A fluidized granular medium as an instance of the Fluctuation Theorem

We study the statistics of the power flux into a collection of inelastic beads maintained in a fluidized steady-state by external mechanical driving. The power shows large fluctuations, including frequent large negative fluctuations, about its average value. The relative probabilities of positive and negative fluctuations in the power flux are in close accord with the Fluctuation Theorem of Gallavotti and Cohen, even at time scales shorter than those required by the theorem. We also compare an effective temperature that emerges from this analysis to the kinetic granular temperature.Comment: 4 pages, 5 figures, submited to Physical Review Letters; Revised versio

Fluctuation theorem applied to Dictyostelium discoideum system

In this paper, we analyze the electrotactic movement of Dictyostelium discoideum from the viewpoint of non-equilibrium statistical mechanics. Because we can observe fluctuating behavior of cellular trajectories, we analyze the probability distribution of the trajectories with the aid of the fluctuation theorem. Recently, the validity of the fluctuation theorem was verified in a colloidal system, and it has also been applied to granular systems, turbulent systems and chemical oscillatory waves to investigate some of their statistical properties that are not yet completely understood. Noting that the fluctuation theorem is potentially applicable to cellular electrotaxis, here we employ it to help us obtain a phenomenological model of this biological system.Comment: 2 pages, to appear in J. Phys. Soc. Jp

DODAB and DODAC bilayer-like aggregates in the micromolar surfactant concentration domain

In the millimolar concentration domain (typically 1 mM), dioctadecyldimethylammonium bromide and chloride (DODAX, X representing Br- or Cl- counterions) molecules assemble in water as large unilamellar vesicles. Differential scanning calorimetry (DSC) is a suitable technique to obtain the melting temperature (Tm) characteristic of surfactant bilayers, while fluorescence spectroscopy detects formation of surfactant aggregates, like bilayers. These two techniques were combined to investigate the assemble of DODAX molecules at micromolar concentrations, from 10 to 100 micromolar. At 1 mM surfactant, Tm ~ 45 ºC and 49 oC, respectively for DODAB and DODAC. DSC and fluorescence of Nile Red were used to show the formation of DODAX aggregates, at the surfactant concentration as low as 10 micromolar, whose Tm decreases monotonically with increasing DODAX concentration to attain the value for the ordinary vesicles. The data indicate that these aggregates are organized as bilayer-like structures.Fundação para a Ciência e a Tecnologia (FCT

Atributos físicos e químicos de argissolo amarelo sob cultivo orgânico.

A utilização de sistemas orgânicos de produção agrícola tem ganhado destaque no cenário mundial principalmente devido à busca por alimentos de maior qualidade, mas também por outros benefícios como a conservação/melhoria de características físicas, químicas e biológicas do solo, aliada ao menor impacto ambiental. O presente trabalho propõe a avaliar a qualidade física e química de um Argissolo após dois anos de cultivo orgânico de videira de vinho, tendo como referência uma área de pousio. A avaliação se deu através da análise da estabilidade de agregados, dos cálculos dos índices de e de dispersão floculação do solo, da densidade do solo e do teor de carbono orgânico, a partir de amostras coletadas nas linhas e entrelinhas da videira e área de pousio, nas profundidades de 0-0,10, 0,10-0,20; 0,20-0,30 m e 0,30-0,60 m. Observou-se que o sistema influenciou a agregação do solo; o manejo nas linhas com a implantação de coquetéis vegetais possivelmente elevou o conteúdo de matéria orgânica quando comparado à entrelinha e pousio; e foram encontrados maiores teores dos elementos Mg e Ca na área de pousio e na linha de plantio, o mesmo não ocorrendo para K e Na

Injected Power Fluctuations in 1D Dissipative Systems

Using fermionic techniques, we compute exactly the large deviation function (ldf) of the time-integrated injected power in several one-dimensional dissipative systems of classical spins. The dynamics are T=0 Glauber dynamics supplemented by an injection mechanism, which is taken as a Poissonian flipping of one particular spin. We discuss the physical content of the results, specifically the influence of the rate of the Poisson process on the properties of the ldf.Comment: 18 pages, 8 figure

Genetic diversity analysis of mangaba (Hancornia speciosa Gomes), an exotic braxilian tropical species.

Twenty genotypes from natural population of mangaba located in Itaporanga D’Ajuda (Sergipe state - Brazil) were subjected to analysis using RAPD markers. Polymorphism, genetic diversity and structure parameters were determined to characterize the differences between plants. 60 DNA fragments were generated by 10 primers, 85% of which were polymorphic. Results show a quantitative genetic diversity value of 0.35 and a Shannon index of 0.46 in the population. The similarity among the specimens according to Jaccard’s coefficient ranged from 0.36 to 0.87. Using cluster analysis it was possible to indentify five groups. Three individuals also stand out since they presented significant divergence from the groups. The PCoA formed four groups, with three of the groups isolated from the others. This investigation showed that genetic diversity was relatively large among these individuals. In addition, the results demonstrated that RAPD markers are a useful tool for evaluating the genetic diversity and relationships among mangaba

The pharmacological profile of ovalbumin-induced paw oedema in rats.

Rats are commonly used in anaphylaxis models, mainly in intestinal anaphylaxis. Hypersensitivity mechanisms are complex and they are not clearly defined. Ovalbumin (OVA) is commonly used for studies on the hypersensitivity mechanism. However, the potential pro-inflammatory mediators induced by this antigen in the model of paw oedema in immunized rats are still not completely understood. This work examines the pharmacological modulation of several mediators involved in rat hind paw immune oedema induced by OVA. Wistar rats were previously immunized (14-18 days) with OVA (30 microg, intraperitoneally) or sham-sensitized with aluminum hydroxide (control). The paw volumes were measured before the antigenic stimuli and 1, 2, 3 and 4 h after the intraplantar injection of OVA (10 microg/paw). Subcutaneous injection of dexamethasone, diphenhydramine, cyproheptadine, chlorpromazine or methysergide significantly inhibited (p < 0.05) the allergic paw oedema. The dual inhibitor of cyclooxygenase and lipoxygenase (NDGA), the cyclooxygenase inhibitor (indomethacin), the lipoxygenase inhibitor (MK-886), the PAF antagonist (WEB 2086), the mast cell stabilizer (ketotifen), and the anti-histamine (meclizine) did not inhibit the immune oedema. In addition, thalidomide and pentoxifylline (anti-tumour necrosis factor drugs) were ineffective against OVA-induced oedema. The fact that indomethacin, MK-886, NDGA and WEB 2086 are unable to inhibit this allergic oedema indicates that the dexamethasone action seems not to be via phospholipase A2, but possibly due to the synthesis and/or the inhibitory activity of cytokines. The paw oedema inhibition by diphenhydramine, but not by meclizine, may suggest a different mechanism, which is independent of the effect of histamine. These data indicate that allergic oedema is more sensitive to anti-serotonin drugs, mainly anti-5-HT2, suggesting that the principal mediator of this inflammatory response is serotonin

Self-diffusion in dense granular shear flows

Diffusivity is a key quantity in describing velocity fluctuations in granular materials. These fluctuations are the basis of many thermodynamic and hydrodynamic models which aim to provide a statistical description of granular systems. We present experimental results on diffusivity in dense, granular shear in a 2D Couette geometry. We find that self-diffusivities are proportional to the local shear rate with diffusivities along the mean flow approximately twice as large as those in the perpendicular direction. The magnitude of the diffusivity is D \approx \dot\gamma a^2 where a is the particle radius. However, the gradient in shear rate, coupling to the mean flow, and drag at the moving boundary lead to particle displacements that can appear sub- or super-diffusive. In particular, diffusion appears superdiffusive along the mean flow direction due to Taylor dispersion effects and subdiffusive along the perpendicular direction due to the gradient in shear rate. The anisotropic force network leads to an additional anisotropy in the diffusivity that is a property of dense systems with no obvious analog in rapid flows. Specifically, the diffusivity is supressed along the direction of the strong force network. A simple random walk simulation reproduces the key features of the data, such as the apparent superdiffusive and subdiffusive behavior arising from the mean flow, confirming the underlying diffusive motion. The additional anisotropy is not observed in the simulation since the strong force network is not included. Examples of correlated motion, such as transient vortices, and Levy flights are also observed. Although correlated motion creates velocity fields qualitatively different from Brownian motion and can introduce non-diffusive effects, on average the system appears simply diffusive.Comment: 13 pages, 20 figures (accepted to Phys. Rev. E