Photoionization mass-spectrometry of benzene and benzaldehyde molecules with an excimer KrF laser

A laser photoionization time-of-flight mass-spectrometer has been developed and used to investigate the photoionization and photofragmentation of benzene and benzaldehyde molecules by an excimer KrF laser radiation at the wavelength of 249 nm in the intensity range from 5·10⁴ to 5·10⁹ W/cm². It has been found that at low laser intensity ions formed by two-step photoionization are most abundant in mass spectra. By increasing laser intensity an extensive fragmentation of molecules, up to C⁺ ions, was observed. The maximum ionization yield of benzaldehyde comes to 0.1% of the number of molecules in the photoionization volume and, according to calculations, to 10% for benzene molecules, when the radiation intensity is 5·10⁹ W/cm².     

Multiple current states of two phase-coupled superconducting rings

The states of two phase-coupled superconducting rings have been investigated. Multiple current states have been revealed in the dependence of the critical current on the magnetic field. The performed calculations of the critical currents and energy states in a magnetic field have made it possible to interpret the experiment as the measurement of energy states into which the system comes with different probabilities because of the equilibrium and nonequilibrium noises upon the transition from the resistive state to the superconducting state.     

Theoretical analysis of <Superscript>6</Superscript>He + <Superscript>12</Superscript>C scattering by means of the model of microscopic optical potential

The ⁶He + ¹²C elastic scattering at E = 3.0, 38.3, and 41.6 MeV/nucleon is analyzed using the microscopic model of optical potential. According to this approach, two or three parameters are fitted that renormalize the depth of real, imaginary, and surface parts of the calculated optical potential. In this case, the ambiguity of the obtained sets of fitting parameters remains, but can be reduced by introducing an additional criterion of selection: the dependence of the volume integrals of the optical potential on the energy. The structure of the obtained optical potential, the role of the nuclear medium, the formation of the imaginary part of the optical potential, and the interconnection between the surface potential and the ⁶He breakup channels are discussed.     

Polarization dependence of Fano resonances in impurity photoconductivity of quantum wells doped with shallow donors

The spectrum of impurity photoabsorption of a heterostructure with quantum wells doped with shallow donors has been calculated in the energy range close to the optical phonon energy. It has been shown that the resonant feature of photoconductivity (Fano resonance) caused by the interaction of electrons with polar optical phonons depends strongly on radiation polarization when the resonance state energy is higher than the energy of the bottom of the second quantum-well subband. This dependence on polarization has been experimentally revealed in the impurity photoconductivity spectrum of the AlGaAs/GaAs heterostructure.     

Initial-boundary-value problems for the generalized multi-term time-fractional diffusion equation

In this paper, the initial-boundary-value problems for the generalized multi-term time-fractional diffusion equation over an open bounded domain G×(0,T), G∈Rn are considered. Based on an appropriate maximum principle that is formulated and proved in the paper, too, some a priory estimates for the solution and then its uniqueness are established. To show the existence of the solution, first a formal solution is constructed using the Fourier method of the separation of the variables. The time-dependent components of the solution are given in terms of the multinomial Mittag-Leffler function. Under certain conditions, the formal solution is shown to be a generalized solution of the initial-boundary-value problem for the generalized time-fractional multi-term diffusion equation that turns out to be a classical solution under some additional conditions. Another important consequence from the maximum principle is a continuously dependence of the solution on the problem data (initial and boundary conditions and a source function) that - together with the uniqueness and existence results - makes the problem under consideration to a well-posed problem in the Hadamard sense.     

Structure and properties of Si nanostructures on highly oriented pyrolitic graphite surface

The morphology, electronic structure, and optical properties of self-assembled silicon nanostructures grown on the surface of highly oriented pyrolitic graphite (HOPG) by molecular beam epitaxy have been studied by ultra-high-vacuum scanning tunneling microscopy and X-ray photoemission spectroscopy in situ, as well as by Raman spectroscopy ex situ. At a coverage of less than one monolayer, formation of monolayer silicon nanoislands with an atomic structure similar to that of graphene has been observed.     

Frequency characteristics of viscoelastic damper models and evaluation of a damper influence on induced oscillations of mechanical system elements

Meccanica - A generalized model of the damper is proposed in the form of the equivalent Voigt model for viscoelastic materials, which fully correlates with the differential equation for induced...