Thermally stimulated currents as a measure of degradation of zinc oxide varistors

ZnO varistor degradation phenomena was studied using thermally stimulated current (TSC) method. It is believed that asymmetrical degradation of V-I characteristics caused by DC biasing is due to charge accumulation on the reverse biased side of ZnO grain barrier. The TSCs' measuring system and cryostat apparatus used in experiment were described. The thermally stimulated currents observed in this study for varistor samples doped with different amounts of Co, due to their recovery from asymmetrical electric stress, could not be controlled by movement of Zn interstitials with activation energy 0.55 v eV, as it is widely believed, for the TSC activation energy determined in this experiment was 0.39 v eV.     

Cholesterol Peroxidation as a Special Type of Lipid Oxidation in Photodynamic Systems

Like other unsaturated lipids in cell membranes and lipoproteins, cholesterol (Ch) is susceptible to oxidative modification, including photodynamic oxidation. There is a sustained interest in the pathogenic properties of Ch oxides such as those generated by photooxidation. Singlet oxygen (¹O₂)‐mediated Ch photooxidation (Type II mechanism) gives rise to three hydroperoxide (ChOOH) isomers: 5α‐OOH, 6α‐OOH and 6β‐OOH, the 5α‐OOH yield far exceeding that of the others. 5α‐OOH detection is relatively straightforward and serves as a definitive indicator of ¹O₂ involvement in a reaction, photochemical or otherwise. Like all lipid hydroperoxides (LOOHs), ChOOHs can disrupt membrane or lipoprotein structure/function on their own, but subsequent light‐independent reactions may either intensify or attenuate such effects. Such reactions include (1) one‐electron reduction to redox‐active free radical intermediates, (2) two‐electron reduction to redox‐silent alcohols and (3) translocation to other lipid compartments, where (1) or (2) may take place. In addition to these effects, ChOOHs may act as signaling molecules in reactions that affect cell fates. Although processes a‐c have been well studied for ChOOHs, signaling activity is still poorly understood compared with that of hydrogen peroxide. This review focuses on these various aspects Ch photoperoxidation and its biological consequences.     

Conformational Dynamics in the Core of Human Y145Stop Prion Protein Amyloid Probed by Relaxation Dispersion NMR

Microsecond to millisecond timescale backbone dynamics of the amyloid core residues in Y145Stop human prion protein (PrP) fibrils were investigated by using ¹⁵N rotating frame (R_1ρ) relaxation dispersion solid-state nuclear magnetic resonance spectroscopy over a wide range of spin-lock fields. Numerical simulations enabled the experimental relaxation dispersion profiles for most of the fibril core residues to be modelled by using a two-state exchange process with a common exchange rate of 1000 s⁻¹, corresponding to protein backbone motion on the timescale of 1 ms, and an excited-state population of 2 %. We also found that the relaxation dispersion profiles for several amino acids positioned near the edges of the most structured regions of the amyloid core were better modelled by assuming somewhat higher excited-state populations (∼5–15 %) and faster exchange rate constants, corresponding to protein backbone motions on the timescale of ∼100–300 μs. The slow backbone dynamics of the core residues were evaluated in the context of the structural model of human Y145Stop PrP amyloid.     

Unusual behavior of Tb3+ in K3YF6 green-emitting phosphor

We report on photoluminescence studies of Tb3+ in a polycrystalline cryolite type K3YF6 host. The location of the Tb3+ in the center of inversion forbids the electric-dipole transitions of terbium ions in this material. As a consequence almost the entire luminescence intensity is related to the 5D4-(7)F5 magnetic-dipole transition, and it is contained in the extremely narrow spectral bandwidth amounting to 1.7 nm at 8K and to 18 nm at room temperature. The phosphor under study can be efficiently excited making use of intense f-d transitions of Tb3+ in the UV-vacuum-UV region and may be of interest for applications requiring high spectral purity of the emission.     

A granular time series approach to long-term forecasting and trend forecasting

To overcome the “curse of dimensionality” (which plagues most predictors (predictive models) when carrying out long-term forecasts) and cope with uncertainty present in many time series, in this study, we introduce a concept of granular time series which are used to long-term forecasting and trend forecasting. A technique of fuzzy clustering is used to construct information granules on a basis of available numeric data present in the original time series. In the sequel, we develop a forecasting model which captures the essential relationships between such information granules and in this manner constructs a fundamental forecasting mechanism. It is demonstrated that the proposed model comes with a number of advantages which manifest when processing a large number of data. Experimental evidence is provided through a series of examples using which we quantify the performance of the forecasting model and provide with some comparative analysis.     

On the reaction of bis(phosphothioyl)disul‐fanes with hydroxamic acids,part I: Ionic versus radical reaction pathways

Among sodium N‐alkyl‐4‐chlorobenzo‐hydroxamates treated with bis(phosphothioyl)disul‐fanes >P(S)SSP(S)< (where >P(S) is phosphorothioyl, phosphonothioyl, and phosphinothioyl), only the N‐methyl one yields quantitatively the respective O‐phosphothioyl derivatives exhibiting complete inversion of configuration at phosphorus in a reaction whose products are inert toward dithiophosphate arising in the reaction. For branched N‐alkyl benzohydroxamates, products of a SET process predominated. The mechanism of the title reaction is discussed. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:271–282, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20423     

Gas-Phase Reactions of Dimethyl Disulfide with Aliphatic Carbanions - A Mass Spectrometry and Computational Study

Ion-molecule reactions of Me₂S₂ with a wide range of aliphatic carbanions differing by structure and proton affinity values have been studied in the gas phase using mass spectrometry techniques and DFT calculations. The analysis of the spectra shows a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the carbanion. Product ions of thiophilic reaction (m/z 47), S_N2 (m/z 79), and E2 elimination – addition sequence of reactions (m/z 93) can be observed. Primary products of thiophilic reaction can undergo subsequent S_N2 and proton transfer reactions. Gibbs free energy profiles calculated for experimentally observed reactions using PBE0/6-311+G(2d,p) method show good agreement with experimental results.

Open image in new window

Graphical Abstract ?

     

Absolute Borel sets and function spaces

An internal characterization of metric spaces which are absolute Borel sets of multiplicative classes is given. This characterization uses complete sequences of covers, a notion introduced by Frolík for characterizing Cech-complete spaces. We also show that the absolute Borel class of is determined by the uniform structure of the space of continuous functions ; however the case of absolute metric spaces is still open. More precisely, we prove that, for metrizable spaces and , if is a uniformly continuous surjection and is an absolute Borel set of multiplicative (resp., additive) class , , then is also an absolute Borel set of the same class. This result is new even if is a linear homeomorphism, and extends a result of Baars, de Groot, and Pelant which shows that the \v{C}ech-completeness of a metric space is determined by the linear structure of .

     

Ion flux through membrane channels--an enhanced algorithm for the Poisson-Nernst-Planck model

A novel algorithmic scheme for numerical solution of the 3D Poisson-Nernst-Planck model is proposed. The algorithmic improvements are universal and independent of the detailed physical model. They include three major steps: an adjustable gradient-based step value, an adjustable relaxation coefficient, and an optimized segmentation of the modeled space. The enhanced algorithm significantly accelerates the speed of computation and reduces the computational demands. The theoretical model was tested on a regular artificial channel and validated on a real protein channel-alpha-hemolysin, proving its efficiency.     

Application of Image Analysis Technique for the Determination of Organophosphorus Pesticides by Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - A simple and convenient thin-layer chromatography (TLC) method combined with image analysis technique was developed to determine...