scholarly journals Probing of molecular replication and accumulation in shallow heat gradients through numerical simulations

2016 ◽  
Vol 18 (30) ◽  
pp. 20153-20159 ◽  
Author(s):  
Lorenz Keil ◽  
Michael Hartmann ◽  
Simon Lanzmich ◽  
Dieter Braun
Keyword(s):  
Numerical Simulations ◽  
Temperature Gradients ◽  
Porous Rocks ◽  
Highly Efficient ◽  
Temperature Oscillations ◽  
Molecular Replication

Shallow temperature gradients across porous rocks drive highly efficient molecular accumulation processes while simultaneously subjecting them to frequent temperature oscillations.

scholarly journals Cardiac Spiral Wave Drifting Due to Spatial Temperature Gradients – a Numerical Study

2018 ◽  
Author(s):  
Guy Malki ◽  
Sharon Zlochiver
Keyword(s):  
Numerical Simulations ◽  
Single Cell ◽  
Numerical Study ◽  
Spiral Wave ◽  
Spiral Waves ◽  
Temperature Gradients ◽  
Effect Of Temperature ◽  
Local Perturbation ◽  
Marginal Effect ◽  
Spatial Temperature

ABSTRACTCardiac rotors are believed to be a major driver source of persistent atrial fibrillation (AF), and their spatiotemporal characterization is essential for successful ablation procedures. However, electrograms guided ablation have not been proven to have benefit over empirical ablation thus far, and there is a strong need of improving the localization of cardiac arrhythmogenic targets for ablation. A new approach for characterize rotors is proposed that is based on induced spatial temperature gradients (STGs), and investigated by theoretical study using numerical simulations. We hypothesize that such gradients will cause rotor drifting due to induced spatial heterogeneity in excitability, so that rotors could be driven towards the ablating probe. Numerical simulations were conducted in single cell and 2D atrial models using AF remodeled kinetics. STGs were applied either linearly on the entire tissue or as a small local perturbation, and the major ion channel rate constants were adjusted following Arrhenius equation. In the AF-remodeled single cell, recovery time increased exponentially with decreasing temperatures, despite the marginal effect of temperature on the action potential duration. In 2D models, spiral waves drifted with drifting velocity components affected by both temperature gradient direction and the spiral wave rotation direction. Overall, spiral waves drifted towards the colder tissue region associated with global minimum of excitability. A local perturbation with a temperature of T=28°C was found optimal for spiral wave attraction for the studied conditions. This work provides a preliminary proof-of-concept for a potential prospective technique for rotor attraction. We envision that the insights from this study will be utilize in the future in the design of a new methodology for AF characterization and termination during ablation procedures.

Analytical description of low-frequency electron density and temperature oscillations

1996 ◽  
Vol 55 (1) ◽  
pp. 25-34 ◽  
Author(s):  
P. Frank ◽  
M. Beckmann ◽  
G. Himmel
Keyword(s):  
Electron Density ◽  
Fluid Model ◽  
Low Frequency ◽  
Analytical Description ◽  
Frequency Instability ◽  
Temperature Gradients ◽  
Temperature Oscillations ◽  
Electron Density And Temperature ◽  
Two Fluid Model ◽  
The Magnetic Field

Low-frequency density and temperature oscillations (ω « νj, ωcj, where νj is the collision frequency with neutrals and ωcj is the cyclotron frequency; j = i, e) observed in magnetized radiofrequency-produced plasmas with electron density and temperature gradients across the magnetic field are analysed using a local two-fluid model. This model incorporates the electron energy equation. The resulting dispersion relation permits study of the parameter dependence of the complex angular wave frequency. Instability is found in the case where the election density and temperature gradients have opposite signs. This instability is classified as a low-frequency drift wave, and the criteria for its onset are obtained.

Generalization of Gassmann equations for porous media saturated with a solid material

Geophysics ◽  
2007 ◽  
Vol 72 (6) ◽  
pp. A75-A79 ◽  
Author(s):  
Radim Ciz ◽  
Serge A. Shapiro
Keyword(s):  
Numerical Simulations ◽  
Elastic Properties ◽  
Pore Space ◽  
Viscoelastic Model ◽  
Solid Material ◽  
Filling Material ◽  
Porous Rocks ◽  
Pore Filling ◽  
Effective Elastic Properties ◽  
New Model

Gassmann equations predict effective elastic properties of an isotropic homogeneous bulk rock frame filled with a fluid. This theory has been generalized for an anisotropic porous frame by Brown and Korringa’s equations. Here, we develop a new model for effective elastic properties of porous rocks — a generalization of Brown and Korringa’s and Gassmann equations for a solid infill of the pore space. We derive the elastic tensor of a solid-saturated porous rock considering small deformations of the rock skeleton and the pore infill material upon loading them with the confining and pore-space stresses. In the case of isotropic material, the solution reduces to two generalized Gassmann equations for the bulk and shear moduli. The applicability of the new model is tested by independent numerical simulations performed on the microscale by finite-difference and finite-element methods. The results show very good agreement between the new theory and the numerical simulations. The generalized Gass-mann model introduces a new heuristic parameter, characterizing the elastic properties of average deformation of the pore-filling solid material. In many cases, these elastic moduli can be substituted by the elastic parameters of the infill grain material. They can also represent a proper viscoelastic model of the pore-filling material. Knowledge of the effective elastic properties for such a situation is required, for example, when predicting seismic velocities in some heavy oil reservoirs, where a highly viscous material fills the pores. The classical Gassmann fluid substitution is inapplicable for a configuration in which the fluid behaves as a quasi-solid.

scholarly journals Dynamic seismic signatures of saturated porous rocks containing two orthogonal sets of fractures: theory versus numerical simulations

2018 ◽  
Vol 213 (2) ◽  
pp. 1244-1262 ◽  
Author(s):  
Junxin Guo ◽  
J Germán Rubino ◽  
Stanislav Glubokovskikh ◽  
Boris Gurevich
Keyword(s):  
Numerical Simulations ◽  
Porous Rocks ◽  
Theory Versus

Experimental and Numerical Study of Solidification in Constant and Oscillating Temperature Gradients

2003 ◽  
Author(s):  
Y. Shu ◽  
B. Q. Li
Keyword(s):  
Numerical Simulations ◽  
Numerical Study ◽  
Numerical Models ◽  
Experimental System ◽  
Temperature Gradients ◽  
Working Fluid ◽  
Set Up ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Planar Solidification

Transient finite element models are developed to describe solidification of materials in constant and oscillating temperature gradients. Both moving grids and fixed methods are applied, with the former intended to model the near-planar solidification front, while the latter for complex solid-liquid interface morphology. Extensive numerical simulations are conducted for various configurations. To validate the model predictions, an experimental system has been set up with Succinonitrile (SCN) as a working fluid. The melt flows and solidification are measured using a laser PIV system. The measurements are compared well with numerical results obtained from the numerical models. Reasonably good agreement between the experimental measurements and numerical simulations is obtained.

Unexpected segregation patterns in high speed granular flows

2020 ◽  
Author(s):  
Alexandre Valance ◽  
Renaud Delannay ◽  
Aurelien Neveu
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Granular Flows ◽  
Temperature Gradients ◽  
Dense Core ◽  
Segregation Pattern ◽  
Granular Temperature ◽  
Confined Geometry ◽  
Large Particles ◽  
Convection Rolls

<p align="JUSTIFY">Classically, for free surface flows of binary granular mixture, large particles migrate at the top of the flow while small ones percolate to the bottom. The key mechanisms at the origin of this segregation behavior have been identified as a combination of squeeze expulsion and kinetic sieving (Savage & Lun J. Fluid Mech. 1988). In this case, the segregation process is governed by the gravity. We <span>discovered</span> here by means of numerical simulations a new segregation pattern in high speed granular flows where size segregation is driven mostly by granular temperature gradients rather than gravity, which highlight the complexity of providing a complete description of segregation processes.</p><p align="JUSTIFY">High speed granular flows are obtained by means of discrete numerical simulations (DEM) in a confined geometry with lateral frictional side-walls. Recently, Brodu et al. (Phys. Rev. E 2013, J. Fluid Mech. 2015) highlighted that this confined geometry allows to produce steady and fully-developed flows at relatively high angles of inclination, including a rich and broad variety of new regimes. In particular, they showed the existence of supported regimes, characterized by a dense and cold (in terms of granular temperature) core floating over a dilute and highly agitated layer of grains, accompanied with longitudinal convection rolls.</p><p align="JUSTIFY">We performed extensive numerical simulations within this geometry with binary mixture of spheres with a given size ratio of 2. We analyzed segregation patterns of steady and fully-developed flows for inclination angles ranging from 18° to 50° and various mixture proportions of large particles ranging from 0 to 100%. We evidenced a new segregation pattern that emerge in the supported flow regimes: large particles no longer accumulate in the upper layers of the flow but are trapped in the dense core and localized at the center of the convection rolls. The strong temperature gradients that develop between the dense core and the surrounding dilute layer seem to govern the segregation mechanism. The accumulation of large particles in the dense core, which is the fastest region of the flow, also tends to enhance the total mass flux in comparison with similar mono-disperse flows.</p>

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