Polyhedral monocarbaborane chemistry. Some C-phenylated seven, eight, nine, ten, eleven and twelve-vertex species

Some synthetic and structural systematics for monocarbaboranes, using the C-phenylated motif as the example, are investigated. The 10-vertex [6-Ph-nido-6-CB(9)H(11)](-) anion 1, from reaction of PhCHO with B(10)H(14) in KOH/H(2)O, is a useful entry synthon into C-phenyl monocarbaborane chemistry. Treatment of anion 1 with Na/thf yields the 10-vertex [1-Ph-closo-1-CB(9)H(9)](-) anion 2a, whereas treatment of anion 1 with iodine in alkaline solution yields the isomeric 10-vertex [2-Ph-closo-2-CB(9)H(9)](-) anion 2b, which isomerises quantitatively to 2a on heating under reflux in DME. Thermolysis of anion 1 yields the 9-vertex [4-Ph-closo-4-CB(8)H(8)](-) anion 5, whereas treatment of anion 1 with FeCl(3)/HCl gives neutral 9-vertex [4-Ph-arachno-4-CB(8)H(13)] 3. Compound 3 gives neutral 9-vertex [1-Ph-nido-1-CB(8)H(11)] 4 in refluxing toluene, and gives the 7-vertex [2-Ph-closo-2-CB(6)H(6)](-) anion 7 and the 8-vertex [1-Ph-closo-1-CB(7)H(7)](-) anion 6 in refluxing toluene with NEt(3). Reaction of 1 with [BH(3)(thf)] yields the 11-vertex [7-Ph-nido-7-CB(10)H(12)](-) anion 8 which can be converted to the 12-vertex [1-Ph-closo-1-CB(11)H(11)](-) anion 10 using [BH(3)(SMe(2))]; alternatively, anion 1 yields anion 10 directly on treatment with [BH(3)(NEt(3))]. Treatment of anion 8 with I(2)/KOH yields the 11-vertex [2-Ph-closo-2-CB(10)H(10)](-) anion 9. The structures of anions 1, 2a, 2b, 5, 6, 7, 8, 9 and 10 have been established by single-crystal X-ray diffraction analyses of their [NEt(4)](+) salts, and those of neutral 3 and 4 estimated by DFT calculations at the B3LYP/6-31G* level; similar calculations have also been applied to the new anionic closo species 2a, 2b, 5, 6, 7, 9 and 10. Crystals of the [NEt(4)](+) salt of the [2-Ph-closo-2-CB(6)H(6)](-) anion 7 required synchrotron X-radiation for sufficient diffraction intensity for molecular-structure elucidation. The syntheses are in principle generally applicable to give extensive derivative C-aryl and C-alkyl chemistries.     

Model of CW pumped passively Q-switched laser

An analytical model of a CW pumped passively Q-switched laser in plane wave approximation is presented. The model was based on possibility to express the analytical solution of simplified rate equations with the help of LambertW function. The LambertW function is now commonly available in most of mathematical software and became to be easy to use. The significant simplification of saturable absorber dynamics is made and its presence is described only by its initial and saturated transmission. Using this model it is possible to estimate giant pulse parameters, like pulse length and energy density, the pulse repetition rate, and the laser input-output power characteristic. The validity limits of this model were verified using numerical solution of more complicated rate equations model which included nonlinear response of the modulator. The model was compared with experimental results obtained for passively Q-switched diode pumped Nd:YAG/V:YAG microchip laser.     

Long-Range Processing Correlation and Morphological Fractality of Compatibilized Blends of PS/ HDPE/ SEBS Block Copolymer

Summary: Processing and compatibilization effects of a commercially available styrene/ ethylene-butylene/ styrene (SEBS) compatibilizer on the morphological structure, rheological and mechanical properties of blends of polystyrene (PS) and high density polyethylene (HDPE) were investigated. The rheological behaviour of the blends melt during processing was followed by measuring torque; extrusion capacity output and melts back-pressure in a twin screw extruder. The processing parameters were decreased with the HDPE content. The results show that SEBS compatibilizer can yield compatibilization by substantially reducing torque and increasing the back-pressure. However, the Hurst indices of melt processing parameters are increased with compatibilization. Near-infrared spectra had been described by the Hurst index H_NIR which is then related to HDPE content in the blends. The correlation between the blend compositions, morphological structure, mechanical and rheological properties and processing parameters was established and discussed on base of correlation with the fractal indices obtained from the SEM microphotographs of PS/HDPE/SEBS blends.     

Visible cw laser emission of GaN-diode pumped Pr:YAlO3 crystal

In the present work we report on spectroscopic properties and laser results of GaN laser diode pumped Pr:YAlO₃ crystal at room temperature. The polarization-resolved absorption and emission spectra have been recorded and the decay time of the ³ P ₀ manifold has been measured. Three samples with different Pr³⁺-ion concentrations in YAP matrix have been tested and compared. The best results were achieved for 0.6 at. % Pr³⁺-ion doping: an output power of 91 mW at 746.9-nm wavelength with a maximum slope efficiency of 45% with respect to the absorbed power.     

Hybrid computer simulations: electrical charging of dust particles in low-temperature plasma

This paper is focused on the study of the electrical charging process of micron-sized particles immersed into low-temperature argon plasma by the methods of computer modelling. The hybrid computer simulations are performed for a set of particles with the radius up to in order to determine the dependence of the electric charge on the surface of the particulate on its radius. This dependence seems to be linear. The distribution of the electric potential in the vicinity of the particulate is obtained from the fluid model. Afterwards, the non self-consistent particle simulation is performed in order to determine both the reaction rates and the electric charge on the surface of the particulate. The most important collision processes of charged particles in plasma and the appropriate dependence of the collision cross-section on the particle energy are considered (elastic scattering of electrons on neutrals, excitation of neutrals into all important energetic states, ionisation of Argon atoms by fast electrons, elastic scattering of positively charged ions etc.). The presented algorithm provides an effective way, how the key quantity in dusty plasma physics – electric charge on the surface of the particulate – can be determined.     

Computational study of impulsively generated standing slow acoustic waves in a solar coronal loop

We numerically investigated standing slow acoustic waves impulsively excited in a solar coronal loop by gas pressure and mass density perturbations in one-dimensional space. The corresponding computer model is described by the hydrodynamic equations that are solved numerically by means of the so-called flux limiters methods on uniformly structured mesh. We discuss the fundamental mode and the first harmonic mode which are generated in dependence on position of the initial perturbation in the numerical box. We show how the standing slow acoustic waves are generated in the corona, where they are trapped in space between two dense layers as in the resonator, and how their energy leaks from the corona to the dense layers. We found that this leakage increases with the decrease of the density jump at the transition region. We also studied the case when the perturbation is initiated at the transition region. We found that even in this case the standing wave is formed, but their energetics is influenced by the evaporation of the plasma from the transition region into the corona.     

Chiral analysis of biogenic DL-amino acids derivatized by urethane - protected alpha-amino acid N-carboxyanhydride using capillary zone electrophoresis and micellar electrokinetic chromatography

A new analytical method for enantioselective separation of DL-amino acids derivatized by N-fluorenylmethoxycarbonyl-L-alanyl N-carboxyanhydride (FMOC-L-Ala-NCA) using capillary electrophoresis was developed. Separation parameters, such as composition and pH of the background electrolyte, and concentration of gamma-cyclodextrin (in capillary zone electrophoresis) and sodium dodecyl sulfate (in micellar electrokinetic chromatography) were optimized. The separation method was validated and it suits well for purity analysis. Detection limit of the method was 0.2% of the minor enantiomer in the major one. The level of racemization in coupling during solid-phase peptide synthesis was studied using capillary electrophoresis with gamma-cyclodextrin as a chiral selector. The anchorage of the first (C-terminal) amino acid derivative to the solid supports bearing the hydroxylic groups is the key step of the synthesis affecting the extent of its racemization. FMOC-L-phenylalanine was chosen as the suitable model amino acid derivative making it possible to study the degree of racemization of N-fluorenylmethoxycarbonyl-L-alanine-L-phenylalanine synthesized on different polymer resins, using the different condensation agents.     

High-power Nd:YAG laser picosecond pulse delivery by a polymer-coated silver hollow-glass waveguide

An oscillator-amplifier high-power Nd:YAG laser system was used for transmission of a single 50-ps-long pulse or a train of pulses through a cyclic olefin polymer-coated silver hollow-glass waveguide. The maximum energy that was transmitted was 150 mJ for the train of pulses and 40 mJ for the single pulse, from which followed a delivered power of 100 GW/cm(2) . The characteristics that were obtained make these waveguides promising for the delivery of high-power laser pulses in medical as well as other applications.