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Stability Analysis of Switched Linear Systems via Numeric Computations of Continuous Piecewise Affine and Continuous Piecewise Quadratic Lyapunov Functions
(University of Iceland, School of Engineering and Natural Sciences, Faculty of Physical Sciences, 2026-11-20) Andersen, Stefania; Sigurður Hafstein; Faculty of Physical Sciences (UI); Raunvísindadeild (HÍ); School of Engineering and Natural Sciences (UI); Verkfræði- og náttúruvísindasvið (HÍ)
In this dissertation we present numerical methods for computing continuous piecewise affine (CPA) and continuous piecewise quadratic (CPQ) Lyapunov functions via linear programming (LP) for switched linear systems. We discuss the application of these methods to both arbitrary switching signals and signals subject to average dwell-time (ADT) constraints. Further, we discuss the challenges of computing the minimum average dwell-time (MADT) and present a search algorithm for its computation. Finally, we discuss our approach to computing CPQ functions via LP, rather than semidefinite programming (SDP).
Verk
Geothermal fluid extraction and injection-related fracture slip susceptibility and seismicity in naturally fractured rocks
(2024-11) Cao, Wenzhuo; Durucan, Sevket; Shi, Ji Quan; Korre, Anna; Ratouis, Thomas; Hjörleifsdóttir, Vala; Department of Engineering
Understanding fracture slip susceptibility in geothermal reservoirs is central to the control of fluid injection-induced seismicity. To investigate the role of regional fracture systems on induced seismicity, a coupled thermo-hydro-mechanical (THM) model containing fracture networks was developed, which features direct coupling between different physics for explicit fractures, fractured rocks (porous matrix blocks with small-scale fractures) and their interactions, as well as indirect coupling through changes of material properties, such as stress-dependent fracture and rock permeabilities. The model was applied to simulate geothermal fluid extraction and re-injection in a natural fracture system comprised of three dominant fracture sets at the Hellisheiði geothermal field over a 10-year period (2011–2021), utilising field recorded monthly production and re-injection rates. Based on the model results, the slip susceptibility of regional fracture systems was examined under reservoir conditions before and after the start of fluid re-injection across different time scales, i.e., over short (1 month), intermediate (1 year) and long-term (10 years). Two model scenarios, one with cooling contraction and one without, were considered to examine the relative contribution of cooling contraction and fluid overpressure on fracture slip susceptibility. Results have shown that fracture networks act as preferential fluid flow paths that influence fluid pressure and stress distribution and fracture slip susceptibility in geothermal reservoirs. NE-SW and N-S trending fractures at Hellisheiði are susceptible to slippage before the start of fluid re-injection. During fluid re-injection, the distribution of fractures with enhanced slip susceptibility gradually shifts from surrounding the re-injection region to forming a two-lobed pattern in the fault-normal direction around the re-injection region, indicating the dominant role of cooling contraction over fluid overpressure on the fracture slip susceptibility in the intermediate- and long-term.
Verk
Pseudo-Scientist : Towards Narrative Interventions for Imposter Syndrome
(2024-10-15) Grasse, Katelyn M.; Junius, Nic; Weatherwax, Kevin; Sisodiya, Shweta; Martin, Amanda; Carstensdottir, Elin; Department of Computer Science
Imposter syndrome (IS) is a mental state that can severely inhibit a person’s productivity and well-being. Although IS is extremely common (especially in high achievers, e.g., academics), few studies offer effective modes of support and recovery. In response, we introduce the application of relatable narrative as a way to help people overcome IS. We present a randomized group comparison study exploring the impact of various design factors – specifically, choice-based interactivity and character relatability – on our story’s capacity to engage and impact 107 STEM undergraduates. Almost all participants enthusiastically endorsed the story as a valuable learning experience, and a majority reported positive impacts to mood and feelings of relatedness to peers. We discuss 1) how our specific digital story design can support positive changes in mental health at both individual and institutional levels and 2) how our findings can inform efficient design of interactive narrative content for educational applications.
Verk
‘Supporting the Support Staff’: A Narrative Review of Nutritional Opportunities to Enhance Recovery and Wellbeing in Multi-Disciplinary Soccer Performance Staff
(2024-10-14) Curtis, Christopher; Carling, Christopher; Tooley, Edward; Russell, Mark; Department of Sport Science
Verk
Community, Storytelling, and Play : Making and Breaking Rituals in Destiny 2
(Association for Computing Machinery, 2024-05-11) Larsen, Bjarke Alexander; Carstensdottir, Elin; Department of Computer Science
Modern video game development relies increasingly on live service models and storytelling, putting strain on developer-player interactions and community management, the success of which is key to the success of such games. In this paper we report on a 2.5-year ethnography study on the Destiny player community, specifically on how players and developers interact and communicate about the game, and how is this interaction is affected by and affects ongoing rituals and storytelling in that game. Our findings indicate that rituals of play are fundamental. They reinforce the players' collective experiences, created by the ongoing relationship between the players and developers. Players test and break boundaries of rituals, and developers continually adjust and experiment with those boundaries in turn. Our findings show that developers create positive feedback loops from the community when they lean into creativity efforts and boundary-breaking from players, and use storytelling directly as a community management tool.

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