E. A. Tropp

Fragmentation of adenine and uracyl molecules through electron captures in collisions with ions

The time-of-flight mass spectrometry method is used to study processes occurring when 36-keV multiply charged Ar ions (Ar6+) capture electrons from adenine and uracyl molecules. Adenine and uracyl constitute one of two base pairs entering into the RNA composition. The fragmentation scheme of resulting molecular ions is derived by analyzing correlations between the detection times of all fragment ions. Fragmentation patterns for molecular ions resulting from molecule ionization by photons, electrons, protons, and multiply charged ions are compared.

The collision integral kernels of the scalar nonlinear Boltzmann equation for pseudopower potentials

Analytic expressions are obtained for the collision integral kernels of the isotropic nonlinear Boltzmann equation for pseudopower interaction potentials. It is shown that for an arbitrary power exponent, the kernels can be expressed in terms of hypergeometric functions. In some cases, the kernels can be expressed in terms of elementary functions.

Interaction of 3He2+ and Ar6+ ions with acetylene, ethylene, and ethane molecules

Time-of-flight mass spectroscopy methods are employed for studying processes occurring during capture of electrons by 3He2+ and Ar6+ multiply charged ions with energy 6z keV (z is the ion charge) from C2Hn molecules (n = 2, 4, 6) with different multiplicities of C-C bonds. Fragmentation schemes of the molecular ions formed in such processes are established from analysis of correlations of recording times for all fragment ions. The absolute values of the cross sections of capture of an electron and capture with ionization are measured, as well as the cross sections of formation of fragment ions in these processes. The absolute values of total capture cross sections for several electrons are determined.

Calculation of thermoelastic stresses near the crystallization front for melt-grown single-crystal rods with a circular cross section

Approximate expressions for the thermoelectric stress tensor components in an isotropic crystal rod of a circular cross section, applicable in the entire crystal including the region near the crystallization front, are obtained. Using the resultant approximate formulas, the stress fields in leucosapphire single crystals are calculated for model temperature fields. It is shown that exactly near the crystallization front, thermoelastic stresses reach maximal values.

Capture of an Electron by Ions in Methionine and Norleucine Molecules

The relative cross sections of processes taking place when H+ and He2+ ions with an energy of 6z keV (z is the ionic charge) capture an electron from molecules of C5H11NO2S methionine (proteogenic amino acid) and C6H13NO2 norleucine (nonproteogenic amino acid) are measured by time-of-flight mass spectrometry (a methionine molecule transforms into a norleucine molecule by substituting the CH2 group for the S heteroatom). The fragmentation pattern of resulting molecular ions is established from correlation analysis of the detection times of all fragment ions. The results are compared with experimental data for fragmentation of the same molecules ionized by electrons and photons. In these amino acids, the pattern of molecular ion fragmentation is found to depend on the type of molecule ionization. However, the detachment cross section of the COOH neutral group or residue (neutral or charged) R of a side chain of the amino acid is invariably among the largest. The relative cross sections of capture with single and double ionization of molecules are measured.

Calculation of thermal stresses in profiled single crystals taking into account the temperature dependence of thermal expansion

Approximate expressions for stress tensor components in cylindrical and ribbon crystals are obtained taking into account the temperature dependence of the thermal expansion coefficient. These expressions are used for estimating the effect of the thermal expansion nonlinearity factor on the stress level. It is shown that the stresses emerging in linear temperature fields due to this factor are comparable with critical stresses for defect formation.

Approximate expressions that describe the profiles of sessile and pendent drops for the cases of small Bond numbers and strong wetting

Variational formulations of the problems of sessile and pendent drops are given taking into account the force of gravity in the axially symmetric case. Approximate expressions that describe the surface profiles of these drops by the asymptotic method for small Bond numbers have been obtained by the linearization method in the case of strong wetting.

Onset of rotating stall in induction magnetohydrodynamic flows

The possible onset of unsteady induction magnetohydrodynamic (MHD) flows in wide channels or in channels of annular cross section is discovered on the basis of a proposed two-dimensional mathematical model. Such secondary flows have the character of rotating stall, which was previously known in high-pressure axial compressors. The existing experimental data confirm the possibility of observing this phenomenon, which can be interpreted as a new type of symmetry loss. It is shown for certain relations between the parameters that the system has a lower margin of stability against disturbances of the rotating-stall type than against steady-state disturbances. In particular, a loss of stability of a steady uniform flow can occur on the descending portion of the external characteristic of the machine.

Cylindrical MHD induction device in the “ideal pressure source” regime

The causes for the onset of a specific operating regime of MHD induction devices which arises after a loss of stability of the uniform flow are investigated. A modification of the original method of studying singularly perturbed dynamical systems in the neighborhood of a bifurcation point is used to construct the asymptotic behavior of the characteristic pressure for various limiting cases.

Separation of angular and energy relaxations of nonequilibrium electrons in a solid

We demonstrate that the collision integral of the kinetic equation for the interaction of hot electrons with phonons can be split into substantially different parts that correspond to elastic and inelastic collisions. In particular, this applies to electrons with energies of about 1 eV that propagate in semiconductors. The difference in the characteristic energy and momentum relaxation times makes it possible to separate the angular and energy relaxation processes. If the differential cross section of elastic scattering depends, not on the scattering angle, but on the directions of incident and scattered electrons (which is observed, e.g., for the interaction of an electron with piezoelectric lattice vibrations in AIIIBV compounds), the Laplacian in the equation that describes the spatial and energy distributions of electrons can be replaced by an elliptical operator; i.e., the electron diffusion turns out to be anisotropic.