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891.
王周琼 《中国科学D辑(英文版)》2002,45(Z1)
Only by providing the good conditions for the growth of plants can a favorable ecologicalenvironment on which human beings rely for existence be created. The upside-down-T dou-ble-layer water-conserving afforestation way is developed according to the situation of the short-age of water resources, low soil fertility and vast land in the arid areas. The characteristics of theafforestation way are to change the microenvironment in the root area of the plants, provide thefavorable conditions for the growth of plants, and reduce the necessary conditions for the growth ofplants in large areas in the arid regions. Meanwhile, the size of its water-conserving layer can bechanged according to the size of the planted trees. The different ways of the bottom wa-ter-conserving layer can be used according to the requirements. The afforestation way is suitablefor planting trees on a small scale and also for afforesting on a large scale under the adverse cir-cumstances in the arid areas, and has been effectively used in the afforestation in the hinterland ofTaklamakan Desert and the southern marginal zone of Gurbantonggut Desert. The prospects ofthe afforestation way are broad in afforestation and desertification control in the desert regions. 相似文献
892.
The salinized sandy lands are the important reclaimable reserve wastelands in thesouth area of the Xinjiang Uygur Autonomous Region of China. But it is necessary that the eco-logical environment of the area is not destroyed by action of oasis development. The main factor tohinder oasis development is land salinization. Rational oasis establishment rebuilds wastelandswith lower productivity and utilization efficiency for the growth of agriculture, forestry, and stock raising. The results of surveying sub-soil environment of Aimugaike. Awati oasis in Hotian County ofthe Xinjiang Uygur Autonomous Region show that the underground water and soil environment arenot deteriorated under the rational management and administration, which could be coordinatedfor obtaining economic and environmental benefit. During the oasis establishment period from1997 to 1999, the plowland area has reached 166.7 hm2, and the seed cotton yield per unit areahas reached 2250 kg @ hm-2, the area of timber forest and active sand break forest has reached 20hm2, the area of fruit trees is 71.5 hm2; and the soil moisture has decreased from 22.07% to18.12%. In the first year of oasis establishment, the soil type has changed salt soil into light saltsoil, in the second year the soil has been out of salt harm; and the content of soil organic matter intopsoil has increased obviously. 相似文献
893.
根据前文所述的测试结果 ,本文主要分析了隔震构造、橡胶支座水平刚度、地震输入频谱特性、地震烈度、输入方向、桥墩高度、桥墩嵌固程度等因素对隔震效果的影响 ,揭示了隔震体系耗散地震能量输入的机理 ,所得出的结论对工程实践具有指导意义。 相似文献
894.
These last 10 years, numerical models of mantle convection have emphasized the role of the 670 km endothermic phase change in generating avalanches that trigger catastrophic mass transfers between upper and lower mantle. On the other hand, scientists have emphasized the concomitance of large-scale worldwide geophysical and tectonic events, which could find their deep thermal roots in the huge mass transfers induced by the avalanches. In particular, the paleontological records show two periods of length of day (l.o.d.) shortening between 420 and 360, and 200 and 80 Myr BP. This last event is synchronous with a strong true polar wander and a global warming of the upper mantle. In order to study the potential effects of the avalanche on the main component of the Earth’s rotation, the Liouville equation has been solved and the l.o.d. evolution has been calculated from the perturbations of the inertia tensor. The results show that the inertia tensor of the Earth’s is mainly sensitive to the global transfers through the 670 km discontinuity. The l.o.d. perturbations will be synchronous with the global thermal effects of the avalanche. These theoretical results allow proposing a self-consistent physical mechanism to explain periods of the Earth’s rotation acceleration. Within this context, the l.o.d. shortening during the Cenozoic and Cretaceous brings one more clue to the possible participation of a mantle avalanche in generating the concomitant large scale events which have occurred during this very particular period of the Earth’s history. 相似文献
895.
We examined the hypothesis that minima in local recurrence time, TL, or equivalently maxima in local probability, PL, may map asperities in the Kanto and Tokai areas of Japan, where the earthquake catalog of the National Research Institute for Earth Science and Disaster Prevention (NIED) is complete at the M=1.5 (M1.5) level. We mapped TL (PL) based on the a- and b-values of the nearest earthquakes within 20 km of every node of a grid spaced 0.01° for M7 target events. Only earthquakes within the top 33 km were used. The b-values increase strongly with depth, in several areas. Therefore, some of the TL (PL) anomalies are not revealed if data from the entire crustal seismogenic zone are mixed. Thus, we mapped TL (PL) separately for the top 15 km and the rest of the depth range, as well as for the entire seismogenic crust. The resulting TL- and PL-maps show that approximately 12% of the total area shows anomalously short recurrence times. Out of six shallow target events with M≥6.5 and which occurred since 1890, five are located within the anomalous areas with TL <450 years. We interpret this to mean that areas with anomalously short TL map asperities, which are more likely than other areas to generate future target events. The probability that this result is due to chance is vanishingly small. The great Kanto rupture of 1923 appears to have initiated in the most significant asperity we mapped in the study area. One anomaly is located in the northeastern part of the area of the proposed future rupture of the Tokai earthquake, and another one at its southwestern corner. The absolute values of TL calculated are uncertain because they depend on the size of the volume used for the calculation. 相似文献
896.
A two‐dimensional simulation model of travel distances of individual particles in a gravel‐bed river is presented. The model is based on a number of rules, which include particle size, entrainment, trajectory, distance of movement and entrapment. Particle interactions are controlled by resistance fields defined about each obstacle and critical elevation defined in the model. Resistance fields, particle dropping and critical elevation rules control particle interactions. The interaction rules cause the particles to develop pebble clusters, stone cells and transverse structures (transverse ribs). The simulated travel distances of individual particles are consistent with reported field results. Individual particle travel distances were simulated using two different models; one without interactions between the individual particles and the stationary bed and one with interactions. The case without interactions demonstrates the random nature of sediment transport, and narrow ranges of travel distances. Wider ranges of travel distances, similar to those for natural situations, were obtained for the cases with interactions. The more intense the interaction between the mobile stones and the stationary ones, the wider the range of distances of travel for a given particle size. Modelling the mean travel distance yielded a result similar to that published previously, which was based on empirical data. Well developed bed‐surface structures were obtained for relatively poorly sorted sediment with intense interactions between particles. Transverse structures developed when relatively large particles were allowed to move. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
897.
弹性反射波频谱分析对比法检测浆砌片石挡墙质量 总被引:2,自引:0,他引:2
钟世航 《CT理论与应用研究》2002,11(1):1-5
大量的浆砌片石挡墙需要作快速质量检测,作者比较了利用弹性波速、瑞利面波和弹性波频谱分析法后,认为后者分辨率高,方法简单,并作了几百个点的检测,得到了成功。 相似文献
898.
X线侧位片与高分辨率CT对鼻骨骨折的对比研究 总被引:17,自引:0,他引:17
目的 通过86例鼻骨骨折的鼻骨X线侧位片与高分辨率CT(HRCT)对比研究,确定HRCT检查对鼻骨骨折的诊断价值。材料与方祛 86例鼻外伤或/和He、面外伤的患者均进行了鼻骨X线侧位摄影、HRCT扫描检查,经集体讨论,由有经验的放射医师对全部影像资料进行分析并进行统计学处理。结果HRCT显示所有的86例鼻骨骨折,但在此86例骨折中X线平片只显示了35例阳性,包括15例鼻骨汇合部骨折,7例双侧鼻骨骨折,3例复合骨折(鼻骨汇合部及双侧鼻骨骨折),l0例鼻区骨折。X线平片显示5l例为阴性。结论 对鼻骨骨折的诊断,HRCT明显优于鼻骨X线侧位片,HRCT扫描检查可提高X线隐性鼻骨骨折的诊断,并可明确鼻骨骨折的类型、范围和程度,为临床诊断和治疗提供可靠的依据。 相似文献
899.
扩频通信技术是基于信息容量和信息传输差错概率理论而建立的先进的无线通讯方式、多次野外实地证实它具有抗干扰性强、可实现码分多址等优点。通过分析传输试验数据,我们有理由相信扩频通信技术在遥测地震台风中具有较高的应用和广阔的发展前景。 相似文献
900.
利用OLE自动化方法,将MapInfo集成在VB中,在手工地震交切定位的基础上,开发了计算机定位程序,该程序与传统的定位方法相比,精度和效率都有较大幅度的提高。并在地震应急中发挥了作用。 相似文献