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  • 11
    ISSN: 1090-6487
    Keywords: 52.25.Wz ; 52.30.−q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An analytical solution of the Vlasov equation for the electrons and the hydrodynamic equations for the ions in a self-consistent electric field is constructed in the quasineutral approximation. This solution is valid for a finite electron-to-ion mass ratio. It permits describing the expansion into vacuum of a collisionless plasma with cold ions and arbitrary initial electron velocity distribution, forming a plasmoid that is bounded and, in the general case, spherically asymmetric in space.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Technical physics letters 25 (1999), S. 374-376 
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The suppression of large-scale vortex formations under gas-saturation conditions is detected on the basis of measurements of the pulsation component of the surface friction when an axisymmetric hot jet of a fluid impinges on an obstacle. The conditions for the resonant enhancement of coherent structures and the suppression of broad-band turbulence are determined for single-phase and gas-saturated impact jets. The evolution of various pulsation components in the gradient region of an impact jet is analyzed.
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  • 13
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Lasing is discovered in the direction perpendicular to the surface in quantum-size InGaN/GaN multilayer heterostructures grown by vapor-phase epitaxy. At high excitation densities one of the modes in the luminescence spectrum, which is modulated by modes of the Fabry-Pérot cavity formed by the GaN/air and GaN/sapphire-substrate interfaces, is sharply amplified and begins to dominate the spectrum. The dependence of the luminescence intensity on pump density has a clearly expressed threshold character. The threshold excitation density in the vertical direction is 5–6 times greater than the stimulated-emission threshold for observation from an end surface of the structure. The gain coefficient in the active region at the threshold for surface-emitting lasing is estimated as 2×105 cm−1. The interaction between the cavity modes and the gain spectrum is detected in the form of displacement (by up to 2.6 nm) of modes on the short-wavelength edge of the luminescence spectrum toward higher photon nergies. The characteristic temperature (T 0) measured in the range from 16 to 120 K is 480 K. At higher temperatures T 0 K.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Technical physics letters 23 (1997), S. 758-759 
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is made of the so-called dynamic state of a metastable substance, characterized by the onset of a nonequilibrium energy interaction (interchange), involving various waves, in the excited material. The intensity of the optical emission is used to analyze the dynamic state; an investigation is made of the propagation of its leading and trailing edges. Various propagation characteristics and natural solitary-wave forms are identified; their similarity to ionization waves allows making some assumptions about the essential nature of this process. The observed effects are important for establishing the physical conditions for the formation of the substance of ball lightning and are also interesting for the physics of flames, electrical breakdown, and electrode spots.
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  • 15
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Results of observations of the anomalous transmission of x-rays in tungsten single crystals are presented. The dislocation density (2–4)×105 cm−2 was determined from an analysis of the dynamic diffraction characteristics.
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  • 16
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: It is known that an increase in plasma density in sources of multicharged ions leads to a substantial increase of ion current and slightly improves the ion distribution over charge states. The validity of this statement was verified in experiments with plasma densities not exceeding several units of 1012 cm−3. In the present work it is demonstrated experimentally that, for the electron densities exceeding 1013 cm−3, the regime of plasma confinement in a trap changes significantly and the quasigasdynamic regime of plasma confinement is realized. Comparison of numerical simulations and experimental data showed the essential influence of the anisotropy of electron velocity distribution in a plasma on the ion charge state distribution. This allows looking for the optimal conditions for the creation of highly charged ions in plasma. In this article we also address problems of plasma stability in an axisymmetric mirror trap under powerful microwave pumping. First experiments on ion extraction from a dense plasma pumped by millimeter wave radiation are described. © 2000 American Institute of Physics.
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  • 17
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using Mössbauer spectroscopy and the magneto-optical Kerr effect, we investigate how magnetic order arises and develops in Fe/C and Fe/Cr layered mixtures prepared by pulsed laser deposition. Two different magnetic transformations are found to occur in these systems under their thermal annealing. The first is the paramagnetic–ferromagnetic crossover that takes place at annealing temperatures of 420–570 K in dependence on the average iron content. Varying the latter quantity, we also observed the same crossover to the ferromagnetic state. The second transformation is magnetic hardening at 700–800 K. The specific feature of both transformations is that they occur within narrow ranges of annealing temperature (〈10 K). The first transformation is supposed to result from an additional iron enrichment of Fe-rich clusters and is associated with magnetic phase transition near the Curie temperature. The cluster enrichment was directly observed with transmission electron microscopy and was also shown in small angle x-ray scattering patterns of the compositionally modulated structures. The observed sharpening of the magnetic behavior near the Curie temperature is presumably a manifestation of the clustered structure. The second transformation is found to be induced by the onset of crystallization and the formation of particles of the new Fe-rich phase. © 1996 American Institute of Physics.
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  • 18
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3844-3846 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new kind of large dispersion lower order blaze grating spectrometer is built. The design is based on the use of uncustomary large angles of incidence and diffraction approaching 80°. The double diffraction optical scheme is employed to fit the design conception. A set of compact size grating spectrometers of various focal lengths and grating ruled widths has been manufactured and explored. The measured grating efficiency related to different blaze angles shows the evidence for the instrument gainful operation. The spectrometer imaging properties are much promising to enable a fine spectral resolution to 0.005 nm under a short focal length ∼100 mm. The estimation of flux luminosity is made in comparison with Fabry–Perot interferometer. © 1999 American Institute of Physics.
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  • 19
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 635-637 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: One of the major trends in the development of ECR sources of multicharged ions is an increase of the extracted ion current. The main factor affecting the current of an ion beam produced by such a source is, obviously, the density of the plasma from which ions are extracted. In the present article the mean ion charge, the ion current density, and the minimal microwave power required to sustain needed electron temperature are calculated for a broad range of plasma densities (up to 1014 cm−3, which corresponds to 90 GHz cutoff frequency of microwave pumping). The electron temperature is taken as granted and no effects due to instabilities are considered. The distinguishing future of the analysis performed is that it takes into account alteration of the regime of plasma confinement, which occurs as the plasma density is increased. If the plasma density exceeds a certain threshold, the classical Pastukhov's regime of plasma confinement is replaced by the quasi-gas-dynamic regime. It is demonstrated, in particular, that within the framework of a common approach it's possible to analyze qualitatively conventional ECR sources with pumping frequencies up to 18 GHz as well as experiments where microwave radiation with the frequency of 37.5 GHz was used. © 2002 American Institute of Physics.
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  • 20
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2122-2128 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamical behavior of a balance sampling gate, consisting of two directly serially connected Josephson junctions and a common shunt resistor, has been investigated by numerical simulations and approximated equations of the resistive shunted junction model. A reduced damping parameter has been found which determines the sampler behavior alone and enables an optimization. A 2.4-ps rise time of the response to a step-function signal predicted by the approximated theory has been verified by numerical simulations. The sampling gate can be driven directly by a room-temperature generator with a rise time of a few hundred picoseconds.
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