New approach of diffraction of electromagnetic waves by a rough surface

We consider the diffraction of a plane wave by a rough surface. In the sake of simplicity the study is restricted to the case of perfectly conducting surfaces. Solving this problem is only possible by limiting the infinite rough surface to a window of width D. We show that we can obtain the diffraction pattern at infinity in the Fraunhofer zone from the modeling of diffraction by a grating with period D whose elementary pattern coincides with the rough surface in the window D. We give some numerical results for triangular profiles or rectified cosine. We show that for small heights we find that the most widely Kirchhoff approximation is very well checked. This modeling can be applied to Fraunhofer diffraction problem by a non-planar metal strip and the complementary problem of diffraction by a perfectly conducting screen, infinitely thin and with a slit of one or more periods

DETERMINATION OF INERTIA ELEMENTS FOR THE LOWER LIMBS

INTRODUCTION: For kinematic and dynamic studies of the lower limbs, using a three dimensional model is useful. Such models allow one to determine segment movements and forces acting on joints. Inverse Dynamic Analysis can be used to calculate the biomechanical loads applied (Elftman,1939). The reliability of the results depends on the degree of accuracy of the kinematic and anthropometric data (Kingma et al.,1996).The purpose of this paper is to explain a simple way to determine inertia elements of the lower limbs using anthropometric data available in the literature. METHODS: Body mass and stature are the only anthropometric parameters known for a subject. Body segment inertia parameters are obtained from cadavers and we use here de Leva (1996) segmental data for males to perform our calculations. We consider each segment of the lower limb (foot, shank and thigh) as rigid and independent. The model supposes a knowledge of the relative mass and the spatial coordinates of at least three points for each segment. A mathematical method is developed in order to obtain data which take into account the individual characteristics of the subjects. For each segment we have to determine three successive elements:- the localization of the center of mass,- a coordinate system assigned, - an inertia matrix assigned. RESULTS: The main difficulty is to place the markers properly on subjects. A simple test, allowing distance determination between markers, was proposed previously to further calculations. The mathematical model is developed in such a way as to be easily used. Conclusions: These simple-to-use methods presuppose a reducing hypothesis. We assume that for each joint a geometrical center exists. This point lies on the longitudinal axis of the segments and has a fixed three dimensional position relative to the segments forming the joint. The localization of the ‘joint center’ is not referenced to the sagittal and transversal axis. We use data reported by de Leva (1996). This supposes that the lower limb is a standard limb, reducing accuracy for subjects with some pathological segment orientation or for young, old and female subjects. As the error introduced by using inappropriate segment parameters could be substantial, the choice of the biomechanical model, as well as the optimal measurement method, is absolutely necessary to obtain for example a good evaluation of the forces acting on the different joints

Vers un renouveau de l’étude des sociétés agraires grecques ? Julien Zurbach et la paysannerie grecque.

À propos de : J. Zurbach, Les hommes, la terre et la dette en Grèce. c. 1400-c. 500 a.C. – Bordeaux : Ausonius, 2017. – 2 vol., 850 p. : bibliogr., index, fig. – (Scripta Antiqua, ISSN : 1298.1990 ; 95). – ISBN : 978.2.35613.179.9.International audienc

SPINE MOVEMENT DURING HALF SQUAT EXERCISE

INTRODUCTION .Postural variations of the spine can be studied using radiological technique, but in order to minimize the ionizing radiation we suggested previously to use a non-invasive method. The aim of this study is to describe the movement of the different vertebral segments during half squat exercise. MATEFUAL AND METHOD As described previously external markers are glued to the projecting contours of the spinous processes on 20 voluntary subjects (10 males, 10 females). Markers were implanted on T7, T12, L1, L3, L5 and S1 vertebra levels. This technique was designed to locate angular displacement. Three positions were studied: neutral (vertical trunk, without additional charge), in charge (vertical trunk + 50 kg) and half squat with 50 kg on the shoulders. From the photos were measured, in the sagittal plane, the angular variations at each vertebral segment. RESULTS In standing position the barbell weight induces a general flexion on the cervical and thoracic levels. A verticalization of S1 with an extension of L5 is noticed. In squat position, the main displacement occurs in S1 according to the important movement of the coxo-femoral joint. L5 remains in a constant position. An important flexion is noticed in L3 and L1. T12 seems well fixed. T7 angulation is dependent of head position and of general trunk flexion. DISCUSSION In physical training session emphasis should be laid on the voluntary development of muscles surrounding pelvis, but also of muscles allowing the fixation of thoraco-lumbar joint

The Interpretation of DreamsAn Ancient Dream Manual: Artemidorus’ The Interpretation of Dreams

Le traité d’interprétation des rêves d’Artémidore de Daldis, rédigé en grec vers 200 ap. J.‑C., ne fait incontestablement pas partie du canon des sources des historiens ; le style très prosaïque de cet auteur lui retire aussi toute chance d’être lu pour ses qualités littéraires. Ni la Collection des Universités de France, ni la Loeb Classical Library ne l’ont encore fait entrer dans leur catalogue. Ce n’est pourtant pas un texte oublié, seulement un texte négligé. Depuis une quinzaine d’année..

Diffraction gratings of isotropic negative phase-velocity materials

Diffraction of electromagnetic plane waves by the gratings made by periodically corrugating the exposed planar boundaries of homogeneous, isotropic, linear dielectric--magnetic half--spaces is examined. The phase velocity vector in the diffracting material can be either co-parallel or anti-parallel to the time-averaged Poynting vector, thereby allowing for the material to be classified as of either the positive or the negative negative phase-velocity (PPV or NPV) type. Three methods used for analyzing dielectric gratings - the Rayleigh-hypothesis method, a perturbative approach, and the C formalism - are extended here to encompass NPV gratings by a careful consideration of field representation inside the refracting half--space. Corrugations of both symmetric as well as asymmetric shapes are studied, as also the diversity of grating response to the linear polarization states of the incident plane wave. The replacement of PPV grating by its NPV analog affects only nonspecular diffraction efficiencies when the corrugations are shallow, and the effect on specular diffraction efficiencies intensifies as the corrugations deepen. Whether the type of the refracting material is NPV or PPV is shown to affect surface wave propagation as well as resonant excitation of surface waves.Comment: 28 pages, 10 figures in 27 file

INFLUENCE OF REST PERIOD ON ELECTRICAL STIMULATION EFFICIENCY

INTRODUCTION: Electrical stimulation (ES) is now widely used as a modality of strengthening in healthy subjects and highly trained athletes. Most of the previous studies have reported that training by ES induces strength gains (Portmann, 1991; Fredon & Poumarat, 1995). Pulse parameters and stimulus regimens are well documented, especially for frequency of stimulation and electrode localization (Ferry & Poumarat, 1994; Ferry et al., 1994). There is a lack of information on training protocols. These should include periodic rest periods to minimize muscle fatigue and maintain an adequate level of contraction during the training session. The aim of this paper is to clarify the effect of rest periods on muscular performance

MECHANICAL STRESS ON KNEES DURING HALF-SQUAT EXERCISES

INTRODUCTION Articular forces and moments have been found to be affected by the lifting technique in ergonomics (Trafirnow et al., 1993) and in weight-training (Poumarat et al.,1989).While these researchers have improved our understanding of biomechanical aspects of lifting as related to the spine and the lower extremities, most of them remain related to either static orquasi-static conditions. The purpose of this study was to determine the mechanical stress on the knee joint using a 3-D dynamic model. MATERIALS AND METHODS Three male volunteer students participated in the study. They were asked to perform three different sets of 10 half-squat exercises: no load, 100% and 120% of total body mass of the subject additional weight. To determine kinematic data, the movement of the half-squat exercises was recorded using the Mac Reflex optoelectronic system (4 cameras) with markers on the left lower extremity at the fust metatarsal, the external rnalleolus, the external lateral femoral condyle and the greater trochanter. A six components force-plate (AMTI) provided kinetic data. Compressive and the shear forces acting on the thigh at the knee joint were calculated where; Fx represents the compressive force; Mx, the external rotatory moment of the thigh; Fy, the medio-lateral shear force; My, the extension moment of the thigh; Fz, the antero-posterior shear force; and Mz, the abductor moment of the thigh. The resultant knee force, in all subjects, increases when lifted load increases. A similar increase in the resultant moment at the knee joint was found. These pic values were calculated for a knee angle of 108. The medio-lateral shear force (Fy) was not affected by the load. However, during the middle phase of the exercise, the mtero-posterior shear force increased from 0.72 to 0. 88 times body weight when lifted mass increased from 1 to 1.20 times body weight. For the compressive component (Fx), no clear variation as a function of load was found in this study in all subjects. Even for the heaviest load (120% body weight), no increase in forces and moments was recorded from the first to the last repetition of one set. CONCLUSION The results of this study demonstrated that mechanical stress acting on knee joint in half-squat exercise increased with lifted barbell. For knee force components, load was found to affect only the antero-posterior shear force. The medio-lateral shear force was independent of this variable. Force and moment values were affected by REFERENCES Poumarat, G., Dabonneville, M., Chandezon, R., & Roddier, P. (1989). Les squats: Forces induites sur I'articulation du genou et sur L5 S 1 en fonction des postures adoptCes. CinCsiologie, 69-74. Trafimow, J.H., Schipplein, O.D., Novak, G.H.,& Andersson, G.B.J. (1993). The effects ofquadriceps fatigue on the technique of lifting. Spine, 18,364-367

Ernest Beulé (1826-1874). Archéologie classique, histoire romaine et politique sous Napoléon III

Dans la nuit du 3 au 4 avril 1874, vers minuit, un homme qui fut l’un des pionniers de l’archéologie française en Grèce et que la politique avait fini par séduire au point de faire de lui un éphémère ministre de l’Intérieur se suicide chez lui, à Paris. Le geste par lequel Ernest Beulé met fin à ses jours est digne de l’Antique. Souffrant depuis quelques semaines d’une douloureuse maladie au cœur, il saisit un poignard d’une panoplie qui ornait sa chambre et se l’enfonce dans la poitrine. Il ..

Why is lateral root growth so variable? A framework to analyze growth variability among lateral roots and the possible roles of auxin and carbon

International audienceLateral root (LR) development is a major component of the efficiency of a plant to capture soil resources. A remarkable facet of lateral root behavior is stochasticity affecting the different stages of LR growth, leading to a large range of lateral root lengths along the primary root. It has been argued that such variability among LR could be an adaptive trait enabling a greater plasticity and efficiency of the root system in front of the spatial and temporal heterogeneity of soil resources (Forde, 2009). In order to characterize variability in LR growth and evaluate the role of hormonal and biochemical signals that might influence it, we analyzed the patterns of development of hundreds of lateral roots in a set of maize seedlings grown in rhizotrons. The SmartRoot toolbox was used to provide a comprehensive recording of individual root growth dynamics. Using a clustering method based on growth variables such as elongation rate and growth duration, we could identify 3 main different elongation patterns in maize LRs composed of accelerating, slowly decelerating and rapidly arrested LRs, as found in other species (Pagès, 1995). The molecular and cellular characterization of these root types revealed differences in meristem size, apical diameters as well as apical diameter variation. Moreover, fast growing roots showed increased sugar content along their tips. Finally, by affecting either the sugar or the auxin status (by pruning seminal roots or using auxin transport mutants) we differentially altered the proportion of the different root types, suggesting that both signals contribute to shape the root system in response to variations of environmental conditions.FORDE, B. (2009), J. Exp. Bot. 60 (14): 3989-4002PAGES, L. (1995), New Phytologist, 130: 503–50