2,469 Works

Metamaterial emitter for thermophotovoltaics stable up to 1400 °C

Manohar Chirumamilla, Gnanavel Vaidhyanathan Krishnamurthy, Katrin Knopp, Tobias Krekeler, Matthias Graf, Dirk Jalas, Martin Ritter, Michael Störmer, Alexander Petrov & Manfred Eich
High temperature stable selective emitters can significantly increase efficiency and radiative power in thermophotovoltaic (TPV) systems. However, optical properties of structured emitters reported so far degrade at temperatures approaching 1200 °C due to various degradation mechanisms. We have realized a 1D structured emitter based on a sputtered W-HfO 2 layered metamaterial and demonstrated desired band edge spectral properties at 1400 °C. To the best of our knowledge the temperature of 1400 °C is the highest...

Increasing tightness by introduction of intertemporal constraints in MILP unit commitment

Tobias Zimmermann, Tobias Cors, Gerrit Erichsen & Alfons Kather

Integrating local scale drainage measures in meso scale hydrological modelling of backwater affected catchments

Sandra Hellmers

Mobility as a Service: ein Angebot auch für Einkommensarme? (Geo-Datensatz, aktualisiert)

Christoph Aberle
--Update: The first .csv version was stored in an unhandy format (had to be transponed to be useful for GIS applications). This has been corrected with the updated .csv file. file Geographic datasets that represent ride-pooling service area in Hamburg as of May 2019: CleverShuttle, Ioki, MOIA, mytaxi match / FREE NOW Including MOIA planned service area extension. All layers have been digitised in May 2019 by using public data provided by the ride-pooling operators....

Three-fluid heat exchanger as evaporator in multi-source heat pumps with viable options for alternative defrosting methods

Thore Oltersdorf, Gerhard Schmitz & Hans-Martin Henning

Neue Mobilitätsangebote: Gewährleisten sie gesellschaftliche Teilhabe für Einkommensarme?

Stephan Daubitz & Christoph Aberle

Experimental investigation of a ground coupled desiccant assisted air conditioning system during winter mode

Peter Niemann & Gerhard Schmitz

Self-assembly of liquid crystals in nanoporous solids for adaptive photonic metamaterials

Kathrin Sentker, Arda Yildirim, Milena Lippmann, Arne Zantop, Florian Bertram, Tommy Hofmann, Oliver H. Seeck, Andriy V. Kityk, Marco G. Mazza, Andreas Schönhals & Patrick Huber

Synthesis and thermal stability of ZrO2@SiO2 core-shell submicron particles

Maik Finsel, Maria Hemme, Sebastian Döring, Jil S. V. Rüter, Gregor Thomas Dahl, Tobias Krekeler, Andreas Kornowski, Martin Ritter, Horst Weller & Tobias Vossmeyer
ZrO2@SiO2 core-shell submicron particles are promising candidates for the development of advanced optical materials. Here, submicron zirconia particles were synthesized using a modified sol-gel method and pre-calcined at 400 °C. Silica shells were grown on these particles (average size: ∼270 nm) with well-defined thicknesses (26 to 61 nm) using a seeded-growth Stöber approach. To study the thermal stability of bare ZrO2 cores and ZrO2@SiO2 core-shell particles they were calcined at 450 to 1200 °C. After...

Synthesis of uniform bulk nanoporous palladium with tunable structure

Shan Shi, Jürgen Markmann & Jörg Weißmüller
This work presents systematic investigations on the synthesis of hierarchical nanoporous Pd via electrochemical dealloying of CuPd alloys in sulfuric acid. The impact of electrode potential, dealloying temperature, and additional annealing on microstructure and morphology is explored. Dealloying Cu85Pd15 in 1M sulfuric acid at elevated temperature provides a facile strategy to produce bulk nanoporous Pd samples which are uniform, hierarchically nanoporous, and free of macro-scale cracks. The question “Why will one-step template-free dealloying yield a...

Dataset of ptychographic X-ray computed tomography of inverse opal photonic crystals produced by atomic layer deposition

Kaline P. Furlan, Emanuel Larsson, Ana Diaz, Mirko Holler, Tobias Krekeler, Martin Ritter, Alexander Yu. Petrov, Manfred Eich, Robert Blick, Gerold A. Schneider, Imke Greving, Robert Zierold & Rolf Janßen
This data article describes the detailed parameters for synthesizing mullite inverse opal photonic crystals via Atomic Layer Deposition (ALD), as well as the detailed image analysis routine used to interpret the data obtained by the measurement of such photonic crystals, before and after the heat treatment, via Ptychographic X-ray Computed Tomography (PXCT). The data presented in this article are related to the research article by Furlan and co-authors entitled "Photonic materials for high-temperature applications: Synthesis...

Photonic materials for high-temperature applications: synthesis and characterization by X-ray ptychographic tomography

Kaline P. Furlan, Emanuel Larsson, Ana Diaz, Mirko Holler, Tobias Krekeler, Martin Ritter, Alexander Yu. Petrov, Manfred Eich, Robert Blick, Gerold A. Schneider, Imke Greving, Robert Zierold & Rolf Janßen
Photonic materials for high-temperature applications need to withstand temperatures usually higher than 1000 °C, whilst keeping their function. When exposed to high temperatures, such nanostructured materials are prone to detrimental morphological changes, however the structure evolution pathway of photonic materials and its correlation with the loss of material's function is not yet fully understood. Here we use high-resolution ptychographic X-ray computed tomography (PXCT) and scanning electron microscopy (SEM) to investigate the structural changes in mullite...

Highly porous α-Al 2 O 3 ceramics obtained by sintering atomic layer deposited inverse opals

Kaline P. Furlan, Robert M. Pasquarelli, Tobias Krekeler, Martin Ritter, Robert Zierold, Kornelius Nielsch, Gerold A. Schneider & Rolf Janßen
A process for generating highly porous α-Al2O3 ceramics has been developed. In this paper, a combination of self-assembly and atomic layer deposition is demonstrated as a means to fabricate inverse alumina opals, which have their structures transformed via sintering. The resulting highly porous structure is stable even after a 4 h dwell time at 1400 °C, in contrast to structures generated by conventional powder metallurgy, sol-gel or colloidal powder suspension infiltration methods. TEM analysis reveals...

Controlling thermal emission with refractory epsilon-near-zero metamaterials via topological transitions

Pavel N. Dyachenko, Sean Molesky, Alexander Petrov, Michael Störmer, Tobias Krekeler, Slawa Lang, Martin Ritter, Zubin Jacob & Manfred Eich
Control of thermal radiation at high temperatures is vital for waste heat recovery and for high-efficiency thermophotovoltaic (TPV) conversion. Previously, structural resonances utilizing gratings, thin film resonances, metasurfaces and photonic crystals were used to spectrally control thermal emission, often requiring lithographic structuring of the surface and causing significant angle dependence. In contrast, here, we demonstrate a refractory W-HfO2 metamaterial, which controls thermal emission through an engineered dielectric response function. The epsilon-near-zero frequency of a metamaterial...

Exceptionally strong, stiff and hard hybrid material based on an elastomer and isotropically shaped ceramic nanoparticles

Prokopios Georgopanos, Gerold A. Schneider, Axel Dreyer, Ulrich A. Handge, Volkan Filiz, Artur Feld, Ezgi D. Yilmaz, Tobias Krekeler, Martin Ritter, Horst Weller & Volker Abetz
In this work the fabrication of hard, stiff and strong nanocomposites based on polybutadiene and iron oxide nanoparticles is presented. The nanocomposites are fabricated via a general concept for mechanically superior nanocomposites not based on the brick and mortar structure, thus on globular nanoparticles with nanosized organic shells. For the fabrication of the composites oleic acid functionalized iron oxide nanoparticles are decorated via ligand exchange with an α,ω-polybutadiene dicarboxylic acid. The functionalized particles were processed...

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 A. 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...

Silver-rich clusters in nanoporous gold

Tobias Krekeler, Anastasia V. Straßer, Matthias Graf, Ke Wang, Christian Hartig, Martin Ritter & Jörg Weissmüller
Herein we report on how to render Ti3C2Tx (MXene) monolayers deposited on SiO2/Si wafers, with different SiO2 thicknesses, visible. Inputting the effective thickness of a Ti3C2Tx monolayer (1 ± 0.2 nm) measured by atomic force microscopy, and its refractive index into a Fresnel-law-based simulation software, we show that the optical contrast of Ti3C2Tx monolayers deposited on SiO2/Si wafers depends on the SiO2 thickness, number of MXene layers, and the light’s wavelength. The highest contrast was...

Alumina-doped zirconia submicro-particles : synthesis, thermal stability, and microstructural characterization

Gregor Thomas Dahl, Sebastian Döring, Tobias Krekeler, Rolf Janßen, Martin Ritter, Horst Weller & Tobias Vossmeyer
Zirconia nanoceramics are interesting materials for numerous high-temperature applications. Because their beneficial properties are mainly governed by the crystal and microstructure, it is essential to understand and control these features. The use of co-stabilizing agents in the sol-gel synthesis of zirconia submicro-particles should provide an effective tool for adjusting the particles’ size and shape. Furthermore, alumina-doping is expected to enhance the particles’ size and shape persistence at high temperatures, similar to what is observed in...

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

Using an interactive lattice Boltzmann solver in fluid mechanics instruction

Mirjam Sophia Glessmer & Christian F. Janßen
This article gives an overview of the diverse range of teaching applications that can be realized using an interactive lattice Boltzmann simulation tool in fluid mechanics instruction and outreach. In an inquiry-based learning framework, examples are given of learning scenarios that address instruction on scientific results, scientific methods or the scientific process at varying levels of student activity, from consuming to applying to researching. Interactive live demonstrations on portable hardware enable new and innovative teaching...

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...

Complexity of spatially interconnected systems

Fatimah Al-Taie
Im Gegensatz zu konzentriert-parametrischen Systemen haben räumlich verteilte (räumlich vernetzte) Systeme sowohl Zeit- als auch Raumkoordinaten als unabhängige Variablen. Räumlich vernetzte Systeme, d.h. Systeme, die aus räumlich verteilten, interagierenden Subsystemen bestehen, sind in der Regel komplex und erfordern eine Modellreduktion, um Analyse- und Syntheseprobleme numerisch lösen zu können. Dabei muss die Struktur der räumlichen Interaktion erhalten werden. Hierbei ist zu unterscheiden zwischen zeit- und rauminvarianten (parameterinvarianten) und zeit- und raumveränderlichen (parameterveränderlichen) Systemen. Was die Modellreduktion...

Time-variant rule-based reliability of corroded structures by Monte Carlo simulation

Karoline M. Neumann, B. J. Leira, Ole Tom Vårdal & Sören Ehlers

The Performance of One-Way Clutch in a Cam-Based Infinitely Variable Transmission

Amjad Al-Hamood, Hazim U. Jamali, Oday Ibraheem Abdullah & Josef Schlattmann

Genetic variability of mutans streptococci revealed by wide whole-genome sequencing

Lifu Song, Wei Wang, Georg Conrads, Anke Rheinberg, Helena Sztajer, Michael Reck, Irene Wagner-Döbler & An-Ping Zeng
Background: Mutans streptococci are a group of bacteria significantly contributing to tooth decay. Their genetic variability is however still not well understood.Results: Genomes of 6 clinical S. mutans isolates of different origins, one isolate of S. sobrinus (DSM 20742) and one isolate of S. ratti (DSM 20564) were sequenced and comparatively analyzed. Genome alignment revealed a mosaic-like structure of genome arrangement. Genes related to pathogenicity are found to have high variations among the strains, whereas...

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