Disjoint skolem sequences and related disjoint structures

A Skolem sequence of order n is a sequence S = (s₁, s₂…, s²ⁿ) of 2n integers satisfying the following conditions: (1) for every k ∈ {1, 2,… n} there exist exactly two elements s_i,S_j such that S_i = S_j = k; (2) If s_i = s_j = k,i < j then j ? i = k. In this article we show the existence of disjoint Skolem, disjoint hooked Skolem, and disjoint near-Skolem sequences. Then we apply these concepts to the existence problems of disjoint cyclic Steiner and Mendelsohn triple systems and the existence of disjoint 1-covering designs. © 1993 John Wiley & Sons, Inc.     

Some new bounds and values for van der Waerden-like numbers

Numbers similar to those of van der Waerden are studied. We consider increasing sequences of positive integers {x ₁,x ₂,...,x _n } that either form an arithmetic progression or for which there exists a polynomialf with integer coefficients and degree exactlyn – 2, andx _j+1 =f(x _j ). We denote byq(n, k) the least positive integer such that if {1, 2,...,q(n, k)} is partitioned intok classes, then some class must contain a sequence of the type just described. Upper bounds are obtained forq(n, 3), q(n, 4), q(3, k), andq(4, k). A table of several values is also given.     

The Embedding Theorem for Cantor Varieties

Let m and n be fixed integers, with 1 m < n. A Cantor variety C _m,n is a variety of algebras with m n-ary and n m-ary basic operations which is defined in a signature ={g₁,...,g_m,f₁,...,f_n} by the identities f_ig₁x₁,...,x_n),...,g_mx₁,...,x_n) = x_i, _i=1,...,n, g_jf₁x₁,...,x_m),...,f_nx₁,...,x_m)) = x_j, _j=1,...,m. We prove the following: (a) every partial C _m,n-algebra A is isomorphically embeddable in the algebra G= A; S(A) of C _m,n; (b) for every finitely presented algebra G= A; S in C _m,n, the word problem is decidable; (c) for finitely presented algebras in _{C m}, the occurrence problem is decidable; (d) _{C m,n} has a hereditarily undecidable elementary theory.     

Dimensional results for Cartesian products of homogeneous Moran sets

M(J, {m _s * n _s }, {c _s }) be the collection of Cartesian products of two homogenous Moran sets with the same ratios {c _s } where J = [0, 1]×[0, 1]. Then the maximal and minimal values of the Hausdorff dimensions for the elements in M are obtained without any restriction on {m _s n _s } or {c _s }.     

On Hong’s conjecture for power LCM matrices

A set S={x ₁,...,x _n } of n distinct positive integers is said to be gcd-closed if (x _i , x _j ) ∈ S for all 1 ⩽ i, j ⩽ n. Shaofang Hong conjectured in 2002 that for a given positive integer t there is a positive integer k(t) depending only on t, such that if n ⩽ k(t), then the power LCM matrix ([x _i , x _j ] ^t ) defined on any gcd-closed set S={x ₁,...,x _n } is nonsingular, but for n ⩾ k(t) + 1, there exists a gcd-closed set S={x ₁,...,x _n } such that the power LCM matrix ([x _i , x _j ] ^t ) on S is singular. In 1996, Hong proved k(1) = 7 and noted k(t) ⩾ 7 for all t ⩾ 2. This paper develops Hong’s method and provides a new idea to calculate the determinant of the LCM matrix on a gcd-closed set and proves that k(t) ⩾ 8 for all t ⩾ 2. We further prove that k(t) ⩾ 9 iff a special Diophantine equation, which we call the LCM equation, has no t-th power solution and conjecture that k(t) = 8 for all t ⩾ 2, namely, the LCM equation has t-th power solution for all t ⩾ 2.     

The minimum diameter of orientations of complete multipartite graphs

Given a graphG, letB be the family of strong orientations ofG, and define A pair {p,q} of integers is called aco-pair if 1 p q . A multiset {p, q, r} of positive integers is called aco-triple if {p, q} and {p, r} are co-pairs. LetK(p₁, p₂,..., p_n) denote the completen-partite graph havingp _i vertices in theith partite set.In this paper, we show that if {p ₁, p₂,...,p_n} can be partitioned into co-pairs whenn is even, and into co-pairs and a co-triple whenn is odd, then(K(p₁, p₂,..., p_n)) = 2 provided that (n,p ₁, p₂, p₃, p₄) (4, 1, 1, 1, 1). This substantially extends a result of Gutin [3] and a result of Koh and Tan [4].     

Density Modulo 1 of Sublacunary Sequences

We prove the existence of real numbers badly approximated by rational fractions whose denominators form a sublacunar sequence. For example, for the ascending sequence s _n , n = 1, 2, 3, ..., generated by the ordered numbers of the form 2ⁱ3^j, i, j = 1, 2, 3, ..., we prove that the set of real numbers α such that inf _n∈ℕ n‖s _n α‖ > 0 is a set of Hausdorff dimension 1. The divergence of the series implies that the Lebesgue measure of those numbers is zero.__________Translated from Matematicheskie Zametki, vol. 77, no. 6, 2005, pp. 803–813.Original Russian Text Copyright ©2005 by R. K. Akhunzhanov, N. G. Moshchevitin.     

White noise eliminates instability

Let x₁,..., x_n be points in the d-dimensional Euclidean space E^d with || x_i-x_j|| ￡ 1\| x_{i}-x_{j}\| \le 1 for all 1 \leqq i,j \leqq n1 \leqq i,j \leqq n, where || .||\| .\| denotes the Euclidean norm. We ask for the maximum M(d,n) of \mathop?_i, j=1ⁿ|| x_i-x_j|| ²\textstyle\mathop\sum\limits _{i,\,j=1}^{n}\| x_{i}-x_{j}\| ^{2} (see [4]). This paper deals with the case d = 2. We calculate M(2, n) and show that the value M(2, n) is attained if and only if the points are distributed as evenly as possible among the vertices of a regular triangle of edge-length 1. Moreover we give an upper bound for the value \mathop?_i, j=1ⁿ|| x_i-x_j|| \textstyle\mathop\sum\limits _{i,\,j=1}^{n}\| x_{i}-x_{j}\| , where the points x₁,...,x_n are chosen under the same constraints as above.     

Marcinkiewicz multiplier theorem for the Weyl functional calculus

Let {X _j , Y _j , T : 1 ≤ j ≤ n} be a basis satisfying the commutation relation for the Heisenberg Lie algebra . Then we obtain a multi-parameter Marcinkiewicz multiplier theorem for the operator defined by m(X ₁,..., X _n , Y ₁,..., Y _n , T).     

Solution of generalized bisymmetry type equations without surjectivity assumptions

Summary. The solution of the rectangular m ×n m \times n generalized bisymmetry equation¶¶F(G₁(x₁₁,...,x_1n),..., G_m(x_m1,...,x_mn))     =     G(F₁(x₁₁,..., x_m1),...,  F_n(x_1n,...,x_mn) ) F\bigl(G_1(x_{11},\dots,x_{1n}),\dots,\ G_m(x_{m1},\dots,x_{mn})\bigr) \quad = \quad G\bigl(F_1(x_{11},\dots, x_{m1}),\dots, \ F_n(x_{1n},\dots,x_{mn}) \bigr) (A)¶is presented assuming that the functions F, G_j, G and F_i (j = 1, ... , m , i = 1, ... , n , m S 2, n S 2) are real valued and defined on the Cartesian product of real intervals, and they are continuous and strictly monotonic in each real variable. Equation (A) is reduced to some special bisymmetry type equations by using induction methods. No surjectivity assumptions are made.     

LEGENDRE TRANSFORMATIONS AND CARTAN FORMS IN THE CALCULUS OF VARIATIONS OF MULTIPLE INTEGRALS

ABSTRACT

(PART I): A field-theoretic treatment of variational problems in n independent variables {x^j} and N dependent variables {ψ^A)} is presented that differs substantially from the standard field theories, such as those of Carathéodory [4] and Weyl [10], inasmuch as it is not stipulated ab initio that the Lagrangian be everywhere positive. This is accomplished by the systematic use of a canonical formalism. Since the latter must necessarily be prescribed by appropriate Legendre transformations, the construction of such transformations is the central theme of Part I.—The underlying manifold is M = M_n x M_N, where M_n, M_N are manifolds with local coordinates {x^j}, {ψ^A}, respectively. The basic ingredient of the theory consists of a pair of complementary distributions D_n, D_N on M that are defined respectively by the characteristic subspaces in the tangent spaces of M of two sets of smooth 1-forms {π^A:A = 1,…, N}, {π^j = 1,…, n} on M. For a given local coordinate system on M the planes of 4, have unique (adapted) basis elements B_j = (?/?_x ^j) + B^A _j (?/?ψ^A), whose coefficients B^A _j will assume the role of derivatives such as ?ψ^A/?x^j in the final analysis of Part II. The first step toward a Legendre transformation is a stipulation that prescribes B^A _j as a function of the components {π^j _h,π^j _A} of {π^j}—these components being ultimately the canonical Variables—in such a manner that B^A _j is unaffected by the action of any unimodular transformation applied to the exterior system {π^j}. A function H of the canonical variables is said to be an acceptable Hamiltonian if it satisfies a similar invariance requirement, together with a determinantal condition that involves its Hessian with respect to π^j _A. The second part of the Legendre transformation consists of the identification in terms of H and the canonical variables of a function L that depends solely on B^A _j and the coordinates on M. This identification imposes a condition on the Hessian of L with respect to B^A _j. Conversely, any function L that satisfies these requirements is an acceptable Lagrangian, whose Hamiltonian is uniquely determined by the general construction.     

Resolvability in circulant graphs

A set W of the vertices of a connected graph G is called a resolving set for G if for every two distinct vertices u, v ∈ V (G) there is a vertex w ∈ W such that d(u, w) ≠ d(v, w). A resolving set of minimum cardinality is called a metric basis for G and the number of vertices in a metric basis is called the metric dimension of G, denoted by dim(G). For a vertex u of G and a subset S of V (G), the distance between u and S is the number min s∈S d(u, s). A k-partition Π = {S 1 , S 2 , . . . , S k } of V (G) is called a resolving partition if for every two distinct vertices u, v ∈ V (G) there is a set S i in Π such that d(u, Si )≠ d(v, Si ). The minimum k for which there is a resolving k-partition of V (G) is called the partition dimension of G, denoted by pd(G). The circulant graph is a graph with vertex set Zn , an additive group of integers modulo n, and two vertices labeled i and j adjacent if and only if i-j (mod n) ∈ C , where CZn has the property that C =-C and 0 ■ C. The circulant graph is denoted by Xn, Δ where Δ = |C|. In this paper, we study the metric dimension of a family of circulant graphs Xn, 3 with connection set C = {1, n/2 , n-1} and prove that dim(Xn, 3 ) is independent of choice of n by showing that dim(Xn, 3 ) ={3 for all n ≡ 0 (mod 4), 4 for all n ≡ 2 (mod 4). We also study the partition dimension of a family of circulant graphs Xn,4 with connection set C = {±1, ±2} and prove that pd(Xn, 4 ) is independent of choice of n and show that pd(X5,4 ) = 5 and pd(Xn,4 ) ={3 for all odd n ≥ 9, 4 for all even n ≥ 6 and n = 7.     

A determinantal description of GCD-closed sets and k-sets

Let S={x ₁,x ₂,…,x_n } be a naturally ordered set of distinct positive integers. S is called a k-set if k= gcd(x_i ,x_j ) for x_i ≠x_j any in S. In this paper k-sets are characterized by certain conditions on the determinants of some matrices associated with S.     

Banded perturbations of the unit vector basis in some sequence spaces

Perturbations of the unit vector basis of the formX _n =Σ_|j−n|≦m a _nj e _j wherem is a fixed positive integer are investigated. It is shown that if |a _nj |≦1 and if {x _n } possesses a biorthogonal sequence uniformly bounded inl _p for some 1<=p<∞, then {x _n } is a seminormalized basic sequence in some reflexive Orlicz spacel _N, then {x_n} is equivalent to {e _n} inl _N.     

Matrices associated with arithmetical functions

Let f be an arithmetical function and S={x ₁,x ₂,…,x_n } a set of distinct positive integers. Denote by [f(x_i ,x_j }] the n×n matrix having f evaluated at the greatest common divisor (x_i ,x_j ) of x_i , and x_j as its i j-entry. We will determine conditions on f that will guarantee the matrix [f(x_i ,x_j )] is positive definite and, in fact, has properties similar to the greatest common divisor (GCD) matrix

[(x_i ,x_j )] where f is the identity function. The set S is gcd-closed if (x_i ,x_j )∈S for 1≤ i j ≤ n. If S is gcd-closed, we calculate the determinant and (if it is invertible) the inverse of the matrix [f(x_i ,x_j )]. Among the examples of determinants of this kind are H. J. S. Smith's determinant det[(i,j)].     

Perpendicular Rectangular Latin Arrays

A set {A ₁, A ₂,..., A _t } of rectangular arrays, each defined on a symbol set X, is said to be t-perpendicular if each t-element subset of X occurs precisely once when the arrays are superimposed. We investigate the existence of sets of r by s rectangular arrays which are row-Latin, column-Latin and t-perpendicular. For example, we show that for all odd n, there exists a pair of row- and column-Latin 2-perpendicular r by s arrays with symbol set X of size n if and only if and r, s ≤ n.     

非对称Cantor集的Hausdorff中心测度

§ 1　 IntroductionThe class of Cantor sets is a typical one of sets in fractal geometry.Mathematicianshave paid their attentions to such sets for a long time.Itis well known that the Hausdorffmeasure of the Cantor middle- third set is1(see[1]) .Recently,Feng[3] obtained the exactvalues of the packing measure for a class of linear Cantor sets.Using Feng s method,Zhuand Zhou[5] obtained the exactvalue of Hausdorff centred measure of the symmetry Cantorsets.In this papar,we consider the Ha…     

Determinants of Matrices Associated with Incidence Functions on Posets

Let S = x ₁,...,x _n} be a finite subset of a partially ordered set P. Let f be an incidence function of P. Let denote the n × n matrix having f evaluated at the meet of x _i and x _j as its i, j-entry and denote the n × n matrix having f evaluated at the join of x _i and x _j as its i, j-entry. The set S is said to be meet-closed if for all 1 i, j n. In this paper we get explicit combinatorial formulas for the determinants of matrices and on any meet-closed set S. We also obtain necessary and sufficient conditions for the matrices and on any meet-closed set S to be nonsingular. Finally, we give some number-theoretic applications.     

Extended skolem sequences

A k-extended Skolem sequence of order n is an integer sequence (s₁, s₂,…, s_2n+1) in which s_k = 0 and for each j ? {1,…,n}, there exists a unique i ? {1,…, 2n} such that s_i = s_i+j = j. We show that such a sequence exists if and only if either 1) k is odd and n ≡ 0 or 1 (mod 4) or (2) k is even and n ≡ 2 or 3 (mod 4). The same conditions are also shown to be necessary and sufficient for the existence of excess Skolem sequences. Finally, we use extended Skolem sequences to construct maximal cyclic partial triple systems. © 1995 John Wiley & Sons, Inc.     

Diophantine inequalities with mixed powers

Let {λ_i}_{i = 1}^s (s ≥ 2) be a finite sequence of non-zero real numbers, not all of the same sign and in which not all the ratios $\text{λ}{}_{\mathrm{i}}\text{λ}{}_{\mathrm{j}}$ are rational. A given sequence of positive integers {n_i}_{i = 1}^s is said to have property (P) (($\text{P}{}^1$) respectively) if for any {λ_i}_{i = 1}^s and any real number η, there exists a positive constant σ, depending on {λ_i}_{i = 1}^s and {n_i}_{i = 1}^s only, so that the inequality |η + Σ_{i = 1}^sλ_ix_iⁿⁱ| < (max x_i)^?σ has infinitely many solutions in positive integers (primes respectively) x₁, x₂,…, x_s. In this paper, we prove the following result: Given a sequence of positive integers {n_i}_{i = 1}^∞, a necessary and sufficient condition that, for any positive integer j, there exists an integer s, depending on {n_i}_{i = j}^∞ only, such that {n_i}_{i = j}^{j + s ? 1} has property (P) (or ($\text{P}{}^1$)), is that Σ_{i = 1}^∞n_i^?1 = ∞. These are parallel to some striking results of G. A. Fre?man, E. J. Scourfield and K. Thanigasalam.