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  • Disputas: 2020-01-20 15:00 Magnélisalen, Kemiska övningslaboratoriet, Stockholm
    Cortés González, Miguel Ángel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Development of new Fluorination Methods Directed to Fluorine-18 Labelling2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with the development of new fluorination reactions and their application to fluorine-18 labelling. Fluorine-18 labelled compounds are employed as tracers in Positron Emission Tomography (PET), which is a powerful non-invasive imaging method in medical diagnostics.

    The first part of this thesis focuses on the development of a late-stage halogen exchange-based fluorination method for the synthesis of trifluoromethylated molecules. The first project in this area relies on the application of a copper(I)-based fluorinating reagent to furnish trifluoroacetates, trifluorotoluenes and trifluoroacetamides. The second project involves the translation of this methodology into the fluorine-18 labelling of tertiary and secondary trifluoroacetamides. The targeted substrates were labelled in high radiochemical yield and high molar activity using [18F]Bu4NF as fluorine source in the presence of an organic activator.

    In the second part, the development of electrophilic fluorination reactions using a hypervalent iodine-based reagent is discussed. The first project in this area addresses the development of an electrophilic fluorine-18 fluorination reagent: [18F]fluoro-benziodoxole. The utility of this reagent was demonstrated in the labelling of [18F]fluoro-benzoxazepines. In the second project, the same [18F]fluoro-benziodoxole reagent was used in the rhodium-mediated synthesis of α-[18F]fluoroethers. High molar activities were obtained in these electrophilic labelling processes. In the third project, the fluorine-19 analog fluoro-benziodoxole was used in the palladium-catalyzed iodofluorination of allyl benzenes, styrenes and cycloalkenes. Both iodine and fluorine atoms in the product arise from the same reagent.

  • Disputas: 2020-01-22 10:00 William-Olssonsalen, Geovetenskapens hus, Stockholm
    Jansen, Joachim
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Carbon trace gas dynamics in subarctic lakes2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Northern lakes are important sources of greenhouse gases carbon dioxide and methane to the atmosphere. Emissions are expected to increase as the climate continues to warm. Even so, lake carbon budgets are currently poorly constrained. This is in part because of a limited understanding of the processes that govern the flux. This thesis focuses on the physical and biogeochemical drivers of carbon trace gas emissions from three small, post-glacial lakes situated within the Stordalen Mire, a subarctic peatland underlain by thawing permafrost in northern Sweden. A unique, multiyear dataset is used to quantify the importance of different emission pathways – ebullition, turbulence-driven diffusion and release from storage – on short and long timescales. In summer and on seasonal to interannual timescales, emissions are robust functions of thermal energy input. Short-term storage-and-release cycles are governed by kinetic drivers, such as turbulence fuelled by wind shear and, to a lesser extent, by thermal convection. In winter, when the lakes are ice-covered, persistent anoxia and density-driven currents enable methane accumulation at rates exceeding summer emissions. Release at ice-off in spring can constitute the majority of annual methane emissions and scales predictably with ice-cover season length, except in warm winters when snowmelt displaces lake water. Most lake flux studies focus on the warmest summer months and omit the spring efflux, as well as emissions in the colder ice-free months which, because of the well-known temperature-dependency of carbon cycling processes, tend to be low. The latter sampling bias may lead to a substantial overestimation of the ice-free flux in regional and global lake emission budgets. Temperature proxies, potentially combined with gas transfer models, can efficiently gap-fill colder months to arrive at a more representative flux estimate, but important feedbacks, such as lake degassing with increasing wind speed, must be taken into account. The mechanisms emerging from intense study of the Stordalen lakes are likely to be found in a majority of northern lakes, which are small, seasonally ice-covered and of post-glacial origin. However, because gas transfer velocity and temperature sensitivity are spatiotemporally variable, field observations remain essential for the development and calibration of models, and to predict future emissions.

  • Disputas: 2020-01-24 10:00 Ahlmannsalen, Geovetenskapens hus, Stockholm
    Lebeck, Carl
    Stockholms universitet, Juridiska fakulteten, Juridiska institutionen.
    De konstitutionella gränserna för tillämpning av överstatlig rätt: En komparativ studie2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    This doctoral dissertation analyses the constitutional limitations on application of supranational law (in particular EU- and EEA-law) in German, Swedish, Danish and Norwegian law. The analysis focuses on how constitutional limitations in national law concerning application of supranational law are relevant regarding the allocation of powers between national and supranational authorities, separation/division of powers within national law, protection of fundamental rights and requirements of legality in national constitutional law. While there are examples of refusals by national courts to apply supranational law on the basis of national constitutional law such refusals are uncommon. The conclusion in this thesis is that constitutional limitations on application of supranational law differ between different fields of law, and that limitations which are limited, temporary and procedural are more common than limitations which are extensive, permanent and substantive in their effects on application of supranational law. There is also a strong functional dependency between national legal orders and supranational law which limit the scope of national constitutional constraints on the application of supranational norms. That means that supranational law in certain respects undermines the effectiveness of national constitutional law and hence contributes to a kind of “constitutional deficit” in national law.

  • Disputas: 2020-01-24 13:00 De Geersalen, Geovetenskapens hus, Stockholm
    Kring, Elisabeth
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Barn- och ungdomsvetenskapliga institutionen.
    Spaces of appearance: Intergenerational and interspecies relations in the Anthropocene2020Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The thesis brings together childhood studies and the problems of environmental degradation and climate change. It focuses on intergenerational and interspecies relations and aspects connected to environmental sustainability. The discussions centre on three contexts: a sea (the Öresund region), a desert (the Sonoran Desert), and the school strikes for the climate (global). Taking an approach inspired by phenomenology, these contexts are examined using the notion of appearance. Questions are asked about which subjects and objects (can) appear – where, when and to whom – and about the conditions for and implications of those appearances (or their absence). The project is twofold: i) developing a conceptualisation of appearance that can serve ethico-political theorising, especially in regard to children, generations and non-human species in times of environmental degradation, and ii) discussing appearance(s) in relation to specific sustainability activities, linked to the three mentioned contexts. Central scholars drawn upon are Hannah Arendt and Maurice Merleau-Ponty, as well as feminist scholars’ development of their theorising.

    Proposing a dual take on acting, it is suggested that creating change in regard to environmental degradation is a matter of both collective political action (creating an Arendtian inter-subjective space of appearance) and an individual body-subject’s way of interacting with objects that appear to it. Further, the reversibility of acting is emphasised, that is, that one who can act can also be acted on, and in this way, capacity (acting) is interlinked with susceptibility and vulnerability (being acted on). However, it is argued that different human and non-human subjects are not equally vulnerable, nor equally responsible, with regard to environmental degradation. Given differences between generations and between species in relation to temporal and spatial “points of appearance” – the points where one appears, or will appear – it is proposed that we should also discuss how the world itself appears to different subjects from their respective point of appearance.

  • Disputas: 2020-01-25 10:00 Hörsal 9, hus D, Södra huset, Stockholm
    LaMonica, Clelia R.
    Stockholms universitet, Humanistiska fakulteten, Engelska institutionen.
    A Combined Perceptual and Acoustical Account of US Dialect Distance2020Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    This study examines the influence of attitudinal, perceptual, and acoustic factors on the categorization of US dialects by comparing acoustic-vocalic and perceived accent distances. The results of native and non-native listeners’ perceived distances between US regional accents are investigated in light of how acoustic-phonetic markers, attitudinal judgments, and identifiability may together impact how similar or different accents are perceived to be. Responses from 80 native and 40 non-native listeners provided perceived distance scores, attitudinal judgements, and categorization results for seven regional, and one non-regional, samples. A comparison of the regional distributions through hierarchical cluster analyses for vowel formant measurements and perceptual results, accompanied by an exploratory factor analysis, reveals a combination of several factors which result in groupings similar to those evident in perceptual distances: 1) markedness, 2) attitude, 3) associations with ‘standardness’, and 4) identifiability. These demonstrate the involvement of perceptions of and pre-existing associations with an identified accent when making a judgement of similarity/difference between varieties, which may furthermore override the initial acoustic information. Based on this investigation, judgements of relatedness between accents are furthermore shown to support previous qualitative models of dialect perception and comprehension.

  • Disputas: 2020-01-27 13:00 L30, NOD-huset, Kista
    Weegar, Rebecka
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Institutionen för data- och systemvetenskap.
    Mining Clinical Text in Cancer Care2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Health care and clinical practice generate large amounts of text detailing symptoms, test results, diagnoses, treatments, and outcomes for patients. This clinical text, documented in health records, is a potential source of knowledge and an underused resource for improved health care. The focus of this work has been text mining of clinical text in the domain of cancer care, with the aim to develop and evaluate methods for extracting relevant information from such texts. Two different types of clinical documentation have been included: clinical notes from electronic health records in Swedish and Norwegian pathology reports.

    Free text, and clinical text in particular, is considered as a kind of unstructured information, which is difficult to process automatically. Therefore, information extraction can be applied to create a more structured representation of a text, making its content more accessible for machine learning and statistics. To this end, this thesis describes the development of an efficient and accurate tool for information extraction for pathology reports.

    Another application for clinical text mining is risk prediction and diagnosis prediction. The goal for such prediction is to create a machine learning model capable of identifying patients at risk of a specific disease or some other adverse outcome. The motivation for cancer diagnosis prediction is that an early diagnosis can be beneficial for the outcome of treatment. Here, a disease prediction model was developed and evaluated for prediction of cervical cancer. To create this model, health records of patients diagnosed with cervical cancer were processed in two steps. First, clinical events were extracted from free text clinical notes through the use of named entity recognition. The extracted events were next combined with other event types, such as diagnosis codes and drug codes from the same health records. Finally, machine learning models were trained for predicting cervical cancer, and evaluation showed that events extracted from the free text records were the most informative event type for the diagnosis prediction.

  • Disputas: 2020-01-30 13:00 Gröjersalen, hus 3, Kräftriket, Stockholm
    Kheirollah, Amir
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Företagsekonomiska institutionen.
    The Art of Discretion: Essays on Earnings Management, Governance, and Capital Structure2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This dissertation is a compilation of three articles on earnings management, governance and capital structure. In addition to these three articles, the introductory chapter establishes the link between these articles and summarizes them.

    Article I investigates the joint effect of governance mechanisms on earnings management. This study finds evidence in support of imperfect substitution and complement effects of corporate governance and industry regulation on earnings management.

    Article II investigates the role of the discretionary environment for earnings management, using several measures of governance and contextual mechanisms. The findings of this article show that the discretionary environment matters in explaining earnings management practices. Therefore, the use of a tractable and quantifiable measure of the discretionary environment has the potential to refine measures of earnings management and mitigate the mixed inferences made from these measures in the literature. Hence, this study contributes to the literature by augmenting accrual-based earnings management models with governance and contextual mechanisms.

    Article III examines the role of managerial traits in the active management of capital structure within the boundaries of a system of financial and governance constraints. The findings of this article show that the managerial discretionary index as a measure of managerial traits is associated with leverage growth and the satisficing effect is statistically significant. The results also show that the association is nonlinear under some combinations of financial and governance constraints (relatively low and high constraints), and linear in others.

  • Disputas: 2020-01-31 10:00 Magnélisalen, Kemiska övningslaboratoriet, Stockholm
    Broomé, Sara
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Stockholm University.
    Atlantic Water in the Nordic Seas: A satellite altimetry perspective on ocean circulation2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Atlantic Water in the Nordic Seas contributes to the mild climate of Northern Europe and is the main oceanic source of heat for the Arctic. The northward bound transport of the warm and saline Atlantic Water is mediated by a topographically constrained cyclonic boundary current along the Norwegian continental slope. The analysis within this thesis is based on satellite observations of dynamic Sea Surface Heights (SSH) from 1993 to the recent present, combined with both hydrographic observations and modelling. It provides some new perspectives and results, as well as corroborates the essential role of bottom topography for the circulation in the Nordic Seas.

    In the first part of the thesis, the topographic constraint is used in the analysis by examining the satellite-derived SSH along topographic contours. We find stationary along-contour anomalies that indicate deviations from strict topographic steering. However, we show that these deviations are dynamically consistent with, and can be explained by, potential vorticity conservation in an adiabatic steady-state model for flow over a topographic slope. The analysis along topographic contours is further developed to study northward-propagating, low-frequency ocean temperature signals. These signals have an expression in the SSH and their propagation speed is remarkably slow compared to the current speed. We propose a conceptual model of shear dispersion effects, in which the effective advection speed of a tracer is determined not only by the rapid current core, but by a mean velocity taken over the cross-flow extent of Atlantic Water. The model predicts a reduced effective tracer advection velocity, comparable to the one observed.

    The close connection between anomalies in SSH and heat content is further used to study decadal variability in the Nordic Seas. There is a shift in decadal trends in the mid-2000s, from a period of strong increase in SSH and heat content to a more stagnant period. We find this variability to be forced remotely, rather than by local air-sea heat fluxes. By developing a conceptual model of ocean heat convergence, we are able to explain the broad features of the decadal changes with the temperature variability of the inflowing Atlantic Water from the subpolar North Atlantic.

    In the final part of the thesis, satellite-derived surface geostrophic velocity fields are used as input to a Lagrangian trajectory model. Based on this, we study the fractionation of the Atlantic Water in the Nordic Seas between the two straits towards the Arctic Ocean: the Barents Sea Opening and the Fram Strait. This Lagrangian approach also provides insights on the origin of the water that reach the straits. We find that it is the frontal current branch, rather than the slope current, that contributes to the variability of the Barents Sea Opening inflow of warm Atlantic Water, and thus potentially to the climate of the Barents Sea and its sea ice cover.

  • Disputas: 2020-01-31 13:00 hörsalen, Frescati backe, Stockholm
    Eriksson, Christine
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Barn- och ungdomsvetenskapliga institutionen.
    A preschool that brings children into public spaces: Onto-epistemological research methods of vocal strolls, metaphors, mappings and preschool displacements2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The interest of this doctoral thesis in early childhood education concerns the discourse on the need to integrate as well as include the youngest children in society. The overall purpose is to produce methodological experimentations on the possibilities of constructing a preschool which facilitates for preschool and preschool children to be present and take place in, and thereby participate in the construction of public spaces, together with other actors and the places themselves. The aim is to experiment with displacing preschool practices from their institutionalised place into public spaces, inspired by various site-specific artistic place-based methods, in order to develop situated onto-epistemological research methods for early childhood education research. These emerging methods aim to enhance interaction between the preschool institution – including the children – and public spaces, as spaces of societal interaction and transaction between different actors.

    The preschool institution was founded in a modernist era which set out to construct a society that could offer safe and appropriate places for all citizens. The institutional preschool was organised as such a separate and reserved place for children in society, but the physical preschool walls and doors simultaneously separate children from the non-institutional places of society – the public places. The public space upholds the potential for interaction, exchange and public action for change.

    In the empirical fieldwork enacted for this project, I as a researcher, a group of the youngest preschool children (1-3 years), and a number of educators, enacted together so-called vocal strolls in the public transport system in Stockholm. The research project functions as a method-producing practice, where children’s places – the preschool practices – are brought into adult’s places – public spaces – outside the preschool. The study thus produces emerging and situated – in situ – research methods in collaboration with a preschool (and its children and practices) and the public spaces we encountered and interacted with. The thesis takes an onto-epistemological theoretical stance, to define the research, not as separated from the world, but as one of many practices collaborating in the production of methods on how to take place in public spaces (cf. Stengers, 2018; Barad, 2007).

    The thesis consists of three published research papers which delineate vocal strolls, vocal mappings, metaphors and displacements as early childhood education research methods that facilitate a preschool which enables children to take place in public spaces. The onto-epistemological research methods which emerged in this study have been inspired by artistic site-specific practices, which have a long tradition of developing methods on how to move art out from art institutions, e.g. museums, galleries and art-studios. These research methods are embodied methods, which produce a direct knowledge and always transform in relation to the situation and the spatial conditions of a place. Vocal metaphors, strolls, mappings and displacements are constructed in the process of collaboration between multiple different ways of enacting a place and being enacted by the place. This study has shown the possibility of developing place-based research methods for early childhood education research with the aim of understanding how they might transform our notions and practices of preschool.

  • Disputas: 2020-01-31 13:00 Nordenskiöldsalen, Geovetenskapens hus, Stockholm
    Qviström, Linda
    Stockholms universitet, Humanistiska fakulteten, Institutionen för arkeologi och antikens kultur.
    Rum utan utsikt: Fönster och ljus i medeltida byggnader2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Windows, light and a view are self-evident parts of contemporary interiors. This was not the case in Scandinavia during the Middle Ages (c. 1050–1520 CE), when closed spaces without wall openings were standard. Windows fulfilling modern needs and regulations, providing rooms with light and a view, did not come into common use until the 18th century, and in some contexts even later.

    The perception of light and darkness, and of what is understood to be light or dark, is changeable – as are people’s sensorial experiences and their definitions of the senses. The provision of as much light as possible has not always been the most desirable quality in buildings, even in rooms provided with windows. The importance of and need for light have varied a lot over time and in different situations. During the Middle Ages, light openings were used in a more distinct and direct way, to meet specific requirements – not to provide rooms with an ambient level of light. Looking at the use of lighting equipment during the same period, it seems that both daylight and artificial light were used in similar, more specific and situational ways. When it comes to a view, this was not something that was expected in any room, or from any window, during the medieval period.

    An overall purpose with the thesis is to discuss how people have related to windows, light and lighting inside buildings during the Middle Ages, both in Sweden generally and in the two regional research areas of Gotland and Uppland in particular. One of the starting points is that the materiality of windows and the use of artificial light were closely bound up with people’s perceptions of and attitudes to light in indoor environments. 

    In addition to past approaches to light and darkness, the thesis also discusses how windows and light were used in different contexts, what sorts of lighting conditions and contact surfaces between outside and inside they created, and how the use of windows interacted with the relationship between outdoor and indoors.

    The primary medium for this study is the material design and placement of windows. The source material consists mainly of standing buildings, archaeologically investigated building remains, and finds of window glass and lighting aids. Lighting equipment and window glass preserved in other contexts, mainly churches, are also considered, as are written sources and medieval images.

    The thesis contains six chapters, including an introduction and concluding discussion. Of the four central chapters, two are thematic, discussing windows and lighting from a long-term perspective, and two present in-depth regional studies of Uppland and Gotland respectively.

  • Disputas: 2020-02-04 13:00 De Geersalen, Geovetenskapens hus, Stockholm
    Stoltz, Jonathan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Perceived Sensory Dimensions: A Human-Centred Approach to Environmental Planning and Design2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Increased urbanization, stress and lifestyle related illness, and biodiversity loss are some of the most urgent challenges today. The potential contributions from green spaces and infrastructures in relation to these challenges are several. In addition to benefits such as climate and water regulation, air purification, food production, and biodiversity conservation, certain aesthetic, i.e. perceived, qualities of green features and natural settings have been shown important for people’s health and wellbeing. The potential of such qualities to aid restoration from stress and attention fatigue is well documented. It has also been suggested that they could support pro-environmental behaviours, promote physical activity, and increase general wellbeing. A difference between grey/urban and green/natural settings has been highlighted in previous research. There is a need however for a more nuanced understanding of the most important qualities in the environment to consider in order to support human health and wellbeing over time.

    Through a universal, human-centred approach, where needs, motivations, and meaningful experiences are considered before specific means of physical implementation, this thesis adopts a framework of eight aesthetic qualities, termed perceived sensory dimensions, accounting for basic human needs in relation to green areas. This framework is investigated and developed in different contexts and at different scales to aid an evidence-based approach to environmental design, planning, and evaluation from a human health and wellbeing perspective. A dialectic model based on the framework is suggested as a means to facilitate the inclusion of this level of analysis in, e.g. trans- and interdisciplinary research settings, and in environmental design and planning practices.

  • Disputas: 2020-02-06 09:30 Magnélisalen, Kemiska övningslaboratoriet, Stockholm
    Zhang, Zhe
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Enhancing membrane and secretory protein production yields in Escherichia coli2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Proteins fulfill essential functions in living cells. To produce sufficient amounts of a protein is essential to study the structure and function of a protein, or to use it for medical purposes. Escherichia coli is a Gram-negative bacterium that is widely used for recombinant protein production. The aim of my PhD studies was to enhance membrane and secretory protein production yields using E. coli. The T7-based protein production system BL21(DE3)/pET was mainly used in my studies. BL21(DE3) contains a strong IPTG-inducible lacUV5 promoter governing the expression of the t7rnap gene encoding the T7RNAP on its chromosome. The target gene is under control of the T7 promoter on the pET plasmid. T7RNAP specifically recognizes the T7 promoter and transcribes the target gene more efficiently than the bacterial RNAP. Unfortunately, the biogenesis machinery for membrane and secretory proteins is usually saturated by the high protein production intensity when the BL21(DE3)/pET system is induced with IPTG, thereby negatively affecting protein production yields. In the first study, we found that when using the BL21(DE3)/pET system omitting the inducer IPTG improved membrane and secretory protein production yields. In previous studies, Lemo21(DE3) was developed to facilitate the production of membrane and secretory proteins. Lemo21(DE3) contains the pLemo plasmid in which the gene encoding the inhibitor of T7RNAP, T7 lysozyme, is under the control of the rhaBAD promoter. The activity of T7RNAP is regulated by synthesizing different levels of T7 lysozyme by adding different amounts of rhamnose. Thus, the production intensity can be modulated such that the biogenesis machinery of membrane and secretory proteins is not saturated upon IPTG induction. In the second study, we combined the key elements from both the pLemo and pET vectors to create the pReX (Regulated eXpression) plasmid to facilitate the use of helper plasmids encoding e.g., chaperones when it is necessary. In the third study, we used the rhaBAD promoter to direct the production of membrane and secretory proteins in a rhamnose metabolism and active uptake deficient strain. The protein production rate can be truly tuned in this setup. Therefore, the production of membrane and secretory proteins can be enhanced by using the right amount of rhamnose in the culture medium. BL21(DE3) contains the λDE3 prophage that carries the t7rnap gene under the control of the lacUV5 promoter. The λDE3 prophage is thought to be stably inserted into the chromosome, but the lytic cycle of the prophage can still be induced by the SOS response inducing antibiotic mitomycin C in the mitomycin C-based bacteriophage test. In the fourth study, we engineered BL21T7 by deleting in BL21(DE3) lysis related genes from the prophage. BL21T7 has similar recombinant protein production characteristics as its ancestor BL21(DE3).

  • Disputas: 2020-02-07 09:00 Magnélisalen, Kemiska övningslaboratoriet, Stockholm
    Olsén, Jon
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Additive metallurgy - Thermal influences on structure and properties of stainless steel 316L2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Additive manufacturing (AM) as a manufacturing process has, in recent years, become widely accepted as capable of manufacturing parts that will be used in end products. In this thesis, stainless steel grade 316L parts are manufactured using two different powder bed fusion techniques, selective laser melting (SLM) and electron beam melting (EBM). It is recognized that parts made using these processes will have unique microstructures and mechanical properties that have not been seen in bulk parts produced with other methods. The driving force behind the formation of these structures is the fast cooling speed that induces segregation of elements, forming an inhomogeneous microstructure. How these structures react to thermal treatment is less well known and an essential aspect in many applications. Parts manufactured using SLM was treated with hot isostatic pressing (HIP) to investigate if the material retains its unique features. Two different HIP cycles were used, one with 1150 °C and one with 1040 °C. In both cases, the cellular sub-grain structure fades. The cycle utilizing the high temperature is found to coarsen the grain structure and thus lowering the mechanical properties significantly. As manufactured parts show yield strength (615±1 MPa), tensile strength (725±2 MPa) and microhardness (211±10 Hv), compared to values of yield strength (284±2 MPa), tensile strength (636±1 MPa) and microhardness (178±8 Hv) after 1150 °C HIP. Using HIP at 1040 °C, the material will retain a finer grain structure resulting in higher yield strength (417±7 MPa) compared to 1150 °C HIP temperature, while the UTS and hardness have a similar value. It is also observed that the dispersed inclusions formed during SLM are still present after HIP to increase the mechanical properties compared to a conventionally annealed bar (TS: 515 MPa, YS: 205 MPa). Samples manufactured using EBM was investigated to understand the influence of the in-situ heat treatment that is present in the EBM process. The material possesses a long-range heterogeneous structure in addition to the cellular structure, where the cellular structure is present at the top and disappears further down the sample. Samples with different geometries were produced to study the effect of heat flux, cooling speed and the elevated temperature of 800 °C that is present during the EBM process. The thickness of the cell boundaries is measured in different areas, revealing that geometry and size of manufactured parts have a significant impact on the evolving microstructure. It is also revealed that the tensile strength (562±4 MPa) and microhardness (161±11 Hv) is not affected by the change in microstructure, resulting in a very homogeneous material concerning these parameters. Heat treating the material at 800 °C show that the cellular structure becomes diffuse after several hours, but the grain morphology stays the same.

  • Disputas: 2020-02-07 10:00 De Geersalen, Geovetenskapens hus, Stockholm
    Coll Mora, Claudia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap.
    How to estimate environmental persistence: Understanding persistence of organic micropollutants in rivers from a multidisciplinary perspective2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Organic micropollutants such as food additives, pharmaceuticals and personal care products are found in rivers worldwide. Persistence is a key criteria in chemical risk assessment as micropollutants that are persistent pose an exposure hazard to humans and the environment. As biodegradation is the most relevant removal process for many micropollutants in rivers, persistence assessment relies on the estimation of the biodegradation half-life.  This thesis presents new approaches to understand the biodegradation of organic pollutants in rivers.

    The application of Junge relationships (previously established for atmospheric pollutants), to river systems, was investigated in paper I to assess if biodegradation half-lives in the Danube river are correlated with variability in measured concentrations. Model scenarios show Junge relationships could potentially be found in measurements performed near the mouth of the river, but Junge relationships were not found in currently available monitoring data. In paper II an experimental design and response surface model were developed to study the effect of hyporheic exchange (induced by flowing water) and bacterial diversity in sediment on dissipation half-lives of two micropollutants in flumes. Faster dissipation was observed in flumes with high bacterial diversity and higher hyporheic exchange, and thus both variables are relevant to study dissipation processes in rivers. The influence of biological factors beyond bacteria diversity is explored in papers III and IV, by characterizing the bacteria community composition of sediment in OECD 308 bottle incubations (a standard test that is often recommended in risk assessment guidelines). In paper III, higher variation in half-lives (e.g. relative standard deviations > 50%) were found for micropollutants with longer half-lives (e.g. from 40 to more than 120 days). Higher variation in half-lives also corresponded to differences in bacteria community composition and specifically to increased or decreased abundance of certain bacteria genera. Although the exact bacteria genera involved in the biodegradation of the micropollutants cannot be determined in papers II or III, our results suggest bacteria community composition and diversity should be considered in the interpretation of biodegradation half-lives since they are related to variability in biodegradation and to understand extrapolation from laboratory to the field. Finally in paper IV, it is investigated if the bacteria communities are affected by the OECD 308 test conditions. Changes in the bacteria communities in the sediment between the initial river community, the beginning and the end of the incubation, at high and a low concentrations are reported. Overall, 8% of bacteria genera increased or decreased in relative abundance in all comparisons, and it is unclear if these small changes in bacteria communities could have had an effect on the observed half-lives in paper III.

    This thesis contributes to the understanding of physical and biological factors influencing biodegradation and potential implications for risk assessment of organic micropollutants in rivers.