Structure and Multi-Center Bonding: From Atomic Clusters to Solid Phase Materials

The work presented in this dissertation has been focused on structure, stability, electronic properties, and chemical bonding of atomic clusters and solid-state compounds. The common thread was development of chemically intuitive models and theoretical methods capable of describing and interpreting bonding and hence, structures of these compounds. Understanding how interactions between atoms in sub-nano clusters and solid-state compounds of certain compositions determine their structures, physical properties, and reactivities is essential for rational design of new materials, catalysts, and molecular devices. A significant part of this work presents joint experimental and theoretical studies of doped boron clusters. Several projects on carbon- and aluminum-substituted boron clusters were aimed at establishing their structures, energetic and electronic properties, and understanding bonding interactions. The dissertation introduces a series of peculiar clusters containing transition metal atoms inside perfectly symmetrical boron rings. These clusters, featuring planar octa-, nona-, and decacoordinated transition metal atoms, were designed based on a simple chemical bonding model governing stabilities of such species. One of the most important parts of this dissertation deals with chemical bonding in the solid state. The Adaptive Natural Density Partitioning method previously developed by the Boldyrev group at Utah State University has proven very efficient for understanding chemical bonding in clusters and complex molecules. In this work, a periodic implementation of this method has been developed, yielding a new theoretical tool capable of interpretation of bonding in solid state in chemically intuitive terms of localized and multi-center bonds

Turbulent Contributions to Ohm's Law in Axisymmetric Magnetized Plasmas

The effect of magnetic turbulence in shaping the current density in axisymmetric magnetized plasma is analyzed using a turbulent extension of Ohm's law derived from the self-consistent action-angle transport theory. Besides the well-known hyper-resistive (helicity-conserving) contribution, the generalized Ohm's law contains an anomalous resistivity term, and a turbulent bootstrap-like term proportional to the current density derivative. The numerical solution of the equation for equilibrium and turbulence profiles characteristic of conventional and advanced scenarios shows that, trough "turbulent bootstrap" effect and anomalous resistivity turbulence can generate power and parallel current which are a sizable portion (about 20-25%) of the corresponding effects associated with the neoclassical bootstrap effect. The degree of alignment of the turbulence peak and the pressure gradient plays an important role in defining the steady-state regime. In fully bootstrapped tokamak, the hyper-resistivity is essential in overcoming the intrinsic limitation of the hollow current profile.Comment: 19 pages, 6 figures, journal pape

Modeling of a fast-flowing CO2 laser with longitudinal discharge in a tube of variable cross section

A mathematical model of axial-flow gas laser in a tube of variable cross section is proposed. The dependence of the energy characteristics of the laser on the discharge tube geometry is studied. It is shown that the output radiation power and electrooptical efficiency may be increased by means of a conical tube tapering along the flow. © 1996 MAEe Cyrillic signK Hayκa/Interperiodica Publishing

Theoretical analysis of a fast-axial-flow CO2 laser with the conical discharge tube

A mathematical model of the fast axial flow carbon-dioxide laser (FAFL) with the glow discharge in a conical tube has been developed. The investigations of the dependence of the laser output power on the discharge tube geometry have been carried out. It is shown that the output power and the electrical-to-optical efficiency can be increased due to the conical discharge tube converging along the flow

Absolute and convective instabilities of parallel propagating circularly polarized Alfven waves: Beat instability

Ruderman and Simpson [Phys. Plasmas 11, 4178 (2004)] studied the absolute and convective decay instabilities of parallel propagating circularly polarized Alfven waves in plasmas where the sound speed c(S) is smaller than the Alfven speed upsilon(A). We extend their analysis for the beat instability which occurs in plasmas with c(S)>upsilon(A). We assume that the dimensionless amplitude of the circularly polarized Alfven wave (pump wave), a, is small. Applying Briggs' method we study the problem analytically using expansions in power series with respect to a. It is shown that the pump wave is absolutely unstable in a reference frame moving with the velocity U with respect to the rest plasma if U-lU-r, the instability is convective. The signaling problem is studied in a reference frame where the pump wave is convectively unstable. It is shown that the spatially amplifying waves exist only when the signaling frequency is in two narrow symmetric frequency bands with the widths of the order of a(3). These results enable us to extend for the case when c(S)>upsilon(A) the conclusions, previously made for the case when c(S)<upsilon(A), that circularly polarized Alfven waves propagating in the solar wind are convectively unstable in a reference frame of any spacecraft moving with the velocity not exceeding a few tens of km/s in the solar reference frame. The characteristic scale of spatial amplification for these waves exceeds 1 a.u

Numerical simulation of gas discharge CO 2 lasers with conic tubes

The results of numerical simulation for fast-axial-flow gas discharge CO 2 lasers are presented. Quasi-one-dimensional consideration of the processes for powerful CO 2 lasers with conic discharge tubes shows that laser operation may be more effective in the case of tubes which are narrowed down from anode to cathode provided that gas flow is directed towards the cathode. On the contrary, when tube is narrowed down from cathode to anode, no any advantage in the laser operation may be received. The calculated quantities are in satisfactory agreement with the available experimental data

Numerical simulation of the processes in fast flow gas discharge CO 2 lasers

In the report the results of numerical simulation of the processes in discharge chambers (DC) of fast flow CO 2 lasers, are presented. The investigations for longitudinal glow discharge (quasi-one-dimensional and two-dimensional flow) using four- and six-temperature models, were performed. Distributions of gas dynamic quantities, densities of charged parti cles, electric field strength, as well as vibrational temperatures of CO 2, N 2 and CO species, within the DC were calcu lated. Quasi-one-dimensional consideration of processes for powerful CO 2 lasers with conic discharge tubes has shown that narrowed along the gas flow tubes must be more effective for laser operation than cylindrical ones. The calculated quantities are in satisfactory agreement with available experimental data

Architectural control of construction materials with application of man-made wastes

© 2016 AIP Publishing LLC.The article considers the principles of construction materials formation based on non-organic and organic raw materials when material matrix is filled with particulate fillers from man-made wastes of various nature formed in different conditions. Qualitative and quantitative requirements for mineral, chemical and material composition of wastes to modify construction materials are detailed. The ways to use them as modifiers of construction materials are shown by the example of wastes group belonging to slags

Microscopic vortices in classical liquids

In the present article we introduce the notions about the microscopic vortices (MV) in classical liquids. The infinite exact chain of engaging kinetic equations of non-Markov type were obtained for the time correlation function (TCF) MV. For its closing and solving the so-called orthogonal dynamic variables of the first, second, third and higher levels are introduced. The consequent usage of this variables let the "quasi-hydrodynamic" approximation for the memory function of the third level M3(t) be used. In the case M3(t) is presented as the linear combination of memory functions of the lowest levels. The coefficients in this expansion may be described by means of the relaxation frequency and even moments TCF MV. The present theory can be compared with the molecular-dynamic (MD)-data of different authors for the transverse currents in liquid argon. It is in accordance with the experimental MD-data frequency spectrum MV the liquid argon; it gives an opportunity to determine a spectrum of vortex excitation and relaxation parameters (the lifetime and the excitation relaxation time), a spectrum of non-Markov's MV parameter and its spatial dispersion. We obtained data to prove the existence of considerably fluctuating MV in liquids. Their relaxation is characterized by considerably expressed non-Markov's kinetic properties. © 1994

A theoretical study of aerosol sampling by an idealized spherical sampler in calm air

The performance of an idealized spherical sampler operating in calm air for an inlet arbitrarily oriented relative to the gravity force is studied theoretically. Under potential flow assumption the air velocity field is obtained by using a model of a finite-size sink on a sphere. The particle motion equations are solved to find the limiting trajectory surface and to calculate the aspiration efficiency. The singular points of the motion equations as a function of settling velocity of particles and the sampler orientation angle are investigated. The connection between the pattern of typical zones of particle trajectories around the sampler and the location of the singular points is illustrated. The effects of partial sampling from zones without particles and of particle screening are discussed. The results of parametrical investigations of the dependence of the aspiration efficiency on the Stokes number and their analysis are presented. In the case of vertically upwards orientation of the sampler the proposed mathematical model gives fair agreement with experimental data from the work by Su and Vincent (Abstracts of sixth international aerosol conference, Taipei, Taiwan, 2002a, pp. 639-640). © 2003 Elsevier Ltd. All rights reserved