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Now showing 1 - 10 of 2780
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    Effects of (complementary) polyelectrolytes characteristics on composite calcium carbonate microparticles properties
    (Bucureşti : [Verlag nicht ermittelbar], 2017) Mic, Cristian Barbu; Mihai, Marcela; Varganici, Cristian Dragos; Schwarz, Simona; Scutaru, Dan; Simionescu, Bogdan C.
    This study follows the possibility to tune the thermal stability of some CaCO3/polymer composites by crystal growth from supersaturated solutions controlled by polymer structure or by using nonstoichiometric polyelectrolyte complexes (NPECs). As the ratio between the organic and inorganic parts in the composites controls the Ca2+/polymer network crosslinking density, the CaCO3/polymer weight ratio was kept constant at 50/1, varying the initial concentration of the polyanions solutions (0.05 or 0.06 wt.%), the NPECs molar ratio , n+/n- (0.2 or 0.4), or the inorganic precursors concentration (0.25 or 0.3 M). Poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid) (PSA) and chondroitin-4-sulfate (CSA) were used as polyanions. Some NPEC dispersions, prepared with the same polyanions and poly(allylamine hydrochloride) (PAH), were also used for calcium carbonate crystallization. The characteristics of the prepared composites were investigated by scanning electron microscopy (SEM), flow particle image analysis (FPIA), particles charge density (CD), zeta-potential (ZP). The thermal stability of the composite particles was investigated as compared to bare CaCO3 microparticles prepared at the same initial inorganic concentrations.
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    A new bifunctional hybrid nanostructure as an active platform for photothermal therapy and MR imaging
    (London : Nature Publishing Group, 2016) Khafaji, Mona; Vossoughi, Manouchehr; Hormozi-Nezhad, M. Reza; Dinarvand, Rassoul; Börrnert, Felix; Irajizad, Azam
    As a bi-functional cancer treatment agent, a new hybrid nanostructure is presented which can be used for photothermal therapy by exposure to one order of magnitude lower laser powers compared to similar nanostructures in addition to substantial enhancment in magnetic resonance imaging (MRI) contrast. This gold-iron oxide hybrid nanostructure (GIHN) is synthesized by a cost-effective and high yield water-based approach. The GIHN is sheilded by PEG. Therefore, it shows high hemo and biocompatibility and more than six month stability. Alongside earlier nanostructures, the heat generation rate of GIHN is compareable with surfactnat-capped gold nanorods (GNRs). Two reasons are behind this enhancement: Firstly the distance between GNRs and SPIONs is adjusted in a way that the surface plasmon resonance of the new nanostructure is similar to bare GNRs and secondly the fraction of GNRs is raised in the hybrid nanostructure. GIHN is then applied as a photothermal agent using laser irradiation with power as low as 0.5 W.cm−2 and only 32% of human breast adenocarcinoma cells could survive. The GIHN also acts as a dose-dependent transvers relaxation time (T2) MRI contrast agent. The results show that the GINH can be considered as a good candidate for multimodal photothermal therapy and MRI.
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    Efficient coupling of inhomogeneous current spreading and dynamic electro-optical models for broad-area edge-emitting semiconductor devices
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2017) Radziunas, Mindaugas; Zeghuzi, Anissa; Fuhrmann, Jürgen; Koprucki, Thomas; Wünsche, Hans-Jürgen; Wenzel, Hans; Bandelow, Uwe
    We extend a 2 (space) + 1 (time)-dimensional traveling wave model for broad-area edgeemitting semiconductor lasers by a model for inhomogeneous current spreading from the contact to the active zone of the laser. To speedup the performance of the device simulations, we suggest and discuss several approximations of the inhomogeneous current density in the active zone.
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    Simulation of the future sea level contribution of Greenland with a new glacial system model
    (Katlenburg-Lindau : Copernicus, 2018) Calov, Reinhard; Beyer, Sebastian; Greve, Ralf; Beckmann, Johanna; Willeit, Matteo; Kleiner, Thomas; Rückamp, Martin; Humbert, Angelika; Ganopolski, Andrey
    We introduce the coupled model of the Greenland glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dynamics, the model of basal hydrology HYDRO and a parameterization of submarine melt for marine-terminated outlet glaciers. The aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, imposing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961-1990 standard climatology derived from simulations of the regional atmosphere model MAR with ERA reanalysis boundary conditions. For the palaeo-part of the spin-up, we add the temperature anomaly derived from the GRIP ice core to the years 1961-1990 average surface temperature field. For our projections, we apply surface temperature and surface mass balance anomalies derived from RCP 4.5 and RCP 8.5 scenarios created by MAR with boundary conditions from simulations with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Further on, the impact of elevation-surface mass balance feedback, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute between 1.9 and 13.0 cm to global sea level rise until the year 2100 and between 3.5 and 76.4 cm until the year 2300, including our simulated additional sea level rise due to elevation-surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7 cm, and in the year 2300 it ranges from 1.7 to 21.8 cm. Additionally, taking the Helheim and Store glaciers as examples, we investigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temperature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.
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    Chirped photonic crystal for spatially filtered optical feedback to a broad-area laser
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2018) Brée, Carsten; Gailevicius, Darius; Purlys, Vytautas; Werner, Guillermo Garre; Staliunas, Kestutis; Rathsfeld, Andreas; Schmidt, Gunther; Radziunas, Mindaugas
    We derive and analyze an efficient model for reinjection of spatially filtered optical feedback from an external resonator to a broad area, edge emitting semiconductor laser diode. Spatial filtering is achieved by a chirped photonic crystal, with variable periodicity along the optical axis and negligible resonant backscattering. The optimal chirp is obtained from a genetic algorithm, which yields solutions that are robust against perturbations. Extensive numerical simulations of the composite system with our optoelectronic solver indicate that spatially filtered reinjection enhances lower-order transversal optical modes in the laser diode and, consequently, improves the spatial beam quality.
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    Mechanics of Materials: Mechanics of Interfaces and Evolving Microstructure
    (Zürich : EMS Publ. House, 2016) McDowell, David L.; Müller, Stefan; Werner, Ewald A.
    Emphasis in modern day efforts in mechanics of materials is increasingly directed towards integration with computational materials science, which itself rests on solid physical and mathematical foundations in thermodynamics and kinetics of processes. Practical applications demand attention to length and time scales which are sufficiently large to preclude direct application of quantum mechanics approaches; accordingly, there are numerous pathways to mathematical modelling of the complexity of material structure during processing and in service. The conventional mathematical machinery of energy minimization provides guidance but has limited direct applicability to material systems evolving away from equilibrium. Material response depends on driving forces, whether arising from mechanical, electromagnetic, or thermal fields. When microstructures evolve, as during plastic deformation, progressive damage and fracture, corrosion, stress-assisted diffusion, migration or chemical/thermal aging, the associated classical mathematical frameworks are often ad hoc and heuristic. Advancing new and improved methods is a major focus of 21st century mechanics of materials of interfaces and evolving microstructure.
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    Semantic modelling of video annotations – the TIB AV-Portal's metadata structure
    (Zenodo, 2018) Saurbier, Felix
    The TIB AV-Portal (https://av.tib.eu) is an online platform for sharing scientific videos operated by the German National Library of Science and Technology (TIB). Besides the allocation of Digital Object Identifiers (DOI) and Media Fragment Identifiers (MFID) for video citation, long-term preservation of all material and open licenses like Creative Commons, the core feature of the TIB AV-Portal are its various methods of automated metadata extraction to fundamentally improve search functionalities (e.g. fine-grained search and faceting). These comprise of an automated chaptering, extraction of superimposed text, speech to text recognition, and the detection of predefined visual concepts. In addition, extracted metadata are consequently mapped against authority files like the German “Gemeinsame Normdatei” and knowledge bases like DBpedia and Library of Congress Subject Headings via a process of automated named entity linking (NEL) to enable semantic and cross-lingual search. The results of this process are expressed as temporal and/or spatial video annotations, linking extracted metadata to certain key frames and video segments. In order to structure the data, express relations between single entities, and link to external information resources, several common vocabularies, ontologies and knowledge bases are being used. These include amongst others the Open Annotation Data Model, the NLP Interchange Format (NIF), BIBFRAME, the Friend of Friend Vocabulary (FOAF), and Schema.org. Furthermore, all data is stored adhering to the Resource Description Framework (RDF) data model and published as linked open data. This provides third parties with an interoperable and easy to reuse RDF graph representation of the AV-Portal’s metadata. On our poster we illustrate the general structure of the TIB AV-Portal’s comprehensive metadata both authoritative and extracted automatically. Here, the main focus is on the underlying video annotation graph model and on semantic interoperability and reusability of the data. In particular we visualize how the use of vocabularies, ontologies and knowledge bases allows for rich semantic descriptions of video materials as well as for easy metadata publication, interlinking, and opportunities of reuse by third parties (e.g. for information retrieval and enrichment). In doing so, we present the AV-Portal’s metadata structure as an illustrative example for the complexity of modelling temporal and spatial video metadata and as a set of best practices in the field of audio-visual resources.
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    Electrolytic Surface Treatment for Improved Adhesion between Carbon Fibre and Polycarbonate
    (Basel : MDPI, 2018) Kamps, Jan Henk; Henderson, Luke C.; Scheffler, Christina; Van der Heijden, Ruud; Simon, Frank; Bonizzi, Teena; Verghese, Nikhil
    To achieve good mechanical properties of carbon fibre-reinforced polycarbonate composites, the fibre-matrix adhesion must be dialled to an optimum level. The electrolytic surface treatment of carbon fibres during their production is one of the possible means of adapting the surface characteristics of the fibres. The production of a range of tailored fibres with varying surface treatments (adjusting the current, potential, and conductivity) was followed by contact angle, inverse gas chromatography and X-ray photoelectron spectroscopy measurements, which revealed a significant increase in polarity and hydroxyl, carboxyl, and nitrile groups on the fibre surface. Accordingly, an increase in the fibre-matrix interaction indicated by a higher interfacial shear strength was observed with the single fibre pull-out force-displacement curves. The statistical analysis identified the correlation between the process settings, fibre surface characteristics, and the performance of the fibres during single fibre pull-out testing.
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    Effect of Alloying Elements in Melt Spun Mg-alloys for Hydrogen Storage
    (São Carlos : SciELO - Scientific Electronic Library Online, 2016) Rozenberg, Silvia; Saporiti, Fabiana; Lang, Julien; Audebert, Fernando; Botta, Pablo; Stoica, Mihai; Huot, Jacques; Eckert, Jürgen
    In this paper we report the effect of alloying elements on hydrogen storage properties of melt-spun Mg-based alloys. The base alloys Mg90Si10, Mg90Cu10, Mg65Cu35 (at%) were studied. We also investigated the effect of rare earths (using MM: mischmetal) and Al in Mg65Cu25Al10, Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys. All the melt-spun alloys without MM show a crystalline structure, and the Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys showed an amorphous and partially amorphous structure respectively. At 350˚C all the alloys had a crystalline structure during the hydrogen absorption-desorption tests. It was observed that Si and Cu in the binaries alloys hindered completely the activation of the hydrogen absorption. The partial substitution of Cu by MM or Al allowed activation. The combined substitution of Cu by MM and Al showed the best results with the fastest absorption and desorption kinetics, which suggests that this combination can be used for new Mg-alloys to improve hydrogen storage properties.
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    Endurance of quantum coherence due to particle indistinguishability in noisy quantum networks
    (London : Nature Publ. Group, 2018) Perez-Leija, Armando; Guzmán-Silva, Diego; León-Montiel, Roberto de J.; Gräfe, Markus; Heinrich, Matthias; Moya-Cessa, Hector; Busch, Kurt; Szameit, Alexander
    Quantum coherence, the physical property underlying fundamental phenomena such as multi-particle interference and entanglement, has emerged as a valuable resource upon which modern technologies are founded. In general, the most prominent adversary of quantum coherence is noise arising from the interaction of the associated dynamical system with its environment. Under certain conditions, however, the existence of noise may drive quantum and classical systems to endure intriguing nontrivial effects. In this vein, here we demonstrate, both theoretically and experimentally, that when two indistinguishable non-interacting particles co-propagate through quantum networks affected by non-dissipative noise, the system always evolves into a steady state in which coherences accounting for particle indistinguishabilty perpetually prevail. Furthermore, we show that the same steady state with surviving quantum coherences is reached even when the initial state exhibits classical correlations.