Effect of particle polydispersity on the irreversible adsorption of fine particles on patterned substrates

We performed extensive Monte Carlo simulations of the irreversible adsorption of polydispersed disks inside the cells of a patterned substrate. The model captures relevant features of the irreversible adsorption of spherical colloidal particles on patterned substrates. The pattern consists of (equal) square cells, where adsorption can take place, centered at the vertices of a square lattice. Two independent, dimensionless parameters are required to control the geometry of the pattern, namely, the cell size and cell-cell distance, measured in terms of the average particle diameter. However, to describe the phase diagram, two additional dimensionless parameters, the minimum and maximum particle radii are also required. We find that the transition between any two adjacent regions of the phase diagram solely depends on the largest and smallest particle sizes, but not on the shape of the distribution function of the radii. We consider size dispersions up-to 20% of the average radius using a physically motivated truncated Gaussian-size distribution, and focus on the regime where adsorbing particles do not interact with those previously adsorbed on neighboring cells to characterize the jammed state structure. The study generalizes previous exact relations on monodisperse particles to account for size dispersion. Due to the presence of the pattern, the coverage shows a non-monotonic dependence on the cell size. The pattern also affects the radius of adsorbed particles, where one observes preferential adsorption of smaller radii particularly at high polydispersity.Comment: 9 pages, 5 figure

Recent advances and open challenges in percolation

Percolation is the paradigm for random connectivity and has been one of the most applied statistical models. With simple geometrical rules a transition is obtained which is related to magnetic models. This transition is, in all dimensions, one of the most robust continuous transitions known. We present a very brief overview of more than 60 years of work in this area and discuss several open questions for a variety of models, including classical, explosive, invasion, bootstrap, and correlated percolation

Neutron Charge Radius: Relativistic Effects and the Foldy Term

The neutron charge radius is studied within a light-front model with different spin coupling schemes and wave functions. The cancellation of the contributions from the Foldy term and Dirac form factor to the neutron charge form factor is verified for large nucleon sizes and it is independent of the detailed form of quark spin coupling and wave function. For the physical nucleon our results for the contribution of the Dirac form factor to the neutron radius are insensitive to the form of the wave function while they strongly depend on the quark spin coupling scheme.Comment: 12 pages, 5 figures, Latex, Int. J. Mod. Phys.

Screening effects in flow through rough channels

A surprising similarity is found between the distribution of hydrodynamic stress on the wall of an irregular channel and the distribution of flux from a purely Laplacian field on the same geometry. This finding is a direct outcome from numerical simulations of the Navier-Stokes equations for flow at low Reynolds numbers in two-dimensional channels with rough walls presenting either deterministic or random self-similar geometries. For high Reynolds numbers, when inertial effects become relevant, the distribution of wall stresses on deterministic and random fractal rough channels becomes substantially dependent on the microscopic details of the walls geometry. In addition, we find that, while the permeability of the random channel follows the usual decrease with Reynolds, our results indicate an unexpected permeability increase for the deterministic case, i.e., ``the rougher the better''. We show that this complex behavior is closely related with the presence and relative intensity of recirculation zones in the reentrant regions of the rough channel.Comment: 4 pages, 5 figure

Genetic variation and correlation of agronomic traits in meadow bromegrass (Bromus riparius Rehm) clones.

Meadow bromegrass (Bromus riparius Rehm.) is a recently introduced pasture grass in western Canada. Its leafy production and rapid regrowth have made it a major grass species for pasturing beef animals in this region. As relatively little breeding work kas been done on this species, there is little information on its breeding behaviour. The main objective of this study was to estimate total genetic variability, broad-sense heritability, phenotypic and genetic correlations. Forty-four meadow bromegrass clones were evaluated for agronomic characters. Genetic variation for dry matter yield, seed yield, fertility index, harvest index, plant height, plant spread, crude protein, neutral de ter gent fiber and acid de ter gent fiber, was significant. Broad-sense heritability estimates exceeded 50% for all characters. Heritability estimates were at least 3.5 times greater than their standard errors. Phenotypic and genetic correlation between all possible characters were measured There was general agreement in both sign and magnitude between genetic and phenotypic correlations. Correlations between the different characters demonstrated that it is possible to simultaneously improve seed and forage yield. Based on the results, it appears that the development of higher yielding cultivars with higher crude protein, and lower acid and neutral detergent fibers concentration should be possible

Desenvolvimento de mudas de pinhão-manso (Jatropha curcas L.) submetidas a diferentes substratos e sombreamentos.

Este trabalho teve como objetivo avaliar o efeito de diferentes substratos e níveis de sombreamento no desenvolvimento de mudas de pinhão-manso (Jatropha curcas L. Os frutos foram colhidos em uma área comercial. Após beneficiamento e assepsia, duas sementes foram semeadas em sacos de polietileno de aproximadamente 3 litros, preenchidos com quatro diferentes substratos. Sendo eles, solo (S); areia (A); S1-A1-NPK (solo + areia, na proporção de 1:1, com 5 g de NPK 6:24:12 por litro de substrato); S1-A2-NPK (solo + areia, na proporção de 1:2, com 5 g de NPK 6:24:12 por litro de substrato); S1-A1-E1 (solo + areia + esterco curtido, na proporção de 1:1:1); S1-A1-E1 NPK (solo + areia + esterco curtido, na proporção de 1:1:1, com 5 g de NPK 6:24:12 por litro de substrato). O experimento foi conduzido em três diferentes intensidades de sombreamento: 0% (a céu aberto), 25% e 75% (em telado, com tela sombrite). O delineamento utilizado foi em blocos casualizados, em um esquema fatorial 4 x 3 (quatro substratos x três sombreamentos), perfazendo um total de 12 tratamentos. As plântulas mantidas em sombreamento de 25% apresentaram, em geral, melhores resultados para todas as variáveis avaliadas. Conclui-se que tanto o sombreamento como o substrato interferiram na emergência da espéci

Avaliação fenológica do pinhão manso (Jatropha curcas L.) no Município de Teresina-PI.

O pinhão manso (Jatropha curcas L.), também conhecido como pinhão do paraguai, pinhão-de-cerca ou pinhão bravo é uma planta arbórea de pequeno porte, da família das Euphorbiaceae, originária do México e América Central e que apresenta potencial como uma fonte de óleo não comestível. O conhecimento da fenologia de uma planta possibilita prever a época de reprodução, deciduidade, ciclos de crescimento vegetativo e sua relação com os fatores climáticos, auxiliando operações agrícolas como poda, colheita, etc. O presente trabalho foi desenvolvido no Campo Experimental da Embrapa Meio Norte, município de Teresina-PI. Sortearam-se 21 plantas de pinhão-manso (Jatropha curcas L.) para o acompanhamento mensal da fenologia no período de janeiro a dezembro de 2007. A intensidade dos eventos fenológicos foi estimada para cada planta, seguindo-se os métodos de Fournier (Fournier, 1976) e o índice de atividade. A queda foliar ocorreu ao longo do ano, com picos no período seco e chuvoso. Os picos de emissão de flores em Jatropha curcas foi observada nos meses de julho, outubro e novembro. De acordo com o percentual de Fournier os picos de ocorrência de frutos verdes e maduros foram observados nos meses de março a setembro e março a outubro, respectivamente