Luleå University of Technology Publications
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High-Temperature Corrosion Behavior of Martensitic Steels in Ammonia Environment
No full textGlobally, energy consumption remains dominated by hydrocarbons (coal, oil and natural gas), while the shipping industry remains a hard-to-abate sector reliant on petroleum-based fuels and a major contributor to greenhouse gas emissions. Against this backdrop, ammonia has emerged as a promising carbon-free fuel and hydrogen carrier due to its favourable chemical properties, established industrial supply chain and alignment with decarbonisation strategies. However, materials used in ammonia-fuelled engines face a particularly demanding degradation environment: elevated combustion temperatures and cyclic pressure loads combine with ammonia-induced corrosion, such that thermo-mechanical fatigue, stress-corrosion cracking and corrosion-fatigue may act concurrently and accelerate damage even at stresses well below yield strength. This thesis investigates the corrosion behavior of three martensitic steels (327F – 42CrMo4; 280T – 19MnV6; 297A – Hybrid 55) in both a dilute ammonia aqueous solution at ambient temperature and a gaseous ammonia environment at elevated temperature. Specimens were prepared as conventional coupons and Hybrid 55 additionally as stress-concentrated forms (designed U-bend and clip coupon). Corrosion resistance in 5% dilute ammonia was ranked: Hybrid 55 > 327F > 280T. In the stressed U-bend coupon of Hybrid 55, aggressive corrosion was observed in the stress-concentrated surface region where micro-pittings and accumulation of corrosion products were spotted, attributed to passive-film rupture. In ammonia-nitrided specimens, a stratified nitrided layer structure was revealed. Porous bands within the compound layer provided favourable sites for crack initiation and propagation. Though crack networks were confined within the compound layer in the conventional plate sample, several branched cracks penetrated into the substrate under tensile stress, indicating that a nitrided layer under stress is prone to SCC failure
The Arabic psychosocial impact of assistive devices scale: Development, translation, and evaluation
No full textThis paper describes the development, translation, and early evaluation of the Arabic Psychosocial Impact of Assistive Devices Scale (AR-PIADS), an outcome measure instrument for the subjective impact of Assistive Technology on a person with a disabilities&apos; quality of life. Developing the AR = PIADS instrument involved forward and backward translation by two independent teams of bilingual, Arabic-English speakers (n = 5) and a quality and usability review by a panel of people with disabilities (n = 18). The emergent version was evaluated with a group of experienced Arabic-speaking Assistive Technology users (n = 67) for its psychometric properties. Initial results demonstrate a favorable comparison for 16 of the 26 questionnaire items with scores recorded for the original, English language version. Internal consistency, measured using Cronbach&apos;s alpha, yielded a range of 0.97-0.99 for AR-PIADS while the new instrument&apos;s reliability was assessed using an intraclass correlation coefficient resulting in scores within the range of 0.86-0.97 for the overall instrument. Despite these positive results however, the translation process did highlight a number of challenges with language and cultural interpretation of the translated instrument. This suggests that further work is warranted to explore its utility in service provision.Godkänd;2025;Nivå 0;2025-03-18 (u4);Funder: RESPECT and the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013); Research Executive Agency (REA) (PCOFUND-GA-2013-608728);Full text license: CC BY-NC-ND</p
Mathematics education in preschool : A study about preschool teachers’ approaches and strategies
No full textDenna studie undersöker förskollärarnas arbete med matematikundervisning som sker planerat och spontant. Syftet är att belysa vilka strategier förskollärarna använder för att väcka barnens intresse och arbetet med matematikundervisning. Studien är av en kvalitativ ansats där fyra förskollärare intervjuades med semistrukturerade intervjuer för att få en fördjupad syn av deras erfarenheter och perspektiv. Analysen är baserad på variationsteorin och tematisk analys för att identifiera teman. Resultatet visar att förskollärarna varierade i sina arbetssätt samt hur de balanaserade planerade och spontana undervisningar. Strategierna som används är språk, material som är konkret och barnens intresse vilket är nyckelfaktorerna för att skapa matematikundervisning som är meningsfull för barnen. Studien framhäver förskollärarnas behov av matematiska och didaktiska kunskaper och balansen mellan spontan och planerad undervisning. Slutsatserna bidrar till en djupare förståelse för matematikundervisning som finns i förskolan och barnens utveckling och lärande.
Decoding the barriers for a circular plastics industry: An equation framework
No full textEmpirical research on barriers to a circular plastics economy has predominantly relied on case study approaches. While research has provided insights into the conceptual and anecdotal aspects of these barriers, a gap remains in the application of formalized methodologies to systematically understand and address them. This paper seeks to bridge this gap by developing an equation system tailored to the plastics industry, bringing clarity to the complex interplay of factors that constitute barriers to a circular economy. The study identifies four primary barriers to the circular economy, as documented in the literature between 2017 and 2024: economic, institutional and regulatory, technological, and social. The results include 24 equations, synthesized into four master equations. A mathematical case study demonstrates how numerical weights, and the relative importance of variables can differ between countries, offering a practical guide for applying the framework across diverse contexts. The study concludes that reducing regulatory ambiguity, scaling recycling infrastructure, and fostering consumer trust in recycled materials are critical steps. However, each country will face unique challenges, requiring policymakers to adopt tailored approaches and variable weighting.Validerad;2025;Nivå 2;2025-02-11 (u2);Full text: CC BY license;</p
An experimental pilot-study on dynamic versus isometric resistance training of grip strength.
No full textIntroduktion: Styrketräning används för att förbättra styrka, kraft, muskelmassa och uthållighet, där träningsdoseringen avgör resultaten. Traditionellt utförs styrketräning med hög belastning och få repetitioner, medan uthållighetsträning fokuserar på låg belastning och många repetitioner. Både statisk och dynamisk träning påverkar muskelfunktionen, men deras effekter skiljer sig åt. Tidigare studier visar att dynamisk träning ger bättre resultat för funktionella rörelser, medan statisk träning är effektivare för uthållighet. Dock saknas forskning om dynamisk mot isometrisk träning för greppstyrka respektive uthållighet. I arbets- och vardagslivet ställs krav på båda dessa funktioner, vilken form av träning som förbättrar dessa är relevant för olika professioner, bland annat fysioterapeuter. Syfte: Jämföra dynamisk mot isometrisk styrketräning och analysera resultatet gällande maximal isometrisk styrka respektive uthållighet. Metod: Den här experimentella studien inkluderade 7 friska deltagare i åldrarna 20-40 år. Två interventionsgrupper, varav en grupp tränade dynamisk greppstyrka och den andra isometrisk greppstyrka. Isometrisk maximal samt uthållighetsstyrka mättes i början och slut av interventionsperioden med dynamometer samt deadhangtest. Interventionerna pågick i 6 veckor, 15-20 minuter, 3 gånger i veckan. Resultat: Den dynamiska gruppen ökade icke dominanta hands max styrka med i medel 2,2 kg respektive den dominanta handens med 2,1 kg, uthålligheten genom deadhang test var oförändrad. Den isometriska gruppens icke dominanta hands max styrka var i stort sett oförändrad, den dominanta handens styrka ökade med 2,6 kg, uthålligheten visade en stor genomsnittlig ökning på 17,5 DHV. Konklusion: Vidare studier behövs med ett större urval för att påvisa effekterna av dynamisk och isometrisk träning för greppstyrka och uthållighet.Introduction: Strength training is used to improve strength, power, muscle mass, and endurance, with training dosage determining the results. Traditionally, strength training is performed with high loads and few repetitions, while endurance training focuses on low loads and many repetitions. Both static and dynamic training affect muscle function, but their effects differ. Previous studies show that dynamic training yields better results for functional movements, while static training is more effective for endurance. However, research comparing dynamic versus isometric training for grip strength and endurance is lacking. Both of these functions are required in both work and everyday life, and determining which type of training improves them is relevant for various professions, including physiotherapists. Aim: To compare dynamic versus isometric strength training and analyze the results regarding maximal isometric strength and endurance. Method: This experimental study included 7 healthy participants aged 20-40 years. Two intervention groups were formed, one group trained dynamic grip strength, and the other trained isometric grip strength. Maximal isometric strength and endurance strength were measured at the beginning and end of the intervention period using a dynamometer and deadhang test. The interventions lasted for 6 weeks, 15-20 minutes, 3 times a week. Results: The dynamic group increased their non-dominant hand's maximum strength by an average of 2.2 kg, and the dominant hand's by 2.1 kg. Endurance, measured through the deadhang test, remained unchanged. The isometric group’s non-dominant hand's maximum strength was largely unchanged, while the dominant hand's strength increased by 2.6 kg. Endurance showed a large average increase of 17.5 DHV. Conclusion: Further studies are needed with a larger sample size to demonstrate the effects of dynamic and isometric training on grip strength and endurance
Accessibility at public places
No full textDen svenska funktionshinderpolitiken har som mål att alla ska ha möjlighet att kunna delta i samhällslivet. Tillgänglighet är en viktig del att förbättra för att kunna uppnå delaktighet. Utöver att vara en aspekt av delaktighet är tillgänglighet även en viktig aspekt i social hållbarhet samt grundläggande förutsättning för stadsplanering som gynnar alla. Bristande tillgänglighet är en form av diskriminering. Inom stadsplanering finns många styrande dokument för att se till att brister i tillgängligheten för personer med nedsatt rörelse- och orienteringsförmåga inte sker. Historiskt sett och även än idag utgår mycket av stadsplaneringen från en genomsnittsmänniska som egentligen inte finns. Denna genomsnittsmänniska är baserat på normer och värderingar om hur människor lever och fungerar. Då det fortfarande finns stora brister i den fysiska utformningen av städer krävs en bättre förståelse kring upplevelser av tillgänglighet för personer med nedsatt rörelse- och orienteringsförmåga. Rapportens syfte är därför att studera den upplevda tillgängligheten för personer med nedsatt rörelseförmåga, syn eller hörsel på handelsområden i Borlänge och Luleå samt vilka krav som ställs på tillgänglighet inom stadsplanering. Studiens utförande har delats in i två delar, en litteraturstudie och en kvalitativ studie. Litteraturstudien var nödvändig för att få bättre kunskap inom studiens fokusområde och har varit en bra grund för den kvalitativa delen av studien. Litteraturstudien har fokuserat på begreppsförklaringar och besvarat frågor vad gäller upplevelsen av tillgänglighet, och hur det förändras i och med säsongsvariationer samt krav som finns gällande tillgänglighet. Den kvantitativa studien består av en dokumentsstudie samt en intervjustudie och studerar två städer i Sverige. Denna del av studien har genomförts för att få kvalitativ information gällande upplevelser av tillgänglighet samt hur kommuner arbetar med tillgänglighet. Intervjustudien genomfördes som en gåtur och totalt deltog sju informanter i studien. Upplevelsen av tillgänglighet på allmänna platser för personer med nedsatt rörelse- och orienteringsförmåga påverkas av den fysiska utformningen och underhåll av miljön samt samspel med andra trafikanter. Många brister finns fortfarande på allmänna platser och dessa behöver åtgärdas. Resultatet från intervjustudierna lyfter bland annat fram bristerna i handikapparkeringar och utformningen av ledstråk i Borlänge, och avsaknad av signalerade övergångställen i Luleå. Tillgänglighetsarbetet handlar inte bara om att planera och konstruera miljöer utan också underhållningen av dem, men även bemötandet av andra behöver bli bättre för att upplevelsen av tillgänglighet ska bli mer positiv. Sveriges alla säsonger och väglag bör beaktas vid konstruktion av tillgänglighetsanpassade områden då den upplevda tillgängligheten förändras vid olika väglag så som barmark, snö och is. Dagens krav gällande tillgänglighet är bristfälliga och större vikt behöver läggas på att stärka dessa krav samt se till att de uppfylls. Kraven behöver baseras på upplevelserna av tillgänglighet för personer med nedsatt rörelse- och orienteringsförmåga och denna grupp av människor bör aktivt vara med när kraven sätts. Detta för att kraven inte ska bygga på normer av denna grupp. The Swedish disability policy aims to have everyone to be able to participate in social life. Accessibility is an important prerequisite to achieve participation. In addition to being an aspect of participation, accessibility is an important aspect of social sustainability as well as a basic prerequisite for urban planning that benefit everyone. Lack of accessibility is a form of discrimination. In urban planning there are many governing documents to ensure that deficiencies in accessibility for people with reduced movement and orientation do not occur. Historically, and even today, much of urban planning is based on an average person that doesn’t really exist. This average person is based on norms and values about how people live and function. Since there are still major deficiencies in the physical design of cities, a better understanding of experiences with accessibility from persons with impaired movement and orientation is needed. The purpose of the report is therefore to study the perceived accessibility for people with reduced movement, vision or hearing in trade areas in Borlänge and Luleå and what requirements are placed on accessibility in urban planning. The study’s execution has been divided into two parts, a literature study and a qualitative study. The literature study was necessary to gain better knowledge on the study's focus area and has been a good basis for the qualitative part of the study. The literature study has focused on explaining key concepts to the study as well as answering questions regarding the experience of accessibility, and how it changes with different seasons, as well as requirements about accessibility. The quantitative study consists of a document study as well as an interview study and studies two cities in Sweden. This part of the study has been carried out to receive qualitative information regarding experiences from to the participants and how municipalities work with accessibility. The interview study was conducted as a walking interview and a total of seven people participated in the study. The experience of the accessibility in public places for people with reduced movement and orientation is affected by the physical design and maintenance of a space as well as the teamwork with other road users. There is still a lot of deficiencies are in public places and these need to be addressed. The result from the interview study presents, among other things, the deficiencies in disabled parking spots and the design of tactile paths in Borlänge, and the lack of signaled crossings in Luleå. The accessibility work is not only about planning and constructing environments but also maintaining them, but also the treatment of others needs to be improved for the experience of accessibility to be more positive. All of Sweden's seasons and road conditions should be considered when constructing accessibility -adapted areas as the perceived accessibility varies at various road conditions such as bare ground, snow and ice. Today's requirements regarding accessibility are inadequate and greater emphasis needs to be placed on strengthening these requirements and ensuring that they are met. The requirements need to be based on the experiences of people with impaired movement and orientation and this group of people should be actively involved when the requirements are set. This is so that the requirements do not longer based on norms of this group
Exploiting agri-food residues for kombucha tea and bacterial cellulose production
No full textBio-valorization of agri-food wastes lies in their possible conversion into fermented foodstuffs/beverages and/or biodegradable polymers such as bacterial cellulose.In this study, three different kombucha cultures were formulated using agri-food waste materials, citrus fruit residues and used coffee grounds, as alternative carbon and nitrogen sources, respectively. Over 21 days of fermentation, the kinetic profile was followed by monitoring cell density, pH variation, minerals, trace elements and production of bacterial cellulose. Moreover, the total phenolic and radical scavenging capacity was measured by spectrophotometric tests on the beverage and bacterial cellulose. Several classes of compounds were detected by gas chromatography coupled with mass spectrometry performing extractions on the headspace above fresh kombucha beverages and their lyophilized fractions, using solid phase micro extraction and liquid phase extraction, respectively. The obtained results allowed assessing molecular profiles of each kombucha beverages. A chemometric meta-analysis of the data revealed the individual impacts of the single ingredients and the effects of the fermentation process.Validerad;2025;Nivå 2;2025-02-17 (u4);For funding information, see link: https://www.sciencedirect.com/science/article/pii/S0141813025008426?via%3Dihub#s0115;Fulltext license: CC BY-NC-ND</p
RIS-Assisted Joint Differential Polarization and Phase Modulation for Non-Coherent Receivers
No full textThis letter introduces a reconfigurable intelligent surface (RIS)-assisted modulation scheme tailored for non-coherent receivers. Employing a RIS of dual-polarized elements, we manipulate the polarization state of the reflected signals to enable a differential polarization shift keying modulation scheme while simultaneously beamforming the reflected signal towards the receiver. Subsequently, an additional differential phase shift keying (DPSK) modulation layer is superimposed under two distinct deployments, where either the source or the RIS performs the DPSK modulation. Furthermore, the analytical performance is investigated, and a comparison with benchmark schemes is evaluated.Validerad;2025;Nivå 2;2025-01-17 (signyg);Full text license: CC BY;Funder: European Project Hexa-X-II (101095759); InterReg Aurora project Arctic 6G;</p
Utilization of Non-Metallic Inclusion to Induce Intragranular Acicular Ferrite Formation Contributing to “Oxide Metallurgy”: Effect of Ti/Al Content on the Microstructure Evolution
No full textNon-metallic inclusion is generally aimed to be removed during the refining process of steel production. The steelmakers always intend to produce clean steel to optimize the final product properties. However, the fine size inclusion is hard to remove completely; alternatively, it could be served as the nucleation site to induce the formation of intragranular acicular ferrite (IAF). This is an optimal microstructure with the “interlock” morphology and has been reported to be able to improve mechanical property, e.g., low-temperature impact toughness, according to the concept of “oxide metallurgy.” In this work, the low-alloy steels with different amounts of Ti and Al contents are prepared, and the inclusion characteristics (i.e., composition, size, distribution, etc.) are quantitatively investigated. Furthermore, high-temperature confocal laser scanning microscopy is applied to observe the IAF formation in situ with controlled isothermal holding and cooling conditions. The effect of nature of inclusions on IAF formation is investigated in the proposed steels. Subsequently, the theoretical model according to classical nucleation theory is utilized to evaluate the capability of different kinds of inclusions to induce IAF. Last but not least, the microstructure features in different steels are also investigated.Validerad;2025;Nivå 2;2025-11-06 (u5);Special Issue: Dedicated to Seshadri Seetharaman on the Occasion of his 80th Birthday;Full text license: CC BY;Funder: Åforsk foundation (23-540); Jernkontoret; </p
Switched control barrier functions-based safe docking control strategy for a planar floating platform
No full textIn this article, we present and experimentally validate a safe docking control strategy designed for an experimental planar floating platform, called the Slider. Three degrees-of-freedom (DOF) platforms like the Slider are used extensively in space industry and academia to emulate micro-gravity conditions on Earth, for validating in-plane Guidance, Navigation and Control (GNC) algorithms. The Slider uses an air cushion (induced by air bearings) to levitate on a smooth flat table, thus emulating the in-plane zero-gravity motion of a spacecraft in orbit. The proposed docking control strategy is applicable in the in-plane approach and docking phases of space docking missions, and is based on the Control Barrier Functions (CBF) approach, where a safe set (a Cardioid), capturing the clearance and direction-of-approach constraints, is rendered positively forward invariant. To enable precise and safe docking in the presence of unmodeled dynamics, disturbances induced by the tether and drifts induced by the non-flat floating surface, we present a switching strategy among the zero and positive level sets of a Cardioid function. In the approach phase, the positive contour of the Cardioid function smoothly steers the Slider platform into the neighborhood of a deadlock point, which is designed to be at a safe distance from the docking port. In the neighborhood of the deadlock point, Slider corrects its proximity and heading until its configuration is well-suited to enter the docking phase. The docking maneuver is initiated by the CBF switching mechanism (positive to zero contour), which expands the safe zone to include the final docking configuration. We present an analysis of the Quadratic program defining the CBF filter, and identify two deadlock points (an asymptotically stable point in the vicinity of the docking port and an unstable point diametrically opposite on the CBF boundary). Both the approach and docking phases are validated through experimentation on the Slider platform, in the presence of tether-induced disturbances and drifts induced by the non-ideal floating surface. In the docking phase, the CBF switching condition effectively handles experimental non-idealities and recovers the slider platform from unsafe configurations. The proposed docking strategy caters to the in-plane (3DOF) approach and docking phases of real space docking missions and is scalable to three-dimensional 6DOF operations, in conjunction with controllers that stabilize the attitude and the out-of-plane degree-of-freedom. Link to the video of experimental demonstration: https://youtu.be/eBiWvnKtG7U?si=QFPD-vm11wydyZSd.Validerad;2025;Nivå 2;2025-02-28 (u4);Fulltext license: CC BY</p