955 resultados para Formation and seed viability


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Thesis (Ph.D.)--University of Washington, 2016-06

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What are the components that control the assembly of subcellular organelles in eukaryotic cells? Although membranes can clearly be distorted by cytosolic factors, very little is known about the intrinsic mechanisms that control the biogenesis, shape, and organization of organellar membranes. Here, we found that the unconventional phospholipid lysobisphosphatidic acid (LBPA) could induce the formation of multivesicular liposomes that resembled the multivesicular endosomes that exist where this lipid is found in vivo. This process depended on the same pH gradient that exists across endosome membranes in vivo and was selectively controlled by Alix. In turn, Alix regulated the organization of LBPA-containing endosomes in vivo.

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Not all myocardium involved in a myocardial infarction is dead or irreversibly damaged. The balance between the amount of scar and live tissue, and the nature of the live tissue, determine the likelihood that contractile function will improve after revascularisation. This improvement (which defines viability) may be predicted with about 80% accuracy using several techniques. This review examines the determinants of functional recovery and how they may be integrated in making decisions regarding revascularisation. (Intern Med J 2005; 35: 118–125)

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Semisolid metal forming has now been accepted as a viable technology for production of components with complex shape and high integrity. The advantages of semisolid metal forming can only be achieved when the feedstock material has a non-dendritic semisolid structure. A controlled nucleation method has been developed to produce such structures for semisolid forming. By controlling grain nucleation and growth, fine-grained and non-dendritic microstructures that are suitable for semisolid casting can be generated. The method was applied to hypoeutectic and hypereutectic Al-Si casting alloys, Al wrought alloys and a Mg alloy. Parameters such as pouring temperature, cooling rate and grain refiner addition were controlled to achieve copious nucleation, nuclei survival and dendritic growth suppression during solidification. The influences of the controlling parameters on the formation of semisolid structure were different for each of these alloy groups. The as-cast structures were then partially remelted and isothermally held. Semisolid structures were developed and followed by semisolid casting into a stepped die.

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Weather damage reduces the value of commercial mungbean, but hard-seededness can reduce the level of damage. However, attempts to breed large- and hard-seeded mungbean varieties have been unsuccessful. To understand the relationship between seed weight and hard-seededness, these traits were investigated using a quantitative trait loci (QTL) mapping approach with a recombinant inbred population derived from a cross between a completely soft-seeded variety and a completely hard-seeded genotype. The two parental genotypes also had a sixfold difference in seed weight. QTL analyses revealed four loci for hard-seededness and I I loci for seed weight. Two of the hardseededness loci co-localized with seed weight QTL. When seed weight was used as a covariate in the analysis of hard-seededness from the field data, two of the four hard-seeded QTL remained significant with the effect at one of these remaining unchanged. These results explain why retaining hard-seededness in large seeded mungbean lines has been unsuccessful. The existence of a persistent locus, however, indicated that breeding large and persistently hard-seeded varieties of mungbean may be possible.

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Mg65Cu25Er10 and Mg65Cu15Ag10Er10 bulk amorphous alloys were produced by a copper mould casting method. The alloys have high glass-forming ability and good thermal stability. The maximum diameter of glass formation (D-c), glass transition temperature (T-g), crystallization onset temperature (T-x), temperature interval of the supercooled region (Delta T-x), melting temperature (T-m), liquidus temperature (T-1) as well as heats of crystallization (Delta H-x) and melting (Delta H-m) are reported for these alloys. Both alloys exhibit high hardness and high strength at room temperature. (c) 2005 Elsevier B.V. All rights reserved.

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A computer model was developed to simulate the cake formation and growth in cake filtration at an individual particle level. The model was shown to be able to generate structural information and quantify the cake thickness, average cake solidosity, filtrate volume, filtrate flowrate for constant pressure filtration or pressure drop across the filter unit for constant rate filtration as a function of filtration time. The effects of particle size distribution and key operational variables such as initial filtration flowrate, maximum pressure drop and initial solidosity were examined based on the simulated results. They are qualitatively comparable to those observed in physical experiments. The need for further development in simulation was also discussed. (c) 2006 Elsevier Ltd. All rights reserved.

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The leaf growth, dry matter production, and seed yield of 11 wild mungbean ( Vigna radiata ssp. sublobata) accessions of diverse geographic origin were observed under natural and artificial photoperiod temperature conditions, to determine the extent to which genotypic differences could be attributed to adaptive responses to photo-thermal environment. Environments included serial sowings in the field in SE Queensland, complemented by artificial photoperiod extension and controlled-environment growth rooms. Photo-thermal environment influenced leaf growth, total dry matter production ( TDM), and seed yield directly, through effects of ( mainly cool) temperature on growth, and indirectly, through effects on phenology. In terms of direct effects, leaf production, leaf expansion, and leaf area were all sensitive to temperature, with implied base temperatures higher than usually observed in cultivated mungbean ( V. radiata ssp. radiata). Genotypic sensitivity to temperature varied systematically with accession provenance and appeared to be of adaptive significance. In terms of the indirect effects of photo-thermal environment, genotypic and environmental effects on TDM were positively related to changes in total growth duration, and harvest index was negatively related to the period from sowing to flowering, similar to cultivated mungbean. However, seed yield was positively related to the duration of reproductive growth, reflecting the indeterminate growth habit of the wild accessions. As a consequence, the wild accessions are more responsive to favourable environments than typically observed in cultivated mungbean, which is determinate in habit. It is suggested that the introduction of the indeterminate trait into mungbean from the wild subspecies would increase the responsiveness of mungbean to favourable environments, analogous to that of black gram ( V. mungo). Although the wild subspecies appeared more sensitive to cool temperature than cultivated mungbean, it may provide a source of tolerance to the warmer temperatures experienced during the wet season in the tropics.

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The dynamics of drop formation and pinch-off have been investigated for a series of low viscosity elastic fluids possessing similar shear viscosities, but differing substantially in elastic properties. On initial approach to the pinch region, the viscoelastic fluids all exhibit the same global necking behavior that is observed for a Newtonian fluid of equivalent shear viscosity. For these low viscosity dilute polymer solutions, inertial and capillary forces form the dominant balance in this potential flow regime, with the viscous force being negligible. The approach to the pinch point, which corresponds to the point of rupture for a Newtonian fluid, is extremely rapid in such solutions, with the sudden increase in curvature producing very large extension rates at this location. In this region the polymer molecules are significantly extended, causing a localized increase in the elastic stresses, which grow to balance the capillary pressure. This prevents the necked fluid from breaking off, as would occur in the equivalent Newtonian fluid. Alternatively, a cylindrical filament forms in which elastic stresses and capillary pressure balance, and the radius decreases exponentially with time. A (0+1)-dimensional finitely extensible nonlinear elastic dumbbell theory incorporating inertial, capillary, and elastic stresses is able to capture the basic features of the experimental observations. Before the critical "pinch time" t(p), an inertial-capillary balance leads to the expected 2/3-power scaling of the minimum radius with time: R-min similar to(t(p)-t)(2/3). However, the diverging deformation rate results in large molecular deformations and rapid crossover to an elastocapillary balance for times t>t(p). In this region, the filament radius decreases exponentially with time R-min similar to exp[(t(p)-t)/lambda(1)], where lambda(1) is the characteristic time constant of the polymer molecules. Measurements of the relaxation times of polyethylene oxide solutions of varying concentrations and molecular weights obtained from high speed imaging of the rate of change of filament radius are significantly higher than the relaxation times estimated from Rouse-Zimm theory, even though the solutions are within the dilute concentration region as determined using intrinsic viscosity measurements. The effective relaxation times exhibit the expected scaling with molecular weight but with an additional dependence on the concentration of the polymer in solution. This is consistent with the expectation that the polymer molecules are in fact highly extended during the approach to the pinch region (i.e., prior to the elastocapillary filament thinning regime) and subsequently as the filament is formed they are further extended by filament stretching at a constant rate until full extension of the polymer coil is achieved. In this highly extended state, intermolecular interactions become significant, producing relaxation times far above theoretical predictions for dilute polymer solutions under equilibrium conditions. (C) 2006 American Institute of Physics

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Tungsten oxide microtubules, arrayed in a radial flower-like structure, were synthesized by simply using W powders reacting with Ni(NO3)(2) center dot 6H(2)O at a elevated temperature. The formed microtubules, with lengths more than 100 pin and outer diameters of 1-5 mu m, have irregular open ends, showing clear grooves along the growth direction on the tubule surface. A novel aggregation mechanism based on chemical-vapor-deposit process was proposed to describe the growth process of the synthesized tubules, and the possible mechanism for the arrangement of the radial flower-like morphology was discussed.

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