| 1. |
- Kádár, Roland, 1982, et al.
(author)
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Challenges in nano-structured fluid flows for assembly into hierarchical biomaterials
- 2023
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In: AIP Conference Proceedings. - 0094-243X .- 1551-7616. - 9780735445475 ; 2997
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Conference paper (peer-reviewed)abstract
- Hierarchical biomaterials have their place in the context of developing novel material systems particularly in the framework of sustainability. The key to their development is in controlling their assembly into hierarchical orders at various lengthscales. Thus, flow can be an asset in e.g. controlling orientation, however, resolving the hierarchical orientation dynamics of such systems remains a challenge. We focus here mainly on cellulose nanocrystals water-based suspensions, however, the outline is representative of numerous nanostructured fluids.
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| 2. |
- Hosseini, Seyedehsan, 1994
(author)
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Additive-Driven Improvements in Interfacial Properties and Processing of TMP-Polymer Composites
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Efforts to address environmental concerns have resulted in new regulations designed to plan the reduction of plastic and synthetic polymer usage, necessitating the search for sustainable natural alternatives with comparable cost-effectiveness and mechanical performance. Thermomechanical pulp (TMP) fibres are one of the most affordable natural fibres that have no chemical refining in production, production have a high yield of 90-98% and TMP fibres have been demonstrated to improve the mechanical characteristics (strength, stiffness and toughness) of wood-polymer composites (WPCs) compared to the pure polymer. The integration of TMP fibres with non-polar synthetic polymers remains a challenge due to surface polarity differences. This PhD thesis aims to ease the processing of TMP fibre composites through the incorporation of additives. The hypothesis posits that incorporating magnesium stearate (MgSt), molybdenum disulfide (MoS2) and alkyl ketene dimer (AKD) as additives in TMP composites will enhance interfacial properties, resulting in improved processability and flow behaviour at high temperatures. MoS2 is known for its interaction with lignin, which exists in TMP and MgSt is recognised for its ability to improve flow in pharmaceutical processing when combined with cellulose, also a component of TMP. AKD modifies the hydrophilic properties of lignocellulosic surfaces. The experimental work explores the effect of these additives on the properties of TMP composites of ethylene acrylic acid copolymer (EAA) and polypropylene (PP) matrices. The dynamic mechanical analysis (DMA) and mechanical analysis results reveal that MoS2 exhibits superior interaction with TMP fibres, yielding enhanced interfacial properties compared to MgSt in between EAA and TMP fibres. Rheological studies elucidate the transition from a fluid-like state to a network-like structure upon the incorporation of TMP into the PP matrix. The incorporation of AKD with C18 reduces the viscosity of TMP-PP composites and PP itself, and, as determined through theoretical Hansen solubility parameter (HSP) calculations, increases compatibility between cellulose in TMP fibres and PP. The addition of AKD influences both the colour (lighter) and shape (smoother surface) of the extrudate filaments in the TMP-PP composites, indicative of improved processing. In addition, frictional analysis demonstrates the reduction of the coefficient of friction (COF) between metal and TMP fibre by MgSt and AKD treatments.
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| 3. |
- Blanch, Krister, 1991
(author)
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Beyond-application datasets and automated fair benchmarking
- 2023
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Licentiate thesis (other academic/artistic)abstract
- Beyond-application perception datasets are generalised datasets that emphasise the fundamental components of good machine perception data. When analysing the history of perception datatsets, notable trends suggest that design of the dataset typically aligns with an application goal. Instead of focusing on a specific application, beyond-application datasets instead look at capturing high-quality, high-volume data from a highly kinematic environment, for the purpose of aiding algorithm development and testing in general. Algorithm benchmarking is a cornerstone of autonomous systems development, and allows developers to demonstrate their results in a comparative manner. However, most benchmarking systems allow developers to use their own hardware or select favourable data. There is also little focus on run time performance and consistency, with benchmarking systems instead showcasing algorithm accuracy. By combining both beyond-application dataset generation and methods for fair benchmarking, there is also the dilemma of how to provide the dataset to developers for this benchmarking, as the result of a high-volume, high-quality dataset generation is a significant increase in dataset size when compared to traditional perception datasets. This thesis presents the first results of attempting the creation of such a dataset. The dataset was built using a maritime platform, selected due to the highly dynamic environment presented on water. The design and initial testing of this platform is detailed, as well as as methods of sensor validation. Continuing, the thesis then presents a method of fair benchmarking, by utilising remote containerisation in a way that allows developers to present their software to the dataset, instead of having to first locally store a copy. To test this dataset and automatic online benchmarking, a number of reference algorithms were required for initial results. Three algorithms were built, using the data from three different sensors captured on the maritime platform. Each algorithm calculates vessel odometry, and the automatic benchmarking system was utilised to show the accuracy and run-time performance of these algorithms. It was found that the containerised approach alleviated data management concerns, prevented inflated accuracy results, and demonstrated precisely how computationally intensive each algorithm was.
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| 4. |
- Säwén, Toivo, 1993
(author)
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Early Stage Architectural Design Practice Perspectives on Life Cycle Building Performance Assessment
- 2023
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Licentiate thesis (other academic/artistic)abstract
- Architectural practitioners can avoid negative social and environmental impacts of new construction by making decisions supported by impact quantification during design processes. However, most software tools developed for such quantification see little use in practice, especially in early design stages when decisions have the greatest influence. To identify ways for software developers to overcome this situation, a thorough literature meta-review of previously performed tool reviews was combined with interviews applying a practice lens. The first key finding is that a possible explanation for the low tool uptake in practice could be a missing practice perspective in previous tool development efforts. In a literature meta-review of publications on life cycle building performance tools identifying previously applied perspectives, most previous tool reviews were found to support tool development and selection, while disregarding how tools can be integrated in existing practices and design processes. As a proposed solution, a framework for defining software requirements using a practice perspective was developed. The second key finding is that a practice perspective could be applied during software development by implementing qualitative methodologies. Nine architectural practitioners in Sweden, Norway and France were interviewed using the interview to the double, a projective technique in which the interviewee is asked to describe their next workday in detail so that their tasks can be assumed by an imagined body double. The design activities described by the respondents were sequenced into user narratives which could serve as starting points for participatory software development processes within the architectural practice. The outcomes - a proposed framework for practice-centric software requirements, and a proposed methodology for collecting these requirements using a practice lens - indicate a research direction toward software development efforts which aligns with design process, architectural practice, and tool user needs. In the next stage of the research this direction will be pursued through application of the developed methodologies in participatory development case studies in early-stage architectural design practice.
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| 5. |
- Zubritskaya, Irina, 1984, et al.
(author)
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Dynamically Tunable Optical Cavities with Embedded Nematic Liquid Crystalline Networks
- 2023
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:13
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Journal article (peer-reviewed)abstract
- Tunable metal–insulator–metal (MIM) Fabry–Pérot (FP) cavities that can dynamically control light enable novel sensing, imaging and display applications. However, the realization of dynamic cavities incorporating stimuli-responsive materials poses a significant engineering challenge. Current approaches rely on refractive index modulation and suffer from low dynamic tunability, high losses, and limited spectral ranges, and require liquid and hazardous materials for operation. To overcome these challenges, a new tuning mechanism employing reversible mechanical adaptations of a polymer network is proposed, and dynamic tuning of optical resonances is demonstrated. Solid-state temperature-responsive optical coatings are developed by preparing a monodomain nematic liquid crystalline network (LCN) and are incorporated between metallic mirrors to form active optical microcavities. LCN microcavities offer large, reversible and highly linear spectral tuning of FP resonances reaching wavelength-shifts up to 40 nm via thermomechanical actuation while featuring outstanding repeatability and precision over more than 100 heating–cooling cycles. This degree of tunability allows for reversible switching between the reflective and the absorbing states of the device over the entire visible and near-infrared spectral regions, reaching large changes in reflectance with modulation efficiency ΔR = 79%.
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| 6. |
- Fadavi Roudsari, Anita, 1978, et al.
(author)
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Three-wave mixing traveling-wave parametric amplifier with periodic variation of the circuit parameters
- 2023
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 122:5
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Journal article (peer-reviewed)abstract
- We report on the implementation of a near-quantum-limited, traveling-wave parametric amplifier that uses three-wave mixing (3WM). To favor amplification by 3WM, we use superconducting nonlinear asymmetric inductive element (SNAIL) loops, biased with a dc magnetic flux. In addition, we equip the device with dispersion engineering features to create a stopband at the second harmonic of the pump and suppress the propagation of the higher harmonics that otherwise degrade the amplification. With a chain of 440 SNAILs, the amplifier provides up to 20 dB gain and a 3-dB bandwidth of 1 GHz. The added noise by the amplifier is found to be less than one photon.
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| 7. |
- Kuznecovs, Artjoms, 1990, et al.
(author)
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Consequence analyses of collision-damaged ships — damage stability, structural adequacy and oil spills
- 2023
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In: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1744-5302 .- 1754-212X. ; 18:4, s. 567-
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Journal article (peer-reviewed)abstract
- A ship collision accident may pose a threat to human lives, the environment and material assets. A damaged ship can suffer from the loss of ship stability, reduced global structural strength, and the loss of the integrity of internal tanks carrying polluting liquids. This study presents a methodology as a framework that can be used to analyze the related consequences of ship-ship collision events using simulations and evaluations. The methodology includes nonlinear finite element analyses of the collision event, a METOCEAN data analysis module, damage stability simulations, analyses of the damaged ship’s ultimate strength and structural integrity, oil spill drift simulations, and finally, an evaluation of the three abovementioned consequences. A case study with a chemical tanker subjected to collision demonstrates the methodology. The collision event was assumed to occur in the Kattegat area (between Sweden and Denmark) at a ship route intersection with high ship traffic density. © 2022 The Author(s).
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| 8. |
- Llacer Navarro, Saül, 1990
(author)
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Role of Sulfate Half Ester Groups on Modifications and Network Formation of Cellulose Nanocrystals
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Cellulose nanocrystals (CNCs) are nanomaterials with unique mechanical, physical, and chemical properties, which make them suitable as films and foams. To tap into the potential of CNCs and develop materials with tailored properties and a wider range of applications, it is essential to overcome existing challenges. These include surface-specific chemical modification, detailed analysis of functional groups, and stable CNC dispersion in water without aggregation. The present doctoral thesis addresses these challenges by investigating the role of sulfate half-ester groups, found on CNC surfaces, and in the chemical or enzymatic oxidative modification of CNCs. Moreover, the thesis explores the properties of CNC networks in water suspensions and as part of gel matrices. The results reveal that sulfate half-ester groups, which are negatively charged and bulky, have varied effects on oxidation reactions, highlighting the need to consider functional groups when working with nanomaterials. Furthermore, the thesis emphasizes the importance of analyzing both solid and soluble products for accurate conclusions. The work presented herein also illustrates the methods used to modify the CNC-CNC interaction governed by sulfate half-ester groups. The findings in this thesis advance our knowledge of CNC modifications, as well as our understanding of the mechanisms underlying CNC network formation. This will contribute to the development of green nanotechnologies rooted in nature's renewable resources.
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| 9. |
- Mebarki, Mohamed Aniss, 1993, et al.
(author)
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GaN High-Electron-Mobility Transistors with Superconducting Nb Gates for Low-Noise Cryogenic Applications
- 2023
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In: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 220:8
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Journal article (peer-reviewed)abstract
- The successful integration of superconducting niobium (Nb) gate electrodes into cryogenic gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs) is reported. This is achieved through a specifically developed microfabrication process. The device's DC, microwave, and noise performances at cryogenic temperatures, down to 4 K, are studied and presented. The superconductivity of the gate is tested using DC end-to-end measurements. A clear superconducting state transition at a critical temperature, Tc, of ≈9.2 K is shown. This is further verified with GaN HEMTs with two gate fingers and a gate length of 0.2 μm, through the extraction and validation of a small-signal model at T < Tc. Additionally, the superconductivity of the gate is verified for several gate widths and lengths, showing a significant reduction of the gate resistance independently of its dimensions. Finally, a comparative study of the cryogenic microwave noise performances of the GaN HEMTs with gold (Au) and Nb gates is presented. The Au-gated device presents a competitive optimum noise temperature, Tmin-opt, of ≈8 K at 5 GHz, demonstrating the potential of this technology for cryogenic low-noise applications. The Nb-gated device presents a 5 K higher Tmin-opt, which is found to be related to the suppression of the superconductivity of the Nb gate at the optimum-noise bias.
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| 10. |
- Bergenram, Felicia, et al.
(author)
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Parametric Optimization of Slab Frame Bridges Considering Investment Cost, Environmental Impact and Buildability
- 2023
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In: Procedia Computer Science. - 1877-0509.
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Conference paper (peer-reviewed)abstract
- This paper presents research performed on set-based multi-criteria optimization for the preliminary design of slab frame bridges. As a result of immense CO2 emissions emerging from concrete production, there is a need for optimization methods decreasing the volume of concrete without affecting the function of the structure. Previous research suggests a general correlation between CO2 footprint- and cost reduction, due to minimized material use. However, the aspect of buildability may conflict with lessened material, as optimized designs might simultaneously be less buildable. This research aimed to develop an optimization method with respect to the investment cost and environmental impact while also considering buildability cost aspects. The optimization algorithm shows the possibilities of reducing the environmental impact by up to 13.7% for a slightly increased cost of 2.3%. Thus, by implementing optimization procedures in the early stages of the planning process the holistic cost effects related to green solutions can be presented, favoring the choice of sustainable designs amongst clients during tendering procedures.
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