421 research outputs found
Loop Bifurcation and Magnetization Rotation in Exchange Biased Ni/FeF2
Exchange biased Ni/ FeF2 films have been investigated using vector coil
vibrating sample magnetometry as a function of the cooling field strength H_FC.
In films with epitaxial FeF2, a loop bifurcation develops with increasing H_FC
as it divides into two sub-loops shifted oppositely from zero field by the same
amount. The positively biased sub-loop grows in size with H_FC until only a
single positively shifted loop is found. Throughout this process, the
negative/positive (sub)loop shift has maintained the same discrete value. This
is in sharp contrast to films with twinned FeF2 where the exchange field
gradually changes with increasing H_FC. The transverse magnetization shows
clear correlations with the longitudinal sub-loops. Interestingly, over 85% of
the Ni reverses its magnetization by rotation, either in one step or through
two successive rotations. These results are due to the single crystal nature of
the antiferromagnetic FeF2, which breaks down into two opposite regions of
large domains.Comment: 16 pages, 3 figures, to appear in PR
Probing the dynamics of quasicrystal growth using synchrotron live imaging
The dynamics of quasicrystal growth remains an unsolved problem in condensed
matter. By means of synchrotron live imaging, facetted growth proceeding by the
tangential motion of ledges at the solid-melt interface is clearly evidenced
all along the solidification of icosahedral AlPdMn quasicrystals. The effect of
interface kinetics is significant so that nucleation and free growth of new
facetted grains occur in the melt when the solidification rate is increased.
The evolution of these grains is explained in details, which reveals the
crucial role of aluminum rejection, both in the poisoning of grain growth and
driving fluid flow
X-ray white beam topography of self-organized domains in flux-grown BaTiO3 single crystals
The phenomenon of self-organization of domains into a âsquare-net patternâ in single-crystal, flux-grown BaTiO3 several degrees below the ferroelectric to paraelectric phase transition was investigated using in situ synchrotron x-ray topography. The tetragonal distortion of the crystal was determined by measuring the angular separation between the diffraction images received from 90° a and c domains in the projection topographs, and shows a rapid decrease towards 110â°C, the onset temperature for self-organization. The onset of self-organization is accompanied by bending of the {100} lattice planes parallel to the crystal surface, which produces a strain that persists up to and beyond the Curie temperature, where the crystal becomes cubic and the self-organized domains disappear. At the Curie point, the bending angle α100=8.1(±0.3)mrad is at a maximum and corresponds to the radius of curvature of the surface being 16.3(±0.6) mm
Reconstruction 3D en tomographie par rayonnement synchrotron coherent
Un systÚme de microtomographie 3D utilisant le rayonnement synchrotron trÚs cohérent de l'ESRF de Grenoble, a été développé. Nous discutons ici les spécificités de ce type d'imagerie tomographique. En effet, la cohérence spatiale de la source de rayons X de l'ESRF, engendre outre les effets d'atténuation conventionnels, des phénomÚnes dits de « contraste de phase ». Ceux-ci sont liés à des interférences entre les ondes diffractées par l'échantillon aprÚs propagation, lorsque 1' échantillon est placé à une distance non nulle du détecteur. Nous montrons que sous certaines conditions, les algorithmes de reconstruction conventionnels sont utilisables. L'image reconstruite possÚde alors une contribution liée à l'atténuation, et une contribution liée aux brusques variations dans l'indice de réfraction
Structural defects in Hg1âxCdxI2 layers grown on CdTe substrates by vapor phase epitaxy
Hg1âxCdxI2 20â25-ÎŒm-thick layers with a uniform composition in the range of x = 0.1â0.2 were grown on CdTe substrates by vapor phase epitaxy (VPE). The growth was carried out using an α-HgI2 polycrystalline source at 200â°C and in the time range of 30â100 h. The layers were studied by scanning electron microscopy (SEM) and high resolution synchrotron x-ray topography (SXRT). The SEM and SXRT images of Hg1âxCdxI2 VPE layers allow one to identify the defects affecting the layer structure. The two main types of structural defects in the layers are subgrain boundaries and densely spaced striations similar to those referred generally to as vapor grown HgI2 bulk crystals. The effect of the growth time on these defects has been analyzed and on the basis of this it has been possible to grow Hg1âxCdxI2 layers with low defect [email protected]
Prognostic study of continuous variables (white blood cell count, peripheral blast cell count, haemoglobin level, platelet count and age) in childhood acute lymphoblastic leukaemia. Analysis of a population of 1545 children treated by the French Acute Lymphoblastic Leukaemia Group (FRALLE)
Many cutpoints have been proposed to categorize continuous variables in childhood acute lymphoblastic leukaemia (white blood cell count, peripheral blast cell count, haemoglobin level, platelet count and age), and have been used to define therapeutic subgroups. This variation in the choice of cutpoints leads to a bias called the âWill Rogers phenomenonâ. The aim of this study was to analyse variations in the relative risk of relapse or death as a function of continuous prognostic variables in childhood ALL and to discuss the choice of cutpoints. We studied a population of 1545 children with ALL enrolled in three consecutive protocols named FRALLE 83, FRALLE 87 and FRALLE 89. We estimated the risk of relapse or death associated with different values of each continuous prognostic variable by dividing the sample into quintiles of the distribution of the variables. As regards age, a category of children under 1 year of age was distinguished and the rest of the population was divided into quintiles. The floated variance method was used to calculate the confidence interval of each relative risk, including the reference category. The relation between the quantitative prognostic factors and the risk was monotonic for each variable, except for age. For the white blood cell count (WBC), the relation is log linear. The risk associated with WBC values in the upper quintile was 1.9 times higher than that in the lower quintile. The peripheral blast cell count correlated strongly with WBC (correlation coefficient: 0.99). The risk increased with the haemoglobin level, and the risk in the upper quintile was 1.3 times higher than that in the lower quintile. The risk decreased as the platelet count increased: the risk in the lower quintile was 1.2 times higher than that in the upper quintile. The risk increased gradually with increasing age above one year. The small subgroup of patients (2.5% of the population) under 1 year of age at diagnosis had a risk 2.6 times higher than the reference category of patients between 3 and 4.3 years of age. When the risk associated with a quantitative prognostic factor varies monotonously, the selection of a cutpoint is arbitrary and represents a loss of information. Despite this loss of information, such arbitrary categorization may be necessary to define therapeutic stratification. In that case, consensus cutpoints must be defined if one wants to avoid the Will Rogers phenomenon. The cutpoints proposed by the Rome workshop and the NCI are arbitrary, but may represent an acceptable convention. © 2000 Cancer Research Campaign http://www.bjcancer.co
Prognostic value of Oncogenetic mutations in pediatric T Acute Lymphoblastic Leukemia: a comparison of UKALL2003 and FRALLE2000T protocols
MicroRNA-106b similar to 25 cluster is upregulated in relapsed MLL-rearranged pediatric acute myeloid leukemia
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