The Oberbeck–Boussinesq Approximation as a Singular Limit of the Full Navier–Stokes–Fourier System

We consider the asymptotic limit for the complete Navier–Stokes–Fourier system as both Mach and Froude numbers tend to zero. The limit is investigated in the context of weak variational solutions on an arbitrary large time interval and for the ill-prepared initial data. The convergence to the Oberbeck–Boussinesq system is shown.      

Solvent extraction of microamounts of strontium and barium into nitrobenzene by using synergistic mixture of hydrogen dicarbollylcobaltate and dicyclohexano-18-crown-6

Extraction of microamounts of strontium and barium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B^?) in the presence of dicyclohexano-18-crown-6 (DCH18C6, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, $ {\text{HL}}_{ 2}^{ + } $ , ML²⁺ and $ {\text{ML}}_{ 2}^{ 2+ } $ (M²⁺ = Sr²⁺, Ba²⁺) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined. It was found that in the mentioned medium the stability constants of the complexes BaL²⁺ and $ {\text{BaL}}_{2}^{2 + }, $ where L = DCH18C6, are somewhat higher than those of the species SrL²⁺ and $ {\text{SrL}}_{2}^{2 + } $ with the same ligand L.     

Pump Effect of a Capillary Discharge in Electrically Conductive Liquids

Among the configurations to generate plasma in electrically conductive liquids only the diaphragm and the capillary discharge schemes allow to generate plasma which is not in contact with one of the electrodes. Based on this concept, this work reports for the first time the development of an underwater plasma pump, in which the periodic electrical breakdown inside an asymmetrical (sub-)millimetre hole results in a net flow of aqueous solution through the hole without the use of any moving parts such as valves or diaphragms typically used in micropumps. Certain capillary geometries feature very stable flow rates and even allow altering flow direction by changing the power. By varying the hole’s dimensions, the range of time-independent flow rates covers more than one order of magnitude and as the discharge produces some of the strongest oxidants available, we believe that this concept might find application in fields as water decontamination and sterilization.     

On validity of a new definition of the threshold condition for injection lasers

Equations describing coupled electron and photon kinetics in the semiconductor laser can be represented by a causal diagram containing closed path — feedback loop. A recently proposed definition of the lasing threshold condition states that the so-called transmission function of this loop equals minus one. This definition has been verified for an idealized model taking into account only simple monomolecular and bimolecular recombination. A more realistic case is studied now, with terms proportional to higher order powers in carrier concentration added on the right-hand side of the electron kinetic equation. The numerical simulation also encompasses the situation where parasitic leakage currents are present and localization of optical field in the laser waveguide is not complete. The results suggest that the appearance of both the Auger recombination and electron drift across the heterostructure barriers does not interfere with the definition. Neither does incomplete radiation localization. Inclusion of the leakage currents, on the other hand, is not compatible with the approximations underlying it.This work has been supported by the Grant Agency of the Czech Republic, project No. 102/93/0642.