Mavromatis V.,University of Graz |
Mavromatis V.,French National Center for Scientific Research |
Purgstaller B.,University of Graz |
Dietzel M.,University of Graz |
And 3 more authors.
Earth and Planetary Science Letters | Year: 2017
Various marine calcifiers form exoskeletons via an amorphous calcium carbonate (ACC) precursor phase and magnesium plays an important role in the temporary stabilization of this metastable phase. Thus, the use of Mg isotope ratios of marine biogenic carbonates as a proxy to reconstruct past seawater chemistry calls for a detailed understanding of the mechanisms controlling Mg isotope signatures during the formation and transformation of ACC to the final crystalline carbonate mineral. For this purpose we have investigated the Mg isotope fractionation between (Ca,Mg)CO3 solids and aqueous fluids at 25 °C and pH = 8.3 during (i) the direct precipitation of crystalline Mg-calcite and (ii) the formation of Mg-rich ACC (Mg-ACC) and its transformation to Mg-calcite. The outcome documents that the small Mg isotope fractionation between Mg-ACC and reactive fluid (#x0394;MgACC-fluid26=−1.0±0.1‰) is not preserved during the transformation of the ACCs into Mg-calcite. Following a pronounced isotopic shift accompanying the transformation of Mg-ACC into Mg-calcite, Δ26Mgcalcite-fluid progressively decreases with reaction progress from #x223C;−3.0‰ to #x2212;3.6‰, reflecting both the approach of isotopic equilibrium and the increase of calcite Mg content (to near 20 mol % Mg). In contrast the crystalline Mg-calcite precipitated directly from the reacting fluid, i.e. lacking a discernable formation of an amorphous precursor, exhibits only small temporal variations in Δ26Mgcalcite-fluid which overall is affected by the precipitation kinetics. The values found in this study at the onset of Mg-ACC precipitation for Mg isotope fractionation between Mg-ACC and the fluid (ΔMgACC-fluid26=−1.0‰) and between Mg-ACC and Mg2+(aq) (ΔMgACC-Mg2+(aq)26=+2.0‰) are consistent with the formation of a hydrated Ca nanoporous solid accommodating Mg bicarbonate/carbonate species in combination with hydrated magnesium. This material crossed by percolating channels filled with the reacting fluid easily converts to Mg-rich calcite via exchange and/or dissolution/precipitation reactions. The results of this study provide new insights on the acquisition of the Mg chemical and isotopic signatures by the skeletal marine carbonates precipitated in confined media from strongly supersaturated fluids. They also offer new guides for the interpretation of the isotopic signature of these organisms for paleo-environmental reconstructions. © 2017 Elsevier B.V.
Fang Z.,Ruhr University Bochum |
Durholt J.P.,Ruhr University Bochum |
Kauer M.,Universitatsstrasse 150 |
Zhang W.,Ruhr University Bochum |
And 11 more authors.
Journal of the American Chemical Society | Year: 2014
A series of defect-engineered metal-organic frameworks (DEMOFs) derived from parent microporous MOFs was obtained by systematic doping with defective linkers during synthesis, leading to the simultaneous and controllable modification of coordinatively unsaturated metal sites (CUS) and introduction of functionalized mesopores. These materials were investigated via temperature-dependent adsorption/desorption of CO monitored by FTIR spectroscopy under ultra-high-vacuum conditions. Accurate structural models for the generated point defects at CUS were deduced by matching experimental data with theoretical simulation. The results reveal multivariate diversity of electronic and steric properties at CUS, demonstrating the MOF defect structure modulation at two length scales in a single step to overcome restricted active site specificity and confined coordination space at CUS. Moreover, the DEMOFs exhibit promising modified physical properties, including band gap, magnetism, and porosity, with hierarchical micro/mesopore structures correlated with the nature and the degree of defective linker incorporation into the framework. © 2014 American Chemical Society.
Dullmann J.,Ruhr University Bochum |
Dullmann J.,Universitatsstrasse 150 |
Alber M.,Ruhr University Bochum |
Plinninger R.J.,PG Dr. Plinninger Geotechnik
Geomechanik und Tunnelbau | Year: 2014
The evaluation of the abrasiveness of soil is not unified or standardised at the moment. Mostly used are complex index processes with greatly simplified model bodies and simplified test conditions such as the LCPC abrasimeter test. These processes can however at best measure the efficiency of the wear mechanism and are not capable of reflecting the strength of the bonding of the internal fabric, an essential factor determining the level of operational demands, i.e. the resistance to excavation. These index processes therefore offer no advantages over evaluation processes based on conventional soil mechanics parameters. Quite the opposite, these mostly prototype tests imply new problems that are inevitable with the testing methods. The paper thus presents at the end an extended method of evaluating wear to excavation tools and the conveyance or transport of excavated spoil. © 2014 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.
Beste C.,Ruhr University Bochum |
Dinse H.R.,Universitatsstrasse 150
Current Biology | Year: 2013
Achieving high-level skills is generally considered to require intense training, which is thought to optimally engage neuronal plasticity mechanisms. Recent work, however, suggests that intensive training may not be necessary for skill learning. Skills can be effectively acquired by a complementary approach in which the learning occurs in response to mere exposure to repetitive sensory stimulation. Such training-independent sensory learning induces lasting changes in perception and goal-directed behaviour in humans, without any explicit task training. We suggest that the effectiveness of this form of learning in different sensory domains stems from the fact that the stimulation protocols used are optimized to alter synaptic transmission and efficacy. While this approach directly links behavioural research in humans with studies on cellular plasticity, other approaches show that learning can occur even in the absence of an actual stimulus. These include learning through imagery or feedback-induced cortical activation, resulting in learning without task training. All these approaches challenge our understanding of the mechanisms that mediate learning. Apparently, humans can learn under conditions thought to be impossible a few years ago. Although the underlying mechanisms are far from being understood, training-independent sensory learning opens novel possibilities for applications aimed at augmenting human cognition. © 2013 Elsevier Ltd.
Peters M.,Ruhr University Bochum |
Kohler-Bachmann S.,Ruhr University Bochum |
Lenz-Habijan T.,Universitatsstrasse 150 |
Bufe A.,Ruhr University Bochum
American Journal of Respiratory Cell and Molecular Biology | Year: 2016
We showed previously that sensitization of mice with dendritic cells (DCs) via the airways depends on activation of these cells with LPS. Allergen-pulsedDCs that were stimulated with lowdoses of LPS induce a strong Th2 response in vivo. Our objective was to investigate whether airway sensitization ofmice by the application ofDCs with a phenotype that is able to induce Th17 cells results in increased remodeling of the airways.We generated DCs fromthe bone marrow ofmice and pulsed them with LPS-free ovalbumin. Subsequently, cells were activated with LPS with or without ATP for inflammasome activation. The activated cellswere used to sensitizemice via the airways. Intranasal instillation of DCs thatwere activated with 0.1ng/ml LPS induced aTh2 response with airway eosinophilia. High doses of LPS, particularly when given in combinationwithATP, led to induction of a mixed Th2/Th17 response. Interestingly, we found a correlation between IL-17A production and the remodeling of the airways. Stimulation ofmouse fibroblasts with purified IL-17A protein in vitro resulted in transforming growth factor-b1 secretion and collagen transcription. Interestingly, we found enhanced secretion of transforming growth factor-b1 by fibroblasts after costimulation with IL-17A and the profibrotic factor winglesstype MMTV integration site family, member 5A (Wnt5a). We showed that an allergen-specific Th17 response in the airway is accompanied by increased airway remodeling. Furthermore, we revealed that increased remodeling is not only based on neutrophilic inflammation, but also on the direct impact of IL-17A on airway structural cells. Copyright © 2016 by the American Thoracic Society.
Hussong J.,Universitatsstrasse 150 |
Lindken R.,ZBT GmbH |
Faulhammer P.,Justus Liebig University |
Noreikat K.,University of Leipzig |
And 3 more authors.
Journal of Biomechanics | Year: 2013
To date, there is only a fragmentary understanding of the fundamental mechanisms of airway mucociliary transport. Application of the latest measurement techniques can aid in deciphering the complex interplay between ciliary beat and airway surface liquid (ASL) transport. In the present study, direct, quasi-simultaneous measurements of the cilia-induced fluid and bead transport were performed to gain a better insight into both transport mechanisms. In this study cilia-induced periciliary liquid (PCL) transport is measured by means of micro Particle Image Velocimetry (μPIV) with neutrally buoyant tracers. Particle Tracking Velocimetry (PTV) with heavier polystyrene-ferrite beads is performed to simulate particle transport. Contrary to recent literature, in which the presence of mucus was deemed necessary to maintain periciliary liquid (PCL) transport, effective particle and fluid transport was measured in our experiments in the absence of mucus. In response to muscarine or ATP stimulation, maximum fluid transport rates of 250 μm/s at 15 μm distance to the tracheal epithelia were measured while bead transport rates over the epithelia surfaces reached 200 μm/s. We estimated that the mean bead transport is dominated by viscous drag compared to inertial fluid forces. Furthermore, mean bead transport velocities appear to be two orders of magnitude larger compared to bead sedimentation velocities. Therefore, beads are expected to closely follow the mean PCL flow in non-ciliated epithelium regions. Based on our results, we have shown that PCL transport can be directly driven by the cilia beat and that the PCL motion may be capable of driving bead transport by fluid drag. © 2012.
Morawietz T.,Universitatsstrasse 150 |
Behler J.,Universitatsstrasse 150
Zeitschrift fur Physikalische Chemie | Year: 2013
Water clusters have attracted a lot of attention as prototype systems to study hydrogen bonded molecular aggregates but also to gain deeper insights into the properties of liquid water, the solvent of life. All these studies depend on an accurate description of the atomic interactions and countless potentials have been proposed in the literature in the past decades to represent the potential-energy surface (PES) of water. Many of these potentials employ drastic approximations like rigid water monomers and fixed point charges, while on the other hand also several attempts have been made to derive very accurate PESs by fitting data obtained in high-level electronic structure calculations. In recent years artificial neural networks (NNs) have been established as a powerful tool to construct high-dimensional PESs of a variety of systems, but to date no full-dimensional NN PES for water has been reported. Here, we present NN potentials for water clusters containing two to six water molecules trained to density functional theory (DFT) data employing two different exchange-correlation functionals, PBE and RPBE. In contrast to other potentials fitted to first principles data, these NN potentials are not based on a truncated many-body expansion of the energy but consider the interactions between all water molecules explicitly. For both functionals an excellent agreement with the underlying DFT calculations has been found with binding energy errors of only about 1%.© by Oldenbourg Wissenschaftsverlag, München.
Wichmann A.,Universitatsstrasse 150 |
Rummel N.,Universitatsstrasse 150
Computers and Education | Year: 2013
Wiki-based writing possesses a great deal of educational potential, yet students face difficulties while writing a shared document. Revising a shared document, in particular, seems to be a demanding activity for students. This study investigated whether collaboration scripts can help to improve students' revision activities and overall text quality. We compared scripted (script+) with unscripted (script-) collaboration in a wiki-based writing setting that was adapted for educational purposes. Students from two university courses participated in a one-week collaborative writing activity. Results showed that students in the scripted condition outperformed students in the unscripted condition with respect to revision behavior and text coherence. Furthermore, we found that students' revision behavior correlated positively with text coherence. Results from analyzing students' discussions during the writing activity revealed more frequent coordination with respect to task division and increased communication frequency for students in the scripted condition. Results also indicate that collaboration scripts can foster coordination. Our findings suggest that collaboration scripts are promising means of structuring collaboration during wiki-based writing. © 2012 Elsevier Ltd. All rights reserved.
Lob C.,Universitatsstrasse 150 |
Mutterlose J.,Universitatsstrasse 150
Revue de Micropaleontologie | Year: 2012
The Frielingen clay pit, situated approximately 20km northwest of Hannover (northern Germany) exposes sediments of Early Cretaceous age (Hauterivian, Barremian). Rhythmic alternations of dark mudstones and pale marls of late Hauterivian age (Simbirskites discofalcatus ammonite Zone) dominate the lithology. These bedding rhythms are overlain by laminated dark shales and lighter mudstones, assigned to the lowermost Barremian (Praeoxyteuthis pugio belemnite Zone). For this study 27 samples covering the Hauterivian/Barremian boundary interval were investigated with respect to their CaCO3 and total organic contents (TOC), stable isotope composition (δ13Corg, δ13CCaCO3, δ18OCaCO3) and their micropalaeontology (foraminifera). The samples were analysed in order to better understand the onset of the Barremian anoxic conditions in the Boreal Realm. The data obtained show that shifts of the environmental parameters are reflected by the mudstone-marl alternation. The dark mudstones reflect cooler surface water temperatures and a lower oxygen content, while the pale marls were deposited under warm surface water conditions. These bedding rhythms are thought to be the result of climatic variations in the Milankovitch Band (10Ka-1Ma). This study further documents that the Hauterivian/Barremian transition is characterised by a deterioration of the living conditions for benthic organisms. This is indicated by the decline of several foraminiferal genera, by decreasing generic richness and by a coeval increase in the abundances of specific taxa. The TOC content and the isotopic composition of the organic carbon support these findings. A morphogroup analysis of the benthic foraminifera indicates changes of the habitats from mainly infaunal in the late Hauterivian to more epifaunal in the early Barremian. Due to this dramatic decline of infaunal forms in the laminated, TOC-rich mudstones of the lowermost Barremian, suboxic to anoxic conditions are postulated for these sediments. The bottom water must, however, have contained some oxygen at least, as is indicated by a few epifaunal genera that became very abundant (e.g. Ammodiscus). A major regression around the Hauterivian/Barremian boundary caused a closing of the seaway to the Tethys, resulting in a significantly reduced water exchange and the establishment of anoxic conditions. © 2012 Elsevier Masson SAS.
Stocker C.,Universitatsstrasse 150 |
Lunze J.,Universitatsstrasse 150 |
Ngo C.,Universitatsstrasse 150
At-Automatisierungstechnik | Year: 2012
Eventbased control aims at reducing the communication effort within a control loop by closing the feedback only if an event indicates a significant control error. This paper derives a condition to the structure of the event-based control of interconnected systems on that the difference between the behavior of event-based control loop and a continuous reference system is bounded. Based on this condition, two novel methods for distributed and decentralized event-based control are developed. Both approaches are evaluated by means of their simulative and experimental application to a thermofluid process. © Oldenbourg Wissenschaftsverlag.