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

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

Radiocarbon and blue optically stimulated luminescence chronologies of the Oitavos consolidated dune (Western Portugal)

The dune of Oitavos, the underlying paleosol, and Helix sp. gastropod shells found within the paleosol were dated using a combination of radiocarbon and blue optically stimulated luminescence (OSL). The organic component of the paleosol produced a significantly older age (~20,000 cal BP) than the OSL age measurement (~15,000 yr), while 14C age measurements on the inorganic component and the gastropods produced ages of ~35,000 yr and ~34,000 yr, respectively. Rare-earth element analyses provide evidence that the gastropods incorporate geological carbonate, making them an unreliable indicator of the age of the paleosol. We propose that the 14C age of the small organic component of the paleosol is also likely to be unreliable due to incorporation of residual material. The OSL age measurement of the upper paleosol (~15,000 yr) is consistent with the age for the base of the dune (~14,500 yr). The younger OSL age for the top of the dune (~12,000 yr) suggests that it was built up by at least 2 sand pulses or that there was a remobilization of material at the top during its evolution, prior to consolidation

Non-additivity of decoherence rates in superconducting qubits

We show that the relaxation and decoherence rates 1/T_1 and 1/T_2 of a qubit coupled to several noise sources are in general not additive, i.e., that the total rates are not the sums of the rates due to each individual noise source. To demonstrate this, we calculate the relaxation and pure dephasing rates 1/T_1 and 1/T_\phi of a superconducting (SC) flux qubit in the Born-Markov approximation in the presence of several circuit impedances Z_i using network graph theory and determine their deviation from additivity (the mixing term). We find that there is no mixing term in 1/T_\phi and that the mixing terms in 1/T_1 and 1/T_2 can be positive or negative, leading to reduced or enhanced relaxation and decoherence times T_1 and T_2. The mixing term due to the circuit inductance L at the qubit transition frequency \omega_{01} is generally of second order in \omega_{01}L/Z_i, but of third order if all impedances Z_i are pure resistances. We calculate T_{1,2} for an example of a SC flux qubit coupled to two impedances.Comment: 5 pages, 2 figure