76 Works

Switchable imbibition in nanoporous gold

Yahui Xue, Jürgen Markmann, Huiling Duan, Jörg Weißmüller & Patrick Huber
Spontaneous imbibition enables the elegant propelling of nano-flows because of the dominance of capillarity at small length scales. The imbibition kinetics are, however, solely determined by the static host geometry, the capillarity, and the fluidity of the imbibed liquid. This makes active control particularly challenging. Here we show for aqueous electrolyte imbibition in nanoporous gold that the fluid flow can be reversibly switched on and off through electric potential control of the solid-liquid interfacial tension,...

Scaling laws of nanoporous metals under uniaxial compression

Norbert Huber, R. N. Viswanath, Nadiia Mameka, Jürgen Markmann & Jörg Weißmüller
This study is motivated by discrepancies between recent experimental compression test data of nanoporus gold and the scaling laws for strength and elasticity by Gibson and Ashby. We present a systematic theoretical investigation of the relationship between microstructure and macroscopic behaviour of nanoporous metals. The microstructure is modelled by four-coordinated spherical nodes interconnected by cylindrical struts. The node positions are randomly displaced from the lattice points of a diamond lattice. We report scaling laws for...

The JamBerry - a stand-alone device for networked music performance based on the Raspberry Pi

Florian Meier, Marco Fink & Udo Zölzer
Today’s public Internet availability and capabilities allow manifold applications in the field of multimedia that were not possible a few years ago. One emerging application is the so-called Networked Music Performance, standing for the online, low-latency interaction of musicians. This work proposes a stand-alone device for that specific purpose and is based on a Raspberry Pi running a Linux-based operating system.

A Tale of three cities : urban culture and social change in the Palestinian West Bank

Thomas Malsch & Hilke Rebenstorf
Based on survey data of adolescents and parents from three major Palestinian cities, this article is a contribution to an ongoing debate on urban Arab culture and social change in the Middle East. Starting with a critical review of scholarly articles on the three West Bank cities of Hebron, Nablus, and Ramallah, we draw on evolutionary concepts of change from below, assuming varieties of urban modernization instead of global convergence of city cultures. In adopting...

Aging of a Pt/Al2O3 exhaust gas catalyst monitored by quasi in situ X-ray micro computed tomography

Georg Hofmann, Amélie Rochet, Elen Ogel, Maria Casapu, Stephan Ritter, Malte Ogurreck & Jan-Dierk Grunwaldt
Catalyst aging effects were analyzed using X-ray absorption micro-computed tomography in combination with conventional characterization methods on various length scales ranging from nm to mmto gain insight into deactivation mechanisms. For this purpose, a 4 wt% Pt/Al2O3 model exhaust gas catalyst was coated on a cordierite honeycomb and subjected to sequential thermal aging in static air at 950 C for 4, 8, 12 and 24 hours. The aging was followed on the one hand by...

Identification of fully coupled anisotropic plasticity and damage constitutive equations using a hybrid experimental–numerical methodology with various triaxialities

Z. M. Yue, Celal Soyarslan, H. Badreddine, K. Saanouni & A. E. Tekkaya
A hybrid experimental–numerical methodology is presented for the parameter identification of a mixed nonlinear hardening anisotropic plasticity model fully coupled with isotropic ductile damage accounting for microcracks closure effects. In this study, three test materials are chosen: DP1000, CP1200, and AL7020. The experiments involve the tensile tests with smooth and notched specimens and two types of shear tests. The tensile tests with smooth specimens are conducted in different directions with respect to the rolling direction....

The effect of in situ/in vitro three-dimensional quantitative computed tomography image voxel size on the finite element model of human vertebral cancellous bone

Yongtao Lu, Klaus Engelke, Claus-C Glueer, Michael Morlock & Gerd Huber
Quantitative computed tomography-based finite element modeling technique is a promising clinical tool for the prediction of bone strength. However, quantitative computed tomography-based finite element models were created from image datasets with different image voxel sizes. The aim of this study was to investigate whether there is an influence of image voxel size on the finite element models. In all 12 thoracolumbar vertebrae were scanned prior to autopsy (in situ) using two different quantitative computed tomography...

Dominant damping effects in friction brake noise, vibration and harshness : the relevance of joints

Merten Tiedemann, Sebastian Kruse & Norbert Hoffmann
The experimental analysis of a single component of a brake system and an assembly consisting of three components is used to clarify the relevance of joints in terms of damping and non-linearity in state-of-the-art brake systems. For this purpose a series of experimental modal analyses are conducted. A comparison of the results obtained from the single component and from the assembly strongly indicate that the joints which necessarily exist in an assembled structure have a...

Common beliefs and reality about PLS : comments on Rönkkö and Evermann (2013)

Jörg Henseler, Theo K. Dijkstra, Marko Sarstedt, Christian M. Ringle, Adamantios Diamantopoulos, Detmar W. Straub, David J. Ketchen, Joseph F. Hair, G. Tomas M. Hult & Roger J. Calantone
This article addresses Ro¨nkko¨ and Evermann’s criticisms of the partial least squares (PLS) approach to structural equation modeling. We contend that the alleged shortcomings of PLS are not due to problems with the technique, but instead to three problems with Ro¨nkko¨ and Evermann’s study: (a) the adherence to the common factor model, (b) a very limited simulation designs, and (c) overstretched generalizations of their findings. Whereas Ro¨nkko¨ and Evermann claim to be dispelling myths about...

A method to simplify perturbation analyses of periodical flows

Heinrich Söding
Perturbation methods up to first order with respect to motion or wave amplitude are common in seakeeping predictions. For higher than first order, lengthy theoretical analyses are required. They result in complicated formulae requiring high programming effort, and often the well-established numerical methods for first-order quantities fail when applied to second-order flow quantities. Both the derivation of the required expressions and their programming are simplified by using mathematical entities called perturbators. The concept of perturbators...

Recent developments and future challenges in fatigue strength assessment of welded joints

Wolfgang Fricke
Fatigue is an important design criterion for welded structures subjected to cyclic loading. Several approaches for fatigue strength assessment have been developed which are either based onWoehler S–N curves and damage accumulation rule or on crack propagation law. The paper briefly reviews the different approaches, highlighting their advantages and limitations. In this connection, the problematic distinction between crack initiation and propagation phases is discussed, followed by considerations about some parameters which have large influence on...

Modification of magnesium alloys by ceramic particles in gravity die casting

Urs Haßlinger, Christian Hartig, Norbert Hort & Robert Günther
A critical drawback for the application of magnesium wrought alloys is the limited formability of semifinished products that arises from a strong texture formation during thermomechanical treatment. The ability of second phase particles embedded into the metal matrix to alter this texture evolution is of great interest. Therefore, the fabrication of particle modified magnesium alloys (particle content 0.5–1 wt.-%) by gravity die casting has been studied. Five different types of micron sized ceramic powders (AlN,...

Innovation education programs : toward a conceptual framework

Alex Maritz, Anton De Waal, Stephan Buse, Cornelius Herstatt, Astrid Lassen & Ross Maclachlan
Innovation education has been identified as a key contributor to enhancing the innovative behavior of individuals, organizations and economies; yet very little literature exists on the development and assessment of innovation education programs (IEPs). This is particularly so in the higher education and vocational education domains. The purpose of this paper is to bridge the gap in the literature, by proposing a conceptual framework of a multi-dimensional IEP.

How to determine losses in a flow field: A paradigm shift towards the second law analysis

Heinz Herwig & Bastian Schmandt
Assuming that CFD solutions will be more and more used to characterize losses in terms of drag for external flows and head loss for internal flows, we suggest to replace single-valued data, like the drag force or a pressure drop, by field information about the losses. These information are gained when the entropy generation in the flow field is analyzed, an approach that often is called second law analysis (SLA), referring to the second law...

The entropic potential concept: a new way to look at energy transfer operations

Tammo Wenterodt & Heinz Herwig
Energy transfer operations or processes are systematically analyzed with respect to the way they can be assessed. It turns out that the energy transfer should not only be characterized by the operation or process itself but that it should be seen in a wider context. This context is introduced as the entropic potential of the energy that is transferred. It takes into account the overall transfer from the energy in its initial and finite states,...

Digitale Bildungsmedien in der Ausbildung zur Fachpraktikerin und zum Fachpraktiker

Henning Klaffke
Digital educational media in inclusive teaching concepts are still not very well represented in everyday vocational school life. This paper presents a critical classification of digital educational media in inclusive offerings, and highlights the fact that didactic deployment scenarios for the inclusive teaching needs to be developed in order to assist the teaching staff to implement and use digital educational media.

Indian Investments in Germany: Promising Prospects and Still Untapped Potential

Rajnish Tiwari
In the reporting period between August 2013 and July 2014 several Indian companies continued to invest in Germany. The “evident pace” of investments, however, did not match the overall growth in India’s outward foreign direct investments. Also, firms from other emerging economies increased their investment activities threatening to overshadow India’s leading position in Germany. With the new Indian government’s thrust on the manufacturing sector and its explicit efforts to foster partnership with Germany, new avenues...

German Mittelstand discovers BRIC: A Survey of Product Strategies of German ‘Hidden Champions’ in China and India

Rajnish Tiwari & Stephan Buse
An empirical survey conducted at the Hamburg University of technology (TUHH) shows the BRIC markets are perceived to be of high and growing strategic importance by German “Hidden Champions”. The survey suggests that many firms belonging to the German “Mittelstand” have just begun to realize the potentials of India as a strategic market. The survey reveals that such companies often try to target high-end, premium segments with products developed at the headquarters. An exclusive focus...

Effect of high pressure on hydrocarbon-degrading bacteria

Martina Schedler, Robert Hiessl, Ana Gabriela Valladares Juárez, Giselher Gust & Rudolf Müller
The blowout of the Deepwater Horizon in the Gulf of Mexico in 2010 occurred at a depth of 1500 m, corresponding to a hydrostatic pressure of 15 MPa. Up to now, knowledge about the impact of high pressure on oil-degrading bacteria has been scarce. To investigate how the biodegradation of crude oil and its components is influenced by high pressures, like those in deep-sea environments, hydrocarbon degradation and growth of two model strains were studied...

TiO2 photocatalyst nanoparticle separation: flocculation in different matrices and use of powdered activated carbon as a precoat in low-cost fabric filtration

Carlos F. Liriano Jorge, Uğur Söhmen, Altan Özkan, Holger Gulyas & Ralf Otterpohl
Separation of photocatalyst nanoparticles is a problem impeding widespread application of photocatalytic oxidation. As sedimentation of photocatalyst particles is facilitated by their flocculation, the influence of common constituents of biologically pretreated wastewaters (NaCl, NaHCO3, and their combination with humic acid sodium salt) on flocculation was tested by the pipetmethod. Results showed that the impact of these substances on TiO2 nanoparticle flocculation is rather complex and strongly affected by pH.When humic acid was present, TiO2 particles...

An Extended analytical approach to evaluating monotonic functions of fuzzy numbers

Arthur Seibel & Josef Schlattmann
This paper presents an extended analytical approach to evaluating continuous, monotonic functions of independent fuzzy numbers. The approach is based on a parametric α-cut representation of fuzzy numbers and allows for the inclusion of parameter uncertainties into mathematical models.

Pretreating stored human urine for solar evaporation by low-technology ammonia stripping

Holger Gulyas, Shidong Zhang & Ralf Otterpohl
In order to avoid the loss of ammonia during solar drying of stored urine, low-tech stripping is suggested as a pretreatment process for ammonia recovery. The mass transfer of ammonia from stored urine with an initial pH of about 9 was tested in a simple closed vessel operated at 72˚C, 74˚C and 85˚C. The specific urine/gas interface was 16.97 m−1. For ammonia absorption, a beaker with sulfuric acid was positioned in the gas phase of...

Forschungsschwerpunkt Maritime Systeme - Zukunft gestalten - Forschung und wissenschaftliche Ausbildung

Sven-Brian Müller, Stefan Krüger, Moustafa Abdel-Maksoud, Thomas Rung, Günter Ackermann, Wolfgang Fricke, Alexander Düster, Friedrich Wirz, Edwin Kreuzer, Marc-André Pick, Hermann Lödding, Axel Friedewald, Jürgen Grabe, Carlos Jahn & Claus Emmelmann
Broschüre des Forschungsschwerpunkts Maritime Systeme zur Forschungsausrichtung der beteiligten Institute.

Laserthermoschockversuche - Durchführung und Auswertung für unterschiedliche Hochleistungskeramiken

Robert Pulz
In this thesis, a laser beam thermal shock rig was fundamentally enhanced to realize heating-up thermal shock tests on different advanced ceramics. The testing technique of the rig was extended with respect to testing media, i.e. testing in vacuum is possible now in addition to air. Heating takes place continuously and very rapidly by a laser beam, which moves helically from the center of the sample to the outside. The measurement of the time and...

Via array modeling for application in fast, energy-efficient digital systems

Sebastian Müller
This thesis studies the application of physics-based via models for an efficient modeling of large via arrays in multilayer PCBs. Three main aspects are addressed: the study and improvement of the modeling accuracy, the study and improvement of the model efficiency, and the application of the model in a systematic evaluation of via array design alternatives for high speed links. With regard to the modeling accuracy, the application of an improved local field model is...

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Publication Year

  • 2014
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  • 2018
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