14 research outputs found
Optical analysis of c-Si quantum dots embedded in a silica matrix
No full textPhotovoltaic Material and Devices GroupElectrical Engineering, Mathematics and Computer Scienc
Scaling and Modelling Photoluminescence of Si Nanoparticles Embedded in Silicon Oxide
No full textSilicon nanoparticles (NPs) embedded in a dielectric matrix, such as silicon oxide, pose a promising candidate for all-silicon multi-junction solar cells. This material is often analysed with photoluminescence (PL) measurements. In literature, the intensities of different PL measurements are either directly compared or normalized. Normalization leads to loss of information, and direct comparison is questionable because of the many factors influencing intensity. In this thesis, a study is performed on PL spectra of Si NPs embedded in intrinsic silicon oxide, fabricated with plasma enhanced chemical vapour deposition. A novel way of scaling PL to the amount Si-Si bonds is proposed, using the phonon modes of a-Si and c-Si. Both the PL spectum and the phonon modes are measured simultaneously with a Raman spectroscope. This method makes comparison of intensities between different measurements possible.Electrical Engineering, Mathematics and Computer ScienceElectrical Sustainable EnergyPhotovoltaic Materials and Devices (PVMD
Upconversion: Kinetics of a model system
No full textPhotochemical upconversion is a process upon which the photons of low energy are converted into photons of higher energy by means of sensitized triplet triplet annihilation. Photochemical upconversion has a potential application in the eld of photovoltaics, where it can signicantly improve the eciency of solar cells by exploiting the energy of near infrared band of solar radiation. In order to design highly ecient chromophores for photochemical upconversion, better understanding of the elementary processes is crucial. Current thesis is an attempt to do so by studying the kinetics and eciency of photochemical upconversion in a model system metal-OEP/DPA utilizing time resolved transient absorption and photoluminescence spectroscopic techniques.Opto-electronic MaterialsChemical EngineeringApplied Science
Bmi1 Is Expressed in Postnatal Myogenic Satellite Cells, Controls Their Maintenance and Plays an Essential Role in Repeated Muscle Regeneration
No full textPMCID: PMC3212532This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Lagrangian sediment transport modelling as a tool for investigating Coastal connectivity
No full textEstuaries and coasts can be conceptualized as connected networks of water and sediment fluxes. These dynamic geomorphic systems are governed by waves, tides, wind, and river input, and evolve according to complex nonlinear transport processes. To predict their evolution, we need to better understand the pathways that sediment takes from source through temporary storage areas to sink. Knowledge of these pathways is essential for predicting the response of such systems to climate change impacts or human interventions (e.g., dredging and nourishment). The conceptual framework of sediment connectivity has the potential to expand our system understanding and address practical coastal management problems (Pearson et al., 2020). Connectivity provides a structured framework for analyzing these sediment pathways, schematizing the system as a series of geomorphic cells or nodes, and the sediment fluxes between those nodes as links (Heckmann et al., 2015). Once organized in this fashion, the resulting network can be expressed algebraically as an adjacency matrix: sediment moving from a given source to different receptors. There is a wealth of pre-existing statistical tools and techniques that can be used to interpret the data once it is in this form, drawing on developments in other scientific disciplines (Newman, 2018; Rubinov & Sporns, 2010). Lagrangian flow networks have been increasingly used to analyze flow and transport pathways in oceanographic and geophysical applications (Padberg-Gehle & Schneide, 2017; Reijnders et al., 2021; Ser-Giacomi et al., 2015). However, this approach has not yet been adopted to analyze coastal or estuarine sediment transport, and requires a multitude of field measurements or numerical model simulations. Lagrangian particle tracking has been widely used to assess connectivity in the context of oceanography and marine ecology (Hufnagl et al., 2016; van Sebille et al., 2018), because the models record the complete history of a particle’s trajectory, not only its start and end points. Particle tracking models are also relatively fast and lend themselves well to parallel computing (Paris et al., 2013). This approach thus permits a faster and more detailed analysis of sediment connectivity than existing Eulerian approaches (e.g., Pearson et al., (2020)). Although several Lagrangian sediment transport models have been developed (e.g., (MacDonald & Davies, 2007; Soulsby et al., 2011)), they have not been used to support connectivity studies. Hence, there is a need for Lagrangian sediment particle tracking tools tailored to predicting sediment transport pathways and determining connectivity of complex coastal systems. To meet this need, we developed a Lagrangian sediment transport model, SedTRAILS (Sediment TRAnsport vIsualization & Lagrangian Simulator) and used it to develop a sediment connectivity network. Our approach provides new analytical techniques for distilling relevant patterns from the chaotic, spaghetti-like network of sediment pathways that often characterize estuarine and coastal systems. We demonstrate a proof of concept for our approach by applying it to a case using these tools
Photochemical upconversion in metal-based octaethyl porphyrin-diphenylanthracene systems
No full textThis paper studies photochemical upconversion in solutions of octaethyl porphyrin (OEP) and diphenyl anthracene (DPA). The system has been widely used as a standard model system in the field of photochemical upconversion. Although, the kinetics of elementary processes contributing to photochemical upconversion in it have been extensively studied, there has been no research on the efficiency of upconversion in the system, despite of the fact that this parameter is detrimental for potential applications of photochemical upconversion process. We determine the yield of photochemical upconversion in a number of metal based OEP/DPA systems. Additionally, we studied the dependence of kinetic, and efficiency parameters of the process on the core metal of the porphyrin. We showed that the overall efficiency of photochemical upconversion depends significantly on the core metal of the triplet sensitizer porphyrin molecule. We attribute this effect to the differences in efficiency of triplet energy transfer from metal based OEP to DPA depending on the core metal.ChemE/Opto-electronic MaterialsPhotovoltaic Materials and Device
Lagrangian ocean analysis: Fundamentals and practices
No full textLagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.Accepted Author ManuscriptMathematical Physic
Wet-chemical Treatment for Improved Surface Passivation of Textured Silicon Heterojunction Solar Cells
No full textSilicon heterojunction (SHJ) solar cells constantly gain more attention due to their low cost and relatively high efficiency. An important aspect of these solar cells is the incorporation of intrinsic hydrogenated amorphous silicon (a-Si:H) layers at each side of the c-Si wafer, which has increased the efficiency potential due to the excellent surface passivation. By applying a randomly textured instead of a double-side polished wafer, optical enhancement is achieved resulting in significant reflection reduction and high short-circuit current densities (Jsc). However, texturing-induced defects lead to an a-Si:H/c-Si interface with increased recombination, which limits the open circuit voltage (Voc) of the SHJ device after using the same cleaning treatment as for the flat wafer. Thus, a one-to-one transfer of process parameters from flat to textured c-Si substrate is not necessarily appropriate and a different wet-chemical treatment is needed. In this work, a chemical treatment is demonstrated, which leads to an improved surface passivation.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Optimizing Silicon Oxide Embedded Silicon Nanocrystal Inter-particle Distances
No full textWe demonstrate an analytical method to optimize the stoichiometry and thickness of multilayer silicon oxide films in order to achieve the highest density of non-touching and closely spaced silicon nanocrystals after annealing. The probability of a nanocrystal nearest-neighbor distance within a limited range is calculated using the stoichiometry of the as-deposited film and the crystallinity of the annealed film as input parameters. Multiplying this probability with the nanocrystal density results in the density of non-touching and closely spaced silicon nanocrystals. This method can be used to estimate the best as-deposited stoichiometry in order to achieve optimal nanocrystal density and spacing after a subsequent annealing step.Photovoltaic Materials and DevicesQN/Zandbergen LabElectrical Sustainable Energ
