124 research outputs found
A mathematical model of the vertical dual-mass hydroimpulsive mechanism
In this paper, the model of a hydroimpulsive mechanism for boring machines was presented. Differential equations describing the processes occurring in the mechanism were derived
Quasi-Elastic Scattering, Random Fields and phonon-coupling effects in PbMg1/3Nb2/3O3
The low-energy part of the vibration spectrum in PbMgNbO
(PMN) relaxor ferroelectric has been studied by neutron scattering above and
below the Burns temperature, T. The transverse acoustic and the lowest
transverse optic phonons are strongly coupled and we have obtained a model for
this coupling. We observe that the lowest optic branch is always underdamped. A
resolution-limited central peak and quasi-elastic scattering appear in the
vicinity of the Burns temperature. It is shown that it is unlikely that the
quasi-elastic scattering originates from the combined effects of coupling
between TA and TO phonons with an increase of the damping of the TO phonon
below T. The quasi-elastic scattering has a peak as a function of
temperature close to the peak in the dielectric constant while the intensity of
the central peak scattering increases strongly below this temperature. These
results are discussed in terms of a random field model for relaxors
Stationary Kolmogorov Solutions of the Smoluchowski Aggregation Equation with a Source Term
In this paper we show how the method of Zakharov transformations may be used
to analyze the stationary solutions of the Smoluchowski aggregation equation
for arbitrary homogeneous kernel. The resulting massdistributions are of
Kolmogorov type in the sense that they carry a constant flux of mass from small
masses to large. We derive a ``locality criterion'', expressed in terms of the
asymptotic properties of the kernel, that must be satisfied in order for the
Kolmogorov spectrum to be an admissiblesolution. Whether a given kernel leads
to a gelation transition or not can be determined by computing the mass
capacity of the Kolmogorov spectrum. As an example, we compute the exact
stationary state for the family of
kernels, which includes both gelling and
non-gelling cases, reproducing the known solution in the case .
Surprisingly, the Kolmogorov constant is the same for all kernels in this
family.Comment: This article is an expanded version of a talk given at IHP workshop
"Dynamics, Growth and Singularities of Continuous Media", Paris July 2003.
Updated 01/04/04. Revised version with additional discussion, references
added, several typographical errors corrected. Revised version accepted for
publication by Phys. Rev.
Absorption of Soluble Gases by Atmospheric Nanoaerosols
We investigate mass transfer during absorption of atmospheric trace soluble
gases by a single droplet whose size is comparable to the molecular mean free
path in air at normal conditions. It is assumed that the trace reactant
diffuses to the droplet surface and then reacts with the substances inside the
droplet according to the first order rate law. Our analysis applies a
flux-matching theory of transport processes in gases and assumes constant
thermophysical properties of the gases and liquids. We derive an integral
equation of Volterra type for the transient molecular flux density to a liquid
droplet and solve it numerically. Numerical calculations are performed for
absorption of sulfur dioxide (SO2), dinitrogen trioxide (N2O3) and chlorine
(Cl2) by liquid nanoaerosols accompanied by chemical dissociation reaction. It
is shown that during gas absorption by nanoaerosols the kinetic effects play
significant role, and neglecting kinetic effects leads to significant
overestimation of the soluble gas flux into a droplet during all the period of
gas absorption.Comment: 9 pages, 9 figure
Strong Collapse Turbulence in Quintic Nonlinear Schr\"odinger Equation
We consider the quintic one dimensional nonlinear Schr\"odinger equation with
forcing and both linear and nonlinear dissipation. Quintic nonlinearity results
in multiple collapse events randomly distributed in space and time forming
forced turbulence. Without dissipation each of these collapses produces finite
time singularity but dissipative terms prevents actual formation of
singularity. In statistical steady state of the developed turbulence the
spatial correlation function has a universal form with the correlation length
determined by the modulational instability scale. The amplitude fluctuations at
that scale are nearly-Gaussian while the large amplitude tail of probability
density function (PDF) is strongly non-Gaussian with power-like behavior. The
small amplitude nearly-Gaussian fluctuations seed formation of large collapse
events. The universal spatio-temporal form of these events together with the
PDF for their maximum amplitudes define the power-like tail of PDF for large
amplitude fluctuations, i.e., the intermittency of strong turbulence.Comment: 14 pages, 17 figure
Concentration for One and Two Species One-Dimensional Reaction-Diffusion Systems
We look for similarity transformations which yield mappings between different
one-dimensional reaction-diffusion processes. In this way results obtained for
special systems can be generalized to equivalent reaction-diffusion models. The
coagulation (A + A -> A) or the annihilation (A + A -> 0) models can be mapped
onto systems in which both processes are allowed. With the help of the
coagulation-decoagulation model results for some death-decoagulation and
annihilation-creation systems are given. We also find a reaction-diffusion
system which is equivalent to the two species annihilation model (A + B ->0).
Besides we present numerical results of Monte Carlo simulations. An accurate
description of the effects of the reaction rates on the concentration in
one-species diffusion-annihilation model is made. The asymptotic behavior of
the concentration in the two species annihilation system (A + B -> 0) with
symmetric initial conditions is studied.Comment: 20 pages latex, uuencoded figures at the en
Solution of classical stochastic one dimensional many-body systems
We propose a simple method that allows, in one dimension, to solve exactly a
wide class of classical stochastic many-body systems far from equilibrium. For
the sake of illustration and without loss of generality, we focus on a model
that describes the asymmetric diffusion of hard core particles in the presence
of an external source and instantaneous annihilation. Starting from a Master
equation formulation of the problem we show that the density and multi-point
correlation functions obey a closed set of integro-differential equations which
in turn can be solved numerically and/or analyticallyComment: 2 figure
How much laser power can propagate through fusion plasma?
Propagation of intense laser beams is crucial for inertial confinement
fusion, which requires precise beam control to achieve the compression and
heating necessary to ignite the fusion reaction. The National Ignition Facility
(NIF), where fusion will be attempted, is now under construction. Control of
intense beam propagation may be ruined by laser beam self-focusing. We have
identified the maximum laser beam power that can propagate through fusion
plasma without significant self-focusing and have found excellent agreement
with recent experimental data, and suggest a way to increase that maximum by
appropriate choice of plasma composition with implication for NIF designs. Our
theory also leads to the prediction of anti-correlation between beam spray and
backscatter and suggests the indirect control of backscatter through
manipulation of plasma ionization state or acoustic damping.Comment: 15 pages, 4 figures, submitted to Plasma Physics and Controlled
Fusio
EQUIVALENCES BETWEEN STOCHASTIC SYSTEMS
Time-dependent correlation functions of (unstable) particles undergoing
biased or unbiased diffusion, coagulation and annihilation are calculated. This
is achieved by similarity transformations between different stochastic models
and between stochastic and soluble {\em non-stochastic} models. The results
agree with experiments on one-dimensional annihilation-coagulation processes.Comment: 15 pages, Latex. Some corrections made and an appendix adde
Dynamics of cubic-tetragonal phase transition in KNbO perovskite
The low-energy part of the vibration spectrum in KNbO was studied by cold
neutron inelastic scattering in the cubic phase. In addition to acoustic
phonons, we observe strong diffuse scattering, which consists of two
components. The first one is quasi-static and has a temperature-independent
intensity. The second component appears as quasi-elastic scattering in the
neutron spectrum indicating a dynamic origin. From analysis of the inelastic
data we conclude that the quasi-elastic component and the acoustic phonon are
mutually coupled. The susceptibility associated with the quasi-elastic
component grows as the temperature approaches T
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