69 Works

Three-dimensional Aerographite-GaN hybrid networks: single step fabrication of porous and mechanically flexible materials for multifunctional applications

Arnim Schuchardt, Tudor Braniste, Yogendra Kumar Mishra, Mao Deng, Matthias Mecklenburg, Marion A. Stevens-Kalceff, Simion Raevschi, Karl Schulte, Lorenz Kienle, Rainer Adelung & Ion Tiginyanu
Three dimensional (3D) elastic hybrid networks built from interconnected nano- and microstructure building units, in the form of semiconducting-carbonaceous materials, are potential candidates for advanced technological applications. However, fabrication of these 3D hybrid networks by simple and versatile methods is a challenging task due to the involvement of complex and multiple synthesis processes. In this paper, we demonstrate the growth of Aerographite-GaN 3D hybrid networks using ultralight and extremely porous carbon based Aerographite material as...

Nanoporous gold : testing macro-scale samples to probe small-scale mechanical behavior

Nadiia Mameka, Ke Wang, Jürgen Markmann, Erica Lilleodden & Jörg Weißmüller
Nanoporous gold made by dealloying exemplifies how the exciting mechanical properties of nanoscale objects can be exploited in designing materials from which macroscopic things can be formed. The homogeneous microstructure and the possibility of adjusting the ligament size, L, between few and few hundred nm, along with the high deformability and reproducible mechanical behavior predestine the material for model studies of small-scale plasticity using reliable macroscopic testing schemes on mm- or cm-size samples. Such experiments...

Joint analysis of TDMA and geographic routing for a large scale wireless mesh network

Tobias Lübkert
Wireless Mesh Networks are a promising technique for large scale networks with low-power and high reliability requirements such as in industrial plants. The shared transmission medium requires a medium access control mechanism which reduces the amount of parallel transmission, because nearby simultaneous transmitting devices hinder the successful reception at the destination device. The common CSMA-CA mechanism cannot satisfy the reliability requirement of an industrial plant, as many messages get dropped when the channel is busy...

Synthesis and thermal stability of zirconia and yttria-stabilized zirconia microspheres

Elisabeth Leib, Ulla Vainio, Robert M. Pasquarelli, Jonas Kus, Christian Czaschke, Nils Walter, Rolf Janßen, Martin Müller, Andreas Schreyer, Horst Weller & Tobias Vossmeyer
Zirconia microparticles produced by sol-gel synthesis have great potential for photonic applications. To this end, identifying synthetic methods that yield reproducible control over size uniformity is mportant. Phase transformations during thermal cycling can disintegrate the particles. Therefore, understanding the parameters driving these transformations is essential for enabling high-temperature applications. Particle morphology is expected to influence particle processability and stability. Yttria-doping should improve the thermal stability of the particles, as it does in bulk zirconia.

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...

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...

Experimental and numerical analysis of fillet-welded joints under low-cycle fatigue loading by means of full-field techniques

Pasqualino Corigliano, Vincenzo Crupi, Wolfgang Fricke, Nils Friedrich & Eugenio Guglielmino
The welded structures used in the naval field are generally subjected to fluctuating stress over time. In some structural welded details, due to changing loading conditions, significant elastic-plastic deformation can arise, which may lead to the failure of the structure after a relatively low number of cycles. The aim of this scientific work was to investigate the behavior of welded T-joints under low-cycle fatigue using full-field techniques: digital image correlation and infrared thermography. Low-cycle fatigue...

Reconstruction of the magnetic particle imaging system matrix using symmetries and compressed sensing

A. Weber & T. Knopp
Magnetic particle imaging (MPI) is a tomographic imaging technique that allows the determination of the 3D spatial distribution of superparamagnetic iron oxide nanoparticles. Due to the complex dynamic nature of these nanoparticles, a time-consuming calibration measurement has to be performed prior to image reconstruction. During the calibration a small delta sample filled with the particle suspension is measured at all positions in the field of view where the particle distribution will be reconstructed. Recently, it...

Transport in nanoporous materials including MOFs : the applicability of Fick’s laws

Tobias Titze, Alexander Lauerer, Lars Heinke, Christian Chmelik, Nils E. R. Zimmermann, Frerich Keil, Douglas M. Ruthven & Jörg Kärger
Die Diffusion in nanoporösen Wirt-Gast-Systemen wird oft als viel zu kompliziert angesehen, als dass sie mit so “einfachen” Beziehungen wie dem ersten und zweiten Fickschen Gesetz vereinbar sein könnte. Wir zeigen nun, dass die mikroskopischen Diffusionsmesstechniken, vor allem die NMR-Spektroskopie mit gepulsten Feldgradienten (PFG) und die Mikrobildgebung mittels Interferenzmikroskopie (IFM) und IR-Mikroskopie (IRM), den direkten experimentellen Nachweis für die Anwendbarkeit der Fickschen Gesetze auf solche Systeme liefern. Dies gilt oft auch dann noch, wenn die...

On the road to biopolymer aerogels - dealing with the solvent

Subrahmanyam Raman, Pavel Gurikov, Paul Dieringer, Miaotian Sun & Irina Smirnova
Aerogels are three-dimensional ultra-light porous structures whose characteristics make them exciting candidates for research, development and commercialization leading to a broad scope of applications ranging from insulation and catalysis to regenerative medicine and pharmaceuticals. Biopolymers have recently entered the aerogel foray. In order to fully realize their potential, progressive strategies dealing with production times and costs reduction must be put in place to facilitate the scale up of aerogel production from lab to commercial scale....

Towards online visualization and interactive monitoring of real-time CFD simulations on commodity hardware

Nils Koliha, Christian F. Janßen & Thomas Rung
Real-time rendering in the realm of computational fluid dynamics (CFD) in particular and scientific high performance computing (HPC) in general is a comparably young field of research, as the complexity of most problems with practical relevance is too high for a real-time numerical simulation. However, recent advances in HPC and the development of very efficient numerical techniques allow running first optimized numerical simulations in or near real-time, which in return requires integrated and optimized visualization...

Characterization of the microstructure evolution in IF-Steel and AA6016 during plane-strain tension and Simple Shear

Gregory Gerstein, Benjamin Klusemann, Swantje Bargmann & Mirko Schaper
In the current work, the evolutions of grain and dislocation microstructures are investigated on the basis of plane strain tension and simple shear tests for an interstitial free steel (DC06) and a 6000 series aluminum alloy (AA6016-T4). Both materials are commonly-used materials in the automobile industry. The focus of this contribution is on the characterization and comparison of the microstructure formation in DC06 and AA6016-T4. Our observations shed light on the active mechanisms at the...

Large-scale parallel alignment of platelet-shaped particles through gravitational sedimentation

Sebastian Behr, Ulla Vainio, Martin Müller, Andreas Schreyer & Gerold A. Schneider
Parallel and concentric alignment of microscopic building blocks into several orders of magnitude larger structures is commonly observed in nature. However, if similarly aligned structures are artificially produced their thickness is generally limited to just about one or two orders of magnitude more than the dimensions of the smallest element. We show that sedimentation provides a promising approach to manufacture solid materials consisting of well-aligned platelet-shaped particles while being more than 30 000 times thicker...

Rissbildung in fugenlosen Kaianlagen - ein Berechnungsmodell für massige Bauteile aus Stahlbeton

Jens Wasner
The thesis contributes to the determination of the effective restraint action in large jointless quays. The focus is on the particular cracking behaviour of the voluminous reinforced concrete superstructures. For this purpose special mechanical models are developed. With those the non-linear material behaviour and bond relation are mapped to reality. After an introduction about the development of container shipping different types of quays with jointless superstructure are presented. Then the material properties of concrete and...

Bioressourceninventur – Analyse von Stoffströmen zur Bestimmung urbaner Biomassepotenziale in einem Geoinformationssystem (GIS)

Helmut Adwiraah
Zur effizienten Nutzung des energetischen und stofflichen Potenzials der im urbanen Raum anfallenden Bioressourcen sind Menge, Entstehungsort und Zusammensetzung von größter Bedeutung. Es werden die spezifischen räumlichen Abhängigkeiten zwischen geographischen Daten und den verwertungsrelevanten Eigenschaften der Bioressourcen untersucht und Berechnungsparameter sowie Einflussfaktoren für die geodatenbasierte Bioressourceninventur in einem GIS bestimmt.

Life cycle assessment of electricity production from airborne wind energy

Stefan Wilhelm
Global energy supply is closely linked with some of the greatest challenges of our society. A rising demand has to be met whereas conventional energy sources are depleting and emit considerable amounts of greenhouse gases. Renewable energy technologies are increasingly promoted to face these issues, especially in the electricity industry. Research has shown, that renewables are superior to conventional energy technologies in many environmental aspects but are not free of burdens. However, the main causes...

RAMIRAN 2015 : 16th International Conference Rural-Urban Symbiosis : proceedings book : 8th-10th September 2015, Hamburg University of Technology, Germany

Ina Körner
Residues originate in rural and in urban systems. Many contain biogenic ingredients, e.g. food and green waste, livestock manure, feces, sewage and other sludge’s, harvest residues, digestates, agro-industry residues, and more. Commonly residues are known to pollute environments, causes hygienic problems or they are cost-intensive to collect and treat. Since fossil raw materials are becoming scarce, biogenic residues are more and more a topic of utilization. Application options are manifold. They range from energetic utilization,...

Indian Companies in Germany - A Report on Investment Activities in 2014-15

Rajnish Tiwari
In the previous fiscal year (April 2014 to March 2015) the level of outward foreign direct investments (FDI) by Indian firms witnessed some moderation. The gross outflow of FDI from India in FY 2014-15 stood at US $8.5 billion as per data released by the Reserve Bank of India. At March-end 2015, the cumulative stock of FDI from India stood at US $130.5 billion, which was only slightly higher from US $128.7 at the end...

Smart Mobility for India: Needs, Opportunities & Challenges

Rajnish Tiwari
India finds itself in a precarious situation. While the lack of efficient and effective mediums of mobility for public-at-large outside metropolitan cities continues to cause loss of productivity and stifle economic growth in a considerable manner; the economic growth in major urban centres and the resultant growth of passenger vehicles and two-wheelers is leading to heavy traffic jams and pollution, again causing loss of productivity and chocking of economic growth. This article argues that a...

USB - an attack surface of emerging importance

Frieder Steinmetz
USB is one of the most widely adopted standards for buses. Little work regarding its security implications has been published. This work provides a brief summary of known issues as well as a documentation of new problems and possible future threats. The discovered issues have been classified and possible solutions have been discussed. During the research a secret channel for data exfiltration, as well as command and control has been designed and implemented. The results...

RAMIRAN 2015 : 16th International Conference Rural-Urban Symbiosis : abstract book : 8th-10th September 2015, Hamburg University of Technology, Germany

Ina Körner
Rückstände stammen aus ländlichen und aus städtischen Systemen. Viele enthalten biogene Bestandteile, z.B. Nahrungs- und Gartenabfälle, Rückstände aus Nutztierhaltungen, Abwasser und andere Schlämme, Ernterückstände, Gärreste, Agro-Industrie Rückstände und mehr. Allgemein ist bekannt, dass diese Rückstände die Umwelt verunreinigen und hygienische Probleme hervorrufen können und dass ihre Einsammlung und Behandlung kostenintensiv ist. Seitdem fossile Rohstoffe knapper werden, sind biogene Rückstände und deren Nutzung mehr und mehr ein Thema. Die Verwendungsmöglichkeiten sind vielfältig. Sie reichen von der...

Die Spannung steigern : Laborpraktika didaktisch gestalten

Zentrum Für Lehre Und Lernen (ZLL), Mirjam Sophia Gleßmer, Sönke Knutzen & Peter Salden
Laboratory classes are an important part of the curriculum in STEM (Science, Technology, Engineering, Mathematics) courses. In laboratory classes students develop an understanding of connections between theory and application in an experimental and research-oriented manner. In this brochure, a team of instructional designers offer suggestions on how to design laboratory courses to maximise student learning. We focus on didactical planning of laboratory classes, considerations when running the laboratory class concerning methods for e.g. group work,...

Friction-based injection clinching joining (F-ICJ): a new joining method for hybrid lightweight structures

André Bastos Abibe
Friction-based Injection Clinching Joining (F-ICJ) is a new advanced staking joining technology for lightweight hybrid structures. This PhD work was devised to understand the fundamental scientific and engineering aspects of F-ICJ. The joint formation mechanisms, process-related changes in the joined materials, and quasi-static mechanical behavior were clarified. This knowledge was used to establish relationships between processing conditions, microstructure, and global joint properties. A proof of concept of the F-ICJ process was explored by optimizing the...

Court rulings as evidence for social engineering research

Ngoc-Minh Michal Pham
This paper is about the question whether court rulings can be used as evidence for Social Engineering research. It goes into the methodology of acquiring and analysing the material and presents the results.

Fatigue Performance of Laser Additive Manufactured Ti–6al–4V in Very High Cycle Fatigue Regime up to 1E9 Cycles

Eric Wycisk, Shafaqat Siddique, Dirk Herzog, Frank Walther & Claus Emmelmann
Additive manufacturing technologies are in the process of establishing themselves as an alternative production technology to conventional manufacturing, such as casting or milling. Especially laser additive manufacturing (LAM) enables the production of metallic parts with mechanical properties comparable to conventionally manufactured components. Due to the high geometrical freedom in LAM, the technology enables the production of ultra-light weight designs, and therefore gains increasing importance in aircraft and space industry. The high quality standards of these...

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