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## Distribuição de corrente entre semicondutores em retificadores de alta corrente - estudo de casos reais.; Current distribution in high current rectifier semiconductors - real case study.

Fonte: Biblioteca Digitais de Teses e Dissertações da USP
Publicador: Biblioteca Digitais de Teses e Dissertações da USP

Tipo: Dissertação de Mestrado
Formato: application/pdf

Publicado em 26/09/2008
PT

Relevância na Pesquisa

65.87%

Nos processos industriais envolvendo eletrólise, como na produção de alumínio, cobre, zinco, níquel, manganês, carbeto de silício, cloro e seus derivados, as correntes envolvidas em geral atingem patamares que excedem o valor nominal de um único semicondutor, exigindo a associação de componentes em paralelo com uma distribuição de corrente equilibrada. Este trabalho apresenta uma análise comparativa da distribuição de corrente em associações de semicondutores em paralelo em vinte retificadores de alta potência com diferentes tipos de arquitetura física de barramentos. A particularidade deste estudo é a medição simultânea das correntes em todos os semicondutores de todos os ramos do retificador obtendo-se uma imagem da distribuição real de correntes do conversor.; The industrial electrolytic processes to produce, aluminum, cooper, zinc, nickel, manganese, silicon carbide, chlorine and its derivative, require current values which greatly exceed the capability of single rectifying devices and paralleled combinations of semiconductors or equipments are necessary. This study evaluated through a comparative analyzes twenty rectifiers, with different busbar geometries, in order to verify the current distribution in paralleled devices. The differential of this study is the simultaneous measurement of currents in all semiconductors of each branch in order to obtain a real representation of the rectifiers current distribution.

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## Co-ocorrência, interações tróficas e distribuição potencial da onça-pintada (Panthera onca) no bioma Amazônia; Co-occurrence, trophic interactions and potential distribution of jaguar (Panthera onca) in the Amazon biome

Fonte: Biblioteca Digitais de Teses e Dissertações da USP
Publicador: Biblioteca Digitais de Teses e Dissertações da USP

Tipo: Tese de Doutorado
Formato: application/pdf

Publicado em 27/05/2015
PT

Relevância na Pesquisa

45.8%

#Apex predator#Co-occurrence#Co-ocorrência#Controle top-down#Distribuição potencial#Liberação mesopredador#Mesopredator release#Potential distribution#Predador de topo#Rede trófica#Top-down control

Predadores de topo desempenham um papel importante na manutenção dos sistemas em que eles ocorrem porque influenciam diretamente a estrutura e a dinâmica de comunidades. Desta forma, este estudo descreveu alguns mecanismos de co-ocorrência espaço-temporal entre a onça-pintada (Panthera onca) e duas espécies de mesopredadores (Puma concolor e Leopardus pardalis), o seu controle top-down na comunidade de mamíferos e os requerimentos ambientais que determinam a sua distribuição no bioma Amazônia. Para as análises de co-ocorrência espaço-temporal foram utilizados o modelo de ocupação e a densidade de Kernel utilizando os registros de armadilhamento fotográfico (2008-2011). Para descrever o controle top-down foi elaborada uma rede trófica utilizando os itens alimentares consumidos pelas espécies e disponíveis na literatura (1983-2014). Para indicar quais as áreas mais adequadas foi utilizado o modelo de distribuição de espécies utilizando as localizações geográficas de ocorrência da espécie que foram compiladas de três diferentes bases de dados (2000-2013). A ocorrência das duas espécies de mesopredadores não foi diferente nos sítios com e sem a onça-pintada nas quatro temporadas de amostragem. A probabilidade de detecção da jaguatirica foi maior nos sítios com a presença da onça-pintada em apenas uma temporada de amostragem. A sobreposição no período de atividade das espécies de mesopredadores com a onça-pintada foi baixa...

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## Assessing the areas under risk of invasion within islands through potential distribution modelling: the case of Pittosporum undulatum in São Miguel, Azores

Fonte: Elsevier
Publicador: Elsevier

Tipo: Artigo de Revista Científica

Publicado em 09/11/2009
ENG

Relevância na Pesquisa

45.79%

#Invasive Species#Species Distribution Models#Islands#Azorean Laurel Forest#Conservation#Risk Assessment

Copyright © 2009 Elsevier GmbH. All rights reserved.; Non-indigenous plant species have been frequently reported as successful invaders in island environments, changing plant community composition and structure. This is the case of the sweet pittosporum (Pittosporum undulatum), native from Australia, which is one of the most successful plant invaders in the Azores archipelago. Data extracted from recent forestry inventories were used to model and map the potential distribution of P. undulatum in São Miguel, the larger island of the Azores. Current distribution of P. undulatum is related to climate, altitude and some human activity effects. Further analysis of the areas under risk of invasion showed that protected areas are under potential threat, although only a few native forest remnants seem to be threatened due to future expansion of P. undulatum, since the current distribution of these native communities has been reduced due to clearing and competition with invasive plants. We discuss the threats that any further expansion of the species will represent for low-altitude native forests, as well as the utility of species distribution models in the assessment of the areas under risk of invasion.

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## Influence of intercellular clefts on potential and current distribution in a multifiber preparation.

Fonte: PubMed
Publicador: PubMed

Tipo: Artigo de Revista Científica

Publicado em /05/1980
EN

Relevância na Pesquisa

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A theoretical model is presented for current and voltage clamp of multifiber bundles in a double sucrose gap. Attention is focused on methodological errors introduced by the intercellular cleft resistance. The bundle is approximated by a continuous geometry. Voltage distribution, as a function of radial distance and time, is defined by a parabolic partial differential equation which is specified for different membrane characteristics. Assuming a linear membrane, analytical solutions are given for current step and voltage step conditions. The theoretical relations (based on Bessel functions) may be used to calculate membrane conductance and capacity from experimental clamp data. The case of a nonlinear membrane with standard Hodgkin-Huxley kinetics for excitatory Na current is treated assuming maximum Na conductances (gNa) of 120, 10, and 1 mmho/cm2. Numerical simulations are presented for potential and current distribution in a bundle of 60 microns diameter during depolarizing voltage steps. Adequate voltage control is restricted to the peripheral fibers of the bundle whereas the membrane potential of the inner fibers deviates from the command level during early inward current, tending to the Na equilibrium potential. In the peak current-voltage diagram the loss of voltage control is reflected by an increased steepness of the negative region and a decreased slope conductance of the positive region. With gNa = 120 mmho/cm2...

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## A primary current distribution model of a novel micro-electroporation channel configuration

Fonte: Springer US
Publicador: Springer US

Tipo: Artigo de Revista Científica

EN

Relevância na Pesquisa

45.78%

Traditional macro and micro-electroporation devices utilize facing electrodes, which generate electric fields inversely proportional to their separation distance. Although the separation distances in micro-electroporation devices are significantly smaller than those in macro-electroporation devices, they are limited by cell size. Because of this, significant potential differences are required to induce electroporation. These potential differences are often large enough to cause water electrolysis, resulting in electrode depletion and bubble formation, both of which adversely affect the electroporation process. Here, we present a theoretical study of a novel micro-electroporation channel composed of an electrolyte flowing over a series of adjacent electrodes separated by infinitesimally small insulators. Application of a small, non-electrolysis inducing potential difference between the adjacent electrodes results in radially-varying electric fields that emanate from these insulators, causing cells flowing through the channel to experience a pulsed electric field. This eliminates the need for a pulse generator, making a minimal power source (such as a battery) the only electrical equipment that is needed. A non-dimensional primary current distribution model of the novel micro-electroporation channel shows that decreasing the channel height results in an exponential increase in the electric field magnitude...

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## Evidence of environmental niche differentiation in the striped mouse (Rhabdomys sp.): inference from its current distribution in southern Africa

Fonte: Blackwell Publishing Ltd
Publicador: Blackwell Publishing Ltd

Tipo: Artigo de Revista Científica

Publicado em /05/2012
EN

Relevância na Pesquisa

45.89%

The aim of this study was to characterize environmental differentiation of lineages within Rhabdomys and provide hypotheses regarding potential areas of contact between them in the Southern African subregion, including the Republic of South Africa, Lesotho, and Namibia. Records of Rhabdomys taxa across the study region were compiled and georeferenced from the literature, museum records, and field expeditions. Presence records were summarized within a 10 × 10 km grid covering the study area. Environmental information regarding climate, topography, land use, and vegetation productivity was gathered at the same resolution. Multivariate statistics were used to characterize the current environmental niche and distribution of the whole genus as well as of three mitochondrial lineages known to occur in southern Africa. Distribution modeling was carried out using MAXENT in order to generate hypotheses regarding current distribution of each taxa and their potential contact zones. Results indicate that the two species within Rhabdomys appear to have differentiated across the precipitation/temperature gradient present in the region from east to west. R. dilectus occupies the wettest areas in eastern southern Africa, while R. pumilio occupies the warmer and drier regions in the west...

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## Anomalous statistical properties of the critical current distribution in superconductor containing fractal clusters of a normal phase

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/01/2003

Relevância na Pesquisa

45.81%

Statistical properties of the critical current distribution in superconductor
with fractal clusters of a normal phase are considered. It is found that there
is the range of fractal dimensions in which the variance and expectation for
this distribution increases infinitely. Simple technique of avoiding such a
divergence by the use of truncated distributions is proposed. It is suggested
that the most current-carrying capability of a superconductor can be achieved
by modifying the cluster area distribution in such a way that the regime of
giant variance of critical currents will be realized.; Comment: 11 pages with 6 figures

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## Current distribution and transition width in superconducting transition-edge sensors

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/12/2012

Relevância na Pesquisa

45.92%

Present models of the superconducting-to-normal transition in transition-edge
sensors (TESs) do not describe the current distribution within a biased TES.
This distribution is complicated by normal-metal features that are integral to
TES design. We present a model with one free parameter that describes the
evolution of the current distribution with bias. To probe the current
distribution experimentally, we fabricated TES devices with different current
return geometries. Devices where the current return geometry mirrors current
flow within the device have sharper transitions, thus allowing for a direct
test of the current-flow model. Measurements from these devices show that
current meanders through a TES low in the resistive transition but flows across
the normal-metal features by 40% of the normal-state resistance. Comparison of
transition sharpness between device designs reveals that self-induced magnetic
fields play an important role in determining the width of the superconducting
transition. [http://dx.doi.org/10.1063/1.4771984]; Comment: 5 pages, 4 figures

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## Current Distribution in the Three-Dimensional Random Resistor Network at the Percolation Threshold

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 11/08/1995

Relevância na Pesquisa

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We study the multifractal properties of the current distribution of the
three-dimensional random resistor network at the percolation threshold. For
lattices ranging in size from $8^3$ to $80^3$ we measure the second, fourth and
sixth moments of the current distribution, finding {\it e.g.\/} that
$t/\nu=2.282(5)$ where $t$ is the conductivity exponent and $\nu$ is the
correlation length exponent.; Comment: 10 pages, latex, 8 figures in separate uuencoded file

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## Soft-boundary graphene nanoribbon formed by a graphene sheet above a perturbed ground plane: conductivity profile and SPP modal current distribution

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.78%

An infinite sheet of graphene lying above a perturbed ground plane is
studied. The perturbation is a two dimensional ridge, and a bias voltage is
applied between the graphene and the ground plane, resulting in a graphene
nanoribbonlike structure with a soft-boundary (SB) The spatial distribution of
the graphene conductivity forming the soft-boundary is studied as a function of
the ridge parameters and the bias voltage. The current distribution of the
fundamental TM surface plasmon polariton (SPP) is considered. The effect of the
ridge parameters and shape of the soft boundary on the current distributions
are investigated, and the conditions are studied under which the mode remains
confined to the vicinity of the ridge region.

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## Current Distribution and random matrix ensembles for an integrable asymmetric fragmentation process

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/05/2004

Relevância na Pesquisa

45.81%

We calculate the time-evolution of a discrete-time fragmentation process in
which clusters of particles break up and reassemble and move stochastically
with size-dependent rates. In the continuous-time limit the process turns into
the totally asymmetric simple exclusion process (only pieces of size 1 break
off a given cluster). We express the exact solution of master equation for the
process in terms of a determinant which can be derived using the Bethe ansatz.
From this determinant we compute the distribution of the current across an
arbitrary bond which after appropriate scaling is given by the distribution of
the largest eigenvalue of the Gaussian unitary ensemble of random matrices.
This result confirms universality of the scaling form of the current
distribution in the KPZ universality class and suggests that there is a link
between integrable particle systems and random matrix ensembles.; Comment: 11 pages

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## Local Current Distribution and "Hot Spots" in the Integer Quantum Hall Regime

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.83%

In a recent experiment, the local current distribution of a two-dimensional
electron gas in the quantum Hall regime was probed by measuring the variation
of the conductance due to local gating. The main experimental finding was the
existence of "hot spots", i.e. regions with high degree of sensitivity to local
gating, whose density increases as one approaches the quantum Hall transition.
However, the direct connection between these "hot spots" and regions of high
current flow is not clear. Here, based on a recent model for the quantum Hall
transition consisting of a mixture of perfect and quantum links, the relation
between the "hot spots" and the current distribution in the sample has been
investigated. The model reproduces the observed dependence of the number and
sizes of "hot spots" on the filling factor. It is further demonstrated that
these "hot spots" are not located in regions where most of the current flows,
but rather, in places where the currents flow both when injected from the left
or from the right. A quantitative measure, the harmonic mean of these currents
is introduced and correlates very well with the "hot spots" positions.

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## Sheet-current distribution in a dc SQUID washer probed by vortices

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.84%

We present a novel method, based on vortex imaging by low-temperature
scanning electron microscopy (LTSEM), to directly image the sheet-current
distribution in YBa2Cu3O7 dc SQUID washers. We show that the LTSEM vortex
signals are simply related to the scalar stream function describing the
vortex-free circulating sheet-current distribution J. Unlike previous inversion
methods that infer the current distribution from the measured magnetic field,
our method uses pinned vortices as local detectors for J. Our experimental
results are in very good agreement with numerical calculations of J.; Comment: 4 pages, 3 figures; submitted to Physical Review Letters

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## Current distribution and ac loss for a superconducting rectangular strip with in phase alternating current and applied field

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/10/2005

Relevância na Pesquisa

45.78%

The case of ac transport at in-phase alternating applied magnetic fields for
a superconducting rectangular strip with finite thickness has been
investigated. The applied magnetic field is considered perpendicular to the
current flow. We present numerical calculations assuming the critical state
model of the current distribution and ac loss for various values of aspect
ratio, transport current and applied field amplitude. A rich phenomenology is
obtained due to the metastable nature of the critical state. We perform a
detailed comparison with the analytical limits and we discuss their
applicability for the actual geometry of superconducting conductors. We also
define a loss factor which allow a more detailed analysis of the ac behavior
than the ac loss. Finally, we compare the calculations with experiments,
showing a significant qualitative and quantitative agreement without any
fitting parameter.; Comment: 21 pages, 12 figures in 15 extra pages/files. Submitted to Physical
Review B

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## A 128-channel picoammeter system and its application on charged particle beam current distribution measurements

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/09/2015

Relevância na Pesquisa

45.8%

A 128-channel picoammeter system is constructed based on instrumentation
amplifiers. Taking the advantages of high electric potential and narrow
bandwidth in DC energetic charged beam measurements, current resolution better
than 5 fA can be achieved. Two 128-channel Faraday cup arrays are built, and
are employed for ion and electron beam current distribution measurements. Tests
with 60 keV O3+ ions and 2 keV electrons show that it can provide exact
boundaries when a positive charged particle beam current distribution is
measured.; Comment: 6 piges, 8 figures; Submitted to Review of Scientific Instruments

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## Critical Current Distribution in Spin Transfer Switched Magnetic Tunnel Junctions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 15/04/2005

Relevância na Pesquisa

45.91%

The spin transfer switching current distribution within a cell was studied in
magnetic tunnel junction based structures having alumina barriers with
resistance-area product (RA) of 10 to 30 Ohm-um2 and tunneling
magneto-resistance (TMR) of ~20%. These were patterned into current
perpendicular to plane configured nano-pillars having elliptical cross-sections
of area ~0.02 um2. The width of the critical current distribution
(sigma/average of distribution), measured using 30 ms current pulse width, was
found to be 7.5% and 3.5% for cells with thermal factor (KuV/kBT) of 40 and 65
respectively. The distribution width did not change significantly for pulse
widths between 1 s and 4 ms. An analytical expression for probability density
function, p(I/Ico) was derived considering the thermally activated spin
transfer model, which supports the experimental observation that the thermal
factor is the most significant parameter in determining the within cell
critical current distribution width.; Comment: 12 pages, 4 figures

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## Quantum Hall Effect: Current Distribution and Existence of Extended States

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.81%

We present a consistent description of the current distribution in the
quantum Hall effect, based on two main ingredients: the location of the
extended states and the distribution of the electric field. We show that the
interaction between electrons produces a boundary line below the Fermi energy,
which extends from source to drain. The existence of this line and that of a
physical boundary are responsible for the formation of a {\em band} of extended
states that carry the Hall current. The number and density of these extended
states are determined by the difference between the energy of this
equipotential boundary line and the energy of the single extended state that
would exist in an infinite system. This is used to prove that the band of
extended states is distributed through the bulk of the sample. We explore the
distribution of the Hall currents and electric fields in by presenting a model
that captures the main features of the charge relaxation processes. Theoretical
predictions based on this model and on the preceding theory are used to
unambiguously explain recent experimental findings.; Comment: 12 pages, 8 eps figures (in paper)

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## Generation of Relativistic Electron Bunches with Arbitrary Current Distribution via Transverse-to-Longitudinal Phase Space Exchange

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 26/07/2010

Relevância na Pesquisa

45.78%

We propose a general method for tailoring the current distribution of
relativistic electron bunches. The technique relies on a recently proposed
method to exchange the longitudinal phase space emittance with one of the
transverse emittances. The method consists of transversely shaping the bunch
and then converting its transverse profile into a current profile via a
transverse-to-longitudinal phase-space-exchange beamline. We show that it is
possible to tailor the current profile to follow, in principle, any desired
distributions. We demonstrate, via computer simulations, the application of the
method to generate trains of microbunches with tunable spacing and
linearly-ramped current profiles. We also briefly explore potential
applications of the technique.; Comment: 13 pages, 17 figures

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## Universal Scaling of Optimal Current Distribution in Transportation Networks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 03/05/2009

Relevância na Pesquisa

45.84%

Transportation networks are inevitably selected with reference to their
global cost which depends on the strengths and the distribution of the embedded
currents. We prove that optimal current distributions for a uniformly injected
d-dimensional network exhibit robust scale-invariance properties, independently
of the particular cost function considered, as long as it is convex. We find
that, in the limit of large currents, the distribution decays as a power law
with an exponent equal to (2d-1)/(d-1). The current distribution can be exactly
calculated in d=2 for all values of the current. Numerical simulations further
suggest that the scaling properties remain unchanged for both random injections
and by randomizing the convex cost functions.; Comment: 5 pages, 5 figures

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## Historical climate modelling predicts patterns of current biodiversity in the Brazilian Atlantic forest

Fonte: Blackwell Publishing Ltd
Publicador: Blackwell Publishing Ltd

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.84%

#Keywords: biodiversity#climate modeling#endemism#genetic variation#geographical distribution#Holocene#mitochondrial DNA#paleoclimate#palynology#phylogeography#Pleistocene

Aim: We aim to propose validated, spatially explicit hypotheses for the late Quaternary distribution of the Brazilian Atlantic forest, and thereby provide a framework for integrating analyses of species and genetic diversity in the region. Location: The Atlantic forest, stretching along the Brazilian coast. Methods: We model the spatial range of the forest under three climatic scenarios (current climate, 6000 and 21,000 years ago) with BIOCLIM and MAXENT. Historically stable areas or refugia are identified as the set of grid cells for which forest presence is inferred in all models and time projections. To validate inferred refugia, we test whether our models are matched by the current distribution of the forest and by fossil pollen data. We then investigate whether the location of inferred forest refugia is consistent with current patterns of species endemism and existing phylogeographical data. Results: Forest models agree with pollen records and predict a large area of historical forest stability in the central corridor (Bahia), as well as a smaller refuge (Pernambuco) along the Brazilian coast, matching current centres of endemism in multiple taxa and mtDNA diversity patterns in a subset of the species examined. Less historical stability is predicted in coastal areas south of the Doce river...

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