@misc{9632, author = {{Tönnies, Merle}}, booktitle = {{Anglistik. International Journal of English Studies}}, number = {{1}}, pages = {{201--203}}, title = {{{Baumbach, S. / Neumann, B. / Nünning, A.: A History of British Drama}}}, volume = {{24}}, year = {{2013}}, } @article{9705, author = {{Beutner, Marc and Fortmann, L. M.}}, journal = {{Kölner Zeitschrift für Wirtschaft und Pädagogik}}, number = {{54}}, title = {{{COR-VET – Career Orientation in Vocational Education and Training in Europe}}}, volume = {{28}}, year = {{2013}}, } @article{9706, author = {{Beutner, Marc and Kundisch, Dennis and Magenheim, J and Hermann, P and Reinhardt, W and Zoyke, A}}, journal = {{Informatik Spektrum}}, number = {{3}}, pages = {{389 -- 393}}, title = {{{Classroom Response Systeme}}}, volume = {{36}}, year = {{2013}}, } @book{9713, author = {{Strauß, Sara}}, publisher = {{WVT}}, title = {{{"This Bright Inward Cinema of Thought" – Stream of Consciousness in Contemporary English Fiction}}}, year = {{2013}}, } @inbook{9724, author = {{Flotmann, Christina}}, booktitle = {{Monstrous Geographies: Places and Spaces of the Monstrous}}, editor = {{Montin, Sarah and Tsitas, Evelyn}}, pages = {{75--96}}, publisher = {{Inter-Disciplinary Press}}, title = {{{‘Monstrous’ Homes: How Private Spaces Shape Characters’ Identities in 19th-century Sensation Fiction}}}, year = {{2013}}, } @book{9725, author = {{Flotmann, Christina}}, publisher = {{transcript}}, title = {{{Ambiguity in ‘Star Wars’ and ‘Harry Potter’: A (Post-)Structuralist Reading of Two Popular Myths}}}, year = {{2013}}, } @misc{9732, abstract = {{Interview 2 Feb. 2013}}, author = {{Flotmann, Christina}}, publisher = {{radioeins rbb Berlin, Die Profis}}, title = {{{Populäre Mythen bei Star Wars und Harry Potter}}}, year = {{2013}}, } @article{9794, abstract = {{A piezoelectric cantilever beam with a tip mass at its free end is a common energy harvester configuration. This article introduces a new principle of designing such a harvester that increases the generated power without changing the resonance frequency of the harvester: the attraction force between two permanent magnets is used to add stiffness to the system. This magnetic stiffening counters the effect of the tip mass on the efficient operation frequency. Five set-ups incorporating piezoelectric bimorph cantilevers of the same type in different mechanical configurations are compared theoretically and experimentally to investigate the feasibility of this principle: theoretical and experimental results show that magnetically stiffened harvesters have important advantages over conventional set-ups with and without tip mass. They generate more power while only slightly increasing the deflection in the piezoelectric harvester and they can be tuned across a wide range of excitation frequencies.}}, author = {{Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Journal of Intelligent Material Systems and Structures}}, number = {{11}}, pages = {{1332--1342}}, title = {{{Increasing the power of piezoelectric energy harvesters by magnetic stiffening}}}, doi = {{10.1177/1045389X13483021}}, volume = {{24}}, year = {{2013}}, } @article{9795, abstract = {{Power and bandwidth of piezoelectric harvesters can be increased by using multiple piezoelectric elements in one harvester. In this contribution, a novel energy harvesting cantilever array with magnetic tuning including three piezoelectric bimorphs is investigated theoretically and experimentally, with a good agreement between model and experiment. Other than harvester designs proposed before, this array is easy to manufacture and insensitive to manufacturing tolerances because its optimum operation frequency can be re-adjusted after fabrication. Using the superposition principle, the Butterworth-Van Dyke model and a mechanical lumped parameters model, the generated voltage and current are determined analytically. Formulas for calculating the power generated by array harvesters with an arbitrary number of piezoelectric elements connected in series or in parallel are derived. It is shown that optimum harvester design must take both the connected load and the operating frequency into account. Strategies for connecting multiple bimorphs to increase the maximum generated power and/or enhance the bandwidth compared to a single bimorph harvester are investigated. For bandwidth enhancement it is essential that individual rectifiers are used for the bimorphs. An example with three bimorphs shows that, depending on the chosen tuning strategy, the power is increased by about 340\% or the bandwidth is increased by about 500\%, compared to one single bimorph.}}, author = {{Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Sensors and Actuators A: Physical}}, keywords = {{Energy harvesting, Cantilever array, Bandwidth, Power increase}}, pages = {{138 -- 146}}, title = {{{Enhanced energy harvesting using multiple piezoelectric elements: Theory and experiments}}}, doi = {{10.1016/j.sna.2013.01.008}}, volume = {{200}}, year = {{2013}}, } @inproceedings{9796, abstract = {{A basic autonomous system powered by a piezoelectric harvester contains three components apart from the harvester: a fullwave rectifier, a reservoir capacitor and an electronic device performing the primary task of the system. In this contribution, a model describing the operation of such a system is derived. It is found that in steady-state operation, the piezoelectric harvester experiences two alternating load conditions due to the rectification process. These alternating load conditions can have a significant effect on the operation of the harvester and must be considered in the design of autonomous systems. The results also show that such an autonomous system works efficiently if it is connected to a high impedance load and excited by a frequency matching the anti-resonance frequency of the piezoelectric harvester.}}, author = {{Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013}}, keywords = {{Energy harvesting, harvester modeling, load dependence, generated voltage}}, number = {{05/2013}}, pages = {{159--161}}, title = {{{Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems}}}, year = {{2013}}, } @inproceedings{9797, abstract = {{A model approach for wedge/wedge bonding copper wire is presented. The connection between wire and substrate is based on a variety of physical effects, but the dominant one is the friction based welding while applying ultrasound. Consequently, a friction model was used to investigate the welding process. This model is built up universal and can be used to describe the formation of micro welds in the time variant contact area between wire and substrate. Aim of the model is to identify the interactions between touchdown, bond normal force, ultrasonic power and bonding time. To do so, the contact area is discretized into partial areas where a Point Contact Model is applied. Based on this approach it is possible to simulate micro and macro slip inside the contact area between wire and substrate. The work done by friction force is a main criterion to define occurring micro joints which influence the subsequent welding.}}, author = {{Althoff, Simon and Neuhaus, Jan and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{IMAPS 2013, 46th International Symposium on Microelectronics}}, keywords = {{Wire bonding, friction modeling, wire bond quality, contact element modeling}}, title = {{{A friction based approach for modeling wire bonding}}}, doi = {{10.4071/isom-2013-TA67}}, year = {{2013}}, } @inproceedings{9799, abstract = {{Ultrasonic wire bonding is a common technology for manufacturing electrical interconnects. In the field of power electronics, new thermal and electrical obligations arose due to increasing power density requirements. One approach to achieve these aims is replacing the wire material for heavy wire bonds from aluminum to copper. This material change leads to challenging tasks and problems, for instance the occurring wear of the bond tool. The wear is significantly higher using copper wire instead of aluminum and results in a dramatic loss in the amount of interconnects which can be produced reliable by a single tool. To reduce setting-up time in the production and minimizing costs, an enlarged bonding tool lifetime is desirable. Therefore, the paper discusses the influences of bonding parameters on the wear. The key question is which of the tasks cannot be fulfilled with increased wear of the tool, e.g. loss of process capability. The main functions are fixing the wire in the tool groove, predeformation, applying normal force and transmission of ultrasonic oscillation to the wire. To identify the most affecting factors, four bonding parameters are varied and their influences are investigated. These parameters are: (I) ultrasonic power, (II) tool geometry, (III) the way of tangential force transmission and (IV) loop trajectory.}}, author = {{Eichwald, Paul and Sextro, Walter and Althoff, Simon and Eacock, Florian and Schnietz, Mark and Guth, Karsten and Brökelmann, Michael}}, booktitle = {{15th Electronics Packaging Technology Conference}}, title = {{{Influences of Bonding Parameters on the Tool Wear for Copper Wire Bonding}}}, doi = {{10.1109/EPTC.2013.6745803}}, year = {{2013}}, } @inproceedings{9801, author = {{Hunstig, Matthias and Al-Ashtari, Waleed and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{9. Paderborner Workshop Entwurf mechatronischer Systeme}}, editor = {{Gausemeier, Jürgen and Dumitrescu, Roman and Rammig, Franz and Schäfer, Wilhelm and Trächtler, Ansgar}}, pages = {{359--372}}, publisher = {{Heinz Nixdorf Institut, Universität Paderborn}}, title = {{{Leistungs- und Bandbreitensteigerung von Energy-Harvesting-Generatoren für Energieautarke Systeme}}}, year = {{2013}}, } @inproceedings{9802, abstract = {{It has been shown previously that ``slip-slip'' operation of piezoelectric inertia motors allows higher velocities and smoother movements than classic ``stick-slip'' operation. One very promising driving option is to use a superposition of multiple sinusoidal signals. In this contribution, previous theoretical results are validated experimentally. The results confirm the theoretical result that for a given maximum frequency, usually defined by the actuator characteristics, a signal with high fundamental frequency and consisting of two superposed sine waves leads to the highest velocity and the smoothest motion. This result is of fundamental importance for the further development of high-velocity piezoelectric inertia motors.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, booktitle = {{Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop}}, keywords = {{Piezoelectric inertia motor, stick-slip motor, driving signal, velocity, smoothness}}, pages = {{16--18}}, title = {{{High-Velocity Slip-Slip Operation of Piezoelectric Inertia Motors - Experimental Validation}}}, year = {{2013}}, } @article{9803, abstract = {{Piezoelectric inertia motors, also known as stickslip drives or (smooth) impact drives, use the inertia of a body to drive it by a friction contact in small steps, in the majority of motors composed of a stick phase and a slip phase between the friction partners. For optimizing inertia motors, it is important to understand the friction contact correctly and to measure its properties appropriately. This contribution presents experimental set-ups for measuring the contact force, friction force and relative displacement in an actual inertia motor with a dry friction contact and numerical simulations of the motor operation. The motor uses a pre-stressed multilayer actuator with a displacement in the range of 20 $\mu$ m. It is shown that a previously postulated condition for the applicability of simple kinetic friction models is well fulfilled for the investigated motor. The friction contact in the motor is simulated using different kinetic friction models. The input for the friction models is the measured motion of the rod. The models qualitatively reproduce the measured motion but show quantitative deviations varying with frequency. These can be explained by vibrations of the driving rod that are experimentally investigated.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Journal of Intelligent Material Systems and Structures}}, keywords = {{Actuator, friction, motor, piezoelectric}}, number = {{11}}, pages = {{1380--1391}}, title = {{{Modelling the friction contact in an inertia motor}}}, doi = {{10.1177/1045389X12474354}}, volume = {{24}}, year = {{2013}}, } @article{9804, abstract = {{This contribution provides a systematic investigation and performance comparison of different modes of operation for piezoelectric inertia drives. The movement of these motors is classically assumed to consist of steps involving stiction and sliding, resulting in the term ``stick-slip drives''. In the first part of this contribution it has been found that using ideal driving signals, ``slip-slip'' operation without phases of stiction allows very high velocities, while the maximum velocity is limited principally in stick-slip operation. In this part it is shown that slip-slip operation is also suitable for use with real actuators, driven with frequency-limited versions of the ideal signals presented in part I. The motional performance of the motor as well as its wear and the required electric power are investigated for operation with different signals. It is found that for high velocity inertia motors it is recommendable to use actuators with large stroke and to drive them with a signal consisting of two harmonics at a high fundamental frequency, a result that is supported by similar setups implemented experimentally by other authors. Using Lanczos' \sigma factors to calculate the frequency-limited excitation signals instead of standard Fourier series additionally increases the motor performance significantly. The results help motor designers to choose the appropriate mode of operation and to optimise the motor parameters for their individual applications.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Sensors and Actuators A: Physical}}, keywords = {{Inertia motor}}, pages = {{79 -- 89}}, title = {{{Stick-slip and slip-slip operation of piezoelectric inertia drives - Part II: Frequency-limited excitation}}}, doi = {{10.1016/j.sna.2012.11.043}}, volume = {{200}}, year = {{2013}}, } @article{9805, abstract = {{Piezoelectric inertia motors, also known as ``stick--slip drives'', use the inertia of a body to drive it in small steps by means of a friction contact. While these steps are classically assumed to involve stiction and sliding, the motors can also operate in ``slip--slip'' mode without any phase of static friction. This contribution provides a systematic investigation and performance comparison of different stick--slip and slip--slip modes of operation. Different criteria for comparing the motional performance of inertia motors are defined: Steady state velocity, smoothness of motion, and start-up time. Using the example of a translational inertia motor excited by an ideal displacement signal, it is found that the maximum velocity reachable in stick--slip operation is limited principally, while continuous slip--slip operation allows very high velocities. For the investigated driving signals, the motor velocity is proportional to the square root of the actuator stroke. The motor performance with these ideal signals defines an upper boundary for the performance of real motors.}}, author = {{Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}}, journal = {{Sensors and Actuators A: Physical}}, keywords = {{Inertia motor, Stick--slip drive, Mode of operation, Performance indicator, Velocity maximization, Actuator stroke}}, pages = {{90 -- 100}}, title = {{{Stick-slip and slip-slip operation of piezoelectric inertia drives - Part I: Ideal Excitation.}}}, doi = {{10.1016/j.sna.2012.11.012}}, volume = {{200}}, year = {{2013}}, } @article{9807, abstract = {{Recently, focus on maintenance strategies has been shifted towards prognostic health management (PHM) and a number of state of the art algorithms based on data-driven prognostics have been developed to predict the health states of degrading components based on sensory data. Amongst these algorithms, Multiclass Support Vector Machines (MC-SVM) has gained popularity due to its relatively high classification accuracy, ability to classify multiple patterns and capability to handle noisy /incomplete data. However, its application is limited by the difficulty in determining the required kernel function and penalty parameters. To address this problem, this paper proposes a hybrid differential evolution -- particle swarm optimization (DE-PSO) algorithm to optimize the MC-SVM kernel function and penalty parameters. The differential algorithm (DE) obtains the search limit for the SVM parameters, while the particle swarm optimization algorithm (PSO) determines the global optimum parameters for a given training data set. Since degrading machinery components display several degradation stages in their lifetime, the MC-SVM trained with optimum parameters are used to estimate the health states of a degrading machinery component, from which the remaining useful life (RUL) is predicted. This method improves the classification accuracy of MC-SVM in predicting the health states of a machinery component and consequently increases the accuracy of RUL predictions. The feasibility of the method is validated using bearing prognostic run-to-failure data obtained from NASA public data repository. A comparative study between MC-SVM with parameters obtained using simple grid search with n-fold cross validation and MCSVM with DE-PSO based on prognostic performance metrics reveals that the proposed method has better performance, with all the cases considered falling within a 10 \% error margin. The method also outperforms other soft computing methods proposed in literature.}}, author = {{Kimotho, James Kuria and Sondermann-Wölke, Christopher and Meyer, Tobias and Sextro, Walter}}, journal = {{Chemical Engineering Transactions}}, pages = {{619--624}}, title = {{{Machinery Prognostic Method Based on Multi-Class Support Vector Machines and Hybrid Differential Evolution -- Particle Swarm Optimization}}}, doi = {{10.3303/CET1333104}}, volume = {{33}}, year = {{2013}}, } @article{9808, abstract = {{This study presents the methods employed by a team from the department of Mechatronics and Dynamics at the University of Paderborn, Germany for the 2013 PHM data challenge. The focus of the challenge was on maintenance action recommendation for an industrial machinery based on remote monitoring and diagnosis. Since an ensemble of data driven methods has been considered as the state of the art approach in diagnosis and prognosis, the first approach was to evaluate the performance of an ensemble of data driven methods using the parametric data as input and problems (recommended maintenance action) as the output. Due to close correlation of parametric data of different problems, this approach produced high misclassification rate. Event-based decision trees were then constructed to identify problems associated with particular events. To distinguish between problems associated with events that appeared in multiple problems, support vector machine (SVM) with parameters optimally tuned using particle swarm optimization (PSO) was employed. Parametric data was used as the input to the SVM algorithm and majority voting was employed to determine the final decision for cases with multiple events. A total of 165 SVM models were constructed. This approach improved the overall score from 21 to 48. The method was further enhanced by employing an ensemble of three data driven methods, that is, SVM, random forests (RF) and bagged trees (BT), to build the event based models. With this approach, a score of 51 was obtained . The results demonstrate that the proposed event based method can be effective in maintenance action recommendation based on events codes and parametric data acquired remotely from an industrial equipment.}}, author = {{Kimotho, James Kuria and Sondermann-Wölke, Chritoph and Meyer, Tobias and Sextro, Walter}}, journal = {{International Journal of Prognostics and Health Management}}, keywords = {{maintenance decision, Bagged trees, Decision trees, PSO-SVM, Random forests}}, number = {{2}}, title = {{{Application of Event Based Decision Tree and Ensemble of Data Driven Methods for Maintenance Action Recommendation}}}, volume = {{4}}, year = {{2013}}, } @article{9819, author = {{Herzig, Bardo and Klar, Tilman-Mathies}}, journal = {{Lernende Schule - Medienkompetenz entwickeln}}, number = {{64}}, pages = {{7--11}}, title = {{{Grundlagen medienbezogener Schulentwicklung}}}, year = {{2013}}, }