3,469 research outputs found
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
The Earth as an extrasolar planet: The vegetation spectral signature today and during the last Quaternary climatic extrema
The so-called Vegetation Red-Edge (VRE), a sharp increase in the reflectance
around , is a characteristic of vegetation spectra, and can therefore
be used as a biomarker if it can be detected in an unresolved extrasolar
Earth-like planet integrated reflectance spectrum. Here we investigate the
potential for detection of vegetation spectra during the last Quaternary
climatic extrema, the Last Glacial Maximum (LGM) and the Holocene optimum, for
which past climatic simulations have been made. By testing the VRE
detectability during these extrema when Earth's climate and biomes maps were
different from today, we are able to test the vegetation detectability on a
terrestrial planet different from our modern Earth. Data from the Biome3.5
model have been associated to visible GOME spectra for each biome and cloud
cover to derive Earth's integrated spectra for given Earth phases and observer
positions. The VRE is then measured. Results show that the vegetation remains
detectable during the last climatic extrema. Compared to current Earth, the
Holocene optimum with a greener Sahara slightly increases the mean VRE on one
hand, while on the other hand, the large ice cap over the northern Hemisphere
during the LGM decreases vegetation detectability. We finally discuss the
detectability of the VRE in the context of recently proposed space missions.Comment: 31-page manuscript, 12 figures, accepted for publication in Int. J.
of Astrobiolog
Plant image retrieval using color, shape and texture features
We present a content-based image retrieval system for plant image retrieval, intended especially for the house plant identification problem. A plant image consists of a collection of overlapping leaves and possibly flowers, which makes the problem challenging.We studied the suitability of various well-known color, shape and texture features for this problem, as well as introducing some new texture matching techniques and shape features. Feature extraction is applied after segmenting the plant region from the background using the max-flow min-cut technique. Results on a database of 380 plant images belonging to 78 different types of plants show promise of the proposed new techniques
and the overall system: in 55% of the queries, the correct plant image is retrieved among the top-15 results. Furthermore, the accuracy goes up to 73% when a 132-image subset of well-segmented plant images are considered
Inspiral, merger and ringdown of unequal mass black hole binaries: a multipolar analysis
We study the inspiral, merger and ringdown of unequal mass black hole
binaries by analyzing a catalogue of numerical simulations for seven different
values of the mass ratio (from q=M2/M1=1 to q=4). We compare numerical and
Post-Newtonian results by projecting the waveforms onto spin-weighted spherical
harmonics, characterized by angular indices (l,m). We find that the
Post-Newtonian equations predict remarkably well the relation between the wave
amplitude and the orbital frequency for each (l,m), and that the convergence of
the Post-Newtonian series to the numerical results is non-monotonic. To leading
order the total energy emitted in the merger phase scales like eta^2 and the
spin of the final black hole scales like eta, where eta=q/(1+q)^2 is the
symmetric mass ratio. We study the multipolar distribution of the radiation,
finding that odd-l multipoles are suppressed in the equal mass limit. Higher
multipoles carry a larger fraction of the total energy as q increases. We
introduce and compare three different definitions for the ringdown starting
time. Applying linear estimation methods (the so-called Prony methods) to the
ringdown phase, we find resolution-dependent time variations in the fitted
parameters of the final black hole. By cross-correlating information from
different multipoles we show that ringdown fits can be used to obtain precise
estimates of the mass and spin of the final black hole, which are in remarkable
agreement with energy and angular momentum balance calculations.Comment: 51 pages, 28 figures, 16 tables. Many improvements throughout the
text in response to the referee report. The calculation of multipolar
components in Appendix A now uses slightly different conventions. Matches
version in press in PR
Van der Waals Engineering of Ferromagnetic Semiconductor Heterostructures for Spin and Valleytronics
The integration of magnetic material with semiconductors has been fertile
ground for fundamental science as well as of great practical interest toward
the seamless integration of information processing and storage. Here we create
van der Waals heterostructures formed by an ultrathin ferromagnetic
semiconductor CrI3 and a monolayer of WSe2. We observe unprecedented control of
the spin and valley pseudospin in WSe2, where we detect a large magnetic
exchange field of nearly 13 T and rapid switching of the WSe2 valley splitting
and polarization via flipping of the CrI3 magnetization. The WSe2
photoluminescence intensity strongly depends on the relative alignment between
photo-excited spins in WSe2 and the CrI3 magnetization, due to ultrafast
spin-dependent charge hopping across the heterostructure interface. The
photoluminescence detection of valley pseudospin provides a simple and
sensitive method to probe the intriguing domain dynamics in the ultrathin
magnet, as well as the rich spin interactions within the heterostructure.Comment: Supplementary Materials included. To appear in Science Advance
Beyond topological persistence: Starting from networks
Persistent homology enables fast and computable comparison of topological
objects. However, it is naturally limited to the analysis of topological
spaces. We extend the theory of persistence, by guaranteeing robustness and
computability to significant data types as simple graphs and quivers. We focus
on categorical persistence functions that allow us to study in full generality
strong kinds of connectedness such as clique communities, -vertex and
-edge connectedness directly on simple graphs and monic coherent categories.Comment: arXiv admin note: text overlap with arXiv:1707.0967
The three dimensional skeleton: tracing the filamentary structure of the universe
The skeleton formalism aims at extracting and quantifying the filamentary
structure of the universe is generalized to 3D density fields; a numerical
method for computating a local approximation of the skeleton is presented and
validated here on Gaussian random fields. This method manages to trace well the
filamentary structure in 3D fields such as given by numerical simulations of
the dark matter distribution on large scales and is insensitive to monotonic
biasing. Two of its characteristics, namely its length and differential length,
are analyzed for Gaussian random fields. Its differential length per unit
normalized density contrast scales like the PDF of the underlying density
contrast times the total length times a quadratic Edgeworth correction
involving the square of the spectral parameter. The total length scales like
the inverse square smoothing length, with a scaling factor given by 0.21 (5.28+
n) where n is the power index of the underlying field. This dependency implies
that the total length can be used to constrain the shape of the underlying
power spectrum, hence the cosmology. Possible applications of the skeleton to
galaxy formation and cosmology are discussed. As an illustration, the
orientation of the spin of dark halos and the orientation of the flow near the
skeleton is computed for dark matter simulations. The flow is laminar along the
filaments, while spins of dark halos within 500 kpc of the skeleton are
preferentially orthogonal to the direction of the flow at a level of 25%.Comment: 17 pages, 11 figures, submitted to MNRA
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