Pyroelectric Applications of the VDF-TrFE Copolymer

VDF/TrFe pyroelectric sensors have now definitely reached the level of a product. Based on a bidimensional staring array, it can be considered as a whole system with a monolithic technology processed on a silicon substrate provided with the integrated read out circuit. The paper will describe the main procedure dealing with the elaboration of a 32 x 32 focal plane array developed, in the context of the PROMETHEUS PROCHIP European Program (EUREKA), as a passive infrared obstacle detection applied to automotive. Additional experimental data suggest that this microsystem could operate in space environment

Growth and characterization studies of Fe 4 N thin films prepared by ion beam assisted evaporation

International audienceThin films of iron nitrides have been prepared using an ion beam assisted evaporation method. X-ray diffraction and Mössbauer spectrometry show that the films generally consist in a mixture of Fe and Fe 4 N phases. For high source powers and temperatures higher than 300 °C it was possible to obtain the pure Fe 4 N phase

Influence of carbon and nitrogen on electronic structure and hyperfine interactions in fcc iron-based alloys

Carbon and nitrogen austenites, modeled by Fe8N and Fe8C superstructures are studied by full-potential LAPW method. Structure parameters, electronic and magnetic properties as well as hyperfine interaction parameters are obtained. Calculations prove that Fe-C austenite can be successfully modeled by ordered Fe8C superstructure. The results show that chemical Fe-C bond in Fe8C has higher covalent part than in Fe8N. Detailed analysis of electric field gradient formation for both systems is performed. The calculation of electric field gradient allow us to carry out a good interpretation of Moessbauer spectra for Fe-C and Fe-N systems.Comment: 8 pages, 3 figures, IOP-style LaTeX, submitted to J. Phys. Condens. Matte

Size Matters: Origin of Binomial Scaling in Nuclear Fragmentation Experiments

The relationship between measured transverse energy, total charge recovered in the detector, and size of the emitting system is investigated. Using only very simple assumptions, we are able to reproduce the observed binomial emission probabilities and their dependences on the transverse energy.Comment: 14 pages, including 4 figure

Exploring the Nature of Weak Chandra Sources near the Galactic Centre

We present results from the first near-IR imaging of the weak X-ray sources discovered in the Chandra/ACIS-I survey (Wang et al. 2002) towards the Galactic Centre (GC). These ~800 discrete sources, which contribute significantly to the GC X-ray emission, represent an important and previously unknown population within the Galaxy. From our VLT observations we will identify likely IR counterparts to a sample of the hardest sources, which are most likely X-ray binaries. With these data we can place constraints on the nature of the discrete weak X-ray source population of the GC.Comment: In Proc. of ``Interacting Binaries: Accretion, Evolution, and Outcomes'', eds. L. A. Antonelli et al., AIP, Cefalu, Sicily, 200

Implications of an arithmetical symmetry of the commutant for modular invariants

We point out the existence of an arithmetical symmetry for the commutant of the modular matrices S and T. This symmetry holds for all affine simple Lie algebras at all levels and implies the equality of certain coefficients in any modular invariant. Particularizing to SU(3)_k, we classify the modular invariant partition functions when k+3 is an integer coprime with 6 and when it is a power of either 2 or 3. Our results imply that no detailed knowledge of the commutant is needed to undertake a classification of all modular invariants.Comment: 17 pages, plain TeX, DIAS-STP-92-2

THE IRON SPIN TEXTURE IN ANNEALED AMORPHOUS Fe/Tb MULTI-LAYERS

Fe/Tb multilayers have been obtained by vacuum evaporation with Tb-layer thickness fixed to 40Å and amorphous Fe-layer thickness fixed to 19Å. 57Fe-Mössbauer spectrometry was used to obtain information on the structure and the spin texture of the multilayers before and after annealing at 530K for different durations of the annealing. The Mössbauer results indicate that the Perpendicular Magnetic Anisotropy (PMA) was stabilised and reinforced after annealing.Fe/Tb multilayers have been obtained by vacuum evaporation with Tb-layer thickness fixed to 40Å and amorphous Fe-layer thickness fixed to 19Å. 57Fe-Mössbauer spectrometry was used to obtain information on the structure and the spin texture of the multilayers before and after annealing at 530K for different durations of the annealing. The Mössbauer results indicate that the Perpendicular Magnetic Anisotropy (PMA) was stabilised and reinforced after annealing

Size effect on magnetism of Fe thin films in Fe/Ir superlattices

In ferromagnetic thin films, the Curie temperature variation with the thickness is always considered as continuous when the thickness is varied from $n$ to $n+1$ atomic planes. We show that it is not the case for Fe in Fe/Ir superlattices. For an integer number of atomic planes, a unique magnetic transition is observed by susceptibility measurements, whereas two magnetic transitions are observed for fractional numbers of planes. This behavior is attributed to successive transitions of areas with $n$ and $n+1$ atomic planes, for which the $T_c$'s are not the same. Indeed, the magnetic correlation length is presumably shorter than the average size of the terraces. Monte carlo simulations are performed to support this explanation.Comment: LaTeX file with Revtex, 5 pages, 5 eps figures, to appear in Phys. Rev. Let

Beating of monopole modes in nuclear dynamics

Time-dependent Hartree-Fock simulations of the evolution of excited gold fragments have been performed. The observed dynamics appears more complex than the collective expansion picture. The minimum density is often not reached during the first density oscillation because of the beating of several collective compression modes.Comment: 14 Latex pages including 4 figures. Nucl. Phys. A (in press