강화학습을 이용한 공항 임시폐쇄 상황에서의 항공 일정계획 복원

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 산업공학과, 2021. 2. 문일경.An airline scheduler plans flight schedules with efficient resource utilization. However, unpredictable events, such as the temporary closure of an airport, disrupt planned flight schedules. Therefore, recovering disrupted flight schedules is essential for airlines. We propose Q-learning and Double Q-learning algorithms using reinforcement learning approach for the aircraft recovery problem (ARP) in cases of temporary closures of airports. We use two recovery options: delaying departures of flights and swapping aircraft. We present an artificial environment of daily flight schedules and the Markov decision process (MDP) for the ARP. We evaluate the proposed approach on a set of experiments carried out on a real-world case of a Korean domestic airline. Computational experiments show that reinforcement learning algorithms recover disrupted flight schedules effectively, and that our approaches flexibly adapt to various objectives and realistic conditions.항공사는 보유하고 있는 자원을 최대한 효율적으로 사용하여 항공 일정계획을 수립하기 위해 비용과 시간을 많이 소모하게 된다. 하지만 공항 임시폐쇄와 같은 긴급 상황이 발생하면 항공편의 비정상 운항이 발생하게 된다. 따라서 이러한 상황이 발생하였을 때, 피해를 최대한 줄이기 위해 항공 일정계획을 복원하게 된다. 본 연구는 강화학습을 이용하여 공항 임시폐쇄 상황에서 항공 일정계획 복원 문제를 푼다. 본 연구에서는 항공기 복원 방법으로 항공편 지연과 항공기 교체의 두 가지 방법을 채택하였으며, 항공 일정계획 복원 문제에 강화학습을 적용하기 위해서 마르코프 결정 과정과 강화학습 환경을 구축하였다. 본 실험을 위해 대한민국 항공사의 실제 국내선 항공 일정계획을 사용하였다. 강화학습 알고리즘을 사용하여 기존의 연구에 비해 항공 일정계획을 효율적으로 복원하였으며, 여러 현실적인 조건과 다양한 목적함수에 유연하게 적용하였다.Abstract i Contents iv List of Tables v List of Figures vi Chapter 1 Introduction 1 Chapter 2 Literature Review 7 Chapter 3 Problem statement 11 3.1 Characteristics of aircraft, flights, and flight schedule requirements 11 3.2 Definitions of disruptions and recovery options and objectives of the problem 13 3.3 Assumptions 16 3.4 Mathematical formulations 19 Chapter 4 Reinforcement learning for aircraft recovery 24 4.1 Principles of reinforcement learning 24 4.2 Environment 27 4.3 Markov decision process 29 Chapter 5 Reinforcement learning algorithms 33 5.1 Q-learning algorithm 33 5.2 Overestimation bias and Double Q-learning algorithm 36 Chapter 6 Computational experiments 38 6.1 Comparison between reinforcement learning and existing algorithms 39 6.2 Performance of the TLN varying the size of delay arcs 46 6.3 Aircraft recovery for a complex real-world case: a Korean domestic airline 48 6.4 Validation for different objectives 54 6.5 Managerial insights 57 Chapter 7 Conclusions 59 Bibliography 61 국문초록 69Maste

Relationship between Serum Alkaline Phosphatase and Low Muscle Mass Index Among Korean Adults: A Nationwide Population-Based Study

Sarcopenia has attracted interest due to its impact on various health problems. Chronic inflammation is an important contributor to sarcopenia. Thus, we aimed to investigate the association between serum alkaline phosphatase (ALP), which is a novel inflammatory marker, and muscle mass. This study included 15,579 adults from the 2008-2011 Korea National Health and Nutrition Survey. Low skeletal muscle mass index (LSMI) was defined as body mass index-adjusted appendicular skeletal muscle mass less than 0.789 for men and 0.512 for women. Multiple logistic regression revealed that the highest ALP tertile was significantly associated with LSMI compared with the lowest ALP tertile in both men [Odds ratio (OR): 1.41; 95% confidence interval (CI): 1.04-1.91] and women (OR: 1.45; 95% CI: 1.00-2.10) after adjusting for other confounders. On the receiver operating characteristic curve analysis, the predictive power was significantly higher for ALP levels than for white blood cell count in women (p < 0.001), whereas the difference was not significant in men (p = 0.515). Our findings suggest the potential use of serum ALP as an inflammatory marker and a predictor of sarcopenia.ope

Difference of Low Skeletal Muscle Index According to Recommended Protein Intake in Korean

Background: Sarcopenia has become a major concern owing to its association with a high risk of fall or fracture and metabolic impairments. There is insufficient evidence to support the role of dietary protein intake in reducing the prevalence of sarcopenia. This study was conducted to investigate the variation in low skeletal muscle index (SMI) with the dietary levels of protein intake. Methods: This study analyzed data of 3,482 male and 4,838 female aged 50 years or older from the Korean National Health and Nutrition Examination Survey (KNHNES) database (2008–2011). Low SMI was indicated by a value <0.789 in male and <0.512 in female. Multiple logistic regression was performed to analyze the association of SMI with protein intake, whereby it was tested whether the dietary intake of proteins met the estimated average requirement (EAR) or the reference nutrient intake (RNI) as stated in the dietary reference intake (DRI) for Koreans, 2015. Results: Irrespective of sex, the prevalence of low SMI was significantly high when the protein intake did not meet the EAR or RNI. Following adjustment for covariates, the odds ratio (OR) for low SMI in subjects with unmet EARs was 1.63 (1.28–2.09) in male and 1.35 (1.10–1.66) in female. The OR for low SMI in subjects with unmet RNI was 1.74 (1.38–2.18) in male and 1.39 (1.14–1.69) in female. Conclusion: The prevalence of low SMI was significantly higher when the protein intake did not meet the EAR or RNI as stated in the DRI for Koreans.ope

Inverse association between triglyceride glucose index and muscle mass in Korean adults: 2008-2011 KNHANES

Background: Since sarcopenia is an important risk factor for falls or cardiovascular disease, early detection and prevention of sarcopenia are being increasingly emphasized. Emerging evidence has indicated relationships between sarcopenia, insulin resistance, and inflammation. The triglyceride glucose (TyG) index, a novel surrogate marker of insulin resistance and systemic inflammation, has not yet been shown to be associated with sarcopenia. This study aimed to examine the relationship between the TyG index and muscle mass in Korean adults. Methods: This study included 15,741 non-diabetic adults over 19 years old using data from the 2008-2011 Korea National Health and Nutrition Examination Survey. Participants were divided into three groups according to tertiles of the TyG index. A low skeletal muscle mass index (LSMI) was defined by the Foundation for the National Institutes of Health Sarcopenia Project criteria. A weighted multivariate logistic regression model was used to analyze relationships between TyG index tertiles and LSMI. Results: The ORs (95% CIs) for LSMI in the second and third TyG tertiles, compared to the first tertile, were 1.463 (1.131-1.892) and 1.816 (1.394-2.366), respectively, after adjusting for confounding factors. Higher TyG index values were also associated with increased odds of LSMI in adults under 65 years who did not exercise regularly, who consumed less than 30 g of alcohol per day, who did not currently smoke, and who ate less than 1.5 g of protein/kg/day. Conclusion: The TyG index was significantly and positively associated with LSMI in Korean adults.ope

Relationship of Low Density Lipoprotein Cholesterol Level and Interest Nutrition on Nutrition Label in Korean Adults: 2008–2011 Korea National Health and Nutrition Examination Survey

Low density lipoprotein (LDL) cholesterol is an important metabolic marker, and it is suggested to be closely related with dietary habits. The use of nutrition labels is beneficial for making healthier food choices. In addition, dietary habits and nutrients of interest vary among nutrient label users. This study investigated the association between different nutrients of interest and LDL cholesterol levels in Korean adults. Methods: This cross-sectional study included 21,870 adults from the 2008–2011 Korea National Health and Nutrition Examination Survey (KNHANES). Participants were divided into five groups according to the nutrients they were most interested in: 1) total calories, 2) carbohydrates, 3) protein, 4) fat, and 5) non-users of nutrition label. LDL cholesterol target level was set according to individual cardiovascular risk level. Multivariate logistic regression analysis was used to verify which nutrient of interest is related to the achievement of LDL cholesterol target level. Results: Participants who were interested in total calories consumed lesser total calories and carbohydrates daily than those in the other groups did. Moreover, compared with the “not reading nutrition label” group, the odds ratios (95% confidence intervals) for achieving LDL cholesterol target level was 1.29 (1.05–1.58, P=0.015) in the “total calories” group after adjusting for confounding variables. Conclusion: Participants who were interested in total calories were more likely to achieve optimal LDL cholesterol levels than those who did not read nutrition labels. Therefore, reading nutrition labels, especially focusing on total calories, can be helpful for reducing cardiovascular risk.ope

Relationship between Skipping Meals and Impaired Fasting Glucose in Non-Diabetic Korean Adults

Background: Regular eating patterns play a crucial role in blood glucose control and irregular eating habits, particularly skipping breakfast, have been reported to increase the risk of developing type 2 diabetes mellitus (T2DM). This study examined the correlation between skipping meals and impaired fasting glucose among non-diabetic adults, as part of a wider aim to reduce the risk of developing diabetes through educational programs targeting eating-habits. Methods: This study was based on data derived from the Sixth Korea National Health and Nutrition Examination Survey (KNHANES VI-1, 2), 2013–2014, Koera Centers for Disease Control and Prevention and involved 6,731 non-diabetic adults between 19 and 64 years of age. Participants were categorized into a skipping meal group (SMG) and a non-SMG, according to their eating habits. To assess the correlation between eating habits and impaired fasting glucose we performed complex sample logistic regression analysis, adjusting for age, sex, body mass index, exercise, income, occupation, marital status, and education. Results: The incidence of impaired fasting glucose was higher in the SMG (odds ratio, 1.27; 95% confidence interval, 1.02–1.58) than in the Non-SMG (P<0.05). Conclusion: Among non-diabetic adults, irregular eating patterns increased the risk of developing impaired fasting glucose, a recognized risk factor for T2DM. Educational strategies promoting regular eating patterns may contribute to the prevention of T2DM.ope

Positive Association of Serum Alkaline Phosphatase Level with Severe Knee Osteoarthritis: A Nationwide Population-Based Study

Serum alkaline phosphatase (ALP), a well-known marker of hepatobiliary and bone disorders, has recently been discovered to be a biochemical marker of cardiometabolic diseases and chronic low-grade inflammation. We aimed to evaluate the association of serum ALP level with knee osteoarthritis in the general population. The study included 3060 men and women aged ≥50 years who participated in the 2009-2011 Korea National Health and Nutrition Examination Survey. The participants were categorized into three groups based on log-transformed serum ALP level as follows: T1 (1.74-2.32), T2 (2.33-2.43), and T3 (2.44-3.01). Their radiographs were evaluated by two well-trained radiologists using the Kellgren-Lawrence (KL) grading system. After excluding those with KL Grade 0, we categorized the remaining participants into two groups, a severe osteoarthritis group (KL Grade 4) and a non-severe osteoarthritis group (KL Grades 1 to 3). The odds ratios (ORs) with 95% confidence intervals (CIs) of severe osteoarthritis according to the tertiles of log-transformed serum ALP levels of patients with osteoarthritis were calculated using a weighted multivariate logistic regression analysis. Compared with T1, the adjusted ORs (95% CIs) for severe osteoarthritis of the T3 serum ALP group was 1.613 (1.087-2.394; p = 0.018) after adjusting for the confounding variables. Conclusively, serum ALP activity was independently and positively associated with severe knee osteoarthritis in middle-aged and older adults.ope

Relationship between White Blood Cell Count and Pulmonary Function Test Results in Korean Adults: The 2007-2009 Korea National Health and Nutrition Examination Survey

Background: Systemic inflammation is associated with impaired pulmonary function. In this study, we investigated the relationship between white blood cell (WBC) count and pulmonary function test (PFT) result. Methods: We analyzed data from the 2007–2009 Korea National Health and Nutrition Examination Survey. Finally, 8,464 patients with no history of asthma or chronic obstructive pulmonary disease (COPD), with WBC counts ranging from 3,000 to 10,000 cells/μL, and ability to interpret lung function test results were finally selected. The WBC counts were divided into four groups according to quartiles. The PFT results were divided into three groups as follows: normal, obstructive, and restrictive patterns. A weighted multinomial logistic regression analysis was performed to calculate the odds ratio for abnormal PFT patterns. Results: The odds ratios were Q2 vs. Q1 1.196 (0.877–1.630), Q3 vs. Q1 1.338 (0.968–1.848), and Q4 vs. Q1 1.670 (1.224–2.280) for the obstructive pattern, and Q2 vs. Q1 0.987 (0.737–1.312), Q3 vs. Q1 1.066 (0.803–1.413), and Q4 vs. Q1 1.329 (1.001–1.766) for the restrictive pattern after being adjusted for age, sex, body mass index, waist circumference, smoking status, high-risk drinking, regular exercise, mean blood pressure, serum fasting blood glucose, total cholesterol, triglyceride, and diabetes mellitus, hypertension, and hyperlipidemia medication. Conclusion: The highest WBC quartile was associated with an increased odds ratio for obstructive and restrictive patterns in subjects without asthma and COPD. The odds ratio of the obstructive pattern was higher than that of the restrictive pattern.ope

Relationship between Muscle Mass and Non-Alcoholic Fatty Liver Disease

Although sarcopenia is known to be a risk factor for non-alcoholic fatty liver disease (NAFLD), whether NAFLD is a risk factor for the development of sarcopenia is not clear. We investigated relationships between NAFLD and low skeletal muscle mass index (LSMI) using three different datasets. Participants were classified into LSMI and normal groups. LSMI was defined as a body mass index (BMI)-adjusted appendicular skeletal muscle mass <0.789 in men and <0.512 in women or as the sex-specific lowest quintile of BMI-adjusted total skeletal muscle mass. NAFLD was determined according to NAFLD liver fat score or abdominal ultrasonography. The NAFLD groups showed a higher hazard ratios (HRs) with 95% confidence intervals (CIs) for LSMI than the normal groups (HRs = 1.21, 95% CIs = 1.05-1.40). The LSMI groups also showed a higher HRs with 95% CIs for NAFLD than normal groups (HRs = 1.56, 95% CIs = 1.38-1.78). Participants with NAFLD had consistently less skeletal muscle mass over 12 years of follow-up. In conclusion, LSMI and NAFLD showed a relationship. Maintaining muscle mass should be emphasized in the management of NAFLD.ope

Association between nutrition education, dietary habits, and body image misperception in adolescents

Background and objectives: In adolescents, adequate nutrition education is essential for making decisions regarding healthy eating habits. We aimed to investigate differences in dietary habits and body image misperception according to nutrition education status. Methods and study design: We analyzed 60,389 adolescents aged 12-18 years old, using the 2017 Korea Youth Risk Behavior Web-based Survey data. Participants were divided into nutrition-educated (EDU) and uneducated (non-EDU) groups, according to nutrition education status within the past year. Skipping breakfast was defined as skipping breakfast ≥5 times/week. Desirable dietary behaviors were divided into the frequency of consumption of 3 items: vegetables ≥1 time/day, milk ≥1 time/day, and fruits ≥1 time/day. Participants with normal weight who reported being slightly fat or very fat were defined as having body image misperception. Results: Compared to the non-EDU group, the odds ratio (OR) and 95% confidence interval (CI) for desirable dietary behaviors in the EDU group were 1.08 (1.04-1.13), 1.14 (1.09-1.19), and 1.16 (1.12-1.20) for the intake of fruits, milk, and vegetables, respectively. The EDU group was less associated with skipping breakfast than the non-EDU group (OR=0.91, 95% CI: 0.87-0.95, p<0.001). The OR and 95% CI of body image misperception in the EDU group were lower than in the non-EDU group (OR=0.92, 95% CI: 0.87- 0.97, p<0.001). Conclusions: Nutrition education have positive effects on healthy dietary behaviors. It also shows a negative association with body image misperception, confirming the importance of nutrition education at school.ope