Rare-earth elements in groundwaters from the Osamu Utsumi mine and Morro do Ferro analogue study sites, Poços de Caldas, Brazil     

N. Miekeley  H. Coutinho de Jesus  C.L. Porto da Silveira  P. Linsalata  R. Morse 《Journal of Geochemical Exploration》1992,45(1-3)

Data are presented on rare-earth elements (REE) in prefiltered (<450 nm) near-surface and deeper groundwaters and in corresponding particulate matter (>450 nm) from the Osamu Utsumi uranium mine and the Morro do Ferro thorium-REE-deposit. Groundwaters from both sites typically contain between 1–50 μg/l of total REE, but can reach values of up to 160 μg/l in the deepest borehole F4 (U-Mine: 150–415 m). Even higher REE concentrations of up to 29 mg/l were measured in acidic, sulfate-rich near-surface waters of the same site. The chondrite-normalized REE patterns in deeper, more reducing groundwaters and in their corresponding suspended particle fractions are similar to those observed in the bedrock (phonolites), indicating that bedrock leaching and secondary mineral sorption occurred without significant fractionation between these elements, in accordance with the only small variations in the stability constants of the expected REE-sulfate complexes in these waters. Groundwaters from the unsaturated zone of both sites show a very characteristic cerium depletion (less pronounced than that observed in the corresponding suspended particulate fractions), which is most probably related to the oxidation of Ce (III) under the prevailing E_h-conditions of these waters (600 to 800 mV), and to sorption/precipitation reactions of the much less soluble Ce(IV) species. Coarse particulate matter (>450 nm), composed mainly of amorphous ferric hydrous oxides, has a strong capacity for sorption of REE. This is shown by its very high REE concentrations, in some boreholes > 8,000 μg/g (total REE), and by the calculated association ratios R_a (ml/g), which are in the order of 10⁵ to 10⁶. The implications of these findings for the migration behavior of REE in both environments are discussed.  相似文献   

Chemical and physical characterization of suspended particles and colloids in waters from the Osamu Utsumi mine and Morro do Ferro analogue study sites, Poços de Caldas, Brazil     

N. Miekeley  H. Coutinho de Jesus  C.L. Porto da Silveira  C. Degueldre 《Journal of Geochemical Exploration》1992,45(1-3)

Data are presented on suspended particles and colloids in groundwaters from the Osamu Utsumi mine and the Morro do Ferro analogue study sites. Cross-flow ultrafiltration with membranes of different pore sizes (450 nm to 1.5 nm) was used to prepare colloid concentrates and ultrafiltrates for analyses of major and trace elements and U- and Th-isotopic compositions. Additional characterization of colloidal and particulate material was performed by ESCA, SEM and X-ray diffraction. The results indicate the presence of low concentrations of colloids in these waters (typically < 500 μg/l), composed mainly of iron/organic species. Minor portions of uranium and other trace elements, but significant fractions of the total concentrations of Th and REE in prefiltered waters (< 450 nm) were associated with these colloids.Suspended particles (> 450 nm), also composed mainly of hydrous ferric oxides and humic-like compounds, show the same trend as the colloids with respect to U, Th and REE associations, but elemental concentrations were typically higher by a factor of 1,000 or more. In waters of low pH and with high sulphate content, these associations are considerably lower. Due to the low concentrations of suspended particles in groundwaters from the Osamu Utsumi uranium mine (typically <0.5 mg/l), these particles carry only a minor fraction of U and the REE (<10% of the total concentrations in unfiltered groundwaters), but a significant, usually predominant fraction of Th (30–70%). The suspended particle load in groundwaters from the Morro do Ferro environment is typically higher than in those from the mine by a factor of 5 to 10. This suggests that U, Th and the REE could be transported predominantly by particulate matter. However, these particles and colloids seem to have a low capacity for migration.  相似文献   

新磁重联理论     

李晓卿  章振大 《紫金山天文台台刊》1999,18(3):338-342

本文研究了磁流体力学与高频等离子体波（ 包括纵横模式） 之间的精巧的相互作用。研究表明,这些等离激元会在电流片内诱发一种阻抗不稳定,并最终导至磁重联,出现爆发性不稳定。在高涨的离声湍动情况下,高温电流片模型必须采用反常电导率,而非库仑电导率。理论估算的结果与观测相一致。因此这种计及等离激元有质动力作用的新磁重联理论,基本上能解释耀斑现象。  相似文献   

已知e或a的先验值的初轨迭代算法   总被引：1，自引：0，他引：1  

贾沛璋  吴连大 《紫金山天文台台刊》1999,18(1):18-25

本文讨论由短弧测角资料,已知偏心率ｅ 或半长轴ａ 的先验值时,初轨的迭代算法。某根数的先验值可看作是对该根数的具有一定精度的观测量,在加权残差平方和达到极小意义下,本文导出了最小二乘估计的迭代算法。仿真结果显示,周期的估计精度主要取决于偏心率先验值的精度;当ｅ 足够小时,可用园轨道计算的ａ′作为ａ 的先验值,定出的初轨有较高精度。  相似文献   

The ocean–continent boundary off the western continental margin of Iberia—II. Crustal structure in the Tagus Abyssal Plain     

L. M. Pinheiro  R. B. Whitmarsh  P. R. Miles 《Geophysical Journal International》1992,109(1):106-124

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El Niño may affect growth behaviour of Amazonian tress     

Roland E. Vetter  Paulo C. Botosso 《GeoJournal》1989,19(4):419-421

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Angular dislocation of the earth principal axes of inertia     

W. C. C. Silva  H. U. Pilchowski  L. D. D. Ferreira 《Journal of Geodesy》1980,54(2):181-189

The coefficientsC ₂₁ andS ₂₁ are usually considered to be zero in theory (e.g. the axis of earth rotation was used as the principal axis of inertia). However, satellite measurements show thatC ₂₁ as well asS ₂₁ are non-zero, indicating that the axis of rotation of the earth is not the principal axis of inertia. This work determines the angles by which the principal axes of inertia must be rotated in relation to the geocentric coordinate system (where theZ axis coincides with the rotating axis of the earth).  相似文献   

Seismic qualification of electrical equipment using a uniaxial test     

Clarence W. De Silva 《地震工程与结构动力学》1980,8(4):337-348

The analytical development of a uniaxial test for the seismic qualification of electrical equipment is presented. This method comprises a single test using a uniaxial excitation having certain minimum intensity applied at the base of the test package in a predetermined optimal direction. It is anticipated that the proposed procedure would be more economical and less time consuming than, but functionally equivalent to, presently employed series of multiaxial tests. The test is shown to be superior to the symmetric tests. The determination of the minimum intensity of the optimal orientation of the base excitation requires a preliminary frequency response test which is a slightly more elaborate version of the sine sweep test presently employed to determine the resonance frequencies of the test package. A simulated test is presented to compare the proposed method with the uncorrelated triaxial test and the symmetric uniaxial test.  相似文献   

DDTs in Balaenopterids (Cetacea) from the Chilean coast     

Silvio Pantoja  Luis Pastene  Jose Becerra  Mario Silva  Victor A. Gallardo 《Marine pollution bulletin》1984,15(12):451

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Transient convection over the Amazon/Bolivia Region and the cynamics of droughts over Northeast Brazil     

Dr. J. Buchmann  Prof. Dr. Pedro L. da Silva Dias  Dr. A. D. Moura 《Meteorology and Atmospheric Physics》1986,34(3-4):367-384

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