5,020 research outputs found
Momentum Space Regularizations and the Indeterminacy in the Schwinger Model
We revisited the problem of the presence of finite indeterminacies that
appear in the calculations of a Quantum Field Theory. We investigate the
occurrence of undetermined mathematical quantities in the evaluation of the
Schwinger model in several regularization scenarios. We show that the
undetermined character of the divergent part of the vacuum polarization tensor
of the model, introduced as an {\it ansatz} in previous works, can be obtained
mathematically if one introduces a set of two parameters in the evaluation of
these quantities. The formal mathematical properties of this tensor and their
violations are discussed. The analysis is carried out in both analytical and
sharp cutoff regularization procedures. We also show how the Pauli Villars
regularization scheme eliminates the indeterminacy, giving a gauge invariant
result in the vector Schwinger model.Comment: 10 pages, no figure
Quantitative sampling of freshwater shrimps : comparison of two electrofishing procedures in a Caribbean stream
Two electrofishing procedures (point abundance sampling and removal sampling) for estimating community structure and the abundance of freshwater shrimps (#Decapoda : #Natantia) were compared at five sites in the Grand-Carbet River, Guadeloupe, French West Indies, on the basis of species richness, species frequency and the length of caught individuals. Sampling was carried out using battery-powered portable electric fishing gear. Both point abundance sampling and removal procedures highlighted a steep longitudinal gradient related to the shrimp fauna and non consistent discrepancy was observed between the two procedures in the different sites. Thus, the choice of one of these two procedures will depend only on the study objective. The benefits and disadvantages of these two electrofishing procedures are concisely discussed. (Résumé d'auteur
Phase Transition and Monopoles Densities in a Nearest Neighbors Two-Dimensional Spin Ice Model
In this work, we show that, due to the alternating orientation of the spins
in the ground state of the artificial square spin ice, the influence of a set
of spins at a certain distance of a reference spin decreases faster than the
expected result for the long range dipolar interaction, justifying the use of
the nearest neighbor two dimensional square spin ice model as an effective
model. Using an extension of the model presented in ref. [Scientific Reports 5,
15875 (2015)], considering the influence of the eight nearest neighbors of each
spin on the lattice, we analyze the thermodynamics of the model and study the
monopoles and string densities dependence as a function of the temperature.Comment: 11 pages, 8 figure
Current-driven and field-driven domain walls at nonzero temperature
We present a model for the dynamics of current- and field-driven domain-wall
lines at nonzero temperature. We compute thermally-averaged drift velocities
from the Fokker-Planck equation that describes the nonzero-temperature dynamics
of the domain wall. As special limits of this general description, we describe
rigid domain walls as well as vortex domain walls. In these limits, we
determine also depinning times of the domain wall from an extrinsic pinning
potential. We compare our theory with previous theoretical and experimental
work
Phase Transition in Asymmetrical Superfluids I: Equal Fermi Surfaces
In this paper, we study phase transitions in asymmetrical fermion
superfluids. In this scenario, the candidates to form pair are particles with
mismatched masses and chemical potentials. We derive an expression for the
critical temperature in terms of the gap and masses (or chemical potentials)
when the constraint of equal Fermi surfaces is imposed.Comment: RevTex, 11 pages, 2 figures, typos corrected and an appendix added,
accepted for publication in Phys. Rev.
Capacidade de combinação e heterose em hÃbridos intervarietais de milho adaptados a solos ácidos.
Comportamiento de cinco poblaciones de maiz y de sus respectivos hibridos interpoblacionales en suelos fertiles y acidos.
El objetivo del presente trabajo fue verificar el comportamiento de cinco poblaciones de maiz (Zea mays L.), selecionados en condiciones de suelo cerrado no corregido (acido) (CMS 36 y CMS 30) y en suelo de cerrado corregido (CMS 14, CMS 04 y CMS 13), sus cruzamientos y cuatro hibridos comerciais en dos ambientes: suelo acido y fertil. Los utilizados en este estudio fueron, peso de mazorca (PE), altura de planta (AP), altura de mazorca (AE) y dias a la floracion masculina (DFM). Todos los caracteres fueron afectados por el tipo de ambiente. Para PE las poblaciones CMS 36 y CMS 30, presentaron buen despeno en suelo acido mas no en suelo fertil y las poblaciones CMS 04, CMS 14 y CMS 13 fueron mejores en suelo fertil. El hibrido CMS 36 x CMS 30 fue el mejor en suelo acido y el CMS 14 x CMS 36 fue el mejor en suelo fertil. La poblacion CMS 36 fue superior a los cuatro hibridos comerciales en suelo acido. El analisis conjunto de variancia nostro efectos altamente significativos (P < 0,001) para localidades (PE, AP, AE y DFM), poblacion (AP y AE) Y localidad x poblacion (PE); y significativos (P < 0,05) para cultivares (PE, AP y AE), poblaciones (PE y DFM), heterosis media (PE, DFM), y localidad por cultivar (PE), localidad x poblacion (dfm). Para el caracter PE la mayor estimacion de los efectos de localidades por heterosis de poblacion fue de la CMS 36 en suelo fertil y en suelo acido fue la CMS 04. Los hibridos CMS 30 x CMS 13 Y cms 36 X CMS 30 presentaron el mayor y menor efecto de localidad por heterosis especifica para suelo fertil y acido, respectivamente. para eterosis de poblacion la CMS 30 presento el mayor efecto, en tanto que la CMS 04 presento el menor. mayores efectos pra heterosis especifica fueron detectados para los hibridos CMS 30 x CMS 13 y CMS 13 X cms 36
Avaliação do potencial ornamental de espécies de antúrio para folhagem de corte pela visão do florista.
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