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71.
For a fixed multigraph H, possibly containing loops, with V(H)={h1, . . . , hk}, we say a graph G is H-linked if for every choice of k vertices v1, . . . , vk in G, there exists a subdivision of H in G such that vi represents hi (for all i). This notion clearly generalizes the concept of k-linked graphs (as well as other properties). In this paper we determine, for a connected multigraph H and for any sufficiently large graph G, a sharp lower bound on δ(G) (depending upon H) such that G is H-linked. 相似文献
72.
Let H be a multigraph and G a graph containing a subgraph isomorphic to a subdivision of H, with S ⊂ V(G) (the ground set) the image of V(H) under the isomorphism. We consider connectivity and minimum degree or degree sum conditions sufficient to imply there is
a spanning subgraph of G isomorphic to a subdivision of H on the same ground set S. These results generalize a number of theorems in the literature. 相似文献
73.
J. Links K. Hibberd M. Gould A. Foerster 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):309-312
A new model for correlated electrons is presented which is integrable in one-dimension. The symmetry algebra of the model
is the Lie superalgebra gl(2|1) which depends on a continuous free parameter. This symmetry algebra contains the pairing algebra as a subalgebra which is used to show that the model exhibits Off-Diagonal Long-Range Order in any number
of dimensions.
Received: 9 December 1997 / Revised: 12 February 1998 / Accepted: 17 March 1998 相似文献
74.
How good are projection methods for convex feasibility problems? 总被引:2,自引:0,他引:2
We consider simple projection methods for solving convex feasibility problems. Both successive and sequential methods are
considered, and heuristics to improve these are suggested. Unfortunately, particularly given the large literature which might
make one think otherwise, numerical tests indicate that in general none of the variants considered are especially effective
or competitive with more sophisticated alternatives.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.
This work was supported by the EPSRC grant GR/S42170. 相似文献
75.
76.
H.W Gould 《Journal of Combinatorial Theory, Series A》1977,23(3):351-353
In this paper a general identity is proved which includes among its special cases a recurrence formula for Catalan numbers given by J. Touchard in 1924. 相似文献
77.
The voltage power spectrum of NbSe3 has been studied in the upper charge-density wave (CDW) state where only one CDW exists. In the non-Ohmic regime sharp spikes appear in the spectrum. The frequency of these spikes increases monotonically with current as in the lower CDW state. We study the “fine structure” of the spectrum and find evidence for “frequency pulling” between the modes. A linear coupled-mode treatment is used to model this effect. There is also evidence of heterodyning of an intrinsic (current independent) 2MHz mode. We briefly discuss these phenomena in terms of Fröhlich sliding conductivity. Difficulties with the simple two-fluid model as well as models based on solid state turbulence are pointed out. 相似文献
78.
CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
79.
R.D. Gould 《Journal of Non》1983,55(3):363-386
Electrical conduction through relatively low resistance filaments has been proposed as the mechanism whereby current-controlled negative resistance (CCNR), voltage-controlled negative resistance (VCNR), switching and memory effects take place, particularly in amorphous insulators and semiconductors. Two types of filament are considered: uniform filaments (in which the applied voltage is assumed to drop uniformly along the filament's length) and non-uniform filaments (in which the applied voltage drop occurs primarily at a higher resistance flaw within the filament). By regarding heat dissipation as taking place either uniformly or preferentially at flaws, depending on the filament type, expressions are derived for the temperature within the non-conducting insulator or semiconductor regions, filament or flaw temperature, and voltage at which a filament will cease to conduct. It is shown that for uniform filamentary conduction in thin films the conduction in individual filaments is influenced by the number and proximity of neighbouring filaments, while flawed filaments are essentially isolated from their neighbours. An illustration in the application of the model is given (in the case of uniform filaments) for an assembly of conducting filaments, and various filamentary parameters are calculated.Experimental evidence for a range of different systems is reviewed, and shown to be consistent with the model. 相似文献
80.
Let G be a graph, and let v be a vertex of G. We denote by N(v) the set of vertices of G which are adjacent to v, and by 〈N(v)〉 the subgraph of G induced by N(v). We call 〈N(v)〉 the neighborhood of v. In a paper of 1968, Agakishieva has, as one of her main theorems, the statement: “Graphs in which every neighborhood is an n-cycle exist if and only if 3?n?6.” It it is the object of this note to provide a list of counter examples to this statement. 相似文献