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Exponential Decay Curve (exponential + decay_curve)
Selected AbstractsTime-resolved spectroscopy in an undoped GaN (1-101)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Eunhee Kim Abstract Time-resolved photoluminescence spectroscopy was performed at 77 K in a GaN (1-101) grown on a 7 degree off-axis (001) Si substrate. The sample was grown by metal-organic-vapour-phase-epitaxy (MOVPE) and was un-intentionally doped with O, C and Si. By using photoluminescence intensity correlation method, the energy relaxation process of the photogenerated carriers near the band edge was investigated in pico-second regime. The correlation signal was represented by a single exponential decay curve and the energy relaxation time was determined, which depended strongly on the kinetic energy of the excess carriers. At low energies, the relaxation time was around 700 ps, while it was as short as a few ps at the highest energy under study. The correlation signals obtained for carriers of which kinetic energy was less than 80 meV showed an anti-correlation behaviour suggesting the occurrence of carrier accumulation. The time constants for the accumulation were of several picoseconds depending on the kinetic energy, which was nearly equal to the decay time constants determined at high energies. This fact shows that the energy relaxation at high energies is controlled by the emission of an LO phonon. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Evaluation of Cytotoxic and Cytostatic Effects in Saccharomyces cerevisiae by Poissoner Quantitative Drop TestBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 1 2009Nadine Paese Poletto Current assay techniques, however, typically require the use of expensive technological equipment or chemical reagents, or they lack adequate testing sensitivity. The poissoner quantitative drop test (PQDT) assay is a sensitive, inexpensive and accurate method for evaluation of cytotoxicity and/or cytostatic effects of multiple chemical compounds in a single experiment. In this study, the sensitivity of the PQDT assay was evaluated in a wild-type Saccharomyces cerevisiae strain using 4-nitroquinoline-N - oxide (4-NQO) and methyl methanesulfonate (MMS), both cytotoxic and genotoxic standard compounds, and cytostatic 5-fluorouracil, an antitumoral drug. Yeast cell colony growth was measured in culture media containing increasing concentrations of the three chemical agents. The results showed that the PQDT assay was able to clearly differentiate the cytotoxic effect of 4-NQO and MMS from the cytostatic effect of 5-fluorouracil. Interestingly, the cytostatic effect of 5-fluorouracil followed an exponential decay curve with increasing concentrations, a phenomenon not previously described for this drug. The PQDT assay, in this sense, can be applied not only for cytotoxic/cytostatic assays, but also for pharmacodynamic studies using Saccharomyces cerevisiae as a model. [source] Use of electron spin resonance measurements on irradiated sperma lentil seeds to indicate accidental irradiationINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2003Mustafa Korkmaz Summary The results of electron spin resonance studies on ,-irradiated micro- and macrosperma lentil seeds are reported. Spectra of non-irradiated intact sperma were composed of an equally spaced sextet originating from the presence of Mn2+ ions and a single weak resonance line. Irradiation produced a linear increase in the radical signal intensity in the radiation dose range (0.5,5 kGy) studied, without affecting the Mn2+ signal. Signal intensities of both sperma followed compound exponential decay curves originating from the presence of three different radical species. Heating the sperma cause irreversible decreases in both radical and Mn2+ signal intensities. Two radical species, described in the present work, and a radical of unknown origin were used to explain the experimental results. [source] Absorption of polyethylene glycol (PEG) polymers: The effect of PEG size on permeabilityJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2009Hema Gursahani Abstract Polyethylene glycol (PEG) polymers are large amphiphilic molecules that are highly hydrated in solution. To explore the permeability properties of different sized PEG polymers across epithelial membranes in vivo, we examined the absorption of fluorescently labeled PEG conjugates sized 0.55,20 kDa from the lung, since this system provides a reservoir that limits rapid diffusion of molecules away from the site of delivery and enables permeability over longer times to be examined. Following intratracheal delivery in rats, the PEG polymers underwent absorption with first-order kinetics described by single exponential decay curves. PEG size produced a marked influence on the rate of uptake from the lung, with half-lives ranging from 2.4 to 13 h, although above a size of 5 kDa, no further change in rate was observed. PEG size likewise affected retention in alveolar macrophages and in lung tissue; whereas smaller PEG sizes (<2 kDa) were effectively cleared within 48 h, larger PEG sizes (>5 kDa) remained in lung cells and tissue for up to 7 days. These data demonstrate that PEG polymers can be absorbed across epithelial membranes and that PEG size plays a dominant role in controlling the rate and mechanism of absorption. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2847,2856, 2009 [source] | ||||||||||