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Stimulated Brillouin scattering in a non-suspended ultra-low-loss thick-SOI platform
Get PDFSilicon photonics, with its CMOS compatibility and high integration density, has enabled a wide range of novel applications. Harnessing stimulated Brillouin scattering (SBS), an optomechanic interaction between optical and gigahertz acoustic waves, in silicon-on-insulator (SOI) platforms attracts great interest for its potential in narrow-linewidth lasers and microwave photonics. However, the poor optoacoustic overlap in silicon nanowires on conventional SOI platforms has previously restricted the observation of SBS signals to suspended silicon waveguide structures. In this work, we report, for the first time, the SBS response in a non-suspended ultra-low-loss thick-SOI waveguide platform. The backward SBS process in this 3 μm thick SOI platform is enabled by a leaky acoustic mode that coexists with the optical mode in the waveguide core, resulting in an enhanced optoacoustic overlap. We measured Brillouin gain coefficients of 2.5 and 1.9 m−1 W−1 at 37.6 GHz for the rib and strip waveguides, respectively. This work paves the way for Brillouin-based applications in non-suspended ultra-low-loss silicon photonics systems
Critical evaluation of torsion rheometry to characterize the anisotropic intraply shear resistance of unidirectional thermoplastic composites in melt
Get PDFThis study critically evaluates oscillatory and transient torsion bar techniques for characterizing the in-plane shear resistance of unidirectional thermoplastic composites in melt. Small-strain oscillatory torsion tests, analyzed using a linear viscoelastic model, showed good agreement with the initial slope of the torque-rotation curve obtained from transient torsion tests. However, the limited strain range restricts the model's applicability to small deformations. Deformation measurements on specimens subjected to larger strains by means of the transient torsion tests revealed anisotropic and inhomogeneous behavior, with significant through-thickness shear rather than the intended in-plane shear. This observed anisotropy contradicts the transverse isotropy assumption originally used in modeling. To address this, a nonlinear anisotropic viscoelastic model was proposed, offering improved accuracy. Despite this enhancement, the inability to precisely control or monitor the desired deformations during testing raises concerns about the reliability of the transient torsion rheometry method.</p
Emerging trade-offs in saltmarsh ecosystem services under sea-level rise
Get PDFCoastal defence and carbon storage by coastal wetlands provide an increasingly recognised means of adaptation and mitigation in the face of climate change, yet these same services are threatened by the impacts against which they protect. Our understanding to date tends to consider impacts of rising sea levels on individual marsh services but fails to consider trade-offs and potential interactions between them. For instance, sea-level rise has the potential to enhance carbon storage but may decrease soil stability, erosion resistance and wave-attenuation capacity by creating sub-optimal growth conditions, causing plants to be weaker and smaller. As such, we aim to answer the question: will rising sea levels drive unidirectional impacts, or contrasting ‘trade-offs’, between saltmarsh carbon storage and coastal defence? We conducted a field experiment across increasing inundation durations beyond the usual seaward limit of Spartina anglica growth, mimicking SLR at established vegetation patches, and measured (1) carbon decomposition rates using the teabag index as proxy, (2) sediment stability, and (3) biomechanical traits of S.anglica as proxy for wave-attenuation capacity. With increasing inundation duration, rates of carbon decomposition slowed, supporting carbon storage, and therefore positively impacted climate change mitigation. In contrast, both sediment stability and vegetation stiffness decreased and hence negatively impacted climate change adaptation. Our findings point to a short-term trade-off in climate ecosystem services with SLR, where positive impacts on carbon storage may offset negative impacts on coastal defence services. However, since lower sediment stability increases the chance of marsh erosion under extreme events, this will increase over time the likelihood of sediment resuspension and the ultimate rerelease of previously stored carbon into the marine carbon cycle. Thus, the interaction between ecosystem services may lead to a net negative impact of SLR on climate mitigation services. Overall, we highlight the necessity of taking a multi-service approach to considering the impact of global change effects on ecosystem services.</p
Towards explainable orchid flower identification
Get PDFOrchidaceae is one of the largest families in the plant kingdom. It has more than 25,000 orchid species. Compared with other parts of the orchid plant, e.g., leaf, fruit, and root, the orchid flowers have distinct features such as color, shape, texture, etc., that can be used to distinguish between species. Taxonomists and botanists often use these unique characteristics to identify plants.Automated flower identification systems have been developed in recent years. However, all of these systems operate as blackboxes, making it difficult to understand the reasons behind a decision. Recent studies only focus on image processing techniques and machine learning methods, while taxonomist knowledge is not taken into account.This thesis presents a new method for explainable plant identification based on flower characteristics by incorporating taxonomist knowledge into artificial intelligence models. The initial solution for realizing the idea is discussed, starting with a decision tree. In order to build specific classifiers that can directly extract flower characteristics from images, we first constructed a new dataset that consists of images, flower characteristics, and names of species. Afterwards, we built a color classifier using deep learning. How to construct classifiers of other features than color is also explained, and we also investigates the classifiers’ effectiveness. Some relatively basic Bayesian-network classification algorithms are applied to study the effect of several combinations of image features. A more knowledge-based approach is made to incorporate uncertain taxonomic knowledge into the classification process, by combining human knowledge with structure learning. The resulting Bayesian networks are combined with an image-based deep neural network to obtain an excellently performing classification method that is also provided with the capability of explanation.Methods proposed in this thesis can help taxonomists, botanists, and plant enthusiasts to easily and quickly identify plants, while also providing an explanation of solutions with an additional indication of their trustworthiness. The methods can also be used as learning aids for plant enthusiasts, in particular those with an interest in orchids. Furthermore, with respect to ‘Explainable Artificial Intelligence’(XAI), the methods developed in this thesis could be useful in a variety of domains outside plant recognition
Overcoming barriers and leveraging opportunities to scale up landscape-scale restoration in Europe
Get PDFStepping up ecosystem restoration is critical to achieving pressing policy targets, but as well as significant benefits, there are also multiple challenges particularly associated with restoring at landscape scale. These relate to the complexity of ecosystems, land uses, and social factors within a landscape and the scale at which sustainable funding and effective monitoring are required. Here we present a summary of discussions from a symposium at the Society for Ecological Restoration—Europe conference, addressing five key topics related to scaling up restoration in Europe: implementation, stakeholder engagement, local economies, financing, and monitoring. Common barriers include inflexible political systems and traditional conservation project thinking, as well as the complexities and time required to work effectively and sustainably across disciplines, sectors, and geographical boundaries. However, opportunities are identified in relation to innovative financing systems and monitoring technologies, the development of nature-based economies, and the strength and sustainability that comes from effectively and deeply engaging a wide diversity of stakeholders. Capitalizing on these prospects could enable landscape-scale ecosystem restoration to play a significant role in meeting global targets for nature, climate, and people.</p
Integrating quality requirements in agile software development at scale:Challenges, approach and validation
Get PDFThis dissertation focuses on the engineering of Quality Requirements (QRs)—also known as non-functional requirements—within agile software development, particularly in Agile Large-Scale Distributed (ALSD) environments. While agile methods adopt a Just-In-Time approach where functional requirements evolve incrementally, this model is not well-suited to QRs. Unlike functional requirements, QRs represent long-term objectives like performance, security, and scalability, which must be addressed early in the Software Development Life Cycle to ensure they are embedded in the system architecture.Agile methods were originally designed for small, co-located teams to counter the inflexible and document-heavy nature of traditional waterfall models. As agile gained popularity, large and distributed organizations began adopting these methods. However, this transition introduced new challenges, especially in handling QRs. Empirical studies show that QRs are often neglected in agile projects, a problem exacerbated in large-scale distributed settings due to increased complexity and communication barriers.In response, this research investigates the specific challenges that agile teams face in managing QRs in ALSD environments. Fifteen key challenges were identified, along with their root causes and the mitigation strategies currently employed by agile teams. The study also evaluated existing Agile Scaled Frameworks (ASFs) to determine their effectiveness in addressing QR-related challenges. While ASFs offer partial solutions, significant gaps remain, particularly in cross-team communication and consistent QR handling.To address these shortcomings, the dissertation introduces the Agile Quality Requirements Elaboration (AQRE) approach. AQRE is a Goal-Oriented Requirements Engineering method designed to facilitate early identification and continuous management of QRs throughout agile projects. The approach supports structured discussion of QRs from the outset and ensures their integration throughout development.AQRE was validated through its application in a real-world agile project and assessed via Focus Group sessions with agile practitioners. Feedback indicated that AQRE is both practical and potentially cost-effective, offering a structured means to enhance QR handling in complex agile environments
Designing on a level playing field:Innovative approaches to eHealth design with older adults
Get PDFAs the global population ages, the concept of “healthspan”—years lived in good health—has gained importance. This shift emphasizes preventive health practices like exercise, nutrition, and mental well-being. eHealth technologies play a key role in supporting these efforts, but older adults often face barriers in using them, including low digital literacy, poorly designed interfaces, and exclusion from the design process. This dissertation addresses these issues by exploring how older adults can be more meaningfully involved in the co-design of eHealth technologies.The central question is how to create equal partnerships between designers, researchers, and older adults during the co-design process. While co-design is often promoted as a way to make technology more user-centered, many initiatives still treat older adults as passive participants. The research argues that older adults should be seen as experts of their own experiences and involved in every stage of design appropriately.The dissertation includes a scoping review and several case studies. These studies highlight challenges like tokenism and ageism, and they explore methods to overcome them, including remote co-design, scenario-based design, and low-contact engagement via newspapers. One case study examines using AI-generated “synthetic users” to simulate older adults’ input early in the design phase, while acknowledging that real user input remains essential.Together, these findings advocate for a flexible, inclusive approach to co-design. By centering the real needs and experiences of older adults, the dissertation outlines practical methods for creating more effective and widely adopted eHealth technologies. It ultimately calls for a paradigm shift: from viewing older adults as passive users to recognizing them as active co-creators of their own health solutions
Microbubble acoustic cavitation and soft matter
Get PDFThis thesis aims to advance our understanding of ultrasound-driven microbubble dynamics, focusing on interactions with viscoelastic media and confined environments. By combining theoretical modeling and experimental observations, we explore microbubble resonance, scattering, and oscillation across different configurations, including bulk media and microchannels. The findings aim to improve the use of microbubbles in clinical applications, enhancing ultrasound imaging and therapeutic precision.After introducing bubble dynamics and viscoelastic tissue models, Chapter 2 investigates how microbubble oscillations influence the rheological properties of the surrounding medium. Tissue behavior at high strain rates (106 s-1) - typical of microbubble activity - is not well understood. To address this, we examine polyacrylamide (PAM) hydrogels as tissue mimicking material, using microbubbles as probes. By analyzing ultra-high-speed imaging data and fitting them to coated bubble simulations, we extract the shear modulus and viscosity of soft and stiff hydrogels. Results show viscosity is highly strain-rate dependent, while the elastic modulus remains comparable to low-frequency values.In Chapter 3, the focus shifts to how the viscoelastic medium’s shear modulus influences the behavior of phospholipid-coated microbubbles. Using a Rayleigh-Plesset-type model, we simulate the scattered pressure from bubbles and study the impact of medium elasticity on resonance frequency, harmonic generation, and subharmonic oscillations.Chapter 4 builds on this by introducing a microbubble scattering spectroscopy technique to experimentally validate simulation findings. We correlate hydrogel stiffness with microbubble resonance frequency, quantify damping, and demonstrate how the gels affect microbubble stability.Chapter 5 explores microbubbles in confined environments, such as small blood vessels, using silicone microchannels (15-100 µm). Ultra-high-speed imaging reveals a decrease in resonance frequency and increased damping as confinement increases. Optical data on radial oscillations is compared with theoretical predictions.Together, these studies enhance our understanding of how microbubbles interact with soft and structured environments, providing a foundation for more accurate clinical models and improved therapeutic outcomes
Ready for the worst:awaiting disaster in ageing rural Japan
Get PDFInami, a small seaside town in Wakayama Prefecture, Japan, is getting ready for the next Nankai Trough earthquake, which is expected to involve multiple events of magnitude 7.0+ on the maximum seismic intensity scale, causing landslides and tsunamis. This paper is concerned with the capabilities and challenges of an elderly community in this highly prepared rural town. The results show that the continued mainstreaming of disaster preparedness practices has led to widespread awareness of evacuation sites and basic knowledge of disaster evacuation needs. Arguably, however, insufficient support is provided to the elderly as current procedures often do not consider how their reduced mobility, physical strength, and psychological discomfort might impact on evacuation itself and life at the shelters. This paper contributes to the literature on disaster and vulnerability by critically assessing and expanding on perceptions of ageing and disasters in rural areas vis-à-vis the traditional depiction of the elderly as ‘vulnerable and helpless’.<br/