83 Works

Fourth-order strain-gradient phase mixture model for nanocrystalline fcc materials

Benjamin Klusemann, Swantje Bargmann & Yuri Estrin
The proposed modeling approach for nanocrystalline materials is an extension of the local phase mixture model introduced by Kim et al (2000 Acta Mater. 48 493–504). Local models cannot account for any non-uniformities or strain patterns, i.e. such models describe the behavior correctly only as long as it is homogeneous. In order to capture heterogeneities, the phase mixture model is augmented with gradient terms of higher order, namely second and fourth order. Different deformation mechanisms...

A principle curvatures analysis of the isothermal evolution of nanoporous gold: Quantifying the characteristic length-scales

Markus Ziehmer, Kaixiong Hu, Ke Wang & Erica Lilleodden
A study of the isothermal evolution of a nanoporous gold (npg) microstructure after dealloying has been performed. In order to adequately characterize its complex three-dimensional bicontinuous ligamentring structure, an analysis of the scaled principle curvatures k1 and k2 based on representative volumes of meshed 3D reconstructions was applied. Five npg samples, as obtained from an electrolytical dealloying process, with different mean ligament diameters ranging from ca. 25 nm (as-dealloyed) to ca. 420 nm (from annealing...

Interface elasticity effects in polymer-filled nanoporous metals

Jana Wilmers, Andrew McBride & Swantje Bargmann
A continuum formulation for electroactive composites made from nanoporous gold and ionconducting polymer is proposed. A novel extension of surface elasticity theory is developed to account for the high surface-to-volume ratio of nanoporous gold, and to capture the chemoelectromechanical coupling that occurs on the interface between the metal and the polymer. This continuum formulation accounts for the fully non-linear behaviour exhibited by the composite. The balance of linear momentum, Gauß's flux theorem and a relation...

Local flow stresses in interpenetrating-phase composites based on nanoporous gold — in situ diffraction

Ke Wang, Christian Hartig, Malte Blankenburg, Martin Müller, Robert Günther & Jörg Weißmüller
We report a synchrotron in situ diffraction experiment exploring stress evolution during compression of interpenetrating-phase nanocomposites based on nanoporous gold and polymer.While previous experiments provided indirect indication of local flow conditions based on macroscopic effective flow stress and micromechanics models such as Gibson-Ashby scaling law, the lattice parameter data of our experiment access the flow stress directly. At small structure size we find excellent agreement with previous reports, supporting thematch between material andmodel of those...

Strong light scattering and broadband (UV to IR) photoabsorption in stretchable 3D hybrid architectures based on Aerographite decorated by ZnO nanocrystallites

Ion Tiginyanu, Lidia Ghimpu, Jorit Gröttrup, Vitalie Postolache, Matthias Mecklenburg, Marion A. Stevens-Kalceff, Veaceslav Ursaki, Nader Payami, Robert Feidenhan'L, Karl Schulte, Rainer Adelung & Yogendra Kumar Mishra
In present work, the nano- and microscale tetrapods from zinc oxide were integrated on the surface of Aerographite material (as backbone) in carbon-metal oxide hybrid hierarchical network via a simple and single step magnetron sputtering process. The fabricated hybrid networks are characterized for morphology, microstructural and optical properties. The cathodoluminescence investigations revealed interesting luminescence features related to carbon impurities and inherent host defects in zinc oxide. Because of the wide bandgap of zinc oxide and...

Automatic three-dimensional geometry and mesh generation of periodic representative volume elements for matrix-inclusion composites

Konrad Schneider, Benjamin Klusemann & Swantje Bargmann
This paper introduces an efficient method to automatically generate and mesh a periodic three- dimensional microstructure for matrix-inclusion composites. Such models are of major importance in the field of computational micromechanics for homogenization purposes utilizing unit cell models. The main focus of this contribution is on the creation of cubic representative volume elements (RVEs) featuring a periodic geometry and a periodic mesh topology suitable for the application of periodic boundary condi- tions in the framework...

Low powered, tunable and ultra-light aerographite sensor for climate relevant gas monitoring

Oleg Lupan, V. Postica, Matthias Mecklenburg, Karl Schulte, Yogendra Kumar Mishra, Bodo Fiedler & Rainer Adelung
Increasing atmospheric CO2 gas pollution and emergence of new types of green energy sources require continuous environmental monitoring. In this context, fast, efficient, light, robust, and reliable gas sensors that can work at room temperature are in high demand. We report on a low-powered type of ultra-light sensor, based on a 3-D-microtube network from a 2-D graphene/nanographite, called aerographite, and a method to tune the nanosensor’s selectivity by a simple variation of the applied bias...

High-temperature stable Zirconia particles doped with Yttrium, Lanthanum, and Gadolinium

Elisabeth Leib, Robert M. Pasquarelli, Malte Blankenburg, Martin Müller, Andreas Schreyer, Rolf Janßen, Horst Weller & Tobias Vossmeyer
Zirconia microspheres synthesized by a wet-chemical sol–gel process are promising building blocks for various photonic applications considered for heat management and energy systems, including highly effi cient refl ective thermal barrier coatings and absorbers/emitters used in thermophotovoltaic systems. As previously shown, pure zirconia microparticles deteriorate at working temperatures of ≥1000 °C. While the addition of yttrium as a dopant has been shown to improve their phase stability, pronounced grain growth at temperatures of ≥1000 °C...

Surface excess elasticity of gold: ab initio coefficients and impact on the effective elastic response of nanowires

Beatrix A. M. Elsner, Stefan Müller, Swantje Bargmann & Jörg Weißmüller
Predicting the influence of the surface on the effective elastic properties of nanoscale structures and nanomaterials remains a challenge, which we here address on both levels, continuum and atomic. Density Functional Theory (DFT) computation at the atomic level yields the first reliable surface excess elastic parameters for the (111) and (001) surfaces of gold. At the continuum level, we derive closed-form expressions for the effective elastic behavior that can be combined with the DFT-derived excess...

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...

Prototyping and testing of composite riser joints for deepwater application

Yu Chen, Ralf Seemann, Dieter Krause, Tong-Earn Tay & Vincent B. C. Tan
The high strength to weight ratio, good corrosion resistance, and excellent fatigue property make carbon fiber-reinforced plastics a competitive material solution to replace steel in deepwater riser application. In this work, scaled-down composite riser joints were fabricated using a filament-winding machine. The prototypes comprise several carbon fiber-reinforced plastic layers wound over an aluminum liner. They consist of a middle tubular section and two metal-composite interface end fittings for the transfer of load between joints. A...

Assembly force and taper angle difference influence the relative motion at the stem-neck interface of bi-modular hip prostheses

Henning Haschke, Sabrina Y. Jauch-Matt, Kay Sellenschloh, Gerd Huber & Michael Morlock
Bi-modular hip arthroplasty prostheses allow adaptation to the individual patient anatomy and the combination of different materials but introduce an additional interface, which was related lately to current clinical issues. Relative motion at the additional taper interface might increase the overall risk of fretting, corrosion, metallic debris and early failure. The aim of this study was to investigate whether the assembly force influences the relative motion and seating behaviour at the stem-neck interface of a...

Data aggregation of mobile M2M traffic in relay enhanced LTE-A networks

Safdar Nawaz Khan Marwat, Yasir Mehmood, Carmelita Görg & Andreas Timm-Giel
Machine-to-machine (M2M) communication is becoming an increasingly essential part of mobile traffic and thus also a major focus of the latest 4G and upcoming 5G mobile networks. M2M communication offers various ubiquitous services and is one of the main enablers of the Internet-of-things (IoTs) vision. Nevertheless, the concept of mobile M2M communication has emerged due to the wide range, coverage provisioning, high reliability as well as decreasing costs of future mobile networks. Resultantly, M2M traffic...

M2M Potentials in logistics and transportation industry

Yasir Mehmood, Safdar Nawaz Khan Marwat, Koojana Kuladinithi, Anna Förster, Yasir Zaki, Carmelita Görg & Andreas Timm-Giel
All over the world, road congestion is among the most prevalent transport challenges usually in urban environments which not only increases fuel consumption and emission of harmful gases, but also causes stress for the drivers. Intelligent Transportation System (ITS) enables a better use of the infrastructure by connecting vehicles to other vehicles as well as infrastructure and thus delivers a faster communication opportunity to ensure safe and secure driving. Machine-to-machine (M2M) communication is one of...

Investigation of the unsteady flow behaviour on a wind turbine using a BEM and a RANSE method

Israa Alesbe, Moustafa Abdel-Maksoud & Sattar Aljabair
Analyses of the unsteady flow behaviour of a 5 MW horizontal-axis wind turbine (HAWT) rotor (Case I) and a rotor with tower (Case II) are carried out using a panel method and a RANSE method. The panel method calculations are obtained by applying the in-house boundary element method (BEM) panMARE code, which is based on the potential flow theory. The BEM is a three-dimensional first-order panel method which can be used for investigating various steady and...

8th International Congress on Biocatalysis (Biocat2016), Hamburg, Germany, 28 August - 1 September, 2016 : meeting report

Skander Elleuche, Petra Esselun, Ralf Grote, Barbara Klippel, Anna Krüger, Andreas Liese, Margit Ostrop, Christian Schäfers, Carola Schröder & Garabed Antranikian
The “8th International Congress on Biocatalysis (biocat2016)” is part of a biennial conference series. Biocatalysis is a topic based on the edge of biology and chemistry, which brings together scientists from the life sciences, engineers and computer scientists. This international conference serves as a platform to meet researchers from all over the world, to find collaboration partners for future projects and to gain novel insights into modern topics and techniques. Biocat covers the most exciting...

Wireless blood pressure measurement implant electronics for integration in a stent craft

Bibin John, Rajeev Ranjan, Clemens Spink, Dietmar Schroeder, Andreas Koops, Gerhard Adam & Wolfgang Krautschneider
This paper describes the design, implementation and testing of a wireless blood pressure sensing implant. The implant is mounted on a stent graft. The implant along with the stent graft must fit into a 16F applicator stent delivery system. The implant is powered using the energy harvested from wireless power transmission. The measured pressure data is sent wirelessly to an external data reader hardware. The pressure measurement must have resolution of 1 mmHg.

Dynamic behavior of coal-fired power plants with postcombustion CO2 capture

Kai Wellner, Thomas Marx-Schubach & Gerhard Schmitz
Der kombinierte Betrieb einer Post-Combustion CO2-Abscheideanlage und einem Kohlekraftwerk ist ein komplexer Prozess mit deutlichen gegenseitigen Auswirkungen. Auch wenn der Betrieb einer CO2-Abscheideanlage den Wirkungsgrad des Kraftwerks herabsetzt, ergibt sich dadurch die Möglichkeit das Kraftwerk flexibler zu betreiben. Um diesen Prozess zu untersuchen, wird ein detailliertes Modell einer Post-Combustion CO2-Abscheideanlage entwickelt und validiert mit Messdaten. Danach wird das Modell mit dem Modell eines Kohlekraftwerks gekoppelt, um die Effekte des zusammenhängenden Betriebs zu untersuchen. In einem...

Enhancement of alkaline protease activity and stability via covalent immobilization onto hollow core-mesoporous shell silica nanospheres

Abdelnasser S. S. Ibrahim, Ali A. Al-Salamah, Ahmed Mohamed El-Toni, Khalid S. Almaary, Mohamed A. El-Tayeb, Yahya B. Elbadawi & Garabed Antranikian
The stability and reusability of soluble enzymes are of major concerns, which limit their industrial applications. Herein, alkaline protease from Bacillus sp. NPST-AK15 was immobilized onto hollow core-mesoporous shell silica (HCMSS) nanospheres. Subsequently, the properties of immobilized proteases were evaluated. Non-, ethane- and amino-functionalized HCMSS nanospheres were synthesized and characterized. NPST-AK15 was immobilized onto the synthesized nano-supports by physical and covalent immobilization approaches. However, protease immobilization by covalent attachment onto the activated HCMSS–NH2 nanospheres showed...

Correction: Raman Subrahmanyam, et al. On the road to biopolymer aerogels—dealing with the solvent. Gels 2015, 1, 291–313

Subrahmanyam Raman, Pavel Gurikov, Paul Dieringer, Miaotian Sun & Irina Smirnova
The authors wish to make the following correction to their paper [1].[...]

What exactly is the Nusselt Number in convective heat transfer problems and are there alternatives?

Heinz Herwig
The often used Nusselt number is critically questioned with respect to its physical meaning. Based on a rigorous dimensional analysis, alternative assessment numbers are found that in a systematic way separately account for the quantitative and qualitative aspect of a heat transfer process. The qualitative aspect is related to the entropy generated in the temperature field of a real, irreversible heat transfer. The irreversibility can be quantified by referring it to the so-called entropic potential...

Wissenskonstruktion : durch aktivierende Lehre nachhaltiges Verständnis in MINT-Fächern fördern

Zentrum Für Lehre Und Lernen, Abteilung Für Fachdidaktik Der Ingenieurwissenschaften & Christian H. Kautz
Die Broschüre gibt einen Einblick darüber, unter welchen Bedingungen der Lernerfolg bei Studierenden in technischen Fächern durch den Einsatz aktivierender Methoden gesteigert werden kann. Dabei wird ein Überblick über ausgewählte Methoden zur Förderung von qualitativem Verständnis bei Studierenden gegeben sowie häufige Fragen zum Einsatz der aktivierenden Methoden beantwortet. Die Wirksamkeit dieser Methoden wird anhand von empirischen Forschungsergebnissen diskutiert.

Nanofiltration for safe drinking water in underdeveloped regions – a feasibility study

Sreenivasan Ramaswami, Zafar Navid Ahmad, Maximilian Slesina, Joachim Behrendt & Ralf Otterpohl
The fact from the United Nations that in 2015, about 663 million people worldwide did not have access to an improved drinking water source, does not resemble the reality wherein more than 1.8 billion people worldwide were consuming water which is unsafe for drinking. Nanofiltration, with the ability to reject several trace organic compounds, heavy metals and viruses at a lower energy demand than reverse osmosis, has found application for the production of high quality...

Gerichtete MWCNT/ Polypyrrol Hybride als Material für anisotrope Aktuatoren

Thea Schnoor
In dieser Arbeit wird die Herstellung vertikal und horizontal gerichteter Multi Walled Carbon Nanotube (MWCNT)/ Polypyrrol Hybride beschrieben und die richtungsabhängige Aktuation untersucht. Die für die Aktuation verantwortliche Komponente des Hybrids ist hierbei das Polypyrrol; bei geringen Potentialdifferenzen und Strömen wird das Polymer reversibel reduziert bzw. oxidiert. Dieser Vorgang wird begleitet vom Aus- bzw. Eindiffundieren solvatisierter Ionen aus der umgebenden Elektrolytlösung in die Polymermatrix, das Volumen des Polymers schwillt bzw. zieht sich zusammen. Da Polypyrrol...

What is frugal innovation? Three defining criteria

Timo Weyrauch & Cornelius Herstatt
Recently, the innovation management literature has witnessed a rising interest in the so-called frugal innovation. The term was initially discussed in the context of emerging markets, giving non-affluent customers opportunities to consume affordable products and services suited to their needs. However, the meaning of frugal innovation is fuzzy. Further, the increasing appearance of frugal innovation in developed markets challenges earlier definitions that often characterised frugal innovation particularly in the context of emerging markets. So far,...

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  • 2016

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