3,510 research outputs found
Determining the luminosity function of Swift long gamma-ray bursts with pseudo-redshifts
The determination of luminosity function (LF) of gamma-ray bursts (GRBs) is
of an important role for the cosmological applications of the GRBs, which is
however hindered seriously by some selection effects due to redshift
measurements. In order to avoid these selection effects, we suggest to
calculate pseudo-redshifts for Swift GRBs according to the empirical L-E_p
relationship. Here, such a relationship is determined by reconciling
the distributions of pseudo- and real redshifts of redshift-known GRBs. The
values of E_p taken from Butler's GRB catalog are estimated with Bayesian
statistics rather than observed. Using the GRB sample with pseudo-redshifts of
a relatively large number, we fit the redshift-resolved luminosity
distributions of the GRBs with a broken-power-law LF. The fitting results
suggest that the LF could evolve with redshift by a redshift-dependent break
luminosity, e.g., L_b=1.2\times10^{51}(1+z)^2\rm erg s^{-1}. The low- and
high-luminosity indices are constrained to 0.8 and 2.0, respectively. It is
found that the proportional coefficient between GRB event rate and star
formation rate should correspondingly decrease with increasing redshifts.Comment: 5 pages, 5 figures, accepted for publication in ApJ
Dynamic dissipative cooling of a mechanical oscillator in strong-coupling optomechanics
Cooling of mesoscopic mechanical resonators represents a primary concern in
cavity optomechanics. Here in the strong optomechanical coupling regime, we
propose to dynamically control the cavity dissipation, which is able to
significantly accelerate the cooling process while strongly suppressing the
heating noise. Furthermore, the dynamic control is capable of overcoming
quantum backaction and reducing the cooling limit by several orders of
magnitude. The dynamic dissipation control provides new insights for tailoring
the optomechanical interaction and offers the prospect of exploring macroscopic
quantum physics.Comment: accepetd in Physical Review Letter
Statistics of Chaotic Resonances in an Optical Microcavity
Distributions of eigenmodes are widely concerned in both bounded and open
systems. In the realm of chaos, counting resonances can characterize the
underlying dynamics (regular vs. chaotic), and is often instrumental to
identify classical-to-quantum correspondence. Here, we study, both
theoretically and experimentally, the statistics of chaotic resonances in an
optical microcavity with a mixed phase space of both regular and chaotic
dynamics. Information on the number of chaotic modes is extracted by counting
regular modes, which couple to the former via dynamical tunneling. The
experimental data are in agreement with a known semiclassical prediction for
the dependence of the number of chaotic resonances on the number of open
channels, while they deviate significantly from a purely
random-matrix-theory-based treatment, in general. We ascribe this result to the
ballistic decay of the rays, which occurs within Ehrenfest time, and
importantly, within the timescale of transient chaos. The present approach may
provide a general tool for the statistical analysis of chaotic resonances in
open systems.Comment: 5 pages, 5 figures, and a supplemental informatio
2-(Carboxymethylsulfanyl)pyridine-3-carboxylic acid monohydrate
The title compound, C8H7NO4S·H2O, was obtained by reaction of 2-mercaptopyridine-3-carboxylic acid with chloroacetic acid. In the molecular structure, the dihedral angle between the two least-squares planes defined by the pyridine ring and the carboxy group is 8.32 (9)°. The carboxymethylsulfanyl group makes a torsion angle of 82.64 (12)° with the pyridine ring. An intramolecular O—H⋯N hydrogen bond between the acidic function of the carboxymethylsulfanyl group and the pyridine N atom stabilizes the conformation, whereas intermolecular O—H⋯O hydrogen bonding with the uncoordinated water molecules is responsible for packing of the structure, leading to chains propagating in [001]
Summarization and Analysis on Commercial Bank Risk Management
Risk management of commercial banks is an important part of their operation activity. The risk management development of commercial banks in the world is a process from single risk management to integrated risk management, while the risk management technology has been developed from qualitative analysis to comprehensive measurement and analysis with various quantitative methods. Currently, the world advance commercial banks already have more mature ways and results in concepts, organization settings and risk management technologies. For the late development of risk management in our country, a scientific and complete risk management system has not been established. At present stage, we are making efforts in introducing and establishing a scientific risk management system step by step. Key words: Commercial bank; risk management; risk management technology Résumé: La gestion des risques est une partie importante des activités d’opération des banques commerciales. Le développement de la gestion des risques des banques commerciales dans le monde est un processus qui va de la gestion simple à la gestion intégrée, quand la technologie de la gestion des risques a développé de l’analyse qualitative à la mesure globale et l’analyse avec des méthodes quantitatives diverses. Aujourd’hui, les banques commerciales avancées du monde ont déjà plus de méthodes et résultats mûrs en concept, organisation et technologie de la gestion des risques. A cause du développement retardé de la gestion des risques dans notre pays, un système scientifique et complet n’a pas encore été établi. Actuellement, nous sommes en train de faire des efforts pour introduire et établir pas à pas un système scientifique de la gestion des risques. Mots-Clés: banque commerciale, gestion des risques, technologie de la gestion des risque
Broadband enhancement of light harvesting in luminescent solar concentrator
Luminescent solar concentrator (LSC) can absorb large-area incident sunlight,
then emit luminescence with high quantum efficiency, which finally be collected
by a small photovoltaic (PV) system. The light-harvesting area of the PV system
is much smaller than that of the LSC system, potentially improving the
efficiency and reducing the cost of solar cells. Here, based on Fermi-golden
rule, we present a theoretical description of the luminescent process in
nanoscale LSCs where the conventional ray-optics model is no longer applicable.
As an example calculated with this new model, we demonstrate that a slot
waveguide consisting of a nanometer-sized low-index slot region sandwiched by
two high-index regions provides a broadband enhancement of light harvesting by
the luminescent centers in the slot region. This is because the slot waveguide
can (1) greatly enhance the spontaneous emission due to the Purcell effect, (2)
dramatically increase the effective absorption cross-section of luminescent
centers, and (3) strongly improve the quantum efficiency of luminescent
centers. It is found that about 80% solar photons can be ultimately converted
to waveguide-coupled luminescent photons even for a low luminescent quantum
efficiency of 0.5. This LSC is potential to construct a tandem structure which
can absorb nearly full-spectrum solar photons, and also may be of special
interest for building integrated nano-PV applications
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