Articoli di riviste sul tema "Non-Linear wave scattering"
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1
Savotchenko, S. E. "THE LINEAR WAVE SCATTERING BY A NON-LINEAR DEFECT". Belgorod State University Scientific bulletin Mathematics Physics 50, n. 3 (30 settembre 2018): 283–91. http://dx.doi.org/10.18413/2075-4639-2018-50-3-283-291.
2
PETER, MALTE A., e MICHAEL H. MEYLAN. "Water-wave scattering by a semi-infinite periodic array of arbitrary bodies". Journal of Fluid Mechanics 575 (marzo 2007): 473–94. http://dx.doi.org/10.1017/s0022112006004319.
Abstract (sommario):
We consider the scattering by a semi-infinite array of bodies of arbitrary geometry excited by an incident wave in the linear water-wave formulation (which reduces to the simpler case of Helmholtz scattering if the depth dependence can be removed). The theory presented here is extremely general, and we present example calculations for an array of floating elastic plates (a highly non-trivial scatterer). The solution method follows closely from the solution for point scatterers in a medium governed by Helmholtz's equation. We have made several extensions to this theory, considering water-wave scattering, allowing for bodies of arbitrary scattering geometry and showing how to include the effects of bound waves (called Rayleigh–Bloch waves in the water-wave context) in the formulation. We present results for scattering by arrays of cylinders that show the convergence of our methods and also some results for the case of scattering by floating elastic plates and fixed docks.
3
Ghodake, Pravinkumar. "The complexity of harmonically scattered nonlinear waves from triangular, circular, and rectangular corners of the 2-D domain". Journal of the Acoustical Society of America 154, n. 4_supplement (1 ottobre 2023): A262. http://dx.doi.org/10.1121/10.0023468.
Abstract (sommario):
Considering recent advancements in the nonlinear pulse-echo technique, understanding reflected nonlinear waves from inaccessible edges and surfaces becomes important. A unique geometrical model solved numerically using the finite element method is proposed and studied via extensive numerical experiments to gain insight into harmonically scattered waves from different shapes of the 2-D spaced corners considering the challenges of theoretical solutions that can capture the interplay between multiple phenomena. Tang et al. (2012), Kube (2017-18), and Achenbach and Wang (2017-18) studied the harmonic scattering of waves from nonlinear inclusions using analytical techniques. Linear longitudinal waves scattered from the triangular, circular, and rectangular-shaped free and fixed edges of the 2-D spaced corner show mode conversion and energy transfer between bulk wave modes at fundamental frequencies. The interaction of nonlinear ultrasonic waves with the edges makes things complex due to an interplay between harmonic generation, linear scattering, harmonic scattering, bulk wave mode conversion, and harmonic energy redistribution between all harmonics of the scattered longitudinal and transverse waves. This results in non-intuitive interesting responses. These studies are extended to explore one-way and two-way two-wave mixing of longitudinal waves and their interesting nonlinear effects. Phase difference introduced during harmonic scattering distinguishes the sensitivity of fundamental harmonics.
4
Belibassakis, Kostas, e Julien Touboul. "A Nonlinear Coupled-Mode Model for Waves Propagating in Vertically Sheared Currents in Variable Bathymetry—Collinear Waves and Currents". Fluids 4, n. 2 (30 marzo 2019): 61. http://dx.doi.org/10.3390/fluids4020061.
Abstract (sommario):
A novel coupled-mode model is developed for the wave–current–seabed interaction problem, with application in wave scattering by non-homogeneous, sheared currents over general bottom topography. The formulation is based on a velocity representation defined by a series of local vertical modes containing the propagating and evanescent modes, able to accurately treat the continuity condition and the bottom boundary condition on sloping parts of the seabed. Using the above representation in Euler equations, a coupled system of differential equations on the horizontal plane is derived, with respect to the unknown horizontal velocity modal amplitudes. In the case of small-amplitude waves, a linearized version of the above coupled-mode system is obtained, and the dispersion characteristics are studied for various interesting cases of wave–seabed–current interaction. Keeping only the propagating mode in the vertical expansion of the wave potential, the present system is reduced to a one-equation, non-linear model, generalizing Boussinesq models. The analytical structure of the present coupled-mode system facilitates extensions to treat non-linear effects and further applications concerning wave scattering by inhomogeneous currents in coastal regions with general 3D bottom topography.
5
Wongthongsiri, Supawat, e Sohichi Hirose. "Scattering Analysis and Detection of Layered Plate Debonding Using Guided SH Waves with Boundary Element Method". Shock and Vibration 2022 (16 luglio 2022): 1–10. http://dx.doi.org/10.1155/2022/8799555.
Abstract (sommario):
This paper investigates the scattering behavior of guided shear horizontal (SH) waves in a two-dimensional, isotropic, and linear elastic layered plate with partially debonded interface by analyzing the reflection and transmission coefficients of scattered waves. The partial wave technique is established to form the displacement and stress of guided wave functions, and the boundary element method (BEM) is utilized to handle the numerical calculation with elastodynamic fundamental solutions in the frequency domain. After applying proper boundary conditions including continuity condition on the interface with traction-free debonding, the scattering coefficients can be obtained in terms of boundary element solutions. Two different materials (steel and aluminum) with various debonding lengths and locations in a 1 mm double-layered plate are considered. With several modes of the incident wave over a frequency range up to 4.5 MHz, the variations of scattering coefficients and scattering phenomena are numerically investigated as several parameters such as mode of the incident wave, materials, locations, and length of debonding are changed. The numerical results also suggest the potential of the suitable wave mode for the debonding detection, which can be useful for non-destructive inspection.
6
Baltenkov, Arkadiy S., e Igor Woiciechowski. "Interference Phenomenon in Electron-Molecule Collisions". Atoms 10, n. 4 (1 ottobre 2022): 105. http://dx.doi.org/10.3390/atoms10040105.
Abstract (sommario):
This article discusses how the pattern of elastic scattering of an electron on a pair of identical atomic centers is modified if we abandon the assumption, standard in molecular physics, that outside of some molecular sphere surrounding the centers, the wave function of the molecular continuum is atomic-like, being a linear combination of the regular and irregular solutions of the wave equation. For this purpose, the elastic scattering of slow particles by a pair of non- overlapping short-range potentials has been studied. The continuum wave function of the particle is represented as a combination of a plane wave and two spherical s-waves propagating freely throughout space. The asymptotic behavior of this function determines the amplitude of elastic particle scattering in closed form. It is demonstrated that this amplitude can be represented as a partial expansion in a set of the orthonormal functions Zλ(r) other than spherical harmonics Ylm(r). General formulas for these functions are obtained. The coefficients of the scattering amplitude expansion into a series of functions Zλ(r) and determine the scattering phases ηλ(k) for the considered two- atomic target. The special features of the S-matrix method for the case of arbitrary non-spherical potentials are discussed.
7
Li, Hong Liang. "Far Field Solution of Circular Inclusion and Linear Crack by SH-Wave". Key Engineering Materials 462-463 (gennaio 2011): 455–60. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.455.
Abstract (sommario):
Circular inclusion exists widely in natural media, engineering materials and structures, and defects are usually found around the inclusion. When a composite material with circular inclusion and cracks is impacted by the dynamic load, on the one hand, the scattering field produced by the circular inclusion and cracks determines the dynamic stress concentration factor around the circular inclusion, and therefore determines whether the material is damaged or not; on the other hand, the scattering field also presents many characteristic parameters of the inclusion and cracks such as defect composition, location and shape, so the research on the scattering far-field is important to the geological prospects, seismological investigation, non-destruction evaluation and the other fields. In the ocean acoustics, the scattering far-field of the acoustic wave is also used in the under-water survey, object distinguishing and so on. In theory, the scattering solution of elastic waves is one of the basic topics of reverse problems on elastic wave. On the basis of literature, few paper concentrates on the scattering far-field solution of SH-wave by a circular inclusion and a linear crack around the inclusion. In the paper a new model and a new method are presented in order to investigate deeply on this kind problem. The paper uses the Green’s function to study the scattering far-field of an elastic wave by a circular inclusion and a linear crack. The Green’s function should be a fundamental solution of displacement field for an elastic space possessing a circular inclusion while bearing out-of-plane harmonic line source force at any point. In terms of the solution of SH-wave’s scattering by an elastic space with a circular inclusion, anti-plane stresses which are the same in quantity but opposite in direction to those mentioned before, are loaded at the region where the linear crack is in existent actually; Then, the expressions of the displacement and stresses are given when the circular inclusion and linear crack exist at the same time. When the special Green’s function has been constructed and close field solution has been illustrated, the far field of scattered wave is studied. The displacement mode of scattered wave at far field and scattering cross-section are given. At last, an example is given and its numerical results are discussed.
8
Meylan, M. H., e L. G. Bennetts. "Three-dimensional time-domain scattering of waves in the marginal ice zone". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, n. 2129 (20 agosto 2018): 20170334. http://dx.doi.org/10.1098/rsta.2017.0334.
Abstract (sommario):
Three-dimensional scattering of ocean surface waves in the marginal ice zone (MIZ) is determined in the time domain. The solution is found using spectral analysis of the linear operator for the Boltzmann equation. The method to calculate the scattering kernel that arises in the Boltzmann model from the single-floe solution is also presented along with new identities for the far-field scattering, which can be used to validate the single-floe solution. The spectrum of the operator is computed, and it is shown to have a universal structure under a special non-dimensionalization. This universal structure implies that under a scaling wave scattering in the MIZ has similar properties for a large range of ice types and wave periods. A scattering theory solution using fast Fourier transforms is given to find the solution for directional incident wave packets. A numerical solution method is also given using the split-step method and this is used to validate the spectral solution. Numerical calculations of the evolution of a typical wave field are presented. This article is part of the theme issue ‘Modelling of sea-ice phenomena’.
9
Grimshaw, R., L. A. Ostrovsky, A. S. Topolnikov e K. R. Khusnutdinova. "Influence of Internal Wave on the Sound Propagation in the Subsurface Bubble Layer". Proceedings of the Mavlyutov Institute of Mechanics 8, n. 1 (2011): 54–64. http://dx.doi.org/10.21662/uim2011.1.005.
Abstract (sommario):
In the paper the influence of non-linear internal wave on the propagation of acoustic signal in the subsurface ocean layer containing gas bubbles is considered. During interaction with surface waves the internal wave causes its collapse and influences the structure of bubble layer. Inhomogeneous structure of the layer promotes the local speed of sound and intensity of scattering near the ocean surface to modulate by internal wave with slight shift in phase in the direction of its propagation, which agree with recent experimental observations made on the shelf of Japan Sea.
10
ATASSI, O. V., e J. J. GILSON. "Acoustic mode scattering from a heat source". Journal of Fluid Mechanics 651 (30 aprile 2010): 1–26. http://dx.doi.org/10.1017/s0022112010000261.
Abstract (sommario):
The scattering of an incident acoustic wave by a non-uniform mean flow resulting from a heat source is investigated. The heat source produces gradients in the mean flow and the speed of sound that scatter the incident duct acoustic mode into vortical, entropic, and higher-order acoustic modes. Linear solutions utilizing the compact source limit and nonlinear solutions to the Euler equations are computed to understand how variations in the amplitude and axial extent of the heat source as well as the incident acoustic wave propagation angle and amplitude modify the scattered solution. For plane wave excitation, significant entropy waves are produced as the net heat addition increases at the expense of the transmitted acoustic energy. When the net heat addition is held constant, increasing the axial extent of the heat source results in a reduction of the entropy waves produced downstream and a corresponding increase in the downstream scattered acoustic energy. For circumferential acoustic mode excitations the incident acoustic wave angle, characterized by the cutoff ratio, significantly modifies the scattered acoustic energy. As the propagating mode cutoff ratio approaches unity, a rise in the scattered vortical disturbance and a decrease in the entropic disturbance amplitude is observed. As the cutoff ratio increases, the scattered solution approaches the plane wave results. Moreover, incident acoustic waves with different frequencies and circumferential mode orders but similar cutoff ratios yield similar scattered wave coefficients. Finally, for large amplitude incident acoustic waves the scattered solution is modified by nonlinear effects. The pressure field exhibits nonlinear steepening of the wavefront and the nonlinear interactions produce higher harmonic frequency content which distorts the sinusoidal variation of the outgoing scattered acoustic waves.
11
Zhan, Hanyu, Hanwan Jiang e Ruinian Jiang. "Three-dimensional images generated from diffuse ultrasound wave: detections of multiple cracks in concrete structures". Structural Health Monitoring 19, n. 1 (13 marzo 2019): 12–25. http://dx.doi.org/10.1177/1475921719834045.
Abstract (sommario):
The simultaneous detection of multiple defects in concrete structures is a task of pivotal importance for non-destructive testing and evaluation. Diffuse waves experiencing multiple scattering inside media are demonstrated to be sensitive to weak defects. Here, an analytic model is presented for diffuse wave decorrelation associated with sensitivity kernel that describes the time-of-flight distribution in strongly scattering environments. The model is then used for generating three-dimensional images that involve estimating perturbations at each localized position through an iterative, non-linear algorithm. With the consideration of loads and micro-cracks effects on diffuse waves, an application of the approach to a real-size concrete beam shows features that denote the positions and depths of multiple existing cracks. Extension of the approach to other strongly scattering media such as tissues and volcanos is straightforward. This study offers great potential for practical applications such as structural health monitoring, medical image generation, and seismic monitoring.
12
Kadowaki, H., H. Takatsu, T. Taniguchi, B. Fåk e J. Ollivier. "Composite Spin and Quadrupole Wave in the Ordered Phase of Tb2+xTi2-xO7+y". SPIN 05, n. 02 (giugno 2015): 1540003. http://dx.doi.org/10.1142/s2010324715400032.
Abstract (sommario):
The hidden ordered state of the frustrated pyrochlore oxide Tb 2+x Ti 2-x O 7+y is possibly one of the two electric multipolar, or quadrupolar, states of the effective pseudospin-1/2 Hamiltonian derived from crystal-field ground state doublets of non-Kramers Tb 3+ ions. These long-range orders are antiparallel or parallel alignments of transverse pseudospin components representing electric quadrupole moments, which cannot be observed as magnetic Bragg reflections by neutron scattering. However, pseudospin waves of these states are composite waves of the magnetic-dipole and electric-quadrupole moments, and can be partly observed by inelastic magnetic neutron scattering. We calculate these spin-quadrupole waves using linear spin-wave theory and discuss previously observed low-energy magnetic excitation spectra of a polycrystalline sample with x = 0.005(T c = 0.5 K).
13
Sergievskaya, Irina, Stanislav Ermakov, Alexey Ermoshkin, Ivan Kapustin, Alexander Molkov, Olga Danilicheva e Olga Shomina. "Modulation of Dual-Polarized X-Band Radar Backscatter Due to Long Wind Waves". Remote Sensing 11, n. 4 (19 febbraio 2019): 423. http://dx.doi.org/10.3390/rs11040423.
Abstract (sommario):
Investigation of microwave scattering mechanisms is extremely important for developing methods for ocean remote sensing. Recent studies have shown that a common two-scale scattering model accounting for resonance (Bragg) scattering has some drawbacks, in particular it often overestimates the vertical-to-horizontal polarization radar return ratio and underestimates the radar Doppler shifts if the latter are assumed as associated with quasi linear resonance surface waves. It is supposed nowadays that radar backscattering at moderate incidence angles is determined not only by resonance Bragg mechanism but also contains non polarized (non Bragg) component which is associated supposedly with wave breaking but which is still insufficiently studied. Better understanding of the scattering mechanisms can be achieved when studying variations of radar return due to long wind waves. In this paper, results of experiments from an Oceanographic Platform on the Black Sea using dual co-polarized X-band scatterometers working at moderate incidence are presented and variations of Bragg and non-Bragg components (BC and NBC, respectively) and radar Doppler shifts are analysed. It is established that BC and NBC are non-uniformly distributed over profile of dominant (decametre-scale) wind waves (DWW). Variations of BC are characterized by some “background” return weakly modulated with the dominant wind wave periods, while NBC is determined mostly by rare and strong spikes occurred near the crests of the most intense individual waves in groups of DWW. We hypothesize that the spikes are due to intensification of nonlinear structures on the profile of short, decimetre-scale wind waves when the latter are amplified by intense DWW. Bragg scattering in slicks under the experimental conditions was suppressed stronger than NBC and spikes dominated in total radar return. It is obtained that radar Doppler shifts at HH-polarization are larger than at VV-polarization, particularly in slicks, the same relation is for NBC and BC Doppler shifts, thus indicating different scattering mechanisms for these components.
14
Tsidulko, Yuriy A., e Ivan S. Chernoshtanov. "Nonlinear Stage of Alfvén Ion-Cyclotron Instability". Siberian Journal of Physics 5, n. 3 (1 ottobre 2010): 90–94. http://dx.doi.org/10.54362/1818-7919-2010-5-3-90-94.
Abstract (sommario):
A model describing nonlinear saturated state of Alfvén ion-cyclotron instability is presented. Spirally symmetric exact solutions of Vlasov – Maxwell equations describing nonlinear Alfvén waves in collisionless plasmas are presented. On their basis the equation describing ion distribution function in non-linear equilibrium of a weak-collision plasma with the wave is obtained, taking into account an uniform fast ion injection, ion drag caused by electrons and neglecting ion angle scattering. A solution of this equation and relations of the wave parameters with the injection parameters are obtained analytically in the case of the infinitely narrow velocity distribution of the injected ions
15
Ginibre, J., e G. Velo. "Scattering theory in the energy space for a class of non-linear wave equations". Communications in Mathematical Physics 123, n. 4 (dicembre 1989): 535–73. http://dx.doi.org/10.1007/bf01218585.
16
Singh, Mansi, e R. Gayen. "Hydrodynamic response of dual obliquely submerged non-uniform flexible thin plates". IOP Conference Series: Materials Science and Engineering 1288, n. 1 (1 agosto 2023): 012008. http://dx.doi.org/10.1088/1757-899x/1288/1/012008.
Abstract (sommario):
Abstract Examining inclined flexible plates with variable thickness becomes crucial when it comes to optimizing or achieving controlled reflection and transmission of waves, especially for the construction of breakwaters. Unlike horizontal breakwaters, inclined barriers have the ability to penetrate through numerous layers of the fluid, having different particle velocities and foster their interactions. This causes wave breaking which leads to loss of wave energy. Also, despite exhibiting a similar behavior, vertical structures do not attenuate waves as effectively as inclined ones do. Additionally, the resonant motion of the fluid trapped between two structures proves to enhance the attenuation, thus it is recommended to include dual structures in the model rather than just one. Therefore in the present study, we examine the water wave scattering phenomenon by a pair of symmetric flexible thin plates with non-uniform thickness obliquely submerged in deep water. We use the linear water wave theory and Kirchhoff’s thin plate theory to model the physical problem. The boundary value problem is converted into a system of coupled integral equations using repeated integration and Green’s integral theorem. Using appropriate approximations, this system is solved and its solutions are used to determine numerical values of different hydrodynamic quantities. Results of two horizontal as well as two vertical plates could be obtained from the present model, thus it is a very general model. Also results are illustrated to analyze the contribution of the thickness variation and the inclinations of the two flexible plates towards the wave scattering process and some related physical quantities.
17
Goel, D., P. Chauhan, A. Varshney e V. Sajal. "Parametric excitation of surface plasma waves by stimulated Compton scattering of laser beam at metal-free space interface". Laser and Particle Beams 34, n. 3 (27 giugno 2016): 467–73. http://dx.doi.org/10.1017/s0263034616000343.
Abstract (sommario):
AbstractAn obliquely incident high-power laser (ω0,k0z) on the metallic surface can resonantly excite a surface plasma wave (SPW) (ω1,k1z) and a quasi-electrostatic plasma wave (ω,kz) inside the skin layer at the phase-matching conditions of frequency ω1= ω − ω0and wave numberk1z=kz−k0z. The oscillating electrons in the skin layer couples with the seed SPW and exert non-linear ponderomotive force on electrons at the frequency of quasi-static mode. Density perturbations due to quasi-static mode and ponderomotive force associate with the motion of electrons (due to incident laser) and give rise to a non-linear current by feedback mechanism. At ω/kz~vF(wherevFis the Fermi velocity of metal) this non-linear current is responsible for the growth of SPW. The maximum growth of the present process (≅1.5 × 1012s−1) is achieved at incident angle θ = 42° for laser frequency ω0= 2 × 1015rad/s. Growth of SPW enhances from 1.62 × 1011to ≅1.5 × 1012s−1as the magnetic field changes from 12 to 24 MG. The excited SPW can be utilized for surface heating and diagnostics purpose.
18
Riaz, Muhammad Bilal, Ali Raza Ansari, Adil Jhangeer, Muddassar Imran e Choon Kit Chan. "The Fractional Soliton Wave Propagation of Non-Linear Volatility and Option Pricing Systems with a Sensitive Demonstration". Fractal and Fractional 7, n. 11 (9 novembre 2023): 809. http://dx.doi.org/10.3390/fractalfract7110809.
Abstract (sommario):
In this study, we explore a fractional non-linear coupled option pricing and volatility system. The model under consideration can be viewed as a fractional non-linear coupled wave alternative to the Black–Scholes option pricing governing system, introducing a leveraging effect where stock volatility corresponds to stock returns. Employing the inverse scattering transformation, we find that the Cauchy problem for this model is insolvable. Consequently, we utilize the Φ6-expansion algorithm to generate generalized novel solitonic analytical wave structures within the system. We present graphical representations in contour, 3D, and 2D formats to illustrate how the system’s behavior responds to the propagation of pulses, enabling us to predict suitable parameter values that align with the data. Finally, a conclusion is given.
19
Schubert, Christian. "The worldline formalism in strong-field QED". Journal of Physics: Conference Series 2494, n. 1 (1 maggio 2023): 012020. http://dx.doi.org/10.1088/1742-6596/2494/1/012020.
Abstract (sommario):
Abstract The worldline formalism provides an alternative to Feynman diagrams that has been found particularly useful for external-field calculations in quantum electrodynamics. Here I summarize its present range of applications, which includes Schwinger pair creation, photon splitting in constant fields and plane-wave backgrounds, as well as non-linear Compton scattering in constant fields.
20
Kenig, Carlos E., e Frank Merle. "Global well-posedness, scattering and blow-up for the energy-critical focusing non-linear wave equation". Acta Mathematica 201, n. 2 (2008): 147–212. http://dx.doi.org/10.1007/s11511-008-0031-6.
21
Fonseca, N., e C. Guedes Soares. "Time-Domain Analysis of Large-Amplitude Vertical Ship Motions and Wave Loads". Journal of Ship Research 42, n. 02 (1 giugno 1998): 139–53. http://dx.doi.org/10.5957/jsr.1998.42.2.139.
Abstract (sommario):
The vertical motions and wave induced loads on ships with forward speed are studied in the time domain, considering non-linear effects associated with large amplitude motions and hull flare shape. The method is based on a strip theory, using singularities distributed on the cross sections which satisfy the linear free surface condition. The solution is obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. In this way the linear radiation forces are represented in terms of impulse response functions, infinite frequency added masses and radiation restoring coefficients. The diffraction forces associated with incident wave scattering are linear. The hydrostatic and Froude-Krylov forces are evaluated over the instantaneous wetted surface of the hull to account for the large amplitude motions and hull flare. The radiation contribution for wave loads is also obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. Results of motions and wave loads for the S175 container ship are presented and analyzed. The results from the present method are compared with linear results.
22
Thejappa, G., e R. J. MacDowall. "High frequency ion sound waves associated with Langmuir waves in type III radio burst source regions". Nonlinear Processes in Geophysics 11, n. 3 (21 settembre 2004): 411–20. http://dx.doi.org/10.5194/npg-11-411-2004.
Abstract (sommario):
Abstract. Short wavelength ion sound waves (2-4kHz) are detected in association with the Langmuir waves (~15-30kHz) in the source regions of several local type III radio bursts. They are most probably not due to any resonant wave-wave interactions such as the electrostatic decay instability because their wavelengths are much shorter than those of Langmuir waves. The Langmuir waves occur as coherent field structures with peak intensities exceeding the Langmuir collapse thresholds. Their scale sizes are of the order of the wavelength of an ion sound wave. These Langmuir wave field characteristics indicate that the observed short wavelength ion sound waves are most probably generated during the thermalization of the burnt-out cavitons left behind by the Langmuir collapse. Moreover, the peak intensities of the observed short wavelength ion sound waves are comparable to the expected intensities of those ion sound waves radiated by the burnt-out cavitons. However, the speeds of the electron beams derived from the frequency drift of type III radio bursts are too slow to satisfy the needed adiabatic ion approximation. Therefore, some non-linear process such as the induced scattering on thermal ions most probably pumps the beam excited Langmuir waves towards the lower wavenumbers, where the adiabatic ion approximation is justified.
23
Tant, Katherine M. M., Anthony J. Mulholland, Matthias Langer e Anthony Gachagan. "A fractional Fourier transform analysis of the scattering of ultrasonic waves". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, n. 2175 (marzo 2015): 20140958. http://dx.doi.org/10.1098/rspa.2014.0958.
Abstract (sommario):
Many safety critical structures, such as those found in nuclear plants, oil pipelines and in the aerospace industry, rely on key components that are constructed from heterogeneous materials. Ultrasonic non-destructive testing (NDT) uses high-frequency mechanical waves to inspect these parts, ensuring they operate reliably without compromising their integrity. It is possible to employ mathematical models to develop a deeper understanding of the acquired ultrasonic data and enhance defect imaging algorithms. In this paper, a model for the scattering of ultrasonic waves by a crack is derived in the time–frequency domain. The fractional Fourier transform (FrFT) is applied to an inhomogeneous wave equation where the forcing function is prescribed as a linear chirp, modulated by a Gaussian envelope. The homogeneous solution is found via the Born approximation which encapsulates information regarding the flaw geometry. The inhomogeneous solution is obtained via the inverse Fourier transform of a Gaussian-windowed linear chirp excitation. It is observed that, although the scattering profile of the flaw does not change, it is amplified. Thus, the theory demonstrates the enhanced signal-to-noise ratio permitted by the use of coded excitation, as well as establishing a time–frequency domain framework to assist in flaw identification and classification.
24
PELEG, YOAV. "4-DIMENSIONAL AND 2-DIMENSIONAL EVAPORATING DILATONIC BLACK HOLES". Modern Physics Letters A 09, n. 34 (10 novembre 1994): 3137–48. http://dx.doi.org/10.1142/s0217732394002963.
Abstract (sommario):
The picture of S-wave scattering from a 4-D extremal dilatonic black hole is examined. Classically, a small matter shock wave will form a non-extremal black hole. In the “throat region” the r-t geometry is exactly that of a collapsing 2-D black hole. The 4-D Hawking radiation (in this classical background) gives the 2-D Hawking radiation exactly in the throat region. The 4-D geometry outside the throat region is almost the extremal one, and the deviations can be calculated using a linear approximation. Inclusion of the back-reaction changes this picture: the linear approximation is valid only at the beginning of the evaporating process. We give (explicitly) that linear 4-D solution. The linear approximation breaks down even before an apparent horizon is formed, which suggests that the 4-D semiclassical solution may be quite different from the 2-D one.
25
Stenkamp, D. "Quantitative determination of imaging parameters and composition from high-resolution transmission electron microscopy lattice images". Proceedings, annual meeting, Electron Microscopy Society of America 54 (11 agosto 1996): 96–97. http://dx.doi.org/10.1017/s0424820100162946.
Abstract (sommario):
A quantitative method for the direct determination of defocus Δf, local sample thickness t and local composition x from high-resolution transmission electron microscopy (HRTEM) lattice images of wedge-shaped samples is described. The method is applicable to a wide class of crystalline materials comprising elemental semiconductors, elemental metals and substitutional random alloys composed of these elements. The proposed method relies on the functional dependence of linear and non-linear image Fourier coefficients on the parameters defocus Δf, sample thickness t and composition x. This relationship is analytically derived by application of the Bloch wave formalism and the non-linear imaging theory to the HRTEM imaging process. Influences of inelastic electron scattering and partially coherent illumination conditions are taken into account explicitly.
26
Mašek, M., e K. Rohlena. "Kinetics of the Raman scattering in a laser corona using a transform method". Laser and Particle Beams 35, n. 4 (6 novembre 2017): 687–98. http://dx.doi.org/10.1017/s0263034617000696.
Abstract (sommario):
AbstractThis paper is an extension of our previous paper (Mašek and Rohlena, 2015), where we applied a transform method for the solution of Vlasov–Maxwell set of equations in a one-dimensional geometry to describe the Raman backscattering of the heating ns laser wave in the external corona of the generated laser plasma in a strongly non-linear regime. The method is stabilized by a simplified Fokker–Planck collision term, which, in turn, is used for a study of the influence of collisional and collisionless damping mechanisms of the daughter electron plasma wave (EPW) on the instability development and their competition resulting in a different instability behavior in various plasma configurations. The physics of trapped electrons is studied in detail and compared to the resulting Raman reflectivity. The Raman reflectivity was found to depend strongly on the intensity of laser irradiation in the different regions of the plasma corona. This is discussed in detail from the point of view of trapped electrons behavior in the EPW. Moreover, a study of the Raman reflectivity dependence on the electron–ion collision frequency (average plasma ionization) is presented, too. The results supplement the physical picture of the collision and collisionless processes influencing the Raman instability non-linear development.
27
SHALAEV, VLADIMIR, V. A. MARKEL, V. P. SAFONOV e R. BOTET. "RESONANT OPTICS OF FRACTALS". Fractals 02, n. 02 (giugno 1994): 201–9. http://dx.doi.org/10.1142/s0218348x94000193.
Abstract (sommario):
Fractal objects can sustain strongly localized optical modes with high quality-factor. Intense local fields associated with the dipolar eigenmodes in fractals ultimately result in significant enhancement of a number of optical effects. In particular, such basic optical processes as Rayleigh and Raman scattering, degenerate four-wave mixing and harmonic generation, two-photon absorption and non-linear photoemission can be enhanced by several orders of magnitude in small-particle fractal composites and self-affine films.
28
Cummins, C. P., G. T. Scarlett e C. Windt. "Numerical analysis of wave–structure interaction of regular waves with surface-piercing inclined plates". Journal of Ocean Engineering and Marine Energy 8, n. 1 (22 novembre 2021): 99–115. http://dx.doi.org/10.1007/s40722-021-00219-6.
Abstract (sommario):
AbstractThe Mocean wave energy converter consists of two sections, hinged at a central location, allowing the device to convert energy from the relative pitching motion of the sections. In a simplified form, the scattering problem for the device can be modelled as monochromatic waves incident upon a thin, inclined, surface-piercing plate of length $$L'$$ L ′ in a finite depth $$d'$$ d ′ of water. In this paper, the flow past such a plate is solved using a Boundary Element Method (BEM) and Computational Fluid Dynamics (CFD). While the BEM solution is based on linear potential flow theory, CFD directly solves the Navier–Stokes equations. Problems of this type are known to exhibit near-perfect reflection (indicated by a reflection coefficient $$|R|\approx 1$$ | R | ≈ 1 ) of waves at specific wavenumbers $$k'$$ k ′ . In this paper, we show that the resonant motion of the fluid induces large hydrodynamic forces on the plate. Furthermore, we argue that this low-frequency resonance resembles Helmholtz resonance, and that Mocean’s device being able to tune to these low frequencies does not act like an attenuator. For the case where the water is deep ($$d'>\lambda '/2$$ d ′ > λ ′ / 2 , where $$\lambda '=2\pi /k'$$ λ ′ = 2 π / k ′ ), we find excellent agreement between our simulations and previous semi-analytical studies on the value of the resonant wave periods in deep water. We also find excellent agreement between the excitation forces on the plate computed using the BEM model, analytical results, and CFD for large inclination angles ($$\alpha > 45^\circ $$ α > 45 ∘ ). For $$\alpha \le 15^\circ $$ α ≤ 15 ∘ , both methods show the same trend, but the CFD predicts a significantly smaller peak in the excitation force compared with BEM, which we attribute to non-linear effects such as the non-linear Froude–Krylov force
29
Mindrinos, Leonidas. "The Electromagnetic Scattering Problem by a Cylindrical Doubly-Connected Domain at Oblique Incidence: An Inverse Problem". Journal of Advances in Applied & Computational Mathematics 10 (7 agosto 2023): 18–25. http://dx.doi.org/10.15377/2409-5761.2023.10.2.
Abstract (sommario):
In this work, we examine the inverse problem to reconstruct the inner boundary of a cylindrical doubly-connected infinitely long medium from measurements of the scattered electromagnetic wave in the far-field. We consider the integral representation of the solution to derive a non-linear system of equations for the unknown radial function. We propose an iterative scheme using linearization and regularization techniques.
30
Rebora, Giacomo, Dario Ferraro, Ramiro H. Rodriguez, François D. Parmentier, Patrice Roche e Maura Sassetti. "Electronic Wave-Packets in Integer Quantum Hall Edge Channels: Relaxation and Dissipative Effects". Entropy 23, n. 2 (22 gennaio 2021): 138. http://dx.doi.org/10.3390/e23020138.
Abstract (sommario):
We theoretically investigate the evolution of the peak height of energy-resolved electronic wave-packets ballistically propagating along integer quantum Hall edge channels at filling factor equal to two. This is ultimately related to the elastic scattering amplitude for the fermionic excitations evaluated at different injection energies. We investigate this quantity assuming a short-range capacitive coupling between the edges. Moreover, we also phenomenologically take into account the possibility of energy dissipation towards additional degrees of freedom—both linear and quadratic—in the injection energy. Through a comparison with recent experimental data, we rule out the non-dissipative case as well as a quadratic dependence of the dissipation, indicating a linear energy loss rate as the best candidate for describing the behavior of the quasi-particle peak at short enough propagation lengths.
31
KAUR, GURMEET, M. L. SINGH e M. S. PATTERH. "THEORETICAL INVESTIGATIONS TO MINIMIZE BIT ERROR RATE BY OPTIMIZING SYSTEM PARAMETERS IN OPTICAL DWDM TRANSMISSION SYSTEMS AT DIFFERENT DATA RATES". Journal of Nonlinear Optical Physics & Materials 18, n. 03 (settembre 2009): 501–19. http://dx.doi.org/10.1142/s0218863509004750.
Abstract (sommario):
The amplifier separation and channel separation has conflicting effects on the noise generated due to the fiber non-linear effects (Stimulated Raman scattering SRS and Four wave mixing FWM) and the Amplified spontaneous emission (ASE) noise introduced by inline optical amplifications. While designing an efficient Dense Wavelength Division Multiplexing (DWDM) system, optimization of the channel separation and amplifier separation are required to minimize the non-linear effects (FWM and SRS) along with the ASE noise. In this paper, theoretical investigations of the optical DWDM systems have been presented to minimize the bit error rate (BER) by optimizing inter-channel separation and inter-amplifier separation at different data rates considering the combined effect of SRS, FWM, ASE, receiver and beat noises.
32
Yin, Junjun, e Jian Yang. "Framework for Reconstruction of Pseudo Quad Polarimetric Imagery from General Compact Polarimetry". Remote Sensing 13, n. 3 (2 febbraio 2021): 530. http://dx.doi.org/10.3390/rs13030530.
Abstract (sommario):
Pseudo quad polarimetric (quad-pol) image reconstruction from the hybrid dual-pol (or compact polarimetric (CP)) synthetic aperture radar (SAR) imagery is a category of important techniques for radar polarimetric applications. There are three key aspects concerned in the literature for the reconstruction methods, i.e., the scattering symmetric assumption, the reconstruction model, and the solving approach of the unknowns. Since CP measurements depend on the CP mode configurations, different reconstruction procedures were designed when the transmit wave varies, which means the reconstruction procedures were not unified. In this study, we propose a unified reconstruction framework for the general CP mode, which is applicable to the mode with an arbitrary transmitted ellipse wave. The unified reconstruction procedure is based on the formalized CP descriptors. The general CP symmetric scattering model-based three-component decomposition method is also employed to fit the reconstruction model parameter. Finally, a least squares (LS) estimation method, which was proposed for the linear π/4 CP data, is extended for the arbitrary CP mode to estimate the solution of the system of non-linear equations. Validation is carried out based on polarimetric data sets from both RADARSAT-2 (C-band) and ALOS-2/PALSAR (L-band), to compare the performances of reconstruction models, methods, and CP modes.
33
Wójcik, Grażyna, e Jolanta Holband. "Variable-temperature studies of the 4-isopropylphenol crystal structure from X-ray diffraction. Comparison of thermal expansion and molecular dynamics with spectroscopic results". Acta Crystallographica Section B Structural Science 58, n. 4 (30 luglio 2002): 684–89. http://dx.doi.org/10.1107/s0108768102004573.
Abstract (sommario):
Crystalline 4-isopropylphenol, C9H12O, an optically non-linear material, was studied by X-ray diffraction in order to determine its structure at several temperatures in the 95–300 K range. The thermal expansion coefficients have been calculated from the lattice parameters' dependence on temperature. The rigid-body analysis of the anisotropic displacement parameters including the correlation with the internal motion of large amplitude provided the values of the molecular translation and libration tensors at the temperatures studied and was used to characterize the torsional motion of the isopropyl group. The calculated normal modes and internal torsion frequency were compared with the wave numbers at the maximum of bands in the low-frequency Raman scattering, FTIR and inelastic neutron scattering spectra.
34
Michelis, T., C. de Koning e M. Kotsonis. "On the interaction of Tollmien–Schlichting waves with a wall-embedded Helmholtz resonator". Physics of Fluids 35, n. 3 (marzo 2023): 034104. http://dx.doi.org/10.1063/5.0141685.
Abstract (sommario):
The influence of a wall-embedded Helmholtz resonator on the development and stability of Tollmien–Schlichting (TS) waves is investigated numerically and experimentally for a range of frequencies extending from below to above resonance. Interactions are found to be limited in the near-wall region and toward the trailing edge of the resonator orifice while at the same time being linear nature. The dynamic response of the flow-excited resonator is shown to have a fixed phase relation with respect to the TS-waves, indicating that only amplification of the latter can be achieved. The same resonant behavior is maintained regardless of whether the resonator is flow-excited or acoustically excited. Thus, it is suggested that pressure perturbations propagate perpendicularly and acoustically within the resonator throat and cavity. The amplification observed in the vicinity of the resonator displays features typical of TS-wave scattering; however, it is confirmed that this is not solely the result of mean flow distortion due to the geometry and recirculation region. Instead, the results indicate that the phenomenology is a consequence of the combination of scattering, localized non-modal growth, and wall-forcing in the wall-normal direction due to resonance.
35
Buckingham, AD. "Linear and Nonlinear Light Scattering from the Surfaces of Liquids". Australian Journal of Physics 43, n. 5 (1990): 617. http://dx.doi.org/10.1071/ph900617.
Abstract (sommario):
The linear optical properties of matter, e.g. the refractive index, the absorption coefficient and the reflectivity, can be interpreted in terms of the oscillating charge and current densities induced by the optical field. For most purposes, it is sufficient to consider the oscillating dipole moment 11= OI.E = OI.E(O) exp(-ioot+ik. r), where 01. is the mean polarisability of a molecule, or of a unit cell, in a plane wave propagating with wave vector k, angular frequency 00 and amplitude E(O). A static electric field F polarises the material and may affect the reflected light linearly in F. If F is in the plane of incidence there is a change of phase of the reflected light, and if F is perpendicular to the plane of incidence there is a change in polarisation and intensity. If the intensity of the optical field is high, nonlinear scattering is observed from the surface of a liquid. The surface breaks the symmetry of the fluid, leading to partial molecular orientation and hence to a non�vanishing first hyperpolarisability P that gives the induced dipole at the frequency 200 proportional to the square of E. With intense laser sources a molecular monolayer or sub-monolayer can be detected. Surface selectivity can be achieved by tuning an infrared laser of frequency oolR to a vibrational frequency of the monolayer and detecting a coherent beam at the sum frequency oo+ooIR, when the surface is simultaneously subjected to pulses at 00 and oolR.
36
Warren, Thomas L. "Interaction effects from the elastodynamic scattering by two symmetric spherical cavities". AIP Advances 13, n. 2 (1 febbraio 2023): 025156. http://dx.doi.org/10.1063/5.0116877.
Abstract (sommario):
The scattering of harmonic waves has been studied extensively for problems in quantum mechanics, acoustics, electromagnetics, and elasticity. Solutions to elastodynamic problems are the basis for ultrasonic non-destructive evaluation measurement models. Therefore, in this study, we investigate the use of the boundary element method (BEM) in the frequency domain using an off-boundary technique in which the observation points are taken inside the scattering object. This methodology removes both non-integrable singularities from the domain of integration along with avoiding ill-conditioning effects that occur at fictitious eigenfrequencies of which both require using special computationally demanding procedures to obtain solutions. Additionally, we employ both free and half-space fundamental solutions (Green’s displacement tensors) to investigate the elastodynamic scattering of an incident, plane, time-harmonic longitudinal wave in the frequency domain of a homogeneous, isotropic, and linear elastic solid with one or two spherical cavities. The half-space fundamental solution reduces the number of required boundary elements in half, which significantly reduces computational resource requirements. We only consider spherical cavities in this paper to illustrate the full and half-space off-boundary BEM and analyze the interaction effects associated with the elastodynamic scattering by two symmetric spherical cavities. To verify the validity of the free and half-space off-boundary BEM formulations, surface displacement results are compared with existing surface displacement results and show good agreement. Finally, the half-space off-boundary BEM is used to illustrate the interaction effects of the back and forward scattered displacement fields as a function of the distance from the spherical cavities.
37
LEE, SEUNG-JOON, JOON-HYUN LEE e JOON-HYUNG BYUN. "EXPERIMENTAL NON-CONTACT EVALUATION OF DELAMINATION IN CFRP COMPOSITE PLATES BY LASER GENERATION/AIR-COUPLED DETECTION ULTRASONIC SYSTEM". Modern Physics Letters B 22, n. 11 (10 maggio 2008): 827–32. http://dx.doi.org/10.1142/s0217984908015450.
Abstract (sommario):
The objective of this research is to develop non-contact and real time inspection technique based on laser generated ultrasound for evaluating near-surface delamination in Carbon/Epoxy composite fabricated from automated fiber placement system. In this study, A hybrid laser generation/air-coupled detection ultrasonic system for detection and visualization of delamination in composite plates with simulated delamination of the area of 20 mm × 20 mm between the first and the second layer. Optical fiberized Nd :YAG pulse laser (532 nm, 32 mJ) with linear slit array is used to generate ultrasonic guided wave in unidirectional CFRP specimen (24 plies, 2.85 mm thickness). The characteristic of time domain waveform and frequency spectrum of guided wave is discussed. Two- dimensional images are obtained from these characteristics. The convergence of received signal using the pitch-catch and the scattering-reflection technique is discussed.
38
Mokhtarzadeh, Mahsa, e Karl F. Ludwig. "Simulations of Co-GISAXS during kinetic roughening of growth surfaces". Journal of Synchrotron Radiation 24, n. 6 (5 ottobre 2017): 1187–94. http://dx.doi.org/10.1107/s1600577517011924.
Abstract (sommario):
The recent development of surface growth studies using X-ray photon correlation spectroscopy in a grazing-incidence small-angle X-ray scattering (Co-GISAXS) geometry enables the investigation of dynamical processes during kinetic roughening in greater detail than was previously possible. In order to investigate the Co-GISAXS behavior expected from existing growth models, calculations and (2+1)-dimension simulations of linear Kuramoto–Sivashinsky and non-linear Kardar–Parisi–Zhang surface growth equations are presented which analyze the temporal correlation functions of the height–height structure factor. Calculations of the GISAXS intensity auto-correlation functions are also performed within the Born/distorted-wave Born approximation for comparison with the scaling behavior of the height–height structure factor and its correlation functions.
39
Xu, Jingyuan, e James A. Kenar. "Rheological and Micro-Rheological Properties of Chicory Inulin Gels". Gels 10, n. 3 (28 febbraio 2024): 171. http://dx.doi.org/10.3390/gels10030171.
Abstract (sommario):
As a soluble fiber, inulin is present in many plants and has many applications in food and non-food products. In this work, we investigated the rheological properties of inulin dispersions at seven concentrations. The linear viscoelastic properties of inulin were determined using a conventional mechanical rheometer. At 25 wt%, inulin exhibited fluid-like viscoelastic liquid behavior. However, when concentrations were ≥27.5 wt%, inulin exhibited gel-like viscoelastic properties. The viscoelastic properties (moduli and viscosities) increased with increasing inulin concentration. The high-frequency linear rheological properties of inulin were also investigated using the modern light scattering technique, diffusion wave spectroscopy (DWS). The diffusion wave spectroscopy (DWS) measurements showed the amplitude of complex moduli (|G*(ω)|) of inulin gels (≥27.5 wt%) to be proportional to ½ power law of the frequency, which suggests inulin gels behave similarly to flexible polymers. The non-linear steady shear experiments demonstrated that inulin exhibited shear-thinning behavior that was well fitted by a power law constitutive model. The trend of the power law exponent from the experiments indicated that the shear-thinning extent for inulin was greater as the inulin concentration increased. The results of this work indicated that the properties of inulin gel can be manipulated by altering its concentration. Therefore, the desired inulin product can be designed accordingly. These results can be used to direct further food and non-food applications, such as wound healing materials for inulin gels.
40
BLAZQUEZ, J. F. MIRAMAR. "Application of solitons to the study of laser propagation into a thermonuclear plasma in inertial confinement fusion". Laser and Particle Beams 20, n. 1 (gennaio 2002): 153–57. http://dx.doi.org/10.1017/s0263034602201238.
Abstract (sommario):
In this work, we study the laser propagation in a thermonuclear plasma corresponding to implosion of deuterium-tritium pellets in inertial confinement fusion, by injecting energy provided by high-power laser devices into a quiescent plasma and generating solitons. Having in mind that the electric field inside of plasma can be studied by means of a particular non-linear Schrödinger equation, we solve this equation as an inverse problem, using the Inverse Scattering Transform method, that is a 2 × 2 eigenvalue problem, known as the AKNS scheme, developed by Ablovitz, Kamp, Newell, and Shabat. We obtain the pseudopotentials q and r if we suppose that the eigenvalue is invariant in time, and is representative of a wave eigenvector, obtaining a solution that has a structure of the soliton type. In the process, one change of variable for space and another for time are applied, and the relation between the pseudopotentials is given by r = −q*. Discretization of the non-linear Schrödinger equation, solved by inverse scattering transform are given by Ablovitz et al. (1999). These solitons are generated near the critical layer where w0 ≅ wp, w0 being the laser frequency and wp the plasma frequency, exhibit a change in electronic density profile and are caused by the ponderomotive force of laser radiation.
41
Morgan, R. V., O. A. Likhachev e J. W. Jacobs. "Rarefaction-driven Rayleigh–Taylor instability. Part 1. Diffuse-interface linear stability measurements and theory". Journal of Fluid Mechanics 791 (15 febbraio 2016): 34–60. http://dx.doi.org/10.1017/jfm.2016.46.
Abstract (sommario):
Theory and experiments are reported that explore the behaviour of the Rayleigh–Taylor instability initiated with a diffuse interface. Experiments are performed in which an interface between two gases of differing density is made unstable by acceleration generated by a rarefaction wave. Well-controlled, diffuse, two-dimensional and three-dimensional, single-mode perturbations are generated by oscillating the gases either side to side, or vertically for the three-dimensional perturbations. The puncturing of a diaphragm separating a vacuum tank beneath the test section generates a rarefaction wave that travels upwards and accelerates the interface downwards. This rarefaction wave generates a large, but non-constant, acceleration of the order of $1000g_{0}$, where $g_{0}$ is the acceleration due to gravity. Initial interface thicknesses are measured using a Rayleigh scattering diagnostic and the instability is visualized using planar laser-induced Mie scattering. Growth rates agree well with theoretical values, and with the inviscid, dynamic diffusion model of Duff et al. (Phys. Fluids, vol. 5, 1962, pp. 417–425) when diffusion thickness is accounted for, and the acceleration is weighted using inviscid Rayleigh–Taylor theory. The linear stability formulation of Chandrasekhar (Proc. Camb. Phil. Soc., vol. 51, 1955, pp. 162–178) is solved numerically with an error function diffusion profile using the Riccati method. This technique exhibits good agreement with the dynamic diffusion model of Duff et al. for small wavenumbers, but produces larger growth rates for large-wavenumber perturbations. Asymptotic analysis shows a $1/k^{2}$ decay in growth rates as $k\rightarrow \infty$ for large-wavenumber perturbations.
42
Wang, Jiong-Hao, Yu-Liang Tao e Yong Xu. "Anomalous Transport Induced by Non-Hermitian Anomalous Berry Connection in Non-Hermitian Systems". Chinese Physics Letters 39, n. 1 (1 gennaio 2022): 010301. http://dx.doi.org/10.1088/0256-307x/39/1/010301.
Abstract (sommario):
Non-Hermitian materials can exhibit not only exotic energy band structures but also an anomalous velocity induced by non-Hermitian anomalous Berry connection as predicted by the semiclassical equations of motion for Bloch electrons. However, it is unclear how the modified semiclassical dynamics modifies transport phenomena. Here, we theoretically demonstrate the emergence of anomalous oscillations driven by either an external dc or ac electric field, which arise from non-Hermitian anomalous Berry connection. Moreover, it is a well-known fact that geometric structures of electric wave functions can only affect the Hall conductivity. However, we are surprised to find a non-Hermitian anomalous Berry connection induced anomalous linear longitudinal conductivity independent of the scattering time. We also show the emergence of a second-order nonlinear longitudinal conductivity induced by non-Hermitian anomalous Berry connection, violating a well-known fact of its absence in a Hermitian system with symmetric energy spectra. These anomalous phenomena are illustrated in a pseudo-Hermitian system with large non-Hermitian anomalous Berry connection. Finally, we propose a practical scheme to realize the anomalous oscillations in an optical system.
43
Susanti, Hesty, S. Suprijanto e Deddy Kurniadi. "ANALYTICAL MODELLING BASED ON RESONANCE SCATTERING THEORY EXPLAINING THE NEEDLE VISIBILITY INCONSISTENCY IN B-MODE ULTRASOUND". Journal of the Serbian Society for Computational Mechanics 15, n. 1 (1 novembre 2021): 131–48. http://dx.doi.org/10.24874/jsscm.2021.15.01.09.
Abstract (sommario):
In an ultrasound-guided needle insertion, physicians should adjust a certain insertion angle and the position of the transducer to ensure that the initial point and final target are in-plane inside the imaging plane. One of the crucial problems in this interventional procedure is poor and inconsistent needle visibility in B-mode ultrasound. In this research, some potential physical parameters, i.e., ultrasound frequency, the incident angle of the ultrasound beam, needle density, and dimension, are investigated through analytical modeling based on the resonance scattering model to understand their behavior in affecting needle visibility. 25G non-echogenic needle is used as a model object and assumed as stainless-steel hollow cylinder insonified by oblique incident plane wave varied within the frequency of 0–10 MHz and incident angle of 0°–45°. The results suggest that those physical parameters simultaneously affect the occurrence possibility of the resonant modes, which eventually affect the total scattering pressure field Ps in a non-linear way. These observed behaviors in the form of the spectrum map of resonance scattering pressure amplitude can be used to adapt a more beneficial combination of those physical parameters to obtain a higher possibility of good needle visibility through practical insertion application and potential echogenic technology or adaptive beamforming.
44
Karamanos, T. D., A. I. Dimitriadis e K. Nikolaos V. "Polarizability Matrix Extraction of a Bianisotropic Metamaterial from the Scattering Parameters of Normally Incident Plane Waves". Advanced Electromagnetics 1, n. 3 (22 novembre 2012): 64. http://dx.doi.org/10.7716/aem.v1i3.73.
Abstract (sommario):
In this paper, a polarizability matrix retrieval method for bianisotropic metamaterials is presented. Assuming that scatterers can be modeled by electric and magnetic pointdipoles located at their centers, the induced dipole moments are analytically related to the normally incident fields, while the scattered fields are also analytically obtained for two individual cases of normal wave incidence. The latter can be combined with the incident fields, to express the desired polarizabilities, with regard to the measured or simulated scattering parameters. In this way, the polarizability matrix can be extracted by solving the resulting non-linear system of equations. The proposed technique is applied to two different split-ring resonator structures and reveals very good agreement with previously reported techniques.
45
Sterbenz, Jacob. "Global regularity and scattering for general non-linear wave equations II. (4+1) dimensional Yang-Mills equations in the Lorentz gauge". American Journal of Mathematics 129, n. 3 (2007): 611–64. http://dx.doi.org/10.1353/ajm.2007.0020.
46
HOWISON, SAM, JOHN KING, ANDREW LACEY e MICHAEL WARD. "Preface". European Journal of Applied Mathematics 26, n. 5 (8 settembre 2015): 561–62. http://dx.doi.org/10.1017/s0956792515000431.
Abstract (sommario):
In this special issue of the European Journal of Applied Mathematics we celebrate the 75th birthday of its founding editor, Professor John Ockendon.John started his research career with his D.Phil., awarded in 1965, working with Alan Tayler at the University of Oxford. John's background was in fluid mechanics, covering a wide range of topics, including, lubrication flows, flows in porous media, hypersonic aerodynamics, sloshing phenomena, and flow separation. He soon became involved in industrial research which led, in particular, to his interest in the field of free boundary problems, an area in which he became a driving force, through papers, conferences, and particularly through the fostering of regular international meetings and personal interactions. His pioneering work in the field was particularly concentrated in diffusion-controlled moving boundary problems that arise in various applications, such as in phase change problems, elastic-contact problems and the fundamental Hele-Shaw free boundary problem. The industrial collaborations also led to mathematical studies of lens design, fibre extrusion, fluidised beds, glass manufacture and semiconductor devices, to name but a few, and to problems in scattering and wave theory, non-linear wave propagation and non-linear oscillations, as well as mechanics and heat and mass transfer. He continues to work on PDEs and asymptotics applied to new well-founded models from the real world, with a particular focus in the physical and earth sciences.
47
Mascali, D., G. Torrisi, L. Di Donato, G. Sorbello, E. Naselli, S. C. Pavone e S. Ceccuzzi. "Preliminary evaluation of inverse scattering-based plasma-profilometry application to fusion plasmas". Journal of Instrumentation 17, n. 06 (1 giugno 2022): C06006. http://dx.doi.org/10.1088/1748-0221/17/06/c06006.
Abstract (sommario):
Abstract A new diagnostic method able to perform plasma profilometry is investigated in this work to retrieve the plasma electron density profile in front of the Ion Cyclotron Range of Frequencies (ICRF) antennas. As a reference scenario for our numerical study, the Divertor Tokamak Test (DTT [1]) ICRF antennas and plasma will be considered. Specifically, the profilometry needs to solve an inverse scattering problem, which is non-linear and ill-posed. In some recent papers [2, 3], plasma imaging profilometry in compact plasma reactors, such as the electron cyclotron ion sources (ECRIS), has been proposed and tested numerically by means of proof-of-concept examples. In particular, proper formulation of electromagnetic inverse scattering techniques have been proposed, requiring measurements of the reflection coefficient in presence of a metallic reflecting surface or, alternatively, both the reflection and transmission coefficients through two antennas facing one each other. In this paper, we would like to investigate this method also for large-size (scale-length) fusion reactors by addressing the profilometry of DTT-like plasma, assuming a very high-frequency probing regime (∼0.5 THz) for the accessibility of both O and X-modes in the DTT plasma (electron density up to 1020 m−3 and magnetic field up to 9 T). To this aim, we adopt COMSOL Wave Optics® module based on beam propagation method (or slowly varying envelope approximation) for simulating the wave propagation and to determine the probing frequencies. A proper formulation allowed to reconstruct a tiny scrape-off plasma layer, approximated as an isotropic medium, thanks to the high probing frequency.
48
Huang, Zhangfeng, e Xuesong Wu. "A local scattering approach for the effects of abrupt changes on boundary-layer instability and transition: a finite-Reynolds-number formulation for isolated distortions". Journal of Fluid Mechanics 822 (6 giugno 2017): 444–83. http://dx.doi.org/10.1017/jfm.2017.287.
Abstract (sommario):
We investigate the influence of abrupt changes on boundary-layer instability and transition. Such changes can take different forms including a local porous wall, suction/injection and surface roughness as well as junctions between rigid and porous walls. They may modify the boundary conditions and/or the mean flow, and their effects on transition have usually been assessed by performing stability analysis for the modified base flow and/or boundary conditions. However, such a conventional local linear stability theory (LST) becomes invalid if the change occurs over a relatively short scale comparable with, or even shorter than, the characteristic wavelength of the instability. In this case, the influence on transition is through scattering with the abrupt change acting as a local scatter, that is, an instability mode propagating through the region of abrupt change is scattered by the strong streamwise inhomogeneity to acquire a different amplitude. A local scattering approach (LSA) should be formulated instead, in which a transmission coefficient, defined as the ratio of the amplitude of the instability wave after the scatter to that before, is introduced to characterize the effect on instability and transition. In the present study, we present a finite-Reynolds-number formulation of LSA for isolated changes including a rigid plate interspersed by a local porous panel and a wall suction through a narrow slot. When the weak non-parallelism of the unperturbed base flow is ignored, the local scattering problem can be cast as an eigenvalue problem, in which the transmission coefficient appears as the eigenvalue. We also improved the method to take into account the non-parallelism of the unperturbed base flow, where it is found that the weak non-parallelism has a rather minor effect. The general formulation is specialized to two-dimensional Tollmien–Schlichting (T–S) waves. The resulting eigenvalue problem is solved, and full direct numerical simulations (DNS) are performed to verify some of the predictions by LSA. A parametric study indicates that conventional LST is valid only when the change is sufficiently gradual, and becomes either inaccurate or invalid when the scale of the local distortion is short. A local porous panel enhances T–S waves, while a local suction with a moderate mass flux significantly inhibits T–S waves. In the latter case, a comprehensive comparison is made between the theoretical predictions and experimental data, and a satisfactory quantitative agreement was observed.
49
Bénisti, Didier. "Self-consistent theory for the linear and nonlinear propagation of a sinusoidal electron plasma wave. Application to stimulated Raman scattering in a non-uniform and non-stationary plasma". Plasma Physics and Controlled Fusion 60, n. 1 (15 novembre 2017): 014040. http://dx.doi.org/10.1088/1361-6587/aa9671.
50
Iurov, Andrii, Liubov Zhemchuzhna, Godfrey Gumbs e Danhong Huang. "Application of the WKB Theory to Investigate Electron Tunneling in Kek-Y Graphene". Applied Sciences 13, n. 10 (16 maggio 2023): 6095. http://dx.doi.org/10.3390/app13106095.
Abstract (sommario):
In this paper, we have constructed a WKB approximation for graphene having a Y-shaped Kekulé lattice distortion and a special folding of the K and K′ valleys, which leads to very specific linear energy dispersions with two non-equivalent pairs of subbands. These obtained semi-classical results, which include the action, electron momentum and wave functions, are utilized to analyze the dynamics of electron tunneling through non-square potential barriers. In particular, we explore resonant scattering of an electron by a potential barrier built on Kekulé-distorted graphene. Mathematically, a group of consecutive equations for a semi-classical action have been solved by following a perturbation approach under the condition of small strain-induced coupling parameter Δ0≪1 (a good fit to its actual value Δ0∽ 0.1). Specifically, we consider a generalized model for Kek-Y graphene with two arbitrary Fermi velocities. The dependence of the electron transmission amplitude on the potential profile V(x) and band parameters of Kekulé-patterned graphene has been explored and analyzed in detail.