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981.
In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky.This characteristic of compressional surface MHD waves is inherent for the spectrum ω = (k6k)VA(k26 + 2k2)12, obtained by Nenovski (1978) in the cold plasma limit VA ? VS(VA is Alfvén velocity, and VS, sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed.  相似文献   
982.
We propose a zero-point photometric calibration of the data from the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) on board the Hubble Space Telescope , based on a spectrum of Vega and the most up-to-date in-flight transmission curves of the camera. This calibration is accurate at the level of a few hundredths of a magnitude. The main purpose of this effort is to transform the entire set of evolutionary models into a simple observational photometric system for ACS/WFC data, and to make them available to the astronomical community. We provide the zero-points for the most used ACS/WFC bands, and give basic recipes for calibrating both the observed data and the models. We also present the colour–magnitude diagram from ACS data of five Galactic globular clusters, spanning the metallicity range  −2.2 <[Fe/H] < −0.04  , and we provide fiducial points representing their sequences from several magnitudes below the turn-off to the red giant branch tip. The observed sequences are compared with the models in the newly defined photometric system.  相似文献   
983.
984.
Uranium was measured by fission track analysis in meteoritic troilite and graphite. The distribution is extremely heterogeneous, with a few high-U grains dominating the total abundances. U/He ages cannot be estimated from such a distribution pattern, and therefore previously reported excessive ages are not valid.  相似文献   
985.
An estimate for the anisotropy of the turbulent viscositys is given in a convective layer heated from below and rotating around a vertical axis. In the case of two-dimensional convection, there is a stationary regime withs⊇2 regardless of the rotation. In the case of three-dimensional convection in a slowly rotating layer (with the Taylor number equal to 1600), nonstationary turbulent regimes take place withs⊇1.6 forR=2.5×104 (R is the Rayleigh number) ands⊇1.2 forR=104. The parameters plays an, important role in the theory of differential rotation of the convective solar or stellar envelopes. So far, it has been evaluated empirically or semi-empirically. Some prospects in the development of the theory of differential rotation are discussed here in terms of the moment theory of hydrodynamic fields. The relation between this strict approach and an anisotropic viscosity approximation is considered.  相似文献   
986.
987.
988.
Vertical measurements of NH4+, NO3? and N2O concentrations, NO3? and NH4+ uptake, and NH4+ oxidation rates were measured at 5 sites in western Cook Strait, New Zealand, between 31 March and 3 April 1983. Nitrate increased with depth at all stations reaching a maximum of 10.5 μg-atom NO3?N l?1 at the most strongly stratified station whereas NH4+ was relatively constant with depth at all stations (~0.1 μg-atom NH4+N l?1). The highest rates of NH4+ oxidation generally occurred in the near surface waters and decreased with depth. N2O levels were near saturation with respect to the air above the sea surface and showed no obvious changes during 24 h incubation. NH4+ oxidation by nitrifying bacteria may account for about 30% of the total NH4+ utilization (i.e. bacterial+agal) and, assuming oxidation through to NO3?, may supply about 40% of the algal requirements of NO3? in the study area. These results suggest that bacterial nitrification is of potential importance to the nitrogen dynamics of the western Cook Strait, particularly with respect to the nitrogen demands of the phytoplankton.  相似文献   
989.
990.
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