9,339 research outputs found
Estimating the turning point location in shifted exponential model of time series
We consider the distribution of the turning point location of time series
modeled as the sum of deterministic trend plus random noise. If the variables
are modeled by shifted exponentials, whose location parameters define the
trend, we provide a formula for computing the distribution of the turning point
location and consequently to estimate a confidence interval for the location.
We test this formula in simulated data series having a trend with asymmetric
minimum, investigating the coverage rate as a function of a bandwidth
parameter. The method is applied to estimate the confidence interval of the
minimum location of the time series of RT intervals extracted from the
electrocardiogram recorded during the exercise test. We discuss the connection
with stochastic ordering
Locally convex quasi C*-algebras and noncommutative integration
In this paper we continue the analysis undertaken in a series of previous
papers on structures arising as completions of C*-algebras under topologies
coarser that their norm and we focus our attention on the so-called {\em
locally convex quasi C*-algebras}. We show, in particular, that any strongly
*-semisimple locally convex quasi C*-algebra (\X,\Ao), can be represented in
a class of noncommutative local -spaces.Comment: 12 page
Riesz-like bases in rigged Hilbert spaces
The notions of Bessel sequence, Riesz-Fischer sequence and Riesz basis are
generalized to a rigged Hilbert space \D[t] \subset \H \subset
\D^\times[t^\times]. A Riesz-like basis, in particular, is obtained by
considering a sequence \{\xi_n\}\subset \D which is mapped by a one-to-one
continuous operator T:\D[t]\to\H[\|\cdot\|] into an orthonormal basis of the
central Hilbert space \H of the triplet. The operator is, in general, an
unbounded operator in \H. If has a bounded inverse then the rigged
Hilbert space is shown to be equivalent to a triplet of Hilbert spaces
Trend extraction in functional data of R and T waves amplitudes of exercise electrocardiogram
The R and T waves amplitudes of the electrocardiogram recorded during the
exercise test undergo strong modifications in response to stress. We analyze
the time series of these amplitudes in a group of normal subjects in the
framework of functional data, performing reduction of dimensionality, smoothing
and principal component analysis. These methods show that the R and T
amplitudes have opposite responses to stress, consisting respectively in a bump
and a dip at the early recovery stage. We test these features computing a
confidence band for the trend of the population mean and analyzing the zero
crossing of its derivative.
Our findings support the existence of a relationship between R and T wave
amplitudes and respectively diastolic and systolic ventricular volumes
Fractional Sobolev Regularity for the Brouwer Degree
We prove that if is a bounded open set and
, then the Brouwer degree
deg of any H\"older function belongs to the Sobolev space
for every . This extends a
summability result of Olbermann and in fact we get, as a byproduct, a more
elementary proof of it. Moreover we show the optimality of the range of
exponents in the following sense: for every and with
there is a vector field with \mbox{deg}\, (v, \Omega, \cdot)\notin
W^{\beta, p}, where is the unit ball.Comment: 12 pages, 1 figur
- …