8,295 research outputs found
Survival of branching random walks in random environment
We study survival of nearest-neighbour branching random walks in random
environment (BRWRE) on . A priori there are three different
regimes of survival: global survival, local survival, and strong local
survival. We show that local and strong local survival regimes coincide for
BRWRE and that they can be characterized with the spectral radius of the first
moment matrix of the process. These results are generalizations of the
classification of BRWRE in recurrent and transient regimes. Our main result is
a characterization of global survival that is given in terms of Lyapunov
exponents of an infinite product of i.i.d. random matrices.Comment: 17 pages; to appear in Journal of Theoretical Probabilit
Lagrangian formulation of classical fields within Riemann-Liouville fractional derivatives
The classical fields with fractional derivatives are investigated by using
the fractional Lagrangian formulation.The fractional Euler-Lagrange equations
were obtained and two examples were studied.Comment: 9 page
Vigor, floração, produção e qualidade de pêssegos 'Chimarrita' e 'Maciel' em função de diferentes porta-enxertos.
O objetivo deste trabalho foi avaliar o vigor, a floração, a produção e a qualidade de pêssegos das cultivares 'Chimarrita' e 'Maciel' sobre oito porta-enxertos. O diâmetro do tronco, acompanhamento da floração, produção e qualidade de pêssegos foram os parâmetros estudados nas safras de 2008 e 2009, na Universidade Federal de Pelotas, Pelotas, RS. De acordo com os resultados obtidos, as cultivares 'Chimarrita' e 'Maciel', enxertadas sobre Umezeiro, apresentam menor vigor e sintomas de incompatibilidade quando comparadas com a enxertia nos demais porta-enxertos. A floração de ambas as cultivares foi influenciada pelos portaenxertos, podendo retardar ou antecipar o início e a plena floração em até cinco dias. A cultivar ?Maciel? enxertada sobre Tsukuba 1 foi a mais produtiva e a cultivar 'Chimarrita' apresentou maior produção quando enxertada sobre Aldrighi e Capdeboscq. O porta-enxerto Umezeiro proporcionou frutos com maior relação SS/AT para a cultivar 'Maciel' e, para 'Chimarrita', os pêssegos apresentaram maior conteúdo de sólidos solúveis
The type N Karlhede bound is sharp
We present a family of four-dimensional Lorentzian manifolds whose invariant
classification requires the seventh covariant derivative of the curvature
tensor. The spacetimes in questions are null radiation, type N solutions on an
anti-de Sitter background. The large order of the bound is due to the fact that
these spacetimes are properly , i.e., curvature homogeneous of order 2
but non-homogeneous. This means that tetrad components of are constant, and that essential coordinates first appear as
components of . Covariant derivatives of orders 4,5,6 yield one
additional invariant each, and is needed for invariant
classification. Thus, our class proves that the bound of 7 on the order of the
covariant derivative, first established by Karlhede, is sharp. Our finding
corrects an outstanding assertion that invariant classification of
four-dimensional Lorentzian manifolds requires at most .Comment: 7 pages, typos corrected, added citation and acknowledgemen
Decay of metastable phases in a model for the catalytic oxidation of CO
We study by kinetic Monte Carlo simulations the dynamic behavior of a
Ziff-Gulari-Barshad model with CO desorption for the reaction CO + O
CO on a catalytic surface. Finite-size scaling analysis of the fluctuations
and the fourth-order order-parameter cumulant show that below a critical CO
desorption rate, the model exhibits a nonequilibrium first-order phase
transition between low and high CO coverage phases. We calculate several points
on the coexistence curve. We also measure the metastable lifetimes associated
with the transition from the low CO coverage phase to the high CO coverage
phase, and {\it vice versa}. Our results indicate that the transition process
follows a mechanism very similar to the decay of metastable phases associated
with {\it equilibrium} first-order phase transitions and can be described by
the classic Kolmogorov-Johnson-Mehl-Avrami theory of phase transformation by
nucleation and growth. In the present case, the desorption parameter plays the
role of temperature, and the distance to the coexistence curve plays the role
of an external field or supersaturation. We identify two distinct regimes,
depending on whether the system is far from or close to the coexistence curve,
in which the statistical properties and the system-size dependence of the
lifetimes are different, corresponding to multidroplet or single-droplet decay,
respectively. The crossover between the two regimes approaches the coexistence
curve logarithmically with system size, analogous to the behavior of the
crossover between multidroplet and single-droplet metastable decay near an
equilibrium first-order phase transition.Comment: 27 pages, 22 figures, accepted by Physical Review
Processo de craqueamento termocatalítico do óleo de palma (ELAEIS guineensis) bruto em escala semi-piloto: aplicação do óxido de cálcio (CaO).
Electrons in Dry DNA from Density Functional Calculations
The electronic structure of an infinite poly-guanine - poly-cytosine DNA
molecule in its dry A-helix structure is studied by means of density-functional
calculations. An extensive study of 30 nucleic base pairs is performed to
validate the method. The electronic energy bands of DNA close to the Fermi
level are then analyzed in order to clarify the electron transport properties
in this particularly simple DNA realization, probably the best suited candidate
for conduction. The energy scale found for the relevant band widths, as
compared with the energy fluctuations of vibrational or genetic-sequence
origin, makes highly implausible the coherent transport of electrons in this
system. The possibility of diffusive transport with sub-nanometer mean free
paths is, however, still open. Information for model Hamiltonians for
conduction is provided.Comment: 8 pages, 4 figure
Numerical Analysis of an Overtopping Wave Energy Converter Subjected to the Incidence of Irregular and Regular Waves from Realistic Sea States
The present study aims to evaluate the difference in the fluid-dynamic behavior of an overtopping wave energy converter under the incidence of irregular waves based on a realistic sea state when compared to the incidence of regular waves, representative of this sea state. Thus, the sea data of three regions from the Rio Grande do Sul coast, Brazil, were considered. Fluent software was employed for the computational modeling, which is based on the finite volume method (FVM). The numerical generation of waves occurred through the imposition of the velocity boundary conditions using transient discrete values through the WaveMIMO methodology. The volume of fluid (VOF) multiphase model was applied to treat the water–air interaction. The results for the water amount accumulated in the device reservoir showed that the fluid-dynamic behavior of the overtopping converter has significant differences when comparing the two proposed approaches. Differences up to 240% were found for the water mass accumulated in the overtopping device reservoir, showing evidence that the results can be overestimated when the overtopping device is analyzed under the incidence of the representative regular waves. Furthermore, for all studied cases, it was possible to approximate the water volume accumulated over time in the overtopping reservoir through a first-degree polynomial function
Spontaneous Bacterial Pericarditis and Coronary Sinus Endocarditis Caused by Oxacillin-Susceptible Staphylococcus aureus
This paper describes a case of a 44-year-old male patient previously healthy admitted with an unusual spontaneous acute bacterial pericarditis associated with coronary sinus mass. Two-dimensional echocardiography showed large loculated pericardial effusion with signs of diastolic restriction and an image suggesting vegetation in topography of the right atrium coronary sinus. Pericardial drainage, coronary sinus vegetation resection, and antibiotic therapy with Oxacillin were performed due to Oxacillin-susceptible Staphylococcus aureus identified on the pericardial effusion and blood culture. This is a rare condition and a unique combination of a spontaneous acute bacterial pericarditis with coronary sinus endocarditis without cardiac valve compromise
Estrutura fitossociológica de um área de cerrado sensu stricto em Sete Lagoas, MG.
Este trabalho teve como objetivo avaliar a composição, estrutura e diversidade da flora arbustivo arbórea em uma área de Cerrado sensu stricto em Sete Lagoas, MG, visando verificar sua similaridade com outras áreas de Cerrado em Minas Gerais. Foram estabelecidas 12 parcelas de 0,1 ha (20×50 m), totalizando 1,2 ha amostrados, sendo inclusas no estudo todas as árvores vivas com circunferência ?15 cm a 0.30 m do solo. Foram registrados 1.689 indivíduos. Os valores de riqueza (48 espécies e 29 famílias), de diversidade de Shannon (3,09) e de uniformidade de Pielou (0,8) evidenciaram grande heterogeneidade e baixa dominância ecológica. Plathymenia reticulata (Fabaceae) apresentou 203 indivíduos, sendo a espécie mais abundante. Fabaceae (10) Bignoniaceae (5), e Vochysiaceae (4) foram as famílias mais ricas em espécie. Os índices qualitativos de similaridade apontaram baixa diversidade entre os ambientes
- …