The formation of shock waves in the recombination era of the universe

The formation and the evolution of shock waves in a two-component fluid during the recombination era of the Universe is studied. The fluid consists of photons and ionized hydrogen gas with interaction due to Thomson scattering. The analysis uses the expansion procedure in powers of the coordinates near the travelling wave front. Incorporating discontinuities in the first derivatives of the physical quantities, we are able to give the analytical solution which answers the questions as to when the discontinuities appear in the physical quantities themselves. Of the two possible waves (a radiation- and a matter-dominated wave) only the matter-dominated wave shows the shock phenomena. However, the shock is induced by the radiation due to Thomson scattering. Therefore, the time for the shock formation depends on the initial amplitude of the wave (as in usual shock phenomena) and on the collision frequency of the photons.     

On the formation of the planetary system the titius-bode law

The linear density and velocity perturbations are analyzed in a differentially rotating thin gravitating disc consisting of gas and dust. For the radial behaviour of the equilibrium density and the velocity of sound we assume a power law. The zeros of these perturbations have a distance behaviour like the distances of the planets and their satellites known as the Titius-Bode rule. It is suggested, that the knots of the velocity disturbances are the places where ring like dust accumulations occur. The mechanism is the same as in the Kundt's tube, where collisions between the dust and the oscillating gas are responsible for this effect.     

A coupled transport and reaction model for long column experiments simulating bank filtration

Within the scope of the interdisciplinary Natural and Artificial Systems for Recharge and Infiltration research project dealing with riverbank filtration processes at the Berlin water works, a semi‐technical column experiment has been ongoing since January 2003. Here, a 30 m long soil column is infiltrated with surface water sampled from Lake Tegel (Berlin, Germany) under saturated flow conditions. Changes in pore water hydrochemistry sampled on 21 non‐equidistant distributed points are verified by coupled transport and reaction modelling. The objective of reactive transport modelling was to identify the main biogeochemical processes within the soil column during the flushing experiment as a conceptual model for riverbank filtration. Modelling was done with a combination of MATLAB and PHREEQC. The main processes identified are: (1) biogeochemical degradation due to interaction of natural surface water with the soil matrix; (2) continuous dissolution of refractory air bubbles from the soil column matrix. Copyright © 2006 John Wiley & Sons, Ltd.     

Inversions Beneath the thermocline in the north-western Mediterranean

Summary Vertical temperature traces in the north-western Mediteranean show remarkably leafy structures at depths between 100 m and 300 m. The individual layers are stable over several days. Their horizontal extension is larger than 20 nm. The thickness amounts to 25–50 m. It is suggested that these interleavings of slightly different water masses are due to lateral mixing processes in the vicinity of the working area.

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Inversionen unterhalb der Sprungschicht im nordwestlichen Mittelmeer

Zusammenfassung Temperaturprofile im nordwestlichen Mittelmeer weisen eine auffällig blättrige Struktur in Tiefen von 100–300 m auf. Die einzelnen Schichten sind über mehrere TAge stabil. Ihre horizontale Ausdehnung ist größer als 20 sm. Die vertikale Mächtigkeit beträgt 25–50 m. Es wird angenommen, daß die schichtförmigen Einschübe schwach unterschiedlicher Wassermassen durch Vermischung in der Umgebung des Arbeitsgebietes entstanden sind.

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Inversions du gradient de température au-dessous de la thermocline dans le Nord Ouest de la Méditerranée

Résumé Les tracés verticaux de la température, dans le Nord Ouest de la Méditerranée ont des structures remarquablement superposées en minces feuillets, à des profondeurs comprises entre 100 et 300 mètres. Les couches individuelles sont stables pendant plusieurs jours. Elles s'étendent horizontalement sur plus de 20 milles nautiques. Leur épaisseur atteint 25 à 50 mètres. On suppose que ces superpositions de masses d'eau légèrement différentes sont dues à des processus de mélange latéral au voisinage de la région d'opération.