580 research outputs found
Large Scale Structures a Gradient Lines: the case of the Trkal Flow
A specific asymptotic expansion at large Reynolds numbers (R)for the long
wavelength perturbation of a non stationary anisotropic helical solution of the
force less Navier-Stokes equations (Trkal solutions) is effectively constructed
of the Beltrami type terms through multi scaling analysis. The asymptotic
procedure is proved to be valid for one specific value of the scaling
parameter,namely for the square root of the Reynolds number (R).As a result
large scale structures arise as gradient lines of the energy determined by the
initial conditions for two anisotropic Beltrami flows of the same helicity.The
same intitial conditions determine the boundaries of the vortex-velocity tubes,
containing both streamlines and vortex linesComment: 27 pages, 2 figure
Nonlinear Dynamics of Capacitive Charging and Desalination by Porous Electrodes
The rapid and efficient exchange of ions between porous electrodes and
aqueous solutions is important in many applications, such as electrical energy
storage by super-capacitors, water desalination and purification by capacitive
deionization (or desalination), and capacitive extraction of renewable energy
from a salinity difference. Here, we present a unified mean-field theory for
capacitive charging and desalination by ideally polarizable porous electrodes
(without Faradaic reactions or specific adsorption of ions) in the limit of
thin double layers (compared to typical pore dimensions). We illustrate the
theory in the case of a dilute, symmetric, binary electrolyte using the
Gouy-Chapman-Stern (GCS) model of the double layer, for which simple formulae
are available for salt adsorption and capacitive charging of the diffuse part
of the double layer. We solve the full GCS mean-field theory numerically for
realistic parameters in capacitive deionization, and we derive reduced models
for two limiting regimes with different time scales: (i) In the
"super-capacitor regime" of small voltages and/or early times where the porous
electrode acts like a transmission line, governed by a linear diffusion
equation for the electrostatic potential, scaled to the RC time of a single
pore. (ii) In the "desalination regime" of large voltages and long times, the
porous electrode slowly adsorbs neutral salt, governed by coupled, nonlinear
diffusion equations for the pore-averaged potential and salt concentration
The profile of a narrow line after single scattering by Maxwellian electrons: relativistic corrections to the kernel of the integral kinetic equation
The frequency distribution of photons in frequency that results from single
Compton scattering of monochromatic radiation on thermal electrons is derived
in the mildly relativistic limit. Algebraic expressions are given for (1) the
photon redistribution function, K(nu,Omega -> nu',Omega'), and (2) the spectrum
produced in the case of isotropic incident radiation, P(nu -> nu'). The former
is a good approximation for electron temperatures kT_e < 25 keV and photon
energies hnu < 50 keV, and the latter is applicable when hnu(hnu/m_ec^2) < kT_e
< 25 keV, hnu < 50 keV. Both formulae can be used for describing the profiles
of X-ray and low-frequency lines upon scattering in hot, optically thin
plasmas, such as present in clusters of galaxies, in the coronae of accretion
disks in X-ray binaries and AGNs, during supernova explosions, etc. Both
formulae can also be employed as the kernels of the corresponding integral
kinetic equations (direction-dependent and isotropic) in the general problem of
Comptonization on thermal electrons. The K(nu,Omega -> nu',Omega') kernel, in
particular, is applicable to the problem of induced Compton interaction of
anisotropic low-frequency radiation of high brightness temperature with free
electrons in the vicinity of powerful radiosources and masers.
Fokker-Planck-type expansion (up to fourth order) of the integral kinetic
equation with the P(nu -> nu') kernel derived here leads to a generalization of
the Kompaneets equation. We further present (1) a simpler kernel that is
necessary and sufficient to derive the Kompaneets equation and (2) an
expression for the angular function for Compton scattering in a hot plasma,
which includes temperature and photon energy corrections to the Rayleigh
angular function.Comment: 29 pages, 17 figures, accepted for publication in ApJ, uses
emulateapj.sty, corrects misprints in previous astro-ph versio
Anomalous temperature dependence of surface tension and capillary waves at liquid gallium
The temperature dependence of surface tension \gamma(T) at liquid gallium is
studied theoretically and experimentally using light scattering from capillary
waves. The theoretical model based on the Gibbs thermodynamics relates the
temperature derivative of \gamma to the surface excess entropy -\Delta S.
Although capillary waves contribute to the surface entropy with a positive sign
the effect of dipole layer on \Delta S is negative. Experimental data collected
at a free Ga surface in the temperature range from 30 to 160 C show that the
temperature derivative of the tension changes sign near 100 C.Comment: 11 pages, 1 Postscript figure, submitted to J. Phys.
Statics and Dynamics of an Interface in a Temperature Gradient
The response and nonconserved dynamics of a two-phase interface in the
presence of a temperature gradient oriented normally to the interface are
considered. Two types of boundary conditions on the order parameter are
considered, and the structure of the effective free energy and the Langevin
equation for the collective coordinate specifying the interface position are
analyzed.Comment: 15 pages, Revtex 3.0, 5 figures available upon reques
Quantum Kinetic Theory of Condensate Growth---Comparison of Experiment and Theory
In a major extension of our previous model (C.W. Gardiner, P. Zoller,
R.J. Ballagh and M.J. Davis, Phys. Rev. Lett. 79, 1793 (1997)) of condensate
growth, we take account of the evolution of the occupations of lower trap
levels, and of the full Bose-Einstein formula for the occupations of higher
trap levels. We find good agreement with experiment, especially at higher
temperatures. We also confirm the picture of the ``kinetic'' region of
evolution, introduced by Kagan et al, for the time up to the initiation of the
condensate. The behavior after initiation essentially follows our original
growth equation, but with a substantially increased rate coefficient W^{+}.Comment: RevTeX, 4 pages and 4 eps figure
Random Sequential Adsorption: From Continuum to Lattice and Pre-Patterned Substrates
The random sequential adsorption (RSA) model has served as a paradigm for
diverse phenomena in physical chemistry, as well as in other areas such as
biology, ecology, and sociology. In the present work, we survey aspects of the
RSA model with emphasis on the approach to and properties of jammed states
obtained for large times in continuum deposition versus that on lattice
substrates, and on pre-patterned surfaces. The latter model has been of recent
interest in the context of efforts to use pre-patterning as a tool to improve
selfassembly in micro- and nanoscale surface structure engineering
Quantum Kinetic Theory V: Quantum kinetic master equation for mutual interaction of condensate and noncondensate
A detailed quantum kinetic master equation is developed which couples the
kinetics of a trapped condensate to the vapor of non-condensed particles. This
generalizes previous work which treated the vapor as being undepleted.Comment: RevTeX, 26 pages and 5 eps figure
ЕКСПЕРИМЕНТАЛЬНО-ТЕОРЕТИЧНІ ПІДХОДИ ДО СТВОРЕННЯ КОМП'ЮТЕРНОЇ ПРОГРАМИ ДЛЯ ВІРТУАЛЬНОГО СКРИНІНГУ СКАВЕНДЖЕРІВ NO В РЯДУ АЗАГЕТЕРОЦИКЛІВ
The creation of computer programs for virtual screening is an urgent task for modern pharmacology and medicine. The article shows some experimental and theoretical approaches to the creation of a computer program for virtual screening of scavengers NO in a range of azageterocycles. Methods for estimating antioxidant activity, quantum mechanical and statistical calculations are presented. Prospects and advantages of computer simulation of the activity of compounds are considered.Создание компьютерных программ для виртуального скрининга является актуальной задачей для современной фармакологии и медицины. В статье показаны некоторые экспериментально-теоретические подходы к созданию компьютерной программы для виртуального скрининга скавенджеров NO в ряду азагетероциклов. Приведены методы оценки антиоксидантной активности, квантово-механические и статистические расчеты. Рассмотрены перспективы и преимущества компьютерного моделирования активности соединений.Створення комп'ютерних програм для віртуального скринінгу є актуальним завданням для сучасної фармакології і медицини. У статті показані деякі експериментально-теоретичні підходи до створення комп'ютерної програми для віртуального скринінгу скавенджерів NO в ряду азагетероциклів. Наведено методи оцінки антиоксидантної активності, квантово-механічні та статистичні розрахунки. Розглянуто перспективи і переваги комп'ютерного моделювання активності сполук
Probing liquid surface waves, liquid properties and liquid films with light diffraction
Surface waves on liquids act as a dynamical phase grating for incident light.
In this article, we revisit the classical method of probing such waves
(wavelengths of the order of mm) as well as inherent properties of liquids and
liquid films on liquids, using optical diffraction. A combination of simulation
and experiment is proposed to trace out the surface wave profiles in various
situations (\emph{eg.} for one or more vertical, slightly immersed,
electrically driven exciters). Subsequently, the surface tension and the
spatial damping coefficient (related to viscosity) of a variety of liquids are
measured carefully in order to gauge the efficiency of measuring liquid
properties using this optical probe. The final set of results deal with liquid
films where dispersion relations, surface and interface modes, interfacial
tension and related issues are investigated in some detail, both theoretically
and experimentally. On the whole, our observations and analyses seem to support
the claim that this simple, low--cost apparatus is capable of providing a
wealth of information on liquids and liquid surface waves in a non--destructive
way.Comment: 25 pages, 12 figures, to appear in Measurement Science and Technology
(IOP
- …