617 research outputs found
Scattering Phases and Density of States for Exterior Domain
For a bounded open domain with connected complement and
piecewise smooth boundary, we consider the Dirichlet Laplacian -\DO on
and the S-matrix on the complement . Using the restriction
of to the boundary of , we establish that
is trace class when is negative and
give bounds on the energy dependence of this difference. This allows for
precise bounds on the total scattering phase, the definition of a
-function, and a Krein spectral formula, which improve similar results
found in the literature.Comment: 15 pages, Postscript, A
Description of nuclear systems with a self-consistent configuration-mixing approach. I: Theory, algorithm, and application to the C test nucleus
Although self-consistent multi-configuration methods have been used for
decades to address the description of atomic and molecular many-body systems,
only a few trials have been made in the context of nuclear structure. This work
aims at the development of such an approach to describe in a unified way
various types of correlations in nuclei, in a self-consistent manner where the
mean-field is improved as correlations are introduced. The goal is to reconcile
the usually set apart Shell-Model and Self-Consistent Mean-Field methods. This
approach is referred as "variational multiparticle-multihole configuration
mixing method". It is based on a double variational principle which yields a
set of two coupled equations that determine at the same time the expansion
coefficients of the many-body wave function and the single particle states. The
formalism is derived and discussed in a general context, starting from a
three-body Hamiltonian. Links to existing many-body techniques such as the
formalism of Green's functions are established. First applications are done
using the two-body D1S Gogny effective force. The numerical procedure is tested
on the C nucleus in order to study the convergence features of the
algorithm in different contexts. Ground state properties as well as
single-particle quantities are analyzed, and the description of the first
state is examined. This study allows to validate our numerical algorithm and
leads to encouraging results. In order to test the method further, we will
realize in the second article of this series, a systematic description of more
nuclei and observables obtained by applying the newly-developed numerical
procedure with the same Gogny force. As raised in the present work,
applications of the variational multiparticle-multihole configuration mixing
method will however ultimately require the use of an extended and more
constrained Gogny force.Comment: 22 pages, 18 figures, accepted for publication in Phys. Rev. C. v2:
minor corrections and references adde
Temporal relation between quiet-Sun transverse fields and the strong flows detected by IMaX/SUNRISE
Localized strongly Doppler-shifted Stokes V signals were detected by
IMaX/SUNRISE. These signals are related to newly emerged magnetic loops that
are observed as linear polarization features. We aim to set constraints on the
physical nature and causes of these highly Doppler-shifted signals. In
particular, the temporal relation between the appearance of transverse fields
and the strong Doppler shifts is analyzed in some detail. We calculated the
time difference between the appearance of the strong flows and the linear
polarization. We also obtained the distances from the center of various
features to the nearest neutral lines and whether they overlap or not. These
distances were compared with those obtained from randomly distributed points on
observed magnetograms. Various cases of strong flows are described in some
detail. The linear polarization signals precede the appearance of the strong
flows by on average 84+-11 seconds. The strongly Doppler-shifted signals are
closer (0.19") to magnetic neutral lines than randomly distributed points
(0.5"). Eighty percent of the strongly Doppler-shifted signals are close to a
neutral line that is located between the emerging field and pre-existing
fields. That the remaining 20% do not show a close-by pre-existing field could
be explained by a lack of sensitivity or an unfavorable geometry of the
pre-existing field, for instance, a canopy-like structure. Transverse fields
occurred before the observation of the strong Doppler shifts. The process is
most naturally explained as the emergence of a granular-scale loop that first
gives rise to the linear polarization signals, interacts with pre-existing
fields (generating new neutral line configurations), and produces the observed
strong flows. This explanation is indicative of frequent small-scale
reconnection events in the quiet Sun.Comment: 11 pages, 8 figure
A note on the Landauer principle in quantum statistical mechanics
The Landauer principle asserts that the energy cost of erasure of one bit of
information by the action of a thermal reservoir in equilibrium at temperature
T is never less than . We discuss Landauer's principle for quantum
statistical models describing a finite level quantum system S coupled to an
infinitely extended thermal reservoir R. Using Araki's perturbation theory of
KMS states and the Avron-Elgart adiabatic theorem we prove, under a natural
ergodicity assumption on the joint system S+R, that Landauer's bound saturates
for adiabatically switched interactions. The recent work of Reeb and Wolf on
the subject is discussed and compared
The formation and disintegration of magnetic bright points observed by Sunrise/IMaX
The evolution of the physical parameters of magnetic bright points (MBPs)
located in the quiet Sun (mainly in the interwork) during their lifetime is
studied. First we concentrate on the detailed description of the magnetic field
evolution of three MBPs. This reveals that individual features follow
different, generally complex, and rather dynamic scenarios of evolution. Next
we apply statistical methods on roughly 200 observed MBP evolutionary tracks.
MBPs are found to be formed by the strengthening of an equipartition field
patch, which initially exhibits a moderate downflow. During the evolution,
strong downdrafts with an average velocity of 2.4 km/s set in. These flows,
taken together with the concurrent strengthening of the field, suggest that we
are witnessing the occurrence of convective collapses in these features,
although only 30% of them reach kG field strengths. This fraction might turn
out to be larger when the new 4 m class solar telescopes are operational as
observations of MBPs with current state of the art instrumentation could still
be suffering from resolution limitations. Finally, when the bright point
disappears (although the magnetic field often continues to exist) the magnetic
field strength has dropped to the equipartition level and is generally somewhat
weaker than at the beginning of the MBP's evolution. Noteworthy is that in
about 10% of the cases we observe in the vicinity of the downflows small-scale
strong (exceeding 2 km/s) intergranular upflows related spatially and
temporally to these downflows.Comment: 19 pages, 13 figures; final version published in "The Astrophysical
Journal
A Goldstone Theorem in Thermal Relativistic Quantum Field Theory
We prove a Goldstone Theorem in thermal relativistic quantum field theory,
which relates spontaneous symmetry breaking to the rate of space-like decay of
the two-point function. The critical rate of fall-off coincides with that of
the massless free scalar field theory. Related results and open problems are
briefly discussed
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