The gas fired absorption heat pump provides a potentially more efficient alternative to the standard gas fired central heating boiler. The working fluid consists of a mixture of a volatile solute and an involatile solvent, whose thermodynamic properties play a key role in the economics of the pump.

Ontario Hydro's three principal nuclear power plants, Pickering, Bruce and Darlington GS incorporate a sequence of pressure relief structures linking all reactors to a vacuum building where accident produced volatile radioactive substances are contained. The paper discusses the design of Pickering's elevated pressure relief duct and its connection to the reactors by rupture panels. The development of the Pickering prototype pressure relief valve is described. At Bruce and Darlington a linear duct cuts through solid rock beneath the reactors, serving both as an access tunnel for their fuelling machines and as part of the pressure relief system. Its continuation, the reinforced concrete manifold, comprises an above-ground toroidal structure partially or fully encircling the vacuum building. The nature of the manfold and its supporting structures is outlined, with emphasis on the special loading conditions at Darlington arising from high seismic forces, hydrostatic uplift, tornado, and explosion.

The physical and statistical properties of backscattered signals in medical ultrasonic imaging are reviewed in terms of: 1) the radiofrequency signal; 2) the envelope (video or magnitude) signal; and 3) the density of samples in simple and in compounded images. I INTRODUCTION There is a wealth of physical information in backscattered signals in medical ultrasound. This information is contained in the radiofrequency spectrum--which is not typically displayed to the viewer--as well as in the higher statistical moments of the envelope or video signal--which are not readily accessed by the human viewer of typical B-scans. This information may be extracted from the detected backscattered signals by straightforward signal processing techniques at low resolution. II THE RADIOFREQUENCY SIGNAL In the weak scattering regime of medical ultrasonic imaging (1), (2) the Born approximation is valid and yields the frequency dependence of back-scattered radiofrequency signals from a diffuse cloud of similar scatterers. The result in the acoustic application (3) is similar to that found in electro-magnetic wave scattering and the frequency dependence of the backscattered intensity is given by I cc f4 F 2 (1) where the frequency to the fourth power is the dependence associated with Rayleigh scattering, and I F I 2 is the square of the scattering form factor: the Fourier transform of the distribution of the scattering potential, here the change in compressibility or acoustic impedance of the medium. F I 2 has the form of a low pass filter. Some examples of Eq.(1) are given in Figure la for Gaussian form factors with diameters (four standard deviations) as shown, and in reference (4) this simplified treatment is shown to agree well with an exact calculation after the method of Faran when the product of the wave number k and particle radius a is less than unity. In Figure lb the same curves are presented after spatial attenuation by a factor exp(-,2.cx(2x) f), a reasonable approximation to the round trip attenuation at a depth x and at fre-quency f. The attenuation has appreciable effect only at the higher frequencies, as in many other applications.

The paper describes the consequences of new design requirements for the Darlington vacuum building on its structural configuration, analytical procedures and reinforcing steel layout. Attention focuses on the ring girder where the juncture of dome and perimeter wall produces a complex post-tensioning layout, and attendant difficulties in design and construction. At the wall base, full fixity imposes large local stresses. Long-term, shrinkage and creep, and temperature effects become significant. A research program and in-house analytical procedure established time-dependent concrete behaviour and corresponding wall-sectional stresses. The outcome is examined in terms of reinforcement, temperature controls, and wall liner requirements.

This paper describes the evolution of the internal structure from initial concept to final design. Fundamental changes to the original configuration were precipitated by the action of large seismic forces acting on a top-heavy configuration. Prestressing was eliminated in deference to high humidity. Aspects of the elevated water tank's peripheral support beam are discussed vis-à-vis an adjacent slipforming operation, and practical construction limitations on steel placement. Also reviewed are the shortening of peripheral columns due to shrinkage and creep, and considerations of crack control for purposes of water-tightness. The authors justify the choice of stainless steel for fabrication of the siphon system's riser pipes. The foundation slab must resist the combined effects of vacuum pressure, hydrostatic uplift, and the seismic reactions of the internal structure and perimeter wall. The dependency of a key foundation component, the gallery roof slab, on the dome tendon layout is high-lighted; and aspects of its constructability are reviewed in light of congestion of vertical tendon anchorages, and of reinforcement. The design of the air-tight slab liner is reviewed, attention focusing on weld design under vacuum and accident temperature loads; on corrosion protection; and on the related construction access bulkhead - its ASME requirements and fabrication tolerances.

In aviation we are concerned with vehicles which, for the majority of their journey time, are well separated from the community by a vertical distance of some 5-8 miles. Over most of their flight they are the cleanest and quietest form of transport. The aircraft noise problem therefore is confined to the regions around the terminal area. The object of this paper is to define aircraft noise sources and to discuss means by which the terminal noise of advanced air-transport systems can be limited, in order to minimize the noise nuisance. From the mid-1950’s to the mid-19603 there had been a steady build-up in the noise of commercial aircraft operations due to the introduction of jet transports and the steady increase in both aircraft size and number of movements. In the early part of the last decade public reaction to the noise situation was slow. Jet transports were seen as an advance in technology and many were proud to be associated with their introduction. Although manufacturers were aware of the undesirable noise characteristics of the jet engine, technological advances were aimed more at improving thrust performance and cruise efficiency in order to achieve significant increases in range. The first step towards noise improvement was the introduction of the low by-pass/turbofan engines in the early 1960’s, which although quieter, did not make a significant impact on the noise scene. However, the introduction of the advanced high by-pass ratio engines which power today’s wide-bodied airliners has improved the noise situation dramatically (see Figure 1). Initially the use of high by-pass ratios was probably aimed more at the improvement of performance and economics than at noise reduction. However, as time went by and the environmental lobby became stronger, the emphasis on design for low noise increased. Regulatory bodies like the FAA and ICAO formulated noise requirements and certification rules which reflected public pressures to curtail the aircraft noise.

La littérature, concernant le mouvement scientifique des événements stressants de la vie dans leur relation à la maladie, a pris naissance, véritablement, en 1957 avec les travaux de Holmes et Rahe. Parallèlement à l'évolution de la conceptualisation des événements, les méthodologies se sont affinées, allant des premières listes d'événements avec attribution de poids standard aux différents événements, indépendamment du vécu des sujets (1957), aux guides d'entretien clinique (1978) visant à effectuer une évaluation contextuelle de l'importance de chaque événement, pour chaque sujet. Les qualités psychométriques des instruments (validité, fidélité) se sont améliorées parallèlement à l'évolution des méthodologies. Les choix de stratégie de recherche (étude rétrospective, prospective) ont petit à petit été faits de façon plus judicieuse et l'exigence de groupes témoins a fini par s'imposer. Malgré la disparité des méthodologies employées au cours des années et encore actuellement la majorité des auteurs s'accorde pour trouver une relation temporelle entre événement et maladie. Cette relation positive va dans le sens d'une progression suivant les types de pathologie : maladies somatiques, psychosomatiques et mentales. Le crédit que nous pouvons apporter aux résultats mentionnés dans la littérature dépend des méthodologies utilisées dans l'obtention de ces résultats. Le secteur de la pathologie mentale, particulièrement de la dépression, du suicide et de la schizophrénie, est celui dans lequel les auteurs ont unanimement montré une relation entre le déclenchement du premier épisode de maladie ou de rechutes et la présence d'événements stressants dans les mois précédents. Ce secteur est celui dans lequel les résultats sont les plus faciles à mettre en évidence, les différences entre malades et témoins étant importantes. Toutefois, l'emploi d'une méthodologie de qualité permettra au chercheur d'affiner ses résultats. Les secteurs des maladies somatiques et psychosomatiques, pour lesquels les différences entre malades et témoins sont faibles, exigent des méthodologies cliniques complexes pour parvenir à mettre en évidence une relation événement/maladie et qui plus est, tenter d'en identifier les arcanes.The literature on scientific research into stressful life events and their relations to disease made its first real debut in 1957 with the studies by Holmes and Rahe. In parallel with changes in the conceptualization of events, methodologies became increasingly refined over time, going from lists of events with standard weightings independent from the perceptions of the subjects (1957) to clinical interview guidelines (1978) aimed at achieving a contextual evaluation of the importance of each event in each individual. The psychometric properties of measurement instruments (validity, reliability) improved in parallel with these changes in methodology. The choices of research strategies (retrospective, prospective) slowly became more discerning, and the need for a control group was finally accepted. Despite the wide variations in methodologies used over time and even across current studies, most studies suggested a chronological relationship between life events and disease. This positive association supports a progression based on the nature of the disease: somatic, psychosomatic, or mental. The credibility of published results depends on the methodologies used to obtain them. In the area of mental diseases, most notably depression, suicide, and schizophrenia, studies have consistently found a relation between the onset of the disease or occurrence of relapses and the presence of stressful life events during the previous months. This is the area in which the effect of life events is easiest to demonstrate, as the differences between patients and controls are large. However, high-quality study designs should provide further refinements in the results. In the areas of somatic and psychosomatic diseases, differences between patients and controls are small, so that complex study designs are needed to detect associations between events and diseases and to unravel the underlying mechanisms.

Kozeny–Carman (KC) equation is a well-known relation between hydraulic conductivity and pore properties in porous material. The applications of KC equation to predicting saturated hydraulic conductivities of sands and non-expansive soils are well documented. However, KC equation is incapable of predicting saturated hydraulic conductivity of expansive soil (e.g. bentonite) well. Based on a new dual-pore system, this study modified KC equation for improving the prediction of saturated hydraulic conductivities of bentonites. In this study, an assumption that inter-layer space (micropore) has limited effect on fluid flow performance of compacted bentonite was adopted. The critical parameters including total porosity and total tortuosity in conventional KC equation were replaced by macroporosity and tortuosity of macropore, respectively. Macroporosity and microporosity were calculated by basal spacing of compacted bentonite, which was estimated by assuming that specific surface area is changeable during saturation process. A comprehensive comparison of bentonite's saturated hydraulic conductivity predictions, including modified KC equation proposed in this study, conventional KC equation, and prediction method based on diffuse double layer (DDL) theory, was carried out. It was found that the predicted saturated hydraulic conductivity of bentonites calculated using modified KC equation fitted the experimental data better than others to a certain extent.