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81.
82.
宁晰春 《地球科学与环境学报》1987,(1)
形成旋扭构造的动力可概括为五个方面:地块随着地球自转速率的变化,局部发生的旋扭;漂移在软流圈之上的地块遇到上拱的“热柱”受到局部牵制而旋扭;地幔熔融体物质对流循环产生蠕动式旋扭;岩石圈拖曳牵动引起旋扭;重力控制下密度分异所引起的水平漫流碰接于上升物质而旋转。欧亚大陆上分布着涡轮状、帚状、莲花状、连环状等各种旋扭构造。 相似文献
83.
84.
A sample of 51 separated binary systems with measured apsidal periods and rotational velocities of the components is examined. The ranges of the angles of inclination of the equatorial planes of the components to the orbital plane are estimated for these systems. The observed apsidal velocities can be explained by assuming that the axes of rotation of the stars are nonorthogonal to the orbital plane in roughly 47% of the systems (24 of the 51) and the rotation of the components is not synchronized with the orbital motion in roughly 59% of the systems (30 of 51). Nonorthogonality and nonsynchrony are defined as deviations from 90° and a synchronized angular velocity, respectively, at levels of 1 or more. 相似文献
85.
86.
Peter J. Huber 《Journal of Geodesy》2006,80(6):283-303
The stochastic behavior of the length of day (LOD) process is analyzed and is modeled within statistical accuracy on a time-scale ranging from weeks to millennia by a three-component model comprising a global Brownian motion process, decadal fluctuations, and a 50-day Madden–Julian oscillation. While the model is intended to be phenomenological, some possible physical models underlying the three components are speculated upon. The model is applied to estimate long-range extrapolation errors. For example, it predicts a standard error of 1 h in the clock-time correction ΔT for extrapolation by 1,500 years from 500 to 2000 BC. 相似文献
87.
H. Greiner-Mai J. Hagedoorn L. Ballani I. Wardinski D. Stromeyer R. Hengst 《Studia Geophysica et Geodaetica》2007,51(4):491-513
We investigate the temporal behaviour of the axial component of the electromagnetic core-mantle coupling torque that is associated
with the poloidal part of the geomagnetic field observable at the Earth surface. For its computation, we use different models
of the geomagnetic field, expanded into spherical harmonics (Wardinski and Holme, 2006; Sabaka et al., 2004), and the mantle
conductivity. The geomagnetic field, which we have to know at the core-mantle boundary for the associated computations, will
be inferred from the field at the Earth surface by the non-harmonic field continuation through a conducting mantle shell.
The aims of this investigation are (i) to check how sensitive is the computation of the torque with respect to the different
geomagnetic field models, (ii) to check its dependence on the spherical harmonic degree n, and (iii) to determine the difference
between the mechanical torque derived from the observed length-of-day variations (atmospheric influence subtracted) and the
poloidal electromagnetic torque in dependence on the assumed conductivity. To use the non-harmonic field continuation for
the torque calculation and to obtain an insight into the influence of the different geomagnetic field models on the EM torques
are the major aspects of this paper.
grm@gfz-potsdam.de 相似文献
88.
We use the rotation curves of 13 galaxies to test the nonsymmetric gravitaional theory (NGT). If we follow Moffat's assumption of a constant mass-to-light for all galaxies then we shall find that the two supposedly universal constants r0, L0 to show a large scatter. By regarding the mass-to-light ratio as a free parameter for each galaxy, and adjusting the values of r0, L0, we find that NGT can well account for the observed rotation curves. Further, the mass-to-light ratios so found show the well-known trend along the Hubble morphological sequence. 相似文献
89.
A 29-year time-series of four-times-daily atmospheric effective angular momentum (EAM) estimates is used to study the atmospheric
influence on nutation. The most important atmospheric contributions are found for the prograde annual (77 μas), retrograde
annual (53 as), prograde semiannual (45 as), and for the constant offset of the pole (δψsinɛ0=−86 as, δɛ=77 as). Among them only the prograde semiannual component is driven mostly by the wind term of the EAM function,
while in all other cases the pressure term is dominant. These are nonnegligible quantities which should be taken into account
in the new theory of nutation. Comparison with the VLBI corrections to the IAU 1980 nutation model taking into account the
ocean tide contribution yields good agreement for the prograde annual and semiannual nutations. We also investigated time
variability of the atmospheric contribution to the nutation amplitudes by performing the sliding-window least-squares analysis
of both the atmospheric excitation and VLBI nutation data. Almost all detected variations of atmospheric origin can be attributed
to the pressure term, the biggest being the in-phase annual prograde component (about 30 as) and the retrograde one (as much
as 100200 as). These variations, if physical, limit the precision of classical modeling of nutation to the level of 0.1 mas.
Comparison with the VLBI data shows significant correlation for the retrograde annual nutation after 1989, while for the prograde
annual term there is a high correlation in shape but the size of the atmospherically driven variations is about three times
less than deduced from the VLBI data. This discrepancy in size can be attributed either to inaccuracy of the theoretical transfer
function or the frequency-dependent ocean response to the pressure variations. Our comparison also yields a considerably better
agreement with the VLBI nutation data when using the EAM function without the IB correction for ocean response, which indicates
that this correction is not adequate for nearly diurnal variations.
Received: 10 September 1997 / Accepted: 5 March 1998 相似文献
90.
Raymond Hide 《Geophysical Journal International》1998,135(3):1150-1152
Several dynamic agencies control differential rotation between various regions of a rotating gravitating body such as a planet, namely advection of angular momentum (within fluid regions) and torques due not only to (a) viscous forces, (b) dynamic pressure forces and (c) gravitational forces, but also to (d) Lorentz forces (involving the flow of electric currents in electrically conducting regions), (e) magnetostatic forces (when magnetized material is present) and (f) electrostatic forces (due to the presence of electric charges). Torques due to (a), (b), (c) and (d) have already been treated in the literature, some extensively. It is of general theoretical interest to derive from first principles mathematical expressions for torques due to (e) and (f), even though they turn out to be quantitatively insignificant in the case of the Earth. 相似文献