Effectifs des diverses sequences de polyedres 3-valents convexes ayant moins de 11 faces et de polyedres sans face triangulaire ayant de 11 a 14 faces

A table is presented of various sequences of 3-valent convex polyhedra, a sequence being defined by p₃p₄???p_i??? where p_i is the number of faces with i edges. These sequences are given for polyhedra with 6, 7, 8, 9, 10 faces and the sequences where p₃=0 are given for polyhedra having 11, 12, 13, 14 faces. The number of polyhedra is also given for each sequence.     

Products of EP matrices

Necessary and sufficient conditions are given for a matrix to be a product of an EP_r matrix by an EP_s matrix. It is shown that a given square matrix is a product of more than two EP matrices of specified ranks (and hence nullities) if and only if its rank is less than or equal to the minimum of the given ranks and its nullity is less than or equal to the sum of the given nullities. It is also shown that given two EP matrices, the rank of their product is independent of the order of the factors.     

A BIVARIATE EXTENSION OF BLEIMANN－BUTZER－HAHN OPERATOR

Let C( R ^2) be a class of continuous functions f on R ^2.A bivariate extension Ln(f,x,y)of Bleiman-Butzer-Hahn operator is defined and its standard convergence properties are given.Moreover,a local analogue of Voronovskaja theorem is also give for a subclass of C(R ^2).     

Geometric fit of a point set by generalized circles

In our paper we approximate a set of given points by a general circle. More precisely, given two norms k ₁ and k ₂ and a set of points in the plane, we consider the problem of locating and scaling the unit circle of norm k ₁ such that the sum of weighted distances between the circumference of the circle and the given points is minimized, where the distance is measured by a norm k ₂. We present results for the general case. In the case that k ₁ and k ₂ are both polyhedral norms, we are able to solve the problem by investigating a finite candidate set.     

Finite-time boundedness and L2-gain analysis for switched delay systems with norm-bounded disturbance

Finite-time boundedness and finite-time weighted L₂-gain for a class of switched delay systems with time-varying exogenous disturbances are studied. Based on the average dwell-time technique, sufficient conditions which guarantee the switched linear system with time-delay is finite-time bounded and has finite-time weighted L₂-gain are given. These conditions are delay-dependent and are given in terms of linear matrix inequalities. Detail proofs are given by using multiple Lyapunov-like functions. An example is employed to verify the efficiency of the proposed method.     

<Emphasis Type="Italic">H</Emphasis><Subscript>∞</Subscript> Observer-Based Control for a Class of Uncertain Neutral Time-Delay Systems via LMI Optimization Approach

In this paper, the H_∞ observer-based control for a class of uncertain neutral time-delay systems is considered. The linear matrix inequality (LMI) optimization approach is used to design the H_∞ robust control with disturbance attenuation. Two classes of observer-based controls are proposed and their H_∞-norm bounds are given. The control and observer gains are given from the LMI feasible solutions. A numerical example is given to illustrate the results. The research reported here was supported by the National Science Council of Taiwan under Grant NSC 93-2213-E-214-020.     

Functional Equations and Weierstrass Transforms

The purpose of this article is to illustrate the utility of the Weierstrass transform in the study of functional equations (and systems) of the form 1 $${\mathop \sum^N\limits_{k=0}}\alpha_{k}f(x+r_{k})=f_{0}(x)\ \ \ \, x\in\ {\rm R}.$$ One may think of α₀, α₁,…, α_N as given complex numbers, r₀, r₁,…, r_N as given real numbers, ?₀: ? → C as a given function and ? as the unknown.     

Closure Operators in Convergence Spaces

We define two closure operators of some well-known topological categories and investigate the relationships between these closure operators and the one that is given in [9]. As a consequence, we characterize separation properties T ₀, T ₁, and T ₂ for these well-known categories and compare them with the ones that are given in [3] and [6]. Finally, we characterize the epimorphisms in the subcategories of these given categories. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nonlinear Elliptic Variational Inequalities

We consider the problem of finding a solution to a class of nonlinear elliptic variational inequalities. These inequalities may be defined on bounded or unbounded domains Ω, and the nonlinearity can depend on gradient terms. Appropriate definitions of sub-and supersolutions relative to the constraint sets are given. By using a mixture of maximal monotone operator theory and compactness arguments we prove the existence of a H²(Ω) solution lying between a given subsolution φ₁ and a given supersolution φ₂≧φ₁, when Ω is bounded, and a H¹(Ω) solution when Ω is unbounded.     

Inverse NO-matrices

Results similar to those of Thomas L. Markham concerning inverse M-matrices are shown to hold for inverse N_Omatrices. A more general result and an alternate method of proof using Schur complements are given for one of Markham's theorems. Conditions are given to transform a nonpositive matrix to an N_O-amtrix by multiplication by Householder transformations. Also, an LU factorization of an inverse N_O-matrix is given.     

Graphs without K4 and well-quasi-ordering

It is proved that given an infinite sequence G₁, G₂, G₃,…, of series-parallel graphs there are indices i < j such that G_j contains an induced subgraph contractable onto G_i. An example is given showing that for planar graphs the preceding theorem fails.     

On normal two-dimensional double point singularities

Letq be a plane curve singularity and letp be the corresponding normal two-dimensional double point singularity. Let Γ and Γ₁ be the topological types of the minimal and of the canonical resolutions ofp respectively. An algorithm is given for finding the equisingular type ofq in terms of Γ₁. An algorithm is also given for finding all Γ₁ corresponding to a given Γ. There is at most one such Γ₁ in case Γ has no 1-cycles. This research was partially supported by the National Science Foundation. The author also is an Alfred P. Sloan Research Fellow.     

A quenching criterion for a multi-dimensional parabolic problem due to a concentrated nonlinear source

A multi-dimensional parabolic first initial-boundary value problem with a concentrated nonlinear source is studied. A criterion for its solution to quench, in a finite time t_q, everywhere on the concentrated nonlinear source only is given. An upper bound for t_q is also deduced. For illustration, an example is given.     

Function cones and interpolation

We consider interpolation of operators acting on functions that belong to a given cone Q with the so‐called decomposition property. The set of all positive functions whose level sets are the level sets of a given function is the main example, and the cone of all decreasing functions is a particular case. As applications, we obtain conditions for the identity (E₀ ∩ Q,E₁ ∩ Q)_θ,p = (E₀,E₁)_θ,p ∩ Q and interpolation results for operators which are bounded when restricted to a given family of characteristic funcions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The convergence of three spline methods for scattered data interpolation and fitting

The convergences of three L₁ spline methods for scattered data interpolation and fitting using bivariate spline spaces are studied in this paper. That is, L₁ interpolatory splines, splines of least absolute deviation, and L₁ smoothing splines are shown to converge to the given data function under some conditions and hence, the surfaces from these three methods will resemble the given data values.     

Regular Subgraphs in Graphs and Rooted Graphs and Definability in Monadic Second - Order Logic

We investigate the definability in monadic ∑₁¹ and monadic Π₁¹ of the problems REG_k, of whether there is a regular subgraph of degree k in some given graph, and XREG_k, of whether, for a given rooted graph, there is a regular subgraph of degree k in which the root has degree k, and their restrictions to graphs in which every vertex has degree at most k, namely REG_k^k and XREG_k^k, respectively, for k ≥ 2 (all our graphs are undirected). Our motivation partly stems from the fact (which we prove here) that REG_k^k and XREG_k^k are logspace equivalent to CONN and REACH, respectively, for k ≥ 3, where CONN is the problem of whether a given graph is connected and REACH is the problem of whether a given graph has a path joining two given vertices. We use monadic first - order reductions, monadic ∑₁¹ games and a recent technique due to Fagin, Stockmeyer and Vardi to almost completely classify whether these problems are definable in monadic ∑₁¹ and monadic Π₁¹, and we compare the definability of these problems (in monadic ∑₁¹ and monadic Π₁¹ with their computational complexity (which varies from solvable using logspace to NP - complete).     

A bivariate extension of Bleimann-Butzer-Hahn operator

Let C(R2+ ) be a class of continuous functions f on R2+. A bivariate extension L.(f ,x,y) of BleimannButzer-Hahn operator is defined and its standard convergence properties are given. Moreover, a local analogue of Voronovskaja theorem is also given for a subclass of C(R2+).     

Minimum nastiness curve fitting

The ‘nastiness’ of a function φ(x) is defined. We then discuss minimum nastiness interpolation to a set of given points (x _k, φ_k), as well as minimum nastiness curve fitting, where the given valuesφ _k have errorsδ _k.     

A free boundary problem for three-dimensional harmonic vector fields

We study in this paper a free boundary value problem ( FB ), where a region G_o in R ³ is determined by the condition that there exists a vector field v_o in G_o which satisfies div v_o = e_o, curl v_o = g_o in G_o and v_o = E on the boundary ?G_o with a given scalar function e_o and given vector fields g_o and E. We give two equivalent formulations for this problem. Then we characterize the solutions by a non-linear integral equation. In order to solve the latter by a Newton method we linearize this equation. We investigate the ensuing linear integral equation. In case of axisymmetric configurations this is a singular integral equation whose index can be easily determined from the given data. We obtain a related equation, if we try to construct a field v in a region G which is on the boundary perpendicular to a given field B . Finally we use this method to investigate an astrophysical problem, which arises in the theory of pulsar magnetospheres.