7,218 research outputs found
Risk hull method and regularization by projections of ill-posed inverse problems
We study a standard method of regularization by projections of the linear
inverse problem , where is a white Gaussian noise,
and is a known compact operator with singular values converging to zero
with polynomial decay. The unknown function is recovered by a projection
method using the singular value decomposition of . The bandwidth choice of
this projection regularization is governed by a data-driven procedure which is
based on the principle of risk hull minimization. We provide nonasymptotic
upper bounds for the mean square risk of this method and we show, in
particular, that in numerical simulations this approach may substantially
improve the classical method of unbiased risk estimation.Comment: Published at http://dx.doi.org/10.1214/009053606000000542 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Evidence for magnetoplasmon character of the cyclotron resonance response of a two-dimensional electron gas
Experimental results on the absolute magneto-transmission of a series of high
density, high mobility GaAs quantum wells are compared with the predictions of
a recent magnetoplasmon theory for values of the filling factor above 2. We
show that the magnetoplasmon picture can explain the non-linear features
observed in the magnetic field evolution of the cyclotron resonance energies
and of the absorption oscillator strength. This provides experimental evidence
that inter Landau level excitations probed by infrared spectroscopy need to be
considered as many body excitations in terms of magnetoplasmons: this is
especially true when interpreting the oscillator strengths of the cyclotron
transitions
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