Über den Einfluss der Fußgeometrie auf die Energieeffizienz beim zweibeinigen Gehen

Die Energieeffizienz beim Gehen ist ein wichtiger Aspekt bei der Entwicklung zweibeiniger Roboter. Diese verfügen nur über einen begrenzten Energiespeicher, mit dem ein möglichst langer Betrieb angestrebt wird. Die Energieeffizienz wird einerseits von der konstruktiven Gestaltung und den Modellparametern beeinflusst, andererseits jedoch auch von der verwendeten Regelung, mit der die Bewegung erzeugt und stabilisiert wird. In einem Entwicklungsprozess werden daher bei der Konzeption und der konstruktiven Gestaltung bereits früh Modelle zur Simulation und Methoden zur Optimierung benötigt. Da in diesem Entwicklungsstadium erst wenige Details konkretisiert und festgelegt sind, eignen sich einfache Mehrkörpermodelle für diese Fragestellung. Durch eine Regelung auf Basis der hybriden Nulldynamik können für solche Systeme stabile Gehbewegungen mit hoher Energieeffizienz erzeugt werden, die die natürliche Dynamik des Systems ausnutzen. In dieser Arbeit wird untersucht, welchen Einfluss die Fußgeometrie auf die Energieeffizienz beim zweibeinigen Gehen hat und wie diese bei der Entwicklung eines zweibeinigen Roboters optimiert werden kann. Hierfür wird ein Modell für einen konvexen, starren Fuß entwickelt, dessen Kontaktpunkt mit dem Boden explizit berechnet werden kann. Dadurch ist eine Beschreibung der Abrollbewegung in Minimalkoordinaten möglich und für die Dynamik des Gesamtsystems kann eine gewöhnliche Differentialgleichung abgeleitet werden. Für das Fußmodell werden zwei Parametrierungen entwickelt, bei denen jeweils von einem Polygon ausgegangen wird, dessen Kanten abgerundet werden, damit sich eine kontinuierliche Abrollbewegung ergibt. Auf diese Weise wird ein flacher Fuß, und ein Fuß mit zusätzlichem Zehenbereich beschrieben. Der Roboter wird durch ein ebenes Mehrkörpersystem beschrieben, das aus einem Oberkörper, Oberschenkeln, Unterschenkeln und dem konvexen Fuß besteht, die jeweils durch Drehgelenke in Hüfte, Knie und Sprunggelenk miteinander verbunden sind. Für dieses System wird eine Regelung auf Basis der hybriden Nulldynamik entworfen. Dieses Regelungskonzept wird somit auf Systeme mit beliebiger Fußgeometrie erweitert. Mittels numerischer Optimierung werden optimale Gehbewegungen erzeugt und zugleich die Fußgeometrie optimiert. Zur Durchführung von Parameterstudien wird eine numerische Fortsetzungsmethode für dieses nichtglatte Problem entwickelt. Durch die Optimierung der Fußgeometrie kann der durchschnittliche Energieverbrauch eines 80 kg schweren und 1,80 m großen Roboters im Geschwindigkeitsbereich 0,3 bis 2,3 m/s gegenüber einem Modell mit Punktfüßen um 81 % reduziert werden

Über den Einfluss der Fußgeometrie auf die Energieeffizienz beim zweibeinigen Gehen

Der Einfluss der Fußgeometrie auf die Energieeffizienz beim zweibeinigen Gehen wird untersucht. Es wird eine Methode zur Optimierung der Fußgeometrie für einen zweibeinigen Roboter entwickelt. Grundlage ist ein ebenes Modell mit beliebieger, konvexer Fußgeometrie in Kombination mit einer Regelung auf Basis der hybriden Nulldynamik. Es werden optimale Bewegungen und Fußgeometrien ermittelt. Im Vergleich zu einem Modell mit Punktfüßen ergeben sich Energieeinsparungen von über 80%

Vortical flow structures induced by red blood cells in capillaries

Objective Knowledge about the flow field of the plasma around the red blood cells in capillary flow is important for a physical understanding of blood flow and the transport of micro- and nanoparticles and molecules in the flowing plasma. We conducted an experimental study on the flow field around red blood cells in capillary flow that is complemented by simulations of vortical flow between red blood cells. Methods Red blood cells were injected in a 10 × 12 µm rectangular microchannel at a low hematocrit, and the flow field around one or two cells was captured by a high-speed camera that tracked 250 nm nanoparticles in the flow field, acting as tracers. Results While the flow field around a steady “croissant” shape is found to be similar to that of a rigid sphere, the flow field around a “slipper” shape exhibits a small vortex at the rear of the red blood cell. Even more pronounced are vortex-like structures observed in the central region between two neighboring croissants. Conclusions The rotation frequency of the vortices is to a good approximation, inversely proportional to the distance between the cells. Our experimental data are complemented by numerical simulations

Lipid Reorganization Induced by Shiga Toxin Clustering on Planar Membranes

The homopentameric B-subunit of bacterial protein Shiga toxin (STxB) binds to the glycolipid Gb3 in plasma membranes, which is the initial step for entering cells by a clathrin-independent mechanism. It has been suggested that protein clustering and lipid reorganization determine toxin uptake into cells. Here, we elucidated the molecular requirements for STxB induced Gb3 clustering and for the proposed lipid reorganization in planar membranes. The influence of binding site III of the B-subunit as well as the Gb3 lipid structure was investigated by means of high resolution methods such as fluorescence and scanning force microscopy. STxB was found to form protein clusters on homogenous 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/cholesterol/Gb3 (65∶30∶5) bilayers. In contrast, membranes composed of DOPC/cholesterol/sphingomyelin/Gb3 (40∶35∶20∶5) phase separate into a liquid ordered and liquid disordered phase. Dependent on the fatty acid composition of Gb3, STxB-Gb3 complexes organize within the liquid ordered phase upon protein binding. Our findings suggest that STxB is capable of forming a new membrane phase that is characterized by lipid compaction. The significance of this finding is discussed in the context of Shiga toxin-induced formation of endocytic membrane invaginations

Leveling up? An inter-neighborhood experiment on parochialism and the efficiency of multi-level public goods provision

Many public goods can be provided at different spatial levels. Evidence from social identity theory and in-group favoritism raises the possibility that where higher-level provision is more efficient, subjects’ narrow concern for local outcomes (parochialism) could harm efficiency. Building on the experimental paradigm of multi-level public good games and the ‘neighborhood attachment’ concept, we conduct an artefactual field experiment with 600 participants in a setting conducive to parochial behavior. In an inter-neighborhood intra-region design, subjects allocate an endowment between a personal account, a local, and a regional public good account. The between-subjects design varies across two dimensions: One informs subjects that the smaller local group consists of members from their own neighborhood (‘neighbors’). The other varies the relative productivity at the two public goods provision levels. We find evidence for parochialism, but contrary to our hypothesis, parochialism does not interfere with efficiency: The average subject responds to a change in relative productivities at the local and regional level in the same way, whether aware of their neighbors’ presence in the small group or not. The results even hold for subjects with above-median neighborhood attachment and subjects primed on neighborhood attachment

Inter-charity competition under spatial differentiation: sorting, crowding, and spillovers

We study spatially differentiated competition between charities by partnering with two foodbanks in two neighboring cities to conduct a field experiment with roughly 350 donation appeals. We induce spatial differentiation by varying the observability of charities’ location such that each donor faces a socially close ‘home’ and a distant ‘away’ charity. We find that spatially differentiated competition is characterized by sorting, crowding-in, and an absence of spillovers: Donors sort themselves by distance; fundraising (through matching) for one charity raises checkbook giving to that charity, irrespective of distance; but checkbook giving to the unmatched charity is not affected. For lead donors, this implies that the social distance between donors and charities is of limited strategic important. For spatially differentiated charities, matching ‘home’ donations maximizes overall charitable income. Across both charities, however, the additional funds raised fail to cover the cost of the match, despite harnessing social identity for giving

Novel targets, treatments, and advanced models for intracerebral haemorrhage

Intracerebral haemorrhage (ICH) is the second most common type of stroke and a major cause of mortality and disability worldwide. Despite advances in surgical interventions and acute ICH management, there is currently no effective therapy to improve functional outcomes in patients. Recently, there has been tremendous progress uncovering new pathophysiological mechanisms underlying ICH that may pave the way for the development of therapeutic interventions. Here, we highlight emerging targets, but also existing gaps in preclinical animal modelling that prevent their exploitation. We particularly focus on (1) ICH aetiology, (2) the haematoma, (3) inflammation, and (4) post-ICH pathology. It is important to recognize that beyond neurons and the brain, other cell types and organs are crucially involved in ICH pathophysiology and successful interventions likely will need to address the entire organism. This review will spur the development of successful therapeutic interventions for ICH and advanced animal models that better reflect its aetiology and pathophysiology

Intramedullary Mg2Ag nails augment callus formation during fracture healing in mice

Intramedullary stabilization is frequently used to treat long bone fractures. Implants usually remain unless complications arise. Since implant removal can become technically very challenging with the potential to cause further tissue damage, biodegradable materials are emerging as alternative options. Magnesium (Mg)-based biodegradable implants have a controllable degradation rate and good tissue compatibility, which makes them attractive for musculoskeletal research. Here we report for the first time the implantation of intramedullary nails made of an Mg alloy containing 2% silver (Mg2Ag) into intact and fractured femora of mice. Prior in vitro analyses revealed an inhibitory effect of Mg2Ag degradation products on osteoclast differentiation and function with no impair of osteoblast function. In vivo, Mg2Ag implants degraded under non-fracture and fracture conditions within 210 days and 133 days, respectively. During fracture repair, osteoblast function and subsequent bone formation were enhanced, while osteoclast activity and bone resorption were decreased, leading to an augmented callus formation. We observed a widening of the femoral shaft under steady state and regenerating conditions, which was at least in part due to an uncoupled bone remodeling. However, Mg2Ag implants did not cause any systemic adverse effects. These data suggest that Mg2Ag implants might be promising for intramedullary fixation of long bone fractures, a novel concept that has to be further investigated in future studies