An R-matrix approach for plasma modelling and the interpretation of astrophysical observation

Over the last decade an Auburn-Rollins-Strathclyde consortium has developed several suites of parallel R-matrix codes [1, 2, 3] that can meet the fundamental data needs required for the interpretation of astrophysical observation and/or plasma experiments. Traditionally our collisional work on light fusion-related atoms has been focused towards spectroscopy and impurity transport for magnetically confined fusion devices. Our approach has been to provide a comprehensive data set for the excitation/ionization for every ion stage of a particular element. As we progress towards a burning fusion plasma, there is a demand for the collisional processes involving tungsten, which has required a revitalization of the relativistic R-matrix approach. The implementation of these codes on massively parallel supercomputers has facilitated the progression to models involving thousands of levels in the close-coupling expansion required by the open d and f sub-shell systems of mid Z tungsten. This work also complements the electron-impact excitation of Fe-Peak elements required by astrophysics, in particular the near neutral species, which offer similar atomic structure challenges. Although electron-impact excitation work is our primary focus in terms of fusion application, the single photon photoionisation codes are also being developed in tandem, and benefit greatly from this ongoing work.

Experimental and theoretical photoionization cross sections for Se + from 18 eV to 31 eV

Absolute Se photoionization cross-section measurements and Dirac-Coulomb R -matrix calculations are reported for the photon energy range 18.0 eV – 31.0 eV, which spans the ionization thresholds of the 4 S 0 3/2 ground state and the low-lying 2 D 0 3/2,5/2 and 2 P 0 1/2,3/2 metastable states. The determination of the photoionization and recombination properties of n -capture element ions is motivated by their astrophysical detection and the importance of their elemental abundances in testing theories of nucleosynthesis and stellar structure.

Generalized collisional radiative model for light elements: C: Data for the B isonuclear sequence

A first stage collision database is assembled which contains electron-impact excitation, ionization,\r and recombination rate coefficients for B, B + , B 2+ , B 3+ , and B 4+ . The first stage database\r is constructed using the R-matrix with pseudostates, time-dependent close-coupling, and perturbative\r distorted-wave methods. A second stage collision database is then assembled which contains\r generalized collisional-radiative ionization, recombination, and power loss rate coefficients as a\r function of both temperature and density. The second stage database is constructed by solution of\r the collisional-radiative equations in the quasi-static equilibrium approximation using the first\r stage database. Both collision database stages reside in electronic form at the IAEA Labeled Atomic\r Data Interface (ALADDIN) database and the Atomic Data Analysis Structure (ADAS) open database.

High-resolution photoionization of Xe + ions: Experiment and theory

High-resolution photoionization measurements of Xe + ions have been performed at the Advanced Light Source in Berkeley, California, USA. The experimental cross sections are compared with results from Dirac-Coulomb R-matrix calculations.

Photoionization of Cl-like Argon using the Breit-Pauli R-matrix method

Here we present the photoionization cross sections for the ground and metastable states of Cl-like Argon by exploiting the fully relativistic Breit-Pauli R-matrix computer codes to determine these transitions of interest. We compare our work with previous theoretical and experimental results and present a detailed investigation into the model of Ar III, the resonant structure and identification process.

Electron-impact excitation of open d-shell ions

Astrophysics is driven by observations, and in the present era there are a wealth of state-of-the-art ground-based and satellite facilities. The astrophysical spectra emerging from these are of exceptional quality and quantity and cover a broad wavelength range. To meaningfully interpret these spectra, astronomers employ highly complex modelling codes to simulate the astrophysical observations. Important input to these codes include atomic data such as excitation rates, photoionization cross sections, oscillator strengths, transition probabilities and energy levels/line wavelengths. Due to the relatively low temperatures associated with many astrophysical plasmas, the accurate determination of electron-impact excitation rates in the low energy region is essential in generating a reliable spectral synthesis. Hence it is these atomic data, and the main computational methods used to evaluate them, which we focus on in this publication. We consider in particular the complicated open d- shell structures of the Fe-peak ions in low ionization stages. While some of these data can be obtained experimentally, they are usually of insufficient accuracy or limited to a small number of transitions.

Electron impact excitation of the Fe-peak ions Ni III and Ni IV

Accurate determination of electron excitation rates for the Fe-peak elements is complicated by the presence of an open 3d-shell in the description of the target ion, which can lead to hundreds of target state energy levels. Furthermore, the low energy scattering region is dominated by series of Rydberg resonances, which require a very fine energy mesh for their delineation. These problems have prompted the development of a suite of parallel R-matrix codes. In this work we report recent applications of these codes to the study of electron impact excitation of Ni III and Ni IV.

Ni II: A comprehensive atomic data study with emphasis on astrophysical applications

In this work we report both the calculation of atomic collision data for the electron-impact excitation of Ni II using parallel R-matrix codes and the computation of atomic transition data using the general atomic structure package CIV3.

Comparison of Parallelised R-matrix codes for electron impact excitation of Cr II

A comparison of collision strengths and effective collision strengths has been undertaken for the Cr II ion based on the model of Wasson et al [2010 A & A. 524 A35]. Calculations have been completed using the Breit-Pauli, RMATRX II and DARC suites of codes.

Measurement of Fast Electrons Spectra Generated by Interaction between Solid Target and Peta Watt Laser

Fast electron energy spectra have been measured for a range of intensities between 1018 Wcm−2 and 1021 Wcm−2 and for different target materials using electron spectrometers. Several experimental campaigns were conducted on peta watt laser facilities at the Rutherford Appleton Laboratory and Osaka University. In these experimental campaigns, the pulse duration was varied from 0.5 ps to 5 ps. The laser incident angle was also changed from normal incidence to 40° in p-polarized. The results show a reduction from the ponderomotive scaling on fast electrons over 1020 Wcm−2.

A influência do terrorismo nos comportamentos de viagem internacionais

A partir de uma amostra de 600 turistas internacionais que circulam em Portugal, Espanha e Itália, este estudo identifica as principais os conceitos chave relacionados com o terrorismo, a percepção de risco, envolvimento e motivação para a segurança dos turistas internacionais. Diferentes níveis de preocupação relativamente à segurança pode influenciar as decisões dos turistas. No seu processo de decisão, os turistas avaliam vários factores, nomeadamente, o nível de risco ou de segurança que consideram nos destinos (Sonmez, 1998). Os turistas adoptam uma atitude protectora alterando os seus comportamentos durante os processos de decisão, substituindo os destinos que consideram inseguros por outros associados a uma maior segurança (Gu & Martin, 1992; Mansfeld, 1996). O terrorismo exacerbado pelos media tem efeitos graves nas receitas dos destinos turísticos (Taylor, 2006). Através da publicidade negativa, um destino turístico que experiencia um incidente terrorista pode ver a sua reputação danificada e a actividade turística severamente comprometida (Sonmez, 1998). Inclusivamente, a imageme negativa de um destino pode ser generalizada e pode também afectar outros países ou regiões por períodos de tempo indeterminados (Taylor, 2006). Um modelo de equações estruturais revela que os turistas são motivados para adquirir informação sobre o terrorismo nos media, nomeadamente mostram atenção e interesse sobre essas notícias e esse facto influencia directamente o seu risco percebido. A percepção de risco influencia directamente o envolvimento dos turistas no planeamento da viagem, especificamente a procura de informação antes da viagem e quando estão no destino. A percepção de risco e o envolvimento dos turistas influencia a percepção da importância da segurança.A discussão foca as implicações deste modelo para a teoria e para as instituições e organizações turísticas. São igualmente apresentadas recomendações para os gestores e promotores dos destinos e para os gestores das organizações turísticas. Direcções futuras de investigação são igualmente apresentadas.

Potencial de utilização de Cistus ladanifer L. na vegetalização de áreas mineiras

Dissertação de mest., Gestão e Conservação da Natureza, Faculdade de Ciências do Mar e do Ambiente, Univ. do Algarve, 2007