1,045 research outputs found
An Analysis of the Quasicontinuum Method
The aim of this paper is to present a streamlined and fully three-dimensional
version of the quasicontinuum (QC) theory of Tadmor et al. and to analyze its
accuracy and convergence characteristics. Specifically, we assess the effect of
the summation rules on accuracy; we determine the rate of convergence of the
method in the presence of strong singularities, such as point loads; and we
assess the effect of the refinement tolerance, which controls the rate at which
new nodes are inserted in the model, on the development of dislocation
microstructures.Comment: 30 pages, 16 figures. To appear in Jornal of the Mechanics and
Physics of Solid
Liquid State Anomalies for the Stell-Hemmer Core-Softened Potential
We study the Stell-Hemmer potential using both analytic (exact and
approximate ) solutions and numerical simulations. We observe in the
liquid phase an anomalous decrease in specific volume and isothermal
compressibility upon heating, and an anomalous increase in the diffusion
coefficient with pressure. We relate the anomalies to the existence of two
different local structures in the liquid phase. Our results are consistent with
the possibility of a low temperature/high pressure liquid-liquid phase
transition.Comment: 4 pages in one gzipped ps file including 11 figures; One RevTex and
11 gzipped eps figure
Matter Wave Scattering and Guiding by Atomic Arrays
We investigate the possibility that linear arrays of atoms can guide matter
waves, much as fiber optics guide light. We model the atomic line as a quasi-1D
array of s wave point scatterers embedded in 2D. Our theoretical study reveals
how matter wave guiding arises from the interplay of scattering phenomena with
bands and conduction along the array. We discuss the conditions under which a
straight or curved array of atoms can guide a beam focused at one end of the
array.Comment: Submitted to Phys. Rev.
On the equation of state of a dense columnar liquid crystal
An accurate description of a columnar liquid crystal of hard disks at high
packing fractions is presented using an improved free-volume theory. It is
shown that the orientational entropy of the disks in the one-dimensional fluid
direction leads to a different high-density scaling pressure compared to the
prediction from traditional cell theory. Excellent quantitative agreement is
found with recent Monte-Carlo simulation results for various thermodynamic and
structural properties of the columnar state.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let
Driven Morse Oscillator: Model for Multi-photon Dissociation of Nitrogen Oxide
Within a one-dimensional semi-classical model with a Morse potential the
possibility of infrared multi-photon dissociation of vibrationally excited
nitrogen oxide was studied. The dissociation thresholds of typical driving
forces and couplings were found to be similar, which indicates that the results
were robust to variations of the potential and of the definition of
dissociation rate.
PACS: 42.50.Hz, 33.80.WzComment: old paper, 8 pages 6 eps file
Molecular Dynamic Simulation of Water Vapor and Determination of Diffusion Characteristics in the Pore
One of the varieties of pores, often found in natural or artificial building materials, are the so-called blind pores of dead-end or saccate type. Three-dimensional model of such kind of pore has been developed in this work. This model has been used for simulation of water vapor interaction with individual pore by molecular dynamics in combination with the diffusion equation method. Special investigations have been done to find dependencies between thermostats implementations and conservation of thermodynamic and statistical values of water vapor – pore system. The two types of evolution of water – pore system have been investigated: drying and wetting of the pore. Full research of diffusion coefficient, diffusion velocity and other diffusion parameters has been made
A new parametric equation of state and quark stars
It is still a matter of debate to understand the equation of state of cold
supra-nuclear matter in compact stars because of unknown on-perturbative strong
interaction between quarks. Nevertheless, it is speculated from an
astrophysical view point that quark clusters could form in cold quark matter
due to strong coupling at realistic baryon densities. Although it is hard to
calculate this conjectured matter from first principles, one can expect the
inter-cluster interaction to share some general features to nucleon-nucleon
interaction. We adopt a two-Gaussian component soft-core potential with these
general features and show that quark clusters can form stable simple cubic
crystal structure if we assume Gaussian form wave function. With this
parameterizing, Tolman-Oppenheimer-Volkoff equation is solved with reasonable
constrained parameter space to give mass-radius relation of crystalline solid
quark star. With baryon densities truncated at 2 times nuclear density at
surface and range of interaction fixed at 2fm we can reproduce similar
mass-radius relation to that obtained with bag model equations of state. The
maximum mass ranges from about 0.5 to 3 solar mass. Observed maximum pulsar
mass (about 2 solar mass) is then used to constrain parameters of this simple
interaction potential.Comment: 5 pages, 2 figure
The effects of psilocybin on cognitive and emotional functions in healthy participants : Results from a phase 1, randomised, placebo-controlled trial involving simultaneous psilocybin administration and preparation
Background: Psilocybin, a psychoactive serotonin receptor partial agonist, has been reported to acutely reduce clinical symptoms of depressive disorders. Psilocybin's effects on cognitive function have not been widely or systematically studied. Aim: The aim of this study was to explore the safety of simultaneous administration of psilocybin to healthy participants in the largest randomised controlled trial of psilocybin to date. Primary and secondary endpoints assessed the short- and longer-term change in cognitive functioning, as assessed by a Cambridge Neuropsychological Test Automated Battery (CANTAB) Panel, and emotional processing scales. Safety was assessed via endpoints which included cognitive function, assessed by CANTAB global composite score, and treatment-emergent adverse event (TEAE) monitoring. Methods: In this phase 1, randomised, double-blind, placebo-controlled study, healthy participants (n=89; mean age 36.1 years; 41 females, 48 males) were randomised to receive a single oral dose of 10 or 25 mg psilocybin, or placebo, administered simultaneously to up to six participants, with one-to-one psychological support - each participant having an assigned, dedicated therapist available throughout the session. Results: In total, 511 TEAEs were reported, with a median duration of 1.0 day; 67% of all TEAEs started and resolved on the day of administration. There were no serious TEAEs, and none led to study withdrawal. There were no clinically relevant between-group differences in CANTAB global composite score, CANTAB cognitive domain scores, or emotional processing scale scores. Conclusions: These results indicate that 10 mg and 25 mg doses of psilocybin were generally well tolerated when given to up to six participants simultaneously and did not have any detrimental short- or long-term effects on cognitive functioning or emotional processing.Peer reviewe
Casimir-Polder interaction between an excited atom and a gas dielectric medium
The Casimir-Polder potential for interaction between an excited atom and a
ground-state one in the retarded case obtained with the help of perturbation
technique drops as R^-2 with the distance between the atoms [E.A. Power,
T.Thirunamachandran, Phys. Rev. A, 47, 2539 (1993)]. It results in diverdent
integrals for interaction between an excited atom and a dilute gas medium. We
investigate interaction between two atoms embedded in a dielectric medium with
the help of non-perturbative approach. We take into account absorption of
photons in the medium. This approach solves the problem of divergence. We
consider interaction between an excited atom and a planar dielectric gas medium
of ground-state atoms. We show that the retarded interaction between an excited
atom and a gas of ground-state atoms is not oscillating but follows a simple
power law. We show that to obtain coventional non-retarded expression for the
van der Waals force between an excited atom and a dilute gas the distance
between the atom and the interface should be much smaller than the free mean
pass of a photon in the medium. Interaction between an excited atom and a
hemisphere of ground-state atoms is considered.Comment: 23 pages, 6 figure
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