Search

The aims of the Aegean Hydrothermal Fluxes and Biological Production project were to estimate the fluxes of fluids, chemicals, heat and bacteria from hydrothermal vents, establish the controls on venting dynamics, measure the productivity in the region of the vents and establish the effect of the vents on biodiversity of both prokaryotes and eukaryotes. This paper presents an initial synthesis of the project results. Research was done both by land-based SCUBA diving and from several vessels at a number of active sites in the near-shore coastal regions of Milos and Kos, with some additional studies at Methana, Lesbos and Santorini. Vent water composition showed very large variations. This was due to the mixing, of hydrothermal reservoir fluids, vapour condensate and seawater altered by interactions of fluid-sediment-bacteria in different proportions, in the gasohydrothermal vents. The composition ranged from nearly sea water with only slightly reduced pH, to higher or lower salinity fluids with a pH as low as 3 and with large enrichments in heavy and trace metals. Phase separation was a common feature at these shallow vents. The dry gas phase was mainly CO2, but with significant amounts of H2S, CH4 and H2. These fluids commonly passed through soft sediments before venting from the seafloor and induced a convection cell of pore-water entrainment from deeper sediment layers into the water column with a consequent 're-charge' down-flow of seawater into the sediment around the vent outlets. Such complex conditions may well explain the high biodiversity of Bacteria, Archaea and epifaunal species surrounding the vents. As many as 44 % of the archaeal lineages detected were found to represent novel phyla. Epifaunal diversity was particularly high with over 200 species recorded at the shallower Milos vents. These vents may form a 'stepping-stone' for warmer water species to colonise the surrounding areas when water temperatures permit.

The structure of the insulant barrier of Nb Pb and Nb (PbIn) thin film Josephson tunnel junctions is studied in detail by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis. The properties of these two types of junction are strictly related to the thin (2–3 nm) oxide acting as a barrier between the superconducting electrodes. Two oxides were found in each barrier: Nb2O5 and PbO in the Nb Pb junction and Nb2O5 and In2O3 in the Nb (PbIn) junction. In addition, the present analysis shows a change with time of the PbO in contact with Nb2O5: this result is correlated with junction aging. Finally, a comparison in terms of the stability of the two junctions is made: Nb (PbIn) devices seem to display a more stable behaviour with time.

X-ray topography using both reflection and transmission geometry and scanning electron microscopy in the transmission cathodoluminescence mode have been used for studying a characteristic inclusion-like defect in InP single crystals grown by the liquid encapsulated Czochralski technique. The experiments were performed on a number of crystals which differed from each other in their doping and crystal orientation. The images confirm a previously postulated model which assumes that the defect consists of a central core from which prismatic dislocation loops are punched out in the «110a directions. The possible role of gaseous inclusions as being responsible for the observed defect is discussed.

The usefulness of E-beam equipment in VLSI validation have been overstressed. However, only recently the necessity of a full integration between the CAD (Computer Aided Design) world and E-Beam world has been felt. The next step further is the complete automation of an E-beam debugging procedure. This paper presents a description of an integrated E-beam debugging system, developed under Esprit Project 271 .

Thin-film-deposited Nb-NbxOy-Pb Josephson tunnel junctions have been adopted at the Istituto Elettrotecnico Nazionale in recent years to improve the monitoring of the Italian voltage standard.

The electrical characteristics of ruthenium-based thick-film resistors with different conductive terminations (PtAu and Ag based compositions) and with different aspect ratios were examined. The purpose is to understand the effects of resistivity decrease and TCR variation caused by the migration of metal particles from the terminations into the resistor film.The majority of the data were collected by using silver-based terminations since Ag diffusion processes, and then the relevant electrical effects, are emphasized.Scanning electron microscopy, electron microprobe analysis and X-ray diffraction analysis have been used to analyze the diffusion processes and the thick-film microstructures. It is shown that the experimental data is simply explained by a conduction model which assumes percolative tunneling of electrons through conductive grains embedded in the glass matrix of the resistors. Using simple hypotheses the model theory gives a good quantitative fit of the experimental results.