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991.
???????????????????????????????????????????????????80 cm??130 cm??????????????????????仯??????0.02×10-8 ms-2/cm??????????仯????仯??????????????????????FG5??A10???????????????????????????????????????????????????仯???????? 相似文献
992.
The most promising approach for studying soil moisture is the assimilation of observation data and computational modeling.However,there is much uncertainty in the assimilation process,which affects the assimilation results.This research developed a one-dimensional soil moisture assimilation scheme based on the Ensemble Kalman Filter(EnKF)and Genetic Algorithm(GA).A two-dimensional hydrologic model-Distributed Hydrology-Soil-Vegetation Model(DHSVM)was coupled with a semi-empirical backscattering model(Oh).The Advanced Synthetic Apertture Radar(ASAR)data were assimilated with this coupled model and the field observation data were used to validate this scheme in the soil moisture assimilation experiment.In order to improve the assimilation results,a cost function was set up based on the distance between the simulated backscattering coefficient from the coupled model and the observed backscattering coefficient from ASAR.The EnKF and GA were used to re-initialize and re-parameterize the simulation process,respectively.The assimilation results were compared with the free-run simulations from hydrologic model and the field observation data.The results obtained indicate that this assimilation scheme is practical and it can improve the accuracy of soil moisture estimation significantly. 相似文献
993.
Autonomous vehicles are being developed to replace the conventional, manned surface vehicles that tow mine hunting towed platforms. While a wide body of work exists that describes numerical models of towed systems, they usually include relatively simple models of the towed bodies and neglect the dynamics of the towing vehicle. For systems in which the mass of the towing vehicle is comparable to that of the towed vehicle, it becomes important to consider the dynamics of both vehicles. In this work, we describe the development of a numerical model that accurately captures the dynamics of these new mine hunting systems. We use a lumped mass approximation for the towcable and couple this model to non-linear numerical models of an autonomous surface vehicle and an actively controlled towfish. Within the dynamics models of the two vehicles, we include non-linear controllers to allow accurate maneuvering of the towed system. 相似文献
994.
Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamic triaxial tests with multi-stage cyclic loading process. The relationship between dynamic shear stress and dynamic shear strain of frozen soil of subgrade under train loading and the influence of freezing temperatures on dynamic constitutive relation, dynamic shear modulus and damping ratio are observed in this study. Test results show that the dynamic constitutive relations of the frozen soils with different freezing temperatures comply with the hyperbolic model, in which model parameters a and b decrease with increasing freezing temperature. The dynamic shear modulus of the frozen soils decreases with increasing dynamic shear strains initially, followed by a relatively smooth attenuation tendency, whereas increases with decreasing freezing temperatures. The damping ratios decrease with decreasing freezing temperatures. Two linear functions are defined to express the linear relationships between dynamic shear modulus (damping ratio) and freezing temperature, respectively, in which corresponding linear coefficients are obtained through multiple regression analysis of test data. 相似文献
995.
996.
太湖流域土壤重金属元素污染历史的重建:以Pb、Cd为例 总被引:4,自引:1,他引:4
太湖是位于长江下游的一个大型浅水湖泊,通过对4个代表太湖不同沉积环境的湖底沉积剖面的137Cs和210Pb沉积定年,重建太湖湖底沉积物和太湖来水流域土壤Cd、Pb的污染历史。结果显示:1980年以前,太湖底积物中Cd、Pb含量与流域内的自然背景含量相当,1980年以后,湖底沉积物中的Cd、Pb含量显著增高,这与我国大规模工业化进程的起始时间基本一致,推测工业化进程是湖底沉积物中Cd、Pb含量增加的主要原因。1900年以来太湖湖底沉积物中累积含有Cd和Pb分别为146t和25980t,其中苕溪来水提供的Cd和Pb分别为40t、6777t,宜溧河来水提供的Cd、Pb分别为36t、6023t,其他来水(洮、滆、运河)提供的Cd、Pb分别为71t、13179t,其他来水是太湖Cd、Pd累积的主要输入途径。Cd、Pb累积的高峰期为20世纪80—90年代,1980年以来,运河来水Cd、Pb的输出通量为28.26t、3419t;苕溪流域Cd、Pb的输出总量分别为13.70t、1585t,其中人为源的Cd、Pb为8.90t、610t,人为源输出的Cd、Pb通量占总输出量的64.96%和38.47%;宜溧河流域Cd、Pb的输出总量分别为10.09t、1063t,人为源的Cd、Pb分别6.96t和500t,人为源输出的Cd、Pb通量占总输出量的68.68%和47.08%,表明太湖流域人类活动所导致的Cd已超过自然剥蚀过程,因此削减工业化进程中的Cd、Pb排放总量,控制太湖运河来水的输出通量是改善太湖底积物Cd、Pb环境质量的关键措施。 相似文献
997.
文章主要研究和讨论青海省格尔木市昆仑河第五级阶地的三岔河组河湖相沉积,特别是其上部的一套典型的湖相沉积。根据野牛沟和纳赤台西北两剖面三岔河组沉积样品的ESR和U系法年龄测定结果,三岔河组堆积于约355~95kaB.P.间,而被称为昆仑古湖的湖相沉积大致开始于约 200~160kaB.P.(ESR)或约150kaB.P.(U系),结束于约 150~120kaB.P.(ESR)或约95kaB.P.(U系)左右,其中深湖时期约为190kaB.P.(ESR)或约110~100kaB.P.(U系)左右。此外,纳赤台东北昆仑河第三级阶地剖面上部的湖相沉积,则是约90(ESR)/72~25kaB.P.(U系)的末次冰期期间形成,可称为纳赤台古湖。根据昆仑古湖湖相沉积地层中的沉积构造和所发现的介形类化石,讨论了湖泊的沉积环境;根据区域对比,认为三岔河组发育于约355~95kaB.P.,而其中约120~95kaB.P.的末次间冰期的早中期则是昆仑古湖的发育时期与青藏高原的羌塘东湖等古大湖发育早期的最高湖面时期,而40~30kaB.P.的MIS3的后半段只是这些大湖分解过程中的一个阶段。 相似文献
998.
Integrated Ocean Drilling Program (IODP) Expeditions 304/305 recovered a total of 1.4 km sequence of lower crustal gabbroic and minor ultramafic rocks from the Atlantis Massif oceanic core complex on the western flank of the Mid Atlantic Ridge (MAR) at 30°N. We conducted an integrated paleomagnetic and rock magnetic study on this sequence to help address the interplay between magmatism and detachment faulting. Detailed thermal and alternating-field demagnetization results demonstrate that stable components of magnetization of mainly reversed polarity with unblocking temperatures below the Curie temperature of magnetite are retained in gabbroic rocks at IODP Site U1309. Several samples also contain multicomponent remanences of both normal and reversed polarities that were acquired over sharply defined blocking temperature intervals, providing evidence for localized reheating of some intervals during both normal and reversed polarity periods. Results from a series of rock magnetic measurements corroborate the demagnetization behavior and show that titanomagnetites are the main magnetic carrier rocks recovered at Site U1309D. The overall magnetic inclination of Hole U1309D is -35°, implying significant (up to ~ 50° counterclockwise, viewed to the north) rotation of the footwall around a horizontal axis parallel to the rift axis (010°) may have occurred. The tectonic rotations inferred by the paleomagnetic data suggest that the original fault orientation dipped relative steeply toward the spreading axis and subsequently rotated to a shallower angle. Coupled with the newly published U–Pb zircon ages for Hole U1309D rocks [Grimes, C.B., John, B.E., Wooden, J.L., 2008. Protracted construction of gabbroic crust at a slow-spreading ridge: Constraints from 206Pb/238U zircon ages from Atlantis Massif and IODP Hole 1309D, (30°N, MAR). Geochem. Geophys. Geosyst. 9, Q08012. doi:1029/2008GC002063], the new paleomagnetic data provide temporal and thermal constraints on the accretion history of the Atlantis Massif. 相似文献
999.
1000.
二连盆地侏罗系地层热演化史研究 总被引:4,自引:1,他引:4
本文应用磷灰石裂变径迹,镜质体动力学模型等方法恢复二连盆地侏罗系地层的热演化史,二连盆地图参1井磷灰石退火浓度为1600-2774m,对应的退火温度为64-102.7℃,图参1井现今温度小于最高古地温,这是由于二连盆地地温梯度逐渐降低及地层发生抬升和剥蚀所致。根据磷灰石裂变径迹分析和镜质体动力学模型模拟图参1井的热演化史,在晚侏罗世时其经受的最高地温梯度分别为7℃/hm和6℃/hm。侏罗系地层在晚 相似文献