Long-wavelength electromagnetic propagation in heterogeneous media

1980 ◽  
Vol 21 (6) ◽  
pp. 2248-2266 ◽  
Author(s):  
W. Lamb ◽  
D. M. Wood ◽  
N. W. Ashcroft
Keyword(s):  
Heterogeneous Media ◽  
Electromagnetic Propagation ◽  
Long Wavelength

scholarly journals Homogenization of piezoelectric planar Willis materials

2021 ◽  
Author(s):  
Alan Muhafra ◽  
Majd Kosta ◽  
Daniel Torrent Martí ◽  
René Pernas Salomón ◽  
Gal Shmuel
Keyword(s):  
Heterogeneous Media ◽  
Effective Properties ◽  
Constitutive Relations ◽  
Piezoelectric Composites ◽  
Long Wavelength ◽  
Equivalent Models ◽  
Homogenized Model ◽  
Arbitrary Frequency ◽  
Momentum Coupling ◽  
Physical Laws

Homogenization theories provide models that simplify the constitutive relations of heterogeneous media while retaining their macroscopic features. These theories have shown how the governing fields can be macroscopically coupled, even if they are microscopically independent. A prominent example is the Willis theory which predicted the strain-momentum coupling in elastodynamic metamaterials. Recently, a theory that is based on the Green’s function method predicted analogous electro-momentum coupling in piezoelectric metamaterials. Here, we develop a simpler scheme for fibrous piezoelectric composites undergoing antiplane shear waves. We employ a source- driven approach that delivers a unique set of effective properties for arbitrary frequency-wavevector pairs. We numerically show how the resultant homogenized model recovers exactly the dispersion of free waves in the composite. We also compute the effective properties in the long-wavelength limit and off the dispersion curves, and show that the resultant model satisfy causality, reciprocity and energy conservation. By contrast, we show how equivalent models that neglect the electromomentum coupling violate these physical laws.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

Modern optics of long-wavelength neutrons

1991 ◽  
Vol 161 (11) ◽  
pp. 95 ◽  
Author(s):  
A.I. Frank
Keyword(s):  
Long Wavelength
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