Heat and mass transfer under laser sintering of a powder mixture

A model of heat and mass transfer during the sintering process of a two-component powder mixture under the action of laser beam irradiation was formulated and numerically investigated. The model accounts for the movement of solid particles in a shrinkage caused by the changed density of the powder mixture, as well as for convective fluxes caused by surface forces and gravity. The flow of the liquid phase of the low-melting component of the mixture was described by the generalized Darcy law. The space-inhomogeneous and non-steady distributions of the phase saturations and the temperature field were estimated to predict the dynamics of the phase change process depending on the properties of the powder mixture (porosity, penetration, and thermal properties of components), and depending on the parameters of the laser beam. The effect of surface subsidence of the powder mixture has been considered.     

Hydrodynamic Aspects of Heterogeneous Reduction and Dissolution Reactions with the Evolution of Gas Bubbles

Theoretical Foundations of Chemical Engineering - The mechanism of a heterogeneous reaction that occurs during the bubbling of gas bubbles released during the reaction has been investigated....     

Thermophysical processes in the burden zone of submerged arc furnaces

Heat exchange processes in the cooling of flue gases with a moving burden bed were experimentally studied. The reasons for the nonuniform distribution of gas temperature over the subroof space of a furnace were revealed, and some measures against it were proposed.     

Metamaterials and superdirectivity of antennas

It is shown that application of metamaterials near elementary radiators can increase antenna gain and form a multilobe pattern. Conditions for the appearance of resonances are determined.     

Effect of laser ablation on the mechanical impulse formation in capillary discharge plasma

Within studies on the creation of new types of engines for small-sized space vehicles, we have experimentally studied the effect of the laser ablation of an electrode (insulator) material on the mechanical impulse of capillary discharge plasma. It is demonstrated that laser pulses can be used to reliably initiate of lowvoltage capillary discharge at low pressures, that is, under conditions where the usual discharge initiation is complicated. The proposed combined scheme allows the weight and size characteristics of plasma thrusters operating in pulsed and pulse-train regimes to be reduced.     

Improved sample complexity estimates for statistical learningcontrol of uncertain systems

Probabilistic methods and statistical learning theory have been shown to provide approximate solutions to “difficult” control problems. Unfortunately, the number of samples required in order to guarantee stringent performance levels may be prohibitively large. This paper introduces bootstrap learning methods and the concept of stopping times to drastically reduce the bound on the number of samples required to achieve a performance level. We then apply these results to obtain more efficient algorithms which probabilistically guarantee stability and robustness levels when designing controllers for uncertain systems     

Discharge lasers pumped by generators with inductive energy storage

Generators with inductive energy storage units and semiconductor opening switches designed for laser excitation are described. Operation of the generators on a gas-discharge load is considered and possible excitation modes are discussed. A longitudinal N₂ laser, transverse discharge nonchain HF laser, and CO₂ laser are developed based on this pumping technique. Output energies of 0.6 J and 3.2 J and laser efficiencies of 5.5% and over 17% were demonstrated on H ₂-SF₆ and He-CO₂-N₂ gas mixtures, respectively. High laser parameters obtained demonstrate the considerable promise of such inductive generators for pumping different gas lasers