8,885 research outputs found
Thermodynamic anomalies in a lattice model of water: Solvation properties
We investigate a lattice-fluid model of water, defined on a 3-dimensional
body-centered cubic lattice. Model molecules possess a tetrahedral symmetry,
with four equivalent bonding arms. The model is similar to the one proposed by
Roberts and Debenedetti [J. Chem. Phys. 105, 658 (1996)], simplified by
removing distinction between "donors" and "acceptors". We focus on solvation
properties, mainly as far as an ideally inert (hydrophobic) solute is
concerned. As in our previous analysis, devoted to neat water [J. Chem. Phys.
121, 11856 (2004)], we make use of a generalized first order approximation on a
tetrahedral cluster. We show that the model exhibits quite a coherent picture
of water thermodynamics, reproducing qualitatively several anomalous properties
observed both in pure water and in solutions of hydrophobic solutes. As far as
supercooled liquid water is concerned, the model is consistent with the second
critical point scenario.Comment: 12 pages, 9 figures, 1 tabl
Cluster-variation approximation for a network-forming lattice-fluid model
We consider a 3-dimensional lattice model of a network-forming fluid, which
has been recently investigated by Girardi and coworkers by means of Monte Carlo
simulations [J. Chem. Phys. \textbf{126}, 064503 (2007)], with the aim of
describing water anomalies. We develop an approximate semi-analytical
calculation, based on a cluster-variation technique, which turns out to
reproduce almost quantitatively different thermodynamic properties and phase
transitions determined by the Monte Carlo method. Nevertheless, our calculation
points out the existence of two different phases characterized by long-range
orientational order, and of critical transitions between them and to a
high-temperature orientationally-disordered phase. Also, the existence of such
critical lines allows us to explain certain ``kinks'' in the isotherms and
isobars determined by the Monte Carlo analysis. The picture of the phase
diagram becomes much more complex and richer, though unfortunately less
suitable to describe real water.Comment: 10 pages, 9 figures, submitted to J. Chem. Phy
Revisiting waterlike network-forming lattice models
In a previous paper [J. Chem. Phys. 129, 024506 (2008)] we studied a 3
dimensional lattice model of a network-forming fluid, recently proposed in
order to investigate water anomalies. Our semi-analytical calculation, based on
a cluster-variation technique, turned out to reproduce almost quantitatively
several Monte Carlo results and allowed us to clarify the structure of the
phase diagram, including different kinds of orientationally ordered phases.
Here, we extend the calculation to different parameter values and to other
similar models, known in the literature. We observe that analogous ordered
phases occur in all these models. Moreover, we show that certain "waterlike"
thermodynamic anomalies, claimed by previous studies, are indeed artifacts of a
homogeneity assumption made in the analytical treatment. We argue that such a
difficulty is common to a whole class of lattice models for water, and suggest
a possible way to overcome the problem.Comment: 13 pages, 12 figure
Hydrophobic organization of membrane proteins
Membrane-exposed residues are more hydrophobic than buried interior residues in the transmembrane regions of the photosynthetic reaction center from Rhodobacter sphaeroides. This hydrophobic organization is opposite to that of water-soluble proteins. The relative polarities of interior and surface residues of membrane and water soluble proteins are not simply reversed, however. The hydrophobicities of interior residues of both membrane and water-soluble proteins are comparable, whereas the bilayer-exposed residues of membrane proteins are more hydrophobic than the interior residues, and the aqueous-exposed residues of water-soluble proteins are more hydrophilic than the interior residues. A method of sequence analysis is described, based on the periodicity of residue replacement in homologous sequences, that extends conclusions derived from the known atomic structure of the reaction center to the more extensive database of putative transmembrane helical sequences
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OAO1.01. Are complementary therapies and integrative care cost-effective? A comprehensive systematic review of economic evaluations
Diffusional Relaxation in Random Sequential Deposition
The effect of diffusional relaxation on the random sequential deposition
process is studied in the limit of fast deposition. Expression for the coverage
as a function of time are analytically derived for both the short-time and
long-time regimes. These results are tested and compared with numerical
simulations.Comment: 9 pages + 2 figure
Measurement Theory in Lax-Phillips Formalism
It is shown that the application of Lax-Phillips scattering theory to quantum
mechanics provides a natural framework for the realization of the ideas of the
Many-Hilbert-Space theory of Machida and Namiki to describe the development of
decoherence in the process of measurement. We show that if the quantum
mechanical evolution is pointwise in time, then decoherence occurs only if the
Hamiltonian is time-dependent. If the evolution is not pointwise in time (as in
Liouville space), then the decoherence may occur even for closed systems. These
conclusions apply as well to the general problem of mixing of states.Comment: 14 pages, IASSNS-HEP 93/6
Deformation Energy Minima at Finite Mass Asymmetry
A very general saddle point nuclear shape may be found as a solution of an
integro-differential equation without giving apriori any shape parametrization.
By introducing phenomenological shell corrections one obtains minima of
deformation energy for binary fission of parent nuclei at a finite (non-zero)
mass asymmetry. Results are presented for reflection asymmetric saddle point
shapes of thorium and uranium even-mass isotopes with A=226-238 and A=230-238
respectively.Comment: 5 pages, 2 Postscript figures, REVTeX, Version 4.
Randomized clinical trial of the effects of screening and brief intervention for illicit drug use: the Life Shift/Shift Gears study.
BackgroundAlthough screening, brief intervention, and referral to treatment (SBIRT) has shown promise for alcohol use, relatively little is known about its effectiveness for adult illicit drug use. This randomized controlled trial assessed the effectiveness of the SBIRT approach for outcomes related to drug use among patients visiting trauma and emergency departments (EDs) at two large, urban hospitals.MethodsA total of 700 ED patients who admitted using illegal drugs in the past 30 days were recruited, consented, provided baseline measures of substance use and related problems measured with the Addiction Severity Index-Lite (ASI-Lite), and then randomized to the Life Shift SBIRT intervention or to an attention-placebo control group focusing on driving and traffic safety (Shift Gears). Both groups received a level of motivational intervention matched to their condition and risk level by trained paraprofessional health educators. Separate measurement technicians conducted face-to-face follow-ups at 6 months post-intervention and collected hair samples to confirm reports of abstinence from drug use. The primary outcome measure of the study was past 30-day drug abstinence at 6 months post-intervention, as self-reported on the ASI-Lite.ResultsOf 700 participants, 292 (42%) completed follow-up. There were no significant differences in self-reported abstinence (12.5% vs. 12.0% , p = 0.88) for Life Shift and Shift Gears groups, respectively. When results of hair analyses were applied, the abstinence rate was 7 percent for Life Shift and 2 percent for Shift Gears (p = .074). In an analysis in which results were imputed (n = 694), there was no significant difference in the ASI-Lite drug use composite scores (Life Shift +0.005 vs. Shift Gears +0.017, p = 0.12).ConclusionsIn this randomized controlled trial, there was no evidence of effectiveness of SBIRT on the primary drug use outcome.Trial registrationClinicalTrials.gov NCT01683227
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