Ionospheric Joule dissipation as a damping mechanism for high latitude ULF pulsations: Observational evidence

On 9 January 1979 an SI-excited pulsation event was observed by the Scandinavian Magnetometer Array. The pulsation period shows a clear variation with latitude which suggests decoupled oscillations of individual magnetic field shells. The pulsation amplitudes exhibit an e-fold decay with the damping rate γ varying both in longitudinal and latitudinal directions. Assuming Joule heating in the ionosphere as the dominant damping mechanism (and thus γ ～ Σ^?1_p) approximate height-integrated Pedersen conductivity profiles were calculated which fit well with previously observed Σ_p distributions. This is interpreted as observational evidence for ionosopheric Joule dissipation as the major damping mechanism for high-latitude ULF-pulsations.     

Tropospheric Ozone in a Global-Scale Three-Dimensional Lagrangian Model and Its Response to NOX Emission Controls

A three-dimensional Lagrangian tropospheric chemistry modelis used toinvestigate the impact of human activities on the tropospheric distributionofozone and hydroxyl radicals. The model describes the behaviour of 50 speciesincluding methane, carbon monoxide, oxides of nitrogen, sulphur dioxide andnineorganic compounds emitted from human activities and a range of other sources.Thechemical mechanism involves about 100 chemical reactions of which 16 arephotochemical reactions whose diurnal dependence is treated in full. The modelutilises a five minute chemistry time step and a three hour advection timestepfor the 50,000 air parcels. Meteorological data for the winds, temperatures,clouds and so on are taken from the UK Meteorological Office global model for1994 onwards. The impacts of a 50% reduction in European NO_Xemissions onglobal ozone concentrations are assessed. Surface ozoneconcentrations decrease in summertime and rise in wintertime, but to differentextents.     

Hα emission objects in Circinus

We present a new survey for Hα emission objects in the Circinus cloud complex and introduce an efficient photometric method for detecting Hα emission via observations in a narrow‐band filter. The observed flux is compared to a blackbody fit of the continuum. Our search strategy reveals 20 stars with strong Hα emission (EW > 10 Å), eight of them being new detections. All Hα stars display infrared excess corroborating their youth. On the other hand, the region contains a number of infrared excess objects that do not show Hα emission. Our results support the picture that accretion – as witnessed by Hα emission – is a highly variable phenomenon. Therefore, Hα surveys can only trace the temporarily active objects. In contrast, infrared excess is a more robust tracer that reveals most of the population of young stellar objects in a star forming region. Our analysis of the general stellar content of the region yields a reliable distance of 450 pc for the Circinus cloud. Moreover, we find a ratio of total‐to‐selective extinction of R^V = 2.8 suggesting that smaller‐than‐normal dust grains may be present. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependence of the cation distribution in nickel aluminate (NiAl2O4) spinel: a powder XRD study

NiAl₂O₄ is a largely inverse spinel, which in detail shows increasing randomisation with temperature of Ni and Al between the octahedral and tetrahedral cation sites of the spinel structure. We have used powder XRD to determine this cation distribution in various samples of NiAl₂O₄ quenched after annealing between 700 and 1400° C. The inversion parameter (x) can be measured with a precision of ± 0.004 (one standard deviation), and a comparison of different methods of synthesis, X-ray diffraction and refinement techniques, suggests a probable accuracy of better than 0.01. The results are supported by some preliminary single crystal refinements on flux-grown samples.Below 800° C the rate of cation ordering becomes very slow, and, despite reaching an apparently steady state, it is doubtful if our samples attained complete internal equilibrium. Above 1250° C the cation redistribution becomes so fast that the quenching method becomes unreliable. Between 800 and 1250° C inclusive, the degree of inversion changes smoothly from 0.87 at 800° C to 0.79 at 1250° C, and is accompanied by linear changes in u, the oxygen parameter, from 0.2555 to 0.2563 (±0.0002), and a₀, the lattice parameter, from 8.0462 to 8.0522 Å (±0.0002 Å).     

Occurrence and characteristics of sporadic sodium layer observed by lidar at a mid-latitude location

Na lidar observations of SSL during the past 5 years at a mid-latitude location (Wuhan, China, 31°N, 114°E) are reported in this paper. From 26 SSL events detected in about 230 h of observation, an SSL occurrence rate of 1 event/9 h at our location was obtained. This result, combined with that reported by Nagasawa and Abo (Geophys. Res. Lett. 22 (1995) 263) at Tokyo, Japan, reveals that the SSL occurrence can be relatively frequent at some mid-latitude locations. The statistical analyses of main parameters for the 26 SSL events were made, and the results were compared with those previously reported. By examining the corresponding data from a nearby ionosonde, it was found that there was a fairly good correlation between SSL and Es. Of the 18 pairs of SSL and Es events checked, 15 of SSL were accompanied by Es, and 8 pairs of them were correlated within 1 h in time and within 5 km in altitude. From the analyses of observed perturbations during SSL development, the role of dynamic processes of atmosphere in the SSL formations were emphasized.     

Mineralogical, chemical, and crystallographic properties of supergene jarosite-group minerals from the Xitieshan Pb-Zn sulfide deposit, northern Tibetan Plateau, China

Supergene jarosite-group minerals are widespread in weathering profiles overlying Pb-Zn sulfide ores at Xitieshan, northern Tibetan Plateau, China. They consist predominantly of K-deficient natrojarosite, with lesser amounts of K-rich natrojarosite and plumbojarosite. Electron microprobe (EMP) analyses, scanning electron microcopy (SEM) investigation, and X-ray mapping reveal that the jarosite-group minerals are characterized by spectacular oscillatory zoning composed of alternating growth bands of K-deficient and K-bearing natrojarosite (K₂O >1 wt.%). Plumbojarosite, whenever present, occurs as an overgrowth in the outermost bands, and its composition can be best represented by K_0.29Na_0.19Pb_0.31Fe_2.66Al_0.22(SO₄)_1.65(PO₄)_0.31(AsO₄)_0.04(OH)_7.37. The substitution of monovalent for divalent cations at the A site of plumbojarosite is charge balanced by the substitution of five-valent for six-valent anions in XO₄ at the X site. Thermogravimetric analysis (TGA) of representative samples reveal mass losses of 11.46 wt.% at 446.6 °C and 21.42 wt.% at 683.4 °C due to dehydroxylation and desulfidation, respectively. TGA data also indicate that the natrojarosite structure collapses at 446.6 °C, resulting in the formation of NaFe(SO₄)₂ and minor hematite. The decomposition products of NaFe(SO₄)₂ are hematite and Na₂SO₄. Powder X-ray diffraction (XRD) analyses show that the jarosite-group minerals have mean unit-cell parameters of a?=?7.315 Å and c?=?016.598 Å. XRD and EMP data support the view that substitutions of Na for K in the A site and full Fe occupancy in the B site can considerably decrease the unit-cell parameter c, but only slightly increase a. The results from this study suggest that the observed oscillatory zoning of jarosite-group minerals at Xitieshan resulted mainly from substitutions of K for Na at the A site and P for S at the X site.     

Qualitätsanforderungen an Oberflächengewässer: Zielvorgaben,Qualitätsziele und chemische Gewässergüteklassifizierung

Quality Requirements for Fresh Waters: Water Quality Targets, Water Quality Objectives, and Chemical Water Quality Classification In the Federal Republic of Germany, water quality requirements for the protection of inland surface waters against hazardous substances are formulated on the basis of a quality targets derivation concept developed jointly by the Federal Government and the Federal States. The quality requirements were termed “water quality targets” in order to make it clear that the values derived are orientational values rather than legally binding limit values. The international comparison of quality requirements for surface waters shows that, on the whole, the national quality targets ensure a high level of protection. According to present scientific knowledge, impairments of uses, such as supply of drinking water, or risks to aquatic communities need not to be expected if the quality targets are complied with. A comparison of water quality data with the water quality targets makes it possible, on the one hand, to identify those substances whose inputs must be further reduced; on the other hand, it also shows that, for a number of substances, there is no need at present for concern over their adversely water quality. A further differentiation of the aquatic hazard potential of pollutants allows a water quality classification system to be developed on the basis of the quality targets derivation concept. The basic elements of this water quality classification system are presented, and its application is explained by way of examples.     

Die Radialgeschwindigkeit des Am Sternes 68 Tau

The radial velocity of the star 68 Tau is searched in dependence on the light variation period. No variations have been proved. The mean radial velocity of 22 spectra is 40.4 km/sec ± 0.7 km/sec.     

Closed-form solution of P4P or the three-dimensional resection problem in terms of Möbius barycentric coordinates

 The perspective 4 point (P4P) problem - also called the three-dimensional resection problem - is solved by means of a new algorithm: At first the unknown Cartesian coordinates of the perspective center are computed by means of M?bius barycentric coordinates. Secondly these coordinates are represented in terms of observables, namely space angles in the five-dimensional simplex generated by the unknown point and the four known points. Substitution of M?bius barycentric coordinates leads to the unknown Cartesian coordinates (2.8)–(2.10) of Box 2.2. The unknown distances within the five-dimensional simplex are determined by solving the Grunert equations, namely by forward reduction to one algebraic equation (3.8) of order four and backward linear substitution. Tables 1.–4. contain a numerical example. Finally we give a reference to the solution of the 3 point (P3P) problem, the two-dimensional resection problem, namely to the Ansermet barycentric coordinates initiated by C.F. Gau? (1842), A. Schreiber (1908) and A.␣Ansermet (1910). Received: 05 March 1996; Accepted: 15 October 1996     

Depositional history of the Main Tuff Interval of the Wittenoom Formation, late Archean—early Proterozoic Hamersley Group, Western Australia

The Main Tuff Interval (MTI) is a 3.5 to 16.4 m thick sequence of pyroclastic turbidites in the Wittenoom Formation of the late Archean to early Proterozoic Hamersley Group, Western Australia. The Hamersley Group accumulated in a basin located on the Archean Pilbara Craton, Western Australia. MTI pyroclasts formed via hydrovolcanic eruption processes from a magma that was likely intermediate in composition. Eruption took place in a shallow subaqueous setting. The MTI was deposited by high- and low- concentration turbidity currents in four overlapping regional depositional packages. Paleocurrent and stratigraphic data indicate the MTI source lay to the north of the present exposure limits of the Hamersley Group on the Pilbara Craton, and was likely to have been a single volcano. Reflection of turbidity currents in the southeastern part of the study area and westward travel of the reflected flows indicate that the Hamersley Group depositional basin shallowed to the east and south at the time of MTI deposition. The presence of the MTI source volcano on the northern Pilbara Craton indicates that the subsidence and marine deposition recorded by the Hamersley Group may be limited to the southern portion of the craton, and that volcanism may have continued on the northern Pilbara Craton.