Fluorescence (TALIF) measurement of atomic hydrogen concentration in a coplanar surface dielectric barrier discharge

Spatially and temporally resolved measurements of atomic hydrogen concentration above the dielectric of coplanar barrier discharge are presented for atmospheric pressure in 2.2% H2/Ar. The measurements were carried out in the afterglow phase by means of two-photon absorption laser-induced fluorescence (TALIF). The difficulties of employing the TALIF technique in close proximity to the dielectric surface wall were successfully addressed by taking measurements on a suitable convexly curved dielectric barrier, and by proper mathematical treatment of parasitic signals from laser–surface interactions. It was found that the maximum atomic hydrogen concentration is situated closest to the dielectric wall from which it gradually decays. The maximum absolute concentration was more than 10^22 m-3. In the afterglow phase, the concentration of atomic hydrogen above the dielectric surface stays constant for a considerable time (10 us - 1 ms), with longer times for areas situated farther from the dielectric surface. The existence of such a temporal plateau was explained by the presented 1D model: the recombination losses of atomic hydrogen farther from the dielectric surface are compensated by the diffusion of atomic hydrogen from regions close to the dielectric surface. The fact that a temporal plateau exists even closest to the dielectric surface suggests that the dielectric surface acts as a source of atomic hydrogen in the afterglow phase

Facies development across the Late Silurian Lau Event based on temperate carbonates of the Prague Basin (Czech Republic)

The facies development through the stratigraphical interval of the Silurian (late Ludlow) Lau Event and the associated major δ13C record excursion have been studied in the Prague Basin. The investigated sections consist of temperate-water carbonates (Kopanina Formation) that were deposited in shallow as well as deeper parts of the basin. In both areas, the facies evolution reflects a major shallowing of sea-level during the early part of the event, which resulted in weathering (karstification) and erosion in the shallower parts of the basin, leading to stratigraphic gaps there. Paleokarst features and dolomitization are associated with these strata in the vicinity of Prague, where the δ13C record displays a strong diagenetic overprint and palynomorphs are very poorly preserved. A transition from deep-water shale to subtidal, thick-bedded limestone facies in the deeper parts of the basin, close to Kosov, signals the same sea-level drop, indicating that it was basin-wide. Detailed lithologic descriptions for the studied sections are provided and the development in the Prague Basin is compared with the coeval succession on Gotland, Sweden, which was located in the tropical realm at this times