Isothermal compression of low-cordierite to 30 kbar (25° C)     

P. W. Mirwald  M. Malinowski  Heinz Schulz 《Physics and Chemistry of Minerals》1984,11(3):140-148

The compression of cordierite (Mg, Fe)₂Al₄Si₅O₁₈·n (H₂O, CO₂; Na⁺, K⁺) has been studied up to 30 kbar (25° C) by volumetric measurements with a piston cylinder apparatus and by X-ray measurements with a diamond-anvil cell. Natural cordierite of intermediate Mg-Fe composition and synthetic Mg-cordierite served as samples. Two discontinuities at 2.2±0.3 and 9.0±0.6 kbar which are correlated with very small volume changes (0.3?0.05%) have been found. The X-ray data indicate, however, no symmetry change of the crystal structure. The two discontinuities are interpreted as phase transitions. The two discontinuities establish three pressure dependent phases referred to as low-pressure (LP)-, first high-pressure (HP1)- and second high-pressure (HP2)-phase. The gross compressibility of cordierite decreases from 1.1 Mbar^?1 at low pressure to 0.7 Mbar^?1 at 30 kbar for the intermediate Mg-Fe cordierite, and to 0.4 Mbar^?1 for Mg-cordierite. Depending on the pressure transmitting medium used in the two different compression techniques, two kinds of compression behavior are observed for cordierite. The measurements with the piston cylinder apparatus where lead is used as quasihydrostatic pressure medium indicate normal compression properties. The X-ray data, however, obtained with the diamond anvil cell where a methanol-ethanol mixture provides hydrostatic pressure conditions yield, e.g. for the HP1-phase a dramatic decrease in compressibility to almost zero. IR-spectra from samples of augmenting experiments with methanol, deuteromethanol and D₂O as pressure media indicate that pressure media of which the molecule size is comparable with the dimensions of the cordierite channels may be incorporated in the structure. This suggests that under such hydrostatic conditions the compression of cordierite is modified by a structure internal component which is acting via the channel system.  相似文献   

Forecasting in the social and natural sciences: An overview and analysis of isomorphisms   总被引：1，自引：0，他引：1  

Kenneth C. Land  Stephen H. Schneider 《Climatic change》1987,11(1-2):7-31

This article identifies and analyzes several points of similarity in the structure and context of forecasting in the social and natural sciences. These include: the limits of identities or universal laws as a basis for forecasts; the corresponding need for simplifying parametric representations of one or more of the variables that enter into identities; various sources of uncertainty about parameterizations; intrinsic limitations on predictability or forecasting accuracy in large-scale systems; the need for sensitivity analyses of model responses to changes in exogenous variables and/or parametric structures; problems of model linkage; and the social (organizational and political) context of forecasts. Suggestions for future lines of inquiry are made in each case. Several of these are such that they can benefit from a sharing of experience and expertise across disciplinary lines.The research reported herein was supported in part by the IC² Institute, The University of Texas at Austin, and in part by National Science Foundation Grant Number SES-8411702. However, the opinions expressed in the paper are those of the authors and do not necessarily reflect those of the sponsoring organizations. We appreciate the advice and comments of Jesse H. Ausubel, Robert S. Chen, Judith Jacobsen, and Richard C. Rockwell on earlier versions of this paper.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Editorial: Three essays of remembrance on the life of Helmut Landsberg     

Stephen H. Schneider 《Climatic change》1986,9(3):259-259

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Das Relief des Mars' Versuch einer zusammenfassenden Übersicht     

Dr. Heinz -Peter Jons 《International Journal of Earth Sciences》1986,75(2):461-493

The analysis of the martian relief leads to the conclusion that some of the most important relief elements are either concentrically or radially arranged with respect to a central structure and hence form aureoles. In this paper four different types of aureoles are identified and described:

1. impact aureoles (as result of extradynamics),
2. volcanic aureoeles (as result of lava flow through vents),
3. tectonic aureoles (as result of isostatic adjustment and/or settlement),
4. permafrost-related aureoles and mega-aureoles (as result of migration above thawing permafrost in areas with high relief).

The spatial distribution of these different types of aureoles indicates the predominant type of relief-forming dynamics in the area of their distribution (impact-related aureoles occur predominantly in the area of the Southern Uplands; volcanic, tectonic and permafrost-related aureoles in the area of large-scale updomings-TaNoVa, Elysiumand their volcanic provinces).  相似文献   

Climatology and glaciology: An interdisciplinary opportunity—An editorial     

Stephen H. Schneider 《Climatic change》1982,4(4):327-328

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A deuterium-hydrogen fractionation mechanism in magnesium oxide     

Friedemann Freund  Heinz Wengeler  Reinhard Martens 《Geochimica et cosmochimica acta》1982,46(10):1821-1829

Water dissolved in a nominally anhydrous oxide like MgO forms not only OH^? ions, as is usually assumed, but also molecular H₂ and peroxy anions O₂^2?. The specific lattice site where this reaction occurs has been identified for the model-type MgO structure: it is the fully OH^? compensated cation vacancy. In partially deuterated synthetic MgO, molecular D₂ forms preferentially to H₂, by a factor of the order of 4. Three methods have been used to study this very large D/H fractionation experimentally: mass spectrometry, electron spin resonance and infrared spectroscopy. All give consistent results and confirm that internal D/H fractionation occurs and is a function of the temperature. Theoretically the D/H fractionation is explained by the lower zeropoint energy of D₂ with respect to H₂, amplified by secondary processes through which the molecular hydrogen species become mobilized and eventually lost via diffusion. The possible consequences of such internal D/H fractionation processes are indicated for the interpretation of water and hydrogen release patterns, with varying D/H ratios, from terrestrial and extraterrestrial samples.  相似文献   

Orientation of the stress field from breakouts in a crystalline well in a seismic active area     

P. Blümling  K. Fuchs  T. Schneider 《Physics of the Earth and Planetary Interiors》1983,33(4):250-254

The orientation of the regional stress field in the Swabian Jura was determined from borehole breakouts caused by stress accumulation at the borehole wall. The analysis is based on caliper data recorded in the Urach 3 geothermal well within an intervall of about 1450 m. The azimuths of the breakouts are consistent with depth and indicate a stress direction which is in good agreement with the interpretation of fault plane solutions of nearby earthquakes.  相似文献   

Velocity constraints for the inner core inferred from long-period PKP amplitudes     

Heinz Häge 《Physics of the Earth and Planetary Interiors》1983,31(2):171-185

Long-period PKP amplitudes from 16 earthquakes in the distance range 110– 170° are compared with theoretical amplitudes which are derived from synthetic seismograms calculated for 56 systematic modifications of Earth model 1066B in the inner core. A suitable normalization procedure allows for the common representation of all observed amplitudes as a function of epicentral distance. Using the theoretical amplitude distributions it can be shown that the parameters of a regression line through the logarithmic and normalized amplitudes between 110 and 134° are related to the velocity and density jump at the inner-core boundary (ICB). The analysis shows that the dominant influence on the PKP amplitudes is the P-velocity jump which can be restricted to 0.64 ± 0.05 km s^?1. There exists a trade-off between the S-velocity jump and the density jump. Restricting the latter to the reasonable range 0–1.2 g cm^?3 the S-velocity jump at the ICB can be inferred to be 2.5–3.0 km s^?1. A rather strong S-velocity gradient below the ICB follows from the condition that the S-wave travel-time through the inner core agrees with that implied by free oscillation observations. This leads to central S-velocities between 3.81 and 4.15 km s^?1, assuming a parabolic velocity law.  相似文献   

Volcanic dust veils and climate: How clear is the connection? — An editorial     

Stephen H. Schneider 《Climatic change》1983,5(2):111-113

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Anthropogenic effects on sedimentary facies in Lake Baldeney,West Germany     

Peter Neumann-Mahlkau  Heinz Theo Niehaus 《Environmental Geology》1983,5(4):169-176

Analysis of well logs of Lake Baldeney, a reservoir of the Ruhr River, yields four facies factors that reflect the effect of anthropogenic processes on the sediment. First, the sedimentation rate is directly related to the subsidence caused by mining. The extent of the subsidence was such that the sediment load of the river could not compensate for the sinking of the lake bottom. Discharged sediment filled about one-fifth of the basin within 40 years. In certain areas of the basin the sedimentation rate reached up to 10 cm per year. Second, the grain-size distribution of the sediment was influenced by long-term and short-term events. During the subsidence, grain-size distribution remained relatively constant. The destruction of the Möhne River dam during World War II resulted in the presence of an extremely large grain size as evidenced by the so-calledMöhnelage. The filling of the lake after 1961 was accompanied by a continual increase in medium grain size. Third, until 1975, the mode of the lake sediment reflects the effect of mining in the vicinity of the lake. High coal content can be traced to its origin. The introduction of modern production processes, modernization of coal dressing, and hydraulic hauling is documented in the sediment. Finally, the heavy metal content of the sediment corresponds to the industrial development in the drainage area the Ruhr River. The accumulation of Cd reached an extreme concentration, exceeding the natural content by a thousand times. Variation in concentration reflects an increase in industrial production, as well as measures undertaken to restore water quality.  相似文献