29,073 research outputs found
Frequency-Domain Stochastic Modeling of Stationary Bivariate or Complex-Valued Signals
There are three equivalent ways of representing two jointly observed
real-valued signals: as a bivariate vector signal, as a single complex-valued
signal, or as two analytic signals known as the rotary components. Each
representation has unique advantages depending on the system of interest and
the application goals. In this paper we provide a joint framework for all three
representations in the context of frequency-domain stochastic modeling. This
framework allows us to extend many established statistical procedures for
bivariate vector time series to complex-valued and rotary representations.
These include procedures for parametrically modeling signal coherence,
estimating model parameters using the Whittle likelihood, performing
semi-parametric modeling, and choosing between classes of nested models using
model choice. We also provide a new method of testing for impropriety in
complex-valued signals, which tests for noncircular or anisotropic second-order
statistical structure when the signal is represented in the complex plane.
Finally, we demonstrate the usefulness of our methodology in capturing the
anisotropic structure of signals observed from fluid dynamic simulations of
turbulence.Comment: To appear in IEEE Transactions on Signal Processin
Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
We present a retrieval method based on Bayesian analysis to infer the
atmospheric compositions and surface or cloud-top pressures from transmission
spectra of exoplanets with general compositions. In this study, we identify
what can unambiguously be determined about the atmospheres of exoplanets from
their transmission spectra by applying the retrieval method to synthetic
observations of the super-Earth GJ 1214b. Our approach to infer constraints on
atmospheric parameters is to compute their joint and marginal posterior
probability distributions using the MCMC technique in a parallel tempering
scheme. A new atmospheric parameterization is introduced that is applicable to
general atmospheres in which the main constituent is not known a priori and
clouds may be present. Our main finding is that a unique constraint of the
mixing ratios of the absorbers and up to two spectrally inactive gases (such as
N2 and primordial H2+He) is possible if the observations are sufficient to
quantify both (1) the broadband transit depths in at least one absorption
feature for each absorber and (2) the slope and strength of the molecular
Rayleigh scattering signature. The surface or cloud-top pressure can be
quantified if a surface or cloud deck is present. The mean molecular mass can
be constrained from the Rayleigh slope or the shapes of absorption features,
thus enabling to distinguish between cloudy hydrogen-rich atmospheres and high
mean molecular mass atmospheres. We conclude, however, that without the
signature of Rayleigh scattering--even with robustly detected infrared
absorption features--there is no reliable way to tell if the absorber is the
main constituent of the atmosphere or just a minor species with a mixing ratio
of <0.1%. The retrieval method leads us to a conceptual picture of which
details in transmission spectra are essential for unique characterizations of
well-mixed atmospheres.Comment: 23 pages, 13 figures, accepted at ApJ, submitted to ApJ on Nov 4,
201
Single-trial multiwavelet coherence in application to neurophysiological time series
A method of single-trial coherence analysis is presented, through the application of continuous muldwavelets. Multiwavelets allow the construction of spectra and bivariate statistics such as coherence within single trials. Spectral estimates are made consistent through optimal time-frequency localization and smoothing. The use of multiwavelets is considered along with an alternative single-trial method prevalent in the literature, with the focus being on statistical, interpretive and computational aspects. The multiwavelet approach is shown to possess many desirable properties, including optimal conditioning, statistical descriptions and computational efficiency. The methods. are then applied to bivariate surrogate and neurophysiological data for calibration and comparative study. Neurophysiological data were recorded intracellularly from two spinal motoneurones innervating the posterior,biceps muscle during fictive locomotion in the decerebrated cat
The binned bispectrum estimator: template-based and non-parametric CMB non-Gaussianity searches
We describe the details of the binned bispectrum estimator as used for the
official 2013 and 2015 analyses of the temperature and polarization CMB maps
from the ESA Planck satellite. The defining aspect of this estimator is the
determination of a map bispectrum (3-point correlator) that has been binned in
harmonic space. For a parametric determination of the non-Gaussianity in the
map (the so-called fNL parameters), one takes the inner product of this binned
bispectrum with theoretically motivated templates. However, as a complementary
approach one can also smooth the binned bispectrum using a variable smoothing
scale in order to suppress noise and make coherent features stand out above the
noise. This allows one to look in a model-independent way for any statistically
significant bispectral signal. This approach is useful for characterizing the
bispectral shape of the galactic foreground emission, for which a theoretical
prediction of the bispectral anisotropy is lacking, and for detecting a
serendipitous primordial signal, for which a theoretical template has not yet
been put forth. Both the template-based and the non-parametric approaches are
described in this paper.Comment: Latex 42 pages with 10 figures and JCAP macros. v2: corrected small
mistake in section 5.3, changed colour scale of slice figures, other minor
changes and additions, matches published versio
- …