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Coming dissertations at Uppsala university

  • Network Optimization of Evolving Mobile Systems with Presence of Interference Coupling Author: Lei You Link: Publication date: 2019-09-10 10:45

    The rapid development from 4G to 5G of mobile communications poses significant challenges in providing high rate and capacity, making it more crucial for efficient utilization of time-frequency resource via optimally configuring the network. Mathematical optimization serves as a powerful tool for addressing this type of problems. However, gauging its potential in large-scale cellular networks is non-trivial due to the inherent coupling relation of interference among cells. To address this issue, the dissertation adopts a so-called load-coupling system that mathe-matically formulates the mutual influence caused by radio resource allocation among cells. The model defines the time-frequency resource consumption in each cell as the cell load. The load of one cell governs the interference that the cell generates to the others, since the cell trans-mits more frequently with higher load. The model enables joint optimization of resource al-location in multiple cells with respect to the dynamics of resource occupancy of cells. Under the load coupling model, the dissertation applies mathematical optimization to resolve resource management problems with respect to a number of evolving technologies, such as coordinated multipoint (CoMP) transmission, wireless relays, cloud radio access networks (C-RAN), and non-orthogonal multiple access (NOMA). Six research papers are included in the dissertation. Paper I addresses the question of how network planning and coordination may increase the ef-ficiency of spectrum usage, by jointly optimizing user association and resource allocation with CoMP. Paper II investigates the potential of relay cooperation for energy saving. As an extension of Paper I, Paper III studies the capacity maximization for a target group of users, while keep-ing the quality-of-service (QoS) of other users being strictly met. Paper IV provides a general framework and a series of theoretical analysis for algorithmically enabling resource optimization in multi-cell NOMA with load coupling, where users are allowed to group together for sharing time-frequency resource by successive interference cancellation (SIC). Under this framework, Paper V explores the potential of NOMA networks. For a restricted setup of NOMA, the paper achieves globally optimal resource usage efficiency, in terms of power allocation, user pair se-lection, and time-frequency resource allocation. Finally, Paper VI, serving as a complementary note, overcomes a key obstacle in analyzing convergence of applying load coupling in NOMA networks.

  • Heterocystous cyanobacteria, Dps proteins and H2 production Author: Christoph Howe Link: Publication date: 2019-09-10 10:16

    To mitigate climate change, CO2-emitting technologies have to be exchanged by renewable alternatives such as H2. H2 can be produced by cyanobacteria, but major efforts to enhance H2 production yields by genetic modifications or optimised cultivation conditions resulted in energetic photo-to-H2 conversion efficiencies of 4.0 %, far from its theoretical maximum. New concepts to enhance photobiological H2 production are described in two separate thesis chapters.

    In photobioreactors, photosynthesis can lead to high O2 concentrations promoting oxidative stress that decreases the photosynthetic efficiency. Genetic modifications could potentially increase the cellular robustness facing oxidative stress e.g. by the introduction of Dps proteins. This protein class is known to mitigate oxidative stress, but cyanobacterial Dps proteins are fairly unexplored. In the 1st thesis chapter, I searched to identify the function of five Dps proteins from the filamentous and heterocystous cyanobacterium Nostoc punctiforme. Since the physiologically active Dps proteins are twelve subunit complexes, various methods were utilised to verify their multimeric state and stability. All five NpDps formed high multimeric complexes that allowed for further enzymatic characterisations. In spectroscopic analyses NpDps1-3 were found to utilise H2O2 for Fe2+ oxidation, whereas NpDps4 only used O2. NpDps4 crystal structures revealed an uncommon ferroxidase center (FOC) with a His character. This His-type FOC was found across the cyanobacterial phylum. Based on their O2 and H2O2 consumption, all four NpDps display interesting candidates to enhance the cellular robustness in photobioreactors.

    To enhance H2 production yields, a reallocation of photosynthetic energy from cell growth to H2 production is required. In the 2nd thesis chapter, Nostoc PCC 7120 ΔhupW was set under iron starvation to evaluate this cultivation strategy for the purpose of H2 production. The Fe-limited culture comprised a ~ 5.3 fold lower chlorophyll a and a ~ 4.5 fold higher specific carbohydrate concentration as compared to the control. The Fe-limited cells retained long filaments with high heterocyst frequency of ~ 6 %. The microoxic environment inside heterocysts enables efficient H2-production from O2-senstive photo fermentative pathways. Therefore, iron-starvation could display the basis of enhanced H2 production on the cost of growth. For this purpose a biofilm-containing photobioreactor was designed.

  • Speaking Other Times : Hannah Arendt and the Temporality of Politics Author: Frida Buhre Link: Publication date: 2019-09-09 14:22

    Political rhetoric frequently utilizes imaginaries of time. Ideas of an eternally sanctioned principle, a historical tradition, a future to come, or a radical change in the present are all part of the temporal toolkit of political rhetoric. The role of these imaginaries has provoked growing interest in rhetorical and political theory, and this thesis contributes to this line of scholarship by offering the first comprehensive examination of political temporalities in the works of Hannah Arendt. 

    In Arendt’s political thought, the temporal imaginaries differ depending on forms of government, and each chapter of the thesis addresses, in turn: tyranny as depending on an eternal principle introduced into contingent worldly time; authority as legitimized by reiterations of tradition; totalitarianism as justified by a trans-historical and ever-changing future; and finally, politics as empowered by the present’s antagonistic negotiations with past memories and future anticipations. Important observations are that the temporal imaginaries of tyranny, authority, and totalitarianism facilitate rhetorical practices that utilize force, violence, hierarchy, and domination. And, in contrast, that the temporalities of politics enable antagonistic speech, action, and formation of public opinion through judgment. The thesis thus provides a systematic account of the political imaginary of eternity, past, future, and present in the thought of Arendt, and contributes to conceptual development in the field of Arendtian scholarship, rhetorical theory, and political temporalities.

    The study concludes that each examined temporal imaginary is comprised of plural and intersecting temporal logics where, for example, eternal principles can utilize the futurity of threat, memories of the past can spark revolutions, and anticipations of the future can stabilize the present. By mobilizing the concept of anachronism, the thesis argues that these conflicting temporal intersections carry persuasive and performative potential. In Arendt’s discussions of temporality, power, and modes of rhetorical expression, certain anachronistic imaginaries take form that carry freedom-enabling potential: by speaking other times, politics can mobilize the power to realize freedom.