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Reddy M.V.,National University of Singapore | Tse L.Y.,National University of Singapore | Tse L.Y.,Raffles Institution | Bruce W.K.Z.,National University of Singapore | And 2 more authors.
Materials Letters | Year: 2015

We conduct the synthesis of nano-sized tin oxides by the one-pot molten salt method at low temperature. A sample of SnO2 is obtained by heating a mixture of tin (II) chloride, lithium hydroxide and lithium nitrate at 180 °C. The nano-sized SnO2 powder is characterized using the techniques of X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, scanning and transmission electron microscopy and density analysis. The electrochemical properties are analysed using galvanostatic cycling and cyclic voltammetry. The results show that the SnO2 prepared is a single phase material and shows reversible capacities of 471 and 767 mA h g-1 in the voltage ranges 0.005-1.0 V and 0.005-3.0 V vs. Li respectively, at a current rate of 100 mA g-1. Reduction of Sn4+ to Sn at characteristic cathodic peak potentials is observed in the initial and subsequent cycles of cathodic scan. Alloying and de-alloying reactions of Sn are observed at ∼0.25 and ∼0.5 V vs. Li in the voltage range 0.005-1.0 V, and the formation of Sn to SnO and SnO2 is observed in the voltage range 0.005-3.0 V vs. Li. Lower capacity fading is observed when cycled in the voltage range 0.005-1.0 V as compared to 0.005-3.0 V. © 2014 Elsevier B.V. All rights reserved.

Madhaiyan M.,National University of Singapore | Jin T.Y.,Raffles Institution | Roy J.J.,National University of Singapore | Kim S.-J.,South Korean National Institute of Animal Science | And 3 more authors.
International Journal of Systematic and Evolutionary Microbiology | Year: 2013

A novel aerobic, non-motile, pleomorphic, Gram-negative and nitrogen-fixing bacterial strain, designated R5-392T, was isolated from surface-sterilized root tissue of Jatropha curcas. The organism grew optimally at 30 °C in media containing 1 % (w/v) NaCl and at pH 6.0-8.0. The predominant ubiquinone was Q-10 and the major fatty acids were C18: 1ω7c/C18: 1ω6c, C16: 0 and C19: 0 cyclo ω8c. The DNA G+C content was 63.2 mol%. Analysis of the 16S rRNA gene sequence suggested that strain R5-392T is affiliated with the order Rhizobiales within the class Alphaproteobacteria and is most closely related to Pleomorphomonas oryzae F-7T (98.8 % similarity) and Pleomorphomonas koreensis Y9T (98.3 % similarity). Analysis of partial nifH gene sequences also revealed a monophyletic lineage within the class Alphaproteobacteria, and strain R5-392T was most closely related to P. oryzae F-7T (98 %). Highest nitrogenase activity was detected in the presence of low-level organic nitrogen or in the presence of nitrogenase co-factors (Fe/Mo) in N-free media. Phenotypic and chemotaxonomic data suggest that strain R5-392T represents a novel species within the genus Pleomorphomonas, for which the name Pleomorphomonas diazotrophica sp. nov. is proposed. The type strain is R5-392T (= KACC 16233T = DSM 25022T). © 2013 IUMS.

Yeo R.W.Y.,Singapore Institute of Medical Biology | Yeo R.W.Y.,National University of Singapore | Yang K.,Raffles Institution | Li G.,Singapore General Hospital | And 2 more authors.
PLoS ONE | Year: 2012

Chronic high glucose (HG) inflicts glucotoxicity on vulnerable cell types such as pancreatic β cells and contributes to insulin resistance and impaired insulin secretion in diabetic patients. To identify HG-induced cellular aberrations that are candidate mediators of glucotoxicity in pancreatic β cells, we analyzed gene expression in ERoSHK6, a mouse insulin-secreting cell line after chronic HG exposure (six-day exposure to 33.3 mM glucose). Chronic HG exposure which reduced glucose-stimulated insulin secretion (GSIS) increased transcript levels of 185 genes that clustered primarily in 5 processes namely cellular growth and proliferation; cell death; cellular assembly and organization; cell morphology; and cell-to-cell signaling and interaction. The former two were validated by increased apoptosis of ERoSHK6 cells after chronic HG exposure and reaffirmed the vulnerability of β cells to glucotoxicity. The three remaining processes were partially substantiated by changes in cellular morphology and structure, and instigated an investigation of the cytoskeleton and cell-cell adhesion. These studies revealed a depolymerized actin cytoskeleton that lacked actin stress fibers anchored at vinculin-containing focal adhesion sites as well as loss of E-cadherin-mediated cell-cell adherence after exposure to chronic HG, and were concomitant with constitutive ERK1/2 phosphorylation that was refractory to serum and glucose deprivation. Although inhibition of ERK phosphorylation by PD98059 promoted actin polymerization, it increased apoptosis and GSIS impairment. These findings suggest that ERK phosphorylation is a proximate regulator of cellular processes targeted by chronic HG-induced gene expression and that dynamic actin polymerization and depolymerization is important in β cell survival and function. Therefore, chronic HG alters gene expression and signal transduction to predispose the cytoskeleton towards apoptosis and GSIS impairment. © 2012 Yeo et al.

Tan Y.Y.,Raffles Institution | Tu W.H.,Anderson Junior College | Manzhos S.,National University of Singapore
Chemical Physics Letters | Year: 2014

We present rational design of phenothiazine dyes by controlled quinoidization of the thiophene unit. We systematically study the effect of electron-withdrawing functional groups including pseudo- and super-halogens. We propose a new dye where a fumaronitrile unit induces an increase in the bond length alternation and a concurrent red shift in the absorption spectrum vs. the parent dye. The visible absorption peak is predicted at 520 nm, in CH 2Cl2 vs. 450 nm for the parent dye. The LUMO and HOMO levels of the new dye are suitable for injection into TiO2 and regeneration by available redox shuttles, respectively. © 2014 Elsevier B.V. All rights reserved.

Wang Y.Z.,National University of Singapore | Wang Q.,National University of Singapore | Xie H.Y.,Raffles Institution | Ho L.P.,Raffles Institution | And 4 more authors.
Nanoscale | Year: 2012

In this paper, we successfully demonstrated the fabrication of highly ordered and large-scale P3HT:PCBM nanowires via a slow-drying method, which allows for the convenient and cost-effective preparation of well-defined P3HT:PCBM nanostructures with large domains. The formation of the organic nanowires can be explained by the self-organization of polymer chains under favorable thermodynamic conditions in the slow-drying process. Furthermore, the C-V measurements revealed that the P3HT:PCBM nanowires possess high capacitance. This supercapacitive behavior of the nanowires is related to their large surface area and open structure, which can facilitate ion transport and accumulation. Owing to their extremely easy preparation and excellent capacitance performance, the P3HT:PCBM nanowires offer a promising electrode material for supercapacitor devices. This journal is © 2013 The Royal Society of Chemistry.

Zhou J.,National University of Singapore | Hu S.-E.,Centers for Disease Control and Prevention | Tan S.-H.,National University of Singapore | Cao R.,Raffles Institution | And 6 more authors.
Autophagy | Year: 2012

Suppression of autophagy has been increasingly recognized as a novel cancer therapeutic approach. Andrographolide (Andro), a diterpenoid lactone isolated from an herbal plant Andrographis paniculata, is known to possess anti-inflammatory and anticancer activity. In this study, we sought to examine the effect of Andro on autophagy, and to evaluate whether such effect is relevant to the sensitization effect of Andro on apoptosis induced by DNA damage agents in cancer cells. First, we found that Andro is able to significantly enhance autophagic markers in various cancer cell lines, including GFP-LC3 puncta and LC3-II level. Interestingly, Andro treatment also led to marked increase of p62 protein level and addition of chloroquine (CQ) failed to further enhance either LC3-II or p62 level, indicating that Andro is likely to suppress autophagic flux at the maturation and degradation stage. Next, we provided evidence that Andro inhibits autophagosome maturation not by affecting the lysosomal function, but by impairing autophagosome-lysosome fusion. Lastly, we demonstrated that treatment with cisplatin, a DNA damage agent, induces autophagy in cancer cells. Importantly, Andro is capable of sensitizing cisplatin-induced cell killing determined with both short-term apoptosis assays and long-term clonogenic test, via suppression of autophagy, a process independent of p53. In summary, these observations collectively suggest that Andro could be a promising anti-cancer agent in combination therapy via its potent inhibitory effect on autophagy by disrupting autophagosome-lysosome fusion. © 2012 Landes Bioscience.

Lee P.W.Q.,Institute for Infocomm Research | Seah W.K.G.,Victoria University of Wellington | Tan H.-P.,Institute for Infocomm Research | Yao Z.,Raffles Institution
Measurement Science and Technology | Year: 2010

Motion and intrusion detection are often cited as wireless sensor network (WSN) applications with typical configurations comprising clusters of wireless nodes equipped with motion sensors to detect human motion. Currently, WSN performance is subjected to several constraints, namely radio irregularity and finite on-board computation/energy resources. Radio irregularity in radio frequency (RF) propagation rises to a higher level in the presence of human activity due to the absorption effect of the human body. In this paper, we investigate the feasibility of monitoring RF transmission for the purpose of intrusion detection through experimentation. With empirical data obtained from the Crossbow TelosB platform in several different environments, the impact of human activity on the signal strength of RF signals in a WSN is evaluated. We then propose a novel approach to intrusion detection by turning a constraint in WSN, namely radio irregularity, into an advantage for the purpose of intrusion detection, using signal fluctuations to detect the presence of human activity within the WSN. Unlike RF fingerprinting, the 'intruders' here neither transmit nor receive any RF signals. By enabling existing wireless infrastructures to serve as intrusion detectors instead of deploying numerous costly sensors, this approach shows great promise for providing novel solutions. © 2010 IOP Publishing Ltd.

Lim Y.H.,Raffles Institution | Tan G.,Raffles Institution | Chua S.-L.,DSO National Laboratories
Procedia Engineering | Year: 2016

With the rapid progress of fiber lasers, there is an increasing demand to develop optical waveguides with large mode area to reduce non-linear affects such as stimulated Raman scattering. This is most easily attained by increasing the core size. However, a larger core supports more higher-order modes which in turn worsen the beam quality. The inclusion of a ring surrounding the core (and within the cladding), combined with coiling, is one known method for removing higher-order modes. In this work, we further this approach by first coupling the core modes to the ring, and subsequently inducing losses through implementation of an absorbing material. However, such single-ring design only allows for coupling with one of the two core LP11 modes, leaving the second unaffected. We proposed a windmill fiber design that is able to simultaneously couple to both LP11 modes. It consists of four annular sectors that strongly couple to the targeted core modes, resulting in an effective single-mode fiber. Importantly, the windmill design is optimized to increase its tolerance to fluctuations in the refractive indices to within current fabrication limits of 1x10-4, and proves itself to be more effective than the single-ring design for out-coupling of higher-order modes. © 2016 The Authors.

Sun D.D.,Nanyang Technological University | Wu Y.,Raffles Institution | Gao P.,Nanyang Technological University
Chemical Engineering Journal | Year: 2014

This paper reports the performance of bacterial disinfection using 3D dendritic titanium dioxide with nanoribbon structures (3DD-TiO2), which is newly developed by the researchers. Characterization of 3DD-TiO2 using SEM and TEM shows that the diameter of nanoribbons is nearly 18nm only, resulting in an aspect ratio of more than 50. The hierarchical porous structure of the 3DD-TiO2 would greatly favor the improvement of photocatalytic activity via enlarging the specific surface area. In comparison with the same-sized microspheres and commercial Degussa P25, which are both spherically structured, 3DD-TiO2 displays a consistently better performance under the tested environment. Without UV illumination, the removal efficiency of Escherichia coli by 3DD-TiO2 is 6.4% and 8.7% higher than that of microspheres and P25, respectively. Under UV radiation, the disinfection kinetic constant k of the disinfection reaction using 3DD-TiO2 is 23.2% and 33.9% higher than that of using microspheres and P25, respectively. A series of optimization studies have been carried out to identify the optimum operating parameters of a photocatalytic process using 3DD-TiO2. The results tend to suggest: (a) optimum catalyst concentration is around 100mg/L; (b) the optimum temperature for bacteria inactivation ranges between 10°C and 20°C; (c) presence of humic acid and anions (SO4 2-) exhibits an inhibitory effect on water disinfection process; and (d) cations (Ca2+) enhance the disinfection rate. These optimum operating parameters could be directly referenced for full-scale applications in future. © 2014 Elsevier B.V.

Sun D.D.,Nanyang Technological University | Wu Y.,Nanyang Technological University | Wu Y.,Raffles Institution
Membrane Water Treatment | Year: 2012

This study employed the modified fouling index (MFI) to determine the performance of a two-step recycling system - a membrane filtration integrated laminar flow water storage (LFWS) tank followed by an ion exchange process to reclaim ultrapure water (UPW) from the wastewater generated from semiconductor wafer backgrinding and sawing processes. The first step consisted of the utilization of either ultrafiltration (UF) or nanofiltration (NF) membranes to remove solids in the wastewater where the second step consisted of an ion exchanger to further purify the filtrate. The system was able to produce high purity water in a continuous operating mode. However, higher recycling cost could be incurred due to membrane fouling. The feed wastewater used for this study contained high concentration of fine particles with low organic and ionic contents, hence membrane fouling was mainly attributed to particulate deposition and cake formation. Based on the MFI results, a LFWS tank that was equipped with a turbulence reducer with a pair of auto-valves was developed and found effective in minimizing fouling by discharging concentrated wastewater prior to any membrane filtration. By comparing flux behaviors of the improved system with the conventional system, the former maintained a high flux than the latter at the end of the experiment.

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