Influence of the energy and velocity spread in the electron beam on the starting conditions and efficiency of a gyrotron

We study theoretically the influence of the spread of initial energies and velocities in the electron beam on the starting conditions and efficiency of a gyrotron. We compare various analytical and numerical models and the results of experimental studies of gyrotrons in which the interaction takes place at the first and second harmonics of the cyclotron frequency. The aftercavity interaction of the electron beam with the high-frequency field in the output waveguide transition is taken into account. The influence of the energy spread on the recuperation efficiency is estimated. Permissible spreads of the initial energies and electron velocities are determined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 2, pp. 121–133, February 2006.     

An unusual transformation of perfluorinated 1- and 3-phenylpropenes to polyfluorochloroindanes by the action of AlCl3

The reaction of perfluorinated 1- and 3-phenylpropenes with AlCl₃ gives polyfluorochloroindanes as the result of an intramolecular cyclization, apparently, by an electrophilic pathway.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2854–2857, December, 1989.     

Orthogonal decompositions of a space of symmetric tensors on an almost-Kählerian manifold

Kemerovo. Translated from Sibirskii Matematicheskii Zhurnal, Vol. 30, No. 3, pp. 131–139, May–June, 1989.     

Reconstruction of an acoustically sound-soft obstacle from one incident field and the far-field pattern

The problem considered is that of determining the shape of aplane acoustically sound-soft obstacle from the knowledge ofthe far-field pattern for one time-harmonic incident field.An iterative procedure is proposed based on two boundary integralsrepresenting the incident field and the far-field pattern, respectively.Numerical examples are included which show that the proceduregives accurate numerical approximations in relatively few iterations.     

Structure and molecular motion of poly(ethylene oxide) chains adsorbed on a silica-tethered poly(methyl methacrylate) by the spin label method

The spin-label method was used to study the structure and molecular motion of poly(ethylene oxide) (PEO) chains adsorbed on a silica-tethered poly(methyl methacrylate) (PMMA). Spin-labelled PEO with a narrow molecular weight distribution, having number averaged molecular weight (M _N)=6.0×10³, was adsorbed on the surface of the silica-tethered PMMA with various grafting ratios in carbon tetrachloride solution at 35?°C. ESR spectra were measured at various temperatures after the samples were completely dried. The ESR spectra are composed of two spectra arising from spin-labels attached to “train” and “tail” segments, which are strongly and weakly interacted with the silica surface, respectively. The fractional amount of the “tail” segments increases extremely with the grafting ratio of PMMA. Molecular mobility of the PEO chains estimated from the temperature dependence of the ESR spectra also decreases significantly with the grafting ratio of PMMA. Structure and molecular motion of the PMMA chains tethered on the silica were also studied using the spin-labelled PMMA. Consequently, parts of the PEO segments penetrate into the PMMA chains and is adsorbed on the silica surface (“train” segments), whereas parts of the PMMA segments protrude from the surface. The other PEO segments are entangled with the tethered PMMA chains (“tail” segments).     

Evaluating Zn2SiO4:Mn phosphor for use in medical imaging radiation detectors

2 SiO₄:Mn phosphor was evaluated for use in radiation detectors of medical imaging systems. Zn₂SiO₄:Mn was used in the form of laboratory-prepared fluorescent layers (screens) with coating weights from 18 to 150 mg/cm². The phosphor was excited to luminescence by low-energy X-raysusing X-raytube voltages ranging from 15 to 50 kVp. The number of emitted optical photons per incident X-rayquantum was thus determined for various X-rayenergies and phosphor coating weights. The optical emission spectrum was also measured and it was used to evaluate the spectral compatibility of Zn₂SiO₄:Mn with radiographic films, photocathodes and the Si photodiode. Finally, phosphor optical properties were estimated by fitting a theoretical model to experimental data. Results showed that Zn₂SiO₄:Mn is more efficient for low-energy X-rays. Its intrinsic conversion efficiency was found equal to 0.08, which is comparable to that of actually used phosphors. Zn₂SiO₄:Mn was also adequately compatible with orthochromatic films and the ES-20 photocathode, thus being appropriate for low-voltage radiography and fluoroscopy. Received: 31 July 1998/Accepted: 3 August 1998     

On the moment characteristics of distributions

We study different moment characteristics of (mostly discrete) distributions: general, central, binomial, and factorial moments, and also ordinary and factorial semi-invariants. We establish the relations that connect various kinds of “moments” of arbitrary order, and we derive recursion formulas. Translated fromMetody Matematicheskogo Modelirovaniya, pp. 34–41, 1998.