37,568 research outputs found
Pseudoscalars Mesons in Hot, Dense Matter
Phase transitions in hot and dense matter and the in--medium behavior of
pseudoscalar mesons () are investigated, in the framework of the three flavor Nambu--Jona-Lasinio
model, including the 't Hooft interaction, which breaks the symmetry.
Three different scenarios are considered: zero density and finite temperature,
zero temperature and finite density in quark matter with different degrees of
strangeness, and finite temperature and density. At T=0, the role of strange
valence quarks in the medium is discussed, in connection with the phase
transition and the mesonic behavior. It is found that the appearance of strange
quarks, above certain densities, leads to meaningful changes in different
observables, especially in matter with \betaT-\rho$ plane is analyzed in connection with possible signatures
of restoration of symmetries.Comment: 33 pages, 12 figures, PRC versio
Effective restoration of chiral and axial symmetries at finite temperature and density
The effective restoration of chiral and axial symmetries is investigated
within the framework of the SU(3) Nambu-Jona-Lasinio model. The topological
susceptibility, modeled from lattice data at finite temperature, is used to
extract the temperature dependence of the coupling strength of the anomaly. The
study of the scalar and pseudoscalar mixing angles is performed in order to
discuss the evolution of the flavor combinations of pairs and its
consequences for the degeneracy of chiral partners. A similar study at zero
temperature and finite density is also realized.Comment: 5 pages, 1 figure. Talk given at Strange Quark Matter 2004, Cape
Town, South Africa, 15-20 September, 200
Quantum Topology Change in (2 + 1)d
The topology of orientable (2 + 1)d spacetimes can be captured by certain
lumps of non-trivial topology called topological geons. They are the
topological analogues of conventional solitons. We give a description of
topological geons where the degrees of freedom related to topology are
separated from the complete theory that contains metric (dynamical) degrees of
freedom. The formalism also allows us to investigate processes of quantum
topology change. They correspond to creation and annihilation of quantum geons.
Selection rules for such processes are derived.Comment: LaTeX file, 33 pages, 10 postscript figures, some typos corrected,
references updated, and other minor change
Universal relaxation function in nonextensive systems
We have derived the dipolar relaxation function for a cluster model whose
volume distribution was obtained from the generalized maximum Tsallis
nonextensive entropy principle. The power law exponents of the relaxation
function are simply related to a global fractal parameter and for
large time to the entropy nonextensivity parameter . For intermediate times
the relaxation follows a stretched exponential behavior. The asymptotic power
law behaviors both in the time and the frequency domains coincide with those of
the Weron generalized dielectric function derived from an extension of the Levy
central limit theorem. They are in full agreement with the Jonscher
universality principle. Moreover our model gives a physical interpretation of
the mathematical parameters of the Weron stochastic theory and opens new paths
to understand the ubiquity of self-similarity and power laws in the relaxation
of large classes of materials in terms of their fractal and nonextensive
properties.Comment: Two figures. Submitted for publicatio
Avoided crossings in mesoscopic systems: electron propagation on a non-uniform magnetic cylinder
We consider an electron constrained to move on a surface with revolution
symmetry in the presence of a constant magnetic field parallel to the
surface axis. Depending on and the surface geometry the transverse part of
the spectrum typically exhibits many crossings which change to avoided
crossings if a weak symmetry breaking interaction is introduced. We study the
effect of such perturbations on the quantum propagation. This problem admits a
natural reformulation to which tools from molecular dynamics can be applied. In
turn, this leads to the study of a perturbation theory for the time dependent
Born-Oppenheimer approximation
Motor‐evoked potentials reveal a motor‐cortical readout of evidence accumulation for sensorimotor decisions
Many everyday activities require time-pressured sensorimotor decision making. Traditionally, perception, decision, and action processes were considered to occur in series, but this idea has been successfully challenged, particularly by neurophysiological work in animals. However, the generality of parallel processing requires further elucidation. Here, we investigate whether the accumulation of a decision can be observed intrahemispherically within human motor cortex. Participants categorized faces as male or female, with task difficulty manipulated using morphed stimuli. Transcranial magnetic stimulation, applied during the reaction-time interval, produced motor-evoked potentials (MEPs) in two hand muscles that were the major contributors when generating the required pinch/grip movements. Smoothing MEPs using a Gaussian kernel allowed us to recover a continuous time-varying MEP average, comparable to an EEG component, permitting precise localization of the time at which the motor plan for the responding muscle became dominant. We demonstrate decision-related activity in the motor cortex during this perceptual discrimination task, suggesting ongoing evidence accumulation within the motor system even for two independent actions represented within one hemisphere
Adubação nitrogenada para pastagens do gênero Brachiaria em solos do Cerrado.
Introdução; Gênero Brachiaria; Matéria orgânica do solo e sua relação com a disponibilidade de N; Adições de nitrogênio ao sistema solo-pastagem; Importância da adubação nitrogenada em pastagens; Concentrações de nitrogênio e estimativa do teor de clorofila; Dinâmica do nitrogênio em pastagens; Perdas de nitrogênio do sistema solo-pastagem; Eficiência e recuperação do nitrogênio; Eficiência do nitrogênio na produção animal; Recomendação de adubação nitrogenada; Recomendação de adubação nitrogenada para o gênero Brachiaria de acordo com a fertilidade do solo; Recomendação de adubação nitrogenada para o gênero Brachiaria de acordo com o sistema de pastejo; Formas de aplicação de nitrogênio para pastagens; Considerações finais.bitstream/CNPAF/25514/1/doc_192.pd
Dataplane Specialization for High-performance OpenFlow Software Switching
OpenFlow is an amazingly expressive dataplane program-
ming language, but this expressiveness comes at a severe
performance price as switches must do excessive packet clas-
sification in the fast path. The prevalent OpenFlow software
switch architecture is therefore built on flow caching, but
this imposes intricate limitations on the workloads that can
be supported efficiently and may even open the door to mali-
cious cache overflow attacks. In this paper we argue that in-
stead of enforcing the same universal flow cache semantics
to all OpenFlow applications and optimize for the common
case, a switch should rather automatically specialize its dat-
aplane piecemeal with respect to the configured workload.
We introduce ES WITCH , a novel switch architecture that
uses on-the-fly template-based code generation to compile
any OpenFlow pipeline into efficient machine code, which
can then be readily used as fast path. We present a proof-
of-concept prototype and we demonstrate on illustrative use
cases that ES WITCH yields a simpler architecture, superior
packet processing speed, improved latency and CPU scala-
bility, and predictable performance. Our prototype can eas-
ily scale beyond 100 Gbps on a single Intel blade even with
complex OpenFlow pipelines
Vortex behavior near a spin vacancy in 2D XY-magnets
The dynamical behavior of anisotropic two dimensional Heisenberg models is
still a matter of controversy. The existence of a central peak at all
temperatures and a rich structure of magnon peaks are not yet understood. It
seems that the central peaks are related, in some way, to structures like
vortices. In order to contribute to the discussion of the dynamical behavior of
the model we use Monte Carlo and spin dynamics simulations as well analytical
calculations to study the behavior of vortices in the presence of nonmagnetic
impurities. Our simulations show that vortices are attracted and trapped by the
impurities. Using this result we show that if we suppose that vortices are not
very much disturbed by the presence of the impurities, then they work as an
attractive potential to the vortices explaining the observed behavior in our
simulations.Comment: 4 pages, 6 figure
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