97 10 25 8 v 1 2 3 O ct 1 99 7 Metal systems of the Lyman forest
An extremely careful analysis of the forest of weak metal-line systems at z ∼ 2 has allowed the separation into individual 'single-phase ionization' components with accurate parameters. The systems typically span several hundred km s −1 and within each the components show a strong coherence in their ioniza-tion properties. A general feature of the observed systems is the presence of high ionization broad components which co-exist in velocity space with more numerous, narrow, lower ionization components. From a sample of components extending to z ∼ 3.5, taken either individually or as system totals, no rapid evolution is found in the column density ratio N(Si IV)/N(C IV), contrary to previous indication of a large change near z = 3.1. Comparisons of component ion ratios including Si IV, C IV, C II and Si II from the sample at z ∼ 2 with CLOUDY derived values using several model ionizing spectra show the general dominance of the metagalactic ionizing background over local stellar radiation and give Si/C distributed 1–3 times the solar value. Indications of the evolution of structure are highlighted.
Cold Gas at High Redshift Netherlands Foundation for Research in Astronomy
We discuss the current observational and theoretical issues concerning cold gas at high redshift and present simulations showing how a number of observational issues can be resolved with planned future instrumentation.
An analytical approach to the design of electrodes in high-power, fast-transverse-flow CO2 lasers
Abstract Usually, the design of the electrodes of fast-transverse-flow CO 2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrodes that achieves a quasi uniform gain distribution. The analysis, based on a two-temperature model and the gas-transport equations, computes the electron density that supports a flat gain pattern. Combining the desired electron density with the electron-balance equations, the model determines the required electric field. The results were used to design a new set of electrodes for a home-made fast transverse flow CO 2 laser. A stable, large volume discharge ( 4 × 8 × 90 cm 3 ) with very good uniformity was obtained. The resulting gain distribution was registered in a bi-dimensional map. The peak gain rose from 1.2 m - 1 , attained with the old electrode set, to 1.6 m - 1 with the new one and the gain showed a homogeneous profile.