154092 research outputs found
Sort by
Focussing of concentric free-surface waves
Get PDFGravito-capillary waves at free surfaces are ubiquitous in several natural and industrial processes involving quiescent liquid pools bounded by cylindrical walls. These waves emanate from the relaxation of initial interface distortions, which often take the form of a cavity (depression) centred on the symmetry axis of the container. The surface waves reflect from the container walls leading to a radially inward propagating wavetrain converging (focussing) onto the symmetry axis. Under the inviscid approximation and for sufficiently shallow cavities, the relaxation is well-described by the linearised potential-flow equations. Naturally, adding viscosity to such a system introduces viscous dissipation that enervates energy and dampens the oscillations at the symmetry axis. However, for viscous liquids and deeper cavities, these equations are qualitatively inaccurate. In this study, we decompose the initial localised interface distortion into several Bessel functions and study their time evolution governing the propagation of concentric gravito-capillary waves on a free surface. This is carried out for inviscid as well as viscous liquids. For a sufficiently deep cavity, the inward focussing of waves results in large interfacial oscillations at the axis, necessitating a second-order nonlinear theory. We demonstrate that this theory effectively models the interfacial behaviour and highlights the crucial role of nonlinearity near the symmetry axis. This is rationalised via demonstration of the contribution of bound wave components to the interface displacement at the symmetry axis Contrary to expectations, the addition of slight viscosity further intensifies the oscillations at the symmetry axis although the mechanism of wavetrain generation here is quite different compared with bubble bursting where such behaviour is well known (Duchemin et al., Phys. Fluids, vol. 14, issue 9, 2002, pp. 3000-3008). This finding underscores the limitations of the potential flow model and suggests avenues for more accurate modelling of such complex free-surface flows.</p
Going from Inner-Skinned to Outer-Skinned Polyelectrolyte Multilayer Based Hollow Fiber Nanofiltration Membranes
Get PDFRecently, hollow fiber polyelectrolyte multilayer membranes (PEMMs) have shown great potential for removing organic micropollutants from wastewater streams. Currently, these PEMMs are made with the selective layer on the inside of the hollow fiber. However, to reduce the physical footprint of PEMM modules, it would be beneficial to have the selective layer on the outside. This will lead to an increased surface area per fiber and enable the use of smaller mechanically stronger fibers, which further increases the surface area per membrane module. To prove that the concept of an outer-skinned PEMM is feasible, the dry-jet wet-spinning process is used to fabricate charged outer-skinned hollow fiber supports, and they are coated through the layer-by-layer self-assembly process to form a PEMM. Scanning electron microscopy images of the hollow fibers confirm the existence of an asymmetric structure with an outer skin, while fluorescence imaging confirms that the polyelectrolyte multilayer is located on the outside of the hollow fiber. Filtration experiments showed that the PEMMs exhibited nanofiltration properties similar to the conventional inner-skinned PEMMs. Overall, these membranes show a 3.8x increase in active membrane surface area to volume ratio compared to commercial PEMMs, clearly highlighting the benefits in terms of footprint.</p
Seismic and environmental controls on slow-moving landslides:Insights from the 2008 Wenchuan earthquake
Get PDFEarthquakes can initiate slow-moving landslides and cause them to transition into rapid failures. Although observations are limited, the literature suggests that strong earthquakes are more likely to trigger nearby failures, while smaller earthquakes may increase susceptibility. However, understanding the role of seismic disturbances requires considering other environmental conditions. This study focuses on the 2008 Mw 7.9 Wenchuan earthquake, using a data-driven multivariate approach to analyze slow-moving landslides. Our findings highlight topographic relief, road proximity, river distance, average monthly precipitation, lithology, and distance to the earthquake surface rupture as key factors. While the distance to the surface rupture is inversely related to landslide occurrence, it is the least influential variable, suggesting that most slow-moving landslides near the rupture may not have failed during the earthquake. Our finding also suggests that persistent disturbances from road networks may be as significant as the impact of a strong earthquake in influencing the existence of slow-moving landslides.</p
Entropy-driven inductance on the surface of a topological insulator
Get PDFNew opportunities for energy harvesting can be found in a century-old thought experiment known as Maxwell's demon, which suggests that energy can be extracted from information. Although systems resembling Maxwell's demon have been experimentally realized, scalability remains a challenge. A scalable solution can be found in the interfacial states of topological insulators, which could resemble Maxwell's demon due to the interaction between spin-momentum locked electrons and nuclear spins. In these systems, information - nuclear spin polarization - can be directly used to store and harvest energy. In this thesis, we focused on thin films of the three-dimensional topological insulator (Bi1-xSbx)2Te3 (BST), which can act as an ‘information engine’ to extract electrical work. Theoretical predictions reveal that the interaction between surface states and nuclear spins in BST leads to an inductive effect, directly coupled to the entropy of the system. This ‘entropic inductance’ has potential applications in microelectronics. Experiments with Hall bar devices fabricated from molecular beam epitaxy (MBE)-grown BST were conducted to investigate this phenomenon under various source-drain bias voltages and temperatures. Despite challenges with high current densities and Joule heating, the study demonstrated finite current-induced nuclear polarization in BST, but the expected inductive signal was small. To enhance the inductive signal, the study explored magnetic doping using vanadium-doped BST (VBST), and searched for the quantum spin Hall effect in ultrathin BST where diffusive losses would be reduced. In future research, the principle of the information engine can be applied to other material systems such as Fermi arc surface states, and future developments in electronic materials could therefore provide the key to a scalable information engine. <br/
Identifying story types of PhD candidates lecturing in higher professional education:“ups and downs”, “turnaround”, “continuous growth”, and “scholarly recognition”
Get PDFPurpose: Guided by the quest concept, this study aims to explore how profession-focused PhD candidates, who are concurrently lecturing at a Dutch University of Applied Sciences (UAS), make sense of change while pursuing doctoral objectives. The research question was: How do these PhD candidates navigate, experience and evaluate their enduring profession-focused doctoral quests across the nexus of research, education and professional fields, considering their aspirations? Design/methodology/approach: Eight PhD candidates shared one-year quest experiences, illustrating how interactions with ‘actors’, ‘settings’ and ‘events’ shape doctoral transitions. These narratological concepts guided within-case and cross-case analyses, while grounded theory methodologies served to explore candidates’ sense-making of change over time. Findings: Four story types of doctoral transitions emerged: “ups and downs”, “turnaround”, “continuous growth” and “scholarly recognition”. Candidates valued the Dutch UASs’ formal policy of supporting academic research with professional relevance. Across the story types, differences in aligning doctoral expectations among research and workplace supervisors and candidates affected knowledge exchange throughout the doctorate. When available, engagement in varied and comprehensive doctoral learning resources advanced candidates’ research competencies, including bridging diverse knowledge types. Autonomous candidate navigation was crucial for building partnerships, accessing dispersed learning resources and responding to uncertainties. Collaborative learning involving BSc-MSc students, colleagues and practitioners varied in strength across the story types, but enhanced the doctorate’s relevance, visible outcomes, feasibility and sustainability. The story types represent transition patterns that shaped how candidates developed new knowledge and contributed to their fields. While passion was a key motivator for candidates, it also heightened their vulnerability. Practical implications: Analysing patterns in doctoral transitions provided actionable insights for optimising conditions and candidate navigation within the science–profession nexus. Originality/value: The findings highlight that diverse actors can contribute to and benefit from profession-focused doctorates, driving momentum in integrating this research into education and innovation.</p
The LiverTwin: a novel ex-vivo experimental platform for multi-modal image-guided liver cancer treatment studies
Get PDFSoftware. Reproducible results. Wastewater-based epidemiology framework:Collaborative modeling for sustainable disease surveillance
No full textThis repository provides access to the materials (code-data), software-environments (NetLogo, Rstudio, Docker containers), and the steps for reproducing the results from the publication: Wastewater-based epidemiology framework: Integrating modeling for disease surveillanc
Monotonicity of the jump set and jump amplitudes in one-dimensional TV denoising
Get PDFWe revisit the classical problem of denoising a one-dimensional scalar-valued function by minimizing the sum of an fidelity term and the total variation, scaled by a regularization parameter. This study focuses on proving that the jump set of solutions, corresponding to discontinuities or edges, as well as the amplitude of the jumps are nonincreasing as the regularization parameter increases. Our results apply to input functions in with left and right approximate limits everywhere, extending beyond the traditional setting of functions of bounded variation. The proof leverages competitor constructions and convexity properties of the taut string problem, a well-known equivalent formulation of the TV model. Such a monotonicity property reflects that the extent to which geometric and topological features of the original signal are preserved is consistent with the amount of smoothing desired when formulating the denoising method
Effect of physical exercise on white matter microstructure in chemotherapy-treated breast cancer patients:a randomized controlled trial (PAM study)
Get PDFPhysical exercise is a promising intervention to improve brain white matter integrity. In the PAM study, exercise intervention effects on white matter integrity were investigated in breast cancer patients. Chemotherapy-treated breast cancer patients with cognitive problems were randomized 2–4 years post-diagnosis to an exercise (n = 91) or control group (n = 90). The 6-month exercise intervention consisted of four hours/week of aerobic and resistance training. White matter integrity was measured at baseline and 6-month follow-up with fractional anisotropy (FA) and mean diffusivity (MD), which were derived from magnetic resonance diffusion tensor imaging (DTI). Both DTI metrics were analyzed whole brain and voxel-wise with a modified tract based spatial statistics (TBSS) procedure. Other measurements included cognition and physical fitness. Exercise effects were analyzed with multiple regression analyses. An explorative analysis was conducted in highly fatigued patients. DTI scans were available for 69 patients of the intervention (age = 52.3 ± 8.9yrs.) and 72 patients of the control group (age = 53.2 ± 8.6yrs.). Whole brain and voxel-wise analyses revealed no significant intervention effects on FA and MD. In highly fatigued patients (exercise: n = 32; control: n = 24), significant clusters of decreased FA post-intervention were observed in the left inferior and superior longitudinal fasciculus. Mean FA in these clusters was not predictive of cognition. A 6-month exercise intervention did not affect white matter integrity in chemotherapy-treated breast cancer patients. However, in highly fatigued breast cancer patients a significant FA decrease was observed post-intervention. The direction of these results is unexpected, and more research is needed to further understand these results.</p