17,775 research outputs found
Far-infrared photometric observations of the outer planets and satellites with Herschel-PACS
We present all Herschel PACS photometer observations of Mars, Saturn, Uranus,
Neptune, Callisto, Ganymede, and Titan. All measurements were carefully
inspected for quality problems, were reduced in a (semi-)standard way, and were
calibrated. The derived flux densities are tied to the standard PACS photometer
response calibration, which is based on repeated measurements of five fiducial
stars. The overall absolute flux uncertainty is dominated by the estimated 5%
model uncertainty of the stellar models in the PACS wavelength range between 60
and 210 micron. A comparison with the corresponding planet and satellite models
shows excellent agreement for Uranus, Neptune, and Titan, well within the
specified 5%. Callisto is brighter than our model predictions by about 4-8%,
Ganymede by about 14-21%. We discuss possible reasons for the model offsets.
The measurements of these very bright point-like sources, together with
observations of stars and asteroids, show the high reliability of the PACS
photometer observations and the linear behavior of the PACS bolometer source
fluxes over more than four orders of magnitude (from mJy levels up to more than
1000 Jy). Our results show the great potential of using the observed solar
system targets for cross-calibration purposes with other ground-based,
airborne, and space-based instruments and projects. At the same time, the PACS
results will lead to improved model solutions for future calibration
applications.Comment: 25 pages, 11 figures, 11 table
Enhancing Transport Efficiency by Hybrid Routing Strategy
Traffic is essential for many dynamic processes on real networks, such as
internet and urban traffic systems. The transport efficiency of the traffic
system can be improved by taking full advantage of the resources in the system.
In this paper, we propose a dual-strategy routing model for network traffic
system, to realize the plenary utility of the whole network. The packets are
delivered according to different "efficient routing strategies" [Yan, et al,
Phys. Rev. E 73, 046108 (2006)]. We introduce the accumulate rate of packets,
{\eta} to measure the performance of traffic system in the congested phase, and
propose the so-called equivalent generation rate of packet to analyze the
jamming processes. From analytical and numerical results, we find that, for
suitable selection of strategies, the dual- strategy system performs better
than the single-strategy system in a broad region of strategy mixing ratio. The
analytical solution to the jamming processes is verified by estimating the
number of jammed nodes, which coincides well with the result from simulation.Comment: 6 pages, 3 figure
Entanglement in bipartite quantum systems: Euclidean volume ratios and detectability by Bell inequalities
Euclidean volume ratios between quantum states with positive partial
transpose and all quantum states in bipartite systems are investigated. These
ratios allow a quantitative exploration of the typicality of entanglement and
of its detectability by Bell inequalities. For this purpose a new numerical
approach is developed. It is based on the Peres-Horodecki criterion, on a
characterization of the convex set of quantum states by inequalities resulting
from Newton identities and from Descartes' rule of signs, and on a numerical
approach involving the multiphase Monte Carlo method and the hit-and-run
algorithm. This approach confirms not only recent analytical and numerical
results on two-qubit, qubit--qutrit, and qubit--four-level qudit states but
also allows for a numerically reliable numerical treatment of so far unexplored
qutrit--qutrit states. Based on this numerical approach with the help of the
Clauser-Horne-Shimony-Holt inequality and the Collins-Gisin inequality the
degree of detectability of entanglement is investigated for two-qubit quantum
states. It is investigated quantitatively to which extent a combined test of
both Bell inequalities can increase the detectability of entanglement beyond
what is achievable by each of these inequalities separately.Comment: 29 pages, 4 figure
Factores internos y externos que afectan el rendimiento académico del agente policial en formación
Se realizó un estudio con alumnos del Instituto Superior Policial, para examinar sus contextos académico y familiar, sus percepciones acerca del apoyo que les brinda su familia, los problemas que enfrentan en su proceso académico, las expectativas propias y las familiares hacia su carrera.Los datos muestran que existe relación entre el apoyo que los estudiantes perciben y su desempeño académico, así como la importancia que tiene incluir a la familia, para promover y elevar el rendimiento académico.
Conocer los factores internos y externos intervinientes en el rendimiento académico de los estudiantes es de vital importancia, para mejorar el proceso de enseñanza aprendizaje y la calidad de enseñanza.
Esta investigación busca identificar los posibles factores que intervienen en el rendimiento académico de los estudiantes del Instituto Superior Policial. El estudio pretende determinar cuáles son los factores que están afectándole directamente a los estudiantes de este Centro de Formación. Con este estudio se pretende poder mejorar la calidad enseñanza y las infraestructuras del Instituto Superior Policial tomando como base las normas legales que rigen este instituto
Behaviors of susceptible-infected epidemics on scale-free networks with identical infectivity
In this article, we proposed a susceptible-infected model with identical
infectivity, in which, at every time step, each node can only contact a
constant number of neighbors. We implemented this model on scale-free networks,
and found that the infected population grows in an exponential form with the
time scale proportional to the spreading rate. Further more, by numerical
simulation, we demonstrated that the targeted immunization of the present model
is much less efficient than that of the standard susceptible-infected model.
Finally, we investigated a fast spreading strategy when only local information
is available. Different from the extensively studied path finding strategy, the
strategy preferring small-degree nodes is more efficient than that preferring
large-degree nodes. Our results indicate the existence of an essential
relationship between network traffic and network epidemic on scale-free
networks.Comment: 5 figures and 7 page
R-symmetry and Supersymmetry Breaking at Finite Temperature
We analyze the spontaneous symmetry breaking at finite temperature
for the simple O'Raifeartaigh-type model introduced in [1] in connection with
spontaneous supersymmetry breaking. We calculate the finite temperature
effective potential (free energy) to one loop order and study the thermal
evolution of the model. We find that the R-symmetry breaking occurs through a
second order phase transition. Its associated meta-stable supersymmetry
breaking vacuum is thermodynamically favored at high temperatures and the model
remains trapped in this state by a potential barrier, as the temperature lowers
all the way until T=0.Comment: 19 pages, 4 figures - Minor revisions, references added. To appear in
JHE
Magnetism and unconventional superconductivity in CeMIn heavy-fermion crystals
We review magnetic, superconducting and non-Fermi-liquid properties of the
structurally layered heavy-fermion compounds CeMIn (M=Co, Rh,
Ir). These properties suggest d-wave superconductivity and proximity to an
antiferromagetic quantum-critical point.Comment: submitted 23rd International Conference on Low Temperature Physics
(LT-23), Aug. 200
One-loop effects in a self-dual planar noncommutative theory
We study the UV properties, and derive the explicit form of the one-loop
effective action, for a noncommutative complex scalar field theory in 2+1
dimensions with a Grosse-Wulkenhaar term, at the self-dual point. We also
consider quantum effects around non-trivial minima of the classical action
which appear when the potential allows for the spontaneous breaking of the U(1)
symmetry. For those solutions, we show that the one-loop correction to the
vacuum energy is a function of a special combination of the amplitude of the
classical solution and the coupling constant.Comment: Version to appear in JHE
Measurement of the Surface Gravity of Boo
Direct angular size measurements of the G0IV subgiant Boo from the
Palomar Testbed Interferometer are presented, with limb-darkened angular size
of mas, which indicate a linear
radius of . A bolometric flux estimate of erg cms is computed, which indicates
an effective temperature of K and luminosity of for this object. Similar data are established for a check
star, HD 121860. The Boo results are compared to, and confirm, similar
parameters established by the {\it MOST} asteroseismology satellite. In
conjunction with the mass estimate from the {\it MOST} investigation, a surface
gravity of [cm s] is established for
Boo.Comment: To appear in March 1, 2007 ApJ v657 n
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