Posture and muscular behaviour in emergency braking: An experimental approach

In the field of numerical crash simulations in road safety research, there is a need to accurately define the initial conditions of a frontal impact for the car occupant. In particular, human models used to simulate such impacts barely take into account muscular contracting effects. This study aims to quantify drivers’ behaviour in terms of posture and muscular activity just before a frontal impact.Experiments on volunteers were performed in order to define these conditions, both on a driving simulator and on a real moving car. Brake pedal loads, lower limbs kinematics and muscle activation were recorded.Coupling instantaneous data from both experimental protocols (simulator versus Real car), a standard emergency braking configuration could be defined as (1) joint flexion angles of 96°, 56° and 13° for the right hip, knee and ankle respectively; (2) a maximum brake pedal load of 780 N; (3) a muscular activation of 55% for the anterior thigh, 26% for the posterior thigh, 18% for the anterior leg and 43% for the posterior leg.The first application of this research is the implementation of muscle tone in human models designed to evaluate new safety systems.     

Nuclear susceptibility of liquid3He-4He solutions along the demixing line

Pulsed NMR measurements of the nuclear magnetic susceptibility of liquid³He-⁴He solutions at saturated vapor pressure are presented. They extend over the whole temperature range between 50 mK and 825 mK, for both concentrations of the coexisting dilute and³He-rich phases. The results have been compared to those obtained with pure³He, and the temperature dependence of the ratio of molar susceptibilities of coexisting phases is derived. The consequences on the efficiency of fractional distillation as a method to enhance nuclear polarization are discussed.     

Different ways for grafting ester derivatives of poly(ethylene glycol) onto chitosan: related characteristics and potential properties

The grafting of poly(ethylene glycol) functionalized by ester groups (MeO-PEG-ester) onto chitosan was studied and optimized using different reaction conditions. In a first procedure, the grafting was made from 6-O-triphenylmethyl-chitosan after protection of primary hydroxyl groups and in a second one, it was made directly onto chitosan. NMR spectroscopy was an important tool to study these reactions and the grafting is unequivocally showed up. Moreover, for each procedure, the solubility and surface properties of the obtained copolymers were evaluated and compared.     

Characterization of spin polarized dilute3He-4He solutions below 500 mK

We have prepared a large sample of spin polarized liquid ³ He- ⁴ He at 500 mK. Polarization is obtained by laser optical pumping, and studied by pulsed NMR. We have observed a nuclear magnetization lifetime T ₁ longer than 1 hour, and an anomalously long, non linear decay of tranverse magnetization.Unité de recherche de l'Ecole Normale Supérieure et de l'Université Pierre et Marie Curie, associé au CNRS (URA 18).     

Wetting properties of liquid helium on rubidium metal

Wetting properties of liquid helium on rubidium metal have been investigated in the temperature range 1.0–1.7 K using a heat conduction method. The rubidium surface is found to be wetted under saturated vapor conditions. Prewetting transitions have been observed for rather weak offsets from saturation, indicating that rubidium is close to the nonwetting limit at T = 0 K. Presumably because of substrate inhomogeneities, the prewetting transitions are experimentally found to be continuous and hysteretic. No evidence for the prewetting critical point has been found up to 1.7 K. The prewetting line verifies a simple linear relation between the liquid-vapour surface tension and the two third power of the chemical potential offset, but does not conform quantitatively to the simple model currently used.On leave of Rochester University.Laboratoire de L'Ecole Normale Supérieure et de l'Universté Pierre et Marie Curie, associé au CNRS (URA 18).     

Investigation of electrostrictive polymer efficiency for mechanical energy harvesting

The purpose of this paper is to propose new means for harvesting energy using electrostrictive polymers. Recent trends in energy conversion mechanisms have demonstrated the abilities of electrostrictive polymers for converting mechanical vibrations into electricity. In particular, such materials present advantageous features such as a high productivity, high flexibility, and ease of processing; hence, the application of these materials for energy harvesting purposes has been of significant interest over the last few years. This paper discusses the development of a model that is able to predict the energy harvesting capabilities of an electrostrictive polymer. Moreover, the energy scavenging abilities of an electrostrictive composite composed of terpolymer poly(vinylidenefluoride-trofluoroethylene- chlorofluoroethylene) [P(VDF-TrFE-CFE)] filled with 1 vol% carbon black (C) is evaluated. Experimental measurements of the harvested power and current have been compared with the theoretical behavior predicted by the proposed model. A good agreement was observed between the two sets of data, which consequently validated the proposed modeling to optimize the choice of materials. It was also shown that the incorporation of nanofillers in P(VDF-TrFE-CFE) increased the harvested power.     

Analysis of ac-dc conversion for energy harvesting using an electrostrictive polymer P(VDF-TrFE-CFE)

Harvesting systems capable of transforming unused environmental energy into useful electrical energy have been extensively studied for the last two decades. The recent development of electrostrictive polymers has generated new opportunities for harvesting energy. The contribution of this study lies in the design and validation of electrostrictive polymer- based harvesters able to deliver dc output voltage to the load terminal, making the practical application of such material for self-powered devices much more realistic. Theoretical analysis supported by experimental investigations showed that an energy harvesting module with ac-to-dc conversion allows scavenging power up to 7 μW using a bias electric field of 10 V/μm and a transverse strain of 0.2%. This represents a power density of 280 μW/cm(3) at 100 Hz, which is much higher than the corresponding values of most piezo-based harvesters.     

Technologie et organisation : le hasard et la nécessité

Evolution of ict in organizations are following two contradictory trends. On the one hand, definition and concepts defining these technologies are loosing specificity, on the other hand, these technologies take a growing place in organizational life. Characterization of ict is particularly difficult as ict are especially flexible and can be substituted easily to one another. The reasons are numerous : supply structure, organizational uses, applications structuring mixing technical devices, organization design, set of procedures and implementation process rules. The argument of the paper analyzes the nature and difficulties of ict characterization. It develops, then, some organizational consequences, concerning, in particular, implementation and equipment decision.