R. Mayo

Measured Stark widths of several Ni II spectral lines

The Stark broadening parameters of 17 lines of Ni II have been measured in a plasma produced by ablation of an Al–Ni alloy with a Nd:YAG laser. The broadening parameters were obtained with the target placed in molecular argon at 6 Torr, which provides appropriate measurement conditions. A Boltzmann plot was used to obtain the plasma temperature (16 500 ± 2100 K) and published values of the Stark broadening in Al II to obtain the electron density ((1.07 ± 0.10)1017cm−3); with these values, the plasma composition was determined by means of the Saha equation. The local thermodynamic equilibrium condition was checked. Contributions to broadening arising from a mechanism different from the Stark broadening as well as self-absorption influence were estimated for every studied line. A comparison was made with previous experimental values and recent theoretical estimates of the Stark broadening where possible.

Measurement of the Stark broadening for several lines of singly ionized gold

The Stark broadening parameters of 26 lines of Au II have been measured in a plasma produced by ablation of a gold target with a Nd:YAG laser. In order to obtain suitable experimental conditions for the homogeneity and stability of the plasma, a study of the temporal plasma evolution in helium, argon and nitrogen at different pressures was made. The broadening parameters were obtained with the gold target placed in molecular argon at 6.5 Torr, which provides appropriate measurement conditions. A Boltzmann plot was used to obtain the plasma temperature [16 200 ± 1400 K] and by means of the Saha equation the electron density [(1.45 ± 0.23) × 1017 cm−3] and the plasma composition were determined. The local thermodynamic equilibrium condition was checked. Contributions to broadening arising from a mechanism different from the Stark broadening as well as self-absorption influence were estimated for every studied line.

Using a Simple Prioritisation Mechanism to Effectively Interoperate Service and Opportunistic Grids in the EELA-2 e-Infrastructure

Grids currently in production can be broadly classified as either service Grids, composed of dedicated resources, or opportunistic Grids that harvest the computing power of non-dedicated resources when they are idle. While a service Grid provides high and well defined levels of quality of service, an opportunistic Grid provides only a best-effort service. Nevertheless, since opportunistic Grids do not require resources to be fully dedicated to the Grid, they have the potential to assemble a much larger number of resources. Moreover, these Grids cater very well to the execution of the so-called embarrassingly parallel applications, a type of application that is frequently found in practice, and that comprises the largest portion of the typical workload processed in production Grid systems. The EELA-2 e-infrastructure is comprised of a service Grid and an opportunistic Grid that federates computing resources from scientific institutions in both Europe and Latin America. Due to the complementary characteristics of these two types of Grids, a lot of attention has recently been placed in how to interoperate them. In this paper we focus on the less studied problem of assessing the feasibility of such interoperation. We analyse different prioritisation policies that define when the resources of one Grid can be used to run jobs originating from the other. Our results show that in the absence of a suitable prioritisation policy, the benefits that the users of one Grid may have, frequently come with an important negative impact on the users of the other Grid. We also show that a simple reciprocation mechanism is capable of arbitrating the interoperation in such a way that, whenever possible, users profit from the interoperation and, in no case, this benefit leads to a noticeable reduction on the quality of service that the users would experience were the Grids not to interoperate. We conclude discussing how we have implemented, in the context of the EELA-2 project, this prioritisation mechanism, allowing the effective interoperation of a service Grid based on the gLite middleware with an opportunistic Grid that uses the OurGrid middleware.

Radiative parameters for some transitions arising from the 3d94d and 3d84s2 electronic configurations in Cu II spectrum

Transition probabilities of 41 transitions originating from the 3d94d and 3d84s2 electronic configurations of singly ionized copper have been determined using laser-induced breakdown spectroscopy. The Cu II ions have been produced by laser ablation. The experimental relative transition probabilities have been converted into an absolute scale using measured branching fractions and theoretical radiative lifetimes of the corresponding upper states obtained by a relativistic Hartree–Fock method taking core-polarization and configuration interaction effects into account. Comparison of the new results with previously available data is also presented.

Experimental stark widths of six UV lines of ZnII

The Stark broadening parameters of six lines of ZnII (four measured for the first time) have been experimentally determined in a plasma produced by ablation of a Cd?Zn alloy with a Nd:YAG laser and a Zn content under 10%. The broadening parameters were obtained with the target placed in molecular argon at 6 Torr, which provides appropriate measurement conditions. A Boltzmann plot was used to obtain the plasma temperature (30?400 ? 6400 K) and published values of the Stark broadening in CdII to obtain the electron density ((5.38 ? 0.54)1016 cm?3); with these values the plasma composition was determined by means of the Saha equation. The local thermodynamic equilibrium condition was checked. Contributions to broadening arising from a mechanism different from the Stark broadening as well as self-absorption influence were estimated for every studied line. A comparison is made with previous experimental values and recent theoretical estimates of the Stark broadening where possible.

Possibility of LIBS for transition probabilities determination

Laser Induced Breakdown Spectroscopy (LIBS) is a one of the successfully used technique for measuring experimental atomic and ionic transition probabilities. This is due to the excitation procedure easily provides highly ionised species and neutral atoms. Nevertheless, its range also extends to another applications such as the industry or in astrophysics. In this work, we explain a specific experimental set-up -consist of fomred by a Nd:YAG laser and grating monochromator coupled with a time-resolved optical multichannel analyser. The employment of the time and spatial spectroscopy in a laser produced plasma for obtaining transition probabilities is also described. From the laser produced plasmas it is also possible to determine some of their properties such as the temperature or the composition. Besides, due to the high emission and temperature, it can be proved the existence of Local Thermodynamic Equilibrium allows determination of absolute values for the transition probabilities and the evaluation of some characteristics such as the self-absorption. The experimental data treatment for obtaining the transition probabilities and the different plasma properties that can be derived was explained.

Transition probabilities for lines from 4d96s, 4d95d of Ag II spectrum and from 3d94d of Cu II lines

Experimental transition probabilities for lines arising from 4d9 6s, 4d9 5d configurations of Ag II spectrum and from 3d9 4d configuration of CuII spectrum were determined from measurements of emission-line intensities in a laser produced plasma. Theoretical calculations of the transition probabilities of these lines were made by HF method with relativistic effects and core polarization taking into account. Absolute transition probabilites were obtained by measured branching ratio and theoretical and data for radiative lifetimes. A comparison of the present results with the available theoretical and experimental values was made.

Radiative data in the Zr I spectrum obtained by Laser Induced Fluorescence

Radiative lifetimes of 17 excited states in Zr I, in the energy interval 29000 - 40974 cm-1, have been investigated using the Time-Resolved Laser-Induced Fluorescence (TR-LIF) method. The levels belong to the 4d25s5p, 4d35p and 4d5s25p electronic configurations were excited in a single - step process from levels belonging to the ground 4p25s2 a 3F or to low-lying 4p25s2 a 3P, a 5F terms. For 14 levels, the lifetimes have been measured for the first time. Experimental results are compared with theoretical calculations performed with a multiconfigurational relativistic Hartree-Fock method including core polarization effects.

Experimental and Theoretical Stark Widths for Au II

In the present work, we have reviewed and compared our experimental and theoretical Au II Stark widths. The interest in Au II resides not only on the knowledge of its atomic structure, or to check the adequacy of theoretical models, but also on its astrophysical importance because its lines are present in spectra of chemically peculiar stars.The plasma source of Au II spectrum was produced by laser ablation on pure gold, using the Laser Induced Breakdown Spectroscopy (LIBS) technique.The theoretical results were obtained using the modified semiempirical approach. Obtained experimental and theoretical results were compared and discussed, in order to prepare the new measurements and to analyze the astrophysical applications for CP star spectra modelling.

3p photoabsorption spectra of Mn{sup 2+} and Mn{sup 3+}

Time-resolved extreme ultraviolet photoabsorption spectra of a manganese plasma have been recorded using the dual laser plasma technique. The 43-73 eV photon energy range is dominated by the 3p-3d giant resonance and to a lesser extent the 3p-4s resonances in both Mn{sup 2+} and Mn{sup 3+}, recorded at interplasma time delays of 80 and 30 ns, respectively. These experimentally observed resonances are well reproduced by synthetic spectra calculated using the Hartree-Fock method. The synthetic spectra allow for absorption from excited states of the Mn{sup 2+} and Mn{sup 3+} ions.