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  • Public defence: 2020-04-24 09:00
    Gutefeldt, Kerstin
    Linköping University, Department of Health, Medicine and Caring Sciences, Division of Diagnostics and Specialist Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Endocrinology.
    Upper extremity impairments in type 1 diabetes in comparison to matched controls without diabetes: associations to the IGF-system, metabolic factors, disability and quality of life2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Compared with the general population, people with type 1 diabetes (T1D) more often exhibit pathological alterations in musculoskeletal tissue (impairments). Some of these impairments involve the upper extremities, i.e., the shoulders, hands, and fingers. Although present in diabetes, these complications are underdiagnosed and not actively searched for during routine clinical examinations. Furthermore, much is still unclear about these impairments, specifically regarding their etiology, risk factors, and consequences on daily life activities and quality of life. The growth hormone (GH)/insulinlike growth factor (IGF)-system is known to be affected in diabetes, but whether this is involved in upper extremity impairments (UEIs) is unclear. The aim of this thesis was to describe the prevalence of UEIs in patients with diabetes compared with controls. Furthermore, we aimed to search for risk factors of UEIs, and elucidate the impact of UEIs on daily life activities and health-related quality of life (HRQOL). We used two cohorts; the LedIG cohort (papers I–III), a large population-based study in which all patients with a long duration of T1D (>20 years), aged <67 years, living in the south-east region of Sweden were invited to participate, as well as matched controls without diabetes. This study was based on questionnaires as well as blood samples from the participants. The last paper (IV) included a smaller cohort (n=69) of patients with T1D, who both completed a questionnaire and were the subjects of a clinical examination.

    Paper I: The UEIs were common in diabetes, with a prevalence of up to 48%. Hand paresthesia was the most common impairment, followed by shoulder pain and stiffness. The prevalence of UEIs was 2–4 times higher in patients than in controls and was associated with more activity limitations. Risk factors were heterogeneous for the different UEIs and included female sex, increasing age, longer duration of diabetes, and poor glycemic control.

    Paper II: The GH-IGF-axis is important for the growth and function of musculoskeletal tissues. We examined differences in the IGF system between patients with T1D on subcutaneous insulin treatment and controls. We found lower levels of IGF-I and insulinlike growth factor-binding protein (IGFBP)-3 and higher levels of GH and IGFBP-1 in patients with T1D than in controls. The largest difference was found in IGFBP-1, and this probably reflected insulin deficiency. The IGF-I levels were increased with increasing insulin doses. However, even at very high insulin doses (>1 U/kg) the IGF-I Z-score was subnormal, indicating that IGF-I cannot be normalized by subcutaneous insulin treatment. Residual endogenous insulin secretion counteracted these alterations. Furthermore, we investigated possible relationships between UEIs and IGF-I, and found no association.

    Paper III: The HRQOL was lower in patients with T1D than in controls. Patients with shoulder impairments, hand paresthesia, and hand stiffness, but not finger impairments, had lower HRQOL scores than patients without these impairments. The patients with T1D showed a higher frequency of sick leave than controls, and a common reason for this was musculoskeletal impairments.

    Paper IV: In addition to the self-reported UEIs, the prevalence of UEIs was also investigated by clinical examination. Clinical UEIs were found in 65% of the participants, with shoulder test (hands against back), prayer sign test, and the Phalen’s and Tinel’s tests being most prevalent. We compared self-reported UEIs to clinical UEIs and found that self-reported impairments were associated with clinical examination. We also found that self-reported shoulder impairments, reduced hand strength, and previous surgery for carpal tunnel syndrome and trigger finger were associated with several other UEIs.

    In current diabetic care, there is no established routine to capture UEIs, as opposed to other known diabetes complications. We show that UEIs are more common in patients with T1D than in controls, and that they are related to impaired HRQOL and daily life activity limitations. Clinical routines including self-reported UEIs, e.g. shoulder stiffness and reduced hand strength, might be used to identify patients with UEIs in need of clinical investigation, enhanced preventive and therapeutic strategies, as well as rehabilitative interventions.

    List of papers
    1. Upper extremity impairments in type 1 diabetes with long duration: common problems with great impact on daily life
    Open this publication in new window or tab >>Upper extremity impairments in type 1 diabetes with long duration: common problems with great impact on daily life
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    2019 (English)In: Disability and Rehabilitation, ISSN 0963-8288, E-ISSN 1464-5165, Vol. 41, no 6, p. 633-640Article in journal (Refereed) Published
    Abstract [en]

    PURPOSE: To investigate the prevalence, activity limitations and potential risk factors of upper extremity impairments in type 1 diabetes in comparison to controls.

    METHODS: In a cross-sectional population-based study in the southeast of Sweden, patients with type 1 diabetes <35 years at onset, duration ≥20 years, <67 years old and matched controls were invited to answer a questionnaire on upper extremity impairments and activity limitations and to take blood samples.

    RESULTS: Seven hundred and seventy-three patients (ages 50 ± 10 years, diabetes duration 35 ± 10 years) and 708 controls (ages 54 ± 9 years) were included. Shoulder pain and stiffness, hand paraesthesia and finger impairments were common in patients with a prevalence of 28-48%, which was 2-4-folds higher than in controls. Compared to controls, the patients had more bilateral impairments, often had coexistence of several upper extremity impairments, and in the presence of impairments, reported more pronounced activity limitations. Female gender (1.72 (1.066-2.272), p = 0.014), longer duration (1.046 (1.015-1.077), p = 0.003), higher body mass index (1.08 (1.017-1.147), p = 0.013) and HbA1c (1.029 (1.008-1.05), p = 0.007) were associated with upper extremity impairments.

    CONCLUSIONS: Compared to controls, patients with type 1 diabetes have a high prevalence of upper extremity impairments, often bilateral, which are strongly associated with activity limitations. Recognising these in clinical practise is crucial, and improved preventative, therapeutic and rehabilitative interventions are needed. Implications for rehabilitation Upper extremity impairments affecting the shoulder, hand and fingers are common in patients with type 1 diabetes, the prevalence being 2-4-fold higher compared to non-diabetic persons. Patients with diabetes type 1 with upper extremity impairments have more pronounced limitations in daily activities compared to controls with similar impairments. Recognising upper extremity impairments and activity limitations are important and improved preventive, therapeutic and rehabilitation methods are needed.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2019
    Keywords
    Dupuytren’s disease, Type 1 diabetes, carpal tunnel syndrome, frozen shoulder, trigger finger disorder
    National Category
    Endocrinology and Diabetes
    Identifiers
    urn:nbn:se:liu:diva-144020 (URN)10.1080/09638288.2017.1397202 (DOI)000461521100002 ()29105514 (PubMedID)2-s2.0-85033477270 (Scopus ID)
    Note

    Funding agencies: Medical Research Council of Southeast Sweden (FORSS); County council of Region Ostergotland, Sweden; Stiftelseforvaltningen of Region Ostergotland, Sweden

    Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2020-03-24Bibliographically approved
    2. Dysregulated growth hormone-insulin-like growth factor-1 axis in adult type 1 diabetes with long duration
    Open this publication in new window or tab >>Dysregulated growth hormone-insulin-like growth factor-1 axis in adult type 1 diabetes with long duration
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    2018 (English)In: Clinical Endocrinology, ISSN 0300-0664, E-ISSN 1365-2265, Vol. 89, no 4, p. 424-430Article in journal (Refereed) Published
    Abstract [en]

    ContextIn type 1 diabetes (T1D), dysregulation of the GH-IGF-1 axis has been reported. Whether this is related to upper extremity impairments (UEI) is unknown. ObjectiveExamine differences in GH-IGF-1 axis between T1D on subcutaneous insulin treatment and matched controls without diabetes and possible associations between GH-IGF-1 axis and UEI. DesignCross-sectional population-based study. Patients with T1D, onset amp;lt;35years, duration 20years, amp;lt;67years old and controls were invited to answer questionnaires and take blood samples. SubjectsA total of 605 patients with T1D and 533 controls accepted to participate. OutcomesFasting levels of IGF-1, IGF-1 Z-score, IGFBP-1, IGFBP-3, C-peptide, GH and UEI. ResultsPatients with T1D had lower IGF-1 and IGFBP-3 and higher IGFBP-1 and GH than controls. The difference in IGF-1 persisted with age. Insulin dose was associated with increasing IGF-1 Z-score but even at a very high insulin dose (amp;gt;1U/kg) IGF-1 Z-score was subnormal compared to controls. IGF-1 Z-score was unaffected by glycaemic control (HbA1c) but increased with residual insulin secretion, (C-peptide 1-99 pmol/L). IGFBP-1 was associated with fasting blood glucose, negatively in controls and positively in patients with T1D probably reflecting insulin resistance and insulin deficiency, respectively. There was no association between lower IGF-1 Z-score and UEI in T1D. ConclusionIn adult T1D with fair glycaemic control, the GH-IGF-1 axis is dysregulated exhibiting GH resistance, low IGF-1 and elevated IGFBP-1. Subcutaneous insulin cannot normalize these changes while endogenous insulin secretion has marked effects on IGF-1 pointing to a role of portal insulin.

    Place, publisher, year, edition, pages
    WILEY, 2018
    Keywords
    GH; insulin-like growth factor-1; insulin-like growth factor-binding protein-1; insulin; type 1 diabetes; upper extremity impairments
    National Category
    Endocrinology and Diabetes
    Identifiers
    urn:nbn:se:liu:diva-151773 (URN)10.1111/cen.13810 (DOI)000444539600006 ()29989677 (PubMedID)
    Note

    Funding Agencies|Medical Research Council of Southeast Sweden FORSS; County council and Stiftelseforvaltningen of Region Ostergotland, Sweden

    Available from: 2018-10-08 Created: 2018-10-08 Last updated: 2020-03-24
    3. Low health-related quality of life is strongly linked to upper extremity impairments in type 1 diabetes with a long duration
    Open this publication in new window or tab >>Low health-related quality of life is strongly linked to upper extremity impairments in type 1 diabetes with a long duration
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    2020 (English)In: Disability and Rehabilitation, ISSN 0963-8288, E-ISSN 1464-5165Article in journal (Refereed) Epub ahead of print
    Abstract [en]

    Purpose: To compare health-related quality of life (HRQOL) in type 1 diabetes and non-diabetic controls and possible links to upper extremity impairments (UEIs). Prevalence of sick-leave and causes were investigated.

    Materials and methods: This Swedish population-based case-control study included type 1 diabetes patients <67 years old and with a diabetes duration ≥20 years. Participants completed a postal questionnaire including Short Form 36, and questions regarding UEIs, and sick-leave.

    Results: In total, 773 patients, aged 50 ± 10 years (diabetes duration 35 ± 10 years), and 708 non-diabetic controls, aged 54 ± 9 years, completed the study. Patients reported significantly lower HRQOL compared with controls. The difference was greatest for general health, vitality, and bodily pain. Patients with shoulder or hand but not finger impairments scored significantly lower than asymptomatic patients. The prevalence of sick leave was higher in patients vs. controls (23% vs. 9%, p < 0.001), and nearly half cited impairments from back, muscles, or joints as the main reason.

    Conclusions: Health-related quality of life is lower in type 1 diabetes than controls and in patients with shoulder and hand impairments than in asymptomatic. Musculoskeletal impairments (back/muscle/joints) have impact on work ability. Identification of UEIs is important for initiating preventative-, therapeutic-, and rehabilitative interventions.

    • Implications for rehabilitation
    • Upper extremity impairments (UEIs) that are common in type 1 diabetes, and associated with reduced health-related quality of life, should preferably be screened for on a regular basis along with other known diabetes complications.

    • Early identification of UEIs is important to improve health by initiating preventive as well as therapeutic multi-professional rehabilitative interventions.

    • Sick leave is higher in type 1 diabetes than in controls. Musculoskeletal impairments, including the back, muscles, and joints, are a common cause for sick leave warranting further studies.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2020
    Keywords
    Quality of life; type 1 diabetes; upper extremity impairments; work ability; disability
    National Category
    General Practice
    Identifiers
    urn:nbn:se:liu:diva-163405 (URN)10.1080/09638288.2019.1705924 (DOI)000505880400001 ()31906725 (PubMedID)2-s2.0-85078623672 (Scopus ID)
    Note

    Funding Agencies|Medical Research Council South-east Sweden (FORSS); County Council; Stiftelseforvaltningen of Region Ostergotland, Sweden

    Available from: 2020-02-04 Created: 2020-02-04 Last updated: 2020-03-24Bibliographically approved
    4. Clinical Examination and Self-Reported Upper Extremity Impairments in Patients with Long-Standing Type 1 Diabetes Mellitus
    Open this publication in new window or tab >>Clinical Examination and Self-Reported Upper Extremity Impairments in Patients with Long-Standing Type 1 Diabetes Mellitus
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    2020 (English)In: Journal of Diabetes Research, ISSN 2314-6745, E-ISSN 2314-6753, Journal of Diabetes Research, Vol. 2020, article id 4172635Article in journal (Refereed) Published
    Abstract [en]

    Aim. The aims of the current study were (1) to determine the prevalence of upper extremity impairments (UEIs) in patients with type 1 diabetes by clinical investigation; (2) to investigate if self-reported impairments were concordant with clinical findings and if key questions could be identified; and (3) to investigate if answers to our self-reported questionnaire regarding UEIs are reliable. Methods. Patients with type 1 diabetes were invited to participate in a cross-sectional study of clinical and self-reported (12 items) UEIs in adjunction to ordinary scheduled clinical visit. Before the visit, a questionnaire on UEIs was filled in twice (test-retest) followed by clinical testing at the planned visit. Results. In total, 69 patients aged and with diabetes duration were included in the study. In the clinical examination, two-thirds (65%) of the patients showed one or more UEI, with failure to perform hand against back as the most common clinical finding (40%) followed by positive Phalen’s test (27%), Tinel’s test (26%), and Prayer’s sign (24%). UEIs observed by clinical examination were often bilateral, and multiple impairments often coexisted. Self-reported shoulder stiffness was associated with impaired shoulder mobility and with Prayer’s sign. Self-reported reduced hand strength was associated to lower grip force, Prayer’s sign, trigger finger, fibrosis string structures, and reduced thenar strength as well as reduced shoulder mobility. In addition, self-reporting previous surgery of carpal tunnel and trigger finger was associated with several clinical UEIs including shoulder, hand, and finger. The test-retest of the questionnaire showed a high agreement of 80-98% for reported shoulder, hand, and finger impairments. Conclusion. UEIs are common in type 1 diabetes. Self-reported shoulder stiffness and reduced hand strength might be used to capture patients with UEIs in need of clinical investigation and enhanced preventive and therapeutic strategies, as well as rehabilitative interventions.

    Place, publisher, year, edition, pages
    Hindawi Publishing Corporation, 2020
    National Category
    Physiotherapy
    Identifiers
    urn:nbn:se:liu:diva-164549 (URN)10.1155/2020/4172635 (DOI)
    Available from: 2020-03-24 Created: 2020-03-24 Last updated: 2020-03-31Bibliographically approved
  • Public defence: 2020-04-24 10:15 Planck, F Building, LinköpingOrder onlineBuy this publication >>
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Electronic transitions and correlation effects: From pure elements to complex materials2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Macroscopic properties of real materials, such as conductivity, magneticproperties, crystal structure parameters, etc. are closely related or evendetermined by the configuration of their electrons, characterized by electronicstructure. By changing the conditions, e.g, pressure, temperature, magnetic/electric field, chemical doping, etc. one can modify the electronic structure ofsolids and therefore induce a phase transition(s) between different electronic andmagnetic states. One famous example is a Mott metal-to-insulator phase transition,at which a material undergoes a significant, often many orders of magnitude, changeof conductivity caused by the interplay between itineracy and localization of thecarriers.

    Electronic topological transitions (ETT) involvechanges in the topology of a metal's Fermi surface. This thesis investigates theeffect of such electronic transitions in various materials, ranging from pureelements to complex compounds.

    To describe the interplay between electronic transitionsand properties of real materials,different state-of-the-art computational methods are used. The densityfunctional theory(DFT), as well as the DFT + U method, is used to calculatestructural properties. The validity of recently introduced exchange-correlationfunctionals, such as the strongly constrained and appropriately normed (SCAN)functional, is also assessed for magnetic elements. In order toinclude dynamical effects of electron interactions we use the DFT + dynamical meanfield theory (DFT + DMFT) method.

    Experiments in hcp-Os have reported peculiarities in the ratio betweenlattice parameters at high pressure. Previous calculations have suggested these transitions maybe related to ETTs and even crossings of core levels at ultra high pressure. Inthis thesis it is shownthat the crossing of core levels is a general feature of heavy transitionmetals. Experiments have therefore been performed to look for indications ofthis transition in Ir using X-ray absorption spectroscopy. In NiO, strongrepulsion between electrons leads to a Mott insulating state at ambientconditions. It has long been predicted that high pressure will lead to aninsulator-to-metal transition. This has been suggested to be accompanied by aloss of magnetic order, and a structural phase transition. In collaboration withexperimentalists we look for thistransition by investigating the X-ray absorption spectra as well as themagnetic hyperfine field. We find no evidence of a Mott transition up to 280GPa. In the Mott insulator TiPO4, application of external pressure has beensuggested to lead to a spin-Peierls transition at room temperature. Weinvestigate the dimerisation and the magnetic structure of TiPO4 at high pressure.As pressure is increased further, TiPO4 goes through a metal to insulatortransition before an eventual crystallographic phase transition. Remarkably, thenew high pressure phases are found to be insulators; the Mott insulating stateis restored.

    MAX phases are layered materials that combinemetallic and ceramic properties and feature layers of M-metal and X-C or N atomsinterconnected by A-group atoms. Magnetic MAX-phases with their low dimensionalmagnetism are promising candidates for applications in e.g., spintronics.The validity of various theoretical approaches are discussed in connection tothe magnetic MAX-phase Mn2GaC. Using DFT and DFT + DMFT we consider the hightemperature paramagnetic state, and whether the magnetic moments are formed bylocalized or itinerant electrons.

    List of papers
    1. Assessing the SCAN functional for itinerant electron ferromagnets
    Open this publication in new window or tab >>Assessing the SCAN functional for itinerant electron ferromagnets
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    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 9, article id 094413Article in journal (Refereed) Published
    Abstract [en]

    Density functional theory is a standard model for condensed-matter theory and computational material science. The accuracy of density functional theory is limited by the accuracy of the employed approximation to the exchange-correlation functional. Recently, the so-called strongly constrained appropriately normed (SCAN) [Sun, Ruzsinszky, and Perdew, Phys. Rev. Lett. 115, 036402 (2015)] functional has received a lot of attention due to promising results for covalent, metallic, ionic, as well as hydrogen- and van der Waals-bonded systems alike. In this work, we focus on assessing the performance of the SCAN functional for itinerant magnets by calculating basic structural and magnetic properties of the transition metals Fe, Co, and Ni. We find that although structural properties of bcc-Fe seem to be in good agreement with experiment, SCAN performs worse than standard local and semilocal functionals for fcc-Ni and hcp-Co. In all three cases, the magnetic moment is significantly overestimated by SCAN, and the 3d states are shifted to lower energies, as compared to experiments.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2018
    National Category
    Theoretical Chemistry
    Identifiers
    urn:nbn:se:liu:diva-151640 (URN)10.1103/PhysRevB.98.094413 (DOI)000444348500004 ()
    Note

    Funding Agencies|Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) through the International Career Grant [20146336]; Marie Sklodowska CurieActions, Cofund, Project [INCA 600398]; Swedish Foundation for Strategic Research (SSF) through the Future Research Leaders 6 program; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; competence center FunMat-II - Vinnova [201605156]; Russian Science Foundation [18-12-00492]

    Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2020-03-17
    2. Pressure-induced crossing of the core levels in 5d metals
    Open this publication in new window or tab >>Pressure-induced crossing of the core levels in 5d metals
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    2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 20, p. 205150-Article in journal (Refereed) Published
    Abstract [en]

    A pressure-induced interaction between core electrons, the core-level crossing (CLC) transition, has been observed in hcp Os at P approximate to 400 GPa [L. Dubrovinsky et al., Nature (London) 525, 226 (2015)]. By carrying out a systematic theoretical study for all metals of the 5d series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at approximate to 1500 GPa, at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2016
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-129490 (URN)10.1103/PhysRevB.93.205150 (DOI)000376638700004 ()
    Note

    Funding Agencies|Swedish Government Strategic Research Area Grant Swedish e-Science Research Centre (SeRC); Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of MISiS; Swedish Foundation for Strategic Research (SSF) program SRL [10-0026]; Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; German Research Foundation (DFG); Federal Ministry of Education and Research (BMBF), Germany; DFG [DU 954-8/1]; BMBF (PT-DESY) [5K13WC3, O5K2013, 2]; Act 211 Government of the Russian Federation [02.A03.21.0006]; Knut and Alice Wallenberg Foundation [2012.0083, 2014-2019]

    Available from: 2016-06-21 Created: 2016-06-20 Last updated: 2020-03-17
    3. Topological transitions of the Fermi surface of osmium under pressure: an LDA plus DMFT study
    Open this publication in new window or tab >>Topological transitions of the Fermi surface of osmium under pressure: an LDA plus DMFT study
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    2017 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 19, article id 033020Article in journal (Refereed) Published
    Abstract [en]

    The influence of pressure on the electronic structure of Os has attracted substantial attention recently due to reports on isostructural electronic transitions in this metal. Here, we theoretically investigate the Fermi surface of Os from ambient to high pressure, using density functional theory combined with dynamical mean field theory. Weprovide a detailed discussion of the calculated Fermi surface and its dependence on the level of theory used for the treatment of the electron-electron interactions. Although we confirm that Os can be classified as weakly correlated metal, the inclusion of local quantum fluctuations between 5d electrons beyond the local density approximation explains the most recent experimental reports regarding the occurrence of electronic topological transitions in Os.

    Place, publisher, year, edition, pages
    IOP PUBLISHING LTD, 2017
    Keywords
    electronic topological transitions; strong correlations; Fermi surfaces
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-136604 (URN)10.1088/1367-2630/aa5f8e (DOI)000398666100004 ()
    Note

    Funding Agencies|Swedish Foundation for Strategic Research SSF (SRL) [10-0026]; Swedish Research Council (VR) grant [2015-04391]; Knut and Alice Wallenberg Foundation [2014-2019]; Swedish Government Strategic Research Area SeRC; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFOMatLiU) [2009 00971]; Ministry of Education and Science of the Russian Federation of NUST MISIS [K2-2016-013]; PHD DALEN Project [26228RM]; Swedish National Infrastructure for Computing (SNIC)

    Available from: 2017-04-21 Created: 2017-04-21 Last updated: 2020-03-17
    4. Phase stability and electronic structure of iridium metal at the megabar range
    Open this publication in new window or tab >>Phase stability and electronic structure of iridium metal at the megabar range
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    2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8940Article in journal (Refereed) Published
    Abstract [en]

    The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.

    Place, publisher, year, edition, pages
    Nature Publishing Group, 2019
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-158862 (URN)10.1038/s41598-019-45401-x (DOI)000472137700036 ()31222067 (PubMedID)2-s2.0-85067628529 (Scopus ID)
    Note

    Funding Agencies|Spanish Ministry of Science, Innovation and Universities; Spanish Research Agency (AEI); European Fund for Regional Development (FEDER) [MAT2016-75586-C4-1/2-P]; Generalitat Valenciana [Prometeo/2018/123]; Spanish Mineco Project [FIS2017-83295-P]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Ministry of Science and High Education of the Russian Federation [K2-2019-001]; "Juan de la Cierva" fellowship [FJCI-2016-27921]; "Ramon y Cajal" fellowship [RYC-2015-17482]

    Available from: 2019-07-16 Created: 2019-07-16 Last updated: 2020-03-19Bibliographically approved
    5. Magnetic interactions in NiO at ultrahigh pressure
    Open this publication in new window or tab >>Magnetic interactions in NiO at ultrahigh pressure
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    2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 20, p. 201110-Article in journal (Refereed) Published
    Abstract [en]

    Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to similar to 24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2016
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-129492 (URN)10.1103/PhysRevB.93.201110 (DOI)000376638400001 ()
    Note

    Funding Agencies|National Science Foundation-Earth Sciences [EAR-1128799]; Department of Energy-GeoSciences [DE-FG02-94ER14466]; DOE Office of Science [DE-AC02-06CH11357]; Helmholtz Association; Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy; Swedish Government Strategic Research Area Grants Swedish e-Science Research Center (SeRC) and in Materials Science on Functional Materials at Linkoping University [2009 00971]; Knut and Alice Wallenbergs Foundation project Strong Field Physics and New States of Matter; Swedish Foundation for Strategic Research program SRL Grant [10-0026]; Swedish Research Council (VR) [2015-04391]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D.I. Mendeleev Fund Program

    Available from: 2016-06-20 Created: 2016-06-20 Last updated: 2020-03-17
    6. Inverse pressure-induced Mott transition in TiPO4
    Open this publication in new window or tab >>Inverse pressure-induced Mott transition in TiPO4
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    2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 24, article id 245132Article in journal (Refereed) Published
    Abstract [en]

    TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2019
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-158863 (URN)10.1103/PhysRevB.99.245132 (DOI)000471984200002 ()
    Note

    Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Russian Science Foundation [18-12-00492]

    Available from: 2019-07-16 Created: 2019-07-16 Last updated: 2020-03-17
  • Public defence: 2020-04-24 10:15 ACAS, A-Building, LinköpingOrder onlineBuy this publication >>
    Johansson, Henrik
    Linköping University, Department of Management and Engineering, Logistics & Quality Management. Linköping University, Faculty of Science & Engineering.
    Customer Benefits in City Logistics: Towards Viable Urban Consolidation Centres2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Urban Consolidation Centre (UCC) is a city logistics initiative that has the potential to increase the efficiency of urban freight delivery systems while reducing negative environmental and social effects caused by freight vehicles. One important issue that have hindered longevity of this initiative is its viability, both the financial viability and acceptance from affected stakeholders (also called UCC customers). The UCC customers in focus in this thesis are receivers of goods and municipalities. To satisfy both types of stakeholders, their requests and, in particular, the benefits they can gain from using UCCs need to be studied. The types of benefits to be given priority differ between the stakeholders, where municipalities strive towards more societal benefits, and the main goals of receivers are an increase in efficiency and financial sustainability. In response, the purpose of this thesis is to deepen the understanding of benefits for customers of UCCs, with a particular focus on customer needs and benefits that UCCs can provide.

    This thesis consists of five appended papers, each of which uses a different methodology. The methodologies applied in the papers include a multiple interview study of five UCCs, a surveybased interview study of retail stores, and a case study of an operating UCC. Regarding customer needs, this thesis takes the customer perspective, in order to identify needs that UCCs can meet. The results presented in this thesis also highlight the importance for UCCs to give priority to meeting customer needs that stem from some type of problem. Regarding benefits that UCCs can provide, the thesis suggests how different types of benefits can be distinguished. This can give guidance to UCC operators regarding which benefits should be given priority in communication with UCC customers. However, the results highlight that it is also important to understand the situation of the customer to be able to communicate the most relevant benefits that UCCs can provide. Furthermore, the results illustrate different improvement areas that can affect the benefits for UCC customers. These identified areas are: improved understanding by both UCCs and its customers of each other’s operation, communication, developing a more holistic view for UCC customers, and developing new UCC services to match customer needs.

    The results provide a foundation for customer needs that UCCs can meet, and the benefits that UCCs can provide. This foundation can be important for UCC customers to gain a better understanding of what a UCC is and how it can affect their operation, something that this thesis contributes towards. It can also assist initiators of UCCs to determine which customer needs they should focus on. Lastly, the results and contribution also address the potential role of municipalities, and it is argued that their role should change from a more supportive role to that of a paying UCC customer. All of these aspects can increase the probability that a UCC, when established becomes viable.

    List of papers
    1. Urban consolidation centre - a literature review, categorisation, and a future research agenda
    Open this publication in new window or tab >>Urban consolidation centre - a literature review, categorisation, and a future research agenda
    2018 (English)In: International Journal of Physical Distribution & Logistics Management, ISSN 0960-0035, E-ISSN 1758-664X, Vol. 48, no 8, p. 745-764Article, review/survey (Refereed) Published
    Abstract [en]

    Purpose Urban consolidation centre (UCC) is a popular initiative targeting the challenge of negative environmental and social impacts from freight transports in cities. Despite this, UCC often fails in practice, which indicates a knowledge gap. Furthermore, research within the field can be described as fragmented, transdisciplinary and fast growing. The purpose of this paper is to provide an overview of the field by describing dominant categories and themes within the area, identify gaps in order to propose a future research agenda, and provide insights into the needs of practitioners. Design/methodology/approach A systematic literature review (SLR) targeting journal articles based on UCCs has been constructed with a supplementary snowball approach. A content analysis was performed to categorise themes in the research on UCCs and to identify research gaps, both within and outside the categories identified. Findings Despite substantial research on UCC, very little research ends up in academic journals. In all, 56 articles address UCC. The most common topics were the role of stakeholders, design of distribution structures and transport resources, environmental and social consideration, and economic considerations. Much focus is directed towards finding optimal solutions and designs for potential initiatives with very little, if any, consideration to financial viability or the management of the UCC initiative. Research limitations/implications This research points out existing gaps in the literature and proposes a future research agenda with UCCs as the focus. For example, although environmental and social arguments are often applied to justify the implementation of UCCs, few studies measure or evaluate their impact. Another important research gap is the economical consideration, both how to generate revenue and how to consider economies of scale. Practical implications The practical contribution of most studies is directed towards municipalities. Few findings are presented in a way to support companies. Additionally, by bridging the gaps related to how stakeholders can collaborate and describe what is happening in a UCC, practitioners can use such information as guidelines. Originality/value The results provide a research agenda for the fragmented research targeting UCCs, supporting the viability of future initiatives.

    Place, publisher, year, edition, pages
    EMERALD GROUP PUBLISHING LTD, 2018
    Keywords
    Content analysis; City logistics; Urban freight; Urban consolidation centre; Structural literature review
    National Category
    Business Administration
    Identifiers
    urn:nbn:se:liu:diva-151808 (URN)10.1108/IJPDLM-01-2017-0050 (DOI)000444391000002 ()
    Note

    Funding Agencies|Swedish Energy Agency

    Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2020-03-20
    2. Critical factors for viable business models for urban consolidation centres
    Open this publication in new window or tab >>Critical factors for viable business models for urban consolidation centres
    2017 (English)In: Research in Transportation Economics, ISSN 0739-8859, E-ISSN 1875-7979, Vol. 64, p. 36-47Article in journal (Refereed) Published
    Abstract [en]

    Abstract Although urban consolidation centres (UCC) worldwide have improved urban freight distribution and reduced externalities, other UCC initiatives have not materialised due to problems such as for example, business model limitations. All the same, researchers have rarely described business model components relevant to city logistics. In response, the purpose of this article is to analyse critical factors for viable business models of city logistics initiatives involving UCCs. Following an extensive literature review and multiple-case study of five initiatives with UCCs, we identified seven critical factors of viable city logistics business models: the ability to scale up and down the UCC solution; an ability to continuously develop and adapt to a dynamic environment; the important entrepreneurial role of the initiator as well; the acknowledgment of society; ability to innovate new services; logistics and supply chain management competence; and the ability to take full advantage of advanced IT. All seven factors describe continuously redeveloped business models seeking to seize new and unexpected opportunities, yet also indicate that city logistics systems require local authorities and municipalities to act as initiators, enablers, and customers. The models also underscore differences between purely commercial and purely municipal city logistics initiatives.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    Urban logistics, Business models, Critical factors, Urban consolidation centres
    National Category
    Transport Systems and Logistics
    Identifiers
    urn:nbn:se:liu:diva-144226 (URN)10.1016/j.retrec.2017.09.009 (DOI)
    Funder
    VINNOVA
    Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2020-03-20
    3. Urban consolidation centres: retail stores demands for UCC services
    Open this publication in new window or tab >>Urban consolidation centres: retail stores demands for UCC services
    2017 (English)In: International Journal of Physical Distribution & Logistics Management, ISSN 0960-0035, E-ISSN 1758-664X, Vol. 47, no 7, p. 646-662Article in journal (Refereed) Published
    Abstract [en]

    Purpose - Urban consolidation centres (UCCs) are often conceived to improve services in retail stores and potentially reduce costs. However, few studies have examined how retail stores perceive the services a UCC could provide. The purpose of this paper is to explore retail stores potential demands for different services that a UCC could provide in order to foster the development and implementation of UCC solutions aimed towards more economically feasible business models. Design/methodology/approach - Structured interviews were conducted with employees at 72 retail stores. Qualitative, as well as quantitative analyses, were conducted to identify the potential demands of the retail stores. Findings - The authors have provided arguments why retail stores might be interested in UCC services, and thereby potentially pay for them. Improved customer service to stores customers might not be a valid argument. The authors point to the cost aspect: stores expend resources that a UCC could provide in a more cost-efficient manner. Research limitations/implications - The findings contradict previous studies to some extent, as it indicates that a UCC may actually not enhance customer service in retail stores. Instead, the findings point to the importance of considering the potential advantages according to economies of scale that are facilitated by UCC services. Practical implications - Taking the perspective of the stores is important in order to identify arguments for why they should pay for the services provided by a UCC. Social implications - Financially viable UCC solutions are needed in order for the initiatives to be maintained and thereby provide a long-term decrease in the environmental and social footprints caused by urban freight. Originality/value - This study answers the call for research addressing retailers perspective in urban logistics, as it takes a demand-driven perspective of the development of UCC services. Furthermore, by highlighting services requested by retail stores, it can guide the financing of UCC initiatives, an aspect that has been lacking.

    Place, publisher, year, edition, pages
    EMERALD GROUP PUBLISHING LTD, 2017
    Keywords
    Customer service; Business model; Urban freight; City logistics; Receivers; Urban consolidation centre; Urban distribution
    National Category
    Business Administration
    Identifiers
    urn:nbn:se:liu:diva-140529 (URN)10.1108/IJPDLM-02-2017-0114 (DOI)000407286000005 ()
    Conference
    Annual Nordic Logistics and SCM Researchers Conference (NOFOMA)
    Note

    Funding Agencies|VINNOVA; Swedens Innovation Agency

    Available from: 2017-09-11 Created: 2017-09-11 Last updated: 2020-03-20
    4. Designing a business model for redistribution of surplus food
    Open this publication in new window or tab >>Designing a business model for redistribution of surplus food
    2018 (English)Conference paper, Published paper (Refereed)
    National Category
    Transport Systems and Logistics
    Identifiers
    urn:nbn:se:liu:diva-148837 (URN)
    Conference
    NoFoMa 2018, Kolding, Denmark, 13-15 June, 2018
    Funder
    VINNOVA, 2017-03156
    Available from: 2018-06-20 Created: 2018-06-20 Last updated: 2020-03-20Bibliographically approved
  • Public defence: 2020-04-29 13:15 Ada Lovelace, hus B, LinköpingOrder onlineBuy this publication >>
    Andersson, Olov
    Linköping University, Department of Computer and Information Science, Artificial Intelligence and Integrated Computer Systems. Linköping University, Faculty of Science & Engineering.
    Learning to Make Safe Real-Time Decisions Under Uncertainty for Autonomous Robots2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Robots are increasingly expected to go beyond controlled environments in laboratories and factories, to act autonomously in real-world workplaces and public spaces. Autonomous robots navigating the real world have to contend with a great deal of uncertainty, which poses additional challenges. Uncertainty in the real world accrues from several sources. Some of it may originate from imperfect internal models of reality. Other uncertainty is inherent, a direct side effect of partial observability induced by sensor limitations and occlusions. Regardless of the source, the resulting decision problem is unfortunately computationally intractable under uncertainty. This poses a great challenge as the real world is also dynamic. It  will not pause while the robot computes a solution. Autonomous robots navigating among people, for example in traffic, need to be able to make split-second decisions. Uncertainty is therefore often neglected in practice, with potentially catastrophic consequences when something unexpected happens. The aim of this thesis is to leverage recent advances in machine learning to compute safe real-time approximations to decision-making under uncertainty for real-world robots. We explore a range of methods, from probabilistic to deep learning, as well as different combinations with optimization-based methods from robotics, planning and control. Driven by applications in robot navigation, and grounded in experiments with real autonomous quadcopters, we address several parts of this problem. From reducing uncertainty by learning better models, to directly approximating the decision problem itself, all the while attempting to satisfy both the safety and real-time requirements of real-world autonomy.

    List of papers
    1. Model-Predictive Control with Stochastic Collision Avoidance using Bayesian Policy Optimization
    Open this publication in new window or tab >>Model-Predictive Control with Stochastic Collision Avoidance using Bayesian Policy Optimization
    2016 (English)In: IEEE International Conference on Robotics and Automation (ICRA), 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 4597-4604Conference paper, Published paper (Refereed)
    Abstract [en]

    Robots are increasingly expected to move out of the controlled environment of research labs and into populated streets and workplaces. Collision avoidance in such cluttered and dynamic environments is of increasing importance as robots gain more autonomy. However, efficient avoidance is fundamentally difficult since computing safe trajectories may require considering both dynamics and uncertainty. While heuristics are often used in practice, we take a holistic stochastic trajectory optimization perspective that merges both collision avoidance and control. We examine dynamic obstacles moving without prior coordination, like pedestrians or vehicles. We find that common stochastic simplifications lead to poor approximations when obstacle behavior is difficult to predict. We instead compute efficient approximations by drawing upon techniques from machine learning. We propose to combine policy search with model-predictive control. This allows us to use recent fast constrained model-predictive control solvers, while gaining the stochastic properties of policy-based methods. We exploit recent advances in Bayesian optimization to efficiently solve the resulting probabilistically-constrained policy optimization problems. Finally, we present a real-time implementation of an obstacle avoiding controller for a quadcopter. We demonstrate the results in simulation as well as with real flight experiments.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2016
    Series
    Proceedings of IEEE International Conference on Robotics and Automation, ISSN 1050-4729
    Keywords
    Robot Learning, Collision Avoidance, Robotics, Bayesian Optimization, Model Predictive Control
    National Category
    Robotics Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-126769 (URN)10.1109/ICRA.2016.7487661 (DOI)000389516203138 ()
    Conference
    IEEE International Conference on Robotics and Automation (ICRA), 2016, Stockholm, May 16-21
    Projects
    CADICSELLIITNFFP6CUASSHERPA
    Funder
    Linnaeus research environment CADICSELLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsEU, FP7, Seventh Framework ProgrammeSwedish Foundation for Strategic Research
    Available from: 2016-04-04 Created: 2016-04-04 Last updated: 2020-03-26Bibliographically approved
    2. Receding-Horizon Lattice-based Motion Planning with Dynamic Obstacle Avoidance
    Open this publication in new window or tab >>Receding-Horizon Lattice-based Motion Planning with Dynamic Obstacle Avoidance
    Show others...
    2018 (English)In: 2018 IEEE Conference on Decision and Control (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 4467-4474Conference paper, Published paper (Refereed)
    Abstract [en]

    A key requirement of autonomous vehicles is the capability to safely navigate in their environment. However, outside of controlled environments, safe navigation is a very difficult problem. In particular, the real-world often contains both complex 3D structure, and dynamic obstacles such as people or other vehicles. Dynamic obstacles are particularly challenging, as a principled solution requires planning trajectories with regard to both vehicle dynamics, and the motion of the obstacles. Additionally, the real-time requirements imposed by obstacle motion, coupled with real-world computational limitations, make classical optimality and completeness guarantees difficult to satisfy. We present a unified optimization-based motion planning and control solution, that can navigate in the presence of both static and dynamic obstacles. By combining optimal and receding-horizon control, with temporal multi-resolution lattices, we can precompute optimal motion primitives, and allow real-time planning of physically-feasible trajectories in complex environments with dynamic obstacles. We demonstrate the framework by solving difficult indoor 3D quadcopter navigation scenarios, where it is necessary to plan in time. Including waiting on, and taking detours around, the motions of other people and quadcopters.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2018
    Series
    Conference on Decision and Control (CDC), ISSN 2576-2370 ; 2018
    Keywords
    Motion Planning, Optimal Control, Autonomous System, UAV, Dynamic Obstacle Avoidance, Robotics
    National Category
    Control Engineering
    Identifiers
    urn:nbn:se:liu:diva-152131 (URN)10.1109/CDC.2018.8618964 (DOI)9781538613955 (ISBN)9781538613948 (ISBN)9781538613962 (ISBN)
    Conference
    2018 IEEE 57th Annual Conference on Decision and Control (CDC),17-19 December, Miami, Florida, USA
    Funder
    VINNOVAKnut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research ELLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsSwedish Research CouncilLinnaeus research environment CADICSCUGS (National Graduate School in Computer Science)
    Note

    This work was partially supported by FFI/VINNOVA, the Wallenberg Artificial Intelligence, Autonomous Systems and Software Program (WASP) funded by Knut and Alice Wallenberg Foundation, the Swedish Foundation for Strategic Research (SSF) project Symbicloud, the ELLIIT Excellence Center at Linköping-Lund for Information Technology, Swedish Research Council (VR) Linnaeus Center CADICS, and the National Graduate School in Computer Science, Sweden (CUGS).

    Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2020-03-26Bibliographically approved
    3. Deep Learning Quadcopter Control via Risk-Aware Active Learning
    Open this publication in new window or tab >>Deep Learning Quadcopter Control via Risk-Aware Active Learning
    2017 (English)In: Proceedings of The Thirty-first AAAI Conference on Artificial Intelligence (AAAI) / [ed] Satinder Singh and Shaul Markovitch, AAAI Press, 2017, Vol. 5, p. 3812-3818Conference paper, Published paper (Refereed)
    Abstract [en]

    Modern optimization-based approaches to control increasingly allow automatic generation of complex behavior from only a model and an objective. Recent years has seen growing interest in fast solvers to also allow real-time operation on robots, but the computational cost of such trajectory optimization remains prohibitive for many applications. In this paper we examine a novel deep neural network approximation and validate it on a safe navigation problem with a real nano-quadcopter. As the risk of costly failures is a major concern with real robots, we propose a risk-aware resampling technique. Contrary to prior work this active learning approach is easy to use with existing solvers for trajectory optimization, as well as deep learning. We demonstrate the efficacy of the approach on a difficult collision avoidance problem with non-cooperative moving obstacles. Our findings indicate that the resulting neural network approximations are least 50 times faster than the trajectory optimizer while still satisfying the safety requirements. We demonstrate the potential of the approach by implementing a synthesized deep neural network policy on the nano-quadcopter microcontroller.

    Place, publisher, year, edition, pages
    AAAI Press, 2017
    Series
    Proceedings of the AAAI Conference on Artificial Intelligence, ISSN 2159-5399, E-ISSN 2374-3468 ; 5
    National Category
    Computer Vision and Robotics (Autonomous Systems) Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-132800 (URN)978-1-57735-784-1 (ISBN)
    Conference
    Thirty-First AAAI Conference on Artificial Intelligence (AAAI), 2017, San Francisco, February 4–9.
    Projects
    ELLIITCADICSNFFP6SYMBICLOUDCUGS
    Funder
    Linnaeus research environment CADICSELLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsEU, FP7, Seventh Framework ProgrammeCUGS (National Graduate School in Computer Science)Swedish Foundation for Strategic Research
    Available from: 2016-11-25 Created: 2016-11-25 Last updated: 2020-03-26Bibliographically approved
    4. Deep RL for Autonomous Robots: Limitations and Safety Challenges
    Open this publication in new window or tab >>Deep RL for Autonomous Robots: Limitations and Safety Challenges
    2019 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    With the rise of deep reinforcement learning, there has also been a string of successes on continuous control problems using physics simulators. This has lead to some optimism regarding use in autonomous robots and vehicles. However, to successful apply such techniques to the real world requires a firm grasp of their limitations. As recent work has raised questions of how diverse these simulation benchmarks really are, we here instead analyze a popular deep RL approach on toy examples from robot obstacle avoidance. We find that these converge very slowly, if at all, to safe policies. We identify convergence issues on stochastic environments and local minima as problems that warrant more attention for safety-critical control applications.

    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-164581 (URN)
    Conference
    European Symposium on Artificial Neural Networks, Computational Intelligence and Machine Learning
    Funder
    Wallenberg AI, Autonomous Systems and Software Program (WASP)Swedish Foundation for Strategic Research ELLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Available from: 2020-03-26 Created: 2020-03-26 Last updated: 2020-04-06
    5. Model-Based Reinforcement Learning in Continuous Environments Using Real-Time Constrained Optimization
    Open this publication in new window or tab >>Model-Based Reinforcement Learning in Continuous Environments Using Real-Time Constrained Optimization
    2015 (English)In: Proceedings of the Twenty-Ninth AAAI Conference on Artificial Intelligence (AAAI) / [ed] Blai Bonet and Sven Koenig, AAAI Press, 2015, p. 2497-2503Conference paper, Published paper (Refereed)
    Abstract [en]

    Reinforcement learning for robot control tasks in continuous environments is a challenging problem due to the dimensionality of the state and action spaces, time and resource costs for learning with a real robot as well as constraints imposed for its safe operation. In this paper we propose a model-based reinforcement learning approach for continuous environments with constraints. The approach combines model-based reinforcement learning with recent advances in approximate optimal control. This results in a bounded-rationality agent that makes decisions in real-time by efficiently solving a sequence of constrained optimization problems on learned sparse Gaussian process models. Such a combination has several advantages. No high-dimensional policy needs to be computed or stored while the learning problem often reduces to a set of lower-dimensional models of the dynamics. In addition, hard constraints can easily be included and objectives can also be changed in real-time to allow for multiple or dynamic tasks. The efficacy of the approach is demonstrated on both an extended cart pole domain and a challenging quadcopter navigation task using real data.

    Place, publisher, year, edition, pages
    AAAI Press, 2015
    Keywords
    Reinforcement Learning, Gaussian Processes, Optimization, Robotics
    National Category
    Computer Sciences Computer Vision and Robotics (Autonomous Systems)
    Identifiers
    urn:nbn:se:liu:diva-113385 (URN)978-1-57735-698-1 (ISBN)
    Conference
    Twenty-Ninth AAAI Conference on Artificial Intelligence (AAAI), January 25-30, 2015, Austin, Texas, USA.
    Funder
    Linnaeus research environment CADICSeLLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsSwedish Foundation for Strategic Research VINNOVAEU, FP7, Seventh Framework Programme
    Available from: 2015-01-16 Created: 2015-01-16 Last updated: 2020-03-26Bibliographically approved
    6. Real-Time Robotic Search using Structural Spatial Point Processes
    Open this publication in new window or tab >>Real-Time Robotic Search using Structural Spatial Point Processes
    Show others...
    2019 (English)Conference paper, Published paper (Refereed)
    National Category
    Computer and Information Sciences
    Identifiers
    urn:nbn:se:liu:diva-159698 (URN)
    Conference
    Proceedings of the 35th Conference on Uncertainty in Artificial Intelligence (UAI 2019), Tel Aviv, Israel, July 22-25, 2019
    Available from: 2019-08-19 Created: 2019-08-19 Last updated: 2020-03-26Bibliographically approved
  • Public defence: 2020-04-30 13:15 I:101, I-Building, LinköpingOrder onlineBuy this publication >>
    Palmqvist, Lisa
    Linköping University, Department of Behavioural Sciences and Learning, Disability Research. Linköping University, Faculty of Arts and Sciences.
    Time to Plan: How to support everyday planning in adolescents with intellectual disability2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Children and adolescents with intellectual disability (ID) have difficulties in executive functioning and when coping with everyday planning tasks. However, the literature cannot explain whether individuals with ID perform according to their developmental level or not. The studies in this thesis investigated if life experience could be a contributing factor to the diversity seen in the literature. Planning performance can be improved by either using external or internal support. Assistive technology for cognition (ATC) is an example of external support. This thesis investigated how the ATC is being used in an everyday planning situation which has not been investigated before. Furthermore, this thesis explored whether the internal supports of cognitive abilities and life experience correlate with planning ability in adolescents with ID, and if planning ability can be trained using a cognitive training program for everyday planning. Results showed that ATC supported cognitive functions, but that the children did not formulate the plans themselves. Furthermore, the results support the difference model of ID since planning correlated with different cognitive measures and life experience in adolescents with ID compared to children with a typical development. Adolescents with ID got better at the planning tasks in the training program, however, no transfer effects to untrained planning tasks were found. To conclude, the planning was supported by external and internal support. However, ATC needs to be designed and prescribed in a way that increases independence. Practitioners should actively support in training planning and should be cautious when introducing cognitive interventions if the transfer gap is too large.  

    List of papers
    1. Parents act as intermediary users for their children when using assistive technology for cognition in everyday planning: Results from a parental survey
    Open this publication in new window or tab >>Parents act as intermediary users for their children when using assistive technology for cognition in everyday planning: Results from a parental survey
    2019 (English)In: Assistive technology, ISSN 1040-0435, E-ISSN 1949-3614, p. 1-9Article in journal (Refereed) Published
    Abstract [en]

    Assistive Technology for Cognition (ATC) is employed by children with and without disabilities. However, how the ATC is used in everyday life has not been studied. The current study investigated ATC-usage in everyday planning in three groups: 1) children qualifying for Swedish habilitation centers (ID/ASD), 2) children with disability not qualifying for habilitation service (ADHD), and 3) children with typical development (TD). A parental survey was conducted (n = 192) and answers were analyzed with statistical tests and inductive thematic text analysis. Results showed that all groups used ATC, most in the Habilitation group and least in the TD group. According to parents, ATC supported cognitive functions in all groups, but it became evident that the parents were responsible for planning by setting up the ATC, whilst the children merely executed the plans. This was linked to several limitations, for example the design was not appropriately adapted for these groups. The implications for the practitioners are 1) evaluate the users? cognitive abilities and choose an ATC suitable for that individual rather focusing on the diagnosis, and 2) follow up usage to see if it is the parent or the child that are using the ATC.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2019
    Keywords
    Activities of daily living, assessment, cognitive impairment, developmental disability, electronic aids to daily living, usability
    National Category
    Pediatrics
    Identifiers
    urn:nbn:se:liu:diva-164915 (URN)10.1080/10400435.2018.1522523 (DOI)
    Available from: 2020-04-01 Created: 2020-04-01 Last updated: 2020-04-01Bibliographically approved
    2. Cognitive abilities and life experience in everyday planning in adolescents with intellectual disabilities: Support for the difference model
    Open this publication in new window or tab >>Cognitive abilities and life experience in everyday planning in adolescents with intellectual disabilities: Support for the difference model
    2020 (English)In: Journal of Intellectual Disability Research, ISSN 0964-2633, E-ISSN 1365-2788Article in journal (Refereed) Epub ahead of print
    Abstract [en]

    Background The literature on planning ability in individuals with intellectual disability (ID) provides no clarity on whether their ability matches their mental age (MA) or not. Perhaps can planning experience explain the mixed results. The current study investigated to what extent cognitive abilities and life experience can explain everyday planning ability in individuals with ID and to what extent results from everyday planning tasks support the developmental or the difference model of ID. Method Planning tests, cognitive ability tasks and a self-rated life experience form were administered to 71 adolescents with ID and 62 children with a typical development matched on MA. Results Adolescents with ID exhibited planning ability according to their MA. Regression analyses showed that the predictors of planning differed between the groups. The cognitive measures could predict planning in both groups, but life experience only contributed positively to planning in the MA group, whereas chronological age was negatively correlated with successful planning in the ID group. Conclusions and discussion The results support the difference model of ID. When matched on MA, the individuals with ID will solve the planning task in a qualitatively different manner. Additionally, the participants with ID could not utilise their life experience when solving the planning task, contrary to the MA group. Practitioners should be aware that individuals with ID might need more everyday planning training throughout adolescence. To support adolescents with ID, practitioners may focus on supporting the individuals cognitive abilities rather than relying on their prior knowledge.

    Place, publisher, year, edition, pages
    WILEY, 2020
    Keywords
    cognitive abilities; difference model; errand task; everyday planning; intellectual disability
    National Category
    Occupational Therapy
    Identifiers
    urn:nbn:se:liu:diva-163409 (URN)10.1111/jir.12710 (DOI)000505491500001 ()31898385 (PubMedID)
    Note

    Funding Agencies|Stiftelsen Savstaholm [ST 2016-030]

    Available from: 2020-02-04 Created: 2020-02-04 Last updated: 2020-04-01
  • Public defence: 2020-05-05 09:00 Berzeliussalen, Building 463, LinköpingOrder onlineBuy this publication >>
    Toll, Rani
    Linköping University, Department of Biomedical and Clinical Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Local Health Care Services in Central Östergötland, Department of Emergency Medicine in Linköping.
    To See or Not to See: A Study on Capillary Refill2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Background: Assessment of the critically ill is traditionally based on vital signs (blood pressure, pulse, respiratory rate, temperature and level of consciousness). Altered vital signs are, however, late indicators of deranged hemodynamics pointing to a need for additional, more sensitive markers of circulatory compromise. In the beginning of the 20th century, the capillary refill (CR) time evolved as a possible, non-invasive adjunct to early prediction of the outcome in the critically ill. The manoeuvre entails application of blanching pressure on the skin of the finger pulp or sternum for 5 seconds. After release of the pressure, the observer estimates time in seconds for the skin to return to original colour. This time is hypothesized to reflect the dynamics of the microcirculation and its possible connection with hemodynamics. In the 1980s the “normal capillary refill time” was set to < 2 seconds and later extended to 3 seconds, without a clear scientific foundation. Naked-eye estimations of CR time met increasing scepticism in the 1990s due to subjectivity and poor prognostic value for shock or death. Several basic traits, such as age and sex, as well as ambient temperature, were also shown to independently influence the CR time. Various methods have evolved with the capability to measure CR time quantitatively, one of which is Polarisation Spectroscopy Imaging (PSI). PSI measures the Red Blood Cell (RBC) concentration in tissue (e.g. the skin) and can be used to measure CR time.

    Objectives: The purpose of this study was to establish basic characteristics for quantified CR (qCR), identify possible influencing factors in healthy subjects and to investigate how this relates to current practice. We also sought to identify technical demands for transfer of the technique into clinical studies. In paper I we analysed the (qCR) time characteristics at 5 different skin sites (forehead, sternum, volar forearm, finger pulp and dorsum finger). The objective of paper II was to investigate the inter- and intra-observer variability of naked eye CR assessments of different professions, nurses, doctors and secretaries (representing laymen). In paper III we observed the effect of low ambient temperature on the qCR time in different skin sites. In paper IV, we transferred the equipment from a laboratory to a clinical setting in the Emergency Department (ED) for application on potentially critically ill patients. In this study we evaluated the most important factors determining a reliable data collection and influencing the amount of data possible to analyse.

    Methods: qCR time was measured in a total of 38 volunteers and 10 patients in different skin sites (2-5 skin sites) at different ambient temperatures. PSI (TiVi 600 and 700, WheelsBridge AB, Linköping, Sweden) was used to determine the rapid temporal changes in RBC concentration in skin during the CR manoeuvre. Films using a range of the first measurements from paper I were shown for assessment to 48 observers working in the ED.

    Results: In paper I we could delineate qCR curves and suggest 2 possible equivalents to the naked-eye observed CR time which we named Time to Return to Baseline 1 (tRtB1) and Time to Peak (tpk). We demonstrated differences in qCR-curves depending on skin site and possibly due to skin temperature. In paper II we showed a poor inter- and intra-observer reproducibility in visually estimating the CR time regardless of profession (clinicians or laymen). Paper III demonstrated a rapid effect of ambient temperature on qCR time in peripheral skin sites such as finger pulp. The forehead, regarded as a more central skin site was the most temperature stable site and showed least variability in qCR time as determined using tRtB1. Paper IV, a study on patients in an ED setting, yielded assayable data in 80% of the measurements. We identified critical performance parameters to address in the further development of a more robust, easy-to-use device for future validation of the possible relevance of qCR in patient triage and monitoring.

    Conclusions: CR time can be quantified using PSI. Quantified CR time demonstrated a large variability between different skin sites, specifically, skin temperature was shown to be an important factor influencing qCR time, particularly at the fingertip. Naked-eye estimates of CR time were highly variable, both within and between observers. Agreement between quantified CR time and naked-eye estimates was poor. The prototypic PSI technique was feasible in a clinical setting and, with further improvements, clinical evaluation of qCR in relation to relevant patient outcomes will be possible.

    List of papers
    1. Reflectance spectroscopy: to shed new light on the capillary refill test
    Open this publication in new window or tab >>Reflectance spectroscopy: to shed new light on the capillary refill test
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    2018 (English)In: Journal of Biophotonics, ISSN 1864-063X, E-ISSN 1864-0648, Vol. 11, no 1, article id e201700043Article in journal (Refereed) Published
    Abstract [en]

    To use Bioengineering methodology is used to achieve, at five anatomical sites, a detailed, quantitative assessment of the return of blood content to the blanched area, during the Capillary Refill (CR) test. An observational, non-randomized, experimental study on 23 healthy subjects (14 females) was performed in our climate controlled skin physiology laboratory. Our main outcome measures were based on the chronological assessment and quantification of red blood cell concentration (RBC) after the release of blanching pressure in the CR test, using Tissue Viability Imaging (TiVi), a digital photographic technique based on polarisation spectroscopy. TiVi enabled collection of detailed data on skin RBC concentration during the CR test. The results were shown as curves with skin blood concentration (TiVi-value) on the y-axis and the time on the x-axis. Quantitative CR responses showed site and temperature variability. We also suggest possible objective endpoint values from the capillary refill curve. Detailed data on skin RBC concentration during the CR test is easily obtained and allows objective determination of end points not possible to achieve by naked eye assessment. These findings have the potential to place the utility of the CR test in a clinical setting in a new light. Picture: Regular photograph and TiVi Image showing CR test and corresponding graph for the CR response. [GRAPHICS] .

    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2018
    Keywords
    Capillary refill; microvasculature; circulation; skin imaging; gender variability; blood concentration
    National Category
    Dermatology and Venereal Diseases
    Identifiers
    urn:nbn:se:liu:diva-145478 (URN)10.1002/jbio.201700043 (DOI)000425294600022 ()28544641 (PubMedID)2-s2.0-85019540776 (Scopus ID)
    Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2020-04-01Bibliographically approved
    2. Man versus machine: comparison of naked-eye estimation and quantified capillary refill
    Open this publication in new window or tab >>Man versus machine: comparison of naked-eye estimation and quantified capillary refill
    2019 (English)In: Emergency Medicine Journal, ISSN 1472-0205, E-ISSN 1472-0213, Vol. 36, no 8, p. 465-471Article in journal (Refereed) Published
    Abstract [en]

    Background Capillary refill (CR) time is traditionally assessed by naked-eye inspection of the return to original colour of a tissue after blanching pressure. Few studies have addressed intra-observer reliability or used objective quantification techniques to assess time to original colour. This study compares naked-eye assessment with quantified CR (qCR) time using polarisation spectroscopy and examines intra-observer and interobserver agreements in using the naked eye. Method A film of 18 CR tests (shown in a random fixed order) performed in healthy adults was assessed by a convenience sample of 14 doctors, 15 nurses and 19 secretaries (Department of Emergency Medicine, Linkoping University, September to November 2017), who were asked to estimate the time to return to colour and characterise it as fast, normal or slow. The qCR times and corresponding naked-eye time assessments were compared using the Kruskal-Wallis test. Three videos were shown twice without observers knowledge to measure intra-observer repeatability. Intra-observer categorical assessments were compared using Cohens Kappa analysis. Interobserver repeatability was measured and depicted with multiple-observer Bland-Altman plotting. Differences in naked-eye estimation between professions were analysed using ANOVA. Results Naked-eye assessed CR time and qCR time differ substantially, and agreement for the categorical assessments (naked-eye assessment vs qCR classification) was poor (Cohens kappa 0.27). Bland-Altman intra-observer repeatability ranged from 6% to 60%. Interobserver agreement was low as shown by the Bland-Altman plotting with a 95% limit of agreement with the mean of +/- 1.98 s for doctors, +/- 1.6 s for nurses and +/- 1.75 s for secretaries. The difference in CR time estimation (in seconds) between professions was not significant. Conclusions Our study suggests that naked-eye-assessed CR time shows poor reproducibility, even by the same observers, and differs from an objective measure of CR time.

    Place, publisher, year, edition, pages
    BMJ PUBLISHING GROUP, 2019
    National Category
    Anesthesiology and Intensive Care
    Identifiers
    urn:nbn:se:liu:diva-159714 (URN)10.1136/emermed-2018-207948 (DOI)000478913300006 ()31308133 (PubMedID)
    Note

    Funding Agencies|Region Ostergotland [LIO-532001, LIO-700271]

    Available from: 2019-08-19 Created: 2019-08-19 Last updated: 2020-04-01
    3. A cool response: the influence of ambient temperature on capillary refill time
    Open this publication in new window or tab >>A cool response: the influence of ambient temperature on capillary refill time
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    2018 (English)In: Journal of Biophotonics, ISSN 1864-063X, E-ISSN 1864-0648, Vol. 11, no 6Article in journal (Refereed) Published
    Abstract [en]

    Objective

    To describe the effect of low ambient temperature on skin temperature and capillary refill (CR) time in forehead, sternum and finger pulp.

    Methods

    An observational, nonrandomized experimental study on 15 healthy subjects (6 females) in a cold room (8°C). Outcome measures were skin temperature and quantified CR test after application of a standardized blanching pressure (9 N/cm2) using digital photographic polarization spectroscopy to generate CR times.

    Results

    The finger pulp showed marked temperature fall and prolonged CR times (>10 seconds). The CR registrations of the forehead and sternum were more comparable to curves observed in a control material at room temperature, and skin temperature falls were less marked. CR times were not prolonged in forehead measurements. At the sternum, some individuals showed CR times beyond guideline recommendations despite only a marginal reduction in skin temperature.

    Conclusions

    Low ambient temperature is a strong independent factor for CR time at peripheral sites. Reservation about sternum as a site of measurement is warranted since cold provocation produced prolonged CR times in some individuals. We found that the forehead is the most thermostable of the 3 sites and thus the preferred site to avoid ambient temperature artifact in measuring CR time.

    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2018
    National Category
    Atom and Molecular Physics and Optics
    Research subject
    Disaster Medicine
    Identifiers
    urn:nbn:se:liu:diva-145527 (URN)10.1002/jbio.201700371 (DOI)000434641700017 ()29384267 (PubMedID)
    Note

    Funding agencies: Socialstyrelsen; Region Ostergotland

    Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2020-04-01Bibliographically approved
  • Public defence: 2020-05-05 13:15 C3 C-Building, Linköping
    Ekman, Petter
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Important Factors for Accurate Scale-Resolving Simulations of Automotive Aerodynamics2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Road transports are responsible for almost 18 % of the greenhouse gas emission in Europe and are today the leading cause of air pollution in cities. Aerodynamic resistance has a significant effect on fuel consumption and hence the emission of vehicles. For electric vehicles, emissions are not affected by the aerodynamics as such but instead have a significant effect on the effective range of the vehicle.

    In 2017, a new measurement procedure was introduced, Worldwide Harmonized Light Vehicles Test Procedure (WLTP), for measuring emissions, fuel consumption, and range. This procedure includes a new test cycle with increased average driving speed compared to the former procedure, which thereby increases the importance of the aerodynamic resistance, as it drastically increases with speed. A second effect is that the exact car configuration sold to the customer needs to be certified in terms of fuel consumption and emissions. The result is that every possible combination of optional extras, which might affect the aerodynamic resistance, needs to be aerodynamically analyzed and possibly improved. From 2021, the European Commission will introduce stricter emission regulations for new passenger cars, with the fleet-wide average lowered to 95 grams CO2=km, which puts an even higher demand on achieving efficient aerodynamics.

    Virtual development of the aerodynamics of road vehicles is today used to a great extent, using Computational Fluid Dynamics, as it enables faster and cheaper development. However, achieving high accuracy for the prediction of the flow field and aerodynamic forces is challenging, especially given the complexity of both the vehicle geometry in itself and the surrounding flow field. Even for a simplified generic bluff body, accurately predicting the flow field and aerodynamic forces is a challenge. The main reason for this challenge of achieving results with high accuracy is the prediction of the complex behavior of turbulence. Scale-resolving simulation (SRS) methods, such as Large Eddy Simulation (LES), where most of the turbulent structures are resolved has in many studies shown high accuracy but unfortunately to a very high computational cost. It is primarily the small turbulent structures within the near-wall region that requires a _ne resolution in both space (the mesh) and in time. This fine resolution is the reason for the very high computational cost and makes LES unfeasible for practical use in industrial aerodynamic development at present and in the near future. By modeling the turbulent structures within the near-wall region using a Reynolds-Averaged Navier-Stokes (RANS) model, and resolving the turbulence outside the region with a LES model, a coarser resolution is possible to use, resulting in significantly lower computational cost. Which used RANS model is of high importance, and especially how much turbulent viscosity the model generates, as too high values can result in suppression of the resolved turbulence.

    The transitioning between the RANS and LES regions have a significant effect on the results. Faster transition enables more resolved turbulence, favorable for higher accuracy, but needs to be balanced with sufficient shielding of the RANS region. If resolving the turbulence occurs within the near-wall region, and the mesh is not sufficiently fine, it can result in poor accuracy.

    By increasing the time-step size and disregarding best-practice guides, the computational cost can be significantly reduced. The accuracy is reasonably insensitive to the larger time step sizes until a certain degree, thereby enabling computationally cheaper SRS to achieve high accuracy of aerodynamic predictions needed to meet present and future emission regulations.

    List of papers
    1. Aerodynamic Drag Reduction - from Conceptual Design on a Simplified Generic Model to Full-Scale Road Tests
    Open this publication in new window or tab >>Aerodynamic Drag Reduction - from Conceptual Design on a Simplified Generic Model to Full-Scale Road Tests
    2015 (English)In: SAE 2015 World Congress & Exhibition, SAE International , 2015Conference paper, Published paper (Refereed)
    Abstract [en]

    Road transportation by trucks is the major part of the goods transportations system in the European Union (EU), and there is a need for increased fuel efficiency. While truck manufacturers already spend significant resources in order to reduce the emissions from their vehicles, most truck manufacturers do not control the shape of the trailer and/or swap bodies. These devices are usually manufactured by different companies that cannot consider the overall aerodynamics around the complete vehicle.By use of Computational Fluid Dynamics (CFD) and previous wind tunnel experiments, the flow around a simplified generic tractor-trailer model has been investigated. With better understanding of the flow features around the tractor with attached trailer or swap bodies, an improved design of the trailer and swap body can be achieved, which is the aim for the project. Special emphasis is put on achieving simple, easy to install or implement drag-reducing geometrical modifications to the trailer or swap bodies that can be mounted on existing trucks.Reynolds-Averaged Navier-Stokes (RANS) simulations were used for the conceptual development phase where trends in drag reduction due to the modified geometries were studied using a parameter study, while more advanced scale resolving simulations (SRS) were used in order to investigate the details of the flow fields.The investigation indicates that aerodynamic drag reduction is possible with quite simple geometrical modifications. Some of the results have also been verified through road tests of vehicles in commercial use, which has shown reduced fuel consumption of up to 5%.

    Place, publisher, year, edition, pages
    SAE International, 2015
    National Category
    Vehicle Engineering
    Identifiers
    urn:nbn:se:liu:diva-164920 (URN)10.4271/2015-01-1543 (DOI)
    Conference
    SAE 2015 World Congress & Exhibition
    Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
    2. Aerodynamic Drag Reduction of a Light Truck - from Conceptual Design to Full Scale Road Tests
    Open this publication in new window or tab >>Aerodynamic Drag Reduction of a Light Truck - from Conceptual Design to Full Scale Road Tests
    2016 (English)In: SAE 2016 World Congress and Exhibition, SAE International , 2016Conference paper, Published paper (Refereed)
    Abstract [en]

    Considerable amounts of the everyday goods transports are done using light trucks. In the last ten years (2005-2015), the number of light trucks has increased by 33 % in Sweden. The majority of these light trucks are fitted with a swap body and encounter the same problem as many other truck configurations, namely that several different manufacturers contribute to the final shape of the vehicle. Due to this, the aerodynamics of the final vehicle is often not fully considered. Hence there appears to be room for improving the aerodynamic performance. In this study the flow around a swap body fitted to a light truck has been investigated using Computational Fluid Dynamics. The focus has been on improving the shape of the swap body in order to reduce both the aerodynamic drag and fuel consumption, while still keeping it usable for daily operations. Reynolds-Averaged Navier-Stokes simulations were used for concept evaluation while more advanced Detached Eddy Simulations were performed on the best concept in order to investigate details of the flow. Various concepts were evaluated from which it could be seen that a more streamlined top of the swap body together with a lowered top trailing edge had a significant positive effect on the aerodynamic drag. A full scale light truck was equipped with a swap body with with these modifications for road tests. During a test period, a mean fuel consumption reduction of 12 % was measured, thus indicating a significantly reduced aerodynamic drag.

    Place, publisher, year, edition, pages
    SAE International, 2016
    National Category
    Vehicle Engineering
    Identifiers
    urn:nbn:se:liu:diva-164923 (URN)10.4271/2016-01-1594 (DOI)
    Conference
    SAE 2016 World Congress and Exhibition
    Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
    3. Aerodynamics of an Unloaded Timber Truck - A CFD Investigation
    Open this publication in new window or tab >>Aerodynamics of an Unloaded Timber Truck - A CFD Investigation
    2016 (English)In: SAE International Journal of Commercial Vehicles, ISSN 1946-391X, E-ISSN 1946-3928, Vol. 9, no 2, p. 217-223Article in journal (Refereed) Published
    Abstract [en]

    Reducing energy consumption and emissions are ongoing challenges for the transport sector. The increased number of goods transports emphasize these challenges even more, as greenhouse gas emissions from these vehicles increased by 20 % between 1990 and 2013, in Sweden. One special case of goods transports is the transport of timber. Today in Sweden, around 2000 timber trucks transport around six billion ton kilometers every year. For every ton kilometer these vehicles use around 0.025 liter diesel, and there should exist large possibilities to reduce the fuel consumption and the emissions for these vehicles. Timber trucks spend most of their operation time travelling in speeds of around 80 km/h. At this speed aerodynamic drag contributes to around 30 % of the total vehicle resistance, which makes the aerodynamic drag a significant part of the energy consumption. One of the big challenges with timber trucks is that they travel unloaded half of the time. This put higher demands on possible drag reduction modifications, as they need to function and be practical for both when the timber truck is loaded and unloaded. In this study an unloaded timber truck has been investigated by use of computational fluid dynamics. The recently released Stress Blended Eddy Simulation model has been used for simulating the flow over a timber truck at a Reynolds number of 1.1 million, based on the square root of its frontal area. From the results it could be seen that 52.8 % of the drag is generated by the cab. By investigating a drag reduction device that covered the gap between the bulkhead and the first stake pair, a drag reduction up to 6.7 % was possible, which shows potential for simple modifications that not influence the daily usage.

    Place, publisher, year, edition, pages
    SAE INT, 2016
    National Category
    Transport Systems and Logistics
    Identifiers
    urn:nbn:se:liu:diva-163998 (URN)10.4271/2016-01-8022 (DOI)000389233800010 ()
    Available from: 2020-03-05 Created: 2020-03-05 Last updated: 2020-04-02
    4. Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model
    Open this publication in new window or tab >>Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model
    2019 (English)In: WCX SAE World Congress Experience, SAE International , 2019Conference paper, Published paper (Refereed)
    Abstract [en]

    In aerodynamic development of ground vehicles, the use of Computational Fluid Dynamics (CFD) is crucial for improving the aerodynamic performance, stability and comfort of the vehicle. Simulation time and accuracy are two key factors of a well working CFD procedure. Using scale-resolving simulations, accurate predictions of the flow field and aerodynamic forces are possible, but often leads to long simulation time. For a given solver, one of the most significant aspects of the simulation time/cost is the temporal resolution. In this study, this aspect is investigated using the realistic vehicle model DrivAer with the notchback geometry as the test case. To ensure a direct and accurate comparison with wind tunnel measurements, performed at TU Berlin, a large section of the wind tunnel is included in the simulation domain. All simulations are performed at a Reynolds number of 3.12 million, based on the vehicle length. Three spatial resolutions were compared, where it could be seen that a hybrid element mesh consisting of 102 million cells only revealed small differences to the finest mesh investigated, well as showing excellent agreement with wind tunnel measurements. An investigation of the temporal resolution is performed, in order to see its effect on the simulation time/cost and accuracy of the results. The finest temporal resolution resulted in a Courant-Friedrichs-Lewy number less than unity, while the coarsest reached a CFL number of around 100. From these results, it is seen that it is possible to reduce the simulation time with more than 90 % (CFL 20) and still keep sufficient accuracy of the forces and important features of the flow field.

    Place, publisher, year, edition, pages
    SAE International, 2019
    National Category
    Vehicle Engineering
    Identifiers
    urn:nbn:se:liu:diva-164924 (URN)10.4271/2019-01-0639 (DOI)
    Conference
    WCX SAE World Congress Experience
    Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved