5,275 research outputs found
Comparing omnidirectional reflection from periodic and quasiperiodic one-dimensional photonic crystals
We determine the range of thicknesses and refractive indices for which
omnidirectional reflection from quasiperiodic multilayers occurs. By resorting
to the notion of area under the transmittance curve, we assess in a systematic
way the performance of the different quasiperiodic Fibonacci multilayers.Comment: 5 pages, 4 color figures. Comments welcome
Self-modulation of nonlinear Alfven waves in a strongly magnetized relativistic electron-positron plasma
We study the self-modulation of a circularly polarized Alfven wave in a strongly magnetized relativistic electron-positron plasma with finite temperature. This nonlinear wave corresponds to an exact solution of the equations, with a dispersion relation that has two branches. For a large magnetic field, the Alfven branch has two different zones, which we call the normal dispersion zone (where d omega/dk > 0) and the anomalous dispersion zone (where d omega/dk < 0). A nonlinear Schrodinger equation is derived in the normal dispersion zone of the Alfven wave, where the wave envelope can evolve as a periodic wave train or as a solitary wave, depending on the initial condition. The maximum growth rate of the modulational instability decreases as the temperature is increased. We also study the Alfven wave propagation in the anomalous dispersion zone, where a nonlinear wave equation is obtained. However, in this zone the wave envelope can evolve only as a periodic wave train.CONICyT 21100839 74110049FONDECyT 1110135 1110729 1080658 1121144CNPqEuropean Commission for a Marie Curie International Incoming FellowshipInstitute for Fusion Studie
Self-modulation of nonlinear waves in a weakly magnetized relativistic electron-positron plasma with temperature
We develop a nonlinear theory for self-modulation of a circularly polarized electromagnetic wave in a relativistic hot weakly magnetized electron-positron plasma. The case of parallel propagation along an ambient magnetic field is considered. A nonlinear Schrodinger equation is derived for the complex wave amplitude of a self-modulated wave packet. We show that the maximum growth rate of the modulational instability decreases as the temperature of the pair plasma increases. Depending on the initial conditions, the unstable wave envelope can evolve nonlinearly to either periodic wave trains or solitary waves. This theory has application to high-energy astrophysics and high-power laser physics.CONICyTFONDECyT 1110135 1080658Brazilian agency CNPqBrazilian agency FAPESPMarie Curie International Incoming Fellowshiphospitality of Paris ObservatoryInstitute for Fusion Studie
Effective potential in Lorentz-breaking field theory models
We calculate explicitly the one-loop effective potential in different
Lorentz-breaking field theory models. First, we consider a Yukawa-like theory
and, then, some examples of Lorentz-violating extensions of scalar QED. We
observed, for the extended QED models, that the resulting effective potential
converges to the known result in the limit in which Lorentz-symmetry is
restored. Besides, the one-loop corrections to the effective potential in all
the cases we studied depend on the background tensors responsible for the
Lorentz symmetry violation. This have consequences in physical quantities like,
for example, in the induced mass due to Coleman-Weinberg mechanism.Comment: Version accepted for publication in EPJ
Impact of Diet and Quality Grade on Shelf Life of Beef Steaks
Steers were fed a diet containing dry rolled corn, steam flaked corn, dry rolled corn with 30% dried distillers grains, or steam flaked corn with 30% dried distillers grains. Strip loins from upper 2/3 Choice and Select- grade carcasses were obtained to evaluate the effects of diet and quality grade on shelf life characteristics. Strip loins were aged for 2, 9, 16, or 23 days. Results suggest that steaks from cattle fed steam flaked corn (with or without dried distillers grains) and from cattle fed dried distillers grains (regardless of corn type) had higher levels of many unsaturated fatty acids, more discoloration, and greater lipid oxidation compared to the dry rolled corn treatments or the no dried distillers grains treatments, respectively. Feeding of dry rolled corn or diets without dried distillers grains maintained red color better during retail display. Choice- grade steaks had significantly higher levels of unsaturated fatty acids like 18:2 and total polyunsaturated fatty acids than Select- grade steaks but did not diff er in color stability or oxidation. These data indicate the longest shelf life will occur when cattle are fed diets containing dry rolled corn (versus steam flaked corn) or without dried distillers grains (versus with dried distillers grains) and that both steam flaked corn and distillers grains have a negative impact on shelf life. Quality grade did not affect color stability
Minimum of and the phase transition of the Linear Sigma Model in the large-N limit
We reexamine the possibility of employing the viscosity over entropy density
ratio as a diagnostic tool to identify a phase transition in hadron physics to
the strongly coupled quark-gluon plasma and other circumstances where direct
measurement of the order parameter or the free energy may be difficult.
It has been conjectured that the minimum of eta/s does indeed occur at the
phase transition. We now make a careful assessment in a controled theoretical
framework, the Linear Sigma Model at large-N, and indeed find that the minimum
of eta/s occurs near the second order phase transition of the model due to the
rapid variation of the order parameter (here the sigma vacuum expectation
value) at a temperature slightly smaller than the critical one.Comment: 22 pages, 19 figures, v2, some references and several figures added,
typos corrected and certain arguments clarified, revised for PR
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