12,639 research outputs found
Input Design for System Identification via Convex Relaxation
This paper proposes a new framework for the optimization of excitation inputs
for system identification. The optimization problem considered is to maximize a
reduced Fisher information matrix in any of the classical D-, E-, or A-optimal
senses. In contrast to the majority of published work on this topic, we
consider the problem in the time domain and subject to constraints on the
amplitude of the input signal. This optimization problem is nonconvex. The main
result of the paper is a convex relaxation that gives an upper bound accurate
to within of the true maximum. A randomized algorithm is presented for
finding a feasible solution which, in a certain sense is expected to be at
least as informative as the globally optimal input signal. In the case
of a single constraint on input power, the proposed approach recovers the true
global optimum exactly. Extensions to situations with both power and amplitude
constraints on both inputs and outputs are given. A simple simulation example
illustrates the technique.Comment: Preprint submitted for journal publication, extended version of a
paper at 2010 IEEE Conference on Decision and Contro
Pulsar Timing Arrays and their Applications
Millisecond pulsars are intrinsically very stable clocks and precise
measurement of their observed pulse periods can be used to study a wide variety
of astrophysical phenomena. In particular, observations of a large sample of
millisecond pulsars at regular intervals, constituting a Pulsar Timing Array
(PTA), can be used as a detector of low-frequency gravitational waves and to
establish a standard of time independent of terrestrial atomic timescales.
Three major timing array projects have been established: The European Pulsar
Timing Array (EPTA), the North American pulsar timing array (NANOGrav) and the
Parkes Pulsar Timing Array (PPTA). Results from the PPTA project are described
in some detail and future prospects for PTA projects are discussed.Comment: 8 pages, 3 figures, to appear in the AIP Conference Proceedings for
the Pulsar Conference 2010, Sardinia, Italy, October 201
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