893 research outputs found

    Coupling of cytoplasm and adhesion dynamics determines cell polarization and locomotion

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    Observations of single epidermal cells on flat adhesive substrates have revealed two distinct morphological and functional states, namely a non-migrating symmetric unpolarized state and a migrating asymmetric polarized state. These states are characterized by different spatial distributions and dynamics of important biochemical cell components: F-actin and myosin-II form the contractile part of the cytoskeleton, and integrin receptors in the plasma membrane connect F-actin filaments to the substratum. In this way, focal adhesion complexes are assembled, which determine cytoskeletal force transduction and subsequent cell locomotion. So far, physical models have reduced this phenomenon either to gradients in regulatory control molecules or to different mechanics of the actin filament system in different regions of the cell. Here we offer an alternative and self-organizational model incorporating polymerization, pushing and sliding of filaments, as well as formation of adhesion sites and their force dependent kinetics. All these phenomena can be combined into a non-linearly coupled system of hyperbolic, parabolic and elliptic differential equations. Aim of this article is to show how relatively simple relations for the small-scale mechanics and kinetics of participating molecules may reproduce the emergent behavior of polarization and migration on the large-scale cell level.Comment: v2 (updates from proof): add TOC, clarify Fig. 4, fix several typo

    TCT investigation of the one-sided depletion of low-temperature covalently bonded silicon sensor P-N diodes

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    In the context of particle detectors, low-temperature covalent wafer-wafer bonding allows for integration of high-Z materials as absorbing layers with readout chips produced in standard CMOS processes. This enables for instance the fabrication of novel highly efficient X-ray imaging sensors. In order to investigate the effects of the covalent bonding on the signal generated in such sensors, wafer-wafer bonded silicon-silicon P-N pad diodes have previously been produced. The behaviour of these test samples is being investigated with transient current technique (TCT) measurements. In this paper we present an overview of the TCT setup as well as a custom sandwich-type sample holder used for these measurements. A review of the results presented in a previous paper shows, that the bonded P-N structures show a highly asymmetric depletion behaviour under reverse bias. IR edge TCT measurements confirm that only the P-side of the samples is being depleted. Comparing the integral of the TCT signals with the expected values based on the Shockley-Ramo theorem reveals an excess of signal being collected. This excess seems to be linked to a long exponential tail which is observed in the time domain TCT signals.Comment: To be submitted to JINST, 18 pages, 10 figures, 2 table

    “The whole is greater than the sum of its parts” – Exploring teachers’ technology readiness profiles and its relation to their emotional state during COVID-19 emergency remote teaching

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    With the rapid spread of the Coronavirus (COVID-19), schools around the world came to a shutdown. This resulted in an abrupt transition from face-to-face instruction to emergency remote teaching (ERT), resulting in numerous challenges that have greatly affected teachers. Even though research has identified key factors for teachers to effectively implement ERT in the context of the COVID-19 school shutdown, there is still little research on the factors (and their interrelations) that account for the differences between teachers’ experiences. Following a theoretical model of technology readiness, this study aimed to investigate teacher profiles based on domains of technology acceptance, technology competence and technology control. In addition, this study seeks to explore whether teachers’ emotional state during ERT varies between the teacher technology readiness profiles. A total of 124 teachers participated voluntarily in an online survey stemming from the research project “Students-Parents-Teachers in Homeschooling” in Germany. Results from a two-step cluster analysis revealed three distinct teacher technology readiness profiles. Moreover, the findings also revealed gender differences between the three technology readiness profiles. Lastly, an analysis of variance indicated that teachers’ positive emotional state during ERT varied significantly across the clusters. Implications of the results for teacher education and teacher professional development, as well as further lines of research are discussed.Peer Reviewe
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