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181.
182.
In this paper we apply the Wiener-Hopf technique combined with the method of the Laplace transform, to derive an exact solution of the transport equation for neutron diffusion in an isotropically scattering plane-parallel medium of finite thickness in which are situated a plane source at the middle and a uniformly distributed point source, there being flux of beams normally incident from outside on the two extreme parallel surfaces of the medium. 相似文献
183.
The ability to deduce exhumation mechanisms from thermochronological data is hampered by the fact that assumptions on the thermal state of the lithosphere have to be made. Additional argumentation is generally required to discriminate between erosion-controlled and tectonically induced exhumation. This problem can be overcome by studying the spatial distribution of zircon and apatite (U-Th)/He and fission track data. In this work the variation of four different low temperature isotopic systems generating age trends along a sampling line is used to infer mechanisms of Quaternary exhumation in the Central High Himalayan Metamorphic Belt. Observed zircon age trends with southwards increasing cooling ages (from 0.5 to 1.7 Ma) are attributed to tectonically induced exhumation. The uniform apatite cooling ages clustered c. 0.5 Ma are attributed to erosion. 相似文献
184.
S. K. Gupta P. V. Ramana Murthy S. C. Tonwar P. R. Vishwanath 《Astrophysics and Space Science》1985,115(1):163-183
Detection of cosmic sources of very high energy gamma rays based on the atmospheric Cerenkov technique is discussed. Very high energy gamma-rays initiate, on entering the terrestrial atmosphere, electron-photon cascade showers with in turn produce Cerenkov photons in the air. Parabolic reflectors are used to focus these photons onto fast photomultipliers. Two methods of deployment of parabolic reflectors are in vogue: one in which all the reflectors are located close to each other in a compact array and the other in which the reflectors are spread out farther apart forming a distributed array. In the latter mode, the arrival direction of individual showers can be determined accurately by using the measured relative arrival times between different detectors. Detailed studies with the distributed array helped us to understand the various parameters in the two designs and evaluate their relative merits in reaching the ultimate goals of lowering the energy threshold and improving the signal to background ratio for the detection of gamma-ray sources. It is found that the relative superiority among the two types of arrays is a function of the exponent assumed for the differential power law energy spectrum for the gamma ray source. It is also seen that with the type of reflectors commonly used in atmospheric Cerenkov work, lower energy thresholds can be achieved with use of larger aperture. 相似文献
185.
Spectrophotometric observations of Cornet Hartley-Good (19851) during five nights in 1985 are presented in the wavelength range 3200–7000 ». The emission bands due to CN, CH, C2, and C3 molecules are observed. The abundances (N) and production rates (Q) of the molecules are derived. 相似文献
186.
Landslide Lake Outburst Floods (LLOFs) are common in the Himalayan river basins. These are caused by breaching of lakes created
by landslides. The active and palaeo-landslide mapping along the Satluj and Spiti Rivers indicate that these rivers were blocked
and breached at many places during the Quaternary period. In the present article, we document LLOFs during 2000 and 2005 caused
by the breaching of landslide lakes created in the Trans-Himalayan region along the Satluj River and Paree Chu (stream), respectively,
both in the Tibetan region of China and its impact on the channel and infrastructure in the Kinnaur district of Himachal Pradesh,
India. It has been observed that the loss of life and property due to these LLOFs is directly related to the disposition of
the Quaternary materials and the different morphological zones observed in the area. 相似文献
187.
188.
In order to consider the effect of anisotropy on the periods of the oscillations of the Earth, the problem of toroidal oscillations
of a transradially isotropic elastic sphere is considered. At each point, the medium is assumed to be transversely isotropic
about the radius through the point. The roots of the frequency equation are obtained for different values of the anisotropy
parameter α. It is found that, for large order oscillations, the percentage change in the frequency of the toroidal oscillations
on account of the anisotropy is nearly equal to |α-1| × 100. 相似文献
189.
The nepheline-diopside join defines the ultra-alkaline portion of the basalt tetrahedron and the bulk composition of nephelinitic
rocks lie in this join. Schairer and others established that under atmospheric pressure, the join cuts through the primary
phase volumes of oliviness, carnegieitess and nepheliness. Melilite coexists with nepheliness, oliviness and diopsidess below 1160±10°C and olivine reacts out at low temperature.
Experimental studies on seven compositions show the presence of a pseudoeutectic at Ne70Di30 and 1420°C, where diopsidess, nepheliness and liquid are in equilibrium. Olivine and melilite do not appear in the system and the assemblage below 1225±20°C is diopsidess+nepheliness. 相似文献
190.
While evaluating the chromospheric variability (solar cycle related or any other) using the Ca II K line (3933.684 Å) as an indicator, an essential prerequisite is the knowledge of the profile of a truly quiet Sun in the integrated light. Such a profile can serve as a bench mark over which enhancements can be measured, particularly when modelling variability. This paper describes how such a K-line profile has been derived for the quiet Sun using disc-integrated light. 相似文献