3,263 research outputs found
Formation of van der Waals molecules in buffer gas cooled magnetic traps
We show that a large class of helium-containing cold polar molecules form
readily in a cryogenic buffer gas, achieving densities as high as 10^12 cm^-3.
We explore the spin relaxation of these molecules in buffer gas loaded magnetic
traps, and identify a loss mechanism based on Landau-Zener transitions arising
from the anisotropic hyperfine interaction. Our results show that the recently
observed strong T^6 thermal dependence of spin change in buffer gas trapped
silver (Ag) is accounted for by the formation and spin change of AgHe, thus
providing evidence for molecular formation in a buffer gas trap.Comment: 4 pages, 4 figure
Kraus representation in the presence of initial correlations
We examine the validity of the Kraus representation in the presence of
initial correlations and show that it is assured only when a joint dynamics is
locally unitary.Comment: REVTeX4, 12 page
Data model issues in the Cherenkov Telescope Array project
The planned Cherenkov Telescope Array (CTA), a future ground-based
Very-High-Energy (VHE) gamma-ray observatory, will be the largest project of
its kind. It aims to provide an order of magnitude increase in sensitivity
compared to currently operating VHE experiments and open access to guest
observers. These features, together with the thirty years lifetime planned for
the installation, impose severe constraints on the data model currently being
developed for the project.
In this contribution we analyze the challenges faced by the CTA data model
development and present the requirements imposed to face them. While the full
data model is still not completed we show the organization of the work, status
of the design, and an overview of the prototyping efforts carried out so far.
We also show examples of specific aspects of the data model currently under
development.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Quartz Cherenkov Counters for Fast Timing: QUARTIC
We have developed particle detectors based on fused silica (quartz) Cherenkov
radiators read out with micro-channel plate photomultipliers (MCP-PMTs) or
silicon photomultipliers (SiPMs) for high precision timing (Sigma(t) about
10-15 ps). One application is to measure the times of small angle protons from
exclusive reactions, e.g. p + p - p + H + p, at the Large Hadron Collider, LHC.
They may also be used to measure directional particle fluxes close to external
or stored beams. The detectors have small areas (square cm), but need to be
active very close (a few mm) to the intense LHC beam, and so must be radiation
hard and nearly edgeless. We present results of tests of detectors with quartz
bars inclined at the Cherenkov angle, and with bars in the form of an "L" (with
a 90 degree corner). We also describe a possible design for a fast timing
hodoscope with elements of a few square mm.Comment: 24 pages, 14 figure
Charge transfer state emission dynamics in blue-emitting functionalized silicon nanocrystals
We explore the dynamics of blue emission from dodecylamine and ammonia functionalized silicon nanocrystals (Si NCs) with average diameters of ∼3 and ∼6 nm using time-resolved photoluminescence (TRPL) spectroscopy. The Si NCs exhibit nanosecond PL decay dynamics that is independent of NC size and uniform across the emission spectrum. The TRPL measurements reveal complete quenching of core state emission by a charge transfer state that is responsible for the blue PL with a radiative recombination rate of ∼5 × 10^7 s^(−1). A detailed picture of the charge transfer state emission dynamics in these functionalized Si NCs is proposed
The unidentified TeV source (TeVJ2032+4130) and surrounding field: Final HEGRA IACT-System results
The unidentified TeV source in Cygnus is now confirmed by follow-up
observations from 2002 with the HEGRA stereoscopic system of Cherenkov
Telescopes. Using all data (1999 to 2002) we confirm this new source as steady
in flux over the four years of data taking, extended with radius 6.2 arcmin
(+-1.2 arcmin (stat) +-0.9 arcmin (sys)) and exhibiting a hard spectrum with
photon index -1.9. It is located in the direction of the dense OB stellar
association, Cygnus OB2. Its integral flux above energies E>1 TeV amounts to
\~5% of the Crab assuming a Gaussian profile for the intrinsic source
morphology. There is no obvious counterpart at radio, optical nor X-ray
energies, leaving TeVJ2032+4130 presently unidentified. Observational
parameters of this source are updated here and some astrophysical discussion is
provided. Also included are upper limits for a number of other interesting
sources in the FoV, including the famous microquasar Cygnus X-3.Comment: 7 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
Nonequilibrium wetting
When a nonequilibrium growing interface in the presence of a wall is
considered a nonequilibrium wetting transition may take place. This transition
can be studied trough Langevin equations or discrete growth models. In the
first case, the Kardar-Parisi-Zhang equation, which defines a very robust
universality class for nonequilibrium moving interfaces, with a soft-wall
potential is considered. While in the second, microscopic models, in the
corresponding universality class, with evaporation and deposition of particles
in the presence of hard-wall are studied. Equilibrium wetting is related to a
particular case of the problem, it corresponds to the Edwards-Wilkinson
equation with a potential in the continuum approach or to the fulfillment of
detailed balance in the microscopic models. In this review we present the
analytical and numerical methods used to investigate the problem and the very
rich behavior that is observed with them.Comment: Review, 36 pages, 16 figure
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