| 1. |
- Fuchs, Alexander, 1985-
(författare)
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Assessment of predicting blood flow and atherosclerosis in the aorta and renal arteries
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cardiovascular diseases (CVD) are the most common cause of death in large parts of the world. Atherosclerosis (AS) has a major part in most CVDs. AS is a slowly developingdisease which is dependent on multiple factors such as genetics and life style (food, smoking, and physical activities). AS is primarily a disease of the arterial wall and develops preferentially at certain locations (such as arterial branches and in certain vessels like thecoronary arteries). The close relation between AS sites and blood flow has been well established over the years. However, due to multi-factorial causes, there exist no early prognostic tools for identifying individuals that should be treated prophylactically or followed up. The underlying hypothesis of this thesis was to determine if it is possible to use bloodflow simulations of patient-specific cases in order to identify individuals with risk for developing AS. CT scans from patients with renal artery stenosis (RAS) were used to get the affected vessels geometry. Blood flow in original and “reconstructed” arteries were simulated. Commonly used wall shear stress (WSS) related indicators of AS were studied to assess their use as risk indicators for developing AS. Divergent results indicated urgent need to assess the impact ofsimulation related factors on results. Altogether, blood flow in the following vessels was studied: The whole aorta with branches from the aortic arch and the abdominal aorta, abdominal aorta as well as the renal arteries, and separately the thoracic aorta with the three main branching arteries from the aortic arch. The impact of geometrical reconstruction, employed boundary conditions (BCs), effects of flow-rate, heart-rate and models of blood viscosity as function of local hematocrit (red blood cell, RBC, concentration) and shear-rate were studied in some detail. In addition to common WSS-related indicators, we suggested the use of endothelial activation models as a further risk indicator. The simulations data was used to extract not only the WSS-related data but also the impact of flow-rate on the extent of retrograde flow in the aorta and close to its walls. The formation of helical motion and flow instabilities (which at high flow- and heart-rate lead to turbulence) was also considered.Results:A large number of simulations (more than 100) were carried out. These simulations assessed the use of flow-rate specified BCs, pressure based BCs or so called windkessel (WK) outlet BCs that simulate effects of peripheral arterial compliance. The results showed high sensitivity of the flow to BCs. For example, the deceleration phase of the flow-rate is more prone to flow instabilities (as also expressed in terms of multiple inflection points in the streamwise velocity profile) as well as leading to retrograde flow. In contrast, the acceleration phase leads to uni-directional and more stable flow. As WSS unsteadiness was found to be pro-AS, it was important to assess the effect flow-rate deceleration, under physiological and pathological conditions. Peaks of retrograde flow occur at local temporal minima in flow-rate. WK BCs require ad-hoc adjusted parameters and are therefore useful only when fully patient specific (i.e. all information is valid for a particular patient at a particular point of time) data is available. Helical flows which are considered as atheroprotective, are formed naturally, depending primarily on the geometry (due to the bends in the thoracic aorta). Helical flow was also observed in the major aortic branches. The helical motion is weaker during flow deceleration and diastole when it may locally also change direction. Most common existing blood viscosity models are based on hematocrit and shear-rate. These models show strong variation of blood (mixture) viscosity. With strong shear-rate blood viscosity is lowest and is almost constant. The impact of blood viscosity in terms of dissipation is counter balanced by the shear-rate; At low shear-rate the blood has larger viscosity and at high shear-rate it is the opposite. This effect and due to the temporal variations in the local flow conditions the effect of blood rheology on the WSS indicators is weak. Tracking of blood components and clot-models shows that the retrograde motion and the flow near branches may have so strong curvature that centrifugal force can become important. This effect may lead to the transport of a thrombus from the descending aorta back to the branches of the aortic arch and could cause embolic stroke. The latter results confirm clinical observation of the risk of stroke due to transport of emboli from the proximal part of the descending aorta upstream to the vessels branching from the aortic arch and which lead blood to the brain.Conclusions:The main reasons for not being able to propose an early predictive tool for future developmentof AS are four-folded:i. At present, the mechanisms behind AS are not adequately understood to enable to define aset of parameters that are sensitive and specific enough to be predictive of its development.ii. The lack of accurate patient-specific data (BC:s) over the whole physiological “envelop”allows only limited number of flow simulations which may not be adequate for patientspecificpredictive purposes.iii. The shortcomings of current models with respect to material properties of blood andarterial walls (for patient-specific space- and time-variations) are lacking.iv. There is a need for better simulation data processing, i.e. tools that enable deducinggeneral predictive atherosclerotic parameters from a limited number of simulations, throughe.g. extending reduced modeling and/or deep learning.The results do show, however, that blood flow simulations may produce very useful data thatenhances understanding of clinically observed processes such as explaining helical- andretrograde flows and the transport of blood components and emboli in larger arteries.
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| 2. |
- Owiredu, Maria, 1982-
(författare)
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Sveriges politiska partier och Israel-Palestinafrågan : En analys av svenska partiers agerande 2006–2021
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis studies political parties in Sweden and their attitudes toward the Israel-Palestine issue during the period from 2006-2021. The analysis assumes that political parties act strategically, guided by their party goals across different arenas: parliamentary, internal, and electoral. Five key party goals—policy, vote-seeking, position, party cohesion, and international credibility—are used to analyze the strategic behavior of these parties. The Israel-Palestine issue holds strategic relevance for several political parties. Left-leaning parties (such as the Green Party, Social Democrats, and Left Party) benefit the most from strategically engaging with this issue. Even parties like the Christian Democrats and the Liberal Party recognize strategic relevance in addressing the Israel-Palestine issue. Notably, the Center Party påsy the least attention to this issue. The most relevant party goals are policy and international credibility. The study also reveals significant relationships between parties and their sympathizers. In addition, the results offer concrete examples of how the party strategy works within the political parties, thus contributing to party strategy research, Swedish foreign policy and the Israel-Palestine issue in a Swedish context. In conclusion, the Israel-Palestine issue is deeply ideological. While it serves as a political tool in foreign policy debates, its impact is even more pronounced in domestic discussions, where parties use it to underscore their ideological stances. Overall, the Israel-Palestine issue remains to be one of the most polarized topics in the Swedish foreign policy debate.
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| 3. |
- Persson, Anders
(författare)
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Cognition and the Machine : Exploring Human-AI Interaction via Predictive Processing
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Artificial Intelligence is rapidly becoming ubiquitous in both professional settings and everyday life. The prospect is that modern machine-learning technology of Generative AI could help with decision-making, and thinking and reasoning alike. However, our understanding of human cognition, particularly thinking and reasoning, remains limited. This thesis proposes a conceptual framework for understanding the interaction between humans and AI, drawing on the cognitive theory of Predictive Processing. Predictive Processing posits that the brain constructs and employs models to predict and interpret the external world based on past experiences. It operates through a top-down simulation, where sensory feedback primarily highlights discrepancies between predictions and reality. This simulation extends to imagination, reasoning, and thinking, facilitated by offline mental simulations using domain-specific predictive models. Prediction models are structured hierarchically, with lower levels corresponding to concrete sensory input, while higher levels represent abstract, generalized relationships within specific domains. In human communication, abstract predictions play a crucial role, as individuals mentally simulate predictions and convey them through language to peers who then interpret them based on their own domain-models. Chatbots has the potential of being a similar kind of dialogue partner, evaluating your predictions of the world, helping you with interpretations or mutual examinations of problems. For human users it may seem as if it is a shared dialogue, but what AI based on current technology most of all lack, is the worldly connection and adaptive flexibility of the model it is based upon.
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| 4. |
- Sandstedt, Mårten, 1972-
(författare)
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Computed Tomography of the Coronary Arteries : Developmental and Prognostic Investigations
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computed tomography (CT) is an increasingly used modality for investigations of patients with suspected coronary artery disease (CAD). Technical advances could improve diagnostic accuracy and lead to clinical workflow improvements. Also, more prognostic information can optimize clinical follow-up strategies and treatments.The general aim of this thesis was to explore the use of CT for CAD investigations. Three studies aimed to examine new technologies, including the evaluation of an on-site, computed tomography-based fractional flow reserve (CT-FFR) software (study I), the evaluation of an AI-based, calcium scoring computed tomography (CSCT) software (study III), and the evaluation of an photon-counting detector (PCD)-CT (study IV). One study aimed to evaluate the long-term prognostic value of coronary computed tomography angiography (CCTA) in symptomatic patients with no history of CAD (study II).The software evaluation studies (study I and III) and the prognostic study (study II) utilized CT data from clinical patients, while the PCD-CT evaluation study (study IV) used CT data from cadaveric specimens. The performances of both software programs were compared with standard references, being represented by fractional flow reserve (FFR) measurements (study I), and coronary artery calcification (CAC) scores from a semi-automatic software (study III), respectively. The PCD-CT performance on CAC quantification was compared with corresponding results from an energy integrating detector (EID)-CT, using micro-CT as the standard reference (study IV). The prognostic study merged registries to identify major adverse cardiac events (MACE), having a follow-up time of up to 7.5 years (study II).The CT-FFR and CSCT software correlation and agreement to corresponding standard references were good and excellent, respectively. Also, both software programs had time-saving potential (study I and III). The CAC quantification was more accurate using PCD-CT than EID-CT (study IV). The prognosis was excellent in patients with normal coronary arteries, and progressively impaired in non-obstructive and obstructive CAD (study II).The results in this thesis convey developmental, technical CT technology advances for CAD investigations. In addition, prognostic follow-up data is communicated. The results may benefit patients by an increased accuracy in the CT evaluation of CAD and can contribute to improve clinical follow-up strategies. Furthermore, the results suggest possibilities to improve the workflow in clinical radiology, which potentially could impact health care costs.
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| 5. |
- Seton, Ragnar, 1985-
(författare)
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Fundamentals and applications of microplasma sources : Actuating, Sensing, and Nonlinearly Approximating.
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research presented in this thesis covers a wide range of applications for, and integrations of, a stripline split-ring resonator (SSRR) microplasma source. Common throughout the presented works is the always present, but sometimes secondary, focus on analyzing the light and matter that is emitted as gas is flowed through theplasma of the SSRR.When evaluated as a heater in a cold-gas microthruster intended for attitude adjustment and orbit maintenance of miniaturized satellites, the plasma was shown to be a more efficient than two modes of resistive heating in improving the specific impulse of the thruster. Furthermore, the ionized exhaust plume of the thruster was used to derive a novel method of estimating its efficiency. In further analysis of the plasma parameters, correlations between supplied power, ion density, and thrust efficiency were uncovered and verified by Langmuir probe measurements.In subsequent experiments, the use of the SSRR as a residual gas analyzer was explored, first by comparing different classes of regression methods for determining gas species concentrations from emitted UV-NIR spectra from the plasma. In a second study, the wide range spectrometer was replaced with an optical filter and a photodetector, in a differential gas sensor setup where the regression methods were replaced with peak intensity differentiation.With the SSRR’s prospects as a gas sensor confirmed, further work focused on integrating it in a transcutaneous blood gas monitoring (TBM) system. To address the shortcomings of existing systems, a series of three studies covered the fabrication and evaluation of (i) A soft gas-collecting patch that, with its accompanying microfluidics, transported the gas that permeates the skin to the sensor, (ii) A novel fabrication technique to integrate an electrical interface in the bulk of the patch, and a prototype out-of-plane skin heater, and (iii) A theoretical model that related the transcutaneous gas composition to blood gas concentration based on a computational fluid dynamics model. Finally, the sensor and gas collector were integrated in a fully functional TBM system.In conclusion, the thesis explores the use of an SSRR throughout the three cornerstone configurations of microsystem technology: as an actuator for microsatellite propulsion, as a sensor for gas measurements, and integrated in a system for blood gas monitoring.
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