Temperature investigation of low-frequency Raman spectra of monocrystalline malononitrile

The Raman spectroscopy method is used to investigate phase transition in crystalline malononitrile. Polarized phonon spectra of a substance are studied in three crystalline phases: T, F, and T'. It is shown that phase transitions are not accompanied by significant restructuring of the crystal lattice, which, probably, preserves monoclinic syngony.Kuzbass Polytechnical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 21–24, December, 1992.     

Laser action in some single and binary organic scintillator solutions

Experimental results are presented, which show that it is necessary to consider the absorption of pump radiation by electronically excited molecules for a proper interpretation of the operation of liquid organic lasers. The possibility of the use of binary organic scintillator solutions to obtain laser action in a rather broad spectral region is shown.     

Calorimetric study of the reactions of n-alkylphosphonic acids with metal oxide surfaces

The reaction enthalpies for the solution-phase self-assembly of n-alkylphosphonic acids on the surfaces of TiO2 and ZrO2 have been determined using isothermal titration calorimetry at 298 K. The reaction enthalpies were negative (exothermic) for methyl- and n-octylphosphonic acids and positive (endothermic) for n-octadecylphosphonic acid with both metal oxides. The enthalpy/energy analysis showed that the net enthalpy of the formation of self-assembled monolayers (SAMs) at solid-liquid interface can be presented as follows: DeltaHr=-D-(DeltaHsol+DeltaHdil)-(ES-ESAM), where D is the binding energy of the SAM molecules with the solid; DeltaHsol and DeltaHdil are the enthalpies of dissolution and dilution; ES and ESAM are the surface energies of bare solid and SAM, respectively. This equation predicted an increase (and the sign change) of the reaction enthalpy as the alkyl group in n-alkylphosphonic acid increased, which explained the experimental data. Using this equation, the binding energy (D) in the SAMs of n-octyl- and n-octadecylphosphonic acids were estimated: 55+/-5 kJ/mol (for ZrO2) and 58+/-7 kJ/mol (for TiO2).     

Thermal stability of organic monolayers chemically grafted to minerals

The thermal degradation of monolayers of alkylsilicon hydrides (RSiH(3)), alkylphosphonic acids (RP(O)(OH)(2)), and alkyldimethylchlorosilanes (R(CH(3))(2)SiCl) supported on silica, alumina, titania, zirconia, and calcium hydroxyapatite particles was investigated using thermal gravimetric analysis (TGA). The common feature in the TGA was a dramatic weight loss between approximately 200 and approximately 600 degrees C (N(2) atmosphere), which was not present for bare minerals, and, thus, was assigned to the degradation of the surface grafted organic species. The onset of weight loss and the temperature of maximal weight loss rate (T(MAX)) showed no dependence on the mineral and were determined by the nature of the chemical group directly attached to the surface. The T(MAX) values were approximately 400-450 degrees C (monolayers of RSiH(3) and RP(O)(OH)(2)) and approximately 250 degrees C (monolayers of RSi(CH(3))(2)Cl). The activation energies (E(A)) of the degradation processes were determined using TGA at multiple heating rates. Surprisingly, the substrate material did not show a significant effect on E(A). For example, all the monolayers of octadecyl groups (R=C(18)H(37)) supported on silica, alumina, titania, and zirconia showed closed E(A) values approximately 265+/-15 kJ/mol. The weight loss, IR, MS, and chemical analysis data suggested that monolayer degradation occurred through pyrolysis of the hydrocarbon moieties (R groups) via cleavage of the CC and SiC (monolayers of silanes) or CC and PC bonds (monolayers of phosphonic acids). The inorganic portion of the molecule remained attached to the surface of the mineral (presumably as silicates or phosphates).     

Numerical study of mathematical models of micromechanics with periodic impulse action

We consider the results of the numerical study of the mathematical models of two microelectromechanical systems (MEMS). The models as initial boundary value problems describe the cylindrical flexure of an elastic beam as a movable electrode under action of a repetitive intensity impulse of the electrostatic field between the movable and fixed electrodes in a microgap. In the first problem, both ends of the beamare rigidly fixed, while in the second problemwe consider a cantilever beam. The range of the parameters is found where the model has two periodic solutions with periods of impulse action one of which is stable and the other is unstable.     

Algorithm for reduced grid generation on a sphere for a global finite-difference atmospheric model

A reduced latitude-longitude grid is a modified version of a uniform spherical grid in which the number of longitudinal grid points is not fixed but depends on latitude. A method for constructing a reduced grid for a global finite-difference semi-Lagrangian atmospheric model is discussed. The key idea behind the algorithm is to generate a one-dimensional latitude grid and then to find a reduced grid that not only has a prescribed resolution structure and an admissible cell shape distortion but also minimizes a certain functional. The functional is specified as the rms interpolation error of an analytically defined function. In this way, the interpolation error, which is a major one in finite-difference semi-Lagrangian models, is taken into account. The potential of the proposed approach is demonstrated as applied to the advection equation on a sphere, which is numerically solved with various velocity fields on constructed reduced grids.     

Low energy α+<Superscript>16</Superscript>O scattering in the orthogonality condition model

The orthogonality condition model (OCM) is used to describe α+¹⁶O scattering at low energies. A double folding potential with density-dependent effective NN interactions is used as the local potential of the model. The energies and widths of α-cluster resonances and differential cross sections are calculated. The results are compared to one obtained using the standard potential approach, without the nonlocal interaction of the OCM.