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  • 1990-1994  (57)
  • 1975-1979  (48)
  • 1965-1969  (26)
  • 1
    Digitale Medien
    Digitale Medien
    A model of beam–plasma discharge in a nonuniform plasma (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3562-3568 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper presents a model of beam–plasma discharge resulting from the quasilinear heating of plasma electrons by Langmuir waves which are excited by beam–plasma interactions. The heating is made possible by the spectral transformation of waves propagating radially from the central beam-occupied region toward the region of lower plasma density. In this paper equations describing the wave spectral density, the distribution function of a high-energy electron tail, and its stationary density profile are obtained and numerically solved; to do so a balanced diffusion and ionization is assumed. The possibility of significant plasma density enhancement in beam–plasma discharge is demonstrated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.860363
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  • 2
    Digitale Medien
    Digitale Medien
    Wave collapse at the lower-hybrid resonance (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3148-3162 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The modulational instability and collapse of waves in the vicinity of the lower-hybrid resonance including both magnetosonic and lower-hybrid waves are investigated by analytical and numerical methods. The mechanism leading to the modulational instability is the nonlinear coupling of lower-hybrid waves with the much lower-frequency quasineutral density perturbations via the ponderomotive force. The result is a filamentation of the high-frequency field producing elongated, cigar-shaped nonlinear wave packets aligned along the magnetic field with the plasma expelled outside (cavities). The analytical self-similar solutions describing cavity collapse are obtained and compared with the results of numerical simulation for both two- and three-dimensional cavity geometries. It is shown that in three-dimensional solutions the transverse, with respect to the magnetic field, contraction remains prevailing. The possibility of ion acceleration as the result of the lower-hybrid collapse is discussed and detailed comparison is made with the observations of the phenomena in the auroral ionosphere.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.860652
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  • 3
    Digitale Medien
    Digitale Medien
    Theory of wave activity occurring in the AMPTE artificial comet (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1728-1738 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: One of the main experiments of the Active Magnetospheric Particle Tracer Explorers (AMPTE) [J. Geophys. Res. 91, 10013 (1986)] satellite mission was the release of neutral barium atoms in the solar wind. The barium atoms ionized by photoionization extremely rapidly forming a dense, expanding, plasma cloud that interrupted the solar wind flow creating diamagnetic cavities. On the upstream side of the cavity a region of compressed plasma and enhanced magnetic field was created as the result of being produced by the slowing down and deflection of the solar wind, and magnetic field line draping. Intense electrostatic and magnetic turbulence was observed by both the IRM [J. Geophys. Res. 91, 10 013 (1986)] and UKS [J. Geophys. Res. 91, 1320 (1986)] satellites at the boundary of the diamagnetic cavity, with the most intense waves being detected near the outer boundary of the compressed region. This paper examines how the newly created expanding plasma couples to the solar wind by means of plasma–beam and current-driven instabilities. In particular, it is shown how lower-hybrid and lower-hybrid drift waves are generated by cross-field proton–barium streaming instabilities and cross-field electron currents. The saturation mechanism for these waves is considered to be the modulational instability, this instability can also lead to filamentation and coupling to magnetosonic modes, which are also observed. As the result of modulational instability the k(parallel) component increases, which allows the heating and acceleration of electrons that is consistent with the observations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.859984
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  • 4
    Digitale Medien
    Digitale Medien
    Reply to "Comment on ‘Peeling of convection cells and the generation of sheared flow' [Phys. Fluids B 4, 488 (1992)]'' (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 658-658 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The comments of Montgomery and Matthaeus on the authors' paper1, have been answered. The results do not contradict those of Montgomery and Matthaeus but for simple case considered, transition to shear flow state and shape of initial vortices is explained. (AIP)
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.860501
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  • 5
    Digitale Medien
    Digitale Medien
    Peeling of convection cells and the generation of sheared flow (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 488-491 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A periodic array of convection cells is subject to a "shear flow'' instability. The generation of the sheared flow is a consequence of "peeling'' of the convection cells. Fluid simulations demonstrate that the efficiency of shear flow generation is high. Implications for understanding poloidal rotation in tokamaks are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.860246
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  • 6
    Digitale Medien
    Digitale Medien
    The solar wind interaction with comet P/Grigg-Skjellerup (1993)
    Springer
    Earth, moon and planets 60 (1993), S. 31-40 
    Details
    ISSN: 1573-0794
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract The Giotto spacecraft is scheduled to intercept comet P/Grigg-Skjellerup on July 10, 1992. The observed outgassing rate of this comet is over an order of magnitude smaller than comet Giacobini-Zinner and over two orders of magnitude smaller than that of comet Halley. Consequently, the new data obtained during the upcoming encounter will strengthen our understanding of how the solar wind interaction with comets depends upon the neutral gas production rate. In this brief note, we make predictions of the location of the flow transition regions — i.e., the bow shock and the ionopause, and discuss the expected level of wave turbulence.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00612178
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  • 7
    Digitale Medien
    Digitale Medien
    Comparison of the biological activity of fusicoccin in higher plants with its binding to plasma membranes (1991)
    Springer
    Planta 183 (1991), S. 315-320 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Fusicoccin (activity, binding) ; Plasmalemma (fusicoccin binding) ; Protoplast (fusicoccin binding) ; Vicia (fusicoccin binding) ; Zea (fusicoccin binding)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The concentration dependences of the binding of fusicoccins (FCs) A, B, C, D, J and H to plasma membranes isolated from maize (Zea mays L.) roots have been studied in parallel with the effects of these compounds on elongation and 86Rb transport in detached maize roots. The dissociation constants obtained showed a good correlation between the affinity of the FCs for the plasmalemma and their biological activity. However, the range of physiologically active FC concentrations proved to be about two orders of magnitude higher than that calculated from the dissociation constants. It was also shown that Vicia faba L. mesophyll protoplasts, unlike isolated plasma membranes, have two FC-binding sites, one with a K D similar to that of the isolated plasmalemma while the other has a substantially higher K D , apparently corresponding to the physiologically active state of the FC-binding proteins.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00197727
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  • 8
    Digitale Medien
    Digitale Medien
    Astroorientation inLethrus (Coleoptera, Scarabaeidae) (1977)
    Springer
    Journal of comparative physiology 121 (1977), S. 253-271 
    Details
    ISSN: 1432-1351
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary 1. Providing the nest with vegetable food,Lethrus performs repeated excursions of about l m from the hole and returns home. 2. Homing by the straight line,Lethrus walks in compass direction toward the nest; the distance traveled is equal to the estimated distance to the hole, and in a case of faultLethrus begins the circling search.Lethrus is able to integrate over the complex path. 3. Lethrus sets direction relative to celestial cues: the sun and the polarized skylight. 4. Lethrus has two photoreceptor systems: the green-sensitive and UV-sensitive one; only an ultraviolet polarization pattern is used for polarotaxis. 5. The eye ofLethrus evolved from the superpositional prototype; it is adapted to diurnal vision by shortening of the clear zone and by thickening of the light-guiding tracts from the cone to the rhabdom. 6. Lethrus is different from other Lamellicorns possessing a typical multilobed rhabdom in thatLethrus has a crustacean-type rhabdom. It is assumed that this specialization of rhabdom provides the perfect analysis of polarized light and polarotaxis. 7. The complex orientational and nest behavior ofLethrus is not accompanied by enlargement of the brain and its presumed associative centres, the mushroom bodies. Among several scarabaeid beetles of comparable size (Amphimallon solstitialis, Geotrupes stercorosus)Lethrus apterus gains the first place in behavioral complexity but the last in number of sensilla on the antennal dumb, number of ommatidia, and the volume of mushroom globuli.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00609615
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  • 9
    Digitale Medien
    Digitale Medien
    Periodic phenomena in Ae / Be Herbig stars light curves (1993)
    Springer
    Astrophysics and space science 202 (1993), S. 121-136 
    Details
    ISSN: 1572-946X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Light curves of 78 Herbig Ae/Be stars were studied by digital analysis methods. Twenty-five thousand photoelectricUBVR observations of these stars were made by the authors in 1978–1990. A star was usually observed once a night. The stars were observed between 70 and 770 nights and on average each star was observed at more than 300 nights. The mean epoch for a star is 5 years. A morphologic classification of the light curves is suggested. The method of digital analysis are briefly described. To estimate the reliability of cyclic phenomena discovered in our study, a large number of them has been examined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00626922
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  • 10
    Digitale Medien
    Digitale Medien
    Periodic phenomena in Ae / Be Herbig stars light curves (1993)
    Springer
    Astrophysics and space science 202 (1993), S. 137-154 
    Details
    ISSN: 1572-946X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The results of Herbig Be-star periodicity search are discussed. The cyclic phenomena can be roughly divided into the following three types: P0 - long-term periodic variability with periods of more than one year and amplitudes of 0 . m 4-4 . m 0V. The following stars show this type of variability (PO in years are presented in parenthesis): VX Cas (4.46), UX Ori (3.70), BF Ori (6.3), VV Ser (2.87), V517 Cyg (8.9-9.6), V373 Cep (7.7), and the others. P1 - middle-scale quasi-cyclic variability with periods of 10-100 days and amplitudes of 0 . m 05-0 . m 5V. Twenty-three stars show this type of cyclicity. 7 stars are suspected to have this type of variability. P2 - short-periodic and quasi-cyclic variability with amplitudes of 0 . m 05-0 . m 5V and periods of less than 10 days. In some cases the periodicity correlates with variations in strong emission line profiles. As an example, the properties of AB Aur are discussed. A total of 14 objects are suspected to have short-periodic quasi-cyclicity. Four of them show a high probability of periods (0.85 〈 II 〈 0.99). The discovered cyclic phenomena are interpreted in terms of Keplerian rotation of various structures in accretion disks and formations. The hypothesis of giant protocomets is suggested to explain the periods P0. Short-period cyclicity is associated with the changing of hot compact shell shapes modulated by rotation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00626923
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