Luleå University of Technology Publications
Not a member yet
39356 research outputs found
Sort by
Biogas upgrading using aqueous bamboo-derived activated carbons
No full textCO2/CH4 separation is crucial for biogas upgrading. In this study, the bamboo-derived activated carbons (BACs) were prepared with different ratios of potassium hydroxide (KOH)/bamboo charcoal (BC), and the hybrid sorbents of aqueous BACs were developed for CO2/CH4 separation. Both the gas solubility and sorption rate were measured, and Henry’s constant and liquid-side mass-transfer coefficient as well as the CO2/CH4 selectivity were calculated. Meanwhile, the comprehensive performances of aqueous BACs were evaluated using a novel index, and the cost of biogas upgrading using the aqueous BACs was estimated and compared to the commercialized technology. The results proved the effectiveness of aqueous BACs, and the comprehensive performance of 7.0 wt% aqueous BAC with the KOH/BC mass ratio of 2:1 was 4.2 times than that of H2O, having the potential to decrease the average CO2/CH4 separation cost by 65.0% compared to the commercialized technology.Validerad;2025;Nivå 2;2025-01-28 (hanlid);Full text licens: CC BY;Funder: Fundamental Research Funds of CAF (CAFYBB2023MB025); National Natural Science Foundation of China (22478415 and 22108115); Natural Science Foundation of Jiangsu Province (BK20241744); Major Science and Technology Project of Yunnan Province (202402AE090027); National Bamboo Industry Research and Development Project (2023YJY05); Fundamental Research Funds of CAF (No. CAFYBB2021ZA003)</p
“My team made me do it”: the differential influence of team amotivation on leaders’ destructive leadership behavior, from a gender perspective
No full textDestructive leadership does not occur in a vacuum; rather, these behaviors are part of a social process in which leader and follower interact and influence each other. Still, knowledge regarding followers’ behaviors as antecedents to destructive leadership behavior is limited, even more so from a gender perspective. In this study, we investigate the relationship between perceived lack of team motivation and destructive leadership behavior, with the leader’s gender as a moderator. Together with Statistic Sweden, we collected data using a two-wave survey design. We included 784 participants in the analysis, using structural equation modeling (SEM). The results showed that perceived lack of team motivation was associated with active and passive destructive leadership behaviors. Beyond that, the leader’s gender moderated the relationship between leaders’ perception of team amotivation and active destructive leadership. The results show that male leaders are more prone to act destructively when they perceive a lack of team motivation. These results suggest that male leaders may be more susceptible to engaging in destructive leadership behaviors due to identity threat than female leaders. Therefore, we examine how the construction of gender and identity and the close association between masculinity and leader identity contribute to the risk of engaging in destructive leadership behavior.Validerad;2025;Nivå 1;2025-02-03 (hanlid);Full text license: CC BY</p
Konsekvenser av lättnader i byggkrav för ombyggnation av lokaler till studentbostäder : En studie om konsekvenserna av Boverkets förslag för lättnader på byggkraven för studentbostäder för arkitekter och studenter
No full textHållbart byggande är ett aktivt mål för arkitekter och ombyggnation är en del av lösningen. Ombyggnation av lokaler till studentbostäder främjar både hållbart byggande och dämpar studentbostadsbristen. Det finns dock ett antal utmaningar med ombyggnation som hämmar antalet projekt. Boverket fick 2023 i uppdrag av regeringen att se över byggkraven för studentbostäder för att skapa ett ökat och ett mer differentierat utbud. Boverkets förslag på lättnader på byggkraven för studentbostäder kan vara en lösning som behövs för att minska utmaningarna vid ombyggnation av lokaler till studentbostäder. Boverkets förslag ser att lättnader kan göras i tillgänglighetskraven. Förslaget presenterar flera påverkade aktörer men inte arkitekter och belyser brister i uppföljning av studenters hälsa efter byggkravsändringar, vilket motiverar att denna studie undersöker arkitekters och studenters åsikter om förslaget. Studien baseras på en kvalitativ ansats med litteraturstudie, intervjustudie och fokusgrupp som metodval. Litteraturstudien genomfördes för att få en grundförståelse för området och kunskap om utmaningar med ombyggnation från tidigare studier samt en grund till intervjustudien och fokusgruppen. Intervjustudien med erfarna arkitekter i ombyggnation av lokaler till studentbostäder gav insikter i åsikter gällande förslaget och en grund till fokusgruppen. Fokusgruppen med studenter som tidigare bott i en mindre studentbostad gav insikter i deras erfarenheter och hur förslaget kommer påverka framtida studenter. Empirin från intervjustudien och fokusgruppen analyserades med hjälp av kodning och kategorisering. Resultatet visa att respondenterna och deltagarna i fokusgruppen ser positivt på förslaget när det gäller ombyggnation och en ökad tillgång till studentbostäder men nämner risker med diskriminering och psykisk ohälsa hos studenter med och utan nedsatt rörelse- eller orienteringsförmåga. Den kategoriserade empirin jämfördes sedan med litteraturen för att besvara studiens forskningsfrågor. Litteraturen instämmer med empirin när det gäller ombyggnation och anser att Boverkets förslag kommer underlätta ombyggnationsprocessen men är delad när det gäller implementering av förslaget och risk för diskriminering. Studien bidrar till en ökad förståelse för hur byggkravsändringar påverkar arkitekter och studenter med fokus på tillgänglighet i ett ombyggnationsperspektiv. Boverkets förslag innebär en möjlighet att förenkla och främja ombyggnation av lokaler till studentbostäder så att fler studentbostäder kan byggas. Det kan främja hållbart byggande men fokus på eventuella negativa effekter för studenter med nedsatt rörelse- eller orienteringsförmåga får inte glömmas bort, för att säkerställa en inkluderande studentbostadsmarknad. Sustainable house building is an active goal for architects and converting buildings is part of the solution. Converting buildings into student housing is a form of conversion that both promotes sustainable house building and reduce the student housing shortage. However, there are several challenges with converting buildings that inhibit the number of actual projects. In 2023, Boverket was commissioned by the government to review the building requirements for student housing to create an increased and more differentiated supply. Boverket’s proposal with changes of the building requirements for student housing can be a solution to the challenges. Boverket’s proposal present changes in the accessibility requirements. The proposal presents several actors that are affected but not architects and highlights shortcomings in the follow-up of student’s health after building requirement changes, which motivates this study to examine architect’s and student’s opinions about the proposal. The study is based on a qualitative approach with a method choice of a literature study, interviews and focus group. The literature study was carried out to gain a basic understanding of the subject and knowledge of previous challenges with converting buildings as well as a basis for the interviews and the focus group. The interviews were conducted with architects that have experience with converting buildings to student housing and provided insights into opinions regarding the proposal. The focus group with students who previously lived in a smaller student housing provided insights into their experiences and how the proposal could affect students. The data from the interviews and the focus group was analyzed using coding and categorization. The results show that the respondents and participants in the focus group approve the proposal in terms of converting and increased access to student housing but mention the risks of discrimination and mental illness for students with and without disability. The categorized data was then compared with the literature to answer the study's research questions. The literature agrees with the data regarding converting and believes that the Boverket’s proposal will facilitate the conversion process but is divided when it comes to implementation of the proposal and the risk of discrimination. The study contributes to an understanding of how changes in building requirements affect architects and students with a focus on accessibility in a conversion perspective. Boverket’s proposal give opportunity to simplify and promote converting of buildings into student housing and more can be built. This could promote sustainable construction, but the focus on possible negative effects for students with disabilities must not be forgotten to ensure an inclusive student housing market
"We’re calling mom!" Guardians' participation in preschool : A qualitative study with a focus on equality
No full textSyftet med denna studie har varit att skapa förståelse för vilka implikationer vårdnadshavares delaktighet får för förskollärares samarbete med hemmet. Studien utgick från en socialkonstruktionistisk teori med ett jämställdhetsfokus där fäders, mödrars och förskollärares upplevelser av delaktighet och samarbete granskats. Metoden för studien var kvalitativ och bestod av semistrukturerade intervjuer som sedan transkriberades och analyserades genom tematisering. De teman som återfanns var följande: Innebörden av delaktighet, kommunikation, makt och trygghet. Dessa genererades till följd av intervjudeltagarnas gemensamma upplevelser av vad som gör, eller inte gör dem delaktiga i förskolan samt upplevelserna av vad som skapar ett fungerande eller icke fungerande samarbete. Utifrån resultatet drogs slutsatserna att förskollärare behöver finna arbetssätt för att ge vårdnadshavare inflytande över förskolan eftersom vårdnadshavarna i denna studie upplevde en avsaknad av makt. I och med studiens funna resultat gällande trygghet anses även förskollärares sociala relationsbyggande kompetenser som väsentliga för delaktighetsarbetet. Slutligen behöver förskollärare finna strategier för att bryta könsnormativa mönster i sina ageranden att ringa mödrar före fäder när barn på förskolan insjuknar.
Continuous and rapid preparation of urea-formaldehyde resin microspheres with adjustable sizes and structures in a microchannel reactor
No full textUrea-formaldehyde (UF) resin microspheres prepared by polymerization of urea and formaldehyde have broad applications because of their unique properties. In this paper, we present the preparation of UF microspheres with particle sizes of several microns at 100–180 °C and 1.5 MPa in 6–24 s in a simple microchannel reactor. A urea aqueous solution and formaldehyde solution containing formic acid as the catalyst were used as raw materials. Porous and flower-like UF microspheres as well as dense ones can be readily produced, with the former obtained mainly at lower temperatures, shorter residence times, and lower reactant concentrations. The porous microspheres can further grow to dense ones by prolonging the residence time, increasing the reaction temperature, or using reactants with higher concentrations. Compared with the present mainly used batch process to prepare UF microspheres using the same raw materials which need 3 h at 50 °C, this preparation method is swift and versatile in adjusting the particle size and structure. Moreover, flower-like UF microspheres could be produced and the pore size could be adjusted without additives. The results indicate a more environmentally friendly and economical synthesis method we developed. A possible formation mechanism of UF microspheres with various structures was proposed.Validerad;2025;Nivå 2;2025-02-10 (u4);Fulltext license: CC BY</p
Konstruktion av ram för kompakt CNC-fräs
No full textDetta examensarbete består en konceptstudie av en kompakt datorstyrd fräs. Fräsen är avsedd att användas för snabb prototyptillverkning i mindre verkstäder eller kontorsmiljöer. Den föreslagna fräsen har funktioner jämförbara med befntliga maskiner på marknaden, tillsammans med förbättringar inom vissa områden. Genom en analys av teorin bakom fräsning samt maskin- och materialegenskaper har ett koncept framställts i CAD. Konceptets duglighet har utvärderats med både analytiska och numeriska metoder, och förslag på lämpligafräsningsparametrar har presenterats. Vid jämförelse med befntliga lösningar på marknaden har konceptet visatsig har ett bättre förhållande mellan arbetsyta och maskinstorlek.This thesis presents a design study of a compact computer nummerical controlled (CNC) milling machine.The mill is desiged for rapid prototyping in small workshops or ofce environments. The proposed design hascapabilites comparable to those of existing machines on the market, in addition to offering improvements incertain areas. Through analysis of machine design, material properties, and milling theory, a concept has been created in CAD. The feasability of the concept has been evaluated using both analytical and nummerical methods, andsuitable milling parameters have been proposed. In comparision to existing solutions on the market, this conceptdemonstrates an improved ratio between useful working area and overall machine size
Effects of electrolytes on electrochemical behaviour and performance of Ti6Al4V alloy prepared by laser directed energy deposition
No full textThis study investigates the influence of electrolytes on the electrochemical (EC) performance of Ti6Al4V alloy fabricated via laser directed energy deposition (LDED). The EC dissolution efficiencies and surface roughnesses of the alloy are assessed, and the surface passivation films are analyzed through impedances, vacancy concentrations, compositions, and nanostructures. The results demonstrate that the NaCl + EDTA-2Na electrolyte attains a moderate EC machining efficiency and the optimal surface roughness of 0.31 μm at its best performance. Transmission electron microscopy reveals distinct dissolution variations between the α and β phases during ECM. The average film thickness on the α-phase is approximately 400 nm in NaCl + NaNO3 electrolyte, 35 nm in NaCl + EDTA-2Na electrolyte, and merely 10 nm in NaCl + NaBr electrolyte. Furthermore, the anionic effects on transpassive dissolution in different electrolytes are illustrated based on the point defect model. These findings reveal that, when compared to the NaCl + NaBr electrolyte, the average ECM efficiency in NaCl + EDTA-2Na drops by 4.3%, whereas the surface roughness experiences a significant reduction of 76.3%. Especially, the dissolution difference between α and β phases can be suppressed in NaCl + EDTA-2Na electrolyte. These insights can guide the selection of electrolytes for efficient and precise ECM of LDED-prepared dual-phase titanium alloy in industrial applications.Validerad;2025;Nivå 2;2025-02-10 (u5);Full text license: CC BY-NC-ND 4.0;Funder: National Natural Science Foundation of China (52105401, U22A20189);</p
Jämförelse av effekter på fotfunktion, gångsträcka, smärta vid stående och smärta vid gång efter lågintensiv respektive högintensiv träning vid hallux valgus : en pilotstudie med randomiserad kontrollerad design
No full textBackground: Hallux valgus (HV) is a common foot deformity. Conservative treatments with a multidisciplinary approach including exercise are recommended. However, there is no consensus regarding the training regimen. This study aims to evaluate the design of an upcoming RCT comparing foot function, walking distance, pain when standing, and pain during walking after a training period with digitally supervised high-load versus low-load exercise for individuals with mild to moderate hallux valgus. Method: Twenty-one participants with mild or moderate HV were randomly assigned to a low-load exercise group (LLEG) or a high-load exercise group (HLEG). Both groups received supervised follow-up via video calls once a week. The LLEG performed exercises twice per day for eight weeks. The HLEG started performing exercises twice daily for four weeks. With increased intensity, they switched to training three times per week for the remaining four weeks. Study design evaluation included training compliance and participant feedback from evaluation questionnaire. Further, the 6-minute walk test, pain when standing and walking, and the self-reported Foot and Ankle Score were compared between groups before and after the training period. The study is conducted in collaboration with another physiotherapist evaluating additional outcomes in a parallel study. Results: Participant feedback was positive, indicating contentment with the study design, and training compliance was satisfactory in both groups. Preliminary results suggest that digitally supervised exercise may reduce pain and improve self-reported foot function in individuals with hallux valgus, although no significant differences were observed between the LLEG and HLEG. Conclusion: This study design provides a foundation for a larger RCT. Although no significant differences between the training intensities were found, the findings indicate that digitally supervised exercise could be a promising approach for managing hallux valgus. Given the ceiling effects of the 6MWT in this population, a more challenging test may be preferable. Future studies with a more impaired participants and a placebo control group, could clarify the results and identify the most effective exercise regimen for hallux valgus
Sharing to Learn and Learning to Share : Meta-learning to Enhance Multi-task Learning
No full textMulti-Task Learning (MTL) enables simultaneous learning of multiple tasks in a shared framework following the principle of ‘sharing to learn,’ to improve the performance of all the tasks. Despite its advantages, MTL also comes with several challenges. One critical issue is negative transfer, where training on one task may degrade the performance of other tasks due to conflicts in feature representations or the sharing of incompatible knowledge between tasks. MTL requires careful optimization of knowledge sharing between tasks, as over-sharing may lead to task interference, and under-sharing may prevent important knowledge transfer. Additionally, MTL systems also struggle with scalability when adapting to new tasks without retraining. The main contributions of this thesis focus on how meta-learning can enhance MTL by addressing the above-mentioned key challenges. Meta-learning leverages the knowledge from learning multiple tasks to dynamically adapt the learning process for newtasks. Thereby focusing on ‘learning (what) to share.’ This work introduces solutions to create a unified framework by combining the adaptability of meta-learning with the task-sharing capabilities of MTL to promote effective MTL. The contributions of this thesis are organized in three dimensions. The first dimension focuses on combining MTLand meta-learning, resulting in the Multi-Task Meta-Learning (MTML) framework. The second dimension introduces structured sparsity to MTL, leading to the development of Layer-Optimized Multi-Task (LOMT) models, Structured Parameter Sparsity for Efficient Multi-Task Learning (SPARSE-MTL), and, finally, meta-sparsity. The third dimension investigates soft parameter sharing for multi-modal, multi-task feature alignment, enabling effective collaboration between different modalities. The first major contribution (C1) is MTML, a framework that employs meta-learning to enable adaptive and efficient knowledge sharing across tasks in MTL. It uses a bi-level meta-optimization strategy to dynamically balance task-specific and shared knowledge; thereby allowing the network to learn faster and generalize better to unseen tasks while maintaining good performance across multiple tasks. This thesis further introduces the structured sparsity technique, particularly channel-wise group sparsity in multi-task settings, resulting in LOMT models (C2) and SPARSE-MTL (C3). Structured sparsity reduces redundant parameters in shared architectures of MTL, with the aim of preventing over-sharing by optimizing feature sharing across all the tasks. However, managing the sparsity level across tasks is a challenge, as the optimal degree of sparsification varies for different tasks and task combinations. To address this, meta-sparsity (C4), an extension of SPARSE-MTL and MTML, incorporates meta-learning to dynamically learn the optimal sparsity patterns across tasks. This ensures the efficient sharing of features while minimizing task interference. In addition to the hard parameter sharing approaches, this thesis also explores soft parameter sharing for multi-modal data through a multi-task multi-modal feature alignment approach (C5). This method focuses on object detection tasks across RGB and infrared (IR) modalities. This approach aims to achieve effective knowledge sharing by employing channel-wise structured regularization to higher network layers to align semantic features between modalities and retain modality-specific features in lower layers. Therefore, it leverages the complementary strengths of RGB and IR data to enhance object detection performance across diverse conditions. In summary, this thesis demonstrates how the integration of meta-learning and structured sparsity addresses fundamental challenges in MTL, resulting in more adaptable, efficient, and scalable systems. On a broader scale, this thesis also paves the way for parsimonious multi-task models, contributing to sustainable machine learning
Solvent-free valorization of sugarcane bagasse fibers into nitrogen-doped microporous carbons: Efficient contenders for selective carbon dioxide capture
No full textNitrogen-doped porous carbons have been widely explored for CO₂ storage and separation, but expensive precursors and intricate synthetic approaches often limit their practical deployment. Here, we report a facile, one-step, solvent-free method to design nitrogen-doped microporous carbons (SBF-BC-KMx) for efficient CO₂ capture from sugarcane bagasse fibers (SBF) as a low-cost precursor. Melamine and KOH were used as a nitrogen-doping source and an activator, respectively. The specimen (SBF-BC-KM0.5), prepared with optimized melamine loading, possessed efficient textural features, including a specific surface area (SSA) of 1138 m² g⁻¹ , a micropore volume of 0.396 cm³ g⁻¹ , high concentration of ultra-micropores (<0.6 nm) (89 %) and high content of pyrrolic-N functionality (35 %). These properties enhanced the CO₂ capture performance, achieving 244.4 mg g⁻¹ at 273 K, 170.0 mg g⁻¹ at 293 K and 1 bar, and 351.5 mg g⁻¹ at 293 K and 10 bar. The optimized material exhibited a moderate isosteric heat of adsorption and an effective CO₂/N₂ selectivity at 293 K. The high ultra-micropore density significantly boosted CO₂ uptake and maintained stable CO₂ uptake over five adsorption cycles. Overall, this work devoted efforts to sustainable environment, biowaste management, and possible practical applicability of designed adsorbent for CO2 storage.Validerad;2025;Nivå 2;2025-02-17 (u4);Excellent Postdoctoral Fellowship Program (228121); Korea Energy (No. 2024-Research and Development in Field Technology, Yeongheung-01); National Research Foundation of Korea (NRF) (2023R1A2C1004109);Fulltext license: CC BY</p