1,721,094 research outputs found
RESIDUAL STRESS BEHAVIOR OF ISOMERIC PMDA ODA POYIMIDES
No full textPoly(3,4'-oxydiphenylene pyromellitimide) (PMDA-3,4'-ODA), an isomer of poly(4,4'-oxydiphenylene pyromellitimide) (PMDA-4,4'-ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4'-oxydiphenylene diamine (3,4'-ODA). For these two polyimide isomers and their poly(amic acid) precursors in the condensed state on Si wafers, residual stress behaviour over the range 25-400-degrees-C was investigated by the dynamic measurement of wafer bending. During thermal imidization both isomers did not show any difference in stress versus temperature behaviour. Once imidized, however, one isomer exhibited a quite different stress behaviour from that of the other during cool-down: the stress of PMDA-3,4'-ODA increased rapidly from zero at 400-degrees-C to almost-equal-to 45 MPa at 40-degrees-C, whereas that of PMDA-4,4'-ODA rose gradually from zero to almost-equal-to 27 MPa. For both cured isomers, stress-temperature profile on heating was the same as that on cooling, with some deviation due to moisture uptake over the temperature range 25-150-degrees-C, indicating that their stresses were insensitive to thermal cycling or thermal annealing. From independently measured properties (thermal expansion coefficient, modulus, Poisson's ratio of 0.34) of both polyimides, the thermal stresses were calculated and compared with the measured overall stresses. It is concluded that for both polyimides the overall residual stress results primarily from the thermal stress. In comparison with PMDA-4,4'-ODA, PMDA-3,4'-ODA showed a much higher stress despite its slightly lower thermal expansion coefficient. This leads to the conclusion that the large difference between the stresses of the isomers results from the large difference in their moduli (5.0 GPa for PMDA-3,4'-ODA and 3.0 GPa for PMDA-4,4'-ODA). This behaviour is further supported by the difference in morphological structures of these two isomers as determined by wide-angle X-ray diffraction: PMDA-3,4'-ODA showed a well-developed crystalline structure, whereas the PMDA-4,4'-ODA did not. In addition, the interfacial adhesion between polyimide film and Si wafer primed with A1100 was investigated.1156Nsciescopu
RODLIKE, CROSSLINKED, FLEXIBLE POLYIMIDE SEMI-INTERPENETRATING POLYMER NETWORK COMPOSITES: MISCIBILITY AND PROPERTIES
No full textSynchrotron Radiation Facilities in Korea: Pohang Light Source and Future XFEL Project
No full text11scopu
Self-Assembled Thermally Highly Stable 1-Dimensional Proton Arrays
No full textFrom a red proton complex of aldehyde derivatives of polyaromatic hydrocarbon with strong intermolecular hydrogen bonding, which are novel examples of intermolecular proton-bonded aldehydes of polyaromatic hydrocarbons, we find one-dimensional proton arrangement. The complex formed as 9-antraldehyde (Ant-CHO) reacts with HAuCl4, to form [(Ant-CHO)(2)H](+) [AuCl4](-) under dry condition, which are confirmed by single-crystal structure determination and infrared spectra analysis at varying temperatures. Since the compounds of distinctively hydrophobic nature are soluble only in limited organic polar solvents, the strong hydrogen bonds are clearly observed from both the electron density of X-ray analysis and the characteristic signature of the IR frequency. The proton complex units have the typical O-H+-O distance of the strong hydrogen bond similar to the Zundel-like cationic hydrogen bond (where two O atoms share a proton in the midpoint of the short O-O distance of similar to 2.4 angstrom). The chemical shift of 20.18 ppm originated from the protons of the O-H+-O hydrogen bonds would be the largest downfield shifted value among those of protons in O-H center dot center dot center dot O bonds reported in various solid materials. indicating very short strong hydrogen bonds for the O-H+-O. The complexes are stabilized with the pi-pi intermolecular interactions of the polyaromatic hydrocarbon ligands, resulting in layered structures. The spectral signatures around similar to 900, similar to 1200, and similar to 1700 cm(-1) for the Zundel-like proton bond are clearly characterized.X1165sciescopu
High performance polyimides for applications in microelectronics and flat panel displays
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Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
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