Katsuo Isaka

Childhood leukemia and magnetic fields in Japan: A case-control study of childhood leukemia and residential power-frequency magnetic fields in Japan

Residential power‐frequency magnetic fields (MFs) were labeled as a possible human carcinogen by the International Agency for Research on Cancer panel. In response to great public concern, the World Health Organization urged that further epidemiologic studies be conducted in high‐exposure areas such as Japan. We conducted a population‐based case‐control study, which covered areas inhabited by 54% of Japanese children. We analyzed 312 case children (0–15 years old) newly diagnosed with acute lymphoblastic leukemia (ALL) or acute myelocytic leukemia (AML) in 1999–2001 (2.3 years) and 603 controls matched for gender, age and residential area. Weekly mean MF level was determined for the childs bedroom. MF measurements in each set of a case and controls were carried out as closely in time as possible to control for seasonal variation. We evaluated the association using conditional logistic regression models. The odds ratios for children whose bedrooms had MF levels of 0.4 μT or higher compared with the reference category (MF levels below 0.1 μT) was 2.6 (95% CI = 0.76–8.6) for AML + ALL and 4.7 (1.15–19.0) for ALL only. Controlling for some possible confounding factors did not alter the results appreciably. Even an analysis in which selection bias was maximized did not fully explain the association. Most of the leukemia cases in the highest exposure category had MF levels far above 0.4 μT. Our results provided additional evidence that high MF exposure was associated with a higher risk of childhood leukemia, particularly of ALL.

Application of Finite Element Method to Analysis of Induced Current Densities Inside Human Model Exposed to 60-Hz Electric Field

The finite eleiment method(FEM) has been applied bt the analysis of the indiced current densities inside axisyrmtrical h. buman medels. It is assumed in the calculations that those models are made of a biological organism whose corndctivity and permittivity are on the sare order as those of humah body tissues. In the experiments, they are made of wood and insulating material covered with aluminium foil.The finite eleiment method(FEM) has been applied bt the analysis of the indiced current densities inside axisyrmtrical h. buman medels. It is assumed in the calculations that those models are made of a biological organism whose corndctivity and permittivity are on the sare order as those of humah body tissues. In the experiments, they are made of wood and insulating material covered with aluminium foil.

Analysis of 60 Hz magnetic fields near ground level in 187 kV switchyard of a 187/66 kV AC substation

To improve understanding of 60 Hz magnetic field characteristics in AC power substations, a numerical calculation of a 60 Hz magnetic field in the 187 kV switchyard of a 187/66 kV substation in service is conducted by using a simple analytical method. The magnetic field profiles near ground level are calculated for various current conditions, and described in terms of the contour maps of magnetic flux density. Effects of the line and bus current conditions, the bus phasing arrangement, and the line and bus geometrical configuration on the substation magnetic field profiles are also investigated. >

Development of real-time system for simultaneous observation of visual discharges and leakage current on contaminated DC insulators

A novel real-time observation system has been developed. It is capable of simultaneously recording visual partial discharge arcs and leakage currents on insulator surfaces under wet-contaminated conditions during a 2-h test. Since this system uses a video recording system uses a video recording system, the discharges and currents can be reproduced repeatedly even at a slowed-down speed. To permit simultaneous recording and accurate data processing of leakage currents, a personal computer is also employed. It was found that the sampling frequency of 1.0 kHz was satisfactory for the recording of the leakage current. Another function of the computer is to exhibit the contours of insulators to be tested in a dark room so that the locations where the arcs stay can be clearly identified. Tests by the clean fog procedure confirmed the good performance of the system at the time of the design. Some experimental results and the applicability of this system are discussed. >

Power-Frequency Magnetic Fields and Childhood Brain Tumors: A Case-Control Study in Japan

Background The strength of the association between brain tumors in children and residential power-frequency magnetic fields (MF) has varied in previous studies, which may be due in part to possible misclassification of MF exposure. This study aimed to examine this association in Japan by improving measurement techniques, and by extending measurement to a whole week. Methods This population-based case-control study encompassed 54% of Japanese children under 15 years of age. After excluding ineligible targeted children, 55 newly diagnosed brain tumor cases and 99 sex-, age-, and residential area-matched controls were included in the analyses. The MF exposures of each set of matching cases and controls were measured in close temporal proximity to control for seasonal variation; the average difference was 12.4 days. The mean interval between diagnosis and MF measurements was 1.1 years. The weekly mean MF level was defined as the exposure. The association was evaluated using conditional logistic regression analysis that controlled for possible confounding factors. Results The odds ratios (95% CI) for exposure categories of 0.1 to 0.2, 0.2 to 0.4, and above 0.4 µT, against a reference category of <0.1 µT, were 0.74 (0.17–3.18), 1.58 (0.25–9.83), and 10.9 (1.05–113), respectively, after adjusting for maternal education. This dose-response pattern was stable when other variables were included in the model as possible confounding factors. Conclusions A positive association was found between high-level exposure—above 0.4 µT—and the risk of brain tumors. This association could not be explained solely by confounding factors or selection bias.

Visualization of Contact Vibration generated on Turbine Model using Fast Haar Wavelet Transform

In this paper we present the results of fundamental study to introduce the in-place fast Haar wavelet transform to vibration diagnosis for a turbine and a generator. It is required to detect typical vibration of the turbine and the generator accurately. Modern power plants usually use one-high pressure and one or two lower pressure turbines. We made the turbine model with 3 rotors supported with journal bearings to simulate rotor-to-stator contact. The contact vibration was measured with displacement meters, acoustic emission sensors and accelerometers. The acceleration signals accompanied by the contact were visualized in the time-frequency domain by the in-place fast Haar wavelet transform. The in-place fast Haar wavelet transform can clearly detect the components accompanied by the contact

Discrimination of Vibration Phenomena on Model Turbine Rotor using In-Place Fast Haar Wavelet Transform

In this paper we present the results of applying the in-place fast Haar wavelet transform to visualization of vibration phenomena on a model turbine rotor. It is required to detect typical vibration of the turbine and the generator accurately. Modern power plants usually use one-high pressure and one or two lower pressure turbines. We made the model turbine with three rotors supported with journal bearings and simulated abnormal conditions. The vibrations accompanied by the abnormal conditions were measured with accelerometers, displacement meters and acoustic emission sensors. The acceleration signals were visualized in the time-frequency domain by the in-place fast Haar wavelet transform. The in- place fast Haar wavelet transform can clearly detect the components accompanied by the abnormal conditions.

Fundamental study on vibration diagnosis for turbine generators using wavelet transform

We presented results of the fundamental study to introduce the wavelet transform to the vibration diagnosis for turbine generators. It is required to detect the vibration of turbine generators more accurately. The wavelet transform is used in many fields because it is able to visualize a phenomenon in the time-frequency domain and to detect the beginning time and the duration of it. We made a model rotor supported with two journal bearings to simulate typical vibrations as contact vibration, clearance vibration, and oil whip. The vibration phenomena were measured with displacement meters at the rotor and accelerometers at the rotor bearing, and then, visualized in the time-frequency domain by the wavelet transform. It is found that the dynamic spectra obtained by the wavelet transform of the contact vibration, the clearance vibration, and the oil whip, are different respectively. Therefore, this method is able to distinguish the typical vibration phenomena. The vibration phenomena can be detected and distinguished at the early stage.

Numerical evaluation of currents induced in a worker by ELF non‐uniform electric fields in high voltage substations and comparison with experimental results

An ungrounded human, such as a substation worker, receives contact currents when touching a grounded object in electric fields. In this article, contact currents and internal electric fields induced in the human when exposed to non-uniform electric fields at 50 Hz are numerically calculated. This is done using a realistic human model standing at a distance of 0.1-0.5 m from the grounded conductive object. We found that the relationship between the external electric field strength and the contact current obtained by calculation is in good agreement with previous measurements. Calculated results show that the contact currents largely depend on the distance, and that the induced electric fields in the tissues are proportional to the contact current regardless of the non-uniformity of the external electric field. Therefore, it is concluded that the contact current, rather than the spatial average of the external electric field, is more suitable for evaluating electric field dosimetry of tissues. The maximum induced electric field appears in the spinal cord in the central nervous system tissues, with the induced electric field in the spinal cord approaching the basic restriction (100 mV/m) of the new 2010 International Commission on Non-Ionizing Radiation Protection guidelines for occupational exposure, if the contact current is 0.5 mA.

Effects of tissue conductivity and electrode area on internal electric fields in a numerical human model for ELF contact current exposures

Contact currents flow through the human body when a conducting object with different potential is touched. There are limited reports on numerical dosimetry for contact current exposure compared with electromagnetic field exposures. In this study, using an anatomical human adult male model, we performed numerical calculation of internal electric fields resulting from 60 Hz contact current flowing from the left hand to the left foot as a basis case. Next, we performed a variety of similar calculations with varying tissue conductivity and contact area, and compared the results with the basis case. We found that very low conductivity of skin and a small electrode size enhanced the internal fields in the muscle, subcutaneous fat and skin close to the contact region. The 99th percentile value of the fields in a particular tissue type did not reliably account for these fields near the electrode. In the arm and leg, the internal fields for the muscle anisotropy were identical to those in the isotropy case using a conductivity value longitudinal to the muscle fibre. Furthermore, the internal fields in the tissues abreast of the joints such as the wrist and the elbow, including low conductivity tissues, as well as the electrode contact region, exceeded the ICNIRP basic restriction for the general public with contact current as the reference level value.