804 research outputs found
A thermodynamically self-consistent theory for the Blume-Capel model
We use a self-consistent Ornstein-Zernike approximation to study the
Blume-Capel ferromagnet on three-dimensional lattices. The correlation
functions and the thermodynamics are obtained from the solution of two coupled
partial differential equations. The theory provides a comprehensive and
accurate description of the phase diagram in all regions, including the wing
boundaries in non-zero magnetic field. In particular, the coordinates of the
tricritical point are in very good agreement with the best estimates from
simulation or series expansion. Numerical and analytical analysis strongly
suggest that the theory predicts a universal Ising-like critical behavior along
the -line and the wing critical lines, and a tricritical behavior
governed by mean-field exponents.Comment: 11 figures. to appear in Physical Review
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
S98RS SGR No. 14 (Finals)
A RESOLUTION
To recommend to Executive Vice-Chancellor and Provost Dan Fogel, Robert Doolos of the University Registrars Office, and the University Calendar Committee to begin finals the Saturday after Dead Week and end the following Friday
Collateral donor artery physiology and the influence of a chronic total occlusion on fractional flow reserve
Backgroundâ The presence of a concomitant chronic total coronary occlusion (CTO) and a large collateral contribution might alter the fractional flow reserve (FFR) of an interrogated vessel, rendering the FFR unreliable at predicting ischemia should the CTO vessel be revascularized and potentially affecting the decision on optimal revascularization strategy. We tested the hypothesis that donor vessel FFR would significantly change after percutaneous coronary intervention of a concomitant CTO. Methods and Resultsâ In consecutive patients undergoing percutaneous coronary intervention of a CTO, coronary pressure and flow velocity were measured at baseline and hyperemia in proximal and distal segments of both nontarget vessels, before and after percutaneous coronary intervention. Hemodynamics including FFR, absolute coronary flow, and the coronary flow velocityâpressure gradient relation were calculated. After successful percutaneous coronary intervention in 34 of 46 patients, FFR in the predominant donor vessel increased from 0.782 to 0.810 (difference, 0.028 [0.012 to 0.044]; P=0.001). Mean decrease in baseline donor vessel absolute flow adjusted for rate pressure product: 177.5 to 139.9 mL/min (difference â37.6 [â62.6 to â12.6]; P=0.005), mean decrease in hyperemic flow: 306.5 to 272.9 mL/min (difference, â33.5 [â58.7 to â8.3]; P=0.011). Change in predominant donor vessel FFR correlated with angiographic (%) diameter stenosis severity (r=0.44; P=0.009) and was strongly related to stenosis severity measured by the coronary flow velocityâpressure gradient relation (r=0.69; P<0.001). Conclusionsâ Recanalization of a CTO results in a modest increase in the FFR of the predominant collateral donor vessel associated with a reduction in coronary flow. A larger increase in FFR is associated with greater coronary stenosis severity
Liquid-Liquid Phase Transition for an Attractive Isotropic Potential with Wide Repulsive Range
Recent experimental and theoretical results have shown the existence of a
liquid-liquid phase transition in isotropic systems, such as biological
solutions and colloids, whose interaction can be represented via an effective
potential with a repulsive soft-core and an attractive part. We investigate how
the phase diagram of a schematic general isotropic system, interacting via a
soft-core squared attractive potential, changes by varying the parameters of
the potential. It has been shown that this potential has a phase diagram with a
liquid-liquid phase transition in addition to the standard gas-liquid phase
transition and that, for a short-range soft-core, the phase diagram resulting
from molecular dynamics simulations can be interpreted through a modified van
der Waals equation. Here we consider the case of soft-core ranges comparable
with or larger than the hard-core diameter. Because an analysis using molecular
dynamics simulations of such systems or potentials is too time-demanding, we
adopt an integral equation approach in the hypernetted-chain approximation.
Thus we can estimate how the temperature and density of both critical points
depend on the potential's parameters for large soft-core ranges. The present
results confirm and extend our previous analysis, showing that this potential
has two fluid-fluid critical points that are well separated in temperature and
in density only if there is a balance between the attractive and repulsive part
of the potential. We find that for large soft-core ranges our results satisfy a
simple relation between the potential's parameters
Gel transitions in colloidal suspensions
The idealized mode coupling theory (MCT) is applied to colloidal systems
interacting via short-range attractive interactions of Yukawa form. At low
temperatures MCT predicts a slowing down of the local dynamics and ergodicity
breaking transitions. The nonergodicity transitions share many features with
the colloidal gel transition, and are proposed to be the source of gelation in
colloidal systems. Previous calculations of the phase diagram are complemented
with additional data for shorter ranges of the attractive interaction, showing
that the path of the nonergodicity transition line is then unimpeded by the
gas-liquid critical curve at low temperatures. Particular attention is given to
the critical nonergodicity parameters, motivated by recent experimental
measurements. An asymptotic model is developed, valid for dilute systems of
spheres interacting via strong short-range attractions, and is shown to capture
all aspects of the low temperature MCT nonergodicity transitions.Comment: 12 pages, LaTeX, 5 eps figures, uses ioplppt.sty, to appear in J.
Phys.: Condens. Matte
A model for the atomic-scale structure of a dense, nonequilibrium fluid: the homogeneous cooling state of granular fluids
It is shown that the equilibrium Generalized Mean Spherical Model of fluid
structure may be extended to nonequilibrium states with equation of state
information used in equilibrium replaced by an exact condition on the two-body
distribution function. The model is applied to the homogeneous cooling state of
granular fluids and upon comparison to molecular dynamics simulations is found
to provide an accurate picture of the pair distribution function.Comment: 29 pages, 11 figures Revision corrects formatting of the figure
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