Technical University of Dortmund

About: Technical University of Dortmund is a education organization based out in Dortmund, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Context (language use) & Large Hadron Collider. The organization has 13028 authors who have published 27666 publications receiving 615557 citations. The organization is also known as: Dortmund University & University of Dortmund.

Stochastic Tunneling Approach for Global Minimization of Complex Potential Energy Landscapes

Abstract: We investigate a novel stochastic technique for the global optimization of complex potential energy surfaces (PES) that avoids the freezing problem of simulated annealing by allowing the dynamical process to tunnel energetically inaccessible regions of the PES by way of a dynamically adjusted nonlinear transformation of the original PES. We demonstrate the success of this approach, which is characterized by a single adjustable parameter, for three generic hard minimization problems.

Students' misconceptions—Looking for a pattern

Abstract: This article describes four chemical terms that students with well-considered reasons use in a way that is not accepted in chemistry. The studies identified students' misconceptions using multiple-choice tests. The distractors of the questions were keyed to the errors observed in a pilot study. From 4300–7500 German senior high school students completed the written tests. They were asked to select an option and give reasons for their answers. Furthermore, discussions were conducted with additional groups of students. It emerged that students limit the term isomerism to compounds of the same class. This idea, however, is not compatible with the modern definition of isomerism. Yet, in practice, only isomers belonging to the same class of compounds are dealt with. Students apparently conclude from the syllable “ox” in redox that oxygen is involved in all redox reactions. Oxygen only had a predominant position in the old oxidation concept. This concept has, however, been extended and oxygen has lost its special position. The idea that in any reaction between an acid and a base a neutral solution is formed has been found to be quite common among students. The term neutralization, coined 300 years ago, can no longer be used in this way. However, words like neutralization or neutral seem to keep the old idea alive. Many students hold the misconception that conjugate acid-base pairs consist of positively and negatively charged ions, which can somehow neutralize each other. The test questions developed can be easily used by teachers to find out whether the misconceptions described appear in a learning group. As it is known which misconceptions might occur teachers can reflect on how to respond to students' incorrect answers before entering the classroom. Discussions among the students have been found to be a good way of dealing with these problems. For further research the question is raised as to whether there are other concepts and terms that cause difficulties for students. © 1997 John Wiley & Sons, Inc. Sci Ed 81:123–135, 1997.

Quickest Flows Over Time

Abstract: Flows over time (also called dynamic flows) generalize standard network flows by introducing an element of time. They naturally model problems where travel and transmission are not instantaneous. Traditionally, flows over time are solved in time-expanded networks that contain one copy of the original network for each discrete time step. While this method makes available the whole algorithmic toolbox developed for static flows, its main and often fatal drawback is the enormous size of the time-expanded network. We present several approaches for coping with this difficulty. First, inspired by the work of Ford and Fulkerson on maximal $s$-$t$-flows over time (or “maximal dynamic $s$-$t$-flows”), we show that static length-bounded flows lead to provably good multicommodity flows over time. Second, we investigate “condensed” time-expanded networks which rely on a rougher discretization of time. We prove that a solution of arbitrary precision can be computed in polynomial time through an appropriate discretization leading to a condensed time-expanded network of polynomial size. In particular, our approach yields fully polynomial-time approximation schemes for the NP-hard quickest min-cost and multicommodity flow problems. For single commodity problems, we show that storage of flow at intermediate nodes is unnecessary, and our approximation schemes do not use any.

The NOMAD experiment at the CERN SPS

Abstract: The NOMAD experiment is a short base-line search for νμ − ντ oscillations in the CERN neutrino beam. The ντ's are searched for through their charged current interactions followed by the observation of the resulting τ− through its electronic, muonic or hadronic decays. These decays are recognized using kinematical criteria necessitating the use of a light target which enables the reconstruction of individual particles produced in the neutrino interactions. This paper describes the various components of the NOMAD detector: the target and muon drift chambers, the electromagnetic and hadronic calorimeters, the preshower and transition radiation detectors and the veto and trigger scintillation counters. The beam and data acquisition system are also described. The quality of the reconstruction and individual particles is demonstrated through the ability of NOMAD to observe Ks0's, Λ0's and π0's. Finally, the observation of τ− through its electronic decay being one of the most promising channels in the search, the identification of electrons in NOMAD is discussed.