TU Delft Repository

    Hidden information in ill-posed inverse problems

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    It is well known that parameter updating of large-scale numerical reservoir flow models (a.k.a. ‘computer assisted history matching’) is an ill-posed inverse problem. Typically the number of uncertain parameters in a reservoir flow model is very large whereas the available information for estimating these parameters is limited. The classic solution to this problem is to regularize the unknowns, e.g. by penalizing deviations from a prior model. Attempts to estimate all uncertain parameters from production data without regularization typically lead to unrealistically high parameter values and therefore to updated parameter fields that have little or no geological realism. However, it has been suggested that the application of unregularized reservoir parameter estimation may still add value, because it, sometimes, gives an indication of the location of significant missing features in the model. We investigated under which conditions this perceived added value might occur. We conducted several twin experiments and applied unregularized parameter estimation to update uncertain parameters in a simple two-dimensional reservoir model that contained a major deficiency in the form of a missing high or low permeability feature. We found that in case of low-permeability barriers or high-permeability streaks it is indeed sometimes possible to localize the position of the model deficiency. To further analyze this behavior we conducted onedimensional experiments using a transfer function formalism to characterize the identifiability of the location and magnitude of model deficiencies (flow barriers).Geoscience and EngineeringCivil Engineering and Geoscience

    The sweetness of discomfort: Designing the journey

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    Industrial DesignIndustrial Design Engineerin

    Evaluation of innovative land tools in sub-Saharan Africa: Three cases from a peri-urban context

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    Sub-Saharan Africa is urbanizing rapidly, but most countries lack appropriate tools to manage their urban growth. This creates both risks and opportunities for prospective land holders, resulting in a tangle of insecure land rights and claims under multiple tenure systems. Recently, innovative land tools have been proposed and implemented to formalize land tenure. It is envisaged that tenure security for land holders will increase and in turn contribute to poverty reduction. This study evaluates such tools in three peri-urban areas in Lusaka (Zambia), Oshakati (Namibia) and Gaborone (Botswana), with a focus on the perspective of the land holders. It is concluded that the tools are to some extent pro-poor, so recommendations for further improvements are made. Furthermore, these innovative land tools are considered a necessary addition to conventional land administration tools.Geo-information and land managementOTB Research Institute for the Built Environmen

    Thermal Expansion and Aging Effects in Neuromorphic Signal Processor

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    In this paper, we propose an efficient methodology based on a real-time estimator and predictor-corrector scheme for accurate thermal expansion profile and aging evaluation of a neuromorphic signal processor circuit components. As the experimental results indicate, for comparable mesh size, the proposed method is 1~2 order of magnitude more accurate than corresponding, generalized finite element method.Circuits and System

    Optical coherence elastography for measuring the deformation within glass fiber composite

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    Optical coherence elastography (OCE) has been applied to the study of microscopic deformation in biological tissue under compressive stress for more than a decade. In this paper, OCE has been extended for the first time, to the best of our knowledge, to deformation measurement in a glass fiber composite in the field of nondestructive testing. A customized optical coherence tomography system, combined with a mechanical loading setup, was developed to provide pairs of prestressed and stressed structural images. The speckle tracking algorithm, based on 2D cross correlation, was used to estimate the local displacements in micrometer scale. The algorithm was first evaluated by a test of rigid body translation. Then the experiments were carried out with the tensile test and three point bending on a set of glass fiber composites. The structural features and structural variations during the mechanical loadings are clearly observed with the presented displacement maps. The advantages and prospects for OCE application on glass fiber composites are discussed at the end of this paper.Aerospace Structures & MaterialsAerospace Engineerin

    Architecture for the perceptive in the unpoetic city

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    Architecture and The Built Environmen

    Periodicity of alpha-continued fractions

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    In the regular case, the continued fraction expansion of a number x is (eventually) periodic if and only if x is a quadratic irrational. In this thesis, we will see if this theorem holds for a special type of continued fraction; the alpha-continued fraction.Applied mathematicsApplied mathematicsElectrical Engineering, Mathematics and Computer Scienc

    Development of four-terminal mechanically-stacked solar cells utilising hydrogenated amorphous silicon oxide (a-SiO<sub>x</sub>:H) and crystalline silicon cells

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    A tremendous amount of research in improving the efficiency of the single junction crystalline silicon (c-Si) based solar cells has brought its efficiency (26.6%) close to the theoretical maximum achievable conversionefficiency (29.43%) [1–3]. Thus to further improve the efficiency, new avenues of reducing losses need to be opened up. One of the major loss, spectral mismatch loss, can be reduced by utilising tandem structures. Still, there are shortcomings associated with the conventional tandem device structure.This thesis describes how higher efficiencies can be achieved by utilising four terminal mechanically stacked structures. This structure utilises two solar cells, which are electrically isolated but optically connected. Isolating the cells electrically negates the problem of current matching which is presentin conventional tandem cells. This structure also removes constraints such as lattice matching for the two cells. Hence many different types of four terminal cells can be developed.In this work, high bandgap hydrogenated amorphous silicon oxide (a-SiO፱:H) thin film top cell was fabricated using plasma-enhanced chemical vapor deposition (PECVD). Three different types of c-Si cells namely, poly-Si, interdigitated back contact (IBC) and silicon heterojunction (SHJ (Hybrid)) wereutilised as the bottom cells. This is the first instance where an a-SiO፱:H based cell has been used with c-Si cells in a four terminal application.Before actual fabrication, theoretical calculations using two parameters called as Response 4T and Spectral Response 4T were made to determine the optimal configuration as well as the efficiency enhancement for the four-terminal device. From this theoretical calculation, an efficiency gain of almost 4% can be obtained when an a-SiOx:H top cell is used with a poly-Si cell in four terminalconfiguration. Gain between 1% and 2% can be realised by utilising four terminal topology for IBC and SHJ (Hybrid) bottom cells. These gains in efficiency are in comparison to the efficiency of the bottom cell alone.A first of its kind- bifacial a-SiO፱:H cell with the efficiency of 6.60% (Voc:0.97 V, Jsc:10.31 mA/cm2 and fill factor:0.66) was developed. Using this cell as the top cell four terminal devices were fabricated. A gain in efficiency of 0.46% was obtained for the four terminal device based on the poly-Si bottom cell.Further analysis of the four terminal devices using GenPro4 simulation tool was also performed. The analysis pointed to the reflection due to the top cell substrate glass as the limiting factor in improving the efficiency of the four terminal cell further. Parasitic absorption in the carrier selective layers of thethin film cell was another contributor to the losses. Through this work, the potential of four terminal device concept was analysed and actual development of the device was carried out. From the work done, future steps in improving the efficiency of the four terminal device were also deduced.Present work positively brought hope for further improvement in efficiency of crystalline silicon solar cells.Electrical Engineering | Sustainable Energy Technolog

    Using Big Data in the Public Sector. Uncertainties and Readiness in the Dutch Public Executive Sector

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    SEPAMPolicy, Organization, Law & GamingTechnology, Policy and Managemen

    Verwachte tijd tot verwachting

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    Medici zijn geïnteresseerd in de tijdsduur die een vrouw nodig heeft om zwanger te worden. De tijdsduur die een vrouw nodig heeft om zwanger te worden, wordt gezien als een belangrijk instrument voor het vaststellen van de vruchtbaarheid van de desbetreffende vrouw. In dit verslag wordt gezocht naar de verdeling van deze tijdsduur. De meest voorkomende methoden om tot een verdeling van de tijdsduur te komen zijn de prospectieve en retrospectieve cohort studie. De prospectieve cohort studie volgt de vrouw vooruit in de tijd. De vrouw wordt gevolgd vanaf het moment waarop zij stopt met het gebruik van anticonceptie. Eindpunt van de studie is het tijdstip waarop de vrouw daadwerkelijk in verwachting is. Het verkrijgen van de data wordt in het geval van een prospectieve cohort studie bemoeilijkt, doordat het tijdstip waarop besloten wordt om zwanger te willen worden per vrouw varieert. Voor de één is dit kort van tevoren, voor de ander lang van tevoren. De retrospectieve cohort studie volgt de vrouw terug in de tijd. Beginpunt van de studie is nu het moment waarop de vrouw in verwachting raakt. Gekeken wordt wanneer de vrouw is gestopt met het gebruik van anticonceptie. Het interpreteren van een retrospectieve cohort studie wordt bemoeilijkt, doordat onvruchtbare vrouwen niet in de studie worden opgenomen. Het mag duidelijk zijn dat beide methoden moeilijkheden met zich meebrengen. In het artikel van Keiding wordt een alternatieve methode aangedragen: het current duration model. Het current duration model zit als volgt in elkaar. Aan een vrouw wordt gevraagd of zij zwanger probeert te worden, en zo ja sinds wanneer. Deze tijdsduur wordt de current duration genoemd. Het blijkt mogelijk te zijn om op basis van de verdeling van deze current duration, de verdeling van de tijdsduur die een vrouw nodig heeft om zwanger te worden vast te stellen. In hoofdstuk 1 wordt het current duration model uitgebreid beschouwd en geanalyseerd. Vervolgens worden in hoofdstuk 2, 3 en 4 verschillende schatters beschouwd. Tenslotte worden in hoofdstuk 5 deze schatters toegepast op data om zo de verdeling van de tijdsduur die een vrouw nodig heeft om zwanger te worden te verkrijgen.Applied mathematicsElectrical Engineering, Mathematics and Computer Scienc
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