Flows in clumpy planetary nebulae

The dynamics of clumps observed in planetary nebulae are considered. The possibility that SiO maser spots in evolved stars and the planetary nebula clumps are formed by the Parker instability behind shocks in pulsating stars' atmospheres is raised. Molecular observations of the clumps are suggested. The effects of the ablation of clumps on the global flow structure of a more tenuous plasma in which they are embedded are reviewed.     

Tribute to Justus Perthes

Conclusion The above account is just a selection of Perthes' multifarious activities. As such it is fragmentary and incomplete. Many other publications and collaborators could have been mentioned. Even in its incompleteness the report may justify the statement that the success of Justus Perthes Geographische Verlagsanstalt, was apart from the managing qualities of its governors, undoubtedly due to the long series of scholarly competent collaborators whom they succeeded in engaging. As illustrated above most of theme were among the avant garde of the profession. Apparently they were at ease with Justus Perthes where they were granted enough freedom of action to realise their ambitious projects under the vigilant eye of the management. In fact the history of the firm is a continuous story of their achievements. Their combined effort initiated modern scientific atlas-making, laid down the foundation of methodic school cartography and accelerated the growth of thematic cartography. The Justus Perthes maps and atlasses stand for intellectual honestly and have an authoritative appearance of truth and exactness. For a long time to come the name of the firm will be considered as a classical example of the promotion of geography and cartography by private enterprise.     

Variations in the natural abundance of 15N in estuarine suspended particulate matter: A specific indicator of biological processing

In this study, the ¹⁴N:¹⁵N ratio of suspended particulate material collected from the Tamar river estuary, south-west England, is described. Three populations of particles, distinguishable by their ¹⁵N content, were observed. This investigation has shown that populations of estuarine particles are generated by biological transformations in situ and that the ¹⁵N content of estuarine particles does not merely reflect hydrodynamic mixing of the freshwater and seawater source particulate material.     

Acoustic oceanography by remote sensing

Ocean dynamical processes exist over a wide range of temporal and spatial scales. Remotely stationed acoustic devices are being used to "sense" the interior of the oceans at previously unattainable scales. The method is similar to computer-aided tomography (CAT) scans of the brain, but the measurement difficulties are far more severe. The results of a demonstration experiment are reviewed and some directions for acoustic oceanography are discussed.     

Deep-ocean piezometer probe technology for geotechnical investigations

Two single-sensor piezometer probes, 8 mm in diameter, were developed for deep-ocean geotechnical investigations. These probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi). Testing was performed for a period of five weeks under high hydrostatic pressure with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. During deep-ocean simulated pressure tests, the sensors exhibited excellent sensitivity and stability. These developments in piezometer-probe technology provide a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits.     

Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog,New Zealand,and implications for tephra correlation

This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies. The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.     

A sapphirine–phlogopite–cordierite paragenesis in a low-P amphibolite facies terrain, Arunta Inlier, Australia

Summary Silica-undersaturated phlogopite schists from the Cackleberry Metamorphics, Arunta Inlier, central Australia, preserve relatively low-temperature sapphirine-bearing parageneses that developed during low-pressure upper amphibolite facies metamorphism. Peak metamorphic phlogopite–cordierite–sapphirine assemblages are interpreted to have formed during the same event recorded in nearby metapelites, at c.3 kbar and 650–700 °C. Initial cooling of the terrain resulted in the breakdown of sapphirine to corundum–chlorite–phlogopite and corundum–spinel–chlorite assemblages. Further retrogression at greenschist facies conditions resulted in the replacement of sapphirine by diaspore–chlorite intergrowths. The reaction textures are consistent with a near-isobaric heating-cooling path at low-pressure, and provide evidence for the stability of sapphirine at c.700 °C at low pressures in rocks of an appropriate Mg- and Fe³⁺-rich bulk composition. Received August 15, 2001 accepted December 27, 2001     

Comparison of results from several AOGCMs for global and regional sea-level change 1900–2100

 Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need for detailed analysis and intercomparison in order to understand and reduce the disagreements. Received: 1 September 2000 / Accepted: 20 April 2001