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We present results of a Monte Carlo simulation of the time evolution of the ordering process in an f.c.c. A 3 B alloy, which undergoes the order-disorder phase transition. In our model system, nearest neighbor interactions are assumed to favor pair formation of A and B atoms. A and B atoms are initially arranged randomly on the f.c.c. lattice sites, then the system is quenched to and to be evolved at a finite temperature T . Exchanges of position of atoms are allowed between nearest neighboring atoms with the Markovian transition probability.The time variations of the distribution function of cluster size and the average value of cluster size are obtained. These are compared with the results obtained from X-ray diffraction studies. Near the transition temperature, the relaxation time for the number of ordered cells shows a kind of slowing down behavior.

The number of patients due to ischemic heart disease seems to be growing rapidly in Japan. Coronary angiography by Judkins' or Soncs' method is very invasive as is well known and thus imposes a burden on patients and physicians. The K-edge subtraction technique is considered to be applicable to intravenous angiography of coronary arteries. A feasibility study of K-edge subtraction with monochromatized SR has been initiated at Photon Factory since 1984. In 1985, a real time observation of intravenous angiography of a cat, utilizing a monochromatic beam with a size of 64 mm by 55 mm, was performed. This paper describes some results of our preliminary experiments and our future systems of clinical application.

This paper describes an x‐ray K‐edge subtraction television system for noninvasive angiography utilizing synchrotron radiation. The phantom, including contrast material (iodine), is irradiated by monochromatized dual‐energy x‐ray flux, alternately, using a high speed monochromator. The monochromator consists of a silicon crystal plate vibrating at 15 Hz so that the phantom is irradiated by the x‐ray flux of 150 eV above and below the K‐edge photon energy of iodine, 15 times per second. As an x‐ray detector, TV cameras optically coupled to an x‐ray image intensifier are used and the video signal is processed to display the subtraction image of pairs of successive images in real time. This system was fully implemented and moving phantoms were examined. Both the time interval between the energy change and the exposure time of each image has been shortened to 2 ms.

The transitional process in the Cu 3 Au alloy from the disordered to the ordered state and the relaxation process in the phase change in Cu 3 Au have been investigated by measuring the time dependence of the X-ray superstructure line width and the electrical resistivity. The process is realized by a rapid change of the sample temperature in comparison with the relaxation time of this process. The average cluster size increases in proportion to t 1/2 irrespective of the ageing temperature. This is compared with the theoretical result of Kawasaki et al. The change of the distribution function of the size of the ordered clusters is obtained from the superstructure line shape. We observe two kinds of relaxation times τ D→0 and τ 0→D . τ D→0 from the disordered to the ordered state is comparatively long and shows a kind of the showing down phenomenon. In contrast to this, τ 0→D from the ordered to the disordered state does not show such slowing down near T t . By assuming an appropriate model, this relaxation ...

We observed the ESR signal of Cr 3+ ions in triglycine-sulphate. It is found that a pair of lines gradually approach to each other with increasing temperature in the ferroelectric phase and converge at the Curie temperature. The results are interpreted by using the concept of motional narrowing on the basis of the model of order-disorder type. The linewidth for the applied magnetic field nearly parallel to the principal axis z shows an anomalous increase near the Curie temperature. The critical exponent of the linewidth in the ferroelectric region is determined to be 0.5 in the vicinity of the Curie temperature and to be 2.0 far from the Curie temperature.

The aim of this study is to visualize the coronary artery with the intravenus injection of contrast media. We propose a method of rapid and successive acquisition of two‐dimensional images in a digital processing system which uses a pair of video cameras, a shutter operation, and a beam‐splitting apparatus. A prototype of the high‐speed acquisition system was constructed. The two‐monochromatic video‐camera method was very suitable for quick acquisition. Electro‐optical shutters (PLZT) were found practical with respect to the dynamic range and response time. The field blanking method was essential for the data acquisition.

The behavior of carriers trapped around doped Ti ions in VO 2 is investigated by means of the electron spin resonance in a temperature range between liquid nitrogen and room temperature. The line shapes are examined for different concentration of Ti. At lower concentration well resolved hyperfine lines are observed and a broad background line is superposed to them. With increasing impurity concentration, however, the single broad line grows up and the hfs lines diminish. At higher concentration only a single broad line of the Lorentz type is observed. The temperature dependences of the linewidth and the intensity for the hfs and broad lines are measured. The width of the broad line which does not vary at low temperature starts to increase at a temperature above which the intensity deviates from the Curie law. The motion of carriers localized around Ti impurity centers is discussed from these results.

In order to investigate the spin relaxation mechanism in Ti-doped VO 2 in relation to the itineracy of electrons associated with Ti impurities substituted for V 4+ , the linewidth and line intensity of ESR absorption at 24 GHz have been measured on samples doped with various concentrations of Ti in a temperature range between 4.2 and 250 K. The spectrum with h f s lines is observed at low concentration of Ti, while a single narrowed line of absorption is found at higher concentration. The temperature dependence of linewidth and line intensity of this single absorption line are discussed with respect to the staying time of electrons in the impurity state and their motions between impurity centers. The hopping frequency of electrons and the staying time in the impurity state are determined.

The d c and 24 GHz conductivities of VO 2 containing various amounts of Ti have been measured below the semiconductor-to-metal transition point. Above 290 K the activation energy for d c conductivity is not affected by the small amounts of Ti impurity and the 24 GHz conductivity coincides with the d c conductivity. The pronounced frequency dispersion of conductivity is observed at low temperature, where the impurity conduction arises from hopping motion of electrons between impurity sites. The 24 GHz conductivity can be explained as a function of temperature by the formula expressing the dielectric loss due to the hopping diffusion of electrons between pair centers given by Pollak.

The ordering process in the Cu3Au alloy from the disordered state is examined experimentally. The time evolution of the cluster size is observed by measuring the X-ray superstructure line width at several temperatures. It is found that the cluster size grows very slowly in the early stage, and then increases more rapidly in obedience to the t 1 2 law which is apparently explained by the theory of Kawasaki et al.

We examined conformation and dynamics of a variety of fibrous and membrane proteins by means of the conformation-dependent displacements of 13C nuclear magnetic resonance (NMR) chemical shifts and their relaxation parameters, respectively, as recorded by high-resolution solid-state 13C NMR. Determination of three-dimensional structure of atomic resolution is also briefly described for a simple peptide on the basis of precise measurements of interatomic distances.

Ischemic heart disease is one of the most popular and lethal diseases for aged peoples in the world, and is usually diagnosed by transarterial selective coronary arteriography. However, it is rather invasive and somewhat dangerous, so that the selective coronary arteriography is not feasible for prospective screening of coronary occlusive heart disease. Conventional digital subtraction angiography (DSA) is widely known as a relatively noninvasive and useful technique is making a diagnosis of arterial occlusive disease, especially in making the diagnosis of ischemic heart disease. Conventional intravenous subtraction angiography by temporal subtraction, however, has several problems when applying to the moving objects. Digital subtraction method using high‐speed switching above and below the K edge could be the ideal approach to this solution. We intend to make a synchrotron radiation digital K‐edge subtraction angiography in the above policy, and to apply it to the human coronary ischemic disease on an ou...

A heating apparatus for hyperthermia therapy using 800 kHz focused ultrasound was developed in order to heat the well defined deep region. The ultrasound was generated from four spherical bowl transducers, the center axes of which are crossed at one point. The heating patterns were measured in phantom and rabbit muscle in vivo. Computer programs were also developed with which the ultrasonic fields in the medium with attenuation could be calculated. The parameter dependences of the intensity distribution were studied.

An X-ray K-edge subtraction television system utilizing synchrotron radiation is investigated. The phantom is irradiated by two monochromatized X-ray beams closely bracketing the K-absorption edge of iodine (33.17 keV) alternately, by means of a vibrating single crystal monochromator combined with a white synchrotron X-ray beam. The subtraction of the successive two images produced by these beams results in images that enhance signals arising from attenuation by iodine and suppresses signals by other materials. The prototype system is fully implemented using two kinds of real time image processing subsystems. The results are compared with those obtained by the conventional (nonreal time) processing system.