2,246 Works

M03.002 Determination of pesticides in food by LC-MS/MS

Alina Stahl & Heike Frerichs
For the preparation of aqueous and solid samples QuEChERS method is used. Therefore, samples are homogenised by means of dry ice, extracted with acetonitrile and cleaned up by dispersive solid phase extraction. The final acidified extract can be analysed directly by LC-MSMS. The concentration of pesticides in samples is quantified with an external calibration and results are reported in mg/l or mg/kg.

Dealloying progress during nanoporous structure evolution analyzed by In situ resistometry

Eva-Maria Steyskal, Michael Seidl, Matthias Graf & Roland Würschum
The progress of dealloying, an electrochemical synthesis method capable of producing nanoporous structures with bulk outer dimensions, is studied by in situ resistometry. The resistance increases by three orders of magnitude while nanoporous gold or platinum is formed. Simultaneous monitoring of charge flow and electrical resistance increase proves to be an ideal combination for analyzing the etching progress, which in accordance with recent studies can be demonstrated to occur in two steps referred to as...

Ultrasonic joining of through-the-thickness reinforced metal-composite hybrid structures

Eduardo Etzberger Feistauer
Verbindungskonzepte, die traditionell für den Verbinden von Metall-Verbundstoff-Strukturen verwendet werden, weisen mehrere Beschränkungen in Bezug auf den Lasttransfer zwischen den Materialien. Die vorliegende Doktorarbeit zielt auf die Einführung von Ultrasonic Joining (U-Joining) ab, einem neuen Fügeverfahren zur Herstellung von throught-the-thickness verstärkten Hybridverbindungen aus Metall und Faserverbundwerkstoff mit verbesserter out-of-plane Festigkeit. Um die Machbarkeit des Fügeprozesses zu demonstrieren und die Korrelation zwischen Prozess- und Fügeeigenschaften zu beschreiben, wurde ein Fallstudienansatz gewählt, der kommerziell erhältliches glasfaserverstärktes Polyetherimid...

Friction-induced vibrations during tightening of bolted joints : analytical and experimental results

Nicolaj Baramsky, Arthur Seibel & Josef Schlattmann
Bolted joints are one of the most used machine elements. Holding together structures of all sizes, the integrity rests on their shoulders. Thus, an accurate and reliable assembly of the joint is crucial. While it is the aim to not experience friction-induced vibrations at all, at some situations, it is unavoidable. These cases, however, have yet been out of the focus of control algorithms due to the volatile nature of the process. This contribution delivers...

Comparison of analytical approaches predicting the compressive strength of fibre reinforced polymers

Christian Leopold, Sergej Harder, Timo Philipkowski, Wilfried Liebig & Bodo Fiedler
Common analytical models to predict the unidirectional compressive strength of fibre reinforced polymers are analysed in terms of their accuracy. Several tests were performed to determine parameters for the models and the compressive strength of carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP). The analytical models are validated for composites with glass and carbon fibres by using the same epoxy matrix system in order to examine whether different fibre types are taken...

Experimental and numerical investigation of reactive species transport around a small rising bubble

Andre Weiner, Jens Timmermann, Chiara Pesci, Jana Grewe, Marko Hoffmann, Michael Schlüter & Dieter Bothe
In this article, we present experimental and numerical techniques to investigate the transfer, transport, and reaction of a chemical species in the vicinity of rising bubbles. In the experiment, single oxygen bubbles of diameter d b =0.55…0.85mm are released into a measurement cell filled with tap water. The oxygen dissolves and reacts with sulfite to sulfate. Laser-induced fluorescence is used to visualize the oxygen concentration in the bubble wake from which the global mass transfer...

Connections between topology and macroscopic mechanical properties of three-dimensional open-pore materials

Norbert Huber
This work addresses a number of fundamental questions regarding the topological description of materials characterized by a highly porous three-dimensional structure with bending as the major deformation mechanism. Highly efficient finite-element beam models were used for generating data on the mechanical behavior of structures with different topologies, ranging from highly coordinated bcc to Gibson–Ashby structures. Random cutting enabled a continuous modification of average coordination numbers ranging from the maximum connectivity to the percolation-cluster transition of...

Part load behaviour of power plants with a retrofitted post-combustion CO2 capture process

Volker Roeder & Alfons Kather
The flexible and part load operation of fossil-fuelled power plants will increase due to the higher share of fluctuating renewable energies, like wind and solar power. In this work the part load behaviour of the post-combustion CO2 capture (PCC) process is evaluated. The net efficiency of the conventional hard-coal-fired power plant decreases from 45.6% at full load to 41.5% at 40% load. The net efficiency with PCC using 7 m MEA (monoethanolamine) as solvent decreases...

Assessment tool for the hybridisation of minigrids - Case study in Niger

Cédric Le Gal, Andreas Wiese & Paul Freunscht
Minigrids are a great electrification strategy for developing countries. [1] Formerly operated only by diesel generators, they could be equipped with renewable energy and storage systems to become more reliable and competitive. Since resources are limited, it is not possible to hybridise all minigrids at the same time. An MS-EXCEL-based multi-criteria decision analysis (MCDA) tool offers a rational and impartial way of decision-making presenting the most eligible minigrids for a hybridisation. For the demonstration purposes,...

Non-stationary 13C metabolic flux analysis of Chinese hamster ovary cells in batch culture using extracellular labeling highlights metabolic reversibility and compartmentation

Averina Nicolae, Judith Wahrheit, Janina Stephanie Bahnemann, An-Ping Zeng & Elmar Heinzle
Mapping the intracellular fluxes for established mammalian cell lines becomes increasingly important for scientific and economic reasons. However, this is being hampered by the high complexity of metabolic networks, particularly concerning compartmentation.

First Glycoside Hydrolase Family 2 Enzymes from Thermus antranikianii and Thermus brockianus with β-Glucosidase Activity

Carola Schröder, Saskia Blank & Garabed Antranikian
Two glycoside hydrolase encoding genes (tagh2 and tbgh2) were identified from different Thermus species using functional screening. Based on amino acid similarities, the enzymes were predicted to belong to glycoside hydrolase (GH) family 2. Surprisingly, both enzymes (TaGH2 and TbGH2) showed twofold higher activities for the hydrolysis of nitrophenol-linked β-D-glucopyranoside than of -galactopyranoside. Specific activities of 3,966 U/mg for TaGH2 and 660 U/mg for TbGH2 were observed. In accordance, K m values for both enzymes...

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...

Mobilisation of organic compounds from reservoir rocks through the injection of CO2 - comparison of baseline characterization and laboratory experiments

Ann Kathrin Scherf, Carsten Zetzl, Irina Smirnova, Michael Zettlitzer & Andrea Vieth-Hillebrand
In the framework of CO2 storage activities, the aim of our investigations is mainly to evaluate the effects of supercritical CO2 (scCO2) on the quantitative and qualitative extraction of organic compounds from reservoir rocks. Within the scope of the CO2 storage project CO2SINK the major task was to identify key mechanisms occurring in the reservoir as a result of the injection of CO2 into a saline aquifer. Here, it is of special interest what types...

Frequency versus time domain immunity testing of Smart Grid components

Frank Gronwald
Smart Grid components often are subject to considerable conducted current disturbances in the frequency range 2-150 kHz and, as a consequence, it is necessary to provide reliable immunity test methods. The relevant basic standard IEC 61000-4-19 that is currently under discussion focusses on frequency domain test methods. It is remarked in this contribution that in the context of frequency domain testing the chosen frequency spacing is related to the resonance response of the system under...

Scaling effects in the mechanical behaviour of carbon nanoparticle modified fibre reinforced polymers

Christian Leopold
Diese Arbeit betrachtet den Einfluss einer Nanopartikelmodifikation auf das Schadensverhalten und die resultierenden mechanischen Eigenschaften von Epoxidmatrix und Faser-Kunststoff-Verbunden (FKV). Ein Vergleich verschiedener Nanopartikel - Morphologien im Hinblick auf ihr Potential für den Einsatz in FKV wird durchgeführt. Da die Volumina zwischen den Fasern in FKV sehr klein sind, liegt der Fokus der Untersuchungen auf Größeneffekten. Der Einfluss wird anhand der Schädigungsmechanismen in Abhängigkeit von der Partikelmorphologie diskutiert. Ein bedarfsgerechter Modifizierungsansatz erlaubt die exakte Analyse...

Factors affecting multifunctional teams in innovation processes

Xin Shen
Structuring the innovation process and managing multifunctional teams is a basic prerequisite successful innovation. A well-structured process gives the possibility to implement effective multifunctional teamwork. Meanwhile, multifunctional teamwork helps to optimise and accomplish the innovation process.
Organizational support is necessary to achieve effective teamwork. Designing or changing the organizational structures for multifunctional collaboration is an important issue. Changing the system of performance measurement and setting up a multifunctional organizational culture gives employees strong signals that...

Rigorose Fehlerschranken für das Elektronenstrukturproblem

Kai Torben Ohlhus
Die vorliegende Doktorarbeit behandelt die Berechnung rigoroser Fehlerschranken für konische Optimierungsprobleme, einer Spezialform der konvexen Optimierung. Der Anwendungsschwerpunkt ist die Berechnung der Elektronenstruktur, insbesondere deren Grundzustandsenergie. Dies ist bis heute eine schwierig lösbare Problemstellung der Quantenchemie und kann als konisches Optimierungsproblem relaxiert werden. Es werden rigorose untere Fehlerschranken für das Elektronenstrukturproblem hergeleitet, welche alle Rundungsfehler miteinbeziehen und mit vernachlässigbarem Speicher- und Zeitaufwand für eine Vielzahl von Molekülen berechnet werden.

Inducing predefined nonlinear rogue waves on basis of breather solutions

Andy Witt
The Peregrine Breather, an analytical solution of the Nonlinear Schroedinger Equation, is modified to induce locally and temporally accurate, predefined extreme wave events in an arbitrary directed sea state. To this end, a parameter study of the distortion term of the unstable Peregrine modulation is performed to enforce form, height, and steepness of the rogue wave. In addition, the phase modulation is identified to be the crucial perturbation for the nonlinear Breather dynamic. With this...

Hierarchical supercrystalline nanocomposites through the self-assembly of organically-modified ceramic nanoparticles

Berta Domènech Garcia, Michael Kampferbeck, Emanuel Larsson, Tobias Krekeler, Büsra Bor, Diletta Giuntini, Malte Blankenburg, Martin Ritter, Martin Müller, Tobias Vossmeyer, Horst Weller & Gerold Schneider
Biomaterials often display outstanding combinations of mechanical properties thanks to their hierarchical structuring, which occurs through a dynamically and biologically controlled growth and self-assembly of their main constituents, typically mineral and protein. However, it is still challenging to obtain this ordered multiscale structural organization in synthetic 3D-nanocomposite materials. Herein, we report a new bottom-up approach for the synthesis of macroscale hierarchical nanocomposite materials in a single step. By controlling the content of organic phase during...

High-temperature stable inverse opal photonic crystals via mullite-sol-gel infiltration of direct photonic crystals

Priscila Bueno, Kaline Pagnan Furlan, Dachamir Hotza & Rolf Janßen
Three-dimensionally ordered macroporous materials for photonic or refractory applications have been developed by an innovative approach based on mullite sol-gel infiltration of direct photonic crystals followed by burn-out and calcination. Direct photonic crystals were obtained using polystyrene spheres templates either by vertical convective self-assembly or by drop casting. The samples were then infiltrated by spin coating with mullite sol-gels prepared with two different compositions (74 wt.% Al 2 O 3 , 26 wt.% SiO 2...

Influence of laser cutting parameters on CFRP part quality

André Goeke & Claus Emmelmann
Material processing of Carbon Fibre Reinforced Plastics (CFRP) parts by means of shape-cutting or jet-cutting technologies is state of the art today. These processes still perform in some applications with lack of part quality such as delamination and low productivity. Therefore, laser cutting processes have a great potential in material processing of CFRP. Laser process parameters have to be adjusted carefully in order to reduce the heat affected zone at cutting edge and influence on...

Property optimization of porous metallic glasses via structural design

Baran Sarac, Jana Wilmers & Swantje Bargmann
Systematization of material parameters is essential for property optimization. In this work, a gradient-extended continuum mechanical model implemented into a finite element code is utilized to analyze the influence of pore hierarchy on the overall mechanical response of porous metallic glasses. A spectrum of samples with randomized (stochastic) pore designs is comparatively studied with their periodic counterparts. It is shown that the pore design as well as the volume fraction has a strong effect on...

In situ high-energy X-ray diffraction during hot-forming of a multiphase TiAl alloy

Andreas Stark, Marcus Willi Rackel, Aristide Tchouaha Tankoua, Michael Oehring, Norbert Schell, Lars Lottermoser, Andreas Schreyer & Florian Pyczak
Intermetallic γ-TiAl based alloys exhibit excellent high-temperature strength combined with low density. This makes them ideal candidates for replacing the twice as dense Ni base super-alloys, currently used in the medium temperature range (~700 °C) of industrial and aviation gas turbines. An important step towards the serial production of TiAl parts is the development of suitable hot-forming processes. Thermo-mechanical treatments often result in mechanical anisotropy due to the formation of crystallographic textures. However, with conventional...

Supply chain sustainability performance indicators : a content analysis based on published standards and guidelines

Muhammad Amad Saeed & Wolfgang Kersten
The goal of this paper is to provide researchers and practitioners with the required guidance to achieve a better assessment of the sustainability-related performance of an organization and its supply chain (SC). In order to achieve this, standards and guidelines covering three sustainability dimensions (economic, social, and environmental) were analyzed for the identification of sustainability performance indicators (SPIs). A content analysis approach was applied for the data collection and analysis. Twelve international standards and guidelines...

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