A near infrared speckle imaging study of T Tauri Stars

The results of a speckle imaging survey of T Tauri stars suggest that most, if not all, young low mass stars have companions. Repeated observations of these young binary stars have revealed orbital motion in the closest pairs (0.3), proving that these systems are indeed gravitationally bound and providing the basis for mass estimates in the upcoming years. These mass estimates are necessary to distinguish between the various binary star formation mechanisms that have been proposed to date.     

Porous rock deformation and fluid flow — numerical FE-simulation of the coupled system

Elastic compaction is characterized by the interaction of the deforming rock matrix and fluid flow for a given environment. The basic theory was developed by Biot. However, Biot's theory has to be extended in order to account for the effective pressure dependent, tensorial nature of permeability.Fluid flow in a deformable rock matrix is controlled by a nonlinear, time dependent permeability. Permeability is defined as a function of the rock matrix pressure as well as the excess fluid pressure. A two-dimensional Finite Element approximation of this process has been developed. Based on numerical experiments the consequences of structural and physical heterogeneities of permeability are investigated and discussed.The numerical calculations emphasize the temporal and spatial significance of permeability variations due to the interaction of rock matrix deformation and fluid flow. The influence of these permeability changes on transient fluid flow cannot be understood without the tool of numerical simulation.

---

Zusammenfassung Das Phänomen der elastischen Kompaktion ist durch die Wechselwirkung zwischen deformierender Gesteinsmatrix und Flüssigkeitsbewegung bei entsprechenden mechanischen Bedingungen charakterisiert. Die grundlegende Theorie hierzu wurde von Biot entwickelt. Um dem druckabhängigen, tensoriellen Charakter der Permeabilität für eine geeignete Beschreibung der Wechselwirkung gerecht zu werden, ist eine Erweiterung der Biot'schen Theorie notwendig.In einem zweidimensionalen Finite Elemente Programm wird der Fließvorgang durch eine nichtlineare, zeitabhängige Permeabilität bestimmt, die eine Funktion von Gesteinsdruck und Fluidüberdruck ist. Anhand von Modellexperimenten wird der Einfluß struktureller und physikalischer Permeabilitätsvariationen untersucht und diskutiert. Die numerischen Rechnungen machen deutlich, daß Permeabilitätsänderungen durch die Wechselwirkung von Gesteinsmatrix und Fluid sowohl von räumlicher als auch von zeitlicher Signifikanz sind. Ihr Einfluß auf die entsprechenden Fließvorgänge ist allgemein kaum ohne das Hilfsmittel numerischer Simulation richtig erfaßbar.

---

Résumé Le phénomène de compaction élastique est caractérisé par l'interaction entre la matrice de la roche et le flux de fluide, dans des conditions mécaniques déterminées. La théorie en a été développée par Biot. Un développement de cette théorie s'avère nécessaire si on veut tenir compte de la nature tensorielle de la perméabilité.Le flux de fluide dans une matière rocheuse déformable a été représenté en termes de perméabilité non linéaire fonction du temps dans un programme d'éléments finis bidimensionnel. La perméabilité est une fonction de la pression de la roche et de la surpression du fluide.Les effets de variations structurelles et physiques de la perméabilité sont étudiées et discutées à partir d'expériences modélisées. Les calculs numériques montrent la signification spatiale et temporelle des variations de perméabilité. Les processus non linéaires ainsi mis en évidence n'auraient guère pu l'être sans l'emploi de simulations quantitatives.

---

. , , , . / Finite elemente programm / , , , . . , , , . - .

---

     

Southern Hemisphere Westerly Winds have modulated the formation of laminations in sediments in Lago Fagnano (Tierra del Fuego,Argentina) over the past 6.3 ka

Tierra del Fuego in Argentina is a unique location to examine past Holocene wind variability since it intersects the core of the Southern Hemisphere Westerly Winds (SHWW). The SHWW are the most powerful prevailing winds on Earth. Their variation plays a role in regulating atmospheric CO₂ levels and rainfall amounts and distribution, both today and in the past. We obtained a piston core (LF06-PC8) from Bahía Grande, a protected sub-basin at the southern margin of Lago Fagnano, the largest lake in Tierra del Fuego. This article focuses on the uppermost 185 cm of this core, corresponding to laminated sediment from the last ~6.3 ka. Laminations consist of millimetre-scale paired dark and light layers. Previous studies and new geochemical analysis show that the dark and light layers are characterized by differing concentrations of Mn and Fe. We attribute the distribution of Mn and Fe to episodic hypolimnic oxic–anoxic variations. The age model suggests an approximately bidecadal timescale for the formation of each layer pair. We propose a new model of these redox changes with the SHWW variations. The most likely phenomenon to produce complete water-column mixing is thermobaric instability, which occurs in colder winters with low-intensity SHWW (El Niño-like conditions). In contrast, windier winters are characterized by higher temperatures and reduced mixing in the water column, facilitating a decline in oxygen concentration. Laminations, and the inferred presence of periodic hypolimnion redox changes, are common features of the past ~6.3 ka. Geochemical proxy variability is compatible with an intensification of El Niño/Southern Oscillation activity during the past ~2 ka.     

Rheologische Gesichtspunkte bei der Verformung der Lithosphäre unter Lasten

Zusammenfassung Die Deformation der Erdoberfläche durch Auflasten ist eine Funktion der jeweiligen Last sowie der rheologisch-mechanischen Eigenschaften der Lithosphäre und des oberen Mantels der Erde.Erklärungsversuche beobachteter Deformationen als Folge von Lasten auf der Grundlage linearer rheologischer Gesetzmäßigkeiten führen im allgemeinen zu unzureichenden Resultaten. Hinzu kommen theoretische und experimentelle Resultate über das nichtlineare Materialverhalten von Gesteinen.Daher werden numerische Modellrechnungen in Ansatz gebracht, um entsprechende rheologische, strukturelle und kinematische Größen in Zusammenhang zu bringen. Diese Berechnungen erbringen deutliche Hinweise, daß der nichtlineare Theologische Ansatz sehr viel weitreichendere Erklärungen der Beobachtungen zuläßt.

---

The deformation of the earth's surface in response to loads is a function of the corresponding loads as well as the rheological constitution of the lithosphere and the upper mantle.Proposed explanations of observations on the base of linear rheologies lead to unsatisfactory results. In addition theoretical and experimental considerations claim nonlinear dependence of the creep rate of rocks on the shear stress.Numerical models have been adopted to bring appropriate rheological, structural and loading conditions together. The numerical results evidently favour the nonlinear rheology statement because this assumption allows more extensive explanations of data.

---

Résumé La déformation de la surface de la terre en tant que réaction due aux charges est une fonction de la charge correspondante ainsi que des propriétés rhéologico-dynamiques de la lithosphère et du manteau supérieur.Des essais d'explication de déformations sous l'effet de charge sur la base de régularités linéaires rhéologiques donnent en général des résultats non satisfaisants. A ceci s'ajoutent des résultats théoriques et expérimentaux sur le comportement non-linéaire des roches.Des calculs de modèle numériques sont adoptés pour conférer une cohésion entre les valeurs rhéologiques, structurelles et cinématique correspondantes. Ces calculs apportents des indications claires telles, que la mise en équation non-linéare rhéologique permet des explications beaucoup plus générales des observations.

---

, .. - . , . , , .

     

The earthquake of 250 a.d. in Augusta Raurica, A real event with a 3D site-effect?

The Roman city Augusta Raurica is located East of Basel, Switzerland. One important topic of the city’s history concerns the hypothesis of an earthquake striking the city in the middle of the third century a.d. This idea had been formulated according to archaeological features and findings, but had not been tested so far. A selection of the archaeological features were reviewed and dated in order to test the hypothesis of a single event. However, archaeological investigations do not draw a conclusive picture; it could not be proven that all features of possible destruction date to the same event. Detailed seismological investigations were performed. These included geological and geotechnical mapping of the unconsolidated sediments. Important parameters such as the thickness and composition of the unconsolidated sediments, the terrain topography and the topography of the bedrock surface were mapped. Ambient vibration H/V measurements provided the fundamental frequency of resonance for the unconsolidated sediments. The velocity of shear waves traveling through sediments is the controlling parameter for amplification of seismic waves. This material property is estimated using the relation between the ellipticity of the fundamental mode Rayleigh wave and the H/V curve. From all information we compiled a three-dimensional model of the surface geology. This model is used to simulate earthquake ground motion and amplification effects in the city, and to map the variability of the amplification. In the part of the city where possible earthquake damage was recognized, amplification occurs in the frequency band of building resonance (2–8 Hz). In the other part of the city amplification occurs much above the building’s resonance. From 1D modelling we estimate a difference in spectral amplification of about a factor of 2.5 to 3 between the two parts of the city. This corresponds approximately to a difference in macroseismic intensity of one unit. 3D modelling showed a large variability of ground motion within very close distance in the part of the city where possible earthquake damage was recognized. The maximum amplification reaches values up to a factor of nine, which is due to 3D effects and the choice of using vertically incident waves. Finally, all paleoseismological findings in the area of Basel were reviewed in order to find indications of a large event in the time-period of interest. Paleoseismological findings provide no hints to a large earthquake in the third century. If we assume that an earthquake caused at least part of the identified damage in Augusta Raurica, we have to assign to this event a magnitude Mw of about 6.0 or even lower, that is much smaller than the value of 6.9 that is actually in the Swiss earthquake catalogue. The earthquake source of this event must then be very close to the site of Augusta Raurica and a strong site-effect occurred in one part of the city.     

Hydrogen-line profiles of six λ Bootis stars

Based on high resolution spectroscopic observations hydrogen-line profiles of six Bootis stars: HD 31295, HD 101108, HD 105058, HD 106223, HD 142703 and HD 183324 are presented. Peculiar line profiles with weak cores and broad but shallow wings are found for four of the stars. Influence of metallicity parameter [Z/H] and effective temperature on the appearance of the observed hydrogen lines is discussed.     

CELIAS - Charge, Element and Isotope Analysis System for SOHO

The CELIAS experiment on SOHO is designed to measure the mass, ionic charge and energy of the low and high speed solar wind, of suprathermal ions, and of low energy flare particles. Through analysis of the elemental and isotopic abundances, the ionic charge state, and the velocity distributions of ions originating in the solar atmosphere, the investigation focuses on the plasma processes on various temporal and spatial scales in the solar chromosphere, transition zone, and corona. CELIAS includes 3 mass- and charge-discriminating sensors based on the time-of-flight technique: CTOF for the elemental, charge and velocity distribution of the solar wind, MTOF for the elemental and isotopic composition of the solar wind, and STOF for the mass, charge and energy distribution of suprathermal ions. The instrument will provide detailed in situ diagnostics of the solar wind and of accelerated particles, which will complement the optical and spectroscopic investigations of the solar atmosphere on SOHO. CELIAS also contains a Solar Extreme Ultraviolet Monitor, SEM, which continously measures the EUV flux in a wide band of 17 – 70 nm, and a narrow band around the 30.4 nm He II line.Principal-InvestigatorPrincipal-Investigator for data phase     

The rotations opening the Central and Northern Atlantic Ocean: compilation, drift lines, and flow lines

We provide an up-to-date compilation of Euler rotations that model the evolution of the Central and Northern Atlantic Ocean (Table 1). The data basis forms seafloor spreading magnetic anomalies of the Atlantic. We checked the published rotations and selected those that form a consistent model. The increments of the Euler rotations going back in time from magnetic anomaly to magnetic anomaly can be illustrated by chains of points on “drift lines” that are paths of motions from continent to continent. Along these paths, the continents bordering the Atlantic Ocean can be moved back to their Mesozoic position within Pangea. Other figures exhibit the early rifting of the North Atlantic, the drift of Iberia, and the evolution of the Greenland-Ellesmere region. The points on the drift lines do not correspond directly to the lines of magnetic anomalies or their “picks” displayed today symmetrically in the Atlantic Ocean. To acquire correspondence, symmetric “flow lines” are constructed analogous to the spreading procedure. But points on the flow lines constructed by half of the increments partially also deviate from the expected symmetric position and in this way quantify displacements or jumps of the axis of rifting or spreading. Most of the selected rotations are from the excellent analyses of previous work. Essential deviations from published rotations are the M 0 rotations of Eurasia and of the Porcupine unit with respect to North America (EUR-NAM and POR-NAM). They lead to a better coincidence between the back-rotated M 0 magnetic anomalies in the Bay of Biscay on the one side and a change of the first transform motions between Greenland and Svalbard on the other side. Through this explanation, an overlap in Pangea SW of Svalbard is avoided and transform motions instead of strong extension are predicted. Some additional data are needed to complete the model: the earliest part of the path of Iberia to North America (IBA-NAM) up to M 4 is calculated assuming that Iberia moved parallel to the African plate, though with slower spreading rates. The evolution of the Central and North Atlantic Ocean system is described in short. This model of the Central and North Atlantic was produced with the primary intention of clearing and fixing the positions of Africa, Iberia, and Eurasia as a framework for an improved reconstruction of the Western Tethys evolution.