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1.
We strengthen G. Rauzy’s characterization of normal sets by observing that the so-called elementary sets are precisely the Fσδ sets. This answers in the affirmative Rauzy’s open question: Are finite unions of normal sets necessarily normal? We also generalize the notion and characterization of normal sets from subsets of ? to subsets of ? d . This allows us to answer a question of E. Lesigne and M. Wierdl with the following construction: There exist two sequences of real numbersU=(u n ) nε?,V=(v n ) nε? such thatαU+βV=(αu n +βv n ) nε? is uniformly distributed mod 1 if and only if exactly one of the real numbers α, β vanishes. Additionally, we provide the ‘ultimate’ counter-example (stronger than that of H. G. Meijer and R. Sattler) to a conjecture of S. Uchiyama by constructing a sequence of integersU which is u.d. in ? (i.e. u.d. modk for allk ε ?), but such that for all realα, αU is not u.d. mod 1.  相似文献   

2.
We call A ? $ \mathbb{E} $ n cone independent of B ? $ \mathbb{E} $ n , the euclidean n-space, if no a = (a 1,..., a n ) ∈ A equals a linear combination of B \ {a} with non-negative coefficients. If A is cone independent of A we call A a cone independent set. We begin the analysis of this concept for the sets P(n) = {A ? {0, 1} n ? $ \mathbb{E} $ n : A is cone independent} and their maximal cardinalities c(n) ? max{|A| : AP(n)}. We show that lim n → ∞ $ \frac{{c\left( n \right)}}{{2^n }} $ > $\frac{1}{2}$ , but can't decide whether the limit equals 1. Furthermore, for integers 1 < k < ? ≤ n we prove first results about c n (k, ?) ? max{|A| : AP n (k, ?)}, where P n (k, ?) = {A : A ? V n k and V n ? is cone independent of A} and V n k equals the set of binary sequences of length n and Hamming weight k. Finding c n (k, ?) is in general a very hard problem with relations to finding Turan numbers.  相似文献   

3.
A family (V a k ) of summability methods, called generalized Valiron summability, is defined. The well-known summability methods (Bα,γ), (E ρ, (Tα), (S β) and (V a) are members of this family. In §3 some properties of the (B α,γ) and (V a k ) transforms are established. Following Satz II of Faulhaber (1956) it is proved that the members of the (V a k ) family are all equivalent for sequences of finite order. This paper is a good illustration of the use of generalized Boral summability. The following theorem is established: Theorem.If s n (n ≥ 0) isa real sequence satisfying $$\mathop {lim}\limits_{ \in \to 0 + } \mathop {lim inf}\limits_{m \to \infty } \mathop {min}\limits_{m \leqslant n \leqslant m \in \sqrt m } \left( {\frac{{S_n - S_m }}{{m^p }}} \right) \geqslant 0(\rho \geqslant 0)$$ , and if sns (V a k ) thens n → s (C, 2ρ).  相似文献   

4.
A successivity in a linear order is a pair of elements with no other elements between them. A recursive linear order with recursive successivities U is recursively categorical if every recursive linear order with recursive successivities isomorphic to U is in fact recursively isomorphic to U. We characterize those recursive linear orders with recursive successivities that are recursively categorical as precisely those with order type k1+g1+k2+g2+…+gn-1+kn where each kn is a finite order type, non-empty for i?{2,…,n-1} and each gi is an order type from among {ω,ω*,ω+ω*}∪{k·η:k<ω}.  相似文献   

5.
Consider random k-circulants A k,n with n????,k=k(n) and whose input sequence {a l } l??0 is independent with mean zero and variance one and $\sup_{n}n^{-1}\sum_{l=1}^{n}\mathbb{E}|a_{l}|^{2+\delta}<\infty$ for some ??>0. Under suitable restrictions on the sequence {k(n)} n??1, we show that the limiting spectral distribution (LSD) of the empirical distribution of suitably scaled eigenvalues exists, and we identify the limits. In particular, we prove the following: Suppose g??1 is fixed and p 1 is the smallest prime divisor of g. Suppose $P_{g}=\prod_{j=1}^{g}E_{j}$ where {E j }1??j??g are i.i.d. exponential random variables with mean one. (i) If k g =?1+sn where s=1 if g=1 and $s=o(n^{p_{1}-1})$ if g>1, then the empirical spectral distribution of n ?1/2 A k,n converges weakly in probability to $U_{1}P_{g}^{1/(2g)}$ where U 1 is uniformly distributed over the (2g)th roots of unity, independent of P g . (ii) If g??2 and k g =1+sn with $s=o(n^{p_{1}-1})$ , then the empirical spectral distribution of n ?1/2 A k,n converges weakly in probability to $U_{2}P_{g}^{1/(2g)}$ where U 2 is uniformly distributed over the unit circle in ?2, independent of P g . On the other hand, if k??2, k=n o(1) with gcd?(n,k)=1, and the input is i.i.d. standard normal variables, then $F_{n^{-1/2}A_{k,n}}$ converges weakly in probability to the uniform distribution over the circle with center at (0,0) and radius $r=\exp(\mathbb{E}[\log\sqrt{E}_{1}])$ .  相似文献   

6.
Let Ω ?C be an open set with simply connected components and suppose that the functionφ is holomorphic on Ω. We prove the existence of a sequence {φ (?n)} ofn-fold antiderivatives (i.e., we haveφ (0)(z)∶=φ(z) andφ (?n)(z)= (?n?1)(z)/dz for alln ∈ N0 and z ∈ Ω) such that the following properties hold:
  1. For any compact setB ?Ω with connected complement and any functionf that is continuous onB and holomorphic in its interior, there exists a sequence {n k} such that {φ?nk} converges tof uniformly onB.
  2. For any open setU ?Ω with simply connected components and any functionf that is holomorphic onU, there exists a sequence {m k} such that {φ?mk} converges tof compactly onU.
  3. For any measurable setE ?Ω and any functionf that is measurable onE, there exists a sequence {p k} such that {φ (-Pk)} converges tof almost everywhere onE.
  相似文献   

7.
A natural exponential family (NEF)F in ? n ,n>1, is said to be diagonal if there existn functions,a 1,...,a n , on some intervals of ?, such that the covariance matrixV F (m) ofF has diagonal (a 1(m 1),...,a n (m n )), for allm=(m 1,...,m n ) in the mean domain ofF. The familyF is also said to be irreducible if it is not the product of two independent NEFs in ? k and ? n-k , for somek=1,...,n?1. This paper shows that there are only six types of irreducible diagonal NEFs in ? n , that we call normal, Poisson, multinomial, negative multinomial, gamma, and hybrid. These types, with the exception of the latter two, correspond to distributions well established in the literature. This study is motivated by the following question: IfF is an NEF in ? n , under what conditions is its projectionp(F) in ? k , underp(x 1,...,x n )∶=(x 1,...,x k ),k=1,...,n?1, still an NEF in ? k ? The answer turns out to be rather predictable. It is the case if, and only if, the principalk×k submatrix ofV F (m 1,...,m n ) does not depend on (m k+1,...,m n ).  相似文献   

8.
Convergence of weighted sums of tight random elements {Vn} (in a separable Banach space) which have zero expected values and uniformly bounded rth moments (r > 1) is obtained. In particular, if {ank} is a Toeplitz sequence of real numbers, then | Σk=1ankf(Vk)| → 0 in probability for each continuous linear functional f if and only if 6Σk=1ankVk 6→ 0 in probability. When the random elements are independent and max1≤k≤n | ank | = O(n?8) for some 0 < 1s < r ? 1, then |Σk=1ankVk 6→ 0 with probability 1. These results yield laws of large numbers without assuming geometric conditions on the Banach space. Finally, these results can be extended to random elements in certain Fréchet spaces.  相似文献   

9.
We propose an answer to a question raised by F. Burstall: Is there any interesting theory of isothermic submanifolds of ? n of dimension greater than two? We call an n-immersion f(x) in ? m isothermic k if the normal bundle of f is flat and x is a line of curvature coordinate system such that its induced metric is of the form $\sum_{i=1}^{n} g_{ii}\,\mathrm{d} x_{i}^{2}$ with $\sum_{i=1}^{n} \epsilon_{i} g_{ii}=0$ , where ?? i =1 for 1??i??n?k and ?? i =?1 for n?k<i??n. A smooth map (f 1,??,f n ) from an open subset ${\mathcal{O}}$ of ? n to the space of m×n matrices is called an n-tuple of isothermic k n-submanifolds in ? m if each f i is an isothermic k immersion, $(f_{i})_{x_{j}}$ is parallel to $(f_{1})_{x_{j}}$ for all 1??i,j??n, and there exists an orthonormal frame (e 1,??,e n ) and a GL(n)-valued map (a ij ) such that $\mathrm{d}f_{i}= \sum_{j=1}^{n} a_{ij} e_{j}\,\mathrm {d} x_{j}$ for 1??i??n. Isothermic1 surfaces in ?3 are the classical isothermic surfaces in ?3. Isothermic k submanifolds in ? m are invariant under conformal transformations. We show that the equation for n-tuples of isothermic k n-submanifolds in ? m is the $\frac{O(m+n-k,k)}{O(m)\times O(n-k,k)}$ -system, which is an integrable system. Methods from soliton theory can therefore be used to construct Christoffel, Ribaucour, and Lie transforms, and to describe the moduli spaces of these geometric objects and their loop group symmetries.  相似文献   

10.
The local behavior of the iterates of a real polynomial is investigated. The fundamental result may be stated as follows: THEOREM. Let xi, for i=1, 2, ..., n+2, be defined recursively by xi+1=f(xi), where x1 is an arbitrary real number and f is a polynomial of degree n. Let xi+1?xi≧1 for i=1, ..., n + 1. Then for all i, 1 ≦i≦n, and all k, 1≦k≦n+1?i, $$ - \frac{{2^{k - 1} }}{{k!}}< f\left[ {x_1 ,... + x_{i + k} } \right]< \frac{{x_{i + k + 1} - x_{i + k} + 2^{k - 1} }}{{k!}},$$ where f[xi, ..., xi+k] denotes the Newton difference quotient. As a consequence of this theorem, the authors obtain information on the local behavior of the solutions of certain nonlinear difference equations. There are several cases, of which the following is typical: THEOREM. Let {xi}, i = 1, 2, 3, ..., be the solution of the nonlinear first order difference equation xi+1=f(xi) where x1 is an arbitrarily assigned real number and f is the polynomial \(f(x) = \sum\limits_{j = 0}^n {a_j x^j } ,n \geqq 2\) . Let δ be positive with δn?1=|2n?1/n!an|. Then, if n is even and an<0, there do not exist n + 1 consecutive increments Δxi=xi+1?xi in the solution {xi} with Δxi≧δ. The special case in which the iterated polynomial has integer coefficients leads to a “nice” upper bound on a generalization of the van der Waerden numbers. Ap k -sequence of length n is defined to be a strictly increasing sequence of positive integers {x 1, ...,x n } for which there exists a polynomial of degree at mostk with integer coefficients and satisfyingf(x j )=x j+1 forj=1, 2, ...,n?1. Definep k (n) to be the least positive integer such that if {1, 2, ...,p k (n)} is partitioned into two sets, then one of the two sets must contain ap k -sequence of lengthn. THEOREM. pn?2(n)≦(n!)(n?2)!/2.  相似文献   

11.
We examine a family of graphs called webs. For integers n ? 2 and k, 1 ? k ? 12n, the web W(n, k) has vertices Vn = {1, …, n} and edges {(i, j): j = i+k, …, i+n ? k, for i?Vn (sums mod n)}. A characterization is given for the vertex packing polyhedron of W(n, k) to contain a facet, none of whose projections is a facet for the lower dimensional vertex packing polyhedra of proper induced subgraphs of W(n, k). Simple necessary and sufficient conditions are given for W(n, k) to contain W(n′, k′) as an induced subgraph; these conditions are used to show that webs satisfy the Strong Perfect Graph Conjecture. Complements of webs are also studied and it is shown that if both a graph and its complement are webs, then the graph is either an odd hole or its complement.  相似文献   

12.
Let K n h = (V, ( h V )) be the complete h-uniform hypergraph on vertex set V with ¦V¦ = n. Baranyai showed that K n h can be expressed as the union of edge-disjoint r-regular factors if and only if h divides rn and r divides \((_{h - 1}^{n - 1} )\) . Using a new proof technique, in this paper we prove that λK n h can be expressed as the union \(\mathcal{G}_1 \cup ... \cup \mathcal{G}_k \) of k edge-disjoint factors, where for 1≤ik, \(\mathcal{G}_i \) is r i -regular, if and only if (i) h divides r i n for 1≤ik, and (ii) \(\sum\nolimits_{i = 1}^k {r_i = \lambda (_{h - 1}^{n - 1} )} \) . Moreover, for any i (1≤ik) for which r i ≥2, this new technique allows us to guarantee that \(\mathcal{G}_i \) is connected, generalizing Baranyai’s theorem, and answering a question by Katona.  相似文献   

13.
Let U be a UHF-algebra of Glimm type n, and {αg: g?G} a strongly continuous group of 1-automorphisms of product type on U, for G compact. Let Uα be the C1-subalgebra of fixed elements of U. We show that any extremal normalized trace on Uα arises as the restriction of a symmetric product state ? on U of the form ? = ?k?1 ω. As an example we classify the extremal traces on Uα for the case G = SU(n), αg = ?k ? 1 Ad(g).  相似文献   

14.
The paper gives a new interpretation and a possible optimization of the wellknown k-means algorithm for searching for a locally optimal partition of the set A = {a i ∈ ? n : i = 1, …, m} which consists of k disjoint nonempty subsets π1, …, π k , 1 ? k ? m. For this purpose, a new divided k-means algorithm was constructed as a limit case of the known smoothed k-means algorithm. It is shown that the algorithm constructed in this way coincides with the k-means algorithm if during the iterative procedure no data points appear in the Voronoi diagram. If in the partition obtained by applying the divided k-means algorithm there are data points lying in the Voronoi diagram, it is shown that the obtained result can be improved further.  相似文献   

15.
For Pm ∈ ?[z1, …, zn], homogeneous of degree m we investigate when the graph of Pm in ?n+1 satisfies the Phragmén-Lindelöf condition PL(?n+1, log), or equivalently, when the operator $i{\partial \over \partial_{x_{n+1}}}+P_{m}(D)$ admits a continuous solution operator on C(?n+1). This is shown to happen if the varieties V+- ? {z ∈ ?n: Pm(z) = ±1} satisfy the following Phragmén-Lindelöf condition (SPL): There exists A ≥ 1 such that each plurisubharmonic function u on V+- satisfying u(z) ≤ ¦z¦+ o(¦z¦) on V+- and u(x) ≤ 0 on V+- ∩ ?n also satisfies u(z) Im on V+-. Necessary as well as sufficient conditions for V+- to satisfy (SPL) are derived and several examples are given.  相似文献   

16.
A topological space is called paranormal if any countable discrete system of closed sets {Dn:n = 1, 2, 3,...} can be expanded to a locally finite system of open sets {Un:n = 1, 2, 3,...}, i.e., Dn is contained in Un for all n, and DmUn≠ Ø if and only if Dm = Dn. It is proved that if X is a countably compact space whose cube is hereditarily paranormal, then X is metrizable.  相似文献   

17.
Given a non-singular quadratic form q of maximal Witt index on $V := V(2n+1,\mathbb{F})$ , let Δ be the building of type B n formed by the subspaces of V totally singular for q and, for 1≤kn, let Δ k be the k-grassmannian of Δ. Let ε k be the embedding of Δ k into PG(? k V) mapping every point 〈v 1,v 2,…,v k 〉 of Δ k to the point 〈v 1v 2∧?∧v k 〉 of PG(? k V). It is known that if $\mathrm{char}(\mathbb{F})\neq2$ then $\mathrm{dim}(\varepsilon_{k})={{2n+1}\choose k}$ . In this paper we give a new very easy proof of this fact. We also prove that if $\mathrm{char}(\mathbb{F}) = 2$ then $\mathrm{dim}(\varepsilon_{k})={{2n+1}\choose k}-{{2n+1}\choose{k-2}}$ . As a consequence, when 1<k<n and $\mathrm{char}(\mathbb{F}) = 2$ the embedding ε k is not universal. Finally, we prove that if $\mathbb{F}$ is a perfect field of characteristic p>2 or a number field, n>k and k=2 or 3, then ε k is universal.  相似文献   

18.
An unbounded 1-derivation δ on a C1-algebra U is called approximately bounded if there is an increasing sequence of full matrix subalgebras {Un} whose union is dense in the domain of U and a sequence {hn} of self-adjoint elements of U such that hn implements δ on Un for every n, and {∥hn ? Qn(hn)∥} is a bounded sequence where Qn is the canonical conditional expectation of U onto Un. We prove that a quasi-free derivation on the Canonical Anticommutation Relation algebra is approximately bounded if the self-adjoint operator from which it arises is of finite multiplicity and bounded. We conjecture that all quasi-free derivations are approximately bounded. We also prove that a quasi-free derivation is bounded if and only if the self-adjoint operator from which it arises is of the trace class.  相似文献   

19.
Let ? n be a linear hyperplane arrangement in ? n . We define two corresponding posetsG k (? n andV k (? n ) of oriented matroids, which approximate the GrassmannianG k (? n ) and the Stiefel manifoldV k (? n ). The basic conjectures are that the “OM-Grassmannian”G k (? n ) has the homotopy type ofG k (? n ), and that the “OM-Stiefel bundle” Δπ: ΔV k (? n ) → ΔG k (? n ) is a surjective map. These conjectures can be proved in some cases: we survey the known results and add some new ones. The conjectures fail if they are generalized to nonrealizable oriented matroids ? n .  相似文献   

20.
The Hirzebruch functional equation is \(\sum\nolimits_{i = 1}^n {\prod\nolimits_{j \ne i} {(1/f({z_j} - {z_i})) = c} } \) with constant c and initial conditions f(0) = 0 and f'(0) = 1. In this paper we find all solutions of the Hirzebruch functional equation for n ≤ 6 in the class of meromorphic functions and in the class of series. Previously, such results have been known only for n ≤ 4. The Todd function is the function determining the two-parameter Todd genus (i.e., the χa,b-genus). It gives a solution to the Hirzebruch functional equation for any n. The elliptic function of level N is the function determining the elliptic genus of level N. It gives a solution to the Hirzebruch functional equation for n divisible by N. A series corresponding to a meromorphic function f with parameters in U ? ?k is a series with parameters in the Zariski closure of U in ?k, such that for the parameters in U it coincides with the series expansion at zero of f. The main results are as follows: (1) Any series solution of the Hirzebruch functional equation for n = 5 corresponds either to the Todd function or to the elliptic function of level 5. (2) Any series solution of the Hirzebruch functional equation for n = 6 corresponds either to the Todd function or to the elliptic function of level 2, 3, or 6. This gives a complete classification of complex genera that are fiber multiplicative with respect to ?Pn?1 for n ≤ 6. A topological application of this study is an effective calculation of the coefficients of elliptic genera of level N for N = 2,..., 6 in terms of solutions of a differential equation with parameters in an irreducible algebraic variety in ?4.  相似文献   

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