• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.7-11
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• 2017

This paper describes a design concept of NPC1 power stack for 1500VDC megawatt level solar inverter. This stack uses three latest half-bridge IGBT modules with highest power density and operation junction temperature, which enable realization of power level beyond 1MW without paralleling. Critical design concept on loop inductance is explained. Dynamic characteristics are verified by double-pulse test. Thermal characteristics and output power limits are verified by thermal test. Temperature-sensitive component on PCB as output power constraint is identified. Different PCB repositioning solutions are tested to give the overall output power thermal derating curves, which enable output power of 1.15MW at $T_A=55^{\circ}C$ with $15^{\circ}C$ thermal margin. The power stack characteristic and performance change under different thermal environment is further analyzed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.781-788
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• 2011

This paper proposes a boost-input self-driven active clamp ZVS converter eliminating the extra dirve circuit for the active clamp switch. The converter used the auxiliary winding of the transformer to drive the active clamp switch and to achieve asymmetrical duty control. This paper presents the operation principle and the analyzed results of dynamic characteristics including steady state characteristics of the converter proposed. The experimental results were used to verify the theoretical predictions. A 300W (15V/20A) prototype converter that only exhibited 2-turn winding number in the auxiliary winding was sufficient to drive the active clamp switch on the input voltage of 80V. Finally, the maximum efficiency of 91.2% was achieved for the prototype converter and the proposed converter had stable closed loop characteristic with phase margin $55^{\circ}$.

• Archives of Plastic Surgery
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• v.32 no.5
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• pp.641-644
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• 2005

Cutaneous squamous cell carcinoma has a high incidence. However, regional metastasis occurs infrequently because skin cancer is usually recognized and treated early. We report the case of squamous cell carcinoma around the earlobe in a 74-year-old male patient. The cutaneous squamous cell carcinoma invaded ipsilateral parotid gland directly without lymphatic spreading. Wide excision was made with 1.5 cm margin and immediate reconstruction was performed with radial forearm fasciocutaneous free flap. During operation facial nerve was preserved. No recurrence was noted for 5 years and the patient was satisfied with good aesthetic result. Cutaneous squamous cell carcinoma spreads to the parotid gland usually through lymph nodes and there are few reports of invasive organ damage by direct invasion. We experienced a case of direct invasion to parotid gland without lymph node involvement of cutaneous squamous cell carcinoma and treated the cancer adequately with wide excision and free flap coverage.

• Journal of Chest Surgery
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• v.22 no.5
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• pp.781-787
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• 1989

Seven patients [six cases of left atrial myxoma, one case of right atrial myxoma] from 24 to 66 years of age [4 male and 3 female, mean age 48 years] underwent excision of atrial myxoma between 1982 and 1989 at Keimyung University Dongsan Medical Center. All patients presented with congestive heart failure, six with cardiac murmur, three with syncope, two with sinus tachycardia, one each with sinus arrhythmia, atrial fibrillation, pleural effusion, peripheral embolization. Symptoms were present from 1 month to 8 years before operation [mean 28 months], All tumors originated from atrial septum and pedunculated. The myxomas were successfully removed in all patients, either shaving them from atrial septum [n=3] or by excising a portion at normal atrial septum with tumor [n=4]. One case was replaced mitral valve with carbomedics-31mm due to severe mitral regurgitation. Follow up is current. No recurrent myxoma has been identified clinically or by echocardiography. In this series, excellent results were obtained by simple excision of the tumor, with or without a margin of normal atrial septum.

• Journal of Chest Surgery
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• v.22 no.5
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• pp.829-833
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• 1989

Congenital coronary arteriovenous fistula is relatively uncommon, but with widespread use of cardiac catheterization, angiography and selective coronary arteriography are being recognized with increasing frequency. Recently we experienced one case of congenital coronary artery fistula which originated from the right coronary artery. The case was 25 year-old-male, who complained of dyspnea on exertion and continuous murmur was heard, and diagnosed as right coronary artery fistula by the cardiac catheterization and aortography. On the operation field, the right coronary artery was markedly dilated from aorta to the middle segment at acute margin of the right ventricle, which the hen-egg sized aneurysm was noticed. The dilated coronary ostium and fistular site were obliterated with several horizontal mattress sutures. And the dilated tortuous right coronary artery with aneurysm was excised. Postoperative course was uneventful and discharged without problem.

• Journal of Chest Surgery
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• v.25 no.7
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• pp.756-762
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• 1992

From August 1990 to October 1991, we performed operation on 5 patients with cardiac myxoma, which was located in the left atrium, There was 1 male and 4 female patients ranging in age 45 years to 61 years. Chief complaints included exertional dyspnea, palpitation, cough, orthopnea, general weakness. M-mode and two dimensional echocardiography provided an accurate diagnosis in all cases which was utilized as safe, reliable and noninvasive imaging modalities. In all cases, myxoma was excised successfully. Follow up is current. No recurrent myxoma has been identified clinically or by echocardiography. In this series, excellent results were obtained by simple excision of the tumor, with or without a margin of normal atrial septum.

• Progress in Superconductivity and Cryogenics
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• v.8 no.2
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• pp.17-19
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• 2006

A novel clock distribution technique for pipelined-RSFQ logics using variable Bias Currents of JTLs as delay-medium is newly proposed. RSFQ logics consist of several logic gates or blocks connected in a pipeline structure. And each block has variable delay difference. In the structure, this clock distribution method generates a set of clock signals for each logic blocks with suitable corresponding delays. These delays, in the order of few to tens of pS, can be adjusted through controlling bias current of JTL of delay medium. While delays with resistor value and JJ size are fixed at fabrication stage, delay through bias current can be controlled externally, and thus, is heavily investigated for its range as well as correct operation within current margin. Possible ways of a standard delay library with modular structure are sought for further modularizing Pipelined-RSFQ applications. Simulations and verifications are done through WRSpice with Hypres 3-um process parameters.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3787-3800
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• 2023

Reactivity Initiated Accident (RIA) scenarios require special attention using advanced simulation techniques due to their complexity and importance for nuclear power plant (NPP) safety. While the conservative approach has traditionally been used for safety analysis, it may lead to unrealistic results which calls for the use of best estimate plus uncertainty (BEPU) approach, especially with the current advances in computational power which makes the BEPU analysis feasible. In this work an Uncontrolled Control Element Assembly (CEA) Withdrawal at Full Power accident scenario is analyzed using the BEPU approach by loosely coupling the thermal hydraulics best-estimate system code (RELAP5/SCDAPSIM/MOD3.4) to the statistical analysis software (DAKOTA) using a Python interface. Results from the BEPU analysis indicate that a realistic treatment of the accident scenario yields a larger safety margin and is therefore encouraged for accident analysis as it may enable more economic and flexible operation.

• Journal of information and communication convergence engineering
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• v.22 no.2
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• pp.98-108
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• 2024

Scrypt is a password-based key derivation function proposed by Colin Percival in 2009 that has a memory-hard structure. Scrypt has been intentionally designed with a memory-intensive structure to make password cracking using ASICs, GPUs, and similar hardware more difficult. However, in this study, we thoroughly analyzed the operation of Scrypt and proposed strategies to maximize computational parallelism in GPU environments. Through these optimizations, we achieved an outstanding performance improvement of 8284.4% compared with traditional CPU-based Scrypt computations. Moreover, the GPU-optimized implementation presented in this paper outperforms the simple GPU-based Scrypt processing by a significant margin, providing a performance improvement of 204.84% in the RTX3090. These results demonstrate the effectiveness of our proposed approach in harnessing the computational power of GPUs and achieving remarkable performance gains in Scrypt calculations. Our proposed implementation is the first GPU implementation of Scrypt, demonstrating the ability to efficiently crack Scrypt.

• Management & Information Systems Review
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• v.17
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• pp.107-133
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• 2005

The purpose of this study was to analyze a trend of profitability classified by characteristics of hospitals and to analyze related factors. The data for this study were derived from survey material conducted by the Korean Hospital Association on 33 hospitals in Korea between 1993 and 2002. Profitability was measured in the aspect of investment profit rate and operation profit rate with net profit to total assets, normal profit to total assets and operating margin to gross revenue as dependent variables. Independent variables were classified by general factors (ownership, number of beds, period of establishment, region), financial factors (total asset turnover, liabilities to total assets, current ratio, fixed ratio, inventories turnover, personnel costs per operation profit, material costs per operation profits), composition of manpower and facilities(personnel and area per beds), productivity index(the number of daily patients per medical doctor, the number of daily patients per nurse), the score of quality assurance activities. First, Concerning the specialists per beds or area per beds and profitability of hospitals there was not statistically significant. Second, Those hospitals having the most daily patients per nurse had significantly higher profitability than the others, but the number of daily patients per medical doctor had little effect on the profitability. Thirds, Those hospitals having a higher proportion total asset turnover tended to show significantly higher profitability compared to other hospitals, but the liabilities to total assets and liquidity ratio had a little difference to the profitability. Those hospitals having a higher proportion personnel costs per operation profit and material costs per operation profits tended to show significantly lower hospital profitability compared to other hospitals. Fourth, In regression analysis, hospital profitability had negative relationship with personnel costs per operation profit or material costs per operation profits. While it had positive relationship with total asset turnover, the number of daily patients per nurse. In conclusion, private hospitals had higher profitability than that of public hospitals. Though factors related to profitability of hospital were different according to ownership, it is important for securing appropriate profitability by operating appropriate number of nurse, raising total asset turnover, and reducing personnel costs, material costs per operation profits. This study can be used as a baseline data for planning of hospital management. But the study may be limited in that the results cannot be generalized due to its small sample size. However, this longitudinal observation of 33 hospitals over ten year period has significant merit alone.