520 research outputs found
Phase diagram of a two-dimensional system with anomalous liquid properties
Using Monte Carlo simulation techniques, we calculate the phase diagram for a
square shoulder-square well potential in two dimensions that has been
previously shown to exhibit liquid anomalies consistent with a metastable
liquid-liquid critical point. We consider the liquid, gas and five crystal
phases, and find that all the melting lines are first order, despite a small
range of metastability. One melting line exhibits a temperature maximum, as
well as a pressure maximum that implies inverse melting over a small range in
pressure.Comment: 11 pages, 13 figure
The liquid-glass transition of silica
We studied the liquid-glass transition of by means of replica theory,
utilizing an effective pair potential which was proved to reproduce a few
experimental features of silica. We found a finite critical temperature ,
where the system undergoes a phase transition related to replica symmetry
breaking, in a region where experiments do not show any transition. The
possible sources of this discrepancy are discussed.Comment: 14 pages, 6 postscript figures. Revised version accepted for
pubblication on J.Chem.Phy
Energy landscape of a simple model for strong liquids
We calculate the statistical properties of the energy landscape of a minimal
model for strong network-forming liquids. Dynamics and thermodynamic properties
of this model can be computed with arbitrary precision even at low
temperatures. A degenerate disordered ground state and logarithmic statistics
for the energy distribution are the landscape signatures of strong liquid
behavior. Differences from fragile liquid properties are attributed to the
presence of a discrete energy scale, provided by the particle bonds, and to the
intrinsic degeneracy of topologically disordered networks.Comment: Revised versio
Non-Gaussian energy landscape of a simple model for strong network-forming liquids: accurate evaluation of the configurational entropy
We present a numerical study of the statistical properties of the potential
energy landscape of a simple model for strong network-forming liquids. The
model is a system of spherical particles interacting through a square well
potential, with an additional constraint that limits the maximum number of
bonds, , per particle. Extensive simulations have been carried out
as a function of temperature, packing fraction, and . The dynamics
of this model are characterized by Arrhenius temperature dependence of the
transport coefficients and by nearly exponential relaxation of dynamic
correlators, i.e. features defining strong glass-forming liquids. This model
has two important features: (i) landscape basins can be associated with bonding
patterns; (ii) the configurational volume of the basin can be evaluated in a
formally exact way, and numerically with arbitrary precision. These features
allow us to evaluate the number of different topologies the bonding pattern can
adopt. We find that the number of fully bonded configurations, i.e.
configurations in which all particles are bonded to neighbors, is
extensive, suggesting that the configurational entropy of the low temperature
fluid is finite. We also evaluate the energy dependence of the configurational
entropy close to the fully bonded state, and show that it follows a logarithmic
functional form, differently from the quadratic dependence characterizing
fragile liquids. We suggest that the presence of a discrete energy scale,
provided by the particle bonds, and the intrinsic degeneracy of fully bonded
disordered networks differentiates strong from fragile behavior.Comment: Final version. Journal of Chemical Physics 124, 204509 (2006
Ocular transient receptor potential channel function in health and disease
Transient receptor potential (TRP) channels sense and transduce environmental
stimuli into Ca2+ transients that in turn induce responses essential for cell
function and adaptation. These non-selective channels with variable Ca2+
selectivity are grouped into seven different subfamilies containing 28
subtypes based on differences in amino acid sequence homology. Many of these
subtypes are expressed in the eye on both neuronal and non-neuronal cells
where they affect a host of stress-induced regulatory responses essential for
normal vision maintenance. This article reviews our current knowledge about
the expression, function and regulation of TRPs in different eye tissues. We
also describe how under certain conditions TRP activation can induce responses
that are maladaptive to ocular function. Furthermore, the possibility of an
association between TRP mutations and disease is considered. These findings
contribute to evidence suggesting that drug targeting TRP channels may be of
therapeutic benefit in a clinical setting. We point out issues that must be
more extensively addressed before it will be possible to decide with certainty
that this is a realistic endeavor. Another possible upshot of future studies
is that disease process progression can be better evaluated by profiling
changes in tissue specific functional TRP subtype activity as well as their
gene and protein expression
Distributions of inherent structure energies during aging
We perform extensive simulations of a binary mixture Lennard-Jones system
subjected to a temperature jump in order to study the time evolution of
fluctuations during aging. Analyzing data from 1500 different aging
realizations, we calculate distributions of inherent structure energies for
different aging times and contrast them with equilibrium. We find that the
distributions initially become narrower and then widen as the system
equilibrates. For deep quenches, fluctuations in the glassy system differ
significantly from those observed in equilibrium. Simulation results are
partially captured by theoretical predictions only when the final temperature
is higher than the mode coupling temperature.Comment: 5 pages, 4 figure
Relation Between the Widom line and the Strong-Fragile Dynamic Crossover in Systems with a Liquid-Liquid Phase Transition
We investigate, for two water models displaying a liquid-liquid critical
point, the relation between changes in dynamic and thermodynamic anomalies
arising from the presence of the liquid-liquid critical point. We find a
correlation between the dynamic fragility transition and the locus of specific
heat maxima (``Widom line'') emanating from the critical point.
Our findings are consistent with a possible relation between the previously
hypothesized liquid-liquid phase transition and the transition in the dynamics
recently observed in neutron scattering experiments on confined water. More
generally, we argue that this connection between and dynamic
crossover is not limited to the case of water, a hydrogen bond network forming
liquid, but is a more general feature of crossing the Widom line. Specifically,
we also study the Jagla potential, a spherically-symmetric two-scale potential
known to possess a liquid-liquid critical point, in which the competition
between two liquid structures is generated by repulsive and attractive ramp
interactions.Comment: 6 pages and 5 figure
Temperature-Sensitive Transient Receptor Potential Channels in Corneal Tissue Layers and Cells
We here provide a brief summary of the characteristics of transient receptor potential channels (TRPs) identified in corneal tissue layers and cells. In general, TRPs are nonselective cation channels which are Ca ²⁺ permeable. Most TRPs serve as thermosensitive molecular sensors (thermo-TRPs). Based on their functional importance, the possibilities are described for drug-targeting TRP activity in a clinical setting. TRPs are expressed in various tissues of the eye including both human corneal epithelial and endothelial layers as well as stromal fibroblasts and stromal nerve fibers. TRP vanilloid type 1 (TRPV1) heat receptor, also known as capsaicin receptor, along with TRP melastatin type 8 (TRPM8) cold receptor, which is also known as menthol receptor, are prototypes of the thermo-TRP family. The TRPV1 functional channel is the most investigated TRP channel in these tissues, owing to its contribution to maintaining tissue homeostasis as well as eliciting wound healing responses to injury. Other thermo-TRP family members identified in these tissues are TRPV2, 3 and 4. Finally, there is the TRP ankyrin type 1 (TRPA1) cold receptor. All of these thermo-TRPs can be activated within specific temperature ranges and transduce such inputs into chemical and electrical signals. Although several recent studies have begun to unravel complex roles for thermo-TRPs such as TRPV1 in corneal layers and resident cells, additional studies are needed to further elucidate their roles in health and disease
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