Comment on "Tricritical Behavior in Rupture Induced by Disorder"

In their letter, Andersen, Sornette, and Leung [Phys. Rev. Lett. 78, 2140 (1997)] describe possible behaviors for rupture in disordered media, based on the mean field-like democratic fiber bundle model. In this model, fibers are pulled with a force which is distributed uniformly. A fiber breaks if the stress on it exceeds a threshold chosen from a probability distribution, and the force is then redistributed over the intact fibers. Andersen et al. claim the existence of a tricritical point, separating a "first-order" regime, characterized by a sudden global failure, from a "second-order" regime, characterized by a divergence in the breaking rate. We show that a first-order transition is an artifact of a (large enough) discontinuity put by hand in the disorder distribution. Thus, in generic physical cases, a first-order regime is not present. This result is obtained from a graphical method, which, unlike Andersen at al.'s analytical solution, enables us to distinguish the various classes of qualitatively different behaviors of the model.Comment: 1 page, 1 figure included, revte

Estudo dos solos do município de Pelotas.

bitstream/item/41392/1/Pelotas.pdf; bitstream/item/41393/1/mapa-geomorfologia.pdf; bitstream/item/41394/1/mapa-solos.pdf; bitstream/item/41395/1/mapa-uso-das-terras.pd

Estudo dos solos do município de Capão do Leão.

bitstream/item/41388/1/Capao-do-leao.pdf; bitstream/item/41389/1/mapa-geomorfologia.pdf; bitstream/item/41390/1/mapa-solos.pdf; bitstream/item/41391/1/mapa-uso-da-terra.pd

Aroeira-vermelha (Schinus terebinthifolius Raddi).

bitstream/item/32431/1/Aroeira.Vermelha.pdfOrganizado por: Joel Henrique Cardoso, João Vicente da Luz Silveira, Comitê Local de Gestão Ambiental

Formation and Stability of Synaptic Receptor Domains

Neurotransmitter receptor molecules, concentrated in postsynaptic domains along with scaffold and a number of other molecules, are key regulators of signal transmission across synapses. Employing experiment and theory, we develop a quantitative description of synaptic receptor domains in terms of a reaction-diffusion model. We show that interactions between only receptor and scaffold molecules, together with the rapid diffusion of receptors on the cell membrane, are sufficient for the formation and stable characteristic size of synaptic receptor domains. Our work reconciles long-term stability of synaptic receptor domains with rapid turnover and diffusion of individual receptors.Comment: 5 pages, 3 figures, Supplementary Materia

Características químicas de um latossolo cultivado com feijão submetido a diferentes sistemas de preparo.

O objetivo deste trabalho foi avaliar o valor do pH e os teores de Ca, Mg, P e K de um latossolo vermelho distrófico cultivado com feijão irrigado, sob dois sistemas de manejo do solo: plantio direto e preparo convencional