154092 research outputs found
Sort by
Aspect ratio effect on side and basal melting in fresh water
No full textThe aspect ratio effect on side and basal melting in fresh water is systematically investigated across a range of Rayleigh numbers and ambient temperatures using direct numerical simulations. The side mean melt rate follows a scaling relation in the side-melting dominant regime, where is the Rayleigh number, and is the width-To-height aspect ratio of the ice block. In the basal-melting dominant regime, the basal mean melt rate follows a scaling relation at low Rayleigh numbers, but transitions to a scaling relation at higher Rayleigh numbers. This scaling transition is attributed to the formation of a bottom cavity resulting from flow separation at high Rayleigh numbers. The overall mean melt rate exhibits a non-monotonic dependence on the aspect ratio, driven by the competition between side and basal melting. The proposed theoretical model successfully captures the observed non-monotonic behaviour, and accurately predicts the overall mean melt rate over the considered range of Rayleigh numbers and ambient temperatures, especially in the side-and basal-melting dominant regimes. More specifically, the side, basal and overall mean melt rates follow a linear scaling relation for ambient temperatures, with being the Stefan number (the ratio between sensible heat and latent heat), but deviations from this scaling relation and a non-monotonic dependence on the ambient temperature are observed at lower ambient temperatures, which can be attributed to the density anomaly effect.</p
Intelligent Human Computer Interaction:Intelligent Human Computer Interaction 16th International Conference, IHCI 2024, Twente, The Netherlands, November 13–16, 2024, Revised Selected Papers, Part II
No full textQuantum transport in tin telluride nanowire devices
Get PDFAt the intersection of curiosity-driven fundamental research and the hunt for practical applications lies the field of quantum computation. Quantum computers would solve specialized problems intractable for supercomputers. However, current quantum processors are highly error-prone due to decoherence. Majorana zero modes are a promising platform for fault-tolerant quantum computing, and could be realized by inducing superconductivity in a topological insulator: a class of materials that behave as electrical insulators in the bulk, while having conducting surface states. A specific subclass is the topological crystalline insulator. In this thesis, topological crystalline insulator SnTe nanowires are studied in transport experiments to investigate and characterize their surface states and bulk properties. The small diameter of SnTe nanowires complicates Hall device fabrication, and high bulk carrier density, due to spontaneous Sn vacancies, limits the effectiveness of field-effect transistor configurations. This thesis presents the successful fabrication of Hall configuration nanowire devices to determine the carrier density. Despite the high carrier density, quantum transport phenomena are observed, among which Fabry-Pérot oscillations. Supported by a model, we attribute the Fabry-Pérot oscillations to ballistic 2D surface state transport. These specific devices also exhibit resistance variations in a parallel magnetic field, indicative of Aharonov-Bohm-type transport due to the surface states in the nanowires. Finally, we investigate Josephson junctions to understand SnTe properties in the superconducting regime, including the critical current behavior as a function of magnetic field and temperature and the skewed current-phase relation. The ability to push the limits of nanostructured devices in combination with the obtained knowledge on SnTe opens new device architectures. We provide an outlook on an alternative device structure to detect Majorana zero modes, employing the high carrier density as an advantage instead of a challenge. While SnTe nanowires may not have immediate practical applications, their study contributes to curiosity-driven exploration of topological phases.<br/
The global spectrum of tree crown architecture
Get PDFTrees can differ enormously in their crown architectural traits, such as the scaling relationships between tree height, crown width and stem diameter. Yet despite the importance of crown architecture in shaping the structure and function of terrestrial ecosystems, we lack a complete picture of what drives this incredible diversity in crown shapes. Using data from 374,888 globally distributed trees, we explore how climate, disturbance, competition, functional traits, and evolutionary history constrain the height and crown width scaling relationships of 1914 tree species. We find that variation in height–diameter scaling relationships is primarily controlled by water availability and light competition. Conversely, crown width is predominantly shaped by exposure to wind and fire, while also covarying with functional traits related to mechanical stability and photosynthesis. Additionally, we identify several plant lineages with highly distinctive stem and crown forms, such as the exceedingly slender dipterocarps of Southeast Asia, or the extremely wide crowns of legume trees in African savannas. Our study charts the global spectrum of tree crown architecture and pinpoints the processes that shape the 3D structure of woody ecosystems
C-SHAP for time series: An approach to high-level temporal explanations
Get PDFTime series are ubiquitous in domains such as energy forecasting, healthcare, and industry. Using AI systems, some tasks within these domains can be efficiently handled. Explainable AI (XAI) aims to increase the reliability of AI solutions by explaining model reasoning. For time series, many XAI methods provide point- or sequence-based attribution maps. These methods explain model reasoning in terms of low-level patterns. However, they do not capture high-level patterns that may also influence model reasoning. We propose a concept-based method to provide explanations in terms of these high-level patterns. In this paper, we present C-SHAP for time series, an approach which determines the contribution of concepts to a model outcome. We provide a general definition of C-SHAP and present an example implementation using time series decomposition. Additionally, we demonstrate the effectiveness of the methodology through a use case from the energy domain
Flexible robotic endoscopes for minimally invasive surgery applications
Get PDFAccurate endoscopic camera control is essential for the success of many minimally invasive procedures. Various research efforts have introduced soft actuators to improve the maneuvering performance of flexible endoscopic tools while also enhancing safety due to their inherent mechanical compliance. To advance soft endoscopic tools towards clinical practice, improvements must be made with respect to their control precision, repeatability, and the amount of force that the soft actuator can exert. Furthermore, incorporating a robotic control interface addresses the main drawback of using flexible endoscopes, namely their nonintuitive control, reducing the learning time required for new clinicians to become proficient in using flexible endoscopes.The first part of this thesis contains the research work performed in order to improve the soft actuator performance to meet minimally invasive surgery needs. The soft pneumatic actuator designs and control method are presented with the goal of improving its size, motion, and force characteristics. The second part of this thesis focuses on the development and evaluation of a robotic interface for flexible endoscopes. The developed control and haptic interface aims to provide a more intuitive control and guidance method for surgeons to use a flexible endoscope. These advancements can help improve robotic flexible endoscope capabilities, ease of use, and ergonomics, which ultimately will lead to a better standard of care in the operating room
Effect of particle shape on the discharge from a mono-layer hopper
Get PDFIn this work, we performed experiments with spheres, rice-shaped particles with different aspect ratios, and macaroni-shaped particles in a quasi-two-dimensional hopper, where the thickness was adjusted to the minor dimensions of the particles such that a mono-layered system is created. We quantitatively investigate the vertical velocity and solid fraction profiles at the orifice and determine how these are influenced by the slope of the hopper. Interestingly, where the hopper angle hardly influences the velocity profile for rice-shaped particles, the magnitude of the velocity profile increases for spherical particles and decreases for macaroni particles with the steepness of the hopper. The spheres have flat solid fraction profiles for all hopper angles, but a transition from flat to dome-shaped profiles is observed with decreasing hopper steepness for all non-spherical particles. The discharge rate determined by integrating the product of the velocity and solid fraction profiles has good agreement with the experimentally measured discharge rate for all particle shapes.</p
FRAME-PRO:Framework for the responsible and accountable mapping of deprived urban areas
Get PDFOver the past two decades, there has been increasing work being done in the mapping of deprived urban areas (otherwise known as slums and informal settlements) in the Global South. These mapping initiatives are performed by private companies, academic researchers, non-governmental organizations and governmental institutions, utilizing technologies including satellites, drones, mobiles phones, wearable devices and artificial intelligence. These actors engage in the mapping of deprived urban areas for a variety of purposes such as improving capacity building efforts, urban planning, understanding sociodemographic conditions and measuring international policy commitments such as monitoring the Sustainable Development Goals. While most of the literature written about these mapping initiatives focus on the technical aspects, there is also a growing need to highlight the social, political and ethical issues involved. The focus of my PhD project, FRAME-PRO, is to address such issues, through an interdisciplinary lens and presenting the mapping of deprived urban areas as a geographic and philosophical problem. This project stemmed from the Behavioural, Management and Social Sciences (BMS) Faculty Board Signature PhD call in 2019, and collaboration between the Philosophy section of BMS and the Department of Urban and Regional Planning and Geo-Information Management of ITC. The chapters comprising my dissertation focus on: i) reviewing ethical guidelines for the use of artificial intelligence (AI) and geographic information technologies; ii) a genealogical and postphenomenological analysis of cartographic practices and the unique challenges of AI-assisted humanitarian mapping; iii) the potential trade-offs between ethical and practical concerns in the use of geographic information during crises (such as COVID-19); and iv) the hermeneutics of geographic information used for waste management processes. And the insights gained from these chapters contribute to developing a framework for the responsible and accountable mapping of deprived urban areas
Socially Sustainable Home Environments for Older Adults Ageing in Place: A Scoping Review (Embase).
No full textWhat drives individuals to initiate donation-based crowdfunding appeals?:An application of the charity disintermediation typology
No full textThe term ‘disintermediation’ is well understood in the commercial sector and is defined as the elimination of the ‘middleman’ (usually via digital means) in business transactions. The concept of disintermediation is less clear-cut in the non-profit context and is complicated further by a wider array of stakeholders who are involved in the conversion of philanthropic contributions into goods and services in aid of beneficiaries. This chapter presents recent scholarship on the development of a typology of disintermediation in the non-profit sector. This typology allows us to identify the significant changes, challenges, and opportunities that disintermediating actors and technologies pose for the future of charity marketing. The second part of the chapter looks at applying and unpacking the typology further. Specifically, it explores inter-disciplinary literature to try and understand what drives individuals to initiate donation-based crowdfunding appeals: Type Bi category within MacQuillin et al.’s (2023) typology. The typology points to two growing trends: donation-based crowdfunding is set to replace some of the more traditional fundraising methods in the future whilst donors’ growing influence and proactive behaviour within the non-profit sphere highlights a shift in power balance away from the charity sector to the individual philanthropist. Understanding the motivations behind disintermediated giving, will help charities orientate themselves in this new philanthropic landscape