15,173 research outputs found
Statistical mechanics of warm and cold unfolding in proteins
We present a statistical mechanics treatment of the stability of globular
proteins which takes explicitly into account the coupling between the protein
and water degrees of freedom. This allows us to describe both the cold and the
warm unfolding, thus qualitatively reproducing the known thermodynamics of
proteins.Comment: 5 pages, REVTex, 4 Postscript figure
Reentrant phase diagram of branching annihilating random walks with one and two offsprings
We investigate the phase diagram of branching annihilating random walks with
one and two offsprings in one dimension. A walker can hop to a nearest neighbor
site or branch with one or two offsprings with relative ratio. Two walkers
annihilate immediately when they meet. In general, this model exhibits a
continuous phase transition from an active state into the absorbing state
(vacuum) at a finite hopping probability. We map out the phase diagram by Monte
Carlo simulations which shows a reentrant phase transition from vacuum to an
active state and finally into vacuum again as the relative rate of the
two-offspring branching process increases. This reentrant property apparently
contradicts the conventional wisdom that increasing the number of offsprings
will tend to make the system more active. We show that the reentrant property
is due to the static reflection symmetry of two-offspring branching processes
and the conventional wisdom is recovered when the dynamic reflection symmetry
is introduced instead of the static one.Comment: 14 pages, Revtex, 4 figures (one PS figure file upon request)
(submitted to Phy. Rev. E
Avalanche Behavior in an Absorbing State Oslo Model
Self-organized criticality can be translated into the language of absorbing
state phase transitions. Most models for which this analogy is established have
been investigated for their absorbing state characteristics. In this article,
we transform the self-organized critical Oslo model into an absorbing state
Oslo model and analyze the avalanche behavior. We find that the resulting gap
exponent, D, is consistent with its value in the self-organized critical model.
For the avalanche size exponent, \tau, an analysis of the effect of the
external drive and the boundary conditions is required.Comment: 4 pages, 2 figures, REVTeX 4, submitted to PRE Brief Reports; added
reference and some extra information in V
Critical behavior of a one-dimensional monomer-dimer reaction model with lateral interactions
A monomer-dimer reaction lattice model with lateral repulsion among the same
species is studied using a mean-field analysis and Monte Carlo simulations. For
weak repulsions, the model exhibits a first-order irreversible phase transition
between two absorbing states saturated by each different species. Increasing
the repulsion, a reactive stationary state appears in addition to the saturated
states. The irreversible phase transitions from the reactive phase to any of
the saturated states are continuous and belong to the directed percolation
universality class. However, a different critical behavior is found at the
point where the directed percolation phase boundaries meet. The values of the
critical exponents calculated at the bicritical point are in good agreement
with the exponents corresponding to the parity-conserving universality class.
Since the adsorption-reaction processes does not lead to a non-trivial local
parity-conserving dynamics, this result confirms that the twofold symmetry
between absorbing states plays a relevant role in determining the universality
class. The value of the exponent , which characterizes the
fluctuations of an interface at the bicritical point, supports the
Bassler-Brown's conjecture which states that this is a new exponent in the
parity-conserving universality class.Comment: 19 pages, 22 figures, to be published in Phys. Rev
Onset of criticality and transport in a driven diffusive system
We study transport properties in a slowly driven diffusive system where the
transport is externally controlled by a parameter . Three types of behavior
are found: For the system is not conducting at all. For intermediate
a finite fraction of the external excitations propagate through the system.
Third, in the regime the system becomes completely conducting. For all
the system exhibits self-organized critical behavior. In the middle of
this regime, at , the system undergoes a continuous phase transition
described by critical exponents.Comment: 4 latex/revtex pages; 4 figure
Synchronization Model for Stock Market Asymmetry
The waiting time needed for a stock market index to undergo a given
percentage change in its value is found to have an up-down asymmetry, which,
surprisingly, is not observed for the individual stocks composing that index.
To explain this, we introduce a market model consisting of randomly fluctuating
stocks that occasionally synchronize their short term draw-downs. These
synchronous events are parameterized by a ``fear factor'', that reflects the
occurrence of dramatic external events which affect the financial market.Comment: 4 pages, 4 figure
Pair contact process with diffusion - A new type of nonequilibrium critical behavior?
Recently Carlon et. al. investigated the critical behavior of the pair
contact process with diffusion [cond-mat/9912347]. Using density matrix
renormalization group methods, they estimate the critical exponents, raising
the possibility that the transition might belong to the same universality class
as branching annihilating random walks with even numbers of offspring. This is
surprising since the model does not have an explicit parity-conserving
symmetry. In order to understand this contradiction, we estimate the critical
exponents by Monte Carlo simulations. The results suggest that the transition
might belong to a different universality class that has not been investigated
before.Comment: RevTeX, 3 pages, 2 eps figures, adapted to final version of
cond-mat/991234
A Model for the Thermodynamics of Globular Proteins
Comments: 6 pages RevTeX, 6 Postscript figures. We review a statistical
mechanics treatment of the stability of globular proteins based on a simple
model Hamiltonian taking into account protein self interactions and
protein-water interactions. The model contains both hot and cold folding
transitions. In addition it predicts a critical point at a given temperature
and chemical potential of the surrounding water. The universality class of this
critical point is new
- …