• 산업경영시스템학회지
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• 제44권2호
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• pp.140-152
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• 2021

During the shift from gasoline vehicles to electric ones, auto parts manufacturing companies have realized the importance of improvement in the manufacturing process that does not require any layout changes nor extra investments, while maintaining their current production rate. Due to these reasons, for the auto part manufacturing company, I-company, this study has developed the simulation model of the PUSH system to conduct a process analysis in terms of production rate, WIP level, and logistics work's utilization rate. In addition, this study compares the PUSH system with other three manufacturing systems -KANBAN, DBR, and CONWIP- to compare the performance of these production systems, while satisfying the company's target production rate. With respect to lead-time, the simulation results show that the improvement of 77.90% for the KANBAN system, 40.39% for the CONWIP system, and 69.81% for the DBR system compared to the PUSH system. In addition, with respect to WIP level, the experimental results demonstrate that the improvement of 77.91% for the KANBAN system, 40.41% for the CONWIP system, and 69.82% for the DBR system compared to the PUSH system. Since the KANBAN system has the largest impacts on the reduction of the lead-time and WIP level compared to other production systems, this study recommends the KANBAN system as the proper manufacturing system of the target company. This study also shows that the proper size of moving units is four and the priority allocation of bottleneck process methods improves the target company's WIP and lead-time. Based on the results of this study, the adoption of the KANBAN system will significantly improve the production process of the target company in terms of lead-time and WIP level.

• Journal of Korean Biological Nursing Science
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• 제23권2호
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• pp.91-99
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• 2021

Purpose: This study aimed to identify occupational stress and health problems as well as turnover reasons among leavers in novice nurses and to estimate factors which might affect turnover by comparing them to stayers. Methods: In this study, secondary analysis of data gathered from the Shift Work Nurse's Health and Turnover studies, was carried out. The data were collected from 204 stayers who have been working for 18 months since 2018 and 48 leavers who left within the same period at two tertiary hospitals in Seoul. The reasons for turnover, occupational stress, and 8 types of health problems were recorded. The data were analyzed using SAS 9.4 to obtain descriptive statistics. In parallel, Pearson's chi-squared test, Fisher's exact test, and independent t-test were also conducted. Results: The main reasons for turnover were job stress and difficult interpersonal relationships in the workplace. Occupational stress of leavers was higher than stayers, especially in the subscales of interpersonal conflict, organizational system, lack of reward, and occupational climate. Among the 8 types of health problems, the depression prevalence of leavers was higher compared to stayers and showed marginal significance. Unexpectedly, the sleep disturbance prevalence of stayers was significantly higher compared to leavers. Conclusion: To reduce the turnover rate of novice nurses, education on how to cope with occupational stress is needed. A customized program for novice nurses to overcome the difficulties of interpersonal relations would be helpful.

• 한국컴퓨터정보학회논문지
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• 제27권1호
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• pp.157-166
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• 2022

본 연구는 철로 복합화물 운송 시 환적 작업으로 인해 발생하는 소요 시간과 비용을 줄이고 운송속도 향상이 가능한 피기백시스템의 도입 타당성을 분석하는 것을 목표로 한다. 이를 위해 국내외 문헌검토를 통해 타당성 분석방법론을 검토한다. 타당성 분석 값을 정량적으로 도출하기 위해 교통 데이터베이스를 적용하여 운송거리가 200KM이상인 주요 화물 운송 O-D 노선에 화물 운송 시뮬레이션 모델과 운송 수단별 화물 수요 예측 모델을 개발하였다. 2025년 주요 화물 운송 O-D 노선에 피기백시스템이 도입된다는 전제로 분석기간을 15년으로 설정하여 경제적 타당성을 분석한 결과 NPV 값이 양수이고 B/C값이 1.18로 도출되어 피기백시스템이 경제성이 있는 것으로 나타났다. 제안된 연구 방법은 철도운송의 경쟁력을 향상할 수 있는 교통 정책 수립에 유의미한 자료가 될 수 있다.

• Safety and Health at Work
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• 제13권2호
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• pp.148-154
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• 2022

Background: Bus driving is a mentally demanding activity that requires prolonged attention to ensure safety. The aim of the study was to assess mental fatigue caused by driving a public bus and to find a profile of workers at higher risk. Methods: We evaluated changes of critical flicker fusion (CFF) (index of central arousal) and heart rate variability (HRV) (index of autonomic balance) in a 6-hour driving shift on a real route, in 31 professional bus drivers, and we tested the influence of personal factors such as sleep quality, BMI, and age. Paired t-test was used to test differences of CFF and HRV between both initial and final phase of driving, while multiple linear regression tested the influence of personal variables on the indexes of mental fatigue. Results: Results showed that CFF significantly decreased after 6 hours of bus driving (41.91 Hz, sd 3.31 vs. 41.15 Hz, sd 3.15; p = 0.041), and heart rate significantly decreased in the final phase of driving, with respect to the initial phase (85 vs. 78 bpm, p = 0.027). Increasing age (beta = -0.729, p = 0.022), risk of obstructive sleep apnea syndrome (beta = -0.530, p = 0.04), and diurnal sleepiness (beta = -0.406, p = 0.017) showed a significant effect on influencing mental fatigue. Conclusion: Elderly drivers at higher risk of sleep disorders are more prone to mental fatigue, when exposed to driving activity. Monitoring indexes of central arousal and autonomic balance, coupled with the use of structured questionnaires can represent a useful strategy to detect profile of workers at higher risk of mental fatigue in such duty.

• Advances in nano research
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• 제13권2호
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• pp.187-197
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• 2022

The synthesis of organic and hybrid organic-inorganic perovskites directly from solution improves the cost- and energy-efficiency of processing. To date, numerous research efforts have been devoted to investigating the influence of the various solvent parameters for the synthesis of lead halide perovskites, focused on the effects of different single solvents on the efficiency of the resulting perovskites. In this work, we investigated the effect of solvent blends for the first time on the structure and phase of perovskites produced via the Lewis base vapor diffusion method to develop a new synthetic approach for water-stable CsPbBr₃ particles with nanometer-sized dimensions. Solvent blends prepared with DMF and water-miscible solvents with different Gutmann's donor numbers (D_N) affect the Pb ions differently, resulting in a variety of lead bromide species with various colors. The use of a DMF/isopropanol solvent mixture was found to induce the formation of the Ruddlesden-Popper perovskite based on lead bromide. This perovskite undergoes a blue color shift in the solvated state owing to the separation of nanoplatelets. In contrast, the replacement of isopropanol with DMSO, which has a high DN, induces the formation of spherical CsPbBr₃ perovskite nanoparticles that exhibit green emission. Finally, the integration of acetone in the solvent system leads to the formation of lead bromide complexes with a yellow-orange color and the perovskite CsPbBr₃.

• Steel and Composite Structures
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• 제41권5호
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• pp.761-773
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• 2021

This study presents a 3D non-linear finite element (FE) assessment of dynamic soil-structure interaction (SSI). The numerical investigation has been performed on the time domain through a Finite Element (FE) system, while considering the nonlinear behavior of soil and the multi-directional nature of genuine seismic events. Later, the FE outcomes are analyzed to the recorded in-situ free-field and structural movements, emphasizing the numerical model's great result in duplicating the observed response. In this work, the soil response is simulated using an isotropic hardening elastic-plastic hysteretic model utilizing HSsmall. It is feasible to define the non-linear cycle response from small to large strain amplitudes through this model as well as for the shift in beginning stiffness with depth that happens during cyclic loading. One of the most difficult and unexpected tasks in resolving soil-structure interaction concerns is picking an appropriate ground motion predicted across an earthquake or assessing the geometrical abnormalities in the soil waves. Furthermore, an artificial neural network (ANN) has been utilized to properly forecast the non-linear behavior of soil and its multi-directional character, which demonstrated the accuracy of the ANN based on the RMSE and R² values. The total result of this research demonstrates that complicated dynamic soil-structure interaction processes may be addressed directly by passing the significant simplifications of well-established substructure techniques.

• 정보보호학회논문지
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• 제32권6호
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• pp.1183-1192
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• 2022

정보 및 정보를 생산, 처리, 폐기하는 시스템은 정보의 총수명주기에 걸쳐 일정수준의 보안이 유지되어야 한다. 일정수준의 보안을 유지하기 위해 소프트웨어 및 자동차 개발, 미국 연방정부 정보체계 등 시스템 수명주기의 보안관리 프로세스를 적용하고 있으나, 우리나라에는 이와 유사한 보안관리 프로세스가 전무한 실정이다. 본 논문에서는 국방 분야 정보 및 정보 처리시스템의 총수명주기에 걸쳐 일정수준의 보안을 유지하기 위한 한국형 보안위험관리 프레임워크를 제안한다. 국방 분야에 적용할 수 있는 한국형 보안위험관리 프레임워크의 개발 목적과 적용방안을 소개함으로써 향후 국방 보안업무가 나가야 할 방향을 제시하고 보안 패러다임의 전환을 유도하고자 한다

• 한국컴퓨터정보학회논문지
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• 제27권6호
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• pp.123-130
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• 2022

본 연구는 신종감염병인 COVID-19 팬데믹 상황에서 환자를 간호하는 국내 병원 간호사들의 소진과 관련요인들을 관리하기 위한 방안이 필요함을 제안하였고 COVID-19 유행 기간동안 국내 임상 간호사의 소진과 관련된 요인을 파악하기 위해 체계적 문헌고찰을 실시하였다. 체계적 문헌고찰을 위해 문헌 검색과 분석은 2019년 12월 1일부터 2022년 4월 30일까지 RISS, KISS, DBPIA, 교보스콜라의 데이터베이스를 사용하였고 '임상 간호사의 소진', '간호사의 소진'의 키워드를 사용하였다. 총 55편의 연구 논문이 검색되었고 자료선정기준에 따라 최종 7편의 논문이 선별되었다. 임상간호사 소진 정도와 소진과 관련된 요인을 살펴보면, COVID-19 동안 임상 간호사는 중등도 이상의 소진을 경험하였고 소진과 관련된 요인은 개인적 특성인 신체증상, 우울, 공감만족, 공감피로, 회복탄력성과 직업적 특성인 교대근무와 직무스트레스로 나타났다. 추후 임상 간호사 소진과 관련된 요인들을 조절할 수 있도록 역량 강화 프로그램 개발 및 적용하고 일관성 있는 간호인력 간호인력관리지관리지침이나 정책을 제시하여 간호사 부족 현상을 해소될 수 있기를 기대해 본다.

• Current Photovoltaic Research
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• 제11권3호
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• pp.67-74
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• 2023

The earth-abundant element-based Cu₂ZnSn(S,Se)₄ (CZTSSe) thin film solar cells (TFSCs) have attracted greater attention in the photovoltaic (PV) community due to their rapid development in device power conversion efficiency (PCE) >13%. In the present work, we demonstrated the fine-tuning of the bandgap in the CZTSSe TFSCs by altering the sulfur (S) to the selenium (Se) chalcogenide ratio. To achieve this, the CZTSSe absorber layers are fabricated with different S/(S+Se) ratios from 0.02 to 0.08 of their weight percentage. Further compositional, morphological, and optoelectronic properties are studied using various characterization techniques. It is observed that the change in the S/(S+Se) ratios has minimal impact on the overall Cu/(Zn+Sn) composition ratio. In contrast, the S and Se content within the CZTSSe absorber layer gets altered with a change in the S/(S+Se) ratio. It also influences the overall absorber quality and gets worse at higher S/(S+Se). Furthermore, the device performance evaluated for similar CZTSSe TFSCs showed a linear increase and decrease in the open circuit voltage (V_oc) and short circuit current density (J_sc) of the device with an increasing S/(S+Se) ratio. The external quantum efficiency (EQE) measured also exhibited a linear blue shift in absorption edge, increasing the bandgap from 1.056 eV to 1.228 eV, respectively.

• Safety and Health at Work
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• 제14권3호
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• pp.279-286
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• 2023

Background: This study aimed to evaluate the association between exposure to occupational hazards and the metabolic syndrome. A secondary objective was to analyze the additive and multiplicative effects of exposure to risk factors. Methods: This retrospective cohort was based on 31,615 health examinees at the Pusan National University Yangsan Hospital in Republic of Korea from 2012-2021. Demographic and behavior-related risk factors were treated as confounding factors, whereas three physical factors, 19 organic solvents and aerosols, and 13 metals and dust were considered occupational risk factors. Time-dependent Cox regression analysis was used to calculate hazard ratios. Results: The risk of metabolic syndrome was significantly higher in night shift workers (hazard ratio = 1.45: 95% confidence interval = 1.36-1.54) and workers who were exposed to noise (1.15:1.07-1.24). Exposure to some other risk factors was also significantly associated with a higher risk of metabolic syndrome. They were dimethylformamide, acetonitrile, trichloroethylene, xylene, styrene, toluene, dichloromethane, copper, antimony, lead, copper, iron, welding fume, and manganese. Among the 28 significant pairs, 19 exhibited both positive additive and multiplicative effects. Conclusions: Exposure to single or combined occupational risk factors may increase the risk of developing metabolic syndrome. Working conditions should be monitored and improved to reduce exposure to occupational hazards and prevent the development of the metabolic syndrome.