Search results for "Viscosity."

Investigation and modeling of the anomalous yield point phenomenon in pure tantalum

2014

International audience; The monotonic and cyclic behavior of commercially pure tantalum has been investigated at room temperature, in order to capture and understand the occurrence of the anomalous yield point phenomenon. Interrupted tests have been performed, with strain reversals (tensile or compressive loading) after an aging period. The stress drop is attributed to the interactions between dislocations and solute atoms (oxygen) and its macroscopic occurrence is not systematically observed. InfraRed Thermography (IRT) measurements supported by Scanning Electron Microscopy (SEM) pictures of the polished gauge length of a specimen during an interrupted tensile test reveal the nucleation an…

Quality control of manufacturing and hot storage of crumb rubber modified binders

2020

The ultimate performance of crumb rubber modified (CRM) binders is linked to the accurate control of the properties during manufacturing and hot storage. However, due to their complexity, asphalt technologists find the characterisation of these materials still challenging. In this study, the adoption of a Dual Helical Ribbon (DHR), a novel mixing/measuring device for rotational viscometers, is proposed for the real-time monitoring of CRM binders during manufacturing and hot storage. According to the laboratory results, manufacturing periods of 45-60 min at 195 degrees, as well as storage temperatures not exceeding 150 degrees C, are recommended for this type of modified binders. (C) 2019 El…

Navier-Stokes equations on an exterior circular domain: construction of the solution and the zero viscosity limit

1997

Abstract In this Note, we consider the limit of Navier-Stokes equations on a circular domain. By an explicit construction of the solution, it is proved that, when viscosity goes to zero, solution converges to the Euler solution outside the boundary layer and to the Prandtl solution inside the boundary layer.

Optimal Impulse Control When Control Actions Have Random Consequences

1997

We consider a generalised impulse control model for controlling a process governed by a stochastic differential equation. The controller can only choose a parameter of the probability distribution of the consequence of his control action which is therefore random. We state optimality results relating the value function to quasi-variational inequalities and a formal optimal stopping problem. We also remark that the value function is a viscosity solution of the quasi-variational inequalities which could lead to developments and convergence proofs of numerical schemes. Further, we give some explicit examples and an application in financial mathematics, the optimal control of the exchange rate…

Verzweigungsgrad und viskositätszahl bei polystyrolen

1961

Das Quadrat des Tragheitsradius r2 eines verzweigten Molekuls ist gegenuber dem des unverzweigten Molekuls r02 um den Faktor g = r2/r02 herabgesetzt. Hieraus ergibt sich nach ZIMM und KILB eine Verringerung der Viskositatszahl (STAUDINGER-Index) um den Betrag Diese Beziehung wird an Polystyrolen verschiedenen Verzweigungsgrades nachgepruft. Hierzu werden trifunktionell verzweigte Polystyrole mit definiertem Verzweigungsgrad hergestellt. Die relative Ubertragungskonstante am Polystyrol wurde fruher durch reaktionskinetische Messungen zu Cpol = 1,9·10−4 bei 60°C bestimmt. Die Kenntnis dieser Grose ermoglicht es, durch thermische Polymerisation bis zu verschieden hohen Umsatzen unverzweigte Po…

Computer Simulations of the Dynamics of Amorphous Silica

1999

We present the results of a large scale computer simulation we performed to investigate the dynamical properties of supercooled silica. We show that parallel supercomputers such as the CRAY-T3E are very well suited to solve these type of problems. We find that at low temperatures the transport properties such as the diffusion constants and the viscosity agree well with the experimental data. At high temperatures this simulation predicts that in the transport quantities significant deviations from the Arrhenius law should be observed. Finally we show that such types of simulations can be used to investigate also complex dynamical quantities, such as the dynamical structure factor, and that t…

Magnetic microrods as a tool for microrheology

2015

International audience; Dynamics of superparamagnetic rods in crossed constant and alternating magnetic fields as a function of field frequency are studied and it is shown that above the critical value of the amplitude of the alternating field the rod oscillates around the direction of the alternating field. The fit of the experimentally measured time dependence of the mean orientation angle of the rod allows one to determine the ratio of magnetic and viscous torques which act on the rod. The protocol of microrheological measurements consists of recording the dynamics of the orientation of the rod when the magnetic field is applied at an angle to the rod and observing its relaxation due to …

Discontinuous thinning in active microrheology of soft complex matter

2016

Employing theory and numerical simulations, we demonstrate discontinuous force thinning due to the driven motion of an external probe in a host medium. We consider two cases: an ideal structureless medium (modeling ultrasoft materials such as polymer melts) and a dilute bath of interacting repulsive particles. When the driving of the probe exceeds a critical force, the microviscosity of the medium drops abruptly by about an order of magnitude. This phenomenon occurs for strong attractive interactions between a large probe and a sufficiently dense host medium.

Red cell phospholipids and membrane microviscosity in diabetics

2016

Fluorescence Probes Exhibit Photoinduced Structural Planarization: Sensing <i>in vitro</i> and <i>in vivo</i> Microscopic Dyn…

2019

We demonstrate the construction of wavelength λ-ratiometric images that allow visualizing the distribution of microscopic dynamics within living cells and tissues by using the newly developed principle of fluorescence response. The bent-to-planar motion in the excited state of incorporated fluorescence probes leads to elongation of the π-delocalization, resulting in microviscosity-dependent but polarity-insensitive interplay between well-separated blue and red bands in emission spectra. This allows constructing the exceptionally contrasted images of cellular dynamics. Moreover, the application of probes with increased affinity towards biological membranes allowed detecting the differences i…