385 research outputs found
Cerebral tissue pO2 response to stimulation is preserved with age in awake mice
Published in final edited form as: Neurosci Lett. 2019 April 23; 699: 160–166. doi:10.1016/j.neulet.2019.02.007.Compromised oxygen supply to cerebral tissue could be an important mechanism contributing to age-related cognition decline. We recently showed in awake mice that resting cerebral tissue pO2 decreases with age, a phenomenon that manifests mainly after middle-age. To extend these findings, here we aimed to study how tissue pO2 response to neuronal stimulation is affected by aging. We used two-photon phosphorescence lifetime microscopy to directly measure the brain tissue pO2 response to whisker stimulation in healthy awake young, middle-aged and old mice. We show that despite a decrease in baseline tissue pO2, the amplitude of the tissue pO2 response to stimulation is well preserved with age. However, the response dynamics are altered towards a slower response with reduced post-stimulus undershoot in older ages, possibly due to stiffer vessel wall among other factors. An estimation of the net oxygen consumption rate using a modified Krogh model suggests that the O2 overshoot during stimulation may be necessary to secure a higher capillary O2 delivery to the tissue proportional to increased CMRO2 to maintain the capillary tissue pO2. It was observed that the coupling between the CMRO2 and capillary O2 delivery is preserved with age.Accepted manuscrip
Wall slip of complex fluids: interfacial friction or slip length?
Using a dynamic Surface Force Apparatus, we demonstrate that the notion of
slip length used to describe the boundary flow of simple liquids, is not
appropriate for viscoelastic liquids. Rather, the appropriate description lies
in the original Navier's partial slip boundary condition, formulated in terms
of an interfacial friction coefficient. We establish an exact analytical
expression to extract the interfacial friction coefficient from oscillatory
drainage forces between a sphere and a plane, suitable for dynamic SFA or
Atomic Force Microscopy non-contact measurements. We use this model to
investigate the boundary friction of viscoelastic polymer solutions over 5
decades of film thicknesses and one decade in frequency. The proper use of the
original Navier's condition describes accurately the complex hydrodynamic force
up to scales of tens of micrometers, with a simple "Newtonian-like" friction
coefficient, not frequency dependent, and reflecting closely the dynamics of an
interfacial depletion layer at the solution/solid interface.Comment: 7 pages, 5 figure
Inférence doublement robuste en présence de données imputées dans les enquêtes
L'imputation est souvent utilisée dans les enquêtes pour traiter la non-réponse partielle. Il est bien connu que traiter les
valeurs imputées comme des valeurs observées entraîne une
sous-estimation importante de la variance des estimateurs
ponctuels. Pour remédier à ce problème, plusieurs méthodes
d'estimation de la variance ont été proposées dans la littérature,
dont des méthodes adaptées de rééchantillonnage telles que le
Bootstrap et le Jackknife. Nous définissons le concept de
double-robustesse pour l'estimation ponctuelle et de variance
sous l'approche par modèle de non-réponse et l'approche par modèle
d'imputation. Nous mettons l'emphase sur l'estimation de la
variance à l'aide du Jackknife qui est souvent utilisé dans la
pratique. Nous étudions les propriétés de différents estimateurs
de la variance Ă l'aide du Jackknife pour l'imputation par la
régression déterministe ainsi qu'aléatoire. Nous nous penchons
d'abord sur le cas de l'échantillon aléatoire simple. Les cas de
l'échantillonnage stratifié et à probabilités inégales seront
aussi étudiés. Une étude de simulation compare plusieurs méthodes
d'estimation de variance Ă l'aide du Jackknife en terme de biais
et de stabilité relative quand la fraction de sondage n'est pas
négligeable. Finalement, nous établissons la normalité
asymptotique des estimateurs imputés pour l'imputation par
régression déterministe et aléatoire.Imputation is often used in surveys to treat item nonresponse. It
is well known that treating the imputed values as observed values
may lead to substantial underestimation of the variance of the
point estimators. To overcome the problem, a number of variance
estimation methods have been proposed in the literature, including
appropriate versions of resampling methods such as the jackknife
and the bootstrap. We define the concept of doubly robust point
and variance estimation under the so-called nonresponse and
imputation model approaches. We focus on jackknife variance
estimation, which is widely used in practice. We study the
properties of several jackknife variance estimators under both
deterministic and random regression imputation. We first consider
the case of simple random sampling without replacement. The case
of stratified simple random sampling and unequal probability
sampling is also considered. A limited simulation study compares
various jackknife variance estimators in terms of bias and
relative stability when the sampling fraction is not negligible.
Finally, the asymptotic normality of imputed estimator is
established under both deterministic and random regression
imputation
Deep multi-scale architectures for monocular depth estimation
This paper aims at understanding the role of multi-scale information in the
estimation of depth from monocular images. More precisely, the paper
investigates four different deep CNN architectures, designed to explicitly make
use of multi-scale features along the network, and compare them to a
state-of-the-art single-scale approach. The paper also shows that involving
multi-scale features in depth estimation not only improves the performance in
terms of accuracy, but also gives qualitatively better depth maps. Experiments
are done on the widely used NYU Depth dataset, on which the proposed method
achieves state-of-the-art performance
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