159 research outputs found
Shear-induced dynamics of polymeric globules at adsorbing homogeneous and inhomogeneous surfaces
The dynamics and adsorption behavior of a single collapsed homopolymer on a
surface in shear flow is investigated by means of Brownian hydrodynamics
simulations. We study different homogeneous and inhomogeneous surface models
and determine dynamic state diagrams as a function of the cohesive strength,
the adhesive strength, and the shear rate. We find distinct dynamical adsorbed
states that are classified into rolling and slipping states, globular and
coil-like states, as well as isotropic and prolate states. We identify two
different cyclic processes based on trajectories of the polymer stretching and
the polymer separation from the surface. For adsorption on an inhomogeneous
surface consisting of discrete binding sites, we observe stick-roll motion for
highly corrugated surface potentials. Although the resulting high surface
friction leads to low drift velocities and reduced hydrodynamic lift forces on
such inhomogeneous surfaces, a shear-induced adsorption is not found in the
presence of full hydrodynamic interactions. A hydrodynamically stagnant
surface model is introduced for which shear-induced adsorption is observed in
the absence of hydrodynamic interactions
Shear-enhanced adsorption of a homopolymeric globule mediated by surface catch bonds
The adsorption of a single collapsed homopolymer onto a planar smooth surface
in shear flow is investigated by means of Brownian hydrodynamics simulation.
While cohesive intra-polymer forces are modeled by Lennard-Jones potentials,
surface-monomer interactions are described by stochastic bonds whose two-state
kinetics is characterized by three parameters: bond formation rate, bond
dissociation rate and an effective catch bond parameter that describes how the
force acting on a surface-monomer bond influences the dissociation rate. We
construct adsorption state diagrams as a function of shear rate and all three
surface-monomer bond parameters. We find shear-induced adsorption in a small
range of parameters for low dissociation and association rates and only when
the surface-monomer bond is near the transition between slip and catch bond
behavior. By mapping on a simple surface-monomer interaction model with
conservative pair potentials we try to estimate the conservative potential
parameters necessary to observe shear-induced surface adsorption phenomena
Internal tension in a collapsed polymer under shear flow and the connection to enzymatic cleavage of von Willebrand factor
By means of Brownian hydrodynamics simulations we show that the tension
distribution along the contour of a single collapsed polymer in shear flow is
inhomogeneous and above a threshold shear rate exhibits a double-peak
structure when hydrodynamic interactions are taken into account. We argue that
the tension maxima close to the termini of the polymer chain reflect the
presence of polymeric protrusions. We establish the connection to shear-
induced globule unfolding and determine the scaling behavior of the maximal
tensile forces and the average protrusion length as a function of shear rate,
globule size, and cohesive strength. A quasi-equilibrium theory is employed in
order to describe the simulation results. Our results are used to explain
experimental data for the shear-sensitive enzymatic degradation of von
Willebrand factor
Cloud Chamber: A Performance with Real Time Two-Way Interaction between Subatomic Particles and Violinist
âCloud Chamberâ - a composition by Alexis Kirke, Antonino Chiaramonte, and Anna Troisi - is a live performance in which the invisible quantum world becomes visible as a violinist and subatomic particle tracks interact together. An electronic instrument was developed which can be âplayedâ live by radioactive atomic particles. Electronic circuitry was developed enabling a violin to create a physical force field that directly affects the ions generated by cosmic radiation particles. This enabled the violinist and the ions to influence each other musically in real time. A glass cloud chamber was used onstage to make radioactivity visible in bright white tracks moving within, with the tracks projected onto a large screen
Physical activity intensity and surrogate markers for cardiovascular health in adolescents
We examined the impact of physical activity (PA) on surrogate markers of cardiovascular health in adolescents. 52 healthy students (28 females, mean age 14.5±0.7years) were investigated. Microvascular endothelial function was assessed by peripheral arterial tonometry to determine reactive hyperemic index (RHI). Vagal activity was measured using 24h analysis of heart rate variability [root mean square of successive normal-to-normal intervals (rMSSD)]. Exercise testing was performed to determine peak oxygen uptake ( ) and maximum power output. PA was assessed by accelerometry. Linear regression models were performed and adjusted for age, sex, skinfolds, and pubertal status. The cohort was dichotomized into two equally sized activity groups (low vs. high) based on the daily time spent in moderate-to-vigorous PA (MVPA, 3,000-5,200 counts.minâ1, model 1) and vigorous PA (VPA, >5,200 counts.minâ1, model 2). MVPA was an independent predictor for rMSSD (ÎČ=0.448, P=0.010), and VPA was associated with maximum power output (ÎČ=0.248, P=0.016). In model 1, the high MVPA group exhibited a higher vagal tone (rMSSD 49.2±13.6 vs. 38.1±11.7ms, P=0.006) and a lower systolic blood pressure (107.3±9.9 vs. 112.9±8.1mmHg, P=0.046). In model 2, the high VPA group had higher maximum power output values (3.9±0.5 vs. 3.4±0.5 Wkgâ1, P=0.012). In both models, no significant differences were observed for RHI and . In conclusion, in healthy adolescents, PA was associated with beneficial intensity-dependent effects on vagal tone, systolic blood pressure, and exercise capacity, but not on microvascular endothelial functio
The Influence of Alloy Composition and Liquid Phase on Foaming of AlâSiâMg Alloys
The foaming behaviour of aluminium alloys processed by the powder compaction technique depends crucially on the exact alloy composition. The AlSi8Mg4 alloy has been in use for a decade now, and it has been claimed that this composition lies in an âisland of good foamingâ. We investigated the reasons for this by systematically studying alloys around this composition by varying the Mg and Si content by a few percent. We applied in situ X-ray 2D and 3D imaging experiments combined with a quantitative nucleation number and expansion analysis, X-ray tomography of solid foams to assess the pore structure and pore size distribution, and in situ diffraction experiments to quantify the melt fraction at any moment. We found a correlation between melt fraction and expansion height and verified that the âisland of good foamingâ actually exists, and foams outside a preferred range for the liquid fractionâjust above TS and between 40â60%âshow a poorer expansion performance than the reference alloy AlSi8Mg4. A very slight increase of Si and decrease of Mg content might further improve this foam
Ratchet effect for nanoparticle transport in hair follicles
The motion of a single rigid nanoparticle inside a hair follicle is investigated by means of Brownian dynamics simulations. The cuticular hair structure is modeled as a periodic asymmetric ratchet-shaped surface. Induced by oscillating radial hair motion we find directed nanoparticle transport into the hair follicle with maximal velocity at a specific optimal frequency and an optimal particle size. We observe flow reversal when switching from radial to axial oscillatory hair motion. We also study the diffusion behavior and find strongly enhanced diffusion for axial motion with a diffusivity significantly larger than for free diffusion
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