Showing papers in "Technical Physics in 2017"

NMR studies of the sedimentation of ferromagnetic nanoparticles in a magnetic fluid

Abstract: A method has been proposed for studying the sedimentation of ferromagnetic nanoparticles in a magnetic fluid from the rate of decrease in its magnetization measured by the NMR technique. The dependence of the rate of variations in the magnetization of the magnetic fluid over time on the concentration of the stabilizer is investigated. A colloidal aqueous solution of magnetite nanoparticles with varying concentrations of the sodium oleate stabilizer was used as the magnetic fluid. It has been found that the ratio of the mass concentrations of the stabilizer and magnetite in a stable magnetic fluid must satisfy the condition C ≥ 0.7, which corresponds to the formation of a double layer of stabilizer on the surface of magnetite nanoparticles.

Phenomenon of statistical instability of the third type systems—complexity

Abstract: The problem of the existence and special properties of third type systems has been formulated within the new chaos–self-organization theory. In fact, a global problem of the possibility of the existence of steady-state regimes for homeostatic systems has been considered. These systems include not only medical and biological systems, but also the dynamics of meteorological parameters, as well as the ambient parameters of the environment in which humans are located. The new approach has been used to give a new definition for homeostatic systems (complexity).

Plastic flow instability: Chernov–Lüders bands and the Portevin—Le Chatelier effect

Abstract: We have studied the regularities in the evolution of macroscopic nonuniformities in the plastic flow of metals in the form of the Chernov–Luders bands and the Portevin—Le Chatelier effect. The regularities in the evolution of strain inhomogeneity in these two cases have been established, and the kinetics of motion of the Chernov–Luders fronts and abrupt deformation in the Portevin–Le Chatelier effect has been analyzed. It has been shown that the Chernov–Luders fronts and Portevin–Le Chatelier jumpwise straining can be treated as macroscopic autowave processes of switching and excitation, respectively, in deformed media of various origins.

Plasma-chemical reactor based on a low-pressure pulsed arc discharge for synthesis of nanopowders

Abstract: A reactor for producing nanopowders in the plasma of a low-pressure arc discharge has been developed. As a plasma source, a pulsed cold-cathode arc evaporator has been applied. The design and operating principle of the reactor have been described. Experimental data on how the movement of a gaseous mixture in the reactor influences the properties of nanopowders have been presented.

Simulation of synaptic coupling of neuron-like generators via a memristive device

Abstract: A physical model of synaptically coupled neuron-like generators interacting via a memristive device has been presented. The model simulates the synaptic transmission of pulsed signals between brain neurons. The action on the receiving generator has been performed via a memristive device that demonstrates adaptive behavior. It has been established that the proposed coupling channel provides the forced synchronization with the parameters depending on the memristive device sensitivity. Synchronization modes 1: 1 and 2: 1 have been experimentally observed.

On electric-pulse well drilling and breaking of solids

Abstract: Research work has been carried out to determine the power-efficient regime of operation of an electric-pulse setup for breaking and crushing natural stones. The optimal energy and geometrical parameters of the method (dependence of the degree of breakdown of materials on the voltage and the electrode spacing in the switching unit) have been established. The proposed method makes it possible to effectively perform drilling in vertical wells for installing heat exchangers of thermal pumps.

Effect of the discharge parameters on the generation of deuterium ions in the plasma of a high-current pulsed vacuum arc with a composite zirconium deuteride cathode

Abstract: We have studied the mass and charge composition of an ion beam extracted from the plasma of a vacuum arc with a zirconium deuteride cathode for various durations of the arc current pulse (half width at half amplitude) of 2, 4, 7, and 17 μs It has been established that the fraction of deuterium ions in the vacuum arc plasma increases with the current and the dependence achieve saturation for current of about 1 kA For the fraction of deuterium atoms in the cathode at a level of 40%, the fraction of deuterium ions in the vacuum arc plasma can exceed 80% The experimental results have been interpreted theoretically It has been shown that the main sources of deuterium ions in a microsecond arc discharge are cathode spots We have developed a model of deuterium desorption during the operation of cathode spots for quantitatively estimating the concentration of deuterium ions in the arc plasma

Variation of elastic characteristics of metastable austenite steel under cycling straining

Abstract: We have analyzed the effect of elastoplastic cyclic straining on anisotropy of elastic properties of 08Kh18N10T metastable austenite steel. The possibility of determining the strain amplitude of the fatigue loading cycle by an acoustic method involving measuring the elastic characteristic of the material has been demonstrated. The resulting experimental dependences that can be used to estimate the number of cycles before failure using ultrasonic measurements have been revealed.

Effect of high-temperature thermomechanical treatment in the austenite region on microstructure and mechanical properties of low-activated 12% chromium ferritic-martensitic steel EK-181

Abstract: The effect of high-temperature thermomechanical treatment with deformation in the austenite region on the microstructure and mechanical properties in low-activated 12% chromium ferritic-martensitic steel EK-181 (Fe–12Cr–2W–V–Ta–B) has been investigated. This treatment leads to a significant increase (compared to traditional regime of treatment) in the density of dislocations, dispersity, and volume fraction of nanosized particles V(C,N) and, as a consequence, to an increase in the yield strength while maintaining a sufficient reserve of ductility.

Mechanical properties of polymeric composites with carbon dioxide particles

Abstract: Nanocomposites consisting of a polymethylmethacrylate or polystyrene matrix with embedded silicon dioxide nanoparticles surface-modified by silazanes have been prepared by melting technology. The influence of particles on viscoelastic properties of the nanocomposites has been studied using dynamic mechanical analysis. It has been revealed that the addition of 20 wt % of SiO2 raises the flexural modulus of the nanocomposites by 30%.

Parameters of the beam plasma formed by a forevacuum plasma source of a ribbon beam in zero-field transportation system

Abstract: We have studied the generation of the beam plasma formed by a forevacuum plasma source of a ribbon electron beam in the conditions of its transportation without an accompanying magnetic field. The ignition conditions in the beam transportation region of the beam–plasma discharge producing a plasma formation of the plasma sheet type with a plasma concentration of ~1016 m–3 and an electron temperature of 1–2.5 eV have been determined. The attained values of parameters and the sizes of the plasma formation make it possible to use it in technologies of the surface modification of planar extended articles.

Physical operating principles of scandate cathodes for microwave devices

Abstract: The electronic structure of barium oxide crystallites determining the emission properties of both dispenser and scandate cathodes has been studied using electron spectroscopy for chemical analysis, electron energy loss spectroscopy, and optical spectroscopy. It has been established that the other elements (calcium, aluminum, scandium, and tungsten) contained in cathode materials are diluted in barium oxide and significantly affect its electronic structure and, consequently, emission properties. The obtained results give an idea about the physical and physicochemical mechanisms of the effect of scandium on the reduction of the work function of scandate cathodes relative to that of the cathodes of other types.

SiC-Based Composite Materials Obtained by Siliconizing Carbon Matrices

Abstract: We have developed a method for fabrication of parts of complicated configuration from composite materials based on SiC ceramics, which employs the interaction of silicon melt with the carbon matrix having a certain composition and porosity. For elevating the operating temperatures of ceramic components, we have developed a method for depositing protective silicon-carbide coatings that is based on the interaction of the silicon melt and vapor with carbon obtained during thermal splitting of hydrocarbon molecules. The new structural ceramics are characterized by higher operating temperatures; chemical stability; mechanical strength; thermal shock, wear and radiation resistance; and parameters stability.

Coupled Soliton States and Localization of Cnoidal Waves at the Interface of Nonlinear and Linear Media

Abstract: Contact effects at the interface of linear and nonlinear media are studied. The problem of different stationary states in two-level system with different parameters of the dispersion relation is considered. A model that employs the nonlinear Shrodinger equation is used to show coupled states of solitons, localization of waves on one side of a defect, and transformation of nonlinear wave into linear wave upon transition through interface for the system under study due to variation in energy. Dispersion relations that determine the energies of such states are derived.

Photostimulation of conductivity and electronic properties of field-emission nanocarbon coatings on silicon

Abstract: The electronic structure of island carbon films on silicon, which are capable of low-voltage field electron emission (at the mean electric-field strength above several hundreds of V/mm), have been investigated. It has been shown by tunnel spectroscopy that islands of these coatings are characterized by a continuous spectrum of the allowed delocalized states near the Fermi level, i.e., they contain carbon in the sp 2 state. The photoconductivity of the coatings under study has been observed. Based on the current and spectral characteristics of this phenomenon, it has been shown that islands are separated from each other by tunnel barriers and from the substrate by a Schottky barrier.

Simulation of the thermal conductivity of a nanofluid with small particles by molecular dynamics methods

Abstract: The thermal conductivity of nanoliquids has been simulated by molecular dynamics method. We consider nanofluids based on argon with aluminum and zinc particles with sizes of 1–4 nm. The volume concentration of nanoparticles is varied from 1 to 5%. The dependence of the thermal conductivity on the volume concentration of nanoparticles has been analyzed. It has been shown that the thermal conductivity of a nanofluid cannot be described by classical theories. In particular, it depends on the particle size and increases with it. However, it has been established that the thermal conductivity of nanofluids with small particles can even be lower than that of the carrier fluid. The behavior of the correlation functions responsible for the thermal conductivity has been studied systematically, and the reason for the increase in the thermal conductivity of nanofluid has been explained qualitatively.

Composition and properties of nanoscale Si structures formed on the CoSi 2 /Si(111) surface by Ar + ion bombardment

Abstract: The variations in the composition and structure of CoSi2/Si(111) surface layers under Ar+ ion bombardment with subsequent annealing has been studied. It has been demonstrated that nanocluster phases enriched with Si atoms form on the CoSi2 surface at low doses D ≤ 1015 cm–2, and a pure Si nanofilm forms at high doses.

Wavelet correlations of nonstationary signals

Abstract: Two approaches to the analysis of nonstationary random signals are proposed and studied. The first approach is based on the adaptive Morlet wavelet that allows variations in time and frequency resolution of signals using an auxiliary control parameter. The second approach is related to the application of double correlation function that represents correlation of continuous wavelet transforms of two signals calculated in time and frequency domains. The advantages of the proposed correlation function in comparison with alternative correlation functions, in particular, analysis of both time and frequency correlations of nonstationary signals are outlined. Applications of the proposed approaches in the analysis of various transient processes in physics are discussed.

Change in the lattice properties and melting temperature of a face-centered cubic iron under compression

Abstract: All four parameters of the Mie–Lennard-Jones pair interatomic potential have been determined, and the state equation (P) and baric dependences of the lattice properties of an fcc iron are calculated using a previously proposed method. The dependences have been studied for the following properties: Debye temperature; the first, second, and third Gruneisen parameters; isothermal bulk modulus B T and B′(P); isochoric specific heat C v and C v ′(P); isobaric specific heat C p ; coefficient of thermal expansion α p and α p ′(P); specific surface energy σ and σ′(P). Calculations performed along two isotherms (1500 and 3000 K) have shown good agreement with the experimental data. Analytical approximations of the baric dependences for B′(P), α p (P), C p (P), and σ′(P) have been obtained, and it is shown that at P → ∞ the functions B T (P) and σ(P) change linearly, while the functions α p′(P) and C p ′(P) tend to zero. The calculated baric dependence of the melting temperature shows good agreement with the experimental data.

Anisotropy of optical, electrical, and photoelectrical properties of amorphous hydrogenated silicon films modified by femtosecond laser irradiation

Abstract: Two types of independent anisotropic structures have been formed simultaneously in amorphous hydrogenated films by applying a femtosecond laser pulse to them, i.e., a structure with a period of several micrometers to several tens of micrometers and a structure with a period of several hundred nanometers. The formation mechanisms of these strictures are different, which allows us to orient them relative to each other in a desirable way. Both structures independently influence the optical properties of the modified films, which causes the diffraction of transmitted light and making the films polarization-sensitive. The conductivity of the modified films correlates with the mutual orientation of the anisotropic structures, whereas no interrelation between the photoconductivity and optical performance of the modified films has been observed.

Experiment neutrino-4 on searching for a sterile neutrino with multisection detector model

Abstract: A laboratory for searching for oscillations of reactor antineutrinos has been created based on the SM-3 reactor in order to approach the problem of the possible existence of a sterile neutrino. The multisection detector prototype with a liquid scintillator volume of 350 L was installed in mid-2015. This detector can move inside the passive shield in a range of 6–11 m from the active core of the reactor. The antineutrino flux was measured for the first time at these short distances from the active core of the reactor by the movable detector. The measurements with the multisection detector prototype demonstrated that it is possible to measure the antineutrino flux from the reactor in the complicated conditions of cosmic background on the Earth’s surface.

Variations in thermal properties of diamond under isothermal compression

Abstract: State equation P(V/V 0, T) and baric dependences of thermal properties of diamond have been obtained without any fitting parameters from the interatomic pair Mie–Lennard-Jones potential and the Einstein model of a crystal Calculations have been performed along two isotherms (at T = 300 and 3000 K) up to P = 10000 kbar = 1000 GPa, ie, to a relative volume of V/V 0 = 05 The baric dependences have been obtained for the following characteristics: isothermal elastic modulus B T and B'(P), isochoric heat capacity C v and C v ' (P), isobaric heat capacity C p ; thermal expansion coefficient α p and α p ' (P); and specific surface energy σ, as well as its derivatives σ'(P) and σ'(T) It is shown that for P → ∞, functions B T (P) and σ(P) vary linearly, functions B'(P), α p (P), C v (P), C p (P) and σ'(P) tend to constants, while functions α p '(P), C v '(P), and difference C p (P)–C v (P) tend to zero Good agreement with experimental data has been demonstrated

Features of an underexpanded pulsed impact gas-dispersed jet with a high particle concentration

Abstract: We have reported on the results of a numerical simulation of the inflow of an underexpanded pulsed gas-dispersed jet with a high particle concentration onto a rigid obstacle unbounded in the transverse direction. The characteristic features of such interaction, in particular, the anomalous formation of the shock-wave structure of the two-phase flow at the subsonic velocity of the carrier gas and the evolution of self-sustained oscillations, have been investigated.

The structure, conductive properties, and reflective properties of amorphous granulated (Co 45 Fe 45 Zr 10 ) x (ZrO) 1 – x composite films

Abstract: The micro- and nanostructure of 328–772-nm-thick amorphous granulated (Co45Fe45Zr10) x (ZrO)1 – x (0.27 < x < 0.61) composite films deposited in argon on a lavsan substrate has been examined using atomic force microscopy, magnetic force microscopy, and scanning electron microscopy. It has been shown that the mean sizes of the grain and the metallic phase content govern the conductive and reflective properties of the films in the microwave range.

Dynamics of a nanoparticle rotating in the near field of a heated solid surface

Abstract: General expressions for the force of attraction to the surface and the projections of torque exerted on a particle rotating near a solid surface at an arbitrary orientation of the angular velocity vector have been found. It has been shown that the particle decelerates over time and the angular velocity vector tends to be oriented perpendicularly to the surface at any initial conditions.

Modification of the texture of a polymer material surface in dust plasma

Abstract: We have analyzed the modification of the texture of polymer particle surface in a dust plasma. Monodisperse spherical melamine formaldehyde particles were injected into the glow discharge plasma in neon. At a certain discharge current and gas pressure in the discharge tube, the particles were suspended in dust-plasma traps and experienced the action of the plasma of 5–25 min. Then, the particles were extracted and the collected material was studied using the scanning electron microscope. Among the results, a change in the diameter and roughness of the surface depending on the residence time of particles in the dust plasma was established. It was found that the absolute deviation of all points of the surface profile averaged over the evaluation length were in the nanometer range. The time of complete degradation of particles in the experimental conditions has been established.

The Dielectric properties of polypropylene/Na+ montmorillonite nanoclays upon heating and cooling

Abstract: The dielectric properties of polypropylene/Na+ montmorillonite nanoclay composites have been studied under conditions of heating and cooling. The e(T) and tanδ(T) parameters have been measured as functions of temperature at frequencies of 103–106 Hz in the heating–cooling mode. A comparative analysis of the measured and calculated e parameters reveals that the best agreement between the theory and experiment has been provided by the Lichteneker model. As has been established, the values of e parameter decrease with an increase in the frequency to 6 × 104 Hz, then increase, while the dielectric losses tanδ(ν) are characterized by curves with a diffused maximum at 104 Hz, which increases with a rise in the nanomontmorillonite filler content. As has been shown, high montmorillonite concentrations in polypropylene favor the acceleration of dipole–relaxation processes and associated dielectric losses, as well as the whole conductivity of nanocomposites.

Failure-delay effect in destruction of steel samples under spalling conditions

Abstract: Dynamic spalling tests have been run on two batches of 30KhN4M steel samples. Experimental data have been processed with the classical technique based on solution of the elastic wave equation. Three samples have been revealed that demonstrated the failure-delay effect under testing. The incubation-time criterion has been used to show the conditions of emergence of failure delay with the example of triangular loading pulses. A rate strength curve has been constructed for the other samples. It has been shown that the limiting strengths under dynamic loads considerably differ for samples from different batches despite the same chemical composition and static strength.

The coffee-drop phenomenon and its time fluctuations: Self-sustained oscillations in colloidal liquids

Abstract: The instant coffee model has been taken to study self-sustained oscillations in liquid dispersive media using dynamic self-organization processes in drying droplets that stay sessile on a solid wetted substrate. The width of the formed ring and the dynamics of mechanical properties of the drying sediment and the way they fluctuated over 11 h of the experiment have been measured. Analysis has shown a high degree of correlation between these indicators. This dynamics reflects processes that develop in the examined liquid medium. The possible mechanism of self-sustained oscillations, which is related to the aggregation–disaggregation of the colloidal phase and fluctuations of the interphase tension, has been discussed. The practical significance of this work is that fluctuation processes in liquid dispersive media need to be taken into account as a natural source of systematic measurement error.

Microstructure of the regions on a plane copper electrode surface affected by a spark discharge in air in the point–plane gap

Abstract: The microstructure of the regions affected by spark discharge on the surface of a plane copper electrode in atmospheric air in the point–plane gap has been studied using a scanning electron microscope for both the positive and negative polarity of the point electrode. It has been found that the affected regions have the shape of round spots or groups of spots with diameters of individual spots varying in the range of 20–200 μm. It has been revealed that the spots have an internal spatial structure in the form of an aggregate of concentric rings. These rings are aggregates of a large number of microscopic craters with diameters of 0.1–1.0 μm.