4,040 research outputs found
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 (). We characterize the motion of individual grains,
which becomes super-diffusive at the jamming transition , 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
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