881 research outputs found
Leave-one-out prediction error of systolic arterial pressure time series under paced breathing
In this paper we show that different physiological states and pathological
conditions may be characterized in terms of predictability of time series
signals from the underlying biological system. In particular we consider
systolic arterial pressure time series from healthy subjects and Chronic Heart
Failure patients, undergoing paced respiration. We model time series by the
regularized least squares approach and quantify predictability by the
leave-one-out error. We find that the entrainment mechanism connected to paced
breath, that renders the arterial blood pressure signal more regular, thus more
predictable, is less effective in patients, and this effect correlates with the
seriousness of the heart failure. The leave-one-out error separates controls
from patients and, when all orders of nonlinearity are taken into account,
alive patients from patients for which cardiac death occurred
Numerical methods for fluctuation driven interactions between dielectrics
We develop a discretized theory of thermal Casimir interactions to
numerically calculate the interactions between fluctuating dielectrics. From a
constrained partition function we derive a surface free energy, while handling
divergences that depend on system size and discretization. We derive analytic
results for parallel plate geometry in order to check the convergence of the
numerical methods. We use the method to calculate vertical and lateral Casimir
forces for a set of grooves.Comment: revtex, 20 page
Redundant variables and Granger causality
We discuss the use of multivariate Granger causality in presence of redundant
variables: the application of the standard analysis, in this case, leads to
under-estimation of causalities. Using the un-normalized version of the
causality index, we quantitatively develop the notions of redundancy and
synergy in the frame of causality and propose two approaches to group redundant
variables: (i) for a given target, the remaining variables are grouped so as to
maximize the total causality and (ii) the whole set of variables is partitioned
to maximize the sum of the causalities between subsets. We show the application
to a real neurological experiment, aiming to a deeper understanding of the
physiological basis of abnormal neuronal oscillations in the migraine brain.
The outcome by our approach reveals the change in the informational pattern due
to repetitive transcranial magnetic stimulations.Comment: 4 pages, 5 figures. Accepted for publication in Physical Review
Coarsening in surface growth models without slope selection
We study conserved models of crystal growth in one dimension [] which are linearly unstable and develop a mound
structure whose typical size L increases in time (). If the local
slope () increases indefinitely, depends on the exponent
characterizing the large behaviour of the surface current (): for and for
.Comment: 7 pages, 2 EPS figures. To be published in J. Phys. A (Letter to the
Editor
An Easy Route to Enantiomerically Enriched 7- and 8-Hydroxystearic Acids by Olefin Metathesis - Based Approach
The synthesis of enantiomerically enriched 7- and 8-hydroxystearic acids (7- and 8-HSA) has been successfully accomplished starting from chiral non racemic 1-pentadecen-4-ol and 1-tetradecen-4-ol respectively. Their Yamaguchi\u2019s esterification with 4-pentenoic and 5-hexenoic acids respectively afforded the suitable dienic esters which were submitted to ring closing metathesis reaction. After hydrogenation and basic hydrolysis of the complex reaction mixture, chiral non racemic 7- and 8-HSA were obtained in about 40% total yield
Cost functions for pairwise data clustering
Cost functions for non-hierarchical pairwise clustering are introduced, in
the probabilistic autoencoder framework, by the request of maximal average
similarity between the input and the output of the autoencoder. The partition
provided by these cost functions identifies clusters with dense connected
regions in data space; differences and similarities with respect to a well
known cost function for pairwise clustering are outlined.Comment: 5 pages, 4 figure
Steady-state visual evoked potentials and phase synchronization in migraine
We investigate phase synchronization in EEG recordings from migraine
patients. We use the analytic signal technique, based on the Hilbert transform,
and find that migraine brains are characterized by enhanced alpha band phase
synchronization in presence of visual stimuli. Our findings show that migraine
patients have an overactive regulatory mechanism that renders them more
sensitive to external stimuli.Comment: 4 page
Deterministic Annealing as a jet clustering algorithm in hadronic collisions
We show that a general purpose clusterization algorithm, Deterministic
Annealing, can be adapted to the problem of jet identification in particle
production by high energy collisions. In particular we consider the problem of
jet searching in events generated at hadronic colliders. Deterministic
Annealing is able to reproduce the results obtained by traditional jet
algorithms and to exhibit a higher degree of flexibility.Comment: 13 pages, 6 figure
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