Tsunami generated by a granular collapse down a rough inclined plane

In this Letter, we experimentally investigate the collapse of initially dry granular media into water and the subsequent impulse waves. We systematically characterize the influence of the slope angle and the granular material on the initial amplitude of the generated leading wave and the evolution of its amplitude during the propagation. The experiments show that whereas the evolution of the leading wave during the propagation is well predicted by a solution of the linearized Korteweg-de Vries equation, the generation of the wave is more complicated to describe. Our results suggest that the internal properties of the granular media and the interplay with the surrounding fluid are important parameters for the generation of waves at low velocity impacts. Moreover, the amplitude of the leading wave reaches a maximum value at large slope angle. The runout distance of the collapse is also shown to be smaller in the presence of water than under totally dry conditions. This study provides a first insight into tsunamis generated by subaerial landslides at low Froude number

Effondrement granulaire dans l'eau : application à la génération de tsunami

Qu'il s'agisse du remplissage d'un silo à grain ou de la distance parcouru par un glissement de terrain, la dynamique des écoulements granulaires est présente aussi bien dans des domaines industriels que géophysiques. Si les différentes configurations d'écoulements granulaires secs sont assez bien prédites par la rhéologie mu(I), il en est tout autrement lorsqu'on ajoute de l'eau. L'objectif de cette étude est de caractériser le comportement d'un effondrement granulaire initialement sec dans l'eau le long d'une pente d'angle variable et de déterminer son influence sur les vagues générées. Pour cela plusieurs séries d'expériences ont été menées dans un aquarium de 2.20 m de long, 0.40 m de haut et 0.20 m de large. Afin de quantifier l'influence des principaux paramètres de ce type d'écoulement, l'angle de la pente, la hauteur d'eau, la masse initiale de granulaire ainsi que le type de grains utilisés ont été modifiés. Pour assurer une condition de non-glissement, les pentes et fonds ont été réalisés en collant à chaque fois le même type de matériaux que l'effondrement. Une caméra rapide a été utilisée pour enregistrer l'évolution du front granulaire au cours du temps. La propagation des vagues générées est enregistrée à l'aide de quatre sondes réparties le long de l'aquarium. Les expériences montrent que l'amplitude maximale atteint par la première vague dépend directement de la masse de granulaire et de la pente. D'autres résultats moins intuitifs ont également été observés comme le fait que la vitesse et l'épaisseur du glissement granulaire restent constant au cours de l'effondrement. Afin d'interpréter ces résultats expérimentaux, une étude numérique est en cours en modélisant l'écoulement granulaire par un fluide non-Newtonien. Le développement d'une loi d'échelle sur l'amplitude de la vague générée est également menée en parallèle

Spin noise and Bell inequalities in a realistic superconductor-quantum dot entangler

Charge and spin current correlations are analyzed in a source of spin-entangled electrons built from a superconductor and two quantum dots in parallel. In addition to the ideal (crossed Andreev) channel, parasitic channels (direct Andreev and cotunneling) and spin flip processes are fully described in a density matrix framework. The way they reduce both the efficiency and the fidelity of the entangler is quantitatively described by analyzing the zero-frequency noise correlations of charge current as well as spin current in the two output branches. Spin current noise is characterized by a spin Fano factor, equal to 0 (total current noise) and -1 (crossed correlations) for an ideal entangler. The violation of the Bell inequalities, as a test of non-locality (entanglement) of split pairs, is formulated in terms of the correlations of electron charge and spin numbers counted in a specific time window $\tau$. The efficiency of the test is analyzed, comparing $\tau$ to the various time scales in the entangler operation.Comment: 8 pages, 5 figures, references added, to appear in Phys. Rev.

Contribution of vertical and horizontal components of ground reaction forces on global motor moment during a golf swing: a preliminary study

No abstract availabl

Biomechanical analysis of the golf swing: methodological effect of angular velocity component on the identification of the kinematic sequence

The golf swing is a complex whole-body motion for which a proximal-to-distal transfer of the segmental angular velocitiesfrom the pelvis to the club is believed to be optimal for maximizing the club head linear velocity. However, previous experimental resultsabout such timing (or kinematic sequence) are contradictory. Nevertheless, methods that were used in these studies differed significantly,in particular, those regarding the component of the angular velocity vector selected for the identification of the kinematic sequence.Hence, the aim of this study was to investigate the effect of angular velocity vector component selection on the identified kinematicsequence. Methods: Thirteen golfers participated in this study and performed driver swings in a motion capture laboratory. Seven meth-ods based on different component selection of segmental angular velocities (vector norm, component normal-to-sagittal, frontal, trans-versal and swing planes, segment longitudinal component and a method mixing longitudinal and swing plane components) were tested.Results: Results showed the critical influence of the component chosen to identify the kinematic sequence with almost as many kine-matic sequences as the number of tested methods for every golfer. Conclusion: One method seems to show the strongest correlation toperformance but none of them can be assessed as a reference method for the identification of the golf swing kinematic sequence. Re-garding the limited time lag between the different peak occurrences and the uncertainty sources of current materials, development ofsimulation studies would be more suitable to identify the optimal kinematic sequence for the golf swin

Effect of shoulder model complexity in upper-body kinematics analysis of the golf swing

The golf swing is a complex full body movement during which the spine and shoulders are highly involved. In order to determine shoulder kinematics during this movement, multibody kinematics optimization (MKO) can be recommended to limit the effect of the soft tissue artifact and to avoid joint dislocations or bone penetration in reconstructed kinematics. Classically, in golf biomechanics research, the shoulder is represented by a 3 degrees-of-freedom model representing the glenohumeral joint. More complex and physiological models are already provided in the scientific literature. Particularly, the model used in this study was a full body model and also described motions of clavicles and scapulae. This study aimed at quantifying the effect of utilizing a more complex and physiological shoulder model when studying the golf swing. Results obtained on 20 golfers showed that a more complex and physiologically-accurate model can more efficiently track experimental markers, which resulted in differences in joint kinematics. Hence, the model with 3 degrees-of-freedom between the humerus and the thorax may be inadequate when combined with MKO and a more physiological model would be beneficial. Finally, results would also be improved through a subject-specific approach for the determination of the segment lengths

Determination of the intervertebral spinal axial rotation in a golf player population: a preliminary study

No abstract availabl

Influence of the projection plane and the markers choice on the X-factor computation of the golf swing X-factor: a case study

Study of variability induced by the methology choice on the X-factor computation of the golf swing. Based on optoelectronic measurements. Variability of the choice of upper limb, plane of projection and instant of computation

Variability of motor moment during golf swing: study of a female professional player

Study of th intra-individual variability of the motor moment during the golf swing. It highlighted the variability induced by horizontal ground reaction forces which are rarely taken into account in field

Effect of Horizontal Ground Reaction Forces during the Golf Swing: Implications for the development of technical solutions of golf swing analysis

The swing is a key movement for golf. Its in-field performance could be estimated by embedded technologies, but often only vertical ground reaction forces (VGRF) are estimated. However, as the swing plane is inclined, horizontal ground reaction forces (HGRF) are expected to contribute to the increase of the club angular velocity. Thus, this study aimed at investigating the role of the HGRF during the golf swing. Twenty-eight golf players were recruited and performed 10 swings with their own driver club, in a motion analysis laboratory, equipped with a full body marker set. Ground reaction forces (GRF) were measured with force-plates. A multibody kinematic optimization was performed with a full body model to estimate the instantaneous location of the golfer’s center of mass (CoM). Moments created by the GRF at the CoM were investigated. Results showed that horizontal forces should not be neglected regarding to VGRF because of their lever arm. Analyzing golf swing with only VGRF appeared not enough and further technological developments are still needed to ecologically measure other components