101 research outputs found
Interfacial instability and DNA fork reversal by repair proteins
A repair protein like RecG moves the stalled replication fork in the
direction from the zipped to the unzipped state of DNA. It is proposed here
that a softening of the zipped-unzipped interface at the fork results in the
front propagating towards the unzipped side. In this scenario, an ordinary
helicase destabilizes the zipped state locally near the interface and the fork
propagates towards the zipped side. The softening of the interface can be
produced by the aromatic interaction, predicted from crystal structure, between
RecG and the nascent broken base pairs at the Y-fork. A numerical analysis of
the model also reveals the possibility of a stop and go type motion.Comment: 7 pages, revtex, 5 eps figures; v2:shorter title, 2 additional
schematic figures in introductio
Critical Phenomena: An Introduction from a modern perspective
Our aim in this set of lectures is to give an introduction to critical
phenomena that emphasizes the emergence of and the role played by diverging
length-scales. It is now accepted that renormalization group gives the basic
understanding of these phenomena and so, instead of following the traditional
historical trail, we try to develop the subject in a way that emphasizes the
length-scale based approach.Comment: Revtex, 26 pages, 2 figures. Lectures given at the SERC School on
"Field theoretic methods in Condensed matter physics", held at MRI,
Allahabad, Indi
Entropy and perpetual computers
A definition of entropy via the Kolmogorov algorithmic complexity is
discussed. As examples, we show how the meanfield theory for the Ising model,
and the entropy of a perfect gas can be recovered. The connection with
computations are pointed out, by paraphrasing the laws of thermodynamics for
computers. Also discussed is an approach that may be adopted to develop
statistical mechanics using the algorithmic point of view.Comment: Based on Chanchal Majumdar memorial lectures given in Kolkata. 9
pages, 3 eps figures. For publication in "Physics Teacher"; v2. Sec 3
fragmented into smaller subsection
Unzipping DNA - towards the first step of replication
The opening of the Y-fork - the first step of DNA replication - is shown to
be a critical phenomenon under an external force at one of its ends. From the
results of an equivalent delocalization in a non-hermitian quantum-mechanics
problem we show the different scaling behavior of unzipping and melting. The
resultant long-range critical features within the unzipped part of Y might play
a role in the highly correlated biochemical functions during replication.Comment: 4 pages, revtex, 2 eps figure
Nonequilibrium Growth problems
We discuss the features of nonequilibrium growth problems, their scaling
description and their differences from equilibrium problems. The emphasis is on
the Kardar-Parisi-Zhang equation and the renormalization group point of view.
Some of the recent developments along these lines are mentioned.Comment: 9 pages, revtex, A brief overview as published in Current Science 77,
394 (1999
Incommensuration in quantum antiferromagnetic chain
A dimerized quantum Heisenberg or XY antiferromagnetic chain has a gap in the
spectrum. We show that a weak incommensurate modulation around a dimerized
chain produces a zero temperature quantum critical point. As the
incommensuration wavelength is varied, there is a transition to a modulated
gapless state. The critical behaviour is in the universality class of the
classical commensurate-incommensurate (Pokrovsky-Talapov) transition. An
analogous metal-insulator transition can also take place for an incommensurate
chain.Comment: 5 pages, revtex, no figures, to appear in J. Phys A Letter
- …