498 Works

Damage due to rolling in total knee replacement : the influence of tractive force

Markus A. Wimmer, Lars Birken, Kay Sellenschloh & Erich Schneider
© 2013, The author(s). The femoral condyles of a knee prosthesis articulate with a combination of rolling and sliding on the tibial polyethylene plateau. Little is known about potential polyethylene damage due to rolling motion. Since rolling does not exclude the presence of tangential surface loads, this study sought to investigate the influence of tractive rolling on the wear of polyethylene. A “wheel-on-flat” apparatus, consisting of a metal wheel and a polyethylene flat, mimicked contact...

Near-field radiative heat transfer with hyperbolic metamaterials

Slawa Lang
Max Plancks bedeutende Schwarzkörper Theorie kann den Anstieg der strahlenden Wärmeübertragung zwischen eng aneinanderliegenden Körpern, bekannt als Nahfeld Wärmeübertragung, nicht erklären. Wir demonstrieren diesen Effekt mit Hilfe einer neuen, dynamischen Messmethode und messen Wärmeströme bis zu 16-mal größer als die Schwarzkörper Grenze. Wir zeigen, dass thermische Strahlung in hyperbolischen Metamaterialien (HMMs) – äußerst anisotropen Nanostrukturen – sehr stark ist und ihre Eigenschaften sich von Schwarzkörper Strahlung deutlich unterscheiden. Schließlich erweisen sich Nahfeld Wärmeströme zwischen HMMs...

Thermal behavior of friction clutch disc based on uniform pressure and uniform wear assumptions

Oday Ibraheem Abdullah & Josef Schlattmann
High temperatures appear in the contacting surfaces of a single-disc clutch system (friction clutch disc, flywheel and pressure plate) due to the relative motion between these parts during the sliding period. These high temperatures are responsible for several disadvantages such as increasing wear rate, surface cracks and permanent distortions. In some cases, these disadvantages may lead the contacting surfaces to failure before the expected lifetime. In this work, mathematical models of the friction clutch system...

Thy-1 deficiency augments bone loss in obesity by affecting bone formation and resorption

Ann-Kristin Picke, Graeme Michael Campbell, Felix N. Schmidt, Björn Busse, Martina Rauner, Jan C. Simon, Ulf Anderegg, Lorenz C. Hofbauer & Anja Saalbach
Healthy bone remodeling results from a balanced bone formation and bone resorption realized by bone-forming osteoblasts and bone-resorbing osteoclasts, respectively. Recently, Thy-1 (CD90) was identified as positive regulator of osteoblast differentiation and activation, thus, promoting bone formation while concurrently inhibiting adipogenesis and obesity in mice. Additionally, Thy-1 did not affect bone resorption. An obesity-related co-morbidity that is increasing in prevalence is a disturbed bone formation resulting in an increased fracture risk. The underlying mechanisms of...

Analysis of the influence of burst-mode laser ablation by modern quality tools

Claus Emmelmann & Juan Pablo Calderón Urbina
The development of lasers in terms of pulse length and ablation quality has made wider the perspective of material processing. Ablation using picosecond lasers offers an almost "cold material removal", which causes minimal heat affected zones and enables sublimation without melt formation. Moreover, burst-mode intensifies these effects by the partition of pulses into groups of micro-pulses. Therefore, removal rate and surface quality are improved with an appropriate combination of burst-mode and other relevant process parameters....

Smart control for functional electrical stimulation with optimal pulse intensity

Aljoscha Reinert, Jan C. Loitz, Fanny Quandt, Dietmar Schröder & Wolfgang H. Krautschneider
Transcutaneous electrical stimulation is a common treatment option for patients suffering from spinal cord injury or stroke. Two major difficulties arise when employing electrical stimulation in patients: Accurate stimulation electrode placement and configuration of optimal stimulation parameters. Optimizing the stimulation parameters has the advantage to reduce muscle fatigue after repetitive stimulation. Here we present a newly developed system which is able to automatically find the optimal individual stimulation intensity by varying the pulse length. The...

Geometrical effects on the concentrated behavior of heat flux in metamaterials thermal harvesting devices

Guoqiang Xu, Haochun Zhang, Ming Xie & Yan Jin
Thermal harvesting devices based on transformation optics, which can manipulate the heat flux concentration significantly through rational arrangements of the conductivities, have attracted considerable interest owing to several great potential applications of the technique for high-efficiency thermal conversion and collection. However, quantitative studies on the geometrical effects, particularly wedge angles, on the harvesting behaviors are rare. In this paper, we adopt wedge structure-based thermal harvesting schemes, and focus on the effects of the geometrical parameters...

Primary hip replacement stem taper fracture due to corrosion in 3 patients

Michael Morlock, Dennis Bünte, Harmen Ettema, Cees C. Verheyen, Åke Hamberg & Jeremy Gilbert

Temperature analysis of a pin-on-disc tribology test using experimental and numerical approaches

Oday Ibraheem Abdullah & Josef Schlattmann
The high thermal stresses generated at the interface between the contacting surfaces due to the sliding between parts of sliding system such as friction clutches and brakes. In this work, pin-on-disc test rig was built to find the temperature field during the sliding operation using experimental and numerical approaches. In the experimental approach, infrared camera was used to find the temperature distribution, while in the numerical approach a finite element technique has been used. Analysis...

Influence of application parameters of ultrasonic-assisted bone instruments on the tear force of a substitute material for spinal dura mater

Marie C. Foelkel, Vitali Herzog, Markus Meier & Michael Morlock
An ultrasonic-assisted bone instrument can be used for the dissection of bone in spinal surgery. During surgery, the tip of such a bone instrument can touch spinal dura mater. Especially during critical re-operations, high forces can be unintentionally applied on spinal dura mater. To prevent dural tears, the influence of application parameters on the tear force shall be analyzed. Collagen foil is used as a substitute material for spinal dura mater because of its similar...

Transparency induced in opals via nanometer thick conformal coating

Guoliang Shang, Kaline P. Furlan, Robert Zierold, Robert Blick, Rolf Janßen, Alexander Petrov & Manfred Eich
Self-assembled periodic structures out of monodisperse spherical particles, so-called opals, are a versatile approach to obtain 3D photonic crystals. We show that a thin conformal coating of only several nanometers can completely alter the reflection properties of such an opal. Specifically, a coating with a refractive index larger than that of the spherical particles can eliminate the first photonic band gap of opals. To explain this non-intuitive effect, where a nm-scaled coating results in a...

Mobility as a Service: ein Angebot auch für Einkommensarme? (Geo-Datensatz, aktualisiert)

Christoph Aberle
-- Aktualisierung: Der erste .csv-Datensatz war in einem unpraktischen Format abgelegt (musste transponiert werden, um ihn in GIS-Anwendungen zu nutzen). Dies wird mit der vorliegenden .csv-Datei korrigiert. Geografischer Datensatz, der die Bedienungsgebiete vierer Ridepooling-Angebote in Hamburg enthält: CleverShuttle, Ioki, MOIA, mytaxi match / FREE NOW. Inklusive der geplanten Erweiterung des MOIA-Bedienungsgebiets. Alle Bedienungsgebiete wurden im Mai 2019 georeferenziert. Grundlage waren öffentliche Karten der Anbieter. Der Datensatz ergänzt das Paper "Mobility as a Service: ein Angebot...

Drift stability of HyStOH semi-submersible supported by airfoil shaped structures

Andreas Manjock & Stefan Netzband
This study presents the results of the German research project HyStOH funded by German Federal Ministry of Economic Affairs and Energy (BMWi). The project consortium of German universities, wind turbine designers, wind farm developers and certification bodies design a novel semi-submersible steel structure with a single point mooring and self-aligning capabilities. The tower, which carries a 6 MW two-bladed downwind turbine, has an airfoil shaped cover, which supports the self-alignment of the full structure towards...

Carbon nanoparticles’ impact on processability and physical properties of epoxy resins : a comprehensive study covering rheological, electrical, thermo-mechanical, and fracture properties (mode I and II)

Hauke Meeuw, Johann Körbelin, Valea Kim Wisniewski, Ali Shaygan Nia, Adrián Romaní Vázquez, Martin Rudolf Lohe, Xinliang Feng & Bodo Fiedler
A trade-off between enhancement of physical properties of the final part and the processability during manufacturing always exists for the application of nanocarbon materials in thermoset-based composites. For different epoxy resins, this study elaborates the impact of nanocarbon particle type, functionalization, and filler loading on the resulting properties, i.e., rheological, electrical, thermo-mechanical, as well as the fracture toughness in mode I and mode II loading. Therefore, a comprehensive set of carbon nanoparticles, consisting of carbon...

Decision-makers’ underestimation of user innovation

Philip Bradonjic, Nikolaus Franke & Christian Lüthje
In the past few decades, much research has documented the importance of users as sources of innovations. Over the last 10 years, Research Policy alone has published 56 research articles investigating this phenomenon. We ask to what degree the findings of users as innovators have been absorbed by decision-makers responsible for new product development (managers) and by those who shape the contextual conditions for innovation (policy makers and public administration). A realistic perception of the...

Bio-inspired solution for optimal adhesive performance

Antonio Papangelo
In recent years there has been a growing interest into high performance bioinspired adhesives. This communication focuses on the adhesive behavior of a rigid cylinder that indents an elastic layer coated on a rigid substrate. With the assumption of short range adhesive interactions (JKR type) the adhesive solution is obtained very easily starting from the adhesiveless one. We show that ultrastrong adhesion (up to theoretical material strength) can be reached in line contact by reducing...

Thinner and better: (Ultra-)low grammage bacterial cellulose nanopaper-reinforced polylactide composite laminates

Martin Hervy, Frederic Bock & Koon-Yang Lee
One of the rate-limiting steps in the large-scale production of cellulose nanopaper-reinforced polymer composites is the time consuming dewatering step to produce the reinforcing cellulose nanopapers. In this work, we show that the dewatering time of bacterial cellulose (BC)-in-water suspension can be reduced by reducing the grammage of BC nanopaper to be produced. The influence of BC nanopaper grammage on the tensile properties of BC nanopaper-reinforced polylactide (PLLA) composites is also investigated in this work....

Dynamic simulation and investigation of the startup process of a postcombustion-capture plant

Thomas Marx-Schubach & Gerhard Schmitz
Carbon capture is an important possibility to reduce carbon dioxide emissions. To be able to study the startup process of such an amine-scrubbing process, a startup model of a postcombustion-capture plant (pcc-plant) was developed in the Modelica language and validated with measured data from a pilot plant in Heilbronn, Germany. Afterward, the process was scaled up in the model to handle the entire flue-gas flow of a 875 MW coal-fired power plant, resulting in three...

Stabilization Columns for Embankment Support - Investigation, Verification and Further Development of Analytical Analyses

Holger Pankrath, Hatice Kaya & Ralf Thiele
As a technical and economical alternative to foundations on piles, but also to shallow foundations on improved soil, in recent decades a high number of soil improvement methods have been developed and established. Many of these methods use non-reinforced, cylindrical load bearing elements. A very common application of stabilizing columns is the improvement of a few meters thick soft soils below dams and embankments. But especially for this application, many failure cases are documented worldwide....

Biosorption of neodymium on Chlorella vulgaris in aqueous solution obtained from hard disk drive magnets

Mehmet Ali Kücüker, Nils Wieczorek, Kerstin Kuchta & Nadim K. Copty
In recent years, biosorption is being considered as an environmental friendly technology for the recovery of rare earth metals (REE). This study investigates the optimal conditions for the biosorption of neodymium (Nd) from an aqueous solution derived from hard drive disk magnets using green microalgae (Chlorella vulgaris). The parameters considered include solution pH, temperature and biosorbent dosage. Best-fit equilibrium as well as kinetic biosorption models were also developed. At the optimal pH of 5, the...

Optimization of solvent-free enzymatic esterification in eutectic substrate reaction mixture

Magdalena Pätzold, Anna Weimer, Andreas Liese & Dirk Holtmann
The Candida rugosa lipase catalyzed esterification of (-)-menthol and lauric acid (LA) was studied in a eutectic mixture formed by both substrates((-)-menthol:LA 3:1, mol/mol). No additional reaction solvent was necessary, since the (-)-menthol:LA deep eutectic solvent (DES) acts as combined reaction medium and substrate pool. Therefore, the esterification is conducted under solvent-free conditions. The thermodynamic water activity (aw) was identified as a key parameter affecting the esterification performance in the (-)-menthol:LA DES. A response surface...

Desiccant-assisted air conditioning system relying on solar and geothermal energy during summer and winter

Peter Niemann, Finn Richter, Arne Speerforck & Gerhard Schmitz
At Hamburg University of Technology the combination of an open cycle desiccant-assisted air conditioning system and a geothermal system is investigated in the framework of different research projects for several years. The objective of this study is to investigate the energy efficiency of the overall system and to evaluate the geothermal system during summer and winter mode, based on data measured for a temperate climate region. Monitoring results of the performance for dehumidification and remoistening...

Fine bubble-based CO2 capture mediated by triethanolamine coupled to whole cell biotransformation

Daniel Ohde, Benjamin Thomas, Simon Matthes, Zeynep Percin, Claudia Engelmann, Paul Bubenheim, Koichi Terasaka, Michael Schlüter & Andreas Liese
Carbon capture technology can be set up in combination with biocatalysis to utilize the bound CO2 as substrate in the Kolbe-Schmitt like enzymatic reaction. The exemplary whole cell biotransformation of catechol to 2,3-dihydroxybenzoic acid in a triethanolamine-mediated multiphase system shows increased equilibrium conversion. Apart from the beneficial thermodynamics, the inherent fluid properties of triethanolamine is enabling easy application of CO2 fine bubbles as highly efficient gassing method to minimize the CO2 demand and CO2 emissions.

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