1,545 Works

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...

Complexity and variety in mass customization systems: analysis and recommendations

Thorsten Blecker & Nizar Abdelkafi
To identify and examine the origins of complexity in a mass customization system and to propose an effective application sequence of variety management strategies in order to cope with this complexity.

Weblog campaigning in the German Bundestag election 2005

Steffen Albrecht, Maren Lübcke & Rasco Hartig-Perschke
Election campaigns are catalysts for new forms of political communication. They are a field of experimentation for new techniques and technologies to reach target groups and influence voters. This article explores how weblogs were used in the 2005 Bundestag election campaign in Germany, examining their effect on the mediatized political field. It is based on an empirical analysis of 317 campaign weblogs.

Quantized self-assembly of discotic rings in a liquid crystal confined in nanopores

Kathrin Sentker, Arne Zantop, Milena Lippmann, Tommy Hofmann, Oliver H. Seeck, Andriy V. Kityk, Arda Yildirim, Andreas Schoenhals, Marco G. Mazza & Patrick Huber
Disklike molecules with aromatic cores spontaneously stack up in linear columns with high, one-dimensional charge carrier mobilities along the columnar axes making them prominent model systems for functional, self-organized matter. We show by high-resolution optical birefringence and synchrotron-based X-ray diffraction that confining a thermotropic discotic liquid crystal in cylindrical nanopores induces a quantized formation of annular layers consisting of concentric circular bent columns, unknown in the bulk state. Starting from the walls this ring self-assembly...

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...

A three-component model of the control error in manual tracking of continuous random signals

Hans Gerisch, Gerhard Staude, Werner Wolf & Gerhard Bauch
The performance of human operators acting within closed-loop control systems is investigated in a classic tracking task. The dependence of the control error (tracking error) on the parameters display gain, k(display), and input signal frequency bandwidth, f(g), which alter task difficulty and presumably the control delay, is studied with the aim of functionally specifying it via a model.

A framework for the alignment of new product development and supply chains

Margherita Pero, Nizar Abdelkafi, Andrea Sianesi & Thorsten Blecker
The purpose of this paper is to develop a framework that explains how new product development and supply chain variables are related to one another and how they affect performance.

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...

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...

Regelung in Energienetzen mit Kraft-Wärme-Kopplung zur hohen Ausnutzung erneuerbarer Energien

Pascal Dubucq
Die verstärkte Nutzung von erneuerbaren Energien erfordert eine Flexibilisierung des elektrischen Energiesystems. In der Arbeit wird durch eine Kombination von linearer Optimierung und Systemsimulation untersucht, welche Maßnahmen die Netzstabilität und die Ausnutzung der erneuerbaren Energien verbessern können. Es zeigt sich, dass Energiespeicher, Verbrauchersteuerung und ein angepasster Einsatz von Anlagen in Kraft-Wärme-Kopplung dazu geeignet sind. Bei der Regelung und Steuerung müssen die Wechselwirkungen zwischen Erzeugereinsatz, teilweise gesteuertem Verbrauch und Wirkleistungs-Frequenz-Regelung berücksichtigt werden. Dies wird durch das...

A knowledge-based approach for design and modelling of high lift actuation systems

M. Pfennig & F. Thielecke
High lift actuation system design is a highly iterative process. Especially the preliminary design phase, which sets the course for the following design steps, is characterized by uncertain and changing data input. Despite the importance of this early design phase, a specialized and integrated computational support is not available. The objective of the research project WissBaSys is to offer knowledge-based design assistance focused on the preliminary design of high lift actuation systems. Moreover, information concerning...

In-depth study of the influence of host-framework flexibility on the diffusion of small gas molecules in one-dimensional zeolitic pore systems

N. E. R. Zimmermann, S. Jakobtorweihen, E. Beerdsen, B. Smit & F. J. Keil
Molecular-dynamics simulations are performed to understand the role of host-framework flexibility on the diffusion of methane molecules in the one-dimensional pores of AFI, LTL, and MTW-type zeolites. In particular, the impact of the choice of the host model is studied. Dynamically corrected Transition State Theory is used to provide insights into the diffusion mechanism on a molecular level. Free-energy barriers and dynamical correction factors can change significantly by introducing lattice flexibility. In order to understand...

On the effects of the external surface on the equilibrium transport in zeolite crystals

N. E. R. Zimmermann, B. Smit & F. J. Keil
With the aid of molecular simulation techniques (molecular dynamics [MD], Grand-Canonical Monte Carlo [GCMC], and reactive flux correlation function [RFCF]), the influence of the external surface on the equilibrium permeation of methane and ethane into and out of an AFI-type zeolite crystal has been studied. In particular, “extended dynamically corrected transition state theory”, that has been proven to describe the transport of tracers in periodic crystals correctly, has been applied to surface problems. The results...

Surface barriers of hydrocarbon transport triggered by ideal zeolite structures

Nils E. R. Zimmermann, Sayee P. Balaji & Frerich J. Keil
Shedding light on the nature of surface barriers of nanoporous materials, molecular simulations (Monte Carlo, Reactive Flux) have been employed to investigate the tracer-exchange characteristics of hydrocarbons in defect-free single-crystal zeolite membranes. The concept of a critical membrane thickness as quantitative measure of surface barriers is shown to be appropriate and advantageous. Nanopore smoothness, framework density, and thermodynamic state of the fluid phase have been identified as the most important influencing variables of surface barriers....

Predicting local transport coefficients at solid-gas interfaces

Nils E. R. Zimmermann, Berend Smit & Frerich J. Keil
The regular nanoporous structure make zeolite membranes attractive candidates for separating molecules on the basis of differences in transport rates (diffusion). Since improvements in synthesis have led to membranes as thin as several hundred nanometers by now, the slow transport in the boundary layer separating bulk gas and core of the nanoporous membrane is becoming increasingly important. Therefore, we investigate the predictability of the coefficient quantifying this local process – the surface permeability α –...

Transport into nanosheets : diffusion equations put to test

Nils E. R. Zimmermann, Timm J. Zabel & Frerich J. Keil
Ultrathin porous materials, such as zeolite nanosheets, are prominent candidates for performing catalysis, drug supply, and separation processes in a highly efficient manner due to exceptionally short transport paths. Predictive design of such processes requires the application of diffusion equations that were derived for macroscopic, homogeneous surroundings to nanoscale, nano-structured host systems. Therefore, we tested different analytical solutions of Fick’s diffusion equations for their applicability to methane transport into two different zeolite nanosheets (AFI, LTA)...

The effect of quality management on the service quality and business success of logistics service providers

Wolfgang Kersten & Jan Koch
The purpose of the paper is to analyse empirically the causal relationships between quality management, service quality and business success in German logistics companies.

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...

A statistical study of scattering in periodic and random helix layers

Christian Meiners & Arne F. Jacob
This paper aims at providing information on scattering in layers composed of periodic and non-periodic arrangements of small metal helices. Metal helices exhibit a pronounced resonance and are thus very effective scatterers.

Integration of demand forecasts in ABC‐XYZ analysis : practical investigation at an industrial company ; reflective practice

Bernd Scholz-Reiter, Jens Heger, Christian Meinecke & Johann Bergmann
Item classification based on ABC-XYZ analysis is of high importance for strategic supply and inventory control. It is common to perform the analysis with past consumption data. In this context, the purpose of this study is to test the hypothesis that an integration of demand forecasts can improve the performance of item classification, in particular the performance of ABC-XYZ analysis.

On the optimization of laser shock peening induced residual stresses

Sergey Chupakhin
There is a strong economic motivation of the aircraft industry to explore novel residual stress-based approaches for the fatigue life extension, repair, and maintenance of the growing fleet of ageing aircrafts, although the effect of residual stresses is not taken into account by the established damage tolerance evaluation methods. Laser shock peening — the most promising life enhancement technique — has already demonstrated great success in regard to the mitigation of fatigue crack growth via...

Framework for internet‐supported inter‐organizational product development collaboration

Eva‐Maria Kern & Wolfgang Kersten
The purpose of this article is to introduce a framework for internet supported inter-organizational product development, which enables companies to efficiently configure their development processes according to their needs.

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