Nonlinear dynamics of a plasma torch generated by a laser pulse of large width

Experimental data on the nonlinear dynamics of a plasma torch generated by a laser pulse of large width acting upon a graphite target are presented and discussed. The mushroom shape of the luminous region and the duration of emission observed in experiment are explained by the development of the Richtmyer-Meshkov instability at the carbon plasma-air interface and by the formation of nanoparticles in the plasma expanding into the buffer gas.     

Inside Front Cover: Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning (Adv. Mater. 6/2007)

Columnar liquid crystals (LCs) are found to spontaneously form homeotropically‐aligned films when deposited on surfaces fabricated via friction transfer of polytetrafluoroethylene. The inside cover schematically shows the film structure of a phthalocyanine derivative together with the corresponding X‐ray diffraction pattern (inset). The results, reported on p. 815 by Dmitri Ivanov and co‐workers, indicate that not only are the columns homeotropically oriented but also that they form a single monodomain of macroscopic size. These findings can have an important impact for fabrication of LC‐based organic solar cells.     

Improving the accuracy of measurements of rotation of the plane of polarization

The feasibility of improving the accuracy of measurement of the angle of rotation of the polarization plane in the application of diffraction methods is investigated. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 32–34, April, 1996.     

Angle measurement by the rolling method

A method of measuring the angle of rotation of the microscope stage of a measuring instrument or of the object being monitored by the method of rolling the measurement disk is proposed. An estimate of the main components of the measurement error is given and methods of reducing it are suggested. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 29–33, October, 1996.     

Artificial abortions in Bulgaria and their prevention

Authors go into one extremely important problem for the family, woman, natality and family planning in Bulgaria. Scarcely during the last years it can be observed a slight reduction of the frequency of induced abortions. The average age of women having an abortion is high--about 30, which shows, that induced abortion is still a method of regulation fertility in intergenetic interval. The rate of those who have induced abortion under the age of 19 in Bulgaria is 7.8 to 53.3%, in Czechoslovakia, 6.7%, in DDR--50.0%, Greece--68%, Hungary--8.9%, Sweden--15.8%. The rate of done again induced abortion is higher, that is a result of bad preventing activities during the first abortion. Similar is the tendency of growing number of unmarried women having an induced abortion, as it is in the other countries: from 16.4% in 1980 to 21.7% in 1987. Bulgaria is on the third place in Europe according to the absolute number of dead cases after abortion (maternity death, after Rumania and USSR). It can be mentioned that in Bulgaria women do not use the most modern and safest devices, medicines for interruption of pregnancy.     

Surface tension nonuniformity effect on fluid distribution in a porous body

Surface forces nonuniformity within the volume of a capillary system for a given structure has been examined in terms of its effect on a wetting fluid distribution. This approach enables the distribution for a porous body with a uniform structure to be quantified using a specific function for the pore volume size distribution. The surface forces nonuniformity effect is illustrated using a fibrous structure impregnated with molten copper.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 8(368), pp. 66–69, August, 1993.     

Explosion resistance of welded cylindrical titanium shells

Results are provided for an experimental study of the reaction to internal explosive loading of titanium alloy PT-3V welded cylindrical shells filled with air or water. It is established that shell failure develops a strong scale effect in the form of a sharp reduction in explosion resistance with an increase in dimensions. Recommendations are made for weakening the effect of the scale factor and increasing shell explosion resistance. Semi-empirical equations are obtained which are recommended for evaluating explosion deformation parameters for the shell of a cylindrical explosion protection chamber made of titanium alloy.VNIIÉF, Arzamas-16 607200. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 148–156, July–August, 1994.     

Investigation and simulation of foam aluminum obtained from secondary aluminum raw materials by mechanical doping

The structure and phase composition of the samples of foam aluminum based on the AMg6 alloy (Al-6%Mg-0.7%Mn) obtained in a high-energy planetary mill are investigated. Mechanical doping provides high dispersity and homogeneity of all structural components including particles of the foam agent TiH₂, which allows one to obtain foam aluminum with a pore size of 1–5 mm at a density of 1.20–0.80 g/cm³. Mechanical properties of foam aluminum were estimated based on the results of compression tests. Based on preliminary investigations, an imitation model of foam formation is suggested that well describes the process of foam formation.     

Method of increasing the output signal-to-noise ratio in passive multi-element antenna arrays

A method of processing complex signals in passive multi-element antenna arrays based on an analysis of the natural values of the correlation matrix of the signal is considered. By means of the method it is possible to substantially increase the output signal-to-noise ratio. An iterational process by means of which optimal estimators of both the signal and the amplitude-phase distribution may be obtained, is proposed. Theoretical estimators of the efficiency of the method are given. It is proved that, in terms of the efficiency, the approach considered in the article comes close to the technique of matched filtration. Results of statistical modeling that confirm the statistical results are presented.     

Crack propagation in ceramic composites with layered granular structure

Fracture experiments under conditions of subcritical crack extension were performed with double torsion and single-edge notched bend specimens of different alumina-based ceramic composites having layered granular structure. It is shown that it is possible to increase significantly the work-of-fracture as a result of layered granular structure organization. The pecularities of structure influence on the crack propagation kinetics were investigated, and the possibilities of acceleration and deceleration of subcritical crack growth are reported.