전이금속칼코겐 전계효과 트랜지스터의 불순물에 의한 전기적 특성 변화에 대한 연구

학위논문 (박사) -- 서울대학교 대학원 : 자연과학대학 물리·천문학부(물리학전공), 2021. 2. 이탁희.Two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides (TMDCs), have been attracted remarkable attention due to their novel electronic features coming from their thin nature. While graphene is hard to utilize as a semiconductor due to its zero electrical bandgap nature, TMDCs have been considered as a promising candidate for the next-generation electronic device due to their thickness dependent tunable bandgap. In particular, semiconducting TMDCs have shown desirable field effect transistor (FET) properties, such as the high on-off ratio, high mobility and low subthreshold voltage swing voltage. In this regard, numerous studies have been reported for the application of TMDCs in various field, such as electronics, optoelectronics and thermoelectrics. However, due to a large number of intrinsic defects of TMDCs (~1012 cm-2) comparing to graphene (~1010 cm-2), the performance of TMDCs devices has been far behind to the theoretically predicted device performance. Furthermore, due to the 2D nature of TMDCs, interface absorbents also can act as impurities. Therefore, understanding the effect of defects to the charge transport of TMDCs is essential to fully realize the potential of TMDCs devices. In this manner, first, I investigated the noise generation and electric conduction at grain boundaries in CVD-grown MoS2 field effect transistor. For application of MoS2 as various devices, understanding the effect of grain boundaries which are unavoidable structure defect is essential. Through electrical characteristics and noise measurements, I confirmed that the grain boundary hinders the charge transport of CVD-grown MoS2, which can be considered as a dominant noise source. The noise characteristics showed that the noise generation mechanism of CVD-grown MoS2 at grain boundary is different from the single grain regions of MoS2. Also, I observed that the noise generated at the grain boundary concealed the percolative noise characteristics of the single grain regions of MoS2. Secondly, I investigated the molecular dopant dependent charged impurity scattering in WSe2 field effect transistor. In general, dopants counterions which are generated by charge transfer process can decrease the mobility of the materials. After doping, the mobility of WSe2 was decreased at low temperature, which means that dopant counterions can act as Coulomb scattering center. Using theoretical model and density functional theory calculation, I investigate the dopant dependent Coulomb scattering of dopant counterions and the microscopic origin of charge transfer process between molecular dopants and WSe2. Additionally, I conducted research on the trap mediated charge transport of pentacene/MoS2 heterojunction p-n device. I confirmed that charge transport of the pentacene/MoS2 heterojunction devices is explained by space-charge-limited conduction. Also, as the temperature goes higher, the variable range hopping transport of the pentacene/MoS2 heterojunction device was transformed to thermally activated transport.그래핀이나 전이 금속 칼코겐 화합물 물질을 포함한 이차원 물질은 얇다는 특징에서 오는 장점들 덕분에 많은 주목을 받아 왔다. 그래핀의 경우에는 전기적 밴드갭이 없어 반도체 소자로서 이용하기 힘든 반면에, 전이 금속 칼코겐 화합물들은 두께에 따라 바뀌는 밴드갭 때문에 차세대 소자로서 각광 받고 있다. 특히 반도체 성질을 가지는 전이 금속 칼코젠 화합물의 경우에는 높은 온/오프 전류비, 높은 이동도, 낮은 문턱 전압 이하 스윙값 등 전계효과 트랜지스터로서 좋은 성능을 보여준다. 이러한 이유로, 다양한 분야에 소자로 활용하기 위해 많은 연구가 활발히 진행되어오고 있다. 하지만 전이 금속 칼코겐 화합물의 경우에는 그래핀과는 다르게 많은 고유결함을 가지고 있기 때문에, 이론적으로 예측된 성능보다 아직 모자란 값들을 보여주고 있다. 게다가, 이차원이라는 구조적 특성 때문에 표면에 붙은 흡착물들 또한 불순물로 작용할 수 있다. 이러한 점으로 볼 때, 차세대 나노 전자 소자 구현에 있어서 결함이 전이금속 칼코겐 화합물의 전자 수송에 어떠한 영향을 주는지에 대한 연구가 필수적이다. 이러한 측면에서, 본 학위논문에서 첫 번째로 화학 기상 증착법으로 만든 이황화 몰리브덴 전계 효과 트랜지스터의 전기적, 노이즈 특성이 결정 입자 경계에 어떠한 영향에 받는지에 대해 논하고자 한다. 이황화 몰리브덴을 다양한 분야에 소자로 활용하기 위해서는, 대면적으로 합성할 때 필연적으로 만들어지는 결정 경계의 효과에 대한 이해가 필요하다. 이를 위해 전기적 측정과 노이즈 측정을 이용하여 결정 경계가 전하 수송을 방해하고 전기적 노이즈를 발생시키는 요인이라는 것을 확인했다. 이러한 결정경계에서 발생한 노이즈는 단일 결정에서 발생한 노이즈와 발생 원인이 다르다는 것을 밝혀냈다. 또, 결정경계에서 발생한 노이즈는 단일 결정의 네트워크 전하수송의 네트원크 경향을 가린다는 것 또한 확인 할 수 있었다. 두 번째로, 텅스텐 셀레늄 화합물 전계 효과 트랜지스터의 분자 마다 다른 대전된 불순물에 의한 산란에 대하여 기술하고자 한다. 일반적으로, 전하 교환에 의해 생기는 도펀트 이온들은 물질의 이동도를 감소시킨다. 도핑 후에 저온에서 텅스텐 셀레늄 화합물의 이동도가 감소하는 것을 확인했는데, 이는 앞에서 언급한 것처럼 도펀트 이온들이 산란을 일으켜 이동도를 감소시킨 것이다. 이러한 특성을 이론 모델과 밀도 함수 이론 계산을 통해 분석하여, 분자 마다 다른 도펀트 이온들에 의한 산란 정도를 확인 할 수 있었고 전하 교환 특성의 미시적인 원인을 알아 볼 수 있었다. 추가적으로, 전이 금속 칼코겐 화합물 물질은 아니지만, 유기 반도체 물질인 펜타센과 이황화 몰리브덴으로 이루어진 p-n 접합 소자에서의 trap에 의한 전하 수송 특성에 대한 연구도 기술하고자 한다. 물질과 물질이 결합하면 물질 사이의 표면에 trap 상태들이 생길 수 있다. 이러한 표면의 trap 상태들에 의한 펜타센/이황화 몰리브덴 p-n 접합 소자의 전하 수송 특성이 space-charge-limited conduction의 특징이라 알려진 경향들과 잘 일치 하는 것을 확인 하였다. 게다가 펜타센/이황화 몰리브덴 p-n 접합 소자가 저온에서는 variable range hopping transport의 경향을 보이다가 점점 온도가 올라 갈수록 thermally activated transport로 변하는 것을 확인 할 수 있었다.List of Contents Abstract i List of Contents iii List of Figures vi Chapter 1. Introduction 1 1.1. Brief introduction of TMDCs 1 1.2. Origin of the disorder in TMDCs 1 1.3. The effect of defects in electrical characteristics of TMDCs 3 1.4. Outline of this thesis 4 References 5 Chapter 2. Analysis of noise generation and electric conduction at grain boundaries in CVD-grown MoS2 field effect transistors 7 2.1. Introduction 7 2.2. Experiments 9 2.2.1. Growth of monolayer MoS2 and device fabrication 9 2.2.2. Raman and Photoluminescence characteristics of CVD-grown monolayer MoS2 11 2.2.3. Current-voltage (I-V) characteristics 11 2.2.4. Electrical noise characteristics 12 2.3. Results and discussions 12 2.3.1. Electrical characteristics of MoS2 FETs with and without grain boundary 12 2.3.2. Electrical noise characteristics of CVD-grown MoS2 with and without grain boundary 14 2.3.3. Hooge parameter analysis and network properties of CVD-grown MoS2 FETs 15 2.3.4. Schematics of conduction network of CVD-grown MoS2 FETs with and without grain boundary 19 2.4. Conclusion 20 References 21 Chapter 3. Molecular Dopant-dependent Charge Transport in Surface-charge-transfer-doped WSe2 Field Effect Transistor 24 3.1. Introduction 25 3.2. Experiments 27 3.2.1. Device fabrication and doping process 27 3.2.2. Dopant molecules and 4-point probe measurement 28 3.2.3. Thickness effect to doping 30 3.2.4. Theoretical model for density of the charged impurity denisty (nimp) calculation 31 3.3. Results and discussions 33 3.3.1. Transfer curves of pristine and doped WSe2 and threshold voltage shifts 33 3.3.2. Temperature dependent conductance and intrinsic mobility of WSe2 FET 35 3.3.3. Dopant dependent charged impurity density 38 3.3.4. DFT Calculation 41 3.4. Conclusion 44 References 45 Chapter 4. Trap-mediated electronic transport properties of gate-tunable pentacene/MoS2 p-n heterojunction diodes 48 4.1. Introduction 48 4.2. Experiments 50 4.2.1. Device fabrication process 50 4.2.2. Electrical characterization 51 4.3. Results and discussions 52 4.3.1. Electrical characteristics of MoS2 FET and pentacene FETs 52 4.3.2. Gate-tunable electrical characteristics of the pentacene/MoS2 p-n junction device 54 4.3.3. Space-charge-limited conduction of the penatene/MoS2 p-n heterojunction device 57 4.3.4. Variable-range hopping conduction of the pentacene/MoS2 heterjunction device 59 4.3.5. Energy band schematics 62 4.4. Conclusion 64 References 65 Chapter 5. Summary 69 국문초록(Abstract in Korean) 71 감사의 글 73Docto

Analysis of Childrens Experiences in Plants and Their Relationship with Ecological Literacy

This study was conducted for investigating the characteristics of childrens experiences in plants and their relationship with ecological literacy. 578 primary students participated in our survey, who consisted of 240 urban and 338 semi-rural children. The questionnaire for this study was composed of items about their experiences in plants and ecological literacy. Childrens experiences in plants were classified to 5 factors; indirect/observable, living, investigative, negative, and active experiences in plants. The most important factor of them is indirect/ observable experience which tends to be passive. Childrens ecological literacy and experiences in plants were not different with a place of residence but had difference with sexual. Most childrens experiences in plants had correlation with ecological literacy. Ecological sensibility was the most important variable for explanation of the relation between childrens ecological literacy and experiences in plants. It is recommended that supplying experiments in plants to children is important for promoting their ecological literacy.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000026049/10SEQ:10PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000026049ADJUST_YN:YEMP_ID:A075900DEPT_CD:719CITE_RATE:0FILENAME:2013ese32(4)juej.pdfDEPT_NM:생물교육과EMAIL:[email protected]_YN:NCONFIRM:

An Analysis of Illustrations in the Unit The Human in the Nature of High School Life Science Textbooks

교과서의 삽화는 학생들에게 중요한 영향을 미치는 자료 중 하나이다. 이 연구에서는 생명 과학Ⅰ 교과서 Ⅳ. 자연 속의 인간 단원의 삽화의 빈도,종류, 용도를 분석하였다. 제시된 삽화의 종류에 있어서는 사진이 49.3 %로 가장 많았고, 그림과 그래프가 다수 사용되었다. 삽화가 사용된 주된용도는 과학 개념을 학습자에게 이해시키기 위한 자료 제공2가 가장 많았고, 이어 동기 유발, 자료 제공1을 위해 사용되었다. 삽화의 종류에 따라사용된 용도를 분석한 결과, 사진의 경우에는 주로 동기 유발과 자료 제공의 용도로 사용되었고, 그림, 그래프 등 나머지 삽화 종류는 주로 자료제공의 용도로 사용되었다. 삽화의 빈도에 관한 연구 결과는 기존의 연구와 유사하였으나, Ⅳ. 자연 속의 인간 단원은 다양한 요소 간의 관계를 요구하는 분량이 많아 여타 과목보다 많은 그래프 자료를 활용하였다. 학습자가 이해하기 쉽고 재미있으며 활용하기 편한 구성의 교과서를 제공하기 위해서는실험에 사용되는 삽화의 수와 실험의 수를 늘려야 한다. 교과 내용에 흥미를 갖고 이해하도록 하기 위해 상황에 맞는 다양한 삽화를 도입해야 한다.Illustrations in text books are the most influential material to students. So we have to analyze illustrations in text books. In this study, the number, sort, purposes of illustrations in the Unit The Human in the nature of highschool Life Science textbooks was analyzed. The sort consists of photograph (49.3 %) and many of drawings and graphs. The main purpose of illustrations is for providing materials 2, followed by motivation, providing materials 1. According to the analysis of the purpose depending on the sort, photograph is mainly used for motivation, providing materials, other illustrations like drawing and graph are mainly used for providing materials. The result of this study was very similar to existing studies, but there are some differences in graph. The Unit The Human in the nature uses more graphs than any other subjects because it contains connections between various factors. For providing understandable and easily usable textbook, we have to increase the number of illustrations used for experiments. And we need more various illustrations that suit the learning situations for motivating students effectively.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/0000026049/3SEQ:3PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:0000026049ADJUST_YN:YEMP_ID:A075900DEPT_CD:719FILENAME:2014schoolscij8(1).pdfDEPT_NM:생물교육과EMAIL:[email protected]_YN:NCONFIRM:

Effect of Plant Life Cycle on Plant Settlement in Diverse Water Level

본 연구에서는 정수 환경에 정착한 3생활형 9분류군의 식물을 대상으로 1년동안 정기적으로 모니터링을 실시하였으며, 이를 통해 식물 생활형이 수위 조건에 따라 식물 정착에 어떠한 영향을 미치는지 밝히고자 하였다. 18개의 실험구를 셋으로 나누어 16주 범람 기간 동안 0, 20, 60cm로 수위를 각각 유지하였으며, 범람 기간을 제외한 기간은 0cm로수위를 모두 동일하게 유지하였다. 1차년에 식재한 다년생 식물인 큰고랭이(Scirpus tabernaemontani), 줄(Zizaniacaduciflora), 부들속 2종(Typha angustifolia, T. orientalis)은 종자에 의한 추가적인 정착은 없었으며, 수문 조건이 밀도 및 초고 생장에 큰 영향을 미치지 않았다. 그러나 1년생 식물인 고마리(Persicaria thunbergii), 여뀌(Persicariahydropiper), 사마귀풀(Aneilema japonicum)과 2년생인 벼룩나물(Stellaria uliginosa), 뚝새풀(Alopecurus aequalis), 개피(Beckmannia syzigachne)는 상대적으로 수문 조건에 의한 영향을 크게 받았다. 정수 환경에서 침수 수위 및 침수 기간은 상대적으로 지하경을 형성하지 못하는 1, 2년생 식물 종들의 정착 및 생육에 큰 영향을 미치는 것으로 보인다.The purpose of this study is to reveal the effect of plant life cycle to plant settlement by 1 year monitoring. The subjects of monitoring are the plants (3 plant life cycle, 9 taxa) well established in the mesocosm. 18 mesocosms were divided into 3 sets and water levels were maintained at 0, 20 and 60 cm during 16 weeks from mid-May, respectively and at 0 cm except these 16 weeks. Height and population size of transplanted perennial plants (Scirpus tabernaemontani, Zizania caduciflora, Typha (Typha angustifolia and Typha orientalis)) at 1st year were not affected by diverse water level, though any more seedlings of these species were not settled at this condition. In contrast, water level condition strong influenced annual and biennial plant, relatively. As a result, timing and duration of flooding have great effect on successful settlement of annual and biennial plant without rhizome.OAIID:oai:osos.snu.ac.kr:snu2015-01/102/0000026049/3SEQ:3PERF_CD:SNU2015-01EVAL_ITEM_CD:102USER_ID:0000026049ADJUST_YN:YEMP_ID:A075900DEPT_CD:719CITE_RATE:0FILENAME:2015jwr17(1)namjm.pdfDEPT_NM:생물교육과SCOPUS_YN:NCONFIRM:

Effects of Micro-topography on Vegetation Pattern in Dunchon-dong Wetland

본 연구에서는 둔촌동 습지에서 미지형이 식물 군락 구성에 미치는 영향을 연구하기 위하여 2007~2008년에 걸쳐 지형에따른 수위 변화와 식물 군락의 변화를 조사하였다. 조사 지역을 지대가 낮은 지형부터 높은 지형까지 4개 구역으로구분하여 조사하였으며, 각각의 구역은 조사 지역 면적 대비 약 11%, 10%, 18%, 24%의 면적을 가지고 있었다. 조사 기간동안 수환경의 pH는 6.10(±0.13), 전기전도도는 51.5(±6.0)㎲/cm이었으며, PO4-P, NO3-N, NH4-N은 각각 0.04(±0.02)mg/L,0.14(±0.07)mg/L 그리고 0.01mg/L 이하로 유지되었다. 2008년 3~4월 누적 강수량이 2007년 대비 약 56%로 적었던 것이지대가 낮은 지형에서 수위 환경 차이를 유발하여 식물 군락 형성에 매우 큰 영향을 미쳤으며, 지형의 높이에 따라 해당구역을 우점하는 식물 길드가 다르게 나타났다. 이러한 결과는 종자로부터 생활사가 시작되는 1년생 식물 종들이 조사지역을 전체적으로 우점하였기 때문이며, 다양한 길드의 식물들이 혼재하기 위해서는 높이 구배가 있는 미지형이조성되어야 한다는 것을 의미한다.The purpose of this study is to investigate the efect of micro-topography to vegetation patern in Dunchon-dong wetland. To characterize the efect of micro-topography, changes in water level and vegetation patern were monitored from 207 to 208. Depending on the relative elevation, the study site was divided into 4 sectors. The relative areas of sectors in ascending order were 1%, 10%, 18% and 24%, respectively. During investigation period, average water pH was 6.10 (±0.13), electron conductivity was 51.5 (±6.0)㎲/cm, PO4-P, NO3-N and NH4-N concentration were 0.04 (±0.02)mg/L, 0.14 (±0.07)mg/L, and lower than 0.01mg/L, respectively. Water level was very changeable in low-water season because the area of lowest sector was smal. This characteristic increased the efect of diference of acumulated precipitation from March to April in 207 and 208 to plant community compositon in lower sectors. Diferent plant guilds dominated respective sectors and anual plants were major dominant species in the study site. This study sugested that the elevation gradients are necesary to create the habitats for various plant guilds in wetland.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/0000026049/13SEQ:13PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:0000026049ADJUST_YN:YEMP_ID:A075900DEPT_CD:719CITE_RATE:0FILENAME:2014jwr16(4)nam.pdfDEPT_NM:생물교육과SCOPUS_YN:NCONFIRM:

경제정의교육에 대한 교사의 신념과 수업

학위논문 (박사)-- 서울대학교 대학원 사범대학 사회교육과, 2017. 8. 조영달.This study examined the relationship between social studies teachers beliefs about economic justice education and their pedagogy on economic justice. Prior to the actual empirical research, I discussed what I have called the mainstream Subject-oriented approach to economic justice and the alternative Others-oriented approach to construct a theoretical framework through which the study could explore teachers beliefs and pedagogy. In doing so, this study suggested an economic justice education to respond to the vocation of the Others, and citizenship education to attend to the alterity of the Others. To determine the relationship between teachers beliefs and pedagogy, an explanatory-convergent design of mixed methods research was employed. The first stage of quantitative research identified six clusters based on cluster analysis, and the analysis of variance showed that social studies teachers beliefs on economic justice education differ according to the clusters. For the second stage of qualitative research, three particular clusters were selected: an Average-group, a Subject-oriented group, and an Others-oriented group. Three teachers (one from each cluster) were sampled from the three clusters to represent each, and a multiple case study was conducted with them. The qualitative examination of three teachers worlds revealed diverse but complicated relationships between beliefs and pedagogy. However, with all the quantitative and qualitative explorations and the detailed research findings, I could not convince myself that the findings fully explored the research question, and I had to return to square one to address the question of what the deeper relationship between teachers beliefs and pedagogy is. This question pushed me towards an ontological exploration. Deleuzian ontology was an essential lens to re-interpret the collected data. From the Deleuzian perspective, teaching is an event, an event of surge. Potential changes which have been unnoticed suddenly soar up into the classroom. This surge is the actualization of what was subsisting/insisting at the level of virtuality. As we understand the ontology of teaching as an aleatory point, empty place, singularity, and an event of surge, we can eventually reimagine the relationship between teachers beliefs and pedagogy as event of surge. As teachings arise into the classroom, a teachers beliefs also surge into his/her teaching. In the springing up events of teachings, beliefs reveal and expose themselves tearing off the ontological rigidity. This ontological understanding of teachers beliefs and pedagogy presented the significance of teachers beliefs: they keep pedagogy active and alive. The moment teachers beliefs stop moving around and being alive, pedagogy remains virtual and fossilized. The importance of teachers beliefs in pedagogy and the significance of an event of surge is that without it, pedagogy is no better than dead. But the empty place cannot remain empty for long. As Levinas (1969) reminds us, the metaphysical desire for the Other awakened by the face of the other should be situated in the aleatory points and empty places that will move around the structure. The reconciliation of soaring up events of teachers beliefs and pedagogy with Others-oriented approach to economic justice education occurs here. The pedagogy to respond to the vocation of the others, and to attend to the alterity of the Others, can gain a life when the beings and beliefs of teachers soar up and permeate the classroom, and thereby affect students, and therefore hopefully, change the world.CHAPTER 1. INTRODUCTION 1 1. Economic justice in crisis 1 2. Economic justice education afoot 2 3. Research question 3 CHAPTER 2. LITERATURE REVIEW 6 1. Mainstream approach to economic justice 6 Principle of desert 7 Principle of needs 8 Principle of equality 9 Utilitarianism 10 The difference principle 11 Libertarianism 12 2. Critical review on the mainstream approach to economic justice 13 3. Others-oriented approach to economic justice 18 Justice as unconditional hospitality for the Other 18 Unconditional hospitality and asymmetric responsibility 22 Economic justice education as a response to the vocation of the Other 24 4. Comparison of the two approaches 28 5. Teachers beliefs and pedagogy 32 Teachers beliefs: Meanings and significance 32 Relationship between belief and pedagogy 34 6. Deleuzian Ontology 39 CHAPTER 3. METHODOLOGY 42 1. Overview of the research: Mixed methods research 42 The philosophical foundation of mixed method 43 Rationale for the mixed method 45 Challenges in using mixed method 48 2. Research design 49 3. Research procedure 53 Quantitative phase 54 Qualitative phase 61 CHAPTER 4. RESEARCH RESULTS 70 1. Quantitative research results 70 Demographic information 70 Teachers beliefs about economic justice education: Descriptive statistics 73 Cluster analysis results 77 Analysis of variance results 91 Sampling for the qualitative case study 93 2. Qualitative research results 95 The story of Y (Cluster 1: Average Group) 97 The story of S (Cluster 3: Others-oriented group) 119 The story of H (Cluster 5: Subject-oriented group) 146 Converged story: The results of the qualitative case study 166 CHAPTER 5. REIMAGINING THE ONTOLOGY OF PEDAGOGY 170 1. Aporia: What is the answer? 170 2. Beyond the representational thought about pedagogy 171 3. Beliefs and pedagogy as an event 174 Ontology of event 174 Teaching: an event of surge 176 Teaching: an aleatory point 178 Reimagining the relationship between teachers beliefs and pedagogies about economic justice education 182 4. Ethics of pedagogy 185 CHAPTER 6. SUMMARY AND CONCLUSION 189 Reference 194 Appendix A: Learning to teach for social justice-beliefs scale 215 Appendix B: Survey Questionnaire 216 Appendix C: Descriptive Statistics of 6 Clusters 219 Appendix D: Email Message to social studies teachers with Link to Online Survey 243 Appendix E: Information/Consent Letter for Interviewees 244 Appendix F: Interview Question Guide 246 Abstract in Korean 248Docto

Relationship between Environmental Characteristics andthe Big 5 Personality Traits in Elementary School Students

The purpose of the present study was to explore the relationship between environmental variables including environmental attitudes, environmental sensitivity, and environmental behaviors, and the Big 5 personality traits of children. Thus, the relationship in a sample of 279 elementary school students was examined using correlation and multi-regression analysis. The results of this study revealed that environmental variables were positively correlated with the personality traits, indicating that the relationship in boys were much higher than in girls. Regression results indicated that the envi- ronmental variables can be significantly predicted by the Big 5 personality traits and conscientiousness is the trait most strongly linked to environmental sensitivity and behavior. However, the amount of the variance explained by personality seemed to be different between gender and was likely to decrease with school year.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/0000026049/11SEQ:11PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:0000026049ADJUST_YN:YEMP_ID:A075900DEPT_CD:719CITE_RATE:0FILENAME:201409kimht_biologyeducation.pdfDEPT_NM:생물교육과SCOPUS_YN:NCONFIRM:

The Construction and Management of Artificial Wetland Using Emergent Macrophytes for High Biomass Production

높은 생산성을 위한 인공습지 조성 및 관리 방안 제시를 위해 세 가지 대형정수식물(갈대, 애기부들, 줄)을 두 가지 매질조건(개별 매질과 혼합 매질)과 두 가지 수위 조건(5 cm와 20 cm)에 식재한 뒤 3년간의 모니터링을 수행하였다. 그 결과줄의 경우 조성 환경에 상관없이 첫 해 초기 생육(최대 초고, 약 200 cm; 최대 지상부 생산성 약 500 g/m2)뿐만 아니라 3년경과 후 최종 생육(줄, 약 1,100 g/m2; 애기부들, 770 g/m2; 갈대, 450 g/m2)에 있어, 전반적으로 갈대나 애기부들에 비해월등하게 나타났다. 특히 초기 생육이 좋았던 줄은 자연적으로 유입돼 발생하는 잡초들에 의한 피해가 거의 없었던 반면갈대나 애기부들의 경우 다년생 잡초를 포함한 여러 잡초와의 종간 경쟁으로 생육이 다소 부진하였다. 특히 얕은 수심환경과 moss peat를 포함한 혼합 매질 조건에선 식재종들의 생육이 전반적으로 부진하였으며, 그로 인해 잡초들의 생육이상대적으로 좋았다. 높은 지상부 생산성을 위한 인공습지 조성을 위해선 줄과 같이 생육 환경에 크게 구애받지 않으며초기 생육이 뛰어난 종의 선발을 통해 자연유입 잡초나 야생동물 등에 의한 피해를 최소화시켜야 할 것이다. 만약 줄이아닌 갈대나 애기부들과 같은 종을 식재하고자 한다면 온실과 같은 환경에서 일정 수준 이상 생육시킨 뒤 식재함으로써더욱 경쟁력을 제고시킬 수 있을 것이다. 더불어 높은 지상부 생산성을 위한 인공습지를 지속적으로 유지시키기 위해선한두 가지 선택지가 아닌 제초와 관련된 최적의 관리방안들을 적시에 활용하는 통합적 잡초 관리 시스템의 적용을 제안하는 바이다.To present a guideline on the construction and management of artificial wetlands for high biomass production, three emergent macrophytes (Phragmites australis, PA; Typha angustifolia, TA; and Zizania latifolia, ZL) were planted under two substrates conditions (general soil with and without moss peat) and two water levels (5 cm and 20 cm) and monitored for three years. ZL showed greater growth performance rather than the others not only at early growth phase in the first year [shoot height, 200 cm; above-ground dry weight (AGDW), 500 g/m2] but also in the last year (ZL, 1,100g/m2; TA, 770g/m2; and PA, 450 g/m2 of AGDW). ZL with rapid growth at the early growth phase was not affected by naturally introduced weeds, whereas slower and poorer growth of PA and TA at the early growth phase resulted in relatively higher introduction and establishment of natural weeds. In turn, such introduced weeds negatively contributed to the growth of PA and TA particularly under shallow water (5 cm) with the substrate condition including moss peat. We suggest a plant material with rapid and great growth at the early phase such as ZL for reducing possible negative influences by the natural weeds and wild animals for high biomass production in constructed wetlands. A pre-growing process in greenhouse prior to planting might be an useful option to raise the competitiveness of those species when planting PA and/or TA. In addition, we recommend that integrated weed management system with utilizing various options at the most appropriate timing must be applied for maintaining sustainable high biomass production at the artificial wetlands.본 연구는 환경부 산하 수생태복원사업단의 Eco-STAR project(EW33-08-12)의 연구비 지원을 통해 수행되었음.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/0000026049/1SEQ:1PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:0000026049ADJUST_YN:YEMP_ID:A075900DEPT_CD:719FILENAME:2014jwr16(1)hongmg_constructedwetland.pdfDEPT_NM:생물교육과EMAIL:[email protected]_YN:NCONFIRM:

Study on Characteristics of Seed Germination and Seedling Growth in Salix gracilistyla for Invasive Species Management

To suggest ecological management plans for invasion of Salix gracilistyla, stepwise environmental sieve of seed dispersal, germination, seedling and juvenile stages were investigated. About 84% of total seeds were released between May 6 and 10. Germination rates significantly declined with decrease of light intensity from 100% to 30% and 0% (p<.001), but above 60% of seeds germinated in all treatments. Difference of germination rates with 0 and 2cm water level was not significant (p = .571). With increase of elapsed time after seed dispersal, germination rates significantly decreased (p<.001), and seed viability was lost within 16 days. Considering both germination rate of seed and survival rate of seedling, survival rate of all dispersed seeds was only 5% when 8 days passed after seed dispersal. All 22-day-old seedlings (height: 1cm) died under flooding of twice level as its height. With decrease of light intensity from 100% to 30%, survival rates of seedling decreased from 90% to 33% (p<.001). In the case of 45-day-old juvenile (height: 20cm), survival rate was 70% under the water level same as its height. There was significant interactive effect of water level and light intensity on the growth of juvenile (height: p<.001, dry weight: p<.01), and survival rate of juvenile was 10% under +20cm-water level and 30%-light intensity condition. The following management plans for invasion of S. gracilistyla are recommended from these results. (1) Dry condition should be maintained at fringe of wetlands for about two weeks at seed dispersal and germination stage (early May∼mid May). (2) Water level should be raised to about 5cm at fringe of wetlands for about two weeks at seedling stage (mid May∼early June). (3) Water level should be raised to over 20cm at fringe of wetlands for a long time at juvenile stage. Planting trees for shading can raise management effectiveness (mid June∼). (4) As water level manipulating is performed as fast as possible for controlling seedling and juvenile, management become easier and more effective.OAIID:oai:osos.snu.ac.kr:snu2015-01/102/0000026049/8ADJUST_YN:YEMP_ID:A075900DEPT_CD:719CITE_RATE:0FILENAME:2015jkert_choih.pdfDEPT_NM:생물교육과SCOPUS_YN:NCONFIRM:

Postoperative nutritional effects of early enteral feeding compared with total parental nutrition in pancreaticoduodectomy patients: a prosepective, randomized study

The benefits of early enteral feeding (EEN) have been demonstrated in gastrointestinal surgery. But, the impact of EEN has not been elucidated yet. We assessed the postoperative nutritional status of patients who had undergone pancreaticoduodenectomy (PD) according to the postoperative nutritional method and compared the clinical outcomes of two methods. A prospective randomized trial was undertaken following PD. Patients were randomly divided into two groups; the EEN group received the postoperative enteral feed and the control group received the postoperative total parenteral nutrition (TPN) management. Thirty-eight patients were included in our analyses. The first day of bowel movement and time to take a normal soft diet was significantly shorter in EEN group than in TPN group. Prealbumin and transferrin were significantly reduced on post-operative day (POD) 7 and were slowly recovered until POD 90 in the TPN group than in the EEN group. EEN group rapidly recovered weight after POD 21 whereas it was gradually decreased in TPN group until POD 90. EEN after PD is associated with preservation of weight compared with TPN and impact on recovery of digestive function after PDope