6,013 research outputs found
Parallel structurally-symmetric sparse matrix-vector products on multi-core processors
We consider the problem of developing an efficient multi-threaded
implementation of the matrix-vector multiplication algorithm for sparse
matrices with structural symmetry. Matrices are stored using the compressed
sparse row-column format (CSRC), designed for profiting from the symmetric
non-zero pattern observed in global finite element matrices. Unlike classical
compressed storage formats, performing the sparse matrix-vector product using
the CSRC requires thread-safe access to the destination vector. To avoid race
conditions, we have implemented two partitioning strategies. In the first one,
each thread allocates an array for storing its contributions, which are later
combined in an accumulation step. We analyze how to perform this accumulation
in four different ways. The second strategy employs a coloring algorithm for
grouping rows that can be concurrently processed by threads. Our results
indicate that, although incurring an increase in the working set size, the
former approach leads to the best performance improvements for most matrices.Comment: 17 pages, 17 figures, reviewed related work section, fixed typo
Magnetoelectric effects in an organo-metallic quantum magnet
We observe a bilinear magnetic field-induced electric polarization of 50 in single crystals of NiCl-4SC(NH) (DTN). DTN forms a
tetragonal structure that breaks inversion symmetry, with the highly polar
thiourea molecules all tilted in the same direction along the c-axis.
Application of a magnetic field between 2 and 12 T induces canted
antiferromagnetism of the Ni spins and the resulting magnetization closely
tracks the electric polarization. We speculate that the Ni magnetic forces
acting on the soft organic lattice can create significant distortions and
modify the angles of the thiourea molecules, thereby creating a magnetoelectric
effect. This is an example of how magnetoelectric effects can be constructed in
organo-metallic single crystals by combining magnetic ions with electrically
polar organic elements.Comment: 3 pages, 3 figure
Electron Spin Resonance of defects in the Haldane System Y(2)BaNiO(5)
We calculate the electron paramagnetic resonance (EPR) spectra of the
antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different
values of x and temperature T much lower than the Haldane gap (~100K). The
low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all
parameters determined from experiment, has been solved using DMRG. The observed
EPR spectra are quantitatively reproduced by this model. The presence of
end-chain S=1/2 states is clearly observed as the main peak in the spectrum and
the remaining structure is completely understood.Comment: 5 pages, 4 figures include
Crescimento e nutrição na abobrinha-de-moita em plantio direto utilizando cobertura do solo com fitomassa de leguminosa arbustiva com e sem uréia.
Objetivou-se estudar aspectos do crescimento inicial e nutricional da abobrinha com uso de fitomassa da leguminosa arbustiva flemíngia cobrindo o solo (CF), com e sem uréia, em plantio direto sobre um Latossolo Amarelo muito argiloso, em Manaus-AM (julho de 2011), utilizando delineamento experimental em blocos casualizados com quatro repetições.Edição dos Resumos do 52º Congresso Brasileiro de Olericultura, Salvador, jul. 2012
Avaliação fenológica de Gossypium hirsutum L. E Hibiscus sabdariffa L. pertencentes à família Malvaceae.
Diagnose e perdas na cadeia produtiva da manga causadas por Neofusicoccum parvum.
Considerada uma das principais culturas do poloagrícola Petrolina, PE/Juazeiro, BA, a mangueira éresponsável por grande parte da absorção de mão-de-obra e de geração de divisas para a região. Este polocontribui com mais de 90% da exportação nacional demanga (ARAÚJO; CORREIA, 2004; PINTOet al.,2004). Entretanto, diferentes patógenos têm colocadoem risco o agronegócio da manga, a exemplo daspodridões causadas por fungos. Agentes de doençasque possuem a fase quiescente podem comprometer acredibilidade de produtores e fornecedores da fruta emrelação ao mercado consumidor. Podridões podemafetar a cultura da manga, e dentre os agentes causaispodem-se destacar os fungos Colletotrichumgloeosporioides, Alternariaalternata, Lasiodiplodiatheobromae(CHOUDHURY; COSTA, 2004) e o maisrecente, Neofusicoccum parvum (COSTA, 2008). Alémde podridão mole e/ou peduncular em manga, oNeofusicoccum parvum pode causar morte descendentee queima de inflorescência (SAAIMAN, 1997; PLOETZ;FREEMAN, 2009), ocasionando grandes perdas naprodução de manga.bitstream/item/17590/1/Comunicado-Neofusicoccum.pd
Dejetos líquidos de suínos como fonte suplementar de nitrogênio mineral na cultura do milho em sistema de sequeiro.
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