scholarly journals Nonlinear hydromagnetic convection in a moderate prandtl number fluid

1981 ◽  
Vol 23 (3) ◽  
pp. 321-338 ◽  
Author(s):  
N. Riahi
Keyword(s):  
Prandtl Number ◽  
Lorentz Force ◽  
Strong Field ◽  
Inertial Force ◽  
Weak Field ◽  
Wave Number ◽  
Boundary Layer Method ◽  
Horizontal Wave ◽  
Moderate Field ◽  
Moderate Prandtl Number Fluid

Nonlinear hydromagnetic connection is investigated using the modal equations for cellular convection. The boundary layer method is used assuming large Rayleigh number R, moderate Prandtl number σ and for different ranges of the Chandrasekhar number Q. The heat flux F is determined for the value of the horizontal wave number which maximizes F. For a weak field, the inertial force dominates over the Lorentz force. F is independent of Q, but it increases with R and σ. For a moderate field, the Lorentz force is significant. F increases with R and σ and decreases as Q increases. For a strong field, the Lorentz force dominates over the inertial force. F is independent of σ, but it increases with R and decreases as Q increases.

scholarly journals Nonlinear Magnetic Convection at Small Prandtl Numbers

1981 ◽  
Vol 34 (3) ◽  
pp. 251 ◽  
Author(s):  
N Riahi
Keyword(s):  
Strong Field ◽  
Weak Field ◽  
Wave Number ◽  
Layer Method ◽  
Boundary Layer Method ◽  
Moderate Field ◽  
Magnetic Convection ◽  
Prandtl Numbers ◽  
Chandrasekhar Number ◽  
Large Rayleigh Number

Nonlinear magnetic convection is investigated using the modal equations for cellular convection. The boundary layer method is used assuming large Rayleigh number R and small Prandtl number a for different ranges of the Chandrasekhar number Q. The heat flux F is determined for the value of the wave number which maximizes F. For a weak field, F is independent of Q but increases with Ra; for a moderate field, F decreases with Q but increases with R and a; for a strong field, F decreases with Q, increases with R and is ndependent of a. F eventually becomes 0(1) as Q 4- OCR), and the layer becomes stable.

Spherical shell rotating convection in the presence of a toroidal magnetic field

1995 ◽  
Vol 448 (1933) ◽  
pp. 245-268 ◽  
Keyword(s):  
Magnetic Field ◽  
Prandtl Number ◽  
Spherical Shell ◽  
Lorentz Force ◽  
Thermal Convection ◽  
Toroidal Magnetic Field ◽  
Wave Number ◽  
Convective Motions ◽  
Magnetic Convection ◽  
Convection Rolls

Convective instabilities of a self-gravitating, rapidly rotating fluid spherical shell are investigated in the presence of an imposed azimuthal axisymmetric magnetic field in the form of the toroidal decay mode that satisfies electrically insulating boundary conditions and has dipole symmetry. Concentration is on two major questions: how purely thermal convection of the different forms (Zhang 1992, 1994) is affected by the Lorentz force, the strength of which is measured by the Elsasser number ∧, and in what manner purely magnetic instabilities in a spherical shell (Zhang & Fearn 1993, 1994) are associated with magnetic convection. It is found that the two-dimensionality of purely thermal convection (Busse 1970) survives under the influence of a strong Lorentz force. Convective motions always attempt to satisfy the Proudman–Taylor constraint and remain predominantly two-dimensional in the whole range of ∧, 0 ≤ ∧ ≤ ∧ c , where ∧ c ═ O (10) is the critical Elsasser number for purely magnetic instabilities. Though the optimum azimuthal wave number m of convection rolls decreases drastically, from m ~ O ( T 1/6 ) at ∧ ═ 0 to m ═ O (5) at ∧ ═ O (1). We show that there exist no optimum values of ∧ that can give rise to an overall minimum of the (modified) Rayleigh number R *; the optimum value of R * is a monotonically, smoothly decreasing function of ∧, from R * ═ O ( T 1/6 ) at ∧ < O ( T -1/6 ) to R * ═ O (–10) at ∧ ═ 20. We also show that the influence of the magnetic field on thermal convection is crucially dependent on the size of the Prandtl number. At sufficiently small Prandtl number, the Poincaré convection mode (Zhang 1994) is preferred in the region 0 ≤ ∧ < ∧ c , and is only slightly affected by the presence of the toroidal magnetic field. Analytical solutions of the magnetic convection problem are then obtained based on a perturbation analysis, showing a good agreement with the numerical solution.

Nonlinear Double-diffusive Convection in a Moderate Prandtl Number Fluid

1981 ◽  
Vol 34 (2) ◽  
pp. 185
Author(s):  
N Riahi
Keyword(s):  
Rayleigh Number ◽  
Prandtl Number ◽  
Double Diffusive Convection ◽  
Layer Method ◽  
Diffusive Convection ◽  
Solute Fluxes ◽  
Boundary Layer Method ◽  
Moderate Prandtl Number Fluid ◽  
Large Rayleigh Number ◽  
Double Diffusive

Recent work on nonlinear double-diffusive convection in a low Prandtl number fluid is extended to the case of a moderate Prandtl number G'. The boundary layer method is used by assuming a large Rayleigh number R for different ranges of the diffusivity ratio -c and the solute Rayleigh number R; It is found that the heat and solute fluxes F and F; increase with G', Rand n;', and that F; F- 1 is independent of G'. The flow is shown to have a solute layer of thickness proportional to F-1-2, The horizontal wavenumber which maximizes F is found to be independent of G', but it increases with Rand R;1

Thermocapillary convection in a differentially heated annular pool for moderate Prandtl number fluid

2004 ◽  
Vol 43 (6) ◽  
pp. 587-593 ◽  
Author(s):  
You-Rong Li ◽  
Lan Peng ◽  
Shuang-Ying Wu ◽  
Dan-Ling Zeng ◽  
Nobuyuki Imaishi
Keyword(s):  
Prandtl Number ◽  
Thermocapillary Convection ◽  
Annular Pool ◽  
Moderate Prandtl Number Fluid

scholarly journals The confrontation between general relativity and experiment

2009 ◽  
Vol 5 (S261) ◽  
pp. 198-199
Author(s):  
Clifford M. Will
Keyword(s):  
General Relativity ◽  
Gravitational Wave ◽  
Equivalence Principle ◽  
Gamma Ray ◽  
Strong Field ◽  
Weak Field ◽  
X Ray ◽  
Spacetime Geometry ◽  
Tests Of General Relativity ◽  
Laser Interferometric

AbstractWe review the experimental evidence for Einstein's general relativity. A variety of high precision null experiments confirm the Einstein Equivalence Principle, which underlies the concept that gravitation is synonymous with spacetime geometry, and must be described by a metric theory. Solar system experiments that test the weak-field, post-Newtonian limit of metric theories strongly favor general relativity. Binary pulsars test gravitational-wave damping and aspects of strong-field general relativity. During the coming decades, tests of general relativity in new regimes may be possible. Laser interferometric gravitational-wave observatories on Earth and in space may provide new tests via precise measurements of the properties of gravitational waves. Future efforts using X-ray, infrared, gamma-ray and gravitational-wave astronomy may one day test general relativity in the strong-field regime near black holes and neutron stars.

scholarly journals Iron Complexes of a Proton-Responsive SCS Pincer Ligand with Sensitive Electronic Structure

2021 ◽  
Author(s):  
Kazimer Skubi ◽  
Reagan Hooper ◽  
Brandon Mercado ◽  
Melissa Bollmeyer ◽  
Samantha MacMillan ◽  
...  
Keyword(s):  
Strong Field ◽  
Alkali Metal Cation ◽  
Weak Field ◽  
Pincer Ligands ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Pincer Ligand ◽  
Intermediate Spin ◽  
X Ray Absorption ◽  
Phosphine Complex

SCS pincer ligands have an interesting combination of strong-field and weak-field donors that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a protonresponsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex. The N–H bond dissociation free energy can be quantitated as 56 ± 2 kcal/mol. EPR spectroscopy and SQUID magnetometry measurements show that the iron(III) complexes with S and N as the fourth donors have an intermediate spin (S = 3/2) ground state with large zero field splitting, and X-ray absorption spectra show high Fe–S covalency. The Mössbauer spectrum changes drastically with the position of a nearby alkali metal cation in the iron(III) amido complex, and DFT calculations explain this phenomenon through a change between having the doubly-occupied orbital as dz2 or dyz, as the former is more influenced by the nearby positive charge.

scholarly journals Maintaining Constant Pulse-Duration in Highly Dispersive Media Using Nonlinear Potentials

Photonics ◽  
2021 ◽  
Vol 8 (12) ◽  
pp. 570
Author(s):  
Haider Zia
Keyword(s):  
Strong Field ◽  
Propagation Distance ◽  
Weak Field ◽  
Dispersive Media ◽  
Signal Pulse ◽  
Nonlinear Phenomenon ◽  
Numerical Example ◽  
Ultrafast Optical ◽  
Nonlinear Potentials ◽  
Temporal Broadening

A method is shown for preventing temporal broadening of ultrafast optical pulses in highly dispersive and fluctuating media for arbitrary signal-pulse profiles. Pulse pairs, consisting of a strong-field control-pulse and a weak-field signal-pulse, co-propagate, whereby the specific profile of the strong-field pulse precisely compensates for the dispersive phase in the weak pulse. A numerical example is presented in an optical system consisting of both resonant and gain dispersive effects. Here, we show signal-pulses that do not temporally broaden across a vast propagation distance, even in the presence of dispersion that fluctuates several orders of magnitude and in sign (for example, within a material resonance) across the pulse’s bandwidth. Another numerical example is presented in normal dispersion telecom fiber, where the length at which an ultrafast pulse does not have significant temporal broadening is extended by at least a factor of 10. Our approach can be used in the design of dispersion-less fiber links and navigating pulses in turbulent dispersive media. Furthermore, we illustrate the potential of using cross-phase modulation to compensate for dispersive effects on a signal-pulse and fill the gap in the current understanding of this nonlinear phenomenon.

scholarly journals Experimental Investigation on Hydrodynamic Coefficients of a Column-Stabilized Fish Cage in Waves

2019 ◽  
Vol 7 (11) ◽  
pp. 418
Author(s):  
Zhao ◽  
Chen ◽  
Bi ◽  
Cui
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Drag Force ◽  
Inertial Force ◽  
Element Model ◽  
Wave Force ◽  
Hydrodynamic Coefficients ◽  
Horizontal Wave ◽  
Horizontal Wave Force ◽  
The Finite Element Model

This study on hydrodynamic coefficients of a column-stabilized fish cage under wave action plays an important role in the anti-wave design of cages. The regular wave test was used to study the horizontal wave force of the jacket and column-stabilized fish cage under different wave heights, periods, and incident angles; the finite element model of the jacket and the column-stabilized fish cage was established according to the test model. On the basis of the calculation of the finite element model, combined with the wave force obtained from the experiment, the hydrodynamic coefficients of the structure was fitted by the least squares method, and then the drag force, inertial force, and total force of the structure under different conditions were calculated. The results show that the hydrodynamic coefficients of the jacket and netting under the wave condition were more obvious with the change of the KC number and wave incident angles. And as the wave height increased, the drag force, the inertial force, and the proportion of the drag force to the horizontal wave force both increased. When the wavelength was large, the same trend occured as the wave period increased. When the wave incident angles were different, the forces of the jacket and the column-stabilized fish cage were always small in lateral low-frequency waves, which is consistent with the change law of hydrodynamic coefficients of the jacket and netting.

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