| 1. |
- Hauser, Tobias, et al.
(författare)
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Material transitions within multi-material laser deposited intermetallic Iron Aluminides
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- Laser Metal Deposition is a near-net-shape processing technology, which allows remarkable freedom in multi-material processing. In the present work, the multi-material processing of two intermetallic iron aluminides, Fe28Al(at.%) and Fe30Al5Ti0.7B(at.%), was investigated. It has been shown that multi-material processing of the two alloys via discrete as well as via gradual material transition is possible without any cracks for manufacturing small cubes. Cross-sections of manufactured parts and tracks showed that a preheating temperature of at least 400 °C is necessary to process crack free samples. EDX-analyses indicated that if a discrete material transition is required in multi-material processing, the material transition should be implemented in the vertical build-up direction because the mixing zone in this direction is significantly smaller than the mixing zone in the horizontal direction. Due to the stronger mixing effects in the horizontal direction, a gradual material transition by a linear progression should be implemented in this direction rather than in the vertical direction. The mixing effects are mainly caused by melt flow, while diffusion effects can be neglected.
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| 2. |
- Heinze, Christoph, et al.
(författare)
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ESD Reviews : Climate feedbacks in the Earth system and prospects for their evaluation
- 2019
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Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 10:3, s. 379-452
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Forskningsöversikt (refereegranskat)abstract
- Earth system models (ESMs) are key tools for providing climate projections under different scenarios of human-induced forcing. ESMs include a large number of additional processes and feedbacks such as biogeochemical cycles that traditional physical climate models do not consider. Yet, some processes such as cloud dynamics and ecosystem functional response still have fairly high uncertainties. In this article, we present an overview of climate feedbacks for Earth system components currently included in state-of-the-art ESMs and discuss the challenges to evaluate and quantify them. Uncertainties in feedback quantification arise from the interdependencies of biogeochemical matter fluxes and physical properties, the spatial and temporal heterogeneity of processes, and the lack of long-term continuous observational data to constrain them. We present an outlook for promising approaches that can help to quantify and to constrain the large number of feedbacks in ESMs in the future. The target group for this article includes generalists with a background in natural sciences and an interest in climate change as well as experts working in interdisciplinary climate research (researchers, lecturers, and students). This study updates and significantly expands upon the last comprehensive overview of climate feedbacks in ESMs, which was produced 15 years ago (NRC, 2003).
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| 3. |
- Heinze, Christoph, et al.
(författare)
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The ocean carbon sink – impacts, vulnerabilities, and challenges
- 2015
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Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 6, s. 327-358
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide (CO 2 ) is, next to water vapour, considered to be the most important natural green- house gas on Earth. Rapidly rising atmospheric CO 2 concentrations caused by human actions such as fossil fuel burning, land-use change or cement production over the past 250 years have given cause for concern that changes in Earth’s climate system may progress at a much faster pace and larger extent than during the past 20 000 years. Investigating global carbon cycle pathways and finding suitable adaptation and mitigation strate- gies has, therefore, become of major concern in many research fields. The oceans have a key role in regulating atmospheric CO 2 concentrations and currently take up about 25 % of annual anthropogenic carbon emissions to the atmosphere. Questions that yet need to be answered are what the carbon uptake kinetics of the oceans will be in the future and how the increase in oceanic carbon inventory will affect its ecosystems and their services. This requires comprehensive investigations, including high-quality ocean carbon measurements on different spatial and temporal scales, the management of data in sophisticated databases, the application of Earth system models to provide future projections for given emission scenarios as well as a global synthesis and outreach to policy makers. In this paper, the current understanding of the ocean as an important carbon sink is reviewed with re- spect to these topics. Emphasis is placed on the complex interplay of different physical, chemical and biological processes that yield both positive and negative air–sea flux values for natural and anthropogenic CO 2 as well as on increased CO 2 (uptake) as the regulating force of the radiative warming of the atmosphere and the gradual acidification of the oceans. Major future ocean carbon challenges in the fields of ocean observations, modelling and process research as well as the relevance of other biogeochemical cycles and greenhouse gases are discussed
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| 4. |
- Heinze, Christoph, et al.
(författare)
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The quiet crossing of ocean tipping points
- 2021
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:9
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic climate change profoundly alters the ocean's environmental conditions, which, in turn, impact marine ecosystems. Some of these changes are happening fast and may be difficult to reverse. The identification and monitoring of such changes, which also includes tipping points, is an ongoing and emerging research effort. Prevention of negative impacts requires mitigation efforts based on feasible research-based pathways. Climate-induced tipping points are traditionally associated with singular catastrophic events (relative to natural variations) of dramatic negative impact. High-probability high-impact ocean tipping points due to warming, ocean acidification, and deoxygenation may be more fragmented both regionally and in time but add up to global dimensions. These tipping points in combination with gradual changes need to be addressed as seriously as singular catastrophic events in order to prevent the cumulative and often compounding negative societal and Earth system impacts.
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| 5. |
- Langhamer, Lukas, et al.
(författare)
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Response of lacustrine glacier dynamics to atmospheric forcing in the Cordillera Darwin
- 2024
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; , s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Calving glaciers respond quickly to atmospheric variability through ice dynamic adjustment. Particularly, single weather extremes may cause changes in ice-flow velocity and terminus position. Occasionally, this can lead to substantial event-driven mass loss at the ice front. We examine changes in terminus position, ice-flow velocity, and calving flux at the grounded la-custrine Schiaparelli Glacier in the Cordillera Darwin using geo-referenced time-lapse camera images and remote sensing data (Sentinel-1) from 2015 to 2022. Lake-level records, lake discharge measurements, and a coupled energy and mass balance model provide insight into the subglacial water discharge. We use downscaled reanalysis data (ERA-5) to identify climate extremes and track land-falling atmospheric rivers to investigate the ice-dynamic response on possible atmospheric drivers.
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| 6. |
- Moritz, Juliane, et al.
(författare)
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Influence of Two-Step Heat Treatments on Microstructure and Mechanical Properties of a β-Solidifying Titanium Aluminide Alloy Fabricated via Electron Beam Powder Bed Fusion
- 2023
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Ingår i: Advanced Engineering Materials. - : John Wiley & Sons. - 1438-1656 .- 1527-2648. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing technologies, particularly electron beam powder bed fusion (PBF-EB/M), are becoming increasingly important for the processing of intermetallic titanium aluminides. This study presents the effects of hot isostatic pressing (HIP) and subsequent two-step heat treatments on the microstructure and mechanical properties of the TNM-B1 alloy (Ti–43.5Al–4Nb–1Mo–0.1B) fabricated via PBF-EB/M. Adequate solution heat treatment temperatures allow the adjustment of fully lamellar (FL) and nearly lamellar (NL-β) microstructures. The specimens are characterized by optical microscopy and scanning electron microscopy (SEM), X-ray computed tomography (CT), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The mechanical properties at ambient temperatures are evaluated via tensile testing and subsequent fractography. While lack-of-fusion defects are the main causes of failure in the as-built condition, the mechanical properties in the heat-treated conditions are predominantly controlled by the microstructure. The highest ultimate tensile strength is achieved after HIP due to the elimination of lack-of-fusion defects. The results reveal challenges originating from the PBF-EB/M process, for example, local variations in chemical composition due to aluminum evaporation, which in turn affect the microstructures after heat treatment. For designing suitable heat treatment strategies, particular attention should therefore be paid to the microstructural characteristics associated with additive manufacturing.
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| 7. |
- Olsen, Are, 1972, et al.
(författare)
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The Arctic Carbon Cycle: Patterns, Impacts and Possible Changes
- 2015
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Ingår i: The New Arctic. Evengård, Birgitta et al (eds.). - Switzerland : Springer International Publishing. - 9783319176017 ; , s. 95-115
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Bokkapitel (refereegranskat)abstract
- Land and ocean uptake and release of carbon dioxide and methane play important roles for regulating their atmospheric concentrations. For example, over the industrialised period the terrestrial biosphere and global oceans have acted as net sinks of carbon dioxide, having absorbed CO2 corresponding to more than 50 % of the accumulated emissions from fossil fuel burning, cement production and land-use change. This uptake has clearly reduced the human footprint on climate development. However, we cannot expect that the strength of these sinks will remain unaltered in the future as the processes that are involved are sensitive to climate change. This is in particular the case for the Arctic where ocean circulation changes, sea-ice and permafrost thaw and increased land and ocean primary production—all excerting direct influence on CO2 and methane—are expected to occur. Further, the ocean uptake of CO2 leads to ocean acidification that may have deletorious effects on many marine organisms. The Arctic Ocean appears particularly vulnerable to this threat. In this contribution we provide an overview of the land and ocean components of the Arctic carbon cycle and their climate change sensitivities.
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| 8. |
- Seland, Øyvind, et al.
(författare)
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Overview of the Norwegian Earth System Model (NorESM2) and key climate response of CMIP6 DECK, historical, and scenario simulations
- 2020
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 13:12, s. 6165-6200
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Tidskriftsartikel (refereegranskat)abstract
- The second version of the coupled Norwegian Earth System Model (NorESM2) is presented and evaluated. NorESM2 is based on the second version of the Community Earth System Model (CESM2) and shares with CESM2 the computer code infrastructure and many Earth system model components. However, NorESM2 employs entirely different ocean and ocean biogeochemistry models. The atmosphere component of NorESM2 (CAM-Nor) includes a different module for aerosol physics and chemistry, including interactions with cloud and radiation; additionally, CAM-Nor includes improvements in the formulation of local dry and moist energy conservation, in local and global angular momentum conservation, and in the computations for deep convection and air-sea fluxes. The surface components of NorESM2 have minor changes in the albedo calculations and to land and sea-ice models. We present results from simulations with NorESM2 that were carried out for the sixth phase of the Coupled Model Intercomparison Project (CMIP6). Two versions of the model are used: one with lower (similar to 2 degrees) atmosphere-land resolution and one with medium (similar to 1 degrees) atmosphere-land resolution. The stability of the pre-industrial climate and the sen- sitivity of the model to abrupt and gradual quadrupling of CO2 are assessed, along with the ability of the model to simulate the historical climate under the CMIP6 forcings. Compared to observations and reanalyses, NorESM2 represents an improvement over previous versions of NorESM in most aspects. NorESM2 appears less sensitive to greenhouse gas forcing than its predecessors, with an estimated equilibrium climate sensitivity of 2.5 K in both resolutions on a 150-year time frame; however, this estimate increases with the time window and the climate sensitivity at equilibration is much higher. We also consider the model response to future scenarios as defined by selected Shared Socioeconomic Pathways (SSPs) from the Scenario Model Intercomparison Project defined under CMIP6. Under the four scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5), the warming in the period 2090-2099 compared to 1850-1879 reaches 1.3, 2.2, 3.0, and 3.9 K in NorESM2-LM, and 1.3, 2.1, 3.1, and 3.9 K in NorESM-MM, robustly similar in both resolutions. NorESM2-LM shows a rather satisfactory evolution of recent sea-ice area. In NorESM2-LM, an ice-free Arctic Ocean is only avoided in the SSP1-2.6 scenario.
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| 9. |
- Watson, Andrew J., et al.
(författare)
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Tracking the Variable North Atlantic Sink for Atmospheric CO2
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 326:5958, s. 1391-1393
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Tidskriftsartikel (refereegranskat)abstract
- The oceans are a major sink for atmospheric carbon dioxide (CO2). Historically, observations have been too sparse to allow accurate tracking of changes in rates of CO2 uptake over ocean basins, so little is known about how these vary. Here, we show observations indicating substantial variability in the CO2 uptake by the North Atlantic on time scales of a few years. Further, we use measurements from a coordinated network of instrumented commercial ships to define the annual flux into the North Atlantic, for the year 2005, to a precision of about 10%. This approach offers the prospect of accurately monitoring the changing ocean CO2 sink for those ocean basins that are well covered by shipping routes.
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