• Progress in Superconductivity and Cryogenics
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• v.15 no.3
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• pp.40-48
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• 2013

Cryoablation device is a surgical instrument to produce the cooling effect to destroy detrimental biological tissue by utilizing low temperature around 110 K. Usually, this device has the concentrated cooling region, so that it is suitable for concentrated and thick target. Accordingly, it is hard to apply this device for the target which is distributed and thin target. In this study, the design procedure of a closed-loop cryoablation device with multiple J-T expansion part is developed for the treatment of incompetent of great saphenous vein. The developed cyoablation device is designed with the analysis of 1-dimensional (1-D) bio-heat equation. The energy balance is considered to determine the minimum mass flow rate of refrigerant for consecutive flow boiling to develop the uniform cooling temperature. Azeotropic mixed refrigerant R410A and zeotropic mixed refrigerant (MR) of R22 ($CHClF_2$) and R23 ($CHF_3$) are utilized as operating fluids of the developed cryoablation device to form the sufficient temperature and to verify the quality of the inside of cryoablation probe. The experimental results of R410A and the zeotropic MR show the temperature non-uniformity over the range are $244.8K{\pm}2.7K$ and $239.8K{\pm}4.7K$ respectively. The experimental results demonstrate that the probe experiences the consecutive flow boiling over the target range of 200 mm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.203-206
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• 2004

For the realization of PRAM, $Ge_2Sb_2Te_5$ (GST) has been employed for the phase transition between the crystal and amorphous states by electrical joule heating. Although there has been a vast amount of results concerning the GST in material aspect for the laser-induced optical storage disc applications, the process-related issues of GST for the PRAM applications have not been reported. In this work, the etching behaviors of GST were investigated when the processing conditions were varied in the high-density helicon plasma. The etching parameters of RF main power, RF bias power, and chamber pressure were fixed at 600 W, 150 W, and 5 mTorr, respectively. For the etching processes, gas mixtures of $Ar/Cl_2$, $Ar/CF_4$, and $Ar/CHF_3$ were employed, in which the etching rates and etching selectivities of GST thin film in given gas mixtures were evaluated. From obtained results, it is found that we can arbitrarily design the etching process according to given cell structures and material combinations for PRAM cell fabrications.

• Journal of Advanced Marine Engineering and Technology
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• v.10 no.2
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• pp.156-164
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• 1986

In the case of boiling on high temperature wall, vapor film covers fully or parcially the surface. This phenomenon, film boiling or transition boiling, is very important in the surface heat treatment of metal, design of cryogenic heat exchanger and emergency cooling of nuclear reactor. Mainly supposed hydraulic-thermal accidents in nuclear reactor are LCCA (Loss of Coolant Accident) and PCM (Power-Cooling Mismatch). Recently, world-wide studies on reflooding of high temperature rod bundles after the occurrence of the above accidents focus attention on wall temperature history and required time in transient cooling process, wall superheat at rewet point, heat flux-wall superheat relationship beyond the transition boiling region, and two-phase flow state near the surface. It is considered that the further systematical study in this field will be in need in spite of the previous results in ref. (2), (3), (4). The paper is the study about the fast transient cooling process following the wall temperature excursion under the CHF (Critical Heat Flux) condition in a forced convective subcooled boiling system. The test section is a vertically arranged concentric annulus of 800 mm long and 10 mm hydraulic diameter. The inner tube, SUS 304 of 400 mm long, 8 mm I.D, and 7 mm O.D., is heated uniformly by the low voltage AC power. The wall temperature measurements were performed at the axial distance from the inlet of the heating tube, z=390 mm. 6 chromel- alumel thermocouples of 76 .mu.m were press fitted to the inner surface of the heating tube periphery. To investigate the heat transfer characteristics during the fast transient cooling process, the outer surface (fluid side) temperature and the surface heat flux are computed from the measured inner surface temperature history by means of a numerical method for inverse problems of transient heat conduction. Present cooling (boiling) curve is sufficiently compared with the previous results.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.302-310
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• 2011

A fluid in an enclosure can be heated by electric heating, chemical reaction, or fission heat. In order to remove the volumetric heat of the fluid, the walls surrounding the enclosure must be cooled. In this case, a natural convection occurs in the pool of the fluid, and it has a dominant role in heat transfer to the surrounding walls. It can augment the heat transfer rates tens to hundreds times larger than conductive heat transfer. The heat transfer by a natural convection in a regular shape such as a square cavity or semi-circular pool has been studied experimentally and numerically for many years. A pool of an inverted triangular shape with 10 degree inclined bottom walls has a good cooling performance because of enhanced boiling critical heat flux (CHF) compared to horizontal downward surface. The coolability of the pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the pool. In this study, turbulence models with modifications for buoyancy effect were validated for unsteady natural convections by volumetric heating. And natural convection in the triangular pool was evaluated by using the models.

• Journal of Chest Surgery
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• v.19 no.4
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• pp.618-626
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• 1986

Univentricular heart is a rare congenital cardiac anomaly in which the atrial chambers are connected to only one ventricular chamber and it consists of a diverse group of cardiac malformation characterized by both AV valves or a common AV valve opening into the same ventricle, or the presence of only a solitary AV valve. In spite of recent development in cardiac surgery, corrective operations for univentricular heart still have high mortality and complication rate. Twenty eight patients underwent corrective operation for univentricular heart at Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital from February 1979 to July 1986. Of the 28 patients, 7 patients were operated on by ventricular septation and 21 patients by modified Fontan operation. Of the 28 patients, 19 patients were male and 9 patients female and ages ranged from 5 months to 18 years old with the average age of 7.3 years. There were 2 mortalities in 7 patients operated on by septation with the mortality rate of 28.6% and 5 complications, 3 complete AV block, 1 low cardiac output and 1 arrhythmia. All survived patients are being followed up without specific problem till now. There were 10 mortalities in 21 patients operated on by modified Fontan operation with the mortality rate of 47.6% and 10 complications, 2 low cardiac output, 2 respiratory failure necessitating tracheostomy, 2 persistent cyanosis, 2 arrhythmia, 1 missing of left AV valve in situs inversus patient due to misdiagnosis and one rupture of closed right AV valve. Incremental risk factors for operative mortality are young age less than 5 years old, anomalous pulmonary and systemic venous drainage and atrial septation procedure. In 11 survived patients, 9 patients show good follow-up results but one patient complains of persistent cyanosis and another one patient is suffered from CHF. In our series, results of corrective operation for univentricular heart shows continuing improvement but still high mortality and complication rate. So there must be continuing improvement in surgical result by selection of patient, by adequate decision making for timing and method of operation and by improving operative methods.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.459-459
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• 2012

Recently, the discharge of global warming gases in dry etching process of TFT-LCD display industry is a serious issue because perfluorocarbon compound (PFC) gas causes global warming effects. PFCs including CF4, C2F6, C3F8, CHF3, NF3 and SF6 are widely used as etching and cleaning gases. In particular, the SF6 gas is chemically stable compounds. However, these gases have large global warming potential (GWP100 = 24,900) and lifetime (3,200). In this work, we chose C3F6O gas which has a very low GWP (GWP100 = <100) and lifetime (< 1) as a replacement gas. This study investigated the effects of the gas flow ratio of C3F6O/O2 and process pressure in dual-frequency capacitively coupled plasma (CCP) etcher on global warming effects. Also, we compared global warming effects of C3F6O gas with those of SF6 gas during dry etching of a patterned positive type photo-resist/silicon nitride/glass substrate. The etch rate measurements and emission of by-products were analyzed by scanning electron Microscopy (SEM; HITACI, S-3500H) and Fourier transform infrared spectroscopy (FT-IR; MIDAC, I2000), respectively. Calculation of MMTCE (million metric ton carbon equivalents) based on the emitted by-products were performed during etching by controlling various process parameters. The evaluation procedure and results will be discussed in detail.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.3
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• pp.194-200
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• 2011

In this work, nucleate pool boiling heat transfer coefficients(HTCs) of pure water are measured on horizontal 26 fpi low fin, Turbo-B and Thermoexcel-E square surfaces of 9.53 mm length. HTCs are taken from 10 $kW/m^2$ to critical heat flux for all surfaces. Test results show that critical heat fluxes(CHFs) of all enhanced surfaces are greatly improved as compared to that of a plain surface. CHFs of water on the 26 fpi low fin surface, Thermoexcel-E surface, and Turbo-B are increased up to 320%, 275%, and 150% as compared to that of the plain surface, respectively. CHF of the Turbo-B enhanced surface is lower than that of the 26 fpi low fin surface due to the surface geometry. The heat transfer enhancement ratios of the Thermoexcel-E surface, low fin surface and Turbo-B enhanced surface are 1.6~2.9, 1.6~2.1, 1.4~1.7 respectively in the range of heat fluxes tested. Judging from these results, it can be said that these types of enhanced surfaces can be used in heat transfer applications at high heat fluxes.

• Korean Journal of Clinical Pharmacy
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• v.24 no.2
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• pp.115-125
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• 2014

Purpose: The purpose of the present study was to assess the incidence of the potentially inappropriate medication (PIM) use in Korean elderly patients with heart failure, and to evaluate factors that influence PIM use. Method: Korean National Health Insurance claims database between January 2009 and December 2009 was used. Using 2012 updated Beers criteria, PIM use in heart failure patients aged 65 years or older was examined. Result: The incidence of PIM use in elderly heart failure patients was higher than in overall elderly patients. Among the 12,759 elderly patients with heart failure, 46.2% of study subjects were prescribed PIM(s) at least once. The number of PIM per 10 medications that patients received per patient was 1.53. The most commonly used PIMs in elderly heart failure patients were benzodiazepines (30.9%), non-steroidal anti-inflammatory drugs (NSAIDs) including COX-2 inhibitors (16.3%), digoxin (9.9%), and spironolactone (9.0%). Women (odds ratio, 1.20; 95% CI, 1.17-1.24), medical aid (odds ratio, 1.11; 95% CI, 1.08-1.13), and long-term facilities (odds ratio, 2.69; 95% CI, 2.44-2.96) were revealed to be important factors associated with PIM use. In addition, patient's age also seems to influence PIM use. Conclusion: Elderly heart failure patients are at a greater risk for adverse drug events attributed by inappropriate medication use. Efforts to increase awareness of PIM use in elderly heart failure patients are needed. In addition, various comprehensive strategies and policies to identify and prevent PIM use should be established nationwide.

• Journal of computational fluids engineering
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• v.16 no.3
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• pp.66-74
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• 2011

A fluid in an enclosure can be heated by electric heating, chemical reaction, or fission heat. In order to remove the volumetric heat of the fluid, the walls surrounding the enclosure must be cooled. In this case, a natural convection occurs in the pool of the fluid, and it has a dominant role in heat transfer to the surrounding walls. It can augment the heat transfer rates tens to hundreds times larger than conductive heat transfer. The heat transfer by a natural convection in a regular shape such as a square cavity or semi-circular pool has been studied experimentally and numerically for many years. A pool of an inverted triangular shape with 10 degree inclined bottom walls has a good cooling performance because of enhanced boiling critical heat flux (CHF) compared to horizontal downward surface. The coolability of the pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the pool. In this study, turbulence models with modifications for buoyancy effect were validated for unsteady natural convections by volumetric heating. And natural convection in the triangular pool was evaluated by using the models.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.9
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• pp.685-692
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• 2012

In this work, nucleate pool boiling heat transfer coefficients(HTCs) of 5 refrigerants of different vapor pressure are measured on horizontal Thermoexcel-E square surface of 9.53 mm length. Tested refrigerants are R32, R22, R134a, R152a and R245fa. HTCs are taken from 10 $kW/m^2$ to critical heat fluxes for all refrigerant at $7^{\circ}C$. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and in the liquid pool. Test results show that critical heat fluxes(CHFs) of Thermoexcel-E enhanced surface are greatly improved as compared to that of a plain surface in all tested refrigerants. CHFs of all refrigerants on the Thermoexcel-E surface are increased up to 100% as compared to that of the plain surface. The improvement of Thermoexcel-E surface in CHF, however, is lower than that of the low fin surface. HTCs on Thermoexcel-E surface increase with heat flux. But after certain heat flux, HTCs began to decrease due to the difficulty in bubble removal caused by the inherent complex nature of this surface. Therefore, at heat fluxes close to the critical one, sudden decrease in HTCs needs to be considered in thermal design with Thermoexcel-E surface.