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Otakaari 1 grandhall. Photo: Esa Kapila
 

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Recent Submissions

Cities as carbon sinks - biogenic carbon sequestration and storage
(2024) Kinnunen, Antti
 School of Engineering | Doctoral dissertation (article-based)
In an era marked by escalating environmental and social crises, transforming urban systems is necessary. Currently, urban environments epitomise the degenerative impacts of anthropogenic activities—net-consumers of natural resources and ecosystem functions, contributing little to their production. However, this need not be the case. By harnessing the internal transformative capacity of the built environment, urban systems can contribute to environmental benefits. This dissertation explores biogenic carbon sequestration and storage (CSS) in redefining the built environment's role in climate regulation, embodying restorative and regenerative urban planning principles. Integrating natural and built structures, the research explores enhancing carbon sink capacity within urban landscapes, offering mitigation and adaptation benefits in the face of rapid urbanisation and accelerating climate change. The research presents a case study of biogenic CSS capacity in the built environment. It employs theoretical and empirical approaches, broad literature reviews, and precise case studies to build the key findings and main argument. The research uses quantitative and qualitative perspectives, mixing them to increase the robustness and credibility of the presented causal argumentation. The ensuing results are reflected upon the identified theoretical and conceptual frameworks and used to draw connections across all the studied scopes, accounting for inherent limitations, uncertainties, and potential weak points in the adopted research approach. Through this comprehensive analysis, the dissertation concludes that significant capacity exists for biogenic CSS improvement in the built environment. Integrating natural and built components into the urban carbon pool by increasing green space and canopy cover, using biogenic materials, and mimicking natural ecosystems' structure and functions presents potential to match or exceed pre-development CSS rates. This requires considering intertwined causal drivers, suggesting that increasing the carbon sink capacity of the built environment is best achieved in tandem with broader urban sustainability transformation. However, contemporary planning and development strategies characterised by simple heuristics often fail to harness this potential. The findings propose that these strategies inadvertently compromise the ecological quality of the built environment by neglecting urban complexity and its functionalities. Thus, the dissertation argues for a fundamental shift in urban planning and development strategies—from singular, performance-targeted approaches to holistic, multicriteria perspectives that embrace urban systems' complexity. The thesis significantly contributes to advancing urban carbon accounting discourse, conceptualising cities as active producers of carbon sink capacity.
Statistically Robust and Sparsity Promoting Inference and Estimation for Large-Scale Data
(2024) Mozafari Majd, Emadaldin
 School of Electrical Engineering | Doctoral dissertation (article-based)
The proliferation of data at a massive rate has led to the generation of massive heterogeneous datasets that are now being collected and analyzed in almost every business, industry, and science area. With datasets expanding in volume and dimensionality, many traditional procedures in signal processing, statistics, and machine learning face difficulties such as high computational complexity, lack of robustness, and reduced statistical performance. Furthermore, the probability of having missing and outlying data points grows when observing large-scale data, which further complicates estimation and inference tasks. The realization of sophisticated inference and estimation procedures that are compatible with distributed computing architectures, robust against outlying data points, and maintain reliable or even optimal statistical performance when sample size, dimensionality, or both grow is of paramount importance. This dissertation addresses two commonly arising problems in the analysis of large-scale data, which are possibly high-dimensional. It introduces new contributions in terms of theory and algorithms to the fields of inference and estimation. First, we develop two-stage robust and distributed statistical inference procedures for sparse linear regression models. These procedures combine a collaborative variable selection process, which identifies relevant variables, with computationally low-complexity and robust adjusted one-step bootstrap methods applied to data with only selected relevant variables. This approach allows for leveraging distributed computation and storage architectures while remaining robust to outlying data points and heavy-tailed distributions. The inferential tasks considered in this dissertation include the construction of confidence intervals for estimated parameter values within the identified support set (the subset of parameters associated with relevant variables) and estimating standard errors for the underlying estimator in the bootstrap method. This dissertation also provides theoretical results by establishing the bootstrap consistency and robustness properties of the proposed inference procedures. Second, we introduce a new regularization-based estimator for high-dimensional sparse linear models in the face of heavy-tailed distributions and outlying data points. The proposed adaptive τ-Lasso estimator possesses desirable oracle properties. This estimator is asymptotically normal when applied to data with its design matrix restricted to truly relevant variables. Moreover, it achieves variable selection consistency in the asymptotic sense. Furthermore, we establish the finite-sample breakdown point and characterize the influence function. Simulation results are presented to verify the analytical robustness results and demonstrate the competitive performance of the class of τ-Lasso and adaptive τ-Lasso in prediction RMSE and variable selection criteria, particularly in scenarios involving adversarial contamination.
Role of conserved and non-conserved residues of Escherichia coli formate dehydrogenase H in the CO2–formate interconversion
(2024) Li, Feilong
 School of Chemical Technology | Doctoral dissertation (article-based)
Molybdenum-dependent formate dehydrogenases (Mo-FDHs) have come to prominence as promising electrocatalysts for CO2 conversion owing to their ability to operate at low redox potentials. Nevertheless, engineering of these enzymes is required prior to application in industrial processes as these differ from physiological conditions under which Mo-FDHs have naturally evolved to increase host fitness. These engineering efforts are currently hampered by the limited understanding of the catalysis of the CO2–formate interconversion and motivated the research presented in this thesis.In publication I, the conserved active-site selenocysteine (U) residue 140 of Escherichia coli formate dehydrogenase H (EcFDH-H) was replaced with cysteine (C) and serine to study its role in catalysis. Kinetic characterization of U140C variants indicated that U140 stabilizes the reduced Mo(IV)–SH state that is required for CO2 reduction. Publication II focuses on the conserved residue lysine (K) 44 in EcFDH-H that is proximal to the Mo and [4Fe-4S] cofactors. The study investigates the role of K44 in catalysis by substitution with six structurally diverse residues. Subsequent kinetic characterization and molecular dynamics simulation of K44 variants suggested that K44 may stabilize the active forms of these cofactors. In publication III, a growth-based screening strategy was developed to extend the structure–function analysis of EcFDH-H beyond conserved residues. This strategy employs the complementation of an incomplete E. coli formate hydrogenlyase complex with EcFDH-H to establish a positive correlation between EcFDH-H variant activity and cell growth. As a proof of concept, five non-conserved residues were analyzed by the designed strategy and the variant A12G with an 82% increased formate oxidation activity was identified. Additionally, unpublished research is included in this thesis that aims at resolving the electron transfer conduit between cathodes and the catalytic center of EcFDH-H. This research was initiated by mapping seventeen potential electrode attachment sites on the EcFDH-H surface by individual replacement of non-conserved residues with cysteine. The formate oxidation activity of EcFDH-H variants was determined and was found to be preserved for the majority of them, providing a basis for the planned bio-electrochemical trials. Overall, the presented results increase the understanding of the role of conserved and non-conserved residues in EcFDH-H catalysis, providing important insights into the reaction mechanism of CO2–formate interconversion by Mo-FDHs. Additionally, this thesis identified potential targets for future engineering works aiming at improving the catalytic properties of Mo-FDHs, thereby promoting the development of proficient catalysts for CO2 utilization.
Modeling of Charged Polymers in Aqueous Solutions in the Presence of Salt Ions and Substrates
(2024) Vahid, Hossein
 School of Science | Doctoral dissertation (article-based)
Polyelectrolytes (PEs) are charged macromolecules. They interact with surrounding ions in aqueous solutions, playing a pivotal role in various scientific and industrial applications. Examples of PEs include biologically relevant molecules such as DNA, RNA, and proteins, as well as synthetic PEs like poly(styrene sulfonate) and poly(diallyl dimethyl ammonium chloride), which are widely used in industrial applications. The interactions of PEs with ions and substrates are governed by a complex interplay of electrostatic, steric, and dielectric effects, making it essential to develop a comprehensive understanding of these processes at the molecular level. This thesis aims to enhance our understanding of PE interactions through theoretical models and molecular dynamics simulations. It explores the influence of ion characteristics and investigates how they affect PE behavior in bulk solutions and at interfaces. To this end, a soft-potential-enhanced Poisson-Boltzmann model is developed and optimized using coarse-grained molecular dynamics (CGMD) simulations and atomistic models. This model captures the influence of ion size in monovalent salt solutions, providing accurate predictions of ion distributions around rodlike PEs. Beyond mean-field theory, CGMD simulations are used to study the effect of correlations arising from multivalent ions and ions with varying shapes on PE interactions. The results highlight the critical role of ion shape and concentration in controlling the range of PE interactions, offering valuable insights for designing PE-based systems, with potential applications in drug delivery, material science, and beyond.In addition, the research highlights the role of ion valency on the electrophoretic mobility (EM) of PEs. Contrary to the conventional assumption that EM is controlled by counterion valency, we show that coion valency can significantly influence EM. Specifically, we find that increasing the coion valency can reverse EM in systems with high salt concentrations, revealing a complex, non-monotonic relationship between ion valency and EM. Moreover, we examine how dielectric discontinuities between the solvent and solid substrates influence PE adsorption. The findings demonstrate that the dielectric mismatch, as well as salt concentration, ion valency, and PE charge, play a crucial role in determining whether PEs are attracted to or repelled from the substrate. This understanding provides practical guidelines for optimizing PE adsorption and monolayer formation on neutral, polarizable substrates, which is essential for applications in material science, biotechnology, and beyond. Overall, this thesis contributes to a deeper understanding of the fundamental mechanisms governing PE interactions in complex environments, offering strategies for controlling and optimizing PE behavior in various scientific and industrial applications, paving the way for the development of more efficient and targeted PE-based systems.
Lapset kaupunkisuunnittelukysymyksenä 1950–1970-lukujen Helsingissä
(2024) Moll, Veera
 School of Engineering | Doctoral dissertation (article-based)
This dissertation examines the shaping of childhood as an urban planning issue in Helsinki. It focuses on the most intense decades of urbanization, the 1950s to the 1970s, when urban planning discussions about children, along with legislation on and standardization of children's environments, increased. These discussions have had far-reaching consequences, contributing to the foundation of the contemporary understanding of children's needs and their role in urban environments. The research material consists of a large collection of reports and planning instructions dealing with urban childhood, as well as written memoirs from the capital region. Theoretical tools used in the work include concepts such as independent mobility, affordances, and the spatial politics of children's geographies. The concept of modern childhood is also a key focus of the work. This multidisciplinary research is primarily anchored within two fields. Firstly, the work contributes to the field of urban planning history by focusing on children's perspectives. It examines children's urban spaces, including yards, streets, urban nature, and particularly built playgrounds. Additionally, the study of child-specific norms represents a novel approach within the context of Finnish planning history research and contributes to the wider historical and societal discussions on standardization in urban planning. In the field of the history of childhood, the main contribution of this work is to show that the modern childhood of the 20th century was also constructed through urban planning. Building instructions related to children in the city, as well as the discussions that preceded and followed them, influenced where children spent their time. They also shaped perceptions of suitable and unsuitable environments for children. The study presents five key findings. First of all, in the 20th century, known as the century of the child, 1) children shifted from being a relatively overlooked group to an important focus in urban planning. In addition, 2) the issue of children as an urban planning concern took shape as a result of multi-professional negotiations. Helsinki's childhood as a planning issue is also 3) a history of redirection. This means that children were typically not considered to be in suitable places where they already were, such as courtyards, streets, or other areas in which they found themselves. Childhood as an urban planning issue also developed 4) as a part of suburban development. Additionally, 5) children as an urban planning issue took shape subordinated to the development of a car-centric transport system.