The structural state of iron in oxidized vs. reduced glasses at 1 atm: A57Fe Mössbauer study

A general model for the structural state of iron in a variety of silicate and aluminosilicate glass compositions in the systems Na₂O-Al₂O₃-SiO₂-Fe-O, CaO-Al₂O₃-SiO₂-Fe-O, and MgO-Al₂O₃-SiO₂-Fe-O is proposed. Quenched melts with variable Al/Si and NBO/T (average number of nonbridging oxygens per tetrahedrally coordinated cation), synthesized over a range of temperatures and values of oxygen fugacity, are analyzed with⁵⁷Fe Mössbauer spectroscopy. For oxidized glasses with Fe³⁺/∑Fe>0.50, the isomer shift for Fe³⁺ is in the range ～0.22–0.33 mm/s and ～0.36 mm/s at 298 K and 77 K, respectively. These values are indicative of tetrahedrally coordinated Fe^3?. This assignment is in agreement with the interpretation of Raman, luminescence, and X-ray,K-edge absorption spectra. The values of the quadrupole splitting are ～0.90 mm/s (298 K and 77 K) in the Na-aluminosilicate glasses and compare with the values of 1.3 mm/s and 1.5 mm/s for the analogous Ca- and Mg-aluminosilicate compositions. The variations in quadrupole splittings for Fe³⁺ are due to differences in the degree of distortion of the tetrahedrally coordinated site in each of the systems. The values of the isomer shifts for Fe²⁺ ions in glasses irrespective of Fe³⁺/∑Fe are in the range 0.90–1.06 mm/s at 298 K and 1.0–1.15 mm/s at 77 K. The corresponding range of values of the quadrupole splitting is 1.75–2.10 mm/s at 298 K and 2.00–2.35 mm/s at 77 K. The temperature dependence of the hyperfine parameters for Fe²⁺ is indicative of noninteracting ions, but the values of the isomer shift are intermediate between those values normally attributable to tetrahedrally and octahedrally coordinated Fe²⁺. The assignment of the isomer-shift values of Fe²⁺ to octahedral coordination is in agreement with the results of other spectral studies. For reduced glasses (Fe³⁺/∑Fe≈<0.50), the value of the isomer shift for Fe³⁺ at both 298 K and 77 K increases and is linearly correlated with decreasing Fe³⁺/∑Fe in the range of \(f_{O_2 } \) between 10^?3 and 10^?6 atm when a single quadrupole-split doublet is assumed to represent the absorption due to ferric iron. The increase in value of the isomer shift with decreasing \(f_{O_2 } \) is consistent with an increase in the proportion of Fe³⁺ ions that are octahedrally coordinated. The concentration of octahedral Fe³⁺ is dependent on the \(T - f_{O_2 } \) conditions, and in the range of log \(f_{O_2 } \) between 10^?2.0 and 10^?5 a significant proportion of the iron may occur as iron-rich structural units with stoichiometry similar to that of inverse spinels such as Fe₃O₄, in addition to isolated Fe²⁺ and Fe³⁺ ions.     

Downscaling a twentieth century global climate simulation to the North Sea

The regional ocean model system (ROMS) is used to downscale a 26-year period of the twentieth century 20C3M experiment from the global coupled Bergen climate model (BCM) for the North Sea. Compared to an observational-based climatology, BCM have good results on the mean temperature, except for too low winter temperature. This is connected to a too weak inflow of Atlantic water. The downscaling gives added value to the BCM results by providing regional details, doubling the Atlantic inflow, and improving the mean winter temperature. For mean salinity, BCM has values very close to the climatology, whereas the downscaling becomes too fresh. The downscaling, however, improves the sea surface salinity, the vertical structure, and the Norwegian Coastal Current. It is concluded that the downscaling procedure as presented here is a suitable tool for assessing the future Atlantic inflow and sea temperature in the North Sea based on a global climate projection.     

利用多波段分光仪观测生物有效UV辐射、臭氧总量和云的影响

该文介绍了一种利用紫外分光仪进行辐照度观测获取生物有效UV辐射、臭氧总量和云的光学厚度的方法。这些量是观测的辐照度与辐射传输计算相结合后测定的。该方法被用于具有 4个中心波长为 30 5、32 0、340和 380nm ,宽度为 10nm的 4波段分光仪。将这种仪器与高精度分光光度计在美国圣迭戈不同天气条件下进行了为期 1周的对比观测。当太阳天顶角 (SZA) <80°时 ,CIE 权重UV辐射剂量率的相对误差为 1.4± 3.2 %。晴天条件下 ,当SZA <80°时 ,相对误差为 0 .6± 1.5%。该仪器观测的辐照度推算的臭氧总量对云并不敏感。这种仪器还与Dobson和Brewer仪器在挪威奥斯陆进行了一年多的对比观测。整个观测期间 (包括有云的情况 )获得的臭氧总量相对误差为 0 .3± 2 .9%。当晴天和SZA <6 0°时 ,标准差减小到 1.9%。将仪器观测中所获得的臭氧总量和云的光学厚度输入到辐射传输模式 ,可以计算从 2 90～ 4 0 0nm分辨率为 1nm的整个光谱。这样计算的光谱与同时用高精度分光光度计观测的光谱在晴天及有云的条件下非常一致 ,所以 ,这种光谱可以用于测定任何作用光谱的辐射剂量率。而计算这种光谱只需要一个UV B通道和一个UV A通道     

地倾斜及水文地球化学参数异常与地震活动最佳关系探索

1　ПостановказадачиНадежныйпрогнозвременивозникновенияземлетрясенияможетбытьобеспеченлишькомплексомпрогностическихпараметров. Прогностическаяценностькаждогопараметранеодинакова,какиразличенмеханизмформированияаномальныхэффектоввразличныхполях.Этосоздает…     

Hydrogeologic studies for nuclear-waste disposal in Sweden

Safety Report 1997 (SR 97) of the Swedish Nuclear Fuel and Waste Management Company is a comprehensive performance assessment of three hypothetical radioactive waste repositories in Sweden. It includes hydrogeologic studies (data compilation, parameter synthesis, and groundwater flow modeling) to determine groundwater flow and the associated uncertainties for the three sites. This report reviews and compares the hydrogeologic characterization programs, the site characteristics, and the groundwater flow models used in the SR 97 performance assessment. Although differences in site-characterization programs tend to mask differences in site characteristics, the sites do have notable differences that affect the results of the performance assessment. The effects of model uncertainties evaluated by the variant cases appear to be smaller than the variability of results for the base case (best estimate of site conditions) of each site. Electronic Publication     

Future ocean uptake of CO2: interaction between ocean circulation and biology

We discuss the potential variations of the biological pump that can be expected from a change in the oceanic circulation in the ongoing global warming. The biogeochemical model is based on the assumption of a perfect stoichiometric composition (Redfield ratios) of organic material. Upwelling nutrients are transformed into organic particles that sink to the deep ocean according to observed profiles. The physical circulation model is driven by the warming pattern as derived from scenario computations of a fully coupled ocean-atmosphere model. The amplitude of the warming is determined from the varying concentration of atmospheric CO₂. The model predicts a pronounced weakening of the thermohaline overturning. This is connected with a reduction of the transient uptake capacity of the ocean. It yields also a more effective removal of organic material from the surface which partly compensates the physical effects of solubility. Both effects are rather marginal for the evolution of atmospheric pCO₂. Running climate models and carbon cycle models separately seems to be justified. Received: 9 August 1995 / Accepted: 22 April 1996     

Boundary-layer ozone depletion as seen in the Norwegian Arctic in spring

Several years of measurements of ozone, hydrocarbons, sulphate and meteorological parameters from Spitsbergen in the Norwegian Arctic are presented. Most of the measurements were taken on the Zeppelin Mountain at an altitude of 474 m a.s.l. The focus is the episodes of ozone depletion in the lower troposphere in spring, which are studied in a climatological way. Episodes of very low ozone concentrations are a common feature on the Zeppelin Mountain in spring. The low ozone episodes were observed from late March to the beginning of June. When the effect of transport direction was subtracted, the frequenty of the low ozone episodes was found to peak in the beginning of May, possibly reflecting the seasonal cycle in the actual depletion process. Analyses based on trajectory calculations show that most of the episodes occurred when the air masses were transported from W-N. Ozone soundings show that the ozone depletion may extend from the surface and up to 3–4 km altitude. The episodes were associated with a cold boundary layer beneath a thermally stable layer, suppressing mixing with the free troposphere. The concentration of several individual hydrocarbons was much lower during episodes of low ozone than for the average conditions. The change in concentration ratio between the hydrocarbons was in qualitative agreement with oxidation of hydrocarbons by Br and Cl atoms rather than by OH radicals.     

Calibration of regional pollen data to construct maps of former forest types in southern Sweden

A method was developed to construct maps of former forest types based on regional pollen data in southern Sweden. The considered species were Alnus, Betula, Carpinus, Corylus, Fagus, Fraxinus, Juniperus, Picea, Pinus, Populus, Quercus, Salix, Tilia and Ulmus. A network of 37 regional pollen sites with high data quality from lakes and peat deposits were selected from Sweden south of 60 ° N. Pollen percentage values were calculated and converted into estimates of tree composition. For controlling the reliability of the reconstruction, the estimates from the core-tops were compared with present day forest inventory data, and local pollen diagrams were compared with the regional pollen diagrams. An inverse distance weighted interpolation algorithm was used to generate maps for each tree species distribution at 2000 BP, 1500 BP, 1000 BP, 500 BP and 0 BP. A supervised classification routine was implemented to generate nine different forest types common to the five studied time intervals. The maps show that the amounts and patterns of distribution of the species and the forest types have varied in a significant but systematic manner through time. The changes are due to human activities, migrational patterns and changes in climate. These maps will be of value as a basis for future landscape planning, forestry and conservation of biodiversity.This is the 20th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.     

‘Trapped sea-water’ in Rørholtfjorden

Summary Trapped sea-water in R?rholtfjorden, Telemark, Norway, was discovered in 1951 by?smund Ystad who was a student at the Department of Limnology, University of Oslo. The lake was investigated continuously from August 1951 to July 1952, and the results are found inYstad [12] andStr?m [8, 9, 10, 11]. On 25 February 1971 some water samples were taken from R?rholtfjorden to supply the information from the lake, and if possible record changes in the water for the last 20 years. The tables contain chemical data, pH, temperature and oxygen content. The trapped sea-water is also compared with original sea-water with the same chloride content. It is difficult to say anything about changes in the salt-water because of uncertainty regarding the depth measurements. But a so-called semi-stagnation (Str?m [8]) was not observed (Fig. 3). It is possible that about one meter of the trapped sea-water has been lost during the last 20 years because of the removed semi-stagnation.

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Zusammenfassung Im R?rholtfjord, Telemark, Norwegen, wurde 1951 von?smund Ystad, Universit?t Oslo, ?gefangenes? Meerwasser entdeckt, welches dann von August 1951 bis Juli 1952 kontinuierlich untersucht wurde. Die Resultate sind beiYstad [12] undStr?m [8, 9, 10, 11] publiziert. Im February 1971 wurden erneut Proben aus dem Fjord genommen, um eventuelle Ver?nderungen w?hrend der vergangenen 20 Jahre festzustellen. Es wurden chemische Daten sowie pH, Temperatur und O₂-Gehalt aufgenommen. Das ?gefangene? Wasser wurde auch mit Originalmeerwasser derselben Salinit?t verglichen. Wegen der Ungenauigkeit der Tiefenmessungen ist es schwierig, etwas über Ver?nderungen auszusagen. Indessen wurde eine sog. Semi-Stagnation, wie sieStr?m [8] beschreibt, nicht beobachtet (Fig. 3). M?glicherweise ging etwa 1 m des ?gefangenen? Wassers zufolge des Verschwindens jener Semi-Stagnation verloren.

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Résumé De l’eau de mer ?captivée? dans le R?rholtfjord, Telemark, Norvège, fut découverte en 1951 par?smund Ystad, étudiant en Limnologie à l’Université d’Oslo. Des expériences avec l’eau de ce lac ont été poursuivies continuellement d’ao?t 1951 à juillet 1952 et les résultats ont été publiés parYstad [12] etStr?m [8, 9, 10, 11]. Le 25 février 1971, de nouveaux échantillons d’eau ont été prélevés dans le fjord pour étudier si, dans les 20 dernières années, d’éventuels changements étaient survenus. Les tableaux présentés contiennent les données chimiques, ainsi que le pH, la température et le taux d’oxygène. En plus, l’eau ?captivée? est comparée avec l’eau de mer originale, au même taux de salinité. Il est difficile de s’exprimer sur les changements survenus dans l’eau, à cause de l’incertitude concernant les mesures de profondeur. Cependant, on n’a pas observé une dite semi-stagnation comme l’a décriteStróm [8] (fig. 3). Il est possible qu’environ un mètre de cette eau ?captivée? se soit perdue, durant les 20 dernières années, par la disparition de la semi-stagnation.