Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited

Water activity and its relationship with interactions stabilising lamellar stacks of mixed lipid bilayers in their fluid state are investigated by means of osmotic pressure measurements coupled with small-angle x-ray scattering. The (electrically-neutral) bilayers are composed of a mixture in various proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic cosurfactant with an ethoxylated polar head. For highly dehydrated samples the osmotic pressure profile always exhibits the "classical" exponential decay as hydration increases but, depending on Simulsol to lecithin ratio, it becomes either of the "bound" or "unbound" types for more water-swollen systems. A simple thermodynamic model is used for interpreting the results without resorting to the celebrated but elusive "hydration forces"Comment: 24 pages, 12 figures. Accepted for publication in The European Physical Journal

Contribuição da física do solo aos estudos sobre manejo e conservação do solo.

Identificação morfológica e classificação do solo do local do experimento; Caracterização física e hídrica do solo; Determinação da percentagem de agregados por via úmida (método opcional); Descrição de perfil de solo (modelo); Ficha de análises físicas e químicas do perfil (modelo); Modelos de legenda e de tabelas para apresentação de resultados de caracterização física do solo.bitstream/item/36146/1/Contribuicao-da-Fisica.pd

Determinação da umidade a 1/10 de atmosfera na terra fina pela "mesa de tensão".

É apresentado um método opcional para a determinação da umidade a 1/10 de atmosfera ou para valores mais baixos de tensão, em amostras de solo (terra fina), utilizando-se a "mesa de tensão" desenvolvida por Oliveira.bitstream/item/36224/1/Determinacao.pd

Estudo da estabilidade da linamarase de manihot esculenta crantz sob armazenamento.

A linamarase é uma β-glicosidase que pode ser obtida, dentre outras fontes, da mandioca. Ela é responsável pela hidrólise dos glicosídeos cianogênicos linamarina e lotaustralina, que se supõe estão envolvidos em processos de defesa da planta

The Likelihood Ratio Test and Full Bayesian Significance Test under small sample sizes for contingency tables

Hypothesis testing in contingency tables is usually based on asymptotic results, thereby restricting its proper use to large samples. To study these tests in small samples, we consider the likelihood ratio test and define an accurate index, the P-value, for the celebrated hypotheses of homogeneity, independence, and Hardy-Weinberg equilibrium. The aim is to understand the use of the asymptotic results of the frequentist Likelihood Ratio Test and the Bayesian FBST -- Full Bayesian Significance Test -- under small-sample scenarios. The proposed exact P-value is used as a benchmark to understand the other indices. We perform analysis in different scenarios, considering different sample sizes and different table dimensions. The exact Fisher test for $2 \times 2$ tables that drastically reduces the sample space is also discussed. The main message of this paper is that all indices have very similar behavior, so the tests based on asymptotic results are very good to be used in any circumstance, even with small sample sizes

Spatial patterns and biodiversity in off-lattice simulations of a cyclic three-species Lotka-Volterra model

Stochastic simulations of cyclic three-species spatial predator-prey models are usually performed in square lattices with nearest neighbor interactions starting from random initial conditions. In this Letter we describe the results of off-lattice Lotka-Volterra stochastic simulations, showing that the emergence of spiral patterns does occur for sufficiently high values of the (conserved) total density of individuals. We also investigate the dynamics in our simulations, finding an empirical relation characterizing the dependence of the characteristic peak frequency and amplitude on the total density. Finally, we study the impact of the total density on the extinction probability, showing how a low population density may jeopardize biodiversity.Comment: 5 pages, 7 figures; new version, with new title and figure