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Small repeating earthquakes are thought to represent rupture of isolated asperities loaded by surrounding creep. The observed scaling between recurrence interval and seismic moment, T-r approximate to M-1/6, contrasts with expectation assuming constant stress drop and no aseismic slip (T-r approximate to M-1/3). Here we demonstrate that simple crack models of velocity-weakening asperities in a velocity-strengthening fault predict the M-1/6 scaling; however, the mechanism depends on asperity radius, R. For small asperities ( , where R is the nucleation radius) numerical simulations with rate-state friction show interseismic creep penetrating inward from the edge, and earthquakes nucleate in the center and rupture the entire asperity. Creep penetration accounts for approximate to 25% of the slip budget, the nucleation phase takes up a larger fraction of slip. Stress drop increases with increasing R; the lack of self-similarity being due to the finite nucleation dimension. For 2R<R less than or similar to 6Rsimulations exhibit simple cycles with ruptures nucleating from the edge. Asperities with R6R exhibit complex cycles of partial and full ruptures. Here T-r is explained by an energy criterion: full rupture requires that the energy release rate everywhere on the asperity at least equals the fracture energy, leading to the scaling T-r approximate to M-1/6. Remarkably, in spite of the variability in behavior with source dimension, the scaling of T-r with stress drop , nucleation length and creep rate v(pl) is the same across all regimes: Tr approximate to vpl. This supports the use of repeating earthquakes as creepmeters and provides a physical interpretation for the scaling observed in nature. Plain Language Summary While most earthquake sequences have complex temporal patterns, some small earthquakes are quite predictable: they repeat periodically. The time between consecutive events (recurrence interval) grows with earthquake size: as intuitive, it takes longer to accumulate the mechanical energy for large earthquakes. However, the scaling between the recurrence interval and earthquake energy (seismic moment) is not what simple physical considerations predict. It is often assumed that faults are locked between events and seismic slip must therefore keep up with long-term plate motion. This leads to the scaling: Tr approximate to M01/3, but the observed scaling is . In fact, faults are not fully locked between earthquakes: they can slip slowly, or release part of the energy in smaller quakes between the larger ones. Here we use numerical simulations, and ideas from fracture mechanics, to understand what controls the time between repeating quakes. The main results are (1) analytical expressions of the recurrence interval as a function of earthquake size, predicting the observed scaling; (2) explanation of the differences between the cycle of small and large earthquakes (fraction of slow slip, direction of rupture propagation, and the occurrence of smaller quakes between large ones) and the quantities determining these transitions.
The H.E.S.S. array is a third generation Imaging Atmospheric Cherenkov Telescope (IACT) array. It is located in the Khomas Highland in Namibia, and measures very high energy (VHE) gamma-rays. In Phase I, the array started data taking in 2004 with its four identical 13 m telescopes. Since then, H.E.S.S. has emerged as the most successful IACT experiment to date. Among the almost 150 sources of VHE gamma-ray radiation found so far, even the oldest detection, the Crab Nebula, keeps surprising the scientific community with unexplained phenomena such as the recently discovered very energetic flares of high energy gamma-ray radiation. During its most recent flare, which was detected by the Fermi satellite in March 2013, the Crab Nebula was simultaneously observed with the H.E.S.S. array for six nights. The results of the observations will be discussed in detail during the course of this work. During the nights of the flare, the new 24 m × 32 m H.E.S.S. II telescope was still being commissioned, but participated in the data taking for one night. To be able to reconstruct and analyze the data of the H.E.S.S. Phase II array, the algorithms and software used by the H.E.S.S. Phase I array had to be adapted. The most prominent advanced shower reconstruction technique developed by de Naurois and Rolland, the template-based model analysis, compares real shower images taken by the Cherenkov telescope cameras with shower templates obtained using a semi-analytical model. To find the best fitting image, and, therefore, the relevant parameters that describe the air shower best, a pixel-wise log-likelihood fit is done. The adaptation of this advanced shower reconstruction technique to the heterogeneous H.E.S.S. Phase II array for stereo events (i.e. air showers seen by at least two telescopes of any kind), its performance using MonteCarlo simulations as well as its application to real data will be described.
CPS and the Worker
(2017)
The idea of interlinked, sensor-augmented, self-governing Cyber Physical System (CPS) production processes is gaining momentum. At the same time, the impact of this concept on the workforce remains surprisingly vague. This can be explained by the fact that man is not at the centre of these developments and—even more importantly—automation is geared towards eliminating human activity. Based on the first views in the 1980s, the label of the “process worker” assumed an almost exclusive focus on control and maintenance tasks for this new type of worker in the automated factory. Recent experiences show, however, that as long as robots are not self-learning, man will be the template for these machines and we can already notice the emerging parallelism of fully automated production lines and human workshops. The changing nature of the workforce will gain further momentum if one depicts new, open formats of production. Here, the worker will have to assume new roles in reconfiguring the production processes.
CpG-oligonucleotides modulate sphingosine-1-phosphate metabolism in normal human keratinocytes
(2012)
The Dictyostelium centrosome is a model for acentriolar centrosomes and it consists of a three-layered core structure surrounded by a corona harboring microtubule nucleation complexes. Its core structure duplicates once per cell cycle at the G2/M transition. Through proteomic analysis of isolated centrosomes we have identified CP91, a 91-kDa coiled coil protein that was localized at the centrosomal core structure. While GFP-CP91 showed almost no mobility in FRAP experiments during interphase, both GFP-CP91 and endogenous CP91 dissociated during mitosis and were absent from spindle poles from late prophase to anaphase. Since this behavior correlates with the disappearance of the central layer upon centrosome duplication, CP91 is a putative component of this layer. When expressed as GFP-fusions, CP91 fragments corresponding to the central coiled coil domain and the preceding N-terminal part (GFP-CP91cc and GFP-CP91N, respectively) also localized to the centrosome but did not show the mitotic redistribution of the full length protein suggesting a regulatory role of the C-terminal domain. Expression of all GFP-fusion proteins suppressed expression of endogenous CP91 and elicited supernumerary centrosomes. This was also very prominent upon depletion of CP91 by RNAi. Additionally, CP91-RNAi cells exhibited heavily increased ploidy due to severe defects in chromosome segregation along with increased cell size and defects in the abscission process during cytokinesis. Our results indicate that CP91 is a central centrosomal core component required for centrosomal integrity, proper centrosome biogenesis and, independently, for abscission during cytokinesis. (c) 2016 Elsevier GmbH. All rights reserved.
Dictyostelium centrosomes consist of a layered core structure surrounded by a microtubule-nucleating corona. At the G2/M transition, the corona dissociates and the core structure duplicates, yielding two spindle pole bodies. Finally, in telophase, the spindle poles mature into two new, complete centrosomes. CP55 was identified in a centrosomal proteome analysis. It is a component of the centrosomal core structure, and persists at the centrosome throughout the entire cell cycle. FRAP experiments revealed that during interphase the majority of centrosomal GFP-CP55 is immobile, which indicates a structural task of CP55 at the centrosome. The CP55null mutant is characterized by increased ploidy, a less structured, slightly enlarged corona, and by supernumerary, cytosolic MTOCs, containing only corona proteins and lacking a core structure. Live cell imaging showed that supernumerary MTOCs arise in telophase. Lack of CP55 also caused premature recruitment of the corona organizer CP148 to mitotic spindle poles, already in metaphase instead of telophase. Forces transmitted through astral microtubules may expel prematurely acquired or loosely attached corona fragments into the cytosol, where they act as independent MTOCs. CP55null cells were also impaired in growth, most probably due to difficulties in centrosome splitting during prophase. Furthermore, although they were still capable of phagocytosis, they appeared unable to utilize phagocytosed nutrients. This inability may be attributed to their partially disorganized Golgi apparatus.
The acentriolar Dictyostelium centrosome is a nucleus-associated body consisting of a core structure with three plaque-like layers, which are surrounded by a microtubule-nucleating corona. The core duplicates once per cell cycle at the G2/M transition, whereby its central layer disappears and the two outer layers form the mitotic spindle poles. Through proteomic analysis of isolated centrosomes, we have identified CP39 and CP75, two essential components of the core structure. Both proteins can be assigned to the central core layer as their centrosomal presence is correlated to the disappearance and reappearance of the central core layer in the course of centrosome duplication. Both proteins contain domains with centrosome-binding activity in their N- and C-terminal halves, whereby the respective N-terminal half is required for cell cycle-dependent regulation. CP39 is capable of self-interaction and GFP-CP39 overexpression elicited supernumerary microtubule-organizing centers and pre-centrosomal cytosolic clusters. Underexpression stopped cell growth and reversed the MTOC amplification phenotype. In contrast, in case of CP75 underexpression of the protein by RNAi treatment elicited supernumerary MTOCs. In addition, CP75RNAi affects correct chromosome segregation and causes co-depletion of CP39 and CP91, another central core layer component. CP39 and CP75 interact with each other directly in a yeast two-hybrid assay. Furthermore, CP39, CP75 and CP91 mutually interact in a proximity-dependent biotin identification (BioID) assay. Our data indicate that these three proteins are all required for proper centrosome biogenesis and make up the major structural components of core structure's central layer.
Global change threatens the maintenance of ecosystem functions that are shaped by the persistence and dynamics of populations. It has been shown that the persistence of species increases if they possess larger trait adaptability. Here, we investigate whether trait adaptability also affects the robustness of population dynamics of interacting species and thereby shapes the reliability of ecosystem functions that are driven by these dynamics. We model co‐adaptation in a predator–prey system as changes to predator offense and prey defense due to evolution or phenotypic plasticity. We investigate how trait adaptation affects the robustness of population dynamics against press perturbations to environmental parameters and against pulse perturbations targeting species abundances and their trait values. Robustness of population dynamics is characterized by resilience, elasticity, and resistance. In addition to employing established measures for resilience and elasticity against pulse perturbations (extinction probability and return time), we propose the warping distance as a new measure for resistance against press perturbations, which compares the shapes and amplitudes of pre‐ and post‐perturbation population dynamics. As expected, we find that the robustness of population dynamics depends on the speed of adaptation, but in nontrivial ways. Elasticity increases with speed of adaptation as the system returns more rapidly to the pre‐perturbation state. Resilience, in turn, is enhanced by intermediate speeds of adaptation, as here trait adaptation dampens biomass oscillations. The resistance of population dynamics strongly depends on the target of the press perturbation, preventing a simple relationship with the adaptation speed. In general, we find that low robustness often coincides with high amplitudes of population dynamics. Hence, amplitudes may indicate the robustness against perturbations also in other natural systems with similar dynamics. Our findings show that besides counteracting extinctions, trait adaptation indeed strongly affects the robustness of population dynamics against press and pulse perturbations.
Global change threatens the maintenance of ecosystem functions that are shaped by the persistence and dynamics of populations. It has been shown that the persistence of species increases if they possess larger trait adaptability. Here, we investigate whether trait adaptability also affects the robustness of population dynamics of interacting species and thereby shapes the reliability of ecosystem functions that are driven by these dynamics. We model co‐adaptation in a predator–prey system as changes to predator offense and prey defense due to evolution or phenotypic plasticity. We investigate how trait adaptation affects the robustness of population dynamics against press perturbations to environmental parameters and against pulse perturbations targeting species abundances and their trait values. Robustness of population dynamics is characterized by resilience, elasticity, and resistance. In addition to employing established measures for resilience and elasticity against pulse perturbations (extinction probability and return time), we propose the warping distance as a new measure for resistance against press perturbations, which compares the shapes and amplitudes of pre‐ and post‐perturbation population dynamics. As expected, we find that the robustness of population dynamics depends on the speed of adaptation, but in nontrivial ways. Elasticity increases with speed of adaptation as the system returns more rapidly to the pre‐perturbation state. Resilience, in turn, is enhanced by intermediate speeds of adaptation, as here trait adaptation dampens biomass oscillations. The resistance of population dynamics strongly depends on the target of the press perturbation, preventing a simple relationship with the adaptation speed. In general, we find that low robustness often coincides with high amplitudes of population dynamics. Hence, amplitudes may indicate the robustness against perturbations also in other natural systems with similar dynamics. Our findings show that besides counteracting extinctions, trait adaptation indeed strongly affects the robustness of population dynamics against press and pulse perturbations.
The anti-inflammatory potential of 26 neolignans (14 of the bicyclooctane-type and 12 of the benzofuran-type), isolated from three Lauraceae species (Pleurothyrium cinereum, Ocotea macrophylla and Nectandra amazonum), was evaluated in vitro through inhibition of COX-1, COX-2, 5-LOX and agonist-induced aggregation of rabbit platelets. Benzofuran neolignans were found to be selective COX-2 inhibitors, whereas bicyclooctane neolignans inhibit selectively the PAF- action as well as COX-1 and 5-LOX. The neolignan 9-nor-7,8-dehydro-isolicarin B 15 and cinerin C 7 were found to be the most potent COX-2 inhibitor and PAF-antagonist, respectively. Nectamazin C 10 exhibited dual 5-LOX/COX-2 inhibition.