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11.
Lars Olov Andersson 《Physics and Chemistry of Minerals》2008,35(9):505-520
The EPR spectra of Maxixe-type beryl contain a large number of overlapping signals. The angular dependence of the 1:3:3:1
signal typical for the CH3 radical shows that this radical is located at the center of the channel cavity with its symmetry axis parallel to the crystal
c-axis and is rotating around this axis. Its EPR spectrum is axially symmetric with g
// = 2.00263, g
⊥ = 2.00249 and A// = 2.288 mT, A⊥ = 2.256 mT. These anisotropies have the opposite signs of those found for surface-adsorbed methyl radicals. Hydrogen atoms
are located at position 2a at the center of the beryl cavity and the EPR parameters of the narrow doublet signal are A
0 = 1,407 MHz and g = 2.00230. Another doublet signal, which is broader and has axial symmetry with g
// = 2.00265, g
⊥ = 2.00625 and A// = 0.895 mT, A⊥ = 0.885 mT, could come from a HCO3 radical. One narrow and easily saturated signal with g
// = 2.00227 and g
⊥ = 2.00386 is interpreted to arise from a carbon monoxide radical in the beryl channel, oriented with its axis parallel to
the crystal c-axis. Additional weak doublet lines, which have similar g values as the carbon monoxide radical, are created by nearby hydrogens. A powder spectrum with g
// = 2.0017 and g
⊥ = 2.0004 appears upon UV irradiation of the single crystal and is easily saturated. This spectrum is interpreted to arise
from a carbon dioxide radical, which rotates around its symmetry axis. 相似文献
12.
Experiments were conducted in an oscillatory water tunnel to investigate what effects temporal inertia has on the resistance of a granular medium. The flow law governing stationary porous media flow is reasonably well accepted and understood but the effects of unsteady flow have commonly been neglected. The present research was designed to assess the magnitude of the acceleration effects on media of uniformly packed spheres of equal diameter and on one sample of randomly placed stone.Oscillatory flow tests were made in a large oscillatory flume tunnel with periods varying from 3 to 12 seconds. The influence of properties of the medium (grain size and porosity) were tested by using spheres with two different diameters and packing each size sphere in different geometric arrangements. Tests made on a stone sample provided a qualitative assessment of the effects of more random material properties.For the experiments described in this paper, the Forchheimer unsteady-stationary flow law described the oscillatory measurements well when velocities and energy losses were maximum. Empirical coefficients determined from steady-stationary flow were generally found to apply to the unsteady flow, however some evidence of dependency on the period of oscillation was noted. 相似文献
13.
The concentrations of total carbonate (Ct), sulphate, sulphide, thiols and oxygen, the ratio between the stable sulphur isotopes 34S and 32S in sulphate and sulphide, and the density (used to calculate salinity) were determined on samples from the water column of Framvaren, a superanoxic fjord in southern Norway. From a depth of 18m (the oxic-anoxic boundary) the initial sulphate concentration, ([SO4]init), as calculated from salinity, is significantly higher than the sum of the measured sulphur species. This is attributed to a loss of sulphur from the water column. The amount of total carbonate produced, corrected for the initial concentration (Ct - 2.4 Sal/35) is found to be proportional to the amount of sulphate consumed, ([SO4]init - [SO4]), according to the following relation Ct- 2.4 Sal/35 = 1.84 ([SO4]init - [SO4]). Isotopic fractionation caused by bacterial sulphate reduction in the anoxic part of the water column produces sulphide with a δ34S 40‰ lower than the δ34S for sulphate at corresponding depths. The isotopic fractionation also results in δ34S value for the remaining sulphate at depths below 80 m being considerably higher than the mean value for ocean water, which is close to + 20‰. The δ34S values for sulphate at depths between 10 and 50 m were lower than + 20‰ which indicates oxidation of sulphide, which follows upon diffusion of sulphide from deeper parts of the water column and inflow of oxygenated seawater over the sill into the anoxic water of the fjord. A conclusive scenario of the Framvaren sulphur chemistry is presented. 相似文献
14.
15.
格陵兰东南部和相邻大洋表层气温时序中记录了一个急剧的事件。这一事件大约出现在3100a(模拟年) ,持续约40a ,以温度降低3°C为特征。由于其峰值比平均值高6个标准偏差(σ)以上 ,可以认为降温是急剧的。如果该区域年平均表层气温时序正常排布 ,那么这种异常可能每数亿年出现一次,如此大幅度降温持续那么久的概率极小。如果将不足40a的变化从时序中去掉 ,那么事件高峰期表层气温低于平均值10~11σ。大气层较低层位的这种急剧降温源于海面温度急剧下降。大约3086a开始 ,格陵兰东海岸中部滨外发育了约0.5°C… 相似文献
16.
In the present study, long-term exposure to PCB resulted in marked induction of the xenobiotic biotransformation enzymes UDP glucuronosyl transferase, glutathione transferase and DT-diaphorase (measured as menadione reductase and DCPIP reductase) in rainbow trout 15 or 20 weeks post-injection during the experimental period. The increase of the phase II enzymes were paralleled by a marked increase of the glutathione reductase activity. These results indicate that prolonged exposure to PCB results in increased production of organo-radicals. 相似文献
17.
18.
19.
C. Rabouille H. Stahl F. Bassinot A. Tengberg J. Brunnegard P. Hall K. Kiriakoulakis J. -L. Reyss L. Dezileau P. Crassous P. Roos R. S. Lampitt 《Progress in Oceanography》2001,50(1-4)
Fluxes contributing to the particulate carbonate system in deep-sea sediments were investigated at the BENGAL site in the Porcupine Abyssal Plain (Northeast Atlantic). Deposition fluxes were estimated using sediment traps at a nominal depth of 3000 m and amounted to 0.37±0.1 mmol C m−2 d−1. Dissolution of carbonate was determined using flux of total alkalinity from in situ benthic chambers, is 0.4±0.1 mmol C m−2 d−1. Burial of carbonate was calculated from data on the carbonate content of the sediment and sedimentation rates from a model age based on 14C dating on foraminifera (0.66±0.1 mmol C m−2 d−1). Burial plus dissolution was three times larger than particle deposition flux which indicates that steady-state is not achieved in these sediments. Mass balances for other components (BSi, 210Pb), and calculations of the focusing factor using 230Th, show that lateral inputs play only a minor role in this imbalance. Decadal variations of annual particle fluxes are also within the uncertainty of our average. Long-term change in dissolution may contribute to the imbalance, but can not be the main reason because burial alone is greater than the input flux. The observed imbalance is thus the consequence of a large change of carbonate input flux which has occured in the recent past. A box model is used to check the response time of the solid carbonate system in these sediments and the time to reach a new steady-state is in the order of 3 kyr. Thus it is likely that the system has been perturbed recently and that large dissolution and burial rates reflect the previously larger particulate carbonate deposition rates. We estimate that particulate carbonate fluxes have certainly decreased by a factor of at least 3 and that this change has occurred during the last few centuries. 相似文献
20.
The stochastic properties of the drag force maxima on a circular cylinder subjected to nonlinear random waves are investigated. Unseparated laminar high Reynolds number flow is considered. A simplified approach based on second order Stokes waves is presented, including the sum-frequency effect only. It is demonstrated how a drag force formula valid for regular linear waves can be used to find the cumulative distribution function of individual drag force maxima for nonlinear irregular waves. Here the [Wang, 1968] drag force coefficient is used. 相似文献