Oxygen vacancy‐induced microstructural changes of annealed CeO2−x nanocrystals

Nanocrystalline ceria (CeO₂) is known for its ionic conductivity and oxygen storage properties, which depend on the presence of oxygen ion vacancies. The vacancies cause several important changes in CeO₂ involving microstrain, electronic structure, magnetic properties, etc. In this article, we focus our attention to the microstructural changes of nanocrystalline CeO_2−x annealed at different temperatures in the range 200–500 °C. Structural and vibrational properties were investigated by X‐ray diffraction and Raman spectroscopy. It was observed that the content of oxygen vacancies changed significantly with increasing annealing temperature, which plays an important role in the observed microstructural changes of the annealed samples. We demonstrate that the observed microstrain changes, because of variable defect content, dominate over the crystallite size effect. This finding is opposite to the conclusions made by several other authors. A new mode, classified as a probable surface mode, was observed in the Raman spectra at ∼480 cm⁻¹, the appearance of which can be explained by the large defective structure and disorder in the ceria lattice. Copyright © 2011 John Wiley & Sons, Ltd.     

The use of chromium minerals in the 4th–3rd century BC China? A preliminary study of a bronze Pan unearthed from Jiuliandun Graves,Hubei Province,central southern China

A bronze Pan (water vessel), dating back to the 4th–3rd century BC, was excavated at Jiuliandun in Hubei Province, central southern China, in 2002. The Pan attracts wide attention among the Chinese archaeologists and conservators for its uniqueness in style and color, which turns out to be due to a black‐brown film of about 1 mm thickness. In the present work, a combined use of X‐ray fluorescence (XRF), micro‐Raman, and X‐ray diffraction (XRD) was employed to determine both chemical and physical compositions of the Pan's film. The results are summarized as follows: (1) The film, as XRF analysis indicates, has high concentrations of chromium (Cr) and iron (Fe); (2) Both Raman and XRD analyses suggest that the element Cr probably exists in the film mainly in the form of chromium oxide (Cr₂O₃). Raman analysis also implies the presence of PbCrO₄·PbO in the film; (3) XRD analysis suggests that the element Fe exists in the film in the form of magnetite (Fe₃O₄). Based on these analytical results and Chinese historical records, we propose that, as early as in the 3rd century BC, people in central southern China might have discovered and intentionally used chromium minerals for bronze surface treatment (such as coating). The source of chromium minerals used in this period was likely Cr‐spinel minerals from meteorites. More work remains to be done to test the possibility of using Cr‐spinel minerals for bronze production and decoration. Other issues, such as the possibility of forming a chromium‐rich film during the underground burial, also need to be solved. Copyright © 2011 John Wiley & Sons, Ltd.     

A three‐dimensional surface‐enhanced Raman scattering substrate: Au nanoparticle supramolecular self‐assembly in anodic aluminum oxide template

A three‐dimensional surface‐enhanced Raman scattering (SERS) substrate via the self‐assembly of properly sized Au nanoparticles in anodic aluminum oxide templates was designed and prepared. Au nanoparticles first underwent hydrophobic surface modification. Then, the hydrophobic Au nanoparticles self‐assembled, aggregated and formed many hot spots in the anodic aluminum oxide templates through a supramolecular interaction. We chose thiophenol as a probe molecule to evaluate the SERS enhancement ability of this three‐dimensional substrate. The enhancement factor was calculated to be 4.6 × 10⁶ under the radiation of a 785‐nm laser. By further comparing SERS signals from different points on the same substrate, we confirmed that this substrate possessed good reproducibility and could be applied for SERS detection. Copyright © 2011 John Wiley & Sons, Ltd.     

An authentication case study: Antonio Palomino versus Vicente Guillo paintings in the vaulted ceiling of the Sant Joan del Mercat church (Valencia,Spain)

In 1695, the Valencian artist Vicente Guillo was engaged in painting the vault of the Sant Joan del Mercat church in Valencia, Spain. After preliminary work was carried out, his contract was cancelled. In 1697, Antonio Palomino, renowned for the publication of his technical treatise entitled El Museo Pictorio y Escala Optica, was finally selected as the painter in charge of decorating the vaulted ceiling of Sant Joan del Mercat. This paper reports an analytical study focused on the characterisation and discrimination of the palette and painting procedures used by Palomino and Guillo in the frescoes of Sant Joan del Mercat. For this purpose, Raman spectroscopy combined with light microscopy, scanning electron microscopy–X‐ray microanalysis, voltammetry of microparticles, X‐ray diffraction, Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry has been employed. The use of gypsum as stucco material for the ground layers contrasts with the recommendations made by Palomino in his treatise about the convenience of using slaked lime‐sand mortars according to traditional fresco recipes. Although lead‐based pigments were not traditionally recommended for frescoes because of their empirically known alterations when subjected to strong alkaline fresco medium, both Guillo and Palomino used them. Palomino, probably supported by his personal experience as a painter, recommended and used Naples yellow, which has been found in a good state of preservation. In contrast, white lead areas found on Guillo's paintings have transformed into lead oxides. Other pigments found in the vaulted ceiling such as smalt, goethite, haematite, azurite and malachite have also undergone substantial changes because of the extreme temperature conditions to which they were subjected in the church. Copyright © 2012 John Wiley & Sons, Ltd.     

Building and analyzing the US airport network based on en-route location information

From a complex network perspective, this study sets out two aims around the US airport network (USAN) which is built from en-route location information of domestic flights in the US. First, we analyze the structural properties of the USAN with respect to its binary and weighted graphs, and second we explore the airport patterns, which have wide-ranging implications. Results from the two graphs indicate the following. (1) The USAN exhibits scale-free, small-world and disassortative mixing properties, which are consistent with the mainstream perspectives. Besides, we find (2) a remarkable power relationship between the structural measurements in the binary graph and the traffic measurements in the weighted counterpart, namely degree versus capacity and attraction versus volume. On the other hand, investigation of the airport patterns suggests (3) that all the airports can be classified into four categories based on multiple network metrics, which shows a complete typology of the airports. And it further indicates (4) that there is a subtle relationship between the airport traffic and the geographical constraints as well as the regional socioeconomic indicators.     

Thermodynamic and physical properties of FeAl and Fe3Al: an atomistic study by EAM simulation

With this work we present a newly developed potential for the Fe–Al system, which is based on the analytical embedded atom method (EAM) with long range atomic interactions. The potential yields for the two most relevant phases B2-FeAl and D0₃-Fe₃Al lattice constants, elastic constants, as well as bulk and point defect formation enthalpies, which are in good agreement with experimental and other theoretical data. In addition, the phonon dispersions for B2-FeAl and D0₃-Fe₃Al show a good agreement with available experiments. The calculated lattice constants and formation enthalpy for disordered Fe–Al alloys are in good agreement with experimental data or other theoretical calculations. This indicates that the present EAM potentials of Fe–Al system is suitable for atomistic simulations of structural and kinetic properties for the Fe–Al system.