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  • 1
    Electronic Resource
    Electronic Resource
    Large-scale numerical simulations of ion beam instabilities in unmagnetized astrophysical plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 5171-5181 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Collisionless quasiperpendicular shocks with magnetoacoustic Mach numbers exceeding a certain threshold are known to reflect a fraction of the upstream ion population. These reflected ions drive instabilities which, in a magnetized plasma, can give rise to electron acceleration. In the case of shocks associated with supernova remnants (SNRs), electrons energized in this way may provide a seed population for subsequent acceleration to highly relativistic energies. If the plasma is weakly magnetized, in the sense that the electron cyclotron frequency is much smaller than the electron plasma frequency ωp, a Buneman instability occurs at ωp. The nonlinear evolution of this instability is examined using particle-in-cell simulations, with initial parameters which are representative of SNR shocks. For simplicity, the magnetic field is taken to be strictly zero. It is shown that the instability saturates as a result of electrons being trapped by the wave potential. Subsequent evolution of the waves depends on the temperature of the background protons Ti and the size of the simulation box L. If Ti is comparable to the initial electron temperature Te, and L is equal to one Buneman wavelength λ0, the wave partially collapses into low frequency waves and backscattered waves at around ωp. If, on the other hand, Ti(very-much-greater-than)Te and L=λ0, two high frequency waves remain in the plasma. One of these waves, excited at a frequency slightly lower than ωp, may be a Bernstein–Greene–Kruskal mode. The other wave, excited at a frequency well above ωp, is driven by the relative streaming of trapped and untrapped electrons. In a simulation with L=4λ0, the Buneman wave collapses on a time scale consistent with the excitation of sideband instabilities. Highly energetic electrons were not observed in any of these simulations, suggesting that the Buneman instability can only produce strong electron acceleration in a magnetized plasma. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319640
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  • 2
    Electronic Resource
    Electronic Resource
    The energy injection into waves with a zero group velocity (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2681-2692 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The frequency maxima of electron cyclotron harmonic (ECH) waves provide strong responses to sounding in various plasma regimes in the solar system. The frequency maxima correspond to waves for which the group velocity and thus the energy propagation velocity in the plasma frame of reference is zero. A particle-in-cell (PIC) code is employed to show that the propagation of wave energy at a non-zero velocity, necessary to couple energy from a stationary antenna to the plasma, is accomplished by propagating wave precursors. The undamped waves at the frequency maxima of the ECH branches are nonpropagating hence the waves remain localized. It is demonstrated that the nonpropagating waves, built up by the wave precursors, are standing waves. The standing wave generation is followed from the linear to nonlinear regimes. For nonlinear emission amplitudes the emission causes a plasma density depletion close to the antenna. The depletion is shown to trigger a modulational instability in which the ECH wave collapses. The generated nonlinear standing wave also develops an electromagnetic component which couples the electrostatic ECH waves to the fast extraordinary wave. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873223
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  • 3
    Electronic Resource
    Electronic Resource
    Competition between RNA polymerase and DNA polymerase for the DNA template
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 18 (1965), S. 932-942 
    Details
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0006-291X(65)90870-3
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  • 4
    Electronic Resource
    Electronic Resource
    Impaired T- and B-cell functions in patients with Hodgkin's disease (1987)
    Springer
    Cancer immunology immunotherapy 25 (1987), S. 59-64 
    Details
    ISSN: 1432-0851
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The mitogenic response of T-cell subsets, the production of interleukin-1 (Il-1) and interleukin-2 (Il-2) and in vitro immunoglobulin production was investigated in patients with Hodgkin's disease (HD). The mitogenic response of mononuclear cells (MNC) and the OKT4+ and OKT8+ subsets was greatly reduced in advanced disease stages and could only partially be restored with exogeneous Il-2. In untreated patients with HD — except those with highly advanced disease — the OKT4+ lymphocytes showed normal response to phytohemagglutinin in contrast to the MNC suggesting inhibiting agents or cells within the MNC. These findings corresponded to reduced Il-2 synthesis of MNC, whereas isolated OKT4+ — cells produced normal or elevated amounts of Il-2. MNC or monocytes produced normal or even higher amounts of lipopolysaccharide-induced Il-1 than controls. The results do not confirm a defect in this component of the interleukin system in HD. The immunological impairment was not limited to the T-cell system but involved B-cell activation and differentiation as well. The pokeweed mitogen-induced IgM, IgG and IgG production was highly suppressed in untreated HD, whereas the MNC of previously treated patients produced subnormal amounts of immunoglobulin in vitro. It is not yet clear whether this defect is T-cell-mediated or primarily a B-cell deficiency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199302
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  • 5
    Electronic Resource
    Electronic Resource
    Potassium photoionization laser produced by innershell ionization of excited potassium
    Amsterdam : Elsevier
    Optics Communications 66 (1988), S. 107-110 
    Details
    ISSN: 0030-4018
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0030-4018(88)90043-0
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  • 6
    Electronic Resource
    Electronic Resource
    Thermal conductivity of e-beam coatings (2000)
    Springer
    Applied physics 71 (2000), S. 71-76 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 60; 70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. We present the results of the study on the thermal conductivity of different thin film materials produced by conventional thermal evaporation. The main features of the thermal pulse method employed for the measurement of the thermal conductivity are described. Thermal conductivity can be measured by determining the traveling time of a thermal wave propagating trough the film. A pump laser beam is directed onto a sample consisting of a thin transparent test layer and a totally absorbing substrate for the laser wavelength. As a consequence of the laser pulse, a temperature profile builds up at the substrate–film interface. A thermal pulse starts to diffuse from the substrate–film interface to the surface of the layer. Therefore, the temperature rise at the surface of the test layer starts with a time delay with respect to the laser pulse. The time delay depends on the propagation time of the thermal wave through the layer and is related to the thermal conductivity and the thickness of the layer. Measurements are evaluated by calculations based on the finite difference method. The results show that the analyzed thin films have lower thermal conductivity than the corresponding materials in bulk form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003390050028
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  • 7
    Electronic Resource
    Electronic Resource
    The application of a shift theorem analysis technique to multipoint measurements (1999)
    Springer
    Annales geophysicae 17 (1999), S. 321-327 
    Details
    ISSN: 0992-7689
    Keywords: Electromagnetics (wave propagation) ; Radio science (waves in plasma) ; Space plasma physics (active perturbation experiments)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A Fourier domain technique has been proposed previously which, in principle, quantifies the extent to which multipoint in-situ measurements can identify whether or not an observed structure is time stationary in its rest frame. Once a structure, sampled for example by four spacecraft, is shown to be quasi-stationary in its rest frame, the structure’s velocity vector can be determined with respect to the sampling spacecraft. We investigate the properties of this technique, which we will refer to as a stationarity test, by applying it to two point measurements of a simulated boundary layer. The boundary layer was evolved using a PIC (particle in cell) electromagnetic code. Initial and boundary conditions were chosen such, that two cases could be considered, i.e. a spacecraft pair moving through (1) a time stationary boundary structure and (2) a boundary structure which is evolving (expanding) in time. The code also introduces noise in the simulated data time series which is uncorrelated between the two spacecraft. We demonstrate that, provided that the time series is Hanning windowed, the test is effective in determining the relative velocity between the boundary layer and spacecraft and in determining the range of frequencies over which the data can be treated as time stationary or time evolving. This work presents a first step towards understanding the effectiveness of this technique, as required in order for it to be applied to multispacecraft data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-0321-0
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