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31.
Debajyoti Bhaumik Kamales Bhaumik Binayak Dutta-Roy Meher H. Engineer 《Physics letters. A》1977,62(3):197-200
The system consists of an electric polarisation field coupled on the one hand to an elastic field and on the other to a thermal reservoir. When the polarisation modes are pumped, Bose condensation in the lowest mode occurs, for energy inflow above a certain critical amount. It is shown that elastic forces, called into play to stabilise the excitation of the polar modes, lowers the threshold for Bose condensation. With further increase in the pumping rate the possibility exists for the softening of the polarisation oscillations leading, in the presence of quartic self-interaction of the polarisation field (inserted for stability), to a metastable ferroelectric state. The work represents an attempt to develop a microscopic approach to the Fröhlich model for the dynamics of macromolecules (such as proteins and enzymes) of biological significance. 相似文献
32.
R. K. Mishra K. Bhaumik S. C. Mathur S. Mitra 《International journal of quantum chemistry》1979,16(4):691-706
The problems connected with the transformations of energy in the living systems are reviewed. Possibility of Bose–Einstein condensation by input of radiant energy over a critical level is considered as a route for overcoming the barriers of activation energy under the conditions of a pump and a thermalizing environment. Molecular force fields constitute the pump. Under our scheme excitons constitute the major fraction of bosons to so condense. Instantaneous dipoles of London theory are then examined as excitons. Lastly an energy packet from a quantized dipolar field is suggested rather than the concept of “conformons.” Questions of charge and of other modes of energy transfer are briefly discussed. 相似文献
33.
The phenomenon of Bose-Einstein condensation of phonons in biological structure, predicted by Fröhlich on the basis of rate equations, is approached here from a microscopic point of view. Rough estimates are compared with the recent experimental evidence of the action of coherent millimeter electromagnetic radiation on biological systems. 相似文献
34.
Bikash Sahoo 《Central European Journal of Physics》2010,8(3):498-508
The entrained flow of an electrically conducting non-Newtonian, viscoelastic second grade fluid due to an axisymmetric stretching
surface with partial slip is considered. The partial slip is controlled by a dimensionless slip factor, which varies between
zero (total adhesion) and infinity (full slip). Suitable similarity transformations are used to reduce the resulting highly
nonlinear partial differential equation into an ordinary differential equation. The issue of paucity of boundary conditions
is addressed, and an effective numerical scheme has been adopted to solve the obtained differential equation even without
augmenting the boundary conditions. The important findings in this communication are the combined effects of the partial slip,
magnetic interaction parameter and the second grade fluid parameter on the velocity and skin friction coefficient. It is observed
that in presence of slip, the velocity decreases with an increase in the magnetic parameter. That is, the Lorentz force which
opposes the flow leads to enhanced deceleration of the flow. Moreover, it is interesting to find that as slip increases in
magnitude, permitting more fluid to slip past the sheet, the skin friction coefficient decreases in magnitude and approaches
zero for higher values of the slip parameter, i.e., the fluid behaves as though it were inviscid. 相似文献
35.
Numerical investigation of sound generation due to unsteady laminar flow past elliptic cylinders has been carried out using direct numerical simulation $(DNS)$ approach at a free-stream Mach number of $0.2$. Effects of aspect ratio $(0.6\le AR\le 1.0)$ and Reynolds number $(100\le Re \le 160)$ on the characteristics of radiated sound fields are analyzed. Two-dimensional compressible fluid flow equations are solved on a refined grid using high resolution dispersion relation preserving $(DRP)$ schemes. Using present $DNS$ data, equivalent noise sources as given by various acoustic analogies are evaluated. Amplitudes and frequencies associated with these noise sources are further related to characteristics of disturbance pressure fields. Disturbance pressure fields are intensified with increase in Reynolds number and aspect ratio. Thus, radiated sound power increases with increase in Reynolds number and aspect ratio. Among various cases studied here, minimum and maximum values of radiated sound power are found at $Re=120$ & $AR=0.6$ and $Re=160$ & $AR=1.0$, respectively. Directivity patterns show that the generated sound fields are dominated by the lift dipole for all cases. Next, proper orthogonal decomposition $(POD)$ technique has been implemented for decomposing disturbance pressure fields. The $POD$ modes associated with the lift and the drag dipoles have been identified. $POD$ analyses also clearly display that the radiated sound fields are dominated by the lift dipole only. Further, acoustic and hydrodynamic modes obtained using Doak's decomposition method have confirmed the patterns of radiated sound field intensities. 相似文献
36.
Baishya B Prabhu UR Suryaprakash N 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,192(1):101-111
In general, the proton NMR spectra of chiral molecules aligned in the chiral liquid crystalline media are broad and featureless. The analyses of such intricate NMR spectra and their routine use for spectral discrimination of R and S optical enantiomers are hindered. A method is developed in the present study which involves spin state selective two dimensional correlation of higher quantum coherence to its single quantum coherence of a chemically isolated group of coupled protons. This enables the spin state selective detection of proton single quantum transitions based on the spin states of the passive nuclei. The technique provides the relative signs and magnitudes of the couplings by overcoming the problems of enantiomer discrimination, spectral complexity and poor resolution, permitting the complete analyses of the otherwise broad and featureless spectra. A non-selective 180 degrees pulse in the middle of MQ dimension retains all the remote passive couplings. This accompanied by spin selective MQ-SQ conversion leads to spin state selective coherence transfer. The removal of field inhomogeneity contributes to dramatically enhanced resolution. The difference in the cumulative additive values of chemical shift anisotropies and the passive couplings, between the enantiomers, achieved by detecting Nth quantum coherence of N magnetically equivalent spins provides enhanced separation of enantiomer peaks. The developed methodology has been demonstrated on four different chiral molecules with varied number of interacting spins, each having a chiral centre. 相似文献
37.
Kazuto Takaishi Bikash Dev Nath Yuya Yamada Hiroyasu Kosugi Tadashi Ema 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):10089-10093
Unique self‐assembled macrocyclic multinuclear ZnII and NiII complexes with binaphthyl‐bipyridyl ligands (L) were synthesized. X‐ray analysis revealed that these complexes consisted of an outer ring (Zn3L3 or Ni3L3) and an inner core (Zn2 or Ni). In the ZnII complex, the inner Zn2 part rotated rapidly inside the outer ring in solution on an NMR timescale. These complexes exhibited dual catalytic activities for CO2 fixations: synthesis of cyclic carbonates from epoxides and CO2 and temperature‐switched N‐formylation/N‐methylation of amines with CO2 and hydrosilane. 相似文献
38.
Dinda Soumitra Patra Sarat Chandra Panda Bikash Kumar Ganguly Sanjib 《Transition Metal Chemistry》2019,44(4):341-347
Transition Metal Chemistry - A pyridylhydrazone incorporating an anthracene moiety, designated as HLAnc, has been synthesized in order to examine its coordination behaviour towards rhodium(III).... 相似文献
39.
Arindam Kumar Naskar Mahasin Gazi Chiranjib Barman Saheli Chowdhury Mitali Mondal Debasis Ghosh Bikash Sinha Argha Deb 《Journal of Radioanalytical and Nuclear Chemistry》2018,315(2):273-283
The main aim of the study is to present an evaluation of radon concentration in underground water of Bakreswar and Tantloi geothermal region which is mainly used for drinking purposes of the local people. Water samples were collected from tube-wells at 173 different locations. The radon (222Rn) concentration level was observed to fluctuate widely between 3.3 and 803.8 Bq/l with an average of 106.8 Bq/l. Nearly 42% of the samples had radon concentration above the safe limit of 100 Bq/l recommended by World Health Organisation (WHO) and European Union Commission (EU). Considering the WHO and International Commission on Radiological Protection recommended water consumption rate for adults (730 l/year) the corresponding total annual effective dose of the samples were estimated to assess the probable health risk. Total annual effective dose of the samples were varied between 16.72 and 4079.47 µSv/year with an average value of 541.92 µSv/year. About 95% samples exceed the WHO and EU Commission proposed safe limit of 100 µSv/year. 相似文献
40.
Bikash Debnath Waikhom Somraj Singh Manik Das Sanchari Goswami Mahesh Kumar Singh Debasish Maiti Kuntal Manna 《Materials Today Chemistry》2018
Alkaloids are plant secondary metabolite. They are well known nitrogen-containing natural bioactive compounds. Cutting edge research is going on alkaloids to unravel novel therapeutic approaches. Literature reveals that alkaloids contribute multiple biological activities and some alkaloids transform into active metabolites too. In this review, we have focused on marketed and experimental alkaloids. We have summarized sources and biological activities of reported alkaloids in past decades. 相似文献