First results on the use of a EDXRF scanner for 3D imaging of paintings

A 3D map of chemical elements distribution from energy-dispersive X-ray fluorescence (EDXRF) analysis would be a perfect conclusion in a detailed study of any type of artifact. This map can be easily achieved by using synchrotron light as source of radiation, and microoptics both at the source and at the detector. In such a manner a micro-voxel is irradiated and detected, which can be at any depth with respect to the surface of the artifact. This method is effective but needs a high-intensity X-ray source; therefore, its use in archaeometry is limited. An alternative method is proposed in the present paper, which uses a portable EDXRF-device to measure the altered Kα/Kβ or Lα/Lβ-ratios, which allow to locate the chemical elements. Several examples are described

Markov Switching Garch Models of Currency Crises in Southeast Asia

This paper develops a model which is able to forecast exchange rate turmoil. Our starting point relies on the empirical evidence that exchange rate volatility is not constant. In fact, the modeling strategy adopted refers to the vast literature of the GARCH class of models, where the variance process is explicitly modeled. Further empirical evidence shows that it is possible to distinguish between two different regimes: “ordinary” versus “turbulence”. Low exchange rate changes are associated with low volatility (ordinary regime) and high exchange rate devaluations go together with high volatility. This calls for a regime switching approach. In our model we also allow the transition probabilities to vary over time as functions of economic and financial indicators. We find that real effective exchange rate, money supply relative to reserves, stock index returns and bank stock index returns and volatility are the major indicators.Currency crises, Markov Switching Models, Volatility

Gold and Silver joining technologies in the Moche Tombs “Señor de Sipán” and “Señora de Cao jewelery

About 200 gold and silver funerary ornaments from the Moche tombs “Señor de Sipán” and “Señora de Cao” were analyzed to determine their metallurgic characteristics. Of particular interest was the question about the gold-silver joining process. To this aim, following methods were employed, all based on the use of X-rays: - energy dispersive X-ray fluorescence; - transmission of monoenergetic fluorescent X-rays; - radiography. At least three joining methods were possibly identified: - of gluing gold and silver sheets; - of brazing using a proper solder; - of using a mercury amalgam

Instability and softening in a continuous bi-rod

We present a continuous bi-rod structure composed of two flanges and a pleated web. The structure is characterised by an instability mechanism that couples axial contraction and twisting. In so doing, the latter can be controlled by the former. Moreover, a remarkable softening response is observed immediately after the critical state. A custom testing machine has been designed and manufactured in order to experimentally investigate the mechanical response of the continuous bi-rod. Full scale finite element simulations have been also performed to provide a deeper understanding of the relative contribution of the flanges and the pleated web to the observed mechanical response. The features exhibited by the continuous bi-rod pave the way for innovative technological applications in areas of growing interest (e.g., compliant mechanisms, morphing and deployable structures)

Comparative Molecular Resolution STM Imaging of Thiourea, Ethylthiourea, and Sulfur Self-Assembled Adlayer Structures on Silver (111)

Self-assembled adlayer structures of thiourea (TU), ethylthiourea (ETU), and sulfur (S) adsorbed on Ag(111), from neutral and alkaline aqueous solutions, are investigated with a scanning tunneling microscope operating under potential control. Voltammograms obtained under various different potential routines are very similar for the three substances. At potentials close to −1.2 V (versus saturated calomel electrode), a (√7×√7)R19.1° adlayer structure with superlattice and nearest neighbor distances of ds = 0.76 nm and dn = 0.44 nm, respectively, is imaged, irrespective of the adsorbate molecule. In this potential region, the first pair of conjugated current peaks related to electroadsorption/desorption processes is recorded. As either the electroadsorption time is increased or the applied potential is shifted positively, self-assembled TU and S monolayers evolve into more compact structures. TU adlayers compress into hexagonal arrangements with dn = 0.33 nm, and S forms adsorbed S-trimers with the initial ordered array superstructure and coverage and shorter dn. On the other hand, ETU only presents the hexagonal arrangement with dn = 0.44 nm common to all three adsorbates at the early ordered adsorption stages. The dynamics of adsorbate patterns can be explained by the interplay of adsorbate−substrate and adsorbate−adsorbate interactions, principally hydrogen bonding for TU, steric size effects due to ethyl substituents for ETU, and a clustering process assisted by polymerization for S. As TU on Ag(111) and TU on Au(111) exhibit similar adlayer structures, the electroadsorption free energy difference was estimated from the electrodesorption voltammetric peaks. The resulting value is similar to the desorption energy differences calculated for other sulfur-containing molecules.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada