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  • Public defence: 2019-08-27 09:15 Planck, Fysikhuset, Linköping
    Yuan, Zhongcheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Defects and crystallinity control of perovskite films for light-emitting diodes2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Metal halide perovskites are promising materials for the fabrication of cost-effective and highperformance light-emitting diodes (LEDs), due to their solution processability, high photoluminescence quantum efficiencies (PLQEs) and excellent charge transport properties. Importantly, perovskite LEDs show ultra-pure emission color, which is better than that of the state-of-the-art quantum dot LEDs (QLEDs) and organic LEDs (OLEDs), demonstrating a bright application potential for realizing vivid natural colors display in the future.

    In this thesis, we first incorporate natural molecules, e.g. deoxyribonucleic acid (DNA), to passivate FAPbI3 perovskite films. We notice that the existence of carbonyl and amide groups within DNA are important for efficient passivation of perovskite films. Combining the knowledge, we further introduce amino-functionalized molecules into perovskite films and achieve significantly improved efficiency of 21.6 %, which is a record external quantum efficiency (EQE) of perovskite LEDs. We reveal that by weakening the hydrogen bond strength between passivation molecules and organic cations, the interaction between passivation amino groups and defects improves, contributing to more efficient passivation.

    We also notice that the underlying substrates play important roles on the film quality of perovskite and the device performance of the ensuing LEDs. Here, we reveal that efficient deprotonation of the undesirable organic cations (Methylammonium (MA+) or Formamidinium (FA+)) by a metal oxide interlayer, e.g. ZnO, with a high isoelectric point, is critical to promote the transition from intermediate phases to highly emissive perovskites. We reveal synergistic effects of precursor stoichiometry and interfacial reactions for high-performance perovskite LEDs, and establish useful guidelines for rational device optimisation. With the knowledge we obtain from the deprotonation process, we further push the EL emission from near-infrared (NIR) (around 800 nm) region to deep red emission (around 700 nm) via cation exchange process between cesium (Cs+) and FA+, which promotes enhanced crystallization of the perovskite films and devices performance simultaneously.

    Intensive efforts in the perovskite community have pushed the EQEs of perovskite LEDs to over 20 %for green, red and NIR emission region. However, it is still a long way to go before their practical applications. We believe that efficient control of both the defects and crystallinity of the perovskite films through rational materials development and interfacial modifications is important for the development of perovskite optoelectronic devices. In addition, both our findings on the perovskite film quality control are universal and provide insights to promote the development of perovskites (especially the hybrid ones containing organic components) for the applications of other optoelectronic devices.

    List of papers
    1. Rational molecular passivation for high-performance perovskite light-emitting diodes
    Open this publication in new window or tab >>Rational molecular passivation for high-performance perovskite light-emitting diodes
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    2019 (English)In: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893, Vol. 13, no 6, p. 418-424Article in journal (Refereed) Published
    Abstract [en]

    A major efficiency limit for solution-processed perovskite optoelectronic devices, for example light-emitting diodes, is trap-mediated non-radiative losses. Defect passivation using organic molecules has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures influence the effectiveness of passivation. We show that the so far largely ignored hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring in the perovskite, we significantly enhance the interaction with defect sites and minimize non-radiative recombination losses. Consequently, we achieve exceptionally high-performance near-infrared perovskite light-emitting diodes with a record external quantum efficiency of 21.6%. In addition, our passivated perovskite light-emitting diodes maintain a high external quantum efficiency of 20.1% and a wall-plug efficiency of 11.0% at a high current density of 200 mA cm−2, making them more attractive than the most efficient organic and quantum-dot light-emitting diodes at high excitations.

    Place, publisher, year, edition, pages
    Springer Nature Publishing AG, 2019
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-157707 (URN)10.1038/s41566-019-0390-x (DOI)000468752300019 ()
    Note

    Funding agencies:  ERC Starting Grant [717026]; National Basic Research Program of China (973 Program) [2015CB932200]; National Natural Science Foundation of China [61704077, 51572016, 51721001, 61634001, 61725502, 91733302, U1530401]; Natural Science Foundation of Jiangsu 

    Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-07-01Bibliographically approved
    2. Room-temperature film formation of metal halide perovskites on n-type metal oxides: the catalysis of ZnO on perovskite crystallization
    Open this publication in new window or tab >>Room-temperature film formation of metal halide perovskites on n-type metal oxides: the catalysis of ZnO on perovskite crystallization
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    2018 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 50, p. 6887-6890Article in journal (Refereed) Published
    Abstract [en]

    We investigate the effect of commonly used solution-processed TiOx, SnO2 and ZnO interlayers on the perovskite film crystallization process. We find that the ZnO/perovskite interface can efficiently catalyze the perovskite crystallization even without thermal annealing.

    Place, publisher, year, edition, pages
    ROYAL SOC CHEMISTRY, 2018
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-149712 (URN)10.1039/c8cc02482k (DOI)000436029000052 ()29781476 (PubMedID)
    Note

    Funding Agencies|ERC [717026]; Carl Tryggers Stiftelse; European Commission [691210]; China Scholarship Council; VINNMER Marie Curie Fellowships

    Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2019-06-19
  • Public defence: 2019-09-02 13:00 Belladonnasalen, Linköping
    Bergkvist, Max
    Linköping University, Department of Clinical and Experimental Medicine, Division of Surgery, Orthopedics and Oncology. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Anaesthetics, Operations and Specialty Surgery Center, Department of Hand and Plastic Surgery.
    Studies on Polarised Light Spectroscopy2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis project focuses on measurements of dermal microcirculation during vascular provocations with polarised light spectroscopy. This is done with a non-invasive method commercially available as Tissue viability imaging (TiVi) which measures concentration and oxygenation of red blood cells in the papillary dermis. Three studies were done with human subjects and one with an animal model, to validate and compare the TiVi technique with laser Doppler flowmetry, which is an established method of measuring dermal microcirculation.

    The TiVi consists of a digital camera with polarisation filters in front of the flash and lens, with software for analysis of the picture. When taking a picture with the TiVi, the polarised light that is reflected on the skin surface is absorbed by the second filter over the lens (which is perpendicular to the first filter) but a portion of light penetrates the surface of the skin and is scattered when it is reflected on tissue components. This makes the light depolarised, passes the second filter, and produces a picture for analysis. The red blood cell (RBC) has a distinct absorption pattern that differs between red and green colour compared to melanin and other components of tissue. This difference is used by the software that calculates differences in each picture element and produces a measure of output which is proportional to the concentration of red blood cells. The oxygenation of RBC can also be calculated, as there is a difference in absorption depending on oxygen state.

    The first paper takes up possible sources of error such as ambient light, and the angle and distance of the camera. The main experiment was to investigate how the local heating reaction is detected with TiVi compared to LDF.

    In the second paper arterial and venous stasis are examined in healthy subjects with TiVi.

    The Third paper is an animal study where skin flaps were raised on pigs, and the vascular pedicle is isolated to enable control of inflow and outflow of blood.The measurements were made during partial venous, total venous, and total arterial occlusion. The TiVi recorded changes in the concentration of RBC, oxygenation and heterogeneity and the results were compared with those of laser Doppler flowmetry.

    In the fourth paper oxygenation and deoxygenation of RBC: s was studied. Studies were made on the forearms of healthy subjects who were exposed to arterial and venous occlusion. Simultaneous measurements were made with TiVi and Enhanced perfusion and oxygen saturation or EPOS, which is a new device that combines laser Doppler flowmetry and diffuse reflectance spectroscopy in one probe.

    With TiVi, one can measure RBC concentration and oxygenation in the area of an entire picture or in one or multiple user defined regions of interest (ROI). Methods such as laser Doppler flowmetry makes single point measurements, which is a potential source of error both because of the heterogeneity of the microcirculation, and that the circulation be insufficient in the margins of the investigated area. TiVi has been able to measure venous stasis more accurately than laser Doppler flowmetry, and venous stasis is the more common reason for flaps to fail.

    The TiVi is an accurate way to measure the concentration of RBC and trends in oxygenation of the dermal microcirculation. It has interesting possible applications for microvascular and dermatological research, monitoring of flaps, and diagnosis of peripheral vascular disease. Future clinical studies are needed as well as development of the user interface.  

    List of papers
    1. Polarized Light Spectroscopy for Measurement of the Microvascular Response to Local Heating at Multiple Skin Sites
    Open this publication in new window or tab >>Polarized Light Spectroscopy for Measurement of the Microvascular Response to Local Heating at Multiple Skin Sites
    2012 (English)In: Microcirculation, ISSN 1073-9688, E-ISSN 1549-8719, Vol. 19, no 8, p. 705-713Article in journal (Refereed) Published
    Abstract [en]

    Objective: To evaluate whether TiVi, a technique based on polarized light, could measure the change in RBC concentration during local heating in healthy volunteers. Methods: Using a custom-made transparent heater, forearm skin was heated to 42 degrees C for 40 minutes while the change in RBC concentration was measured with TiVi. The perfusion response during local heating was measured at the same time with Laser Doppler flowmetry. Results: Mean RBC concentration increased (91 +/- 34 vs. 51 +/- 34 A.U. at baseline, p less than 0.001). The spatial heterogeneity of the RBC concentration in the measured skin areas was 26 +/- 6.4% at baseline, and 23 +/- 4.6% after 40 minutes of heating. The mean RBC concentrations in two skin sites were highly correlated (0.98 at baseline and 0.96 after 40 minutes of heating). The change in RBC concentration was less than the change in perfusion, measured with LDF. Unlike with LDF, a neurally mediated peak was not observed with TiVi in most of the test subjects. Conclusions: TiVi is a valuable technique for measuring the microvascular response to local heating in the skin, and offers a high reproducibility for simultaneous measurements at different skin sites, provided carefully controlled experiments are ensured.

    Place, publisher, year, edition, pages
    Informa Healthcare / John Wiley and Sons, 2012
    Keywords
    tissue viability imaging; polarization light spectroscopy; local heating; red blood cell concentration; reproducibility
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-87225 (URN)10.1111/j.1549-8719.2012.00203.x (DOI)000311373400004 ()
    Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2019-07-23
    2. Assessment of microcirculation of the skin using Tissue Viability Imaging: A promising technique for detecting venous stasis in the skin
    Open this publication in new window or tab >>Assessment of microcirculation of the skin using Tissue Viability Imaging: A promising technique for detecting venous stasis in the skin
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    2015 (English)In: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 101, p. 20-25Article in journal (Refereed) Published
    Abstract [en]

    Background: : Venous occlusion in the skin is difficult to detect by existing measurement techniques. Our aim was to find out whether Tissue Viability Imaging (TiVi) was better at detecting venous occlusion by comparing it with results of laser Doppler flowmetry (LDF) during graded arterial and venous stasis in human forearm skin. Methods: : Arterial and venous occlusions were simulated in 10 healthy volunteers by inflating a blood pressure cuff around the upper right arm. Changes in the concentration of red blood cells (RBC) were measured using TiVi, while skin perfusion and concentration of moving red blood cells (CMBC) were measured using static indices of LDF during exsanguination and subsequent arterial occlusion, postocclusive reactive hyperaemia, and graded increasing and decreasing venous stasis. Results: : During arterial occlusion there was a significant reduction in the mean concentration of RBC from baseline, as well as in perfusion and CMBC (p less than 0.008). Venous occlusion resulted in a significant 28% increase in the concentration of RBC (p = 0.002), but no significant change in perfusion (mean change -14%) while CMBC decreased significantly by 24% (p = 0.02). With stepwise increasing occlusion pressures there was a significant rise in the TiVi index and reduction in perfusion (p = 0.008), while the reverse was seen when venous flow was gradually restored. Conclusion: : The concentration of RBC measured with TiVi changes rapidly and consistently during both total and partial arterial and venous occlusions, while the changes in perfusion, measured by LDF, were less consistent This suggests that TiVi could be a more useful, non-invasive clinical monitoring tool for detecting venous stasis in the skin than LDF.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Tissue viability imaging; Laser Doppler flowmetry; Post-occusive hyperaemia; Venous occlusion; Arterial occlusion
    National Category
    Clinical Medicine
    Identifiers
    urn:nbn:se:liu:diva-121302 (URN)10.1016/j.mvr.2015.06.002 (DOI)000360028500004 ()26092681 (PubMedID)
    Note

    Funding Agencies|County Council of Ostergotland, Sweden [2014JZ0004]

    Available from: 2015-09-16 Created: 2015-09-14 Last updated: 2019-07-23Bibliographically approved
    3. Vascular Occlusion in a Porcine Flap Model: Effects on Blood Cell Concentration and Oxygenation.
    Open this publication in new window or tab >>Vascular Occlusion in a Porcine Flap Model: Effects on Blood Cell Concentration and Oxygenation.
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    2017 (English)In: Plastic and reconstructive surgery. Global open, ISSN 2169-7574, Vol. 5, no 11, article id e1531Article in journal (Refereed) Published
    Abstract [en]

    Background: Venous congestion in skin flaps is difficult to detect. This study evaluated the ability of tissue viability imaging (TiVi) to measure changes in the concentration of red blood cells (CRBC), oxygenation, and heterogeneity during vascular provocations in a porcine fasciocutaneous flap model.

    Methods: In 5 pigs, cranial gluteal artery perforator flaps were raised (8 flaps in 5 pigs). The arterial and venous blood flow was monitored with ultrasonic flow probes. CRBC, tissue oxygenation, and heterogeneity in the skin were monitored with TiVi during baseline, 50% and 100% venous occlusion, recovery, 100% arterial occlusion and final recovery, thereby simulating venous and arterial occlusion of a free fasciocutaneous flap. A laser Doppler probe was used as a reference for microvascular perfusion in the flap.

    Results: During partial and complete venous occlusion, increases in CRBC were seen in different regions of the flap. They were more pronounced in the distal part. During complete arterial occlusion, CRBC decreased in all but the most distal parts of the flap. There were also increases in tissue oxygenation and heterogeneity during venous occlusion.

    Conclusions: TiVi measures regional changes in CRBC in the skin of the flap during arterial and venous occlusion, as well as an increase in oxygenated hemoglobin during venous occlusion that may be the result of reduced metabolism and impaired delivery of oxygen to the tissue. TiVi may provide a promising method for measuring flap viability because it is hand-held, easy to-use, and provides spatial information on venous congestion.

    Place, publisher, year, edition, pages
    Wolters Kluwer, 2017
    National Category
    Radiology, Nuclear Medicine and Medical Imaging Surgery
    Identifiers
    urn:nbn:se:liu:diva-145391 (URN)10.1097/GOX.0000000000001531 (DOI)29263951 (PubMedID)2-s2.0-85038559789 (Scopus ID)
    Available from: 2018-02-27 Created: 2018-02-27 Last updated: 2019-07-23Bibliographically approved
  • Public defence: 2019-09-06 09:00 Originalet, Qulturum, Jönköping
    Taxbro, Knut
    Linköping University, Department of Medical and Health Sciences, Division of Drug Research. Linköping University, Faculty of Medicine and Health Sciences.
    Vascular access in cancer patients – clinical implications2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Central venous catheters (CVC) are vital for patients receiving chemotherapy not compatible with peripheral infusion. Thousands of centrally and peripherally inserted central venous catheters are inserted into patients with cancer each year. All types of intravascular catheters are associated with complications. These complications may be divided into infectious, thrombotic, mechanical and occlusive events. All of these events have the potential to harm patients and cause additional expense for the health-care system. Furthermore, the above-mentioned complications are largely avoidable through proper patient selection, insertion technique, hygiene precautions and catheter maintenance.

    Catheter-related infections and deep venous thrombosis are the two most common and feared CVC related complications. Infection in a catheter can cause lifethreatening bacteraemia, and thrombosis can lead to pulmonary embolisation, post-thrombotic syndrome and stenosis of the vessel affected. Many studies describing methods to minimise infectious complications associated with central venous catheters have been carried out. These methods appear to have been implemented in most modern advanced healthcare facilities resulting in a continual decrease in catheter-related infections over the last two decades. New implantation techniques, fewer infections and better catheter materials are likely to have contributed to the reduction in the incidence of catheter-related deep venous thrombosis (CR-DVT). Peripherally inserted central venous catheters (PICC) and subcutaneously implanted vascular access ports (PORT) are two very commonly used catheter devices for delivery of chemotherapy. International guidelines are unclear as to which device to choose due to the paucity of controlled trials.

    The aim of this thesis was to study complications related to central venous access devices used over long periods of time, usually for the delivery of chemotherapy. Vascular access in cancer patients – clinical implications We prospectively studied PORT complications (Study 1) over a six-month follow- up period. In Study 2, we assessed the number of common CVC-related micro- organisms that are transferred across PORT membrane contaminated by a controlled suspension of micro-organisms when a non-coring access needle is inserted using two different techniques. In the largest randomised controlled trial published on this topic (Study 3), we compared PICC with PORT regarding CRDVT and other catheter-related complications. The economic implications of using PICC or PORT were assessed from health-care system´s perspective (Study 4), using data on adverse events and clinical factors (implantation, treatments and dwell-time) from Study 3.

    Chemotherapy against various forms of cancer is very common. Implantation of PORT is one of the ten most common surgical procedures in Sweden according to the Swedish Perioperative Register. Hence, the topic in this thesis may be clinically relevant to many patients and their health care providers.

    We found that the incidence of catheter-related blood stream infection was very low in the cohorts studied. In general, PICCs are associated with significantly more CR-DVTs and adverse events than PORTs. The cost to the health-care system when using PICC is higher than for PORT when complications are included. Given the choice, patients about to commence chemotherapy appear to prefer PORT to PICC. PORT implantation is more painful than PICC insertion, but PICC appears to influence activities of daily life more than PORT.

    List of papers
    1. A prospective observational study on 249 subcutaneous central vein access ports in a Swedish county hospital
    Open this publication in new window or tab >>A prospective observational study on 249 subcutaneous central vein access ports in a Swedish county hospital
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    2013 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 52, no 5, p. 893-901Article in journal (Refereed) Published
    Abstract [en]

    Background. Reliable central vein access is a fundamental issue in modern advanced oncological care. The aim of this study was to determine the incidence of complications and patient perception regarding central vein access ports. Methods. We prospectively studied 249 single lumen access ports implanted between 1 July 2008 and 15 March 2010 in a mixed patient population at a 500-bed secondary level hospital in Sweden. We determined the number of catheter days, infection rate and mechanical complications, as well as patient satisfaction regarding the access port, over a six-month follow-up period. Results. Two hundred and forty-four different patients received 249 ports yielding a total of 37 763 catheter days. Ultrasound and fluoroscopic guidance was used in 98% of procedures. Vein access was obtained percutanously by an anaesthesiologist in all cases. There was no case of pneumo- or haemothorax. The incidence of catheter-related bloodstream infection, was 0.05/1000 catheter days and the incidence of pocket/tunnel infection was 0.39/1000 catheter days. Clinically apparent deep vein thrombosis occurred in four patients (1.6%). Patient satisfaction was overall high. Conclusion. These results confirm that our team-based approach with written easily accessible evidence-based guidelines and a structured education programme leads to a very low complication rate and a high degree of patient satisfaction.

    Place, publisher, year, edition, pages
    Informa Healthcare, 2013
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-93959 (URN)10.3109/0284186X.2013.770601 (DOI)000318655300003 ()
    Note

    Funding Agencies|Futurum - the Academy for Healthcare, Jonkoping County Council, Jonkoping, Sweden||

    Available from: 2013-06-13 Created: 2013-06-13 Last updated: 2019-07-23
    2. Clinical impact of peripherally inserted central catheters vs implanted port catheters in patients with cancer: an open-label, randomised, two-centre trial
    Open this publication in new window or tab >>Clinical impact of peripherally inserted central catheters vs implanted port catheters in patients with cancer: an open-label, randomised, two-centre trial
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    2019 (English)In: British Journal of Anaesthesia, ISSN 0007-0912, E-ISSN 1471-6771, Vol. 122, no 6, p. 734-741Article in journal (Refereed) Published
    Abstract [en]

    Background

    Centrally inserted totally implanted vascular access ports (PORTs) and peripherally inserted central catheters (PICCs) are widely used for the administration of chemotherapy. Our aim was to study the incidence of catheter-related deep venous thrombosis in patients with cancer receiving chemotherapy through either a PICC or a PORT.

    Methods

    Adults with non-haematological cancer (mainly breast and colorectal) from two Swedish oncology centres were included and followed for up to 1 yr. Patients were randomly assigned to receive a single-lumen PICC or PORT. The primary end point was the occurrence of a clinically significant catheter-related deep venous thrombosis, and the secondary end point was a composite of adverse events related to the catheter: insertion complication, thrombosis, occlusion, infection, and mechanical problems.

    Results

    The trial recruited 399 participants (PICC, n=201; PORT, n=198) between March 2013 and February 2017. The PICCs were associated with 16 (8%) deep venous thromboses compared with two (1%) in the PORT group (HR=10.2; 95% confidence interval, 2.3–44.6; P=0.002). The overall incidence of composite adverse events was higher for patients with a PICC compared with those with a PORT (HR=2.7; 95% confidence interval, 1.6–4.6; P<0.001).

    Conclusions

    PICCs are associated with higher risk for catheter-related deep venous thrombosis and other adverse events when compared with PORTs. This increased risk should be considered when choosing a vascular access device for chemotherapy, especially in patients with solid malignancy.

    Place, publisher, year, edition, pages
    Elsevier, 2019
    Keywords
    central venous catheter; central venous catheter thrombosis; peripherally inserted central catheter line insertion; vascular access devices
    National Category
    Surgery
    Identifiers
    urn:nbn:se:liu:diva-158319 (URN)10.1016/j.bja.2019.01.038 (DOI)000467806400034 ()31005243 (PubMedID)2-s2.0-85064326103 (Scopus ID)
    Note

    Funding Agencies|Futurum (Academy for Healthcare, Jonkoping County Council, Sweden) [767451]; FORSS (Research Council in South East Sweden) [295881]

    Available from: 2019-07-02 Created: 2019-07-02 Last updated: 2019-08-12Bibliographically approved
  • Public defence: 2019-09-09 10:00 ACAS, A-huset, Linköping
    Farhad, Nandita
    Linköping University, Department of Management and Engineering, Industrial Economics. Linköping University, Faculty of Science & Engineering.
    Supply Chain Governance for Social Sustainability: A Study of the Ready-Made Garment Industry in Bangladesh2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This PhD thesis approaches the phenomenon of supply chain governance for social sustainability in the ready-made garment industry in Bangladesh. This research is based on a study of eight large multinational corporations (e.g. clothing brands and retailers) and their ready-made garment suppliers. The purpose of this research is to understand how supply chain governance mechanisms and governance structures improve social sustainability performance when stakeholders are engaged.

    The study identifies four main governance systems, namely, market-based, hierarchical controlbased, collaborative multi-stakeholder-based and relational cross-sectoral-based. These governance systems are employed in the supply chain by the multinational corporations in combination with different stakeholders, such as suppliers, multi-stakeholder-initiatives, and non-government organisations. The study focuses on the challenges faced by the multinational corporations to ensure social sustainability, whilst at the same time, incorporating suppliers’ viewpoints on the consequences of different governance systems for social sustainability.

    This research shows the choice of governance structures from market-based, hierarchy-based, collaboration-based and relational-based depend on the cost of managing relationships with the stakeholders and potential risks of governance in a given situation. An effective governance structure for a multinational corporation in a particular context is determined by how well the structure supports governance mechanisms to reduce associated transaction risks that results from potential opportunistic behaviour of the suppliers. In this research, it is argued that governance structure provides the platform for practicing a set of governance mechanisms.

    The study claims that social sustainability governance incorporates three mechanisms with separate outcomes: one consists of buyer-driven control-based mechanisms which include codes of conduct, supplier assessment and monitoring, and supplier training for regular social compliance; the second consists of multi-stakeholder-based governance mechanisms for structural compliance when unexpected problems occur, for example, building collapse, electrical and fire safety risks emerge; and the third comprises cross-sectoral governance mechanisms when the multinational corporations involve with non-government organisations for social development of the garment workers and community by facilitating drinking water, health-hygiene, education, and so on.

    This thesis contributes to the Sustainable Supply Chain Management literature by expanding knowledge of supply chain governance through bringing an understanding of governance mechanisms, governance structures and stakeholder engagements for social sustainability. As the demand for supply chain governance for social sustainability are growing, this thesis can help responsible corporate sourcing managers to develop a deeper understanding of how supply chain governance can affect social sustainability. 

  • Public defence: 2019-09-12 09:00 Berzeliussalen, Linköping
    Vahdat Shariatpanahi, Aida
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    The Importance of Macrophages, Lipid Membranes and Seeding in Experimental AA Amyloidosis2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Amyloidosis is a group of protein misfolding diseases caused by tissue deposition of fibrillary protein aggregates termed amyloid. Amyloid A (AA) amyloidosis is a systemic form of amyloidosis that occurs as a complication of chronic inflammatory diseases, such as rheumatoid arthritis, familial Mediterranean fever and chronic infections, such as tuberculosis. AA amyloid is derived from the precursor protein serum amyloid A and is deposited in several organs preferably kidneys, liver and spleen. AA amyloidosis can be induced in mice by long standing inflammatory stimulation and concurrent administration of tissue extracts of AA amyloid, referred to as amyloid enhancing factor (AEF), reduces the time for amyloid deposition in the marginal zone of the spleen from 5 weeks to 2 days. The general aim of this thesis was to investigate the mechanisms involved in the development of AA amyloid in the mouse model of AA amyloidosis.

    Amyloid was induced in inflamed mice by injection of AEF and amyloid toxicity to splenic macrophages was investigated. We found that the marginal zone macrophages were very sensitive to amyloid formation and increasing amyloid load caused progressive depletion of these cells, whereas red pulp macrophages and metallophilic marginal zone macrophages appeared unaffected. To clarify the role of splenic macrophages in amyloidogenesis, macrophages were depleted by clodronate containing liposomes. We displayed that in the absence of splenic macrophages, especially marginal zone macrophages, amyloid formation was delayed implying a crucial role of macrophages in amyloid formation.

    The effect of lipid membranes on amyloid formation was studied and we showed that liposomes exhibited an amyloidogenic effect in inflamed mice although not as powerful as AEF. Following the fate of the liposomes, we showed that liposomes were rapidly cleared by uptake in the spleen and liver and colocalized with lysosomes. A tentative mechanism might be that accumulation of liposomes in lysosomes interfere with the SAA degradation process facilitating amyloid formation.

    Finally the conformational properties of two AEF (AEF1 and AEF2) preparations were studied using conformation sensitive luminescent-conjugated oligothiophenes (LCOs). We found that AEF1 and AEF2 displayed significantly different ultrastructure as well as conformation and consequently induced different cytotoxicity in vitro. Inducing amyloid formation in inflamed mice by AEF1 and AEF2 revealed that the polymorph of the amyloid aggregates was replicated in vivo.

    In summary, the results obtained in this thesis indicate an important role for macrophages for the formation of amyloid. The existence of amyloid strains has long been an in vitro finding, but the finding that AEF ultrastructure drives the morphology of newly formed amyloid in vivo opens up for new studies that can help us to understand the formation of homologous and heterologous fibrils. Thus, the fundamental mechanisms of various amyloid diseases are similar and the results presented in the thesis can increase the understanding of other amyloid diseases.

    List of papers
    1. Depletion of Spleen Macrophages Delays AA Amyloid Development: A Study Performed in the Rapid Mouse Model of AA Amyloidosis
    Open this publication in new window or tab >>Depletion of Spleen Macrophages Delays AA Amyloid Development: A Study Performed in the Rapid Mouse Model of AA Amyloidosis
    2013 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 11, p. e79104-Article in journal (Refereed) Published
    Abstract [en]

    AA amyloidosis is a systemic disease that develops secondary to chronic inflammatory diseases Macrophages are often found in the vicinity of amyloid deposits and considered to play a role in both formation and degradation of amyloid fibrils. In spleen reside at least three types of macrophages, red pulp macrophages (RPM), marginal zone macrophages (MZM), metallophilic marginal zone macrophages (MMZM). MMZM and MZM are located in the marginal zone and express a unique collection of scavenger receptors that are involved in the uptake of blood-born particles. The murine AA amyloid model that resembles the human form of the disease has been used to study amyloid effects on different macrophage populations. Amyloid was induced by intravenous injection of amyloid enhancing factor and subcutaneous injections of silver nitrate and macrophages were identified with specific antibodies. We show that MZMs are highly sensitive to amyloid and decrease in number progressively with increasing amyloid load. Total area of MMZMs is unaffected by amyloid but cells are activated and migrate into the white pulp. In a group of mice spleen macrophages were depleted by an intravenous injection of clodronate filled liposomes. Subsequent injections of AEF and silver nitrate showed a sustained amyloid development. RPMs that constitute the majority of macrophages in spleen, appear insensitive to amyloid and do not participate in amyloid formation.

    Place, publisher, year, edition, pages
    Public Library of Science, 2013
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-102982 (URN)10.1371/journal.pone.0079104 (DOI)000327254700092 ()
    Note

    Funding Agencies|Swedish Research Council|GTW5343|County Council of Ostergotland Magnus Bergvalls research foundation||Ingrid Svenssons research foundation||Broderna Karlssons research foundation||Hildur Pettersons research foundation||

    Available from: 2014-01-09 Created: 2014-01-09 Last updated: 2019-08-15
    2. Lipid membranes accelerate amyloid formation in the mouse model of AA amyloidosis
    Open this publication in new window or tab >>Lipid membranes accelerate amyloid formation in the mouse model of AA amyloidosis
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    2019 (English)In: Amyloid: Journal of Protein Folding Disorders, ISSN 1350-6129, E-ISSN 1744-2818, Vol. 26, no 1, p. 34-44Article in journal (Refereed) Published
    Abstract [en]

    Introduction: AA amyloidosis develops as a result of prolonged inflammation and is characterized by deposits of N-terminal proteolytic fragments of the acute phase reactant serum amyloid A (SAA). Macrophages are usually found adjacent to amyloid, suggesting their involvement in the formation and/or degradation of the amyloid fibrils. Furthermore, accumulating evidence suggests that lipid membranes accelerate the fibrillation of different amyloid proteins.

    Methods: Using an experimental mouse model of AA amyloidosis, we compared the amyloidogenic effect of liposomes and/or amyloid-enhancing factor (AEF). Inflammation was induced by subcutaneous injection of silver nitrate followed by intravenous injection of liposomes and/or AEF to accelerate amyloid formation.

    Results: We showed that liposomes accelerate amyloid formation in inflamed mice, but the amyloidogenic effect of liposomes was weaker compared with AEF. Regardless of the induction method, amyloid deposits were mainly found in the marginal zones of the spleen and coincided with the depletion of marginal zone macrophages, while red pulp macrophages and metallophilic marginal zone macrophages proved insensitive to amyloid deposition.

    Conclusions: We conclude that increased intracellular lipid content facilitates AA amyloid fibril formation and show that the mouse model of AA amyloidosis is a suitable system for further mechanistic studies.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2019
    Keywords
    Amyloid; liposomes; lipid membrane; macrophages; AA amyloidosis
    National Category
    Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
    Identifiers
    urn:nbn:se:liu:diva-157278 (URN)10.1080/13506129.2019.1576606 (DOI)000466218300001 ()30929476 (PubMedID)2-s2.0-85063746690 (Scopus ID)
    Note

    Funding Agencies|County Council of Ostergotland; Magnus Bergvalls Research Foundation; Broderna Karlssons Research Foundation; K. Molins Minnesfond and Hildur Pettersons Research Foundation

    Available from: 2019-06-12 Created: 2019-06-12 Last updated: 2019-08-15Bibliographically approved
  • Public defence: 2019-09-12 10:15 Planck, Fysikhuset, Linköping
    Shi, Yuchen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Growth of 3C-SiC and Graphene for Solar Water-Splitting Application2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Silicon carbide (SiC) is regarded as an important semiconductor for a variety of applications including high-temperature, high-power and high-frequency devices. The most common polytypes of SiC are hexagonal (4H- or 6H-SiC) and cubic silicon carbide (3C-SiC), which differ from each other by the ordering of the Si–C bilayers along the c-axis crystal direction. Among different polytypes of SiC, 3C-SiC has attracted specific interest due to its prominent properties such as high electron mobility and low interface trap density in MOSFET devices. Moreover, with a relatively small bandgap of 2.36 eV and suitable conduction and valence band positions, 3C-SiC has also been considered as a promising material for solar water splitting application, which provides a completely renewable approach to convert solar energy into storable hydrogen fuel. However, the growth of high-quality 3C-SiC remains a great challenge for decades.

    Graphene, a single layer of sp2-bonded carbon atoms, has shown outstanding electronic properties and becomes the most promising candidate for next-generation electronic and optoelectronic devices. Epitaxial growth of graphene on SiC substrates by sublimation of Si from SiC provides a feasible route to fabricate wafer-scale device-quality graphene. The most advantage of this method is that a variety of devices can be processed directly on graphene/SiC without any transfer process, which is needed in the case of graphene produced by exfoliation or CVD on metals. During past years, the growth of monolayer (ML) graphene on hexagonal SiC (6H-SiC, 4H-SiC) substrates has been extensively studied. However, it is challenging to grow large-area and uniform multilayer graphene on hexagonal SiC substrates due to the stepbunching issue during the sublimation growth.

    Multilayer graphene has recently attracted great interest due to its tunable electronic properties for various electronic and optoelectronic applications. It has been shown that the electronic properties of multilayer graphene are strongly influenced by its stacking sequence. In particular, the rhombohedral stacking sequence (ABC stacking) has shown its potential to introduce a flat band energy dispersion at the K points of the Brillouin zone, which would result in many exotic phases of matter such as superconductivity. Among various SiC polytypes, 3CSiC is predicted to be the most suitable substrate for the epitaxial growth of rhombohedral multilayer graphene.

    This thesis work mainly covers the sublimation growth of high-quality Si-face and C-face 3C-SiC on off-oriented 4H-SiC, exploring the proper parameter window for the growth of homogeneous graphene layers ranging from monolayer to multilayer on Si-face off-oriented 3C-SiC and the growth of graphene on C-face 3C-SiC, as well as the characterizations on 3CSiC and graphene. Moreover, as a proof of concept, photoelectrochemical (PEC) water splitting cells based on the Si-face and C-face 3C-SiC have been fabricated to study the conversion of solar energy into chemical fuel, hydrogen.

    Firstly, the high-quality bulk-like Si-face and C-face 3C-SiC(111) were grown on 4- degree off-oriented 4H-SiC substrates by the sublimation epitaxy technique. The C-face sample exhibited a smoother surface with a step height of one-unit cell without the step bunching. In contrast, the Si-face 3C-SiC showed larger steps with a height of two-unit cells of 3C-SiC due to the pronounced step bunching. The cross-sectional studies showed that C-face 3C-SiC exhibited less polytype-transition layer than the Si-face sample. This would help the lateral enlargement of 3C-SiC domains. We also demonstrated that the crystalline quality of C-face 3C-SiC was comparable to the Si-face sample.

    Secondly, we systematically studied the growth of monolayer and multilayer graphene on off-axis 3C-SiC(111). Taking advantage of the synergistic effect of periodic SiC step edges as graphene nucleation sites and the unique thermal decomposition energy of 3C-SiC steps, we demonstrated that the step bunching was fully eliminated during graphene growth on Si-face 3C-SiC and large-area monolayer, bilayer, and four-layer graphene were controllably obtained on high-quality off-axis Si-face 3C-SiC(111). The growth of uniform four-layer graphene over areas of tens of square micrometers was demonstrated. The electronic structures of multilayer graphene with different stacking sequences were systematically studied by experimental and theoretical analysis. It was demonstrated that the four-layer graphene exhibited rhombohedral stacking sequence, which introduced a flat band near the Fermi level. Moreover, the flat-band width and bandgap can be tuned by the interlayer spacing of graphene. In contrast, graphene layers grown on the off-axis C-face 3C-SiC(1̄1̄1̄) showed 1ML to 4ML graphene domains with large-area coverage over several of square micrometers and there was no buffer layer underneath. The low energy electron diffraction pattern collected on the monolayer graphene domain demonstrated four sets of graphene (1 x 1) spots, indicating the existence of rotational disorders within the monolayer graphene. To compare with graphene growth on the off-oriented 3C-SiC, the growth of graphene on off-oriented 4H-SiC epilayers was also explored. The 4HSiC epilayers were first grown on 4-degree off-oriented 4H-SiC substrates and periodically inclined step facets in-between terraces were induced on 4H-SiC epilayers due to the pronounced step bunching. The graphene grown on such step-structured surface of off-oriented 4H-SiC showed that the terraces were mainly covered by monolayer graphene and the buffer layer underneath it while on the step facets, graphene was strongly buckled and appeared to be largely decoupled from the surface.

    Finally, the PEC water splitting performance based on the Si-face and C-face 3C-SiC was systematically studied. It was found that the SiC surface polarity played an important role in the PEC performance. The influence of both Si-face and C-face on surface proton transfer was investigated. It was demonstrated that the Si-face SiC was more energy-favorable, thus making oxygen evolution reaction operate at a very low overpotential. Furthermore, the PEC watersplitting performance was significantly enhanced by using NiO/3C-SiC p-n junction as a photoanode. A high photovoltage of 1.0 V, a photocurrent density of 1.01 mA/cm-2 at 0.55 V versus reversible hydrogen electrode (VRHE), a low onset potential of 0.20 VRHE and a high fill factor of 57% were demonstrated in the PEC water splitting cell under AM1.5G 100 mW cm-2 illumination.

    List of papers
    1. A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates
    Open this publication in new window or tab >>A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates
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    2019 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 34Article in journal (Refereed) Published
    Abstract [en]

    We present a comparative study of the C-face and Si-face of 3C-SiC(111) grown on off-oriented 4H-SiC substrates by the sublimation epitaxy. By the lateral enlargement method, we demonstrate that the high-quality bulk-like C-face 3C-SiC with thickness of ~1 mm can be grown over a large single domain without double positioning boundaries (DPBs), which are known to have a strongly negative impact on the electronic properties of the material. Moreover, the C-face sample exhibits a smoother surface with one unit cell height steps while the surface of the Si-face sample exhibits steps twice as high as on the C-face due to step-bunching. High-resolution XRD and low temperature photoluminescence measurements show that C-face 3C-SiC can reach the same high crystalline quality as the Si-face 3C-SiC. Furthermore, cross-section studies of the C- and Si-face 3C-SiC demonstrate that in both cases an initial homoepitaxial 4H-SiC layer followed by a polytype transition layer are formed prior to the formation and lateral expansion of 3C-SiC layer. However, the transition layer in the C-face sample is extending along the step-flow direction less than that on the Si-face sample, giving rise to a more fairly consistent crystalline quality 3C-SiC epilayer over the whole sample compared to the Si-face 3C-SiC where more defects appeared on the surface at the edge. This facilitates the lateral enlargement of 3C-SiC growth on hexagonal SiC substrates.

    Place, publisher, year, edition, pages
    Biopress Ltd, 2019
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-159101 (URN)10.1088/1361-6463/ab2859 (DOI)000475964100002 ()
    Note

    Funding agencies:  Swedish Research Council (Vetenskapsradet) [621-2014-5461, 2018-04670, 2016-05362, 621-2014-5825]; Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) [2016-00559]; Swedish Foundation for International Cooperation

    Available from: 2019-07-24 Created: 2019-07-24 Last updated: 2019-08-07
    2. Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)
    Open this publication in new window or tab >>Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)
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    2018 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, p. 533-542Article in journal (Refereed) Published
    Abstract [en]

    Multilayer graphene has exhibited distinct electronic properties such as the tunable bandgap for optoelectronic applications. Among all graphene growth techniques, thermal decomposition of SiC is regarded as a promising method for production of device-quality graphene. However, it is still very challenging to grow uniform graphene over a large-area, especially multilayer graphene. One of the main obstacles is the occurrence of step bunching on the SiC surface, which significantly influences the formation process and the uniformity of the multilayer graphene. In this work, we have systematically studied the growth of monolayer and multilayer graphene on off-axis 3CSiC(111). Taking advantage of the synergistic effect of periodic SiC step edges as graphene nucleation sites and the unique thermal decomposition energy of 3CSiC steps, we demonstrate that the step bunching can be fully eliminated during graphene growth and large-area monolayer, bilayer, and four-layer graphene can be controllably obtained on high-quality off-axis 3CSiC(111) surface. The low energy electron microscopy results demonstrate that a uniform four-layer graphene has been grown over areas of tens of square micrometers, which opens the possibility to tune the bandgap for optoelectronic devices. Furthermore, a model for graphene growth along with the step bunching elimination is proposed.

    Place, publisher, year, edition, pages
    Elsevier, 2018
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-151054 (URN)10.1016/j.carbon.2018.08.042 (DOI)000450120200057 ()
    Note

    Funding agencies: Swedish Research Council (Vetenskapsradet) [621-2014-5461, 621-2014-5825]; Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) [2016-00559]; Swedish Foundation for International Cooperation in Research and Higher 

    Available from: 2018-09-12 Created: 2018-09-12 Last updated: 2019-07-24
    3. Flat-Band Electronic Structure and Interlayer Spacing Influence in Rhombohedral Four-Layer Graphene
    Open this publication in new window or tab >>Flat-Band Electronic Structure and Interlayer Spacing Influence in Rhombohedral Four-Layer Graphene
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    2018 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 9, p. 5862-5866Article in journal (Refereed) Published
    Abstract [en]

    The stacking order of multilayer graphene significantly influences its electronic properties. The rhombohedral stacking sequence is predicted to introduce a flat band, which has high density of states and the enhanced Coulomb interaction between charge carriers, thus possibly resulting in superconductivity, fractional quantum Hall effect, and many other exotic phases of matter. In this work, we comprehensively study the effect of the stacking sequence and interlayer spacing on the electronic structure of four-layer graphene, which was grown on a high crystalline quality 3C-SiC(111) crystal. The number of graphene layers and coverage were determined by low energy electron microscopy. First-principles density functional theory calculations show distinctively different band structures for ABAB (Bernal), ABCA (rhombohedral), and ABCB (turbostratic) stacking sequences. By comparing with angle-resolved photoelectron spectroscopy data, we can verify the existence of a rhombohedral stacking sequence and a nearly dispersionless electronic band (flat band) near the Fermi level. Moreover, we find that the momentum width, bandgap, and curvature of the flat-band region can be tuned by the interlayer spacing, which plays an important role in superconductivity and many other exotic phases of matter. © 2018 American Chemical Society.

    Place, publisher, year, edition, pages
    American Chemical Society, 2018
    Keywords
    flat-band; Graphene; interlayer spacing; rhombohedral stacking; superconductor
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-151307 (URN)10.1021/acs.nanolett.8b02530 (DOI)30136852 (PubMedID)2-s2.0-85052867510 (Scopus ID)
    Available from: 2018-09-17 Created: 2018-09-17 Last updated: 2019-07-24
  • Public defence: 2019-09-13 10:15 Planck, Fysikhuset, Linköping
    Engberg, David L. J.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Atom Probe Tomography of Hard Nitride and Boride Thin Films2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hard ceramic thin films, including TiSiN, ZrAlN, ZrB2, and ZrTaB2, with applications for wear-resistant coatings, have been studied using atom probe tomography and correlated with several other analytical techniques, including X-ray diffraction, electron microscopy, and elastic recoil detection analysis. Outstanding obstacles for quantitative atom probe tomography of ceramic thin films have been surmounted.

    Mass spectral overlaps in TiSiN, which make 28Si indistinguishable from 14N, was resolved by isotopic substitution with 15N, and the nanostructural distribution of elements was thus revealed in 3-D, which enabled the identification of additional structural elements within the nanostructured Ti0.81Si0.1915N film. Improvements to the growth model of TiSiN by cathodic arc deposition was suggested.

    A self-organized nanolabyrinthine structure of ZrAlN, consisting of standing lamellae of fcc-ZrN and hexagonal AlN, was investigated with focus on the onset and limits of the self-organization. The local crystallographic orientational relationships were (001)ZrN || (0001)AlN and <110>ZrN || <2-1-10>AlN. Close to the MgO substrates, a smooth transition region was formed, going from segregated and disordered to the self-organized nanolabyrinthine structure. With increased growth temperature, coarse (111)-oriented ZrN grains occasionally precipitated and locally replaced the nanolabyrinthine structure. Significant local magnification effects rendered the Zr and N signals unusable, thereby inhibiting quantitative compositional analysis of the constituent phases, but the nanostructure was resolved using the Al signal.

    Ceramic materials are often affected by correlated evaporation, which can result in losses due to the detector dead-time/space. A compositional correction procedure was suggested, tested against an established procedure, and applied to ZrB2. The correction was found to be less dependent on the isotope abundances and background correction compared to the established procedure. While losses due to dead-time/space occur in atom probe tomography of all materials, the correlative field evaporation behavior of ceramics significantly increases the compositional error. The evaporation behavior of ZrB2 was therefore thoroughly investigated and evidence of preferential retention, correlated evaporation, and inhomogeneous field distributions at a low-index pole was presented. The high mass resolution, relatively low multiple events percentage, and quality of the co-evaporation correlation data was partly attributed to the crystal structure and film orientation, which promoted a layer-by-layer field evaporation.

    The evaporation behavior of the related ZrTaB2 films was found to be similar to that of ZrB2. The distribution of Ta in relation to Zr was investigated, showing that the column boundaries were both metal- and Ta-rich, and that there was a significant amount of Ta in solid solution within the columns.

    In addition, an instrumental artefact previously not described in atom probe tomography was found in several of the materials investigated in this thesis. The artefact consists of high-density lines along the analysis direction, which cannot be related to pole artefacts. The detection system of the atom probe was identified as the cause, because the artefact patterns on detector histograms coincided with the structure of the microchannel plate. Inconsistencies in the internal boundaries of the microchannel plate multifibers from the manufacturing process can influence the signal to the detector and locally increase the detection efficiency in a pattern characteristic to the microchannel plate in question.

    Altogether, this thesis shows that atom probe tomography of nitride and boride thin films is burdened by several artefacts and distortions, but that relevant material outcomes can nevertheless be achieved by informed choices of film isotopic constituents and analytical parameters, exclusion of heavily distorted regions (such as pole artefacts), and the use of compositional correction procedures when applicable.

    List of papers
    1. Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
    Open this publication in new window or tab >>Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
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    2018 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 184, p. 51-60Article in journal (Refereed) Published
    Abstract [en]

    Mass spectral overlaps in atom probe tomography (APT) analyses of complex compounds typically limit the identification of elements and microstructural analysis of a material. This study concerns the TiSiN system, chosen because of severe mass-to-charge-state ratio overlaps of the 14N+ and 28Si2+ peaks as well as the 14N and 28Si2+ peaks. By substituting 14N with 15N, mass spectrum peaks generated by ions composed of one or more N atoms will be shifted toward higher mass-to-charge-state ratios, thereby enabling the separation of N from the predominant Si isotope. We thus resolve thermodynamically driven Si segregation on the nanometer scale in cubic phase Ti1-xSix15N thin films for Si contents 0.08 ≤ x ≤ 0.19 by APT, as corroborated by transmission electron microscopy. The APT analysis yields a composition determination that is in good agreement with energy dispersive X-ray spectroscopy and elastic recoil detection analyses. Additionally, a method for determining good voxel sizes for visualizing small-scale fluctuations is presented and demonstrated for the TiSiN system.

    Place, publisher, year, edition, pages
    Elsevier, 2018
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-122721 (URN)10.1016/j.ultramic.2017.08.004 (DOI)000415650200007 ()28850866 (PubMedID)
    Note

    Funding Agencies:VINN Excellence Center on Functional Nanoscale Materials (FunMat) [2007-00863]; Swedish Research Council (VR) project [2013-4018]; Swedish Government Strategic Research Area Grant in Materials Science (Grant SFO Mat-LiU) on Advanced Functional Materials [2009-00971]; Knut and Alice Wallenberg Project Isotope

    Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2019-08-01Bibliographically approved
    2. Self-organized Nanostructuring in Zr0.64Al0.36N Thin Films Studied by Atom Probe Tomography
    Open this publication in new window or tab >>Self-organized Nanostructuring in Zr0.64Al0.36N Thin Films Studied by Atom Probe Tomography
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    2016 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, p. 233-238Article in journal (Refereed) Published
    Abstract [en]

    We have applied atom probe tomography (apt) to analyze the selforganized structure of wear-resistant Zr0.64Al0.36N thin films grown by magnetron sputtering. Transmission electron microscopy shows that these films grow as a two-dimensional nanocomposite, consisting of interleaved lamellae in a labyrinthine structure, with a size scale of ∼ 5 nm. The structure was recovered in the Al apt signal, while the Zr and N data lacked structural information due to severe local magnification effects. The onset of the self-organized growth was observed to occur locally by nucleation, at 5-8 nm from the MgO substrate, after increasing Zr-Al compositional fluctuations. Finally, it was observed that the self-organized growth mode could be perturbed by renucleation of ZrN.

    Place, publisher, year, edition, pages
    Elsevier, 2016
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-84258 (URN)10.1016/j.tsf.2016.07.034 (DOI)000381939700037 ()
    Note

    Funding agencies: VINN Excellence Center on Functional Nanoscale Materials; Swedish Research Council; Swedish Government Strategic Faculty Grant in Materials Science (SFO Mat-LiU) at Linkoping University; Swedish Governmental Agency for Innovation Systems (Vinnova) [2011-0

    Vid tiden för disputationen förelåg publikationen som manuskript

    Available from: 2012-10-03 Created: 2012-10-03 Last updated: 2019-08-02Bibliographically approved
    3. Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1-xTaxBy thin films
    Open this publication in new window or tab >>Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1-xTaxBy thin films
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    2019 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, no 3, article id 031506Article in journal (Refereed) Published
    Abstract [en]

    Refractory transition-metal diborides exhibit inherent hardness. However, this is not always sufficient to prevent failure in applications involving high mechanical and thermal stress, since hardness is typically accompanied by brittleness leading to crack formation and propagation. Toughness, the combination of hardness and ductility, is required to avoid brittle fracture. Here, the authors demonstrate a strategy for simultaneously enhancing both hardness and ductility of ZrB2-rich thin films grown in pure Ar on Al2O3(0001) and Si(001) substrates at 475 degrees C. ZrB2.4 layers are deposited by dc magnetron sputtering (DCMS) from a ZrB2 target, while Zr1-xTaxBy alloy films are grown, thus varying the B/metal ratio as a function of x, by adding pulsed high-power impulse magnetron sputtering (HiPIMS) from a Ta target to deposit Zr1-xTaxBy alloy films using hybrid Ta-HiPIMS/ZrB2-DCMS sputtering with a substrate bias synchronized to the metal-rich portion of each HiPIMS pulse. The average power P-Ta (and pulse frequency) applied to the HiPIMS Ta target is varied from 0 to 1800W (0 to 300 Hz) in increments of 600W (100 Hz). The resulting boron-to-metal ratio, y = B/(Zr+Ta), in as-deposited Zr1-xTaxBy films decreases from 2.4 to 1.5 as P-Ta is increased from 0 to 1800W, while x increases from 0 to 0.3. A combination of x-ray diffraction (XRD), glancing-angle XRD, transmission electron microscopy (TEM), analytical Z-contrast scanning TEM, electron energy-loss spectroscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and atom-probe tomography reveals that all films have the hexagonal AlB2 crystal structure with a columnar nanostructure, in which the column boundaries of layers with 0 amp;lt;= x amp;lt; 0.2 are B-rich, whereas those with x amp;gt;= 0.2 are Ta-rich. The nanostructural transition, combined with changes in average column widths, results in an similar to 20% increase in hardness, from 35 to 42 GPa, with a simultaneous increase of similar to 30% in nanoindentation toughness, from 4.0 to 5.2MPa root m. Published by the AVS.

    Place, publisher, year, edition, pages
    A V S AMER INST PHYSICS, 2019
    National Category
    Inorganic Chemistry
    Identifiers
    urn:nbn:se:liu:diva-159001 (URN)10.1116/1.5093170 (DOI)000472182400035 ()
    Note

    Funding Agencies|Swedish Research Council VR [2014-5790, 2018-03957, 642-2013-8020]; Knut and Alice Wallenbergs foundation [KAW 2015.0043]; VINNOVA [2018-04290]; Aforsk Foundation [16-359]; Carl Tryggers Stiftelse [CTS 15: 219, CTS 17: 166, CTS 14: 431]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]

    Available from: 2019-07-19 Created: 2019-07-19 Last updated: 2019-08-01
  • Public defence: 2019-09-13 13:15 Ada Lovelace, B-huset, Linköping
    Ghasemi Zinatabadi, Fatemeh
    Linköping University, Department of Mathematics, Computational Mathematics. Linköping University, Faculty of Science & Engineering.
    Stability, dual consistency and conservation of summation-by-parts formulations for multiphysics problems2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, we consider the numerical solution of initial boundary value problems (IBVPs). Boundary and interface conditions are derived such that the IBVP under consideration is well-posed. We also study the dual problem and the related dual boundary/interface conditions. Once the continuous problem is analyzed, we use finite difference operators with the Summation- By-Parts property (SBP) and a weak boundary/interface treatment using the Simultaneous-Approximation-Terms (SAT) technique to construct high-order accurate numerical schemes. We focus in particular on stability, conservation and dual consistency. The energy method is used as our main analysis tool for both the continuous and numerical problems.

    The contributions of this thesis can be divided into two parts. The first part focuses on the coupling of different IBVPs. Interface conditions are derived such that the continuous problem satisfy an energy estimate and such that the discrete problem is stable. In the first paper, two hyperbolic systems of different size posed on two domains are considered. We derive the dual problem and dual interface conditions. It is also shown that a specific choice of penalty matrices leads to dual consistency. As an application, we study the coupling of the Euler and wave equations. In the fourth paper, we examine how to couple the compressible and incompressible Navier-Stokes equations. In order to obtain a sufficient number of interface conditions, the decoupled heat equation is added to the incompressible equations. The interface conditions include mass and momentum balance and two variants of heat transfer. The typical application in this case is the atmosphere-ocean coupling.

    The second part of the thesis focuses on the relation between the primal and dual problem and the relation between dual consistency and conservation. In the second and third paper, we show that dual consistency and conservation are equivalent concepts for linear hyperbolic conservation laws. We also show that these concepts are equivalent for symmetric or symmetrizable parabolic problems in the fifth contribution. The relation between the primal and dual boundary conditions for linear hyperbolic systems of equations is investigated in the sixth and last paper. It is shown that for given well-posed primal/dual boundary conditions, the corresponding well-posed dual/primal boundary conditions can be obtained by a simple scaling operation. It is also shown how one can proceed directly from the well-posed weak primal problem to the well-posed weak dual problem.  

    List of papers
    1. Coupling Requirements for Multiphysics Problems Posed on Two Domains
    Open this publication in new window or tab >>Coupling Requirements for Multiphysics Problems Posed on Two Domains
    2017 (English)In: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 55, no 6, p. 2885-2904Article in journal (Refereed) Published
    Abstract [en]

    We consider two hyperbolic systems in first order form of different size posed on two domains. Our ambition is to derive general conditions for when the two systems can and cannot be coupled. The adjoint equations are derived and well-posedness of the primal and dual problems is discussed. By applying the energy method, interface conditions for the primal and dual problems are derived such that the continuous problems are well posed. The equations are discretized using a high order finite difference method in summation-by-parts form and the interface conditions are imposed weakly in a stable way, using penalty formulations. It is shown that one specic choice of penalty matrices leads to a dual consistent scheme. By considering an example, it is shown that the correct physical coupling conditions are contained in the set of well posed coupling conditions. It is also shown that dual consistency leads to superconverging functionals and reduced stiffness.

    Place, publisher, year, edition, pages
    Society for Industrial and Applied Mathematics, 2017
    Keywords
    well posed problems, high order finite diffrences, stability, summation-by-parts, weak interface conditions, dual consistency, stiffness, superconvergence
    National Category
    Computational Mathematics
    Identifiers
    urn:nbn:se:liu:diva-143261 (URN)10.1137/16M1087710 (DOI)000418663500015 ()
    Available from: 2017-11-28 Created: 2017-11-28 Last updated: 2019-08-01Bibliographically approved
    2. On the relation between conservation and dual consistency for summation-by-parts schemes
    Open this publication in new window or tab >>On the relation between conservation and dual consistency for summation-by-parts schemes
    2017 (English)In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 344, p. 3p. 437-439Article in journal (Refereed) Published
    Abstract [en]

    n/a

    Publisher
    p. 3
    Keywords
    Initial boundary value problems Summation-by-parts Conservation, Dual consistent, Multi-block, Multi-element
    National Category
    Mathematics
    Identifiers
    urn:nbn:se:liu:diva-137545 (URN)10.1016/j.jcp.2017.04.072 (DOI)000402481300021 ()
    Note

    Classified in the journal as "Short note"

    Available from: 2017-05-21 Created: 2017-05-21 Last updated: 2019-08-01
    3. Corrigendum to “On the relation between conservation and dual consistency for summation-by-parts schemes”[J. Comput. Phys. 344 (2017) 437–439]
    Open this publication in new window or tab >>Corrigendum to “On the relation between conservation and dual consistency for summation-by-parts schemes”[J. Comput. Phys. 344 (2017) 437–439]
    2018 (English)In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 360, p. 247-247Article in journal (Refereed) Published
    Place, publisher, year, edition, pages
    Academic Press, 2018
    National Category
    Mathematics
    Identifiers
    urn:nbn:se:liu:diva-145718 (URN)10.1016/j.jcp.2018.02.046 (DOI)000428966300014 ()
    Available from: 2018-03-19 Created: 2018-03-19 Last updated: 2019-08-01Bibliographically approved
    4. An energy stable coupling procedure for the compressible and incompressible Navier-Stokes equations
    Open this publication in new window or tab >>An energy stable coupling procedure for the compressible and incompressible Navier-Stokes equations
    2019 (English)In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 396, p. 280-302Article in journal (Refereed) Epub ahead of print
    Abstract [en]

    The coupling of the compressible and incompressible Navier-Stokes equations is considered. Our ambition is to take a first step towards a provably well posed and stable coupling procedure. We study a simplified setting with a stationary planar interface and small disturbances from a steady background flow with zero velocity normal to the interface. The simplified setting motivates the use of the linearized equations, and we derive interface conditions such that the continuous problem satisfy an energy estimate. The interface conditions can be imposed both strongly and weakly. It is shown that the weak and strong interface imposition produce similar continuous energy estimates. We discretize the problem in time and space by employing finite difference operators that satisfy a summation-by-parts rule. The interface and initial conditions are imposed weakly using a penalty formulation. It is shown that the results obtained for the weak interface conditions in the continuous case, lead directly to stability of the fully discrete problem.

    Keywords
    Compressible fluid, Incompressible fluid, Navier-Stokes equations, Energy estimate, Interface conditions, Stability
    National Category
    Mathematics
    Identifiers
    urn:nbn:se:liu:diva-159116 (URN)10.1016/j.jcp.2019.07.022 (DOI)
    Available from: 2019-07-29 Created: 2019-07-29 Last updated: 2019-08-01
    5. On conservation and dual consistency for summation-by-parts based approximations of parabolic problems
    Open this publication in new window or tab >>On conservation and dual consistency for summation-by-parts based approximations of parabolic problems
    2019 (English)Report (Other academic)
    Abstract [en]

    We consider the coupling of parabolic problems discretized using difference operators on summation-by-parts (SBP) form with interface conditions imposed weakly. In, it was shown that conservation and dual consistency are equivalent concepts for linear conservation laws. Here, we show that these concepts are equivalent also for symmetric or symmetrizable parabolic problems, exemplified by the heat equation. We rewrite the heat equation as first order system as in the local discontinuous Galerkin method and show the equivalence of dual consistency and conservation for both the first and second order forms.

    Place, publisher, year, edition, pages
    Linköping: Linköping University Electronic Press, 2019. p. 9
    Series
    LiTH-MAT-R, ISSN 0348-2960 ; 2019:5
    National Category
    Computational Mathematics Mathematics
    Identifiers
    urn:nbn:se:liu:diva-158903 (URN)LiTH-MAT-R--2019/05--SE (ISRN)
    Available from: 2019-07-17 Created: 2019-07-17 Last updated: 2019-08-12Bibliographically approved
    6. The Relation Between Primal and Dual Boundary Conditions for Hyperbolic Systems of Equations
    Open this publication in new window or tab >>The Relation Between Primal and Dual Boundary Conditions for Hyperbolic Systems of Equations
    2019 (English)Report (Other academic)
    Abstract [en]

    In this paper we study boundary conditions for linear hyperbolic systems of equations and the corresponding dual problems. In particular, we show that the primal and dual boundary conditions are related by a simple scaling relation. It is also shown that the weak dual problem can be derived directly from the weak primal problem.

    Based on the continuous analysis, we discretize and perform computations with a high-order finite difference scheme on summation-by-parts form with weak boundary conditions. It is shown that the results obtained in the continuous analysis lead directly to stability results for the primal and dual discrete problems. Numerical experiments corroborate the theoretical results.

    Place, publisher, year, edition, pages
    Linköping: Linköping University Electronic Press, 2019. p. 22
    Series
    LiTH-MAT-R, ISSN 0348-2960 ; 2019:6
    Keywords
    Hyperbolic systems, boundary conditions, primal problem, dual problem, well-posedness, dual consistency
    National Category
    Computational Mathematics Mathematics
    Identifiers
    urn:nbn:se:liu:diva-158904 (URN)LiTH-MAT-R--2019/06--SE (ISRN)
    Available from: 2019-07-17 Created: 2019-07-17 Last updated: 2019-08-12Bibliographically approved
  • Public defence: 2019-09-17 13:15 ACAS, A-huset, Linköping
    Petersson, Johan
    Handelshögskolan, Örebro universitet, Örebro, Sverige.
    Elektroniska marknadsplatser: IT-stöd för små och medelstora leverantörer2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The aim of this dissertation is to identify what constitutes a desirable design for electronic marketplaces from the perspective of small and medium-sized suppliers. The specific marketplace category under study is business-oriented marketplaces, which are marketplaces that mediate commercial transactions between organizations (in a so-called business-to-business setting). An important justification for the study is the fact that research has shown a disproportionately small interest in studying the issue from this perspective, despite there being both scientific and practical needs for greater knowledge in this area. That is to say, there are a number of important and unanswered questions regarding marketplace suppliers in general and the situation of small suppliers in specific.

    The overarching research question is: “What kind of electronic marketplace design is preferable in order to support the needs of small suppliers” and this question has been answered through the development, presentation and application of a set of seven design criteria. The research project was comprised of several sub-studies and characterized by a qualitative approach. Practice theory has been used as the central theoretical perspective of the study. The object of study in the primary case was the Scandinavian marketplace Proceedo and the practical work undertaken involved collecting and analyzing data in the form of interviews, documents and system tests.

    The study’s contribution to knowledge is made up of four parts: a set of criteria for electronic marketplace design, a conceptualization of marketplace practices, a categorization of SME supplier needs and finally a suggested set of generic design principles for work practices. The design criteria are presented as seven prescriptive statements that may be used to aid practical marketplace design. The set of criteria therefore also directly answers the overarching research question. For the purposes of observing, analyzing and understanding the phenomenon of electronic marketplaces, this study also presents the two concepts of marketplace practice and sales practice.

    When it came to the resulting categorization of supplier needs, the study found that the primary need was for compliance with customer desires and demands. Furthermore, the analysis also revealed two main areas within electronic marketplace interaction in which SME suppliers have particular needs. The first concerns business information – suppliers need to be able to examine and change their own business information. The second relates to business harmonization – there is a need for marketplace activities to harmonize with the regular business activities of suppliers. The study has also resulted in a contribution on a more theoretical and abstract level. It has produced a presentation of a prescriptive extension of an existing work practice model. The extension is a set of generic design principles that stem from the information systems domain and socio-technical theory.

  • Public defence: 2019-09-20 09:00 Berzeliussalen, Linköping
    Carlén, Anna
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Exercise Testing in Firefighters: Work Capacity and Cardiovascular Risk Assessment in a Low-Risk Population2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Background. Firefighting is one of the most physically demanding occupations and it requires a high cardiorespiratory fitness level.

    Pre-duty medical evaluation of firefighters includes fitness testing and assessment of cardiac health to ensure that firefighters meet the minimum physical fitness standard and to ensure that they are not at increased risk of cardiac events. The medical evaluation methods for Swedish firefighters are regulated by the Swedish Work Environment Authority and include a 6 min constant workload treadmill (TM) test for fitness evaluation in which the firefighter wears full smoke diving equipment and a maximal effort exercise electrocardiography test (ExECG) at cycle ergometer (CE) for assessment of cardiac health. Previously, fitness was also evaluated by cycle ergometry.

    The standard parameter for evaluation of ischaemic heart disease (IHD) is exercise-induced ST depression. In general, exercise testing of asymptomatic low-risk individuals is discouraged due to low sensitivity and specificity for IHD, generating both false-positive and false-negative test results. Heart rate (HR) adjustment of the ST-segment response has been shown to be superior to simple ST depression to evaluate cardiac ischaemia in some populations, but has not been extensively evaluated in an occupational setting.

    Methods. We retrospectively analysed a cohort of 774 firefighters who were asymptomatic at the time of the testing.

    In paper I, test approval, HR response, and calculated oxygen uptake from TM tests and CE tests for 424 firefighters (44±10 years) were compared.

    Paper II methodologically described the process for data extraction, processing, and calculation of ExECG data from a clinical database. Procedures for noise assessment, error checking, and computerized calculation of ST/HR parameters were described.

    In paper III, ExECG and medical records of 521 male firefighters (44±10 years) were studied. During 8.4 ± 2.1 years of follow-up, IHD was verified angiographically in 12 subjects. The predictive value of HR-adjusted ST variables (ST/HR index, ST/HR slope, and ST/HR loop) for IHD was evaluated.

    In paper IV, subjects with objectively verified IHD were excluded and factors associated with exercise-induced nonischaemic ST depression were studied in the remaining 509 males (46±11 years).

     

    Results. The firefighters had an average maximal exercise capacity of 281 ± 36 W (range 186-467 W) achieved by incremental CE exercise. To enable comparison, the maximal workload was converted to the workload sustainable for 6 min. It was more common to pass the 6 min TM fitness test but to fail the supposedly equivalent CE test rather than vice versa.

    Twenty percent of the firefighters developed an ST depression of ≥o.1 mV in at least one lead during exercise and half of the firefighters had a horizontal or downsloping ST depression. While an abnormal ST response associated with an increased risk for IHD only in V4, both an abnormal ST/HR index and an abnormal ST/HR slope associated with IHD in three leads each. Clockwise rotation of the ST/HR loop was infrequent in all precordial leads (1%), but it associated with an increased risk for IHD.

    In the subgroup without evidence of coronary artery disease, age and the HR response associated with ST depression, whereas hypertension, hyperlipidaemia, diabetes, blood pressure response, and exercise capacity did not.

     

    Conclusions. Even though the calculated oxygen uptake was higher for the TM test than for the supposedly equivalent CE test, the higher treadmill approval rate may indicate that the fitness requirement for Swedish firefighters has been lowered by changing the test modality.

    Exercise-induced ST depression was common in asymptomatic physically active men, although there were only a few cases of IHD during follow-up. If performing ExECG in asymptomatic, low-risk populations, ST/HR analysis could be given more importance. However, the limited clinical value of ExECG in low-risk populations was emphasised and needs to be reconsidered.

    In asymptomatic, physically active men without coronary artery disease, false-positive ST depressions can be partially explained by HR variables rather than by common cardiovascular risk factors and blood pressure response to exercise.

    List of papers
    1. Loaded treadmill walking and cycle ergometry to assess work capacity: a retrospective comparison in 424 firefighters.
    Open this publication in new window or tab >>Loaded treadmill walking and cycle ergometry to assess work capacity: a retrospective comparison in 424 firefighters.
    2017 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 37, no 1, p. 37-44Article in journal (Refereed) Published
    Abstract [en]

    The fitness of firefighters is regularly evaluated using exercise tests. We aimed to compare, with respect to age and body composition, two test modalities for the assessment work capacity. A total of 424 Swedish firefighters with cycle ergometer (CE) and treadmill (TM) tests available from Jan 2004 to Dec 2010 were included. We compared results from CE (6 min at 200 W, 250 W or incremental ramp exercise) with TM (6 min at 8° inclination, 4·5 km h(-1) or faster, wearing 24-kg protective equipment). Oxygen requirements were estimated by prediction equations. It was more common to pass the TM test and fail the supposedly equivalent CE test (20%), than vice versa (0·5%), P<0·001. Low age and tall stature were significant predictors of passing both CE and TM tests (P<0·05), while low body mass predicted accomplishment of TM test only (P = 0·006). Firefighters who passed the TM but failed the supposedly equivalent CE test within 12 months had significantly lower body mass, lower BMI, lower BSA and shorter stature than did those who passed both tests. Calculated oxygen uptake was higher in TM tests compared with corresponding CE tests (P<0·001). Body constitution affected approval differently depending on the test modality. A higher approval rate in TM testing suggests lower cardiorespiratory requirements compared with CE testing, even though estimated oxygen uptake was higher during TM testing. The relevance of our findings in relation to the occupational demands needs reconsidering.

    National Category
    Sport and Fitness Sciences
    Identifiers
    urn:nbn:se:liu:diva-120004 (URN)10.1111/cpf.12265 (DOI)000390688200006 ()26096157 (PubMedID)
    Note

    Funding agencies: ALF grants; County Council of Ostergotland, Sweden; Olav Axelssons memorial fund

    Available from: 2015-07-02 Created: 2015-07-02 Last updated: 2019-08-21
    2. ST/HR variables in firefighter exercise ECG - relation to ischemic heart disease
    Open this publication in new window or tab >>ST/HR variables in firefighter exercise ECG - relation to ischemic heart disease
    2019 (English)In: Physiological Reports, E-ISSN 2051-817X, Vol. 7, no 2, article id e13968Article in journal (Refereed) Published
    Abstract [en]

    Exercise electrocardiography (ExECG) is regularly performed by Swedish firefighters by law. Heart rate-corrected analysis of ST segment variables (ST/HR) has shown improved prediction of ischemic heart disease (IHD) compared to ST depression alone. This has not previously been extensively studied in asymptomatic persons with a low probability of IHD. We therefore evaluated the predictive performance of ST/HR analysis in firefighter ExECG. ExECG was studied in 521 male firefighters. During 8.4 ± 2.1 years, 2.3% (n = 12) were verified with IHD by catheterization or myocardial scintigraphy (age 51.5 ± 5.5 years) and were compared with firefighters without imaging proof of IHD (44.2 ± 10.1 years). The predictive value of ST depression, ST/HR index, ST/HR slope, and area and rotation of the ST/HR loop was calculated as age-adjusted odds ratios (OR), in 10 ECG leads. Predictive accuracy was analyzed with receiver operating characteristics (ROC) analysis. ST/HR index ≤-1.6 μV/bpm and ST/HR slope ≤-2.4 μV/bpm were associated with increased IHD risk in three individual leads (all OR > 1.0, P < 0.05). ST/HR loop area lower than the fifth percentile of non-IHD subjects indicated IHD risk in V4, V5, aVF, II, and -aVR (P < 0.05). ST depression ≤-0.1 mV was associated with IHD only in V4 (OR, 9.6, CI, 2.3-40.0). ROC analysis of each of these variables yielded areas under the curve of 0.72 or lower for all variables and leads. Clockwise-rotated ST/HR loops was associated with increased risk in most leads compared to counterclockwise rotation. The limited clinical value of ExECG in low-risk populations was emphasized, but if performed, ST/HR analysis should probably be given more importance.

    Keywords
    Electrocardiography, ST depression, ST/HR variables, low risk
    National Category
    Cardiac and Cardiovascular Systems
    Identifiers
    urn:nbn:se:liu:diva-159752 (URN)10.14814/phy2.13968 (DOI)30688031 (PubMedID)
    Available from: 2019-08-20 Created: 2019-08-20 Last updated: 2019-08-21
    3. Exercise-induced ST depression in an asymptomatic population without coronary artery disease
    Open this publication in new window or tab >>Exercise-induced ST depression in an asymptomatic population without coronary artery disease
    2019 (English)In: Scandinavian Cardiovascular Journal, ISSN 1401-7431, E-ISSN 1651-2006, Vol. 53, no 4, p. 206-212Article in journal (Refereed) Published
    Abstract [en]

    Objectives. Exercise electrocardiogram (ExECG) in low risk populations frequently generates false positive ST depression. We aimed to characterize factors that are associated with exercise-induced ST depression in asymptomatic men without coronary artery disease. Design. Cycle ergometer exercise tests from 509 male firefighters without imaging proof of significant coronary artery disease were analysed. Analysed test data included heart rate at rest before exercise, and workload, blood pressure, heart rate, ST depression and ST segment slope at peak exercise. ST depression of amp;gt;0.1 mV was considered significant (STdep). With a mean follow-up of 6.1 +/- 1.7 years, medical records were reviewed for cardiovascular diagnoses, hyperlipidemia and diabetes. Logistic regression analysis was used for risk assessment. Results. In total, 22% had STdep in amp;gt;= 1 lead. Subjects with STdep were older than those with normal ExECG (p amp;lt; .001). Downsloping STdep was more common in extremity leads (9%) than in precordial leads (2%). STdep was categorized according to location (precordial/extremity) and slope direction into eight categories. Larger age-adjusted heart rate increase predicted STdep in seven categories (p amp;lt; .05). Age-adjusted peak heart rate correlated with STdep in five categories, predominantly where the ST slope was positive. Peak blood pressure and exercise capacity were both associated with STdep in few categories. We found no association between STdep and hypertension, hyperlipidemia or diabetes (all p amp;gt; .05). Conclusions. In asymptomatic men with a physically demanding occupation and no coronary artery disease, both age and heart rate response were associated with ST depression, whereas common cardiovascular risk factors, blood pressure response and exercise capacity were not.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2019
    Keywords
    Stress test; false positive; electrocardiography; heart rate; ST segment deviation; firefighters; low risk
    National Category
    Cardiac and Cardiovascular Systems
    Identifiers
    urn:nbn:se:liu:diva-158872 (URN)10.1080/14017431.2019.1626021 (DOI)000472278700001 ()31144537 (PubMedID)
    Note

    Funding Agencies|County Council of Ostergotland, Sweden [LIO-711261]; ALF grant [700731]

    Available from: 2019-07-15 Created: 2019-07-15 Last updated: 2019-08-21
  • Public defence: 2019-09-20 10:15 ACAS, Linköping
    Larsson, L. Viktor
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Control of Hybrid Hydromechanical Transmissions2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with control aspects of complex hybrid hydromechanical transmissions for heavy mobile working machines. Control problems are identified and solved to facilitate the implementation and use of these systems.

    Fuel prices and environmental concerns have increased the interest in hybrid hydromechanical transmissions for heavy mobile working machines. Hybridisation, the introduction of a secondary energy source in the transmission, offers attractive improvements in terms of both fuel efficiency and performance. These improvements are, in turn, enabled by software control. A complex transmission architecture has several components that need to interact in a stable manner. In addition, optimal utilisation of the added energy source is required to maximise fuel savings. Meanwhile, there is a strong trend towards automation, where many of the operator’s difficult control tasks need to be managed by computers. Sophisticated control strategies are therefore needed, along with a deeper understanding of dynamic properties.

    Previous research on the control of hybrid hydromechanical transmissions has primarily focussed on on-road applications. The working conditions of heavy working machines place different requirements on the transmission, which is also reflected in the control strategy.

    This thesis highlights the importance of fast response of the variable displacement pump/motors used in hybrid hydromechanical transmissions. Their central position in the interface between hydraulics and mechanics makes their dynamic performance a limiting factor both for the stability of the transmission control loops and in the realisation of smooth mode shifts in multiplemode transmissions. Dynamic models and control strategies for displacement actuators are derived and validated in simulation and experiments. A linear model for dynamic analysis of a general hybrid hydromechanical transmission for heavy working machines is derived and a powertrain control strategy based on decoupled control is proposed. The strategy is verified in simulations and experiments in hardware-in-the-loop simulations, and may be used in a working machine with or without a human operator.

    List of papers
    1. Mode Shifting in Hybrid Hydromechanical Transmissions
    Open this publication in new window or tab >>Mode Shifting in Hybrid Hydromechanical Transmissions
    2015 (English)In: ASME/BATH 2015 Symposium on Fluid Power and Motion Control, ASME Press, 2015, p. 13-Conference paper, Published paper (Refereed)
    Abstract [en]

    Demands for low cost sustainable solutions have increased the use of and interest in complex hydromechanical transmissions for heavy off-road vehicles. In transmissions with multiplemodes, an important condition is to maintain the tractive force during the mode shifting event. For hybrid hydromechanical transmissions, with a direct connection to a hydraulic accumulator, the impressed system pressure caused by the hydraulic accumulator has not yet been observed to interfere with this condition. In this paper, a black box model approach is used to modify the hydraulic system after obtaining knowledge regarding how it is affected by a mode shift. A comparative study is carried out where a full vehicle model of a mobile working machine is simulated with two different hydraulic systems. The results show that different system solutions imply different demands on the included components, and that the mode shifting event is not a negligible factor in heavy hydraulic hybrid vehicles.

    Place, publisher, year, edition, pages
    ASME Press, 2015
    Keywords
    Mode shifting, hydromechanical transmissions, fluid power, heavy construction machinery
    National Category
    Other Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-126556 (URN)10.1115/FPMC2015-9583 (DOI)000373970500045 ()978-0-7918-5723-6 (ISBN)
    Conference
    ASME/BATH 2015 Symposium on Fluid Power and Motion Control, Chicago, Illinois, USA, October 12–14, 2015
    Projects
    Research on Hydromechanical Transmissions and Hybrid Motion systems, RHYTHM
    Funder
    Swedish Energy Agency, P39367-1
    Available from: 2016-03-30 Created: 2016-03-30 Last updated: 2019-08-21
    2. Modelling of the Swash Plate Control Actuator in an Axial Piston Pump for a Hardware-In-the-Loop Simulation Test Rig
    Open this publication in new window or tab >>Modelling of the Swash Plate Control Actuator in an Axial Piston Pump for a Hardware-In-the-Loop Simulation Test Rig
    2016 (English)In: Proceedings of the 9th FPNI Ph.D. Symposium on Fluid Power, FPNI2016, ASME Press, 2016, article id UNSP V001T01A044Conference paper, Published paper (Refereed)
    Abstract [en]

    Hydraulic hybrid system solutions are promising in the quest for energy efficiency in heavy construction machines. Hardware-in-the-loop simulations, where hardware is included in software simulations in real time, may be used to facilitate the development process of these systems without the need to build expensive prototypes. In this paper, the displacement actuator of a prototype pump used in a hardware-in-the-loop simulation test rig is modelled and validated against hardware, in order to draw conclusions regarding its dynamic behaviour in a future control design. The results show that the dynamic response of the modelled displacement actuator is mainly determined by the system pressure as well as the response and geometry of the control valve.

    Place, publisher, year, edition, pages
    ASME Press, 2016
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-133328 (URN)10.1115/FPNI2016-1570 (DOI)000398986900044 ()978-0-7918-5047-3 (ISBN)
    Conference
    The 9th FPNI Ph.D. Symposium on Fluid Power
    Projects
    Research on Hydromechanical Transmissions and Hybrid Motion systems, RHYTHM
    Funder
    Swedish Energy Agency, P39367-1
    Note

    The authors would like to thank the Swedish Energy Agency for contributing funds for the research project. Thanks also go to Bosch Rexroth for providing the prototype machines.

    Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2019-08-21
    3. Displacement Control Strategies of an In-Line Axial-Piston Unit
    Open this publication in new window or tab >>Displacement Control Strategies of an In-Line Axial-Piston Unit
    2017 (English)In: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Ericson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, p. 244-253Conference paper, Published paper (Refereed)
    Abstract [en]

    The need for efficient propulsion in heavy vehicles has led to an increased interest in hybrid solutions. Hydraulic hybrids rely on variable hydraulic pumps/motors to continuously convert between hydraulic and mechanical power. This process is carried out via the implementation of secondary control which, in turn, is dependent on a fast displacement controller response. This paper reports on a study of a prototype axial piston pump of the in-line type, in which the displacement is measured with a sensor and controlled using a software-based controller. A pole placement control approach is used, in which a simple model of the pump is used to parametrise the controller using desired resonance and damping of the closed loop controller as input. The controller’s performance is tested in simulations and hardware tests on the prototype unit. The results show that the pole placement approach combined with a lead-compensator controller architecture is flexible, easy to implement and is able to deliver a fast response with high damping. The results will in the future be used in further research on full-vehicle control of heavy hydraulic hybrids.

    Place, publisher, year, edition, pages
    Linköping: Linköping University Electronic Press, 2017
    Series
    Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 144
    Keywords
    Hydraulic hybrids, displacement control, pole placement
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-139854 (URN)10.3384/ecp17144244 (DOI)9789176853696 (ISBN)
    Conference
    The 15th Scandinavian International Conference on Fluid Power, SICFP’17, June 7-9, 2017, Linköping, Sweden
    Available from: 2017-08-17 Created: 2017-08-17 Last updated: 2019-08-21Bibliographically approved
    4. A General Approach to Low-Level Control of Heavy Complex Hybrid Hydromechanical Transmissions
    Open this publication in new window or tab >>A General Approach to Low-Level Control of Heavy Complex Hybrid Hydromechanical Transmissions
    2018 (English)In: BATH/ASME 2018 Symposium on Fluid Power and Motion Control, 2018Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper focuses on the low-level control of heavy complex hydraulic hybrids, taking stability and the dynamic properties of the included components into account. A linear model which can describe a high number of hybrid configurations in a straightforward manner is derived and used for the development of a general multiple input multiple output (MIMO) decoupling control strategy. This strategy is tested in non-linear simulations of an example vehicle and stability requirements for the low-level actuators are derived. The results show that static decoupling may be used to simplify the control problem to three individual loops controlling pressure, output speed and engine speed. In particular, the pressure and output speed loops rely on fast displacement controllers for stability. In addition, it was found that the decoupling is facilitated if the hydrostatic units have equal response. The low-level control of heavy complex hydraulic hybrids may thus imply other demands on actuators than what is traditionally assumed.

    Keywords
    Control, Multiple input multiple output control, heavy hydraulic hybrids, hydromechanical transmissions
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-154306 (URN)10.1115/FPMC2018-8877 (DOI)000460491500042 ()2-s2.0-85058056485 (Scopus ID)978-0-7918-5196-8 (ISBN)
    Conference
    BATH/ASME 2018 Symposium on Fluid Power and Motion Control, Bath, United Kingdom, September 12-14, 2018
    Funder
    Swedish Energy Agency, P39367-2
    Note

    Funding agencies: Swedish Energy Agency

    Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-08-21Bibliographically approved
    5. Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines
    Open this publication in new window or tab >>Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines
    2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 9, article id 1683Article in journal (Refereed) Published
    Abstract [en]

    Fuel efficiency has become an increasingly important property of heavy mobile working machines. As a result, Hybrid Hydromechanical Transmissions (HMTs) are often considered for the propulsion of these vehicles. The introduction of hybrid HMTs does, however, come with a number of control-related challenges. To date, a great focus in the literature has been on high-level control aspects, concerning optimal utilization of the energy storage medium. In contrast, the main topic of this article is low-level control, with the focus on dynamic response and the ability to realize requested power flows accurately. A static decoupled Multiple-Input-Multiple-Output (MIMO) control strategy, based on a linear model of a general hybrid HMT, is proposed. The strategy is compared to a baseline approach in Hardware-In-the-Loop (HWIL) simulations of a reference wheel loader for two drive cycles. It was found that an important benefit of the decoupled control approach is that the static error caused by the system’s cross-couplings is minimized without introducing integrating elements. This feature, combined with the strategy’s general nature, motivates its use for multiple-mode transmissions in which the transmission configuration changes between the modes. 

    Place, publisher, year, edition, pages
    MDPI, 2019
    Keywords
    hydromechanical transmissions, hybridization, control, construction machinery; decoupled control, hardware-in-the-loop
    National Category
    Other Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-157504 (URN)10.3390/en12091683 (DOI)000469761700099 ()
    Funder
    Swedish Energy Agency, P39367-2
    Note

    Funding agencies: Swedish Energy Agency (Energimyndigheten) [P39367-2]

    Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-08-21Bibliographically approved
  • Public defence: 2019-09-24 13:00 Belladonna, Linköping
    Bratengeier, Cornelia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Mechanisms of mechanically induced Osteoclastogenesis: in a novel in vitro model for bone implant loosening2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Total joint arthroplasty is the primary intervention in the treatment of end-stage osteoarthritis. Despite the high success rate, in some patients, the replacement will fail during their lifetime requiring a revision of the implant. These revisions are strenuous for the patient and costly for health care. Joint replacement at a younger age, in combination with a more active lifestyle, increases the need for an early revision of the joint prosthesis. The main reason for revision surgeries is aseptic loosening, a condition where the prosthesis is loosening due to bone degradation at the peri-prosthetic interface in the absence of infections. The most well-established pathological mechanism for aseptic loosening is related to wear particles, generated from different parts of the prosthesis that will trigger bone degradation and bone loss. In addition, early micromotions of the prosthesis and resulting local pressurized fluid flow in the peri-prosthetic interface (supraphysiological loading) have also been identified as a cause for aseptic loosening. However, it remains unknown what cells are the primary responders to supraphysiological loading, and what underlying physical, cellular and molecular mechanism that triggers osteoclast differentiation and osteolysis.

    In this thesis, we intended to shed light on three currently unknown aspects of mechanical loading-induced peri-prosthetic osteolysis, leading to aseptic loosening of orthopedic prostheses: (1)Which cells are the primary responder to supraphysiological loading? (2)What characteristics of the mechanical stimulus induce an osteo-protective or osteo-destructive response? (3)Which cellular mechano-sensing mechanisms are involved in an osteo-destructive response?

    We successfully implemented supraphysiological mechanical loading, mimicking the periprosthetic pressurized fluid flow around a loosening implant, in an in vitro model for bone implant loosening. Using this model, we uncovered the involvement of mesenchymal stem cells and myeloid progenitor cells (monocytes) in mechanical loading-induced peri-prosthetic osteolysis. Applying supraphysiological loading on cells from patients undergoing primary hip arthroplasty, successfully validated the in vitro model for the use of cells of human origin. We further identified in murine myeloid progenitor cells that a combination of high loading amplitude (3.0±0.2Pa), prolonged active loading duration per cycle (duty cycle 22%-50%), and rapid alterations in minimum/maximum values of the loading profile (square wave) is necessary to induce an osteo-destructive response. Further, the loading-induced ATP release and subsequent activation of the P2X7 receptor was essential for the release of soluble factors modulating osteoclastogenesis.

    In conclusion, we expect that the proposed new in vitro model is a helpful tool to further advance the knowledge in aseptic loosening, by uncovering the mechanoresponsive cellular mechanism to supraphysiological mechanical loading. The identification of the respondent cells in mechanical loading-induced prosthetic loosening gives the opportunity to deliver targeted treatment strategies. Furthermore, identifying the physical parameters that define the shift towards an osteo-destructive response emphasizes the importance of the prosthetic design and surgical technique to reduce mechanical loading-induced bone degradation around a prosthesis.

    List of papers
    1. Supraphysiological loading induces osteocyte-mediated osteoclastogenesis in a novel in vitro model for bone implant loosening
    Open this publication in new window or tab >>Supraphysiological loading induces osteocyte-mediated osteoclastogenesis in a novel in vitro model for bone implant loosening
    Show others...
    2018 (English)In: Journal of Orthopaedic Research, ISSN 0736-0266, E-ISSN 1554-527X, Vol. 36, no 5, p. 1425-1434Article in journal (Refereed) Published
    Abstract [en]

    We aimed to develop an in vitro model for bone implant loosening, allowing analysis of biophysical and biological parameters contributing to mechanical instability-induced osteoclast differentiation and peri-implant bone loss. MLO-Y4-osteocytes were mechanically stimulated for 1h by fluid shear stress using regimes simulating: (i) supraphysiological loading in the peri-prosthetic interface (2.9 +/- 2.9Pa, 1Hz, square wave); (ii) physiologic loading in the cortical bone (0.7 +/- 0.7Pa, 5Hz, sinusoidal wave); and (iii) stress shielding. Cellular morphological parameters, membrane-bound RANKL expression, gene expression influencing osteoclast differentiation, nitric oxide release and caspase 3/7-activity were determined. Either Mouse bone marrow cells were cultured on top of loaded osteocytes or osteocyte-conditioned medium was added to bone marrow cells. Osteoclast differentiation was assessed after 6 days. We found that osteocytes subjected to supraphysiological loading showed similar morphology and caspase 3/7-activity compared to simulated physiological loading or stress shielding. Supraphysiological stimulation of osteocytes enhanced osteoclast differentiation by 1.9-fold compared to physiological loading when cell-to-cell contact was permitted. In addition, it enhanced the number of osteoclasts using conditioned medium by 1.7-fold, membrane-bound RANKL by 3.3-fold, and nitric oxide production by 3.2-fold. The stimulatory effect of supraphysiological loading on membrane-bound RANKL and nitric oxide production was higher than that achieved by stress shielding. In conclusion, the in vitro model developed recapitulated the catabolic biological situation in the peri-prosthetic interface during instability that is associated with osteoclast differentiation and enhanced RANKL expression. The model thus provides a platform for pre-clinical testing of pharmacological interventions with potential to stop instability-induced bone implant loosening. (c) 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1425-1434, 2018.

    Place, publisher, year, edition, pages
    WILEY, 2018
    Keywords
    osteocyte; osteoclast; implant; osteolysis; RANKL
    National Category
    Cell and Molecular Biology
    Identifiers
    urn:nbn:se:liu:diva-150301 (URN)10.1002/jor.23780 (DOI)000434360700015 ()29068483 (PubMedID)
    Note

    Funding Agencies|Swedish Research Council [521-2013-2593, 2016-01822, 2016-06097]; Swedish Governmental Agency for Innovation Systems [2012-04409]

    Available from: 2018-08-16 Created: 2018-08-16 Last updated: 2019-08-21
    2. Mechanical loading releases osteoclastogenesis-modulating factors through stimulation of the P2X7 receptor in hematopoietic progenitor cells
    Open this publication in new window or tab >>Mechanical loading releases osteoclastogenesis-modulating factors through stimulation of the P2X7 receptor in hematopoietic progenitor cells
    2019 (English)In: Journal of Cellular Physiology, ISSN 0021-9541, E-ISSN 1097-4652, Vol. 234, no 8, p. 13057-13067Article in journal (Refereed) Published
    Abstract [en]

    Mechanical instability of bone implants stimulate osteoclast differentiation and peri-implant bone loss, leading to prosthetic loosening. It is unclear which cells at the periprosthetic interface transduce mechanical signals into a biochemical response, and subsequently facilitate bone loss. We hypothesized that mechanical overloading of hematopoietic bone marrow progenitor cells, which are located near to the inserted bone implants, stimulates the release of osteoclast-inducing soluble factors. Using a novel in vitro model to apply mechanical overloading, we found that hematopoietic progenitor cells released adenosine triphosphate (ATP) after only 2min of mechanical loading. The released ATP interacts with its specific receptor P2X7 to stimulate the release of unknown soluble factors that inhibit (physiological loading) or promote (supraphysiological loading) the differentiation of multinucleated osteoclasts derived from bone marrow cultures. Inhibition of ATP-receptor P2X7 by Brilliant Blue G completely abolished the overloading-induced stimulation of osteoclast formation. Likewise, stimulation of P2X7 receptor on hematopoietic cells by BzATP enhanced the release of osteoclastogenesis-stimulating signaling molecules to a similar extent as supraphysiological loading. Supraphysiological loading affected neither gene expression of inflammatory markers involved in aseptic implant loosening (e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor-, and PTGES2) nor expression of the osteoclast modulators receptor activator of nuclear factor -B ligandand osteoprotegerin. Our findings suggest that murine hematopoietic progenitor cells are a potential key player in local mechanical loading-induced bone implant loosening via the ATP/P2X7-axis. Our approach identifies potential therapeutic targets to prevent prosthetic loosening.

    Place, publisher, year, edition, pages
    WILEY, 2019
    Keywords
    fluid flow; implant loosening; mechanoresponsive hematopoietic progenitor cells; osteolysis; purinergic signaling
    National Category
    Cell and Molecular Biology
    Identifiers
    urn:nbn:se:liu:diva-158040 (URN)10.1002/jcp.27976 (DOI)000467240800083 ()30536959 (PubMedID)
    Note

    Funding Agencies|Swedish Research Council [2016-01822, 2016-06097, 521-2013-2593]; Swedish Governmental Agency for Innovation Systems [2012-04409]

    Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-08-21
  • Public defence: 2019-09-25 13:15 Planck, Linköping
    Kargén, Ulf
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Scalable Dynamic Analysis of Binary Code2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years, binary code analysis, i.e., applying program analysis directly at the machine code level, has become an increasingly important topic of study. This is driven to a large extent by the information security community, where security auditing of closed-source software and analysis of malware are important applications. Since most of the high-level semantics of the original source code are lost upon compilation to executable code, static analysis is intractable for, e.g., fine-grained information flow analysis of binary code. Dynamic analysis, however, does not suffer in the same way from reduced accuracy in the absence of high-level semantics, and is therefore also more readily applicable to binary code. Since fine-grained dynamic analysis often requires recording detailed information about every instruction execution, scalability can become a significant challenge. In this thesis, we address the scalability challenges of two powerful dynamic analysis methods whose widespread use has, so far, been impeded by their lack of scalability: dynamic slicing and instruction trace alignment. Dynamic slicing provides fine-grained information about dependencies between individual instructions, and can be used both as a powerful debugging aid and as a foundation for other dynamic analysis techniques. Instruction trace alignment provides a means for comparing executions of two similar programs and has important applications in, e.g., malware analysis, security auditing, and plagiarism detection. We also apply our work on scalable dynamic analysis in two novel approaches to improve fuzzing — a popular random testing technique that is widely used in industry to discover security vulnerabilities.

    To use dynamic slicing, detailed information about a program execution must first be recorded. Since the amount of information is often too large to fit in main memory, existing dynamic slicing methods apply various time-versus-space trade-offs to reduce memory requirements. However, these trade-offs result in very high time overheads, limiting the usefulness of dynamic slicing in practice. In this thesis, we show that the speed of dynamic slicing can be greatly improved by carefully designing data structures and algorithms to exploit temporal locality of programs. This allows avoidance of the expensive trade-offs used in earlier methods by accessing recorded runtime information directly from secondary storage without significant random-access overhead. In addition to being a standalone contribution, scalable dynamic slicing also forms integral parts of our contributions to fuzzing. Our first contribution uses dynamic slicing and binary code mutation to automatically turn an existing executable into a test generator. In our experiments, this new approach to fuzzing achieved about an order of magnitude better code coverage than traditional mutational fuzzing and found several bugs in popular Linux software. The second work on fuzzing presented in this thesis uses dynamic slicing to accelerate the state-of-the-art fuzzer AFL by focusing the fuzzing effort on previously unexplored parts of the input space.

    For the second dynamic analysis technique whose scalability we sought to improve — instruction trace alignment — we employed techniques used in speech recognition and information retrieval to design what is, to the best of our knowledge, the first general approach to aligning realistically long program traces. We show in our experiments that this method is capable of producing meaningful alignments even in the presence of significant syntactic differences stemming from, for example, the use of different compilers or optimization levels.

    List of papers
    1. Efficient Utilization of Secondary Storage for Scalable Dynamic Slicing
    Open this publication in new window or tab >>Efficient Utilization of Secondary Storage for Scalable Dynamic Slicing
    2014 (English)In: Proceedings of the 2014 IEEE 14th International Working Conference on Source Code Analysis and Manipulation / [ed] Randall Bilof, IEEE , 2014, p. 155-164Conference paper, Published paper (Refereed)
    Abstract [en]

    Dynamic program slicing is widely recognized as a powerful aid for e.g. Program comprehension during debugging. However, its widespread use has been impeded in part by scalability issues that occur when constructing the dynamic dependence graph necessary to compute dynamic slices. A few seconds of execution time on a modern CPU can easily yield dynamic dependence graphs on the order of tens of gigabytes in size. Existing methods either produce imprecise slices, incur large time overheads during slice computation, or run out of memory for long program executions. By carefully designing our method to take advantage of locality, we are able to efficiently use secondary storage for dynamic dependence graphs, thus allowing our method to scale to long program executions. Our prototype implementation runs directly on x86 executables, eliminating problems with e.g. Binary-only libraries. We show in our experiments that graphs can be constructed for program runs with billions of executed instructions, at slowdowns ranging from 62x to 173x. Our optimized format also allows graphs to be traversed at speeds of several million dependence edges per second.

    Place, publisher, year, edition, pages
    IEEE, 2014
    Keywords
    binary analysis, debugging, dynamic dependence graph, dynamic slicing, x86
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-117289 (URN)10.1109/SCAM.2014.24 (DOI)000358876700020 ()978-0-7695-5304-7 (ISBN)
    Conference
    14th IEEE International Working Conference on Source Code Analysis and Manipulation, Victoria, British Columbia, Canada, September 28-29, 2014
    Available from: 2015-04-22 Created: 2015-04-22 Last updated: 2019-08-16
    2. Towards Robust Instruction-Level Trace Alignment of Binary Code
    Open this publication in new window or tab >>Towards Robust Instruction-Level Trace Alignment of Binary Code
    2017 (English)In: PROCEEDINGS OF THE 2017 32ND IEEE/ACM INTERNATIONAL CONFERENCE ON AUTOMATED SOFTWARE ENGINEERING (ASE17), IEEE , 2017, p. 342-352Conference paper, Published paper (Refereed)
    Abstract [en]

    Program trace alignment is the process of establishing a correspondence between dynamic instruction instances in executions of two semantically similar but syntactically different programs. In this paper we present what is, to the best of our knowledge, the first method capable of aligning realistically long execution traces of real programs. To maximize generality, our method works entirely on the machine code level, i.e. it does not require access to source code. Moreover, the method is based entirely on dynamic analysis, which avoids the many challenges associated with static analysis of binary code, and which additionally makes our approach inherently resilient to e.g. static code obfuscation. Therefore, we believe that our trace alignment method could prove to be a useful aid in many program analysis tasks, such as debugging, reverse-engineering, investigating plagiarism, and malware analysis. We empirically evaluate our method on 11 popular Linux programs, and show that it is capable of producing meaningful alignments in the presence of various code transformations such as optimization or obfuscation, and that it easily scales to traces with tens of millions of instructions.

    Place, publisher, year, edition, pages
    IEEE, 2017
    Series
    IEEE ACM International Conference on Automated Software Engineering, ISSN 1527-1366
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-143959 (URN)10.1109/ASE.2017.8115647 (DOI)000417469700038 ()978-1-5386-2684-9 (ISBN)978-1-5386-3976-4 (ISBN)
    Conference
    32nd IEEE/ACM International Conference on Automated Software Engineering (ASE)
    Available from: 2017-12-29 Created: 2017-12-29 Last updated: 2019-08-16
    3. Turning programs against each other: high coverage fuzz-testing using binary-code mutation and dynamic slicing
    Open this publication in new window or tab >>Turning programs against each other: high coverage fuzz-testing using binary-code mutation and dynamic slicing
    2015 (English)In: 2015 10TH JOINT MEETING OF THE EUROPEAN SOFTWARE ENGINEERING CONFERENCE AND THE ACM SIGSOFT SYMPOSIUM ON THE FOUNDATIONS OF SOFTWARE ENGINEERING (ESEC/FSE 2015) PROCEEDINGS, New York, NY, USA: Association for Computing Machinery (ACM), 2015, p. 782-792Conference paper, Published paper (Refereed)
    Abstract [en]

    Mutation-based fuzzing is a popular and widely employed black-box testing technique for finding security and robustness bugs in software. It owes much of its success to its simplicity; a well-formed seed input is mutated, e.g. through random bit-flipping, to produce test inputs. While reducing the need for human effort, and enabling security testing even of closed-source programs with undocumented input formats, the simplicity of mutation-based fuzzing comes at the cost of poor code coverage. Often millions of iterations are needed, and the results are highly dependent on configuration parameters and the choice of seed inputs. In this paper we propose a novel method for automated generation of high-coverage test cases for robustness testing. Our method is based on the observation that, even for closed-source programs with proprietary input formats, an implementation that can generate well-formed inputs to the program is typically available. By systematically mutating the program code of such generating programs, we leverage information about the input format encoded in the generating program to produce high-coverage test inputs, capable of reaching deep states in the program under test. Our method works entirely at the machine-code level, enabling use-cases similar to traditional black-box fuzzing. We have implemented the method in our tool MutaGen, and evaluated it on 7 popular Linux programs. We found that, for most programs, our method improves code coverage by one order of magnitude or more, compared to two well-known mutation-based fuzzers. We also found a total of 8 unique bugs.

    Place, publisher, year, edition, pages
    New York, NY, USA: Association for Computing Machinery (ACM), 2015
    Keywords
    Fuzz testing, fuzzing, black-box, dynamic slicing, program mutation
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-128810 (URN)10.1145/2786805.2786844 (DOI)000382568700067 ()978-1-4503-3675-8 (ISBN)
    Conference
    10th Joint Meeting on Foundations of Software Engineering
    Available from: 2016-05-31 Created: 2016-05-31 Last updated: 2019-08-16
    4. Speeding Up Bug Finding using Focused Fuzzing
    Open this publication in new window or tab >>Speeding Up Bug Finding using Focused Fuzzing
    2019 (English)In: Proceedings of the 13th International Conference on Availability, Reliability and Security, ACM Digital Library, 2019, article id 7Conference paper, Published paper (Refereed)
    Abstract [en]

    Greybox fuzzing has recently emerged as a scalable and practical approach to finding security bugs in software. For example, AFL — the current state-of-the-art greybox fuzzer — has found hundreds of vulnerabilities in popular software since its release in 2013. The combination of lightweight coverage instrumentation and a simple evolutionary algorithm allows AFL to quickly generate inputs that exercise new code. AFL also obviates the need to manually set ad-hoc fuzzing ratios, which has been a major limitation of classical black-box fuzzers. Instead, AFL's first fuzzing pass exhaustively applies a set of mutations to every byte of a program input. While this approach allows for more thorough exploration of the input space, and therefore improves the chances of finding complex bugs, it also drastically slows down the fuzzing progress for "heavyweight" programs, or programs that take large inputs. This makes AFL less suitable for fuzzing input formats with large size overhead, such as various document formats. In this paper, we propose focused fuzzing as a practical trade-off between thoroughness and speed, for fuzzers that employ input mutation. We extend the notion of code coverage to individual bytes of input, and show how forward dynamic slicing can be used to efficiently determine the set of program instructions that are affected by a particular input byte. This information can then be used to restrict expensive mutations to a small subset of input bytes. We implement focused fuzzing on top of AFL, and evaluate it on four "real-life" Linux programs. Our evaluation shows that focused fuzzing noticeably improves bug discovery, compared to vanilla AFL.

    Place, publisher, year, edition, pages
    ACM Digital Library, 2019
    Keywords
    fuzzing, AFL, dynamic slicing, focused fuzzing
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-152737 (URN)10.1145/3230833.3230867 (DOI)000477981800013 ()978-1-4503-6448-5 (ISBN)
    Conference
    13th International Conference on Availability, Reliability and Security, Hamburg, Germany, August 27 - 30, 2018
    Available from: 2018-11-19 Created: 2018-11-19 Last updated: 2019-08-19
  • Public defence: 2019-09-27 09:00 Hasselqvistsalen, Hus 511, Linköping
    Lundgren, Linda
    Linköping University, Department of Clinical and Experimental Medicine, Division of Surgery, Orthopedics and Oncology. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Surgery in Linköping.
    Incidental Gallbladder Cancer: Incidence, predictors, management and outcome in a Swedish population2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Background: Cholecystectomy is a common surgical procedure and incidental gallbladder cancer is a rare and unexpected finding at a cholecystectomy performed upon benign indications. Whether to perform routine or selective histopathology of the gallbladder specimen is still a subject for discussion. The prognosis of gallbladder cancer is largely affected by tumour stage and treatment.

    Aims: The overall aim was to study whether routine histological examination of the gallbladder specimen is of clinical and health economic value; determine if there are any predictive factors of incidental gallbladder cancer at benign cholecystectomy and compare the management and outcome of incidental gallbladder cancer patients in Sweden.

    Methods: All studies were based on registry data from GallRiks (The Swedish Registry for Gallstone Surgery and Endoscopic Retrograde Cholangiopancreatography) between 2007 and 2016, with some modifications between studies. Complemental cross-linkage was made to national registries, and medical records were reviewed. Papers I, II and III were population-based observational studies with prospectively and retrospectively collected data. Paper IV was a health economic evaluation based on the results from papers I and III.

    Results and conclusions: Hospitals submitting >75 per cent of gallbladder specimens diagnosed a higher proportion of incidental gallbladder cancer than did hospitals submitting ≤25 per cent of samples (paper I). Incidental gallbladder cancer was more prevalent in older patients, women and patients with acute or previous cholecystitis, as well as ongoing jaundice. The risk model based on predictive preoperative factors was further improved by adding a macroscopic assessment of the gallbladder (paper II). Predictive factors for gallbladder cancer appeared to have an impact on which specimens were submitted in hospitals with a selective approach of histopathology (paper I). For pT2 and pT3 patients, re-resection improved diseasespecific survival, although these groups differed in terms of age and comorbidity (paper III). Residual disease was an independent factor for impaired survival. A change to routine histopathology of gallbladder specimens in Sweden would lead to increased costs with little improved health outcomes. Instead, a more standardized approach to selective histology would be needed (paper IV).

    List of papers
    1. Are Incidental Gallbladder Cancers Missed with a Selective Approach of Gallbladder Histology at Cholecystectomy?
    Open this publication in new window or tab >>Are Incidental Gallbladder Cancers Missed with a Selective Approach of Gallbladder Histology at Cholecystectomy?
    Show others...
    2018 (English)In: World Journal of Surgery, ISSN 0364-2313, E-ISSN 1432-2323, Vol. 42, no 4, p. 1092-1099Article in journal (Refereed) Published
    Abstract [en]

    Incidental gallbladder cancer (IGBC) is an unexpected finding when a cholecystectomy is performed upon a benign indication, and the use of routine or selective histological analysis of gallbladder specimen is still debated. The aim of this study was to investigate whether the proportion of submitted gallbladder specimens for pathological investigation influences the proportion of IGBC found, and what possible factors preoperatively or perioperatively could influence the selection process. All cholecystectomies between January 2007 and September 2014 registered in the Swedish Registry of Gallstone Surgery and ERCP (GallRiks) were included. Proportion of histological analysis was divided into four subgroups (0-25%, amp;gt; 25-50%, amp;gt; 50-75%, amp;gt; 75-100%). A total of 81,349 cholecystectomies were registered, and 36,010 (44.3%) gallbladder specimens were sent for histological analysis. A total of 213 cases of IGBC were discovered, which constituted 0.26% of all cholecystectomies performed and 0.59% of the number of gallbladder specimens sent for histological analysis. Hospitals submitting amp;gt; 75-100% of the gallbladder specimens had significantly more IGBC/1000 cholecystectomies performed (p = 0.003). Hospitals with the most selective approach had a significantly higher proportion of IGBC/1000 gallbladders that were sent for histological analysis (p amp;lt; 0.001). Factors such as higher age (p amp;lt; 0.001), female gender (p = 0.048) and macroscopic cholecystitis (p amp;lt; 0.001) were more common in gallbladder specimens from hospitals that had a selective approach to histological analysis. A routine approach to histological analysis in cholecystectomies with a benign indication for surgery can uncover a higher proportion of IGBC cases. When a selective approach is used, risk factors should be taken into account.

    Place, publisher, year, edition, pages
    SPRINGER, 2018
    National Category
    Surgery
    Identifiers
    urn:nbn:se:liu:diva-147095 (URN)10.1007/s00268-017-4215-0 (DOI)000427050900023 ()28900706 (PubMedID)
    Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2019-08-23
    2. Predictors of incidental gallbladder cancer in patients undergoing cholecystectomy for benign gallbladder disease: Results from a population-based gallstone surgery registry
    Open this publication in new window or tab >>Predictors of incidental gallbladder cancer in patients undergoing cholecystectomy for benign gallbladder disease: Results from a population-based gallstone surgery registry
    Show others...
    2017 (English)In: Surgery, ISSN 0039-6060, E-ISSN 1532-7361, Vol. 162, no 2, p. 256-263Article in journal (Refereed) Published
    Abstract [en]

    Background. Gallbladder cancer is a rare neoplasm with a poor prognosis. Early diagnosis and correct treatment strategy is important. The aim of this study was to identify predictors for incidental gallbladder cancer. Methods. Data from cholecystectomies registered in the nationwide Swedish Register for Gallstone Surgery between 2007 and 2014 were analyzed for incidental gallbladder cancer. Exclusion criteria were patients with a gallbladder not sent for histopathology, preoperative suspicion of polyps/gallbladder cancer, and indication for operation for other reasons than gallstone disease. Predictive factors for incidental gallbladder cancer were identified using multivariable logistic regression. Results. A total of 86,154 procedures were registered in the Swedish Register for Gallstone Surgery. Of these, 36,355 patients were included in the analysis, and 215 of the included patients had incidental gallbladder cancer (0.59%). Mean age was 70 11 years for index cases and 54 16 years for the control group, and 80% of cases and 60% of controls were female. Predictors for incidental gallbladder cancer were older age (odds ratio = 1.08; P amp;lt; .001), female sex (odds ratio = 3.58; P amp;lt; .001), previous cholecystitis (odds ratio = 1.37; P = .045), and the combination of acute cholecystitis without jaundice (odds ratio = 1.39; P = .041) and jaundice without acute cholecystitis (odds ratio = 2.02; P = .009). A preoperative risk model including these factors gave an area under receiver operating characteristic curve of 0.82. By adding macroscopic evaluation of the gallbladder by the surgeon, the area under receiver operating characteristic curve increased to 0.87. Intraoperatively suspected gallbladder cancer was confirmed as cancer in 31 % of the cases. Conclusion. Incidental gallbladder cancer is more likely to be diagnosed in older patients, women, and after previous cholecystitis. Jaundice and acute cholecystitis were also shown to be important risk factors. Intraoperative inspection of the gallbladder improved the risk model.

    Place, publisher, year, edition, pages
    MOSBY-ELSEVIER, 2017
    National Category
    Surgery
    Identifiers
    urn:nbn:se:liu:diva-139810 (URN)10.1016/j.surg.2017.02.009 (DOI)000406087900006 ()28400123 (PubMedID)
    Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2019-08-23
    3. Management of incidental gallbladder cancer in a national cohort
    Open this publication in new window or tab >>Management of incidental gallbladder cancer in a national cohort
    Show others...
    2019 (English)In: British Journal of Surgery, ISSN 0007-1323, E-ISSN 1365-2168, Vol. 106, no 9, p. 1216-1227Article in journal (Refereed) Published
    Abstract [en]

    Background Incidental gallbladder cancer is a rare event, and its prognosis is largely affected by the tumour stage and treatment. The aim of this study was to analyse the management, treatment and survival of patients with incidental gallbladder cancer in a national cohort over a decade. Methods Patients were identified through the Swedish Registry of Gallstone Surgery (GallRiks). Data were cross-linked to the national registry for liver surgery (SweLiv) and the Cancer Registry. Medical records were collected if registry data were missing. Survival was measured as disease-specific survival. The study was divided into two intervals (2007-2011 and 2012-2016) to evaluate changes over time. Results In total, 249 patients were identified with incidental gallbladder cancer, of whom 92 (36 center dot 9 per cent) underwent re-resection with curative intent. For patients with pT2 and pT3 disease, median disease-specific survival improved after re-resection (12 center dot 4 versus 44 center dot 1 months for pT2, and 9 center dot 7 versus 23 center dot 0 months for pT3). Residual disease was present in 53 per cent of patients with pT2 tumours who underwent re-resection; these patients had a median disease-specific survival of 32 center dot 2 months, whereas the median was not reached in patients without residual disease. Median survival increased by 11 months for all patients between the early and late periods (P = 0 center dot 030). Conclusion Re-resection of pT2 and pT3 incidental gallbladder cancer was associated with improved survival, but survival was impaired when residual disease was present. A higher re-resection rate and more R0 resections in the later time period may have been associated with improved survival.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2019
    National Category
    Surgery
    Identifiers
    urn:nbn:se:liu:diva-159068 (URN)10.1002/bjs.11205 (DOI)000474059700001 ()31259388 (PubMedID)
    Available from: 2019-07-22 Created: 2019-07-22 Last updated: 2019-08-23
  • Public defence: 2019-09-27 10:15 Planck, House B, Linköping
    Kasebzadeh, Parinaz
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Learning Human Gait2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Pedestrian navigation in body-worn devices is usually based on global navigation satellite systems (GNSS), which is a sufficient solution in most outdoor applications. Pedestrian navigation indoors is much more challenging. Further, GNSS does not provide any specific information about the gait style or how the device is carried. This thesis presents three contributions for how to learn human gait parameters for improved dead-reckoning indoors, and to classify the gait style and how the device is carried, all supported with extensive test data.

    The first contribution of this thesis is a novel approach to support pedestrian navigation in situations when GNSS is not available. A novel filtering approach, based on a multi-rate Kalman filter bank, is employed to learn the human gait parameters when GNSS is available using data from an inertial measurement unit (IMU). In a typical indoor-outdoor navigation application, the gait parameters are learned outdoors and then used to improve the pedestrian navigation indoors using dead-reckoning methods. The performance of the proposed method is evaluated with both simulated and experimental data.

    Secondly, an approach for estimating a unique gait signature from the inertial measurements provided by IMU-equipped handheld devices is proposed. The gait signatures, defined as one full cycle of the human gait, are obtained for multiple human motion modes and device carrying poses. Then, a parametric model of each signature, using Fourier series expansion, is computed. This provides a low-dimensional feature vector that can be used in medical diagnosis of certain physical or neurological diseases, or for a generic classification service outlined below.

    The third contribution concerns joint motion mode and device pose classification using the set of features described above. The features are extracted from the received IMU gait measurement and the computed gait signature. A classification framework is presented which includes standard classifiers, e.g. Gaussian process and neural network, with an additional smoothing stage based on hidden Markov model.

    There seems to be a lack of publicly available data sets in these kind of applications. The extensive datasets developed in this work, primarily for performance evaluation, have been documented and published separately. In the largest dataset, several users with four body-worn devices and 17 body-mounted IMUs performed a large number of repetitive experiments, with special attention to get well annotated data with ground truth position, motion mode and device pose.

  • Public defence: 2019-10-04 13:00 K2, Kåkenus, Norrköping
    Frejd, Johanna
    Linköping University, Department of Social and Welfare Studies, Learning, Aesthetics, Natural science. Linköping University, Faculty of Educational Sciences.
    Encountering Evolution: Children’s Meaning-Making Processes in Collaborative Interactions2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis explores preschool class children’s meaning making processes when they encounter evolution. By adopting social semiotic and sociocultural perspectives on meaning making, three group-based tasks were designed. Video data from the activities were analysed using a multimodal approach. The analysis focuses on how the communicated science content affects the science focus of the tasks, how different materials function as semiotic resources and influence meaning making, and interactive aspects of doing science in the meaning-making processes.

    The findings reveal that, by using the provided materials and their previous experiences, the children argue for different reasons for animal diversity and evolution. Throughout the tasks, a child-centric view of life emerged in a salient manner. This means that, apart from the science focus, the children also emphasise other aspects that they find important. The child-centric perspective is suggested to be a strength that enables children to engage in science activities.

    The results show that the provided materials had three functions. Children use materials as resources providing meaning. This means that the children draw on the meaning potential of the materials, a process that is influenced by their previous experiences. Moreover, in interaction with peers, the materials also serve as communicative and argumentative tools. Thus, access to materials influences the children’s meaning making and enables them to discuss evolution and “do science”.

    The findings also reveal an intimate relationship between task context and interaction. More scripted tasks convey more child–adult interaction (scaffolding) while less scripted tasks, during which children build on previous experiences instead of communicated science content, stimulates child–child interaction (mutual collaboration). In scaffolding interactions, a greater emphasis is placed on the science topic of the task due to guidance from the adult. Consequently, meanings made by children in more scripted tasks are more likely to be “scientifically correct”. However, if the teacher or the adult steps back and allows the children to engage in mutual collaboration, they engage in multiple ways of doing science through evaluating, observing, describing and comparing.

    Overall, the research reported in this thesis suggests that task contexts and materials have a great impact on children’s meaning making and how science is done.

    List of papers
    1. “If It Lived Here, It Would Die.” Children’s Useof Materials as Semiotic Resources in GroupDiscussions About Evolution
    Open this publication in new window or tab >>“If It Lived Here, It Would Die.” Children’s Useof Materials as Semiotic Resources in GroupDiscussions About Evolution
    2018 (English)In: Journal of Research in Childhood Education, ISSN 0256-8543, E-ISSN 2150-2641, Vol. 32, no 3, p. 251-267Article in journal (Refereed) Published
    Abstract [en]

    With the aim of exploring how children discuss underlying reasons forevolution and how materials function in children’s meaning making processes,this article provides insight into how evolution theory can beintroduced in preschool and in the early years of primary school. Videodata from eight group discussions (N = 27) were analyzed using a multimodalperspective. Despite not having had any formal instruction aboutevolution theory, the 6-year-old children in this study made use of theirprevious experiences and the materials to make meaning and argue fordifferent reasons for animal diversity. The results show that the children’sdiscussions concerned four conceptual themes: animals are differentbecause of kinship and heredity, environmental effects, the need for adaptation,and the need for geographic separation. The children used theprovided materials, comprising photographs, figurines, and a topographicworld map, as resources for providing meaning, as argumentative tools, andas tools for communication. By making observations in a logical and scientificway, the children spontaneously discussed similarities and differencesin traits, which implies that variation might be a fruitful way to introduceevolution theory to preschool children.

    Place, publisher, year, edition, pages
    London and New York: Taylor & Francis, 2018
    Keywords
    Early childhood; group discussion; materials; meaning making; science
    National Category
    Didactics
    Identifiers
    urn:nbn:se:liu:diva-150935 (URN)10.1080/02568543.2018.1465497 (DOI)
    Available from: 2018-09-05 Created: 2018-09-05 Last updated: 2019-08-21
    2. When Children Do Science: Collaborative Interactions in Preschoolers’ Discussions About Animal Diversity
    Open this publication in new window or tab >>When Children Do Science: Collaborative Interactions in Preschoolers’ Discussions About Animal Diversity
    2019 (English)In: Research in science education, ISSN 0157-244X, E-ISSN 1573-1898Article in journal (Refereed) Published
    Abstract [en]

    With the aim of exploring how science is done in collaborative interactions when children discuss reasons for animal diversity, this paper provides insight into the relationships between acts of doing science and collaborative interactions. Video data from four small-group discussions (N = 14) were analysed using Lemke’s (1990) talking science framework and Granott’s (1993) collaborative interaction framework. During their interactions, the children make use of their prior experiences and the materials provided as they engage in acts of doing science. The findings reveal that 6-year-old children are able to engage in science dialogue as they use observations and comparisons as data to generate, describe and discuss ideas. Moreover, while engaged in highly collaborative interactions, the children use observations to evaluate, challenge and question each other. Overall, the study sheds light on how acts of doing science can be perceived in young students’ discussions about science phenomena. The study indicates that the character of the collaborative interactions is an important factor for how acts of doing science are carried out.

    Keywords
    Early Childhood, Biology, Group discussion, Interaction, Multimodality
    National Category
    Didactics
    Identifiers
    urn:nbn:se:liu:diva-158505 (URN)10.1007/s11165-019-9822-3 (DOI)
    Available from: 2019-07-02 Created: 2019-07-02 Last updated: 2019-08-21