Präparationstechnik für Aufbereitungsprodukte zur quantitativen erzmikroskopischen Untersuchung     

Gerhard Ludwig 《Mineralium Deposita》1966,1(3):193-200

Zusammenfassung Mikroskopische Anschliffe feinkörniger Aufbereitungsprodukte können nur dann quantitativ ausgewertet werden, wenn ihre Schliffqualität so hoch ist, daß auch feinste Partien sicher zu bestimmen sind. Daneben muß gewährleistet sein, daß die an der Schliffoberfläche erfaßten Körner die tatsächliche Verteilung der Mineralien der Probe repräsentieren. Diese Forderung kann nur durch zweckentsprechende Präparation, die dem eigentlichen Schleif- und Polierprozeß vorausgeht, erfüllt werden. Als günstigste Lösung erscheint es, das Korngemisch exakt als Einkornschicht zu präparieren und anschließend wie Stückproben anzuschleifen. Die Schliffe können dann nach den gleichen statistischen Gesetzmäßigkeiten ausgewertet werden, wie sie bei praktisch zweidimensionalen Dünnschliffen oder bei Streupräparaten nichtopaker Korngemische vorliegen.

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Quantitative examination of fine-grained ore dressing products depends on good quality of the sections and on whether very small particles and areas of grains can be determined. Besides, it must absolutely be guaranteed that the grains at the section surface represent the actual distribution of the minerals in the sample. This condition can only be realized by suitable grain mounting prior to grinding and polishing. The best method for this purpose appears to be the preparation of a mono-grain layer. The polished sections can then be examined according to the same statistical laws as two-dimensional thin sections or immersion-liquid slides of non-opaque mixtures of grains.

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Mitteilung Nr. 141 aus dem Forschungsinstitut für Aufbereitung der Deutschen Akademie der Wissenschaften zu Berlin, Freiberg (Sachsen). Direktor: Prof. Dr.-Ing. habil. H. Kirchberg.  相似文献   

Composition-Induced Variations in SIMS Instrumental Mass Fractionation during Boron Isotope Ratio Measurements of Silicate Glasses     

Martin Rosner  Michael Wiedenbeck  Thomas Ludwig 《Geostandards and Geoanalytical Research》2008,32(1):27-38

An analytical artefact is reported here related to differences in instrumental mass fractionation between NIST SRM glasses and natural geological glasses during SIMS boron isotope determinations. The data presented demonstrated an average 3.4‰ difference between the NIST glasses and natural basaltic to rhyolitic glasses mainly in terms of their sputtering-induced fractionation of boron isotopes. As no matrix effect was found among basaltic to rhyolitic glasses, instrumental mass fractionation of most natural glass samples can be corrected by using appropriate glass reference materials. In order to confirm the existence of the compositionally induced variations in boron SIMS instrumental mass bias, the observed offset in SIMS instrumental mass bias has been independently reproduced in two laboratories and the phenomenon has been found to be stable over a period of more than one year. This study highlights the need for a close match between the chemical composition of the reference material and the samples being investigated.  相似文献   

Solar irradiance modulation by active regions during 1980     

Sabatino Sofia  Ludwig Oster  Kenneth Schatten 《Solar physics》1982,80(1):87-98

The solar irradiance modulation due to active regions during 1980 has been investigated in detail. Specifically, we estimate the uncertainties caused by ground-based data used as input in the modeling effort, and by our currently incomplete knowledge of the proper parameters that describe the angular variation of sunspot and facular contrasts. We conclude that the most significant uncertainties are due to errors in area measurements and, possibly, varying spot and facular brightness. A standard model for later use is derived by a best-fit technique of the currently available ACRIM irradiance data and the predictions of our models with appropriately varied parameters. Finally, we compute the expected irradiance for the entire year of 1980.NRC Senior Research Associate on leave from the Joint Institute for Laboratory Astrophysics and the Astro-Geophysics Department, University of Colorado at Boulder, Colo., U.S.A.  相似文献   

A Permeable Reactive Barrier for Treatment of Heavy Metals   总被引：8，自引：0，他引：8  

Ralph D. Ludwig  Rick G. McGregor  David W. Blowes  Shawn G. Benner  Keith Mountjoy 《Ground water》2002,40(1):59-66

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Cyclic sedimentation and climatically caused sea-level changes in the Late Palaeozoic of Central Europe     

A. O. Ludwig 《International Journal of Earth Sciences》1994,83(4):799-810

Significant short-term fluctuations are characteristic of geological history since Precambrian times. Only the younger Quaternary climatic fluctuations are known in more detail as a result of a high grade time resolution. Climatic change can also be postulated with respect to older, cold periods during which polar inland ice sheets developed. From a discussion of endogene and exogene interpretations it is shown that global climatic changes, and the sea-level changes induced by them, as well as changes in the position and extent of climatic zones throughout the world provide a control mechanism for sedimentation which is consistent with cyclic sedimentation in Late Palaeozoic times, and also if the basin subsides non-cyclically. The model allows an explanation of the development of the Permo-Carboniferous sedimentary cycles without numerous short-term vertical oscillations of the earth's crust. In reality, exogene and endogene controls on sedimentation act together in great variety of combinations.  相似文献   

Desalinization of running waters: III. Changes in the structure of diatom assemblages caused by a decreasing salt load and changing ion spectra in the river Wipper (Thuringia, Germany)     

Horst Ziemann  Ludwig Kies  Claus-Jürgen Schulz   《Limnologica》2001,31(4):257-280

Salt-loaded effluents were introduced into the river Wipper during the mining period for almost a century. Beginning with the year 1990, the waste water load was strongly reduced due to the termination of the potash industry. Prior to 1990, monthly means of the chloride concentrations at times exceeded 6,000 mg l⁻¹ in the strongly polluted sections. Maximum concentrations reached twice these values. Up to 1998, mean annual chloride concentrations decreased to values below 2,000 mg l⁻¹. This led to more balanced fluctuations in salinity which had been pronounced before, depending on discharge and short-term changes in production. Similarly, the physiologically adverse ion conditions improved due to decrasing potassium and increasing calcium proportions.

In 1963/64, 1986 and 1998, samples of epilithic, epiphytic and epipsammic diatoms were taken at locations of different salinities along the river and examined for the effects of the salinization on the structure of the diatom assemblages. These structures changed in dependence on salinity. Increasing salt concentrations coincided with decreasing oligohalophilic and increasing mesohalophilic and polyhalophilic species numbers. Above a chloride concentration of about 3,000 mg l⁻¹, the proportion of the latter exceed that of the former (halobion index > 50). Corresponding to different conditions of salinization along the river, characteristic diatom assemblages occur differring from each other and which are specific for the river section. Spring and autumn aspects of the diatom assemblages show also salt-dependent differences. The assemblages found in 1998 after decrease of salinization have changed markedly in comparison to those from 1963/64 and 1986. Halobiontic species predominating formerly occurred only occasionally or not at all. They were replaced by oligohalobic-indifferent forms.

An ecological assessment of the changes was performed based on the halobion index calculated from all the samples. For the strongly salinized section of the river Wipper, a shift from -mesohalobic/polyhalobic conditions in 1963/64 and 1986 to -oligohalobic/β-mesohalobic conditions in 1998 was found. However, constant -oligohalobic conditions are still not given. With regard to the transition from -oligohalobic (limnetic) to β-mesohalobic (brackish) conditions, a maximum chloride concentration of 600 mg l⁻¹ was found. To guarantee -oligohalobic conditions, a maximum chloride concentration of 400 mg l⁻¹ should not be exceeded.  相似文献   

Sr-Isotope record of Quaternary marine terraces on the California coast and off Hawaii     

Kenneth R. Ludwig  Daniel R. Muhs  Kathleen R. Simmons  James G. Moore 《Quaternary Research》1992,37(3)

Strontium-isotopic ratios of dated corals have been obtained from submerged reefs formed during Quaternary glacial periods off the Hawaiian islands. These data, combined with data from deep-sea sediments, tightly constrain the secular variation of marine ⁸⁷Sr/⁸⁶Sr for the past 800,000 yr. Although long-term trends are apparent, no significant (>0.02‰), rapid (<100,000 yr) excursions in ⁸⁷Sr/⁸⁶Sr were resolved nor did we observe any samples with ⁸⁷Sr/⁸⁶Sr greater than that of modern seawater. Strontium in mollusks from elevated marine terraces formed during interglacial periods on the southern California coast show resolvable and consistent variations in ⁸⁷Sr/⁸⁶Sr which, when compared to the trend of Quaternary marine ⁸⁷Sr/⁸⁶Sr, can be used to infer uplift rates and define approximate ages for the higher terraces. The Sr-isotope age estimates indicate that uplift rates vary among crustal blocks and were not necessarily constant with time. No contrast in Sr-isotopic ratios between similar-age Hawaiian and California fossils was observed, confirming that any change in marine ⁸⁷Sr/⁸⁶Sr from glacial to interglacial periods must be small. A realistic appraisal of the potential of Sr-isotope stratigraphy for chronometric applications in the Quaternary suggests that the technique will be limited to relatively coarse distinctions in age.  相似文献   

New approaches to European loess: a stratigraphic and methodical review of the past decade     

Ludwig Zoeller 《Central European Journal of Geosciences》2010,2(1):19-31

This review paper intends to summarize the state of the art in loess research at the first international “Loess-fest’99” conference and to outline progress in loess research during the past decade. The focus is on loess as a terrestrial archive of climatic and environmental change during the Quaternary. The review highlights remarkable new results from regional investigations into European loess, as well as the emergence of new methods and refinements of established techniques, focussing on stratigraphy, dating and palaeoenvironment. It is concluded that loess research during the past decade not only has developed rapidly to take an outstanding place in Quaternary sciences, but also promises exciting perspectives for the next decade, in particular when combined approaches are applied to benefit from the now comprehensive pool of established and new methods.  相似文献   

Excitation of Radial P-Modes in the Sun and Stars     

Robert Stein  Dali Georgobiani  Regner Trampedach  Hans-Günter Ludwig  Åke Nordlund 《Solar physics》2004,220(2):229-242

P-mode oscillations in the Sun and stars are excited stochastically by Reynolds stress and entropy fluctuations produced by convection in their outer envelopes. The excitation rate of radial oscillations of stars near the main sequence from K to F and a subgiant K IV star have been calculated from numerical simulations of their surface convection zones. P-mode excitation increases with increasing effective temperature (until envelope convection ceases in the F stars) and also increases with decreasing gravity. The frequency of the maximum excitation decreases with decreasing surface gravity.  相似文献   

Has climate change opened new opportunities for wheat cropping in Argentina?     

Senthold Asseng  Maria I. Travasso  Fulco Ludwig  Graciela O. Magrin 《Climatic change》2013,117(1-2):181-196

As a result of climate change, and in particular rainfall changes, agricultural production is likely to change across the globe. Until now most research has focused on areas which will become unsustainable for agricultural production. However, there are also regions where climate change might actually improve conditions for growth. In the western Pampas region of Argentina, average annual rainfall has increased by 100–200 mm over the last 70 years, mainly during summer. Wheat is grown during winter, primarily on stored soil water and the main factor limiting plant production in this area is rainfall. Using the well tested simulation model APSIM-NWheat, we studied whether recent climate change has potentially opened new opportunities for wheat cropping in Argentina. Simulation results indicated that the additional rainfall in the Pampas of Argentina has increased the achievable yield (defined as the yield limited by solar radiation, temperature, water and nitrogen supply) of wheat in the currently cropped region, but less than expected based on the large amount of additional rainfall. The higher achievable yield from additional rainfall could potentially allow an expansion of profitable wheat cropping into currently non-cropped areas, where the achievable wheat yield increased in average from 1 t/ha to currently 2 t/ha. However, the poor water-holding capacity of the sandy soils which dominate the region outside the current cropping area limits the systems ability to use most of the increased summer rainfall. Nevertheless, the current higher achievable yield indicates a suitability of the region for cropping, which will slightly decline or remain unchanged depending on summer rainfall storage, with current and future climate change, including projected changes in rainfall, temperature and atmospheric CO₂ concentration. Factors other than just the achievable yield will eventually influence any future development of this region for cropping, including the high sensitivity of the sandy soils to erosion and nutrient leaching, current relatively high land prices, restrictions on clearing for cropping, the distance to the nearest port and current unsuitable cultivars withstanding the high frost risk.  相似文献