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  • 1
    Electronic Resource
    Electronic Resource
    Calcium-regulated appressorium formation of the entomopathogenic fungusZoophthora radicans (1991)
    Springer
    Protoplasma 160 (1991), S. 77-88 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Calmodulin ; Appressorium formation ; Zoophthora radicans ; Entomopathogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The fungusZoophthora radicans (Zygomycetes: Entomophthorales) requires external Ca2+ for appressorium formation but not for conidial germination. The number of appressoria formed depends on the Ca2+ concentration of the medium. At low [Ca2+] (100 pM) nuclear division and germ tube growth are significantly reduced compared to higher Ca2+ concentrations (10 and 1,000 μM). By contrast, neither external K+ nor external Cl− is needed for germination or appressorium formation. Treatment of conidia with a Ca2+-antagonist, Nd3+, and a Ca2+-channel blocker, nifedipine, inhibits appressorium formation, showing that a Ca2+ influx is required for appressorium formation. Furthermore, the partial yet saturating inhibition by nifedipine and complete inhibition by Nd3+ indicates that at least two kinds of Ca2+ channels are involved in appressorium formation. A contribution of intracellular Ca2+ to the signal transduction chain for the formation of appressoria is demonstrated by the inhibitory effect of the intracellular Ca2+ antagonist TMB-8. The calmodulin antagonists R24571, TFP, W-7, and W-5 inhibit appressorium formation at concentrations which have no effect on germination. The data presented in this paper are consistent with the hypothesis that a Ca2+/calmodulin system is involved in regulating appressorium formation. However, since the direct effects of the drugs were not specifically tested on their proposed binding sites, we leave room for alternative hypotheses that have yet to be formulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01539959
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  • 2
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    Quasi-periodic transverse plasma flow associated with an evolving MHD vortex street in the outer heliosphere (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We study a transverse plasma flow induced by the evolution of a Karman vortex street using a Chebyshev-Fourier spectral algorithm to solve both the compressible Navier-Stokes and MHD equations. The evolving vortex street is formed by the nonlinear interaction of two vortex sheets initially in equilibrium. We study spatial profiles of the total plasma velocity, the density, the meridional flow angle and the location of sector boundaries and find generally good agreement with Voyager 2 measurements of quasi-periodic transverse flow in the outer heliosphere. The pressure pulses associated with the meridional flows in the simulation are too small, although they are correctly located, and this may be due to the lack of any 'warp' in the current sheet in this model. A strong, flow-aligned magnetic field, such as would occur in the inner heliosphere, is shown to lead to weak effects that would be masked by the background interplanetary turbulence. We also study the plasma and magnetic transport resulting from the meridional flow and find that deficits of magnetic quantities do occur near the ecliptic. While the effect is relatively small, it is in general agreement with the most recent analysis of 'flux deficit' in the outer heliosphere.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A8; p. 13,233-13,246.
    Format: text
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  • 3
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    The structure of helical interplanetary magnetic fields (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The interplanetary magnetic field is known to be highly helical. Although the detailed spatial structure of the fields has yet to be elucidated, the helicity spectrum has been conjectured to result from a random walk in the direction of a constant magnitude magnetic field vector. A model using three-dimensional fluctuations with variations in B is demonstrated giving a good fit to the helicity spectrum as well as to other properties of the interplanetary magnetic field.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 1505-150
    Format: text
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  • 4
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    A survey of the milliarcsecond polarization properties of BL Lacertae objects at 5 GHz (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Consideration is given to millarcsecond-resolution total-intensity and linear polarization maps at 5 GHz presented for 11 BL Lacertae objects. In every BL Lacertae object in which polarization structure was detected, the polarization position angle of the knots is nearly parallel to the VLBI structural axis. The direction of the polarization in the cores of these sources appears to be random. The preferred polarization direction in the jets is explained by the fact that plane perpendicular shock waves are common in these sources; the origin of the absence of the preferred polarization direction in the core components is unclear. These results support an early conclusion that it cannot be the case that a significant number of BL Lacertae objects are gravitationally microlensed images of more distant quasars, since the characteristic VLBI polarization structures observed in these two types of objects are very different.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 388; 40-54
    Format: text
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  • 5
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    Is 1308+326 A BL Lacertae object or a quasar? (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The active galaxy 1308+326 (z = 0.996) has been classified as a BL Lacertae object because of its nearly featureless optical continuum and high and variable polarization. New VLBI polarization images of 1308+326, however, show both VLBI polarization structure and tentative superluminal motions that are characteristic of quasars rather than BL Lacertae objects. These data strongly suggest that this source is simply a quasar with emission lines of small equivalent width. We discuss the possibility that the optical continuum is enhanced by microlensing in a foreground galaxy, as suggested by Stickel et al.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 410; 1; p. 39-43.
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  • 6
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    Radio constraints on the nature of BL Lacertae objects and their parent population (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: 5 GHz VLA observations of 17 BL Lac objects with bright radio cores at both high and low resolution are reported. Extended emission is detected around most objects. None of the sources observed at low resolution show evidence of giant halos on the scale of tens of arcmin. In general, the sources with the most luminous extended emission exhibit FR II characteristics in both morphology and polarization, and less luminous sources exhibit FR I characteristics. Thus, the parent population of the BL Lac objects contains both FR I and FR II radio sources. No BL Lac objects are found that clearly exhibit quasarlike polarization at milliarcsec resolution. This argues against the view that the more luminous BL Lac objects are simply an extension of the quasar/OVV population, or that most BL Lac objects are gravitationally microlensed images of distant quasars. Other properties are generally consistent with the view the BL Lac objects are normal radio galaxies whose jets make a small angle to the line of sight.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 104; 5; p. 1687-1705.
    Format: text
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  • 7
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    Physical consistency in modeling interplanetary magnetohydrodynamic fluctuations (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The validity of the Velli, Grappin and Mangeney (1989) model is evaluated. It is argued that the model is incorrect because it mixes different dynamical models, assumes weak nonlinearities, makes predictions that vary with observations, and violates causality. It is proposed that self-similar behavior in the coronal source region of the magnetohydrodynamic fluctuations cause the Kolmogorov-like spectra.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters (ISSN 0031-9007); 64; 2591; Au
    Format: text
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