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Kolkata, India

Routh J.,IISER Kolkata | Hjelmquist P.,University of Stockholm
Applied Geochemistry | Year: 2011

Sediments from a core retrieved during installation of a shallow drinking water well in Ambikanagar (West Bengal, India) were analyzed for various physical and chemical parameters. The geochemical analyses included: (1) a 4-step sequential extraction scheme to determine the distribution of As between different fractions, (2) As speciation (As 3+ vs. As 5+), and (3) C, N and S isotopes. The sediments have a low percentage of organic C and N (0.10-0.56% and 0.01-0.05%, respectively). Arsenic concentration is between 2 and 7mgkg -1, and it is mainly associated with the residual fraction, less susceptible to chemical weathering. The proportion of As 3+ in these sediments is high and ranges from 24% to 74%. Arsenic in the second fraction (reducible) correlates well with Mn, and in the residual fraction As correlates well with several transition elements. The stable isotope results indicate microbial oxidation of organic matter involving SO 4 reduction. Oxidation of primary sulfide minerals and release of As from reduction of Fe-(oxy)hydroxides do not seem important mechanisms in As mobilization. Instead, the dominance of As 3+ and presence of As 5+ reducing microorganisms in this shallow aquifer imply As remobilization involving microbial processes that needs further investigations. © 2011 Elsevier Ltd. Source

Wallenburg M.A.,Ontario Cancer Institute | Wood M.F.G.,Ontario Cancer Institute | Ghosh N.,IISER Kolkata | Vitkin I.A.,Ontario Cancer Institute | Vitkin I.A.,University of Toronto
Optics Letters | Year: 2010

Recently, we have used polarimetry as a method for assessing the linear retardance of infarcted myocardium. While linear retardance reflects tissue anisotropy, experimental geometry has a confounding effect due to dependence of the linear retardance on the orientation of the sample with respect to the probing beam. Here, polarimetry imaging of an 8 mm diameter birefringent polystyrene sphere of known anisotropy axis was used to test a dual-projection method by which the anisotropy axis and its true magnitude can be reconstructed, thus eliminating the confounding effect of anisotropy axis orientation. Feasibility is demonstrated in ex-vivo tissue imaging. © 2010 Optical Society of America. Source

Chattopadhyay D.,IISER Kolkata | Zuschin M.,University of Vienna | Tomasovych A.,Slovak Academy of Sciences
Paleobiology | Year: 2014

Edge-drilling is an unusual predation pattern in which a predatory gastropod drills a hole on the commissure between the valves of a bivalve. Although it is faster than wall drilling, it involves the potential risk of amputating the drilling organ. We therefore hypothesize that this risky strategy is advantageous only in environments where predators face high competition or predation pressure while feeding. The high frequency of edge-drilling (EDF, relative to the total number of drilled valves) in a diverse Recent bivalve assemblage from the Red Sea enables us to test this hypothesis, predicting (1) a low EDF in infaunal groups, (2) a high EDF in bivalves with elongated shape, (3) high incidence of edge-drilling in groups showing a high wall-drilling frequency, and (4) high EDF in shallow habitats. We evaluate these predictions based on >15,000 bivalve specimens. Among ecological attributes, we found substrate affinity and predation intensity of a species to be good predictors of edge-drilling incidence. Infaunal taxa with high length/width ratio have a low EDF, in accordance with our predictions. Predation intensity is also a significant predictor of edge-drilling; groups with high predation intensity show higher incidence of edge-drilling, confirming our prediction. Although water depth fails to show any significant effect on EDF, this analysis generally supports the high-risk hypothesis of edge-drilling incidence because shallow depths have considerable microhabitat variability. Classically the drill hole site selection has often been linked to predatory behavior. Our study indicates that prey attributes are also crucial in dictating the behavioral traits of a driller such as site selection. This calls for considering such details of the prey to fully understand predation in modern and fossil habitats. Moreover, this perspective is important for tackling the longstanding riddle of the limited temporal and spatial distribution of edge-drilling. © 2014 The Paleontological Society. All rights reserved. Source

Soni J.,IISER Kolkata | Mansha S.,Nanyang Technological University | Dutta Gupta S.,University of Hyderabad | Banerjee A.,IISER Kolkata | Ghosh N.,IISER Kolkata
Optics Letters | Year: 2014

The longitudinal and transverse beam shifts, namely, the Goos-Hänchen (GH) and the Spin-Hall (SH) shifts are usually observed at planar interfaces. It has recently been shown that the transverse SH shift may also arise due to scattering of plane waves. Here, we show that analogous in-plane (longitudinal) shifts also exist in the scattering of plane waves from micro/nano systems. We study both the GH and the SH shifts in plasmonic metal nanoparticles/ nanostructures and dielectric micro-particles employing a unified framework that utilizes the transverse components of the Poynting vector of the scattered wave. The results demonstrate that the interference of neighboring resonance modes in plasmonic nanostructures (e.g., electric dipolar and quadrupolar modes in metal spheres) leads to great enhancement of the GH shift in scattering from such systems. We also unravel interesting correlations between these shifts with the polarimetry parameters, diattenuation and retardance. © 2014 Optical Society of America. Source

Nanda A.K.,IISER Kolkata | Hazra N.K.,IISER Kolkata
Operations Research Letters | Year: 2013

Optimum lifetime of a series system with active spares always depends on the allocation of spares at component /system level. We prove that under some sufficient conditions, component redundancy offers greater reliability than the system redundancy in likelihood ratio ordering for n-component matching spares. We also show that this principle holds under some sufficient conditions in likelihood ratio ordering for 2-component non-matching spares of iid components and iid spares. Further, we give some sufficient conditions under which reversed hazard rate order does not exist between two 2-component systems of matching spares. © 2013 Elsevier B.V. All rights reserved. Source

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