403 research outputs found
Efficient room temperature cw Yb:glass laser pumped by a 946nm Nd:YAG laser
By pumping with a cw diode-pumped Nd:YAG laser operating at 946nm laser operation of a new Yb-doped phosphate glass with 440mW cw output power and a slope efficiency of 48% with respect to the absorbed pump power was achieved at room temperature
Mass Parameterizations and Predictions of Isotopic Observables
We discuss the accuracy of mass models for extrapolating to very asymmetric
nuclei and the impact of such extrapolations on the predictions of isotopic
observables in multifragmentation. We obtain improved mass predictions by
incorporating measured masses and extrapolating to unmeasured masses with a
mass formula that includes surface symmetry and Coulomb terms. We find that
using accurate masses has a significant impact on the predicted isotopic
observables.Comment: 12 pages, 4 figure
Garvey-Kelson Relations for Nuclear Charge Radii
The Garvey-Kelson relations (GKRs) are algebraic expressions originally
developed to predict nuclear masses. In this letter we show that the GKRs
provide a fruitful framework for the prediction of other physical observables
that also display a slowly-varying dynamics. Based on this concept, we extend
the GKRs to the study of nuclear charge radii. The GKRs are tested on 455 out
of the approximately 800 nuclei whose charge radius is experimentally known. We
find a rms deviation between the GK predictions and the experimental values of
only 0.01 fm. This should be contrasted against some of the most successful
microscopic models that yield rms deviations almost three times as large.
Predictions - with reliable uncertainties - are provided for 116 nuclei whose
charge radius is presently unknown.Comment: 4 pages and 3 figure
Comparisons of Statistical Multifragmentation and Evaporation Models for Heavy Ion Collisions
The results from ten statistical multifragmentation models have been compared
with each other using selected experimental observables. Even though details in
any single observable may differ, the general trends among models are similar.
Thus these models and similar ones are very good in providing important physics
insights especially for general properties of the primary fragments and the
multifragmentation process. Mean values and ratios of observables are also less
sensitive to individual differences in the models. In addition to
multifragmentation models, we have compared results from five commonly used
evaporation codes. The fluctuations in isotope yield ratios are found to be a
good indicator to evaluate the sequential decay implementation in the code. The
systems and the observables studied here can be used as benchmarks for the
development of statistical multifragmentation models and evaporation codes.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume
"Dynamics and Thermodynamics with Nuclear Degrees of Freedo
Caloric Curves and Nuclear Expansion
Nuclear caloric curves have been analyzed using an expanding Fermi gas
hypothesis to extract average nuclear densities. In this approach the observed
flattening of the caloric curves reflects progressively increasing expansion
with increasing excitation energy. This expansion results in a corresponding
decrease in the density and Fermi energy of the excited system. For nuclei of
medium to heavy mass apparent densities ~ 0.4 rho_0 are reached at the higher
excitation energies.Comment: 4 pages, 3 figure
Distributed phase-covariant cloning with atomic ensembles via quantum Zeno dynamics
We propose an interesting scheme for distributed orbital state quantum
cloning with atomic ensembles based on the quantum Zeno dynamics. These atomic
ensembles which consist of identical three-level atoms are trapped in distant
cavities connected by a single-mode integrated optical star coupler. These
qubits can be manipulated through appropriate modulation of the coupling
constants between atomic ensemble and classical field, and the cavity decay can
be largely suppressed as the number of atoms in the ensemble qubits increases.
The fidelity of each cloned qubit can be obtained with analytic result. The
present scheme provides a new way to construct the quantum communication
network.Comment: 5 pages, 4 figure
Magnetic Branes in Gauss-Bonnet Gravity
We present two new classes of magnetic brane solutions in
Einstein-Maxwell-Gauss-Bonnet gravity with a negative cosmological constant.
The first class of solutions yields an -dimensional spacetime with a
longitudinal magnetic field generated by a static magnetic brane. We also
generalize this solution to the case of spinning magnetic branes with one or
more rotation parameters. We find that these solutions have no curvature
singularity and no horizons, but have a conic geometry. In these spacetimes,
when all the rotation parameters are zero, the electric field vanishes, and
therefore the brane has no net electric charge. For the spinning brane, when
one or more rotation parameters are non zero, the brane has a net electric
charge which is proportional to the magnitude of the rotation parameter. The
second class of solutions yields a spacetime with an angular magnetic field.
These solutions have no curvature singularity, no horizon, and no conical
singularity. Again we find that the net electric charge of the branes in these
spacetimes is proportional to the magnitude of the velocity of the brane.
Finally, we use the counterterm method in the Gauss-Bonnet gravity and compute
the conserved quantities of these spacetimes.Comment: 17 pages, No figure, The version to be published in Phys. Rev.
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Machine Learning in Automated Text Categorization
The automated categorization (or classification) of texts into predefined
categories has witnessed a booming interest in the last ten years, due to the
increased availability of documents in digital form and the ensuing need to
organize them. In the research community the dominant approach to this problem
is based on machine learning techniques: a general inductive process
automatically builds a classifier by learning, from a set of preclassified
documents, the characteristics of the categories. The advantages of this
approach over the knowledge engineering approach (consisting in the manual
definition of a classifier by domain experts) are a very good effectiveness,
considerable savings in terms of expert manpower, and straightforward
portability to different domains. This survey discusses the main approaches to
text categorization that fall within the machine learning paradigm. We will
discuss in detail issues pertaining to three different problems, namely
document representation, classifier construction, and classifier evaluation.Comment: Accepted for publication on ACM Computing Survey
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