14,756 research outputs found
Ising Spin Glass in a Transverse Magnetic Field
We study the three-dimensional quantum Ising spin glass in a transverse
magnetic field following the evolution of the bond probability distribution
under Renormalisation Group transformations. The phase diagram (critical
temperature {\em vs} transverse field ) we obtain shows a finite
slope near , in contrast with the infinite slope for the pure case. Our
results compare very well with the experimental data recently obtained for the
dipolar Ising spin glass LiHoYF, in a transverse field.
This indicates that this system is more apropriately described by a model with
short range interactions than by an equivalent Sherrington-Kirkpatrick model in
a transverse field.Comment: 7 pages, RevTeX3, Nota Cientifica PUC-Rio 23/9
Magnetism and Pairing in Hubbard Bilayers.
We study the Hubbard model on a bilayer with repulsive on-site interactions,
, in which fermions undergo both intra-plane () and inter-plane ()
hopping. This situation is what one would expect in high-temperature
superconductors such as YBCO, with two adjacent CuO planes. Magnetic and
pairing properties of the system are investigated through Quantum Monte Carlo
simulations for both half- and quarter-filled bands. We find that in all cases
inter-planar pairing with symmetry is dominant over planar
pairing with symmetry, and that for large enough pair
formation is possible through antiferromagnetic correlations. However, another
mechanism is needed to make these pairs condense into a superconducting state
at lower temperatures. We identify the temperature for pair formation with the
spin gap crossover temperature. [Submitted to Phys. Rev. B]Comment: 7 pages, uuencoded self-unpacking PS file with text and figures
Suppression of Anderson localization of light and Brewster anomalies in disordered superlattices containing a dispersive metamaterial
Light propagation through 1D disordered structures composed of alternating
layers, with random thicknesses, of air and a dispersive metamaterial is
theoretically investigated. Both normal and oblique incidences are considered.
By means of numerical simulations and an analytical theory, we have established
that Anderson localization of light may be suppressed: (i) in the long
wavelength limit, for a finite angle of incidence which depends on the
parameters of the dispersive metamaterial; (ii) for isolated frequencies and
for specific angles of incidence, corresponding to Brewster anomalies in both
positive- and negative-refraction regimes of the dispersive metamaterial. These
results suggest that Anderson localization of light could be explored to
control and tune light propagation in disordered metamaterials.Comment: 4 two-column pages, 3 figure
Análise in silico de genes envolvidos no transporte de nitrato, amônio e uréia em cafeeiro.
O nitrogênio (N) é o nutriente mais requerido pelo cafeeiro, sendo adquirido principalmente pelas raízes. As formas de N mais abundantes em solos agrícolas são nitrato (NO3-) e amônio (NH4+), enquanto que a uréia [CO(NH)2 O nitrato (NO] é a principal forma de N utilizada na adubação do cafeeiro. Devido a participação significativa da adubação nitrogenada nos custos de produção do café, é de interesse a identificação de genes envolvidos na absorção radicular e translocação de nitrogênio no cafeeiro, visando uma otimização da eficiência do uso do nitrogênio pela cultura. Neste trabalho foram encontradas etiquetas de sequências expressas (ESTs) no banco de dados do Projeto Genoma Café relacionadas ao transporte das formas mais relevantes na aquisição do N. O número de contigs/singlets para as diferentes famílias de transportadores decresceu na ordem: nitrato (NRT) > amônio (AMT) > uréia (DUR3). A maior expressão e diversidade de transportadores de nitrato refletem a importância desta forma de N na nutrição e fisiologia do cafeeiro, assim como na maioria das outras espécies de plantas
Fixação biológica de nitrogênio na cultura do arroz irrigado por inundação: Parte I: bactérias endofíticas diazotróficas isoladas das cultivares BRS 7 "Taim" e BRS Pelota.
bitstream/item/44624/1/documento-303.pd
Avaliação do desempenho produtivo de ovinos SRD em pastagens de capim-búffel, sob duas variedades e três ofertas de biomassa no Semiárido de Pernambuco.
Desempenho agronômico de cultivares de batata-doce em Palmas, TO.
O presente trabalho teve como objetivo avaliar o desempenho agronômico de oito cultivares utilizando mudas que passaram pela limpeza clonal.Suplemento. Edição dos Anais do 53 Congresso Brasileiro de Olericultura
Equation of state of charged colloidal suspensions and its dependence on the thermodynamic route
The thermodynamic properties of highly charged colloidal suspensions in
contact with a salt reservoir are investigated in the framework of the
Renormalized Jellium Model (RJM). It is found that the equation of state is
very sensitive to the particular thermodynamic route used to obtain it.
Specifically, the osmotic pressure calculated within the RJM using the contact
value theorem can be very different from the pressure calculated using the
Kirkwood-Buff fluctuation relations. On the other hand, Monte Carlo (MC)
simulations show that both the effective pair potentials and the correlation
functions are accurately predicted by the RJM. It is suggested that the lack of
self-consistency in the thermodynamics of the RJM is a result of neglected
electrostatic correlations between the counterions and coions
Multi-critical point in a diluted bilayer Heisenberg quantum antiferromagnet
The S=1/2 Heisenberg bilayer antiferromagnet with randomly removed
inter-layer dimers is studied using quantum Monte Carlo simulations. A
zero-temperature multi-critical point (p*,g*) at the classical percolation
density p=p* and inter-layer coupling g* approximately 0.16 is demonstrated.
The quantum critical exponents of the percolating cluster are determined using
finite-size scaling. It is argued that the associated finite-temperature
quantum critical regime extends to zero inter-layer coupling and could be
relevant for antiferromagnetic cuprates doped with non-magnetic impurities.Comment: 4 pages, 6 figures. v2: only minor changes; accepted for publication
in Phys. Rev. Let
Influence of application time on survival, establishment and ability of Clonostachys Rosea to control Botrytis Cinerea on roses.
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