liu.seSearch for publications in DiVA
1 - 6 of 6
rss atomLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
  • Public defence: 2018-01-26 10:15 KEY1, Hus KEY, Linköping
    Gustavsson, Erik
    Linköping University, Department of Culture and Communication, Culture and Aesthetics. Linköping University, Faculty of Arts and Sciences.
    Characterising Needs in Health Care Priority Setting2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The focus of this thesis is needs in the context of health care priority setting. The notion of needs has a strong standing in health care policy; however, how the idea should be understood more specifically and how it should guide decisions about priority setting remain contentious issues. The aim of this thesis is to explore how needs should be characterised in health care priority setting. This matter is approached by, first, exploring and developing the conceptual structure of health care needs, and second, discussing and suggesting solutions to normative questions that arise when needs are characterised as a distributive principle.

    In the first article, the conceptual structure of needs in general and health care needs in particular is explored, and it is argued that a specific characterisation of health care needs is required.

    In the second article, the notion of health care needs is explored in relation to preferences for health care within the context of shared decision-making. The paper further discusses a number of queries that arise in the intersection between what the patient needs and what the patient wants.

    The third article discusses how a principle of need should handle questions about interpersonal aggregation. The paper characterises a principle of need which strikes a reasonable balance between giving priority to the worst off and the distribution of benefits with regard to interpersonal aggregation.

    The fourth article discusses how a principle of need should account for the fact that patients often are badly off due to several conditions rather than one single condition. It is argued that how badly off patients are should be understood as a function of how badly off these patients are when all of their conditions (for which they need health care) are considered.

    The frame story provides the terminological, theoretical, contextual, and methodological background for the discussion undertaken in this thesis. The conclusions of the articles are brought together and the discussion extended in the concluding discussion by sketching a number of conditions of adequacy for the concept and principle of need relevant for health care priority setting.  

    List of papers
    1. From Needs to Health Care Needs
    Open this publication in new window or tab >>From Needs to Health Care Needs
    2014 (English)In: Health Care Analysis, ISSN 1065-3058, E-ISSN 1573-3394, Vol. 22, no 1, 22-35 p.Article in journal (Refereed) Published
    Abstract [en]

    One generally considered plausible way to allocate resources in health care is according to people’s needs. In this paper I focus on a somewhat overlooked issue, that is the conceptual structure of health care needs. It is argued that what conceptual understanding of needs one has is decisive in the assessment of what qualifies as a health care need and what does not. The aim for this paper is a clarification of the concept of health care need with a starting point in the general philosophical discussion about needs. I outline three approaches to the concept of need and argue that they all share the same conceptual underpinnings. The concept of need is then analyzed in terms of a subject x needing some object y in order to achieve some goal z. I then discuss the relevant features of the object y and the goal z which make a given need qualify as a health care need and not just a need for anything.

    Place, publisher, year, edition, pages
    Springer, 2014
    Keyword
    Harm; Health; Health care; Health care need; Need; Priority-setting; Rationing; Well-being
    National Category
    Philosophy, Ethics and Religion Other Medical Sciences
    Identifiers
    urn:nbn:se:liu:diva-106476 (URN)10.1007/s10728-013-0241-8 (DOI)000331640900003 ()
    Available from: 2014-05-08 Created: 2014-05-08 Last updated: 2018-01-10Bibliographically approved
    2. Health-care needs and shared decision-making in priority-setting
    Open this publication in new window or tab >>Health-care needs and shared decision-making in priority-setting
    2015 (English)In: Medicine, Health care and Philosophy, ISSN 1386-7423, E-ISSN 1572-8633, Vol. 18, no 1, 13-22 p.Article in journal (Refereed) Published
    Abstract [en]

    In this paper we explore the relation between health-care needs and patients desires within shared decision-making (SDM) in a context of priority setting in health care. We begin by outlining some general characteristics of the concept of health-care need as well as the notions of SDM and desire. Secondly we will discuss how to distinguish between needs and desires for health care. Thirdly we present three cases which all aim to bring out and discuss a number of queries which seem to arise due to the double focus on a patients need and what that patient desires. These queries regard the following themes: the objectivity and moral force of needs, the prediction about what kind of patients which will appear on a micro level, implications for ranking in priority setting, difficulties regarding assessing and comparing benefits, and implications for evidence-based medicine.

    Place, publisher, year, edition, pages
    Springer Verlag (Germany), 2015
    Keyword
    Needs; Health-care needs; Shared decision-making; Desires; Priority setting; Rationing
    National Category
    Clinical Medicine
    Identifiers
    urn:nbn:se:liu:diva-114234 (URN)10.1007/s11019-014-9568-7 (DOI)000347699000003 ()24807745 (PubMedID)
    Available from: 2015-02-16 Created: 2015-02-16 Last updated: 2018-01-10Bibliographically approved
    3. Principles of Need and the Aggregation Thesis.
    Open this publication in new window or tab >>Principles of Need and the Aggregation Thesis.
    2017 (English)In: Health Care Analysis, ISSN 1065-3058, E-ISSN 1573-3394Article in journal (Refereed) Epub ahead of print
    Abstract [en]

    Principles of need are constantly referred to in health care priority setting. The common denominator for any principle of need is that it will ascribe some kind of special normative weight to people being worse off. However, this common ground does not answer the question how a plausible principle of need should relate to the aggregation of benefits across individuals. Principles of need are sometimes stated as being incompatible with aggregation and sometimes characterized as accepting aggregation in much the same way as utilitarians do. In this paper we argue that if one wants to take principles of need seriously both of these positions have unreasonable implications. We then characterize and defend a principle of need consisting of sufficientarian elements as well as prioritarian which avoids these unreasonable implications.

    Place, publisher, year, edition, pages
    Springer, 2017
    Keyword
    Aggregation, Needs, Principles of need, Prioritarianism, Priority setting, Sufficiency
    National Category
    Ethics
    Identifiers
    urn:nbn:se:liu:diva-144208 (URN)10.1007/s10728-017-0346-6 (DOI)28866792 (PubMedID)
    Available from: 2018-01-10 Created: 2018-01-10 Last updated: 2018-01-10
  • Public defence: 2018-01-26 13:15 Ada Lovelace, B-huset, Linköping
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    High-End Performance with Low-End Hardware: Analysis of Massive MIMO Base Station Transceivers2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Massive MIMO (multiple-input–multiple-output) is a multi-antenna technology for cellular wireless communication, where the base station uses a large number of individually controllable antennas to multiplex users spatially.  This technology can provide a high spectral efficiency.  One of its main challenges is the immense hardware complexity and cost of all the radio chains in the base station.  To make massive MIMO commercially viable, inexpensive, low-complexity hardware with low linearity has to be used, which inherently leads to more signal distortion.  This thesis investigates how the degenerated linearity of some of the main components—power amplifiers, analog-to-digital converters (ADCs) and low-noise amplifiers—affects the performance of the system, with respect to data rate, power consumption and out-of-band radiation. The main results are: Spatial processing can reduce PAR (peak-to-average ratio) of the transmit signals in the downlink to as low as 0B; this, however, does not necessarily reduce power consumption.  In environments with isotropic fading, one-bit ADCs lead to a reduction in effective signal-to-interference-and-noise ratio (SINR) of 4dB in the uplink and four-bit ADCs give a performance close to that of an unquantized system.  An analytical expression for the radiation pattern of the distortion from nonlinear power amplifiers is derived.  It shows how the distortion is beamformed to some extent, that its gain never is greater than that of the desired signal, and that the gain of the distortion is reduced with a higher number of served users and a higher number of channel taps.  Nonlinear low-noise amplifiers give rise to distortion that partly combines coherently and limits the possible SINR.  It is concluded that spatial processing with a large number of antennas reduces the impact of hardware distortion in most cases.  As long as proper attention is paid to the few sources of coherent distortion, the hardware complexity can be reduced in massive MIMO base stations to overcome the hardware challenge and make massive MIMO commercial reality.

    List of papers
    1. Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion and Performance
    Open this publication in new window or tab >>Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion and Performance
    2016 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 46, no 12, 5050-5063 p.Article in journal (Refereed) Published
    Abstract [en]

    In massive multiple-input multiple-output (MIMO), most precoders result in downlink signals that suffer from high peak-to-average ratio (PAR), independently of modulation order and whether single-carrier or orthogonal frequency-division multiplexing (OFDM) transmission is used. The high PAR lowers the power efficiency of the base-station amplifiers. To increase the power efficiency, low-PAR precoders have been proposed. In this paper, we compare different transmission methods for massive MIMO in terms of the power consumed by the amplifiers. It is found that: 1) OFDM and single-carrier transmission have the same performance over a hardened massive MIMO channel and 2) when the higher amplifier power efficiency of low-PAR precoding is taken into account, conventional and low-PAR precoders lead to approximately the same power consumption. Since downlink signals with low PAR allow for simpler and cheaper hardware, than signals with high PAR, therefore, the results suggest that low-PAR precoding with either single-carrier or OFDM transmission should be used in a massive MIMO base station.

    Place, publisher, year, edition, pages
    IEEE, 2016
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-130514 (URN)10.1109/TCOMM.2016.2557781 (DOI)000391694500013 ()
    Funder
    EU, FP7, Seventh Framework Programme, ICT-619086Swedish Research CouncilELLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Note

    Funding agencies: European Union [ICT-619086]; Swedish Research Council (Vetenskapsradet); ELLIIT

    Available from: 2016-08-11 Created: 2016-08-11 Last updated: 2018-01-03
    2. Multiuser MIMO Precoding with Per-Antenna Continuous-Time Constant-Envelope Constraints
    Open this publication in new window or tab >>Multiuser MIMO Precoding with Per-Antenna Continuous-Time Constant-Envelope Constraints
    2015 (English)In: 2015 IEEE 16th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Institute of Electrical and Electronics Engineers (IEEE), 2015, 261-265 p.Conference paper, Published paper (Refereed)
    Abstract [en]

    A transmission scheme for the multiuser MIMO downlink, where the transmit signal from each antenna has constant envelope and a limited bandwidth, is proposed in order to enable the use of highly efficient, nonlinear amplifiers at the base station. To evaluate its performance, an achievable rate is derived and the necessary transmit power of the proposed scheme is computed for a system with 40 antennas that serves 4 users at data rates around 1 bpcu. For this system and 40% excess 30 dB-bandwidth, approximately 3 dB more transmit power is required to achieve the same sum-rate as without the constantenvelope constraints.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2015
    Series
    IEEE International Workshop on Signal Processing Advances in Wireless Communications, ISSN 2325-3789
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-120251 (URN)10.1109/SPAWC.2015.7227040 (DOI)000380547100053 ()978-1-4799-1931-4 (ISBN)
    Conference
    SPAWC 2015 The 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, June 28 – July 1, 2015, Stockholm, Sweden
    Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2018-01-03Bibliographically approved
    3. Uplink Performance of Wideband Massive MIMO With One-Bit ADCs
    Open this publication in new window or tab >>Uplink Performance of Wideband Massive MIMO With One-Bit ADCs
    2017 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 1, 87-100 p.Article in journal (Refereed) Published
    Abstract [en]

    Analog-to-digital converters (ADCs) stand for a significant part of the total power consumption in a massive multiple-input multiple-output (MIMO) base station. One-bit ADCs are one way to reduce power consumption. This paper presents an analysis of the spectral efficiency of single-carrier and orthogonal-frequency-division-multiplexing (OFDM) transmission in massive MIMO systems that use one-bit ADCs. A closed-form achievable rate, i.e., a lower bound on capacity, is derived for a wideband system with a large number of channel taps that employ low-complexity linear channel estimation and symbol detection. Quantization results in two types of error in the symbol detection. The circularly symmetric error becomes Gaussian in massive MIMO and vanishes as the number of antennas grows. The amplitude distortion, which severely degrades the performance of OFDM, is caused by variations between symbol durations in received interference energy. As the number of channel taps grows, the amplitude distortion vanishes and OFDM has the same performance as single-carrier transmission. A main conclusion of this paper is that wideband massive MIMO systems work well with one-bit ADCs.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2017
    Keyword
    MIMO, Channel estimation, Wideband, Quantization (signal), Distortion, Fading channels, One-bit ADCs
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-135783 (URN)10.1109/TWC.2016.2619343 (DOI)000393876200007 ()2-s2.0-85009814512 (Scopus ID)
    Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2018-01-03Bibliographically approved
    4. Achievable Uplink Rates for Massive MIMO with Coarse Quantization
    Open this publication in new window or tab >>Achievable Uplink Rates for Massive MIMO with Coarse Quantization
    2017 (English)In: 2017 IEEE InternationalConference on Acoustics, Speech,and Signal Processing Proceedings, 2017, 6488-6492 p.Conference paper, Published paper (Refereed)
    Abstract [en]

    The high hardware complexity of a massive MIMO base station, which requires hundreds of radio chains, makes it challenging to build commercially.  One way to reduce the hardware complexity and power consumption of the receiver is to lower the resolution of the analog-to-digital converters (ADCs).  We derive an achievable rate for a massive MIMO system with arbitrary quantization and use this rate to show that ADCs with as low as 3 bits can be used without significant performance loss at spectral efficiencies around 3.5 bpcu per user, also under interference from stronger transmitters and with some imperfections in the automatic gain control.

    Series
    Acoustics, Speech and Signal Processing (ICASSP), E-ISSN 2379-190X ; 2017
    Keyword
    ADC, channel estimation, low resolution, massive MIMO, quantization
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-135787 (URN)10.1109/ICASSP.2017.7953406 (DOI)000414286206131 ()9781509041176 (ISBN)9781509041169 (ISBN)9781509041183 (ISBN)
    Conference
    International Conference on Acoustics, Speech, and Signal Processing, March 5–9, 2017, New Orleans, USA
    Note

    Funding agencies: European Union Seventh Framework Programme [ICT-619086]; Swedish Research Council (Vetenskapsradet); National Science Foundation [NSF-CCF-1527079]; ICT R&D program of MSIP/IITP [2016 (B0717-16-0002)]

    Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2018-01-12Bibliographically approved
  • Public defence: 2018-01-26 13:15 Planck, Hus F, Linköping
    Ivanova, Valentina
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Fostering User Involvement in Ontology Alignment and Alignment Evaluation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The abundance of data at our disposal empowers data-driven applications and decision making. The knowledge captured in the data, however, has not been utilized to full potential, as it is only accessible to human interpretation and data are distributed in heterogeneous repositories.

    Ontologies are a key technology unlocking the knowledge in the data by providing means to model the world around us and infer knowledge implicitly captured in the data. As data are hosted by independent organizations we often need to use several ontologies and discover the relationships between them in order to support data and knowledge transfer. Broadly speaking, while ontologies provide formal representations and thus the basis, ontology alignment supplies integration techniques and thus the means to turn the data kept in distributed, heterogeneous repositories into valuable knowledge.

    While many automatic approaches for creating alignments have already been developed, user input is still required for obtaining the highest-quality alignments. This thesis focuses on supporting users during the cognitively intensive alignment process and makes several contributions.

    We have identified front- and back-end system features that foster user involvement during the alignment process and have investigated their support in existing systems by user interface evaluations and literature studies. We have further narrowed down our investigation to features in connection to the, arguably, most cognitively demanding task from the users’ perspective—manual validation—and have also considered the level of user expertise by assessing the impact of user errors on alignments’ quality. As developing and aligning ontologies is an error-prone task, we have focused on the benefits of the integration of ontology alignment and debugging.

    We have enabled interactive comparative exploration and evaluation of multiple alignments at different levels of detail by developing a dedicated visual environment—Alignment Cubes—which allows for alignments’ evaluation even in the absence of reference alignments.

    Inspired by the latest technological advances we have investigated and identified three promising directions for the application of large, high-resolution displays in the field: improving the navigation in the ontologies and their alignments, supporting reasoning and collaboration between users.

    List of papers
    1. Requirements for and Evaluation of User Support for Large-Scale Ontology Alignment
    Open this publication in new window or tab >>Requirements for and Evaluation of User Support for Large-Scale Ontology Alignment
    2015 (English)In: The Semantic Web. Latest Advances and New Domains: 12th European Semantic Web Conference, ESWC 2015, Portoroz, Slovenia, May 31 -- June 4, 2015. Proceedings, Springer Science+Business Media B.V., 2015, 3-20 p.Chapter in book (Refereed)
    Abstract [en]

    Currently one of the challenges for the ontology alignment community is the user involvement in the alignment process. At the same time, the focus of the community has shifted towards large-scale matching which introduces an additional dimension to this issue. This paper aims to provide a set of requirements that foster the user involvement for large-scale ontology alignment tasks.Further, we present and discuss the results of a literature study for 7 ontology alignments systems as well as a heuristic evaluation and an observational user study for 3 ontology alignment systems to reveal the coverage of the requirements in the systems and the support for the requirements in the user interfaces.

    Place, publisher, year, edition, pages
    Springer Science+Business Media B.V., 2015
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743 (print), 1611-3349 (online) ; 9088
    Keyword
    knowledge representation, ontologies, ontology alignment, user interfaces
    National Category
    Computer Sciences Human Computer Interaction
    Identifiers
    urn:nbn:se:liu:diva-118273 (URN)10.1007/978-3-319-18818-8_1 (DOI)000362439200001 ()978-3-319-18817-1 (ISBN)978-3-319-18818-8 (ISBN)
    Funder
    CUGS (National Graduate School in Computer Science)Swedish e‐Science Research Center
    Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2018-01-11Bibliographically approved
    2. User validation in ontology alignment
    Open this publication in new window or tab >>User validation in ontology alignment
    Show others...
    2016 (English)In: The Semantic Web - ISWC 2016: 15th International Semantic Web Conference, Kobe, Japan, October 17–21, 2016, Proceedings, Part I / [ed] Paul Groth, Elena Simperl, Alasdair Gray, Marta Sabou, Markus Krötzsch, Freddy Lecue, Fabian Flöck and Yolanda Gil, Cham, Switzerland: Springer Publishing Company, 2016, 200-217 p.Chapter in book (Refereed)
    Abstract [en]

    User validation is one of the challenges facing the ontology alignment community, as there are limits to the quality of automated alignment algorithms. In this paper we present a broad study on user validation of ontology alignments that encompasses three distinct but interrelated aspects: the profile of the user, the services of the alignment system, and its user interface. We discuss key issues pertaining to the alignment validation process under each of these aspects, and provide an overview of how current systems address them. Finally, we use experiments from the Interactive Matching track of the Ontology Alignment Evaluation Initiative (OAEI) 2015 to assess the impact of errors in alignment validation, and how systems cope with them as function of their services.

    Place, publisher, year, edition, pages
    Cham, Switzerland: Springer Publishing Company, 2016
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 9981
    Keyword
    knowledge representation, user interfaces, ontology engineering, ontology alignment
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-131806 (URN)10.1007/978-3-319-46523-4_13 (DOI)000389086500013 ()9783319465227 (ISBN)9783319465234 (ISBN)
    Funder
    Swedish e‐Science Research CenterCUGS (National Graduate School in Computer Science)EU, FP7, Seventh Framework Programme, FP7-IP-608142
    Available from: 2016-10-07 Created: 2016-10-07 Last updated: 2018-01-14Bibliographically approved
    3. A unified approach for aligning taxonomies and debugging taxonomies and their alignments
    Open this publication in new window or tab >>A unified approach for aligning taxonomies and debugging taxonomies and their alignments
    2013 (English)In: The Semantic Web: Semantics and Big Data: 10th International Conference, ESWC 2013, Montpellier, France, May 26-30, 2013. Proceedings / [ed] Philipp Cimiano, Oscar Corcho, Valentina Presutti, Laura Hollink, Sebastian Rudolph, Springer Berlin/Heidelberg, 2013, 1-15 p.Chapter in book (Refereed)
    Abstract [en]

    With the increased use of ontologies in semantically-enabled applications, the issues of debugging and aligning ontologies have become increasingly important. The quality of the results of such applications is directly dependent on the quality of the ontologies and mappings between the ontologies they employ. A key step towards achieving high quality ontologies and mappings is discovering and resolving modeling defects, e.g., wrong or missing relations and mappings. In this paper we present a unified framework for aligning taxonomies, the most used kind of ontologies, and debugging taxonomies and their alignments, where ontology alignment is treated as a special kind of debugging. Our framework supports the detection and repairing of missing and wrong is-a structure in taxonomies, as well as the detection and repairing of missing (alignment) and wrong mappings between ontologies. Further, we implemented a system based on this framework and demonstrate its benefits through experiments with ontologies from the Ontology Alignment Evaluation Initiative.

    Place, publisher, year, edition, pages
    Springer Berlin/Heidelberg, 2013
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743 (print), 1611-3349 (online) ; 7882
    Keyword
    Computer science, Database management, Information storage and retrieval systems, Artificial intelligence, Database Management, Database Management, Computer Science, general
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-93643 (URN)10.1007/978-3-642-38288-8_1 (DOI)978-3-642-38287-1 (ISBN)978-3-642-38288-8 (ISBN)
    Funder
    Swedish e‐Science Research CenterSwedish Research Council, 2010-4759CUGS (National Graduate School in Computer Science)
    Available from: 2013-06-04 Created: 2013-06-04 Last updated: 2018-01-11Bibliographically approved
    4. Applications of Large Displays: Advancing User Support in Large Scale Ontology Alignment
    Open this publication in new window or tab >>Applications of Large Displays: Advancing User Support in Large Scale Ontology Alignment
    2016 (English)In: Proceedings of the Doctoral Consortium at the 15th International Semantic Web Conference (ISWC 2016) Kobe, Japan, October 18, 2016 / [ed] Philippe Cudre-Mauroux, Natasha Noy and Riichiro Mizoguchi, Aachen, Germany: CEUR Workshop Proceedings , 2016, 50-57 p.Conference paper, Published paper (Refereed)
    Abstract [en]

    Producing alignments of the highest quality requires ‘humans in the loop’, however, user involvement is currently one of the challenges for the ontology alignment community. Ontology alignment is a cognitively intensive task and could be efficiently supported by user interfaces encompassing well-designed visualizations and interaction techniques. This work investigates the applicationof large, high-resolution displays to improve users’ cognitive support and identifies several promising directions for their application - improving ontologies’ and alignments’ navigation, supporting users’ thinking process and collaboration.

    Place, publisher, year, edition, pages
    Aachen, Germany: CEUR Workshop Proceedings, 2016
    Series
    CEUR Workshop Proceedings, ISSN 1613-0073 ; 1733
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-134161 (URN)
    Conference
    Doctoral Consortium at the 15th International Semantic Web Conference, October 18, Kobe, Japan
    Funder
    CUGS (National Graduate School in Computer Science)Swedish e‐Science Research CenterEU, FP7, Seventh Framework Programme, FP7-IP-608142
    Available from: 2017-01-26 Created: 2017-01-26 Last updated: 2018-01-13
    5. Experiences from the Anatomy track in the Ontology Alignment Evaluation Initiative
    Open this publication in new window or tab >>Experiences from the Anatomy track in the Ontology Alignment Evaluation Initiative
    2017 (English)In: Journal of Biomedical Semantics, ISSN 2041-1480, E-ISSN 2041-1480, Vol. 8, 56Article, review/survey (Refereed) Published
    Abstract [en]

    Background: One of the longest running tracks in the Ontology Alignment Evaluation Initiative is the Anatomy track which focuses on aligning two anatomy ontologies. The Anatomy track was started in 2005. In 2005 and 2006 the task in this track was to align the Foundational Model of Anatomy and the OpenGalen Anatomy Model. Since 2007 the ontologies used in the track are the Adult Mouse Anatomy and a part of the NCI Thesaurus. Since 2015 the data in the Anatomy track is also used in the Interactive track of the Ontology Alignment Evaluation Initiative.

    Results: In this paper we focus on the Anatomy track in the years 2007-2016 and the Anatomy part of the Interactive track in 2015-2016. We describe the data set and the changes it went through during the years. Further, we give an overview of all systems that participated in the track and the techniques they have used. We discuss the performance results of the systems and summarize the general trends.

    Conclusions: About 50 systems have participated in the Anatomy track. Many different techniques were used. The most popular matching techniques are string-based strategies and structure-based techniques. Many systems also use auxiliary information. The quality of the alignment has increased for the best performing systems since the beginning of the track and more and more systems check the coherence of the proposed alignment and implement a repair strategy.Further, interacting with an oracle is beneficial.

    Place, publisher, year, edition, pages
    BioMed Central, 2017
    Keyword
    ontologies, ontology matching, OAEI, anatomy
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-139775 (URN)10.1186/s13326-017-0166-5 (DOI)000416915300001 ()29202830 (PubMedID)
    Funder
    Swedish e‐Science Research CenterCUGS (National Graduate School in Computer Science)EU, FP7, Seventh Framework Programme, FP7-IP-608142
    Note

    Funding agencies: Swedish e-Science Research Centre (SeRC); Swedish national graduate school in computer science (CUGS); EU project VALCRI [FP7-IP-608142]

    Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2018-01-13
    6. Alignment Cubes: Towards Interactive Visual Exploration and Evaluation of Multiple Ontology Alignments
    Open this publication in new window or tab >>Alignment Cubes: Towards Interactive Visual Exploration and Evaluation of Multiple Ontology Alignments
    2017 (English)In: The Semantic Web: ISWC 2017 - 16th International Semantic Web Conference, Vienna, Austria, October 21-25, 2017, Proceedings, Part I / [ed] Claudia d'Amato, Miriam Fernandez, Valentina A. M. Tamma, Freddy Lecue, Philippe Cudre-Mauroux, Juan F. Sequeda, Christoph Lange and Jeff Heflin, Cham, Switzerland: Springer Publishing Company, 2017, 400-417 p.Chapter in book (Refereed)
    Abstract [en]

    Ontology alignment is an area of active research where many algorithms and approaches are being developed. Their performance is usually evaluated by comparing the produced alignments to a reference alignment in terms of precision, recall and F-measure. These measures, however, only provide an overall assessment of the quality of the alignments, but do not reveal differences and commonalities between alignments at a finer-grained level such as, e.g., regions or individual mappings. Furthermore, reference alignments are often unavailable, which makes the comparative exploration of alignments at different levels of granularity even more important. Making such comparisons efficient calls for a “human-in-the-loop” approach, best supported through interactive visual representations of alignments. Our approach extends a recent tool, Matrix Cubes, used for visualizing dense dynamic networks. We first identify use cases for ontology alignment evaluation that can benefit from interactive visualization, and then detail how our Alignment Cubes support interactive exploration of multiple ontology alignments. We demonstrate the usefulness of Alignment Cubes by describing visual exploration scenarios, showing how Alignment Cubes support common tasks identified in the use cases.

    Place, publisher, year, edition, pages
    Cham, Switzerland: Springer Publishing Company, 2017
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 10587
    Keyword
    Ontology alignment evaluation, Visual exploration, Multiple alignment comparison
    National Category
    Computer Sciences Human Computer Interaction
    Identifiers
    urn:nbn:se:liu:diva-141986 (URN)10.1007/978-3-319-68288-4_24 (DOI)9783319682877 (ISBN)9783319682884 (ISBN)9783319682884 (ISBN)
    Funder
    Swedish e‐Science Research CenterCUGS (National Graduate School in Computer Science)EU, FP7, Seventh Framework Programme, P7-IP-608142
    Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2018-01-13Bibliographically approved
  • Public defence: 2018-02-02 10:15 Planck, Fysikhuset, Linköping
    Lü, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
    Nano- and mesoscale morphology evolution of metal films on weakly-interacting surfaces2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thin films are structures consisting of one or several nanoscale atomic layers of material that are used to either functionalize a surface or constitute components in more complex devices. Many properties of a film are closely related to its microstructure, which allows films to be tailored to meet specific technological requirements. Atom-by-atom film growth from the vapor phase involves a multitude of atomic processes that may not be easily studied experimentally in real-time because they occur in small length- (≤ Å) and timescales (≤ ns). Therefore, different types of computer simulation methods have been developed in order to test theoretical models of thin film growth and unravel what experiments cannot show. In order to compare simulated and experimental results, the simulations must be able to model events on experimental time-scales, i.e. on the order of microseconds to seconds. This is achievable with the kinetic Monte Carlo (kMC) method.

    In this work, the initial growth stages of metal deposition on weakly-interacting substrates is studied using both kMC simulations as well as experiments whereby growth was monitored using in situ probes. Such film/substrate material combinations are widely encountered in technological applications including low-emissivity window coatings to parts of microelectronics components. In the first part of this work, a kMC algorithm was developed to model the growth processes of island nucleation, growth and coalescence when these are functions of deposition parameters such as the vapor deposition rate and substrate temperature. The dynamic interplay between these growth processes was studied in terms of the scaling behavior of the film thickness at the elongation transition, for both continuous and pulsed deposition fluxes, and revealed in both cases two distinct growth regimes in which coalescence is either active or frozen out during deposition. These growth regimes were subsequently confirmed in growth experiments of Ag on SiO2, again for both pulsed and continuous deposition, by measuring the percolation thickness as well as the continuous film formation thickness. However, quantitative agreement with regards to scaling exponents in the two growth regimes was not found between simulations and experiments, and this prompted the development of a method to determine the elongation transition thickness experimentally. Using this method, the elongation transition of Ag on SiO2 was measured, with scaling exponents found in much better agreement with the simulation results. Further, these measurement data also allowed the calculation of surface properties such as the terrace diffusion barrier of Ag on SiO2 and the average island coalescence rate.

    In the second part of this thesis, pioneering work is done to develop a fully atomistic, on-lattice model which describes the growth of Ag on weakly-interacting substrates. Simulations performed using this model revealed several key atomic-scale processes occurring at the film/substrate interface and on islands which govern island shape evolution, thereby contributing to a better understanding of how 3D island growth occurs at the atomic scale for a wide class of materials. The latter provides insights into the directed growth of metal nanostructures with controlled shapes on weakly-interacting substrates, including twodimensional crystals for use in catalytic and nano-electronic applications.

    List of papers
    1. Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films
    Open this publication in new window or tab >>Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films
    2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 4, 044302- p.Article in journal (Refereed) Published
    Abstract [en]

    The initial formation stages (i.e., island nucleation, island growth, and island coalescence) set characteristic length scales during growth of thin films from the vapour phase. They are, thus, decisive for morphological and microstructural features of films and nanostructures. Each of the initial formation stages has previously been well-investigated separately for the case of Volmer-Weber growth, but knowledge on how and to what extent each stage individually and all together affect the microstructural evolution is still lacking. Here we address this question using growth of Ag on SiO2 from pulsed vapour fluxes as a case study. By combining in situ growth monitoring, ex situ imaging and growth simulations we systematically study the growth evolution all the way from nucleation to formation of a continuous film and establish the effect of the vapour flux time domain on the scaling behaviour of characteristic growth transitions (elongation transition, percolation and continuous film formation). Our data reveal a pulsing frequency dependence for the characteristic film growth transitions, where the nominal transition thickness decreases with increasing pulsing frequency up to a certain value after which a steady-state behaviour is observed. The scaling behaviour is shown to result from differences in island sizes and densities, as dictated by the initial film formation stages. These differences are determined solely by the interplay between the characteristics of the vapour flux and time required for island coalescence to be completed. In particular, our data provide evidence that the steady-state scaling regime of the characteristic growth transitions is caused by island growth that hinders coalescence from being completed, leading to a coalescence-free growth regime.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-103920 (URN)10.1063/1.4890522 (DOI)000340710700078 ()
    Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2018-01-11
    2. Dynamic competition between island growth and coalescence in metal-on-insulator deposition
    Open this publication in new window or tab >>Dynamic competition between island growth and coalescence in metal-on-insulator deposition
    2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 16, 163107-1-163107-5 p.Article in journal (Refereed) Published
    Abstract [en]

    The morphology of thin metal films and nanostructures synthesized from the vapor phase on insulating substrates is strongly influenced by the coalescence of islands. Here, we derive analytically the quantitative criterion for coalescence suppression by combining atomistic nucleation theory and a classical model of coalescence. Growth simulations show that using this criterion, a coalescence-free growth regime can be reached in which morphological evolution is solely determined by island nucleation, growth, and impingement. Experimental validation for the ability to control the rate of coalescence using this criterion and navigate between different growth regimes is provided by in situ monitoring of Ag deposition on SiO2. Our findings pave the way for creating thin films and nanostructures that exhibit a wide range of morphologies and physical attributes in a knowledge-based manner.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2014
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-112133 (URN)10.1063/1.4900575 (DOI)000344363000073 ()
    Available from: 2014-11-17 Created: 2014-11-17 Last updated: 2018-01-11Bibliographically approved
    3. Coalescence-controlled and coalescence-free growth regimes during deposition of pulsed metal vapor fluxes on insulating surfaces
    Open this publication in new window or tab >>Coalescence-controlled and coalescence-free growth regimes during deposition of pulsed metal vapor fluxes on insulating surfaces
    2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 13, 134304Article in journal (Refereed) Published
    Abstract [en]

    The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the processes of island nucleation, growth, and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. These regimes can be accessed by tuning deposition conditions; however, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we derived the quantitative criterion to stop coalescence during continuous metal vapor flux deposition on insulating surfaceswhich typically yields 3-dimensional growthby describing analytically the competition between island growth by atomic incorporation and the coalescence rate of islands [Lu et al., Appl. Phys. Lett. 105, 163107 (2014)]. Here, we develop the analytical framework for entering a coalescence-free growth regime for metal vapor deposition on insulating substrates using pulsed vapor fluxes, showing that there exist three distinct criteria for suppressing coalescence that correspond to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using atomistic nucleation theory for pulsed vapor deposition to control morphology of thin films beyond the point of island density saturation. (C) 2015 AIP Publishing LLC.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2015
    National Category
    Manufacturing, Surface and Joining Technology
    Identifiers
    urn:nbn:se:liu:diva-117792 (URN)10.1063/1.49169831 (DOI)000352645100033 ()
    Note

    Funding Agencies|Linkoping University via the "LiU Research Fellows" program; Swedish Research Council [VR 621-2011-5312]; AForsk through the project "Towards Next Generation Energy Saving Windows"

    Available from: 2015-05-11 Created: 2015-05-08 Last updated: 2018-01-11
    4. Scaling of elongation transition thickness during thin-film growth on weakly interacting substrates
    Open this publication in new window or tab >>Scaling of elongation transition thickness during thin-film growth on weakly interacting substrates
    2017 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, no 8, 084101Article in journal (Refereed) Published
    Abstract [en]

    The elongation transition thickness (hElong) is a central concept in the theoretical description of thin-film growth dynamics on weakly interacting substrates via scaling relations of hElong with respect to rates of key atomistic film-forming processes. To date, these scaling laws have only been confirmed quantitatively by simulations, while experimental proof has been left ambiguous as it has not been possible to measure hElong. Here, we present a method for determining experimentally hElong for Ag films growing on amorphous SiO2: an archetypical weakly interacting film/substrate system. Our results confirm the theoretically predicted hElong scaling behavior, which then allow us to calculate the rates of adatom diffusion and island coalescence completion, in good agreement with the literature. The methodology presented herein casts the foundation for studying growth dynamics and cataloging atomistic-process rates for a wide range of weakly interacting film/substrate systems. This may provide insights into directed growth of metal films with a well-controlled morphology and interfacial structure on 2D crystals-including graphene and MoS2-for catalytic and nanoelectronic applications. Published by AIP Publishing.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2017
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-140966 (URN)10.1063/1.4993252 (DOI)000408570000044 ()2-s2.0-85028308625 (Scopus ID)
    Note

    Funding Agencies|Linkoping University (LiU) [Dnr-LiU-2015-01510]; Swedish research council [VR-2011-5312, VR-2015-04630]; Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC)

    Available from: 2017-09-19 Created: 2017-09-19 Last updated: 2018-01-11Bibliographically approved
  • Public defence: 2018-02-09 09:00 Berzeliussalen, Linköping
    Wilhelms, Susanne
    Linköping University, Department of Clinical and Experimental Medicine, Division of Surgery, Orthopedics and Oncology. Linköping University, Faculty of Medicine and Health Sciences.
    The epidemiology of severe sepsis in Sweden: Methodological aspects on the use of ICD coding in national registries2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Severe sepsis is characterized by acute organ dysfunction caused by an infection. Despite advanced treatment with antibiotics and organ support the mortality remains high. The epidemiological research on severe sepsis has expanded over the years but has led to conflicting results. In this thesis, we present evidence that some of these conflicting results may be explained by inappropriate methods used in epidemiological studies on severe sepsis. The definition of severe sepsis relies on consensus criteria including a number of clinical signs, parameters and laboratory findings. To facilitate large nation-wide studies on the incidence of severe sepsis in already existing administrative datasets, several investigators have attempted to mirror the clinical criteria by using combinations of the International Classification of Diseases (ICD) codes for infection and organ dysfunction. In paper I of this thesis, however, we found that three different ICD code abstraction strategies applied on the same dataset (the Swedish National Patient Register) generated three almost separate cohorts of patients. Furthermore, in paper II, where we followed intensive care unit (ICU)-treated patients with severe sepsis according to clinical consensus criteria to discharge, we observed that most patients did not meet any ICD code abstraction strategies for severe sepsis when reviewing their ICD codes registered at discharge from the hospital. In conclusion, the ICD code abstraction strategies previously used in the epidemiological research on sepsis seem to be inaccurate in the Swedish setting.  

    Sepsis may also result in poor long-term outcomes, and contribute to an increased risk of late mortality. However, the actual causes of late mortality in sepsis remain unclear. In paper III, we investigated causes of death over 1 year after treatment of sepsis in the ICU. In this study, a matched control group consisting of ICU-treated patients without sepsis was included. The most common causes of late mortality in both the sepsis group and the control group were heart diseases and cancer. The sepsis group, however, had a significantly increased incidence of infectious-related deaths compared with the control group, even over 1 year after the initial ICU event.   

    List of papers
    1. Assessment of incidence of severe sepsis in Sweden using different ways of abstracting International Classification of Diseases codes: Difficulties with methods and interpretation of results
    Open this publication in new window or tab >>Assessment of incidence of severe sepsis in Sweden using different ways of abstracting International Classification of Diseases codes: Difficulties with methods and interpretation of results
    2010 (English)In: CRITICAL CARE MEDICINE, ISSN 0090-3493, Vol. 38, no 6, 1442-1449 p.Article in journal (Refereed) Published
    Abstract [en]

    Objective: To compare three International Classification of Diseases code abstraction strategies that have previously been reported to mirror severe sepsis by examining retrospective Swedish national data from 1987 to 2005 inclusive. Design: Retrospective cohort study. Setting: Swedish hospital discharge database. Patients: All hospital admissions during the period 1987 to 2005 were extracted and these patients were screened for severe sepsis using the three International Classification of Diseases code abstraction strategies, which were adapted for the Swedish version of the International Classification of Diseases. Two code abstraction strategies included both International Classification of Diseases, Ninth Revision and International Classification of Diseases, Tenth Revision codes, whereas one included International Classification of Diseases, Tenth Revision codes alone. Interventions: None. Measurements and Main Results: The three International Classification of Diseases code abstraction strategies identified 37,990, 27,655, and 12,512 patients, respectively, with severe sepsis. The incidence increased over the years, reaching 0.35 per 1000, 0.43 per 1000, and 0.13 per 1000 inhabitants, respectively. During the International Classification of Diseases, Ninth Revision period, we found 17,096 unique patients and of these, only 2789 patients (16%) met two of the code abstraction strategy lists and 14,307 (84%) met one list. The International Classification of Diseases, Tenth Revision period included 46,979 unique patients, of whom 8% met the criteria of all three International Classification of Diseases code abstraction strategies, 7% met two, and 84% met one only. Conclusions: The three different International Classification of Diseases code abstraction strategies generated three almost separate cohorts of patients with severe sepsis. Thus, the International Classification of Diseases code abstraction strategies for recording severe sepsis in use today provides an unsatisfactory way of estimating the true incidence of severe sepsis. Further studies relating International Classification of Diseases code abstraction strategies to the American College of Chest Physicians/Society of Critical Care Medicine scores are needed.

    Place, publisher, year, edition, pages
    Williams and Wilkins, 2010
    Keyword
    epidemiology, sepsis, International Classification of Diseases, incidence, mortality, multiple organ failure
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-57412 (URN)10.1097/CCM.0b013e3181de4406 (DOI)000278231700008 ()
    Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2018-01-11
    2. Severe sepsis in the ICU is often missing in hospital discharge codes.
    Open this publication in new window or tab >>Severe sepsis in the ICU is often missing in hospital discharge codes.
    2017 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 61, no 2Article in journal (Refereed) Published
    Abstract [en]

    BACKGROUND: Different International Classification of Diseases (ICD)-based code abstraction strategies have been used when studying the epidemiology of severe sepsis. The aim of this study was to compare three previously used ICD code abstraction strategies to the American College of Chest Physicians/Society of Critical Care Medicine (ACCP/SCCM) consensus criteria for severe sepsis, in a setting of intensive care patients.

    METHODS: All patients (≥ 18 years of age) with severe sepsis according to the ACCP/SCCM criteria registered in the Swedish Intensive Care Registry (2005-2009) were included in the study. Using the Swedish National Patient Register, we investigated whether these patients fulfilled an ICD code compilation for severe sepsis at hospital discharge.

    RESULTS: Overall, 9271 patients with severe sepsis were registered in the Swedish Intensive Care Registry. A majority of these patients (55.4%) were discharged from the hospital with ICD codes that did not correspond to any of the ICD code compilations. A minority of patients (10.3%) were discharged with ICD codes corresponding to all three code abstraction strategies applied. Overall, the proportion of patients discharged with ICD codes corresponding to the criteria of Angus et al. was 15.1%, to the criteria of Flaatten was 39.8%, and to the criteria of Martin et al. was 16.0%.

    CONCLUSIONS: A majority of patients with severe sepsis according to the ACCP/SCCM criteria were not discharged with ICD codes corresponding to the ICD code abstraction strategies; thus, the abstraction strategies did not identify the correct patients.

    National Category
    Clinical Medicine
    Identifiers
    urn:nbn:se:liu:diva-133993 (URN)10.1111/aas.12814 (DOI)000394910200007 ()27699759 (PubMedID)
    Note

    Funding agencies: Region Ostergotland

    Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2018-01-11
  • Public defence: 2018-03-23 10:15 ACAS, A-huset, Linköping
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Cracks in superalloys2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Gas turbines are widely used in industry for power generation and as a power source at hard to reach locations where other possibilities for electrical power supplies are insufficient. New ways of producing greener energy is needed to reduce emission levels. This can be achieved by increasing the combustion temperature of gas turbines. High combustion temperatures can be detrimental and degrade critical components. This raises the demands on the high temperature performance of the superalloys used in gas turbine components. These components are frequently subjected to different cyclic loads combined with for example dwell-times and overloads at elevated temperatures, which can influence the crack growth. Dwell-times have been shown to accelerate crack growth and change cracking behaviour in both Inconel 718, Haynes 282 and Hastelloy X. On the other hand, overloads at the beginning of a dwell-time cycle have been shown to retard the dwell-time effect on crack growth in Inconel 718. More experiments and microstructural investigations are needed to better understand these effects.

    The work presented in this thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", where I have mainly looked at fatigue crack growth mechanisms in superalloys subjected to dwell-fatigue, which can have a devastating effect on crack propagation behaviour. Mechanical testing was performed under operation-like cycles in order to achieve representative microstructures and material data for the subsequent microstructural work. Microstructures were investigated using light optical microscopy and scanning electron microscopy (SEM) techniques such as electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). 

    The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at maximum load (0 % overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. The crack growth rate decreases with increasing overload levels in Inconel 718 when an overload is applied prior to the dwell-time. At high temperature, intergranular crack growth was observed in Inconel 718 as a result of oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along δ-phase boundaries with subsequent oxidation of the δ-phase. 

    This thesis comprises two parts. Part I gives an introduction to the field of superalloys and the acting microstructural mechanisms related to fatigue and crack propagation. Part II consists of five appended papers, which report the work completed as part of the project.

    List of papers
    1. Influence of Overloads on Dwell Time Fatigue Crack Growth in Inconel 718
    Open this publication in new window or tab >>Influence of Overloads on Dwell Time Fatigue Crack Growth in Inconel 718
    2014 (English)In: Materials Science and Engineering: A, Vol. 612, 398-405 p.Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ~700 °C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 °C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of branches in each crack. It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload. When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keyword
    nickel based superalloys, fatigue, fracture, mechanical charcterization, electron microscopy
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-109348 (URN)10.1016/j.msea.2014.06.068 (DOI)000340331300049 ()
    Available from: 2014-08-14 Created: 2014-08-14 Last updated: 2018-01-18Bibliographically approved
    2. Time- and Cycle-Dependent Crack Propagation in Haynes 282
    Open this publication in new window or tab >>Time- and Cycle-Dependent Crack Propagation in Haynes 282
    2016 (English)In: Journal of Materials Science and Engineering: A, ISSN 2161-6213, Vol. 658, 463-471 p.Article in journal (Refereed) Published
    Abstract [en]

    Haynes 282 is a promising superalloy candidate for several high-temperature applications in both aero and land-based gas turbine engines. To study the crack growth behaviour under time-dependent conditions relevant to such applications, a test program was carried out at room temperature up to 700 °C with conditions ranging from pure cyclic to sustained tensile loading. At 650 °C and high stress intensity factors the crack growth was fully time-dependent for dwell-times of 90 s and longer. At lower stress intensities, the behaviour was mainly controlled by the cyclic loading, even under dwell conditions. The behaviour under dwell-fatigue conditions was well described by a liner superposition model.

    Place, publisher, year, edition, pages
    Elsevier, 2016
    Keyword
    Nickel based superalloys, fatigue, fracture, mechanical characterisation, electron microscopy
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-126922 (URN)10.1016/j.msea.2016.01.111 (DOI)000372560800054 ()
    Note

    At the time for thesis presentation publication was in status: Manuscript

    Name of manuscript was: Time-dependent crack propagation in Haynes 282

    Funding agencies: Agora Materiae, graduate school, Faculty grant SFO-MAT-LiU [2009-00971]; Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research program TURBO POWER

    Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2018-01-18Bibliographically approved
    3. Anisotropy Effects During Dwell-fatigue Caused by δ-phase Orientation in Forged Inconel 718
    Open this publication in new window or tab >>Anisotropy Effects During Dwell-fatigue Caused by δ-phase Orientation in Forged Inconel 718
    2017 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, no 692, 174-181 p.Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is a commonly used superalloy for turbine discs in the gas turbine industry. Turbine discs are often subjected to dwell-fatigue as a result of long constant load cycles. The effect of anisotropy on dwell-fatigue cracking in forged turbine discs have not yet been thoroughly investigated. Crack propagation behaviour was characterised using compact tension (CT) samples cut in different orientations from a real turbine disc forging. Samples were also cut in two different thicknesses in order to investigate the influence of plane strain and plane stress condition on the crack propagation rates. The samples were subjected to dwell-fatigue tests at 550 °C with 90 s or 2160 s dwell-times at maximum load. Microstructure characterisation was done using scanning electron microscopy (SEM) techniques such as electron channelling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and light optical microscopy (LOM). The forged alloy exhibits strong anisotropic behaviour caused by the non-random δ-phase orientation. When δ-phases were oriented perpendicular compared to parallel to the loading direction, the crack growth rates were approximately ten times faster. Crack growth occurred preferably in the interface between the γ-matrix and the δ-phase.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keyword
    Anisotropy, Nickel-based superalloys, Fatigue, Mechanical characterisation, Scanning electron microscopy
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-135825 (URN)10.1016/j.msea.2017.03.063 (DOI)000400718400021 ()
    Note

    Funding agencies: Agora Materiae, graduate school, Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Sy

    Available from: 2017-03-24 Created: 2017-03-24 Last updated: 2018-01-18
    4. Grain Size Depending Dwell-Fatigue Crack Growth in Inconel 718
    Open this publication in new window or tab >>Grain Size Depending Dwell-Fatigue Crack Growth in Inconel 718
    2018 (English)In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, 1-7 p.Article in journal (Refereed) Published
    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2018
    Keyword
    electron microscopy, fatigue, fracture, mechanical characterzation, nickel base superalloys
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-144395 (URN)10.1002/adem.201700930 (DOI)
    Available from: 2018-01-18 Created: 2018-01-18 Last updated: 2018-01-18