• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.28-39
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• 2018

In this study, numerical simulations were performed for steady and unsteady state characteristics of length effects on linear pintle nozzles using the overset grid method. Nozzles and pintles are created separately by an auto grid generation program to use the overset grid method. Appropriate turbulent models and numerical methods are selected for the validation of simulations. Pintle shapes are chosen from five types, with differences in the ratio of length and diameter. The longer the pintle length, the greater the thrust and thrust coefficient. The chamber pressure tendency of steady-state and unsteady-state are different for various pintle velocities. The thrust of the nozzle exit responds to changes in the nozzle throat in the unsteady-state, and the speed of pressure propagation wave generated by movement of the pintle is considered to predict the major factor of performance.

• The Journal of Pediatrics of Korean Medicine
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• v.19 no.2
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• pp.31-40
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• 2005

Objectives: This study was performed to investigate the character of childhood common cold according to four seasons. Methods: We made an investigation into medical record of 432 children under fifteen years of age who visited pediatrics or emergency room suffering from common cold. We analyzed the principal and secondary symptoms of the children classifying four seasons by $SPSS^{\circledR}$ 12.0 for windows. Results: Male to female ratio were 1.42:1, the average of age was 3.86 years old. Distribution of principal symptoms was that nasal discharge was 231(56.1%), cough was 233(54.1%), nasal obstruction was 162(39.3%), secretion and sputum were 126(30.6%), fever was 121(29.4%), and headache was 13(3.2%). Out of these fever occurred in high frequency during spring and summer, nasal obstruction occurred in high frequency during spring and autumn. Distribution of secondary symptoms was that throat pain was 93(22.6%), otalgia was 39(9.5%), vomiting was 35(8.5%), abdominal pain was 30(7.3%), anorexia was 23(5.6%), sweating was 21(5.1%), diarrhea was 19(4.6%), and startle was 11(2.7%). Out of these otalgia occurred in high frequency during spring and summer, diarrhea occurred in high frequency during autumn and winter. Conclusions: A few symptoms can be the character according to four seasons.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.1-7
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• 2017

The performance of a MEMS solid propellant thruster was predicted and analyzed through internal ballistics model and CFD analysis. The nozzle throat was $416{\mu}m$, and the area ratio of the nozzle was 1.85. As a result of the internal ballistics model, chamber pressure increased up to 197 bar and the maximum thrust was 3,836 mN. In CFD analysis, the chamber pressure of the internal ballistics model was applied as the operating pressure, and the CFD model was divided into an adiabatic and a heat loss model. As a result, the maximum thrust of the adiabatic model was 14.92% lower than that of the internal ballistics model, and the effect of heat loss was insignificant.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.3
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• pp.28-34
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• 2019

The thrust control calculation according to the operation of plug nozzle for cold air test and the analysis of the flow characteristics of the pintle shape and operation pressure are performed. The numerical computation was verified by comparing the flow structure and the coefficient of thrust with the experimental data. It was confirmed that the nozzle throat was formed at the design position on each pintle shape, and thrust control up to 1:8 was achieved only by the stroke change. Finally, although the aerospike nozzle is autonomous, it is unfavorable in the under_expansion condition, if it is designed for a very low nozzle pressure ratio.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.66-72
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• 2018

A numerical study was conducted to investigate the performance characteristics of a STED with various pressure ratios (PRs) and cone shapes. Due to momentum loss, the pressure in vacuum chamber increased with cone angle for a PR of 75. Also, the STED is started between PRs of 36 and 37 in the case of a cone angle of $15^{\circ}$ and a blockage ratio (BR) of 15%. The results for various PRs and cone shapes are presented, and the optimal cone shape is found to have a cone angle of between $5{\sim}20^{\circ}$ and a BR of between 15~40%.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.78-84
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• 2020

The performance of pintle thruster is analyzed by using the pintle thruster performance analysis model which integrating the element models introduced in Part I. To verify the performance analysis, the results of the developed program are compared with the experimental data of kerosene/hydrogen peroxide liquid pintle thrusters. Based on the results, the characteristics of the pintle thruster are analyzed. The sensitivity analysis is performed to investigate the effect of thruster shape and operation parameters on performance characteristics using both OAT and scatter plot methods. The four performance parameters such as droplet diameter, film flow rate, O/F ratio, and nozzle throat diameter are evaluated to investigate their effects on characteristic speed, combustor pressure, and specific thrust.

• Journal of Preventive Medicine and Public Health
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• v.56 no.5
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• pp.431-439
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• 2023

Objectives: Numerous studies have explored the causes and spread of outbreaks, yet there is a lack of research on post-coronavirus disease 2019 condition (PCC) in Korea. The goal of this study was to identify the various types of PCC and associated factors in discharged patients and to provide directions for the ongoing health management of confirmed patients. Methods: A telephone survey was conducted among 680 coronavirus disease 2019 (COVID-19) patients diagnosed between July 7, 2021 and August 26, 2021, in Dangjin, Chungnam, Korea. A descriptive analysis of characteristics, univariate analysis, and regression were performed using data from basic epidemiological surveys conducted at the time of diagnosis and post-discharge questionnaires. Results: Of the 585 patients who responded, 159 (27.2%) developed PCC. Of the 211 patients with no initial symptoms, 27 (12.8%) developed PCC, versus 132 (35.3%) of the 374 patients with initial symptoms. Among the initial symptoms, fever or chills, cough or sputum, loss of smell, and sore throat were associated with PCC. Compared to patients with less than 10 days of hospitalization, those with a hospitalization period of 21 days to 30 days (odds ratio [OR], 2.3; 95% confidence interval [CI], 1.0 to 5.2) and 31 days or more (OR, 5.8; 95% CI, 1.9 to 18.1) had a higher risk of PCC. Conclusions: More than a quarter of COVID-19 patients, including those who had no initial symptoms, experienced PCC in Korea. People with the initial symptoms of fever, chills, and respiratory symptoms and those who had prolonged hospital stays had a high risk of PCC.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.2
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• pp.183-190
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• 2015

An ejector is a type of non-powered pump that is used to supply a secondary flow via the ejection of a primary flow. It is utilized in many industrial fields, and is used for fueling the vehicle because of less failures and simple structure. Since most of ejectors in industry are gas-to-gas and liquid to gas ejector, many research activities have been reported in optimization of gas ejector. On the other hand, the liquid ejector is also applied in many industry but few research has been reported. The liquid ejector occurs cavitation, and it causes damage of parts. Cavitation has bees observed at the nozzle throat at the specified pressure. In this study, a two-dimensional axisymmetric simulation of a liquid-liquid ejector was carried out using five different parameters. The angle of the nozzle plays an important role in the cavitation of a liquid ejector, and the performance characteristics of the flow ratio showed that an angle of $35^{\circ}$ was the most advantageous. The simulation results showed that the performance of the liquid ejector and the cavitation effect have to be considered simultaneously.

• Journal of Korean Society for Atmospheric Environment
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• v.25 no.1
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• pp.26-37
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• 2009

Recently rapid environmental changes due to desertification and industrialization in China make a threat to Korea, especially during Asian Dust Event (ADE). This study was aimed to compare symptoms and behaviors related to ADE between Korea and China. We conducted questionnaires on self-reported symptoms and behaviors before and during ADE. Korean and Chinese subjects were grouped into children, adults, and elderly by nation (n=791). Statistical analyses were performed by $X^2$-test, Fisher's exact test, t-test and chow's test for comparing differences between Korean and Chinese. We estimated the odds ratio for perceived symptoms during ADE by preventive behavior, using Generalized Estimation Equation (GEE). The study indicated that there were significant differences between symptoms in Korea and those in China such as cold, cough, and sore throat, especially in elderly. Preventive behaviors such as avoiding outdoor activity and wearing sunglasses were more often performed in China than Korea. However wearing mask was more often performed in Korea than China. After adjusting for age, sex, educational level, and smoking status, the odds ratio (OR) of dry cough symptom in Korea was significantly decreased by closing the windows and wearing a mask during ADE. In China, the OR of dry cough symptom was decreased by wearing a mask and avoiding outdoor activity. We found that China which had higher performance of preventive behavior showed lower prevalence of symptoms during ADE than Korea. Also preventive behaviors could affects prevalence of symptoms during ADE. This results suggest that preventive behavior. could reduce symptoms during ADE and there are needed for. more attentions to reduce a threat of ADE.

• Clinical and Experimental Pediatrics
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• v.51 no.11
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• pp.1191-1197
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• 2008

Purpose : Previously, Epstein-Barr virus (EBV) infection was diagnosed by serological examination; currently, many EBV antigen detection methods have been developed and applied clinically for diagnosing EBV infection. To delineate the clinical characteristics of EBV infection, clinical and laboratory findings were evaluated for patients who tested positive in EBV polymerase chain reaction (PCR). Methods : EBV PCR was conducted in 352 patients admitted to the pediatric ward from January 2004 to December 2006, with more than 2 clinical signs such as fever (${\geq}37.5^{\circ}C$), exudative throat infection, lymphadenopathy, hepatitis of unknown etiology, and splenomegaly. The EBV viral gene was detected by PCR in 115 patients (32%), and the clinical characteristics of these patients were evaluated. Laboratory findings such as leukocytosis, thrombocytopenia, atypical lymphocyte, and alteration in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in peripheral blood were examined. The EBV-specific immunoglobulin M antibody (EBV-IgM Ab) was also tested. Results : Most of the children were younger than 8 years (89%), and the male to female ratio was 1.3:1. Exudative throat infection and fever (${\geq}37.5^{\circ}C$) were observed in all patients. Cervical lymph node enlargement was seen in 36 patients (31 %); leukocytosis ($WBC{\geq}10,000/mm^3$), in 54 patients (47%); and atypical lymphocyte (${\geq}20%$), in 28 patients (24%). EBV-IgM Ab was positive in 33 patients (29%). The younger patients had higher ALT levels and higher incidence of positive EBV-IgM Ab than the older patients. Conclusion : The cumulative number of patients diagnosed to have EBV infection by PCR increased markedly for those under 8 years. ALT was higher and EBV-IgM Ab was detected more in younger patients with EBV infection.