273,511 research outputs found
Precursors of extreme increments
We investigate precursors and predictability of extreme increments in a time
series. The events we are focusing on consist in large increments within
successive time steps. We are especially interested in understanding how the
quality of the predictions depends on the strategy to choose precursors, on the
size of the event and on the correlation strength. We study the prediction of
extreme increments analytically in an AR(1) process, and numerically in wind
speed recordings and long-range correlated ARMA data. We evaluate the success
of predictions via receiver operator characteristics (ROC-curves). Furthermore,
we observe an increase of the quality of predictions with increasing event size
and with decreasing correlation in all examples. Both effects can be understood
by using the likelihood ratio as a summary index for smooth ROC-curves
Variational Bayesian Inference of Line Spectra
In this paper, we address the fundamental problem of line spectral estimation
in a Bayesian framework. We target model order and parameter estimation via
variational inference in a probabilistic model in which the frequencies are
continuous-valued, i.e., not restricted to a grid; and the coefficients are
governed by a Bernoulli-Gaussian prior model turning model order selection into
binary sequence detection. Unlike earlier works which retain only point
estimates of the frequencies, we undertake a more complete Bayesian treatment
by estimating the posterior probability density functions (pdfs) of the
frequencies and computing expectations over them. Thus, we additionally capture
and operate with the uncertainty of the frequency estimates. Aiming to maximize
the model evidence, variational optimization provides analytic approximations
of the posterior pdfs and also gives estimates of the additional parameters. We
propose an accurate representation of the pdfs of the frequencies by mixtures
of von Mises pdfs, which yields closed-form expectations. We define the
algorithm VALSE in which the estimates of the pdfs and parameters are
iteratively updated. VALSE is a gridless, convergent method, does not require
parameter tuning, can easily include prior knowledge about the frequencies and
provides approximate posterior pdfs based on which the uncertainty in line
spectral estimation can be quantified. Simulation results show that accounting
for the uncertainty of frequency estimates, rather than computing just point
estimates, significantly improves the performance. The performance of VALSE is
superior to that of state-of-the-art methods and closely approaches the
Cram\'er-Rao bound computed for the true model order.Comment: 15 pages, 8 figures, accepted for publication in IEEE Transactions on
Signal Processin
The power spectrum of galaxies in the 2dF 100k redshift survey
We compute the real-space power spectrum and the redshift-space distortions
of galaxies in the 2dF 100k galaxy redshift survey using pseudo-Karhunen-Loeve
eigenmodes and the stochastic bias formalism. Our results agree well with those
published by the 2dFGRS team, and have the added advantage of producing
easy-to-interpret uncorrelated minimum-variance measurements of the
galaxy-galaxy, galaxy-velocity and velocity-velocity power spectra in 27
k-bands, with narrow and well-behaved window functions in the range 0.01h/Mpc <
k < 0.8h/Mpc. We find no significant detection of baryonic wiggles, although
our results are consistent with a standard flat Omega_Lambda=0.7
``concordance'' model and previous tantalizing hints of baryonic oscillations.
We measure the galaxy-matter correlation coefficient r > 0.4 and the
redshift-distortion parameter beta=0.49+/-0.16 for r=1 (beta=0.47+/- 0.16
without finger-of-god compression). Since this is an apparent-magnitude limited
sample, luminosity-dependent bias may cause a slight red-tilt in the power
spectum. A battery of systematic error tests indicate that the survey is not
only impressive in size, but also unusually clean, free of systematic errors at
the level to which our tests are sensitive. Our measurements and window
functions are available at http://www.hep.upenn.edu/~max/2df.html together with
the survey mask, radial selection function and uniform subsample of the survey
that we have constructed.Comment: Replaced to match accepted MNRAS version, with new radial/angular
systematics plot and sigma8 typo corrected. High-res figures, power spectra,
windows and our uniform galaxy subsample with mask at
http://www.hep.upenn.edu/~max/2df.html or from [email protected]. 26
journal pages, 28 fig
Post-WMAP Assessment of Infrared Cutoff in the Primordial Spectrum from Inflation
The recent Cosmic Microwave Background (CMB) measurements indicate that there
is power deficiency of the CMB anisotropies at large scales compared with the
CDM model. We have investigated the possibility of explaining such
effects by a class of primordial power spectra which have infrared cutoffs
close to the horizon scale. The primordial power spectrum recovered by direct
deconvolution of the observed CMB angular spectrum indicates that the data
prefers a sharp infrared cutoff with a localized excess (bump) just above the
cutoff. We have been motivated to assess plausible extensions of simplest
inflationary scenarios which readily accommodate similar form of infrared
cutoff. We carry out a complete Bayesian analysis of the parameter space using
{\it Markov Chain Monte Carlo} technique with such a class of primordial power
spectra. We show that primordial power spectrum that have features such as an
infrared cutoff followed by a subsequent excess in power give better fit to the
observed data compared to a nearly scale-invariant power law or power spectrum
with just a monotonic infrared cutoff. However, there is substantial room for
improvement in the match to data and calls for exploration of other mechanisms
that may lead to infrared cutoff even closer to that recovered by direct
deconvolution approach.Comment: Changes to match version accepted for publication in PR
SUCCESS VERSUS DECISIVENESS: CONCEPTUAL DISCUSSION AND CASE STUDY
In this paper, we vindicate the relevance of the notion of success or satisfaction for the normative assessment of voting rules. We provide arguments in support of this view and emphasize the conceptual and analytical differences between this notion and that of decisiveness. The conclusions are illustrated in the case study provided by three different voting rules that have been proposed for the Council of Ministers of the European Union.Voting, European Union, Power indices
Bayesian model selection for dark energy using weak lensing forecasts
The next generation of weak lensing probes can place strong constraints on
cosmological parameters by measuring the mass distribution and geometry of the
low redshift universe. We show that a future all-sky tomographic cosmic shear
survey with design properties similar to Euclid can provide the statistical
accuracy required to distinguish between different dark energy models. Using a
fiducial cosmological model which includes cold dark matter, baryons, massive
neutrinos (hot dark matter), a running primordial spectral index and possible
spatial curvature as well as dark energy perturbations, we calculate Fisher
matrix forecasts for different dynamical dark energy models. Using a Bayesian
evidence calculation we show how well a future weak lensing survey could do in
distinguishing between a cosmological constant and dynamical dark energy.Comment: 12 pages, 4 figures, accepted for publication by MNRA
How to take the interstellar weather with you in pulsar timing analysis
Here we present a Bayesian method of including discrete measurements of
dispersion measure due to the interstellar medium in the direction of a pulsar
as prior information in the analysis of that pulsar. We use a simple simulation
to show the efficacy of this method, where the inclusion of the additional
measurements results in both a significant increase in the precision with which
the timing model parameters can be obtained, and an improved upper limit on the
amplitude of any red noise in the dataset. We show that this method can be
applied where no multi-frequency data exists across much of the dataset, and
where there is no simultaneous multi-frequency data for any given observing
epoch. Including such information in the analysis of upcoming International
Pulsar Timing Array (IPTA) and European Pulsar Timing Array (EPTA) data
releases could therefore prove invaluable in obtaining the most constraining
limits on gravitational wave signals within those datasets.Comment: 7 pages, 1 Table, 3 Figures. arXiv admin note: substantial text
overlap with arXiv:1310.212
Disentangling the Determinants of Successful Demobilization and Reintegration
Since 1989, international efforts to end protracted conflicts in Africa, Latin America, and Asia have included sustained investments in the disarmament, demobilization, and reintegration (DDR) of combatants from the warring parties. Yet, while policy analysts have debated the organizational factors that contribute to a successful DDR program, little is known about the factors that account for successful DDR at the micro level. Using a new dataset of ex-combatants in Sierra Leone, this paper analyzes, for the first time, the individual level determinants of demobilization and reintegration. Conventional views about the importance of age and gender for understanding reintegration find little support in the data. Instead, we find that an individualâs prospect of gaining acceptance from family and neighbors depends largely on the abusiveness of the unit in which he or she fought. Finally, while internationally-funded programs designed to assist the demobilization and reintegration process may have had an effect at the macro-level, we find no evidence that those who participated in DDR programs had an easier time gaining acceptance from their families or communities as compared to those who did not participate.demobilization, reintegration, conflict, disarmament, Sierra Leone
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