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.

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.

scholarly journals Exploring the Partonic Phase at Finite Chemical Potential in and out-of Equilibrium

Particles ◽  
2020 ◽  
Vol 3 (1) ◽  
pp. 178-192 ◽  
Author(s):  
O. Soloveva ◽  
P. Moreau ◽  
L. Oliva ◽  
V. Voronyuk ◽  
V. Kireyeu ◽  
...  
Keyword(s):  
Cross Sections ◽  
Chemical Potential ◽  
Transport Coefficients ◽  
Gluon Plasma ◽  
Entropy Density ◽  
Baryon Chemical Potential ◽  
Equilibrium Study ◽  
200 Gev ◽  
Quasiparticle Model ◽  
Scattering Cross Sections

We study the influence of the baryon chemical potential μ B on the properties of the Quark–Gluon–Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature T c from lattice Quantum Chromodynamics (QCD). We study the transport coefficients such as the ratio of shear viscosity η and bulk viscosity ζ over entropy density s, i.e., η / s and ζ / s in the ( T , μ ) plane and compare to other model results available at μ B = 0 . The out-of equilibrium study of the QGP is performed within the Parton–Hadron–String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections based on the DQPM and the evaluated at actual temperature T and baryon chemical potential μ B in each individual space-time cell where partonic scattering takes place. The traces of their μ B dependences are investigated in different observables for symmetric Au + Au and asymmetric Cu + Au collisions such as rapidity and m T -distributions and directed and elliptic flow coefficients v 1 , v 2 in the energy range 7.7 GeV ≤ s N N ≤ 200 GeV.

scholarly journals Universal mobility characteristics of graphene originating from charge scattering by ionised impurities

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jonathan H. Gosling ◽  
Oleg Makarovsky ◽  
Feiran Wang ◽  
Nathan D. Cottam ◽  
Mark T. Greenaway ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Carrier Density ◽  
Carrier Mobility ◽  
Carrier Transport ◽  
Analytical Models ◽  
Pristine Graphene ◽  
High Electron ◽  
Boltzmann Transport ◽  
Transport Parameters ◽  
Wide Range

AbstractPristine graphene and graphene-based heterostructures can exhibit exceptionally high electron mobility if their surface contains few electron-scattering impurities. Mobility directly influences electrical conductivity and its dependence on the carrier density. But linking these key transport parameters remains a challenging task for both theorists and experimentalists. Here, we report numerical and analytical models of carrier transport in graphene, which reveal a universal connection between graphene’s carrier mobility and the variation of its electrical conductivity with carrier density. Our model of graphene conductivity is based on a convolution of carrier density and its uncertainty, which is verified by numerical solution of the Boltzmann transport equation including the effects of charged impurity scattering and optical phonons on the carrier mobility. This model reproduces, explains, and unifies experimental mobility and conductivity data from a wide range of samples and provides a way to predict a priori all key transport parameters of graphene devices. Our results open a route for controlling the transport properties of graphene by doping and for engineering the properties of 2D materials and heterostructures.

Molten fatty acid salts as model ionic liquids. I. Thermodynamic and transport parameters of some organic sodium salts

1971 ◽  
Vol 322 (1550) ◽  
pp. 281-299 ◽  
Keyword(s):  
Electrical Conductivity ◽  
Transport Parameters ◽  
Sodium Propionate ◽  
Isotropic Liquid ◽  
Enthalpy Changes ◽  
Physical Measurements ◽  
Ionic Melts ◽  
Ionic Solids ◽  
Steep Decrease ◽  
Transition Points

Procedures are described for maintaining good chemical stability in molten alkali-metal carboxylates, up to about 350 °C. Valid physical measurements can be made and the fluids can be used up to about this temperature, above which spontaneous decomposition of the anions is difficult to repress. Molten sodium propionate has a useful liquid range of about 60 °C and sodium isobutyrate of about 90 °C. Sodium n -butyrate transforms into a ‘liquid crystal’ at about 250 °0 and into the isotropic liquid at 324 °C. For sodium isovalerate corresponding transition points are respectively 188 and 280 °C. Thermodynamic measurements are reported of volume and enthalpy changes at transition and melting points. Transport parameters measured include the viscosity and the electrical conductivity. The viscosity of these ionic melts undergoes a steep decrease at the transition from mesomorphic to isotropic liquids. Jumps in ionic conductivity are found both at the melting and clearing points. Even for the isotropic liquids, the ratio of viscosity to electrical conductivity is exceptionally high, compared with the other ionic melts. Mechanisms of melting for these ionic solids are discussed.

scholarly journals Shear viscosity η to electrical conductivity σel ratio for an anisotropic QGP

2017 ◽  
Vol 95 (9) ◽  
Author(s):  
Lata Thakur ◽  
P. K. Srivastava ◽  
Guru Prakash Kadam ◽  
Manu George ◽  
Hiranmaya Mishra
Keyword(s):  
Electrical Conductivity ◽  
Shear Viscosity

scholarly journals Turbulent drag reduction by polymer additives in parallel-shear flows

2017 ◽  
Vol 827 ◽  
Author(s):  
Bayode E. Owolabi ◽  
David J. C. Dennis ◽  
Robert J. Poole
Keyword(s):  
Drag Reduction ◽  
Cross Sections ◽  
Shear Flows ◽  
Extensional Flow ◽  
Relaxation Times ◽  
Weissenberg Number ◽  
Mechanical Degradation ◽  
Turbulent Drag Reduction ◽  
Time Resolved ◽  
Turbulent Drag

In this study, we experimentally investigate the turbulent drag-reduction (DR) mechanism in flow through ducts of circular, rectangular and square cross-sections using two grades of polyacrylamide in aqueous solution having different molecular weights and various semidilute concentrations. Specifically, we explore the relationship between drag reduction and fluid elasticity, purposely exploiting the mechanical degradation of polymer molecules to vary their rheological properties. We also obtain time-resolved velocity data for various DR levels using particle image velocimetry and laser Doppler velocimetry. Elasticity is quantified via relaxation times determined from uniaxial extensional flow using a capillary breakup apparatus. A plot of DR against Weissenberg number ($Wi$) is found to approximately collapse the data, with the onset of DR occurring at $Wi\approx 0.5$ and the maximum drag-reduction asymptote being approached for $Wi\gtrsim 5$. Thus quantitative predictions of DR in a range of shear flows can be made from a single measurable material property of a polymer solution, at least for this particular flexible linear polymer.

The Effects of Hall and Ion Slip on the Electrical Conductivity of Partially Ionized Gases for Magnetohydrodynamic Re-Entry Vehicle Application

1962 ◽  
Vol 84 (2) ◽  
pp. 177-184 ◽  
Author(s):  
M. J. Brunner
Keyword(s):  
Electrical Conductivity ◽  
Cross Sections ◽  
Effective Conductivity ◽  
Ionized Gas ◽  
Equilibrium Conditions ◽  
Degree Of Ionization ◽  
Slip Effects ◽  
Wide Range ◽  
Ion Slip ◽  
Partially Ionized

The presence of a partially ionized gas around a hypersonic vehicle permits the application of magnetohydrodynamic (MHD) devices during re-entry. The operation of such MHD devices on a re-entry vehicle will largely depend on the magnitude of the electrical conductivity of the gas between the electrodes. In some cases it may be necessary to seed the air in order to insure high conductivity. The operation of the re-entry vehicle at relatively low gas densities and high magnetic fields will produce Hall and ion slip effects which may materially reduce the effective conductivity between the electrodes. The electrical conductivity including Hall and ion slip effects for air is presented for a wide range of pressures and temperatures and for a typical re-entry vehicle, with and without seeding. The electrical conductivity is evaluated for equilibrium conditions considering the number density and collision cross sections for electrons, neutrals, and ions. The Hall and ion slip effects are evaluated from the degree of ionization, the cyclotron frequency, and the time between collisions for electrons, neutrals, and ions.

scholarly journals Quark-flavor dependence of the shear viscosity in a quasiparticle model

2019 ◽  
Vol 100 (3) ◽  
Author(s):  
Valeriya Mykhaylova ◽  
Marcus Bluhm ◽  
Krzysztof Redlich ◽  
Chihiro Sasaki
Keyword(s):  
Shear Viscosity ◽  
Quark Flavor ◽  
Quasiparticle Model
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