Structural and optical properties of CaTiO3 perovskite-based materials obtained by microwave-assisted hydrothermal synthesis: An experimental and theoretical insight

CaTiO₃ powders were synthesized using both a polymeric precursor method (CT_ref) and a microwave-assisted hydrothermal (CT_HTMW) method in order to compare the chemical and physical properties of the perovskite-based material as a function of the synthesis method. To this end, X-ray diffraction, Raman spectroscopy, inductively coupled plasma atomic emission spectroscopy and experimental Ti and Ca K-edge X-ray absorption near-edge structure spectroscopy, as well as measurements of photoluminescence (PL) emission, were used to characterize the typical bottom-up process of the CaTiO₃ perovskite phase at different times. Detailed Rietveld refinements show a random polycrystalline distortion in the powder structure, which can be associated with the tilting (α angle < O–Ti–O) between adjacent TiO₆ octahedra (intermediate range) for CT_HTMW samples and an intrinsic TiO₆ distortion (short range) in relation to the polymeric precursor CT_ref sample. These properties were further investigated by first-principles calculations based on the density functional theory at the B3LYP level. The relationship between this tilting on the PL profile is highlighted and discussed. Thus, a structural model derived from both experimental results and theoretical simulations reveals a close relationship between this tilting and the presence of intermediate energy states within the band gap which are mainly responsible for PL emissions.     

Delegated dispatching of wind farms: an optimal approach considering continuous control and interruption capabilities

In grids with high wind power penetration, the System Operator may curtail the power injected at critical moments for security reasons. An intermediate operator can optimize this power reduction for a group of wind farms under its control, attending to their controllability. In this way, resources may be used efficiently, and in cooperation with the system operation. In this paper, an optimization‐based procedure is proposed to allocate the power reductions among the wind farms of a region. Application examples based on the Spanish situation are shown, because in that country, these intermediate entities (called Delegated Dispatches) are about to begin their full operation. Copyright © 2008 John Wiley & Sons, Ltd.     

Thinking about the future moves attention to the right.

Previous studies have shown that past and future temporal concepts are spatially represented (past being located to the left and future to the right in a mental time line). This study aims at further investigating the nature of this space–time conceptual metaphor, by testing whether the temporal reference of words orient spatial attention or rather prime a congruent left/right response. A modified version of the spatial cuing paradigm was used in which a word’s temporal reference must be kept in working memory whilst participants carry out a spatial localization (Experiment 1) or a direction discrimination, spatial Stroop task (Experiment 2). The results showed that the mere activation of the past or future concepts both oriented attention and primed motor responses to left or right space, respectively, and these effects were independent. Moreover, in spite of the fact that such time-reference cues were nonpredictive, the use of a short and a long stimulus onset asynchrony in Experiment 3 showed that these cues modulated spatial attention as typical central cues like arrows do, suggesting a common mechanism for these two types of cuing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

MASS TRANSFER WITH CHEMICAL REACTION IN PARTIALLY WETTED FLAT PLATE CATALYST PELLETS: RIVULET FLOW ANALYSIS

Mass transfer with chemical reaction is analyzed in a system formed by a flat plate solid catalyst, partially wetted by a flowing rivulet of a liquid in contact with a stagnant pure gas. The paper solves the fluid dynamic problem of the liquid phase first, and afterwards incorporates the mass transfer and the chemical reaction. The system is assumed to be isothermal and at steady state, with a first order kinetics whose limiting reactant is in the gas phase. This work studies the influence of the gas-liquid surface tension, the liquid reactant flow rate, the liquid viscosity and the angle of inclination of the solid, upon the wetting factor. The model proposed also predicts the effect of these parameters and the Thiele modulus on the overall effectiveness factor and the molar flux of the limiting gaseous reactant at the catalytic solid-liquid interface in a direct way. This approach makes the wetting factor a non-manipulated variable.     

Scaling law for the radius of gyration of poly[bis(2-naphthoxyphosphazene)] (PBNP)

A numerical procedure that allows for the evaluation of the scaling law between radius of gyration and molecular weight,2> _i ^1/2 =Q M _i ^q , of ideally monodisperse fractions of any polymer is proposed. The method is similar to that previously used to determine viscometric constants and chromatographic calibration functions and is based on the combination of experimental results obtained by Static Light Scattering and Size Exclusion Chromatography on polydisperse samples. The method is used to study poly[bis(2-naphthoxyphosphazene)] in THF solution at 25°C for which the relationship2> _i ^1/2 =0.557 M _i ^0.29 is obtained. The comparison between the dimensions computed with this equation and those obtained by viscometric measurements, performed under the same experimental conditions, suggest the formation of intermolecular aggregates in the solutions of this polymer.     

Helmholtz-Gauss waves

A detailed study of the propagation of an arbitrary nondiffracting beam whose disturbance in the plane z = 0 is modulated by a Gaussian envelope is presented. We call such a field a Helmholtz-Gauss (HzG) beam. A simple closed-form expression for the paraxial propagation of the HzG beams is written as the product of three factors: a complex amplitude depending on the z coordinate only, a Gaussian beam, and a complex scaled version of the transverse shape of the nondiffracting beam. The general expression for the angular spectrum of the HzG beams is also derived. We introduce for the first time closed-form expressions for the Mathieu-Gauss beams in elliptic coordinates and for the parabolic Gauss beams in parabolic coordinates. The properties of the considered beams are studied both analytically and numerically.     

Ince-Gaussian beams in a quadratic-index medium

The propagation of Ince-Gaussian beams in media where the refractive index varies quadratically with the distance from the optical axis is studied. Explicit expressions for the complex beam parameter and the longitudinal phase shift are derived and discussed. Ince-Gaussian eigenmodes with constant width can be obtained by satisfying a relation between the beam width and the quadratic-medium coefficient. The derivation has included the possibility of propagation of Ince-Gaussian beams in complex lenslike media having quadratic transverse variations of the index of refraction and the gain or loss.