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971.
Summary A geometrically simple volcano is considered, havig a spherical magma chamber of 2.5 km radius centred at 10 km depth. The Curie point isotherm is assumed to be a plane at 20 km depth, except for the spherical volume which is also non-magnetic. The stress pattern in the vicinity of the spherical chamber, due to regional stress of sufficient intensity to cause an eruptions, is used to calculate the change in magnetization which results from the piezomagnetic effect through the volume of solid rock. The consequent magnetic field anomaly at the surface is then obtaied by numerical integration of the dipole law of force over the stressed volume. For rocks of the type found on the volcanic island of St. Vincent (West Indies), this model gives a maximum local volcano-magnet c effect of about 7 gammas. 相似文献
972.
Summary The present note, as its title implies, is concerned with the investigation of disturbances in an infinite elastic medium containing an initial magnetic field in the axial direction. The equations ofMaxwell, those of elasticity have been effectively made use of to solve the problem. 相似文献
973.
Gully erosion has for many years been a problem in Rhodesia1s Tribal Trust Lands. This paper describes how Soil Conservation Service staff, with no previous ground knowledge of these areas, used good quality 1/25,000 scale aerial photographs to measure the extent of the gully erosion and to pinpoint erosion “black spots.” This enabled quick and reliable estimates of the cost of reclamation work to be made without the need for time-consuming field survey. The survey method discussed is capable of wide application wherever gully erosion occurs and needs to be brought under control. 相似文献
974.
The long-wave outgoing radiation, effective cloudiness equal to the product of the total cloud amount by their optical density,
and the sea-surface temperature determined from the satellites are used to determine the annual course of the components of
external heat balance on the sea surface whose climatic anomalies, parallel with the meridional heat and water transfer in
the ocean-atmosphere system, specify the intraannual and interannual large-scale variations of weather in different regions
of the Earth. The development of these studies is connected with the progress of satellite hydrophysics because the data obtained
from the space become sufficiently exact, regular, and global. The increase in the existing data array on the external heat
balance of the oceans from ∼15–20 to 100 yr and more would promote the solution of the problem of oscillations of Earth's
climate. We present examples of coordinated numerical analysis of the heat balance of the upper (0–100 m ) layer of the Black
Sea performed on the basis of the shipborne and satellite data.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 59–75, November–December, 2007. 相似文献
975.
Isotopic variation of fishes in freshwater and estuarine zones of a large subtropical coastal lagoon
A.M. Garcia D.J. Hoeinghaus J.P. Vieira K.O. Winemiller 《Estuarine, Coastal and Shelf Science》2007,73(3-4):399-408
We used stable C and N isotope ratios of tissues from 29 fish species from a large subtropical lagoon in southern Brazil to examine spatial variability in isotopic composition and vertical trophic structure across freshwater and estuarine habitats. Nitrogen isotope ratios indicated a smooth gradation in trophic positions among species, with most fishes occupying the secondary and tertiary consumer level. Fish assemblages showed a significant shift in their carbon isotopic signatures between freshwater and estuarine sites. Depleted carbon signatures (from −24.7‰ to −17.8‰) were found in freshwater, whereas more enriched signatures (from −19.1‰ to −12.3‰) were obtained within the estuarine zone downstream. Based on our survey of the C3 and C4 plants and isotopic values for phytoplankton and benthic microalgae reported for ecosystems elsewhere, we hypothesized that the observed δ13C differences in the fish assemblage between freshwater and estuarine sites is due to a shift from assimilating organic matter ultimately derived from C3 freshwater marsh vegetation and phytoplankton at the freshwater site (δ13C ranging from −25‰ to −19‰), to C4 salt-marsh (e.g. Spartina) and widgeon grass (Ruppia maritima), benthic microalgae and marine phytoplankton at the estuarine sites (from −18‰ to −12‰). Our results suggested that fish assemblages are generally supported by autochthonous primary production. Freshwater fishes that likely were displaced downstream into the estuary during periods of high freshwater discharge had depleted δ13C values that were characteristic of the upper lagoon. These results suggest that spatial foodweb subsidies can occur within the lagoon. 相似文献
976.
The hydroelastic responses of a very-long floating structure (VLFS) placed behind a reverse T-shape freely floating breakwater with a built-in oscillating water column (OWC) chamber are analyzed in two dimensions. The Bernoulli–Euler beam equation is coupled with the equations of rigid and elastic motions of the breakwater and the VLFS. The interaction of waves between the floating rigid breakwater and the elastic VLFS is formulated in a consistent manner. It has been shown numerically that the structural deflections of the VLFS can be reduced significantly by a suitably designed reverse T-shape floating breakwater. 相似文献
977.
978.
The motion and the drift force of a floating OWC (oscillating water column) wave energy device in regular waves are studied taking account of the oscillating surface-pressure due to the pressure drop across the duct of the air chamber. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine-type Green function while the outer problem with the Kelvin-type Green function. The added mass, wave damping and excitation coefficients as well as the motion and drift force of the OWC device are calculated for various values of parameter related to the pressure drop. 相似文献
979.
Numerical simulation of undersea cable dynamics 总被引:7,自引:0,他引:7
A fully three-dimensional code has been written to compute the motion of a towed cable. The code is based on a robust and stable finite difference approximation to the differential equations derived from basic dynamics. A 3500-ft (1.07 km) cable pulled at 18.5 knots (34.3 km hr−1) through a circular turn of 700 yd (0.64 km) radius has been computed in about half of the real time of the maneuver. The computed displacements are close to the measured ones; the changes in depth are within 2%. 相似文献
980.
E.R. Jefferys 《Applied Ocean Research》1983,5(3):145-149
The solution to the problem of calculating the hydrodynamic forces on multiple floating bodies is summarised. The complex coefficients which characterise the forces at each frequency of oscillation are expensive to compute; interpolation of intermediate values and extrapolation to high frequencies appear difficult since the coefficients seem to vary arbitrarily with frequency. Interpolation and extrapolation schemes based on a novel representation of the coefficients are proposed and tested. The excellent numerical results indicate that the values of the coefficients at a few frequency points can characterise the hydrodynamics at all frequencies. These techniques can save economically significant amounts of computer time and permit investigations which would otherwise be prohibitively expensive. 相似文献