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Offline Planning for Autonomous Forest Regeneration of Mixed Tree Species
No full textSweden has 23.4 million hectares of productive forest land, primarily managed through even-aged forestry, with 96% of nursery seedlings being Scots pine and Norway spruce. Regeneration efforts are supported by mechanized site preparation techniques, such as mounding and disc trenching. However, the reliance on monocultures increases vulnerability to pests, pathogens, and climate-related stress. Mixed-species regeneration offers significant ecological and economic benefits but introduces operational complexity and higher costs. Despite its labor intensity, manual planting remains the dominant method, especially for small private forest holdings, due to its affordability. This research seeks to advance sustainable forest regeneration by integrating automation and digital decision-support tools. While commercial mechanized solutions have been tested in Nordic countries since the 1960s, high operational and investment costs, coupled with the relatively low cost of manual planting, have limited the widespread adoption of mechanized planting. Recent autonomous planting initiatives, such as Autoplant and Södra BraSatt, demonstrate the potential to improve safety and efficiency while reducing environmental impact. When paired with intelligent planning tools, these systems facilitate species diversification and enable site-adapted regeneration strategies, offering a promising future for sustainable forestry practices. A primary contribution of this study is the development of the Digital Precision Planning Tool (DiPPT), which determines the distribution of mixed-species planting based on species-specific site productivity and user-defined density constraints. By using site index maps, DiPPT generates spatially explicit planting maps through either a productivity method or an iterative balancing process tailored to user constraints. The tool allows users to optimize the placement of species adapted for within-site variations, promoting biodiversity and improving forest resilience, and sustaining site productivity. To advance automation in forest operations, a metaheuristic coverage path planner (CPP) was developed specifically for forest terrain, aiming to minimize travel distances for ground-based vehicles. Using a Genetic Algorithm (GA), the CPP considers roll, pitch, and soil moisture thresholds to ensure paths are navigable safely. It was tested on both synthetic and real terrains, demonstrating its effectiveness to safely plan paths through challenging sites. Tests on steep terrain showed that the genetic algorithm successfully navigated the terrain while minimizing vehicle path length and ensuring operational safety. Since the CPP with GA took a long time to calculate, an improved CPP named TerraTrail was developed as a faster alternative. TerraTrail was later evaluated alongside another CPP, Pathfinder, for both autonomous planting operations and as a support tool for manual operators. These tools utilized Digital Elevation Models (DEM), Depth-to-Water (DTW) maps, and vehicle kinematics to generate terrain-aware routes, offering coverage and path efficiency comparable to that of manually operated vehicles. Tests with real-world data from a manually operated planting machine, PlantMax, showed that both Pathfinder and TerraTrail achieved better coverage compared to manual planting systems. On average, TerraTrail achieved up to 18% higher coverage than the manually operated PlantMax, with a similar path distance when working under constrained environmental conditions (e.g., wet zones and steep slopes). Similarly, Pathfinder demonstrated up to 19% improvement in coverage and a 14% reduction in normalized path length compared to PlantMax, highlighting the efficiency of automated coverage path planning. Together, these advancements tackle key challenges in autonomous forest regeneration, focusing on decision-making and CPP. By integrating digital planning tools, automation, and CPP, this research helps offload forest managers, enabling better on-site decisions and improving biodiversity and forest resilience. This thesis promotes ecological sustainability by supporting the planting of mixed tree species instead of monocultures, increasing coverage for planting vehicles, and minimizing path distances, which in turn supports economic sustainability. Additionally, autonomy allows operators to work remotely, improving safety and reducing full body vibrations, which contributes to social sustainability.Trees For M
Numerical study of mixing dynamics in controlled coaxial jets
No full textProducing iron ore pellets in grate-kiln plants involves several steps in order to obtain the final product. During the induration, the pellets are fired inside a rotary kiln; a large rotating oven, with two channels through which secondary process air enters. The secondary air channels are divided by the so-called back plate, causing an area of reduced velocity to form as the air flows past it. Current plants use coal to produce a flame inside the rotary kiln which heats the pellets. The coal flame is long and stable, and gives an even temperature profile inside the rotary kiln, something that is important for the quality of the pellets. As industries are transitioning towards more environmentally friendly processes and solutions, there is a desire to eliminate the use of fossil fuels such as coal. One alternative fuel of interest is hydrogen, since it can be produced and used without CO2 emissions. The issue with replacing the coal with hydrogen directly in the rotary kiln is that mixing with the surrounding secondary process air, necessary for combustion, occurs too quickly. This results in a flame that is short and intense, negatively impacting the pellet quality. Hence, different methods of injecting the hydrogen into the rotary kiln need to be investigated. This thesis investigates the use of a so-called coaxial jet to control the mixing of fuel and secondary air. The coaxial jet consists of a central round jet mounted in the back plate, through which hydrogen is issued. Surrounding the inner jet is an annular outer jet, issuing either hydrogen or a different fluid. By altering the parameters of the coaxial jet, mixing of the hydrogen fuel and the surrounding secondary air can be controlled, making it possible to tune the resulting flame. To investigate the effect of different parameter values, Computational Fluid Dynamics (CFD) simulations are used. As a first step a simplified, axisymmetric model of the rotary kiln is modeled in 2D. This approach reduces the computational effort, enabling large amounts of parameter values to be evaluated. The so-called momentum flow ratio of the outer jet to the inner jet, Mjet, is used to compare different configurations of the coaxial jet. By increasing or decreasing the outer jet velocity, the value of Mjet is increased or decreased, respectively. Two scenarios for the coaxial jet are considered; the first is using hydrogen through both the inner and the outer jet, and the second is using air instead of hydrogen through the outer jet. In Paper A, it is found that when using hydrogen through both the inner and outer jet, the potential core can be extended by decreasing the value of Mjet. This is achieved by decreasing the velocity of the outer jet, and thus providing a more gradual change in velocity between the high velocity inner jet, and the relatively slow secondary air. As a result the shear is reduced and the mixing is delayed. Among the values considered, Mjet = 0.25 produces the longest jet core and least mixing. This configuration, however, experiences recirculation and accumulation of hydrogen in a wake behind the back plate. If the outer jet fluid is substituted for air (Paper B) a different trend is seen, in which an increase of Mjet is beneficial for the jet length. The increased outer jet velocity, and thus momentum, enables the inner jet to be protected over a greater distance. Mjet = 2, the highest considered value, provides the longest hydrogen jet potential core and the most contained jet close to the jet exit. This is an indication that mixing with the secondary air is delayed. Further downstream, on the other hand, the increased shear that comes with higher Mjet -values contributes to increased mixing and spread. Lastly, a three-dimensional model is simulated in Paper C, offering insights into a more complete view of the flow field inside the rotary kiln. Three-dimensional as well as transient characteristics of the flow are scrutinized, showing that there are effects not captured by the simplified steady-state 2D model. Unsteadiness along the jet core boundary, as well as a difference in the prediction of the flow behind the back plate, contribute to a difference in the jet evolution between the 3D model and the 2D model. The main conclusion from this investigation is that the simplified axisymmetric model of the rotary kiln fails to capture important features of the flow field, making it unsuitable to use for predicting accurate details about the coaxial jet evolution. The findings from this thesis will be used as a basis for the continued work, which includes investigating the influence of additional parameters on the mixing and flow field, as well as conducting experiments to enable validation of the numerical simulations.Funder: Swedish Mining Innovation</p
Physics-Informed Neural Network Framework for Wheel-Rail Contact Analysis: Toward an Intelligent Maintenance Workflow in Railway Systems
No full textRailway transportation traffic is rapidly growing, which demands a more effective and efficient generation analysis for more reliable predictive maintenance planning. This is achievable if prognostic indicators are known, e.g. stress, deformation and displacement fields. These parameter values unlock the underlying physics knowledge about fault modes and mechanisms to solve the wheel-rail deterioration. Commercial multi-physics software lack source code accessibility, flexibility and interoperability between computing platforms. On the other hand, physics-informed neural networks (PINNs), which belong to the second AI revolution and scientific ML (SciML) that combines physical and machine learning models, show promise in computational fluid dynamics and electrodynamics; however, their application to railwayremains largely unexplored. This study addresses these research gaps through a comprehensive open-source and reproducible PINN PhysicsNeMo framework for 3D wheel-rail contact analysis as proof of concept. Current railway maintenance often relies on reactive approaches; this PhysicsNeMo framework supports integration by providing predictive stress analyses. The aim is to explore the PhysicsNeMo simulations for railway, establishing a foundation for an interpretable, explainable and trustworthy AI. Results demonstrate detailed and intuitive 3D wheel visualisations of stress distributions and displacement fields, with insights into damage mechanisms for railway designers and maintainers, facilitating more efficient maintenance workflows.Full text license: CC BY 4.0Academics4Rai
Levelling-up walking as a mode of transport - a case for changing hierarchies
No full textIntroduction Walking has a key role in achieving the compact and 15-min city, improving public health, and reaching sustainability goals. However, whilst walking is placed at the top of the transport hierarchy in public documents throughout Scandinavia, in reality, walking as a mode of transport is consistently downplayed and hierarchically placed in the bottom of the transport hierarchy. Focus in the public and planning discourse is instead commonly on either motorised transport, public transport, or cycling, regardless of whether the focus is on city planning, logistics or safety. Methods To better understand why this is the case – as well as attempting to suggest solutions to levelling-up walking as a mode of transport – academics, policymakers, and practitioners from across Scandinavia were strategically selected to contribute with their knowledge through focus groups and individual surveys during 2021 and 2023. Results In the analysis of the material, it became clear that walking was largely viewed in the parallel perspectives of two fields: planning and safety. These fields coexist as disparate and disconnected fields, basing their work on different methodologies and input data, resulting in an incoherent understanding of walking as a mode of transport. However, the analysis also enabled the development of a thematic model: realising walking as a mode of transport, illustrating an ideal construct in which planning and safety perspectives work coherently. Conclusion The results suggest that there is a strong desire to level-up walking as a mode of transport and change the status and hierarchy in the transport system. However, to do so requires a more holistic and multi-disciplinary view.Fulltext license: CC BY</p
Impact of MV reserve path operation on LV network hosting capacity
No full textThe hosting capacity of low-voltage (LV) networks is influenced by existing consumption and production in adjacent LV networks under the same medium-voltage (MV) network. Since LV transformers typically lack automatic on-load tap changers, both voltage and current limits require a joint assessment covering the MV network and all underlying LV networks. This paper introduces a methodology to include different MV operating conditions, like reserve operating paths, in the calculation of the hosting capacity for new production at LV networks. The MV voltage profile before the connection of new production, called the background voltage, is modelled to enable such analysis. The methodology is applied to an existing MV/LV network. The hosting capacity was lower, for the studied reserve operating paths, and the limitation was due to overvoltage issues. The proposed methodology is a valuable tool for distribution network planning. It was also shown that it is essential to use an accurate model of the background voltage for hosting capacity calculation of distribution networks.Funder: Skellefteå Kraft;Fulltext license: CC BY</p
Sustainable regeneration of cellulose gels and fibration of powder materials via eco-friendly dissolution–regeneration process
No full textThe development of sustainable biomass resources is key to achieving “dual carbon” goals. Waste wood powder, a by-product of traditional wood processing, is often discarded due to its complex structure, leading to resource waste and pollution. In this study, a lithium bromide (∼ 60 wt%) system was used to dissolve and regenerate waste wood powder into three cellulose hydrogels without prior removal of hemicellulose and lignin: OWP-RC, RC, and P-RC. To uncover the mechanisms of dissolution and regeneration, various characterization methods were used to compare regenerated cellulose with the original fibers, at scales ranging from macroscopic to molecular. During dissolution, cellulose reached nanoscale dispersion. The dissolution–regeneration process transformed the cellulose from type I to type II, which exhibited decreased crystallinity and thermal stability. However, the presence of organic powder in OWP-RC improved properties, including crystallinity (27.43 %) and thermal stability. Additionally, the potential for cellulose solution as a medium for integrating other types of waste powders was investigated. Waste wood powder, elemental powders, and compound powders were successfully incorporated into cellulose solutions to facilitate fibration of materials without phase separation. The fibrillated powder composite hydrogels exhibited an increase in compressive strength by 1.8 times and reached a biodegradation rate of 99.15 % under enzymatic conditions. The dissolution–regeneration process yielded a lignin-rich by-product (∼ 54 % of the residue), which can be reused. This work offers an efficient green method for upcycling waste powders and developing functional regenerated cellulose composites.Funder: Key Research and Development Program of Shandong Province (2024TZXD078), Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX24_1301);Full text license: CC BY-NC-ND</p
Safe and Field Resilient Risk-Aware Path Planning with Dynamic Obstacle Avoidance in Unknown and Uncontrolled Environments
No full textThis PhD thesis advances robotic autonomy by developing novel path-planning and collision-avoidance solutions that enable resilient missions in complex, unstructured real-world environments. The primary contribution is D*+, a risk-aware path planner extending the D*-lite framework for ground and aerial robots. D*+ introduces a risk layer around occupied and unknown spaces, ensuring traversable paths with safety margins while operating on imperfect maps from real data. Its dynamic mapping supports adaptive replanning, enabling exploration missions in unknown environments, and is excellent for waypoint navigation. Real-world trials with a UAV and quadrupedal robot confirm its versatility across diverse scenarios. The second contribution is the Detect Track and Avoid Architecture (DTAA), which tackles dynamic obstacles using YOLO-based detection, Kalman filter state estimation, and a nonlinear model predictive controller (NMPC) for anticipatory avoidance maneuvers. DTAA effectively handles fast-moving objects while following D*+ paths; however, it is limited by a short predictive horizon and susceptible to local minima. To overcome these weaknesses, this thesis introduces A*+T, a distributed, time-dependent multi-agent path planner. Built on an A*framework, A*+T integrates D*+ 's risk layers and DTAA's dynamic obstacle handling, adding a temporal dimension to the planning process, enabling collision checks in time and space. The temporal dimension enables distributed autonomous robots to plan collision-free paths in shared spaces based on other robots' planned paths. Leveraging shared paths and predicted paths from DTAA, A*+T plans collision-free paths around the dynamic obstacles. Validated through simulations and real-world experiments, A*+T enhances mission readiness for multi-agent scenarios. Beyond these, the thesis integrates these modules into complete robotic systems, enhancing mission control for large-scale applications. Demonstrations include mining inspections (visual and gas detection) and search-and-rescue missions (locating humans/objects). These original advancements offer robust, practical solutions for robotic navigation, validated through extensive real-world testing, and contribute significantly to autonomous systems in high-stakes environments
An investigation of mechanical, corrosion and high-temperature oxidation behaviors on designed Ti-based entropic alloys
No full textTo satisfy the high performance requirements of new generation materials in application of aerospace and automotive industries, a series of TiZrHf-based entropic (i.e., entropy-stabilized) alloys with α+β dual-phase microstructure were designed using the CALPHAD (CALculation of PHAse Diagram) methodology. The present work aimed to achieve an balanced performance between mechanical properties, corrosion resistance, and high-temperature oxidation stability by tailoring Zr/Hf ratios. The alloys were comprehensively characterized using X-ray diffraction (XRD), electron channeling contrast imaging (ECCI), and high angle annular dark field scanning transmission electron microscope (HAADF-STEM). Due to the effect of transformation-induced plasticity (TRIP), the homogenized and cryogenic alloys exhibit balanced mechanical properties (i.e., high strength and ductility). Electrochemical tests in 3.5 wt% NaCl solution demonstrated good corrosion resistance, and the stability of the passive film was slightly compromised by both cryogenic treatment and Zr/Hf additions. Moderate high-temperature oxidation tests at 500 and 600 °C showed that the alloys have good oxidation resistance result from the formation of protective scales dominated by TiO2 and Al2O3. However, the formation of less-protective Zr/Hf-oxides at higher temperatures (700 °C) was found to be detrimental. This work provide a CALPHAD-guided design strategy for developing Ti-based entropic alloys with a well-balanced properties for applying in different severe environments.Full text: CC BY license;For funding information, see: https://doi.org/10.1016/j.jmrt.2025.12.182</p
Direct conversion of N2 by contact-electrocatalysis (CEC): A highly efficient dual-pathway approach for tunable co-production of nitrate and ammonia
No full textNitrogen fixation is crucial for agriculture and environmental sustainability, but conventional methods, such as the Haber–Bosch process, suffer from high energy demands, a complex synthesis process, and significant carbon emissions. Here, we report an innovative direct conversion of N2 from water and air via contact-electro-catalysis (CEC) for nitrogen fixation, where dielectric fluorinated ethylene propylene (FEP) micropowder, water, and ultrasonication synergistically enable efficient, simultaneous synthesis of ammonia (NH₃) and nitrate (NO₃⁻), with hydrogen peroxide (H₂O₂) as byproduct under ambient conditions. Another key finding is the role of surfactant, which not only regulates reaction pathways in the nitrogen cycle but also improves the performance of FEP in water. With the assistance of fluorocarbon surfactant (Capstone FS-30), this method achieves a nitrogen fixation rate at 7.9 × 10 ³ μmol L⁻¹ h⁻¹ gcat−1, significantly enhancing the efficiency of current interface-driven nitrogen fixation techniques, and it offers a simplified synthetic process with lower carbon emissions than the traditional method. Our study provides a sustainable and highly efficient catalytic platform, broadening the scope and practicality of nitrogen fixation technologies.Full text: CC BY license;For funding information, see: https://doi.org/10.1016/j.nanoen.2025.111661</p
Sustainable development in English textbooks : A qualitative analysis of Agenda 2030 in teaching materials for year 6
No full textHållbar utveckling är en central del av skolans uppdrag, och enligt Läroplan för grundskolan, förskoleklassen och fritidshemmet 2022, i fortsättningen kallad Lgr22, och Agenda 2030, förväntas elever ges möjlighet att utveckla kunskaper, förhållningssätt och handlingsberedskap för en mer hållbar framtid. I denna studie undersöks hur hållbarhetsfrågor gestaltas i textböcker för ämnet engelska i årskurs 6, med utgångspunkt i mål 4.7 i Agenda 2030 samt skolans värdegrundsuppdrag. Åtta vanligt förekommande textböcker i engelskämnet granskades genom en kvalitativ innehållsanalys med kvantitativa inslag. Analysen utgick från tre perspektiv, vilka hållbarhetsteman som förekommer, hur dessa uttrycks tematiskt och språkligt, samt vilka möjligheter och begränsningar dessa material ger vid undervisning mot hållbar utveckling. Resultatet visar att samtliga böcker på ett eller annat sätt berör hållbarhet, men i varierande omfattning. Ekologiska teman överväger med ämnen som rör klimat, miljö och återvinning, medan de sociala och ekonomiska dimensionerna förekommer i mindre utsträckning. De nyare läromedlen som förvisso innehåller fler hållbarhetsrelaterade teman saknar dock koppling till de globala målen och erbjuder färre möjligheter till elevreflektioner, samt är ytterst begränsade i val av tema. Studien visar på att det finns stor potential att integrera engelskundervisningen med utbildning för hållbar utveckling, men att det i nuläget förutsätter att läraren själv skapar sammanhang och mening. Slutsatserna lyfter ett behov av att vidareutveckla läromedel i engelska och stärka hållbarhetsdidaktiken i lärarutbildningen samt öka integreringen av ämnen knutna till Agenda 2030 i grundskolans undervisning