250 research outputs found
Large Time Step and DC Stable TD-EFIE Discretized with Implicit Runge-Kutta Methods
No full textThe time domain-electric field integral equation (TD-EFIE) and its differentiated version are widely used to simulate the transient scattering of a time dependent electromagnetic field by a perfect electric conductor (PEC). The time discretization of the TD-EFIE can be achieved by a space-time Galerkin approach or, as it is considered in this contribution, by a convolution quadrature using implicit Runge-Kutta methods. The solution is then computed using the marching-on-in-time (MOT) algorithm. The differentiated TD-EFIE has two problems: 1) the system matrix suffers from ill-conditioning when the time step increases (low frequency breakdown) and 2) it suffers from the DC instability, i.e., the formulation allows for the existence of spurious solenoidal currents that grow slowly in the solution. In this article, we show that 1) and 2) can be alleviated by leveraging quasi-Helmholtz projectors to separate the Helmholtz components of the induced current and rescale them independently. The efficacy of the approach is demonstrated by numerical examples including benchmarks and real-life applications.Numerical Analysi
Newton polygons and curve gonalities
No full textWe give a combinatorial upper bound for the gonality of a curve that is defined by a bivariate Laurent polynomial with given Newton polygon. We conjecture that this bound is generically attained, and provide proofs in a considerable number of special cases. One proof technique uses recent work of M. Baker on linear systems on graphs, by means of which we reduce our conjecture to a purely combinatorial statement.sponsorship: We are very grateful to an anonymous referee for his valuable comments, which led to the proof of Theorem 11. We would also like to thank Marc Coppens, Hendrik Hubrechts, Bjorn Poonen, Jan Schepers, Jan Tuitman and Wim Veys for some helpful discussions. The first author thanks the Massachusetts Institute of Technology for its hospitality. Both authors where supported by the Fund for Scientific Research Flanders (F.W.O. Vlaanderen). (Fund for Scientific Research Flanders (F.W.O. Vlaanderen))status: Publishe
Literature and the nugget of knowledge : an interview with Derek Attridge and Peter Lamarque
No full textAbstract: The idea of an interview with Peter Lamarque and Derek Attridge on the cognitive value of literary fiction arose in the wake of an aesthetics course on the relation between literature and truth at the University of Antwerp. In Spring 2015 Peter Lamarque contributed to this course with the lecture \u201cThe Opacity of Narrative and Fine-grained Reading\u201d. In Spring 2017 Derek Attridge elaborated his view on the relation between literature and truth in his lecture \u201cThe Event of Truth : Literature\u2019s Singular Relation to Knowledge\u201d. After each lecture, we had the occasion to discuss with the author the stakes of the debate and we were rapidly convinced by the many points of convergences between their views. We intended to explore these similarities and differences through a face to face interaction and were happy that both philosophers accepted our invitation for an interview. This interview was conducted by Arthur Cools and Leen Verheyen in York on 9 July 2018
The Antwerp Jesuit Cornelius Hazart as an author of dialogue pamphlets
No full textThe Antwerp Jesuit Cornelius Hazart as an author of dialogue pamphlets
Cornelius Hazart (1617-1690) was a prolific author. Amongst many another things, he published a monumental four volume Church History (De Kerckelyke Historie vanden Gheheelen Wereldt, 1667-1671) and dozens of pamphlets in which he argued that only roman Catholics could expect salvation and that their church was by far superior to the various competing protestant institutions (Martens, 2012). Many of these pamphlets were presented as imaginary, but seemingly realistic dialogues between various characters.
In recent years, Dutch scholars have paid attention to the genre of dialogue pamphlets (Dingemanse 2008). They have argued that such dialogue pamphlets were a typical feature of the ‘discussion culture’ that characterized the Dutch Republic (Frijhoff and Spies, 1999). In the Habsburg Netherlands power relations were more vertically structured than in the Dutch Republic. But just as in the Republic, literacy levels in these regions remained high and a reading culture was firmly rooted amongst urban populations (Jacobs and Verberckmoes, 2006). Therefore authorities made use of pamphlets to win over public opinion. Due to their realistic settings, dialogue pamphlets were particularly suited to enact power relations and to enhance the confessionalisation process.
In this paper, I shall analyze Hazart’s dialogue pamphlets. As a preacher of the Antwerp St Ignatius church he was a well-known polemicist. In particular, after the Peace of Munster, when relationships with the Dutch Republic were restored, Hazart used this form. Apparently, he and his fellow clergymen feared that Catholics, who had frequent contacts with northerners, would be lured into Protestantism. Not surprisingly, a detailed reading of Hazart’s dialogue pamphlets reveals that he emphasized the catholic stance on controversial points of doctrine. Moreover, and maybe more importantly, he ridiculed his counterparts, the protestant ministers. Thereby he created powerful stereotypes that would be deeply rooted in the collective imagery of the post Tridentine Catholic Netherlands.
Source material
A corpus of dialogue pamphlets by Cornelius Hazart has been compiled by searches into the STCV-database.
Basic references
C. Dingemanse, Rap van tong, scherp van pen: Literaire discussiecultuur in Nederlandse praatjespamfletten (circa 1600-1750). (Hilversum, 2008).
W. Frijhoff and M. Spies, 1650. Bevochten eendracht (The Hague, 1999).
M. Jacobs and J. Verberckmoes, ‘Populair drukwerk’ in P. Janssens ed. België in de 17de eeuw. De Spaanse Nederlanden en het Prinsbisdom Luik. Band II: Cultuur en Leefwereld (Brussels and Gent, 2006) 106-110.
B. Martens, ‘Nederlandse religieuze controversepublicaties en de kunst van het argumenteren in de Zuidelijke Nederlanden (ca. 1591-c. 1688)’, in Trajecta, 19-20 (2012), 241-272.status: Publishe
Performances of the HL (Hyperloop) transport system
No full textThis paper deals with an analysis of performances of the HL (Hyperloop) transport system considered as an advanced transport alternative to the existing APT (Air Passenger Transport) and HSR (High Speed Rail) systems. The considered performances are operational, financial, social and environmental. The operational performance include capacity and quality of service provided to the system’s users-passengers with attributes such as door-to-door travel time consisting of the access and egress time, schedule delay, in-vehicle time, and interchange time. The economic performances embrace the costs and revenues of operating the system. The costs include that for infrastructure, vehicles, traffic management facilities and equipment, and employees. The revenues embrace earnings from pricing users/passengers. The environmental performances include energy consumption and related emissions of GHGs (Green House Gases), and land use. The social performances are considered to be noise and safety. The analytical models of indicators of these performances are developed and applied to the scenario of operating the HL system on the short- to medium-haul travel distances/routes. These are then compared to the corresponding performances of the HSR and APT. This comparison has shown that the HL system may possess some advantages but also disadvantages regarding particular performances.Transport and PlanningOLD Urban and Regional Developmen
The environmental impact of a shift to rail from short-haul flights
No full textIn the context of mitigating climate change, a shift from air to rail is proposed for short-haul journeys. The impact of this policy on the GHG emissions of aviation is small and will be even marginal if only journeys < 500 km are involved. These journeys account for 2.2% of the mileage of air travel, and the impact on emissions will be even smaller than this figure, mainly because not all air travellers (likely) will shift, and part of the emission reduction will be undone by increasing emissions of rail transport. When the upper limit of involved distances increases, the impact increases significantly as well; but even at a limit of 1200 km, which is about the upper limit of the market range of the train, the impact will likely be smaller than the opposite impact of the annual growth of air travel. Policy intentions seem to be prompted by just to do something that doesn’t hurt people so much rather than by a systematic analysis of possible measures and their effectiveness.Transport and Plannin
Analyse van het Meteorologische Getij op de Noordzee m.b.v. de Theorie van Systemen
No full textHet probleem onder studie handelt over het vastleggen van het verband tussen het waargenomen meteorologische getij op een bepaalde plaats aan de Nederlandse kust en haar oorsprong: luchtdruk- en/of de hieruit voortvloeiende windvariaties over de Noordzee. De bepaling van dit verband geschiedt met behulp van de theorie van systemen. Ligt dit verband eenmaal vast, dan kunnen aan de hand van werkelijke of fictieve depressies, voorspellingen gemaakt worden over de grootte van het meteorologische getij op die bepaalde plaats. Met het meteorologische getij (surges) wordt bedoeld de vertikale waterstandsverandering ten gevolge van de weersomstandigheden, dit in tegenstelling tot het astronomische getij (tides), dat veroorzaruct wordt door de beweging van hemellichamen als de zon, de maan en de aarde. Het eerste getij wordt gevonden door het laatste getij, dat door haar deterministische karakter voldoende bekend is, op de waargenomen waters.tand in mindering te brengen. Deze formulering gaat voorbij aan een eventuele interaktie die tussen de beide getijden kan optreden en volgens bovenstaande definitie in het meteorologisch getij gerntroduceerd wordt. Bijde analyse van de resultaten zal hiermee rekening moeten worden gehouden. Voorspellen betekent in deze studie het berekenen van de waterstanden uit bekende meteorologische gegevens, m.b.v. het eerder vastgelegde verband hiertussen. Dit in tegenstelling tot het voorspellen (extrapoleren) van de waterstanden uit meteorologische gegevens uit het verleden bijbekend verband, hetgeen een andere methode vereist.Hydraulic EngineeringCivil Engineering and Geoscience
A custom-made percutaneous flow-restrictor to manage a symptomatic congenital porto-systemic shunt in an infant
No full textPortosystemic shunts allow splanchnic blood to bypass the liver unfiltered, and may cause serious pulmonary and cerebral dysfunction; closure is therefore recommended. In patients where the portal system is hypoplastic, closure by a staged approach with a flow reducer may be necessary. We report a new, reliable, short, and adjustable device that can be delivered through a small 8-Fr sheath.sponsorship: Eddy Merckx Research Grant, Belgian Foundation for Pediatric Cardiac Research FNRCP (Eddy Merckx Research Grant, Belgian Foundation for Pediatric Cardiac Research FNRCP)status: Publishe
Application of Wavefront Sensorless Methods to Shack-Hartmann Patterns for Wavefront Reconstruction: A Two-step Method for Single-Frame Phase Retrieval
No full textCounter-acting image quality degradation caused by phase aberrations through physical correction requires the phase field to be known. As imaging hardware captures real-valued intensity, defined as the wave amplitude squared, obtaining this lost phase information is known as the phase retrieval problem and is a non-linear and non-convex optimisation problem. Literature treats this problem from two points of view: reconstruction using indirect phase sampling, and reconstruction using Fourier amplitude sampling. The former employs wavefront sensors such as the Shack-Hartmann sensor, which encodes phase gradient information in the form of the displacement of imaged spots. These methods, while fast, discard information such as interference and are limited to low-order reconstruction. The latter, also called wavefront sensorless phase retrieval, uses the full point-spread function (PSF) to obtain high-accuracy reconstruction at the cost of computational speed, number of intensity images required, or limited aberration magnitude. These two points of view have remained largely separated, but can be made compatible through a modelling technique called Shack-Hartmann diversity. This thesis explores the merging of wavefront sensorless methods with Shack-Hartmann intensity patterns to leverage more information from a single captured image frame.Firstly, a low-order modal reconstruction technique is presented applied to phase gradient fields obtained from Fourier demodulation of a Shack-Hartmann intensity pattern. A method of minimising the amount of redundant data-points used for reconstruction is illustrated through the removal of Fourier-interpolated data to speed up performance.Secondly, a novel extension of the Fourier demodulation technique to hexagonal Shack-Hartmann arrays is presented, allowing phase gradient extraction and modal reconstruction of hexagonal array intensity images using Fourier demodulation.Thirdly, Shack-Hartmann diversity is used to extend intensity-based modal phase retrieval using Taylor approximation of the intensity function to Shack-Hartmann intensity patterns. This bridges the gap between wavefront sensorless methods and Shack-Hartmann intensity patterns.Lastly, a novel hybrid method is presented for high-accuracy phase reconstruction based on applying the above intensity-based method to a single Shack-Hartmann intensity pattern with low-order pre-conditioning obtained from Fourier demodulation. The method is demonstrated to obtain highly accurate reconstruction on low-order aberrations, and better reconstruction accuracy on small-magnitude high-order aberrations with dominating large-magnitude low-order terms than traditional methods. Potential use cases are discussed, such as open-loop turbulence reconstruction for use in turbulence modelling.Mechanical Engineering | Systems and Contro
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