1,620 Works

Ethics and technology : some issues ; a booklet

Mirko Daniel Garasic & Steffen Steinert
Bioethical questions have a crucial role both in people’s personal choices and in the political domain. The aim of this booklet is to introduce you to the main controversies in contemporary bioethics, especially to those concerning the intersection between ethics and technology. At the end of reading the booklet, you will be equipped with the conceptual tools required to understand the main debates in ethics and technology and the most relevant positions in the debate....

Elastic and plastic poisson’s ratios of nanoporous gold

Lukas Lührs, Celal Soyarslan, Jürgen Markmann, Swantje Bargmann & Jörg Weißmüller
We explore the elastic and plastic Poisson’s ratios, mE and mP, of nanoporous gold, using digital image correlation during compression experiments including load/unload segments. The two coefficients differ significantly, with mE independent of the ligament size, L, and with a trend for mP / L at not too large L. Disorder in the network of ligaments may explain why mE is smaller than predicted by lattice-based models. Finite element simulations, based on the Deshpande–Fleck constitutive...

Elastic behaviour at the nanoscale of innovative composites of nanoporous gold and polymer

Emma Griffiths, Swantje Bargmann & B. Dayanand Reddy
Nanoporous gold is a material with unique properties that make it attractive for use in multiple areas. It has an extremely high compressive strain capability but is very brittle in tension which limits its usage. One means of addressing this limitation is to fill the voids of the nanoporous material with a polymer, resulting in a more ductile and stronger material. In this work, the mechanical properties of a nanocomposite representative sample are studied numerically....

Exceptionally strong, stiff and hard hybrid material based on an elastomer and isotropically shaped ceramic nanoparticles

Prokopios Georgopanos, Gerold A. Schneider, Axel Dreyer, Ulrich A. Handge, Volkan Filiz, Artur Feld, Ezgi D. Yilmaz, Tobias Krekeler, Martin Ritter, Horst Weller & Volker Abetz
In this work the fabrication of hard, stiff and strong nanocomposites based on polybutadiene and iron oxide nanoparticles is presented. The nanocomposites are fabricated via a general concept for mechanically superior nanocomposites not based on the brick and mortar structure, thus on globular nanoparticles with nanosized organic shells. For the fabrication of the composites oleic acid functionalized iron oxide nanoparticles are decorated via ligand exchange with an α,ω-polybutadiene dicarboxylic acid. The functionalized particles were processed...

On the impact of capillarity for strength at the nanoscale

Nadiia Mameka, Jürgen Markmann & Jörg Weißmüller
The interior of nanoscale crystals experiences stress that compensates for the capillary forces and that can be large, in the order of 1 GPa. Various studies have speculated on whether and how this surface-induced stress affects the stability and plasticity of small crystals. Yet, experiments have so far failed to discriminate between the surface contribution and other, bulk-related size effects. To clarify the issue, here we study the variation of the flow stress of a nanomaterial...

Effect of nodal mass on macroscopic mechanical properties of nanoporous metals

Jingsi Jiao & Norbert Huber
The current work investigates the effect of the nodal mass on the macroscopic mechanical behavior of nanoporous metals using the Finite Element Method. A nodal corrected beam modeling concept is introduced that allows local incorporation of the effective elastoplastic mechanical behavior of the nodal mass in the nodal area of a representative volume element (RVE). The calibration to the corresponding Finite Element solid model is achieved by integrating additional geometry and material parameters to the...

Hydrogen bonding and thermoplastic elastomers - a nice couple with temperature-adjustable mechanical properties

Elisabeth Wittenberg, Andreas Meyer, Steffen Eggers & Volker Abetz
Styrene-butadiene copolymers are modified with varying fractions of benzoic acid moieties being able to perform hydrogen bonding. This is done by using a simple synthetic approach which utilizes click hemistry. Temperature-dependent dynamic mechanical properties are studied, and it turns out that even the apparently rather simple ydrogen bonding motif has a marked impact on the material properties due to the fact that it facilitates the formation of a supramolecular polymer network. Besides a glass transition,...

A ferroelectric liquid crystal confined in cylindrical nanopores : reversible smectic layer buckling, enhanced light rotation and extremely fast electro-optically active Goldstone excitations

Mark Busch, Andriy V. Kityk, Wiktor Piecek, Tommy Hofmann, Dirk Wallacher, Sylwia Calus, Przemyslaw Kula, Martin Steinhart, Manfred Eich & Patrick Huber
The orientational and translational order of a thermotropic ferroelectric liquid crystal (2MBOCBC) imbibed in self-organized, parallel, cylindrical pores with radii of 10, 15, or 20 nm in anodic aluminium oxide monoliths (AAO) are explored by high-resolution linear and circular optical birefringence as well as neutron diffraction texture analysis. The results are compared to experiments on the bulk system. The native oxidic pore walls do not provide a stable smectogen wall anchoring. By contrast, a polymeric...

Controlling thermal emission with refractory epsilon-near-zero metamaterials via topological transitions

Pavel N. Dyachenko, Sean Molesky, Alexander Petrov, Michael Störmer, Tobias Krekeler, Slawa Lang, Martin Ritter, Zubin Jacob & Manfred Eich
Control of thermal radiation at high temperatures is vital for waste heat recovery and for high-efficiency thermophotovoltaic (TPV) conversion. Previously, structural resonances utilizing gratings, thin film resonances, metasurfaces and photonic crystals were used to spectrally control thermal emission, often requiring lithographic structuring of the surface and causing significant angle dependence. In contrast, here, we demonstrate a refractory W-HfO2 metamaterial, which controls thermal emission through an engineered dielectric response function. The epsilon-near-zero frequency of a metamaterial...

The perfect match: the role of categorical fit between venture capitalists and their startup investments

Jan-Frederik Arnold
This dissertation sheds light on how the categorical fit between venture capitalists and startups affect the matching process before a funding round. The study uses market categories to measure new venture’s distinctiveness and the cultural distance between venture capitalists and new ventures. The empirical analysis of 11 years of venture capital investment data in the USA confirms that experienced and high status investors prefer more distinctive new ventures and that the negative effect of cultural...

3D stochastic bicontinuous microstructures: generation, topology and elasticity

Celal Soyarslan, Swantje Bargmann, Marc Pradas & Jörg Weißmüller
Motivated by recent experimental investigations of the mechanical behavior of nanoporous metal we explore an efficient and robust method for generating 3D representative volume elements (RVEs) with strikingly similar behavior. Our approach adopts Cahn's method of generating a Gaussian random field by taking a superposition of standing sinusoidal waves of fixed wavelength but random in direction and phase. In its theory part, our study describes closed-form xpressions for how the solid volume fraction affects the...

Noise impact in powered respirators

Klaus-Dieter Fröhner & Ze Li
In respirators the users are closely linked with the apparatus. The new types of respirators use powered ventilators so that the technical layout and the used elements have strong effects on the users. The most unwanted effect is noise that influences not only the hearing bility of the user but also impairs the communication between users. This study aims at a systematic investigation of influencing factors based on a study evaluating methods for measurements. It...

Wie kommt das Repositorium in die Suchmaschine?

Beate Rajski
Publication repositories use a special interface for the provision of their metadata: OAI-PMH ("Protocol for Metadata Harvesting" of the Open Archive Initiative). Since this is not used by search engines such as Google Scholar, metadata is also provided in the machine-readable HTML header for a publication.

Stress and strain of aging innovators in the product development process

Kerstin Nawroth
Workforces in industrialized countries in general are becoming older because the babyboom generation is reaching an advanced age and the percentage of young employees is constantly decreasing.

Interlaminar Fracture Energy of Laminates Made of Thermoplastic Impregnated Fiber Bundles

Hans Wittich & Klaus Friedrich
Interlaminar mode I- and II-fracture energy measurements (in terms of the strain energy release rate) were carried out with different laminates of a glass fiber/thermoplastic PA 12- and aramid fiber/PA 12-composite system. Specimens were prepared from fiber bundles interspersed with polymer powder and a polymer sheath around them. The results, obtained from two different test procedures and data reduction methods, reflect a good interlaminar fracture toughness of the different laminates. This can be attributed to...

Influence of connector design on fracture probability of ceramic fixed-partial dentures

Won‐Suck Oh, Nils Götzen & Kenneth J. Anusavice
Fracture of ceramic fixed-partial dentures (FPDs) tends to occur in the connector area because of stress concentrations. The objective of this study was to test the hypothesis that the radius of curvature at the gingival embrasure of the FPD connector significantly affects the fracture resistance of three-unit FPDs. Two three-dimensional finite element models (FEMs), representing two FPD connector designs, were created in a manner corresponding to that described in a previous experimental study (Oh, 2002)....

Identification of fully coupled anisotropic plasticity and damage constitutive equations using a hybrid experimental–numerical methodology with various triaxialities

Z. M. Yue, Celal Soyarslan, H. Badreddine, K. Saanouni & A. E. Tekkaya
A hybrid experimental–numerical methodology is presented for the parameter identification of a mixed nonlinear hardening anisotropic plasticity model fully coupled with isotropic ductile damage accounting for microcracks closure effects. In this study, three test materials are chosen: DP1000, CP1200, and AL7020. The experiments involve the tensile tests with smooth and notched specimens and two types of shear tests. The tensile tests with smooth specimens are conducted in different directions with respect to the rolling direction....

Ships may encounter high wind loads—a statistical assessment

Werner Blendermann
The wind loads on ships are treated under long-term wind conditions. Probabilities of high forces and moments are given. A probabilistic criterion for wind heeling levers is proposed.

Biogas and nutrients from blackwater, lawn cuttings and grease trap residues : experiments for Hamburg’s Jenfelder Au district

Saskia Hertel, P. Navarro, Stefan Deegener & Ina Körner
Background: The project KREIS focuses on a new combination of renewable energy provision with innovative wastewater treatment, called the “Hamburg Water Cycle®” (HWC) which will be applied in Hamburg’s neighbourhood Jenfelder Au. HWC includes a separate collection of rainwater, greywater and blackwater. Vacuum toilets are used to concentrate the blackwater. Biogas will be produced from the blackwater in an anaerobic digestion process together with co-substrates. The blackwater will be transported to the anaerobic pre-treatment facility...

Numerical analysis of propeller-induced higher-order pressure fluctuations on the ship hull

Stephan Berger
Gegenstand der vorliegenden Arbeit ist die Entwicklung und Validierung einer hybriden Simulationsmethode zur Untersuchung propellerinduzierter Druckschwankungen höherer Ordnung in kavitierender Strömung. Es werden zwei Arten von Propellerkavitation berücksichtigt: Schichtkavitation auf den Flügeln des Propellers und Spitzenwirbelkavitation. Dabei stellt sich heraus, dass insbesondere die Interaktion zwischen Schicht- und Spitzenwirbelkavitation zu stärkeren Druckschwankungen höherer Ordnung führen kann. Herzstück der neu entwickelten Methode ist das Paneelverfahren panMARE, welches zur Bestimmung der Propellerumströmung und von Schichtkavitation eingesetzt wird. Darüber...

Deformation of press-fitted metallic resurfacing cups. Part 2: Finite element simulation

A. Yew, Zhongmin Jin, A. Donn, Michael Morlock & Graham H. Isaac
The deformation of metallic acetabular cups employed for metal-on-metal hip resurfacing procedures was considered theoretically using the finite element method in the present study, following on the experimental investigation reported in Part 1. Three representative cups, characterized by the cup wall thickness as thin, intermediate, and thick, were considered. For the intermediate cup, the effects of both the size and the diametral interference on the cup deformation were investigated. Both two-dimensional axisymmetric and three-dimensional finite...

Deformation of press-fitted metallic resurfacing cups. Part 1: Experimental simulation

Zhongmin Lin, Steven Meakins, Michael Morlock, Peter A. Parsons, Catherine Hardaker, Magnus Flett & Graham H. Isaac
The interference press fit of a metallic one-piece acetabular cup employed for metal-on-metal hip resurfacing procedures was investigated experimentally under laboratory conditions in the present study, in particular regarding the cup deformation. Tests were carried out in cadavers as well as polyurethane foams of various grades with different elastic moduli to represent different cancellous bone qualities. The cadaver test was used to establish the most suitable configuration of the foam model representing realistic support and...

Fracture toughness of short fiber/thermoplastic matrix composites, compared on the basis of different test methods

Klaus Friedrich, R. Walter, J. Voigt & M. Grosso
A variety of thermoplastic matrices, including Polyethersulfone (PES), Polyoxymethylene (POM), and toughness modified Polyethylenterephthalate (PET), and their short glass fiber reinforced composites have been tested with respect to their impact resistance. Test methods applied, all characterize in some respects the "toughness" of these materials. It turns out, however, that the ranking order of their toughnesses varies quite remarkably, depending on the particular testing procedure. In a fracture mechanics test with compact tension specimens, the fracture...

From the World Brain to the first transatlantic information dialogue : activities in information and documentation in Germany in the first half of the 20 th Century

Thomas Hapke
It is not enough to found libraries. It is necessary, by means of lectures and bibliographic. lists, to instruct those eager for knowledge in the best methods of utilizing their treasures. And this is by no means so easy as it sounds!

Cross-cultural comparison of company organization structure

Bakri Osman Hamad & Klaus-Dieter Fröhner
This study tends to quantify some differences of developed and developing countries in the field of human resources. Due to different social and cultural milieus, no global solution is available to fit each country. This fact necessitates a special examination for countries according to their cultural context. In this part of the study, the cultural and social influential elements of the working force in a developing country were examined. The specific elements of satisfaction and...

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