First results obtained with DENIS

We briefly report on the first astronomical results obtained with the DENIS camera at the ESO 1 meter telescope.     

Dynamics of an Abra alba population (bivalve-scrobiculariidae) in the Bay of Brest

The Abra population studied, lived in a muddy-sand Melinna palmata community in the vicinity of the harbour of Brest. There were two periods of spawning in the year: June to August and end of autumn. Individuals 12 mm long can spawn after the first winter. Recruitment was regularly observed in 1 mm mesh sieves in May and September–October. Growth rings were formed in winter; a second growth ring in summer was correlated with spawning. The modal analysis showed a decreasing growth rate and maximum length for the successive cohorts over the three years surveyed. Growth characteristics observed in this population seem to be due to disturbances brought about by neighbouring dredgings which had just ended at the beginning of the study.     

The effects of source rocks and chemical weathering on the petrogenesis of siliciclastic sand from the Neto River (Calabria, Italy): implications for provenance studies

Plutonic and gneissic rocks of the Sila Massif in the uppermost portion of the Neto drainage basin (Calabria, Southern Italy) weather and erode under a humid Mediterranean climate. During the development of weathering profiles, a combination of chemical weathering and granular disintegration processes occurred. Chemical weathering involves a loss of both plagioclase (mainly during grus generation) and K-feldspar (mainly during soil formation). This loss is attributed to transformation of plagioclase to clay minerals and to leaching and dissolution of K-feldspar. Sand composition is quartzofeldspathic and nearly homogeneous along the main channel of the Neto River, even where the river cuts across a blanket of sedimentary cover. Thus, fluvial transport does not alter sand composition within the Neto drainage basin. Petrographic indices are effective in (1) discriminating between contributions from similar (granite and gneiss) source rocks (Qm/F); (2) relating the provenance of plutoniclastic and gneissiclastic sand found in the headwaters to grus horizons (Qm/F; Q/Rg); and (3) distinguishing between upstream first-cycle and downstream multicycle sand (Q/Rg). This last distinction is further emphasized by considering both aphanitic and phaneritic varieties of rock fragments (RgRmRs diagram). Chemical weathering is the main sand producer within the regolithic environment in northern Calabria. In addition, rapid erosion resulting from steep slopes removes weathered products, and rapid and short transport leads to minimal sediment maturation. In general, the F/Q index is climate and relief dependent; thus, it should be used in conjunction with palaeoclimatic and palaeophysiographic evidence for provenance interpretations of ancient quartzofeldspathic sandstones.     

Tritium-Verteilung,Durchmischungsverhältnisse und Altersstruktur der Wassermasse im Vierwaldstättersee

Tritium of thermonuclear origin was measured in four different depth profiles in the Lake of Lucerne. Its concentration distribution yielded information on the mixing within the water mass under observation. A simple model was established for approximating the age structure of the water layers.     

Temperature and heat flow measurements in a fumarolic area: Vulcano Island (Italy)

Vulcano, the southern Aeolian Island, is in fumarolic activity. The possibilities of measurements are limited by the field conditions as well as by the technological feasibility. In the presente work different tests were made in the field to measure temperature continuously: only the measurements made in dry steam gave good results because they avoid corrosion, and solution of the acid gases in the condensed in the ground. Field measurement show that the heat transfer is mainly due to convection. The values obtained in the field can be used to quantify the remote sensing of heat transfer.     

The chemistry of magmatic gases from Erta'Ale,Ethiopia

The chemical composition of the gases emitted from a hornito close to the active lava lake of Erta'Ale, Ethiopia, as derived from chemical analyses on 18 samples collected on 23 January 1974, was found to be (in mol-%): H₂O: 79.4, CO₂: 10.4, total S: 7.36, HCl: 0.42, H₂: 1.49, N₂: 0.18, Ar: 0.001, CO: 0.46, and COS: 0.009. Thermodynamic considerations, based on the equilibria CO₂ + H₂ ? CO + H₂O and CO₂ + 3H₂ + SO₂ ? COS + 3H₂O show that the analytical values represent the equilibrium composition of a gas mixture at the measured temperature of around 1130°C under close to the surface pressure conditions. Comparison of the Erta'Ale gas emissions with those from other volcanoes suggests a close similarity in their chemical composition. This similarity is considered to be due to common processes governing the release of gaseous species from a magma.     

地面沉降对工程沉降监测数据的影响及分析

该文通过对工程沉降监测中的作业方法及其监测数据进行分析，由此得出在工程沉降监测中，地面沉降的影响因素不容忽视。