Z. Jin

An equivalent circuit grid model for no-insulation HTS pancake coils

An equivalent circuit grid (ECG) model is proposed to analyse the time-varying characteristics of no-insulation (NI) ReBCO pancake coils. In the model, each turn of the coil is subdivided into fine elements in the azimuthal direction, and each element is equivalent to a circuit parameter. Then, the coil is equivalent to a circuit grid. A math model based on Kirchhoffs law is proposed to solve the circuit grid model. The distribution of the electrical current inside the NI coil is analysed for the charging and discharging process. A finite element method (FEM) model is coupled to calculate the magnetic field induced by the coil. To validate the model, a double pancake (DP) coil is fabricated by coated conductor ReBCO tapes. Charging and discharging tests are performed on the coil at 77 K. The results from simulations and experiments exhibit a good agreement. Then, this model is used for more studies on the current distribution inside the NI coil in the charging and discharging process. The charging and discharging delay of NI coil is analysed and explained by the model. The model can also be applied to partial insulated (PI) coils and magnets consisting of NI coils.

Design and Application of a Superconducting Fault Current Limiter in DC Systems

A dc resistive type superconducting fault current limiter (SFCL) is presented in this paper. This SFCL is designed for the HVDC system. Experiments are conducted to prove the current limiting ability of superconducting materials in dc system. Uniform current and voltage sharing among the SFCL modules can be observed through contact resistance tests, dc flow-through tests, and ac flow-through tests. Results of tests show that each limiting module has good uniformity in higher current system. Then, system simulation model based on these experimental data is built in PSCAD, and simulations are carried out to determine the value of shunt resistor. Results of simulation show that SFCL has fast responding time and good current limiting performance in dc network.

Design and Experimental Results of a DC Induction Heater Prototype for Aluminum Billets

The advantages of dc induction heating in high efficiency and good heating quality have been proved and studied worldwide in past decades. In this paper, a laboratory-scale dc induction heater with iron yoke for aluminum billets is designed and tested in detail. The billet to be heated is placed in the air gap of the yoke and is driven by a motor. The magnetic field in the gap is built up by copper windings with direct currents. The whole heating processes under different conditions are observed. Various surface temperature distributions have been achieved by changing several heating parameters including heating time, rotating speed, and dc magnetic field. Numerical analysis for calculating the heating process is also carried out in a commercial finite-element software. Results show that all the heating parameters will affect the final heating effects. Also, the numerical results agree well with the experimental results.

Anorectal functional outcome after repeated transanal endoscopic microsurgery

AIM To evaluate the status of anorectal function after repeated transanal endoscopic microsurgery (TEM). METHODS Twenty-one patients undergoing subtotal colectomy with ileorectal anastomosis were included. There were more than 5 large (> 1 cm) polyps in the remaining rectum (range: 6-20 cm from the anal edge). All patients, 19 with villous adenomas and 2 with low-grade adenocarcinomas, underwent TEM with submucosal endoscopic excision at least twice between 2005 and 2011. Anorectal manometry and a questionnaire about incontinence were carried out at week 1 before operation, and at weeks 2 and 3 and 6 mo after the last operation. Anal resting pressure, maximum squeeze pressure, maximum tolerable volume (MTV) and rectoanal inhibitory reflexes (RAIR) were recorded. The integrity and thickness of the internal anal sphincter (IAS) and external anal sphincter (EAS) were also evaluated by endoanal ultrasonography. We determined the physical and mental health status with SF-36 score to assess the effect of multiple TEM on patient quality of life (QoL). RESULTS All patients answered the questionnaire. Apart from negative RAIR in 4 patients, all of the anorectal manometric values in the 21 patients were normal before operation. Mean anal resting pressure decreased from 38 ± 5 mmHg to 19 ± 3 mmHg (38 ± 5 mmHg vs 19 ± 3 mmHg, P = 0.000) and MTV from 165 ± 19 mL to 60 ± 11 mL (165 ± 19 mL vs 60 ± 11 mL, P = 0.000) at month 3 after surgery. Anal resting pressure and MTV were 37 ± 5 mmHg (38 ± 5 mmHg vs 37 ± 5 mmHg, P = 0.057) and 159 ± 19 mL (165 ± 19 mL vs 159 ± 19 mL, P = 0.071), respectively, at month 6 after TEM. Maximal squeeze pressure decreased from 171 ± 19 mmHg to 62 ± 12 mmHg (171 ± 19 mmHg vs 62 ± 12 mmHg, P = 0.000) at week 2 after operation, and returned to normal values by postoperative month 3 (171 ± 19 vs 166 ± 18, P = 0.051). RAIR were absent in 4 patients preoperatively and in 12 (χ(2) = 4.947, P = 0.026) patients at month 3 after surgery. RAIR was absent only in 5 patients at postoperative month 6 (χ(2) = 0.141, P = 0.707). Endosonography demonstrated that IAS disruption occurred in 8 patients, and 6 patients had temporary incontinence to flatus that was normalized by postoperative month 3. IAS thickness decreased from 1.9 ± 0.6 mm preoperatively to 1.3 ± 0.4 mm (1.9 ± 0.6 mm vs 1.3 ± 0.4 mm, P = 0.000) at postoperative month 3 and increased to 1.8 ± 0.5 mm (1.9 ± 0.6 mm vs 1.8 ± 0.5 mm, P = 0.239) at postoperative month 6. EAS thickness decreased from 3.7 ± 0.6 mm preoperatively to 3.5 ± 0.3 mm (3.7 ± 0.6 mm vs 3.5 ± 0.3 mm, P = 0.510) at month 3 and then increased to 3.6 ± 0.4 mm (3.7 ± 0.6 mm vs 3.6 ± 0.4 mm, P = 0.123) at month 6 after operation. Most patients had frequent stools per day and relatively high Wexner scores in a short time period. While actual fecal incontinence was exceptional, episodes of soiling were reported by 3 patients. With regard to the QoL, the physical and mental health status scores (SF-36) were 56.1 and 46.2 (50 in the general population), respectively. CONCLUSION The anorectal function after repeated TEM is preserved. Multiple TEM procedures are useful for resection of multi-polyps in the remaining rectum.

Study on a Numerical Method for Calculating the Heating Process of HTS DC Induction Heater

A commercial HTS dc induction heater for aluminium billets is going to be built in Shanghai Jiao Tong University, China. To achieve an optimal design, a numerical model is proposed to accurately calculate the heating process of the billets due to induced current. The model is based on two physics fields i.e. including thermodynamics and electromagnetism. The changes of relevant parameters with increase of billets temperature are taken into account. In the model, the billets rotate in a dc magnetic field generated by a HTS magnet with iron cores. The induction heating power and temperature distribution inside the billets can be calculated accurately. In order to validate the calculation, a small laboratory-scale prototype dc inductive heater for aluminium billets is built. The coils are immersed in liquid nitrogen to flow higher current, and the billet is rotated by a motor. Comparison is carried out on the results of numerical model and experiment and analysis is made for the discrepancy between them. The discrepancy is acceptable for engineering applications. Finally, some examples of using the numerical model to calculate the electromagnetic behaviour for a commercial industry-scale dc induction heater are given.

The chemokine CXCL9 expression is associated with better prognosis for colorectal carcinoma patients

The chemokine CXCL9 has been demonstrated to play an important role in the development of human malignancies. However, its prognostic significance in cancer patients remains unclear and less is known about its role in colonrectal carcinoma (CRC) patients. In this study, we found that the relative mRNA expression level of CXCL9 in primary colorectal tumor tissues was significantly higher than that in corresponding normal colon tissues. CXCL9 protein expression was also detected in 102 of 130 primary CRC patients by immunochemistry. Thus, CXCL9 might play a vital role in the progression of colorectal cancer. By analyzing the correlation between clinicopathological factors of patients and expression of CXCL9 protein, we showed that the expression of CXCL9 was significantly associated with tumor differentiation, tumor invasion, lymph node metastasis, distant metastasis, and vascular invasion, but not with other factors of CRC patients including age, gender, tumor location and tumor size. Furthermore, by performing Kaplan-Meier method as well as Coxs univariate and multivariate hazard regression model, we found that the higher the CXCL9 expression, the higher overall survival rate was observed, and CXCL9 expression was a significant independent prognostic factor for CRC patients. Therefore, CXCL9 is a useful predictor of better clinical outcome in CRC patients.

Fabrication and Characteristic Tests of a Novel Low-Resistance Joint Structure for YBCO Coated-Conductors

Joints play an important role in the application of YBaCuO-coated conductors. Given the limited length and various requirements of tapes, large numbers of joints are needed in some applications. Therefore, developing stable joints between tapes and achieving low joint resistance has become an important issue for the application of YBCO tapes. In this paper, we propose a novel superconducting joint production process and fabricate these joints with a lamination machine. A few meters or more than 10 m of joint overlapping length can be achieved, and the joint resistance can be as low as 2.25 nΩ when the overlapping length reaches 8 m. A series of experiments has been carried out to explore the joint resistance changing law, with overlap length increases, and the joint characteristics. The results show that joint resistance is inversely proportional to the overlap length. Although long bridge joints cost more, they have an incomparable advantage in that the joint resistance is distributed over the bridge joint, which allows for more stable operation and less liquid nitrogen boiloff. After joint lamination processing, the burnout current rises from 276 to 523 A. Critical current and joint resistance are not affected by the overcurrent before the joint burns out.

Design of a HTS Magnet With Iron Core for DC Induction Heater

This paper presents an electromagnetic design of a HTS magnet with iron core for DC induction heater. The heater is designed for aluminium billets with diameter of 60 mm and length less than 500 mm. The magnet is designed to generate 0.5 T DC magnetic fields in its air gap. The coil is wound with YBCO tapes produced by AMSC, and its operating temperature is 50 K. A numerical model is proposed to get an optimal design. The model couples MATLAB code and FEM model and considers the nonlinearity of iron core and the field dependence of tapes Jc. The FEM model is built from commercial software. It can analyze the electromagnetic characteristics of magnet with complex geometry easily. The MATLAB code is used to analyse results from the FEM model, update the design variables to get an optimal solution. Finally, the specifications of design results are shown. The accuracy of the FEM model is the key of the optimization process. A magnet by cooper wires is built to validate the FEM model. Its iron core has same dimension as the designed HTS one. The data from FEM model and experiment show a good agreement.

Characteristic Tests and Electromagnetic Analysis of an HTS Partial Core Transformer

An experimental high temperature superconducting (HTS) transformer has been designed and built using GdBCO HTS tapes. The transformer is unique in that the magnetic circuit is comprised of air and an iron partial core. The HTS windings and iron core were immersed in a liquid nitrogen environment. Fundamental characteristics were obtained by no-load and load tests. The transformer had a smaller exciting current compared with the HTS air core transformer, and the voltage regulation was 1.67% at full load. A lumped parameter equivalent circuit that takes the ac loss was proposed and testified by tests. A 3-D “field-circuit” coupled model built in COMSOL was used to successfully analyze the electromagnetic characteristics of the transformer. The experimental results were consistent with the calculated and simulation values. The detail results will describe in this paper.

Study of Surface Flashover and Breakdown Characteristics in Liquid Nitrogen for SFCL Application

With the rapid development of commercial use of superconducting fault current limiters (SFCLs), higher and higher voltage use is being taken into consideration. Insulation property is crucial and limits the development at high voltage level. G10, as an excellent insulation material for cryogenic use, can be applied in high voltage SFCL module. Based on the fundamental design of SFCL module in Shanghai Jiao Tong University, flashover characteristics of G10 in LN2 are researched to design the SFCL module. In addition, ac breakdown strength of SFCL module terminals is investigated to design module distance to ensure insulation safety and do not make SFCL too large. Simulations are conducted to study the theoretical electric field distribution. Partial discharge voltage and ac surface flashover breakdown voltage of different electrodes are measured. SFCL module terminal electrodes and triangle-plane electrodes are applied. How the surface flashover breakdown strength would be affected is studied by changing the electrode gap. Breakdown strength property of SFCL module terminal is also studied by altering the distance of electrodes. The experiment results show that gas gap and surface length do influence the partial discharge charge and flashover breakdown voltage. Bubbles also affect breakdown strength between terminals. These results are conducive to design SFCL module.