Mechanical and Damping Properties of Graphene-Modified Polyurethane-Epoxy Composites for Structures

Yi Su,Ting Li,Yanyan Liu 한국고분자학회 2021 폴리머 Vol.45 No.4

Polyurethane (PU) has received extensive attention in structural engineering due to its excellent mechanical properties and damping properties. In this research, graphene-modified PU-epoxy composites are prepared for the application in structural engineering. The mechanical properties and damping properties of the composites with different contents of graphene are investigated. The damping properties of the composites were also investigated by performing dynamic mechanical analysis (DMA). The results showed that with the increase of graphene content, the tear strength of the composites decreased from 52 to 39 ㎫. Due to the enhancement of appropriate amount of graphene, the tensile strength and elongation at break increase to the maximum value, being 16 ㎫ and 675%, respectively. And DMA tests showed that the damping properties reach the optimal values when the graphene content is 0.2%. The large damping temperature range (ΔT0.5) is 33 ℃, from -2.9 to 30.1 ℃. The peak of loss factor (ηmax) is 0.92 and the integral area (TA) is 36 ℃, much higher than those of the pure PU-epoxy composites. In addition, scanning electron microscopy (SEM) results show that agglomeration appears with higher graphene content.

Educational choice and marketization in Hong Kong: the case of direct subsidy scheme schools

Yisu Zhou,Yi-Lee Wong,Wei Li 서울대학교 교육연구소 2015 Asia Pacific Education Review Vol.16 No.4

Direct subsidy scheme (DSS) schools are a product of Hong Kong’s market-oriented educational reform, mirroring global reform that champions parental choice and school marketization. Such schools have greater autonomy in matters of curricula, staffing, and student admission. Although advocates of the DSS credit it with increasing educational diversity and competition, little empirical is available to back up such claim. In this study, we use data from the Program for International Student Assessment to compare student achievements in DSS schools with those in traditional public schools. We find that while DSS students’ test scores in math, reading, and science have improved significantly over time, though the variation is much greater. Changes in mean performance have been anchored by a substantial change in student composition. DSS schools have a higher proportion of students with high socioeconomic status than with medium and low socioeconomic status. DSS schools also amplify the effects that family background have on student achievement. These findings raise concerns that the DSS approach favors a small minority of students.

Stability study on tenon-connected SHS and CFST columns in modular construction

Yisu Chen,Chao Hou,Jiahao Peng 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.30 No.2

Modular construction is an emerging technology to accommodate the increasing restrictions in terms of construction period, energy efficiency and environmental impacts, since each structural module is prefabricated offsite beforehand and assembled onsite using industrialized techniques. However, some innate structural drawbacks of this innovative method are also distinct, such as connection tying inaccessibility, column instability and system robustness. This study aims to explore the theoretical and numerical stability analysis of a tenon-connected square hollow section (SHS) steel column to address the tying and stability issue in modular construction. Due to the excellent performance of composite structures in fire resistance and buckling prevention, concrete-filled steel tube (CFST) columns are also taken into account in the analysis to evaluate the feasibility of adopting composite sections in modular buildings. Characteristic equations with three variables, i.e., the length ratio, the bending stiffness ratio and the rotational stiffness ratio, are generated from the fourth-order governing differential equations. The rotational stiffness ratio is recognized as the most significant factor, with interval analysis conducted for its mechanical significance and domain. Numerical analysis using ABAQUS is conducted for validation of characteristic equations. Recommendations and instructions in predicting the buckling performance of both SHS and CFST columns are then proposed.

Preprocessing Technique Using an Interpolation Matrix in Direction Finding

Yisu Wang,Weiwei Zhou,Woojin Jang,Jinhwan Koh 한국통신학회 2005 한국통신학회 학술대회논문집 Vol.2005 No.6

Protect the forest House

Wang Yisu 한국콘텐츠학회 2023 한국콘텐츠학회 ICCC 논문집 Vol.2023 No.12

5 · 18광주항쟁과 5 · 18의 두 법정

김이수(Yisu Kim) 서울대학교 법학평론 편집위원회 2021 법학평론 Vol.11 No.-

5 · 18광주항쟁은 1980년 5월 18일 오전에 시작하여 5월 27일 새벽까지 열흘간 광주와 전남에서 벌어진 시민들의 항쟁이었다. 광주시민들은 국가폭력에 의해 인간의 존엄과 가치가 짓밟힐 때 인간의 존엄성을 위해, 공동체의 보전을 위해 죽음의 위기에 직면해서도 연대정신을 발휘하여 국가폭력에 저항하였다. 시민들의 항쟁은 나중에 사법절차에서도 헌정질서를 수호하기 위한 행위로 그 정당성을 인정받았다. 항쟁은 비록 실패로 끝난 것처럼 보였지만 이후 한국사회가 질적으로 변화할 수 있는 계기가 되었으며, 한국 현대사의 물줄기를 바꾸어 놓을 변혁적 에너지를 생산하였다. 이 글에서는 5 · 18광주항쟁에 관련된 사람들을 처벌했던 서로 다른 두 법정을 살펴보고자 한다. 광주항쟁이 진압된 직후, 무자비한 진압을 하는 계엄군에 대항하여 5 · 18광주항쟁에 가담한 시민들 중 409명은 내란죄, 소요죄, 계엄법위반죄 등으로 군사법원의 재판을 받았다. 반면에 광주항쟁에 대해 무자비한 진압을 계획하고 시행한 핵심 책임자인 전두환과 노태우 등에 대한 처벌은 항쟁이 종료된 지 15년이 훨씬 지난 뒤에야 비로소 이루어졌다. 이렇듯 15년여의 시간이 지나는 동안, 진상이 밝혀져 항쟁 진압의 핵심 책임자들이 처벌되고, 시민들의 행위가 헌정질서를 수호하기 위한 정당행위로 평가받아 재심 무죄선고가 이루어지는 등 큰 변화가 이루어지게 된 가장 큰 동력은 국민이 연대한 힘이었다. 그리고 국회의 5 · 18특별법 제정과 헌법재판소의 결정, 법원의 판결이 중요한 역할을 했다. 특히 최근 들어 2020년 11월 30일 전두환의 사자명예훼손 사건에서 광주지방법원이 헬기 사격 사실을 인정하거나, 2021년 1월 5일 5 · 18민주화운동에 대한 허위사실을 유포한 자를 처벌하는 내용의 ‘5 · 18민주화운동 등에 관한 특별법’ 제8조가 신설되는 등 진실을 밝혀내고 허위주장을 배척하기 위한 다양한 노력들이 이어져왔다. 그럼에도 여전히 도청 앞 집단발포 경위나 광주 파견부대 지휘체계 이원화 여부, 광주 외곽 피해의 진상, 사망자 수와 관련한 사체 암매장 등의 의문점은 해소되지 않은 실정이다. 2020년부터 본격적으로 활동을 개시한 5 · 18민주화운동 진상규명조사위원회가 새롭게 제기된 문제나 아직 해소되지 아니한 의문점들을 분명하게 규명하길 기대한다. 마지막으로 살림, 나눔, 연대 그리고 희생의 광주항쟁 정신이 현실에서 제대로 실현되고 이어지기를 바라면서 이 글을 마치고자 한다. The May 18th Democratic Uprising, which began in the morning of May 18, 1980 and lasted for ten days until the dawn of May 27, 1980, was a protest of citizens in Gwangju and Jeonllanam-do. When human dignity and value were trampled by state violence, the citizens of Gwangju resisted by demonstrating solidarity even at risk of death, for the sake of human dignity and the preservation of community. The uprising was later recognized for its legitimacy in judicial proceedings as an act to protect constitutional order. Although the uprising seemed to have ended in failure, it later served as a major momentum for qualitative change in Korean society and generated revolutionary energy that would change the course of modern Korean history. This article examines two different courts that punished people involved in the May 18th Democratic Uprising. Shortly after the protests were suppressed, 409 of the citizens who participated in the uprising were tried by the military court on charges of rebellion, sedition and violation of martial law. On the other hand, punishment for Chun Doo-hwan and Roh Tae-woo, the key managers who planned and implemented a ruthless crackdown on the May 18th Democratic Uprising, was only carried out 16 years after the end of the uprising. In the meantime, people’s solidarity has been the biggest driving force for the punishment of key figures responsible for the suppression, and the acquittal of the retrial which evaluated citizens’ protests as self-defense to protect constitutional order. The enactment of the Special Act On The May 18 Democratization Movement, the Constitutional Court’s decisions and the court’s decisions also played important roles. Various efforts have been made to reveal the truth and to reject false claims. On November 30, 2020, in Chun Doo-hwan’s defamation of dead person case, the Gwangju District Court approved helicopter gunship attacks. The Article 8 of the Special Act On the May 18 Democratization Movement was newly established to punish those who distribute false information regarding the May 18th Democratic Uprising. Still, questions regarding the details of mass firing in front of the Jeonnam Provincial Office building, the command system’s dualization of the troops dispatched to Gwangju, the actual damage to the outskirts of Gwangju, and the secret burial of dead bodies remain unanswered. Hopefully, the May 18 Democratization Movement Truth Commission, which began its full-scale activities in 2020, will clarify the newly raised issues and questions that have not yet been resolved. Finally, I hope that the May 18th Democratic Uprising spirit of living, sharing, solidarity and sacrifice will be realized and passed on in our reality.

Protect the forest House

Wang Yisu 한국콘텐츠학회 2023 ICCC International Digital Design Invitation Exhib Vol.2023 No.12

패러글라이더 캐노피 주변의 유동 특성

신이수(Yisu Shin),신정한(Jeonghan Shin),채석봉(Seokbong Chae),김주하(Jooha Kim) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12

In the present study, a flow visualization experiment was conducted on a paraglider canopy with a form of a curved airfoil. The experiment was performed at Re = 3.3 ×10<SUP>5</SUP> and the angles of attack of 0° to 14°. It was observed that flow separation did not occur on the canopy surface at a low angle of attack, and a flow separation region grew from the center of the canopy surface at a high angle of attack. By comparison with the model of this experiment and the NACA 23021, which has the most similar cross section, the change of the local Reynolds number by the chord length of the canopy was shown to have no significant effect on the flow characteristics of the canopy. The present study showed that the dominant parameter affecting the flow-separation characteristics is the spanwise variation of the local angle of attack caused by the curvature of the canopy.

Let’s stop the war

Wang Yisu 한국콘텐츠학회 2023 ICCC International Digital Design Invitation Exhib Vol.2023 No.5

그물망을 이용한 로터 후류의 재순환 유동 제어

황성윤(Seongyun Hwang),신이수(Yisu Shin),김주하(Jooha Kim) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11