The redox transformations and nucleophilic replacements as possible metabolic reactions of the drug “Triazaverin”. The chemical modeling of the metabolic processes

As a model of metabolic transformations of antiviral drug “Triazaverin” and its analogues‑2-alkylthio‑6-nitro‑1,2,4-triazolo[5,1-c][1,2,4]triazine‑7-ones 1a-d examined the oxidation of alkylthio groups to the corresponding sulfoxides 2a-d and sulfones 3a-d, as well as the process of nucleophilic substitution sulfonyloxy group of cysteine and cysteamine with the formation of compounds 5 and 6

Environment quality management in green cities

The article is devoted to the issues of improvement of quality of urban environment during realization of the project of development of green cities, which combines economic and ecological advantages. The article substantiates top-priority directions of change of approaches to management of urban territories and integration of efforts of science, business, and society in promotion of green technologies. The main methodological approach to provision of ecological balance in green cities consists in development of the most comprehensive complex of ecological and economic indicators of development of the city in view of implementation of progressive technologies of filtration of industrial emissions into the atmosphere, sewage water treatment, waste processing, etc. The article offers methodological substantiation of the system of indicators which include evaluation of anthropogenic influence on urban environment and calculation of integrated economic effect from implementation of green technologies which minimize unfavorable effect of these influences. These indicators include emissions release into the atmosphere, soil pollution, development of green areas, use of urban territories which are taken out from the system of natural use, use of city public transport, etc. The developed indicators can not only reflect the existing ecological state and economic development of the city fully but be used for development of perspective scenarios of development of green urban economy on the basis of industrially developed middle-sized cities of Russia and the CIS.peer-reviewe

Canted Ferromagnetism in Double Exchange Model with on-site Coulomb Repulsion

The double exchange model with on-site Coulomb repulsion is considered. Schwinger-bosons representation of the localized spins is used and two spin-singlet Fermion operators are introduced. In terms of the new Fermi fields the on-site Hund's interaction is in a diagonal form and the true magnons of the system are identified. The singlet fermions can be understood as electrons dressed by a cloud of repeatedly emitted and reabsorbed magnons. Rewritten in terms of Schwinger-bosons and spin-singlet fermions the theory is U(1) gauge invariant. We show that spontaneous breakdown of the gauge symmetry leads to \emph{\textbf{canted ferromagnetism with on-site spins of localized and delocalized electrons misaligned}}. On-site canted phase emerges in double exchange model when Coulomb repulsion is large enough. The quantum phase transition between ferromagnetism and canted phase is studied varying the Coulomb repulsion for different values of parameters in the theory such as Hund's coupling and chemical potential.Comment: 8 pages, 6 figure

Electronic band structure and carrier effective mass in calcium aluminates

First-principles electronic band structure investigations of five compounds of the CaO-Al2O3 family, 3CaO.Al2O3, 12CaO.7Al2O3, CaO.Al2O3, CaO.2Al2O3 and CaO.6Al2O3, as well as CaO and alpha-, theta- and kappa-Al2O3 are performed. We find that the conduction band in the complex oxides is formed from the oxygen antibonding p-states and, although the band gap in Al2O3 is almost twice larger than in CaO, the s-states of both cations. Such a hybrid nature of the conduction band leads to isotropic electron effective masses which are nearly the same for all compounds investigated. This insensitivity of the effective mass to variations in the composition and structure suggests that upon a proper degenerate doping, both amorphous and crystalline phases of the materials will possess mobile extra electrons

Structure peculiarities of cementite and their influence on the magnetic characteristics

The iron carbide $Fe_3C$ is studied by the first-principle density functional theory. It is shown that the crystal structure with the carbon disposition in a prismatic environment has the lowest total energy and the highest energy of magnetic anisotropy as compared to the structure with carbon in an octahedron environment. This fact explains the behavior of the coercive force upon annealing of the plastically deformed samples. The appearance of carbon atoms in the octahedron environment can be revealed by Mossbauer experiment.Comment: 10 pages, 3 figures, 3 tables. submitted to Phys.Rev.

Electric field gradients in s-, p- and d-metal diborides and the effect of pressure on the band structure and Tc_c in MgB2_2

Results of FLMTO-GGA (full-potential linear muffin-tin orbital -- generalized gradient approximation) calculations of the band structure and boron electric field gradients (EFG) for the new medium-T$_c$ superconductor (MTSC), MgB$_2$, and related diborides MB$_2$, M=Be, Al, Sc, Ti, V, Cr, Mo and Ta are reported. The boron EFG variations are found to be related to specific features of their band structure and particularly to the M-B hybridization. The strong charge anisotropy at the B site in MgB$_2$ is completely defined by the valence electrons - a property which sets MgB$_2$ apart from other diborides. The boron EFG in MgB$_2$ is weakly dependent of applied pressure: the B p electron anisotropy increases with pressure, but it is partly compensated by the increase of core charge assymetry. The concentration of holes in bonding $\sigma$ bands is found to decrease slightly from 0.067 to 0.062 holes/B under a pressure of 10 GPa. Despite a small decrease of N(E$_F$), the Hopfield parameter increases with pressure and we believe that the main reason for the reduction under pressure of the superconducting transition temperature, T$_c$, is the strong pressure dependence of phonon frequencies, which is sufficient to compensate the electronic effects.Comment: 12 pages, 3 figure

Softening and hardening of ECAP nickel under ultrasonic treatment

Commercially pure nickel was processed by equal channel angular pressing (ECAP) through route Bc for 12 passes to obtain an ultrafine grained (UFG) microstructure and further subjected to an ultrasonic treatment (UST) which introduced a maximum amplitude equivalent to anormal stresses of 100 MPa in a steady state regime. It was observed that the microstructure of UFG Ni can be differently altered depending on the position in the sample, i.e. on the amplitude of the ultrasonic wave. The microstructural analysis demonstrated a lower dislocation density (due to the activation of recovery) at the cross section of the specimen subjected to UST at an amplitude equal to 0.8 of the maximum one, plus enhanced hardening in the cross section at the maximum amplitude.Preprin

Multi-component Transparent Conducting Oxides: Progress in Materials Modelling

Transparent conducting oxides (TCOs) play an essential role in modern optoelectronic devices through their combination of electrical conductivity and optical transparency. We review recent progress in our understanding of multi-component TCOs formed from solid-solutions of ZnO, In2O3, Ga2O3 and Al2O3, with a particular emphasis on the contributions of materials modelling, primarily based on Density Functional Theory. In particular, we highlight three major results from our work: (i) the fundamental principles governing the crystal structures of multi-component oxide structures including (In2O3)(ZnO)n, named IZO, and (In2O3)m(Ga2O3)l(ZnO)n, named IGZO; (ii) the relationship between elemental composition and optical and electrical behaviour, including valence band alignments; (iii) the high-performance of amorphous oxide semiconductors. From these advances, the challenge of the rational design of novel electroceramic materials is discussed.Comment: Part of a themed issue of Journal of Physics: Condensed Matter on "Semiconducting Oxides". In Press (2011

Dielectric functions and collective excitations in MgB_2

The frequency- and momentum-dependent dielectric function $\epsilon{(\bf q,\omega)}$ as well as the energy loss function Im[-$\epsilon^{-1}{(\bf q,\omega)}$\protect{]} are calculated for intermetallic superconductor $MgB_2$ by using two {\it ab initio} methods: the plane-wave pseudopotential method and the tight-binding version of the LMTO method. We find two plasmon modes dispersing at energies $\sim 2$-8 eV and $\sim 18$-22 eV. The high energy plasmon results from a free electron like plasmon mode while the low energy collective excitation has its origin in a peculiar character of the band structure. Both plasmon modes demonstrate clearly anisotropic behaviour of both the peak position and the peak width. In particular, the low energy collective excitation has practically zero width in the direction perpendicular to boron layers and broadens in other directions.Comment: 3 pages with 10 postscript figures. Submitted to PRB on May 14 200

Generalized stacking fault energetics and dislocation properties: compact vs. spread unit dislocation structures in TiAl and CuAu

We present a general scheme for analyzing the structure and mobility of dislocations based on solutions of the Peierls-Nabarro model with a two component displacement field and restoring forces determined from the ab-initio generalized stacking fault energetics (ie., the so-called $\gamma$-surface). The approach is used to investigate dislocations in L1$_{0}$ TiAl and CuAu; predicted differences in the unit dislocation properties are explicitly related with features of the $\gamma$-surface geometry. A unified description of compact, spread and split dislocation cores is provided with an important characteristic "dissociation path" revealed by this highly tractable scheme.Comment: 7 two columns pages, 2 eps figures. Phys. Rev. B. accepted November 199