The Effects of Collisions with Neutral Particles on the Instability of Two Superposed Composite Plasmas Streaming Through Porous Medium

1999 ◽  
Vol 54 (6-7) ◽  
pp. 411-416 ◽  
Author(s):  
Mohamed Fahmy El-Sayed
Keyword(s):  
Porous Medium ◽  
Unstable Mode ◽  
Instability Criterion ◽  
Stable Configuration ◽  
Neutral Particles ◽  
Fluid Velocities ◽  
Stability And Instability ◽  
The Stability ◽  
The Magnetic Field

Abstract The effects of collisions with neutral atoms on the hydromagnetic stability of the plane interface separating two streaming superposed composite plasmas of uniform densities in a porous medium are investigated. In the absence of fluid velocities, it is found, for a potentially stable configuration, that the system remains stable, while for a potentially unstable configuraion, the unstable system becomes stable under a certain condition of the wavenumber depending on the values of the fluid densities, Alfvén velocities, and the orientation of the magnetic field. The porosity of the porous medium does not have any significant effect on the stability criterion. In the presence of fluid velocities, it is found that, the instability criterion is independent of the permeability of the medium and the collision effects with neutral particles. The criterion determing the stability does not depend on the permeability of the medium but depends on the density of neutral particles. The porosity of the medium is found to have a significant effect on both the stability and instability criteria in this case. The role of the permeability of the medium, the collisional frequency, and the porosity of the porous medium on the growth rate of the unstable mode is examined analitically. Routh’s test of stability is applied to confirm the above results.

Magnetohydrodynamic Stability of Two Streaming Superposed Viscoelastic Conducting Fluids

2001 ◽  
Vol 56 (6-7) ◽  
pp. 416-439
Author(s):  
Mohamed Fahmy El
Keyword(s):  
Magnetic Field ◽  
Stable Configuration ◽  
Retardation Time ◽  
Horizontal Magnetic Field ◽  
Fluid Velocities ◽  
Unstable Configuration ◽  
The Stability ◽  
The Magnetic Field ◽  
Conducting Fluids ◽  
Alfven Velocity

Abstract The stability of the plane interface separating two Oldroydian viscoelastic superposed moving fluids of uniform densities when immersed in a uniform horizontal magnetic field has been in­ vestigated. The stability analysis has been carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities. It is found that the potentially stable configuration remains stable if the fluids are at rest, while it becomes unstable if the fluids move. The stability criterion is found to be independent of the viscosity and viscoelasticity, and to be dependent on the orientation of the magnetic field and the magnitudes of the fluids and Alfven velocities. It is also found that the potentially unstable configuration remains unstable in the absence of average fluid velocities, or in the presence of fluid velocities and absence of a magnetic field. The magnetic field is found to stabilize a certain wavenumbers range of the unstable configuration even in the presence of the effects of viscoelasticity. The behaviour of growth rates with respect to the stress relaxation time, strain retardation time, fluid and Alfven velocity parameters is examined analytically, and the stability conditions are obtained and discussed. -Pacs: 47.20.-k; 47.50.+d; 47.65.+a.

scholarly journals Hydromagnetic Instability of Two Viscoelastic Dusty-Fluids in Porous Medium

2021 ◽  
Vol 16 ◽  
pp. 137-144
Author(s):  
Pardeep Kumar ◽  
Sumit Gupta
Keyword(s):  
Magnetic Field ◽  
Porous Medium ◽  
Suspended Particles ◽  
Stable Configuration ◽  
Number Density ◽  
Horizontal Magnetic Field ◽  
Two Fluids ◽  
Medium Permeability ◽  
The Stability ◽  
The Magnetic Field

An attempt has been made to investigate the instability of the plane interface between two viscoelastic superposed conducting fluids in the presence of suspended particles and variable horizontal magnetic field through porous medium is studied. The cases of two fluids of uniform densities, viscosities, magnetic fields, and suspended particles number densities separated by a horizontal boundary; and of exponentially varying density, viscosity, suspended particles number density, and magnetic field are considered. It is found that the stability criterion is independent of the effects of viscoelasticity, medium porosity, and suspended particles but is dependent on the orientation and magnitude of the magnetic field. The magnetic field succeeds in stabilizing a certain range of wavenumbers which were unstable in the absence of the magnetic field. The system is found to be stable for potentially stable configuration/stratification. The growth rates are found to increase (for certain wavenumbers) and decrease (for other wavenumbers) with the increase in kinematic viscosity, suspended particles number density, magnetic field, medium permeability and stress relaxation time.

scholarly journals Instability of compressible drops and jets

2012 ◽  
Vol 700 ◽  
pp. 441-458 ◽  
Author(s):  
Umpei Miyamoto
Keyword(s):  
Surface Tension ◽  
Unstable Mode ◽  
Mode Analysis ◽  
Instability Criterion ◽  
Classic Problem ◽  
Perfect Fluids ◽  
Spatial Dimensions ◽  
Minimal Radius ◽  
The Stability ◽  
Self Gravity

AbstractWe revisit the classic problem of the stability of drops and jets held by surface tension, while regarding the compressibility of bulk fluids and spatial dimensions as free parameters. By mode analysis, it is shown that there exists a critical compressibility above which the drops (and discs) become unstable for a spherical perturbation. For a given value of compressibility (and of the surface tension and the density at equilibrium), this instability criterion provides a minimal radius below which the drop cannot be in stable equilibrium. According to the existence of the above unstable mode of the drop, which corresponds to a homogeneous perturbation of a cylindrical jet, the dispersion relation of Rayleigh–Plateau instability for cylinders drastically changes. In particular, we identify another critical compressibility above which the homogeneous unstable mode is predominant. The analysis is carried out for non-relativistic and relativistic perfect fluids, the self-gravity of which is ignored.

Hydromagnetic stability of a compressible jet

1975 ◽  
Vol 14 (3) ◽  
pp. 443-448 ◽  
Author(s):  
B. B. Chakraborty ◽  
H. K. S. Iyengar
Keyword(s):  
Magnetic Field ◽  
Dispersion Relation ◽  
Magnetic Fields ◽  
Axial Direction ◽  
Vortex Sheet ◽  
Fluid Velocities ◽  
The Stability ◽  
Axisymmetric Disturbances ◽  
Jet Velocities ◽  
The Magnetic Field

This paper studies the hydromagnetic stability of a cylindrical jet of a perfectly-conducting, inviscid and compressible fluid. The fluid velocities and magnetic fields, inside and outside the jet, are uniform and in the axial direction, with possible discontinuities in their values across the jet surface. For large wavelength disturbances, the jet behaves as though it were incompressible. Numerical evaluation of the roots of the dispersion relation for a number of different magnetic-field strengths and jet velocities, but for disturbances of finite ranges of wavenumbers, indicates that the jet is stable against axisymmetric disturbances, but instability is present for asymmetric disturbances when the magnetic fields are sufficiently small. The magnetic field is found to have a stabilizinginfluence when compressibility is not very large; for high compressibility, it may have even a destabilizing effect. The paper explains physically the roles of compressibility and the magnetic field in bringing about the stability of the jet. When the wavelengths of disturbances are small, the dispersion relation reduces to that for a two-dimensional jet and a vortex sheet; and the results for these cases are known from earlier studies.

scholarly journals CHEMISORPTION OF ENROFLOXACIN ON RUTILE-TIO2 (110) SURFACE: A THEORETICAL INVESTIGATION

2019 ◽  
Vol 57 (4) ◽  
pp. 449
Author(s):  
Trung Tien Nguyen ◽  
Tri Ngoc Nguyen ◽  
Dai Quoc Ho
Keyword(s):  
Hydrogen Bond ◽  
Chemical Analysis ◽  
Dft Calculations ◽  
Quantum Chemical ◽  
Adsorption Process ◽  
Stable Configuration ◽  
Quantum Chemical Analysis ◽  
Rutile Tio2 ◽  
The Stability

We investigated the adsorption of enrofloxacin (ENR) antibiotic on rutile-TiO2 (r-TiO2­) (110) surface using DFT calculations. Stable configurations of the adsorption of ENR on r-TiO2 (110) were observed. The origin and role of interactions in stablizing the configurations are thoroughly analyzed using NBO and AIM analyses. Obtained results indicate that the adsorption process is characterized as a strong chemisorption with an associated energy of ca. -35.1 kcal.mol-1 for the most stable configuration. Quantum chemical analysis shows that the stability of configurations is mainly determined by >C=O∙∙∙Ti5f electrostatic interaction along with supplement of H∙∙∙Ob hydrogen bond.

Determinism and Stability in Physics

2018 ◽  
pp. 61-81
Author(s):  
Yemima Ben-Menahem
Keyword(s):  
Quantum Mechanics ◽  
Statistical Mechanics ◽  
Chaos Theory ◽  
Physical Sciences ◽  
Stability And Instability ◽  
Conceptual Relations ◽  
The Stability

This chapter examines the role of stability and determinism in physical theories such as statistical mechanics. In the physical sciences, the notions of stability and instability, no longer camouflaged in the language of necessity and contingency, are often used in a variety of contexts, from chaos theory to quantum mechanics. Physicists consider questions about the stability of states, orbits, and structures to be as fundamental as questions about determinism. Before expounding on the conceptual relations between stability and determinism in physics, the chapter discusses three interconnected problems that statistical mechanics has had to tackle: the meaning of probability in statistical mechanics, the link between probability and a system's dynamics, and the origin of directionality. It shows that the notions of determinism and stability are often conflated, giving rise to teleological thinking.

Rayleigh Taylor instability of a viscous Hall plasma with magnetic field

1972 ◽  
Vol 7 (1) ◽  
pp. 117-132 ◽  
Author(s):  
G. Bhowmik
Keyword(s):  
Magnetic Field ◽  
Variational Principle ◽  
Larmor Frequency ◽  
Field Vector ◽  
Stable Configuration ◽  
Horizontal Magnetic Field ◽  
Wave Numbers ◽  
Hall Plasma ◽  
The Stability ◽  
The Magnetic Field

The influence of finite Larmor frequency on the stability of a viscous, finitely conducting liquid in a downward gravitational field under the influence of a uniform magnetic field directed along or normal to gravity, is investigated. The solution in each case is shown to be characterized by a variational principle Based on the variational principle, an approximate solution is obtained for the stability of a layer of fluid of constant kinematic viscosity and an exponentia density distribution. It has been found that finite resistivity and finite Larmor frequency do not introduce any instabifity in a potentially stable configuration. However, for a potentially unstable configuration we find that, for an ideal Hal plasma, the results depend on the orientation of the magnetic field, though the instability persists for all wave-numbers in the presence of non-ideal (finite resistivity and viscosity) effects. For the field aligned with gravity, it is found that a potentially unstable field-free configuration is stabilized if the buoyancy number B ( = gβ/12 V2) is less than unity. For B > 1, the instability arises for wave-numbers exceeding a critical value, which decreases on allowing for Hall terms in the generalized Ohm's law, suggesting a destabilizing influence of finite Larmor frequency. For an ambient horizontal magnetic field, it is found that an ideal plasma is stable, even for B > 0, for perturbations confined to a cone about the magnetic field vector. The angle of the cone of stable propagation, however, decreases on account of finite Larmor frequency.

scholarly journals The role of curvature in modifying frontal instabilities, part 2

2020 ◽  
Author(s):  
Christian E. Buckingham ◽  
Jonathan Gula ◽  
Xavier Carton
Keyword(s):  
Simple Expression ◽  
Instability Criterion ◽  
Small Scale ◽  
Buoyancy Forcing ◽  
Coherent Vortices ◽  
Stability Maps ◽  
Cyclonic Flow ◽  
The Stability ◽  
Earth System Models

AbstractWe continue our study of the role of curvature in modifying frontal stability. In Part 1, we obtained an instability criterion valid for curved fronts and vortices in gradient wind balance (GWB): Φ′ = L′q′ < 0, where L′ and q′ are the non-dimensional absolute angular momentum and Ertel potential vorticity (PV), respectively. In Part 2, we investigate this criterion in a parameter space representative of low-Richardson number fronts and vortices in GWB. An interesting outcome is that, for Richardson numbers near one, anticyclonic flows increase in q′, while cyclonic flows decrease in q′, tending to stabilize anticyclonic and de-stabilize cyclonic flow. Although stability is marginal or weak for anticyclonic flow (owing to multiplication by L′), the de-stabilization of cyclonic flow is pronounced, and may help to explain an observed asymmetry in the distribution of small-scale, coherent vortices in the ocean interior. We are referring mid-latitude submesoscale and polar mesoscale vortices that are generated by friction and/or buoyancy forcing within boundary layers but that are often documented outside these layers. A comparison is made between several documented vortices and predicted stability maps, providing support for the proposed mechanism. Finally, a simple expression, which is a root of the stability discriminant, Φ′, explains the observed asymmetry in the distribution of vorticity. In conclusion, the generalized criterion is consistent with theory, observations and recent modeling studies, and demonstrates that curvature in low-stratified environments can de-stabilize cyclonic and stabilize anticyclonic fronts and vortices to symmetric instability. The results may have implications for Earth system models.

Nonlinear Electrohydrodynamic Stability of Two Superposed Walters B′ Viscoelastic Fluids in Relative Motion Through Porous Medium

2013 ◽  
Vol 29 (4) ◽  
pp. 569-582 ◽  
Author(s):  
M. F. El-Sayed ◽  
N. T. Eldabe ◽  
M. H. Haroun ◽  
D. M. Mostafa
Keyword(s):  
Surface Tension ◽  
Porous Medium ◽  
Electric Fields ◽  
Multiple Scales ◽  
Landau Equation ◽  
Three Dimensions ◽  
Surface Charges ◽  
Fluid Velocities ◽  
Medium Permeability ◽  
The Stability

ABSTRACTA nonlinear stability of two superposed semi-infinite Walters B′ viscoelastic dielectric fluids streaming through porous media in the presence of vertical electric fields in absence of surface charges at their interface is investigated in three dimensions. The method of multiple scales is used to obtain a Ginzburg-Landau equation with complex coefficients describing the behavior of the system. The stability of the system is discussed both analytically and numerically in linear and nonlinear cases, and the corresponding stability conditions are obtained. It is found, in the linear case, that the surface tension and medium permeability have stabilizing effects, and the fluid velocities, electric fields and kinematic viscoelastici-ties have destabilizing effects, while the porosity of porous medium and kinematic viscosities have dual role on the stability. In the nonlinear case, it is found that the fluid velocities, kinematic viscosities, kinematic viscoelasticities, surface tension and porosity of porous medium have stabilizing effects; while the electric fields and medium permeability have destabilizing effects.

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