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Hugli, India

Majumder M.,Saha Institute of Nuclear Physics | Ghoshray K.,Saha Institute of Nuclear Physics | Ghoshray A.,Saha Institute of Nuclear Physics | Bandyopadhyay B.,Saha Institute of Nuclear Physics | Ghosh M.,Hooghly Womens College
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

L 139 a NMR study was performed in grain-aligned (c→|| H→0) sample of LaCoPO and polycrystalline LaFePO. Knight shift is isotropic and temperature independent in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The spin-lattice relaxation rate in LaCoPO clearly reveals the existence of three-dimensional spin fluctuations both in the paramagnetic and ferromagnetic state over and above the dominant two-dimensional spin fluctuations in the paramagnetic state, observed earlier from P 31 NMR measurements in the same oriented sample. The spin fluctuation parameters in LaCoPO determined from L 139 a NMR relaxation and magnetization data, using the self-consistent renormalization theory, are in close agreement and follow the universal Rhodes-Wohlfarth curve. © 2010 The American Physical Society.

Haldar S.,Hooghly Womens College | Chakraborty K.,Information Services Group | Das K.,Sashinara High School | Kar T.K.,Indian Institute of Science
Nonlinear Dynamics | Year: 2015

This paper describes the dynamics of an infectious disease transmission modified Leslie–Gower type eco-epidemiological system in both deterministic and stochastic fluctuating environments with harvesting. The dynamics of the deterministic system is extensively investigated around coexistence equilibria. Sufficient conditions are derived for local and global stability of the system. The existence of Hopf bifurcation phenomenon is examined around interior equilibria of the system. Subsequently, we use normal form method and center manifold theorem to examine the nature of the Hopf bifurcation. The obtained results are useful to extract the criteria for disease extinction and control perspective. Later, a white noise term is incorporated to the system to describe the dynamics of the system in stochastic fluctuating environment. Sufficient conditions are derived for the mean square stability (MSS) of the system which can be used to evaluate necessary conditions for the asymptotic MSS and a threshold condition between asymptotic MSS and unstable system. Finally, some numerical simulations are carried out, and graphical illustrations are given in support of the analytical results obtained in both deterministic and stochastic systems. © 2015, Springer Science+Business Media Dordrecht.

Haldar S.,Hooghly Womens College
Zeitschrift fur Angewandte Mathematik und Physik | Year: 2016

The stability of thin electrically conducting viscoelastic fluid film flowing down on a non-conducting inclined plane in the presence of electromagnetic field is investigated under induction-free approximation. Surface evolution equation is derived by long-wave expansion method. The stabilizing role of Hartman number M (magnetic field) and the destabilizing role of the viscoelastic property (Formula presented.) and the electric parameter E on such fluid film are established through the linear stability analysis of the surface evolution equation. Investigation shows that at small values of Hartman number (M), the influence of electric parameter (E) on the viscoelastic parameter (Formula presented.) is insignificant, while for large values of M, E introduces more destabilizing effect at low values of (Formula presented.) than that at high values of (Formula presented.). An interesting result also perceived from our analysis is that the stabilizing effect of Hartman number (M) is decreasing with the increase of the values of (Formula presented.) and E, even it gives destabilizing effect after a certain high value of the electric field depending on the high value of (Formula presented.). The weakly nonlinear study reveals that the increase of (Formula presented.) decreases the explosive and subcritical unstable zones but increases the supercritical stable zone keeping the unconditional zone almost constant. © 2016, Springer International Publishing.

Chakraborty K.,Information Services Group | Haldar S.,Hooghly Womens College | Kar T.K.,Indian Institute of Science
Journal of Biological Systems | Year: 2015

This paper describes a prey-predator fishery model incorporating partial closure for the populations. It is assumed that the predator population partially dependent on a logistically growing resource with Beddington-De Angelis type functional response. The proposed system also reflects the dynamic interaction between the net economic revenue and the fishing effort used to harvest the populations. The steady states of the system are determined and the dynamic behavior of the system is discussed. The existence of Hopf bifurcation phenomenon is examined at the interior equilibrium point of the proposed system. We have adopted partial closure for the populations as a controlling instrument to regulate the harvesting of the populations. A dynamic framework towards the optimal utilization of the resource is developed using Pontryagin's maximum principle. The optimal system is numerically solved using an iterative method with Runge-Kutta fourth-order scheme. Simulation results show that the optimal control scheme can achieve a sustainable ecosystem. Results are analyzed with the help of graphical illustrations. © 2015 World Scientific Publishing Company.

Das N.,Nabadwip Vidyasagar College | Majumdar U.,Hooghly Womens College | Mazumdar A.,University of Burdwan | Hazra N.,University of Burdwan
Oriental Insects | Year: 2015

Life stages of eight new species of Chironomus Meigen are described from the Eastern Himalaya of India. These are, Chironomus acutus sp. nov., Chironomus alternus sp. nov., Chironomus clavipenis sp. nov., Chironomus confectus sp. nov., Chironomus culterus sp. nov., Chironomus fortibracchius sp. nov., Chironomus hemicyclius sp. nov. and Chironomus lurilatus sp. nov. With these, number of species of the genus is raised to 26 in India. A key to adult males of the species of Chironomus of the study area is presented here. © 2015 Taylor & Francis.

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