1,721,002 research outputs found
A model of composite objects for information mesh
Get PDFThesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 87-88).by Felix Tun-Han Lo.M.Eng
Effects of SiO2 and Star Architecture on Crystallization Behavior of PLLA
No full text本研究主要探討添加無機物SiO2以及星狀聚乳酸，對左旋聚乳酸兩結晶結構α與α’結晶行為以及結晶型態學上的影響。
聚乳酸結晶時，會因結晶溫度的不同而產生不同的結晶結構，在較高的結晶溫度下形成排列較緊密的α晶體結構；在較低的結晶溫度下，形成排列相對較鬆散的α’晶體結構；而在這之間的溫度，則形成兩相共存的晶體結構。我們將左旋聚乳酸混摻二氧化矽，以及合成三臂的星狀左旋聚乳酸，利用POM、DSC、XRD等儀器觀察其結晶共存區間的有何改變。
當左旋聚乳酸加入SiO2顆粒，其提供了異質成核的表面，加速結晶晶核的形成；星狀左旋聚乳酸則因為含有核心結構，在結晶時核心會被視為雜質而排到晶片之外，不易形成穩定的晶核，結晶時需要更久的時間進行，兩種結晶結構受到的影響程度不同，導致共存區的結晶競爭能力改變，PLLA/SiO2系統的α與α’共存區溫度範圍跟單純PLLA系統比較似乎沒有差異，而星狀左旋聚乳酸的共存區溫度範圍則劇烈下移，為了更進一步了解線性與星狀構型之間的差異，我們做了不同比例的線性與星狀PLLA混摻系統來連結兩者，並藉由玻璃轉移溫度、平衡熔點等提供的訊息，由分子鏈運動能力、過冷度與結晶時晶片摺疊鏈端表面自由能來探討競爭的差異。
結晶型態方面，摻入SiO2顆粒後的左旋聚乳酸仍是典型黑十字球晶，星狀PLLA則在較高結晶溫度球晶會開始出現環狀結構，線性與星狀PLLA混摻系統球晶環狀結構出現的溫度則隨線性PLLA比例增加而提高。The focus of this research is how SiO2-added and architecture affect α and α’crystal structures and morphology of PLLA. PLLA polymer chains packed closely α form crystal structure at higher crystallization temperature, and loosely α’ form crystal structure at lower crystallization temperature. Two crystal structures can co-exist at moderate temperatue. It is investigated by POM, DSC and XRD to observe the crystal structures changes of PLLA/ SiO2 and 3-ram PLLA, then compared with typical linear PLLA system.
When SiO2 is added, it provides heterogenous nucleation surface to accelerate the formation of crystal nuclei; in the contrast, star-shaped PLLA is difficult to form stable nuclei and requires longer crystallization time due to the core unit which is considered as impurity and is excluded from lamellae. The two factors affect the two crystal structures in varying degree, resulting in coexistence zone change. The α and α’ coexistence zone of PLLA/SiO2 system seems the same to pure PLLA system and that is much lower of star-shaped PLLA system. In order to further understand the variations from linear to star-shaped PLLA, different proportion blends of linear and star PLLA are used to link the relationship. Furthermore, it is discussed by the aspects of chain mobility, degree of undercooling and surface free energy of chain folding from the information of glass transition temperature, equilibrium melting temperature and the other basic physical properties.
On the morphology of PLLA, it is typical Maltese cross type spherulite in PLLA/SiO2 system, while there is ring-banded type spherulite appearing in Star-shaped PLLA system. In the blended system of linear and star PLLA, the temperature of ring-banded spherulite appearing is rasing with the proportion of linear PLLA increasing
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Get PDFWe 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
- …
