3,447 Works

Helical milling of bore holes in Ti6Al4V parts produced by selective laser melting with simultaneous support structure removal

Wolfgang Hintze, Robert Schötz, Jan Philipp Mehnen, Lars Köttner & Carsten Möller
Selective Laser Melting (SLM) is a powder bed based Additive Manufacturing (AM) process that is currently being established in the series production of Ti6Al4V components in the aviation industry. One advantage is the significantly lower Buy-to-Fly ratio. However, subsequent machining is necessary in order to remove support structures of the SLM process and to fulfill quality requirements. Experimental results on support structure removal and simultaneous finishing of holes by helical milling are presented. Engagement conditions...

Extreme scale-dependent tensile properties of epoxy fibers

Xiaomeng Sui, Mayank Tiwari, Israel Greenfeld, Rafail L. Khalfin, Hauke Meeuw, Bodo Fiedler & H. Daniel Wagner
Epoxy fibers with different diameters were prepared by hot drawing and their mechanical properties were measured under tension. The stiffness, strength, ultimate strain, and toughness revealed substantial scale-dependent effects as they all significantly increased with a decrease in size. Compared to bulk epoxy, an intrinsically brittle material, thin epoxy fibers displayed a highly ductile behavior under tension. A drop in stress observed immediately beyond the yield point was followed by the development of a stable...

Dynamics of postcombustion CO2 capture plants : modeling, validation, and case study

Adam van de Haar, Carsten Trapp, Kai Wellner, Rrobert de Kler, Gerhard Schmitz & Piero Colonna

Laser scored machining of fiber reinforced plastics to prevent delamination

Wolfgang Hintze, Marcel Cordes, Tobias Geis, Melchior Frieder Blühm, Claus Emmelmann & Marten Canisius

Ein Ansatz zur nachvollziehbaren Verifikation medizinisch-cyber-physikalischer Systeme

Julia Padberg, Alexander Schlaefer & Sibylle Schupp

Modeling of the German National Standard for High Pressure Natural Gas Flow Metering in Modelica

Michael von der Heyde, Gerhard Schmitz & Bodo Mickan
The German national metrological institute Physikalisch-Technische Bundesanstalt uses a High Pressure Piston Prover as the primary standard for high pressure natural gas flow meters. The High Pressure Piston Prover measures the gas flow rate using the time a piston needs to displace a defined enclosed volume of gas in a cylinder. Fluctuating piston velocity during measurement can be a significant source of uncertainty if not considered in an appropriate way (Mickan et al., 2010). A...

Combinatorial n-fold integer programming and applications

Dušan Knop, Martin Koutecký & Matthias Mnich
Many fundamental NP-hard problems can be formulated as integer linear programs (ILPs). A famous algorithm by Lenstra solves ILPs in time that is exponential only in the dimension of the program, and polynomial in the size of the ILP. That algorithm became a ubiquitous tool in the design of fixed-parameter algorithms for NP-hard problems, where one wishes to isolate the hardness of a problem by some parameter. However, in many cases using Lenstra’s algorithm has...

Inexact iterative projection methods for linear and nonlinear eigenvalue problems

Nicolai Rehbein
Wir geben einen allgemeinen Ansatz für das Jacobi-Davidson-Verfahren basierend auf einem beliebigen iterativen Verfahren zum Lösen eines linearen oder nichtlinearen Eigenwertproblems. Die Auswirkung eines inexakten Lösens der Korrekturgleichung wird betrachtet und hieraus kann lineare Konvergenz für drei Fälle von verschiedene Vorbedingungen bewiesen werden. Abschließend wird noch für ein Zwei-Parameter-Eigenwertproblem, welches durch dynamische Systeme mit Totzeit entsteht, ein Funktional eingeführt, welches ähnliche Eigenschaften wie das Rayleigh-Funktional aufweist.

Iron(II)-catalyzed biomimetic aerobic oxidation of alcohols

Arnar Guðmundsson, Kim Elisabeth Schlipköter & Jan-E. Bäckvall

4D spatio-temporal deep learning with 4D fMRI data for autism spectrum disorder classification

Marcel Bengs, Nils Thorben Gessert & Alexander Schlaefer
Autism spectrum disorder (ASD) is associated with behavioral and communication problems. Often, functional magnetic resonance imaging (fMRI) is used to detect and characterize brain changes related to the disorder. Recently, machine learning methods have been employed to reveal new patterns by trying to classify ASD from spatio-temporal fMRI images. Typically, these methods have either focused on temporal or spatial information processing. Instead, we propose a 4D spatio-temporal deep learning approach for ASD classification where we...

Advanced Modeling of Electric Components in Integrated Energy Systems with the TransiEnt Library

Jan-Peter Heckel & Christian Becker
Integrated Energy Systems (IES) with the coupling of electricity, gas and heat are assumed to be a suitable concept for future energy systems. For the necessary energy system analysis with respect to dynamics and stability, powerful tools are needed. Such tools should be provided in open toolboxes to make the research more transparent, comprehensive and communicative. It is aimed that scientists collaborate on models for multimodal energy system analysis. The dynamic simulation is a method...

Electrical double layer capacitance of curved graphite electrodes

Jannes Seebeck, Peter Schiffels, Sabine Schweizer, Jörg-Rüdiger Hill & Robert Meißner
To improve the understanding of the relation between electrode curvature and energy storage mechanisms, a systematic investigation of the correlation between convex and concave electrode surfaces and the differential capacitance of an electrochemical double layer capacitor using molecular dynamics simulations is presented. Each electrode consists of three layers of curved graphene sheets with a convex and concave surface to which the constant potential method was applied. The differential capacitance shows a fluctuating behavior with respect...

Wireless energy and data transmission ASIC for blood pressure measurement in an aneurysm implant

Rajeev Ranjan, Bibin John, Dipal Gosh, Soumil Kumar, Lait Abu Saleh, Dietmar Schröder & Wolfgang Krautschneider
Aneurysm implant requires multiple pressure sensors integrated into the stent graft for recording pressure profile inside an aneurysm sac. This paper details the design of an ASIC which receives power wirelessly using inductive coupling, fetches pressure data from a seperate chip and transmits data wirelessly. Besides, the ASIC extends the functionality of the external pressure measurement chip to support up to four pressure sensors by using an analog multiplexer. Error detection and forward error correction...

Stochastic analysis of ocean wave states with and without rogue waves

Ali Hadjihosseini, Joachim Peinke & Norbert Hoffmann

Multi-domain design structure matrix approach applied to urban system modeling

Peter Hoffmann, Yutaka Nomaguchi, Keishiro Hara, Kana Sawai, Ingenuin Gasser, Myriam Albrecht, Benjamin Bechtel, Jana Fischereit, Kikuo Fujita, Philine Gaffron, Anne Caroline Krefis, Markus Quante, Jürgen Scheffran, Katharina Heinke Schlünzen & Malte von Szombathely
Modeling the urban system for urban health and well-being with the aim of finding ways to optimize the well-being of urban dwellers is a complex task. Different modeling approaches that consider specific parts of the urban system, e.g., environmental stressors, urban society, and urban morphology, need to be integrated. The conceptual model of health-related urban well-being (UrbWellth) has been constructed to provide a structure for an integrated modeling framework. However, interfaces between the different modeling...

Reader architectures for wireless surface acoustic wave sensors

Fabian Lurz, Thomas Ostertag, Benedict Scheiner, Robert Weigel & Alexander Kölpin
Wireless surface acoustic wave (SAW) sensors have some unique features that make them promising for industrial metrology. Their decisive advantage lies in their purely passive operation and the wireless readout capability allowing the installation also at particularly inaccessible locations. Furthermore, they are small, low-cost and rugged components on highly stable substrate materials and thus particularly suited for harsh environments. Nevertheless, a sensor itself does not carry out any measurement but always requires a suitable excitation...

A clinically evaluated interferometric continuous-wave radar system for the contactless measurement of human vital parameters

Fabian Michler, Kilin Shi, Sven Schellenberger, Tobias Steigleder, Anke Malessa, Laura Hameyer, Nina Neumann, Fabian Lurz, Christoph Ostgathe, Robert Weigel & Alexander Kölpin
Vital parameters are key indicators for the assessment of health. Conventional methods rely on direct contact with the patients’ skin and can hence cause discomfort and reduce autonomy. This article presents a bistatic 24 GHz radar system based on an interferometric six-port architecture and features a precision of 1 µm in distance measurements. Placed at a distance of 40 cm in front of the human chest, it detects vibrations containing respiratory movements, pulse waves and...

Radar-Based Heart Sound Detection

Christoph Will, Kilin Shi, Sven Schellenberger, Tobias Steigleder, Fabian Michler, Jonas Fuchs, Robert Weigel, Christoph Ostgathe & Alexander Kölpin
This paper introduces heart sound detection by radar systems, which enables touch-free and continuous monitoring of heart sounds. The proposed measurement principle entails two enhancements in modern vital sign monitoring. First, common touch-based auscultation with a phonocardiograph can be simplified by using biomedical radar systems. Second, detecting heart sounds offers a further feasibility in radar-based heartbeat monitoring. To analyse the performance of the proposed measurement principle, 9930 seconds of eleven persons-under-tests’ vital signs were acquired...

A 24 GHz Waveguide based Radar System using an Advanced Algorithm for I/Q Offset Cancelation

Christoph Will, Sarah Linz, Sebastian Mann, Fabian Lurz, Stefan Lindner, Robert Weigel & Alexander Kölpin
Precise position measurement with micrometer accuracy plays an important role in modern industrial applications. Herewith, a guided wave Six-Port interferometric radar system is presented. Due to limited matching and discontinuities in the radio frequency part of the system, the designers have to deal with DC offsets. The offset voltages in the baseband lead to worse relative modulation dynamics relating to the full scale range of the analog-To-digital converters and thus, considerably degrade the system performance....

A dataset of radar-recorded heart sounds and vital signs including synchronised reference sensor signals

Kilin Shi, Sven Schellenberger, Christoph Will, Tobias Steigleder, Fabian Michler, Jonas Fuchs, Robert Weigel, Christoph Ostgathe & Alexander Kölpin
Radar systems allow for contactless measurements of vital signs such as heart sounds, the pulse signal, and respiration. This approach is able to tackle crucial disadvantages of state-of-the-art monitoring devices such as the need for permanent wiring and skin contact. Potential applications include the employment in a hospital environment but also in home care or passenger vehicles. This dataset consists of synchronised data which are acquired using a Six-Port-based radar system operating at 24 GHz,...

Six-port based interferometry for precise radar and sensing applications

Alexander Kölpin, Fabian Lurz, Sarah Linz, Sebastian Mann, Christoph Will & Stefan Lindner
Microwave technology plays a more important role in modern industrial sensing applications. Pushed by the significant progress in monolithic microwave integrated circuit technology over the past decades, complex sensing systems operating in the microwave and even millimeter-wave range are available for reasonable costs combined with exquisite performance. In the context of industrial sensing, this stimulates new approaches for metrology based on microwave technology. An old measurement principle nearly forgotten over the years has recently gained...

Distributed formation control of multi-agent systems

Marcus Bartels
Diese Dissertation behandelt die verteilte Regelung von Multi-Agenten-Systemen mit Formationsflügen als Schwerpunkt. Ein wesentlicher Beitrag ist ein neuer Ansatz zur Reglersynthese auf der Grundlage einer Deskriptordarstellung des Multi-Agenten-Systems, welcher in dieser Arbeit entwickelt und erfolgreich in Simulationen getestet wurde. Zudem wurden bestehende Ansätze in einer Simulationsstudie untersucht und eine neue Reglerarchitektur eingeführt, welche die Vorteile der bestehenden Ansätze vereint. Mit dem Ziel der experimentellen Validierung dieser Ergebnisse wurden Versuchsplattformen mit mehreren Quadrokoptern entwickelt. Diese werden...

Analytical and numerical investigation of the airflow in face masks used for protection against COVID-19 virus : implications for mask design and usage

Robinson Peric & Milovan Perić
Der Einsatz von Atemschutzmasken für die breite Öffentlichkeit wurde in der Literatur als ein möglicher Ansatz vorgeschlagen, um die Virusausbreitung während der weltweiten COVID-19 Pandemie zu reduzieren. Allerdings deuten Literaturdaten darauf hin, dass viele Atemschutzmasken keinen verlässlichen Schutz vor einer Infektion bieten. Dieser Artikel untersucht die Hypothese, dass der Hauptgrund für diese eingeschränkte Schutzwirkung der nicht-passgenaue Sitz der Masken ist, wodurch Virus-transportierende Tröpfchen mit dem Luftstrom durch Spalte zwischen Dichtung und Gesicht eintreten oder austreten...

Solving packing problems with few small items using rainbow matchings

Max Bannach, Sebastian Berndt, Marten Maack, Matthias Mnich, Alexandra Lassota, Malin Rau & Malte Skambath
An important area of combinatorial optimization is the study of packing and covering problems, such as Bin Packing, Multiple Knapsack, and Bin Covering. Those problems have been studied extensively from the viewpoint of approximation algorithms, but their parameterized complexity has only been investigated barely. For problem instances containing no “small” items, classical matching algorithms yield optimal solutions in polynomial time. In this paper we approach them by their distance from triviality, measuring the problem complexity...

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