Radiative rates and electron impact excitation rates for H-like Ar XVIII

Aims. In this paper we report on calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for<br/>transitions among the lowest 25 levels of the n ≤ 5 configurations of H-like Ar xviii.<br/>Methods. The general-purpose relativistic atomic structure package (grasp) andDirac atomic R-matrix code (darc) are adopted for<br/>the calculations.<br/>Results. Radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric<br/>quadrupole (E2), and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective<br/>collision strengths are listed for all 300 transitions among the above 25 levels over a wide energy (temperature) range up to 800 Ryd<br/>(107.4 K).

Characterization of a high-density, direct-current reflex discharge plasma source operating in Ar and N-2

The characterization of a direct current, low-pressure, and high-density reflex discharge plasma source operating in argon and in nitrogen, over a range of pressures 1.0-10(-2) mbar, discharge currents 20-200 mA, and magnetic fields 0-120 G, and its parametric characterization is presented. Both external parameters, such as the breakdown potential and the discharge voltage-current characteristic, and internal parameters, like the charge carrier's temperature and density, plasma potential, floating potential, and electron energy distribution function, were measured. The electron energy distribution functions are bi-Maxwellian, but some structure is observed in these functions in nitrogen plasmas. There is experimental evidence for the existence of three groups of electrons within this reflex discharge plasma. Due to the enhanced hollow cathode effect by the magnetic trapping of electrons, the density of the cold group of electrons is as high as 10(18) m(-3), and the temperature is as low as a few tenths of an electron volt. The bulk plasma density scales with the dissipated power. Another important feature of this reflex plasma source is its high degree of uniformity, while the discharge bulk region is free of electric field. (C) 2002 American Institute of Physics.

Argon metastable state densities in inductively coupled plasma in mixtures of Ar and O2

We have measured the densities of 1s5 and 1s3 argon metastables as a function of the abundance of molecular oxygen in an inductively coupled plasma (ICP) in mixtures of Ar and O2. Laser absorption spectroscopy was used to determine the densities of the metastables. It was found that even small abundances of oxygen lead to large increases in metastable density, mostly due to the reduction in the electron number density, since electron-induced quenching determines the metastable density. At abundances higher than 7% to 15% for powers between 50 and 150W, quenching by oxygen molecules begins to dominate and the metastable density drops again.

Short pulse pumped X-ray lasers

Double laser pulses of duration similar to 75 ps and short laser pulses similar to 1 ps superimposed on longer duration background pulses have been shown to efficiently pump lasing in Ne-like and Ni-like ions. For the 75 ps pumping, X-ray laser output without travelling wave pumping is shown to be well-described by a model of ASE output. With I ps pumping, the X-ray laser output with different velocity travelling wave pumping is well-fitted with an extension to the ASE model allowing for travelling wave excitation of the gain along the plasma line. The model is used to investigate the production of short (&lt;1 ps) x-ray laser pulses and the effects of non-ideal travelling wave velocities on the X-ray laser output. Resonance line spectra of emission perpendicular to the plasma line are measured and simulated. It is shown that an accurate opacity model for the more intense Ne-like ions is needed to correctly simulate the spectra.

Ar Drywydd Pererin: Gwaith Dafydd Benfras, Cerdd 36

This article identifies the author of a hitherto anonymous poem and supplies its ending, previously believed to be missing. It adds a sixth poem to the surviving work of Einion ap Gwalchmai.

Nebular and Auroral Emission Lines of [Ar IV] in the Optical Spectra of Planetary Nebulae

<p>Recent R-matrix calculations of electron impact excitation rates in Ar IV are used to calculate the emission-line ratio: ratio diagrams (R₁, R₂), (R_1, R₃), and (R_1, R₄), where K₁ = I(4711 Ã…)/I(4740 Ã…), R₂ = I(7238 Ã…)/I(4711 + 4740 Ã…), R₃ = I(7263 Ã…)/I(4711 + 4740 Ã…), and R₄ = I(7171 Ã…)/I(4711 + 4740 Ã…), for a range of electron temperatures (T_e = 5000-20,000 K) and electron densities (N_e = 10-10⁶ cm^-3) appropriate to gaseous nebulae. These diagrams should, in principle, allow the simultaneous determination of T_e and N_e from measurements of the [Ar IV] lines in a spectrum. Plasma parameters deduced for a sample of planetary nebulae from (R_1, R₃) and (R_1, R₄), using observational date obtained with the Hamilton echelle spectrograph on the 3 m Shane Telescope at the Lick Observatory, are found to show excellent internal consistency and to be in generally good agreement with the values of T_e and N_e estimated from other line ratios in the echelle spectra. These results provide observational support for the accuracy of the theoretical ratios and, hence, the atomic data adopted in their derivation. In addition, they imply that the 7171 Ã… line is not as seriously affected by telluric absorption as previously thought. However, the observed values of R₂ are mostly larger than the theoretical high-temperature and density limit, which is due to blending of the Ar IV 7237.54 Ã… line with the strong C II transition at 7236 Ã…. </p>

Eochaid ua Flainn is Eochaid ua Flannucáin: Súil Úr ar an bhFianaise

The evidence for two poets on record in the tenth century is reconsidered. The argument is made that they can be identified as one person, the poet Eochaid ua Flannucáin, a member of the religious community of Armagh and founder of a dynasty which governed the centre of the Irish church for over 150 years.

Discretization of highly persistent correlated AR(1) shocks

The finite state Markov-chain approximation methods developed by Tauchen (1986) and Tauchen and Hussey (1991) are widely used in economics, finance and econometrics to solve functional equations in which state variables follow autoregressive processes. For highly persistent processes, the methods require a large number of discrete values for the state variables to produce close approximations which leads to an undesirable reduction in computational speed, especially in a multivariate case. This paper proposes an alternative method of discretizing multivariate autoregressive processes. This method can be treated as an extension of Rouwenhorst's (1995) method which, according to our finding, outperforms the existing methods in the scalar case for highly persistent processes. The new method works well as an approximation that is much more robust to the number of discrete values for a wide range of the parameter space.