Holomorphic extension of CR functions from quadratic cones

It is proved that CR functions on a quadratic cone M in , n > 1, admit one-sided holomorphic extension if and only if M does not have two-sided support, a geometric condition on M which generalizes minimality in the sense of Tumanov. A biholomorphic classification of quadratic cones in is also given.     

Linear extension majority cycles on partial orders

Let P define a partial order on a set X of cardinalityn. A linear extensionL ofP is a linear order withP G L, and is the set of all linear extensions ofP. denotes that subset of withxLy forx, y X. A linear extension majority (LEM) relationM onX is defined byxMy if . Similarly,M is defined byxMy if . An LEM cycle exists if there arex, y, z X withxMyMzMx, and an LEM quasi-cycle exists ifxMyMzMx and the equality part of the definition ofM holds for exactly one pair in the triple. The study shows that no semiorders have LEM cycles or LEM quasi-cycles, and that every interval order has a maximal element under theM relation. LEM cycles and LEM quasi-cycles are also considered for partial orders with specific structures. Simulation is used to determine the relative likelihood with which LEM cycles and LEM quasi-cycles are observed when connected partial orders are generated at random by a specific procedure.Dr. Gehrlein's research was supported through a fellowship from the Center for Advanced Study of the University of Delaware.     

On weak completeness of products and direct sums in locally convex cones

We discuss the weak completeness of product and direct sum cones in the lower, upper and symmetric topologies. For the weak lower, upper and symmetric topology of a direct sum cone, there correspond bases of upper, respectively lower and symmetric, closed members in a coarser topology which leads us to investigate the weak completeness of direct sum cones.

     

Linear sums of two composition operators on the Fock space

Linear sums of two composition operators of the multi-dimensional Fock space are studied. We show that such an operator is bounded only when both composition operators in the sum are bounded. So, cancelation phenomenon is not possible on the Fock space, in contrast to what have been known on other well-known function spaces over the unit disk. We also show the analogues for compactness and for membership in the Schatten classes. For linear sums of more than two composition operators the investigation is left open.     

Ramanujan sums as supercharacters

The theory of supercharacters, recently developed by Diaconis-Isaacs and André, is used to derive the fundamental algebraic properties of Ramanujan sums. This machinery frequently yields one-line proofs of difficult identities and provides many novel formulas. In addition to exhibiting a new application of supercharacter theory, this article also serves as a blueprint for future work since some of the abstract results we develop are applicable in much greater generality.     

Generalized valuations on MTL-algebras

In this paper, we study some kinds of generalized valuations on MTL-algebras, discuss the relationship between the cokernel of generalized valuations and types of filters on MTL-algebras. Then, we give some equivalent characterizations of positive implicative generalized valuations on MTL-algebras. Finally, we characterize the structure theory of quotient MTL algebras based on the congruence relation, which is constructed by generalized valuations. The results of this paper not only generalize related theories of generalized valuations, but also enrich the algebraic conclusion of probability measure, on algebras of triangular norm based fuzzy logic.     

The single-valued extension property for sums and products of commuting operators

It is shown that the sum and the product of two commuting Banach space operators with Dunford's property (C) have the single-valued extension property.     

Rectangles as sums of squares

In this paper we examine generalisations of the following problem posed by Laczkovich: Given an n×m rectangle with n and m integers, it can be written as a disjoint union of squares; what is the smallest number of squares that can be used? He also asked the corresponding higher dimensional analogue. For the two dimensional case Kenyon proved a tight logarithmic bound but left open the higher dimensional case. Using completely different methods we prove good upper and lower bounds for this case as well as some other variants.     

Matrices as sums of squares

How many squares are needed to represent elements in a matrix ring? A matrix over a field of characteristic two is a sum of two squares if and only if its trace is a square, otherwise it is not a sum of squares. Any proper matrix over a field of characteristic not two is always a sum of three squares. If the order of a matrix is even the matrix is a sum of two squares, but an odd order matrix which is q times the identity matrix is a sum of two squares if and only ifq is a sum of two squares in the field. Matrices of order 2,3 and 4 over the integers can always be written as the sum of three squares.     

Blowing-ups and valuations on surfaces

In this paper, we show that all the nontrivial valuations on surfaces can be given by the infinite sequences of blowing-ups, and give the process of blowing-ups.     

Real-valued valuations on Sobolev spaces

Continuous, SL(n) and translation invariant real-valued valuations on Sobolev spaces are classified.The centro-affine Hadwiger’s theorem is applied. In the homogeneous case, these valuations turn out to be L~p-norms raised to p-th power(up to suitable multipication scales).     

Arc valuations on smooth varieties

Let X be a nonsingular variety (with $\dim X?2$) over an algebraically closed field k of characteristic zero. Let $\alpha :\mathrm{Spec}\mathbf{k}?t?\to X$ be an arc on X, and let $v={\mathrm{ord}}_{\alpha }$ be the valuation given by the order of vanishing along α. We describe the maximal irreducible subset $C(v)$ of the arc space of X such that ${\mathrm{val}}_{C(v)}=v$. We describe $C(v)$ both algebraically, in terms of the sequence of valuation ideals of v, and geometrically, in terms of the sequence of infinitely near points associated to v. As a corollary, we get that v is determined by its sequence of centers. Also, when X is a surface, our construction also applies to any divisorial valuation v, and in this case $C(v)$ coincides with the one introduced in [L. Ein, R. Lazarsfeld, M. Musta?ǎ, Contact loci in arc spaces, Compos. Math. 140 (2004) 1229–1244, Example 2.5].     

Even valuations on convex bodies

The notion of even valuation is introduced as a natural generalization of volume on compact convex subsets of Euclidean space. A recent characterization theorem for volume leads in turn to a connection between even valuations on compact convex sets and continuous functions on Grassmannians. This connection can be described in part using generating distributions for symmetric compact convex sets. We also explore some consequences of these characterization results in convex and integral geometry.