Global axisymmetric Magnetorotational Instability with density gradients

We examine global incompressible axisymmetric perturbations of a differentially rotating MHD plasma with radial density gradients. It is shown that the standard magnetorotational instability, (MRI) criterion drawn from the local dispersion relation is often misleading. If the equilibrium magnetic field is either purely axial or purely toroidal, the problem reduces to finding the global radial eigenvalues of an effective potential. The standard Keplerian profile including the origin is mathematically ill-posed, and thus any solution will depend strongly on the inner boundary. We find a class of unstable modes localized by the form of the rotation and density profiles, with reduced dependence on boundary conditions.Comment: 22 pages, 5 figure

Technology requirements for post-1985 communications satellites

The technical and functional requirements for commercial communication satellites are discussed. The need for providing quality service at an acceptable cost is emphasized. Specialized services are postulated in a needs model which forecasts future demands. This needs model is based upon 322 separately identified needs for long distance communication. It is shown that the 1985 demand for satellite communication service for a domestic region such as the United States, and surrounding sea and air lanes, may require on the order of 100,000 MHz of bandwith. This level of demand can be met by means of the presently allocated bandwidths and developing some key technologies. Suggested improvements include: (1) improving antennas so that high speed switching will be possible; (2) development of solid state transponders for 12 GHz and possibly higher frequencies; (3) development of switched or steered beam antennas with 10 db or higher gain for aircraft; and (4) continued development of improved video channel compression techniques and hardware

Technology requirements for communication satellites in the 1980's

The key technology requirements are defined for meeting the forecasted demands for communication satellite services in the 1985 to 1995 time frame. Evaluation is made of needs for services and technical and functional requirements for providing services. The future growth capabilities of the terrestrial telephone network, cable television, and satellite networks are forecasted. The impact of spacecraft technology and booster performance and costs upon communication satellite costs are analyzed. Systems analysis techniques are used to determine functional requirements and the sensitivities of technology improvements for reducing the costs of meeting requirements. Recommended development plans and funding levels are presented, as well as the possible cost saving for communications satellites in the post 1985 era

Numerical study of Yang-Mills classical solutions on the twisted torus

We use the lattice cooling method to investigate the structure of some gauge fixed SU(2) Yang-Mills classical solutions of the euclidean equations of motion which are defined in the 3-torus with symmetric twisted boundary conditions.Comment: 20pp (fig.included

Hot-dip-zinc-coating of prefabricated structural steel components

This JRC-Scientific and Technical Report gives information from pre-normative research for methods to prevent liquid metal assisted cracking of prefabricated structural components during zinc-coating in the liquid zinc melt, that may impair the structural safety of structures in which the components are built in. This information provides a platform upon which further European design and product specifications can be developed. It may in particular affect the further developments of EN 1993, EN 1090, EN ISO 1461 and EN ISO 14713. This report gives the state-of-the-art in understanding the mechanism of liquid metal assisted cracking in the zinc bath and methods and models that may be used to avoid it. It could be a basis to propose rules for the design of steel components intended to be hot-dip-zinc-coated in such a way that the design is consistent with execution rules for hot-dip-zinc-coating. The workability of the rules proposed for all metal works and steel works that are fabricated under EN 1090 and galvanized according to the rules in this report is demonstrated by worked examples.JRC.DG.G.5-European laboratory for structural assessmen

Needs to Achieve Improved Fire Protection as regards the Implementation and Development of the EN Eurocodes

The work reported is a deliverable within the framework of the Administrative Arrangement between DG ENTR and JRC on support to the implementation, harmonization and further development of the Eurocodes. The report encompasses the results achieved during the three-year work on Sub-task 5.2 'Needs for fire protection' of the Administrative Arrangement with DG ENTR. The report consists of three self-contained sections, namely: - Research needs to achieve improved fire design using the Eurocodes, - Implementation and use of fire-parts of the Eurocodes, and - Survey on the progress in the National implementation of the Eurocodes fire design parts. The present report has been prepared by the JRC in collaboration with the two ad-hoc groups on fire design convened by the JRC and in consultation with DG ENTR, Member States and individual experts and organizations involved in fire design.JRC.G.5-European laboratory for structural assessmen

Choice of steel material for bridge bearings to avoid brittle fracture

Bridge bearings need verification against brittle failure at low temperatures. The design of bearings according to EN 1337 may lead to structural components with thicknesses no longer covered in the relevant technical construction regulations. Due to its specific geometry, the loading and stressing and the fabrication process the prerequisites for using the rules in EN 1993 1 10 lead to conservative restrictions or uneconomical choice of steel material. For an economical bearing design further modifications of the existing rules are necessary. This report adapts the fracture mechanical approach used in EN 1993 1 10 and gives information for a “safe-sided” choice of steel material for bearings. The main modifications refer to the hypothetical design crack scenario and the definition of the “nominal design stress” at the geometric “hot-spot”. An advanced methodology using Finite Elements and a simplified method using linear bending theory are evaluated.JRC.G.5-European laboratory for structural assessmen

Environmental controls on the post-Permian recovery of benthic, tropical marine ecosystems in western Palaeotethys (Aggtelek Karst, Hungary)

Climate warming during the late Permian is associated with the most severe mass extinction event of the Phanerozoic, and the expansion of hypoxic and anoxic conditions in shallow shelf settings. It has been hypothesised that wave aeration provided a ‘habitable zone’ in the shallowest environments that allowed the survival and rapid recovery of benthic invertebrates during the Early Triassic.We test this hypothesis by studying the rock and fossil records of the Aggtelek Karst, Hungary. Nearshore settings recorded in the Bódvaszilas Sandstone Formation and units A and D of the Szin Marl Formation are characterised by taxonomically homogenous fossil assemblages of low diversity and low evenness. Ecological and taxonomic recovery in this environmental setting was hampered by persistent environmental stress. This stress is attributed to increased runoff related to climate warming during the Early Triassic that resulted in large salinity fluctuations, increased sedimentation rates and eutrophication that led to seasonal hypoxia and an environment only favourable for opportunistic taxa. In contrast, shoal andmid-ramp settings further offshore are characterised by high diversity faunaswith a greater functional complexity. Prior to the late Spathian Tirolites carniolicus Zone, the shelly fossils and trace fossils are limited to settings aerated by wave activity, which supports the habitable zone hypothesis. In the Tirolites carniolicus Zone, however, the oxygen minimum zone retreats offshore and the habitable deeper shelf settings are rapidly colonised by shallowwater taxa, evidenced by the highest levels of diversity and bioturbation recorded in the study. Locally, full recovery of marine ecosystems is not recorded until the Illyrian, with the establishment of a sponge reef complex

EFFECTS OF NUTRIENT ENRICHMENT ON THE AUCHENORRHYNCHA (HOMOPTERA) IN CONTRASTING GRASSLAND COMMUNITIES

SUMMARY (1) Auchenorrhyncha were sampled from control, fertilizer-and sludge-treated plots within agricultural and fourth-year old-field communities. (2) Nutrient enrichment significantly increased net primary productivity in both plant communities. (3) Functional plant community properties (e.g. net primary production) were more robust indicators of nutrient enrichment than were structural properties (e.g. plant species diversity). (4) Nutrient-enriched plots generally exhibited higher Auchenorrhyncha population densities than control plots in both community types; differences were more frequent in the more mature old-field community. (5) There were significant differences in Auchenorrhyncha species richness only in the nutrient-enriched plots in the old-field community. (6) Changes in Auchenorrhyncha density and diversity were attributed to changes in plant composition, productivity and probably plant quality and vegetational architecture. (7) Auchenorrhyncha within the more mature old-field community exhibited a greater response to nutrient subsidy than within the agricultural community; these differences were attributed to plant-insect life-history characteristics