Propagation of MHD body and surface waves in magnetically structured regions of the solar atmosphere     

S. T. Wu  Y. C. Xiao  Z. E. Musielak  S. T. Suess 《Solar physics》1996,163(2):291-307

The fact that magnetically structured regions exist in the solar atmosphere has been known for a number of years. It has been suggested that different kinds of magnetohydrodynamic (MHD) waves can be efficiently damped in these regions and that the dissipated wave energy may be responsible for the observed enhancement in radiative losses. From a theoretical point of view, an important task would be to investigate the propagation and dissipation of MHD waves in these highly structured regions of the solar atmosphere. In this paper, we study the behavior of MHD body and surface waves in a medium with either a single or double (slab) magnetic interface by use of a nonlinear, two-dimensional, time-dependent, ideal MHD numerical model constructed on the basis of a Lagrangean grid and semi-implicit scheme. The processes of wave confinement and wave energy leakage are discussed in detail. It is shown that the obtained results depend strongly on the type of perturbations imposed on the interface or slab and on the plasma parameter, . The relevance of the obtained results to the heating problem of the upper parts of the solar atmosphere is also discussed.  相似文献   

A nonlinear tensor field and the second metric tensor     

L. Sh. Grigorian  S. Gottlöber 《Astrophysics》1996,39(1):71-77

In our preceding paper {see [L. Sh. Grigorian and S. Gottlöber, Astrofizika (in press)]} we investigated a self-gravitating system consisting of a scalar field and a linear tensor field _ik= _ki with minimal coupling and with allowance for the action of vacuum polarization effects. In the present paper we investigate the case of a nonlinear tensor field _ik. The action S ⁽⁾ of the field _ik is determined by the difference R_ik — _ik, where R_ik is the space-time Ricci tensor and Rik is the analogous quantity constructed using the metric _ik=g_ik+_ik induced by _ik ( is a free parameter). Here S ⁽⁾ coincides with the previously known expression for the action of a linear field _ik. Equations of motion are derived for _ik in curved space-time. The energy-momentum metric tensor, determining the contribution of _ik to the gravitational field equations, is calculated.Translated from Astrofizika, Vol. 39, No. 1, pp. 135–144, January-March, 1996.  相似文献   

Effects of water on strength and failure mode of coarse-grained granites at 300°C   总被引：1，自引：0，他引：1  

E. Althaus  A. Friz-Töpfer  Dr. rer. nat. Ch. Lempp  O. Natau 《Rock Mechanics and Rock Engineering》1994,27(1):1-21

Summary Deformation experiments have been performed in a triaxial compression cell at a temperature of 300°C and confining pressures up to 65 MPa using samples of homogeneous, fresh two-mica-granite (RM) and monzogranite (CM). The cylindrical specimens (d=70 mm, h=140 mm, V=540 cm³) were tested undrained under dry (105°C), as received, and water saturated conditions at deformation rates between and . The mechanical behaviour of the two types of coarse-grained, crystalloblastic granites is critically influenced by mineralogical composition, porosity, and the amount of intergranular water present in the samples. The failure stress of the CM granite is at about 65% of that of the RM granite; in both rocks strength decreases with increasing porosity and water content.The presence of interstitial water causes a failure mode of non-localized, homogeneously distributed microcracking in the central parts of the samples, whereas, in runs with dry granites, strain localization along a single shear fracture was observed. When aqueous fluids are present, the macroscopic style of deformation of granites appears to be ductile even at lowP andT conditions. Strength and angle of internal friction are reduced to very low values. The style of deformation, as well as the reduction of strength of the water-saturated rock samples, is due to mechanical and chemical effects of intergranular water at elevated temperatures.The maximum differential stresses measured for these coarse-grained granites are much lower than the strength commonly reported for other granites, e. g. Westerly and Charcoal granites. Our data suggest that the strength of the granitic crust under differential stress is lower than currently deduced from laboratory experiments.  相似文献   

Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers   总被引：11，自引：0，他引：11  

Summons RE  Jahnke LL  Roksandic Z 《Geochimica et cosmochimica acta》1994,58(13):2853-2863

Experiments with cultured aerobic methane oxidising bacteria confirm that their biomarker lipids will be significantly depleted in 13C compared to the substrate. The methanotrophic bacteria Methylococcus capsulatus and Methylomonas methanica, grown on methane and using the RuMP cycle for carbon assimilation, show maximum 13C fractionation of approximately 30% in the resultant biomass. In M. capsulatus, the maximum fractionation is observed in the earliest part of the exponential growth stage and decreases to approximately 16% as cells approach stationary phase. This change may be associated with a shift from the particulate form to the soluble form of the methane monooxygenase enzyme. Less than maximum fractionation is observed when cells are grown with reduced methane availability. Biomass of M. capsulatus grown on methanol was depleted by 9% compared to the substrate. Additional strong 13C fractionation takes place during polyisoprenoid biosynthesis in methanotrophs. The delta 13C values of individual hopanoid and steroid biomarkers produced by these organisms were as much as l0% more negative than total biomass. In individual cultures, squalene was 13C-enriched by as much as 14% compared to the triterpane skeleton of bacteriohopaneaminopentol. Much of the isotopic dispersion in lipid metabolites could be attributed to shifts in their relative abundances, combined with an overall reduction in fractionation during the growth cycle. In cells grown on methanol, where there was no apparent effect of growth stage on overall fractionation there were still significant isotopic differences between closely related lipids including a 5.3% difference between the hopane and 3 beta-methylhopane skeletons. Hopane and sterane polyisoprenoids were also 13C-depleted compared to fatty acids. These observations have significant implications for the interpretation of specific compound isotopic signatures now being measured for hydrocarbons and other lipids present in sediments and petroleum. In particular, biomarker lipids produced by a single organism do not necessarily have the same carbon isotopic composition.  相似文献   

Early Cretaceous volcaniclastic and quartzose sandstones from north central Nepal: composition,sedimentology and geotectonic significance     

Sören B. Dürr  Martin R. Gibling 《International Journal of Earth Sciences》1994,83(1):62-75

Early Cretaceous sandstones and shales from the Thakkhola region (Chukh and Tangbe Formations) were deposited on the subsiding northern (Tethyan) margin of Gondwana; current directions indicate a source area to the south. Whereas the Berriasian Chukh Formation is dominated by quartz arenites, volcaniclastic sandstones and minor conglomerates dominate the Tangbe Formation of Valanginian to Aptian age. Upsection, the composition of the volcaniclastic components changes from mainly basaltic to dominantly dacitic/rhyolitic. Magmatism was preceded and accompanied by strong uplift in the source area of the Chukh and Tangbe clastics, resulting in the erosion of probably more than several hundred meters of pre-Cretaceous sedimentary, metamorphic and plutonic rocks. A geochemical whole rock analysis of basaltic pebble fragments shows their alkaline character and suggests a within-plate geotectonic setting for the volcanic source. This volcanotectonic event is probably related to rifting between Australia and Greater India, where seafloor spreading began in late Valanginian/Hauterivian times.  相似文献   

A quantitative model of coherent,stimulated emission in astrophysical jets     

J. C. Wang  G. Z. Xie  J. Lin 《Astrophysics and Space Science》1994,213(2):257-271

On the basis of issues raised by observations of BL Lac objects and the qualitative jet model proposed by Bakeret al. in 1988, we have been led to consider the quantitative role of coherent, stimulated emission in jets and construct a new jet model of blazars in which a relativistic electron beam with an axial symmetric, power-law distribution is injected from the central engine into the jet plasma. We study quantitatively the synchrotron emission of the relativistic electron beams. Using the weak turbulent theory of plasma, we discuss the interaction between relativistic electron beams and jet plasma, and the roles of stimulated emission. The main results are:

1. The synchrotron emission increases sensitively with the increase of the angle between the direction of the beam and the magnetic field. When the direction of the beam is vertical to the magnetic field, the synchrotron emission reaches its maximum, i.e. the emitted waves are beamed in the direction of the jet axis. We suggest that radio selected BL Lac objects belong to this extreme classification.
2. The synchrotron emission of the relativistic beam increases rapidly with the increase of the Lorentz factor of the relativistic electron,γ, whenγ ≤ 22.5, then decreases rapidly with increase ofγ.
3. The stimulated emission also increases with increasing Lorentz factorγ of the relativistic electrons whenγ ≤ 35 and then decreases with the increasingγ. The maximum stimulated emission and the maximum synchrotron emission occur at different frequencies. Stimulated emission is probably very important and reasonable flare mechanism in blazars.
4. The rapid polarization position angle (PA) swings may arise from the interaction between the relativistic electron beam and the turbulent plasma.

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Partitioning of silver,beryllium and molybdenum among chemical fractions in the sediments from the Labe (Elbe) river in Central Bohemia,Czech Rep.     

Z. Borovec 《GeoJournal》1993,29(4):359-364

Sequential extraction of the fine fraction (63 µm) of the bottom sediments of the Labe river in Central Bohemia indicates that the readily reducible sediment fraction is a major reservoir of silver for release into the aqueous phase. Molybdenum is preferentially mobilized by ion-exchange, while beryllium is accumulated in all the chemical fractions of the sediments, especially in the moderately reducible and the organic/sulphidic phases.Contamination of the aquatic system from anthropogenic sources is characterized by the formation of relatively unstable chemical forms and only a small portion of these elements remain in the stable residual fraction.  相似文献   

Fossil carotenoids and paleolimnology of meromictic Mahoney Lake,British Columbia,Canada     

Jörg Overmann  Gerhard Sandmann  Ken J. Hall  Tom G. Northcote 《Aquatic Sciences - Research Across Boundaries》1993,55(1):31-39

Vertical distribution of fossil carotenoids in a sediment core from meromictic Mahoney Lake was studied. Besides okenone and demethylated okenone, lutein and zeaxanthin and-carotene isomers were identified. No carotenoids typical for purple nonsulfur or green sulfur bacteria were detected. The ratio of zeaxanthin to lutein (above 1:1 in all samples) indicates a dominance of cyanobacteria over green algae in the phytoplankton assemblages of the past. Okenone, which is found exclusively in Chromatiaceae, was the dominating carotenoid in all sediment zones.The oldest sediment layers containing okenone were deposited 11 000 years ago. Between 9000 and 7000 and since 3000 years b.p., Chromatiaceae reached a considerable biomass in the lake. Vertical changes in okenone concentration were not related to changes of paleotemperatures. In contrast, okenone concentrations decreased during periods of volcanic ash input. During most of the lake history, however, mean okenone concentrations were positively correlated with sedimentation rates. This indicates that vertical changes of okenone concentration in the sediment reflect past changes of purple sulfur bacterial biomass in the lake.According to these results, the past limnology of Mahoney Lake resembled that of the present with a sulfide-containing monimolimnion and a well-developed population of okenone-bearing purple sulfur bacteria.  相似文献   

Alkaline and ultramafic carbonate lamprophyres in Central Bohemian carboniferous basins,Czech Republic     

Dr. J. Ulrych  Dr. E. Pivec  Dr. K. Zák  Dr. J. Bendl  Dr. P. Bosák 《Mineralogy and Petrology》1993,48(1):65-81

Summary Dykes of alkaline and ultramafic carbonate lamprophyres (monchiquite-ouachitite and aillikite) intrude the Carboniferous sediments of Central Bohemia. Their characteristic feature is the presence of substantial amounts of a sodalite group mineral (presumably haüyne), carbonate and barite. Isotopic compositions of ¹³C (–3.4 to –6.2) and ¹⁸O ( + 13.5 to + 15.9) indicate that the carbonate is of primary magmatic origin and that fluids were formed at temperatures of 500 to 350°C. High contents of CO₂ (3.6 to 17.6 wt.%) and incompatible elements, high LREE/HREE ratios (30.0 to 57.7), and low Rb/Sr (0.025 to 0.078) and⁸⁷Sr/⁸⁶Sr (0.7038 to 0.7042) ratios suggest the ultramafic lamprophyres are related to deep-seated carbonated magmas of mantle origin. Low degree of partial melting ( < 1%) of the mantle peridotite is envisaged, with additional transport of fluids rich in incompatible elements into the crustal chamber. Alkaline lamprophyres are fractionated derivatives which originated from the same source. Magma intrusion from different levels of a magma chamber into fracture zones under horizontal tension without a central intrusion could result in variability in lamprophyre composition (cumulates or evolved derivatives).

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Alkalische und ultramafische Karbonat-Lamprophyre der zentralen böhmischen Karbonbecken, Tschische Republik

Zusammenfassung Alkalische und ultramafische Karbonat-Lamprophyrgänge (Monchiquit-Ouachitit und Aillikit) intrudieren in karbonische Sedimente Zentralböhmens. Sie sind charakterisiert durch das Auftreten von beträchtlichen Mengen an Mineralen der Sodalith-Gruppe (v.a. Haüyn), Karbonaten und Baryt. Ihre Isotopenzusammensetzung von ¹³C (–3.4 bis –6.2) und ¹⁸O (13.5 bis 15.9) zeigt, daß die Karbonate primär magmatischen Ursprungs sind und daß assoziierte Fluide in einem Temperaturbereich von 350 bis 500°C gebildet wurden. Hohe Gehalte an CO₂ (3.6 bis 17.6 Gew. %), inkompatiblen Elementen, hohe LREE/HREE-Verhältnisse (30.0 bis 57.7), sowie niedrige Rb/Sr—(0.025 bis 0.078) und⁸⁷Sr/⁸⁶Sr-(0.7038 bis 0.7042) Verhältnisse lassen vermuten, daß die ultramafischen Lamprophyre mit karbonatischen Magmen des Mantels in Beziehung stehen. Eine niedrige Aufschmelzungsrate ( < 1%) von Mantelperidotit mit zusätzlichem Transport von, an inkompatiblen Elementen angereicherten Fluiden, in die krustale Magmenkammer wird diskutiert. Alkalische Lamprophyre sind als stärker fraktionierte Magmen, die derselben Quelle entstammen, zu verstehen. Die Intrusion der aus verschiedenen Bereichen der Magmenkammer stammenden Magmen in durch horizontale Dehnung verursachte Störungszonen könnte das Fehlen eines zentralen Intrusionskörpers und die unterschiedliche Zusammensetzung der Lamprophyre (Kumulate oder entwickelte Derivate) erklären.

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With 8 Figures  相似文献   

Synthetic zeolites formed from expanded perlite: Type,formation conditions and properties     

Dr. Ulrike Barth-Wirsching  Dr. H. Höller  Dr. D. Klammer  Dr. B. Konrad 《Mineralogy and Petrology》1993,48(2-4):275-294

Summary The starting material used was expanded perlite with a grain size < 40 m (74.5 wt.% SiO₂; 12.5 wt.% Al₂O₃). This material is a waste product obtained during the production of expanded perlite. The experiments were carried out with KOH solutions, mixtures of KOH and NaOH solutions (1:1) as well as NaOH solutions in the concentration range 0.5 N to 6.0 N at temperatures of between 100° and 140°C and with reaction periods of 2 hours to 13 days in closed system. In the experiments with KOH containing solutions zeolite ZK-19 (phillipsite), W (merlinoite), G (chabazite) and F (edingtonite) formed. Without addition of aluminium high percentages of zeolite ZK-19 (80–100 wt.%) and zeolite W (90–100 wt.%) were obtained. The addition of aluminium rendered possibly the formation of 90 to 100 wt.% of zeolite G and 85 to 100 wt.% of zeolite F, respectively. In the experiments with NaOH solutions analcime, zeolite Na-Pc (gismondine), zeolite HS (sodalite hydrate) and zeolite A formed. High percentages of zeolite Na-Pc (90–100 wt.%), zeolite HS (up to 100 wt.%) and analcime (up to 100 wt.%) were synthesized without addition of aluminium. The formation of high percentages of zeolite A (95–100 wt.%), however, needs the addition of aluminium, NaCI and seed crystals. The temperature stability of the zeolites decreases in the following sequence: K-F > K-W K-ZK-19 (Na), K-W Na, K-F G_si-rich (Na), K-ZK-19 >> Na-Pc G_si-poor. Zeolite A has a very good temperature stability up to temperatures of } 550 °C similar to that of zeolite K-W. At higher temperatures, however, its stability is very poor. The NH₄ ⁺-exchange capacities (meq/g) of the different zeolites amount to the following values: ZK-19:2.8 - 3.2; W:3.0 - 3.2; G:2.3 - 3.6; A:3.1 - 3.2; Na-Pc:3.5 - 3.6; F : 3.9 - 4.8.

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Zeolithsynthese aus Blähperlit—Art, Bildungsbedingungen und Eigenschaften

Zusammenfassung Ausgangsmaterial der experimentellen Untersuchungen war Blähperlit mit einer Korngröße < 40 ,m (74,5 Gew.-% SiO₂; 12,5 Gew.-% Al₂O₃). Dieses Material ist ein Abfallprodukt, das bei der Produktion von Blähperlit anfällt. Die Experimente wurden mit KOH-Lösungen, Lösungsgemischen aus KOH und NaOH (1:1) sowie mit NaOH-Losungen im Konzentrationsbereich 0,5 n-6,0 n bei Temperaturen von 100° – 140°C und über Reaktionszeiten von 2 Stunden bis zu 13 Tagen im geschlossenen System durchgeführt. In den Experimenten mit KOH-hältigen Lösungen bildeten sich die Zeolithe ZK-19 (Phillipsit), W (Merlinoit), G (Chabasit) und F (Edingtonit). Hohe Prozentgehalte an Zeolith ZK-19 (80 – 100 Gew.-%) und Zeolith W (90–100 Gew.-%) entstehen nur ohne Zugabe von Aluminium. Die Bildung von 90–100 Gew.-% Zeolith G bzw. 85–100 Gew. % Zeolith F ist dagegen durch die Zugabe von Aluminium möglich. In den Experimenten mit NaOH-Lösungen bildeten sich die Zeolithe Analcim, Na-Pc (Gismondin), HS (Sodalithhydrat) und Zeolith A. Hohe Prozentanteile an Zeolith Na-Pc (90–100 Gew.-%), HS (bis zu 100 Gew. %) und Analcim (bis zu 100 Gew.-%) wurden ohne Aluminium-Zugabe synthetisiert. Die Bildung von hohen Gehalten an Zeolith A (95–100 Gew. %) ist jedoch nur unter Zugabe von Aluminium, NaCl und Kristallkeimen möglich.Die Temperaturbeständigkeit der Zeolithe nimmt in der folgenden Reihenfolge ab: K-F > K-W - K-ZK-19 (Na), K-W Na, K-F G_si-reich (Na), K-ZK-19 >> Na-Pc G_si-am. Zeolith A weist bis zu Temperaturen von etwa 550°C eine gute Temperaturbeständigkeit auf, die in etwa der von Zeolith K-W entspricht. Bei höheren Temperaturen ist die Beständigkeit jedoch sehr gering.Die NH⁴⁺-Austauschkapazitäten (mÄqu/g) der verschiedenen Zeolithe erreichen folgende Werte: ZK-19:2,8 - 3,2; W:3,0 - 3,2; G:2,3 - 3,6; A:3,1 - 3,2; Na-Pc:3,5 -3,6; F:3,9 - 4,8.

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With 2 Figures  相似文献