Der Stabbogen bei stählernen Straßenbrücken – Entwicklungstendenzen der letzten 50 Jahre – Teil I

The strut arch in using of steel road bridges mainly in Germany – trends of developments into the last 50 years. By the presentation is given a survey about the development of the designing the arch construction for steel road bridges inclusive the constructive details. In the detail are considerd the suspensions with their connections, the cross‐sections of the arch, springing arch, arch model and the roadway‐constructions into different phases. At last of the investigation are presented some typical erection‐examples.     

Application of GC-HRMS and GC×GC-TOFMS to aid in the understanding of a dioxin assay's performance for soil and sediment samples

There have been numerous attempts to correlate results obtained by gas chromatography-mass spectrometry (GC-MS) to alternative techniques such as immunoassays and bioassays for the analysis of dioxins in environmental samples. In spite of these efforts, uncertainties about the performance of these methods remain. Following a series of performance studies of various dioxin assays, an in-depth evaluation of sample extracts from the Procept Rapid Dioxin Assay was conducted to provide users with a clearer understanding of the differences in the assay's results compared to traditional mass spectrometry. Two powerful analytical techniques [high-resolution mass spectrometry (HRMS) and two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS)] were used to provide a unique perspective about the assay's underlying analytical performance. HRMS analyses demonstrated that the target dioxin and furans were consistently captured in the assay's extracts. TOFMS analyses revealed that interferents in the sample extracts resulting from inconsistencies in the sample preparation process appear to be the primary factor contributing to the assay's imprecision. The conclusion of this research was the assay results cannot be expected to correlate directly with HRMS and should only be utilized as a screening technique (e.g., to identify the relative ranking of contamination, to determine if samples are above/below threshold levels, or to monitor a cleanup) for environmental matrices such as soil and sediment.     

Issues in satellite personal communication systems

In the paper various issues in personal satellite communications are addressed. Basic geostationary and non‐geostationary satellite constellations are considered. The narrowband and wideband characterization of the mobile satellite channel and related system implications are discussed. Satellite diversity is presented as a measure to overcome signal shadowing. The capacity of TDMA and CDMA multiple access is estimated, taking into account co‐channel interference. Various network issues, such as mobility management, radio resource management, call control, routing, and network integration are addressed. Finally, some regulatory and political issues are mentioned which may be most relevant for market development and financial success of satellite personal communication systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Solder metallization interdiffusion in microelectronicinterconnects

We investigated the growth of intermetallic compounds in Cu/Ni/Au/PbSn solder joints. The substrates that we investigated had been Au plated by one of two different techniques. The Au finish thicknesses ranged from 0.25 to 2.6 μm. After solder renew, structural examinations using optical and electron microscopy of cross-sectioned solder joints revealed the growth of Ni₃Sn ₄ at the solder/Ni interface after reflow. Solder joints with thicker layers of Au annealed in Ar gas at a temperature of 150°C for up to 450 h, displayed an appreciable growth of Au_0.5Ni _0.5Sn₄ at the Ni₃Sn₄/solder interface. Previous investigators correlated growth of a Au-Sn alloy with the degradation of the mechanical properties of the solder joint. The determination of the stoichiometry of the Au_0.5Ni_0.5 Sn₄ phase provides some understanding of why this phase grew at the Ni₃Sn₄/solder interface, as Sn, Au and Ni are all readily available at this interface. The growth of this ternary alloy is also consistent with trends observed in the kinetics of formation of solder alloys     

Spurious Signal Response of Broadband Solid–State Frequency Multipliers at Millimeter and Submillimeter Wavelengths

Heterodyne instruments at millimeter and submillimeter wavelengths often use wideband fixed-tuned frequency multipliers, in conjunction with broadband power amplifiers driven by frequency synthesizers, as the local oscillator (LO) source. At these frequencies the multipliers use Gallium Arsenide (GaAs) based Schottky varactor diodes as the nonlinear element, and like most other harmonic generators are susceptible to spurious signal interference. The state-of-the-art LO sources at these wavelengths use high power MMIC amplifiers at the initial stages, and are used to drive the subsequent multiplier stages to have enough LO power to pump the mixers. Because of the high input power environment and the presence of noise in the system, the multipliers become vulnerable to spurious signal interference. As the spurious signals propagate through the receiver system, they generate inter-modulation products which might fall in the passband of the heterodyne instrument and seriously degrade its performance. In this paper spurious signal response of solid-state frequency multipliers at millimeter and submillimeter wavelengths is investigated. Results of numerical harmonic balance simulations and laboratory experiments, which were found to show good agreement, are presented here.