17,197 research outputs found
Crystallization of the Wahnstr\"om Binary Lennard-Jones Liquid
We report observation of crystallization of the glass-forming binary
Lennard-Jones liquid first used by Wahnstr\"om [G. Wahnstr\"om, Phys. Rev. A
44, 3752 (1991)]. Molecular dynamics simulations of the metastable liquid on a
timescale of microseconds were performed. The liquid crystallized
spontaneously. The crystal structure was identified as MgZn_2. Formation of
transient crystallites is observed in the liquid. The crystallization is
investigate at different temperatures and compositions. At high temperature the
rate of crystallite formation is the limiting factor, while at low temperature
the limiting factor is growth rate. The melting temperature of the crystal is
estimated to be T_m=0.93 at rho=0.82. The maximum crystallization rate of the
A_2B composition is T=0.60+/-0.02.Comment: 4 pages, 4 figures; corrected typo
Inflammation and changes in cytokine levels in neurological feline infectious peritonitis.
Feline infectious peritonitis (FIP) is a progressive, fatal, predominantly Arthus-type immune-mediated disease that is triggered when cats are infected with a mutant enteric coronavirus. The disease presents variably with multiple organ failure, seizures, generalized effusion, or shock. Neurological FIP is clinically and pathologically more homogeneous than systemic 'wet' or 'dry' FIP; thus, comparison of cytokine profiles from cats with neurological FIP, wet FIP, and non-FIP neurological disease may provide insight into some baseline characteristics relating to the immunopathogenesis of neurological FIP. This study characterizes inflammation and changes in cytokines in the brain tissue of FIP-affected cats. Cellular infiltrates in cats with FIP included lymphocytes, plasma cells, neutrophils, macrophages, and eosinophils. IL-1 beta, IL-6, IL-12, IL-18, TNF-alpha, macrophage inhibitory protein (MIP)-1 alpha, and RANTES showed no upregulation in the brains of control cats, moderate upregulation in neurological FIP cats, and very high upregulation in generalized FIP cats. Transcription of IFN-gamma appeared upregulated in cats with systemic FIP and slightly downregulated in neurological FIP. In most cytokines tested, variance was extremely high in generalized FIP and much less in neurological FIP. Principal components analysis was performed in order to find the least number of 'components' that would summarize the cytokine profiles in cats with neurological FIP. A large component of the variance (91.7%) was accounted for by levels of IL-6, MIP-1 alpha, and RANTES. These findings provide new insight into the immunopathogenesis of FIP and suggest targets for immune therapy of this disease
Strong pressure-energy correlations in liquids as a configuration space property: Simulations of temperature down jumps and crystallization
Computer simulations recently revealed that several liquids exhibit strong
correlations between virial and potential energy equilibrium fluctuations in
the NVT ensemble [U. R. Pedersen {\it et al.}, Phys. Rev. Lett. {\bf 100},
015701 (2008)]. In order to investigate whether these correlations are present
also far from equilibrium constant-volume aging following a temperature down
jump from equilibrium was simulated for two strongly correlating liquids, an
asymmetric dumbbell model and Lewis-Wahnstr{\"o}m OTP, as well as for SPC water
that is not strongly correlating. For the two strongly correlating liquids
virial and potential energy follow each other closely during the aging towards
equilibrium. For SPC water, on the other hand, virial and potential energy vary
with little correlation as the system ages towards equilibrium. Further proof
that strong pressure-energy correlations express a configuration space property
comes from monitoring pressure and energy during the crystallization (reported
here for the first time) of supercooled Lewis-Wahnstr{\"o}m OTP at constant
temperature
A repulsive reference potential reproducing the dynamics of a liquid with attractions
A well-known result of liquid state theory is that the structure of dense
fluids is mainly determined by repulsive forces. The WCA potential, which cuts
intermolecular potentials at their minima, is therefore often used as a
reference. However, this reference gives quite wrong results for the viscous
dynamics of the Kob-Andersen binary Lennard-Jones liquid [Berthier and Tarjus,
Phys. Rev. Lett. 103, 170601 (2009)]. We show that repulsive inverse-power law
potentials provide a useful reference for this liquid by reproducing its
structure, dynamics, and isochoric heat capacity
Pressure-energy correlations in liquids. V. Isomorphs in generalized Lennard-Jones systems
This series of papers is devoted to identifying and explaining the properties
of strongly correlating liquids, i.e., liquids with more than 90% correlation
between their virial W and potential energy U fluctuations in the NVT ensemble.
Paper IV [N. Gnan et al., J. Chem. Phys. v131, 234504 (2009)] showed that
strongly correlating liquids have "isomorphs", which are curves in the phase
diagram along which structure, dynamics, and some thermodynamic properties are
invariant in reduced units. In the present paper, using the fact that
reduced-unit radial distribution functions are isomorph invariant, we derive an
expression for the shapes of isomorphs in the WU phase diagram of generalized
Lennard-Jones systems of one or more types of particles. The isomorph shape
depends only on the Lennard-Jones exponents; thus all isomorphs of standard
Lennard-Jones systems (with exponents 12 and 6) can be scaled onto to a single
curve. Two applications are given. One is testing the prediction that the
solid-liquid coexistence curve follows an isomorph by comparing to recent
simulations by Ahmed and Sadus [J. Chem. Phys. v131, 174504 (2009)]. Excellent
agreement is found on the liquid side of the coexistence, whereas the agreement
is worse on the solid side. A second application is the derivation of an
approximate equation of state for generalized Lennard-Jones systems by
combining the isomorph theory with the Rosenfeld-Tarazona expression for the
temperature dependence of potential energy on isochores. It is shown that the
new equation of state agrees well with simulations.Comment: 12 pages, 14 figures, Section on solid-liquid coexistence expande
Estimating the density scaling exponent of viscous liquids from specific heat and bulk modulus data
It was recently shown by computer simulations that a large class of liquids
exhibits strong correlations in their thermal fluctuations of virial and
potential energy [Pedersen et al., Phys. Rev. Lett. 100, 015701 (2008)]. Among
organic liquids the class of strongly correlating liquids includes van der
Waals liquids, but excludes ionic and hydrogen-bonding liquids. The present
note focuses on the density scaling of strongly correlating liquids, i.e., the
fact their relaxation time tau at different densities rho and temperatures T
collapses to a master curve according to the expression tau propto
F(rho^gamma/T) [Schroder et al., arXiv:0803.2199]. We here show how to
calculate the exponent gamma from bulk modulus and specific heat data, either
measured as functions of frequency in the metastable liquid or extrapolated
from the glass and liquid phases to a common temperature (close to the glass
transition temperature). Thus an exponent defined from the response to highly
nonlinear parameter changes may be determined from linear response
measurements
Impact of comorbidity on the association between surgery delay and mortality in hip fracture patients:A Danish nationwide cohort study
Commuting self-adjoint extensions of symmetric operators defined from the partial derivatives
We consider the problem of finding commuting self-adjoint extensions of the
partial derivatives {(1/i)(\partial/\partial x_j):j=1,...,d} with domain
C_c^\infty(\Omega) where the self-adjointness is defined relative to
L^2(\Omega), and \Omega is a given open subset of R^d. The measure on \Omega is
Lebesgue measure on R^d restricted to \Omega. The problem originates with I.E.
Segal and B. Fuglede, and is difficult in general. In this paper, we provide a
representation-theoretic answer in the special case when \Omega=I\times\Omega_2
and I is an open interval. We then apply the results to the case when \Omega is
a d-cube, I^d, and we describe possible subsets \Lambda of R^d such that
{e^(i2\pi\lambda \dot x) restricted to I^d:\lambda\in\Lambda} is an orthonormal
basis in L^2(I^d).Comment: LaTeX2e amsart class, 18 pages, 2 figures; PACS numbers 02.20.Km,
02.30.Nw, 02.30.Tb, 02.60.-x, 03.65.-w, 03.65.Bz, 03.65.Db, 61.12.Bt,
61.44.B
Einstein-Weyl structures corresponding to diagonal K\"ahler Bianchi IX metrics
We analyse in a systematic way the four dimensionnal Einstein-Weyl spaces
equipped with a diagonal K\"ahler Bianchi IX metric. In particular, we show
that the subclass of Einstein-Weyl structures with a constant conformal scalar
curvature is the one with a conformally scalar flat - but not necessarily
scalar flat - metric ; we exhibit its 3-parameter distance and Weyl one-form.
This extends previous analysis of Pedersen, Swann and Madsen , limited to the
scalar flat, antiself-dual case. We also check that, in agreement with a
theorem of Derdzinski, the most general conformally Einstein metric in the
family of biaxial K\"ahler Bianchi IX metrics is an extremal metric of Calabi,
conformal to Carter's metric, thanks to Chave and Valent's results.Comment: 15 pages, Latex file, minor modifications, to be published in Class.
Quant. Gra
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