325 research outputs found
Activité physique et vieillissement : il n'est jamais trop tard!
Cet article propose une démarche pratique permettant à partir d'une évaluation initiale de leur niveau d'activité physique d'informer, de conseiller et de convaincre les personnes âgées sédentaires qui nous consultent des bénéfices à retirer d'une activité physique adaptée pour le maintien de leur indépendance, de leur autonomie et de leur qualité de vie
L'occupation humaine de l'abri Pataud (Les Eyzies-de-Tayac, Dordogne) il y a 22 000 ans : problématique et résultats préliminaires des fouilles du niveau 2
In this paper, we present the first elements of response to the question: "What is the status of the human remains in the Final Gravettian Level (Level 2) at Abri Pataud?" In 2005, more than forty years after the excavations of H. L. Movius, a new project concerning level 2 was initiated at Abri Pataud. This project was conceived according to three simultaneous and complementary approaches: 1) a detailed analysis of archives; 2) a study of the Movius collections; 3) a new excavation with both archaeological and geoarchaeological objectives. The initial results of the 2005 and 2006 excavations have confirmed that we can indeed appreciably improve our understanding of this archaeological level. Certain elements, such as the presence of very small backed bladelets, already permit us to more precisely define the originality of this culture. A first approach to the human remains (more than 250, MNI=6) led us to consider the hypothesis of a "disturbed primary burial". This hypothesis is confirmed by preliminary results concerning the significant assemblage of "particular artefacts" associated with the human remains, most notably mammoth ivory beads.Cet article présente les premiers éléments de réponse à la question : " Quel est le statut des vestiges humains du Gravettien final (niveau 2) de l'abri Pataud ? ". En 2005, plus de quarante ans après l'arrêt des fouilles de H. L. Movius, a débuté une opération archéologique programmée portant sur le niveau 2 de l'abri Pataud. Cette opération a été conçue selon trois démarches simultanées et complémentaires : 1) analyse des archives ; 2) étude des collections Movius ; 3) reprise de la fouille elle-même, dans une double perspective archéologique et géoarchéologique. Les premiers résultats obtenus en 2005 et 2006 ont confirmé que nous pouvions sensiblement améliorer la compréhension de ce niveau archéologique. Nous avons d'ores et déjà des éléments permettant de mieux documenter ce faciès culturel original, comme par exemple la présence de lamelles à dos de dimensions millimétriques. Une première approche des vestiges humains (plus de 250 restes, NMI = 6), nous a conduits à envisager l'hypothèse de " dépôts primaires remaniés ". Cette hypothèse est confortée par l'analyse préliminaire de l'importante série d'" objets particuliers " associée aux restes humains, notamment des perles en ivoire de mammouth
The flow of a very concentrated slurry in a parallel-plate device: influence of gravity
We investigate, both experimentally and theoretically, the fow and structure
of a slurry when sheared between 2 horizontal plates. The slurry, otherwise
called a "wet granular material", is made of non-Brownian particles immersed in
a viscous fluid. The particles are heavier than the fluid, consequently,
gravity influences the structure and flow profiles of the sheared material.
Experiments are carried out in a plane Couette device, with a model slurry
composed of approximately monodisperse spherical PMMA particles in oil, at high
average solid concentration (about 58%). Optical observation reveals a typical
2-phase configuration, with a fluidized layer in contact with the upper plate
and on top of an amorphous solid phase. We provide data on velocity profiles,
wall-slip and shear stress versus the average shear rate. To interpret the
data, we propose a model for the ideal case of infinite horizontal flat plates.
The model, of mean field type, is based on local constitutive equations for the
tangential and normal components of the stress tensor and on expressions
relating the material viscometric coefficients (the shear viscosity eta and the
normal viscosity psi) with the local concentration (phi) and the local shear
rate. 1-,2- and 3-phase configurations are predicted, with non linear flow and
concentration profiles. We conclude that the model equations correctly describe
the experimental data, provided that appropriate forms are chosen for the
divergence of eta and psi near the packing concentration (phi_max), namely a
(phi_max-phi)^-1 singularity.Comment: 26 pages, 12 figures ; submitted to Physics of Fluid
Passive remote sensing of tropospheric aerosol and atmospheric correction for the aerosol effect
The launch of ADEOS in August 1996 with POLDER, TOMS, and OCTS instruments on board and the future launch of EOS-AM 1 in mid-1998 with MODIS and MISR instruments on board start a new era in remote sensing of aerosol as part of a new remote sensing of the whole Earth system (see a list of the acronyms in the Notation section of the paper). These platforms will be followed by other international platforms with unique aerosol sensing capability, some still in this century (e.g., ENVISAT in 1999). These international spaceborne multispectral, multiangular, and polarization measurements, combined for the first time with international automatic, routine monitoring of aerosol from the ground, are expected to form a quantum leap in our ability to observe the highly variable global aerosol. This new capability is contrasted with present single-channel techniques for AVHRR, Meteosat, and GOES that although poorly calibrated and poorly characterized already generated important aerosol global maps and regional transport assessments. The new data will improve significantly atmospheric corrections for the aerosol effect on remote sensing of the oceans and be used to generate first real-time atmospheric corrections over the land. This special issue summarizes the science behind this change in remote sensing, and the sensitivity studies and applications of the new algorithms to data from present satellite and aircraft instruments. Background information and a summary of a critical discussion that took place in a workshop devoted to this topic is given in this introductory paper. In the discussion it was concluded that the anticipated remote sensing of aerosol simultaneously from several space platforms with different observation strategies, together with continuous validations around the world, is expected to be of significant importance to test remote sensing approaches to characterize the complex and highly variable aerosol field. So far, we have only partial understanding of the information content and accuracy of the radiative transfer inversion of aerosol information from the satellite data, due to lack of sufficient theoretical analysis and applications to proper field data. This limitation will make the anticipated new data even more interesting and challenging. A main concern is the present inadequate ability to sense aerosol absorption, from space or from the ground. Absorption is a critical parameter for climate studies and atmospheric corrections. Over oceans, main concerns are the effects of white caps and dust on the correction scheme. Future improvement in aerosol retrieval and atmospheric corrections will require better climatology of the aerosol properties and understanding of the effects of mixed composition and shape of the particles. The main ingredient missing in the planned remote sensing of aerosol are spaceborne and ground-based lidar observations of the aerosol profiles
G Electronics and Data Acquisition (Forward-Angle Measurements)
The G parity-violation experiment at Jefferson Lab (Newport News, VA) is
designed to determine the contribution of strange/anti-strange quark pairs to
the intrinsic properties of the proton. In the forward-angle part of the
experiment, the asymmetry in the cross section was measured for
elastic scattering by counting the recoil protons corresponding to the two
beam-helicity states. Due to the high accuracy required on the asymmetry, the
G experiment was based on a custom experimental setup with its own
associated electronics and data acquisition (DAQ) system. Highly specialized
time-encoding electronics provided time-of-flight spectra for each detector for
each helicity state. More conventional electronics was used for monitoring
(mainly FastBus). The time-encoding electronics and the DAQ system have been
designed to handle events at a mean rate of 2 MHz per detector with low
deadtime and to minimize helicity-correlated systematic errors. In this paper,
we outline the general architecture and the main features of the electronics
and the DAQ system dedicated to G forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section
A. It has been written with Latex using \documentclass{elsart}. Nuclear
Instruments and Methods in Physics Research Section A: Accelerators,
Spectrometers, Detectors and Associated Equipment In Press (2007
An improved chronology for the Middle Stone Age at El Mnasra cave, Morocco
North African coastal Middle Stone Age (MSA) sites are key to study the development and expansion of early H. sapiens. El Mnasra cave on the Atlantic coast of Morocco (Témara region) is a crucial site associated with MSA archaeological materials considered advanced cognitive hallmarks of behavioural innovation, such as numerous Nassariidae perforated shells, hematite pigments, bones industry and coastal resources exploitation. We provide new trapped-charges dates (OSL and combined US-ESR ages). Our Bayesian modelling strengthens the new lithostratigraphic interpretation of the cave stratigraphic units (US) and we propose an updated chronostratigraphic model for the Middle Stone Age archaeo-sequence of El Mnasra Cave. We confirm a human presence between 124–104 ka, earlier than what the previous OSL and US-ESR data showed. Our time range intervals allowed us to also extend the age of the MSA occupations considerably to the MIS 4/3 (~62–30 ka), marked by the disappearance of the Nassariidae perforated shells. Outstandingly, our model pushed back the age of the largest record of Nassariidae perforated shells and placed the age of their use by the Aterian groups at El Mnasra from the MIS 5d-5b (~115–94 ka)
Effective surface albedo due to snow cover of the surrounding area
Albedo inversion techniques are investigated in this work. Several methods are applied to spectral irradiance data from a measurement campaign held in the German Alps during the spring of 1999. One first method is based on the comparison of measurements of absolute levels of UV irradiance with model calculations. The second method takes advantage of changes in the spectral slope of spectral UV irradiance, which is a function of the surface albedo. In the third method, the surrounding area is partitioned into snow-covered and snow-free regions, and the effective albedo estimated by applying a higher or lower reflectivity to each facet before integrating over the surroundings. We present sensitivity analysis, the differences and the correlations between the various methods as well as the results for the different locations
Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering
We have measured the beam-normal single-spin asymmetry in elastic scattering
of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 =
0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely
using the elastic nucleon intermediate state, and generally agree with
calculations with significant inelastic hadronic intermediate state
contributions. A_n provides a direct probe of the imaginary component of the
2-gamma exchange amplitude, the complete description of which is important in
the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened
to meet PRL length limit, clarified some text after referee's comment
Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment
We have measured parity-violating asymmetries in elastic electron-proton
scattering over the range of momentum transfers 0.12 < Q^2 < 1.0 GeV^2. These
asymmetries, arising from interference of the electromagnetic and neutral weak
interactions, are sensitive to strange quark contributions to the currents of
the proton. The measurements were made at JLab using a toroidal spectrometer to
detect the recoiling protons from a liquid hydrogen target. The results
indicate non-zero, Q^2 dependent, strange quark contributions and provide new
information beyond that obtained in previous experiments.Comment: 5 pages, 2 figure
The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles
In the G0 experiment, performed at Jefferson Lab, the parity-violating
elastic scattering of electrons from protons and quasi-elastic scattering from
deuterons is measured in order to determine the neutral weak currents of the
nucleon. Asymmetries as small as 1 part per million in the scattering of a
polarized electron beam are determined using a dedicated apparatus. It consists
of specialized beam-monitoring and control systems, a cryogenic hydrogen (or
deuterium) target, and a superconducting, toroidal magnetic spectrometer
equipped with plastic scintillation and aerogel Cerenkov detectors, as well as
fast readout electronics for the measurement of individual events. The overall
design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method
- …