Numerical study of the influence of surface reaction probabilities on reactive species in an rf atmospheric pressure plasma containing humidity

International audienceThe quantification and control of reactive species (RS) in atmospheric pressure plasmas (APPs) is of great interest for their technological applications, in particular in biomedicine. Of key importance in simulating the densities of these species are fundamental data on their production and destruction. In particular, data concerning particle-surface reaction probabilities in APPs are scarce, with most of these probabilities measured in low-pressure systems. In this work, the role of surface reaction probabilities, gamma, of reactive neutral species (H, O and OH) on neutral particle densities in a He-H2O radio-frequency micro APP jet (COST-mu APPJ) are investigated using a global model. It is found that the choice of gamma, particularly for low-mass species having large diffusivities, such as H, can change computed species densities significantly. The importance of gamma even at elevated pressures offers potential for tailoring the RS composition of atmospheric pressure microplasmas by choosing different wall materials or plasma geometries

What happens when we remove GRACE or Ocean Bottom pressure from a GRACE+GPS+OBP joint inversion? Roelof Rietbroek, Sandra-Esther Brunnabend, Madlen Gebler, Mathias Fritsche, Jürgen Kusche, Christoph Dahle, Frank Flechtner, Schröter Jens, and Dietrich Reinhard

The movement of large masses, originating from hydrological and oceanographic variations, causes detectable variations in gravity and surface deformation. These may be detected by satellite gravimetry and a network of permanent GPS stations respectively. Alternatively, additional information on ocean bottom pressure(OBP) variations may be retrieved from simulations. Joint inversions offer a way to combine different data sources in order to obtain improved estimates of surface loading. This technique can be used to compensate for weaknesses in one dataset, by the strengths of the others. But what happens when one datasets is taken out of the equation? Here, we compute a joint inversion using a GPS+GRACE+OBP combination. Additionally, we purposely deteriorate the solution by removing either data from GRACE or OBP. The accuracy and resolution of the solutions is discussed. Furthermore, regions are identified where the restricted inversion is consistent with the full inversion, and where the results show strong hydrological signals

National Ecosystem Assessments in Europe: A Review

National ecosystem assessments form an essential knowledge base for safeguarding biodiversity and ecosystem services. We analyze eight European (sub-)national ecosystem assessments (Portugal, United Kingdom, Spain, Norway, Flanders, Netherlands, Finland, and Germany) and compare their objectives, political context, methods, and operationalization. We observed remarkable differences in breadth of the assessment, methods employed, variety of services considered, policy mandates, and funding mechanisms. Biodiversity and ecosystem services are mainly assessed independently, with biodiversity conceptualized as underpinning services, as a source of conflict with services, or as a service in itself. Recommendations derived from our analysis for future ecosystem assessments include the needs to improve the common evidence base, to advance the mapping of services, to consider international flows of services, and to connect more strongly to policy questions. Although the context specificity of national ecosystem assessments is acknowledged as important, a greater harmonization across assessments could help to better inform common European policies and future pan-regional assessments

Biophysical characterization of DNA origami nanostructures reveals inaccessibility to intercalation binding sites

Intercalation of drug molecules into synthetic DNA nanostructures formed through self-assembled origami has been postulated as a valuable future method for targeted drug delivery. This is due to the excellent biocompatibility of synthetic DNA nanostructures, and high potential for flexible programmability including facile drug release into or near to target cells. Such favourable properties may enable high initial loading and efficient release for a predictable number of drug molecules per nanostructure carrier, important for efficient delivery of safe and effective drug doses to minimise non-specific release away from target cells. However, basic questions remain as to how intercalation-mediated loading depends on the DNA carrier structure. Here we use the interaction of dyes YOYO-1 and acridine orange with a tightly-packed 2D DNA origami tile as a simple model system to investigate intercalation-mediated loading. We employed multiple biophysical techniques including single-molecule fluorescence microscopy, atomic force microscopy, gel electrophoresis and controllable damage using low temperature plasma on synthetic DNA origami samples. Our results indicate that not all potential DNA binding sites are accessible for dye intercalation, which has implications for future DNA nanostructures designed for targeted drug delivery

The formation of atomic oxygen and hydrogen in atmospheric pressure plasmas containing humidity : picosecond two-photon absorption laser induced fluorescence and numerical simulations

Atmospheric pressure plasmas are effective sources for reactive species, making them applicable for industrial and biomedical applications. We quantify ground-state densities of key species, atomic oxygen (O) and hydrogen (H), produced from admixtures of water vapour (up to 0.5%) to the helium feed gas in a radio-frequency-driven plasma at atmospheric pressure. Absolute density measurements, using two-photon absorption laser induced fluorescence, require accurate effective excited state lifetimes. For atmospheric pressure plasmas, picosecond resolution is needed due to the rapid collisional de-excitation of excited states. These absolute O and H density measurements, at the nozzle of the plasma jet, are used to benchmark a plug-flow, 0D chemical kinetics model, for varying humidity content, to further investigate the main formation pathways of O and H. It is found that impurities can play a crucial role for the production of O at small molecular admixtures. Hence, for controllable reactive species production, purposely admixed molecules to the feed gas is recommended, as opposed to relying on ambient molecules. The controlled humidity content was also identified as an effective tailoring mechanism for the O/H ratio

Chemical kinetics and density measurements of OH in an atmospheric pressure He + O2 + H2O radiofrequency plasma

This work presents experiments and modelling of OH densities in a radio-frequency driven atmospheric-pressure plasma in a plane-parallel geometry, operated in helium with small admixtures of oxygen and water vapour (He+O2+H2O). The density of OH is measured under a wide range of conditions by absorption spectroscopy, using an ultra-stable laser-driven broad-band light source. These measurements are compared with 0D plasma chemical kinetics simulations adapted for high levels of O2 (1%). Without O2 admixture, the measured density of OH increases from 1.0×1014 to 4.0×1014 cm-3 for H2O admixtures from 0.05% to 1%. The density of atomic oxygen is about 1×1013 cm-3 and grows with humidity content. With O2 admixture, the OH density stays relatively constant, showing only a small maximum at 0.1% O2. The simulations predict that the atomic oxygen density is strongly increased by O2 addition. It reaches ~1015 cm-3 without humidity, but is limited to ~1014 cm-3 beyond 0.05% water content. The addition of O2 has a weak effect on the OH density because, while atomic oxygen becomes a dominant precursor for the formation of OH, it makes a nearly equal contribution to the loss processes of OH. The small increase in the density of OH with the addition of O2 is instead due to reaction pathways involving increased production of HO2 and O3. The simulations show that the densities of OH, O and O3 can be tailored relatively independently over a wide range of conditions. The densities of O and O3 are strongly affected by the presence of small quantities (0.05%) of water vapour, but further water addition has little effect. Therefore, a greater range and control of the reactive species mix from the plasma can be obtained by the use of well-controlled multiple gas admixtures, instead of relying on ambient air mixing

Mass transfer in the lower crust: Evidence for incipient melt assisted flow along grain boundaries in the deep arc granulites of Fiordland, New Zealand

Knowledge of mass transfer is critical in improving our understanding of crustal evolution, however mass transfer mechanisms are debated, especially in arc environments. The Pembroke Granulite is a gabbroic gneiss, passively exhumed from depths of >45 km from the arc root of Fiordland, New Zealand. Here, enstatite and diopside grains are replaced by coronas of pargasite and quartz, which may be asymmetric, recording hydration of the gabbroic gneiss. The coronas contain microstructures indicative of the former presence of melt, supported by pseudosection modeling consistent with the reaction having occurred near the solidus of the rock (630–710°C, 8.8–12.4 kbar). Homogeneous mineral chemistry in reaction products indicates an open system, despite limited metasomatism at the hand sample scale. We propose the partial replacement microstructures are a result of a reaction involving an externally derived hydrous, silicate melt and the relatively anhydrous, high-grade assemblage. Trace element mapping reveals a correlation between reaction microstructure development and bands of high-Sr plagioclase, recording pathways of the reactant melt along grain boundaries. Replacement microstructures record pathways of diffuse porous melt flow at a kilometer scale within the lower crust, which was assisted by small proportions of incipient melt providing a permeable network. This work recognizes melt flux through the lower crust in the absence of significant metasomatism, which may be more common than is currently recognized. As similar microstructures are found elsewhere within the exposed Fiordland lower crustal arc rocks, mass transfer of melt by diffuse porous flow may have fluxed an area >10,000 km2

Chemical kinetics in an atmospheric pressure helium plasma containing humidity

Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultra-violet high-resolution Fourier-transform absorption spectroscopy and ultra-violet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H 2 O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 × 10 14 cm −3 for OH and 3 × 10 13 cm −3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH + by proton transfer to H 2 O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H 2 O + by proton transfer to H 2 O and by electron impact dissociation of H 2 O. It is lost by reactions with other OH molecules to form either H 2 O + O or H 2 O 2 . Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications