2,936 research outputs found
Detecting periodicities with Gaussian processes
We consider the problem of detecting and quantifying the periodic component of
a function given noise-corrupted observations of a limited number of input/output
tuples. Our approach is based on Gaussian process regression, which provides a
flexible non-parametric framework for modelling periodic data. We introduce a novel
decomposition of the covariance function as the sum of periodic and aperiodic kernels.
This decomposition allows for the creation of sub-models which capture the periodic
nature of the signal and its complement. To quantify the periodicity of the signal,
we derive a periodicity ratio which reflects the uncertainty in the fitted sub-models.
Although the method can be applied to many kernels, we give a special emphasis to
the Matérn family, from the expression of the reproducing kernel Hilbert space inner
product to the implementation of the associated periodic kernels in a Gaussian process
toolkit. The proposed method is illustrated by considering the detection of periodically
expressed genes in the arabidopsis genome
Global testing against sparse alternatives in time-frequency analysis
In this paper, an over-sampled periodogram higher criticism (OPHC) test is
proposed for the global detection of sparse periodic effects in a
complex-valued time series. An explicit minimax detection boundary is
established between the rareness and weakness of the complex sinusoids hidden
in the series. The OPHC test is shown to be asymptotically powerful in the
detectable region. Numerical simulations illustrate and verify the
effectiveness of the proposed test. Furthermore, the periodogram over-sampled
by is proven universally optimal in global testing for
periodicities under a mild minimum separation condition.Comment: Published at http://dx.doi.org/10.1214/15-AOS1412 in the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Evidence for 9 planets in the HD 10180 system
We re-analyse the HARPS radial velocities of HD 10180 and calculate the
probabilities of models with differing numbers of periodic signals in the data.
We test the significance of the seven signals, corresponding to seven
exoplanets orbiting the star, in the Bayesian framework and perform comparisons
of models with up to nine periodicities. We use posterior samplings and
Bayesian model probabilities in our analyses together with suitable prior
probability densities and prior model probabilities to extract all the
significant signals from the data and to receive reliable uncertainties for the
orbital parameters of the six, possibly seven, known exoplanets in the system.
According to our results, there is evidence for up to nine planets orbiting HD
10180, which would make this this star a record holder in having more planets
in its orbits than there are in the Solar system. We revise the uncertainties
of the previously reported six planets in the system, verify the existence of
the seventh signal, and announce the detection of two additional statistically
significant signals in the data. If of planetary origin, these two additional
signals would correspond to planets with minimum masses of 5.1
and 1.9 M on orbits with 67.55 and
9.655 days periods (denoted using the 99% credibility
intervals), respectively.Comment: 12 pages, 7 figures, accepted for publication in the Astronomy and
Astrophysic
Searching data for periodic signals
We present two statistical tests for periodicities in the time series. We
apply the two tests to the data taken from Glasgow prototype interferometer in
March 1996. We find that the data contain several very narrow spectral
features. We investigate whether these features can be confused with
gravitational wave signals from pulsars.Comment: 7 pages, 2 figure
The evidence for and against astronomical impacts on climate change and mass extinctions: A review
Numerous studies over the past 30 years have suggested there is a causal
connection between the motion of the Sun through the Galaxy and terrestrial
mass extinctions or climate change. Proposed mechanisms include comet impacts
(via perturbation of the Oort cloud), cosmic rays and supernovae, the effects
of which are modulated by the passage of the Sun through the Galactic midplane
or spiral arms. Supposed periodicities in the fossil record, impact cratering
dates or climate proxies over the Phanerozoic (past 545 Myr) are frequently
cited as evidence in support of these hypotheses. This remains a controversial
subject, with many refutations and replies having been published. Here I review
both the mechanisms and the evidence for and against the relevance of
astronomical phenomena to climate change and evolution. This necessarily
includes a critical assessment of time series analysis techniques and
hypothesis testing. Some of the studies have suffered from flaws in
methodology, in particular drawing incorrect conclusions based on ruling out a
null hypothesis. I conclude that there is little evidence for intrinsic
periodicities in biodiversity, impact cratering or climate on timescales of
tens to hundreds of Myr. Furthermore, Galactic midplane and spiral arm
crossings seem to have little or no impact on biological or climate variation
above background level. (truncated)Comment: 51 pages, 7 figures, 140 references. To appear in the International
Journal of Astrobiology. For hyperref version with full resolution figures
see http://www.mpia-hd.mpg.de/homes/calj/astimpact_ija.pd
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