| 1. |
- Andersson, Erik, 1984-
(författare)
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PHYSIOLOGICAL AND BIOMECHANICAL FACTORS DETERMINING CROSS-COUNTRY SKIING PERFORMANCE
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cross-country (c.c.) skiing is a complex sport discipline from both physiological and biomechanical perspectives, with varying course topographies that require different proportions of the involved sub-techniques to be utilised. A relatively new event in c.c. skiing is the sprint race, involving four separate heats, each lasting 2-4 min, with diverse demands from distance races associated with longer durations. Therefore, the overall aim of the current thesis has been to examine the biomechanical and physiological factors associated with sprint c.c. skiing performance through novel measurements conducted both in the field (Studies I-III) and the laboratory (Studies IV and V).In Study I sprint skiing velocities and sub-techniques were analysed with a differential global navigation satellite system in combination with video recording. In Studies II and III the effects of an increasing velocity (moderate, high and maximal) on the biomechanics of uphill classical skiing with the diagonal stride (DS) (Study II) and herringbone (HB) (Study III) sub-techniques were examined.In Study I the skiers completed the 1,425 m (2 x 712 m) sprint time trial (STT) in 207 s, at an average velocity of 24.8 km/h, with multiple technique transitions (range: 21-34) between skiing techniques (i.e., the different gears [G2-7]). A pacing strategy involving a fast start followed by a gradual slowing down (i.e., positive pacing) was employed as indicated by the 2.9% faster first than second lap. The slower second lap was primarily related to a slower (12.9%) uphill velocity with a shift from G3 towards a greater use of G2. The maximal oxygen uptake ( O2max) was related to the ability to maintain uphill skiing velocity and the fastest skiers used G3 to a greater extent than G2. In addition, maximal speed over short distances (50 and 20 m) with the G3 and double poling (DP) sub-techniques exerted an important impact on STT performance.Study II demonstrated that during uphill skiing (7.5°) with DS, skiers increased cycle rate and cycle length from moderate to high velocity, while cycle rate increased and cycle length decreased at maximal velocity. Absolute poling, gliding and kick times became gradually shorter with an elevated velocity. The rate of pole and leg force development increased with elevated velocity and the development of leg force in the normal direction was substantially faster during skiing on snow than previous findings for roller skiing, although the peak force was similar in both cases. The fastest skiers applied greater peak leg forces over shorter durations.Study III revealed that when employing the HB technique on a steep uphill slope (15°), the skiers positioned their skis laterally (“V” between 25 to 30°) and planted their poles at a slight lateral angle (8 to 12°), with most of the propulsive force being exerted on the inside forefoot. Of the total propulsive force, 77% was generated by the legs. The cycle rate increased across all three velocities (from 1.20 to 1.60 Hz), while cycle length only increased from moderate to high velocity (from 2.0 to 2.3 m). Finally, the magnitude and rate of leg force generation are important determinants of both DS and HB skiing performance, although the rate is more important in connection with DS, since this sub-technique involves gliding.In Studies IV and V skiers performed pre-tests for determination of gross efficiency (GE), O2max, and Vmax on a treadmill. The main performance test involved four self-paced STTs on a treadmill over a 1,300-m simulated course including three flat (1°) DP sections interspersed with two uphill (7°) DS sections.The modified GE method for estimating anaerobic energy production during skiing on varying terrain employed in Study IV revealed that the relative aerobic and anaerobic energy contributions were 82% and 18%, respectively, during the 232 s of skiing, with an accumulated oxygen (O2) deficit of 45 mL/kg. The STT performance time was largely explained by the GE (53%), followed by O2 (30%) and O2 deficit (15%). Therefore, training strategies designed to reduce energetic cost and improve GE should be examined in greater detail.In Study V metabolic responses and pacing strategies during the four successive STTs were investigated. The first and the last trials were the fastest (both 228 s) and were associated with both a substantially larger and a more rapid anaerobic energy supply, while the average O2 during all four STTs was similar. The individual variation in STT performance was explained primarily (69%) by the variation in O2 deficit. Furthermore, positive pacing was employed throughout all the STTs, but the pacing strategy became more even after the first trial. In addition, considerably higher (~ 30%) metabolic rates were generated on the uphill than on the flat sections of the course, reflecting an irregular production of anaerobic energy. Altogether, a fast start appears important for STT performance and high work rates during uphill skiing may exert a more pronounced impact on skiing performance outdoors, due to the reduction in velocity fluctuations and thereby overall air-drag.
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| 2. |
- Björklund, Erik
(författare)
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Avoiding ageing : Surface degradation of commercial electrode materials in lithium-ion batteries
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The battery market today expands rapidly, not least for electric vehicles. But to compete against the combustion engine, the cost of batteries must be reduced. After years of usage, the batteries degrade and need to be exchanged, increasing the cost over the vehicle lifecycle. This can be mitigated by tailoring the usage conditions and the battery materials. Understanding and avoiding ageing can be key to a more sustainable transport system. This thesis contains studies on degradation processes in Li-ion batteries utilizing the LiNixMnyCozO2 (NMC) cathode material, and suggests strategies for the improvement of battery life time.When cycling different negative electrodes – including graphite, lithium foil and lithium titanium oxide (LTO) – against NMC electrodes, only minor capacity fading was observed in the NMC-LTO and NMC-graphite cells, in contrast to the NMC-Li-metal cells. The capacity fading for Li-metal cells was determined to be caused by degradation products formed at the lithium foil which thereafter diffused to the NMC electrode, leading to a higher resistance. Commercial NMC/LiMn2O4-graphite cells were also investigated after cycling in limited state of charge (SOC)-intervals. The cycle life was far longer in the low-SOC cell than in the high-SOC cell. Photoelectron spectroscopy revealed increased manganese dissolution in the high-SOC cell, likely causing a less stable solid electrolyte interphase layer on the negative electrode. This, in turn, limits the capacity. How temperature influence ageing in NMC-LTO was analysed in cells cycled at -10 °C, 30 °C and 55 °C. It was found that the initial side reactions at the LTO electrode limited the cell capacity, but that these also stabilized the NMC electrode. At 55 °C, excessive side reactions at LTO caused capacity fading due to loss of active lithium. At -10 °C, high cell resistance limited the capacity. Switching to a PC based electrolyte allowed stable low temperature cycling, although it was found that PC degraded and formed thick electrode surface layers. Also sulfolane-based electrolytes were investigated, showing thinner surface layers than the EC containing reference electrolyte at high potentials, thus indicating a more stable electrolyte system.
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| 3. |
- Björklund, Erik, 1967-
(författare)
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Early Risk Stratification, Treatment and Outcome in ST-elevation Myocardial Infarction
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We evaluated, in patients with ST-elevation myocardial infarction (STEMI) treated with thrombolytics, admission Troponin T (tnT), ST-segment resolution and admission N-terminal pro-brain natriuretic peptide (NT-proBNP) for early risk stratification as well as time delays and outcome in real life patients according to prehospital or in-hospital thrombolytic treatment. Also, baseline characteristics, treatments and outcome in patients enrolled in the ASSENT-2 trial in Sweden and in patients not enrolled were evaluated.TnT (n=881) and NT-proBNP (n=782) on admission and ST-resolution at 60 minutes (n=516) in patients from the ASSENT-2 and ASSENT-PLUS trials were analysed. Elevated levels of NT-proBNP and tnT on admission were both independently related to one-year mortality. However, when adding information on ST-resolution (We investigated consecutive STEMI patients included in the RIKS-HIA registry between 2001 and 2004, if they were ambulance transported and had received prehospital (n=1690) or in-hospital (n=3685) thrombolytic treatment. Prehospital diagnosis and thrombolysis reduced the time to thrombolysis by almost one hour, were associated with better left ventricular function and fewer complications and reduced the adjusted one-year mortality by 30% compared with in-hospital thrombolysis.Prospective data from the RIKS-HIA registry on STEMI patients treated with thrombolytics were linked to data on trial participants in the ASSENT-2 trial of thrombolytic agents and used for direct comparisons. Patients treated with thrombolytics and not enrolled in a clinical trial at trial hospitals (n=2048) had higher risk characteristics, more early complications and twice as high adjusted one-year mortality compared to those enrolled (n=729). One major reason for the difference in outcome appeared to be the selection of less critically ill patients to the trial.
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| 4. |
- Björklund, Erik
(författare)
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Platelet inhibition and secondary prevention in cardiac surgery patients
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- ABSTRACT Background and objective Coronary artery bypass grafting (CABG) is the most common cardiac surgery procedure. Dual antiplatelet therapy (DAPT) reduces the risk for ischaemic events in patients with acute coronary syndrome (ACS) but increases the bleeding risk, both for spontaneous bleedings and procedure-related bleedings for the subset of ACS patients undergoing urgent CABG. Statins, beta-blockers, and renin-angiotensin-system (RAS) inhibitors are commonly prescribed after CABG but the scientific evidence for their use after CABG is scarce. The objective of this thesis is to investigate how different aspects of pharmacotherapy are associated with short- and long-term risk for adverse events after CABG. Methods Study I: Platelet function before and after cardiac surgery was analysed using impedance aggregometry in patients treated with acetylsalicylic acid and the P2Y12-inhibitor ticagrelor. Associations between pre- and postoperative platelet function and risk for severe postoperative bleeding were investigated. Study II-IV: Individual patient data from the Swedish Cardiac Surgery Registry, the National Patient Register, the Swedish Prescribed Drug Register, LISA register and the Cause of Death Register was merged to obtain data on procedural aspects, baseline comorbidities, adverse events and mortality after CABG. Study II investigated associations between use of statins, beta-blockers, RAS-inhibitors and platelet inhibitors and mortality risk. Study III investigated if the combination of ASA and ticagrelor was associated with improved clinical outcome compared to ASA monotherapy in patients with acute coronary syndrome undergoing CABG. Study IV investigated the associations between post-discharge major bleeding and myocardial infarction respectively with subsequent mortality risk. Results Study I: Postoperative platelet aggregation induced by adenosin diphosphate (ADP) had an area under curve (AUC) of 0.75 (95% CI 0.62-0.87) in predicting severe bleeding. The corresponding value for preoperative testing was AUC of 0.77 (95% CI 0.65-0.89). Study II: Utilization of secondary prevention medication was high early after CABG but decreased significantly over time. Ongoing use of statins, RAS inhibitors and platelet inhibitors were associated with reduced mortality risk after CABG. Use of beta-blockers was not associated with lower mortality risk. Study III: The combination of acetylsalicylic acid (ASA) and ticagrelor was not associated with lower risk for ischaemic events but increased the bleeding risk compared with ASA monotherapy. Study IV: Post-discharge major bleeding was associated with increased mortality risk, comparable to the increase in mortality risk associated with post-discharge myocardial infarction. Conclusions Adding a postoperative test of platelet aggregation did not improve accuracy in predicting severe bleeding. Improving long-term utilization of statins, RAS inhibitors and platelet inhibitors poses an opportunity to improve long-term survival after CABG. Prospective, randomized controlled trials are warranted to establish the clinical outcome of DAPT with ticagrelor after CABG in ACS patients, especially considering the increased mortality risk associated with post-discharge major bleeding events.
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| 5. |
- Björklund, Elisabet, 1983-
(författare)
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The Most Delicate Subject : A History of Sex Education Films in Sweden
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this dissertation is to present a history of sex education films in Sweden, from their beginnings until the late 1970s, relating the films to the changing historical context of the Swedish welfare society. Within this framework, the dissertation explores two main sets of questions. First, utilizing a contextual understanding of genre, the dissertation analyzes how the films were produced, exhibited, and censored, what position and status they had, and where the borders were understood to be to kindred types of film, such as exploitation and pornography. Second, the norms and ideas about sexuality that the films construct are explored from a social constructionist perspective and put in historical context. Apart from the films themselves, the material used consists of censorship records, archival material, and articles and reviews from the daily press and the trade press.The study demonstrates that the sex education film has always been a delicate genre, and that this delicacy is related to the medium and to the fact that cinema is part of the commercial market. The sex education film came to Sweden through imported films during the silent era and was relatively common at Swedish movie theaters from the 1920s to the early 1970s. Very quickly, it became a contested genre thought to be in need of regulation, which can be seen in the censorship procedures. For instance, until the 1950s, screenings were often restricted through gender segregation. When film censorship was liberalized in the 1960s, sex education films could show more than before, and when the films in the sexually explicit Language of Love series (1969–1972) were released, their relationship to pornography became a central point of discussion. The changing views on using film in school sex education are also examined. Here, it is shown that if film was seen as a potentially helpful tool in the 1920s and 1930s, this view had changed into a more skeptical position by the early 1970s.In the analysis of the content of the films, only Swedish examples are studied. In the first group of theatrically shown films of this kind, which appeared in the 1940s and 1950s, sexuality is represented as problematic through the themes of venereal disease and abortion. Here, casual sex is seen as immoral and abortion is condemned. At the same time, the films display how traditional and modern views on sexuality and gender were under negotiation during this period. While reproduction was the dominating perspective in school films well into the 1970s, the Language of Love films display a radically different perspective on sex, not least because of their focus on sexual pleasure. However, while the films advocate a liberal idea about sexuality according to which science leads to liberation, a focus on romantic long-term relationships can also be noted. Throughout the period, there is an emphasis on rationality and science and on a secular perspective on sex in which love is seen as more important than matrimony. In this way, the films in general reflect a strong belief in modernity and progress that was characteristic of Sweden during the welfare era.
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| 6. |
- Björklund, Lars-Erik, 1953-
(författare)
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Från novis till expert : förtrogenhetskunskap i kognitiv och didaktisk belysning
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Syftet med den här avhandlingen är att bidra till förståelsen av beprövad erfarenhetsbaserad kunskap, det vi förknippar med fårdigheter, förmågor och förtrogenhet. Avhandlingen är enintegrerande forskningsöversikt, fntegrative research review. Genom att sammanställa, jämföra och integrera resultat från psykologins, beteendevetenskapens, neuromedicinens och neurofysiologins forskningsfålt synliggör författaren en neurodidaktisk modell för hur experters egenskaper och förmågor byggs upp under praktisk erfarenhet i en specifik kontext.När en engagerad individ utsätts för en upprepad variation av upplevelser skapas kunskap som består av utfallsmärkta sensoriska mönster i framför allt de basala ganglierna men även i amygdala och cerebellum. Dessa sammantaget utgör ett implicit, omedvetet inlärningssystem parallellt med det medvetna explicita. Det implicita systemet jämför det vi betraktar med tidigare lagrade mönster vilket gör att vi snabbt kan upptäcka vad som är relevant i komplexa, stressade situationer. Med dess hjälp blir vi mer kompetenta i vår roll som lärare, hantverkare, läkare etc. Den här kunskapen blir omedveten, dold och tyst, det som Polanyi kallar Tacit knowledge och som bröderna Dreyfus refererar till som holistic pattern recognition. När vårt medvetande uppmärksammar ett igenkännande i det implicita systemet upplever vi en känsla, intuition eller gut feeling. Det implicita bedömningssystemet hämmas inte av arbetsminnets begränsningar i hastighet och antal detaljer och blir med tiden en resurs som visar sig som förtrogenhet inom en praktik. Mycket talar för att de mönster och erfarenheter som lagras i det implicita systemet används vid problemlösning. Detta leder till implikationer för hur undervisning och lärandemiljöer i exempelvis teknikämnet ska planeras för att befrämja en kreativ utveckling hos den lärande.Det implicita systemet ger oss en omedveten kapacitet att tolka andra människors kroppsspråk och aktiveras av kända kontexter och artefakter. Detta påverkar de svar vi som forskare får från våra informanter i en intervjusituation. För att nå expertens tysta kunskap om t.ex. bedömningskriterier kan en speciell intervjumetod; Repertory Grid Technique, användas.
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| 7. |
- Demandt, Marnie H
(författare)
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Biodiversity in Swedish Cyprinid Fish: Insights Into Processes of Divergence
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Uncovering and understanding the processes that have led to the biological diversity we observe today are of fundamental interest in biology. Since direct observation of speciation is usually impossible, knowledge about the processes behind species formation can be gathered by studying mutations, natural/sexual selection, and genetic drift. In this thesis I aim to identify evolutionary processes that cause species divergence and, ultimately, speciation using Swedish cyprinid fish as a model system. Assuming that the demographic history of a population is mirrored in the genome, I studied the effects of a bottleneck on genetic variability in populations of roach. As expected, I found that a decrease in population size caused a decrease in genetic variability, a pattern that was obtained from both microsatellite and mitochondrial data. The importance of hybridization for speciation is debated, however, by analyzing morphology and microsatellites I could show that common bream and white bream and their interspecific hybrids are phenotypically and genetically differentiated and that ongoing geneflow is mainly unidirectional. Ongoing geneflow antagonizes the effect of genetic drift, but by studying isolated populations (= no gene flow) the impact of genetic drift can be assessed. Long-term isolated populations of roach and perch surprisingly showed stable levels of genetic diversity over time despite decreasing effective population size. However, each population genetically diverged during the period of investigation, a finding that is consistent with the effect of drift. An analysis of the systematic relationship of the 18 species of Swedish cyprinids revealed low congruence of phylogenies based on two different genetic markers. The position of the tench remains unresolved and the relationship of common bream and white bream as sister species cannot be confirmed. Within cyprinid fishes, diversification rates reveal a slowdown with time, a pattern that I found also in other fish clades and that is consistent with density-dependent cladogenesis. Overall, based on the findings presented in this thesis I emphasize that the maintenance of genetic variation in populations is essential since genetic variation is the key element for processes of divergence to act upon.
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| 8. |
- Stolpe, Karin
(författare)
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Att uppmärksamma det väsentliga : Lärares ämnesdidaktiska förmågor ur ett interaktionskognitivt perspektiv
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Den här avhandlingen syftar till att belysa lärares ämnesdidaktiska förmågor i naturvetenskap. Jag fokuserar på tre olika förmågor som är centrala för lärare, nämligen lärares professionella seende, deras automatiska agerande samt deras förmåga att berätta narrativ. Den teoretiska utgångspunkten för avhandlingen är det som jag kallar för det interaktionskognitiva perspektivet. Tre olika aspekter av interaktion behandlas, interaktion mellan individen och hennes omgivning, interaktion mellan individen och andra individer samt interaktion mellan två olika kunskapsformer – den deklarerbara och den intuitiva kunskapen – som bearbetas i det explicita respektive det implicita minnessystemet. Modellen om de två minnessystemen är således central i den här avhandlingen och jag behandlar hur dessa båda minnessystem samverkar så att deklarerbara och intuitiva kunskaper tar sig i uttryck i form av förmågor. Informanterna i de ingående studierna utgörs av såväl lärarstudenter som erfarna lärare som undervisar om, berättar om eller löser problem med ett naturvetenskapligt innehåll, med särskild tyngdpunkt på ekologi. Datainsamlingen har främst bestått i intervjuer, såväl semistrukturerade som stimulated recall-intervjuer. Dessutom har data samlats in genom att undervisning har videofilmats och att informanter har beskrivit sin undervisning i loggböcker. Resultaten visar att vi kan urskilja tre olika aspekter av lärares professionella seende: uppmärksamma, identifiera och känna igen. Förmågan att uppmärksamma det väsentliga i en komplex miljö, exempelvis att finna en viss typ av gräs bland andra gräs, är starkt förknippad med förmågan att känna igen. Dessa förmågor bygger på intuitiv kunskap och är därmed en långlivad förmåga. Att identifiera, dvs. att kunna sätta ett namn på gräset, är däremot en deklarerbar kunskap som är snabbt avklingande relativt lärtillfället. Vidare visar resultaten att förmågan att agera automatiskt är starkt situerad och därmed sammanlänkad med lärandemiljön, elevgruppen och det specifika innehållet. Automatiskt agerande bygger på erfarenhet (igenkänning) av en specifik situation vartill ett beteende är kopplat. En lärare behöver inte själv vara medveten om sitt agerande eftersom detta är en intuitiv kunskap. Den intuitiva kunskapen verkar dessutom vara en viktig del av berättelser. Studenterna kunde upp till ett år efter lärtillfället återberätta grunddragen i en historia. Däremot visade det sig att de exakta vetenskapliga termerna, dvs. den deklarerbara kunskapen, till stor del hade bytts ut mot mer vanligt förekommande termer. Jag vill poängtera värdet av både intuitiv och deklarerbar kunskap i lärarutbildningen.
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