• Journal of Aerospace System Engineering
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• v.11 no.4
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• pp.48-53
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• 2017

Liquid rocket engines (LREs) are very complex systems that include combustion chambers, turbopumps, gas generators, ducts and tubes, valves and etc. Most components of the LREs require higher than or equal to level 6 IT (ISO Tolerance). The components along with pipe line and/or tubing must dispose not to interfere each other. In addition, effectiveness of maintenance and service after assembling should be considered when the allocation of the components are determined. Especially at the stage of the development, tolerance accumulations or unpredictable errors may result in misalignment and/or mismatches at interfaces of the parts. Namely, it is the engine assembling process that many inherent risks are realized and crises or incidents occur. Therefore, a rapid reaction system should be prepared. In this research, 7 tonf class liquid rocket assembling process was studied and actual building steps were introduced.

• Journal of the Korean Institute of Gas
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• v.25 no.3
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• pp.1-8
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• 2021

Among the flare systems that handle discharged substances from safety valves, the knockout drum was a key facility for safety, but the installation standards were not clear, so it was necessary to review the standards acceptable to the workplace and regulatory agencies. After investigating the domestic and foreign technical standards of knockout drums and the deficiencies of previous studies, research was first conducted on the degree of mass discharge, the installation location of the intermediate knockout drum, and the effect of changes in the composition of the discharged material. As a result of the study under the process simulation conditions, the gas-liquid separation of the knockout drum was completed in a small amount of less than 7,500kg/hr. However, when more than that was released, the gas-liquid separation effect was small even with the addition of an intermediate knockout drum. In addition, when the composition ratio of the material easily condensed was increased (molar fraction 10%), the gas-liquid separation effect of the knockout drum increased in the case of mass release. The gas-liquid separation effect was analyzed to be greater when the knockout drum was installed adjacent to the stack than the knockout drum was installed adjacent to the process equipment.

• Journal of the Korean Institute of Gas
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• v.22 no.6
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• pp.76-89
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• 2018

The distribution of the combined heat and power system is active as a solution to the instability of energy supply and environmental pollution caused by continuous industrial development. In Korea, the safety standards for combined heat and power system using a gas engine are insufficient therefore the study on this is needed. In this study, the safety performance and structural/material assessment items of domestic and international standards applied to the combined heat and power system were analyzed to carry out a standardization study on safety performance applicable to 20 kW gas engine combined heat and power system. In addition, the safety performance assessment (plan) of the gas engine combined heat and power system was derived by performing risk analysis and risk assessment using HAZOP. Assessment items include engine ignition systems related to safety performance, piping tight performance, watering and temperature rise performance, combustion performance, electrical efficiency, thermal efficiency, overall efficiency and humidity performance. Gas and water pipes, gas control and shut-off valves, durability, heat resistance, and cold resistance of metal or non-metallic materials related to the structure and materials of the gas engine combined heat and power systems.

• Journal of Chest Surgery
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• v.55 no.5
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• pp.388-396
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• 2022

Background: In this study, we present recent trends in heart valve surgery in Korea through analyses of data from the Korea Heart Valve Surgery Registry (KHVSR). Methods: We enrolled 8,981 patients who were registered in the KHVSR from 2017 to 2020. Yearly trends in patients' baseline characteristics, surgical profiles, and early mortality rates were explored. The observed/expected mortality ratio (O/E ratio), calculated from the actual mortality in the KHVSR and the predicted mortality estimated using the EuroSCORE II, was also analyzed. Results: The proportion of aortic valve surgery significantly increased from 56.8% in 2017 to 60.3% in 2020. The proportion of all combined procedures and minimally invasive surgery significantly increased over the 4-year study period. The operative mortality rate was 2.9% in the entire cohort, while mitral valve repair showed the lowest mortality risk (0.9%). The mortality rates of isolated aortic valve replacement (AVR) significantly decreased from 2.1% in 2017 to 0.8% in 2020 (p=0.016). Overall, the O/E ratio was 0.784 (95% confidence interval [CI], 0.677-0.902) demonstrating significantly lower actual mortality risks than expected based on the EuroSCORE II. In particular, the O/E ratios were as low as 0.364 (95% CI, 0.208-0.591) for isolated AVR. Conclusion: The recent data from the KHVSR showed increasing trends for complex procedures and minimally invasive surgery in heart valve surgery in Korea, and demonstrated remarkably low risks of operative mortality.

• Korean Journal of Plant Taxonomy
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• v.52 no.3
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• pp.184-195
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• 2022

The invasive alien species Brassica tournefortii Gouan (Brassicaceae) is herein reported for the first time in Korea, from Gunsan-si, Gochang-gun, and Jeju-si. Brassica tournefortii can easily be distinguished from B. juncea and B. napus by its dense stiff hairs at the base of the stem and leaves, basally and distally branched stems, partially dehiscent fruits, and seeds that become mucilaginous in the presence of moisture. Although some taxonomists have classified this species as belonging to Coincya Rouy based on its fruit and seed characteristics, the existence of one vein on the fruit valves and our maximum likelihood analysis using internal transcribed spacer sequences placed it in Brassica. Distribution data, photographs, and a description of B. tournefortii are presented herein. Moreover, potential changes in the distribution of B. tournefortii were predicted under different climate scenarios, but our analysis showed that the probability of the spreading of this species is low. Nevertheless, continuous monitoring is necessary for an accurate assessment. The results of the present study can be used to conduct an invasion risk assessment and can assist with the effective management of this invasive alien species.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.39 no.9
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• pp.41-51
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• 2010

건물의 배수 및 통기시스템에서 나타나는 현상중에 확실한 내용이 아직 밝혀지지 않은 부분이 몇 가지 남아 있다. 이것은 19세기 말엽의 근대 위생공학의 시작 단계에서부터 잘 알려진 사실이다. 건물의 배수 및 통기시스템 운용에 대한 내용은 일반 공학과 특정 유체역학의 범위 내에서 가장 잘 이해할 수 있다. 건물의 배수 및 통기시스템의 운영에 종사했던 초기의 기술진들은 이러한 점을 잘 알고 있었으며 유체역학에 적합하게 응용한 많은 사례를 확인할 수 있었다. 제2차 세계대전이 끝나고 이에 대한 많은 연구가 진행되어 왔으며 특히 유럽에서 시작된 전후 재건 붐을 통해 배수 및 통기시스템의 설계에 좀 더 효율적인 접근이 진척되게 되었다. 이러한 배수시스템의 중심에는 배수관 내부의 오염된 공기가 배수구 또는 위생기구를 통하여 주거 공간으로 유입되는 것을 방지하는 트랩(Water Trap)이 있다. 배수트랩의 주요 기능인 봉수는 일반적으로 깊이가 40 mm에서 50 mm 정도로 위생기구의 종류에 따라 봉수의 깊이는 다소 차이가 있다. 배수관내 공기의 흐름이 중요한 것처럼 트랩의 봉수 메커니즘이 중요하기 때문에 이 메커니즘을 소홀히 여긴다면 안전한 배수시스템의 운영을 기대하기는 어렵다. 배수관 내의 공기의 흐름은 배수에 의해 유입되거나 또는 배출된다. 배수관에서 내부 압력의 불규칙한 변화로 인하여 야기되는 불안정한 배수의 흐름은 트랩의 봉수를 파괴하고 나아가 주거공간으로 오염된 공기가 새어 나갈 수 있는 통로를 제공하게 된다. 관내압력의 천이는 이로 인한 문제가 발생할 가능성이 있는 위치에 그 압력을 완화할 수 있는 장치를 설계단계에 반영하여 적용함으로써 제어할 수 있다. 건물 내부에 상당한 길이의 통기배관을 설치하는 것은 배관의 마찰손실로 인하여 천이 현상을 효과적으로 제어할 수 있는 확실한 방법이 되지는 못한다. 그렇지만 통기밸브를 설치하는 것과 같이 배수관 내로 공기를 공급해주는 유입구를 건물 내부에 분산 설치하는 것이 효율적인 통기방식이 될 수 있고, 정압 천이로 인한 위험을 줄여줄 수 있다. 통기밸브는 정압 발생의 원인이 되지 않으며 단지 정압에 반응하여 더욱 기밀하게 닫히며, 약화된 압력파를 반사할 뿐이다. 고층 건물에서 배수입상관과 평행하게 설치된 통기입상관(Parallel Vent Pipe)의 경우 극히 일부분의 정압 천이 현상을 완화할 수 있다. (통기 배관의 직경이 배수 입상배관과 동일한 경우 대략 1/3 정도임), 그러므로 정압의 천이로 인한 압력 파동은 배수 시스템의 나머지 부분을 통해 전파되어 배수 트랩에 영향을 미치게 된다. 정압의 천이가 예상되는 위치에 정압천이 완화 장치(Positive Air Pressure Transient Alleviation Device)를 사용하면 배관 내부압력의 급격한 상승을 방지하여 연결된 트랩의 봉수를 보호할 수 있다. 이렇게 되면 순간적으로 발생하는 배관내 압력의 급등 현상을 90% 정도까지 완화 시킬 수 있다. 경험적으로 배수시스템에서 배관이 완전하게 막혀 과도한 정압이 발생하는 경우는 거의 없다. 이러한 경우에는 가장 낮은 위치에 있는 배수 트랩의 봉수가 깨지면서 자연스럽게 배수시스템의 압력이 해소되게 된다. 이러한 사례는 통기 방식과 상관없이 발생할 수 있다. 실제와 유사한 시뮬레이션을 통하여 통기 밸브(Air Admittance Valves)는 전면 통기 시스템 (Fully Vented System)에서 최소한 트랩의 봉수 보호용으로 적합한 것이 확인 되었다. 어떤 경우 에는 고층 건물에 더욱 적합하다는 것을 확인할 수 있었다. 부압 해소용으로 통기밸브를 이용하고 정압완화용으로 정압 완화장치(PAPAs: Positive Air Pressure Transient Attenuators)를 사용하는 전면적 능동 제어시스템(Fully Engineered Designed Active Control System)이 사용자에게 육안으로는 확인하지 못하는 기능을 보장하면서 배수 시스템의 안전과 효율성에 대한 효과적인 방법을 제공하고 있다.

• Journal of the Korean Electrochemical Society
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• v.26 no.4
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• pp.43-55
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• 2023

Mass transport through nanoporous structures such as nanopores or nanochannels has fundamental electrochemical implications and many potential applications as well. These structures can be particularly useful for water treatment, energy conversion, biosensing, and controlled delivery of substances. Earlier research focused on creating nanopores with diameters ranging from tens to hundreds of nanometers that can selectively transport cationic or anionic charged species. However, recent studies have shown that nanopores with diameters of a few nanometers or even less can achieve more complex and versatile transport control. For example, nanopores that mimic biological channels can be functionalized with specific receptors to detect viruses, small molecules, and even ions, or can be made hydrophobic and responsive to external stimuli, such as light and electric field, to act as efficient valves. This review summarizes the latest developments in nanopore-based systems that can control mass transport based on the size of the nanopores (e.g., length, diameter, and shape) and the physical/chemical properties of their inner surfaces. It also provides some examples of practical applications of these systems.

• Journal of the Korean Society of Radiology
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• v.81 no.2
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• pp.324-336
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• 2020

Cardiovascular calcifications can occur in various cardiovascular diseases and can serve as a biomarker for cardiovascular event prediction. Advances in CT have enabled evaluation of calcifications in cardiovascular structures not only on ECG-gated CT but also on non-ECG-gated CT. Therefore, many studies have been conducted on the clinical relevance of cardiovascular calcifications in patients. In this study, we divided cardiovascular calcifications into three classes, i.e., coronary artery, thoracic aorta, and cardiac valve calcifications, which are closely associated with cardiovascular events. Further, we briefly described pericardial calcifications, which can be found incidentally. Since the start of lung cancer screening in Korea in the second half of 2019, the number of non-enhanced, non-ECG-gated, low-dose chest CT has been increasing, and the number of incidentally found cardiovascular calcifications has also been increasing. Therefore, understanding the relevance of cardiovascular calcifications on non-enhanced, non-ECG-gated, low-dose chest CT and their proper reporting are important for radiologists.

• Journal of the Korean Society of Radiology
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• v.84 no.6
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• pp.1324-1336
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• 2023

Purpose This study aimed to compare the diagnostic performance of cardiac CT and transthoracic echocardiogram (TTE) depending on the degree of valvular calcification and bicuspid aortic valve (BAV) subtype. Materials and Methods This retrospective study included 266 consecutive patients (106 with BAV and 160 with tricuspid aortic valve) who underwent cardiac CT and TTE before aortic valve replacement. Cardiac CT was used to evaluate the morphology of the aortic valve, and a calcium scoring scan was used to quantify valve calcium. The aortic valves were classified into fused and two-sinus types. The diagnostic accuracy of cardiac CT and TTE was calculated using a reference standard for intraoperative inspection. Results CT demonstrated significantly higher sensitivity, negative predictive value, and accuracy than TTE in detecting BAV (p < 0.001, p < 0.001, and p = 0.003, respectively). The TTE sensitivity tended to decrease as valvular calcification increased. The error rate of TTE for CT was 10.9% for the twosinus type of BAV and 28.3% for the fused type (p = 0.044). Conclusion Cardiac CT had a higher diagnostic performance in detecting BAV than TTE and may help diagnose BAV, particularly in patients with severe valvular calcification.

• Korean Circulation Journal
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• v.53 no.11
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• pp.744-755
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• 2023

Background and Objectives: Aortic valve replacement (AVR) is considered a class I indication for symptomatic severe aortic stenosis (AS). However, there is little evidence regarding the potential benefits of early AVR in symptomatic patients diagnosed with normal-flow, low-gradient (NFLG) severe AS. Methods: Two-hundred eighty-one patients diagnosed with symptomatic NFLG severe AS (stroke volume index ≥35 mL/m², mean transaortic pressure gradient <40 mmHg, peak transaortic velocity <4 m/s, and aortic valve area <1.0 cm²) between January 2010 and December 2020 were included in this retrospective study. After performing 1:1 propensity score matching, 121 patients aged 75.1±9.8 years (including 63 women) who underwent early AVR within 3 months after index echocardiography, were compared with 121 patients who received conservative care. The primary outcome was a composite of all-cause death and heart failure (HF) hospitalization. Results: During a median follow-up of 21.9 months, 48 primary outcomes (18 in the early AVR group and 30 in the conservative care group) occurred. The early AVR group demonstrated a significantly lower incidence of primary outcomes (hazard ratio [HR], 0.52; 95% confidence interval [CI], 0.29-0.93; p=0.028); specifically, there was no significant difference in all-cause death (HR, 0.51; 95% CI, 0.23-1.16; p=0.110), although the early AVR group showed a significantly lower incidence of hospitalization for HF (HR, 0.43; 95% CI, 0.19-0.95, p=0.037). Subgroup analyses supported the main findings. Conclusions: An early AVR strategy may be beneficial in reducing the risk of a composite outcome of death or hospitalization for HF in symptomatic patients with NFLG severe AS. Future randomized studies are required to validate and confirm our findings.