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  • Grönlund, Erik (författare)
  • Microalgae at wastewater pond treatment in cold climate an ecological engineering approach
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Three types of wastewater ponds in subarctic climates were investigated, each of them highly dependent on microalgae. They were fellingsdams, i.e. wastewater stabilization ponds complemented with chemical precipitation, high-rate algal ponds (HRAPs), and a type of aquaculture interface ponds between a wastewater treatment plant and the natural surrounding.From a microalgae taxa perspective green algae and cryptophytes were dominant in the wastewater ponds. Green algae and cryptophytes were also, together with chryso- and haptophytes, dominating the hypereutrophic and eutrophic stages of the natural lakes. Biomasses in the different types of ponds were of very different order of magnitude. From 100-1000 mg/l in the stabilization ponds during summer and 10-100 mg/l in spring and autumn, 70- 90 mg/l in a HRAP in autumn, to 5-30 mg/l in the most hypereutrophic stage in the natural ponds, 1-10 mg/l in the eutrophic stage, and below 1 mg/l in the oligotrophic stage.The connection between wastewater pond treatment and the field of ecological engineering was recognized. Future development of pond technology may benefit from a stronger connection to the theoretical framework of systems ecology developed in collaboration with the field of ecological engineering and ecotechnology.
  • Hansson, Örjan, 1965- (författare)
  • Studying the views of preservice teachers on the concept of function
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This thesis consists of an overview of the subject, where in particular five papers are put into a frame. The research conducted for the thesis concerns the views of preservice teachers on the concept of function. Preservice teachers’ conceptions of the function concept are in particular examined in relation to mathematical statements that can be related to different topics on a variety of levels in mathematics; in this research, concept mapping technique is a research tool of interest. Questions concerning preservice teachers’ conceptions of the significance of functions in mathematics, and the presence of functions in school mathematics, are also considered relevant aspects of their views of functions. The final part of the research study includes an intervention study regarding the concept of function, located to a calculus course as one of the concluding courses in mathematics on the educational programme.There is a range of findings from the study that is summarized and further discussed in the overview part of the thesis. One result, is that preservice teachers in their reasoning show signs of knowledge compartmentalization which is an issue of concern in their development of conceptual frameworks rich in meaningful connections. This might have consequences for their abilities to operate in a constructivist environment and reason with their students from different points of view. The function concepts’ large network of relations to other concepts is frequently omitted in the preservice teachers’ reasoning. One reason for this is that to preservice teachers, properties of functions seem to be results of isolated procedures, associated with operational conceptions rather than structural conceptions of functions. The findings imply that preservice teachers should encounter functions in a variety of context, to develop their views of the concept of function – including frameworks rich of meaningful relations – and realize that the concept of function is one of the underlying concepts of mathematics, and an important concept to introduce to their future students. The preservice teachers’ reflections concerning functions in school mathematics contribute to emphasize the significance of the process of transformation of subject matter knowledge to pedagogical content knowledge. Further results of the research study, and an outline of the implications, are included in the concluding discussion of the overview part of the thesis.The preservice teachers participating in the study are enrolled in a four and a half year teacher preparation program in mathematics and science, grades 4 to 9. The five papers included in the thesis, describe parts of a larger study essentially conducted until the sixth term during the concluding mathematics courses of the program.
  • Wingstedt, Johnny, 1954- (författare)
  • Making music mean on functions of, and knowledge about, narrative music in multimedia
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Narrative media music - music used for narrative purposes in multimedia such as film and computer games - is often, especially for young people, the largest source of daily musical experience. This PhD thesis is based on three articles, in different ways exploring functions of, and knowledge about, narrative media music. The overarching research question of the thesis is: ‘How can meaning-making functions of narrative media music be described - and how are attitudes, awareness and knowledge about such functions expressed through the different modes of musical sound and speech?' The first article discusses how the musical underscore in narrative media achieves meaning in multimodal interplay with the visuals and other available modes of representation. Three short film scenes are examined from the perspectives of ideational, interpersonal and textual meanings. Even if music in such situations usually does not attain a high degree of conscious salience, it is clear that it often contributes meaning that is essential for the understanding of the overall narrative. It is concluded that what we (think we) see is often to a large degree determined by what we hear. The second article presents the first part of a study, where 23 young participants (12-13 years old), using a software tool, were given the task of adapting musical expression to make it ‘fit as well as possible' different visual scenes shown on a computer screen. They also answered a questionnaire, asking about their musical training and media habits. Numerical data from the trial sessions, representing differences in musical expression, were analyzed statistically. The results indicated a strong degree of in-group conformity and consensus, indicating knowledge of culturally available functions and conventions of narrative media music. The third article describes the second part of the study. Each participant was interviewed in a stimulated recall situation where they commented and reflected on their own musical expressions of their completed trials. From the analysis of the interviews, examining the verbal expression of ideational, interpersonal and textual meanings, five different types of statements could be discerned: the Unclear, Intuitive, Associative, Analytical and Transformative types. These statements were also seen as reflecting various aspects of Swanwick's (1994) concepts of intuitive and analytical knowledge. Combining the verbal statements with how each participant musically had demonstrated conformity or non-conformity to narrative conventions, contributed to a fuller and more nuanced account of their expressed musical knowledge. The thesis concludes with a discussion of the learning opportunities offered by narrative multimedia in the escalating media society and of its implications for formal music education.
  • Dahlén, Leon (författare)
  • Numerical and experimental study of performance of a hydraulic motor
  • 2003
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The aim of this study was to develop an understanding of the fluid properties that influence the efficiency of hydraulic systems in a steady-state, especially components in hydrostatic transmission systems under different running conditions. The aim has also been to investigate and model the sources of losses in hydraulic machines, in order to estimate the losses, taking fluid properties into account. Finally, the technique of optimization has been introduced in order to improve the efficiency of a distributor valve in a radial piston hydraulic motor, Marathon M200. From an experimental field-test, which was performed on a belt conveyer using a hydrostatic transmission system, the overall efficiency of the hydrostatic transmission was compared when using a mineral oil, Shell Tellus TX 68, a synthetic fluid, Mobil SHC 526, and a vegetable fluid, Binol Hydrap II. The experimental field-test showed that vegetable and synthetic fluids improve the efficiency compared to mineral oil. The three fluids have the same viscosity but experimental tests showed that the temperature (?)- and pressure(?) -viscosity coefficient differs between them. It was also found that the pressure-viscosity coefficient (?) of mineral oil was higher compared to vegetable and synthetic fluids. The proposed steady-state model gives greater accuracy regarding overall efficiency than the Wilson model, when examining fluid properties that differ in other aspects than their viscosity. The study has focused on losses in lubricated sliding contacts within a radial piston hydraulic motor, Marathon M200, and an analysis of the losses has been made using the finite element method (FEM). A FEM software package, Solvia, which takes into account fluid properties, such as temperature- and pressure- viscosity coefficient, heat conduction and specific heat, has been used to simulate the behaviour and to estimate the losses in tribological contact. This approach of simulation has been applied to two different tribological contact within the hydraulic motor: to a journal bearing contact and to a hydrostatic annular multi-recess plane thrust bearing. By using an FEM software package linked to an optimization algorithm, the losses in the tribological contact in a distributor valve were reduced significantly. The study shows that the optimized geometry of the distributor valve in the motor can successfully be improved, with regard to losses, by small changes in the geometry. Combining an FEM software package with the optimization routine offers an effective tool for designers to simulate and improve the efficiency of a hydraulic unit.
  • Isaksson, Per (författare)
  • On crack growth under compressive stresses
  • 2001
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This thesis concerns fractures subjected to compressive stresses. In the four papers appended fracture behavior in brittle as well as ductile materials is studied. In the first paper, an expression for the mode II stress intensity factor at a straight extended kink has been calculated under the condition that crack opening is suppressed during crack growth. The expression has been found as a function of the mode II stress intensity factor K2 at the parent crack, the direction and length of the kink, and the difference between the remote compressive normal stresses perpendicular to, and parallel with, the plane of the parent crack. Crack growth directions have been suggested based on the result. At a sufficiently high non-isotropic compressive normal stress, so that the crack remains closed, the crack will propagate along a curved path maximizing the mode II stress intensity factor. Only at an isotropic compressive normal stress will the crack continue straight ahead in its original plane without directional change. By analyzing experimental crack growth patterns in paper two, the conclusion is that crack paths experimentally observed indicate that mode II crack growth under compression in some brittle materials follow a propagation path described by a function y=gx^b. In fact, the agreement between the experiments and the propagation path prescribed by the model, in which b=3/2, is astonishingly good since b was found in the interval [1.43-1.58] in all the experiments studied. Further, the investigation of the curvature parameter g has revealed that g also agree with the simplified model, even though not as good as the exponent b. However, the experimentally observed g differs in general less than 15% from the theoretical value predicted by the analytical model discussed in paper I. In paper three, a directional crack growth criterion in a compressed elastic perfectly-plastic material is considered. A slip-line solution is derived for evaluation of the stresses at the crack tip, which considers hydrostatic pressure and friction between the crack surfaces. Based upon the slip-line solution a projection stress based model is discussed for prediction of the direction of initiated crack growth. The opening displacement of an extended kink has been examined in paper four, using a finite element procedure. The conclusion is that an over-critical pressure in the plastic zone surrounding the crack tip suppresses crack opening regardless the direction of crack growth. The only possibility seems to be shear mode crack growth, which occur straight ahead in the crack plane if the crack is assumed to follow the plane of maximum shear stress. At a sub-critical hydrostatic pressure, or lower friction between the crack surfaces, the crack can extend via a kink subjected to local opening mode. An expression for the critical value determining fracture mode has been found as a function of hydrostatic pressure and friction between the crack surfaces assuming the fracture process to be predominantly controlled by local tensile stresses at the crack tip. The crack growth directions predicted by the projection stress based criterion in paper three are comparable with the directions maximizing the opening displacement of an extended kink computed in paper four.
  • Juter, Kristina (författare)
  • Limits of functions university students' concept development
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Avhandlingen består av sex artiklar som föregås av en kappa. Kappan sammanfattar de teorier som använts i artiklarna, empiridelen samt resultat och slutsatser. Fem av artiklarna är publicerade i tidskrifter eller accepterade för publikation i tidskrifter och den återstående är accepterad för publicering i en konferensrapport. Gränsvärden är väldigt centrala i matematisk analys och därför viktiga att förstå för studenter som ska syssla med matematik. Avhandlingen handlar om studenter som läser sin första matematiktermin på universitetsnivå. Två studentgrupper har undersökts med avseende på hur de hanterar gränsvärden av funktioner under 10 respektive 20 veckor. Utländsk litteratur har visat att detta begrepps komplexitet försvårar studenternas inlärning. Undersökningen genomfördes för att ytterligare klargöra hur studenterna resonerar kring gränsvärden, speciellt i Sverige där liknande undersökningar inte gjorts tidigare. Undersökningen genomfördes år 2002 med en grupp på våren och en på hösten. Studenterna fick tre enkäter med gränsvärdesproblem och attitydfrågor om matematik. Femton studenter från den andra gruppen intervjuades vid två tillfällen vardera. Dessutom gjordes fältanteckningar. De olika sätten att samla in data gav en bred bild av verksamheten i klassrummen och föreläsningssalen samt hur studenterna resonerade i olika situationer. Undersökningen visade att kontinuiteten i studenternas inlärningssituation brutits på flera nivåer och skapat stora problem för studenterna. Det fanns till exempel klyftor mellan gymnasiets hantering av gränsvärden och universitetets hantering av gränsvärden och mellan teoretisk hantering av gränsvärden och problemlösning. Studenterna var bra på att lösa standardproblem, men de hade svårigheter att koppla den formella teorin till problemen de löste och att lösa problem som var formulerade något annorlunda än studenterna var vana vid. Resultaten visar på att det behövs större variation i studenternas inlärning så de blir varse om sina egna uppfattningar och kan korrigera det som är felaktigt. Många studenter tyckte själva att de hade kontroll över begreppet trots att undersökningen visade att de inte hade det.
  • Johansson Falck, Marlene, et al. (författare)
  • Technology, Language and Thought Extensions of Meaning in the English Lexicon
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • In this thesis, the relationship between technological innovation and the development of language and thought is analysed. For this purpose, three different fields of technology are investigated: 1) the steam engine, 2) electricity, and 3) motor vehicles, roads and ways. They have all either played an extremely important part in people’s lives, or they are still essential to us. The overall aim is to find out in what ways these inventions and discoveries have helped people to develop abstract thinking and given speakers of English new possibilities to express themselves. Questions being asked are a) if the correlations in experience between the inventions and other domains have motivated new conceptual mappings? b) if the experiences that they provide people with may be used to re-experience certain conceptual mappings, and hence make them more deeply entrenched in people’s minds? and c) if the uses of them as cognitive tools have resulted in meaning extension in the English lexicon? The study is based on metaphoric and metonymic phrases collected from a number of different dictionaries. In the material a large number of metaphorical and metonymic expressions including terms connected to the inventions and discoveries that are part of this thesis are found. As is clear from the expressions, the steam engine, electricity, motor vehicles, roads and ways have all provided us with ample tools for structuring our thoughts, and for conveying our thoughts to others. Primarily, it seems to be the different functions of the discoveries and inventions, or the effects that they have on other objects that have motivated the mappings. In addition to analysing the cognitive role of the inventions that are part of this thesis, some general conclusions concerning the relationship between language, thought and world are suggested.
  • Andersson Chan, Anneli (författare)
  • Biofiltration of odorous gas emissions
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Biologisk gasreningsteknik kan vara ett intressant behandlingsalternativ för förorenade gasströmmar. Till skillnad från traditionella tekniker, såsom adsorption, skrubbers, eller förbränning, kan biofilter erbjuda en effektiv behandling till relativt låga investerings- och driftskostnader, och utan att generera sekundära föroreningsproblem. Nackdelarna med biofilter har varit de stora ytor som krävs samt att filtermaterialet har behövts bytas relativt ofta på grund av nedbrytning och ökade tryckfall. Omfattande forskning och utveckling har ägt rum de senaste 20 åren inom biologisk gasreningsteknik internationellt, men relativt lite har gjorts i Sverige. Majoriteten av studierna är laborativa där man behandlar enstaka föroreningar i relativt höga koncentrationer under konstanta och kontrollerade förhållanden. Ute i fält är sådana förhållanden väldigt ovanliga och få studier inriktar sig på behandling av komplexa gasströmmar med mycket låga koncentrationer, vilket är fallet för många illaluktande gasemissioner.Syftet med denna avhandling var att minska kunskapsklyftan mellan laborativa studier och tillämpningar inom biologisk gasreningsteknik för luktproblem. Flera operativa och processrelaterade problem identifierades, såsom varierande flöden, temperaturer och föroreningskoncentrationer. Dessa påverkade biofiltrets prestanda genom att skapa suboptimala förhållanden för mikroorganismerna i filtret. Ett kompakt pilotskalefilter med ny design användes i tre olika verksamheter med luktproblem: restaurang, massabruk, och avloppspumpstation. Gasemissionerna från dessa verksamheter var komplexa blandningar bestående av föroreningar med kemiskt olika egenskaper där koncentrationerna varierade över tiden. Aldehyder dominerade i restaurangemissionerna, medan reducerade svavelföreningar, i första hand dimetylsulfid, dominerade i emissionerna från massafabriken och avloppspumpstationen. I allmänhet återfanns enskilda föreningar i väldigt låga koncentrationer (ppb-nivå) och väldigt låg eller ingen reduktion kunde påvisas i biofiltret. Begränsningar av tillgänglig biomassa i filtret är en rimlig förklaring, eftersom föroreningskoncentrationer på ppb-nivå kan ha varit för låga för att kunna bygga upp och försörja en tillräckligt omfattande bakteriekultur. Många av de identifierade föroreningarna har låg löslighet och uppehållstiderna i filtret kan ha varit för korta för infångning och transport mellan gas och biofilm. Uttorkning av filtermaterialet var delvis ett problem, vilket indikerar att ett bättre befuktningssystem eller användandet av en kontinuerlig vätskeström kan bli nödvändig.En metod för att utvärdera luktproblem utvecklades i en fallstudie vid ett avloppsreningsverk. Lokala observatörer användes i en luktpanel där de fick ringain när de kände lukt. Aktuella väderdata och processparametrar från verket hämtades in och relaterades till varje luktsamtal. Luktpanelen var engagerade och de lärde sig mer om komplexiteten i luktproblem och kring vad och varför det luktar. Det visade sig dock vara svårt att använda panelens luktrapporter för att hitta källan till luktepisoden och samtalen stämde inte alltid överens med aktuella vindriktningar.
  • Bergström, David (författare)
  • The Absorption of Laser Light by Rough Metal Surfaces
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • In Laser Material Processing of metals, an understanding of the fundamental absorption mechanisms plays a vital role in determining the optimum processing parameters and conditions. The absorptance, which is the fraction of the incident laser light which is absorbed, depends on a number of different parameters. These include laser parameters such as intensity, wavelength, polarisation and angle of incidence and material properties such as composition, temperature, surface roughness, oxide layers and contamination. The vast theoretical and experimental knowledge of the absorptance of pure elements with smooth, contamination-free surfaces contrasts with the relatively sparse information on the engineering materials found in real processing applications. In this thesis a thorough investigation of the absorption mechanisms in engineering grade materials has been conducted, both experimentally and theoretically. Integrating sphere reflectometry has been employed to study the impact of surface conditions on Nd:YAG and Nd:YLF laser absorptance of some of the most common ferrous and non-ferrous metallic alloys found in Laser Material Processing. Mathematical modelling and simulations using ray-tracing methods from scattering theory have been used to analyze the influence of surface topography on light absorption. The Doctoral thesis consists of six papers: Paper 1 is a short review of some of the most important mathematical models used in describing the interaction between laser light and a metal surface. Paper 2 is a review of experimental methods available for measuring the absorptance of an opaque solid such as a metal. Papers 3 and 4 are experimental investigations of the absorptance of some of the most frequently found metallic alloys used in Laser Material Processing today. Paper 5 presents results from 2D ray-tracing simulations of random rough metal surfaces in an attempt to investigate the influence of surface roughness on laser scattering and absorption. Paper 6 is a full 3D ray-tracing investigation of the interaction of laser light with a rough metallic surface, where some comparisons also are made to the previous 2D model.
  • Fors, Vaike, 1969- (författare)
  • The Missing Link in Learning in Science Centres
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Science centres have been identified as an important resource in encouraging teenagers to choose higher education in science and technology. This is of interest to society, since there seems to be a problem in getting sufficient numbers to do so. And accomplishing this is sometimes described as a fatal question for a nation’s future prosperity and development. Still, there is an international trend where teenagers fail to visit science centres. Through research, little is known about what is interesting or useful to the public, as well as how to reach those who are ‘unengaged’. Considering teenagers as exponents for what distinguishes today’s society makes their apparent unwillingness to participate in science centres interesting to study with regards to what culture, history and ideology these centres were initially produced. Hence, from this point of view, what is missing in science centres that would make them interesting for the young people of today? Many studies of learning in science centres have come to focus on visitors who visit voluntarily and how well the embedded messages in the exhibits have been acknowledged by these visitors. This study focuses instead on teenagers who are reluctant to participate in science centres, with their perspective of science centres as the point of departure, specifically what kind of social activities are formed in their encounters with science centre exhibits. This encounter is regarded as an encounter between the two different practices of the science centre and the teenagers. The applied theoretical perspective is mainly assembled from socio-cultural theories of learning. This research is a microanalytic study of five teenagers who were equipped with video cameras and asked to film a visit to the local science centre, Teknikens Hus. The films were later discussed in a focus-group interview consisting of the teenagers and the researcher. Visual ethnography provided the theoretical framework for this research design. The results showed that the teenagers want to use exhibits to have the authority of interpretations and the possibilities to contribute to the meaning of the activity. At the same time, they want to use the exhibits in a way that the activities become places for developing social identity. To negotiate the meaning of the exhibits there is a need for an openness that may be constrained by too inflexible and limiting exhibit designs. This pattern is described as two different forms of participation in the exhibits; ignoring or extending the intended meaning of the exhibits. Meaningfulness also demands a closeness created by connections between the exhibit and the user’s personal experiences. This pattern is described as two different ways in which the teenagers identified the exhibits; exhibits which they dissociated from or to which they had an ongoing relationship. Providing a space for negotiation seems crucial to inviting teenagers into opportunities of meaningful experiences, even more significant than any specific physical feature in the exhibit. The teenagers’ agenda, in which forming practices where they can express themselves and contribute to the meaning seem to be very important, appears not to be greatly enabled by science centre exhibits. In this situation they learn to not participate. Science and technology represented in this matter show a ‘ready-made’ world that they cannot change. The missing link in learning in science centres is here described as the part of the meaning making process where the teenagers get to re-negotiate the meaning of the activities in the centre and use the exhibits as tools to accomplish this.
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