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  • Disputation: 2019-08-27 09:15 Planck, Fysikhuset, Linköping
    Yuan, Zhongcheng
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Defects and crystallinity control of perovskite films for light-emitting diodes2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. Rational molecular passivation for high-performance perovskite light-emitting diodes
    Öppna denna publikation i ny flik eller fönster >>Rational molecular passivation for high-performance perovskite light-emitting diodes
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    2019 (Engelska)Ingår i: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893, Vol. 13, nr 6, s. 418-424Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Springer Nature Publishing AG, 2019
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:liu:diva-157707 (URN)10.1038/s41566-019-0390-x (DOI)000468752300019 ()
    Anmärkning

    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 

    Tillgänglig från: 2019-06-19 Skapad: 2019-06-19 Senast uppdaterad: 2019-07-01Bibliografiskt granskad
    2. Room-temperature film formation of metal halide perovskites on n-type metal oxides: the catalysis of ZnO on perovskite crystallization
    Öppna denna publikation i ny flik eller fönster >>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 (Engelska)Ingår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, nr 50, s. 6887-6890Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    ROYAL SOC CHEMISTRY, 2018
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-149712 (URN)10.1039/c8cc02482k (DOI)000436029000052 ()29781476 (PubMedID)
    Anmärkning

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

    Tillgänglig från: 2018-07-24 Skapad: 2018-07-24 Senast uppdaterad: 2019-06-19
  • Disputation: 2019-09-02 13:00 Belladonnasalen, Linköping
    Bergkvist, Max
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för Kirurgi, Ortopedi och Onkologi. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Sinnescentrum, Hand- och plastikkirurgiska kliniken US.
    Studies on Polarised Light Spectroscopy2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.  

    Delarbeten
    1. Polarized Light Spectroscopy for Measurement of the Microvascular Response to Local Heating at Multiple Skin Sites
    Öppna denna publikation i ny flik eller fönster >>Polarized Light Spectroscopy for Measurement of the Microvascular Response to Local Heating at Multiple Skin Sites
    2012 (Engelska)Ingår i: Microcirculation, ISSN 1073-9688, E-ISSN 1549-8719, Vol. 19, nr 8, s. 705-713Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Informa Healthcare / John Wiley and Sons, 2012
    Nyckelord
    tissue viability imaging; polarization light spectroscopy; local heating; red blood cell concentration; reproducibility
    Nationell ämneskategori
    Medicin och hälsovetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-87225 (URN)10.1111/j.1549-8719.2012.00203.x (DOI)000311373400004 ()
    Tillgänglig från: 2013-01-14 Skapad: 2013-01-14 Senast uppdaterad: 2019-07-23
    2. Assessment of microcirculation of the skin using Tissue Viability Imaging: A promising technique for detecting venous stasis in the skin
    Öppna denna publikation i ny flik eller fönster >>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 (Engelska)Ingår i: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 101, s. 20-25Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2015
    Nyckelord
    Tissue viability imaging; Laser Doppler flowmetry; Post-occusive hyperaemia; Venous occlusion; Arterial occlusion
    Nationell ämneskategori
    Klinisk medicin
    Identifikatorer
    urn:nbn:se:liu:diva-121302 (URN)10.1016/j.mvr.2015.06.002 (DOI)000360028500004 ()26092681 (PubMedID)
    Anmärkning

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

    Tillgänglig från: 2015-09-16 Skapad: 2015-09-14 Senast uppdaterad: 2019-07-23Bibliografiskt granskad
    3. Vascular Occlusion in a Porcine Flap Model: Effects on Blood Cell Concentration and Oxygenation.
    Öppna denna publikation i ny flik eller fönster >>Vascular Occlusion in a Porcine Flap Model: Effects on Blood Cell Concentration and Oxygenation.
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    2017 (Engelska)Ingår i: Plastic and reconstructive surgery. Global open, ISSN 2169-7574, Vol. 5, nr 11, artikel-id e1531Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Wolters Kluwer, 2017
    Nationell ämneskategori
    Radiologi och bildbehandling Kirurgi
    Identifikatorer
    urn:nbn:se:liu:diva-145391 (URN)10.1097/GOX.0000000000001531 (DOI)29263951 (PubMedID)2-s2.0-85038559789 (Scopus ID)
    Tillgänglig från: 2018-02-27 Skapad: 2018-02-27 Senast uppdaterad: 2019-07-23Bibliografiskt granskad
  • Disputation: 2019-09-06 09:00 Originalet, Qulturum, Jönköping
    Taxbro, Knut
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för läkemedelsforskning. Linköpings universitet, Medicinska fakulteten.
    Vascular access in cancer patients – clinical implications2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. A prospective observational study on 249 subcutaneous central vein access ports in a Swedish county hospital
    Öppna denna publikation i ny flik eller fönster >>A prospective observational study on 249 subcutaneous central vein access ports in a Swedish county hospital
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    2013 (Engelska)Ingår i: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 52, nr 5, s. 893-901Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Informa Healthcare, 2013
    Nationell ämneskategori
    Medicin och hälsovetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-93959 (URN)10.3109/0284186X.2013.770601 (DOI)000318655300003 ()
    Anmärkning

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

    Tillgänglig från: 2013-06-13 Skapad: 2013-06-13 Senast uppdaterad: 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
    Öppna denna publikation i ny flik eller fönster >>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 (Engelska)Ingår i: British Journal of Anaesthesia, ISSN 0007-0912, E-ISSN 1471-6771, Vol. 122, nr 6, s. 734-741Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2019
    Nyckelord
    central venous catheter; central venous catheter thrombosis; peripherally inserted central catheter line insertion; vascular access devices
    Nationell ämneskategori
    Kirurgi
    Identifikatorer
    urn:nbn:se:liu:diva-158319 (URN)10.1016/j.bja.2019.01.038 (DOI)000467806400034 ()31005243 (PubMedID)2-s2.0-85064326103 (Scopus ID)
    Anmärkning

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

    Tillgänglig från: 2019-07-02 Skapad: 2019-07-02 Senast uppdaterad: 2019-08-12Bibliografiskt granskad
  • Disputation: 2019-09-09 10:00 ACAS, A-huset, Linköping
    Farhad, Nandita
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell ekonomi. Linköpings universitet, Tekniska fakulteten.
    Supply Chain Governance for Social Sustainability: A Study of the Ready-Made Garment Industry in Bangladesh2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Denna doktorsavhandling tar sig an fenomenet leverantörsstyrning för social hållbarhet i klädindustrin i Bangladesh. Forskningen baseras på en studie av åtta stora multinationella företag, tillika återförsäljare av kläder och välkända klädmärken. Syftet med studien är att förstå hur leverantörsstyrningsmekanismer och styrstrukturer kan förbättra socialt hållbarhetsarbete när flera aktörer är engagerade och samverkar.

    Resultatet av studien indikerar att multinationella företag de facto engagerar sig med andra aktörer för att förbättra sin förmåga att bedriva socialt hållbarhetsarbete. Studien identifierar fyra olika typer av leverantörsstyrsystem: ett marknadsbaserat, ett hierarkiskt kontrollbaserat, ett kollaborativt multi-intressentbaserat samt ett relationellt sektorsövergripande system. Dessa styrningssystem tillämpas i leverantörskedjan av de multinationella företagen i samarbete med andra aktörer såsom leverantörer, ‘multi-intressentinitiativ’ och icke-statliga organisationer. Studien fokuserar dels på de utmaningar som föreligger för de multinationella företagen när det gäller att säkerställa social hållbarhet, dels på hur leverantörer uppfattar konsekvenserna av de olika styrningssystemen för social hållbarhet.

    Denna forskning visar att valet av styrstruktur, från marknadsbaserad, hierarkibaserad, kollaborativ och relationell är beroende dels av kostnaden för att hantera och upprätthålla relationer med de olika aktörerna, dels av de potentiella riskerna som föreligger i en viss situation. Vad som utgör en effektiv styrstruktur för ett multinationellt företag i en viss given kontext avgörs av hur väl strukturen stödjer styrningsmekanismer för att reducera transaktionsrisker som bottnar i ett potentiellt opportunistiskt beteende hos leverantörerna. I denna forskning argumenteras det för att struktur ger en plattform för att tillämpa ett antal styrningsmekanismer.

    Studien visar att styrning av social hållbarhet omfattar tre typer av mekanismer med olika utgång. En består av köparstyrda styrningsmekanismer som omfattar uppförandekoder, leverantörskontroll och leverantörsutbildning. Den andra består av multi-initiativbaserade styrningsmekanismer av hur det strukturella arbetet för att hantera oväntade problem (t.ex. bygg-, el- och brandsäkerhetsrisker) efterföljs. Det tredje omfattar sektorsövergripande styrningsmekanismer där de multinationella företagen samverkar med lokala icke-statliga organisationer i projekt som syftar till social utveckling (tillgång till rent vatten, hälso- & utbildningsinsatser, etc.) för fabriksarbetarna och det omgivande samhället.

    Denna avhandling bidrar till Sustainable Supply Chain Management-litteraturen då den utvidgar kunskapen om leverantörsstyrning för social hållbarhet genom en den ger en ökad förståelse för styrningsmekanismer, styrstrukturer och olika aktörers engagemang för social hållbarhet. I takt med att behovet av leverantörsstyrning för social hållbarhet ökar kan denna avhandling hjälpa ansvariga ‘corporate sourcing managers’ att utveckla en fördjupad förståelse för hur leverantörsstyrning kan påverka social hållbarhet.

  • Disputation: 2019-09-12 09:00 Berzeliussalen, Linköping
    Vahdat Shariatpanahi, Aida
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    The Importance of Macrophages, Lipid Membranes and Seeding in Experimental AA Amyloidosis2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. Depletion of Spleen Macrophages Delays AA Amyloid Development: A Study Performed in the Rapid Mouse Model of AA Amyloidosis
    Öppna denna publikation i ny flik eller fönster >>Depletion of Spleen Macrophages Delays AA Amyloid Development: A Study Performed in the Rapid Mouse Model of AA Amyloidosis
    2013 (Engelska)Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, nr 11, s. e79104-Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Public Library of Science, 2013
    Nationell ämneskategori
    Medicin och hälsovetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-102982 (URN)10.1371/journal.pone.0079104 (DOI)000327254700092 ()
    Anmärkning

    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||

    Tillgänglig från: 2014-01-09 Skapad: 2014-01-09 Senast uppdaterad: 2019-08-15
    2. Lipid membranes accelerate amyloid formation in the mouse model of AA amyloidosis
    Öppna denna publikation i ny flik eller fönster >>Lipid membranes accelerate amyloid formation in the mouse model of AA amyloidosis
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    2019 (Engelska)Ingår i: Amyloid: Journal of Protein Folding Disorders, ISSN 1350-6129, E-ISSN 1744-2818, Vol. 26, nr 1, s. 34-44Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Taylor & Francis, 2019
    Nyckelord
    Amyloid; liposomes; lipid membrane; macrophages; AA amyloidosis
    Nationell ämneskategori
    Medicinsk bioteknologi (med inriktning mot cellbiologi (inklusive stamcellsbiologi), molekylärbiologi, mikrobiologi, biokemi eller biofarmaci)
    Identifikatorer
    urn:nbn:se:liu:diva-157278 (URN)10.1080/13506129.2019.1576606 (DOI)000466218300001 ()30929476 (PubMedID)2-s2.0-85063746690 (Scopus ID)
    Anmärkning

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

    Tillgänglig från: 2019-06-12 Skapad: 2019-06-12 Senast uppdaterad: 2019-08-15Bibliografiskt granskad
  • Disputation: 2019-09-12 10:15 Planck, Fysikhuset, Linköping
    Shi, Yuchen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Growth of 3C-SiC and Graphene for Solar Water-Splitting Application2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates
    Öppna denna publikation i ny flik eller fönster >>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 (Engelska)Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, nr 34Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Biopress Ltd, 2019
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-159101 (URN)10.1088/1361-6463/ab2859 (DOI)000475964100002 ()
    Anmärkning

    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

    Tillgänglig från: 2019-07-24 Skapad: 2019-07-24 Senast uppdaterad: 2019-08-07
    2. Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)
    Öppna denna publikation i ny flik eller fönster >>Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)
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    2018 (Engelska)Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, s. 533-542Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2018
    Nationell ämneskategori
    Materialkemi
    Identifikatorer
    urn:nbn:se:liu:diva-151054 (URN)10.1016/j.carbon.2018.08.042 (DOI)000450120200057 ()
    Anmärkning

    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 

    Tillgänglig från: 2018-09-12 Skapad: 2018-09-12 Senast uppdaterad: 2019-07-24
    3. Flat-Band Electronic Structure and Interlayer Spacing Influence in Rhombohedral Four-Layer Graphene
    Öppna denna publikation i ny flik eller fönster >>Flat-Band Electronic Structure and Interlayer Spacing Influence in Rhombohedral Four-Layer Graphene
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    2018 (Engelska)Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, nr 9, s. 5862-5866Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    American Chemical Society, 2018
    Nyckelord
    flat-band; Graphene; interlayer spacing; rhombohedral stacking; superconductor
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-151307 (URN)10.1021/acs.nanolett.8b02530 (DOI)30136852 (PubMedID)2-s2.0-85052867510 (Scopus ID)
    Tillgänglig från: 2018-09-17 Skapad: 2018-09-17 Senast uppdaterad: 2019-07-24
  • Disputation: 2019-09-13 10:15 Planck, Fysikhuset, Linköping
    Engberg, David L. J.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Atom Probe Tomography of Hard Nitride and Boride Thin Films2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
    Öppna denna publikation i ny flik eller fönster >>Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
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    2018 (Engelska)Ingår i: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 184, s. 51-60Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2018
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:liu:diva-122721 (URN)10.1016/j.ultramic.2017.08.004 (DOI)000415650200007 ()28850866 (PubMedID)
    Anmärkning

    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

    Tillgänglig från: 2015-11-18 Skapad: 2015-11-18 Senast uppdaterad: 2019-08-01Bibliografiskt granskad
    2. Self-organized Nanostructuring in Zr0.64Al0.36N Thin Films Studied by Atom Probe Tomography
    Öppna denna publikation i ny flik eller fönster >>Self-organized Nanostructuring in Zr0.64Al0.36N Thin Films Studied by Atom Probe Tomography
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    2016 (Engelska)Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, s. 233-238Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2016
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-84258 (URN)10.1016/j.tsf.2016.07.034 (DOI)000381939700037 ()
    Anmärkning

    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

    Tillgänglig från: 2012-10-03 Skapad: 2012-10-03 Senast uppdaterad: 2019-08-02Bibliografiskt granskad
    3. Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1-xTaxBy thin films
    Öppna denna publikation i ny flik eller fönster >>Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1-xTaxBy thin films
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    2019 (Engelska)Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, nr 3, artikel-id 031506Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    A V S AMER INST PHYSICS, 2019
    Nationell ämneskategori
    Oorganisk kemi
    Identifikatorer
    urn:nbn:se:liu:diva-159001 (URN)10.1116/1.5093170 (DOI)000472182400035 ()
    Anmärkning

    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]

    Tillgänglig från: 2019-07-19 Skapad: 2019-07-19 Senast uppdaterad: 2019-08-01
  • Disputation: 2019-09-13 13:15 Ada Lovelace, B-huset, Linköping
    Ghasemi Zinatabadi, Fatemeh
    Linköpings universitet, Matematiska institutionen, Beräkningsmatematik. Linköpings universitet, Tekniska fakulteten.
    Stability, dual consistency and conservation of summation-by-parts formulations for multiphysics problems2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Den här avhandlingen handlar om numeriska metoder för att lösa initial och randvärdes problem. Studien fokuserar på härledningen av rand/kopplingsvillkor som garanterar välställdhet. Det duala problemet och dess duala rand/kopplingsvillkor studeras också. Dessa problem diskretiseras genom att använda noggranna finita differensscheman på SBP-form (eng. summation-by-parts), kombinerat med en svag randbehandling benämnd SAT (eng. simultaneous approximation term). Vi fokuserar särskilt på stabilitet, konservation och dualkonsistens. Det främsta analysverktyget för både det kontinuerliga och diskreta problemet är energimetoden.

    Den första delen av avhandlingen behandlar välställdhet och stabilitet för koppling av olika system av ekvationer. Kopplingsvillkoren är härledda så att det kontinuerliga problemet uppfyller en energiuppskattning och så att det diskreta problemet är stabilt. I den första artikeln görs analysen för koppling av två olika hyperboliska system på första ordningens form. Som tillämpning kopplar vi Euler och vågekvationerna. Koppling mellan kompressibla och inkompressibla Navier-Stokes ekvationer studeras i den fjärde artikeln. För att få rätt antal kopplingsvillkor lägger vi till värmeledningsekvationen till de inkompressibla ekvationerna. Kopplingsvillkoren innefattar massans och rörelsemängdens bevarande samt två varianter av värmeöverföring. Den typiska tillämpningen är koppling mellan atmosfär och hav.

    Den andra delen av avhandlingen fokuserar på relationen mellan det primära och duala problemet och relationen mellan dualkonsistens och konservation. I den andra och tredje artikeln visar vi att dualkonsistens och konservation är ekvivalenta koncept för linjära hyperboliska konserveringslagar. I den femte artikeln, visas att dessa koncept är ekvivalenta även för paraboliska problem. Relationen mellan de primära och duala randvilkoren för linjära hyperboliska system av ekvationer i två dimensioner studeras i den sista artikeln. Vi visar att primära/duala välställda randvilkor ger duala/primära välställda randvilkor genom en enkel skalningsoperation. Det visas också att man kan gå direkt från det välställda svaga primära problemet till det välställda svaga duala problemet.

    Delarbeten
    1. Coupling Requirements for Multiphysics Problems Posed on Two Domains
    Öppna denna publikation i ny flik eller fönster >>Coupling Requirements for Multiphysics Problems Posed on Two Domains
    2017 (Engelska)Ingår i: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 55, nr 6, s. 2885-2904Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Society for Industrial and Applied Mathematics, 2017
    Nyckelord
    well posed problems, high order finite diffrences, stability, summation-by-parts, weak interface conditions, dual consistency, stiffness, superconvergence
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-143261 (URN)10.1137/16M1087710 (DOI)000418663500015 ()
    Tillgänglig från: 2017-11-28 Skapad: 2017-11-28 Senast uppdaterad: 2019-08-01Bibliografiskt granskad
    2. On the relation between conservation and dual consistency for summation-by-parts schemes
    Öppna denna publikation i ny flik eller fönster >>On the relation between conservation and dual consistency for summation-by-parts schemes
    2017 (Engelska)Ingår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 344, s. 3s. 437-439Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    n/a

    Förlag
    s. 3
    Nyckelord
    Initial boundary value problems Summation-by-parts Conservation, Dual consistent, Multi-block, Multi-element
    Nationell ämneskategori
    Matematik
    Identifikatorer
    urn:nbn:se:liu:diva-137545 (URN)10.1016/j.jcp.2017.04.072 (DOI)000402481300021 ()
    Anmärkning

    Classified in the journal as "Short note"

    Tillgänglig från: 2017-05-21 Skapad: 2017-05-21 Senast uppdaterad: 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]
    Öppna denna publikation i ny flik eller fönster >>Corrigendum to “On the relation between conservation and dual consistency for summation-by-parts schemes”[J. Comput. Phys. 344 (2017) 437–439]
    2018 (Engelska)Ingår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 360, s. 247-247Artikel i tidskrift (Refereegranskat) Published
    Ort, förlag, år, upplaga, sidor
    Academic Press, 2018
    Nationell ämneskategori
    Matematik
    Identifikatorer
    urn:nbn:se:liu:diva-145718 (URN)10.1016/j.jcp.2018.02.046 (DOI)000428966300014 ()
    Tillgänglig från: 2018-03-19 Skapad: 2018-03-19 Senast uppdaterad: 2019-08-01Bibliografiskt granskad
    4. An energy stable coupling procedure for the compressible and incompressible Navier-Stokes equations
    Öppna denna publikation i ny flik eller fönster >>An energy stable coupling procedure for the compressible and incompressible Navier-Stokes equations
    2019 (Engelska)Ingår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 396, s. 280-302Artikel i tidskrift (Refereegranskat) 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.

    Nyckelord
    Compressible fluid, Incompressible fluid, Navier-Stokes equations, Energy estimate, Interface conditions, Stability
    Nationell ämneskategori
    Matematik
    Identifikatorer
    urn:nbn:se:liu:diva-159116 (URN)10.1016/j.jcp.2019.07.022 (DOI)
    Tillgänglig från: 2019-07-29 Skapad: 2019-07-29 Senast uppdaterad: 2019-08-01
    5. On conservation and dual consistency for summation-by-parts based approximations of parabolic problems
    Öppna denna publikation i ny flik eller fönster >>On conservation and dual consistency for summation-by-parts based approximations of parabolic problems
    2019 (Engelska)Rapport (Övrigt vetenskapligt)
    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.

    Ort, förlag, år, upplaga, sidor
    Linköping: Linköping University Electronic Press, 2019. s. 9
    Serie
    LiTH-MAT-R, ISSN 0348-2960 ; 2019:5
    Nationell ämneskategori
    Beräkningsmatematik Matematik
    Identifikatorer
    urn:nbn:se:liu:diva-158903 (URN)LiTH-MAT-R--2019/05--SE (ISRN)
    Tillgänglig från: 2019-07-17 Skapad: 2019-07-17 Senast uppdaterad: 2019-08-12Bibliografiskt granskad
    6. The Relation Between Primal and Dual Boundary Conditions for Hyperbolic Systems of Equations
    Öppna denna publikation i ny flik eller fönster >>The Relation Between Primal and Dual Boundary Conditions for Hyperbolic Systems of Equations
    2019 (Engelska)Rapport (Övrigt vetenskapligt)
    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.

    Ort, förlag, år, upplaga, sidor
    Linköping: Linköping University Electronic Press, 2019. s. 22
    Serie
    LiTH-MAT-R, ISSN 0348-2960 ; 2019:6
    Nyckelord
    Hyperbolic systems, boundary conditions, primal problem, dual problem, well-posedness, dual consistency
    Nationell ämneskategori
    Beräkningsmatematik Matematik
    Identifikatorer
    urn:nbn:se:liu:diva-158904 (URN)LiTH-MAT-R--2019/06--SE (ISRN)
    Tillgänglig från: 2019-07-17 Skapad: 2019-07-17 Senast uppdaterad: 2019-08-12Bibliografiskt granskad
  • Disputation: 2019-09-17 13:15 ACAS, A-huset, Linköping
    Petersson, Johan
    Handelshögskolan, Örebro universitet, Örebro, Sverige.
    Elektroniska marknadsplatser: IT-stöd för små och medelstora leverantörer2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Den här avhandlingens ämne är elektroniska marknadsplatser och hur sådana bör utformas utifrån mindre leverantörers perspektiv. Med leverantörer avses här de säljande företag som använder marknadsplatser som mellanhand för att sälja varor och tjänster. I den situation som studerats används ofta denna kanal på begäran av kunden och dessutom via en marknadsplats vars utformning primärt är utformad utifrån kundens behov. Den kategori av marknadsplatser som har studerats har vidare inriktning mot inköp och försäljning mellan organisationer och företag.

    En central utgångspunkt och viktig förutsättning för studiens berättigande är uppfattningen om att forskningen kring den här kategorin av elektroniska marknadsplatser visat ett oproportionerlig litet intresse för just leverantörernas situation i allmänhet och de mindre aktörerna i synnerhet. Detta trots att ett reellt kunskapsbehov existerar såväl inomvetenskapligt som i praktikfältet. Det problem som ligger bakom praktikfältets kunskapsbehov har dessutom aktualiserats och accentuerats i Sverige under avhandlingsarbetes absoluta slutfas. Detta genom förändrad lagstiftning som innebär att alla leverantörer till offentlig sektor har krav på sig att kunna kommunicera elektroniskt.

    Den övergripande forskningsfråga som behandlas har formulerats som: ”Vilken utformning bör en elektronisk marknadsplats ha för att stödja mindre leverantörers ändamål?” och sedermera besvarats genom utveckling, presentation och tillämpning av en uppsättning utformningskriterier. Den övergripande forskningsstrategin har omfattat genomförande av en kvalitativ fallundersökning bestående av flera delstudier och praktikteori har utgjort ett centralt teoretiskt perspektiv. Undersökningens primära fall har varit den väletablerade skandinaviska marknadsplatsen Visma Proceedo och det praktiska genomförande har inneburit insamling och analys av data i form av intervjuer, dokument och demosystemtester.

    Kunskapsbidraget studien resulterat i består av fyra delar: en uppsättning utformningskriterier för elektroniska marknadsplatser, en kategorisering av mindre leverantörers ändamål, begreppsutveckling om s.k. marknadsplatspraktiker respektive ett antal praktikteoretiska utformningsprinciper. De två förstnämnda bidragen är riktade mot både praktikfältet och forskarsamhället med de två senare mer teoretiskt och inomvetenskapligt ämnade.

    Utformningskriterierna består av sju preskriptiva utsagor vilka är ämnade att kunna användas som riktningsvisare vid marknadsplatsutformning. Kriterierna utgör därmed det egentliga svaret på den övergripande forskningsfrågan. Studiens identifiering och kategorisering av de mindre leverantörernas ändamål visar att leverantörerna använder marknadsplatsen för att tillmötesgå befintliga kunders önskemål och krav. Vidare visar analysen två huvudkategorier vilka utgör centrala förutsättningar för de mindre leverantörernas aktivitet på den här typen av elektronisk marknadsplats: dels möjligheten till kontroll: att kunna granska och påverka sin egen information och dels behovet av matchning: överensstämmelse mellan marknadsplatsaktiviteten och den övriga (egna) verksamheten.

    I syfte att betrakta, analysera och förstå det studerade fenomenet presenterar avhandlingen också de två praktikteoretiska begreppen marknadsplatspraktik respektive försäljningspraktik. Intressenter för detta bidrag finns primärt bland forskare med intresse praktikteori och interorganisatoriska företeelser som elektroniska marknadsplatser.

    På vägen mot de tillämpningsspecifika utformningskriterierna har avhandlingsarbetet emellertid också inneburit teoriutveckling på ett betydligt mer generiskt plan. Resultatet är att en till karaktären deskriptiv praktikteoretisk modell har utökats med en uppsättning designprinciper. Principerna är resultat av en teoretisk syntes av informationssystemteori, sociotekniska designprinciper och praktikteori. Då principerna och tillämpningen av dem presenteras åtskilt från varandra är det möjligt för andra att tillämpa, testa och vidareutveckla dem helt bortom undersökningens fall och studieområde.

  • Disputation: 2019-09-20 09:00 Berzeliussalen, Linköping
    Carlén, Anna
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för kardiovaskulär medicin. Linköpings universitet, Medicinska fakulteten.
    Exercise Testing in Firefighters: Work Capacity and Cardiovascular Risk Assessment in a Low-Risk Population2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. Loaded treadmill walking and cycle ergometry to assess work capacity: a retrospective comparison in 424 firefighters.
    Öppna denna publikation i ny flik eller fönster >>Loaded treadmill walking and cycle ergometry to assess work capacity: a retrospective comparison in 424 firefighters.
    2017 (Engelska)Ingår i: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 37, nr 1, s. 37-44Artikel i tidskrift (Refereegranskat) 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.

    Nationell ämneskategori
    Idrottsvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-120004 (URN)10.1111/cpf.12265 (DOI)000390688200006 ()26096157 (PubMedID)
    Anmärkning

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

    Tillgänglig från: 2015-07-02 Skapad: 2015-07-02 Senast uppdaterad: 2019-08-21
    2. ST/HR variables in firefighter exercise ECG - relation to ischemic heart disease
    Öppna denna publikation i ny flik eller fönster >>ST/HR variables in firefighter exercise ECG - relation to ischemic heart disease
    2019 (Engelska)Ingår i: Physiological Reports, E-ISSN 2051-817X, Vol. 7, nr 2, artikel-id e13968Artikel i tidskrift (Refereegranskat) 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.

    Nyckelord
    Electrocardiography, ST depression, ST/HR variables, low risk
    Nationell ämneskategori
    Kardiologi
    Identifikatorer
    urn:nbn:se:liu:diva-159752 (URN)10.14814/phy2.13968 (DOI)30688031 (PubMedID)
    Tillgänglig från: 2019-08-20 Skapad: 2019-08-20 Senast uppdaterad: 2019-08-21
    3. Exercise-induced ST depression in an asymptomatic population without coronary artery disease
    Öppna denna publikation i ny flik eller fönster >>Exercise-induced ST depression in an asymptomatic population without coronary artery disease
    2019 (Engelska)Ingår i: Scandinavian Cardiovascular Journal, ISSN 1401-7431, E-ISSN 1651-2006, Vol. 53, nr 4, s. 206-212Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Taylor & Francis, 2019
    Nyckelord
    Stress test; false positive; electrocardiography; heart rate; ST segment deviation; firefighters; low risk
    Nationell ämneskategori
    Kardiologi
    Identifikatorer
    urn:nbn:se:liu:diva-158872 (URN)10.1080/14017431.2019.1626021 (DOI)000472278700001 ()31144537 (PubMedID)
    Anmärkning

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

    Tillgänglig från: 2019-07-15 Skapad: 2019-07-15 Senast uppdaterad: 2019-08-21
  • Disputation: 2019-09-20 10:15 ACAS, Linköping
    Larsson, L. Viktor
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system. Linköpings universitet, Tekniska fakulteten.
    Control of Hybrid Hydromechanical Transmissions2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. Mode Shifting in Hybrid Hydromechanical Transmissions
    Öppna denna publikation i ny flik eller fönster >>Mode Shifting in Hybrid Hydromechanical Transmissions
    2015 (Engelska)Ingår i: ASME/BATH 2015 Symposium on Fluid Power and Motion Control, ASME Press, 2015, s. 13-Konferensbidrag, Publicerat paper (Refereegranskat)
    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.

    Ort, förlag, år, upplaga, sidor
    ASME Press, 2015
    Nyckelord
    Mode shifting, hydromechanical transmissions, fluid power, heavy construction machinery
    Nationell ämneskategori
    Annan maskinteknik
    Identifikatorer
    urn:nbn:se:liu:diva-126556 (URN)10.1115/FPMC2015-9583 (DOI)000373970500045 ()978-0-7918-5723-6 (ISBN)
    Konferens
    ASME/BATH 2015 Symposium on Fluid Power and Motion Control, Chicago, Illinois, USA, October 12–14, 2015
    Projekt
    Research on Hydromechanical Transmissions and Hybrid Motion systems, RHYTHM
    Forskningsfinansiär
    Energimyndigheten, P39367-1
    Tillgänglig från: 2016-03-30 Skapad: 2016-03-30 Senast uppdaterad: 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
    Öppna denna publikation i ny flik eller fönster >>Modelling of the Swash Plate Control Actuator in an Axial Piston Pump for a Hardware-In-the-Loop Simulation Test Rig
    2016 (Engelska)Ingår i: Proceedings of the 9th FPNI Ph.D. Symposium on Fluid Power, FPNI2016, ASME Press, 2016, artikel-id UNSP V001T01A044Konferensbidrag, Publicerat paper (Refereegranskat)
    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.

    Ort, förlag, år, upplaga, sidor
    ASME Press, 2016
    Nationell ämneskategori
    Maskinteknik
    Identifikatorer
    urn:nbn:se:liu:diva-133328 (URN)10.1115/FPNI2016-1570 (DOI)000398986900044 ()978-0-7918-5047-3 (ISBN)
    Konferens
    The 9th FPNI Ph.D. Symposium on Fluid Power
    Projekt
    Research on Hydromechanical Transmissions and Hybrid Motion systems, RHYTHM
    Forskningsfinansiär
    Energimyndigheten, P39367-1
    Anmärkning

    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.

    Tillgänglig från: 2016-12-20 Skapad: 2016-12-20 Senast uppdaterad: 2019-08-21
    3. Displacement Control Strategies of an In-Line Axial-Piston Unit
    Öppna denna publikation i ny flik eller fönster >>Displacement Control Strategies of an In-Line Axial-Piston Unit
    2017 (Engelska)Ingår i: 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, s. 244-253Konferensbidrag, Publicerat paper (Refereegranskat)
    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.

    Ort, förlag, år, upplaga, sidor
    Linköping: Linköping University Electronic Press, 2017
    Serie
    Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 144
    Nyckelord
    Hydraulic hybrids, displacement control, pole placement
    Nationell ämneskategori
    Maskinteknik
    Identifikatorer
    urn:nbn:se:liu:diva-139854 (URN)10.3384/ecp17144244 (DOI)9789176853696 (ISBN)
    Konferens
    The 15th Scandinavian International Conference on Fluid Power, SICFP’17, June 7-9, 2017, Linköping, Sweden
    Tillgänglig från: 2017-08-17 Skapad: 2017-08-17 Senast uppdaterad: 2019-08-21Bibliografiskt granskad
    4. A General Approach to Low-Level Control of Heavy Complex Hybrid Hydromechanical Transmissions
    Öppna denna publikation i ny flik eller fönster >>A General Approach to Low-Level Control of Heavy Complex Hybrid Hydromechanical Transmissions
    2018 (Engelska)Ingår i: BATH/ASME 2018 Symposium on Fluid Power and Motion Control, 2018Konferensbidrag, Publicerat paper (Refereegranskat)
    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.

    Nyckelord
    Control, Multiple input multiple output control, heavy hydraulic hybrids, hydromechanical transmissions
    Nationell ämneskategori
    Maskinteknik
    Identifikatorer
    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)
    Konferens
    BATH/ASME 2018 Symposium on Fluid Power and Motion Control, Bath, United Kingdom, September 12-14, 2018
    Forskningsfinansiär
    Energimyndigheten, P39367-2
    Anmärkning

    Funding agencies: Swedish Energy Agency

    Tillgänglig från: 2019-02-04 Skapad: 2019-02-04 Senast uppdaterad: 2019-08-21Bibliografiskt granskad
    5. Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines
    Öppna denna publikation i ny flik eller fönster >>Low-Level Control of Hybrid Hydromechanical Transmissions for Heavy Mobile Working Machines
    2019 (Engelska)Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 9, artikel-id 1683Artikel i tidskrift (Refereegranskat) 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. 

    Ort, förlag, år, upplaga, sidor
    MDPI, 2019
    Nyckelord
    hydromechanical transmissions, hybridization, control, construction machinery; decoupled control, hardware-in-the-loop
    Nationell ämneskategori
    Annan maskinteknik
    Identifikatorer
    urn:nbn:se:liu:diva-157504 (URN)10.3390/en12091683 (DOI)000469761700099 ()
    Forskningsfinansiär
    Energimyndigheten, P39367-2
    Anmärkning

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

    Tillgänglig från: 2019-06-14 Skapad: 2019-06-14 Senast uppdaterad: 2019-08-21Bibliografiskt granskad
  • Disputation: 2019-09-24 13:00 Belladonna, Linköping
    Bratengeier, Cornelia
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Mechanisms of mechanically induced Osteoclastogenesis: in a novel in vitro model for bone implant loosening2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. Supraphysiological loading induces osteocyte-mediated osteoclastogenesis in a novel in vitro model for bone implant loosening
    Öppna denna publikation i ny flik eller fönster >>Supraphysiological loading induces osteocyte-mediated osteoclastogenesis in a novel in vitro model for bone implant loosening
    Visa övriga...
    2018 (Engelska)Ingår i: Journal of Orthopaedic Research, ISSN 0736-0266, E-ISSN 1554-527X, Vol. 36, nr 5, s. 1425-1434Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    WILEY, 2018
    Nyckelord
    osteocyte; osteoclast; implant; osteolysis; RANKL
    Nationell ämneskategori
    Cell- och molekylärbiologi
    Identifikatorer
    urn:nbn:se:liu:diva-150301 (URN)10.1002/jor.23780 (DOI)000434360700015 ()29068483 (PubMedID)
    Anmärkning

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

    Tillgänglig från: 2018-08-16 Skapad: 2018-08-16 Senast uppdaterad: 2019-08-21
    2. Mechanical loading releases osteoclastogenesis-modulating factors through stimulation of the P2X7 receptor in hematopoietic progenitor cells
    Öppna denna publikation i ny flik eller fönster >>Mechanical loading releases osteoclastogenesis-modulating factors through stimulation of the P2X7 receptor in hematopoietic progenitor cells
    2019 (Engelska)Ingår i: Journal of Cellular Physiology, ISSN 0021-9541, E-ISSN 1097-4652, Vol. 234, nr 8, s. 13057-13067Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    WILEY, 2019
    Nyckelord
    fluid flow; implant loosening; mechanoresponsive hematopoietic progenitor cells; osteolysis; purinergic signaling
    Nationell ämneskategori
    Cell- och molekylärbiologi
    Identifikatorer
    urn:nbn:se:liu:diva-158040 (URN)10.1002/jcp.27976 (DOI)000467240800083 ()30536959 (PubMedID)
    Anmärkning

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

    Tillgänglig från: 2019-06-25 Skapad: 2019-06-25 Senast uppdaterad: 2019-08-21
  • Disputation: 2019-09-27 10:15 Planck, House B, Linköping
    Kasebzadeh, Parinaz
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Learning Human Gait2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    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.