New hydrophobic L‐amino acid salts: maleates of L‐leucine,L‐isoleucine and L‐norvaline

Crystals of maleates of three amino acids with hydrophobic side chains [L‐leucenium hydrogen maleate, C₆H₁₄NO₂⁺·C₄H₃O₄⁻, (I), L‐isoleucenium hydrogen maleate hemihydrate, C₆H₁₄NO₂⁺·C₄H₃O₄⁻·0.5H₂O, (II), and L‐norvalinium hydrogen maleate–L‐norvaline (1/1), C₅H₁₁NO₂⁺·C₄H₃O₄⁻·C₅H₁₂NO₂, (III)], were obtained. The new structures contain C₂²(12) chains, or variants thereof, that are a common feature in the crystal structures of amino acid maleates. The L‐leucenium salt is remarkable due to a large number of symmetrically non‐equivalent units (Z′ = 3). The L‐isoleucenium salt is a hydrate despite the fact that L‐isoleucine is a nonpolar hydrophobic amino acid (previously known amino acid maleates formed hydrates only with lysine and histidine, which are polar and hydrophilic). The L‐norvalinium salt provides the first example where the dimeric cation L‐Nva...L‐NvaH⁺ was observed. All three compounds have layered noncentrosymmetric structures. Preliminary tests have shown the presence of the second harmonic generation (SGH) effect for all three compounds.     

Thermal stability of modified chromium dioxide nanopowders with various magnetic properties obtained by hydrothermal route

Melt modification is a method commonly used when enhancing mechanical and microstructural properties of various alloys. The addition of heterogeneous nucleation sites generally refines the given microstructure and enhances the toughness of the material. Ferroalloys based on high-melting elements require a longer incubation time in the melt which makes them liable candidates for modification agents. A research on the effect of melt modification was conducted on an indefinite chill cast iron alloy commonly used for working layers in rolls. The goal of the research was to determine the effect of ferrovanadium and ferrotungsten melt treatment with the use of thermal analysis along with thermodynamic modelling using the CALPHAD approach. The results show a decrease in the measured liquidus temperature of the modified alloy along with a possible second eutectic reaction hidden inside the main graphite/cementite eutectic reaction. Scanning electron microscopy revealed small and evenly distributed MC type carbides rich in V with W and other carbide-forming elements. The results presented in this work enable a better understanding of the impact melt modification has on the development of microstructure and subsequently the improvement in mechanical properties of the alloy.     

Semiinfinite Cohomology of Quantum Groups

We define a new cohomology theory of associative algebras called semiinfinite cohomology in the derived categories' setting. We investigate the case of a small quantum group u, calculate semiinfinite cohomology spaces of the trivial u-module and express them in terms of local cohomology of the nilpotent cone for the corresponding semisimple Lie algebra. We discuss the connection between the semiinfinite homology of u and the conformal blocks' spaces. Received: 14 October 1996 / Accepted: 25 February 1997     

Mean-value theorem for the modulus of multiple trigonometric sums

A two-dimensional analog of the Vinogradov mean-value theorem for the modulus of trigonometric sums is proven.Translated from Matematicheskie Zametki, Vol. 17, No. 1, pp. 143–153, January, 1975.The author expresses his gratitude fo Prof. A. A. Karatsuba for guidance and Prof. S. B. Stechkin for careful consideration of the paper and useful advice.     

Negative currents caused by injection-controlled polarization

The paper deals with transient currents through the materials whose polarization properties are controlled by injection. It is shown that the negative current can occur if the dielectric constant depends upon the generation rate.