6,095 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
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
Coexistence of localized and itinerant electrons in BaFe2X3 (X = S and Se) revealed by photoemission spectroscopy
We report a photoemission study at room temperature on BaFe2X3 (X = S and Se)
and CsFe2Se3 in which two-leg ladders are formed by the Fe sites. The Fe 2p
core-level peaks of BaFe2X3 are broad and exhibit two components, indicating
that itinerant and localized Fe 3d sites coexist similar to KxFe2-ySe2. The Fe
2p core-level peak of CsFe2Se3 is rather sharp and is accompanied by a
charge-transfer satellite. The insulating ground state of CsFe2Se3 can be
viewed as a Fe2+ Mott insulator in spite of the formal valence of +2.5. The
itinerant versus localized behaviors can be associated with the stability of
chalcogen p holes in the two-leg ladder structure.Comment: 5 pages, 5 figures, Accepted in publication for Physical Review
Ultra-Transparent Antarctic Ice as a Supernova Detector
We have simulated the response of a high energy neutrino telescope in deep
Antarctic ice to the stream of low energy neutrinos produced by a supernova.
The passage of a large flux of MeV-energy neutrinos during a period of seconds
will be detected as an excess of single counting rates in all individual
optical modules. We update here a previous estimate of the performance of such
an instrument taking into account the recent discovery of absorption lengths of
several hundred meters for near-UV photons in natural deep ice. The existing
AMANDA detector can, even by the most conservative estimates, act as a galactic
supernova watch.Comment: 9 pages, Revtex file, no figures. Postscript file also available from
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.Z or from
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.
Non-Gaussianity and large-scale structure in a two-field inflationary model
Single field inflationary models predict nearly Gaussian initial conditions
and hence a detection of non-Gaussianity would be a signature of the more
complex inflationary scenarios. In this paper we study the effect on the cosmic
microwave background and on large scale structure from primordial
non-Gaussianity in a two-field inflationary model in which both the inflaton
and curvaton contribute to the density perturbations. We show that in addition
to the previously described enhancement of the galaxy bias on large scales,
this setup results in large-scale stochasticity. We provide joint constraints
on the local non-Gaussianity parameter and the ratio
of the amplitude of primordial perturbations due to the inflaton and curvaton
using WMAP and SDSS data
Molecular Density Functional Theory for water with liquid-gas coexistence and correct pressure
The solvation of hydrophobic solutes in water is special because liquid and
gas are almost at coexistence. In the common hypernetted chain approximation to
integral equations, or equivalently in the homogenous reference fluid of
molecular density functional theory, coexistence is not taken into account.
Hydration structures and energies of nanometer-scale hydrophobic solutes are
thus incorrect. In this article, we propose a bridge functional that corrects
this thermodynamic inconsistency by introducing a metastable gas phase for the
homogeneous solvent. We show how this can be done by a third order expansion of
the functional around the bulk liquid density that imposes the right pressure
and the correct second order derivatives. Although this theory is not limited
to water, we apply it to study hydrophobic solvation in water at room
temperature and pressure and compare the results to all-atom simulations. With
this correction, molecular density functional theory gives, at a modest
computational cost, quantitative hydration free energies and structures of
small molecular solutes like n-alkanes, and of hard sphere solutes whose radii
range from angstroms to nanometers. The macroscopic liquid-gas surface tension
predicted by the theory is comparable to experiments. This theory gives an
alternative to the empirical hard sphere bridge correction used so far by
several authors.Comment: 18 pages, 6 figure
Nuclear Photoabsorption at Photon Energies between 300 and 850 Mev
We construct the formula for the photonuclear total absorption cross section
using the projection method and the unitarity relation. Our treatment is very
effective when interference effects in the absorption processes on a nucleon
are strong. The disappearance of the peak around the position of the
resonance in the nuclear photoabsorption can be explained with the cooperative
effect of the interference in two-pion production processes,the Fermi motion,
the collision broadenings of and , and the pion distortion in the
nuclear medium. The change of the interference effect by the medium plays an
important role.Comment: 22pages,7figures,revtex
Phenomenological interaction between current quarks
We construct a phenomenological model which describes the dynamical chiral
symmetry breaking (DCSB) of QCD vacuum and reproduces meson spectra. Quark
condensates, the pion decay constant, and meson spectra are well reproduced by
phenomenological interaction which consists of a linear confining potential, a
Coulombic potential, and the 't Hooft determinant interaction. In this model,
the 't Hooft determinant interaction plays a important role not to only
\eta,\eta' mass difference, but other meson masses through DCSB.Comment: 18 pages, LaTe
FEATURE SELECTION APPLIED TO THE TIME-FREQUENCY REPRESENTATION OF MUSCLE NEAR-INFRARED SPECTROSCOPY (NIRS) SIGNALS: CHARACTERIZATION OF DIABETIC OXYGENATION PATTERNS
Diabetic patients might present peripheral microcirculation impairment and might benefit from physical training. Thirty-nine diabetic patients underwent the monitoring of the tibialis anterior muscle oxygenation during a series of voluntary ankle flexo-extensions by near-infrared spectroscopy (NIRS). NIRS signals were acquired before and after training protocols. Sixteen control subjects were tested with the same protocol. Time-frequency distributions of the Cohen's class were used to process the NIRS signals relative to the concentration changes of oxygenated and reduced hemoglobin. A total of 24 variables were measured for each subject and the most discriminative were selected by using four feature selection algorithms: QuickReduct, Genetic Rough-Set Attribute Reduction, Ant Rough-Set Attribute Reduction, and traditional ANOVA. Artificial neural networks were used to validate the discriminative power of the selected features. Results showed that different algorithms extracted different sets of variables, but all the combinations were discriminative. The best classification accuracy was about 70%. The oxygenation variables were selected when comparing controls to diabetic patients or diabetic patients before and after training. This preliminary study showed the importance of feature selection techniques in NIRS assessment of diabetic peripheral vascular impairmen
Vortex matching effect in engineered thin films of NbN
We report robust vortex matching effects in antidot arrays fabricated on thin
films of NbN. The near absence of hysteresis between field sweep directions
indicates a negligible residual pinning in the host thin film. Owing to the
very small coherence length of NbN thin films (), the observations
suggests the possibility of probing physics of vortices at true nanometer
length scales in suitably fabricated structures.Comment: Submitted to Appl. Phys. Let
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