Action current of the heart muscle produces electric field on the body surface and also weak magnetic field around the thorax. Magnetocardiogram (MCG) is a record of this magnetic field by means of a very sensitive magnetometer. We usually record MCG at 36 points of the anterior chest wall by means of a SQUID with the transducer coil for the second gradient of the magnetic field. Electrocardiography has been used widely for the diagnosis of the cardiovascular diseases, but its limitations have also been known. MCG can not be expected to provide different kinds of informations from ECG, because both methods handle such informations related to the electromotive forces of the heart. But there may be some possibility that the MCG can give some diagnostic informations which can not be detected by ECG, because the magnetism is somewhat different from electricity in physical properties. For example diagnostic sensitivity of the right atrial overloading is 13.6% in ECG and 56.6% in MCG, showing higher diagnostic ability of MCG. As for the diagnosis of the right ventricular hypertrophy, diagnostic sensitivity is 31.3% in ECG and 73.3% in MCG, also showing the higher sensitivity in the latter than the former. Sensitivity for the diagnosis of the myocardial damage (abnormal ventricular repolarization) in hypertensive subjects was 20.0% in ECG and 42.5% in MCG. Sensitivity is especially higher in MCG in slight to moderate cases of hypertension. Multiple dipoles were detected in 7.5% in isopotential map and 27.5% in isomagnetic map at the peak of the T wave in lead II of the standard leads. The reason of the higher sensitivity of MCG for the diagnosis of the abnormal ventricular repolarization is thought to be due to the superiority of MCG in detecting multiple dipoles. At present, liquid helium is necessary to record MCG, and the multi-elements MCG system are not available with a reasonable price. It is expected that the MCG may become to be used widely in clinical medicine as a supplementary diagnostic method to the ECG, if these weak points are overcome.
Many projects starting in the 1960's, MHD and nuclear fusion projects, etc., demanded helium refrigerators with large capacity, high efficiency and excellent reliability. The rotating machine is essential to such systems. Since then, the rotating machines has been developed to realize large scale helium refrigerators. In this paper, the conception and the criterion design of rotating machines for the systems are described.
The MRI market has expanded rapidly in Europe and the US, leading to wide spread adoption of super-conducting magnets. Also in Japan the trends are changing from resistive to superconducting systems these days. In this paper we summarize the features and present status of superconducting magnets for MRI and make introduction of HiHo-rampable, Compact, and Active-shielded magnets. Finally, a few words are paid for the prospect of superconducting magnet for MRI in the near future.
A new method has been developed for numerical analysis of quench transients in cable-in-conduit (CIC) forced-flow cooled superconductors. In this method, the quench transients are separated into two time-domains, for which different models are introduced. The first model includes the thermal conduction of the conductor, the heat transfer and the supercritical helium flow, but in the second model two assumptions on the thermal conduction and the heat transfer are introduced so as to omit the calculation of the thermal conduction equation of the conductor. So as to verify the validity of the present method, the present method is compared with the ordinary method, which uses only the first model over all time-domains. Results show that the solution by the present method has almost the same accuracy as that by the ordinary method and that the computing time by the former method is very shorter than that by the latter method. As an application, the influence of the thermal disturbance location on quench transients has been investigated using the present method, and it has been made clear.
Mechanical properties of SUS 304L and 316L aged at 700°C;×75hr were investigated at the temperatures below the ambient temperature, especially at 4K. Cr rich carbides, M23C6, precipitated at grain boundaries and Cr depleted zones were formed during aging though both steels had low content of carbon. 4K tensile properties, notch strength, Charpy absorbed energy and fracture toughness of aged steels were all inferior to those of solutioned ones. Tensile properties showed the smallest degradation while fracture toughness showed the largest. It is evident that the grain boundary precipitation results in degradation of 4K mechanical properties. The degree of degradation corresponds to an extent of tri-axiality of stress which constrained plastic deformation.
The heat fluxes between two parallel plates with prescribed temperatures were compared for two configurations in terms of insulation performance. The first configuration: the plates are separated by a non-radiation-participating gas. The second: the plates contact the surfaces of a solid slab. A chart was prepared to provide designers with a selection criterion.