51,490 research outputs found
Unusual magnetic fields in the interacting spiral NGC 3627
By observing the interacting galaxy NGC 3627 in radio polarization we try to
answer the question to which degree the magnetic field follows the galactic gas
flows. We obtained total power and polarized intensity maps at 8.46 GHz and
4.85 GHz using the VLA in its compact D-configuration. In order to overcome the
zero-spacing problems, the interferometric data were combined with single-dish
measurements obtained with the Effelsberg 100-m radio telescope. The observed
magnetic field structure in NGC 3627 suggests that two field components are
superposed. One component smoothly fills the interarm space and shows up also
in the outermost disk regions, the other component follows a symmetric S-shaped
structure. In the western disk the latter component is well aligned with an
optical dust lane, following a bend which is possibly caused by external
interactions. However, in the SE disk the magnetic field crosses a heavy dust
lane segment, apparently being insensitive to strong density-wave effects. We
suggest that the magnetic field is decoupled from the gas by high turbulent
diffusion, in agreement with the large \ion{H}{i} line width in this region. We
discuss in detail the possible influence of compression effects and
non-axisymmetric gas flows on the general magnetic field asymmetries in NGC
3627. On the basis of the Faraday rotation distribution we also suggest the
existence of a large ionized halo around this galaxy.Comment: 11 pages, 11 figure
One-electron spectral functions of the attractive Hubbard model at intermediate coupling
We calculate the one-electron spectral function of the attractive-U Hubbard
model in two dimensions. We work in the intermediate coupling and low density
regime and evaluate analytically the self-energy. The results are obtained in a
framework based on the self-consistent T-matrix approximation. We also
calculate the chemical potential of the bound pairs as a function of
temperature. On the basis of this calculation we analyze the low-temperature
resistivity and specific heat in the normal state of this system. We compare
our results with recent beautiful tunneling experiments in the underdoped
regime of HTSC-materials.Comment: 2 pages, LT22 Conference paper, phbauth and elsart style files
include
Stress corrosion cracking of titanium alloys: SCC velocity: concentration of TiCl3
Stress corrosion cracking of titanium alloys, velocity of cracking in aqueous and methanol solutions and halogenated organic solvents, concentration of TiCl3 in crack
How multiplicity determines entropy and the derivation of the maximum entropy principle for complex systems
The maximum entropy principle (MEP) is a method for obtaining the most likely
distribution functions of observables from statistical systems, by maximizing
entropy under constraints. The MEP has found hundreds of applications in
ergodic and Markovian systems in statistical mechanics, information theory, and
statistics. For several decades there exists an ongoing controversy whether the
notion of the maximum entropy principle can be extended in a meaningful way to
non-extensive, non-ergodic, and complex statistical systems and processes. In
this paper we start by reviewing how Boltzmann-Gibbs-Shannon entropy is related
to multiplicities of independent random processes. We then show how the
relaxation of independence naturally leads to the most general entropies that
are compatible with the first three Shannon-Khinchin axioms, the
(c,d)-entropies. We demonstrate that the MEP is a perfectly consistent concept
for non-ergodic and complex statistical systems if their relative entropy can
be factored into a generalized multiplicity and a constraint term. The problem
of finding such a factorization reduces to finding an appropriate
representation of relative entropy in a linear basis. In a particular example
we show that path-dependent random processes with memory naturally require
specific generalized entropies. The example is the first exact derivation of a
generalized entropy from the microscopic properties of a path-dependent random
process.Comment: 6 pages, 1 figure. To appear in PNA
Numerically determined transport laws for fingering ("thermohaline") convection in astrophysics
We present the first three-dimensional simulations of fingering convection
performed in a parameter regime close to the one relevant for astrophysics, and
reveal the existence of simple asymptotic scaling laws for turbulent heat and
compositional transport. These laws can straightforwardly be extrapolated to
the true astrophysical regime. Our investigation also indicates that
thermocompositional "staircases," a key consequence of fingering convection in
the ocean, cannot form spontaneously in the fingering regime in stellar
interiors. Our proposed empirically-determined transport laws thus provide
simple prescriptions for mixing by fingering convection in a variety of
astrophysical situations, and should, from here on, be used preferentially over
older and less accurate parameterizations. They also establish that fingering
convection does not provide sufficient extra mixing to explain observed
chemical abundances in RGB stars.Comment: Submitted to ApJ Letters on October 29th. 15 pages, 4 figures. See
Garaud 2010 for companion pape
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