Evaluation of myocardial function and perfusion in ischemic heart disease

Ischemic heart disease is the most frequently encountered cardiac disease. Magnetic resonance imaging (MRI) can be used to investigate several facets of this disease. A number of studies over the past several years have shown the capability of cine MRI for quantifying regional myocardial function and for identifying abnormalities of regional myocardial wall thickening in the basal or vasodilated states due to ischemia. Contrast-enhanced inversion recovery fast gradient echo and echo-planar imaging have been applied for monitoring the first passage of contrast media through the myocardium. This technique has depicted regional perfusion deficits in the basal state or in the vasodilated states induced by vasodilators. Recent studies have also disclosed the feasibility of using MR techniques for displaying the morphology of the major coronary arteries and for measuring blood flow velocity in the coronary arteries and coronary bypass grafts. Thus, MRI has the capability for evaluation of morphology and flow in the coronary arteries and for assessment of function and perfusion of the myocardium.     

Optimization of the measuring conditions for thermal analysis of casting powders and evaluation of the results by means of factor analysis

Thermal analysis is a very powerful method for investigation and characterization of casting powders. The results depend on the measuring conditions to a high degree. That was the reason for the systematic optimization of the measuring conditions of differential thermal analysis and thermogravimetry (DTA/TG) which were used for this study. Especially the temperature program was developed carefully. The factor analysis of the results gives information about the variables which influence the thermal properties of the powders. Factor analysis was also used for cluster formation and identification of casting powders.     

Partial scan and symbolic test at the register-transfer level

This paper presents a partial scan methodology suited for (pipelined) data paths described at the Register-Transfer level. The method is based on feedback elimination by making existing registers scannable or by adding extra transparent scan registers An optimal set (in terms of area cost) of scan registers is selected using an exact branch and bound algorithm. This approach can deal with complex realistic data paths requiring orders of magnitude lower CPU times than gate devel techniques. Furthermore, our symbolic test pattern generation technique can very effectively deal with the delay in the remaining acyclic sequential circuit parts. This symbolic test method makes various scan schemes possible which ensure a correct assembly and application of the test vectors. They are discussed and compared in terms of hardware requirements, test application times and test accuracy.     

OUTLIER DIAGNOSTICS IN TIME SERIES ANALYSIS

Abstract. Cook's likelihood displacement is a convenient measure of the impact of a model perturbation on parameter estimates. A commonly used model perturbation in regression is the deletion of a case , or equation. A natural model perturbation in the time series context is the deletion of an observation , or a group of observations. Diagnostics that measure the impact of individual observations on the time series estimates are explored in this paper. A diagnostic that compares the estimates of the innovation variance with and without a particular observation is studied in detail.     

Theory of high temperature intercrystalline fracture under static or fatigue loads,with or without irradiation damage

Hull and Rimmer’s theory of high temperature creep fracture by grain boundary void growth and Skelton’s theory of high temperature fatigue fracture have been extended. The present theory includes the effect on void growth of volume diffusion and of vacancy generation by irradiation damage or plastic deformation within the grain interiors. The growth rate of cylindrical as well as spherical voids is calculated. We find that the presence of volume diffusion or of vacancy generation within the grain does not increase very much the growth rate of spherical voids but under certain conditions the growth rate of cylindrical voids is increased markedly. Unlike Skelton, we find that vacancy production within the grains does not decrease the critical radius for the growth of a grain boundary void in push-pull fatigue. (Likewise intra-granular vacancy production does not decrease the critical radius of grain boundary voids in creep.) Since in push-pull fatigue void growth is observed in the case of radii smaller than the critical value it is concluded that the stress concentrations that are produced by grain boundary sliding (according to the theory of Raj, Ashby, and Gifkins) are responsible for this growth. Whether voids aided by stress concentrations can continue to grow beyond a certain size depends critically upon the “roughness” of the grain boundary. It is strongly recommended that grain boundary internal friction peak studies be carried out in connection with void growth and high temperature fracture experiments. In particular, grain boundary voids are more likely to grow in push-pull fatigue (or in creep) if the value of the grain boundary sliding activation energy is close to that of volume self diffusion rather than if the sliding activation energy is close to the grain boundary self diffusion activation energy.     

Preparation of Barium Titanates from Oxalates

The decomposition of mixed barium titanium oxalates was studied by means of various thermochemical as well as spectroscopic methods. Infrared (IR) spectra of the mixed oxalates indicate the existence of an octahedral complex with Ti chelated by oxalate groups. In general, the results of both IR and the thermochemical analyses suggest that the oxalates are first converted to unidentate carbonate, then to ionic carbonate, and finally to mixed oxides of perovskite structure. The decomposition processes were found to depend upon the atmosphere. In the presence of oxygen the stoichiometrically mixed oxalates decompose by forming TiO₂ and BaCO₃ as intermediates. Under vacuum, two routes of decomposition occur in parallel. In one route, TiO₂ and BaCO₃ are formed as intermediates; in the other, partially reduced TiO_x(x < 2) is formed, which further reacts with BaCO₃ to produce also BaTiO₃, CO₂ and CO.     

Thin turbomachinery blade design using a finite-volume method

A numerical method is presented for the design of thin turbomachinery blades with specified whirl velocities across the blade span. The numerical scheme involves iteration between the directs solution of a finite-volume method developed earlier on by Soulis¹ and a design solution. The finite-volume method, which is a combination of finite elements and finite differences, solves the three-dimensional, inviscid, steady arid potential flow through turbomachinery blade rows in the incompressible, compressible and transonic flow range. In the design step, the whirl velocity distribution is specified across the blade span (Dirichlet boundary condition). The design procedure yields a new set of co-ordinates for the blade geometry which are used in the next iteration of the direct solution. However, in the present analysis only thin turbomachinery blades are designed, although a fully three-dimensional numerical method is used (the whirl velocity components of the flow field are averaged over the blade suction and pressure surface). The numerical method has been used to design free-vortex thin turbomachinery blades. Results show that the new numerical procedure is a comparatively economic and reliable method for designing thin turbomachinery blades. It may form the baseline for complete three-dimensional turbomachinery blade designs.