1 - 15 of 15
rss atomLink to result list
Permanent link
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
  • Public defence: 2019-10-18 10:00 Magnélisalen, Kemiska övningslaboratoriet, Stockholm
    Elmongy, Hatem
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Analytical Methods For Sports Drugs: Challenges and Approaches2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Drugs used to enhance human performance in sport competitions are prohibited by the world anti-doping association (WADA). Biological samples from athletes are continuously tested for adverse analytical findings regarding the identity and/or quantity of the banned substances. The current thesis deals with the development of new analytical methods to determine the concentrations of certain drugs used by athletes and even by regular users for therapeutic purposes. The developed methods aim to analyze the contents of these drugs in the biological matrices; plasma, serum and saliva to provide a successful approach towards either doping detection or therapeutic monitoring. β-adrenergic blockers such as propranolol and metoprolol are used in sports to relief stress and as therapeutic agents in the treatment of hypertension. Both drugs are in chiral forms and available only as racemic mixtures. The different pharmacology of each enantiomer necessitates the monitoring of each enantiomer by stereoselective analytical technique such as chiral liquid chromatography for separation and mass spectrometry for selective detection. The Endogenous anabolic androgenic steroids (EAAS) on the other hand are only notoriously used in sports to increase muscle mass and strength. A method utilizing high-resolution mass spectrometry (HRMS) coupled to ultra-high performance liquid chromatography (UHPLC) was developed for the simultaneous determination of EAAS and their conjugated metabolites to provide a better insight into the steroidal module of the athlete biological passport (ABP). Moreover, the steroidal profile was assessed in serum using the proposed method after the administration of Growth hormone injection as an approach toward the implementation of a new endocrinological module based on steroids biomarkers to hormone doping.  Biological samples contain many components that may interfere with the analytical measurements. Therefore, sample preparation methods were developed using solid phase extraction (SPE) and miniaturized techniques such as microextraction by packed sorbents (MEPS) for the purification and pre-concentration of analytes prior to LC/MS analysis.

  • Public defence: 2019-10-18 10:00 David Magnussonsalen (U31), Stockholm
    Jonsson, Jakob
    Stockholm University, Faculty of Social Sciences, Department of Psychology.
    Preventing problem gambling: Focus on overconsumption2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A proportion of gamblers experience problems. The role of overconsumption in developing gambling problems is sparsely described in the literature and there is little scientific knowledge about the prevention of gambling problems. There are some promising results regarding personalized feedback on gambling habits, and there is a need for more research. The overall aim of this thesis was to explore the role of overconsumption in problem gambling and target it in a preventive intervention. The preventive intervention was to give gambling consumption feedback to high consumers in order to make them reflect upon their gambling habits and enhance their motivation for change. Study I aimed to explore the dimensionality of GamTest, an online test of gambling behaviour, and validate it against PGSI and the gambler’s own perceived problems. Data came from four Nordic gambling sites, n = 10,402. In an ESEM analyses, GamTest had a high degree of correspondence with the players’ own perceived problems and with the PGSI. In an EFA, GamTest captured five dimensions of problematic gambling (i.e. overconsumption of money and time, and negative financial, social and emotional consequences). A bifactor approach showed a general factor and four specific residual factors, negative emotional consequences contribute to the dominant part of the general factor. Study II aimed to examine both the psychometric properties of the Jonsson-Abbot Scale (JAS) and its predictive validity with respect to increased gambling risk and problem gambling onset. The results are based on repeated interviews with 3,818 participants within the Swedish longitudinal gambling study. The results indicate an acceptable fit of a three-factor solution in a CFA, with ‘Overconsumption (OC),’ ‘Gambling fallacies (GF),’ and ‘Reinforcers (RI)’ as factors. When controlled for risk potential measured at baseline, GF and RI were significant predictors of gambling risk potential, and GF and OC were significant predictors of problem gambling onset at 12-month follow up. Study III’s primary objective was to investigate the effects of providing personalized feedback on gambling intensity among high consumers in Norway. An RCT design was used to evaluate how behavioural feedback by telephone or letters affects subsequent gambling expenditure. A sample of 1,003 statistical matched triplets, from the top 0.5 % of customers, were randomly assigned to telephone, letter, or a no-contact control condition. Over 12 weeks, theoretical loss decreased 29 % for the telephone, and 15 % for the letter, conditions, compared with 3 % for the control group. Study IV was a 12-month follow-up of Study III, aimed to investigate the relative effects over twelve months. The telephone group showed a 30 % reduction in theoretical loss, the letter group 13 %, both outperforming the control group with a 7 % reduction. Less than 1% in all groups stopped playing at Norsk Tipping. These four studies indicate that overconsumption of gambling plays different roles in problem gambling. The role of overconsumption in preventing gambling problems is discussed. Contacting high consumers about their gambling expenditure appears to be an effective method for gambling companies to meet their duty of care for customers. Technical evolution has made it possible for gambling companies to fulfil their duty of care, but this has to be regulated and mandatory if it is to be effective.

  • Public defence: 2019-10-18 10:00 Vivi Täckholmsalen (Q-salen), NPQ-huset, Stockholm
    Leslie, David J.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Regulation of the bacterial cell cycle in response to starvation2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Bacteria have adapted to diverse environments, which are often unpredictable and constantly changing. In order to survive, bacteria need to make the most of nutrients while they are available, while being prepared to rapidly change their behaviour when conditions take a turn for the worse. One of the most central processes that must be regulated to ensure survival when conditions change is the cell cycle, the succession of DNA replication, chromosome segregation and cell division connecting growth and proliferation.

    In this thesis, we investigate how environmental information, specifically nutrient availability, is used to modulate cell cycle progression. In Paper I, we uncover a mechanism used by Caulobacter crescentus to arrest DNA replication in response to nutrient depletion. We find that the essential replication initiator protein DnaA is eliminated under these conditions, and determine that this occurs by a mechanism based on constant degradation of DnaA by the protease Lon. This constant degradation is coupled with regulated translation of the dnaA mRNA to decrease DnaA synthesis as nutrient levels decrease. We found that this regulated translation of dnaA depends on its long 5′ untranslated region.

    The replication initiator DnaA is conserved in almost all bacteria, and although some aspects of its regulation are maintained, others work differently in distantly related bacteria. In Paper II, we investigate how the enteric bacterium Escherichia coli regulates DNA replication at the onset of the stationary phase. We found that although DnaA is eliminated as growth slows, this downregulation is not required to arrest replication. We also found that the signalling molecule ppGpp, which is produced in response to starvation, is required for the elimination of DnaA at entry to stationary phase. High ppGpp levels lead to a block of replication initiation, however we found that chromosome content is still dramatically reduced at the onset of stationary phase in the absence of ppGpp, indicating that a ppGpp-independent mechanism is involved.

    While bacteria are usually studied over short timeframes and under optimal conditions in the laboratory, in nature, bacteria are often found in environments where only very slow growth is possible. In Paper III, we investigate a change in morphology observed to occur in a small subpopulation of cells in cultures of C. crescentus after extended incubation in the stationary phase. These cells form long, helical filaments. We determined that the filamentation arises as a result of a block of DNA replication and cell division while growth continues, and that this can be induced by a combination of conditions in the medium: low phosphate, high pH and excess ammonium. We find that these conditions occur in freshwater lakes during persistent algal blooms in the summer months, indicating that this response might occur in the wild.

    In summary, this thesis provides new insight into the mechanisms bacteria use to adapt their cell cycle, and specifically, DNA replication to changes in their environment, how bacteria are able to change their morphology by disrupting the coupling between growth and the cell cycle, and investigates how this morphological plasticity may be advantageous in natural environments.

  • Public defence: 2019-10-18 13:00 William-Olssonsalen, Geovetenskapens hus, Stockholm
    Uddling, Jenny
    Stockholm University, Faculty of Humanities, Department of Language Education.
    Textsamtalens möjligheter och begränsningar i språkligt heterogena fysikklassrum2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis reports and discusses results from case studies of how two physics teachers process the language and subject content of textbook texts in interaction with their students, several of whom are second language learners. The overall aim is to study and contribute to knowledge about the didactic choices teachers make in relation to text-talks in linguistically diverse physics classrooms. In order to find out what might pose linguistic challenges for the students, the textbook texts used in the classrooms are also analyzed.

    Data was collected through video and audio recordings in a year 5 and a year 8 physics classroom, during a period of nine and seven weeks respectively, where physics was taught by teachers who identified themselves as having a language focus in science instruction. In addition to the classroom observations, semi-structured interviews with the teachers were conducted.

    The study is rooted in socio-cultural theory, including literacy and second language acquisition, and in social semiotics, including systemic functional linguistics (SFL) and multimodal perspectives. In the textbook texts, structural and lexicogrammatical features were analyzed. In the text-talks, the analysis focused on how language and content were processed in interaction with the students and what opportunities and limitations this offered the students.

    The results reveal that the science textbook texts impose great linguistic demands upon the students. The results also reveal that both teachers carried out extensive textual processing in interaction with their students, which showed the teachers’ broad repertoire of didactic choices in connection with the text-talks. The text-talks offered an increased redundancy, opportunities to develop academic registers and to some extent to be socialized into disciplinary reading. Limitations were associated with the teachers not always being sufficiently clear about the purpose and implementation of the text-talks, the language focus sometimes taking the focus off the subject matter and the teachers' use of everyday language not always being an asset.

  • Public defence: 2019-10-18 14:00 De Geersalen, Geovetenskapens hus, Stockholm
    Pronin, Mathias
    Stockholm University, Faculty of Social Sciences, Department of Economics.
    Essays in Macroeconomics and Political Economy2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

        The Response of the Riksbank to House Prices in Sweden

    In the aftermath of the recent financial crisis, an environment of historically low interest rates and extensive household indebtedness in the OECD countries have triggered a vivid debate on whether central banks should react to house-price fluctuations in their pursuit of monetary policy. In Sweden, a period of low policy rates and house-price inflation was halted when the central bank increased the interest rates in 2010. This study investigates whether the Riksbank reacted to house prices in the period from 1993 to 2013. Using Bayesian methods and quarterly data, I estimate a DSGE model with patient and impatient households, where the central bank reacts to house-price inflation. The results suggest that the Riksbank did respond to house prices during the sample period. The findings are robust and plausible from an economic perspective. 

    Wealth Distribution under Heterogeneous Preferences

    The standard macroeconomic framework of uninsurable idiosyncratic income risk fails to generate key features of the aggregate wealth distribution. Although the assumptions of heterogeneity of either impatience rate or risk aversion are common in the literature, they do not reflect the evidence and common belief that both parameters are dispersed across the population. I extend the standard framework by allowing for heterogeneity in both impatience and risk aversion. The results suggest that this richer framework outperforms previous work in terms of matching actual properties of the wealth distribution. In particular, the model presented generates a greater concentration of wealth at the top of the distribution and a greater mass of poor households than models with preference heterogeneity in only one dimension. 

    Political Budget Cycles and Dependence on Foreign Aid 

    This study poses the question of whether countries with a higher share of foreign aid per GDP exhibit larger political budget cycles. Using data on a large sample of countries, I find a significant negative effect of aid dependency on the budget surplus in election years. The effect is quantitatively important and implies that on average, a 1% increase in foreign aid per GDP is associated with a 0.2 percentage point larger deficit in election years. The results are robust to the model specification, inclusion of control variables, and other political budget cycles' determining factors described in the recent literature.

  • Public defence: 2019-10-24 10:00 De Geersalen, Stockolm
    Aldama Campino, Aitor
    Stockholm University, Faculty of Science, Department of Meteorology .
    Atmospheric and oceanic circulation from a thermodynamic perspective2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The climate system is continuously transporting and exchanging heat, freshwater, carbon and other tracers in different spatio-temporal scales. Therefore, analysing the system from a thermodynamic or biogeochemical framework is highly convenient. In this thesis the interaction between the ocean and the atmospheric circulation is analysed using thermodynamical and biogeochemical coordinates. Due to the dimensionality of the climate system stream functions are used to reduce this complexity and facilitate the understanding of the different processes that take place. The first half of this thesis, focuses on the interaction between the atmospheric and the ocean circulation from a thermodynamic perspective. We introduce the hydrothermohaline stream function which combines the atmospheric circulation in humidity-potential temperature (hydrothermal) space and the ocean circulation in salinity-temperature coordinates (thermohaline). A scale factor of 7.1 is proposed to link humidity and salinity coordinates. Future scenarios are showing an increase of humidity in the atmosphere due to the increase of temperatures which results in a widening of the hydrothermal stream function along the humidity coordinate. In a similar way, the ocean circulation in the thermohaline space expands along the salinity coordinate. The link between salinity and humidity changes is strongest at net evaporation regions where the gain of water vapour in the atmosphere results in a salinification in the ocean. In addition, the ocean circulation in latitude-carbon space is investigated. By doing so, we are able to distinguish the roles of different water masses and circulation pathways for ocean carbon. We find that the surface waters in the subtropical gyres are the main drivers of the meridional carbon transport in the ocean. By separating the carbon in its different constituents we show that the carbon transported by the majority of the water masses is a result of the solubility pump. The contribution of the biological pump is predominant in the deep Pacific Ocean. The effects of the Mediterranean Overflow Waters on the North Atlantic are discussed in the final part of the thesis.

  • Public defence: 2019-10-25 10:00 William-Olssonsalen, Geovetenskapens hus, Stockholm
    Ödalen, Malin
    Stockholm University, Faculty of Science, Department of Meteorology .
    Model analysis of ocean carbon storage and transport across climate states2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The ocean carbon cycle plays a fundamental role in the Earth’s climate system, on decadal to multi-millennial timescales. Of the carbon held in the ocean, the atmosphere, and the terrestrial biosphere combined, more than 90% resides in the ocean. Carbon enters the surface ocean through air-sea gas exchange and from terrestrial sources. It is transported to the deep ocean with the ocean circulation and through the so-called biological pump, where carbon is taken up in the surface ocean by photosynthetic organisms that fall down and decompose at depth. This thesis contributes to the understanding of the processes involved in ocean carbon storage and transport. It examines how these processes respond to model perturbations, and how this response influences our attempts to simulate glacial-interglacial fluctuations in atmospheric carbon dioxide (CO2).

    The thesis investigates the response of the simulated ocean carbon storage, and distribution of the isotopic tracer δ13C, to changes in physical and biological parameters. In the included studies, we use observational as well as proxy records of oceanic properties to evaluate our model simulations. In addition, we use a climate model to interpret proxy evidence of glacial-interglacial changes in ocean δ13C. By using a separation framework, we identify the origin of the carbon in the model ocean, and attribute observed changes to the processes involved.

    The results indicate a strong link between ocean carbon storage and the strength of the global ocean overturning circulation. Stronger circulation leads to less carbon storage through a weakening of the biological pump, and through reduced solubility due to an increase in global ocean average temperature.

    In simulations of glacial climate, we find that biological adaptability to the surrounding nutrient conditions, through a flexible carbon-to-phosphorus ratio (C/P) in ocean photosynthesis, increases the ocean carbon storage compared to simulations where fixed C/P is applied. The biological flexibility improves the model’s ability to reproduce glacial atmospheric CO2. In line with previous research, we find freshwater input to the North Atlantic to be an important factor for reproducing glacial proxy records. The ensemble of simulations that achieve a good representation of glacial-interglacial δ13C indicates a deglacial whole-ocean change in δ13C of 0.28 ± 0.06‰.

    The thesis underlines the importance of the initial state, and the choice of model parameterisations, for the outcome of model ensemble, and intercomparison studies. Finally, it proposes a new method for estimation of ocean carbon transport, and attribution of this transport to different water masses and carbon system processes.

  • Public defence: 2019-10-25 10:00 Ahlmannsalen, Geovetenskapens hus, Stockholm
    Aguirre Vidal, Gladis
    Stockholm University, Faculty of Social Sciences, Department of Social Anthropology.
    Mobilising care: Ecuadorian families and transnational lives between Ecuador and Spain2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis focuses on the dynamics of care in the transnational lives of Ecuadorian migrant women in Spain. It is concerned with the various forms of care that take shape and are sustained in the workplace, between friends, and among family members in Ecuador and Spain. Ultimately, it sheds light on how care is mobilised to sustain ideals of solidarity at work as well as togetherness in transnational life. The thesis is set against the background of the economic and political crisis in Ecuador of the late 1990s and early 2000s, which resulted not only in the dollarization of the economy and the removal of the country’s president, but in a dramatic shift of traditional male migration from the southern highlands to the United States, to a new wave of largely middle class female migration to Western Europe, especially Spain. Women from across the country left their children, spouses and elderly parents behind to work in domestic and care jobs abroad. In Ecuador, this disturbed the dominant cultural imaginary of the co-habitating and united family, centred on the presence of the woman as mother and wife. In light of this, the thesis engages with women’s dilemmas in giving and receiving care during years of absence, the role of family members, friends and domestic workers in this process, and the development of long-term goals focused on remittances, reunification, return, and the ultimate goal of creating a better future. Most generally, while challenging a series of dichotomies between love and money, home and work, gift and commodity—which have structured academic discussions concerning the feminization of international migration—the thesis describes the intimate relationship between women’s participation in the gift economy and a global labour market through the lens of care relationships.

  • Public defence: 2019-10-25 14:00 Nordenskiöldsalen, Geovetenskapens hus, Stockholm
    Darougheh, Saman
    Stockholm University, Faculty of Social Sciences, Department of Economics. Stockholm University, Faculty of Social Sciences, Institute for International Economic Studies.
    Search and Mismatch2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    I define occupations that are employed in more industries as “broader” occupations. I study the implications of occupation-level broadness for mismatch of unemployed and vacancies across occupations and industries. In the cross-section, workers in broader occupations are better insured against industry-level shocks and less at risk of being mismatched. Using geographical variation in occupation-level broadness, I show that during the Great Recession, unemployed workers from broader occupations had higher job-finding rates and smaller increases in unemployment than those previously employed in more specialized occupations. I contrast these cross-sectional results to the aggregate implications of mismatch. To that end, I build a model where the resulting mismatch of an industry-level shock depends on how specialized the affected occupations are. The model extends the Lucas (1974) island setting with frictional intra-island labor markets and frictional inter-island mobility. Workers in broader occupations are insured against industry-level productivity shocks because they can stay in their occupation but work in other unaffected industries. When individuals from broad occupations move to other industries, they propagate the shock to more workers. This strong general equilibrium mechanism offsets the direct effect. The results indicate that recessions which cause more mismatch lead to larger unemployment risk for workers in specialized occupations, but do not cause larger fluctuations of the aggregate unemployment rate.   

    I develop a model of the consumer good market where the individual’s search decision is consistent with balanced-growth preferences. Here, optimal search is independent of income but increases with the time endowment. I characterize the potentially multiple equilibria and test whether the model can replicate differences in observed shopping behavior across employed and unemployed individuals. Using the American Time Use Survey, I show that unemployed individuals have an almost 50 % larger time endowment available for leisure and shopping. Meanwhile, they only spend 18 % more time shopping than the employed. In the calibrated model, however, unemployed households will spend around twice as much time shopping as employed households. I argue that consumer-goods search models are not yet ready for business cycle analysis, and discuss ways of reconciling the model with the data.   

    We study the impact of worker protection in an environment with heterogeneous match productivity and a constrained wage setting. Firms can either employ costly screening to determine the match quality, or hire workers out of their applicant pool at random, learn about the match quality, and disengage from bad matches. Thus, layoff protections intervene with a firm’s ability to screen matches. In our calibration, a policy that prevents layoffs reduces unemployment and increases consumption in the new steady state. However, the economy becomes more susceptible to productivity shocks. Two additional channels transmit productivity shocks when layoffs are regulated. First, the value of hiring at random is more volatile when separating bad matches is no longer an option. Second, additional screening in recessions worsens the composition of the unemployed pool. Consequently, recessions will be long lasting and hiring is lower even after the TFP shock has receded. We conclude that economies potentially have a higher average output under layoff regulations, but that this comes at the cost of higher volatility and jobless recoveries.

  • Public defence: 2019-10-28 10:00 David Magnussonsalen (U31), Stockholm
    Zakirova Engstrand, Rano
    Stockholm University, Faculty of Social Sciences, Department of Special Education.
    Families of young children with autism spectrum disorder in Sweden: The role of culture and intergenerational support2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Children with autism spectrum disorder (ASD) have shown high variability in learning outcomes in response to evidence-based interventions, suggesting a need for individualization of intervention programmes for each child and his/her family. To explain this variability and develop effective intervention strategies research suggested focusing on identification of important contextual factors that might influence the effectiveness of a specific intervention for each child such as family cultural characteristics and characteristics of service settings and systems. The overarching aim of the thesis was to identify and describe proximal and distal environmental factors and processes affecting implementation and provision of interventions and services for young children with ASD and their families within the context of the Swedish support system. Two theoretical models guided the research project: Bronfenbrenner’s bioecological model of human development and Wachs’s multiple-influences model of individual variability. The specific objectives addressed using a mixture of qualitative and quantitative methods were: (i) to investigate the scope of reporting ethnicity and other cultural factors in research publications by Swedish scholars involved in empirical research in ASD in children and youth (Study 1); (ii) to explore perceptions of autism, beliefs about its causes, and treatment preferences expressed by parents of children with ASD from culturally, ethnically and linguistically diverse backgrounds (Study 2), and (iii) to explore grandparents’ perceived needs in relation to having a young grandchild with ASD (Study 3).

    The results of data triangulation across the three studies showed that within the context of the Swedish support system, three proximal environmental factors were associated with identification of ASD in young children and families’ use of services and interventions before and after the child was diagnosed with ASD. These were parents’ belief systems (including perceptions about child’s autism, help-seeking behaviours, and treatment preferences); the role of preschool teachers, and the role of other service providers, such as healthcare professionals. Data triangulation singled out seven groups of distal environmental factors: beliefs of extended family; family cultural, ethnic and linguistic background; family socio-economic characteristics (occupation and education level); Swedish formal support system enacted through various legislative acts; international laws and regulations; information sources (mass media and social media), and conceptualization and clinical definition of ASD (as reflected in DSM and ICD classifications). Findings also highlight the importance of taking into consideration of role of ASD researchers as an additional distal environmental factor affecting implementation of interventions and services for culturally and linguistically diverse children with ASD and their families.

    The results of the studies provide insights into understanding of families’ belief systems about ASD causes, treatment preferences, and needs that are essential for planning and provision of family-level early interventions for children with ASD in the cultural context of Sweden. Implications for practice and future research are discussed. 

  • Public defence: 2019-10-28 13:00 FP41, hus 1, AlbaNova universitetscentrum, Stockholm
    de Andrés Prada, Roberto
    Stockholm University, Faculty of Science, Department of Physics. Physics Department and Fribourg Center for Nanomaterials (FriMat), University of Fribourg, Switzerland.
    Pulsed laser deposition and nanofabrication of mesoscopic devices based on cuprates and manganites2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis explores the growth, the nano-fabrication and the study of the magneto-transport properties of Superconductor/Ferromagnet/Superconductor (SFS) structures from complex oxides such as the high Tc superconducting cuprate YBa2Cu3O7 (YBCO) and the ferromagnetic manganites La2/3Ca1/3MnO3 and La2/3Sr1/3MnO3 (LCMO and LSMO), deposited with the pulsed laser deposition (PLD) technique.The present work has been possible thanks to the collaboration between the “Magnetism and Superconductivity” Group at the University of Fribourg, in Switzerland, and the “Experimentell Kondenserade Materiens Fysik” Group at Stockholm University, in Sweden.

    Earlier, the two research groups in Fribourg and Stockholm had studied SFS structures from YBCO/LaMnO3/YBCO multilayers with 20 nm thick ferromagnetic and insulating LaMnO3 barriers, and obtained signs of an unconventional spin-triplet current across these structures. This finding motivated the present thesis work with a focus on two main aspects.

    Firstly, to explore other candidate materials suitable as barriers and optimise their growth conditions as to maintain a large ferromagnetic moment and thus a high spin polarisation of the charge carriers. Secondly, to study what happens when the thickness of the ferromagnetic and insulating LaMnO3 barrier is reduced well below 20 nm to enable larger supercurrents.

    It has been shown for a series of YBCO/LCMO multilayers that the ferromagnetic moment of LCMO depends critically on the PLD growth conditions as well as on the thickness and even structural details of the YBCO layer on which they are grown. Furthermore, a protocol has been established to grow heterostructures with strongly ferromagnetic manganite layers embedded in thick YBCO layers by optimising the PLD growth conditions and by substituting the bottom YBCO layer with a Co and Ca substituted version of YBCO that has a tetragonal structure (tYBCO) instead of the orthorhombic one of plain YBCO.

    Devices suitable for perpendicular magneto-transport measurements have been nano-fabricated from YBCO/manganite/YBCO multilayers with ~10 nm thick LCMO and LSMO layers as the F barriers. While no clear indications of a spin-triplet component of the superconducting order parameter have been obtained yet, a negative and hysteretic magneto-resistance has been observed that is indicative of a strong ferromagnetic order in the thin manganite barrier. The latter suggests a potential memory functionality of such structures that could be exploited in future spintronic memory devices.

    Moreover, devices have been fabricated on SFS structures with a reduced thickness of the LaMnO3 barrier of 10 nm and 5 nm. These samples were grown prior to the beginning of this PhD work using non optimised growth conditions, and it was found that the ferromagnetic properties of these LaMnO3 barriers are strongly deteriorated. It remains to be seen whether the ferromagnetic order of such thin LaMnO3 layers can be also recovered by using the optimised growth conditions as for LSMO and LCMO.

  • Public defence: 2019-10-30 09:00 David Magnussonsalen (U31), Stockholm
    Eklund, Rasmus
    Stockholm University, Faculty of Social Sciences, Department of Psychology.
    Electrophysiological correlates of consciousness2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    How does the brain enable us to experience seeing or hearing a stimulus? If a stimulus is repeatedly presented at the awareness threshold, subjects will report that they are aware of the stimulus on half of the presentations. Electroencephalography (EEG) can be used to non-invasively record neural activity as event-related potentials (ERPs). The contrastive analysis of neural activity to trials rated as aware minus neural activity to trials rated as unaware reveals the neural correlates of consciousness (NCC). Research on the NCC in vision has resulted in two ERPs: an early negative difference wave (visual awareness negativity, VAN) and a subsequent late positivity (LP). Visual awareness may be reflected by one or both of these ERPs. However, the contrastive analysis (aware minus unaware) may not isolate the NCC because it arguably compares aware processing with a combination of unaware processing and no processing. In support, previous research that tried to isolate a comparison between aware processing and unaware processing found that LP was the only NCC. However, subsequent replications suggested VAN and LP as NCC. Because of these mixed results, we followed up on these studies in Study I with a preregistered design that manipulated stimulus size. Results showed VAN and LP as NCC. The findings provide evidence for VAN as an early NCC.

    Another main goal of this thesis was to investigate auditory awareness. In Study II, an auditory threshold task was used, and the contrastive analysis revealed an early negative difference wave (auditory awareness negativity, AAN) and LP. These ERPs are comparable to VAN and LP in vision. Because post-perceptual processes related to responding may confound the NCC in contrastive analysis, no-response tasks can be used to isolate awareness-related activity. In vision, a previous study in which the manual response requirement was manipulated showed effects on LP but not on VAN. In Study III, we used a similar task with auditory stimuli at the awareness threshold. Results suggested that AAN and LP are unaffected by the response manipulation. However, the present no-response task may not be optimal for removing post-perceptual processing because subjects need to reflect on their experience even if they do not need to respond manually. Additional analyses that attempted source localization of the AAN suggested that it is generated in auditory cortex.

    From a theoretical perspective, one view of these results is that VAN and AAN reflect local recurrent processing and that this is the neural signature of awareness, whereas LP reflects global recurrent processing that enables reporting. Other views suggest that VAN and AAN merely reflect preconscious processes, whereas LP and global recurrent processing reflect consciousness. The studies described in this thesis do not support one theory over the other but provide robust evidence for early neural correlates of visual and auditory awareness.

  • Public defence: 2019-11-01 10:00 CCK lecture hall, building R8, Solna
    Sandström, Helena
    Stockholm University, Faculty of Science, Department of Physics.
    Contouring & planning variability in stereotactic radiosurgery: How to assess and address the weakest link in stereotactic radiosurgery?2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of stereotactic radiosurgery (SRS) employing one or a few fractions of high doses of radiation has continuously increased due to the technical development in dose delivery and morphological and functional imaging. As the target volume in SRS is usually defined without margins, the treatment success critically depends on accurate definition and contouring of the target volume and organs at risk (OARs) which are commonly situated in the proximity of the target making their precise delineation particularly important in order to limit possible normal tissue complications. Subsequent treatment planning is reliant on these volumes, which makes the accurate contouring a requisite to high quality treatments. 

    The purpose of this work was to evaluate the current degree of variability for target and OAR contouring and to establish methods for analysing multi-observer data regarding structure delineation variability. Furthermore, this was set in a broader picture including the importance of contouring studies, the clinical implications of contouring errors and the possible mitigation of the variability in contouring by robust treatment planning.

    A multi-centre target and OAR contouring study was initiated. Four complex and six common cases to be treated with SRS were selected and subsequently distributed to centres around the world performing Gamma Knife® radiosurgery for delineation and treatment planning. The resulting treatment plans and the corresponding delineated structures were collected and analysed.

    Results showed a very high variability in contouring for the four complex radiosurgery targets. Similar results indicating high variability in delineating the common targets and OARs were also reported. This emphasised the need of continuous work towards consistent and standardized SRS treatments. Consequently, the results of the OAR analysis were incorporated in an effort to standardize stereotactic radiosurgery (SRS). Variations in treatment planning were as well analysed for several of the indications included in the initial study on contour delineation and the results showed a high variability in planned doses including several plans presenting large volumes of the brain receiving a higher dose than 12 Gy, indicating an elevated risk of normal tissue complications.

    The results of the contouring work were, as a last step of this thesis, used as input for a robust treatment planning approach considering the variability in target delineation. The very preliminary results indicate the feasibility of the probabilistic approach and the potential of robust treatment planning to account for uncertainties in target extent and location.

  • Public defence: 2019-11-06 13:00 Gröjersalen, hus 3, Kräftriket, Stockholm
    Dahlström, Petter
    Stockholm University, Faculty of Social Sciences, Stockholm Business School.
    New Insights on Computerized Trading: Implications of Frequently Revised Trading Decisions2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computerized trading may be viewed as an aspect of modernization of financial markets. This dissertation contains four articles that in different ways examine to what extent the modernization influences the economics of the markets.

    Article 1 investigates transaction costs for large orders which are split up by execution algorithms to be executed in smaller pieces.  I find that the costs associated with not being able to execute all pieces are substantial. These costs can be lowered by speeding up the trading pace but at the expense of higher costs for the successfully executed pieces.

    Article 2 investigates the strategies trading firms pursue in particular cases, known as toxic arbitrage opportunities. We find that trading firms, that otherwise behave as market makers, morph into liquidity takers as toxic arbitrage opportunities emerge. In contrast to common belief, market makers are net beneficiaries of toxic arbitrage, and this finding puts into question whether the amount of toxic arbitrage leads to wider bid-ask spreads.

    Article 3 investigates the information content of limit orders in an alternative way by studying the price impact implied by the depth in the limit order book. I find that the price impact estimates are slightly lower relative to those from a structural vector auto regressive model, but slightly higher compared to those from a price impact regression. Thus, the limit order book implied price impact estimates match those from benchmark models, and this finding contradicts earlier research.

    Article 4 investigates the economic rationale behind limit order cancellations. We put forth a model that explains the frequent limit order cancellations seen in today’s markets, and we test its predictions using a unique data set from Nasdaq. Our results points towards that frequent order cancellations is a benign feature of modern market making, as opposed to different types of manipulative behavior.

  • Public defence: 2019-11-29 13:00 sal FB54, AlbaNova universitetscentrum, Stockholm
    Wallängen, Veronica
    Stockholm University, Faculty of Science, Department of Physics.
    Performance Improvements for Particle Tracking Detectors in Extreme Rate and Radiation Environments2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In order to increase its discovery potential, the Large Hadron Collider (LHC) at CERN is being transformed into a higher luminosity machine expected to be operational around 2026. The number of particle collisions will increase by a factor of 10 beyond the current design value, which means that the detectors installed around the LHC are facing various new challenges. The most demanding challenges include handling the enormous data quantities that will be transferred from the front-end readout modules at significantly higher rates than previously, as well as the radiation effects that arise as a consequence of the intense particle flow and that cause damage to sensor elements and electronics.

    At the ATLAS experiment, a multipurpose detector operating at the LHC, the impact of the luminosity increase is especially severe for the silicon pixel tracking detector, being the central subsystem located closest to the particle interaction point and therefore exposed to the highest radiation dose and hit density. The extreme radiation doses that the pixel modules will be subject to will cause deformation of the sensor material structure and thus loss of the signals, which after subsequent digitization by the pixel readout chip must be transferred over relatively long distances through a low-mass data link, causing further signal distortion.

    The work presented here addresses both major challenges described and outlines solutions for the upcoming upgrade of the ATLAS pixel detector system with regards to these. Firstly, it is demonstrated how improved accuracy of detector simulations and reconstruction of particle trajectories through the detector can be achieved as higher particle fluences are approached, by modeling radiation damage effects that occur in the pixel sensors. Secondly, it is shown how a receiver integrated circuit utilizing an industry standard technique novel within high-energy physics applications has been designed as an integral part of a high-speed transmission link to efficiently restore the signal quality in order to achieve adequate data readout rates.