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It is well known that Moore digraphs do not exist except for trivial cases (degree 1 or diameter 1), but there are digraphs of diameter two and arbitrary degree which miss the Moore bound by one. No examples of such digraphs of diameter at least three are known, although several necessary conditions for their existence have been obtained. In this paper, we prove that digraphs of degree three and diameter k ≥ 3 which miss the Moore bound by one do not exist. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 112–126, 2005 相似文献
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Edy Rivas-Suárez Luiz H. Catalani Etelvino J. H Bechara Giuseppe Cilento 《Photochemistry and photobiology》1983,37(1):93-97
Tyrosine and especially its 3,5-dihalogenoderivatives quench acetone triplets. When the excited acetone is generated free in solution, the Stern-Volmer plots for the quenching by these species, monitored via the sensitized emission of the 9,10-dibromoanthracene-2-sulfonate ion, are linear. When triplet acetone is generated enzymically by the peroxidase-catalyzed aerobic oxidation of isobutyral-dehyde, the Stern-Volmer plots for the quenching of the acetone phosphorescence curve upwards in the case of 3,5-dibromotyrosine and even more markedly with 3,5-diiodotyrosine. Quenching appears likely to occur by triplet-triplet energy transfer and especially in the case of the phenoxide form, also by electron transfer. The curvature denotes a static contribution to quenching favoured by the enzyme. 相似文献
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Abstract 2-Methyl-1,4-naphtoquinone (vitamin K3 ) quenches the phosphorescence from enzyme-generated triplet acetone. Concomitantly the vitamin undergoes a photochemical-like alteration as the result of transfer of the electronic energy ( k ET – 1 ± 105 M-1 ). This transfer appears to be of the long-range type. 相似文献
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Edy I. Rivas Alejandro Paladini Jr Giuseppe Cilento 《Photochemistry and photobiology》1984,40(5):565-568
Abstract —Human and bovine serum albumin quench enzyme-generated acetone phosphorescence ( K sv = ca . 104 M 1 ). Concomitantly, these proteins are altered as shown by diminished tryptophan absorption at 280 nm, appearance of products of the formylkynurenine type (max = ca . 320 nm) and disappearance of tryptophan fluorescence. These alterations—which are similar to those induced photochemically—were also observed with serum albumins exposed to enzyme-generated triplet acetaldehyde. On the other hand, triplet acetone generated by the thermolysis of tetramethyldioxetane failed to induce alterations. Presumably energy transfer occurs from the enzyme-generated triplet species to tryptophan group(s) in the serum albumin associated with the acting enzyme. The detailed mechanism is, however, not yet understood. 相似文献
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F. H. Vupré P. V. Vupré A. Gerasimow R. Bahr Fr. Grützmacher J. H. Walton R. C. Judd A. Stock K. Friederici W. Schuen M. Plüss Th. Paul Poda Jan von Zawidzki M. H. Palo Th. W. Richards G. D. Osgood R. Fänder J. G. Royd H. M. Atkinson W. R. Bousfield A. Whitaker S. H. Collins A. Slator J. Livingston R. Morgan Edy Björnsson Stéphan Jahn Ernest Esclangon P. B. Davis F. W. J. Boekhout H. Albrecht Alex L. Feild H. H. Bunzel H. Hasselbring Christ. gob & Co. 《Analytical and bioanalytical chemistry》1917,56(10-11):511-521
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Mustafa alayan Alessandra Lucini Paioni Edy Abou‐Hamad Genrikh Shterk Alexey Pustovarenko Marc Baldus Abhishek Dutta Chowdhury Jorge Gascon 《Angewandte Chemie (International ed. in English)》2020,59(38):16741-16746
Methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science owing to the inherent harsh reaction conditions and fast catalyst deactivation. To improve this process, understanding the mechanism of the initial C?C bond formation is essential. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic‐angle spinning (MAS) solid‐state NMR spectroscopy, we study in detail the early stages of the reaction over a well‐dispersed Mo/H‐ZSM‐5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C?C bond‐forming product from methane), methylidene, allenes, acetal, and surface‐formate species, along with the typical olefinic/aromatic species, allow us to conclude the existence of at least two independent C?H activation pathways. Moreover, this study emphasizes the significance of mobility‐dependent host–guest chemistry between an inorganic zeolite and its trapped organic species during heterogeneous catalysis. 相似文献
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Edy Tri Baskoro 《Discrete Mathematics》2005,294(3):275-277
For graphs G and H, the Ramsey numberR(G,H) is the smallest positive integer n such that every graph F of order n contains G or the complement of F contains H. For the path Pn and the wheel Wm, it is proved that R(Pn,Wm)=2n-1 if m is even, m?4, and n?(m/2)(m-2), and R(Pn,Wm)=3n-2 if m is odd, m?5, and n?(m-1/2)(m-3). 相似文献
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Bendjeriou-Sedjerari A Pelletier JD Abou-Hamad E Emsley L Basset JM 《Chemical communications (Cambridge, England)》2012,48(25):3067-3069
2D double-quantum (1)H-(1)H NMR unambiguously shows that the "isolated" ≡Si-OH surface silanols of dehydroxylated SBA-15 are converted upon treatment with ammonia into single silylamine surface site ≡Si-NH(2). The "gem" di-silanols (=Si(OH)(2)) remain intact. Treatment using HMDS produces (=Si(OSiMe(3))(2)) but leaves ≡Si-NH(2) untouched. The resulting surface is hydrophobic and stable. 相似文献