On the dependence of the avalanche angle on the granular layer thickness

A layer of sand of thickness h flows down a rough surface if the inclination is larger than some threshold value theta which decreases with h. A tentative microscopic model for the dependence of theta with h is proposed for rigid frictional grains, based on the following hypothesis: (i) a horizontal layer of sand has some coordination z larger than a critical value z_c where mechanical stability is lost (ii) as the tilt angle is increased, the configurations visited present a growing proportion $_s of sliding contacts. Instability with respect to flow occurs when z-z_s=z_c. This criterion leads to a prediction for theta(h) in good agreement with empirical observations.Comment: 6 pages, 2 figure

Lorentz-violating dimension-five operator contribution to the black body radiation

We investigate the thermodynamics of a photon gas in an effective field theory model that describes Lorentz violations through dimension-five operators and Horava-Lifshitz theory. We explore the electrodynamics of the model which includes higher order derivatives in the Lagrangian that can modify the dispersion relation for the propagation of the photons. We shall focus on the deformed black body radiation spectrum and modified Stefan-Boltzmann law to address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL

Non-relativistic electron-electron interaction in a Maxwell-Chern-Simons-Proca model endowed with a timelike Lorentz-violating background

A planar Maxwell-Chern-Simons-Proca model endowed with a Lorentz-violating background is taken as framework to investigate the electron-electron interaction. The Dirac sector is introduced exhibiting a Yukawa and a minimal coupling with the scalar and the gauge fields, respectively. The the electron-electron interaction is then exactly evaluated as the Fourier transform of the Moller scattering amplitude (carried out in the non-relativistic limit) for the case of a purely time-like background. The interaction potential exhibits a totally screened behavior far from the origin as consequence of massive character of the physical mediators. The total interaction (scalar plus gauge potential) can always be attractive, revealing that this model may lead to the formation of electron-electron bound states.Comment: 14 pages, 4 figures, style revtex. To appear in International Journal Modern Physics

Efeitos de doses de resíduos orgânicos e tipos de adubação na biomassa microbiana do solo cultivado com milho.

O trabalho foi conduzido na fazenda escola da UEL com o objetivo de avaliar os efeitos de doses de resíduos orgânicos e de tipos de adubação na biomassa microbiana do solo cultivado com milho. O carbono da biomassa microbiana do solo foi avaliado em cada época de floração e colheita do milho em duas safras, considerando-se o delineamento experimental de blocos casualizados em esquema fatorial 4 x 2, com três repetições, em que os fatores foram quatro doses de resíduos (O, 15, 30 e 45 Mg ha-1), e dois tipos de adubação (AO: adubação orgânica e OM: adubação organomineral). A adubação mineral empregada na semeadura do milho nas duas safras correspondeu à aplicação de 40, 60 e 40 kg ha-1 de N, P2O5 e K2O, respectivamente. O conteúdo de carbono da biomassa microbiana do solo aumentou com as doses de resíduo na primeira safra de milho. O ponto de máximo (777 mg Kg-1 de solo) foi observado na floração do milho da segunda safra e para a dose de 23 Mg ha-1 de resíduo. Na colheita da segunda safra reduziu linearmente com as doses de resíduos nas parcelas que receberam adubação organomineral

Biomassa microbiana do solo e produtividade do feijão submetido a diferentes tipos de adubação.

O experimento foi conduzido na fazenda escola da Universidade Estadual de Londrina em área de área de Nitossolo Vermelho eutroférrico latossólico argiloso, com o objetivo de avaliar os efeitos da adubação orgânica e organomineral na biomassa microbiana do solo, nos componentes de produção e na produtividade da cultura do feijoeiro (IPR Colibri) em sucessão à de milho. O delineamento experimental adotado foi de blocos inteiramente casualizados em arranjo fatorial 4 x 2, em que os fatores foram quatro doses de resíduos orgânicos (O, 15, 30 e 45 Mg ha-\ e dois tipos de adubação (adubação orgânica (AO) e adubação organomineral (OM)). A adubação organomineral correspondeu à associação da adubação orgânica (resíduos de poda de árvores) com a adubação mineral de semeadura e cobertura, recomendada para a cultura, ou seja, 20, 50 e 30 kg ha-1 de N, P2O5 e K2O, respectivamente, na semeadura e 60 kg ha-1 de N (uréia) em cobertura (14 dias após a emergência). O conteúdo de carbono da biomassa microbiana do solo foi maior na época de floração do feijão, com ponto de máximo estimado para a dose de 35,3 Mg ha-1 de resíduos orgânicos. Na época da colheita exceto para a dose de 30 Mg ha-1,0 conteúdo de carbono da biomassa microbiana do solo foi sempre maior nas parcelas que receberam adubação organomineral. A produtividade do feijão (cv IPR Colibri) foi maior com a adubação organomineral, mas somente com a adubação orgânica obteve-se produtividade superior a média da cultura do feijoeiro no estado do Paraná

Critical scaling and heterogeneous superdiffusion across the jamming/rigidity transition of a granular glass

The dynamical properties of a dense horizontally vibrated bidisperse granular monolayer are experimentally investigated. The quench protocol produces states with a frozen structure of the assembly, but the remaining degrees of freedom associated with contact dynamics control the appearance of macroscopic rigidity. We provide decisive experimental evidence that this transition is a critical phenomenon, with increasingly collective and heterogeneous rearrangements occurring at length scales much smaller than the grains' diameter, presumably reflecting the contact force network fluctuations. Dynamical correlation time and length scales soar on both sides of the transition, as the volume fraction varies over a remarkably tiny range ($\delta \phi/\phi \sim 10^{-3}$). We characterize the motion of individual grains, which becomes super-diffusive at the jamming transition $\phi_J$, signaling long-ranged temporal correlations. Correspondingly, the system exhibits long-ranged four-point dynamical correlations in space that obey critical scaling at the transition density.Comment: 4 pages, 8 figure

DRYING STUDY OF EUCALYTPTUS STAIGERIANA LEAVES BY MONITORING THE HUMIDITY OF THE DRYER DISCHARGE

The drying phenomenon can be treated as simultaneous heat and mass transfer in both the light and heavy phases. In the present case, the phenomenons evolution is normally observed through the heating of and moisture removal from the heavy phase. On the other hand, while the material is heating, the light phase is cooling and humidifying. The goal of the present work is to present discharge air humidification curves as a function of the drying time for Eucalyptus staigeriana leaves drying experiments. For the air humidification measurements, a dry bulb thermocouple and relative humidity transducer were installed at both the dryer inlet and outlet. The dryer was linked to a data acquisition system, which recorded the dry bulb temperature and the relative humidity with time. These data were later used to calculate the air moisture content at the dryer inlet and outlet. The data obtained by this methodology are compared with the ones from drying kinetic (moisture content removing of the heavy phase along time), acquired by the evolution of wet material weight through the use of an analytical scale