Growth of YBa2Cu3O7 films with [100] tilt of CuO planes to the surface on SrTiO3 crystals

YBa₂Cu₃O₇ films with CuO planes tilted to the surface have been grown on SrTiO₃ crystals by pulsed laser deposition. The tilt angle was varied in the range from 0° (CuO planes are parallel to the surface) to 70°. At this tilt, the crystalline lattice of the film was rotated by rotating the substrate crystalline lattice around its axis [100], which is oriented parallel to the surface. The zero tilt of CuO planes corresponds to the orientation of the SrTiO₃ surface parallel to the (100) plane. It is established that the CuO planes of the film remain parallel to one or several (100)-type planes of the substrate at an arbitrary tilt angle. In the range of tilt angles from 0° to 41°, the film has a single-crystal structure. At tilt angles above 41°, the film is transformed into a two-domain texture and its surface roughness sharply increases.     

Calculation of Diffusion-limited Growth of Hg1−x Cdx Te Epilayers on CdTe from Te-rich Melts by Step-Cooling LPE

Calculations of layer thicknesses and composition profiles in Hg_1−xCd_xTe layers on CdTe substrates for the growth from Te-rich melts have been carried out for liquidus temperatures of 460 °C, 480 °C, and 500 °C. This has been made on the basis of the multicomponent diffusion model of SMALL and GHEZ and the solid-liquid phase relation of BRICE . It could be shown that growth velocity increases only slightly with rising liquidus temperature. On the other hand, the interdiffusion velocity of Hg and Cd in the solid increases remarkably at a higher temperature. Therefore, to get layers with a constant x-value a higher supersaturation of the melt is necessary. The x-value decreases with rising supercooling by about 0.003 K⁻¹. To demonstrate the thermodynamically and kinetically advantageous properties of CdTe as substrate material, comparative calculations for a “hypothetical” HgTe substrate have been involved.     

Temporal relaxation of plasma electrons acted upon by directcurrent electric and magnetic fields

On the basis of the time-dependent electron Boltzmann equation the temporal relaxation of the electrons in the presence of electric and magnetic fields in weakly ionized, collision dominated plasmas has been studied. The relaxation process is treated by using a strict time-dependent two-term approximation of the velocity distribution function expansion in spherical harmonics. A new technique for solving the time-dependent electron kinetic equation in this two-term approximation for arbitrary angles between the electric and magnetic fields has been developed and the main aspects of the efficient solution method are presented. Using this new approach and starting from steady-state plasmas under the action of time-independent electric fields only, the impact of superimposed DC magnetic fields on the electron relaxation is analyzed with regard to the control of a neon plasma. The investigations reveal an important effect of the magnetic field on the temporal relaxation process. In particular, it has been found that the relaxation time of the electron component with respect to the establishment of steady-state can be enlarged by some orders of magnitude when increasing the magnetic field strength     

Reversible 1,1‐Hydroboration: Boryl Insertion into a CN Bond and Competitive Elimination of HBR2 or RH

Boranes with the general formula of HBR₂ have been found to undergo a facile 1,1‐hydroboration reaction with pyrido[1,2‐a]isoindole ( A ), resulting in insertion of a BR₂ unit into a C? N bond and the formation of a variety of BN heterocycles. Investigation on the thermal reactivity of the BN heterocycles revealed that these molecules have two distinct and competitive thermal elimination pathways: HBR₂ elimination (or retro‐hydroboration) versus R? H elimination, depending on the R group on the B atom and the chelate backbone. Mechanistic aspects of these highly unusual reactions have been established from both experimental and computational evidence. Adduct formation between HBR₂ and A was found to be the key intermediate in 1,1‐hydroboration of A .     

Mass and thermal accommodation during gas-liquid condensation of water

In this Letter we report, for the first time, direct and simultaneous determinations of mass and thermal accommodation coefficients for water vapor condensation in air, based on the observation of droplet growth kinetics in an expansion cloud chamber. Our experiments exclude values below 0.85 for the thermal and below 0.4 for the mass accommodation coefficients at temperatures ranging from 250 to 290 K. Both coefficients are likely to be 1 for all studied conditions. Previously available experimental data on the mass accommodation coefficient for water span about 3 orders of magnitude. Our results provide new and firm insight to cloud microphysics and consequently to the global radiative balance.     

Degree sets ofk-trees: Smallk

Ak-tree is ak-uniform hypergraph constructed from a single edge by the successive addition of edges each containing a new vertex andk−1 vertices of an existing edge. We show that ifD is any finite set of positive integers which includes 1, thenD is the set of vertex degrees of somek-tree fork=2, 3, and 4, and that there is precisely one such set,D={1, 4, 6}, which is not the set of degrees of any 5-tree. We also show for eachk≧2 that such a setD is the set of degrees of somek-tree provided only thatD contains some elementd which satisfiesd≧k (k−1)−2 [k/2]+3.