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排序方式: 共有216条查询结果,搜索用时 31 毫秒
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H. Schmid E. Burkhardt E. Walker W. Brixel M. Clin J. -P. Rivera J. -L. Jorda M. François K. Yvon 《Zeitschrift für Physik B Condensed Matter》1988,72(3):305-322
The ferroelastic domains of the orthorhombic phase of YBa2Cu3O7- have been observed in polarized light on ceramics and single crystals. By combining polarized light microscopy with the X-ray precession technique, the correlation of the orientation of the orthorhombica- andb-axes with that of thea-b-plane bireflectance, reflection dichroism, transmission dichroism (at a thickness of about 1m), reflection tints generated with compensators and upon uncrossing of polars, as well as the orientation of etch pits has been realized on ferroelastic single domains, bi-domains and more complicated domain patterns. Four ferroelastic orthorhombic domain states have been identified, at variance with former group theoretical considerations, predicting only two states. Ensembles of lamellar domains beyond optical resolution generate strong bireflectance with principal axes rotated by 45° relative to the truea, b-directions. 相似文献
3.
Abramowicz H Belusevic R Blondel A Blümer H Böckmann P Brummel HD Buchholz P Burkhardt H Debu P Duda J Dydak F Falkenburg B Fiedler M Geiges R Geweniger C Grant AL Guyot C Hagelberg R Hepp V Hughes EW Kampschulte B Keilwerth H Kleinknecht K Knobloch J Krasny M Królikowski J Kurz N Lipniacka A Merlo J Müller E Para A Perez P Perrier F Pollman D Ranjard F Renk B Schuller J Taureg H Tittel K Turlay R Vallage B Wachsmuth H Wotschack J 《Physical review letters》1986,57(3):298-301
4.
Substituted 2-deoxy-2-acylamino-4-O-methanesulfonyl-hexopyranosiduronates yield, by mild alkaline mesylate (a, e)-β-elimination, the corresponding 4,5-unsaturated 4-deoxyhexopyranosiduronates VIII. This type of aminosugars proved to be the cyclic enol-ether acetal form of the 2,4-dideoxy-2-acylamino-hexos-5-ulosuronates. The structural principle of the latter can be found e.g. in neuraminic acid. These 4,5-unsaturated 4-deoxy-acylamino-hexopyranosiduronates give by reduction with NaBH4 the corresponding 4,5-unsaturated 2,4-dideoxy-2-acylamino-hexopyranosides IX (with an endocyclic double bond on the glycosidic C atom 5). The isomeric 5,6-unsaturated 2,6-dideoxy-2-acylamino-hexopyranosides XVI (with an exocyclic double bond) are furthermore synthesized according to the method of HELFERICH [14] by elimination of a molecule of HI from the corresponding 2,6-dideoxy-2-acylamino-6-iodo-4-O-acylhexopyranoside derivatives XV. The ring stability of the two types of isomeric unsaturated hexopyranosides mentioned (bearing respectively an exo- and an endocyclic 5-enol-ether linkage) has been examined. In accordance with the stability principle of BROWN [16] – on the base of our preliminary experimental indications – the hexopyranosides with endocyclic double bond have been shown to be more stable than those with an exocyclic double bond: the latter (1) decompose slowly at 20°; (2) the α-glycosidic linkage is very easily split by dil. acetic acid at 20° within a few hours, giving 2, G-dideoxy-2-acyl-amino-D -xylo-hcxofuranos-5-ulose derivatives XX. On the other hand, the hcxopyranosides with endocyclic double bond show in the mass spectrometer, besides other fragmentations, a retro-dien decomposition. Some data on the NMR. spectra (100 and 220 MHz) of the above isomeric unsaturated acylamino-hexopyranosides (and hexopyranosiduronates, resp.) are furnished. The ORD./CD. spectra of the 4,5-unsaturated 2,4-dideoxy-2-acylamino-hexopyranosiduronates, which have two «COTTON centres», have been measured. 相似文献
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Theodore W. Burkhardt 《Zeitschrift für Physik B Condensed Matter》1978,31(2):183-186
Exact values are obtained for the slopesK
1
c
(0, 0)/K
2,K
1
c
(0, 0)/K
4 of the critical surface of paramagnetic-ferromagnetic transitionsK
1
c
(K
2,K
4) for the two-dimensional Ising model on a square lattice with first-neighbor, second-neighbor, and four-spin couplingsK
1,K
2, andK
4, respectively. The results are obtained using universality arguments to relate the slopes to known spin-spin correlation functions forK
2=K
4=0. The equivalence of different expressions for the slopes in terms of correlation functions yields sum rules for the divergent part of certain sums over the second-neighbor and four-spin energy-energy correlation functions. 相似文献
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Burkhardt I. Wilke Mark H. Dornan Jon Yeung Christopher N. Boddy Atahualpa Pinto 《Tetrahedron letters》2014
Symmetric diols are useful compounds in the synthesis of natural products, their value often dependent on their successful monoprotection. A general and simple method for the monosilylation of symmetrical primary and secondary diols is reported. The method exploits the solubility differential of diols and their monosilylated counterparts in a binary hexanes/acetonitrile solvent system. 相似文献