Panayia Ematousa II: Political, cultural, ethnic and social relations in Cyprus: Approaches to regional studies

Edited by L. Wriedt Sorensen & K. Winther Jacobse

Thermodynamic modelling of the plutonium–oxygen system

The published data for the thermodynamic functions and phase equilibria of the plutonium–oxygen system have been examined. Some inconsistencies have been found for oxygen chemical potential and vaporization data of [Pu2O3 + PuO2−x] and PuO2−x domains. As the original chemical potential data were not performed at the same temperature and O/Pu ratio, a chart with fixed temperature and composition ranges was built in order to compare all the experimental data. The discrepancies remain difficult to explain. Thermodynamic models of all the phases have been derived by the least-squares minimization procedure using the Thermo-Calc software. The compound energy formalism with the sublattice models (Pu3+, Pu4+)1(O2−, Va)2 and (Pu3+, Pu4+)2(O2−)3(O2−, Va)1 have been chosen to account for the crystal structure, defect chemistry and thermodynamic properties of respectively PuO2−x and PuO1.61 phases. The liquid phase was described using the ionic two-sublattice model (Pu3+)P(O2−, VaQ−, PuO2, O)Q. The reliability of the refined parameters is demonstrated by calculation of the phase diagram, the thermodynamic properties of the phases and the equilibrium partial pressures in the Pu2O3–PuO2 region. Considering the large uncertainties on the experimental information, an overall good agreement was obtained. To improve the thermodynamic description of the system, some missing experimental data are listed

Relationship between the morphology and the light scattering cross section of optically soft aggregates

International audienceThe purpose of this paper is to establish the suitable analytical expressions for the light scattering cross section of aggregates constituted by optically soft primary particles. The used optical approximation is the well-known Rayleigh-Debye-Gans approximation. The geometrical description of the aggregate is based on the pair, or distance, distribution density function describing at once the two spatial scales (primary particle and aggregate). Firstly, a study of the two-particle set is presented. An exact and an approximated formulations are proposed for the distance distribution density and the scattering cross section. Then the corresponding results are extended to the aggregates

T-Matrix Modeling of Linear Depolarization by Morphologically Complex Soot and Soot-Containing Aerosols

We use state-of-the-art public-domain Fortran codes based on the T-matrix method to calculate orientation and ensemble averaged scattering matrix elements for a variety of morphologically complex black carbon (BC) and BC-containing aerosol particles, with a special emphasis on the linear depolarization ratio (LDR). We explain theoretically the quasi-Rayleigh LDR peak at side-scattering angles typical of low-density soot fractals and conclude that the measurement of this feature enables one to evaluate the compactness state of BC clusters and trace the evolution of low-density fluffy fractals into densely packed aggregates. We show that small backscattering LDRs measured with groundbased, airborne, and spaceborne lidars for fresh smoke generally agree with the values predicted theoretically for fluffy BC fractals and densely packed near-spheroidal BC aggregates. To reproduce higher lidar LDRs observed for aged smoke, one needs alternative particle models such as shape mixtures of BC spheroids or cylinders

The environmental dependence of redox energetics of PuO2 and \alpha-Pu2O3: A quantitative solution from DFT+U calculations

We report a comprehensive density functional theory (DFT) + $U$ study of the energetics of charged and neutral oxygen defects in both PuO$_{2}$ and $\alpha$-Pu$_{2}$O$_{3}$, and present a quantitative determination of the equilibrium compositions of reduced PuO$_{2}$ (PuO$_{2-x}$) as functions of environmental temperature and partial pressure of oxygen, which shows fairly agreement with corresponding high-temperature experiments. Under ambient conditions, the endothermic reduction of PuO$_{2}$ to $\alpha$-Pu$_{2}$O$_{3}$ is found to be facilitated by accompanying volume expansion of PuO$_{2-x}$ and the possible migration of O-vacancy, whereas further reduction of $\alpha$-Pu$_{2}$O$_{3}$ is predicted to be much more difficult. In contrast to the endothermic oxidation of PuO$_{2}$,\ the oxidation of $\alpha$-Pu$_{2}$O$_{3}$ is a stable exothermic process.Comment: 5 PLA pages, 4 figure

Modelling optical properties of morphologically complex soot aerosols

Soot containing aerosol has both adverse impacts on the Earth\u27s climate and on human health. Monitoring soot sources, transport pathways and sinks on global scale requires satellite-borne remote sensing techniques.A detailed understanding of the soot particle\u27s optical properties is important to improve the interpretation of remote sensing data as well as the use of lidar remote sensing data in chemical transport modelling. The calculations of the optical properties were carried out using the discrete dipole approximation (DDA). Aim of this thesis is to identify key morphological features, which affect the depolarisation ratio.As soot particles age in the atmosphere, condensation of other compounds from the gas phase onto the particles results in soot aggregates coated by liquid-phase material. Initially, the soot particles are coated by a thin film (i.e., the coating follows the shape of the aggregate). As more liquid phase material is added, the coating becomes increasingly spherical. It is found that this transition from film coating to radial growth of spherical shells is an important process affecting the linear depolarisation ratio. If this transition occurs first at relatively high amounts of coating, then the depolarisation ratio tends to be high. Conversely, if the coating becomes already spherical at low amounts of coating material, then the depolarisation ratio of the coated soot particles is much lower.The linear depolarisation ratio of thickly coated aggregates was found to be sensitive to changes in the complex refractive index of the coating material, which represents changes in the chemical composition.These differences in the optical properties, even after averaging over a particle size distribution, are large enough to clearly distinguish the coating materials

Comprehensive T-Matrix Reference Database: A 2007-2009 Update

The T-matrix method is among the most versatile, efficient, and widely used theoretical techniques for the numerically exact computation of electromagnetic scattering by homogeneous and composite particles, clusters of particles, discrete random media, and particles in the vicinity of an interface separating two half-spaces with different refractive indices. This paper presents an update to the comprehensive database of T-matrix publications compiled by us previously and includes the publications that appeared since 2007. It also lists several earlier publications not included in the original database

Modelling optical properties of morphologically complex aerosols

The interpretation of remote sensing data of atmospheric aerosol particles requires a thorough understanding of the links between microphysical and optical properties. Morphologically complex aerosol models describe the particles’ morphology in detail. Based on the calculations with realistic particle models, simplified models can be devised, which incorporate essential microphysical properties for reproducing the optical properties. In this thesis, such models are developed and tested for soot aerosols, for mineral dust, and for dried and partially dissolved sea salt aerosol.A tunable model for coated soot aggregates is presented, and corresponding uncertainty estimates are performed. One of the main sources of uncertainty for thickly coated soot is the chemical composition of the coating, as represented by its refractive index. These uncertainties are so substantial, they are investigated as a potential source of information. The calculated lidar-measurable (spectral) quantities are distinct for two coating materials.The non-sphericity of a particle is identified as an essential morphological property affecting the linear depolarisation ratio. For coated soot another important property is the amount of carbon interacting with the incident wave, as it affects the absorption cross section. Combining these two insights resulted in the core grey shell dimer (CGS2) model, which is introduced in this thesis.For dry sea salt aerosol different random geometries are investigated, to simultaneously calculate linear depolarisation and extinction-to-backscatter ratio of dried sea salt aerosol particles. The results indicate that convex polyhedra are best suited to represent dried sea salt aerosol particles. Thus, the coated convex polyhedra model is proposed as the basis for modelling dissolving sea salt in a further study. For dissolving sea salt three simplified, equally well-performing models are presented, which identify the change in particle sphericity as a key morphological feature.A spheroidal model with a single refractive index and a single aspect ratio is fitted to laboratory measurements of 131 different dust samples. The scattering of the measurements about the model can mainly be explained by changes in morphology and dielectric properties, and to a lesser degree by the width of the particle size distribution.These results are expected to significantly advance our capacity to exploit and interpret polarimetric remote sensing observations of morphologically complex and chemically heterogeneous aerosol. This will be important for constraining Earth-system climate and air-quality forecasting models, and for evaluating and improving parameterisations of aerosol processes in these environmental modelling system

Volume Integral Formulation for the Calculation of Material Independent Modes of Dielectric Scatterers

In the frame of volume integral equation methods, we introduce an alternative representation of the electromagnetic field scattered by a homogeneous object of arbitrary shape at a given frequency, in terms of a set of modes independent of its permittivity. This is accomplished by introducing an auxiliary eigenvalue problem, based on a volume integral operator. With this modal basis the expansion coefficients of the scattered field are simple rational functions of the permittivity of the scatterer. We show, by studying the electromagnetic scattering from a sphere and a cylinder of dimensions comparable to the incident wavelength, that only a moderate number of modes is needed to accurately describe the scattered far field. This method can be used to investigate resonant scattering phenomena, including plasmonic and photonic resonances, and to design the permittivity of the object to pursue a prescribed tailoring of the scattered field. Moreover, the presented modal expansion is computationally advantageous compared to direct solution of the volume integral equation when the scattered field has to be computed for many different values of the dielectric permittivity, given the size and shape of the dielectric body