Monte-Carlo simulation of Mercury's exosphere

Because of its proximity to the Sun and its small size, Mercury has not been able to retain its atmosphere and only a thin exosphere surrounds the planet. The exospheric pressure at the planetary surface is approximately 10⁻¹⁰ mbar, set by the Mariner 10 occultation experiment. The existence of gaseous species H, He, and O has been established by Mariner 10. In addition Na, K, and Ca have been observed by ground based instrumentation. Other elements are expected to be found in Mercury's exosphere since the total pressure of the known species is almost two orders of magnitude less than the exospheric pressure.It is intended to measure these exospheric particle densities in situ with an instrument on board of ESA's BepiColombo Mercury Planetary Orbiter (MPO) spacecraft. Since the expected exospheric densities are very small we developed a Monte-Carlo computer model to investigate if such a measurement is feasible along the MPO spacecraft orbit. We model energy and ejection angle distributions of the particles at the surface, with the emission process determining the actual distribution functions. Our model follows the trajectory of each particle by numerical integration until the particle hits Mercury's surface again or escapes from the calculation domain. Using a large set of these trajectories bulk parameters of the exospheric gas are derived, e.g., particle densities for various atomic and molecular species. Our study suggests that a mass spectrometric measurement is feasible and, at least at MPO's periherm, all species that are released from the surface will be observed.     

Preparation,collisional decay and transfer of alignment in C2H2 21

Stimulated Raman scattering is used to prepare ensembles of aligned acetylene molecules in thev ₂=1 excited vibrational level. Decay and transfer of the alignment is followed by laser induced fluorescence. Measurements of the initially excited alignment agree well with theoretical calculations. The rate constants for decay decrease as the rotational quantum numberJ of the excited level increases.     

The responses of different ethnic groups in the Sudan to rural-urban migration

The ethnic identities of the various population groups in the Sudan are a product of their specific natural and social environments. The migration of these groups to the towns, especially to Greater Khartoum, involves a drastic change of cultural norms and values. However, the capability of change and the subsequent results are strongly conditioned by the specific background of each ethnic group and by the conditions in its area of origin. This is being proved by a comparative study on three ethnic groups in the Sudan: the Nuba, the Zaghawa and the Hadandawa.     

Kriterien für die anwendung des ertelschen erhaltungssatzes in ionisierten bzw. viskosen medien

Zusammenfassung Es wird gezeigt, dass für ein Gasgemisch, das geladene Komponenten enthält und von einem divergenzfreien und stationären Magnetfeld durchsetzt wird, für eine geladene Komponente (Ionen oder freie Elektronen) näherungsweise der Ertelsche Erhaltungssatz gilt, falls unter bestimmten Voraussetzungen das Verhältnis der Reibungskraft (innere) zur magnetischen Feldkraft sehr klein verbleibt. Weiter wurde nachgewiesen, dass derselbe Erhaltungssatz näherungsweise auch für ein viskoses Medium gilt, falls die Reynoldszahl (Verhältnis der Trägheitskraft zur Reibungskraft (innere)) sehr gross ist. Dies ist bei einem turbulenten Medium der Fall.

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Summary It is shown that in a gas mixture containing charged constituents (ions and free electrons) the conservation theorem of Ertel is valid on certain conditions for one of the charged constituent if the ratio of the friction force between the neutral and charged constituents to the magnetic force is small. The same conservation theorem is also valid for a viscous fluid if the Reynoldsnumber (ratio of inertial force to the viscous force) is large.

     

A New Genus and Species of Rhynchonellid (Brachiopoda, Recent) from Submarine Caves in the Mediterranean Sea

Abstract. A new rhynchonellid brachiopod genus Tethyrhynchia , with type species Tethyrhynchia mediterranea n. sp., is described from specimens discovered in dark zones of submarine caves along the Mediterranean coast of France between Marseille and La Ciotat, and also at Zembra Island, off the Gulf of Tunis, Tunisia. Other brachiopods occurring with this diminutive rhynchonellid are also small and include the megathyridids Argyrotheca cistellula and Megathiris detruncata . This is the first recorded occurrence of a rhynchonellid from the Mediterranean Sea. The new form is apparently neotenous, in that the lophophore in adults never develops beyond the trocholophous stage. A new type of rhynchonellid crus, crescentic in profile and here named the lunifer type, is described. The new genus is assigned to the new family Tethyrhynchiidae , and comparisons are made with other extant rhynchonellid genera.     

Multi-Scale Texture Modeling

Patterns of crystallographic preferred orientation are referred to as texture. The specific subject of texture analysis is the experimental determination and interpretation of the statistical distribution of orientations of crystals within a specimen of polycrystalline material, which could be metals or rocks. The objective is to relate an observed pattern of preferred orientation to its generating processes and vice versa. In geosciences, texture of minerals in rocks is used to infer constraints on their tectono-metamorphic history. Since most physical properties of crystals, such as elastic moduli, the coefficients of thermal expansion, or chemical resistance to etching depends on crystal symmetry and orientation, the presence of texture imparts directional properties to the polycrystalline material. A major issue of mathematical texture analysis is the resolution of the inverse problem to determine a reasonable orientation density function on SO(3) from measured pole intensities on , which relates to the inverse of the totally geodesic Radon transform. This communication introduces a wavelet approach into mathematical texture analysis. Wavelets on the two-dimensional sphere and on the rotational group SO(3) are discussed, and an algorithms for a wavelet decomposition on both domains following the ideas of Ta-Hsin Li is given. The relationship of these wavelets on both domains with respect to the totally geodesic Radon transform is investigated. In particular, it is shown that the Radon transform of these wavelets on SO(3) are again wavelets on . A novel algorithm for the inversion of experimental pole intensities to an orientation density function based on this relationship is developed.     

Crustal structure of the Eastern Alps along the TRANSALP profile from wide-angle seismic tomography

The objective of the TRANSALP project is an investigation of the Eastern Alps with regard to their deep structure and dynamic evolution. The core of the project is a 340-km-long seismic profile at 12°E between Munich and Venice. This paper deals with the P-wave velocity distribution as derived from active source travel time tomography. Our database consists of Vibroseis and explosion seismic travel times recorded at up to 100 seismological stations distributed in a 30-km-wide corridor along the profile. In order to derive a velocity and reflector model, we simultaneously inverted refractions and reflections using a derivative of a damped least squares approach for local earthquake tomography. 8000 travel time picks from dense Vibroseis recordings provide the basis for high resolution in the upper crust. Explosion seismic wide-angle reflection travel times constrain both deeper crustal velocities and structure of the crust–mantle boundary with low resolution. In the resulting model, the Adriatic crust shows significantly higher P-wave velocities than the European crust. The European Moho is dipping south at an angle of 7°. The Adriatic Moho dips north with a gentle inclination at shallower depths. This geometry suggests S-directed subduction. Azimuthal variations of the first-break velocities as well as observations of shear wave splitting reveal strong anisotropy in the Tauern Window. We explain this finding by foliations and laminations generated by lateral extrusion. Based on the P-wave model we also localized almost 100 local earthquakes recorded during the 2-month acquisition campaign in 1999. Seismicity patterns in the North seem related to the Inn valley shear zone, and to thrusting of Austroalpine units over European basement. The alignment of deep seismicity in the Trento-Vicenza region with the top of the Adriatic lower crust corroborates the suggestion of a deep thrust fault in the Southern Alps.     

A thermodynamic model for Fe–Mg dioctahedral K white micas using data from phase-equilibrium experiments and natural pelitic assemblages

The purpose of this study is to derive a solid-solution model for potassic white micas (KWM) encountered in rocks of various bulk compositions, over a wide range of P-T conditions. A compilation of phengite compositions lead us to propose a seven-thermodynamic-component (muscovite, Fe²⁺-Al-celadonite, Mg-Al-celadonite, annite, phlogopite, pyrophyllite and paragonite) ionic solid-solution model which accounts for the Tschermak, Fe-Mg, di/trioctahedral, pyrophyllitic and paragonitic substitutions observed in nature. A four-site mixing model with symmetric Margules parameters to model the Tschermak substitutions, asymmetric Margules parameters to model the other substitutions, and ideal intersite interaction has been adopted. In contrast to previous models, the relevant thermodynamic data and solid-solution properties are calibrated with independent sets of published experiments conducted for the KMASH, KFASH, KFMASH, and KNASH systems, as well as about 200 natural data involving KWM assemblages. The constraints span a wide range of pressure and temperature conditions (150 to 750 °C, 0.5 to 30 kbar), so that our model does not need to be extrapolated outside the calibration range to be used for P-T thermobarometric purposes. The calculated thermodynamic data are interconsistent with the TWQ thermodynamic database and solid-solution models, including that recently published for chlorites.