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We establish an optimal regularity result for parametrized two-dimensional stationary varifolds. Namely, we show that the parametrization map is a smooth minimal branched immersion and that the multiplicity function is constant. We provide some applications of this regularity result, especially in the calculus of variations for the area functional. © 2020 Wiley Periodicals LLC 相似文献
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O. Volkova E. Goodilin A. Vasiliev D. Khomskii N. Tristan P. Kerschl Yu. Skourski K. -H. Mueller B. Buechner 《JETP Letters》2005,82(10):642-645
The ferrimagnetic compounds Ca(CuxMn3?x)Mn4O12 of the double distorted perovskites AC3B4O12 family exhibit a rapid increase of the ferromagnetic component in magnetization at partial substitution of square coordinated (Mn3+)C for (Cu2+)C. In the transport properties, this is seen as a change of the semiconducting type of resistivity for the metallic one. The evolution of magnetic properties of Ca(CuxMn3?x)Mn4O12 is driven by strong antiferromagnetic exchange interaction of (Cu2+)C with (Mn3+/Mn4+)B coordinated octahedra. The competing interactions of (Mn3+)C with (Mn3+/Mn4+)B lead to the formation of noncollinear magnetic structures that can be aligned by magnetic fields. 相似文献
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Transition metal nitrides and carbides (MN/MC) are intriguing materials due to their combination of properties that place them between high-performance ceramics and pure metals. Recent progress in easier synthetic routes toward their production as bulk or nanostructured materials explains the current surge in sustained attention such progress has been receiving. After progressing toward easier syntheses of MN/MC nanosystems as pure phases, coupling MN/MC with a second phase for the production of hybrids and nanocomposites is considered a next important step in the development of these nanosystems. The coupled phase can simply be a different nitride or carbide; it also can be a polymer, a poly(ionic liquid) or a carbon phase, just to give a few examples. The combination of these phases with MN/MC nanoparticles could lead to multifunctional materials. The aim of the present review is to show how far the research concerning the production of MN/MC-based nanocomposites has progressed, especially in terms of controlled composition, morphology and properties. We discuss the most intensely investigated systems and related motivations, as well as partially unexplored yet appealing alternative materials. 相似文献
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Tristan J. Keller Christopher Sterzenbach Joshua Bahr Taria L. Schneiders Markus Bursch Julia Kohn Theresa Eder John M. Lupton Stefan Grimme Sigurd Hger Stefan-S. Jester 《Chemical science》2021,12(27):9352
Molecular spoked wheels with D3h and Cs symmetry are synthesized by Vollhardt trimerization of C2v-symmetric dumbbell structures with central acetylene units and subsequent intramolecular ring closure. Scanning tunneling microscopy of the D3h-symmetric species at the solid/liquid interface on graphite reveals triporous chiral honeycomb nanopatterns in which the alkoxy side chains dominate the packing over the carboxylic acid groups, which remain unpaired. In contrast, Cs-symmetric isomers partially allow for pairing of the carboxylic acids, which therefore act as a probe for the reduced alkoxy chain nanopattern stabilization. This observation also reflects the adsorbate substrate symmetry mismatch, which leads to an increase of nanopattern complexity and unexpected templating of alkoxy side chains along the graphite armchair directions. State-of-the-art GFN-FF calculations confirm the overall structure of this packing and attribute the unusual side-chain orientation to a steric constraint in a confined environment. These calculations go far beyond conventional simple space-filling models and are therefore particularly suitable for this special case of molecular packing.Scanning tunneling microscopy investigations of phenylene-based molecular spoked wheels with D3h and Cs symmetries on graphite show the competitive or complementary effects of carboxylic acid groups and alkoxy chains on the nanopattern formation. 相似文献
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Zhenpin Lu Henrik Quanz Julia Ruhl Georg Albrecht Christian Logemann Derck Schlettwein Peter R. Schreiner Hermann A. Wegner 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4303-4307
We present a new concept to control the conformations of molecules in the excited state through harvesting negative hyperconjugation. The strategy was realized with the 2,3,1,4‐benzodiazadiborinane scaffold, which was prepared by a new synthetic procedure. Photochemical studies identified dual light emission, which was assigned to well‐defined conformers. The emission at longer wavelength can be switched off by restricting the rotational degrees of freedom in the solid state as well as by controlling the energy levels of the excited states through adjusting the solvent polarity. 相似文献
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Bernd Tieke Volker Enkelmann Harald Kapp Günter Lieser Gerhard Wegner 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5):1045-1058
Abstract The topochemical polymerization of diacetylenes and.the dimerization of cinnamic acid derivatives have been studied in Langmuir-Blodgett-multilayers. The resulting polymer films are of controlled thickness and morphology and exhibit excellent stability. Structure, morphology and phase changes occuring in monomer and polymer films have been investigated using spectroscopic methods, electron and x-ray diffraction. Possible applications of the polymer films are discussed. 相似文献
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