Problem of the Rotating Magnetoconvection in Variously Stratified Fluid Layer Revisited     

Šimkanin  Ján  Brestenský  Jozef  Ševčík  Sebastián 《Studia Geophysica et Geodaetica》2003,47(4):827-845

The linear magnetoconvection in the rotating uniformly as well as non-uniformly stratified horizontal layer with azimuthal magnetic field is investigated for the various mechanical and electrical boundary conditions and especially, for various values of Roberts number. The developed diffusive perturbations (modes) are strongly influenced not only by the mentioned properties of boundaries but also by complicated coupling of viscous, thermal and magnetic diffusive processes. The mean electromotive force produced by developed hydromagnetic instabilities is also investigated to determine the hydromagnetic processes which are appropriate for -effect. The presented paper is an unification of hitherto published results of the authors and gives a short survey of many developments of corresponding model by Soward (1979).  相似文献   

Present-day seismicity of the south-eastern Elbe Fault System (NE Bohemian Massif)   总被引：1，自引：0，他引：1  

P. Špaček  Z. Sýkorová  J. Pazdírková  J. Švancara  J. Havíř 《Studia Geophysica et Geodaetica》2006,50(2):233-258

The Variscan Bohemian Massif is disrupted by the NW-SE striking Elbe Fault System in its northern part. The increased tectonic activity associated with this structure is manifested by increased seismicity in the eastern part of the Sudetes. With the use of a temporary local seismic network, the total number of micro-earthquakes located in this region increased to 153 for the period 1996–2003. The local magnitudes vary between −0.6 and 1.8 and the seismic energy was often released in swarm-like sequences. Five seismic events with well-defined P-onset polarities at five or six stations enabled the estimation of focal mechanisms. The present-day activity of the WNW-ESE to NNW-SSE fault systems is discussed on the basis of source mechanisms, the alignment of the epicentres, as well as morphological and geological evidence. The majority of the recent seismic activity is concentrated in a 40–60 km wide zone of a generally NW-SE trend. This structure represents a regional zone of weakness within the SE termination of the Elbe Fault System, defined by a mesh of interconnected faults, of which many are deep-seated and highly permeable and some are associated with light to moderate historical earthquakes. Both in the areas due south and due north of this zone the present-day seismic activity is very low. The increased tectonic activity can be interpreted as a result of the abundance of suitably oriented faults and their interconnection into major fault systems, the proximity of the Outer Carpathian indentor and the Cainozoic volcanic and associated recent post-volcanic activity. The similar character of swarms and their coincidence with the post-volcanic activity in the southeastern part of the Elbe Fault System and in some focal zones of the western Bohemian seismically active area suggests that overpressurized fluids may represent a potential swarm-triggering mechanism.  相似文献   

Detection of the wave-like structures in the F-region electron density: Two station measurements     

P. Šauli  P. Abry  D. Altadill  J. Boška 《Studia Geophysica et Geodaetica》2006,50(1):131-146

Comparative studies of short-term ionospheric variability in the F region ionosphere during rapid sequence sounding campaign “HIRAC/SolarMax” (23–29 April 2001) are presented. The ionospheric short-term fluctuations have been studied in detail using measurements from vertical sounding at Ebro (40.8 °N, 0.5 ° E) and Průhonice (49.9 °N, 14.5 °E) in the period range from 15 minutes to 2 hours. The electron density measurements contain variations that indicate the possible presence of propagating gravity waves. Regular wave-like bursts were found during quiet days at both stations in electron concentration in F region, with an increase of the oscillation activity after sunrise and then during late afternoon, and at sunset and after sunset. Solar Terminator is assumed to be one of the sources of the regular wave bursts detected in the ionosphere during campaign HIRAC. As expected, substantial intensification in longer period gravity waves was found to occur during the disturbed period on April 28. Particular enhancement of the wave-like activity during disturbed day is discussed, being significant evidences of a change of the wave-like activity pattern at a height around 200 km.  相似文献   

Seasonal ecosystem variability in remote mountain lakes: implications for detecting climatic signals in sediment records   总被引：5，自引：0，他引：5  

J. Catalan  M. Ventura  A. Brancelj  I. Granados  H. Thies  U. Nickus  A. Korhola  A.F. Lotter  A. Barbieri  E. Stuchlík  L. Lien  P. Bitušík  T. Buchaca  L. Camarero  G.H. Goudsmit  J. Kopáćek  G. Lemcke  D.M. Livingstone  B. Müller  M. Rautio  M. Šiško  S. Sorvari  F. Šporka  O. Strunecký  M. Toro 《Journal of Paleolimnology》2002,28(1):25-46

Weather variation and climate fluctuations are the main sources of ecosystem variability in remote mountain lakes. Here we describe the main patterns of seasonal variability in the ecosystems of nine lakes in Europe, and discuss the implications for recording climatic features in their sediments. Despite the diversity in latitude and size, the lakes showed a number of common features. They were ice-covered between 5–9 months, and all but one were dimictic. This particular lake was long and shallow, and wind action episodically mixed the water column throughout the ice-free period. All lakes showed characteristic oxygen depletion during the ice-covered-period, which was greater in the most productive lakes. Two types of lakes were distinguished according to the number of production peaks during the ice-free season. Lakes with longer summer stratification tended to have two productive periods: one at the onset of stratification, and the other during the autumn overturn. Lakes with shorter stratification had a single peak during the ice-free period. All lakes presented deep chlorophyll maxima during summer stratification, and subsurface chlorophyll maxima beneath the ice. Phosphorus limitation was common to all lakes, since nitrogen compounds were significantly more abundant than the requirements for the primary production observed. The major chemical components present in the lakes showed a short but extreme dilution during thawing. Certain lake features may favour the recording of particular climatic fluctuations, for instance: lakes with two distinct productive periods, climatic fluctuations in spring or autumn (e.g., through chrysophycean cysts); lakes with higher oxygen consumption, climatic factors affecting the duration of the ice-cover (e.g., through low-oxygen tolerant chironomids); lakes with higher water retention time; changes in atmospheric deposition (e.g., through carbon or pigment burial); lakes with longer stratification, air temperature changes during summer and autumn (e.g., through all epilimnetic species).  相似文献   

Tantalum mineralization in the apical part of the Cínovec (Zinnwald) granite stock     

A. K. Rub  M. Štemprok  M. G. Rub 《Mineralogy and Petrology》1998,63(3-4):199-222

Summary Granite-hosted tantalum mineralization was studied in the apical part of the Cínovec (Zinnwald) granite stock (eastern Kruné hory, Czech Republic). Samples of granite and greisen from drill hole CS-1 (1596m deep), situated in the centre of the granite body were analysed chemically and examined by electron microprobe. The apical, mainly lepidolite granite with 24 to 212 ppm Ta contains Ta-rich Mn columbite, uranmicrolite and strueverite (tantalian rutile). During greisenization the contents of Ta decreased or remained the same, but the newly formed cassiterite has elevated contents of Ta, probably due to remobilization from albitized granites. Niobium and tantalum mineralization can be linked with both magmatic and postmagmatic stages of granite evolution. Ta-rich columbite formed as a result of albitization dominant at the top of the granite cupola, whereas magmatic Nb-rich columbite is present throughout the entire profile of the granite stock.The Cínovec granite stock is similar to some Palaeozoic Ta-bearing granite stocks in the Far East of Russia (Vosnesenka, Pogranichnyi) which are characterized by a vertical sequence of lepidolite, zinnwaldite and protolithionite granites. It shows minor similarities with Mesozoic amazonite-bearing granites in Transbaikalia (Etyka, Orlovka) and differs petrologically and mineralogically from the Palaeozoic lepidolite granite of Beauvoir (Échassieres) in France.

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Tantalvererzung im oberen Teil des Cínovec (Zinnwalder) Granitstocks

Zusammenfassung Eine granitgebundene Tantalvererzung wurde im oberen Teil des Cínovec (Zinnwalder) Granitstocks (östliches Erzgebirge, Tschechische Republik) untersucht. Granit- und Greisenproben aus der Mitte des Granitkörpers wurden chemisch und mittels Elektronenstrahl-Mikrosonde analysiert. Der apikale Lepidolitgranit mit 24-212 ppm Ta führt Ta-reichen Mangancolumbit, Uranmikrolit und Strueverit (Tantalrutil). Im Verlauf der Vergreisung wurden die Tantalgehalte erniedrigt oder blieben gleich. Nur der neugebildete Kassiterit zeigt, wahrscheinlich als Folge der Remobilisierung aus den albitisierten Graniten, erhöhte Tantalgehalte. Die Niob- und Tantalmineralisation ist an das magmatische und postmagmatische Stadium der Granitentwicklung gebunden. Tantalreiche Columbite wurden durch die Albitisierung im Apikalteil des Granitstockes gebildet, während die niobreichen Columbite des magmatischen Stadiums über das ganze Bohrprofil hinweg vorkommen.Der Zinnwalder Granitstock ist einigen paläozoischen Granitstöcken mit Tantalmineralisation im fernen Osten von Russland (Voznesenka, Pogranichnyi) ähnlich, welche durch eine vertikale Zonierung von Lepidolit-, Zinnwaldit- und Protolithionitgranit charakterisiert sind. Der Granitstock zeigt wenig ähnlichkeiten mit den mesozoischen Amazonitgraniten in Transbaikalien (Etyka, Orlovka) und unterscheidet sich petrologisch und mineralogisch vom paläozoischen Granit aus Beauvoir (Échassieres) in Frankreich.

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With 11 Figures  相似文献   

CLIMATE HISTORY INFERRED FROM BOREHOLE TEMPERATURES, DATA FROM THE CZECH REPUBLIC     

JAN ŠAFANDA  VLADIMÌR ČERMÀK  Louise Bodri 《Surveys in Geophysics》1997,18(2-3):197-212

The knowledge of the present-day underground temperatures may be important in the assessments of the past climate change. The method of inversion of the temperature-depth records into the ground surface temperature history is briefly introduced by showing an example of synthetic data and illustrated by a review of existing results obtained from the inversion of temperature logs measured in holes in the Czech Republic. Underground temperatures observed in holes of the depth of at least 1000–1500 m seem to confirm the preinstrumental climate pattern of the past several thousand years. Most of shallower temperature records (500–800 m) revealed general warming of climate followed the Little Ice Age of the 17–18th centuries and a pronounced increase of the soil temperatures by at least 1 K since the beginning of this century.  相似文献   

Explanation of the internal air pressure effect on the worden gravity meter dial constant     

Karel Diviš  Vladimír Tobyáš  Bohumil Chán  Reviewer Z. Šimon 《Studia Geophysica et Geodaetica》1989,33(2):206-209

Summary A model, explaining the effect of air pressure changes in the space of the measuring system on the fine dial counter constant of the Worden and similar gravity meters, is presented. It is based on the changes of the bellows volume with compensating the gravity changes. It is shown that the resetting the gravity meter in the whole range has practically no influence on the fine dial counter constant.

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Determination of tidal torques independently of densities     

Milan Burša  Reviewer Z. Šimon 《Studia Geophysica et Geodaetica》1986,30(2):118-123

Summary The components of the tidal torques along the axes of the inertia ellipsoid of a perfectly elastic Earth have been derived quite independently of the density distribution of masses within the Earth. It has been demonstrated that not only the sectorial, but also the tesseral terms in the tidal forming potential are responsible for the tidal deceleration of the Earth's rotation.

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am ¶rt; mau ma nuu u m u a um unu¶rt;a uuu u¶rt;a n u, auu m ¶rt;a an¶rt;uu nmm a. aa, m nuu a¶rt;u au u a m muau, u mau nuuu au nuua nmua.

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Seismic regime of a single fault model     

A. Špičák  T. Lokajíček  L. Waniek 《Pure and Applied Geophysics》1986,124(4-5):793-810

A special experimental technique enabled us to study in detail seismic events on a fault model in a uniaxial stress field. The recording system used made it possible to investigate the radiation pattern for all the events observed including the precise determination of the dislocation origin.The aim of the present paper is (1) to find the relation between shear and tensile displacements, (2) to check a possible influence of the process of tensile crack generation on the seismic energy release and (3) to compare the seismic regime of a single fault before and after the tensile crack generation, respectively.Results prove the dominating importance of shear mechanism for the seismic energy release. The tensile displacement can be seismoactive only under special contact conditions on the fault plane.The existence of tensile cracks at the fault tips changed the pattern of seismic energy radiation. This feature is probably caused by subsequent changes in contact conditions on the fault plane and in the stress field around the fault.A comparison of some results of the present model experiments with the already published results of geological and seismological measurements and investigations shows the analogous character in laboratory and in nature of the process of tectonic earthquake preparation, the displacement course on the fault during the earthquake and the manner of seismic energy release on faults.  相似文献   

Gravity ideal-body analysis     

Pavel Peška  Reviewers J. Švancara  Reviewers K. Pěč 《Studia Geophysica et Geodaetica》1989,33(4):405-408

Summary This short note contributes to the methods of computing the bounds on some properties of the source of measured data.  相似文献