| 1. |
- Lindvall, Kristoffer
(author)
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Time Spectral Methods - Towards Plasma Turbulence Modelling
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Energy comes in two forms; potential energy and kinetic energy. Energyis stored as potential energy and released in the form of kinetic energy. This process of storage and release is the basic strategy of all energy alternatives in use today. This applies to solar, wind, fossil fuels, and the list goes on. Most of these come in diluted and scarce forms allowing only a portion of the energy to be used, which has prompted the quest for the original source, the Sun.As early as 1905 in the work by Albert Einstein on the connection between mass and energy, it has been seen theoretically that energy can be extracted from the process of fusing lighter elements into heavier elements. Later, this process of fusion was discovered to be the very source powering the Sun. Almost a century later, the work continues to make thermonuclear fusion energy a reality.Looking closer at the Sun, we see that it consists of a hot burning gas subject to electromagnetic fields, i.e. a plasma. The plasma in the Sun is contained by the massive gravitational force which allows for fusion to be created in a stable and continuous process. Taking inspiration from the Sun we see that a hot plasma and its containment are key to achieving fusion. The gravitational force is not present on Earth, and creating it artificially is, a sof today, an insurmountable task. Fortunately, the plasma can be contained in another way; with magnetic fields.The challenges of making fusion a viable energy source are numerous and diverse. To deal with these challenges there are several fields of fusion research; engineering, physics, and numerical analysis. These of course overlap, but serve to illustrate the focus of different groups. This thesis work is focused on the latter two, physics and numerical analysis.The containment of the plasma in a fusion device is degraded by drift wave turbulence. The turbulence in the plasma occurs on the micro-scale, namely on the scale of particles travelling around the magnetic field lines. The physics behind turbulence and the drift waves responsible is a rich field with many future topics.Since the micro-turbulence can quickly grow and diffuse plasma throughout the device in a matter of micro-seconds, it becomes a difficult challenge to numerically resolve the turbulence over a longer span of time. The typical confinement times required in a fusion device is on the order of several seconds. Thus, the main focus of this thesis is on developing a numerical method that can effectively resolve the plasma physics over longer time-intervals. To this effect, a Time-Spectral method has been developed that utilizes the advantageous properties of spectral methods to all domains, specifically the temporal domain. The numerical method has been implemented on compressible Navier-Stokes, ideal magnetohydrodynamics (MHD), and a toroidal two-fluid plasma turbulence model called the Weiland model.
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| 2. |
- Lindvalll, Kristoffer, et al.
(author)
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2D continuous Chebyshev-Galerkin time-spectral method
- 2022
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In: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 271, s. 108217-108217
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Journal article (peer-reviewed)abstract
- A fully spectral multi-domain method has been developed and applied to three applications within ideal MHD, compressible Navier-Stokes, and a two-fluid plasma turbulence model named the Weiland model. The time-spectral method employed is the Generalized Weighted Residual Method (GWRM), where all domains such as space, time, and parameter space are spectrally decomposed with Chebyshev polynomials. The spectral decomposition of the temporal domain allows the GWRM to reach spectral accuracy in all dimensions. The GWRM linear/nonlinear algebraic equations are solved using an Anderson Acceleration (AA) method and a newly developed Quasi Semi-Implicit root solver (Q-SIR). Up to 85% improved convergence rate was obtained for Q-SIR as compared to AA and in certain cases only Q-SIR converged. In the most challenging simulations, featuring steep gradients, the GWRM converged for time intervals roughly two times larger than typical time steps for explicit time-marching schemes, being limited by the CFL condition. Time intervals up to 70 times larger than those of explicit time-marching schemes were used in smooth regions. Furthermore, the most computationally expensive algorithm, namely the product of two Chebyshev series, has been GPU accelerated with speedup gains of several thousands compared to a CPU.
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| 3. |
- Scheffel, Jan, 1954-
(author)
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On the Solvability of the Mind–Body Problem
- 2020
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In: Axiomathes. - : Springer. - 1122-1151 .- 1572-8390. ; 30:3, s. 289-312
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Journal article (peer-reviewed)abstract
- The mind–body problem is analyzed in a physicalist perspective. By combining the concepts of emergence and algorithmic information theory in a thought experiment, employing a basic nonlinear process, it is shown that epistemologically emergent properties may develop in a physical system. Turning to the signi cantly more com- plex neural network of the brain it is subsequently argued that consciousness is epis- temologically emergent. Thus reductionist understanding of consciousness appears not possible; the mind–body problem does not have a reductionist solution. The ontologically emergent character of consciousness is then identi ed from a com- binatorial analysis relating to universal limits set by quantum mechanics, implying that consciousness is fundamentally irreducible to low-level phenomena.
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| 4. |
- Scheffel, Jan, 1954-
(author)
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On the solvability of the mind–body problem
- 2020
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Other publication (pop. science, debate, etc.)abstract
- The mind-body problem is one of the most enigmatic issues in philosophy that has yet to be resolved. Professor Jan Scheffel from KTH Royal Institute of Technology, Sweden analyses the mind–body problem from a physicalist perspective. He finds that consciousness is epistemologically emergent and shows that this result overlaps with the problem of free will. If a theory for consciousness could be constructed, free will would not exist. Professor Scheffel discloses that the mind–body problem cannot be solved reductionistically and evolves the notion of emergence in an argument for free will.
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| 5. |
- Scheffel, Jan, 1954-, et al.
(author)
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Temporal smoothing - A step forward for time-spectral methods
- 2022
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In: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 270
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Journal article (peer-reviewed)abstract
- Time-spectral methods may feature substantial advantages over time-stepping solvers for solution of initial-value ODEs and PDEs, but their efficiency depends on the smoothness of the solution. We present two methods to overcome this problem. The first involves transforming the differential equation to an equation for a new variable, related to the time-integrated solution, before applying the solution algorithm. In the second method, a procedure for transformation to exact differential equations of a running average is outlined. Examples of solution of stiff problems and problems with multiple time scales are presented, employing the time-spectral Generalized Weighted Residual Method (GWRM). It is found that the smoothing algorithms have a significant positive effect on convergence.
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| 6. |
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| 7. |
- Ölmefors, Oscar, et al.
(author)
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High school student perspectives on flipped classroom learning
- 2021
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In: Pedagogy, Culture & Society. - : Informa UK Limited. - 1468-1366 .- 1747-5104. ; , s. 1-18
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Journal article (peer-reviewed)abstract
- Flipped classroom pedagogics has become a widely used approach within blended learning. The aim of the present study is to add students’ perspectives on the flipped classroom as used as a pedagogical method in a Swedish upper secondary school. In this qualitative study, eight students participated in focus group interviews. Problems were found both for neurotypical students as well as for a neurodiverse student. Unless special care is taken, students with neurodiversity may not be given equal opportunities for learning, in conflict with Swedish school legislation. Issues are discussed that need to be addressed when introducing flipped classroom course design at high school level.
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