The transfer of momentum across surfaces drawn perpendicular to the direction of flow in gases under laminar conditions

Zusammenfassung Bei laminarer Strömung eines Gases ist die Übertragung der Bewegungsgrösse quer zu Flächen senkrecht zur Strömungsrichtung berechnet und gleich der transversalen Bewegungsgrösse quer zu Flächen, die parallel zur Strömungsrichtung laufen, gefunden worden. Daraus kann der Schluss gezogen werden, dass ein Flüssigkeitswürfel mit Seiten, die parallel zu den angegebenen Richtungen sind, statisch im Dreh-Gleichgewicht ist.     

Measurement of the thermoelectric power of lead sulphide

The thermoelectric power of natural specimens of lead sulphide crystals has been measured between room temperature and 700° K. Specimens which are of then-type remain as such throughout the temperature range. Thep-type specimens, however, show an initial small rise followed by a gradual decrease and a subsequent change of sign ata temperature which, in some specimens, is well defined. Further increase of temperature results in a negative extremum. From this stage onwards there seems to develop a common behaviour for both types of specimens. Some crystals which were initially of thep-type changed over to then-type and remained as such throughout subsequent investigation. Among the crystals one showed a metallic conduction and an extraordinary large thermoelectric power.     

Inhibition and anti-inhibition effects of electron scavengers in hydrocarbons revisited

Positronium formation experiments inn-hexane were performed with C₂H₅Br and CCl₄ as inhibitors and others (decalin, tetralin, benzene, naphthalene, phenanthrene) as anti-inhibitors. Although the results can be interpreted in terms of the anti-recombination and anti-inhibition, it is necessary to consider further some new aspects of intra-spur reactions such as shallow tapping of e⁺ and secondary reactions of Ps. The data thus interpreted correlate excellently with the data of radiation chemistry.     

Structural, optical and dielectric properties of glass-nanocomposite

Transparent glass-nanocomposite sample [50Li₂B₄O₇-50(SrO-Bi₂O₃-Nb₂O₅)] (mol %) was prepared by a conventional melt-quenching technique. Fluorite (Bi₃NbO₇) and SrBi₂Nb₂O₉ (SBN) was produced by heat-treating the as-prepared sample at 773 K for 6 h (HT773). The nanocrystallites of fluorite and SBN phases in the Li₂B₄O₇ glass matrix were established by differential thermal analysis (DTA) which is confirmed by X-ray powder diffraction (XRD), infrared spectroscopy and transmission electron microscopic (TEM) studies. The influence of heat-treating the as-prepared sample on the optical properties (transmission, optical band gap and Urbach energy) has been investigated. Properties such as dielectric constant and dielectric loss as a function of frequency (120 Hz -100 k Hz) and temperature (300-829 K) are reported.     

Solvent free synthesis of 1,3-diaryl-2-propenones catalyzed by commercial acid-clays under ultrasound irradiation

This paper presents a novel solvent free method of synthesis of trans-chalcones. The method was based on ultrasound irradiation of the reagents (aryl methyl ketones and aryl aldehydes) in presence of commercial acid-montmorillonites as catalysts. The trans-chalcones were synthesized in high yields (85–95%) and excellent selectivity in a short reaction time.     

A novel femtosecond-laser formation of CdS nanocrystallites in zirconia matrices

A novel method for direct laser writing of two-dimensional cadmium sulfide (CdS) semiconductor nanoparticle microstructures is reported. A two photon or a higher-order multiphoton absorption process, originating from femtosecond laser pulses, was used to decompose CdS precursors dispersed in a zirconia thin film previously dip-coated on a glass substrate. The kinetics of nanoparticle formation as a function of laser power were monitored in situ by photoluminescence spectroscopy. Raman spectroscopy was also performed to characterize the structural changes of the zirconia matrix under irradiation and to verify the formation of CdS nanoparticles. Results show that CdS nanoparticles were formed by two-photon absorption (TPA) with or without the help of an additional carbazole photoinitiator.     

Low temperature,atmospheric pressure,direct current microplasma jet operated in air,nitrogen and oxygen

Micro-plasma jets in atmospheric pressure molecular gases (nitrogen, oxygen, air) were generated by blowing these gases through direct current microhollow cathode discharges (MHCDs). The tapered discharge channel, drilled through two 100 to 200 μm thick molybdenum electrodes separated by a 200 μm thick alumina layer, is 150 to 450 μm in diameter in the cathode and has an opening of 100 to 300 μm in diameter in the anode. Sustaining voltages are 400 to 600 V, the maximum current is 25 mA. The gas temperature of the microplasma inside the microhollow cathode varies between ~2000 K and ~1000 K depending on current, gas, and flow rate. Outside the discharge channel the temperature in the jet can be reduced by manipulating the discharge current and the gas flow to achieve values close to room temperature. This cold microplasma jet can be used for surface treatment of heat sensitive substances, and for sterilization of contaminated areas.     

The numerical index of the space

We give a partial answer to the problem of computing the numerical index of for .

     

Solution and solid state studies on the binding of isomeric carboranes C2B10H12 by p-Bu(t)-calix[5]arene

p-Bu(t)-calix[5]arene forms crystalline inclusion complexes with o- and m-carboranes in toluene or dichloromethane-hexane, but not with the p-isomer, the extended structures being based on 1 : 1 host-guest supermolecules, with the p-Bu(t)-substituents creating a snug fit for o- and m-carborane; p-carborane forms a highly hexane soluble complex, induced by grinding, which crystallizes as fibres. Solution phase studies showed the presence of a 1 : 1 host-guest stoichiometry with all three isomeric carboranes as determined from Job plots. The association constants for the o- and m-carborane complexes are 6.4 +/- 0.3 M(-1) and 3.8 +/- 0.1 M(-1) respectively, whereas the p-isomer is only weakly associated. Competition experiments involving all three isomers show rapid exchange on the NMR time scale, and no selectivity in solution is evident. Selective association involving the o- and m-isomers in the solid state is therefore remarkable, and it is a manifestation of crystal packing forces which embodies the differences in dipole moments of the carboranes.