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I De Moortel - One of the best experts on this subject based on the ideXlab platform.
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Transverse Wave induced kelvin helmholtz rolls in spicules
The Astrophysical Journal, 2018Co-Authors: Patrick Antolin, D Schmit, T M D Pereira, Bart De Pontieu, I De MoortelAbstract:In addition to their jet-like dynamic behavior, spicules usually exhibit strong Transverse speeds, multi-stranded structure, and heating from chromospheric to transition region temperatures. In this work we first analyze Hinode and IRIS observations of spicules and find different behaviors in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models, or long-Wavelength torsional Alfven Waves. Others exhibit a Doppler shift sign change at maximum displacement and coherent motion of their strands, suggesting a collective magnetohydrodynamic (MHD) Wave. By comparing with an idealized 3D MHD simulation combined with radiative transfer modeling, we analyze the role of Transverse MHD Waves and associated instabilities in spicule-like features. We find that Transverse Wave induced Kelvin–Helmholtz (TWIKH) rolls lead to coherence of strand-like structure in imaging and spectral maps, as seen in some observations. The rapid Transverse dynamics and the density and temperature gradients at the spicule boundary lead to ring-shaped Mg ii k and Ca ii H source functions in the Transverse cross-section, potentially allowing IRIS to capture the Kelvin–Helmholtz instability dynamics. Twists and currents propagate along the spicule at Alfvenic speeds, and the temperature variations within TWIKH rolls, produce the sudden appearance/disappearance of strands seen in Doppler velocity and in Ca ii H intensity. However, only a mild intensity increase in higher-temperature lines is obtained, suggesting there is an additional heating mechanism at work in spicules.
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Transverse Wave induced kelvin helmholtz rolls in spicules
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Patrick Antolin, T M D Pereira, Bart De Pontieu, D J Schmit, I De MoortelAbstract:In addition to their jet-like dynamic behaviour, spicules usually exhibit strong Transverse speeds, multi-stranded structure and heating from chromospheric to transition region temperatures. In this work we first analyse \textit{Hinode} \& \textit{IRIS} observations of spicules and find different behaviours in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models or long Wavelength torsional Alfv\'en Waves. Others exhibit a Doppler shift sign change at maximum displacement and coherent motion of their strands, suggesting a collective MHD Wave. By comparing with an idealised 3-D MHD simulation combined with radiative transfer modelling, we analyse the role of Transverse MHD Waves and associated instabilities in spicule-like features. We find that Transverse Wave Induced Kelvin-Helmholtz (TWIKH) rolls lead to coherence of strand-like structure in imaging and spectral maps, as seen in some observations. The rapid Transverse dynamics and the density and temperature gradients at the spicule boundary lead to ring-shaped \ion{Mg}{2} k and \ion{Ca}{2} H source functions in the Transverse cross-section, potentially allowing IRIS to capture the KHI dynamics. Twists and currents propagate along the spicule at Alfv\'enic speeds, and the temperature variations within TWIKH rolls produce sudden appearance / disappearance of strands seen in Doppler velocity and in \ion{Ca}{2} H intensity. However, only a mild intensity increase in higher temperature lines is obtained, suggesting there is an additional heating mechanism at work in spicules.
S. K. Tomar - One of the best experts on this subject based on the ideXlab platform.
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Wave propagation in elastic plastic material with voids
Journal of Applied Physics, 2020Co-Authors: S. K. Tomar, Suraj KumarAbstract:Constitutive relations and governing equations have been developed for an elastic–plastic material with voids having single slip-plane and direction. The plasticity of the material is considered through the dislocation of slip-plane. The propagation of unidirectional plane Waves has been explored in an infinite elastic–plastic material with voids, and it has been found that there exist four basic Waves consisting of three coupled elastic–plastic Waves and a lone Transverse Wave. The speeds of propagation of all the coupled elastic–plastic Waves are found to be affected by the plasticity and void parameters, in general, while the Transverse Wave is not affected by the plasticity and void parameters at all and travels with the speed of classical Transverse Waves. Out of the three coupled elastic–plastic Waves, two Waves are the counterpart of the Waves existing in elastic materials with voids, while the third Wave is new and has appeared due to the presence of plasticity in the material. One of the coupled elastic–plastic Waves that is least affected by the plasticity faces a critical frequency, below which the Wave is a nonpropagating Wave. This critical frequency arises due to the presence of voids in the medium. The speed of various Waves is computed for a specific model and the results that are obtained are presented graphically. At large frequencies, all the coupled elastic–plastic Waves propagate with constant speeds, but at low frequencies, they propagate with speeds less than that of the longitudinal Wave of classical elasticity. Several earlier known results have been recovered as special cases from the present formulation.
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plane Waves in nonlocal thermoelastic solid with voids
Journal of Thermal Stresses, 2019Co-Authors: Nantu Sarkar, S. K. TomarAbstract:AbstractThis work is concerned with the propagation of time harmonic plane Waves in an infinite nonlocal thermoelastic solid having void pores. Three sets of coupled dilatational Waves and an independent Transverse Wave may travel with distinct speeds in the medium. All these Waves are found to be dispersive in nature, but the coupled dilatational Waves are attenuating, while Transverse Wave is nonattenuating. Coupled dilatational Waves are found to be influenced by the presence of voids, thermal field and elastic nonlocal parameter. While the Transverse Wave is found to be influenced by the nonlocal parameter, but independent of void and thermal parameters. For a particular model, the effects of frequency, void parameters, thermal parameter and nonlocality have been studied numerically on the phase speeds, attenuation coefficients and specific losses of all the propagating Waves. All the computed results obtained have been depicted graphically and explained.
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Waves in nonlocal elastic solid with voids
Journal of Elasticity, 2017Co-Authors: Gurwinderpal Kaur, Dilbag Singh, S. K. TomarAbstract:In this paper, the governing relations and equations are derived for nonlocal elastic solid with voids. The propagation of time harmonic plane Waves is investigated in an infinite nonlocal elastic solid material with voids. It has been found that three basic Waves consisting of two sets of coupled longitudinal Waves and one independent Transverse Wave may travel with distinct speeds. The sets of coupled Waves are found to be dispersive, attenuating and influenced by the presence of voids and nonlocality parameters in the medium. The Transverse Wave is dispersive but non-attenuating, influenced by the nonlocality and independent of void parameters. Furthermore, the Transverse Wave is found to face critical frequency, while the coupled Waves may face critical frequencies conditionally. Beyond each critical frequency, the respective Wave is no more a propagating Wave. Reflection phenomenon of an incident coupled longitudinal Waves from stress-free boundary surface of a nonlocal elastic solid half-space with voids has also been studied. Using appropriate boundary conditions, the formulae for various reflection coefficients and their respective energy ratios are presented. For a particular model, the effects of non-locality and dissipation parameter (\(\tau \)) have been depicted on phase speeds and attenuation coefficients of propagating Waves. The effect of nonlocality on reflection coefficients has also been observed and shown graphically.
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reflection and transmission of elastic Waves at an elastic porous solid saturated by two immiscible fluids
International Journal of Solids and Structures, 2006Co-Authors: S. K. Tomar, Ashish AroraAbstract:Wave propagation in a porous elastic medium saturated by two immiscible fluids is investigated. It is shown that there exist three dilatational Waves and one Transverse Wave propagating with different velocities. It is found that the velocities of all the three longitudinal Waves are influenced by the capillary pressure, while the velocity of Transverse Wave does not at all. The problem of reflection and refraction phenomena due to longitudinal and Transverse Wave incident obliquely at a plane interface between uniform elastic solid half-space and porous elastic half-space saturated by two immiscible fluids has been analyzed. The amplitude ratios of various reflected and refracted Waves are found to be continuous functions of the angle of incidence. Expression of energy ratios of various reflected and refracted Waves are derived in closed form. The amplitude ratios and energy ratios have been computed numerically for a particular model and the results obtained are depicted graphically. It is verified that during transmission there is no dissipation of energy at the interface. Some particular cases have also been reduced from the present formulation.
Patrick Antolin - One of the best experts on this subject based on the ideXlab platform.
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Transverse Wave induced kelvin helmholtz rolls in spicules
The Astrophysical Journal, 2018Co-Authors: Patrick Antolin, D Schmit, T M D Pereira, Bart De Pontieu, I De MoortelAbstract:In addition to their jet-like dynamic behavior, spicules usually exhibit strong Transverse speeds, multi-stranded structure, and heating from chromospheric to transition region temperatures. In this work we first analyze Hinode and IRIS observations of spicules and find different behaviors in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models, or long-Wavelength torsional Alfven Waves. Others exhibit a Doppler shift sign change at maximum displacement and coherent motion of their strands, suggesting a collective magnetohydrodynamic (MHD) Wave. By comparing with an idealized 3D MHD simulation combined with radiative transfer modeling, we analyze the role of Transverse MHD Waves and associated instabilities in spicule-like features. We find that Transverse Wave induced Kelvin–Helmholtz (TWIKH) rolls lead to coherence of strand-like structure in imaging and spectral maps, as seen in some observations. The rapid Transverse dynamics and the density and temperature gradients at the spicule boundary lead to ring-shaped Mg ii k and Ca ii H source functions in the Transverse cross-section, potentially allowing IRIS to capture the Kelvin–Helmholtz instability dynamics. Twists and currents propagate along the spicule at Alfvenic speeds, and the temperature variations within TWIKH rolls, produce the sudden appearance/disappearance of strands seen in Doppler velocity and in Ca ii H intensity. However, only a mild intensity increase in higher-temperature lines is obtained, suggesting there is an additional heating mechanism at work in spicules.
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Transverse Wave induced kelvin helmholtz rolls in spicules
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Patrick Antolin, T M D Pereira, Bart De Pontieu, D J Schmit, I De MoortelAbstract:In addition to their jet-like dynamic behaviour, spicules usually exhibit strong Transverse speeds, multi-stranded structure and heating from chromospheric to transition region temperatures. In this work we first analyse \textit{Hinode} \& \textit{IRIS} observations of spicules and find different behaviours in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models or long Wavelength torsional Alfv\'en Waves. Others exhibit a Doppler shift sign change at maximum displacement and coherent motion of their strands, suggesting a collective MHD Wave. By comparing with an idealised 3-D MHD simulation combined with radiative transfer modelling, we analyse the role of Transverse MHD Waves and associated instabilities in spicule-like features. We find that Transverse Wave Induced Kelvin-Helmholtz (TWIKH) rolls lead to coherence of strand-like structure in imaging and spectral maps, as seen in some observations. The rapid Transverse dynamics and the density and temperature gradients at the spicule boundary lead to ring-shaped \ion{Mg}{2} k and \ion{Ca}{2} H source functions in the Transverse cross-section, potentially allowing IRIS to capture the KHI dynamics. Twists and currents propagate along the spicule at Alfv\'enic speeds, and the temperature variations within TWIKH rolls produce sudden appearance / disappearance of strands seen in Doppler velocity and in \ion{Ca}{2} H intensity. However, only a mild intensity increase in higher temperature lines is obtained, suggesting there is an additional heating mechanism at work in spicules.
Bertrand Dubus - One of the best experts on this subject based on the ideXlab platform.
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experimental demonstration of the negative refraction of a Transverse elastic Wave in a two dimensional solid phononic crystal
Applied Physics Letters, 2010Co-Authors: Bruno Morvan, Alain Tinel, A C Hladkyhennion, Jerome Vasseur, Bertrand DubusAbstract:The negative refraction of Transverse elastic Waves is demonstrated experimentally in a two-dimensional phononic crystal (PC) made of a square lattice of cylindrical air cavities in an aluminum matrix. Dispersion curves of elastic Waves in this PC exhibit a unique branch with phase and group velocities of opposite signs in a broad frequency range. Measurement of refraction angles through prismatic PC included in an aluminum block demonstrates negative refraction of elastic Transverse Wave.
G C Herman - One of the best experts on this subject based on the ideXlab platform.
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Waves in linear elastic media with microrotations part 2 isotropic reduced cosserat model
Bulletin of the Seismological Society of America, 2009Co-Authors: Elena F Grekova, M A Kulesh, G C HermanAbstract:In this article, we consider a problem of the surface elastic Wave propagation within the framework of the isotropic Cosserat continuum. The medium deformation in this model is described not only by the displacement vector but also by a kinematically independent rotation vector. We discuss the general solution of equations of motion. This solution describes the following Wave types: longitudinal and Transverse bulk Waves, Rayleigh Wave, surface Transverse Wave in a half-space as well as Lamb Wave and Transverse Wave in a thin layer. Within the framework of Cosserat continuum, both the Rayleigh and surface Transverse Waves in a half-space are dispersive. The Transverse Wave in a thin layer and the surface Transverse Wave in a half-space do not have any analogies in the classical elasticity theory.
