Temperature dependence and mechanisms for vortex pinning by periodic arrays of Ni dots in Nb films

Pinning interactions between superconducting vortices in Nb and magnetic Ni dots were studied as a function of current and temperature to clarify the nature of pinning mechanisms. A strong current dependence is found for a square array of dots, with a temperature dependent optimum current for the observation of periodic pinning, that decreases with temperature as (1-T/Tc)3/2. This same temperature dependence is found for the critical current at the first matching field with a rectangular array of dots. The analysis of these results allows to narrow the possible pinning mechanisms to a combination of two: the interaction between the vortex and the magnetic moment of the dot and the proximity effect. Moreover, for the rectangular dot array, the temperature dependence of the crossover between the low field regime with a rectangular vortex lattice to the high field regime with a square configuration has been studied. It is found that the crossover field increases with decreasing temperature. This dependence indicates a change in the balance between elastic and pinning energies, associated with dynamical effects of the vortex lattice in the high field range.Comment: 12 text pages (revtex), 6 figures (1st jpeg, 2nd-6th postscript) accepted in Physical Review

Polymorphism and histochemical characterization of acetylcholinesterase from bees'heads (Hymenoptera)

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Analyse et évolution des déficits cognitifs après rupture des anévrysmes de l'artère communicante antérieure [Analysis and course of cognitive deficits after rupture of aneurysms of the anterior communicating artery]

The aim of this study is to investigate general intellectual and memory performances at the secondary (3 weeks to 4.5 months) and late (10 to 16 months) stages following rupture of anterior communicating artery aneurysms (AACA). Twenty one patients presenting with selective lesion within frontal, or cingulate, callosal, caudate, basal forebrain areas were evaluated. At the secondary stage, the analysis of the general intellectual capacities revealed a drop of performance, prominent on performance IQ, which was more severe than the learning deficit. Specific cognitive evaluations revealed increase of the execution time, but performance was relatively preserved: in the Stroop test, focused attention disorder was moderate: the modified Wisconsin Card Sorting test was correctly performed in most cases; significant deficits of verbal short-term memory, long-term verbal and visuo-spatial learning, and access to semantic memory were observed. At the late stage, general intellectual performance improved, but did not reached the estimated prelesional level in most cases; specific cognitive disorders had most often disappeared. Most performances were best explained by the severity of lesions in the left cingulate cortex and corpus callosum area. These results show that the cognitive profile of AACA patients is different from classical descriptions of the "amnesic syndrome", and is also different at the secondary and late stages; this evolution has to be taken into account in studies describing cognitive deficits of such patients, or comparing them with others presenting with "annesic syndrome"

Screening of glutamate decarboxylase activity and bile salt resistance of human asymptomic carriage, clinical, food, and environmental isolates of Listeria monocytogenes

International audienceFollowing consumption, stomach acidity is the first major barrier encountered by thefood-borne pathogen Listeria monocytogenes. Analysis of low pH sensitivity and glutamatedecarboxylase (GAD) acid resistance system of 14 isolates of L. monocytogenes carriedasymptomatically by humans showed that levels of GAD activity was subjected to strainvariation. Similar variations were observed for strains responsible of 18 listeriosis, whereas incomparison, 13 strains isolated from food and from food-processing plant environmentshowed lower GAD activity. Following survival of the stomach barrier, L. monocytogenesalso has to resist to bile salts encountered in the small intestine. Analysis revealed that allstrains tested were able to grow in presence of bile salts with concentrations as high as thoseencountered in the small intestine and had the previously identified Bile Salt Hydrolase(BSH) activity. Strain variation was observed but there was no relationship between the originof the strains and the ability to degrade bile salts

Dystonie et tremblement dans une lésion bilatérale du mésencéphale postérieur et du vermis [Dystonia and tremor in bilateral lesion of the posterior mesencephalon and the vermis]

The aim of this study is to report the association of diffuse dystonia and tremor in a bilateral and extended lesion of the posterior mesencephalon. After surgery on a meningioma of the upper part of the fourth ventricle, this patient presented with facial dystonia, predominating on orbicularis muscles and peribuccal area, and limb dystonia, with tonic extension of fingers and first toes. The tremor was associated with a rhythmic and most often alternate agonist-antagonist muscular activation, whose frequency varied from 3 to 7 Hz. These disorders were increased by the standing position, voluntary movement, somatosensory stimulations, stress or emotion. Pyramidal and somatosensory tracts were spared. Therapeutic trials showed that both the dystonia and tremor were improved by subcutaneous injection of apomorphine, the dystonia by trihexyphenidyle, and the tremor by carbamazepine and propranolol, but not by levodopa and benserazide. The cerebral blood flow study using HMPAO showed a relatively important activity on the cerebellum, which could play a role in the onset of these disorders

Magnetization Reversal in Arrays of Perpendicularly Magnetized Ultrathin Dots Coupled by Dipolar Interaction

Arrays of micron size perpendicularly magnetized ultrathin Co dots with 20 nm separation were obtained using ion irradiation by a focused ion beam and studied by polar magneto-optical microscopy. Because irradiation induces easy nucleation regions along dot borders, magnetization reversal inside the dots under a perpendicular field is due only to domain wall propagation, driven by applied field and dipolar interactions. Frustrated checkerboard patterns are observed in the demagnetized state, in agreement with numerical simulations. This opens the way to experimental studies on model arrays of interacting Ising dot