유성 기어박스의 진동기반 고장 진단을 위한 저가형 센서의 정량적 성능 평가

학위논문 (석사)-- 서울대학교 대학원 공과대학 기계항공공학부, 2017. 8. 윤병동.A gearbox is one of the critical components in rotating machinery. Timely prediction of gearbox faults become of great importance to minimizing unscheduled machine downtime. Most of gearbox diagnosis studies are focused on the development of gearbox diagnosis algorithms using costly vibration sensors. However, vibration sensor cost matters in some applications, thus pushing to the use of a low-cost accelerometer, such as a knock sensor. This study uses a planetary gearbox with a knock sensor, known to be cheap and good for application (i.e., diesel engines) to detect high frequency. This study develops a quantitative sensor evaluation process for fault diagnosis. The performance of the sensor is evaluated in terms of vibration performance and fault diagnosis performance. Vibration performance evaluates the sensor's noise level through an experiment using an electro-dynamic transducer. The fault diagnosis performance is evaluated by analyzing the vibration signal obtained from the faulty gear through gearbox feature engineering to check whether the fault has been separated or not. In this study, two ideas will be proposed. First, some quantitative metrics will be used to evaluate the performance of the sensor. The vibration performance of the knock sensor is comparatively evaluated with the signal-to-noise ratio (SNR). The stable frequency range of the knock sensor for the fault diagnosis is defined based on the SNR value. From the point of view of the fault diagnosis evaluation, fault separation capability is carried out by probability of separation (PoS) and Fisher discriminant ratio (FDR). Second, a new application of the base signal of feature used for the fault diagnosis will be proposed. The filtered signal obtained by the alternative signal processing method(i.e., autoregressive-minimum entropy deconvolution (AR-MED) and spectral kurtosis (SK)) in the case of no tachometer is used as a difference signal. Analyze the frequency range and periodicity of the fault signal to determine the availability of the feature calculated with the newly applied differential signal. Two case studies are presented to demonstrate the effectiveness of the proposed sensor evaluation process and metric: 1) one-stage planetary gearbox in a wind-turbine rig tester and 2) a swing reduction gear (two-stage planetary gearbox) in an excavator. It is concluded that a knock sensor can be used for the fault diagnosis of a gearbox.Chapter 1. Introduction 1 1.1 Background and Motivation 1 1.2 Scope of Research 2 1.3 Structure of the Thesis 3 Chapter 2. Technical Background 4 2.1 Fault Diagnosis in a Planetary Gearbox 4 2.1.1 Vibration Characteristics of a Faulty Gearbox 4 2.1.2 Signal Processing Methods 6 2.1.3 Features for Fault Diagnosis 9 2.2 Overview of Sensor Selection 11 2.2.1 Specification of Accelerometer 12 2.2.2 Selection of a Knock Sensor 14 Chapter 3. Knock Sensor Evaluation from the Viewpoint of Vibration Measurement 17 3.1 Conventional Sensor Assessment Method 17 3.2 Signal-to-Noise Ratio (SNR) 18 3.3 Method of Estimating the SNR 19 3.4 Results and Discussion 20 Chapter 4. Knock Sensor Evaluation from the Viewpoint of Fault Diagnosis 22 4.1 Review of Fault Diagnosis 22 4.1.1 Model-based Methods 22 4.1.2 Signal Processing Based Methods 23 4.1.3 Discussion 24 4.2 Fault Diagnosis using Two Types of Difference Signals 25 4.2.1 Definition of Difference Signal 25 4.2.2 Methodology for Estimation of the Difference Signal 26 4.3 Results and Discussion 28 4.3.1 Description of Experiments 28 4.3.2 Comparison of Fault Diagnosis using Signal Processing Results 33 4.3.3 Comparison of Diagnostic Performance using Quantitative Metrics 49 Chapter 5. Conclusions and Future Work 54 5.1 Conclusions and Contributions 54 5.2 Future Work 55 Bibliography 57 국문 초록 63Maste

코로나19 이후 기혼 유자녀 여성 무급노동시간 변화의 이중차분법 추정

학위논문(석사) -- 서울대학교대학원 : 사회과학대학 사회복지학과, 2023. 2. 구인회.This study examined the impact of COVID-19 on married mothers domestic labor time, using data from the 5th to 8th wave(2014~2021) of the Korean Longitudinal Survey of Women and Families(KLOWF). It also assessed the change in the gender gap of domestic labor time and determined which theory, either economic exchange theory or the doing gender theory, provides a better explanation for the division of domestic labor after the pandemic. To address these three research questions, Difference-in-Differences(DiD) analysis with marital status, gender, and female-breadwinner models was conducted. The key findings are as follows. First, care work hours of married mothers increased after the pandemic. To answer the first research question, What was the impact of COVID-19 pandemic on the domestic labor hours for married mothers?, the DiD analysis with married mothers as the treatment group and unmarried women as the comparison group was conducted. The results suggest that married mothers experienced a larger increase in care work hours compared to unmarried women, but this was not the case for housework and domestic labor hours. Second, married mothers experienced a larger increase in housework, care work, and domestic labor hours compared to their husbands. To answer the second research question, What was the impact of COVID-19 pandemic on the gender gap of domestic labor hours?, the DiD analysis with married mothers as the treatment group and their husbands as the comparison group was conducted. The results show that married mothers saw a greater rise in the amount of time spent on housework, care work, and domestic labor. That is, the COVID-19 has widened the gender gap in the domestic labor hours. Third, in families in which the wife earns more than their husband, both partners changes in care work and domestic labor hours were not significantly different, and wives housework hours increased more than their husbands. To address the third research question, Which theory, either economic exchange theory or doing gender theory, provides a better explanation for the division of domestic labor after COVID-19 pandemic?, the DiD analysis with married mothers earning more than their husbands as the treatment group and their husbands as the comparison group was conducted. The results suggest that breadwinning wives experienced a larger increase in housework hours than their husbands, while the partners changes in care work and domestic labor hours were not significantly different. It shows that gender norms had a greater influence on the division of domestic labor after the pandemic, than economic rationality. This study made several meaningful contributions to the existing literature. First, The study made a theoretical contribution by demonstrating that the level of defamiliarization in South Korea decreased after the pandemic, as the government shifted its responsibilities of domestic labor to women within families. It also discovered that the gender norms were more influential than economic rationality, in determining the division of domestic labor after the COVID-19. The study makes a methodological contribution by using the quasi-experimental DiD method to analyze KLOWF, which addressed limitations in data and analysis found in previous studies. One of the policy implications of the study is that the aggressive quarantine policies, such as kindergarten and school closure, prevented the spread of the disease but widened the gender gap within families. And given that the division of domestic labor is heavily influenced by gender norms, positive incentives are needed to encourage equal distribution of domestic labor hours. To overcome the ideal worker norm hindering fathers from participating in domestic labor and mothers from pursuing their career, consistent working hours regulation policies should be established to decrease the amount of working hours. The limitations of this study are as follows. The models in the analysis lack some labor market variables, as the sample included non-employed wives to address selection bias and enhance external validity. Also some variables from the economic exchange theory and the time availability theory were not included in the analysis since they would have absorbed the impact of COVID-19 in the DiD estimators. Accordingly, this hindered the identification of the pathways through which COVID-19 affected domestic labor hours.본 연구는 2014년부터 2021년까지 조사된 5차부터 8차까지의 여성가족패널조사를 이용해 코로나19 이후 기혼 유자녀 여성의 무급노동시간 변화를 분석하였다. 또한 코로나19 이후 기혼 유자녀 여성과 남성 배우자의 무급노동시간 격차는 어떻게 변화하였는지, 무급노동시간 배분이 경제적 교환 논리와 젠더 규범 중 무엇에 의해 더 잘 설명될 수 있는지 살펴보고자 하였다. 이러한 세 가지 연구 질문에 답하기 위해, 혼인여부 모형, 젠더 모형, 여성소득상위모형을 설정하여 이중차분법을 활용한 분석을 실시하였다. 본 연구의 분석결과를 요약하면 다음과 같다. 첫째, 코로나19 이후 기혼 유자녀 여성의 돌봄노동시간이 증가한 것을 확인하였다. 이는 코로나19는 기혼 유자녀 여성의 무급노동시간에 어떠한 영향을 미쳤는가?라는 첫 번째 연구문제에 답하기 위해, 기혼 유자녀 여성을 처치집단으로, 미혼 여성을 비교집단으로 둔 이중차분법을 실시하여 도출된 결과이다. 분석 결과, 코로나19 이후 기혼 유자녀 여성의 돌봄노동시간은 미혼 여성에 비해 더 크게 증가하였으나, 무급노동시간과 가사노동시간에는 유의한 증가량의 차이가 없었다. 둘째, 코로나19 이후 기혼 유자녀 여성의 무급, 가사, 돌봄노동시간이 모두 남성 배우자보다 더 크게 증가한 것을 확인하였다. 이는 코로나19 이후 여성과 남성의 무급노동시간 격차는 어떻게 변화하였는가?라는 두 번째 연구문제에 답하기 위해, 기혼 유자녀 여성을 처치집단으로, 이들의 남성 배우자를 비교집단으로 둔 이중차분법을 실시하여 도출된 결과이다. 분석 결과, 코로나19 이후 기혼 유자녀 여성의 무급, 가사, 돌봄노동시간 증가량 모두 남성 배우자보다 큰 것으로 나타났다. 즉, 코로나19는 무급노동시간 배분의 젠더 간 불평등을 더욱 심화시킨 것으로 나타났다. 셋째, 아내의 소득이 남편보다 높은 가구에서 코로나19 이후 기혼 유자녀 여성의 무급노동시간 및 돌봄노동시간 증가량이 남성 배우자보다 작지 않으며, 가사노동시간 증가량은 더 큰 것을 확인하였다. 이는 코로나19로 인한 무급노동 부담은 부부간 경제적 교환 논리에 따라 배분되는가, 젠더 규범에 따라 배분되는가?라는 세 번째 연구문제에 답하기 위해, 분석 대상을 여성의 소득이 남성 배우자보다 더 높은 가구로 한정한 뒤 기혼 유자녀 여성을 처치집단으로, 이들의 남성 배우자를 비교집단으로 둔 이중차분법을 실시하여 도출된 결과이다. 분석 결과, 아내의 소득이 남편보다 높은 가구에서 코로나19 이후 기혼 유자녀 여성의 가사노동시간이 남성 배우자보다 더 크게 증가했지만, 무급노동시간과 돌봄노동시간의 변화량에는 두 집단 간 차이가 없는 것으로 나타났다. 즉, 코로나19 이후 무급노동시간 배분은 경제적 교환 논리보다는 젠더 규범에 따라 이루어졌다고 볼 수 있다. 본 연구의 주요 함의는 다음과 같다. 먼저 이론적 함의로서, 코로나19 이후 국가가 분담하던 무급노동 부담이 가족 내 여성에게 전가되면서, 한국의 탈가족화 수준이 낮아졌음을 밝혀냈다. 또한 코로나19 이후 추가적으로 주어진 무급노동 배분에 있어 경제적 교환 논리보다 젠더 규범의 영향력이 더 강하게 작동하였음을 포착하였다. 본 연구의 방법론적 함의는 준실험설계인 이중차분법을 바탕으로 여성가족패널조사를 분석하여 선행연구가 노정하는 자료와 분석 방법 상의 한계를 보완하였다는 점이다. 이와 같은 엄밀한 추정을 통해 코로나19가 기혼 유자녀 여성의 무급노동부담에 미친 영향에 대한 준실험적 증거를 마련하였다. 본 연구의 분석에 따른 정책적 함의는 적극적 방역정책으로 코로나19의 확산은 억지되었으나, 그 이면에서 한국 사회가 가정 영역의 젠더 격차 심화라는 비용을 치렀음을 밝혀냈다는 점이다. 그리고 본 연구는 젠더 규범이 무급노동 배분에 미치는 강력한 영향력을 고려하면, 남성의 무급노동 분담을 촉진하기 위해서는 성중립적 정책 설계보다는 적극적인 인센티브 제공이 필요함을 강조하였다. 또한 남성의 무급노동수행과 여성의 경제활동참여를 저해하는 이상적 노동자 규범의 해체를 위해, 일관성 있는 근로시간 단축 정책을 통한 장시간 노동 문화 탈피를 제언하였다. 본 연구의 한계는 다음과 같다. 먼저, 선택 편향 문제에 대처하고 외적 타당성을 확보하기 위해 취업 여성뿐만 아니라 비취업 여성을 분석 대상에 포함하였는데, 이로 인해 노동시장 관련 요인이 분석에 포함되지 못했다. 또한 경제적 교환 관점, 가용시간이론에 따른 변수들이 코로나19의 영향을 흡수할 것을 우려하여 이러한 변수들을 분석에 포함하지 않았고, 이에 따라 무급노동시간 변화의 세부적인 경로를 밝혀내지는 못했다. 후속연구를 통해 이러한 한계가 보완되기를 기대한다.제 1 장 서 론 1 제 1 절 문제제기 1 제 2 절 연구문제 5 제 2 장 이론적 배경 6 제 1 절 무급노동시간의 정의 및 중요성 6 제 2 절 코로나19로 인한 변화 12 제 3 절 코로나19와 여성의 무급노동시간 19 제 3 장 연구방법 34 제 1 절 분석방법 및 분석자료 34 제 2 절 연구모형 44 제 3 절 변수설정 47 제 4 장 분석결과 54 제 1 절 혼인여부 모형 54 제 2 절 젠더 모형 67 제 3 절 여성소득상위모형 78 제 5 장 결론 86 제 1 절 분석 결과의 요약 86 제 2 절 연구의 함의 89 제 3 절 연구의 한계와 후속연구에 대한 제언 96 참고문헌 99석

MgAl2O4의 연소합성 중 LiF 첨가물의 영향

학위논문 (석사)-- 서울대학교 대학원 공과대학 재료공학부, 2017. 8. Shinhoo Kang.Due to the excellent mechanical properties and high transparency from near-UV to mid-IR (190<λ<6000nm), MgAl2O4 has been used for optical engineering applications, such as armored window systems, high energy laser windows and lightweight armor. In order to fabricate high quality transparent ceramics, high quality starting powder is necessary. So we focused on the combustion synthesis method which has recently drawn the attention of researchers due to multiply advantages. But the combustion synthesis method still have some disadvantages need to be overcome. Based on the mechanism of spinel formation, we decided to introduce some additive to improve this method. After calculation, the promising of LiF additive was certified. With different amount of LiF, combustion synthesis of MgAl2O4 (MAS) was investigated in relation to the synthesis conditions, powder properties, thermodynamic aspects and sinterability. Using citric acid as a single fuel, only hard-agglomeration MAS was obtained with high carbon contamination and poor sinterability which cannot be used as transparent ceramic raw materials. However, by introducing LiF, good property MAS powder can be synthesized. This is because LiF can effectively reduce the formation energy of MAS, remove the residue carbon, reduce agglomeration degree and promote the crystal growth during the combustion reaction. Through 2-steps calcination, the as-obtain high purity powders have been consolidated into transparent ceramics (T=81.0%) by SPS at T=1200℃ for 20min holding under P=80MPaChapter 1. Introduction 1 1.1. Study Background 1 1.2. Synthesis of MgAl2O4 Powders 4 1.3. LiF Additive 7 1.3.1. Sintering Additive 7 1.3.2. Synthesis additive 7 1.4. Objective of the Study 10 Chapter 2. Experimental Methods 11 2.1. Sample Preparation 11 2.2. Characterization Methods 14 Chapter 3. Results and Discussion 15 3.1. Powder Synthesis 15 3.1.1 Reaction Equation & Thermodynamic Aspects 15 3.1.2. TGA DSC 17 3.2. Material characterization of as obtained MgAl2O4 22 3.2.1. Particle Morphology 22 3.2.2. Different Additives 25 3.2.3. Impurity 27 3.2.4. 2 steps calcination 30 3.3. Sintering 35 3.3.1. Air Sintering 35 3.3.2. SPS 37 Chapter 4. Conclusions 39 Reference 40 국문 초록 42 Acknowledgement 43Maste

탄소 나노튜브를 기반으로 한 나노구조의 전기적 특성에 대한 이론 연구

Thesis(doctoral)--서울대학교 대학원 :물리학부,2005.Docto

Preparation and evaluation of mosapride matrix tablet for sustained release

학위논문 (석사)-- 서울대학교 대학원 : 약학과, 2014. 2. 김대덕.모사프리드는 위장관운동 조절제로 위장관 운동성을 높이는 역할을 하며, 하루에 세 번, 5 mg씩 복용하는 것을 용법으로 한다. 적응증은 기능성소화불량으로 인한 소화기증상(속쓰림, 구역, 구토) 으로, 주로 다른 약물에 의해 유발된 위장관 증상을 완화시키기 위해 처방된다. 하지만 하루 세 번의 빈번한 복용법은 환자의 복약순응도를 낮출 가능성이 있기 때문에 하루 한 번과 같이 복용법을 바꾸는 제형이 필요하다. 이를 위해 복약순응도를 높일 수 있는 모사프리드의 이상적인 용출 양상을 1시간에 33% 이상, 6시간에 약 66%, 9시간에 80% 이상으로 설정하였다. 매트릭스 정제의 무게는 311.19 mg, 경도는 약 80 N으로 맞추어 단발 타정기로 타정하였다. 정제는 지름 11 mm의 원형이었다. 이후 용출기를 사용하여 정제의 용출을 관찰하였다. 모사프리드의 용출 샘플은 HPLC를 사용하여 분석하였다. 처방 조성은 이전 처방의 용출 결과에 따라 바뀌었다. 최종적으로 처방 F17에서 이상적인 용출과 유사한 용출양상을 관찰할 수 있었으며, in vitro 상에서 모사프리드의 지연 방출은 성공적으로 시행되었다.Abstract I List of Tables IV List of Figures V 1. Introduction 1 2. Materials and Methods 6 2.1. Materials 6 2.2. Preparation of mosapride sustained-release tablets 6 2.3. In vitro dissolution test 8 2.4. HPLC analysis and validation 8 3. Results and Discussion 10 3.1. Preparation of mosapride sustained-release tablets 10 3.2. Validation of analytical methods 10 3.3. In vitro dissolution test of mosapride sustained-release tablets 11 4. Conclusion 14 References 16 영문초록 42Maste

해결중심 단기상담을 통한 농촌 고등학생의 자아존중감 향상

학위논문(석사)--아주대학교 교육대학원 :상담심리전공,2004testMaste

Identifying Potentially Avoidable Emergency Department Visits of Long-Term Care Hospital Residents in Korea: A Multicenter Retrospective Cohort Study

The aims of this study were to investigate the reasons of transfers from long-term care hospitals (LTCHs) to emergency departments (EDs) of university hospitals in geriatric patients and to categorize the avoidable causes of these transfers. This retrospective multicenter study involved patients aged 65 years and older who were transferred from LTCHs to 5 EDs of university hospitals located in the metropolitan area of South Korea between January 2017 and December 2017. The expert panel reviewed and categorized the reason of transfers as avoidable or not. Moreover, we also investigated the number of patients with do-not-resuscitate (DNR) documents and the date these DNR documents were written. A total of 255,543 patients visited 5 EDs during the study period. Of these, 1,131 patients were from LTCHs. The number of potentially avoidable transfers was 168/1,131 (14.9%). The most common reason of avoidable transfers was noncritical diagnoses that could be assessed and managed in LTCHs (57.1%). There were 162 patients with DNR orders; of these, 12 had approved the DNR order before transfer. In conclusion, in Korea, potentially avoidable transfers could be reduced by managing noncritical diseases in LTCH and preparing advance care directives, including DNR orders, during admission to LTCH

Characteristics of Elderly Long-Term Care Residents Who Were Injured and Transferred to Hospital Emergency Departments in Korea: A Retrospective Multicenter Study

The objective of this retrospective multicenter study was to investigate the mechanism and characteristics of trauma experienced by patients aged 65 years who were transferred from a long-term care hospital to one of five university hospital emergency departments. Of 255,543 patients seen in one of the five emergency departments, 79 were transferred from a long-term care hospital because of trauma. The most common trauma mechanism was slipping down, with 33 (58.9%) patients, followed by falling from a bed (17.9%), striking an object such as a wall or corner (10.7%), overextending a joint (8.9%), and unknown mechanisms (3.6%). Many cases of slip (39.4%) occurred in relation to the bathroom. Comparing slip and fall from a bed, we found more hip fractures (95.2%) because of slipping down than falling from a bed (57.1%); traumatic brain injury only occurred in slip cases. These traumas cause significant morbidity in elderly patients; therefore, we sought to identify strategies that prevent slip in long-term care hospitals