4,805 research outputs found
A unified view of some representations of imprecise probabilities
International audienceSeveral methods for the practical representation of imprecise probabilities exist such as Ferson's p-boxes, possibility distributions, Neumaier's clouds, and random sets . In this paper some relationships existing between the four kinds of representations are discussed. A cloud as well as a p-box can be modelled as a pair of possibility distributions. We show that a generalized form of p-box is a special kind of belief function and also a special kind of cloud
Detecting event-related recurrences by symbolic analysis: Applications to human language processing
Quasistationarity is ubiquitous in complex dynamical systems. In brain
dynamics there is ample evidence that event-related potentials reflect such
quasistationary states. In order to detect them from time series, several
segmentation techniques have been proposed. In this study we elaborate a recent
approach for detecting quasistationary states as recurrence domains by means of
recurrence analysis and subsequent symbolisation methods. As a result,
recurrence domains are obtained as partition cells that can be further aligned
and unified for different realisations. We address two pertinent problems of
contemporary recurrence analysis and present possible solutions for them.Comment: 24 pages, 6 figures. Draft version to appear in Proc Royal Soc
The opaque nascent starburst in NGC 1377: Spitzer SINGS observations
We analyze extensive data on NGC 1377 from the Spitzer Infrared Nearby Galaxies Survey (SINGS). Within the category of nascent starbursts that we previously selected as having infrared-to-radio continuum ratios in large excess of the average and containing hot dust, NGC 1377 has the largest infrared excess yet measured. Optical imaging reveals a morphological distortion suggestive of a recent accretion event. Infrared spectroscopy reveals a compact and opaque source dominated by a hot, self-absorbed continuum (τ~ 20 in the 10μm silicate band). We provide physical evidence against nonstellar activity being the heating source. H II regions are detected through the single [Ne II] line, probing 85% of ionizing photons are suppressed by dust. The only other detected emission features are molecular hydrogen lines, arguably excited mainly by shocks, besides photodissociation regions, and weak aromatic bands. The new observations support our interpretation in terms of an extremely young starburst (<1 Myr). More generally, galaxies deficient in radio synchrotron emission are likely observed within a few Myr of the onset of a starburst and after a long quiescence, prior to the replenishment of the interstellar medium with cosmic rays. The similar infrared-radio properties of NGC 1377 and some infrared-luminous galaxies suggest that NGC 1377 constitutes an archetype that will be useful to better understand starburst evolution. Although rare locally because observed in a brief evolutionary stage, nascent starbursts may represent a nonnegligible fraction of merger-induced starbursts that dominate deep infrared counts. Since they differ dramatically from usual starburst templates, they have important consequences for the interpretation of deep surveys
Surface Structure of Liquid Metals and the Effect of Capillary Waves: X-ray Studies on Liquid Indium
We report x-ray reflectivity (XR) and small angle off-specular diffuse
scattering (DS) measurements from the surface of liquid Indium close to its
melting point of C. From the XR measurements we extract the surface
structure factor convolved with fluctuations in the height of the liquid
surface. We present a model to describe DS that takes into account the surface
structure factor, thermally excited capillary waves and the experimental
resolution. The experimentally determined DS follows this model with no
adjustable parameters, allowing the surface structure factor to be deconvolved
from the thermally excited height fluctuations. The resulting local electron
density profile displays exponentially decaying surface induced layering
similar to that previously reported for Ga and Hg. We compare the details of
the local electron density profiles of liquid In, which is a nearly free
electron metal, and liquid Ga, which is considerably more covalent and shows
directional bonding in the melt. The oscillatory density profiles have
comparable amplitudes in both metals, but surface layering decays over a length
scale of \AA for In and \AA for Ga. Upon controlled
exposure to oxygen, no oxide monolayer is formed on the liquid In surface,
unlike the passivating film formed on liquid Gallium.Comment: 9 pages, 5 figures; submitted to Phys. Rev.
The GREAT triggerless total data readout method
Recoil decay tagging (RDT) is a very powerful method for the spectroscopy of exotic nuclei. RDT is a delayed coincidence technique between detectors usually at the target position and at the focal plane of a spectrometer. Such measurements are often limited by dead time. This paper describes a novel triggerless data acquisition method, which is being developed for the Gamma Recoil Electron Alpha Tagging (GREAT) spectrometer, that overcomes this limitation by virtually eliminating dead time. Our solution is a total data readout (TDR) method where all channels run independently and are associated in software to reconstruct events. The TDR method allows all the data from both target position and focal plane to be collected with practically no dead-time losses. Each data word is associated with a timestamp generated from a global 100-MHz clock. Events are then reconstructed in real time in the event builder using temporal and spatial associations defined by the physics of the experimen
Mid-Infrared IRS Spectroscopy of NGC 7331: A First Look at the SINGS Legacy
The nearby spiral galaxy NGC 7331 was spectrally mapped from 5-38um using all
modules of Spitzer's IRS spectrograph. A strong new dust emission feature,
presumed due to PAHs, was discovered at 17.1um. The feature's intensity is
nearly half that of the ubiquitous 11.3um band. The 7-14um spectral maps
revealed significant variation in the 7.7 and 11.3um PAH features between the
stellar ring and nucleus. Weak [OIV] 25.9um line emission was found to be
centrally concentrated in the nucleus, with an observed strength over 10% of
the combined neon line flux, indicating an AGN or unusually active massive star
photo-ionization. Two [SIII] lines fix the characteristic electron density in
the HII regions at n_e < ~200 cm^-3. Three detected H_2 rotational lines,
tracing warm molecular gas, together with the observed IR continuum, are
difficult to match with standard PDR models. Either additional PDR heating or
shocks are required to simultaneously match lines and continuum.Comment: 6 pages, 5 figures, accepted for publication in ApJS Spitzer Special
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