Heaping, Secondary Flows and Broken Symmetry in Flows of Elongated Granular Particles

In this paper we report experiments where we shear granular rods in split-bottom geometries, and find that a significant heap of height of least 40% of the filling height can form at the particle surface. We show that heaping is caused by a significant secondary flow, absent for spherical particles. Flow reversal transiently reverses the secondary flow, leading to a quick collapse and slower regeneration of the heap. We present a symmetry argument and experimental data that show that the generation of the secondary flow is driven by a misalignment of the mean particle orientation with the streamlines of the flow. This general mechanism is expected to be important in all flows of sufficiently anisometric grains.Comment: Accepted for Soft Matte

Effects of grain shape on packing and dilatancy of sheared granular materials

Granular material exposed to shear shows a variety of unique phenomena: Reynolds dilatancy, positional order and orientational order effects may compete in the shear zone. We study granular packings consisting of macroscopic prolate, oblate and spherical grains and compare their behaviour. X-ray tomography is used to determine the particle positions and orientations in a cylindrical split bottom shear cell. Packing densities and the arrangements of individual particles in the shear zone are evaluated. For anisometric particles, we observe the competition of two opposite effects. One the one hand, the sheared granulate is dilated, but on the other hand the particles reorient and align with respect to the streamlines. Even though aligned cylinders in principle may achieve higher packing densities, this alignment compensates for the effect of dilatancy only partially. The complex rearrangements lead to a depression of the surface above the well oriented region while neigbouring parts still show the effect of dilation in the form of heaps. For grains with isotropic shapes, the surface remains rather flat. Perfect monodisperse spheres crystallize in the shear zone, whereby positional order partially overcompensates dilatancy effects. However, already slight deviations from the ideal monodisperse sphere shape inhibit crystallization.Comment: 12 pages, 13 figures, accepted in Soft Matte

Evolution of shear zones in granular materials

The evolution of wide shear zones (or shear bands) was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains (e.g. sand) and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e. when the grain shape changes from spherical to irregular (e.g. sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rod like particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear induced density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.Comment: 11 pages, 12 figures, submitted to Phys. Rev.

Investigation of oxygen permeation through composites of PMMA and surface-modified ZnO nanoparticles

Oxygen permeabilities of nanocomposite films consisting of poly(methyl methacrylate) (PMMA) and different amounts of spherical zinc oxide (ZnO) nanoparticles were determined to investigate the barrier effect of this material with respect to particle content. A method was applied which is based on quenching of an excited phosphorescent dye by oxygen. Possible effects of the nanoparticles on the response of the dye molecules were investigated and were ruled out

Public Administration as Positive Example for Transparency in Data Collection and Sharing regarding the Life-Event Birth of Child

Digital self-determination is crucial in a digitalized world. Given the recent advances in e-government and its increased usage, public administration is in a unique position to inform and educate citizens about data sharing and act as a best practice example for digital transparency. We present the results of a project to support citizens\u27 digital sovereignty via interactive prototypes on e-government services (e.g. websites). A digital data sharing fable and a mystery game for the life event birth of a child have been developed that provide information about data sharing between government agencies. They were evaluated using randomized controlled trials (experiments) to determine causal effects of the interventions on digital sovereignty. Results indicate that these applications can foster knowledge about data sharing. Implications on digital sovereignty and future work are discussed

Flow of anisometric particles in a quasi-2D hopper

The stationary flow field in a quasi-two-dimensional hopper is investigated experimentally. The behavior of materials consisting of beads and elongated particles with different aspect ratio is compared. We show, that while the vertical velocity in the flowing region can be fitted with a Gaussian function for beads, in the case of elongated grains the flowing channel is narrower and is bordered with sharper velocity gradient. For this case, we quantify deviations from the Gaussian velocity profile. Relative velocity fluctuations are considerably larger and slower for elongated grains.Comment: 6 pages, 6 figures, submitted to Phys. Rev.

Belastung der Persönlichen Schutzausrüstung und des Löschwassers durch Schwermetalle bei der Brandbekämpfung von Hochvoltspeichern - Evaluierung möglicher Rückhaltemaßnahmen durch Einsatzausrüstung der Feuerwehr

Die steigende Anzahl von Fahrzeugen mit Hochvoltsystem führt zu veränderten Einsatzsituationen für die Feuerwehr bei der Bekämpfung von Fahrzeugbränden und der technischen Hilfeleistung bei Verkehrsunfällen. Probleme stellen die exotherme Reaktion (mit und ohne Flammenerscheinungen) und das Freisetzen des Inhalts des Hochvoltspeichers aufgrund mechanischer Beschädigung oder Brandeinwirkungen dar. Bei einem Thermal Runaway in einem Hochvoltspeicher sind die entweichenden hoch entzündlichen, toxischen Gase sowie die Rauchgase mit Schwermetallen belastet. Das gilt ebenso für anfallendes Lösch- und Tauchwasser sowie feste emittierte Bestandteile. Bei der Brandbekämpfung werden die persönlichen Schutzausrüstungen und Einsatzmittel der Einsatzkräfte mit diesen Stoffen kontaminiert. Mittels chemischer Analysen wird die Gefährdung durch die Metallkontaminationen der Bekleidung in diesem Bericht eingeordnet. Erste Erkenntnisse zu einfachen Waschvorgängen der Bekleidung werden gezeigt. Besagte Einsätze gehen mit kontaminiertem Löschwasser und so mit einer Belastung der Umwelt einher. Deshalb wird empfohlen, das Löschwasser aufzufangen und entsorgen zu lassen. Bisher fehlt eine Beschreibung, wie diese Maßnahme umzusetzen ist. Einsatzempfehlungen zur Rückhaltung des Löschwassers werden, je nach örtlicher Gegebenheit, gegeben. Datei-Upload durch TI

Packing, alignment and flow of shape-anisotropic grains in a 3D silo experiment

Granular material flowing through bottlenecks, like the openings of silos, tend to clog and thus inhibit further flow. We study this phenomenon in a three-dimensional hopper for spherical and shape-anisotropic particles by means of x-ray tomography. The x-ray tomograms provide information on the bulk of the granular filling, and allows us to determine the particle positions and orientations inside the silo. In addition, it allows us to calculate local packing densities in different parts of the container. We find that in the flowing zone of the silo particles show a preferred orientation and thereby a higher order. Similarly to simple shear flows, the average orientation of the particles is not parallel to the streamlines but encloses a certain angle with it. In most parts of the hopper, the angular distribution of the particles did not reach the one corresponding to stationary shear flow, thus the average orientation angle in the hopper deviates more from the streamlines than in stationary shear flows. In the flowing parts of the silo, shear induced dilation is observed, which is more pronounced for elongated grains than for nearly spherical particles. The clogged state is characterized by a dome, i.e. the geometry of the layer of grains blocking the outflow. The shape of the dome depends on the particle shape

Sox10 Activity and the Timing of Schwann Cell Differentiation Are Controlled by a Tle4-Dependent Negative Feedback Loop

The HMG-domain containing transcription factor Sox10 plays a crucial role in regulating Schwann cell survival and differentiation and is expressed throughout the entire Schwann cell lineage. While its importance in peripheral myelination is well established, little is known about its role in the early stages of Schwann cell development. In a search for direct target genes of Sox10 in Schwann cell precursors, the transcriptional co-repressor Tle4 was identified. At least two regions upstream of the Tle4 gene appear involved in mediating the Sox10-dependent activation. Once induced, Tle4 works in tandem with the bHLH transcriptional repressor Hes1 and exerts a dual inhibitory effect on Sox10 by preventing the Sox10 protein from transcriptionally activating maturation genes and by suppressing Sox10 expression through known enhancers of the gene. This mechanism establishes a regulatory barrier that prevents premature activation of factors involved in differentiation and myelin formation by Sox10 in immature Schwann cells. The identification of Tle4 as a critical downstream target of Sox10 sheds light on the gene regulatory network in the early phases of Schwann cell development. It unravels an elaborate regulatory circuitry that fine-tunes the timing and extent of Schwann cell differentiation and myelin gene expression.Supported by grants of the Deutsche Forschungsgemeinschaft (270949263/GRK2162) to M.K.Deutsche Forschungsgemeinschaf