252,599 research outputs found
The creeping motion of a spherical particle normal to a deformable interface
Numerical results are presented for the approach of a rigid sphere normal to a deformable fluid-fluid interface in the velocity range for which inertial effects may be neglected. Both the case of a sphere moving with constant velocity, and that of a sphere moving under the action of a constant non-hydrodynamic body force are considered for several values of the viscosity ratio, density difference and interfacial tension between the two fluids. Two distinct modes of interface deformation are demonstrated: a film drainage mode in which fluid drains away in front of the sphere leaving an ever-thinning film, and a tailing mode where the sphere passes several radii beyond the plane of the initially undeformed interface, while remaining encapsulated by the original surrounding fluid which is connected with its main body by a thin thread-like tail behind the sphere. We consider the influence of the viscosity ratio, density difference, interfacial tension and starting position of the sphere in deter-mining which of these two modes of deformation will occur
Nuclear Incompressibility at Finite Temperature and Entropy
Features of the nuclear isothermal incompressibility and adiabatic
incompressibility are investigated. The calculations are done at
zero and finite temperatures and non zero entropy and for several equations of
state. It is shown that decreases with increasing entropy while the
isothermal increases with increasing . A duality is found between
the adiabatic and the T=0 isothermal . Our isothermal
results are compared with a recent lattice Monte Carlo calculation done at
finite . The necessity of including correlations is shown if is to
have a peak with increasing as seen in the Monte Carlo calculations. A peak
in is linked to attractive scattering correlations in two nucleons
channel in the virial expansion in our approach which are Pauli blocked at low
.Comment: 5 page
Roughening of ion-eroded surfaces
Recent experimental studies focusing on the morphological properties of
surfaces eroded by ion-bombardment report the observation of self-affine
fractal surfaces, while others provide evidence about the development of a
periodic ripple structure. To explain these discrepancies we derive a
stochastic growth equation that describes the evolution of surfaces eroded by
ion bombardment. The coefficients appearing in the equation can be calculated
explicitly in terms of the physical parameters characterizing the sputtering
process. Exploring the connection between the ion-sputtering problem and the
Kardar-Parisi-Zhang and Kuramoto-Sivashinsky equations, we find that
morphological transitions may take place when experimental parameters, such as
the angle of incidence of the incoming ions or their average penetration depth,
are varied. Furthermore, the discussed methods allow us to calculate
analytically the ion-induced surface diffusion coefficient, that can be
compared with experiments. Finally, we use numerical simulations of a one
dimensional sputtering model to investigate certain aspects of the ripple
formation and roughening.Comment: 20 pages, LaTeX, 5 ps figures, contribution to the 4th CTP Workshop
on Statistical Physics "Dynamics of Fluctuating Interfaces and Related
Phenomena", Seoul National University, Seoul, Korea, January 27-31, 199
On the anomalous component
The so-called anomalous cosmic ray component, which occurs at energies of about 10 MeV/nucleon and consists only of He, N, O, and Ne, has been a subject of interest for more than a decade. The origin of this component is generally considered to be interstellar neutral gas that is ionized and accelerated in the solar wind. The mechanism and the location for the acceleration, however, remains an unsolved problem. A model is used which includes the effects of gradient and curvature drifts and considers the implications of observed spatial gradients of the anomalous component for the location of the acceleration region. It is concluded that if drifts are important the acceleration region cannot lie at the solar poles. It is also concluded that there is no single region for the acceleration which can account for both the observed intensities and gradients in models which include drift effects
Liquid-Gas Phase Transition in Nuclear Equation of State
A canonical ensemble model is used to describe a caloric curve of nuclear
liquid-gas phase transition. Allowing a discontinuity in the freeze out density
from one spinodal density to another for a given initial temperature, the
nuclear liquid-gas phase transition can be described as first order. Averaging
over various freeze out densities of all the possible initial temperatures for
a given total reaction energy, the first order characteristics of liquid-gas
phase transition is smeared out to a smooth transition. Two experiments, one at
low beam energy and one at high beam energy show different caloric behaviors
and are discussed.Comment: 12 pages in Revtex including two Postscript figure
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