Décomposition spectrale dans des algèbres munies d'un star-produit

Summary The purpose of this paper is to study, in intrinsic way, the Moyal's product, defined in the flat space R ²ⁿ. This product is defined here with the twisted convolution and the Fourier transform. The S(R ²ⁿ) and L²(R ²ⁿ) spaces are_*5-algebras. Because of this definition, the_*V-product of some tempered distributions is defined. Let O _M ^v be the set of multiplication operators in S(R ²ⁿ). By transposition, the S(R ²ⁿ) space is a right-module on O _M ^v . The support of f_*v g is different from the support of f·g; under large enough hypotheses, there is a Taylor's formula for the star-product function of the v variable. The ^v space of the multiplication operators in L²(R ²ⁿ) is defined here as the space of tempered distributions, the image of which is the set of bounded operators in L²(R ²ⁿ) by the Weyl map. After the study of ^v space, it is possible to show the spectral resolution of the real elements of ^v or of O _M ^v , which satisfies a, probably superfluous, hypothesis.     

Theorems about traces and the extension of distributions

In this paper we present the necessary and sufficient condition of epimorphism of the operator where the Q_i(d) are differential operators with constant coefficients, R^m is a subspace of Rⁿ, and H(Rⁿ) and H^vi(R^m) are distribution spaces introduced in [1]. We prove the existence of a linear continuous operator which is the right inverse of. There are 4 references.Translated from Matematicheskie Zametki, Vol. 2, No. 6, pp. 577–588, December, 1967.     

Toeplitz operators on harmonic Bergman spaces

We study Toeplitz operators on the harmonic Bergman spaceb ^p (B), whereB is the open unit ball inR ⁿ(n2), for 1<p. We give characterizations for the Toeplitz operators with positive symbols to be bounded, compact, and in Schatten classes. We also obtain a compactness criteria for the Toeplitz operators with continuous symbols.     

Multiresolution Approximations and Wavelet Bases of WeightedLpSpaces

We study boundedness and convergence on L ^p (R ⁿ ,d) of the projection operators P _j given by MRA structures with non-necessarily compactly supported scaling function. As a consequence, we prove that if w is a locally integrable function such that w ^-(1/p–1)(x) (1+|x|)^-N is integrable for some N > 0, then the Muckenhoupt A _p condition is necessary and sufficient for the associated wavelet system to be an unconditional basis for the weighted space L ^p (R ⁿ ,w(x) dx), 1 < p < .     

变量核分数次积分在Hardy空间的有界性

§ 1　 Introduction and main resultsLet Sn- 1 be the unitsphere in Rn(n≥ 2 ) equipped with normalized Lebesgue measure dσ= dσ(z′) .We say that a functionΩ(x,z) defined on Rn× Rnbelongs to L∞ (Rn)× Lr(Sn- 1 )(r≥ 1 ) ,ifΩ(x,z) satisfies the following two conditions,(i) for any x,z∈Rnandλ>0 ,there hasΩ(x,λz) =Ω(x,z) ;(ii)‖Ω‖L∞(Rn)× Lr(Sn- 1) :=supx∈ Rn∫Sn- 1|Ω(x,z′) | rdσ(z′) 1 / r<∞ .For 0 <α相似文献   

Modulation spaces and pseudodifferential operators

We use methods from time-frequency analysis to study boundedness and traceclass properties of pseudodifferential operators. As natural symbol classes, we use the modulation spaces onR ^2d , which quantify the notion of the time-frequency content of a function or distribution. We show that if a symbol lies in the modulation spaceM _,1 (R ^2d ), then the corresponding pseudodifferential operator is bounded onL ²(R ^d ) and, more generally, on the modulation spacesM _p,p (R ^d ) for 1p. If lies in the modulation spaceM _2,2 ^s (R ^2d )=L _s ^/2 (R ^2d )H ^s (R ^2d ), i.e., the intersection of a weightedL ²-space and a Sobolev space, then the corresponding operator lies in a specified Schatten class. These results hold for both the Weyl and the Kohn-Nirenberg correspondences. Using recent embedding theorems of Lipschitz and Fourier spaces into modulation spaces, we show that these results improve on the classical Calderòn-Vaillancourt boundedness theorem and on Daubechies' trace-class results.     

Hölder type quasicontinuity

It is proved that a functionuL ^m,p (R ⁿ ) (which coincides with the Sobolev spaceW ^1,p (R ⁿ ) ifm=1) coincides with a Hölder continuous functionw outside a set of smallm,q-capacity, whereq<p. Moreover, ifm=1, then the functionw can be chosen to be close tou in theW ^1,p -norm.     

Additive preservers of idempotence and Jordan homorphisms between rings of square matrices

Suppose R is an idempotence-diagonalizable ring. Let n and m be two arbitrary positive integers with n ≥ 3. We denote by Mn（R） the ring of all n x n matrices over R. Let （Jn（R）） be the additive subgroup of Mn（R） generated additively by all idempotent matrices. Let JJ = （Jn（R）） or Mn（R）. We describe the additive preservers of idempotence from JJ to Mm（R） when 2 is a unit of R. Thereby, we also characterize the Jordan （respectively, ring and ring anti-） homomorphisms from Mn （R） to Mm （R） when 2 is a unit of R.     

Capacitary inequalities for fractional integrals,with applications to partial differential equations and Sobolev multipliers

Some new characterizations of the class of positive measures γ onR ⁿ such thatH _p ^l ∉L _p (γ) are given whereH _p ^l (1<p<∞ 0<l∞) is the space of Bessel potentials This imbed ding as well as the corresponding trace inequality

ltivariate Hausdorff operators on the spaces H1(Rn) and BMO(Rn)

Summary A multivariate Hausdorff operator H = H(, c, A) is defined in terms of a -finite Borel measure on Rⁿ, a Borel measurable function c on Rⁿ, and an n × n matrix A whose entries are Borel measurable functions on rⁿ and such that A is nonsingular -a.e. The operator H*:= H (, c | det A^-1|, A^-1) is the adjoint to H in a well-defined sense. Our goal is to prove sufficient conditions for the boundedness of these operators on the real Hardy space H¹(Rⁿ) and BMO (Rⁿ). Our main tool is proving commuting relations among H, H*, and the Riesz transforms R_j. We also prove commuting relations among H, H*, and the Fourier transform.     

Rigidity theorem for harmonic maps from Riemannian manifold to Grassmannian manifold

We first study the Grassmannian manifoldG _n (R^n+p)as a submanifold in Euclidean space ⁿ (R ^n+p). Then we give a local expression for each map from Riemannian manifoldM toG ⁿ (R ^n+p) ⁿ (R ^n+p), and use the local expression to establish a formula which is satisfied by any harmonic map fromM toG _n (R ^n+p). As a consequence of this formula we get a rigidity theorem.     

ON THE SOLVABILITY OF NONLINEAR BOUNDARY VALUE PROBLEMS FOR FUNCTIONAL DIFFERENTIAL EQUATIONS

Sufficient conditions are established for the solvability of the boundary value problem where p : C(I; R ⁿ) × C(I; R ⁿ) L(I; R ⁿ), q : C(I; R ⁿ) L(I; R ⁿ), l : C(I, R ⁿ) × C(I; R ⁿ) R ⁿ, and c _n : C(I, R ⁿ) R ⁿ are continuous operators, and p(x, ) and l(x, ) are linear operators for any fixed .     

Vertex-reinforced random walk

Summary This paper considers a class of non-Markovian discrete-time random processes on a finite state space {1,...,d}. The transition probabilities at each time are influenced by the number of times each state has been visited and by a fixed a priori likelihood matrix,R, which is real, symmetric and nonnegative. LetS _i (n) keep track of the number of visits to statei up to timen, and form the fractional occupation vector,V(n), where . It is shown thatV(n) converges to to a set of critical points for the quadratic formH with matrixR, and that under nondegeneracy conditions onR, there is a finite set of points such that with probability one,V(n)p for somep in the set. There may be more than onep in this set for whichP(V(n)p)>0. On the other handP(V(n)p)=0 wheneverp fails in a strong enough sense to be maximum forH.This research was supported by an NSF graduate fellowship and by an NSF postdoctoral fellowship     

Induced operators on symmetry classes of tensors

LetV be ann-dimensional inner product space,T _i ,i=1,...,k, k linear operators onV, H a subgroup ofS _m (the symmetric group of degreem), a character of degree 1 andT a linear operator onV. Denote byK(T) the induced operator ofT onV (H), the symmetry class of tensors associated withH and . This note is concerned with the structure of the setK _{, m} ^H (T₁,...,T_k) consisting of all numbers of the form traceK(T ₁ U ₁...T _k U _k ) whereU _i ,i=1,...k vary over the group of all unitary operators onV. For V=ⁿ or ⁿ, it turns out thatK _{, m} ^H (T₁,...,T_k) is convex whenm is not a multiple ofn. Form=n, there are examples which show that the convexity of _{, m} ^H (T₁,...,T_k) depends onH and .The author wishes to express his thanks to Dr. Yik-Hoi Au-Yeung for his valuable advice and encouragement.     

Differential operators for Siegel-Jacobi forms

For any positive integers n and m, H_(n,m):= H_n× C~(m,n) is called the Siegel-Jacobi space, with the Jacobi group acting on it. The Jacobi forms are defined on this space. We compute the Chern connection of the Siegel-Jacobi space and use it to obtain derivations of Jacobi forms. Using these results, we construct a series of invariant differential operators for Siegel-Jacobi forms. Also two kinds of Maass-Shimura type differential operators for H_(n,m) are obtained.     

Linear foliations ofT n

We present a definition of diophantine matrix and use this concept to distinguish two classes of minimal linear foliations ofT ⁿ, the diophantine and the Liouville one. Let _p , 1pn–1, denote a minimal (all leaves are dense) linearp-dimensional foliation ofT ⁿ, andH ^om(T ⁿ, _p ), 1mp, the cohomology group of type (0,m) of the foliated manifold (T ⁿ, _p ). Our main result is the computation of these groups.H ^om(T ⁿ, _p ) is isomorphic to if _p is diophantine and is an infinite dimensional non-Hausdorff vector space if _p is Liouville. Some of these groups were computed before, see [4], [6] and [9].     

Gaussian kernels have only Gaussian maximizers

A Gaussian integral kernelG(x, y) onR ⁿ ×R ⁿ is the exponential of a quadratic form inx andy; the Fourier transform kernel is an example. The problem addressed here is to find the sharp bound ofG as an operator fromL ^p (R ⁿ ) toL ^p (R ⁿ ) and to prove that theL ^p (R ⁿ ) functions that saturate the bound are necessarily Gaussians. This is accomplished generally for 1<pq< and also forp>q in some special cases. Besides greatly extending previous results in this area, the proof technique is also essentially different from earlier ones. A corollary of these results is a fully multidimensional, multilinear generalization of Young's inequality.Oblatum 19-XII-1989Work partially supported by U.S. National Science Foundation grant PHY-85-15288-A03