19,202 research outputs found
Pressure dependence of diffusion coefficient and orientational relaxation time for acetonitrile and methanol in water: DRISM/mode-coupling study
We present results of theoretical description and numerical calculation of
the dynamics of molecular liquids based on the Reference Interaction Site Model
/ Mode-Coupling Theory. They include the temperature-pressure(density)
dependence of the translational diffusion coefficients and orientational
relaxation times for acetonitrile and methanol in water at infinite dilution.
Anomalous behavior, i.e. the increase in mobility with density, is observed for
the orientational relaxation time of methanol, while acetonitrile does not show
any deviations from the usual. This effect is in qualitative agreement with the
recent data of MD simulation and with experimental measurements, which tells us
that presented theory is a good candidate to explain such kind of anomalies
from the microscopical point of view and with the connection to the structure
of the molecules.Comment: 10 pages, 2 eps-figures, 3 table
Superconductivity in S-substituted FeTe
We have successfully synthesized a new superconducting phase of FeTe1-xSx
with a PbO-type structure. It has the simplest crystal structure in iron-based
superconductors. Superconducting transition temperature is about 10 K at x =
0.2. The upper critical field Hc2 was estimated to be ~70 T. The coherent
length was calculated to be ~2.2 nm. Because FeTe1-xSx is composed of nontoxic
elements, this material is a candidate for applications and will activate more
and more research on iron-based superconductor.Comment: 13 pages, 10 figure
Stability criteria of the Vlasov equation and quasi-stationary states of the HMF model
We perform a detailed study of the relaxation towards equilibrium in the
Hamiltonian Mean-Field (HMF) model, a prototype for long-range interactions in
-particle dynamics. In particular, we point out the role played by the
infinity of stationary states of the associated Vlasov dynamics. In this
context, we derive a new general criterion for the stability of any spatially
homogeneous distribution, and compare its analytical predictions with numerical
simulations of the Hamiltonian, finite , dynamics. We then propose and
verify numerically a scenario for the relaxation process, relying on the Vlasov
equation. When starting from a non stationary or a Vlasov unstable stationary
initial state, the system shows initially a rapid convergence towards a stable
stationary state of the Vlasov equation via non stationary states: we
characterize numerically this dynamical instability in the finite system by
introducing appropriate indicators. This first step of the evolution towards
Boltzmann-Gibbs equilibrium is followed by a slow quasi-stationary process,
that proceeds through different stable stationary states of the Vlasov
equation. If the finite system is initialized in a Vlasov stable homogenous
state, it remains trapped in a quasi-stationary state for times that increase
with the nontrivial power law . Single particle momentum distributions
in such a quasi-stationary regime do not have power-law tails, and hence cannot
be fitted by the -exponential distributions derived from Tsallis statistics.Comment: To appear in Physica
Inflation by non-minimal coupling
Inflationary scenarios based on simple non-minimal coupling and its
generalizations are studied. Generalizing the form of non-minimal coupling to
"K(phi)R" with an arbitrary function K(phi), we show that the flat potential
still is obtainable when V(phi)/K^2(phi) is asymptotically constant. Very
interestingly, if the ratio of the dimensionless self-coupling constant of the
inflaton field and the non-minimal coupling constant is small the cosmological
observables for general monomial cases are in good agreement with recent
observational data.Comment: 9 pages, 1 figur
Modulation Mechanism of TeV, GeV, and X-ray Emission in LS5039
The emission mechanism of the gamma-ray binary LS5039 in energy bands of TeV,
GeV, and X-ray is investigated. Observed light curves in LS5039 show that TeV
and GeV fluxes anticorrelate and TeV and X-ray fluxes correlate. However, such
correlated variations have not been explained yet reasonably at this stage.
Assuming that relativistic electrons are injected constantly at the location of
the compact object as a point source, and that they lose energy only by the
inverse Compton (IC) process, we calculate gamma-ray spectra and light curves
by the Monte Carlo method, including the full electromagnetic cascade process.
Moreover, we calculated X-ray spectra and light curves by using the resultant
electron distribution. As a result, we are able to reproduce qualitatively
spectra and light curves observed by HESS, Fermi, and Suzaku for the
inclination angle i = 30 dig and the index of injected electron distribution p
= 2.5. We conclude that TeV-GeV anticorrelation is due to anisotropic IC
scattering and anisotropic gamma-gamma absorption, and that TeV-X correlation
is due to the dependence of IC cooling time on orbital phases. In addition, the
constraint on the inclination angle implies that the compact object in LS5039
is a black hole.Comment: 27 pages, 7 figures, published in The Astrophysical Journa
Photon Mass Bound Destroyed by Vortices
The Particle Data Group gives an upper bound on the photon mass eV from a laboratory experiment and lists, but does not adopt, an
astronomical bound eV, both of which are based on the
plausible assumption of large galactic vector-potential. We argue that the
interpretations of these experiments should be changed, which alters
significantly the bounds on . If arises from a Higgs effect, both limits
are invalid because the Proca vector-potential of the galactic magnetic field
may be neutralized by vortices giving a large-scale magnetic field that is
effectively Maxwellian. In this regime, experiments sensitive to the Proca
potential do not yield a useful bound on . As a by-product, the non-zero
photon mass from Higgs effect predicts generation of a primordial magnetic
field in the early universe. If, on the other hand, the galactic magnetic field
is in the Proca regime, the very existence of the observed large-scale magnetic
field gives kpc, or eV.Comment: 9 pages, discussion of primordial magnetic field adde
Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile
We present results of theoretical study and numerical calculation of the
dynamics of molecular liquids based on combination of the memory equation
formalism and the reference interaction site model - RISM. Memory equations for
the site-site intermediate scattering functions are studied in the
mode-coupling approximation for the first order memory kernels, while
equilibrium properties such as site-site static structure factors are deduced
from RISM. The results include the temperature-density(pressure) dependence of
translational diffusion coefficients D and orientational relaxation times t for
acetonitrile in water, methanol in water and methanol in acetonitrile, all in
the limit of infinite dilution. Calculations are performed over the range of
temperatures and densities employing the SPC/E model for water and optimized
site-site potentials for acetonitrile and methanol. The theory is able to
reproduce qualitatively all main features of temperature and density
dependences of D and t observed in real and computer experiments. In
particular, anomalous behavior, i.e. the increase in mobility with density, is
observed for D and t of methanol in water, while acetonitrile in water and
methanol in acetonitrile do not show deviations from the ordinary behavior. The
variety exhibited by the different solute-solvent systems in the density
dependence of the mobility is interpreted in terms of the two competing origins
of friction, which interplay with each other as density increases: the
collisional and dielectric frictions which, respectively, increase and decrease
with increasing density.Comment: 13 pages, 8 eps-figures, 3 tables, RevTeX4-forma
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