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

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

Avaliação temporal e espacial do balanço de energia na microbacia do córrego do Ipê, no município de Ilha Solteira face a mudança de uso do solo.

O objetivo deste trabalho foi analisar a variação espacial e temporal dos componentes que compõem o balanço de energia na microbacia do Córrego do Ipê, ao longo do período de 2003 a 2011 para o período seco, buscando identificar interferências com a mudança de uso da terra ocorrida com a entrada da cultura da cana de açúcar

Evapotranspiração real para diferentes coberturas vegetais no noroeste paulista em período seco.

A determinação da evapotranspiração é de fundamental importância para o bom manejo da irrigação. No entanto, o uso de estações meteorológicas para se determinar a evapotranspiração muitas vezes pode comprometer a qualidade da informação, devido a distancia em relação às áreas de cultivo. Dentro dessas premissas, o uso do sensoriamento remoto através do algoritmo SEBAL vem apresentando bons resultados para a determinação da evapotranspiração. Dessa forma, este trabalho se propôs a utilizar o algoritmo para determinar a evapotranspiração real das culturas de cana de açúcar e pastagem e de uma área com mata nativa no noroeste paulista no período seco, com as áreas de pastagem apresentando os menores valores de evapotranspiração e os maiores valores de temperatura de superfíci

Onsager-Machlup theory for nonequilibrium steady states and fluctuation theorems

A generalization of the Onsager-Machlup theory from equilibrium to nonequilibrium steady states and its connection with recent fluctuation theorems are discussed for a dragged particle restricted by a harmonic potential in a heat reservoir. Using a functional integral approach, the probability functional for a path is expressed in terms of a Lagrangian function from which an entropy production rate and dissipation functions are introduced, and nonequilibrium thermodynamic relations like the energy conservation law and the second law of thermodynamics are derived. Using this Lagrangian function we establish two nonequilibrium detailed balance relations, which not only lead to a fluctuation theorem for work but also to one related to energy loss by friction. In addition, we carried out the functional integrals for heat explicitly, leading to the extended fluctuation theorem for heat. We also present a simple argument for this extended fluctuation theorem in the long time limit.Comment: 20 pages, 2 figure

A MECHANICAL SPEEDO-METER TO ASSESS SWIMMER’S HORIZONTAL INTRA-CYCLIC VELOCITY: VALIDATION FOR BREASTSTROKE AND BUTTERFLY STROKE

The aim was to validate a system to assess speed-fluctuation at breaststroke and butterfly stroke. 12 boys and 11 undertook a set of maximal 2x25 m swims (Breaststroke and Butterfly stroke). The speedo-meter cable was attached to the subject’s hip and data was acquired on-line. At the same time, subjects were recorded in the sagital plane with an underwater video camera enabling the hip to be digitized. The following were analysed: (i) maximal velocity; (ii) minimal velocity; (iii) difference between maximal and minimal velocity; (iv) coefficient of variation. There were no significant differences for the mean values between methods, except for the coefficient of variation. Linear regression models were highly related. More than 80% of the Bland-Altman plots were within the 1.96 standard-deviation criteria used as a rule of thumb for technique validation

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

Avaliação nutricional do capim-elefante fertilizado com composto orgânico oriundo de resíduos da produção e abate de caprinos e ovinos?.

Resumo: Objetivou-se avaliar a composição química do capim-elefante adubado com crescentes doses de composto orgânico produzido a partir de resíduos da produção e abate de pequenos ruminantes. O delineamento foi em blocos casualizados com 6 tratamentos e 4 blocos, totalizando 24 parcelas, sendo aplicadas as seguintes doses (t ha-1): zero; 13,3; 26,6; 39,9; 53,2 e 79,8. Para a diagnose do estado nutricional do capim-elefante, coletou-se 7 amostras simples por parcela, em zigue-zague, de maneira aleatória. A região avaliada foi a primeira folha recém-expandida, sendo as amostras simples as plantas de uma mesma touceira, ao sexagésimo dia após o corte de uniformização. Avaliou-se a análise de macro e micronutrientes do capim-elefante. Houve efeito significativo para os macronutrientes primários nitrogênio, fósforo e potássio (NPK) e o micronutriente zinco. Conclui-se que a aplicação, na capineira, do composto orgânico proveniente de resíduos da produção e abate de pequenos ruminantes proporciona incremento nos teores foliares de N, P, K e Zn. [Evaluation of elephant grass fertilized with compound organic derived of production and slaugher of sheeps and goats]. Abstract: This study aimed to evaluate the nutritional status of elephant grass under doses of organic compound from production residue and slaughter of small ruminants after composting process. The experimental design was randomized blocks with 6 treatments and 4 blocks, total of 24 plots. The doses (t ha-1) applied were: zero; 13.3; 26.6; 39.9; 53.2 and 79.8. In order to diagnose the nutritional status of elephant grass we collected 40 single samples in random way in each plot. The chosen part was the first newly expanded leaf, and the single samples were plants of the same clump on the sixtieth day after the uniformity cut. We evaluated the chemical analysis of macronutrients and micronutrients in elephant grass. The results showed that there were significant effects on primary macronutrients nitrogen, phosphorus and potassium (NPK) and zinc micronutrient. The results show that the application of organic compound from production residue and slaughter of small ruminants provided an increase in the leaf levels of N, P, K and Zn