On Lelong-Bremermann Lemma

The main theorem of this note is the following refinement of the well-known Lelong-Bremermann Lemma:

Let be a continuous plurisubharmonic function on a Stein manifold of dimension Then there exists an integer , natural numbers , and analytic mappings such that the sequence of functions

converges to uniformly on each compact subset of .

In the case when is a domain in the complex plane, it is shown that one can take in the theorem above (Section 3); on the other hand, for -circular plurisubharmonic functions in the statement of this theorem is true with (Section 4). The last section contains some remarks and open questions.

     

Cohen-Macaulay Properties of Thom-Boardman Strata II: The Defining Ideals of {Sigma}i, j

We consider the Zariski closure of Thom–Boardman strata^{i, j} in the jet space for map-germs (Cⁿ, 0) (C^p, 0). We applythe geometric technique of calculating syzygies to the desingularizationof ^{i, j} constructed by Ronga. We investigate when the normalizationof the coordinate ring of ^{i, j} is rational in the cases i =n – p + 1 or i = j = 1. We also consider when these coordinaterings are normal with rational singularities. 2000 MathematicsSubject Classification 13D02, 14B05, 14M05, 14M12, 58C25 (primary),58K20 (secondary).     

Rado Partition Theorem for Random Subsets of Integers

For an l x k matrix A = (a_ij) of integers, denote by L(A) thesystem of homogenous linear equations a_i1x₁ + ... + a_ikx_k =0, 1 i l. We say that A is density regular if every subsetof N with positive density, contains a solution to L(A). Fora density regular l x k matrix A, an integer r and a set ofintegers F, we write if for any partition F = F₁ ... F_r there exists i {1, 2,..., r} and a column vector x such that Ax = 0 and all entriesof x belong to F_i. Let [n]_N be a random N-element subset of{1, 2, ..., n} chosen uniformly from among all such subsets.In this paper we determine for every density regular matrixA a parameter = (A) such that lim_n P([n]_N (A)_r)=0 if N =O(n) and 1 if N = (n). 1991 Mathematics Subject Classification:05D10, 11B25, 60C05     

Sub- and Superadditive Properties of Fejer's sine Polynomial

Let be Fejér's sine polynomial. We prove the following statements.

1. The inequality holds for all x, y (0, ) with x + y < if and only if 0 and + rß 1.
2. The converse of the above inequality is valid for allx, y (0, ) with x + y < if and only if 0 and + rß 1.
3. For all n N and x, y [0, ] we have . Both bounds are best possible.

2000 Mathematics Subject Classification 42A05, 26D05 (primary),39B62 (secondary).     

Some New and Old Asymptotic Representations of the Jost Solution and the Weyl m-Function For Schrodinger Operators on the Line

For the general one-dimensional Schrödinger operator –d²/dx²+q(x) with real q L₁(R), this paper presents a new series representationof the Jost solution which, in turn, implies a new asymptoticrepresentation of the Weyl m-function for locally summable q.This representation is then applied to smooth potentials q toobtain Weyl m-function power asymptotics. The condition q^(N) L₁(x₀, x₀ + ), for N N₀, allows one to derive the (N + 1)term for almost all x [x₀, x₀ + ), thereby refining a relevantresult by Danielyan, Levitan and Simon. 2000 Mathematics SubjectClassification 34E05, 34L40 (primary), 34B20, 34L25 (secondary).     

Anzai Skew Products with Lebesgue Component of Infinite Multiplicity

Let f be a 1-periodic C¹-function whose Fourier coefficientssatisfy the condition _n|n|³|f(n|² < . For every R\Q andm Z\{0}, we consider the Anzai skew product T(x, y) = (x +, y + mx + f(x)) acting on the 2-torus. It is shown that T hasinfinite Lebesgue spectrum on the orthocomplement L²(dx) ofthe space of functions depending only on the first variable.This extends some earlier results of Kushnirenko, Choe, Lemaczyk,Rudolph, and the author. 1991 Mathematics Subject Classification28D05.     

Chaotic Expansion of Elements of the Universal Enveloping Algebra of a Lie Algebra Associated with a Quantum Stochastic Calculus

The functional Ito formula, in the form df() = f( + d ) –f(),is formulated and proved in the context of a Lie algebra L associatedwith a quantum (non-commutative) stochastic calculus. Here fis an element of the universal enveloping algebra U of L, andf() + d() – f() is given a meaning using the coproductstructure of U even though the individual terms of this expressionhave no meaning. The Ito formula is equivalent to a chaoticexpansion formula for f() which is found explicitly. 1991 MathematicsSubject Classification: primary 81S25; secondary 60H05; tertiary18B25.     

Polynomial systems supported on circuits and dessins d'enfants

We study polynomial systems in which equations have as commonsupport a set of n + 2 points in ⁿ called a circuit. We finda bound on the number of real solutions to such systems whichdepends on n, the dimension of the affine span of the minimalaffinely dependent subset of , and the rank modulo 2 of . Weprove that this bound is sharp by drawing the so-called dessinsd’enfants on the Riemann sphere. We also obtain that themaximal number of solutions with positive coordinates to systemssupported on circuits in ⁿ is n + 1, which is very small comparedto the bound given by the Khovanskii fewnomial theorem.     

The density of rational points on non-singular hypersurfaces, II

For any integers d,n 2, let X Pⁿ be a non-singular hypersurfaceof degree d that is defined over the rational numbers. The mainresult in this paper is a proof that the number of rationalpoints on X which have height at most B is O(B^{n – 1} +), for any > 0. The implied constant in this estimate dependsat most upon d, and n. 2000 Mathematics Subject Classification11D45 (primary), 11G35, 14G05 (secondary).     

Error Bounds for the Truncation of Infinite Linear Differential Systems

An infinite system of linear differential equations of the form = Ax + f, x(0) = y is considered, wherex, y and f are infinite column vectors in E, and A is a constantinfinite matrix defining a bounded operator on E, where E isl₁, (c₀), or l. Explicit error bounds are obtained for the approximationof the solution of the infinite system by the solutions of thefinite truncated systems.     

Common Multiples of Complete Graphs

A graph H is said to divide a graph G if there exists a setS of subgraphs of G, all isomorphic to H, such that the edgeset of G is partitioned by the edge sets of the subgraphs inS. Thus, a graph G is a common multiple of two graphs if eachof the two graphs divides G. This paper considers common multiples of a complete graph oforder m and a complete graph of order n. The complete graphof order n is denoted K_n. In particular, for all positive integersn, the set of integers q for which there exists a common multipleof K₃ and K_n having precisely q edges is determined. It is shown that there exists a common multiple of K₃ and K_nhaving q edges if and only if q 0 (mod 3), q 0 (mod n2) and (1) q 3 n2 when n 5 (mod 6); (2) q (n + 1) n2 when n is even; (3) q {36, 42, 48} when n = 4. The proof of this result uses a variety of techniques includingthe use of Johnson graphs, Skolem and Langford sequences, andequitable partial Steiner triple systems. 2000 MathematicalSubject Classification: 05C70, 05B30, 05B07.     

Mobius Instability of Sampling for Small Weighted Spaces of Analytic Functions

In this paper, the space A (D)is considered, consisting of thoseholomorphic functions f on the unit disk D such that || f ||= sup_{z D} | f(z)|(|z|) < +, with (1) = 0. The sampling problemis studied for weights satisfying ln (r)/ln(1 – r) 0.Möbius stability of sampling is shown to fail in this space.2000 Mathematics Subject Classification 30H05 (primary), 30D60(secondary).     

Metrical Theorems on Prime Values of the Integer Parts of Real Sequences

Let a_n be an increasing sequence of positive reals with a_n as n . Necessary and sufficient conditions are obtained foreach of the sequences to take on infinitely many prime values for almost all > rß.For example, the sequence a_n is infinitely often prime for almostall > 0 if and only if there is a subsequence of the a_n,say b_n, with b_{n + 1} > b_n + 1 and with the series divergent. Asymptotic formulae areobtained when the sequences considered are lacunary. An earlierresult of the author reduces the problem to estimating the measureof overlaps of certain sets, and sieve methods are used to obtainthe correct order upper bounds. 1991 Mathematics Subject Classification:primary 11N05; secondary 11K99, 11N36.     

Identities for Combinatorial Extremal Theory

Let be the set {1, 2, ..., n}, and let Ø be the emptyset. Let G be the family of all non-empty sets of subsets of. For A G and X , put An important discovery is the following. 1991 Mathematics SubjectClassification 05D05.     

A Bohr Phenomenon For Elliptic Equations

In 1914 Bohr proved that there is an r (0,1) such that if apower series converges in the unit disk and its sum has modulusless than 1 then, for |z| < r, the sum of absolute valuesof its terms is again less than 1. Recently, analogous resultshave been obtained for functions of several variables. The aimof this paper is to place the theorem of Bohr in the contextof solutions to second-order elliptic equations satisfying themaximum principle. 2000 Mathematics Subject Classification: 35J15, 32A05, 46A35.     

The Density of Rational Points on Non-Singular Hypersurfaces, I

For any n 3, let F Z[X₀, ..., X_n] be a form of degree d 5that defines a non-singular hypersurface X Pⁿ. The main resultin this paper is a proof of the fact that the number N(F; B)of Q-rational points on X which have height at most B satisfies , for any > 0. The implied constantin this estimate depends at most upon d, and n. New estimatesare also obtained for the number of representations of a positiveinteger as the sum of three dth powers, and for the paucityof integer solutions to equal sums of like polynomials. 2000Mathematics Subject Classification 11G35 (primary), 11P05, 14G05(secondary).     

A Liouville Theorem for Matrix-Valued Harmonic Functions on Nilpotent Groups

Let be a non-degenerate positive M_n-valued measure on a locallycompact group G with |||| = 1. An M_n-valued Borel function fon G is called -harmonic if for all x G. Given such a function f which is bounded and leftuniformly continuous on G, it is shown that every central elementin G is a period of f. Further, it is shown that f is constantif G is nilpotent or central. 2000 Mathematics Subject Classification31C05, 43A05, 45E10, 46G10.     

Convergent and spurious solutions of nonlinear elliptic equations

In this paper we investigate finite element approximations ofnonlinear elliptic equations in three dimensions. By applyingand extending the results of Lopez-Marcos and Sanz-Serna, weprove that the finite element approximation on a mesh of sizeh, has a solution U_k which converges to an exact solution ofthe differential equation as h0. This solution is unique withina suitably defined stability ball Bh. For the particular nonlinearequation u + (u + u^p) we show that the size of B_h depends uponh only if p > 5 when it tends to zero as h 0. In this casewe prove the existence of spurious solutions V_h of the Galerkinapproximation which become unbounded in the maximum norm ash0. The stability ball B_h then acts to separate the convergentand the spurious solutions. We present the results of some numericalexperiments to substantiate our claims.     

The Ok Corral and the Power of the Law (A Curious Poisson-Kernel Formula for a Parabolic Equation)

Two lines of gunmen face each other, there being initially mon one side, n on the other. Each person involved is a hopelessshot, but keeps firing at the enemy until either he himselfis killed or there is no one left on the other side. Let µ(m,n) be the expected number of survivors. Clearly, we have boundaryconditions: We also have theequation This is because theprobability that the first successful shot is made by the sidewith m gunmen is m/(m + n). On using the recurrence relation(1.2) together with the boundary condition (1.1), the computerproduces Table 1 below, in which 1991 Mathematics Subject Classification 60F05.     

A Solution for the Embedding Problem for Partial Transitive Triple Systems

In this paper we solve the embedding problem for partial transitivetriple systems of order n and index , partial TTS(n, ) s, showingthat any partial TTS(n, ) can be embedded in a TTS(v, ) forall -admissible v 2n + 1. This lower bound on v is the bestpossible. A simple proof is also given of a result of Colbournand Harms which shows that every partial triple system of ordern and index 2 is the underlying triple system of a partial TTS(n,). 1991 Mathematics Subject Classification 05B07.