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  • 2801.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Beräkningar av näringsbalanser och kväveförluster vid helträdsutnyttjande1992In: Vattenfall Bioenergi Research, U(B) 1992/16Article in journal (Refereed)
  • 2802.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    The Potential of Energy Utilization from Logging Residues With Regard to the Availability of Ashes2007In: Biomass and Bioenergy 2007; 31: 40-45Article in journal (Refereed)
  • 2803.
    Wikström, Fredrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Karlsson, Mikael
    Karlstad University, Faculty of Social and Life Sciences, Department of Health and Environmental Sciences.
    Hållbar utveckling i skogslandskapet ' med energi i fokus2004Chapter in book (Other academic)
  • 2804.
    Wikström, Fredrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Karlsson, Mikael
    Karlstad University, Faculty of Social and Life Sciences, Department of Health and Environmental Sciences.
    Hållbar utveckling i Värmland - Strategier för lokal och regional hållbar utveckling av energisystem i ett femtioårsperspektiv2002Report (Refereed)
  • 2805.
    Wikström, Fredrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Olsson, A
    Nilsson, F
    Hellström, D
    Bra förpackning skyddar och säljer i hållbart system2011In: Miljöforskning, ISSN 2000-8627, no januariArticle in journal (Other (popular science, discussion, etc.))
  • 2806.
    Wikström, Fredrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Williams, Helén
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Ger mindre förpackningsmaterial mindre avfall?2010In: Återvinnare för industrin 2010 / [ed] Kjell-Arne Larsson, Stockholm: Rekord Media och Produktion , 2010Chapter in book (Other academic)
  • 2807.
    Wikström, Fredrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Williams, Helén
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Potential environmental gains from reducing food losses through development of new packaging – a life cycle model.2010In: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 23, no 7, p. 403-411Article in journal (Refereed)
    Abstract [en]

    The environmental concern and development issues regarding packaging has for 20 years to a high extent been on packaging when it has become waste. To reduce the environmental impact from the whole food packaging system it is also important to develop the packaging’s ability to reduce food waste. In some cases it may be necessary to increase the environmental impact of packaging in order to reduce food waste. In this paper, the environmental impact of packaging and food losses and the balance between the two has been examined for five different food items. The results show that packaging’s that reduce food waste can be an important tool to reduce the total environmental impact, even if there is an increase in impact from the packaging itself. This is especially true for food items where the environ- mental impact of the food is high relative the packaging, for example cheese, and for food items with high losses, for example bread. It is important to analyse the risk of increasing food losses when pack- aging design changes, for example, when the aim is less packaging material, which is the main intention of the packaging and packaging waste directive of the European Union.

  • 2808.
    Wikström, Fredrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Williams, Helén
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Verghese, Karli
    RMIT University, Melbourne.
    Clune, Stephen
    RMIT University, Melbourne.
    The influence of packaging attributes on consumer behaviour in food-packaging LCA studies: a neglected topic2012In: 8th International Conference on Life cycle assessment in the agri-food sector / [ed] Corson, M.S., van der Werf, H.M.G., 2012, p. 287-293Conference paper (Refereed)
  • 2809.
    Wikström, Fredrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Ågren, G.I.
    The relationship between the growth rate of young plants and their total-N concentration is unique and simple: a comment1995In: Annals of Botany 75(1995) 541-544Article in journal (Refereed)
  • 2810.
    Wilke, Caroline
    Karlstad University, Faculty of Technology and Science.
    Fördröja åldrandet av elektrotekniskt papper genom kemikalietillsats: En studie av dicyandiamids påverkan2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Nordic Paper Åmotfors manufactures electro technical paper that is used to isolate the windings in transformers. It is important to maintain the properties of the paper during a long period of time because the life of a transformer is extensive. The purpose of this thesis was to investigate whether or not addition by a chemical consisting of dicyandiamide could delay the ageing of the papers that Nordic Paper manufactures. The aspiration was that their paper would then fulfil the requirements that are applicable to papers that have been aged in oil. The chemical that was utilised is called Cartafix® WE liquid.

    Experiments were conducted where different dosages of the chemical were added to the stock. Sheets of paper were manufactured and the nitrogen level was then measured in order to verify that the chemical had been fused in the finished paper. The paper sheets were then aged in either oil or air and the remaining degree of polymerisation was measured. Bursting strength and conductivity were also evaluated. Papers that Nordic Paper had manufactured were coated with different dosages of the chemical and then investigated in the same manner.

    The results showed that the retention of the chemical was relatively low. The nitrogen level did not exceed 1 %, which occurred at 10-20 % addition of the chemical.

    After ageing in oil, the degree of polymerisation was significantly reduced, which meant that the papers did not fulfil the requirement of a maximum of 50 % reduction. The addition of the chemical did however improve the ageing resistance with nearly 45 % if the unmodified paper is compared to the modified paper with the highest degree of polymerisation (10 % addition, equivalent to 1 % nitrogen).

    Papers that had been modified by addition of chemicals in the stock and had been aged in air exhibited lower degree of polymerisation than unmodified paper. The degree of polymerisation was significantly reduced for papers that had been coated and aged in air.

    Addition of chemicals resulted in both lower bursting strength and lower conductivity.

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    FULLTEXT01
  • 2811.
    Williams, Helén
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Food Packaging for Sustainable Development2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Packaging has been on the environmental agenda for decades. It has been discussed and debated within the society mainly as an environmental problem. Production, distribution and consumption of food and drinks contribute significant to the environmental impact. However, consumers in the EU waste about 20% of the food they buy. The function of packaging in reducing the amount of food losses is an important but often neglected environmental issue.

    This thesis focuses on the functions of packaging that can be used to preserve resources efficiently and reduce the environmental impact of the food-packaging system. The service perspective is used to increase knowledge about consumer interaction with packages. Fifteen packaging attributes, for example, ‘easy to empty’, ‘hygienic’ and ‘contain the right quantity’, were identified as influencing the amount of food losses at the consumer. The result showed that there are potentials to both increase consumer satisfaction and decrease the environmental impact of the food-packaging system, when new packaging design reduces food losses. A model was developed that calculates the balance of environmental impact between reduction of food losses, and more packaging material. The result showed that it can be environmentally motivated to increase the environmental impact of packaging, if the amount of food losses is reduced. This is especially true for food items with high environmental impact, e.g. meat and dairy products, and for food items that have a high share of loss, e.g. bread.

    I have also explored to what extent packaging can influence food losses in households. The study showed that about 20% to 25% of household food waste was related to packaging. The households noted three packaging attributes as the main causes for food losses; ‘too big packaging’, ‘difficult to empty’ and ‘best-before-date’.

    Finally there is a discussion of packaging research in the context of sustainability principles, and suggestions for further research.

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    fulltext
  • 2812.
    Williams, Helén
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Helhetssyn i förpackningsutvecklingen för att minska livsmedelsspill2008Conference paper (Other (popular science, discussion, etc.))
    Abstract [sv]

    Vad händer med miljöpåverkan om man lyssnar mer på konsumenterna i förpackningsutvecklingen?



    Konsumenten i fokus är en trend som har ökat i betydelses för många verksamheter de senaste åren, detta gäller också för förpackningsindustrin. Vi har undersökt vad som händer med miljöpåverkan om förpackningsutvecklare lyssnar mer till vad konsumenten har för behov när det gäller förpackningars funktion.



    Förpackningar har varit med i miljödebatten sedan början på 1990-talet. Särskilt uppmärksammad har förpackningen varit när den används färdigt och blivit avfall. Myndigheterna styr att mängden material i förpackningar ska minska samt hur förpackningar ska återvinnas. Kunskapen om förpackningens miljöpåverkan har sedan dess ökat eftersom många livscykelanalyser presenterats. Förpackningar står för 5-10% av miljöpåverkan från produkter (Tempelman, Joore et al. 2004). Många av livscykelanalyserna har gjorts på själva förpackningen och inte systemet med produkt/förpackning. Det finns risk att ett sådant arbetssätt leder till subotimering i det större systemet som rör förpackning/produkt (Williams, Wikström et al. 2008).



    Förpackningar används för att skydda varor under lagring och transporter från producent till konsument. Förpackningen spelar också en viktig roll i att skapa varumärken och informera konsumenten (Löfgren 2006). Genom att utgå från vad konsumenten tycker är viktigt och samtidigt undersöka miljöpåverkan i hela värdekedjan med mat/förpackning så kunde vi se att förpackningar som medför mindre förluster av mat kan förväntas ge nöjdare kunder och mindre miljöpåverkan. Mat och dryck står för 20-30 % av den totala miljöpåverkan i EU (Tukker, Huppes et al. 2005). I en brittisk studie konstaterades att nästan 30 % av maten som bärs hem till hushållen slängs (Ventour 2008). Att så mycket mat slängs bidrar till en onödig och stor miljöpåverkan.



    Om varumärkesägare och förpackningsutvecklare ser mer till hur förpackningen kan förhindra uppkomst av matspill så kan det innebära att nya förpackningslösningar introduceras. Åtgärder i förpackningsutformningen som påverkar spill är till exempel, hur den skyddar, hur lätt den är att tömma, storleken (konsumenten kan köpa den mängd den har behov av), dosering, information om innehåll eller instruktioner kring förvaring. Dessa lösningar kan medföra, nya tekniska lösningar i produktionen av förpackningen, nya material i ytor och ibland ökad mängd förpackningsmaterial. För att minska miljöpåverkan i hela systemet med mat/förpackning finns det utrymme för att till och med öka miljöbelastningen av förpackningar, då nya lösningar leder till minskade förluster av livsmedel (Williams, Wikström et al. 2008).



    När man vill kartlägga miljöpåverkan på förpackningar genom att göra livscykelanalyser bör dessa alltid också omfatta innehållet i förpackningen samt brukarbeteende/behov.

  • 2813.
    Williams, Helén
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Packaging and losses of food2008Conference paper (Other (popular science, discussion, etc.))
  • 2814.
    Williams, Helén
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Packaging Development and Environmental Effects of Food Losses2008Conference paper (Refereed)
    Abstract [en]

    Consumer-in-focus is a trend that is important for many businesses. We have explored what happens with the environmental impact in the food-packaging systems if packaging developers and brand-owners listen more to what the consumer finds important about packaging. We found that it is possible to increase customer satisfaction and at the same time decrease the environmental impact, especially when the new packaging design reduces food losses

  • 2815.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Lindh, Helena
    Lunds Tekniska Högskola.
    Annika, Olsson
    Lunds Tekniska högskola.
    Consumer perceptions of sustainable packaging - Limited by lack of knowledge?2012Conference paper (Refereed)
    Abstract [en]

    Packaging has great potential to contribute to sustainable development. This is due to its primary role to protect products. This paper reports on how Swedish consumers perceive and select food packages in general, and how environmental aspects of conventional and organic food packaging are perceived in particular. The study is based on a consumer survey. The findings indicate that contrary to research that emphasizes the protective function of packaging as most important, consumers almost exclusively refer to the packaging material when it comes to the environmental impact of packaging. This indicates a lack of knowledge among consumers on sustainable packaging.

  • 2816.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science.
    Lindh, Helena
    Lunds tekniska högskola.
    Olsson, Annika
    Lunds tekniska högskola.
    Consumer Perceptions of Food Packaging: Contributing to or Counteracting Envir onmentally Sustainable Development?2016In: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 29, no 1, p. 3-23Article in journal (Refereed)
    Abstract [en]

    Packaging has a fundamental role in ensuring safe delivery of goods throughout supply chains to the end consumer in good condition. It also has great potential to contribute to sustainable development. This paper explores and provides insights on Swedish consumer perceptions and knowledge of environmental aspects of food packaging and elaborates on how these can contribute to or counteract environmentally sustainable development. A study based on a consumer survey carried out in Sweden is presented. A review of recent packaging research emphasizes the protective function of packaging as its most important contribution to the environmental dimension of sustainable development. Contrary to this, consumers almost exclusively refer to the packaging material when it comes to their perceptions of the environmental impact of packaging. Paper-based packaging is strongly understood by the surveyed consumers to be environmentally advantageous, whereas plastic and metal are not. This study further indicates that a majority of the Swedish consumers surveyed are aware of their shortcomings in judging the environmental status of food packaging, indicating a need for guidance; otherwise, consumer choices can unintendedly counteract environmentally sustainable intentions

  • 2817.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Löfgren, Martin
    Förpackad för hållbar framtid2008Conference paper (Other (popular science, discussion, etc.))
  • 2818.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Environmental impact of packaging and food losses in a life cycle perspective: a comparative analysis of five food items2011In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 19, no 1, p. 43-48Article in journal (Refereed)
    Abstract [en]

    The environmental concern and development issues regarding packaging has for 20 years to a high extent been on packaging when it has become waste. To reduce the environmentalimpact from the whole foodpackaging system it is also important to develop the packaging’s ability to reduce food waste. In some cases it may be necessary to increase the environmentalimpactofpackagingin order to reduce food waste. In this paper, the environmentalimpactofpackagingandfoodlossesand the balance between the two has been examined for five different food items. The results show that packaging’s that reduce food waste can be an important tool to reduce the total environmentalimpact, even if there is an increase inimpact from the packaging itself. This is especially true for food items where the environmentalimpactof the food is high relative the packaging, for example cheese, and for food items with high losses, for example bread. It is important to analyse the risk of increasing foodlosses when packaging design changes, for example, when the aim is less packaging material, which is the main intention of the packagingandpackaging waste directive of the European Union.

  • 2819.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    From sustainable packaging to packaging for sustainable development2009Conference paper (Other (popular science, discussion, etc.))
    Abstract

    From sustainable packaging to packaging for sustainable development

    By moving from:

    Packaging waste, Production-oriented, Product-oriented (packaging), Selective and Regulations on packaging reduction

    to:

    Food waste, Consumption-oriented, Service-oriented(packaging functions), Comprehensive and

    Regulations on packaging optimization

  • 2820.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Potential Environmental Gains from Reducing Food Losses Through Development of New Packaging: A Life-Cycle Model2010In: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 23, no 7, p. 403-411Article in journal (Refereed)
    Abstract [en]

    Food losses are seldom included in life cycle analyses of the food packaging system, nor are they included in the debat on sustainable packaging. The development of packaging that decreases food losses does, however, provide an opportunity to reduce the overall environmental impact. In this paper, we present a model that calculates the environmental impact of the food packaging system as a function of food losses. The model can be used to analyse the potential environmental gains from developing packaging that reduce food losses. The model includes food production and processing, transports, packaging, retailer and consumer issues and waste handling. The results show that it can be environmentally motivated to increase the environmental impact of packaging, if necessary, when new packaging design helps to reduce food losses. However, the waste handling systems of food and packaging are important to consider if packaging are developed in order to reduce the environmental impact of the food-packaging system

  • 2821.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Hellström, Daniel
    Division of Packaging Logistics, Department of Design Sciences, Lund Univerisity.
    Olsson, Annika
    Division of Packaging Logistics, Department of Design Sciences, Lund Univerisity.
    Sustainable Packaging Development: One Step FurtherManuscript (preprint) (Other academic)
  • 2822.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Löfgren, Martin
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Service Research Center. Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Business Administration.
    A life cycle perspective on environmental effects of customer focused packaging development2008In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 16, no 7, p. 853-859Article in journal (Refereed)
    Abstract [en]

    This study explores the possibilities of increasing customer satisfaction and reducing the environmental impact from food-packaging systems in alifecycleperspective using results from a study on consumers' demands on packaging based on Kano's Theory of Attractive Quality. It assesses the environmentaleffects of potential improvements in quality attributes. The results show that there are obvious potentials to increase customer satisfaction and at the same time decrease in the environmental impact of the food-packaging system, especially when the packaging design helps to decrease food losses. There were many connections between quality attributes and environmental impacts.

  • 2823.
    Williams, Helén
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Wikström, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Otterbring, Tobias
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Service Research Center. Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Psychology.
    Löfgren, Martin
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Business Administration. Karlstad University, Faculty of Economic Sciences, Communication and IT, Service Research Center.
    Gustafsson, Anders
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Service Research Center. Norway.
    Reasons for household food waste with special attention to packaging2012In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 24, p. 141-148Article in journal (Refereed)
    Abstract [en]

    The amount of food waste needs to be reduced in order to sustain the world's limited resources and secure enough food to all humans. Packaging plays an important role in reducing food waste. The knowledge about how packaging affects food waste in households, however, is scarce. This exploratory study examines reasons for food waste in household and especially how and to what extent packaging influences the amount of food waste. Sixty-one families measured their amount of food waste during seven days and noted in a diary why each item was wasted. Thirty of the families had participated earlier in an environmental project including education in environmental issues of everyday life. About 20-25% of the households' food waste could be related to packaging. Three packaging aspects dominate the packaging related waste: packages that the consumer noted as being too big and packages that were difficult to empty, and wastage because of passed "best before date". The environmentally educated households wasted less, especially of prepared food. They also wasted less food due to passed "best before date". These households were more observant to packaging aspects in relation to food waste. The observations made could be used to learn more about packaging attributes that affect food waste. Although they recognised packaging influence on food waste, these households expressed lower satisfaction with packaging functions and wanted packaging to a lower extent. (C) 2011 Elsevier Ltd. All rights reserved.

  • 2824.
    Willman, Annica
    Karlstad University, Faculty of Technology and Science.
    Språkets betydelse i matematikundervisningen2008Independent thesis Basic level (professional degree), 10 points / 15 hpStudent thesis
    Abstract [en]

    Language is an important part of mathematics education. Research shows that language is significant for knowledge development and that there is a connection between linguistic and mathematical ability. Investigations have shown, though, that the increased focus on communication and pupil interaction within the mathematics education, recommended in the curriculum and syllabus, have not yet reached the desired effect. In order to find out about teachers’ views on the significance of language in mathematics education, and also to get an update of the current educational situation from a linguistic perspective, a qualitative investigation has been made among six primary-school teachers.

    The investigation shows that all teachers interviewed believe language to be important in mathematics education. They do, however, differ in their opinions of where the significance lies. The main part of mathematics lessons is, as noted in previous investigations, used for individual schoolwork, even though half the group of teachers actively practise mathematical communication amongst the pupils. One of the conclusions that can be drawn from this investigation is that if the syllabus’ objective about communicative ability is to be achieved, the pupils must be allowed to write and discuss mathematical issues on a regular basis.

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    FULLTEXT01
  • 2825.
    Willman, Linda
    Karlstad University, Faculty of Technology and Science. Karlstad University, Faculty of Social and Life Sciences.
    Barn och vinter: En kvalitativ undersökning om barns tankar om vad som händer i naturen på vintern2012Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
  • 2826.
    Windfäll, Åsa
    Karlstad University, Faculty of Technology and Science, Department of Mathematics.
    Some Problems in Kinetic Theory and Applications2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis consists of four papers. the first is devoted to discrete velocity models, the second to hydrodynamic equation beyond Navier-Stokes level, the third to a multi-linear Maxwell model for economic or social dynamics and the fourth is devoted to a function related to the Riemann zeta-function.

    In Paper 1, we consider the general problem of construction and classification of normal, i.e. without spurious invariants, discrete velocity models (DVM) of the classical Boltzman equation. We explain in detail how this problem can be solved and present a complete classification of normal plane DVMs with relatively small number n of velocities (n≤10). Some results for models with larger number of velocities are also presented.

    In Paper 2, we discuss hydrodynamics at the Burnett level. Since the Burnett equations are ill-posed, we describe how to make a regularization of these. We derive the well-posed generalized Burnett equations (GBEs) and discuss briefly an optimal choice of free parameters and consider a specific version of these equations. Finally we prove linear stability for GBE and present some numerical result on the sound propagationbased on GBEs.

    In Paper 3, we study a Maxwell kinetic model of socio-economic behavior. The model can predict a time dependent distribution of wealth among the participants in economic games with an arbitrary, but sufficiently large, number of players. The model depends on three different positive parameters {γ,q,s} where s and q are fixed by market conditions and γ is a control parameter. In particular, we investigate the efficiency of control. Some exact solutions and numerical examples are presented.

    In Paper 4, we study a special function u(s,x), closely connected to the Riemann zeta-function ζ(s), where s is a complex number. We study in detail the properties of u(s,x) and in particular the location of its zeros s(x), for various x≥0. For x=0 the zeros s(0) coincide with non-trivial zeros of ζ(s). We perform a detailed numerical study of trajectories of various zeros s(x) of u(s,x).

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    Some Problems...
  • 2827.
    Winestrand, Sandra
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Industrial applications and properties of oxalate-degrading enzymes2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Oxalate-degrading enzymes were investigated with focus on potential applications in the pulp and paper industry and in active packaging. Changes introduced to make the pulp and paper industry more environmentally friendly, such as recirculation of process-water streams and elementary chlorine free bleaching of pulp, have led to increasing problems with precipitation of calcium oxalate. The potential of using enzymes for degradation of oxalic acid in industrial bleaching filtrates was explored to find a way to decrease the problem.

    The studies included chemical characterization and enzymatic treatments of 34 filtrates from kraft, mechanical, and sulfite pulping. Eight oxalate-degrading enzymes were included in the experiments. The treatments of the filtrates were affected by substances that inhibit oxalate-degrading enzymes. Multivariate data analysis, analytical treatment of filtrates with ion-exchange resins, and analysis of the effects of separate compounds on the enzyme activity were employed as tools to investigate inhibiting substances and groups of inhibitors. The experiments with ion-exchangers indicated that the inhibitors included anions, cations, as well as uncharged substances. Sulfite (≥1 mM) caused complete or almost complete inhibition of all oxalate-degrading enzymes so far examined, while the effects of chlorine oxyanions differed for the various enzymes investigated. A newly discovered oxalate decarboxylase was chosen for experiments performed directly in a mill producing mechanical pulp. The new enzyme degraded 70% of the oxalic acid in one hour, while the well-characterized oxalate decarboxylase from Aspergillus niger degraded <5% of the oxalic acid during the same period of time.

    Oxalate decarboxylase from the white-rot basidiomycete fungus Trametes versicolor was purified by using chromatographic methods and characterized with gel electrophoresis and tandem mass spectrometry. Results indicate that it is a 69-kDa heavily glycosylated enzyme with optimal activity at pH 2.5.

    Experiments designed to investigate the potential of using oxalate oxidase from barley in active packaging showed that it could be entrapped with retained catalytic activity in a latex-polymer matrix. Furthermore, the experiments indicate that oxalate oxidase can be used in active packaging either as an oxalic acid scavenger or as an oxygen scavenger.

  • 2828.
    Winestrand, Sandra
    et al.
    Kemiska institutionen, Department of Chemistry, Umeå Universitet.
    Johansson, Kristin
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Jönsson, Leif J.
    Kemiska institutionen, Department of Chemistry, Umeå Universitet.
    Co-immobilization of oxalate oxidase and catalase in films for scavenging of oxygen or oxalic acid2013In: Biochemical engineering journal, ISSN 1369-703X, E-ISSN 1873-295X, Vol. 72, p. 96-101Article in journal (Refereed)
    Abstract [en]

    Oxalate oxidase has potential to act as an oxygen scavenger in active packaging to increase the shelf-life of food and beverages, while simultaneously producing the protective packaging gas carbon dioxide. This study shows that oxalate oxidase from barley can be immobilized with retained catalytic activity through entrapment in a latex polymer matrix. Conditions for formation of film containing oxalate oxidase have been evaluated as well as effects of storage and latex on enzyme activity, migration of enzyme in films, and the ability of the latex films to resist higher temperatures. Drying of enzyme-containing latex films at 75 °C prior to conditioning at 30 °C resulted in higher activity than drying solely at 30 °C, or drying at 95 °C or 105 °C followed by conditioning at 30 °C. Storage of films in air at 4 °C for 14 days did not negatively affect the enzymatic activity. Inclusion of catalase in films with oxalate oxidase effectively prevented release of hydrogen peroxide. The results suggest that the immobilized enzyme can successfully be used both as an oxygen scavenger and as an oxalic-acid scavenger.

  • 2829.
    Winestrand, Sandra
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Larsson, Simona
    Riga Technical University, Faculty of Civil Engineering, Latvia.
    Cassland, Pierre
    Applied Microbiology, Lund University/Lund Institute of Technology.
    Nilvebrant, Nils-Olof
    Karlstad University, Faculty of Technology and Science.
    Jönsson, Leif J.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Effects of ionic substances in bleaching filtrates and of lignosulfonates on the activity of oxalate oxidase from barley2011In: Engineering in Life Sciences, ISSN 1618-0240, E-ISSN 1618-2863, Vol. 11, no 3, p. 245-252Article in journal (Refereed)
    Abstract [en]

    The effects of ionic substances in seven industrial filtrates from kraft pulping, mechanical pulping, and sulfite pulping on the activity of oxalate oxidase from barley were investigated by pre-treatment of the filtrates with ion-exchange resins prior to enzymatic degradation of the oxalic acid in the filtrates. The pre-treatment resulted in increased oxalic acid degradation rates in all filtrates, except for one that was obtained from sulfite pulping. The possibility that lignosulfonates, which were present in the filtrate from sulfite pulping, could affect oxalate oxidase was investigated in a separate set of experiments involving four different preparations of lignosulfonates. At a lignosulfonate concentration of 50 mg/mL and a pH of 3.8, only 2-16% of the activity of oxalate oxidase remained. The results show the effects of anionic and cationic substances in bleaching filtrates on oxalate oxidase and indicate that there is an interaction between the enzyme, which has a positive net charge at pH 3.8, and the polymeric anionic lignosulfonates.

  • 2830.
    Winestrand, Sandra
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Latha Gandla, Madhavi
    Department of Chemistry, Umeå University.
    Hong, Feng
    College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, China.
    Chen, Qi Zhi
    College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, China.
    Jönsson, Leif J.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Oxalate decarboxylase of Trametes versicolor: biochemical characterization and performance in bleaching filtrates from the pulp and paper industry2012In: Journal of chemical technology and biotechnology (1986), ISSN 0268-2575, E-ISSN 1097-4660, Vol. 87, no 11, p. 1600-1606Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Oxalate decarboxylase (ODC) from acid-induced cultures of the white-rot fungus Trametes versicolor was purified and characterized with respect to its biochemical properties and the possibility to utilize the enzyme for treatment of process water with the intention to prevent problems with calcium-oxalate scaling in the pulp and paper industry. RESULTS: Purified T. versicolor ODC was identified by tandem mass spectrometry. As estimated by using SDS-PAGE, the molecular mass was 69 kDa, and 60 kDa after deglycosylation with N-glycosidase F. The pH optimum was 2.5 and the temperature optimum was 4045 degrees C. The effects of ten potential inhibitors in industrial filtrates were examined. The enzyme was sensitive to low concentrations (0.1 mmol L-1) of chlorite and sulfite. T. versicolor ODC exhibited activity in 16 filtrates collected from mechanical pulping and kraft pulping. It had higher activity than ODC from Aspergillus niger in all of the filtrates and higher activity than oxalate oxidase from barley in all filtrates except two. CONCLUSIONS: The investigation shows basic biochemical properties of T. versicolor ODC and indicates that the enzyme may be useful for treatment of industrial filtrates under acidic conditions. Copyright (c) 2012 Society of Chemical Industry

  • 2831.
    Winestrand, Sandra
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Nilvebrant, Nils-Olof
    Karlstad University, Faculty of Technology and Science.
    The Effects of Oxyanions on the Activity of Oxalate Oxidase2009In: The Open Enzyme Inhibition Journal, ISSN 1874-9402, Vol. 2, p. 36-40Article in journal (Refereed)
  • 2832.
    Wingqvist, Annica
    Karlstad University, Faculty of Technology and Science.
    Extraction, Isolation and Purification of β-carotene2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With focus on purification and isolation, the fat soluble, highly conjugated hydrocarbon β-carotene was investigated. The aim originated from a research project whose objective is an attempt to take better advantage of the planets resources, doing this particularly by refining by-products from the industry, which e.g. include β-carotene. β-carotene, known for its provitamin A activity and potential disease suppression, as well as usage as a colorant, is a sought compound. This high-value compound in this study found in carrot extract originating from pressurized fluid extraction (PFE) have been detected and purified by high performance (pressure) liquid chromatography (HPLC). The extract should prior to usage exhibit profitable and environmental friendly β-carotene concentration. By solid phase extraction (SPE) four times higher concentration than the original one was achieved. Competitive extraction methods were developed and compared with PFE, by amount extracted in correlation to time consumed particularly reflux boiling proved to be a good option. Owing to reactivity β-carotenes instability and degradation are stated in other studies, in this study this is on certain points rejected, e.g. heat instability and the usefulness of an antioxidant (butylated hydroxytoluene (BHT)). The later requires nevertheless more long term studies to actually confirm the pointlessness in using BHT. Further investigation and evaluation of the SPE method and the extraction methods will also be necessary prior to scale-up of the process for industrial application.

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  • 2833.
    Wong, Arne
    Karlstad University, Faculty of Technology and Science.
    Sojamjöl som tillsats vid produktion av träpellets: Effekt på pelletskvalitet, miljöförstöring och energiförbrukning2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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  • 2834.
    Wurtz, Albrecht
    Karlstad University, Faculty of Technology and Science.
    Conformal Field Theory and D-branes2006Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The main topic of this doctoral thesis is D-branes in string theory, expressed in the language of conformal field theory. The purpose of string theory is to describe the elementary particles and the fundamental interactions of nature, including gravitation as a quantum theory. String theory has not yet reached the status to make falsifiable predictions, thus it is not certain that string theory has any direct relevance to physics. On the other hand, string theory related research has led to progress in mathematics.

    We begin with a short introduction to conformal field theory and some of its applications to string theory. We also introduce vertex algebras and discuss their relevance to conformal field theory. Some classes of conformal field theories are introduced, and we discuss the relevant vertex algebras, as well as their interpretation in terms of string theory.

    In string theory, a D-brane specifies where the endpoint of the string lives. Many aspects of string theory can be described in terms of a conformal field theory, which is a field theory that lives on a two-dimensional space. The conformal field theory counterpart of a D-brane is a boundary state, which in some cases has a natural interpretation as constraining the string end point. The main focus of this thesis is on the interpretation of boundary states in terms of D-branes in curved target spaces.

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  • 2835.
    Wäne, Gerd
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Fibre surface properties of kraft pulp: The influence of wood raw material, bleaching and storage2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this thesis was to study the fibre surface properties of Birch (Betula ssp.), Eucalyptus (E. urograndis and E. globulus) and Spruce (Picea Abies) pulps bleached using two different methods: ECF (Elementary Chlorine Free) and TCF (Totally Chlorine Free). The hardwood pulps were subjected to a hot acidic stage prior to ECF bleaching in order to remove hexenuronic acid. The effect of prolonged storage (ageing) on the fibre surface properties was studied for all of the pulps.

    The characteristics of the fibre surfaces were determined by measuring the dynamic contact angle of single fibres (DCA) and by using Electron Spectroscopy for Chemical Analysis (ESCA) and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). The correlation between the fibre surface properties and the sizing efficiency of the hardwood pulps were evaluated by measuring the amount of alkyl ketene dimer (AKD) needed to reach a certain water absorption level(measured as Cobb60).

    The birch pulp was more hydrophilic than the eucalyptus pulps, thus requiring more AKD to reach a certain water absorption value, and also had a lower DCA. The introduction of a hot acidic stage (A stage) in the ECF bleaching sequence applied to the hardwood pulps (i.e. A/D(EP)DD versus D(EP)DD) lowered, as expected, the total fibre charge due to the removal of hexenuronic acids groups (HexA). According to the DCA measurements all of the pulps became more hydrophilic after the A/D(EP)DD bleaching than after the D(EP)DD bleaching sequence. The sizing ability of the pulps, measured as the AKD demand to a certain Cobb60 value, showed that the AKD demand was more or less the same for the eucalyptus pulps regardless of the bleaching sequence used. The birch pulp, on the other hand, required somewhat less AKD in the A/D(EP)DD sequence than in the D(EP)DD.

    The AKD demand to a certain Cobb60 value decreased further for the bleached birch and E. globulus pulps after ageing due to an increase in the fibre surface hydrophobicity. ESCA analysis revealed an increase of surface extractives on the pulps after ageing, which was also supported by ToF-SIMS analysis. It was concluded that there was an increase in fatty acids, fatty acid salts and possibly even sterols and glycerides on the fibre surfaces due to ageing. A migration of these components from the interior of the fibre wall to the fibre surface during ageing was verified in this study.

    The TCF and ECF bleached softwood pulps also showed differences in their fibre surface properties that were tangible and thereby measurable. The dynamic contact angle was highest for the TCF bleached softwood fibres, i.e. these were more hydrophobic. Although changes caused by ageing were much more pronounced for the ECF fibres, all pulps became more hydrophobic upon ageing.

    The hydrophobicity of pulp fibres can be determined using DCA, which is a rather rapid and economically viable analysis. Using this information, a paper/board mill can base its sizing strategy on scientific findings.

    The ageing effects seen on the fibre surfaces in the form of the migration of extractives might be an important parameter from an industrial point of view, especially when pulps are stored and/or transported for a long time period. Nowadays it is quite common for pulps to be shipped around the world and subjected to warm and humid conditions. It is therefore probable that the properties of the pulp change in such a way that the papermaking process requires adjustment.

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  • 2836.
    Wäne, Gerd
    et al.
    Karlstad University, Faculty of Technology and Science.
    Basta, Jiri
    Eka Chemicals AB, Bohus, Sweden.
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    A comparison of the surface properties of ECF and TCF bleached softwood kraft pulp2007In: Appita journal, ISSN 1038-6807, Vol. 60, no 5, p. 396-Article in journal (Refereed)
  • 2837.
    Wäne, Gerd
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Aspects on the AKD demand of hardwood kraft pulps before and after ageing2009In: Appita journal, ISSN 1038-6807, Vol. 62, no 2, p. 123-129Article in journal (Refereed)
  • 2838.
    Wäne, Gerd
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Pulp and Fibre surface properties of bleached hardwood Kraft Pulps: Influence of an A-stage2009In: Paperi ja puu, ISSN 0031-1243, Vol. 91, no 7-8, p. 58-64Article in journal (Refereed)
    Abstract [en]

    Hexenuronic acids in kraft pulps increase the demand for bleaching chemicals and cause brightness reversion of the bleached pulps during storage. They can, however, be removed by the use of hot acid treatments in e.g. the bleaching sequence, which is commonly used for eucalyptus in the pulp industry today. In this work three kraft hardwood pulps (two eucalyptus and one birch) were selected to study the influence on the surface properties of the pulps of a hot acidic stage (A stage) introduced prior to a standard ECF bleaching sequence. The sequences compared were A/D(EP)DD and D(EP)DD. The results were compared before and after the pulps were aged at room temperature for about eight months.

  • 2839.
    Xinzhu, Jin
    Karlstad University, Faculty of Technology and Science.
    Channel Estimation Techniques of SC-FDMA2007Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Abstract

    This master thesis investigates several di®erent channel estimation techniques in an SC-

    FDMA (Single Carrier Frequency Division Multiple Access) system with parameters set

    according to the standards of 3GPP LTE (3rd Generation Partnership Project Long Term

    Evolution). 3GPP LTE is the name given to a project within the 3GPP to improve the

    mobile phone standard to cope with future requirements. In this thesis, we ¯rst introduce

    the SC-FDMA system, which is a transmission technique that utilizes single carrier mod-

    ulation, then ¯ve types of estimators are investigated. Essential to all channel estimatiors

    is the use of pilot symbols. In the last part we compare the performance of the channel

    estimation techniques with each other in di®erent environments by analysing their symbol

    error rates. All simulations are done in a Matlab environment.

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  • 2840.
    Yadoitsev, Igor
    et al.
    Central University of Technology, Free State, Department of Mechanical and Mechatronic Engineering, South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yadroitsava, Ina
    Central University of Technology, Free State, Department of Mechanical and Mechatronic Engineering, South Africa.
    Hierarchical design principles of selective laser melting for high quality metallic objects2015In: Additive manufacturing, ISSN 2214-8604, Vol. 7, p. 45-56Article in journal (Refereed)
  • 2841.
    Yadroitsev, I
    et al.
    Université de Lyon, Ecole Nationale d’Ingénieurs de Saint-Etienne, Saint-Etienne, France.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yadroitsava, I
    Université de Lyon, Ecole Nationale d’Ingénieurs de Saint-Etienne, Saint-Etienne, France.
    Selective laser melting of Ti6Al4V alloy for biomedical applications: Temperature monitoring and microstructural evolution2014In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 583, p. 404-409Article in journal (Refereed)
  • 2842.
    Yadroitsev, I
    et al.
    Université de Lyon, France.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yadroitsava, I
    Université de , France.
    Johansson, S
    Linköpings universitet.
    Smurov, I
    Université de Lyon.
    Energy input effect on morphology and microstructure of selective laser melting single track from metallic powder2013In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 4, p. 606-613Article in journal (Refereed)
  • 2843.
    Yang, Zhenkun
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Alternatives to hard chromium plating on piston rods2011Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
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  • 2844. Yeom, H. W.
    et al.
    Horikoshi, K.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Ono, K.
    Uhrberg, R. I. G.
    Nature of the broken-symmetry phase of the one-dimensional metallic In/Si(111) surface2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 24Article in journal (Refereed)
  • 2845.
    Yngman, Sofie
    Karlstad University, Faculty of Technology and Science.
    Mechanical properties of carbon nanotubes grown by pyrolysis of ferrocene2012Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    Carbon nanotubes (CNTs) have drawn a lot of attention during the last decades due to its promising mechanical and electrical properties. Extensive research regarding the mechanical properties of CNTs has been carried out during the last decades. A lot of effort has been put into developing methods to properly characterize features such as Young’s modulus and the deformation processes of carbon nanotubes. A detailed knowledge of these properties is important for many of the suggested applications of carbon nanotubes.Here we have examined multiwalled carbon nanotubes (MWCNTs) grown by pyrolysis of ferrocene. In some cases the carbon nanotube contained an iron core or traces of iron in the core. The carbon nanotubes ranged from 20 nm to 65 nm in radius and 1000 nm to 4000 nm in length.An atomic force microscope (AFM) was used inside a scanning electron microscope (SEM) for in situ force measurements. The AFM cantilever was used to displace individual carbon nanotubes from their equilibrium positions. The forces used to displace the carbon nanotubes have been plotted against the displacements of the tubes to obtain the characteristic force-displacement curves. From the slope of these curves the spring constants of the carbon nanotubes have been found. Young’s modulus for each tube was derived from the spring constant and the tube dimensions.We found that Young’s modulus ranged from 7 GPa to 340 GPa with no observed dependence on the radius or the length. Previous works suggest that deformation processes such as rippling and buckling will drastically change the spring constant of the tubes when displaced. The maximum values of the applied forces in our measurements were smaller than those needed to push the tubes into the deformation stages. The relatively low values of Young’s modulus indicate that these tubes are rich in defects which dominate their mechanical behaviour.

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  • 2846.
    Yngman, Sofie
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Probing mechanical properties of carbon nanotubes2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose with this c-level thesis is to investigate Young’s modulus of carbon nanotubes (CNTs). The force measurements as well as the imaging are done by an atomic force microscope (AFM). This has been done before by Eric W. Wong et al in 19971. These earlier experiments report techniques using clean-room facilities not available at Karlstad University. Our task is to investigate probabilities in which to perform the experiment by using the available instruments at Karlstad University.The force measurements are done by using the AFM tip to push the CNTs. A force curve is obtained from where it is possible to determine the spring constant of the CNT. By knowing some essential characteristics of the cantilever and the tip, Young’s modulus can be calculated. The CNT needs to be fixed in one end and able to push to the sides in the other end. Our main focuses in this thesis is how to fix the CNTs and what surface to use. Essentially two methods of fixing the tubes have been tried out. Partly we have been looking for large particles on the surface lying on top of a CNT fixing one end, partly we have evaporated gold to achieve an edge under which the CNTs can be attached.In conclusion we can say that it is hard and time-consuming looking for CNTs randomly fixed by particles on the surface. Further we can say that the choice of surface is important. A surface with a low friction was desired but the low friction causes trouble during imaging. The force between the tip and the cantilever during imaging seems to be enough to disturb the CNT and the surface, making measurements hard.

  • 2847.
    Yohan, Noh
    et al.
    Waseda University.
    Wang, C.
    Waseda University.
    Tokumoto, M.
    Waseda University.
    Solis, Jorge
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Ishii, H.
    Waseda University.
    Takanishi, Atsuo
    Waseda University.
    Development of Airway Management Training System WKA-4: Provide Useful Feedback of Trainee Performance to Trainee during Airway Management2012In: Complex Medical Engineering (CME), 2012 ICME International Conference on, IEEE Press, 2012Conference paper (Refereed)
  • 2848.
    zafar, syed hammad
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Modelling and control of large wind turbine2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In order to make the wind energy an economical alternative for energy production, upscaling of turbine to 10 - 15MW may be necessary to reduce the overall cost of energy production. This production target requires a considerable increase in the turbine size and placing the turbines at high wind speed locations. But increase in turbine size also increases the uneven load distribution across the turbine structure. Therefore an efficient load reduction technique is necessary to increase the turbine reliability in high wind speed locations. Variable speed wind turbine offers most desirable load reduction through actively pitch angle control of turbine blades. Research has shown that the Individual Pitch Control (IPC) is most promising option for turbine load reduction.

    This thesis work is focused on modelling of a large wind turbine and implementation of a new mutlivariable control concept for turbine load reduction. A detailed mathematical model is designed which includes turbine blade and tower dynamics and a proposed Linear Quadratic Gaussian (LQG) algorithm is implemented for Individual Pitch Control (IPC) loop of wind turbine. Proposed model in this thesis work is derived from the previous turbine model used in ECN with additional tower dynamics. My contribution in turbine modelling portion is to linearize the equations of motion to form a statespace model and to implement LQG algorithm for turbine active load reduction. This proposed method is compared with the previous control technique used in ECN for turbine fatigue load reduction to measure the overall efficiency of the proposed technique.

    Fatigue load has major effect on the turbine working age. In quantitative way, proposed LGQ design offers 8-10% approx. more fatigue load reduction in comparison with the previous design. In simple convention, decrease in turbine fatigue load increases the turbine age. This 8 - 10% fatigue load reduction offers 8 - 10% minimum increase in turbine working age which means that if a turbine works for 20 years in total for energy production, this proposed technique will add 2 extra years into the turbine working life. This age increase has major economic impact to make the wind turbine a viable alternative for energy production.

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  • 2849.
    Zanganeh, Arjan
    Karlstad University, Faculty of Technology and Science.
    Lyftanordningsbeskrivning för Metso Fiber AB2013Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    The thesis is performed at Metso Fiber in Karlstad which belongs to the Metso coperation. The company is a global supplier of sustainable technology and services for mining, construction, power generation, automation, recycling and the pulp and paper industry.

    Metso Fiber AB has a need to review the lifting and transportation plans for all their machines. In order to solve the assignment in a proper way, the student has to understand how the machines are built and how assembly and disassembly works. It will therefore benefit if the student has contact with different departments of the company. These assignments also include the design and quantification of any lifting lugs / loops etc. Then later determine where the lifting lugs / loops should be placed and what material should be selected. They will also help to determine which parts of the machine that is more or less susceptible to external forces. The objective of this assignment is to expand a procedure for how to lift a certain machine to the correct position.

    After many discussions and experiments, we concluded that an appropriate transportation blueprint would consist of clear views of the machine, 2D and 3D view and the relevant information applicable to the specific machine, in form of charts.

  • 2850.
    Zeb, Hassan
    Karlstad University, Faculty of Technology and Science.
    Bleaching of Old Newsprint Paper at Metsä Tissue2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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