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排序方式: 共有443条查询结果,搜索用时 15 毫秒
51.
W. J. Kirsten 《Mikrochimica acta》1957,45(3-4):289-295
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Phase biaxiality in nematic liquid crystalline side-chain polymers of various chemical constitutions
Severing K Stibal-Fischer E Hasenhindl A Finkelmann H Saalwächter K 《The journal of physical chemistry. B》2006,110(32):15680-15688
In a previous deuterium NMR study conducted on a liquid crystalline (LC) polymer with laterally attached book-shaped molecules as the mesogenic moiety, we have revealed a biaxial nematic phase below the conventional uniaxial nematic phase (Phys. Rev. Lett. 2004, 92, 125501). To elucidate details of its formation, we here report on deuterium NMR experiments that have been conducted on different types of LC side-chain polymers as well as on mixtures with low-molar-mass mesogens. Different parameters that affect the formation of a biaxial nematic phase, such as the geometry of the attachment, the spacer length between the polymer backbone and the mesogenic unit, as well as the polymer dynamics, were investigated. Surprisingly, also polymers with terminally attached mesogens (end-on polymers) are capable of forming biaxial nematic phases if the flexible spacer is short and thus retains a coupling between the polymer backbone and the LC phase. Furthermore, the most important parameter for the formation of a biaxial nematic phase is the dynamics of the polymer backbone, as the addition of a small percentage of low molar mass LC to the biaxial nematic polymer from the original study served to shift both the glass transition and the appearance of detectable biaxiality in a very similar fashion. Plotting different parameters for the investigated systems as a function of T/Tg also reveals the crucial role of the dynamics of the polymer backbone and hence the glass transition. 相似文献
55.
Upper bounds are obtained for the heat content of an open set D in a geodesically complete Riemannian manifold M with Dirichlet boundary condition on ?D, and non-negative initial condition. We show that these upper bounds are close to being sharp if (i) the Dirichlet-Laplace-Beltrami operator acting in L 2(D) satisfies a strong Hardy inequality with weight δ2, (ii) the initial temperature distribution, and the specific heat of D are given by δ?α and δ?β respectively, where δ is the distance to ?D, and 1 < α <2, 1 < β <2. 相似文献
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W. ZIMMERMANN's method of determining sulphur has been investigated and it has been found that the accuracy is not as great as has often been stated. It seems that the errors occur in the decomposition of the sample. In the modification of the method, recently published by ZIMMERMANN, the error is approximately compensated by the use of a titration procedure which gives too high results. 相似文献
58.
Summary Rapid methods for the micro- and semi-micro-determination of halogens by dry combustion are described. Semi-micro-samples are burnt in a quartz capsule. The halogen is expelled from ash-containing compounds by vanadium pentoxide. The halogens are absorbed in hot alkali. Chlorine and bromine are titrated with alcoholic silver-nitrate, mercuric halogenide-diphenylcarbazide being used as indicator. Iodine is titrated with thiosulphate after oxidation to iodate.
With 1 figure. 相似文献
Zusammenfassung Schnell-Methoden für die Mikro- und Halbmikrohalogenbestimmung durch trockene Verbrennung werden beschrieben. Halbmikroeinwaagen werden in einem Quarzeinlegeröhrchen verbrannt. Aus aschehaltigen Substanzen werden die Halogene durch Vanadiumpentoxyd ausgetrieben. Die Halogene werden in heißem Alkali absorbiert. Chlor und Brom werden mit alkoholischer Silbernitratlösung titriert, wobei Quecksilberhalogenid-Diphenylcarbazid als Indikator verwendet wird. Jod wird nach Oxydation zu Jodat mit Thiosulfat titriert.
Résumé On décrit des méthodes rapides de micro et de semimicrodosage des halogènes par combustion sèche. On calcine les semimicroéchantillons dans une capsule de quartz. L'halogène est expulsé des cendres par le pentoxyde de vanadium. On absorbe les halogènes au moyen d'alcali chaud. Le chlore et le brome sont titrés par une solution alcoolique de nitrate d'argent en utilisant comme indicateur de l'halogènure mercuriquediphénylcarbazide. On titre l'iode au thiosulfate après oxydation en iodate.
With 1 figure. 相似文献
59.
Kirsten Knape Anton Beyer Anna Stary Gerhard Buchbauer Peter Wolschann 《Monatshefte für Chemie / Chemical Monthly》2008,454(5):1537-1544
Single nucleotide polymorphisms (SNPs) in odorant receptor genes may influence the protein sequence and consequently also
the function of the receptors. An analysis of the HapMap data for human OR3A1 was performed and provided evidence that genetic
differences subject to ancestry and gender can be recognized. A genomic comparison of individuals shows the diversity of odorant
receptor genes and therefore potentially the variety of the sense of smell. At this time, two complete human genomes are available
in public domain, which we used for this purpose. 相似文献
60.
Kirsten Knape Anton Beyer Anna Stary Gerhard Buchbauer Peter Wolschann 《Monatshefte für Chemie / Chemical Monthly》2008,139(12):1537-1544
Single nucleotide polymorphisms (SNPs) in odorant receptor genes may influence the protein sequence and consequently also
the function of the receptors. An analysis of the HapMap data for human OR3A1 was performed and provided evidence that genetic
differences subject to ancestry and gender can be recognized. A genomic comparison of individuals shows the diversity of odorant
receptor genes and therefore potentially the variety of the sense of smell. At this time, two complete human genomes are available
in public domain, which we used for this purpose.
Correspondence: Anton Beyer, Institute of Theoretical Chemistry, University of Vienna, A-1090 Vienna, Austria. 相似文献