A New Radar-Signal Parameter for Recognition of Wind-Related Weather Hazards

Radiophysics and Quantum Electronics - Wind-related weather hazards remain difficult to recognize targets for weather radars. Methods that use estimates of the width of the reflected-signal...     

On the thermophoresis of a spheroidal solid aerosol particle

The steady motion of a spheroidal aerosol particle with inner nonuniformly distributed heat sources (sinks) that is placed in an external temperature gradient is theoretically studied in the Stokes approximation. The mean temperature of the particle surface is assumed to differ slightly from that of the gaseous environment. An analytic expression for the force and rate of thermophoresis are found by solving the gas-dynamic equations in view of the motion of the environment.     

Molecular Packing in the Crystal Structures of the Mixed-Ligand Complexes [CdPhen{(i-C4H9)2PS2}2] and [Cd(2,2′-Bipy){(i-C4H9)2PS2}2]

Single crystals of the mixed-ligand complex compounds of Cd(i-Bu₂PS₂)₂ with Phen and 2,2-Bipy have been obtained. The crystal structures of the complexes [CdPhen{(i-C₄H₉)₂PS₂}₂] (I) and [Cd(2,2-Bipy){(i-C₄H₉)₂PS₂}₂] (II) were determined by X-ray diffraction (CAD-4 diffractometer, MoK radiation, 1739 F _{F hkl} , R = 0.0417 for I and 2612 F _hkl , R = 0.0442 for II). Monoclinic crystals with unit cell parameters a = 15.640(3), b = 20.797(4), c = 11.559(2) , = 111.21(3)°, V = 3505(1) ³, Z = 4, d _calc = 1.348 g/cm³, space group (I); a = 14.737(3), b = 20.918(4), c = 11.517(2) , = 105.53(3)°, V = 3421(1) ³, Z = 4, d _calc = 1.334 g/cm³, space group (II). The structures consist of discrete monomer molecules. The coordination polyhedra of the Cd atoms are distorted octahedra formed by four S atoms of two cyclic bidentate ligands i-Bu₂ and two N atoms of the cyclic bidentate ligands — Phen or 2, -Bipy molecules. The interaction between molecules I and II in the structures and the packing modes are considered.     

Molecular Packing in the Crystal Structures of Mixed-Ligand Complexes [ZnPhen{(i-C4H9)2PS2}2] and [Zn(2,2′-Bipy){(i-C4H9)2PS2}2]

Volatile mixed-ligand complexes of Zn(i-Bu₂PS₂)₂ with Phen and 2,2-Bipy have been synthesized. The crystal structures of the complexes ZnPhen{(i-C₄H₉)₂PS₂}₂ and Zn(2,2-Bipy){(i-C₄H₉)₂PS₂}₂ were determined by single crystal X-ray diffractometry (CAD-4 diffractometer, MoK radiation, 2100 F_hkl, R = 0.0423 for the first complex and 2003 F_hkl, R = 0.0486 for the second). The crystals are monoclinic with cell dimensions a = 17.580(4), b = 9.969(2), c = 19.175(4) , = 90.33(3)°, V = 3360(1) ³, Z = 4, d _calc = 1.313 g/cm³, space group P2/n (for the Phen complex); a = 24.219(5), b = 11.386(2), c = 24.916(5) , = 97.70(3)°, V = 6809(2) ³, Z = 8, d _calc = 1.249 g/cm³, space group C2/c (for the 2,2-Bipy complex). The complexes are constructed from discrete monomer molecules. The coordination polyhedra of the Zn atoms are distorted tetrahedra formed by two S atoms of the two monodentate i-Bu₂PS ₂ ^- ligands and two N atoms of the cyclic bidentate Phen or 2,2-Bipy molecules. Intermolecular interactions and packings in the structures are analyzed.     

Contact Interactions between Individual Fibers of Cellulose and Its Derivatives: Mechanism of Cationic Surfactant Action

The effect of cationic surfactants (cetyltrimethylammonium bromide and tetrabutylammonium iodide) and cationic polyelectrolyte polyethylenimine on the coefficient of friction and adhesion force p(during shear and tensile testing, respectively) at the point contacts between the individual fibers of cellulose, viscose, and cellulose acetate was studied. The comparison of these data with the results of -potential and adsorption measurements enabled us to relate the nonmonotonic dependence of parameters and pon the surfactant concentration to the changes in electrosurface properties and the hydrophilicity or hydrophobicity of the fibers. The specific free energy of interaction U[mJ/m²] was estimated for cellulose acetate fibers.     

Chlorination features of 1,5-dinitro-3-azabicyclo[3.3.1]non-6-enes

The electrophilic chlorine addition to 3-substituted 1,5-dinitro-3-azabicyclo[3.3.1]-non-6-enes in the tetrachloromethane is accompanied at an intramolecular 3,7-cyclization giving 6-chloro-3-R-1,5-dinitro-3-azoniatricyclo[3.3.1.03,7]nonane chlorides. The reaction of the tricyclic quaternary ammonium salts with sodium methoxide leads to the formation of dealkylated and dehydrohalogenated products, 3-substituted 8-chloro-1,5-dinitro-3-azabicyclo[3.3.1]non-6-enes, bicyclic products with a halogen atom in an allyl position with respect to the double bond.     

Calculation of carbon-carbon bond deformation curves for fluorinated ethylenes and the corresponding carbocations

Carbon-carbon bond deformation curves for fluorinated ethylene molecules and the corresponding carbocations were calculated by the ab initio self-consistent field method in the 5-31G basis set. The maximum force required for bond cleavage was taken as a criterion for bond strength. It has been found that for ethylene, replacement of hydrogen by fluorine insignificantly strengthens the C=C bonds in symmetric molecules. However, in molecules with an asymmetric arrangement of fluorine atoms, the bond is slightly weakened due to different charges on the carbon atoms. The configuration of the corresponding carbocations also depends on the bond polarity: an assymmetric distribution of electron density in the C=C bond region leads to the formation of σ-complexes, while a symmetric distribution of electron density (pure covalent bonding) gives π-complexes. Since the carbon-carbon bond in the σ-complexes is essentially weaker, one should expect significant weakening of the bond in high-acidity media if the bond exhibits any kind of asymmetry (chain branching, defects, etc.). For the considered molecules, an antibatic correlation has been established between the strength criterion F_max (unlike the dissociation energy) and the bond length. Institute of Physical Chemistry, Russian Academy of Sciences, Moscow. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 1, pp. 34–41, January–February, 1995. Translated by I. Izvekova     

Compression of underdetermined data in a 7-piece chess table

Block compression algorithms used for solving the problem of 7-piece chess endings are presented. The algorithms are based on data reordering before compression, the RE-PAIR compression algorithm, and use of the so-called underdetermined value method.     

Finely striped structure at the edges of localized deformation bands

Under conditions of high-rate loading, plastic strain localization is a result of tension in the zone of interference of unloading waves rather than of thermal softening. At stresses close to the dynamic strength of the material, the microstructure of localized strain bands consists of strongly deformed material, with a large number of incipient microdiscontinuities. At stresses below the Hugoniot elastic limit, the microstructure looks as a set of barely visible stripes. The finely striped structure at the edges of the bands of a spall damage arises as a result of the stretching of initially rounded damage centers attached to the matrix material during dynamic deformation.