374 Works

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...

Wissenschaft und Offenheit : Reflexion über Wissenschaft als Teil der Lehre zum wissenschaftlichen Arbeiten und Schreiben

Thomas Hapke
Fostering academic research and writing is more and more part of the services of university libraries within their activities to promote information literacy. The actual challenge and trend to openness, to topics like Open Access and Open Science, emphasizes especially questions of scientificality and the quality of science. A debate on this can enrich learning and teaching academic research and writing. As a holistic view on information literacy includes reflection about the production of information...

Determining periodic orbits via nonlinear filtering and recurrence spectra in the presence of noise

Sebastian Oberst, Steffen Marburg & Norbert Hoffmann
In nonlinear dynamical systems the determination of stable and unstable periodic orbits as part of phase space prediction is problematic in particular if perturbed by noise. Fourier spectra of the time series or its autocorrelation function have shown to be of little use if the dynamic process is not strictly wide-sense stationary or if it is nonlinear. To locate unstable periodic orbits of a chaotic attractor in phase space the least stable eigenvalue can be...

Settlements in unsaturated granular soils induced by changes in saturation and suction

Marius Milatz, Tom Törzs & Jürgen Grabe
In this contribution the hydro-mechanically coupled behaviour of a sand is experimentally investigated with the focus on settlements induced by changes in degree of saturation and suction. This phenomenon, referred to as collapse behaviour, is attributed to rearrangements of the grain skeleton due to changing capillary effects on wetting of the soil. For the experimental investigation of the collapse behaviour of a medium coarse sand cyclic dryingwetting tests are performed under oedometric conditions. In the...

Coupled chemo(enzymatic) reactions in continuous flow

Ruslan Yuryev, Simon Strompen & Andreas Liese
This review highlights the state of the art in the field of coupled chemo(enzymatic) reactions in continuous flow. Three different approaches to such reaction systems are presented herein and discussed in view of their advantages and disadvantages as well as trends for their future development.

Synthesis of uniform bulk nanoporous palladium with tunable structure

Shan Shi, Jürgen Markmann & Jörg Weißmüller
This work presents systematic investigations on the synthesis of hierarchical nanoporous Pd via electrochemical dealloying of CuPd alloys in sulfuric acid. The impact of electrode potential, dealloying temperature, and additional annealing on microstructure and morphology is explored. Dealloying Cu85Pd15 in 1M sulfuric acid at elevated temperature provides a facile strategy to produce bulk nanoporous Pd samples which are uniform, hierarchically nanoporous, and free of macro-scale cracks. The question “Why will one-step template-free dealloying yield a...

Prozessentwicklung einer linearen Reaktionskaskade zur biotechnologischen Herstellung von epsilon-Caprolacton

Christian Scherkus
In der vorliegenden Arbeit wurde die enzymatische Synthese von ε-Caprolacton mittels einer Alkohol-Dehydrogenase und einer sauerstoffabhängigen Baeyer-Villiger-Monooxygenase ausgehend von Cyclohexanol untersucht. Zusätzlich ist eine Lipase zur Hydrolyse sowie zur Polymerisation von ε-Caprolacton eingesetzt worden. Im Rahmen der Prozessentwicklung wurden die einzelnen Reaktionsschritte und Enzyme kinetisch charakterisiert, um ein Prozessdesign mit optimalen Reaktionsbedingungen festzulegen. Hierfür wurden insbesondere Ergebnisse im Satzbetrieb und im Zulaufverfahren gegenübergestellt. Auf der Basis eines kinetischen Modells sind zusätzlich Simulationen durchgeführt und mit...

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...

Analysis and Modeling of Heat Flux into the Tool in Abrasive Circular Cutting of Unidirectional CFRP

Wolfgang Hintze & Christian Klingelhöller
For edge trimming of slightly curved thin walled CFRP parts dry circular cutting is a promising alternative. However, a high fraction of the cutting energy is converted into heat. The study focuses on the determination of the amount of heat dissipated by the tool in circular cutting of unidirectional CFRP with epoxy matrix. An inverse heat conduction model is developed and solved for a set of temperature profiles measured on the tool surface with an...

Forschungsdatenmanagement - Umfrage TUHH

Andreas Pohnke, Inken Feldsien-Sudhaus & Detlev Bieler
Poster mit Auszügen der Ergebnisse der Umfrage zum Forschungsdatemnamagement an der TUHH, Zeitraum: 11. Juli bis 15. August 2016, Zielgruppe: MitarbeiterInnen des wissenschaftlichen Personals der TUHH. Vollständige Auswertung hier abrufbar: https://doi.org/10.15480/882.1326

Inteins, valuable genetic elements in molecular biology and biotechnology

Skander Elleuche & Stefanie Pöggeler
Inteins are internal protein elements that self-excise from their host protein and catalyze ligation of the flanking sequences (exteins) with a peptide bond. They are found in organisms in all three domains of life, and in viral proteins. Intein excision is a posttranslational process that does not require auxiliary enzymes or cofactors. This self-excision process is called protein splicing, by analogy to the splicing of RNA introns from pre-mRNA. Protein splicing involves only four intramolecular...

Relevanz und Potenziale frugaler Innovationen für Österreich

Rajnish Tiwari, Stephan Buse, Katharina Kalogerakis, Jakob Scheitza & Cornelius Herstatt
This qualitative-explorative study set out to investigate potentials and relevance of frugal innovations, as enablers of “affordable excellence”, for Austria. Employing a multi-method approach combining literature review, case studies and expert interviews it sought to generate preliminary insights about the strategic imperative of frugal innovations for Austrian firms. The generated insights were analyzed with experts in a focus group to identify the resulting implications for Austria’s research and innovation system. The study discovered that some...

Analyse von Arbeitsabläufen mit 3D-Kameras

Martin Benter
Productivity analyses are important tools to control labour costs in industrial companies. This work presents a consistent method for determining times and analysing productivity. To achieve this goal, the method accesses motion tracking data acquired by 3D cameras. The method derives worker states and determines relevant state data. By systematically analysing this data, it is capable to provide meaningful results.

LWE-based encryption schemes and their applications In privacy-friendly data aggregation

Daniela Becker
Wir konstruieren neue Verschlüsselungssysteme basierend auf dem Learning With Errors Problem and lösen die folgenden Probleme: Durch datenschutzfreundliche Aggregation lassen sich Daten von mehreren Nutzern unter Wahrung ihrer Privatsphäre aggregieren ohne dem Aggregator zu vertrauen. Unsere Systeme verbessern sowohl Laufzeit als auch Bandbreite der Verschlüsselung, insbesondere die Entschlüsselung ist ca. 150 Mal schneller als zuvor. Überdies stellen wir die erste Lösung für datenschutzfreundliche Werbung auf sozialen Medien vor - unsere Architektur hat hohe Sicherheits- und...

Evaluating the performance of solvers for integer-linear programming

Arno Luppold, Dominic Oehlert & Heiko Falk
Optimizing embedded systems often boils down to solving complex combinatorial optimization problems. Integer-Linear Programming (ILP) turned out to be a powerful tool to solve these problems, as beyond traditional constraints, Boolean variables may be used to model complex logical expressions and conditionals. One of the key technical aspects is to be able to efficiently express these relations within the ILP. This paper presents formalized solutions for these issues, as well as an assessment of common...

Comparison of natural gas combined cycle power plants with post combustion and oxyfuel technology at different CO2 capture rates

Jan Mletzko, Sören Ehlers & Alfons Kather
Within this work a natural gas-fired combined cycle plant is investigated with post-combustion CO2 capture (PCC) and as a semi-closed oxyfuel combustion combined cycle (SCOC-CC) using process simulation tools. In most studies the CO2 capture rate of PCC units is set to 90% while the SCOC-CC is often considered for zero emission plants. To allow a comparison between the processes the capture rate needs to be taken into account. If a certain CO2 emission value...

The influence of pressure on crude oil biodegradation in shallow and deep Gulf of Mexico sediments

Uyen T. Nguyen, Sara A. Lincoln, Ana Gabriela Valladares Juárez, Martina Schedler, Jennifer L. Macalady, Rudolf Müller & Katherine H. Freeman
A significant portion of oil released during the Deepwater Horizon disaster reached the Gulf of Mexico (GOM) seafloor. Predicting the long-term fate of this oil is hindered by a lack of data about the combined influences of pressure, temperature, and sediment composition on microbial hydrocarbon remineralization in deep-sea sediments. To investigate crude oil biodegradation by native GOM microbial communities, we incubated core-top sediments from 13 GOM sites at water depths from 60-1500 m with crude...

Bone-patellar tendon-bone grafts for anterior cruciate ligament reconstruction : an in vitro comparison of mechanical behavior under failure tensile loading and cyclic submaximal tensile loading

Matthias Honl, Volker Carrero, Ekkehard Hille, Erich Schneider & Michael Morlock
There is no difference in the mechanical behavior of reconstructions from method of fixation or method of testing. Secure fixation is an important factor in the success of anterior cruciate ligament reconstruction.

A geometric model for the fracture toughness of porous materials

Hans Jelitto & Gerold A. Schneider
Different models for the fracture toughness, KIC, of porous materials have been proposed to describe KIC as a function of the porosity P. They have in common that beside P at least one additional parameter exists that has to be adjusted to the measured data. Based on the cubic structure, we present a geometrical 3D model without any arbitrary parameter, which predicts the KIC the toughness, GC, and the Young's modulus, E, of a porous...

Additive manufacturing in supply chains – the future of purchasing processes

Stephanie Niehues, Laura Berger & Michael Henke
Additive manufacturing is one of the leading production technologies when it comes to the efficient production of individual parts. This paper explains how additive manufacturing will influence purchasing processes and network structures of producing companies in future supply chain networks. Therefore, an exploratory research of relevant literature and recent studies in a systematic literature review is conducted, giving an overview of how additive manufacturing will change the processes of purchasing. Traditional purchasing and modern processes...

Fabrication of composites via spouted bed granulation process and simulation of their micromechanical properties

Eduard Eichner, Maksym Dosta, Stefan Heinrich & Gerold A. Schneider
In this contribution numerical simulation of Young’s modulus of copper-polymer composites is presented. For the simulation of the composites the Bonded-Particle-Model was applied. The model allows representing of the structure of composite materials realistically. The polymer matrix, which surrounds the particles, was represented as network of solid bonds connecting copper particles. Simulation results were validated based on mechanical determination of modulus of elasticity. The modulus of elasticity was approximated in experiments as well as in...

Investigation on stick phenomena in metal-on-metal hip joints after resting periods

M. A. Wimmer, Roman Nassutt, Christoph Sprecher, J. Loos, Georg Täger & A. Fischer
Insufficient understanding of tribological behaviour in total joint arthroplasty is considered as one of the reasons for prosthesis failure. Contrary to the continuous motion input profiles of hip simulators, human locomotion contains motion interruptions. These occurring resting periods can cause stick phenomena in metal-on-metal hip joints. The aim of the present study was to investigate the tribological sensitivity of all-metal bearings to motion interruptions on in vitro test specimens and retrieved implants. Friction and wear...

RUVIVAL Publication Series Volume 3

Joachim Behrendt, Dario Fröndhoff, Andrea Munoz Ardila, Maria Monina Orlina, Máryeluz Rueda Morales & Ruth Schaldach
RUVIVAL Publication Series is a compilation of literature reviews on topics concerned with the revitalisation of rural areas. RUVIVAL Publication Series is part of the e-learning project RUVIVAL and each of the three contributions in this publication is connected to further interactive multimedia material, which can be reached under www.ruvival.de. The first literature review is concerned with urine utilisation as a fertiliser in agriculture. Urine contains four important nutrients for plant growth: nitrogen (N), phosphorus...

Influence of cooling on curing temperature distribution during cementing of modular cobalt-chromium and monoblock polyethylene acetabular cups

Stephan Rothstock, Mahnaz Saadatmand, Matthias Vollmer, Andreas Paech, Christian Jürgens, Roman Nassutt & Michael Morlock
Total hip replacements for older patients are usually cemented to ensure high postoperative primary stability. Curing temperatures vary with implant material and cement thickness (30°C to 70°C), whereas limits for the initiation of thermal bone damage are reported at 45°C to 55°C. Thus, optimizing surgical treatment and the implant material are possible approaches to lower the temperature. The aim of this study was to investigate the influence of water cooling on the temperature magnitude at...

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...

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