• 대한기계학회논문집B
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• 제33권4호
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• pp.288-297
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• 2009

A serpentine channel geometry often used in a fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from the intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with high aspect ratio of active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compressive forces. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds that of dropwise condensation in cathode channels.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권8호
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• pp.3550-3566
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• 2020

As a widely used way to exfiltrate information, wireless covert channel (WCC) brings a serious threat to communication security, which enables the wireless communication process to bypass the authorized access control mechanism to disclose information. Unlike the covert channel on the network layer, wireless covert channels on the physical layer (WCC-P) is a new covert communication mode to implement and improve covert wireless communication. Existing WCC-P scheme modulates the secret message bits into the Gaussian noise, which is also called covert digital communication system based on the joint normal distribution (CJND). Finding the existence of this type of covert channel remains a challenging work due to its high undetectability. In this paper, we exploit the square autocorrelation coefficient (SAC) characteristic of the CJND signal to distinguish the covert communication from legitimate communication. We study the sharp increase of the SAC value when the offset is equal to the symbol length, which is caused by embedding secret information. Then, the SAC value of the measured sample is compared with the threshold value to determine whether the measured sample is CJND sample. When the signal-to-noise ratio reaches 20db, the detection accuracy can reach more than 90%.

• 설비공학논문집
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• 제28권10호
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• pp.408-413
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• 2016

The objective of this study is to investigate the performance of a heat recovery heat pump dryer using a R245fa refrigerant experimentally. In this study, the main components of the heat pump dryer were an evaporator, a compressor, a condenser, and an expansion valve. As a result, when the amount of refrigerant varied from 15 kg to 16 kg, the hot air outlet temperature in the condenser and the heat transfer rate were almost kept constant. Therefore, the amount of refrigerant at 16 kg was considered to be a suitable amount in the heat pump. As the air inlet velocity varied from 0.5 m/s to 1.5 m/s, the highest temperature in the condenser could be obtained when the air inlet velocity was 0.5 m/s. The heat transfer rate, system (COP), and hot air outlet temperature were 5.6 kW, 3.4, and $102.5^{\circ}C$, respectively, when the bypass ratio and water temperature were 0% and $60^{\circ}C$.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.147-151
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• 2007

A serpentine channel geometry often used in a polymer electrolyte membrane fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with relatively high aspect ratio active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compression conditions. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds to that of dropwise condensation in cathode channels.

• Journal of Chest Surgery
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• 제22권1호
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• pp.32-41
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• 1989

We scrutinized the 64 cases of TGA and Taussig-Bing anomaly who underwent Senning and Mustard operations from Jan. 1981 to May 1988. The ratio of male to female was 45; 19, and the age at operation varied from 2 months to 18 years [mean 18.9*32.9 months]. The in-hospital mortality was in 24 cases [37.5%] and the major causes were myocardial failure and congestive heart failure associated with arrhythmias. The risk factors for hospital mortality were complex TGA, prolonged bypass time and high postoperative CVP. In addition, mortality increased during the first year the procedure was used. Late mortality occurred in 6 cases and the major causes was congestive heart failure, and there was not any significant risk factor noted in late mortality. Early arrhythmia developed in 37.5%, all of which were transient and self limited and 7 cases of early mortality were related to the arrhythmias. Late arrhythmias developed in 8 cases, but 7 cases were transient. One case died with junctional tachycardia. Of significance the one case that died late by arrhythmia had a similar junctional tachycardia in the early postoperative period. The survival rate in all cases disregarding initial in-hospital mortality 1YSR 89.8% and 5YSR 84.3%, but because of short duration of follow up this is not significant. We concluded that early hospital mortality could be decreased by operating at an earlier age and by adjusting the appropriate operation method.

• Journal of Chest Surgery
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• 제24권10호
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• pp.973-978
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• 1991

From January, 1982, to December, 1990, 15 patients underwent pericardiectomy for chronic constrictive pericarditis on Department Of Thoracic and Cardiovascular Surgery, School of Medicine, Pusan National University. There were 9 male and 6 female patients [male to female ratio was 1.5: 1] ranging from 15 years to 63 years old [mean age 35.0]. All patients underwent pericardiectomy through a median sternotomy, partial cardiopulmonary bypass was performed on two patients. There were 3 postoperative death [20%]. Six cases [40%] were tuberculous origin 5 cases [34%] were Idiopathic [nonspecific chronic inflammatory change was considered to idiopathic], 2 cases [13%] were malignant origin, 2 cases [13Yo] were pyogenic origin. Dyspnea on exertion was evident in all patients and abdominal distention, general weakness, palpitation, peripheral edema were found. Eleven patients showed low voltage of QRS wave, 7 patients showed diffuse ST-T wave change, 2 patients showed atrial fibrillation on EKG. There were 6 patient showed pericardial thickening, 5 patients showed evidence of restriction, 5 patients showed pericardial effusion, 4 patients showed low cardiac output on preoperative echocardiogram. Hemodynamic response to pericardiectomy were observed; preoperative CVP 26.8 cmH2O declined to 15.0 cmH2O. Preoperative NYHA Functional class showed class II - 1, class III - 10, class IV - 4, postoperative NYHA functional class showed class I - 7, class II - 4, class Ill - l.

• Journal of Chest Surgery
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• 제19권1호
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• pp.18-24
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• 1986

The mean perfusion pressure produced by 20 different design and size of disposable aortic perfusion cannulas [size range: 18F to 20F] at flow rates of 1 to 5 L/min was compared. A roller pump with perfusion tubing 10mm in inner diameter was used with a mixture of 0.9% normal saline and 100% glycerin [mixing ratio of 6.72:13.28] to make the viscosity as normal blood in 20oC as the test solution. Line pressure in these cannulas at a flow rate of 3L/min ranged from 13.2$\pm$4.47 to 157$\pm$1 34 mmHg in a case of absence of resistance, and from 11.4$\pm$1.14 to 227.2$\pm$4.47 mmHg in a case of presence of resistances 14 cannulas had gradients of less than 100Hg at a flow rate of 3L/min and 9 cannulas less than 100mmHg at 4L/min. The following results were obtained from this experimental study: .1] A wide range of line pressure was observed in disposable aortic perfusion cannulas currently in clinical use; 2] Some cannulas currently used for cardiopulmonary bypass in adults generated excessive line pressure; 3] Both the material and design affect function, with some designs safer than others. Cardiac surgeons should base the choice of aortic perfusion cannula on the best performance and safest design available to avoid cannula-related problems during operation.

• Journal of Chest Surgery
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• 제22권3호
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• pp.384-392
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• 1989

Forty cases of coronary artery bypass grafting treated at the Department of Thoracic and Cardiovascular Surgery, SNUH, Korea were compared with forty cases of the procedure treated at University of Alberta Hospital, Canada, in terms of pathoanatomy. That showed no difference in sex ratio between Korean and Caucasian the average ages, however, were 50.4 years and 60.9 years respectively [p< 0.005]. The leading cause of angina at presentation was unstable angina in Korean, but it was post-infarction angina in Caucasian instead. The incidences of single-vessel disease and double-vessel disease were similar in both countries, but the incidence of so-called triple-vessel disease was higher in Caucasian while left main coronary artery disease was more prevalent in Korean [0.01< P, 0.005]. < The internal diameters of surgically available coronary artery branches had similar characteristics and no significant statistical differences were found between them. The predilection sites of stenoses were proximal left anterior descending artery, left main coronary artery, proximal left circumflex artery and proximal right coronary artery decreasing in incidence respectively, in Korean. The myocardial perfusion score were 6.80 in single-vessel disease, 7.56 in double-vessel disease, 11.27 in triple-vessel disease and 9.77 in left main disease respectively, in Korean.

• Journal of Trauma and Injury
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• 제36권3호
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• pp.180-186
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• 2023

Purpose: The purpose of this study was to report the treatment results of patients with traumatic cardiac tamponade after the opening of Jeju Regional Trauma Center. Methods: We analyzed the treatment outcomes of patients with traumatic cardiac tamponade who were treated at Jeju Regional Trauma Center from January 2018 to August 2022. Results: Seven patients with traumatic cardiac tamponade were treated. The male to female ratio was 1.33:1 (four male and three female patients) and the average age was 60.3±7.2 years. The mechanism of injury was blunt trauma in six cases and penetrating injury in one case. Upon arrival at the emergency department, pericardiostomy was performed in four cases, and an emergency operation was performed in six cases. Pericardiostomy alone was performed in one patient, who had cardiac tamponade due to extrapericardial suprahepatic inferior vena cava rupture. The causes of cardiac tamponade were right atrium appendage rupture in one case, right ventricle rupture in one case, inferior vena cava rupture in two cases, right atrium and left atrium rupture in one case, both atria and left ventricle rupture in one case, and intercostal artery rupture in one case. In three cases, intraoperative cardiopulmonary bypass was required. Two of the seven patients died (mortality rate, 28.5%). Conclusions: Relatively favorable treatment results were observed for traumatic cardiac tamponade patients after Jeju Regional Trauma Center was established.

• Asian-Australasian Journal of Animal Sciences
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• 제14권5호
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• pp.651-654
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• 2001

A study was made of the efficiency of ammonia N retention by Jowar kadbi (sorghum straw), initially 6.41% crude protein (CP), treated with 4% urea solution. After 30 days the CP in straw that was unchaffed and had been left uncovered was 10.02, and in chaffed straw that had been covered with a polythene sheet was 10.9%. The two treated straws were each fed to six crossbred (HF$\times$Deoni) calves, initially $12{\pm}2$ months old and $86.7{\pm}3.2kg$ bodyweight. They were also given two isocaloric (70% TDN) and isonitrogenous (20% CP) concentrate mixtures differing in calculated Rumen Degradable to Undegradable Dietary Protein ratio (RDP:UDP). Those fed the unchaffed uncovered treated straw (treatment C) received 65 RDP:35UDP and the other group (T1) received concentrate with a 55:45 ratio. The T1 group had the higher DM intake (p<0.01) in total (306 vs 268 kg), per day (4.1 vs 3.6 kg) and per unit bodyweight. Digestibility of DM, OM, CP and NDF, but not ADF, was higher in T1 and that group had the higher daily gain (517 vs 333 g) and higher total gain (38.8 vs 25.0 kg) over the 75 d of the feeding trial. It is concluded that chaffing and covering of Jowar kadbi treated with urea, not likely to be adopted by farmers because of financial constraints, does not confer important benefits. A concentrate supplement (estimated 45% of the CP as UDP) to calves given the treated straw has a beneficial effect on their growth and development.