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Braunschweig, Germany

Barth T.,Braunschweig Institute of Technology | Scholz P.,Braunschweig Institute of Technology | Scholz P.,Institute of Fluid Mechanics | Wierach P.,German Aerospace Center | Wierach P.,German Institute of Composite Structures and Adaptive Systems
AIAA Journal

This paper describes a study of dynamical vane vortex generators in a flow over a flat plate. Fluidic vortex generators are more effective when operated dynamically. Thus, it is the aim of this study to find out whether mechanical vortex generators are also superior under dynamic operating conditions. The motion of the vortex generators is generated by piezoceramic actuators constructed in a bimorph configuration, which consists of a carbon-fiber bar covered with piezoceramic face actuators. The actuators exploit the longitudinal piezoelectric effect (d33 effect), they are operated in resonance to reach the required displacement and generate a sinusoidal motion of the vortex generators. Vortex generators and actuators were integrated into a flat plate in a low-speed wind tunnel. A stereo particle image velocimetry system was used to record phase-locked flowfields that were analyzed using vortex classification methods. It was found that the transient development of the vortex core position and circulation is very different from that of static vanes. While vortices from static vortex generators are able to survive over a considerable distance, the vortices from dynamically driven ones decay faster. It is argued that the dynamic vortices have a greater ability to reorganize the momentum in the turbulent boundary layer. Copyright © 2010 by Peter Scholz. Source

Hibbeln M.,Braunschweig Institute of Technology | Jenkins J.L.,Brigham Young University | Schneider C.,City University of Hong Kong | Valacich J.S.,University of Arizona | Weinmann M.,University of Liechtenstein
35th International Conference on Information Systems "Building a Better World Through Information Systems", ICIS 2014

The completion of online forms is the catalyst for many business and governmental processes. However, providing fraudulent information in such forms is pervasive, resulting in costly consequences for organizations and society. Furthermore, detecting fraudulent responses in online forms is often very difficult, time consuming, and expensive. This research proposes that analyzing users' mouse movements may reveal when a person is being fraudulent. Namely, based on neuroscience and deception theory, the paper explains how deception may influence hand movements captured via the computer mouse. In an insurance fraud context, a study is conducted to explore these proposed relationships. The results suggest that being deceptive may increase the normalized distance of movement, decrease the speed of movement, increase the response time, and result in more left clicks. Implications for human-computer interaction research and practice are discussed. Source

Fekete S.P.,Braunschweig Institute of Technology | Mitchell J.S.B.,State University of New York at Stony Brook | Schmidt C.,Braunschweig Institute of Technology
Journal of Combinatorial Optimization

Given a polygon and a visibility range, the Myopic Watchman Problem with Discrete Vision (MWPDV) asks for a closed path P and a set of scan points S, such that (i) every point of the polygon is within visibility range of a scan point; and (ii) path length plus weighted sum of scan number along the tour is minimized. Alternatively, the bicriteria problem (ii) aims at minimizing both scan number and tour length. We consider both lawn mowing (in which tour and scan points may leave P) and milling (in which tour, scan points and visibility must stay within P) variants for the MWPDV; even for simple special cases, these problems are NP-hard. We show that this problem is NP-hard, even for the special cases of rectilinear polygons and L8 scan range 1, and negligible small travel cost or negligible travel cost. For rectilinear MWPDV milling in grid polygons we present a 2.5- approximation with unit scan range; this holds for the bicriteria version, thus for any linear combination of travel cost and scan cost. For grid polygons and circular unit scan range, we describe a bicriteria 4-approximation. These results serve as stepping stones for the general case of circular scans with scan radius r and arbitrary polygons of feature size a, for which we extend the underlying ideas to a φ( r/a + r+1/ 2 ) bicriteria approximation algorithm. Finally, we describe approximation schemes for MWPDV lawn mowing and milling of grid polygons, for fixed ratio between scan cost and travel cost. © Springer Science+Business Media, LLC 2011. Source

Weinmann M.,Braunschweig Institute of Technology | Schneider C.,City University of Hong Kong | Robra-Bissantz S.,Braunschweig Institute of Technology
ECIS 2013 - Proceedings of the 21st European Conference on Information Systems

Given people's differences in preferences, personalities, or demographic factors, building useradaptive systems can aid in providing each individual user with the interface that helps to best achieve the desired outcome. For example, online retailers now have the possibility to offer customized Web sites to individual customers, so as to meet each customer's specific needs. However, online retailers typically only have little data available to segment customers in real-Time. In this study, we propose that observable usage data (such as click path data) can be used to distinguish female and male Web site visitors. Drawing on research in psychology and consumer behavior, we hypothesize that observable differences in Web surfing behavior can be indicative of a user's gender. Our results show that women tend to need less time and have shorter click paths than men in online product configuration tasks, and thus confirm the utility of using observable usage data to distinguish Web site visitors based on their gender. Source

Fekete S.P.,Braunschweig Institute of Technology | Kamphans T.,Braunschweig Institute of Technology | Kroller A.,Braunschweig Institute of Technology | Mitchell J.S.B.,State University of New York at Stony Brook | Schmidt C.,Braunschweig Institute of Technology
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

We consider online and offline problems related to exploring and surveying a region by a swarm of robots with limited communication range. The minimum relay triangulation problem (MRTP) asks for placing a minimum number of robots, such that their communication graph is a triangulated cover of the region. The maximum area triangulation problem (MATP) aims at finding a placement of n robots such that their communication graph contains a root and forms a triangulated cover of a maximum possible amount of area. Both problems are geometric versions of natural graph optimization problems. The offline version of both problems share a decision problem, which we prove to be NP-hard. For the online version of the MRTP, we give a lower bound of 6/5 for the competitive ratio, and a strategy that achieves a ratio of 3; for different offline versions, we describe polynomial-time approximation schemes. For the MATP we show that no competitive ratio exists for the online problem, and give polynomial-time approximation schemes for offline versions. © 2011 Springer-Verlag. Source

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