Electrical conductivity improvement of strontium titanate doped lead vanadate glasses by nanocrystallization

The structural and electrical conductivity (σ) of annealed SrTiO₃–PbO₂–V₂O₅ glasses were studied. The annealing of initially glass samples leads to formation of nanocrystalline grains embedded in the glassy matrix. XRD patterns of the glass–ceramic samples show that nanocrystals were embedded in the glassy matrix with an average grain size of 32 nm. The glass–ceramic nanocrystals obtained by annealing at temperatures close to the crystallization temperature T_c exhibit enhancement of electrical conductivity up to four orders of magnitude than initially glasses. The enhancement of the electrical conductivity due to annealing was attributed to two interdependent factors: (i) an increase of concentration of V⁴⁺–V⁵⁺ pairs; and (ii) formation of defective, well-conducting regions along the glass–crystallites interfaces. From the conductivity temperature relation, it was found that small polaron hopping model was applicable at temperature above θ_D/2 (θ_D, the Debye temperature). The electrical conduction at T >θ_D/2 was due to non-adiabatic small polaron hopping (SPH) of electrons between vanadium ions. The parameters obtained from the fits of the experimental data to this model appear reasonable and are consistent with glass composition.     

Neue Integraldarstellungen aus der Theorie der MacRobertschen und Besselschen Funktionen

Ohne Zusammenfassung     

Integrals involving Whittaker functions

Summary Integrals involving products of two Whittaker functions and Bessel functions are evaluated in §§ 3, 4. Also the integrals are evaluated in § 5 while in § 6 integrals involving the product of three Whittaker functions are established.     

Semi-classical transport for predicting joule heating in carbon nanotubes

A method for predicting the joule heating using Monte Carlo simulation for the electron dynamics is proposed. The joule heating in (10,10) carbon nanotubes is computed. The full energy band is utilized; however the results show that for low temperatures only the lower subband is sufficient, while for temperatures above 900 K, it is important to include all the subbands. Results are compared with a quantum mechanical integral form which uses an approximation for the electron occupation probability. There is a quantitative agreement of the results; however saturation of the heat generated observed in the integral form is not observed.     

Radioprotective and Antitumor Activity of Some Novel Amino Acids and Imidazoles Containing Thieno[2,3-d]pyrimidine Moiety

A variety of novel thieno[2,3-d]pyrimidine derivatives, comprising amino acids 3a–l, imidazothieno-pyrimidines 4A, 4b–h, and 7, were obtained via the reaction of 4-chloro-5,6-dimethylthieno[2,3-d]pyrimidine 1 with a variety of reagents. The structures of these compounds were confirmed by microanalysis, IR, ¹H NMR, and mass spectrometry. Some of the obtained compounds showed promising radioprotective and antitumor activities.     

Simple and convenient routes to new polyheterocycles incorporating pyrazole,thiazole, thiophene,and 1,3,4‐thiadiazole moieties

The cyanothioacetanilide derivative 3 reacted readily with either α‐halocarbonyl compounds 4 or α‐halodicarbonyl compounds 8 to afford the same thiophene derivatives 6 . Compound 3 also reacted with hydrazonoyl chlorides 12 and 16 and furnished the new polyheterocyles 14 and 17 , respectively. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:248–251, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10024