2,877 research outputs found
Modeling sparse connectivity between underlying brain sources for EEG/MEG
We propose a novel technique to assess functional brain connectivity in
EEG/MEG signals. Our method, called Sparsely-Connected Sources Analysis (SCSA),
can overcome the problem of volume conduction by modeling neural data
innovatively with the following ingredients: (a) the EEG is assumed to be a
linear mixture of correlated sources following a multivariate autoregressive
(MVAR) model, (b) the demixing is estimated jointly with the source MVAR
parameters, (c) overfitting is avoided by using the Group Lasso penalty. This
approach allows to extract the appropriate level cross-talk between the
extracted sources and in this manner we obtain a sparse data-driven model of
functional connectivity. We demonstrate the usefulness of SCSA with simulated
data, and compare to a number of existing algorithms with excellent results.Comment: 9 pages, 6 figure
Arm locking performance with the new LISA design
The Laser Interferometer Space Antenna (LISA) is a future space-based
gravitational wave (GW) detector designed to be sensitive to sources radiating
in the low frequency regime (0.1 mHz to 1 Hz). LISA's interferometer signals
will be dominated by laser frequency noise which has to be suppressed by about
7 orders of magnitude using an algorithm called Time-Delay Interferometry
(TDI). Arm locking has been proposed to reduce the laser frequency noise by a
few orders of magnitude to reduce the potential risks associated with TDI. In
this paper, we present an updated performance model for arm locking for the new
LISA mission using 2.5 Gm arm lengths, the currently assumed clock noise,
spacecraft motion, and shot noise. We also update the Doppler frequency pulling
estimates during lock acquisition.Comment: 21 pages, 13 figure
Determination and optimization of mode matching into optical cavities by heterodyne detection
We report on a novel high-sensitivity method to characterize and improve mode matching into optical cavities. This method is based on heterodyne detection of cylindrical transverse cavity modes. A specially designed annular-segmented photodiode is used to measure the amplitude of nonresonant modes reflected by the cavity. Our measurements allow us to optimize cavity mode matching to nearly 99.98% and will play an important diagnostic role in gravitational-wave detectors
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