Kazuyuki Demachi

Tumor growth suppression by gadolinium-neutron capture therapy using gadolinium-entrapped liposome as gadolinium delivery agent

Neutron capture therapy (NCT) is a promising non-invasive cancer therapy approach and some recent NCT research has focused on using compounds containing gadolinium as an alternative to currently used boron-10 considering several advantages that gadolinium offers compared to those of boron. In this study, we evaluated gadolinium-entrapped liposome compound as neutron capture therapy agent by in vivo experiment on colon-26 tumor-bearing mice. Gadolinium compound were injected intravenously via tail vein and allowed to accumulate into tumor site. Tumor samples were taken for quantitative analysis by ICP-MS at 2, 12, and 24 h after gadolinium compound injection. Highest gadolinium concentration was observed at about 2 h after gadolinium compound injection with an average of 40.3 μg/g of wet tumor tissue. We performed neutron irradiation at JRR-4 reactor facility of Japan Atomic Energy Research Institute in Tokaimura with average neutron fluence of 2×10¹² n/cm². The experimental results showed that the tumor growth suppression of gadolinium-injected irradiated group was revealed until about four times higher compared to the control group, and no significant weight loss were observed after treatment suggesting low systemic toxicity of this compound. The gadolinium-entrapped liposome will become one of the candidates for Gd delivery system on NCT.

A study on the relaxation of levitation property in an HTSC magnetic bearing

Abstract For realization of the flywheel system using high T c superconductors (HTSCs), AC loss is one of the serious problems to be solved. An un-uniformity of magnetization of permanent magnets rotating at high speed generates AC field around HTSC. This causes AC losses. In this study we assumed that AC field generated by a rotating permanent magnet is equivalent to AC field generated by coil current. Based on this model the experiments were done. These results were compared with those of numerical simulation. Furthermore, to suppress AC loss, a pre-loading method was suggested.

Numerical and experimental analysis of the rotation speed degradation of superconducting magnetic bearings

The suppression of the rotation speed degradation of the Superconducting Magnetic Bearing (SMB) with the Permanent Magnet (PM) rotor including the layered insulator thin films is studied. The SMB system consists of the superconductor stator and the PM rotor, and is a no-contact bearing system using the levitation force between them. The SMB was expected to be applied to the electric power storage flywheel system because friction causes the rotation speed degradation and decreases the energy storage capability. However, it was found that the electromagnetic friction of the SMB was not zero, due to electromagnetic forces; 1) the magnetic force interaction between the inhomogeneous magnetic field of the PM rotor and the eddy current it induces in the cryostat, 2) the magnetic force between the inhomogeneous magnetic field of the PM rotor and the shielding current it induces in the superconductor, 3) the magnetic force between the magnetic field of superconductors yielding the levitation force and the eddy current induced in the PM rotor. This magnetic field of superconductor is inhomogeneous too, because the superconductors consist of several HTSC bulks. In this research, it was found that the 3rd phenomenon is most significant. So, we use the advanced PM rotor including the layered insulator thin films to suppress its eddy current and the degradation of the rotation speed. Using our SMB equipment, the rotation speed degradation was measured using the PM rotors with/without the insulator thin films and the electromagnetic frictions were compared to each other.

Numerical evaluation of rotational speed degradation in the superconducting magnetic bearing for various superconducting bulk shapes

In constructing the 100 kWh flywheel energy storage systems, the performance of the Superconducting Magnet Bearing (SMB) needs to be calculated to get better technical and practical results. The SMB system mainly consists of the Superconducting (SC) stator and the Permanent Magnet (PM) rotor. The SMB has the advantage that the rotational dragging force between the PM rotor and the SC stator is greatly smaller compared with the usual bearing systems. However, the magnetic friction becomes large enough to cause significant rotational speed degradation. The rotational speed degradation, which cuts down the stored energy, occurring in the PM rotors is one of the most significant problems for the practical use of the SMBs. It is caused mainly by the Lorentz force due to the inhomogeneous magnetic field of the SC stator and the induced eddy current in the PM rotor. In this study, we tried up various shapes of the SC stator to smooth the magnetic field and decrease the energy loss and then evaluated the levitation force, the magnetic field of the SC stator and the energy loss.

Study of magnetic damping effect on dynamic deflection of fusion reactor first wall

Abstract Magnetoelastically coupled vibration of the fusion reactor first wall was investigated in light of the magnetic damping effect. A law of similarity for the coupled vibration is proposed by non-dimensionalizing a set of equations describing the coupled problem between the elastic vibration and the eddy current field. The law was verified through numerical experiments. In addition, the dynamic behavior of the ITER first wall during plasma disruption was simulated, taking into account the magnetic damping effect. It was found that the dynamic stress is overestimated by neglecting the magnetic damping. This effect significantly reduces the dynamic stress in the case of a thin first wall, so that the flexible thin shell structure is found to be applicable to fusion reactor components.

Phase gradient imaging for positive contrast generation to superparamagnetic iron oxide nanoparticle-labeled targets in magnetic resonance imaging

Positive contrast imaging methods produce enhanced signal at large magnetic field gradient in magnetic resonance imaging. Several postprocessing algorithms, such as susceptibility gradient mapping and phase gradient mapping methods, have been applied for positive contrast generation to detect the cells targeted by superparamagnetic iron oxide nanoparticles. In the phase gradient mapping methods, smoothness condition has to be satisfied to keep the phase gradient unwrapped. Moreover, there has been no discussion about the truncation artifact associated with the algorithm of differentiation that is performed in k-space by the multiplication with frequency value. In this work, phase gradient methods are discussed by considering the wrapping problem when the smoothness condition is not satisfied. A region-growing unwrapping algorithm is used in the phase gradient image to solve the problem. In order to reduce the truncation artifact, a cosine function is multiplied in the k-space to eliminate the abrupt change at the boundaries. Simulation, phantom and in vivo experimental results demonstrate that the modified phase gradient mapping methods may produce improved positive contrast effects by reducing truncation or wrapping artifacts.

Numerical simulation of coupled problem of electromagnetic field and heat conduction in superconducting magnetic bearing

Abstract The superconducting magnetic bearing (SMB) system consists of the HTSC stator and the PM rotor, and is a no-contact bearing system using the levitation force between them. The SMB was expected to be applied to the electric power storage flywheel system because no friction causes the rotation speed degradation and decreases the energy storage capability. However, it was found that the electromagnetic friction of the SMB was not zero, due to electromagnetic forces; (1) the magnetic force interaction between the inhomogeneous magnetic field of the PM rotor and the eddy current it induces in the cryostat, (2) the magnetic force between the inhomogeneous magnetic field of the PM rotor and the shielding current it induces in the superconductor, (3) the magnetic force between the magnetic field of superconductors yielding the levitation force and the eddy current induced in the PM rotor. The magnetic field of superconductor is inhomogeneous too, because the superconductors consist of several HTSC bulks. We improved the PM rotor and succeed in suppressing the rotation speed degradation by inhomogeneous magnetic field of HTSC bulks by preventing the eddy current with many insulator thin films in the PM rotor [Trans. Supercond. (in press)]. On the other hand, the rotation speed degradation by inhomogeneous magnetic field of the PM rotor have not been able to be removed. The induced eddy currents generate temperature rise with Joule heat in HTSC bulks. Therefore we are able to estimate the rotation speed degradation by evaluating the temperature rise. Furthermore temperature rise can cause inhomogeneous magnetic field because physical properties is varied by it. The purpose of this research is to develop the electromagnetic field analysis method coupled with thermal analysis.

Cracks measurement using fiber-phased array laser ultrasound generation

A phased array laser ultrasound generation system by using fiber optic delivery and a custom-designed focusing objective lens has been developed for crack inspection. The enhancement of crack tip diffraction by using phased array laser ultrasound is simulated with finite element method and validated by experiment. A non-contact and non-destructive measurement of inner-surface cracks by time-of-flight diffraction method using fiber-phased array laser ultrasound generation and electromagnetic acoustic transducer detection has been studied.

Experimental and numerical evaluation of rotation speed degradation of radial type superconducting magnetic bearing

The degradation of levitation force and rotation speed is one of the most significant problems for the practical use of superconducting magnetic bearing (SMB) for flywheel energy storage system. The degradation are called the rotation losses caused by the AC magnetic field due to the inhomogeneous distribution of magnetic flux density of the permanent magnet (PM) rotor. In this research, our simulation method was improved so that the eddy current flowing in the cryostat around the superconductor was taken into account. The dependency of the rotation losses of radial type SMB with cryostat was evaluated by this new simulation method concerning the amplitude of inhomogeneous component of PM rotors field.

Neural network for inverse mapping in eddy current testing

A neural network mapping approach has been proposed for the inversion problem in eddy-current testing (ECT). The use of a principal component analysis (PCA) data transformation step, a data fragmentation technique, jittering, and of a data fusion approach proved to be instrumental auxiliary tools that support the basic training algorithm in coping with the strong ill-posedness of the inversion problem. The present paper reports on the further improvements brought by a new, randomly generated database used for the training set, proposed for the reconstruction of crack shape and conductivity distribution. Good results were obtained for four levels of conductivity and nonconnected crack shapes even in the presence of high noise levels.