Ca2Mg(NO3)6×12H2O–structural investigations on a new compound retrieved from chimney deposits of a combined heat and power plant

Phase analysis of incrustations retrieved from chimney deposits of a combined heat and power plant in Malchow/Germany by X-ray powder diffraction gave evidence for the existence of a previously unknown hydrous calcium magnesium nitrate. Optical investigations of the sample showed the presence of colorless platy crystals with a maximum diameter of about 250 μm embedded in a partly polycrystalline and partly glassy matrix. Aided by EDX-analysis and Raman spectroscopy, a single-crystal diffraction study performed at ambient conditions demonstrated that the material represents a phase with composition Ca₂Mg(NO₃)₆×12H₂O. Basic crystallographic data are as follows: trigonal symmetry, space group type R \( \overline{3} \) , a?=?10.5583(5) Å, c?=?19.5351(10) Å, V?=?1885.97(16) ų, Z?=?3, (R(|F|) = 0.0248). The magnesium ions are coordinated by water molecules to form distorted Mg(H₂O)₆-octahedra. The calcium atoms are surrounded by nine ligands. The resulting CaO₉ tricapped trigonal prisms involve oxygen atoms from additional water moieties as well as from three different bidentate nitrate groups, respectively. Hydrogen bonds link one octahedron with two adjacent prisms into trimers. The trimers in turn are stacked in columns running parallel to [001]. Further hydrogen bonding between neighboring columns results in the formation of a three-dimensional network. To our best knowledge, Ca₂Mg(NO₃)₆×12H₂O represents a new structure type. However, column-like topologies with rods consisting of different types of polyhedra have been also observed in other trigonal hydrous nitrates. The structural relationships between these compounds are discussed. It is interesting to note that in previous phase equilibrium studies on the ternary system Ca(NO₃)₂-Mg(NO₃)₂-H₂O no other hydrous double salt has been described. Finally, the results of the structure analysis allowed a qualitative and quantitative phase analysis of the crystalline part of the chimney deposit by the Rietveld method.     

Mars surface and atmospheric temperature during the 2001 global dust storm

The dramatic growth and evolution of the 2001 martian global dust storm were captured using the Submillimeter Wave Astronomy Satellite (SWAS). While the lower and middle atmosphere (pressures greater than 50 μbar, up to ∼45 km altitude) showed rapid heating of up to 40 K, the average surface brightness temperature plummeted by ∼20 K at the peak of the storm. The storm appears to have had little impact on the global temperature structure at altitudes above ∼ 10 μbar (∼ 60 km).     

Modelling the cosmological co-evolution of supermassive black holes and galaxies – II. The clustering of quasars and their dark environment

We use semi-analytic modelling on top of the Millennium simulation to study the joint formation of galaxies and their embedded supermassive black holes. Our goal is to test scenarios in which black hole accretion and quasar activity are triggered by galaxy mergers, and to constrain different models for the light curves associated with individual quasar events. In the present work, we focus on studying the spatial distribution of simulated quasars. At all luminosities, we find that the simulated quasar two-point correlation function is fit well by a single power law in the range  0.5 ≲ r ≲ 20  h ⁻¹ Mpc  , but its normalization is a strong function of redshift. When we select only quasars with luminosities within the range typically accessible by today's quasar surveys, their clustering strength depends only weakly on luminosity, in agreement with observations. This holds independently of the assumed light-curve model, since bright quasars are black holes accreting close to the Eddington limit, and are hosted by dark matter haloes with a narrow mass range of a few  10¹²  h ⁻¹ M_⊙  . Therefore, the clustering of bright quasars cannot be used to disentangle light-curve models, but such a discrimination would become possible if the observational samples can be pushed to significantly fainter limits. Overall, our clustering results for the simulated quasar population agree rather well with observations, lending support to the conjecture that galaxy mergers could be the main physical process responsible for triggering black hole accretion and quasar activity.     

Einige Probleme der geoelektrischen Bodenverfestigung

Zusammenfassung 1. Eine Verfestigung über die «kritische Zeit» hinaus ist unwirtschaftlich. Daher sollten Elektroden verwendet werden, bei deren Anwendung die kritische Zeit sehr gross ist, oder die leicht verlegt werden können, wenn die kritische Zeit abgelaufen ist. Bei Stabelektroden geschieht dies durch Umstecken. Man kann aber auch Rollenelektroden verwenden, die über das zu verfestigende Volumen hinwegrollen. Dies ist allerdings nur dann zulässig, wenn nur eine ziemlich schwache Oberflächenschichte zu verfestigen ist. — 2. Um die günstigste Verfestigungsleistung zu erreichen, muss die Elektrodenspannung und der Elektrodenstrom den bodenphysikalischen Bestimmungsstücken richtig angepasst werden. — 3. Die geoelektrische Entwässerung ist nur dann anwendbar, wenn der Boden einen Mindestwassergehalt hat. Dieser ist durch die Kornverteilungskurve bestimmt. — 4. Durch die geoelektrische Behandlung des Bodens wird das Verhältnis zwischen Raumgewicht und Wassergehalt verändert und daher die Verfestigungskurve verformt.

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Summary In this article some geoelectrical problems of soil consolidation are discussed. The principal part of the electrical power is effective only near the electrodes. The resistance in this zone rises quickly during the course of time. After a «critical time» it becomes so high that no further consolidation of soil can be achieved. This time depends on the number, form and configuration of the electrodes. Rollings and plates are preferable to sticks. The voltage of electrodes has to be adapted to the specific resistivity of soil. The content of water of the soil can be reduced by electric means only if it surmounts a certain lowest value. By this geoelectrical consolidation the moisture-density relationship (Proctor-diagram) is deformed.

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Nach einem Vortrag auf der 2. Tagung der «Società Italiana di Geofisica e Meteorologia» in Genova, 23–25 April 1954.