Cornetite: Modulated densely-packed Cu2+ oxysalt

Summary The crystal structure of cornetite, Cu₃(PO₄)(OH)₃, orthorhombic, a = 10.854(1), b = 14.053(3), c = 7.086(2), Å, V = 1080.8(3) ų, Z = 8, space group Pbca, has been refined to an R-index of 3.9% for 1231 observed reflections (I > 3I), measured with MoK X-radiation on an automated four-circle diffractometer. The structure consists of edge sharing zig-zag chains of distorted octahedra, cross-linked by edge-sharing octahedral dimers into complex octahedral layers. Adjacent layers are corner-linked together by neighbouring octahedra and PO₄ tetrahedra into a densely-packed heteropolyhedral framework, in which the phosphate tetrahedra share edges with the octahedral dimers. The polyhedral layers exhibit a commensurate modulation that results from the interaction between local relaxation of Jahn-Teller distorted octahedra and the long-range requirements of translational periodicity.

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Cornetit: Ein moduliertes, dicht gepacktes Oxosalz des zweiwertigen Kupfers

Zusammenfassung Die Kristallstruktur des Cornetits, Cu₃(PO4)(OH)3, orthorhombisch, a = 10,854(1), b = 14,053(3), c = 7,086(2,) Å, V = 1080,8(3) ų, Z = 8, Raumgruppe Pbca, wurde mit 1231 beobachteten Röntgenreflexen (I > 3I), die mit MoK-Strahlung auf einem automatischen Vierkreis-Diffraktometer gesammelt worden waren, auf einen R-Wert von 3,9% verfeinert. Die Struktur besteht aus kantenverknüpften Zickzack-Ketten verzerrter Oktaeder, die über kantenverknüfte Oktaeder-Dimere zu komplizierten Oktaederschichten verbunden sind. Benachbarte Schichten sind über Ecken durch benachbarte Oktaeder und PO₄-Tetraeder zu einem dichtgepackten, heteropolyedrischen Gerüst verknüpft, in welchem die Phosphattetraeder mit den Oktaeder-Dimeren Kanten gemeinsam haben. Die Polyederschichten zeigen eine kommensurable Modulierung, die aus der Wechselwirkung zwischen der lokalen Relaxation von Jahn-Teller-verzerrten Oktaedern und den Forderungen der translatorischen Periodizität über größere Entfernungen resultiert.

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With 5 Figures     

Earthquake response of asymmetric building with MR damper

Plan asymmetric buildings are very susceptible to earthquake induced damage due to lateral torsional coupling, and the corners of these systems suffer heavy damage during earthquakes. Therefore, it is important to investigate the seismic behavior of an asymmetric plan building with MR dampers. In this study, the effectiveness of MR damper-based control systems has been investigated for seismic hazard mitigation of a plan asymmetric building. Furthermore, the infl uence of the building parameters and damper command voltage on the control performance is examined through parametric study. The building parameters chosen are eccentricity ratio and frequency ratio. The results show that the MR damper-based control systems are effective for plan asymmetric systems.     

TRANSIENT ELECTROMAGNETIC FIELD OF A POLARIZABLE HALF-SPACE DUE TO VARIOUS CURRENT PULSES *

In this paper, the expressions for the induced voltage function V(T) and mutual impedance function Z_m(T) have been derived for specific range of time T and specific values of induced polarization parameters a for ramp and saw-tooth type of current pulses. The computed results for various cases are also presented. The low values of induced polarization parameter a represent the medium possessing membrane polarization, whereas high values exhibit electrode polarization medium. The method has practical applicability and is best suited for the interpretation of transient electromagnetic fields over a polarizable half-space.     

Sporadic and recurrent geomagnetic disturbances in 1859–1860 according to the archived data from the Russian network of stations

Based on an analysis of the available archived data from the Russian network of geomagnetic stations, it has been indicated that the known event of August–September 1859 was the first and the greatest event in the series of the recurrent geomagnetic storms. Similar series were repeatedly observed in the next years. These series are caused by the processes on the Sun and in the heliosphere related to the superposition of the solar wind flows. The sporadic and regular components in joint activity of the complex, including active regions and coronal holes on the rotating Sun, play the role of the Bartels M regions responsible for initiation and development of geomagnetic storms. Neither coronal holes nor active regions can separately explain observations. During interpretation, active regions and coronal holes should be considered as a unified complex.     

Demersal Continental Shelf and Upper Slope Cephalopod Assemblages from the Balearic Sea (North-Western Mediterranean). Biological Aspects of Some Deep-Sea Species

The analysis of 79 hauls performed by commercial bottom trawlers from 50 to 800 m depth in the Balearic Sea (north-western Mediterranean) from June 1995 to September 1996 yielded a total of 30 cephalopod species belonging to 12 families. Cluster analysis of these data gave as a result two main groups 50–200 m and 200–800 m each subdivided into two other groups (50–100 vs. 100–200 m and 200–600 vs. 600–800 m). These results suggested the existence of two assemblages that could be associated to the continental shelf (50–100 m) and the upper slope (600–800 m) separated by a wide transitional zone (100–600 m) representing a region of overlapping shelf and slope faunas (ecotone). The faunistic bathymetric gradient showed a continuous substitution of species with depth rather than discrete assemblages separated by distinct boundaries. The more coastal species such as Eledone moschata, Loligo vulgarisSepia officinalis and Octopus vulgaris were found on the continental shelf; on the transitional zone, apart from species characteristic of this zone (Illex coindetii, Sepietta oweniana, Rossia macrosoma, Scaeurgus unicirrhus and Pteroctopus tetracirrhus), we also observed species from both the continental shelf and slope. The upper slope was characterized by typical species of deeper waters, such asBathypolypus sponsalis , Histioteuthis reversa, H. bonnellii, Ancistroteuthis lichtensteinii andOnychoteuthis banksii . The octopod O. vulgaris was the dominant species on the continental shelf and upper transitional zone, being substituted by T. sagittatus on the lower transitional zone and upper slope. Mean biomass decreased abruptly from the continental shelf to the transitional zone and from there to the upper slope. Mean species richness and species diversity were higher in the transitional zone than in the continental shelf and upper slope. Finally, some biological aspects of the more abundant deep-sea cephalopod species are studied: Bathypolypus sponsalis, Octopus salutii,Pteroctopus tetracirrhus , Histioteuthis reversa and H. bonnellii.     

Nitrous oxide production and denitrification rates in estuarine intertidal saltmarsh and managed realignment zones

Increasing concerns over habitat loss and rising costs of sea defence maintenance due to rising sea levels, has seen increases in the practice of managed realignment and reflooding of former reclaimed areas of intertidal saltmarsh and mudflat around the world. These practices are taking place with little knowledge of their impact on soil biogeochemical processes. Rates of denitrification (using the acetylene inhibition technique) and nitrous oxide (N₂O) production were measured from a long-established saltmarsh (SM) and an adjacent, recently re-flooded managed realignment (MR) site comprising former arable land in the estuary of the River Torridge, Devon, UK. Incubations were carried out in closed chambers in which patterns of tidal flooding were simulated automatically. Measurements were made during periods of flood and non-flood over a total of four tidal inundations with estuarine water. During the latter two flooding episodes floodwater was amended with nitrate (NO₃⁻). Nitrous oxide production in the SM soil generally was lower than in the MR soil, with mean values and standard errors over the whole incubation of 0.27 ± 0.16 mg N₂O-N m⁻² h⁻¹ and 0.65 ± 0.15 mg N₂O-N m⁻² h⁻¹ respectively. Denitrification rates demonstrated a similar trend although generally were an order of magnitude higher than N₂O production, with mean rates and standard errors of 2.88 ± 1.12 mg N₂O-N m⁻² h⁻¹ in the SM soil and 3.39 ± 1.16 mg N₂O-N m⁻² h⁻¹ in the MR soil. The data suggest that both soils are net sinks for NO₃⁻ and net sources for N₂O. Both patterns of tidal inundation and floodwater chemistry affect the process rates in each soil differently. The impact of flooding with NO₃⁻ – amended water was greater on the SM soil than the MR soil, and it is likely that decomposing vegetation buried in the accreting sediments following reflooding at the MR site were supplying a source of N in the soil, and so process rates were less dependent upon external supplies. The act of managed realignment in intertidal zones could therefore result in an increase in mean production of N₂O in intertidal zones, at least in the short term.