2,880 research outputs found
Evidential-EM Algorithm Applied to Progressively Censored Observations
Evidential-EM (E2M) algorithm is an effective approach for computing maximum
likelihood estimations under finite mixture models, especially when there is
uncertain information about data. In this paper we present an extension of the
E2M method in a particular case of incom-plete data, where the loss of
information is due to both mixture models and censored observations. The prior
uncertain information is expressed by belief functions, while the
pseudo-likelihood function is derived based on imprecise observations and prior
knowledge. Then E2M method is evoked to maximize the generalized likelihood
function to obtain the optimal estimation of parameters. Numerical examples
show that the proposed method could effectively integrate the uncertain prior
infor-mation with the current imprecise knowledge conveyed by the observed
data
X-ray Lighthouses of the High-Redshift Universe. II. Further Snapshot Observations of the Most Luminous z>4 Quasars with Chandra
We report on Chandra observations of a sample of 11 optically luminous
(Mb<-28.5) quasars at z=3.96-4.55 selected from the Palomar Digital Sky Survey
and the Automatic Plate Measuring Facility Survey. These are among the most
luminous z>4 quasars known and hence represent ideal witnesses of the end of
the "dark age ''. Nine quasars are detected by Chandra, with ~2-57 counts in
the observed 0.5-8 keV band. These detections increase the number of X-ray
detected AGN at z>4 to ~90; overall, Chandra has detected ~85% of the
high-redshift quasars observed with snapshot (few kilosecond) observations. PSS
1506+5220, one of the two X-ray undetected quasars, displays a number of
notable features in its rest-frame ultraviolet spectrum, the most prominent
being broad, deep SiIV and CIV absorption lines. The average optical-to-X-ray
spectral index for the present sample (=-1.88+/-0.05) is steeper than
that typically found for z>4 quasars but consistent with the expected value
from the known dependence of this spectral index on quasar luminosity.
We present joint X-ray spectral fitting for a sample of 48 radio-quiet
quasars in the redshift range 3.99-6.28 for which Chandra observations are
available. The X-ray spectrum (~870 counts) is well parameterized by a power
law with Gamma=1.93+0.10/-0.09 in the rest-frame ~2-40 keV band, and a tight
upper limit of N_H~5x10^21 cm^-2 is obtained on any average intrinsic X-ray
absorption. There is no indication of any significant evolution in the X-ray
properties of quasars between redshifts zero and six, suggesting that the
physical processes of accretion onto massive black holes have not changed over
the bulk of cosmic time.Comment: 15 pages, 7 figures, accepted for publication in A
The reluctant polymorph: investigation into the effect of self-association on the solvent mediated phase transformation and nucleation of theophylline
Little is known concerning the pathway of the crystallization of the thermodynamically stable polymorph of theophylline, form IV. Here we study the reasons why the thermodynamically stable theophylline form IV can be obtained only by slow, solvent mediated phase transformation (SMPT) in specific solvents, and whether the presence of prenucleation aggregates affect the polymorphic outcome. Solution concentration, polymorphic composition and morphology were monitored over time during the transformation from form II to form IV in several solvents. NMR and FTIR spectroscopy were used to detect prenucleation molecular aggregates present in the solutions. It was determined that theophylline self-associates in solvents which are good H-bond donors and the presence of these aggregates hinder the nucleation and phase transformation. SMPT from form II to form IV is a nucleation-growth controlled polymorphic transformation, nucleation is most likely homogenous, and form IV crystals grow along the (001) plane, forming plate-like crystals
Appearance-based localization for mobile robots using digital zoom and visual compass
This paper describes a localization system for mobile robots moving in dynamic indoor environments, which uses probabilistic integration of visual appearance and odometry information. The approach is based on a novel image matching algorithm for appearance-based place recognition that integrates digital zooming, to extend the area of application, and a visual compass. Ambiguous information used for recognizing places is resolved with multiple hypothesis tracking and a selection procedure inspired by Markov localization. This enables the system to deal with perceptual aliasing or absence of reliable sensor data. It has been implemented on a robot operating in an office scenario and the robustness of the approach demonstrated experimentally
Proximal humeral fractures with a severe varus deformity treated by fixation with a locking plate
Identifying dynamical systems with bifurcations from noisy partial observation
Dynamical systems are used to model a variety of phenomena in which the
bifurcation structure is a fundamental characteristic. Here we propose a
statistical machine-learning approach to derive lowdimensional models that
automatically integrate information in noisy time-series data from partial
observations. The method is tested using artificial data generated from two
cell-cycle control system models that exhibit different bifurcations, and the
learned systems are shown to robustly inherit the bifurcation structure.Comment: 16 pages, 6 figure
A population-based approach to background discrimination in particle physics
Background properties in experimental particle physics are typically
estimated using control samples corresponding to large numbers of events. This
can provide precise knowledge of average background distributions, but
typically does not consider the effect of fluctuations in a data set of
interest. A novel approach based on mixture model decomposition is presented as
a way to estimate the effect of fluctuations on the shapes of probability
distributions in a given data set, with a view to improving on the knowledge of
background distributions obtained from control samples. Events are treated as
heterogeneous populations comprising particles originating from different
processes, and individual particles are mapped to a process of interest on a
probabilistic basis. The proposed approach makes it possible to extract from
the data information about the effect of fluctuations that would otherwise be
lost using traditional methods based on high-statistics control samples. A
feasibility study on Monte Carlo is presented, together with a comparison with
existing techniques. Finally, the prospects for the development of tools for
intensive offline analysis of individual events at the Large Hadron Collider
are discussed.Comment: Updated according to the version published in J. Phys.: Conf. Ser.
Minor changes have been made to the text with respect to the published
article with a view to improving readabilit
Rheumatologists' judgements about the efficacy of anti-TNF therapy in two neighbouring regions
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