scholarly journals Scattering mechanisms, relaxation times, and shear viscosity in universal anomalous transport of unitary Fermi gases

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Hang Zhou ◽  
Hang Dong ◽  
Yongli Ma
Keyword(s):  
Shear Viscosity ◽  
Relaxation Times ◽  
Anomalous Transport ◽  
Fermi Gases ◽  
Scattering Mechanisms

Dependence of the dynamic properties of elastohydrodynamic liquids on temperature and pressure (volume)

2010 ◽  
Vol 224 (12) ◽  
pp. 2568-2576 ◽  
Author(s):  
S Bair
Keyword(s):  
Shear Viscosity ◽  
Scaling Function ◽  
Dynamic Properties ◽  
Relaxation Times ◽  
Elastohydrodynamic Lubrication ◽  
Time Dependent ◽  
Essential Property ◽  
Scaling Parameters ◽  
Temperature And Pressure ◽  
Low Shear

Shear viscosity is an essential property of elastohydrodynamic lubrication (EHL) liquids. Relaxation times that govern shear dependence of viscosity, time-dependent shear response, and time-dependent bulk behaviour all scale with temperature and pressure in the same way as does the low-shear viscosity. An accurate description of the temperature, pressure, and shear dependence of viscosity has, however, been missing from EHL analysis since the very beginning of the field resulting in many invalid conclusions. In this article, a generalized version of the Stickel plot is introduced and many empirical models are placed in their relevant region of the temperature and pressure domains by showing where they belong on the Stickel plot. The models that are capable of predicting both temperature and pressure responses are discussed in terms of scaling parameters and an example of a mineral oil from the 1953 ASME viscosity report is used to demonstrate the utility of the scaling parameter models. The Stickel analysis is shown to be extremely useful in identifying the appropriate scaling function.

scholarly journals Electron spin flip scattering in graphene due to substrate impurities

2013 ◽  
Vol 1505 ◽  
Author(s):  
Aditi Goswami ◽  
Yue Liu ◽  
Feilong Liu ◽  
P. Paul Ruden ◽  
Darryl L. Smith
Keyword(s):  
Electric Field ◽  
Cross Sections ◽  
Relaxation Times ◽  
Orbit Interaction ◽  
Spin Orbit ◽  
Spin Orbit Interaction ◽  
Scattering Mechanisms ◽  
Spin Flip ◽  
Perpendicular Component ◽  
Scattering Cross Sections

ABSTRACTGraphene is a promising material for electronic and spintronic applications due to its high carrier mobility and low intrinsic spin-orbit interaction. However, extrinsic effects may easily dominate intrinsic scattering mechanisms. The scattering mechanisms investigated here are associated non-magnetic, charged impurities in the substrate (e.g. SiO2) beneath the graphene layer. Such impurities cause an electric field that extends through the graphene and has a non-vanishing perpendicular component. Consequently, the impurity, in addition to the conventional elastic, spin-conserving scattering can give rise to spin-flip processes. The latter is a consequence of a spatially varying Rashba spin-orbit interaction caused by the electric field of the impurity in the substrate. Scattering cross-sections are calculated and, for assumed impurity distributions, relaxation times are estimated.

Effect of Elastic Properties of the Fluids on the Particle Settling Velocity

2017 ◽  
Author(s):  
Sumanth Kumar Arnipally ◽  
Ergun Kuru
Keyword(s):  
Elastic Properties ◽  
Shear Viscosity ◽  
Settling Velocity ◽  
Relaxation Times ◽  
Average Diameter ◽  
Spherical Particles ◽  
Molecular Weights ◽  
Elastic Fluids ◽  
The Impact ◽  
Elastic Characteristics

An experimental study was performed to investigate the influence of fluid elastic properties on the settling velocity of spherical particles in viscoelastic polymer fluids. The Particle Image Shadowgraph (PIS) technique was used to measure the settling velocity of the spherical particles (with average diameter of 2mm) in the hydrolyzed poly acrylamide (HPAM) polymer test fluids. Test fluids were prepared by mixing 3 different grades of HPAM (with molecular weights of; 500,000; 8,000,000; and 20,000,000) at polymer concentrations of 0.09 and 0.1% by weight. Shear viscosity and oscillatory measurements were carried out to characterize the test fluids. The test fluids were formulated in such a way that they had almost identical shear viscosity characteristics while showing significantly different elastic properties. The relaxation time was used to quantify the elastic characteristics of the fluids. To quantify the impact of elasticity, the experimentally measured settling velocities were compared to the values calculated by using the model developed for predicting settling velocity of spherical particles in power law (visco-inelastic) fluids [1]. Experimental results indicated that the settling velocity of spherical particles in visco-elastic fluids decreased significantly with the increasing elasticity (measured in terms of relaxation times) of the fluids.

Relaxation-Time Approximation

2018 ◽  
Author(s):  
Klaus Morawetz
Keyword(s):  
Thermal Conductivity ◽  
Exact Solution ◽  
Relaxation Time ◽  
Boltzmann Equation ◽  
Band Structure ◽  
Shear Viscosity ◽  
Relaxation Times ◽  
Time Approximation ◽  
Relaxation Time Approximation ◽  
Experimental Values

A conserving relaxation time approximation is presented resulting into a Mermin-type of polarisation functions. The transport properties are calculated for the relaxation time approximation and an arbitrary band structure. The results for metals and gases are discussed and the shortcoming of relaxation time approximation to describe experimental values is outlined. As improvement, the exact solution of the linearised quantum Boltzmann equation is presented leading to momentum-depended relaxation times specific for each observable. Explicit expressions are given for the electric and thermal conductivity as well as the shear viscosity.

Relaxation times of polymer solutions in the semidilute region for zero-shear viscosity

1988 ◽  
Vol 21 (7) ◽  
pp. 2257-2262 ◽  
Author(s):  
Yoshiaki Takahashi ◽  
Masanari Umeda ◽  
Ichiro Noda
Keyword(s):  
Shear Viscosity ◽  
Polymer Solutions ◽  
Relaxation Times ◽  
Zero Shear Viscosity

scholarly journals Shear viscosity to electrical conductivity ratio in the quasiparticle models

2020 ◽  
Vol 229 (22-23) ◽  
pp. 3487-3496
Author(s):  
Valeriya Mykhaylova
Keyword(s):  
Electrical Conductivity ◽  
Cross Sections ◽  
Shear Viscosity ◽  
Relaxation Times ◽  
Conductivity Ratio ◽  
Transport Parameters ◽  
Strange Quarks ◽  
Effective Masses ◽  
Relaxation Time Approximation ◽  
Quasiparticle Model

AbstractWe examine the temperature dependence of the shear viscosity η to electrical conductivity σ ratio, as well as the specific shear viscosity and the scaled electrical conductivity in QCD with light and strange quarks. Our calculations are performed in kinetic theory under the relaxation time approximation combined with the quasiparticle model. We compute all transport parameters using the isotropic and transport cross sections and compare our results to a class of quasiparticle models for the QGP with Nf = 2 + 1. The results depending on different schemes are examined. The ratio (η∕s)∕(σ∕T) quantifies the relation between the relaxation times of gluons and quarks and specifies their comparative role in the evolution of the QGP. We find an excellent agreement with the (η∕s)∕(σ∕T) ratio deduced from the dynamical quasiparticle model in which the quasiparticles are characterized not only by their effective masses but also by finite widths.

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