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Arov D.Z.,South Ukrainian Pedagogical University | Kurula M.,Abo Akademi University | Staffans O.J.,Abo Akademi University
Complex Analysis and Operator Theory | Year: 2011

This work is devoted to the construction of canonical passive and conservative state/signal shift realizations of arbitrary passive continuous time behaviors. By definition, a passive future continuous time behavior is a maximal nonnegative right-shift invariant subspace of the Kreǐn space L2([0, ∞);W), where W is a Kreǐn space, and the inner product in L2([0, ∞);W) is the one inherited from W. A state/signal system Σ = (V; X, W), with a Hilbert state space X and a Kreǐn signal space W, is a dynamical system whose classical trajectories (x, w) on [0, ∞) satisfy x ∈ C1 ([0,∞); X),w ∈ C([0, ∞); W) and (ẋ(t), x(t), w(t)) ∈ V, t ∈ [0, ∞), where the generating subspace V is a given subspace of the node space k: = X × X × W. Passivity of this systems means that V is maximal nonnegative with respect to a certain Kreǐn space inner product on k, and that (z, 0, 0) ∈ V implies z = 0. We present three canonical passive shift models: (a) an observable and co-energy preserving model, (b) a controllable and energy preserving model, and (c) a simple conservative model. In order to construct these models we first introduce the notions of the input map, the output map, and the past/future map of a passive state/signal system. Our canonical passive state/signal shift realizations are analogous to the corresponding de Branges-Rovnyak type input/state/output realizations of a given Schur function. © 2011 Springer Basel AG. Source

Fuks D.,Ben - Gurion University of the Negev | Shapiro D.,Ben - Gurion University of the Negev | Kiv A.,Ben - Gurion University of the Negev | Golovanov V.,South Ukrainian Pedagogical University | And 2 more authors.
International Journal of Quantum Chemistry | Year: 2011

A slab approach in the framework of ab initio calculations was applied to study surface electronic states in In2O3 crystal. Density functional theory (DFT) calculations were carried out employing the WIEN 2k code and using the full potential method with Augmented Plane Waves + local orbitals (APW+lo) formalism. Total and partial DOS (Density of States) were calculated for In and O atoms in two upper (110) surface layers. Comparison of total and partial DOS allowed determining a contribution of electronic states of different In and O surface atoms into formation of surface electronic spectra and corresponding chemical bonds. A dominant ionic character of chemical bonds in In2O3 is found. Calculations were performed for three slab models with different geometry parameters. It was shown that an optimal ratio between the whole vertical size of a supercell and the vertical size of atomic cluster has to be chosen. The size of vacuum region in the slab model influences significantly on the reliability of calculated characteristics of the surface electronic structure. Copyright © 2010 Wiley Periodicals, Inc. Source

Birkenheuer U.,Helmholtz Center Dresden | Ulbricht A.,Helmholtz Center Dresden | Bergner F.,Helmholtz Center Dresden | Gokhman A.,South Ukrainian Pedagogical University
Journal of Physics: Conference Series | Year: 2010

Setting out from the results found in a set of small-angle neutron scattering (SANS) experiments for neutron-irradiated Fe-Cu model alloys, a rate theory model for the simulation of the irradiation-induced time-evolution of Cu-rich precipitates in these model alloys is presented which follows the idea that the precipitate clusters are mixed Cu-vacancy aggregates. This is done by explicitly allowing the defect clusters to absorb vacancies. The resulting Vacancy-Coupled Copper Clustering (V3C) model is calibrated by SANS experiments on two different Fe-Cu model alloys neutron-irradiated at four different doses. Quantitative agreement with the SANS experiments could be achieved by introducing a dependence of the Fe-Cu interface energy on the amount of vacancies in the mixed precipitate clusters. Phenomenologically, this energy can be seen as a function of the weight-percentage of Cu in the iron matrix. An empirical expression for this dependence is suggested. In addition, the new V3C model is used to gain some preliminary insight into the time-evolution of the chemical composition of the mixed Cu-vacancy clusters, confirming qualitatively the experimental findings. The relation of our ansatz to the heterogeneous Cu-precipitation mechanism proposed by others for neutron-irradiated Fe-Cu alloys of low Cu content is discussed. © 2010 IOP Publishing Ltd. Source

Gokhman A.,South Ukrainian Pedagogical University | Bergner F.,Helmholtz Center Dresden
NATO Science for Peace and Security Series A: Chemistry and Biology | Year: 2010

The Lifshitz - Slezov theory is applied to study the metastable states of the matrix damage clusters, MD s, and the copper enriched clusters, CEC s, in neutron irradiated steels. It was found that under irradiation conditions the CEC s are at the Ostwald stage for a neutron fluence of about 0.0002 dpa. The time dependence of number density, MD N, is determined by summarizing all differential equations of the master equation for MD s with neglecting of dimmers concentration in comparison with concentration of the single vacancies and subtraction of the number CEC s that replace the MD s, namely vacancy clusters, due to the diffusivity of copper and other impurity atoms to them. For binary Fe-0.3wt%Cu under neutron irradiation with dose 0.026, 0.051, 0.10 and 0.19 dpa the volume content of the precipitates from the SANS experiment is found to be about 0.229, 0.280, 0.237 and 0.300 vol% respectively. The volume fraction of CEC s in these samples is 0.195 vol% and the calculated volume fraction of MD s is 0.034, 0.085, 0.042 and 0.105 vol% for doses 0.026, 0.051, 0.10 and 0.19 dpa respectively. Source

Smatko V.,Institute of Electrotechnical Engineering | Golovanov V.,South Ukrainian Pedagogical University | Golovanov V.,Case Western Reserve University | Liu C.C.,Case Western Reserve University | And 5 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2010

A structural stability of In 2O 3 films in gas sensors was studied in conditions of intensive exploitation of sensor device at elevated temperatures. Structural changes of In 2O 3 films as well as a surface electromigration of In atoms were observed. The degradation effects are caused by simultaneous influence on In 2O 3 films of elevated temperatures and conditions of the working device. It was found that a structural degradation of In 2O 3 films in a sensor device could be suppressed using thin substrates. Fabrication of sensors with uniform In 2O 3 films led to improvement of their operational parameters. © 2009 Springer Science+Business Media, LLC. Source

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