The Experts below are selected from a list of 3315 Experts worldwide ranked by ideXlab platform
Grzegorz Wyleżek - One of the best experts on this subject based on the ideXlab platform.
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The Huygens Principle and cosmological gravitational waves in the Regge–Wheeler gauge
Classical and Quantum Gravity, 2005Co-Authors: Edward Malec, Grzegorz WyleżekAbstract:We study the propagation of axial gravitational waves in Friedmann universes. The evolution equation is obtained in the Regge–Wheeler gauge. The gravitational waves obey the Huygens Principle in the radiation-dominated era, but in the matter-dominated universe their propagation depends on their wavelengths, with the scale fixed essentially by the Hubble radius. Short waves practically satisfy the Huygens Principle while long waves can backscatter off the curvature of a spacetime.
Thomas W Noonan - One of the best experts on this subject based on the ideXlab platform.
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Huygens' Principle for the self-adjoint scalar wave equation in Einstein spacetimes
Classical and Quantum Gravity, 2001Co-Authors: Thomas W NoonanAbstract:A necessary condition that the self-adjoint scalar wave equation satisfies Huygens' Principle is that the spacetime should be Einstein.
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Some considerations of the scalar wave equation and Huygens' Principle
Classical and Quantum Gravity, 1996Co-Authors: Thomas W NoonanAbstract:If the scalar wave equation satisfies Huygens' Principle, then it may always be written in the form and a necessary condition on the metric is that the Bach tensor vanishes.
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Huygens' Principle for the wave equation of arbitrary rank
Classical and Quantum Gravity, 1995Co-Authors: Thomas W NoonanAbstract:Previous results regarding the wave equation having a Green's function which satisfies Huygens' Principle are extended to fields of arbitrary rank. The Cotton invariant for any rank must vanish. For a self-adjoint operator on any non-zero rank, a necessary and sufficient condition is that spacetime be flat.
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Huygens' Principle in conformally flat spacetimes
Classical and Quantum Gravity, 1995Co-Authors: Thomas W NoonanAbstract:This paper examines conflicting claims in the literature regarding whether the wave equation satisfies Huygens' Principle in a conformally flat spacetime. It is concluded that in general the wave equation does not satisfy Huygens' Principle, but there is an exception for the case of the electromagnetic field tensor.
Edward Malec - One of the best experts on this subject based on the ideXlab platform.
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The Huygens Principle and cosmological gravitational waves in the Regge–Wheeler gauge
Classical and Quantum Gravity, 2005Co-Authors: Edward Malec, Grzegorz WyleżekAbstract:We study the propagation of axial gravitational waves in Friedmann universes. The evolution equation is obtained in the Regge–Wheeler gauge. The gravitational waves obey the Huygens Principle in the radiation-dominated era, but in the matter-dominated universe their propagation depends on their wavelengths, with the scale fixed essentially by the Hubble radius. Short waves practically satisfy the Huygens Principle while long waves can backscatter off the curvature of a spacetime.
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the Huygens Principle and cosmological gravitational waves in the regge wheeler gauge
arXiv: General Relativity and Quantum Cosmology, 2005Co-Authors: Edward Malec, Grzegorz WylezekAbstract:We study the propagation of axial gravitational waves in Friedman universes. The evolution equation is obtained in the Regge-Wheeler gauge. The gravitational waves obey the Huygens Principle in the radiation dominated era, but in the matter dominated universe their propagation depends on their wavelengths, with the scale fixed essentially by the Hubble radius. Short waves practically satisfy the Huygens Principle while long waves can backscatter off the curvature of a spacetime.
Gianluigi Tiberi - One of the best experts on this subject based on the ideXlab platform.
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A Phantom Investigation to Quantify Huygens Principle Based Microwave Imaging for Bone Lesion Detection
Electronics, 2019Co-Authors: Banafsheh Khalesi, Behnaz Sohani, Sandra Dudley, Mohammad Ghavami, Navid Ghavami, Gianluigi TiberiAbstract:This paper demonstrates the outcomes of a feasibility study of a microwave imaging procedure based on the Huygens Principle for bone lesion detection. This study has been performed using a dedicated phantom and validated through measurements in the frequency range of 1–3 GHz using one receiving and one transmitting antenna in free space. Specifically, a multilayered bone phantom, which is comprised of cortical bone and bone marrow layers, was fabricated. The identification of the lesion’s presence in different bone layers was performed on images that were derived after processing through Huygens’ Principle, the S21 signals measured inside an anechoic chamber in multi-bistatic fashion. The quantification of the obtained images was carried out by introducing parameters such as the resolution and signal-to-clutter ratio (SCR). The impact of different frequencies and bandwidths (in the 1–3 GHz range) in lesion detection was investigated. The findings showed that the frequency range of 1.5–2.5 GHz offered the best resolution (1.1 cm) and SCR (2.22 on a linear scale). Subtraction between S21 obtained using two slightly displaced transmitting positions was employed to remove the artefacts; the best artefact removal was obtained when the spatial displacement was approximately of the same magnitude as the dimension of the lesion.
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Phase-weighted UWB Imaging through Huygens Principle
2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring), 2019Co-Authors: Gianluigi Tiberi, Banafsheh Khalesi, Behnaz Sohani, Sandra Dudley, Mohammad Ghavami, Navid GhavamiAbstract:Phase information is used in many imaging modalities to enhance resolution, such as in magnetic resonance imaging. However, its impact in Ultra-wideband (UWB) microwave imaging is still unexplored. Here, examples using analytical simulations are shown to address the impact of phase information in Huygens Principle (HP) based UWB imaging. Conventional amplitude-weighted HP imaging has a resolution, which achieves the optical resolution limit of λ/4, where $A$ represents the wavelength in the investigation domain calculated at the highest frequency. Simulation results show that HP phase-weighted modality leads to an improvement in the resolution of approximately 30% with respect to the HP amplitude-weighted modality, and to an increase in signal-to-average ratio of approximately 40% with respect to the HP amplitude-weighted modality.
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Huygens Principle based UWB microwave imaging method for skin cancer detection
2016 10th International Symposium on Communication Systems Networks and Digital Signal Processing (CSNDSP), 2016Co-Authors: Navid Ghavami, Gianluigi Tiberi, Sandra Dudley, Mohammad Ghavami, Majella LaneAbstract:In recent years, Ultra Wideband (UWB) technology has emerged as a promising alternative for use in a wide range of applications. One of the potential applications of UWB is in healthcare and imaging, motivated by its non-ionizing signals, low cost, low complexity, and its ability to penetrate through mediums. Moreover, the large bandwidth covered by UWB signals permits the very high resolution required in imaging experiments. In this paper, a recently introduced UWB microwave imaging technique based on the Huygens Principle (HP), has been applied to multilayered skin model with an inclusion representing a tumor. The methodology of HP permits the capture of contrast such that different material properties within the region of interest can be discriminated in the final image, and its simplicity removes the need to solve inverse problems when forward propagating the waves. Therefore the procedure can identify and localize significant scatterers inside a multilayered volume. Validation of the technique through simulations on multilayered cylindrical model of the skin with inclusion representing the tumor has been performed.
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Huygens Principle based imaging of multilayered objects with inclusions
Progress In Electromagnetics Research B, 2014Co-Authors: Navid Ghavami, Gianluigi Tiberi, David J. Edwards, Ahmad Safaai-jazi, Agostino MonorchioAbstract:The application of a recently introduced microwave imaging technique based on the Huygens Principle (HP), has been extended to multilayered objects with inclusions in this paper. The methodology of HP permits the capture of contrast such that difierent material properties within the region of interest can be discriminated in the flnal image, and its simplicity removes the need to solve inverse problems when forward propagating the waves. Therefore the procedure can identify and localize signiflcant scatterers inside a multilayered volume, without having apriori knowledge on the dielectric properties of the target object. Additionally, an analytically-based approach for analyzing UltraWide Bandwidth (UWB) body propagation is presented, where the body is modeled as a 3-layer stratifled cylinder with an eccentric inclusion. Validation of the technique through both simulations and measurements on multilayered cylindrical objects with inclusions has been performed.
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Huygens Principle-based approach for UWB medical imaging
2011Co-Authors: Navid Ghavami, Gianluigi Tiberi, David J. EdwardsAbstract:In this paper, the algorithm of a novel imaging method based on Ultra WideBand (UWB) microwave signals has been developed and presented. The method is based on the Huygens Principle (HP), which removes the need to solve inverse problems and consequently, the need for matrix generation and inversion. Aside from the simplicity of the HP, it enables the detection of the extent to which different tissues, or different types of tissues, can be discriminated and render contrast in the final image. It should be pointed out that prior knowledge of electrical properties of the inclusions is not required when performing the imaging. The validation of HP technique through simulations on cylinders with multiple inclusions, representing realistic examples are presented. Simulation results show that the method successfully identifies the presence and location of significant scatterers within a target volume.
Igor Loutsenko - One of the best experts on this subject based on the ideXlab platform.
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Huygens' Principle in Minkowski Spaces and Soliton Solutions of the Korteweg–de Vries Equation
Communications in Mathematical Physics, 1997Co-Authors: Yuri Berest, Igor LoutsenkoAbstract:A new class of linear second order hyperbolic partial differential operators satisfying Huygens' Principle in Minkowski spaces is presented. The construction reveals a direct connection between Huygens' Principle and the theory of solitary wave solutions of the Korteweg–de Vries equation.
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Huygens Principle in minkowski spaces and soliton solutions of the korteweg de vries equation
arXiv: Exactly Solvable and Integrable Systems, 1997Co-Authors: Yuri Berest, Igor LoutsenkoAbstract:A new class of linear second order hyperbolic partial differential operators satisfying Huygens' Principle in Minkowski spaces is presented. The construction reveals a direct connection between Huygens' Principle and the theory of solitary wave solutions of the Korteweg-de Vries equation.