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21.
Inside Cover: A Non‐Exploding Alkali Metal Drop on Water: From Blue Solvated Electrons to Bursting Molten Hydroxide (Angew. Chem. Int. Ed. 42/2016)
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22.
Dehn twists around simple closed curves in oriented surfaces satisfy the braid relations. This gives rise to a group theoretic
map from the braid group to the mapping class group. We prove here that this map is trivial in homology with any trivial coefficients
in degrees less than g/2. In particular this proves an old conjecture of J. Harer. The main tool is categorical delooping in the spirit of (Tillmann
in Invent Math 130:257–175, 1997). By extending the homomorphism to a functor of monoidal 2-categories, is seen to induce a map of double loop spaces on the plus construction of the classifying spaces. Any such map is null-homotopic.
In an appendix we show that geometrically defined homomorphisms from the braid group to the mapping class group behave similarly
in stable homology.
The first author was supported by Inha University research grant. 相似文献
23.
Stephan Tillmann 《Mathematische Zeitschrift》2012,272(3-4):793-823
Let M be a cusped 3-manifold, and let ${\mathcal{T}}$ be an ideal triangulation of M. The deformation variety ${\mathfrak{D}(\mathcal{T})}$ , a subset of which parameterises (incomplete) hyperbolic structures obtained on M using ${\mathcal{T}}$ , is defined and compactified by adding certain projective classes of transversely measured singular codimension-one foliations of M. This leads to a combinatorial and geometric variant of well-known constructions by Culler, Morgan and Shalen concerning the character variety of a 3-manifold. 相似文献
24.
Tillmann Jentsch 《manuscripta mathematica》2012,137(3-4):347-382
We consider parallel submanifolds M of a Riemannian symmetric space N and study the question whether M is extrinsically homogeneous in N, i.e. whether there exists a subgroup of the isometry group of N which acts transitively on M. Provided that N is of compact or non-compact type, we establish the extrinsic homogeneity of every complete irreducible parallel submanifold of N whose dimension is at least three and which is not contained in any flat of N. 相似文献
25.
Christian Balischewski Dr. Biswajit Bhattacharyya Dr. Eric Sperlich Dr. Christina Günter Alkit Beqiraj Prof. Dr. Tillmann Klamroth Dr. Karsten Behrens Stefan Mies Alexandra Kelling Susanne Lubahn Lea Holtzheimer Anne Nitschke Prof. Dr. Andreas Taubert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(64):e202201068
Fifteen N-butylpyridinium salts – five monometallic [C4Py]2[MBr4] and ten bimetallic [C4Py]2[M0.5aM0.5bBr4] (M=Co, Cu, Mn, Ni, Zn) – were synthesized, and their structures and thermal and electrochemical properties were studied. All the compounds are ionic liquids (ILs) with melting points between 64 and 101 °C. Powder and single-crystal X-ray diffraction show that all ILs are isostructural. The electrochemical stability windows of the ILs are between 2 and 3 V. The conductivities at room temperature are between 10−5 and 10−6 S cm−1. At elevated temperatures, the conductivities reach up to 10−4 S cm−1 at 70 °C. The structures and properties of the current bromide-based ILs were also compared with those of previous examples using chloride ligands, which illustrated differences and similarities between the two groups of ILs. 相似文献
26.
Dye DF Köpke T Ramabhadran RO Raghavachari K Zaleski JM 《Journal of the American Chemical Society》2011,133(33):13110-13120
Photolysis of metalated (Cu and Ni) and free base 2-diazo-3-oxochlorins within a frozen matrix (λ = 457.9 nm, toluene, 80 K) generates a single photointermediate with a hypsochromically shifted electronic absorption spectrum relative to the starting diazochlorins. The appearance of ketene (~2131 cm(-1)) and azete (~1670 cm(-1)) vibrations in infrared absorption and Raman spectra, respectively, identifies this intermediate as resulting from the Wolff rearrangement of the diazochlorins upon N(2) loss. Computational modeling of the vibrational spectra and TDDFT simulation of the electronic transitions of potential photointermediates corroborate this assignment. Isolation and analysis of photoproducts of these diazochlorins formed within n-butanol-doped frozen toluene matrices indicate near exclusive formation of azeteoporphyrins. In sharp contrast, room temperature laser photolysis of these materials yields a mixture of photoproducts deriving from the presence of both carbene and ketene intermediates. Computational modeling of the intramolecular reactivity of the proposed sp(2) carbene intermediate shows exclusive bond insertion to the adjacent phenyl group, and no evidence of Wolff rearrangement. Computational reaction profile analyses reveal that the barrierless Wolff rearrangement proceeds via an out-of-plane carbene electronic configuration that is generated directly during the loss of N(2). The formation of out-of-plane carbene, resulting in the exclusive formation of the observed ketene photointermediate at low temperatures, is consistent with orbital symmetry considerations and by the geometric constraints imposed by the frozen matrix. Combined, this leads to a model showing that azeteoporphyrin formation via the Wolff rearrangement is dependent upon the structural disposition of the adjacent framework, and the specific reaction intermediate formed is very sensitive to this feature. 相似文献
27.
With the availability of resolution boosting and delocalization minimizing techniques, for example, spherical aberration correction and exit-plane wave function reconstruction, high-resolution transmission electron microscopy is drawing to a breakthrough with respect to the atomic-scale imaging of common semiconductor materials. In the present study, we apply a combination of these two state-of-the-art techniques to investigate lattice defects in GaAs-based heterostructures at atomic resolution. Focusing on the direct imaging of stacking faults as well as the core structure of edge and partial dislocations, the practical capabilities of both techniques are illustrated. For the first time, we apply the technique of bright-atom contrast imaging at negative spherical aberration together with an appropriate overfocus setting for the investigation of lattice defects in a semiconductor material. For these purposes, the elastic displacements associated with lattice defects in GaAs viewed along the 110 zone axis are measured from experimental images using reciprocal space strain map algorithms. Moreover, we demonstrate the benefits of the retrieval of the exit-plane wave function not only for the elimination of residual imaging artefacts but also for the proper on-line alignment of specimens during operation of the electron microscope--a basic prerequisite to obtain a fair agreement between simulated images and experimental micrographs. 相似文献
28.
Comparative Structural Studies on 4‐Dimethylaminopyridine‐Adducts Lewis acid‐base adducts of the type dmap—MMe3 (M = Al 1 , Ga 2 , In 3 , Tl 4 ) as well as dmap—AlCl3 ( 6 ) and dmap—Al(t‐Bu)3 ( 7 ) were synthesized by reaction of MR3 with 4‐dimethylamino‐pyridine (dmap) whereas dmap—AlH3 ( 5 ) was obtained from AlH3·Et2O. 1 — 7 were characterized by means of NMR (1H, 13C{1H}) and mass spectrometry and elemental analysis. In addition, their solid state structures were determined by single crystal X‐ray diffraction studies. A comparison of the structural parameters reveales the influence of both electronic (Lewis acidity of the group 13 atom) and steric interactions on the structure and stability of as prepared Lewis acid‐base adducts. 相似文献
29.
Gebauer T Beckert R Weiss D Knop K Käpplinger C Görls H 《Chemical communications (Cambridge, England)》2004,(16):1860-1861
Bora-tetraazapentalenes have been synthesised and characterized; the radical anion shows an unusual thermodynamic stability (semiquinone formation constants K(SEM) of ca. 10(14)). 相似文献
30.