Showing papers by "Nanyang Technological University published in 2009"

Differential Evolution Algorithm With Strategy Adaptation for Global Numerical Optimization

Abstract: Differential evolution (DE) is an efficient and powerful population-based stochastic search technique for solving optimization problems over continuous space, which has been widely applied in many scientific and engineering fields. However, the success of DE in solving a specific problem crucially depends on appropriately choosing trial vector generation strategies and their associated control parameter values. Employing a trial-and-error scheme to search for the most suitable strategy and its associated parameter settings requires high computational costs. Moreover, at different stages of evolution, different strategies coupled with different parameter settings may be required in order to achieve the best performance. In this paper, we propose a self-adaptive DE (SaDE) algorithm, in which both trial vector generation strategies and their associated control parameter values are gradually self-adapted by learning from their previous experiences in generating promising solutions. Consequently, a more suitable generation strategy along with its parameter settings can be determined adaptively to match different phases of the search process/evolution. The performance of the SaDE algorithm is extensively evaluated (using codes available from P. N. Suganthan) on a suite of 26 bound-constrained numerical optimization problems and compares favorably with the conventional DE and several state-of-the-art parameter adaptive DE variants.

Two-dimensional digital image correlation for in-plane displacement and strain measurement: a review

Abstract: As a practical and effective tool for quantitative in-plane deformation measurement of a planar object surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. It directly provides full-field displacements to sub-pixel accuracy and full-field strains by comparing the digital images of a test object surface acquired before and after deformation. In this review, methodologies of the 2D DIC technique for displacement field measurement and strain field estimation are systematically reviewed and discussed. Detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided. Measures for achieving high accuracy deformation measurement using the 2D DIC technique are also recommended. Since microscale and nanoscale deformation measurement can easily be realized by combining the 2D DIC technique with high-spatial-resolution microscopes, the 2D DIC technique should find more applications in broad areas.

Atomic‐Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers

Abstract: The optical conductance of monolayer graphene is defined solely by the fine structure constant, α = (where e is the electron charge, is Dirac's constant and c is the speed of light). The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero-gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the graphene thickness. These results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth, and wideband tunability.

An oestrogen-receptor-α-bound human chromatin interactome

Abstract: Genomes are organized into high-level three-dimensional structures, and DNA elements separated by long genomic distances can in principle interact functionally Many transcription factors bind to regulatory DNA elements distant from gene promoters Although distal binding sites have been shown to regulate transcription by long-range chromatin interactions at a few loci, chromatin interactions and their impact on transcription regulation have not been investigated in a genome-wide manner Here we describe the development of a new strategy, chromatin interaction analysis by paired-end tag sequencing (ChIA-PET) for the de novo detection of global chromatin interactions, with which we have comprehensively mapped the chromatin interaction network bound by oestrogen receptor α (ER-α) in the human genome We found that most high-confidence remote ER-α-binding sites are anchored at gene promoters through long-range chromatin interactions, suggesting that ER-α functions by extensive chromatin looping to bring genes together for coordinated transcriptional regulation We propose that chromatin interactions constitute a primary mechanism for regulating transcription in mammalian genomes © 2009 Macmillan Publishers Limited All rights reserved

Force-induced activation of covalent bonds in mechanoresponsive polymeric materials

Abstract: Biology is replete with materials systems that actively and functionally respond to mechanical stimuli and thereby enable physiological processes such as the sense of touch, hearing or the growth of tissue and bone. In contrast, exposing polymers to large stresses tends to result in covalent bond rupture and hence damage or failure. Davis et al. now demonstrate that synthetic materials can be rationally designed to ensure that mechanical stress alters their properties in a useful manner. This is realized by incorporating a chemical group that responds to mechanical stress by changing its colour to red as it undergoes a ring-opening reaction, enabling the team to directly monitor the accumulation of plastic deformation. The principles underpinning this work should enable the development of other force-responsive chemical groups that could impart synthetic materials with desirable functionalities ranging from damage sensing to fully regenerative self-healing. Exposing synthetic materials to large stresses tends to result in simple failure, unlike many biological systems, which respond by enabling physiological processes such as hearing and balance. But by incorporating a chemical group that responds to mechanical stress by changing its colour, it is possible to monitor the accumulation of plastic deformation directly in a synthetic polymer. This principle could be used to design synthetic materials with desirable functionalities ranging from damage sensing to fully regenerative self-healing. Mechanochemical transduction enables an extraordinary range of physiological processes such as the sense of touch, hearing, balance, muscle contraction, and the growth and remodelling of tissue and bone1,2,3,4,5,6. Although biology is replete with materials systems that actively and functionally respond to mechanical stimuli, the default mechanochemical reaction of bulk polymers to large external stress is the unselective scission of covalent bonds, resulting in damage or failure7. An alternative to this degradation process is the rational molecular design of synthetic materials such that mechanical stress favourably alters material properties. A few mechanosensitive polymers with this property have been developed8,9,10,11,12,13,14; but their active response is mediated through non-covalent processes, which may limit the extent to which properties can be modified and the long-term stability in structural materials. Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups—so-called mechanophores—that the directional nature of mechanical forces can selectively break and re-form covalent bonds15,16. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process. We anticipate that force activation of covalent bonds can serve as a general strategy for the development of new mechanophore building blocks that impart polymeric materials with desirable functionalities ranging from damage sensing to fully regenerative self-healing.

Designed Synthesis of Coaxial SnO2@carbon Hollow Nanospheres for Highly Reversible Lithium Storage

Abstract: This publication was based on work supported by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST). We are also grateful to the National Science Foundation (DMR 0404278) for partial support. Facilities available through the Cornell Center for Materials Research (CCMR), and Cornell Integrated Microscopy Center (CIMC) were used for this study. Supporting Information is available online from Wiley InterScience or from the author. This article has been amended for print publication.

A benchmark study on the thermal conductivity of nanofluids

Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

Is the Free Energy Change of Adsorption Correctly Calculated

Abstract: In the study of adsorption, changes in free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) have been most frequently calculated from the Langmuir equilibrium constant. In a strict theoretical sense, the Langmuir equilibrium constant with units of liters per mole and the thermodynamic equilibrium constant without units are not the same. Moreover, the equilibrium constants for thermodynamic calculation have also been derived in different ways in the literature, for example, Frumkin isotherm, Flory−Huggins isotherm, distribution constants, and so on. As a result, values of ΔG°, ΔH°, and ΔS° of adsorption reported in the literature are very confusing. This study shows that for a dilute solution of charged adsorbates or for a solution of uncharged adsorbates at any concentration, the thermodynamic equilibrium constant of adsorption would be reasonably approximated by the Langmuir equilibrium constant, and thus the use of the Langmuir equilibrium constant for calculation of ΔG° and subsequent determination of ...

Robust Finite-Time Consensus Tracking Algorithm for Multirobot Systems

Abstract: This paper studies the finite-time consensus tracking control for multirobot systems. We prove that finite-time consensus tracking of multiagent systems can be achieved on the terminal sliding-mode surface. Also, we show that the proposed error function can be modified to achieve relative state deviation between agents. These results are then applied to the finite-time consensus tracking control of multirobot systems with input disturbances. Simulation results are presented to validate the analysis.

In Situ Synthesis of Metal Nanoparticles on Single-Layer Graphene Oxide and Reduced Graphene Oxide Surfaces

Abstract: A straightforward one-step chemical method to in situ synthesis of Ag nanoparticles (Ag NPs) on single-layer graphene oxide (GO) and reduced graphene oxide (r-GO) surfaces is proposed. After simply heating the single-layer GO or r-GO adsorbed on 3-aminopropyltriethoxysilane (APTES)-modified Si/SiOx substrates in a silver nitrate aqueous solution at 75 °C, Ag NPs are synthesized and grow on the GO or r-GO surface. The obtained Ag NPs are investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Our method is unique and important since no reducing agent is required in the reaction. Au NPs on a GO surface are obtained by simply immersing the obtained Ag NPs on the GO surface in HAuCl4 solution.

Direct Electrochemical Reduction of Single-Layer Graphene Oxide and Subsequent Functionalization with Glucose Oxidase

Abstract: A direct electrochemical method to reduce single-layer graphene oxide (GO) adsorbed on the 3-aminopropyltriethoxysilane (APTES)-modified conductive electrodes is proposed. The reduced GO adsorbed on glassy carbon electrode was modified with glucose oxidase (GOx) by covalent bonding via a polymer generated by electrografting N-succinimidyl acrylate (NSA). The direct electron transfer between the electrode and GOx molecules was realized. The bioactivity of GOx maintains very well on the electrode. The thus-prepared GOx-modified electrode was successfully used to detect glucose.

Error Minimized Extreme Learning Machine With Growth of Hidden Nodes and Incremental Learning

Abstract: One of the open problems in neural network research is how to automatically determine network architectures for given applications. In this brief, we propose a simple and efficient approach to automatically determine the number of hidden nodes in generalized single-hidden-layer feedforward networks (SLFNs) which need not be neural alike. This approach referred to as error minimized extreme learning machine (EM-ELM) can add random hidden nodes to SLFNs one by one or group by group (with varying group size). During the growth of the networks, the output weights are updated incrementally. The convergence of this approach is proved in this brief as well. Simulation results demonstrate and verify that our new approach is much faster than other sequential/incremental/growing algorithms with good generalization performance.

The Effects of Prosocial Video Games on Prosocial Behaviors: International Evidence From Correlational, Longitudinal, and Experimental Studies:

Abstract: Although dozens of studies have documented a relationship between violent video games and aggressive behaviors, very little attention has been paid to potential effects of prosocial games. Theoretically, games in which game characters help and support each other in nonviolent ways should increase both short-term and long-term prosocial behaviors. We report three studies conducted in three countries with three age groups to test this hypothesis. In the correlational study, Singaporean middle-school students who played more prosocial games behaved more prosocially. In the two longitudinal samples of Japanese children and adolescents, prosocial game play predicted later increases in prosocial behavior. In the experimental study, U.S. undergraduates randomly assigned to play prosocial games behaved more prosocially toward another student. These similar results across different methodologies, ages, and cultures provide robust evidence of a prosocial game content effect, and they provide support for the General Learning Model.

Doping single-layer graphene with aromatic molecules.

Abstract: Recently discovered single-layer graphene (SLG) has attracted great attention not only because this perfect 2-dimensional carbon crystalline structure enables unprecedented explorations of fundamental physics but also because of its exciting potentials in the post-silicon nanoeletronics 1-6 . As the electrical properties of SLG films are very sensitive to the local perturbations such as from surface charges 7-9 and adsorbed gas molecules 6 , it is plausible that the electronic structures, hence the performance, of SLG may be tailored by molecular doping on its surface. Herein, we demonstrated that the electronic structures of SLG can be differentially modulated by doping from various aromatic molecules. We also show that a simple spectroscopic method based on the Raman 2D and G band frequency sampling can be used to distinguish the n- and p-doped SLG. Raman spectroscopy is a powerful tool to rapidly and nondestructively examine intrinsic physical properties of various carbon nanostructures, including flat and one-atom thick carbon crystalline layer (graphene monolayer), stacked graphenes (graphite), and roll-up graphene monolayer (single-walled carbon nanotube–SWNT). The characteristic G (~1580-1590 cm -1 ) and 2D (~2690-2710 cm -1 ) Raman bands are able to reveal the number of stacked graphene layer 10-12 and the changes in charge carrier concentration (or Fermi energy shift) induced by static electrical field 13-14 .

Self-assembled cationic peptide nanoparticles as an efficient antimicrobial agent.

Abstract: Antimicrobial cationic peptides are of interest because they can combat multi-drug-resistant microbes. Most peptides form alpha-helices or beta-sheet-like structures that can insert into and subsequently disintegrate negatively charged bacterial cell surfaces. Here, we show that a novel class of core-shell nanoparticles formed by self-assembly of an amphiphilic peptide have strong antimicrobial properties against a range of bacteria, yeasts and fungi. The nanoparticles show a high therapeutic index against Staphylococcus aureus infection in mice and are more potent than their unassembled peptide counterparts. Using Staphylococcus aureus-infected meningitis rabbits, we show that the nanoparticles can cross the blood-brain barrier and suppress bacterial growth in infected brains. Taken together, these nanoparticles are promising antimicrobial agents that can be used to treat brain infections and other infectious diseases.

The Effect of SOX Internal Control Deficiencies on Firm Risk and Cost of Equity

Abstract: The Sarbanes-Oxley Act (SOX) mandates management evaluation and independent audits of internal control effectiveness. The mandate is costly to firms but may yield benefits through lower information risk that translates into lower cost of equity. We use unaudited pre–SOX 404 disclosures and SOX 404 audit opinions to assess how changes in internal control quality affect firm risk and cost of equity. After controlling for other risk factors, we find that firms with internal control deficiencies have significantly higher idiosyncratic risk, systematic risk, and cost of equity. Our change analyses document that auditor-confirmed changes in internal control effectiveness (including remediation of previously disclosed internal control deficiencies) are followed by significant changes in the cost of equity that range from 50 to 150 basis points. Overall, our cross-sectional and intertemporal change test results are consistent with internal control reports affecting investors' risk assessments and firms' cost of equity.

Integrating the theory of planned behaviour and self-determination theory in health behaviour: A meta-analysis

Abstract: Purpose A meta-analysis of studies integrating the theory of planned behaviour (TPB) and self-determination theory (SDT) in health contexts is presented. The analysis aimed to provide cumulative empirical support for a motivational sequence in which self-determined motivation from SDT predicts the proximal predictors of intentions and behaviour from the TPB. Methods A literature search identified 36 integrated studies providing 45 tests of effects between TPB and SDT variables. Hunter and Schmidt's (1994) methods of meta-analysis were used to correct the effect sizes across the studies for statistical artifacts. Age (old versus young), publication status (published versus unpublished), study design (correlational versus experimental/intervention), and behaviour type (physical activity versus other health-related behaviours) were evaluated as moderators of the effects. A path-analysis using the meta-analytically derived correlations was conducted to examine the proposed motivational sequence. Results Statistically significant corrected correlations were evident among the perceived autonomy support and self-determined motivation constructs from SDT and the attitude, subjective norms, perceived behavioural control, intention, and health-related behaviour constructs from the TPB. Only six of the 28 effect sizes were moderated by the proposed moderators. Path analysis revealed that the significant effects of self-determined motivation on intentions and behaviour were partially mediated by the proximal predictors from the TPB. Conclusions Evidence from this synthesis supported the theoretical integration and proposed motivational sequence. Results are discussed with reference to the complementary aspects of the TPB and SDT and the need for integrated experimental or intervention studies on a broader range of health behaviours.

A hybrid approach using ISM and fuzzy TOPSIS for the selection of reverse logistics provider

Abstract: Return of used products is becoming an important logistics activity due to government legislation and increasing awareness among the people to protect the environment and reduce waste. For industries, the management of return flow usually requires a specialized infrastructure with special information systems for tracking and dedicated equipment for the processing of returns. Therefore, industries are turning to third-party reverse logistics providers (3PRLPs). In this study, a multi-criteria group decision-making (MCGDM) model in fuzzy environment is developed to guide the selection process of best 3PRLP. The interactions among the criteria are also analyzed before arriving at a decision for the selection of 3PRLP from among 15 alternatives. The analysis is done through Interpretive Structural Modeling (ISM) and fuzzy technique for order preference by similarity to ideal solution (TOPSIS). Finally the effectiveness of the model is illustrated using a case study on battery manufacturing industry in India.

Mapping human genetic diversity in Asia

Abstract: Asia harbors substantial cultural and linguistic diversity, but the geographic structure of genetic variation across the continent remains enigmatic. Here we report a large-scale survey of autosomal variation from a broad geographic sample of Asian human populations. Our results show that genetic ancestry is strongly correlated with linguistic affiliations as well as geography. Most populations show relatedness within ethnic/linguistic groups, despite prevalent gene flow among populations. More than 90% of East Asian (EA) haplotypes could be found in either Southeast Asian (SEA) or Central-South Asian (CSA) populations and show clinal structure with haplotype diversity decreasing from south to north. Furthermore, 50% of EA haplotypes were found in SEA only and 5% were found in CSA only, indicating that SEA was a major geographic source of EA populations.

Antioxidant Activity and Total Phenolic Content of Moringa oleifera Leaves in Two Stages of Maturity

Abstract: Antioxidants play an important role in inhibiting and scavenging free radicals, thus providing protection to human against infections and degenerative diseases. Current research is now directed towards natural antioxidants originated from plants due to safe therapeutics. Moringa oleifera is used in Indian traditional medicine for a wide range of various ailments. To understand the mechanism of pharmacological actions, antioxidant properties of the Moringa oleifera leaf extracts were tested in two stages of maturity using standard in vitro models. The successive aqueous extract of Moringa oleifera exhibited strong scavenging effect on 2, 2-diphenyl-2-picryl hydrazyl (DPPH) free radical, superoxide, nitric oxide radical and inhibition of lipid per oxidation. The free radical scavenging effect of Moringa oleifera leaf extract was comparable with that of the reference antioxidants. The data obtained in the present study suggests that the extracts of Moringa oleifera both mature and tender leaves have potent antioxidant activity against free radicals, prevent oxidative damage to major biomolecules and afford significant protection against oxidative damage.

Islamic banking: Interest-free or interest-based?

Abstract: A unique feature of Islamic banking, in theory, is its profit-and-loss sharing (PLS) paradigm. In practice, however, we find that Islamic banking is not very different from conventional banking. Our study on Malaysia shows that only a negligible portion of Islamic bank financing is strictly PLS based and that Islamic deposits are not interest-free, but are closely pegged to conventional deposits. Our findings suggest that the rapid growth in Islamic banking is largely driven by the Islamic resurgence worldwide rather than by the advantages of the PLS paradigm and that Islamic banks should be subject to regulations similar to those of their western counterparts.

Dynamic Spectrum Access and Management in Cognitive Radio Networks

Abstract: Are you involved in designing the next generation of wireless networks? With spectrum becoming an ever scarcer resource, it is critical that new systems utilize all available frequency bands as efficiently as possible. The revolutionary technology presented in this book will be at the cutting edge of future wireless communications. Dynamic Spectrum Access and Management in Cognitive Radio Networks provides you with an all-inclusive introduction to this emerging technology, outlining the fundamentals of cognitive radio-based wireless communication and networking, spectrum sharing models, and the requirements for dynamic spectrum access. In addition to the different techniques and their applications in designing dynamic spectrum access methods, you'll also find state-of-the-art dynamic spectrum access schemes, including classifications of the different schemes and the technical details of each scheme. This is a perfect introduction for graduate students and researchers, as well as a useful self-study guide for practitioners.

The Chemical Composition and Biological Properties of Coconut (Cocos nucifera L.) Water

Abstract: Coconut water (coconut liquid endosperm), with its many applications, is one of the world's most versatile natural product. This refreshing beverage is consumed worldwide as it is nutritious and beneficial for health. There is increasing scientific evidence that supports the role of coconut water in health and medicinal applications. Coconut water is traditionally used as a growth supplement in plant tissue culture/micropropagation. The wide applications of coconut water can be justified by its unique chemical composition of sugars, vitamins, minerals, amino acids and phytohormones. This review attempts to summarise and evaluate the chemical composition and biological properties of coconut water.

Antenna-on-Chip and Antenna-in-Package Solutions to Highly Integrated Millimeter-Wave Devices for Wireless Communications

Abstract: Antenna-on-chip (AoC) and antenna-in-package (AiP) solutions are studied for highly integrated millimeter-wave (mmWave) devices in wireless communications. First, the background, regulations, standard, and applications of 60-GHz wireless communications are briefly introduced. Then, highly integrated 60-GHz radios are overviewed as a basis for the link budget analysis to derive the antenna gain requirement. Next, in order to have deep physical insight into the AoC solution, the silicon substrate's high permittivity and low resistivity effects on the AoC efficiency are examined. It is shown that the AoC solution has low efficiency, less than 12% due to large ohmic losses and surface waves, which requires the development of techniques to improve the AoC efficiency. After that, the AiP solution and associated challenges such as how to realize low-loss interconnection between the chip and antenna are addressed. It is shown that wire-bonding interconnects, although inferior to the flip-chip, are still feasible in the 60-GHz band if proper compensation schemes are utilized. An example of the AiP solution in a low-temperature cofired ceramic (LTCC) process is presented in the 60-GHz band showing an efficiency better than 90%. A major concern with both AoC and AiP solutions is electromagnetic interference (EMI), which is also discussed. Finally, the systems level pros and cons of both AoC and AiP solutions are highlighted from the electrical and economic perspectives for system designers.

PeerSoN: P2P social networking: early experiences and insights

Abstract: To address privacy concerns over Online Social Networks (OSNs), we propose a distributed, peer-to-peer approach coupled with encryption. Moreover, extending this distributed approach by direct data exchange between user devices removes the strict Internet-connectivity requirements of web-based OSNs. In order to verify the feasibility of this approach, we designed a two-tiered architecture and protocols that recreate the core features of OSNs in a decentralized way. This paper focuses on the description of the prototype built for the P2P infrastructure for social networks, as a first step without the encryption part, and shares early experiences from the prototype and insights gained since first outlining the challenges and possibilities of decentralized alternatives to OSNs.