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排序方式: 共有73条查询结果,搜索用时 15 毫秒
1.
R. Wieler Th. Graf P. Signer S. Vogt G. F. Herzog C. Tuniz D. Fink L. K. Fifield J. Klein R. Middleton A. J. T. Jull P. Pellas J. Masarik G. Dreibus 《Meteoritics & planetary science》1996,31(2):265-272
Abstract— We determined He, Ne, Ar, 10Be, 26Al, 36Cl, and 14C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ~20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ~65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories. 相似文献
2.
B.L. Herzog R.A. Griffin C.J. Stohr L.R. Follmer W.J. Morse W.J. Su 《Ground Water Monitoring & Remediation》1989,9(2):82-89
Ground water contamination was discovered in 1981 in a monitoring well at the Earthline disposal facility near Wilsonville, Illinois. Organic chemicals had migrated at a rate 100 to 1000 times greater than predicted when the site received its permit to operate in 1978. Postulated failure mechanisms included migration through previously unmapped permeable zones, subsidence of an underground mine, organic-chemical and clay-mineral interactions, acid-mine drainage and clay interactions, trench-cover settlement, and erosion.
In this investigation, the Illinois State Geological Survey found the primary reason for the rapid migration: the presence of previously undetermined fractures and joints in glacial till. The inaccurate predictions of hydraulic conductivity were based on laboratory-determined values that did not adequately measure the effects of fractures and joints on the transit time calculations. Field-measured hydraulic conductivity values were generally 10 to 1000 times greater than their laboratory-measured counterparts, thus largely accounting for the discrepancy between predicted and actual migration rates in the transit time calculations. The problem was compounded, however, by the burial of liquid wastes and by trench covers that allowed excess surface runoff to enter the trenches. Organic-chemical and clay-mineral interactions may also have exacerbated the problem in areas where liquid organic wastes were buried. 相似文献
In this investigation, the Illinois State Geological Survey found the primary reason for the rapid migration: the presence of previously undetermined fractures and joints in glacial till. The inaccurate predictions of hydraulic conductivity were based on laboratory-determined values that did not adequately measure the effects of fractures and joints on the transit time calculations. Field-measured hydraulic conductivity values were generally 10 to 1000 times greater than their laboratory-measured counterparts, thus largely accounting for the discrepancy between predicted and actual migration rates in the transit time calculations. The problem was compounded, however, by the burial of liquid wastes and by trench covers that allowed excess surface runoff to enter the trenches. Organic-chemical and clay-mineral interactions may also have exacerbated the problem in areas where liquid organic wastes were buried. 相似文献
3.
Tilapia is a common fish species inhabiting inland waters and estuarine regions in Hong Kong and Southeast Asia, and useful for bio-monitoring of metal pollution. Metallothionein (MT) gene expression in fish tissues has been useful to sub-lethal risk assessment as biomarker of exposure to metal ions in fishes inhabiting metal contaminated area. To investigate metal inductions of Tilapia MT gene expression in vivo, Tilapias were injected with different concentrations of heavy metals and tissues were then removed for quantitative PCR assay using mimic PCR methods. All of the metal ions tested (Cu(2+), Cd(2+), Hg(2+), Ni(2+), Pb(2+) and Zn(2+)) were able to induce hepatic MT mRNA levels. Renal MT mRNA levels of Cd(2+) and Zn(2+) treated fish was not induced with significant fold induction, however MT mRNA levels in gills were sensitive to the administrations of these metal ions. These data indicated that Tilapia MT mRNA levels in gills and liver are sensitive biomarker of exposure to various metal ions. 相似文献
4.
KAr and/or 40Ar39Ar plateau ages of Allende samples—whole rock, matrix, chondrules, white inclusions–range from 3.8 AE for matrix of ?5 AE for some white inclusions, but cluster strongly near 4.53 AE. This age marks the dominant KAr resetting of Allende materials. Age spectra show disturbances due to 39Ar recoil or some other argon redistribution processes. Possible explanations for the apparent presolar ages (>4.6 AE) include: ?20% loss of 39Ar; ?40% loss of 40K ~3.8 AE ago with no loss of 40Arl trapped argon of unique 40Ar/36Ar isotopic composition; admixture of “very old” presolar grains. 相似文献
5.
6.
Taking continuous spatiotemporal in situ measurements with multi‐probes in fast‐flowing waters/rivers can be problematic because the sensors may be damaged by high shear forces and flotsam. To protect the multi‐probe and to enable easy access for the maintenance and calibration of the sensors, a special multi‐probe holder fixed in a hydrographic slot was developed. The validation of the probe system revealed a “memory effect” at short time scales (< 10 s) within sharp gradients caused by the overflow container of the multi‐probe rack keeping the sensors submerged in the sample water. Continuously recorded data (conductivity, temperature, pH, oxygen concentration and saturation, as well as in vivo fluorescence of chlorophyll‐a) from a research cruise on board the RV ALBIS along the river Elbe (river km 309) and entering the river Saale are presented. This river stretch upstream of the city of Magdeburg to the mouth of the Saale tributary was found to have a complex physicochemical character, which is attributable to the long mixing process of water from the river Saale and the river Elbe. 相似文献
7.
H. -J. Herzog 《Meteorology and Atmospheric Physics》1995,55(3-4):185-204
Summary The application of a radiative upper boundary condition (RUBC) in a mesoscale numerical weather prediction (NWP) model with hybrid vertical coordinate is presented. Results of two- and three-dimensional numerical simulations are discussed. Starting from earlier work by Klemp and Durran (1983) and Bougeault (1983) the radiative upper boundary condition is formally derived for a hybrid vertical coordinate. The basic assumptions include hydrostaticity, linearity, neglect of Coriolis effects and restriction to internal gravity waves. The resulting RUBC is global in space and local in time. In a second step. the RUBC is tested in a twodimensional vertical-plane version of the NWP model, in which essential properties of the full three-dimensional model have been preserved. Gravity wave experiments clearly show the superiority of the RUBC over the commonly used lid-type upper boundary condition. For the setting with an isolated bell-shaped mountain with resolution-independent steepness, the RUBC tends to work more effectively with increasing horizontal resolution. At the same time, the application of a radiative instead of a lid-type, and thus reflecting, upper boundary condition appears to become more important with decreasing mesh width. Finally, the RUBC is introduced into the full three-dimensional NWP model. This requires further approximations. In particular for a limited-area model, the geopotential field at the uppermost model level needs to be bi-periodic. Here, a linear detrending technique is applied. First results for a weather situation with strong northwesterly flow towards the Alps show that application of the RUBC drastically reduces the development of unrealistic standing, hydrostatic mountain waves, which become apprent as distinct mesoscale ridge-trough structures in the simulation with the lid-type upper boundary. Implications of the RUBC on the time-stepping procedure of the NWP model are also discussed. In the experiments whown, the additional RUBC-terms are treated explicitly. 相似文献
8.
Electron microprobe analyses and petrographic observations demonstrate that Almelo Township (L6), Beeler (LL6), Kalvesta (H4), Phillips County (L6), and Yocemento (L5) are typical ordinary chondrites. Selden has abnormally iron-rich silicates and nickel-rich metal, and it may have been a lower petrologic type that has been shocked to an LL5. Shielding corrected exposure ages range from 0.80 m.y. (Kalvesta) to 47.0 m.y. (Yocemento). 相似文献
9.
10.
To determine deformation and strength behaviour of a frozen morainic material uniaxial creep tests with constant load on remoulded samples have been carried out.
From the test results an analytical method describing the mechanical behaviour could be found.
In the following the results of this investigation are presented and an analytical solution is derived. In addition, other experimentally determined curves are compared with the calculated ones. For the material tested the proposed method leads to quite satisfactory results and is expected to do so also for other materials. 相似文献