Journal articles: 'Eikonal systems'

1

Bijker, R., and J. N. Ginocchio. "Eikonal scattering from complex systems." Physical Review C 45, no. 6 (June 1, 1992): 3030–33. http://dx.doi.org/10.1103/physrevc.45.3030.

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KIM, YONG JOO, JONG-KWAN WOO, and MOON HOE CHA. "ANALYTIC FIRST-ORDER EIKONAL MODEL FOR HEAVY-ION ELASTIC SCATTERINGS." International Journal of Modern Physics E 19, no. 10 (October 2010): 1947–60. http://dx.doi.org/10.1142/s0218301310016430.

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We present analytic expressions for the zero-order eikonal phase shift and its first-order correction by approximating a distance between two colliding nuclei. This formalism has been applied to elastic scatterings of the 12 C + 40 Ca and the 12 C + 90 Zr systems at E lab = 420 MeV , and the 16 O + 40 Ca and the 16 O + 90 Zr ones at E lab = 1503 MeV . The calculated angular distributions, taking into account up to the analytic first-order eikonal phase shift, are found to be in fairly good agreement with the observed data. The reaction cross-sections obtained from the present model produce very excellent agreements with ones of exact first-order eikonal model calculations. We have found that analytic eikonal phase shift including the first-order correction is one theoretical method to the analysis of heavy-ion elastic scattering.

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Wereszczyński, A. "Generalized eikonal knots and new integrable dynamical systems." Physics Letters B 621, no. 1-2 (August 2005): 201–7. http://dx.doi.org/10.1016/j.physletb.2005.06.050.

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Al-Khalili, J. S., J. A. Tostevin, and J. M. Brooke. "Beyond the eikonal model for few-body systems." Physical Review C 55, no. 3 (March 1, 1997): R1018—R1022. http://dx.doi.org/10.1103/physrevc.55.r1018.

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BAYE, DANIEL. "THREE AND FOUR-BODY BREAKUP REACTIONS." International Journal of Modern Physics E 17, no. 10 (November 2008): 2301–9. http://dx.doi.org/10.1142/s0218301308011513.

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Breakup reactions provide spectroscopic information on exotic nuclei. Coulomb breakup indirectly measures the astrophysical S factor for radiative-capture reactions. The validity of first-order perturbation theory is limited for extended systems such as halo nuclei. More elaborate reaction models are necessary: semi-classical time-dependent Schrödinger equation, eikonal and dynamical eikonal approximations, continuum-discretized coupled-channel method. Breakup experiments do not provide much information on the structure of a two-cluster halo nucleus but accurate exclusive experiments should be more interesting for three-cluster nuclei.

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Venetskiy, A. S., and V. A. Kaloshin. "On eikonal aberrations in axisymmetric double-reflector telescopic systems." Journal of Communications Technology and Electronics 61, no. 4 (April 2016): 385–94. http://dx.doi.org/10.1134/s1064226916040136.

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KOPIETZ, PETER. "BOSONIZATION AND THE EIKONAL EXPANSION: SIMILARITIES AND DIFFERENCES." International Journal of Modern Physics B 10, no. 17 (July 30, 1996): 2111–24. http://dx.doi.org/10.1142/s0217979296000969.

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We compare two non-perturbative techniques for calculating the single-particle Green’s function of interacting Fermi systems with dominant forward scattering: our recently developed functional integral approach to bosonization in arbitrary dimensions, and the eikonal expansion. In both methods the Green’s function is first calculated for a fixed configuration of a background field, and then averaged with respect to a suitably defined effective action. We show that, after linearization of the energy dispersion at the Fermi surface, both methods yield for Fermi liquids exactly the same non-perturbative expression for the quasi-particle residue. However, in the case of non-Fermi liquid behavior the low-energy behavior of the Green’s function predicted by the eikonal method can be erroneous. In particular, for the Tomonaga-Luttinger model the eikonal method neither reproduces the correct scaling behavior of the spectral function, nor predicts the correct location of its singularities.

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MULHOLLAND, A. J., and J. GOMATAM. "PATTERN FORMATION IN EXCITABLE REACTION–DIFFUSION SYSTEMS: THE EIKONAL ANALYSIS ON THE TORUS." Journal of Biological Systems 03, no. 04 (December 1995): 1013–19. http://dx.doi.org/10.1142/s0218339095000903.

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The excitable reaction–diffusion (R–D) systems of biological and chemical origin harbour a wealth of patterns and structures, not all of which have been modelled by the full R-D equations. The analytical and numerical facility offered by the eikonal approach to the R-D equation is exploited here in the demonstration of existence and stability of a class of solutions on a torus.

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Waheed, Umair bin, Ehsan Haghighat, Tariq Alkhalifah, Chao Song, and Qi Hao. "PINNeik: Eikonal solution using physics-informed neural networks." Computers & Geosciences 155 (October 2021): 104833. http://dx.doi.org/10.1016/j.cageo.2021.104833.

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Soravia, Pierpaolo. "Degenerate Eikonal equations with discontinuous refraction index." ESAIM: Control, Optimisation and Calculus of Variations 12, no. 2 (March 22, 2006): 216–30. http://dx.doi.org/10.1051/cocv:2005033.

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11

CAMILLI, Fabio, and Paola LORETI. "Comparison results for a class of weakly coupled systems of eikonal equations." Hokkaido Mathematical Journal 37, no. 2 (May 2008): 349–62. http://dx.doi.org/10.14492/hokmj/1253539559.

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12

Osetrin, Konstantin, Altair Filippov, and Evgeny Osetrin. "Wave-like spatially homogeneous models of Stäckel spacetimes (2.1) type in the scalar-tensor theory of gravity." Modern Physics Letters A 35, no. 33 (August 26, 2020): 2050275. http://dx.doi.org/10.1142/s0217732320502752.

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Six exact solutions are obtained in the general scalar-tensor theory of gravity related to spatially homogeneous wave-like models of the Universe. Wave-like spacetime models allow the existence of privileged coordinate systems where the eikonal equation and the Hamilton–Jacobi equation of test particles can be integrated by the method of complete separation of variables with the separation of isotropic (wave) variables on which the space metric depends (non-ignored variables). An explicit form of the scalar field and two functions of the scalar field that are part of the general scalar-tensor theory of gravity are found. The explicit form of the eikonal function and the action function for test particles in the considered models is given. The obtained solutions are of type III according to the Bianchi classification and type N according to the Petrov classification. Wave-like spatially homogeneous spacetime models can describe primordial gravitational waves of the Universe.

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13

LIU, YU-LIANG. "EIGEN-FUNCTIONAL METHOD AND EIKONAL-TYPE EQUATIONS IN ONE-DIMENSIONAL STRONGLY CORRELATED ELECTRON SYSTEMS." International Journal of Modern Physics B 16, no. 16 (June 30, 2002): 2201–20. http://dx.doi.org/10.1142/s0217979202010385.

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Using eigen-functional method, we study one-dimensional strongly correlated electron systems with large momentum (2k F and/or 4k F ) transfer term(s), and demonstrate that this kind of problems ends in to solve the Eikonal-type equations, and these equations are universal, and independent of whether or not the system is integrable. In contrast to usual perturbation theory, this method is valid not only for weak electron interaction, but also for strong electron interaction. Comparing with exact solution of some integrable models, it can give correct results in linearization approximation. This method can also be used to study electron-phonon interaction systems, and two coupled spin chain (or quantum wire) systems.

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AHMAD, I., and M. A. ALVI. "EIKONAL PHENOMENOLOGY FOR HEAVY-ION SCATTERING AT INTERMEDIATE ENERGIES." International Journal of Modern Physics E 13, no. 06 (December 2004): 1225–37. http://dx.doi.org/10.1142/s0218301304002685.

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Working within the framework of the Coulomb modified Glauber model and the optical limit approximation, we propose a phenomenological method of analysis for heavy-ion elastic scattering data at intermediate energies. Instead of using the commonly employed Gaussian approximation for the input NN amplitude that is deficient in some respects at low intermediate energies, we evaluate it in terms of a three parameter phenomenological NN phase shift function. The application of the method to some 12 C -nucleus and 16 O -nucleus systems shows that a very good description of the elastic scattering data at several energies can be obtained in this way. In particular, the 12 C –12 C elastic scattering data at 200 MeV/nucleon is very well reproduced. We also calculate the effective NN potential using the phenomenological NN phase shift function by the method of inversion. The calculated potential shows the expected behavior and is found to vary smoothly with energy.

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15

Chen, Hongquan, Tsubasa Onishi, Jaeyoung Park, and Akhil Datta-Gupta. "Computing Pressure Front Propagation Using the Diffusive-Time-of-Flight in Structured and Unstructured Grid Systems via the Fast-Marching Method." SPE Journal 26, no. 03 (January 14, 2021): 1366–86. http://dx.doi.org/10.2118/201771-pa.

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Summary Diffusive-time-of-flight (DTOF), representing the travel time of pressure front propagation, has found many applications in unconventional reservoir performance analysis. The computation of DTOF typically involves upwind finite difference of the Eikonal equation and solution using the fast-marching method (FMM). However, the application of the finite difference-based FMM to irregular grid systems remains a challenge. In this paper, we present a novel and robust method for solving the Eikonal equation using finite volume discretization and the FMM. The implementation is first validated with analytical solutions using isotropic and anisotropic models with homogeneous reservoir properties. Consistent DTOF distributions are obtained between the proposed approach and the analytical solutions. Next, the implementation is applied to unconventional reservoirs with hydraulic and natural fractures. Our approach relies on cell volumes and connections (transmissibilities) rather than the grid geometry, and thus can be easily applied to complex grid systems. For illustrative purposes, we present applications of the proposed method to embedded discrete fracture models (EDFMs), dual-porosity dual-permeability models (DPDK), and unstructured perpendicular-bisectional (PEBI) grids with heterogeneous reservoir properties. Visualization of the DTOF provides flow diagnostics, such as evolution of the drainage volume of the wells and well interactions. The novelty of the proposed approach is its broad applicability to arbitrary grid systems and ease of implementation in commercial reservoir simulators. This makes the approach well-suited for field applications with complex grid geometry and complex well architecture.

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16

Velzel, C. H. F., and J. L. F. de Meijere. "Characteristic functions and the aberrations of symmetric optical systems III Calculation of eikonal coefficients." Journal of the Optical Society of America A 5, no. 8 (August 1, 1988): 1237. http://dx.doi.org/10.1364/josaa.5.001237.

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17

Hoffnagle, John A., and David L. Shealy. "Refracting the k-function: Stavroudis’s solution to the eikonal equation for multielement optical systems." Journal of the Optical Society of America A 28, no. 6 (May 31, 2011): 1312. http://dx.doi.org/10.1364/josaa.28.001312.

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18

Vlad, M. O., and J. Ross. "A stochastic approach to nonequilibrium chain reactions in disordered systems: Breakdown of eikonal approximation." International Journal of Thermophysics 18, no. 4 (July 1997): 957–75. http://dx.doi.org/10.1007/bf02575241.

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19

Osetrin, Konstantin, and Evgeny Osetrin. "Shapovalov Wave-Like Spacetimes." Symmetry 12, no. 8 (August 18, 2020): 1372. http://dx.doi.org/10.3390/sym12081372.

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A complete classification of space-time models is presented, which admit the privileged coordinate systems, where the Hamilton–Jacobi equation for a test particle is integrated by the method of complete separation of variables with separation of the isotropic (wave) variable, on which the metric depends (wave-like Shapovalov spaces). For all types of Shapovalov spaces, exact solutions of the Einstein equations with a cosmological constant in vacuum are found. Complete integrals are presented for the eikonal equation and the Hamilton–Jacobi equation of motion of test particles.

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20

Mulholland, Anthony J., and Jagannathan Gomatam. "The eikonal approximation to excitable reaction-diffusion systems: travelling non-planar wave fronts on the plane." Physica D: Nonlinear Phenomena 89, no. 3-4 (January 1996): 329–45. http://dx.doi.org/10.1016/0167-2789(95)00213-8.

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21

KIM, YONG JOO, and MOON HOE CHA. "OPTICAL POTENTIALS BY INVERSION FOR 16O ION ELASTIC SCATTERINGS AT Elab=1503 MeV." International Journal of Modern Physics E 09, no. 04 (August 2000): 299–307. http://dx.doi.org/10.1142/s0218301300000210.

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The optical potentials by inversion are presented in two ways. The first one is to use the inverse eikonal relations derived from McIntyre phase shifts. The second one is to solve the inversion problem based on McIntyre parametrization of S-matrix corresponding to the Woods-Saxon type optical potentials. The optical potentials obtained from the two inversion methods are applied to the systems 16 O +12 C , 16 O +28 Si , and 16 O +40 Ca at E lab =1503 MeV . The calculated results are compared with those from the optical model analysis. It is shown that both the two methods lead to reasonable agreements, in the surface region, to the results from the optical model analysis.

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22

Velzel, C. H. F., and J. L. F. de Meijere. "Characteristic functions and the aberrations of symmetric optical systems I Transverse aberrations when the eikonal is given." Journal of the Optical Society of America A 5, no. 2 (February 1, 1988): 246. http://dx.doi.org/10.1364/josaa.5.000246.

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23

Maragos, Petros, and Muhammad Akmal Butt. "Curve Evolution, Differential Morphology, and Distance Transforms Applied to Multiscale and Eikonal Problems." Fundamenta Informaticae 41, no. 1,2 (2000): 91–129. http://dx.doi.org/10.3233/fi-2000-411204.

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White, Malcolm C. A., Hongjian Fang, Nori Nakata, and Yehuda Ben-Zion. "PyKonal: A Python Package for Solving the Eikonal Equation in Spherical and Cartesian Coordinates Using the Fast Marching Method." Seismological Research Letters 91, no. 4 (June 3, 2020): 2378–89. http://dx.doi.org/10.1785/0220190318.

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Abstract This article introduces PyKonal: a new open-source Python package for computing travel times and tracing ray paths in 2D or 3D heterogeneous media using the fast marching method for solving the eikonal equation in spherical and Cartesian coordinates. Compiled with the Cython compiler framework, PyKonal offers a Python application program interface (API) with execution speeds comparable to C or Fortran codes. Designed to be accurate, stable, fast, general, extensible, and easy to use, PyKonal offers low- and high-level API functions for full control and convenience, respectively. A scale-independent implementation allows problems to be solved at micro, local, regional, and global scales, and precision can be improved over existing open-source codes by combining different coordinate systems. The resulting code makes state-of-the-art computational capabilities accessible to novice programmers and is efficient enough for modern research problems in seismology.

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Laskin, B. N., and E. A. Bolelov. "THE METHOD OF CALCULATION OF COEFFICIENTS OF THE PHASE ABERRATIONS OF AXIALLY ASYMMETRIC DUAL REFLECTOR ANTENNAS." Civil Aviation High TECHNOLOGIES 22, no. 1 (February 27, 2019): 93–105. http://dx.doi.org/10.26467/2079-0619-2019-22-1-93-105.

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Aerodrome-enroute surveillance radar systems (ARSR) of civil aviation are designed for detection of aerial objects and determination of their range and movement parameters. Meanwhile, the reflector-type antennas are still the main type of_used antenna systems. Radars (ARSR) have, as a rule, antennas with a bidirectional beam, structurally reflector-type antenna is made in the form of a truss welded structure. The use of active phased antenna arrays (APAR) is a promising direction of radars (ARSR) development. Radars (ARSR) based on the phased antenna arrays can significantly improve such critical tactical and technical criteria as: the accuracy of the coordinates determination, the number of simultaneously followed targets. However, the use of APAR does not solve one of the main problems - the presence of a support-rotary device in the radar (ARSR). The principal necessity of a support-rotary device leads to the need of the use of movable joints of feeder lines, which, with a significant number of antenna elements used in the PAR, significantly reduces the potential time before failure. It seems promising to use in the radar antenna systems based on several stationary multi-beam dual-reflector antennas made by axially asymmetric scheme. Methodology of estimation of aberrations of a dual-reflector sensimetrics antenna based on a polynomial expansion of the eikonal function in the plane of the aperture of the main reflector is proposed in the article. Analytical expressions of the functions of display and rotation of the scanning plane of a dual-reflector axially asymmetric antenna with arbitrary parameters, designed based on clippings from centrally symmetric surfaces of rotation of the second order, are obtained. It is shown that the aplanatic antennas lose their scanning features during the transition to the axially asymmetric variant.

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Kuziv, Yaroslav Yu. "Software for the numerical solution of first-order partial differential equations." Discrete and Continuous Models and Applied Computational Science 27, no. 1 (December 15, 2019): 42–48. http://dx.doi.org/10.22363/2658-4670-2019-27-1-42-48.

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Partial differential equations of the first order, arising in applied problems of optics and optoelectronics, often contain coefficients that are not defined by a single analytical expression in the entire considered domain. For example, the eikonal equation contains the refractive index, which is described by various expressions depending on the optical properties of the media that fill the domain under consideration. This type of equations cannot be analysed by standard tools built into modern computer algebra systems, including Maple.The paper deals with the adaptation of the classical Cauchy method of integrating partial differential equations of the first order to the case when the coefficients of the equation are given by various analytical expressions in the subdomains G1, . . . , Gk , into which the considered domain is divided. In this case, it is assumed that these subdomains are specified by inequalities. This integration method is implemented as a Python program using the SymPy library. The characteristics are calculatednumerically using the Runge-Kutta method, but taking into account the change in the expressions for the coefficients of the equation when passing from one subdomain to another. The main functions of the program are described, including those that can be used to illustrate the Cauchy method. The verification was carried out by comparison with the results obtained in the Maple computer algebra system.

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Gimbert, Florent, Ugo Nanni, Philippe Roux, Agnès Helmstetter, Stéphane Garambois, Albanne Lecointre, Andréa Walpersdorf, et al. "A Multi-Physics Experiment with a Temporary Dense Seismic Array on the Argentière Glacier, French Alps: The RESOLVE Project." Seismological Research Letters 92, no. 2A (February 3, 2021): 1185–201. http://dx.doi.org/10.1785/0220200280.

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Abstract Recent work in the field of cryo-seismology demonstrates that high-frequency (>1 Hz) seismic waves provide key constraints on a wide range of glacier processes, such as basal friction, surface crevassing, or subglacial water flow. Establishing quantitative links between the seismic signal and the processes of interest, however, requires detailed characterization of the wavefield, which, at high frequencies, necessitates the deployment of large and dense seismic arrays. Although dense seismic array monitoring has recently become increasingly common in geophysics, its application to glaciated environments remains limited. Here, we present a dense seismic array experiment made of 98 three-component seismic stations continuously recording during 35 days in early spring 2018 on the Argentière Glacier, French Alps. The seismic dataset is supplemented with a wide range of complementary observations obtained from ground-penetrating radar, drone imagery, Global Navigation Satellite Systems positioning, and in situ measurements of basal glacier sliding velocities and subglacial water discharge. We present first results through conducting spectral analysis, template matching, matched-field processing, and eikonal-wave tomography. We report enhanced spatial resolution on basal stick slip and englacial fracturing sources as well as novel constraints on the heterogeneous nature of the noise field generated by subglacial water flow and on the link between crevasse properties and englacial seismic velocities. We outline in which ways further work using this dataset could help tackle key remaining questions in the field.

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Langenbucher, Achim, and Berthold Seitz. "Computerized calculation scheme for bitoric eikonic intraocular lenses." Ophthalmic and Physiological Optics 23, no. 3 (May 2003): 213–20. http://dx.doi.org/10.1046/j.1475-1313.2003.00109.x.

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Noriller, Rafael Martins, and César Augusto Tibúrcio Silva. "IMPACT OF MACROECONOMIC VARIABLES ON THE COMPONENTS OF FINANCIAL STATEMENTS OF LATIN AMERICAN PUBLIC COMPANIES." Revista Universo Contábil 15, no. 3 (September 2, 2020): 47. http://dx.doi.org/10.4270/ruc.2019319.

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This study (i) measures the causal relationship between macroeconomic indicators and the financial statements of Latin American public companies, (ii) and determines the relationship between components of financial statements of Latin American public companies and their respective lagged variables. To carry out the study, estimates GMM of Arellano and Bond and GMM System were adopted, with secondary data extracted from Thomson Reuters Eikon and Word Bank. From the estimates, which had a sample of 150 companies, identified the causal relationships (i) of the Exchange Rate in Total Assets, Net Revenue and Equity, (ii) of the GDP in Equity and Net Income, (iii) and Net Income with its first lag. Thus, this research advances the literature by demonstrating the influence of macroeconomics, in a different way, on the components of financial statements.

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Elrazaz, Tariq Zaglol, Moataz Elmassri, and Yousry Ahmed. "Real earnings manipulation surrounding mergers and acquisitions: the targets’ perspective." International Journal of Accounting & Information Management 29, no. 3 (June 8, 2021): 429–51. http://dx.doi.org/10.1108/ijaim-11-2020-0188.

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Purpose This paper aims to investigate whether UK public targets manage their earnings using real activities manipulation in the period prior to the announcement of a mergers and acquisition (M&A). It also examines whether the payment method in M&As affects the degree to which takeover targets manipulate earnings. Design/methodology/approach Using a sample of 131 UK listed targets acquired over the period 1995–2013, this paper examines real earnings management (REM) by employing OLS regression models. The data related to deals have been mainly collected from Thomson One Banker and Thomson Reuters Eikon databases. REM is examined by investigating abnormal cash flow from operations, abnormal discretionary expenses and abnormal production costs. This analysis was supplemented by conducting additional robustness checks. Findings The results show that UK takeover targets manage earnings upwards through cutting discretionary expenses in the year prior to the acquisition, while they do not do so by manipulating sales or production costs. Moreover, targets of cash-only or mixed-payment deals do not have the same strong motivation to manage their earnings as stock-financed deal target counterparts do. Our results continue to hold after using alternative accrual earnings management (EM) measures, controlling for unobservable firm heterogeneity using the fixed-effect model and controlling for endogeneity using the two-stage Heckman (1979) model. Practical implications The main findings of this study could be beneficial for various parties involved M&As, such as standard setters and regulators. A need arises to improve disclosure rules and enhance overall financial reporting quality in the capital markets with the aim of reducing information asymmetry and agency conflicts. Originality/value As far as the literature on EM around M&As is concerned, only EM by acquirers has been examined, and not much attention has been paid to targets’ EM.

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Purgar, Krešimir. "Nulti stupanj reprezentacije: Umjetnost, tehnika i slikovno pojavljivanje." Ars Adriatica, no. 6 (January 1, 2016): 241. http://dx.doi.org/10.15291/ars.189.

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My starting hypothesis in the theory of pictorial appearing is that Gottfried Boehm’s notion of iconic difference can serve as a sufficiently comprehensive concept for differentiating between image and non-image in all visual artefacts that have been created during the several millennia of visual representation. This era started with the first paleolithic drawings and includes the entire visual production from the period “before art”, as well as all those visual representations that emerged in the early modern period beyond the needs of religious worship, only to be substituted through the technosphere. However, since the technosphere is characterized by increasingly evolved systems of visual immersion, from the all-accessible OLED screen and IMAX cinema theatres to Oculus Rift glasses and further to the experience of total immersion, which recreates synesthetic visual-haptic impressions, ontological differentiation between the visual surface as such and the extra-iconic reality can no longer be established with the idea of difference alone. Namely, the notion of difference can serve as a qualifier for defining the relationship between the separate categories in an object – in our case, the pictorial and non-pictorial ones – only insofar as the reality in which they are situated is identical or equivalent. Thus, nobody questions the clear ontological separation between the two-dimensional represented reality such as established in cinematic fiction and the non-represented, that is actual reality existing outside of that fiction. Many films and artworks count on that implied separation and can therefore afford to question the borderline between the two, primarily within a strictly artistic discourse. Boehm’s theory of iconic difference and Jean-Luc Nancy’s understanding of the cut have helped establish the semiotic-phenomenological criteria for a theoretical differentiation between various experiences that are innate to man’s picture of the world. In other words, the difference or ontological cut between image and non-image can exist only because even a modestly capable individual can empirically grasp these two categories. However, my hypothesis is that iconic difference reveals itself as an inadequate concept for that ontological cut, not only because the status and the possibilities of human experience are radically altered in the time and space of the technosphere, but also because this new type of experience has not yet been “normalized” within the process that Flint Schier has termed “natural generativity”. The space and time of the technosphere require that one should no longer approach the image merely as the ancient Greek eikon, i.e. mirroring or representation, but rather as an experience, event, and a specific type of phenomenon. The modalities of pictorial appearing in the technosphere can be recognized as symptoms of the most recent visual turn, in any case the first in the 21st century, which no longer occurs in an encounter between image and language, as lucidly described by Mitchell and Boehm, but in an encounter between analogue and digital images, between representation and post-representation, reality and virtuality, semiotics and phenomenology. In order to understand this epochally new reality, one can use concepts such as Bolter’s and Grusin’s remediation, or Žarko Paić’s idea of the technosphere, as well as some other approaches, such as Paul Crowther’s categorization of “transhistorical images” or the phenomenologically based interpretation of art and images that Martin Seel has termed “the aesthetics of appearing”.

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"A geometrical approach to wave-type solutions of excitable reaction-diffusion systems." Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences 433, no. 1887 (April 8, 1991): 151–64. http://dx.doi.org/10.1098/rspa.1991.0040.

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We formulate the eikonal equation approximation for travelling waves in excitable reaction-diffusion systems, which have been proposed as models for a large number of biomedical situations. This formulation is particularly suited, in a natural way, to numerical solution by finite difference methods. We show how this solution is independent of the parametric variable used for expressing the eikonal equation, and how a reduction of dimensionality implies a major saving over the time taken to solve the original reaction-diffusion system. Neumann boundary conditions on reactants in the original system translate into a geometric constraint on the wave boundary itself. We show how this leads to geometrically stable stationary wave boundaries in appropriately shaped non-convex domains. This analytical prediction is verified by numerical solution of the eikonal equation on a domain which supports geometrically stable stationary wave boundary configurations. We show how the concepts of geometrical stability and wave-front stability relate to a problem where a bi-stable reaction-diffusion system has a stable stationary wave-front configuration.

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Vázquez, Luis, M. Pilar Velasco, Dumitru Baleanu, J. Luis Vázquez-Poletti, and Salvador Jiménez. "From Eikonal to Antieikonal Approximations: Competition of Scales in the Framework of Schrödinger and Classical Wave Equation." Journal of Computational and Nonlinear Dynamics 17, no. 8 (April 1, 2022). http://dx.doi.org/10.1115/1.4054153.

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Abstract We present a description of certain limits associated with the Schrödinger equation, the classical wave equation, and Maxwell equations. Such limits are mainly characterized by the competition of two fundamental scales. More precisely: (1) The competition of an exploratory wavelength and the scale of fluctuations is associated with the media where the propagation takes place. From that, the universal behaviors arise eikonal and anti-eikonal. (2) In the context above, it is specially relevant and promising the study of propagation of electromagnetic waves in a media with a self-similar structure, like a fractal one. These systems offer the suggestive scenario where the eikonal and anti-eikonal behaviors are simultaneous. This kind of study requires large and massive computations that are mainly possible in the framework of the cloud computing. Recently, we started to carry out this task. (3) Finally and as a collateral aspect, we analyze the Planck constant in the interval 0≤h≤∞.

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Zhou, Pengxiang, Sébastien Chevrot, Maximilien Lehujeur, Shaohong Xia, and Chunquan Yu. "Eikonal surface-wave tomography of central and eastern China." Geophysical Journal International, August 6, 2022. http://dx.doi.org/10.1093/gji/ggac296.

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Summary Eikonal tomography has become a key approach to image lithospheric structures with surface waves recorded by dense regional arrays. Its main advantage is that phase velocities can be determined directly from phase measurements without resolving a tomographic inverse problem. Here, we apply a new smoothing spline eikonal tomography approach to a selection of 40 large (Mw larger than 6.5) teleseismic events recorded by the permanent seismic stations of the CEArray. We first apply a time-frequency filter to isolate the fundamental mode of Rayleigh waves and cross-correlate the cleaned and isolated surface wave records to measure precise relative travel times. The phase measurements are then unwrapped and corrected for cycle skipping. Finally, we derive phase-velocity maps from the gradient of the reconstructed travel time fields, using the eikonal equation. We obtain finely resolved phase-velocity maps from 25 s to 150 s period that are inverted to obtain a 3-D shear wave velocity model which is in good agreement with previous tomographic studies. The lithospheric architecture emerging from the phase-velocity maps and 3-D S-wave velocities correlates with surface geology and major tectonic provinces. In particular, the architecture of the narrow rift systems, the South China Craton, and the North China Craton are revealed with unprecedented details. The South China Craton is characterized by very high velocities beneath the Sichuan Basin. The North China Craton shows more complex structures with two high velocity anomalies beneath the Ordos Basin and the southeastern North China Craton and low velocity anomalies beneath the Cenozoic rift systems.

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Rjasanowa, Kerstin. "Numerical solution of the Eikonal equation for an automatic piping." Georgian Mathematical Journal, October 17, 2019. http://dx.doi.org/10.1515/gmj-2019-2052.

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Abstract The procedure of positioning of pipes, for example for the automobile exhaust construction, by the use of 3D CAD systems is difficult and time consuming because of obstacles in an engine compartment. There are also further strong technical requirements and restrictions. An automatic generation procedure based on the level set method and the numerical solution of the Eikonal equation is proposed. The positions of pipes which satisfy the technical requirements are obtained using spline functions.

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Dierckx, Hans, Olivier Bernus, and Henri Verschelde. "Accurate Eikonal-Curvature Relation for Wave Fronts in Locally Anisotropic Reaction-Diffusion Systems." Physical Review Letters 107, no. 10 (August 31, 2011). http://dx.doi.org/10.1103/physrevlett.107.108101.

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"Diffraction of spherical waves by a toroidal obstacle: eikonal approach to excitable reaction—diffusion systems." Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences 452, no. 1955 (December 31, 1996): 2785–99. http://dx.doi.org/10.1098/rspa.1996.0147.

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Bern, Zvi, Juan Pablo Gatica, Enrico Herrmann, Andres Luna, and Mao Zeng. "Scalar QED as a toy model for higher-order effects in classical gravitational scattering." Journal of High Energy Physics 2022, no. 8 (August 10, 2022). http://dx.doi.org/10.1007/jhep08(2022)131.

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Abstract Quantum Electrodynamics (QED) serves as a useful toy model for classical observables in gravitational two-body systems with reduced complexity due to the linearity of QED. We investigate scattering observables in scalar QED at the sixth order in the charges (two-loop order) in a classical regime analogous to the post-Minkowskian expansion in General Relativity. We employ modern scattering amplitude tools and extract classical observables by both eikonal methods and the formalism of Kosower, Maybee, and O’Connell (KMOC). In addition, we provide a simplified approach to extracting the radial action beyond the conservative sector.

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Andreeva, T. A., W. W. Durgin, and S. E. Wojcik. "Influence of Imperfect Internal Waves on Long-Range Underwater Acoustic Propagation." Journal of Computational and Nonlinear Dynamics 5, no. 1 (November 12, 2009). http://dx.doi.org/10.1115/1.4000322.

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This work presents a numerical analysis of the effect of random fluctuations of internal waves on the chaotic dynamics of ray trajectories in ocean acoustics. The Eikonal equation is considered in a form of the second order, nonlinear ordinary differential equation. Random phase modulations in the form of zero mean Gaussian white noise are considered for modeling an imperfectly periodic single mode internal wave. It is shown that in the presence of random fluctuations the intersection of acoustic rays with the ocean surface occurs sooner and becomes more frequent than predicted by deterministic ocean models.

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Agostini, Pedro, Tolga Altinoluk, and Néstor Armesto. "Effect of non-eikonal corrections on azimuthal asymmetries in the color glass condensate." European Physical Journal C 79, no. 9 (September 2019). http://dx.doi.org/10.1140/epjc/s10052-019-7315-1.

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Abstract We analyse the azimuthal structure of two gluon correlations in the color glass condensate including those effects that result from relaxing the shockwave approximation for the target. Working in the Glasma graph approach suitable for collisions between dilute systems, we compute numerically the azimuthal distributions and show that both even and odd harmonics appear. We study their dependence on model parameters, energy of the collision, pseudorapidity and transverse momentum of the produced particles, and length of the target. While the contribution from non-eikonal corrections vanishes with increasing collision energy and becomes negligible at the energies of the Large Hadron Collider, it is found to be sizeable up to top energies at the Relativistic Heavy Ion Collider.

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Parra-Martinez, Julio, Michael S. Ruf, and Mao Zeng. "Extremal black hole scattering at $$ \mathcal{O} $$(G3): graviton dominance, eikonal exponentiation, and differential equations." Journal of High Energy Physics 2020, no. 11 (November 2020). http://dx.doi.org/10.1007/jhep11(2020)023.

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Abstract We use $$ \mathcal{N} $$ N = 8 supergravity as a toy model for understanding the dynamics of black hole binary systems via the scattering amplitudes approach. We compute the conservative part of the classical scattering angle of two extremal (half-BPS) black holes with minimal charge misalignment at $$ \mathcal{O} $$ O (G3) using the eikonal approximation and effective field theory, finding agreement between both methods. We construct the massive loop integrands by Kaluza-Klein reduction of the known D-dimensional massless integrands. To carry out integration we formulate a novel method for calculating the post-Minkowskian expansion with exact velocity dependence, by solving velocity differential equations for the Feynman integrals subject to modified boundary conditions that isolate conservative contributions from the potential region. Motivated by a recent result for universality in massless scattering, we compare the scattering angle to the result found by Bern et. al. in Einstein gravity and find that they coincide in the high-energy limit, suggesting graviton dominance at this order.

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Bonnans, Frédéric, Guillaume Bonnet, and Jean-Marie Mirebeau. "A linear finite-difference scheme for approximating Randers distances on Cartesian grids." ESAIM: Control, Optimisation and Calculus of Variations, June 2, 2022. http://dx.doi.org/10.1051/cocv/2022043.

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Randers distances are an asymmetric generalization of Riemannian distances, and arise in optimal control problems subject to a drift term, among other applications. We show that Randers eikonal equation can be approximated by a logarithmic transformation of an anisotropic second order linear equation, generalizing Varadhan's formula for Riemannian manifolds. Based on this observation, we establish the convergence of a numerical method for computing Randers distances, from point sources or from a domain's boundary, on Cartesian grids of dimension two and three, which is consistent at order two thirds, and uses tools from low-dimensional algorithmic geometry for best efficiency. We also propose a numerical method for optimal transport problems whose cost is a Randers distance, exploiting the linear structure of our discretization and generalizing previous works in the Riemannian case. Numerical experiments illustrate our results.

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Bellazzini, Brando, Giulia Isabella, Matthew Lewandowski, and Francesco Sgarlata. "Gravitational causality and the self-stress of photons." Journal of High Energy Physics 2022, no. 5 (May 2022). http://dx.doi.org/10.1007/jhep05(2022)154.

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Abstract We study causality in gravitational systems beyond the classical limit. Using on-shell methods, we consider the 1-loop corrections from charged particles to the photon energy-momentum tensor — the self-stress — that controls the quantum interaction between two on-shell photons and one off-shell graviton. The self-stress determines in turn the phase shift and time delay in the scattering of photons against a spectator particle of any spin in the eikonal regime. We show that the sign of the β-function associated to the running gauge coupling is related to the sign of time delay at small impact parameter. Our results show that, at first post-Minkowskian order, asymptotic causality, where the time delay experienced by any particle must be positive, is respected quantum mechanically. Contrasted with asymptotic causality, we explore a local notion of causality, where the time delay is longer than the one of gravitons, which is seemingly violated by quantum effects.

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Raffaelli, Bernard. "Hidden conformal symmetry on the black hole photon sphere." Journal of High Energy Physics 2022, no. 3 (March 2022). http://dx.doi.org/10.1007/jhep03(2022)125.

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Abstract We consider a class of static and spherically symmetric black hole geometries endowed with a photon sphere. On the one hand, we show that close to the photon sphere, a massless scalar field theory exhibits a simple dynamical SL(2, ℝ) algebraic structure which allows to recover the discrete spectrum of the weakly damped quasinormal frequencies in the eikonal approximation, and the associated quasinormal modes from the algebra representations. On the other hand, we consider the non-radial motion of a free-falling test particle, in the equatorial plane, from spatial infinity to the black hole. In the ultrarelativistic limit, we show that the photon sphere acts as an effective Rindler horizon for the geodesic motion of the test particle in the (t, r)-plane, with an associated Unruh temperature Tc = ħΛc/2πkB, where Λc is the Lyapunov exponent that characterizes the unstable circular motions of massless particles on the photon sphere. The photon sphere then appears as a location where the thermal bound on chaos for quantum systems with a large number of degrees of freedom, in the form conjectured a few years ago by Maldacena et al., is saturated. The study developed in this paper could hopefully shed a new light on the gravity/CFT correspondence, particularly in asymptotically flat spacetimes, in which the photon sphere may also be considered as a holographic screen.

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Kaufman, Allan N., and Bruce I. Cohen. "Theoretical plasma physics." Journal of Plasma Physics 85, no. 6 (November 13, 2019). http://dx.doi.org/10.1017/s0022377819000667.

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These lecture notes were presented by Allan N. Kaufman in his graduate plasma theory course and a follow-on special topics course (Physics 242A, B, C and Physics 250 at the University of California Berkeley). The notes follow the order of the lectures. The equations and derivations are as Kaufman presented, but the text is a reconstruction of Kaufman’s discussion and commentary. The notes were transcribed by Bruce I. Cohen in 1971 and 1972, and word processed, edited and illustrations added by Cohen in 2017 and 2018. The series of lectures is divided into four major parts: (i) collisionless Vlasov plasmas (linear theory of waves and instabilities with and without an applied magnetic field, Vlasov–Poisson and Vlasov–Maxwell systems, Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) eikonal theory of wave propagation); (ii) nonlinear Vlasov plasmas and miscellaneous topics (the plasma dispersion function, singular solutions of the Vlasov–Poisson system, pulse-response solutions for initial-value problems, Gardner’s stability theorem, gyroresonant effects, nonlinear waves, particle trapping in waves, quasilinear theory, nonlinear three-wave interactions); (iii) plasma collisional and discreteness phenomena (test-particle theory of dynamic friction and wave emission, classical resistivity, extension of test-particle theory to many-particle phenomena and the derivation of the Boltzmann and Lenard–Balescu equations, the Fokker–Planck collision operator, a general scattering theory, nonlinear Landau damping, radiation transport and Dupree’s theory of clumps); (iv) non-uniform plasmas (adiabatic invariance, guiding-centre drifts, hydromagnetic theory, introduction to drift-wave stability theory).

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Kumar, Jitendra, and Ashish Dutta. "Energy optimal motion planning of a 14-DOF biped robot on 3D terrain using a new speed function incorporating biped dynamics and terrain geometry." Robotica, May 14, 2021, 1–29. http://dx.doi.org/10.1017/s0263574721000515.

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Abstract In this paper, a new method is proposed to find a feasible energy-efficient path between an initial point and goal point on uneven terrain and then to optimally traverse the path. The path is planned by integrating the geometric features of the uneven terrain and the biped robot dynamics. This integrated information of biped dynamics and associated cost (energy) for moving toward the goal point is used to define the value of a new speed function at each point on the discretized surface of the terrain. The value is stored as a matrix called the dynamic transport cost (DTC). The path is obtained by solving the Eikonal equation numerically by fast marching method (FMM) on an orthogonal grid, by using the information stored in the DTC matrix. One step of walk on uneven terrain is characterized by 10 footstep parameters (FSPs); these FSPs represent the position of swinging foot at the starting and ending time of the walk, orientation, and state (left or right) of support foot. A walking dataset was created for different walking conditions (FSPs), which the biped robot is likely to encounter when it has to walk on the uneven terrain. The corresponding energy optimal hip and foot trajectory parameters (HFTPs) are obtained by optimization using a genetic algorithm (GA). The created walk dataset is generalized by training a feedforward neural network (NN) using the scaled conjugate gradient (SCG) algorithm. The Foot placement planner gives a sequence of foot positions and orientations along the obtained path, which is followed by the biped robot by generating real-time optimal foot and hip trajectories using the learned NN. Simulation results on different types of uneven terrains validate the proposed method.

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Nguyen, Linh-TX. "The relationship between corporate sustainability performance and earnings management: evidence from emerging East Asian economies." Journal of Financial Reporting and Accounting, March 29, 2022. http://dx.doi.org/10.1108/jfra-09-2021-0302.

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Purpose This study aims to investigate the relationship between corporate sustainability performance and earnings management in emerging East Asian economies. Design/methodology/approach The authors base on the triple bottom line approach to measure corporate sustainability performance. In terms of earnings management, two models are applied to detect real activities manipulation and discretionary accruals. The authors use panel data analysis of 410 listed non-financial firms in emerging East Asian economies from 2016 to 2020 that are collected from the Thomson Reuters Eikon database. Findings The authors find a negative influence of corporate sustainability performance on real activities manipulation and discretionary accruals. The findings highlight the long-term perspective of sustainable development strategies in relation to earnings management. The authors conclude that sustainable firms in emerging East Asia are less likely to engage in earnings management. Practical implications The study would be of interest to investors who need more detailed assessments of financial reporting quality to facilitate their investment decision-making and to policymakers who need more understanding of business practices and reporting behaviors of East Asian firms. Originality/value The study has shed light on the role of corporate sustainability performance in constraining earnings management and the role of corporate ethics in providing transparent and reliable financial reporting in emerging East Asian economies.

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Journal articles on the topic 'Eikonal systems'

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