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We discuss the concept of a repetitive control system, and recall the main stability theorem for such systems. We give new, improved estimates on the error signal in a repetitive control system. As an extension of repetitive control, we introduce a new control system which is capable of tracking (or rejecting) a superposition of several periodic signals(More)
We survey the literature on well-posed linear systems, which has been an area of rapid development in recent years. We examine the particular subclass of conservative systems and its connections to scattering theory. We study some transformations of well-posed systems, namely duality and time-flow inversion, and their effect on the transfer function and the(More)
We consider infinite-dimensional linear systems without a-priori wellposedness assumptions, in a framework based on the works of M. Livšic, M.S. Brodskĭı, Y.L. Smuljan and others. We define the energy in the system as the norm of the state squared (other, possibly indefinite quadratic forms will also be considered). We derive a number of equivalent(More)
An infinite-dimensional linear system described by ẋ(t) = Ax(t) + Bu(t) (t ≥ 0) is said to be optimizable if for every initial state x(0), an input u ∈ L2 can be found such that x ∈ L2. Here, A is the generator of a strongly continuous semigroup on a Hilbert space and B is an admissible control operator for this semigroup. In this paper we investigate(More)
We examined the relationship among social discrimination, violence, and illicit drug use among an ethnically diverse cohort of young men who have sex with men (YMSM) residing in Los Angeles. Five Hundred twenty-six YMSM (aged 18-24 years) were recruited using a venue-based, stratified probability sampling design. Surveys assessed childhood financial(More)