3,320 research outputs found
Measures with zeros in the inverse of their moment matrix
We investigate and discuss when the inverse of a multivariate truncated
moment matrix of a measure has zeros in some prescribed entries. We
describe precisely which pattern of these zeroes corresponds to independence,
namely, the measure having a product structure. A more refined finding is that
the key factor forcing a zero entry in this inverse matrix is a certain
conditional triangularity property of the orthogonal polynomials associated
with .Comment: Published in at http://dx.doi.org/10.1214/07-AOP365 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Collectively enhanced resonant photoionization in a multi-atom ensemble
Photoionization of an atom via interatomic correlations to N neighboring
atoms may be strongly enhanced due to constructive interference of quantum
pathways. The ionization proceeds via resonant photoexcitation of a neighbor
atom and subsequent interatomic Coulombic decay. The enhancement can scale with
N^2, leading to "super-enhanced photoionization".Comment: 4 pages, 2 figure
An Iterative Receiver for OFDM With Sparsity-Based Parametric Channel Estimation
In this work we design a receiver that iteratively passes soft information
between the channel estimation and data decoding stages. The receiver
incorporates sparsity-based parametric channel estimation. State-of-the-art
sparsity-based iterative receivers simplify the channel estimation problem by
restricting the multipath delays to a grid. Our receiver does not impose such a
restriction. As a result it does not suffer from the leakage effect, which
destroys sparsity. Communication at near capacity rates in high SNR requires a
large modulation order. Due to the close proximity of modulation symbols in
such systems, the grid-based approximation is of insufficient accuracy. We show
numerically that a state-of-the-art iterative receiver with grid-based sparse
channel estimation exhibits a bit-error-rate floor in the high SNR regime. On
the contrary, our receiver performs very close to the perfect channel state
information bound for all SNR values. We also demonstrate both theoretically
and numerically that parametric channel estimation works well in dense
channels, i.e., when the number of multipath components is large and each
individual component cannot be resolved.Comment: Major revision, accepted for IEEE Transactions on Signal Processin
Algorithm Developments for Discrete Adjoint Methods
This paper presents a number of algorithm developments for adjoint methods using the 'discrete' approach in which the discretisation of the non-linear equations is linearised and the resulting matrix is then transposed. With a new iterative procedure for solving the adjoint equations, exact numerical equivalence is maintained between the linear and adjoint discretisations. The incorporation of strong boundary conditions within the discrete approach is discussed, as well as a new application of adjoint methods to linear unsteady flow in turbomachinery
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