20,652 research outputs found
Probability distribution of the order parameter in the directed percolation universality class
The probability distributions of the order parameter for two models in the
directed percolation universality class were evaluated. Monte Carlo simulations
have been performed for the one-dimensional generalized contact process and the
Domany-Kinzel cellular automaton. In both cases, the density of active sites
was chosen as the order parameter. The criticality of those models was obtained
by solely using the corresponding probability distribution function. It has
been shown that the present method, which has been successfully employed in
treating equilibrium systems, is indeed also useful in the study of
nonequilibrium phase transitions.Comment: 6 pages, 4 figure
Produção de madeira de progĂȘnies de segunda geração de grevĂlea na RegiĂŁo de AvarĂ©, SP.
A grevĂlea (Grevillea robusta A. Cunn) Ă© uma espĂ©cie utilizada para o sombreamento de cafezais e de outras culturas agrĂcolas, ĂĄreas de pastagens e apicultura, paisagismo e como cortina quebra-ventos. Sua madeira tambĂ©m Ă© utilizada para desdobro, em serrarias. Um teste com 28 progĂȘnies de meios-irmĂŁos de segunda geração foi instalado no MunicĂpio de AvarĂ©, SĂŁo Paulo. O objetivo principal foi avaliar e selecionar o material genĂ©tico mais produtivo em volume de madeira. Dados de altura e diĂąmetro Ă altura do peito (DAP) foram coletados na ĂĄrea experimental, na idade de trĂȘs anos. Baseando-se nos dados estimados de volume cilĂndrico com casca, as seguintes conclusĂ”es foram obtidas: em AvarĂ©, SP, a progĂȘnie de segunda geração mais produtiva e com maior taxa de sobrevivĂȘncia pertencente Ă procedĂȘncia australiana de Boyd River (NSW). A progĂȘnie de segunda geração mais produtiva, em termos de volume cilĂndrico de madeira com casca, foi 138 % superior Ă media geral do teste. Considerando o valor mĂ©dio de volume de madeira para apenas as doze progĂȘnies de segunda geração mais produtivas, foi possĂvel observar um aumento de 32 % em relação Ă mĂ©dia geral do experimento.Nota tĂ©cnica
Integrable variant of the one-dimensional Hubbard model
A new integrable model which is a variant of the one-dimensional Hubbard
model is proposed. The integrability of the model is verified by presenting the
associated quantum R-matrix which satisfies the Yang-Baxter equation. We argue
that the new model possesses the SO(4) algebra symmetry, which contains a
representation of the -pairing SU(2) algebra and a spin SU(2) algebra.
Additionally, the algebraic Bethe ansatz is studied by means of the quantum
inverse scattering method. The spectrum of the Hamiltonian, eigenvectors, as
well as the Bethe ansatz equations, are discussed
Differential mesenteric fat deposition in bovines fed on silage or concentrate is independent of glycerol membrane permeability
© The Animal Consortium 2011In the meat industry, the manipulation of fat deposition in cattle is of pivotal importance to improve production efficiency, carcass composition and ultimately meat quality. There is an increasing interest in the identification of key factors and molecular mechanisms responsible for the development of specific fat depots. This study aimed at elucidating the influence of breed and diet on adipose tissue membrane permeability and fluidity and their interplay on fat deposition in bovines. Two Portuguese autochthonous breeds, Alentejana and BarrosĂŁ, recognized as late- and early-maturing breeds, respectively, were chosen to examine the effects of breed and diet on fat deposition and on adipose membrane composition and permeability. Twenty-four male bovines from these breeds were fed on silage-based or concentrate-based diets for 11 months. Animals were slaughtered to determine their live slaughter and hot carcass weights, as well as weights of subcutaneous and visceral adipose depots. Mesenteric fat depots were excised and used to isolate adipocyte membrane vesicles where cholesterol content, fatty acid profile as well as permeability and fluidity were determined. Total accumulation of neither subcutaneous nor visceral fat was influenced by breed. In contrast, mesenteric and omental fat depots weights were higher in concentrate-fed bulls relative to silage-fed animals. Membrane fluidity and permeability to water and glycerol in mesenteric adipose tissue were found to be independent of breed and diet. Moreover, the deposition of cholesterol and unsaturated fatty acids, which may influence membrane properties, were unchanged among experimental groups. Adipose membrane lipids from the mesenteric fat depot of ruminants were rich in saturated fatty acids, and unaffected by polyunsaturated fatty acids dietary levels. Our results provide evidence against the involvement of cellular membrane permeability to glycerol on fat accumulation in mesenteric fat tissue of concentrate-fed bovines, which is consistent with the unchanged membrane lipid profile found among experimental groups.This study was supported by Fundação para a CiĂȘncia e a Tecnologia (FCT) through grant PTDC/CVT/2006/66114 and individual fellowships to Ana P. Martins (SFRH/BD/2009/65046), Ana S. H. Costa (SFRH/BD/2009/61068) and Susana V. Martins (SFRH/BPD/2009/63019). Paula A. Lopes is a researcher from the program ââCiĂȘncia 2008ââ from FC
Transport and Strong-Correlation Phenomena in Carbon Nanotube Quantum Dots in a Magnetic Field
Transport through carbon nanotube (CNT) quantum dots (QDs) in a magnetic
field is discussed. The evolution of the system from the ultraviolet to the
infrared is analyzed; the strongly correlated (SC) states arising in the
infrared are investigated. Experimental consequences of the physics are
presented -- the SC states arising at various fillings are shown to be
drastically different, with distinct signatures in the conductance and, in
particular, the noise. Besides CNT QDs, our results are also relevant to double
QD systems.Comment: 5 pages, 5 figure
High-field Electron Spin Resonance of Cu_{1-x}Zn_{x}GeO_{3}
High-Field Electron Spin Resonance measurements were made on powder samples
of Cu_{1-x}Zn_{x}GeO_{3} (x=0.00, 0.01, 0.02, 0.03 and 0.05) at different
frequencies (95, 110, 190, 220, 330 and 440 GHz) at low temperatures. The
spectra of the doped samples show resonances whose positions are dependent on
Zn concentration, frequency and temperature. The analysis of intensity
variation of these lines with temperature allows us to identify them as
originating in transitions within states situated inside the Spin Peierls gap.
A qualitative explanation of the details of the spectra is possible if we
assume that these states in the gap are associated with "loose" spins created
near the Zn impurities, as recently theoreticaly predicted. A new phenomenon of
quenching of the ESR signal across the Dimerized to Incommensurate
phase-boundary is observed.Comment: 4 pages, 5 ps figures in the text, submitted to Phys. Rev. Let
A new investigation of the binary HD 48099
With an orbital period of about 3.078 days, the double-lined spectroscopic
binary HD 48099 is, still now, the only short-period O+O system known in the
Mon OB2 association. Even though an orbital solution has already been derived
for this system, few information are available about the individual stars. We
present, in this paper, the results of a long-term spectroscopic campaign. We
derive a new orbital solution and apply a disentangling method to recover the
mean spectrum of each star. To improve our knowledge concerning both
components, we determine their spectral classifications and their projected
rotational velocities. We also constrain the main stellar parameters of both
stars by using the CMFGEN atmosphere code and provide the wind properties for
the primary star through the study of IUE spectra. This investigation reveals
that HD 48099 is an O5.5 V((f))+O9 V binary with M_1 sin^3 i = 0.70 M_{\sun}
and M_2 sin^3 i = 0.39 M_{\sun}, implying a rather low orbital inclination.
This result, combined with both a large effective temperature and log g,
suggests that the primary star (v sini ~ 91 km s^-1) is actually a fast rotator
with a strongly clumped wind and a nitrogen abundance of about 8 times the
solar value.Comment: 12 pages, 7 figures, accepted by Ap
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