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- Ahlberg, Erik, et al.
(författare)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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| 5. |
- Larsson, Inger, et al.
(författare)
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Interferon production in glia and glioma cell lines
- 1978
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Ingår i: Infection and Immunity. - 1098-5522. ; 22:3, s. 786-789
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Tidskriftsartikel (refereegranskat)abstract
- Interferon (IF) was produced in glia and glioma cell lines in titers comparable to those produced by human fibroblasts. It was inducible by both Sendai virus and polyriboinosinic:polyribocytidylic acid. "Superinduction" resulted in up to 500-fold-higher titers of IF. The IF appeared to be of the fibroblast type, as revealed by experiments using heat treatment, assay of antiviral activity in heterologous cell lines, and neutralization with specific antisera. Since large amounts of IF may easily be produced with glioma cell lines, such cells may be suitable for mass production of IF.
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| 6. |
- Lundgren, Erik, 1988-
(författare)
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Exploring and modeling response process data from PISA : inferences related to motivation and problem-solving
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores and models response process data from large-scale assessments, focusing on test-taking motivation, problem-solving strategies, and questionnaire response validity. It consists of four studies, all using data from PISA (Programme for International Student Assessment) data.Study I processed and clustered log-file data to create a behavioral evaluation of students' effort applied to a PISA problem-solving item, and examined the relationship between students' behavioral effort, self-reported effort, and test performance. Results show that effort invested before leaving the task unsolved was positively related to performance, while effort invested before solving the tasks was not. Low effort before leaving the task unsolved was further related to lower self-reported effort. The findings suggest that test-taking motivation could only be validly measured from efforts exerted before giving up.Study II used response process data to infer students' problem-solving strategies on a PISA problem-solving task, and investigated the efficiency of strategies and their relationship to PISA performance. A text classifier trained on data from a generative computational model was used to retrieve different strategies, reaching a classification accuracy of 0.72, which increased to 0.90 with item design changes. The most efficient strategies used information from the task environment to make plans. Test-takers classified as selecting actions randomly performed worse overall. The study concludes that computational modeling can inform score interpretation and item design.Study III investigated the relationship between motivation to answer the PISA student questionnaire and test performance. Departing from the theory of satisficing in surveys a Bayesian finite mixture model was developed to assess questionnaire-taking motivation. Results showed that overall motivation was high, but decreased toward the end. The questionnaire-taking motivation was positively related to performance, suggesting that it could be a proxy for test-taking motivation, however, reading skills may affect the estimation.Study IV examines the validity of composite scores assessing reading metacognition, using a Bayesian finite mixture model that jointly considers response times and sequential patterns in subitem responses. The results show that, the relatively high levels of satisficing (up to 30%) negatively biased composite scores. The study highlights the importance of considering response time data and subitem response patterns when the validity of scores from the student questionnaire.In conclusion, response process data from international large-scale assessments can provide valuable insights into test-takers’ motivation, problem-solving strategies, and questionnaire validity.
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| 7. |
- Lundgren, Jonas, 1993-, et al.
(författare)
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Flow–heat topology optimization of internally cooled high temperature applications using a voxelization approach for domain initialization
- 2023
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Ingår i: Engineering optimization (Print). - : Taylor & Francis. - 0305-215X .- 1029-0273.
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented for obtaining topology optimized designs for internally cooled high temperature applications, using a flexible geometry description, by means of a voxelization methodology and a novel boundary detection algorithm. A conjugate heat transfer approach is taken; the physics is described by a Stokes-Brinkman model for the flow, weakly coupled with a convection-diffusion model for the heat transfer. A practically relevant optimization formulation, consisting of a maximum temperature objective with a mass flow constraint, is used, and applied to an industrial-relevant non-trivial geometry resembling a guide vane in a gas turbine. Temperatures and velocities from the optimized design are compared with the response from a Stokes flow model with body-fitted mesh and a high-fidelity Reynolds-averaged Navier-Stokes model. A comparison of the performance from a mixed and a penalty approach for solving the flow problem is included. The voxelization approach shows good promise for handling complex design domains.
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| 8. |
- Lundgren, Jonas, 1993-
(författare)
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Internal Cooling Design Using Multiphysics Topology Optimization
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates topology optimization (TO) as a tool for designing optimal internal cooling configurations in components subjected to external hot gas streams. The work is motivated by the challenge of simultaneously considering objectives from multiple physics domains, and the rapid development of additive manufacturing (AM) in the industry, which makes it possible to realize highly complex TO designs. Against this background, a multi-physics TO approach is employed, involving the following physics domains: • Fluid mechanics: describes the flow of the coolant • Heat transfer: describes the coolant and component temperatures • Solid mechanics: describes the structural behaviour of the component Density-based TO is used to parametrize the design, such that the interpolation between solid and fluid material properties is governed by a spatially varying design variable. Temperature measures are considered as objectives in the non-convex optimization problems, and coolant mass flow and structural stiffness measures are considered as constraints. The design process is iterative: for a given design, the flow velocities are computed and used to calculate the temperature distribution, which in turn influences the domain’s structural response. These three equilibrium state problems are solved sequentially, followed by solving corresponding adjoint problems in reversed order, to acquire first-order sensitivity information used by the gradient-based optimization solver. Numerical simulations are carried out for geometries of varying degrees of complexity, resembling gas turbine guide vanes. The simulations cover a range of fidelity levels: from simpler 2D setups to more complex 3D setups with fine resolution, intended for execution on high-performance computing (HPC) clusters. Low-fidelity flow models are utilized in the TO process, while more advanced flow models are employed for design comparisons, and flow and heat response comparisons for given TO designs. The thesis consists of two parts: the first provides the theoretical framework, and the second includes appended papers. In Paper I, only the heat problem is included when modelling convection on internal boundaries identified using the design gradient. Fluid and solid mechanics are introduced in Paper II, where a conjugate heat transfer problem is augmented with a structural model coupled through thermal strains, with numerical examples in 3D. In Paper III, the simultaneous consideration of flow and heat objectives is formulated as a mathematical game between two players trying to minimize the average temperature in the domain and the coolant mass flow through the domain, respectively, with examples in 2D and 3D. The flow problems are the computational bottlenecks, and therefore, Paper IV demonstrates a 3D implementation investigating two different numerical techniques for solving the flow problem, with a voxelization approach for efficient meshing of complex geometries. Paper V presents an efficient, massively parallel HPC implementation for three-field flow-heat-structural models, and addresses further implementation details. This thesis highlights challenging aspects of large-scale multiphysics TO considering fluid mechanics, heat transfer, and solid mechanics.
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| 9. |
- Lundgren, Jonas, et al.
(författare)
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Topology optimization of periodic 3D heat transfer problems with 2D design
- 2019
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Ingår i: Structural and multidisciplinary optimization (Print). - : SPRINGER. - 1615-147X .- 1615-1488. ; 60:6, s. 2295-2303
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Tidskriftsartikel (refereegranskat)abstract
- We consider a model for density-based topology optimization (TO) of stationary heat transfer problems with design-dependent internal convection in 3D structures with periodic design obtained by extruding a 2D design in 3D. The internal convection takes place at the interface between a solid material and a cooling fluid in internal channels through the design domain. The objective of the TO is to minimize the maximum temperature, which is approximated by means of an L-p norm. The finite element method is used to discretize the state problem and the resulting optimization problem is solved using gradient-based methods. The internal convection is modeled to be dependent on the design density gradient in the continuous problem. In discrete form, it is approximated as proportional to the difference in design densities of adjacent elements in the finite element mesh. The theory is illustrated by numerical examples based on a simplified guide vane geometry.
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| 10. |
- Miörner, Håkan, et al.
(författare)
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Regulation of mitogen-induced lymphocyte DNA synthesis by human interferon of different origins
- 1978
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Ingår i: Cellular Immunology. - : Elsevier BV. - 0008-8749. ; 35:1, s. 15-24
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Tidskriftsartikel (refereegranskat)abstract
- Human fibroblast and leukocyte interferons were found to suppress lymphocyte mitogenesis induced by optimal doses of phytohemagglutinin and concanavalin A. In certain situations (low doses of mitogen and/or low doses of interferon), however, interferon significantly enhanced mitogenesis. In experiments using varying concentrations of interferon, dose-response curves with different slopes were obtained for fibroblast and leukocyte interferons. The effect of interferon was apparently exerted during early stages of the lymphocyte cell cycle. There was no inhibitory effect of interferon if the lymphocytes were washed with medium before being exposed to mitogen. Interferon increased the binding of radiolabeled mitogens to cells. The results suggest that the immunological effects of interferon are consequences of actions on lymphoid cells. Fibroblast and leukocyte interferons seem to have different modes of action, or to bind differently to target cells. Possible mechanisms for the suppressive and enhancing effects of interferons on lymphoid cells are discussed.
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