3,893 Works

Combinatorial n-fold integer programming and applications

Dušan Knop, Martin Koutecký & Matthias Mnich
Many fundamental NP-hard problems can be formulated as integer linear programs (ILPs). A famous algorithm by Lenstra solves ILPs in time that is exponential only in the dimension of the program, and polynomial in the size of the ILP. That algorithm became a ubiquitous tool in the design of fixed-parameter algorithms for NP-hard problems, where one wishes to isolate the hardness of a problem by some parameter. However, in many cases using Lenstra’s algorithm has...

Adaptive asset management for flood protection: The FAIR framework in action

Bart Vonk, Wouter Jan Klerk, Peter Fröhle, Berry Gersonius, Frank den Heijer, Philipp Jordan, Ulf Radu Ciocan, Jeroen Rijke, Paul Sayers & Richard Ashley
Uncertainties about climate change consequences, changing societal requirements and system complexity require flood protection asset managers to continuously evaluate their asset management policies and practice to manage risk and improve the resilience of their assets. However, there are many challenges in doing this, with asset operators often facing conflicting interests and major uncertainties about the future needs for asset performance. In the EU Interreg IV FAIR project, flood protection asset owners and operators, with scientific...

Characterization and performance of LbL-coated multibore membranes : zeta potential, MWCO, permeability and sulfate rejection

Saskia Dillmann, Shambhavi Arvind Kaushik, Jakob Stumme & Mathias Ernst
The characterization of membranes is suitable to investigate changes in the membrane properties caused by Layer-by-Layer (LbL) modification. Besides permeability, rejection, and molecular-weight cut-off (MWCO), which give information about the modification of the separation behaviour of the membrane, the zeta potential is capable of describing the surface charge of the membrane and its variation impacted by the properties of the polyelectrolyte multilayers (PEM). In this study, a new method for zeta potential measurement of hollow...

Ca-Zn-Ag alginate aerogels for wound healing applications : swelling behavior in simulated human body fluids and effect on macrophages

Claudia Keil, Christopher Hübner, Constanze Richter, Sandy Lier, Lars Barthel, Vera Meyer, Raman Subrahmanyam, Pavel Gurikov, Irina Smirnova & Hajo Haase
Chronic non-healing wounds represent a substantial economic burden to healthcare systems and cause a considerable reduction in quality of life for those affected. Approximately 0.5–2% of the population in developed countries are projected to experience a chronic wound in their lifetime, necessitating further developments in the area of wound care materials. The use of aerogels for wound healing applications has increased due to their high exudate absorbency and ability to incorporate therapeutic substances, amongst them...

Polyurea-crosslinked biopolymer aerogel beads

Patrina Paraskevopoulou, Irina Smirnova, Tamara Athamneh, Maria Papastergiou, Despoina Chriti, Gregor Mali, Tomaž Čendak, Grigorios Raptopoulos & Pavel Gurikov
Polyurea-crosslinked calcium alginate (X-Ca-alginate) and chitosan (X-chitosan) aerogel beads have been prepared via reaction of an aliphatic triisocyanate (Desmodur N3300) with the –OH groups of calcium alginate or the –NH2 groups of chitosan preformed wet gels, forming surface urethane or urea groups, respectively, and the subsequent formation of a polyurea conformal coating of the network via reaction of the triisocyanate with adsorbed water retained on the inner surfaces of the wet gels. That conformal coating...

Impact of temperature on LVI-damage and tensile and compressive residual strength of CFRP

Johann Körbelin, Chiara Dreiner & Bodo Fiedler
This study investigates the influence of temperature and impact-energy on low-velocity impact damage in CFRP and the resulting residual tensile and compressive strength. Impacts were introduce d at −20 ◦C , 20 ◦C and 80 ◦C , which are moderate temperature compared to the glass transition temperature of 203 ◦C of the used CFRP. A change in temperature leads to a substantial change in damage behaviour. With increasing temperature, the delamination area is reduced, and...

Solving packing problems with few small items using rainbow matchings

Max Bannach, Sebastian Berndt, Marten Maack, Matthias Mnich, Alexandra Lassota, Malin Rau & Malte Skambath
An important area of combinatorial optimization is the study of packing and covering problems, such as Bin Packing, Multiple Knapsack, and Bin Covering. Those problems have been studied extensively from the viewpoint of approximation algorithms, but their parameterized complexity has only been investigated barely. For problem instances containing no “small” items, classical matching algorithms yield optimal solutions in polynomial time. In this paper we approach them by their distance from triviality, measuring the problem complexity...

Operational Parameters of Biogas Plants: A Review and Evaluation Study

Abdullah Nsair, Senem Önen Cinar, Ayah Alassali, Hani Abu Qdais & Kerstin Kuchta
The biogas production technology has improved over the last years for the aim of reducing the costs of the process, increasing the biogas yields, and minimizing the greenhouse gas emissions. To obtain a stable and efficient biogas production, there are several design considerations and operational parameters to be taken into account. Besides, adapting the process to unanticipated conditions can be achieved by adequate monitoring of various operational parameters. This paper reviews the research that has...

Parameter dependence of solutions of the Cauchy–Riemann equation on weighted spaces of smooth functions

Karsten Kruse
Let Ω be an open subset of R2 and E a complete complex locally convex Hausdorff space. The purpose of this paper is to find conditions on certain weighted Fréchet spaces EV(Ω) of smooth functions and on the space E to ensure that the vector-valued Cauchy–Riemann operator ∂¯ : EV(Ω, E) → EV(Ω, E) is surjective. This is done via splitting theory and positive results can be interpreted as parameter dependence of solutions of the...

High-precision calibration of a weld-on-the-fly-system

Claus Emmelmann, Kerstin Schenk, Jörg Wollnack & Marc Kirchhoff
Since 20 years the importance of laser based material processing increases constantly due to its significant higher process speed in comparison to conventional processing technologies. A scanner system for laser-remote-welding mounted on a robot hand to achieve more freedom in positioning the laser spot has been investigated. Additionally the scanner head contains two fixed cameras for measurements and process monitoring. To perform required measurements with maximum accuracy the allover system has to be calibrated precise....

PLAU inferred from a correlation network is critical for suppressor function of regulatory T cells

Feng He, Hairong Chen, Michael Probst-Kepper, Robert Geffers, Serge Eifes, Antonio del Sol, Klaus Schughart, An-Ping Zeng & Rudi Balling
Human FOXP3(+)CD25(+)CD4(+) regulatory T cells (Tregs) are essential to the maintenance of immune homeostasis. Several genes are known to be important for murine Tregs, but for human Tregs the genes and underlying molecular networks controlling the suppressor function still largely remain unclear. Here, we describe a strategy to identify the key genes directly from an undirected correlation network which we reconstruct from a very high time-resolution (HTR) transcriptome during the activation of human Tregs/CD4(+) T-effector...

The Metagenome-derived enzymes LipS and LipT increase the diversity of known lipases

Jennifer Chow, Filip Kovacic, Yuliya Dall Antonia, Ulrich Krauss, Francesco Fersini, Christel Schmeißer, Benjamin Lauinger, Patrick Bongen, Jörg Pietruszka, Marlen Schmidt, Ina Menyes, Uwe Theo Bornscheuer, Marrit Friederike Eckstein, Oliver Thum, Andreas Liese, Jochen Müller-Dieckmann, Karl-Erich Jaeger & Wolfgang R. Streit
Triacylglycerol lipases (EC 3.1.1.3) catalyze both hydrolysis and synthesis reactions with a broad spectrum of substrates rendering them especially suitable for many biotechnological applications. Most lipases used today originate from mesophilic organisms and are susceptible to thermal denaturation whereas only few possess high thermotolerance. Here, we report on the identification and characterization of two novel thermostable bacterial lipases identified by functional metagenomic screenings. Metagenomic libraries were constructed from enrichment cultures maintained at 65 to 75°C...

In silico screening of modulators of magnesium dissolution

Christian Feiler, Di Mei, Bahram Vaghefinazari, Tim Würger, Robert Meißner, Bérengère J.C. Luthringer-Feyerabend, David A. Winkler, Mikhail L. Zheludkevich & Sviatlana V. Lamaka
The vast number of small molecules with potentially useful dissolution modulating properties (inhibitors or accelerators) renders currently used experimental discovery methods time- and resource-consuming. Fortunately, emerging computer-assisted methods can explore large areas of chemical space with less effort. Here we show how density functional theory calculations and machine learning methods can work synergistically to generate robust and predictive models that recapitulate experimentally-derived corrosion inhibition efficiencies of small organic compounds for pure magnesium. We further validate...

Analytical and numerical investigation of the airflow in face masks used for protection against COVID-19 virus : implications for mask design and usage

Robinson Peric & Milovan Perić
Der Einsatz von Atemschutzmasken für die breite Öffentlichkeit wurde in der Literatur als ein möglicher Ansatz vorgeschlagen, um die Virusausbreitung während der weltweiten COVID-19 Pandemie zu reduzieren. Allerdings deuten Literaturdaten darauf hin, dass viele Atemschutzmasken keinen verlässlichen Schutz vor einer Infektion bieten. Dieser Artikel untersucht die Hypothese, dass der Hauptgrund für diese eingeschränkte Schutzwirkung der nicht-passgenaue Sitz der Masken ist, wodurch Virus-transportierende Tröpfchen mit dem Luftstrom durch Spalte zwischen Dichtung und Gesicht eintreten oder austreten...

Compiling for the worst case : memory allocation for multi-task and multi-core hard real-time systems

Arno Luppold, Dominic Oehlert & Heiko Falk
Modern embedded hard real-time systems feature multiple tasks running on multiple processing cores. Schedulability analysis of such systems is usually performed on an abstract system level with each task being represented as a black box with fixed timing properties. If timing constraints are violated, optimizing the system on a code-level in order to achieve schedulability is a tedious task. To tackle this issue, we propose an extension to the WCET-Aware C Compiler framework WCC. We...

OpenMPIData: an initiative for freely accessible magnetic particle imaging data

Tobias Knopp, Patryk Szwargulski, Florian Griese & Matthias Gräser
Magnetic particle imaging is a tomographic imaging technique capable of measuring the local concentration of magnetic nanoparticles that can be used as tracers in biomedical applications. Since MPI is still at a very early stage of development, there are only a few MPI systems worldwide that are primarily operated by technical research groups that develop the systems themselves. It is therefore difficult for researchers without direct access to an MPI system to obtain experimental MPI...

Validation Concept for the Investigation of Effects of Modular Product Families

Lea-Nadine Schwede, Erik Greve & Dieter Krause
In order to meet an increasing internal variety, a solution can be the modularization of products. To motivate modularization projects throughout all phases of life, different effects of modular product families were collected in previous works on a literature basis. In this paper, a validation concept is presented, which will investigate these effects by using statements directly from industry representatives. In particular, the industry background is included in the evaluation to generate a more differentiated...

Towards a framework for the design of variety-oriented product-service systems

Christoph Rennpferdt & Dieter Krause
Due to increasing cost pressure, companies are expanding their product range and therefore increasingly offering so-called product-service systems (PSS) to increase sales. At the same time, PSS can also contribute to an increase in variety-induced complexity in the company, which ultimately further increases cost pressure. In this article, the causes and effects of variety-induced complexity through products, services and PSS are analysed and the need for a new PSS design method is then demonstrated. Finally,...

A Multi-Dimensional Configuration Algorithm for Modular Product Architectures

Florian Seiler & Dieter Krause
With an increasing demand for product individualisation leading to increased product architecture complexity and -costs, modular kits are one common measure to cope with this issue. The management of such a modular kit as well as the methodical determination of a specific product variant is key to the manufacturer's success. As multiple influence factors need to be taken into account when configuring product variants, we propose a multi-dimensional geometric optimisation algorithm, allowing for prioritising varying...

Flocking of linear parameter varying agents: source seeking application with underwater vehicles

Aly Attallah, Adwait Datar & Herbert Werner
A distributed flocking control scheme is proposed for a network of Autonomous Underwater Vehicles (AUVs) which are modeled as Linear Parameter Varying (LPV) systems. This scheme is applied here to the solution of a source seeking problem, i.e. the vehicles (agents) measure the local values of a scalar field and are required to flock to its maximum (source). It is assumed that agents have the gradient and Hessian information of the scalar field at their...

Jet cutting technique for the production of chitosan aerogel microparticles loaded with vancomycin

Clara López-Iglesias, Joana Barros, Inés Ardao, Pavel Gurikov, Fernando Monteiro, Irina Smirnova, Carmen Alvarez-Lorenzo & Carlos A. García-González
Biopolymer-based aerogels can be obtained by supercritical drying of wet gels and endowed with outstanding properties for biomedical applications. Namely, polysaccharide-based aerogels in the form of microparticles are of special interest for wound treatment and can also be loaded with bioactive agents to improve the healing process. However, the production of the precursor gel may be limited by the viscosity of the polysaccharide initial solution. The jet cutting technique is regarded as a suitable processing...

Model uncertainty-based evaluation of process strategies during scale-up of biopharmaceutical processes

Johannes Möller, Tanja Hernández Rodríguez, Jan Müller, Lukas Arndt, Kim Beatrice Kuchemüller, Björn Frahm, Regine Eibl, Dieter Eibl & Ralf Pörtner
Reliable scale-up of biopharmaceutical production processes is key in Quality by Design. In this study, a model-based workflow is described to evaluate the bioprocess dynamics during process transfer and scale-up computationally. First, a mathematical model describes the bioprocess dynamics of different state variables (e.g., cell density, titer). Second, the model parameter probability distributions are de- termined at different scales due to measurement uncertainty. Third, the quantified parameter distribu- tions are statistically compared to evaluate if...

CFRP thin-ply fibre metal laminates : influences of ply thickness and metal layers on open hole tension and compression properties

Benedikt Kötter, Julian Karsten, Johann Körbelin & Bodo Fiedler
Thin-ply laminates exhibit a higher degree of freedom in design and altered failure behaviour, and therefore, an increased strength for unnotched laminates in comparison to thick-ply laminates. For notched laminates, the static strength is strongly decreased; this is caused by a lack of stress relaxation through damage, which leads to a higher stress concentration and premature, brittle failure. To overcome this behaviour and to use the advantage of thin-ply laminates in areas with high stress...

Automated fabrication of elastomeric prepregs for soft robotics applications

Tristan Wienzek & Arthur Seibel
Fluidic elastomer soft robots typically consist of a top and a strain-limiting bottom part. Both parts are usually cast and then glued together. Elastomeric prepregs, which can be stored at low temperatures for several months without significant cross-linking, simplify this manufacturing process. A cured top part of an arbitrary shape is placed on the wet prepreg, which later forms the strain-limiting layer, and the actuator is finally cured in an oven. Herein, a machine is...

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...

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