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- ItemA customizable microfluidic platform for medium-throughput modeling of neuromuscular circuits(Amsterdam [u.a.] : Elsevier Science, 2019) Bellmann, Jessica; Goswami, Ruchi Y.; Girardo, Salvatore; Rein, Nelly; Hosseinzadeh, Zohreh; Hicks, Michael R.; Busskamp, Volker; Pyle, April D.; Werner, Carsten; Sterneckert, JaredNeuromuscular circuits (NMCs) are vital for voluntary movement, and effective models of NMCs are needed to understand the pathogenesis of, as well as to identify effective treatments for, multiple diseases, including Duchenne's muscular dystrophy and amyotrophic lateral sclerosis. Microfluidics are ideal for recapitulating the central and peripheral compartments of NMCs, but myotubes often detach before functional NMCs are formed. In addition, microfluidic systems are often limited to a single experimental unit, which significantly limits their application in disease modeling and drug discovery. Here, we developed a microfluidic platform (MFP) containing over 100 experimental units, making it suitable for medium-throughput applications. To overcome detachment, we incorporated a reactive polymer surface allowing customization of the environment to culture different cell types. Using this approach, we identified conditions that enable long-term co-culture of human motor neurons and myotubes differentiated from human induced pluripotent stem cells inside our MFP. Optogenetics demonstrated the formation of functional NMCs. Furthermore, we developed a novel application of the rabies tracing assay to efficiently identify NMCs in our MFP. Therefore, our MFP enables large-scale generation and quantification of functional NMCs for disease modeling and pharmacological drug targeting. © 2019 The Authors
- ItemA survey on Bluetooth multi-hop networks(Amsterdam [u.a.] : Elsevier Science, 2019) Todtenberg, Nicole; Kraemer, RolfBluetooth was firstly announced in 1998. Originally designed as cable replacement connecting devices in a point-to-point fashion its high penetration arouses interest in its ad-hoc networking potential. This ad-hoc networking potential of Bluetooth is advertised for years - but until recently no actual products were available and less than a handful of real Bluetooth multi-hop network deployments were reported. The turnaround was triggered by the release of the Bluetooth Low Energy Mesh Profile which is unquestionable a great achievement but not well suited for all use cases of multi-hop networks. This paper surveys the tremendous work done on Bluetooth multi-hop networks during the last 20 years. All aspects are discussed with demands for a real world Bluetooth multi-hop operation in mind. Relationships and side effects of different topics for a real world implementation are explained. This unique focus distinguishes this survey from existing ones. Furthermore, to the best of the authors’ knowledge this is the first survey consolidating the work on Bluetooth multi-hop networks for classic Bluetooth technology as well as for Bluetooth Low Energy. Another individual characteristic of this survey is a synopsis of real world Bluetooth multi-hop network deployment efforts. In fact, there are only four reports of a successful establishment of a Bluetooth multi-hop network with more than 30 nodes and only one of them was integrated in a real world application - namely a photovoltaic power plant. © 2019 The Authors
- ItemAn AI-based open recommender system for personalized labor market driven education(Amsterdam [u.a.] : Elsevier Science, 2022) Tavakoli, Mohammadreza; Faraji, Abdolali; Vrolijk, Jarno; Molavi, Mohammadreza; Mol, Stefan T.; Kismihók, GáborAttaining those skills that match labor market demand is getting increasingly complicated, not in the last place in engineering education, as prerequisite knowledge, skills, and abilities are evolving dynamically through an uncontrollable and seemingly unpredictable process. Anticipating and addressing such dynamism is a fundamental challenge to twenty-first century education. The burgeoning availability of data, not only on the demand side but also on the supply side (in the form of open educational resources) coupled with smart technologies, may provide a fertile ground for addressing this challenge. In this paper, we propose a novel, Artificial Intelligence (AI) driven approach to the development of an open, personalized, and labor market oriented learning recommender system, called eDoer. We discuss the complete system development cycle starting with a systematic user requirements gathering, and followed by system design, implementation, and validation. Our recommender prototype (1) derives the skill requirements for particular occupations through an analysis of online job vacancy announcements
- ItemMonitoring the thermally induced transition from sp3-hybridized into sp2-hybridized carbons(Amsterdam [u.a.] : Elsevier Science, 2021) Schüpfer, Dominique B.; Badaczewski, Felix; Peilstöcker, Jan; Guerra-Castro, Juan Manuel; Shim, Hwirim; Firoozabadi, Saleh; Beyer, Andreas; Volz, Kerstin; Presser, Volker; Heiliger, Christian; Smarsly, Bernd; Klar, Peter J.The preparation of carbons for technical applications is typically based on a treatment of a precursor, which is transformed into the carbon phase with the desired structural properties. During such treatment the material passes through several different structural stages, for example, starting from precursor molecules via an amorphous phase into crystalline-like phases. While the structure of non-graphitic and graphitic carbon has been well studied, the transformation stages from molecular to amorphous and non-graphitic carbon are still not fully understood. Disordered carbon often contains a mixture of sp3-, sp2-and sp1-hybridized bonds, whose analysis is difficult to interpret. We systematically address this issue by studying the transformation of purely sp3-hybridized carbons, that is, nanodiamond and adamantane, into sp2-hybridized non-graphitic and graphitic carbon. The precursor materials are thermally treated at different temperatures and the transformation stages are monitored. We employ Raman spectroscopy, WAXS and TEM to characterize the structural changes. We correlate the intensities and positions of the Raman bands with the lateral crystallite size La estimated by WAXS analysis. The behavior of the D and G Raman bands characteristic for sp2-type material formed by transforming the sp3-hybridized precursors into non-graphitic and graphitic carbon agrees well with that observed using sp2-structured precursors.
- ItemEffect of pore geometry on ultra-densified hydrogen in microporous carbons(Amsterdam [u.a.] : Elsevier Science, 2021) Tian, Mi; Lennox, Matthew J.; O’Malley, Alexander J.; Porter, Alexander J.; Krüner, Benjamin; Rudić, Svemir; Mays, Timothy J.; Düren, Tina; Presser, Volker; Terry, Lui R.; Rols, Stephane; Fang, Yanan; Dong, Zhili; Rochat, Sebastien; Ting, Valeska P.Our investigations into molecular hydrogen (H2) confined in microporous carbons with different pore geometries at 77 K have provided detailed information on effects of pore shape on densification of confined H2 at pressures up to 15 MPa. We selected three materials: a disordered, phenolic resin-based activated carbon, a graphitic carbon with slit-shaped pores (titanium carbide-derived carbon), and single-walled carbon nanotubes, all with comparable pore sizes of <1 nm. We show via a combination of in situ inelastic neutron scattering studies, high-pressure H2 adsorption measurements, and molecular modelling that both slit-shaped and cylindrical pores with a diameter of ∼0.7 nm lead to significant H2 densification compared to bulk hydrogen under the same conditions, with only subtle differences in hydrogen packing (and hence density) due to geometric constraints. While pore geometry may play some part in influencing the diffusion kinetics and packing arrangement of hydrogen molecules in pores, pore size remains the critical factor determining hydrogen storage capacities. This confirmation of the effects of pore geometry and pore size on the confinement of molecules is essential in understanding and guiding the development and scale-up of porous adsorbents that are tailored for maximising H2 storage capacities, in particular for sustainable energy applications.
- ItemResolving mobility anisotropy in quasi-free-standing epitaxial graphene by terahertz optical Hall effect(Amsterdam [u.a.] : Elsevier Science, 2021) Armakavicius, Nerijus; Kühne, Philipp; Eriksson, Jens; Bouhafs, Chamseddine; Stanishev, Vallery; Ivanov, Ivan G.; Yakimova, Rositsa; Zakharov, Alexei A.; Al-Temimy, Ameer; Coletti, Camilla; Schubert, Mathias; Darakchieva, VanyaIn this work, we demonstrate the application of terahertz-optical Hall effect (THz-OHE) to determine directionally dependent free charge carrier properties of ambient-doped monolayer and quasi-free-standing-bilayer epitaxial graphene on 4H–SiC(0001). Directionally independent free hole mobility parameters are found for the monolayer graphene. In contrast, anisotropic hole mobility parameters with a lower mobility in direction perpendicular to the SiC surface steps and higher along the steps in quasi-free-standing-bilayer graphene are determined for the first time. A combination of THz-OHE, nanoscale microscopy and optical spectroscopy techniques are used to investigate the origin of the anisotropy. Different defect densities and different number of graphene layers on the step edges and terraces are ruled out as possible causes. Scattering mechanisms related to doping variations at the step edges and terraces as a result of different interaction with the substrate and environment are discussed and also excluded. It is suggested that the step edges introduce intrinsic scattering in quasi-free-standing-bilayer graphene, that is manifested as a result of the higher ratio between mean free path and average terrace width parameters. The suggested scenario allows to reconcile existing differences in the literature regarding the anisotropic electrical transport in epitaxial graphene. © 2020 Elsevier Ltd
- ItemFrom microfluidics to hierarchical hydrogel materials(Amsterdam [u.a.] : Elsevier Science, 2023) Weigel, Niclas; Li, Yue; Fery, Andreas; Thiele, JulianOver the past two decades, microfluidics has made significant contributions to material and life sciences, particularly via the design of nano-, micro- and mesoscale materials such as nanoparticles, micelles, vesicles, emulsion droplets, and microgels. Unmatched in control over a multitude of material parameters, microfluidics has also shed light on fundamental aspects of material design such as the early stages of nucleation and growth processes as well as structure evolution. Exemplarily, polymer hydrogel particles can be formed via microfluidics with exact control over size, shape, functionalization, compartmentalization, and mechanics that is hardly found in any other processing method. Interestingly, the utilization of microfluidics for material design largely focuses on the fabrication of single entities that act as reaction volume for organic and cell-free biosynthesis, cell mimics, or local environment for cell culturing. In recent years, however, hydrogel design has shifted towards structures that integrate a large variety of functions, e.g., to address the demands for sensing tasks in a complex environment or more closely mimicking architecture and organization of tissue by multiparametric cultures. Hence, this review provides an overview of recent literature that explores microfluidics for fabricating hydrogel materials that go well beyond common length scales as well as the structural and functional complexity of microgels necessary to produce hierarchical hydrogel structures. We focus on examples that utilize microfluidics to design microgel-based assemblies, on microfluidically made polymer microgels for 3D bioprinting, on hydrogels fabricated by microfluidics in a continuous fashion, like fibers, and on hydrogel structures that are shaped by microchannels.
- ItemMicrobiome-based biotechnology for reducing food loss post harvest(Amsterdam [u.a.] : Elsevier Science, 2022) Wassermann, Birgit; Abdelfattah, Ahmed; Cernava, Tomislav; Wicaksono, Wisnu; Berg, GabrieleMicrobiomes have an immense potential to enhance plant resilience to various biotic and abiotic stresses. However, intrinsic microbial communities respond to changes in their host's physiology and environment during plant's life cycle. The potential of the inherent plant microbiome has been neglected for a long time, especially for the postharvest period. Currently, close to 50% of all produced fruits and vegetables are lost either during production or storage. Biological control of spoilage and storage diseases is still lacking sufficiency. Today, novel multiomics technologies allow us to study the microbiome and its responses on a community level, which will help to advance current classic approaches and develop more effective and robust microbiome-based solutions for fruit and vegetable storability, quality, and safety.
- ItemDesign of biomimetic collagen matrices by reagent-free electron beam induced crosslinking: Structure-property relationships and cellular response(Amsterdam [u.a.] : Elsevier Science, 2019) Riedel, Stefanie; Hietschold, Philine; Krömmelbein, Catharina; Kunschmann, Tom; Konieczny, Robert; Knolle, Wolfgang; Mierke, Claudia T.; Zink, Mareike; Mayr, Stefan G.Novel strategies to mimic mammalian extracellular matrix (ECM) in vitro are desirable to study cell behavior, diseases and new agents in drug delivery. Even though collagen represents the major constituent of mammalian ECM, artificial collagen hydrogels with characteristic tissue properties such as network size and stiffness are difficult to design without application of chemicals which might be even cytotoxic. In our study we investigate how high energy electron induced crosslinking can be utilized to precisely tune collagen properties for ECM model systems. Constituting a minimally invasive approach, collagen residues remain intact in the course of high energy electron treatment. Quantification of the 3D pore size of the collagen network as a function of irradiation dose shows an increase in density leading to decreased pore size. Rheological measurements indicate elevated storage and loss moduli correlating with an increase in crosslinking density. In addition, cell tests show well maintained viability of NIH 3T3 cells for irradiated collagen gels indicating excellent cellular acceptance. With this, our investigations demonstrate that electron beam crosslinked collagen matrices have a high potential as precisely tunable ECM-mimetic systems with excellent cytocompatibility.
- ItemThe impact of chemical short-range order on the thermophysical properties of medium- and high-entropy alloys(Amsterdam [u.a.] : Elsevier Science, 2024) Andreoli, Angelo F.; Fantin, Andrea; Kasatikov, Sergey; Bacurau, Vinícius P.; Widom, Michael; Gargarella, Piter; Mazzer, Eric M.; Woodcock, Thomas G.; Nielsch, Kornelius; Coury, Francisco G.The unusual behavior observed in the coefficient of thermal expansion and specific heat capacity of CrFeNi, CoCrNi, and CoCrFeNi medium/high-entropy alloys is commonly referred to as the K-state effect. It is shown to be independent of the Curie temperature, as demonstrated by temperature-dependent magnetic moment measurements. CoCrFeNi alloy is chosen for detailed characterization; potential reasons for the K-state effect such as texture, recrystallization, and second-phase precipitation are ruled out. An examination of the electronic structure indicates the formation of a pseudo-gap in the Density of States, which suggests a specific chemical interaction between Ni and Cr atoms upon alloying. Hybrid Monte Carlo/Molecular Dynamic (MC/MD) simulations indicate the presence of non-negligible chemical short-range order (CSRO). Local lattice distortions are shown to be negligible, although deviations around Cr and Ni elements from those expected in a fully disordered structure are experimentally observed by X-ray absorption spectroscopy. The determined bonding distances are in good agreement with MC/MD calculations. A mechanism is proposed to explain the anomalies and calorimetric experiments and their results are used to validate the mechanism.