Fabrication of Seebeck coefficient measurement system and thermoelectric properties in Sn1-xAgxTe compounds

Pb-based materials, which are superior for thermoelectric performance, environmentally have toxicity. Thus the materials should be alternated by non-toxic materials. Tin telluride (SnTe) is isostructural with PbTe and PbSe which are rock salt structure. In addition, SnTe is similar to the electronic band structure (two valence band system) with PbTe and PbSe. Thus, SnTe, which is overcome by low Seebeck coefficient and by large thermal conductivity, can be expected by good thermoelectric material. Thus, Ag-included poly crystals Sn1-xAgxTe (x=0.1, 0.2, 0.3, and 0.4) were prepared by box furnace and by hot press to confirm thermoelectric performance of the samples. By accident, we noticed difference that XRD patterns of Sn1-xAgxTe are changed from two phases (SnTe, AgTe) to mixed phase (SnTe/AgTe) before hot pressing and after. In addition, electrical conductivity of samples is maintained until high temperature. The power factor of sample to include silver(x=0.1) has maximum value (1.1 mW/mK2) at 673K. However, SnTe has higher power factor than Ag-included SnTe. Nevertheless, we can carefully expect that sample to include mixed phase obtain high electrical conductivity. Exceptionally, we developed the measurement of the thermoelectric power in the temperature range from 2K to 300K. By using two heaters, two thermometer, chip resistors, et al, measurement equipment is fabricated exactly. In addition, high density data is obtained by two heaters that are operated by turn. The system is controlled by LabVIEW software. In order to demonstrate this system, reference data of Pt wire and Ca10Nax(Pt3As8)(Fe2As2)5 superconductor were calibrated by developed equipment. Therefore we demonstrated the equipment with superior performance through confirming calculated data. ⓒ 2015 DGISTChapter 1. Introduction 1-- 1.1 Thermoelectric effect 1-- 1.2 Figure of merit (ZT) & Efficiency 2-- 1.3 Carrier concentration 4-- 1.4 Sn1-xAgxTe 5-- Chapter 2. Theory 9-- 2.1 Seebeck effect 9-- 2.2 Effects of charge carrier’s interactions on Seebeck coefficients 11-- 2.3 Thermal conductivity 13-- Chapter 3. Seebeck coefficient measuring equipment 15-- 3.1 Experimental setup 16-- 3.2 Operating principles 17-- 3.3 Calculation of sample Seebeck coefficient 18-- Chapter 4. Thermoelectric property of Sn1-xAgxTe 20-- 4.1 Experimental Methods 20-- 4.1.1 Sample preparation 20-- 4.1.2 Seebeck coefficient, Electrical conductivity measurement 22-- 4.2 Results and Discussion 23-- 4.2.1 X-Ray Diffraction 23-- 4.2.2 Scanning electron microscopy and Energy Dispersive Spectroscopy 26-- 4.2.3 Seebeck coefficient 28-- 4.2.4 Electrical conductivity 29-- 4.2.5 Power factor 30-- Chapter 5. Conclusion 31-- References 33-- Summary (in Korean) 35열전 성능이 우수한 Pb-based 물질은 환경적으로 독성을 가진다. 따라서 Pb-based 물질은 독성이 없는 물질로 대체 되어야 한다. Tin telluride (SnTe) 는 PbTe, PbSe 와 같은 rock salt 구조 이다. 게다가 SnTe 는 PbTe, PbSe 의 전자 밴드 구조 (두 개 밴드 구조)와 유사한 밴드구조를 가졌다. 따라서 작은 제백상수와 큰 열전도도를 극복한 SnTe 좋은 열전재료가 될 것으로 기대된다. 그래서 실버가 포함된 poly crystals 이 박스 퍼니스와 핫프레스에 의해 준비되었다. 우연적으로 우리는 Sn1-xAgxTe 의 XRD 패턴이 핫프레스 전후에 바뀌는 것을 알았다. 그리고 핫프레스 전에는 두개의 사에서 후에는 섞인 패턴이 발견 되었다. 게다가 섞인 패턴 때문에 샘플들의 전기전도도는 높은 온도까지 잘 유지했다. 파워팩터는 실버(x=1)에서 가장 높은 값 (1.1 mW/mK2 ) 을 673K 에서 가졌다. 그러나 parent SnTe 는 실버가 포함된 시료보다 높은 파워팩터를 가졌다. 그럼에도 불구하고, 우리는 샘플이 상이 섞인 상태에서 높은 전기전도도를 가진다고 조심스럽게 예측 해볼 수 있다. 예외적으로 우리는 2K-300K 까지 측정할 수 있는 열전측정 장비를 개발했다. 장비는 두 개의 히터, 두 개 온도계, 칩 저항, 등으로 이루어져있다. 게다가 두 개의 히터가 번갈아 가면서 작동하기 때문에 높은 밀도의 데이터를 얻을 수 있다. 이 시스템은 랩뷰 소프트웨어에 의해 조작된다. 측정 장비를 증명하기 위해 우리는 Pt wire 의 참고 데이터와 실험과 비교하였고, 초전도체인 Ca10Nax(Pt3As8)(Fe2As2)5 으로 비교함으로써 우수한 성능을 확인하였다. ⓒ 2015 DGISTMasterdCollectio

A Design and Development of the Learning Contents Management based on the Personalized Online Learning

Teaching-learning methods are undergoing rapid transformation in terms of new information and communication technology and in accordance with onset of the 4th Industrial Revolution. The educational environment is being transformed into various forms, with examples being found not only in the existing traditional educational environment, but also in online education and blended learning. Existing online learning (LMS, LCMS) is offered in a limited contents transmission online educational environment, and has been limited but the level of support offered to a learner’s personalized learning. This study will overview existing flexible model of contents, suggest possible problems, and attempt to solve these problems. LCMS was designed and realized based on the open source Moodle platform, offering personalized contents to learners. LCMS is composed of the following 3 functions: contents registration of metadata inputted by administrator; search functionality for personalized learner contents; and personalized contents automatically being recommended to learners. As a result of the research, we made online learning environment that can provide customized learning recommendation and self - directed learning by increasing the continuity and efficiency of learning by automatically providing customized online contents to learners. Through this study, the learning of students promises to be effectively initiated by being based on available LCMS functions related to personalized educational contents in online education

Occupational Factors Associated with Changes in the Body Mass Index of Korean Male Manual Workers

OBJECTIVES: This study was carried out to analyze and compare the occupational factors that could influence changes in body mass index (BMI) in male manual workers stratified into short-term and long-term work experience groups. METHODS: The subjects were 299 male manual workers (sampled systematically) from 27 workplaces, who had undergone travelling medical examinations at a university hospital between March 28 and May 10, 2013, and had also undergone medical examinations at the same hospital in 2012. Their general and occupational characteristics were investigated through a structured, self-administered questionnaire. The BMI at each point in time was calculated based on the anthropometric results of the medical examinations. Multiple regression analyses were conducted on outcomes of the BMI change and predictors composed of the general and occupational characteristics, with the subjects stratified into groups with 5 years or less (short-term) versus more than 5 years (long-term) of work experience at the present post. RESULTS: In the short-term work experience group, the BMI increases of 3-shift workers and groups reporting disagreement with feeling “insufficient job control” and “lack of reward” at work, two of the subscales of job stress, were significantly higher than those of daytime workers and high-stress groups, respectively. In the long-term work experience group, However, although the BMI increase for 3-shift workers was also significantly higher than that of daytime workers, none of the job stress factors were significantly associated with a BMI increase, whereas the social factors of education and marital status were significant, and some lifestyle factors (such as smoking and regular exercise) were also significant. CONCLUSION: This study showed that, except for 3-shift work, the factors associated with BMI increase could differ depending on the length of job experience. Consequently, different strategies may be needed for workers with short-term versus long-term job experience when designing interventions for preventing their obesity

Genome sequence of the chromate-resistant bacterium Leucobacter salsicius type strain M1-8T

Leucobacter salsicius M1-8(T) is a member of the Microbacteriaceae family within the class Actinomycetales. This strain is a Gram-positive, rod-shaped bacterium and was previously isolated from a Korean fermented food. Most members of the genus Leucobacter are chromate-resistant and this feature could be exploited in biotechnological applications. However, the genus Leucobacter is poorly characterized at the genome level, despite its potential importance. Thus, the present study determined the features of Leucobacter salsicius M1-8(T), as well as its genome sequence and annotation. The genome comprised 3,185,418 bp with a G+C content of 64.5%, which included 2,865 protein-coding genes and 68 RNA genes. This strain possessed two predicted genes associated with chromate resistance, which might facilitate its growth in heavy metal-rich environments.