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Cell migration is associated with the dynamic protrusion of a thin actin-based cytoskeletal extension at the cell front, which has been shown to consist of two different substructures, the leading lamellipodium and the subsequent lamellum. While the formation of the lamellipodium is increasingly well understood, organizational principles underlying the emergence of the lamellum are just beginning to be unraveled. We report here on a 1D mathematical model which describes the reaction-diffusion processes of a polarized actin network in steady state, and reproduces essential characteristics of the lamellipodium-lamellum system. We observe a steep gradient in filament lengths at the protruding edge, a local depolymerization maximum a few microns behind the edge, as well as a differential dominance of the network destabilizer ADF/cofilin and the stabilizer tropomyosin. We identify simple and robust organizational principles giving rise to the derived network characteristics, uncoupled from the specifics of any molecular implementation, and thus plausibly valid across cell types. An analysis of network length dependence on physico-chemical system parameters implies that to limit array treadmilling to cellular dimensions, network growth has to be truncated by mechanisms other than aging-induced depolymerization, e.g., by myosin-associated network dissociation at the transition to the cell body. Our work contributes to the analytical understanding of the cytoskeletal extension's bisection into lamellipodium and lamellum and sheds light on how cells organize their molecular machinery to achieve motility.
Despite its impressive complexity the cytoskeleton succeeds to persistently organize itself and thus the cells' interior. In contrast to classical man-made machines, much of the cellular organization originates from inherent self-assembly and self-organization allowing a high degree of autonomy for various functional units. Recent experimental and theoretical studies revealed numerous examples of cytoskeleton components that arrange and organize in a self-regulative way. In the present review we want to shortly summarize some of the principle mechanisms that are able to inherently trigger and regulate the cytoskeleton organization. Although taken individually most of these regulative principles are rather simple with intuitively predictable consequences, combinations of two or more of these mechanisms can quickly give rise to very complex, unexpected behavior and might even be able to explain the formation of different functional units out of a common pool of available building blocks.
“Net Zero-Energy Building” has become a popular catchphrase to describe the synergy between energy-efficient building and renewable energy utilisation to achieve a balanced energy budget over an annual cycle. Taking into account the energy exchange with a grid overcomes the limitations of energy-autonomous buildings with the need for seasonal energy storage on-site. Although the expression, “Net Zero-Energy Building,” appears in many energy policy documents, a harmonised definition or a standardised balancing method is still lacking. This paper reports on the background and the various effects influencing the energy balance approach. After discussing the national energy code framework in Germany, a harmonised terminology and balancing procedure is proposed. The procedure takes not only the energy balance but also energy efficiency and load matching into account.
Die Begriffe „Nullenergiehaus“ oder „Plusenergiehaus“ sind in den letzten Jahren national und international zum Inbegriff für die konsequente Zusammenführung von Maßnahmen zur drastischen Energieeinsparung und optimierter, dezentraler Nutzung erneuerbarer Energien geworden. Dabei geht es nicht um energieautarke Gebäude und die dabei große Herausforderung der saisonalen Energiespeicherung. Grundidee ist, dass die von einem Gebäude in ein Netz eingespeiste Energiemenge in der Jahresbilanz mindestens dem Energiebezug entspricht. Sowohl im Kontext der Fortführung der europäischen Gebäuderichtline als auch im aktuellen Energiekonzept und Energieforschungsprogramm der Bundesregierung wird das Thema besetzt.
Seit den ersten nationalen, strategischen Papieren zu Datenmanagement-Fragen in der Wissenschaft in den USA (NSF, 2005), Großbritannien (Lyon, 2007; Swan & Brown, 2008), der EU (Atkinson et al. 2008; OGF22-ET CG, 2008) und vor allem seit den Guidelines der OECD (2007) wird international intensiv über die Erfordernisse der Ausbildung von „Datenspezialisten“ diskutiert. Grundlegende Überlegungen, die einen gewissen internationalen Konsens gefunden haben, wurden im Auftrag von JISC von Swan und Brown (2008, S. 1) entwickelt (vgl. Hank & Davidson, 2009). Sie schlagen vier Rollen im Forschungsdatenmanagement vor. Neben dem Data Creator (datenproduzierender Forscher), dem Data Scientist (Wissenschaftler der bspw. bei der Datenanalyse unterstützt) und dem Data Manager (verantwortlich für alle technischen Aspekte: Lagerung, Zugriff, Aufbewahrung) wurde auch der Data Librarian benannt. Im Weiteren wird, auch unter Beachtung der Tätigkeiten die im Data Curation Lifecycle Model (s. Beitrag von Rümpel. Kap. 1.2) aufgeführt sind, neben dem Data Manager und dem Data Curator insbesondere auf den Data Librarian eingegangen.
Um einen Mehrwert von Forschungsdaten zu erhalten, ist eine adäquate Verwaltung notwendig. Ihr Lebenszyklus erstreckt sich über verschiedene Phasen, die von der Entstehung in wissenschaftlichen Arbeitsprozessen bis zur nachnutzbaren Archivierung reichen. Die Anforderungen an das Management von Forschungsdaten gehen weit über die Langzeitarchivierung hinaus.
In this paper, we present an approach to adopt UMLsec, which is defined for UML 1.5, to support the current UML version 2.3. The new profile UMLsec4UML2 is technically constructed as a UML profile diagram, which is equipped with a number of integrity conditions expressed using OCL. Consequently, the UMLsec4UML2-profile can be loaded in any Eclipse-based EMF- and MDT-compatible UML editing tool to develop and analyze different kinds of security models. The OCL constraints replace the static checks of the tool support for the old UMLsec defined for UML 1.5. Thus, the UMLsec4UML2-profile not only provides the whole expresiveness of UML2.3 for security modeling, it also brings considerably more freedom in selecting a basic UML editing tool, and it integrates modeling and analyzing security models. Since UML2.3 comprises new diagram types, as well as new model elements and new semantics of diagram types already contained in UML1.5, we consider a number of these changes in detail. More specifically, we consider composite structure and sequence diagrams with respect to modeling security properties according to the original version of UMLsec. The goal is to use UMLsec4UML2 to specify architectural security patterns.