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181.
182.
Andreas Krein Holger Klinck Michael Eiden Wolfhard Symader Reinhard Bierl Lucien Hoffmann Laurent Pfister 《地球表面变化过程与地形》2008,33(1):152-163
This article deals with the following two questions. Are acoustic measurements in running waters appropriate for a highly resolved investigation of the bedload transport? Which characterizations of the bedload regarding mass and shape are possible via the acoustic signals? The signals were recorded by means of data recorders (Tascam Inc. DAP1 Portable Data Recorder) and hydrophones (International Transducer Corp. ITC‐4001 A). The ITC‐4001 is a shallow water omnidirectional transducer containing a flexural disc transducer utilizing Channelite‐5400 ceramics mounted in a rugged corrosion‐resistant housing. These hydrophones were screwed onto the bottom side of stainless steel plates, serving as a contact surface for the bedload in motion above them. After more than 100 series of tests in the laboratory, which indicated the basic relations between the dimension, shape and weight of the bedload and the resulting signal, field tests of the measuring system were conducted. By artificially produced flood waves in the small brooks Riverisbach, Olewiger Bach and by a winter flood wave in the River Moselle, it is possible to elaborate similar structures of the signal course of the bedload movement. The highest transport rates can be observed at the beginning of the increasing limbs and behind the peaks of the waves. At the beginning of the waves, the increasing transport power of the water and the loose material can be considered as the cause for this result. The high stream velocity behind the wave peaks explains the increase in the bedload transport so that material from the channel beds is unfastened and will be mobilized. The characterization of the bedload regarding the shape and mass is still limited regarding the field measurements and could be solved only for homogeneous grain sizes and single stones under laboratory conditions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
183.
184.
Experimental results of pressure-induced changes in mean magnetic susceptibility of rock samples from the main KTB borehole are reported. It was found that susceptibility values of rocks from depths between 5200 and 7000 m show unstable behaviour upon application of pressure, showing an increase in susceptibility of between 20 and 120%. This unstable behaviour was only detected in samples from the above mentioned depth interval, which contain both ferrimagnetic and antiferromagnetic phases of pyrrhotite. On the basis of thermomagnetic analysis, magnetic field treatment, optical microscopy and domain observations of undeformed and deformed samples, reasons for this instability are discussed and interpreted in relation to redistribution of internal stresses within the ferrimagnetic phase, resulting in changes in domain wall mobility. 相似文献
185.
This investigation was carried out within the scope of EU-FP5 project MAGPROX. In parallel with the work of Kalinski et al. (2004, submitted), in which the magnetic signatures of the same soil profiles were analysed in more detail. The ‘hot spot’ under investigation was situated in the Lausitz area, Eastern Germany, between two major power plants, Schwarze Pumpe and Boxberg. This heavily industrialized region is known as the Black Triangle, named after the large lignite deposits and the old-technology power plants, among other petrochemical plants, refineries, textile manufacturing and glasswork industries. The relationship between magnetic parameters and heavy metal concentrations (Fe, Mn, Zn, Pb, Cu, Cr, Cd, Co and Ni) in soil profiles was determined statistically using linear regression analysis. Strong positive correlation was observed between heavy metal concentrations as viewed preliminarily from the heavy metal and magnetic susceptibility distributions with depth (soil profiles), and from the correlation coefficients obtained.MAGPROX team–FP5 RTD Project No. EVK2-CT-1999-00019 相似文献
186.
Expansive clay buffers in radioactive waste disposal designs experience cyclic drying and wetting paths during different stages of their design life. Clayey soils subjected to these processes develop swelling and shrinkage deformations, which give rise to the accumulation of compression or expansion strains during suction cycles. Experimental studies were undertaken using oedometer tests on an artificially prepared bentonite-sand mixture (80% bentonite by dry mass). In order to study these processes and to identify the most important features controlling soil behaviour, several wetting-drying cycles with suctions ranging between 130 and 4 MPa were applied using vapour equilibrium technique and covering a wide range of overconsolidation ratios (OCR). The tested samples showed cumulative shrinkage strains along the successive cycles, which became more significant at increasing vertical net stresses (low OCR values). However, no accumulation of expansion strains was detected at elevated OCR values. Test results were interpreted and predicted within the context of an elastoplastic model proposed by Alonso et al., 1999, [Alonso, E.E., Vaunat, J., Gens, A., (1999). Modelling the mechanical behaviour of expansive clays. Engineering Geology, 54, 173-183.] which takes into account the accumulation of strains. A good correspondence between measured soil response and model predictions was observed. The paper also presents the methodology to derive the constitutive parameters. 相似文献
187.
Françoise Vimeux Robert Gallaire Georg Hoffmann 《Earth and Planetary Science Letters》2005,240(2):205-220
Controversy has surrounded the interpretation of the water isotopic composition (δD or δ18O) in tropical and subtropical ice cores in South America. Although recent modeling studies using AGCM have provided useful constraints at interannual time scales, no direct calibration based on modern observations has been achieved. In the context of the recent ice core drilling at Nevado Illimani (16°39′S-67°47′W) in Bolivia, we examine the climatic controls on the modern isotopic composition of precipitation in the Zongo Valley, located on the northeast side of the Cordillera Real, at about 55 km from Nevado Illimani. Monthly precipitation samples were collected from September 1999 to August 2004 at various altitudes along this valley. First we examine the local and regional controls on the common δD signal measured along this valley. We show that (1) local temperature has definitely no control on δD variations, and (2) local rainout is a poor factor to explain δD variations. We thus seek regional controls upstream the Valley potentially affecting air masses distillation. Based on backtrajectory calculations and using satellite data (TRMM precipitation, NOAA OLR) and direct observations of precipitation (IAEA/GNIP), we show that moisture transport history and the degree of rainout upstream are more important factors explaining seasonal δD variations. Analysis of a 92-yr simulation from the ECHAM-4 model (T30 version) implemented with water stable isotopes confirms our observations at seasonal time scale and emphasize the role of air masses distillation upstream as a prominent factor controlling interannual δD variations. Lastly, we focus on the isotopic depletion along the valley when air masses are lifted up. Our results suggest that, if the temperature gradient between the base and the top of the Andes was higher by a few degrees during the Last Glacial Maximum (LGM), less than 10% of the glacial to interglacial isotopic variation recorded in the Illimani ice core could be accounted for by this temperature change. It implies that the rest of the variation would originate from wetter conditions along air masses trajectory during LGM. 相似文献
188.
New trends in marine chemical ecology 总被引:1,自引:0,他引:1
A. Ianora M. Boersma R. Casotti A. Fontana J. Harder F. Hoffmann H. Pavia P. Potin S. A. Poulet G. Toth 《Estuaries and Coasts》2006,29(4):531-551
This essay is the outcome of a colloquium convened in November 2005 at the Benthos Laboratory of the Stazione Zoologica Anton
Dohrn in Ischia, Italy, on chemical ecology and the role of secondary metabolites in the structuring and functioning of marine
biodiversity. The participants of the workshop are part of the European Network of Excellence MarBEF (Marine Biodiversity
and Ecosystem Function), a consortium of 56 European marine institutes to integrate and disseminate knowledge and expertise
on marine biodiversity. Here we review some of the new trends and emerging topics in marine chemical ecology. The first section
deals with microbial chemical interactions. Microbes communicate with each other using diffusible molecules such as N-acylhomoserine
lactones (AHL). These are regulators in cell-density-dependent gene regulation (quorum sensing) controlling microbial processes.
In chemical interactions with higher organisms, microbes can act either as harmful pathogens that are repelled by the host’s
chemical defense or as beneficial symbionts. These symbionts are sometimes the true producers of the host’s secondary metabolites
that have defensive and protective functions for their hosts. We also describe how allelochemicals can shape phytoplankton
communities by regulating competition for available resources, and also interactions among individuals of the same species.
Compounds such as the diatom-derived unsaturated aldehydes have been demonstrated to act as info chemicals, and they possibly
function as a diffusible bloom-termination signal that triggers an active cell death and bloom termination at sea. The same
molecules have also been shown to interfere with the reproductive capacity of grazing animals deterring future generations
of potential predators. Such compounds differ from those that act as feeding deterrents since they do not target the predator
but its offspring. Many of the neurotoxins produced by dinoflagellates act as feeding deterrents, and laboratory experiments
have shown that ingestion of these algae by some microzooplankton and macrozooplankton can cause acute, responses such as
death, incapacitation, altered swimming behavior, and reduced fecundity and egg-hatching success. These effects may rarely
occur in nature because of low individual grazing rates on dinoflagellate cells and grazing on other food sources such as
microflagellates and diatoms. We also consider the nutritional component of marine plant-herbivore interactions, especially
in the plankton, and the information available on the effects of growing conditions of algae on the production of toxic metabolites.
Species producing saxitoxins seem to consistently produce the highest amounts of toxins (on a per cell basis) in the exponential
phase of growth, and there is a decrease in their production under nitrogen, but not under phosphorus stress, where the production
actually increases. We try to explain the circumstances under which organisms defend themselves chemically and argue that
the most likely explanatory model for the production of secondary metabolites used for defense in planktonic organisms is
the carbon nutrient balance hypothesis, which predicts that most algae produce their toxins mainly under conditions where
carbon is in excess and nitrogen (or other nutrients) is limiting. We also discuss chemically mediated macroalgal-herbivore
interactions in the benthos and the large variation in concentration of seaweed defense metabolites at different spatial and
temporal scales. Seaweeds have been shown to produce a large variety of secondary metabolites with highly variable chemical
structures such as terpenoids, acetogenins, amino acid derivates, and polyphenols. Many of these compounds probably have multiple
simultaneous functions for the seaweeds and can act as allelopathic, antimicrobial, and antifouling or ultraviolet-screening
agents, as well as herbivore deterrents. We also provide examples of interactions between marine benthic invertebrates, especially
sponges, molluscs, and cnidarians, that are mediated by specific secondary metabolites and discuss the role of these in shaping
benthic communities. 相似文献
189.
M. Knab V. Hoffmann E. Petrovský A. Kapička N. Jordanova E. Appel 《Environmental Geology》2006,49(4):527-535
Measuring magnetic susceptibility is a method which is used to estimate the amount of magnetic particles in soils, sediments
or dusts. Changes in magnetic susceptibility can be due to various reasons: input from different sources of sediments, e.g.
from different soils or rocks, atmospheric fallout of anthropogenic dusts containing magnetic particles produced by fossil
fuel combustion, steel production or road traffic. In the case of river sediments, input from the catchment is of primary
significance. The main aim of this investigation was to test the potential of magnetic susceptibility screening in identifying
the effect and significance of anthropogenic activities in an area with complex geological conditions. We investigated the
magnetic susceptibility of riverbed sediments of the largest river of the Czech Republic, the Moldau river. Besides that,
the magnetic signal of nearby topsoils as well as of outcropping bedrocks in the vicinity of the river was examined. In the
upper 300 km of the river, the magnetic enhancement of the river sediments can be linked to anthropogenic activities. Positive
correlations were found in the river sediments between the contents of Cu and Zn and magnetic susceptibility, while Fe, Mn
and Ni did not show a correlation with magnetic susceptibility. However, the major geogenic magnetic anomaly in the area around
the Slapy dam has made it impossible to unambiguously interpret the magnetic signal in terms of anthropogenic impact in the
last 80 km downstream. 相似文献
190.
Dr. Christoph Hoffmann 《Contributions to Mineralogy and Petrology》1970,27(4):283-320
In the southern Apennin (= northern part of the region dealt with) and the Coasta Chain (= southern part) there are metabasalts wich are classified in the northern part as:
- Glaucophane rocks of the albite-lawsonite-glaucophane-subfacies with the assemblage glaucophane + pumpellyite + lawsonite ±albite ±aragonite ±muscovite (7 rock analyses, 8 mineral analyses). These rocks are conceived as relics of an older burial metamorphism.
- Rocks with pumpellyite and chlorite or also chlorite alone, that are interpreted as reaction rims between the metastable glaucophane rocks and the country rock (phyllites, quartzites). The assemblages pumpellyite + chlorite and chlorite alone are to be found (2 rock analyses and 2 mineral analyses).
- Rocks with lawsonite and/or epidote belong to the same mineral facies as the country rock: a facies similar to the greenschist facies (called “lawsonite-albite-chlorite-subfacies”) which is characterized by the assemblages lawsonite + albite + chlorite ±calcite and also epidote ±lawsonite + albite + chlorite ± muscovite. These types are attributed to a younger dynamo-metamorphism (2 rock analyses).