2,587 research outputs found
Pearling instability of nanoscale fluid flow confined to a chemical channel
We investigate the flow of a nano-scale incompressible ridge of
low-volatility liquid along a "chemical channel": a long, straight, and
completely wetting stripe embedded in a planar substrate, and sandwiched
between two extended less wetting solid regions. Molecular dynamics
simulations, a simple long-wavelength approximation, and a full stability
analysis based on the Stokes equations are used, and give qualitatively
consistent results. While thin liquid ridges are stable both statically and
during flow, a (linear) pearling instability develops if the thickness of the
ridge exceeds half of the width of the channel. In the flowing case periodic
bulges propagate along the channel and subsequently merge due to nonlinear
effects. However, the ridge does not break up even when the flow is unstable,
and the qualitative behavior is unchanged even when the fluid can spill over
onto a partially wetting exterior solid region.Comment: 17 pages, 12 figures, submitted to Physics of Fluids, fixed equation
numbering after Eq. (17
Depression Care Management: Can Employers Purchase Improved Outcomes?
Fourteen vendors are currently selling depression care management products to US employers after randomized trials demonstrate improved work outcomes. The research team interviewed 10 (71.4%) of these vendors to compare their products to four key components of interventions demonstrated to improve work outcomes. Five of 10 depression products incorporate all four key components, three of which are sold by health maintenance organizations (HMOs); however, HMOs did not deliver these components at the recommended intensity and/or duration. Only one product delivered by a disease management company delivered all four components of care at the recommended intensity and duration. This “voltage drop,” which we anticipate will increase with product implementation, suggests that every delivery system should carefully evaluate the design of its depression product before implementation for its capacity to deliver evidence-based care, repeating these evaluations as new evidence emerges
Wall-liquid and wall-crystal interfacial free energies via thermodynamic integration: A molecular dynamics simulation study
A method is proposed to compute the interfacial free energy of a
Lennard-Jones system in contact with a structured wall by molecular dynamics
simulation. Both the bulk liquid and bulk face-centered-cubic crystal phase
along the (111) orientation are considered. Our approach is based on a
thermodynamic integration scheme where first the bulk Lennard-Jones system is
reversibly transformed to a state where it interacts with a structureless flat
wall. In a second step, the flat structureless wall is reversibly transformed
into an atomistic wall with crystalline structure. The dependence of the
interfacial free energy on various parameters such as the wall potential, the
density and orientation of the wall is investigated. The conditions are
indicated under which a Lennard-Jones crystal partially wets a flat wall.Comment: 15 pages, 11 figure
Mean-field dynamical density functional theory
We examine the out-of-equilibrium dynamical evolution of density profiles of
ultrasoft particles under time-varying external confining potentials in three
spatial dimensions. The theoretical formalism employed is the dynamical density
functional theory (DDFT) of Marini Bettolo Marconi and Tarazona [J. Chem. Phys.
{\bf 110}, 8032 (1999)], supplied by an equilibrium excess free energy
functional that is essentially exact. We complement our theoretical analysis by
carrying out extensive Brownian Dynamics simulations. We find excellent
agreement between theory and simulations for the whole time evolution of
density profiles, demonstrating thereby the validity of the DDFT when an
accurate equilibrium free energy functional is employed.Comment: 8 pagers, 4 figure
Nonlinear dielectric effect of dipolar fluids
The nonlinear dielectric effect for dipolar fluids is studied within the
framework of the mean spherical approximation (MSA) of hard core dipolar Yukawa
fluids. Based on earlier results for the electric field dependence of the
polarization our analytical results show so-called normal saturation effects
which are in good agreement with corresponding NVT ensemble Monte Carlo
simulation data. The linear and the nonlinear dielectric permittivities
obtained from MC simulations are determined from the fluctuations of the total
dipole moment of the system in the absence of an applied electric field. We
compare the MSA based theoretical results with the corresponding Langevin and
Debye-Weiss behaviors.Comment: 10 pages including 4 figure
Exact Three Dimensional Casimir Force Amplitude, -function and Binder's Cumulant Ratio: Spherical Model Results
The three dimensional mean spherical model on a hypercubic lattice with a
film geometry under periodic boundary conditions is
considered in the presence of an external magnetic field . The universal
Casimir amplitude and the Binder's cumulant ratio are calculated
exactly and found to be and
A discussion on the relations
between the finite temperature -function, usually defined for quantum
systems, and the excess free energy (due to the finite-size contributions to
the free energy of the system) scaling function is presented. It is
demonstrated that the -function of the model equals 4/5 at the bulk critical
temperature . It is analytically shown that the excess free energy is a
monotonically increasing function of the temperature and of the magnetic
field in the vicinity of This property is supposed to hold for any
classical -dimensional model with a film geometry under periodic
boundary conditions when . An analytical evidence is also presented to
confirm that the Casimir force in the system is negative both below and in the
vicinity of the bulk critical temperature Comment: 12 pages revtex, one eps figure, submitted to Phys. Rev E A set of
references added with the text needed to incorporate them. Small changes in
the title and in the abstrac
Lactobacilli and bifidobacteria in the prevention of antibiotic-associated diarrhoea and Clostridium difficile diarrhoea in older inpatients (PLACIDE): a randomised, double-blind, placebo-controlled, multicentre trial
BACKGROUND: Antibiotic-associated diarrhoea (AAD) occurs most frequently in older (≥65 years) inpatients exposed to broad-spectrum antibiotics. When caused by Clostridium difficile, AAD can result in life-threatening illness. Although underlying disease mechanisms are not well understood, microbial preparations have been assessed in the prevention of AAD. However, studies have been mostly small single-centre trials with varying quality, providing insufficient data to reliably assess effectiveness. We aimed to do a pragmatic efficacy trial in older inpatients who would be representative of those admitted to National Health Service (NHS) and similar secondary care institutions and to recruit a sufficient number of patients to generate a definitive result. METHODS: We did a multicentre, randomised, double-blind, placebo-controlled, pragmatic, efficacy trial of inpatients aged 65 years and older and exposed to one or more oral or parenteral antibiotics. A computer-generated randomisation scheme was used to allocate participants (in a 1:1 ratio) to receive either a multistrain preparation of lactobacilli and bifidobacteria, with a total of 6 × 10(10) organisms, one per day for 21 days, or an identical placebo. Patients, study staff, and specimen and data analysts were masked to assignment. The primary outcomes were occurrence of AAD within 8 weeks and C difficile diarrhoea (CDD) within 12 weeks of recruitment. Analysis was by modified intention-to-treat. This trial is registered, number ISRCTN70017204. FINDINGS: Of 17,420 patients screened, 1493 were randomly assigned to the microbial preparation group and 1488 to the placebo group. 1470 and 1471, respectively, were included in the analyses of the primary endpoints. AAD (including CDD) occurred in 159 (10·8%) participants in the microbial preparation group and 153 (10·4%) participants in the placebo group (relative risk [RR] 1·04; 95% CI 0·84-1·28; p=0·71). CDD was an uncommon cause of AAD and occurred in 12 (0·8%) participants in the microbial preparation group and 17 (1·2%) participants in the placebo group (RR 0·71; 95% CI 0·34-1·47; p=0·35). 578 (19·7%) participants had one or more serious adverse event; the frequency of serious adverse events was much the same in the two study groups and none was attributed to participation in the trial. INTERPRETATION: We identified no evidence that a multistrain preparation of lactobacilli and bifidobacteria was effective in prevention of AAD or CDD. An improved understanding of the pathophysiology of AAD is needed to guide future studies. FUNDING: Health Technology Assessment programme; National Institute for Health Research, UK
Fluctuation - induced forces in critical fluids
The current knowledge about fluctuation - induced long - ranged forces is
summarized. Reference is made in particular to fluids near critical points, for
which some new insight has been obtained recently. Where appropiate, results of
analytic theory are compared with computer simulations and experiments.Comment: Topical review, 24 pages RevTeX, 6 figure
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.
Phase separation of an asymmetric binary fluid mixture confined in a nanoscopic slit pore: Molecular-dynamics simulations
As a generic model system of an asymmetric binary fluid mixture, hexadecane
dissolved in carbon dioxide is considered, using a coarse-grained bead-spring
model for the short polymer, and a simple spherical particle with Lennard-Jones
interactions for the carbon dioxide molecules. In previous work, it has been
shown that this model reproduces the real phase diagram reasonable well, and
also the initial stages of spinodal decomposition in the bulk following a
sudden expansion of the system could be studied. Using the parallelized
simulation package ESPResSo on a multiprocessor supercomputer, phase separation
of thin fluid films confined between parallel walls that are repulsive for both
types of molecules are simulated in a rather large system (1356 x 1356 x 67.8
A^3, corresponding to about 3.2 million atoms). Following the sudden system
expansion, a complicated interplay between phase separation in the directions
perpendicular and parallel to the walls is found: in the early stages the
hexadecane molecules accumulate mostly in the center of the slit pore, but as
the coarsening of the structure in the parallel direction proceeds, the
inhomogeneity in the perpendicular direction gets much reduced. Studying then
the structure factors and correlation functions at fixed distances from the
wall, the densities are essentially not conserved at these distances, and hence
the behavior differs strongly from spinodal decomposition in the bulk. Some of
the characteristic lengths show a nonmonotonic variation with time, and simple
coarsening described by power-law growth is only observed if the domain sizes
are much larger than the film thickness.Comment: accepted for publication in PR
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