The energetics of interaction between oxygen vacancies in sillimanite: A model for the mullite structure     

S. Padlewski  V. Heine  G. D. Price 《Physics and Chemistry of Minerals》1992,19(3):196-202

A microscopic model is introduced to discuss the modulated structure of mullite. The oxygen vacancies of this aluminosilicate are known to play a central role. In particular, a single vacancy strongly orders its surrounding Al/Si tetrahedral sites. It is shown in this work that if two oxygen vacancies approach too closely to one another, their Al/Si dressing overlap. This situation results in repulsive interaction. The field of interaction between the vacancies is estimated with the use of an atomistic computer simulation. We use a Bragg-Williams type of theory to dicuss the ordering pattern of the vacancies. Due to frustration between the two dominant repulsive interactions, our model predicts a modulated phase transition in agreement with observation.  相似文献   

Mountain restoration: Soil and surface wildlife habitat     

B. N. MacCullum  V. Geist Prof. Dr. 《GeoJournal》1992,27(1):23-46

Much wildlife habitat is being destroyed by extractive resource industries in mountain environments. This article illustrates how mountain wildlife habitat was restored in a devastated area. A strip mine for coal on the east slopes of the Alberta Rockies, occupied during its operations by Rocky Mountain bighorn sheep (Ovis canadensis canadensis, Shaw 1803), was reclaimed as bighorn habitat. By considering the behaviour and habitat requirements of bighorns in conjunction with an operating coal mine and reclamation process, a large coal mining company has been able to reconstruct the mine site restoration to benefit mountain sheep. Although bighorn habitat requirements are well known, it was not until the animal and its requirements were studied against the backdrop of an operating coal mine that obvious recommendations regarding the maintenance and placement of high steep excavated rock faces were made and accepted by the government regulatory agencies. An open pit mine is a devastated landscape; trees, soil and overburden are removed to retrieve coal that may be up to 215 m underground. Overburden and soil are returned, but the disturbance compares to the barren landscapes left behind by glaciers. Contouring of the land, grading of overburden and soil, seeding with grass and legume mixtures and extensive fertilization are designed to speed plant colonization and soil development. By examining the bighorn's biological needs with respect to specific mining operations, a unique opportunity arose to employ McHarg's design with nature concept. This approach incorporates environmental and societal values into every aspect of development, and promotes the evaluation of the constraints and opportunities arising. The sheep numbered about 200. Their seasonal movements were similar to those found on native ranges. They used the reclaimed areas as winter range and for the mineral licks exposed during mining; in summer, the sheep moved to nearby alpine areas. Two thirds of all sightings were confined to 1.3 km² of reclaimed grassland; its average productivity (4190 kg/ha) exceeded native ranges (1700 kg/ha). The body mass of female sheep in autumn equalled that of the largest in Alberta, but the skull dimensions were not larger than those of adjacent ranges. Infestation with lungworms was moderate. Lamb production and survival were high. Design criteria should be: feeding areas should be dry and lie within 300 m of escape terrain, which should have a slope of 40% and contain at least three benches. Rock piles should be placed on grazing areas. Mineral licks, a vital welfare factor, already existed within the high walls created by strip mining.  相似文献   

Electron optical and X-ray powder diffraction study of synthetic and natural potassic cordierites     

P. Daniels  W. V. Maresch  W. Schreyer  K. Sahl 《Contributions to Mineralogy and Petrology》1992,111(4):484-492

The microstructural and X-ray diffraction characteristics of natural K-bearing cordierites in buchites (Blaue Kuppe, Germany), and paralavas (Bokaro, India) are compared to those of three suites of synthetic, K-bearing Mg-cordierite, studied after annealing glasses of the requisite compositions for durations between 5 min and 255 days at 1,290° C and 1 bar. In analogy to pure Mg-cordierite, hexagonal high-cordierite initially crystallizes from the glass and subsequently transforms to orthorhombic low-cordierite. After annealing for 30–60 min, the crystals develop tweed-structure. With prolonged annealing, the pattern coarsens and develops into lamellar twinning. Higher K-contents favour earlier development of tweed-contrast. Distortion indices obtained by X-ray powder diffraction show a sharp initial increase of with annealing time, followed by a levelling off after approximately 10 h. Higher K-contents delay this initial increase, and decrease drastically the maximum distortion index that can be attained. The contrasting observations with respect to increasing K-content are due to the different levels of information yielded by TEM and X-ray diffraction. Analyses of electron diffraction patterns indicate that the metric state of individual crystals in any single sample annealed for more than one hour is highly heterogeneous, while no compositional differences could be detected. Hexagonal and variously distored crystals coexist. Thus intermediate structural states of cordierite in the classical sense are shown to exist, although intermediate distortion indices obtained by routine X-ray powder diffraction are largely due to a summation effect over such structurally heterogeneous populations. Although distinct differences in microstructure between the synthetic and the natural Fe²⁺-bearing cordierites exist, the Bokaro samples most closely resemble the early (1–10 h) tweed-structure of the synthetic products, whereas the Blaue Kuppe samples are comparable to a more mature (1–3 days) stage. It is thus concluded that the cordierite-bearing Bokaro paralavas cooled considerably faster than the Blaue Kuppe buchites.  相似文献   

Using numerical modelling to evaluate tsunami hazard near the Kuril Island     

L. B. Chubarov  Yu. I. Shokin  K. V. Simonov 《Natural Hazards》1992,5(3):293-318

A sequence of computer experiments is used to study questions concerning the tsunami problem as a quantitative estimate of tsunami danger, detailed geographical tsunami classification, determination of the parameters of critical tsunami waves, and the conditions of their development. We call a wave critical, if its impact on the coast is most hazardous.Using the Middle Kuril Island as an example, we present the results of a computer experiment which includes determining the wavefields on the shelf and estimating the effects connected with the deep-water Bussol and Diana Straits.Numerical simulation of tsunami waves of different sources permits the assessment of the extent of tsunami danger in different areas of the coastal zone of Simushir Island, depending on the location of the focus zone and their geometry.The major singularities of the wavefield arise in the zones of the deep-water straits. The distribution of the amplification factors is determined by both the global parameters of the wavefields and the local properties of individual harbours. The results obtained for a particular harbour in the northern part of Simushir Island, formed the basis for the quantitative estimate of tsunami danger for this area.  相似文献   

Seismic hazard monitoring in Kamchatka and its applications to the M = 6.6 earthquake of 6 October 1987     

V. M. Zobin  E. I. Gordeev  V. F. Bakhtiarov  E. I. Ivanova  Yu. M. Khatkevich  V. N. Khodenko  V. E. Levin  V. P. Mityakin 《Natural Hazards》1992,6(1):51-70

The earthquake of 6 October 1987 (M = 6.6), which occurred near the Shipunsky Cape, Kamchatka, was the largest crustal event in the vicinity of the main city of Kamchatka — Petropavlovsk-Kamchatsky — during the last three decades. It was followed by numerous aftershocks. This earthquake allowed us to test the effectiveness of the seismic hazard monitoring in Kamchatka, including the seismological, geodetic and hydrogeochemical surveys. The seismic survey provided the location and source nature of the main shock and aftershocks and the seismic environment of the main shock. The geodetic and hydrogeochemical surveys have yielded data on the response to earthquakes of the Earth's surface deformations, water level, and chemical elements concentration in the underground water. As a result, the following data were obtained:

u

The earthquake of 6 October had a seismic moment 4–10 E18 Nm, thrust type of faulting and the source volume of 20 × 20 × 10 km³. The maximum intensity was VI–VII (MSK-64 scale) and maximum acceleration 88 cm/s².

Before this event, a relative increase in the number of the upper mantle (depth more than 100 km) moderate magnitude earthquakes during 5 years and a one-year period of seismic quiescence for small shallow earthquakes, were recognized. Significant anomalies in HCO₃ and H₃BO₃ concentrations in the underground waters were observed in the wells a week before the main shock.

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Possible ways to decipher spatial distribution of mineral resources     

V. Nemec 《Mathematical Geology》1992,24(6):705-709

Regularity of structural patterns can be connected to planetary disjunctive systems (paleosystems). A computerized universal model of these systems should be developed that may be helpful to predict unknown localities of mineral resources controlled by tectonic processes. The specific character of tectonic phenomena is to be respected in geomathematical models. Some suggestions for applications are given.  相似文献   

Electrical resistivity structure of the eastern Moroccan Atlas System and its Tectonic implications     

G. Schwarz  H. G. Mehl  F. Ramdani  V. Rath 《International Journal of Earth Sciences》1992,81(1):221-235

The electrical resistivity structure of the crust and upper mantle of the Atlas Mountain System was studied using magnetotelluric and geomagnetic deep soundings. Field experiments were done in eastern Morocco along a traverse from the Anti Atlas to the Rides Rifaines in two campaigns in 1983 and 1988.Zones of very low electrical resistivity could be identified in the various structural settings at different depth ranges, most likely connected directly to the tectonic evolution of the mountain belts. A mid-crustal low resistivity layer with total conductance (thickness-resistivity ratio) of about 2000 Siemens stretches from the southern border of the High Atlas towards the Middle Atlas. This layer seems to characterize the base of crustal detachment, e.g., the plane for large horizontal overthrusting, and supports the idea of thick- and thin-skinned tectonics involved in Atlasic mountain building. In the western Middle Atlas an upper-crustal low resistivity layer (at depth < 10 km) was found in the area where volcanic activity was present, pointing towards a direct relation between low electrical resistivity and volcanic or postvolcanic events. North of the Middle Atlas resistivity structures change totally: The Pre and parts of the Sub-Rif have a highly conductive cover, presumably connected to the molasse basin. Total conductance was calculated to reach 6000 Siemens. No further conductive structures, like, e.g., the ones found beneath the High and Middle Atlas, are seen within the resistive crust, but at much greater depth within the upper mantle.

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Zusammenfassung Im marokkanischen Atlas-System wurde der elektrische Widerstand der Kruste und des oberen Mantels mit magnetotellurischen und erdmagnetischen Tiefen-Sondierungen erkundet. Die Feldmessungen wurden in den Jahren 1983 und 1988 im östlichen Marokko entlang einer Traverse vom Anti Atlas bis in das Rif durchgeführt.In den einzelnen strukturellen Einheiten wurden in unterschiedlichen Krustentiefen Schichten sehr kleiner elektrischer Widerstände entdeckt, die direkt mit der tektonischen Entwicklung des Atlasgebirges verknüpft zu sein scheinen. Zwischen dem Südrand des Hohen Atlas und dem Mittleren Atlas im Norden erstreckt sich eine Zone sehr kleiner Widerstände (integrierte Leitfähigkeit etwa 2000 Siemens) in mittleren Krustentiefen. Diese Schicht scheint einen Bereich krustaler Ablösung zu kennzeichnen und kann als Basis einer weitspannigen Überschiebung angenommen werden. Diese Form der »thick- & thin-skinned« Tektonik scheint wesentlich am Prozess der Gebirgsbildung im Atlas beteiligt zu sein. Im westlichen Mittleren Atlas, im Bereich des jungen Vulkanismus, wurde eine gutleitende Zone in der oberen Kruste (Tiefe < 10 km) gefunden. Diese Beobachtung legt einen direkten Zusammenhang zwischen erhöhter elektrischer Leitfähigkeit und vulkanischen bzw. postvulkanischen Ereignissen nahe. Nördlich des Mittleren Atlas ändern sich die Widerstandsstrukturen sehr stark: Im Prä- und teilweise auch noch im Sub-Rif liegt eine sehr gut leitende Deckschicht (integrierte Leitfähigkeit etwa 6000 Siemens) über einem hochohmigen Basement. In der Kruste des Rif werden keine weiteren, tieferliegenden Schichten erhöhter Leitfähigkeit gefunden, wie sie z.B. unter dem Hohen Atlas vorliegen. Dagegen gibt es Hinweise auf Zonen hoher Leitfähigkeit im oberen Mantel.

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Résumé Dans l'Atlas marocain la résistivité électrique de la croûte et du manteau supérieur a été étudiée à l'aide des sondages magnétotelluriques et géomagnétiques. Ces travaux ont été effectués le long d'une traverse menant de l'Anti-Atlas jusqu'au Rif durant les années 1983 et 1988.Dans différentes profondeurs de la croûte terrestre des zones de résistances électriques très basses ont pu être découvertes ce qui peut être attribué à l'évolution tectonique de l'Atlas. Une couche de résistances très basses (conductance vers 2000 Siemens) s'étend entre le bord au sud du Haut Atlas et l'Atlas Moyen au nord. Cette couche peut être le signe d'un détachement de l'écorce et d'une poussée très vaste. Cette forme tectonique »thick- & thin-skinned« semble être essentiellement responsable du processus de la formation orogénique de l'Atlas. Une zone de bonne conductance se trouve dans la croûte terrestre supérieure (profondeur < 10 km) dans l'ouest de l'Atlas Moyen aux environs de l'activité volcanique caractérisant une relation directe entre une haute conductance électrique et des événements volcaniques et post-volcaniques. Vers le nord de l'Atlas Moyen les structures de résistance subissent un changement total: Au Pré- et partiellement aussi au Subrif se trouve une bonne couche guide (conductance vers 6000 Siemens). Aucune autre couche de conductance supérieure — comme au-dessous du Haut Atlas — n'a été découverte dans la croûte du Rif. On en décèle, par contre, dans le manteau supérieur.

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1983 1988 - . , , , . ( 2000 Si). , , . , »thick- & -thin-skinned«, , . , ( 10 ) . , - . : - , , - , : 6000 Si. . .

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TREK: A cosmic-ray experiment on the Russian space station MIR     

P. B. Price  D. M. Lowder  A. J. Westphal  R. D. Wilkes  R. A. Brennen  V. G. Afanasyev  V. V. Akimov  V. G. Rodin  G. K. Baryshnikov  L. A. Gorshkov  N. I. Shvets  O. S. Tsigankov 《Astrophysics and Space Science》1992,197(1):121-143

The goals of the TREK experiment, now in place on the MIR Space Station, are to resolve and measure the composition of both odd-Z and even-Z cosmic-ray nuclei up to uranium, to measure the isotopic composition of Fe-group nuclei, and to search for transuranic nucleic and exotic particles such as strangelets. To collect tracks of ultraheavy cosmic rays, exterior panels holding an array of BP-1 phosphate glass 1.2m² in area and 16 plates thick are now mounted outside the Kvant-2 module on MIR. Heaters and relays regulate the temperature of the glass at 25°±5°C. The detectors will record 10³ cosmic-ray tracks withZ50 during 2.5 years. An interior panel consisting of an array 0.09 m² in area and 32 plates thick and mounted on the inside wall of the Soyuz spacecraft (attached to the Space Station) will collect tracks of about 13000 Fe and 500 Ni nuclei.  相似文献   

Mass ratios of three bodies for stable low-inclination three-dimensional periodic motion     

E. Perodios  V. V. Markellos 《Astrophysics and Space Science》1992,192(2):291-297

The intervals of possible stability, on the -axis, of the basic families of three-dimensional periodie motions of the restricted three-body problem (determined in an earlier paper) are extended into regions of the -m ₃ parameter space of the general three-body problem. Sample three-dimensional periodic motions corresponding to these regions are computed and tested for stability. Six regions, corresponding to the vertical-critical orbitsl1v, m1v,m2v, andilv, survive this preliminary stability test-therefore, emerging as the mass parameters regions allowing the simplest types of stable low inclination three-dimensional motion of three massive bodies.  相似文献   

Nonlinear gravidynamics: Energy-momentum tensor of collapsar field     

Vladimir V. Sokolov 《Astrophysics and Space Science》1992,197(1):87-108

In the bounds of a theoretical scheme treating consistently gravitational interaction as dynamical (gauge) field in flat space-time, an expression was obtained for the density of energy-momentum-tension of gravitational field in vacuum around a collapsed object. A case was studied of an interacting static spherically-symmetric field of a collapsar in vacuum with taking into account of input of all the possible components (spin states of virtual gravitons) into the energy for the symmetric tensor of second rank _ik . The radius of the sphere filled by matter for the collapsar of massM may achieve values up toGM/c ².  相似文献