742 research outputs found
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
Cavascope: the broadband seismological network of the New Hebrides subduction zone and its associated data base
Seismological Research Letters, v. 79, n. 4, p. 498-503, 2008. http://dx.doi.org/10.1785/gssrl.79.4.498International audienc
Searching for overturning convection in penumbral filaments: slit spectroscopy at 0.2 arcsec resolution
Recent numerical simulations of sunspots suggest that overturning convection
is responsible for the existence of penumbral filaments and the Evershed flow,
but there is little observational evidence of this process. Here we carry out a
spectroscopic search for small-scale convective motions in the penumbra of a
sunspot located 5 deg away from the disk center. The position of the spot is
very favorable for the detection of overturning downflows at the edges of
penumbral filaments. Our analysis is based on measurements of the Fe I 709.0 nm
line taken with the Littrow spectrograph of the Swedish 1 m Solar Telescope
under excellent seeing conditions. We compute line bisectors at different
intensity levels and derive Doppler velocities from them. The velocities are
calibrated using a nearby telluric line, with systematic errors smaller than
150 m/s. Deep in the photosphere, as sampled by the bisectors at the 80%-88%
intensity levels, we always observe blueshifts or zero velocities. The maximum
blueshifts reach 1.2 km/s and tend to be cospatial with bright penumbral
filaments. In the line core we detect blueshifts for the most part, with small
velocities not exceeding 300 m/s. Redshifts also occur, but at the level of
100-150 m/s, and only occasionally. The fact that they are visible in high
layers casts doubts on their convective origin. Overall, we do not find
indications of downflows that could be associated with overturning convection
at our detection limit of 150 m/s. Either no downflows exist, or we have been
unable to observe them because they occur beneath tau=1 or the spatial
resolution/height resolution of the measurements is still insufficient.Comment: Accepted for publication in Ap
Dynamics of multi-cored magnetic structures in the quiet Sun
We report on the dynamical interaction of quiet-Sun magnetic fields and
granular convection in the solar photosphere as seen by \textsc{Sunrise}. We
use high spatial resolution (0\farcs 15--0\farcs 18) and temporal cadence (33
s) spectropolarimetric Imaging Magnetograph eXperiment data, together with
simultaneous CN and Ca\,\textsc{ii}\,H filtergrams from \textsc{Sunrise} Filter
Imager. We apply the SIR inversion code to the polarimetric data in order to
infer the line of sight velocity and vector magnetic field in the photosphere.
The analysis reveals bundles of individual flux tubes evolving as a single
entity during the entire 23 minute data set. The group shares a common canopy
in the upper photospheric layers, while the individual tubes continually
intensify, fragment and merge in the same way that chains of bright points in
photometric observations have been reported to do. The evolution of the tube
cores are driven by the local granular convection flows. They intensify when
they are "compressed" by surrounding granules and split when they are
"squeezed" between two moving granules. The resulting fragments are usually
later regrouped in intergranular lanes by the granular flows. The continual
intensification, fragmentation and coalescence of flux results in magnetic
field oscillations of the global entity. From the observations we conclude that
the magnetic field oscillations first reported by \citet{2011ApJ...730L..37M}
correspond to the forcing by granular motions and not to characteristic
oscillatory modes of thin flux tubes.Comment: 12 pages, 7 figures. Accepted in ApJ. Animation 1 can be downloaded
from: http://spg.iaa.es/download
Quantum Hypothesis Testing and Non-Equilibrium Statistical Mechanics
We extend the mathematical theory of quantum hypothesis testing to the
general -algebraic setting and explore its relation with recent
developments in non-equilibrium quantum statistical mechanics. In particular,
we relate the large deviation principle for the full counting statistics of
entropy flow to quantum hypothesis testing of the arrow of time.Comment: 60 page
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