17 results
Search Results
Now showing 1 - 10 of 17
- ItemPolyethylene glycol-modified poly(styrene-co-ethylene/butylene-co-styrene)/carbon nanotubes composite for humidity sensing(Lausanne : Frontiers Media, 2019) Mičušík, Matej; Chatzimanolis, Christos; Tabačiarová, Jana; Kollár, Jozef; Kyritsis, Apostolos; Pissis, Polycarpos; Pionteck, Jürgen; Vegso, Karol; Siffalovic, Peter; Majkova, Eva; Omastová, MáriaPolymeric composites of the linear triblock copolymer poly(styrene-co-ethylene/butylene-co-styrene) grafted with maleic anhydride units (SEBS-MA) or MA modified by hydrophilic polyethylene glycol (PEG) and containing various amounts of multiwall carbon nanotubes (MWCNTs) as conducting filler—were prepared by solvent casting. The MWCNT surface was modified by a non-covalent approach with a pyrene-based surfactant to achieve a homogeneous dispersion of the conducting filler within the polymeric matrix. The dispersion of the unmodified and surfactant-modified MWCNTs within the elastomeric SEBS-MA and SEBS-MA-PEG matrices was characterized by studying the morphology by TEM and SAXS. Dynamical mechanical analysis was used to evaluate the interaction between the MWCNTs and copolymer matrix. The electrical conductivity of the prepared composites was measured by dielectric relaxation spectroscopy, and the percolation threshold was calculated. The prepared elastomeric composites were characterized and studied as humidity sensor. Our results demonstrated that at MWCNTs concentration slightly above the percolation threshold could result in large signal changes. In our system, good results were obtained for MWCNT loading of 2 wt% and an ~0.1 mm thin composite film. The thickness of the tested elastomeric composites and the source current appear to be very important factors that influence the sensing performance. © 2019 Mičušík, Chatzimanolis, Tabačiarová, Kollár, Kyritsis, Pissis, Pionteck, Vegso, Siffalovic, Majkova and Omastová.
- ItemFlexible Transparent Barrier Applications of Oxide Thin Films Prepared by Photochemical Conversion at Low Temperature and Ambient Pressure(Lausanne : Frontiers Media, 2020) With, Patrick C.; Helmstedt, Ulrike; Prager, LutzPhotoconversion of metal-organic precursors to thin film metal oxides using ultraviolet (UV) radiation in oxidative atmosphere is an attractive technology because it can be applied at temperatures <80°C and at ambient pressure. Thus, it enables preparing this class of thin films in a cost-efficient manner on temperature sensitive substrates such as polymer films. In this article, various aspects of research and development in the field of photochemical thin-film fabrication, with particular focus to the application of the produced films as gas permeation barriers for the encapsulation of optoelectronic devices are reviewed. Thereby, it covers investigations on fundamental photochemically initiated reactions for precursor classes containing metal-oxygen and metal-nitrogen bonds, and emphazises the relevance of that understanding for applicative considerations like integration of the single-layer barrier films into relevant encapsulation films. Further perspectives are given concerning integration of additional functionalities like electrical conductivity to the flexible and transparent barrier films. © Copyright © 2020 With, Helmstedt and Prager.
- ItemCorrosion Fatigue Studies on a Bulk Glassy Zr-Based Alloy under Three-Point Bending(Lausanne : Frontiers Media, 2017-1-9) Grell, Daniel; Wilkin, Yannic; Gostin, Petre F.; Gebert, Annett; Kerscher, EberhardCorrosion fatigue (CF) tests were carried out on bulk glassy Zr52.5Cu17.9Al10Ni14.6Ti5 (Vitreloy 105) samples under load-controlled three-point bending conditions with a load ratio of R = 0.1 in 0.01 M Na2SO4 + 0.01 M NaCl electrolyte. During cyclic testing, the bar-shaped specimens were polarized in situ at constant potentials and the current was monitored. Three different anodic potentials within the interval between the pitting potential EP and the repassivation potential ER and three different load amplitudes were applied. In some cases, in situ microscopic observations revealed the formation of black corrosion products in the vicinity of the crack tip during anodic polarization. Fractographic analysis revealed a clear distinction between two modes of crack growth characterized by smooth dissolution induced regions on the one hand and slim fast fracture areas on the other hand. Both alternating features contributed to a broad-striated CF fracture surface. Moreover, further fatigue tests were carried out under free corrosion conditions yielding additional information on crack initiation and crack propagation period by means of the open circuit potential (OCP) changes. Thereby, a slight increase in OCP was detected after rupture of the passive layer due to bare metal exposed to the electrolyte. The electrochemical response increased continuously according to stable crack propagation until fracture occurred. Finally, the fracture surfaces of the CF samples were investigated by energy dispersive X-ray with the objective of analyzing the elemental distribution after anodic dissolution. Interestingly, anodic polarization at a near repassivation potential of −50 mV vs. saturated calomel electrode (SCE), which commands a constant electric potential of E = 0.241 V vs. standard hydrogen electrode (SHE), led to favorable effects on the fatigue lifetime. In conclusion, all results are conflated to a CF model for bulk glassy Vitreloy 105 under anodic polarization in chloride-containing electrolyte and compared to the previously proposed stress corrosion mechanisms under similar conditions. © 2017 Grell, Wilkin, Gostin, Gebert and Kerscher.
- ItemOn the adhesion between thin sheets and randomly rough surfaces(Lausanne : Frontiers Media, 2022) Wang , Anle; Müser, Martin H.Thin, elastic sheets are well known to adapt to rough counterfaces, whereby adhesive interactions and pull-off stresses σp can be significant, yet no generally applicable, quantitative guideline has been suggested hitherto as to when a sheet should be considered thin enough to be sticky. Using computer simulations, we find that the dependence of σp on surface energy γ has a high and a low-pull-off-stress regime. For randomly rough surfaces, we locate the dividing line at the point, where γ is approximately half the elastic energy per unit area needed to make conformal contact, which is the same ratio as for semi-infinite elastic solids. This rule of thumb also applies to a certain degree for single-wavelength roughness, in which case the transition from low to high stickiness occurs when at the moment of maximum tension contact is not only broken at the height maxima but also at the saddle points.
- ItemMicroenvironments designed to support growth and function of neuronal cells(Lausanne : Frontiers Media, 2018) Farrukh, Aleeza; Zhao, Shifang; del Campo, AránzazuStrategies for neural tissue repair heavily depend on our ability to temporally reconstruct the natural cellular microenvironment of neural cells. Biomaterials play a fundamental role in this context, as they provide the mechanical support for cells to attach and migrate to the injury site, as well as fundamental signals for differentiation. This review describes how different cellular processes (attachment, proliferation, and (directional) migration and differentiation) have been supported by different material parameters, in vitro and in vivo. Although incipient guidelines for biomaterial design become visible, literature in the field remains rather phenomenological. As in other fields of tissue regeneration, progress will depend on more systematic studies on cell-materials response, better understanding on how cells behave and understand signals in their natural milieu from neurobiology studies, and the translation of this knowledge into engineered microenvironments for clinical use.
- ItemFluoride-Sulfophosphate/Silica Hybrid Fiber as a Platform for Optically Active Materials(Lausanne : Frontiers Media, 2019) Wang, Wei-Chao; Yang, Xu; Wieduwilt, Torsten; Schmidt, Markus A.; Zhang, Qin-Yuan; Wondraczek, LotharPressure-assisted melt filling (PAMF) of pre-fabricated micro-capillaries has been proven an effective way of fabricating hybrid optical fiber (HOF) from unusual combinations of materials. Here, we extend the applicability of PAMF to multi-anionic fluoride-sulfophosphate (FPS) glasses. FPS glasses provide extended transmission windows and high solubility for various transition metal (TM) and rare earth (RE) ion species. Using PAMF for fabricating FPS/silica HOFs can therefore act as a platform for a broad variety of optically active fiber devices. For the present demonstration purposes, we selected Cr3+- and Mn2+-doped FPS. For both glasses, we demonstrate how the spectral characteristics of the bulk material persist also in the HOF. Using a double-core fiber structure in which waveguiding is conducted in a primary GeO2-SiO2 core, mode coupling to the secondary FPS-filled core allows one to exploit the optical activity of the doped FPS glass even when the intrinsic optical loss is high.Pressure-assisted melt filling (PAMF) of pre-fabricated micro-capillaries has been proven an effective way of fabricating hybrid optical fiber (HOF) from unusual combinations of materials. Here, we extend the applicability of PAMF to multi-anionic fluoride-sulfophosphate (FPS) glasses. FPS glasses provide extended transmission windows and high solubility for various transition metal (TM) and rare earth (RE) ion species. Using PAMF for fabricating FPS/silica HOFs can therefore act as a platform for a broad variety of optically active fiber devices. For the present demonstration purposes, we selected Cr3+- and Mn2+-doped FPS. For both glasses, we demonstrate how the spectral characteristics of the bulk material persist also in the HOF. Using a double-core fiber structure in which waveguiding is conducted in a primary GeO2-SiO2 core, mode coupling to the secondary FPS-filled core allows one to exploit the optical activity of the doped FPS glass even when the intrinsic optical loss is high.
- ItemTowards the Identification and Classification of Solar Granulation Structures Using Semantic Segmentation(Lausanne : Frontiers Media, 2022) Díaz Castillo, S. M.; Asensio Ramos, A.; Fischer, C. E.; Berdyugina, S. V.Solar granulation is the visible signature of convective cells at the solar surface. The granulation cellular pattern observed in the continuum intensity images is characterised by diverse structures e.g., bright individual granules of hot rising gas or dark intergranular lanes. Recently, the access to new instrumentation capabilities has given us the possibility to obtain high-resolution images, which have revealed the overwhelming complexity of granulation (e.g., exploding granules and granular lanes). In that sense, any research focused on understanding solar small-scale phenomena on the solar surface is sustained on the effective identification and localization of the different resolved structures. In this work, we present the initial results of a proposed classification model of solar granulation structures based on neural semantic segmentation. We inspect the ability of the U-net architecture, a convolutional neural network initially proposed for biomedical image segmentation, to be applied to the dense segmentation of solar granulation. We use continuum intensity maps of the IMaX instrument onboard the Sunrise I balloon-borne solar observatory and their corresponding segmented maps as a training set. The training data have been labeled using the multiple-level technique (MLT) and also by hand. We performed several tests of the performance and precision of this approach in order to evaluate the versatility of the U-net architecture. We found an appealing potential of the U-net architecture to identify cellular patterns in solar granulation images reaching an average accuracy above 80% in the initial training experiments.
- ItemInfrared Dual-Line Hanle Diagnostic of the Coronal Vector Magnetic Field(Lausanne : Frontiers Media, 2016) Dima, Gabriel I.; Kuhn, Jeffrey R.; Berdyugina, Svetlana V.Measuring the coronal vector magnetic field is still a major challenge in solar physics. This is due to the intrinsic weakness of the field (e.g., ~4G at a height of 0.1R⊙ above an active region) and the large thermal broadening of coronal emission lines. We propose using concurrent linear polarization measurements of near-infrared forbidden and permitted lines together with Hanle effect models to calculate the coronal vector magnetic field. In the unsaturated Hanle regime both the direction and strength of the magnetic field affect the linear polarization, while in the saturated regime the polarization is insensitive to the strength of the field. The relatively long radiative lifetimes of coronal forbidden atomic transitions implies that the emission lines are formed in the saturated Hanle regime and the linear polarization is insensitive to the strength of the field. By combining measurements of both forbidden and permitted lines, the direction and strength of the field can be obtained. For example, the SiX 1.4301 μm line shows strong linear polarization and has been observed in emission over a large field-of-view (out to elongations of 0.5 R⊙). Here we describe an algorithm that combines linear polarization measurements of the SiX 1.4301 μm forbidden line with linear polarization observations of the HeI 1.0830 μm permitted coronal line to obtain the vector magnetic field. To illustrate the concept we assume that the emitting gas for both atomic transitions is located in the plane of the sky. The further development of this method and associated tools will be a critical step toward interpreting the high spectral, spatial and temporal infrared spectro-polarimetric measurements that will be possible when the Daniel K. Inouye Solar Telescope (DKIST) is completed in 2019.
- ItemImpacts of acoustic and gravity waves on the ionosphere(Lausanne : Frontiers Media, 2022) Zawdie, Kate; Belehaki, Anna; Burleigh, Meghan; Chou, Min-Yang; Dhadly, Manbharat S.; Greer, Katelynn; Halford, Alexa J.; Hickey, Dustin; Inchin, Pavel; Kaeppler, Stephen R.; Klenzing, Jeff; Narayanan, Viswanathan Lakshmi; Sassi, Fabrizio; Sivakandan, Mani; Smith, Jonathon M.; Zabotin, Nikolay; Zettergren, Matthew D.; Zhang, Shun-RongThe impact of regional-scale neutral atmospheric waves has been demonstrated to have profound effects on the ionosphere, but the circumstances under which they generate ionospheric disturbances and seed plasma instabilities are not well understood. Neutral atmospheric waves vary from infrasonic waves of <20 Hz to gravity waves with periods on the order of 10 min, for simplicity, hereafter they are combined under the common term Acoustic and Gravity Waves (AGWs). There are other longer period waves like planetary waves from the lower and middle atmosphere, whose effects are important globally, but they are not considered here. The most ubiquitous and frequently observed impact of AGWs on the ionosphere are Traveling Ionospheric Disturbances (TIDs), but AGWs also affect the global ionosphere/thermosphere circulation and can trigger ionospheric instabilities (e.g., Perkins, Equatorial Spread F). The purpose of this white paper is to outline additional studies and observations that are required in the coming decade to improve our understanding of the impact of AGWs on the ionosphere.
- ItemThe future of auroral E-region plasma turbulence research(Lausanne : Frontiers Media, 2022) Huyghebaert, Devin; Billett, Daniel; Chartier, Alex; Chau, Jorge L.; Hussey, Glenn C.; Hysell, David L.; Ivarsen, Magnus F.; Mesquita, Rafael L. A.; Rojas, Enrique; Vierinen, Juha; Young, MatthewThe heating caused by ionospheric E-region plasma turbulence has documented global implications for the energy transfer from space into the terrestrial atmosphere. Traveling atmospheric disturbances, neutral wind motion, energy deposition rates, and ionospheric conductance have all been shown to be potentially affected by turbulent plasma heating. Therefore it is proposed to enhance and expand existing ionospheric radar capabilities and fund research into E-region plasma turbulence so that it is possible to more accurately quantify the solar-terrestrial energy budget and study phenomena related to E-region plasma turbulence. The proposed research funding includes the development of models to accurately predict and model the E-region plasma turbulence using particle-in-cell analysis, fluid-based analysis, and hybrid combinations of the two. This review provides an expanded and more detailed description of the past, present, and future of auroral E-region plasma turbulence research compared to the summary report submitted to the National Academy of Sciences Decadal Survey for Solar and Space Physics (Heliophysics) 2024–2033 (Huyghebaert et al., 2022a).