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241.
We characterise and enumerate permutations that are sortable by n – 4 passes through a stack. We conjecture the number of permutations sortable by n – 5 passes, and also the form of a formula for the general case n – k, which involves a polynomial expression. 相似文献
242.
Anders O. F. Hendrickson 《代数通讯》2013,41(12):4420-4438
Diaconis and Isaacs have defined the supercharacter theories of a finite group to be certain approximations to the ordinary character theory of the group [7]. We make explicit the connection between supercharacter theories and Schur rings, and we provide supercharacter theory constructions which correspond to Schur ring products of Leung and Man [12], Hirasaka and Muzychuk [10], and Tamaschke [20]. 相似文献
243.
In this paper we propose a new definition of prime ends for domains in metric spaces under rather general assumptions. We compare our prime ends to those of Carathéodory and Näkki. Modulus ends and prime ends, defined by means of the p-modulus of curve families, are also discussed and related to the prime ends. We provide characterizations of singleton prime ends and relate them to the notion of accessibility of boundary points, and introduce a topology on the prime end boundary. We also study relations between the prime end boundary and the Mazurkiewicz boundary. Generalizing the notion of John domains, we introduce almost John domains, and we investigate prime ends in the settings of John domains, almost John domains and domains which are finitely connected at the boundary. 相似文献
244.
245.
In this paper, we study lower bounds on the size of a maximum independent set and a maximum matching in a hypergraph of rank three. The rank in a hypergraph is the size of a maximum edge in the hypergraph. A hypergraph is simple if no two edges contain exactly the same vertices. Let H be a hypergraph and let and be the size of a maximum independent set and a maximum matching, respectively, in H, where a set of vertices in H is independent (also called strongly independent in the literature) if no two vertices in the set belong to a common edge. Let H be a hypergraph of rank at most three and maximum degree at most three. We show that with equality if and only if H is the Fano plane. In fact, we show that if H is connected and different from the Fano plane, then and we characterize the hypergraphs achieving equality in this bound. Using this result, we show that that if H is a simple connected 3‐uniform hypergraph of order at least 8 and with maximum degree at most three, then and there is a connected 3‐uniform hypergraph H of order 19 achieving this lower bound. Finally, we show that if H is a connected hypergraph of rank at most three that is not a complete hypergraph on vertices, where denotes the maximum degree in H, then and this bound is asymptotically best possible. © 2012 Wiley Periodicals, Inc. J. Graph Theory 相似文献
246.
247.
Anders Frankild 《代数通讯》2013,41(2):461-500
In this article we present a systematic study of the reflexivity properties of homologically finite complexes with respect to semidualizing complexes in the setting of nonlocal rings. One primary focus is the descent of these properties over ring homomorphisms of finite flat dimension, presented in terms of inequalities between generalized G-dimensions. Most of these results are new even when the ring homomorphism is local. The main tool for these analyses is a nonlocal version of the amplitude inequality of Iversen, Foxby, and Iyengar. We provide numerous examples demonstrating the need for certain hypotheses and the strictness of many inequalities. 相似文献
248.
L. Lorini N. Ashby A. Brusch S. Diddams R. Drullinger E. Eason T. Fortier P. Hastings T. Heavner D. Hume W. Itano S. Jefferts N. Newbury T. Parker T. Rosenband J. Stalnaker W. Swann D. Wineland J. Bergquist 《The European physical journal. Special topics》2008,163(1):19-35
The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints
of any present-day temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements
of the absolute frequency of the Hg+ single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine
structure constant α to less than 2 · 10−6yr−1 and offers a Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency
ratio of the Al+ and Hg+ optical clocks is reported with a fractional frequency uncertainty of ±5.2 · 10−17. The record of such measurements over the last year sensitively tests for a temporal variation of α and constrains , consistent with zero. 相似文献
249.
Zhipeng Shao Zaiwei Wang Zhipeng Li Yingping Fan Hongguang Meng Ranran Liu Yan Wang Anders Hagfeldt Guanglei Cui Shuping Pang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5643-5647
An easy and scalable methylamine (MA) gas healing method was realized for inorganic cesium‐based perovskite (CsPbX3) layers by incorporating a certain amount of MAX (X=I or Br) initiators into the raw film. It was found that the excess MAX accelerated the absorption of the MA gas into the CsPbX3 film and quickly turned it into a liquid intermediate phase. Through the healing process, a highly uniform and highly crystalline CsPbX3 film with enhanced photovoltaic performance was obtained. Moreover, the chemical interactions between a series of halides and MA gas molecules were studied, and the results could offer guidance in further optimizations of the healing strategy. 相似文献
250.
José Alejandro Arminio-Ravelo Anders W. Jensen Dr. Kim D. Jensen Dr. Jonathan Quinson Prof. Dr. María Escudero-Escribano 《Chemphyschem》2019,20(22):2956-2963
Proton exchange membrane water electrolysers are very promising renewable energy conversion devices that produce hydrogen from sustainable feedstocks. These devices are mainly limited by the sluggish kinetics of the oxygen evolution reaction (OER). Ir-based nanoparticles are both reasonably active and stable for the OER in acidic media. The electrolyte composition and the pH may play a crucial role in electrocatalysis, yet they have been widely overlooked for the OER. Herein, we present a study on the effects of the composition and concentration of the electrolyte on commercial Ir black nanoparticles using concentrations of 0.05 M, 0.1 M and 0.5 M of both sulphuric and perchloric acid. The results show an important effect of the electrolyte composition on the catalytic performance of the Ir nanoparticles. The concentration of H2SO4 interferes on the oxidation of Ir and decreases the catalytic performance of the catalyst. HClO4 does not show strong interferences in the electrochemistry of Ir. Higher catalytic performances are observed in HClO4 electrolytes in comparison to H2SO4 with little effect of the concentration of HClO4. 相似文献