1,430 research outputs found
Myelin figures: the buckling and flow of wet soap
Myelin figures are interfacial structures formed when certain surfactants
swell in excess water. Here, I present data and model calculations suggesting
myelin formation and growth is due to the fluid flow of surfactant, driven by
the hydration gradient at the dry surfactant/water interface; a simple model
based on this idea qualitatively reproduces the various myelin growth behaviors
observed in different experiments. From a detailed experimental observation of
how myelins develop from a planar precursor structure, I identify a mechanical
instability that may underlie myelin formation. These results indicate the
mixed mechanical character of the surfactant lamellar structure, where fluid
and elastic properties coexist, is what enables the formation and growth of
myelins.Comment: 11 pages, 10 figures, to appear in Phys. Rev. E. Corrected
figures/typo
Stability of Biaxial Nematic Phase for Systems with Variable Molecular Shape Anisotropy
We study the influence of fluctuations in molecular shape on the stability of
the biaxial nematic phase by generalizing the mean field model of Mulder and
Ruijgrok [Physica A {\bf 113}, 145 (1982)]. We limit ourselves to the case when
the molecular shape anisotropy, represented by the alignment tensor, is a
random variable of an annealed type. A prototype of such behavior can be found
in lyotropic systems - a mixture of potassium laurate, 1-decanol, and ,
where distribution of the micellar shape adjusts to actual equilibrium
conditions. Further examples of materials with the biaxial nematic phase, where
molecular shape is subject to fluctuations, are thermotropic materials composed
of flexible trimeric- or tetrapod-like molecular units. Our calculations show
that the Gaussian equilibrium distribution of the variables describing
molecular shape (dispersion force) anisotropy gives rise to new classes of the
phase diagrams, absent in the original model. Depending on properties of the
shape fluctuations, the stability of the biaxial nematic phase can be either
enhanced or depressed, relative to the uniaxial nematic phases. In the former
case the splitting of the Landau point into two triple points with a direct
phase transition line from isotropic to biaxial phase is observed.Comment: 18 pages containing 6 figure
Evaluation of calcium absorption by 'yellow' melon with green manure use in the Brazilian Semiarid.
The objective was to evaluate the absorption curve and the calcium contribution by green manure in the development of yellow melon produced in the Brazilian Semiarid region
Statistical models of mixtures with a biaxial nematic phase
We consider a simple Maier-Saupe statistical model with the inclusion of
disorder degrees of freedom to mimic the phase diagram of a mixture of rod-like
and disc-like molecules. A quenched distribution of shapes leads to the
existence of a stable biaxial nematic phase, in qualitative agreement with
experimental findings for some ternary lyotropic liquid mixtures. An annealed
distribution, however, which is more adequate to liquid mixtures, precludes the
stability of this biaxial phase. We then use a two-temperature formalism, and
assume a separation of relaxation times, to show that a partial degree of
annealing is already sufficient to stabilize a biaxial nematic structure.Comment: 11 pages, 2 figure
Plant crude extracts inhibit oviposition of bovine tick Rhipicephalus (Boophilus) microplus.
Parasitism by the bovine tick Rhipicephalus (Boophilus) microplus is one of the main barriers for the development of livestock.04 a 07 dez. EBEQ. Pôster
Nitrate in soil solution with use of plant cocktails as green manure in diferent tillage systems in the brazilian semi-arid
Tillage systems strongly affect nutrient transformations and plant availability. The objective of this study was to assess the nitrate dynamic in soil solution in different tillage systems with use of plant cocktail as green manure in fertilized melon (Cucumis melon) in Brazilian semi-arid. The treatments were arranged in four blocks in a split-plot design and included three types of cover crops and two tillage systems, conventional tillage (CT) and no-till (NT). The data showed no strong effect of plant cocktails composition on NO3-N dynamic in the soil. Mean concentration of NO3-N ranged from 19.45 mg L-1 at 15 cm to 60.16 mg L-1 at 50 cm soil depth, indicating high leachability. No significant differences were observed between NT and CT treatments for 15 cm depth. The high soil moisture content at ~ 30 cm depth concentrated high NO3-N in all treatments, mean of 54.27 mg L-1 to NT and 54.62 mg L-1 to CT. The highest NO3-N concentration was observed at 50 cm depth in TC (60.16 mg L-1). High concentration of NO3-N in CT may be attributed to increase in decomposition of soil organic matter and crop residues incorporated into the soil
Respostas biofísicas, alocação de biomassa e produção de óleo essencial de pimenta longa no Município de Igarapé-Açu, PA.
Trabalhos e palestras apresentados no 40º. Congresso Brasileiro de Olericultura; 2º Congresso Ibero-Americamo sobre Utilização de Plástico na Agricultura; 1º Simpósio Latino-Americano de Produção de Plantas Medicinais, Aromáticas e Condimentares
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