冲击回转碎岩机理试验研究   总被引：2，自引：0，他引：2       下载免费PDF全文

常玉军  殷琨 《探矿工程》2001,(4):62-64

在模拟孔底冲击回转钻进条件的试验台上，对岩石的冲击回转碎岩机理进行了试验研究，提出了大直径潜孔钻头的合理布齿及钻进参数选择依据。  相似文献   

Confidence Intervals of Quantiles in Hydrology Computed by an Analytical Method     

Baâ  Khalidou M.  Díaz-Delgado  Carlos  Caârsteanu  Alin 《Natural Hazards》2001,24(1):1-12

Fitting probability distributions to hydrologic data samples is widely used for quantile estimation purposes. The estimated quantile (X^_T) is related to a return period (T). The confidence interval associated with each of the estimates has been calculated empirically, up until now, supposing that the quantile estimator is normally distributed. In this study, it is shown that the confidence interval follows a normal distribution only in the central part of the distribution. The real confidence limits are computed analytically, by defining and integrating the probability density function of the confidence interval. The results with an important number of hydrologic samples show that the upper confidence limits are significantly underestimated towards the tail of the distribution, when determined using the normality approximation for the quantile estimator.  相似文献   

2050年前气候变暖冰川萎缩对水资源影响情景预估   总被引：42，自引：34，他引：42  

施雅风 《冰川冻土》2001,23(4):333-341

根据有不确定性的综合预测 ,到 2 0 5 0年左右青藏高原温度可比 2 0世纪末升高 2 .5℃左右 ,其导致冰川强烈消融的夏季升温为 1.4℃ ,将使平衡线上升 10 0m以上 .冰舌区消融冰量超过积累区冰运动来的冰量 ,冰川出现变薄后退 ,初期以变薄为主融水量增加 ,后期冰川面积大幅度减少 ,融水量衰退 ,至冰川消亡而停止 .考虑冰川大小 ,冰川类型响应气候变暖的敏感性有重大差别 ,应用新编中国冰川目录的统计数据 ,选择若干区域 ,预估 2 0 5 0年前冰川萎缩对水资源影响情景 .祁连山北麓河西地区 ,天山北麓准噶尔盆地南缘 ,天山南麓吐鲁番 哈密盆地的多数出山河流的冰川 ,以面积小于 2km2 者占绝对优势 ,对气候变暖最为敏感 ,衰退迅速 ,本世纪初期出现融水量高峰 ,中期融水量减少 ,对每条河流的影响以 10 6～ 10 7m3 ·a-1计 .少数流域如疏勒河、玛纳斯河等 ,冰川融水量占河川径流 1/ 3以上 ,有若干 5～ 30km2 左右中等规模冰川存在 ,预期至本世纪中期才出现融水高峰 ,融水增加值以 10 8m3 ·a-1计 .塔里木盆地周围高山冰川总面积达 2 2 0 0 9km2 ,有面积超过 10 0km2 、冰舌为厚表覆盖的大冰川 2 2条 ,退缩缓慢 ,冰川融水量在叶尔羌河、玉龙喀什河与阿克苏河等占 5 0 %～ 80 % .现在塔里木河干流主要靠天山西南部  相似文献   

Anisotropy of the upper mantle in Chinese mainland and its vicinity   总被引：2，自引：1，他引：2  

刘希强  周蕙兰  李红  季爱东 《地震学报(英文版)》2001,14(4):359-370

IntroductionAnisotropy is a universal phenomenon in the upper mantle. The mechanisms, which cause elastic anisotropy of in-situ rocks, include lattice preferred orientation of the minerals composing the rocks and preferred orientation of magma chambers. Lattice preferred orientation (LPO) of olivine is widely believed to be the dominant cause of the upper mantle anisotropy. The observational results of the upper mantle anisotropy can be explained by tectonic process relating to plate motion.…  相似文献   

The channel-geometry method: Guidelines and applications     

Geraldene Wharton 《地球表面变化过程与地形》1995,20(7):649-660

All river engineering schemes require flood discharge estimates as part of the design and appraisal process. Unfortunately, continuous measurement of flood discharges is limited to those river sites with instrumented gauging stations, which constitute only a small proportion of channel reaches where information is required. Therefore, considerable research effort has been devoted to the development of reliable indirect techniques of flood discharge estimation. Research on the interrelationship of stream channel geometry and river discharge has provided the basis for an indirect method of flood estimation – the channel-geometry method – which employs river channel dimensions alone to estimate discharge characteristics at ungauged river sites. Channel-geometry equations are developed empirically by relating streamflow data from gauging stations and channel dimensions measured from natural river reaches in the vicinity of the gauge, and take the form of power function relations. Once regional channel-geometry equations have been defined, a channel width or channel capacity measurement is the only variable needed to estimate the flood flow characteristics at a specified river site. The method is useful as an alternative to traditional catchment-based approaches or as a rapid reconnaissance technique. In addition to the application for flood discharge prediction, channel-geometry equations could prove helpful in the management of river channels, first, by providing a basis for assessing local deviations in the channel form–discharge relation, deviations which could be employed as indicators of the sensitivity of particular stretches of river channel to change, and secondly, in the computation of natural channel dimensions for use in river channel design and river restoration.  相似文献   

A seismic gap in the eastern margin of the Sea of Japan as inferred from the time-space distribution of past seismicity   总被引：3，自引：0，他引：3  

Masakazu  Ohtake 《Island Arc》1995,4(3):156-165

Abstract Based on the spatial distribution of the focal areas from previous large earthquakes, a significant seismic gap was found off the coast of the Akita Prefecture at the eastern margin of the Sea of Japan. We forecast that the 75 km segment of plate boundary may be ruptured by a large thrust earthquake with a magnitude of 7.5 in the near future. The time of occurrence is uncertain, but the recurrence interval of large earthquakes in this region suggests that it will be no later than the end of next century. The time sequence of large earthquakes in the eastern margin of the Sea of Japan shows a systematic shortening of the earthquake interval for the past 250 years. This feature is simulated successfully by a simple mechanical model that represents a plate boundary by segmented blocks, each of which is composed of a spring friction slider system. We further propose to revise the conventionally accepted plate boundary between the Eurasian and Okhotsk plates in the eastern margin of the Sea of Japan; the observed data of seismic activity and recent crustal deformation indicate that the southern part of the plate boundary traverses the land region from Niigata to Otari along the Shinanogawa seismic belt. The fault geometries of previous large earthquakes show that the mode of plate convergence in the eastern margin of the Sea of Japan is a collision type rather than a simple eastward subduction as was postulated in early studies.  相似文献   

变步长显式完全平方守恒差分格式   总被引：8，自引：0，他引：8  

王斌  季仲贞 《气象学报》1995,53(3):299-305

综合隐式完全平方守恒差分格式和显式瞬时平方守恒差分格式的优点，针对一类非线性发展方程构造了一种通过自动调节时间步长来保持平方守恒性的显式差分格式。它基于加小耗散的思想，但又与小耗散法有所不同。本文取的耗散项不是一般的人工耗散，而是取能够弥补由于时间离散所产生的截断误差的所谓（时间）协调耗散。因此，该格式具有较高的时间精度。在数值试验中，该类格式可取得满意的效果。  相似文献   

骨龄评定统计模型的建立     

黄幼才  刘友光  徐亚明  郭祥瑞 《武汉大学学报(信息科学版)》1995,(3)

介绍了手腕骨的筛选，手腕骨发育信息的量化和获取，回归模型的建立和稳健化方法。  相似文献   

GPS在平面控制网加密应用中的若干问题   总被引：1，自引：0，他引：1  

路伯祥 《四川测绘》1995,18(1):9-12

本文讨论ＧＰＳ在平面控制网加密应用中坐标转换的各种方法，综合实例对这些方法进行了评述，产对精度估计中的问题进行了分析。  相似文献   

Automatic parameter estimation applied on a groundwater model: The problem of structure identification     

F. Aschenbrenner  A. Ostin 《Environmental Geology》1995,25(3):205-210

The properties of a Pleistocene aquifer located in NW Germany were evaluated by means of an inverse two-dimensional numerical model in the vertical plane. The steady-state drawdown recorded at the end of a pumping test was used to calibrate the model with a Gauss-Newton parameter estimation method. The results were analyzed within a formal statistical procedure by means of eigenvalues and eigenvectors. Although a mathematically meaningful value for the standard error can be obtained, the resulting set of permeabilities depends strongly upon the choice of the zonation pattern.  相似文献