26,225 research outputs found
Region of the anomalous compression under Bondi-Hoyle accretion
We investigate the properties of an axisymmetric non-magnetized gas flow
without angular momentum on a small compact object, in particular, on a
Schwarzschild black hole in the supersonic region near the object; the velocity
of the object itself is assumed to be low compared to the speed of sound at
infinity. First of all, we see that the streamlines intersect (i.e., a caustic
forms) on the symmetry axis at a certain distance from the center on the
front side if the pressure gradient is neglected. The characteristic radial
size of the region, in which the streamlines emerging from the sonic surface at
an angle no larger than to the axis intersect, is To refine the flow structure in this region, we numerically
compute the system in the adiabatic approximation without ignoring the
pressure. We estimate the parameters of the inferred region with anomalously
high matter temperature and density accompanied by anomalously high energy
release.Comment: 10 pages, 2 figure
Malmheden's theorem revisited
In 1934 H. Malmheden discovered an elegant geometric algorithm for solving
the Dirichlet problem in a ball. Although his result was rediscovered
independently by Duffin 23 years later, it still does not seem to be widely
known. In this paper we return to Malmheden's theorem, give an alternative
proof of the result that allows generalization to polyharmonic functions and,
also, discuss applications of his theorem to geometric properties of harmonic
measures in balls in Euclidean spaces
Two-dimensional shapes and lemniscates
A shape in the plane is an equivalence class of sufficiently smooth Jordan
curves, where two curves are equivalent if one can be obtained from the other
by a translation and a scaling. The fingerprint of a shape is an equivalence of
orientation preserving diffeomorphisms of the unit circle, where two
diffeomorphisms are equivalent if they differ by right composition with an
automorphism of the unit disk. The fingerprint is obtained by composing Riemann
maps onto the interior and exterior of a representative of a shape in a
suitable way. In this paper, we show that there is a one-to-one correspondence
between shapes defined by polynomial lemniscates of degree n and nth roots of
Blaschke products of degree n. The facts that lemniscates approximate all
Jordan curves in the Hausdorff metric and roots of Blaschke products
approximate all orientation preserving diffeomorphisms of the circle in the
C^1-norm suggest that lemniscates and roots of Blaschke products are natural
objects to study in the theory of shapes and their fingerprints
Glaciological and volcanological studies in the Wrangell Mountains, Alaska
There are no author-identified significant results in this report
Cold Atomic Collisions: Coherent Control of Penning and Associative Ionization
Coherent Control techniques are computationally applied to cold (1mK < T < 1
K) and ultracold (T < 1 microK) Ne*(3s,3P2) + Ar(1S0) collisions. We show that
by using various initial superpositions of the Ne*(3s,3P2) M = {-2,-1,0,1,2}
Zeeman sub-levels it is possible to reduce the Penning Ionization (PI) and
Associative Ionization (AI) cross sections by as much as four orders of
magnitude. It is also possible to drastically change the ratio of these two
processes. The results are based on combining, within the "Rotating Atom
Approximation", empirical and ab-initio ionization-widths.Comment: 4 pages, 2 tables, 2 figure
Neutrino emissivity under neutral kaon condensation
Neutrino emissivity from neutron star matter with neutral kaon condensate is
considered. It is shown that a new cooling channel is opened, and what is more,
all previously known channels acquire the greater emissivity reaching the level
of the direct URCA cycle in normal matter.Comment: 7 pages, 1 figure, to be published in Phys.Rev.C, revised version:
the sectioning changed and more discussion adde
Is There a Relationship between the Density of Primordial Black Holes in a Galaxy and the Rate of Cosmological Gamma-Ray Bursts?
The rate of accretion of matter from a solar-type star onto a primordial
black hole (PBH) that passes through it is calculated. The probability that a
PBH is captured into an orbit around a star in a galaxy is found. The mean
lifetime of the PBH in such an orbit and the rate of orbital captures of PBHs
in the galaxy are calculated. It is shown that this rate does not depend on the
mass of the PBH. This mechanism cannot make an appreciable contribution to the
rate of observed gamma-ray bursts. The density of PBHs in the galaxy can reach
a critical value - the density of the mass of dark matter in the galaxy.Comment: 7 page
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