70 research outputs found
Experimental study of pedestrian flow through a bottleneck
In this work the results of a bottleneck experiment with pedestrians are
presented in the form of total times, fluxes, specific fluxes, and time gaps. A
main aim was to find the dependence of these values from the bottleneck width.
The results show a linear decline of the specific flux with increasing width as
long as only one person at a time can pass, and a constant value for larger
bottleneck widths. Differences between small (one person at a time) and wide
bottlenecks (two persons at a time) were also found in the distribution of time
gaps.Comment: accepted for publication in J. Stat. Mec
Diffusion of hydrophobin proteins in solution and interactions with a graphite surface
<p>Abstract</p> <p>Background</p> <p>Hydrophobins are small proteins produced by filamentous fungi that have a variety of biological functions including coating of spores and surface adhesion. To accomplish these functions, they rely on unique interface-binding properties. Using atomic-detail implicit solvent rigid-body Brownian dynamics simulations, we studied the diffusion of HFBI, a class II hydrophobin from <it>Trichoderma reesei</it>, in aqueous solution in the presence and absence of a graphite surface.</p> <p>Results</p> <p>In the simulations, HFBI exists in solution as a mixture of monomers in equilibrium with different types of oligomers. The oligomerization state depends on the conformation of HFBI. When a Highly Ordered Pyrolytic Graphite (HOPG) layer is present in the simulated system, HFBI tends to interact with the HOPG layer through a hydrophobic patch on the protein.</p> <p>Conclusions</p> <p>From the simulations of HFBI solutions, we identify a tetrameric encounter complex stabilized by non-polar interactions between the aliphatic residues in the hydrophobic patch on HFBI. After the formation of the encounter complex, a local structural rearrangement at the protein interfaces is required to obtain the tetrameric arrangement seen in HFBI crystals. Simulations performed with the graphite surface show that, due to a combination of a geometric hindrance and the interaction of the aliphatic sidechains with the graphite layer, HFBI proteins tend to accumulate close to the hydrophobic surface.</p
Mutual Information for the Detection of Crush
Fatal crush conditions occur in crowds with tragic frequency. Event organizers and architects are often criticised for failing to consider the causes and implications of crush, but the reality is that both the prediction and prevention of such conditions offer a significant technical challenge. Full treatment of physical force within crowd simulations is precise but often computationally expensive; the more common method of human interpretation of results is computationally âcheapâ but subjective and time-consuming. This paper describes an alternative method for the analysis of crowd behaviour, which uses information theory to measure crowd disorder. We show how this technique may be easily incorporated into an existing simulation framework, and validate it against an historical event. Our results show that this method offers an effective and efficient route towards automatic detection of the onset of crush
Martensite-to-austenite reversion and recrystallization in cryogenically-rolled type 321 metastable austenitic steel
The annealing behavior of cryogenically-rolled type 321 metastable austenitic steel was established. Cryogenic deformation gave rise to martensitic transformation which developed preferentially within deformation bands. Subsequent annealing in the range of 600 C to 700 C resulted in reversion of the strain-induced martensite to austenite. At 800 C, the reversion was followed by static recrystallization. At relatively-low temperatures, the reversion was characterized by a very strong variant selection, which led to the restoration of the crystallographic orientation of the coarse parent austenite grains. An increase in the annealing temperature relaxed the variant-selection tendency and provided subsequent recrystallization thus leading to significant grain refinement. Nevertheless, a significant portion of the original coarse grains was found to be untransformed and therefore the fine-grain structure was fairly heterogeneous
EBSD characterization of cryogenically rolled type 321 austenitic stainless steel
Electron backscatter diffraction was applied to investigate microstructure evolution during cryogenic rolling of type 321 metastable austenitic stainless steel. As expected, rolling promoted deformation-induced martensitic transformation which developed preferentially in deformation bands. Because a large fraction of the imposed strain was accommodated by deformation banding, grain refinement in the parent austenite phase was minimal. The martensitic transformation was found to follow a general orientation relationship, {111}Îł||{0001}Δ||{110}αâČ and ă110ăÎł||ă11-20ăΔ||ă111ăαâČ, and was characterized by noticeable variant selection
Sample preparation challenges with highly metastable ferritic-austenitic stainless steels
Abstract
The effects of different sample preparation techniques on a set of laboratory hot-rolled and thermally cycled ferritic-austenitic stainless steels containing 19â20 wt.% Cr have been studied. The differences in chemical composition led to different volume fractions of ferrite and austenite and austenite stabilities, which were characterized using composition-based estimates of Md30 and Ms temperatures. The sample preparation methods were combined mechanical and chemical polishing, electrolytical polishing and ion beam cross section polishing. The ferrite-austenite phase ratio and tendency for phase transformation varied with the chemical composition of the steel. Electropolishing is shown to be the only sample preparation method not to cause martensite formation in samples containing metastable austenite.Herausforderungen bei der ProbenprĂ€paration von hochmetastabilen ferritisch-austenitischen EdelstĂ€hlen
Die Auswirkungen unterschiedlicher PrĂ€parationstechniken an einer Reihe von im Labor warmgewalzten und thermisch wechselbelasteten ferritisch-austenitischen EdelstĂ€hlen mit 19â20 wt.% Cr wurden untersucht. Die Unterschiede der chemischen Zusammensetzung fĂŒhrten zu unterschied-lichen Volumenanteilen und ferritischen und austenitischen StabilitĂ€ten, die mithilfe von kompositionsbasierten SchĂ€tzungen der Md30- und Ms-Temperaturen charakterisiert wurden. Die PrĂ€parationsmethode fĂŒr die Probe bestand aus einer Kombination aus mechanischem und chemischem Polieren, elektrolytischem Polieren und Ionenstrahl-Querschliff-Polieren. Das ferritisch-austenitische PhasenverhĂ€ltnis und die Tendenz zur Phasentransformation variierte ja nach chemischer Zusammensetzung des Stahls. Es wird gezeigt, dass Elektropolieren die einzige Methode zur ProbenprĂ€paration ist, bei der sich kein Martensit in den Proben bildet, die metastabilen Austenit enthalten
Structural analysis of vascular endothelial growth factor receptor-2/ligand complexes by small-angle X-ray solution scattering
Receptor tyrosine kinases play essential roles in tissue development and homeostasis, and aberrant signaling by these molecules is the basis of many diseases. Understanding the activation mechanism of these receptors is thus of high clinical relevance. We investigated vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs), which regulate blood and lymph vessel formation. We analyzed the structural changes in the extracellular receptor domain that were induced by ligand binding and that represent the initial step in transmembrane signaling, culminating in the activation of the intracellular receptor kinase domain. High-resolution structural information for the ligand binding domain became available recently, but the flexibility of the extracellular domain and inhomogeneous glycosylation of VEGFRs have prevented the production of highly diffracting crystals of the entire extracellular domain so far. Therefore, we chose to further investigate VEGFR structure by small-angle X-ray scattering in solution (SAXS). SAXS data were combined with independent distance restraint determination obtained by mass spectrometric analysis of chemically cross-linked ligand/receptor complexes. With these data, we constructed a structural model of the entire extracellular receptor domain in the unbound form and in complex with VEGF
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