Showing papers by "National University of Singapore published in 2007"
TL;DR: The literature on cryptic and sibling species is synthesized and trends in their discovery are discussed, suggesting that the discovery of cryptic species is likely to be non-random with regard to taxon and biome and could have profound implications for evolutionary theory, biogeography and conservation planning.
Abstract: The taxonomic challenge posed by cryptic species (two or more distinct species classified as a single species) has been recognized for nearly 300 years, but the advent of relatively inexpensive and rapid DNA sequencing has given biologists a new tool for detecting and differentiating morphologically similar species. Here, we synthesize the literature on cryptic and sibling species and discuss trends in their discovery. However, a lack of systematic studies leaves many questions open, such as whether cryptic species are more common in particular habitats, latitudes or taxonomic groups. The discovery of cryptic species is likely to be non-random with regard to taxon and biome and, hence, could have profound implications for evolutionary theory, biogeography and conservation planning.
2,837 citations
TL;DR: A review on fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows is presented in this article, where the authors identify opportunities for future research.
1,988 citations
TL;DR: In this article, a review of mixed matrix membranes (MMMs) is presented, including two immediate challenges: achieving an optimized interface structure, and forming asymmetric or composite membrane with an ultrathin and defect-free mixed matrix skin.
1,586 citations
TL;DR: In this article, the Euler-Bernoulli, Timoshenko, Reddy, and Levinson beam theories are reformulated using the nonlocal differential constitutive relations of Eringen.
1,519 citations
01 Feb 2007
TL;DR: The findings demonstrate that consumers' perception of the value of M-Internet is a principal determinant of adoption intention, and the other beliefs are mediated through perceived value.
Abstract: This study examines the adoption of Mobile Internet (M-Internet) as a new Information and Communication Technology (ICT) from the value perspective. M-Internet is a fast growing enabling technology for Mobile Commerce. However, despite its phenomenal growth and although M-Internet essentially provides the same services as stationary Internet, its adoption rate in many countries is very low compared to that of stationary Internet. The well-known Technology Adoption Model (TAM) has been used for explaining the adoption of traditional technologies. Most adopters and users of traditional technologies (e.g., spreadsheet, word processor) are employees in an organizational setting who use the technology for work purposes, and the cost of mandatory adoption and usage is borne by the organization. In contrast, adopters and users of M-Internet are individuals who play the dual roles of technology user and service consumer. Most of them adopt and use it for personal purposes, and the cost of voluntary adoption and usage is borne by the individuals. Thus, the adopters of new ICT, especially M-Internet, are also consumers rather than simply technology users. By adopting the theory of consumer choice and decision making from economics and marketing research, this study develops the Value-based Adoption Model (VAM) and explains customers' M-Internet adoption from the value maximization perspective. The findings demonstrate that consumers' perception of the value of M-Internet is a principal determinant of adoption intention, and the other beliefs are mediated through perceived value. The theoretical and practical implications of VAM related to M-Internet are discussed.
1,517 citations
01 Jan 2007
TL;DR: The terms "antioxidant", "oxidative stress" and "oxoidative damage" are widely used but rarely defined as discussed by the authors, and a brief review attempts to define them and to examine the ways in which oxidative stress and oxidative damage can affect cell behaviour both in vivo and in cell culture, using cancer as an example.
Abstract: The terms 'antioxidant', 'oxidative stress' and 'oxidative damage' are widely used but rarely defined. This brief review attempts to define them and to examine the ways in which oxidative stress and oxidative damage can affect cell behaviour both in vivo and in cell culture, using cancer as an example.
1,309 citations
TL;DR: 'Reactive species' of various types are formed in vivo and many are powerful oxidizing agents, capable of damaging DNA and other biomolecules, but increased levels of DNA base oxidation products such as 8OHdg (8-hydroxy-2'-deoxyguanosine) do not always lead to malignancy, although malignant tumours often show increased levels.
Abstract: 'Reactive species' (RS) of various types are formed in vivo and many are powerful oxidizing agents, capable of damaging DNA and other biomolecules. Increased formation of RS can promote the development of malignancy, and the 'normal' rates of RS generation may account for the increased risk of cancer development in the aged. Indeed, knockout of various antioxidant defence enzymes raises oxidative damage levels and promotes age-related cancer development in animals. In explaining this, most attention has been paid to direct oxidative damage to DNA by certain RS, such as hydroxyl radical (OH*). However, increased levels of DNA base oxidation products such as 8OHdg (8-hydroxy-2'-deoxyguanosine) do not always lead to malignancy, although malignant tumours often show increased levels of DNA base oxidation. Hence additional actions of RS must be important, possibly their effects on p53, cell proliferation, invasiveness and metastasis. Chronic inflammation predisposes to malignancy, but the role of RS in this is likely to be complex because RS can sometimes act as anti-inflammatory agents.
1,202 citations
TL;DR: In this article, the authors investigate whether nanoparticles can be used as a vaccine platform by targeting lymph node-residing dendritic cells via interstitial flow and activating these cells by in situ complement activation.
Abstract: Antigen targeting and adjuvancy schemes that respectively facilitate delivery of antigen to dendritic cells and elicit their activation have been explored in vaccine development. Here we investigate whether nanoparticles can be used as a vaccine platform by targeting lymph node-residing dendritic cells via interstitial flow and activating these cells by in situ complement activation. After intradermal injection, interstitial flow transported ultra-small nanoparticles (25 nm) highly efficiently into lymphatic capillaries and their draining lymph nodes, targeting half of the lymph node-residing dendritic cells, whereas 100-nm nanoparticles were only 10% as efficient. The surface chemistry of these nanoparticles activated the complement cascade, generating a danger signal in situ and potently activating dendritic cells. Using nanoparticles conjugated to the model antigen ovalbumin, we demonstrate generation of humoral and cellular immunity in mice in a size- and complement-dependent manner.
1,158 citations
TL;DR: Two easy-to-use methods to determine the number of graphene layers based on contrast spectra are provided: a graphic method and an analytical method, which show that the refractive index of graphene is different from that of graphite.
Abstract: We have clearly discriminated the single-, bilayer-, and multiple-layer graphene (<10 layers) on Si substrate with a 285 nm SiO2 capping layer by using contrast spectra, which were generated from the reflection light of a white light source. Calculations based on Fresnel's law are in excellent agreement with the experimental results (deviation 2%). The contrast image shows the reliability and efficiency of this new technique. The contrast spectrum is a fast, nondestructive, easy to be carried out, and unambiguous way to identify the numbers of layers of graphene sheet. We provide two easy-to-use methods to determine the number of graphene layers based on contrast spectra: a graphic method and an analytical method. We also show that the refractive index of graphene is different from that of graphite. The results are compared with those obtained using Raman spectroscopy.
1,147 citations
TL;DR: The ways in which oxidative stress and oxidative damage can affect cell behaviour both in vivo and in cell culture are examined, using cancer as an example.
Abstract: The terms 'antioxidant', 'oxidative stress' and 'oxidative damage' are widely used but rarely defined. This brief review attempts to define them and to examine the ways in which oxidative stress and oxidative damage can affect cell behaviour both in vivo and in cell culture, using cancer as an example.
1,110 citations
Posted Content•
TL;DR: Li et al. as discussed by the authors examined the relationship between citizenship behaviors and organizational justice in two studies in a Chinese context, using two cultural characteristics (traditionality and modernity) and one individual (gender) characteristic.
Abstract: To understand variations in citizenship behavior within a culture, we examine the relationship between citizenship behaviors and organizational justice in two studies in a Chinese context, using two cultural characteristics (traditionality and modernity) and one individual (gender) characteristic. In Study 1, we develop an indigenous measure of organizational citizenship behavior and explore the similarities and differences of this measure with its Western counterpart. In Study 2, we use this citizenship behavior measure to test its relationship to justice. Results demonstrate that organizational justice (distributive and procedural) is most strongly related to citizenship behavior for individuals who endorse less traditional, or high modernity, values. In addition, we found the relationship between justice and citizenship behavior to be stronger for men than for women. The studies are discussed in terms of the generality of citizenship behavior and its relation to organizational justiqe and cultural characteristics.
TL;DR: (hierarchical, Lagrange) reduced basis approximation and a posteriori error estimation for linear functional outputs of affinely parametrized elliptic coercive partial differential equations are considered.
Abstract: In this paper we consider (hierarchical, La-grange)reduced basis approximation anda posteriori error estimation for linear functional outputs of affinely parametrized elliptic coercive partial differential equa-tions. The essential ingredients are (primal-dual)Galer-kin projection onto a low-dimensional space associated with a smooth “parametric manifold” - dimension re-duction; efficient and effective greedy sampling meth-ods for identification of optimal and numerically stable approximations - rapid convergence;a posteriori er-ror estimation procedures - rigorous and sharp bounds for the linear-functional outputs of interest; and Offine-Online computational decomposition strategies - min-imummarginal cost for high performance in the real-time/embedded (e.g., parameter-estimation, control)and many-query (e.g., design optimization, multi-model/ scale)contexts. We present illustrative results for heat conduction and convection-diffusion,inviscid flow, and linear elasticity; outputs include transport rates, added mass,and stress intensity factors.
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TL;DR: Proton beam (p-beam) writing as discussed by the authors is a direct writing process that uses a focused beam of MeV protons to pattern resist material at nanodimensions, which is similar in many ways to direct writing using electrons.
TL;DR: This paper shows that while retaining the same simplicity, the convergence rate of I-ELM can be further improved by recalculating the output weights of the existing nodes based on a convex optimization method when a new hidden node is randomly added.
TL;DR: The data suggest that mGlu2/3 receptor agonists have antipsychotic properties and may provide a new alternative for the treatment of schizophrenia.
Abstract: Corrigenda: Activation of mGlu2/3 receptors as a new approach to treat schizophrenia: a randomized Phase 2 clinical trial
TL;DR: In this article, the performance of α-Fe2O3 nanoflakes has been evaluated by cyclic voltammery, galvanostatic discharge-charge cycling, and impedance spectral measurements on cells with Li metal as the counter and reference electrodes, at ambient temperature.
Abstract: Nanoflakes of α-Fe2O3 were prepared on Cu foil by using a thermal treatment method. The nanoflakes were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The reversible Li-cycling properties of the α-Fe2O3 nanoflakes have been evaluated by cyclic voltammery, galvanostatic discharge–charge cycling, and impedance spectral measurements on cells with Li metal as the counter and reference electrodes, at ambient temperature. Results show that Fe2O3 nanoflakes exhibit a stable capacity of (680 ± 20) mA h g–1, corresponding to (4.05 ± 0.05) moles of Li per mole of Fe2O3 with no noticeable capacity fading up to 80 cycles when cycled in the voltage range 0.005–3.0 V at 65 mA g–1 (0.1 C rate), and with a coulombic efficiency of > 98 % during cycling (after the 15th cycle). The average discharge and charge voltages are 1.2 and 2.1 V, respectively. The observed cyclic voltammograms and impedance spectra have been analyzed and interpreted in terms of the ‘conversion reaction' involving nanophase Fe0–Li2O. The superior performance of Fe2O3 nanoflakes is clearly established by a comparison of the results with those for Fe2O3 nanoparticles and nanotubes reported in the literature.
TL;DR: In this paper, the authors examined the relationship between investor protection and corporate insiders' incentive to take value-enhancing risks and found empirical confirmation that corporate risk-taking and firm growth rates are positively related to the quality of investor protection.
Abstract: This paper examines the relationship between investor protection and corporate insiders' incentive to take value-enhancing risks. In a poor investor protection environment corporations are often run by entrenched insiders who appropriate considerable corporate resources as personal benefits. When these private benefits are large, insiders may undertake sub-optimally conservative investment decisions to preserve them. Better investor protection reduces these private benefits and may therefore induce riskier but value enhancing investment policy. Such a relationship can also result from risk-averse behavior on the part of dominant shareholders with undiversified exposure in their own firms, which is again more prevalent in countries with poorer investor protection. If prominent non-equity stakeholders such as banks, labor unions or the government can influence corporate investment, and their influence is decreasing in investor protection, that can also give rise to a positive relationship between investor protection and investment risk. We test these predictions using a large cross-country panel. We find empirical confirmation that corporate risk-taking and firm growth rates are positively related to the quality of investor protection. On the other hand, the data do not lead to consistent evidence for the alternative channels.
TL;DR: The present results may improve the existing ones due to a method to estimate the upper bound of the derivative of Lyapunov functional without ignoring some useful terms and the introduction of additional terms into the proposed Lyap unov functional, which take into account the range of delay.
TL;DR: A comprehensive review of recent findings of mechanisms and signaling pathways by which microglial cells are activated in CNS inflammatory diseases and various forms of potential therapeutic options to inhibit the microglia activation which amplifies the inflammation-related neuronal injury in neurodegenerative diseases are summarized.
Abstract: An inflammatory process in the central nervous system (CNS) is believed to play an important role in the pathway leading to neuronal cell death in a number of neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, prion diseases, multiple sclerosis and HIV-dementia. The inflammatory response is mediated by the activated microglia, the resident immune cells of the CNS, which normally respond to neuronal damage and remove the damaged cells by phagocytosis. Activation of microglia is a hallmark of brain pathology. However, it remains controversial whether microglial cells have beneficial or detrimental functions in various neuropathological conditions. The chronic activation of microglia may in turn cause neuronal damage through the release of potentially cytotoxic molecules such as proinflammatory cytokines, reactive oxygen intermediates, proteinases and complement proteins. Therefore, suppression of microglia-mediated inflammation has been considered as an important strategy in neurodegenerative disease therapy. Several anti-inflammatory drugs of various chemical ingredients have been shown to repress the microglial activation and to exert neuroprotective effects in the CNS following different types of injuries. However, the molecular mechanisms by which these effects occur remain unclear. In recent years, several research groups including ours have attempted to explain the potential mechanisms and signaling pathways for the repressive effect of various drugs, on activation of microglial cells in CNS injury. We provide here a comprehensive review of recent findings of mechanisms and signaling pathways by which microglial cells are activated in CNS inflammatory diseases. This review article further summarizes the role of microglial cells in neurodegenerative diseases and various forms of potential therapeutic options to inhibit the microglial activation which amplifies the inflammation-related neuronal injury in neurodegenerative diseases.
TL;DR: The important properties of the biomaterials and the scaffold design in the making of tissue engineered bone constructs are discussed in detail, with special emphasis placed on the new material developments, namely composites made of synthetic polymers and calcium phosphates.
Abstract: Scaffold-based bone tissue engineering aims to repair/regenerate bone defects. Such a treatment concept involves seeding autologous osteogenic cells throughout a biodegradable scaffold to create a scaffold-cell hybrid that may be called a tissue-engineered construct (TEC). A variety of materials and scaffolding fabrication techniques for bone tissue engineering have been investigated over the past two decades. This review aims to discuss the advances in bone engineering from a scaffold material point of view. In the first part the reader is introduced to the basic principles of bone engineering. The important properties of the biomaterials and the scaffold design in the making of tissue engineered bone constructs are discussed in detail, with special emphasis placed on the new material developments, namely composites made of synthetic polymers and calcium phosphates. Advantages and limitations of these materials are analysed along with various architectural parameters of scaffolds important for bone tissue engineering, e.g. porosity, pore size, interconnectivity and pore-wall microstructures.
TL;DR: This study proposes a cost-effective composite consisting of a nanofibrous scaffold directly electrospun onto a polyurethane dressing (Tegaderm, 3M Medical) - which it is called the Tegaderm-nanofiber (TG-NF) construct - for dermal wound healing.
TL;DR: In this article, the current state of the art in filtrations by using the nanofibrous filtering media is addressed. But, the development objectives for improving the Nanofiber based filtering media are lower energy consumption, longer filter life, high filtration capacity and easier maintenance; which are elaborated from manufacturing point of view.
TL;DR: It is found that a quadrilateral element divided into four smoothing cells can avoid spurious modes and gives stable results for integration over the element and the SFEM achieves more accurate results and generally higher convergence rate in energy without increasing computational cost.
Abstract: In the finite element method (FEM), a necessary condition for a four-node isoparametric element is that no interior angle is greater than 180° and the positivity of Jacobian determinant should be ensured in numerical implementation. In this paper, we incorporate cell-wise strain smoothing operations into conventional finite elements and propose the smoothed finite element method (SFEM) for 2D elastic problems. It is found that a quadrilateral element divided into four smoothing cells can avoid spurious modes and gives stable results for integration over the element. Compared with original FEM, the SFEM achieves more accurate results and generally higher convergence rate in energy without increasing computational cost. More importantly, as no mapping or coordinate transformation is involved in the SFEM, its element is allowed to be of arbitrary shape. Hence the restriction on the shape bilinear isoparametric elements can be removed and problem domain can be discretized in more flexible ways, as demonstrated in the example problems.
TL;DR: The measured magnetic moment based on the content of carbide in the films was in agreement with the theoretical prediction, and the magnetism is due to theZn-C system in the ZnO environment.
Abstract: We report ferromagnetism in carbon-doped ZnO. Our first-principles calculations based on density functional theory predicted a magnetic moment of 2.02 mu(B) per carbon when carbon substitutes oxygen in ZnO, and an ferromagnetic coupling among magnetic moments of the carbon dopants. The theoretical prediction was confirmed experimentally. C-doped ZnO films deposited by pulsed-laser deposition showed ferromagnetism with Curie temperatures higher than 400 K. The measured magnetic moment based on the content of carbide in the films [(1.5-3.0) mu(B) per carbon] was in agreement with the theoretical prediction. The magnetism is due to the Zn-C system in the ZnO environment.
TL;DR: In this article, hexagonal phase nanoparticles of NaYF4:Yb,Er,Tm (∼8.5 ± 0.8 nm) were synthesized.
Abstract: Hexagonal phase nanoparticles of NaYF4:Yb,Er and NaYF4:Yb,Tm (∼8.5 ± 0.8 nm) were synthesized. Significant enhancements of upconversion fluorescence were observed after coating with an undoped NaYF4 shell (core/shell ∼ 11.1 ± 1.5 nm). The hydrophobic core/shell nanoparticles were rendered hydrophilic by a subsequent amphiphilic coating of PAA. These nanostructures have great potentials as bio-probes.
TL;DR: A novel method is proposed in this note for stability analysis of systems with a time-varying delay by considering the additional useful terms when estimating the upper bound of the derivative of Lyapunov functionals and introducing the new free-weighting matrices.
Abstract: A novel method is proposed in this note for stability analysis of systems with a time-varying delay. Appropriate Lyapunov functional and augmented Lyapunov functional are introduced to establish some improved delay-dependent stability criteria. Less conservative results are obtained by considering the additional useful terms (which are ignored in previous methods) when estimating the upper bound of the derivative of Lyapunov functionals and introducing the new free-weighting matrices. The resulting criteria are extended to the stability analysis for uncertain systems with time-varying structured uncertainties and polytopic-type uncertainties. Numerical examples are given to demonstrate the effectiveness and the benefits of the proposed method
French Institute of Health and Medical Research1, University College London2, Laval University3, University of Edinburgh4, The Heart Research Institute5, National University of Singapore6, University of Antwerp7, Dresden University of Technology8, Sanofi S.A.9, University of Texas Health Science Center at San Antonio10
TL;DR: Among men and women who consulted primary care physicians, BMI and particularly WC were both strongly linked to CVD and especially to diabetes mellitus, with a stronger relationship for WC than for BMI across regions for both genders.
Abstract: Background— Abdominal adiposity is a growing clinical and public health problem. It is not known whether it is similarly associated with cardiovascular disease (CVD) and diabetes mellitus in different regions around the world, and thus whether measurement of waist circumference (WC) in addition to body mass index (BMI) is useful in primary care practice. Methods and Results— Randomly chosen primary care physicians in 63 countries recruited consecutive patients aged 18 to 80 years on 2 prespecified half days. WC and BMI were measured and the presence of CVD and diabetes mellitus recorded. Of the patients who consulted the primary care physicians, 97% agreed to participate in the present study. Overall, 24% of 69 409 men and 27% of 98 750 women were obese (BMI≥30 kg/m2). A further 40% and 30% of men and women, respectively, were overweight (BMI 25 to 30 kg/m2). Increased WC (>102 for men and >88 cm for women) was recorded in 29% and 48%, CVD in 16% and 13%, and diabetes mellitus in 13% and 11% of men and wo...
TL;DR: The authors investigated whether this is purely an economic-downturn effect or also a fire-sales effect along the lines of Shleifer and Vishny [1992] and found that creditors of defaulted firms recover significantly lower amounts in present-value terms when the industry of a defaulted firm is in distress.
TL;DR: This link between the Canary islands of La Palma and Tenerife has a path length much longer than from LEO satellites to a ground station and serves as a realistic test bed for future quantum communication to space.
Abstract: We report on the experimental implementation of a Bennett-Brassard 1984 (BB84) protocol type quantum key distribution over a 144 km free-space link using weak coherent laser pulses. Optimization of the link transmission was achieved with bidirectional active telescope tracking, and the security was ensured by employing decoy-state analysis. This enabled us to distribute a secure key at a rate of 12.8 bit/s at an attenuation of about 35 dB. Utilizing a simple transmitter setup and an optical ground station capable of tracking a spacecraft in low earth orbit, this outdoor experiment demonstrates the feasibility of global key distribution via satellites.
TL;DR: This work proposes transformations based on the well-established K-anonymity concept to compute exact answers for range and nearest neighbor search, without revealing the query source.
Abstract: The increasing trend of embedding positioning capabilities (for example, GPS) in mobile devices facilitates the widespread use of location-based services. For such applications to succeed, privacy and confidentiality are essential. Existing privacy-enhancing techniques rely on encryption to safeguard communication channels, and on pseudonyms to protect user identities. Nevertheless, the query contents may disclose the physical location of the user. In this paper, we present a framework for preventing location-based identity inference of users who issue spatial queries to location-based services. We propose transformations based on the well-established K-anonymity concept to compute exact answers for range and nearest neighbor search, without revealing the query source. Our methods optimize the entire process of anonymizing the requests and processing the transformed spatial queries. Extensive experimental studies suggest that the proposed techniques are applicable to real-life scenarios with numerous mobile users.