9,220 research outputs found
Chromatographic test facility. Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration
Test facility to verify design concepts and mathematical models of chromatograph for atmospheric composition analysis of Mar
Reduction of chromatographic data and evaluation of a GC model
Gas chromatograph, mass spectrometer system for chemical and biochemical determinations on Mars, and data reduction progra
Universal conductance fluctuations in epitaxial GaMnAs ferromagnets: structural and spin disorder
Mesoscopic transport measurements reveal a large effective phase coherence
length in epitaxial GaMnAs ferromagnets, contrary to usual 3d-metal
ferromagnets. Universal conductance fluctuations of single nanowires are
compared for epilayers with a tailored anisotropy. At large magnetic fields,
quantum interferences are due to structural disorder only, and an unusual
behavior related to hole-induced ferromagnetism is evidenced, for both quantum
interferences and decoherence. At small fields, phase coherence is shown to
persist down to zero field, even in presence of magnons, and an additional spin
disorder contribution to quantum interferences is observed under domain walls
nucleation.Comment: 15 pages, 4 figure
Anharmonicity and asymmetry of Landau levels for a two-dimensional electron gas
We calculate the density of states of a two dimensional electron gas located
at the interface of a GaAlAs/GaAs heterojunction. The disorder potential which
is generally created by a single doping layer behind a spacer, is here enhanced
by the presence of a second delta doped layer of scatterers which can be
repulsive or attractive impurities. We have calculated the density of states by
means of the Klauder's approximation, in the presence of a magnetic field of
arbitrary strength. At low field either band tails or impurity bands are
observed for attractive potentials, depending on the impurity concentration. At
higher field, impurity bands are observed for both repulsive and attractive
potentials. We discuss the effect of such an asymmetrical density of states on
the transport properties in the quantum Hall effect regime.Comment: 22 pages, 12 figures. submitted to Phys. Rev.
NIKEL: Electronics and data acquisition for kilopixels kinetic inductance camera
A prototype of digital frequency multiplexing electronics allowing the real
time monitoring of microwave kinetic inductance detector (MKIDs) arrays for
mm-wave astronomy has been developed. Thanks to the frequency multiplexing, it
can monitor simultaneously 400 pixels over a 500 MHz bandwidth and requires
only two coaxial cables for instrumenting such a large array. The chosen
solution and the performances achieved are presented in this paper.Comment: 21 pages, 14 figure
THE CLINICAL SIGNIFICANCE OF TWO DIFFERENT ELECTROMYOGRAPHY NORMALISATION TECHNIQUES IN PATIENTS WITH ANTERIOR CRUCIATE LIGAMENT INSTABILITY DURING TREADMILL WALKING
The purpose of this study is to investigate the clinical outcome of two normalisation techniques in detecting neuromuscular alterations of the quadriceps muscles between injured and non-injured patients diagnosed with ACL knee instability in their right knee during repeated gait cycles on a treadmill. The ensemble average muscle activity of the vastus lateralis and vastus medialis were normalised to either MVC or maximal activation during the gait cycle in eight male and female subjects. Results indicate that the EMG normalised to MVC was more sensitive in detecting differences in activation between the vastus lateralis and vastus medialis than the normalisation to maximal activity during repeated strides. This study indicates the importance of choosing the appropriate normalisation technique when seeking a clinical outcome measure
Comparaison des diversités génétiques de Dacryodes edulis (G.Don) H.J. Lam et de Dacryodes buettneri (Engel.) H.J. Lam (Burséracées), deux espèces forestières utiles en Afrique centrale
Dacryodes buettneri et Dacryodes edulis sont des espèces à usages multiples en Afrique centrale. Elles servent principalement de bois d’oeuvre et de fruitier. Des échantillons de leurs folioles ont été récoltés sur 694 arbres répartis dans 29 populations au Cameroun et au Gabon, afin d’extraire l’ADNn et amplifier cinq marqueurs microsatellites. Les paramètres génétiques des populations ont été calculés pour évaluer et comparer leur diversité génétique. Les moyennes des nombres d’allèles sont respectivement 4,43 ± 1,37 et 5,36 ± 1,13. Il n’existe pas de différence significative dans la répartition des nombres d’allèles par locus entre les espèces. Les paramètres de la diversité intra-population de D. buettneri (P = 0,76 ± 0,15; Hatt = 0,35 ± 0,06 et Hobs = 0,26 ± 0,04) sont significativement inférieurs à ceux de D. edulis (P = 0,9 ± 0,12; Hatt = 0,47 ± 0,05 et Hobs = 0,41 ± 0,07), alors que le coefficient de consanguinité de D. buettneri (F = 0,25 ± 0,08) est deux fois supérieur à celui de la deuxième espèce (F = 0,12 ± 0,03). Un important flux de gènes inter-espèce a été trouvé, Nm = 0,44. Les analyses ont ressorti trois groupes de populations, séparés par la distance géographique et l’isolement taxonomique. D. edulis se croise parfaitement si les individus sont géographiquement proches, même avec les individus spontanés forestiers. Aucune séparation variétale au sein de D. edulis n’a été détectée. Cette étude est une contribution à la valorisation de la diversité génétique des espèces forestières africaines pour une conservation durable.Mots clés : Espèces à usages multiples, marqueurs microsatellites, génétique de populations, conservation durable
Frustration and sound attenuation in structural glasses
Three classes of harmonic disorder systems (Lennard-Jones like glasses,
percolators above threshold, and spring disordered lattices) have been
numerically investigated in order to clarify the effect of different types of
disorder on the mechanism of high frequency sound attenuation. We introduce the
concept of frustration in structural glasses as a measure of the internal
stress, and find a strong correlation between the degree of frustration and the
exponent alpha that characterizes the momentum dependence of the sound
attenuation . In particular, alpha decreases from
about d+1 in low-frustration systems (where d is the spectral dimension), to
about 2 for high frustration systems like the realistic glasses examined.Comment: Revtex, 4 pages including 4 figure
WHAT CAN WE LEARN FROM IN VIVO BIOMECHANICAL INVESTIGATIONS OF LOWER EXTREMITY?
In vivo biomechanical investigations of human movement are needed to better understand function and injury mechanism of the musculoskeletal system and to validate models or methods that otherwise could not be validated. In this report, we showcase two biomechanical approaches that use in vivo experiments to directly measure skin movement artefacts and the role of hamstring neuromuscular control in protecting the anterior cruciate ligament (ACL). The study on skin movement artefacts revealed that surface markers provided kinematics which can present repeatable patterns within a participant for various movements. However these repeatable patterns must not be misinterpreted as accurately representing skeletal kinematics, at least beyond the sagittal plane of movement. In the second investigation the neuromuscular control of the hamstring and gastrocnemius muscles showed a protective mechanism to prevent excessive ACL elongation, whereas the quadriceps muscles resisted against the collapsing of the knee joint after foot impact with the ground. This paper highlights the value of in vivo experimentation in contributing to our understanding of biomechanical functions or processes
Quantifying year-round nocturnal bird migration with a fluid dynamics model.
To understand the influence of biomass flows on ecosystems, we need to characterize and quantify migrations at various spatial and temporal scales. Representing the movements of migrating birds as a fluid, we applied a flow model to bird density and velocity maps retrieved from the European weather radar network, covering almost a year. We quantified how many birds take-off, fly, and land across Western Europe to (1) track bird migration waves between nights, (2) cumulate the number of birds on the ground and (3) quantify the seasonal flow into and out of the study area through several regional transects. Our results identified several migration waves that crossed the study area in 4 days only and included up to 188 million (M) birds that took-off in a single night. In spring, we estimated that 494 M birds entered the study area, 251 M left it, and 243 M birds remained within the study area. In autumn, 314 M birds entered the study area while 858 M left it. In addition to identifying fundamental quantities, our study highlights the potential of combining interdisciplinary data and methods to elucidate the dynamics of avian migration from nightly to yearly time scales and from regional to continental spatial scales
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