A millimeter-wave monolithic grid amplifier

A 36-element monolithic grid amplifier has been fabricated. The peak gain is 5 dB at 40.8 GHz with a 3-dB bandwidth of 1.4 GHz. The active elements are pairs of heterojunction-bipolar-transistor's (HBT's). The individual transistors in the grid have a maximum oscillation frequency,f _max , of 100 GHz. The grid includes base stabilizing capacitors which result in a highly stable grid. This is the first report of a successful monolithic grid amplifier.     

The esterified plasma fatty acid profile is altered in early HIV-1 infection

The online version of the original article can be found at     

Incidence of hepatitis C infection among donors of femur heads to the tissue bank

A review of a case series of sixteen anaesthetics in eight cases was undertaken to determine whether children with Prader-Willi syndrome present particular problems to the anaesthetist. Children in an early stage of the condition who are below their centile for weight present no specific problems. Children who are heavier than 97th centile weight have problems associated with their obesity: difficult intravenous access and sleep apnoea. Scoliosis was noted in both groups and was not associated with problems after minor surgery.     

Preparation of High - Purity Tl(1223) Ceramics

The influence of changes in the nominal composition and preparation conditions on the formation of Tl(1223) under a high isostatic gas pressure was studied. Optimization of the cation substitution allowed to increase the phase purity, whereas substitution of small amounts of oxygen by fluorine decreased the formation temperature of the Tl(1223) phase and extended the temperature range favorable for grain growth. A two-step reaction involving substantial melting produced well shaped, plate-like grains.     

Web mining based on Growing Hierarchical Self-Organizing Maps: Analysis of a real citizen web portal

This work is focused on the usage analysis of a citizen web portal, Infoville XXI (http://www.infoville.es) by means of Self-Organizing Maps (SOM). In this paper, a variant of the classical SOM has been used, the so-called Growing Hierarchical SOM (GHSOM). The GHSOM is able to find an optimal architecture of the SOM in a few iterations. There are also other variants which allow to find an optimal architecture, but they tend to need a long time for training, especially in the case of complex data sets. Another relevant contribution of the paper is the new visualization of the patterns in the hierarchical structure. Results show that GHSOM is a powerful and versatile tool to extract relevant and straightforward knowledge from the vast amount of information involved in a real citizen web portal.     

Electron effective mass in InuGa1−uPvAs1−v for 0 ≤ v ≤ 1

The electron effective mass in In_uGa_1−uP_vAs_1−v has been measured on seven samples lattice-matched to InP and evenly spaced in values of v between 0 and 1, using the temperature dependence of the amplitude of the Shubnikov-de Haas oscillations at high magnetic fields. Values of the carrier concentrations, Hall mobilities and Dingle temperatures measured on these samples are also reported. Work sponsored in part by the National Science Foundation, Grant No. ENG 76-09586, and in part by International Telephone and Telegraph Electro-Optical Products Division. Work done in part at the M.I.T. Francis Bitter National Magnet Laboratory. Funded in part by the National Science Foundation under Grant No. DMR-76-80895.     

A study on posidonia residue in seawater intakes

The reliability of a sea-water desalination plant relies largely on an efficient intake system. This is not easily ensured in large areas of the Mediterranean, where the residue of a particular seagrass, Posidonia 0ceanica, is often found in large quantities. To separate or avoid this residue, which can cause operational problems, considerable technical and economical efforts are required.

This paper presents the results of a design and operation-oriented experimental study on Posidonia. This study deals with aspects such as concentration in sea-water, distribution of sizes in residue samples, sedimentation properties, bulk densities and resistance of sea-grass cakes to sea-water flow, and is supported by direct practice in desalination in Libya. Experience confirms that the analysis of the behaviour and physical properties of Posidonia residue, together with accurate site survey, enable one to design a tailored solution, thus avoiding an unreliable standardized system or an uneconomical sophisticated or over-dimensioned solution, not necessarily reliable when unassisted by field data.     

Optimum reliabilities and optimum design

The designer's task is to optimize. Designing for an intuitively fixed reliability is almost as arbitrary as designing for an intuitively fixed safety factor. Efforts to improve the calculation of reliabilities of proposed designs are commendable but sterile unless we take the additional step of optimizing the design reliabilities associated with the various potential limit states. Through examples it is shown how these reliabilities depend on the consequences of entrance into limit states and on the marginal initial cost of the reliability and how earthquake design spectra must differ radically from those for fixed return periods. It is further claimed that the optimum reliabilities depend on how a structure enters a limit state. A more realistic aim is not the establishing of design reliabilities but of optimum designs. This is illustrated in connection with progressive collapse.Mistakes (“human” or “gross” errors) are not considered in the present analysis.