Factors Affecting Extra Journey Time of Public Bike

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 건설환경공학부, 2020. 8. 이청원.Considering the severe issue of environmental pollution, the government has attempted low carbon green growth by encouraging the use of the green transportation mode. As the green transportation mode, the revitalization of bike usage attracts remarkable public attention. However, for the acquirement of the effective outcome, the comprehensive analysis of bike usage characteristics should be arranged first. Since the characteristics of public bike usage depend on the journey times, it is necessary to expand the utilization rate considering the journey times. Existing researchers considered the number of usages or utilization rates as a dependent variable when analyzing factors affecting the usage of the public bike. This study aims to analyze the factors that affect the difference between the actual journey times and KAKAO Maps estimated journey times. These journey times from KAKAO Maps were compared with the actual journey times recorded in the dataset to create a new variable called Extra Journey Time. This study was conducted on Yeongdeungpo-gu, a residential-business center district in Seoul. As a results, Trips to and from stations that had a large number of shops within 100 m distance were also found to be likely predictors of the trips with lowest Extra Journey Time. The stations with bike priority road and leisure/cultural facilities are associated with larger Extra Journey Time. This study is helpful to understand the characteristics of public bike by analyzing the effects on journey time, not the effects on the demand for use conducted by previous study.환경오염의 심각성에 따라 정부는 저탄소 녹색성장의 방안으로 친환경 교통수단 활성화에 노력하고 있다. 녹색교통으로서 공공자전거 이용활성화가 사회적으로 큰 조명을 받고 있으나 효과적인 성과를 내기 위해서는 자전거 이용특성에 대한 구체적이고 다양한 분석이 수행되어야 한다. 공공자전거는 단시간, 장시간 이용에 따라 이용특성이 다르므로 이를 고려한 이용률 확대 방안이 필요하다. 기존의 선행연구들은 공공자전거 이용에 영향을 미치는 요인분석의 종속변수로서 이용횟수 혹은 이용률만을 고려하였다. 본 연구는 실제 대비 추정 이용시간의 차이에 영향을 미치는 요인을 분석하였다. 이에 Extra Journey Time은 실제 대비 추정 이용시간의 차이를 비교하기 위한 새로운 변수로서 생성되었다. 본 연구는 서울시 주거업무 중심 지역인 영등포구를 대상으로 연구를 시행하였으며, 그 결과 Extra Journey Time은 주중 대비 주말에 여가/문화 시설이 존재하며 자전거전용도로가 잘 갖춰져 있는 곳에서 증가하였고, 주중 출퇴근 시간대 상점이 많은 곳에서 Extra Journey Time이 감소하였다. 날씨 측면에서 Extra Journey Time은 특정 조건(기온 10°c 이하, 33°c 이상, 미세먼지 나쁨/매우 나쁨 등)에서 감소하는 이용특성을 확인하였다.1. INTRODUCTION 1 1. Research background 1 2. Research purpose 3 2. LITERATURE REVIEW 4 1. Public bike in Seoul 4 2. External factor influences 5 3. Contributions 9 3. METHODOLOGY 10 1. Data collection 11 2. K-means clustering 16 3. Multinomial Logistic Regression 18 4. RESULTS 20 1. Classification results 20 2. Estimation results 25 5. CONCLUSIONS 30Maste

한국의 고령자 노동 연구

학위논문(박사) -- 서울대학교대학원 : 사회과학대학 경제학부, 2021.8. 정종우.The dissertation contains three essays on labor economics of the elderly in Korea. Specifically, I investigate how elderly labor responds to the following three factors: 1) housing wealth, 2) technological change, and 3) minimum retirement age policy. Chapter 1: Housing Wealth, Home Ownership, and Retirement Behavior Using a longitudinal data set from South Korea, I estimate the impact of housing wealth on the labor supply of elderly workers. Estimation results from my model suggest that house wealth variations significantly influence labor force participation, working hours, and expected retirement age of older workers. The housing wealth effect is bigger for people nearing retirement, which influences their retirement behavior. Additionally, this study suggests a mechanism of the housing wealth effect in which home-owning retirees tend to liquidate their housing wealth to finance their retirement. Retirees tend to move to a less-expensive house and utilize the profits from the housing values as a financial cushion to fund their retirement. Chapter 2: Technological Change, Job Characteristics, and Employment of Aged Workers (with Chulhee Lee) We investigate how the adoption of a new production technology differently affects the risk of job separation of young and old employees in South Korea by analyzing establishment-level panel data linked with administrative employment insurance records on individual workers. To address potential endogeneity associated with a firms technology adoption, we conduct instrumental variable estimations with a two-stage residual inclusion (2SRI) approach. The results suggest that technological changes (indicated by newly adopted automation, increased investment in IT, and increased purchase of IT equipment) positively affect the overall employment of incumbent workers. However, the employment of aged workers is less favorably affected by newly adopted technologies compared to that of younger workers. In some conditions, technological changes increase the retirement risk of older workers absolutely as well as relative to that of younger workers. Newly adopted automation negatively affects the employment of aged male workers who are engaged in the manufacturing industry. Investment in IT or IT equipment raises the probability of voluntary retirement of older workers employed in the service industry. Chapter 3: The Impact of the Minimum Retirement Age and Labor Substitutability Since 2016, workplaces in South Korea have been required to set the minimum retirement age at 60 by the amendment of the Act on aged workers employment. Using a set of data combining establishment-level panel data with individual-level employment records, I examined whether the delayed retirement age would increase older workers employment and how it affects the younger generations. A simple analysis shows that birth cohorts affected by the policy are 25.1 percentage points less likely to retire from their original retirement age than the other cohorts. The estimation results suggest that the policy reduces the employment of mid-aged (aged 30-54) workers. Much of the reduction in employment can be accounted for by the changes in male workers working for more than two years. The degree of labor substitution between older and young workers depends on the implementation of a wage-peak system. Firms adopting the wage-peak system tend to show 1) the low proportion of old workers and 2) the existence of a labor union. I found that firms having at least one of these characteristics show lower labor substitutability between generations.본 학위논문은 한국의 고령자 노동에 영향을 미치는 세 가지 요인들에 대한 연구를 담고 있다. 구체적으로 1) 주택자산 시장, 2) 기술 변화, 3) 정년 제도가 고령자의 노동공급 및 은퇴에 미치는 영향을 살펴보았다. 한국 가계의 자산 구성이 부동산 자산에 집중되어 있는 현 상황에서, 주택 가격의 변화는 곧 가구 자산의 변화를 의미하며, 특히 고령 가구의 경우 노후자산 및 가용소득에 지대한 영향을 미치게 된다. 1장은 고령화패널자료 2006-2016 자료와 인구주택총조사(Census) 자료를 이용하여 주택가격의 변화로 인한 자산 효과(wealth effect)가 고령 근로자의 노동공급에 어떠한 영향을 미치는지, 그리고 고령자들이 은퇴 후 노후 생활에서 주택자산을 어떻게 활용하는지 연구하였다. 분석 결과, 주택 자산의 가치 상승은 고령 근로자의 노동공급을 줄이며, 이 효과는 고령자 내에서도 연령이 높은 층에게서 더욱 높아, 은퇴가 가까운 근로자에게서 더욱 큰 것으로 확인되었다. 한편 은퇴자들은 주택자산의 노후 활용에 있어 주택연금 등 금융상품을 통한 현금화 보다는 상대적으로 저렴한 주택으로 이동한 뒤 발생한 차액으로 생활비를 마련하는 경향을 보였다. 이는 한국 고령자들의 주택 소유에 대한 선호, 그리고 향후 주택가격 상승에 대한 기대심리 등이 반영되었을 것으로 추측된다. 최근 자동화 시스템, 로봇, IT, AI 기술 등 다양한 기술이 산업현장에 도입됨에 따라 이들이 고용에 미칠 충격이 매우 클 것으로 예상된다. 기술과 고용 간의 관계에 관해서는 많은 선행연구가 진행됐으나 기술이 고령자 노동, 특별히 한국 고령자 고용에 미칠 영향에 대한 연구는 비교적 심도 있게 다루어지지 못했다. 2장(이철희 공저)은 사업체패널조사 (Workplace Panel Survey)와 연계된 고용보험 자료를 이용하여, 기업의 새로운 기술도입 (자동화 기술 도입, IT 투자확대)이 고용에 어떠한 영향을 미치는지, 특별히 기술로 인한 고령근로자의 퇴직위험이 젊은 근로자들과 비교해 어떠한 차이가 있는지 확인하였다. 분석 결과, 기업의 기술 도입은 소속 근로자의 퇴직위험을 낮추지만, 고령근로자의 위험 감소폭은 젊은 근로자에 비해 낮아 기술도입이 고령자 고용에 상대적으로 비우호적으로 작용하는 것으로 나타났다. 한편 특정 조건 하에서는 기술도입이 고령근로자의 퇴직위험을 절대적으로 낮추는데, 제조업 기업의 자동화 기술 도입은 남성 고령근로자의 퇴직위험을 크게 높이며, 서비스 기업의 IT 기술 도입은 근로자들의 자발적인 퇴직위험을 높이는 것으로 확인되었다. 이러한 기술도입의 부정적 고용효과가 발생한 이유로는 첫째로 기업의 비용 절감 목적, 둘째로 기술 도입으로 인해 변동된 직무와 근로자의 직무 선호 간 부조화가 복합적으로 작용한 것으로 추측된다. 한국은 2013년 고령자고용법 개정에 따라 2016년부터 최소정년을 60세로 정하여 운영 중이다. 정년연장의 효과에 관해 다양한 연구가 진행되는 가운데, 정년연장이 실제로 고령자 고용에 어떠한 영향을 미치는지, 또한 그로 인해 전체 고용시장은 어떠한 변화를 겪게 될지에 대한 논의가 진행 중이다. 3장은 사업체패널조사 (Workplace Panel Survey)와 연계된 고용보험 자료를 이용하여, 정년연장 시행이 고령자 고용에 어떠한 영향을 미쳤는지, 또한 고령자 고용 증가가 중년 및 청년 세대의 고용에 미치는 영향을 집중적으로 살펴보았다. 분석은 크게 두 단계로 진행되었는데, 첫 단계에서는 정년연장이 시행된 직후 고령자 고용의 변화를 살펴보았다. 정년연장의 적용을 받는 출생 코호트와 직전 연도에 태어나 적용을 받지 못한 코호트를 비교분석한 결과 정년연장 적용 코호트의 퇴직율이 정년연장 시점에서 큰 폭으로 감소하는 것을 확인하였다. 다음단계로, 정년연장으로 인해 고용이 유지된 고령 인력이 다른 세대의 고용에 미치는 영향을 살펴보았다. 분석 결과 정년연장 시행은 55세 이상 고령자 고용에 긍정적인 영향을 미쳤으나 이로 인해 30-54세 중년층 고용을 낮추는 것으로 확인되었다. 이러한 부정적 고용효과는 남성 및 2년 이상 종사한 근로자에게서 명확하게 나타났다. 정년연장에 대한 기업의 대표적인 대응책으로 임금피크제가 제시되는데, 임금피크제를 시행한 기업의 경우 정년연장으로 인한 세대간 노동대체가 발생하지 않았다. 반면 임금피크제를 시행하지 않은 기업의 경우 정년연장은 중년층을 비롯해 청년층 고용에도 부정적인 영향을 미치는 것으로 나타났다. 이외에도 기업 내 노동조합의 유무, 사내 고령근로자 비율에 따라 고령인력 증가가 다른 세대 고용에 미치는 영향은 큰 차이를 보여, 정년연장으로 인한 세대 간 노동 대체는 기업 특성과도 관련이 높은 것을 확인하였다.Chapter 1. Housing Wealth, Home Ownership, and Labor Supply of Older Workers 1 1.1. Introduction 1 1.2. Literature Survey and Theoretical Framework 3 1.3. Data and Empirical Strategy 7 1.3.1. Data 7 1.3.2. Empirical Strategy 11 1.4. Results 13 1.4.1. Baseline Results 13 1.4.2. Robustness Checks 14 1.5. Downsizing Channel of Housing Wealth Effect 17 1.6. Conclusion 22 1.A. Appendix 24 Chapter 2. Technological Change, Job Characteristics, and Employment of Aged Workers 25 2.1. Introduction 25 2.2. Conceptual Framework and Related Literature 27 2.3. Data and Empirical Strategy 31 2.3.1. Data 31 2.3.2. Empirical Strategy 32 2.4. Technological Change and Risk of Job Separation by Age: Results 35 2.4.1. Summary Statistics 35 2.4.2. Baseline Results 40 2.4.3. Sensitivity to Choice of Age Cutoff 45 2.4.4. Heterogeneity 47 2.5. Conclusion 52 2.A. Appendix 54 2.A.1. Analyses Using New Instruments: Robot Density 54 2.A.2. Additional Analysis: Multiple Technologies Adopted 57 2.A.3. Technological Change and New Employment 58 Chapter 3. The Impact of the Minimum Retirement Age and Labor Substitutability 59 3.1. Introduction 59 3.2. Literature Survey 61 3.3. Theoretical Framework 64 3.4. Data 66 3.5. The Impact of the MRA on Retirement 67 3.5.1. The Discontinuity of Retirement Age 67 3.5.2. Regression Results 70 3.6. Labor Substitutability Between Old and Young Workers 72 3.6.1. Empirical Strategy 72 3.6.2. Baseline Results 74 3.6.3. Heterogeneity: Job Tenure and Gender 76 3.6.4. Heterogeneity: Labor Cost and Wage-peak System 78 3.7. Conclusion 82 Bibliography 83 Chapter 1 Housing Wealth, Home Ownership, and Labor Supply of Older Workers 83 Chapter 2 Technological Change, Job Characteristics, and Employment of Aged Workers 86 Chapter 3 The Impact of the Minimum Retirement Age and Labor Substitutability 89 Abstract in Korean 92박

서식유형이 다른 학국의 세 동물군에 관한 분자집단 유전학 및 계통지리학적 연구

Thesis(doctoral)--서울대학교 대학원 :생명과학부,2004.Docto

Complete mitochondrial genome of Cyclograpsus intermedius Ortmann, 1894 (Crustacea: Decapoda: Grapsoidea) specimen collected in South Korea

In this study, the complete 16,184 bp mitochondrial genome of Cyclograpsus intermedius was determined from a specimen collected in South Korea. It consists of 13 protein-coding, 22 tRNA, 2 rRNA genes, and a non-coding A + T rich region. The base composition of the heavy strand in the mitochondrial genome was 34.7% A, 10.7% G, 18.7% C, and 35.9% T, resulting in a G + C content of 29.4%. A maximum-likelihood phylogenetic tree based on the 13 mitochondrial protein-coding genes showed that C. intermedius clustered together with the Varunidae. These molecular data will be useful for studying the evolutionary relationships among crab species. © 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group

Genetic variation in a freshwater prawn species, Palaemon paucidens, in South Korea

The biogeography of freshwater biota in the Korean Peninsula has been affected by recent geological processes and anthropogenic activity. The freshwater prawn, Palaemon paucidens, can serve as a non-fish model organism suitable for assessing these factors, as it is found in all river systems in the Korean Peninsula and may have been introduced by humans in some regions. In this study, we investigated the geographical distribution of genetic variation and the genetic structure of P. paucidens populations using mitochondrial DNA sequences and genotypes identified from four microsatellite loci. Our results showed that populations from westward-flowing river systems that drain into the Yellow Sea have more genetic diversity than those from southward-flowing river systems, and that the highest genetic variance revealed by analysis of molecular variance (AMOVA) using both genetic markers was observed in river systems grouped as HAN + GEUM, NAKDONG + JEJU, YOUNGSAN, and SEOMJIN. These results suggest that HAN and GEUM, in which freshwater prawn populations have higher levels of genetic diversity, were the most recently isolated river systems from Asian continental systems. Therefore, populations from HAN and GEUM experienced less severe bottlenecks than those from YOUNGSAN and SEOMJIN. (C) 2016 Elsevier Ltd. All rights reserved

Isolation and characterization of microsatellite markers for the endangered crab species Sesarmops intermedius

Sesarmops intermedius, which is designated as an endangered species in Korea, has been severely threatened by habitat destruction and pollution. From this species, we isolated 9 polymorphic microsatellites, which are independent of each other and represent allele frequencies under the Hardy-Weinberg equilibrium, except for 1 locus. The number of alleles per locus ranged from 7 to 20. The expected and observed heterozygosities ranged from 0.77 to 0.96 and from 0.63 to 0.95, respectively. We also examined cross-species amplification of the 9 developed microsatellite loci in 2 other crabs designated as endangered species in Korea and 6 sesarmid crabs, which live in habitats similar to that of S. intermedius. These markers have the potential to contribute to establishing conservation plans for this endangered crab species. © Springer Science+Business Media B.V. 2011

First record of the complete mitochondrial genome of Aedes koreicus (Edwards, 1917) (Diptera: Culicidae) in South Korea

In this study, we first determined the mitochondrial genome sequence of Aedes koreicus collected in South Korea. Its mitochondrial genome is 15,840 bp in length and consists of 13 protein-coding genes, 22 transfer-RNA genes, 2 ribosomal-RNA genes, and a non-coding A + T rich region. The overall base composition in the heavy strand was as follows: A, 40.1%; G, 8.7%; C, 13.6%; T, 37.5%; and the G + C content was 22.4%. Phylogenetic analysis revealed that Aedes spp. form a monophyletic group

Environmental factors affecting population level genetic divergence of the striped field mouse (Apodemus agrarius) in South Korea

The cognizing of connectivity among small mammal populations across heterogeneous landscapes is complicated due to complex influences of landscape and anthropogenic factors on gene flow. A landscape genetics approach offers inferences on how landscape features drive population structure. Through a landscape genetics approach, we investigated influences of geographical, environmental, and anthropogenic features on populations of Apodemus agrarius, the striped field mouse, the prime vector of hemorrhagic fever by a landscape genetic approach. We identified landscape features that might affect the population structure of striped field mice by analyzing microsatellite markers of 197 striped field mice from 21 populations throughout South Korea. We developed Maximum-likelihood population effects models based on landscape distances and resistance matrices and pairwise F-ST values for meta-populations of striped field mouse. We also conducted Mantel and partial Mantel tests to investigate geographic patterns of genetic similarities. In Mantel and partial Mantel tests, the F-ST was significantly correlated with all three models of movement; movement cost, Euclidian distance and least-cost distance, although the magnitudes of correlations varied. The 4 top-ranked models included three variables; temperature, precipitation and one human disturbance factor (population). We did not attain a significant effect for anthropogenic factors on genetic similarities among populations in the Korean striped field mouse, but we confirmed a significant association for genetic similarity with climatic features (temperature and precipitation)

Genetic differentiation of the Korean striped field mouse, Apodemus agrarius (Muridae, Rodentia), based on microsatellite polymorphism

The striped field mouse (Apodemus agrarius) is one of the most common mammals in Korea, however, limited research has focused on the population structure and biogeography of this mouse throughout Korea. In addition, the taxonomic status of the species remains unresolved. The objectives of our study were to address the inadequacies in understanding the population structure, biogeography, and taxonomic status of A. agrarius. We collected 160 samples from 13 localities throughout the South Korean Peninsula, two nearby islands and two remote islands. We used five microsatellite loci and estimated genetic diversity measures and populations divergence estimates (i.e. FST and RST) to address the objectives. Except for populations on the two remote islands, Jeju and Heuksan, the populations on the peninsula and nearby islands indicated low FST and RST values. The population structure based on microsatellite loci supported only one subspecies opposing three subspecies reported previously on the Korean Peninsula and nearby islands. However, populations on Jeju Island and Heuksan Island showed subspecific differences from each other and the populations on the Korean Peninsula and nearby islands. The information reported on the population genetics of the striped field mouse in Korea will allow resolving the taxonomy and biogeography of this species. © 2017 Walter de Gruyter GmbH, Berlin/Boston

Population Genetic Structure of the Malaria Vector Anopheles sinensis (Diptera: Culicidae) Sensu Stricto and Evidence for Possible Introgression in the Republic of Korea

Anopheles sinensis Wiedemann sensu stricto (s.s.) is a dominant mosquito and considered a secondary malaria vector in the Republic of Korea (ROK). Despite the potential significance for malaria control, population genetics studies have been conducted using only mitochondrial DNA (mtDNA), and studies of the genetics of hybridization have never been attempted. In this study, 346 specimens from 23 localities were subject to experiments. Among them, 305 An. sinensis s.s. specimens from 20 localities were used for mtDNA analysis, and 346 specimens comprising 341 An. sinensis s.s. from 22 localities and five Anopheles kleini Rueda from one locality were examined in the microsatellite study. Neighbor-joining analysis of pairwise F-ST and R-ST based on microsatellite results showed that the populations are divided into two groups, as did the mtDNA results. However, the Bayesian analysis and factorial correspondence analysis plots showed three distinct clusters. Among the mtDNA and microsatellite results, only microsatellites represented small but positive and significant isolation-by-distance patterns. Both molecular markers show the Taebaek and Sobaek Mountain ranges as barriers between the northern and southern parts of the ROK. The newly recognized third group suggests possible introgressive hybridization of An. sinensis s.s. with closely related species. The slightly different composition of populations in each group based on different markers is probably because of different population dynamics in each group. These results imply that there is restricted gene flow of epidemiologically important malaria-related genes between the northern and southern parts of the ROK