Browsing by Author "Ritesh Kumar Dubey"

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A study of thermal denaturation/renaturation in DNA using laser light scattering: A new approach
(2005) Ritesh Kumar Dubey; D.N. Tripathi
The thermal denaturation/renaturation processes in E. coli and eukaryotic DNAs have been studied using the laser light scattering (LS) technique. The differential scattering intensity curve has been utilized to determine the transition temperature Tm. The effect of solution pH on DNA thermal denaturation has been examined. It has been shown clearly that LS is an extremely sensitive method (more than the UV absorption method) and reveals even the subtler effects such as the pretransition fluctuations, and that the DNA denaturation is prominently affected by pH. The dependence of melting temperature (Tm) on composition of DNA, number of base pairs and base sequences has also been investigated. It has been observed that depending upon its base sequence, the Tm decreases in the case of renatured DNAs. The results have been compared with the UV absorption studies.
Application of light scattering for the determination of molecular parameters: Polystyrene balls
(2002) Ritesh Kumar Dubey; R.K. Pandey; D.N. Tripathi
Average molecular weight, radius of gyration and second virial coefficient have been determined for polystyrene balls using the static laser light scattering method. Reported results are quite reasonable and therefore, could be used to estimate other physical parameters for the sample.
Classical Relativistic Extension of Kanai’s Frictional Lagrangian
(The Korean Physical Society, 2018) Ritesh Kumar Dubey; B.K. Singh
Working in an arbitrary Lorentz frame, we address the question of formulating the covariant variational principle for classical, single-particle, dissipative, relativistic mechanics. First, within a Minkowskian geometry, the basic properties of the proper time τ and the covariant velocity uμ are recapitulated. Next, using a scalar function ψ(x) and its negative derivatives ϕμ’s, we construct a covariant Lagrangian Λ that generalizes the famous Bateman-Caldirola-Kanai Lagrangian of nonrelativistic frictional mechanics. Finally, we propose a deterministic model for ψ (involving the drag coefficient A) whose explicit solution leads to relativistic damped Rayleigh motion in the rest frame of the medium. © 2018, The Korean Physical Society.
Debye screening versus Gauss law in electrostatics: Finite size effects
(2007) Ritesh Kumar Dubey; V.J. Menon; M. Mishra; D.N. Tripathi
We revisit the well-known topics of self- and induced-screening in an otherwise isotropic neutral plasma/colloid. It is pointed out that the standard Debye-Hückel (DH) theory (ignoring finite size effects) suffers from many ambiguities related to net ionic numbers, total charge of the system, role of the electrostatic Gauss law, short-distance behaviour of the potential and incorrectly normalized pair correlation functions. We give a new formulation (incorporating finite size effects) such that ionic numbers are maintained, the total charge of the system has physically correct value, the Gauss law boundary conditions are rigorously obeyed, short-distance behaviour of the potential is guaranteed automatically, and correlation functions are correctly normalized. Numerical differences between the two approaches show up if the screening length μ-1 becomes comparable to the size R of the system. © 2007 Elsevier B.V. All rights reserved.
Gauss law constraints on Debye-Hückel screening
(2007) Ritesh Kumar Dubey; V.J. Menon; Madhukar Mishra; Mukesh Kumar Pandey; B.K. Patra
We demand that the Gauss law at the edge must be obeyed by the electric potential Φ(r) generated within a neutral plasma/electrolyte of strictly finite size by the introduction of a test charge qb. Our proposal has the nice features that total ionic numbers are conserved, the point-Coulomb behaviour of Φ(r) is guaranteed at short-distance, and accumulation of induced charges near the centre and the surface can be demonstrated rigorously. In contrast, the standard Debye-Hückel potential ΦD(r) applicable to unbounded plasma has the strange features that the Gauss law cannot be obeyed at the plasma's edge, total ionic numbers themselves are altered, the short-distance Coulomb behaviour has to be imposed by hand, and induced charge appearance at the surface cannot be built-in. © Indian Academy of Sciences.
J / ψ suppression in Au + Au collisions at RHIC: Colour screening scenario in the bag model at variable participant numbers
(2007) M. Mishra; C.P. Singh; V.J. Menon; Ritesh Kumar Dubey
We have modified the colour screening theory of Chu and Matsui by properly incorporating bag model equation of state for quark-gluon plasma (QGP). We have also chosen the pressure parametrization rather than parameterizing energy density in the transverse plane. We assume that the QGP dense medium is expanding in the longitudinal direction obeying Bjorken boost invariant scaling law. Sequential melting of χc, ψ′ and J / ψ is also considered in this scenario. We have applied above formulation to the recent PHENIX experimental data of J / ψ suppression in Au + Au collisions at RHIC. We find that the model gives a good description of data at mid-rapidity in terms of survival probability versus number of participants without any necessity of implementing (3 + 1)-dimensional expansion of the deconfined medium. © 2007 Elsevier B.V. All rights reserved.
New insights into optical Fourier transforms, radial distribution function, and Glatter's method
(2006) Ritesh Kumar Dubey; V.J. Menon; D.N. Tripathi
We address several subtle issues concerning the static scattering of light or x-rays from physical/chemical/biological systems. In the context of Fourier integrals we point out that the Glatter-Moore algorithms can efficiently perform sine inversion between two functions J(q) and L(r) of calculus, and the structure factor S(q) can be correct only if the asymptotic value of the pair correlation function differs from unity. Next, concerning the radial distribution function g(r), we derive a new integral equation for and use it to find the effective potential when the input pair potential is parabolic. Finally, turning to data analysis, we demonstrate that a bump in the underlying distance distribution function P(r) plays a major role in producing attenuated oscillations in the experimental structure factor, and also in the study of a subtle convolution integral. © IOP Publishing Ltd and SISSA.
Non-orthogonality of Lippmann-Schwinger-Low states
(2004) V.J. Menon; B.K. Patra; Ritesh Kumar Dubey
For the general short-ranged potential the Lippmann-Schwinger-Low (LSL) scattering formalism by taking the limit ε → +0 at the end of the analysis, with ε being an infinitesimal adiabatic parameter has been re-examined. It is found that the LSL state |ψ k L〉 does not strictly satisfy the Schrodinger eigen equation, and the pair |ψ n L〉,|ψ k L〉 is mutually non-orthogonal if E n = E k, n ≠ k. For this purpose a new type of projection operator η k o, a non-linear relation among transition amplitudes, and a separable interaction as illustration have been used.
On quantum scattering by δ′(x) and quasi ′(x) distributions
(2007) Ritesh Kumar Dubey; V.J. Menon; M.K. Pandey; D.N. Tripathi
The zero-range interaction U(x) occurring in the one-dimensional, time-independent Schrödinger equation is regarded as a smoothed distribution characterized by a tiny length scale b such that the origin becomes an ordinary point. A neighbourhood around the origin is scanned by defining inner demarcation points a± = ±b/N and outer demarcation points b± ≡ ±Nb with N ≫ 1. Then a sequence of simple Lemmas permits (i) construction of a systematic procedure for simultaneously solving the scattering wave function ψ(0) at the origin, its derivative ψ(0) there, the transmission amplitude B, as well as the reflection amplitude D; and (ii) unambiguous application to scattering by the previously known δ′(x) and newly proposed quasi δ′(x) potentials in the Cauchy representation of various distributions. © 2007 NRC Canada.
On the ε → 0 limit of the Lippmann-Schwinger-Low states
(2004) V.J. Menon; Ritesh Kumar Dubey
The Lippmann-Schwinger-Low (LSL) quantum scattering states involve a resolvent operator depending on an infinitesimal adiabatic parameter ε. We reexamine the LSL formalism by taking the ε → +0 limit at the end of the analysis (rather than at the outset). It is found that the LSL state vector |ψkL〉 does not coincide with the Schrödinger eigen vector in Hilbert space as a whole, and the pair |ψn L〉, |ψkL〉 is mutually nonorthogonal if the energy En = Ek, n ≠ k. For this purpose we carefully use a new type of projection operator ηk, a novel nonlinear relation among transition amplitudes, and a separable interaction as illustration. © 2004 NRC Canada.
Ordering in polystyrene macroions
(2004) Ritesh Kumar Dubey; D.N. Tripathi
Ordering in polystyrene macroions in Benzene, Toluene, triple distilled water and heavy water has been studied using the static laser light scattering method. Liquid-like ordering amongst the polystyrene macroions in benzene, toluene, water and heavy water solvents has been reported. The ordering has been found to depend on the concentration of the particles and the dielectric constant of the solvent.
Proton/antiproton collisions with positronium in the presence of an electric field
(2008) Mukesh Kumar Pandey; Ritesh Kumar Dubey; D.N. Tripathi
Effects of aligned electric field on the hydrogen formation mechanism have been studied. Classical trajectory Monte Carlo (CTMC) method is used to simulate the proton/antiproton collisions with positronium (Ps) in the energy range of 1-200 keV. Total cross section for an electron/positron capture by colliding proton/antiproton has been calculated using the simple Coulomb potential. The hydrogen and antihydrogen formation in these capture processes, as expected, is reported to be charge conjugate. The capture cross sections are in reasonable agreement with the recently reported experimental and theoretical results. The effects of the external electric field are seen to be quite prominent. © 2008 Elsevier B.V. All rights reserved.
Rigorous treatment of scattering by quantum zero-range interactions
(2008) Ritesh Kumar Dubey; V.J. Menon; D.N. Tripathi
A new rigorous treatment of solving the Schrödinger scattering equation for a general contact potential U(x) has been developed. It is proved that if U(x) is regarded as a distribution characterized by a tiny length scale b then the wave function ψ and its derivative ψ′ become continuous across the apparent singular point x = 0. Hence, the reflection and transmission coefficients can be constructed for many cases namely usual δ(x), controversial δ′(x) and entirely new quasi δ′(x) interactions.
Stable galaxies of finite masses in the most probable distribution
(2006) V.J. Menon; Ritesh Kumar Dubey; D.N. Tripathi
Conventional equilibrium statistical mechanics of bound gravitational systems is known to suffer from the serious difficulties that galaxies acquire unbounded radii, become infinitely massive, and evaporate away continuously. We point out that these troubles disappear automatically if we use the exact, most probable, distribution having an inherent upper energy cutoff. © 2005 Elsevier B.V. All rights reserved.
Time dependence of Lippmann-Schwinger states
(2005) Ritesh Kumar Dubey; V.J. Menon; D.N. Tripathi
Due to the presence of an infinitesimal parameter ε in the resolvent, the Lippmann-Schwinger states cannot be strict eigenstates of the Hamiltonian, and their time evolution is very non-trivial (in agreement with Fermi's golden rule). In sharp contrast, strict Schrödinger eigenstates cannot make transitions into free channels. Artefacts such as adiabatic switching, wave packets, or infinite time span are not needed in our analysis.