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31.
Sumana Chakraborty Yew Kam Ho 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):59-65
This work presents an investigation on the doubly excited 1S
e
autoionizing states of screened helium atom lying below the n = 4 threshold of the He+ ion. The potential generated in this system is represented by a Yukawa type potential. We have employed complex-coordinate
rotation method, as it is a powerful scheme to study high lying resonances. Hylleraas type wave function is used to consider
the correlation effect between all the charged particles. Our resonance parameters for the resonances lying below the He+ (n = 2) threshold agree well with those of the existing calculations by using the stabilization method. Resonances associated
with higher thresholds are new calculations. All the present results are well converged with basis length N = 444. 相似文献
32.
Binita Ghosh Purushottam Chakraborty 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(3):518-524
Although electronics technologies have made great advances in device speed, optical devices can function in the time domain inaccessible to electronics. In the time domain less than 1 ps, optical devices have no competition. Photonic or optical devices are designed to switch and process light signals without converting them to electronic form. The major advantages that these devices offer are speed and preservation of bandwidth. The switching is accomplished through changes in refractive index of the material that are proportional to the light intensity. The third-order optical susceptibility, χ(3), known as the optical Kerr susceptibility which is related to the non-linear part of the total refractive index, is the nonlinearity which provides this particular feature. Future opportunities in photonic switching and information processing will depend critically on the development of improved photonic materials with enhanced Kerr susceptibilities, as these materials are still in a relatively early stage of development. Different glass systems are now under investigation to increase their nonlinearity by introducing a variety of modifiers into the glass-network. Ion implantation is an attractive method for inducing colloid formation at a high local concentration unattainable by the melt-glass fabrication process and for confining the non-linearities to specific patterned regions in a variety of host matrices. Recent works on metal-ion implanted colloid generation in bulk fused silica glasses have shown that these nanocluster-glass composites under favourable circumstances have significant enhancement of χ(3) with picosecond to femtosecond temporal responses. 相似文献
33.
Ritabrata Biswas Subenoy Chakraborty 《International Journal of Theoretical Physics》2010,49(1):152-161
We study the black hole solution in Einstein-Maxwell-Gauss-Bonnet (EMGB) gravity theory with a cosmological constant in five dimension. It is a generalization of the Reissner-Nordström-de Sitter (RNdS) or RNAdS (Reissner-Nordström-Anti-de Sitter) black hole solutions (according as the cosmological constant is positive or negative) in the Einstein-Gauss-Bonnet (EGB) theory. We analyze the thermodynamic quantities of EMGB black hole and find a restriction involving the charge and the cosmological constant for the existence of an extremal black hole. Finally, Hawking-Page phase transition has been discussed for the present black hole. 相似文献
34.
Birefringent filters can be used for tuning lasers, with some advantages over prisms, gratings and tilted etalons. In this paper the transmission characteristics of a new mixed birefringent filter are investigated. The term ‘mixed’ is used because both circular birefringence and linear birefringence have been utilized in the fabrication of this filter.It has a loss-less core, formed by a cascaded system of alternate rotators and retarders, and a linear polarizer at each end. The performance of this filter is better because of the more effective suppression of side peaks. Unlike previous birefringent filters, this one may be used inside a linear resonator. 相似文献
35.
Susanto Chakraborty Pranab Krishna Chanda Dipankar Ray 《International Journal of Theoretical Physics》1995,34(11):2223-2244
Under some assumptions and transformations of variables, Yang's equations forR-gauge fields on Euclidean space lead to conformally invariant equations permitting one to obtain infinitely many other solutions from any solution of these conformally invariant equations. These conformally invariant equations closely resemble the mathematically interesting generalized Lund-Regge equations. Some exact solutions of these conformally in variant equations are obtained. Except for some singular situations, these solutions are self-dual. 相似文献
36.
Bhagyashree D. Rao Hirak Chakraborty Sandro Keller Amitabha Chattopadhyay 《Journal of fluorescence》2018,28(4):967-973
pH (low) insertion peptide (pHLIP) is a 36-residue peptide derived from the third transmembrane helix of the membrane protein bacteriorhodopsin. The hydrophobicity of this peptide makes it prone to aggregation even at low concentrations, but this has not been studied in detail. In this work, we characterized monomeric and aggregated forms of pHLIP in aqueous solution (pH 8) at low concentrations (~μM) using fluorescence-based approaches, complemented by circular dichroism (CD) spectroscopy. We show here that monomeric and aggregated pHLIP display differential red edge excitation shift (REES) and CD spectra. These spectroscopic features allowed us to show that pHLIP aggregates even at low concentrations. A detailed knowledge of the aggregation behavior of pHLIP under these conditions will be useful for monitoring and quantifying its interaction with membranes. 相似文献
37.
Mukherjee P Hess CP Xu D Han ET Kelley DA Vigneron DB 《Magnetic resonance imaging》2008,26(2):171-180
Diffusion tensor imaging (DTI) noninvasively depicts white matter connectivity in regions where the Gaussian model of diffusion is valid but yields inaccurate results in those where diffusion has a more complex distribution, such as fiber crossings. q-ball imaging (QBI) overcomes this limitation of DTI by more fully characterizing the angular dependence of intravoxel diffusion with larger numbers of diffusion-encoding directional measurements at higher diffusion-weighting factors (b values). However, the former technique results in longer acquisition times and the latter technique results in a lower signal-to-noise ratio (SNR). In this project, we developed specialized 7-T acquisition methods utilizing novel radiofrequency pulses, eight-channel parallel imaging EPI and high-order shimming with a phase-sensitive multichannel B0 field map reconstruction. These methods were applied in initial healthy adult volunteer studies, which demonstrated the feasibility of performing 7-T QBI. Preliminary comparisons of 3 T with 7 T within supratentorial crossing white matter tracts documented a 79.5% SNR increase for b=3000 s/mm2 (P=.0001) and a 38.6% SNR increase for b=6000 s/mm2 (P=.015). With spherical harmonic reconstruction of the q-ball orientation distribution function at b=3000 s/mm2, 7-T QBI allowed for accurate visualization of crossing fiber tracts with fewer diffusion-encoding acquisitions as compared with 3-T QBI. The improvement of 7-T QBI at b factors as high as 6000 s/mm2 resulted in better angular resolution as compared with 3-T QBI for depicting fibers crossing at shallow angles. Although the increased susceptibility effects at 7 T caused problematic distortions near brain-air interfaces at the skull base and posterior fossa, these initial 7-T QBI studies demonstrated excellent quality in much of the supratentorial brain, with significant improvements as compared with 3-T acquisitions in the same individuals. 相似文献
38.
Sudipta Kumar Sinha Sudip Chakraborty Sanjoy Bandyopadhyay 《Indian Journal of Physics》2009,83(1):49-64
Properties of water in the hydration layer around a protein is intimately correlated with its function. A knowledge of the
thickness of the hydration layer is important to understand its role in guiding the folding-unfolding of the protein. We have
performed atomistic molecular dynamics simulations of the folded native and a partially unfolded molten globule structure
of the villin headpiece subdomain or HP-36 in aqueous solution to estimate the effect of unfolding on the thickness of hydration
layer around different segments of the protein. In particular, several dynamic properties of water around different segments
of the folded native and the unfolded structure have been calculated by varying the thickness of the hydration layers. It
is found that unfolding of a segment of the protein is correlated with the dynamics of water around it, i.e., within the first hydration layer. The effect of unfolding on water properties has been found to diminish when water molecules
present beyond the first hydration layer were included in the calculations.
相似文献
39.
The 6.4 GHz ECR ion source that was indigenously developed a few years ago has been operating continuously for injecting oxygen
and neon beams to the cyclotron since 1997. VEC-ECR is a single stage high magnetic field ion source provided with a negatively
biased electron repeller placed on the axis, near the injection mirror point. The supply of cold electrons and use of low
mass mixing gas improve the stability of ECR plasma. Very recently, the effect of aluminum oxide coating on the copper plasma
chamber wall has been studied. The plasma chamber wall was coated with aluminum by vacuum evaporation method and then exposed
to oxygen gas to form aluminum oxide. It was noticed that the process substantially shifts the charge state distribution to
the higher charge state with an enhancement of ion current by an order of magnitude. With the aluminized plasma chamber, the
VEC-ECR can now produce 12 μA of O7+, 6.5 μA of Ar12+, 1.5 μA of Kr20+ and 1.0 μA of Xe31+. 相似文献
40.
The gravitational field of a higher dimensional global monopole in the context of Brans-Dicke theory of gravity is investigated.
The space time metric and the scalar field generated by a global monopole are obtained using the weak field approximation.
Finally, the geodesic of a test particle due to the gravitational field of the monopole is studied. 相似文献