440 research outputs found
Reanalysis of antiproton production in proton-nucleus and nucleus-nucleus reactions at subthreshold energies
We reanalyse the production of pairs in proton-nucleus and
nucleus-nucleus collisions employing novel elementary cross sections for
baryon-baryon and pion-baryon production channels based on a boson-exchange
model. In contrast to previous transport studies performed in the literature
the secondary pion induced channel is found to be most important in both p+A
and A+A collisions at subthreshold energies. A detailed comparison with the
experimental data available indicates that sizeable attractive
potentials in the order of - 100 to - 150 MeV at normal nuclear matter density
are needed to reproduce the size and shape of the experimental spectra.Comment: 25 pages, latex, including 15 ps-figures, UGI-97-21, submitted to
Nucl. Phys.
Espécies Arbóreas De Papilionoideae (leguminosae) Na Região Noroeste Do Estado De São Paulo, Brasil
In this study, we collected woody plants of Papilionoideae, Leguminosae, in the northwest region of São Paulo state, southeastern Brazil. The study area has one of the most fragmented vegetation within the context of the region, and it is still poorly known about the flora. Nineteen species were recorded in eleven genera and three tribes. The most representative tribes were Sophoreae, with the genus Bowdichia, Leptolobium, Myroxylon, Sweetia and Ormosia; tribe Dalbergieae, with Andira, Centrolobium, Machaerium and Platypodium, and tribe Dipterygeae represented by Dipteryx and Pterodon. Machaerium presented the highest number of species, with eight, followed by Leptolobium, with two species. The other genera were represented by one species each. The species distribution data showed that the regional flora consists of species with wide distribution in the Cerrado, in central Brazil, and species that occur primarily in the Atlantic forest in eastern Brazil. Keys.6718510
Semiclassical Trace Formulas for Noninteracting Identical Particles
We extend the Gutzwiller trace formula to systems of noninteracting identical
particles. The standard relation for isolated orbits does not apply since the
energy of each particle is separately conserved causing the periodic orbits to
occur in continuous families. The identical nature of the particles also
introduces discrete permutational symmetries. We exploit the formalism of
Creagh and Littlejohn [Phys. Rev. A 44, 836 (1991)], who have studied
semiclassical dynamics in the presence of continuous symmetries, to derive
many-body trace formulas for the full and symmetry-reduced densities of states.
Numerical studies of the three-particle cardioid billiard are used to
explicitly illustrate and test the results of the theory.Comment: 29 pages, 11 figures, submitted to PR
Dislocations and the critical endpoint of the melting line of vortex line lattices
We develop a theory for dislocation-mediated structural transitions in the
vortex lattice which allows for a unified description of phase transitions
between the three phases, the elastic vortex glass, the amorphous vortex glass,
and the vortex liquid, in terms of a free energy functional for the dislocation
density. The origin of a critical endpoint of the melting line at high magnetic
fields, which has been recently observed experimentally, is explained.Comment: 4 pages, 1 figur
Quantum Computing of Quantum Chaos in the Kicked Rotator Model
We investigate a quantum algorithm which simulates efficiently the quantum
kicked rotator model, a system which displays rich physical properties, and
enables to study problems of quantum chaos, atomic physics and localization of
electrons in solids. The effects of errors in gate operations are tested on
this algorithm in numerical simulations with up to 20 qubits. In this way
various physical quantities are investigated. Some of them, such as second
moment of probability distribution and tunneling transitions through invariant
curves are shown to be particularly sensitive to errors. However,
investigations of the fidelity and Wigner and Husimi distributions show that
these physical quantities are robust in presence of imperfections. This implies
that the algorithm can simulate the dynamics of quantum chaos in presence of a
moderate amount of noise.Comment: research at Quantware MIPS Center http://www.quantware.ups-tlse.fr,
revtex 11 pages, 13 figs, 2 figs and discussion adde
Global well-posedness for the KP-I equation on the background of a non localized solution
We prove that the Cauchy problem for the KP-I equation is globally well-posed
for initial data which are localized perturbations (of arbitrary size) of a
non-localized (i.e. not decaying in all directions) traveling wave solution
(e.g. the KdV line solitary wave or the Zaitsev solitary waves which are
localized in and periodic or conversely)
The Library of Babel: On the origin of gravitational thermodynamics
We show that heavy pure states of gravity can appear to be mixed states to
almost all probes. For AdS_5 Schwarzschild black holes, our arguments are made
using the field theory dual to string theory in such spacetimes. Our results
follow from applying information theoretic notions to field theory operators
capable of describing very heavy states in gravity. For half-BPS states of the
theory which are incipient black holes, our account is exact: typical
microstates are described in gravity by a spacetime ``foam'', the precise
details of which are almost invisible to almost all probes. We show that
universal low-energy effective description of a foam of given global charges is
via certain singular spacetime geometries. When one of the specified charges is
the number of D-branes, the effective singular geometry is the half-BPS
``superstar''. We propose this as the general mechanism by which the effective
thermodynamic character of gravity emerges.Comment: LaTeX, 6 eps figures, uses young.sty and wick.sty; Version 2: typos
corrected, minor rewordings and clarifications, references adde
β1-Adrenergic Receptor and Sphingosine- 1-Phosphate Receptor 1 Reciprocal Down-Regulation Influences Cardiac Hypertrophic Response and Progression Toward Heart Failure: Protective Role of S1PR1 Cardiac Gene Therapy
YesThe Sphingosine-1-phosphate receptor 1 (S1PR1) and β1-adrenergic receptor
(β1AR) are G protein-coupled receptors (GPCRs) expressed in the heart. These two GPCRs have
opposing actions on adenylyl cyclase due to differential G protein-coupling. Importantly, both of
these receptors can be regulated by the actions of GPCR kinase-2 (GRK2), which triggers
desensitization and down-regulation processes. Although, classical signaling paradigms suggest
that simultaneous activation of β1ARs and S1PR1s in a myocyte would simply be opposing action
on cAMP production, in this report we have uncovered a direct interaction between these two
receptors with a regulatory involvement of GRK2.
In HEK293 cells overexpressing both β1AR and S1PR1, we
demonstrate that β1AR down-regulation can occur after sphingosine 1-phosphate (S1PR1 agonist)
stimulation while S1PR1 down-regulation can be triggered by isoproterenol (βAR agonist)
treatment. This cross-talk between these two distinct GPCRs appears to have physiological
significance since they interact and show reciprocal regulation in mouse hearts undergoing chronic
βAR stimulation and also in a rat model of post-ischemic heart failure (HF).
We demonstrate that restoring cardiac plasma membrane levels of S1PR1
produce beneficial effects counterbalancing deleterious β1AR overstimulation in HF
Analysis of the efficiency of a cloth cyclone: the effect of the permeability of the filtering medium
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