Left ventricular outflow tract obstruction after mitral valve replacement

A method of posterior mitral annulus remodeling is presented. The posterior annulus is divided into three segments, each segment encircled by a suture that is passed in a tourniquet. Coaptation of the leaflets can be achieved by tightening the tourniquets while the ventricle is being filled. This technique is simple and quick, avoids the use of foreign material, and requires less expertise and judgment than traditional annuloplasties.     

Seroepidemiologic indicators for the evaluation of campaigns for the control of foot-and-mouth disease

A sero-epidemiological survey was conducted in two districts in Argentina between 1993 and 1995, to provide additional information on the epidemiology of foot and mouth disease (FMD) in Argentina and to assess the level of immunity in cattle populations, and the circulation of FMD virus. As part of the final stage of this survey, a comparison was made of the results obtained by the enzyme-linked immunosorbent assay (ELISA) and agar gel immunodiffusion techniques. Levels of population immunity against the four types of virus included in the vaccine increased progressively during the period of the survey until, in 1995, at the end of the vaccination period, the percentage of animals possessing adequate levels of protection was approximately 77% in yearlings, and more than 94% in cattle over one year old. During the three-year study, there was a clear tendency for viral activity to diminish, until in 1995 when between 3% and 0.6% were positive to the agar gel immunodiffusion test for the antigen associated with viral infection. By contrast, the ELISA detected antibody in about five times as many animals. The authors show how the increase in the level of population immunity was accompanied by a fall in viral activity.     

Hydrogen-assisted cracking

This article reviews a number of case studies involving hydrogen-assisted cracking in steels. Before the case studies are presented, the current state of understanding of hydrogen-assisted cracking is briefly reviewed. At present there are two leading approaches to the development of a mechanism of hydrogen-assisted cracking, one based upon bond weakening, and the other upon strain localization. As the case studies illustrate, hydrogen-assisted cracking can lead to failures in perhaps unexpected circumstances. The need for the wider dissemination of information about hydrogen cracking to design engineers is indicated.     

Transient dynamics of cylinders under wave slamming

Large diameter slender cylindrical shells used as buoyancy chambers and support legs for compliant marine structures experience a variety of impact loadings which could induce significant levels of dynamic response. By examining the response of a typical range of cylindrical shell geometries to a simulation of the impact loading typical of wave slamming, the paper examines the likely levels and practical significance of the transient dynamic response. It shows that the levels of dynamic response are sufficiently severe to have important implications for the triggering of buckling and fatigue collapse characteristics. It is suggested that this phenomenon requires additional more-detailed consideration, including the provision of reliable predictions of transient slam pressure distributions and the levels and forms of hydrodynamic damping, as well as the effects of more practical shell and stiffening geometries, and ambient stress levels.     

Temperature-induced phase change in a fat. A study by electron spin resonance

Electron Spin Resonance, Differential Scanning Calorimetry and rheological techniques have been used to study the physical changes induced by temperature in lard and in the solid and liquid fractions obtained by fractionation of lard at 15 C. The mobilization process of a C18 fatty acid nitroxide derivative dispersed in the molten fat has been observed in the temperature range −50 to +70 C. The mobilization of the probe seemed to be concomitant with the melting of the low melting point glycerides. Above this temperature, all the probes were in the liquid phase and their mobility reflected the viscosity of their liquid environment, or the viscosity of the bulk fat when crystal was no longer present. Probe mobility was temperature dependent, and it was identical for the three fats at the same temperature, despite their different triglyceride compositions.     

Utilisation de couples d'hydrocarbures dans les frigopompes et les thermofrigopompes à absorptionUtilisation of hydrocarbon pairs in absorption heat pumps in cooling applications

The performances of two systems using hydrocarbon pairs are compared. The first system is an absorption heat pump, comprising a rectification column separator and a mixer comprising a single-stage cell. In this case, five hydrocarbon pairs are used. In the second system, the authors compare the performances of three hydrocarbon pairs in two heat pumps with one or two stages in the mixer. It was shown that the best performances are obtained using pairs with the most similar chemical compositions.