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61.
Augmenting forests to meet odd diameter requirements 总被引:1,自引:0,他引:1
Given a graph G=(V,E) and an integer D≥1, we consider the problem of augmenting G by the smallest number of new edges so that the diameter becomes at most D. It is known that no constant approximation algorithms to this problem with an arbitrary graph G can be obtained unless P=NP. For a forest G and an odd D≥3, it was open whether the problem is approximable within a constant factor. In this paper, we give the first constant factor approximation algorithm to the problem with a forest G and an odd D; our algorithm delivers an 8-approximate solution in O(|V|3) time. We also show that a 4-approximate solution to the problem with a forest G and an odd D can be obtained in linear time if the augmented graph is additionally required to be biconnected. 相似文献
62.
LetW be an open Riemann surface and
ap-sheeted (1<p<∞) unlimited covering surface ofW. Denote by Δ1 (resp.,
) the minimal Martin boundary ofW (resp.,
). For ζ ∈ Δ, let
ζ be the (cardinal) number of the set of pionts
which lie over ζ and
the class of open connected subsetsM ofW such thatM∪{ζ} is a minimal fine neighborhood of ζ. Our main result is the following:
, where
is the number of components of π-1
M and π is the projection of
ontoW. Moreover, some applications of the above results are discussed whenW is the unit disc. 相似文献
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69.
Nagasato S Sunatsuki Y Ohsato S Kido T Matsumoto N Kojima M 《Chemical communications (Cambridge, England)》2002,(1):14-15
The assembly reaction arising from hydrogen bonding between a chiral C3 symmetric cobalt(III) complex and a tripod-ligand involving three imidazolate groups [tris[2-(((2-methylimidazolato-4-yl)methylidene)amino)ethyl]amine]cobalt(III) and either hydroquinone or resorcinol gave the 1:3 adducts, with 3D extended structures showing the template effect of the complex. 相似文献
70.
Shigeyuki Yagi Ryuhei Yamada Norihiro Tsuji Shinji Murakami Toru Takagishi 《Supramolecular chemistry》2013,25(3):293-297
Abstract A porphyrin dimer with a polyether linkage was newly synthesized and its conformational change triggered by complexation with an sodium cation was examined. It was confirmed by 1H NMR titration experiments that the dimer bearing a pentaoxyehtylene linkage (1b) was effectively formed a 1:1 complex with a sodium perchlorate. A detailed investigation of the CIS values for the protons confirmed that the complex of 1b?Na+ adopts a slipped face-to-face conformation. 相似文献