Reactive oxygen and hydrogen species generation in radio-frequency atmospheric pressure plasmas - Experimental and numerical investigations

Atmospheric pressure plasmas (APPs) are known to be effective sources for reactive oxygen and nitrogen species (RS), making them potentially suitable for applications in biomedicine, where these species are believed to play a crucial role. However, in order to fully establish plasma sources in biomedicine, detailed characterisation of the RS produced is required. This is particularly challenging at atmospheric pressure, because of high collision rates among particles leading to fast de-excitation of excited states (quenching), complex gas mixing, and the small physical dimensions of the investigated systems, which effectively limits the accurate application of several commonly used diagnostic techniques applicable in low pressure systems. The motivation of this work is therefore to investigate the chemical kinetics in APPs, using a combination of simulations and experimental diagnostics, which are able to overcome the above-mentioned challenges. Experimentally, absolute RS species densities such as O, OH, H2O2, N, and NO, are determined using absorption spectroscopy in the UV and VUV spectral range, a technique independent on quenching and providing high spectral resolution. Spatially resolved two-photon absorption laser-induced fluorescence with sub-nanosecond temporal resolution enables the determination of atomic species densities (O and H) in the plasma effluent. Experimental values are benchmarked against zero-dimensional plasma-chemical kinetics simulations, which are used to investigate the principal reaction mechanisms leading to the formation and consumption of the investigated species. It is generally found that formation pathways depend strongly on the concentration of molecules in the feed gas, and the position in the plasma jet, as well as potential impurities being present in the feed gas, which is an important aspect for consideration for the applications of APPs. The results are used to propose possible tailoring schemes to optimise RS productions in APPs

Plasma-liquid interactions: a review and roadmap

Plasma-liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas

Breaking down Global and Regional Sea Level Budgets: what Satellite Observations can tell us

A thorough understanding of sea level rise requires the quantification of the underlying drivers. Using satellite gravimetry and radar altimetry we can split up the global mean sea level budget into components induced by mass changes (e.g. melting and water cycle variations) and volumetric changes (thermo and halosteric variations). But, is this also possible in terms of regional sea level budgets? Furthermore, can we resolve for even smaller contributions, such as, individual ice sheets, glacier groups, and dominant modes of terrestrial hydrology, and steric variations? In this study, we use satellite gravimetry from GRACE and radar altimetry from Jason-1 and Jason-2 to break down the sea level budgets on both global and regional scales over the years 2002-2014. Auxiliary data from hydrological and ocean models are used to create time invariant patterns which are scaled by time series which are estimated from the data. The inversion scheme, ensures that the sea level budget closes in a consistent way, respecting geometry and mass conservation. The solution is then evaluated in terms of sea level rise and its variation. To investigate the contribution of the deeper ocean, we subtract an independent steric estimate (top 700m, ARGO) from the estimated steric contribution. In contrast to other studies, we find a significant deep ocean steric component below 700m in the order of 1.2 mm/yr over the years considered

New insights into myosin phosphorylation during cyclic nucleotide-mediated smooth muscle relaxation

Nitrovasodilators and agonists, via an increase in intracellular cyclic nucleotide levels, can induce smooth muscle relaxation without a concomitant decrease in phosphorylation of the regulatory light chains (RLC) of myosin. However, since cyclic nucleotide-induced relaxation is associated with a decrease in intracellular [Ca2+], and hence, a decreased activity of MLCK, we tested the hypothesis that the site responsible for the elevated RLC phosphorylation is not Ser19. Smooth muscle strips from gastric fundus were isometrically contracted with ET-1 which induced an increase in monophosphorylation from 9 +/- A 1 % under resting conditions (PSS) to 36 +/- A 1 % determined with 2D-PAGE. Electric field stimulation induced a rapid, largely NO-mediated relaxation with a half time of 8 s, which was associated with an initial decline in RLC phosphorylation to 18 % within 2 s and a rebound to 34 % after 30 s whereas relaxation was sustained. In contrast, phosphorylation of RLC at Ser19 probed with phosphospecific antibodies declined in parallel with force. LC/MS and western blot analysis with phosphospecific antibodies against monophosphorylated Thr18 indicate that Thr18 is significantly monophosphorylated during sustained relaxation. We therefore suggest that (i) monophosphorylation of Thr18 rather than Ser19 is responsible for the phosphorylation rebound during sustained EFS-induced relaxation of mouse gastric fundus, and (ii) that relaxation can be ascribed to dephosphorylation of Ser19, the site considered to be responsible for regulation of smooth muscle tone

Aging-related alterations in eNOS and nNOS responsiveness and smooth muscle reactivity of murine basilar arteries are modulated by apocynin and phosphorylation of myosin phosphatase targeting subunit-1

Aging causes major alterations of all components of the neurovascular unit and compromises brain blood supply. Here, we tested how aging affects vascular reactivity in basilar arteries from young (22months; o-BA) and old (>22months) heterozygous MYPT1-T-696A/+knock-in mice. In isometrically mounted o-BA, media thickness was increased by approximate to 10% while the passive length tension relations were not altered. Endothelial denudation or pan-NOS inhibition (100 mu mol/L L-NAME) increased the basal tone by 11% in y-BA and 23% in o-BA, while inhibition of nNOS (1 mu mol/L L-NPA) induced approximate to 10% increase in both ages. eNOS expression was approximate to 2-fold higher in o-BA. In o-BA, U46619-induced force was augmented (pEC(50) approximate to 6.9 vs. pEC(50) approximate to 6.5) while responsiveness to DEA-NONOate, electrical field stimulation or nicotine was decreased. Basal phosphorylation of MLC20-S19 and MYPT1-T-853 was higher in o-BA and was reversed by apocynin. Furthermore, permeabilized o-BA showed enhanced Ca2+-sensitivity. Old T-696A/+BA displayed a reduced phosphorylation of MYPT1-T696 and MLC20, a lower basal tone in response to L-NAME and a reduced eNOS expression. The results indicate that the vascular hypercontractility found in o-BA is mediated by inhibition of MLCP and is partially compensated by an upregulation of endothelial NO release