Mohanpur, India
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Soni J.,IISER Kolkata | Purwar H.,IISER Kolkata | Lakhotia H.,IISER Kolkata | Chandel S.,Cochin University of Science and Technology | And 3 more authors.
Optics Express | Year: 2013

A novel spectroscopic Mueller matrix system has been developed and explored for both fluorescence and elastic scattering polarimetric measurements from biological tissues. The 4 × 4 Mueller matrix measurement strategy is based on sixteen spectrally resolved (γ = 400 - 800 nm) measurements performed by sequentially generating and analyzing four elliptical polarization states. Eigenvalue calibration of the system ensured high accuracy of Mueller matrix measurement over a broad wavelength range, either for forward or backscattering geometry. The system was explored for quantitative fluorescence and elastic scattering spectroscopic polarimetric studies on normal and precancerous tissue sections from human uterine cervix. The fluorescence spectroscopic Mueller matrices yielded an interesting diattenuation parameter, exhibiting differences between normal and precancerous tissues. © 2013 Optical Society of America.

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.

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.

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.

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.

Mondal A.,IISER Kolkata | Roy B.,IISER Kolkata | Banerjee A.,IISER Kolkata
Optics Express | Year: 2015

We induce spontaneous motion that is both directed and complex in micron-sized asymmetric Brownian particles in a spherically aberrated optical trap to generate microswimmers. The aberrated optical trap is prepared in a slightly modified optical tweezers configuration where we use a refractive index mismatched cover slip leading to the formation of an annular intensity distribution near the trap focal plane. Asymmetric scattering from a micro-particle trapped in this annular trap gives rise to a net tangential force on the particle causing it to revolve spontaneously in the intensity ring. The rate of revolution can be controlled from sub-Hz to a few Hz by changing the intensity of the trapping light. Theoretical simulations performed using finite-difference time-domain method verify the experimental observations. We also experimentally demonstrate simultaneous spin and revolution of a micro-swimmer which shows that complex motion can be achieved by designing a suitable shape of a micro-swimmer in the optical potential. © 2015 OSA.

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.

Haldar A.,IISER Kolkata | Pal S.B.,IISER Kolkata | Roy B.,IISER Kolkata | Gupta S.D.,University of Hyderabad | Banerjee A.,IISER Kolkata
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Microparticle self assembly under the influence of optical forces produced by higher-order optical beams or by projection of a hologram into the trapping volume is well known. In this paper, we report the spontaneous formation of a ring of identical microspheres (each with diameter 1.1 μm) in conventional single-beam optical tweezers with a usual TEM 00 Gaussian beam coupled into a sample chamber having a standing wave geometry with a cover slip and glass slide. The effects of different experimental parameters on the ring formation are studied extensively. The experimental observations are backed by theoretical simulations based on a plane wave decomposition of the forward- and backward-propagating Gaussian beams. The ring patterns are shown to be caused due to geometrical aberrations produced by focusing the Gaussian beam using a high-numerical-aperture microscope objective into stratified media. It is found that the thickness of the stratified media and the standing wave geometry itself play a critical role in the formation of stable ring structures. These structures could be used in the study of optical binding, as well as of biological interactions between cells in an optical trap. © 2012 American Physical Society.

Hazra N.K.,IISER Kolkata | Nanda A.K.,IISER Kolkata
Operations Research Letters | Year: 2014

We study the system (series/parallel) where the components are randomly chosen from two different batches. We assume that one batch is more reliable than the other in some stochastic sense. In the case of series systems we show that, under certain conditions, lifetime of one system dominates that of the other in different stochastic orders viz. hazard rate, down shifted hazard rate and likelihood ratio orders. Further, we show that the same principle holds for the reversed hazard rate and the likelihood ratio orders in the case of parallel systems. © 2014 Elsevier B.V. All rights reserved.

Roy B.,IISER Kolkata | Bera S.K.,IISER Kolkata | Banerjee A.,IISER Kolkata
Optics Letters | Year: 2014

We describe a simple yet powerful technique of simultaneously measuring both translational and rotational motion of mesoscopic particles in optical tweezers by measuring the backscattered intensity on a quadrant photodiode (QPD). While the measurement of translational motion by taking the difference of the backscattered intensity incident on adjacent quadrants of a QPD is well known, we demonstrate that rotational motion can be measured very precisely by taking the difference between the diagonal quadrants. The latter measurement eliminates the translational component entirely and leads to a detection sensitivity of around 50 mdeg at S/N of 2 for angular motion of a driven microrod. The technique is also able to resolve the translational and rotational Brownian motion components of the microrod in an unperturbed trap and can be very useful in measuring translation-rotation coupling of microobjects induced by hydrodynamic interactions. © 2014 Optical Society of America.

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