1,720,961 research outputs found
Ultra-high-molecular-weight polyethylene as cosmic radiation and hypervelocity impact shielding material for low earth orbit space structures
No full text학위논문(석사) - 한국과학기술원 : 항공우주공학과, 2019.2,[vi, 89 p. :]우주방사선은 양성자, 중핵이온, 전자로 구성된 입자방사선으로 정의된다. 우주방사선은 인공위성 전자장치에 치명적인 영향을 주며, 수명을 감소시킨다. 또한 위성전자장치의 성능을 크게 제한시킨다. 우주인의 장기 우주체류가 불가능하게 만들고, 각종 질병과 암을 유발시킨다. 폴리에틸렌은 우주방사선 차폐에 매우 좋은 성능을 보이는 것으로 알려져 있다. 특히 초고밀도 폴리에틸렌(UHMWPE)은 매우 높은 기계적 성능을 가지고 있다. 한편, 현재 지구 궤도에는 수백만개의 우주 파편이 존재하고 있다. 우주 파편은 궤도에 따라 수에서 수십 km/s 의 초고속 속도를 가지며 우주 구조물의 생존을 크게 위협하고 있다. 국제우주정거장의 경우 이중으로 된 알루미늄 보호 시스템인 Whipple shield 개념을 적용하여 우주 파편 충돌로부터 우주인들을 보호한다. 하지만, 기존 우주구조물은 우주방사선 차폐 설계가 중요하게 고려되지 않았다. 본 연구에서는 초고밀도 폴리에틸렌이 적용된 제안된 우주 구조시스템의 우주방사선 차폐와 초고속 충돌성능을 실험해보았다. 양성자 가속기와 전자 가속기, 초고속 충돌 시험기인 2단 경 가스건을 실험에 사용하였다. 우주 환경 모사를 위해 열선을 이용해 초고밀도 폴리에틸렌을 고온 상태로 만들고, 초고속 충돌 실험을 수행하였다. 저궤도지구환경모사장비를 이용하여 outgassing 실험을 수행하였다. 우주방사선 차폐 해석을 수행하였으며 실험과 오차를 분석하였다. 초고밀도 폴리에틸렌이 적용된 제안된 우주구조물은 기존의 우주구조물보다 우주방사선 차폐와 초고속 충돌에 더 좋은 성능을 보였다. 고온에서 초고밀도 폴리에틸렌의 충돌성능 감소를 확인하였다. 충돌 속도가 증가할수록 온도에 의한 충돌성능 감소효과가 줄어드는 것을 확인했다. 평직 섬유의 기공은 양성자 차폐 성능을 감소시키지만, 전자 차폐에서는 무관한 것을 확인하였다. Outgassing 실험에서 초고밀도 폴리에틸렌은 기존 우주구조물에 사용되는 케블라보다 더 좋은 성능을 갖는 것을 확인했다.한국과학기술원 :항공우주공학과
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
우주 방사선 차폐 및 우주 환경 적용을 위한 기계적 특성이 개선된 다수소 복합재료
No full text학위논문(박사) - 한국과학기술원 : 항공우주공학과, 2023.2,[ix, 114 p. :]In the new space era, cosmic radiation shielding is important for satellites equipped with highly integrated electronic equipment and astronauts participating in long-term space missions. Commercial off -the-shelf is being used as an electronic device for high-performance, low-cost satellites but is vulnerable to cosmic radiation. Because hydrogen-rich benzoxazine (HRB) contains a large amount of hydrogen, it can effectively shield radiation. The mass of an HRB radiation shield is lower than that of an epoxy shield, and its mechanical properties may be enhanced by the addition of amines or carbon nanotubes. However, when HRB is exposed to a space environment, high-energy atomic oxygen erodes its surface, while ultrahigh vacuum combined with high temperature causes outgassing. To improve the mechanical properties of HRB and its space environment resistance, multi-walled carbon nanotube (MWCNT)/HRB nanocomposites with grafted amine groups have been synthesized in this study. The tensile properties of these nanocomposites were evaluated, and their space environment resistance was determined using special equipment that simulates a space environment, including high-energy atomic oxygen irradiation. The obtained results revealed that the proposed NH2–MWCNT/HRB nanocomposites were superior to HRB in terms of their tensile properties, outgassing performance, and atomic oxygen resistance. Therefore, these materials can potentially replace epoxy polymers in space missions that require cosmic radiation shielding. The application of stealth design to satellites provides an advantage in reconnaissance activities by evading ground observation and increasing survivability by preventing attacks from anti-satellite weapons. A shield that absorbs microwave irradiation was developed for incorporation into an ultra-high-molecular-weight polyethylene (UHMWPE)/hydrogen-rich benzoxazine composite for cosmic radiation shielding and to prevent electronic malfunction. Through the application of a polydopamine coating to UHMWPE followed by the grafting of carbon nanotubes, microwave absorption was achieved and the mechanical properties were improved. Moreover, radiation dose analysis confirmed that the proposed material exhibited a higher radiation shielding performance than conventional radar absorbing structures. UHMWPE/hydrogen-rich benzoxazine composite (UHC) exhibits excellent cosmic radiation shielding. However, the low interfacial adhesion of UHMWPE causes low flexural strength and delamination of the UHC. We increased the interlaminar shear strength of UHC via polydopamine coating, MWCNT, and amine grafting on UHMWPE. The total mass loss and collected volatile
condensable material tests were performed on the UHC to confirm for space environmental suitability. The proposed materials are expected to be utilized as a cosmic radiation shielding panel for future spacecraft.한국과학기술원 :항공우주공학과
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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