Effect of temperature on spectroscopic features relevant to laser performance of YVO4:Tm3+, GdVO4:Tm3+, and LuVO4:Tm3+ crystals

Optical spectra and luminescence decay curves were measured for thulium-doped YVO(4), GdVO(4), and LuVO(4) single crystals as a function of temperature in the 300-670 K temperature region. In spite of structural similarity, the three systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found, in particular, that the peak value of the pump band absorption intensity diminishes by about 30% for Tm:YVO(4) and Tm:GdVO(4), and the effective emission cross section for the laser transition of Tm(3+) diminishes by a factor of 2 roughly when temperature increases from 300 to 500 K. An unusually small quantum efficiency of the upper laser level in Tm:LuVO(4) has been derived from the analysis of luminescence decay curves.     

Compact pseudo-Riemannian manifolds with parallel Weyl tensor

It is shown that in every dimension n = 3j + 2, j = 1, 2, 3, . . ., there exist compact pseudo-Riemannian manifolds with parallel Weyl tensor, which are Ricci-recurrent, but neither conformally flat nor locally symmetric, and represent all indefinite metric signatures. The manifolds in question are diffeomorphic to nontrivial torus bundles over the circle. They all arise from a construction that a priori yields bundles over the circle, having as the fibre either a torus, or a 2-step nilmanifold with a complete flat torsionfree connection; our argument only realizes the torus case.     

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.     

A genetic design of linguistic terms for fuzzy rule based classifiers

The determination of fuzzy information granules including the estimation of their membership functions play a significant role in fuzzy system design as well as in the design of fuzzy rule based classifiers (FRBCSs). However, although linguistic terms are fundamental elements in the process of elucidating expert’s knowledge, the problem of linguistic term design along with their fuzzy-set-based semantics has not been fully addressed, since term-sets of attributes have not been interpreted as a formalized structure. Thus, the essential relationship between linguistic terms, as syntax, and the constructed fuzzy sets, as their quantitative semantics, or in other words, the problem of the natural semantics of terms behind the linguistic literal has not been addressed. In this paper, we introduce the problem of the design of optimal linguistic terms and propose a method of the design of FRBCSs which may incorporate with the design of linguistic terms to ensure that the presence of linguistic literals are supported not only by data but also by their natural semantics. It is shown that this problem plays a primordial role in enhancing the performance and the interpretability of the designed FRBCSs and helps striking a better balance between the generality and the specificity of the desired fuzzy rule bases for fuzzy classification problems. A series of experiments concerning 17 Machine Learning datasets is reported.     

Saturation recovery EPR and ELDOR at W-band for spin labels

A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE₀₁₁ cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW^−1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T_1e previously reported for these molecules in the range of 2–35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T₁ values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524–9529]. The values of T_1e decrease at 94 GHz relative to values at 35 GHz.     

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