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"Kim, Woo Chang"
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Predicting Mobile Payment Behavior Through Explainable Machine Learning and Application Usage Analysis
In the increasingly competitive mobile ecosystem, understanding user behavior is essential to improve targeted sales and the effectiveness of advertising. With the widespread adoption of smartphones and the increasing variety of mobile applications, predicting user behavior has become more complex. This study presents a comprehensive framework for predicting mobile payment behavior by integrating demographic, situational, and behavioral factors, focusing on patterns in mobile application usage. To address the complexity of the data, we use a combination of machine-learning models, including extreme gradient boosting, light gradient boosting machine, and CatBoost, along with Shapley additive explanations (SHAP) to improve interpretability. An analysis of extensive panel data from Korean Android users reveals that incorporating application usage behavior in such models considerably improves the accuracy of mobile payment predictions. The study identifies key predictors of payment behavior, indicated by high Shapley values, such as using social networking services (e.g., KakaoTalk and Instagram), media applications (e.g., YouTube), and financial and membership applications (e.g., Toss and OK Cashbag). Moreover, the results of the SHAP force analysis reveal the individual session-level drivers of mobile purchases. These findings advance the literature on mobile payment prediction and offer practical insights for improving targeted marketing strategies by identifying key behavioral drivers of mobile transactions.
Journal Article
Coxiella burnetii infection in a patient with tick bite
Introduction: We report the case of a 60-year-old male who was hospitalized with fever, headache, fatigue, nausea, and myalgia for six days. Methodology: Polymerase chain reactions (PCR) were performed on patient blood samples, and four ticks were collected from the area the patient mowed. Indirect immunofluorescence assays (IFAs) were performed on serum samples to detect specific antibodies. Results: The collected ticks were identified as Haemaphysalis longicornis. Coxiella species-specific nested PCR (N-PCR) and sequencing confirmed the presence of Coxiella burnetii in the patient, and Coxiella-like bacteria were identified in three of the four ticks. IFA results showed ≥ 4-fold increases in both IgM and IgG antibody titers against Q fever. Conclusions: Despite positive PCR results for Coxiella species in both the patient and the ticks, different bacterial species were isolated, suggesting that the patient was not infected with C. burnetii through tick bites. Further investigation is required to identify the carriers or transmitters of the infection.
Journal Article
Long-term oncologic outcomes of single-incision laparoscopic surgery for colon cancer
BackgroundStudies find similar perioperative outcomes between single-incision laparoscopic surgery (SILS) and conventional laparoscopic surgery (CLS) for colon cancer. However, few have reported long-term outcomes of SILS versus CLS. We aimed to compare long-term postoperative and oncologic outcomes as well as perioperative outcomes between SILS and CLS for colon cancer.MethodsA total of 641 consecutive patients who underwent laparoscopic surgery for colon cancer from July 2009 to September 2014 were eligible for the study. Data from 300 of these patients were used for analysis after propensity score-matching (n = 150 per group). Variables associated with short- and long-term outcomes were analyzed.ResultsThe SILS group had a shorter mean total incision length, less postoperative pain, and a similar mean rate of incisional hernia (2.7% versus 3.3%) compared with the CLS group. The 7-year overall and disease-free survival rates were 92.7% versus 94% (p = 0.673) and 85.3% versus 84.7% (p = 0.688) in the SILS and CLS groups, respectively.ConclusionsCompared with CLS, SILS for colon cancer appeared to be safe in terms of perioperative and long-term postoperative and oncologic outcomes. The results suggested that SILS is a reasonable treatment option for colon cancer for a selected group of patients.
Journal Article
Musculoskeletal Pain, Physical Activity, Muscle Mass, and Mortality in Older Adults: Results from the Korean Longitudinal Study on Health and Aging (KLoSHA)
Background and objectives: Musculoskeletal (MSK) pain significantly impacts physical activity and quality of life in older adults, potentially influencing mortality. This study explored the relationship between MSK pain, physical activity, muscle mass, and mortality among older adults. Material and Methods: We studied 1000 participants in the Korean Longitudinal Study on Health and Aging (KLoSHA), a prospective, population-based cohort study of people aged 65 years or older. Survival status was tracked over a 5-year period. Correlations between low back pain (LBP), knee pain, regular exercise, appendicular skeletal muscle mass (ASM), and other variables were analyzed. Logistic regression analyses were used to identify independent risk factors for mortality. Results: Of the total participants, 829 (82.9%) survived over a 5-year period. Survivors tended to be younger, had a higher BMI, and were more active in regular exercise. In contrast, non-survivors exhibited a higher prevalence of both LBP and knee pain, along with increased instances of multiple MSK pains. Lower ASM correlated moderately with LBP and knee pain, whereas higher ASM was associated with regular exercise. There was a moderate correlation between LBP and knee pain, both of which were associated with a lack of regular exercise. Age, sex, ASM, and regular exercise were significant predictors, even though MSK pain itself did not directly predict all-cause mortality. Conclusions: This study demonstrated the independent association between ASM, regular exercise, and mortality. Although MSK pain did not directly correlate with all-cause mortality, the non-survivor group had higher levels of both single and multiple MSK pains. Recognizing the interplay of MSK pain, physical activity, and muscle mass for older adults, the research underscores the need for holistic strategies to enhance health outcomes in older individuals with MSK pain.
Journal Article
Ultra-wideband power divider using three parallel-coupled lines and one shunt stub
An ultra-wideband power divider with out-of-band filtering and DC blocking functions is presented. The divider consists of three parallel-coupled lines, a short-circuited shunt stub and a resistor. The divider was implemented in a two-layer printed circuit board with a high dielectric constant. The measurements show a minimum insertion loss of −0.4 dB in the middle band and a rejection of −17 to −18 dBc at 1.5 and 11.5 GHz, respectively.
Journal Article
System-Level Fault Diagnosis for an Industrial Wafer Transfer Robot with Multi-Component Failure Modes
In the manufacturing industry, robots are constantly operated at high speed, which degrades their performance by the degradation of internal components, eventually reaching failure. To address this issue, a framework for system-level fault diagnosis is proposed, which consists of extracting useful features from the motor control signal acquired during the operation, diagnosing the current health of each component using the features, and estimating the associated degradation in the robot system’s performance. Finally, a maintenance strategy is determined by evaluating how well the system performance is restored by the replacement of each component. The framework is demonstrated using the example of a wafer transfer robot in the semiconductor industry, in which the robot is operated under faults with various severities for two critical components: the harmonic drive and the timing belt. Features are extracted for the motor signal using wavelet packet decomposition, followed by feature selection by considering the trendability and separability of the fault severity. An artificial neural network model and Gaussian process regression are employed for the diagnosis of the components’ health and the system’s performance, respectively.
Journal Article
Deciphering the Impact of COVID-19 on Korean Sector ETFs: Insights from an ARIMAX and Granger Causality
The COVID-19 pandemic caused major disruptions to worldwide financial markets, which resulted in market instability and unpredictability. South Korean investors used sector-specific exchange-traded funds (ETFs) to handle the market challenges. This research examines the connection between COVID-19 statistics, including total confirmed cases and deaths, and Korean sector ETF market performance. The research uses the ARIMAX model to evaluate how external variables affect ETF price volatility. The research uses Granger causality tests to determine the direction of relationships between pandemic metrics and sectoral performance, while K-means clustering identifies patterns across different sectors. The analysis reveals significant statistical connections between pandemic disruptions and three sectors, including communication services, healthcare, and IT. The research shows that COVID-19 metrics strongly affected the performance of sector-specific ETFs throughout the analyzed time period. The research establishes a basis for additional studies about external shock effects on financial instruments and delivers valuable information to investors and policymakers who need to manage global crisis risks.
Journal Article
Robust equity portfolio management + website : formulations, implementations, and properties using MATLAB
\"The book will be most helpful for readers who are interested in learning about the quantitative side of equity portfolio management, mainly portfolio optimization and risk analysis. Mean-variance portfolio optimization is covered in detail, leading to an extensive discussion on robust portfolio optimization. Nonetheless, readers without prior knowledge of portfolio management or mathematical modeling should be able to follow the presentation since basic concepts are covered in each chapter. Furthermore, the main quantitative approaches are presented with MATLAB examples, allowing readers to easily implement portfolio problems in MATLAB or similar modeling software. There is an online appendix that provides the MATLAB codes presented in the chapter boxes (www.wiley.com/go/robustequitypm)\"--
eBook
Operating Characteristic Analysis and Verification of Short-Stroke Linear Oscillating Actuators Considering Mechanical Load
Linear oscillating machines are electric devices that reciprocate at a specific frequency and at a specific stroke. Because of their linear motion, they are used in special applications, such as refrigerators for home appliances and medical devices. In this paper, the structure and electromagnetic characteristics of these linear oscillating machines are investigated, and the stroke is calculated according to voltage and motion equations. In addition, static and transient behavior analysis is performed, considering mechanical systems such as springs, damping systems, and mover mass. Furthermore, in this study, the magnetic force is analyzed, experiments are conducted according to the input power, and the current magnitude and stroke characteristics are analyzed according to the input frequency. Finally, the study confirmed that the most efficient operation is possible when the electrical resonance frequency matches the resonance frequency of the linear oscillating machines.
Journal Article