1,977 research outputs found
Eelco Visser - An Exceptional SLE Researcher
No full textThese notes honor Eelco Visser as an exceptional member of the Software Language Engineering (SLE) community. The notes are authored from the perspective of an SLE co-founder and a continuous SLE supporter. As an inevitable side effect, a short history of SLE is captured. The commemoration begins with Eelco’s role in launching the SLE conference. The commemoration continues with Eelco’s contributions as an author and his involvement with running the conference and working towards an SLE Body of Knowledge (SLEBoK). The commemoration ends with recalling Eelco’s role as the de-facto SLE photographer
Interview mit Prof. Wolfgang Wahlster, Leiter des DFKI und Professor an der Universität des Saarlandes
No full textByline: Ubbo Visser (1) Author Affiliation: (1) Department of Computer Science, University of Miami, Coral Gables, FL, 33124, USA Article History: Registration Date: 10/10/2011 Online Date: 19/10/2011Academi
Interview mit Prof. Kerstin Schill, Professorin an der Universität Bremen
No full textByline: Ubbo Visser (1) Author Affiliation: (1) Department of Computer Science, University of Miami, Coral Gables, FL, 33124, USA Article History: Registration Date: 10/10/2011 Online Date: 19/10/2011Academi
Application of sediment transport formulae to sand-dike breach erosion
No full textThe Technical Advisory Committee on Water Defences in the Netherlands has decided to develop a mathematical model for breach erosion in dunes and dikes, with which it will be possible to predict the growth of the breach and the discharge rate through the breach in case of a dike-burst. An essential part of such a mathematical model is the description of the entrainment of the sediment (sand or clay) and its transport through the breach. The process of breach erosion, especially in the first phases, is characterized by relatively steep slopes and large flow velocities. None of the existing sediment transport formulae has been derived and tested for these circumstances. This report presents the results of an investigation into the applicability of sediment transport formulae to sand-dike breach erosion. In view of the steep slopes and the large flow velocities, the following sediment transport conceptions have been included in the study: formulae for sand-water mixture flows: Wilson (1966), Wilson (1987), Mastbergen and Winterwerp (1987); formulae for sediment transport in flows on relatively steep slopes: Mizuyama (1977), Smart and Jaeggi (1983), Bathurst et al. (1987), Takahashi (1987), Rickenmann (1991); formulae for river regimes which have been tested for (relatively) large flow velocities (large shear stress velocities): Engelund and Hansen (1967), Van Rijn (1984a, 1984c); energetics-based sediment transport conceptions: Bagnold (1963, 1966), Yang (1979), Bagnold-Bailard, see Bailard (1981), Bagnold-Visser, see Visser (1988), these last two formulae are modifications of the original conception of Bagnold (1963, 1966); formulae for debris flows: Takahashi (1978, 1980, 1987, 1991). These sediment transport formulae, combined with Galappatti's model (1983) for the pickup of sediment, are compared with the data of two laboratory experiments (Schelde Flume experiments, see Steetzel and Visser, 1992a, 1992b) and the data of a field experiment (Zwin'89 experiment, see Visser et al., 1990). Experimental sediment transport rates have been determined as volumes of sand eroded over a certain period of time. All tests concern super-critical flow (Froude number Fr > 1, i.e. here 2.8<5 Fr<5 4.1), large values for Shields' mobility parameter (10 < theta < 100) and high concentrations (depth-averaged values rising up to about 0.25 by volume). Most of the tested sediment transport formulae predict sand transport rates being much larger than the observed quantities. Only the Bagnold-Visser formula, see Visser (1988), predicts sand transport rates within a factor two of the experimental values. With the formulation of Van Rijn (1984a, 1984c) this is possible within about a factor three. All other formulae give larger deviations from the experimental data. These conclusions hold for the three initial phases of the process of breach erosion, when the flow is supercritical, and confirm the good results obtained up to now with the BagnoldVisser formula, see Visser (1988, 1994). Once more it should be emphasized that this formula has not been derived for a situation where the rate of sand entrainment is so large as in the first three phases of the breach erosion process (this applies to both the energeticsbased method and the semi-empirical determination of the efficiency factor). The relatively large entrainment of sediment causes a relatively large increase of both the flow rate and the sediment concentration of the sand-water mixture along the inner slope (so that the effect of 'hindered entrainment' is possibly not negligible). Further study is necessary to establish the effects of the large rate of sediment entrainment on the breach erosion process. For the time being it is recommended to apply the formula of Bagnold-Visser in a mathematical breach growth model for the description of the first phases (i.e. as long as the flow is supercritical) of the breach erosion process. The present study does not recommend a formula for the important later phases of breach growth (when the flows becomes subcritical), in which most of the breach erosion takes place and in which also the dimensions of the ultimate breach are determined. Probably the data of the recent Zwin'94 field experiment (see Visser et al, 1995) will allow such a recommendation in the near future. For the present the conclusion of Voogt et al. (1991) is still valid, i.e. that the formulae of Engelund and Hansen (1967) and in particular Van Rijn (1984a, 1984c) can also be applied for relatively large current velocities in subcritical flow.Civil Engineering and Geoscience
SNP data of 556 isolates of the wheat leaf rust fungus, Puccinia triticina from 11 world-wide regions
No full textWe provide variant calls in VCF and fasta format. Fasta formatted data were used with the deposited python script to calculate the average number of pairwise differences between sequences. GBS SNP calls in Variant Call Format (bgzipped) GBS Haplotype sequence in fasta format (tarballed directory) Python script for calculating average number of pairwise differences using the fasta haplotypes as input. Names dependency file for python script. The excel file gives the virulence/virulence of the same isolates to 20 lines of Thatcher wheat that differ for single leaf rust resistance genes.This dataset includes SNPs of 556 isolates of the wheat leaf rust fungus, Puccina triticina from 11 worldwide regions that were mapped to the reference genome. This data was used to examine the population structure of Puccinia triticina on a worldwide basis, and to examine the evolutionary relationship between collections from a wheat progenitor, collections from durum wheat, and collections from common wheat. Groups of isolates that were highly related were found in distant continental regions, indicating past and current migration of this important wheat pathogen. Data is being released now in conjunction with publication of a primary research paper that describes this research.Kolmer, James; Herman, Adam; Ordonez, Maria; German, Silvia; Morgounov, Alexy; Pretorius, Zack; Visser, Botma; Anikster, Yehoshoa; Acevedo, Maricelis. (2019). SNP data of 556 isolates of the wheat leaf rust fungus, Puccinia triticina from 11 world-wide regions. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/0f8c-k469
KI und Robotik fur das Human Brain Project
No full textByline: Ubbo Visser (1) Author Affiliation: (1) Department of Computer Science, University of Miami, Coral Gables, FL, 33146, USA Article History: Registration Date: 17/09/2014 Online Date: 02/10/2014Academi
Discussie. Mondialisering, groei en ongelijkheid. Antwoord aan Hans Visser en Robert Went
No full textGlobalization, Growth, and Inequality: A Response to Hans Visser and Robert Went.
In a reply to criticisms by Hans Visser and Robert Went (2002) of the author\u27s "Mondialisering en de mondiale welvaartskloof: trends in inkomensverschillen in de wereld, 1950-1998" ([Globalization and the Global Welfare Gap: Trends in Income Disparities in the World, 1950-1998] 2002), it is argued that the author and his critics are speaking of different things. Visser approves of globalization "under certain conditions," whereas Went aligns himself with antiglobalists. It is acknowledged that the definition of globalization is a problematic one, and that it can be argued that globalization as a process began in 1492. What is at issue is the prevalence of poverty in the world, and whether the globalized economies of the world ameliorate or perpetuate this poverty. 11 References. A. Siege
A model for breach growth in a sand-dike and its prediction for the Zwin 94 experiment
No full textA mathematical model for breach growth in sand-dikes and dunes is described. The model is based on the five-step breach erosion process as observed in several laboratory experiments and the Zwin 89 field experiment. A simplified Galappatti (1983) pick up mechanism for sand from the bed is combined with Bagnold's (1963) modified (Visser, 1988) energetics-based sand transport conception to describe the breach erosion. The test of the model to the data of the Zwin 89 experiment shows good agreement. Finally, a prediction for the growth of the breach width in the Zwin 94 experiment is given.Hydraulic EngineeringCivil Engineering and Geoscience
Global Nonlinear Model Identification with Multivariate Splines
No full textAt present, model based control systems play an essential role in many aspects of modern society. Application areas of model based control systems range from food processing to medical imaging, and from process control in oil refineries to the flight control systems of modern aircraft. Central to a model based control system is a mathematical model of the physical system or process that is being controlled. The field of science concerned with the identification of models of physical systems is called system identification. In this thesis, a new methodology is proposed for the identification of models of nonlinear systems using multivariate simplex splines. This new methodology has the potential to increase the performance of any model based control system by improving the quality of system models. Multivariate simplex splines consist of polynomial basis functions, called B-form polynomials, which are defined on geometric structures called simplices. Every simplex supports a single B-form polynomial which itself consists of a linear combination of Bernstein basis polynomials. Each individual Bernstein basis polynomial is scaled by a single coefficient called a B-coefficient. The B-coefficients have a special property in the sense that they have a unique spatial location inside their supporting simplex. This spatial structure, also known as the B-net, provides a number of unique capabilities that add to the desirability of the simplex splines as a tool for data approximation. For example, the B-net simplifies local model modification by directly relating specific model regions to subsets of B-coefficients involved in shaping the model in those regions. This particular capability has the potential to play an important role in future adaptive model based control systems. In such a control system, an on-board simplex spline model can be locally adapted in real time to reflect changes in system dynamics. The approximation power of the multivariate simplex splines can be increased by joining any number of simplices together into a geometric structure called a triangulation. Triangulations come in many shapes and sizes, ranging from configurations consisting of just two simplices to configurations containing millions of simplices. Triangulations can be optimized by locally increasing or decreasing the density of simplices to reflect local system complexity. The new methodology was applied in the identification of a complete set of aerodynamic models for the Cessna Citation II laboratory using flight data obtained during seven test flights. In total, 247 flight test maneuvers were flown which together provided a significant coverage of the flight envelope of the Citation II. The complete identification dataset consisted of millions of measurements on more than sixty flight parameters. More than 2000 prototype spline based aerodynamic models were identified using a newly developed, highly optimized software implementation of the simplex spline identification algorithm. Using the developed methods for simplex spline model validation it was proved that the models are both accurate and of guaranteed numerical stability inside the spline domain. The identification and validation results of the simplex spline models were compared with those of ordinary polynomial models identified using standard identification methods. These results showed that the multivariate simplex spline based aerodynamic models were of significantly higher quality than the aerodynamic models based on ordinary polynomials.Control & OperationsAerospace Engineerin
BEPSys 2.0: Central Registration Tool for Projects and Groups
No full textThe following report outlines the research, development, and delivery phases of the BEPSys 2.0 application. The application aims to provide central project registration and management for courses at the TU Delft. The request for the development stemmed from Otto Visser, who was the acting coordinator for the Computer Science Final Project Course. A system named ”BEPSys” already existed for this purpose, but it was deemed insecure and unreliable, and warranted a redesign
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