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931.
Atrazine, an herbicide widely used for selective control of grassy weeds in the fields where maize is grown, is a potential ground water contaminant in China and, consequently, there is interest in predicting its mobility in agricultural soils. In this study, we determined the nonequilibrium transport characteristics of atrazine in Shahe soil (Beijing sandy loam) using the advection-dispersion equation, and using a sensitivity analysis, we evaluated the contribution of the uncertainty in a given input parameter to the overall uncertainty in model results. The asymmetrical shape and tailing of the atrazine breakthrough curve (BTC) showed that atrazine was subject to nonequilibrium transport. The observed atrazine BTC was best fitted by the chemical nonequilibrium model with a nonlinear least-squares optimization approach. Results from the sensitivity analysis indicated that the retardation factor was the most sensitive parameter. Considering the reliability of the estimated parameters, the best fit to the atrazine BTC was obtained by fixing the retardation factor based on the linear distribution coefficient, and by calculating the dispersion coefficient from the bromide BTC and the average pore water velocity from the measured data; nonequilibrium parameters were the only unknown parameters that were optimized. Model verification procedures were based on best-fit parameters optimized from one soil column experiment and applied to simulate the transport of atrazine in the duplicate experiment. The results showed there was good agreement between measured and simulated concentrations for atrazine leaching in the soil column. 相似文献
932.
Paleomagnetic and rock magnetic study has been conducted on the Early Triassic red beds of Liujiagou Formation from Jiaocheng,
Shanxi Province. Hematite was shown as the main magnetic mineral. After eradicating an initial viscous component at room temperature
to ~100°C–200°C, thermal demagnetization shows that most samples contain two remanence components, intermediate-temperature
remanence component at 250°C–500°C and high-temperature component at 500°C–680°C. The intermediate-temperature component has
a negative fold test at the 95% confidence level. And the pole position of the intermediate-temperature component in geographic
coordinates is correlated with the Middle Jurassic reference pole of the North China Block (NCB) within the 95% confidence,
suggesting that it might be a remagnetization component acquired during the Yanshanian period. The high-temperature component
contains both reversal and normal polarities with positive fold test and C-level positive reversal test at the 95% confidence
level, which suggests that this high-temperature component can be regarded as primary magnetization. Comparison of this newly
obtained Early Triassic paleopole with the coeval mean pole of the Ordos Basin suggests that a locally relative rotation may
have happened between the Ordos and the Jiaocheng area of Shanxi Province. This rotation may be related with two faults: one
is Lishi big fault separating Ordos from Shanxi and the other is Jiaocheng big fault, which is situated in the southeast of
sampling locality and was still in motion during the Cenozoic. 相似文献
933.
Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors 总被引:2,自引:0,他引:2
~~Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors@马宗晋
@任金卫
@张进~~ 相似文献
934.
土壤墒情是反映一地土壤含水量多少的主要指标,墒情的好坏直接影响着农作物的生长。对于土壤墒情的计算和编报,曲沃县气象站经历了从完全的由人工查算计算编报,到用Basic语言编程计算编报,再到以后的Excel表格计算几个阶段。但这几种方法要么是计算量大,要么是界面不友好不易控制,要么是对操作计算机人员水平要求过高,稍不留心可能造成计算错误等多种不便。应用VFP语言可容易的编出具有Windows风格的程序,既方便操作,又能保证计算的精确度。 相似文献
935.
用sPn计算内蒙地震的震源深度 总被引:11,自引:6,他引:11
震源深度是地震定位的一个重要参数。本文讨论了用sPn测定震源深度的可能性。sPn对于测定地壳内震源深度具有重要意义。本文笔者利用记录到的sPn震相计算了2003年8月16日发生在我国内蒙地区地震的震源深度,并对该方法在日常工作中的应用进行了讨论。 相似文献
936.
Steve P. Schilling Paul E. Carrara Ren A. Thompson Eugene Y. Iwatsubo 《Quaternary Research》2004,61(3):325-329
The cataclysmic eruption of Mount St. Helens on May 18, 1980, resulted in a large, north-facing amphitheater, with a steep headwall rising 700 m above the crater floor. In this deeply shaded niche a glacier, here named the Amphitheater glacier, has formed. Tongues of ice-containing crevasses extend from the main ice mass around both the east and the west sides of the lava dome that occupies the center of the crater floor. Aerial photographs taken in September 1996 reveal a small glacier in the southwest portion of the amphitheater containing several crevasses and a bergschrund-like feature at its head. The extent of the glacier at this time is probably about 0.1 km2. By September 2001, the debris-laden glacier had grown to about 1 km2 in area, with a maximum thickness of about 200 m, and contained an estimated 120,000,000 m3 of ice and rock debris. Approximately one-third of the volume of the glacier is thought to be rock debris derived mainly from rock avalanches from the surrounding amphitheater walls. The newly formed Amphitheater glacier is not only the largest glacier on Mount St. Helens but its aerial extent exceeds that of all other remaining glaciers combined. 相似文献
937.
938.
固体潮研究是研究地震成因、地震前兆与地震预测的重要内容.在开展固体潮地震预测研究之前,固体潮主要用于地球动力学研究.然而固体潮地震预测研究与固体潮地球动力学研究的目标截然不同.地球动力学从大的时间尺度和地球整体运动(包括地球内部及表面的构造运动)来探讨其动力演化过程,进而寻求其驱动机制.固体潮地震预测研究则是研究小时间尺度、区域性地壳构造运动中与地震有关的固体潮异常现象.二者相差甚远.在现行地震预测体系中,固体潮研究也远不能与测震学研究的重要性相比.为什么会出现这种情况?固体潮地震预测研究有什么特点?这些问题的讨论,有助于帮助我们强化地震预测的目标和概念、改进固体潮地震监测技术系统、探索新的数字信号处理方法. 相似文献
939.
Xinrong Ren Hartwig Harder Monica Martinez Ian C. Faloona David Tan Robert L. Lesher Piero Di Carlo James B. Simpas William H. Brune 《Journal of Atmospheric Chemistry》2004,47(2):169-190
Accurate OH and HO2 (collectively called HOx) measurements by laser-induced fluorescence (LIF) may be contaminated by spurious signals from interfering atmospheric chemicals or from the instrument itself. Interference tests must be conducted to ensure that observed OH signal originates solely from ambient OH and is not due to instrument artifacts. Several tests were performed on the Penn State LIF HOx instrument, both in the laboratory and in the field. Theseincluded measurements of the instrument's zero signal by using either zero air or perfluoropropylene to remove OH, examination of spectral interferences from naphthalene, sulfur dioxide, and formaldehyde, and tests of interferences by addition of suspected interfering atmospheric chemicals, including ozone, hydrogen peroxide, nitrous acid, formaldehyde, nitric acid, acetone, and organic peroxy radicals (RO2). All tests lacked evidence ofsignificant interferences for measurements in the atmosphere, including highly polluted urban environments. 相似文献
940.
Numerical Method for Modeling the Constitutive Relationship of Sand under Different Stress Paths 总被引:1,自引:0,他引:1
Ren Qingyang Wang Jingtao 《中国地质大学学报(英文版)》2005,16(3):268-270
Overonehundredconstitutivemodelsforsand havebeenproposed,howeveronlyafewmodelsare widelyappliedinengineering.Therearetwochief reasonsforthis.(1)Sandiscomposedofgeological materialsandsituatedinaneutralenvironmentthat hassufferedvariousactions.Therefore,itisdifficult todescribethecomplexbehaviorofsoilsbyusinga simplemathematicalmodelwithonlyafewparame ters.(2)Therealsoexistsabasicparadoxintradi tionalmodelingmethods.Oneaspectofthemodelsis neededtodescribetheconstitutiverelationofsoilac curatel… 相似文献