1 - 5 of 5
rss atomLink to result list
Permanent link
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
  • Public defence: 2018-05-29 13:00 Kappa, Västerås
    Tumwesigye, Alex Behakanira
    Mälardalen University, School of Education, Culture and Communication, Educational Sciences and Mathematics.
    Dynamical Systems and Commutants in Non-Commutative Algebras2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis work is about commutativity which is a very important topic in Mathematics, Physics, Engineering and many other fields. In Mathematics, it is well known that matrix multiplication (or composition of linear operators on a finite dimensional vector space) is not always commutative. Commuting matrices or more general linear or non-linear operators play an essential role in Mathematics and its applications in Physics and Engineering. Many important relations in Mathematics, Physics and Engineering are represented by operators satisfying a number of commutation relations. Such commutation relations are key in areas such as representation theory, dynamical systems, spectral theory, quantum mechanics, wavelet analysis and many others.

    In Chapter 2 of this thesis we treat commutativity of monomials of operators satisfying certain commutation relations in relation to one-dimensional dynamical systems. We derive explicit conditions for commutativity of the said monomials in relation to the existence of periodic points of certain onedimensional dynamical systems.

    In Chapter 3, we treat the crossed product algebra for the algebra of piecewise constant functions on given set and describe the commutant of this algebra of functions which happens to be the maximal commutative subalgebra of the crossed product containing this algebra.

    In Chapters 4 and 5, we give a characterization of the commutant for the algebra of piecewise constant functions on the real line, by comparing commutants for a non-decreasing sequence of algebras.

    In Chapter 6 we give a description of the centralizer of the coefficient algebra in the Ore extension of the algebra of functions on a countable set with finite support.

  • Public defence: 2018-06-01 13:00 Pi, Västerås
    Mörndal, Marie
    Mälardalen University, School of Business, Society and Engineering, Industrial Economics and Organisation.
    "Vi måste takta!": En studie av organisering för samverkan.2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Organizational collaboration is perceived as a positive phenomenon in the public sector and is often seen as a way of facing societal challenges despite limited resources. This positive view on organizational collaboration seems to persist, although research shows that collaborative projects bring various difficulties. These are related to boundaries, both between organizations and professions. How boundaries are understood and managed are thus central aspects of organizing for collaboration. This thesis describes and discusses the preparation – the organizing – for collaboration and the purpose of the thesis is to explore and deepen an understanding of the practice developed in organizing for collaboration.

    A municipality’s work to improve internal collaboration and prepare for external collaboration has been studied. The work was led by two project managers in collaboration with various members of the municipality. A practice-oriented approach has been applied, which involves a focus on the activities carried out during the organizing work. The empirical material was created through participatory observations of the project managers’ work.

    The project managers’ practice developed into five activity patterns called planning, navigating, interacting, documenting and, what in Swedish was called, “takta”. The term “takta” was used to denote activities related to adaptation and synchronization to the municipality’s activities; to pace the activities.

    The analysis shows that the activity pattern of pacing was a superior activity pattern that managed and organized the other four patterns. The concept pacing contributes to the understanding of how activities create rhythms in an organization and how these are adapted to the overall pace. People responsible for pacing must be aware of the rhythms of other activities that affect the pacing. Pacing is a complex concept that can be described in several dimensions: temporal, social, boundary-crossing, emotional, holistic, and in a situated dimension. These dimensions contribute to the understanding of how pacing is done, what it means when pacing and also facilitate an analysis when pacing fails.

    The conclusion of the thesis is that an awareness of pacing activities in organizing across boundaries increases the opportunities to implement activities in the “right” order, time and place. Thus, the multidimensional concept of pacing may be used as a planning-tool when organizing across boundaries and as an analytical instrument when the organizing becomes unsynchronized with other activities. A practice-oriented perspective enables the exploration of the activity patterns created in organizing for collaboration and increases the understanding of how organizing across boundaries is done.

  • Public defence: 2018-06-15 13:00 Filen, Eskilstuna
    Stålberg, Lina
    Mälardalen University, School of Innovation, Design and Engineering, Innovation and Product Realisation.
    Adapting to dynamic conditions through continuous innovation in manufacturing2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The speed of change increases due to the pace of technological change and globalisation, and many industries that usually have acted in more stable settings will in the future act in more dynamic marketplaces. In order to be able to manage dynamic conditions, the organisation needs to continue delivering effectively in existing business areas while developing new systems, products and processes to take advantage of new opportunities in the future. This means that the organisation must be able to use abilities for exploitation and exploration simultaneously or, in other words, strive for continuous innovation including ambidexterity.

    In the traditional manufacturing industry, many companies use some sort of improvement programme for achieving operational excellence. Hence, a trend among multinational manufacturing companies is also to deploy and integrate corporate improvement programmes (XPS). These are based on lean production and inspired by the Toyota Production System. Generally, improvement programmes such as XPS largely support the development of exploitation capabilities but not exploration capabilities, which instead may have to stand back. Previous research states that these are problematic and complex issues that need to be further understood and developed. Therefore, more knowledge and support needs to be developed regarding how manufacturing companies can adapt their production systems to remain resource-efficient while simultaneously adapting to more radical changes.

    The overall purpose of this research project is to contribute to an increased understanding of how XPS integrations can be developed towards continuous innovation to be able to manage more dynamic conditions. Accordingly, the research objective is to develop recommendations supporting continuous innovation in manufacturing. An overall longitudinal study has been carried out containing five case studies at a manufacturing company integrating an XPS during dynamic conditions, i.e., with large variations in volumes and mixes of products together with the introduction of new products and production concepts. The studies conducted and the results are presented in five appended papers.

    The research shows there is a risk that the XPS concept is abandoned due to a lack of understanding of how the XPS contributes to solve the turbulent situation that appears under dynamic conditions. At the same time, it is important to develop and support exploration skills in parallel, as these abilities are not particularly well developed in this context. Furthermore, the research shows that a strategy formulation process striving for high involvement can be used as a means of creating ambidextrous capabilities.

    The full text will be freely available from 2018-05-25 08:00
  • Public defence: 2018-06-18 13:00 Paros, Västerås
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Co-digestion of microalgae and sewage sludge - A feasibility study for municipal wastewater treatment plants2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increased emissions of anthropogenic greenhouse gases over the last 100 years is the reason for the acceleration in the greenhouse effect, which has led to an increase of the globally averaged combined land and ocean surface temperature of 0.85 °C between 1880 and 2012. A small fraction of the increased anthropogenic greenhouse gases originates from municipal wastewater treatment plants (WWTPs).

    This doctoral thesis was part of a larger investigation of using an alternative biological treatment based on the symbiosis of microalgae and bacteria (MAAS-process (microalgae and activated sludge)). This solution could be more energy efficient and potentially consume carbon dioxide from fossil combustion processes and also directly capture carbon dioxide from the atmosphere and thereby reduce the addition of anthropogenic greenhouse gases to the air.

     The objective of the thesis was to explore the effects when the microalgae-derived biomass from the biological treatment were co-digested with sewage sludge. The results from these experimental studies were then used to evaluate the effects on a system level when implementing microalgae in municipal WWTP.

     Microalgae grown from a synthetic medium improved the methane yield with up to 23% in mesophilic conditions when part of the sewage sludge was replaced by the microalgae. The microalgae grown from municipal wastewater showed no synergetic effect.

     In the semi-continuous experiments the methane yield was slightly reduced when implementing the microalgae. Furthermore the digestibility of the co-digestion between sewage sludge and microalgae were lower compared to the digestion of sewage sludge.

     The digestates containing microalgal substrate had higher heavy metals content than digestates containing only sewage sludge. This could have a negative effect on the potential to use this digestate on arable land in future, due to strict limits from the authorities.  Filterability measurements indicated that the addition of microalgae enhanced the dewaterability of the digested sludge and lowered the demand for polyelectrolyte significantly.

     When a hypothetical MAAS-process replaced a conventional ASP-process the amount of feedstock of biomass increased significantly due to the increased production from the autotrophic microalgae. This increased the biogas production by 66-210% and reduced the heavy metal concentration in the digestate due to a dilution effect from the increased biomass production.

     The thesis demonstrates that microalgae in combination with bacteria from a MAAS-process can be a realistic alternative feedstock to WAS in the anaerobic digestion at a municipal WWTP. A few drawbacks need to be considered when choosing a MAAS-process as biological treatment.

    The full text will be freely available from 2018-05-28 08:00
  • Public defence: 2018-06-19 09:00 Delta, Västerås
    Anbalagan, Anbarasan
    Mälardalen University, School of Business, Society and Engineering.
    A passage to wastewater nutrient recovery units: Microalgal-Bacterial bioreactors2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years, the microalgal–bacterial process has been considered to be a very attractive engineering solution for wastewater treatment. However, it has not been widely studied in the context of conventional wastewater treatment design under Swedish conditions. The technology holds several advantages: as a CO2 sink, ability to withstand cold conditions, ability to grow under low light, fast settling without chemical precipitation, and reducing the loss of valuable nutrients (CO2, N2, N2O, PO4). The process also provides the option to be operated either as mainstream (treatment of municipal wastewater) or side stream (treatment of centrate from anaerobic digesters) to reduce the nutrient load of the wastewater. Furthermore, the application is not only limited to wastewater treatment; the biomass can be used to synthesise platform chemicals or biofuels and can be followed by recovery of ammonium and phosphate for use in agriculture.

    In the present study, the feasibility of applying the process in Swedish temperature and light conditions was investigated by implementing microalgae within the activated sludge process. In this context, the supporting operational and performance indicators (hydraulic retention time (HRT), sludge retention time (SRT) and nutrients removal) were evaluated to support naturally occurring consortia in photo-sequencing and continuous bioreactor configuration. Furthermore, CO2 uptake and light spectrum-mediated nutrient removal were investigated to reduce the impact on climate and the technical challenges associated with this type of system.

    The results identified effective retention times of 6 and 4 days (HRT = SRT) under limited lighting to reduce the electrical consumption. From the perspective of nitrogen removal, the process demands effective CO2 input either in the mainstream or side stream treatment. The incorporation of a vertical absorption column demonstrated effective CO2 mass transfer to support efficient nitrogen and phosphorus removal as a side stream treatment. However, the investigation of a continuous single-stage process as the mainstream showed a requirement for a lower SRT in comparison to semi-continuous operation due to faster settlability, regardless of inorganic carbon. Furthermore, the process showed an effective reduction of influent phosphorus and organic compounds (i.e. COD/TOC) load in the wastewater as a result of photosynthetic aeration. Most importantly, the operation was stable at the temperature equivalent of wastewater (12 and 13 ˚C), under different lighting (white, and red-blue wavelengths) and retention times (6 and 1.5 d HRT) with complete nitrification. Additionally, the biomass production was stable with faster settling properties without any physiochemical separation.

    The outcomes of this thesis on microalgal–bacterial nutrient removal demonstrates that (1) photosynthesis-based aeration at existing wastewater conditions under photo-sequential and continuous photobioreactor setup, (2) flocs with rapid settling characteristics at all studied retention times, (3) the possibility of increasing carbon supplementation to achieve higher carbon to nitrogen balance in the photobioreactor, and (4) most importantly, nitrification-based microalgal biomass uptake occurred at all spectral distributions, lower photosynthetic active radiation and existing wastewater conditions.

    The full text will be freely available from 2018-05-29 08:00