58,815 research outputs found
Loopy belief propagation and probabilistic image processing
Estimation of hyperparameters by maximization of the marginal likelihood in probabilistic image processing is investigated by using the cluster variation method. The algorithms are substantially equivalent to generalized loopy belief propagation
Absorption spectrum of (H2O)-O-18 in the range 12 400-14 520 cm(-1)
Fourier transform spectra recorded using (a) natural abundance water vapor, (b) (H2O)-O-18-enriched water vapor, and (c) (H2O)-O-17-enriched water vapor are analyzed. The ratio of intensities in three spectra is used to identify 927 lines due to absorption by (H2O)-O-18. Intensities and self-broadening parameters are derived for these lines. Using theoretical linelists, comparisons with previously assigned (H2O)-O-16 spectra, and automatic searches for combination differences, 747 lines are assigned. These lines belong to 14 vibrational states in the 3nu + delta and 4nu polyads. Newly determined (H2O)-O-18 vibrational band origins include 4nu(1) at 13 793.09 cm(-1), 3nu(1) + nu(3) at 13 795.40 cm(-1), 2nu(1) + 2nu(3) at 14 188.82 cm(-1), nu(1) + 3nu(3) at 14 276.34 cm(-1), and 2nu(2) + 2nu(2) + nu(3) at 13 612.71 cm(-1). These results are compared with data in HITRAN. (C) 2002 Elsevier Science (USA)
Transport through a single Anderson impurity coupled to one normal and two superconducting leads
We study the interplay between the Kondo and Andreev-Josephson effects in a
quantum dot coupled to one normal and two superconducting (SC) leads. In the
large gap limit, the low-energy states of this system can be described exactly
by a local Fermi liquid for the interacting Bogoliubov particles. The phase
shift and the renormalized parameters for the Bogoliubov particles vary
depending on the Josephson phase between the two SC leads. We explore the
precise features of a crossover that occurs between the Kondo singlet and local
Cooper-pairing states as the Josephson phase varies, using the numerical
renormalization group approach.Comment: 4 pages, 4 figures, contribution to SCES 201
Quantum anholonomies in time-dependent Aharonov-Bohm rings
Anholonomies in eigenstates are studied through time-dependent variations of
a magnetic flux in an Aharonov-Bohm ring. The anholonomies in the eigenenergy
and the expectation values of eigenstates are shown to persist beyond the
adiabatic regime. The choice of the gauge of the magnetic flux is shown to be
crucial to clarify the relationship of these anholonomies to the eigenspace
anholonomy, which is described by a non-Abelian connection in the adiabatic
limit.Comment: 6 pages. Fixed typ
Electrophoresis of a rod macroion under polyelectrolyte salt: Is mobility reversed for DNA?
By molecular dynamics simulation, we study the charge inversion phenomenon of
a rod macroion in the presence of polyelectrolyte counterions. We simulate
electrophoresis of the macroion under an applied electric field. When both
counterions and coions are polyelectrolytes, charge inversion occurs if the
line charge density of the counterions is larger than that of the coions. For
the macroion of surface charge density equal to that of the DNA, the reversed
mobility is realized either with adsorption of the multivalent counterion
polyelectrolyte or the combination of electrostatics and other mechanisms
including the short-range attraction potential or the mechanical twining of
polyelectrolyte around the rod axis.Comment: 8 pages, 5 figures, Applied Statistical Physics of Molecular
Engineering (Mexico, 2003). Journal of Physics: Condensed Matters, in press
(2004). Journal of Physics: Condensed Matters, in press (2004
Multi-State Image Restoration by Transmission of Bit-Decomposed Data
We report on the restoration of gray-scale image when it is decomposed into a
binary form before transmission. We assume that a gray-scale image expressed by
a set of Q-Ising spins is first decomposed into an expression using Ising
(binary) spins by means of the threshold division, namely, we produce (Q-1)
binary Ising spins from a Q-Ising spin by the function F(\sigma_i - m) = 1 if
the input data \sigma_i \in {0,.....,Q-1} is \sigma_i \geq m and 0 otherwise,
where m \in {1,....,Q-1} is the threshold value. The effects of noise are
different from the case where the raw Q-Ising values are sent. We investigate
which is more effective to use the binary data for transmission or to send the
raw Q-Ising values. By using the mean-field model, we first analyze the
performance of our method quantitatively. Then we obtain the static and
dynamical properties of restoration using the bit-decomposed data. In order to
investigate what kind of original picture is efficiently restored by our
method, the standard image in two dimensions is simulated by the mean-field
annealing, and we compare the performance of our method with that using the
Q-Ising form. We show that our method is more efficient than the one using the
Q-Ising form when the original picture has large parts in which the nearest
neighboring pixels take close values.Comment: latex 24 pages using REVTEX, 10 figures, 4 table
A Novel Approach in Constraining Electron Spectra in Blazar Jets: The Case of Markarian 421
We report results from the observations of the well studied TeV blazar Mrk
421 with the Swift and the Suzaku satellites in December 2008. During the
observation, Mrk 421 was found in a relatively low activity state, with the
corresponding 2-10 keV flux of erg/s/cm^2. For the purpose
of robust constraining the UV-to-X-ray emission continuum we selected only the
data corresponding to truly simultaneous time intervals between Swift and
Suzaku, allowing us to obtain a good-quality, broad-band spectrum despite a
modest length (0.6 ksec) exposure. We analyzed the spectrum with the parametric
forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different
representations of the underlying electron energy distribution, both well
motivated by the current particle acceleration models: a power-law distribution
above the minimum energy with an exponential cutoff at the
maximum energy , and a modified ultra-relativistic Maxwellian
with an equilibrium energy . We found that the latter implies
unlikely physical conditions within the blazar zone of Mrk 421. On the other
hand, the exponentially moderated power-law electron distribution gives two
possible sets of the model parameters: (i) flat spectrum with low minimum electron energy , and
(ii) steep spectrum with high minimum electron energy
. We discuss different interpretations of
both possibilities in the context of a diffusive acceleration of electrons at
relativistic, sub- or superluminal shocks. We also comment on how exactly the
gamma-ray data can be used to discriminate between the proposed different
scenarios.Comment: 18 pages, 2 figures; accepted for publication in the Astrophysical
Journa
Vacuum Energy Density for Massless Scalar Fields in Flat Homogeneous Spacetime Manifolds with Nontrivial Topology
Although the observed universe appears to be geometrically flat, it could
have one of 18 global topologies. A constant-time slice of the spacetime
manifold could be a torus, Mobius strip, Klein bottle, or others. This global
topology of the universe imposes boundary conditions on quantum fields and
affects the vacuum energy density via Casimir effect. In a spacetime with such
a nontrivial topology, the vacuum energy density is shifted from its value in a
simply-connected spacetime. In this paper, the vacuum expectation value of the
stress-energy tensor for a massless scalar field is calculated in all 17
multiply-connected, flat and homogeneous spacetimes with different global
topologies. It is found that the vacuum energy density is lowered relative to
the Minkowski vacuum level in all spacetimes and that the stress-energy tensor
becomes position-dependent in spacetimes that involve reflections and
rotations.Comment: 25 pages, 11 figure
Collisional energy transfer in two-component plasmas
The friction in plasmas consisting of two species with different temperatures
is discussed together with the consequent energy transfer. It is shown that the
friction between the two species has no effect on the ion acoustic mode in a
quasi-neutral plasma. Using the Poisson equation instead of the
quasi-neutrality reveals the possibility for an instability driven by the
collisional energy transfer. However, the different starting temperatures of
the two species imply an evolving equilibrium. It is shown that the relaxation
time of the equilibrium electron-ion plasma is, in fact, always shorter than
the growth rate time, and the instability can thus never effectively take
place. The results obtained here should contribute to the definite
clarification of some contradictory results obtained in the past
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