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991.
992.
it is said that when Pythagoras discovered his famous theorem, in a right-angled triangle the squares of the smaller sides
sum up to the square of the hypoteneuse, he sacrificed a hundred oxen to thank the gods. 相似文献
993.
We show that, for energies above Mañé’s critical value, minimal magnetic geodesics are Riemannian (A, 0)-quasi-geodesics whereA→1 as the energy tends to infinity. As a consequence, on negatively curved manifolds, minimal magnetic geodesics lie in tubes around Riemannian geodesics.Finally, we investigate a natural metric introduced by Mañé via the so-called action potential. Although this magnetic metric does depend on the magnetic field, the associated magnetic length turns out to be just the Riemannian length. 相似文献
994.
We introduce self-dual codes over the Kleinian four group K=Z
2×Z
2 for a natural quadratic form on K
n
and develop the theory. Topics studied are: weight enumerators, mass formulas, classification up to length 8, neighbourhood graphs, extremal codes, shadows, generalized t-designs, lexicographic codes, the Hexacode and its odd and shorter cousin, automorphism groups, marked codes. Kleinian codes form a new and natural fourth step in a series of analogies between binary codes, lattices and vertex operator algebras. This analogy will be emphasized and explained in detail. 相似文献
995.
In this paper we introduce two tree-width-like graph
invariants. The first graph invariant, which we denote by
=(G), is defined in terms of positive
semi-definite matrices and is similar to the graph invariant
(G), introduced by Colin de Verdière in
[J. Comb. Theory, Ser. B., 74:121–146, 1998]. The second graph
invariant, which we denote by (G), is defined in terms of a certain
connected subgraph property and is similar to (G), introduced by van der Holst,
Laurent, and Schrijver in [J. Comb. Theory, Ser. B., 65:291–304,
1995]. We give some theorems on the behaviour of these
invariants under certain transformations. We show that
=(G)=(G)
for any graph G with
=(G)4, and we give minimal forbidden
minor characterizations for the graphs satisfying
=(G)k
for k=1,2,3,4.This paper is extracted from two chapters of [7].
This work was done while the author was at the Centrum voor
Wiskunde en Informatica, Kruislaan 413, 1098 SJ Amsterdam, The
Netherlands. 相似文献
996.
Denote by
the class of all triangle-free
graphs on n vertices and
m edges. Our main result is
the following sharp threshold, which answers the question for
which densities a typical triangle-free graph is bipartite. Fix
> 0 and let
. If
n/2 m (1 – ) t
3, then almost
all graphs in
are not bipartite, whereas if
m (1 + )t
3, then almost
all of them are bipartite. For m (1 + )t
3, this allows
us to determine asymptotically the number of graphs in
. We also obtain corresponding
results for C
-free graphs, for any
cycle C
of fixed odd length.
Forschergruppe Algorithmen, Struktur, Zufall
supported by Deutsche Forschungsgemeinschaft grant FOR
413/1-1 相似文献
997.
998.
In this work we show that the energy associated to the linear three-dimensional magneto-elastic system decays polynomially to zero as time goes to infinity, provided the initial data is smooth enough. 相似文献
999.
1000.