Spectral properties and anomalous transport in a polygonal billiard

We analyze a class of polygonal billiards, whose behavior is conjectured to exhibit a variety of interesting dynamical features. Correlation functions are numerically investigated, and in a subclass of billiard tables they give indications about a singular continuous spectral measure. By lifting billiard dynamics we are also able to study transport properties: the (normal or anomalous) diffusive behavior is theoretically connected to a scaling index of the spectral measure; the proposed identity is shown to agree with numerical simulations. (c) 2000 American Institute of Physics.     

Size-controllable synthesis of functional heterostructured TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> core–shell nanoparticles

Mono and bicomponent TiO₂ and WO₃ nanoparticles were synthesized inside Vycor^® glass pores, by cycles of impregnation of the glass with the respective oxide precursor followed by its thermal decomposition. The impregnation-decomposition cycle (IDC) methodology promoted a linear mass increase of the glass matrix, and allowed tuning the nanoparticle size. X-ray diffraction and Raman spectroscopy data allowed identifying the formation of TiO₂ as anatase phase, while WO₃ is a mixture of the γ-WO₃ (monoclinic) and δ-WO₃ (triclinic) phases. High resolution transmission electron microscopy images revealed that for 3, 5, and 7 IDC, the TiO₂ nanoparticles obtained presented average diameters of 3.4, 4.3, and 5.1 nm, and the WO₃ nanoparticles have 2.9, 4.6, and 5.7 nm sizes. These TiO₂ and WO₃ monocomponent nanoparticles were submitted to IDC with the other oxide precursor, resulting in bicomponent nanoparticles. The broadening and shift of the Raman bands related to titanium and tungsten oxides suggest the formation of hetero-structure core–shell nanoparticles with tunable core sizes and shell thicknesses.     

Long-lasting exponential spreading in periodically driven quantum systems

Using a dynamical model relevant to cold-atom experiments, we show that long-lasting exponential spreading of wave packets in momentum space is possible. Numerical results are explained via a pseudoclassical map, both qualitatively and quantitatively. Possible applications of our findings are also briefly discussed.     

Stress dependence of paramagnetic point defects in amorphous silicon oxide

Room-temperature red cathodoluminescence (CL) emission (R band) arising from the paramagnetic point-defect population present in amorphous silicon oxide (SiOx) has been characterized with respect to its shift upon applied stress, according to a piezo-spectroscopic (PS) approach. The R band (found at around 630 nm) originates from nonbridging oxygen hole centers (NBOHC; Si-O*) generated in the presence of oxygen-excess sites. It is shown that reliable stress assessments can be obtained in silica glass with a relatively high spatial resolution, provided that appropriate spectroscopic procedures are developed to precisely extract from the CL spectrum the shift upon stress of the R band, isolated from other partly overlapping bands. Macroscopic and microscopic PS calibration procedures are shown to lead to consistent results on silica materials with different chemical characteristics and, thus, with different intrinsic defect populations. In addition, quantitative calibrations of both electron probe size and luminescence emission distribution within the electron probe are given. As an application of the PS technique, the magnitude of the residual stress piled up (mainly due to a thermal expansion mismatch) at a sharp silica/silicon interface has been characterized by taking into account the gradient in defect population developed as a function of distance from the interface. In the Results and Discussion section, brief comments are offered regarding the possible impact of highly spatially resolved stress assessments in silica glass upon the development of new materials and advanced electronic devices.     

Phonon deformation potentials for the corundum structure of sapphire

A theoretical Raman polarization analysis is proposed for the corundum structure of sapphire (α‐Al₂O₃) and validation experiments conducted with the purpose of retrieving the full set of phonon deformation potentials (PDPs). From the theoretical side, the change in force constants under stress/strain has been expressed in matrix form, and close‐form solutions were obtained for the eigenvalues that take into account the local dependence of oblique phonons on crystallographic orientation (i.e. uncoupling the effects of local crystal orientation and stress tensor from the shifts of Raman bands). From the experimental side, controlled (uniaxial) stress fields were applied to sapphire parallelepiped bars (along known crystallographic axes) while Raman spectra were systematically recorded along the bar thickness. An untextured alumina polycrystal with fine grain size was also investigated according to the same procedure. As a result of this set of experiments, PDPs for both A_1g and E_g vibrational bands could be retrieved. Validation of PDP constants was obtained by measuring the steeply graded stress fields developed ahead of a surface crack propagated along an arbitrary crystallographic direction in the R‐plane of the sapphire crystal. Copyright © 2011 John Wiley & Sons, Ltd.     

Phase equilibrium data and thermodynamic modeling of the system (CO2 + biodiesel + methanol) at high pressures

The main objective of this work was to investigate the high pressure phase behavior of the binary systems {CO₂(1) + methanol(2)} and {CO₂(1) + soybean methyl esters (biodiesel)(2)} and the ternary system {CO₂(1) + biodiesel(2) + methanol(3)} were determined. Biodiesel was produced from soybean oil, purified, characterized and used in this work. The static synthetic method, using a variable-volume view cell, was employed to obtain the experimental data in the temperature range of (303.15 to 343.15) K and pressures up to 21 MPa. The mole fractions of carbon dioxide were varied according to the systems as follows: (0.2383 to 0.8666) for the binary system {CO₂(1) + methanol(2)}; (0.4201 to 0.9931) for the binary system {CO₂(1) + biodiesel(2)}; (0.4864 to 0.9767) for the ternary system {CO₂(1) + biodiesel(2) + methanol(3)} with a biodiesel to methanol molar ratio of (1:3); and (0.3732 to 0.9630) for the system {CO₂ + biodiesel + methanol} with a biodiesel to methanol molar ratio of (8:1). For these systems, (vapor + liquid), (liquid + liquid), (vapor + liquid + liquid) transitions were observed. The phase equilibrium data obtained for the systems were modeled using the Peng–Robinson equation of state with the classical van der Waals (PR-vdW2) and Wong-Sandler (PR–WS) mixing rules. Both thermodynamic models were able to satisfactorily correlate the phase behavior of the systems investigated and the PR–WS presented the best performance.     

CuI‐Mediated Trifluoromethylations with Stannanes. Preliminary Communication

(Trifluoromethyl)stannane reagents such as Bu₃SnCF₃ are effective in CuI‐mediated trifluoromethylation reactions of aryl iodides. The reactions proceed via the intermediacy of [CuCF₃] species.     

Mean-Field Limit and Semiclassical Expansion of a Quantum Particle System

We consider a quantum system constituted by N identical particles interacting by means of a mean-field Hamiltonian. It is well known that, in the limit N → ∞, the one-particle state obeys to the Hartree equation. Moreover, propagation of chaos holds. In this paper, we take care of the dependence by considering the semiclassical expansion of the N-particle system. We prove that each term of the expansion agrees, in the limit N → ∞, with the corresponding one associated with the Hartree equation. We work in the classical phase space by using the Wigner formalism, which seems to be the most appropriate for the present problem. Submitted: October 2, 2008., Accepted: December 4, 2008.     

Targeted screening of pesticides, veterinary drugs and mycotoxins in bakery ingredients and food commodities by liquid chromatography-high-resolution single-stage Orbitrap mass spectrometry

In the food industry, it is frequently necessary to check the quality of an ingredient to decide whether to use it in production and/or to have an idea of the final possible contamination of the finished product. The current need to quickly separate and identify relevant contaminants within different classes, often with legal residue limits on the order of 1-100?μg?kg(-1) , has led to the need for more effective analytical methods. With thousands of organic compounds present in complex food matrices, the development of new analytical solutions leaned towards simplified extraction/clean-up procedures and chromatography coupled with mass spectrometry. Efforts must also be made regarding the instrumental phase to overcome sensitivity/selectivity limits and interferences. For this purpose, high-resolution full scan analysis in mass spectrometry is an interesting alternative to the traditional tandem mass approach. A fast method for extracting and purifying bakery matrices was therefore developed and combined with the exploitation of ultra-high-pressure liquid chromatography (UHPLC) coupled to a Orbitrap Exactive? high-resolution mass spectrometer (HRMS). Extracts of blank, naturally contaminated and fortified minicakes, prepared through a combined use of industrial and pilot plant production lines, were analyzed at different concentration levels (1-100?μg?kg(-1) ) of various contaminants: a limit of detection at 10?μg?kg(-1) was possible for most of the analytes within all the categories analyzed, including pesticides, aflatoxins, trichothecene toxins and veterinary drugs. The application of accurate mass targeted screening described in this article demonstrates that current single-stage HRMS analytical instrumentation is well equipped to meet the challenges posed by chemical contaminants in the screening of both bakery raw materials and finished products. Copyright ? 2012 John Wiley & Sons, Ltd.     

Raman tensor analysis of (K0.5Na0.5)NbO3–LiSbO3 lead‐free ceramics and its application to study grain/domain orientation

A quantitative polarized Raman analysis of ferroelectric grain/domain orientation in LiSbO₃ (LS‐modified) (K_0.5Na_0.5)NbO₃ (KNN) ceramics is presented, based on the analysis of the complex orientation dependence in space of their Raman‐active modes. Complete sets of Raman tensor elements of A_g, and E_g phonon modes for orthorhombic/tetragonal structures of KNN have been determined. Through this spectroscopic algorithm, quantitative information could be extracted in terms of three Euler angles in space for KNN samples consisting of mixed phases, thus enabling quantitative visualization of the local distribution of grains/domains in the solid angle. As an application of the method, we quantitatively examined the unknown crystallographic grain orientation patterns on the surfaces of pure KNN and of KNN‐0.05LS ceramics. These two samples were useful to clarify a polymorphic phase transition from the orthorhombic to the tetragonal phase taking place in the LS‐modified KNN system. Thus, we demonstrated that polarized Raman spectroscopy is a valuable and efficient tool for nondestructive three‐dimensional assessments of grain/domain orientation in ferroelectric materials with complex polymorphic structures. We believe that the data shown here represent a typical scenario encountered in grain/domain orientation assessments of piezoelectric perovskites. Copyright © 2012 John Wiley & Sons, Ltd.