Substitute conductors for electromagnetic response estimates   总被引：3，自引：0，他引：3  

Ulrich Schmucker 《Pure and Applied Geophysics》1987,125(2-3):341-367

Various concepts exist to define substitute conductors for empirical response estimates at singular frequencies: Chapman's shell-core model, the Cagniard-Tikhonov apparent resistivity, the Niblett-Bostick and Molochnov transformation, thep ^* —z ^* transformation. They are all interrelated and assign comparable resistivities to the substitute conductor at a given frequency. Applications to synthetic response data of plane and spherical conductors show under which conditions these substitutions come closest to the model and which influence of source dimensions and Earth's sphericity can be expected.p ^* —z ^* transformed global response data forS andDst variations demonstrate how substitute conductors may serve as useful guides in inverse procedures.  相似文献   

Shock effects in melilite     

Helmut Schäfer  Wolfgang Friedrich Müller  Ulrich Hornemann 《Physics and Chemistry of Minerals》1984,10(3):121-124

Shock recovery experiments on melilite samples in the pressure range from 11 to 50.5 GPa have been performed in order to examine the effects of shock waves on this material. The shocked samples were subsequently studied in the transmission electron microscope. All samples displayed the shock-induced amorphous areas, known as diaplectic glass. The amount of diaplectic melilite glass increased from a few percent at 11 GPa to about 85 percent at 50.5 GPa shock pressure. The shock waves also caused deformational effects as planar faults parallel to (001) and dislocations with a density in the order of 10¹⁰ cm^?2. Regarding the present discussion on the origin and nature of diaplectic glass, diaplectic melilite glass is assumed to be the reversion product of a high-density phase produced in the shock front. Deformed melilites in Ca-Al-rich inclusions from chondritic meteorites studied so far do not contain diaplectic glass. It is assumed that the meteoritic melilites were hot (>1,000° C) and thus plastically deformable by shock waves of rather low amplitudes.  相似文献   

Germination and algal-free laboratory culture of widgeon grass,Ruppia maritima     

Ulrich Seeliger  Cesar Cordazzo  Evamaria Wysk Koch 《Estuaries and Coasts》1984,7(2):176-178

A methodology for the isolation ofRuppia maritima L. into algal-free laboratory culture is described. Seeds were surface sterilized with 96% ethyl alcohol of pH 2, kept for several months in cold storage at 7°C, and subsequently transferred to 25°C to induce germination. Basic culture conditions are discussed and a vessel of easy maintenance and sterilization forRuppia culture in ground glass sediments is presented. Minor modifications of this methodology might permit contaminant-free laboratory cultures of other estuarine and marine spermatophytes.  相似文献   

Conceptual study — An improved method to assess acidification in German streams by using benthic macroinvertebrates     

Ulrich Braukmann  Regina Biss 《Limnologica》2004,34(4):433-450

The present study is based mainly upon the authors' hydrochemical and hydrobiological studies of small silicate streams in South-West Germany, principally in the Black Forest and the Odenwald.

The aim of the paper is the adaptation of a practically proven four-level biological classification system of different degrees of acidity using benthic maroinvertebrates to a five-level system of acidification of mainly upland streams with low buffer capacity. The main reason for such a five-class system is the Water Framework Directive of the European Union (EU WFD), which lays down a five-level classification system for the assessment of the ecological quality of waters.

The biological method of assessing the state of acidity for evaluation of the degree of anthropogenic acidification under the directive, and principles of the EU WFD, are also described. A list of 278 taxa of the macrozoobenthos has been reclassified from a four-level system to a five-level biological indication system, based upon the authors' scientific expertise and the latest references from literature of different acid sensitive areas in Germany.  相似文献   

Observation of isotopes in the water cycle—the Swiss National Network (NISOT)     

Schürch  Marc  Kozel  Ronald  Schotterer  Ulrich  Tripet  Jean-Pierre 《Environmental Geology》2003,45(1):1-11

The Swiss National Network for the Observation of Isotopes in the Water Cycle (NISOT) includes eleven precipitation, seven surface water (river) and three groundwater stations, where tritium, deuterium and oxygen-18 are monthly measured in composite samples. The network provides a good overview of the characteristic isotope signatures in recharge waters in Switzerland and of the relations between isotopes and altitude, orography and the amount of precipitation. Mixing of air water vapour and surface waters can be observed along a NW/SE cross section through the Alps. With increasing length of the data series, the network provides a valuable contribution for national and international scientific and practical applications in surface and subsurface hydrology, climatology and biology. The Swiss Geological Survey at the Federal Office for Water and Geology operates the isotope network within the legal framework of the Federal Law on the Protection of Waters and guarantees quality, access and distribution of the isotope data.  相似文献   

Presolar nanodiamonds: faster, cleaner, and limits on platinum-HL     

Silke Merchel  Ulrich Ott  Siegfried Herrmann  Thomas Faestermann  Gunther Korschinek  Anton Wallner 《Geochimica et cosmochimica acta》2003,67(24):4949-4960

We have developed a procedure that allows extraction of clean nanodiamond samples from primitive meteorites for isotopic analyses of trace elements on a timescale of just a week. This procedure includes microwave digestion and optimization of existing isolation techniques for further purification. Abundances of trace elements that are difficult to dissolve using standard procedures (e.g., Ir) are lower in the diamond residues prepared using the new technique. Accelerator mass spectrometry (AMS) was explored as a means for isotopic measurements. Results obtained on diamond fractions from Allende and Murchison show the need for suitable matrix-adjusted standards to correct for fractionation effects; nevertheless they allow putting an upper limit on the abundance of ¹⁹⁸Pt-H in nanodiamonds of ∼1 × 10¹⁴ atoms/g. This limit is on the order of what can be expected from predictions of competing nucleosynthesis models and extrapolation of the apparently mass dependent abundance trend of the associated noble gases.Unfortunately, and unexpectedly, presolar silicon carbide is almost quantitatively dissolved during microwave digestion with HCl/HF/HNO₃. Re-evaluation of the standard extraction technique, however, shows that it also may lead to severe loss of fine-grained SiC, a fact not commonly appreciated. A lower limit to SiC abundance in Murchison is 20 ppm, and previous conclusions that Murchison SiC is unusually coarse-grained compared to SiC in other primitive meteorites seem not to be warranted. Graphite and silicon nitride may survive and possibly can be separated after this step as suggested by a simulation experiment using terrestrial analog material, but the detailed behavior of meteoritic graphite requires further study.  相似文献   

Vegetation response to rapid climate change in central europe during the past 140,000 yr based on evidence from the Füramoos pollen record     

Ulrich C Müller  J.örg ProssErhard Bibus 《Quaternary Research》2003,59(2):235-245

The response of Central European vegetation to rapid climate change during the late Quaternary period (Eemian to Holocene) is assessed by data from the new pollen record of Füramoos, southwestern Germany. This record represents the longest late Quaternary pollen record north of the Alps as currently known. Its high degree of completeness allows detailed correlations with Greenland ice cores and sea-surface temperature records from the North Atlantic. Our data show that if climate deteriorations were not long or severe enough to extirpate refugia of arboreal taxa north of the Alps such as during marine oxygen isotope stage (MIS) 5 (i.e., Würm Stadial A, Stadial B, and Stadial C), reforestation with the onset of warmer conditions in Central Europe occurred on a centennial scale. If arboreal taxa became completely extinct north of the Alps such as during MIS 4 (i.e., Würm Stadial D), several thousand years were necessary for the reimmigration from refugia situated in regions south of the Alps. Thus, Dansgaard-Oeschger interstades (DOIS) 24 to 20 and 15 to 11 are expressed in Central European pollen records, whereas DOIS 19 to 16 are not recorded due to migration lags.  相似文献   

Phosphorus input by upwelling in the eastern Gotland Basin (Baltic Sea) in summer and its effects on filamentous cyanobacteria     

Monika Nausch  Günther Nausch  Hans Ulrich Lass  Volker Mohrholz  Klaus Nagel  Herbert Siegel  Norbert Wasmund   《Estuarine, Coastal and Shelf Science》2009,83(4):434-442

In July 2007, phosphorus input by an upwelling event along the east coast of Gotland Island and the response of filamentous cyanobacteria were studied to determine whether introduced phosphorus can intensify cyanobacterial bloom formation in the eastern Gotland Basin. Surface temperature, nutrient concentrations, phytoplankton biomass and its stoichiometry, as well as phosphate uptake rates were determined in two transects between the coasts of Gotland and Latvia and in a short grid offshore of Gotland. In the upwelling area, surface temperatures of 11–12 °C and average dissolved inorganic phosphorus (DIP) concentrations of 0.26 μM were measured. Outside the upwelling, surface temperatures were higher (15.5–16.6 °C) and DIP supplies in the upper 10 m layer were exhausted. Nitrite and nitrate concentrations (0.01–0.22 μM) were very low within and outside the upwelling region. Abundances of filamentous cyanobacteria were highly reduced in the upwelling area, accounting for only 1.4–6.0% of the total phytoplankton biomass, in contrast to 18–20% outside the upwelling. The C:P ratio of filamentous cyanobacteria varied between 32.8 and 310 in the upwelling region, most likely due to the introduction of phosphorus-depleted organisms into the upwelling water. These organisms accumulate DIP in upwelling water and have lower C:P ratios as long as they remain in DIP-rich water. Thus, diazotrophic cyanobacteria benefit from phosphorus input directly in the upwelling region. Outside the upwelling region, the C:P ratios of filamentous cyanobacteria varied widely, between 240 and 463, whereas those of particulate material in the water ranged only between 96 and 224. To reduce their C:P ratio from 300 to 35, cyanobacteria in the upwelling region had to take up 0.05 mmol m⁻³ DIP, which is about 20% of the available DIP. Thus, a larger biomass of filamentous cyanobacteria may be able to benefit from a given DIP input. As determined from the DIP uptake rates measured in upwelling cells, the time needed to reduce the C:P ratio from 300 to 35 was too long to explain the huge bloom formations that typically occur in summer. However, phosphorus uptake rates increased significantly with increasing C:P ratios, allowing phosphorus accumulation within 4–5 days, a span of time suitable for bloom formation in July and August.  相似文献   

Optical observations of an infrared selected sample of galaxies     

Ulrich Klaas 《Astrophysics and Space Science》1989,157(1-2):245-253

Extragalactic IRAS sources with previously unknown optical counterparts were selected from thePoint Source Catalog within two 300 deg² areas. Deep CCD images have been obtained for 99 objects and long-slit spectroscopy has been performed in 55 fields. The morphological, spectroscopic and photometric properties of these objects are summarized.  相似文献   

S-wave velocity measurements applied to the seismic microzonation of Basel, Upper Rhine Graben     

Hans-Balder Havenith  Donat Fäh  Ulrich Polom  Agathe Roullé 《Geophysical Journal International》2007,170(1):346-358

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