Fracture through cavitation in a metallic glass

The fracture surfaces of a Zr-based bulk metallic glass exhibit exotic multi-affine isotropic scaling properties. The study of the mismatch between the two facing fracture surfaces as a function of their distance shows that fracture occurs mostly through the growth and coalescence of damage cavities. The fractal nature of these damage cavities is shown to control the roughness of the fracture surfaces

Electron Probe X-Ray Microanalysis Applied to Thin Surface Films and Stratified Specimens

The basic principles of X-ray microanalysis of thin surface films and stratified targets are summarized. The influence of the electron beam accelerating voltage on the analyzed depth is discussed. It is shown that in the field of soft X-rays, the effective depth of analysis is most often limited by the absorption of the radiation in the specimen itself. For high energy radiations, the importance of the secondary emission due to fluorescence excited by the continuous radiation and by the characteristic lines is outlined. The main concepts of the recent ø(ρz) models used for quantitation in the recent software packages are reminded. The performance of the technique for the simultaneous determination of the mass thicknesses and the compositions of the layers in a stratified target is illustrated with several examples. These examples also illustrate the capability and the limitations of the iterative procedure used in the recent software packages such as Strata or Multifilm

The convergence method to calculate particles fluxes in x rays spectrometry techniques. Application in nuclear compounds

A method to calculate particle fluxes applicable in most of the spectroscopy techniques is described. Flux intensities of backscattered or absorbed electrons and emitted photons are calculated using a method of convergence to solve the Invariant Embedding equations that are used to describe the particle trajectories inside a solid sample. Our results are found to be helpful to carry out a procedure for quantitative characterization using instrument such as Electron Probe Microanalysis or other probes. Examples of application to calculate the composition of ternary alloys are given and are compared with the same calculations using another procedure.Comment: 15 page

Marco económico del negocio : Análisis de eficiencia empresarial del subsector comercial mayorista en la región de La Plata, Berisso y Ensenada

El desenvolvimiento de la actividad empresarial requiere contar con información sobre la estructura económica y la evolución de los agregados más relevantes del medio en que actúa para la toma de decisiones y ejecutar mejor sus estrategias. Asimismo resulta imprescindible para cualquier interesado en realizar o compartir inversiones y para la definición y ejecución de políticas públicas en general y en particular en su rol de promotor de la actividad económica privada. En la región conformada por los partidos de de La Plata, Berisso y Ensenada es general la carencia de datos sobre estructura y características productivas de la misma, y un desorden significativo de los datos existentes lo que representa una limitación básica y esencial para la toma de decisiones, para identificar o propiciar iniciativas o proyectos, y para su uso en propósitos diversos en el ámbito interno o externo de las organizaciones. En lo que respecta al sector terciario, y en particular, en lo referido al comercio mayorista como objeto de este trabajo, no se dispone de información que exponga la conformación básica del subsector, ni a magnitudes relevantes de su funcionamiento que permita comparaciones significativas. En ese contexto, la estrategia obligada se basa en adaptaciones a los requerimientos del mercado y del cliente, en base a pequeños atisbos de intuición empresarial. En la región, sin una base de datos e información fidedigna que exponga el estado de situación real del sector.Facultad de Ciencias Económica

Encapsulated Single Crystal Growth and Annealing of the High-Temperature Superconductor Tl-2201

Highly-perfect platelet single crystals of Tl_2Ba_2CuO_{6+d} (Tl-2201) were grown by a self-flux technique. A novel encapsulation scheme allowed the precursors to react prior to the sealing required to contain volatile thallium oxides, and permitted the removal of melt at the conclusion of growth, reproducibly producing high yields of clean crystals. The crystals were annealed under well-controlled oxygen partial pressures, then characterised. They have sharp superconducting transitions, narrow X-ray rocking curves and a low 4% substitution of thallium by copper, all evidence of their high perfection and homogeneity. The crystals are orthorhombic at most dopings, and a previously unreported commensurate superlattice distortion is observed.Comment: 8 pages, 5 figures, submitted to Journal of Crystal Growt

Absolute values of the London penetration depth in YBa2Cu3O6+y measured by zero field ESR spectroscopy on Gd doped single crystals

Zero-field electron spin resonance (ESR) of dilute Gd ions substituted for Y in the cuprate superconductor YBa$_2$Cu$_3$O$_{\rm 6+y}$ is used as a novel technique for measuring the absolute value of the low temperature magnetic penetration depth $\lambda(T\to 0)$. The Gd ESR spectrum of samples with $\approx 1$ substitution was obtained with a broadband microwave technique that measures power absorption bolometrically from 0.5 GHz to 21 GHz. This ESR spectrum is determined by the crystal field that lifts the level degeneracy of the spin 7/2 Gd$^{3+}$ ion and details of this spectrum provide information concerning oxygen ordering in the samples. The magnetic penetration depth is obtained by relating the number of Gd ions exposed to the microwave magnetic field to the frequency-integrated intensity of the observed ESR transitions. This technique has allowed us to determine precise values of $\lambda$ for screening currents flowing in the three crystallographic orientations ($\hat a$, $\hat b$ and $\hat c$) in samples of Gd$_{\rm x}$Y$_{\rm 1-x}$Ba$_2$Cu$_3$O$_{6+{\rm y}}$ of three different oxygen contents ${\rm y}=0.993$ ($T_c = 89$ K), ${\rm y}=0.77$ ($T_c=75$ K) and ${\rm y}=0.52$ ($T_c=56$ K). The in-plane values are found to depart substantially from the widely reported relation $T_c\propto 1/\lambda^2$.Comment: 14 pages, 12 figures; version to appear in PR