Place and people: spatializing degrees of bonding and bridging social capital in Lisbon (Portugal)

GeoJournal - Broad academic interest in measuring social relationships within an urban context has grown over recent decades. Significant research attention is focused on where social synergies...     

Origin and composition of fluid responsible for metasomatic processes in shear zones of the Bolshie Keivy tectonic nappe,baltic shield: Carbon isotope composition of graphite

Doklady Earth Sciences -     

The selective replacement of the aluminum silicates by white mica

From considerations of relativeG-T surfaces inferred from publishedP-T data and the occurrence of replacement textures of Al₂SiO₅ polymorphs in rocks, the relative positions of curves representing the following equation in _K+ —T — pH ispace on substituting Al₂SiO₅ different polymorphs are derived.3 Al₂SiO₅ + 3 SiO₂ (quartz) + 2 K⁺ + 3 H₂O 2 KAl₂[AlSi₃O₁₀](OH)₂ (muscovite)+ 2 H⁺. The curves are different because of the differentG-T values for the polymorphs which, in the field, is borne out by the observation that in a rock containing two or three Al₂SiO₅ polymorphs, in nearly all instances only one polymorph is replaced by white mica. Instances of textural relations showing the interpreted selective replacement of one Al₂SiO₅ polymorph by a white mica in the presence of one (or two) other Al₂SiO₅ polymorph(s) are cited both from the literature and various field examples. The selective replacement of kyanite if sillimanite and/or andalusite is/are present, and of andalusite if only sillimanite is present are interpreted to show that generally during the muscovitization reaction, the field of sillimanite in the above reaction (left hand side) at a particular pH (H⁺ concentration) and is larger in _K+ —T space than that of andalusite which in turn is larger than that of kyanite. Theoretically it is shown that variations to this can exist but the field evidence suggests these only occur under rare geological conditions. Although this is not totally conclusive, the selectiveness of the replacement is interpreted to show that the fluid was buffered with respect to K⁺ and H⁺ on or near the curve of the polymorph showing the lowest stability field until that polymorph is totally consumed, after which the fluid composition moves to the next lowest curve for the remaining polymorph(s) present in the rock. The alteration of more than one polymorph by an apparently simultaneous process of alteration is rare and usually occurs at a low grade of metamorphism. This is interpreted to show that the buffering reaction could not keep pace with the influx of fluid and change the composition of this fluid (in most cases).     

Interstellar magnetic field strength and dirty ice grains oriented by paramagnetic relaxation

A method of estimating the orientation parameter and the resulting galactic magnetic field consistent with the observed visual ratio of polarization to extinction has been given. The orientation has been considered in the sense of paramagnetic relaxation envisaged by Davis and Greenstein (1951) and by Jones and Spitzer (1967). It is assumed that the grains, cylindrical in shape, consist of a pair of distinct effective sizes with different number densities. The method has been applied to dirty ice grain as an illustration.     

The GREGOR polarimetric calibration unit

The new Solar telescope GREGOR is designed to observe small‐scale dynamic magnetic structures below a size of 70 km on the Sun with high spectral resolution and polarimetric accuracy. For this purpose, the polarimetric concept of GREGOR is based on a combination of post‐focus polarimeters with pre‐focus equipment for high precision calibration. The Leibniz‐Institute for Astrophysics Potsdam developed the GREGOR calibration unit which is an integral part of the telescope. We give an overview of the function and design of the calibration unit and present the results of extensive testing series done in the Solar Observatory “Einsteinturm” and at GREGOR (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Feldspar in type 4–6 ordinary chondrites: Metamorphic processing on the H and LL chondrite parent bodies

Abstract– We have carried out a study of feldspar compositions in a suite of H and LL ordinary chondrites, of petrologic types 4, 5, and 6, in order to examine the process of recrystallization and equilibration of feldspar as the degree of metamorphism increases. In the H chondrites, there is little variation in feldspar compositions among the petrologic types, suggesting that homogenization of chondrule mesostasis, from which feldspar is presumed to have crystallized, occurred before feldspar crystallization began. The LL chondrites we studied are more complex. In Bjurböle (L/LL4), plagioclase in individual relict chondrules has distinct compositions, with a range of An/Ab ratios and low Or contents. This heterogeneity is most likely attributable to original compositional heterogeneity among chondrule mesostases: localized recrystallization of mesostasis must have occurred before diffusional equilibration took place. In Tuxtuac (LL5), the An/Ab ratio of plagioclase is more homogeneous, and plagioclase includes a significant Or component. In addition, we observe what appears to be exsolution of K‐feldspar from albitic host grains. In Saint Séverin (LL6), the An/Ab ratio of plagioclase is homogeneous, but plagioclase compositions show a range of Or contents, corresponding to a patchy distribution of K in individual feldspar grains. The observations in these LL chondrites are difficult to interpret with a simple model of progressive equilibration with increasing petrologic type. We suggest that the current criteria for assigning petrologic types are poorly defined: it is possible that the assigned petrologic types of these chondrites do not correlate with their peak temperatures. We propose that feldspar compositions might record conditions during the heating stage of metamorphism, and that the early stages of metamorphism may have occurred in the presence of fluids, rather than under the dry conditions that are commonly assumed.     

Photometric and spectroscopic investigation of the B2E Herbig star HD52721: First results

We present first results of the photometric and spectroscopic investigation of the B1/B2 Herbig star HD52721 performed in 2009–2010 at three observatories: Mountain Astronomical Station (Kislovodsk)—photometry, CrAO (Crimea, Ukraine)—spectroscopy, Observatory San Pedro Martyr (Ensenada, Mexico)—high-resolution echelle-spectroscopy. We have also used photometric data from the ASAS survey for 2003–2009. Our analysis has shown that a) the object is a close binary system with the orbital period of 1.610 days composed of two components of similar spectral type (B1–B2); b) the system is surrounded by the common disk-like envelope containing azimuthal inhomogeneity rotating with the orbital period of the system. We present preliminary estimates of the system parameters and discuss its possible nature.