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  • Disputation: 2018-12-13 09:00 Belladonna, Linköping
    Kiwi, Mahin
    Linköpings universitet, Institutionen för samhälls- och välfärdsstudier, Avdelningen för omvårdnad. Linköpings universitet, Medicinska fakulteten.
    Dementia across cultural borders: Reflections and thought patterns of elderly Iranians with dementia in Sweden, their relatives and staff at a culturally profiled nursing home2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Introduction: Today’s multicultural society has resulted in major changes, with healthcare undergoing significant modifications. Healthcare workers and patients are increasingly confronted with “cultural” backgrounds other than their own. The world’s population is ageing, and the number of people with dementia is growing, resulting in a growing number of older people with a foreign background whose care needs have increased at different rates. Migration does not only mean moving from one place to another; it also involves the transition of an individual’s lifestyle, life views, social and economic adjustments that may lead to certain changes. These transitions from the “old” to the “new” way of life and from a life without dementia to a life with dementia involve making sense of life’s changes.

    Aim: The aim of study I was to explore the experiences and perceptions of dementia among Iranian staff working in a culturally profiled nursing home (CPNH). The aim of studies II and III was to explore relatives’ decisions to end caregiving at home, and Iranian families’ and relatives’ attitudes towards CPNHs in Sweden. The aim of study (IV) was to explore how the residents with dementia at the CPNH expressed the feeling of “home”.

    Method: This thesis is based on more than one year’s fieldwork. The empirical material is based on interviews and observations. Three groups of participants were interviewed and observed: 10 people with dementia (IV), 20 family caregivers and relatives (II and III, respectively) and 34 staff members (I). The interviews were conducted in Persian/Farsi, Azerbaijani, English and Swedish. The choice of language was always up to the participants. All the interviews were audio-recorded, transcribed verbatim in the respective languages and then translated later into Swedish. The analysis of the material was based on content analysis blended with ethnography.

    Results: Study I shows that people from different culturally and linguistically diverse backgrounds could have different perceptions of what dementia entails. A lack of knowledge concerning dementia affects how staff approach these people.

    Study II shows that the CPNH is crucial when deciding to cease caregiving at home. It is important to ensure that relatives with dementia are cared for by someone who speaks the same mother tongue. The results indicate that positive feelings of relief or comfort are dominant responses among the participants, some of whom even feel pride in the high standard of care provided by the home.

    In Study III, most participants based their views on a comparison between the CPNH and Iranian nursing homes after the Islamic Revolution. Negative views of the nursing home were evaluated alongside what the respondents considered to be typically Iranian. In Study IV, the results show that people with dementia’s personal experiences of home played a great role, and although none of the participants felt at home, all of them stated that the CPNH was a place to live in.

    Conclusion: Perceptions of dementia can be based on cultural and traditional understanding, although this can shift through transition and knowledge accumulation. A lack of knowledge concerning dementia and residents’ sociocultural background, generational differences and incoherence, aligned with staff members’ different sociocultural backgrounds, created many challenges. The staff wanted to learn more about dementia, to be able to manage daily communication with the residents. On another point, the staff admitted that only being able to speak a person’s native language was not enough to claim that they were actually communicating. Family caregivers’ decisions to end caregiving at home involve mutuality, capability and management, but decision-making sometimes has nothing to do with violating a person’s autonomy and is more about protecting the person. The family caregivers do care for frail elderly family members. What has changed due to a transition is the structure and construction of family caregiving. The consequences of communication difficulties between staff and the residents have led to a small degree of social involvement, which in turn affects residents’ daily social state. Overall, many family members stated that the CPNH resembled Iran too much, which disturbed them.

    The residents thought of home as a geographical location, but also connected it with both positive and negative feelings. Furthermore, the CPNH reminded some of the residents of the nicer side of life back home in Iran, while for others it brought back sad experiences and memories from the past. Nevertheless, the nursing home, due to memories and experiences of life in Iran, “home”, was a place to be and to live.

    Delarbeten
    1. Frankly, None of Us Know What Dementia Is: Dementia Caregiving Among Iranian Immigrants Living in Sweden
    Öppna denna publikation i ny flik eller fönster >>Frankly, None of Us Know What Dementia Is: Dementia Caregiving Among Iranian Immigrants Living in Sweden
    2015 (Engelska)Ingår i: Care Management Journals, ISSN 1521-0987, Vol. 16, nr 2, s. 79-94Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In quite a short amount of time, Sweden has gone from being a relatively homogeneous society to a multicultural one, with a rapid expansion of immigrants having culturally and linguistically diverse (CALD) backgrounds growing old in Sweden. This is particularly interesting in relation to studying age-related dementia diseases. Research shows that not only do CALD persons with dementia diseases tend to mix languages, have difficulties with separation of languages, or revert to speaking only their native tongue as the disease progresses, but they also show tendencies to experience that they live in the cultural environment in which they were brought up, rather than in the current Swedish one. In this article, we explore findings in relation to one such CALD group in Sweden, Iranians. The article is empirically driven and based on data gathered in 2 separate settings with specific ethnocultural profiles, offering dementia care with Middle Eastern, Arab, and/or Persian profile. Observations were carried out in combination with semistructured in-depth interviews (n = 66). By using a combination of content and ethnographic analysis, 4 main findings related to ethnocultural dementia care were elucidated. These include (a) a wider recognition of people from different CALD backgrounds possibly having different perceptions of what dementia is, (b) a possibility that such ascribed meaning of dementia has a bearing on health maintenance and health-seeking behavior as well as the inclination to use formal services or not, (c) choosing to use formal service in the forms of ethnoculturally profiled dementia care facility seems to relate to being able to “live up to ideals of Iranian culture,” and (d) “culture,” however ambiguous and hotly debated a concept it is, appears to be a relevant aspect of people's lives, an aspect that is both acquired as well as ascribed to oneself and to others. As such, we argue that culture needs to be further addressed in relation to dementia care in multicultural societies because ascribing culture boxes people in as well as out. In addition, ethnocultural contextualization of dementia care needs to be understood in relation to this because it affects the care provided.

    Nyckelord
    dementia, caregiving, illness, ethnoculturally profiled care
    Nationell ämneskategori
    Gerontologi, medicinsk/hälsovetenskaplig inriktning
    Identifikatorer
    urn:nbn:se:liu:diva-119110 (URN)10.1891/1521-0987.16.2.79 (DOI)
    Projekt
    Ethnic diversity and dementia: cultural, social and linguistic aspects
    Forskningsfinansiär
    Riksbankens Jubileumsfond
    Tillgänglig från: 2015-06-09 Skapad: 2015-06-09 Senast uppdaterad: 2018-11-20
    2. Deciding upon Transition to Residential Care for Persons Living with Dementia: why Do Iranian Family Caregivers Living in Sweden Cease Caregiving at Home?
    Öppna denna publikation i ny flik eller fönster >>Deciding upon Transition to Residential Care for Persons Living with Dementia: why Do Iranian Family Caregivers Living in Sweden Cease Caregiving at Home?
    2018 (Engelska)Ingår i: Journal of Cross-Cultural Gerontology, ISSN 0169-3816, E-ISSN 1573-0719, Vol. 33, nr 1, s. 21-42Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Previous research has shown how filial piety is strong among people of Iranian background and that traditional Iranian culture result in most families’ preferring to care for their elderly (and sick) family members at home. While acknowledging this, this article highlights what living in diaspora could mean in terms of cultural adaption and changing family values. By interviewing people with Iranian background living in Sweden (n = 20), whom all have been former primary caregivers to a relative living with dementia, we are able to show how the decision to cease caregiving at home is taken, and what underlying factors form the basis for such decision. Results indicate that although the existence of a Persian profiled dementia care facility is crucial in the making of the decision, it is the feeling of ‘sheer exhaustion’ that is the main factor for ceasing care at home. And, we argue, the ability to make such a decision based upon ‘being too tired’ must be understood in relation to transition processes and changes in lifestyle having an affect upon cultural values in relation to filial piety. Because, at the same time the changes on cultural values might not change accordingly among the elderly who are the ones moving into residential care, resulting in them quite often being left out of the actual decision.

    Ort, förlag, år, upplaga, sidor
    Springer-Verlag New York, 2018
    Nyckelord
    Caregiver, Dementia diseases, Iranian immigrants, Care at home, Care at residential nursing home, Transition
    Nationell ämneskategori
    Folkhälsovetenskap, global hälsa, socialmedicin och epidemiologi Omvårdnad
    Identifikatorer
    urn:nbn:se:liu:diva-152760 (URN)10.1007/s10823-017-9337-1 (DOI)000427289500002 ()29170865 (PubMedID)2-s2.0-85034757762 (Scopus ID)
    Tillgänglig från: 2018-11-20 Skapad: 2018-11-20 Senast uppdaterad: 2018-11-30Bibliografiskt granskad
    3. Iranian relatives' attitudes towards culturally profiled nursing homes for individuals living with dementia
    Öppna denna publikation i ny flik eller fönster >>Iranian relatives' attitudes towards culturally profiled nursing homes for individuals living with dementia
    2017 (Engelska)Ingår i: Dementia, ISSN 1471-3012, E-ISSN 1741-2684, s. 1-17Artikel i tidskrift (Refereegranskat) Epub ahead of print
    Abstract [en]

    This article discusses Iranian family members attitudes towards the culturally profiled nursing home, their relationships with the staff, the obstacles, their hopes and their fears. This study is based on qualitative research using 29 semi-structured interviews with family members who had previously been informal caregivers, as well as using fieldwork, all in the same nursing home. The interviews were analysed by the three steps of content analysis. The results show the identification of three main categories with nine main subcategories. The categories and subcategories in the table clarify and explain how the interviewees tended to compare the situation in Iran with that in Sweden, how they perceived the situation in Sweden and finally how they also saw the culturally profiled nursing home.

    Ort, förlag, år, upplaga, sidor
    Sage Publications, 2017
    Nyckelord
    culturally profiled nursing home; nursing home
    Nationell ämneskategori
    Omvårdnad
    Identifikatorer
    urn:nbn:se:liu:diva-144853 (URN)10.1177/1471301217743835 (DOI)29192514 (PubMedID)
    Tillgänglig från: 2018-02-05 Skapad: 2018-02-05 Senast uppdaterad: 2018-11-20Bibliografiskt granskad
  • Disputation: 2018-12-13 10:15 Key 1, Key-huset, Linköping
    Vernqvist, Johanna
    Linköpings universitet, Institutionen för kultur och kommunikation, Avdelningen för språk och litteratur. Linköpings universitet, Filosofiska fakulteten.
    The Androgyne and the Phoenix: Marguerite de Navarre and Gaspara Stampa: Gendering Early Modern Debates on Love2018Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Den här studien undersöker Margareta av Navarras och Gaspara Stampas appropriering av nyplatonska kärleks- och genusideal. Mot en bakgrund av en tidigmodern litterär kanon och genom teoretiska perspektiv från Judith Butler och Michel Foucault, visar studien hur Margareta av Navarra och Gaspara Stampa genom olika litterära strategier destabiliserar ideal såväl som maktrelationer i tidens dominerande diskussioner om kärlek.

    Diskussionerna kretsar till stor del kring klassiska och tidigmoderna traktat om kärlek och är ofta presenterade i dialogform, som hos Platon, Marsilio Ficino, Leone Ebreo och Tullia d’Aragona. De filosofiska idéer om kärlek som gestaltas i dessa verk diskuteras också under den här perioden vid kulturella sammankomster, i exempelvis Venedigs salonger och vid de franska och italienska hoven, vilket ytterligare förstärker deras dialogiska karaktär.

    Genom närläsningar och kontextualiseringar visar studien mer precist hur dessa filosofiska idéer tolkas och omdefinieras i Margareta av Navarras novellsamling Heptaméron (1559) och Gaspara Stampas diktsamling Rime (1554), och då särskilt hur de använder de mytiska figurerna androgynen och fenixen. Även om vi har att göra med två relativt olika författare, den ena är drottning och den andra en virtuosa, det vill säga en skicklig musiker och sångerska som framför lyrisk poesi, så är huvudargumentet i den här studien att deras litterära verk korresponderar ifråga om de litterära strategier de använder i syfte att ge plats för en kvinnlig röst inom en mansdominerad kultur. Därmed förhandlar och destabiliserar Margareta av Navarra och Gaspara Stampa rådande normer inom de tidigmoderna diskurserna om genus och kärlek.

  • Disputation: 2018-12-14 09:00 Hasselquistsalen, Linköping
    Halvarsson, Camilla
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för mikrobiologi och molekylär medicin. Linköpings universitet, Medicinska fakulteten.
    Hypoxia inducible factor 1 alpha: dependent and independent regulation of hematopoietic stem cells and leukemia2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis has studied the role of low oxygen levels, or hypoxia, in hematopoietic stem cells (HSCs) and how, at the molecular level, it regulates stem cell maintenance and protects against oxidative stress induced by reactive oxygen species (ROS). HSCs reside within the bone marrow in specific niches created by a unique vascularized environment, which is suggested to be hypoxic and crucial for HSCs by maintaining a quiescent state of cell cycle and by redirecting metabolism away from the mitochondria to glycolysis. The niches are also believed to limit the production of ROS, which could damage DNA and disrupt the stem cell features. The hypoxia-responsive protein hypoxia-inducible factor 1 alpha (HIF-1α) is a major regulator of the hypoxic cell response in HSCs as well as in leukemic stem cells. Both these cells are thought to reside in the bone marrow where they are protected from stress and chemotherapy by niche cells and hypoxia.

    The thesis demonstrates that pyruvate dehydrogenase kinase 1 regulates a metabolic shift to glycolysis, and maintains the engraftment potential of both HSCs and multipotent progenitors upon transplantation. Furthermore, we wanted to determine whether HIF-1α or other signaling pathways are involved in protecting HSCs from ROS-induced cell death. Overexpression, silencing or a knockout mouse model of Hif-1α could not identify HIF-1α as important for protecting HSCs from oxidative stress-induced cell death through inhibition of synthesis of the antioxidant glutathione. Gene expression analysis instead identified the transcription factor nuclear factor kappa B (NF-κB) as induced by hypoxia. By studying NF- κB signaling we found increased NF-κB activity in cells cultured in hypoxia compared to normoxia. Suppression of inhibitor of kappa B indicated a putative role of NF-κB signaling in hypoxia-induced protection against oxidative stress. The findings show that hypoxia-induced protection to elevated levels of ROS upon glutathione depletion seems to be attributed to activation of the NF-κB signaling pathway independently of HIF-1α.

    To address the question whether hypoxic in vitro cultures support maintenance and promote HSC expansion we performed a limited dilution-transplantation assay. Our data indicate that hypoxic cultures maintain more long-term-reconstituting HSCs than normoxia, but this could not be confirmed statistically. Finally, we wanted to study the mechanisms by which hypoxia protect against chemotherapy. We could demonstrate that hypoxic culture protects leukemic cell lines against apoptosis induced by chemotherapy or inhibitors used for treatment of leukemia. This multidrug resistance seems to be mediated by ATP-binding cassette transporter genes, which are upregulated by hypoxia and whose inhibition has been shown to increase chemosensitivity. In addition, HIF-1α was upregulated in the leukemic cell lines in hypoxia and its inhibition increased the sensitivity to chemotherapy, indicating a role in inducing chemotherapy resistance.

    Conclusively, the results presented in this thesis stress the importance of hypoxia in regulating metabolism, oxidative-stress response and maintenance of both HSCs as well as leukemic cells, especially through the critical transcription factors HIF-1α and NF-κB and their target genes.  

    Delarbeten
    1. Pyruvate dehydrogenase kinase 1 is essential for transplantable mouse bone marrow hematopoietic stem cell and progenitor function
    Öppna denna publikation i ny flik eller fönster >>Pyruvate dehydrogenase kinase 1 is essential for transplantable mouse bone marrow hematopoietic stem cell and progenitor function
    2017 (Engelska)Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, nr 2, artikel-id e0171714Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Background Accumulating evidence suggests that hypoxic areas in the bone marrow are crucial for maintenance of hematopoietic stem cells (HSCs) by supporting a quiescent state of cell cycle and regulating the transplantation capacity of long-term (LT)-HSCs. In addition, HSCs seem to express a metabolic profile of energy production away from mitochondrial oxidative phosphorylation in favor of glycolysis. At oxygen deprivation, hypoxia inducible factor 1 alpha (HIF-1 alpha) is known to induce glycolytic enzymes as well as suppressing mitochondrial energy production by inducing pyruvate dehydrogenase kinase 1 (Pdk1) in most cell types. It has not been established whether PDK1 is essential for HSC function and mediates hypoxia-adapting functions in HSCs. While the Pdk gene family contains four members (Pdk1-4), it was recently shown that Pdk2 and Pdk4 have an important role in regulating LT-HSCs. Principle findings Here we demonstrate that PDK1 activity is crucial for transplantable HSC function. Whereas Pdkl, Pdk2, and Pdk3 transcripts were expressed at higher levels in different subtypes of HSCs compared to differentiated cells, we could not detect any major differences in expression between LT-HSCs and more short-term HSCs and multipotent progenitors. When studying HIF-1 alpha-mediated regulation of Pdk activity in vitro, Pdk1 was the most robust target regulated by hypoxia, whereas Pdk2, Pdk3, and Pdk4 were not affected. Contrary, genetic ablation in a cre-inducible Hif-1 alpha knockout mouse did not support a link between HIF-1 alpha and Pdk1. Silencing of Pdk1 by shRNA lentiviral gene transfer partially impaired progenitor colony formation in vitro and had a strong negative effect on both long-term and short-term engraftment in mice. Conclusions Our study demonstrates that PDK1 has broad effects in hematopoiesis and is a critical factor for engraftment of both HSCs and multipotent progenitors upon transplantation to recipient mice. While Pdk1 was a robust hypoxia-inducible gene mediated by HIF-1 alpha in vitro, we could not find evidence of any in vivo links between Pdk1 and HIF-1 alpha.

    Ort, förlag, år, upplaga, sidor
    PUBLIC LIBRARY SCIENCE, 2017
    Nationell ämneskategori
    Cell- och molekylärbiologi
    Identifikatorer
    urn:nbn:se:liu:diva-136062 (URN)10.1371/journal.pone.0171714 (DOI)000394231800095 ()28182733 (PubMedID)
    Anmärkning

    Funding Agencies|Swedish Research Council; Swedish Cancer Society; Swedish Childhood Cancer Foundation; County Council of Ostergotland; Faculty of Medicine at Linkoping University; Ollie and Elof Ericssons Foundation

    Tillgänglig från: 2017-03-27 Skapad: 2017-03-27 Senast uppdaterad: 2018-10-18
    2. Letter: Hypoxic and normoxic in vitro cultures maintain similar numbers of long-term reconstituting hematopoietic stem cells from mouse bone marrow
    Öppna denna publikation i ny flik eller fönster >>Letter: Hypoxic and normoxic in vitro cultures maintain similar numbers of long-term reconstituting hematopoietic stem cells from mouse bone marrow
    2012 (Engelska)Ingår i: Experimental Hematology, ISSN 0301-472X, E-ISSN 1873-2399, Vol. 40, nr 11, s. 879-881Artikel i tidskrift, Letter (Övrigt vetenskapligt) Published
    Abstract [en]

    n/a

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2012
    Nationell ämneskategori
    Medicin och hälsovetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-85627 (URN)10.1016/j.exphem.2012.07.005 (DOI)000310182400001 ()
    Tillgänglig från: 2012-11-26 Skapad: 2012-11-26 Senast uppdaterad: 2018-10-18
  • Disputation: 2018-12-14 09:15 Domteatern, Visualiseringscenter C, Kungsgatan 54, Norrköping
    Miandji, Ehsan
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Sparse representation of visual data for compression and compressed sensing2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The ongoing advances in computational photography have introduced a range of new imaging techniques for capturing multidimensional visual data such as light fields, BRDFs, BTFs, and more. A key challenge inherent to such imaging techniques is the large amount of high dimensional visual data that is produced, often requiring GBs, or even TBs, of storage. Moreover, the utilization of these datasets in real time applications poses many difficulties due to the large memory footprint. Furthermore, the acquisition of large-scale visual data is very challenging and expensive in most cases. This thesis makes several contributions with regards to acquisition, compression, and real time rendering of high dimensional visual data in computer graphics and imaging applications.

    Contributions of this thesis reside on the strong foundation of sparse representations. Numerous applications are presented that utilize sparse representations for compression and compressed sensing of visual data. Specifically, we present a single sensor light field camera design, a compressive rendering method, a real time precomputed photorealistic rendering technique, light field (video) compression and real time rendering, compressive BRDF capture, and more. Another key contribution of this thesis is a general framework for compression and compressed sensing of visual data, regardless of the dimensionality. As a result, any type of discrete visual data with arbitrary dimensionality can be captured, compressed, and rendered in real time.

    This thesis makes two theoretical contributions. In particular, uniqueness conditions for recovering a sparse signal under an ensemble of multidimensional dictionaries is presented. The theoretical results discussed here are useful for designing efficient capturing devices for multidimensional visual data. Moreover, we derive the probability of successful recovery of a noisy sparse signal using OMP, one of the most widely used algorithms for solving compressed sensing problems.

    Delarbeten
    1. OMP-based DOA estimation performance analysis
    Öppna denna publikation i ny flik eller fönster >>OMP-based DOA estimation performance analysis
    2018 (Engelska)Ingår i: Digital signal processing (Print), ISSN 1051-2004, E-ISSN 1095-4333, Vol. 79, s. 57-65Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this paper, we present a new performance guarantee for Orthogonal Matching Pursuit (OMP) in the context of the Direction Of Arrival (DOA) estimation problem. For the first time, the effect of parameters such as sensor array configuration, as well as signal to noise ratio and dynamic range of the sources is thoroughly analyzed. In particular, we formulate a lower bound for the probability of detection and an upper bound for the estimation error. The proposed performance guarantee is further developed to include the estimation error as a user-defined parameter for the probability of detection. Numerical results show acceptable correlation between theoretical and empirical simulations. (C) 2018 Elsevier Inc. All rights reserved.

    Ort, förlag, år, upplaga, sidor
    ACADEMIC PRESS INC ELSEVIER SCIENCE, 2018
    Nyckelord
    Direction of arrival; Orthogonal Matching Pursuit (OMP); Mutual coherence; Array configuration
    Nationell ämneskategori
    Signalbehandling
    Identifikatorer
    urn:nbn:se:liu:diva-149841 (URN)10.1016/j.dsp.2018.04.006 (DOI)000437386200006 ()
    Tillgänglig från: 2018-08-02 Skapad: 2018-08-02 Senast uppdaterad: 2018-11-23
    2. On Probability of Support Recovery for Orthogonal Matching Pursuit Using Mutual Coherence
    Öppna denna publikation i ny flik eller fönster >>On Probability of Support Recovery for Orthogonal Matching Pursuit Using Mutual Coherence
    2017 (Engelska)Ingår i: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 24, nr 11, s. 1646-1650Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In this paper we present a new coherence-based performance guarantee for the Orthogonal Matching Pursuit (OMP) algorithm. A lower bound for the probability of correctly identifying the support of a sparse signal with additive white Gaussian noise is derived. Compared to previous work, the new bound takes into account the signal parameters such as dynamic range, noise variance, and sparsity. Numerical simulations show significant improvements over previous work and a closer match to empirically obtained results of the OMP algorithm.

    Ort, förlag, år, upplaga, sidor
    IEEE Signal Processing Society, 2017
    Nyckelord
    Compressed Sensing (CS), Sparse Recovery, Orthogonal Matching Pursuit (OMP), Mutual Coherence
    Nationell ämneskategori
    Signalbehandling
    Identifikatorer
    urn:nbn:se:liu:diva-141613 (URN)10.1109/LSP.2017.2753939 (DOI)000412501600001 ()
    Tillgänglig från: 2017-10-03 Skapad: 2017-10-03 Senast uppdaterad: 2018-11-23Bibliografiskt granskad
    3. ON NONLOCAL IMAGE COMPLETION USING AN ENSEMBLE OF DICTIONARIES
    Öppna denna publikation i ny flik eller fönster >>ON NONLOCAL IMAGE COMPLETION USING AN ENSEMBLE OF DICTIONARIES
    2016 (Engelska)Ingår i: 2016 IEEE INTERNATIONAL CONFERENCE ON IMAGE PROCESSING (ICIP), IEEE , 2016, s. 2519-2523Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    In this paper we consider the problem of nonlocal image completion from random measurements and using an ensemble of dictionaries. Utilizing recent advances in the field of compressed sensing, we derive conditions under which one can uniquely recover an incomplete image with overwhelming probability. The theoretical results are complemented by numerical simulations using various ensembles of analytical and training-based dictionaries.

    Ort, förlag, år, upplaga, sidor
    IEEE, 2016
    Serie
    IEEE International Conference on Image Processing ICIP, ISSN 1522-4880
    Nyckelord
    compressed sensing; image completion; nonlocal; inverse problems; uniqueness conditions
    Nationell ämneskategori
    Datorseende och robotik (autonoma system)
    Identifikatorer
    urn:nbn:se:liu:diva-134107 (URN)10.1109/ICIP.2016.7532813 (DOI)000390782002114 ()978-1-4673-9961-6 (ISBN)
    Konferens
    23rd IEEE International Conference on Image Processing (ICIP)
    Tillgänglig från: 2017-01-22 Skapad: 2017-01-22 Senast uppdaterad: 2018-11-23
    4. Compressive Image Reconstruction in Reduced Union of Subspaces
    Öppna denna publikation i ny flik eller fönster >>Compressive Image Reconstruction in Reduced Union of Subspaces
    2015 (Engelska)Ingår i: Computer Graphics Forum, ISSN 1467-8659, Vol. 34, nr 2, s. 33-44Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We present a new compressed sensing framework for reconstruction of incomplete and possibly noisy images and their higher dimensional variants, e.g. animations and light-fields. The algorithm relies on a learning-based basis representation. We train an ensemble of intrinsically two-dimensional (2D) dictionaries that operate locally on a set of 2D patches extracted from the input data. We show that one can convert the problem of 2D sparse signal recovery to an equivalent 1D form, enabling us to utilize a large family of sparse solvers. The proposed framework represents the input signals in a reduced union of subspaces model, while allowing sparsity in each subspace. Such a model leads to a much more sparse representation than widely used methods such as K-SVD. To evaluate our method, we apply it to three different scenarios where the signal dimensionality varies from 2D (images) to 3D (animations) and 4D (light-fields). We show that our method outperforms state-of-the-art algorithms in computer graphics and image processing literature.

    Ort, förlag, år, upplaga, sidor
    John Wiley & Sons Ltd, 2015
    Nyckelord
    Image reconstruction, compressed sensing, light field imaging
    Nationell ämneskategori
    Signalbehandling
    Identifikatorer
    urn:nbn:se:liu:diva-119639 (URN)10.1111/cgf.12539 (DOI)000358326600008 ()
    Konferens
    Eurographics 2015
    Projekt
    VPS
    Forskningsfinansiär
    Stiftelsen för strategisk forskning (SSF), IIS11-0081
    Tillgänglig från: 2015-06-23 Skapad: 2015-06-23 Senast uppdaterad: 2018-11-23Bibliografiskt granskad
    5. Learning Based Compression of Surface Light Fields for Real-time Rendering of Global Illumination Scenes
    Öppna denna publikation i ny flik eller fönster >>Learning Based Compression of Surface Light Fields for Real-time Rendering of Global Illumination Scenes
    2013 (Engelska)Ingår i: Proceedings of ACM SIGGRAPH ASIA 2013, ACM Press, 2013Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    We present an algorithm for compression and real-time rendering of surface light fields (SLF) encoding the visual appearance of objects in static scenes with high frequency variations. We apply a non-local clustering in order to exploit spatial coherence in the SLFdata. To efficiently encode the data in each cluster, we introducea learning based approach, Clustered Exemplar Orthogonal Bases(CEOB), which trains a compact dictionary of orthogonal basispairs, enabling efficient sparse projection of the SLF data. In ad-dition, we discuss the application of the traditional Clustered Principal Component Analysis (CPCA) on SLF data, and show that inmost cases, CEOB outperforms CPCA, K-SVD and spherical harmonics in terms of memory footprint, rendering performance andreconstruction quality. Our method enables efficient reconstructionand real-time rendering of scenes with complex materials and lightsources, not possible to render in real-time using previous methods.

    Ort, förlag, år, upplaga, sidor
    ACM Press, 2013
    Nyckelord
    computer graphics, global illumination, real-time, machine learning
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-99433 (URN)10.1145/2542355.2542385 (DOI)978-1-4503-2629-2 (ISBN)
    Konferens
    SIGGRAPH Asia, 19-22 November 2013, Hong Kong
    Projekt
    VPS
    Forskningsfinansiär
    Stiftelsen för strategisk forskning (SSF), IIS11-0081Vetenskapsrådet
    Tillgänglig från: 2013-10-17 Skapad: 2013-10-17 Senast uppdaterad: 2018-11-23Bibliografiskt granskad
  • Disputation: 2018-12-14 10:00 I101, I-huset, Linköping
    Hagman, William
    Linköpings universitet, Institutionen för beteendevetenskap och lärande, Psykologi. Linköpings universitet, Filosofiska fakulteten.
    When are nudges acceptable?: Influences of beneficiaries, techniques, alternatives and choice architects2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Interventions aimed to change behavior (so called nudges) are becoming more and more popular among policymakers. However, in order to be able to effectively use nudges, it is important to understand when and why people find them acceptable. The objective of this thesis is therefore to improve the understanding of when nudges are judged to be acceptable. The thesis focuses on a model for behavioral change. The model contains two parts, nudge technique and acceptance of nudges. Nudge technique refers to how the nudge is designed to function in regard to psychological mechanism and functionality.

    The nudge technique part of the model is expanded and problematized from an ethical perspective in the first part of this thesis, by exemplifying psychological mechanisms behind different techniques and explaining why they might be intrusive to individuals’ freedom of choice. In the second part of this thesis it is discussed why acceptance is an important component of making nudging legitimate and effective. This is followed by a discussion of how acceptance is empirically measured. The empirical part of the thesis is based on four papers which all use a quantitative online survey approach to study the judgements of nudges from the general public.

    Paper 1 was a first attempt to measure whether nudges which are common in the nudge literature are acceptable interventions according to the general public. We found that the nudges that were categorized as pro-self were more likely to be rated as acceptable and less likely to be perceived as intrusive to freedom of choice compared to pro-social nudges. Furthermore, the effect of decision styles and worldview on acceptance was explored. In paper 2, we explored whether the difference between acceptance found for pro-social nudges and proself nudges could be increased by framing nudges as beneficial for society or individuals. The framing had no effect on acceptance but, as in paper 1, pro-social nudges were found to be more intrusive to freedom of choice compared to pro-self framed nudges. Moreover, different nudge techniques had different rates of acceptance even with the same explicit goal for the nudges. In paper 3, we examined whether the alternative to nudges affects the perceived acceptability and intrusiveness of default-changing nudge techniques. The alternatives given to the nudges were either to enforce the intended behavioral change with legislation or to do nothing at all in order to change the behavior. We find no difference in aggregated acceptance, however, the judgements vary depending on individuals’ worldview. Paper 4 explored if the choice architect’s (the creator/proposer of the nudge) political affiliation affects acceptance rating for proposed nudge interventions and legislation. We find that acceptance of both nudges and legislation increases with the level of matching between people’s political orientation and the choice architect’s political affiliation.

    Taken together, the findings suggest that there is more to creating an acceptable nudge than to merely take a nudge technique that was acceptable in one context and apply it in another. Moreover, nudges that are rated as more beneficial towards individuals compared to society at large are in general more likely to be found acceptable and less intrusive to freedom of choice. It is important to have knowledge about the target population (e.g. their decision styles, world-views, and political orientation) to avoid backfires when implementing nudges.  

    Delarbeten
    1. Public Views on Policies Involving Nudges
    Öppna denna publikation i ny flik eller fönster >>Public Views on Policies Involving Nudges
    2015 (Engelska)Ingår i: Review of Philosophy and Psychology, ISSN 1878-5158, E-ISSN 1878-5166, Vol. 6, nr 3, s. 439-453Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    When should nudging be deemed as permissible and when should it be deemed as intrusive to individuals’ freedom of choice? Should all types of nudges be judged the same? To date the debate concerning these issues has largely proceeded without much input from the general public. The main objective of this study is to elicit public views on the use of nudges in policy. In particular we investigate attitudes toward two broad categories of nudges that we label pro-self (i.e. focusing on private welfare) and pro-social (i.e. focusing on social welfare) nudges. In addition we explore how individual differences in thinking and feeling influence attitudes toward nudges. General population samples in Sweden and the United States (n=952) were presented with vignettes describing nudge-policies and rated acceptability and intrusiveness on freedom of choice. To test for individual differences, measures on cultural cognition and analytical thinking were included. Results show that the level of acceptance toward nudge-policies was generally high in both countries, but were slightly higher among Swedes than Americans. Somewhat paradoxically a majority of the respondents also perceived the presented nudge-policies as intrusive to freedom of choice. Nudge- polices classified as pro-social had a significantly lower acceptance rate compared to pro-self nudges (p<.0001). Individuals with a more individualistic worldview were less likely to perceive nudges as acceptable, while individuals more prone to analytical thinking were less likely to perceive nudges as intrusive to freedom of choice. To conclude, our findings suggest that the notion of “one-nudge- fits-all” is not tenable. Recognizing this is an important aspect both for successfully implementing nudges as well as nuancing nudge theory. 

    Nyckelord
    Nudge; Libertarian Paternalism; Acceptability; Autonomi
    Nationell ämneskategori
    Nationalekonomi
    Identifikatorer
    urn:nbn:se:liu:diva-119071 (URN)10.1007/s13164-015-0263-2 (DOI)
    Projekt
    Neuroekonomi
    Tillgänglig från: 2015-06-08 Skapad: 2015-06-08 Senast uppdaterad: 2018-11-22
  • Disputation: 2018-12-14 10:15 Ada Lovelace, Building B, Linköping
    Andersson Naesseth, Christian
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Machine learning using approximate inference: Variational and sequential Monte Carlo methods2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Automatic decision making and pattern recognition under uncertainty are difficult tasks that are ubiquitous in our everyday life. The systems we design, and technology we develop, requires us to coherently represent and work with uncertainty in data. Probabilistic models and probabilistic inference gives us a powerful framework for solving this problem. Using this framework, while enticing, results in difficult-to-compute integrals and probabilities when conditioning on the observed data. This means we have a need for approximate inference, methods that solves the problem approximately using a systematic approach. In this thesis we develop new methods for efficient approximate inference in probabilistic models.

    There are generally two approaches to approximate inference, variational methods and Monte Carlo methods. In Monte Carlo methods we use a large number of random samples to approximate the integral of interest. With variational methods, on the other hand, we turn the integration problem into that of an optimization problem. We develop algorithms of both types and bridge the gap between them.

    First, we present a self-contained tutorial to the popular sequential Monte Carlo (SMC) class of methods. Next, we propose new algorithms and applications based on SMC for approximate inference in probabilistic graphical models. We derive nested sequential Monte Carlo, a new algorithm particularly well suited for inference in a large class of high-dimensional probabilistic models. Then, inspired by similar ideas we derive interacting particle Markov chain Monte Carlo to make use of parallelization to speed up approximate inference for universal probabilistic programming languages. After that, we show how we can make use of the rejection sampling process when generating gamma distributed random variables to speed up variational inference. Finally, we bridge the gap between SMC and variational methods by developing variational sequential Monte Carlo, a new flexible family of variational approximations.

    Delarbeten
    1. Capacity estimation of two-dimensional channels using Sequential Monte Carlo
    Öppna denna publikation i ny flik eller fönster >>Capacity estimation of two-dimensional channels using Sequential Monte Carlo
    2014 (Engelska)Ingår i: 2014 IEEE Information Theory Workshop, 2014, s. 431-435Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    We derive a new Sequential-Monte-Carlo-based algorithm to estimate the capacity of two-dimensional channel models. The focus is on computing the noiseless capacity of the 2-D (1, ∞) run-length limited constrained channel, but the underlying idea is generally applicable. The proposed algorithm is profiled against a state-of-the-art method, yielding more than an order of magnitude improvement in estimation accuracy for a given computation time.

    Nationell ämneskategori
    Reglerteknik Datavetenskap (datalogi) Sannolikhetsteori och statistik
    Identifikatorer
    urn:nbn:se:liu:diva-112966 (URN)10.1109/ITW.2014.6970868 (DOI)
    Konferens
    Information Theory Workshop
    Tillgänglig från: 2015-01-06 Skapad: 2015-01-06 Senast uppdaterad: 2018-11-09
    2. Sequential Monte Carlo for Graphical Models
    Öppna denna publikation i ny flik eller fönster >>Sequential Monte Carlo for Graphical Models
    2014 (Engelska)Ingår i: Advances in Neural Information Processing Systems, 2014, s. 1862-1870Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    We propose a new framework for how to use sequential Monte Carlo (SMC) algorithms for inference in probabilistic graphical models (PGM). Via a sequential decomposition of the PGM we find a sequence of auxiliary distributions defined on a monotonically increasing sequence of probability spaces. By targeting these auxiliary distributions using SMC we are able to approximate the full joint distribution defined by the PGM. One of the key merits of the SMC sampler is that it provides an unbiased estimate of the partition function of the model. We also show how it can be used within a particle Markov chain Monte Carlo framework in order to construct high-dimensional block-sampling algorithms for general PGMs.

    Nationell ämneskategori
    Datavetenskap (datalogi) Sannolikhetsteori och statistik Reglerteknik
    Identifikatorer
    urn:nbn:se:liu:diva-112967 (URN)
    Konferens
    Neural Information Processing Systems (NIPS)
    Tillgänglig från: 2015-01-06 Skapad: 2015-01-06 Senast uppdaterad: 2018-11-09Bibliografiskt granskad
    3. Nested Sequential Monte Carlo Methods
    Öppna denna publikation i ny flik eller fönster >>Nested Sequential Monte Carlo Methods
    2015 (Engelska)Ingår i: Proceedings of The 32nd International Conference on Machine Learning / [ed] Francis Bach, David Blei, Journal of Machine Learning Research (Online) , 2015, Vol. 37, s. 1292-1301Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    We propose nested sequential Monte Carlo (NSMC), a methodology to sample from sequences of probability distributions, even where the random variables are high-dimensional. NSMC generalises the SMC framework by requiring only approximate, properly weighted, samples from the SMC proposal distribution, while still resulting in a correct SMC algorithm. Furthermore, NSMC can in itself be used to produce such properly weighted samples. Consequently, one NSMC sampler can be used to construct an efficient high-dimensional proposal distribution for another NSMC sampler, and this nesting of the algorithm can be done to an arbitrary degree. This allows us to consider complex and high-dimensional models using SMC. We show results that motivate the efficacy of our approach on several filtering problems with dimensions in the order of 100 to 1 000.

    Ort, förlag, år, upplaga, sidor
    Journal of Machine Learning Research (Online), 2015
    Serie
    JMLR Workshop and Conference Proceedings, ISSN 1938-7228 ; 37
    Nationell ämneskategori
    Datavetenskap (datalogi) Reglerteknik Sannolikhetsteori och statistik
    Identifikatorer
    urn:nbn:se:liu:diva-122698 (URN)
    Konferens
    32nd International Conference on Machine Learning, Lille, France, 6-11 July, 2015
    Tillgänglig från: 2015-11-16 Skapad: 2015-11-16 Senast uppdaterad: 2018-11-09Bibliografiskt granskad
    4. Interacting Particle Markov Chain Monte Carlo
    Öppna denna publikation i ny flik eller fönster >>Interacting Particle Markov Chain Monte Carlo
    Visa övriga...
    2016 (Engelska)Ingår i: Proceedings of the 33rd International Conference on Machine Learning (ICML), 2016Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    We introduce interacting particle Markov chain Monte Carlo (iPMCMC), a PMCMC method based on an interacting pool of standard and conditional sequential Monte Carlo samplers. Like related methods, iPMCMC is a Markov chain Monte Carlo sampler on an extended space. We present empirical results that show significant improvements in mixing rates relative to both non-interacting PMCMC samplers and a single PMCMC sampler with an equivalent memory and computational budget. An additional advantage of the iPMCMC method is that it is suitable for distributed and multi-core architectures.

    Nyckelord
    Sequential Monte Carlo, Probabilistic programming, parallelisation
    Nationell ämneskategori
    Datavetenskap (datalogi) Reglerteknik Sannolikhetsteori och statistik
    Identifikatorer
    urn:nbn:se:liu:diva-130043 (URN)
    Konferens
    International Conference on Machine Learning (ICML), New York, USA, June 19-24, 2016
    Projekt
    CADICS
    Forskningsfinansiär
    Cancer- och Allergifonden
    Tillgänglig från: 2016-07-05 Skapad: 2016-07-05 Senast uppdaterad: 2018-11-09
    5. Reparameterization Gradients through Acceptance-Rejection Sampling Algorithms
    Öppna denna publikation i ny flik eller fönster >>Reparameterization Gradients through Acceptance-Rejection Sampling Algorithms
    2017 (Engelska)Ingår i: Proceedings of the 20th International Conference on Artificial Intelligence and Statistics, 2017Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Variational inference using the reparameterization trick has enabled large-scale approximate Bayesian inference in complex probabilistic models, leveraging stochastic optimization to sidestep intractable expectations. The reparameterization trick is applicable when we can simulate a random variable by applying a differentiable deterministic function on an auxiliary random variable whose distribution is fixed. For many distributions of interest (such as the gamma or Dirichlet), simulation of random variables relies on acceptance-rejection sampling. The discontinuity introduced by the accept-reject step means that standard reparameterization tricks are not applicable. We propose a new method that lets us leverage reparameterization gradients even when variables are outputs of a acceptance-rejection sampling algorithm. Our approach enables reparameterization on a larger class of variational distributions. In several studies of real and synthetic data, we show that the variance of the estimator of the gradient is significantly lower than other state-of-the-art methods. This leads to faster convergence of stochastic gradient variational inference.

    Serie
    Proceedings of Machine Learning Research, ISSN 1938-7228 ; 54
    Nationell ämneskategori
    Datavetenskap (datalogi)
    Identifikatorer
    urn:nbn:se:liu:diva-152645 (URN)
    Konferens
    Artificial Intelligence and Statistics, 20-22 April 2017, Fort Lauderdale, FL, USA
    Tillgänglig från: 2018-11-09 Skapad: 2018-11-09 Senast uppdaterad: 2018-11-21
    6. Variational Sequential Monte Carlo
    Öppna denna publikation i ny flik eller fönster >>Variational Sequential Monte Carlo
    2018 (Engelska)Ingår i: Proceedings of the Twenty-First International Conference on Artificial Intelligence and Statistics, 2018Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Many recent advances in large scale probabilistic inference rely on variational methods. The success of variational approaches depends on (i) formulating a flexible parametric family of distributions, and (ii) optimizing the parameters to find the member of this family that most closely approximates the exact posterior. In this paper we present a new approximating family of distributions, the variational sequential Monte Carlo (VSMC) family, and show how to optimize it in variational inference. VSMC melds variational inference (VI) and sequential Monte Carlo (SMC), providing practitioners with flexible, accurate, and powerful Bayesian inference. The VSMC family is a variational family that can approximate the posterior arbitrarily well, while still allowing for efficient optimization of its parameters. We demonstrate its utility on state space models, stochastic volatility models for financial data, and deep Markov models of brain neural circuits.

    Nationell ämneskategori
    Datavetenskap (datalogi)
    Identifikatorer
    urn:nbn:se:liu:diva-152646 (URN)
    Konferens
    International Conference on Artificial Intelligence and Statistics, Playa Blanca, Lanzarote, Canary Islands, April 9 - 11, 2018
    Tillgänglig från: 2018-11-09 Skapad: 2018-11-09 Senast uppdaterad: 2018-11-16Bibliografiskt granskad
  • Disputation: 2018-12-14 13:00 Berzeliussalen, Linköping
    Vavruch, Ludvig
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för Kirurgi, Ortopedi och Onkologi. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Ortopedkliniken i Linköping.
    Adolescent Idiopathic Scoliosis: A Deformity in Three Dimensions2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Scoliosis is a complex three-dimensional deformity of the spine. Even though it has been known for centuries, treatment of the deformity has focused on correcting only in the frontal plane. In the last decades, the need for three-dimensional assessment regarding scoliosis has been highlighted to better understand the cause and the principles of treating scoliosis. The overall aim of this dissertation is to provide knowledge to assess scoliosis as a three-dimensional problem.

    The severity of scoliosis is measured with the Cobb angle from standing radiographs. Computed tomography (CT) examinations are used throughout this thesis. The first paper investigates the difference in Cobb angle measured from standing radiographs and supine CT examinations. The standing radiographs had larger Cobb angles with a mean difference of 11° and a linear correlation between the two examinations from 128 consecutive patients with adolescent idiopathic scoliosis (AIS) planned for surgery.

    The second paper compares the axial shape of vertebrae in 20 patients with AIS with a reference group. Clear asymmetry was observed in all vertebrae – superior and inferior end vertebrae as well as the apical vertebra – compared with corresponding vertebrae among the reference group. The asymmetry was most pronounced in the apical vertebra. A novel parameter, frontal vertebral body rotation (FVBR), was introduced to describe the internal rotation of the vertebrae in the axial plane.

    Pelvic incidence (PI) is a measurement of the position of the sacrum in relation to the femoral heads. This is relevant in scoliosis because PI determines the pelvic configuration acting as a foundation to the spine. PI has traditionally been measured from standing radiographs. The third study investigates PI three-dimensionally, based on low-dose CT examinations, in 37 patients with Lenke type 1 or 5 curves compared with a reference group. A significantly higher PI was observed in patients with Lenke type 5 curves compared with the reference group and patients with Lenke type 1 curves.

    Severe AIS is treated with corrective surgery. Two approaches are available: the predominant posterior approach and the anterior approach. In the fourth paper, these two approaches are evaluated with regard to three-dimensional correction, how well the correction is maintained over a 2-year follow-up and patient-reported outcome measures. Twenty-seven patients treated with the posterior approach and 26 patients treated with the anterior approach, all with Lenke type 1 curves, were included. Fewer vertebrae were fused in the anterior group, but the posterior group had a better correction of the deformity in the frontal plane. No difference was observed regarding three-dimensional correction and patient-reported outcome measures.

    AIS is truly a complex three-dimensional deformity. More research is needed to fully comprehend the complexity of the scoliotic spine.

    Delarbeten
    1. A Comparison of Cobb Angle: Standing Versus Supine Images of Late-Onset Idiopathic Scoliosis
    Öppna denna publikation i ny flik eller fönster >>A Comparison of Cobb Angle: Standing Versus Supine Images of Late-Onset Idiopathic Scoliosis
    2016 (Engelska)Ingår i: Polish Journal Of Radiology, ISSN 1733-134X, Vol. 81, s. 270-276Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Background: Scoliosis is traditionally evaluated by measuring the Cobb angle in radiograph images taken while the patient is standing. However, low-dose computed tomography (CT) images, which are taken while the patient is in a supine position, provide new opportunities to evaluate scoliosis. Few studies have investigated how the patient's position, standing or supine, affects measurements. The purpose of this study was to compare the Cobb angle in images from patients while standing versus supine.less thanbr /greater thanMaterial/methods: A total of 128 consecutive patients (97 females and 21 males; mean age 15.5 [11-26] years) with late-onset scoliosis requiring corrective surgery were enrolled. One observer evaluated the type of curve (Lenke classification) and measured the Cobb angle in whole-spine radiography (standing) and scout images from low-dose CT (supine) were taken on the same day.less thanbr /greater thanResults: For all primary curves, the mean Cobb angle was 59 (SD 12) while standing and 48 (SD 12) while in the supine position, with a mean difference of 11 (SD 5). The correlation between primary standing and supine images had an r value of 0.899 (95% CI 0.860-0.928) and an intra-class correlation coefficient value of 0.969. The correlation between the difference in standing and supine images from primary and secondary curves had an r value of 0.340 (95% CI 0.177-0.484).less thanbr /greater thanConclusions: We found a strong correlation between the Cobb angle in images obtained while the patient was standing versus supine for primary and secondary curves. This study is only applicable for patients with severe curves requiring surgical treatment. It enables additional studies based on low-dose CT.

    Ort, förlag, år, upplaga, sidor
    Medical Science International, 2016
    Nyckelord
    Scoliosis; Spine; Supine Position
    Nationell ämneskategori
    Radiologi och bildbehandling
    Identifikatorer
    urn:nbn:se:liu:diva-145863 (URN)10.12659/PJR.895949 (DOI)27354881 (PubMedID)
    Tillgänglig från: 2018-03-20 Skapad: 2018-03-20 Senast uppdaterad: 2018-11-23Bibliografiskt granskad
    2. Vertebral Axial Asymmetry in Adolescent Idiopathic Scoliosis.
    Öppna denna publikation i ny flik eller fönster >>Vertebral Axial Asymmetry in Adolescent Idiopathic Scoliosis.
    2018 (Engelska)Ingår i: Spine Deformity, ISSN 2212-1358, Vol. 6, nr 2, s. 112-120.e1Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Study Design

    Retrospective study.

    Objectives

    To investigate parameters of axial vertebral deformation in patients with scoliosis compared to a control group, and to determine whether these parameters correlated with the severity of spine curvature, measured as the Cobb angle.

    Summary of Background Data

    Adolescent idiopathic scoliosis (AIS) is the most common type of spinal deformity. Many studies have investigated vertebral deformation, in terms of wedging and pedicle deformations, but few studies have investigated actual structural changes within vertebrae.

    Methods

    This study included 20 patients with AIS (Lenke 1–3, mean age: 15.6 years, range: 11–20). We compared preoperative low-dose computed tomography(CT) examinations of patients with AIS to those of a control group matched for age and sex. The control individuals had no spinal deformity, but they were admitted to the emergency department for trauma CTs. We measured the Cobb angles and the axial vertebral rotation (AVR), axial vertebral bodyasymmetry (AVBA), and frontal vertebral body rotation (FVBR) for the superior end, inferior end, and apical vertebrae, with in-house–developed software. Correlations between entities were investigated with the Pearson correlation test.

    Results

    The average Cobb angles were 49.3° and 1.3° for the scoliotic and control groups, respectively. The patient and control groups showed significant differences in the AVRs of all three vertebra levels (p < .01), the AVBAs of the superior end and apical vertebrae (p < .008), and the FVBR of the apical vertebra (p = .011). Correlations were only found between the AVBA and FVBR in the superior end vertebra (r = 0.728, p < .001) and in the apical vertebra (r = 0.713, p < .001).

    Conclusions

    Compared with controls, patients with scoliosis showed clear morphologic differences in the midaxial plane vertebrae. Differences in AVR, AVBA, and FVBR were most pronounced at the apical vertebra. The FVBR provided valuable additional information about the internal rotation and deformation of vertebrae.

    Level of Evidence

    Level III.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2018
    Nyckelord
    Scoliosis; Morphology; Three-dimensional; Vertebral rotation; Low-dose CT
    Nationell ämneskategori
    Ortopedi
    Identifikatorer
    urn:nbn:se:liu:diva-145864 (URN)10.1016/j.jspd.2017.09.001 (DOI)29413732 (PubMedID)2-s2.0-85032338953 (Scopus ID)
    Tillgänglig från: 2018-03-20 Skapad: 2018-03-20 Senast uppdaterad: 2018-11-23Bibliografiskt granskad
    3. Three-dimensional pelvic incidence is much higher in (thoraco)lumbar scoliosis than in controls
    Öppna denna publikation i ny flik eller fönster >>Three-dimensional pelvic incidence is much higher in (thoraco)lumbar scoliosis than in controls
    Visa övriga...
    2018 (Engelska)Ingår i: European spine journal, ISSN 0940-6719, E-ISSN 1432-0932Artikel i tidskrift (Refereegranskat) Epub ahead of print
    Abstract [en]

    Purpose

    The pelvic incidence (PI) is used to describe the sagittal spino-pelvic alignment. In previous studies, radiographs were used, leading to less accuracy in establishing the three-dimensional (3D) spino-pelvic parameters. The purpose of this study is to analyze the differences in the 3D sagittal spino-pelvic alignment in adolescent idiopathic scoliosis (AIS) subjects and non-scoliotic controls.

    Methods

    Thirty-seven female AIS patients that underwent preoperative supine low-dose computed tomography imaging of the spine, hips and pelvis as part of their general workup were included and compared to 44 non-scoliotic age-matched female controls. A previously validated computerized method was used to measure the PI in 3D, as the angle between the line orthogonal to the inclination of the sacral endplate and the line connecting the center of the sacral endplate with the hip axis.

    Results

    The PI was on average 46.8° ± 12.4° in AIS patients and 41.3° ± 11.4° in controls (p = 0.025), with a higher PI in Lenke type 5 curves (50.6° ± 16.2°) as compared to controls (p = 0.042), whereas the Lenke type 1 curves (45.9° ± 12.2°) did not differ from controls (p = 0.141).

    Conclusion

    Lenke type 5 curves show a significantly higher PI than controls, whereas the Lenke type 1 curves did not differ from controls. This suggests a role of pelvic morphology and spino-pelvic alignment in the pathogenesis of idiopathic scoliosis. Further longitudinal studies should explore the exact role of the PI in the initiation and progression of different AIS types.

    Ort, förlag, år, upplaga, sidor
    Heidelberg: Springer, 2018
    Nyckelord
    Idiopathic scoliosis, Sagittal alignment, Pelvic incidence, Three-dimensional analysis, Computed tomography
    Nationell ämneskategori
    Ortopedi
    Identifikatorer
    urn:nbn:se:liu:diva-152573 (URN)10.1007/s00586-018-5718-6 (DOI)30128762 (PubMedID)2-s2.0-85051834138 (Scopus ID)
    Tillgänglig från: 2018-11-07 Skapad: 2018-11-07 Senast uppdaterad: 2018-11-23Bibliografiskt granskad
  • Disputation: 2018-12-14 13:00 Belladonna, Linköping
    Ali, Zaheer
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för kardiovaskulär medicin. Linköpings universitet, Medicinska fakulteten.
    Investigating mechanisms of angiogenesis in health and disease using zebrafish models2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Angiogenesis, the growth of blood vessels from an existing vasculature, can occur by sprouting from preexisting vessels or by vessel splitting (intussusception). Pathological angiogenesis drives choroidal neovascularization (CNV) in age related macular degeneration (AMD) which is commonly restricted under the retinal pigment epithelium (RPE), called occult CNV, but may also involve vessels penetrating through the RPE into the sub-retinal space. Pathological vessels are poorly developed, insufficiently perfused and highly leaky, phenotypes that are considered to drive disease progression and lead to poor prognosis. Currently, a number of anti-angiogenic drugs exists, the majority of which target vascular endothelial factor (VEGF), but although they often are highly beneficial for treating eye diseases in the short-term, they are generally of limited efficacy in other diseases such as cancer, and also have poorer efficacy when used for treatment of eye diseases in the long-term. A better understanding of the mechanisms underlying pathological angiogenesis can generate new targets for treatment leading to development of better drugs for cancer and retinopathies, but perhaps also other angiogenesis-dependent diseases, in the future. In this thesis mechanisms involved in developmental angiogenesis or pathological angiogenesis in the choroid, cornea or melanoma was identified. These findings highlight the need to further elaborate our knowledge related to angiogenesis in different tissues/conditions for a more targeted, and potentially effective treatment of diseases in the future.

    In paper I, we for the first time identified the choriocapillaries (CCs) in adult zebrafish and found that occult CNV could be induced by exposing the fish to severe hypoxia. Interestingly, we found that occult CNV relied on intussusception, involving not only de novo generation of intussusceptive pillars but also a previously poorly understood mechanism called pillar splitting. This involved HIF-VEGF-VEGFR2 signaling and evidence that this also occurred in both rats and humans suffering from AMD suggested that the mechanism was conserved and clinically relevant.

    In contrast, we found in paper II that the development of CCs in the zebrafish relies on sprouting angiogenesis, involve continuous remodeling, and delayed maturation of the vasculature in 2D. The initial development was found to occur by a unique process of tissuewide synchronized vasculogenesis. As expected, VEGFA via VEGFR2 was also critical for the development of these vessels in the zebrafish embryo, but surprisingly this was independent on hypoxia-inducible factor (HIF)-1.

    Inflammatory nuclear factor-kB (NF-kB) signaling is involved in the progression of angiogenesis, but this signaling pathway has mainly been studied in the inflammatory cells and the role of NF-kB in the endothelial cells during angiogenesis is poorly understood. In paper III, we found that blocking NF-kB signaling using a specific IKK2 blocker IMD0354, specifically blocks pathological as well as developmental angiogenesis by targeting endothelial cell NF-kB signaling in the endothelial cells. Using a rat model for suture-induced corneal neovascularization, IMD0354 treatment lead to reduced production of inflammatory C-C motif chemokine ligand 2 (CCL2), C-X-C motif chemokine ligand 5 (CXCL5) and VEGF, and thereby reduced pathological corneal angiogenesis in this model.

    Using the zebrafish tumor xenograft model in paper IV, we found an association between Microphthalmia associated transcription factor (MITF) and pigment epithelium derived factor (PEDF), which was involved in pathological tumor angiogenesis and metastasis. Similarly, in paper V we used zebrafish transplantation models to study and investigate the use of biocompatible polymers for the delivery of pro-angiogenic FGF-2 as a potential treatment strategy for ischemic diseases such as myocardial infarction (MI). Conclusively, this thesis provides new insights into diverse fields of angiogenic assays using zebrafish, and reveals new mechanisms of angiogenesis in health and disease. This work will hopefully provide a foundation for further studies into occult CNV related to AMD, a process that has not been possible to study previously in pre-clinical models. In addition, zebrafish xenograft or other transplantation models used in this work will likely be important to study cancer biology and to develop more attractive pharmaceutical preparations based on biocompatible hydrogels formulated as microspheres in the future.

    Delarbeten
    1. Selective IKK2 inhibitor IMD0354 disrupts NF-kappa B signaling to suppress corneal inflammation and angiogenesis
    Öppna denna publikation i ny flik eller fönster >>Selective IKK2 inhibitor IMD0354 disrupts NF-kappa B signaling to suppress corneal inflammation and angiogenesis
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    2018 (Engelska)Ingår i: Angiogenesis, ISSN 0969-6970, E-ISSN 1573-7209, Vol. 21, nr 2, s. 267-285Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Corneal neovascularization is a sight-threatening condition caused by angiogenesis in the normally avascular cornea. Neovascularization of the cornea is often associated with an inflammatory response, thus targeting VEGF-A alone yields only a limited efficacy. The NF-kappa B signaling pathway plays important roles in inflammation and angiogenesis. Here, we study consequences of the inhibition of NF-kappa B activation through selective blockade of the IKK complex I kappa B kinase beta (IKK2) using the compound IMD0354, focusing on the effects of inflammation and pathological angiogenesis in the cornea. In vitro, IMD0354 treatment diminished HUVEC migration and tube formation without an increase in cell death and arrested rat aortic ring sprouting. In HUVEC, the IMD0354 treatment caused a dose-dependent reduction in VEGF-A expression, suppressed TNF alpha-stimulated expression of chemokines CCL2 and CXCL5, and diminished actin filament fibers and cell filopodia formation. In developing zebrafish embryos, IMD0354 treatment reduced expression of Vegf-a and disrupted retinal angiogenesis. In inflammation-induced angiogenesis in the rat cornea, systemic selective IKK2 inhibition decreased inflammatory cell invasion, suppressed CCL2, CXCL5, Cxcr2, and TNF-alpha expression and exhibited anti-angiogenic effects such as reduced limbal vessel dilation, reduced VEGF-A expression and reduced angiogenic sprouting, without noticeable toxic effect. In summary, targeting NF-kappa B by selective IKK2 inhibition dampened the inflammatory and angiogenic responses in vivo by modulating the endothelial cell expression profile and motility, thus indicating an important role of NF-kappa B signaling in the development of pathologic corneal neovascularization.

    Ort, förlag, år, upplaga, sidor
    Springer Netherlands, 2018
    Nyckelord
    Cornea; Neovascularization; NF-kappa B; IMD0354; IKK2; VEGF
    Nationell ämneskategori
    Cell- och molekylärbiologi
    Identifikatorer
    urn:nbn:se:liu:diva-147373 (URN)10.1007/s10456-018-9594-9 (DOI)000428924500007 ()29332242 (PubMedID)2-s2.0-85041334437 (Scopus ID)
    Anmärkning

    Funding Agencies|Swedish Research Council [2012-2472]; Swedish Foundation Stiftelsen Synframjandets Forskningsfond/Ogonfonden; Svenska Sallskapet for Medicinsk Forskning; Linkoping Universitet; Jeanssons Stiftelser

    Tillgänglig från: 2018-05-18 Skapad: 2018-05-18 Senast uppdaterad: 2018-12-07Bibliografiskt granskad
    2. Regulatory and Functional Connection of Microphthalmia-Associated Transcription Factor and Anti-Metastatic Pigment Epithelium Derived Factor in Melanoma
    Öppna denna publikation i ny flik eller fönster >>Regulatory and Functional Connection of Microphthalmia-Associated Transcription Factor and Anti-Metastatic Pigment Epithelium Derived Factor in Melanoma
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    2014 (Engelska)Ingår i: Neoplasia, ISSN 1522-8002, E-ISSN 1476-5586, Vol. 16, nr 6, s. 529-542Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Pigment epithelium-derived factor (PEDF), a member of the serine protease inhibitor superfamily, has potent anti-metastatic effects in cutaneous melanoma through its direct actions on endothelial and melanoma cells. Here we show that PEDF expression positively correlates with microphthalmia-associated transcription factor ( MITF) in melanoma cell lines and human samples. High PEDF and MITF expression is characteristic of low aggressive melanomas classified according to molecular and pathological criteria, whereas both factors are decreased in senescent melanocytes and naevi. Importantly, MITF silencing down-regulates PEDF expression in melanoma cell lines and primary melanocytes, suggesting that the correlation in the expression reflects a causal relationship. In agreement, analysis of Chromatin immunoprecipitation coupled to high throughput sequencing (ChIP-seq) data sets revealed three MITF binding regions within the first intron of SERPINF1, and reporter assays demonstrated that the binding of MITF to these regions is sufficient to drive transcription. Finally, we demonstrate that exogenous PEDF expression efficiently halts in vitro migration and invasion, as well as in vivo dissemination of melanoma cells induced by MITF silencing. In summary, these results identify PEDF as a novel transcriptional target of MITF and support a relevant functional role for the MITF-PEDF axis in the biology of melanoma.

    Ort, förlag, år, upplaga, sidor
    Neoplasia, 2014
    Nationell ämneskategori
    Klinisk medicin
    Identifikatorer
    urn:nbn:se:liu:diva-110497 (URN)10.1016/j.neo.2014.06.001 (DOI)000340553600007 ()25030625 (PubMedID)
    Anmärkning

    Funding Agencies|Ministerio de Ciencia y Competitividad of Spain [SAF-2010-19256, SAF-2011-24225, SAF-2012-32117, FIS 11/02568, RD09/0076/0101, PT13/0010/0012, PI12/01552]; LiU-Cancer; Svenska Sallskapet for Medicinsk Forskning; Ake Wibergs Stiftelse; Goesta Fraenkels Stifelse; Fundacion Cientifica de la Asociacion Espanola Contra el Cancer

    Tillgänglig från: 2014-09-15 Skapad: 2014-09-12 Senast uppdaterad: 2018-12-07
    3. Adjustable delivery of pro-angiogenic FGF-2 by alginate: collagen microspheres
    Öppna denna publikation i ny flik eller fönster >>Adjustable delivery of pro-angiogenic FGF-2 by alginate: collagen microspheres
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    2018 (Engelska)Ingår i: BIOLOGY OPEN, ISSN 2046-6390, Vol. 7, nr 3, artikel-id UNSP bio027060Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Therapeutic induction of blood vessel growth (angiogenesis) in ischemic tissues holds great potential for treatment of myocardial infarction and stroke. Achieving sustained angiogenesis and vascular maturation has, however, been highly challenging. Here, we demonstrate that alginate: collagen hydrogels containing therapeutic, pro-angiogenic FGF-2, and formulated as microspheres, is a promising and clinically relevant vehicle for therapeutic angiogenesis. By titrating the amount of readily dissolvable and degradable collagen with more slowly degradable alginate in the hydrogel mixture, the degradation rates of the biomaterial controlling the release kinetics of embedded proangiogenic FGF-2 can be adjusted. Furthermore, we elaborate a microsphere synthesis protocol allowing accurate control over sphere size, also a critical determinant of degradation/release rate. As expected, alginate: collagen microspheres were completely biocompatible and did not cause any adverse reactions when injected in mice. Importantly, the amount of pro-angiogenic FGF-2 released from such microspheres led to robust induction of angiogenesis in zebrafish embryos similar to that achieved by injecting FGF-2-releasing cells. These findings highlight the use of microspheres constructed from alginate: collagen hydrogels as a promising and clinically relevant delivery system for pro-angiogenic therapy.

    Ort, förlag, år, upplaga, sidor
    COMPANY OF BIOLOGISTS LTD, 2018
    Nyckelord
    Hydrogels; Microspheres; Angiogenesis; Vasculature; Zebrafish
    Nationell ämneskategori
    Cell- och molekylärbiologi
    Identifikatorer
    urn:nbn:se:liu:diva-147419 (URN)10.1242/bio.027060 (DOI)000429100500002 ()29449216 (PubMedID)
    Anmärkning

    Funding Agencies|Svenska Sallskapet for Medicinsk Forskning; Ake-Wiberg Foundation; Goesta Fraenkel Foundation; Ahrens Stiftelse; Ollie och Elof Ericssons Stiftelse; Carmen och Bertil Ragners Stiftelse; KI Stiftelser och fonder; Loo och Hans Ostermans Stiftelse for Medicinsk Forskning; Vetenskapsradet; Linkoping University

    Tillgänglig från: 2018-05-17 Skapad: 2018-05-17 Senast uppdaterad: 2018-12-07
  • Disputation: 2018-12-18 10:15 Planck, Fysikhuset, Linköping
    Lilja, Louise
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    4H-SiC epitaxy investigating carrier lifetime and substrate off-axis dependence2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Silicon carbide (SiC) is a wide bandgap semiconductor with unique material properties making it useful for various device applications using high power, high frequency and high temperature. Compared to Si-based electronics, SiC based electronics have an improved energy efficiency. One of the most critical problems is to reduce this planets power consumption, where large improvements can be made enhancing the energy efficiency. Independent on how the electrical power is generated, power conversion is needed and about 10% of the electrical power is lost for every power conversion step using Si-based electronics. Since the efficiency is related to the performance of the semiconductor device, SiC can make contributions to the efficiency. Compared to Si, SiC has three times larger bandgap, about ten times higher breakdown electric field strength and about three times higher thermal conductivity. The wide bandgap together with the chemical stability of SiC makes it possible for SiC electronic devices to operate at much higher temperatures (>250°C) compared to Si-based devices and do not require large cooling units as with Si power converters.

    The current status for 4H-SiC devices regard unipolar devices (≤ 1700 V), such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes (SBDs), are now on the market for mass production. The research focus is now on high-voltage (>10 kV) bipolar devices, such as, bipolar junction transistors (BJTs), p‑i‑n diodes and insulated-gate bipolar transistors (IGBTs).

    The focus of this thesis are material improvements relevant for the development of 4H-SiC high-voltage bipolar devices. A key parameter for such devices is the minority carrier lifetime, where long carrier lifetimes reduce the on-resistance through conductivity modulation. However, too long carrier lifetimes give long reverse recovery times leading to large switching losses. Thus, a tailored carrier lifetime is needed for the specific application. Carrier lifetimes of the epilayers can both be controlled by the CVD growth conditions and by post-growth processing, such as thermal oxidation and carbon implantation followed by thermal annealing. Emphasis in this thesis (Paper 1‑2) is to find optimal CVD growth conditions (growth temperature, C/Si ratio, growth rate, doping) improving the carrier lifetime. Since the main lifetime limiting defect has shown to be the Z1/2 center, identified as isolated carbon vacancies, growth conditions minimizing the Z1/2 concentration are strived for.

    To achieve high-voltage bipolar devices, thick epilayers of high quality is needed. An important factor is then the growth rate that needs to be relatively high in order to reduce the fabrication time, and thus the cost of the final device. In this thesis the growth process has been optimized for high growth rates (30 µm/h) using standard silane and propane chemistry (Paper 3), compared to other chemistries that includes chlorine, which results in corroded reactor parts and new defects in the epitaxial layers.

    Another important parameter for 4H-SiC bipolar devices is the basal plane dislocations (BPDs) in the substrate and epilayers, since the BPDs can act as source of nucleation and expansion of Shockley stacking faults (SSFs). The expanded SSFs give a lowered carrier lifetime and form a potential barrier for carrier transport leading to an increased forward voltage drop which in turn leads to bipolar degradation. The bipolar degradation is detrimental for 4H-SiC bipolar devices. Several strategies are developed to reduce the density of BPDs including buffer layers, growth interrupts and decreasing the substrates off-cut angle. Paper 4‑6 is focused on developing a CVD growth process for low substrate off-cut angles (1° and 2°) compared to the today’s standard off-cut angle of 4°. By reducing the substrate off-cut angle the number of BPDs intersecting the substrate surface is reduced. In addition, the conversion from BPDs to threading edge dislocations (TEDs) during epitaxial growth is increased with lower off-cut angles.

    Delarbeten
    1. Influence of Growth Temperature on Carrier Lifetime in 4H-SiC Epilayers
    Öppna denna publikation i ny flik eller fönster >>Influence of Growth Temperature on Carrier Lifetime in 4H-SiC Epilayers
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    2013 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Carrier lifetime and formation of defects have been investigated as a function of growth temperature in n-type 4H-SiC epitaxial layers, grown by horizontal hot-wall CVD. Emphasis has been put on having fixed conditions except for the growth temperature, hence growth rate, doping and epilayer thickness were constant in all epilayers independent of growth temperature. An increasing growth temperature gave higher Z1/2 concentrations along with decreasing carrier lifetime. A correlation between growth temperature and D1 defect was also observed.

    Ort, förlag, år, upplaga, sidor
    Trans Tech Publications Inc., 2013
    Nyckelord
    Atomic Force Microscopy, Carrier Lifetime, DLTS, Epitaxial Growth, Horizontal Hot-Wall CVD, Intrinsic Defect, Photoluminescence (PL)
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-88341 (URN)10.4028/www.scientific.net/MSF.740-742.637 (DOI)000319785500151 ()
    Konferens
    9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St Petersburg, Russia
    Tillgänglig från: 2013-02-04 Skapad: 2013-02-04 Senast uppdaterad: 2018-12-10
    2. Smooth 4H-SiC epilayers grown with high growth rates with silane/propane chemistry using 4° off-cut substrates
    Öppna denna publikation i ny flik eller fönster >>Smooth 4H-SiC epilayers grown with high growth rates with silane/propane chemistry using 4° off-cut substrates
    2016 (Engelska)Ingår i: Silicon Carbide and Related Materials 2015 / [ed] Fabrizio Roccaforte, Francesco La Via, Roberta Nipoti, Danilo Crippa, Filippo Giannazzo and Mario Saggio, Trans Tech Publications, 2016, Vol. 858, s. 209-212Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    4H-SiC epilayers with very smooth surfaces were grown with high growth rates on 4° off-cut substrates using standard silane/propane chemistry. Specular surfaces with RMS values below 0.2 nm are presented for epilayers grown with growth rates up to 30 μm/h using horizontal hot-wall chemical vapor deposition, with up to 100 μm thickness. Optimization of in-situ etching conditions and C/Si ratio are presented.

    Ort, förlag, år, upplaga, sidor
    Trans Tech Publications, 2016
    Serie
    Materials Science Forum, ISSN 1662-9752 ; 858
    Nyckelord
    Atomic force microscopy, Chemical vapor deposition, Epitaxial growth, Silicon carbide
    Nationell ämneskategori
    Materialteknik
    Identifikatorer
    urn:nbn:se:liu:diva-153288 (URN)10.4028/www.scientific.net/MSF.858.209 (DOI)
    Konferens
    The 16th International Conference on Silicon Carbide and Related Materials (ICSCRM2015), Giardini Naxos, Sicily, Italy, October 4th October 9th, 2015.
    Tillgänglig från: 2018-12-10 Skapad: 2018-12-10 Senast uppdaterad: 2018-12-10
    3. Improved Epilayer Surface Morphology on 2 degrees off-cut 4H-SiC Substrates
    Öppna denna publikation i ny flik eller fönster >>Improved Epilayer Surface Morphology on 2 degrees off-cut 4H-SiC Substrates
    2014 (Engelska)Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, s. 206-209Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Homoepitaxial layers of 4H-SiC were grown with horizontal hot-wall CVD on 2 degrees off-cut substrates, with the purpose of improving the surface morphology of the epilayers and reducing the density of surface morphological defects. In-situ etching conditions in either pure hydrogen or in a mixture of silane and hydrogen prior to the growth were compared as well as C/Si ratios in the range 0.8 to 1.0 during growth. The smoothest epilayer surface, together with lowest defect density, was achieved with growth at a C/Si ratio of 0.9 after an in-situ etching in pure hydrogen atmosphere.

    Ort, förlag, år, upplaga, sidor
    Trans Tech Publications, 2014
    Serie
    Materials Science Forum, ISSN 1662-9752 ; 778-780
    Nyckelord
    epitaxial growth; horizontal hot-wall CVD; atomic force microscopy; vicinal off angle
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-108194 (URN)10.4028/www.scientific.net/MSF.778-780.206 (DOI)000336634100048 ()
    Konferens
    SILICON CARBIDE AND RELATED MATERIALS 2013
    Tillgänglig från: 2014-06-26 Skapad: 2014-06-26 Senast uppdaterad: 2018-12-10
    4. In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates
    Öppna denna publikation i ny flik eller fönster >>In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates
    2015 (Engelska)Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, nr 6, s. 1319-1324Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    4H-SiC epilayers were grown on 2 degrees off-cut substrates using standard silane/propane chemistry, with the aim of characterizing in-grown stacking faults. The stacking faults were analyzed with low temperature photoluminescence spectroscopy, room temperature photoluminescence mappings, room temperature cathodoluminescence and synchrotron white beam X-ray topography. At least three different types of in-grown stacking faults were observed, including double Shockley stacking faults, triple Shockley stacking faults and bar-shaped stacking faults. Those stacking faults are all previously found in 4 degrees and 8 degrees off-cut epilayers; however, the geometrical size is larger in epilayers grown on 2 degrees off-cut substrates due to lower off-cut angle. The stacking faults were formed close to the epilayer/substrate interface during the epitaxial growth. (C) 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

    Ort, förlag, år, upplaga, sidor
    WILEY-V C H VERLAG GMBH, 2015
    Nyckelord
    chemical vapor deposition; epitaxy; photoluminescence; SiC; stacking faults
    Nationell ämneskategori
    Kemi
    Identifikatorer
    urn:nbn:se:liu:diva-120065 (URN)10.1002/pssb.201451710 (DOI)000355756200018 ()
    Anmärkning

    Funding Agencies|Swedish Research Council (VR); Advanced Functional Materials (AFM); Swedish Foundation for Strategic Research (SSF)

    Tillgänglig från: 2015-07-06 Skapad: 2015-07-06 Senast uppdaterad: 2018-12-10
  • Disputation: 2018-12-19 09:15 Planck, Fysikhuset, Linköping
    Lundström, Maria
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biologi. Linköpings universitet, Tekniska fakulteten.
    Exploring Fennoscandian agricultural history through genetic analysis of aged crop materials2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Crop plants have undergone a multitude of genetic changes during and following their domestication. The spread of agriculture brought the crops to new geographic regions exposing them to new environments and selection pressures along the way. This gave rise to many local variants with traits favoured both by agricultural practices and the environment.

    Agriculture was introduced in Fennoscandia (Norway, Sweden, Finland and Denmark) around 4000 BC. The composition of the archaeobotanical record gives some clues as to which species were cultivated, but macroscale analyses rarely reach beyond that. Therefore, methods like genetic analysis are necessary to expand our knowledge about the history of crop cultivation. Under optimal conditions, DNA can survive in biological samples for several hundred thousand years. The preservation of plant specimens in the Fennoscandian climate has, however, rarely been explored. This thesis therefore attempts to dive deeper into the Fennoscandian cultivation history through genetic analyses of aged plant materials from both museum collections and archaeological sources. Cereal grains from a range of preservation conditions were evaluated to find which ones might be of interest for genetic investigations. Desiccated materials gave the highest success rates, in agreement with previous studies. Waterlogged materials appeared to contain small amounts of endogenous DNA, whereas genetic analysis of charred cereals failed completely in all samples.

    Population structure was investigated in 17-19th century materials of both barley and rye from Sweden and Finland. Northern and southern populations of Finnish six-row barley were distinct from one another. In southern Sweden, genetic analysis suggested conserved population structure extending over 200 years. The genetic composition of rye also seemed mostly conserved, but rye did not show geographic population structure across the investigated region in Sweden and Finland.

    A long-standing question in Fennoscandian crop history has been the interpretation of historical written records mentioning Brassica (cole crops, turnips and mustards), as well as the species identity of archaeobotanical finds of Brassica seeds. Thus, Next Generation Sequencing (NGS) was applied to identify which Brassica types that were cultivated in 17th century Kalmar, Sweden. The analysis corroborated morphological species classification in two of the investigated subfossil seeds, whereas no conclusions could be drawn from the remaining samples. The genome coverages were too low to allow subspecies identification.

    Wheat has been cultivated in Fennoscandia since the introduction of agriculture but has increased dramatically in importance over the last century. The functional allele of the wheat nutrition gene NAM-B1 was found to be particularly prominent in Fennoscandian wheats, likely associated with its effect on grain maturation time. Here the evolutionary history of NAM-B1 was investigated to see if it could truly be considered a domestication gene as suggested in a previous study. By studying extant landrace materials of Mediterranean tetraploid wheat, it was found that the non-functional allele showed signs indicative of a selective sweep. This selection did not, however, appear to have occurred during domestication.

    In conclusion, aged plant specimens from both museum and archaeological contexts could contribute greatly to our knowledge about historical cultivation, extending the investigated period into the mid 17th century. Subfossil and waterlogged archaeobotanical materials do contain endogenous DNA, suggesting that they are better suited for genetic analysis than charred ones, at least as far as cereals are concerned. There is potential for classifying archaeological Brassica remains using NGS, even though further optimisation of sample and library preparation may be necessary. And finally, despite NAM-B1 showing signs of selection it should not be considered a domestication gene in tetraploid wheat.

  • Disputation: 2018-12-19 13:15 Nobel BL32, B-Huset, Linköping
    Maghazeh, Arian
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    System-Level Design of GPU-Based Embedded Systems2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Modern embedded systems deploy several hardware accelerators, in a heterogeneous manner, to deliver high-performance computing. Among such devices, graphics processing units (GPUs) have earned a prominent position by virtue of their immense computing power. However, a system design that relies on sheer throughput of GPUs is often incapable of satisfying the strict power- and time-related constraints faced by the embedded systems.

    This thesis presents several system-level software techniques to optimize the design of GPU-based embedded systems under various graphics and non-graphics applications. As compared to the conventional application-level optimizations, the system-wide view of our proposed techniques brings about several advantages: First, it allows for fully incorporating the limitations and requirements of the various system parts in the design process. Second, it can unveil optimization opportunities through exposing the information flow between the processing components. Third, the techniques are generally applicable to a wide range of applications with similar characteristics. In addition, multiple system-level techniques can be combined together or with application-level techniques to further improve the performance.

    We begin by studying some of the unique attributes of GPU-based embedded systems and discussing several factors that distinguish the design of these systems from that of the conventional high-end GPU-based systems. We then proceed to develop two techniques that address an important challenge in the design of GPU-based embedded systems from different perspectives. The challenge arises from the fact that GPUs require a large amount of workload to be present at runtime in order to deliver a high throughput. However, for some embedded applications, collecting large batches of input data requires an unacceptable waiting time, prompting a trade-off between throughput and latency. We also develop an optimization technique for GPU-based applications to address the memory bottleneck issue by utilizing the GPU L2 cache to shorten data access time. Moreover, in the area of graphics applications, and in particular with a focus on mobile games, we propose a power management scheme to reduce the GPU power consumption by dynamically adjusting the display resolution, while considering the user's visual perception at various resolutions. We also discuss the collective impact of the proposed techniques in tackling the design challenges of emerging complex systems.

    The proposed techniques are assessed by real-life experimentations on GPU-based hardware platforms, which demonstrate the superior performance of our approaches as compared to the state-of-the-art techniques.

    Delarbeten
    1. General Purpose Computing on Low-Power Embedded GPUs: Has It Come of Age?
    Öppna denna publikation i ny flik eller fönster >>General Purpose Computing on Low-Power Embedded GPUs: Has It Come of Age?
    2013 (Engelska)Ingår i: 13th International Conference on Embedded Computer Systems: Architectures, Modeling, and Simulation (SAMOS 2013), Samos, Greece, July 15-18, 2013., IEEE Press, 2013Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    In this paper we evaluate the promise held by low power GPUs for non-graphic workloads that arise in embedded systems. Towards this, we map and implement 5 benchmarks, that find utility in very different application domains, to an embedded GPU. Our results show that apart from accelerated performance, embedded GPUs are promising also because of their energy efficiency which is an important design goal for battery-driven mobile devices. We show that adopting the same optimization strategies as those used for programming high-end GPUs might lead to worse performance on embedded GPUs. This is due to restricted features of embedded GPUs, such as, limited or no user-defined memory, small instruction-set, limited number of registers, among others. We propose techniques to overcome such challenges, e.g., by distributing the workload between GPUs and multi-core CPUs, similar to the spirit of heterogeneous computation.

    Ort, förlag, år, upplaga, sidor
    IEEE Press, 2013
    Nationell ämneskategori
    Datavetenskap (datalogi)
    Identifikatorer
    urn:nbn:se:liu:diva-92626 (URN)10.1109/SAMOS.2013.6621099 (DOI)000332458100004 ()
    Konferens
    SAMOS'13
    Tillgänglig från: 2013-05-14 Skapad: 2013-05-14 Senast uppdaterad: 2018-12-07
    2. Saving Energy without Defying Deadlines on Mobile GPU-based Heterogeneous Systems
    Öppna denna publikation i ny flik eller fönster >>Saving Energy without Defying Deadlines on Mobile GPU-based Heterogeneous Systems
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    2014 (Engelska)Ingår i: 2014 International Conference on Hardware/Software Codesign and System Synthesis, Association for Computing Machinery (ACM), 2014Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    With the advent of low-power programmable compute cores based on GPUs, GPU-equipped heterogeneous platforms are becoming common in a wide spectrum of industries including safety-critical domains like the automotive industry. While the suitability of GPUs for throughput oriented applications is well-accepted, their applicability for real-time applications remains an open issue. Moreover, in mobile/embedded systems, energy-efficient computing is a major concern and yet, there has been no systematic study on the energy savings that GPUs may potentially provide. In this paper, we propose an approach to utilize both the GPU and the CPU in a heterogeneous fashion to meet the deadlines of a real-time application while ensuring that we maximize the energy savings. We note that GPUs are inherently built to maximize the throughput and this poses a major challenge when deadlines must be satisfied. The problem becomes more acute when we consider the fact that GPUs are more energy efficient than CPUs and thus, a naive approach that is based on maximizing GPU utilization might easily lead to infeasible solutions from a deadline perspective.

    Ort, förlag, år, upplaga, sidor
    Association for Computing Machinery (ACM), 2014
    Nationell ämneskategori
    Data- och informationsvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-112689 (URN)10.1145/2656075.2656097 (DOI)978-1-4503-3051-0 (ISBN)
    Konferens
    International Conference on Hardware/Software Codesign and System Synthesis (CODES+ISSS 2014), New Delhi, India, October 12-17, 2014
    Tillgänglig från: 2014-12-08 Skapad: 2014-12-08 Senast uppdaterad: 2018-12-07Bibliografiskt granskad
    3. Perception-aware power management for mobile games via dynamic resolution scaling
    Öppna denna publikation i ny flik eller fönster >>Perception-aware power management for mobile games via dynamic resolution scaling
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    2015 (Engelska)Ingår i: 2015 IEEE/ACM INTERNATIONAL CONFERENCE ON COMPUTER-AIDED DESIGN (ICCAD), IEEE , 2015, s. 613-620Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Modern mobile devices provide ultra-high resolutions in their display panels. This imposes ever increasing workload on the GPU leading to high power consumption and shortened battery life. In this paper, we first show that resolution scaling leads to significant power savings. Second, we propose a perception-aware adaptive scheme that sets the resolution during game play. We exploit the fact that game players are often willing to trade quality for longer battery life. Our scheme uses decision theory, where the predicted user perception is combined with a novel asymmetric loss function that encodes users' alterations in their willingness to save power.

    Ort, förlag, år, upplaga, sidor
    IEEE, 2015
    Serie
    ICCAD-IEEE ACM International Conference on Computer-Aided Design, ISSN 1933-7760
    Nationell ämneskategori
    Datavetenskap (datalogi)
    Identifikatorer
    urn:nbn:se:liu:diva-124543 (URN)10.1109/ICCAD.2015.7372626 (DOI)000368929600084 ()978-1-4673-8388-2 (ISBN)
    Konferens
    Computer-Aided Design (ICCAD), 2015 IEEE/ACM International Conference on 2-6 Nov. 2015 Austin, TX
    Tillgänglig från: 2016-02-02 Skapad: 2016-02-02 Senast uppdaterad: 2018-12-07
    4. Latency-Aware Packet Processing on CPU-GPU Heterogeneous Systems
    Öppna denna publikation i ny flik eller fönster >>Latency-Aware Packet Processing on CPU-GPU Heterogeneous Systems
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    2017 (Engelska)Ingår i: DAC '17 Proceedings of the 54th Annual Design Automation Conference 2017, New York, NY, USA: Association for Computing Machinery (ACM), 2017Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    In response to the tremendous growth of the Internet, towards what we call the Internet of Things (IoT), there is a need to move from costly, high-time-to-market specific-purpose hardware to flexible, low-time-to-market general-purpose devices for packet processing. Among several such devices, GPUs have attracted attention in the past, mainly because the high computing demand of packet processing applications can, potentially, be satisfied by these throughput-oriented machines. However, another important aspect of such applications is the packet latency which, if not handled carefully, will overshadow the throughput benefits. Unfortunately, until now, this aspect has been mostly ignored. To address this issue, we propose a method that considers the variable bit rate of the traffic and, depending on the current rate, minimizes the latency, while meeting the rate demand. We propose a persistent kernel based software architecture to overcome the challenges inherent in GPU implementation like kernel invocation overhead, CPU-GPU communication and memory access overhead. We have chosen packet classification as the packet processing application to demonstrate our technique. Using the proposed approach, we are able to reduce the packet latency on average by a factor of 3.5, compared to the state-of-the-art solutions, without any packet drop.

    Ort, förlag, år, upplaga, sidor
    New York, NY, USA: Association for Computing Machinery (ACM), 2017
    Serie
    Design Automation Conference DAC, ISSN 0738-100X
    Nationell ämneskategori
    Datavetenskap (datalogi)
    Identifikatorer
    urn:nbn:se:liu:diva-141212 (URN)10.1145/3061639.3062269 (DOI)000424895400129 ()2-s2.0-85023612665 (Scopus ID)978-1-4503-4927-7 (ISBN)
    Konferens
    54th ACM/EDAC/IEEE Design Automation Conference (DAC), Austin, TX, USA, June 18-22, 2017
    Tillgänglig från: 2017-09-27 Skapad: 2017-09-27 Senast uppdaterad: 2018-12-07Bibliografiskt granskad
  • Disputation: 2019-01-11 13:00 ACAS, A Building, Linköping
    Odar, Susanne
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell ekonomi. Linköpings universitet, Tekniska fakulteten.
    Managementinitiativ, mening och verksamhetsresultat: En retrospektiv studie av en teknikintensiv verksamhet2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    I denna studie betraktas en organisations utveckling med ett meningsskapande-perspektiv, vilket kort innebär att handlingar skapar mening och mening skapar handlingar. Weicks (1995) inflytelserika tankemodell av meningsskapande har utvecklats till en modell och metod som kan tillämpas på ett empiriskt material. Utvecklingen inom ASEA/ABB reläverksamheten under en trettioårsperiod från tidigt 1980-tal till år 2010 beskrivs och analyseras.

    Studien handlar om att förstå hur organisationer utvecklas, och hur chefer och medarbetare kan påverka en organisations utveckling och bidra till verksamhetsresultat. Syftet har avgränsats genom valet av teoretiskt perspektiv, metod och forskningsfrågor. Forskningsfrågorna rör samspelet mellan så kallade managementinitiativ, mening och verksamhetens utveckling. Managementinitiativ är en typ av handlingar som chefer i en organisation kan besluta om. Hur dessa påverkar och påverkas av de uppfattningar som finns hos chefer och medarbetare i organisationen beskrivs och analyseras. Det valda fallet omfattar 85 stycken initiativ. Studien har visat att en verksamhets utveckling bäst förstås genom en analys av den aktuella verksamheten och dess omvärld, och att det går att finna mönster som upprepas över tid inom ramen för verksamheten

    Metoden och modellen är generaliserbara och kan användas för empiriska studier av meningsskapande i grupper, organisationer och samhällen. Det kanske viktigaste bidraget med modellen och metoden är att samspelet mellan olika nivåer – individ-, interaktions-, struktur- och kulturnivån – kan studeras över tid samt att fokus kan riktas mot substansen, innehållet, i meningsskapandet såväl som processen. Data omfattar handlingar, argument, förväntningar och utfästelser. I denna studie har dessa betraktats som uttryck för meningsskapande, men de kan ses som uttryck för andra perspektiv. Metoden och modellen kan även användas inom andra processtudier där dessa kategoriers utveckling över tiden är av intresse, och där samspelet mellan olika nivåer är av betydelse.

    Ambitionen är i första hand att bidra till det pågående samtalet inom meningsskapande, men en förhoppning är också göra området tillgängligt för forskare inom andra områden och praktiker som inte kommit i kontakt med meningsskapande tidigare.

  • Disputation: 2019-01-23 10:15 BL32, B-huset, Linköping
    Shuaib, Budor
    Linköpings universitet, Matematiska institutionen, Matematik och tillämpad matematik. Linköpings universitet, Tekniska fakulteten.
    Ghostpeakons2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    I denna avhandling studeras peakoner (från engelskans peakons, en förkortning för peaked solitons, dvs. spetsiga solitoner).Detta är en klass av lösningar som förekommer i vissa vågekvationer, t.ex. Camassa–Holm-ekvationen från teorin för vågor i grunt vatten, samt de matematiskt närbesläktade Degasperis–Procesi-, Novikov- och Geng–Xue-ekvationerna. Samtliga dessa fyra ickelinjära partiella differentialekvationer är integrabla system i den meningen att de har Laxpar, oändligt många konserveringslagar, samt multipeakonlösningar som ges av explicita formler.

    I den första artikeln utvecklar vi en metod som använder s.k. spökpeakoner (peakoner med amplituden noll) för att finna explicita formler för de karaktäristiska kurvorna som hör till multipeakonlösningarna till Camassa–Holm-, Degasperis– Procesi- och Novikov-ekvationerna.

    I den andra artikeln använder vi spökpeakonmetoden för att härleda explicita formler för godtyckliga multipeakonlösningar till Geng–Xue-ekvationen, som är en tvåkomponentsekvation.Det allmänna fallet innefattarmånga icke-ekvivalenta peakonkonfigurationer, beroende på i vilken ordning peakonerna kommer i de två komponenterna i lösningen, och tidigare var lösningen känd enbart i det s.k. sammanflätade fallet där peakonerna ligger växelvis i den ena och den andra komponenten. För att erhålla lösningsformlerna för en godtycklig konfiguration inför vi hjälppeakoner som gör konfigurationen sammanflätad.Genom lämpliga gränsövergångar tvingar vi sedan amplituden för dessa hjälppeakoner att gå mot noll, och kvar blir då lösningsformlerna för de resterande vanliga peakonerna  

  • Disputation: 2019-01-25 13:00 ACAS, A-Building, Linköping
    Radits, Markus
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell ekonomi. Linköpings universitet, Tekniska fakulteten.
    A Business Ecology Perspective on Community-Driven Open Source: The Case of the Free and Open Source Content Management System Joomla2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Denna avhandling undersöker fenomenet öppen källkod, ’open source’, ur ett lednings och styrningsperspektiv. Mer konkret studeras aspekter på kommersialisering av ett community-drivet open source projekt (OSS, open source software). Uttrycket ’community-drivet’ hänvisar till open source projekt som drivs och styrs av volontärgrupper, till skillnad från open source projekt som drivs och styrs av enskilda företag.

    Genom att tillämpa ett affärsekologiperspektiv fokuserar denna avhandling på det vidare sammanhang som karaktäriserar kommersialisering av OSS, såsom globala och kollaborativa produktionssystem, värderingarna öppenhet och samarbete, marknadsstrukturer, och diffusa organisationsgränser. Aktiviteterna i open source communityn och dess kringliggande ekosystem kan bidra till många fördelar för företag, och därför kan ett affärsekologiperspektiv vara en användbar analytisk lins för att förstå de möjligheter, utmaningar och risker som företag står inför när de kommersialiserar OSS.

    Två övergripande teman lyfts fram i denna avhandling. Det första temat handlar om de utmaningar som företag står inför när de kommersialiserar community-driven OSS. Det finns i litteraturen om affärsekologier och open source en tendens att betona fördelar, möjligheter och positiva aspekter på beteende på bekostnad av att undersöka utmaningar som företag står inför. Affärsekologier innebär dock inte enbart möjligheter för företag, utan kan också orsaka en rad utmaningar som företag behöver hantera för att lyckas. Med utgångspunkt i denna obalans i litteraturen fokuserar det första temat på de utmaningar med kommersialisering av community-driven OSS. Detta görs för att bidra till en mer balanserad och holistisk förståelse av den på samma gång kollaborativa och konkurrerande dynamiken i affärsekologin runt ett open source projekt.

    Det andra temat handlar om sammanflätningen (intertwining) mellan community-deltagande och vinstdrivande verksamhet. Såsom det framgår i litteraturen har frågan om samverkan mellan företag och communities blivit allt viktigare, eftersom communityernas överlevnad, framgång och hållbarhet har blivit strategiskt viktiga för många organisationer. Även om många strategiska fördelar kan uppstå som en följd av samverkan mellan företag och communities saknas forskning om hur värdeskapande uppstår i en vidare kontext. Med ett bredare perspektiv i åtanke undersöker denna avhandling sammanflätningen av frivilligt community-deltagande och en vinstdrivande verksamhet genom att fokusera på fyra aspekter av sammanflätning som förekommer i litteraturen: förstärkning, komplementaritet, synergi, och ömsesidighet.

    Denna avhandling är utformad som en kvalitativ utforskande fallstudie. Det empiriska fallet är Joomla, ett innehållshanteringssystem som bygger på open source. Inom ramen för avhandlingen undersöks fallet i termer av samspel inom Joomla-communityn och de kommersiella aktiviteterna som sker runt Joomla-plattformen (t.ex., webbutveckling, rådgivning, marknadsföring, anpassningar, och extensions). För att uppnå ett analytiskt djup kompletteras affärsekologiperspektivet med idéer och förslag från andra teoretiska områden, såsom intressentmodellen, community-styrning, företagsidentitet, motivationsteori, prissättning, och buntning.

    Resultaten visar att utmaningarna med kommersialisering av community-driven OSS kretsar kring nio olika faktorer som kan grupperas i tre områden: ekosystemet, communityn, och företaget. Ekosystemsfaktorerna innefattar den globala verksamma miljön, förändringshastigheten och kannibalisering av idéer. Community-faktorerna innefattar plattformspolicy, plattformsimage, och att deltagandet i open source projektet sker på frivillig basis. Slutligen innefattar företagsfaktorerna suddiga gränser mellan privatliv och arbetsliv, svårigheten att uppskatta kostnader samt beroendeförhållanden mellan företag. Baserat på dessa insikter föreslås en modell för att analysera communitybaserad värdeskapande i affärsekologier. Modellen integrerar kollektiv innovation, community-deltagande, och value capture i en holistisk modell för community-baserad värdeskapande i kontexten samverkan mellan företag och communities.

    Vidare beskrivs effekterna av sammanflätningen av frivilligt community-deltagande och vinstdrivande verksamhet i termer av förstärkning, komplementaritet, synergi, och ömsesidighet. Genom att visa att sammanflätningen av frivilligt community-deltagande och vinstdrivande verksamhet kan vara stark i fall där det ofta antas implicit att kommersiella aktiviteter inte förekommer ger denna avhandling en mer nyanserad förståelse av företags roll i kontexten open source.

    Baserat på empiriska och analytiska insikter diskuterar denna avhandling ett antal teoretiska konsekvenser, såsom rollen som intersubjektiv tillit spelar i förhållande till den ovisshet som kommersiella aktörer står inför, ett alternativt sätt att klassificera community-typer, metaforen superorganismer i kontexten open source, community-deltagares välbefinnande, samt hur open source utvecklare hanterar övergången från en community-baserad självidentitet till en entreprenöriell självidentitet vid kommersialisering av OSS. Dessutom ger de sex delstudier som avhandlingen bygger på egna bidrag som presenteras i respektive delstudie.

    I stora drag bidrar denna avhandling till litteraturen om kommersialisering av OSS, affärsmässiga och strategiska aspekter på open source, samspelet mellan community-driven entreprenörsverksamhet samt den framväxande forskning som använder ett affärsekologiperspektiv för att studera kollegial produktion baserad på allmännytta. En mängd olika möjligheter för framtida forskning lyfts fram.