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951.
We present a numerical algorithm designed to study the evolution of a distribution of solid particles orbiting around the Sun that could be applied to similar systems in which f c ≤ Ω/2π, where f c is the frequency of collisions, and Ω is the orbital angular speed. A number of sample particles are used to represent the whole system. Binary collisions are treated in a novel way using a Monte Carlo method that works as follows. Orbits are locally sampled to compute the velocity dispersion. Then the velocity vectors of the sample particles are modified according to random collisions with virtual particles which have velocities taken from a normal distribution computed using the previously found local velocity dispersion. The energy and momentum taken up by the virtual particles are redistributed among the neighbours of the sample particle undergoing the collision, so that conservation laws are satisfied. Simulations using this model give an estimation of the final distribution of inclinations and the associated evolutionary time-scale. 相似文献
952.
The deep oil exploration drillings in Denmark have shown that especially the Danish Embayment contains low enthalpy geothermal resources associated with warm aquifers. The most promising reservoirs have been found in highly permeable Upper Triassic sand and sandstone beds, which cover at least 5000 km2 at depths of 2000–3000 m and at temperatures of 60–100°C. The porosity of the main reservoir is of 15–25%, and the permeability is presumed to be approximately 1 darcy (10–12 m2) or higher. A layer thickness of 30–60 m has been observed on a number of localities. Also the Middle Jurassic and the Lower Triassic contain reservoirs of interest. A major geothermal exploration work is planned with seismic investigations, drillings to depths of 2000–4000 m and probably establishment of pilot district heating plants. 相似文献
953.
The observed relationship between atmospheric vorticity variations and solar magnetic sector boundary passages is examined for a possible connection via ionization changes affecting ozone distributions. A superposed epoch analysis was performed on Umkehr distributions for 18 years from Arosa, Switzerland, with use of more than 500 solar sector boundary passages as keyday zero. No significant responses are observed in any Umkehr level or in total observed ozone amounts. Further analyses on shorter records for Belsk, Poland, and Hohenpeissenberg, West Germany, corroborate these results. Another analysis for Arosa with about 100 type IV solar flares as keyday zero also shows no definitive trend. It is concluded that ozone distribution changes cannot be the primary causative mechanism for vorticity variations.Journal Paper No. J-8838 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 1852. 相似文献
954.
Stream channel development in forested areas is profoundly influenced by large organic debris (logs, limbs and rootwads greater than 10 cm in diameter) in the channels. In low gradient meandering streams large organic debris enters the channel through bank erosion, mass wasting, blowdown, and collapse of trees due to ice loading. In small streams large organic debris may locally influence channel morphology and sediment transport processes because the stream may not have the competency to redistribute the debris. In larger streams flowing water may move large organic debris, concentrating it into distinct accumulations (debris jams). Organic debris may greatly affect channel form and process by: increasing or decreasing stability of stream banks; influencing development of midchannel bars and short braided reaches; and facilitating, with other favourable circumstances, development of meander cutoffs. In steep gradient mountain streams organic debris may enter the channel by all the processes mentioned for low gradient streams. In addition, considerable debris may also enter the channel by way of debris avalanches or debris torrents. In small to intermediate size mountain streams with steep valley walls and little or no floodplain or flat valley floor, the effects of large organic debris on the fluvial processes and channel form may be very significant. Debris jams may locally accelerate or retard channel bed and bank erosion and/or deposition; create sites for significant sediment storage; and produce a stepped channel profile, herein referred to as ‘organic stepping’, which provides for variable channel morphology and flow conditions. The effect of live or dead trees anchored by rootwads into the stream bank may not only greatly retard bank erosion but also influence channel width and the development of small scour holes along the channel beneath tree roots. Once trees fall into the stream, their influence on the channel form and process may be quite different than when they were defending the banks, and, depending on the size of the debris, size of the stream, and many other factors, their effects range from insignificant to very important. 相似文献
955.
The importance of energetic particle precipitation on the chemical composition of the middle atmosphere 总被引:1,自引:0,他引:1
Richard Mansergh Thorne 《Pure and Applied Geophysics》1980,118(1):128-151
An assessment is made of the relative contribution of certain classes of energetic particle precipitation to the chemical composition of the middle atmosphere with emphasis placed on the production of odd nitrogen and odd hydrogen species and their subsequent role in the catalytic removal of ozone. Galactic cosmic radiation is an important source of odd nitrogen in the lower stratosphere but since the peak energy deposition occurs below the region where catalytic removal of O3 is most effective, it is questionable whether this mechanism is important in the overall terrestrial ozone budget. The precipitation of energetic solar protons can periodically produce dramatic enhancement in upper stratospheric NO. The long residence time of NO in this region of the atmosphere, where catalytic interaction with O3 is also most effective, mandates that this mechanism be included in future modelling of the global distribution of O3. Throughout the mesosphere the precipitation of energetic electrons from the outer radiation belt (60°70°) can sporadically act as a major local source of odd hydrogen and odd nitrogen leading to observable O3 depletion. Future satellite studies should be directed at simultaneously measuring the precipitation flux and the concomitant atmosphere modification, and these results should be employed to develop more sophisticated models of this important coupling. 相似文献
956.
G. P. Ayers N. Fukuzaki R. W. Gillett P. W. Selleck J. C. Powell H. Hara 《Journal of Atmospheric Chemistry》1998,30(2):301-310
Rainwater samples (wet-only; event samples) collected in Niigata in late autumn 1996 and springtime 1997 were used to assess the effectiveness of thymol as a biocide in Japanese rainwater. Upon collection each rainwater sample was divided into sub-samples, with thymol added to one sub-sample. Sub-samples with and without thymol were shipped to CSIRO, Australia, for chemical analysis. Comparison of analytical results for each pair of sub-samples proved the effectiveness of thymol in preventing biological action in this region where effects of rainwater microflaura and fauna on rainwater composition have not before been studied. Sub-samples without thymol exhibited lowered electrical conductivity, loss of the cations H+ and NH
4
-
, and loss of the anions HCOO-, CH3COO-, C2O
4
2-
, CH3SO
3
-
and PO
4
3-
. Nitrate showed no change in all but one of the samples, indicating that ammonia was the preferred source of nitrogen for the biological processes that consumed the rainwater organic acids and phosphate. These results suggest that thymol is a suitable rainwater biocide for use under Japanese conditions. 相似文献
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