7,261 research outputs found
Dynamics of nearly spherical vesicles in an external flow
We analytically derive an equation describing vesicle evolution in a fluid
where some stationary flow is excited regarding that the vesicle shape is close
to a sphere. A character of the evolution is governed by two dimensionless
parameters, and , depending on the vesicle excess area, viscosity
contrast, membrane viscosity, strength of the flow, bending module, and ratio
of the elongation and rotation components of the flow. We establish the ``phase
diagram'' of the system on the plane: we find curves corresponding
to the tank-treading to tumbling transition (described by the saddle-node
bifurcation) and to the tank-treading to trembling transition (described by the
Hopf bifurcation).Comment: 4 pages, 1 figur
Triple galaxies and a hidden mass problem
The authors consider a homogeneous sample of 84 triple systems of galaxies with components brighter than m = 15.7, located in the northern sky and satisfying an isolation criterion with respect to neighboring galaxies in projection. The distributions of basic dynamical parameters for triplets have median values as follows: radial velocity dispersion 133 km/s, mean harmonic radius 63 kpc, absolute magnitude of galaxies M sub B equals -20.38, crossing time tau = 0.04 H(sup minus 1). For different ways of estimation the median mass-to-luminosity ratio is (20 - 30). A comparison of the last value with the ones for single and binary galaxies shows the presence of a virial mass excess for triplets by a factor 4. The mass-to-luminosity ratio is practically uncorrelated with linear size of triplets or with morphological types of their components. We note that a significant part of the virial excess may be explained by the presence of nonisolated triple configurations in the sample, which are produced by debris of more populous groups of galaxies
The probability distribution of the number of electron-positron pairs produced in a uniform electric field
The probability-generating function of the number of electron-positron pairs
produced in a uniform electric field is constructed. The mean and variance of
the numbers of pairs are calculated, and analytical expressions for the
probability of low numbers of electron-positron pairs are given. A recursive
formula is derived for evaluating the probability of any number of pairs. In
electric fields of supercritical strength |eE| > \pi m^2/ \ln 2, where e is the
electron charge, E is the electric field, and m is the electron mass, a
branch-point singularity of the probability-generating function penetrates the
unit circle |z| = 1, which leads to the asymptotic divergence of the cumulative
probability. This divergence indicates a failure of the continuum limit
approximation. In the continuum limit and for any field strength, the positive
definiteness of the probability is violated in the tail of the distribution.
Analyticity, convergence, and positive definiteness are restored upon the
summation over discrete levels of electrons in the normalization volume.
Numerical examples illustrating the field strength dependence of the asymptotic
behavior of the probability distribution are presented.Comment: 7 pages, REVTeX, 4 figures; new references added; a short version of
this e-print has appeared in PR
Auxiliary Basis Sets for Grid-Free Density Functional Theory
Density functional theory(DFT) has gained popularity because it can frequently give accurate energies and geometries. The evaluation of DFT integrals in a fully analytical manner is generally impossible; thus, most implementations use numerical quadrature over grid points. The grid-free approaches were developed as a viable alternative based upon the resolution of the identity (RI). Of particular concern is the convergence of the RI with respect to basis set in the grid-free approach. Conventional atomic basis sets are inadequate for fitting the RI, particularly for gradient corrected functionals [J. Chem. Phys. 108, 9959 (1998)]. The focus of this work is on implementation of and selection of auxiliary basis sets. Auxiliary basis sets of varying sizes are studied and those with sufficient flexibility are found to adequately represent the RI
Strong light-matter coupling: parametric interactions in a cavity and free-space
We consider parametric interactions of laser pulses in a coherent macroscopic
ensemble of resonant atoms, which are possible in the strong coupling regime of
light-matter interaction. The spectrum condensation (lasing at collective
vacuum Rabi sidebands) was studied in an active cavity configuration.
Parametric interactions under the strong light-matter coupling were proved even
in free space. In contrast to bichromatic beats in a cavity, they were shown to
appear due to interference between polaritonic wave packets of different group
velocities.Comment: 4 pages, 2 figure
High-throughput synthesis of thermoelectric CaCoO films
Properties of complex oxide thin films can be tuned over a range of values as
a function of mismatch, composition, orientation, and structure. Here, we
report a strategy for growing structured epitaxial thermoelectric thin films
leading to improved Seebeck coefficient. Instead of using single-crystal
sapphire substrates to support epitaxial growth, CaCoO films are
deposited, using the Pulsed Laser Deposition technique, onto AlO
polycrystalline substrates textured by Spark Plasma Sintering. The structural
quality of the 2000 \AA thin film was investigated by Transmission Electron
Microscopy, while the crystallographic orientation of the grains and the
epitaxial relationships were determined by Electron Back Scatter Diffraction.
The use of a polycrystalline ceramic template leads to structured films that
are in good local epitaxial registry. The Seebeck coefficient is about 170
V/K at 300 K, a typical value of misfit material with low carrier density.
This high-throughput process, called combinatorial substrate epitaxy, appears
to facilitate the rational tuning of functional oxide films, opening a route to
the epitaxial synthesis of high quality complex oxides.Comment: Submitted to Applied Physics Letters (2013
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