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The charge phenomena under sine and half‐wave sine voltages within the frequency range of 500 Hz are studied here. Based on the pulsed electro‐acoustic method, the traditional circuit design under high‐frequency voltages is first analysed. It is found that the selection of a 186 pF protection capacitor and a 333 kΩ protection resistor can ensure that the actual voltage applied to the sample is consistent with the expected input. Based on this design, experimental results show that the polarity of the charge accumulated in the depth of the sample is determined by that of the upper electrode. Comparison results under special voltages with different amplitudes and frequencies indicate that the amount of accumulated charge under sine voltages are larger than those under positive and negative half‐wave sine and DC conditions, and the samples under lower‐frequency conditions show more charge accumulation. The maximum electric field strengths appear at 90 and 270 degrees of the sine voltage with a frequency of 10 Hz, and their values are 68.55 and 81.82 kV/mm, respectively. Therefore, the charge characteristics are easily affected by the voltage’s waveform and frequency parameters. The results obtained here can provide guidance for the application of insulating materials under special voltage environments.

This paper reports the effect of DC and pulse wave voltages on space charge characteristics of polyimide material for high-frequency insulation. The pulsed electroacoustic method is used to measure the charge distribution inside the material under the pulse wave voltages with different amplitudes, polarities, frequencies and duty ratios. Comparative results show that positive charge is more likely to accumulate inside the polyimide. The amount of accumulated charge under pulse wave voltages is larger than that under DC voltages. With frequency, more space charge is accumulated under negative pulse wave voltages with a frequency above 50 Hz, while it is not larger than 100 Hz under positive voltages. The maximum distortion of electric field appears under the negative pulse wave voltage with the frequency of 500 Hz, which is 1.19 times the applied field strength. When the duty ratio of the pulse wave voltage exceeds 50%, the distribution of accumulated charge tends to be stable. The research results can provide a reference for the practical application and modification design of polyimide materials in power electronic equipment.

Background/Aim: We aimed to elucidate the prognostic impact of tumor doubling time (DT) and radical surgery when classified by DT in patients with metachronous liver, lung, or peritoneal metastases of colorectal cancer (CRC). Patients and Methods: We reviewed the data of 1941 patients who underwent curative surgery for CRC and calculated DT for recurrences using computed tomography. Results: Short DT was an independent prognostic risk factor in liver (p

Aim Recently, the accessory middle colic artery (AMCA) has been recognized as the vessel that supplies blood to the splenic flexure. However, the positional relationship between the AMCA and inferior mesenteric vein (IMV) has not been evaluated. Herein, we aimed to evaluate the anatomy of the AMCA and the splenic flexure vein (SFV). Method Two hundred and five patients with colorectal cancer who underwent enhanced CT preoperatively were enrolled in the present study. The locations of the AMCA and IMV were evaluated, focusing on the positional relationship between the vessels and pancreas - below the pancreas or to the dorsal side of the pancreas. Results The AMCA was observed in 74 (36.1%) patients whereas the SFV was found in 177 (86.3%) patients. The left colic artery (LCA) was the major artery accompanying the SFV in 87 (42.4%) of patients. The AMCA accompanied the SFV in 65 (32.7%) patients. In 15 (7.8%) patients, no artery accompanied the SFV. The origin of the AMCA was located on the dorsal side of the pancreas in 15 (20.3%) of these 74 patients. Similarly, the destination of the IMV was located on the dorsal side of the pancreas in 65 (31.7%) of patients. Conclusion The SFV was observed in most patients, and the LCA or AMCA was the common accompanying artery. In some patients these vessels were located on the dorsal side of the pancreas and not below it. Preoperative evaluation of this anatomy may be beneficial for lymph node dissection during left-sided hemicolectomy.

Recently, some next-generation semiconductors such as SiC, which can be operated at high temperature under high electric field, have been developed, and power devices using these semiconductors have been reduced in size with higher power output. However, while the semiconductors themselves are available at high temperature under high electric stress, there is no suitable material which shows a good performance as the insulating material under such a severe condition. Therefore, to realize the usage of the next-generation semiconductors with the inherent ability, it is required to develop the insulating material that shows an excellent characteristic even under such severe conditi ons. Generally, epoxy resin is used as such a molding insulation material, and this study also evaluated the insulating performance of the epoxy resin. For this purpose, several imide type hardeners for the epoxy resin were developed provide the characteristics of both high heat resistance and low dielectric properties. A feature of the imide type hardener is that an imide group is introduced into the hardener to maintain high heat resistance without lowering the crosslinking density. In this study, we estimated the insulating properties of those epoxy resins by observing space charge accumulation behaviors in them at high temperature under high electric field. From the measurement results, it is found that some of them shows a good performance as the insulating materials even under such severe conditions.

DC current integrated charge measurement (Q(t) method) is applied to evaluate the performance of insulating layer used in power module at high temperature under high DC stress. It is said that a s pace charge accumulation is one of important factors to evaluate the insulating materials, and the Q(t) measurement is an effective method that is available to the actual devices. Therefore, the Q(t) method was attempted to be applied to evaluate the insulating layers in some actual IGB T modules. As the result, it is found that the Q(t) method is effective to evaluate the insulating materials used for actually devices.

Insulating materials are frequently used in spacecraft's structure and especially as thermal blanket which are protecting the electronic devices. Their behavior in relation to an electron beam irradiation due to space environment must be clearly elucidate. For example, when the electron beam is irradiated to the material, it charged up and a large electric potential difference generate between the charged and uncharged surfaces. If the difference in potential becomes very large, a discharge sometimes occurs between them. Such discharge is very harmful for the spacecraft. Therefore, at designing stage of spacecraft, it is important to understand the charging characteristics of the surface material of the spacecraft. In this paper, we focused on the charge accumulation in the materials under an irradiation of high energy electron beam. In the experiments, some fluorine materials are used which are ordinary used for the spacecraft. Judging from the measurement results, it was found that the amounts of accumulated electrons gradually decreased ever during an electron beam irradiation. In addition, we tried to explain for this phenomenon using an idea of RIC (Radiation Induced Conductivity).

To propose a new and improved surveillance schedule for colorectal cancer (CRC) patients by focusing on the recurrence rate, resectability, and especially, the tumor doubling time (DT) of recurrent tumors. The subjects of this retrospective review were 1774 consecutive patients who underwent radical surgery for stage I–III CRC between January, 2004 and December, 2015. We calculated the DT by measuring the tumor diameter using computed tomography (CT). The median DT for recurrences in the liver, lung, peritoneum, and other locations were 35, 72, 85, and 36 days, respectively, (p

Investigation of space charge accumulation processes in a chemically cross-linked polyethylene for ac usage (XLPE) and a modified XLPE for dc usage (DC-XLPE) at voltage polarity reversal was carried out using pulsed electro-acoustic (PEA) measurement system. We found that a huge amount of so called packet-like charge, some of which partially increased the electric field in the material to more than twice of the average applied stress, generated in XLPE at the polarity reversal of DC stress. It enhanced the electric stress locally in the sample by almost twice of the applied average stress. On the other hand, we also found that the packet-like charge was not observed in DC-XLPE under the same experimental condition.

Space charge accumulation properties were investigated on epoxy resin under high dc stresses at high temperature. Due to the recent improvement in operable temperature of semiconductors, it is required to develop a new insulating material for semiconductor packaging, which exhibit a high insulation performance even at high temperature under the high electric stress. To estimate the insulation performance, it is said that the space charge accumulation is characteristic one of important factors for the evaluation of the materials. Therefore, in this study, the space charge behavior in epoxy resin, that is widely used as a semiconductor packaging material, is evaluated using PEA (Pulsed Electro Acoustic) method at high temperature under high electric field. While there are many demand to know the insulating properties in epoxy resin at relatively high temperature like more than 100 °C the ordinary PEA system was applicable to the measurement at temperature from room temperature to about 80 °C. Therefore, we improved the PEA system available to the measurement at 100 °C. In this report, two types of epoxy plate samples were used: one is made using an amine type curing agent (EP-A) and another is made using acid anhydride curing agent (EP-NH). As a result, it was found that an obvious amount of space charge accumulation was observed in EP-A, while it was not observed in EP-NH even under the dc stress of more than 100 kV/mm at 100 °C.

While many kinds of polymeric materials have been developed for being used at high temperature in various devices, there is a few cases that they are used as an electric insulating material for dc high electric stress. However, according to the development of power electric devices in recent years, the demand of an insulating material which show a good performance even at high temperature more than 100 °C has been increasing. Under such severe condition, especially in HVDC (high voltage DC) systems, the space charge accumulation property must be a key factor to evaluate the performance of them. Therefore, we tried to measure the space charge distributions in many kinds of polymers at high temperature (∼ 140°C) under high electric stress (∼ 120 kV/mm) using the originally developed PEA (pulsed electroacoustic) system for high temperature measurement. Judging from the results, the obtained data can be available to evaluate the performance of them under such severe condition.

In this paper, we tried to evaluate the charge accumulation in insulating materials used for electronic power devices. Space charge accumulation is said that one of important factors to evaluate the insulating materials under dc high electric fields, especially at high temperature. While, the space charge accumulation in insulating materials has been measured using pulse electro acoustic (PEA) method, the PEA method has been mainly applied to sheet shape samples. Therefore, it is difficult to apply the PEA method to an insulating layers used for an actual electronic devices, which are usually composed of complicated shape. Therefore, we have tried to apply a direct current integrated charge measurement which is newly developed measurement method to evaluate the charge accumulation in the insulating layers. Using the method, we tried to estimate the charge accumulation in the insulating layer of actual power electronic devices under various electric stresses at various temperature. As the result, it was found that the method was preferably available to evaluate the characteristics of charge accumulation in the insulation layers of the power electronic devices.

We developed a compact system for evaluating the deterioration of insulating materials used in high-voltage dc power apparatuses. The developed system can be used for simultaneous determination of three basic parameters important for evaluating the deterioration of high-voltage insulation materials, i.e., conductivity, dielectric constant, and charge accumulation. Charge accumulation, which is detrimental to high-voltage dc electrical apparatuses, such as power devices, transformers, and power cables, can be evaluated using this system. With this system, the charges accumulated are measured by integrating the current through a capacitor inserted between the highvoltage power source and the high-voltage apparatus to be tested. The obtained information is transmitted to the unit placed at ground potential. The evaluation is carried out by comparing the amount of initial charges in the insulating material with that of charges accumulated at a certain time after application of a high voltage. When the ratio of the charges accumulated at time (t) to that of the initial charge is 1, it is assumed that there was no charge accumulation; thus, no deterioration of the insulating material is assumed. However, when the ratio is greater than 1, the insulating material is considered to have deteriorated. Using the evaluation system, we developed, we examined the deterioration of insulating materials used in coaxial cables by exposure to 1) γ-rays and 2) high-temperature conditions. From these two experiments using the developed system, the deterioration of insulating materials was found to have advanced substantially when the charge accumulation ratio exceeded approximately over 2.0.

The doubling times of tumor volume and tumor markers are associated with the prognosis of liver or lung metastases from colorectal cancer (CRC). However, no studies have assessed peritoneal metastases. Therefore, we aimed to elucidate the association between doubling time and the prognosis of patients who underwent radical surgery for metachronous peritoneal metastases of CRC. We calculated the tumor doubling times (TDT) of peritoneal metastases and serum carcinoembryonic antigen-doubling times (CEA-DT) in 33 consecutive patients who underwent radical surgery for metachronous peritoneal metastases between January 2006 and April 2017. The impact of short TDT and CEA-DT on overall survival (OS) and relapse-free survival (RFS) was retrospectively reviewed. In long TDT (> 137 days) group, the 5-year OS rate was 74.1% and median OS time was 6.6 years. In long CEA-DT (> 102 days) group, the 5-year OS rate was 50.0% and median OS time was 5.6 years. Conversely, in short TDT (≤ 137 days) and CEA-DT (≤ 102 days) group, the 5-year OS rates and median OS times were both 0.0% and 3.2 years, respectively. In the multivariate analysis, short TDT was an independent risk factor for poor RFS (P = 0.006) and OS (P = 0.010). Similarly, short CEA-DT was also a poor risk factor for RFS (P

In the automotive industry, a reduction in CO 2 and low fuel consumption are required from the environmental point of view. According to such demand, electric vehicle using an inverter fed motor is developed and widely used. However, partial discharge generates in motor winding, when the higher voltage is applied to the windings. Thereby, it may induce a fatal breakdown in the insulating coating layer of the windings. Judging from a published report, it was said that a decrease of partial discharge inception voltage (PDIV) was strongly related with space charge accumulation in the insulating layer. However, only few studies about the space charge accumulation characteristic in the insulating coating for the windings has been carried out in the past. In this study, we proposed a new space charge distribution measurement technique using Pulsed Electro Acoustic (PEA) method to evaluate the space charge accumulation characteristics in such layer. Using this technique, we can observe the pace charge distribution in an insulating film during the application of square wave, square wave with surge shape and half-wave of AC voltages of 50 Hz to the film. Judging from the obtained results, we found that the space charge accumulated in the film by applying above mentioned the voltages, and it might cause of the reduction of PDIV.

AIM Surgery for colorectal cancer located in the splenic flexure is difficult to perform because of the complex anatomy. Recently, in addition to the middle colic artery and left colic artery (LCA), the accessory middle colic artery (AMCA) has been recognized as a feeding artery for the left-sided colon. This study aimed to evaluate the vascular anatomy of the splenic flexure focusing on the AMCA in a large number of patients. METHOD A total of 734 patients who underwent CT before surgery for colorectal cancer were enrolled. We retrospectively evaluated the vascular anatomy using both two- and three-dimensional CT angiography. RESULTS The AMCA existed in 36.4% of the cases (n = 267). In many cases, it originated from the superior mesenteric artery (n = 228, 85.4%). The AMCA had a common trunk with the transverse pancreatic artery in 54 patients (20.2%). The frequency of the presence of the AMCA was associated with the branching pattern of the LCA, and was more frequent when the LCA was absent (P < 0.001). CONCLUSION The presence of the AMCA is not rare and the AMCA has some branching patterns; therefore, recognizing it preoperatively and intra-operatively is important, being especially careful when the LCA is absent.

SUMMARY Space charge behavior and conduction current in polyethylene under dc stress were investigated. One of the reasons for the different breakdown property in cross-linked polyethylene (XLPE) from that in low-density polyethylene (LDPE) may be based on the existence of cross-linking by-products in XLPE. Furthermore, a thermal history in cross-linking process for XLPE may also cause of the difference. It is generally accepted that the existence of the cross-linking by-products increase the conduction current in XLPE under dc stress. It is also said that an anneal treatment in air atmosphere may affect to the electrical properties under dc stress. Therefore, we investigated the effect of the cross-linking by-products and the anneal treatment on space charge behavior and conduction current in polyethylene under dc stress. In our research, it is thought that the increasing dissipation power in XLPE is the cause of the breakdown in it under dc stress. Therefore, to calculate the dissipation power in the bulk of test sample, we measured the space charge distribution and the external circuit current simultaneously. Based on the results, we discussed the reason of the difference of the space charge properties in XLPE and LDPE focusing on the cross-linking by-products and the oxidation of the test samples.

In recent years, improvement of power density of a power semiconductor modules is required. However, it has been reported that dielectric breakdown occurs in the ceramic material used as an insulating substrate for the power semiconductor under the environment currently used. Therefore, to make it reliable and to improve its power density as the power module, it is necessary to elucidate the dielectric breakdown mechanism of the ceramic material. In this research, we tried to investigate the dielectric breakdown mechanism of the ceramic materials by measuring space charge accumulation characteristics using PEA method. However, it was found that the ceramic material a theoretically unexplainable behavior when shows it is measured using the PEA method. Therefore, we tried to estimate the charge behavior inside the ceramic material from a measurement result in multilayer samples composed of ceramic material and polymer material.

In this report, we study of fundamental research for a high positional resolution of pulse electro-acoustic (PEA) method. Positional resolution of PEA method depends on a pulse width of the applied pulse voltage and a traveling time of the acoustic signal through a piezo electric sensor. Our laboratory tried to develop a thin sensor using the polyvinylidene fluoride (PVDF). Consequently, we succeeded in developing a measuring device with a position resolution of ca. 2.5 μm using thin PVDF sensor which is 1 sm thick. However, since PVDF is polymer material, which is difficult to form a film thinner than under 1 sm. So, we focused on a depletion layer in semiconductor as a sensor material for further improvement of the sensor. The depletion layer is formed at the contact interface with the semiconductor and the metal. Which have space charge distribution inside, and it distribution is similar to an electric dipole. So we expect to apply the depletion layer for sensor. In this report, we tried to measure the space charge distribution of the depletion layer which is formed by contact a silicon substrate to an aluminum electrode. As a result, we succeeded in measuring the space charge distribution of depletion layer.

Various findings on color impression have become essential knowledge for professionals who handle colors as elements of design. Similarly, knowledge of memorized colors should be considered by design professionals. Researchers in color psychology have conducted various studies on memorized colors; however, a database on changing of colors cannot be built, because the investigated colors are limited to parts in the color space. In this paper, we propose an experimental method to reveal memorized colors. The apparatus consists of a personal computer and LCD display. The proposed method uses quantitative data on three attributes of memorized colors, and the manipulation of the apparatus is easier than the conventional method. We compare the study results with the findings of previous research papers. The results confirm the validity of the method. This study presents memorized colors of rarely investigated parts in the color space.

As a long distance DC power transmission cable, XLPE (cross-linked polyethylene) insulated cable is considered to be used. Since the cable is supposed to be used at high-temperature because a large current flows in inner conductor, it is necessary to estimate the performance of the insulating material at high temperature. Especially, characteristics of a space charge accumulation and a conduction current in the material under a high DC stress at high-temperature is important to estimate it. Therefore, it has been developed a measuring equipment which is enable to measure the space charge distribution and the external circuit current density simultaneously at high temperature. In this report, several typical measurement results, that are obtained using the developed system, will be introduced. As a result, it is found that the moving speed of the injected packet-like charge increases with increase of temperature. Furthermore, it is found that a current value significantly depends on the polarity of the applied voltage is generated.

In the automotive industry, a reduction in CO 2 and low fuel consumption is required from the view of environment. According to such demand, electric vehicle using an inverter fed motor is developed and diffused. However, partial discharge is generated between motor winding, when the higher voltage is applied to the winding. Thereby, it may induce a fatal breakdown in the cover insulating. Judging from a published report, it is said that a decrease of partial discharge inception voltage are concerned by space charge accumulation in the insulating layer. However, only few studies about the space charge accumulation characteristic in the insulating layer of the windings has been carried out in the past. In this study, we especially focused on the space charge accumulations in polyamide-imide (PAI) under square wave voltage using Pulsed Electro-Acoustic (PEA) method. It is found that, a negative hetero charge accumulated near the anode immediately after DC voltage application. Moreover, even in the short circuit condition, negative charge remained near the anode. It means that the space charge accumulates in the bulk of PAI film within a short time of the DC voltage application. Therefore, even in the inverter drive system, excessive voltage application may affect the performance of the dielectric material. Therefore, in this study, we investigated the effect of the square wave voltage application to the film on the space charge accumulation.

A thin insulating layer is used for motor windings. In an inverter fed motor driving system, an inverter surge voltage generates and it leads a partial discharge on the surface of insulating layer. Since the partial discharge reduces a motor lifetime, it is necessary to investigate a generation mechanism of the partial discharge. In the mechanism of it, we have focused on an effect of space charge accumulation. In this study, we tried to measure the space charge distribution in a specially designed insulating material against the partial discharge to investigate the effect of space charge accumulation on degradation of the insulating material by corona discharge. The material is composed of three layers of the same thickness which are two surface layers including an inorganic filler and one middle layer without the filler. To observe the degradation of the material by corona discharge, the surface of the material was exposed to corona discharge of high voltage pulses using a spherical electrode with frequency of 1 kHz for 2 hours. After the corona discharge treatment, we applied a DC voltage to the material to observe a time dependence of the space charge accumulation in the material. As the results, a positive and a negative space charges were observed at positions of one thirds of the sample thickness from an anode and a cathode electrodes. The charges supposed to be accumulated at the interfaces of the layers. On the other hand, the corona discharged sample showed a complicated space charge behavior followed by a breakdown. We also found that the space charge accumulation behavior strongly affects the corona discharged insulating material.

Volume resistivities of polyimide film under simulated space environment are measured with “charge storage decay method.” The test material was irradiated by electron beam in a vacuum chamber to simulate space environment. Volume resistivity is calculated from the surface potential decay time constant after stopping electron irradiation. This is called “charge storage decay method” and is shown to be the preferred method to determine resistivities of highly insulating materials. As a result of experiments, we have found that volume resistivity of polyimide film is in order of 1016 Ωm, which is one order higher than the result from the conventional resistivity measurement method prescribed in JIS or ASTM. Higher resistivity requires much longer field relaxation time after injection of electron to dissipate through the material. Thus, charging analysis of spacecraft needs to consider this higher resistivity. The effect of injection energy of electron is also examined and it is found that the higher the energy is, the faster the charge decay become.

Charge accumulations in electron-beam (e-beam)-irradiated polymers are investigated by observing them using the pressure wave propagation method. The purpose of our research work is to measure the charge distribution in e-beam-irradiated dielectric materials for spacecrafts. We have been developing a system for measuring such a charge distribution in dielectric materials. Using this system, we tried to measure the charge distribution in various typical polymers (poly(ethylene terephthalate), polystyrene, low-density polyethylene) under e-beam irradiation. As a result, it is found that charging characteristics of insulating material is strongly influenced by the existence of benzene ring in the molecular architecture. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Space charge accumulation behaviors at voltage polarity reversal in cross-linked polyethylene (XLPE) and in improved XLPE for dc cable are observed using pulsed electro-acoustic (PEA) method. A huge amount of so called a packet like charge, which was enough to enhance the electric field significantly, is generated in XLPE at the polarity reversal, while it is not observed in the improved XLPE. It enhanced the electric stress locally in the sample by almost twice of the applied average stress. Since the packet-like charge was not observed in the improved XLPE at the polarity reversal, it is applicable to high voltage direct current (HVDC) network using line commutate converter (LCC) system, in which the voltage polarity reversal is necessary to inverse the current flow.

A generation of PD (partial discharge) in motor windings is a significant problem to develop a high voltage driving system, which is expected to improve the motor efficiency. A space charge accumulation in an insulating material of motor windings has been pointed out as one of reasons, for the PD generation because the space charge accumulation sometimes enhances the electric field in an insulating material. Therefore, measurement of the space charge in the insulating layer of motor windings is required. Space charge accumulation characteristics in film shape sample are usually measured using the PEA (pulsed electro-acoustic) method. However, since a manufacturing process of actual windings wire is different from that for film shape sample, the characteristics are assumed to be different from actual one. It means that it is difficult to evaluate the influences of the space charge on the insulating layer of the actual wire from the measurement result of the film shape sample. Therefore, in this research, we tried to measure the space charge distribution in the insulating material of actual enameled wires using an improved PEA measurement system. As a result, it is found that there are different types of space charge accumulation characteristics, even between nominally same insulating materials.

We investigated the relationship between the space charge accumulation characteristics and the breakdown in a single layer and double layered polyimide films under dc stress using the pulsed electro acoustic (PEA) method. In recent years, there are many examples of multilayered polyimide film is used as the flexible Printed-Circuit Board (PCB) inside an advanced electronic devices. Therefore, it is important to investigate the insulation performance of the multilayered polyimide film. In previous work, it was revealed that a space charge accumulated in a polyimide film under a high stress and it was closely relevant to the electrical breakdown. Therefore, it is also necessary to investigate the space charge accumulation characteristics of the multilayered type sample. Furthermore, we measured the space charge accumulation in various combinations of the multilayered samples under dc high electric field at 80 °C using the PEA method. From the space charge measurement, we found that the multilayered sample had more superior insulating properties than the single layer sample and the breakdown strength was improved by arranging a thin layer putting next to the anode electrode. In this paper, we investigated the influence of the combinations with the various thickness of the layers and the polarities of the contacting electrodes on the space charge behavior. As the results, we found that the space charge accumulation and the breakdown in polyimide films under dc high stress was strongly affected by the polarity of the electrode.

Recently, some accidents in spacecraft due to charging up by irradiation of charged particles have been reported. Some of them are caused by a surface discharge, which normally takes place in a plasma environment in space. Some others seem to be caused by a discharge due to an accumulation of charge in the bulk of materials in a relatively high-altitude environment. To investigate the charge accumulation in the bulk of materials, the authors have been developing an internal charge measurement system. The internal charge accumulation in dielectric materials under irradiation of artificial radioactive rays is observed using the developed system, which employs the so-called pulsed electroacoustic method and pressure wave propagation method based on pulse acoustic measurement techniques. The developed system is applicable to the measurement of the charge distribution in dielectrics in air atmosphere or vacuum environments under electron beam, proton beam, and gamma ray irradiations. Using the system, we measured bulk charge distributions in polymeric films and glass materials. In this paper, summaries of some typical measurement results are presented following a brief explanation of measurement principles

Space charge accumulation for various glass materials under DC stress was studied by using a pulse electroacoustic (PEA) method. We should make an acoustic matching between the sample and electron on the high-voltage side when the hetero-space charge distribution in glass materials is measured. The acoustic pressure wave generated from the induced charge at the high-voltage side is canceled by the reflected one generated from hetero-charge accumulated in the sample. Large hetero-charge is observed in the glass materials containing MgO and CaO compound compared to the quartz glass containing no such compounds. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(1): 19–27, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10260

A positional resolution of space charge measurement system of a pulsed electro acoustic (PEA) method is tried to improve using a newly designed upper electrode unit and a new pulse generator. The improved upper electrode unit with a good terminator contribute to reduce the inductance and it results in reduce a noise. Moreover, in order to apply a pulse voltage to a sample efficiently using a newly adopted pulse generator, the upper electrode diameter was made to be small. In the PEA measurement, we have to take a so-called `reference' signal, which is used for a deconvolution data processing to get an accurate space charge distribution. In the previous system, we needed to take the reference signal using a thicker sample because the original signal is including a relatively long-tail noise. Therefore, to take the reference using a thinner measurement sample, the noise should be shorter. Since, the above mentioned effort to improve made the resolution higher with the shorter noise, we obtained a charge distribution with the resolution of about 1.6 μm in 25 μm-thick PET film. As the result, a typical measurement result of the space charge distribution in a polyimide film with the thickness of 25 μm was introduced in this report.

Spacecraft are sometimes seriously damaged by electrostatic discharge in polymeric materials. Various polymeric materials are used for the surface materials of spacecraft, such as a MultiLayer Insulator (MLI) or an Optical Solar Reflector (OSR). They are charged up by irradiation of solar particles and high-energy charged particles, particularly those such as charged particles like electrons and protons. The accumulations of the charges are the origin of discharge phenomena, and they become a trigger for some anomalies of spacecraft operation or a degradation of the materials. Therefore, it is necessary to investigate the charging effect on the dielectric properties of these materials. Since the dielectric properties like electrical conductivity have a strong correlation with the charge accumulation in the bulk, we especially focused on the space charge behavior in electron beam irradiated dielectric materials, especially in polyimide film used as MLI and fluoride films used for OSR and wire harness. To observe the space charge accumulation processes in polyimide films and fluoride films with and without electron beam irradiation, the pulsed electro-acoustic (PEA) measurement were carried out after irradiation for dozens of days. Furthermore, the conduction current in them were also measured according to the American Society for Testing and Material (ASTM) method (IEC has also same standard). On the basis of the results, we confirm that the charge decay behavior is different between polyimide film and fluoride films. The current density decreased on irradiated polyimide compared with non-irradiated film. This phenomena also was confirmed by the space charge measurement results that was large amount of accumulated charge still remained in the bulk during several hours. On the other hand, the current density of irradiated fluoride films approximately 100 times larger than non-irradiated film. From the results, it is considered that the increasing of current density on fluoride films may influence the charge accumulation in the bulk.

Since the space charge accumulation sometimes enhances the electric field in an insulating material, it can be thought as a reason of unexpected PD (partial discharge) generation. Therefore, measurements of the space charge in the insulating layer of the winding are required. The space charge accumulation in the insulating material is usually carried out using the PEA (pulsed electro-acoustic) method. In this measurement, the space charge distribution in film shape sample was a research object. However, the properties of specially-made film samples may be different from those of the insulating layer with the actual configuration of the winding wire, and it is difficult to evaluate the actual influence of the space charge to the motor windings. In this research, we improved the PEA system which can be applied to measure the space charge distribution in the actual insulating layer of the winding wire. Using the developed system, we found that the space charge accumulated in the actual insulating layer by application of high voltage.

In this study, we observed a space charge accumulation behavior in the covering materials (Polyamideimide: PAI, Polyester-imide: PEI) for motor windings under applied voltage of square wave. In these days, the inverter-fed motor drive using pulse width modulation control is applied to many electric devices for industrial machinery, automotive, railway cars and so on, and it is effective to decrease a dissipation power. For further improvement of the efficiency of the motor, it is said that higher voltage is applied to motors. However, if the high voltage is applied to the motor winding, a partial discharge (PD) is generated between motor windings because of a so-called inverter surge voltage generation. The inverter surge voltage is induced by the mismatching of the impedance and it sometimes becomes twice of the applied voltage. The generated PD induces some degradation of the covering material, and then finally it makes a electrical breakdown in it. It is usually said that the PD inception voltage depends on the value of surge voltage and the kind of insulating material. Furthermore, it is also said a space charge accumulation in the insulating material affects on the PD inception voltage. However, at present, it has not been reported about the effect of the space charge accumulation in the covering material for motor windings on the PD inception voltage. Therefore in this study, we investigated the space charge accumulation property of PAI under square wave voltage by using Pulsed Electro-Acoustic (PEA) method. From the measurement results, it was found that the space charge accumulation in PAI under the square wave voltage with high frequency of 1 kHz.

We investigated the relationship between the space charge accumulation characteristics and the breakdown in various combination of multilayered polyimide samples under dc stress using the pulsed electro acoustic (PEA) method. In recent years, there are many examples which a multilayered polyimide film is used as the flexible Printed-Circuit Board (PCB) inside an advanced electronic devices or motor windings. Therefore, it is necessary to investigate the insulation performance of the multilayered polyimide. In previous work, it has been revealed that a space charge accumulated in polyimide film under a high stress and it is closely related to the electrical breakdown. Therefore, it is also necessary to investigate the space charge accumulation characteristics of the multilayered type sample. In this paper, we measured the space charge accumulation in various combinations of the multilayered samples under dc high electric field at 80°C by using the PEA method. From the space charge measurement, we found that the multilayered sample has more superior insulating properties than the single layer sample. Furthermore, we found that it is hard to have the breakdown by arranging a thin layer putting next to the anode electrode.

Inhibitors of 3-hydroxy,3-methylglutaryl coenzyme A (HMG-CoA) reductase have been reported to decrease the cholesterol saturation index (CSI) in duodenal bile in humans and to prevent formation of cholesterol gallstones in animal studies. We performed a prospective study to evaluate the role of HMG-CoA reductase inhibitors as gallstone-dissolving agents. Fifty patients with radiolucent gallstones in a gallbladder opacifying at drip infusion cholecystography were treated with either 10 mg/day simvastatin plus 600 mg/day ursodeoxycholic acid (group 1, n=26) or 600 mg/day ursodeoxycholic acid alone (group 2, n=24) for 12 months. The ratio of solitary to multiple gallstone cases was 21:29. Plasma lipid levels were assessed and ultrasonographic examination of the gallbladder was performed at baseline and at 3-month intervals during treatment. Duodenal bile sampling was performed in five patients in each group at baseline and after 12 months of treatment. Plasma cholesterol decreased significantly in group 1 but not in group 2. In solitary gallstone cases, no significant difference in dissolution rates was observed between groups 1 (3 of 9, 33%) and 2 (4 of 12, 33%). In contrast, the dissolution rate in multiple gallstone cases was significantly higher in group 1 (12 of 17, 71%) than in group 2 (3 of 12, 25%) (p0.01). Bile cholesterol saturation index was significantly decreased (p0.01) but did not significantly differ between the two groups. These results suggest that combination therapy with simvastatin and ursodeoxycholic acid is more effective for cholesterol gallstone dissolution than ursodeoxycholic acid monotherapy in patients with multiple gallstones.