共查询到20条相似文献,搜索用时 921 毫秒
1.
Marilyn Breen 《Geometriae Dedicata》1991,37(3):317-326
Let be a family of compact starshaped sets in the plane. If every three and every two members of have a union which is connected and simply connected, then {F:F in } is simply connected and nonempty. Of course, if every three and every two members of have a starshaped union, the same result holds.Supported in part by NSF grants DMS-8705336, DMS-8908717 and by a Senior Faculty Summer Research Fellowship, Research Council, University of Oklahoma. 相似文献
2.
Denote by a flock of a quadratic cone of PG(3,q) by S() the spread of PG(3,q) associated with and by l the common line of the base reguli. Suppose that there are two lines not transversal to a base regulus which share the same lines of S() Then we prove that is either linear or a Kantor-Knuth semifield flock. Using this property we can extend the result of J3 on derivable flocks proving that, if a set of q + 1 lines of S() defines a derivable net different from a base regulus-net, then is either linear or a Kantor-Knuth semifield flock. Moreover if l is not a component of the derivable net, then is linear. 相似文献
3.
E. G. Pytkeev 《Mathematical Notes》1992,52(3):953-959
Suppose that is a relatively countably compact subset of B1(X), the space of Baire I functions over a K-analytic space X equipped with the pointwise convergence topology. It is proved that (1) the closure of is a strongly countably compact Frechét-Urysohn space; (2) if is 1 -compact, is a bicompactum; (3) if X is a paracompact space, the closure of is a bicompactum.Translated from Matematicheskie Zametki, Vol. 52, No. 3, pp. 108–116, September, 1992. 相似文献
4.
N. Alon D. Kleitman R. Lipton R. Meshulam M. Rabin J. Spencer 《Graphs and Combinatorics》1991,7(2):97-99
Letq be a prime power. It is shown that for any hypergraph = {F
1,...,F
d(q–1)+1} whose maximal degree isd, there exists Ø 0 , such that 0 (modq). 相似文献
5.
Dines Bjørner 《BIT Numerical Mathematics》1970,10(4):415-442
Let denote a conventional flowchart. Any algorithm can be represented by a flowchart. If action nodes in call then is a recursive flowchart. We show how to decompose arbitrary non-self-modifying programs into structure and atomic parts. We specifically give the synthesis procedure for a controller . can serve as the only sequencer in an execution of . If is recursive then is a pushdown machine, otherwise is a finite state machine. The next-state functionf and the output functiong of represent respectively all of the structure-, i.e. the programmer-oriented-, and all of the atomic-, i.e. the data-oriented-, parts of .f defines the flow or pattern of computations andg the actual transformations or operations on data. Thus we construct and analyze programs by constructing and analyzing their sequencers . 相似文献
6.
P. C. Craighero R. Gattazzo M. C. Ronconi 《Annali di Matematica Pura ed Applicata》1981,129(1):81-130
Summary In this paper we classify the algebraic cubic surfaces of the affine space
is the complex field, whose algebraic curves are set-theoretic complete intersections of ; in other words surfaces such that every prime ideal of height 1in the coordinate ring [] of is the radical of a principal ideal; if is non singular in codimension 1this means that [] is semifactorial. We give the equations of such surfaces within linear isomorphisms of
providing also methods by which one can construct the equations of the surfaces cutting on its curves as set-theoretic complete intersections. Moreover for each of these surfaces we determine the minimum positive number such that every algebraic curve of with multiplicity of intersection , is complete intersection of itself with another surface
§ 8where the results are summarized). We tackle also the problem of such a classification over algebraically closed fields k different from .
Lavoro eseguito nell'ambito del G.N.S.A.G.A. del C.N.R. 相似文献
Lavoro eseguito nell'ambito del G.N.S.A.G.A. del C.N.R. 相似文献
7.
The main result is a control theorem for the space of stable pseudo-isotopies on E with control near the leaves of in M, where : E M is a fiber bundle over a Riemannian manifold M having a compact manifold for fiber and is a smooth foliation of M such that each leaf inherits a flat Riemannian geometry from M. A similar result has been proved by Farrell and Jones under the assumption that each leaf of inherits a geometry with strictly negative curvature from M.Both authors were supported in part by the National Science Foundation. 相似文献
8.
Edwin Perkins 《Probability Theory and Related Fields》1981,56(2):255-281
Summary D. Gilat has shown that any non-negative submartingale (X, .) is equal in law to the absolute value of a martingale (M, .). This result may be strenthened so that the pairs (X,.) and (¦M¦,.) are synonomous. In this paper the question of uniqueness of M is considered. Conditions on a local martingale (M, .) are found that lead to an explicit formula for the finite-dimensional distributions of M in terms of the Doob-Meyer decomposition of the local martingale X. In many cases of interest the conditions on M are unnecessary. For example, if X is the pth power of an Itô integral it is shown that (M) is unique if p> 1 but not in general if p=1. 相似文献
9.
Given a nondecreasing sequence (
n
) of sub--fields and a real or vector valued random variable f, the Lévy Martingale convergence Theorem (LMCT) asserts that E(f/
n
) converges to E(f/) almost surely and in L
1, where stands for the -field generated by the
n
. In the present paper, we study the validity of the multivalued analog this theorem for a random set F whose values are members of (X), the space of nonempty closed sets of a Banach space X, when (X) is endowed either with the Painlevé–Kuratowski convergence or its infinite dimensional extensions. We deduce epi-convergence results for integrands via the epigraphical multifunctions. As it is known, these results are useful for approximating optimization problems. The method relies on countability supportness hypotheses which are shown to hold when the values of the random set E(F/
n
) do not contain any line. On the other hand, since the values of F are not assumed to be bounded, conditions involving barrier and asymptotic cones are shown to be necessary. Moreover, we discuss the relations with other multivalued martingale convergence theorems and provide examples showing the role of the hypotheses. Even in the finite dimensional setting, our results are new or subsume already existing ones. 相似文献
10.
Let M be a compact Riemannian manifold of dimension n, and let be a smooth foliation on M. A topological obstruction is obtained, similar to results of R. Bott and J. Pasternack, to the existence of a metric on M for which is totally geodesic. In this case, necessarily that portion of the Pontryagin algebra of the subbundle must vanish in degree n if is odd-dimensional. Using the same methods simple proofs of the theorems of Bott and Pasternack are given. 相似文献
11.
Dongsu Kim 《Graphs and Combinatorics》1990,6(2):173-178
We give a weight-preserving bijection from
r, µ
m
to, where
r, µ
m
is the set of all plane partitions whose entries are m and whose entries below ther-th row form a column strict plane partition of type, and
µ
m
the set of all column strict plane partitions of type whose entries are m, and the set of all plane partitions with at mostr rows, whose entries are m. This confirms a conjecture of Kadell. 相似文献
12.
For graphsA andB the relationA(B)
r
1
means that for everyr-coloring of the vertices ofA there is a monochromatic copy ofB inA. Forb (G) is the family of graphs which do not embedG. A familyof graphs is Ramsey if for all graphsBthere is a graphAsuch thatA(B)
r
1
. The only graphsG for which it is not known whether Forb (G) is Ramsey are graphs which have a cutpoint adjacent to every other vertex except one. In this paper we prove for a large subclass of those graphsG, that Forb (G) does not have the Ramsey property.This research has been supported in part by NSERC grant 69-1325. 相似文献
13.
Pierre Matet 《Archive for Mathematical Logic》1993,32(3):151-171
Summary We use games of Kastanas to obtain a new characterization of the classC
of all sets that are completely Ramsey with respect to a given happy family . We then combine this with ideas of Plewik to give a uniform proof of various results of Ellentuck, Louveau, Mathias and Milliken concerning the extent ofC
. We also study some cardinals that can be associated with the ideal of nowhere -Ramsey sets.Part of this research was done while the author was visiting I.V.I.C. in Caracas in September 1989. The author would like to thank Carlos Di Prisco for his hospitality. 相似文献
14.
Using a construction of Thomassen [Discrete Math. 9, 91–96 (1974)] we prove that for infinitely manyn there is a family
n
of triangle-free maximally non-hamiltonian graphs of ordern with |
n
| exponentially inn. In particular, for everym 48 we construct such a graph; an infinite number of these provide new almost extremal examples in the sense of minimal size. 相似文献
15.
M. Kiehl 《Applied Mathematics and Optimization》1991,24(1):171-181
The multiple-shooting method for the solution of boundary-value problems is a modified Newton method for the solution of an equation(x) = 0, where is a special function which is differentiable in general, but may occasionally have discontinuities at some points which have to be passed during the iteration process. This is the case especially in optimal control problems and it is a severe handicap for the convergence of the Newton method which can be essentially reduced when replacing by a series of smooth functions
i dependent on the iteration process. 相似文献
16.
L. Bader, G. Lunardon and J. A. Thas have shown that a flock 0 of a quadratic cone in PG(3, q), q odd, determines a set ={0,1,...,q} of q+1 flocks. Each
j
, 1jq, is said to be derived from 0. We show that, by derivation, the flocks with q=3
e
arising from the Ganley planes yield an inequivalent flock for q27. Further, we prove that the Fisher flocks (q odd, q5) are the unique nonlinear flocks for which (q–1)/2 planes of the flock contain a common line. This result is used to show that each of the flocks derived from a Fisher flock is again a Fisher flock. Finally, we prove that any set of q–1 pairwise disjoint nonsingular conics of a cone can be extended to a flock. All these results have implications for the theory of translation planes. 相似文献
17.
B. Maisonneuve 《Probability Theory and Related Fields》1989,80(3):395-405
Summary Given a random closed setM, adapted to a filtration (
t
), we construct a local time ofM which is both (
t
) adapted and (
Dt
) predictable, whereD
t
=inf{s>t: sM}. Similarly an exit system, both (
t
) optional and (
Dt
) predictable, is associated withM and with the process representing the future at each timet. The paper is motivated by the markovian case, where the general results are applied to Ray processes. 相似文献
18.
Mika Watanabe 《Graphs and Combinatorics》1995,11(3):293-303
LetX be ann-element set and be a family of its subsets. Consider the family
x = {F – {x} : F } for a givenx X. We write(m, n) (m – k, n – 1), when for all with || m, there exists an elementx ofX such that|
x| m – k. We show that (m, n) (m – 10,n – 1) for allm 5n and (m, n) (m – 13,n – 1) for allm 29n/5. 相似文献
19.
Given a family of subsets of an arbitrary groundsetE, acover of is any setC E having non-empty intersection with every subset in.
In this paper we deal with thecovering polytope, i.e., the convex hull of the incidence vectors of all the covers of. In Section 2 we review all the known properties of the covering polytope. In Sections 3 and 4 we introduce two new classes of non-Boolean facets of such a polytope. In Sections 5 and 6 we describe some non-sequential lifting procedures. In Section 7 a generalization of the notion ofweb introduced by L.E. Trotter is presented together with the facets of the covering polytope produced by such a structure.Moreover, the strong connections between several combinatorial problems and the covering problem are pointed out and, exploiting those connections, some examples are presented of new facets for the Knapsack and Acyclic Subdigraph polytopes. 相似文献
20.
Self-bounded controlled invariant subspaces: A straightforward approach to constrained controllability 总被引:1,自引:0,他引:1
A lattice-type structure is shown to exist in a particular subset of the set of all (A, )-controlled invariants contained in
and containing
, whereA denotes a linear map inR
n
; ,
are arbitrary subspaces ofR
n
; andD is an arbitrary subspace ofJ, the maximum (A, )-controlled invariant contained in
. In linear system theory, this property can be used for a more direct theoretical and algorithmic approach to constrained controllability and disturbance rejection problems. 相似文献