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991.
Hans‐Georg Weinig Ulrich Koert Burkhard Ziemer 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):e218-e218
The title compound, 2,3‐dimethoxy‐2,3‐dimethyl‐5,6,7,8‐tetrahydro‐4‐oxachroman, C12H22O4, was synthesized as a model compound for substituted diequatorial fixed vicinal trans‐cyclohexanediols. 相似文献
992.
Ahmed El-Rafei Tobias Engelhorn Simone Wärntges Arnd Dörfler Joachim Hornegger Georg Michelson 《Magnetic resonance imaging》2013
Most of the existing methods for diagnosing glaucoma analyze the eye with a main focus on the retina, despite the transsynaptic nature of the fiber degeneration caused by glaucoma. Thus, they ignore a significant part of the visual system represented by the visual pathway in the brain. The advances in neuroimaging, especially diffusion tensor imaging (DTI), enable the identification and characterization of white matter fibers. In this work, we propose a system based on DTI analysis of the visual pathway fibers in the optic radiation for detecting and discriminating different glaucoma entities. The optic radiation is identified semi-automatically. DTI provides information about the fiber orientation as well as a set of derived parameters describing the degree of diffusion anisotropy and diffusivity. Features for each DTI derived measure are extracted from a specified region of interest on the optic radiation. The features are grouped into three sets: Histogram, co-occurrence matrices, and Laws features. For feature selection, the features are ranked using a support vector machine classifier. The highest ranked features are used for classification. A support vector machine classifier is used for classification in a 10-fold cross validation setup. The system is applied to three age-matched subjects’ categories containing 27 healthy, 39 primary open angle glaucoma (POAG), and 18 normal tension glaucoma (NTG) subjects. The discrimination accuracy between healthy and glaucoma (POAG and NTG) subjects is 94.1% with an area under the ROC of 0.97. Classification accuracy of 92.4% is obtained for the normal and the POAG groups while it increased to 100% in case of healthy and NTG groups. In addition, the system could differentiate between glaucoma types (POAG and NTG) with an accuracy of 98.3%. A complementary analysis was performed to estimate the selection bias in the obtained accuracy. The bias ranged from 10% to 20% depending on the group pair under consideration. The classification results indicate the high performance of the system compared to retina-based glaucoma detection systems. The proposed approach utilizes visual pathway analysis rather than the conventional eye analysis which presents a new trend in glaucoma detection. Analyzing the entire visual system could provide significant information that can improve the glaucoma examination flow and treatment. 相似文献
993.
994.
995.
Dr. David Schweinfurth Marcella Mazzolini Dr. Dmytro Neshchadin Carolin Hoyer Roman Geier Dr. Karl Gatterer Dr. Nils Trapp Prof. Dr. Georg Gescheidt Prof. Dr. François Diederich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(21):7152-7157
The synthesis of redox‐active p‐ and o‐quinones 2‐phenylamino‐4‐phenylimino[6]helicene‐1‐one 1 , 2‐phenylamino[6]‐helicene‐1,4‐dione 2 , and 4‐phenyl[6]helicene‐1,2‐dione 3 in their enantiopure forms by post‐functionalization of (P)‐ and (M)‐1,2‐dimethoxy[6]helicene is presented. Structural characterization in solution and in the solid state was accomplished by 2D NMR spectroscopy methods and X‐ray diffraction analysis, respectively. Interpretation of electrochemical redox data was accompanied by a detailed orbital picture, derived from DFT calculations. The electronic structures of compounds 1 – 3 were investigated by UV/Vis and electronic circular dichroism (ECD) spectroscopy, complemented by TD‐DFT calculations. Quinones 1 – 3 were chemically reduced to study the EPR signatures of their respective radical anions. DFT methods were used for the atom assignment of the hyperfine coupling constants. The results are discussed within the context of electrochromic chiral switches and molecular recognition. 相似文献
996.
997.
Push–Pull Buta‐1,2,3‐trienes: Exceptionally Low Rotational Barriers of Cumulenic CC Bonds and Proacetylenic Reactivity
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Przemyslaw Gawel Dr. Yi‐Lin Wu Dr. Aaron D. Finke Dr. Nils Trapp Dr. Michal Zalibera Prof. Dr. Corinne Boudon Dr. Jean‐Paul Gisselbrecht Dr. W. Bernd Schweizer Prof. Dr. Georg Gescheidt Prof. Dr. François Diederich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(16):6215-6225
A variety of asymmetrically donor–acceptor‐substituted [3]cumulenes (buta‐1,2,3‐trienes) were synthesized by developed procedures. The activation barriers to rotation ΔG≠ were measured by variable temperature NMR spectroscopy and found to be as low as 11.8 kcal mol?1, in the range of the barriers for rotation around sterically hindered single bonds. The central C?C bond of the push–pull‐substituted [3]cumulene moiety is shortened down to 1.22 Å as measured by X‐ray crystallography, leading to a substantial bond length alternation (BLA) of up to 0.17 Å. All the experimental results are supported by DFT calculations. Zwitterionic transition states (TS) of bond rotation confirm the postulated proacetylenic character of donor–acceptor [3]cumulenes. Additional support for the proacetylenic character of these chromophores is provided by their reaction with tetracyanoethene (TCNE) in a cycloaddition‐retroelectrocyclization (CA–RE) cascade characteristic of donor‐polarized acetylenes. 相似文献
998.
Georg Berschneider 《Monatshefte für Mathematik》2012,166(3-4):329-340
In this paper we consider bounded, conditionally positive definite functions on commutative hypergroups. We show an integral representation that allows to decompose conditionally positive definite functions as differences of positive definite functions. 相似文献
999.
Georg Berschneider 《Monatshefte für Mathematik》2012,43(1):329-340
In this paper we consider bounded, conditionally positive definite functions on commutative hypergroups. We show an integral representation that allows to decompose conditionally positive definite functions as differences of positive definite functions. 相似文献
1000.
Dr. Tobias Böttcher Simon Steinhauer Dr. Lesley C. Lewis‐Alleyne Beate Neumann Dr. Hans‐Georg Stammler Dr. Bassem S. Bassil Prof. Dr. Gerd‐Volker Röschenthaler Prof. Dr. Berthold Hoge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):893-899
The addition of BCl3 to the carbene‐transfer reagent NHC→SiCl4 (NHC=1,3‐dimethylimidazolidin‐2‐ylidene) gave the tetra‐ and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl3]+ and [(NHC)2SiCl3]+ with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC→SiCl4 served as a transfer reagent for the NHC ligand. The addition of BF3 ? OEt2, on the other hand, gave NHC→BF3 as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C2F5)2SiCl2 was treated with NHC→SiCl4. In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl3]+ and [(NHC)2SiCl3]+ were detected with [(C2F5)SiCl3]? as counterion. A similar result was already reported for the reaction of NHC→SiCl4 with (C2F5)2SiH2, which gave [(NHC)2SiCl2H][(C2F5)SiCl3]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC→Si(C2F5)2Cl2 and NHC→Si(C2F5)2ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron‐poor silylenes. Furthermore, the reactivity of NHC→SiCl4 towards phosphines is discussed. The carbene complex NHC→PCl3 shows similar reactivity to NHC→SiCl4, and may even serve as a carbene‐transfer reagent as well. 相似文献