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991.
We carry out first-principles calculations of the nonlinear dielectric response of short-period ferroelectric superlattices. We compute and store not only the total polarization, but also the Wannier-based polarizations of individual atomic layers, as a function of the electric displacement field, and use this information to construct a model capable of predicting the nonlinear dielectric response of an arbitrary superlattice sequence. We demonstrate the successful application of our approach to superlattices composed of SrTiO3, CaTiO3, and BaTiO3 layers. 相似文献
992.
Ugo Castelli Jean‐Franois Lohier Ines Drukenmüller Agns Mingot Christian Bachman Carole Alayrac Jrme Marrot Karin Stierstorfer Andreas Kornath Annie‐Claude Gaumont Sbastien Thibaudeau 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(5):1369-1374
Unambiguously confirmed by low‐temperature in situ NMR experiments, X‐ray diffraction and vibrational spectroscopy, phosphonium‐carbenium superelectrophiles are shown to be generated in strong acidic conditions. Representing crucial intermediates, their exploitation allows for the synthesis of unprecedented fluorinated (cyclic) phosphine oxides. 相似文献
993.
Wood strength is highly anisotropic and tissue-specific. We herein show how it can be predicted from local failure of the nanoscaled wood component lignin and from the microstructure and the composition of the wood tissue, by means of continuum micromechanics. The suitability of the model is confirmed by the good agreement between model-predicted biaxial strength values of wood and corresponding experimental results. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
994.
During the preparation of plant extracts by a press-slit technique, membranes of cell walls and cell organelles of the plant material form vesicles, which are colloidally dispersed. It was assumed that chlorophyll-containing green extracts enclose lipoidic structures. Vesicles in aqueous mistletoe extracts (extracts of Viscum album L.) were analyzed by cryo-transmission electron microscopy (cryo-TEM) without fixation. For the first time, it was possible to analyze unfixed vesicles in the mistletoe extract. Micrographs of cryo-TEM showed predominantly unilamellar vesicles of different sizes. The quantification of vesicles was established through the analysis of phospholipids, which are major components of membranes. The method was validated mainly according to ICH guidelines for the validation of analytical methods (Q2A and Q2B). For further characterization of the vesicle size, a method was developed which is based on the separation of the vesicles from low molecular weight substances by size exclusion chromatography. Fractions were collected and average sizes were determined by multi-angle laser light scattering (MALLS). Furthermore, the UV-vis absorbance and phospholipid concentration were analyzed. Phospholipid quantification was in agreement with photometrical data. Sizes determined by cryo-TEM and by light scattering showed consistent results. 相似文献
995.
996.
First-principles periodic slab density-functional theory (DFT) calculations with a plane-wave basis are used to predict the properties of S, Pt, and Hf adsorption on NiAl(1 1 0). Stable adsorption sites are identified, and adsorbate binding energies and structures are predicted. We find that while S adsorbs in a threefold site, the metals prefer to adsorb in the Ni-Ni twofold bridge site. The latter finding is consistent with scanning tunneling microscopy experiments for adsorption of various transition metals on NiAl(1 1 0) by Ho and coworkers. S is predicted to easily diffuse between threefold sites. We find that Pt and Hf both induce significant changes in the local surface structure, changing twofold bridge sites into fourfold coordination sites by drawing next-nearest-neighbor atoms nearly equidistant with the nearest-neighbor atoms. We find Pt favors interaction with Al slightly more than Ni, while Hf shows a particularly strong affinity for Ni compared to Al. We also predict that Hf may diffuse one-dimensionally along Ni rows with a barrier of ≈0.6 eV. 相似文献
997.
998.
Crystal Structure of Yellow K3OBr K3OBr was prepared for the first time and investigated by X-ray methods. The yellow compound crystallizes with cubic symmetry, space group Pm3m, a = 521.3(1) pm, Z = 1 and shows like colourless Na3OCl anti-perovskite structure. 相似文献
999.
1000.