1,469 research outputs found
Coherent States of the q--Canonical Commutation Relations
For the -deformed canonical commutation relations for in some Hilbert
space we consider representations generated from a vector
satisfying , where .
We show that such a representation exists if and only if .
Moreover, for these representations are unitarily equivalent
to the Fock representation (obtained for ). On the other hand
representations obtained for different unit vectors are disjoint. We
show that the universal C*-algebra for the relations has a largest proper,
closed, two-sided ideal. The quotient by this ideal is a natural -analogue
of the Cuntz algebra (obtained for ). We discuss the Conjecture that, for
, this analogue should, in fact, be equal to the Cuntz algebra
itself. In the limiting cases we determine all irreducible
representations of the relations, and characterize those which can be obtained
via coherent states.Comment: 19 pages, Plain Te
Modélisation dynamique des risques sanitaires liés aux inondations urbaines influencées par des eaux usées
Water in low-mass star-forming regions with Herschel: HIFI spectroscopy of NGC1333
'Water In Star-forming regions with Herschel' (WISH) is a key programme
dedicated to studying the role of water and related species during the
star-formation process and constraining the physical and chemical properties of
young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on
the Herschel Space Observatory observed three deeply embedded protostars in the
low-mass star-forming region NGC1333 in several H2-16O, H2-18O, and CO
transitions. Line profiles are resolved for five H16O transitions in each
source, revealing them to be surprisingly complex. The line profiles are
decomposed into broad (>20 km/s), medium-broad (~5-10 km/s), and narrow (<5
km/s) components. The H2-18O emission is only detected in broad 1_10-1_01 lines
(>20 km/s), indicating that its physical origin is the same as for the broad
H2-16O component. In one of the sources, IRAS4A, an inverse P Cygni profile is
observed, a clear sign of infall in the envelope. From the line profiles alone,
it is clear that the bulk of emission arises from shocks, both on small (<1000
AU) and large scales along the outflow cavity walls (~10 000 AU). The H2O line
profiles are compared to CO line profiles to constrain the H2O abundance as a
function of velocity within these shocked regions. The H2O/CO abundance ratios
are measured to be in the range of ~0.1-1, corresponding to H2O abundances of
~10-5-10-4 with respect to H2. Approximately 5-10% of the gas is hot enough for
all oxygen to be driven into water in warm post-shock gas, mostly at high
velocities.Comment: Accepted for publication in the A&A HIFI special issu
Combined analysis of 19 common validated type 2 diabetes susceptibility gene variants shows moderate discriminative value and no evidence of gene-gene interaction
Peculiar Motions in the Region of the Ursa Major Supercluster of Galaxies
We have investigated the peculiar motions of clusters of galaxies in the Ursa
Major (UMa) supercluster and its neighborhood. Based on SDSS (Sloan Digital Sky
Survey) data, we have compiled a sample of early-type galaxies and used their
fundamental plane to determine the cluster distances and peculiar velocities.
The samples of early-type galaxies in the central regions (within R_200) of 12
UMa clusters of galaxies, in three main subsystems of the supercluster -- the
filamentary structures connecting the clusters, and in nine clusters from the
nearest UMa neighborhood have similar parameters. The fairly high overdensity
(3 by the galaxy number and 15 by the cluster number) suggests that the
supercluster as a whole is gravitationally bound, while no significant peculiar
motions have been found: the peculiar velocities do not exceed the measurement
errors by more than a factor of 1.5-2. The mean random peculiar velocities of
clusters and the systematic deviations from the overall Hubble expansion in the
supercluster are consistent with theoretical estimates. For the possible
approach of the three UMa subsystems to be confirmed, the measurement accuracy
must be increased by a factor of 2-3.Comment: 21 pages, 4 tables, 7 figure
Influence of Quadrupole and Octupole Electron-Phonon Coupling on the Low-Field Transport Properties of n-type Silicon
Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes
Quantum dots defined in carbon nanotubes are a platform for both basic
scientific studies and research into new device applications. In particular,
they have unique properties that make them attractive for studying the coherent
properties of single electron spins. To perform such experiments it is
necessary to confine a single electron in a quantum dot with highly tunable
barriers, but disorder has until now prevented tunable nanotube-based
quantum-dot devices from reaching the single-electron regime. Here, we use
local gate voltages applied to an ultra-clean suspended nanotube to confine a
single electron in both a single quantum dot and, for the first time, in a
tunable double quantum dot. This tunability is limited by a novel type of
tunnelling that is analogous to that in the Klein paradox of relativistic
quantum mechanics.Comment: 21 pages including supplementary informatio
Statistical Mechanics of Glass Formation in Molecular Liquids with OTP as an Example
We extend our statistical mechanical theory of the glass transition from
examples consisting of point particles to molecular liquids with internal
degrees of freedom. As before, the fundamental assertion is that super-cooled
liquids are ergodic, although becoming very viscous at lower temperatures, and
are therefore describable in principle by statistical mechanics. The theory is
based on analyzing the local neighborhoods of each molecule, and a statistical
mechanical weight is assigned to every possible local organization. This
results in an approximate theory that is in very good agreement with
simulations regarding both thermodynamical and dynamical properties
Annihilation of low energy antiprotons in silicon
The goal of the AEIS experiment at the Antiproton
Decelerator (AD) at CERN, is to measure directly the Earth's gravitational
acceleration on antimatter. To achieve this goal, the AEIS
collaboration will produce a pulsed, cold (100 mK) antihydrogen beam with a
velocity of a few 100 m/s and measure the magnitude of the vertical deflection
of the beam from a straight path. The final position of the falling
antihydrogen will be detected by a position sensitive detector. This detector
will consist of an active silicon part, where the annihilations take place,
followed by an emulsion part. Together, they allow to achieve 1 precision on
the measurement of with about 600 reconstructed and time tagged
annihilations.
We present here, to the best of our knowledge, the first direct measurement
of antiproton annihilation in a segmented silicon sensor, the first step
towards designing a position sensitive silicon detector for the
AEIS experiment. We also present a first comparison with
Monte Carlo simulations (GEANT4) for antiproton energies below 5 MeVComment: 21 pages in total, 29 figures, 3 table
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