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201.
Main problems of water use and transfer of technology 总被引:2,自引:0,他引:2
M. Falkenmark 《GeoJournal》1979,3(5):435-443
Man and water are closely related in a dualistic manner: on one hand water has great influence on man's welfare and social development, on the other man's activities greatly affect water as such. Comparing the present and future water needs with water availability, the author concludes that some world regions should be considered as truly water scarce at least during the next generation. Man's activities create water problems which tend to change with time and exhibit a regional pattern. Many problems can be avoided if advance impact studies were made more regularly for planned water-related activities and projects. The author ends by stressing that differences in climate, hydrology, culture and dominating water problems tend to complicate the important process of transfer of knowledge between temperate and tropical countries. 相似文献
202.
203.
E. A. Kolotilov I. Mikolajewska P. M. Marrese U. Munari S. Yu. Shugarov B. F. Yudin 《Astronomy Letters》2001,27(1):51-57
We present our UBVRI photometry and spectroscopy of AS 338 performed in 1999–2000. Another eclipse of the hot component in this symbiotic binary system, the deepest one ever observed, occurred in September 1999. The U brightness declined by ~2m, the Hβflux decreased by a factor of ~2.3, and the [O III]γ5007 flux did not change. The hot component is eclipsed at orbital phases ?≈0.045–0.057. The U-B color index begins to appreciably fluctuate during an eclipse of the hot component and its circumstellar envelope. About 100 days after a strong outburst of 1995, the mean UBV brightness of AS 338 declined linearly in the ensuing five years at the same rate in all bands (ΔU/Δt≈10?3 mag/day). The brightness of the outer, uneclipsed parts of the circumstellar envelope also decreased, which is attributable to a reduction in the luminosity of the hot component against the rise in its temperature. The appearance of He II lines has not yet been recorded, though the optical brightness of AS 338 has already dropped by ~2m after the outburst. 相似文献
204.
C. M. Giordano A. R. Plastino A. Plastino 《Celestial Mechanics and Dynamical Astronomy》1996,66(2):229-242
Robe's restricted three-body problem is investigated with regards to the effects of a linear drag force. In particular. the stability of the model's equilibrium points is studied in this respect. Two scenarios are envisaged: the one originally discussed by Robe himself and the one suggested by him and recently analyzed by the present authors, that assumes for the fluid body the structure of a Roche's ellipsoid. 相似文献
205.
The spectrum of a magnetic or a gravity anomaly due to a body of a given shape with either homogeneous magnetization or uniform density distribution can be expressed as a product of the Fourier transforms of the source geometry and the Green's function. The transform of the source geometry for any irregularly-shaped body can be accurately determined by representing the body as closely as possible by a number of prismatic bodies. The Green's function is not dependent upon the source geometry. So the analytical expression for its transform remains the same for all causative bodies. It is, therefore, not difficult to obtain the spectrum of an anomaly by multiplying the transform of the source geometry by that of the Green's function. Then the inverse of this spectrum, which yields the anomaly in the space domain, is calculated by using the Fast Fourier Transform algorithm. Many examples show the reliability and accuracy of the method for calculating potential field anomalies. 相似文献
206.
Summary Sets of virtual poles corresponding to sets of geomagnetic field values at equidistant points, lying along circles of latitude, were defined on the basis of the 1980 IGRF extending to degree and order 8. Certain places on the Earth's surface yield virtual poles lying very close together. The segments of the virtual pole paths, corresponding to these places, have a large curvature. The mentioned places of the Earth's surface are supposed to be areas with a low rate of the westward drift. They form continuous zones that show a certain relation to global-tectonics features.
uum ¶rt; 8- n¶rt;a ¶rt;a¶rt; aaumu n 1980 u u nmu uma n, mmmu nm uu n ma, a u¶rt;umam ¶rt; naa m ma nmu nua¶rt;am uma n, m uu ¶rt; ¶rt;. amu u, mmmu mu ma, um uu. ¶rt;naam, m nm ma nmu m amu, m m ana¶rt; ¶rt;a ua. u am n na, m naam a m uua mmuu.相似文献
207.
C.M. Wai 《Geochimica et cosmochimica acta》1974,38(12):1821-1825
Hydrothermal studies indicate that Co and Ge are strongly siderophile when metallic iron is in equilibrium with olivine at 900°C and 500 bars. If the metal is replaced by troilite (FeS), Ge is strongly lithophile whereas Co tends to concentrate in the sulfide phase. If iron meteorites were formed in a core derived from the sulfide phase, they would be depleted in Ge but retain Co. 相似文献
208.
209.
Summary The paper presents comprehensive theory based on the boundary integral method for calculations of the electric potential,
electric field and corresponding magnetic field due to a pair of D.C. source electrodes near a vertical resistivity contact
in the halfspace, indlucing a 3-D disturbing body in the vicinity of the contact. Special attention is paid to the case when
the disturbing body touches the vertical contact. Results of numerical calculations are presented in the form of sounding
curves and a set of isoline graphs for potential, components of the electric and magnetic field (total and anomalous) on the
surface of the Earth. It is shown that the presence of the disturbing body at the contact is most pronounced in the electrical
characteristics. Anomalies in the magnetic field are small in comparison to the field due to the electric current in the electrode
cable and primary currents flowing from the electrodes. 相似文献
210.
Pickering & Hiscott, (1985) have demonstrated amply the presence of reverse-flow units within the thick-bedded calcareous wacke (TCW) beds of the turbiditic Cloridorme Formation (Middle Ordovician, Gaspé Peninsula, Quebec, Canada). These reverse-flow units are underlain and overlain by units which reveal flow in the primary (obverse) direction. In this paper, a model is proposed for this reverse flow, based on the probable nature of the primary turbidity flow. It appears that the initial flow was highly elongated (thickness h? length L), with h~ 500 m, velocity U~ 2 m s-1 and sediment concentration C~ 1·25%o. The rate of momentum loss of the flow is estimated by means of a useful parameter which we call the ‘drag distance’, symbol dD, defined by where h and L are the thickness and length of the flow, respectively; cCd is a combined drag coefficient representing friction on the bottom and at the upper interface; and fCd is a form-drag coefficient related to the shape and size of the head. dD is the distance travelled by a current of constant h and L, flowing over a horizontal bottom and obeying a quadratic friction law, for an e-fold reduction in velocity. Simple considerations, confirmed by our own experiments (described in this paper), show that such an elongated turbidity current cannot be reflected as a whole from an adverse slope: when the nose of the current reaches the slope, it forms a hump, which surges backwards and sooner or later breaks up into a series of internal solitons. The latter, probably numbering 4–7, will cause reverse flow at a given point as they pass by, provided that the residual velocity in the tail is not too great. Flow in the original (obverse) direction will be re-established after the passage of the solitons. Quiescent periods in front of, between and behind the solitons, when soliton-associated currents cancelled out the residual obverse flow, would allow the deposition of thin mud-drapes. Additional flow reversals observed in a few of the TCW beds cannot be explained readily by the re-passage of solitons, since wave breaking at the ends of the basin would cause massive energy loss; internal seiches are the preferred explanation for these later reversals. 相似文献