共查询到20条相似文献,搜索用时 359 毫秒
1.
Thorsten Kröncke 《Integral Equations and Operator Theory》2001,40(1):80-105
Let T- S, be a family of not necessarily bounded semi-Fredholm operators, where T and S are operators acting between Banach spaces X and Y, and where S is bounded with D(S) D(T). For compact sets , as well as for certain open sets , we investigate existence and minimal rank of bounded feedback perturbations of the form F=BE such that min.ind (T-S+F)=0 for all . Here B is a given operator from a linear space Z to Y and E is some operator from X to Z.We give a simple characterization of that situation, when such regularizing feedback perturbations exist and show that for compact sets the minimal rank never exceeds max { min.ind (T-S) }+1. Moreover, an example shows that the minimal rank, in fact, may increase from max {...} to max {...}+1, if the given B enforces a certain structure of the feedbachk perturbation F.However, the minimal rank is equal to max { min.ind (T-S) }, if is an open set such that min.ind (T-S) already vanishes for all but finitely many points . We illustrate this result by applying it to the stabilization of certain infinite-dimensional dynamical systems in Hilbert space. 相似文献
2.
Consider a functionL() defined on an interval of the real axis whose values are linear bounded selfadjoint operators in a Hilbert spaceH. A point 0 and a vector
0 H(
0 0) are called eigenvalue and eigenvector ofL() ifL() ifL(0)
0 = 0. Supposing that the functionL() can be represented as an absolutely convergent Fourier integral, the interval is sufficiently small and the derivative will be positive at some point, it has been proved that all the eigenvectors of the operator-functionL() corresponding to the eigenvalues from the interval form an unconditional basis in the subspace spanned by them. 相似文献
3.
Let {n}
n=0
be the eigenvalue sequence of a symmetric Hilbert-Schmidt operator onL
2(I). WhenI is an open interval, a necessary condition for {n}
n=0
to be in the sequence space is obtained. WhenI is a closed bounded interval, sufficient conditions for {n}
n=0
to be in the sequence space – are obtained. 相似文献
4.
Yin Chen 《Integral Equations and Operator Theory》2001,41(3):255-263
Let (E
0,E
1) be a compatible couple of Banach spaces, and letE
: 0Re1 be the complex interpolation spaces ofE
0,E
1. LetT be a closed linear operator onE
0+E
1, then the restrictionT
ofT to eachE
is closed. If we denote by
the extended spectrum ofT
inE
, then, under appropriate conditions, it is shown that the map
is an analytic multifunction in the strip {C0<Re<1}. We use these results to give some applications to the spectral theory of semigroups. 相似文献
5.
Sharad Sane 《Designs, Codes and Cryptography》2001,23(3):291-296
A proof of the following conjecture of Jungnickel and Tonchev on quasi-multiple quasi-symmetric designs is given: Let D be a design whose parameter set (v,b,r,k,) equals (v,sv,sk,k, s) for some positive integer s and for some integers v,k, that satisfy (v-1) = k(k-1) (that is, these integers satisfy the parametric feasibility conditions for a symmetric (v,k,)-design). Further assume that D is a quasi-symmetric design, that is D has at most two block intersection numbers. If (k, (s-1)) = 1, then the only way D can be constructed is by taking multiple copies of a symmetric (v,k, )-design. 相似文献
6.
u=f(x)+S(u), S — , u-G(u), G —
. B
p,q
s
() -F
p,q
s
(). R
n
—
. — .
p,q
s
F
p,q
s
. 相似文献
7.
D. Y. Ye 《Journal of Optimization Theory and Applications》1993,76(2):287-304
LetA(·) be ann × n symmetric affine matrix-valued function of a parameteruR
m
, and let (u) be the greatest eigenvalue ofA(u). Recently, there has been interest in calculating (u), the subdifferential of atu, which is useful for both the construction of efficient algorithms for the minimization of (u) and the sensitivity analysis of (u), namely, the perturbation theory of (u). In this paper, more generally, we investigate the Legendre-Fenchel conjugate function of (·) and the -subdifferential (u) of atu. Then, we discuss relations between the set (u) and some perturbation bounds for (u).The author is deeply indebted to Professor J. B. Hiriart-Urruty who suggested this study and provided helpful advice and constant encouragement. The author also thanks the referees and the editors for their substantial help in the improvement of this paper. 相似文献
8.
Walter Benz 《Aequationes Mathematicae》1992,43(2-3):177-182
Summary The following theorem holds true.
Theorem.
Let X be a normed real vector space of dimension 3 and let k > 0 be a fixed real number. Suppose that f: X X and g: X × X are functions satisfying x – y = k f(x) – f(y) = g(x, y)(x – y) for all x, y X. Then there exist elements and t X such that f(x) = x + t for all x X and such that g(x, y) = for all x, y X with x – y = k. 相似文献
9.
Michael Sand 《Integral Equations and Operator Theory》1996,26(2):210-221
If is a complex, separable Hilbert space, letL
2 () denote theL
2-space of functions defined on the unit circle and having values in . The bilateral shift onL
2() is the operator (U
f)()=f(). A Hilbert spaceH iscontractively contained in the Hilbert spaceK ifHK and the inclusion mapH–K is a contraction. We describe the structure of those Hilbert spaces, contractively contained inL
2(), that are carried into themselves contractively byU
. We also do this for the subcase of those spaces which are carried into themselves unitarily byU
. 相似文献
10.
In the present paper we consider a selfadjoint and nonsmooth operator-valued function on (c, d)R
1. We suppose that the equation (L()x, x)=0,x0, has exactly one rootp(x) (c, d) and the functionf()=(L()x, x) is increasing at the pointp(x). We discuss questions of the variational theory of the spectrum. Some theorems on the variational properties of the spectrum are proved. 相似文献
11.
Paolo Lipparini 《Archive for Mathematical Logic》1996,35(2):63-87
We develop a method for extending results about ultrafilters into a more general setting. In this paper we shall be mainly concerned with applications to cardinality logics. For example, assumingV=L, Gödel's Axiom of Constructibility, we prove that if > then the logic with the quantifier there exist many is (,)-compact if and only if either is weakly compact or is singular of cofinality<. As a corollary, for every infinite cardinals and , there exists a (,)-compact non-(,)-compact logic if and only if either < orcf<cf or < is weakly compact.Counterexamples are given showing that the above statements may fail, ifV=L is not assumed.However, without special assumptions, analogous results are obtained for the stronger notion of [,]-compactness. 相似文献
12.
Yu. Lyubich 《Integral Equations and Operator Theory》1995,23(2):232-244
If X is a real Banach space, then the inequality x defines so-called hyperbolic cone in E=X. We develop a relevant version of Perron-Frobenius-Krein-Rutman theory. 相似文献
13.
An integer partition {1,2,...,
v
} is said to be graphical if there exists a graph with degree sequence
i
. We give some results corcerning the problem of deciding whether or not almost all partitions of even integer are non-graphical. We also give asymptotic estimates for the number of partitions with given rank. 相似文献
14.
Given a bounded linear operatorA in an infinite dimensional Banach space and a compact subset of a connected component of its semi-Fredholm domain, we construct a finite rank operatorF such that –A+F is bounded below (or surjective) for each ,F
2=0 and rankF=max min{dimN(–A), codimR(–A)}, if ind(–A)0 (or ind(–A)0, respectively) for each . 相似文献
15.
Martin Krüskemper 《manuscripta mathematica》1989,65(2):225-243
In this paper we examine for which Witt classes ,..., n over a number field or a function fieldF there exist a finite extensionL/F and 2,..., n L* such thatT
L/F
()=1 andTr
L/F
(i)=i fori=2,...n. 相似文献
16.
F. A. Sukochev 《Integral Equations and Operator Theory》1996,26(1):102-124
If is a surjective isometry of the separable symmetric operator spaceE(M, ) associated with the approximately finite-dimensional semifinite factorM and if ·
E(M,)
is not proportional to ·
L
2, then there exist a unitary operatorUM and a Jordan automorphismJ ofM such that(x)=UJ(x) for allxME(M, ). We characterize also surjective isometries of vector-valued symmetric spacesF((0, 1), E(M, )).Research supported by the Australian Research Council 相似文献
17.
LetT B(H) be a bounded linear operator on a complex Hilbert spaceH. Let 0 (T) be an isolated point of (T) and let
be the Riesz idempotent for 0. In this paper, we prove that ifT isp-hyponormal or log-hyponormal, thenE is self-adjoint andE
H=ker(H–0)=ker(H–0
*.This research was supported by Grant-in-Aid Research 1 No. 12640187. 相似文献
18.
We give uniform estimates of entire functions of exponential type less than having sufficiently small logarithmic sums over real sequences {
n
} satisfying |
n
–n|L and
n+1–
n
for fixed positive constants L and . We thereby generalize results about logarithmic sums over the set of integers and so-called relatively h-dense sequences. 相似文献
19.
A topological spaceX whose topology is the order topology of some linear ordering onX, is called aninterval space. A space in which every closed subspace is homeomorphic to a clopen subspace, is called aCO space and a space isscattered if every non-empty subspace has an isolated point. We regard linear orderings as topological spaces, by equipping them with their order topology. IfL andK are linear orderings, thenL
*, L+K, L · K denote respectively the reverse ordering ofL, the ordered sum ofL andK and the lexicographic order onL x K (so · 2=+). Ordinals are considered as linear orderings, and cardinals are initial ordinals. For cardinals , l 0, letL(K,)=K+1+*.Theorem: Let X be a compact interval scattered space. Then X is a CO space if and only if X is homeomorphic to a space of the form +1+1
L(K
i
i), where is any ordinal, n , for every ii ,i are regular cardinals and Kii, and if n>0, then max({Ki:i相似文献
20.
Fabio Cipriani 《Potential Analysis》1994,3(2):203-218
We give a general criterion for the intrinsic ultracontractivity of Dirichlet Laplacians –
D
on domainsD ofR
d d 3, based on the Lieb's formula. It applies to various classes of domains (e.g. John, Hölder andL
p-averaging domains) and gives new conditions for intrinsic ultracontractivity in terms of the Minkowski dimension of the boundary D. In particular, isotropic self-similar fractals and domains satisfying a c-covering condition are considered. 相似文献