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Search Results: 1 - 10 of 144635 matches for " B. Raychaudhuri "
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Kinetic Monte Carlo Study of the Type 1/Type 2 Choice in Apoptosis Elucidates Selective Killing of Cancer Cells under Death Ligand Induction  [PDF]
Subhadip Raychaudhuri
Open Journal of Apoptosis (OJApo) , 2015, DOI: 10.4236/ojapo.2015.41003
Abstract: Death ligand mediated apoptotic activation is a mode of cell death that is widely used in cellular and physiological situations. Interest in studying death ligand induced apoptosis has increased due to the promising role of recombinant soluble forms of death ligands (mainly recombinant TRAIL) in anti-cancer therapy. A clear elucidation of how death ligands activate the type 1 and type 2 apoptotic pathways in healthy and cancer cells may help develop better chemotherapeutic strategies. In this work, we use kinetic Monte Carlo simulations to address the problem of type 1/ type 2 choice in death ligand mediated apoptosis of cancer cells. Our study provides insights into the activation of membrane proximal death module that results from complex interplay between death and decoy receptors. Relative abundance of death and decoy receptors was shown to be a key parameter for activation of the initiator caspases in the membrane module. Increased concentration of death ligands frequently increased the type 1 activation fraction in cancer cells, and, in certain cases changed the signaling phenotype from type 2 to type 1. Results of this study also indicate that inherent differences between cancer and healthy cells, such as in the membrane module, may allow robust activation of cancer cell apoptosis by death ligand induction. At the same time, large cell-to-cell variability through the type 2 pathway was shown to provide protection for healthy cells. Such elucidation of selective activation of apoptosis in cancer cells addresses a key question in cancer biology and cancer therapy.
On Topological Defects and Cosmological Constant
B. Raychaudhuri,F. Rahaman,M. Kalam
Physics , 2013, DOI: 10.1142/S0217732314500072
Abstract: Einstein introduced Cosmological Constant in his field equations in an ad hoc manner. Cosmological constant plays the role of vacuum energy of the universe which is responsible for the accelerating expansion of the universe. To give theoretical support it remains an elusive goal to modern physicists. We provide a prescription to obtain cosmological constant from the phase transitions of the early universe when topological defects, namely monopole might have existed.
Accretion disk/corona emission from a radio-loud narrow line Seyfert 1 galaxy PKS 0558-504
R. Ghosh,G. C. Dewangan,B. Raychaudhuri
Physics , 2015, DOI: 10.1093/mnras/stv2682
Abstract: Approximately 10-20% of Active Galactic Nuclei are known to eject powerful jets from the innermost regions. There is very little observational evidence if the jets are powered by spinning black holes and if the accretion disks extend to the innermost regions in radio-loud AGN. Here we study the soft X-ray excess, the hard X-ray spectrum and the optical/UV emission from the radio-loud narrow-line Seyfert 1 galaxy PKS 0558-504 using Suzaku and Swift observations. The broadband X-ray continuum of PKS 0558- 504 consists of a soft X-ray excess emission below 2 keV that is well described by a blackbody (kTe ~ 0.13 keV) and high energy emission that is well described by a thermal Comptonisation (compps) model with kTe ~ 250 keV, optical depth {\tau} ~ 0.05 (spherical corona) or kTe ~ 90 keV, {\tau} ~ 0.5 (slab corona). The Comptonising corona in PKS 0558-504 is likely hotter than in radio-quiet Seyferts such as IC 4329A and Swift J2127.4+5654. The observed soft X-ray excess can be modelled as blurred reflection from an ionised accretion disk or optically thick thermal Comptonisation in a low temperature plasma. Both the soft X-ray excess emission when interpreted as the blurred reflection and the optical/UV to soft X-ray emission interpreted as intrinsic disk Comptonised emission implies spinning (a > 0.6) black hole. These results suggest that disk truncation at large radii and retrograde black hole spin both are unlikely to be the necessary conditions for launching the jets.
Cellotape Birefringent Filter: Some New Demonstrations  [PDF]
Ayantika Khanra, Barun Raychaudhuri
Optics and Photonics Journal (OPJ) , 2016, DOI: 10.4236/opj.2016.67016
Abstract: An easy method is put forward to estimate the optical bandwidth and the wavelength of maximum transmission of Lyot optical filter by measuring the change in phase retardation of birefringent plates as function of thickness. The objective is to demonstrate the experiment with common undergraduate laboratory equipment and thereby provide with an educational aid. The filter is fabricated with cellotape using its birefringence property. The accuracy of measurement is cross-checked with precision spectroradiometric measurements. Some simplification is suggested in the theoretical derivation of the transmitted intensity and a possibility of realizing tunable filter by changing the angle of incidence is indicated.
Motion of Massive and Massless Test particles in Dyadosphere Geometry
B. Raychaudhuri,F. Rahaman,M. Kalam,A. Ghosh
Physics , 2008, DOI: 10.1142/S0217732309029971
Abstract: Motion of massive and massless test particle in equilibrium and non-equilibrium case is discussed in a dyadosphere geometry through Hamilton-Jacobi method. Geodesics of particles are discussed through Lagrangian method too. Scalar wave equation for massless particle is analyzed to show the absence of superradiance.
Radiative Corrections to $\zbb$ from Colored Scalars in a Model with Dynamical Symmetry Breaking
A. Kundu,S. Raychaudhuri,T. De,B. Dutta-Roy
Physics , 1993, DOI: 10.1103/PhysRevD.50.6872
Abstract: Isodoublet color-octet scalar bosons appear in the low-energy limit of a natural extension of the Standard Model in which the electroweak symmetry is broken by a $t\bar t$ condensate. We briefly discuss the model and show that radiative corrections (involving these scalars) to the branching ratio $R_b=\Gamma (Z\rightarrow b\bar b)/\Gamma (Z\rightarrow {\rm hadrons})$ are negative and thus place a stringent lower bound on the masses of the colored scalars. This turns out to be $\sim 400$ GeV with $m_t=150$ GeV and increases quadratically with $m_t$. It is emphasized that $R_b$ is a parameter that is well-determined experimentally and that theoretical estimates are relatively free from uncertainties emanating from hadronic corrections and are comparatively insensitive to the value of the top mass.
Wormhole with varying cosmological constant
F. Rahaman,M. Kalam,M. Sarker,A. Ghosh,B. Raychaudhuri
Physics , 2006, DOI: 10.1007/s10714-006-0380-4
Abstract: It has been suggested that the cosmological constant is a variable dynamical quantity. A class of solution has been presented for the spherically symmetric space time describing wormholes by assuming the erstwhile cosmological constant $\Lambda$ to be a space variable scalar, viz., $\Lambda$ = $\Lambda (r) $ . It is shown that the Averaged Null Energy Condition (ANEC) violating exotic matter can be made arbitrarily small.
Discussion on some characteristics of the Charged Brane-world Black holes
M. Kalam,F. Rahaman,A. Ghosh,B. Raychaudhuri
Physics , 2008, DOI: 10.1142/S0217751X09042542
Abstract: Several physical natures of charged brane-world black holes have been investigated. At first, time-like and null geodesics of the charged brane-world black holes are presented. We also analyze all the possible motions by plotting the effective potentials for various parameters for circular and radial geodesics. Secondly, we investigate the motion of test particles in the gravitational field of charged brane-world black holes using Hamilton-Jacobi (H-J) formalism. We have considered charged and uncharged test particles and examine its behavior both in static and non-static cases. Thirdly, thermodynamics of the charged brane-world black holes are studied. Finally, it has been also shown that there is no phenomenon of superradiance for an incident massless scalar field for this black hole.
Discussions on a special static spherically symmetric perfect fluid solution of Einstein's equations
F. Rahaman,M. Kalam,S. Chakraborty,K. Maity,B. Raychaudhuri
Physics , 2008,
Abstract: In this article, a special static spherically symmetric perfect fluid solution of Einstein's equations is provided. Though pressure and density both diverge at the origin, their ratio remains constant. The solution presented here fails to give positive pressure but nevertheless, it satisfies all energy conditions. In this new spacetime geometry, the metric becomes singular at some finite value of radial coordinate although, by using isotropic coordinates, this singularity could be avoided, as has been shown here. Some characteristics of this solution are also discussed.
Global monopole, dark matter and scalar tensor theory
F. Rahaman,M. Kalam,R. Mondal,B. Raychaudhuri
Physics , 2006, DOI: 10.1142/S0217732307021317
Abstract: In this article, we discuss the space-time of a global monopole field as a candidate for galactic dark matter in the context of scalar tensor theory.
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