1,492 research outputs found
Extensão Supersimétrica do Modelo BF bidimensional e a quantização de laços.
Um dos grandes desafios da física nos últimos cinquenta anos tem sido a conciliação da Mecânica Quântica com a Relatividade Geral, numa teoria Quântica da Gravitação. Teoria que até hoje não foi encontrada, de forma concreta, devido a sua complexidade, sobretudo quando tratamos sistemas gravitação-matéria, e a falta de tecnologias que possam nos dar evidências experimentais. Mas, existem muitos modelos teóricos que procuram explicar esta teoria, entre os quais temos a Gravitação Quântica de Laços. Para entender e simplificar as dificuldades teoricas da Gravitação Quântica de Laços em 3+1 dimensões, estudamos modelos de dimensões mais baixas. Partindo do modelo topológico BF, discutimos nesta tese sistemas gravitação-matéria do espaço-tempo bidimensional, a través de extensões supersimétricas N = 1. Discutimos dois modelos: 1.) Num primeiro modelo, o grupo de calibre da teoria é dado pelo supergrupo super
(anti-)de Sitter, S(A)dS, que é a extensão supersimétrica N = 1 do grupo de calibre (A)dS, a qual possue três geradores bosônicos e dois geradores fermiônicos. 2.) No segundo modelo acoplamos matéria, sendo guiados pela existência de uma supersimétria rígida (estudamos especificamente a gravitação num espaço Riemanniano com constante cosmológica positiva), onde os campos do modelo BF usual são expressos em termos de supercampos, como grupo de calibre sendo uma supersimetrização de SU(2). Neste caso particular quantizamos o modelo extendendo as técnicas usadas na Gravitação Quântica de Laços. Em ambos casos, discutimos a estrutura canônica do modelo, mostramos que a Hamiltoniana do modelo é completamente vinculada, bem como construimos quantidades invariantes de calibre (observáveis de Dirac)
Atomic Processes in Planetary Nebulae and H II Regions
Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have
driven much development in atomic physics. In the last few years the
combination of a generation of powerful observatories, the development of ever
more sophisticated spectral modeling codes, and large efforts on mass
production of high quality atomic data have led to important progress in our
understanding of the atomic spectra of such astronomical objects. In this paper
I review such progress, including evaluations of atomic data by comparisons
with nebular spectra, detection of spectral lines from most iron-peak elements
and n-capture elements, observations of hyperfine emission lines and analysis
of isotopic abundances, fluorescent processes, and new techniques for
diagnosing physical conditions based on recombination spectra. The review is
directed toward atomic physicists and spectroscopists trying to establish the
current status of the atomic data and models and to know the main standing
issues.Comment: 9 pages, 1 figur
Chemical Abundances from the Continuum
The calculation of solar absolute fluxes in the near-UV is revisited,
discussing in some detail recent updates in theoretical calculations of
bound-free opacity from metals. Modest changes in the abundances of elements
such as Mg and the iron-peak elements have a significant impact on the
atmospheric structure, and therefore self-consistent calculations are
necessary. With small adjustments to the solar photospheric composition, we are
able to reproduce fairly well the observed solar fluxes between 200 and 270 nm,
and between 300 and 420 nm, but find too much absorption in the 270-290 nm
window. A comparison between our reference 1D model and a 3D time-dependent
hydrodynamical simulation indicates that the continuum flux is only weakly
sensitive to 3D effects, with corrections reaching <10% in the near-UV, and <2%
in the optical.Comment: 10 pages, 5 figures, to appear in the proceedings of the conference A
Stellar Journey, a symposium in celebration of Bengt Gustafsson's 65th
birthday, June 23-27, 2008, Uppsal
Elliptic flow from color strings
It is shown that the elliptic flow can be successfully described in the color
string picture with fusion and percolation provided anisotropy of particle
emission from the fused string is taken into account. Two possible sources of
this anisotropy are considered, propagation of the string in the transverse
plane and quenching of produced particles in the strong color field of the
string. Calculations show that the second source gives an overwhelming
contribution to the flow at accessible energies.Comment: 23 pages, 11 figure
A New Physical Performance Classification System for Elite Handball Players : Cluster Analysis
The aim of the present study was to identify different cluster groups of handball players according to their physical performance level assessed in a series of physical assessments, which could then be used to design a training program based on individual strengths and weaknesses, and to determine which of these variables best identified elite performance in a group of under-19 [U19] national level handball players. Players of the U19 National Handball team (n=16) performed a set of tests to determine: 10 m (ST(10)) and 20 m (ST(20)) sprint time, ball release velocity (BRv), countermovement jump (CMJ) height and squat jump (SJ) height. All players also performed an incremental-load bench press test to determine the 1 repetition maximum (1RM(est)), the load corresponding to maximum mean power (Load(MP)), the mean propulsive phase power at Load(MP) (P(MPP)MP) and the peak power at Load(MP) (P(PEAK)MP). Cluster analyses of the test results generated four groupings of players. The variables best able to discriminate physical performance were BRv, ST(20), 1RM(est), P(PEAK)MP and P(MPP)MP. These variables could help coaches identify talent or monitor the physical performance of athletes in their team. Each cluster of players has a particular weakness related to physical performance and therefore, the cluster results can be applied to a specific training programmed based on individual needs
Loop Quantization of the Supersymmetric Two-Dimensional BF Model
In this paper we consider the quantization of the 2d BF model coupled to
topological matter. Guided by the rigid supersymmetry this system can be viewed
as a super-BF model, where the field content is expressed in terms of
superfields. A canonical analysis is done and the constraints are then
implemented at the quantum level in order to construct the Hilbert space of the
theory under the perspective of Loop Quantum Gravity methods.Comment: 17 pages, Late
Elliptic flow in proton-proton collisions at 7 TeV
The angular correlations measured in proton-proton collisions at 7 TeV are
decomposed into contributions from back to back emission and elliptic flow.
Modeling the dominant term in the correlation functions as a momentum
conservation effect or as an effect of the initial transverse velocity of the
source, the remaining elliptic flow component can be estimated. The elliptic
flow coefficient extracted from the CMS Collaboration data is 0.04-0.08. No
additional small-angle, ridge-like correlations are needed to explain the
experimental data
Distinct subsets of unmyelinated primary sensory fibers mediate behavioral responses to noxious thermal and mechanical stimuli
Behavioral responses to painful stimuli require peripheral sensory neurons called nociceptors. Electrophysiological studies show that most C-fiber nociceptors are polymodal (i.e., respond to multiple noxious stimulus modalities, such as mechanical and thermal); nevertheless, these stimuli are perceived as distinct. Therefore, it is believed that discrimination among these modalities only occurs at spinal or supraspinal levels of processing. Here, we provide evidence to the contrary. Genetic ablation in adulthood of unmyelinated sensory neurons expressing the G protein-coupled receptor Mrgprd reduces behavioral sensitivity to noxious mechanical stimuli but not to heat or cold stimuli. Conversely, pharmacological ablation of the central branches of TRPV1+ nociceptors, which constitute a nonoverlapping population, selectively abolishes noxious heat pain sensitivity. Combined elimination of both populations yielded an additive phenotype with no additional behavioral deficits, ruling out a redundant contribution of these populations to heat and mechanical pain sensitivity. This double-dissociation suggests that the brain can distinguish different noxious stimulus modalities from the earliest stages of sensory processing
Vacuum effects in an asymptotically uniformly accelerated frame with a constant magnetic field
In the present article we solve the Dirac-Pauli and Klein Gordon equations in
an asymptotically uniformly accelerated frame when a constant magnetic field is
present. We compute, via the Bogoliubov coefficients, the density of scalar and
spin 1/2 particles created. We discuss the role played by the magnetic field
and the thermal character of the spectrum.Comment: 17 pages. RevTe
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