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301.
Frontispiece: Theoretical Modelling and Facile Synthesis of a Highly Active Boron‐Doped Palladium Catalyst for the Oxygen Reduction Reaction
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302.
303.
Patrick Pröhm Willi R. Berg Susanne M. Rupf Patrick Voßnacker Prof. Dr. Sebastian Riedel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(70):17676-17681
A systematic study of halogenate(I/III) anions with polyatomic ligands is presented. The bis(perfluoro-tert-butoxy) halogenates(I) [X(OC4F9)2]−, X=Cl, Br, I, of chlorine, bromine, and iodine are prepared as their tetraethylammonium salts and characterized with IR, Raman, and NMR spectroscopic methods, as well as single-crystal X-ray diffraction analyses. Spectroscopical data are supported by quantum-chemical calculations. Additionally, the bonding situation of the species in question are analyzed and discussed. Furthermore, the oxidation to the corresponding halogenate(III) derivatives was studied. For [Br(OC4F9)2]−, oxidation with elemental fluorine gave [BrF2(OC4F9)2]−. Iodide was directly oxidized by ClOC4F9 to the IIII species [I(OC4F9)4]−, which is a surprisingly inert anion that might be used as a weakly coordinating anion (WCA) in the future. For [Cl(OC4F9)2]−, the decomposition products of the synthetic approaches towards a chlorine(III) system were analyzed. 相似文献
304.
Static and vibration analysis of functionally graded beams using refined shear deformation theory 总被引:1,自引:0,他引:1
Static and vibration analysis of functionally graded beams using refined shear deformation theory is presented. The developed theory, which does not require shear correction factor, accounts for shear deformation effect and coupling coming from the material anisotropy. Governing equations of motion are derived from the Hamilton’s principle. The resulting coupling is referred to as triply coupled axial-flexural response. A two-noded Hermite-cubic element with five degree-of-freedom per node is developed to solve the problem. Numerical results are obtained for functionally graded beams with simply-supported, cantilever-free and clamped-clamped boundary conditions to investigate effects of the power-law exponent and modulus ratio on the displacements, natural frequencies and corresponding mode shapes. 相似文献
305.
Cooling-rate effects in simple monatomic amorphous nanoparticles were studied in a spherical model containing 2469 atoms using a molecular dynamics (MD) method under non-periodic boundary conditions. We used the pair double-well interaction potential developed by Engel and Trebin [Phys. Rev. Lett. 98 225505 (2007)]. To observe the cooling-rate effects, the initial, well-relaxed models at a high temperature (i.e. in liquid state) were cooled to zero temperature at three different cooling rates. Cooling-rate effects on thermodynamic quantities, such as potential and surface energy, were more pronounced than those for static quantities. The potential and surface energy of the nanoparticles decreased with decreasing cooling rate, indicating the formation of more stable configurations with lower cooling rates. The microstructure of amorphous nanoparticles was analyzed via radial distribution function (RDF), coordination number and bond-angle distributions. Relatively weak cooling-rate effects on such quantities were found. Honeycutt–Andersen analysis for different bond pairs was used and discussed. The microstructure of the surface and core of amorphous nanoparticles were analyzed and the evolution of nanoparticle structures upon cooling from the melt discussed. Cooling-rate effects in a short-range interaction system are discussed and compared with those in long-range systems. 相似文献
306.
Stefan Voß 《Annals of Operations Research》1996,63(2):253-275
Tabu search is a metastrategy for guiding known heuristics to overcome local optimality with a large number of successful applications reported in the literature. In this paper we investigate two dynamic strategies, the reverse elimination method and the cancellation sequence method. The incorporation of strategic oscillation as well as a combination of these methods are developed. The impact of the different methods is shown with respect to the traveling purchaser problem, a generalization of the classical traveling salesman problem. The traveling purchaser problem is the problem of determining a tour of a purchaser buying several items in different shops by minimizing the total amount of travel and purchase costs. A comparison of the tabu search strategies with a simulated annealing approach is presented, too. 相似文献
307.
I. O. Troyanchuk D. V. Karpinskiĭ A. N. Chobot D. G. Voĭitsekhovich V. M. Dobryanskiĭ 《JETP Letters》2006,84(3):151-155
The elastic properties and crystal structure of the Pr1?x Sr x CoO3 system are studied. Two types of crystal structure transitions are found. For the composition x = 0.5, the monoclinic phase transforms to a rhombohedral one in the high-temperature transition (T ≈ 310 K), while the unit cell symmetry remains monoclinic though the unit cell parameters change drastically in the low-temperature transformation (T ≈ 110 K). It is suggested that the high-temperature transition is caused by the dimensional effect, while the low-temperature transition is associated with the presence of praseodymium ions actively involved in chemical bonding. 相似文献
308.
Background
The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses. 相似文献309.
In this paper, the following facts are stated in the setting of b-metric spaces.
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- (1)The contraction constant in the Banach contraction principle fully extends to [0, 1), but the contraction constants in Reich’s fixed point theorem and many other fixed point theorems do not fully extend to [0, 1), which answers the early stated question on transforming fixed point theorems in metric spaces to fixed point theorems in b-metric spaces.
- (2) Caristi’s theorem does not fully extend to b-metric spaces, which is a negative answer to a recent Kirk–Shahzad’s question (Remark 12.6) [Fixed Point Theory in Distance Spaces. Springer, 2014].
310.
Quaternary Germanides RE3TRh4Ge4 (RE = Ce,Pr, Nd; T = Nb,Ta) – A New Coloring Variant of the Aristotype AlB2
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Rolf‐Dieter Hoffmann Daniel Voßwinkel Samir F. Matar Rainer Pöttgen 《无机化学与普通化学杂志》2016,642(18):979-986
The quaternary germanides RE3TRh4Ge4 (RE = Ce, Pr, Nd; T = Nb, Ta) were synthesized from the elements by arc‐melting and subsequent annealing in a muffle furnace. The structure of Ce3TaRh4Ge4 was refined from single‐crystal X‐ray diffractometer data: new type, Pbam, a = 719.9(2), b = 1495.0(3), c = 431.61(8), wR2 = 0.0678, 1004 F2 values, and 40 variables. Isotypy of the remaining phases was evident from X‐ray powder patterns. Ce3TaRh4Ge4 is a new superstructure variant of the aristotype AlB2 with an ordering of cerium and tantalum on the aluminum site, whereas the honey‐comb network is built up by a 1:1 ordering of rhodium and germanium. This crystal‐chemical relationship is discussed based on a group‐subgroup scheme. The distinctly different size of tantalum and cerium leads to a pronounced puckering of the [Rh4Ge4] network, which shows the shortest interatomic distances (253–271 pm Rh–Ge) within the Ce3TaRh4Ge4 structure. Another remarkable structural feature concerns the tantalum coordination with six shorter Ta–Rh bonds (265–266 pm) and six longer Ta–Ge bonds (294–295 pm). The [Rh4Ge4] network fully separates the tantalum and cerium atoms (Ce–Ce > 387 pm, Ta–Ta > 431 pm, and Ce–Ta > 359 pm). The electronic density of states DOS from DFT calculations show metallic behavior with large contributions of localized Ce 4f as well as itinerant ones from all constituents at the Fermi level but no significant magnetic polarization on Ce could be identified. The bonding characteristics described based on overlap populations illustrate further the crystal chemistry observations of the different coordination of Ce1 and Ce2 in Ce3TaRh4Ge4. The Rh–Ge interactions within the network are highlighted as dominant. The bonding magnitudes follow the interatomic distances and identify differences of Ta bonding vs. Ce1/Ce2 bonding with the Rh and Ge substructures. 相似文献