A "poor man's" approach for high-resolution three-dimensional topology optimization of natural convection problems

This paper treats topology optimization of natural convection problems. A simplified model is suggested to describe the flow of an incompressible fluid in steady state conditions, similar to Darcy's law for fluid flow in porous media. The equations for the fluid flow are coupled to the thermal convection-diffusion equation through the Boussinesq approximation. The coupled non-linear system of equations is discretized with stabilized finite elements and solved in a parallel framework that allows for the optimization of high resolution three-dimensional problems. A density-based topology optimization approach is used, where a two-material interpolation scheme is applied to both the permeability and conductivity of the distributed material. Due to the simplified model, the proposed methodology allows for a significant reduction of the computational effort required in the optimization. At the same time, it is significantly more accurate than even simpler models that rely on convection boundary conditions based on Newton's law of cooling. The methodology discussed herein is applied to the optimization-based design of three-dimensional heat sinks. The final designs are formally compared with results of previous work obtained from solving the full set of Navier-Stokes equations. The results are compared in terms of performance of the optimized designs and computational cost. The computational time is shown to be decreased to around 5-20% in terms of core-hours, allowing for the possibility of generating an optimized design during the workday on a small computational cluster and overnight on a high-end desktop

Replicating the effect of brain stimulation on mind wandering: A pre-registered study

Mind wandering (MW) is a common mental phenomenon. Despite this, there is still much we don’t know about this pervasive mental state. Transcranial direct current stimulation (tDCS) has been proposed to be able to modulate mind wandering propensity, but a large variability in results paints an inconclusive picture in the current brain stimulation literature, and a satisfactory conclusion is still lacking. Recently, a study by Boayue et al. (2020) reported to successfully reduce mind wandering using high-definition transcranial direct current stimulation (HD-tDCS) over the dorsolateral prefrontal cortex, providing preliminary evidence of the efficacy of HD-tDCS in modulating MW. The current thesis introduces the topic of replicating this elusive effect of non-invasive brain stimulation in depth, as well as reporting a high-powered, pre-registered direct replication attempt of the effect found by Boayue et al. (2020). Additionally, the results of investigating MW with a finger-tapping random sequence generation task that draws heavily on executive resources are reported. We failed to replicate the original effect of reducing MW during HD-tDCS, and in a meta-analytic approach, when the data was combined with Boayue et al. (2020) the original effect of HD-tDCS reducing MW disappeared. These findings and potential problems of brain stimulation studies (in particular their low replicability) and their implications are reviewed and discussed

A "poor man's" approach to topology optimization of natural convection problems

Topology optimization of natural convection problems is computationally expensive, due to the large number of degrees of freedom (DOFs) in the model and its two-way coupled nature. Herein, a method is presented to reduce the computational effort by use of a reduced-order model governed by simplified physics. The proposed method models the fluid flow using a potential flow model, which introduces an additional fluid property. This material property currently requires tuning of the model by comparison to numerical Navier-Stokes based solutions. Topology optimization based on the reduced-order model is shown to provide qualitatively similar designs, as those obtained using a full Navier-Stokes based model. The number of DOFs is reduced by 50% in two dimensions and the computational complexity is evaluated to be approximately 12.5% of the full model. We further compare to optimized designs obtained utilizing Newton's convection law.Comment: Preprint version. Please refer to final version in Structural Multidisciplinary Optimization https://doi.org/10.1007/s00158-019-02215-

Increasing Women's Sexual Agency with Feminist Pornography? A study on and with a feminist organization in Copenhagen on feminist pornography, heterosexuality and sex

Feminist pornography as phenomenon is used as point of departure for discussing and laying out discourses on heterosexuality, sex and sexual agency in women. From a group conversation with the board members of the (for the researcher familiar) feminist organization Selskab for Ligestilling in Copenhagen, I explore if feminist pornography has the potential of contributing to, and increase sexual agency in women. Acknowledging pornography as on/scene suggests that researching (with) a familiar group allows for in-depth conversation and analysis. Queer theory as overall frame gives access to pornographic studies as potential disruptor of what is considered sexual. Besides from legitimizing women as sexual agents pornographic studies thus also opens the opportunity for disrupting heterosexuality. Pornographic studies scholars’ emphasis on authenticity in pornographic material in this case lays out the differing ways women’s sexuality and desires are expressed: from explicit sex to epic films and erotic features to something beyond heterosexual sex acts. This shows that sexual agency is expressed and negotiated in multiple ways. With an emphasis on the contradictions in heterosexuality, queer theory and pornographic studies will thus serve to show how heterosexuality itself possesses the key to its own deconstruction

The effect of transcranial direct current stimulation on the interplay between executive control, behavioral variability and mind wandering: A registered report

Mind wandering (MW) is a mental phenomenon humans experience daily. Yet, we lack a complete understanding of the neural basis of this pervasive mental state. Over the past decade there has been an increase in publications using transcranial direct current stimulation (tDCS) to modulate the propensity to mind wander, but findings are diverse, and a satisfactory conclusion is missing. Recently, Boayue et al. (2020) reported successful reduction of mind wandering using high-definition tDCS (HD-tDCS) over the dorsolateral prefrontal cortex, providing preliminary evidence for the efficacy of HD-tDCS in interfering with mind wandering. The current study is a high-powered, pre-registered direct replication attempt of the effect found by Boayue et al. (2020). In addition, we investigated whether the effects of HD-tDCS on mind wandering would be prolonged and assessed the underlying processes of mind wandering using electroencephalography (EEG) and pupillometry during a finger-tapping random sequence generation task that requires the use of executive resources. We failed to find any evidence of the original effect of reduced MW during and after stimulation. When combining our data with the data from Boayue et al. (2020), the original effect of reduced MW caused by HD-tDCS disappeared. In addition, we observed increased occipital alpha power as task duration increased and increased midfrontal theta power preceding response patterns signaling high executive function use. Finally, tonic and phasic pupil size decreased as task duration increased yet, phasic responses were increased, while tonic responses were reduced preceding reports of MW. Additionally phasic pupil size also showed a tendency to be increased during periods of high executive function use. Importantly, none of the EEG or pupil measures were modulated by HD-tDCS. We conclude that HD-tDCS over the dorsolateral prefrontal cortex does not affect MW propensity and its neural signatures. Furthermore, we recommend that previously reported effects of tDCS on mind wandering and other cognitive functions should only be accepted after a successful pre-registered replication

Intercultural Competence and Postcolonialism in Nye’s Habibi and Gordimer’s “Loot”. Promoting democracy and citizenship through literature in the Norwegian EFL classroom

There is broad agreement that the current use of literature in the Norwegian EFL classroom is not realizing its full educational potential due to a lack of practical approaches and an over ambitious curriculum. Thus, literature has become a rare and limited occurrence where students are asked to read for content and linguistical features, rather than for personal enjoyment and growth. The purpose of this thesis is to investigate the potential of postcolonial literature in facilitating the development of intercultural competence in Norwegian upper-secondary EFL students as a step towards achieving the new interdisciplinary goals of promoting democracy and citizenship. Through providing postcolonial readings of Nadine Gordimer’s short story “Loot” and Naomi Shihab Nye’s young adult novel Habibi and an analysis of the texts in relation to the theories of intercultural competence provided by Barrett et al. and Michael Byram, this thesis seeks to discuss the potential of postcolonial literature as a genre in the development of intercultural competence through personal growth. The thesis found that postcolonial literature lends itself particularly well to the purpose of developing intercultural competence and that the variety within the genre presents a plethora of opportunities for facilitating this development. Specifically, the thesis found that Nye’s Habibi could facilitate intercultural competence through its potential for student identification and imitation of the novel’s main protagonist, and Gordimer’s “Loot” was found to facilitate through challenging the readers preconceptions and focusing on the role of extreme conditions on human behaviour

Gender equality and gender gaps in mathematics performance

In a recent analysis of mathematics performance (Eriksson et al. 2020), national gender egalitarian values were positively associated with an increase in the average mathematics scores of high-school boys relative to girls. This study highlights that progressive gender egalitarian values at a national level might not translate into equality of opportunity at an individual level.PostprintNon peer reviewe

Large scale three-dimensional topology optimisation of heat sinks cooled by natural convection

This work presents the application of density-based topology optimisation to the design of three-dimensional heat sinks cooled by natural convection. The governing equations are the steady-state incompressible Navier-Stokes equations coupled to the thermal convection-diffusion equation through the Bousinessq approximation. The fully coupled non-linear multiphysics system is solved using stabilised trilinear equal-order finite elements in a parallel framework allowing for the optimisation of large scale problems with order of 40-330 million state degrees of freedom. The flow is assumed to be laminar and several optimised designs are presented for Grashof numbers between $10^3$ and $10^6$. Interestingly, it is observed that the number of branches in the optimised design increases with increasing Grashof numbers, which is opposite to two-dimensional optimised designs.Comment: Submitted (18th of August 2015