| 1. |
- Lindwall, Johan, et al.
(author)
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Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting
- 2022
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In: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854 .- 2214-0697. ; 16, s. 1165-1178
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Journal article (peer-reviewed)abstract
- Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.
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| 4. |
- Abelsson, Anna, 1971-
(author)
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Simulering som lärande inom prehospital akutsjukvård
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Den prehospitala akutsjukvården är ett komplext kunskapsfält som innebär att vårdaren skall kunna bemöta patient och närstående, bedöma skada, sjukdom och den aktuella situationen samt avgöra vilka vårdåtgärder som skall prioriteras.Patientens lidande kan lindras genom att vårdaren tränar färdigheter i ett prehospitalt kontext. Detta främjar en god och säker vård samt stärker patientens möjligheter till överlevnad.Resultatet visar på behovet av simulering inom prehospital akutsjukvård. Med simulering lär sig vårdaren att hantera realistiska, dynamiska och komplexa vårdsituationer, vilket skapar kunskaper, färdigheter och erfarenheter av omhändertagande av patient drabbad av högenergitrauma. Simuleringens utformning och miljö skapar förutsättningar för lärandet vilket framkommer i interventionsstudien.Utifrån resultatet i föreliggande forskning utvecklas en modell för lärande med hjälp av simulering.
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| 5. |
- Bergqvist, Tomas, 1962-, et al.
(author)
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Podcasting in School
- 2008
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Reports (other academic/artistic)abstract
- Podcasting is a new phenomenon in Swedish schools. This pa- per describes a project where the main goal is to analyze if the students’ interest in mathematics is affected if the mathematics is made accessible via podcasts and iPods. Teachers at eleven schools were encouraged to produce podcasts as a part of their mathematics teaching in school year eight. The results indicate an increased interest in mathematics and the learning of mathematics among the students. We also found that the tech- nical difficulties for the teachers were underestimated in the project, and that teachers had difficulties in finding time for the production of podcasts.
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| 6. |
- Bergqvist, Tomas, 1962-, et al.
(author)
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Podcasting in school
- 2009
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In: Sixth Research Seminar of the Swedish Society for Research in Mathematics Education (MADIF 6). - In press.
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Conference paper (peer-reviewed)abstract
- Podcasting is a new phenomenon in Swedish schools. This paper describes a project where the main goal is to analyze if the students’ interest in mathematics is affected if the mathematics is made accessible via podcasts and ipods. Teachers at eleven schools were encouraged to produce podcasts as a part of their mathematics teaching in school-year eight. The results indicate an increased interest in mathematics and the learning of mathematics among the students. We also found that the technical difficulties for the teachers were underestimated in the project, and that teachers had difficulties in finding time for the production of podcasts.
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| 7. |
- Chou, Chia-Ying, 1990-
(author)
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Integrated Computational and Experimental Study of Additively Manufactured Steels
- 2023
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Doctoral thesis (other academic/artistic)abstract
- The design freedom Additive Manufacturing (AM) offers provides new solutions for improving functionality in industrial applications. It also offers unique opportunities when it comes to materials design.Powder Bed Fusion – Laser Beam (PBF-LB) is currently one of the most popular commercial AM techniques for metallic materials partly due to the relatively low surface roughness and the large design flexibility. However, the number of materials suitable for the PBF-LB process is still rather low and to accelerate the development of grades tailored for this AM process, dedicated computational tools for alloy design are needed. Of importance for materials design, is computational thermodynamics and kinetics coupled with CALPHAD materials descriptions since it enables calculations for multicomponent materials making it possible to predict the effect of varying composition.In this thesis, computational thermodynamic and kinetics coupled with materials characterization are applied to study the microstructure evolution during PBF-LB. Two material classes are in focus – hot-work tool steels and ferritic stainless steels. For the hot-work tool steel, the cooling rates during PBF-LB processing are high enough to induce martensite transformation and in the as-built microstructure a martensitic matrix is observed and some fraction of retained austenite. A solidification sub-structure due to micro-segregation during printing is also observed. Solidification calculations are performed to predict the micro-segregation showing agreement with experimental measurements. The segregation results are then used as input to a semi-empirical martensite start temperature model making it possible to explain the location and amount of retained austenite.In addition to compositional optimization, a computational framework for AM alloy design needs to include the possibility to tailor the AM post heat treatments. An alternative to the conventional hardening treatment is thus studied in the current work. A model for precipitation kinetics is combined with experimental characterization to explore the effect of tempering on the as-built microstructure in comparison to the tempering effect on an austenitized microstructure. The results show that the precipitation kinetics is strongly dependent on the starting structure and that direct tempering of the as-built microstructure changes the precipitation sequence compared to the conventional heat treatment route. The calculations reproduce this result suggesting that it is a thermodynamic effect stemming from different matrix compositions.The other material class, the ferritic stainless steels, is studied in terms of its response to post-heat treatments. The as-built microstructure is characterized by high dislocation density and a fine grain structure in some cases as well as a solidification sub-structure. The mechanical properties of the as-built material are in general good for these steels, however, stress relieving is most often a required post process for the as-built components which may decrease the mechanical properties. To maximize the gained benefits from the unique process condition of PBF-LB, simulations are applied to study the possibility of post heat treatment optimization.To construct a computational framework for AM materials design, multiscale modeling capabilities are needed. This work shows the value of computational thermodynamics and kinetics for understanding the materials behavior on the microscale and hence, contributes to the construction of such a framework. By understanding the physical metallurgy, and enable modeling of the AM processes, the industrialization of AM can be accelerated.
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| 8. |
- Dahlqvist, Jörgen, et al.
(creator_code:cre_t)
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Praxis
- 2014
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Artistic work (other academic/artistic)
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| 9. |
- Droeser, R. A., et al.
(author)
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Hypoparathyroidism after total thyroidectomy in patients with previous gastric bypass
- 2017
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In: Langenbecks Archives of Surgery. - : Springer Science and Business Media LLC. - 1435-2443 .- 1435-2451. ; 402:2, s. 273-280
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Journal article (peer-reviewed)abstract
- Purpose Case reports suggest that patients with previous gastric bypass have an increased risk of severe hypocalcemia after total thyroidectomy, but there are no population-based studies. The prevalence of gastric bypass before thyroidectomy and the risk of hypocalcemia after thyroidectomy in patients with previous gastric bypass were investigated. Methods By cross-linking The Scandinavian Quality Registry for Thyroid, Parathyroid and Adrenal Surgery with the Scandinavian Obesity Surgery Registry patients operated with total thyroidectomy without concurrent or previous surgery for hyperparathyroidism were identified and grouped according to previous gastric bypass. The risk of treatment with intravenous calcium during hospital stay, and with oral calcium and vitamin D at 6 weeks and 6 months postoperatively was calculated by using multiple logistic regression in the overall cohort and in a 1:1 nested case-control analysis. Results We identified 6115 patients treated with total thyroidectomy. Out of these, 25 (0.4 %) had undergone previous gastric bypass surgery. In logistic regression, previous gastric bypass was not associated with treatment with i.v. calcium (OR 2.05, 95 % CI 0.48-8.74), or calcium and/or vitamin D at 6 weeks (1.14 (0.39-3.35), 1.31 (0.39-4.42)) or 6 months after total thyroidectomy (1.71 (0.40-7.32), 2.28 (0.53-9.75)). In the nested case-control analysis, rates of treatment for hypocalcemia were similar in patients with and without previous gastric bypass. Conclusion Previous gastric bypass surgery was infrequent in patients undergoing total thyroidectomy and was not associated with an increased risk of postoperative hypocalcemia.
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| 10. |
- Ericsson, A., et al.
(author)
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Transient nucleation in selective laser melting of Zr-based bulk metallic glass
- 2020
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In: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 195
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Journal article (peer-reviewed)abstract
- The crystallization rate during selective laser melting (SLM) of bulk metallic glasses (BMG) is a critical factor in maintaining the material's amorphous structure. To increase the understanding of the interplay between the SLM process and the crystallization behavior of BMGs, a numerical model based on the classical nucleation theory has been developed that accounts for the rapid temperature changes associated with SLM. The model is applied to SLM of a Zr-based BMG and it is shown that the transient effects, accounted for by the model, reduce the nucleation rate by up to 15 orders of magnitude below the steady-state nucleation rate on cooling, resulting in less nuclei during the build process. The capability of the proposed modelling approach is demonstrated by comparing the resulting crystalline volume fraction to experimental findings. The agreement between model predictions and the experimental results clearly suggests that transient nucleation effects must be accounted for when considering the crystallization rate during SLM processing of BMGs.
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