137 results
Search Results
Now showing 1 - 10 of 137
- ItemMaking limb and nadir measurements comparable: A common volume study of PMC brightness observed by Odin OSIRIS and AIM CIPS(Amsterdam [u.a.] : Elsevier Science, 2017) Benze, Susanne; Gumbel, Jörg; Randall, Cora E.; Karlsson, Bodil; Hultgren, Kristoffer; Lumpe, Jerry D.; Baumgarten, GerdCombining limb and nadir satellite observations of Polar Mesospheric Clouds (PMCs) has long been recognized as problematic due to differences in observation geometry, scattering conditions, and retrieval approaches. This study offers a method of comparing PMC brightness observations from the nadir-viewing Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument and the limb-viewing Odin Optical Spectrograph and InfraRed Imaging System (OSIRIS). OSIRIS and CIPS measurements are made comparable by defining a common volume for overlapping OSIRIS and CIPS observations for two northern hemisphere (NH) PMC seasons: NH08 and NH09. We define a scattering intensity quantity that is suitable for either nadir or limb observations and for different scattering conditions. A known CIPS bias is applied, differences in instrument sensitivity are analyzed and taken into account, and effects of cloud inhomogeneity and common volume definition on the comparison are discussed. Not accounting for instrument sensitivity differences or inhomogeneities in the PMC field, the mean relative difference in cloud brightness (CIPS - OSIRIS) is −102 ± 55%. The differences are largest for coincidences with very inhomogeneous clouds that are dominated by pixels that CIPS reports as non-cloud points. Removing these coincidences, the mean relative difference in cloud brightness reduces to −6 ± 14%. The correlation coefficient between the CIPS and OSIRIS measurements of PMC brightness variations in space and time is remarkably high, at 0.94. Overall, the comparison shows excellent agreement despite different retrieval approaches and observation geometries.
- ItemGeophysical investigation of a freshwater lens on the island of Langeoog, Germany – Insights from combined HEM, TEM and MRS data(Amsterdam [u.a.] : Elsevier Science, 2017) Costabel, Stephan; Siemon, Bernhard; Houben, Georg; Günther, ThomasA multi-method geophysical survey, including helicopter-borne electromagnetics (HEM), transient electromagnetics (TEM), and magnetic resonance sounding (MRS), was conducted to investigate a freshwater lens on the North Sea island of Langeoog, Germany. The HEM survey covers the entire island and gives an overview of the extent of three freshwater lenses that reach depths of up to 45 m. Ground-based TEM and MRS were conducted particularly on the managed western lens to verify the HEM results and to complement the lithological information from existing boreholes. The results of HEM and TEM are in good agreement. Salt- and freshwater-bearing sediments can, as expected, clearly be distinguished due to their individual resistivity ranges. In the resistivity data, a large transition zone between fresh- and saltwater with a thickness of up to 20 m is identified, the existence of which is verified by borehole logging and sampling. Regarding lithological characterisation of the subsurface, the MRS method provides more accurate and reliable results than HEM and TEM. Using a lithological index derived from MRS water content and relaxation time, thin aquitard structures as well as fine and coarse sand aquifers can be distinguished. Complementing the existing borehole data with the lithology information estimated from MRS, we generate a map showing the occurrence of aquitard structures, which significantly improves the hydrogeological model of the island. Moreover, we demonstrate that the estimates of groundwater conductivity in the sand aquifers from geophysical data are in agreement with the fluid conductivity measured in the boreholes.
- ItemRisk assessment of a cold argon plasma jet in respect to its mutagenicity(Amsterdam [u.a.] : Elsevier Science, 2016) Wende, K.; Bekeschus, S.; Schmidt, A.; Jatsch, L.; Hasse, S.; Weltmann, K.D.; Masur, K.; von Woedtke, T.Cold atmospheric pressure plasmas represent a favorable option for the treatment of heat sensitive materials and human or animal tissue. Beneficial effects have been documented in a variety of medical conditions, e.g., in the treatment of chronic wounds. It is assumed that the main mechanism of the plasma’s efficacy is mediated by a stimulating dissipation of energy via radiation and/or chemical energy. Although no evidence on undesired side effects of a plasma treatment has yet been presented, skepticism toward the safety of the exposure to plasma is present. However, only little data regarding the mutagenic potential of this new treatment option is available. Accordingly, we investigated the mutagenic potential of an argon plasma jet (kinpen) using different testing systems in accordance with ISO norms and multiple cell lines: a HPRT1 mutation assay, a micronucleus formation assay, and a colony formation assay. Moderate plasma treatment up to 180 s did not increase genotoxicity in any assay or cell type investigated. We conclude that treatment with the argon plasma jet kinpen did not display a mutagenic potential under the test conditions applied and may from this perspective be regarded as safe for the use in biomedical applications.
- ItemThermal annealing to influence the vapor sensing behavior of co-continuous poly(lactic acid)/polystyrene/multiwalled carbon nanotube composites(Amsterdam [u.a.] : Elsevier Science, 2020) Li, Yilong; Pionteck, Jürgen; Pötschke, Petra; Voit, BrigitteWith the main purpose of being used as vapor leakage detector, the volatile organic compound (VOC) vapor sensing properties of conductive polymer blend composites were studied. Poly(lactic acid)/polystyrene/multi-walled carbon nanotube (PLA/PS/MWCNT) based conductive polymer composites (CPCs) in which the polymer components exhibit different interactions with the vapors, were prepared by melt mixing. CPCs with a blend composition of 50/50 wt% resulted in the finest co-continuous structure and selective MWCNT localization in PLA. Therefore, these composites were selected for sensor tests. Thermal annealing was applied aiming to maintain the blend structure but improving the sensing reversibility of CPC sensors towards high vapor concentrations. Different sensing protocols were applied using acetone (good solvent for PS and PLA) and cyclohexane (good solvent for PS but poor solvent for PLA) vapors. Increasing acetone vapor concentration resulted in increased relative resistance change (Rrel) of CPCs. Saturated cyclohexane vapor resulted in lower response than nearly saturated acetone vapor. The thermal annealing at 150 °C did not change the blend morphology but increased the PLA crystallinity, making the CPC sensors more resistant to vapor stimulation, resulting in lower Rrel but better reversibility after vapor exposure.
- ItemCarbon leakage in a fragmented climate regime: The dynamic response of global energy markets(Amsterdam [u.a.] : Elsevier Science, 2013) Arroyo-Currás, Tabaré; Bauer, Nico; Kriegler, Elmar; Schwanitz, Valeria Jana; Luderer, Gunnar; Aboumahboub, Tino; Giannousakis, Anastasis; Hilaire, JérômeAs a global climate agreement has not yet been achieved, a variety of national climate policy agendas are being pursued in different parts of the world. Regionally fragmented climate policy regimes are prone to carbon leakage between regions, which has given rise to concerns about the environmental effectiveness of this approach. This study investigates carbon leakage through energy markets and the resulting macro-economic effects by exploring the sensitivity of leakage to the size and composition of pioneering regions that adopt ambitious climate action early on. The study uses the multi-regional energy–economy–climate model REMIND 1.5 to analyze the implications of Europe, China and the United States taking unilateral or joint early action. We find that carbon leakage is the combined effect of fossil fuel and capital market re-allocation. Leakage is limited to 15% of the emission reductions in the pioneering regions, and depends on the size and composition of the pioneering coalition and the decarbonization strategy in the energy sector. There is an incentive to delay action to avoid near-term costs, but the immediate GDP losses after acceding to a global climate regime can be higher in the case of delayed action compared to early action. We conclude that carbon leakage is not a strong counter-argument against early action by pioneers to induce other regions to adopt more stringent mitigation.
- ItemImpacts of a sudden stratospheric warming on the mesospheric metal layers(Amsterdam [u.a.] : Elsevier Science, 2017) Feng, Wuhu; Kaifler, Bernd; Marsh, Daniel R.; Höffner, Josef; Hoppe, Ulf-Peter; Williams, Bifford P.; Plane, John M.C.We report measurements of atomic sodium, iron and temperature in the mesosphere and lower thermosphere (MLT) made by ground-based lidars at the ALOMAR observatory (69°N, 16°E) during a major sudden stratospheric warming (SSW) event that occurred in January 2009. The high resolution temporal observations allow the responses of the Na and Fe layers to the SSW at high northern latitudes to be investigated. A significant cooling with temperatures as low as 136 K around 90 km was observed on 22–23 January 2009, along with substantial depletions of the Na and Fe layers (an ~80% decrease in the column abundance with respect to the mean over the observation period). The Whole Atmosphere Community Climate Model (WACCM) incorporating the chemistry of Na, Fe, Mg and K, and nudged with reanalysis data below 60 km, captures well the timing of the SSW, although the extent of the cooling and consequently the depletion in the Na and Fe layers is slightly underestimated. The model also predicts that the perturbations to the metal layers would have been observable even at equatorial latitudes. The modelled Mg layer responds in a very similar way to Na and Fe, whereas the K layer is barely affected by the SSW because of the enhanced conversion of K+ ions to K atoms at the very low temperatures.
- ItemGround reaction forces and external hip joint moments predict in vivo hip contact forces during gait(Amsterdam [u.a.] : Elsevier Science, 2022) Alves, Sónia A.; Polzehl, Jörg; Brisson, Nicholas M.; Bender, Alwina; Agres, Alison N.; Damm, Philipp; Duda, Georg N.Younger patients increasingly receive total hip arthroplasty (THA) as therapy for end-stage osteoarthritis. To maintain the long-term success of THA in such patients, avoiding extremely high hip loads, i.e., in vivo hip contact force (HCF), is considered essential. However, in vivo HCFs are difficult to determine and their direct measurement is limited to instrumented joint implants. It remains unclear whether external measurements of ground reaction forces (GRFs), a non-invasive, markerless and clinic-friendly measure can estimate in vivo HCFs. Using data from eight patients with instrumented hip implants, this study determined whether GRF time series data, alone or combined with other scalar variables such as hip joint moments (HJMs) and lean muscle volume (LMV), could predict the resultant HCF (rHCF) impulse using a functional linear modeling approach. Overall, single GRF time series data did not predict in vivo rHCF impulses. However, when GRF time series data were combined with LMV of the gluteus medius or sagittal HJM using a functional linear modeling approach, the in vivo rHCF impulse could be predicted from external measures only. Accordingly, this approach can predict in vivo rHCF impulses, and thus provide patients with useful insight regarding their gait behavior to avoid hip joint overloading.
- ItemInfluence of annealing on microstructure and mechanical properties of ultrafine-grained Ti45Nb(Amsterdam [u.a.] : Elsevier Science, 2019) Völker, B.; Maier-Kiener, V.; Werbach, K.; Müller, T.; Pilz, S.; Calin, M.; Eckert, J.; Hohenwarter, A.Beta-Ti alloys have been intensively investigated in the last years because of their favorable low Young's moduli, biocompatibility and bio-inertness, making these alloys interesting candidates for implant materials. Due to their low mechanical strength, efforts are currently devoted to increasing it. A promising way to improve the strength is to tailor the microstructure using severe plastic deformation (SPD). In this investigation high pressure torsion was used to refine the microstructure of a Ti-45wt.%Nb alloy inducing a grain size of ~50 nm. The main focus of the subsequent investigations was devoted to the thermal stability of the microstructure. Isochronal heat-treatments performed for 30 min in a temperature range up to 500 °C caused an increase of hardness with a peak value at 300 °C before the hardness decreased at higher temperatures. Simultaneously, a distinct temperature-dependent variation of the Young's modulus was also measured. Tensile tests revealed an increase in strength after annealing compared to the SPD-state. Microstructural investigations showed that annealing causes the formation of α-Ti. The findings suggest that the combination of severe plastic deformation with subsequent heat treatment provides a feasible way to improve the mechanical properties of SPD-deformed β-Ti alloys making them suitable for higher strength applications.
- ItemDesigning the microstructural constituents of an additively manufactured near β Ti alloy for an enhanced mechanical and corrosion response(Amsterdam [u.a.] : Elsevier Science, 2022) Hariharan, Avinash; Goldberg, Phil; Gustmann, Tobias; Maawad, Emad; Pilz, Stefan; Schell, Frederic; Kunze, Tim; Zwahr, Christoph; Gebert, AnnettAdditive manufacturing of near β-type Ti-13Nb-13Zr alloys using the laser powder bed fusion process (LPBF) opens up new avenues to tailor the microstructure and subsequent macro-scale properties that aids in developing new generation patient-specific, load-bearing orthopedic implants. In this work, we investigate a wide range of LPBF parameter space to optimize the volumetric energy density, surface characteristics and melt track widths to achieve a stable process and part density of greater than 99 %. Further, optimized sample states were achieved via thermal post-processing using standard capability aging, super-transus (900 °C) and sub-transus (660 °C) heat treatment strategies with varying quenching mediums (air, water and ice). The applied heat treatment strategies induce various fractions of α, martensite (α', α'') in combination with the β phase and strongly correlated with the observed enhanced mechanical properties and a relatively low elastic modulus. In summary, our work highlights a practical strategy for optimizing the mechanical and corrosion properties of a LPBF produced near β-type Ti-13Nb-13Zr alloy via careful evaluation of processing and post-processing steps and the interrelation to the corresponding microstructures. Corrosion studies revealed excellent corrosion resistances of the heat-treated LPBF samples comparable to wrought Ti-13Nb-13Zr alloys.
- ItemSurface defects reduce Carbon Nanotube toxicity in vitro(Amsterdam [u.a.] : Elsevier Science, 2019) Requardt, Hendrik; Braun, Armin; Steinberg, Pablo; Hampel, Silke; Hansen, TanjaThe cytotoxicity of two different types of Multi-walled Carbon Nanotubes (MWCNTs)in A549 lung epithelial cells and HepG2 hepatocytes was investigated. One MWCNT still contained iron that was used as a catalyst during production, while the other one had all iron removed in a post-production heat treatment resulting in significantly fewer surface defects. The WST-8 assay was applied to test cell viability. To check the integrity of the cell membrane, we performed the lactate dehydrogenases assay (LDH)and measured the cellular production of reactive oxygen species (ROS). Finally, to examine cell proliferation, we conducted a cell cycle analysis. The results showed a dose- and time-dependent decrease in cell viability for both MWCNTs in both cell types. Moreover, a dose- and time-dependent increase in LDH leakage was detected, thereby indicating a decreased membrane integrity. The production of ROS was significantly increased in the case of the heat-treated MWCNTs. The heat-treated MWCNTs showed significantly stronger adverse effects when compared to the non-treated MWCNTs. Additionally, the heat-treated MWCNTs induced a dose-dependent cell cycle arrest in A549 cells. Both MWCNTs induced a significant cytotoxicity, whereby the heat treatment, leading to a decrease in surface defects, further increased the indicated adverse effects. © 2019 The Authors