Showing papers in "Technical Physics Letters in 2009"
TL;DR: In this paper, an insulated target was irradiated by an electron beam generated by a forevacuum plasma electron source operating in the pressure range of 5-15 Pa. Measurements of the target potential showed that plasma formed in the region of electron beam transport ensured the almost complete neutralization of charge accumulated on the target.
Abstract: An insulated target was irradiated by an electron beam generated by a forevacuum plasma electron source operating in the pressure range of 5–15 Pa. Measurements of the target potential showed that plasma formed in the region of electron beam transport ensured the almost complete neutralization of charge accumulated on the target. This effect results in the possibility of direct electron-beam processing of nonconducting materials, including the melting and welding of ceramics.
62 citations
TL;DR: In this article, a method of converting a high-voltage video pulse into high-frequency oscillations using a nonlinear transmission line with temporal dispersion has been studied, where the dispersion was provided by pulsed magnetization reversal in a ferrite, which was initially magnetized to saturation in an external magnetic field.
Abstract: A new method of converting a high-voltage video pulse into high-frequency oscillations using a nonlinear transmission line with temporal dispersion has been studied. The dispersion was provided by pulsed magnetization reversal in a ferrite, which was initially magnetized to saturation in an external magnetic field. For a 9-ns pulse, an average energy conversion efficiency of about 10% was achieved. It is demonstrated that oscillations at frequencies within 600 MHz-1.1 GHz with a spectral width of about 15% (at a −3 dB level) can be excited using voltage pulses with an amplitude of 110–290 kV. The optimum bias magnetization fields are within 20–40 kA/m.
50 citations
TL;DR: In this article, a gas-flow-driven liquid film driven by friction with a gas flow in a horizontal minichannel and the heat exchange crisis in this film locally heated by a 1 × 1 cm source in the channel wall has been experimentally studied.
Abstract: The rupture of a liquid film driven by friction with a gas flow in a horizontal minichannel and the heat-exchange crisis in this film locally heated by a 1 × 1 cm source in the channel wall has been experimentally studied. A heat flux of 250 W/cm2 is achieved, which is greater by an order of magnitude than the limiting heat flux for a vertically falling liquid film with the same Reynolds number (Rel = 21). These experiments confirmed good prospects for using gas-flow-driven liquid films in cooling systems of devices with intense local heat evolution.
39 citations
TL;DR: In this article, the effect of a gas-permeable material situated in front of a blunt body on the aerodynamic drag of this system in a supersonic airflow with a Mach number of M = 4.85 was investigated.
Abstract: We have experimentally studied the effect of a gas-permeable material situated in front of a blunt body on the aerodynamic drag of this system in a supersonic airflow with a Mach number of M = 4.85. It is established that the porous material significantly reduces the wave drag in the system. Explanation of the observed phenomenon is proposed.
37 citations
TL;DR: The possibility of obtaining hard nanocrystalline coatings using vacuum-arc deposition in a high-frequency discharge stimulated regime has been studied in this paper, where the results of nanoindentation show evidence for a strong inhomogeneity of the coatings, in which regions possessing a hardness of 29-30 GPa alternate with those where the hardness exceeds 45-47 GPa.
Abstract: The possibility of obtaining hard nanocrystalline coatings using vacuum-arc deposition in a high-frequency discharge stimulated regime has been studied. Condensates of the Zr(Ti)-Si-N system obtained by this method contain ZrN and TiN crystalline grains. These grains exhibit a compressive strain of about −1.1% in the film growth plane, which corresponds to compressive stresses up to about 3.5 GPa in the film-substrate system. The results of nanoindentation show evidence for a strong inhomogeneity of the coatings, in which regions possessing a hardness of 29–30 GPa alternate with those where the hardness exceeds 45–47 GPa. This pattern agrees with a two-phase model based on the structural data, according to which the condensed material consists of less hard ZrN grains and harder TiN grains.
37 citations
TL;DR: In this paper, a simple theoretical model is proposed for predicting the dynamics of the hollow liquid drop spreading on the surface, and the results of calculations satisfactorily agree with the data of model experiments.
Abstract: Physical model experiments devoted to visualization of the collision of a hollow liquid drop with a flat surface are described. A new phenomenon is discovered, according to which the impact leads to the formation of a central counter jet of the liquid. A simple theoretical model is proposed for predicting the dynamics of the hollow liquid drop spreading on the surface. The results of calculations satisfactorily agree with the data of model experiments.
30 citations
TL;DR: In this article, the development of thermal (overheat) instabilities during the electric explosion of a conducting wire was studied based on the theory of small perturbations, and it was established that the overheat instabilities are always developed in the course of electric explosions, irrespective of the regime of explosion.
Abstract: The development of thermal (overheat) instabilities during the electric explosion of a conducting wire was studied based on the theory of small perturbations. It is established that (i) the overheat instabilities are always developed in the course of electric explosions, irrespective of the regime of explosion and (ii) a threshold value of the current density exists for each metal, below which the magnetohydrodynamic screw instabilities grow faster than the overheat instabilities; above this threshold, the latter instabilities predominate.
27 citations
TL;DR: In this article, the stability of parallel explosive-emission cathodes driven by a split high-voltage pulse with a subnanosecond leading front was studied and it was established that upon the training of graphite cathodes in vacuum with up to ∼104 pulses, the current pulse fronts of injected high-current electron beams exhibit a mutual temporal dispersion not exceeding ten picoseconds.
Abstract: The stability of operation of parallel explosive-emission cathodes driven by a split high-voltage pulse with a subnanosecond leading front has been studied. It is established that, upon the training of graphite cathodes in vacuum with up to ∼104 pulses, the current pulse fronts of injected high-current electron beams exhibit a mutual temporal dispersion not exceeding ten picoseconds. The dynamics of this parameter during the training stage, the variation of the absolute spread, and the growth of a relative delay of the moments of beam injection have been investigated.
24 citations
TL;DR: The elastic coefficients of layered tetragonal LaFeAsO, SrFe2As2, and LiFeAs crystals, which are potential basic phases for new superconductors of the 1111-, 122-, and 111-FeAs groups, were calculated from first principles using the fullpotential linearized augmented plane wave (FLAPW) method with an exchange-correlation potential in the generalized gradient approximation (GGA) as discussed by the authors.
Abstract: The elastic coefficients (C
ij
), bulk compression moduli (B), and shear moduli (G) of layered tetragonal LaFeAsO, SrFe2As2, and LiFeAs crystals, which are potential basic phases for new superconductors of the 1111-, 122-, and 111-FeAs groups, respectively, have been calculated from first principles using the full-potential linearized augmented plane wave (FLAPW) method with an exchange-correlation potential in the generalized gradient approximation (GGA). Numerical estimates of the bulk moduli, shear moduli, Young’s moduli, and Poisson’s ratios of the corresponding polycrystalline ceramics have been obtained for the first time.
22 citations
TL;DR: In this article, a pilot accelerator-based source of epithermal neutrons, which is intended for wide application in clinics for boron neutron capture therapy, has been constructed at the Budker Institute of Nuclear Physics (Novosibirsk).
Abstract: A pilot accelerator-based source of epithermal neutrons, which is intended for wide application in clinics for boron neutron capture therapy, has been constructed at the Budker Institute of Nuclear Physics (Novosibirsk). A stationary proton beam has been obtained and near-threshold neutron generation regime has been realized. Results of the first experiments on neutron generation using the proposed source are described.
22 citations
TL;DR: In this paper, an original technology for manufacturing polarizers in a single technological cycle has been developed, consisting of a metal (aluminum) film and a dielectric (Al2O3) buffer layer.
Abstract: Plasmon-polariton polarizers on the surface of single-mode channel optical waveguides (OWGs) in lithium niobate crystals have been studied in detail. An original technology for manufacturing polarizers in a single technological cycle has been developed. A polarizer consists of a metal (aluminum) film and a dielectric (Al2O3) buffer layer. An optimum polarizer configuration is found for single-mode channel OWGs matched to a standard optical fiber (SMF-28). A prototype polarizer was manufactured, which was characterized by a polarization extinction ratio of 19 dB/mm and insertion losses on a level of 0.1 dB/mm.
TL;DR: In this paper, the effect of impurities on the density of cavitation centers in water under the conditions of pulsed tension with amplitude of up to −6.0 MPa has been studied.
Abstract: The effect of impurities on the density of cavitation centers in water under the conditions of pulsed tension with amplitude of up to −6.0 MPa has been studied. It is established that the density of cavitation centers in water under these conditions decreases in the presence of dissolved CO2, HCl, and formic acid.
TL;DR: In this article, it was shown that GaAs-based semiconductor heterostructures containing a single layer delta-doped with manganese, obtained by combining the methods of metalorganic chemical vapor deposition (MOCVD) in a hydride system and laser ablation of solid targets in a common technological cycle, possess ferromagnetic properties.
Abstract: It is established that GaAs-based semiconductor heterostructures containing a single layer delta-doped with manganese, obtained by combining the methods of metalorganic chemical vapor deposition (MOCVD) in a hydride system and laser ablation of solid targets in a common technological cycle, possess ferromagnetic properties. The structures demonstrate nonlinear magnetic-field dependences of the Hall resistance with a hysteresis (at a coercivity of about 80 Oe) and show a negative magnetoresistance (up to 4% in a magnetic field of 3000 Oe) at temperatures below the Curie point (TC ≈ 30 K).
TL;DR: In this article, the structural modification of stacking fault tetrahedra (SFTs) upon the absorption of point defects has been studied by the method of molecular dynamics, where the sequential absorption of vacancies by a perfect SFT is accompanied by the following transformations: (i) the formation of a step on one of the SFT faces, (ii) a change in the step sign upon reaching the middle of the face, (iii) formation of an SFT with truncated vertex, and (iv) the forming of the complete SFT.
Abstract: Mechanisms of the structural modification of stacking fault tetrahedra (SFTs) upon the absorption of point defects have been studied by the method of molecular dynamics. The sequential absorption of vacancies by a perfect SFT is accompanied by the following transformations: (i) the formation of a step on one of the SFT faces, (ii) a change in the step sign upon reaching the middle of the face, (iii) the formation of an SFT with truncated vertex, and (iv) the formation of the perfect SFT. Upon the absorption of interstitial atoms, the stages of SFT transformation follow the reverse order.
TL;DR: In this paper, the composition and structure of nongraphite carbon phases in the near-surface region of the crater have been studied using the Raman scattering spectroscopy, electron microdiffraction, and energy-dispersive X-ray analysis.
Abstract: Pulsed laser action upon a sample of highly oriented pyrolytic graphite (HOPG) in a gasostat filled with helium at a pressure above that corresponding to the triple point of carbon, followed by rapid quenching of the liquid phase at a rate of about 106 K/s leads to the formation of a crater with a periodic spatial structure at the surface. The composition and structure of nongraphite carbon phases in the near-surface region of the crater have been studied using the Raman scattering spectroscopy, electron microdiffraction, and energy-dispersive X-ray analysis. It is established that rapidly quenched carbon possesses predominantly a hybrid structure of glassy carbon formed as a result of the high-temperature treatment, with inclusions of crystalline carbyne, chaoite, and a hybrid cubic phase of ultradense carbon (C8). The hybrid phases of glassy carbon and C8 had not been reported until now as possible products of solidification of liquid carbon.
TL;DR: The mechanical and thermodynamic properties of nanocrystalline (NC) titanium have been experimentally studied under the conditions of dynamic compression at a strain rate of (2-5) × 103 s−1 as mentioned in this paper.
Abstract: The mechanical and thermodynamic characteristics of nanocrystalline (NC) titanium have been experimentally studied under the conditions of dynamic compression at a strain rate of (2–5) × 103 s−1. The samples of NC titanium were cut from a rod processed by equal-channel angular pressing and had a characteristic grain size of 300 nm. It is established that a 25% increase in the dynamic limit of elasticity in the NC titanium (compared to an initial coarse-grained sample) is accompanied by qualitative changes in the process of energy absorption and dissipation in the material. The amount of dissipated energy remains approximately constant and independent of the rate and amplitude of loading in the entire range of strain rates studied.
TL;DR: In this article, a nanoperforated magnetic structure based on cobalt films was presented on the surface of a porous aluminum substrate, which exhibited a significant enhancement of the transversal magnetooptical Kerr effect as compared to that in magnetic thin films formed on a usual nonporous substrate.
Abstract: We present the technology of nanoperforated magnetic structures based on cobalt films deposited onto the surface of a porous aluminum substrate. The structures exhibit a significant (by an order of magnitude) enhancement of the transversal magnetooptical Kerr effect as compared to that in magnetic thin films formed on a usual nonporous substrate. The effect increases with the depth of pores.
TL;DR: In this paper, the effect of an electron beam and the related plasma on the structure, phase state, and microhardness of the surface of titanium has been studied in a broad range of beam currents (0.1-2.5 A), electron energies ( 0.1 − 1 keV), and gas pressures (0.01 − 1 Pa).
Abstract: The effect of an electron beam and the related plasma on the structure, phase state, and microhardness of the surface of titanium has been studied in a broad range of beam currents (0.1–2.5 A), electron energies (0.1–1 keV), and gas pressures (0.01–1 Pa). This range was ensured by the grid stabilization of emissive properties of the plasma electron source, which formed a wide (∼40 cm2) electron beam in a space charge layer between the beam-excited plasma and the grid bounding the plasma cathode. The sample temperature (350–900°C) was determined by the electron beam parameters. The plasma density was additionally controlled by changing the gas (N2 or Ar-N2 mixture) pressure. It is established that, during the low-temperature nitriding process in low-energy electron beam plasma, the ion sputtering significantly affects the microhardness of a processed surface and the rate of growth of the hardened layer thickness. The possibility of nitriding at a low (−50 V) or floating potential of the sample eliminates the development of a surface relief and allows the process to be carried out in deep and narrow slits.
TL;DR: In this article, the authors measured the pressure generated by the electric explosion of various metal (Cu, Al, Fe, Ta, Ti, Pb, W, and brass) foils.
Abstract: We have measured the pressure generated by the electric explosion of various metal (Cu, Al, Fe, Ta, Ti, Pb, W, and brass) foils. The pressure amplitude as a function of the specific energy supplied to the exploding foil is well approximated by a linear dependence.
TL;DR: In this article, a supershort avalanche electron beam (SAEB) with a current amplitude of ∼30 A, a current density of ∼20 A/cm2, and a pulse full width at half maximum (FWHM) of ∼100 ps has been observed behind the output foil of an air-filled diode.
Abstract: Optimum conditions for the generation of runaway electron beams with maximum current amplitudes and densities in nanosecond pulsed discharges in air at atmospheric pressure are determined. A supershort avalanche electron beam (SAEB) with a current amplitude of ∼30 A, a current density of ∼20 A/cm2, and a pulse full width at half maximum (FWHM) of ∼100 ps has been observed behind the output foil of an air-filled diode. It is shown that the position of the SAEB current maximum relative to the voltage pulse front exhibits a time shift that varies when the small-size collector is moved over the foil surface.
TL;DR: In this paper, the electron beam was monitored using luminescence of a layer of ZnS-CdS:Ag phosphor placed behind a 20-μm-thick foil anode.
Abstract: Electron beam generation in atmospheric air discharge with a flat cathode has been experimentally studied. The discharge was excited by voltage pulses of negative polarity with an amplitude of 220 kV, a full width at half maximum of 2 ns, and a leading front width of 0.7 ns. The electron beam was monitored using luminescence of a layer of ZnS-CdS:Ag phosphor placed behind a 20-μm-thick foil anode. It was found that the intensity and homogeneity of luminescence of the phosphor layer increased when a dielectric tube with a length smaller than half of the interelectrode distance was placed in the near-cathode part of the air gap. It is concluded that a plasma cathode is formed within the volume confined by the tube and electrons emitted from this region are accelerated in the open part of the gap. In addition, the dielectric tube decreases the divergence of the electron beam.
TL;DR: In this article, it was found that the surface of ND films showing by the maximum field-emission currents contains needle-like carbon structures. And the presence of non-diamond carbon inclusions was determined by the obtained experimental data.
Abstract: Nanodiamond (ND) films on silicon substrates have been synthesized by plasmachemical deposition (PCD). Films with minimum differences in the structure and morphology, which were obtained by varying the PCD process parameters, exhibited significantly (several orders in magnitude) different field-emission currents. It was found that the surface of ND films showing by the maximum field-emission currents contains needle-like carbon structures. Based on the obtained experimental data, it is concluded that the field-emission properties of ND films are determined by the presence of non-diamond carbon inclusions.
TL;DR: In this paper, the authors studied the character of film fracture depending on the level of supplied electric energy W. At high current densities on a level of ∼(1-3) × 1012 A/m2 and explosion times within 50-300 ns, the integral of action to explosion varies within (0.79 − 1.08) × 1.7 A s/m 2 depending upon the rate of energy supply and differs from published data for relatively massive conductors.
Abstract: Pulsed electrodynamic breakage of thin (∼20-nm-thick) aluminum films deposited onto polymer substrates have been experimentally studied. The character of film fracture depends on the level of supplied electric energy W. For 3.5 kJ/g < W < 4.3 kJ/g, discontinuities (striations) are formed in the transverse direction relative to the applied electric field. At high current densities on a level of ∼(1–3) × 1012 A/m2 and explosion times within 50–300 ns, the integral of action to explosion varies within (0.79–1.08) × 1017 A s/m2 depending on the rate of energy supply and differs from published data for relatively massive conductors.
TL;DR: In this paper, the luminescence of TbCl3 · 6H2O and Tb(acac)3 · H2O crystal hydrates under conditions of multibubble sonolysis (20 kHz, 25 W) of corresponding crystal suspensions in perfluorodecalin and undecane has been observed for the first time.
Abstract: The luminescence of TbCl3 · 6H2O and Tb(acac)3 · H2O crystal hydrates under conditions of multibubble sonolysis (20 kHz, 25 W) of the corresponding crystal suspensions in perfluorodecalin and undecane has been observed for the first time. The luminescence spectra contain the lines of emission from Tb3+* ions. No emission lines due to molecular nitrogen have been observed in N2-saturated suspensions. Based on a comparison of the emission accompanying the sonolysis of suspensions, the photoluminescence of terbium crystals, and the tribolumninescence under usual mechanical actions, it is concluded that the nature of the observed phenomenon corresponds to sonotriboluminescence (STL), the mechanism of which is different from that of the recently discovered STL of resorcinol where N2 is predominantly excited. It is suggested that resorcinol-like organic crystals and terbium compounds belong to different types of triboluminescent materials, which are characterized by different susceptibilities to STL activation during the sonolysis of suspensions.
TL;DR: In this article, exact stationary solutions of the Kompaneets kinetic equation were obtained and analyzed for the first time, which describes the spectra of photons interacting with a rarefied electron gas.
Abstract: Exact stationary solutions of the Kompaneets kinetic equation, which describes the spectra of photons interacting with a rarefied electron gas are obtained and analyzed for the first time. Solutions describing the stationary spectra of comptonization in a photon flux along the frequency axis are expressed through the Heun functions. It is shown that the photon input and output points always correspond to finite frequencies.
TL;DR: In this paper, a fractal model of the spatial structure of nanosecond gas discharges is proposed for the generation of high and anomalous energy electrons, which admits the acceleration of electrons both in the stage of interelectrode gap bridging and in conduction.
Abstract: A mechanism responsible for the generation of high- and anomalous-energy electrons is formulated on the basis of a fractal model of the spatial structure of nanosecond gas discharges. The proposed mechanism admits the acceleration of electrons both in the stage of interelectrode gap bridging and in the stage of conduction.
TL;DR: In this article, a Ti-sapphire laser was used to trap a gas bubble in water at a repetition rate of 100 kHz and the trapping force was estimated as ∼200 pN at an average laser power of 20 mW.
Abstract: We have experimentally observed the trapping of a gas bubble in water by focused laser radiation. The optical trap was provided by 200-fs pulses of a Ti-sapphire laser operating at a repetition rate of 100 kHz. The laser radiation was focused in water by an objective with a numerical aperture of 0.5. The trapping force in water is estimated as ∼200 pN at an average laser power of 20 mW, which is by two orders of magnitude greater than the efficiency of a traditional laser tweezers. The trapping force arises upon local heating of gas inside a bubble due to nonlinear absorption in the focal region.
TL;DR: A thermovoltaic effect has been observed for the first time in a polycrystalline sample of samarium sulfide (SmS) with artificially created concentration gradient of excess (overstoichiometric) samarium ions, in which an electric voltage of 12.5 mV was generated in a temperature interval of 370-485 K as discussed by the authors.
Abstract: A thermovoltaic effect has been observed for the first time in a polycrystalline sample of samarium sulfide (SmS) with artificially created concentration gradient of excess (overstoichiometric) samarium ions, in which an electric voltage of 12–22.5 mV was generated in a temperature interval of 370–485 K. It is shown that the specific voltage generation in SmS due to the thermovoltaic effect can be observed in a temperature range of 100–1800 K.
TL;DR: In this paper, the temperature interval ΔTSE of superelasticity in [001]-, [\( \bar 1 \)23]-, and [\bar 1 ε)-oriented Co40Ni21Ga30 (at. %) single crystals strained at compression was studied.
Abstract: The temperature interval ΔTSE of superelasticity in [001]-, [\( \bar 1 \)23]-, and [\( \bar 1 \)24]-oriented Co40Ni21Ga30 (at. %) single crystals strained at compression has been studied. It is established that ΔTSE in the [001]-oriented single crystal amounts to 441 K and the reversible B2-L10 martensite transformations in loaded samples take place at T2 = 698 K. In [\( \bar 1 \)23]- and [\( \bar 1 \)24]-oriented samples, ΔTSE decreases to 233 K and the superelasticity is observed up to T2 = 523 K.
TL;DR: In this paper, a hierarchical scheme for evaluating the defectness of the LSMO material is proposed, which is based on the results of measurements of the minimum dc conductivity (σdc(T)) and the range of its variation with the temperature.
Abstract: We have studied the dynamics of the transport and optical characteristics of epitaxial La0.7Sr0.3MnO3 − δ (LSMO) films with oxygen deficiency varied in the course of a multistage annealing. A hierarchical scheme for evaluating the defectness of the film material is proposed, which is based on the results of measurements of the minimum dc conductivity (σdc(T)) and the range of its variation with the temperature. It is established that the optical conductivity (σopt) at a radiation quantum energy of 2 eV corresponds to the limiting value of minimum σdc(T) in LSMO films without oxygen deficiency. This result does not contradict previously reported optical data and is consistent with the existing notions about the mechanisms of conductivity operative in the system under consideration.