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91.
Wenguang Yang Hongbo Zheng Ke Wang Xin Xie Guocheng Chen Xi Mei 《Frontiers of Earth Science》2008,2(2):170-176
Sediments with high sedimentation rate at site MD05-2905 in the Northeastern slope of the South China Sea provide unique materials
for a high-resolution study on the paleoenvironment. Based on precise dating of AMS 14C, grain size analysis of terrigenous debris at core MD05-2905 was conducted after organic matter, biological carbonate and
biogenic opal were removed. The results show that 15.5–63.5 μm coarse grain size ingredients may indicate East Asian winter
monsoon changes and that 2–9 μm fine grain size ingredients may be used as a proxy of evolution of the East Asian summer monsoon.
The results of grain size analysis, which suggest East Asian monsoon intensity, reveal that a winter monsoon dominated the
glacial regime and a summer monsoon dominated the Holocene regime. It was also shown that the summer monsoon increased gradually,
experienced several abrupt changes and reached a culmination in the early Holocene (11200–8500 a B.P.) since 36 ka. Controlled
by precession periodicity, it may be related with the amount of solar radiation at the highest stage, which needs further
study.
__________
Translated from Advances in Earth Science, 2007, 22(10): 1012–1018 [译自: 地球科学进展] 相似文献
92.
In northern Jiangsu coastal zone area, Guanhe River is the biggest river and has the best navigation conditions among rivers
which flow into the Yellow Sea. The grain sizes show gradual increase from the high intertidal zone to lower intertidal zone.
The heavy metal values have slight changes along both sides of the river mouth, but show an evident change perpendicular to
the tidal flat. In the latter case, they show a good correlation with grain size fluctuation, that is, the heavy metal values
gradually decline when the grain size increases from the high intertidal zone to the lower intra-tidal zone. Analyses of the
heavy metal elements show that on the Guanhe estuary surface sediment, the content of the elements Hg, As and Cu is above
background values; Pb and Zn contents are rather close to the background values; and Cd content is less than the background
values. The element Hg comes out to be harmful in a medium level to ecological environment, while the elements of Cr, As,
Cu, Pb, Zn and Cd fall in a safe range of MPL. On the whole, Guanhe estuary tidal flat is not very harmful to the ecology
in terms of the heavy metals.
__________
Translated from Marine Geology & Quaternary Geology, 2007, 27(5): 23–32 [译自: 海洋地质与第四纪地质] 相似文献
93.
对在上海市建设用地勘测定界过程中涉及的土地权属界线认定、原土地用途划分时所现的若干问题进行了详细探讨,同时从政策角度、技术角度提出了以上问题的相应解决途径。 相似文献
94.
在平顶山矿工路路面改造工程中,使用GX-2型及RD-4000型地下管线探测仪探测地下管网布设情况。根据地下管线种类、管线布设方位、埋置深度、探测难度大小进行了多次试验,在此基础上确定了电磁探测技术与方法:利用直连法提高被测管线中的交变电流,压制邻近平行管线和地下介质中的异常反映;在多管并存、且间距较小的情况下,应选择“梯度法”对磁场水平分量垂直梯度ΔHx进行观测,以得到最大清晰异常;另外,还应根据具体情况,合理选择诸如压制旁侧管线法、选择发射法、偏移感应法、动源发射法等发射方式,保证目标管线中有较强异常呈现。在管线密集区,应尽可能地降低工作频率,以减小旁侧管线中产生的二次电流及二次磁场;为防止信噪比下降,可适当减小收发距,以提高接收机的灵敏度。 相似文献
95.
CSU-RAMS模式在区域气侯模拟中的应用 总被引:1,自引:0,他引:1
将CSU-RAMS(中尺度)数值模式改造成“区域气候数值模式”以及进行区域气候数值模拟的试验研究。说明将有限区域中尺度数值模式与GCM模式嵌套应用到区域气候数值模拟研究上能够取得有意义的结果。它能在一定程度上改善GCM模式的不足。可以更为细致地描述大气环流的变化特征,是了解区域气候变化的有效方法之一。 相似文献
96.
Numerical studies using the displacement discontinuity method show that a single shear crack under compression propagates in its own direction, because such propagation results in the maximum release of strain energy. The methods of linear elastic fracture mechanics may not be used for such a closed crack, and the stress intensity factors are meaningless in that case. Laboratory observations of propagation by means of kinks at an angle of approximately 70° to the crack may be due to heterogeneities, to the effect of a preexisting crack, to end effects, to microcracking, or to some combination of these factors. Such kinks may thus be local phenomena which cannot release most of the strain energy, and are not incompatible with our numerical results which are based on a global energy balance. 相似文献
97.
Xian-Huan Wen 《Mathematical Geology》1994,26(6):717-731
Field tests of hydraulic conductivity (e.g., injection test, pumping test, etc.) in low permeability formations are subject to censoring due to the detection limit of the instruments used. An iterative method of estimating the mean and variance of hydraulic conductivity data with a presumed log-normal distribution function is presented. This method accounts for the data that are actually below the lower detection limit (called truncated data) and thus gives distribution parameters that are more representative for the underlying distribution. The proposed method is then tested on two simulated normally distributed random datasets having different variances. The results show that the means and variances estimated by the proposed method are very accurate. Finally, the method is used to estimate the mean and variance of hydraulic conductivity data from single hole water injection tests in a fractured geological formation. 相似文献
98.
Chang-Jo F. Chung 《Mathematical Geology》1993,25(7):851-865
Multivariate statistical analyses have been extensively applied to geochemical measurements to analyze and aid interpretation of the data. Estimation of the covariance matrix of multivariate observations is the first task in multivariate analysis. However, geochemical data for the rare elements, especially Ag, Au, and platinum-group elements, usually contain observations the below detection limits. In particular, Instrumental Neutron Activation Analysis (INAA) for the rare elements produces multilevel and possibly extremely high detection limits depending on the sample weight. Traditionally, in applying multivariate analysis to such incomplete data, the observations below detection limits are first substituted, for example, each observation below the detection limit is replaced by a certain percentage of that limit, and then the standard statistical computer packages or techniques are used to obtain the analysis of the data. If a number of samples with observations below detection limits is small, or the detection limits are relatively near zero, the results may be reasonable and most geological interpretations or conclusions are probably valid. In this paper, a new method is proposed to estimate the covariance matrix from a dataset containing observations below multilevel detection limits by using the marginal maximum likelihood estimation (MMLE) method. For each pair of variables, sayY andZ whose observations containing below detection limits, the proposed method consists of three steps: (i) for each variable separately obtaining the marginal MLE for the means and the variances,
,
,
, and
forY andZ: (ii) defining new variables by
and
and lettingA=C+D andB=C–D, and obtaining MLE for variances,
and
forA andB; (iii) estimating the correlation coefficient YZ by
and the covariance
YZ
by
. The procedure is illustrated by using a precious metal geochemical data set from the Fox River Sill, Manitoba, Canada. 相似文献
99.
Bruce A. Callander 《GeoJournal》1997,42(1):55-63
IPCCs statement in its 1995 report (IPCC 1996) that a human influence was discernible in global climate has been widely quoted but often misunderstood. The character of the evidence underpinning this detection statement is explained so that its strengths and weaknesses can be better understood and the subtleties of its message better appreciated. To demonstrate the close linkage between the government-approved summary and the underlying chapters of the IPCC report the detailed evolution of the detection statement from first draft through to the form finally approved by the IPCC is described. 相似文献
100.
扬子地台前寒武纪-寒武纪界线地层的微体植物化石群 总被引:10,自引:2,他引:8
前寒武纪一寒武纪界线地层在扬子地台发育良好、分布广泛,并有包括微体植物群、海藻、瓶形原生物、具硬体动物及‘澄江动物群’等化石的发现。因而,扬子地台成为研究前寒武纪-寒武纪界线生物地层的代表地区之一。基于对扬子地台前寒武纪-寒武纪界线地层已知微体植物化石记录的回顾和论定,总结概括了下寒武统微体植物化石组合:寒武系最底部硅质磷块岩中的Micrhystridium-Paracymatiosphaera-Megathrix组合和较高层位页岩的Skiagia-Annulum-Archaeodiscina组合。它们分别与Anabarites-Circotheca-Protohertzina小壳动物化石带和Parabadiella及Eoredlichia三叶虫带相对应。与东欧地台疑源类生物地层相对照,扬子地台Micrhystridium-Paracymatiosphaera-Megathrix组合的纵向分布大体和东欧地台Asteridiumtornatum-Comasphaeridiumvelvetum组合带相一致,而以上两地台的化石组合产出层位可能都略高于纽芬兰东部剖面,依据Phycodespedum所厘定的寒武系底界? 相似文献