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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.

In this paper, space charge behavior over a large range of electric field and temperature, of two kinds of epoxy resins are investigated using an improved pulsed electro-acoustic method. Significant influence of high electric field and high temperature on the space charge accumulation in epoxy are found. Hetero charge accumulation starts to build up at 80 °C under 120 kV/mm for amine-type hardener cured epoxy (EP-AM), while at 140 °C under 60 kV/mm for anhydride-type hardener cured epoxy (EP-AH). The accumulated charge increases with the increasing of electric field and temperature. The maximum enhancement of local electric field of is 135 and 123 % at 140 °C for EP-AM and EP-AH, respectively. Quantum chemical calculation is performed to clarify the mechanism of space charge characteristics in the two types of epoxy. It is indicated that ionization of remnant unreacted hardener and electrode injection may be the main sources of space charge. The interaction between molecular chains of EP-AH is stronger than that of EP-AM, which makes it have better space charge characteristics even under high temperature.

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

The recent expansion of the application environment of power electronics to high-radiation environments will cause the deterioration of insulation materials used in power electronics due to charging caused by cosmic ray irradiation. The charging phenomena should induce malfunctions in power electronics. Therefore, it is important to understand the insulation characteristics of insulation materials irradiated with protons, electrons, etc., to improve the reliability of power electronics. With respect to the above, there are few reports on the RIC (radiation-induced conductivity) of insulation materials irradiated with proton beams. In this paper, we experimentally evaluated the RIC of PI (polyimide) films irradiated with proton beams under various irradiation conditions. We also studied a calculation method to estimate the measured RIC of the PI. As a result, we clarified that the total conductivity of the PI increased under non-penetrating irradiation conditions and saturated under penetrating irradiation conditions. The reason for this is that the higher the irradiation energy, the deeper the maximum proton penetration depth under non-penetrating irradiation conditions. On the other hand, the conductivity characteristics did not change under penetrating conditions because the penetration depth was the same as the sample thickness. We also developed a calculation method to estimate the conductivity of the entire PI irradiated with proton beams. The estimated data calculated by the above method were analytically fitted with the measured data for most irradiation energy conditions. It is suggested that the above calculation method can estimate the conductivity of the entire PI irradiated with proton beams, regardless of penetrating or non-penetrating irradiation, based on the relationship between the RIC and dose rate of the PI irradiated under penetrating conditions. In the future, we will incorporate the results of this study into a computational model of space charge accumulation inside insulation materials to verify the influence of the RIC caused by proton irradiation on space charge accumulation.

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.

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).

Polyimide is widely used insulation materials, such as power equipment, motor windings, multi layer insulated, and so on. As the operation environment is high temperature, high humidity, radiation, the dielectric insulation characteristic is decreased compared with pristine one. Especially, the space charge characteristics are obtained big different. Furthermore, the breakdown phenomenon is frequently produced. In this chapter, we discuss the dielectric phenomena through the viewpoints of charge accumulation under the following environment. High temperature, High humidity, DC application, PWM application, Radio-active rays (electron, proton).

Recently, the high performance and high reliability materials on the power electronics devices have been studied. Those devices are used in severe environments, such as high temperature, radiation, vacuum environment, and so on. In this study, we focused on the effect of space charge accumulation in the bulk of dielectrics by the radiation, such as the proton and/or the electron beams. So, we measured space charge distributions on insulating materials for the power electronics devices irradiated by proton/electron using the pulsed electroacoustic (PEA) method. As a result, the charges due to irradiated protons and electrons were confirmed to accumulate in the bulk at the calculated penetration depth, and the electric fields were emphasized 1.3 and 1.2 times larger than that of non-irradiated samples for the proton and electron irradiations, respectively. It is considered that those appearances of the electric field distribution had been occurred by charge accumulation by irradiation, modification of molecules structure, radio activation, and an increase of conductivity. To clarify this assumption, further investigation will be carried out in our future study.

Polypropylene (PP) is one of the candidate materials for cable insulation instead of XLPE, which is remarked as a thermoplastic material with high melting temperature. In our previous studies, it is shown that space charge injection and conduction current in PP based flexible copolymers are both reduced at high temperatures and under high DC electric fields by adding an inorganic filler or a polar group into them. In this report, we tried to analyze the state of trap sites formed in the PP copolymers using the quantum chemical calculation to understand the effect of the inorganic filler and the polar group added into PP copolymers.

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.

This paper aims at the measurement of the time dependence of the internal space charge and analysis of radiation induced conduction (RIC) in polyimide caused by electron beam irradiation. Both the normal PEA method and an “on-line” PEA system were employed to detect the space charge profiles after and during the electron irradiation. In view of that, a small size PEA device with a ring high voltage electrode was used for the “on-line” measurement. In addition, the electric conduction was discussed by the RIC theory. Negative charge accumulations were introduced by the irradiated electrons, which increase with the increase of electron energy and density. The behaviors of RIC depend on electron energy, indicating an enhancement with high electron energy. These phenomena are closely related to the charge deposition and electron-hole pairs. High energy and density of the electron beams introduced large amounts of negative charge accumulations. Meanwhile, they contributed to the high level of RIC. Consequently, the space charge would maintain the dynamic equilibrium in polyimide film.

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.

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.

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.

We have investigated a space charge distribution and a conduction current characteristics in copolymerized materials of propylene and ethylene under high DC electric field at various temperatures, which are considered as one of candidate insulating materials for HVDC cable. The materials show excellent mechanical flexibility and relatively low conductivity at room temperature. However, at high temperature under very high DC applied electric field, electric field distortion induced by accumulated space charges in the bulk was observed. We attempted to improve the insulating properties of them by adding inorganic fillers into them. In this report, we describe measuring results of space charge distribution and conduction current in the composite materials under high DC electric field at high temperature.

It is said that a space charge accumulation in an insulating material for motor windings decreases the partial discharge inception voltage (PDIV). Therefore, the space charge distribution measurement is important in the insulating material under square wave voltage, which is applied to an actual motor. In this study, we tried to understand the relationship between the space charge accumulation and the change of PDIV by comparing the experimental results obtained using PEA (pulsed electroacoustic) method and PDIV testing systems.