Showing papers in "Technical Physics in 2009"

On the effective viscosity of nanosuspensions

Abstract: The effective viscosity of nanosuspensions is simulated using the molecular dynamics method. It is found that viscosity is controlled not only by the volume concentration of nanoparticles, by also by their mass and diameter. The viscosity of even strongly rarefied nanosuspensions (with a low concentration of nanoparticles) cannot be described by the Einstein relation. This means that the mechanism responsible for the increase in the viscosity of the medium is not of hydrodynamic origin. It is shown that the formation of viscosity of nanosuspensions is associated to a considerable extent with nonequilibrium microfluctuations of density and velocity of the carrier medium, which are induced by the motion of nanoparticles.

Structural evolution of drying drops of biological fluids

Abstract: Qualitative analysis of experimental data for the mechanisms of structuring in drying drops of biological fluids is carried out. It is shown that the structural evolution of the drying drops is a complex process in which two stages can be separated out by convention: events occurring during evaporation of free water and structuring due to evaporation of film water. Consideration of the structural evolution of drying drops on the basis of the physical chemistry of solutions, physics of polymers, mechanics, and materials science makes it possible to explain the phenomenology of the process in terms of well-known physical phenomena.

Elastic-plastic transition in iron: Structural and thermodynamic features

Abstract: The structural and thermodynamic features of the elastic-plastic transition in armco iron and its plastic deformation are studied. Energy storage in iron is shown to have a nonlinear character and be accompanied by wavelike heat dissipation. To describe the energy balance in the plastically deformed metal, a theoretical model is proposed based on a statistical description of the evolution of an ensemble of typical mesodefects (microshears). Moreover, a procedure is developed to experimentally determine the dependence of the potential of the medium on the mesodefect density using infrared scanning data.

Compact group method in the theory of permittivity of heterogeneous systems

Abstract: The static permittivity of macroscopically homogeneous and isotropic heterogeneous systems is analyzed using the concepts of compact groups of inhomogeneities. The method makes it possible to avoid excessive specification of mutual polarization processes in the system, which ensures effective application of this method for concentrated systems with arbitrary relations between the permittivities of system components. By way of example, the Maxwell-Garnett and Bruggeman formulas for the effective permittivity of heterogeneous matrix systems are reconstructed and their interrelation is analyzed. It is shown that the Bruggeman formula is more limited in the sense that it is based on additional model assumptions concerning the properties of the system and the type of averaging of fields over the volume of the system. Generalizations of these formulas are obtained for multicomponent heterogeneous systems consisting of inhomogeneous nonspherical particles or parts.

Low-frequency magnetoelectric effect in a Galfenol-PZT planar composite structure

Abstract: The forward and inverse magnetoelectric (ME) effects are experimentally studied in a two-layer planar structure containing mechanically coupled Galfenol and PZT plates. The process of production of polycrystalline Galfenol plates and their magnetic and magnetostriction characteristics are described. For the forward ME conversion, the dependences of the amplitude of the voltage generated by the structure on the magnitude and orientation of a dc magnetic field and the frequency and amplitude of a modulating magnetic field are measured. For the inverse ME conversion, the dependences of the amplitude of the change in the magnetic induction of the structure on the dc magnetic field and the frequency of an ac electric field applied to the structure are measured. The efficiencies of the forward and inverse ME conversion are estimated for the case of low-frequency field modulation and under conditions of the resonance excitation of bending and longitudinal mechanical vibrations in the structure.

Propagation velocity of longitudinal and transverse acoustic waves and anharmonicity of lattice oscillations

Abstract: A linear correlation between the Gruneisen parameter and ratio of the velocities of longitudinal (νl)and transverse (νt) acoustic waves in crystals is found. It is assumed that velocities νl and νt are severally harmonic parameters, while their ratio νl/νt is an anharmonic quantity and depends on the ratio between the shear and flexural rigidities of interatomic bonds.

Experimental study of the pumping action of helical flow

Abstract: A decrease in hydraulic friction coefficient Σ (Darcy number) is found in the range of smooth tubes. The maximum possible decrease in Σ is observed at Φ = 0.08 for numbers Re D = V x D / ν in the range Re Dx = (5.8−6.6) × 104.

Low-threshold field electron emission from carbon nanoclusters formed upon cold destruction of graphite

Abstract: The field-emission characteristics of carbon nanoclusters (graphenes, nanotubes, their compositions with microdiamonds) produced by the cold destruction of natural graphite are studied. The structure of a coating of carbon nanoclusters on a tungsten cathode is examined by field emission microscopy, transmission electron microscopy, and electron diffraction. The high-intensity stable field emission of these clusters is shown to be characterized by a low field threshold. The mechanism of the low-threshold emission from carbon nanoclusters is discussed.

Multiexponential decay of negative molecular ions as a result of target molecule distribution over vibrational states

Abstract: The lifetimes of long-lived negative molecular ions SF 6 − -, C6H5NO 2 − , and C6F 6 − are measured with a static mass spectrometer. A great spread in published data for the lifetimes of these ions is explained using a concept of multiexponential decay of molecular ions. The influence of the Boltzmann distribution of neutral target molecules over vibrational states on the lifetime of negative molecular ions is studied in terms of the Illenberger-Smirnov-Kompaneits simple statistical model. It is shown that this distribution has a profound effect on the multiexponential decay of molecular anions and, as a consequence, on the lifetime of negative molecular ions measured on different mass spectrometers.

Formation and Dynamics of a Virtual Cathode in a Tubular Electron Beam Placed in a Magnetic Field

Abstract: Mechanisms underlying the formation and dynamics of a virtual cathode (VC) in a tubular electron beam subjected to a magnetic field are studied using a numerical 2D model. Two qualitatively different competing types of space charge dynamics near the VC are discovered. Which of them predominates depends on the magnetic field strength. The beam current critical density at which a nonstationary VC forms in the system is also strongly dependent on the magnetic field. It is shown that the optimal strength of the magnetic field that minimizes the beam current critical density depends on the Brillouin magnetic field.

Inflammation dynamics of thin alcohol films under the action of a surface microwave discharge initiated in atmospheric-pressure air

Abstract: Rapid nonthermal plasma-stimulated inflammation of liquid hydrocarbon (alcohol) films is realized under the conditions of a surface microwave discharge initiated in quiescent atmospheric-pressure air. The induction period is found, and the velocity of the intense combustion front is determined. Combustion is initiated by the low-temperature plasma of the surface microwave discharge that exists at high values of the reduced electric field. It is shown that the induction period varies between 10 and 100 µs depending on the input power, the plasma-stimulated inflammation occurs on the antenna at the site where the surface microwave discharge burns, and the velocity of the intense combustion front near the antenna reaches 300–350 m/s.

Optimization of matching section of an accelerator with a spatially uniform quadrupole focusing

Abstract: A new approach is proposed for determining the matching section profile in an accelerator with spatially uniform quadrupole focusing. The approach based on mathematically formalized optimization problem and considerably extends the class of possible profiles since it is primarily independent of specific laws of variation of rigidity in the matching section and makes it possible to find the values of the aperture at the boundaries and in the cells directly as a solution.

On the model of channel-by-channel magnetization of a granular medium (with a radial permeability profile of a quasi-continuous channel)

Abstract: The features of an “elementary” effective magnetization channel are studied for a chain of spheres as a specific magnet responsible for magnetization of the granular medium as a whole (based on a model differing from the models of traditional averaging of magnetic properties over the volume). Matching experimental and theoretical data on the permeability (radial permeability profile) of a magnet-channel (core of various radii and isolated tubular layers) are compared.

Size effects under martensitic deformation of shape-memory alloys

Abstract: The effect of the grain size and film thickness on the parameters of martensitic transitions and deformation behavior of shape-memory alloys is studied in terms of the theory of smeared martensitic transitions. Comparison of theoretical results with experimental data suggests that the transformation kinetics related to the growth mechanism and shrinkage of martensite lamellas when transformation steps (dislocations) move along their boundaries is most sensitive to the size factor.

Dependence of the macroscopic elastic properties of porous media on the parameters of a stochastic spatial pore distribution

Abstract: The mechanical behavior of porous ceramic materials with a stochastic structure of their pore space is numerically studied during shear loading. The calculations are performed by the mobile cellular automaton method. A procedure is proposed for a numerical description of the internal structure of such materials using the dispersion of the pore distribution in layers that are parallel to the loading direction in a sample. The dependence of the macroscopic elastic properties of porous media on their internal structure is analyzed. Samples with spherical pores and pores extended along the loading direction exhibit a correlation between their average shear modulus and the dispersion of a pore distribution. Thus, the results obtained indicate that the shear modulus of such media is a structure-sensitive property. The proposed approach can be applied to compare the elastic properties of samples using data on their pore structure.

Accelerator mass spectrometer for the Siberian Branch of the Russian Academy of Sciences

Abstract: A concept of an accelerator mass spectrometer intended for the Siberian Branch of the Russian Academy of Sciences is suggested. Preliminary tests have been conducted, and a carbon isotope having a mass of 14 amu has been detected in a charcoal sample.

Electrostatic instability of a heavily charged conducting liquid jet

Abstract: The effect of electric charge on the jet surface on the capillary instability of the jet and its disintegration into drops is analyzed A theoretical explanation is given for the electrostatic mechanism of instability development and jet disintegration that is akin to the mechanisms behind the instability of a heavily charged drop (Rayleigh instability) and flat uniformly charged liquid surface (Tonks-Frenkel instability) but differs qualitatively from the conventional capillary mechanism of instability and disintegration

Effect of bulk modification of polymers in a directional low-temperature plasma flow

Abstract: A mechanism explaining the kinetics of polymer etching and the formation of modified layers in the plasma generated by a high-voltage gas discharge outside the electrode gap is proposed and substantiated from a unified point of view based on the Thomson-Widdington law. The effect of bulk modification of a polymer is discovered, which upgrades the knowledge of the processes occurring during polymer interaction with a low-temperature plasma.

Electric-arc high-capacity reactor for the synthesis of carbon soot with a high content of endohedral metallofullerenes

Abstract: An electric-arc reactor is designed for synthesizing carbon soot containing endohedral metallofullerenes during the sequential evaporation of five composite graphite electrodes. The preparation conditions of the composite graphite electrodes and the electric-arc evaporation parameters are optimized, which increases the reactor capacity and the content of endohedral metallofullerenes in carbon soot.

On the Grüneisen parameter for crystals and glasses

Abstract: Additional data confirming the close relation between the Gruneisen parameter and the Poisson ratio are obtained. The estimate of the Gruneisen parameter based on the Leont’ev formula using the data on density, bulk compression modulus, and velocity of sound is in conformity with the results of calculations based on the Gruneisen and Belomestnykh-Tesleva equations.

Effect of high doses of N + , N + + Ni + , and Mo + + W + ions on the physicomechanical properties of TiNi

Abstract: The surface layer of an equiatomic TiNi alloy, which exhibits the shape memory effect in the martensitic state, is modified with high-dose implantation of 65-keV N+ ions (the implantation dose is varied from 1017 to 1018 ions/cm2) TiNi samples are implanted by N+, Ni+-N+, and Mo+-W+ ions at a dose of 1017–1018 cm−2 and studied by Rutherford backscattering, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction (glancing geometry), and by measuring the nanohardness and the elastic modulus A Ni+ concentration peak is detected between two maxima in the depth profile of the N+ ion concentration X-ray diffraction (glancing geometry) of TiNi samples implanted by Ni+ and N+ ions shows the formation of the TiNi (B2), TiN, and Ni3N phases In the initial state, the elastic modulus of the samples is E = 56 GPa at a hardness of H = 213 ± 030 GPa (at a depth of 150 nm) After double implantation by Ni+-N+ and W+-Mo+ ions, the hardness of the TiNi samples is ∼278 ± 095 GPa at a depth of 150 nm and 495 ± 225 GPa at a depth of 50 nm; the elastic modulus is 59 GPa Annealing of the samples at 550°C leads to an increase in the hardness to 444 ± 145 GPa and a sharp increase in the elastic modulus to 236 ± 39 GPa A correlation between the elemental composition, microstructure, shape memory effect, and mechanical properties of the near-surface layer in TiNi is found

Impedance characteristics of crystal-like structures

Abstract: Simulation of crystal-like structures (CSs) based on the impedance model is considered. It is shown that CSs peculiarly transform the wave impedance, inducing unusual properties of the medium. The impedance characteristics for various CSs are considered.

New acoustooptic effect: Constant high diffraction efficiency in wide range of acoustic power

Abstract: A new effect, viz., acoustooptic Bragg diffraction without the overmodulation mode, in which the efficiency of the Bragg order attains its maximal value (close to 100%) upon an increase in the intensity of an acoustic wave and then remains practically unchanged, is predicted theoretically and observed experimentally. The effect takes place in the case of considerable bending of phase fronts of the acoustic field in the acoustooptic diffraction plane and attains its maximal value at a relatively low frequency of sound, a small width of a piezoelectric transducer, strong acoustic anisotropy of the medium, and a large distance between the light beam and the piezoelectric transducer.

Spectra of electrons and X-ray photons in a diffusive nanosecond discharge in air under atmospheric pressure

Abstract: The spectra of electrons and X-ray photons generated in nanosecond discharges in air under atmospheric pressure are investigated theoretically and experimentally. Data for the discharge formation dynamics in a nonuniform electric field are gathered. It is confirmed that voltage pulses with an amplitude of more than 100 kV and a rise time of 1 ns or less causing breakdown of an electrode gap with a small-radius cathode generate runaway electrons, which can be divided into three groups in energy (their energy varies from several kiloelectronvolts to several hundreds of kiloelectronvolts). It is also borne out that the formation of the space charge is due to electrons appearing in the gap at the cathode and a major contribution to the electron beam behind the foil comes from electrons of the second group, the maximal energy of which roughly corresponds to the voltage across the gap during electron beam generation. X-ray radiation from the gas-filled diode results from beam electron slowdown both in the anode and in the gap. It is shown that the amount of group-3 electrons with an energy above the energy gained by runaway electrons (in the absence of losses) at a maximal voltage across the gap is much smaller than the amount of group-2 electrons.

Experimental assessment of local thermodynamic equilibrium in VKI Plasmatron air plasma jet

Abstract: The thermodynamic state of subsonic air plasma jet, produced by VKI Plasmatron operating at 500 kW and 16 g.s ―1 , in the pressure range 100―300 mbar, is investigated by means of optical emission spectroscopy diagnostics. The N and O atomic lines were recorded, in the visible spectral range at resolution of 0.066 nm, at 16 cm away from the outlet into the test chamber. The temperatures obtained assuming Local Thermodynamic Equilibrium (LTE) and only thermal equilibrium were found to agree quite well, indicating that the plasma is close to thermal equilibrium at temperature of about 10000 K. However electron densities, determined starting from H β line broadening measured on initial air mixture seeded with a small amount of water, were found to be about 10 21 m ―3 , slightly lower than the densities calculated at LTE, similarly to plasma undergoing recombination.

Detonation of CHO working substances in a laser jet engine

Abstract: Laser-induced ablation of materials (including polymers and a variety of polycrystalline substances with a CHO chemical composition) is studied theoretically and experimentally. Based on experimental data, a parametric physicochemical model of detonation of these materials is put forward with the aim to estimate the efficiency of laser thrust formation in jet engines.

Excimer laser-assisted annealing of silicate glass with ion-synthesized silver nanoparticles

Abstract: The effect of KrF excimer laser radiation on a composite layer consisting of sodium-potassium silicate glass with silver nanoparticles is studied as a function of the number of laser nanosecond pulses. The silver nanoparticles are synthesized by ion implantation. The measured optical absorption of the composite layer demonstrates that the silver nanoparticle size decreases monotonically as the number of laser pulses increases. Rutherford backscattering shows that laser annealing is accompanied by silver diffusion into the bulk of the glass and partial metal evaporation from the sample surface. The detected decrease in the silver nanoparticle size is discussed in terms of simultaneous melting of silver nanoparticles and the glass matrix due to the absorption of laser radiation.

Poisson ratio and plasticity of glasses

Abstract: Analysis of experimental data reveals a regular relation between Poisson’s ratio and plastic characteristics of inorganic glasses.

Spectroscopic investigation of an inductively heated CO 2 plasma for Mars entry simulation

Abstract: The principal availability of a high enthalpy ground test facility for the simulation of atmospheric entry into a martian atmosphere based on a CO 2 plasma is shown. The plasma is characterized using both the heat flux and pressure probe techniques. Two different approaches to determine local enthalpies are presented. Results of the plasma characterization using Optical Emission Spectroscopy (OES) are presented and a quantitative comparison of the measurement results, with numerically simulated spectra using the PARADE database, are analysed. In order to create a data basis for further improvement and validation of radiation codes for Mars entry scenarios, emission spectroscopic measurements have been performed. The first qualitative comparison of the measurement data from the 21 MJ/kg condition with numerically created CO 2 spectra has been used to identify the radiating species. Atomic oxygen and atomic carbon could clearly be identified, also there is evidence of oxygen and carbon ions. From the molecule-based radiation, C 2 Swan and CO 3rd Pos. as well as the CO + 1st. Neg. systems could be identified and showed a fairly good agreement with the PARADE data. The CO + Comet Tail system has been added very recently in PARADE and it is shown within this paper that it contributed significantly to the measured radiation.

Classification of shock wave reflections from a wedge. Part 2: Experimental and numerical simulations of different types of Mach reflections

Abstract: Shadowgraph images of different types of irregular reflections that illustrate the suggested classification are presented. The complex forms of the Mach reflection are studied by numerical simulation at various initial parameters. Emphasis is on the near-wall behavior of the contact discontinuity in the main Mach configuration and on intersection between contact discontinuities. Analysis shows that, if an incident shock wave is strong, interaction of the shock wave with an infinite wedge is a nonstationary process.