Structure and properties of solid solutions in the Mg-Al-B system

Compounds with the general formula Mg_1−x Al _x B₂ were obtained by two-step ceramic synthesis. All compounds were characterized by X-ray diffraction, NMR spectroscopy, and by four point probe resistivity measurements in various magnetic fields method. The diborides unit cell parameters were determined as a function of the Al mole fraction. With the vaues of x up to 0.40 (where x is the composition of the stock prepared for sintering), the unit cell parameters of Mg_1−x Al _x B₂ are similar to those of pure MgB₂ and the superconducting transition temperature was lowered. For stock compositions of 0:25 ≤ x ≤ 0:60, the products contain a superstructure, also superconducting phase, which becomes the only product at x = 0:50, and at x > 0:60 this phase is replaced by AlB₂-based solid solutions.     

An equation of state for the detonation product of copper oxide/aluminum nanothermite composites

An equation of state (EOS) for the detonation product of the copper oxide/aluminum (CuO/Al) nanothermite composites is developed based on the Chapman–Jouguet (CJ) theory and the nanothermite detonation experiment. The EOS is implemented into a coupled computational fluid dynamics and computational solid dynamics code through the material point method for the model-based simulations of the detonation response of the CuO/Al nanothermite material placed in a small well. The simulations demonstrate the validity of the formulated EOS to catch the essential feature of the detonation response of the CuO/Al nanothermite. The EOS parameters are determined by comparing simulated and experimentally measured pressure–time histories.     

A novel regiospecific cascade synthesis of sulfonamide derivatives from <Emphasis Type="Italic">N</Emphasis>-(2-polychloroethyl)sulfonamides via chloroaziridine intermediates in the presence of mercaptoethanol

N-(1-Aryl-2-polychloroethyl)arenesulfonamides obtained on the basis of N,N-dichlorosulfoamides and polychloroethenes or phenylacetylene undergo a reaction cascade in the presence of mercaptoethanol. The reaction cascade opens a new route to the series of cyclic or open-chain sulfonamide derivatives. The process includes cyclization to aziridine intermediates, their further recyclization, and isomerization to imidoylchlorides or chloroimines, followed by substitution or reduction under the action of mercaptoethanol or hydrolysis. The final sulfonamide structures depend on the starting N-(polychloroethyl)sulfonamides. N-(2,2-Dichloroethyl)sulfonamides were transformed into sulfonamide-containing 1,4-oxathians while N-(2,2,2-trichloroethyl)sulfonamides were converted to N-(2-arylacetyl)arenesulfonamides. N-(2-Phenyl-2,2-dichloroethyl)sulfonamides form enamide derivatives that were transformed into aromatic ketones.     

BioCores: identification of a drug/natural product-based privileged structural motif for small-molecule lead discovery

The analysis of known drugs (Comprehensive Medicinal Chemistry database (2008 version): ) and natural products (Koch et al., Proc Natl Acad Sci USA 102:17272–17277, 2008) has led to the identification of privileged saturated and aromatic heterocyclic ring pairs that we have termed as “BioCores.” This article explains how the BioCores can be used for the design of novel lead-like scaffolds.     

Enhancement of Lewis Acidity of Cr-Doped Nanocrystalline SnO2: Effect on Surface NH3 Oxidation and Sensory Detection Pattern

Understanding ammonia oxidation over metal oxide surfaces is crucial for improving its detection with resistive type gas sensors. Formation of NO_x during this process makes sensor response and calibration unstable. Cr-doping of nanocrystalline metal oxides has been reported to suppress NO₂ sensitivity and improve response towards NH₃, however the exact mechanism of such chromium action remained unknown. Herein, by using EPR spectroscopy we demonstrate formation of Cr(VI) lattice defects on the surface of nanocrystalline Cr-doped SnO₂. Enhancement of Cr-doped SnO₂ surface acidity and ammonia adsorption as a result has been revealed by using in situ IR spectroscopy. Moreover, a decrease in concentration of free electrons in the conduction band has been shown as a result of substitutional Cr(III) defects formation. Weaker NO_x chemisorption during ammonia oxidation over SnO₂ surface after Cr doping has been found with the use of mass-spectrometry assisted NH₃ thermo-programmed desorption. The given example of surface acidity adjustment and electronic configuration by means of doping may find use in the design of new gas-sensing metal oxide materials.     

Incompatibility of the Dirac-like Field Operators with the Majorana Anzatzen

In the present article we investigate the spin-1/2 and spin-1 cases in different bases. Next, we look for relations with the Majorana-like field operator. We show explicitly incompatibility of the Majorana anzatzen with the Dirac-like field operators in both the original Majorana theory and its generalizations. Several explicit examples are presented for higher spins too. It seems that the calculations in the helicity basis only give mathematically and physically reasonable results.

     

On existence of complete sets for bounded reducibilities

Classical reducibilities have complete sets U that any recursively enumerable set can be reduced to U. This paper investigates existence of complete sets for reducibilities with limited oracle access. Three characteristics of classical complete sets are selected and a natural hierarchy of the bounds on oracle access is built. As the bounds become stricter, complete sets lose certain characteristics and eventually vanish. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bi2−xLnxWO6: a novel layered structure type related to the Aurivillius phases

The crystal structure of Bi_0.7Yb_1.3WO₆ (a representative of the isomorphous series Bi_2−xLn_xWO₆; 0.3<x<1.3, for most lanthanides) has been determined. Contrary to previous suggestions, this structure type (space group A2; a=8.1070(3) Å, b=3.7048(2) Å, c=15.8379(8) Å, β=103.548(4)°) contains layers of stoichiometry WO₄, containing WO₆ octahedra sharing both edges and corners. These layers alternate with fluorite-like (Bi/Yb)₂O₂ sheets; this is a novel and unexpected arrangement and contrasts dramatically with the purely corner-sharing octahedral WO₄-layer in the parent Aurivillius phase Bi₂WO₆.