Investigation of the structure and properties of modified Armenian minerals for polymer-based composites

The results of investigation of the modification of the Armenian minerals with fluorine-containing oligomers show that a modified product appears when the mineral fillers are treated with fluoroalkanes. The product preserves the structure of the fillers with a “grafted” fluoroalkane layer in which chlorine atoms locate mainly over their periphery. The composite materials based on heterochained polymers and the modified fillers possess a stronger wear resistance and a low friction coefficient.     

Galvanomagnetic properties of 3C-SiC epilayers grown on hexagonal SiC substrates

Epitaxial 3C-SiC films have been grown on 6H-SiC substrates by sublimation epitaxy in vacuum. The Hall effect in these heterostructures and their magnetoresistance have been measured in a temperature range from 1.4 to 300 K. At liquid-helium temperatures, the samples are characterized by low resistance and exhibit negative magnetoresistance in weak fields (～1 T). Analysis of the experimental results suggests that the low resistance of samples is most probably due to the metal-insulator transition in the epitaxial 3C-SiC films.     

Experiments on the synthesis of neutron-deficient isotopes of kurchatovium in reactions with accelerated50Ti ions

Conclusions A number of conclusions can be drawn from the aggregate of experimental results.The method of synthesis of transfermium elements in the irradiation of lead isotopes with ions with mass A_I40 atomic units, investigated earlier [12] for the example of the reaction Pb(⁴⁰Ar, xn)Fm, is also extremely effective using⁵⁰Ti ions. The reactions Pb(⁴⁰Ar, 2n)Fm and Pb(⁵⁰Ti, 2n)Ku have approximately equal cross sections, which might have been expected on the basis of theoretical estimates. This permits us to hope that this method can be used successfully for the synthesis of heavier elements in the reactions induced by⁵⁴Cr,⁵⁵Mn, and⁵⁸Fe ions.In all probability, the substantial changes in the systematics of the half-lives for even-even isotopes of kurchatovium are associated with the structure of the barriers to fission of these nuclei. From this standpoint, it seems important to investigate the properties of more neutron-deficient isotopes of kurchatovium, using, in particular, the reactions with²⁰⁴Pb, and to attempt to advance into the region of elements with Z 106. On the other hand, a detailed theoretical analysis must be made of the data obtained on the basis of the modern theory of nuclear fission, which, in our opinion, will aid in a more reliable prediction of the properties of heavy and ultraheavy elements.Translated from Atomnaya Énergiya, Vol. 38, No. 6, pp. 382–390, June, 1975.     

Quantum supercurrent and Andreev reflection in silicon nanostructures

The tunneling spectroscopy is used for studying the hole transport in a sandwich nanostructure of the superconductor-ultra-narrow-self-assembled-p-silicon-quantum-well (Si-QW)-superconductor type on the n-Si (100) surface; the quantum well’s width is less than the coherence length and the Fermi wave-length. The high-resolution tunneling I–V characteristics display the supercurrent quantization, the characteristics of which depend on the positions of the dimensional-quantization levels for holes in the Si-QW. The correlation in the tunneling of single holes and Cooper pairs manifests itself in identical oscillations of the I–V characteristics for the supercurrent at T < T _c and the conductivity at T > T _c . In addition to the Josephson effect, the forward and reverse I–V characteristics for the first time reveal the processes of multiple Andreev reflection of two-dimensional holes in the Si-QW, which cause the microscopic mechanism responsible for the superconducting proximity effect. The investigation of the two-dimensional hole’s conductivity in the Si-QW plane indicates the presence of coherent tunneling under conditions of the spin-dependent multiple Andreev reflection between the superconducting δ] barriers confining it.     

Investigation of vacancy-type complexes in GaN and AlN using positron annihilation

The momentum distribution of electron-positron pairs in GaN and AlN has been investigated for the first time by measuring the one-dimensional angular correlation of the annihilation radiation (1D-ACAR). The characteristic parameter of the electron density r _s ^′ (the radius of the sphere occupied by an electron) estimated from the experimental data differs noticeably from r _s calculated in terms of a standard model of noninteracting particles: r _s ^′ (AlN)≈1.28r _s, and r _s ^′ (GaN)≈1.66r _s, where r _s(AlN)≈1.6091 au, and r _s(GaN)≈1.6568 au. The chemical nature of atoms in the environment of the annihilating positron in AlN and GaN was identified from the electron-positron ionic radius of Al³⁺, Ga³⁺, and N⁵⁺ cores, which were determined from the characteristics of the high-momentum component of 1D-ACAR curves. The analysis was based on a comparison of the electron-positron ionic radii with those considered standard for Al and Ga metals and the related compounds GaP, GaAs, and GaSb. A conclusion is made that positron annihilation dominates in the regions of vacancy-type “nitrogen antisite”-“vacancy” complexes, [N _Ga ⁺ V _Ga] and [N _Al ⁺ V _Al], in GaN and AlN, respectively.     

An Automatic Field Optical Meteorological Station Automatic

An optoelectronic measuring complex is used for prompt measurements of the atmospheric transparency to wavelengths of 0.35–1.03 m and the meteorological optical range of 0.1–300 km under various weather conditions with a relative error of no more than 15%.     

A radiation generator based on the induced transition effect

The possibility of generating electromagnetic radiation using a beam of free electrons in an empty resonator with ideally conducting walls is examined. It is shown that a regime can exist in which the number of photons in the resonator exhibits exponential growth, provided that the electron bunch length is sufficiently large.