Search results for "kinetics"
showing 10 items of 2224 documents
Modeling the interactions between light and crystallizing polymer during fast cooling
2004
In this work, an experimental set-up able to quench thin polymer films whilst recording the sample thermal history as well as the overall and depolarized light intensities of a laser beam emerging from the sample is described. The interactions between the light beam and the crystallizing material have been modeled accounting for absorption and scattering phenomena. The proposed model was found to be able to reproduce the ex- perimentally observed behavior of light intensities and it was validated by comparison with conventional DSC analysis. On the basis of this model, a method to obtain crystallinity evo- lution is proposed and applied to some fast cooling runs. The method was applied to q…
Kinetics of phase separation in polymer blends for deep quenches
1986
Electro microscopy was used to study the phase separation kinetics of a polystyrene/polyvinylmethylether system subjected to a critical deep quench. The size of the phase-separated domains was found to increase linearly with time, implying that hydrodynamic effects control the rate of growth of the domains in the time scale and temperature range under consideration. From these measurements the growth velocity and approximate diffusion constants can be determined for three different temperatures. Comparison of these results with those obtained by light scattering on other systems and with theoretical predictions is possible by replotting in dimensionless units.
Biowaiver monographs for immediate release solid oral dosage forms: quinidine sulfate.
2009
Literature data are reviewed relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing quinidine sulfate. Quinidine sulfate's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. The available data are not fully conclusive, but do suggest that quinidine sulfate is highly soluble and moderately to highly permeable and would likely be assigned to BCS Class I (or at worst BCS III). In view of the inconclusiveness of the data and, more imp…
A combined molecular dynamics and Monte Carlo study of the approach towards phase separation in colloid-polymer mixtures.
2011
A coarse-grained model for colloid-polymer mixtures is investigated where both colloids and polymer coils are represented as point-like particles interacting with spherically symmetric effective potentials. Colloid-colloid and colloid-polymer interactions are described by Weeks-Chandler-Andersen potentials, while the polymer-polymer interaction is very soft, of strength k(B)T/2 for maximum polymer-polymer overlap. This model can be efficiently simulated both by Monte Carlo and molecular dynamics methods, and its phase diagram closely resembles that of the well-known Asakura-Oosawa model. The static and dynamic properties of the model are presented for systems at critical colloid density, va…
Reversion of 7-methylguanosine 5′-phosphate inhibition of mRNA translation by polysomal and soluble factors isolated from Saccharomyces cerevisiae
1987
Abstract Protein fractions that overcome m7GMP inhibition of mRNA translation have been purified from the yeast S. cerevisiae . An active fraction isolated from polysomes contains two polypeptides of 220- and 190-kDa. The active fraction isolated from postribosomal supernatant contains a major polypeptide of 28-kDa and other species of 32-, 24-, 22- and 21-kDa, and sediments in sucrose gradients as a high molecular weight complex of about 200000. This fraction restored yeast mRNA translation in reticulocyte lysates under conditions of yeast and globin mRNA competition; however, this effect was not observed with the 220- and 190-kDa polypeptides from polysomes. Nevertheless, translation of y…
Arabinose nucleoside triphosphates are no inhibitors for DNA-dependent RNA polymerases.
1976
1-Beta-D-arabinofuranosylcytosine-5' -triphosphate and 9-beta-D-arabinofuranosyladenosine-5' -triphosphate were found to have no inhibitory potency for both mammalian DNA-dependent RNA polymerase II and E. coli DNA-dependent RNA polymerase.
Stability of the radiopharmaceutical []DMSA: Study of the ligand exchange reaction with [99Tc]EDTA
1983
Abstract A kinetic study was made of the ligand exchange reaction between [ 99 m Tc]EDTA and DMSA. The results of this study indicate that this exchange reaction is closely related to temperature and pH. Kinetic and thermodynamic parameters demonstrate that both complexes—[ 99 m Tc]EDTA and [ 99 m Tc]DMSA—have a similar stability. Furthermore, the existence of an acid-basic catalysis for the global exchange reaction was established, and the catalytic parameters were calculated. These data were obtained by radiochromatography and visible spectrophotometry.
Controlled release of tyrosol and ferulic acid encapsulated in chitosan–gelatin films after electron beam irradiation
2016
Abstract This work deals with the study of the release kinetics of antioxidants (ferulic acid and tyrosol) incorporated into chitosan–gelatin edible films after irradiation processes. The aim was to determine the influence of electron beam irradiation (at 60 kGy) on the retention of antioxidants in the film, their release in water (pH=7) at 25 °C, in relation with the barrier and mechanical properties of biopolymer films. The film preparation process coupled to the irradiation induced a loss of about 20% of tyrosol but did not affect the ferulic acid content. However, 27% of the ferulic acid remained entrapped in the biopolymer network during the release experiments whereas all tyrosol was …
Trap Spectroscopy by the Glow Rate Technique using Bleaching of Colour Centres
2002
An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF 3 :Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F A and F…
Accumulation and discharge behavior of Cs-137 by zebra fish (Brachydanio rerio) in different aquatic environments
1990
The uptake and release kinetics of137Cs from water by the tropical fishBrachydanio rerio has been studied under controlled laboratory condition. The accumulation of this radionuclide from food was avoided by feeding the fishes separately in an inactive environment. A steep inverse dependence of bioconcentration factor (BCF) with potassium concentration has been observed. This can formally be described by the equation BCF=5.2 · [K+]−0.44. The elimination rate constant K in fresh water conditions has been found to have a magnitude of 0.014±0.03 d−1 which corresponds to a biological half-life of 51±10 days. The uptake and release kinetics ofBrachydanio rerio has been compared with earlier stud…