156 Works

Size affected dislocation activity in crystals : advanced surface and grain boundary conditions

Edgar Husser, Celal Soyarslan & Swantje Bargmann
Extended crystal plasticity theories are well established to study size-dependent hardening of metals. Surface and inner grain boundary conditions play a significant role for crystals at small scales as they affect the dislocation activity and, hence, alter strength and strain hardening behavior. Conventional micro boundary conditions, i.e., microhard and microfree, are unable to capture the underlying physics as they describe ideal and over-simplified surface/interface conditions. In this work, advanced boundary conditions for gradient extended crystal...

A nanoporous gold-polypyrrole hybrid nanomaterial for actuation

Ke Wang, Charlotte Stenner & Jörg Weißmüller
We discuss actuation with a hybrid nanomaterial that is made by electro-polymerizing pyrrole on the internal surfaces of dealloying-derived nanoporous gold and then letting aqueous electrolyte be imbibed in the remaining pore space. In this way, active polypyrrole films are contacted by two separate but individually contiguous conduction paths, providing efficient transport of ions in the electrolyte channels and of electrons in the metal skeleton. The metal skeleton also serves to enhance the mechanical behavior...

COLIBRI MODULE O17 : documentation of project results : final report

Jens Myrup Pedersen
During 2014 and 2017 the project COLIBRI (Collaboration and Innovation for Better, Personalised and IT-Supported Teaching) was carried out between seven European Universities, two companies, and a national documentation center. The aim was to develop and try out new and innovative teaching methods. You can read more about the project at www.erasmus-colibri.eu . The purpose of this document is to share the experiences we had during the three years, in a way that is useful...

Nanomechanics of individual aerographite tetrapods

Raimonds Meija, Stefano Signetti, Arnim Schuchardt, Kerstin Meurisch, Daria Smazna, Matthias Mecklenburg, Karl Schulte, Donats Erts, Oleg Lupan, Bodo Fiedler, Yogendra Kumar Mishra, Rainer Adelung & Nicola M. Pugno
Carbon-based three-dimensional aerographite networks, built from interconnected hollow tubular tetrapods of multilayer graphene, are ultra-lightweight materials recently discovered and ideal for advanced multifunctional applications. In order to predict the bulk mechanical behaviour of networks it is very important to understand the mechanics of their individual building blocks. Here we characterize the mechanical response of single aerographite tetrapods via in situ scanning electron and atomic force microscopy measurements. To understand the acquired results, which show that...

Effect of surface slasticity on the elastic response of nanoporous gold

Celal Soyarslan, Edgar Husser & Swantje Bargmann
In this work, the effect of surface elasticity on the effective elastic properties of nanoporous gold is studied. To this end, a theoretical framework for surface elasticity effects in submicron-sized solids is implemented as a user-defined finite element subroutine. This allows the use of the theory in large-scale engineering problems. The theory suggests a zero-thickness surface accommodating unique energetic properties and surface tension. For the example of ball-and-stick diamond cubic unit cell structures for nanoporous...

Cross-disciplinary communication among Ph.D. candidates : how to make it work

Ulrike Herzog, Alette Winter & Christian H. Kautz
Cross-disciplinary research settings are highly challenging for young scientists. In our research centre, Ph.D. candidates with various disciplinary backgrounds are expected to cooperate. To support cooperation, we designed a Ph.D. programme that fosters cross-disciplinary communication. The programme uses an innovative teaching format that aims to broaden the participants’ understanding of technical basics and to improve their academic teaching skills. Being faced with dissatisfaction among the Ph.D. candidates at first, we introduced a targeted feedback process...

Deformation mechanisms in nanoporous metals : effect of ligament shape and disorder

Jingsi Jiao & Norbert Huber
The current work presents a numerical modelling approach for investigating the effect of ligament shape and disorder on the macroscopic mechanical response of nanoporous gold (NPG). The approach starts from a ‘single ligament’ analysis with respect to three fundamental deformation modes, bending, torsion, and compression, that depend on the ligament shape. It can be shown that the predictive capability of the highly computationally efficient beam model is sufficient for a large variation in ligament shapes....

Silver-rich clusters in nanoporous gold

Tobias Krekeler, Anastasia V. Straßer, Matthias Graf, Ke Wang, Christian Hartig, Martin Ritter & Jörg Weißmüller
Herein we report on how to render Ti3C2Tx (MXene) monolayers deposited on SiO2/Si wafers, with different SiO2 thicknesses, visible. Inputting the effective thickness of a Ti3C2Tx monolayer (1 ± 0.2 nm) measured by atomic force microscopy, and its refractive index into a Fresnel-law-based simulation software, we show that the optical contrast of Ti3C2Tx monolayers deposited on SiO2/Si wafers depends on the SiO2 thickness, number of MXene layers, and the light’s wavelength. The highest contrast was found for SiO2...

Die Architektur von Offenheit - Überlegungen zur Gestaltung der digitalen Transformation

Axel Dürkop
Vortragstext der Nachwuchskeynote auf dem Jungen Forum für Medien und Hochschulentwicklung 2017 an der Uni Hamburg. Die Potenziale der Gestaltung von Offenheit sozio-technischer Systeme bilden sich in der Architektur ab. Entscheidungen im Entwicklungsprozess dieser Systeme sind nicht nur gestalterischer, sondern auch politischer Art. Am Ende des Beitrags werden Beispiele für dezentrale und föderierte Architekturen entfaltet.

Finite element simulation of pole vaulting

Sven Drücker, Konrad Schneider, Navneet-Kaur Ghothra & Swantje Bargmann
Pole vaulting is one of the most spectacular disciplines in athletics. The evolution of world record heights is strongly influenced by the development of advanced poles and subsequent materials. Employing advanced, load-adjusted composites has resulted in a steady increase of the world record height. This study provides a framework for finite element simulations of pole vaulting with focus on the initial and boundary conditions as well as finite element choices. The influence of the pole...

Adsorption-induced deformation of nanoporous materials : a review

Gennady Y. Gor, Patrick Huber & Noam Bernstein
When a solid surface accommodates guest molecules, they induce noticeable stresses to the surface and cause its strain. Nanoporous materials have high surface area and, therefore, are very sensitive to this effect called adsorption-induced deformation. In recent years, there has been significant progress in both experimental and theoretical studies of this phenomenon, driven by the development of new materials as well as advanced experimental and modeling techniques. Also, adsorptioninduced deformation has been found to manifest...

Highly porous α-Al 2 O 3 ceramics obtained by sintering atomic layer deposited inverse opals

Kaline P. Furlan, Robert M. Pasquarelli, Tobias Krekeler, Martin Ritter, Robert Zierold, Kornelius Nielsch, Gerold A. Schneider & Rolf Janßen
A process for generating highly porous α-Al2O3 ceramics has been developed. In this paper, a combination of self-assembly and atomic layer deposition is demonstrated as a means to fabricate inverse alumina opals, which have their structures transformed via sintering. The resulting highly porous structure is stable even after a 4 h dwell time at 1400 °C, in contrast to structures generated by conventional powder metallurgy, sol-gel or colloidal powder suspension infiltration methods. TEM analysis reveals...

A Comparison of German and Indian innovation pathways in the auto component industry

Katharina Kalogerakis, Luise Fischer & Rajnish Tiwari
This paper is a part of a series of analyses conducted within a BMBF-funded research project to investigate potentials of frugal innovations for Germany. One of the objectives of this project has been to identify innovation pathways that foster frugal innovations. Since auto component suppliers based in India are known to contribute significantly to the development of “affordable and good quality” vehicles, it was considered useful to conduct comparative studies of the prevalent innovation pathways...

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...

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...

Integrating cell on chip : novel waveguide platform employing ultra-long optical paths

Lena Simone Fohrmann, Gerrit Sommer, Giampaolo Pitruzzello, Thomas F. Krauss, Alexander Petrov & Manfred Eich
Optical waveguides are the most fundamental building blocks of integrated optical circuits. They are extremely well understood, yet there is still room for surprises. Here, we introduce a novel 2D waveguide platform which affords a strong interaction of the evanescent tail of a guided optical wave with an external medium while only employing a very small geometrical footprint. The key feature of the platform is its ability to integrate the ultra-long path lengths by combining...

Cemented tibial tray fixation

Katrin Nagel
Die totale Kniearthroplastie ist ein erfolgreicher chirurgischer Eingriff, führte aber in 2013 in Deutschland zu etwa 25 000 Revisionseingriffen. Häufig ist die tibiale Komponente der Prothese betroffen. Die Vermeidung oder ein Hinauszögern des Revisionseingriffes ist im Hinblick auf das erhöhte Infektionsrisiko und den Knochenverlust bei der Implantatextraktion im Interesse des Patienten. Bis zu ein Drittel der Revisionen werden aufgrund einer aseptischen Lockerung der Prothesenkomponenten durchgeführt, die durch eine unzureichende Implantatfixation ausgelöst wird. Die Fixierung der Implantate...

Improvement of the process stability of arylmalonate decarboxylase by immobilization for biocatalytic profen synthesis

Miriam Aßmann, Carolin Mügge, Sarah Katharina Gaßmeyer, Junichi Enoki, Lutz Hilterhaus, Robert Kourist, Andreas Liese & Selin Kara
The enzyme arylmalonate decarboxylase (AMDase) enables the selective synthesis of enantiopure (S)-arylpropinates in a simple single-step decarboxylation of dicarboxylic acid precursors. However, the poor enzyme stability with a half-life time of about 1.2 h under process conditions is a serious limitation of the productivity, which results in a need for high catalyst loads. By immobilization on an amino C2 acrylate carrier the operational stability of the (S)-selective AMDase variant G74C/M159L/C188G/V43I/A125P/V156L was increased to a half-life...

Forwarding strategies for 6LoWPAN-fragmented IPv6 datagrams

Andreas Weigel
Diese Arbiet untersucht verschiedene Implementierungsstrategien für den Weiterleitungsaspekt des 6LoWPAN protocols für „low power and lossy networks“ (LLNs). Die Leistungsfähigkeit in Hinblick auf Latenz und Zuverlässigkeit wird für das LLN-typische Datensammlung- Verkehrsmuster für direkte und reassemblierende Strategien untersucht. Ein neuartiger Ansatz basierend auf Lauschen und dem Aussetzen von Transmissionen wird entwickelt und es wird gezeigt, dass dieser die Ende-zu-Ende-Zuverlässigkeit in einem Großteil der untersuchten Simulationsszenarien und Testnetzwerken signifikant verbessert.

BDD-based value analysis for X86 executables

Sven Mattsen
Wir präsentieren eine abstrakte Domäne zur Ganzzahlanalyse, die für maschinennahen Code, wo Präzision besonders wichtig ist, geeignet ist. Ganzzahlanalysen approximieren Ganzzahlmengen normalerwise durch konvexe Mengen, wobei Präzision verloren geht, aber Effizienz gewonnen wird. Unsere Ganzzahlanalyse basiert auf modifizierten binären Entscheidungsbäumen (BDD), die ein effizientes Speichern von Ganzzahlmengen ermöglichen. Die zugehörigen Transferfunktionen definieren wir auf der Struktur der BDDs, was sie selbst für sehr große Mengen effizient macht. Wir stellen die Domäne in Form einer Bibliothek...

Structural and differential analysis for program comprehension of executables

Arne Wichmann
Wir führen eine strukturelle Analyse (StA), die Schlüsselstellen für das Programmverständnis von ausführbaren Programmen identifiziert, und eine differenzielle Analyse (DiA), die Ähnlichkeiten zwischen solchen ausführbaren Programmen identifiziert, ein. Unsere StA basiert auf einer neuen Abstraktion von Kontrollflussinformationen auf Statementebene zu einer Repräsentation mit einer graphischen Ansicht, die eine intuitive Identifizierung von mitgelieferten Mustern ermöglicht. Unsere DiA basiert auf Sequenzalignments und benötigt nur die Position und Größe der Funktionen. Wir validieren die StA manuell mit einer...

PGE production in Southern Africa, part II: Environmental aspects

Benedikt Buchspies, Lisa Thormann, Charles Mbohwa & Martin Kaltschmitt
Platinum group elements (PGEs, 6E PGE = Pt + Pd + Rh + Ru + Ir + Au) are used in numerous applications that seek to reduce environmental impacts of mobility and energy generation. Consequently, the future demand for PGEs is predicted to increase. Previous studies indicate that environmental impacts of PGE production change over time emphasizing the need of up-to-date data and assessments. In this context, an analysis of environmental aspects of PGE production...

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Publication Year

  • 2017
    156

Registration Year

  • 2018
    27
  • 2017
    129