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

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

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

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

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

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

Twisted Bundles on Noncommutative T4T^4 and D-brane Bound States

We construct twisted quantum bundles and adjoint sections on noncommutative $T^4$, and investigate relevant D-brane bound states with non-Abelian backgrounds. We also show that the noncommutative $T^4$ with non-Abelian backgrounds exhibits SO$(4,4|Z)$ duality and via this duality we get a Morita equivalent $T^4$ on which only D0-branes exist. For a reducible non-Abelian background, the moduli space of D-brane bound states in Type II string theory takes the form $\prod_a (T^4)^{q_a}/S_{q_a}$.Comment: 19 pages, Latex. v2: Title is changed. Minor corrections. A reference adde

Design of Lightweight Footbridges for Human Induced Vibrations

Nowadays, it is well-known that for the structural safety verification of footbridges, and for the comfort guarantee of its users, it is fundamental to consider the effect of human induced vibrations, particularly: vibrations due to pedestrian traffic should be within acceptable limits for users; the lock-in phenomenon should be prevented; and, the footbridge structural safety should be guaranteed if subjected to intentional excitations. Recognizing a gap in lightweight footbridges design procedures, a guideline is presented in this document proposal for footbridges design taking into account human induced vibrations. First, the proposed methodology is detailed. Attention is devoted also to the response measurements, identification tests and instrumentation used in the evaluation of the dynamic properties of footbridges. The potential strategies to control the vibration response of footbridges are reviewed. Finally, three worked examples of application of the proposed design methodology are exposed, namely a simply supported beam and two existing footbridges. Keywords: Footbridges; Design procedures; Human induced vibrations; Structural safety; Human comfort; Dynamic properties; Vibration controlJRC.G.5 - European laboratory for structural assessmen

Choice of Steel Material to Avoid Brittle Fracture for Hollow Section Structures

European cold-formed hollow sections in general exhibit better toughness properties than required by EN 10219. However, limits in applying the toughness related rules for the choice of steel material in EN 1993 1 10 to cold-formed hollow sections still constitute barriers to free marketing. By requests from European producers a conservative assessment procedure has been developed which is based on toughness measurements and a concept using effective strains. Due to the cold-forming process such plastic strains may occur in the bent areas of the profiles associated with a noticeable reduction in material toughness. For the degradation of these toughness properties an appropriate temperature shift Delta Tcf has been derived for both circular and rectangular hollow sections. In order to guarantee the proper application of this temperature shift Table 2.1 in EN 1993 1 10 had to be extended to lower temperatures down to -120 °C.JRC.G.5-European laboratory for structural assessmen