Potential Theory of Geometric Stable Processes

In this paper we study the potential theory of symmetric geometric stable processes by realizing them as subordinate Brownian motions with geometric stable subordinators. More precisely, we establish the asymptotic behaviors of the Green function and the Lévy density of symmetric geometric stable processes. The asymptotics of these functions near zero exhibit features that are very different from the ones for stable processes. The Green function behaves near zero as 1/(|x|^d log ²|x|), while the Lévy density behaves like 1/|x|^d. We also study the asymptotic behaviors of the Green function and Lévy density of subordinate Brownian motions with iterated geometric stable subordinators. As an application, we establish estimates on the capacity of small balls for these processes, as well as mean exit time estimates from small balls and a Harnack inequality for these processes. The research of this author is supported in part by MZT grant 0037118 of the Republic of Croatia and in part by a joint US-Croatia grant INT 0302167. The research of this author is supported in part by a joint US-Croatia grant INT 0302167. The research of this author is supported in part by MZT grant 0037107 of the Republic of Croatia and in part by a joint US-Croatia grant INT 0302167.     

On Minimizing Some Merit Functions for Nonlinear Complementarity Problems under <Emphasis Type="Italic">H</Emphasis>-Differentiability

In this paper, we describe the H-differentials of some well known NCP functions and their merit functions. We show how, under appropriate conditions on an H-differential of f, minimizing a merit function corresponding to f leads to a solution of the nonlinear complementarity problem. Our results give a unified treatment of such results for C ¹-functions, semismooth-functions, and locally Lipschitzian functions. Illustrations are given to show the usefulness of our results. We present also a result on the global convergence of a derivative-free descent algorithm for solving the nonlinear complementarity problem. The first author is deeply indebted to Professor M. Seetharama Gowda for his numerous helpful suggestions and encouragement. Special thanks to Professor J.-P. Crouzeix and an anonymous referees for their constructive suggestions which led to numerous improvements in the paper. The research of the first author was supported in part by the Natural Sciences and Engineering Research Council of Canada and Scholar Activity Grant of Thompson Rivers University. The research of the second author was supported by the Natural Sciences and Engineering Research Council of Canada.     

Potential theory of subordinate killed Brownian motion in a domain

 Subordination of a killed Brownian motion in a bounded domain D⊂ℝ ^d via an α/2-stable subordinator gives a process Z _t whose infinitesimal generator is −(−Δ| _D )^α/2, the fractional power of the negative Dirichlet Laplacian. In this paper we study the properties of the process Z _t in a Lipschitz domain D by comparing the process with the rotationally invariant α-stable process killed upon exiting D. We show that these processes have comparable killing measures, prove the intrinsic ultracontractivity of the generator of Z _t , prove the intrinsic ultracontractivity of the semigroup of Z _t , and, in the case when D is a bounded C ^1,1 domain, obtain bounds on the Green function and the jumping kernel of Z _t . Received: 4 April 2002 / Revised version: 1 July 2002 / Published online: 19 December 2002 This work was completed while the authors were in the Research in Pairs program at the Mathematisches Forschungsinstitut Oberwolfach. We thank the Institute for the hospitality. The research of the first author is supported in part by NSF Grant DMS-9803240. The research of the second author is supported in part by MZT grant 037008 of the Republic of Croatia. Mathematics Subject Classification (2000): Primary 60J45; Secondary 60J75, 31C25 Key words or phrases: Killed Brownian motions – Stable processes – Subordination – Fractional Laplacian     

The existence of identity of orthodox semigroup rings

The existence of identity of orthodox semigroup rings is investigated. The author characterizes the existence of identity in anN-perfect band ring and in anN-perfect orthodox semigroup ring. This research was supported by the National Natural Science Foundation of China. This paper formed a part of the author's doctoral dissertation [4], written under the direction of Professor Y. Q. Guo at Lanzhou University. The author is very grateful to Professor J. S. Ponizovskii for his valuable words of advice.     

Congruence lattices ofp-algebras

T. Kartriák proved the following theorem:Every finite distributive lattice is the congruence lattice of a finite p-algebra. We provide a short proof, and a generalization, of this result.Presented by J. Berman.The research of the first author was supported by the NSERC of Canada.The research of the second author was supported by the Hungarian National Foundation for Scientific Research, under Grant No. 1903.     

An efficient algorithm for guard placement in polygons with holes

In this paper we consider the problem of placing guards to supervise an art gallery with holes. No gallery withn vertices andh holes requires more than [(n+h)/3] guards. For some galleries this number of guards is necessary. We present an algorithm which places the [(n+h)/3] guards inO(n ²) time. Work by the first author was done at Rutgers University and was supported in part by a DIMACS research assistantship. The second author was supported in part by National Science Foundation Grants CCR-88-03549 and CCR-91-04732.     

Groups with small Dehn functions and bipartite chord diagrams

We introduce a new invariant of bipartite chord diagrams and use it to construct the first examples of groups with Dehn function n²log n. Some of these groups have undecidable conjugacy problem. Our groups are multiple HNN extensions of free groups. We show that n²log n is the smallest Dehn function of a multiple HNN extension of a free group with undecidable conjugacy problem. Both authors were supported in part by the NSF grants DMS 0245600 and DMS 0455881. In addition, the research of the first author was supported in part by the Russian Fund for Basic Research 05-01-00895, the research of the second author was supported in part by the NSF grant DMS 9978802 and the US-Israeli BSF grant 1999298. Received: February 2005; Revision: September 2005; Accepted: September 2005     

Non-amenable finitely presented torsion-by-cyclic groups

Abstract. – We construct a finitely presented non-amenable group without free non-cyclic subgroups thus providing a finitely presented counterexample to von Neumann’s problem. Our group is an extension of a group of finite exponent n ≫ 1 by a cyclic group, so it satisfies the identity [x,y] ⁿ = 1. Manuscrit reĉu le 8 février 2001. RID="*" ID="*"Both authors were supported in part by the NSF grant DMS 0072307. In addition, the research of the first author was supported in part by the Russian Fund for Basic Research 99-01-00894 and by the INTAS grant, the research of the second author was supported in part by the NSF grant DMS 9978802.     

On the dual Stiefel-Whitney classes of some Grassmann manifolds

We present some non-vanishing dual Stiefel-Whitney classes of the Grassmann manifolds O(n)/O(4) × O(n − 4) for n = 2 ^s + 2 and n = 2 ^s + 3 (s ≧ 3), providing a supplement to results of Hiller, Stong, and Oproiu. Some applications are also mentioned. Part of this research was carried out while the first author was a member of three research teams supported in part by the grant agencies VEGA and APVV, and the second author was a member of a research team supported in part by VEGA.     

Some existence results for solutions to SU(3) Toda system

We study SU(3) Toda system in non-abelian relativistic self-dual gauge theory. In the range of parameters where the corresponding Trudinger-Moser inequality fails, we show the existence of the solution by a different variational formulation from Lucia-Nolasco's [15]. This work was supported by a grant of the Japan-Korea Scientific Cooperation Program - Joint Research “Mathematical analysis and mathematical science for self-interacting particles.” The second author was partially supported by Grant-in-Aid for Scientific Research (No. 16740103), Japan Society for the Promotion of Science. Mathematics Subject Classification (2000) 35B40 - 35J50 - 35J60 - 49Q99 - 58E15 - 58J05 - 70S15     

The Goursat problem for a generalized Helmholtz operator in the plane

We consider the Goursat problem in the plane for partial differential operators whose principal part is the pth power of the standard Laplace operator. The data is posed on a union of 2p distinct lines through the origin. We show that the solvability of this Goursat problem depends on Diophantine properties of the geometry of lines on which the data is posed. The first author is supported in part by DMS-0401215. The second author is supported in part by Grant MTM2006-13000-C03-03 of the D.G.I. of Spain.     

There exist 6n/13 ordinary points

In 1958 L. M. Kelly and W. O. J. Moser showed that apart from a pencil, any configuration ofn lines in the real projective plane has at least 3n/7 ordinary or simple points of intersection, with equality in the Kelly-Moser example (a complete quadrilateral with its three diagonal lines). In 1981 S. Hansen claimed to have improved this ton/2 (apart from pencils, the Kelly-Moser example and the McKee example). In this paper we show that one of the main theorems used by Hansen is false, thus leavingn/2 open, and we improve the 3n/7 estimate to 6n/13 (apart from pencils and the Kelly-Moser example), with equality in the McKee example. Our result applies also to arrangements of pseudolines.The research of J. Csima was supported in part by NSERC Grant A4078. E. T. Sawyer's research was supported in part by NSERC Grant A5149.     

Branching in the enumeration degrees of the Σ 2 0 sets

We show that every incomplete Σ ₂ ⁰ enumeration degree is meet-reducible in the structure of the enumeration degrees of the Σ ₂ ⁰ sets. The first author was partially supported by NSF-grant DMS-9500983. The second author was partially supported by the HC&M research networkComplexity, Logic and Recursion Theory (COLORET), contract no. ERBCHRXCT930415, and by MURST 60%.     

Geometry of homogeneous convex cones,duality mapping,and optimal self-concordant barriers

We study homogeneous convex cones. We first characterize the extreme rays of such cones in the context of their primal construction (due to Vinberg) and also in the context of their dual construction (due to Rothaus). Then, using these results, we prove that every homogeneous cone is facially exposed. We provide an alternative proof of a result of Güler and Tunç el that the Siegel rank of a symmetric cone is equal to its Carathéodory number. Our proof does not use the Jordan-von Neumann-Wigner characterization of the symmetric cones but it easily follows from the primal construction of the homogeneous cones and our results on the geometry of homogeneous cones in primal and dual forms. We study optimal self-concordant barriers in this context. We briefly discuss the duality mapping in the context of automorphisms of convex cones and prove, using numerical integration, that the duality mapping is not an involution on certain self-dual cones.Research of this author was supported in part by a Summer Undergraduate Research Assistantship Award from NSERC (Summer 2001) and a research grant from NSERC while she was an undergraduate student at Faculty of Mathematics, University of Waterloo.Research of this author was supported in part by a PREA from Ontario, Canada and research grants from NSERC. Corresponding author.Mathematics Subject Classification (2000): 90C25, 90C51, 90C60, 90C05, 65Y20, 52A41, 49M37, 90C30     

A topological proof of the bott periodicity theorems

Summary A proof is given of theBott periodicity theorems using only well known techniques of algebrdbc topology. To Enrico Bompiani on his scientific Jubilee. This research was done in part while the first author held a Sloan Foundation Fellowship and the second author held a Senior National Science Foundation Fellowhip. It was also supported in part by the National Science Foundation under contract number G-10369.     

Star-linear equational theories of groupoids

We prove that there are precisely six equational theories E of groupoids with the property that every term is E-equivalent to a unique linear term. Presented by J. Berman. Received November 11, 2004; accepted in final form March 12, 2006. The first and third authors were supported by the Ministry of Science and Environment of Serbia, grant no. 144011; the second and fifth authors were supported by MŠMT, research project MSM 0021620839, and by the Grant Agency of the Czech Republic, grant #201/02/0594; the fourth author was supported by the NSF grant #DMS-0245622.     

Instability of exponential Collet-Eckmann maps

Given λ ∈ ℂ \ {0} let the entire function f _λ: ℂ → ℂ be defined by the formula

Hurwitz continued fractions with confluent hypergeometric functions

Many new types of Hurwitz continued fractions have been studied by the author. In this paper we show that all of these closed forms can be expressed by using confluent hypergeometric functions ₀ F1(;c;z). In the application we study some new Hurwitz continued fractions whose closed form can be expressed by using confluent hypergeometric functions. This research was supported in part by the Grant-in-Aid for Scientific research (C) (No. 18540006), the Japan Society for the Promotion of Science.     

Seshadri constants and Fano manifolds

In memory of Meeyoung Kim In this paper, we give a lower bound of Seshadri constants on smooth Fano varieties. More precisely, we show that on a smooth Fano manifold of dimension n whose anticanonical system is base point free, Seshadri constants of ample divisors are bounded from below by one over n–2. As a corollary we recover the earlier result on Fano threefolds. Mathematics Subject Classification (2000):14J45, 14N30.The author was supported in part by KOSEF Grant R14-2002-007-01001-0(2002).     

A boundary property of semimartingale reflecting Brownian motions

Summary We consider a class of reflecting Brownian motions on the non-negative orthant inR ^K . In the interior of the orthant, such a process behaves like Brownian motion with a constant covariance matrix and drift vector. At each of the (K-1)-dimensional faces that form the boundary of the orthant, the process reflects instantaneously in a direction that is constant over the face. We give a necessary condition for the process to have a certain semimartingale decomposition, and then show that the boundary processes appearing in this decomposition do not charge the set of times that the process is at the intersection of two or more faces. This boundary property plays an essential role in the derivation (performed in a separate work) of an analytical characterization of the stationary distributions of such semimartingale reflecting Brownian motions.Research performed in part while the second author was visiting the Institute for Mathematics and Its Applications with support provided by the National Science Foundation and the Air Force Office of Scientific Research. R.J. William's research was also supported in part by NSF Grant DMS 8319562.