathematical properties of the measures of quantum correlations are reviewed, related to each other, and the classical-quantum division that is common among them is discussed. In the second half, it is shown that the measures identify and quantify the deviation from classicality in various quantum-information- processing tasks, quantum thermodynamics, open-system dynamics, and many-body physics. It is shown that in many cases quantum correlations indicate an advantage of quantum methods over classical ones. © 2012 American Physical Society.

Pham Q.-C.,Nanyang Technological University
IEEE Transactions on Robotics | Year: 2014

Finding the time-optimal parameterization of a given path subject to kinodynamic constraints is an essential component in many robotic theories and applications. The objective of this paper is to provide a general, fast, and robust implementation of this component. For this, we give a complete solution to the issue of dynamic singularities, which are the main cause of failure in existing implementations. We then present an open-source implementation of the algorithm in C++/Python and demonstrate its robustness and speed in various robotics settings. © 2014 IEEE.

Low Y.M.,Nanyang Technological University
Structural Safety | Year: 2013

The problem of constructing a probability density function (pdf) from four prescribed moments arises in many fields, including engineering. This problem may be addressed by the Pearson and Johnson systems of distribution, but systems are complicated to implement and have other drawbacks. This article presents a new unimodal distribution characterized by four parameters. This distribution has a rich flexibility in shape, nearly encompassing the entire skewness-kurtosis region permissible for unimodal densities. This versatility enables it to approximate many well known distributions, and moreover, it specializes to several important cases such as the normal and the lognormal. The density and cumulative distribution function have proper analytical forms, unlike, for example the generalized lambda distribution. Moreover, the parameters can be easily computed from the moments, thus obviating the need for tables. The proposed distribution is applied to fit several theoretical distributions, as well as actual datasets, with very favorable results. In addition, we demonstrate the effectiveness of the distribution in an assortment of engineering problems, including nonlinear ocean waves, non-Gaussian stochastic processes, moment-based reliability analysis, and fatigue damage uncertainty prediction. © 2013 Elsevier Ltd.

Nguyen N.-T.,Nanyang Technological University
Biomicrofluidics | Year: 2010

This review presents a systematic perspective on the development of microoptofluidic lenses. The progress on the development of micro-optofluidic lenses are illustrated by example from recent literature. The advantage of micro-optofluidic lenses over solid lens systems is their tunability without the use of large actuators such as servo motors. Depending on the relative orientation of light path and the substrate surface, micro-optofluidic lenses can be categorized as in-plane or out-ofplane lenses. However, this review will focus on the tunability of the lenses and categorizes them according to the concept of tunability. Micro-optofluidic lenses can be either tuned by the liquid in use or by the shape of the lens. Microoptofluidic lenses with tunable shape are categorized according to the actuation schemes. Typical parameters of micro-optofluidic lenses reported recently are compared and discussed. Finally, perspectives are given for future works in this field. © 2010 American Institute of Physics.

Huang H.,Nanyang Technological University
Nanoscale | Year: 2012

SnO(2) nanorod arrays have been deposited on 4 inch SiO(2)/Si and Si wafers and stainless steel substrates by plasma-enhanced chemical vapor deposition without any high temperature treatment or additional catalysis. The SnO(2) nanorods grow up from seed nanocrystals along the [110] preferential direction by a self-catalyzed vapor-solid growth mechanism. The surface of the SnO(2) nanorods was modified by ZnO, Pt and Ni nanocrystals. After surface modification, the field emission properties of the SnO(2) nanorod arrays are improved. The Ni nanocrystal with sharp tips and edges act as additional field emission sites to SnO(2) nanorods and thus the Ni/SnO(2)/SiO(2)/Si outperforms other samples due to the synergistic effects of good conductivity and hierarchical sharp apexes. The field enhancement factor of the Ni/SnO(2)/SiO(2)/Si increased around 3 times while the turn-on field of 8.0 V μm(-1) is about one third of the SnO(2)/SiO(2)/Si device.

Gruber G.,Nanyang Technological University
Structure | Year: 2015

Deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) are essential for hypusination of eukaryotic translation initiation factor 5A (eIF-5A). In this issue, Han et al. use X-ray crystallograpy and UV/Vis and Mössbauer spectroscopy to provide insights into the fundamental mechanism of the hypusination of eIF-5A and a peroxo intermediate state. © 2015 Elsevier Ltd.

Chiba S.,Nanyang Technological University
Bulletin of the Chemical Society of Japan | Year: 2013

This personal account highlights the remarkable versatility of the Cu-O2 systems for promoting oxidative/oxygenative molecular transformation of imine and enamine derivatives toward efficient construction of azaheterocycles. © 2013 The Chemical Society of Japan.

Zhang J.,Nanyang Technological University
Proceedings - International Conference on Advanced Information Networking and Applications, AINA | Year: 2011

There is an urgent need of effective trust management for vehicular ad-hoc networks (VANETs), given the dire consequences of acting on false information sent out by malicious peers in this context. In this paper, we first discuss the challenges for trust management caused by the important characteristics of VANET environments. We then survey existing trust models in multi-agent systems, mobile ad-hoc networks (MANETs) and VANETs, and point out their key issues. Based on these studies, we suggest desired properties towards effective trust management in VANETs, setting up clear goals for researchers in this area. © 2011 IEEE.

Agarwal S.,Nanyang Technological University
Telemedicine journal and e-health : the official journal of the American Telemedicine Association | Year: 2010

Diabetes and hypertension have become very common perhaps because of increasingly busy lifestyles, unhealthy eating habits, and a highly competitive workplace. The rapid advancement of mobile communication technologies offers innumerable opportunities for the development of software and hardware applications for remote monitoring of such chronic diseases. This study describes a remote health-monitoring service that provides an end-to-end solution, that is, (1) it collects blood pressure readings from the patient through a mobile phone; (2) it provides these data to doctors through a Web interface; and (3) it enables doctors to manage the chronic condition by providing feedback to the patients remotely. This article also aims at understanding the requirements and expectations of doctors and hospitals from such a remote health-monitoring service.

Patil V.S.,National University of Singapore | Patil V.S.,Nanyang Technological University | Kai T.,National University of Singapore
Current Biology | Year: 2010

The Piwi-interacting RNAs (piRNAs) have been shown to safeguard the animal germline genome against deleterious retroelements [1-9]. Many factors involved in the production of piRNAs localize to nuage, a unique perinuclear structure in animal germline cells [10], suggesting that nuage may function as a site for processing of germline piRNAs [1, 3-6, 11-14]. Here we report a conserved yet uncharacterized component of the germline piRNA pathway, Tejas (Tej), which localizes to nuage. tej is required for the repression of some retroelements and for the production of sufficient germline piRNAs. The localization of Tej to nuage depends on vasa (vas) [15] and spindle-E (spn-E) [1, 16, 17] while it regulates the localization of Spn-E, Aubergine (Aub) [3, 4, 14], Argonaute3 (Ago3) [5], Krimper (Krimp) [13], and Maelstrom (Mael) [18] to nuage. Aub, Vas, and Spn-E physically interact with Tej through the N terminus containing the conserved tejas domain, which is necessary and sufficient for its germline function. Aub and Spn-E also bind to the tudor domain at the C terminus. Our data suggest that Tej contributes to the formation of a macromolecular complex at perinuclear region and engages it in the production of germline piRNAs. © 2010 Elsevier Ltd. All rights reserved.

Hu G.,Nanyang Technological University
Systems and Control Letters | Year: 2012

In this paper, we study the problem of robust consensus tracking for a class of second-order multi-agent dynamic systems with disturbances and unmodeled agent dynamics. Contrary to previous approaches, we design continuous distributed consensus protocols to enable global asymptotic consensus tracking. Our focus is on consensus protocol design and stability analysis which also leads to the derivation of sufficient conditions for consensus tracking. We first consider the case of undirected information exchange with a symmetric and positive definite information-exchange matrix. We develop an identifier for each agent to estimate the unknown disturbances and unmodeled agent dynamics. Based on the identifier, we develop a consensus tracking protocol to enable global asymptotic consensus tracking using local information obtained from neighboring agents. The closed-loop stability is proven using Lyapunov analysis theory and an invariance-like theorem. We then extend the approach to the case of directed information exchange, whose information-exchange matrix is only of full rank so that the approach for undirected graphs cannot be directly applied. We show that global asymptotic consensus tracking can still be enabled under the new derived sufficient conditions by designing a new identifier, which utilizes the estimated information exchanged from neighboring agents, and constructing a new Lyapunov function. Examples and numerical simulations are provided to validate the effectiveness of the proposed robust consensus tracking method. © 2011 Elsevier B.V. All rights reserved.

Phan V.-T.,Nanyang Technological University | Lee H.-H.,University of Ulsan
IEEE Transactions on Power Electronics | Year: 2011

This paper proposes a new control strategy of effective fifth and seventh harmonic elimination in the stator output voltage at the point of common coupling for a stand-alone doubly fed induction generator (DFIG) feeding a three-phase diode rectifier. This load regularly causes such harmonic distortions, which harmfully affect the performance of other loads connected to the DFIG. In order to allow the DFIG to deliver a pure sinusoidal stator output voltage, these harmonics must be rejected. The proposed elimination method is investigated based on the rotor current controller employing a proportional integral and a resonant controller, which is implemented in the fundamental reference frame. In this frame, both positive seventh and negative fifth voltage harmonic can be eliminated by using only single resonant compensator tuned at six multiples of synchronous frequency in the rotor current controller. The control scheme is developed in the rotor-side converter for the control and operation of the DFIG. Simulations and experimental results with 2.2-kW DFIG feeding a nonlinear load are shown to verify prominent features of the proposed control method. © 2010 IEEE.

Lai X.,Hangzhou Dianzi University | Lin Z.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2012

Infinite impulse response (IIR) digital filters with prescribed magnitude and phase responses have been used in many applications. To approximate the prescribed magnitude and phase responses, we propose a new approach to the design of general IIR filters by minimizing the maximum phase error subject to a prescribed or simultaneously minimized maximum magnitude error, where the phase error and magnitude error are controlled by two elliptic constraints respectively with major and minor axes along the desired frequency response. The sequential constrained least-squares method and Levy-Sanathanan-Koerner strategy are used to convert the nonconvex constraints into convex ones, resulting in a series of convex optimization subproblems. Design examples and comparisons with recent methods demonstrate the flexibility and effectiveness of the proposed methods. © 2011 IEEE.

Zhou J.,Swinburne University of Technology | Wen C.,Nanyang Technological University | Li T.,Dalian Maritime University
IEEE Transactions on Automatic Control | Year: 2012

In this note, we consider a class of uncertain dynamic nonlinear systems preceded by Bouc-Wen type of hysteresis nonlinearity. A new perfect inverse function of the hysteresis is constructed and used to cancel the hysteresis effects in controller design with backstepping technique. For the design and implementation of the controller, no knowledge is assumed on system parameters. It is shown that the proposed controller not only guarantees asymptotic stability, but also transient performance. © 2012 IEEE.

Mn(III)-catalyzed formal [3+2]- and [3+3]-annulations have been developed using readily available vinyl azides with 1,3-dicarbonyl compounds and cyclopropanols. Vinyl azides were successfully applied as a threeatom unit including one nitrogen to prepare various azaheterocycles via Mn(III)-catalyzed radical reactions. © Schweizerische Chemische Gesellschaft.

Chiba S.,Nanyang Technological University
Synlett | Year: 2012

In this account, recent advances made on the reactions of several types of organic azides, such as vinyl azides, cyclic 2-azido alcohols, α-azido carbonyl compounds, towards the synthesis of nitrogen-containing molecules are described. 1 Introduction 2 Chemistry of Vinyl Azides 2.1 Thermal [3+2]-Annulation of Vinyl Azides with 1,3-Dicarbonyl Compounds 2.2 Manganese(III)-Catalyzed Formal [3+2]-Annulation with 1,3-Dicarbonyl Compounds 2.3 Manganese(III)-Mediated/Catalyzed Formal [3+3]-Annulation with Cyclopropanols 2.4 Synthesis of Isoquinolines from α-Aryl-Substituted Vinyl Azides and Internal Alkynes by Rhodium-Copper Bimetallic Cooperation 3 Chemistry of Cyclic 2-Azido Alcohols 3.1 Manganese(III)-Catalyzed Ring Expansion of 2-Azido-cyclobutanols 3.2 Palladium(II)-Catalyzed Ring Expansion of Cyclic 2-Azido Alcohols 4 Chemistry of α-Azido Carbonyl Compounds 4.1 Orthogonal Synthesis of Isoindole and Isoquinoline Derivatives 4.2 Generation of Iminylcopper Species and Their Catalytic Carbon-Carbon Bond Cleavage under an Oxygen Atmosphere 4.3 Copper(II)-Catalyzed Aerobic Synthesis of Azaspirocyclohexadienones 5 Conclusion. © Georg Thieme Verlag Stuttgart. New York.

Ou J.-Y.,University of Southampton | Plum E.,University of Southampton | Zhang J.,University of Southampton | Zheludev N.I.,University of Southampton | Zheludev N.I.,Nanyang Technological University
Nature Nanotechnology | Year: 2013

Current efforts in metamaterials research focus on attaining dynamic functionalities such as tunability, switching and modulation of electromagnetic waves. To this end, various approaches have emerged, including embedded varactors, phase-change media, the use of liquid crystals, electrical modulation with graphene and superconductors, and carrier injection or depletion in semiconductor substrates. However, tuning, switching and modulating metamaterial properties in the visible and near-infrared range remain major technological challenges: indeed, the existing microelectromechanical solutions used for the sub-terahertz and terahertz regimes cannot be shrunk by two to three orders of magnitude to enter the optical spectral range. Here, we develop a new type of metamaterial operating in the optical part of the spectrum that is three orders of magnitude faster than previously reported electrically reconfigurable metamaterials. The metamaterial is actuated by electrostatic forces arising from the application of only a few volts to its nanoscale building blocks - the plasmonic metamolecules - that are supported by pairs of parallel strings cut from a flexible silicon nitride membrane of nanoscale thickness. These strings, of picogram mass, can be driven synchronously to megahertz frequencies to electromechanically reconfigure the metamolecules and dramatically change the transmission and reflection spectra of the metamaterial. The metamaterial's colossal electro-optical response (on the order of 10-5-10 -6 m V-1) allows for either fast continuous tuning of its optical properties (up to 8% optical signal modulation at up to megahertz rates) or high-contrast irreversible switching in a device only 100 nm thick, without the need for external polarizers and analysers. Copyright © 2013 Macmillan Publishers Limited. All rights reserved.

Qu X.,Nanyang Technological University
Gait and Posture | Year: 2012

The uncontrolled manifold (UCM) analysis has been demonstrated to be a powerful tool for understanding motor variability. The purpose of this study was to use the UCM analysis to investigate the effects of load carriage and fatigue on gait variability. Whole-body kinematic data during treadmill walking were collected from 12 healthy male participants when fatigue and load carriage were applied. The task-level variable for the UCM analysis was selected to be the whole-body COM. We chose to analyze the whole-body COM data at two important gait events: right heel contact and right toe off, and the UCM analysis was carried out in the sagittal and frontal planes, separately. The dependent measures were UCM variability measures and UCM ratio. Three-way ANOVA was performed to determine the main and interaction effects of back-carrying load, fatigue, and gait events on the dependent measures. The results showed that frontal UCM ratio significantly changed with the application of back-carrying load and fatigue, indicating that both factors had effects on motor performance in stabilizing the whole-body COM in the frontal plane. These findings can facilitate a better understanding of the nature of motor variability due to load carriage and fatigue. © 2012 Elsevier B.V.

Yea S.,Nanyang Technological University
Environment and Planning D: Society and Space | Year: 2013

In this paper I examine the local mobilisation of the dominant global framing of the problem of human trafficking through 'the female child victim' in child sex trafficking advocacy campaigns. The child victim is a symbolic and emotive frame embodied in the Third World female child and enacted through her helplessness and experiences of extreme violence and (sexual) abuse in trafficking situations across diverse contexts globally. I use The Body Shop's (TBS's) 2009-12 global campaign against child sex trafficking as my site for discussion of the way frames in global human rights activism move into local contexts, often coming to define the ways contemporary human rights problems are understood and reproduced locally. I draw on ethnographic research on human trafficking in Singapore to explore the ways in which the child victim frame is mobilised in a specific locale through the involvement of a local nongovernmental organisation and university student actors as part of TBS's campaign strategy. Although recent geographical scholarship on social movements has embraced a networked approach, I argue for heightened attention to the geographies of scaled (re)iteration, or local mobilisation that occurs as transnational activism connects with particular places. The role of framing in embedding global human rights issues locally in transnational activism is central to this process.

Sandin S.,Nanyang Technological University | Rhodes D.,Proteos, Inc.
Current Opinion in Structural Biology | Year: 2014

The telomerase reverse transcriptase has an essential role in telomere maintenance and in cancer biology. Progress during the last year has revealed the three-dimensional architecture of both human and ciliate telomerase at about 25. Å resolution, obtained using single particle electron microscopy (EM). The structural analysis of the two holoenzyme complexes isolated from cells shows that whilst the ciliate telomerase is monomeric, the human telomerase is dimeric and only functional as a dimer. We critically discuss the approaches taken to assign the location of protein and RNA subunits, as well as fitting the crystal structure of the catalytic protein subunit in the medium resolution EM density maps. Comparison of the two structural interpretations reveals not only a common RNA/reverse transcriptase core, but also significant differences due to different RNA subunit size and protein composition. These differences suggest that the oligomeric state and subunit composition of telomerase in evolutionary distant organism have evolved. © 2014.

Hu H.,Xidian University | Liu Y.,Nanyang Technological University
IEEE Transactions on Automation Science and Engineering | Year: 2014

In the framework of automated manufacturing systems (AMS), Petri nets are widely used to model, analyze, and control them. Resolving deadlocks is of paramount significance because their emergence may likely zero a systems throughput, if not necessarily. Supervisory control technique is the most widely adopted method to resolve them. A control policy can be converted into satisfying a set of inequalities, each of which corresponds to a siphon in a Petri net structure. The number of siphons can be exponential in the worst case, so does the number of inequalities. Taking into account the independent and dependent inequalities, this paper proposes a method to remove all the dependent inequalities, while preserving only the independent ones. This method can significantly reduce the size of a supervisory controller. Examples are presented to illustrate the effectiveness and efficiency of this method. © 2013 IEEE.

Tan E.L.,Nanyang Technological University
IEEE Microwave and Wireless Components Letters | Year: 2010

This letter presents the acceleration of locally one-dimensional finite-difference time-domain (LOD-FDTD) method using fundamental scheme on graphics processor units (GPUs). Compared to the conventional scheme, the fundamental LOD-FDTD (denoted as FLOD-FDTD) scheme has its right-hand sides cast in the simplest form without involving matrix operators. This leads to a substantial reduction in floating-point operations as well as field and coefficient memory access. To reap further advantages of FLOD-FDTD, certain field updates are embedded in the implicit solutions while exploiting the reuse of field data. Using FLOD-FDTD, it is found that significant speed-up is achievable for the method on GPUs. © 2010 IEEE.

Hew K.F.,Nanyang Technological University
Computers in Human Behavior | Year: 2011

The purpose of this article is to review current published research studies focusing on the use of Facebook by students and teachers. The aim of the review is not to solely discuss Facebook in relation to teaching or learning purposes, or about its educational value per se, but also to present a detailed account of the participants' Facebook usage profile or the extent to which users are engaged in Facebook activities. The emphasis of this review will be upon empirical findings rather than opinion- or theoretical explanations. Following the review guidelines set by Creswell (Research Design Qualitative and Quantitative Approaches, 1994), I summarize the hitherto accumulated state of knowledge concerning Facebook and highlight questions or issues that research has left unresolved. This review is organized into three sections that cover the major topics of current research: (a) students' Facebook usage profile or extent of Facebook use (e.g.; time students spend on Facebook each day, students' motives for using Facebook, as well as various factors that may affect these usage profiles), (b) the effects of Facebook use (e.g.; effects of Facebook self-disclosure on teacher credibility, effects of Facebook use on student social presence and discussion, and effects of Facebook on students' academic performance), and (c) students' attitudes toward Facebook. The conclusions overall suggest that Facebook thus far has very little educational use, that students use Facebook mainly to keep in touch with known individuals, and that students tend to disclose more personal information about themselves on Facebook; hence attracting potential privacy risks upon themselves. © 2010 Elsevier Ltd. All rights reserved.

Controversy remains regarding the suitable density functionals for the calculation of vitamin B 12 systems that contain cobalt. To identify the optimum functionals, geometry optimization calculations were performed on a full-size model of methylcobalamin (MeCbl) using the B3LYP, B3LYP-D, BP86, and BP86-D methods in conjunction with the 6-31G* basis set. Single-point energy evaluations were also performed with the 6-311+G(2d,p) basis set. Consistent with previous studies, the BP86-optimized geometry showed fairly good agreement with the experimental geometry. Various factors that may influence the homolytic bond dissociation energy (BDE) of the Co-C bond of MeCbl were systematically evaluated with these methods. Our analysis demonstrated that dispersion was the largest correction term that influenced the magnitude of BDE. Previous studies have shown that B3LYP significantly underestimates BDE, whereas BP86 gives BDE values that are fairly close to the experimental values (36-37 kcal/mol). The same trend in the relative magnitudes of the BDEs was observed in the present calculations. However, BP86 underestimated the BDE for a full model of MeCbl. When the amount of Hartree-Fock exchange in the B3LYP functional was reduced to 15% and the dispersion correction was made (i.e., B3LYP-D), the calculated BDE was in good accord with experimental values. B3P86-D also performed well. A detailed analysis was undertaken to determine which atoms in cobalamin have large dispersion interactions with a methyl fragment of MeCbl. © 2011 American Chemical Society.

Su P.-C.,Nanyang Technological University | Prinz F.B.,Stanford University
Electrochemistry Communications | Year: 2012

This paper presents a fabrication method for a low temperature micro-solid oxide fuel cell (μ-SOFC), featuring a large number of free-standing nano thin film electrolyte membranes. The μ-SOFC was fabricated by simple silicon-based MEMS processes to create a membrane array structure that renders high surface area density and mechanically stable support for yttria-stablized zirconia (YSZ) with only 70 nm in thickness. A total number of 765 to 6885 circular YSZ electrolyte membranes with a diameter of 50 μm were enclosed within 2 mm to 6 mm square arrays. The active membrane area density on a silicon wafer surface was increased up to 20 times higher than that of previously reported structures. A 2 mm μ-SOFC array was tested at 350, 400, and 450 °C, and maximum power outputs of 1.78 mW, 2.43 mW, and 2.98 mW were obtained, respectively. Total power output of the high performance micro-SOFCs was increased from microwatts up to the milliwatt scale, and can be easily scaled up further for higher power output by this method. © 2011 Elsevier B.V. All rights reserved.

Ambrogio M.W.,Northwestern University | Thomas C.R.,University of California at Los Angeles | Zhao Y.-L.,Nanyang Technological University | Zink J.I.,University of California at Los Angeles | Stoddart J.F.,Northwestern University
Accounts of Chemical Research | Year: 2011

Medicine can benefit significantly from advances in nanotechnology because nanoscale assemblies promise to improve on previously established therapeutic and diagnostic regimes. Over the past decade, the use of delivery platforms has attracted attention as researchers shift their focus toward new ways to deliver therapeutic and/or diagnostic agents and away from the development of new drug candidates. Metaphorically, the use of delivery platforms in medicine can be viewed as the "bow-and-arrow" approach, where the drugs are the arrows and the delivery vehicles are the bows. Even if one possesses the best arrows that money can buy, they will not be useful if one does not have the appropriate bow to deliver the arrows to their intended location.Currently, many strategies exist for the delivery of bioactive agents within living tissue. Polymers, dendrimers, micelles, vesicles, and nanoparticles have all been investigated for their use as possible delivery vehicles. With the growth of nanomedicine, one can envisage the possibility of fabricating a theranostic vector that could release powerful therapeutics and diagnostic markers simultaneously and selectively to diseased tissue.In our design of more robust theranostic delivery systems, we have focused our attention on using mesoporous silica nanoparticles (SNPs). The payload "cargo" molecules can be stored within this robust domain, which is stable to a wide range of chemical conditions. This stability allows SNPs to be functionalized with stimulus-responsive mechanically interlocked molecules (MIMs) in the shape of bistable rotaxanes and psuedorotaxanes to yield mechanized silica nanoparticles (MSNPs).In this Account, we chronicle the evolution of various MSNPs, which came about as a result of our decade-long collaboration, and discuss advances in the synthesis of novel hybrid SNPs and the various MIMs which have been attached to their surfaces. These MIMs can be designed in such a way that they either change shape or shed off some of their parts in response to a specific stimulus, such as changes in redox potential, alterations in pH, irradiation with light, or the application of an oscillating magnetic field, allowing a theranostic payload to be released from the nanopores to a precise location at the appropiate time. We have also shown that these integrated systems can operate not only within cells, but also in live animals in response to pre-existing biological triggers. Recognizing that the theranostics of the future could offer a fresh approach to the treatment of degenerative diseases including cancer, we aim to start moving out of the chemical domain and into the biological one. Some MSNPs are already being tested in biological systems. © 2011 American Chemical Society.

Wang Y.,Nanyang Technological University
Nature communications | Year: 2010

A central theme in nanotechnology is to advance the fundamental understanding of nanoscale component assembly, thereby allowing rational structural design that may lead to materials with novel properties and functions. Nanoparticles (NPs) are often regarded as 'artificial atoms', but their 'reactions' are not readily controllable. Here, we demonstrate a complete nanoreaction system whereby colloidal NPs are rationally assembled and purified. Two types of functionalized gold NPs (A and B) are bonded to give specific products AB, AB(2), AB(3) and AB(4). The stoichiometry control is realized by fine-tuning the charge repulsion among the B-NPs. The products are protected by a polymer, which allows their isolation in high purity. The integration of hetero-assembly, stoichiometry control, protection scheme and separation method may provide a scalable way to fabricate sophisticated nanostructures.

Hirao H.,Nanyang Technological University | Morokuma K.,Kyoto University
Journal of the American Chemical Society | Year: 2011

Why can enzymes provide different products from only slightly different substrates? While the reaction of 2-hydroxyethylphosphonate (2-HEP) catalyzed by 2-hydroxyethylphosphonate dioxygenase (HEPD) yields hydroxymethylphosphonate and formic acid, the HEPD-catalyzed reaction of 1-HEP gives acetylphosphate. ONIOM(DFT:MM) was used to uncover the distinct reaction mechanisms for the different substrates. Calculations show that, in both reactions, similar radical intermediates are generated by the same process. After the formation of common radical intermediates, proton-coupled electron transfer (PCET) operates in the 1-HEP reaction, whereas in the 2-HEP reaction, it cannot occur and an alternative pathway sets in. Thus, the PCET plays a critical role in defining the fates of the substrates. © 2011 American Chemical Society.

Nakamura E.,University of Tokyo | Yoshikai N.,Nanyang Technological University
Journal of Organic Chemistry | Year: 2010

Figure presented. The use of iron as a catalyst for organic synthesis has been increasingly attracting the interest of chemists from economical and ecological points of view. While Fe(III) and Fe(II) catalysts have long been used as Lewis acids for synthesis, we have been interested in exploration of catalysis based on rather unexplored organoiron chemistry since the late 1990s. This Perspective summarizes a series of iron-catalyzed C-C bond formation reactions developed by us, which include (asymmetric) carbometalation of olefins, cross-coupling of alkyl halides, and activation of sp2 and sp3 C-H bonds. © 2010 American Chemical Society.

Wang G.,Nanyang Technological University | Forsyth D.,University of Illinois at Urbana - Champaign | Hoiem D.,University of Illinois at Urbana - Champaign
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2013

Due to the intrinsic long-tailed distribution of objects in the real world, we are unlikely to be able to train an object recognizer/detector with many visual examples for each category. We have to share visual knowledge between object categories to enable learning with few or no training examples. In this paper, we show that local object similarity information - statements that pairs of categories are similar or dissimilar - is a very useful cue to tie different categories to each other for effective knowledge transfer. The key insight: Given a set of object categories which are similar and a set of categories which are dissimilar, a good object model should respond more strongly to examples from similar categories than to examples from dissimilar categories. To exploit this category-dependent similarity regularization, we develop a regularized kernel machine algorithm to train kernel classifiers for categories with few or no training examples. We also adapt the state-of-the-art object detector to encode object similarity constraints. Our experiments on hundreds of categories from the Labelme dataset show that our regularized kernel classifiers can make significant improvement on object categorization. We also evaluate the improved object detector on the PASCAL VOC 2007 benchmark dataset. © 1979-2012 IEEE.

Zhao B.,Soochow University of China | Loh T.-P.,Nanyang Technological University
Organic Letters | Year: 2013

An efficient catalytic enantioselective hetero-Diels-Alder reaction of Danishefsky's dienes with α-carbonyl esters using a chiral In(III)-pybox complex has been demonstrated. This protocol offers several advantages, including mild reaction conditions, relatively low catalyst loading, and good to excellent enantioselectivities. Furthermore, the absolute configurations of the new alkynyl-containing products were determined by CD spectra in combination with TD-DFT calculations. © 2013 American Chemical Society.

Poon K.K.,Nanyang Technological University
Journal of Intellectual Disability Research | Year: 2011

Background This study sought to describe the activities and participation of adolescents with autism spectrum disorders (ASD) in Singapore and to examine the suitability of the Activity and Participation component of the International Classification of Functioning, Disability and Health for achieving this purpose. This information may guide the development of intervention programmes for adolescents and adults as well as the provision of a means to document meaningful outcomes. Methods Parents of 20 adolescents with ASD attending special schools in Singapore were interviewed using the Vineland Adaptive Behavioural Scales - Second Edition and the Activities and Participation Rating Scale (APRS), which was developed for this study. Results The adolescents with ASD were rated to have more difficulties with participation than with the engagement of activities. Individual domain analyses indicate no difficulties with mobility and mild difficulties with self-care. The performance of general tasks and demands were rated as less problematic than domestic, major life areas, communication and interpersonal interactions. The adolescents with ASD were rated to have more difficulties in communication and community environments than in at home. In addition, analysis of associations between the APRS and Vineland Adaptive Behavioural Scales - Second Edition reveal a pattern of strong relationships between sub-tests. Conclusion This study highlights the imperative for researchers and practitioners alike to develop a focus on strengths, generalisation and the quality of life of adolescents with ASD. The APRS also shows promise in helping document outcomes for adolescents with ASD in Asia and further development of this instrument is needed. © 2011 The Author. Journal of Intellectual Disability Research © 2011 Blackwell Publishing Ltd.

Bhattacharjya S.,Nanyang Technological University
Current Medicinal Chemistry | Year: 2010

Lipopolysaccharide (LPS), the glycolipid of the outer membrane of Gram-negative bacteria, is critically involved in health and diseases. LPS facilitates the survival of pathogens by imposing a permeability barrier against antibiotics and antimicrobial peptides. LPS, also termed as endotoxin, functions as a potent inducer of innate immunity. Interception of endotoxin in systemic circulation by immune cells e.g. macrophages is essential to mount surveillance against invading microbes. However, a hyper-activated immune response may lead to the overwhelming production of tissue damaging cytokines TNF-α, IL-1, IL-6 and free radicals that may cause multiple organ failures or septic shock syndromes. The sepsis or septic shock is the major cause of mortality; 120,000 deaths/year occur in the United States alone, in the intensive care units. To-date, no therapeutic is available to combat sepsis mediated lethality. Furthermore, bacterial resistance against commonly used antibiotics has been increasing at an alarming rate necessitating a search for antibacterial agents with novel mode of actions. LPS could be a valid drug target for the development of antiendotoxic and antimicrobial compounds. In this article, recent advances in structural basis of LPS recognition by its receptor proteins and mode of actions of antimicrobial peptides defensins and cathelicidins are reviewed. Our research has identified, through de novo design, antimicrobial and endotoxin interacting β-boomerang peptides. Structure-activity correlations (SAR) of these peptides have been discussed, highlighting future design to achieve potent LPS neutralizing molecules. © 2010 Bentham Science Publishers Ltd.

Hong L.,Nanyang Technological University
Nanotechnology | Year: 2013

The finite element method is used to simulate light absorption in periodic hybrid Si nanohole (SiNH)/PEDOT:PSS arrays. The structural periodicity (P) and hole diameter (D) of the hybrid SiNH structure are varied to maximize light absorption. In terms of the solar cell performance under the AM1.5G spectrum, the highest ultimate efficiency achieved is 30.5%, when the D/P ratio is 0.8 and P is 600 nm. We have successfully fabricated the SiNH structure based on a low cost electroless chemical etching approach using a silver catalyst. The SiNH diameters formed vary from ∼200 to 300 nm, with periodicities from ∼300 to 1000 nm. The SiNH structure reveals a low average reflectance of 4% for incident light in the range 300 to 1100 nm.

Lu M.-Z.,Hefei University of Technology | Loh T.-P.,Hefei University of Technology | Loh T.-P.,Nanyang Technological University
Organic Letters | Year: 2014

An iron-catalyzed carbodi- and trichloromethylation of activated alkenes with readily available dichloro- and tetrachloromethane has been developed. A diaryliodonium salt is used as an efficient oxidant in this transformation. This reaction tolerates a variety of functional groups and allows for a highly efficient synthesis of various chloro-containing oxindoles. © 2014 American Chemical Society.

Wang X.,East China University of Science and Technology | Zhou K.,Nanyang Technological University
International Journal of Engineering Science | Year: 2013

We investigate the internal electroelastic field within a three-phase piezoelectric inclusion of arbitrary shape when the piezoelectric matrix is subjected to remote uniform electroelastic loadings. It is observed that in the presence of the intermediate interphase layer, the internal electroelastic field within an inclusion of non-elliptical shape can be conditionally or unconditionally uniform. In order to ensure that the internal electroelastic field is conditionally uniform, the thickness of the interphase layer should be properly designed for given electroelastic constants of the three-phase piezoelectric composite, and the remote uniform electric displacements should be dependent on the applied remote uniform stresses. To ensure an unconditionally uniform internal electroelastic field, the electroelastic constants of the interphase layer can be uniquely determined by given thickness of the interphase layer and given electroelastic constants of both the internal inclusion and the surrounding matrix. Interestingly, our analysis indicates that even in the absence of the interphase layer, the internal electroelastic field within a piezoelectric inclusion of arbitrary shape can still be conditionally uniform if the electroelastic constants of the two-phase composite satisfy a restriction. © 2012 Elsevier Ltd. All rights reserved.

Unluer C.,Nanyang Technological University | Al-Tabbaa A.,University of Cambridge
Cement and Concrete Research | Year: 2013

Reactive magnesia (MgO) cements have emerged as a potentially more sustainable and technically superior alternative to Portland cement due to their lower production temperature and ability to sequester significant quantities of CO2. Porous blocks containing MgO were found to achieve higher strength values than PC blocks. A number of variables are investigated to achieve maximum carbonation and associated high strengths. This paper focuses on the impact of four different hydrated magnesium carbonates (HMCs) as cement replacements of either 20 or 50%. Accelerated carbonation (20 C, 70-90% RH, 20% CO2) is compared with natural curing (20 C, 60-70% RH, ambient CO2). SEM, TG/DTA, XRD, and HCl acid digestion are utilized to provide a thorough understanding of the performance of MgO-cement porous blocks. The presence of HMCs resulted in the formation of larger size carbonation products with a different morphology than those in the control mix, leading to significantly enhanced carbonation and strength. © 2013 Elsevier Ltd.

Pumera M.,Nanyang Technological University
Chemical Record | Year: 2012

Voltammetry of carbon nanotubes and graphene underwent significant development in the first decade of the 21st century. The initial excitement concerning the performance of the new materials was replaced with increasing crises in the field caused by the use of impure materials. Here, I provide a personal view of these developments and some "reality checks" for the electrochemistry of these nanomaterials. Copyright © 2012 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Skote M.,Nanyang Technological University
Physics of Fluids | Year: 2011

Direct numerical simulations have been performed to study the effect of a stationary distribution of spanwise wall-velocity that oscillates in the streamwise direction on a turbulent boundary layer. For the first time, a spatially developing flow with this type of forcing is studied. The part of the boundary layer which flows over the alternating wall-velocity section is greatly affected with a drag reduction close to 50% which exhibits an oscillatory distribution with a wavenumber which is twice that of the imposed wall-velocity. The maximum in drag reduction occurs where the wall velocity is at its maximum (or minimum) and the minimum occurs where the wall velocity is zero. Comparisons of the mean spanwise velocity profiles with the analytical solution to the laminar Navier-Stokes equations show very good agreement. The streamwise velocity profile indicates a thickening of the viscous sub-layer when scaled with the local friction velocity and an upward shifting of the logarithmic region when scaled with the reference (unmanipulated) friction velocity. An estimation of the idealized power consumption shows that-with the present wall forcing magnitude-more energy is required for the spatial oscillation than what is saved by drag reduction. © 2011 American Institute of Physics.

Hong Z.,Nanyang Technological University | Lee C.,Hong Kong Polytechnic University
Decision Support Systems | Year: 2013

In the presence of spot market, this paper presents a decision support system to model risks for procurement processes and to design a robust purchasing plan, including supplier selection and order allocation. Taking advantages of contract supplier and spot market, the buyer can better meet business requirements in this dynamic business environment. However, there are limitations of existing methods for modeling multiple correlated risks to support decision makers for allocating orders among multiple suppliers in the presence of spot market. Therefore, Monte Carlo simulation algorithm termed as Expected Profit-Supply at Risk (A-EPSaR) is proposed to quantify each supplier's risk so as to let decision maker realize the trade-off between profit and risk. The goal programming model helps to allocate orders among the supplier pool and the contract-spot allocation model can assign orders between the spot market and the supplier pool, respectively. The significance of this paper is to propose a novel decision support framework which helps the buyer to make optimal and robust procurement decision including supplier selection and order allocation among multiple supplier sources in the existence of correlated demand, yield and spot price uncertainties. A case study is used to illustrate the performance of the proposed framework and the proposed methods show the promising result. © 2012 Elsevier B.V. All rights reserved.

Zeng Y.,Nanyang Technological University
Journal of Aircraft | Year: 2012

Flowchoke usually occurs in the cells of a grid fin at transonicMach numbers and results in a significant increase in drag force. Compared to a typical baseline grid-fin configuration, an improved configuration with sweptback lattice alone was proposed and illustrated a moderate beneficial effect on drag reduction.With the aim to further reduce the high drag resulting from the transonic flow choke within the fin cells, an additional benefit of sharpening the original blunt leading edges of the sweptback grid fin was investigated. Viscous computational fluid dynamic (CFD) simulations were performed to study the flows over a missilewith baseline, sweptback gridfinwith blunt leading edges (SBblunt), and sweptback grid fin with sharp leading edges (SB-sharp) models under supersonic and transonic conditions at 0 incidences. The results confirm the notion that the combination of sweptback and leading-edge sharpness contributes a more significant effect on suppressing the flow choke and reducing the drag experienced by grid fins. Because of complicated grid generation and long computation time, however, the present study considers only one sweptback angle and one sharpness angle, which may not be the optimal ones. To determine the optimal angles,more studies on different sweptback and sharpness angles will be conducted in future works. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Feng C.,Nanyang Technological University | Loh T.-P.,Anhui University of Science and Technology
Angewandte Chemie - International Edition | Year: 2014

The rhodium(III)-catalyzed ortho C-H alkynylation of non-electronically activated arenes is disclosed. This process features a straightforward and highly effective protocol for the synthesis of functionalized alkynes and represents the first example of merging a hypervalent iodine reagent with rhodium(III) catalysis. Notably, this reaction proceeds at room temperature, tolerates a variety of functional groups, and more importantly, exhibits high selectivity for monoalkynylation. Hot rhod: A rhodium-catalyzed, electronically reversed Sonogashira reaction between unbiased arenes and the hypervalent iodine reagent 1 proceeds through C-H activation. This reaction displays excellent functional-group tolerance and high efficiency, and thus opens a new synthetic pathway to access functionalized alkynes. Cp*=C5Me5, DCE=1,2-dichloroethane, Piv=pivaloyl, TIPS=triisopropylsilyl. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yoshikai N.,Nanyang Technological University
Synlett | Year: 2011

While chelation-assisted C-H bond activation by a transition-metal complex serves as a versatile platform for the development of regioselective C-H bond-functionalization reactions, the capability of first-row transition metals to catalyze such transformations has scarcely been explored. This highlight article illustrates how cobalt has recently emerged as a promising metal for chelation-assisted C-H bond functionalization. © Georg Thieme Verlag Stuttgart - New York.

Triantafyllou M.S.,Massachusetts Institute of Technology | Weymouth G.D.,University of Southampton | Miao J.,Nanyang Technological University
Annual Review of Fluid Mechanics | Year: 2016

The fluid mechanics employed by aquatic animals in their escape or attack maneuvers, what we call survival hydrodynamics, are fascinating because the recorded performance in animals is truly impressive. Such performance forces us to pose some basic questions on the underlying flow mechanisms that are not yet in use in engineered vehicles. A closely related issue is the ability of animals to sense the flow velocity and pressure field around them in order to detect and discriminate threats in environments where vision or other sensing is of limited or no use. We review work on animal flow sensing and actuation as a source of inspiration and as a way to formulate a number of basic problems and investigate the flow mechanisms that enable animals to perform these remarkable maneuvers. We also describe some intriguing mechanisms of actuation and sensing. © Copyright 2016 by Annual Reviews. All rights reserved.

Tsai F.S.,Nanyang Technological University
Expert Systems with Applications | Year: 2012

Data visualization of high-dimensional data is possible through the use of dimensionality reduction techniques. However, in deciding which dimensionality reduction techniques to use in practice, quantitative metrics are necessary for evaluating the results of the transformation and visualization of the lower dimensional embedding. In this paper, we propose a manifold visualization metric based on the pairwise correlation of the geodesic distance in a data manifold. This metric is compared with other metrics based on the Euclidean distance, Mahalanobis distance, City Block metric, Minkowski metric, cosine distance, Chebychev distance, and Spearman distance. The results of applying different dimensionality reduction techniques on various types of nonlinear manifolds are compared and discussed. Our experiments show that our proposed metric is suitable for quantitatively evaluating the results of the dimensionality reduction techniques if the data lies on an open planar nonlinear manifold. This has practical significance in the implementation of knowledge-based visualization systems and the application of knowledge-based dimensionality reduction methods. © 2011 Elsevier Ltd. All rights reserved.

Adams D.H.,Nanyang Technological University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

A new formulation of chiral fermions on the lattice is presented. It is a version of overlap fermions, but built from the computationally efficient staggered fermions rather than the previously used Wilson fermions. The construction reduces the four quark flavors described by the staggered fermion to two quark flavors; this pair can be taken as the up and down quarks in Lattice QCD. A domain wall formulation giving a truncation of this overlap construction is also outlined. © 2011 Elsevier B.V.

Lin R.M.,Nanyang Technological University
Mechanical Systems and Signal Processing | Year: 2012

A continuum-based plate model is proposed to study the nanoscale vibration characteristics of multi-layered graphene sheets (MLGSs) that are increasingly being proposed for important engineering applications such as THz resonators. Generalized Differential Quadrature (GDQ) method is used to predict the natural frequencies and their associated vibration modes of single-layered and triple-layered graphene sheets, as well as general MLGSs. Numerical simulations are carried out to examine the effects of van der Waals (vdW) interactions, which are present as bonding forces between the layers, on nanoscale vibration natural frequencies and their mode shapes. The results show that for a general MLGSs, vibration modes can be classified into 3 families - lower classical synchronized modes which are independent of van der Waals forces, middle van der Waals enhanced modes which are largely determined by the presence of van der Waals interactions and higher mixed modes which are combinations of the classical synchronized modes and van der Waals enhanced modes. Detailed characterizations of these modes from their derived mode shapes have been achieved for the typical case of triple-layered GSs, as well as general MLGSs. Effects of different boundary conditions, aspect ratios and the number of layers on nanoscale vibration properties have been examined in detail. The results presented in this paper, for the first time, provide accurate and wholesome studies and characterizations on the interesting nanoscale vibration properties of multi-layered graphene sheets and the results obtained will certainly be useful to those who are concerned with the dynamics of graphene sheets which are increasingly being deployed for various innovative engineering applications. © 2012 Elsevier Ltd.

Tjahjowidodo T.,Nanyang Technological University
Mechanical Systems and Signal Processing | Year: 2012

Depending on the application, friction in mechanical systems can be a desirable or an undesirable thing. In order to optimally utilize or compensate for the frictional effect in the system, characterization of the frictional behavior is a crucial task. Unfortunately, friction force exhibits strong (hysteretic) nonlinear relationship with sliding velocity, displacement and time, which makes the characterization to become a difficult task to fulfill. The classical Coulomb friction has been widely used, especially in the field of control engineering to compensate for the static force in a system. However, despite its simplicity, the effectiveness of the Coulomb model in capturing the frictional behavior of friction in the presliding regime is very low. This paper deals with the derivation of equivalent modal parameters, namely the stiffness and damping elements, to represent the hysteresis friction element on mechanical systems. The analysis is carried out using the skeleton technique, which employs the instantaneous amplitude and frequency of the excitation input and the response of the system. Subsequently, the dynamic analysis is performed on the equivalent system and the result is compared to that of the original system. The results show good agreement between the equivalent system and the original system for wide range of excitation. © 2011 Elsevier Ltd. All rights reserved.

Qu B.Y.,Zhongyuan University of Technology | Suganthan P.N.,Nanyang Technological University | Das S.,Indian Statistical Institute
IEEE Transactions on Evolutionary Computation | Year: 2013

Multimodal optimization amounts to finding multiple global and local optima (as opposed to a single solution) of a function, so that the user can have a better knowledge about different optimal solutions in the search space and when needed, the current solution may be switched to a more suitable one while still maintaining the optimal system performance. Niching particle swarm optimizers (PSOs) have been widely used by the evolutionary computation community for solving real-parameter multimodal optimization problems. However, most of the existing PSO-based niching algorithms are difficult to use in practice because of their poor local search ability and requirement of prior knowledge to specify certain niching parameters. This paper has addressed these issues by proposing a distance-based locally informed particle swarm (LIPS) optimizer, which eliminates the need to specify any niching parameter and enhance the fine search ability of PSO. Instead of using the global best particle, LIPS uses several local bests to guide the search of each particle. LIPS can operate as a stable niching algorithm by using the information provided by its neighborhoods. The neighborhoods are estimated in terms of Euclidean distance. The algorithm is compared with a number of state-of-the-art evolutionary multimodal optimizers on 30 commonly used multimodal benchmark functions. The experimental results suggest that the proposed technique is able to provide statistically superior and more consistent performance over the existing niching algorithms on the test functions, without