| 1. |
- Kamenetzky, J., et al.
(författare)
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CARBON MONOXIDE IN THE COLD DEBRIS OF SUPERNOVA 1987A
- 2013
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Ingår i: ASTROPHYS J LETT. - 2041-8205. ; 773:2, s. L34-
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Tidskriftsartikel (refereegranskat)abstract
- We report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J = 1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J = 13-12, collectively measured from the Atacama Large Millimeter Array, the Atacama Pathfinder EXperiment, and the Herschel Spectral and Photometric Imaging REceiver. Simple models show the lines are emitted from at least 0.01 M-circle dot of CO at a temperature >14 K, confined within at most 35% of a spherical volume expanding at similar to 2000 km s(-1). Moreover, we locate the emission within 1 '' of the central debris. These observations, along with a partial observation of SiO, confirm the presence of cold molecular gas within supernova remnants and provide insight into the physical conditions and chemical processes in the ejecta. Furthermore, we demonstrate the powerful new window into supernova ejecta offered by submillimeter observations.
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| 2. |
- Kamenetzky, J., et al.
(författare)
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CARBON MONOXIDE IN THE COLD DEBRIS OF SUPERNOVA 1987A
- 2013
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 773:2
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Tidskriftsartikel (refereegranskat)abstract
- We report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J = 1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J = 13-12, collectively measured from the Atacama Large Millimeter Array, the Atacama Pathfinder EXperiment, and the Herschel Spectral and Photometric Imaging REceiver. Simple models show the lines are emitted from at least 0.01 M-circle dot of CO at a temperature >14 K, confined within at most 35% of a spherical volume expanding at similar to 2000 km s(-1). Moreover, we locate the emission within 1 '' of the central debris. These observations, along with a partial observation of SiO, confirm the presence of cold molecular gas within supernova remnants and provide insight into the physical conditions and chemical processes in the ejecta. Furthermore, we demonstrate the powerful new window into supernova ejecta offered by submillimeter observations.
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| 4. |
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| 5. |
- Hopwood, Mark J., et al.
(författare)
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Experiment design and bacterial abundance control extracellular H2O2 concentrations during four series of mesocosm experiments
- 2020
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 17, s. 1309-1326
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Tidskriftsartikel (refereegranskat)abstract
- © Author(s) 2020. The extracellular concentration of H2O2 in surface aquatic environments is controlled by a balance between photochemical production and the microbial synthesis of catalase and peroxidase enzymes to remove H2O2 from solution. In any kind of incubation experiment, the formation rates and equilibrium concentrations of reactive oxygen species (ROSs) such as H2O2 may be sensitive to both the experiment design, particularly to the regulation of incident light, and the abundance of different microbial groups, as both cellular H2O2 production and catalase-peroxidase enzyme production rates differ between species. Whilst there are extensive measurements of photochemical H2O2 formation rates and the distribution of H2O2 in the marine environment, it is poorly constrained how different microbial groups affect extracellular H2O2 concentrations, how comparable extracellular H2O2 concentrations within large-scale incubation experiments are to those observed in the surface-mixed layer, and to what extent a mismatch with environmentally relevant concentrations of ROS in incubations could influence biological processes differently to what would be observed in nature. Here we show that both experiment design and bacterial abundance consistently exert control on extracellular H2O2 concentrations across a range of incubation experiments in diverse marine environments. During four large-scale (> 1000 L) mesocosm experiments (in Gran Canaria, the Mediterranean, Patagonia and Svalbard) most experimental factors appeared to exert only minor, or no, direct effect on H2O2 concentrations. For example, in three of four experiments where pH was manipulated to 0.4-0.5 below ambient pH, no significant change was evident in extracellular H2O2 concentrations relative to controls. An influence was sometimes inferred from zooplankton density, but not consistently between different incubation experiments, and no change in H2O2 was evident in controlled experiments using different densities of the copepod Calanus finmarchicus grazing on the diatom Skeletonema costatum (< 1 % change in [H2O2] comparing copepod densities from 1 to 10 L-1). Instead, the changes in H2O2 concentration contrasting high-and low-zooplankton incubations appeared to arise from the resulting changes in bacterial activity. The correlation between bacterial abundance and extracellular H2O2 was stronger in some incubations than others (R2 range 0.09 to 0.55), yet high bacterial densities were consistently associated with low H2O2. Nonetheless, the main control on H2O2 concentrations during incubation experiments relative to those in ambient, unenclosed waters was the regulation of incident light. In an open (lidless) mesocosm experiment in Gran Canaria, H2O2 was persistently elevated (2-6-fold) above ambient concentrations; whereas using closed high-density polyethylene mesocosms in Crete, Svalbard and Patagonia H2O2 within incubations was always reduced (median 10 %-90 %) relative to ambient waters.
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| 6. |
- Hopwood, Mark J., et al.
(författare)
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Fe(II) stability in coastal seawater during experiments in Patagonia, Svalbard, and Gran Canaria
- 2020
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 17, s. 1327-1342
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Tidskriftsartikel (refereegranskat)abstract
- © Author(s) 2020. The speciation of dissolved iron (DFe) in the ocean is widely assumed to consist almost exclusively of Fe(III)-ligand complexes. Yet in most aqueous environments a poorly defined fraction of DFe also exists as Fe(II), the speciation of which is uncertain. Here we deploy flow injection analysis to measure in situ Fe(II) concentrations during a series of mesocosm/microcosm/multistressor experiments in coastal environments in addition to the decay rate of this Fe(II) when moved into the dark. During five mesocosm/microcosm/multistressor experiments in Svalbard and Patagonia, where dissolved (0.2 μ m) Fe and Fe(II) were quantified simultaneously, Fe(II) constituted 24 %-65 % of DFe, suggesting that Fe(II) was a large fraction of the DFe pool. When this Fe(II) was allowed to decay in the dark, the vast majority of measured oxidation rate constants were less than calculated constants derived from ambient temperature, salinity, pH, and dissolved O2. The oxidation rates of Fe(II) spikes added to Atlantic seawater more closely matched calculated rate constants. The difference between observed and theoretical decay rates in Svalbard and Patagonia was most pronounced at Fe(II) concentrations < 2 nM, suggesting that the effect may have arisen from organic Fe(II) ligands. This apparent enhancement of Fe(II) stability under post-bloom conditions and the existence of such a high fraction of DFe as Fe(II) challenge the assumption that DFe speciation in coastal seawater is dominated by ligand boundFe(III) species.
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| 7. |
- Lundin, Daniel
(författare)
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The HiPIMS Process
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis involves experimental and theoretical studies related to a thin film deposition technique called high power impulse magnetron sputtering (HiPIMS), and more specifically the plasma properties and how they influence the coating. HiPIMS is an ionized physical vapor deposition technique based on conventional direct current magnetron sputtering (DCMS). The major difference between the two methods is that HiPIMS has the added advantage of providing substantial ionization of the sputtered material, and thus presents many new opportunities for the coating industry. Understanding the dynamics of the charged species and their effect on thin film growth in the HiPIMS process is therefore essential for producing high-quality coatings.In the first part of the thesis a new type of anomalous electron transport was found. Investigations of the transport resulted in the discovery that this phenomenon could quantitatively be described as being related and mediated by highly nonlinear waves, likely due to the modified two-stream instability, resulting in electric field oscillations in the MHz-range (the lower hybrid frequency). Measurements in the plasma confirmed these oscillations as well as trends predicted by the theory of these types of waves. Using electric probes, the degree of anomalous transport in the plasma could also be determined by measuring the current density ratio between the azimuthal current density (of which the Hall current density is one contribution) and the discharge current density, Jϕ / JD. The results were verified in another series of measurements using Rogowski probes to directly gain insight into the internal currents in the HiPIMS discharge. The results provided important insights into understanding the mechanism behind the anomalous transport.It was furthermore demonstrated that the current ratio Jϕ / JD is inversely proportional to the transverse resistivity, η⊥ , which governs how well momentum in the direction of the current is transferred from the electrons to the ions in the plasma. By looking at the forces involved in the charged particle transport it was expected that the azimuthally rotating electrons would exert a volume force on the ions tangentially outwards from the circular race track region. The effect of having an anomalous transport would therefore be that the ions were transported across the magnetic field lines and to a larger extent deflected sideways, instead of solely moving from the target region towards a substrate placed in front of the target some distance away. From the experiments it was confirmed that a substantial fraction of sputtered material is transported radially away from the cathode and lost to the walls in HiPIMS as well as in DCMS, but more so for HiPIMS giving one possible explanation to why the deposition rate is lower for HiPIMS compared to DCMS. Moreover, in a separate investigation on the energy flux it could be determined that the heating due to radial energy flux reached as much as 60 % of the axial energy flux, which is likely a result of the anomalous transport of charged species present in the HiPIMS discharge. Also, the recorded ion energy flux confirmed theoretical estimations on this type of transport regarding energy and direction.In order to gain a better understanding of the complete discharge regime, as well as providing a link between the HiPIMS and DCMS processes, the current and voltage characteristics were investigated for discharge pulses longer than 100 μs. The current behavior was found to be strongly correlated with the chamber gas pressure. Based on these experiments it was suggested that high-current transients commonly seen in the HiPIMS process cause a depletion of the working gas in the area in front of the target, and thereby a transition to a DCMS-like high voltage, lower current regime, which alters the deposition conditions.In the second part of the thesis, using the results and ideas from the fundamental plasma investigations, it was possible to successfully implement different coating improvements. First, the concept of sideways deposition of thin films was examined in a dual-magnetron system providing a solution for coating complex shaped surfaces. Here, the two magnetrons were facing each other having opposing magnetic fields forcing electrons, and thereby also ionized material to be transported radially towards the substrate. In this way deposition inside tubular substrates can be made in a beneficial way.Last, the densification process of thin films using HiPIMS was investigated for eight different materials (Al, Ti, Cr, Cu, Zr, Ag, Ta, and Pt). Through careful characterization of the thin film properties it was determined that the HiPIMS coatings were approximately 5-15 % denser compared to the DCMS coatings. This could be attributed to the increased ion bombardment seen in the HiPIMS process, where the momentum transfer between the growing film and the incoming ions is very efficient due to the equal mass of the atoms constituting the film and the bombarding species, leading to a less pronounced columnar microstructure. The deposition conditions were also examined using a global plasma model, which was in good agreement with the experimental results.
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