To optimally use wind farms, thorough understanding of wind patterns is needed. Recently, a lot of attention in the scientific community is turned to the Current FeedBack effect, where oceanic currents influence the atmosphere above. It has been shown that this also applies to tidal currents in the English Channel where the induced tidal winds have an amplitude of one-third of the underlying current. In this report focus is moved to the Dutch coast. Using a numerical integration model of a vertical grid, the horizontal wind speeds above a small area of the Dutch coast are modelled. The model is based on the 1-dimensional Navier-Stokes equations in combination with Prandtl's mixing length model to account for turbulence. The horizontal wind speeds are found to reach up to one-fourth of the amplitude of the tidal currents at a height of z = 10 m above the sea surface and 1/20 at z = 50 m. This is similar to what was found in earlier research, but a lot of assumptions were made in this model. Therefore, further research could focus on addressing some of these assumptions such that the understanding of tidal induced wind velocities can be even better understood.

¹⁶¹Tb is considered a promising alternative to ¹⁷⁷Lu in the treatment of neuroendocrine tumors and prostate cancer. It is produced via neutron irradiation of ¹⁶⁰Gd targets and its subsequent separation from said targets. Current separation methods have limitations so a fast removal method of the Gd bulk is desired. Such a method is developed in this research using solvent extraction techniques. Three extractants were investigated, the one with the highest potential, DEHPA, was used to optimize the extraction. This yielded a Tb extraction efficiency of 98.6 ± 0.2 % and a Gd extraction efficiency of 85.7 ± 5.5 % followed by a Tb back-extraction efficiency of 98.2 ± 0.1 % and a Gd back-extraction efficiency of more than 98.2 ± 0.1 %. The Tb/Gd separation was increased by adding the reverse size selective chelator MACROPA to the aqueous phase to preferentially complex Gd in the aqueous phase. This yielded a Tb and Gd extraction efficiency of 95.0 ± 0.2 % and 53.1 ± 3.0 % respectively. The ratio between total EEs of Tb and Gd after three subsequent extractions was approximately 10 demonstrating the potential of using sequential extractions to remove a bulk of Gd from Tb. The procedure of doing consecutive extractions must however be further optimized as nearly 80% of Tb was not extracted. Finally, it was shown that the resulting solution after bulk Gd removal can still be further purified using an ion exchange column. In future research, it is highly advised to investigate the recycling of Gd and MACROPA from the aqueous phase after extraction to allow for further irradiation of the Gd and re-usability of the MACROPA.

This study explores the electrokinetic properties of zinc-alginate beads in the context of a zinc-air solid- mediated flow battery, as there has been a renewed interest in zinc–air batteries due to their potential for high energy density, safety, and environmental benefits [43]. On the contrary, there are several challenges related to both the anode and the cathode of the Zn-air battery. This research focuses on the challenges related to the anode side which consists of zinc dendrite formation, reducing the battery’s lifetime. Also, Zn passivation increases internal resistance and reduces active capacity. Additionally, hydrogen evolution reaction during charging decreases the coulombic efficiency and leads to safety risks due to gas pressure build-up [40][43]. Trying to solve these issues, a European pathfinder project, ReZilient, has proposed a Zinc-Air Solid Mediated Flow Battery. In the anolyte tank, alginate beads are introduced to encapsulate zinc, aiming to prevent these parasitic reactions. Besides, the encapsulation of solid ZnO microparticles overcomes the limited solubility of ZnO and could significantly enhance the system’s energy density. This study explores the electrokinetic and mechanical properties of Zn/ZnO beads and the capability of preventing these parasitic reactions. Experimental research, including thermogravimetric analysis, scanning elec- tron microscopy, cyclic voltammetry and electrical impedance spectroscopy was used to characterize and evaluate the bead’s electrochemical and mechanical behaviour. After synthesizing the beads it was found that beads consisting of 2.5% and 5% w/v sodium alginate demonstrated a strong structure of which the last one was used for further experimental research. The synthesized beads were uniformly sized, with diameters mainly between 3.3 mm and 3.5 mm. Besides, thermogravimetric analysis was performed on beads produced from a 5% w/v sodium alginate, 3% carbon black and 10% ZnO solution. The analysis revealed that the bead consisted of 82.7% water, 7.4% organic alginate and carbon black, and 9.9% metal oxides including ZnO and CaO, although the specific ratio of calcium remains to be determined. Additionally, the diffusion rates for alkali metal hydroxides like NaOH and KOH were measured at 0.0464 s−1 and 0.0435 s−1, respectively. Conductivity assessments via cyclic voltammetry identified a con- ductivity of 0.01 S/m at a 3% KS4 graphite concentration, which aligned with literature studies. Addi- tionally, hydrogen evolution was observed within the beads during voltammetry experiments conducted between 0 and -1.4 V (vs Ag/AgCl), indicating that the alginate’s carboxylic acid groups do not suffi- ciently increase the overpotential for the reduction of water to mitigate hydrogen evolution. Still, cyclic voltammetry of the bead was performed with a technique, called film voltammetry, inspired by the study of Yoon et al. (2019). The measurement showed that the Zn/ZnO could perform a redox reaction while situating in the bead. it exhibited a redox potential of around -1.4 V (vs Ag/AgCl) at a pH of 12, indicating Zn/Zn(OH)−2 4 . However, it suffered from very low zinc utilization of 0.0007% and limited reversibility as the reduction kinetics were unfavourable. The Zn-Ca-crosslinked bead demonstrated faster reaction kinetics and achieved a redox potential of -1.05 V (vs Ag/AgCl), indicating Zn/Zn+2, yet it also experienced zinc loss and declining efficiency over time as it shifted to similar electrochemical behaviour as the Zn/ZnO bead. To improve zinc utilization, ZnO was encapsulated with a carbon micro-shell before being added to the alginate beads to increase ionic and electronic conductivity. However, it only showed slightly enhanced reduction currents, while zinc utilization remained low. Next to the electrochemical behaviour, were the mechanical properties of the beads tested as well, with a Young’s modulus of 0.58 MPa for the 5% w/v Na-Alg with 3% w/v KS4 graphite bead. These findings show that strong beads were synthesised and Zn/ZnO is electrochemically reactive within the bead. Nevertheless, the low zinc utilization and dogged parasitic reactions require further research. This research provides a foundation for improving the performance of Zn beads in zinc-air solid-mediated flow batteries by addressing their electrochemical behaviour and mechanical properties.

Drop-on-Demand Inkjet Printing requires jetting ink particles at 100kHz at velocities of 10m/s from sub-millimeter-scale printhead assemblies, and represents a physics-rich engineering problem. CFD simulations have been used to study the jetting process. From meniscus deformation at the nozzle, to the presence of entrained particles in the jet, modelling contact line dynamics is very important.
Color-Gradient Lattice Boltzmann (CG-LBM) simulations can capture surface tension between fluids. Contact angles with solids are often imposed on geometrical grounds as boundary conditions. Alternative energy-based wetting, based on solid-liquid surface tension/energy arguments, is investigated for its applicability in the inkjet printing regime.
CG-LBM fluid-fluid interfaces are diffuse, despite modelling macroscopically sharp interfaces. This requires interpolation of viscosity in the interface region: new arguments are given to support the idea that this interpolation is free, and can be chosen, for example, on the basis of validation results.
New theory on CG-LBM for any number N of fluids is developed, and broadens the applicability of known N-fluid algorithms, allowing the use of in-simulation phase definitions that are more suitable for large density ratios among fluids.
The use of superviscous particles is investigated, where an N-fluid CG-LBM implementation is leveraged by using very viscous fluids to model solids. Wetting would then be mediated by the CG-LBM fluid-fluid interaction framework. The way CG-LBM maintains fluid-fluid interfaces is now also extended to the solid-fluid interfaces, and can lead to catastrophic spurious smearing of physical features.
Separately, recognizing the fundamental physical similarity of surface-tension across fluid-fluid and fluid-solid interfaces, wetting phenomena were simulated with additional fluid-fluid-like interactions near walls. This solid-phase perturbation approach was consistently formulated thanks to the new N-fluid CG-LBM theory developed earlier. Inaccuracies arise when these interactions are not paired with a diffuse fluid-solid interface, similar to those maintained between fluids in CG-LBM.
Sufficient results are obtained to motivate future development of solid-phase perturbation, which indeed describes solid-fluid and fluid-fluid surface-tensile interaction in a unified framework.

This thesis investigates the implementation of three-dimensional nudging into large-eddy simulation (LES) to assimilate observed atmospheric data into an LES model. 3D-nudging 'pushes' the thermodynamic fields in a simulation towards the desired observed fields. The aim is to test if such a method is useful in improving solar forecasts of stratocumulus-topped boundary layers. For this purpose 3D-nudging LES solar forecasts are compared to persistence forecasts and conventional LES-based forecasts. As a proxy for observations, exact thermodynamic fields from LES were used in this research. Using LES fields is advantageous as it provides full 3D thermodynamic fields but also dynamic fields for checking the turbulence in the different methods. Results show that 3D-nudging is quite capable of replicating the desired thermodynamic fields. Unfortunately, nudging comes with a penalty as it causes the turbulence built up in a simulation to be flawed. This effect is mitigated by the design of variations on the nudging technique, the most promising of which is multiple time fields nudging, which nudges the thermodynamic fields in a simulation to subsequent desired fields every 10 minutes during the nudging period. Solar forecasts found by this method are found to be more accurate than the persistence and regular LES methods on forecast horizons of 30 minutes and larger. Approaches proposed in this study to approximate thermodynamic fields from observational data estimate thermodynamic fields to a reasonable accuracy but are far from perfect, and thus it should be noted that solar forecast accuracy of the discussed methods will be less accurate when applied to real observations. Further research is recommended to focus on the use of the 3D-nudging methods in more LES case studies, and on devising better methods for the estimation of thermodynamic fields from observations.

In the realm of fluid dynamics and particle transport, the control of particle trajectories represents a formidable challenge. It would be useful to be able to optimally navigate an oceanographic float from one pre-set location to another by solely changing its buoyancy. In this thesis, a first step in discovering whether this is possible and what optimization strategy can be used is taken.
To do so, first, the physical situation is translated into a mathematical model. Then, an optimization strategy for changing the buoyancy to optimally travel to a set location is constructed. The strategy is based on gradient descent and implemented in Python. Four different definitions of an optimal trajectory to a target location are considered, those are 1) any trajectory that leads to the target location, 2) the most time-efficient trajectory, 3) the most energy-efficient trajectory, and 4) a trajectory that is both time and energy-efficient.
The optimization strategy is tested for five different starting and target locations for a small spherical float in an idealized two-dimensional linear flow field. It is concluded that it is possible to use the optimization strategy to navigate a float using buoyancy changes for all four optimization objectives, although the current implementation is not efficient enough for targets far away.
The first objective of future research should be to increase the coding efficiency. Thereafter, other steps toward a more realistic situation can be taken, such as testing for non-linear flow fields, three-dimensional fields, and bigger floats.

River estuaries are strongly modified by human interventions, such as dredging. For example the Ems river (Germany and Netherlands) has been deepened between in 1965 and 2005. As a result the sediment (sand and dirt) concentration has increased enormously \cite{Ems_data}. The muddiness of this sediment blocks sunlight and decreases the friction of the water with the bed level. The transport of sediment into the river is mainly caused by non-linearity in tidal waves. As a result of the elevation of the bed level and the friction change of the Ems river, the amplitude of the M2 and M4 tide has changed, which was concluded in previous research. In this study the M2 and M4 tide are studied individually, subjected to deepening, widening and friction change. The main research question in this study is '\textit{How does the propagation of the M2 and M4 tide change, subjected to deepening, change in width and change in friction?}' The result to this question can be applied to tidal rivers. To illustrate this, the results are compared to historical data of the Ems river. The sub question in this study is; '\textit{Can historical observations of the amplitude of the M2 and M4 tides in the Ems river over the years be explained with the change in propagation of the M2 and M4 tides, subjected to deepening and friction change?}'.

The questions are answered with help of a model. The model is constructed with the one dimensional water equations, where boundary conditions are used. Next the equations can be used in two cases. In the first case, which is used to answer the main question, the variables width, depth and friction of the river basin are taken to be length independent variables. In the second case, the width, depth and friction of the river basin are taken to be length dependent variables. This second case is used to model the propagation of the M2 and M4 tide for the Ems river. For the first case an analytical and numerical solution exist. From the error, the optimal grid size for the numerical model is obtained, which is taken as $N=100$. For the second case only a numerical solution exists.

With the model it is concluded that widening and an increasing friction cause a damping effect on the propagation of the M2 and M4 tide. Deepening, however, has a different effect on the M2 and M4 tide. It was seen that for certain value change in depth the M2 tide shows an amplification in amplitude, while the M4 tide shows an damping in amplitude for the same value change. The plots obtained in this part of the study can be used to see what is expected to happen to the amplitude of the M2 and M4 tide when a variable is varied in a tidal river basin. The latter is done for the Ems river.


An important observation made with the $x$-dependent model is that the amplification in amplitude from 1965 to 2005 can be explained by the decreased friction, due to increasing muddiness in the Ems river. Secondly, relatively, it was seen that the amplitude of the M4 tide shows a much greater amplification in amplitude at the beginning of the river than the amplitude of the M2 tide. This could be explained by the different change in amplitude of the M2 and M4 tide subjected to deepening, which was concluded from the $x$-independent model as well. However, the difference in M2 and M4 tide between 1965 and 2005 is not due to deepening on its own. Namely, the change in amplitude due to deepening highly depends on the value of the friction, which is different for the years 1965 and 2005. It is concluded that the exact amplitude of the M2 and M4 tide cannot be predicted with the $x$-independent model. However, it is concluded that the results from the $x$-independent model can be used to predict how the M2 and M4 tide will change due to deepening relatively to each other.


The results of this study are strongly influenced by the assumptions made to derive the model. Before the one dimensional, $x$-independent model was compared to the observations for the Ems river between 1965 and 2005 a few decisions had to be made regarding $x$-dependent to $x$-independent variables. This process needs to be further researched, before applying the x-independent model to other tidal rivers, which is left for further research.

Radiometals re-emerge as a promising alternative in nuclear imaging. Cyclotron production of such radiometals using liquid targets solve critical impurity problems seen with current conventional production methods. Purification employing liquid-liquid extraction in microfluidic environments has recently been investigated. Fluid behaviour in microfluidic environments are deeply laminar, and one of the dominant factors in mass transfer in such environments is diffusion. For optimal design, numerical models are being developed to theoretically describe mass transfer in a microfluidic environment. To achieve this, diffusion coefficients of radiometals in their respective liquid target solutions need to be known. Exploiting the laminar flow properties in microfluidics, microfluidic devices have been employed in determining diffusion coefficients. This study presents a simplified 2D theoretical description of mass transfer in single phase flows in microfluidic channels. It has been attempted to verify the proposed model by determining the diffusion coefficient with methylene blue in an aqueous solution for direct comparison with literature. The method was tested for microfluidic devices of varying geometries, different flow rates and alternative setups, and yielded overestimations of a factor of two regarding literature. Consistently finding this overestimation, along with the discovery of several small mistakes in work presented in literature, does not render the method inaccurate. Further research in what range microfluidic devices remain an appropriate tool for determining diffusion coefficients is required. Diffusion coefficients for 68Ga in target solutions of varying concentrations of zinc nitrate, dissolved in aqueous solutions of varying concentrations of nitric acid were investigated. The influence on concentration of nitric acid was minimal, while the diffusion coefficient was found to be inversely proportional to the viscosity of the target solution, in correspondence with the general behaviour of several empirical correlation relations for finding the diffusion coefficient.

FLASH proton therapy is a growing field of research, especially due to its biological benefits in radiation oncology: sparing healthy tissue while delivering the treatment within a millisecond. However, instead of sparing healthy tissue, the conventional FLASH approach, using transmission beams, damages the tissue behind the distal edge of a tumour. Therefore, this approach is less attractive in some clinical applications of FLASH proton therapy. To solve this problem, the use of a ridge filter and patient-specific range compensator, to shift the spread-out Bragg peak (SOBP) of the proton beam to the tumour, is proposed. In this research, the clinical feasibility and acceptability of FLASH-compatible treatment plans, optimized with multiple, Monte Carlo-simulated ridge filter beams, is analysed. An SOBP-database is generated using energy spectrum approximations and interpolations of energy spectra retrieved from Monte Carlo simulations in TOPAS. To obtain optimized FLASH-compatible treatment plans for neuro-oncological targets, this database is implemented in the in-house treatment planning software of the Erasmus Medical Center, iCycle.  The resulting treatment plans show that it is possible to generate FLASH-compatible treatment plans using a ridge filter. A FLASH enhancement ratio between 1.4 and 2.1 would potentially give clinically acceptable plans for the three patients considered. In some optimized plans, the homogeneity of the tumour dose is also increased. A limitation of this research is that configuration of a stable ridge filter beam treatment plan optimizer appears to be challenging. Besides this, the FLASH enhancement ratio and the dose rate are not taken into account to find the regions in the patient where the FLASH conditions (dose > 8 Gy, dose rate > 40 Gy/s and treatment time < 0.1 s) are met.  Recommendations for future research include: implementing the FLASH enhancement ratio and the dose rate optimization in treatment plan optimization; investigating the influence of fractionation ofa FLASH treatment plan on the tumour control and the healthy tissue irradiated; study the relative biological effectiveness (RBE) and the biological character of FLASH radiotherapy, and investigate the clinical potential of a combination of FLASH and non-FLASH treatment.

Radionuclides are important in the diagnosis and treatment of, amongst others, cancer. A promising therapy is targeted radionuclide therapy, where the radionuclide is brought to the tumor by a targeting specific
vector. Bringing the radionuclide directly to the tumor, should reduce the dose to the healthy tissue. For targeted radionuclide therapy, a radionuclide with a high specific activity is required. Some radionuclides,
with promising half-lives and decay energies, are currently not produced with the required specific activity. This problem occurs mainly for radionuclides that are produced via (n,γ) reactions in nuclear reactors. For radionuclides that are produced via this reaction, it is nearly impossible to do a chemical separation between the target material and the produced radionuclide, because these are of the same element. This is why new production routes have to be investigated. In this thesis a feasibility study has been done for a new production method, which should increase the specific activity of radionuclides that are produced via a (n,γ) reaction. For this production method, the target material is labeled with a chelator. Due to the Szilard-Chalmers effect the bond with the chelator will be broken, when the target material is activated by a neutron. This enables the separation of the produced radionuclide from the target complex and therefore, the extraction of the radionuclide. The production method will be loop-based, in order to enable continuous activation of the target material and extraction of the radionuclide. Furthermore, the loop-based design should minimize the effect of radiolysis and relabeling. The loop will be placed close to the reactor core. In this thesis, the elements holmium and lutetium have been used. It has been determined which chelator is most suitable to label with holmium and lutetium. Furthermore, the stability of this complex has been investigated for: higher temperatures, time and the effect of the γ-radiation. The effect of the γ-radiation was determined because this results in radiolysis. The extraction of the radionuclide has also been investigated. These parameters have been used in the calculation of the possible achievable specific activity of 166Ho and 177Lu, when using this loop-based production method. Labeling was possible with the chelator DOTA, which resulted in a stable complex, even for higher temperatures. Labeling happened fast, which also results in fast relabeling. The effect of radiolysis, due to the γ-radiation, was determined by fitting the experimental data. The fit gave negative values for short irradiation times, which is not possible. Therefore, two possible fits were made, which did not give negative results. The first fit was shifted over the y-axis and for the second fit the negative values were assigned to be zero....

Er wordt geschat dat 80% van al het zuurstof op aarde geproduceerd wordt door fytoplankton. Dit is een soort eencellige plant die voorkomen in wateren over de hele wereld. Deze kleine planten worden voornamelijk gegeten door zoöplankton, kleine organismen bestaand uit meestal enkele cellen. Afsterving of overbevolking van fytoplankton heeft ook verregaande gevolgen voor de rest van het maritieme ecosysteem. Fyto- en zoöplankton hebben populaties die een oscillerend patroon kunnen volgen. De groei van de ene beïnvloed het voorkomen van de ander en zo ontstaat een interessante wisselwerking. Er zijn vele modellen die dit gedrag proberen te simuleren om zo inzicht te krijgen in de verschillende patronen die zichtbaar zijn in planktonpopulaties. Een van deze modellen is het model van Steele en Henderson uit 1992. Dat model is echter gemaakt voor wateren zonder ruimtelijke structuren. Om het model van Steele en Henderson ook toe te passen op stromend water in een rivier wordt in dit onderzoek een model beschreven voor planktonpopulaties in rivieren, waarbij de volgende onderzoeksvragen zijn gesteld:
- Welke patronen zijn er te vinden in het model van Steele en Henderson zonder convectie en diffusie?
- Wat is het effect van convectie in een rivier op de uitkomsten van het plankton model van Steele en Henderson?
- Wat is het effect van diffusie in een rivier op de uitkomsten van het plankton model van Steele en Henderson?
- Wat is het effect van convectie én diffusie

In the search for new large-scale battery technologies that are cheap, safe and durable, in this research it is found that the state of the art semi-solid redox flow battery (“SSRFB”) technology shows perspective. Therefore, a novel, cheap and safe aqueous SSRFB design is introduced based on iron- and manganese hydroxide materials. This design was subsequently tested in the lab through which it was concluded that it is not possible to effectively make a SSRFB based on FeOOH and Mn(OH)2 semi-solid electrode (“SSE”) suspensions. Systematic proof is provided on how this can be attributed to the specific combination of the active materials in the highly alkaline environment, but that in itself, both the tested SSRFB configuration and SSE suspensions are functional. On the one hand, a complex chemical system of the active species consisting of multiple thermodynamic equilibria had the consequence that the open circuit voltage (“OCV”) had a very low value of 0.2 V instead of the expected 0.63 V. On the other hand, it was shown that both the FeOOH and the Mn(OH)2 SSE suspension could be separately cycled versus respectively a solid zinc and copper electrode and that a cheap microfiltration membrane suffices in the design of a SSRFB (on the condition that ionic active species are not apparent in the system). In sum, this research demonstrates that the SSRFB by its very nature is a suitable battery technology in which cheap and safe materials can be used for large-scale energy storage. However, that the combination and optimization of the right active materials in the right environment proves to be fundamental for proper operation and is in fact a complex balance between electric and ionic conductivity, colloidal stability, viscosity and (electro)chemical stability.