Degenerate thermal ignition of gaseous suspensions

Study has been made of the effect of a reduction of the heat of reaction per unit mass on the critical conditions for ignition of a gaseous suspension. Calculations are presented to show the relation between critical ignition temperature and the particle diameter and concentration.     

Molecular structures of acetylene derivatives of tin: Part III. Gas phase electron diffraction study of tetrakis(trifluoropropynyl)-tin,Sn(CC-CF3)4

A gas phase electron diffraction study of tetrakis(trifluoropropynyl)tin is reported. The model, based on T_d symmetry for the carbon—tin skeleton and C_3v symmetry for the CF₃ groups, refines to the following parameters (bond lengths, r_a, in nm; valence angles in degrees): Sn—C0.2070(7), CC 0.1215(6), C—C 0.1460(7), C—F 0.1343(2), CCF 111.3(0.2). The uncertainties (given in parentheses) represent three times the standard deviation values. The results obtained point to practically free rotation of the CF₃ groups. The presence of electronegative CF₃ causes shortening of the Sn-C bonds in Sn(CC—CF₃)₄ from Me₃SnCCH and Me₃ SnCCSnMe₃. The triple CC bond length is larger than in hexafluoro-2-butyne and nearly the same as in dimethylacetylene.     

Gas-phase electron diffraction study of tris(trimethylstannyl)amine,N(SnMe3)3

The geometrical parameters of tris(trimethylstannyl)amine have been determined by gas-phase electron diffraction. The _a structure has been refined using mean amplitude values calculated from the force fields of a number of tin derivatives.The experimental data are consistent with a planar bond configuration at the nitrogen in N(SnMe₃)₃. The final set of geometrical parameters is as follows (average bond distances, r_g , in Å, angles in degrees): SnC 2.166(5), SnN 2.038(3), CH 1.117(17). NSnC 108.5(1.5), SnCH 112.1(1.6). Mean amplitude values have been varied for those distances which give considerable contributions to scattering.The results obtained fill a gap in the knowledge of structures of Group IV element μ-nitrido derivatives. They confirm the conclusion that lowering of ligand MR_n electro-negativity weakens the tendency to deviation from planarity in the central fragment NM₃. This tendency may be considered as a manifestation of the second-order Jahn-Teller effect.     

Performance of slotted pores in particle manufacture using rotating membrane emulsification

This paper addresses the use of different slotted pores in rotating membrane emulsification technology.Pores of square and rectangular shapes were studied to understand the effect of aspect ratio (1-3.5) and their orientation on oil droplet formation.Increasing the membrane rotation speed decreased the droplet size,and the oil droplets produced were more uniform using slotted pores as compared to circular geometry.At a given rotation speed,the droplet size was mainly determined by the pore size and the fluid velocity of oil through the pore (pore fluid velocity).The ratio of droplet diameter to the equivalent diameter of the slotted pore increased with the pore fluid velocity.At a given pore fluid velocity and rotation speed,pore orientation significantly influences the droplet formation rate: horizontally disposed pores (with their longer side perpendicular to the membrane axis) generate droplets at double the rate of vertically disposed pores.This work indicates practical benefits in the use of slotted membranes over conventional methods.     

Characteristics of Radio Telescopes with Multielement Microstrip Focal Arrays

We calculate beam patterns (BPs) and power characteristics of radio telescopes in the multibeam regime with the use of different types of microstrip focal arrays. A terrace design of focal array for illumination of the asymmetric secondary mirror of the RATAN-600 radio telescope and a symmetric paraboloid dish is proposed. Ways for optimization of this type of array are considered. Characteristics of a radio telescope with a millimeter-wave planar circularly polarized focal array are calculated. Some applications of multibeam microstrip focal arrays are considered.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,Vol.48, No. 2, pp. 95–109, February 2005     

Quantum-chemical calculations and electron diffraction study of the equilibrium molecular structure of vitamin K3

The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K₃) having C _s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.     

Quantum-chemical calculations for silyl- and alkyl-pseudohalides X3YNCZ (X = H or CH3; Y = C or Si; Z = O,S, or Se) and electron diffraction study of the equilibrium molecular structure of (CH3)3SiNCSe

The equilibrium structures and force fields of the twelve simplest silyl- and alkyl-pseudo halides are calculated by means of B3LYP and MP2(full) quantum-chemical methods with the use of the aug-cc-pVTZ basis. Some regularities in their structure are established. Using these data, the equilibrium structure of the (CH₃)₃SiNCSe molecule with symmetry C _3v is described experimentally for the first time via gas electron diffraction. The following values of the main r _e parameters are determined (uncertainty 3σ is in parentheses): C=Se, 1.709(14) Å; N=C, 1.190(10) Å; N-Si, 1.767(15) Å; Si-C, 1.847(13) Å; N-Si-C, 106.4°; C-Si-C, 112.4°.     

Gas phase electron diffraction study of trimethylstannylacetylene

Trimethylstannylacetylene has been studied by gas phase electron diffraction. The bond lengths, r_a (Å), and valence angles (degrees) determined with errors represented by three times standard deviation values are as follows:

.The results are compared with the structural data on organotin compounds studied earlier. The

bond lengths are shown subject to different substituent effects.