Role of vibrational entropy in the stabilization of the high-temperature phases of iron

The phonon dispersions of the bcc and fcc phases of pure iron ({\alpha}-Fe, {\gamma}-Fe and {\delta}-Fe) at ambient pressure were investigated close to the respective phase transition temperatures. In the open bcc structure the transverse phonons along T1 [{\xi}{\xi}0] and T1 [{\xi}{\xi}2{\xi}] are of particularly low energy. The eigenvectors of these phonons correspond to displacements needed for the transformation to the fcc {\gamma}-phase. Especially these phonons, but also all other phonons soften considerably with increasing temperature. Comparing thermodynamic properties of the fcc and the two bcc phases it is shown that the high temperature bcc phase is stabilized predominantly by vibrational entropy, whereas for the stabilization of the fcc phase electronic entropy provides an equal contribution.Comment: to appear in Physical Review

Première évaluation du risque toxique lié aux cyanobactéries d'eau douce en France : le programme " EFFLOCYA "

Une enquête menée à l'aide d'un questionnaire couvrant l'ensemble du territoire français ainsi que l'étude spécifique d'écosystèmes aquatiques de type lacs et réservoirs ont permis de montrer que les proliférations de cyanobactéries toxiques pouvaient a priori affecter n'importe quel plan d'eau de l'Héxagone. Les genres rencontrés responsables de la production de toxines, le plus souvent hépatiques, sont Microcystis, Planktothrix, Anabœna et Cylindrospermopsis.Les efflorescences peuvent se produire tout au long de l'année car certaines espèces sont adaptées aux eaux froides et elles ne sont pas liées de manière univoque à un état eutrophe de l'écosystème.La production toxinique est la plus élevée lorsque les populations cyanobactériennes sont peu ou pas diversifiées et à la lumière de travaux récents, cette production serait favorisée, en ce qui concerne les microcystines, par un milieu riche en nitrate, pauvre en ammonium et fortement carencé en fer.La suite à donner à ce travail pourrait être la création d'un observatoire national des efflorescences toxiques.An inquiry covering the whole French territory together with specific studies of natural and artificial reservoirs has been made to assess the human health risk related to the prolifération of toxin producing blue green algae (cyanobacteria). The conclusions show that any lentic ecosystem can be affected like it has been shown already in other countries all over the world and more specifically within the EU. The main genus concemed are: Microcystis, Planktothrix, Anabœna and Cylindrospermopsis.Blooms can occur juring the whole year since some species are well adapted to cold water and are not clearly linked with the trophic status of the aquatic ecosystem.The toxinic production is the largest when the cyanobacteria populations contain only a few number of species. The results of recent works are well correlated with our findings which show that the production of toxic heptapeptides (microcystins) could be correlated with high levels of nitrate and depletions of ammonium and iron.The follow up of this work should now include the set up of a national observatory of toxic algal blooms

Allowing for detachment processes in market innovation. The case of short food supply chains

The purpose of this paper is to study the place of detachment processes in market agencing. The authors draw on the case of short food supply chains, especially those established to provide local produce to mass catering. They characterise short food supply chains as “market innovations through withdrawal”, i.e. market innovations aiming at detaching farmers and consumers from the middlemen of mainstream markets and reducing the number of food miles. They argue that detachment from mainstream market mediators generally calls for the creation of new mediators and highlight the difficulties of this agencing work. In line with the research on path dependence and lock-ins, they also show that existing attachments are binding and may impede detachments. Finally, the authors show that short food supply chains combine the establishment of new and pre-existing attachments and of new and pre-existing detachments. They sum up this combination of processes with the term “quasi-detachment”

Atomic dynamics of the i-ScZnMg and its 1/1 approximant phase: experiment and simulation

International audienceQuasicrystals are long range ordered materials which lack translational invariance so that the study of their physical properties remains a challenging problem. In order to study the respective influence of the local order and of the long range order (periodic or quasiperiodic) on lattice dynamics, we have carried out inelastic x-ray and neutron scattering experiments on single grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant. Besides the overall similarities and the existence of a pseudo gap in the transverse dispersion relation, marked differences are observed, the pseudo gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of pseudo Brillouin zone in the quasicrystal. These results are compared to simulations on atomic models and using oscillating pair potentials which have been fitted against ab-initio data. The simulated response function reproduces both the dispersion relation but also the observed intensity distribution in the measured spectra. The partial vibrational density of states, projected on the cluster shells, is computed from this model

L'INTERRUPTION VOLONTAIRE DE GROSSESSE DU PREMIER TRIMESTRE

LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF

Inelastic neutron scattering investigation of magnetic excitations in the spin-Peierls ground state of(TMTTF)2 PF6

We present the first inelastic neutron scattering investigation of magnetic excitations in a one- dimensional (1D) organic conductor. This experiment is conducted in the spin-Peierls (SP) ground state of (TMTTF)2PF6. The study, performed with a 98% deuterated powder, reveals the double gap structure of magnetic excitation soft the SP chain. These responses, as well as the observation of a high erenergy mode, occur at energies consistent with microscopic coupling deduced from magnetic measurements performed on the same sample

A Visuo-Haptic Device - Telemaque - Increases Kindergarten Children's Handwriting Acquisition

The objective of the present research was to show that incorporating a visuo-haptic device ‘Telemaque' may increase the fluency of handwriting production of cursive letters in kindergarten children i.e., before formal handwriting learning begins. Forty two 5 year-old children were assigned an intervention involving either Telemaque (experimental training; VH group) or not (control training; C group). The fluency of handwriting was tested before and after both interventions. Fluency was analysed by kinematic parameters: Average velocity, number of velocity peaks, and number of breaks during the production of six cursive letters (a,b,f,i,l,s). The results showed that the fluency of handwriting production for all letters was higher after the VH training than after the C training: The movements were faster, exhibited less velocity peaks and children lifted the pen less often during the letter production. These results showed that the Telemaque device may help kindergarten children to increase the proactive strategy to control handwriting movements