Two-fluid large-eddy simulation approach for particle-laden turbulent flows

In this paper, effects of particles on the subgrid scales of turbulence are properly accounted for during the modeling of subgrid scale stresses in the large-eddy simulation (LES) of fluid phase. In doing so, we propose closed filtered kinetic equations for phase space density of the particle. The various moments of these equations give the `fluid' equations which can be considered as the LES equations for the particle phase. The influence of subgrid scales motion on the particles is included in these `fluid' equations.     

Contents

This article explains the basic issues that are facing the global community regarding the emission of carbon dioxide (CO/sub 2/) gas that is degrading our environment and, most significantly, the environment of generations to come. This article deals with the current state of a potential international agreement to curtail greenhouse gases and the subsequent underlying issues. A theory suggests that apparent reluctance to agree to an international treaty by the United States is directly tied to the process of electric utility reforms. The proposed Kyoto Treaty is explained as well as the consequences of its implementation. The current facts surrounding electric utility generation and CO/sub 2/ gas emissions are explained, as are some mitigation efforts.     

Theoretical analysis of control properties for the brushless doubly fed reluctance machine

The brushless doubly fed induction machine (BDFIM) has been extensively researched for approximately 30 years, but a related machine [the brushless doubly fed reluctance machine (BDFRM)], has not. This was mainly due to the fact that reluctance rotor designs were not capable of generating saliency ratios large enough to make the BDFRM competitive with other machines. However, recent developments in reluctance rotors, spurred on by research into synchronous reluctance machines, has resulted in high saliency ratio rotors that are economic to build. This, together with the promise of higher efficiency and simpler control compared to the BDFIM, means that further investigation of the BDFRM is warranted. A relatively limited amount of work to date has been published on the BDFRM. This paper attempts to fill this void by presenting a theoretical analysis of some of the important control properties of the ideal BDFRM.     

Performance and modeling of advanced Ti:LiNbO3 digitaloptical switches

High-performance Y-branch digital optical switches realized in Ti:LiNbO₃ are presented. Their switching response functions have been optimized in terms of switch voltage and crosstalk ratio. The optimization is based on analyzing different types of waveguide shaping and switching arrangements using coupled mode theory and computer simulations. Excellent switching characteristics are achieved with devices exploiting a specially shaped waveguide branch in a dilated switch arrangement. Demonstrated performances include switching voltage as low as 9 V with crosstalk suppression better than 45 dB and fiber-to-fiber losses as low as 4 dB. Polarization independence with crosstalk suppression better than 40 dB over a 1520- to 1570-nm wavelength range is achieved for any applied switch voltage greater than 18 V. These optimized digital optical switches have further demonstrated the capability to reshape electrical input signals at switching rates of several hundred megahertz     

Interactions of electron beams with surfaces of MgO crystals

The strong interaction of electrons with the flat surfaces of small crystals has been investigated by high resolution CTEM and STEM instruments. When cubic crystals of MgO smoke with edges 20–300 nm are oriented so that the ?001? or ?011? zone axis is parallel to the optical axis, then two kinds of external fringes are observed at (100) surfaces. One kind is parallel to the surface, having spacings up to 0.4 nm. These are caused by interference among the electron channelled along the surface. Fresnel-diffracted ones and the remnant of the incident beam. Fringes of the other kind, which appear as fine structure in the first kind of fringes, are perpendicular to the crystal edge. When an electron beam is parallel to the ?011? axis, the second kind of fringe, whose spacing is 0.3 nm corresponding to d₀₁₁, shows the difference of the surface potential between magnesium atoms and oxygen atoms. Selected area diffraction patterns and microdiffraction patterns also show the same periodicities as in the two kinds of fringes. Simulated images, using the scattering amplitudes for ions, are compared with observations.     

Comparison of Solutions of the Problems of Elasticity Theory for Different Near-Boundary Elements

We consider three types of near-boundary elements: curvilinear quadrangles and families of arcs and points, and their application to a two-dimensional problem of the static theory of elasticity with boundary conditions in displacements. The comparison of the theoretical and numerical aspects of the obtained solutions is performed. It is shown that the accuracy of evaluation of the components of the vector of displacements increases in the following cases: in the case of complete quantization of the near-boundary region (but not in the case of its partial quantization or quantization with overlapping), in the case where the numbers of arcs and points increase, and in the case of simultaneous application of different types of near-boundary elements (specifically, quadrangles and families of arcs).