Anion emission from water molecules colliding with positive ions: Identification of binary and many-body processes

It is shown that negative ions are ejected from gas-phase water molecules when bombarded with positive ions at keV energies typical of solar-wind velocities. This finding is relevant for studies of planetary and cometary atmospheres, as well as for radiolysis and radiobiology. Emission of both H- and heavier (O- and OH-) anions, with a larger yield for H-, was observed in 6.6-keV 16O+ + H2O collisions. The ex-perimental setup allowed separate identification of anions formed in collisions with many-body dynamics from those created in hard, binary collisions. Most of the ani-ons are emitted with low kinetic energy due to many-body processes. Model calcu-lations show that both nucleus-nucleus interactions and electronic excitations con-tribute to the observed large anion emission yield.Comment: 5 pages, 4 figure

Disorder-induced microscopic magnetic memory

Using coherent x-ray speckle metrology, we have measured the influence of disorder on major loop return point memory (RPM) and complementary point memory (CPM) for a series of perpendicular anisotropy Co/Pt multilayer films. In the low disorder limit, the domain structures show no memory with field cycling--no RPM and no CPM. With increasing disorder, we observe the onset and the saturation of both the RPM and the CPM. These results provide the first direct ensemble-sensitive experimental study of the effects of varying disorder on microscopic magnetic memory and are compared against the predictions of existing theories.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review Letters in Nov. 200

Spin density wave dislocation in chromium probed by coherent x-ray diffraction

We report on the study of a magnetic dislocation in pure chromium. Coherent x-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.Comment: 8 pages, 7 figure

Anion and cation emission from water molecules after collisions with 6.6-keV 16 O+ ions

DOI: https://doi.org/10.1103/PhysRevA.100.032713arXiv link: http://arxiv.org/abs/1910.00657International audienceAnion and cation emission following water dissociation was studied for 6.6-keV $^{16}$O$^{+}$ + H$_{2}$O collisions. Absolute cross sections for the emission of all positively and negatively charged fragments, differential in both energy and observation angle, were measured. The fragments formed in hard, binary collisions appearing in peaks were distinguishable from those created in soft collisions with many-body dynamics that result in a broad energy spectrum. A striking feature is that anions and cations are emitted with similar energy and angular distributions, with a nearly constant ratio of about 1:100 for H$^{-}$ to H$^{+}$. Model calculations were performed at different levels of complexity. Four-body scattering simulations reproduce the measured fragment distributions if adequate kinetic-energy release of the target is taken into account. Providing even further insight into the underlying processes, predictions of a thermodynamic model indicate that transfer ionization at small impact parameters is the dominant mechanism for H$^{+}$ creation. The present findings confirm our earlier observation that in molecular fragmentation induced by slow, singly charged ions, the charge states of the emitted hydrogen fragments follow a simple statistical distribution independent of the way they are formed

Lifelong testicular differentiation in Pleurodeles waltl (Amphibia, Caudata)

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Effect of sensory education on willingness to taste novel food in children

As part of 'EduSens', a project aiming to measure the effect of a sensory education program developed in France on the food behaviour of school children, the present paper shows the results regarding neophobia. One hundred and eighty children (8-10 years old) were involved in the study. Half of them (experimental group) were educated during school-time with the 12 sessions of taste lessons Les classes du gout by J. Puisais. The others served as a control group. Food neophobia was evaluated before and after the education period of the experimental group and once again 10 months later. An adapted food neophobia scale was used (AFNS) and the willingness to taste novel food (WTNF) was evaluated by the presentation of eight unknown foods. To improve involvement in the expressed willingness to taste new foods, the children were told that they would have to eat one of the not rejected unknown foods afterwards. Results revealed that, at the end of the education period, in the educated group, declarative food neophobia decreased significantly and participants' willingness to taste novel food seemed to increase compared to the control group. Nevertheless, these effects had disappeared 10 months later. Thus, we have shown that sensory education can influence childrens' food neophobia, but does so only temporarily. This is especially true for the WTNF test, which measures the expression of neophobia in concrete situations, whereas neophobia measured as a psychological trait by the AFNS test hardly changes

Scaling laws for single and double electron capture in A^q+ + He collisions (q>~Z_A−2) at low impact velocities

International audienceWe present empirical scaling laws, as a function of the projectile charge state, for single and double electron capture in slow collisions between highly charged ions and He atoms at impact velocities of 0.1 and 0.5 a.u. The fitting parameters are shown to be suitable for predicting the populated states in single and double electron capture. The scaling law for single capture is found to be nearly independent of the projectile velocity in the range 0.1–0.5 a.u. The same fitting procedure is followed for double electron capture at the velocity of 0.5 a.u. since independent monoelectronic transitions, due to electron-nucleus interactions, are dominant. At this velocity, the scaling law for the projectile charge dependence of double electron capture cross sections is found to be similar to that for single electron capture. At the lower velocity of 0.1 a.u., where dielectronic processes caused by the electron-electron interaction gain importance, the charge dependence of double capture cross sections is strongly modified