132571 research outputs found
Sort by
Lateral-torsional buckling resistance of non-prismatic and prismatic mono-symmetric I-section steel beams based on stress utilization
No full textThe lateral-torsional resistance of prismatic double-symmetric I-section beams is accurately predicted using a mechanically consistent Ayrton-Perry approach, combined with a calibrated generalized imperfection. The corresponding design formulation was recently adopted in the revised version of Eurocode 3. However, for prismatic mono-symmetric I-section beams, the General Case shall be used while for non-prismatic beams only the General Method is available. Both methods present a very large scatter and highly underestimate the lateral-torsional buckling resistance. This paper proposes an extension to the General Formulation for non-prismatic beams with arbitrary boundary conditions, partial lateral restraints, and arbitrary loading for mono-symmetric I-sections. Using an advanced numerical model calibrated with experimental test results, a large parametric study is undertaken, and its results are used to assess the available design methodologies and the proposed method. It is concluded that the General Formulation provides excellent safe-sided estimates of the LTB resistance, and it is confirmed the very poor performance of the General Case and the General Method.Steel & Composite Structure
Green Health: Examining the role of green space characteristics and their proximity in green space health pathways
No full textThis doctoral thesis critically examines green space characteristics and their proximity to residents in their ability to help reduce the global disease burden of non-communicable diseases. By dissecting three pivotal pathways of theorized green space health effects through increased physical activity, increased social cohesion, and reduced air pollution, the thesis aims to provide new insights into which green space characteristics drive these relationships and in which distance they occur. To achieve these aims, this thesis develops reporting guidelines for the research field, a QGIS script for automatization of green space indicator development and uses two complementary sources for data collection. It builds on the self-reported data on physical activity, social cohesion, air pollution, health and mental health from the URBiNAT project and its case studies in the four European satellite neighbourhoods Nantes-Nord (France), Porto-Campanhã (Portugal), Sofia-Nadezhda (Bulgaria), and Høje-Taastrup (Denmark) and complements it with a rigorous spatial analysis. This enabled a rigorous sensitivity analysis based on up to 135 structural equation models per pathway. The results of this doctoral research revealed distinct green space characteristics and proximities that drive each pathway, including thresholds where these associations disappear or even change direction. It concludes that interconnected, multi-use green corridors are more beneficial than isolated patches for all analysed health pathways, challenging current municipal green space strategies to shift focus from mere ratios to green mobility infrastructures. Although rooted primarily in European contexts and of a cross-sectional nature, the doctoral research provides new evidence for urban planning and public health. It emphasizes the practical implications of how to design green spaces to address health concerns. The results not only resonate with the WHO's Urban Health Research Agenda but also provide tangible recommendations for a healthier human habitat.Heritage & Architectur
On-Demand Magnetically-Activated Drug Delivery from Additively Manufactured Porous Bone Implants to Tackle Antibiotic-Resistant Infections
No full textThis study proposes a new concept for an on-demand drug releasing device intended for integration into additively manufactured (i.e., 3D printed) orthopedic implants. The system comprises a surface with conduits connected to a subsurface reservoir used for storage and on-demand release of antimicrobial agents, covered with a cap that prevents the antibacterial agents from being released until alternating magnetic field (AMF) raises the temperature of the cap, thus, releasing the stored drug. To demonstrate this concept, Ti6Al4V specimens are directly 3D printed using selective laser melting and their surface, reservoirs, and drug releasing properties are characterized. A new synthetic antimicrobial peptide, SAAP-148, is thereafter tested for its cytotoxic, osteogenic, and immunomodulatory effects at concentrations relevant for its minimal bactericidal concentration (MBC) and is compared with its natural analogue, LL-37. The results showed that AMF successfully activated the release from the 3D printed loaded samples. Both peptides demonstrated to be non-cytotoxic within the MBC levels for macrophages and preosteoblasts and did not influence their osteoimmunomodulatory behavior. The findings of this study indicate that the proposed concept is technically feasible and has the potential to be used for the development of bone implants with on-demand delivery systems to fight IAI without systemic or continuous local release of antibiotics.Biomaterials & Tissue Biomechanic
Crashworthiness in preliminary design: Mean crushing force prediction for closed-section thin-walled metallic structures
No full textTo design crash structures for disruptive aircraft designs, it is required to have fast and accurate methods that can predict crashworthiness of aircraft structures early in the design phase. Axial crushing is one of the key energy absorbing mechanisms during a crash event. In this study, various analytical models proposed for calculation of mean crushing force for thin-walled tubular structures are compared with a database of numerical and experimental values to ascertain their accuracy. Improvements to some of the models have also been proposed. Finally a generalized model based on the studied and improved analytical models for prediction of mean crushing force for closed section thin-walled tubular structures is introduced. The generalized model demonstrates high accuracy when compared against experimental/numerical dataset as evidenced by a high coefficient of determination (R2) value of 0.97 and can therefore be used to estimate the mean crushing force for closed-section thin-walled metallic tubular structures with various cross-sectional shapes and crushing modes early in the design phase.Group Giovani Pereira CastroGroup Alderlieste
Moving measurements: Measurements of the turbulent/non-turbulent interface of a round jet in a co-moving frame of reference
No full textAt the turbulent/non-turbulent interface (TNTI) of a jet flow, momentum is transferred from the turbulent jet fluid to the fluid at rest. This transfer is governed by two mechanisms. One of them is related to the large scales of the flow and the other relates to the small scales of the flow. Which of the two is dominant is still a point of discussion. To analyse the TNTI the instantaneous information of the flow and the location of the interface is of great importance. However, the interface simultaneously develops and travels downstream from the nozzle. With stationary measurement techniques this limits the number of frames the interface can be seen developing as it travels in and out of the FOV. In this thesis the TNTI is measured using a camera system that moves along with the TNTI to get high resolution instantaneous measurements of the same part of the evolving interface. The measurement techniques that are used for this experiment are Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF). The cameras for these measurements are mounted to a motorised frame to keep the same part of the interface in view of the cameras as it develops. Three Reynolds numbers are measured with this setup and the cameras move approximately 50Dn at a velocity close to the velocity of the interface along a diagonal path to follow the evolution of the TNTI. One measurement with a Reynolds number of approximately 1.2 × 104 has been processed to show the quality of the results that can be obtained from such a measurement. The velocities are computed by an in-house interrogation analysis program in MATLAB to overcome the wide range of particle displacement found in this experiment, due to the presence of both the centreline and the TNTI of the jet. The TNTI is detected using the LIF data and a threshold detection method from literature that determines a threshold value. The results from the PIV and LIF processing is combined to compute the average conditional vorticity over the interface. The results show that the PIV analysis is able to compute the velocities of almost the entire jet. Only showing a lot of spurious vectors close to the nozzle in the core of the jet. The LIF edge detection algorithm, on the other hand, does not perform as expected. In multiple instances, an internal interface is detected instead of the TNTI. The TNTI is also determined by identifying a threshold value through a visual inspection of the LIF images. This manually determined TNTI is used as a point of comparison for the average conditional vorticity profiles. The average conditional vorticity profiles support the conclusion that an interface internal to the jet is detected when comparing the interface from the algorithm to the interface determined manually. Although not quantified in this thesis, there are moving measurements that show the same section of the TNTI evolving for many frames. This gives the co-moving measurements a clear advantage in measurement time compared to stationary measurements when trying to measure the moving TNTI. Refinements to the experimental setup, the behaviour of these internal interfaces and the detection of the TNTI can be of interest for future research.https://www.youtube.com/watch?v=O-WBgnZn_l0 A video of the raw LIF images from the co-moving measurementsMechanical Engineerin
Towards reusable building blocks for agent-based modelling and theory development
No full textDespite the increasing use of standards for documenting and testing agent-based models (ABMs) and sharing of open access code, most ABMs are still developed from scratch. This is not only inefficient, but also leads to ad hoc and often inconsistent implementations of the same theories in computational code and delays progress in the exploration of the functioning of complex social-ecological systems (SES). We argue that reusable building blocks (RBBs) known from professional software development can mitigate these issues. An RBB is a submodel that represents a particular mechanism or process that is relevant across many ABMs in an application domain, such as plant competition in vegetation models, or reinforcement learning in a behavioural model. RBBs need to be distinguished from modules, which represent entire subsystems and include more than one mechanism and process. While linking modules faces the same challenges as integrating different models in general, RBBs are “atomic” enough to be more easily re-used in different contexts. We describe and provide examples from different domains for how and why building blocks are used in software development, and the benefits of doing so for the ABM community and to individual modellers. We propose a template to guide the development and publication of RBBs and provide example RBBs that use this template. Most importantly, we propose and initiate a strategy for community-based development, sharing and use of RBBs. Individual modellers can have a much greater impact in their field with an RBB than with a single paper, while the community will benefit from increased coherence, facilitating the development of theory for both the behaviour of agents and the systems they form. We invite peers to upload and share their RBBs via our website - preferably referenced by a DOI (digital object identifier obtained e.g. via Zenodo). After a critical mass of candidate RBBs has accumulated, feedback and discussion can take place and both the template and the scope of the envisioned platform can be improved.Energie and IndustriePolicy Analysi
Understanding students’ adoption of the ChatGPT chatbot in higher education: the role of anthropomorphism, trust, design novelty and institutional policy
No full textThe present research aims to highlight the underlying factors that drive students’ adoption of the ChatGPT chatbot in higher education. This study extends the meta-UTAUT framework by including additional exogenous factors of anthropomorphism, trust, design novelty, and institutional policy. Empirical examination with Structural Equation Modelling among 355 students in Dutch higher education institutions revealed attitude and behavioural intention as significant positive predictors of students’ ChatGPT use behaviour. Institutional policy negatively moderated the effect of behavioural intention on use behaviour. Behavioural intention was significantly and positively influenced by attitude, performance expectancy, social influence, and facilitating conditions. Anthropomorphism, design novelty, trust, performance expectancy, and effort expectancy were unveiled as significant positive antecedents of attitude. The central theoretical contributions of this research include investigating students’ use behaviour instead of behavioural intention, establishing attitude as a core construct, underlining additional antecedents of attitude, and highlighting the importance of institutional policy. The present study contributes to prior research on technology adoption, especially in the area of artificial intelligence in education. The findings yield valuable insights for chatbot designers, product managers, and higher education policy writers.BT/Biotechnology and SocietyEconomics of Technology and Innovatio
Cross-coupled iterative learning control: A computationally efficient approach applied to an industrial flatbed printer
No full textCross-coupled iterative learning control (ILC) can improve the contour tracking performance of manufacturing systems significantly. This paper aims to develop a framework for norm-optimal cross-coupled ILC that enables intuitive tuning of time- and iteration-varying weights of the exact contour error and its tangential counterpart. This leads to an iteration-varying ILC algorithm for which convergence conditions are developed. In addition, a resource-efficient implementation is developed that reduces the computational load significantly and enables the use of long reference signals. The approach is experimentally validated on an industrial flatbed printer.Team Jan-Willem van Wingerde
Low disorder and high valley splitting in silicon
No full textThe electrical characterisation of classical and quantum devices is a critical step in the development cycle of heterogeneous material stacks for semiconductor spin qubits. In the case of silicon, properties such as disorder and energy separation of conduction band valleys are commonly investigated individually upon modifications in selected parameters of the material stack. However, this reductionist approach fails to consider the interdependence between different structural and electronic properties at the danger of optimising one metric at the expense of the others. Here, we achieve a significant improvement in both disorder and valley splitting by taking a co-design approach to the material stack. We demonstrate isotopically purified, strained quantum wells with high mobility of 3.14(8) × 105 cm2 V−1 s−1 and low percolation density of 6.9(1) × 1010 cm−2. These low disorder quantum wells support quantum dots with low charge noise of 0.9(3) μeV Hz−1/2 and large mean valley splitting energy of 0.24(7) meV, measured in qubit devices. By striking the delicate balance between disorder, charge noise, and valley splitting, these findings provide a benchmark for silicon as a host semiconductor for quantum dot qubits. We foresee the application of these heterostructures in larger, high-performance quantum processors.QCD/Scappucci LabQRD/Kouwenhoven LabBUS/TNO STAFFQCD/Veldhorst LabQN/Vandersypen LabQN/Veldhorst La
Two-layer gravity inversion on Mars: Three different inversion methods to obtain a global density model of the crust and upper mantle of Mars
No full textThe origin of the Martian dichotomy is subject to question and no substantial evidence exists. Some surface and interior features that are not visible in, e.g., topography data, can show up in gravity data. Therefore, this research inverts gravity data to find a crustal and mantle global density model. Previous research performed a one-layer inversion, assuming equal mass in all columns. Also, missions like InSight do not provide global interior information, but only at the landing site. The aim of this research is to provide a global density model of both the Martian crust and upper mantle. The inversion is performed using a weighted, regularized least-squares algorithm. The gravity input consists of the residual between the MRO120F data set and the state-of-the-art gravity field model of the TU Delft. The design matrix is built using Green’s functions, which define the influence of a mass element in all different directions on a measurement point. Using this least-squares algorithm, three different methods for inversion are used. The separate two-layer inversion, the combined independent two-layer inversion and the combined dependent two-layer inversion. All three inversion methods are performed on synthetic planets as well, for verification purposes. By performing all inversions on the synthetic planets, it was found that the combined independent two-layer inversion results in a strong decoupling of short and long wavelength signals, but is not able to attribute gravity signals to different features in the crust and mantle. The combined dependent two-layer inversion does lead to a result that shows decoupling of crust and mantle features. The hypothesis is that adding different gravity components to the combined dependent two-layer inversion will further increase its accuracy. The results of the inversion methods applied to Mars are in agreement with existing research in terms of standard deviations of the crust and mantle density anomalies. The maps were also analysed geologically, where the most important conclusion is the evidence of potential impact basins in the north polar region. These can be evidence to accept the several impact theory for the origination of the Martian dichotomy. Increasing the resolution and refining the third inversion method with multiple gravity components will increase the potential of gravity inversion to define geological features of Mars.Aerospace Engineerin
Data sources:
Access Repository Dashboard
Do you manage Open Research Online? Become a CORE Member to access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard! 👇