24,802 research outputs found
Lens Galaxy Properties of SBS1520+530: Insights from Keck Spectroscopy and AO Imaging
We report on an investigation of the SBS 1520+530 gravitational lens system
and its environment using archival HST imaging, Keck spectroscopic data, and
Keck adaptive-optics imaging. The AO imaging has allowed us to fix the lens
galaxy properties with a high degree of precision when performing the lens
modeling, and the data indicate that the lens has an elliptical morphology and
perhaps a disk. The new spectroscopic data suggest that previous determinations
of the lens redshift may be incorrect, and we report an updated, though
inconclusive, value z_lens = 0.761. We have also spectroscopically confirmed
the existence of several galaxy groups at approximately the redshift of the
lens system. We create new models of the lens system that explicitly account
for the environment of the lens, and we also include improved constraints on
the lensing galaxy from our adaptive-optics imaging. Lens models created with
these new data can be well-fit with a steeper than isothermal mass slope (alpha
= 2.29, with the density proportional to r^-alpha) if H_0 is fixed at 72
km/s/Mpc; isothermal models require H_0 ~ 50 km/s/Mpc. The steepened profile
may indicate that the lens is in a transient perturbed state caused by
interactions with a nearby galaxy.Comment: 12 pages, 10 figures, submitted to Ap
Interference effects in f-deformed fields
We show how the introduction of an algeabric field deformation affects the
interference phenomena. We also give a physical interpretation of the developed
theory.Comment: 6 pages, Latex file, no figures, accepted by Physica Script
Relativistic Modification of the Gamow Factor
In processes involving Coulomb-type initial- and final-state interactions,
the Gamow factor has been traditionally used to take into account these
additional interactions. The Gamow factor needs to be modified when the
magnitude of the effective coupling constant increases or when the velocity
increases. For the production of a pair of particles under their mutual
Coulomb-type interaction, we obtain the modification of the Gamow factor in
terms of the overlap of the Feynman amplitude with the relativistic wave
function of the two particles. As a first example, we study the modification of
the Gamow factor for the production of two bosons. The modification is
substantial when the coupling constant is large.Comment: 13 pages, in LaTe
Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies
Using the technique of quantum transport of the interfering pair we examine
the Hanbury-Brown-Twiss (HBT) interferometry signatures for the
particle-emitting sources of pions and kaons produced in the heavy ion
collisions at GSI-FAIR energies. The evolution of the sources is described by
relativistic hydrodynamics with the system equation of state of the first-order
phase transition from quark-gluon plasma (QGP) to hadronic matter. We use
quantum probability amplitudes in a path-integral formalism to calculate the
two-particle correlation functions, where the effects of particle decay and
multiple scattering are taken into consideration. We find that the HBT radii of
kaons are smaller than those of pions for the same initial conditions. Both the
HBT radii of pions and kaons increase with the system initial energy density.
The HBT lifetimes of the pion and kaon sources are sensitive to the initial
energy density. They are significantly prolonged when the initial energy
density is tuned to the phase boundary between the QGP and mixed phase. This
prolongations of the HBT lifetimes of pions and kaons may likely be observed in
the heavy ion collisions with an incident energy in the GSI-FAIR energy range.Comment: 16 pages, 4 figure
Dissociation rates of J/psi's with comoving mesons - thermal vs. nonequilibrium scenario
We study J/psi dissociation processes in hadronic environments. The validity
of a thermal meson gas ansatz is tested by confronting it with an alternative,
nonequilibrium scenario. Heavy ion collisions are simulated in the framework of
the microscopic transport model UrQMD, taking into account the production of
charmonium states through hard parton-parton interactions and subsequent
rescattering with hadrons. The thermal gas and microscopic transport scenarios
are shown to be very dissimilar. Estimates of J/psi survival probabilities
based on thermal models of comover interactions in heavy ion collisions are
therefore not reliable.Comment: 12 pages, 6 figure
Optimisation of neural network with simultaneous feature selection and network prunning using evolutionary algorithm
Most advances on the Evolutionary Algorithm optimisation of Neural Network are on recurrent neural network using the NEAT optimisation method. For feed forward network, most of the optimisation are merely on the Weights and the bias selection which is generally known as conventional Neuroevolution. In this research work, a simultaneous feature reduction, network pruning and weight/biases selection is presented using fitness function design which penalizes selection of large feature sets. The fitness function also considers feature and the neuron reduction in the hidden layer. The results were demonstrated using two sets of data sets which are the cancer datasets and Thyroid datasets. Results showed backpropagation gradient descent error weights/biased optimisations performed slightly better at classification of the two datasets with lower misclassification rate and error. However, features and hidden neurons were reduced with the simultaneous feature/neurons switching using Genetic Algorithm. The number of features were reduced from 21 to 4 (Thyroid dataset) and 9 to 3 (cancer dataset) with only 1 hidden neuron in the processing layer for both network structures for the respective datasets. This research work will present the chromosome representation and the fitness function design
Strong Color Field Baryonic Remnants in Nucleus-Nucleus Collisions at 200A GeV
The effects of strong color electric fields (SCF) on the baryon production at
RHIC are studied in the framework of HIJING/B\=B (v2.0) model. The particle
species dependence of nuclear modification factors (NMF) are analyzed for Au+Au
collisions at 200A GeV. A doubling of the string tension leading to a
modification of the strangeness suppression according to Schwinger mechanism is
shown to provide an alternate explanation to coalescence models for the
interpretation of the observed baryon and meson production at moderate
and results in a predicted enhancement in the (multi)strange (anti)hyperon
production.Comment: 6 pages, Latex(Revtex), 4 figures;Added new references, one figure,
text slightly modified. final version accepted for publication in Pnys. Rev.
C (october,05
Color mixing in high-energy hadron collisions
The color mixing of mesons propagating in a nucleus is studied with the help
of a color-octet Pomeron partner present in the two-gluon model of the Pomeron.
For a simple model with four meson-nucleon channels, color mixings are found to
be absent for pointlike mesons and very small for small mesons. These results
seem to validate the absorption model with two independent color components
used in recent analyses of the nuclear absorption of mesons produced
in nuclear reactions.Comment: 3 journal-style page
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