9,774 research outputs found
A new hypothesis of sunspot formation
The process of sunspot formation is considered with the account of heat
effects. According to the Le Chatelier principle, a local overheating must
precede to the cooling of solar surface in the places of sunspot formation. The
sunspot dynamics is a process close to the surface nucleate-free boiling in a
thin layer with formation of bubbles (or craters), so we focus on the analogy
between these two processes. Solar spots and surface nucleate-free boiling in a
thin layer have similarities in formation conditions, results of impact on the
surface were they have been formed, periodicity, and their place in the
hierarchy of self-organization in complex systems. The difference is in the
working medium and method of channelling of extra energy from the overheated
surface -for boiling process, the energy is forwarded to generation of vapor,
and in sunspots the solar energy is consumed to formation of a strong magnetic
field. This analogy explains the problem of a steady brightness (temperature)
of a spot that is independent of the spot size and other characteristics.Comment: 10 pages in LaTeX, 5 figures (JPEG
Microscopic Theory for Emission of Elementary Excitations into He II from a Heated Solid
I develop here the microscopic quantum theory for description of creation of
phonons and rotons in superfluid helium by a solid heater. Starting with
correct transfer Hamiltonian describing a coupling between the solid and liquid
He the probabilities of transformation of a single phonon in the solid into
i) single helium phonon, ii) two helium phonons, and iii) single helium roton
are found out. All the obtained expressions account for different polarizations
of phonons in the solid. The heat transfer associated with single phonon and
single roton channels are calculated. Particularly, the obtained expression for
heat flux via the single phonon channel calculated in the framework of present
microscopic theory exactly coincides with the well known Khalatnikov formula
obtained initially in the framework of acoustic-mismatch theory. The
impossibility of direct creation of R rotons becomes clear in the used
framework due to accurate account of the boundary conditions at the solid --
liquid helium interface, which is in agreement with recent experimental
results.Comment: 13 pages, 4 eps figure
Lagrangian subspaces, delta-matroids and four-term relations
Finite order invariants (Vassiliev invariants) of knots are expressed in
terms of weight systems, that is, functions on chord diagrams satisfying the
four-term relations. Weight systems have graph analogues, so-called
-invariants of graphs, i.e. functions on graphs that satisfy the four-term
relations for graphs. Each -invariant determines a weight system. The notion
of weight system is naturally generalized for the case of embedded graphs with
an arbitrary number of vertices. Such embedded graphs correspond to links; to
each component of a link there corresponds a vertex of an embedded graph.
Recently, two approaches have been suggested to extend the notion of
-invariants of graphs to the case of combinatorial structures corresponding
to embedded graphs with an arbitrary number of vertices. The first approach is
due to V.~Kleptsyn and E.~Smirnov, who considered functions on Lagrangian
subspaces in a -dimensional space over endowed with a
standard symplectic form and introduced four-term relations for them. On the
other hand, the second approach, the one due to Zhukov and Lando, suggests
four-term relations for functions on binary delta-matroids. In this paper, we
prove that the two approaches are equivalent
Relaxation times hierarchy in two-component quasiparticle gas
A quasiparticle description of various condensed media is a very popular tool
in study of their transport and thermodynamic properties. I present here a
microscopic theory for the description of diffusion processes in two-component
gas of quasiparticles with arbitrary dispersion law and statistics.
Particularly, I analyze the role of interaction within each subsystem (i.e.
between identical quasiparticles) in relaxation of the whole system. The
approach for solution of such kinetic problem allows to study the most
important limiting cases and to clarify their physical sense. Classical results
for diffusion coefficient of light particles in a massive gas (Lorentz model)
and of massive particles in a light gas (Rayleigh model) are obtained directly
from the general solution without using artificial approaches, as it was done
earlier. This particularly provide a possibility to generalize these popular
models on quasiparticle systems.Comment: 10 pages, REVTe
Internal Spatial Oscillations in a Single Trapped Bose--Einstein Condensate
I predict the existence of internal spatial currents in a {\it single}
macroscopic quantum system, namely in trapped dilute-gas at sufficiently low
temperatures, when a Bose-Einstein condensation occurs. The spatial profiles of
the wavefunctions of low-lying states in such a system are different due to the
inhomogeneity, caused by an asymmetry of external trapping potential. This is
the reason for appearing of Josephson--like oscillations between atomic
subsystems in different states including the ground state as well. Using a
simple model for the wavefunctions of three low-lying states we demonstrate how
essential this effect can be. The possible applications of the predicted effect
are briefly discussed. Particularly, this effect opens the possibility to
identify experimentally the low lying excited states of a system.Comment: 7 REVTeX pages, 4 ps figure
Continuum excitations of O in a three-body model: and states
The structure and decay dynamics for and continuum excitations of
O are investigated in a three-body O++ model. The validity
of a simple approximation for the cross section profile for long-lived
emission is demonstrated. A sequence of three monopole ("breathing mode"
type) excited states is predicted. These states could probably be interpreted
as analogues of Efimov states pushed in the continuum due to insufficient
binding. The calculated energies of the states are related to the
excitation spectrum of O. We discuss the correlation between the
predicted O spectrum and experimental observations.Comment: 9 pages, 8 figure
Confinement of Cosmic Rays in Dark Matter clumps
Some part of the relic Dark Matter is distributed in small-scale clumps which
survived structure formation in inflation cosmological scenario. The
annihilation of DM inside these clumps is a strong source of stable charged
particles which can have a substantial density near the clump core. The
streaming of the annihilation products from the clump can enhance
irregularities in the galactic magnetic field. This can produce small scale
variations in diffusion coefficient affecting propagation of Cosmic Rays.Comment: Contribution to the 30 ICRC, July 2007, Merida, Mexic
GK Per and EX Hya: Intermediate polars with small magnetospheres
Observed hard X-ray spectra of intermediate polars are determined mainly by
the accretion flow velocity at the white dwarf surface, which is normally close
to the free-fall velocity. This allows to estimate the white dwarf masses as
the white dwarf mass-radius relation M-R and the expected free-fall velocities
at the surface are well known. This method is widely used, however, derived
white dwarf masses M can be systematically underestimated because the accretion
flow is stopped at and re-accelerates from the magnetospheric boundary R_m, and
therefore, its velocity at the surface will be lower than free-fall.To avoid
this problem we computed a two-parameter set of model hard X-ray spectra, which
allows to constrain a degenerate M - R_m dependence. On the other hand,
previous works showed that power spectra of accreting X-ray pulsars and
intermediate polars exhibit breaks at the frequencies corresponding to the
Keplerian frequencies at the magnetospheric boundary. Therefore, the break
frequency \nu_b in an intermediate polar power spectrum gives another relation
in the M - R_m plane. The intersection of the two dependences allows,
therefore, to determine simultaneously the white dwarf mass and the
magnetospheric radius. To verify the method we analyzed the archival Suzaku
observation of EX Hya obtaining M /M_sun= 0.73 \pm 0.06 and R_ m / R = 2.6 \pm
0.4 consistent with the values determined by other authors. Subsequently, we
applied the same method to a recent NuSTAR observation of another intermediate
polar GK~Per performed during an outburst and found M/M_sun = 0.86 \pm 0.02 and
R_ m / R = 2.8 \pm 0.2. The long duration observations of GK Per in quiescence
performed by Swift/BAT and INTEGRAL observatories indicate increase of
magnetosphere radius R_m at lower accretion rates.Comment: 12 pages, 17 figures, submitted to Astronomy and Astrophysic
Anomalous pH-gradient in Ampholyte Solution
A mathematical model describing a steady pH-gradient in the solution of
ampholytes in water has been studied with the use of analytical, asymptotic,
and numerical methods. We show that at the large values of an electric current
a concentration distribution takes the form of a piecewise constant function
that is drastically different from a classical Gaussian form. The correspondent
pH-gradient takes a stepwise form, instead of being a linear function. A
discovered anomalous pH-gradient can crucially affect the understanding of an
isoelectric focusing process.Comment: 5 pages, 2 figure
Mathematical Model of a pH-gradient Creation at Isoelectrofocusing. Part II. Numerical Solution of the Stationary Problem
The mathematical model describing the natural textrm{pH}-gradient arising
under the action of an electric field in an aqueous solution of ampholytes
(amino acids) is constructed and investigated. This paper is the second part of
the series papers \cite{Part1,Part3,Part4} that are devoted to pH-gradient
creation problem. We present the numerical solution of the stationary problem.
The equations system has a small parameter at higher derivatives and the
turning points, so called stiff problem. To solve this problem numerically we
use the shooting method: transformation of the boundary value problem to the
Cauchy problem. At large voltage or electric current density we compare the
numerical solution with weak solution presented in Part 1.Comment: 14 pages, 8 figure
- …