244 research outputs found
Assessing extrema of empirical principal component functions
The difficulties of estimating and representing the distributions of
functional data mean that principal component methods play a substantially
greater role in functional data analysis than in more conventional
finite-dimensional settings. Local maxima and minima in principal component
functions are of direct importance; they indicate places in the domain of a
random function where influence on the function value tends to be relatively
strong but of opposite sign. We explore statistical properties of the
relationship between extrema of empirical principal component functions, and
their counterparts for the true principal component functions. It is shown that
empirical principal component funcions have relatively little trouble capturing
conventional extrema, but can experience difficulty distinguishing a
``shoulder'' in a curve from a small bump. For example, when the true principal
component function has a shoulder, the probability that the empirical principal
component function has instead a bump is approximately equal to 1/2. We suggest
and describe the performance of bootstrap methods for assessing the strength of
extrema. It is shown that the subsample bootstrap is more effective than the
standard bootstrap in this regard. A ``bootstrap likelihood'' is proposed for
measuring extremum strength. Exploratory numerical methods are suggested.Comment: Published at http://dx.doi.org/10.1214/009053606000000371 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Parameter tuning in pointwise adaptation using a propagation approach
This paper discusses the problem of adaptive estimation of a univariate
object like the value of a regression function at a given point or a linear
functional in a linear inverse problem. We consider an adaptive procedure
originated from Lepski [Theory Probab. Appl. 35 (1990) 454--466.] that selects
in a data-driven way one estimate out of a given class of estimates ordered by
their variability. A serious problem with using this and similar procedures is
the choice of some tuning parameters like thresholds. Numerical results show
that the theoretically recommended proposals appear to be too conservative and
lead to a strong oversmoothing effect. A careful choice of the parameters of
the procedure is extremely important for getting the reasonable quality of
estimation. The main contribution of this paper is the new approach for
choosing the parameters of the procedure by providing the prescribed behavior
of the resulting estimate in the simple parametric situation. We establish a
non-asymptotical "oracle" bound, which shows that the estimation risk is, up to
a logarithmic multiplier, equal to the risk of the "oracle" estimate that is
optimally selected from the given family. A numerical study demonstrates a good
performance of the resulting procedure in a number of simulated examples.Comment: Published in at http://dx.doi.org/10.1214/08-AOS607 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Global smoothness estimation of a Gaussian process from regular sequence designs
We consider a real Gaussian process having a global unknown smoothness
,
r_{\scriptscriptstyle 0}\in \mathds{N}_0 and , with (the mean-square derivative of
if ) supposed to be locally stationary with
index . From the behavior of quadratic variations
built on divided differences of , we derive an estimator of
based on - not
necessarily equally spaced - observations of . Various numerical studies of
these estimators exhibit their properties for finite sample size and different
types of processes, and are also completed by two examples of application to
real data.Comment: 28 page
Assessing the number of mean-square derivatives of a Gaussian process
28 pagesInternational audienceWe consider a real Gaussian process with unknown smoothness \ro\in\n_{Ăte 0} where the mean-square derivative X^{(\ro)} is supposed to be H\"{o}lder continuous in quadratic mean. First, from the discrete observations , we study reconstruction of , with , a piecewise polynomial interpolation of degree . We show that the mean-square error of interpolation is a decreasing function of but becomes stable as soon as r\ge \ro. Next, from an interpolation-based empirical criterion, we derive an estimator of \ro and prove its strong consistency by giving an exponential inequality for P(\widehat{r}\not=\ro). Finally, we prove the strong consistency of with an almost optimal rate
Flows at the Edge of an Active Region: Observation and Interpretation
Upflows observed at the edges of active regions have been proposed as the
source of the slow solar wind. In the particular case of Active Region (AR)
10942, where such an upflow has been already observed, we want to evaluate the
part of this upflow that actually remains confined in the magnetic loops that
connect AR10942 to AR10943. Both active regions were visible simultaneously on
the solar disk and were observed by STEREO/SECCHI EUVI. Using Hinode/EIS
spectra, we determine the Doppler shifts and densities in AR10943 and AR10942,
in order to evaluate the mass flows. We also perform magnetic field
extrapolations to assess the connectivity between AR10942 and AR10943. AR10943
displays a persistent downflow in Fe XII. Magnetic extrapolations including
both ARs show that this downflow can be connected to the upflow in AR10942. We
estimate that the mass flow received by AR10943 areas connected to AR10942
represents about 18% of the mass flow from AR10942. We conclude that the
upflows observed on the edge of active regions represent either large-scale
loops with mass flowing along them (accounting for about one-fifth of the total
mass flow in this example) or open magnetic field structures where the slow
solar wind originates.Comment: 20 pages, 9 figures, accepted for publication in Astrophys.
Rapid and Efficient Methods to Isolate, Type Strains and Determine Species of Agrobacterium spp. in Pure Culture and Complex Environments
International audienc
Les choix organisationnels des propriétaires de chevaux de loisir dans les espaces ruraux
La possession dâĂ©quidĂ©s de loisir a rĂ©cemment connu un essor important. Pour entretenir ces animaux, leurs propriĂ©taires peuvent soit les prendre en charge eux-mĂȘmes, soit faire appel Ă des prestataires de services marchands. Les assimilant Ă des producteurs de leur propre loisir, nous proposons dâĂ©tudier les dĂ©terminants de leur choix organisationnel grĂące aux thĂ©ories traitant habituellement des frontiĂšres de la firme. Les 251 enquĂȘtes rĂ©alisĂ©es dĂ©montrent la pertinence de lâapplication de ces cadres dâanalyse Ă la production domestique. Les propriĂ©taires dâĂ©quidĂ©s poursuivent un objectif dâefficience. Ils cherchent Ă maximiser leur utilitĂ©, tout en minimisant leurs coĂ»ts de production et de transaction et en sâadaptant aux ressources auxquelles ils peuvent avoir accĂšs.The number of recreational Equidae owners has recently increased sharply. These owners can choose between stabling and caring for their animals domestically, on their own property, or using professional service suppliers. By considering them as producers of their own leisure activity, we proposed to study the parameters involved in this choice using theories usually employed to analyze firm boundaries. Results from our 251 inquiries demonstrated the relevance of transposing these theoretical tools to domestic production. Equidae owners pursue an objective of efficiency. They aim at maximizing their utility while minimizing their production and transaction costs and adapting to resources they can access
Comparison of the cellular and biochemical properties of Plasmodium falciparum choline and ethanolamine kinases.
International audienceThe proliferation of the malaria-causing parasite Plasmodium falciparum within the erythrocyte is concomitant with massive phosphatidylcholine and phosphatidylethanolamine biosynthesis. Based on pharmacological and genetic data, de novo biosynthesis pathways of both phospholipids appear to be essential for parasite survival. The present study characterizes PfCK (P. falciparum choline kinase) and PfEK (P. falciparum ethanolamine kinase), which catalyse the first enzymatic steps of these essential metabolic pathways. Recombinant PfCK and PfEK were expressed as His6-tagged fusion proteins from overexpressing Escherichia coli strains, then purified to homogeneity and characterized. Using murine polyclonal antibodies against recombinant kinases, PfCK and PfEK were shown to be localized within the parasite cytoplasm. Protein expression levels increased during erythrocytic development. PfCK and PfEK appeared to be specific to their respective substrates and followed Michaelis-Menten kinetics. The Km value of PfCK for choline was 135.3+/-15.5 microM. PfCK was also able to phosphorylate ethanolamine with a very low affinity. PfEK was found to be an ethanolamine-specific kinase (Km=475.7+/-80.2 microM for ethanolamine). The quaternary ammonium compound hemicholinium-3 and an ethanolamine analogue, 2-amino-1-butanol, selectively inhibited PfCK or PfEK. In contrast, the bis-thiazolium compound T3, which was designed as a choline analogue and is currently in clinical trials for antimalarial treatment, affected PfCK and PfEK activities similarly. Inhibition exerted by T3 was competitive for both PfCK and PfEK and correlated with the impairment of cellular phosphatidylcholine biosynthesis. Comparative analyses of sequences and structures for both kinase types gave insights into their specific inhibition profiles and into the dual capacity of T3 to inhibit both PfCK and PfEK
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