10,256 research outputs found
Natural entropy fluctuations discriminate similar looking electric signals emitted from systems of different dynamics
Complexity measures are introduced, that quantify the change of the natural
entropy fluctuations at different length scales in time-series emitted from
systems operating far from equilibrium. They identify impending sudden cardiac
death (SD) by analyzing fifteen minutes electrocardiograms, and comparing to
those of truly healthy humans (H). These measures seem to be complementary to
the ones suggested recently [Phys. Rev. E {\bf 70}, 011106 (2004)] and
altogether enable the classification of individuals into three categories: H,
heart disease patients and SD. All the SD individuals, who exhibit critical
dynamics, result in a common behavior.Comment: Published in Physical Review
Reweighting of the form factors in exclusive B --> X ell nu decays
A form factor reweighting technique has been elaborated to permit relatively
easy comparisons between different form factor models applied to exclusive B
--> X l nu decays. The software tool developped for this purpose is described.
It can be used with any event generator, three of which were used in this work:
ISGW2, PHSP and FLATQ2, a new powerful generator. The software tool allows an
easy and reliable implementation of any form factor model. The tool has been
fully validated with the ISGW2 form factor hypothesis. The results of our
present studies indicate that the combined use of the FLATQ2 generator and the
form factor reweighting tool should play a very important role in future
exclusive |Vub| measurements, with largely reduced errors.Comment: accepted for publication by EPJ
Penguin decays of B mesons
Penguin, or loop, decays of B mesons induce effective flavor-changing neutral
currents, which are forbidden at tree level in the Standard Model. These decays
give special insight into the CKM matrix and are sensitive to non-standard
model effects. In this review, we give a historical and theoretical
introduction to penguins and a description of the various types of penguin
processes: electromagnetic, electroweak, and gluonic. We review the
experimental searches for penguin decays, including the measurements of the
electromagnetic penguins b -> s gamma and B -> K* gamma and gluonic penguins B
-> K pi, B+ -> omega K+ and B -> eta' K, and their implications for the
Standard Model and New Physics. We conclude by exploring the future prospects
for penguin physics.Comment: 49 pages, LATEX, 30 embedded figures, submitted to Annual Reviews of
Nuclear and Particle Scienc
Analysis of electroencephalograms in Alzheimer's disease patients with multiscale entropy
The aim of this study was to analyse the electroencephalogram (EEG) background activity of Alzheimer’s disease (AD) patients using the Multiscale Entropy (MSE). The MSE is a recently developed method that quantifies the regularity of a signal on different time scales. These time scales are inspected by means of several coarse-grained sequences formed from the analysed signals. We recorded the EEGs from 19 scalp electrodes in 11 AD patients and 11 age-matched controls and estimated the MSE profile for each epoch of the EEG recordings. The shape of the MSE profiles reveals the EEG complexity, and it suggests that the EEG contains information in deeper scales than the smallest one. Moreover, the results showed that the EEG background activity is less complex in AD patients than control subjects. We found significant difference
Hyperactivity, impulsivity, and inattention in boys with cleft lip and palate: relationship to ventromedial prefrontal cortex morphology
The purpose of this study is to evaluate quantitative structural measures of the ventromedial prefrontal cortex (vmPFC) in boys with isolated clefts of the lip and/or palate (ICLP) relative to a comparison group and to associate measures of brain structure with quantitative measures of hyperactivity, impulsivity, and inattentiveness. A total of 50 boys with ICLP were compared to 60 healthy boys without clefts. Magnetic resonance imaging brain scans were used to evaluate vmPFC structure. Parents and teachers provided quantitative measures of hyperactivity, impulsivity, and inattentiveness using the Pediatric Behavior Scale. Boys with ICLP had significantly higher ratings of hyperactivity/impulsivity/inattention (HII) and significantly increased volume of the right vmPFC relative to the comparison group. There was a direct relationship between HII score and vmPFC volume in both the ICLP group and control group, but the relationship was in the opposite direction: in ICLP, the higher the vmPFC volume, the higher the HII score; for the comparison group, the lower the vmPFC volume, the greater the HII score. The vmPFC is a region of the brain that governs behaviors of hyperactivity, impulsivity and inattention (HII). In boys with ICLP, there are higher levels of HII compared to the controls and this is directly related to a significantly enlarged volume of the right vmPFC. Enlargement of this region of the brain is therefore considered to be pathological in the ICLP group and supports the notion that abnormal brain structure (from abnormal brain development) is the underlying etiology for the abnormal behaviors seen in this population
Scaling Behaviour and Complexity of the Portevin-Le Chatelier Effect
The plastic deformation of dilute alloys is often accompanied by plastic
instabilities due to dynamic strain aging and dislocation interaction. The
repeated breakaway of dislocations from and their recapture by solute atoms
leads to stress serrations and localized strain in the strain controlled
tensile tests, known as the Portevin-Le Chatelier (PLC) effect. In this present
work, we analyse the stress time series data of the observed PLC effect in the
constant strain rate tensile tests on Al-2.5%Mg alloy for a wide range of
strain rates at room temperature. The scaling behaviour of the PLC effect was
studied using two complementary scaling analysis methods: the finite variance
scaling method and the diffusion entropy analysis. From these analyses we could
establish that in the entire span of strain rates, PLC effect showed Levy walk
property. Moreover, the multiscale entropy analysis is carried out on the
stress time series data observed during the PLC effect to quantify the
complexity of the distinct spatiotemporal dynamical regimes. It is shown that
for the static type C band, the entropy is very low for all the scales compared
to the hopping type B and the propagating type A bands. The results are
interpreted considering the time and length scales relevant to the effect.Comment: 35 pages, 6 figure
Granular Rheology in Zero Gravity
We present an experimental investigation on the rheological behavior of model
granular media made of nearly elastic spherical particles. The experiments are
performed in a cylindrical Couette geometry and the experimental device is
placed inside an airplane undergoing parabolic flights to cancel the effect of
gravity. The corresponding curves, shear stress versus shear rate, are
presented and a comparison with existing theories is proposed. The quadratic
dependence on the shear rate is clearly shown and the behavior as a function of
the solid volume fraction of particles exhibits a power law function. It is
shown that theoretical predictions overestimate the experiments. We observe, at
intermediate volume fractions, the formation of rings of particles regularly
spaced along the height of the cell. The differences observed between
experimental results and theoretical predictions are discussed and related to
the structures formed in the granular medium submitted to the external shear.Comment: 10 pages, 6 figures to be published in Journal of Physics : Condensed
Matte
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Instantaneous venous oxygenation estimation using the Photoplethysmograph (PPG) waveform
In this study oesophageal photoplethysmograph data from eight patients under positive pressure ventilation were analysed in order to test the hypothesis that the modulations created by the ventilation in the AC Photoplethysmograph (PPG) signal could be used to estimate venous oxygen saturation. In order to estimate the instantaneous arterial and venous oxygen saturation Smoothed-pseudo Wigner-Ville Distribution (SPWVD) was utilised. The result from this study showed that there was no significant different in the conventional (time domain) arterial saturation and the instantaneous arterial saturation. However, the instantaneous venous oxygen saturation estimated with the ventilator modulation were significantly lower then the conventional arterial saturation (P=0.008) and also from the instantaneous arterial saturation (P=0.008)
An algorithmic approach to the existence of ideal objects in commutative algebra
The existence of ideal objects, such as maximal ideals in nonzero rings,
plays a crucial role in commutative algebra. These are typically justified
using Zorn's lemma, and thus pose a challenge from a computational point of
view. Giving a constructive meaning to ideal objects is a problem which dates
back to Hilbert's program, and today is still a central theme in the area of
dynamical algebra, which focuses on the elimination of ideal objects via
syntactic methods. In this paper, we take an alternative approach based on
Kreisel's no counterexample interpretation and sequential algorithms. We first
give a computational interpretation to an abstract maximality principle in the
countable setting via an intuitive, state based algorithm. We then carry out a
concrete case study, in which we give an algorithmic account of the result that
in any commutative ring, the intersection of all prime ideals is contained in
its nilradical
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