Morphological effects in liquid phase epitaxy (The C8H5O4K-C8H5O4Rb-H2O system)

The results of the complex study of the morphology and defect state of the crystals of the isomorphous potassium acid phthalate-rubidium acid phthalate (KAP-RbAP) series formed in aqueous solutions are presented. The crystals are characterized by heteroepitaxial porous and solid textures formed as a result of the exchange reaction between the crystals and solution. The interaction of the KAP and RbAP crystals with saturated RbAP and KAP aqueous solutions is studied both in situ and in vitro under optical and atomic force microscopes. The results obtained are used to create a theoretical model of formation of characteristic morphological textures in liquid phase epitaxy, including their formation from the aqueous solutions of the respective salts.     

Refinement of the atomic structure of specimens cut out from different growth pyramids of a K(H0.052D0.948)2 PO4 single crystal

The structures of two crystalline specimens cut out from the pyramidal and prismatic growth sectors of a K(H_0.052D_0.948)₂PO₄ single crystal have been studied by diffuse neutron scattering and precision diffuse X-ray scattering. Diffuse scattering is concentrated in the vicinity of the Bragg reflections and is practically the same in specimens cut out from different growth sectors of a single crystal. X-ray diffraction analysis using the extinction parameters provided the establishment of a higher perfection of the specimen cut out from the prismatic growth sector. The precision X-ray studies revealed different configurations of hydrogen bonds in the specimens.     

Growth of single crystals of NaH2PO4 (NaDP), NaH2PO4 · H2O (NaDP · H2O), and NaH2PO4 · 2H2O (NaDP · 2H2O) sodium dihydrogenphosphate based on the analysis of the Na2O-P2O5-H2O phase diagram

The crystallization conditions for the NaH₂PO₄, NaH₂PO₄ · H₂O, and NaH₂PO₄ · 2H₂O solid phases have been established from the analysis of the phase diagram of solubility of the ternary Na₂O-P₂O₅-H₂O system in the temperature range from 0 to 100°C. Based on these data, the methods for growing sodium dihydrogenphosphate single crystals of the above compositions are developed. The initial components for preparing mother solutions were H₃PO₄ and NaOH solutions taken in certain weight ratios. For the first time, NaDP, NaDP · H₂O, and NaDP · 2H₂O single crystals were grown on a seed by the method of temperature decrease. The habits of the NaDP and NaDP · H₂O single crystals are determined. __________ Translated from Kristallografiya, Vol. 47, No. 5, 2002, pp. 937–944. Original Russian Text Copyright ? 2002 by Soboleva, Voloshin.     

Photo- and thermochromic spiranes. 31.* Photochromic cationic spiropyrans with a pyridinium fragment in the aliphatic side chain*2

Syntheses are reported for cationic indoline spiropyrans with a quaternized pyridinium fragment in the aliphatic side chain, which display photochromic properties in solution. The major effect of introducing a quaternized pyridinium fragment into the benzopyran part of the spiropyran entails a significant decrease in the rate of thermal relaxation processes. ^*For Communication 30 see [1]. ^*2Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1513-1522, October, 2008.     

Ozone production and losses in N<Subscript>2</Subscript>/O<Subscript>2</Subscript> mixtures in an ozone generator

Nonunique ozone concentrations at the output of an ozone generator under identical external conditions of barrier discharge activation of N₂/O₂ mixtures but with different prehistories of operating practice and employed gas mixtures are investigated theoretically. An analytical approach is developed to determine the ozone yield with regard for its heterogeneous loss. Plasma-chemical and electron kinetics in the N₂/O₂-mixtures are calculated numerically. The results of numerical calculations are compared to experimental data obtained by the authors. It is noted that the heterogeneous loss of ozone is the probable reason for the observed variety of behavior of О₃ concentrations, depending on prehistory of ozone generator operation, along with the N₂ and O₂ gas flow rates and the specific active power.     

A superconducting direct-current limiter with a power of up to 8 MVA

A resistive switching superconducting fault current limiter (SFCL) for DC networks with a nominal voltage of 3.5 kV and a nominal current of 2 kA was developed, produced, and tested. The SFCL has two main units—an assembly of superconducting modules and a high-speed vacuum circuit breaker. The assembly of superconducting modules consists of nine (3 × 3) parallel–series connected modules. Each module contains four parallel-connected 2G high-temperature superconducting (HTS) tapes. The results of SFCL tests in the short-circuit emulation mode with a maximum current rise rate of 1300 A/ms are presented. The SFCL is capable of limiting the current at a level of 7 kA and break it 8 ms after the current-limiting mode begins. The average temperature of HTS tapes during the current-limiting mode increases to 210 K. After the current is interrupted, the superconductivity recovery time does not exceed 1 s.     

Gas phase activation energy for unimolecular dissociation of biomolecular ions determined by focused RAdiation for gaseous multiphoton ENergy transfer (FRAGMENT)

We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd.     

Anharmonicity of short-wavelength acoustic phonons in silicon at high temperatures

Second-order Raman spectra corresponding to transverse acoustic phonons are studied in detail for crystalline Si over the temperature range 20–620°C. The largest relative softening and anharmonicity at the boundaries of the Brillouin zone were observed for the TA(X) mode. Extrapolation of the TA(X) frequency to high temperatures suggests that the Si lattice should be dynamically unstable at temperatures on the order of a doubled melting temperature. It is found that the main contribution to the softening of the transverse acoustic phonons in silicon comes from the anharmonicity and not from the volume expansion.     

Phase separation in La-Pr manganites and its evolution in a magnetic field

The self-consistent harmonic oscillator model including the three-dimensional cranking term is extended to describe collective excitations in the random phase approximation. It is found that quadrupole collective excitations associated with wobbling motion in rotating nuclei lead to the appearance of two-or three-dimensional rotation.     

Threshold Effects of the Magnetic Influence on the Microhardness of KDP Crystals

JETP Letters - The threshold of the magnetic effect on the microhardness of potassium dihydrogen phosphate (KDP) crystals has been found. It was previously shown that the preliminary exposure of...