Comparison Theorems on Convex Hypersurfaces in Hadamard Manifolds

In a Hadamard manifold with sectional curvaturebounded from below by –k ₂ ², we give sharp upper estimates for the difference circumradius minus inradiusof a compact k ₂-convex domain, and we getalso estimates for the quotient (Total d-mean curvature)/Area of a convex domain.     

Nuclear spin polarization in silicon nanostructures with charge carrier injection

We theoretically examine injection polarization of nuclear spins in silicon nanostructures with hyperfine interaction of nuclei with excited triplet states. We predict the possibility of the appearance of self-sustaining nuclear spin polarization, initiated by an external field. We show that if the external magnetic field is varied, we observe up to a 600-fold jump in the number of spin-polarized nuclei. A similar up to 40-fold jump also appears as the charge carrier injection rate increases. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 647–653, September–October, 2006.     

Influence of the Miniband Width on the Relaxation Time of Superlattice Electrons Scattered by Impurity Ions

Based on the Boltzmann equation, the influence of the miniband width on the relaxation time of nondegenerate electrons scattered by impurity ions in the GaAs/Al _x Ga_1–x As superlattice with doped quantum wells is numerically analyzed. The wave function being the eigenfunction of the ground state of the lower miniband of the superlattice is used to calculate the scattering probability. The dispersion of the longitudinal and transverse relaxation times versus the longitudinal wave vector is investigated.     

On compact submanifolds of nonpositive external curvature in Riemannian spaces

In this paper we consider compact multidimensional surfaces of nonpositive external curvature in a Riemannian space. If the curvature of the underlying space is ≥ 1 and the curvature of the surface is ≤ 1, then in small codimension the surface is a totally geodesic submanifold that is locally isometric to the sphere. Under stricter restrictions on the curvature of the underlying space, the submanifold is globally isometric to the unit sphere. Translated fromMatematicheskie Zametki, Vol. 60, No. 1, pp. 3–10, July, 1996.     

Recrystallization and ageing of undoped and strontium-doped potassium chloride crystals after incomplete polymorphic transformation under pressure

This paper reports on the results of investigations into the room-temperature recrystallization and ageing of undoped and doped potassium chloride crystals after incomplete polymorphic transformation under high pressure. It is demonstrated that the recrystallization proceeds through several stages. The first stage involves nucleation and growth of grains with twin orientations with respect to the orientation of the initial single crystal. It is found that, after the transformation, the doped crystals undergo ageing at room temperature. This process is accompanied by the precipitation of orthorhombic strontium chloride and complex potassium strontium chloride (KSr₂Cl₅) phases. Depending on the strontium concentration in the initial crystal, particles of the precipitated phases can substantially impede the growth of recrystallized grains. The high-pressure phase is revealed under normal conditions. The diffusion coefficient of strontium in the materials after the polymorphic transformation is estimated. The kinetics and mechanisms of recrystallization and ageing in pure crystals and crystals with the same doping level after compression and treatment under high hydrostatic pressure are analyzed.     

The sorption properties of carbon nanotubes modified with tetraphenylmethylenediphosphine dioxide in nitric acid media

The distribution of microamounts of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y nitrates between aqueous solutions of HNO₃ and multiwalled carbon nanotubes noncovalently modified with tetraphenylmethylenediphosphine dioxide (L) was considered depending on the concentration of HNO₃ in the aqueous phase and L in the sorbent phase. Ln(III) ions were shown to pass to the sorbent phase in the form of solvated nitrates Ln(NO₃)₃L₃. The effectiveness of the extraction of such complexes decreases along the series of rare-earth metals as the atomic number of the element in the Periodic Table increases.     

Josephson effect in hybrid oxide heterostructures with an antiferromagnetic layer

Josephson coupling between an s- and d-wave superconductor through a 50 nm thick Ca1-xSrxCuO2 antiferromagnetic layer was observed for the hybrid Nb/Au/Ca1-xSrxCuO2/YBa2Cu3O7-delta heterostructures and investigated as a function of temperature, magnetic field, and applied millimeter-wave electromagnetic radiation. The magnetic field dependence of the supercurrent I(c)(H) exhibits anomalously rapid oscillations, which is the first experimental evidence of the theoretically predicted giant magneto-oscillations in Josephson junctions with antiferromagnetic interlayers.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-vinyl-2-pyrrolidone–3-butenoic acid copolymers as drug carriers

New water-soluble copolymers of N-vinylpyrrolidone with 3-butenoic acid were prepared by radical copolymerization initiated with azobis(isobutyronitrile) or γ-radiation. The relative activities of the monomers in copolymerization were determined. The distribution of the units in the copolymer macrochains was calculated. The composition, molecular and hydrodynamic characteristics, and acute toxicity of the copolymers were determined. The copolymers were used as carriers for rifampicin antibiotic.     

Effect of post-deformation ageing on the recrystallization of KCl-SrCl2 crystals

Room-temperature recrystallization of KCl single crystals, both pure and doped with 0.02 and 0.06 wt % Sr, deformed preliminarily at 250°C is studied. It is found that annealing of the original single crystals at 650°C results in the precipitation of the SrCl₂ phase from the solid solution. X-ray diffraction studies reveal that the deformed crystals undergo ageing at room temperature, which is accompanied by a change in the phase composition. In the first place, particles of the KSr₂Cl₅ phase are formed instead of the phase SrCl₂ observed in the original and deformed crystals. These particles, which are located at the boundaries of growing recrystallized grains (twins of the original single crystal) occupying not more than 8% of the volume, impede the motion of grain boundaries and hamper further recrystallization. Second, it is shown that post-deformation ageing occurring in the remaining 92% of the deformed crystal region that has not undergone recrystallization lends stability to the strain-hardened state of alkali halide crystals over a period of at least two years at room temperature.