| 1. |
- Egelkraut, Dagmar D., 1989-
(författare)
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Long-lasting ecological legacies of reindeer on tundra vegetation
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reindeer can have strong effects on the plant species composition and functioning of tundra ecosystems, and often promote a transition towards a graminoid-dominated vegetation type. As a result, they influence many ecological processes, such as nutrient dynamics, soil biotic composition and functioning, and carbon storage. Several studies suggest that the effect of reindeer on vegetation may follow predictable patterns and could induce an alternative stable vegetation state. However, little empirical data on the long-term stability of reindeer effects on vegetation exist, as it is inherently challenging to study these ecological processes experimentally on a sufficiently long timescale. The main objective of this thesis was therefore to gain a better understanding of the long-term ecological processes following reindeer-induced vegetation shifts.In order to gain a more mechanistic insight in what initially drives this transition, I used a field-based grazing simulation experiment in which I separated defoliation, trampling, moss removal and the addition of feces. This allowed me to test the relative contribution of reindeer-related activities to initiating the shift from moss and heath- dominated tundra towards a graminoid-dominated vegetation state. Additionally, I studied the long-term ecological stability following such a vegetation shift. I did this by addressing historical milking grounds (HMGs): sites where high reindeer concentrations associated with historical traditional reindeer herding practices induced a vegetation transition from shrubs towards graminoids several centuries earlier, but which were abandoned a century ago. Studying HMGs allowed me to address: 1. The potential stability of reindeer-induced vegetation shifts; 2. The ecological mechanisms contributing to the long-term stability of these vegetation shifts; and 3. How such long-lasting vegetation changes influence soil carbon- and nutrient cycling.I found that trampling by reindeer is an important mechanism by which reindeer cause vegetation change. Addressing HMGs further revealed that this vegetation change can be hightly persistent, as the studied HMGs showed only a low encroachment at the surrounding borders in the last 50 years. The vegetation in the core areas of all studied HMGs had remained strikingly stable, and were hardly invaded by surrounding shrubs. Interestingly, soil nutrient concentrations and microbial activities were still different from the surrounding area as well, and even comparable to actively grazed areas. Even after many centuries of changed vegetation composition and soil processes, there was no difference in total carbon sequestration. This suggests that the environmental conditions for microbial decomposition were more important than vegetation composition for the soil carbon stocks, in our study site.After studying the contemporary habitat use of HMGs by reindeer and other herbivores, investigating the potential plant-soil feedbacks mechanisms and detailed soil analyses, I concluded that several ecological mechanisms contribute to the long-term stability of HMGs: first, the altered soil biotic and abiotic conditions appear to have a stronger advantage for HMG vegetation than for the surrounding tundra vegetation. Furthermore, I found a clear browsing preference of small rodents on single shrubs proliferating in HMGs, causing a strong limitation on shrub expansion. Moreover, the dense established sward of graminoids likely poses a strong direct competition for space and nutrients, hindering seedling establishment. Finally, I conclude that HMGs are highly stable on relevant ecological timescales, and propose how the concepts of historical contingency and ASS can be applied to understand stability of these reindeer-induced vegetation transitions.
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| 2. |
- Liljegren, Sofie
(författare)
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Stellar Winds of Cool Giants : Investigating the Mass-Loss Mechanism of AGB Stars
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Asymptotic giant branch (AGB) stars are luminous cool giants of low to intermediate mass that are strongly pulsating and non-spherical, with heavy mass loss through a stellar wind. The mass loss makes these stars important for galactic chemistry, as the wind enriches the interstellar medium with new elements and dust, and it determines the final fate of these stars.The winds of AGB stars are believed to be driven by a combination of pulsation-induced shocks and radiation pressure on dust grains, which form in the atmospheres. The two processes, pulsation and mass loss, are usually simulated using different computational codes, as the physical environment of the atmosphere, where the wind is driven, is vastly different from the interior, where the pulsations originate. In this work we try to bridge this gap.The dynamical atmosphere and wind code DARWIN is used to study dust driven winds. An extensive grid of DARWIN models is constructed to investigate how the mass-loss rates depend on different stellar parameters. The models reproduce observed dynamical properties and we find a strong correlation between mass-loss rates and luminosities.The simplified description of stellar pulsation in standard DARWIN models, however, introduces free parameters that need to be constrained. The atmosphere models are highly non-linear and even moderate changes to the pulsation properties may have significant impact on the mass-loss rate and wind velocity.To self-consistently model the pulsation process, and to study atmospheric structures caused by the convection, the radiation hydrodynamical code CO5BOLD is used to produce an exploratory grid of 3D star-in-a-box models. The resulting models have realistic radii and periods, and give important insights into the complex non-spherical structure of AGB stars. Pulsation properties are derived from the CO5BOLD models and used as input in the DARWIN models. Average wind properties from models with CO5BOLD input agree with the standard DARWIN models, however the winds show large density variations with time, which may affect comparisons with observations.
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| 3. |
- Olofsson, Hans, 1960-
(författare)
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Historia på högstadiet : Historiekulturella yttringar i och utanför ett klassrum i Sverige hösten 2009
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- How do students use schools´ history education to develop their historical consciousness? In which ways could history education be regarded as a historical-culture expression, i.e. as a part of a society’s interest in the past? This thesis takes its point of departure in these overarching questions. More specifically the research was carried out as a contextualised case study of sixteen history lessons in a Swedish Year 9 class, in the autumn of 2009. The contextualisation consists of an analysis on historical-culture expressions in Sweden at that time. Despite conflicting opinions, the major finding was the common view of Sweden as a country that solves her problems in a peaceful way, both in the past, the present and the future. The classroom study was conducted with an ethnographical approach with close attention to teacher-student interactions. The research was guided by an analytical model inspired by the historian Jörn Rüsen’s theories on history learning processes.The results show in detail the complicated learning processes in the classroom but also the connection with the historical-culture expressions in Sweden at that moment. One major finding was the tendency to react to the rise of contemporary islamophobia and nationalism in Sweden by making comparisons with the development in Weimar Germany in the beginning of the 1930s. This tendency was present both in and outside the classroom.
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| 4. |
- Olofsson, Magnus, 1971-
(författare)
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Microbiological Surveillance in Primary Health Care : New Aspects of Antimicrobial Resistance and Molecular Epidemiology in an Ageing Population
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundThe inexorable rise in antimicrobial resistance (AMR) interferes with the goals of health care services around the world, given how critical the antibacterials are in making infections treatable and surgical procedures doable. Nursing homes residents have been identified as a reservoir for AMR, possibly due to the combination of being physically and mentally frail, frequently treated with antibacterials, and frequently moved between nursing home and hospital. Microbiological surveillance is a key countermeasure against further AMR development. Yet, surveillance data is easily biased due to precision problems regarding how the data is collected and evaluated.MethodsBeginning in 2008, we launched two programmes (“SHADES” and “MIDIO”) aimed to gathering AMR data in a systematic fashion from elderly nursing home residents and elderly people living in their own place of residence. In doing so, we focused on colonizing strains of the two most important nosocomial infectious agents, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The bacteria were collected from multiple body sites and analysed with respect to antimicrobial susceptibility and genetic diversity.ResultsActive surveillance of AMR showed that (i) a S. aureus isolate could be retrieved from 1 in every 2 individuals given a single round of sampling, but aggregating several rounds of sampling, this figure might reach 7 in every 10 individuals, (ii) an E. coli isolate could be retrieved from 4 in every 5 individuals, (iii) the overall prevalence of AMR was favourable when compared to the situation in many other countries, (iv) the genetic diversity of S. aureus was generally high and provided only limited evidence of clonal expansion or contraction, and (v) diabetes mellitus was one of very few patient-level factors to show an association with the degree of genetic diversity in S. aureus.ConclusionsThe prevalence of colonization with S. aureus and E. coli was somewhat higher than expected, but the degree of AMR was very low. The genetic diversity of S. aureus was generally high. Diabetes mellitus emerged as the only patient-level factor associated with a higher degree of genetic diversity in S. aureus.
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| 5. |
- Ramstedt, Sofia, 1974-
(författare)
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Molecules and Dust around AGB stars : Mass-loss rates and molecular abundances
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- All stars with a stellar mass of about 0.8–8 MSun will end their lives as asymptotic giant branch (AGB) stars. Through their extensive mass loss the AGB stars constitutes an important source of nuclear processed material. They also provide us with fascinating systems where an interchange of different physical and chemical processes occur, making them excellent astrophysical laboratories.Being the most important process for the evolution of an AGB star, the mass loss is well established, but its details are less well known. On the AGB, the mass-loss rate can span several orders of magnitude, reaching 10−4 MSun yr−1 toward the end of the AGB. It is challenging to find reliable methods to estimate the mass-loss rates of individual objects. Nevertheless, it is important, since the mass-loss rate affects the derived abundances of other molecules in the circumstellar envelope, and therefore the estimates of the amount and composition of the recycled material. In the first part of the thesis the reliability of mass-loss rate estimates is evaluated using two main methods; the observations and radiative transfer analysis of CO radio line emission, and dust radiative transfer combined with a dynamical model.The second part of the thesis focuses on a particular chemical type of AGB stars; the S-type. The S-stars are believed to have approximately the same amount of carbon as oxygen in the photosphere, and to be an intermediate evolutionary stage as the star evolves from an oxygen-rich M-star into a carbon star. As possible transition objects the S-stars might give important clues to the mass-loss mechanisms and to the chemical evolution along the AGB. Using observations of circumstellar radio line emission in combination with detailed radiative transfer analysis, we have estimated mass-loss rates and abundances of chemically important molecules for a sample of 40 S-stars. The results are compared to previous results for M- and carbon stars.
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| 6. |
- Humbert, Marion, et al.
(författare)
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Functional SARS-CoV-2 cross-reactive CD4+ T cells established in early childhood decline with age
- 2023
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 120:12
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Tidskriftsartikel (refereegranskat)abstract
- Pre-existing SARS-CoV-2-reactive T cells have been identified in SARS-CoV-2-unexposed individuals, potentially modulating COVID-19 and vaccination outcomes. Here, we provide evidence that functional cross-reactive memory CD4+ T cell immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is established in early childhood, mirroring early seroconversion with seasonal human coronavirus OC43. Humoral and cellular immune responses against OC43 and SARS-CoV-2 were assessed in SARS-CoV-2-unexposed children (paired samples at age two and six) and adults (age 26 to 83). Pre-existing SARS-CoV-2-reactive CD4+ T cell responses targeting spike, nucleocapsid, and membrane were closely linked to the frequency of OC43-specific memory CD4+ T cells in childhood. The functional quality of the cross-reactive memory CD4+ T cell responses targeting SARS-CoV-2 spike, but not nucleocapsid, paralleled OC43-specific T cell responses. OC43-specific antibodies were prevalent already at age two. However, they did not increase further with age, contrasting with the antibody magnitudes against HKU1 (β-coronavirus), 229E and NL63 (α-coronaviruses), rhinovirus, Epstein–Barr virus (EBV), and influenza virus, which increased after age two. The quality of the memory CD4+ T cell responses peaked at age six and subsequently declined with age, with diminished expression of interferon (IFN)-γ, interleukin (IL)-2, tumor necrosis factor (TNF), and CD38 in late adulthood. Age-dependent qualitative differences in the pre-existing SARS-CoV-2-reactive T cell responses may reflect the ability of the host to control coronavirus infections and respond to vaccination. Copyright © 2023 the Author(s).
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| 7. |
- Knief, Ulrich, et al.
(författare)
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Highly pathogenic avian influenza causes mass mortality in Sandwich Tern Thalasseus sandvicensis breeding colonies across north-western Europe
- 2024
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Ingår i: Bird conservation international. - : Cambridge University Press. - 0959-2709 .- 1474-0001. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- In 2022, highly pathogenic avian influenza (HPAI) A(H5N1) virus clade 2.3.4.4b became enzootic and caused mass mortality in Sandwich TernThalasseus sandvicensis and other seabird species across north-western Europe. We present data on the characteristics of the spread of the virus between and within breeding colonies and the number of dead adult Sandwich Terns recorded at breeding sites throughout north-western Europe. Within two months of the first reported mortalities, 20,531 adult Sandwich Terns were found dead, which is >17% of the total north-western European breeding population. This is probably an under-representation of total mortality, as many carcasses are likely to have gone unnoticed and unreported. Within affected colonies, almost all chicks died. After the peak of the outbreak, in a colony established by late breeders, 25.7% of tested adults showed immunity to HPAI subtype H5. Removal of carcasses was associated with lower levels of mortality at affected colonies. More research on the sources and modes of transmission, incubation times, effective containment, and immunity is urgently needed to combat this major threat for colonial seabirds.
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| 8. |
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| 9. |
- Olofsson, Hans, 1960-
(författare)
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Fatta historia : En explorativ fallstudie om historieundervisning och historiebruk i en högstadieklass
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Studiens huvudsyfte är att utforska hur historieämnet konstitueras av lärare och eleverunder arbetet med ett ämnesområde, i det här fallet första världskrigets och mellankrigstidenshistoria. Närmare bestämt undersöker den hur informanterna gemensamt skaparhistorisk mening genom att erfara och tolka det förflutna i klassrummet. En teoretiskutgångspunkt är att skolans historieundervisning bör betraktas som ett organiserat kollektivtbruk av det förflutna som står i nära förbindelse med andra samhälleliga historiebruk.Studien omfattar data från 16 observerade lektioner, intervjuer med läraren och elevernaoch analyser av elevernas essäskrivningar.Studien visar hur realhistoriska kunskaper i, metahistoriska kunskaper om ochvärdeförmedlande kunskaper av historia framträder och tvinnas samman till en helheti undervisningen. En hypotetisk slutats är att dessa tre kunskapsformer är ömsesidigtberoende av varandra i den konkreta undervisningssituationen. En didaktisk implikationär indikationer på att olika metaperspektiv i historieundervisningen kan behöva utvecklas.Särkilt gäller det om de historiska aktörsperspektiven som förefaller vara viktiga för attstärka elevers förmåga att artikulera sitt historiemedvetande. Ett teoretiskt bidrag rörstudiens medvetet eklektiska användning av (”tyska”) teorier om historiemedvetande och(”anglosaxisiska”) teorier om historiskt tänkande.Hans Olofsson är verksam som lärare i historia, religionskunskap och svenska påAbrahamsbergsskolan i Stockholm och forskarstuderande vid Karlstads universitet.Han är också aktiv som läromedelsförfattare. ”Fatta historia – en explorativ fallstudie omhistorieundervisning och historiebruk i en högstadieklass” är hans licentiatavhandling.Licentiatavhandlingen har skrivits inom Forskarskolan för lärare i historia ochsamhällskunskap, en särskild fortbildningssatsning för yrkesverksamma lärare. Centrumför de samhällsvetenskapliga ämnenas didaktik vid Karlstads universitet har ansvarat förforskarskolan i samarbete med Högskolan Dalarna.
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| 10. |
- Olofsson, Jenny, 1980-
(författare)
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Amoebae as Hosts and Vectors for Spread of Campylobacter jejuni
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Campylobacter jejuni is the leading bacterial cause of gastrointestinal diarrheal disease in humans worldwide. This zoonotic pathogen has a complex epidemiology due to its presence in many different host organisms. The overall aim of this thesis was to explore the role of amoebae of the genus Acanthamoeba as an intermediate host and vector for survival and dissemination of C. jejuni. Earlier studies have shown that C. jejuni can enter, survive and replicate within Acanthamoebae spp. In this thesis, I have shown that C. jejuni actively invades Acanthamoeba polyphaga. Once inside, C. jejuni could survive within the amoebae by avoiding localization to degradative lysosomes. We also found that A. polyphaga could protect C. jejuni in acid environments with pH levels far below the range in which the bacterium normally survives. Furthermore, low pH triggered C. jejuni motility and invasion of A. polyphaga. In an applied study I found that A. polyphaga also could increase the survival of C. jejuni in milk and juice both at room temperature and at +4ºC, but not during heating to recommended pasteurization temperatures. In the last study we found that forty environmental C. jejuni isolates with low bacterial concentrations could be successfully enriched using the Acanthamoeba-Campylobacter coculture (ACC) method. Molecular genetic analysis using multilocus sequence typing (MLST) and sequencing of the flaA gene, showed no genetic changes during coculture. The results of this thesis have increased our knowledge on the mechanisms behind C. jejuni invasion and intracellular survival in amoebae of the genus Acanthamoeba. By protecting C. jejuni from acid environments, Acanthamoebae could serve as important reservoirs for C. jejuni e.g. during acid sanitation of chicken stables and possibly as vectors during passage through the stomach of host animals. Furthermore, Acanthamoeba spp. could serve as a vehicle and reservoir introducing and protecting C. jejuni in beverages such as milk and juice. Validation of the ACC method suggests that it is robust and could be used even in outbreak investigations where genetic fingerprints are compared between isolates. In conclusion, Acanthamoeba spp. are good candidates for being natural hosts and vectors of C. jejuni.
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| 11. |
- Olofsson, Jan, et al.
(författare)
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Overall Project Guide : Sustainable Bridges - Assessment for Future Traffic Demands and Longer Lives SB9.2
- 2007
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Rapport (refereegranskat)abstract
- This Overall Project Guide gives a general overview of the main outputs of the Integrated Research Project "Sustainable Bridges - Assessment for Future Traffic Demands and Longer Lives" founded by the European Commission within its 6th Framework Programme. It guides the bridge engineers, operators and managers through the number of technical guidelines and reports developed within the project, and it shows where to find relevant technical information for the specific activity related to operation, maintenance and management of existing railway bridges. Furthermore, it gives some guidance on the number of possible approaches and methods, presented in the project guidelines and reports that might be helpful in upgrading existing railway bridges for higher speeds and loads or that might help to extend their service life.
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