455 research outputs found
A modern Fizeau experiment for education and outreach purposes
On the occasion of the laser's 50th anniversary, we performed a modern Fizeau
experiment, measuring the speed of light with a laser beam passing over the
city centre of Marseille. For a round trip distance of almost five kilometers,
the measurement has reached an uncertainty of about 10, mainly due to
atmospheric fluctuations. We present the experimental and pedagogical
challenges of this brilliant outreach experiment.Comment: accepted by Eur J Phys in november 201
Postural control and cognitive decline in older adults: Position versus velocity implicit motor strategy
The present study explored the impact of cognitive decline on postural control strategies in older adults with and without cognitive decline from mild cognitive impairment (MCI) to mild-to-moderate Alzheimer disease (MMAD). We hypothesized that the cognitive decline affected the postural control leading to higher bounding limits of COP velocity dynamics. Based on a cross-sectional design, 175 non-faller older adults were recruited in Angers University Hospital, France, including 50 cognitively healthy individuals [CHI] (mean age 76.42 +/- 4.84 years; 30% women), 64 age-and body mass index-matched participants with MCI (mean age 77.51 +/- 6.32 years; 39% women), and 61 age- and body mass index-matched participants with MMAD (mean age 78.44 +/- 3.97 years; 62% women). For all data collection of postural sway, the participants were asked to maintain quiet stance on force platform. The postural test consisted of two trials of quiet stance, with eyes open and with eyes closed. The COP parameters were mean and standard deviation (SD) of position, velocity and average absolute maximal velocity (AAMV) in anteroposterior and medio-lateral directions. Overall, the analysis concerning all COP parameters revealed a significant main effect of cognitive status on velocity-based variables, with post hoc comparisons evidencing that SD velocity and AAMV increased with cognitive impairment. The current findings suggest an active control (or corrective process) of COP velocity dynamics for CHI, whereas MCI and MMAD are affected by COP movements. (C) 2013 Elsevier B.V. All rights reserved
Lateral differentiation of Albeluvisols under the impact of subsurface drainage
Albeluvisols are temporarily waterlogged due to the argillic horizon that limits downward movement of rainfall water. These soils are hence frequently drained for cropping. Drainage modifies water movement in both direction and velocity, inducing a gradient in waterlogging conditions perpendicularly to the drain. Over time, it may induce a lateral differentiation of the soil solid phase with the distance from the drain. This study aims at characterising and quantifying this differentiation. Albeluvisols are characterised by the following horizon succession: A, Eg&BT, BTgd. The two last horizons exhibit a complex juxtaposition of white-grey, ochre and pale-brown volumes, and numerous black concretions or impregnations. In order to study the impact of drainage on the evolution of such soils, we have to characterise the soil differentiation perpendicularly to the drain by quantifying changes in the quality and the abundance of the different pedological volumes
Use of the neutrophil-to-lymphocyte ratio as a component of a score to predict postoperative mortality after surgery for hip fracture in elderly subjects
Peer reviewedPublisher PD
Impact of drainage on soil-forming mechanisms in a French Albeluvisol: Input of mineralogical data in mass-balance modelling
International audienceResearch on soil pedogenesis has mainly focused on the long-term soil formation and has most often neglected recent soil evolutions in response to human practices. Such recent soil evolutions are however of considerable interest to study the timing of soil forming processes in response to changes in environmental conditions. In this paper, we model the Albeluvisol evolution in response to agricultural drainage. This was considered as a model case to study the velocity of mineralogical changes in soil as a result of eluviation and redox processes. We used a space-for-time substitution approach in combination with mass balance modelling based on mineralogical data in order to identify and characterise the mineralogical transformations responsible for the recent soil evolution in response to subsurface drainage. This approach allowed demonstrating that the main effects of subsurface drainage are (i) increasing precipitation of Mn oxides and Mn-rich ferrihydrite with decreasing distance to the drain as a result of the change in redox conditions and (ii) increasing loss of clay-sized oxides and smectites due to the enhanced eluviation in the vicinity of the drain. Both processes induce significant matter fluxes in comparison with those that occurred over the long-term soil formation. Nowadays, the precipitation of Mn oxides and Mn-rich ferrihydrite seems to still be active in the studied soil. On the opposite, the eluviation process appears less active than immediately after the drainage network installation, if not totally inactive. It thus demonstrates that some soil processes may have significant impact on the soil mineralogical composition even if they are only active over very short periods of time after a change in environmental conditions
Long Cycles in a Perturbed Mean Field Model of a Boson Gas
In this paper we give a precise mathematical formulation of the relation
between Bose condensation and long cycles and prove its validity for the
perturbed mean field model of a Bose gas. We decompose the total density
into the number density of
particles belonging to cycles of finite length () and to
infinitely long cycles () in the thermodynamic limit. For
this model we prove that when there is Bose condensation,
is different from zero and identical to the condensate density. This is
achieved through an application of the theory of large deviations. We discuss
the possible equivalence of with off-diagonal long
range order and winding paths that occur in the path integral representation of
the Bose gas.Comment: 10 page
A multipurpose machine to study paramagnetic species on well defined single crystal surfaces
A new ultrahigh vacuum (UHV) electron paramagnetic resonance (EPR)
spectrometer operating at 94 GHz to investigate paramagnetic centers on single
crystal surfaces is described. It is particularly designed to study
paramagnetic centers on well-defined model catalysts using epitaxial thin
oxide films grown on metal single crystals. The EPR setup is based on a
commercial Bruker E600 spectrometer, which is adapted to ultrahigh vacuum
conditions using a home made Fabry Perot resonator. The key idea of the
resonator is to use the planar metal single crystal required to grow the
single crystalline oxide films as one of the mirrors of the resonator. EPR
spectroscopy is solely sensitive to paramagnetic species, which are typically
minority species in such a system. Hence, additional experimental
characterization tools are required to allow for a comprehensive investigation
of the surface. The apparatus includes a preparation chamber hosting
equipment, which is required to prepare supported model catalysts. In
addition, surface characterization tools such as low energy electron
diffraction (LEED)/Auger spectroscopy, temperature programmed desorption
(TPD), and infrared reflection absorption spectroscopy (IRAS) are available to
characterize the surfaces. A second chamber used to perform EPR spectroscopy
at 94 GHz has a room temperature scanning tunneling microscope attached to it,
which allows for real space structural characterization. The heart of the UHV
adaptation of the EPR experiment is the sealing of the Fabry-Perot resonator
against atmosphere. To this end it is possible to use a thin sapphire window
glued to the backside of the coupling orifice of the Fabry Perot resonator.
With the help of a variety of stabilization measures reducing vibrations as
well as thermal drift it is possible to accumulate data for a time span, which
is for low temperature measurements only limited by the amount of liquid
helium. Test measurements show that the system can detect paramagnetic species
with a density of approximately 5 × 1011 spins/cm2, which is comparable to the
limit obtained for the presently available UHV-EPR spectrometer operating at
10 GHz (X-band). Investigation of electron trapped centers in MgO(001) films
shows that the increased resolution offered by the experiments at W-band
allows to identify new paramagnetic species, that cannot be differentiated
with the currently available methodology
Large deviations for many Brownian bridges with symmetrised initial-terminal condition
Consider a large system of Brownian motions in with some
non-degenerate initial measure on some fixed time interval with
symmetrised initial-terminal condition. That is, for any , the terminal
location of the -th motion is affixed to the initial point of the
-th motion, where is a uniformly distributed random
permutation of . Such systems play an important role in quantum
physics in the description of Boson systems at positive temperature .
In this paper, we describe the large-N behaviour of the empirical path
measure (the mean of the Dirac measures in the paths) and of the mean of
the normalised occupation measures of the motions in terms of large
deviations principles. The rate functions are given as variational formulas
involving certain entropies and Fenchel-Legendre transforms. Consequences are
drawn for asymptotic independence statements and laws of large numbers.
In the special case related to quantum physics, our rate function for the
occupation measures turns out to be equal to the well-known Donsker-Varadhan
rate function for the occupation measures of one motion in the limit of
diverging time. This enables us to prove a simple formula for the large-N
asymptotic of the symmetrised trace of , where
is an -particle Hamilton operator in a trap
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