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Patna, India

Shwetanshumala S.,Birla Institute of Technology | Shwetanshumala S.,An College | Konar S.,Birla Institute of Technology
Physica Scripta | Year: 2011

This paper presents an investigation of the modulation instability (MI) of a broad optical beam in biased centro-symmetric two-photon photorefractive media under undepleted pump approximation. From the evolution equation of the perturbation field, we obtain the expression for growth rate of the sidebands. The occurrence of MI has been found to be constrained by the system parameters. The MI gain function, its maximum value, critical frequency andbandwidth have been evaluated in the unstable region. © 2011 The Royal Swedish Academy of Sciences. Source


Shwetanshumala S.,Birla Institute of Technology | Shwetanshumala S.,An College | Konar S.,Birla Institute of Technology | Biswas A.,Delaware State University
Applied Physics B: Lasers and Optics | Year: 2013

In this paper, we have shown the existence of large amounts of quintic nonlinearity in asymmetric three-coupled quantum wells, which arise due to a probe pulse and two controlling laser beams. The possibilities of generation and propagation of ultraslow bright optical solitons in these systems have been examined in situations of both Kerr and quintic nonlinearities. We have also demonstrated numerically that these solitons are stable. The modulation instability of a continuous or quasi-continuous wave probe beam has been also investigated and the role of quintic nonlinearity in suppressing this instability has been addressed. © 2013 Springer-Verlag Berlin Heidelberg. Source


Mukherjee A.,Indian Institute of Technology Kharagpur | Mukherjee A.,University of Texas at Austin | Scanlon B.R.,University of Texas at Austin | Fryar A.E.,University of Kentucky | And 4 more authors.
Geochimica et Cosmochimica Acta | Year: 2012

Information on groundwater chemistry in the central Ganges basin can provide insights into recharge, provenance, and fate of solutes in arsenic (As)-affected areas upstream of the more intensively studied Bengal basin. The geological and geomorphological units of the region are much more discernible than the Bengal basin aquifers. Moreover, the region is less affected by groundwater abstraction, which complicates interpretation of As distributions in the Bengal basin. The study area extends from the northern edge of the Indian craton outcrops to the foothills of the Himalayas. Geologic units in the area can be broadly classified as pre-Cenozoic metamorphics and volcanics (PC), older alluvial deposits of the Ganges and its tributaries (OA), younger or active alluvial deposits of the Ganges and its tributaries in the basin (YA), and sediments of the Himalayan foothills (piedmont, PD). Stable-isotopic analyses indicate groundwater in these units has been recharged by meteoric or surface water that has generally undergone some evaporation. The hydrochemical facies is generally a Ca-HCO 3 type. While most of the solutes in the YA groundwater are derived from carbonate dissolution, many of the PD, PC and OA groundwater samples are influenced by silicate weathering, suggesting that leaching of metamorphics and volcanics acts as a major source of solutes. Redox conditions are highly spatially variable (oxic to methanic, dominated by metal reduction), with no systematic depth variation within sampled aquifers. More than 75% of YA and PD groundwater samples have As≥0.01mg/L, but As was detected in only one OA sample and no PC samples. Arsenic is probably mobilized by reductive dissolution of Fe-Mn (oxyhydr)oxides in the alluvium, with possibility of competitive anionic mobilization. Hence, relative to the Bengal basin, in addition to lower groundwater abstraction influence, groundwater chemistry in the study area reflects a greater variety of differences in the geological and geomorphological settings of the aquifers. © 2012 Elsevier Ltd. Source


Shwetanshumala S.,Birla Institute of Technology | Shwetanshumala S.,An College | Asif N.,Birla Institute of Technology | Konar S.,Birla Institute of Technology | Biswas A.,Delaware State University
Optik | Year: 2013

This paper presents an investigation on the propagation characteristics of optical spatial solitons in a biased centro-symmetric photorefractive medium. Unlike earlier attempts on photorefractive solitons, in the present investigation, we have given equal significance to the effects of charge drift and their diffusion. We have obtained dynamical equations for solitons employing paraxial ray approximation and examined criteria for stationary propagation. Trajectories of stationary solitons have been examined. © 2011 Elsevier GmbH. Source


Shwetanshumala S.,An College
Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences | Year: 2016

Evolution of bright optical spatial solitons in biased photovoltaic photorefractive (PVPR) medium is investigated in the present work. The space-charge field developed in the medium is comprised of local and nonlocal parts. Lowest order charge drift results in the buildup of the local space-charge field, whereas higher order drift and charge diffusion are responsible for nonlocal field development. The dynamical equation for solitons in the closed circuit PVPR medium is obtained under Akhmanov's paraxial ray approximation. Conditions for stationary propagation are obtained, and the path of soliton in the medium is examined. The asymmetry in the nonlinear refractive index introduced by nonlocal contribution to the space-charge field causes a soliton to deflect from its straight line path in the medium. The roles of charge diffusion and higher order drift on soliton trajectory are examined. Source

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