Sampling variance of a T-year flood estimated by curve-fitting     

S. X. Wang  Vijay P. Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》1994,8(3):233-258

The sampling variance of a T-year flood when estimated using a curve-fitting method results from the errors in hydrologic observations, plotting positions, and model-fitting. This paper develops a method to quantify the contribution of plotting positions to the sampling variance of the T-year flood magnitude. Application of the method to 150 flood-flow data sets of 41 rivers in the People's Republic of China show that the errors due to plotting positions contribute more to the sampling variance than others.  相似文献   

试论干旱区流域开发中人口、资源、环境和经济发展的协调   总被引：5，自引：1，他引：5  

张兴平  张林源  韩魁哲 《干旱区地理》1994,17(2):38-43

本文讨论了干旱区流域开发中的人口承载力、人口超载和移民问题；资源开发和人类活动的强度及其环境问题。认为要解决和预防这些问题，必须协调人口、资源、环境和经济发展（PRED）。在对PRED协调的必要性，可能性，理论基础和一般模式，有关措施作了初步分析之后，以宁夏黄河干流流域开发为例，讨论了干旱区流域开发中PRED的协调问题。  相似文献   

Seismic wave propagation in complex crust-upper mantle media using 2-D finite-difference synthetics   总被引：1，自引：0，他引：1  

S. O. Hestholm  E. S. Husebye  B. O. Ruud 《Geophysical Journal International》1994,118(3):643-670

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Investigations of S_n and P_n phases in the area of the upper Rhine Graben and northern Switzerland     

T. Plenefisch  S. Faber  K.-P. Bonjer 《Geophysical Journal International》1994,119(2):402-420

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Changes in the structural and magnetic properties of Ni–substituted hematite prepared from metal oxinates     

C.?SaragoviEmail author  J.?Arpe  E.?Sileo  R.?Zysler  L. C.?Sanchez  C. A.?Barrero 《Physics and Chemistry of Minerals》2004,31(9):625-632

Samples prepared by the novel method based on the thermal decomposition at 700 °C in air of mixed Fe and Ni oxinates were characterized by thermogravimetric analysis, X-ray diffraction, magnetization measurements, and variable-temperature Mössbauer spectroscopy. It is found that the combustion treatment produces Ni-hematite and trevorite, the fraction of the latter increasing with the increment of Ni in the metal oxinates. Results indicate that the substitution of Ni²⁺ for Fe³⁺ in the hematite structure, which was found to be less than 5.3 mol%, is accompanied by the presence of oxygen and structural vacancy sites. Both the metal replacement and the presence of defects cause the a and c cell hematite parameters to decrease. The Néel temperature and the difference between the saturation fields for the antiferromagnetic AF and the weakly ferromagnetic WF phases are also found to decrease with nickel content. These effects are due to the fact that the magnetic behavior of hematite depends on the presence of Ni, vacancy sites, and lattice distortion. The large decrease in the Néel temperature with Ni doping suggests that structural vacancies are also present On the contrary, Ni incorporation does not appreciably affect the Morin temperature and the temperature range in which both AF and WF phases coexist. It is suggested that these effects are probably due to the differing effects that Ni and defects can produce on the magnetic dipolar and the single ion anisotropies.  相似文献   

三峡库区坡地物质的地球化学特征--以三峡草堂河流域为例     

陈可锋杨达源  姜洪涛周彬徐永辉  刘庆友董杰 《华东地质学院学报》2004,27(2):141-146

三峡水库建成后,三峡坡地物质成为三峡水库泥沙主要来源之一,三峡坡地物质的地球化学特征的研究对于三峡坡地水土保持与管理利用具有重要的意义。通过分析各坡度段物质的常量元素全量、磁化率特征以及粘土矿物种类等地球化学的特征,定性地说明了各坡度段从缓坡一斜坡一陡坡段风化作用强度依次减弱,相应的坡面侵蚀作用逐渐增强。而在相同坡度段,表层与一定深度物质的地球化学特征值变化不大,这说明土壤年轻化,成土作用比较弱。  相似文献   

Middle Permian palaeobiogeography study in East Kunlun,A’nyêmaqên and Bayan Har     

Wang?Yongbiao?Email author  Yang?Hao 《中国科学D辑(英文版)》2004,47(12):1120-1126

Three regions can easily be identified in the study area according to the Middle Permian palaeobiogeographic distribution of biota, they are the southern slope of East Kunlun, A'nyêmaqên and Bayan Har. Biotic constitution and ecology in the southern slope of East Kunlun and Bayan Har are very similar. Both the diversity and abundance of organisms in these two areas are very high and reefs are widely developed. However, biotic diversity and abundance in A'nyêmaqên which is between the above two areas are obviously low. Differentiation of palaeobiogeographic distribution in these areas should be due to the baring of A'nyêmaqên ocean in the time of Middle Permian. Middle Permian radiolarian chert and thick abyssal red ooze are widely spread in A'nyêmaqên, implying that the A'nyêmaqên ocean had a great scale in size. Vast scale of deep ocean basin became an impassable gulf for some of the benthos, and as a result, only part of the organisms could have the chance to get to the isolated islands situated in ocean basin. Small living space and hard conditions in the islands further limited the abundance and diversity of biota. Tectonic background reflected by the geochemical study of basalt in the three areas is coupling well enough with the palaeobiogeographic division.  相似文献   

Static compression of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>: linear incompressibility of lattice parameters and high-pressure transformations     

H.?Liu  W. A.?Caldwell  L. R.?Benedetti  W.?Panero  R.?JeanlozEmail author 《Physics and Chemistry of Minerals》2003,30(9):582-588

The high-pressure behavior of -Fe₂O₃ has been studied under static compression up to 60 GPa, using a laser-heated diamond anvil cell. Synchrotron-based angular-dispersive X-ray diffraction shows that the sample remains in the corundum structure up to 50 GPa, but with the appearance of coexisting diffraction lines from a high-pressure phase at pressures above 45 GPa. A least-squares fit of low-pressure phase data to an Eulerian finite-strain equation of state yields linear incompressibilities of K _{a 0}=749.5 (± 18.4) GPa and K _{c 0}= 455.7 (± 21.4) GPa, differing by a factor of 1.6 along the two directions. The enhanced compressibility of the c axis may lead to breaking of vertex- or edge-sharing bonds between octahedra, inducing the high-pressure phase transformation at 50 GPa. Analysis of linear compressibilities suggests that the high-pressure phase above 50 GPa is of the Rh₂O₃ (II) structure. Continuous laser heating reveals a new structural phase transformation of -Fe₂O₃ at 22 GPa, to an orthorhombic structure with a=7.305(3) Å, b=7.850(3) Å, and c=12.877(14) Å, different from the Rh₂O₃ (II) structure.  相似文献   

网状河流的构型、流量-宽深比关系和能耗率   总被引：6，自引：0，他引：6  

王随继 《沉积学报》2003,21(4):565-570

网状河流作为一类新河型,已经受到研究者的关注,但对其研究还不充分.该研究基于目前已经报道过的资料及新近取得的研究成果,从河流构型、河道过水断面宽深比与流量关系及能耗率等方面对该河型展开论述,期望引起大家对该河型的兴趣.网状河流在许多方面表现出了独有的特色.从平面构型来看,它以相互连通的多河道围绕非常稳定的泛滥盆地为特征,其中泛滥盆地上植被发育、沼泽湖泊可见.从河道纵、横剖面来看,它具有非常小的河道比降和一般小于40的河道宽深比,总体上属于各类河型中最小的.从沉积体系的剖面构型来看,它以多个孤立的河道砂体"漂浮"在细粒泥质沉积物中为特征.在河道过水断面宽深比与流量的半对数图中可见,其宽深比随流量的增大而减小,并且其散点位于各类河流的最下部.由于其河道比降一般很小,多河道体系中的单个河道的流量相对于其决口前的老河道显然较小,从而其能耗率就相对很小.文中所讨论到的长江三口分流网状河道:东松滋河、西松滋河、虎渡河、藕池河、北藕池河和松澧合流,其能耗率分别为3.0 W/m2,5.5 W/m2,2.8 W/m2,6.4 W/m2,3.7 W/m2和2.7 W/m2,显然都小于10 W/m2,这与长江主河道在枝江附近的140 W/m2相比,差两个数量级.所有这些特征都预示着网状河流与以长江中下游为代表的分汊河流之间有着完全不同的特性,与其他河型更是大相径庭.  相似文献   

长江芦家河浅滩段石泓大开挖方案的研究   总被引：2，自引：1，他引：1       下载免费PDF全文

陈立  崔承章  谢葆玲 《水科学进展》2003,14(3):341-344

三峡水库蓄水运用后,长江芦家河浅滩段将出现局部坡陡流急的航道问题,石泓大开挖为解决此问题的方案之一.采用全沙动床模型实验方法,研究了石泓大开挖方案实施后对改善航道条件、对本河段及上游河段河势变化可能产生的影响等.研究表明:石泓大开挖方案将改善本河段的航行条件;也将使本河段枯水期的主、支汊易位;改变松滋河的分流特性;与此同时石泓大开挖方案将加剧上游水位的下降,并可能因此影响葛洲坝船闸的正常运行;挖槽中推移质泥沙的回淤有待于今后的进一步研究.  相似文献