3,893 Works

Production of starch aerogel in form of monoliths and microparticles

Victor Baudron, Martha Taboada, Pavel Gurikov, Irina Smirnova & Steve Whitehouse
Pea and amylomaize starches were used to produce aerogel in form of monoliths and microparticles. The formation of starch gel was investigated, and we showed that each starch needed a different pasting temperature for its complete dissolution. The gelation kinetics was investigated with oscillatory rheometry for both systems as a function of the starch concentration. The gelation and retrogradation temperature of the starch gel were varied and its impact on the final aerogel evaluated. The...

Iron(II)-catalyzed biomimetic aerobic oxidation of alcohols

Arnar Guðmundsson, Kim Elisabeth Schlipköter & Jan-E. Bäckvall
We report the first FeII-catalyzed biomimetic aerobic oxidation of alcohols. The principle of this oxidation, which involves several electron-transfer steps, is reminiscent of biological oxidation in the respiratory chain. The electron transfer from the alcohol to molecular oxygen occurs with the aid of three coupled catalytic redox systems, leading to a low-energy pathway. An iron transfer-hydrogenation complex was utilized as a substrate-selective dehydrogenation catalyst, along with an electron-rich quinone and an oxygen-activating Co(salen)-type complex as...

Electrical double layer capacitance of curved graphite electrodes

Jannes Seebeck, Peter Schiffels, Sabine Schweizer, Jörg-Rüdiger Hill & Robert Meißner
To improve the understanding of the relation between electrode curvature and energy storage mechanisms, a systematic investigation of the correlation between convex and concave electrode surfaces and the differential capacitance of an electrochemical double layer capacitor using molecular dynamics simulations is presented. Each electrode consists of three layers of curved graphene sheets with a convex and concave surface to which the constant potential method was applied. The differential capacitance shows a fluctuating behavior with respect...

Inconsistency Management for Product Families with many Varients through a Model-Based Approach in Modular Lightweight Design

Michael Hanna, Johann Schwenke & Dieter Krause
In methodical product development, numerous data are used and linked with each other, especially variant-related data. This paper presents a model-based solution for avoiding inconsistencies in the development of product families with many variants and extends it to modular lightweight design. In addition, the inconsistencies in methodical product development were classified and solution approaches were shown. Thus, inconsistencies can be avoided with the presented elaborated data model for an integrated product and process model based...

Optimal temperature-based condition monitoring system for wind turbines

Payam Teimourzadeh Baboli, Davood Babazadeh, Amin Raeiszadeh, Susanne Horodyvskyy & Isabel Koprek
With the increasing demand for the efficiency of wind energy projects due to challenging market conditions, the challenges related to maintenance planning are increasing. In this paper, a condition-based monitoring system for wind turbines (WTs) based on data-driven modeling is proposed. First, the normal condition of the WTs key components is estimated using a tailor-made artificial neural network. Then, the deviation of the real-time measurement data from the estimated values is calculated, indicating abnormal conditions....

BIM-based description of intelligent transportation systems for roads

Mahsa Mirboland & Kay Smarsly
Intelligent transportation systems (ITS) provide safer, greener, and more convenient mobility, while reducing the impact on the environment. In recent years, simulation platforms have been employed to study ITS applications, mostly focusing on traffic-related simulations. Despite several research studies on ITS applications and simulation platforms, formal semantic descriptions of intelligent transportation systems have not been addressed yet. In this paper, a semantic model describing intelligent transportation systems for roads is proposed. The semantic model is...

Modelling shear wave propagation in soft tissue surrogates using a finite element‐ and finite difference method

Jakob Ohlsen, Maximilian Neidhardt, Alexander Schlaefer & Norbert Hoffmann
Abstract Shear Wave Elasticity Imaging (SWEI) has become a popular medical imaging technique [1] in which soft tissue is excited by the acoustic radiation forces of a focused ultrasonic beam. Tissue stiffness can then be derived from measurements of shear wave propagation speeds [2]. The main objective of this work is a comparison of a finite element (FEM) and a finite difference method (FDM) in terms of their computational efficiency when modeling shear wave propagation...

A Note on the Harmonic Extension Approach to Fractional Powers of non‐densely defined Operators

Jan Meichsner & Christian Seifert
We show to what extend fractional powers of non‐densely defined sectorial operators on Banach spaces can still be described by the harmonic extension approach.

Begleitung eines agilen Lernprozesses bei kleineren und mittleren Unternehmen : ein Diskussionspapier

Henning Klaffke, Vanessa Kortegast & Thomas Greve
In dieser Veröffentlichung wird die Begleitung eines agilen Lernprozesses bei kleinen und mittleren Unternehmen durch die Integration einer Lernkoordination mithilfe des vorgestellten Frameworks konzeptionell beschrieben und mit konkreten Vorgehensweisen, Beispielen und Erfahrungen konkretisiert. In dem Framework nimmt die Lernkoordination eine Schnittstellenfunktion zwischen den Mitarbeiter:innen eines Unternehmens sowie dem Unternehmen und externen Know-How-Träger:innen ein und unterstützt und begleitet damit den agilen Lernprozess im Unternehmen. Kennzeichnend für das Framework ist die Berücksichtigung der Anforderungen an Lernsysteme im...

Estimating the spatial orientation of immobilized magnetic nanoparticles with parallel-aligned easy axes

Martin Möddel, Florian Griese, Tobias Kluth & Tobias Knopp
Advances in micromachinery and nanotechnology, such as magnetically actuated microrobots for navigating in viscous environments, are important driving forces in medicine. Recently, it has been shown that the spatial orientation of an ensemble of immobilized nanoparticles with parallel-aligned magnetic easy axes has an effect on the magnetization response to an external dynamic magnetic field. Here, we introduce a method that allows us to estimate the spatial orientation of this axis from the magnetization response and...

Welches Lehrverhalten zeigen geschulte Tutor/innen? Eine explorative Analyse selbst- und fremdwahrnehmungsbasierter Reflexionsberichte

Jenny Alice Rohde & Nadine Stahlberg
Der Einsatz von Tutor/innen in der universitären Lehre ist weit verbreitet. Um sie auf die Übernahme von Lehraufgaben vorzubereiten, ist ihre Schulung von großer Bedeutung. Es hat sich gezeigt, dass geschulte Tutor/innen über ein höheres Niveau von didaktischem Wissen, selbsteingeschätzter Kompetenz und Selbstwirksamkeit verfügen (Glathe, 2017). Weitere Untersuchungen stützen sich meist allein auf Evaluationsbögen, die jedoch vorwiegend die Zufriedenheit erfassen und keinen Aussagewert über den Praxistransfer enthalten. Dieser Beitrag schließt diese Forschungslücke, indem er 40...

Understanding interfaces in metal-oxide/organic-acid hybrid materials from first-principles calculations

Kai Sellschopp
Grenzflächen zwischen Metall-Oxiden und organischen Säuren beeinflussen eine Reihe von verschiedenen Anwendungen, von Hybridmaterialien bis hin zu Katalyse. Die vorliegende Arbeit untersucht die Struktur und Energetik dieser Grenzflächen auf der atomaren Skala. Mit Hilfe von ab-initio Rechnungen und einem neuartigen Werkzeug für Struktursuche werden die stabilsten Grenzflächenstrukturen bestimmt, wodurch eine Restrukturierung von Magnetit (Fe3O4) Oberflächen gefunden und formbeeinflussende Faktoren für Titandioxid (TiO2)-Nanopartikel identifiziert werden. Schließlich wird die Facettenabhängigkeit der mechanischen Grenzflächeneigenschaften untersucht, was tiefere Einblicke...

Adjoint-based shape optimization for the minimization of flow-induced hemolysis in biomedical applications

Georgios Bletsos, Niklas Kühl & Thomas Rung
This paper reports on the derivation and implementation of a shape optimization procedure for the minimization of hemolysis induction in biomedical devices. Hemolysis is a blood damaging phenomenon that may occur in mechanical blood-processing applications where large velocity gradients are found. An increased level of damaged blood can lead to deterioration of the immune system and quality of life. It is, thus, important to minimize flow-induced hemolysis by improving the design of next-generation biomedical machinery....

Bildgebende UV/VIS‐Spektroskopie zur Untersuchung des Einflusses der Fluiddynamik auf die Entstehung von Haupt‐ und Nebenprodukt in schnellen konkurrierenden konsekutiven Gas‐Flüssig‐Reaktionen

Felix Kexel, Alexandra von Kameke, Martin Oßberger, Marko Hoffmann, Peter Klüfers & Michael Schlüter
Zur Bildung vieler Bulk‐Chemikalien müssen gasförmige Stoffe mit einer kontinuierlichen flüssigen Phase vermischt und zur Reaktion gebracht werden. Häufig kommt es dabei zur Entstehung unerwünschter Nebenprodukte. Wie die Entstehung eines Nebenprodukts einer schnellen konkurrierenden Folgereaktion durch die Zeitskalen der Vermischung beeinflusst werden kann wird untersucht. Zum Einsatz kommt ein Taylor‐Blasen‐Experiment, bei dem die Zeitskalen der Vermischung systematisch und reproduzierbar variiert werden können. Es zeigt sich, dass der Vermischung in der Wirbelschleppe einer Blase hinsichtlich der...

Experimental investigation of sustainable and energy efficient management of a geothermal field as a heat source and heat sink for a large office building

Kristian Duus & Gerhard Schmitz
The new construction of a large office building in Hamburg, which is the subject of this investigation, has been closely monitored over a period of about 5 years. In addition to evaluating and optimising the energy demands and user comfort, the focus was on the management of the energy from an exceptionally large geothermal field which is used for heating and cooling the building. The possibilities for sustainable, energy efficient use of the geothermal field...

A novel dry treatment for municipal solid waste incineration bottom ash for the reduction of salts and potential toxic elements

Marco Abis, Martina Bruno, Franz-Georg Simon, Raul Grönholm, Michel Hoppe, Kerstin Kuchta & Silvia Fiore
The main obstacle to bottom ash (BA) being used as a recycling aggregate is the content of salts and potential toxic elements (PTEs), concentrated in a layer that coats BA particles. This work presents a dry treatment for the removal of salts and PTEs from BA particles. Two pilot-scale abrasion units (with/without the removal of the fine particles) were fed with different BA samples. The performance of the abrasion tests was assessed through the analyses...

The impact of time delays for power hardware-in-the-loop investigations

Jana Ihrens, Stefan Möws, Lennard Wilkening, Thorsten A. Kern & Christian Becker
Power hardware-in-the-loop (PHiL) simulations provide a powerful environment in the critical process of testing new components and controllers. In this work, we aim to explain the impact of time delays in a PHiL setup and recommend how to consider them in different investigations. The general concept of PHiL, with its necessary components, is explained and the benefits compared to pure simulation and implemented field tests are presented. An example for a flexible PHiL environment is...

Intercropping in rice farming under the system of rice intensification : an agroecological strategy for weed control, better yield, increased returns, and social-ecological sustainability

Tavseef Mairaj Shah, Sumbal Tasawwar, M. Anwar Bhat & Ralf Otterpohl
Rice is the staple food for more than half of the world’s population. In South Asia, rice farming systems provide food to the majority of the population, and agriculture is a primary source of livelihood. With the demand for nutritious food increasing, introducing innovative strategies in farming systems is imperative. In this regard, intensification of rice farming is intricately linked with the challenges of water scarcity, soil degradation, and the vagaries of climate change. Agroecological...

Agroecology for food and water security in times of climate consciousness : a bibliometric analysis of peer-reviewed literature published from 1990 to 2020

Tavseef Mairaj Shah, Sumbal Tasawwar & Ralf Otterpohl
The discrepancies in our food systems have become more pronounced in the last couple of years due to natural disasters of huge magnitude and the current pandemic, that have served to make them visible to a wider range of population. As a result, a shift to agroecological food and farming systems is currently being advocated at different levels. An agroecological approach to food systems involves consideration of all their interactions with the major challenges of...

Extracellular riboflavin induces anaerobic biofilm formation in Shewanella oneidensis

Miriam Edel, Gunnar Sturm, Katrin Sturm-Richter, Michael Wagner, Julia Novion Ducassou, Yohann Couté, Harald Horn & Johannes Gescher
Background: Some microorganisms can respire with extracellular electron acceptors using an extended electron transport chain to the cell surface. This process can be applied in bioelectrochemical systems in which the organisms produce an electrical current by respiring with an anode as electron acceptor. These organisms apply flavin molecules as cofactors to facilitate one-electron transfer catalyzed by the terminal reductases and in some cases as endogenous electron shuttles. Results: In the model organism Shewanella oneidensis, riboflavin...

Structural degradation of tungsten sandwiched in hafnia layers determined by in-situ XRD up to 1520 °C

Gnanavel Vaidhyanathan Krishnamurthy, Manohar Chirumamilla, Surya Snata Rout, Kaline Pagnan Furlan, Tobias Krekeler, Martin Ritter, Hans Werner Becker, Alexander Petrov, Manfred Eich & Michael Störmer
The high-temperature stability of thermal emitters is one of the critical properties of thermophotovoltaic (TPV) systems to obtain high radiative power and conversion efficiencies. W and HfO are ideal due to their high melting points and low vapor pressures. At high temperatures and given vacuum conditions, W is prone to oxidation resulting in instantaneous sublimation of volatile W oxides. Herein, we present a detailed in-situ XRD analysis of the morphological changes of a 3-layer-system: HfO...

Simultaneous enhancement of actuation strain and mechanical strength of nanoporous Ni–Mn actuators

Chuan Cheng, Lukas Lührs & Tobias Krekeler
Metallic electrochemical actuators convert electrical energy into mechanical energy via charge-induced strain at the nanoporous metal/electrolyte interface. To enhance the actuation amplitude, a general choice is to increase the electrode surface area to elevate the charge capacity. However, a large surface area is detrimental to the actuation stability and mechanical strength of the actuator, such as irreversible volume shrinkage due to surface coarsening. Here, this critical issue can be mitigated by introducing a secondary actuation...

MRIReco.jl: an MRI reconstruction framework written in Julia

Tobias Knopp & Mirco Grosser
Purpose: The aim of this work is to develop a high-performance, flexible, and easy-to-use MRI reconstruction framework using the scientific programming language Julia. Methods: Julia is a modern, general purpose programming language with strong features in the area of signal/image processing and numerical computing. It has a high-level syntax but still generates efficient machine code that is usually as fast as comparable C/C++ applications. In addition to the language features itself, Julia has a sophisticated...

Mechanical homeostasis in tissue equivalents: a review

Jonas Eichinger, Lea J. Haeusel, Daniel Paukner, Roland C. Aydin, Jay Dowell Humphrey & Christian J. Cyron
There is substantial evidence that growth and remodeling of load bearing soft biological tissues is to a large extent controlled by mechanical factors. Mechanical homeostasis, which describes the natural tendency of such tissues to establish, maintain, or restore a preferred mechanical state, is thought to be one mechanism by which such control is achieved across multiple scales. Yet, many questions remain regarding what promotes or prevents homeostasis. Tissue equivalents, such as collagen gels seeded with...

Microstructure and mechanical behavior of TiO₂-MnO-doped alumina/alumina laminates

Marcelo Daniel Barros, Hans Jelitto, Dachamir Hotza & Rolf Janßen
Tapes of TiO2-MnO-doped alumina (d-Al2O3) and pure alumina (Al2O3) were shaped via tape casting. Laminates with three different layer numbers and respective thicknesses were produced and sintered at 1200°C. The microstructure and mechanical behavior of laminates were investigated and compared to the respective monolithic references (d-Al2O3 and Al2O3). The use of dopants in alumina decreased the initial sintering temperature, leading to higher densification at 1200°C (~98% theoretical density (TD)) when compared to Al2O3 (~73% TD)....

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