2,200 research outputs found
Dimensionality effects in the LDOS of ferromagnetic hosts probed via STM: spin-polarized quantum beats and spin filtering
We theoretically investigate the local density of states (LDOS) probed by a
STM tip of ferromagnetic metals hosting a single adatom and a subsurface
impurity. We model the system via the two-impurity Anderson Hamiltonian. By
using the equation of motion with the relevant Green functions, we derive
analytical expressions for the LDOS of two host types: a surface and a quantum
wire. The LDOS reveals Friedel-like oscillations and Fano interference as a
function of the STM tip position. These oscillations strongly depend on the
host dimension. Interestingly, we find that the spin-dependent Fermi wave
numbers of the hosts give rise to spin-polarized quantum beats in the LDOS.
While the LDOS for the metallic surface shows a damped beating pattern, it
exhibits an opposite behavior in the quantum wire. Due to this absence of
damping, the wire operates as a spatially resolved spin filter with a high
efficiency.Comment: revised tex
A experiência da metodologia camponês a camponês em territórios de identidade rural no Nordeste do Brasil.
A pesquisa teve por objetivo a promoção da transição agroeocológica em territórios de identidade rural por meio do ajuste da metodologia ?campesino a campesino? visando à promoção do desenvolvimento sustentável e solidário nas condições do Nordeste do Brasil. Foram identificadas famílias agricultoras camponesas com perfil para inserção em redes de transição agroecológica, potenciais promotores de intercâmbios entre elas para a troca de experiências e saberes. O trabalho foi realizado no Território de identidade rural Sul Sergipano localizado nos tabuleiros costeiros do estado de Sergipe. A realização das ações resultou de uma parceria efetiva entre Colegiado Territorial, Empresa Brasileira de Pesquisa Agropecuária (Embrapa), Instituto Nacional de Colonização e Reforma Agrária (INCRA-SE), Movimento dos Trabalhadores Sem Terra (MST), Universidade Federal de Sergipe (UFS), Universidade Federal de Viçosa (UFV) e Centro de Formação e Assistência Comunitária (CFAC). Para a operacionalização do trabalho e ajuste da metodologia foram potencializadas as redes sociais de agroecologia existentes na região. Os resultados referem-se à identificação das principais experiências de transição agroecológica da região, a consolidação das redes existentes e a criação de formas inovadoras de intercâmbio de experiências potencializadas pela metodologia ajustada, então denominada ?camponês a camponês?. Os aprendizados referem-se à forma de construção coletiva necessária para a introdução de conhecimento agroecológico e, principalmente, de conceitos de maior complexidade, como agrofloresta sucessional e, a perspectiva de construção de uma nova abordagem para a extensão rural em agricultura familiar e camponesa em territórios de identidade rural
Magnetization plateau in a two-dimensional multiple-spin exchange model
We study a multiple-spin exchange model on a triangular lattice, which is a
possible model for low-density solid 3He films. Due to strong competitions
between ferromagnetic three-spin exchange and antiferromagnetic four-spin one,
the ground states are highly degenerate in the classical limit. At least
2^{L/2}-fold degeneracy exists on the L*L triangular lattice except for the
SO(3) symmetry. In the magnetization process, we found a plateau at
m/m_{sat}=1/2, in which the ground state is "uuud state" (a collinear state
with four sublattices). The 1/2-plateau appears due to the strong four-spin
exchange interaction. This plateau survives against both quantum and thermal
fluctuations. Under a magnetic field which realizes the "uuud" ordered state, a
phase transition occurs at a finite temperature. We predict that low-density
solid 3He thin films may show the 1/2-plateau in the magnetization process.
Experimental observation of the plateau will verify strength of the four-spin
exchange. It is also discussed that this magnetization plateau can be
understood as an insulating-conducting transition in a particle picture.Comment: 10 pages, RevTeX, 12 figures, added a reference and corrected typos,
to be published in Phys.Rev.B (01 APR 99
Um modelo baseado no indivíduo para estudo da transmissão da anemia infecciosa equina por mutuca no Pantanal brasileiro.
Resumo. A Anemia Infeciosa Equina (AIE) é uma doença causada por um retrovírus e transmitida pelo inseto hematófago conhecido como mutuca (tabanídeo), sendo observada nas últimas décadas a prevalência de 50% entre os animais de serviço no Pantanal brasileiro. Este trabalho apresenta um modelo baseado no indivíduo para analisar a dinâmica de transmissão da AIE pela mutuca no Pantanal. Considerando um período de 40 anos de simulação, os resultados mostram que a mutuca não pode ser responsável sozinha pela alta prevalência da doença na região, sendo necessário estudos mais detalhados das práticas de manejo usadas.SBIAgro 2013
Uso da modelagem baseada no indivíduo para estudo da dinâmica de propagação de doença no cavalo pantaneiro.
Este trabalho objetiva o uso da modelagem baseada no indivíduo (MBI) para analisar a dinâmica de propagação da anemia infecciosa equina (AIE) em cavalos de serviço usando o software TerraME, desenvolvido pelo INPE.CIIC 2013. No 13605
Predicting Thermoelectric Power Plants Diesel/Heavy Fuel Oil Engine Fuel Consumption Using Univariate Forecasting and XGBoost Machine Learning Models
Monitoring and controlling thermoelectric power plants (TPPs) operational parameters have become essential to ensure system reliability, especially in emergencies. Due to system complexity, operating parameters control is often performed based on technical know-how and simplified analytical models that can result in limited observations. An alternative to this task is using time series forecasting methods that seek to generalize system characteristics based on past information. However, the analysis of these techniques on large diesel/HFO engines used in Brazilian power plants under the dispatch regime has not yet been well-explored. Therefore, given the complex characteristics of engine fuel consumption during power generation, this work aimed to investigate patterns generalization abilities when linear and nonlinear univariate forecasting models are used on a representative database related to an engine-driven generator used in a TPP located in Pernambuco, Brazil. Fuel consumption predictions based on artificial neural networks were directly compared to XGBoost regressor adaptation to perform this task as an alternative with lower computational cost. AR and ARIMA linear models were applied as a benchmark, and the PSO optimizer was used as an alternative during model adjustment. In summary, it was possible to observe that AR and ARIMA-PSO had similar performances in operations and lower error distributions during full-load power output with normal error frequency distribution of −0.03 ± 3.55 and 0.03 ± 3.78 kg/h, respectively. Despite their similarities, ARIMA-PSO achieved better adherence in capturing load adjustment periods. On the other hand, the nonlinear approaches NAR and XGBoost showed significantly better performance, achieving mean absolute error reductions of 42.37% and 30.30%, respectively, when compared with the best linear model. XGBoost modeling was 8.7 times computationally faster than NAR during training. The nonlinear models were better at capturing disturbances related to fuel consumption ramp, shut-down, and sudden fluctuations steps, despite being inferior in forecasting at full-load, especially XGBoost due to its high sensitivity with slight fuel consumption variations
High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP~1
The globular cluster HP~1 is projected at only 3.33 degrees from the Galactic
center. Together with its distance, this makes it one of the most central
globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a
metallicity of [Fe/H]~-1.0. This means that it probably is one of the oldest
objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern
of the first stars as well as the early chemical enrichment and early formation
of stellar populations. High-resolution spectra obtained for six stars were
analyzed to derive the abundances of the light elements C, N, O, Na, and Al,
the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y , Zr, Ba,
La, and Eu.} High-resolution spectra of six red giants that are confirmed
members of the bulge globular cluster HP~1 were obtained with the 8m VLT
UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration.
The spectroscopic parameter derivation was based on the excitation and
ionization equilibrium of FeI and FeII. We confirm a mean metallicity of [Fe/H]
= -1.06~0.10, by adding the two stars that were previously analyzed in HP~1.
The alpha-elements O and Mg are enhanced by about +0.3<[O,Mg/Fe]<+0.5 dex, Si
is moderately enhanced with +0.15<[Si/Fe]<+0.35dex, while Ca and Ti show lower
values of -0.04<[Ca,Ti/Fe]<+0.28dex. The r-element Eu is also enhanced with
[Eu/Fe]~+0.4, which together with O and Mg is indicative of early enrichment by
type II supernovae. Na and Al are low, but it is unclear if Na-O are
anticorrelated. The heavy elements are moderately enhanced, with
-0.20<[La/Fe]<+0.43dex and 0.0<[Ba/Fe]<+0.75~dex, which is compatible with
r-process formation. The spread in Y, Zr, Ba, and La abundances, on the other
hand, appears to be compatible with the spinstar scenario or other additional
mechanisms such as the weak r-process.Comment: 15 pages, 8 figures In press in Astronomy & Astrophysics (2016
Estudo sobre o comportamento de cultivares de milho na região semi-árida do Estado de Sergipe.
bitstream/item/80184/1/CPATC-COM.-TEC.-16-84.pd
Thermofield Dynamics for Twisted Poincare-Invariant Field Theories: Wick Theorem and S-matrix
Poincare invariant quantum field theories can be formulated on
non-commutative planes if the statistics of fields is twisted. This is
equivalent to state that the coproduct on the Poincare group is suitably
twisted. In the present work we present a twisted Poincare invariant quantum
field theory at finite temperature. For that we use the formalism of
Thermofield Dynamics (TFD). This TFD formalism is extend to incorporate
interacting fields. This is a non trivial step, since the separation in
positive and negative frequency terms is no longer valid in TFD. In particular,
we prove the validity of Wick's theorem for twisted scalar quantum field at
finite temperature.Comment: v1: 25 pages, no figure v2: references added; typos corrected; typo
in title correcte
Balanço hidrológico da microbacia do córrego lageado, Município de Uberaba-MG, para o ano de 2012.
O manejo integrado em microbacia hidrográfica implementa uma nova maneira de se planejar e usar os recursos naturais, indo de encontro ao desenvolvimento sustentável. A compreensão do balanço hídrico, mesmo que de forma simplificada, é importante para o entendimento dos processos de degradação e conservação dos recursos naturais relacionados ao uso do solo e da água. Dentro deste contexto, o presente estudo teve por objetivo fazer o balanço hídrico da microbacia do córrego Lageado, situada no município de Uberaba, MG, para o ano de 2012. A escolha desta microbacia para este trabalho baseou-se na sua importância como terceiro maior manancial pertencente à APA (Área de Proteção Ambiental) do rio Uberaba e por estar parcialmente dentro do perímetro urbano. Nas últimas décadas, esta microbacia hidrográfica passou por intensas transformações relacionadas ao uso e à ocupação do solo
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