Evolution of nappes in the eastern margin of the Bohemian Massif: a kinematic interpretation

The entire pile of nappes in the eastern margin of the Bohemian massif is characterized by two stages of Variscan nappe emplacement each exhibiting a different kinematic and metamorphic evolution.The older emplacement (D1) probably occurred around 350-340 Ma ago and was synmetamorphic. The nappes show a typical systematic superposition of higher grade metamorphic units over lower grade ones. Thus, the crystalline complexes showing a HT-MP Barrovian imprint (Svratka allochthonous unit and Moldanubicum) were thrust over an intermediate unit affected by MTMP recrystallization (Bíte orthogneiss and its country rock), and at the base of the D1 nappe pile the Inner Phyllite Nappe (Biý Potok Unit) is characterized by LT/LP metamorphism.The second stage of tectonic evolution (D2) is characterized by a thin-skinned northward-oriented nappe emplacement that occurred under LT-LP conditions dated at 320-310 Ma. The whole nappe sequence formed during the first tectonometamorphic period (D1) was transported northward over the autochthonous »Deblín polymetamorphic and granitic complex« of Upper Proterozoic age and its Devonian sedimentary cover with very low metamorphism. During this second tectonic event the Brno granite massif (580 Ma) was only marginally incorporated in the Variscan nappe tectonics which resulted in kilometer-scale cover and basement duplexes. The tectonic evolution of the nappe pile ended with stage D3, represented by large- to medium-scale east-vergent folds with limited displacement.

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Zusammenfassung Der Deckenbau am Ostrand der Böhmischen Masse erfolgte in zwei aufeinanderfolgenden Stadien, die sich sowohl in ihrer Kinematik als auch in ihrer Metamorphoseentwicklung deutlich voneinander unterschieden.Die ältere Phase (D1 ca. 350-340 Ma) ist durch synmetamorphe Überschiebungen charakterisiert. Sie führt zu einer metamorphen Inversion der überschobenen Deckeneinheiten, so daß generell hohe metamorphe Einheiten schwach metamorphe tektonisch überlagern. Der Svratka Komplex und das Moldanubikum als hangendste Decken sind durch MP/HT Paragenesen vom Barrow-Typ gekennzeichnet. Beide Einheiten sind auf den MP/MT-metamorphen Bite-Gneis und seine Rahmengesteine überschoben. Die Bílý potok Einheit als liegende Decke zeigt nur noch eine LP/ LT Regionalmetamorphose.Das jüngere Stadium (D2 ca. 320-310 Ma) ist durch eine Thin-skinned Tektonik mit nordvergentem Deckentransport unter LP/LT Bedingungen charakterisiert. Der gesamte, invers metamorphe D1-Deckenstapel wird dabei nach N über den autochtonen Deblín Komplex bzw. seine devonische Sedimenthülle überschoben.Das Brno Granit Massiv (580 Ma) wird nur randlich in diesen variszischen Deckenbau einbezogen. Die tektonische Entwicklung endet mit einem mittel bis großräumigen E-vergenten Faltenbau (D3 phase).

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Résumé L'empilement des nappes a la bordure orientale du Massif de Bohème est caractérisé par deux stades de mise en place présentant différentes évolutions cinématiques et métamorphiques.La tectonique majeure de mise en place des nappes crustales intervient lors d'un métamorphisme de type barrowien, calé autour de 350-340 Ma. L'empilement qui en résulte montre une superposition systématique d'unités à fort degré de métamorphisme sur des unités moins métamorphiques. Ainsi les complexes cristallins, montrant des reliques de métamorphisme de haute à moyenne pression-haute température (unités cristallines de Svratka et du Moldanubien), chevauchent une unité intermédiaire affectée par un métamorphisme de moyenne à basse pression-moyenne température (l'orthogneiss de Bíte et son encaissant). A la base de cette pile édifiée durant la tectonique D1, l'unité des phyllites internes (unité de Bílý potok) est caractérisée par un métamorphisme de basse témperature-basse pression.Le second stade D2 de l'évolution tectonique est caractérisé par une tectonique pelliculaire à vergence nord datée à 320-310 Ma. L'empilement résultant de D1 est ainsi transporté vers le nord, au dessus du complexe autochtone d'âge protérozoïque supérieur (groupe de Deblín) et sa couverture sédimentaire dévonienne très faiblement métamorphisée.Le massif granitique de Brno (580 Ma) n'est que marginalement incorporé à cette tectonique de nappe varisque. Ceci se traduit par des duplex socle-couverture d'échelle plurikilométrique. L'évolution tectonique s'achève lors d'une troisième phase, marquée par de grands plis à vergence est. Le déplacement associé est alors d'amplitude limitée.

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The maximum limit of the density variation parameter λ for a stable neutron star

A static spherically-symmetric model, based on an exact solution of Einstein's equation, gives the permissible matter density 2×10¹⁴ g cm^–3. If we use the change in the ratio of central density to the radiusr=a (i.e., central density per unit radius (₀/a), we call it radius density) minimum, we have estimated the upper limit of the density variation parameter () and minimum mass limit of a superdense star like a neutron star. This limit gives an idea of the domain where the neutron abundance with negligible number of electrons and protons (may be treated as pure neutrons) and equilibrium in neutrons begins.     

Surface distribution of M stars with different IRAS colour

The surface distribution of M stars is studied by differentiating them according to whether they show a circumstellar dust shell (CS) or not. Analysis shows that galactic latitudinal and longitudinal distributions are not determined by spectral subclasses alone. The study also indicates that M-type stars with CS have higher luminosities in the K band than those without CS. The M stars used in the study are obtained from theTwo-Micron Sky-Survey Catalogue (IRC) which is a most unbiased sample with respect to the interstellar extinction. The CS feature is identified by the ratio of flux densities at 12 and 25 m in the IRAS point source catalog.     

Spectrophotometric observations of delta Capricorni

Spectrophotometric observations of the eclipsing binary system Capricorni, covering the wavelength interval 3300–7300 Å, have been presented. Comparison of the standard spectral scans of Cap with the spectral scans of the stars of known spectral types and luminosity classes taken from the Breger (1976) catalogue shows that, near the phase of secondary eclipse, Cap shows the spectral-luminosity type as A8-9III. This is in agreement with the photometric findings of Srivastava (1987b). H emission is not visible convincingly, however, some irregularities are apparent, at least in two scans, around the H region.     

The even-odd systematics inR-process nuclide abundances

We report and discuss solar systemN _R abundances for nuclidesA>70, obtained as differences between measured solar system abundances and calculatedS-process contributions. The abundance peak atA163 in the rare Earth element region reveals properties which are similar to those of theR-process peaks corresponding to magic neutron numbersN=82 andN=126. We observe that systematic differences in theN _R abundances of even-A and odd-A nuclides are restricted to specific mass regions. We discuss possible interpretations and conclude that these differences are most probably related to the properties of nuclear species during _– to the stability valley.... A genesis of the elements such as is sketched out would not be confined to our little Solar System, but would probably follow the same general sequence of events in every center of energy now visible as a Star. Sir William Crookes (1886)Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

The stability parameters of three-dimensional periodic three-body orbits

Formulae containing the elements of the variational matrix are obtained which determine the linear isoenergetic stability parameters of three-dimensional periodic orbits of the general three-boy problem. This requires the numerical integration of the variational equations but produces the stability parameters with the effective accuracy of the numerical integration. The conditions for stability, criticality, and bifurcations are briefly examined and the stability determination procedure is tested in the determination of some three-dimensional periodic orbits of low inclination bifurcating from vertical-critical coplanar orbits.     

Space charge sheath in plasma-neutral gas interaction

A space charge sheath is found to be formed whenever a high-velocity magnetized plasma stream penetrates a gas cloud. The sheath is always located at the head of the plasma stream, and its thickness is very small compared to the length of the plasma stream. Soon after the sheath is formed it quickly slows down to the Alfvén critical velocity. The plasma behind the sheath continues to move at higher velocity until the whole plasma stream is retarded to the critical velocity. In the interaction at gas density 10¹⁹ m^–3 the sheaths are observed to be accompanied by a single loop of current with current density of 10⁵ Å m^–2. Maximum potential in the sheath ranges between 50 and 200 V.Presently available models for the sheath may explain the initiation of the sheath formation. Physical processes like heating of the electrons and ionization of the gas cloud which come into play at a later stage of the interaction are not included in these models. These processes considerably alter the potential structure in the sheath region. A schematic model of the observed sheath is presented here.Experiments reveal a threshold value of the magnetic field for plasma retardation to occur. This seems to correspond to the threshold condition for excitation of the modified two-stream instability which can lead to the electron heating. The observed current are found sufficient to account for the plasma retardation at a gas density of 10¹⁷ m^–3.     

A spectroscopic study of the microorganism model of interstellar grains

The microorganism model of interstellar grains is investigated by spectroscopy from the infrared (IR), visible to the ultraviolet (UV) wave regions.E. coli, yeast and spores ofBacillus subtilis exhibit absorption bands at =3.1 and 9.7 m; they also exhibit several absorptions at 68 m which are in agreement with the observed IS extinction curves.To obtain the extinction curves in the visible and UV regions, dry films of microorganism are prepared on a MgF₂ plate or synthesized quartz plate and their spectra measured. In the wavelength region 190400 nm, conventional spectrophotometers are adopted for the measurement. The extinction curve of the film ofE. coli is similar to the observed IS curve.For the wave-range 100<<400 nm, a vacuum UV spectrometer is adopted to avoid absorptions due to O₂ in the atmosphere. The extinction spectra by this method are in agreement with the result obtained by the conventional method where comparison is possible. The extinction curves ofE. coli and yeast are such that they incrase towards the short wavelength and exhibit a peak at -190 nm, which is different from the well-known IS peak at =220 nm. It remains to be seen whether interstellar low temperatures (1040 K) can shift the peak position in the extinction curve of biochemical materials.     

Development of a real-time algorithm for detection of solar wind discontinuities

A study is presented of an algorithm, based on the statistical analysis of interplanetary magnetic field data, for the real-time detection of discontinuities in the solar wind. The analysis is based on the application of a sliding or searching algorithm together with a minimum variance treatment. A demonstration is given for a Pioneer data set from 29 August, 1966. This particular data set was chosen because it has been extensively studied (in terms of the fast forward MHD shock wave) by previous groups who utilized the three-dimensional Rankine-Hugoniot shock equations after identifying the shock on a subjective basis. Our procedure differs in that it is perfectly objective because of its searching technique. For this particular data set we identify the original shock with excellent agreement with the earlier studies of its normal vector, as well as an additional shock and tangential discontinuity, neither of which had been identified previously.     

Converging magnetogasdynamic cylindrical shock waves in a uniform atmosphere

A self-similar solution to the problem of the implosion of a cylindrical shock wave in the presence of a magnetic field has been investigated. A strong shock wave in a cylindrically-symmetric flow travels to the axis of symmetry through a gas of uniform initial density ₀ and zero-pressure. A comparative study has been made between the results obtained in ordinary gasdynamics and magnetogasdynamics with transverse and axial components of the magnetic field. The value of similarity exponent has been assigned from that found in the paper of Whitham (1958).