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Aged individuals with Down syndrome (DS) develop Alzheimer's disease (AD) neuropathology by the age of 40 years. The purpose of the current study was to measure age-associated changes in APP processing in 36 individuals with DS (5 months-69 years) and in 26 controls (5 months-100 years). Alpha-secretase significantly decreased with age in DS, particularly in cases over the age of 40 years and was stable in controls. The levels of C-terminal fragments of APP reflecting alpha-secretase processing (CTF-alpha) decreased with age in both groups. In both groups, there was significant increase in beta-secretase activity with age. CTF-beta remained constant with age in controls suggesting compensatory increases in turnover/clearance mechanisms. In DS, young individuals had the lowest CTF-beta levels that may reflect rapid conversion of beta-amyloid (Abeta) to soluble pools or efficient CTF-beta clearance mechanisms. Treatments to slow or prevent AD in the general population targeting secretase activity may be more efficacious in adults with DS if combined with approaches that enhance Abeta degradation and clearance.

We present a detailed magnetic and magnetotransport investigation of spinel zinc ferrite ZnxFe3-xO4-y (0.1⩽x⩽0.6) thin films grown by pulsed laser deposition on various substrates. The films are ranging from polycrystalline to (001)- or (111)-oriented. It is shown associating magnetic and resistivity measurements to x-ray and ion beam scattering analyses that the magnetic and electrical properties are tightly linked to the chemical composition and crystallinity/ microstructure of the films, as they result from the choice of substrate and growth conditions. The use of oxidizing conditions (O2 pressure≈10-4-10-2 mbar) is highly detrimental to the crystalline quality and thus to the ferromagnetism. On the contrary, a partial O2 pressure of 3 × 10-7 mbar combined to a growth temperature of 500 °C allows obtaining ZnxFe3-xO4-y films displaying very good ferromagnetic features. The SiO2/Si substrates, promoting (111) growth without interfacial effects, lead to better film properties than Al2O3(0001), MgO(001), or SrTiO3(001) substrates: higher Curie temperatures and higher magnetization values (≈490 kAm-1) at room temperature. Above a Verwey-type critical temperature, a thermally activated spin polarized charge transport is observed, while in the low temperature range, the resistivity is well described by the variable range hopping model. However, the negative magnetoresistance response at low field remains modest and a monotonous decrease with increasing magnetic field is observed. We show that a steeper low field magnetoresistance decrease may be obtained in polycrystalline stoichiometric layers formed by a specific two-step growth process, which significantly reduces the density of grain/antiphase boundaries. [ABSTRACT FROM AUTHOR]

Pulsed-laser deposition is known as a well-suited method for growing thin films of oxide compounds presenting a wide range of functional properties. A limitation of this method for industrial process is the very anisotropic expansion dynamics of the plasma plume, which induces difficulties to grow on large scale films with homogeneous thickness and composition. The specific aspect of the crystalline or orientation uniformity has not been investigated, despite its important role on oxide films properties. In this work, the crystalline parameters and the texture of zinc oxide films are studied as a function of position with respect to the central axis of the plasma plume. We demonstrate the existence of large non-uniformities in the films. The stoichiometry, the lattice parameter, and the distribution of crystallites orientations drastically depend on the position with respect to the plume axis, i.e., on the oblique incidence of the ablated species. The origin of these non-uniformities, in particular, the unexpected tilted orientation of the ZnO c-axis may be attributed to the combined effects of the oblique incidence and of the ratio between oxygen and zinc fluxes reaching the surface of the growing film. [ABSTRACT FROM AUTHOR]

The composition, structure, microstructure, and properties of indium tin oxide films grown by pulsed laser deposition at room temperature and under vacuum were studied. The films are highly nonstoichiometric, with about 20% oxygen deficiency, and present a semiconductor behavior between 300 and 15 K, followed by a superconducting transition at about 7 K related to the presence of In or In-Sn nanoclusters embedded in a stoichiometric indium tin oxide matrix, i.e., nanocomposite films are formed by the phase separation of oxygen deficient metastable indium tin oxide. The solid-liquid and liquid-solid phase transitions of the metallic nanoclusters were evidenced by resistivity measurements in the 300 to 450 K range. The films grown at room temperature are partially crystallized. Actually, stoichiometric indium tin oxide crystallites are observed in the as grown films. After thermal treatment (<450 K), both stoichiometric indium tin oxide crystallites and the tetragonal phase of the metallic In are observed in the nanocomposite films. The size of nanoclusters (from 5 to 30 nm), which depends on the thermal treatments and crystallization, and the microstructure of the nanocomposite films were confirmed by HRTEM measurements. [ABSTRACT FROM AUTHOR]

We report on the formation and transport properties of ZnO thin films which are grown by pulsed-electron beam deposition under a low residual oxygen pressure (10-5 mbar). ZnO films presenting metallic conductivity at room temperature, and a metal-semiconductor transition at low temperature, were epitaxially grown on Al2O3 single crystal substrates for growth temperatures in the 300–450 °C range. These results have been interpreted through the quantum corrections to conductivity in a disordered oxide conductor, implying first a high density of carriers leading to degenerate semiconductor ZnO films, and then a sufficient disorder in these films. These characteristics could be related to the nature of the ZnO films formed by pulsed-electron deposition: a high density of carriers related to an oxygen deficiency in the films and a high density of defects related to the high deposition rate of the pulsed-electron beam deposition method. [ABSTRACT FROM AUTHOR]