排序方式： 共有35条查询结果，搜索用时 15 毫秒
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射线透射成像中重物质遮挡下的轻物质检测技术研究 总被引：2，自引：2，他引：0
本文研究了不同厚度轻重物质在射线透射成像中的图像灰度关系，根据提取轻物质轮廓线的要求，找出了在不同厚度重物质遮挡下的可检测出轻物质的最小厚度曲线。 相似文献
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Georg Houben Torge Tünnermeier Naim Eqrar Thomas Himmelsbach 《Hydrogeology Journal》2009,17(4):935-948
Shallow groundwater is the main source for drinking water in Kabul, Afghanistan. It comes from a multitude of shallow hand-pumped wells spread over the whole city area. The groundwater is characterised by slightly oxic redox conditions. Interactions with aquifer carbonates lead to near-neutral pH and high degrees of hardness. The mostly negative water budget of the Kabul Basin is the result of strong evaporation which leads to an increase in salt and also of some undesirable constituents, e.g. borate. Several years of drought have aggravated this problem. The shallow groundwater in the city has received tremendous amounts of pollution due to a lack of proper waste disposal and sewage treatment. Common indicators are elevated concentrations of nutrients such as nitrate and faecal bacteria. The high infant mortality can at least partially be attributed to the insufficient water hygiene. Acid generated during the mineralisation of the wastewater is hidden due to the strong pH buffering capacity of the groundwater system. Redox and pH conditions preclude significant mobilisation of trace metals and metalloids. 相似文献
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CBS图像重建中的数据修正 总被引：2，自引：1，他引：1
本文依据康普顿背散射扫描原理,给出了图像重建算法,讨论了有关的数据修正因子,得出了检测深度增大时误差累积传播的数据修正模型。 相似文献
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Houben Georg J. Wachenhausen Julia Guevara Morel Carlos R. 《Hydrogeology Journal》2018,26(4):1285-1294
Hydrogeology Journal - Well ageing is mostly caused by mechanical and biogeochemical clogging processes, which affect the gravel pack, screen slots and casing. Clogging deposits increase head... 相似文献
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Hydrogeology Journal - Coefficients B and C of the Jacob (1947) equation, usually derived from step-drawdown tests, are commonly attributed to “aquifer losses” and “well... 相似文献
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Houben GJ 《Ground water》2006,44(5):668-675
In many cases, the operation of wells is hampered by the formation of mineral incrustations. From field studies, it is known that the distribution of incrustations in wells is quite inhomogeneous. Flow models were calculated to assess the hydraulic background of this phenomenon. For horizontal flow, the screen section facing the natural flow direction receives the majority of the total inflow. This phenomenon increases with increasing natural gradients of flow. The vertical distribution of water intake is also quite inhomogeneous. In partially penetrating wells, the uppermost part of the screen receives much more inflow than the deeper screen sections. These flow inhomogenities involve elevated flow velocities and may cause increased influx of shallow, oxygenated water, all conditions favorable for incrustation growth. Field investigations on incrusting wells clearly show that the identified screen areas of elevated flow are indeed much more prone to incrustation deposition. Such sections require more attention during rehabilitations. A suction flow control device can help to homogenize the inflow but can cause elevated entrance loss when affected by incrustation buildup itself. 相似文献
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Peter Houben Norbert Kühl Rainer Dambeck Jan Overath 《Boreas: An International Journal of Quaternary Research》2013,42(4):947-958
We document the Lateglacial to Holocene sedimentation and vegetation history of a small, infilled crater landform in the West‐Eifel Volcanic Field (WEVF; western Germany). We analysed geomorphological landform change, sedimentological and geochronological data, pollen, and plant macrofossils of a 16‐m‐long sediment core from the Eichholz Maar (EHM). The EHM erupted between ～20 and 15 ka ago (MIS 2). Lacustrine siliclastic infilling was completed about 7500 years ago. Lateglacial rates of sedimentation are generally 2 to 5 times higher than in other maar lakes of the WEVF. Local factors, therefore, overprint the relative efficacy of the climate‐controlled variance of sedimentation rates at the Lateglacial/Holocene transition. The predominance of local factors relates to inherent geomorphological process–response mechanisms that were triggered by the EHM eruption. Rapid crater infilling and its completion by the mid‐Holocene are attributed to a combination of small storage capacity and geomorphological activity. A late Boreal interval of significant lake‐level fall can, however, be attributed to a period of continental‐scale climate change as recorded in other European lacustrine settings. Our findings highlight the importance of utilizing geomorphological information to reveal the relative significance of local controls as opposed to climate control when investigating small‐sized lake settings with active sediment supply systems. 相似文献
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CBS扫描图像的直接重建与处理 总被引：4，自引：1，他引：4
本文详细的介绍了CBS扫描图像直接重建技术的原理，列出了利用该原理设计DHB2115医用CT机中出现的主要技术问题和解决方法，并简单介绍系统的主控程序，给出模拟结果。 相似文献