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排序方式: 共有233条查询结果,搜索用时 15 毫秒
31.
The critical cooling rates required to form glass have been measured for Na2OSiO2 compositions containing 15.4, 20.6, 29.9 and 34.0 wt% Na2O and for K2OSiO2 compositions containing 15.3, 21.7, 34.3, 41.8 and 43.9 wt% K2O. Pronounced minima in critical cooling rate are observed in the ranges about 25 wt% Na2O and 33 wt% K2O. The locations of these minima correlate with regions of low liquidus temperatures (near eutectics) in the phase diagrams.Calculations of critical cooling rates have been carried out using the analysis of crystallization statistics and the simplified model of glass formation. In both cases, the models predict well the measured critical cooling rates and their variation with composition. 相似文献
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R. J. Matyi D. R. Uhlmann J. A. Koutsky 《Journal of Polymer Science.Polymer Physics》1980,18(5):1053-1063
The small-angle x-ray scattering (SAXS) from an Epon 812 and two Epon 828 (one amine-cured and one anhydride-cured) epoxy resins has been measured using a Bonse-Hart system. The data cover the angular range (2θ) between 20 sec and 60 min. After correction for absorption, background and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a previously studied polycarbonate sample. The corrected absolute intensity decreases strongly with increasing angle between 20 sec and 2 min, decreases more gradually between 2 and 20–30 min, and reaches a nearly constant asymptotic value at larger angles. The magnitude of the intensity in the constant-intensity region is close to the value predicted by thermodynamic fluctuation theory for fluids applied at the glass transition temperature. The increase in intensity at angles smaller than 20–30 min is associated with heterogeneities in the cured resins. These heterogeneities cover a range of sizes in all samples, from less than 100 Å to more than 1000 Å, with the most frequently occurring size in the range 100–200 Å. 相似文献
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In this paper we investigate conditions under which two finite-dimensional density matrices can be transformed simultaneously into two other ones by means of a positive linear map which maps density matrices into density matrices. The result of this paper provides a complete answer in case of the matrix algebra of two-by-two matrices. 相似文献
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We prove the local invertibility, up to potential fields, and stability of the geodesic X-ray transform on tensor fields of order 1 and 2 near a strictly convex boundary point, on manifolds with boundary of dimension n ≥ 3. We also present an inversion formula. Under the condition that the manifold can be foliated with a continuous family of strictly convex surfaces, we prove a global result which also implies a lens rigidity result near such a metric. The class of manifolds satisfying the foliation condition includes manifolds with no focal points, and does not exclude existence of conjugate points. 相似文献
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Variability of UV irradiance in Europe 总被引:1,自引:1,他引:0
Seckmeyer G Pissulla D Glandorf M Henriques D Johnsen B Webb A Siani AM Bais A Kjeldstad B Brogniez C Lenoble J Gardiner B Kirsch P Koskela T Kaurola J Uhlmann B Slaper H den Outer P Janouch M Werle P Gröbner J Mayer B de la Casiniere A Simic S Carvalho F 《Photochemistry and photobiology》2008,84(1):172-179
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Philipp Seitz Dr. Manik Bhosale Luisa Rzesny Anselm Uhlmann Dr. Jan S. Wössner Robin Wessling Prof. Dr. Birgit Esser 《Angewandte Chemie (International ed. in English)》2023,62(43):e202306184
With their bent π-systems, cyclic conjugation and inherent cavities, conjugated nanohoops are attractive for organic electronics applications. For ease of processing and morphological stability, an incorporation into polymers is desirable, but to date was hampered with few exceptions by synthetic difficulties. We herein present a unique strategy for the synthesis of conjugated nanohoop polymers using a dibenzo[a,e]pentalene (DBP) as central connector. We demonstrate this versatility by synthesizing three electronically diverse copolymers with dithienyldiketo(pyrrolopyrrol), fluorene and carbazole comonomers, and report the first donor-acceptor nanohoop polymer. Optoelectronic investigations reveal the prevalence of cyclic or linear conjugation, depending on the comonomer unit, and ambipolar electrochemical properties through the antiaromatic character of the DBP units. As the first report on using conjugated nanohoops for charge storage as positive electrode materials, we show a significant improvement in battery performance in a nanohoop-containing polymer compared to an equivalent nanohoop-free reference polymer. We believe this study will pave the way for the synthesis of a diverse range of nanohoop polymers and further stimulate their exploration for charge storage in batteries. 相似文献