[en] The counting efficiency and detection limit of an in vivo thyroid ¹³¹I monitoring system using an imaging plate (IP) was estimated using an anthropomorphic thyroid neck phantom. The counting efficiency of the IP system was approximately constant for thyroid volumes between 11.7 and 20 ml and neck diameters between 10 and 14 cm. The detection limits were distributed from 288 to 451 Bq depending on the combination of neck diameter, thyroid volume and tissue thickness. The IP monitoring system gives a reliable counting efficiency notwithstanding the variation of thyroid volume and neck diameter. The IP system is a new option for thyroid ¹³¹I monitoring. (author)

[en] Waves in shear flows exhibit highly complicated behavior in both space and time, which appears transient and asymptotically grows or decays with algebraic power of time. The decomposition into eigenmodes is generally difficult due to the presence of the continuous spectrum and the nonorthogonal property of eigenmodes of non-Hermitian operators. In particular, the degeneracy of some spectra into the continuous spectrum requires mathematically nontrivial consideration. Although one can expect the resonant interaction among the eigenmodes, the spectral resolution of the continuous spectrum is not yet understood for general non-Hermitian operators. In this talk, we introduce a basic model which mathematically represents the degeneracy of point (i.e. discrete) and continuous spectra. This situation occurs in various hydrodynamic and magnetohydrodynamic waves. In fluid mechanics, vorticity fluctuations convected by shear flow embody a continuous spectrum, which transforms into the Doppler-shifted Alfven continuous spectrum in the case of plasmas. The acoustic waves and the (subcritical) Kelvin- Helmholtz and interchange modes play the role of point spectra that are possible to be degenerated into the continuous spectrum. The solution of our model indicates that there are some varieties of such wave-wave interaction. Depending on the structure of the non- Hermitican operator, the wave corresponding to the point spectrum exhibits any one of (a) exponential growth, (b) the Landau damping and (c) algebraic growth and saturation. Another possibility is (d) algebraic growth of a local mode corresponding to the continuous spectrum. It is interesting to observe these phenomena in terms of the wave energy. As in the case with many Hamiltonian systems, the exponential growth occurs if the sign of the wave energy for the point spectrum is opposite to that for the continuous spectrum. The same sign leads to the Landau damping. The case (d) occurs if the continuous spectrum has 'zero' energy. The case (c) is attributed to the noncanonical property of our Hamiltonian system. (author)

[en] An imaging plate (IP) system was applied to in vivo thyroid radioactive iodine 131 (¹³¹I) monitoring. Thyroid contamination by ¹³¹I occurs when medical staffs and patient's families take in ¹³¹I used as treatment agent for thyroid cancer and hyperthyroidism in nuclear medicine, inhabitants take in ¹³¹I released into environment by an accident of nuclear facilities, or worker take in ¹³¹I used by experiment of research. The IP system is a two-dimensional integrating radiation detector which is a plate thinly coated plastic sheet with a kind of phosphore. The IP was exposed to a neck-thyroid phantom loaded ¹³¹I aqueous solution. The IP system displayed a thyroid image that reflects a unique shape characteristic of the thyroid gland. A ¹³¹I thyroid imaging allows visual confirmation of thyroid contamination by ¹³¹I. The counting efficiency was approximately constant when neck diameter, thyroid volume and prethyroid tissue thickness varied within the normal adult. The detection limit of 450Bq was about 1/65 of the screening level of 30kBq. The IP system is applicable for thyroid ¹³¹I monitoring

[en] A preparation method has been developed for thin foils for transmission electron microscopy (TEM) from powdered intermetallic compounds as a result of hydrogenation, in which powder samples are embedded in a Ni plate formed by electroless plating and then the assembly consisting of the Ni plate and the embedded powder samples are ion-milled. This method is successfully applied to some typical hydrogen-absorbing intermetallic compounds such as LaNi₅, FeTi and TiMn₂. In this method, Ni plating is carried out at ambient temperature, at which possible rearrangement of lattice defects that are introduced during hydrogenation is minimized and areas thin and wide enough for TEM observations are successfully produced because of the small difference in the sputtering yield between the Ni plate and these intermetallics. For thin foils produced by this method, not only lattice defects such as dislocations introduced into the bulk of powder samples can be characterized but also the crystallography of cracking and surface layers of powder samples can be characterized

[en] Comparison of postoperative QOL was made between 42 patients who underwent breast-preserving surgery followed by irradiation and TAM administration (BPT group) and 35 patients who underwent mastectomy without adjuvant therapy (MST group). The results of this comparison showed that, although there was a slight elevation in QOL in the BPT group in terms of the level of disappointment, due to the economic burden of postoperative adjuvant therapy and to functional disorder arising from the synergistic effects of axillary lymph node dissection and irradiation, to the residual breast the QOL in the BPT group was inferior to that in the MST group. In view of these results, in order to improve the postoperative QOL in the BPT group, it is considered necessary to reduce postoperative adjuvant therapy and to eliminate postoperative irradiation and axillalry lymph node dissection. (author)

[en] Energy of waves (or eigenmodes) in an ideal fluid and plasma is formulated in the noncanonical Hamiltonian context. By imposing the kinematical constraint on perturbations, the linearized Hamiltonian equation provides a formal definition of wave energy not only for eigenmodes corresponding to point spectra but also for singular ones corresponding to a continuous spectrum. The latter becomes dominant when mean fields have inhomogeneity originating from shear or gradient of the fields. The energy of each wave is represented by the eigenfrequency multiplied by the wave action, which is nothing but the action variable and, moreover, is associated with a derivative of a suitably defined dispersion relation. The sign of the action variable is crucial to the occurrence of Hopf bifurcation in Hamiltonian systems of finite degrees of freedom [M. G. Krein, Dokl. Akad. Nauk SSSR, Ser. A 73, 445 (1950)]. Krein's idea is extended to the case of coalescence between point and continuous spectra

[en] Stabilization/destabilization of magnetohydrodynamic (MHD) waves are formulated in terms of wave energy, where the waves are subject to Alfven and sound resonances and also influenced by small resistivity at conductive wall. Negative energy wave, which may exist in the presence of mean flow, is shown to be destabilized by the resistive wall, where its growth rate is characterized by the energy dissipation rate. The effect of resonance is examined as well based on a recent knowledge of wave energy for Alfven and sound continuum modes. Resonant coupling between an eigenmode and a continuum mode having the same sign of energy results in phase mixing (or continuum) damping. In contrast, if their signs are opposite, such resonance triggers an instability. (magnetically confined plasma)

[en] Nonlinear mode coupling of the (shear) Alfven eigenmodes (AEs) is studied both analytically and numerically to understand the effect of the magnetohydrodynamic nonlinearity on the saturation mechanism. The energy transfer via the mode coupling can restrict the amplitude to a level that is estimated by the frequency mismatch and the coupling coefficient among the coupled modes. For the cases of cylindrical and toroidal geometries, new numerical codes are developed to calculate the coupling coefficient directly according to the Lagrangian theory of weakly nonlinear perturbations. It is shown that the shear AEs can couple with each other through the small compressional components of their eigenfunctions. By assuming low-β plasma, an analytic estimation of the coupling coefficient (∝√(β)) is derived in the cylindrical case. A coupling of reversed shear AEs in toroidal geometry indicates a more effective energy transfer at a lower amplitude level owing to the enhanced compressional perturbations in the poloidal sidebands.

[en] Hamiltonian aspects of linear waves in plasmas are generally reviewed and discussed. Action-angle representation of linear waves is a fundamental problem, but it requires a careful mathematical consideration in the presence of continuum mode (continuous spectrum). We introduce a novel spectral technique that can treat continuous spectrum as well as discrete spectrum in a unified manner. Our method facilitates the derivation of action-angle variables, which is demonstrated for the Van Kampen mode in electrostatic plasma.

[en] Full text: Three-mode coupling due to magnetohydrodynamic (MHD) nonlinearity is studied for the understanding of saturation mechanism of the toroidal Alfven eigenmode (TAE) that is destabilized by energetic particles. An analytic expression of the coupling coefficient among ideal MHD eigenmodes is derived in a general manner, which quantifies the effectiveness of the nonlinear mode coupling (i.e., the parametric decay). This formulation for the first time enables the analysis of the global mode coupling in real geometry. The well-known equation of the displacement vector field in linear MHD theory is rigorously extended to nonlinear regime by taking the Lagrangian approach. The coupling coefficient is written in terms of the linear displacement vector fields, so that it can be directly and systematically evaluated by utilizing the existing linear stability code. (author)