Volume 61, Nº 4 (2016)
- Ano: 2016
- Artigos: 26
- URL: https://journals.rcsi.science/1063-7842/issue/view/12319
Theoretical and Mathematical Physics
Generalization of the Bennett equilibrium condition for a relativistic electron beam propagating in the Ohmic plasma channel and ion focusing regime along an external magnetic field
Resumo
The problem of formulating the generalization of the Bennett equilibrium condition is considered for a relativistic electron beam propagating in the Ohmic plasma channel, as well as in the ion focusing regime in the presence of an external longitudinal uniform magnetic field. We assume that the electron component of the background plasma is not completely removed from the region occupied by the beam. This equilibrium condition is derived using the mass and momentum transport equations obtained for a paraxial monoenergetic beam from the Fokker–Planck kinetic equation.
Analysis of the properties of the molecular–cluster xenon mixture in the mesoscopic phase transition region
Resumo
We report on the results of calculation of the concentrations of cluster subcomponents in a molecular–cluster xenon mixture at temperatures and pressures at which the gas experiences a mesoscopic phase transition. The existence of such a transition follows from singularities of the temperature dependence of viscosity, from the behavior of the cluster thermodiffusion coefficient, and from the features of the distributions of cluster subcomponents in the centrifuge. The mesoscopic phase transition is manifested in the intermediate position of the molecular–cluster mixture between the gas and the liquid judging from its properties in the transition region.
Recurrence procedure for calculating kernels of the nonlinear collision integral of the Boltzmann equation
Resumo
A recurrence procedure for a sequential construction of kernels \(G_{{l_1},{l_2}}^l\) (c, c1, c2) appearing upon the expansion of a nonlinear collision integral of the Boltzmann equation in spherical harmonics is developed. The starting kernel for this procedure is kernel G0,00 (c, c1, c2) of the collision integral for the distribution function isotropic with respect to the velocities. Using the recurrence procedure, a set of kernels \(G_{{l_1},{l_2}}^{ + l}\) (c, c1, c2) for a gas consisting of hard spheres and Maxwellian molecules is constructed. It is shown that the resultant kernels exhibit similarity and symmetry properties and satisfy the relations following from the conservation laws.
Gases and Liquids
Stability of a velocity field tangential discontinuity in a three-layer density-stratified liquid with a moving middle layer
Resumo
A dispersion relation is analytically derived for gravitational waves in an ideal incompressible threelayer liquid with a free surface in the presence of a velocity field tangential discontinuity between the layers. The discontinuity results from the motion of the middle layer. The instability of the tangential discontinuity is shown to depend on the relative velocity of contacting layers, which, in turn, depends on the ratio of their densities. The closer the density ratio to unity, the lower the moving layer velocity causing instability. In the given case, instability involves internal waves arising at the second and third interfaces in accordance with the Kelvin–Helmholtz concept of instability development. Internal waves with wavelengths far exceeding the thickness of the middle layer are found to interact with each other. Surface waves only change their frequencies.
Plasma
Electric discharge in air in a deeply subcritical field of a quasi-optical microwave beam
Resumo
We describe the results of experiments on initiation of an electric discharge in air in a quasi-optical microwave beam by an electromagnetic vibrator fixed above the screen. This method for initiating the electrical breakdown makes it possible to obtain a discharge at a level of the electric field component in the microwave, which two orders of magnitude lower than the minimal critical field of the electrodeless breakdown of air. In our experiments, the threshold value of the air pressure determining the low- and high-temperature forms of the microwave discharge are determined depending on the field level.
Generation of wakefields in a dielectric structure filled with plasma
Resumo
The effect of plasma on the amplitude of the wakefield excited in a dielectric structure by a relativistic electron bunch train is studied. The structure under study is a dielectric cylindrical waveguide with an axial drift channel filled with plasma. The dependences of the amplitude of a longitudinal electric field on the plasma density are obtained for the following three cases: the parameters of the dielectric structure and bunches are fixed; the inside or outside radius of the dielectric tube changes according a change in the plasma frequency, and the bunch repetition frequency is adjusted to the plasma frequency and the frequency of the first radial mode of a dielectric wave. It is shown that, when the eigenwave frequencies are adjusted to the bunch repetition frequency via a change in the structure radii, the maximum of the accelerating field is determined by a plasma wave, and there is a plasma density range where a dielectric wave significantly contributes to the total field amplitude. In the case of changing the outside radius, this range is substantially wider.
Relaxation of heavy ions in collisionless shock waves in cosmic plasma
Resumo
We report on the results of hybrid particle-in-cell simulation of shock waves (SWs) in the cosmic plasma with admixture of heavy weakly charged ions. The dependence of ion relaxation and the SW structure on the angle between the magnetic field and the normal to the wavefront is analyzed. The conditions for invariability of the anisotropic ion velocity distribution behind the front of quasi-transverse SWs are indicated on scales substantially exceeding the width of the collisionless SW front (up to the Coulomb relaxation length). The obtained results are essential for determining the effectiveness of heating of heavy ions and observation diagnostic of collisionless SWs in the cosmic plasma.
Reconstruction of the energy spectrum of electrons accelerated in the April 15, 2002 solar flare based on IRIS X-ray spectrometer measurements
Resumo
We reconstruct the energy distribution of electrons accelerated in the April 15, 2002 solar flare on the basis of the data from the IRIS X-ray spectrometer onboard the CORONAS-F satellite. We obtain the solution to the integral equations describing the transformation of the spectrum of X-ray photons during the recording and reconstruction of the spectrum of accelerated electrons in the bremsstrahlung source using the random search method and the Tikhonov regularization method. In this event, we detected a singularity in the electron spectrum associated with the existence of a local minimum in the energy range 40–60 keV, which cannot be detected by a direct method.
Solid State
Spatial distortions of the orientational structure of a ferronematic in the presence of external fields
Resumo
Spatial distortions of the director field and magnetization of a ferronematic (suspension of magnetic nanoparticles in a nematic liquid crystal) that are induced by simultaneous action of electric and magnetic fields are studied with allowance for the flexoelectric polarization of the liquid-crystalline matrix. Soft coupling of liquid crystal and magnetic particles and layer boundaries is considered. The dependence of the phase lag of the transmitted light on the external magnetic field is analyzed.
Pyroelectric effect in layered magnetoelectric PZT/Ni–Zn ferrite composites
Resumo
The electric response of layered 2-2 connectivity magnetoelectric composites to the action of a modulated heat flow, which is detected by a dynamic method, is studied. The kinetics of the pyroelectric response of the composite material to a pulsed thermal action is calculated. The experimental results and calculation data suggest that a modulated heat action induces a signal due to both the pyroelectric and piezoelectric effects. The latter effect is caused by the mechanical interaction of the layers of lead zirconate titanate ceramic and nickel–zinc (Ni–Zn) ferrite.
Effect of gallium alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni–Mn–Ga alloys
Resumo
The effect of gallium alloying on the structure, the phase composition, and the properties of quasibinary Ni50Mn50–zGaz (0 ⩽ z ⩽ 25 at %) alloys is studied over a wide temperature range. The influence of the alloy composition on the type of crystal structure in high-temperature austenite and martensite and the critical martensitic transformation temperatures is analyzed. A general phase diagram of the magnetic and structural transformations in the alloys is plotted. The temperature–concentration boundaries of the B2 and L21 superstructures in the austenite field, the tetragonal L10 (2M) martensite, and the 10M and 14M martensite phases with complex multilayer crystal lattices are found. The predominant morphology of martensite is shown to be determined by the hierarchy of the packets of thin coherent lamellae of nano- and submicrocrystalline crystals with planar habit plane boundaries close to {011}B2. Martensite crystals are twinned along one of the 24 \(24\left\{ {011} \right\}{\left\langle {01\bar 1} \right\rangle _{B2}}\) “soft” twinning shear systems, which provides coherent accommodation of the martensitic transformation–induced elastic stresses.
Effect of copper on the structure–phase transformations and the properties of quasi-binary TiNi–TiCu alloys
Resumo
The effect of copper alloying up to 25 at % on the structure–phase transformations and the physicomechanical properties of ternary alloys from the quasi-binary TiNi–TiCu section is studied by measuring the physicomechanical properties, transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction (XRD). The data of temperature measurements of the electrical resistivity and the magnetic susceptibility and XRD data are used to plot a general diagram for the thermoelastic B2 ↔ B19', B2 ↔ B19 ↔ B19', and B2 ↔ B19 martensitic transformations, which occur in the alloys upon cooling as the copper content increases in the ranges 0–8, 8–15, and 15–25 at % Cu, respectively. The experimental results are compared to the well-known data, including differential scanning calorimetry data, obtained for these alloys. The changes in the mechanical properties and the microstructure of the alloys in the state of B19 or B19' martensite are discussed.
Use of dynamic speckle interferometry for contactless diagnostics of fatigue crack initiation and determining its growth rate
Resumo
Steel 09G2S specimens are subjected to cyclic tests, and real-time monitoring of the initiation of a fatigue crack and its growth kinetics is performed by dynamic speckle interferometry. The time averaging of speckles are used to reveal a relation between the parameters that characterize random and deterministic changes in the relief height and speckle images of the surface near the notch during crack initiation.
Physics of Nanostructures
Effect of thermal annealing on the structure of ZnSe/Al2O3 nanocomposite films
Resumo
The ZnSe/Al2O3 nanocomposite films synthesized by laser evaporation followed by heat treatment are studied. X-ray diffraction and electron-microscopic investigations of the as-deposited films demonstrate the presence of ZnSe crystallites in an Al2O3 amorphous matrix. Annealing changes the structures of ZnSe and Al2O3, increases the ZnSe crystallite size, and causes the appearance of the ZnSeO4 phase. The presence of aluminum oxide layers decreases the phase transformation temperature of zinc selenide.
Effect of temperature on the growth rate of tin dioxide whiskers formed by physical vapor deposition
Resumo
The effect of temperature on the vertical growth rate of functional tin dioxide nanostructures formed by physical vapor deposition from a gas phase is studied. A model is proposed to describe the formation of tin dioxide nanocrystals. This model adequately describes the experimentally detected effect of the deposition zone temperature on the nanocrystal growth rate in the temperature range under study. An analytical relation between the growth rate of a nanowhisker, its geometric parameters, the nanowhisker material, the substrate material, and the technological parameters of its formation is revealed. The crystal growth rate is found to increase with the deposition zone temperature, which can be caused by an activation character of nucleation processes and precursor mass transport along the substrate surface and the lateral nanocrystal surface.
Specific features of the laser irradiation of thin molybdenum films
Resumo
Laser irradiation of thin molybdenum films with a thickness of less than 100 nm is studied. An experimental hypothesis in accordance with which films of refractory metals can be laser-ablated owing to the formation of an intermediate oxide phase is experimentally proven. A threefold decrease in the thickness of the ablation region under the action of scanning laser radiation is interpreted.
Optics
Threshold intensity and coefficient of raman scattering amplification in a high-Q bilayer microresonator during the formation of internal and external submicron photonic jets: A photonic nanojet in the near field
Resumo
Using quantum and semiclassical approaches, the energy excitation threshold for induced Raman scattering is estimated and a relationship between the excitation threshold and the concentration of optically active molecules in a bilayer microresonator is established. Estimates are made during the formation of specially configured optical fields: internal and external photonic nanojets. Based on the amount of stored energy per mode and the value of the threshold intensity, an additional generalized selection rule for whispering gallery modes is suggested. It is shown that the bilayer microresonator can focus incident radiation (laser pumping) into a submicron focal volume at a low threshold intensity.
Spatially nonuniform distribution of magnetization in laser-irradiated ferromagentic materials
Resumo
Ferromagnetic austenite–martensite steels are laser-irradiated to obtain spatially nonuniform distribution of magnetization. An original setup that employs the Faraday effect in epitaxial ferrite-garnet films is used to visualize and measure the spatial distribution of magnetization in steels that are processed with the aid of a fiber laser at different scanning rates. It is demonstrated that rapid laser heating of samples causes modification of the microstructure from the martensite state to the austenite state that provides paramagnetic properties.
Acoustics, Acoustoelectronics
Passive broadband acoustic thermometry
Resumo
The 1D internal (core) temperature profiles for the model object (plasticine) and the human hand are reconstructed using the passive acoustothermometric broadband probing data. Thermal acoustic radiation is detected by a broadband (0.8–3.5 MHz) acoustic radiometer. The temperature distribution is reconstructed using a priori information corresponding to the experimental conditions. The temperature distribution for the heated model object is assumed to be monotonic. For the hand, we assume that the temperature distribution satisfies the heat-conduction equation taking into account the blood flow. The average error of reconstruction determined for plasticine from the results of independent temperature measurements is 0.6 K for a measuring time of 25 s. The reconstructed value of the core temperature of the hand (36°C) generally corresponds to physiological data. The obtained results make it possible to use passive broadband acoustic probing for measuring the core temperatures in medical procedures associated with heating of human organism tissues.
Experimental Instruments and Technique
Vacuum test bench for high-voltage tests of storage chambers in the electric dipole moment spectrometer
Resumo
We describe the structure of the high-voltage test bench for checking individual insulators and their assemblies with separate control of leakage currents in each insulator. The test bench is mainly intended for preparing the high-voltage block of the spectrometer for the search for the electric dipole moment (EDM) of the neutron. The main part of the bench is the high-voltage source with controllable polarity and voltages up to 200 kV with complex control over parameters. An analogous converter is used in experiment on measuring the EDM of the neutron. We report on the results of testing the new design of the storage chambers of the EDM spectrometer operating with a high voltage; we also test the maximal potentialities of the converter under nearly working conditions; its optimization and calibration are performed.
Ultracold neutron detector for the spectrometer of a neutron lifetime measuring
Resumo
The gas-discharge detector is designed for the neutron lifetime spectrometer. The detector is intended for ultracold neutron flux monitoring in measurement cycles at the specrtometer (ILL, Grenoble, France). The detector has been successively tested with a Pu–Be neutron source under laboratory conditions and as a part of the spectrometer.
Short Communications
On the mechanism of own rotation of dust particles
Resumo
We analyze the physical reason for own rotation of dust particles. We propose from analysis of literature data and our previous studies that own rotation of dust particles is due to azimuth-symmetric flow of ions to the particle surface, which is associated with a nonuniform distribution of the surface charge. This assumption is in conformity with the results of experiments in which the plasma flow is changed by introducing particles in the horizontal plane (horizontal cluster) and particles aligned along the discharge current (vertical cluster) and with the observation of the rotation threshold for the discharge current and the magnetic field. The experiments are performed with spherical particles using the coordinate tracing method. Our results make it possible to construct a model of spinning of charged dust tops for describing magnetic properties of a complex plasma.
Influence of current ripple on the tungsten cathode erosion
Resumo
The erosion of a thermionic tungsten cathode is studied. Arc burning conditions under which gas–vapor erosion causes cathode mass losses are determined. It is shown that erosion does not depend on the current ripple amplitude and is roughly equal to 2 ng/C. In experiments, the current ripple amplitude ranges from ±1% to ±50%.
Electro-optic study of PZT ferroelectric ceramics using modulation of reflected light
Resumo
Electro-optic coefficients of variations in the refractive index of PZT and PLZT ceramic materials induced by ac electric field are estimated using modulation of reflected light. The electro-optic coefficients of PLZT ceramics measured with the aid of conventional birefringence using the phase shift of transmitted radiation and the proposed method of birefringence using the modulation of reflected light are compared.
Acoustic emission upon spontaneous polarization in triglycine sulfate single crystals
Resumo
We report on the results of analysis of acoustic emission (AE) under thermal action on a triglycine sulfate (NH2CH2COOH)3 ⋅ H2SO4 crystal. The triglycine sulfate single crystals grown from solution and not subjected to mechanical treatment are heated to a temperature above the Curie point (TC = 49°C). During natural cooling of the crystal, a transition from the paraelectric to ferroelectric phase is accompanied by intense AE. In the temperature range ∼28–30°C, an anomalous drop of the mean-square voltage in the AE signal is observed against the background of monotonic accumulation of AE events.