On Lie ideals with derivations as homomorphisms and anti-homomorphisms

In [2, Theorem 3], Bell and Kappe proved that if d is a derivation of a prime ring R which acts as a homomorphism or an anti-homomorphism on a nonzero right ideal I of R, then d = 0 on R. In the present paper our objective is to extend this result to Lie ideals. The following result is proved: Let R be a 2-torsion free prime ring and U a nonzero Lie ideal of R such that u ² ∈ U, for all u ∈ U. If d is a derivation of R which acts as a homomorphism or an anti-homomorphism on U, then either d=0 or U ?Z(R).     

On Lie ideals with generalized derivations

Let R be a prime ring with characteristic different from 2, let U be a nonzero Lie ideal of R, and let f be a generalized derivation associated with d. We prove the following results: (i) If a ∈ R and [a, f(U)] = 0 then a ∈ Z or d(a) = 0 or U ? Z; (ii) If f ²(U) = 0 then U ? Z; (iii) If u ² ∈ U for all u ∈ U and f acts as a homomorphism or antihomomorphism on U then either d = 0 or U ? Z.     

Conditional limiting distribution of Type III elliptical random vectors

In this paper we consider elliptical random vectors in R^d,d≥2 with stochastic representation RAU where R is a positive random radius independent of the random vector U which is uniformly distributed on the unit sphere of R^d and A∈R^d×d is a non-singular matrix. When R has distribution function in the Weibull max-domain of attraction we say that the corresponding elliptical random vector is of Type III. For the bivariate set-up, Berman [Sojurns and Extremes of Stochastic Processes, Wadsworth & Brooks/ Cole, 1992] obtained for Type III elliptical random vectors an interesting asymptotic approximation by conditioning on one component. In this paper we extend Berman's result to Type III elliptical random vectors in R^d. Further, we derive an asymptotic approximation for the conditional distribution of such random vectors.     

Reduced convex bodies in the plane

A convex bodyR of Euclideand-spaceE ^d is called reduced if there is no convex body properly contained inR of thickness equal to the thickness Δ(R) ofR. The paper presents basic properties of reduced bodies inE ². Particularly, it is shown that the diameter of a reduced bodyR?E ² is not greater than √2Δ(R), and that the perimeter is at most (2+½π)Δ(R). Both the estimates are the best possible.     

Derivations with nilpotent values

IfR is a semiprme ring andd a derivation ofR such thatd(x) ⁿ=0 for allx∈R, wheren≥1 is a fixed integer, thend=0.     

Ombres Convexité, régularité et sous-harmonicité

Letf:V→R be a function defined on a subsetV ofR ⁿ ×R ^d let?:x→inf{f(x t);t such that(x t)∈V} denote theshadow off and letΦ={(x t)∈V; f(x t)=?(x)} This paper deals with the characterization of some properties of ? in terms of the infinitesimal behavior off near points ζ∈Φ proving in particular a conjecture of J M Trépreau concerning the cased=1 Characterizations of this type are provided for the convexity the subharmonicity or theC ^{1 1} regularity of ? in the interior ofI={x∈ R ⁿ;εR ^d (x t)∈V} and in theC ^{1 1} case an expression forD ²? is given To some extent an answer is given to the following question: which convex function ?:I→R I interval ?R (resp which function √:I→R of classC ^{1 1}) is the shadow of aC ² functionf:I×R→R?     

Cardinal hermite interpolation with box splines

The study of cardinal interpolation (CIP) by the span of the lattice translates of a box spline has met with limited success. Only the case of interpolation with the box spline determined by the three directionsd ₁=(1, 0),d ₂=(0, 1), andd ₃=(1, 1) inR ² has been treated in full generality [2]. In the case ofR ^d,d ≥ 3, the directions that define the box spline must satisfy a certain determinant condition [6], [9]. If the directions occur with even multiplicities, then this condition is also sufficient. For Hermite interpolation (CHIP) both even multiplicities and the determinant condition for the directions does not prevent the linear dependence of the basis functions. This leads to singularities in the characteristic multiplier when using the standard Fourier transform method. In the case of derivatives in one direction, these singularities can be removed and a set of fundamental splines can be given. This gives the existence of a solution to CHIP inL ^p (R ^d) for data inl ^p (Z ^d), 1≤p≤2.     

The rate of the normal approximation for jackknifingU-statistics

Let U_n be a U-statistic with symmetric kernel h(x,y) such that Eh(X_1,X_2)=θ and Var E[h(X_1,X_2)-θ|X_j]>0.Let f(x) be a function defined on R and f″ be bounded.If f(θ) is the parameterof interest,a natural estimator is f(U_n).It is known that the distribution function of z_n=(n~(1/2){Jf(U_n)-f(θ)})/(S_n~*) converges to the standard normal distribution Φ(x) as n→∞,where Jf(U_n) isthe jackknife estimator of f(U_n),and S_n~(*2) is the jackknife estimator of the asymptotic variance ofn~(1/2) Jf(U_n).It is of theoretical value to study the rate of the normal approximation of the statistic.In this paper,assuming the existence of fourth moment of h(X_1,X_2),we show that(?)|P{z_n≤x}-Φ(x)|=O(n~(-1/2)log n).This improves the earlier results of Cheng(1981).     

Proper holomorphic maps between Reinhardt domains and strictly pseudoconvex domains

LetR be a Reinhardt domain andD a bounded simply connected strictly pseudoconvex domain withC ^∞ boundary. We prove that any proper holomorphic mapF:R →D is, up to biholomorphism ofD, of the form \((z_1^{d_1 } , z_2^{d_2 } , \ldots , z_n^{d_n } )\) withd ₁,d ₂,…,d _n ∈ IN.     

Gitterpunktsanzahl und Parallelkörpervolumen von Eikörpern

LetΛ={x=(x ₁,...,x _d )|x _i ∈?} be a lattice in euclideand-spaceR ^d with respect to a rectangular coordinate system with unit vectors. Then for instance the following theorem holds: The number of lattice pointsG(K)=card (K∩Λ) of an arbitrary convex bodyK?R ^d is less or equal the volumeV(K _λd) of the outer parallel bodyK _λd ofK at a distance λ _d =ω _d ^-1/d (ω _d =Volume of thed-unitsphere, 2≤d≤5). The number λ is best possible.     

Some remarks on the existence of optimal controls for quasilinear systems

Let a quasilinear control system having the state space \(\bar X \subseteq R^n \) be governed by the vector differential equation $$\dot x = G(u(t))x,$$ wherex(0) =x ₀ andU is the family of all bounded measurable functions from [0,T] intoU, a compact and convex subset ofR ^m.LetG:U ?R be a bounded measurable nonlinear function, such thatG(U) is compact and convex.G ^?1 can be convex onG(U) or concave. The main results of the paper establish the existence of a controlu ∈U which minimizes the cost functional $$I(u) = \int_0^T {L(u(t))x(t)dt,} $$ whereL(·) is convex. A practical example of application for chemical reactions is worked out in detail.     

Distance-hereditary graphs and signpost systems

An ordered pair (U,R) is called a signpost system if U is a finite nonempty set, R⊆U×U×U, and the following axioms hold for all u,v,w∈U: (1) if (u,v,w)∈R, then (v,u,u)∈R; (2) if (u,v,w)∈R, then (v,u,w)∉R; (3) if u≠v, then there exists t∈U such that (u,t,v)∈R. (If F is a (finite) connected graph with vertex set U and distance function d, then U together with the set of all ordered triples (u,v,w) of vertices in F such that d(u,v)=1 and d(v,w)=d(u,w)−1 is an example of a signpost system). If (U,R) is a signpost system and G is a graph, then G is called the underlying graph of (U,R) if V(G)=U and xy∈E(G) if and only if (x,y,y)∈R (for all x,y∈U). It is possible to say that a signpost system shows a way how to travel in its underlying graph. The following result is proved: Let (U,R) be a signpost system and let G denote the underlying graph of (U,R). Then G is connected and every induced path in G is a geodesic in G if and only if (U,R) satisfies axioms (4)-(8) stated in this paper; note that axioms (4)-(8)-similarly as axioms (1)-(3)-can be formulated in the language of the first-order logic.     

On Jordan Left Derivations of Lie Ideals in Prime Rings

Let R be a prime ring with characteristic different from two and U be a Lie ideal of R such that u² U for all u U. In the present paper it is shown that if d is an additive mappings of R into itself satisfying d(u²) = 2ud(u), for all u U, then either U Z(R) or d(U) = (0).1991 Mathematics Subject Classification 16W25 16N60     

Approximation of convex bodies by polytopes with uniformly bounded valences

Given any convex bodyK in Euclideann-spaceR ⁿ and any number ?>0, does there always exist a polytopeP(K, ?)?R ⁿ such that the number of vertices of a facet ofP and the number of facets meeting in a common vertex are bounded by a constant depending on the dimensiond only and such that the Hausdorff-distance ? (K, P) ofK andP is less than ?? This question of Ewald posed at the Durham symposium in 1975 is answered in the affirmative.     

Inequalities for convex bodies and polar reciprocal lattices inR n II: Application ofK-convexity

The paper is a supplement to [2]. LetL be a lattice andU ano-symmetric convex body inR ⁿ . The Minkowski functional? ⁿ ofU, the polar bodyU ⁰, the dual latticeL ^*, the covering radius μ(L, U), and the successive minima λ _i ,i=1, …,n, are defined in the usual way. Let $\mathcal{L}_n $ be the family of all lattices inR ⁿ . Given a convex bodyU, we define $$\begin{gathered} mh(U){\text{ }} = {\text{ }}\sup {\text{ }}\max \lambda _i (L,U)\lambda _{n - i + 1} (L^* ,U^0 ), \hfill \\ {\text{ }}L \in \mathcal{L}_n 1 \leqslant i \leqslant n \hfill \\ lh(U){\text{ }} = {\text{ }}\sup {\text{ }}\lambda _1 (L,U) \cdot \mu (L^* ,U^0 ), \hfill \\ {\text{ }}L \in \mathcal{L}_n \hfill \\ \end{gathered} $$ and kh(U) is defined as the smallest positive numbers for which, given arbitrary $L \in \mathcal{L}_n $ andx∈R ⁿ /(L+U), somey∈L ^* with ∥y∥ _U ⁰?sd(xy,Z) can be found. It is proved $$C_1 n \leqslant jh(U) \leqslant C_2 nK(R_U^n ) \leqslant C_3 n(1 + \log n),$$ , for j=k, l, m, whereC ₁,C ₂,C ₃ are some numerical constants andK(R _U ⁿ ) is theK-convexity constant of the normed space (R ⁿ , ∥∥U). This is an essential strengthening of the bounds obtained in [2]. The bounds for lh(U) are then applied to improve the results of Kannan and Lovász [5] estimating the lattice width of a convex bodyU by the number of lattice points inU.     

Solutions ofLu=u α dominated byL-harmonic functions

LetL be a second order elliptic differential operator on a differentiable manifoldM and let 1 <α≤2. We investigate connections bewween classU of all positive solutions of the equationLu=u ^α and classH of all positiveL-harmonic functions (i.e., solutions of the equationsLh=0). Putu∈U ⁰ ifu∈U and ifu≤h for someh∈H. To everyu∈U ⁰ there corresponds the minimalL-harmonic functionh _u which dominatesu andu→h _u is a 1–1 mapping fromU ⁰ onto a subsetH ⁰ ofH. The inverse mapping associates with everyh∈H ⁰ the maximal element ofU dominated byh. Supposeg(x, dy) is Green's kernel,k(x, y) is the Martin kernel and ?M is the Martin boundary associated withL. A subset Γ of ?M is calledR-polar if it is not hit by the rangeR of the (L, α)-superdiffusion. It is calledM-polar if $\int\limits_M {g\left( {c,dx} \right)[\int\limits_\Gamma {k(x,y)v(dy)]^\alpha } } $ is equal to 0 or ∞ for everyc∈M and every measure ρ. Everyh∈H has a unique representation $h(x) = \int\limits_{\partial M} {k\left( {x,y} \right)v\left( {dy} \right)} $ where ρ is a measure concentrated on the minimal partM ^* of ?M. We show that the condition:

1. ρ(Γ)=0 for allR sets Γ is necessary and the condition:
2. ρ(Γ)=0 for allM-polar sets Γ is sufficient forh to belong toH ⁰. IfM is a bounded domain of classC ^{2, λ} in ? ^d , then conditions (a) and (b) are equivalent and therefore each of them characterizesH ⁰. This was conjectured by Dynkin a few years ago and proved in a recent paper of Le Gall forL=Δ, α=2 and domains of classC ⁵.

     

Upper bounds for configurations and polytopes inR d

We give a new upper bound onn ^d(d+1)n on the number of realizable order types of simple configurations ofn points inR ^d , and ofn2d ² n on the number of realizable combinatorial types of simple configurations. It follows as a corollary of the first result that there are no more thann ^d(d+1)n combinatorially distinct labeled simplicial polytopes inR ^d withn vertices, which improves the best previous upper bound ofn ^{cn d/2}.Supported in part by NSF Grant DMS-8501492 and PSC-CUNY Grant 665258.Supported in part by NSF Grant DMS-8501947.     

Simulated annealing with a potential function with discontinuous gradient on Rd

In this paper, we have proven that the simulated annealing processdX _t = ?β(t) ?U (X _t ) + √2dW _tt with a potential function on R^d, of which the gradient is discontinuous, converges in probability to a neighborhood of the global minima of the potential function.     

NP-completeness of some problems of partitioning and covering in graphs

Given a digraph G = (X,U) such that ? x ∈ X, d⁺ (x) = d^- (x) = 2, we prove that the problem of determining whether U can be decomposed into two hamiltonian circuits is an NP-complete problem. From there, we deduce that it is NP-complete to determine the path-numbers of graphs and digraphs, even if these graphs have maximum degree four.