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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 844-852 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coalescence of two parallel current loops in an electron–positron plasma is investigated by a three-dimensional electromagnetic relativistic particle code. Instead of mixing uniformly in the dissipation region as observed for current coalescence in an electron–ion plasma, electrons and positrons initially in the loops are driven to move separately by the magnetic gradient drift. Redistribution of the current-carrying electrons and positrons creates new current loops, which coalesce again, if the initial drift velocities remain greater than a critical value after coalescence. It was found that the energy stored in the current loops dissipates gradually through several coalescences. Consequently, the electrons and positrons near the current loops are heated through the coalescence. This process is qualitatively different from the explosive energy release during coalescence in an electron–ion plasma. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3501-3508 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Excitation of large-amplitude Alfvén waves in an anisotropic electron–positron plasma is investigated with a two-and-one-half-dimensional (2〈fraction SHAPE="CASE"〉12-D), electromagnetic particle code. If the plasma distribution is a bi-Maxwellian with T⊥/T(parallel)〉1, where the subscript symbols denote directions perpendicular and parallel to the ambient magnetic field, Alfvén waves with arbitrary polarization are generated. Simulations show that the amplitude of the waves increases both with increasing temperature anisotropy and parallel plasma β(parallel). The stabilization of individual wave modes occurs sequentially, from higher values of wave number down to lower ones, in the evolution of the temperature anisotropy instability. Wave–particle scattering by the enhanced waves maintains the initially bi-Maxwellian character throughout the simulation, even as it reduces T⊥ and increases T(parallel). After saturation of wave magnetic energy a large residual temperature anisotropy still remains and persists through the end of the simulation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3906-3911 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results from a three-dimensional electromagnetic and relativistic particle simulation of a relativistic electron-positron plasma cloud (Lorentz factor γ=5/3) moving perpendicular to an ambient magnetic field with background plasmas are presented. It is shown that, in addition to the charge sheaths created at both sides of the cloud, secondary charge structures are created in the central region of the cloud and many cloud particles expand along the magnetic field. The Alfvén waves with large amplitude (δB/B0≈0.03) and linear polarization are excited dominantly with wave number kzc/Ωc〈1, while the electromagnetic waves are weakly excited because of the relativistic effect of the cloud particles. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1452-1455 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Donor-assisted resonant tunneling in nominally symmetric GaAs/(AlGa)As large area double-barrier diodes is investigated. The log(I)–V characteristics are used to evaluate doping density in the quantum well and are investigated in connection with donor cluster-assisted resonant tunneling. The single-donor-related feature in the resonant-tunneling characteristics is used to detect the presence of donors in the quantum well, even at concentrations of the order of the lowest achieved so far in molecular beam epitaxy GaAs. Expected effects of the presence of donors in the quantum well on the log(I) vs V characteristics are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 178 (1998), S. 43-53 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigate plasma heating associated with the effect of recombination and the filamentation instability of Alfvén waves propagating along homogeneous magnetic field in low-beta plasmas, by using an MHD simulation code. The linear instability of Alfvén waves leading to the filamentation is investigated by imposing small density perturbations across a magnetic field. We show results of the nonlinear stage of the above filamentation instability and the plasma heating through a two-dimensional simulation. It is shown that the plasma heating is caused by localized heating and whole heating, which are associated with the filamentation instability and the effect of recombination, respectively. We discuss the implication of these results for plasma heating processes observed in the chromosphere of the Sun.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary. The complete nucleotide sequence of a sweet potato feathery mottle virus severe strain (SPFMV-S) genomic RNA was determined from overlapping cDNA clones and by directly sequencing viral RNA. The viral RNA genome is 10 820 nucleotides long, excluding the poly(A) tail and contains one open reading frame (ORF) starting at nucleotide 118 and ending at 10 599, potentially encoding a polyprotein of 3 493 amino acids (Mr 393 800). The ORF was followed by a 3 untranslated region of 221 nucleotides. The deduced polyprotein includes P1 (74K), HC-Pro (52K), P3 (46K), 6K1, CI (72K), 6K2, NIa-VPg (22K), NIa-Pro (28K), NIb (60K) and coat (35K) proteins, after an analysis of protein cleavage sites analogous to other potyvirus polyproteins. The polyprotein had a high level of amino acid identity with those of other potyviruses, except in the regions of P1 and P3. The P1 of SPFMV-S RNA has 664 amino acid residues, and is the largest and least similar to those of other potyviruses. HC-Pro and CI show high identity with those of other potyviruses. P3 has relatively low identity, however, the length of P3 was within the range of variability among other potyviruses. The 6K1 protein between P3 and C1 is also highly similar to those of other potyviruses. This is the first report on the complete nucleotide sequence of the sweet potato-infecting virus.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Recombinant DNA molecules containing cDNA of a sweet potato feathery mottle virus severe strain (SPFMV-S) RNA genome were constructed and the partial nucleotide sequences were determined for three DNA inserts, which cover 4.2 kb from the 3′-terminus excluding the poly (A) tail. This region of the genome consists of an open reading frame of 1340 amino acids (a.a.) and a 3′-non-translated region of 224 nucleotides. The protein products expected were 6K2 (53 a.a.) NIa, (435 a.a.), NIb (521 a.a) and CP (315 a.a.). Among NIa, NIb and coat proteins, the NIb protein was found to be the most conserved (59–68%) when compared to the corresponding proteins of other distinct potyviruses.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Shock waves 9 (1999), S. 423-427 
    ISSN: 1432-2153
    Keywords: Key words:Galilean transformation, Shock-capturing scheme, Artificial wind
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract. We introduce and apply a new way for the construction of efficient non-oscillatory shock-capturing schemes for fluid dynamic and magneto-hydro-dynamic simulations. The basic idea is to solve the governing equations in different steadily moving frames of reference chosen in such a way that the flow would be supersonic there resulting in simple upwind formulas for fluxes across control volume faces. An extra velocity (artificial wind) is added to the velocity of the flow under simulation when the system of coordinates is changed. The approach allows to simplify existing schemes and to get new modifications. Test problems demonstrate that the derived schemes provide accurate results while being simple and efficient.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 246 (1996), S. 107-118 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider that single loop flares can be caused by the rotation of loop footpoints. Choosing a typical geometry for this case we find from MHD equations self-consistent expressions and a set equations governing behaviour of all physical quantities. Numerical simulations have revealed that under the determined conditions for the initial azimuthal velocity and current the pinch instability takes place. The most important parameters of the problem are the plasma β and the ratio of the initial values of longitudinal and poloidal components of the magnetic field-B 1. Thus, calculations show that the critical pinch time increases with the increase ofB 1 and decreases with the increase of plasma β. So the most effective flares are probable for the most high loops with strong currents. ForB 1=10 and β=0.01 the critical pinch time is ≈2.5 s. The critical twist angle for magnetic field depends on the initial one. For low intial twist which corresponds to bigB 1 the critical one is more less. For exampleB 1=30 gives Φ≈1.8π (when ratio of loop length and radius is 10). Geometrical analysis shows that the present model can explain (for high photospheric rotation) single loop flares taking place on different parts of the loop as on the top of it as closer to one of the footpoints. It depends on the relative rotation momentum of loop footpoints. Subject headings: MHD-Sun:flares.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Graefe's archive for clinical and experimental ophthalmology 237 (1999), S. 928-933 
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract   · Background: Onset of experimental autoimmune uveoretinitis (EAU) is believed to involve a CD4-positive type 1 T helper cell (Th1) immune response, with inhibition involving a Th2 immune response. Development of Th1 and Th2 responses involves the participation of the costimulatory molecules B7-1 and B7-2, respectively. The purpose of this study was to investigate the role of B7-1 and B7-2 in the EAU model in mice. · Methods: B10.A mice were immunized with interphotoreceptor retinoid-binding protein (IRBP) and given daily intraperitoneal injections of either phosphate-buffered saline (control), mouse monoclonal antibody (mAb) to B7-1, mAb to B7-2, or mAb to both B7-1 and B7-2. Eyes were evaluated by histopathological criteria and cytokines were assayed in culture medium of IRBP-stimulated lymphocytes. Cellular immune responses were measured by cell proliferation assay under IRBP stimulation.  · Results: Rates of EAU onset were 5/10 (50%) for control mice, 1/9 (11%) for mice treated with anti-B7-1 mAb, 5/6 (83%) for mice treated with anti-B7-2 mAb, and 2/6 (33%) for mice treated with both anti-B7-1 and anti-B7-2 mAb. Mean histopathological severity scores were 2.4±0.8, 1.0±0, 2.6±1.0, and 1.0±0, respectively. Production of IL-5 was significantly increased in mice treated with anti-B7-1 mAb, while IFN-γ was increased in mice treated with anti-B7-2 mAb. Spleen cell proliferation was significantly reduced in mice treated with anti-B7-1 mAb.  · Conclusions: These results suggest that the costimulatory molecules B7-1 and B7-2, via their influence on generating Th1 and Th2 immune responses, play an important role in the clinical outcome of EAU in mice immunized with IRBP.
    Type of Medium: Electronic Resource
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