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101.
Skylab EUV observations of an active region near the solar limb were analyzed. Both cool (T < 106 K) and hot (T > 106 K) loops were observed in this region. For the hot loops the observed intensity variations were small, typically a few percent over a period of 30 min. The cool loops exhibited stronger variations, sometimes appearing and disappearing in 5 to 10 min. Most of the cool material observed in the loops appeared to be caused by the downward flow of coronal rain and by the upward ejection of chromospheric material in surges. The frequent EUV brightenings observed near the loop footpoints appear to have been produced by both in situ transient energy releases (e.g. subflares) and the infall/impact of coronal rain. The physical conditions in the loops (temperatures, densities, radiative and conducting cooling rates, cooling times) were determined. The mean energy required to balance the radiative and conductive cooling of the hot loops is approximately 3 × 10–3 erg cm–3 s–1. One coronal heating mechanism that can account for the observed behavior of the EUV emission from McMath region 12634 is heating by the dissipation of fast mode MHD waves. 相似文献
102.
Magnetic stratigraphy observed in ferromanganese crust 总被引:1,自引:0,他引:1
Summary. A sample of ferromanganese crust deposit (SCHW-1D) was cut into two sets of 1 mm slices for palaeomagnetic study. Alternating field and thermal demagnetization, and isothermal remanent magnetization analyses were performed on each thin slice. The results reveal the presence of a stable magnetism and both normal and reversed polarity intervals in the specimens. The observed polarity intervals cannot be confidently correlated with the geomagnetic polarity time-scale of the last 10 Myr due to the polarity overlap inherent in the sampling technique. But the results confirm the slow accretion rate of ferromanganese deposit determined by 10 Be method and suggest potential use of ferromanganese deposits in palaeomagnetic and tectonic studies. 相似文献
103.
Summary. Exact spherical harmonic expansions are given for calculating the gravitational and magnetic fields associated with certain uniform solids of revolution. The figures are those made by rotating a conic section about one of its principal axes. The coefficients in the expansions can be computed accurately and efficiently and this approach leads to a very satisfactory method for calculating the fields of geological bodies with approximate circular symmetry about a vertical axis. A complete theory of convergence is given for the expansions. Somewhat unexpectedly, the sphere of convergence is determined by the location of a number of equivalent point or line sources that lie within the body or on its edges. 相似文献
104.
105.
106.
Report of the International Astronomical Union Division I Working Group on Precession and the Ecliptic 总被引:1,自引:0,他引:1
J. L. Hilton N. Capitaine J. Chapront J. M. Ferrandiz A. Fienga T. Fukushima J. Getino P. Mathews J.-L. Simon M. Soffel J. Vondrak P. Wallace J. Williams 《Celestial Mechanics and Dynamical Astronomy》2006,94(3):351-367
The IAU Working Group on Precession and the Equinox looked at several solutions for replacing the precession part of the IAU
2000A precession–nutation model, which is not consistent with dynamical theory. These comparisons show that the (Capitaine
et al., Astron. Astrophys., 412, 2003a) precession theory, P03, is both consistent with dynamical theory and the solution most compatible with the IAU 2000A
nutation model. Thus, the working group recommends the adoption of the P03 precession theory for use with the IAU 2000A nutation.
The two greatest sources of uncertainty in the precession theory are the rate of change of the Earth’s dynamical flattening,
ΔJ2, and the precession rates (i.e. the constants of integration used in deriving the precession). The combined uncertainties
limit the accuracy in the precession theory to approximately 2 mas cent−2.
Given that there are difficulties with the traditional angles used to parameterize the precession, zA, ζA, and θA, the working group has decided that the choice of parameters should be left to the user. We provide a consistent set of parameters
that may be used with either the traditional rotation matrix, or those rotation matrices described in (Capitaine et al., Astron.
Astrophys., 412, 2003a) and (Fukushima Astron. J., 126, 2003).
We recommend that the ecliptic pole be explicitly defined by the mean orbital angular momentum vector of the Earth–Moon barycenter
in the Barycentric Celestial Reference System (BCRS), and explicitly state that this definition is being used to avoid confusion
with previous definitions of the ecliptic.
Finally, we recommend that the terms precession of the equator and precession of the ecliptic replace the terms lunisolar precession and planetary precession, respectively. 相似文献
107.
Diurnal variation of the dayside, ionospheric, mid-latitude trough in the southern hemisphere at 800 km: Model and measurement comparison 总被引:1,自引:0,他引:1
J.J. Sojka W.J. Raitt R.W. Schunk J.L. Parish F.J. Rich 《Planetary and Space Science》1985,33(12):1375-1382
Our high latitude ionospheric model predicts the existence of a pronounced “dayside” trough in plasma concentration equatorward of the auroral oval in both the Northern and Southern Hemispheres for solar maximum, winter, and low geomagnetic activity conditions. The trough in the Southern Hemisphere is much deeper than that in the Northern Hemisphere, with the minimum trough density at 800 km being 2 × 103 cm−3 in the Southern Hemisphere and 104 cm−3 in the Northern Hemisphere. The dayside trough has a strong longitudinal (diurnal) dependence and appears between 11:00 and 19:00 U.T. in the Southern Hemisphere and between 02:00 and 08:00 U.T. in the Northern Hemisphere. This dayside trough is a result of the auroral oval moving to larger solar zenith angles at those universal times when the magnetic pole is on the antisunward side of the geographic pole. As the auroral ionization source moves to higher geographic latitudes, it leaves a region of declining photoionization on the dayside. For low convection speeds, the ionosphere decays and a dayside trough forms. The trough is deeper in the Southern Hemisphere than in the Northern Hemisphere because of the greater offset between the geomagnetic and geographic poles. Satellite data taken in both the Northern and Southern Hemispheres confirm the gross features of the dayside trough, including its strong longitudinal dependence, its depth, and the asymmetry between the Northern and Southern Hemisphere troughs. 相似文献
108.
The paper considers the random phase errors in the phase shifters which are used in an antenna array to steer the beam in the look direction, and analyzes the effect of these errors on the performance of the optimal processor which maximizes the output SNR by deriving the expressions for the output signal power, residual interference power, output SNR, and the array gain as a function of the variance of these errors. The paper also considers the phase quantization error which arises in the digital phase shifters and shows how the performance of the optimal processor depends on the number of bits of the digital phase shifters. 相似文献
109.
The present work applies the method of characteristics to study the behaviour of planar and cylindrical wave-heads propagating through a perfectly electrically conducting and thermally radiating inviscid gas under the optically thin limit in the presence of a transverse magnetic field. The true nonlinear progress of the flow variable gradients at the wavefront is predicted and the critical distance at which the characteristics pile up at the wavefront to form a shock wave is obtained. It is investigated as to how the effects of radiative flux, the magnetic field strength and the specific heat ratio influence the process of steepening or flattening of the characteristic wavefront. 相似文献
110.
The paper models the suprathermal plasma as the concatenation of two different gravitating fluids each having its own separate density and pressure. One of the fluids has isotropic pressure while the other has an anisotropic pressure. The system is subjected to a uniform magnetic field which is frozen with the fluids. The gravitational instability of the model for low frequency plane waves has been investigated in a linear framework for plasma parameters relevant to the spiral arms of the galaxy and the cosmic gas clouds. The analysis shows that the wavelength of the instability is strongly dependent upon the anisotropy of the non-thermal plasma. 相似文献