63 research outputs found
Critical Behavior of the Widom-Rowlinson Lattice Model
We report extensive Monte Carlo simulations of the Widom-Rowlinson lattice
model in two and three dimensions. Our results yield precise values for the
critical activities and densities, and clearly place the critical behavior in
the Ising universality class.Comment: 6 pages, LaTeX, 5 figures available upon reques
Phase Diagram of the Lattice Restricted Primitive Model
We present a comprehensive study of the lattice restricted primitive model,
i.e., a lattice gas consisting of an equal number of positively and negatively
charged particles interacting via on-site exclusion and a 1/r potential. On the
cubic lattice, Monte Carlo simulations show a line of Neel points separating a
disordered, high-temperature phase from a phase with global antiferromagnetic
order. At low temperatures the (high-density) ordered phase coexists with the
(low-density) disordered phase. The Neel line meets the coexistence curve at a
tricritical point, T_t \simeq 0.14, rho_t \simeq 0.4. A simple mean-field
analysis is in qualitative agreement with simulations.Comment: Contribution to the AIP Conference on Treatment of Electrostatic
Interactions in Computer Simulations of Condensed Media 25 pages, 16 figure
First-Passage Time Distribution and Non-Markovian Diffusion Dynamics of Protein Folding
We study the kinetics of protein folding via statistical energy landscape
theory. We concentrate on the local-connectivity case, where the
configurational changes can only occur among neighboring states, with the
folding progress described in terms of an order parameter given by the fraction
of native conformations. The non-Markovian diffusion dynamics is analyzed in
detail and an expression for the mean first-passage time (MFPT) from non-native
unfolded states to native folded state is obtained. It was found that the MFPT
has a V-shaped dependence on the temperature. We also find that the MFPT is
shortened as one increases the gap between the energy of the native and average
non-native folded states relative to the fluctuations of the energy landscape.
The second- and higher-order moments are studied to infer the first-passage
time (FPT) distribution. At high temperature, the distribution becomes close to
a Poisson distribution, while at low temperatures the distribution becomes a
L\'evy-like distribution with power-law tails, indicating a non-self-averaging
intermittent behavior of folding dynamics. We note the likely relevance of this
result to single-molecule dynamics experiments, where a power law (L\'evy)
distribution of the relaxation time of the underlined protein energy landscape
is observed.Comment: 26 pages, 10 figure
Diffusion Dynamics, Moments, and Distribution of First Passage Time on the Protein-Folding Energy Landscape, with Applications to Single Molecules
We study the dynamics of protein folding via statistical energy-landscape
theory. In particular, we concentrate on the local-connectivity case with the
folding progress described by the fraction of native conformations. We obtain
information for the first passage-time (FPT) distribution and its moments. The
results show a dynamic transition temperature below which the FPT distribution
develops a power-law tail, a signature of the intermittency phenomena of the
folding dynamics. We also discuss the possible application of the results to
single-molecule dynamics experiments
Final Progress Report for THERMOPHYSICAL PROPERTIES OF FLUIDS AND FLUID MIXTURES
The DOE supported research is a theoretical statistical-mechanical based study of the thermophysical properties of fluids and fluid mixtures. It focuses upon thermodynamic and transport properties in particular. In addition the study covers the development of new ways for predicting the microscopic structure of fluids in a wide range of thermodynamic state parameters, including the critical point
SCOZA for Monolayer Films
We show the way in which the self-consistent Ornstein-Zernike approach
(SCOZA) to obtaining structure factors and thermodynamics for Hamiltonian
models can best be applied to two-dimensional systems such as thin films. We
use the nearest-neighbor lattice gas on a square lattice as an illustrative
example.Comment: 10 pages, 5 figure
Studies by electron-paramagnetic-resonance spectroscopy of the molybdenum centre of aldehyde oxidase
Phase equilibria and glass transition in colloidal systems with short-ranged attractive interactions. Application to protein crystallization
We have studied a model of a complex fluid consisting of particles
interacting through a hard core and a short range attractive potential of both
Yukawa and square-well form. Using a hybrid method, including a self-consistent
and quite accurate approximation for the liquid integral equation in the case
of the Yukawa fluid, perturbation theory to evaluate the crystal free energies,
and mode-coupling theory of the glass transition, we determine both the
equilibrium phase diagram of the system and the lines of equilibrium between
the supercooled fluid and the glass phases. For these potentials, we study the
phase diagrams for different values of the potential range, the ratio of the
range of the interaction to the diameter of the repulsive core being the main
control parameter. Our arguments are relevant to a variety of systems, from
dense colloidal systems with depletion forces, through particle gels,
nano-particle aggregation, and globular protein crystallization.Comment: 20 pages, 10 figure
Archaeological Assessment of Second World War Anti-Torpedo Close Protection Pontoons in Scapa Flow, Orkney
This paper presents the outcomes of sidescan sonar and archaeological diving surveys in 2015 of two wrecked vessels located off Flotta Island, Orkney, North Scotland. Archival research indicates these are the remains of Anti-Torpedo Close Protection Pontoons (ATCPP), an experimental protection device used for close protection of naval vessels at anchor in Scapa Flow from attack by aircraft-launch torpedoes. The pontoons were only in operation in Scapa Flow for 13 months (March 1941-April 1942) and few were brought into service. As such they represent a rare heritage resource, for which very little is known about their operation
The low temperature interface between the gas and solid phases of hard spheres with a short-ranged attraction
At low temperature, spheres with a very short-ranged attraction exist as a
close-packed solid coexisting with an infinitely dilute gas. We find that the
ratio of the interfacial tension between these two phases to the thermal energy
diverges as the range of the attraction goes to zero. The large tensions when
the interparticle attractions are short-ranged may be why globular proteins
only crystallise over a narrow range of conditions.Comment: 6 pages, no figures (v2 has change of notation to agree with that of
Stell
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