共查询到20条相似文献,搜索用时 31 毫秒
1.
Daniel J. Rudolph 《Israel Journal of Mathematics》1978,30(3):255-263
LetT acting on (Ω, ℱ, μ) be afinite entropy Bernoulli shift. AT invariant factor
is “relatively finite” if a.e. fiber of
has a finite, hence constantk, number of points. We say two factors
, “sit the same” if there is a measurable measure preserving map ϕ with
and
. We show here that up to sitting the same there are only finitely many relatively finite factors withk point fibers in a Bernoulli shift, and that they are classified by a certain algebraic structure in the symmetric group onk-points.
This work was supported in part by the Miller Institute for Basic Research, U. C. Berkeley. 相似文献
2.
K. R. Apt 《Israel Journal of Mathematics》1978,29(2-3):221-238
The connections between inductive definability and models of comprehension are studied. Let
= 〈A, R
l, ...,R
n 〉 be an infinite structure and letI
φ
be a set inductively defined by a formulaφ of the second order language
. We prove that if
is a model of Δ
1
1
-Comprehension relativized toφ, andφ is
-absolute, then for everyη smaller than the height of
(h(
)),I
φ
is in
. If
is aβ-structure which satisfies Σ
1
1
-Comprehension relativized toφ and WF(X), and φ is
-absolute, thenI
φ
is in
and ‖φ| <h (
). These results imply that Barwise-Grilliot theorem is false in the case of uncountable acceptable structures. We also study
the notion of invariant definability over models1 of Δ
1
1
-Comprehension.
This paper is registered as Report ZW 69/76 of the Mathematical Centre. 相似文献
3.
Evgeni Ja. Gabovič 《Semigroup Forum》1972,4(1):335-340
A semigroup S is calledE-semigroup (
-semigroup) if every (finitely generated) subsemigroup of S is an endomorphic image of S and Ē-semigroup (
-semigroup) if every subsemigroup of S is an E-semigroup
-semigroup. All classes X ε {Ē,
, E,
} are distinct even in the case of semilattices. It is established when a free band (semilattice) is an X-semigroup.
-,
- and Ē-chains and E-chains with identity or zero, Ē-and
, X-bands with identity and X-semigroups with identity and zero are found. 相似文献
4.
For an arbitrary uniformly continuous completely positive semigroup (
t
:t0) on the space of bounded operators on a Hilbert space, we construct a family (U(t)t0) of unitary operators on a Hilbert space and a conditional expectation from to, such that, for arbitraryt0,. The unitary operatorsU(t) satisfy a stochastic differential equation involving a noncommutative generalisation of infinite dimensional Brownian motion. They do not form a semigroup.Part of this work was completed when the first author was visiting research associate at the Center for Relativity, Physics Department, The University of Texas at Austin, Austin, TX 78712, U.S.A., supported in part by NSF PHY 81-01381. 相似文献
5.
R. Schneider 《Discrete and Computational Geometry》1995,13(1):609-627
Let
be an infinite discrete system ofk-dimensional flats inn-dimensional Euclidean space. If the totalk-dimensional volume of the flats in
intersected with the ball of center 0 and radiusr, divided by the volume of that ball, tends to a limit forr→∞, then this limit is called thedensity of
. We consider isoperimetric problems of the following kind. If
is a hyperplane system of positive density, find sharp upper bounds for the density of the system ofk-flats (k∈{0, ...,n−2}) that are generated as intersections of hyperplanes in
. Ideas from the theory of uniform distribution of sequences are employed to define a large class of hyperplane systems, calleduniform, for which all necessary densities exist, isperimetric inequalities can be proved, and systems with extremal intersection
densities can be characterized. 相似文献
6.
Let
be a family of two-valued functions defined on ann-element set in which each pair of functions in
satisfy a given intersection condition. For certain intersection conditions we determine the maximal value of
. 相似文献
7.
E. Steingrímsson 《Discrete and Computational Geometry》1994,12(1):465-479
The 2-weak vertex-packing polytope of a loopless graphG withd vertices is the subset of the unitd-cube satisfyingx
i
+x
j
≤1 for every edge (i,j) ofG. The dilation by 2 of this polytope is a polytope
with integral vertices. We triangulate
with lattice simplices of minimal volume and label the maximal simplices with elements of the hyperoctahedral groupB
d
. This labeling gives rise to a shelling of the triangulation
of
, where theh-vector of
(and the Ehrharth
*-vector of
can be computed as a descent statistic on a subset ofB
d
defined in terms ofG. A recursive way of computing theh-vector of
is also given, and a recursive formula for the volume of
.
This work was partially supported by grants from the Icelandic Council of Science and the Royal Swedish Academy of Sciences,
respectively. 相似文献
8.
Lars Hörmander 《Israel Journal of Mathematics》1973,16(1):103-116
Two extensions of a classical theorem of Rellich are proved: (1) LetP=P(−iϖ/ϖx) be a partial differential operator with constant coefficients in
, let the manifolds contained in
have codimension ≧k>0, and denote by Γ an open cone in
intersecting each normal plane of every such manifold. If
,Pu=0 and
it follows thatu=0. (2) Assume in addition that each irreducibe lfactor ofP van shes on a real hypersurface and that Γ contains both normal directions at some such point. If
andP(D) u has compact support, the same condition withk=1 implies thatu has compact support. In both results the hypotheses on the cone Γ and on the operatorP are minimal. 相似文献
9.
This paper introduces the concept of ‘symmetric centres’ of braided monoidal categories. LetH be a Hopf algebra with bijective antipode over a fieldk. We address the symmetric centre of the Yetter-Drinfel’d module category:
and show that a left Yetter-Drinfel’d moduleM belongs to the symmetric centre of
and only ifM is trivial. We also study the symmetric centres of categories of representations of quasitriangular Hopf algebras and give
a sufficient and necessary condition for the braid of,
Hℳ to induce the braid of
, or equivalently, the braid of
, whereA is a quantum commutativeH-module algebra 相似文献
10.
It
and
are two families of pairwise disjoint simple closed curves in the plane such that each curve in
intersects each curve in
, then the total number of points of intersection in
is at least 2(m−1)n, where
, and this bound is best possible. We use this to show that the cartesian product of two 5-cycles has crossing number 15. 相似文献
11.
Geoffrey S. Watson 《Annals of the Institute of Statistical Mathematics》1983,35(1):303-319
Summary A distribution on the unit sphere inℝ
q
with a densityf(‖x
v
‖) is considered where
is ans(<q) dimensional subspace andx
v
is the part ofx in
. For a large sample the estimation of
, a test that
and a test for rotational symmetry within
is given. For several samples with possibly different subspaces
but the samef, a test that
is given. For all tests power functions for contiguous alternatives are given. For the special density proportional to expk‖x
v
‖
2, additional results are given.
Research supported in part by a Contract with the Office of Naval Research N00014-81-K-0146 awarded to Princeton University,
Princeton, New Jersey 08544. 相似文献
12.
Satoru Fujishige 《Mathematical Programming》1984,29(2):125-141
The present paper shows that for any submodular functionf on a crossing family
with
, if the polyhedron
is nonempty, then there exist a unique distributive lattice
with
and a unique submodular function
with
such thatB(f) coincides with the base polyhedron
associated with the submodular system
. Here, iff is integer-valued, thenf
1 is also integer-valued.
Based on this fact, we also show the relationship between the independent-flow problem considered by the author and the minimum
cost flow problem considered by J. Edmonds and R. Giles. 相似文献
13.
Le Tu Quoc Thang 《Discrete and Computational Geometry》1995,14(1):31-70
The existence of different kinds of local rules is established for many sets of pentagonal quasi-crystal tilings. For eacht∈ℝ there is a set
of pentagonal tilings of the same local isomorphism class; the caset=0 corresponds to the Penrose tilings. It is proved that the set
admits a local rule which does not involve any colorings (or markings, decorations) if and only ift=m+nτ. In other words, this set of tilings is totally characterized by patches of some finite radius, orr-maps. When
the set
admits a local rule which involvescolorings. For the set of Penrose tilings the construction here leads exactly to the Penrose matching rules. Local rules for the caset=1/2 are presented. 相似文献
14.
Nondas E. Kechagias 《manuscripta mathematica》1994,84(1):261-290
Given an increasing sequence of integersN=(0,n
1,n
2,...), a functorG
N
is constructed from the category
of based spaces of the homotopy type ofCW compleces and based maps to a subcategory
of
in analogy to May's approximation modelC. A family of homology operationsRN is associated toG
N
and its algebraic structure is described in terms of modular coinvariants of parabolic subgroups. 相似文献
15.
J. A. S. Martins 《Annali di Matematica Pura ed Applicata》1977,115(1):271-294
Summary Piecewise polynomial and Fourier approximation of functions in the Sobolev spaces
on unbounded domains Θ ⊂ Rn are applied to the study of the type of compact embeddings into appropriate Lebesgue and Orlicz spaces. It is shown that
if Θ and s satisfy certain conditions, the embeddings
, m/n+1/q−1/p>0 and
, Φ being an Orlicz function subordinate to both φ(t)=|t|p
exp |t|n/(n−m) and Φσ(t)=exp |t|σ−1, σ ⩾ 1, m/n>1/p, are of type ls. One result dealing with multiplications maps from
into Lq(Θ) is also obtained.
Entrata in Redazione il 14 ottobre 1976. 相似文献
16.
Automatic groups were introduced in connection with geometric problems, in particular with the study of fundamental groups
of 3-manifolds. In this article the class of automatic groups is extended to include the fundamental group of every compact
3-manifold which satisfies Thurston's geometrization conjecture. Toward this end, the class
of asynchronously
groups is introduced and studied, where
is an arbitrary full abstract family of languages. For example
may be the family of regular languagesReg, context-free languagesCF, or indexed languagesInd. The class
consists of precisely those groups which are asynchronously automatic. It is proved that
contains all of the above fundamental groups, but that
does not. Indeed a virtually nilpotent group belongs to
if and only if it is virtually abelian.
The first author was partially supported by NSF grant DMS-9203500 and FNRS (Suisse). He also wishes to thank the University
of Geneva for its hospitality while this paper was being written. The second author thanks the Institute for Advanced Study
for its hospitality while this paper was being written. 相似文献
17.
Given a self-concordant barrier function for a convex set
, we determine a self-concordant barrier function for the conic hull
of
. As our main result, we derive an “optimal” barrier for
based on the barrier function for
. Important applications of this result include the conic reformulation of a convex problem, and the solution of fractional
programs by interior-point methods. The problem of minimizing a convex-concave fraction over some convex set can be solved
by applying an interior-point method directly to the original nonconvex problem, or by applying an interior-point method to
an equivalent convex reformulation of the original problem. Our main result allows to analyze the second approach showing
that the rate of convergence is of the same order in both cases. 相似文献
18.
Gil Kalai 《Israel Journal of Mathematics》1983,45(4):337-351
Let
(n, k) be the class of all simplicial complexesC over a fixed set ofn vertices (2≦k≦n) such that: (1)C has a complete (k−1)-skeleton, (2)C has precisely (
k
n−1
)k-faces, (3)H
k
(C)=0. We prove that for
,H
k−1(C) is a finite group, and our main result is:
. This formula extends to high dimensions Cayley’s formula for the number of trees onn labelled vertices. Its proof is based on a generalization of the matrix tree theorem. 相似文献
19.
William M. Kantor 《Israel Journal of Mathematics》1976,23(1):8-18
Generalized quadrangles
are studied in whichs ort is prime and Aut
has rank 3 on points.
This research was supported in part by NSF grant GP 37982X. 相似文献
20.
Takaaki Nomura 《Annals of Global Analysis and Geometry》1994,12(1):237-260
We study the set of rankp idempotents in a topologically simple Hilbert Jordan algebra (JH-algebra for short). To produce the differential geometric structure on, we establish Jordan algebraic results concerning the structure of some two-generator subalgebras. We identify geodesics, the Riemannian distance and the sectional curvature of by using the Jordan algebraic structure. 相似文献