Risk assessment method for the implementation of materials divided up to the nanometric scale

International audienceA new approach of assessing the risks inherent in the implementation of powders, including nanomaterials has been developed. This tool is based on the method of the OHB (Occupational Hazard Band) widely spread in the chemical industry. The European classification and CLP scales of toxicity have not been modified; only the control of exposure has been worked at. The method applies essentially to the prevention of the exposures by airborne materials, whatever their particle size. The skin exposure is not treated there specifically for the time being. The method considers exposure based on seven parameters to take into account the characteristics of the materials used, their emission potential, the conditions of use, as well as classic parameters of the characterization of the exposure as the duration and the frequency. The method stresses on a pragmatic exploitation of the current knowledge and of the available data, bearing in mind that a lot of them are not easily accessible to plant operators. The product of the reflection is then positioned on a hazard x exposure matrix from which 3 levels of priority of action are defined, as in the classical OHB method applied to pure chemical risk. This approach fills in a gap in term of risk assessment and avoids jeopardizing all that had been set up for years, while introducing newelements of reflection accessible to all operators

Accumulation of IL-17+ Vgamma6+ gamma-delta T cells in pregnant mice is not associated with spontaneous abortion

Introduction. Pregnancy is an immune paradox. While the immune system is required for embryo implantation, placental development and progression of gestation, excessive inflammation is associated with pregnancy failure. Similarly, the cytokine IL-17A plays an important role in defence against extracellular pathogens, but its dysregulation can lead to pathogenic inflammation and tissue damage. Although expression of IL-17 has been reported during pregnancy, the cellular source of this cytokine and its relevance to gestation are not clear. Objectives. Here we define the kinetics and cellular source of IL-17A in the uterus during healthy and abortion-prone murine pregnancy. Methods. The CBA/J x DBA/2J abortion-prone mating was used and compared to CBA/J x BALB/c control mating. Results. We demonstrate that, irrespective of gestational health, the number of IL-17-producing cells peaks during midterm pregnancy and is largely derived from the gd T-cell lineage. We identify cd T, Th17, CD8 T and NKT cells as the cellular source of IL-17A in pregnant mice. Furthermore, we positively identify the Vc6+ subset of uterine gd T cells as the main producer of IL-17A during both healthy pregnancy and abortive pregnancy. Conclusions. To conclude, the accumulation of uterine IL-17+ innate-like T cells appears not to adversely impact the developing foetus. Collectively, our results show that IL-17+ gd T cells are present in the uterus throughout the course of normal gestation and therefore may play an important role in healthy pregnancy. Keywords: abortion, gamma delta T cells, interleukin-17, pregnancy.Implantation and Tolerance of the Embry

Enhancing Micrometric Aluminum Reactivity by Mechanical Activation

The pursuit of solid rocket motor and hybrid rocket engine performance enhancements is pushing toward the research of novel energetic materials replacing the conventional micron-sized aluminum. Nanotechnology opened the way to new concepts, introducing very promising ingredients like nano-sized aluminum powders. Their effectiveness in increasing energetic system performance has been already proven at lab-scale level. However, the high cost, the dispersion difficulties, and the increased handling risk hinder a widespread application of nanomaterials. On the other hand, activation techniques offer the possibility of micron-sized additives reactivity enhancement while maintaining high safety levels and reduced costs. This work deals with the design, the production, and the characterization of mechanically activated ingredients for solid propellants and hybrid rocket fuels. General guidelines for the powder processing implementation are critically discussed. Additives are characterized in the pre-burning phase, and their effects on the ballistic response of solid propellants and hybrid fuels are investigated. Activated powders improved hybrid fuel regression rate and reduced the size of the condensed combustion products of solid propellants, confirming their suitability for the micron-sized aluminum replacement

Le role des forces à longues distances dans la determination de la libération d'énergie cinétique translationnelle. La formation de cations C4H4+ à partir du Benzène et de la Pyridine.

Kinetic energy release distributions (KERDs) for the benzene ion fragmenting into C4H4+ and C2H2 have been recorded by double-focussing mass spectrometry in the metastable energy window and by a retarding field experiment up to an energy of 5 eV above the fragmentation threshold. They are compared with those resulting from the HCN loss reaction from the pyridine ion. Both reactions display a similar variation of the kinetic energy release as a function of the internal energy: the average release is smaller than statistically expected, with a further restriction of the phase-space sampling for the C5H5N+ dissociation. Ab initio calculations of the potential-energy profile have been carried out. They reveal a complicated reaction mechanism, the last step of which consists in the dissociation of a weakly bound ion-quadrupole or ion-dipole complex. The KERDs have been analyzed by the maximum entropy method. The fraction of phase-space effectively sampled by the pair of fragments has been determined and is similar for both dissociations. Both reactions are constrained by the square root of the released kinetic energy, epsilon1/2. This indicates that in the latter stage of the dissociation process, the reaction coordinate is adiabatically decoupled from the bath of the bound degrees of freedom. For the C6H6+ fragmentation, the analysis of the experimental results strongly suggests that, just as for the symmetric interaction potential, the translational motion is confined to a two-dimensional subspace. This dimensionality reduction of the translational phase space is due to the fact that the Hamiltonian of both weakly bound complexes contains a cyclic coordinate

Attosecond hole migration in benzene molecules surviving nuclear motion

Hole migration is a fascinating process driven by electron correlation, in which purely electronic dynamics occur on a very short time scale in complex ionized molecules, prior to the onset of nuclear motion. However, it is expected that due to coupling to the nuclear dynamics, these oscillations will be rapidly damped and smeared out, which makes experimental observation of the hole migration process rather difficult. In this Letter, we demonstrate that the instantaneous ionization of benzene molecules initiates an ultrafast hole migration characterized by a periodic breathing of the hole density between the carbon ring and surrounding hydrogen atoms on a subfemtosecond time scale. We show that these oscillations survive the dephasing introduced by the nuclear motion for a long enough time to allow their observation. We argue that this offers an ideal benchmark for studying the influence of hole migration on molecular reactivity

Dynamique de la dissociation des états fondamental et excité du 1,1-difluoroéthylène ionisé.

The kinetic energy release distributions (KERDs) for the fluorine atom loss from the 1,1-difluoroethene cation have been recorded with two spectrometers in two different energy ranges. A first experiment uses dissociative photoionization with the He(I) and Ne(I) resonance lines, providing the ions with a broad internal energy range, up to 7 eV above the dissociation threshold. The second experiment samples the metastable range, and the average ion internal energy is limited to about 0.2 eV above the threshold. In both energy domains, KERDs are found to be bimodal. Each component has been analyzed by the maximum entropy method. The narrow, low kinetic energy components display for both experiments the characteristics of a statistical, simple bond cleavage reaction: constraint equal to the square root of the fragment kinetic energy and ergodicity index higher than 90%. Furthermore, this component is satisfactorily accounted for in the metastable time scale by the orbiting transition state theory. Potential energy surfaces corresponding to the five lowest electronic states of the dissociating 1,1-C2H2F2+ ion have been investigated by ab initio calculations at various levels. The equilibrium geometry of these states, their dissociation energies, and their vibrational wavenumbers have been calculated, and a few conical intersections between these surfaces have been identified. It comes out that the ionic ground state (X) over tilde B-2(1) is adiabatically correlated with the lowest dissociation asymptote. Its potential energy curve increases in a monotonic way along the reaction coordinate, giving rise to the narrow KERD component. Two states embedded in the third photoelectron band ( (B) over tilde (2)A(1), at 15.95 eV and (C) over tilde B-2(2) at 16.17 eV) also correlate with the lowest asymptote at 14.24 eV. We suggest that their repulsive behavior along the reaction coordinate be responsible for the KERD high kinetic energy contribution