7,176 research outputs found

    Integrated Geophysical Analysis of Passive Continental Margins: Insights into the Crustal Structure of the Namibian Margin from Magnetotelluric, Gravity, and Seismic Data

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    Passive continental margin research amalgamates the investigation of many broad topics, such as the emergence of oceanic crust, lithospheric stress patterns and plume-lithosphere interaction, reservoir potential, methane cycle, and general global geodynamics. Central tasks in this field of research are geophysical investigations of the structure, composition, and dynamic of the passive margin crust and upper mantle. A key practice to improve geophysical models and their interpretation, is the integrated analysis of multiple data, or the integration of complementary models and data. In this thesis, I compare four different inversion results based on data from the Namibian passive continental margin. These are a) a single method MT inversion; b) constrained inversion of MT data, cross-gradient coupled with a fixed structural density model; c) cross-gradient coupled joint inversion of MT and satellite gravity data; d) constrained inversion of MT data, cross-gradient coupled with a fixed gradient velocity model. To bridge the formal analysis of geophysical models with geological interpretations, I define a link between the physical parameter models and geological units. Therefore, the results from the joint MT and gravity inversion (c) are correlated through a user-unbiased clustering analysis. This clustering analysis results in a distinct difference in the signature of the transitional crust south of- and along the supposed hot-spot track Walvis Ridge. I ascribe this contrast to an increase in magmatic activity above the volcanic center along Walvis Ridge. Furthermore, the analysis helps to clearly identify areas of interlayered massive, and weathered volcanic flows, which are usually only identified in reflection seismic studies as seaward dipping reflectors. Lastly, the clustering helps to differentiate two types of sediment cover. Namely, one of near-shore, thick, clastic sediments, and one of further offshore located, more biogenic, marine sediments

    Analog Photonics Computing for Information Processing, Inference and Optimisation

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    This review presents an overview of the current state-of-the-art in photonics computing, which leverages photons, photons coupled with matter, and optics-related technologies for effective and efficient computational purposes. It covers the history and development of photonics computing and modern analogue computing platforms and architectures, focusing on optimization tasks and neural network implementations. The authors examine special-purpose optimizers, mathematical descriptions of photonics optimizers, and their various interconnections. Disparate applications are discussed, including direct encoding, logistics, finance, phase retrieval, machine learning, neural networks, probabilistic graphical models, and image processing, among many others. The main directions of technological advancement and associated challenges in photonics computing are explored, along with an assessment of its efficiency. Finally, the paper discusses prospects and the field of optical quantum computing, providing insights into the potential applications of this technology.Comment: Invited submission by Journal of Advanced Quantum Technologies; accepted version 5/06/202

    ICEBEAR-3D: An Advanced Low Elevation Angle Auroral E region Imaging Radar

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    The Ionospheric Continuous-wave E region Bistatic Experimental Auroral Radar (ICEBEAR) is an auroral E~region radar which has operated from 7 December 2017 until the September 2019. During the first two years of operation, ICEBEAR was only capable of spatially locating E~region scatter and meteor trail targets in range and azimuth. Elevation angles were not determinable due to its East-West uniform linear receiving antenna array. Measuring elevation angles of targets when viewing from low elevation angles with radar interferometers has been a long standing problem. Past high latitude radars have attempted to obtain elevation angles of E~region targets using North-South baselines, but have always resulted in erroneous elevation angles being measured in the low elevation regime (0° to ≈30° above the horizon), leaving interesting scientific questions about scatter altitudes in the auroral E~region unanswered. The work entailed in this thesis encompasses the design of the ICEBEAR-3D system for the acquisition of these important elevation angles. The receiver antenna array was redesigned using a custom phase error minimization and stochastic antenna location perturbation technique, which produces phase tolerant receiver antenna arrays. The resulting 45-baseline sparse non-uniform coplanar T-shaped array was designed for aperture synthesis radar imaging. Conventional aperture synthesis radar imaging techniques assume point-like incoherent targets and image using a Cartesian basis over a narrow field of view. These methods are incompatible with horizon pointing E~region radars such as ICEBEAR. Instead, radar targets were imaged using the Suppressed Spherical Wave Harmonic Transform (Suppressed-SWHT) technique. This imaging method uses precalculated spherical harmonic coefficient matrices to transform the visibilities to brightness maps by direct matrix multiplication. The under sampled image domain artefacts (dirty beam) were suppressed by the products of differing harmonic order brightness maps. From the images, elevation and azimuth angles of arrival were obtained. Due to the excellent phase tolerance of ICEBEAR new light was shed on the long standing low elevation angle problem. This led to the development of the proper phase reference vertical interferometry geometry, which allowed horizon pointing radar interferometers to unambiguously measure elevation angles near the horizon. Ultimately resulting in accurate elevation angles from zenith to horizon

    The Forward Physics Facility at the High-Luminosity LHC

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    Electromagnetic scattering by lossy plasmonic and non-plasmonic half-spaces from vertically polarized incident waves

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    In this research, approximate analytical solutions for the scattered electromagnetic (EM) fields radiated by a vertical electric dipole (VED) antenna in the presence of a lossy half-space for ordinary and plasmonic media are investigated. First, an approximate analytical solution for the wave scattering above a lossy half-space with a smooth interface is proposed for frequencies below the very high frequency (VHF) band. The solution to the problem is given in terms of two-dimensional Fourier transforms, which leads to Sommerfeld-type integrals. The solution is decomposed into three terms. Two terms are expressed with hyperbolic functions and the third term is presented using the Gauss error function. A numerical evaluation of the integrals validates the accuracy and efficiency of the proposed solution at various frequencies and distances from the source. Second, an approximate analytical solution of the problem with a smooth interface is proposed for frequencies below 10 GHz. The solution for the intermediate Hertz potential is decomposed into two integrals and a rigorous approximate closed-form solution in the near and far field regions is presented for each term. Then, the scattered electric field (E-field) components are calculated from the intermediate Hertz potential. A numerical evaluation of the solution for different lossy half-spaces, i.e., seawater, wet earth, dry earth and lake water, validates the accuracy of the proposed solution at various frequencies and distances from the antenna. Following this work, a new asymptotic solution for the scattered EM fields above a lossy half-space with a smooth interface for ordinary and plasmonic media is proposed using the modified saddle point method. The new formulations are applied to calculate radiation patterns of different impedance half- planes for both ordinary media (e.g., seawater, silty clay soil, silty loam soil and lake water) and plasmonic media (e.g., silver and gold). A numerical evaluation of the proposed solution at various frequencies and comparisons with two alternative state- of-the-art solutions show that the proposed solution has higher accuracy for plasmonic and non-plasmonic structures. Lastly, random roughness is added to the interface, and a solution for EM scattering over a two-dimensional random rough surface with large roughness height using the generalized functions approach is proposed. The EM field derivation incorporates an arbitrary rough surface profile with small slope, a radiation source and involves all scattering orders of the scattered E-field for high and moderate contrast media. Subsequently, the first-order scattered E-field is calculated using the Neumann series solution for transverse magnetic (TM) polarization. By considering a pulsed dipole antenna and a two-dimensional Gaussian rough surface distribution with different root mean square heights and correlation lengths, the scattered E-field along with the radar cross-section is calculated. Using the result of the method of moments (MoM) as reference, a numerical evaluation of the solution for different roughness heights and contrast media demonstrates that the proposed solution is better than those of the small perturbation method (SPM), Kirchhoff approximation (KA) and small-slope approximation (SSA)

    Infrared Spectroelectrochemical Studies of Redox-Active Self Assembled Monolayers: Structure and Kinetics

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    Long-range bridge-mediated electron transfer proceeding through outer-sphere pathways attracts scientific interest beyond fundamental studies due to its relevance in technological systems like molecular electronics and biosensors. Deep knowledge of the structure and dynamics of these molecular interfaces and the kinetics of the electron transfer processes are critical to improving the performance of such technological systems. Interfacial charge transfer between the electrode and redox molecules can be manipulated as an outer sphere electron transfer process by employing organic molecules as bridging moieties between the electron donor and acceptor. Electrode surfaces can be made suitable for charge transfer studies via the self assembled monolayers (SAMs) of redox-substituted alkanethiols. Alternatively, redox species can be covalently tethered to the terminals of preformed monolayers of alkane chains. Electroactive surfaces prepared via both methodologies are explored for studying heterogeneous electron transfer (ET) processes using conventional electrochemical techniques such as cyclic voltammetry and chronocoulometry. Butler-Volmer (BV) formalism and Marcus-Hush-Chidsey (MHC) theory are some of the widely accepted models to predict the kinetic parameters of electron transfer processes. In-situ surface characterization techniques such as surface-enhanced infrared absorption spectroscopy (SEIRAS) offer the potential to provide deeper insights into molecular processes occurring in organized systems during electron transfer. Time-resolved SEIRAS technique is an advanced method capable of correlating structural changes in both the redox-active moiety and the scaffold supporting the redox centre preceding/during/following the electron transfer process. This thesis reports a combination of time-resolved SEIRAS with conventional electrochemistry techniques to study the electron transfer process across different electroactive layers. The time-resolved SEIRAS technique is applied here to follow the molecular restructuring of alkane-bridging moieties during the electron transfer process in ferrocene-SAM systems. The behaviour of surrounding SAM structures to the redox moieties during the electron transfer process is also explored using deuterated alkanethiols as diluents. An amide-coupling reaction is explored to link electroactive moieties to prefabricated alkanethiol SAM terminals. Studying the reaction mechanism of the amide-coupling process offers an opportunity to improve the reaction efficiency. Therefore, the potential of electrochemical-SEIRAS has been leveraged to monitor the amide-coupling process on the monolayers under various reaction conditions. SEIRAS analysis identified that the reaction intermediates change their rate of formation under the electrode potential control, which establishes proof for potential-dependent reaction pathways for amide-coupling reactions. Another redox species studied in this body of research is 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO ̇ ), a prominent organic free radical used as a catalyst in various industrial-scale processes. Electron transfer studies of TEMPO ̇ tethered to various lengths of alkanethiols are reported in this thesis using conventional electrochemical techniques. Time-resolved SEIRAS studies of TEMPO ̇ -alkanethiol monolayers for structural and kinetic analysis are reported here for the first time. The SEIRAS analysis provides a molecular model showing the conformational change of TEMPO ̇ moieties along with structural reorientation of the alkane chain adlayers during the electron transfer process

    Crashworthiness Optimization using difference-based equivalent static Loads - Sizing and Topology Optimization of Structures subjected to Crash

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    Structural optimization of crash related problems usually involves nonlinearities in geometry, material, and contact. For such kinds of problems, the sensitivities are either not available or very expensive to compute. Efficient gradient-based optimizers can then not be employed directly. The Difference-based Equivalent Static Load (DiESL) method provides a procedure to circumvent the sensitivity calculation of the original nonlinear dynamic problem by creating linear auxiliary load cases enabling gradient-based optimization. Each linear auxiliary load case then represents one specific time step of the original nonlinear dynamic problem. In this thesis various extensions of the DiESL method are presented and the method is compared to several other relevant approaches in this field. It is demonstrated how an appropriate selection of the time steps in each cycle can improve the DiESL method's approximation quality. For this purpose, the time steps are selected adaptively such that an appropriate curve, indicating the structure's nonlinear behavior, is fitted by the selected time steps. It turns out that this leads to better optimization results and more reliable convergence behavior. The DiESL method also enables the adaption of path-dependent structural properties of the original nonlinear dynamic problem like material stiffness in each linear auxiliary load case. In this thesis, an adaption of the Young’s modulus and Poisson's ratio on element level in the linear auxiliary load cases corresponding to the local plasticization in the nonlinear dynamic problem is tested. Therefore, a bilinear material model is employed in the auxiliary load cases. Here, the test examples indicate that an observable improvement can only be obtained if the material of the nonlinear dynamic problem is also idealized bilinearily and the portion of elements in the elastic and the plastic range is balanced such that the structure’s behavior is not dominated by one of both. Crashworthiness design usually involves two contradictory objectives: the structure's stiffness as well as its energy absorption behavior. To be able to address the latter, an approach for handling crash forces with the DiESL method is developed and tested using sizing optimization examples. The respective results are validated by comparing them to the theoretically known optimum or other state of the art methods. Moreover, the DiESL method is extended to topology optimization utilizing the Solid Isotropic Material with Penalization approach (SIMP). The method is tested using three examples. The first is a rigid pole colliding with a simple beam structure, where the intrusion of the pole is minimized. The initial velocity of the pole is varied in order to examine the influence of inertia effects on the optimized structures. It is shown that the results differ significantly depending on the chosen initial velocity and, consequently, that they exhibit inertia effects. Moreover, considerable improvement in terms of the resulting objective function's value could be achieved employing the DiESL method when compared with the standard ESL method for high initial velocities. The second example is an extruded rocker colliding with a rigid pole, where also the intrusion of the pole is minimized. The DiESL method yields equally good results as the Graph and Heuristic Topology optimization (GHT) approach does. However, the number of nonlinear analyses necessary to achieve convergence is significantly smaller when using the DiESL method. Finally, a rail reinforced by an additive manufactured rib is optimized. Here, several optimization runs are executed. The reaction force is maximized, while the mass of the rib is constrained to various fractions of the original rib's mass. This formulation aims to find designs where the original rib's mass and thus the related production cycle time is reduced, while its stiffness is almost maintained. In doing so a mass reduction of 30% could be achieved

    Digital materials design of solid oxide fuel cell anodes

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    This PhD-Thesis was presented to the Faculty of Science and Medicine of the University of Fribourg (Switzerland) in consideration for the award of the academic grade of Doctor of Philosophy in Physics (Thesis No: 5369). The doctorate was mainly pursued at the Institute of Computational Physics ICP at Zurich University of Applied Sciences ZHAW in Winterthur, Switzerland PhD Presentation: https://zhaw.mediaspace.cast.switch.ch/mediashare/d430305eb29a01af/media/t/0_8py1hjfn GeoDict User Meeting 2021 Presentation: https://www.youtube.com/watch?v=AIROVKq5yocThe storage and efficient conversion of energy is one of the key issues for a successful transition to renewable energies. Solid oxide cell (SOC) technology is a promising solution for the conversion of electrical energy to storable chemical energy (power-to-gas) in the solid oxide electrolysis cell (SOEC) mode, and for the on-demand supply of electrical energy using synthetic gas or biogas (or natural gas) as input in the solid oxide fuel cell (SOFC) mode. To significantly improve on the unavoidable degradation of state-of-the-art anodes like Ni-YSZ, we elaborate on new nickel-free electrode concepts, which are based on mixed ionic and electronic conductors (MIEC) like doped ceria and perovskite (e.g., titanate) materials. However, the anode performance is governed by complex physico-chemical processes including transport of gas in the pores, transport of ions and electrons in both solid phases and fuel oxidation reaction on the surface of the MIECs, which are not yet fully understood. Hence, there are numerous conflicting requirements and lack of knowledge complicating the development and optimization process. These challenges are addressed in this thesis in two ways. First, a Digital Materials Design (DMD) framework for the systematic and model-based optimization of MIEC SOC-electrodes is elaborated. In our DMD approach we combine stochastic microstructure modeling, virtual testing of 3D microstructures and a multiscale-multiphysics electrode model to explore the available design space by performing parametric studies. The basis for the DMD process is a set of fabricated solid oxide cells. Their real microstructures are reconstructed using FIB-SEM tomography. Stochastic digital microstructure twins with matching microstructure properties are then constructed for each real structure using a pluri-Gaussian method. On that basis, the microstructure can be virtually varied for a large parameter space in a realistic way. The real and subsequently the virtual 3D structures need to be characterized quantitatively by means of image analysis and numerical simulations. Hence, a standardized and automated microstructure characterization has been developed, which enables the fast determination of an extensive set of microstructure properties relevant for SOC electrodes. Moreover, specific microstructure properties like the ‘composite conductivity’ crucial for novel composite MIEC electrodes are introduced and discussed. A multiphysics continuum simulation model is then used to predict the impact of the microstructure variation on the electrode performance, using the previously determined microstructure properties as an input. In addition, the kinetic reaction parameters of the model are calibrated to the experimental performance characterizations of the cells (e.g., EIS results). This model-based performance prediction enables to establish the relationship between materials choices and compositions, fabrication parameters, microstructure properties and cell-performance. Due to the integration of stochastic modeling (pluri-Gaussian method) and its combination with automated characterization and model-based performance prediction, the number of the involved 3D microstructures can be significantly increased. This approach is thus capable to explore a much larger design space than it would be possible with experimental methods only. On this basis, design guidelines for the fabrication of electrodes with improved performances can be provided, which closes the loop of this iterative workflow. This DMD workflow is made available for the research community by the release of two software apps for the standardized microstructure characterization and stochastic microstructure modeling for SOC electrodes. Detailed information on these methodologies is also provided by the corresponding publications. Second, this DMD workflow is applied for the optimization of titanate based LSCT-CGO SOFC-anodes with a noble metal catalyst impregnation. Based on the performance and microstructure characterization of fabricated cells, several DMD studies are performed. Thereof, design guidelines for titanate-CGO anodes are provided including different microstructure design concepts and parameter specifications like appropriate material compositions and porosity. Moreover, the new opportunities as well as the current limitations of these nickel-free electrodes are discussed in great detail

    The Impact of Heterogenous Cell Populations on Impedance-Based Cell Analysis

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    Many in vitro studies for drug development are based on population-averaging measurement techniques without giving information about cell-to-cell variability within the cell ensembles under study. However, such heterogeneities in cell cultures are omnipresent and can arise by several causes, like spontaneous genetic mutations, different metabolic situations or different cell cycle states of individual cells. Moreover, microenvironmental conditions, like cell crowding, might force cell ensembles to form subpopulations with distinct characteristics. Therefore, single phenotypically different subpopulations may be overseen or averaged responses across different subpopulations might not reflect the majority of the cells, leading to misinterpretations of data – one possible reason for the high failure rate in clinical trials. This thesis addressed the fundamental question of how cell-to-cell variability in populations influence the signal of population-based assays by using three different approaches. The first project addressed the impact of evenly distributed heterogeneities within cell populations, introduced by mixing a cell line expressing a certain G protein-coupled receptor (GPCR) with a cell line not expressing this receptor type, on the impedance-based cell analysis. The second project focused on the development of an impedance-based assay for the future purpose of spatiotemporally introducing heterogeneities in an isogenic cell population, expressing a certain GPCR, by switching an appropriate, photochromic ligand by illumination. The third project addressed the quantification of the impact of heterogeneities within cell populations on the impedance-based cell analysis in a theoretical manner. The first project focused on the impact of cell-to-cell variability on the population-based impedance signal by mixing cell lines in different ratios prior to the seeding onto the co-planar gold electrodes. The evenly distributed heterogeneities in the resulting cell populations were generated by co-culturing two cell lines with one of them expressing a GPCR predominantly coupled to one of the three main canonical G-protein pathways (Gq, Gs, Gi/o). A protocol was established to obtain co-cultures with distinct cell ratios resulting in well-defined areal receptor densities (ARD) as verified by supported microscopic staining studies. The stimulation of cell ensembles with varying ARD by the GPCR's endogenous ligands was analyzed in detail by wholistic impedance-based cell assays. Efficacies and potencies, which describe the maximal agonist effect and the activity of a drug, were compared to those of the pure and original cell lines. It was shown that both parameters were dependent on the ARD and the coupled signaling cascades in distinct ways: for the Gq pathway, efficacy decreased non-linearly with decreasing ARD, while the Gs- and Gi/o-pathways exhibited an almost linear dependency of efficacy on the ARD. The potencies observed for the Gq- and Gi/o-coupled signaling pathway decreased with decreasing ARD, while the potency of the Gs-pathway was almost independent of the ARD. Simple simulations indicated that underlying communication processes between stimulated and non-stimulated cells within the populations under study may be responsible for these trends. Additionally, two proximal assay techniques were used to assist the interpretation of impedance analysis and to assign the impact of the ARD on the signal to a certain part of the signaling cascade. The radioligand competition binding assay confirmed the correct co-culturing strategy for such heterogeneous cell populations and confirmed the corresponding potency to be independent of the population composition. Population-based Ca2+ imaging highlighted the impact of altering the ARD on second messenger mobilization. Again, the ARD did not affect the potency, but the analysis of the response on a single-cell level proposed cell communication as a potential mechanism explaining the dependency of impedance on ARD. Moreover, the stimulation of a co-culture, consisting of two GPCR-expressing cell lines, was analyzed impedimetrically. The outcomes indicated that the potency dependency on the ARD was caused by the simultaneous activation of two different signaling pathways. The obtained data confirmed that the impact of artificially introduced heterogeneities in the cell population under study on the obtained impedance signal was indeed significant. Nevertheless, it remains elusive, whether these results can be translated to other cell lines or other GPCRs. This project addressed the fundamental question of areal heterogeneities influencing the impedance signal. However, further studies on cell ensembles with different compositions and other measurement techniques have to be carried out to obtain a broader picture of such impacts on population-based measurements and its significance for the drug development process. In the second project of this thesis, an assay was developed for the future purpose of introducing cell-to-cell variability within isogenic cell populations by spatiotemporal illumination of photochromic GPCR-ligands, which can be toggled between their bioactive and -inactive isomer. Thus, it was required to establish a protocol to active in situ such a ligand by online irradiation with light and to monitor the cell responses in a time-resolved manner. The wholistic impedance-based cell assay was appropriate to monitor the in situ toggling of a model photoswitchable ligand for a Gq-coupled receptor. To accomplish the superordinate goal, it will be necessary to establish a measurement setup, which is capable of spatiotemporal illumination of the cell culture, so that a small subpopulation can be stimulated in a spatiotemporally well-defined manner after the systemic addition of the bioinactive species of a photoswitchable ligand. The third part of this thesis addressed the impact of heterogeneous cell populations on the impedance readout by theoretical means. For this purpose, a MATLAB-based algorithm was developed, capable of simulating different cell types following the electric cell-substrate impedance sensing (ECIS) model. In contrast to the conventional mode, which assumes global cell-related parameters (α for the cell-substrate contacts, Rb for the cell-cell contacts, Cm for the cell membrane capacitances) for the whole population, the new approach emulated cell populations by cell-related parameters, each showing a Gaussian distribution with a mean and a deviation value. After successful validation of the underlying algorithm, discrepancies from the ECIS model using global parameters were found for such populations with heterogeneous cell-related parameters for three distinct cell types, emulating leaky, moderately tight, and tight cells. Especially the deviation of the Gaussian-distributed parameters α and Rb had a big impact on the spectra. In direct comparison to the reference, which was a homogenous cell population with global parameter values being equal to the mean values of the Gaussian distribution, a systematical misestimation could be found for α (up to 110 % of the reference value) and underestimation for Rb (down to 78 % of the reference value) when the deviation values were set to 30 % of the mean values. In contrast, Cm was found to be very robust for deviations up to 30 % (100 % of the reference value). In summary, the thesis has demonstrated in an experimental and theoretical manner that cell-to-cell variability has indeed major impacts on the population-based impedance signal, having the potential to misdirect data interpretation. These can affect fundamental as well as pharmacological research. Thus, it is crucial to address such heterogeneities within cell populations in future studies using population- as well as single-cell-based assay techniques
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