Technical Physics最新文献

The sizes of dust particles capable of levitating in dust traps in striations in a glow discharge in all inert gases are quantitatively determined for the same discharge parameters. A more than twofold decrease in the particle size was established upon passing from the gas with the maximum ionization potential (He) to Xe. The dependence found in the experiment is interpreted from the point of view of the conditions of particle levitation. It is shown that in gases with a low ionization potential in the balance of forces, the ion drag force exceeds the force of gravity, while the absolute values of the forces decrease with decreasing particle size. The discovered effect can be used for fine trapping of dust particles in plasma traps.

It is shown that the application of the universal Lindhard function for calculating the scattering cross section of atomic particles is, as a rule, limited to the region of scattering angles less than 20°. The results obtained for various popular interaction potentials are compared with the available experimental data. It is shown that the presence of inelastic channels in scattering leads to the appearance of additional maxima in the scattering cross section. Recommendations are given on the use of the universal Lindhard function to describe quasi-elastic scattering in the region η = εsin(θ/2) > 0.01, ε is the reduced impact energy, θ is the scattering angle. At high energies, the scattering is well described by screened Coulomb potentials, and the application of the Lindhard function provides an accuracy of 10% for calculating the scattering cross sections.

The method of mirror reflections of electrostatics for a point charge located next to a plane-layered medium consisting of a single film on a dielectric half-space is formulated. The method is generalized to the case of an arbitrary system of charges. The proposed approach is applied to mathematically similar problems of electrostatics and stationary heat conduction of plane-layered media. In particular, the problems of finding distributions of the electrostatic potential around a conducting sphere, an ellipsoid of revolution and a drop-shaped body located near the dielectric film on the dielectric half-space. It is shown how to apply the results obtained for electrostatic problems to similar problems of finding the temperature distribution of uniformly heated bodies of the same geometry located near a heat-conducting film in a heat-conducting half-space.

Impact peril for warm-blooded organisms produced by a sequence of ultra-wideband electromagnetic sub-nanosecond pulses, used in various scientific and technological applications, is assessed by calculation methods of radiophysics and classical mechanics. Threshold values of the sequence parameters whose long time excess can be perilous for human have been determined.

The paper presents the results of ice strengthening by means of ultrafme silica nanoparticles introduced to distilled water prior to its crystallization. Stable SiO₂ particles suspensions with concentrations ranging from 0.003 to 5 wt % have been prepared, and nanoparticles size distribution and zeta potential have been monitored in them. Both values remain almost constant for a week. Concentration dependences of maximal stress, Young’s modulus and inelastic deformation at and after reaching peak stress in uniaxial compression test have been studied. The highest rate of change with the particles concentration for these properties is between 0.01 and 1 wt % while beyond the above range the concentration sensitivity is much weaker. The strongest effect of silica concentration is on inelastic deformation, and the weakest effect is on Young’s modulus. Concentration sensitivity of the properties has been estimated by the power index of the best fitted power function for each of the property. Dependence of strength upon average grain size, that diminishes sixfold with growing concentration, is well approximated by power function also, but with negative power index –1/2. Additive constant in this dependence is found to be much lower than the strength of large grain pure ice and is close to zero within experiment accuracy. Hence, the strength of studied polycrystalline ice and ice composites is limited by the nucleation and subsequent propagation of Griffiths cracks with characteristic length proportional to average size of ice grain.

The possibility of fixing velocities of fluid motion in model porous medium (glass beads) by measuring the transverse relaxation time T₂ by spin echo method is shown. The magnetic field gradient arising due to the difference in the magnetic permeability of the fluid and the porous medium causes a decrease in the average time T₂, which makes it possible to fix the fluid motion in the absence of an external magnetic field gradient. The addition of magnetic nanoparticles to the fluid under study increases the dependence of T₂ on fluid velocity and increases the sensitivity in determining the permeability of porous medium by NMR-relaxometry.

A technique has been developed and, for the first time, sufficiently complete data on the radiation-induced conductivity (RIC) of polystyrene (PS) at a temperature of 79 K, close to the boiling point of liquid nitrogen (77 K). RIC has been studied under pulsed and continuous exposure to electrons with an energy of 50 keV. It is shown that the RIC of PS at a temperature of 79 K, as well as at room temperature, determined by the sum of two components: prompt and delayed. Both components at 79 K are much smaller than at 298 K. The total signal falls off by a factor of 40, while the delayed component falls off by a factor of almost 200, and the prompt component dominant in the RIC signal. The possibility of the occurrence of electrostatic discharges (ESD) in PS with decreasing temperature was studied. It has been shown that PS, which is capable of resisting the occurrence of ESD at room temperature, at 79 K passes into the category of materials in which ESD is possible.

The features of the probe technique are described and the results of measuring the parameters of plasma generated by a planar magnetron sputtering system with a pure boron target during coating deposition are presented. A feature of probe measurements was the use of heating the collecting surface of a single Langmuir probe. Heating led to a decrease in the electrical resistance of the boron film on the surface, which made it possible to carry out in situ probe measurements of the magnetron discharge plasma parameters during the entire process of boron coating.

In this work, the effect of the action of gamma quanta and neutrons on the magnetic properties of Ta/feromagnet/IrMn/Ta bilayer films with an exchange bias of the hysteresis loop is studied. The samples were fabricated by magnetron sputtering, and their structure was studied by small-angle X-ray reflectometry and X-ray diffractometry. The measurement of the magnetic hysteresis loops of the irradiated and non-irradiated samples was carried out by the methods of magneto-optical Kerr magnetometry. As a result, the effect of broadening of the magnetic hysteresis loop after irradiation was found. The maximum broadening of the hysteresis loop was observed in the NiFe/IrMn film under neutron irradiation; in this case, the loop width increased by more than 2.5 times. No noticeable change in the field of the exchange bias of the hysteresis loops was observed in the entire range of radiation exposure.