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  • Disputas: 2019-04-25 13:00 M102, Sundsvall
    Razaz, Ghadir
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Problems in the Aluminium DC Casting Process Associated with Melt Treatment Operations2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The quality of DC cast Al alloys is highly dependent on melt batch composition and impurity level in the molten alloy. The chemical composition and cleanliness of a melt is controlled through the melt treatment operations, carried out while the melt is still in the furnace before casting starts. The present work has studied some of these operations and associated problems such as slow dissolution of alloying elements, non-reproducibility in chemical composition analysis and inclusions.

     The results of the dissolution of the alloy elements Mn and Fe showed different behaviors.  For Mn three intermediate phases were involved, all of which exhibited a smooth interface between Mn and the liquid. These three phases were identified as the γ2, Al11Mn4, and µ phases, which grow slowly towards the dissolving Mn particles. The results from the Fe dissolution revealed that only one phase dominates the process, Al5Fe2, which penetrates the Fe particles with an irregular interface.

    The interaction between Mn and Ti additions to AA3003 alloys and consequences for the solidification and precipitation behavior was investigated. The study could map the limits for formation of an earlier unknown AlMnTi phase, which formed large particles, detrimental for subsequent rolling operations.

    Different sampling procedures for chemical composition analysis were studied, and a novel approach was proposed. A mould with an insulated periphery provided one-dimensional solidification, which gave compositions close to nominal.

     Inclusion distributions along as-cast billets were studied as a function of different holding times, and thus different grades of sedimentation. Holding times longer than 30 minutes did not show any improvements.  It was also shown that if melt remaining in the furnace at end of casting is less than about 3000 kg, the sedimented inclusions are stirred into the bulk again, and can enter into the end of the billet.

    The impact on hot tearing susceptibility of different Cu and Fe contents for AA3000 alloys was studied. Cu contents in a range from 0.3 to 1.2 wt%  significantly increase the hot tearing tendency, which was attributed to bad feeding at end of solidification. Decreasing of the Fe content below 0.2 wt%, gives a strong cracking tendency, owing to decreased precipitations of the Al6(Mn,Fe) phase, which contributes to early bridging and thus reinforcement between grains.

  • Disputas: 2019-05-03 10:00 F 234, Östersund
    Weimer, Kerstin
    Mittuniversitetet, Fakulteten för humanvetenskap, Institutionen för psykologi och socialt arbete.
    Behavior Change Towards a Sustainable Lifestyle – Effects of Interventions and Psychological Factors on Pro-Environmental Behaviors2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Climate changes due to human-caused global warming are serious challenges for the planet. Changes in individual human behavior towards more pro-environmental actions are thus highly necessary. Human behavior is complex, however, and promoting behavior change requires a solid understanding of how people behave in different situations and contexts.

    Previous research has pointed out several reasons why people do not behave in accordance with our knowledge about the threat of climate change. Besides structural barriers, other reasons may be related to psychological barriers, such as beliefs, values, and social norms, which limit us in adopting more pro-environmental choices and behaviors. The overall aims of this thesis were to investigate the effects of interventions on energy conservation and ecological food consumption in promoting pro-environmental behavior, to explore the experiences of an energy-saving intervention from the perspective of the participants, and to investigate how values, attitudes, and other psychological factors predict pro-environmental behavior and pro-environmental intentions.

    This thesis is built on four studies. The first study was a survey, where an investigation was made of the predictive power of value orientation, awareness of consequences, environmental concern, moral judgment competence, locus of control, and sense of coherence, on eight pro-environmental behaviors and behavioral intentions. The results showed that only the value type universalism predicts pro-environmental behaviors and behavioral intentions, with attitudes, awareness of consequences for the biosphere, and environmental concern for the biosphere as intermediate or transmitting variables. The results indicate that found determinants of one single behavior may not be applied to other behaviors as dependent variables. Thus, a separate analysis for every type of both actual and intentional lifestyle might have been more successful in confirming these independent variables as determinants of pro-environmental behaviors and behavioral intentions.

    The second study was a randomized quasi-experimental field study. This field intervention investigated the effect of feedback on residential electricity use in households. For a period of eight weeks, differentiated energy use for daily domestic behaviors was monitored by 15 residents via an internet-based system. Feedback based on Relational Frame Theory was used to enhance motivation for energy conservation, and follow-up studies analyzed the maintenance of change for another three months. Psychological factors, including values, attitudes, moral judgment competence, locus of control, and sense of coherence, were simultaneously assessed by web surveys. No significant effects of the feedback on reduction of energy use were found. The small sample size, and the fact that warm water energy use was not monitored, were discussed as explanatory factors.

    In the third study, semi-structured interviews were conducted among eight households having participated in the intervention in the second study. The interview transcripts were subject to qualitative content analysis with the purpose of exploring the experiences of the participants. Those experiences were, on the one hand, described as a struggle to overcome internal and external barriers as well as feelings of contradiction and ambivalence, representing the limitations imposed by participating. On the other hand, there were also descriptions of feelings of ability and motivation, and interaction between satisfaction and improvements, representing the opportunities available to a participant in this kind of intervention. These results support the importance of specific strategies in developing the design of future interventions for promoting residential energy conservation.

    Finally, in the fourth study, an experimental field study was conducted to investigate the effects of behavioral interventions, commonly known as nudges, in promoting the consumption of organic fruits and vegetables. The consumption of both organically and conventionally produced fruits and vegetables was measured during four days (one day every other week) in a grocery store, where consumers were exposed to informational messages in combination with either emotional images or social norm messages. Measurements of daily consumption without exposure to nudges were carried out during four other days (one day every other week, alternated with the nudging days). The results showed that the proportion of sold organic products in the total sale of the selected fruits and vegetables was slightly higher during nudging days when price differences between conventional and organic products were low. This limited effect of nudging disappeared when the price of organic products was considerably higher than the price of conventionally produced products. The results indicate that there is a need to take measures to compensate for the prevailing differences in price between organic and conventional products. Such measures are, for example, the application of a combination of all available nudging tools to strengthen the effects of nudging, as well as collecting psychological data from the participants to be aware of their attitudes towards choices of organic products.

    Taken together, the overall findings of the studies in this thesis confirm the complexity of behavior and of behavior change. Many questions remain unanswered and suggestions on how to develop the research on these issues are discussed.