172 research outputs found
Author Correction: New perspectives on Neanderthal dispersal and turnover from Stajnia Cave (Poland)
Get PDFThe Author contributions section now reads:“W.N., A.N. and S.T. designed research; A.P., M.H., W.N., S.B., M.U., A.M., H.F., M.D.B., P.S., K.S., M.Ż., A.W., A.N. and S.T. performed research; A.P., M.H., W.N., S.B., M.U., A.M., H.F., M.D.B., P.S., K.S., M.Ż., A.W., A.N. and S.T. analysed data; A.P., M.H., S.T., W.N. and S.B. wrote the paper with the collaboration of all the co-authors.
Measurement system analysis for categorical measurements: agreement and kappa type indices
Get PDFTitle Measurement system analysis for categorical data: Agreement and kappa-type indices Author(s) J. de Mast, W.N. extern van Wieringe
Author Correction:A 41,500 year-old decorated ivory pendant from Stajnia Cave (Poland)
No full textCorrection to: Scientific Reports https://doi.org/10.1038/s41598-021-01221-6, published online 25 November 2021The original version of this Article contained errors in the author list where Marjolein D. Bosch was omitted from the author list, and Mikołaj Urbanowski was incorrectly listed as an author of the original Article, and has subsequently been removed.The Author contributions section now reads:“S.T. W.N. and A.N. conceived the project; S.T., W.N., A.P., M.B., S.C., M.D., H.F., A.M., M.D. B., D.P., M.P.R., C.M.R., V.S-M., G.M.S., P.S., M.S., K.S., A.V., F.W., H.W., A.W., M.Z., S.B., A.N., J-J. H., performed research; S.T., A.P., W.N., M.B., M.D.B., S.C., M.D., H.F., A.M., D.P., M.P.R., C.M.R., V.S-M., G.M.S., P.S., M.S., K.S., A.V., F.W., H.W., A.W., M.Z., S.B., A.N., J-J. H. analysed all archaeological data; S.T. and A.P. wrote the paper with the collaboration of all the co-authors.”The original Article and its accompanying Supplementary Information file have been corrected
The political economy of hedge fund regulation
Get PDFThe currency crises and episodes of market unrest of the 1990s sparked a series of regulatory initiatives to reform the Global Financial Architecture. One of these initiatives tackled the activities of hedge funds, a type of investment vehicle that was frequently cited as one of the causes of these crises. The key research question of this thesis is why efforts to regulate an apparently destabilising aspect of financial markets failed, despite the setting up of an ad hoc forum at the international level (the Financial Stability Forum) and various domestic initiatives in the US, the country where most hedge funds operate.
The thesis develops a theoretical framework that examines this regulatory inaction through three explanatory models. The first model draws upon mainstream economic accounts and argues that the empirical evidence did not justify more interventionist public regulation of hedge funds. The second model assumes that a form of relational power has been exercised at the regulatory table: those actors with an interest in leaving hedge funds unregulated prevailed over those that favoured a more mandatory approach. The third model argues that it was not just relational power that determined outcomes, but mainly the power of the structure of meaning within which discussions took place and problems were framed. This structure of meaning led to a particular formulation of the problem at stake, which excluded other concerns and actors from the regulatory agenda.
Each model is analysed for its policy implications. The first model leads to regulatory solutions that rely upon private actors' due diligence and self-assessment of risk. The second model leads to policy options that favour a greater inclusion of developing countries and other stakeholder groups in decision-making processes in global finance. The third model leads to a rethinking of the very tenets of financial market regulation and of the financial theories used to explain and govern the market. The thesis argues that the third model is better able to grasp the complexity of power beyond the seemingly technical nature of financial regulation. For this reason, it is deemed more suitable to provide policy solutions that challenge the current neo-liberal framework of regulation
On the principles, assumptions and methods of geodetic very long baseline interferometry
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On the "great circle reduction" in the data analysis for the astrometric satellite Hipparcos
No full textCivil Engineering and Geoscience
Hydrothermal Synthesis and Characterization of 3R Polytypes of Mg-Al Layered Double Hydroxides
No full textLayered Double Hydroxides (LDH) is a unique group of clays that have an anionic exchange capability. This research explored the hydrothermal method as an alternative method to synthesize Mg-Al LDH. It is a simple and more environmentally friendly compared to the conventional method of co-precipitation. Furthermore, depending on the synthesis condition, two different polytypes, namely 3R1 and 3R2 can be synthesized. The first part of the research was focused on the optimization of the hydrothermal synthesis. Various pre-treatment techniques of the reactants were investigated. The use of a microwave system as an alternative energy source resulted in the formation of a unique donut-shaped crystal which provides enlargement of the specific surface area of the {hk0} faces, needed for adsorption application. The growth mechanism of such donut-like crystals is studied by AFM as well as by STEM-EDX. The interrelation of polytype 3R1 and 3R2 along with the chemical composition and structure of polytype 3R2 is addressed in the second part. The transition temperature is approximately at 110 ºC with 3R1 being stabile at lower temperatures and 3R2 at higher temperatures. Polytype 3R2 was also found to have more aluminum content compared to 3R1. The excess aluminium is the presence as tetrahedrally coordinated aluminate ion located in the interlayer as charge compensation. The apical oxygen of the aluminate is grafted onto the octahedral metal layer, inducing the formation of 3R2 stacking. This grafted structure might explain the reluctance of polytype 3R2 to be ion exchanged compared to 3R1.Process and EnergyMechanical, Maritime and Materials Engineerin
Quantification of Modelling Uncertainties in Turbulent Flow Simulations
No full textThe goal of this thesis is to make predictive simulations with Reynolds-Averaged Navier-Stokes (RANS) turbulence models, i.e. simulations with a systematic treatment of model and data uncertainties and their propagation through a computational model to produce predictions of quantities of interest with quantified uncertainty. To do so, we make use of the robust Bayesian statistical framework, in which the uncertainty is represented by probability. The first step toward our goal concerned obtaining estimates for the error in RANS simulations based on the Launder-Sharma k-e turbulence closure model, for a limited class of flows. In particular we searched for estimates grounded in uncertainties in the space of model closure coefficients, for wall-bounded flows at a variety of favourable and adverse pressure gradients. In order to estimate the spread of closure coefficients which reproduces these flows accurately, we performed 13 separate Bayesian calibrations. Each calibration was at a different pressure gradient, using measured boundary-layer velocity profiles, and a statistical model containing a multiplicative model inadequacy term in the solution space. The results are 13 joint posterior distributions over coefficients and hyper-parameters. To summarize this information we compute Highest Posterior-Density (HPD) intervals, and subsequently represent the total solution uncertainty with a probability box (p-box). This p-box represents both parameter variability across flows, and epistemic uncertainty within each calibration. A prediction of a new boundary-layer flow is made with uncertainty bars generated from this uncertainty information, and the resulting error estimate is shown to be consistent with measurement data. However, although consistent with the data, the obtained error estimates were very large. This is due to the fact that a p-box constitutes a unweighted prediction, essentially saying that every posterior distribution is equally applicable to the predictive scenario at hand, which is unlikely to be an accurate assumption. To improve upon this, we developed another approach still based on variability in model closure coefficients across multiple flow scenarios, but also across multiple closure models. The variability is again estimated using Bayesian calibration against experimental data for each scenario, but now Bayesian Model-Scenario Averaging (BMSA) is used to collate the resulting posteriors in an unmeasured (prediction) scenario. Unlike the p-boxes, this is a weighted approach involving turbulence model probabilities which are determined from the calibration data. Furthermore, BMSA incorporates scenario probabilities which are chosen using a sensor which automatically weights those scenarios in the calibration set which are similar to the prediction scenario. The methodology was applied to the class of turbulent boundary-layers subject to various pressure gradients. For all considered prediction scenarios the standard-deviation of the stochastic estimate is consistent with the measurement ground truth. Furthermore, the mean of the estimate is more consistently accurate than the individual model predictions. The BMSA approach results in reasonable error bars, which can also be decomposed into separate contributions due to coefficient uncertainty, model inadequacy and variability of posteriors over different scenarios. However, to apply it to more complex topologies outside the class of boundary-layer flows, surrogate modelling techniques must be applied. The Simplex-Stochastic Collocation (SSC) method is a robust surrogate modelling technique used to propagate uncertain input distributions through a computer code. However, its use of the Delaunay triangulation can become prohibitively expensive for problems with dimensions higher than 5. We therefore investigated means to improve upon this bad scalability. In order to do so, we first proposed an alternative interpolation stencil technique based upon the Set-Covering problem, which resulted in a significant speed up when sampling the full-dimensional stochastic space. Secondly, we integrated the SSC method into the High-Dimensional Model-Reduction framework in order to avoid sampling high-dimensional spaces all together. Finally, with the use of our efficient surrogate modelling technique, we applied the BMSA framework to the transonic flow over an airfoil. With this we are able to make predictive simulations of computationally expensive flow problems with quantified uncertainty due to various imperfections in the turbulence models.AerodynamicsAerospace Engineerin
Fabrieksschema: Argonwinning uit lucht
No full textDocument(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science
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