374 Works

Highly effective inhibition of biofilm formation by the first metagenome-derived AI-2 quenching enzyme

Nancy Weiland-Bräuer, Johannes Martin Kisch, Nicole Pinnow, Andreas Liese & Ruth Schmitz-Streit
Bacterial cell-cell communication (quorum sensing, QS) represents a fundamental process crucial for biofilm formation, pathogenicity, and virulence allowing coordinated, concerted actions of bacteria depending on their cell density. With the widespread appearance of antibiotic-resistance of biofilms, there is an increasing need for novel strategies to control harmful biofilms. One attractive and most likely effective approach is to target bacterial communication systems for novel drug design in biotechnological and medical applications. In this study, metagenomic large-insert...

Shear design of concrete members without shear reinforcement - A solved problem?

Günter A. Rombach, Matthias Kohl & Vu Hong Nghiep
The design of concrete members for shear without stirrups has become a major issue worldwide especially for bridge decks as the shear capacity according to the 'new' regulations like the Eurocode often gives significant smaller values than the one predicted by former codes. Therefore nowadays stirrups are required in bridge decks. In addition the safety of existing structures mainly build without shear reinforcement has been brought into focus. The lack of the available design models...

Advances in porous biomaterials for dental and orthopaedic applications

Meenakshi Mour, Debarun Das, Thomas Winkler, Elisa Hoenig, Gabriela Mielke, Michael Morlock & Arndt Schilling
The connective hard tissues bone and teeth are highly porous on a micrometer scale, but show high values of compression strength at a relatively low weight. The fabrication of porous materials has been actively researched and different processes have been developed that vary in preparation complexity and also in the type of porous material that they produce. Methodologies are available for determination of pore properties. The purpose of the paper is to give an overview...

Gypsum scaling during reverse osmosis desalination − characterization and effects of natural organic matter

Jan Benecke
Zur Sicherstellung regionaler Wasserbedürfnisse gewinnt die Entsalzung von Brack- und Salzwasser mittels Umkehrosmose (UO) zunehmend an Bedeutung. Eine wesentliche Einschränkung stellt dabei die Kristallisation schwerlöslicher Salze in der Nähe oder auf der Membranoberfläche (‚Scaling‘) insbesondere bei hohen Permeatausbeuten dar. Diese Dissertation charakterisiert das Scaling durch Gips (CaSO4∙2H2O) und die Wechselwirkungen mit natürlichem organischem Material (NOM) mithilfe von Cross-Flow UO- und gerührten Becherglasexperimenten. Die Ergebnisse zeigen, dass das Gips-Scaling und die damit verbundenen Leistungsverluste in der...

Magnetic particle / magnetic resonance imaging: in-vitro MPI-guided real time catheter tracking and 4D angioplasty using a road map and blood pool tracer approach

Johannes Salamon, Martin Hofmann, Caroline Jung, Michael Kaul, Franziska Werner, Kolja Them, Rudolph Reimer, Peter Nielsen, Annika Vom Scheidt, Gerhard Adam, Tobias Knopp & Harald Ittrich
In-vitro evaluation of the feasibility of 4D real time tracking of endovascular devices and stenosis treatment with a magnetic particle imaging (MPI) / magnetic resonance imaging (MRI) road map approach and an MPI-guided approach using a blood pool tracer.

Thermal modelling of new Li-ion cell design modifications

Martin Sievers, Uwe Sievers & Samuel S. Mao
The effects of material and design modifications on the temperature distribution of Li-ion cells are simulated numerically. A two-dimensional anisotropic cylindrical coordinate model with linear triangular finite elements is used to simulate the steady-state temperature distribution within the cell. The cell's material and geometry are changed. New cell materials are investigated for thermal performance: a negative electrode of variously-oriented carbon nanotubes, as well as separators made of Separion, of Al 2O3 containing Cr particles or...

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...

Subcritical bifurcation in a self-excited single-degree-of-freedom system with velocity weakening-strengthening friction law: analytical results and comparison with experiments

Antonio Papangelo, Michele Ciavarella & Norbert Hoffmann
The dynamical behavior of a single-degree-of-freedom system that experiences friction-induced vibrations is studied with particular interest on the possibility of the so-called hard effect of a subcritical Hopf bifurcation, using a velocity weakening–strengthening friction law. The bifurcation diagram of the system is numerically evaluated using as bifurcation parameter the velocity of the belt. Analytical results are provided using standard linear stability analysis and nonlinear stability analysis to large perturbations. The former permits to identify the...

Analytical and semi-analytical solutions of some fundamental nonlinear stochastic differential equations

Leo Dostal & Edwin Kreuzer
We are interested in perturbed Hamiltonian systems in a plane, which are damped and excited by an absolutely regular non-white Gaussian process. We use two methods for the determination of analytical and semi-analytical solutions to such nonlinear stochastic differential equations (SDE). The first method is based on a limit theorem by Khashminskii, from which a class of methods was derived known as stochastic averaging. From the drift and diffusion of the resulting averaged process, probability...

Optimization of a composite latent heat storage (CLHS) with non-uniform heat fluxes using a genetic algorithm

Henrik Veelken & Gerhard Schmitz
The scope of this work is to show optimization potential for regularly structured composite latent heat storage (CLHS) devices with non-uniform heat loads by varying the distribution of fins on the contact surface to an electronic component. The modeling of the CLHS is carried out in 2D using Matlab in combination with Comsol and the effective heat capacity method for the melting process. The link between Matlab and Comsol is carried out with the Comsol–Matlab...

Synthesis of heat exchanger networks taking into account cost and dynamic considerations

Matthias Rathjens, Timo Bohnenstädt, Georg Fieg & Ole Engel
In this work an approach is presented for the synthesis of near cost optimal heat exchanger networks with a high controllability. The presented methodology is based on a sequential approach utilizing different algorithms and mathematical models. The procedure is carried out in three steps. A genetic algorithm is used to produce a high diversity of promising structures that suffice the needs for cost reduction and controllability characteristics. For selected structures controllability evaluations are carried out,...

Occurrence of micropollutants in the wastewater streams of cruise ships

Lena Westhof, Stephan Köster & Margrit Reich
Nowadays the protection of the marine environment raises increasing academic and public attention. The issue of organic micropollutants is of equally high importance for the marine ecosystems. Maritime vessels are considered to significant sources of micropollutants especially if the ship carries many passengers, which is often true for cruise ships which frequent attractive and sensitive sea areas. The emission pathways for micropollutants include wastewater discharges and sewage sludge disposal. The findings of the German research...

Computing Fault-Containment Times of Self-Stabilizing Algorithms Using Lumped Markov Chains

Volker Turau
The analysis of self-stabilizing algorithms is often limited to the worst case stabilization time starting from an arbitrary state, i.e., a state resulting from a sequence of faults. Considering the fact that these algorithms are intended to provide fault tolerance in the long run, this is not the most relevant metric. A common situation is that a running system is an a legitimate state when hit by a single fault. This event has a much...

Volcanic SO2 and SiF4 visualization using 2-D thermal emission spectroscopy ; Part 1: Slant-columns and their ratios

Wolfgang Stremme, Arne Krueger, Roland Harig & Michel Grutter
The composition and emission rates of volcanic gas plumes provide insight of the geologic internal activity, atmospheric chemistry, aerosol formation and radiative processes around it. Observations are necessary for public security and the aviation industry. Ground-based thermal emission infrared spectroscopy, which uses the radiation of the volcanic gas itself, allows for continuously monitoring during day and night from a safe distance. We present measurements on Popocatépetl volcano based on thermal emission spectroscopy during different campaigns...

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,...

Adsorption-induced deformation of nanoporous materials : a review

Gennady Y. Gor, Patrick Huber & Noam Bernstein
When a solid surface accommodates guest molecules, they induce noticeable stresses to the surface and cause its strain. Nanoporous materials have high surface area and, therefore, are very sensitive to this effect called adsorption-induced deformation. In recent years, there has been significant progress in both experimental and theoretical studies of this phenomenon, driven by the development of new materials as well as advanced experimental and modeling techniques. Also, adsorptioninduced deformation has been found to manifest...

Information-Bottleneck Decoding of High-Rate Irregular LDPC Codes for Optical Communication Using Message Alignment

Maximilian Stark, Jan Lewandowsky & Gerhard Bauch
In high-throughput applications, low-complexity and low-latency channel decoders are inevitable. Hence, for low-density parity-check (LDPC) codes, message passing decoding has to be implemented with coarse quantization—that is, the exchanged beliefs are quantized with a small number of bits. This can result in a significant performance degradation with respect to decoding with high-precision messages. Recently, so-called information-bottleneck decoders were proposed which leverage a machine learning framework (i.e., the information bottleneck method) to design coarse-precision decoders with...

Comparison of NF-RO and RO-NF for the treatment of mature landfill leachates: a guide for landfill operators

Sreenivasan Ramaswami, Joachim Behrendt & Ralf Otterpohl
Reverse osmosis (RO) and nanofiltration (NF) are among the state-of-the-art technologies for treating landfill leachates. Due to the complexity and variance in the composition of leachates, numerous combinations of multiple technologies are used for their treatment. One process chain for the treatment of raw leachate is RO followed by further concentration of RO-retentate using NF (RO-NF scheme). The aptness of this process train used by some landfill sites around the world (usually with the aim...

Non-conventional methods for gelation of alginate

Pavel Gurikov & Irina Smirnova
This review presents and critically evaluates recent advances in non-conventional gelation method of native alginate. A special focus is given to the following three methods: cryotropic gelation, non-solvent induced phase separation and carbon dioxide induced gelation. A few other gelation approaches are also briefly reviewed. Results are discussed in the context of subsequent freeze and supercritical drying. The methods are selected so as to provide the readers with a range of novel tools and tactics...

Polysaccharide-based aerogel bead production via jet cutting method

Imke Preibisch, Philipp Niemeyer, Yusuf Yusufoğlu, Pavel Gurikov, Barbara Milow & Irina Smirnova
The aim of this work is to develop a method to produce spherical biopolymer-based aerogel particles, which is capable for scale-up in the future. Therefore, the jet cutting method is suggested. Amidated pectin, sodium alginate, and chitosan are used as a precursor (a 1–3 wt. % solution) for particle production via jet cutting. Gelation is realized via two methods: the internal setting method (using calcium carbonate particles as cross-linkers and citric and acidic acid for...

High-temperature stable Zirconia particles doped with Yttrium, Lanthanum, and Gadolinium

Elisabeth Leib, Robert M. Pasquarelli, Malte Blankenburg, Martin Müller, Andreas Schreyer, Rolf Janßen, Horst Weller & Tobias Vossmeyer
Zirconia microspheres synthesized by a wet-chemical sol–gel process are promising building blocks for various photonic applications considered for heat management and energy systems, including highly effi cient refl ective thermal barrier coatings and absorbers/emitters used in thermophotovoltaic systems. As previously shown, pure zirconia microparticles deteriorate at working temperatures of ≥1000 °C. While the addition of yttrium as a dopant has been shown to improve their phase stability, pronounced grain growth at temperatures of ≥1000 °C...

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...

Ein technisches System für die kollaborative OER-Entwicklung im Experimentierfeld der TUHH

Axel Dürkop, Andreas Böttger, Tina Ladwig & Sönke Knutzen
Der Artikel führt ein in ein umgesetztes Konzept zur kollaborativen Entwicklung von Open Educational Ressources (OER) im Experimentierfeld der HOOU an der TUHH. Dabei werden Erfahrungen sowohl aus dem sozialen und organisatorischen Prozess berichtet als auch informationstechnische Systeme und ihr Zusammenspiel vorgestellt.

Hydrological impacts of climate change on flood probability in small urban catchments and possibilities of flood risk mitigation

Sandra Hellmers
Die Auswirkungen des Klimawandels auf die Ökologie, den Menschen und die Ökonomie sind bereits spürbar und werden voraussichtlich in Zukunft erheblich zunehmen. Veränderungen der Häufigkeit und Intensität von Starkniederschlägen sind dabei zu erwarten, die wiederum erhebliche Auswirkungen auf die Hochwasserverhältnisse in Flusseinzugsgebieten zur Folge haben können. Insbesondere Überschwemmungen von kleinen Einzugsgebieten in urbanen Räumen durch Gewässer und Entwässerungsnetze werden durch Starkniederschläge verursacht. Die Entwicklung einer umfassenden und detaillierten Methodik zur Quantifizierung der hydrologischen Auswirkungen des...

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