14 research outputs found
Wetting transitions of Ne
We report studies of the wetting behavior of Ne on very weakly attractive
surfaces, carried out with the Grand Canonical Monte Carlo method. The Ne-Ne
interaction was taken to be of Lennard-Jones form, while the Ne-surface
interaction was derived from an ab initio calculation of Chizmeshya et al.
Nonwetting behavior was found for Li, Rb, and Cs in the temperature regime
explored (i.e., T < 42 K). Drying behavior was manifested in a depleted fluid
density near the Cs surface. In contrast, for the case of Mg (a more attractive
potential) a prewetting transition was found near T= 28 K. This temperature was
found to shift slightly when a corrugated potential was used instead of a
uniform potential. The isotherm shape and the density profiles did not differ
qualitatively between these cases.Comment: 22 pages, 12 figures, submitted to Phys. Rev.
Density Distribution in the Liquid Hg-Sapphire Interface
We present the results of a computer simulation study of the liquid density
distribution normal to the interface between liquid Hg and the reconstructed
(0001) face of sapphire. The simulations are based on an extension of the
self-consistent quantum Monte Carlo scheme previously used to study the
structure of the liquid metal-vapor interface. The calculated density
distribution is in very good agreement with that inferred from the recent
experimental data of Tamam et al (J. Phys. Chem. Lett. 1, 1041-1045 (2010)). We
conclude that, to account for the difference in structure between the liquid
Hg-vapor and liquid-Hg-reconstructed (0001) Al2O3 interfaces, it is not
necessary assume there is charge transfer from the Hg to the Al2O3. Rather, the
available experimental data are adequately reproduced when the van der Waals
interactions of the Al and O atoms with Hg atoms and the exclusion of electron
density from Al2O3 via repulsion of the electrons from the closed shells of the
ions in the solid are accounted for.Comment: 26 pages, 11 figure
Radiologist experience and CT examination quality determine metastasis detection in patients with esophageal or gastric cardia cancer
We aimed to separate the influence of radiologist experience from that of CT quality in the evaluation of CT examinations of patients with esophageal or gastric cardia cancer. Two radiologists from referral centers ('expert radiologists') and six radiologists from regional non-referral centers ('non-expert radiologists') performed 240 evaluations of 72 CT examinations of patients diagnosed with esophageal or gastric cardia cancer between 1994 and 2003. We used conditional logistic regression analysis to calculate odds ratios (OR) for the likelihood of a correct diagnosis. Expert radiologists made a correct diagnosis of the presence or absence of distant metastases according to the gold standard almost three times more frequently (OR 2.
Monte Carlo Methods for Estimating Interfacial Free Energies and Line Tensions
Excess contributions to the free energy due to interfaces occur for many
problems encountered in the statistical physics of condensed matter when
coexistence between different phases is possible (e.g. wetting phenomena,
nucleation, crystal growth, etc.). This article reviews two methods to estimate
both interfacial free energies and line tensions by Monte Carlo simulations of
simple models, (e.g. the Ising model, a symmetrical binary Lennard-Jones fluid
exhibiting a miscibility gap, and a simple Lennard-Jones fluid). One method is
based on thermodynamic integration. This method is useful to study flat and
inclined interfaces for Ising lattices, allowing also the estimation of line
tensions of three-phase contact lines, when the interfaces meet walls (where
"surface fields" may act). A generalization to off-lattice systems is described
as well.
The second method is based on the sampling of the order parameter
distribution of the system throughout the two-phase coexistence region of the
model. Both the interface free energies of flat interfaces and of (spherical or
cylindrical) droplets (or bubbles) can be estimated, including also systems
with walls, where sphere-cap shaped wall-attached droplets occur. The
curvature-dependence of the interfacial free energy is discussed, and estimates
for the line tensions are compared to results from the thermodynamic
integration method. Basic limitations of all these methods are critically
discussed, and an outlook on other approaches is given