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901.
提高气介式超声波水位计测量精度的探讨 总被引:1,自引:0,他引:1
分析了影响气介式超声波水位计水位测量精度的各种因素,提出了消除这些影响因素的对策措施。其中,对超声波水位计测量回波因距离、反射角和发射面的变化带来的误差进行了分析,提出了一种利用数字采样技术对超声波测量回波前沿进行分析补偿来提高测量精度的方法。采用该技术的气介式超声波水位计在回波信号强弱变化时,数据重复性明显提高,使较短时间的采样就可获得较好测量精度,适合野外功耗要求小而采用间歇工作的方式。 相似文献
902.
The process of drilling, in general, always produces sound. Though sound is used as a diagnostic tool in mechanical industry, its application in predicting rock property is not much explored. In this study, an attempt has been made to estimate rock properties such as uniaxial compressive strength, Schmidt rebound number and Young's modulus using sound level produced during rotary drilling. For this purpose, a computer numerical controlled vertical milling centre was used for drilling holes with drill bit diameters ranging from 6 to 20 mm with a shank length of 40 mm. Fourteen different rock types were tested. The study was carried out to develop the empirical relations using multiple regression analysis between sound level produced during drilling and rock properties considering the effects of drill bit diameter, drill bit speed and drill bit penetration rate. The F-test was used to check the validity of the developed models. The measured rock property values and the values calculated from the developed regression model are fairly close, indicating that the developed models could be efficiently used with acceptable accuracy in prediction of rock properties. 相似文献
903.
Longitudinal profiles and knickzones: the example of the rivers of the Cher basin in the northern French Massif Central 总被引:1,自引:0,他引:1
Jean-Pierre Larue 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(1):125-142
This work examines the longitudinal profiles of 27 rivers in the upper Cher basin, of various lengths, in order to characterize their shape and the knickzones (high gradient sections) that disrupt their longitudinal profiles. No smooth, concave-upwards long profile has been found in the study area, located at the contact between the Massif Central basement rocks and the Paris Basin sedimentary rocks, because of the heterogeneous geological structure and lithology. The analysis of the main knickzone parameters allows us to distinguish two knickzone assemblages: the 53 knickzones of the first have a lithological origin and are characterized by a gradient equal to or lower than that given by the power curve y = 63.306 × −0.4392; the 30 knickzones of the second assemblage, which have a higher gradient than that of the curve, and give clear outliers in the DS (distance-slope) plot, are due to active faulting. The locations of this second group of knickzones delimit the areas that have experienced important local vertical crustal motions, too rapid for fluvial incision to have reduced the effect of knickzones caused by active faulting. In these uplifted areas, headward erosion has been arrested by knickzones of the second type, allowing the preservation of shallow-dell valley heads without any incision. 相似文献
904.
KIM M. COHEN 《Sedimentology》2011,58(6):1453-1485
This study presents a detailed reconstruction of the palaeogeography of the Rhine valley (western Netherlands) during the Holocene transgression with systems tracts placed in a precise sea‐level context. This approach permits comparison of actual versus conceptual boundaries of the lowstand, transgressive and highstand systems tracts. The inland position of the highstand Rhine river mouth on a wide, low‐gradient continental shelf meant that base‐level changes were the dominant control on sedimentation for a relatively short period of the last glacial cycle. Systems in such inland positions predominantly record changes in the balance between river discharge and sediment load, and preserve excellent records of climatic changes or other catchment‐induced forcing. It is shown here that the transgressive systems tract‐part of the coastal prism formed in three stages: (i) the millennium before 8·45 ka bp , when the area was dominated by fluvial environments with extensive wetlands; (ii) the millennium after 8·45 ka, characterized by strong erosion, increasing tidal amplitudes and bay‐head delta development; and (iii) the period between 7·5 and 6·3 ka bp when the Rhine avulsed multiple times and the maximum flooding surface formed. The diachroneity of the transgressive surface is strongly suppressed because of a pulse of accelerated sea‐level rise at 8·45 ka bp . That event not only had a strong effect on preservation, but has circum‐oceanic stratigraphical relevance as it divides the early and middle Holocene parts of coastal successions worldwide. The palaeogeographical reconstruction offers a unique full spatial–temporal view on the coastal and fluvial dynamics of a major river mouth under brief rapid forced transgression. This reconstruction is of relevance for Holocene and ancient transgressive systems worldwide, and for next‐century natural coasts that are predicted to experience a 1 m sea‐level rise. 相似文献
905.
不良工程地质组合导致房屋地基开裂或滑移,墙体承重失衡导致房屋结构性破裂。煤矿开采直接导致地下水位下降,部分影响建筑物地基稳定性及地面塌陷。 相似文献
906.
In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size).The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone.When Mindulle moved to the area of the upper jet entrance,where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle.The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex.The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast,and the west.With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern. 相似文献
907.
908.
河南省城市化水平综合评价及区域格局分析 总被引:2,自引:1,他引:1
根据城市化的内涵构建城市化水平综合评价指标体系,采用多目标决策TOPSIS法结合信息熵赋权法,对河南2001-2009年各地市的城市化水平进行综合评价分析;继而采用ESDA-GIS方法,对河南城市化综合水平的地域空间格局演化特征进行探讨。研究表明,河南各地市城市化综合水平虽然自2001年以来均获得了不同程度的提升,但地市间城市化水平的绝对差异和相对差异均呈拉大趋势;城市化热点地区在空间上表现出由集中分布向随机分布的演变态势,但整体上仍呈现出以中原城市群地区为核心的热点区和以外围地市为冷点区的核心—边缘型空间格局,由此认为着力推进边缘化传统农区的城市化进程是实现河南城市化区域协调发展的关键。 相似文献
909.
Atmospheric air temperature data from 92 stations in China’s radiosonde network were used to analyze changes in the freezing
level height (FLH), glacier snow line, and ice edge from 1958–2005 (48 years) and to examine the impact of these changes on the
cryosphere. In general, the FLH, glacier snow line, and ice edge exhibited latitudinal zonation, declining from south to north.
Trends in the FLH, glacier snow line, and ice edge showed spatial heterogeneity during the study period, with prevailing upward
trends. Temporally, the FLH, glacier snow line, and ice edge trends differed on various time scales. 相似文献
910.
利用淮南市朱集东矿井新生界松散层供水水文地质勘探成果和抽水试验资料,查明了区内新生界松散层供水含水层的供水水文地质条件,认为第一含水层埋藏浅,易受污染,水量随季节变化大,不宜作为生活饮用水供水水源,第三含水层水质较差,亦不作为生活饮用水供水水源,确定了第二含水层为矿区主要供水层位。采用解析法对第二含水层的水量进行了计算,并设计了布井方案,计算了井群水量;水位预报结果表明,开采50a后,3#、4#井中的水位最大降深为35.229m,小于其顶板埋深,说明拟建井群布置是合适的。评价结果为矿井供水设计提供了依据。 相似文献