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961.
We report on a year's study of spatial and seasonal patterns of zooplankton abundance in Port Phillip and Westernport Bays, July 1982 to August 1983. These two bays, closely adjacent on the southern coast of Victoria, Australia, differ in several respects: Port Phillip is a nearly landlocked bay with a broad basin, while Westernport is an open tidal embayment with extensive mud and seagrass banks. Both bays have a resident zooplankton fauna distinct from that of Bass Strait. Although these resident communities have many species in common, patterns of abundance and dominance are quite different. We found that the holoplankton of Port Phillip was about half copepods, mostly Paracalanus indicus, with 23% Caldocera and 21% larvaceans. Westernport Bay zooplankton was dominated by Acartia tranteri, with no resident cladoceran fauna. Bass Strait species were more often found in Westernport than in Port Phillip Bay, but the resident community of Port Phillip Bay was more similar to that of Bass Strait than to that of Westernport.Although this study was undertaken in an exceptionally dry year, the available historical data show that the overall patterns found in 1982–1983 are typical for these bays. The differences in community composition probably relate to differences in depth profile, predator abundance, and suspended matter between the bays. 相似文献
962.
The problem of collapse of a dust ball has been studied in detail from the point of view of an external observer (O). It is seen that although there is no material pressure from the point of view of the comoving observer, there is a non-vanishing material pressure in the ball from the point of view of O. In the early stages of collapse (w.r.t. O), this pressure is positive everywhere inside the ball, while during the later stages, if one goes outwards from the centre towards the surface of the ball, this pressure is negative up to a certain value of the radial coordinate, and then changes its sign thereafter. On the basis of this pressure, one can understand the physics of the whole scenario of collapse w.r.t. O; in particular, the important feature is that in the ultimate stages an event horizon is formed asymptotically and there is no collapse to a point (as takes place from the point of view of the comoving observer). 相似文献
963.
Al. A. Suchkov 《Astrophysics》1985,23(1):452-458
964.
An analysis previously developed for rough surface scattering with narrow-beam reception is extended to wide-beam or omnidirectional reception. The source is considered to be a pulsed electric dipole. The analysis includes multipathing effects on the received signal. The results are used to develop a model for the backscattered radar cross section of the ocean surface, up to a second-order approximation. 相似文献
965.
The Zürich sunspot relative number R
z
series has been analysed by the cyclogram method. The amplitude and the frequency variations of the Fourier 11 yr component between 1700–1983 A.D., were determined in a continuous way.Four distinct time intervals with significantly different characteristics of the periodicities are observed and discussed.Their second harmonics are also considered. The periodicity changes are contemporary to those of the 11 yr cycles.Around the year 1903 it seems that an important event has happened in the Sun. In fact the 11.4 yr cycle periodicity, that was very stable since at least 1825 started to change gradually to smaller values and similarly it happened to the second harmonic which also stopped and abruptly changed of phase of 90°. 相似文献
966.
967.
Summary. The elastodynamic fields of point forces and shear dislocations of finite source duration are analysed with the aim of establishing the frequency and time-domain characteristics of the field in the near-source region. Criteria are obtained for amplitude dominance in regions where the source–sensor distance is much smaller than the wavelength.
It is shown that in the frequency domain , the Green's tensor (and hence the displacement field of a single point force) attenuates like R−1 in the near-source region and there exists no region in which the 'near-field' term becomes dominant such that the 'far-field' term can be neglected. Hence, there is no real 'near-field' term for the elastodynamic Green's tensor. The near-field terms of the displacements, velocities and accelerations excited by a shear dislocation attenuate like R −2 , since the R −3 and R −4 terms tend to be eliminated due to mutual cancellation of P and S motions in the near-source region.
In the time domain , the corresponding near field of the displacement field is defined for the steady amplitude interval (away from transients) R /β < t < R /α+ T by the condition R ≤βT where β is the shear velocity and T is the source's duration. The relative strengths of all other arrivals will depend on the particular time window under consideration.
The particle motion patterns due to a single force in the near-source region are shown to be similar to rotating hyperbolas with an axis along the force direction, which are quite different from the 'smoke ring' motion patterns of the so-called 'near-field' term itself. 相似文献
It is shown that in the frequency domain , the Green's tensor (and hence the displacement field of a single point force) attenuates like R
In the time domain , the corresponding near field of the displacement field is defined for the steady amplitude interval (away from transients) R /β < t < R /α+ T by the condition R ≤βT where β is the shear velocity and T is the source's duration. The relative strengths of all other arrivals will depend on the particular time window under consideration.
The particle motion patterns due to a single force in the near-source region are shown to be similar to rotating hyperbolas with an axis along the force direction, which are quite different from the 'smoke ring' motion patterns of the so-called 'near-field' term itself. 相似文献
968.
S.I. Akasofu 《Planetary and Space Science》1985,33(1):81-87
We examine time variations of the total magnetospheric output UT and the two geomagnetic indices AE and Dst during the magnetospheric storm of 31 December 1967–1 January 1968. A unique feature of this particular storm is that the solar-wind magnetosphere dynamo power ε was nearly constant for about 24 h by maintaining a high value of ~1019 erg s?1. It is found that UT was also nearly constant during that period, indicating that the magnetosphere is primarily a directly driven system. However, during an early epoch of the storm, the electrojet intensity levelled off, while the ring current began to grow during the same epoch. Subsequently, there occurred a sudden surge of the electrojet intensity, while the growth of the ring-current levelled off. Later variations of both the AE and Dst indices were very complex. After the surge, the AE index continued to decline and became as low as ~250 nT during the maximum epoch of this major storm (when the Dst decrease attained the maximum values). This trend can also be seen in many other major storms, but is often masked by changes of ε. One possible cause for such features for ε ? 1019erg/s?1 is that the neutral wind is generated by the motion in the lower ionosphere, reducing the electrojet intensity and enhancing the ring-current particle-injection rate. 相似文献
969.
970.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献