[en] A new non-invasive method for investigating total coronary blood supply is presented. This method is based on the principle of indicator dilution of a radio-nuclide bolus (⁹⁹Tc), requiring a scintillation camera with high sensitivity and high picture resolution. The first findings obtained from 83 patients are shown. With 4.61+-1.19% of cardiac output the mean values of the rates of coronary perfusion obtained at rest in subjects with a normal heart differed significantly from those obtained for patients with certain coronary occlusions (8.18+-3.99% of cardiac output) and from those obtained for hypertensive patients (Stages I-III). Double examinations carried out on 20 patients yielded an adequate reproducibility. The main deviation of the double examinations from one another was 16%. (orig.)

[en] High power microwave systems operating in vacuum or near vacuum run the risk of multipactor breakdown. In order to avoid multipactor, it is necessary to make theoretical predictions of critical parameter combinations. These treatments are generally based on the assumption of electrons moving in resonance with the electric field while traversing the gap between critical surfaces. Through comparison with experiments, it has been found that only for small system dimensions will the resonant approach give correct predictions. Apparently, the resonance is destroyed due to the statistical spread in electron emission velocity, and for a more valid description it is necessary to resort to rather complicated statistical treatments of the electron population, and extensive simulations. However, in the limit where resonance is completely destroyed it is possible to use a much simpler treatment, here called non-resonant theory. In this paper, we develop the formalism for this theory, use it to calculate universal curves for the existence of multipactor, and compare with previous results. Two important effects that leads to an increase in the multipactor threshold in comparison with the resonant prediction are identified. These are the statistical spread of impact speed, which leads to a lower average electron impact speed, and the impact of electrons in phase regions where the secondary electrons are immediately reabsorbed, leading to an effective removal of electrons from the discharge.

No abstract available

[en] A theoretical investigation is made of the effect of finite pulse length on the multipactor breakdown condition for microwave signals. The analysis considers the case of multipactor between two parallel metallic plates, using the classical resonance theory. It is found that decreasing pulse length tends to successively eliminate higher order resonance zones and lead to a ‘pulse hardening’ of lower order modes where the multipactor-prone resonance zones shrink and the lower boundary breakdown field of the zones smoothly increases as the pulse becomes shorter, eventually to completely eliminate the multipactor effect for sufficiently short pulses. (paper)

[en] The products of 99m-TcO₄^- reaction with dmpe 2 HCl were investigated at different reaction conditions. Four compounds, TcCl₂dmpe₂⁺ (II), Tc0₂dmpe₂⁺ (III), Tcdmpe₃⁺⁺ (IV) and a neutral or weakly cationic species were identified. II, III, and IV accumulate in the rat myocardium but also in different glands and in the periosteum of the bones. Only II is rapidly cleared from the blood. 150 min p.i. a good delineation of the pig heart was obtained with clear-cut separation of the myocardium and the blood pool. (Author)

No abstract available

[en] An analysis is made of the basic physical conditions under which a small local microwave-induced breakdown region in a gas may develop to extended 'global' breakdown. The analysis describes the different nonlinear stages of the microwave breakdown process. In the first stage, the increasing breakdown plasma density suppresses the electric field in the breakdown region to reach a quasi-stationary state with constant electron density. The subsequent heating of the gas due to absorption of microwave power in the breakdown plasma is then analysed and the corresponding steady state for the thermal evolution is found including the temperature dependence of the breakdown electric field. The stability properties of the stationary state are examined and it is found that there exists a critical (unstable) radius of the initial breakdown plasma region such that initial regions smaller than this critical dimension will shrink to ultimately vanish whereas plasma regions larger than the critical dimension will grow indefinitely and transform the local breakdown region into full scale 'global' breakdown. The practical implication of this model is to give an order of magnitude estimate for the critical size of hot spots, regions of enhanced field and intensified heating in rf systems.

[en] Within the last two years a number of highly refined measurements have been performed on H targets which have yielded accurate absolute data for a range of energies and geometries and it would appear that the experimental situation for this, the simplest of atomic targets is now resolved. The theoretical situation is however far from satisfactory and in this paper we will analysis some of the main approaches and characterize their strengths and their weaknesses. We have developed a numerical method which allows us to evaluate triple differential cross sections (TDCS) using the most complex position dependent analytic ansatz wave function and we will present results, using this for low energy (e,2e) processes. We will see that this approach fails when incident channel effects, such as target polarization are likely to be strong

[en] A simplified analytical model is developed to predict the spectrum of electric current induced by the multipacting electrons between two parallel electrodes exposed to an rf voltage of fixed amplitude. The model is based on the resonant multipactor theory and makes it possible to calculate the relative spectral amplitudes of electric current at different harmonics and sub-harmonics of the applied rf frequency. The theoretical predictions are confirmed by numerical simulations of multipactor inside a rectangular waveguide. Specifically it is seen that the relative height of the spectral peaks decreases with increasing gap height. (paper)

[en] The main physical properties of gas breakdown in inhomogeneous high frequency microwave electric fields are investigated using both analytical and numerical analysis. In particular, the interplay between diffusion and attachment in redistributing electrons from high field regions to low field regions and the concomitant effect on the breakdown threshold is studied using three different examples of ionization profiles. The results give a clear physical picture of the dependence of breakdown electric field on pressure showing a high pressure branch determined by conditions in the high field region, a low pressure branch determined by the properties of the low field region only, and a more or less smooth transition region for intermediate pressures. Simple estimates for the extension of the transition region are given in good agreement with the numerical simulations, and a comparison of the theoretical breakdown threshold with previous experimental results also shows good agreement.