362 research outputs found
Ătude ThĂ©orique et ExpĂ©rimentale des Flux de Neutrons Thermiques dans des Hydrocarbures et Application des RĂ©sultats Ă la Mesure de Leur DensitĂ© et Ă la Recherche de Leur Composition. EUR 3624. = Theoretical and Experimental Study of Flows of Thermal Neutrons in Hydrocarbons and Application of Results to the Measurement of Their Density and the Search for Their Composition. EUR 3624.
MĂ©decine physique et de rĂ©adaptation et cancer : Ă©tat de lâart et analyse de la littĂ©rature
Sobre el problema geomorfolĂłgico del alineamiento de las cumbres en la region del lago Buenos Aires y la determinaciĂłn de las lĂneas tectĂłnicas en la parte sur de la Cordillera de Los Andes
En el presente trabajo se desarrolla un método de análisis geomorfológico-estadístico aplicado a la deducción de hechos geológicos generales. Es el método estadístico de los alineamientos, que se ha empleado para determinar las direcciones tectónicas de la región cordillerana del lago Buenos Aires, valiéndose del trazado de los alineamientos de las cumbres de la región considerada. De ese modo se ha inferido la existencia de cuatro direcciones tectónicas predominantes, caracterizadas por ángulos de 27°, 55°, 100° y 175°, medidos a partir de la dirección Norte y en ei sentido del movimiento de las agujas del reloj.The purpose of this work is to develope a method of a morphologic-statistical analysis applied to the deduction of general geological fats. This is the statistical method of the alinements, which has been applied to determine the tectonic directions of the Andes región in the vecinity of the Buenos Aires lalte, by establishing the alinements of the tops of the mountains in the above mentioned región. In this way it has possible to deduce the existance of four main tectonic directions, distinguished by angles of 27°, 55°, 100° and 175°, measured from the North and moving like of the hands of a dock
Diagnosis and treatment of osteoporosis in spinal cord injury patients: A literature review
AbstractObjectiveTo present an up-to-date literature review of osteoporosis in spinal cord injury (SCI) patients, in view of the seriousness of this complication (with a high risk of fractures) and the complexity of its diagnosis, evaluation and treatment.MethodsA Medline search with the following keywords: immobilization osteoporosis, spinal cord injury, bone loss, dual energy X-ray absorptiometry (DEXA), bisphosphonate.ResultsOur analysis of the literature noted a bone metabolism imbalance in SCI patients, with accelerated early bone resorption (particularly during the first 6months post-injury). Although dual energy X-ray absorptiometry constitutes the âgold standardâ diagnostic method, the decrease in bone mineral density only becomes significant 12months after the injury. Bisphosphonate therapy has proven efficacy. Despite the frequent use of various physical therapies, these methods have not been found to be effective.ConclusionAlthough our literature review did not identify any guidelines on the strategy for diagnosing and treating osteoporosis in SCI patients, several findings provide guidance on procedures for early diagnosis and preventive treatment
Experimental application of sum rules for electron energy loss magnetic chiral dichroism
We present a derivation of the orbital and spin sum rules for magnetic
circular dichroic spectra measured by electron energy loss spectroscopy in a
transmission electron microscope. These sum rules are obtained from the
differential cross section calculated for symmetric positions in the
diffraction pattern. Orbital and spin magnetic moments are expressed explicitly
in terms of experimental spectra and dynamical diffraction coefficients. We
estimate the ratio of spin to orbital magnetic moments and discuss first
experimental results for the Fe L_{2,3} edge.Comment: 11 pages, 2 figure
Lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion
The erosion of major mountain ranges is thought to be largely cannibalistic, recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift. Despite this recognition, it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean. Here, we have analyzed the Li content and isotope composition (View the MathML source) of suspended sediments sampled along river depth profiles and bed sands in three of the largest Earth's river systems (Amazon, Mackenzie and GangaâBrahmaputra rivers). The View the MathML source values of river-sediments transported by these rivers range from +5.3 to â3.6â° and decrease with sediment grain size. We interpret these variations as reflecting a mixture of unweathered rock fragments (preferentially transported at depth in the coarse fraction) and present-day weathering products (preferentially transported at the surface in the finest fraction). Only the finest surface sediments contain the complementary reservoir of Li solubilized by waterârock interactions within the watersheds. Li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks. A mass budget approach, based on Li isotopes, Li/Al and Na/Al ratios, solved by an inverse method allows us to estimate that, for the large rivers analyzed here, the part of solid weathering products formed by present-day weathering reactions and transported to the ocean do not exceed 35%. Li isotopes also show that the sediments transported by the Amazon, Mackenzie and GangaâBrahmaputra river systems are mostly sourced from sedimentary rocks (>60%) rather than igneous rocks. This study shows that Li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present-day weathering processes. Overall, Li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering
Reliability of 2D ultrasound imaging associated with transient ShearWave Elastography method to analyze spastic gastrocnemius medialis muscle architecture and viscoelastic properties
PurposeThe aim of the study was to assess the reliability of pennation angle (PA) and muscle thickness (MT) 2D measurements and of shear elastic modulus measurement, using ultrasound imaging (US). Those measurements were made on spastic gastrocnemius medialis muscle at rest and at maximal passive stretching, in post-stroke hemiplegic patients. The paretic side measurements were compared to non-paretic side.Material and methodsFourteen patients took part in 2 inter-session reliability experiments, realized at a 7 days interval by the same operator. The AixplorerŸ Supersonic US scanner with the transient ShearWave Elastography (SWE) software was used. The stretching experiments were made manually and controlled by a goniometer.ResultsThe reliability of the 2D measurements was good. The coefficient of variation (CV) was 6.30% for MT measurement at rest, 6.40% and 8.26% for PA at rest and at maximal passive stretching respectively. The reliability of the shear elastic modulus measurement in the sagittal plane was good only at rest with a CV of 9.86%, versus 40.58% at stretching. None of the shear elastic modulus measurements in the axial plane were good. At rest, MT and PA were weaker on the paretic side (14.25±3.12mm and 17.32±5.10°) versus non-paretic side (16.30±3.19mm and 21.08±5.05°) (P<0.0001 and P=0.006). At rest, there was a small difference in the shear elastic modulus between the paretic side and the non-paretic side (5.40±1.67kPa versus 6.20±2.18kPa, P=0.041).DiscussionThis is the first description of muscle spastic structure using SWE with Supersonic Shear Imaging. 2D US associated with SWE shows promise in terms of muscular atrophy quantification and muscle histological quality assessment. These structural properties reflect some of the functional abilities regardless of motor control. It should enable further research on therapies, which impact muscle tissue quality, such as botulinum neurotoxin injections
Energy-loss magnetic chiral dichroism (EMCD): Magnetic chiral dichroism in the electron microscope
A new technique called energy-loss magnetic chiral dichroism (EMCD) has recently been developed [P. Schattschneider, et al. Nature 441, 486 (2006)] to measure magnetic circular dichroism in the transmission electron microscope (TEM) with a spatial resolution of 10 nm. This novel technique is the TEM counterpart of x-ray magnetic circular dichroism, which is widely used for the characterization of magnetic materials with synchrotron radiation. In this paper we describe several experimental methods that can be used to measure the EMCD signal [P. Schattschneider, et al. Nature 441, 486 (2006); C. HĂ©bert, et al. Ultramicroscopy 108(3), 277 (2008); B. Warot-Fonrose, et al. Ultramicroscopy 108(5), 393 (2008); L. Calmels, et al. Phys. Rev. B 76, 060409 (2007); P. van Aken, et al. Microsc. Microanal. 13(3), 426 (2007)] and give a review of the recent improvements of this new investigation tool. The dependence of the EMCD on several experimental conditions (such as thickness, relative orientation of beam and sample, collection and convergence angle) is investigated in the transition metals iron, cobalt, and nickel. Different scattering geometries are illustrated; their advantages and disadvantages are detailed, together with current limitations. The next realistic perspectives of this technique consist of measuring atomic specific magnetic moments, using suitable spin and orbital sum rules, [L. Calmels, et al. Phys. Rev. B 76, 060409 (2007); J. Rusz, et al. Phys. Rev. B 76, 060408 (2007)] with a resolution down to 2 to 3 n
Singular Structure and Enhanced Friedel Oscillations in the Two-Dimensional Electron Gas
We calculate the leading order corrections (in ) to the static
polarization , with dynamically screened interactions, for the
two-dimensional electron gas. The corresponding diagrams all exhibit singular
logarithmic behavior in their derivatives at and provide significant
enhancement to the proper polarization particularly at low densities. At a
density of , the contribution from the leading order {\em fluctuational}
diagrams exceeds both the zeroth order (Lindhard) response and the self-energy
and exchange contributions. We comment on the importance of these diagrams in
two-dimensions and make comparisons to an equivalent three-dimensional electron
gas; we also consider the impact these finding have on computed
to all orders in perturbation theory
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