• Journal of Power Electronics
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• v.16 no.6
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• pp.2119-2128
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• 2016

Due to detection and control errors, some high-frequency harmonics with voltage-source characteristics cause circulating currents in modular inverters. Moreover, the circulating currents are usually affected by the output filters (OF) of each module due to their filter and resonance properties. The interaction among the circulating currents in the modules increase the power loss and reduce system stability and control precision. Therefore, this paper reports the results of a study on the SPWM high-frequency harmonics circulating currents for a double-module VSI. In the paper, an analysis of the circulating-current circuits is briefly described. Next, a mathematic model of the single-module output voltage based on the carrier frequency of SPWM is built. On this basis, through mathematic modeling of high-frequency harmonic circulating currents, the formation mechanism and distribution characteristics of circular currents and their influences are studied in detail. Finally, the influences of the OF on the circulating currents are studied by mainly taking an LC-type filter as an example. A theoretical analysis and experimental results demonstrate some important characteristics. First, the carrier phase shifting of the SPWM for each module is the major cause of the SPWM harmonic circulating currents, and the circulating currents are in an odd distribution around n-times the carrier frequency $n{\omega}_s$, where n = 1, 2, 3, ${\ldots}$. Second, the harmonic circular currents do not flow into the parallel system. Third, the OF can effectively suppress the non-circulating part of the high-frequency harmonic currents but is ineffective for the circulation part, and actually reduces system stability.

• Journal of IKEEE
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• v.18 no.2
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• pp.282-290
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• 2014

This paper presents the design of embedded electrical power control unit for Personal Electrical Vehicle(PEV). The embedded unit is designed using PIC18F8720 processor, 16Mb flash ROM, 32Mb SDRAM and signal condition circuits. The proposed PEV consists of 4KW in-wheel Brushless DC Motor(BLDCM), 3 phase voltage source inverter with the $180^{\circ}$ conduction space vector PWM method, PID speed controller and the embedded control unit. The PEV has mechanical manufacture of inverse 3 wheel system, which is applied by the in-wheel BLDCM and steering mechanism with tilting function. Also, the performances of the proposed embedded electrical power control unit are verified through the lab experiment and road driving test of PEV.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.5
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• pp.423-431
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• 2001

This paper proposes a new active common-mode voltage damper circuit that is capable of suppressing a common-mode voltage produced in the PWM VSI-fed induction motor drives. The new active common mode voltage damper is consists of a four-level half-bridge Inverter and a common mode transformer with a blocking capacitor. In order to reduce the common mode voltage and high frequency leakage current the active common mode damper applies to the PWM inverter system the compensated voltage of which the amplitude is the same as the common mode voltage and of which the polarity is opposite to the common mode voltage. Simulated using P-SPICE and experimental results show that common-mode voltage damper makes contributions to reducing a high frequency leakage current and common-mode voltage.

• Journal of the Korean Vacuum Society
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• v.20 no.6
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• pp.403-408
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• 2011

To develop the MFX (Micro-Focus X-ray) tube, the trajectories of electrons emitted from the field emission cathode was simulated using SIMION program. Regardless of starting position of the electron in emitter, we found out the fact that there is the optimum extractor voltage Ve, which can focus the electron beam on one place. Extractor voltage Ve varies depending on the source voltage Vs, but the ratio of two voltages (Ve/Vs) is always constant, its value was 99.4%. When the ratio of two voltages (Ve/Vs) was 99.4%, the beam diameter in the cross-over point was $1.2{\mu}m$. Because the focal spot size in MFXG (Micro-Focus X-ray Generator) can not be less than the cross-over diameter within MFX tube, it is important to find out the conditions that can make a smaller beam diameter. Therefore, the above results is considered to be a very important ones in the development of the MFXG.

• Vascular Specialist International
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• v.34 no.4
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• pp.103-108
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• 2018

Purpose: Surgery is the most common risk factor for pulmonary embolism (PE) in patients with a recent venous thromboembolism (VTE). This study reviewed clinical outcomes of preoperative inferior vena cava filter (IVCF) use in patients with acute VTE during abdominal-pelvic cancer or lower extremity orthopedic surgeries. Materials and Methods: We retrospectively analyzed 122 patients with a recent VTE who underwent IVCF replacement prior to abdominal-pelvic cancer or lower extremity orthopedic surgery conducted between January 2010 and December 2016. Demographics, clinical characteristics, postoperative IVCF status, risk factors for a captured thrombus, and clinical outcomes were collected for these subjects. Results: Among the 122 study patients who were diagnosed with acute VTE in the prior 3 months and underwent preoperative IVCF replacement, 70 patients (57.4%) received abdominal-pelvic cancer surgery and 52 (42.6%) underwent lower extremity orthopedic surgery. There were no perioperative complications associated with IVCF in the study population and no cases of symptomatic PE postoperatively. A captured thrombus in the filter was identified postoperatively in 16 patients (13.1%). Logistic regression analysis indicated that postoperative anticoagulation within 48 hours significantly reduced the risk of a captured thrombus (odds ratio [OR], 0.28; 95% confidence interval [CI], 0.08-0.94; P=0.032). Conclusion: A captured thrombus in preoperative IVCF was identified postoperatively in 16 patients (13.1%). Postoperative anticoagulation within 48 hours reduces the risk of captured thrombus in these cases.

• Vascular Specialist International
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• v.34 no.4
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• pp.83-87
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• 2018

Purpose: Thrombosis of the portal vein, known as pylephlebitis, is a rare and fatal complication caused by intraperitoneal infections. The disease progression of superior mesenteric venous thrombosis (SMVT) is not severe. This study aimed to determine the clinical features, etiology, and prognosis of SMVT. Materials and Methods: We retrospectively reviewed the medical records of 41 patients with SMVT from March 2000 to February 2017. We obtained a list of 305 patients through the International Classification of Disease-9 code system and selected 41 patients with SMVT with computed tomography. Data from the medical records included patient demographics, comorbidities, review of system, laboratory results, clinical courses, and treatment modalities. Results: The causes of SMVT were found to be intraperitoneal inflammation in 27 patients (65.9%), malignancy in 7 patients (17.1%), and unknown in 7 patients (17.1%). Among the patients with intraperitoneal inflammation, 14 presented with appendicitis (51.9%), 7 with diverticulitis (25.9%), and 2 with ileus (7.4%). When comparing patients with and without small bowel resection, the differences in symptom duration, bowel enhancement and blood culture were significant (P=0.010, P=0.039, and P=0.028, respectively). Conclusion: SMVT, caused by intraperitoneal inflammation, unlike portal vein thrombosis including pylephlebitis, shows mild prognosis. In addition, rapid symptom progression and positive blood culture can be the prognostic factors related to extensive bowel resection. Use of appropriate antibiotics and understanding of disease progression can help improve the outcomes of patients with SMVT.

• Vascular Specialist International
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• v.34 no.4
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• pp.109-116
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• 2018

Purpose: Diabetic foot wound (DFW) is known as a major contributor of nontraumatic lower extremity amputation. We aimed to evaluate overall amputation rates and risk factors for amputation in patients with DFW. Materials and Methods: From January 2014 to December 2017, 141 patients with DFW were enrolled. We determined rates and risk factors of major amputation in DFW and in DFW with peripheral arterial occlusive disease (PAOD). In addition, we investigated rates and predictors for amputation in diabetic foot ulcer (DFU). Results: The overall rate of major amputation was 26.2% in patients with DFW. Among 141 DFWs, 76 patients (53.9%) had PAOD and 29 patients (38.2%) of 76 DFWs with PAOD underwent major amputation. Wound state according to Wagner classification, congestive heart failure, leukocytosis, dementia, and PAOD were the significant risk factors for major amputation. In DFW with PAOD, Wagner classification grades and leukocytosis were the predictors for major amputation. In addition, amputation was performed for 28 patients (38.4%) while major amputation was performed for 5 patients (6.8%) of 73 DFUs. Only the presence of osteomyelitis (OM) showed significant difference for amputation in DFU. Conclusion: This study represented that approximately a quarter of DFWs underwent major amputation. Moreover, over half of DFW patients had PAOD and about 38.2% of them underwent major amputation. Wound state and PAOD was major predictors for major amputation in DFW. Systemic factors, such as CHF, leukocytosis, and dementia were identified as risk factors for major amputation. In terms of DFU, 38.4% underwent amputation and the presence of OM was a determinant for amputation.

• Vascular Specialist International
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• v.34 no.4
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• pp.88-93
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• 2018

Purpose: This study aimed to compare surgical revisions and balloon angioplasty after surgical thrombectomy on thrombosed dialysis access as a first event. Materials and Methods: Records of patients undergoing creation of arteriovenous grafts (AVGs) at the Gachon University Gil Medical Center between March 2008 and February 2016 were reviewed. Among them, patients who underwent treatment on first-time thrombotic occlusion after AVG creation were identified. Outcomes were primary, primary-assisted, and secondary patency. The patency was generated using the Kaplan-Meier method, and patency rates were compared by log-rank test. Results: A total of 59 de novo interventions (n=26, hybrid interventions; n=33, surgical revisions) for occlusive AVGs were identified. The estimated 1-year primary patency rates were 47% and 30% in the surgery and hybrid groups, respectively. The estimated primary patency rates were not different between the two groups (log-rank test, P=0.73). The Kaplan-Meier estimates of 6 and 12 months for primary-assisted patency rates were 68% and 57% in the surgery group and 56% and 56% in the hybrid group. The Kaplan-Meier estimates of 12 and 24 months secondary patency rates were 90% and 71% in the surgery group and 79% and 62% in the hybrid group. There were no differences in the estimated primary-assisted and secondary patency rates between the two groups. Conclusion: Our results showed no significant difference between the two groups in terms of primary patency (P=0.73), primary-assisted patency (P=0.85), and secondary patency (P=0.78). However, percutaneous transluminal angioplasty can give more therapeutic options for both surgeons and patients.

• Journal of Aquaculture
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• v.7 no.1
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• pp.63-76
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• 1994

The effects of different dietary lipids on growth, body chemical composition, and nutrient partition of the Korean rockfish (43 g of initial mean weight) were studied. Fish were fed three experimental diets containing 1) $4.5\%$ squid liver oil, 2) $1\%$ squid liver oil and $3.5\%$ beef tallow, and 3) $1\%$ squid liver oil and $3.5\%$ soybean oil. Growth and feed efficiency were detarmined during a 19-week feeding period at water temperature of $15.5^{\circ}C$, and at the end of which body chemical compositions were analyzed. Remained fish were fasted for 45 days, and four fish were taken at 6, 12 and 24 hours, and 3, 15 and 45 days after the fasting to determine tissue compositions and hematological changes. Growth, feed efficiency, protein and lipid retention efficiency, hepatosomatic index(HSI), viscerosomatic index (VSI), and chemical composition of whole body and dorsal muscle were not affected by the different dietary lipids. Liver moisture content of fish fed squid liver oil diet was higher than that of fish fed beef tallow or soybean oil diet. Liver lipid content of fish fed beef tallow diet was higher than that of fish fed the other diets. Fatty acid composition of dorsal muscle and liver were affected by the different dietary lipids ; high levels of 20 : 5n-3 and 22 : 6n-3 from fish fed the diet containing squid liver oil, 18 : 1 from fish fed the diet containing beef tallow, and high 18 : 2n-6 and 18 : 3n-3 from fish fed the diet containing soybean oil were observed. Both HSI and VSI of fish fed three diets decreased with time after the begining of starvation. Liver glycogen did not change during the first 15 days of starvation and decreased thereafter, and that was not affected by the different dietary lipids. Lipid and protein contents in the dorsal muscle of fish decreased up to 15 days of starvation and remained unchanged thereafter, these were not different from each other. Glucose, free fatty acid, triglyceride and phospholipid concentrations in Fish serum were varied for the first 15 days of starvation, after that the concentrations of fish serum remained relatively stable in all the treatment groups with prolonged starvation. The results indicate that Korean rockfish can utilize fish oil, animal fat or vegetable oil equally as energy source when n-3HUF A is adquate.

• Journal of Aquaculture
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• v.16 no.3
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• pp.190-195
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• 2003

Dietary optimum ratio of frozen raw fish and commercial compound meal (CCM) in moist pellet (MP) were investigated to improve the growth rate, and feed and economical efficiency in the flounder, Paralichthys olivaceus. Experimental fish (average body weight, about 48 g) were divided into 6 groups and each group was fed with raw fish (FRF), and MPs (ratio of raw fish and CCM=9:1, 8:2, 7:3, 6:4 and 5:5) for 10 weeks. The 9:1, 8:2, 7:3, 6:4, 5:5 groups showed no significant difference in weight gain as 203.5~217.3%, while the FRF group showed significantly low growth rate as 183.1%(P<0.05). The feed efficiency gradually increased with the increase in the ratio of CCM and was the highest in the 5:5 group as 89.7%. As a result of analysis of body composition after the experiment, moisture was significantly low in the 7:3 group (P<0.05) and crude protein was significantly low in the 9:1 group (P<0.05). The crude lipid increased as the ratio of raw fish increased, and it was the highest in the raw fish group (8.3%) and the lowest in the 5:5 group (4.6%). There were no significant difference in hepatosomatic index (HSI) and condition factor(CF) among the experimental groups. Visceralsomatic index (VSI) increased with the increase in the ratio of raw fish and was significantly high in the raw fish group as 5.49 (P<0.05). For the unit cost of feed, it was found that raw fish was economical when mackerel, a source of raw feed, was 400 won/kg, while the ratio of 5:5 was economical when it was more than 500 won/kg. Results of this study concluded that sole use of raw feed is not desirable in view of growth, environment and economy, and the 5:5 group showed highest effect under the least use of raw feed.