Vesicles in solutions of hard rods

The surface free energy of ideal hard rods near curved hard surfaces is determined to second order in curvature for surfaces of general shape. In accordance with previous results for spherical and cylindrical surfaces it is found that this quantity is non-analytical when one of the principal curvatures changes signs. This prohibits writing it in the common Helfrich form. It is shown that the non-analytical terms are the same for any aspect ratio of the rods. These results are used to find the equilibrium shape of vesicles immersed in solutions of rod-like (colloidal) particles. The presence of the particles induces a change in the equilibrium shape and to a shift of the prolate-oblate transition in the vesicle phase diagram, which are calculated within the framework of the spontaneous curvature model. As a consequence of the special form of the energy contribution due to the rods these changes cannot be accounted for by a simple rescaling of the elastic constants of the vesicle as for solutions of spherical colloids or polymers.Comment: 11 pages, 7 figures, submitted to Phys. Rev.

Dynamic Phase Transitions in Cell Spreading

We monitored isotropic spreading of mouse embryonic fibroblasts on fibronectin-coated substrates. Cell adhesion area versus time was measured via total internal reflection fluorescence microscopy. Spreading proceeds in well-defined phases. We found a power-law area growth with distinct exponents a_i in three sequential phases, which we denote basal (a_1=0.4+-0.2), continous (a_2=1.6+-0.9) and contractile (a_3=0.3+-0.2) spreading. High resolution differential interference contrast microscopy was used to characterize local membrane dynamics at the spreading front. Fourier power spectra of membrane velocity reveal the sudden development of periodic membrane retractions at the transition from continous to contractile spreading. We propose that the classification of cell spreading into phases with distinct functional characteristics and protein activity patterns serves as a paradigm for a general program of a phase classification of cellular phenotype. Biological variability is drastically reduced when only the corresponding phases are used for comparison across species/different cell lines.Comment: 4 pages, 5 figure

Phase ordering and shape deformation of two-phase membranes

Within a coupled-field Ginzburg-Landau model we study analytically phase separation and accompanying shape deformation on a two-phase elastic membrane in simple geometries such as cylinders, spheres and tori. Using an exact periodic domain wall solution we solve for the shape and phase ordering field, and estimate the degree of deformation of the membrane. The results are pertinent to a preferential phase separation in regions of differing curvature on a variety of vesicles.Comment: 4 pages, submitted to PR

Tilt Texture Domains on a Membrane and Chirality induced Budding

We study the equilibrium conformations of a lipid domain on a planar fluid membrane where the domain is decorated by a vector field representing the tilt of the stiff fatty acid chains of the lipid molecules, while the surrounding membrane is fluid and structureless. The inclusion of chirality in the bulk of the domain induces a novel budding of the membrane, which preempts the budding induced by a decrease in interfacial tension.Comment: 5 pages, 3 figure

Fatores a serem considerados na interpretação de valores analíticos de fósforo inorgânico no soro sanguíneo de bovinos

The factors studied included 1) the effects of temperature after collection of the blood sample, 2) the time interval between collection and separation of serum, 3) the effect of storage at room temperature and in refrigeration for differing periods of time, and 4) influence of different degrees of haemolysis on the inorganic phosphorus level. Inorganic phosphorus was also determined in plasma and whole blood, and the values were compared with those found Iii the serum. The inorganic phosphorus values were elevated significanty when the serum was separated after the blood had remained at room temperature for more than 3 hours; there was no significant difference when the serum was separated after the blood had been refrigerated for up to 24 hours. The phosphorus values were not altered when the serum was kept up to 7 days in the refrigerator, deep freezer, or at room temperature with one drop of formalin for each 3 ml of serum. Slight or moderate haemolysis did not, influence the serum inorganic phosphorus values, when the serum was separated within 24 hours after the collection of the blood. When serum with slight or moderate haemolysis was examined there was no difference because of storage for 7 days, of storage in the refrigerator or storage at room temperature with formalin. Serum with severe haemolysis had significantly higher phosphorus values following all three types of storage. Inorganic phosphorus estimation in the serum gave significantly higher values than those from plasma or whole blood, with a regression coefficient of Y (phosphorus of plasma) ═ -0.44 + 0.907 X (phosphorus of serum) and Y (phosphorus of serum) ═ 1.38 + 1.07 X (phosphorus of whole blood).Foi estudada a influência da temperatura e do intervalo de tempo de separação do soro após a coleta do sangue, a influência da temperatura e do tempo na conservação do soro e a influência da hemólise sobre o valor real de fósforo inorgânico no soro sanguíneo de bovinos. Através de dosagens desse elemento também no plasma e sangue total foram comparados os valores dessas análises com os encontrados no soro. Os valores de fósforo inorgânico aumentaram significativamente quando o soro era separado depois de ter o sangue permanecido em temperatura ambiente por mais de três horas; não houve diferença significativa quando o soro era separado após o sangue ter sido mantido refrigerado até 24 horas. O teor de fósforo não sofreu influência substancial quando o soro era estocado, até 7 dias, em geladeira ou congelador, ou em temperatura ambiente com uma gota de formol p.a. para 3 ml de soro. Hemólise leve ou moderada não interferiu no teor de fósforo inorgânico do soro, quando este foi separado até 24 horas após a coleta do sangue. O tempo de estocagem do até 7 dias não influenciou o teor de fósforo no soro com hemólise leve ou moderada, tanto no mantido em geladeira ou em temperatura ambiente com uma gota de formol p.a. para 3 ml de soro. O soro com grau de hemólise acentuada apresentou níveis de fósforo significativamente mais elevados que os demais. O soro apresentou um teor de fósforo inorgânico significativamente mais alto do que o plasma ou sangue total, sendo as equações de regressão, respectivamente, Y (fósforo no plasma) ═ -0,440 + 0,907 X (fósforo no soro) e Y (fósforo no soro) ═ 1.38 + 1.07 X (fósforo no sague total)

Seleção de genótipos de milho e arroz mais eficientes quanto ao ganho de N através de fixação biológica de N2.

Milho. Arroz. Resultados referentes ao ano de 1997. Experimento 1: Interação de níveis de nitrogênio (N) e fósforo (P) em diferentes variedades de milho. Experimento 2: Efeito da inoculação em milho com bactérias diazotróficas, no incremento da produção de grãos, absorção de nitrogênio e atividade das enzimas glutamina sintetase e nitrato redutase. Quantificação da FBN associada com a cultura de arroz irrigado. Quantificação da FBN em 40 genótipos de arroz inundado, em solo marcado com 15N, através da técnica de diluição isotópica de 15N - rendimento de grãos, produção de matéria seca e índice de colheita. Contagem de bactérias diazotróficas. Quantificação da FBN em arroz de sequeiro com e sem a inoculação de bactérias diazotróficas. Experimento de vasos contendo 15N.bitstream/CNPAB-2010/27270/1/doc073.pd

Critical adsorption on curved objects

A systematic fieldtheoretic description of critical adsorption on curved objects such as spherical or rodlike colloidal particles immersed in a fluid near criticality is presented. The temperature dependence of the corresponding order parameter profiles and of the excess adsorption are calculated explicitly. Critical adsorption on elongated rods is substantially more pronounced than on spherical particles. It turns out that, within the context of critical phenomena in confined geometries, critical adsorption on a microscopically thin `needle' represents a distinct universality class of its own. Under favorable conditions the results are relevant for the flocculation of colloidal particles.Comment: 52 pages, 10 figure