arXiv subjects

Anirvan M. Sengupta

Publications and source records attributed to Anirvan M. Sengupta.

47 records · Page 3Linked to original sources

arXiv2005

Quantitative modeling and data analysis of SELEX experiments

SELEX (Systematic Evolution of Ligands by Exponential Enrichment) is an experimental procedure that allows extracting, from an initially random pool of DNA, those oligomers with high affinity for a given DNA-binding protein. We address what is a suitable experimental and computational procedure to infer parameters of transcription factor-DNA interaction from SELEX experiments. To answer this, we use a biophysical model of transcription factor-DNA interactions to quantitatively model SELEX. We show that a standard procedure is unsuitable for obtaining accurate interaction parameters. However, we theoretically show that a modified experiment in which chemical potential is fixed through different rounds of the experiment allows robust generation of an appropriate data set. Based on our quantitative model, we propose a novel bioinformatic method of data analysis for such modified experiment and apply it to extract the interaction parameters for a mammalian transcription factor CTF/NFI. From a practical point of view, our method results in a significantly improved false positive/false negative trade-off, as compared to both the standard information theory based method and a widely used empirically formulated procedure.

q-bio.GN↗

arXiv2004

Optimal Path to Epigenetic Switching

We use large deviation methods to calculate rates of noise-induced transitions between states in multistable genetic networks. We analyze a synthetic biochemical circuit, the toggle switch, and compare the results to those obtained from a numerical solution of the master equation.

q-bio.MN↗

arXiv2000

Communication through a Diffusive Medium: Coherence and Capacity

Coherent wave propagation in disordered media gives rise to many fascinating phenomena as diverse as universal conductance fluctuations in mesoscopic metals and speckle patterns in light scattering. Here, the theory of electromagnetic wave propagation in diffusive media is combined with information theory to show how interference affects the information transmission rate between antenna arrays. Nontrivial dependencies of the information capacity on the nature of the antenna arrays are found, such as the dimensionality of the arrays and their direction with respect to the local scattering medium. This approach provides a physical picture for understanding the importance of scattering in the transfer of information through wireless communications.

cond-mat.mes-hall↗

arXiv1998

Hall effect in the perovskite manganites

We compute the zero temperature phase diagram and the Hall response of the doped perovskite manganites within the model of double exchange and Jahn-Teller coupling, employing the large dimensionality approximation proposed by Millis et al. We find that in this scenario a ``hole - like'' $R_H$ for the hole doped manganites, as observed at low temperature by Matl et al., can be obtained only when lattice distortions persist in the metallic state at zero temperature. The calculated temperature dependence of $R_H$ seems to be consistent with the measured ``normal'' Hall coefficient in thin films.

cond-mat.str-el↗

arXiv1997

Spin in a Fluctuating Field: The Bose (+Fermi) Kondo models

I consider models with an impurity spin coupled to a fluctuating gaussian field with or without additional Kondo coupling of the conventional sort. In the case of isotropic fluctuations, the renormalisation group flows for these models have controlled fixed points when the autocorrelation of the gaussian field $h(t)$, $ \sim {1\over t^{2-ε}}$ with small positive $ε$. In absence of any additional Kondo coupling, I get powerlaw decay of spin correlators, $ \sim {1\over t^ε}$ . For negative $ε$, the spin autocorrelation is constant in long time limit. The results agree with calculations in Schwinger Boson mean field theory. In presence of a Kondo coupling to itinerant electrons, the model shows a phase transition from a Kondo phase to a field fluctuation dominated phase. These models are good starting points for understanding behaviour of impurities in a system near a zero-temperature magnetic transition. They are also useful for understanding the dynamical local mean field theory of Kondo lattice with Heisenberg (spin-glass type) magnetic interactions.

cond-mat.str-el↗

arXiv1996

Overscreened Single Channel Kondo Problem

We consider the single channel Kondo problem with the Kondo coupling between a spin $S$ impurity and conduction electrons with spin $j$. These problems arise as multicritical points in the parameter spaces of two- and higher-level tunneling systems, and some impurity models of heavy fermion compounds. In contrast to the previous Bethe-anstaz conjectures, it turns out that the dynamics of the spin sector is the same as that of a spin $S$ impurity coupled to $k(j)$ channels of spin $1/2$ electrons with $k(j) = 2j(j+1)(2j+1)/3$. As a result, for $2S < k(j)$, the system shows non-Fermi liquid behavior with the same exponents for the thermodynamic quantities as those of $k(j)$ channel Kondo problem. However, both the finite-size spectrum and the operator content are different due to the presence of the other sectors and can be obtained by conformal field theory techniques.

cond-mat↗

arXiv1995

Non-equilibrium Dynamics Following a Quench to the Critical Point in a Semi-infinite System

We study the non-equilibrium dynamics (purely dissipative and relaxational) in a semi-infinite system following a quench from the high temperature disordered phase to its critical temperature. We show that the local autocorrelation near the surface of a semi-infinite system decays algebraically in time with a new exponent which is different from the bulk. We calculate this new non-equilibrium surface exponent in several cases, both analytically and numerically.

cond-mat↗

arXiv1995

Non Fermi Liquid Behaviour near a $T=0$ spin-glass transition

In this paper we study the competition between the Kondo effect and RKKY interactions near the zero-temperature quantum critical point of an Ising-like metallic spin-glass. We consider the mean-field behaviour of various physical quantities. In the `quantum- critical regime' non-analytic corrections to the Fermi liquid behaviour are found for the specific heat and uniform static susceptibility, while the resistivity and NMR relaxation rate have a non-Fermi liquid dependence on temperature.

cond-mat↗

arXiv1993

On the Emery-Kivelson Solution of the two channel Kondo problem

We consider the two channel Kondo model in the Emery-Kivelson approach, and calculate the total susceptibility enhancement due to the impurity $χ_{imp}=χ-χ_{bulk}$. We find that $χ_{imp}$ exactly vanishes at the solvable point, in a completely analogous way to the singular part of the specific heat $C_{imp}$. A perturbative calculation around the solvable point yields the generic behaviour $χ_{imp} \sim \log {1 \over T}$, $C_{imp} \sim T\log T $ and the known universal value of the Wilson ratio $R_W={8 \over 3}$. From this calculation, the Kondo temperature can be identified and is found to behave as the inverse-square of the perturbation parameter. The small field, zero-temperature behaviour $χ_{imp}\sim log {1 \over h}$ is also recovered.

cond-mat↗

arXiv1992

Target Space Interpretation of New Moduli in 2D String Theory

We analyze the new states that have recently been discovered in 2D string theory by E. Witten and B. Zwiebach. Since the Liouville direction is uncompactified, we show that the deformations by the new ghost number two states generate equivalent classical solutions of the string fields. We argue that the new ghost number one states are responsible for generating transformations which relate such equivalent solutions. We also discuss the possible interpretation of higher ghost number states of those kinds.

hep-th↗

arXiv1991

Instabilities in the gravitational background and string theory

We indicate the tentative source of instability in the two-dimensional black hole background. There are relevant operators among the tachyon and the higher level vertex operators in the conformal field theory. Connection of this instability with Hawking radiation is not obvious. The situation is somewhat analogous to fields in the background of a negative mass Euclidean Schwarzschild solution (in four dimensions). Speculation is made about decay of the Minkowski black hole into finite temperature flat space.

hep-th↗