13,427 research outputs found
Electric field inversion asymmetry: Rashba and Stark effects for holes in resonant tunneling devices
We report experimental evidence of excitonic spin-splitting, in addition to
the conventional Zeeman effect, produced by a combination of the Rashba
spin-orbit interaction, Stark shift and charge screening. The
electric-field-induced modulation of the spin-splitting are studied during the
charging and discharging processes of p-type GaAs/AlAs double barrier resonant
tunneling diodes (RTD) under applied bias and magnetic field. The abrupt
changes in the photoluminescence, with the applied bias, provide information of
the charge accumulation effects on the device.Comment: 4 pages, 2 figure
Density Fluctuations in an Electrolyte from Generalized Debye-Hueckel Theory
Near-critical thermodynamics in the hard-sphere (1,1) electrolyte is well
described, at a classical level, by Debye-Hueckel (DH) theory with (+,-) ion
pairing and dipolar-pair-ionic-fluid coupling. But DH-based theories do not
address density fluctuations. Here density correlations are obtained by
functional differentiation of DH theory generalized to {\it non}-uniform
densities of various species. The correlation length diverges universally
at low density as (correcting GMSA theory). When
one has as
where the amplitudes compare informatively with experimental data.Comment: 5 pages, REVTeX, 1 ps figure included with epsf. Minor changes,
references added. Accepted for publication in Phys. Rev. Let
Influence of organic fertilization and fertigation on quality of ?Syrah? tropical wine produced in the São Francisco Valley, Brazil.
The vitiviniculture in the São Francisco Valley is a recent activity, but with great social and economic importance to the region. The region is located in a tropical semi-arid zone and it is important the study of management practices for its unique soil and climate conditions. Therefore, this study aimed to evaluate the influence of the addition of organic matter and potassium fertigation on physic-chemical quality of Syrah (Vitis vinifera L.) tropical wines produced in the São Francisco Valley
A Transfer Matrix Method for Resonances in Randall-Sundrum Models
In this paper we discuss in detail a numerical method to study resonances in
membranes generated by domain walls in Randall-Sundrum-like scenarios. It is
based on similar works to understand the quantum mechanics of electrons subject
to the potential barriers that exist in heterostructures in semiconductors.
This method was used recently to study resonances of a three form field and
lately generalized to arbitrary forms. We apply it to a lot of important
models, namely those that contain the Gauge, Gravity and Spinor fields. In many
cases we find a rich structure of resonances which depends on the parameters
involved.Comment: 25 pages, 17 figure
Efeito da adubação nitrogenada no algodoeiro em sistema integrado lavoura-pecuária e plantio direto.
Modeling Quasi-Static and Fatigue-Driven Delamination Migration
An approach was proposed and assessed for the high-fidelity modeling of progressive damage and failure in composite materials. It combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. Delamination, matrix cracking, and migration were captured failure and migration criteria based on fracture mechanics. Quasi-static and fatigue loading were modeled within the same overall framework. The methodology proposed was illustrated by simulating the delamination migration test, showing good agreement with the available experimental data
Seleção de genótipos em uma população de melhoramento de manga rosa usando o método multivariado biplot.
Mango (Mangifera indica L.) trees stand out among the main fruit trees cultivated in Brazil. The mango rosa fruit is a very popular local variety (landrace), especially because of their superior technological characteristics such as high contents of Vitamin C and soluble solids (SS), as well as attractive taste and color. The objective of this study was to select a breeding population of mango rosa (polyclonal variety; ≥5 individuals) that can simultaneously meet the fresh and processed fruit Vmarkets, using the multivariate method of principal components and the biplot graphic
Real Time Analysis of Thermal Activation via Sphaleron Transitions
We study the process of thermal activation mediated by sphaleron transitions
by analyzing the real-time dynamics of the decay out of equilibrium in a
dimensional field theory with a metastable state. The situation considered is
that of a rapid supercooling in which the system is trapped in a metastable
state at a temperature larger than the mass of the quanta, but smaller than the
energy to create a critical droplet. The initial density matrix is evolved in
time and the nucleation rate (probability current at the saddle point) is
computed. The nucleation rate is {\it time dependent}, vanishing at early
times, reaching a maximum at a time with the mass of quanta
in the metastable state, and decreasing at long times as a consequence of
unitarity. An estimate for the average number of particles of ``true vacuum''
produced as a function of time during the nucleation process is obtained.Comment: 26 pages 6 figures (available upon request), PITT-93-06, LATE
HCG 16 Revisited: Clues About Galaxy Evolution in Groups
We present new spectroscopic observations of 5 galaxies, members of the
unusually active compact group HCG 16, observed using the Palomar 5m telescope.
The high signal to noise ratios (S/N ) of the spectra allow us to
study the variation of the emission line characteristics and the stellar
populations in the nucleus and the circumnuclear regions of the galaxies. The
emission line characteristics of these galaxies are complex, varying between
Seyfert 2 and LINERs or between LINERs and starbursts. All of the galaxies show
traces of intermediate age stellar populations, supporting our previous result
that post-starburst galaxies are common in compact groups. The galaxies
HCG16--4 and HCG16--5 show double nuclei and therefore could be two cases of
recent merger. Our observations support a scenario where HCG 16 was formed by
the successive merger of metal poor, low mass galaxies. The galaxies HCG16--1
and HCG16--2, which are more evolved, form the old core of the group. Galaxies
HCG16--4 and HCG16--5 are two more recent additions still in a merging phase.
Galaxy HCG16--5 is a starburst galaxy which is just beginning to fall into the
core. If HCG 16 is representative of compact groups in their early stage, the
whole set of observations implies that the formation of compact groups is the
result of hierarchical galaxy formation. HCG 16 could be one example of this
process operating in the local universe.Comment: tar file containing text and figures is available at
http://www.daf.on.br/~reinaldo/paper.htm
Knotting probabilities after a local strand passage in unknotted self-avoiding polygons
We investigate the knotting probability after a local strand passage is
performed in an unknotted self-avoiding polygon on the simple cubic lattice. We
assume that two polygon segments have already been brought close together for
the purpose of performing a strand passage, and model this using Theta-SAPs,
polygons that contain the pattern Theta at a fixed location. It is proved that
the number of n-edge Theta-SAPs grows exponentially (with n) at the same rate
as the total number of n-edge unknotted self-avoiding polygons, and that the
same holds for subsets of n-edge Theta-SAPs that yield a specific
after-strand-passage knot-type. Thus the probability of a given
after-strand-passage knot-type does not grow (or decay) exponentially with n,
and we conjecture that instead it approaches a knot-type dependent amplitude
ratio lying strictly between 0 and 1. This is supported by critical exponent
estimates obtained from a new maximum likelihood method for Theta-SAPs that are
generated by a composite (aka multiple) Markov Chain Monte Carlo BFACF
algorithm. We also give strong numerical evidence that the after-strand-passage
knotting probability depends on the local structure around the strand passage
site. Considering both the local structure and the crossing-sign at the strand
passage site, we observe that the more "compact" the local structure, the less
likely the after-strand-passage polygon is to be knotted. This trend is
consistent with results from other strand-passage models, however, we are the
first to note the influence of the crossing-sign information. Two measures of
"compactness" are used: the size of a smallest polygon that contains the
structure and the structure's "opening" angle. The opening angle definition is
consistent with one that is measurable from single molecule DNA experiments.Comment: 31 pages, 12 figures, submitted to Journal of Physics
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