Evolution of the domain structure of thin magnetic films during ideal magnetization

Thin uniaxial ferromagnetic films with the easy-magnetization axis oriented perpendicularly to the film plane are considered. The process of ideal magnetization of films with a twisted unipolar periodic domain structure is investigated by computer simulation. It is shown that during film magnetization the degree of twistedness of domain walls decreases and the magnetic structure becomes domainless.     

Investigation of the electronic properties of Au nanoclusters in SiO<Subscript>2</Subscript> by combined scanning tunneling/atomic force microscopy

The tunneling of electrons through Au nanoc lusters formed by pulsed laser deposition in a SiO₂ thin film on a Si substrate has been investigated by combined scanning/atomic force microscopy (STM/AFM). Conducting Pt-coated Si cantilevers were used. The feedback was maintained via the AFM channel, and the current-voltage (I-V) characteristics of the tunnel contact between the AFM probe and the n ⁺-Si substrate through a =4-nm-thick SiO₂ film with Au nanoclusters =2 nm in diameter were measured simultaneously. The current image of the structure contained areas of increased current (tunnel-current channels) 2–15 nm in size, related to tunneling of electrons through Au nanoclusters in SiO₂. The I-V characteristics recorded in the tunnel-current channels exhibit specific features related to the Coulomb blockade of electron tunneling through Au nanoclusters.     

Study of resonant tunneling in Au nanoclusters on the surface of SiO2/Si thin films using the combined scanning tunneling microscopy and atomic-force microscopy technique

The morphology and electronic properties of Au nanoclusters on the surface of SiO₂ thin films on n ⁺-Si substrates are studied using the combined scanning tunneling microscopy (STM) and atomic-force microscopy (AFM) technique. The peaks associated with the resonant tunneling of electrons from the states of the valence band of the probe material to the states of the conduction band of the substrate material through Au nanoclusters are observed on the current-voltage characteristics for the contact of a p ⁺-Si AFM probe with Au nanoclusters. Experimental results are interpreted by calculating the tunnel transparency of the SiO₂/Au/SiO₂ double barrier structure in a strong electric field.     

Mixing gasdynamic laser with nonequilibrium arc excitation

A mixing gasdynamic laser with nonuniform arc excitation is investigated using a model setup. Tentative analysis of the results indicates the appropriateness of using plasmatrons to improve the efficiency of mixing gasdynamic lasers by making carbon dioxide molecules vibrationally more nonuniform. In addition, a plasmatron serves as a preionization source both for a fast-flow gas-discharge laser and for a gasdynamic laser with combined pumping.     

Acousto-optic deflector: A new method to increase the efficiency and bandwidth

A new type of acousto-optic deflector based on anisotropic diffraction in paratellurite crystal is developed. Specific features of the method and proposed device are related to the broadening of the angular scanning range at a relatively high diffraction efficiency. The method is based on the application of the properties of the Bragg diffraction at phase modulation indices of 3π. Significant broadening of the frequency band at a relatively high diffraction efficiency is observed at high phase-modulation indices. Simultaneous application of indices of π and 3π allows a decrease in the control power to practically acceptable levels that provide continuous operation.     

Determination of temperature and concentration of a vapor–gas mixture in a wake of water droplets moving through combustion products

Characteristic temperatures and concentrations of a vapor–gas mixture in a wake of water droplets moving through combustion products (initial temperature 1170 K) were determined using the Ansys Fluent mathematical modeling package. We investigated two variants of motion: motion of two droplets (with sizes from 1 mm to 3 mm), consecutive and parallel, and motion of five staggered droplets. The influence of the relative position of droplets and also of distances between them (varied from 0.01 mm to 5 mm) on temperatures and concentrations of water vapor was established. The distances determine the relation between the evaporation areas and the total volume occupied by a droplet aggregate in the gas medium. The results of modeling for conditions that take into account vaporization on the droplet surface at average constant values of evaporation rate and also with consideration of the change in the latter, depending on the droplet temperature field, are compared. We determined conditions under which the modeling results are comparable for the assumption of a constant vaporization rate and with regard to the dependence of the latter on temperature. The earlier hypothesis on formation of a buffer vapor layer (“thermal protection”) around a droplet, which decreases the thermal flow from the external gas medium, was validated.     

Micronization of levofloxacin by supercritical antisolvent precipitation

The process of micronization of levofloxacin (LF, an antibacterial agent of the fluoroquinolone group) by the supercritical antisolvent precipitation technique (SAS) was investigated. It was shown that LF particles of different sizes (from 1 to 10 μm) and of various morphologies (from thin plates to elongated parallelepipeds) can be produced depending on the type of solvent used for conducting micronization. Investigation of the micronized LF preparations using the methods of IR-Fourier spectroscopy, Raman scattering, and circular dichroism showed that the LF micronization caused neither changes in its chemical structure nor racemization. Micronization of LF significantly affects the rate of its dissolution in model systems exhibiting effects dependent on the type of the solvent used for micronization. For example, the highest rate of dissolution at pH 4 was observed for LF preparations micronized with the help of chlorohydrocarbons. It was shown that the rate of dissolution of all micronized LF preparations was higher by 15–30% in comparison with the initial LF, which likely was related to the changes in the degree of crystallinity/amorphousness, as well as of morphologies of microparticles formed in the SAS process.     

Study of the energy spectrum and mass composition of primary cosmic rays in the energy range of 10<Superscript>18</Superscript>–10<Superscript>20</Superscript> eV using a balloon setup in antarctica (SPHERE-antarctica project)

An Antarctic balloon experiment for measuring the energy spectrum and elemental composition of cosmic rays in the ultrahigh-energy range (10¹⁸–10²⁰) eV is proposed. Scientific equipment will measure fluorescence caused by an extensive air shower formed in the atmosphere by an ultrahigh energy particle and Cherenkov light of this shower reflected from a snow surface. It is assumed that the balloon will fly in the circumpolar orbit in Antarctica at a height of ~25 km for (2–3) winter (in the Southern Hemisphere)months. For this time, ~3000 events caused by particles with energies above 10¹⁸ eV and (200–300) events caused by particles with energies above 10¹⁹ eV will be detected.     

Phase equilibria in water-protein-polysaccharide systems

Summary Phase separation and thermodynamic stability of water (W) — casein (C) — neutral polysaccharide (NPS) systems have been studied. Dextrans of different molecular weights D40, D150, D500 and D2000 (10^–3 M _w =40, 150, 500, 2000), ficoll (10^–3 M _w =400) and amylopectin (10-^–6 M _w = 38) have been used as neutral polysaccharides. Phase diagrams of W-C-NPS systems, as well as their effect on the thermodynamic stability of the molecular weight and structural features of polysaccharides, low-molecular salts, pH and temperature have been considered. There has been shown the similarity of conditions under which the stability of W-C-NPS systems is disturbed, resulting in their separation, as well as conditions favorable to self-association of casein. A decrease in the pH value, an increase in the ionic strength and a rise in temperature are favorable both to self-association of casein and separation of W-C-NPS systems. Proceeding from this fact and from the results obtained earlier for W-C-acidic polysaccharide and W-albumin-D-glucan systems, a conclusion is drawn as to the common nature of the relationship between self-association of polymers and their compatibility. At constant temperature and pH, the stability limit of W-C-NPS systems is determined by the concentrations of polymers (w ₂ andw ₃) and salt (C₄). The totality of cloud points C ₄ ^* (pH) at givenw ₂ andw ₃ being considered as the stability limit. It is also shown that the relationship C ₄ ^* (pH) is an increasing function within the range of pH values from 6.5 to 11.5 and in all cases where lim C ₄ ^* (pH)=0. The sequence of values 947-1PHPH IEP C ₄ ^* is determined by the nature of the low-molecular salt (Na₂SO₄ NaCl KSCN) and the specific nature of the polysaccharides (D2000 amylopectin < D 150 < ficoll < D 40).W-C-NPS-NaCl have been found to possess a lower critical point in a system of coordinates: temperature-composition. W-C-NPS-urea (6M) systems feature, in a system of coordinates: pH-polymer concentration, two areas of separation, overlapping at sufficiently high total concentrations. This fact is indicative of the specific nature of interaction of casein macromolecules capable of association near the isoelectric point due to interaction of charge fluctuations and, in the acid region, due to interaction of non-ionized carboxyl groups. The obtained results are discussed with the stability limit being expressed in terms of second virial coefficients.With 13 figures and 2 tables