arXiv subjects

Debanjan Chowdhury

Publications and source records attributed to Debanjan Chowdhury.

94 records · Page 6Linked to original sources

arXiv2010

Adiabatic dynamics in passage across quantum critical lines and gapless phases

It is well known that the dynamics of a quantum system is always non-adiabatic in passage through a quantum critical point and the defect density in the final state following a quench shows a power-law scaling with the rate of quenching. However, we propose here a possible situation where the dynamics of a quantum system in passage across quantum critical regions is adiabatic and the defect density decays exponentially. This is achieved by incorporating additional interactions which lead to quantum critical behavior and gapless phases but do not participate in the time evolution of the system. To illustrate the general argument, we study the defect generation in the quantum critical dynamics of a spin-1/2 anisotropic quantum XY spin chain with three spin interactions and a linearly driven staggered magnetic field.

cond-mat.stat-mech↗

arXiv2010

Searching for targets on a model DNA: Effects of inter-segment hopping, detachment and re-attachment

For most of the important processes in DNA metabolism, a protein has to reach a specific binding site on the DNA. The specific binding site may consist of just a few base pairs while the DNA is usually several millions of base pairs long. How does the protein search for the target site? What is the most efficient mechanism for a successful search? Motivated by these fundamental questions on intracellular biological processes, we have developed a model for searching a specific site on a model DNA by a single protein. We have made a comparative quantitative study of the efficiencies of sliding, inter-segmental hoppings and detachment/re-attachments of the particle during its search for the specific site on the DNA. We also introduce some new quantitative measures of {\it efficiency} of a search process by defining a relevant quantity, which can be measured in {\it in-vitro} experiments.

cond-mat.stat-mech↗

arXiv2009

Stochastic kinetics of ribosomes: single motor properties and collective behavior

Synthesis of protein molecules in a cell are carried out by ribosomes. A ribosome can be regarded as a molecular motor which utilizes the input chemical energy to move on a messenger RNA (mRNA) track that also serves as a template for the polymerization of the corresponding protein. The forward movement, however, is characterized by an alternating sequence of translocation and pause. Using a quantitative model, which captures the mechanochemical cycle of an individual ribosome, we derive an {\it exact} analytical expression for the distribution of its dwell times at the successive positions on the mRNA track. Inverse of the average dwell time satisfies a ``Michaelis-Menten-like'' equation and is consistent with the general formula for the average velocity of a molecular motor with an unbranched mechano-chemical cycle. Extending this formula appropriately, we also derive the exact force-velocity relation for a ribosome. Often many ribosomes simultaneously move on the same mRNA track, while each synthesizes a copy of the same protein. We extend the model of a single ribosome by incorporating steric exclusion of different individuals on the same track. We draw the phase diagram of this model of ribosome traffic in 3-dimensional spaces spanned by experimentally controllable parameters. We suggest new experimental tests of our theoretical predictions.

physics.bio-ph↗

arXiv2008

The effect of long range interactions on the stability of classical and quantum solids

We generalise the celebrated Peierls' argument to study the stability of a long-range interacting classical solid. Long-range interaction implies that all the atomic oscillators are coupled to each other via a harmonic potential, though the coupling strength decays as a power-law $1/x^α$, where $x$ is the distance between the oscillators. We show that for the range parameter $α<2$, the long-range interaction dominates and the one-dimensional system retains a crystalline order even at a finite temperature whereas for $α\geq2$, the long-range crystalline order vanishes even at an infinitesimally small temperature. We also study the effect of quantum fluctuations on the melting behaviour of a one-dimensional solid at T=0, extending Peierls' arguments to the case of quantum oscillators.

cond-mat.stat-mech↗