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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. Source


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. Source


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. Source


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. Source


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. Source

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