The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Peter Berg - One of the best experts on this subject based on the ideXlab platform.
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Technical note: Measurements and data analysis of sediment–water Oxygen Flux using a new dual-optode eddy covariance instrument
Biogeosciences, 2020Co-Authors: Markus Huettel, Peter Berg, Alireza MerikhiAbstract:Abstract. Sediment–water Oxygen Fluxes are widely used as a proxy for organic carbon production and mineralization at the seafloor. In situ Fluxes can be measured non-invasively with the aquatic eddy covariance technique, but a critical requirement is that the sensors of the instrument are able to correctly capture the high-frequency variations in dissolved Oxygen concentration and vertical velocity. Even small changes in sensor characteristics during deployment as caused, e.g. by biofouling can result in erroneous Flux data. Here we present a dual-optode eddy covariance instrument (2OEC) with two fast Oxygen fibre sensors and document how erroneous Flux interpretations and data loss can effectively be reduced by this hardware and a new data analysis approach. With deployments over a carbonate sandy sediment in the Florida Keys and comparison with parallel benthic advection chamber incubations, we demonstrate the improved data quality and data reliability facilitated by the instrument and associated data processing. Short-term changes in Flux that are dubious in measurements with single Oxygen sensor instruments can be confirmed or rejected with the 2OEC and in our deployments provided new insights into the temporal dynamics of benthic Oxygen Flux in permeable carbonate sands. Under steady conditions, representative benthic Flux data can be generated with the 2OEC within a couple of hours, making this technique suitable for mapping sediment–water, intra-water column, or atmosphere–water Fluxes.
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Technical note: Measurements and data analysis of sediment-water Oxygen Flux using a new dual-optode eddy covariance instrument
2020Co-Authors: Markus Huettel, Peter Berg, Alireza MerikhiAbstract:Abstract. Sediment-water Oxygen Fluxes are widely used as a proxy for organic carbon production and mineralization at the seafloor. In-situ Fluxes can be measured non-invasively with the aquatic eddy covariance technique, but a main weakness of the commonly used instrumentation is the susceptibility of the delicate Oxygen microsensors required for the high frequency measurements to disturbances. Even small changes in sensor characteristics during deployment as caused e.g. by biofouling can result in erroneous Flux data. Here we present a dual-optode eddy covariance instrument (2OEC) with two fast Oxygen fiber sensors and document how erroneous Flux interpretations and data loss can effectively be reduced by this hardware and a new data analysis approach. With deployments over a carbonate sandy sediment in the Florida Keys and comparison with parallel benthic advection-chamber incubations, we demonstrate the improved data quality and data reliability facilitated by the instrument and associated data processing. Short-term changes in Flux that are questionable in single Oxygen sensor instruments can be confirmed or rejected with the 2OEC and in our deployments provided new insights into the temporal dynamics of benthic Oxygen Flux in permeable carbonate sands. With the 2OEC, reliable benthic Flux data can be generated within a couple of hours, making this technique suitable for mapping sediment-water, intra-water column, or atmosphere-water Fluxes.
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Stream Oxygen Flux and metabolism determined with the open water and aquatic eddy covariance techniques
Limnology and Oceanography, 2015Co-Authors: Dirk Koopmans, Peter BergAbstract:We quantified Oxygen Flux in a coastal stream in Virginia using a novel combination of the conventional open water technique and the aquatic eddy covariance technique. The latter has a smaller footprint (sediment surface area that contributes to the Flux; ∼ 10 m2), allowing measurements to be made at multiple sites within the footprint of the open water technique (∼ 1000 m2). Sites included an unvegetated stream pool with cohesive sediment, a macrophyte bed with sandy sediment, and an unvegetated sand bed with rippled bedforms. Nighttime eddy covariance Oxygen uptake was always smaller than uptake produced by the open water technique. At the pool and unvegetated sand bed sites, nighttime eddy covariance uptake was 20-fold smaller than open water uptake. At the macrophyte bed site, gross primary production quantified with the two techniques was similar but eddy covariance uptake was 2.4-fold smaller. The difference in Oxygen uptake between eddy covariance and open water techniques could not be accounted for by uncertainties in the gas transfer velocity but could be accounted for by anoxic groundwater inflow through stream banks outside of the eddy covariance footprint. Nighttime Oxygen uptake was also measured with eddy covariance in a tidal freshwater part of the stream, where pore space in the sandy sediment near the sediment–water interface was flushed with stream water at peak water velocities. As a result of this advective hyporheic exchange, nighttime Oxygen Flux increased fourfold with a doubling of water velocity.
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Eddy correlation measurements of Oxygen Fluxes in permeable sediments exposed to varying current flow and light
Limnology and Oceanography, 2013Co-Authors: Peter Berg, Markus Huettel, Matthew H. Long, Jennie E. Rheuban, Karen J. Mcglathery, Robert W. Howarth, Kenneth H. Foreman, Anne E. Giblin, Roxanne MarinoAbstract:Based on noninvasive eddy correlation measurements at a marine and a freshwater site, this study documents the control that current flow and light have on sediment–water Oxygen Fluxes in permeable sediments. The marine sediment was exposed to tidal-driven current and light, and the Oxygen Flux varied from night to day between 229 and 78 mmol m22 d21. A fitting model, assuming a linear increase in Oxygen respiration with current flow, and a photosynthesis–irradiance curve for light-controlled production reproduced measured Fluxes well (R2 5 0.992) and revealed a 4-fold increase in Oxygen uptake when current velocity increased from , 0t o 20 cm s 21. Application of the model to a week-long measured record of current velocity and light showed that net ecosystem metabolism varied substantially among days, between 227 and 31 mmol m22 d21, due to variations in light and current flow. This variation is likely typical of many shallow-water systems and highlights the need for long-term Flux integrations to determine system metabolism accurately. At the freshwater river site, the sediment–water Oxygen Flux ranged from 2360 to 137 mmol m22 d21. A direct comparison during nighttime with concurrent benthic chamber incubations revealed a 4.1 times larger eddy Flux than that obtained with chambers. The current velocity during this comparison was 31 cm s 21 , and the large discrepancy was likely caused by poor imitation by the chambers of the natural pore-water flushing at this high current velocity. These results emphasize the need for more noninvasive Oxygen Flux measurements in permeable sediments to accurately assess their role in local and global carbon budgets.
Thierry Chartier - One of the best experts on this subject based on the ideXlab platform.
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Improvement of Oxygen Flux through perovskite membranes using a coating of ultra-divided particles
Chemical Engineering Science, 2016Co-Authors: L. Guironnet, Pierre-marie Geffroy, Nicolas Richet, Thierry ChartierAbstract:Abstract In the last decades, numerous mixed ionic and electronic conducting materials with a perovskite structure have been investigated for their potential applications as membrane materials for Oxygen separation applications. This work shows that significant improvement of electrochemical properties of two perovskite materials, La0.6Sr0.4Fe0.8Co0.2O3-δ (LSFCo6482) and La0.5Sr0.5Fe0.7Ga0.3O3-δ (LSFG5573) is obtained using ultra-divided particles perovskite coating. This coating is obtained by dip-coating thanks to a derived sol-gel synthesis route. The ultra-divided particles have a grain size distribution from 300 to 500 nm. The Oxygen Flux measured using a specific setup shows that the Oxygen surface exchange kinetics and bulk diffusion coefficient depend on the microstructure and the chemical composition of the coating material. The relation established between chemical formulation, microstructure, and Oxygen Flux were used to design optimized membranes.
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New route for high Oxygen semi-permeation through surface-modified dense La1−xSrxFe1−yGayO3−δ perovskite membranes
Journal of Membrane Science, 2014Co-Authors: Aurélien Vivet, Elsa Thune, Claire Bonhomme, Nicolas Richet, Fabrice Rossignol, Pierre-marie Geffroy, Thierry ChartierAbstract:La1−xSrxFe1−yGayO3−δ perovskite membranes are promising candidates for catalytic membrane reactors applications due to their potential high Oxygen semi-permeation Fluxes and good chemical stability in working conditions. The Oxygen Flux through La1−xSrxFe1−yGayO3−δ perovskite membranes is mainly governed by Oxygen exchanges at the membrane surface. This work shows how to strongly increase such an Oxygen Flux while developing a dedicated ultra-divided surface coating. Such a coating is obtained by following a route derived from sol-gel and allowing an elementary grain diameter control in the 5-10 nm range. In this way, the Oxygen Fluxes through the coated membrane can be increased of more than an order of magnitude in comparison to uncoated membranes. This paper clearly shows that the Oxygen Flux through the uncoated membrane is governed by Oxygen surface exchange, while for coated membranes it is governed by a balance between surface exchange and bulk diffusion. Our surface-modified dense La1−xSrxFe1−yGayO3−δ membranes show good performance in long term in working conditions (high temperature and large Oxygen partial pressure gradients).
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Influence of Oxygen surface exchanges on Oxygen semi-permeation through La(1-x)SrxFe(1-y)GayO3- dense
Journal of The Electrochemical Society, 2011Co-Authors: Pierre-marie Geffroy, Aurélien Vivet, Pascal Del-gallo, Nicolas Richet, Jacques Fouletier, Thierry ChartierAbstract:Because of high Oxygen semi-permeation and very good chemical stability, La0.8Sr0.2Fe0.7Ga0.3O3 d perovskite is one of the most promising materials as a catalytic membrane reactor for hydrogen production. In this paper, Oxygen semi-permeation of La0.8Sr0.2Fe0.7Ga0.3O3 d membranes with different architectures is studied over a large range of temperatures in order to identify the rate determining step of the Oxygen Flux through the membrane. We show that the Oxygen Flux through the membrane is governed by the surface exchanges on the membrane reducing face. Besides, these results are confirmed by potentiometric measurements of Oxygen activity on both membrane faces under Oxygen partial pressure gradient. Finally, new architectures with La0.8Sr0.2Fe0.7Ni0.3O3 d porous catalytic layer on membrane reducing surface are tested to improve the performances of Oxygen semi-permeation.
S. Geis - One of the best experts on this subject based on the ideXlab platform.
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Transepidermal Oxygen Flux during arterial occlusion using ratiometric luminescence imaging.
Clinical hemorheology and microcirculation, 2017Co-Authors: M. Ranieri, S. Klein, Christian D. Taeger, A. Kotrade, J. Dolderer, L. Prantl, S. GeisAbstract:BACKGROUND: A physiological Oxygen transport through a circulatory and microcirculatory system is essential for execution of cellular functions. Several pathological conditions e.g. infections, ischemia, cancer, diabetes, hypertension or chronic wounds show a change of Oxygen distribution and Oxygen tension in cellular microenvironment. Additionally complex operative procedures in order to reconstruct tissue defects require a reliable monitoring of microcirculation. OBJECTIVE: Target of this study was to evaluate skin Oxygenation during an ischemia-reperfusion experiment using transepidermal Oxygen Flux imaging. METHODS: Twelve patients at the Department of Plastic and Reconstructive surgery of the University hospital of Regensburg underwent to elective hand operations. During the operation a tourniquet is standardly set on the upper arm to create ischemia in order to facilitate the operative procedure. Measurements were performed at the different time intervals: in rest, under ischemia and after reperfusion. RESULTS: The transepidermal Oxygen Flux increased during the ischemic condition compared to normal condition and decreased to a lower value during reperfusion (rest: 0.043 +/- 0.007, ischemia: 0.063 +/- 0.014, reperfusion: 0.030 +/- 0.028). CONCULSION: Transepidermal Oxygen Flux imaging by ratiometric luminescence imaging seems to be a reliable tool to assess skin Oxygenation. However dynamic changes seem to be more informative than absolute thresholds. Further investigations are necessary to prove these promising results.
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Transepidermal Oxygen Flux measurement – First clinical application for postoperative wound monitoring
Clinical hemorheology and microcirculation, 2017Co-Authors: M. Ranieri, S. Klein, Christian D. Taeger, A. Kotrade, Michael Nerlich, J. Dolderer, L. Prantl, S. GeisAbstract:BACKGROUND: Measurement of skin Oxygen is of great interest in diverse fields of medicine. Different pathologies, e.g. infection, ischemia cancer or chronic wounds show a characteristic Oxygen distribution and skin Oxygen tension. Additionally diverse operative procedures require a reliable postoperative monitoring in order to ensure success of the therapy. OBJECTIVE: Aim of this study was to assess transepidermal Oxygen Flux for postoperative wound monitoring after operative treatment of fractures close to the hip. METHODS: 22 patients underwent transepidermal Oxygen Flux measurement at the first postoperative day. Transepidermal Oxygen Flux measurement was performed using ratiometric luminescence imaging. Examination was conducted in close proximity to the operation wound. The corresponding area at the contralateral side served as reference. RESULTS: Oxygen Flux in the operation area was higher (0.084 +/- 0.021) than the contralateral side (0.071 +/- 0.029). CONCLUSIONS: Transepidermal Oxygen Flux imaging by ratiometric luminescence imaging seems to be a reliable tool to assess postoperative wound healing. However further investigations in greater populations and under pathologic conditions have to be performed to prove these first results.
Markus Huettel - One of the best experts on this subject based on the ideXlab platform.
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Technical note: Measurements and data analysis of sediment–water Oxygen Flux using a new dual-optode eddy covariance instrument
Biogeosciences, 2020Co-Authors: Markus Huettel, Peter Berg, Alireza MerikhiAbstract:Abstract. Sediment–water Oxygen Fluxes are widely used as a proxy for organic carbon production and mineralization at the seafloor. In situ Fluxes can be measured non-invasively with the aquatic eddy covariance technique, but a critical requirement is that the sensors of the instrument are able to correctly capture the high-frequency variations in dissolved Oxygen concentration and vertical velocity. Even small changes in sensor characteristics during deployment as caused, e.g. by biofouling can result in erroneous Flux data. Here we present a dual-optode eddy covariance instrument (2OEC) with two fast Oxygen fibre sensors and document how erroneous Flux interpretations and data loss can effectively be reduced by this hardware and a new data analysis approach. With deployments over a carbonate sandy sediment in the Florida Keys and comparison with parallel benthic advection chamber incubations, we demonstrate the improved data quality and data reliability facilitated by the instrument and associated data processing. Short-term changes in Flux that are dubious in measurements with single Oxygen sensor instruments can be confirmed or rejected with the 2OEC and in our deployments provided new insights into the temporal dynamics of benthic Oxygen Flux in permeable carbonate sands. Under steady conditions, representative benthic Flux data can be generated with the 2OEC within a couple of hours, making this technique suitable for mapping sediment–water, intra-water column, or atmosphere–water Fluxes.
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Technical note: Measurements and data analysis of sediment-water Oxygen Flux using a new dual-optode eddy covariance instrument
2020Co-Authors: Markus Huettel, Peter Berg, Alireza MerikhiAbstract:Abstract. Sediment-water Oxygen Fluxes are widely used as a proxy for organic carbon production and mineralization at the seafloor. In-situ Fluxes can be measured non-invasively with the aquatic eddy covariance technique, but a main weakness of the commonly used instrumentation is the susceptibility of the delicate Oxygen microsensors required for the high frequency measurements to disturbances. Even small changes in sensor characteristics during deployment as caused e.g. by biofouling can result in erroneous Flux data. Here we present a dual-optode eddy covariance instrument (2OEC) with two fast Oxygen fiber sensors and document how erroneous Flux interpretations and data loss can effectively be reduced by this hardware and a new data analysis approach. With deployments over a carbonate sandy sediment in the Florida Keys and comparison with parallel benthic advection-chamber incubations, we demonstrate the improved data quality and data reliability facilitated by the instrument and associated data processing. Short-term changes in Flux that are questionable in single Oxygen sensor instruments can be confirmed or rejected with the 2OEC and in our deployments provided new insights into the temporal dynamics of benthic Oxygen Flux in permeable carbonate sands. With the 2OEC, reliable benthic Flux data can be generated within a couple of hours, making this technique suitable for mapping sediment-water, intra-water column, or atmosphere-water Fluxes.
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Eddy correlation measurements of Oxygen Fluxes in permeable sediments exposed to varying current flow and light
Limnology and Oceanography, 2013Co-Authors: Peter Berg, Markus Huettel, Matthew H. Long, Jennie E. Rheuban, Karen J. Mcglathery, Robert W. Howarth, Kenneth H. Foreman, Anne E. Giblin, Roxanne MarinoAbstract:Based on noninvasive eddy correlation measurements at a marine and a freshwater site, this study documents the control that current flow and light have on sediment–water Oxygen Fluxes in permeable sediments. The marine sediment was exposed to tidal-driven current and light, and the Oxygen Flux varied from night to day between 229 and 78 mmol m22 d21. A fitting model, assuming a linear increase in Oxygen respiration with current flow, and a photosynthesis–irradiance curve for light-controlled production reproduced measured Fluxes well (R2 5 0.992) and revealed a 4-fold increase in Oxygen uptake when current velocity increased from , 0t o 20 cm s 21. Application of the model to a week-long measured record of current velocity and light showed that net ecosystem metabolism varied substantially among days, between 227 and 31 mmol m22 d21, due to variations in light and current flow. This variation is likely typical of many shallow-water systems and highlights the need for long-term Flux integrations to determine system metabolism accurately. At the freshwater river site, the sediment–water Oxygen Flux ranged from 2360 to 137 mmol m22 d21. A direct comparison during nighttime with concurrent benthic chamber incubations revealed a 4.1 times larger eddy Flux than that obtained with chambers. The current velocity during this comparison was 31 cm s 21 , and the large discrepancy was likely caused by poor imitation by the chambers of the natural pore-water flushing at this high current velocity. These results emphasize the need for more noninvasive Oxygen Flux measurements in permeable sediments to accurately assess their role in local and global carbon budgets.
Jong Hoon Joo - One of the best experts on this subject based on the ideXlab platform.
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elucidation of the Oxygen surface kinetics in a coated dual phase membrane for enhancing Oxygen permeation Flux
ACS Applied Materials & Interfaces, 2017Co-Authors: Jeong Hwan Park, Jong Hyuk Park, Jong Hoon JooAbstract:The dual-phase membrane has received much attention as the solution to the instability of the Oxygen permeation membrane. It has been reported that the Oxygen Flux of the dual-phase membrane is greatly enhanced by the active coating layer. However, there has been little discussion about the enhancement mechanism by surface coating in the dual-phase membrane. This study investigates the Oxygen Flux of the Ce0.9Gd0.1O2−δ–La0.7Sr0.3MnO3±δ (GDC 80 vol %/LSM 20 vol %) composite membrane depending on the Oxygen partial pressure (PO2) to elucidate the mechanism of enhanced Oxygen Flux by the surface modification in the fluorite-rich phase dual-phase membrane. The Oxygen permeation resistances were obtained from the Oxygen Flux as a function of PO2 using the Oxygen permeation model. The surface exchange coefficient (k) and the bulk diffusion coefficient (D) were calculated from these resistances. According to the calculated k and D values, we concluded that the active coating layer (La0.6Sr0.4CoO3−δ) significantl...
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Substantial Oxygen Flux in Dual-Phase Membrane of Ceria and Pure Electronic Conductor by Tailoring the Surface
ACS applied materials & interfaces, 2015Co-Authors: Jong Hoon Joo, Kyong Sik Yun, Jung-hwa Kim, Younki Lee, Chung-yul YooAbstract:The Oxygen permeation Flux of dual-phase membranes, Ce0.9Gd0.1O2−δ–La0.7Sr0.3MnO3±δ (GDC/LSM), has been systematically studied as a function of their LSM content, thickness, and coating material. The electronic percolation threshold of this GDC/LSM membrane occurs at about 20 vol % LSM. The coated LSM20 (80 vol % GDC, 20 vol % LSM) dual-phase membrane exhibits a maximum Oxygen Flux of 2.2 mL·cm–2·min–1 at 850 °C, indicating that to enhance the Oxygen permeation Flux, the LSM content should be adjusted to the minimum value at which electronic percolation is maintained. The Oxygen ion conductivity of the dual-phase membrane is reliably calculated from Oxygen Flux data by considering the effects of surface Oxygen exchange. Thermal cycling tests confirm the mechanical stability of the membrane. Furthermore, a dual-phase membrane prepared here with a cobalt-free coating remains chemically stable in a CO2 atmosphere at a lower temperature (800 °C) than has previously been achieved.
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Dramatically Enhanced Oxygen Fluxes in Fluorite-Rich Dual-Phase Membrane by Surface Modification
Chemistry of Materials, 2014Co-Authors: Jong Hoon Joo, Kyong Sik Yun, Younki Lee, Jaewon Jung, Chung-yul YooAbstract:Dual-phase ceramic membranes with very high Oxygen Flux have been designed by taking into account the volume fraction of the fluorite phase, membrane thickness, and surface modification. The Oxygen Flux of Ce0.9Gd0.1O2−δ–La0.6Sr0.4Co0.2Fe0.8O3−δ (GDC–LSCF) dual-phase membranes has been systematically investigated as a function of membrane thickness and volume fraction of the fluorite phase with or without surface modification. The percolation threshold of the composites for electronic conduction has been determined to be about 20 vol % of LSCF by general effective-medium theory. The Oxygen Flux of uncoated fluorite phase-rich membrane (80 vol % GDC–20 vol % LSCF) with 30-μm thickness exhibits a low Oxygen Flux (8.0 × 10–3 mL·cm–2·min–1 at 850 °C) under an air/He gradient, indicating that the permeation is controlled by only the surface-exchange kinetics of GDC. With both sides coated with La0.6Sr0.4CoO3−δ (LSC), the Flux of the membrane (3.6 mL·cm–2·min–1 at 850 °C) has been dramatically enhanced by about...
