Regio- and Stereoselective Addition of Selenium Dichloride to Alkyl Propiolates

Russian Journal of Organic Chemistry - The reaction of selenium dichloride with methyl and ethyl propiolates leads to formation of anti-Markovnikov adducts. The regio- and stereoselective synthesis...     

Design and investigation of UV image detectors

The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.     

Sturm-Liouville’s problem with discontinuous nonlinearity

We establish a theorem on the existence of solutions of the Sturm-Liouville problem with nonlinearity discontinuous in the phase variable. By way of application, we consider a one-dimensional analog of the Gol’dshtik model of separated flows of an incompressible fluid.     

On one problem of electrophysics with discontinuous nonlinearity

We consider a conductor heating problem in the following setting: a constant voltage and a constant temperature are maintained on the conductor surface, and the electric conductivity of the material experiences jumps when passing through certain temperatures. Earlier-obtained results for problems with a spectral parameter for equations of elliptic type with discontinuous nonlinearities are applied to this problem of electrophysics. We weaken the conditions imposed on the set of points of discontinuity of the nonlinearity (the electric conductivity of the conductor) occurring in the equation.     

Estimates for a spectral parameter in elliptic boundary value problems with discontinuous nonlinearities

Under study are the two classes of elliptic spectral problems with homogeneous Dirichlet conditions and discontinuous nonlinearities (the parameter occurs in the nonlinearity multiplicatively). In the former case the nonlinearity is nonnegative and vanishes for the values of the phase variable not exceeding some positive number c; it has linear growth at infinity in the phase variable u and the only discontinuity at u = c. We prove that for every spectral parameter greater than the minimal eigenvalue of the differential part of the equation with the homogeneous Dirichlet condition, the corresponding boundary value problem has a nontrivial strong solution. The corresponding free boundary in this case is of zero measure. A lower estimate for the spectral parameter is established as well. In the latter case the differential part of the equation is formally selfadjoint and the nonlinearity has sublinear growth at infinity. Some upper estimate for the spectral parameter is given in this case.     

A Regioselective Synthesis of Novel Functionalized Organochalcogen Compounds by Chalcogenocyclofunctionalization Reactions Based on Chalcogen Halides and Natural Products

The regioselective synthesis of novel functionalized condensed organochalcogen compounds by chalcogenocyclofunctionalization reactions based on chalcogen halides and the natural products thymol and carvacrol has been developed. The reactions of selenium dibromide with allyl thymol and allyl carvacrol proceeded in methylene chloride at room temperature in the presence of NaHCO₃ affording bis[(7-isopropyl-4-methyl-2,3-dihydro-1-benzofuran-2-yl)methyl] and bis[(4-isopropyl-7-methyl-2,3-dihydro-1-benzofuran-2-yl)methyl] selenides in 90–92% yield. Similar sulfides were obtained in 70–72% yields by the reaction of sulfur dichloride in chloroform under reflux. Trihalotellanes containing the same organic moieties were synthesized from allyl thymol, allyl carvacrol and tellurium tetrachloride or tetrabromide in quantitative yields. Corresponding functionalized ditellurides were prepared in 91–92% yields by the reduction of the trichlorotellanes with sodium metabisulfite in two-phase solvent system. The comparison of reactivity of sulfur, selenium and tellurium halides in chalcogenocyclofunctionalization and distinguishing features of each reaction were discussed.     

An experimental investigation of the effect of oxygen on the erosion of a multichannel tungsten cathode

The problem of the preservation of electrodes and the reduction of their depletion to a minimum has decisive significance among the practical questions of maintaining the efficiency of steady sources and plasma accelerators during an extended period of operation. For this purpose electrodes are made, as a rule, out of the refractory metals in familiar designs. In particular, tungsten, which has the highest phase-transition; temperatures among all the metals, thus permitting an appreciable reduction in the evaporation rate of the material under the thermally stressed operating conditions of these devices, is attractive. However, there exist other factors besides evaporation which affect the integrity of hot tungsten electrodes and their ablation (chemical processes, erosion in microarcs, ion bombardment, and so on). One of these factors requiring special investigation is the chemical interaction of tungsten with the oxygen contained in the working medium as an industrial impurity. Such an impurity can, for example, be present in industrially pure alkali and alkali-earth metals used as the working media. In addition, these metals can be contaminated by the oxygen of the air in the process of different industrial operations, in particular, in connection with the servicing of the supply system. The entrance into the working material of oxygen liberated from the structural elements of the supply route and the operating cavities of the plasma source is not excluded. In practice it is impossible to eliminate oxygen, even when using contemporary methods of deep cleaning of lithium, due to its great affinity for oxygen. The actual role of the oxygen impurity and the necessity for taking it into account in connection with the creation and operation of plasma devices can only be revealed as a result of direct experimental investigation on samples having an electrode. geometry similar to the class of sources or accelerators in question. Results are presented in this article of an experimental investigation of the erosion of a multichannel tungsten electrode [1–4] and a coaxial source of lithium plasma [5]. The use of lithium as the main plasma-forming material ensured the maintainance of a discharge distributed over the electrodes and having a small value of the potential drop next to the cathode, which lies below the threshold of cathode erosion upon bombardment of the surface of polycrystalline tungsten by lithium ions [6]. Thus, the phenomena of cathode destruction associated with microarcs and ion bombardment could be exluded from consideration in practice. Thus evaporation and chemical ablation due to interaction with the oxygen of the working medium remain the principal, competing processes contributing to the erosion of the cathode mass. Therefore, in order to obtain reliable quantitative relationships which characterize differential erosion due to oxidation and evaporation, the oxygen content in the working medium was varied in the experiments described within limits extending beyond the framework of the usual industrial impurity, which does not exceed tenths of a percent. One should note that in the process of investigating the role of an industrial oxygen impurity in causing the erosion of a tungsten cathode in a lithium plasma its direct effect was revealed on the anomalous current of a hollow cathode, which is characterized by the recorded average densities of the discharge current exceeding significantly the values of the emission current given at the same surface temperature by the Richardson-Schottky equation [7–9].Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 67–73, May–June, 1979.The authors express their gratitude to S. S. Kellin, N. P. Mezhevov, and V. N. Belinskii for their participation in the preparation and performance of the experiment.     

Force action of a shock wave on a sphere or a cylinder in numerical and physical experiments

The results of an investigation of the unsteady and steady stages of the action of a plane shock v/ave on a sphere or a cylinder are given. The volume compression force which determines the signal amplitude of a nondirectional spherical transducer [1] and the force acting on the body in the direction of the shock wave motion are analyzed. Good agreement of the results is obtained between the numerical and physical experiments and with the data of other authors.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 134–139, November–December, 1985.The authors are grateful to B. I. Zaslavskii for the discussion of the results and to O. V. Zonovaya for the formulation and presentation of the calculated material.     

Approximate solution to a time optimal boundary control problem for the wave equation

The paper provides some examples of mutually dual unconstrained optimization problems originating from regularization problems for systems of linear equations and/or inequalities. The solution of each of these mutually dual problems can be found from the solution of the other problem by means of simple formulas. Since mutually dual problems have different dimensions, it is natural to solve the unconstrained optimization problem of the smaller dimension.