频率域单程方程三维叠前正演中的波场替换     

周亚同  董恩清  贺振华 《煤田地质与勘探》2001,29(1):49-52

利用定位原理进行三维叠前正演,仅靠单程声波方程的延拓即可形成复杂地质条件下的正演记录,运算效率高无多次反射出现。但速度模型中对于过大或过小的速度常使波场在延拓时有频率和波数成分的损失,这种损失引起波场畸变并严重影响正演记录的质量。本文采用波场替换技术,在每次延拓时用零相位子波形成一个同时保留了原波场的动力学特征与空间位置信息的新波场,然后用新波场取代原畸变波场并参与正演记录合成。在频率域单程方程三维叠前正演中特别适合做波场替换,因为震源脉冲与接收响应(均可视为点脉冲)的延拓波场在形态上相似,而且在延拓波场中每道记录之振幅包络只有一个极值点。理论试算结果表明,采用波场替换技术后最终正演记录质量比替换前有了很大改善。   相似文献   

中国气候变化的植物信号和生态证据   总被引：4，自引：2，他引：4  

袁婧薇  倪健 《干旱区地理》2007,30(4):65-473

全球平均气温上升、降水格局变化、极端天气事件发生的频率和强度增大等气候变化现象已经对陆地生态系统产生了影响,物种、群落和生态系统响应于气候变化而发生的改变,可以作为气候变化的间接生物学和生态学证据,对未来气候变化的影响评价有重要的价值,尤其是对减缓和适应全球气候变化的"地球系统科学"研究以及可持续生态系统管理与发展对策的制订,具有重要的意义。在国际气候变化的生物学证据研究的大背景下,总结了中国陆地生态系统响应过去气候变化的植物学信号和生态学证据:(1)物种水平:气候变暖导致中国33°N以北大部分地区植物春季物候期包括萌芽、展叶、开花期等显著提前,植被生长季延长;(2)群落水平:群落物种组成和分布发生改变,主要表现在长白山等高山群落交错带物种组成和林线位置的变化以及青藏高原高寒草甸的退化;(3)生态系统水平:全国总体植被盖度增加,植被活动加强,生产力增加;北方和西部地区农业植被的耕作制度、种植结构、耕种面积和产量发生变化,东北地区水稻种植面积和产量增加,但全国大部分地区农作物产量和温度呈负相关,这将威胁到未来的粮食安全。  相似文献   

干振碎石桩处理地基技术及应用实践     

张光立  孙健 《安徽地质》2006,16(4):305-307

干振碎石桩作为软地基处理的手段之一,目前在国内外已得到广泛应用,笔者根据多年来的施工实践,并结合工程实例,对该工艺技术方法对其作用机理进行了探讨,并通过工程实例的分析,对该技术的应用前景作了展望。  相似文献   

偏最小二乘回归法在强夯置换深度估算上的应用     

解华明  丁华 《水文地质工程地质》2003,30(6):62-64

简述了单因变量偏最小二乘回归的基本方法,并对一组工程实例,利用该方法回归建模,得到强夯置换深度回归方程,结果明显好于文中所述的其它两种方法,表明该方法是可靠、有效的。  相似文献   

吉林省双阳水库灌区灌溉水源置换可行性研究   总被引：1，自引：0，他引：1  

迟宝明  戴长雷  易树平  李治军 《世界地质》2003,22(3):284-289,312

双阳水库供水为优先满足城区需求和农业可持续发展,其水库灌区需进行灌溉水源置换。基于时序分析与回归分析的迭合模型模拟预测双阳水库来水量和区间降水量,并采用迦辽金有限单元数值差分法对区间地下水系统进行模拟求解,计算结果表明,新条件下灌区可能获得的水资源量为4 026.6×104m3/a;大于总需水量3 314.6×104 m3/a;从资源承载力的角度看,水源置换是可行的。对区内现状及规划中的取供水工程分析计算可知,灌区工程供水能力可达3 536.0×104 m3/a,大于总需水量;从工程承载力的角度看,水源置换亦是可以实现的。同时注意到,即使在水源置换以后,灌区的水供应对双阳水库的依赖程度仍然很高,如果水库对城区的供水量大幅增加,则灌区在置换后建立的水资源平衡将可能被打破。  相似文献   

Subsea-floor replacement in volcanic-hosted massive sulfide deposits   总被引：1，自引：0，他引：1  

Mark G. Doyle  Rodney L. Allen   《Ore Geology Reviews》2003,23(3-4):183-222

Recent research on volcanic-hosted massive sulfide (VMS) deposits indicates that syngenetic subsea-floor replacement ores form an important component of many deposits. In the context of VMS deposits, subsea-floor replacement can be defined as the syn-volcanic formation of sulfide minerals within pre-existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces (fractures, inter- and intra-granular porosity) as well as replacement of solid materials.There are five criteria for distinguishing subsea-floor replacement in massive sulfide deposits: (1) mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies (lavas, intrusions, subaqueous mass-flow deposits, pyroclastic fallout); (2) relics of the host facies occur within the mineral deposit; (3) replacement fronts occur between the mineral deposit and the host lithofacies; (4) the mineral deposit is discordant to bedding; and (5) strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity. Criteria 1–3 are diagnostic of replacement, whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic. Because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow(s) during transport, criteria 2 can only be applied to massive, semi-massive, disseminated or vein style deposits, and not clastic ores.The spectrum of VMS deposit types includes deposits that have accumulated largely subsea-floor, and others in which sedimentation and volcanism were synchronous with hydrothermal activity, and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system. Deposits that formed largely subsea-floor are mainly hosted by syn-eruptive or post-eruptive volcaniclastic facies (gravity flow deposits, water-settled fall, autoclastic breccia). However, some subsea-floor replacement VMS deposits are hosted by lavas and syn-volcanic intrusions (sills, domes, cryptodomes). Burial of sea-floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea-floor mineralization and promote subsea-floor replacement and zone-refining.The distance below the sea floor at which infiltration and replacement took place is rarely well constrained, with published estimates ranging from less than 1 to more than 500 m, but mainly in the range 10–200 m. The upper few tens to hundreds of metres in the volcano-sedimentary pile are the favoured position for replacement, as clastic facies are wet, porous and poorly consolidated in this zone, and at greater depths become progressively more compacted, dewatered, altered, and less amenable to large scale infiltration and replacement by hydrothermal fluids. Furthermore, sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in VMS systems, and this mixing process generally becomes less effective with increasing depth in the volcanic pile.The relative importance of subsea-floor replacement in VMS systems is related principally to four factors: the permeability and porosity patterns of host lithofacies, sedimentation rate, the relative ease of replacement of host lithofacies (especially glassy materials) and early formed alteration minerals during hydrothermal attack, and physiochemical characteristics of the hydrothermal fluid.  相似文献   

钻机易磨损件更换时间间隔的灰色预测   总被引：1，自引：0，他引：1       下载免费PDF全文

王书庆 《探矿工程》1998,(3):34-36

提出了采用铁谱分析技术、运用灰色预测理论对钻机易磨损件的更换时间间隔进行灰色预测。通过实例计算,证明本方法效果良好。  相似文献   

内蒙朱拉扎嘎金矿成矿地质条件及找矿方向初探   总被引：4，自引：0，他引：4  

孟二根  张有宽  陈旺 《矿产与地质》2002,16(3):168-173

朱拉扎嘎金矿床产于中元古界渣尔泰山群浅变质细碎屑岩中 ,矿层赋存在阿古鲁沟组一段中部层位 ,选择性的产于变质粉砂岩和变质钙质石英粉砂岩等孔隙度较好的岩性层中 ,矿区构造复杂 ,金与岩浆热液关系密切 ,且与 Ag、Cu呈正相关 ,金矿物主要是自然金和银金矿 ,围岩蚀变为中低温热液蚀变类型 ,属层控微细浸染热液交代大型金矿床。  相似文献   

Photogrammetric calibration of a C-arm X-ray system as a verification tool for orthopaedic navigation systems     

H. Broers  H. Hemken  T. Luhmann  P. Ritschl 《ISPRS Journal of Photogrammetry and Remote Sensing》2002,56(5-6)

For the total replacement of the knee joint, the precise reconstruction of the mechanical axis is significantly determined by the alignment of the cutting tool with respect to the rotation centre of the femur head. Operation techniques supported by navigation allow for the precise three-dimensional location of the hip centre by cinematic analysis.Recent results permit the reconstruction of the femur axis to be better than 0.7°. Therefore, conventional verification methods such as the post-operative recording of the complete leg are not suitable due to their limited system accuracy of about 2°.As the femur head cannot be accessed directly during the operation, an X-ray method has been used to verify alignment. The paper presents a method and the results achieved for the calibration of a C-arm system by introducing photogrammetric parameters. Since the method is used during operation, boundary conditions such as minimal invasive surgical intervention and sterility have been considered for practical applications of patients.  相似文献   

置换深度估算的一维波动方程法     

罗嗣海  龚晓南等 《地球科学》2002,27(1):115-119

强夯置换的应用已逐渐广泛，但其设计是高度经验性的。强夯置换的理论研究较为肤浅，特别是置换深度的计算尚无较好的方法。为此，提出了模拟夯击过程的一维波动方程理论模型；初步建议了模型中有关参数的取值并用工程实例进行了验证；用所提出的模型探讨了置换体形成与扩展的基本规律；给出了应用的简化形式。结果表明，一维波动方程法及其简化形式与实际吻合较好，可应用于强夯置换的置换深度估算。  相似文献