Mid-infrared, spatially resolved spectroscopy of the nucleus of the Circinus galaxy

High spatial resolution spectroscopy at 8–13 μm with T-ReCS on Gemini-S has revealed striking variations in the mid-infrared emission and absorption in the nucleus of the Circinus galaxy (hereafter Circinus) on subarcsecond scales. The core of Circinus is compact and obscured by a substantial column of cool silicate dust. Weak extended emission to the east and west coincides with the coronal line region and arises from featureless dust grains which are probably heated by line emission in the coronal emission zone. The extended emission on the east side of the nucleus displays a much deeper silicate absorption than that on the west, indicating significant columns of cool material along the line of sight and corresponding to an additional extinction of   A_V ∼ 25 mag  . Emission bands from aromatic hydrocarbons are not subject to this additional extinction, are relatively weak in the core and in the coronal line region, and are much more spatially extended than the continuum dust emission; they presumably arise in the circumnuclear star-forming regions. These data are interpreted in terms of an inclined disc-like structure around the nucleus extending over tens of parsecs and possibly related to the inner disc found from observations of water masers by Greenhill et al..     

溃变图的业务操作系统简介

按溃变理论［１］的不连续或非均匀信息不仅可以预测天气系统的移动性变化和转折性变化，也可以预测降水等天气现象。并已被多次历史例案和应用实践所验证。为了便于投入业务运用，我们利用数据库系统，实现了体现资料信息非均匀和不连续的广义参数在微机、填图机上的自动化处理，完成了收报、计算和填图分析的自动化。本方法体现了预报工具的改革也充分地利用了现有的资料资源     

Analysis of mapping coverage obtained from spacecraft

An exact analysis of the coverage obtained by spacecraft using cross-track scanning and nadir-centered conical imaging, under imposed viewing obliqueness and resolution requirements, is presented. In addition to exact expressions for the area acquired and the area acquisition rate, envelope theory is introduced to obtain the boundary of the imaged area. These expressions are relatively compact, allowing rapid machine computation. The effects of the sun phase angle, and of imaging system limitations are also examined. The Galileo mission encounter with Callisto is used as a numerical example, from which certain general conclusions are drawn regarding optimal imaging trajectories.     

Detrital barytes in the Karoo Supergroup of Southern Africa

Beds of sedimentary barytes are found in late Paleozoic sediments in the northeasternmost part of South Africa and adjoining parts of Rhodesia. The baryte horizon consists of 2 beds of composite thickness of up to 50 cm within a sequence of partly porcellaneous shales. It is dark gray to redbrown in colour, in places also black, and then contains traces of H₂S. It usually consists of fine-grained subrounded tabular grains of detrital origin. This horizon frequently contains aggregates of upward diverging acicular baryte which formed diagenetically within the detrital baryte. The deposit was formed through reworking of semiconsolidated clays containing baryte concretions. Such shales are known to occur to the west of the baryte deposit in contemporaneous sediments.

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Zusammenfassung In spätpaläozoischen Sedimenten im Nordosten Südafrikas und dem angrenzenden Bereich Rhodesiens treten sedimentäre Barytlagen auf. Die Barytzone besteht aus zwei Lagen mit einer gemeinsamen größten Mächtigkeit von 50 cm, innerhalb einer Abfolge teilweise verkieselter Tonschiefer. Der Baryt ist dunkelgrau bis rotbraun, stellenweise auch schwarz, und enthält dann Spuren von H₂S. Er besteht meist aus feinkörnigen kantengerundeten schwach plattigen Kristallen detritischer Herkunft. Die Zone enthält häufig Aggregate aus nach oben divergierenden nadeligen Barytkristallen, die sich frühdiagenetisch im detritischen Baryt bildeten. Das Vorkommen entstand durch Aufarbeitung von Barytkonkretionen in schwach verfestigten Tonen. Entsprechende Tonschiefer treten in gleichaltrigen Sedimenten westlich des Barytvorkommens auf.

     

Quaternary sediments in the axial zone of the Brazil Basin

Lithological and micropaleontological studies of sediments were carried out along the meridional profile across the Brazil Basin. Based on nannoplankton and diatom assemblages, the sediments represented by oxidized miopelagic clays, differently reduced hemipelagic clays, and clayey-siliceous (Ethmodiscus) and calcareous (coccolith-foraminiferal) oozes are attributed to the Pleistocene-Holocene. Specific features of sedimentary material indicate its redeposition by Antarctic bottom waters, mudflows, slumps, and rockslides. It is shown that sedimentation in the Brazil Basin corresponds to the incomplete pelagic (miopelagic) type of oceanic lithogenesis transitional to the near-continental one.     

Modelling groundwater contamination above the Asse 2 medium-level nuclear waste repository,Germany

The medium-level radioactive waste deposited in the Asse 2 salt mine, Germany, has a total activity of 1.2 × 10¹⁵ Bq (1 January 2002). The waste lies in a former mining chamber on the −511 m mining level close to the contact between the Mesozoic country rock and the Zechstein salt dome. The Mesozoic country rock is strongly faulted but the geometry of the fault pattern is incompletely known. Two tectonic cases are considered: a pessimistic case, which assumes that the radioactive source is linked to the surface by a single fault, and an optimistic case, which assumes that the radioactive source is not connected to any fault at all. The potential groundwater contamination by radioactive fluids expelled from the cavity is simulated with the TOUGH2 code for periods of up to 6,000 years, when the potential contamination reaches its greatest vertical extent. Two types of driving forces are considered: convergence of the rock salt surrounding the cavity and generation of H₂ gas by the corrosion of iron, steel and other metallic components of the waste at low O₂ fugacities. Rock-salt creep has the greatest potential impact, as it leads to a radioactive plume whose 1 Bq/L activity contour rises up to 240 m below the surface in the pessimistic tectonic case. The value of the model for the assessment of the environmental risk is limited. The knowledge of the hydrogeological situation is incomplete and the pessimistic tectonic case may not be pessimistic enough for a realistic worst-case scenario.     

Palaeozoic Victoria,Australia: Igneous rocks,ages and their interpretation

A reconnaissance traverse across Victoria yields 160 K‐Ar dates on igneous rocks from 94 localities. These are supplemented by Rb‐Sr dating in critical cases, and major‐element analyses (some new) on a proportion of the samples. All dates quoted in text and tables, new and previously‐published, have been revised in terms of the latest decay‐constant conventions.

The dates range from Early Ordovician (480 Ma) in the west to Late Devonian (360 Ma) among the high‐level intrusives of Central Victoria. The relatively complex age pattern, and the petrochemical character of the rocks, are compared with the published chronology of neighbouring States, and are interpreted in terms of a long‐duration regime of westwards compression, which began in the deformations of the Adelaide System of South Australia, and continued until the Mid‐Devonian Tabberabberan Movement.