On definability of completely decomposable torsion-free Abelian groups by certain groups of homomorphisms

Let C be an Abelian group. An Abelian group A from a class X of Abelian groups is said to be _C H-definable in X if, for any group B ∈ X, the isomorphism Hom(C,A) ≅ Hom(C,B) implies that A ≅ B. If every group from X is _C H-definable in X, then X is called an _C H-class. In this paper, we study conditions under which a class of completely decomposable torsion-free Abelian groups is an _C H-class, where C is a vector group.     

The Green-Kehayopulu relation H in le-semigroups

The definition of the Green—Kehayopulu relation H in le -semigroups mimics the definition of the usual Green relation H in plain semigroups. We show, however, that certain properties of H -classes essentially differ from those of H-classes: a non-singleton H -class cannot be a subgroup and an H -class H satisfying ``Green's condition' (there exist a,b ∈ H such that a, b ∈ H) need not constitute a subsemigroup. We provide various conditions that ensure that an H -class forms a subsemigroup.     

Remarks on the structure of the multiplicative monoid of integers modulom

This note presents some results concerningH-classes, Schützenberger groups, and regular elements in the multiplicative monoid ℤ _m of integers modulom. It also shows that in ℤ _m , the product of twoH-classes is anH-class.     

Schatten Class Hankel Operators on the Harmonic Bergman Space of the Unit Ball

We give a necessary and sufficient condition for Hankel operators H_f on the harmonic Bergman space of the unit ball to be in the Schatten p-class for 2 ≤ p < ∞. A special case when symbol f is a harmonic function is also considered.     

H∞ robust control based on event‐triggered sampling for hybrid systems with singular Markovian jump

The problem of H_∞ robust control based on event‐triggered sampling for a class of singular hybrid systems with Markovian jump is considered in this paper. The primary object of this paper here is to design the event‐triggered sampling controller for a class of uncertain singular Markovian systems, and two fundamental issues on mean square exponential admissibility and H_∞ robust performance are fully addressed. By making use of a suitable Lyapunov functional, in combination with both infinitesimal operator and linear matrices inequalities(LMIs), the sufficient criteria are derived to guarantee the controlled singular hybrid system with Markovian jump is robustly exponentially mean‐square admissible and has a prescribed H_∞ performance γ. Finally, a typical RLC circuit system is given to show the effectiveness of the proposed control method.     

Reduction of the number of associate classes of hypercubic association schemes

The reduction of the number of associate classes of some hypercubic association schemes by clubbing certain associate classes has been studied in the paper. It has been found that the reduction of anm-class hypercubic association scheme forv=2 ^m treatments into a 2-class association scheme is always possible. Further it is proved herein that them-class hypercubic association scheme forv=s ^m treatments is reducible (i) to a 3-class association scheme, whens=3 and (ii) to a 2-class association scheme, whens=4, which really hasp ₁₁ ¹ =p ₁₁ ² and hence leads to a series of balanced incomplete block designs.     

Complex structured singular value analysis using fixed-structure dynamic D-scales

Models of systems are always inexact. Hence, to better predict the performance of a system it is necessary to take into account uncertainty in a nominal model of a system. The structured singular value was developed to nonconservatively analyze robust stability and performance for systems with multiple-block uncertainty. In practice, optimization techniques are used to compute an upper bound on the structured singular value. For dynamic uncertainty with bounded magnitude and arbitrary phase (i.e., "complex uncertainty"), the standard approach to computing an upper bound involves finding diagonal scaling matrices D(jω) that minimize σ_max (D(jω)G(jω)D^-1(jω)) over a (theoretically) infinite number of frequencies. The order of the corresponding stable, minimum phase, rational function D(s) (if it exists) is hence arbitrary, which can lead to very high order controllers when D(s) is used for controller synthesis. This paper develops a fixed-structure approach to computing an upper bound for the complex structured singular value. In particular, by relying on results from mixed-norm H₂/H_∞ analysisD(s) is a priori constrained to be a rational matrix function of a chosen order and a new approach to computing an upper bound on the structured singular value is developed. The results are illustrated using two examples which clearly demonstrate the suboptimality of standard curve fitting. The proposed approach can be extended to mixed uncertainty and structured singular value controller synthesis without D — K type iteration.     

The product of the idempotents and an $\mathcal{H}$-class of the finite full transformation semigroup

We investigate the set products S=EH, where E is the set of idempotents of a finite full transformation semigroup T _X and H is an arbitrary H\mathcal{H}-class of T _X . We show that S is a semigroup and is a union of H\mathcal{H}-classes of T _X . We determine the nature of this union through use of Hall’s Marriage Lemma. We describe Green’s relations and thereby show that S has regular elements of all possible ranks and that \operatornameReg(S)\operatorname{Reg}(S) forms a right ideal of S.     

Correctors for some asymptotic problems

In the theory of anisotropic singular perturbation boundary value problems, the solution u _ɛ does not converge, in the H ¹-norm on the whole domain, towards some u ₀. In this paper we construct correctors to have good approximations of u _ɛ in the H ¹-norm on the whole domain. Since the anisotropic singular perturbation problems can be connected to the study of the asymptotic behaviour of problems defined in cylindrical domains becoming unbounded in some directions, we transpose our results for such problems.     

Nonself-Adjoint Operators with Almost Hermitian Spectrum: Weak Annihilators

We consider nonself-adjoint nondissipative trace class additive perturbations L=A+iV of a bounded self-adjoint operator A in a Hilbert space ,H. The main goal is to study the properties of the singular spectral subspace N _i ⁰ of L corresponding to part of the real singular spectrum and playing a special role in spectral theory of nonself-adjoint nondissipative operators.To some extent, the properties of N _i ⁰ resemble those of the singular spectral subspace of a self-adjoint operator. Namely, we prove that L and the adjoint operator ,L ^* are weakly annihilated by some scalar bounded outer analytic functions if and only if both of them satisfy the condition N _i ⁰ =H. This is a generalization of the well-known Cayley identity to nonself-adjoint operators of the above-mentioned class.     

Approximate identities from Laguerre functions and singular integrals on the Heisenberg group

Suitably scaled Laguerre functions are an approximate identity for multiplicative convolution with test functions on the half line. As an application, we derive a precise connection between the Mikhlin-type expansion of a singular integral operator on a Heisenberg groupH _n and its natural restriction toH _n modulo the center. Research supported by NSF Grant DMS-9800605 and by NSERC Grant OGP0003017.     

Transfer of absolute continuity by a flow generated by a stochastic equation with reflection

Let ϕ_t(x), x ∈ ℝ₊ be a value taken at time t ≥ 0 by a solution of a stochastic equation with normal reflection from a hyperplane starting at initial time from x. We characterize the absolutely continuous (with respect to Lebesgue measure) component and the singular component of a stochastic measure-valued process μ_t = μ ○ ϕ _t ⁻¹ that is the image of a certain absolutely continuous measure μ under random mapping ϕ_t(·). We prove that the restriction of the Hausdorff measure H ^d−1 to the support of the singular component is σ-finite and give sufficient conditions guaranteeing that the singular component is absolutely continuous with respect to H ^d−1. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 12, pp. 1663–1673, December, 2006.     

Superoptimal singular values and indices of matrix functions

LetG be a matrix-valued function on the unit circle which is the sum of a continuous function and anH function. We establish an inequality between corresponding terms of the sequence of singular values of the Hankel operator {s _j (H _G )} and a sequence formed from the superoptimal singular values ofG with repetitions. The number of times each superoptimal singular value is repeated is a positive integer index which is the winding number of a related scalar function on the circle and gives information about the superoptimal error functionG-Q withQH . In the second part of the paper we establish a property of invariance of the sum of the indices corresponding to a particular superoptimal singular value. This establishes the truth of two conjectures made in [PeY].The research was supported by an NSF grant in modern analysis.     

Comparison Theorems for the Eigenvalue Gap of Schr?dinger Operators on the Real Line

We establish several comparison results on the eigenvalue gap for Schr?dinger operators on the real line. The potentials we consider here include symmetric single-well, double-well, U _c -class, M _c -class as well as their perturbations. Some related results on the eigenvalue ratio are also discussed.     

Spectral analysis for convolution operators on locally compact groups

We consider operators H_μ of convolution with measures μ on locally compact groups. We characterize the spectrum of H_μ by constructing auxiliary operators whose kernel contain the pure point and singular subspaces of H_μ, respectively. The proofs rely on commutator methods.     

The narrow class groups of the ℤ<Subscript>17</Subscript>- and ℤ<Subscript>19</Subscript>-extensions over the rational field

Let p be either 17 or 19, let ℤ _p denote the ring of p-adic integers, and let l be a prime number which is a primitive root modulo p ². We shall prove, with the help of a computer, that the l-class group of the ℤ _p -extension over the rational field is trivial. We shall also prove the triviality of the narrow 2-class group of the same ℤ _p -extension.     

Bounded cohomology of group constructions

It is proved that the singular partH _b ^2/(2) (G) of the second group of bounded homology of the discrete groupG is isomorphic to the space of 2-cocycles that vanish on the diagonal. For groupsG representable as HNN-extensions or free products with amalgamation, as well as for groupsG with one defining relation, conditions for the infinite-dimensionality ofH _b ^2/(2) (G) are found. Some applications of bounded cohomology to the width problem for verbal subgroups and to the boundedness problem for group presentations are indicated. Translated fromMatematicheskie Zametki, Vol. 59, No. 4, pp. 546–550, April, 1996. This research was supported by the Russian Foundation for Basic Research under grant No. 93-01-00239.     

Robust H ∞ control for singular systems with time-varying uncertainties

In this paper, we investigate the problem of robust H _∞ control for singular systems with polytopic time-varying parameter uncertainties. By introducing the notion of generalized quadratic H _∞ performance, the relationship between the existence of a robust H _∞ dynamic state feedback controller and that of a robust H _∞ static state feedback controller is given. By using matrix inequalities, the existence conditions of robust H _∞ static state feedback and dynamic output feedback controllers are derived. Moreover, the design methods for such controllers are provided in terms of the solutions of matrix inequalities. An example is also presented to demonstrate the validity of the proposed methods. __________ Translated from Journal of Northeastern University (Natural Science), 2004, 25(2): 110–113     

On Kato's inequality for the Weyl quantized relativistic Hamiltonian

In this note we give a simpler proof of Kato's inequality for the Weyl quantized relativistic HamiltonianH _A ^m of a spinless particle with a more singular vector potentialA(x) than in a previous paper of one of the authors. This article was processed by the author using the Springer-Verlag T_EX mamath macro package 1990