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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.

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

In this paper, we studied the space charge phenomena of a solid polymer under thermal and electrical stresses with different frequencies and waveforms. By analyzing the parameter selection method of a protection capacitor and resistor, the newly built pulsed electro-acoustic (PEA) system can be used for special electrical stresses under 500 Hz, based on which the charge phenomena are studied in detail under positive and negative DC and half-wave sine and rectangular wave voltages. Experimental results show that the charge accumulated in the polyimide polymer under DC conditions mainly comes from the grounded electrode side, and the amount of charge accumulated with electric field distortion becomes larger in a high-temperature environment. At room temperature, positive charges tend to accumulate in low-frequency conditions under positive rectangular wave voltages, while they easily appear under high-frequency situations of negative ones. In contrast, the maximum electric field distortion and charge accumulation under both half-wave sine voltages occur at 10 Hz. When the measurement temperature increases, the accumulated positive charge decreases, with a more negative charge appearing under rectangular wave voltages, while a more positive charge accumulates at different frequencies of half-wave sine voltages. Therefore, our study of the charge characteristics under different voltage and temperature conditions can provide a reference for applications in the corresponding environments.

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.

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.

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.

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.