The results of spectroscopic studies of plasmas generated in dielectric barrier discharges between flat ceramic electrodes supplied by AC voltage in pure hydrogen atmosphere under low-pressure conditions are presented. Stark splitting of the H α Balmer line was used to measure the electric field strengths in the discharge volume. The optical instrumentation and the detection system allow to perform spatial and time resolved measurements separately for the π and σ Stark components. The measured spatial light intensity distributions are averaged data obtained by integrating signals from many half-periods of the AC voltage supply. This fact has been taken into account when comparing our averaged data with results of theoretical models which are yielding time dependent results.

Experimental and theoretical Stark broadening studies of the Paschen beta line of hydrogen (lambda=1.28 microm) are reported. Line shape measurements were performed at electron densities of the plasma between 3.5 x 10(15) cm(-3) and 7.5 x 10(15) cm(-3), applying as the light source a wall-stabilized arc operated at atmospheric pressure in a helium-hydrogen gas mixture. The radiation of the plasma, emitted from nearly homogeneous plasma layers in the end-on direction, was registered with the use of a grating spectrometer equipped with a charge coupled device detector. The measured light outputs were calibrated against signals obtained from a tungsten strip radiation standard. The experimentally determined line profiles are compared with results of new Stark broadening calculations based on simulation techniques. The measured broadening, shift, and asymmetry parameters are also compared with results of previous Stark broadening calculations and other experimental data obtained at electron densities higher as well as lower than ours.

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We give a formulation of quantum cosmology with pressureless dust and arbitrary additional matter fields. The system has the property that its Hamiltonian constraint is linear in the dust momentum. This feature provides a natural time gauge, leading to a physical Hamiltonian that is not a square root. Quantization leads to a Schrödinger equation for which unitary evolution is directly linked to geodesic completeness. Our approach simplifies the analysis of both Wheeler-deWitt and loop quantum cosmology (LQC) models and significantly broadens the applicability of the latter. This is demonstrated for arbitrary scalar field potential and cosmological constant in LQC.