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

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Dynamics and charge density wave collective excitations of the blue bronze

Recent neutron scattering investigations of the pretransitional dynamics and of the phase and amplitude excitations of the charge density wave (CDW) condensate of the blue bronze are reviewed. It is shown that the dynamics of the Peierls transition is dominated by the intrachain fluctuations. The key role of Coulomb forces in the intrachain deformation process of the phase of the CDW is also emphasized

Segmental motion of alkyl chains grafted on silica gel, studied by neutron scattering

The quasielastic neutron scattering spectra of CnH2n+ 1 grafted on silica are obtained for n = 4, 8,12, 16,18, 22. The well known difficulty in determining the mass in the beam is overcome by using (as a reference) the integrated elastic and quasielastic scattering function, extrapolated to q = 0. A correction for the coherent scattering contribution is applied. It is thus possible to determine the molar scattering functions of the chains Sn(q, ω). Assuming that in all chains there is a constant number ne of end atoms contributing Se to Sn for all n and that the remaining middle CH2 are all equivalent, each contributing S m to Sn, we obtain Sn = Se + (n - n e) Sm. This relationship is verified for the elastic incoherent structure factor and used to calculate Sm. The n = 22 case is left apart, its anomalous behaviour is explained by interaction between neighbouring chains. The data agree with a 3-bonds jump model with a time between jumps equal to 1.9 x 10-11 s at room temperature.Les spectres de diffusion quasi-élastique de neutrons par CnH 2n+1 greffé sur silice, ont été mesurés pour n = 4, 8,12,16,18, 22. La masse d'échantillon dans le faisceau est déterminée en utilisant la fonction de diffusion élastique et quasi-élastique, intégrée et extrapolée à q = 0, après correction de la diffusion cohérente. On obtient ainsi les fonctions de diffusion molaires des chaines Sn(q, ω). En admettant que toutes les chaines, quel que soit n, contiennent à leurs extrémités un même nombre ne de maillons contribuant la même quantité S e à Sn et que les CH2 restant au milieu sont tous équivalents et contribuent chacun Sm, on obtient Sn = Se + (n - ne) Sm. Cette relation est vérifiée pour le facteur de structure incohérent élastique et utilisée pour calculer Sm. L'échantillon n = 22 a un comportement anormal en raison de l'interaction entre chaines voisines qui devient possible. Les données sont en accord avec un modèle de saut impliquant 3 ou 5 liaisons à condition que la conformation à 5 liaisons dure trop peu pour pouvoir effectuer plusieurs sauts consécutifs. Le temps moyen entre sauts est, à température ambiante, 1,9 x 10-11 s

Fine-scale spatial genetic structuring and relatedness in a natural population of an European fossorial vole (Arvicola terrestris)

*INRA Biologie et gestion des populations 34980 Montferrier sur Lez (FRA) Diffusion du document : INRA Biologie et gestion des populations 34980 Montferrier sur Lez (FRA)International audienc