Revising the multipole moments of numerical spacetimes, and its consequences

Identifying the relativistic multipole moments of a spacetime of an astrophysical object that has been constructed numerically is of major interest, both because the multipole moments are intimately related to the internal structure of the object, and because the construction of a suitable analytic metric that mimics a numerical metric should be based on the multipole moments of the latter one, in order to yield a reliable representation. In this note we show that there has been a widespread delusion in the way the multipole moments of a numerical metric are read from the asymptotic expansion of the metric functions. We show how one should read correctly the first few multipole moments (starting from the quadrupole mass-moment), and how these corrected moments improve the efficiency of describing the metric functions with analytic metrics that have already been used in the literature, as well as other consequences of using the correct moments.Comment: article + supplemental materia

Modeling of Coastal Erosion in Exposed and Groin-Protected Steep Beaches

Process-based models are suitable tools for reproducing storm-driven erosion. However, their performance has been mainly examined on mild-slope sandy beaches and their use on steep beaches still represents a challenge. Here, open-source process-based model XBeach experiments were combined with topographical measurements collected for two storms (16- and 5-year return period) to obtain a reliable model. The model parameters "facua"(parameterized wave asymmetry and skewness sediment transport component), "bermslope"(upslope transport term for semireflective beaches), and "wetslope"(critical avalanching submerged slope) were utilized for calibration and validation. The 16-year storm simulations on an exposed beach revealed that whether bermslope increased and "facua"must be reduced, and vice versa, to properly simulate erosion. Adding bermslope provided excellent results for these storms when using facua and wetslope values close to the recommended values. In a groin-protected site, XBeach was successfully calibrated and validated for the tested storms using these parameters, although with different values. These experiments demonstrated that the appropriate use of these parameters can satisfactorily simulate morphological changes on steep beaches for different hydrodynamic conditions and coastal settings (exposed and groin protected). © 2022 This work is made available under the terms of the Creative Commons Attribution 4.0 International license

Modeling of coastal erosion in exposed and groin-protected steep beaches

Process-based models are suitable tools for reproducing storm-driven erosion. However, their performance has been mainly examined on mild-slope sandy beaches and their use on steep beaches still represents a challenge. Here, open-source process-based model XBeach experiments were combined with topographical measurements collected for two storms (16- and 5-year return period) to obtain a reliable model. The model parameters “facua” (parameterized wave asymmetry and skewness sediment transport component), “bermslope” (upslope transport term for semireflective beaches), and “wetslope” (critical avalanching submerged slope) were utilized for calibration and validation. The 16-year storm simulations on an exposed beach revealed that whether bermslope increased and “facua” must be reduced, and vice versa, to properly simulate erosion. Adding bermslope provided excellent results for these storms when using facua and wetslope values close to the recommended values. In a groin-protected site, XBeach was successfully calibrated and validated for the tested storms using these parameters, although with different values. These experiments demonstrated that the appropriate use of these parameters can satisfactorily simulate morphological changes on steep beaches for different hydrodynamic conditions and coastal settings (exposed and groin protected).info:eu-repo/semantics/acceptedVersio

Dark matter-wave solitons in the dimensionality crossover

We consider the statics and dynamics of dark matter-wave solitons in the dimensionality crossover regime from 3D to 1D. There, using the nonpolynomial Schr\"{o}dinger mean-field model, we find that the anomalous mode of the Bogoliubov spectrum has an eigenfrequency which coincides with the soliton oscillation frequency obtained by the 3D Gross-Pitaevskii model. We show that substantial deviations (of order of 10% or more) from the characteristic frequency $\omega_{z}/\sqrt{2}$ ($\omega_{z}$ being the longitudinal trap frequency) are possible even in the purely 1D regime.Comment: Phys. Rev. A, in pres

Impact of anisotropy on vortex clusters and their dynamics

We investigate the effects of anisotropy on the stability and dynamics of vortex cluster states which arise in Bose-Einstein condensates. Sufficiently strong anisotropies are shown to stabilize states with arbitrary numbers of vortices that are highly unstable in the isotropic limit. Conversely, anisotropy can be used to destabilize states which are stable in the isotropic limit. Near the linear limit, we identify the bifurcations of vortex states including their emergence from linear eigenstates, while in the strongly nonlinear limit, a particle-like description of the dynamics of the vortices in the anisotropic trap is developed. Both are in very good agreement with numerical results. Collective modes of stabilized many vortex cluster states are demonstrated.Comment: 6 pages, 6 figure

Tunable Vibrational Band Gaps in One-Dimensional Diatomic Granular Crystals with Three-Particle Unit Cells

We investigate the tunable vibration filtering properties of one-dimensional diatomic granular crystals composed of arrays of stainless steel spheres and cylinders interacting via Hertzian contact. The arrays consist of periodically repeated three-particle unit cells (steel-cylinder-sphere) in which the length of the cylinder is varied systematically. We apply static compression to linearize the dynamic response of the crystals and characterize their linear frequency spectrum. We find good agreement between theoretical dispersion relation analysis (for infinite systems), state-space analysis (for finite systems), and experiments. We report the observation of up to three distinct pass bands and two finite band gaps and show their tunability for variations in cylinder length and static compression

Stationary states of a nonlinear Schrödinger lattice with a harmonic trap

We study a discrete nonlinear Schrödinger lattice with a parabolic trapping potential. The model, describing, e.g., an array of repulsive Bose-Einstein condensate droplets confined in the wells of an optical lattice, is analytically and numerically investigated. Starting from the linear limit of the problem, we use global bifurcation theory to rigorously prove that – in the discrete regime – all linear states lead to nonlinear generalizations thereof, which assume the form of a chain of discrete dark solitons (as the density increases). The stability of the ensuing nonlinear states is studied and it is found that the ground state is stable, while the excited states feature a chain of stability/instability bands. We illustrate the mechanisms under which discreteness destabilizes the dark-soliton configurations, which become stable only in the continuum regime. Continuation from the anti-continuum limit is also considered, and a rich bifurcation structure is revealed

Stealth Acoustic Materials

[EN] We report the experimental design of a one-dimensional stealth acoustic material, namely a material that suppresses the acoustic scattering for a given set of incident wave vectors. The material consists of multiple scatterers, rigid diaphragms, located in an air-filled acoustic waveguide. The position of the scatterers has been chosen such that in the Born approximation a suppression of the scattering for a broad range of frequencies is achieved and thus a broadband transparency. Experimental results are found in excellent agreement with the theory despite the presence of losses and the finite size of the material, features that are not captured in the theory. This robustness as well as the generality of the results motivates realistic potential applications for the design of transparent materials in acoustics and other fields of wave physics.This work has been funded by RFI Le Mans Acoustique (Region Pays de la Loire) in the framework of the APA-MAS project, by the project HYPERMETA funded under the program Etoiles Montantes of the Region Pays de la Loire as well as by the Ministerio de Economia y Competitividad (Spain) and European Union FEDER through project FIS2015-65998-C2-2-P. V. Romero-Garcia and L. M. Garcia-Raffi acknowledge the short-term scientific mission (STSM) funded by the COST (European Cooperation in Science and Technology) Action DENORMS - CA15125.Romero-García, V.; Lamothe, N.; Theocharis, G.; Richoux, O.; García-Raffi, LM. (2019). Stealth Acoustic Materials. Physical Review Applied. 11(5):1-9. https://doi.org/10.1103/PhysRevApplied.11.054076S19115Shen, C., Xu, J., Fang, N. X., & Jing, Y. (2014). 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Nature Photonics, 2(8), 465-473. doi:10.1038/nphoton.2008.146Kaya, O. A., Cicek, A., & Ulug, B. (2012). Self-collimated slow sound in sonic crystals. Journal of Physics D: Applied Physics, 45(36), 365101. doi:10.1088/0022-3727/45/36/365101Theocharis, G., Richoux, O., García, V. R., Merkel, A., & Tournat, V. (2014). Limits of slow sound propagation and transparency in lossy, locally resonant periodic structures. New Journal of Physics, 16(9), 093017. doi:10.1088/1367-2630/16/9/093017Groby, J.-P., Pommier, R., & Aurégan, Y. (2016). Use of slow sound to design perfect and broadband passive sound absorbing materials. The Journal of the Acoustical Society of America, 139(4), 1660-1671. doi:10.1121/1.4945101Wiersma, D. S. (2013). Disordered photonics. Nature Photonics, 7(3), 188-196. doi:10.1038/nphoton.2013.29Hu, H., Strybulevych, A., Page, J. H., Skipetrov, S. E., & van Tiggelen, B. A. (2008). Localization of ultrasound in a three-dimensional elastic network. Nature Physics, 4(12), 945-948. doi:10.1038/nphys1101Sperling, T., Bührer, W., Aegerter, C. M., & Maret, G. (2012). Direct determination of the transition to localization of light in three dimensions. Nature Photonics, 7(1), 48-52. doi:10.1038/nphoton.2012.313Fan, Y., Percus, J. K., Stillinger, D. K., & Stillinger, F. H. (1991). Constraints on collective density variables: One dimension. Physical Review A, 44(4), 2394-2402. doi:10.1103/physreva.44.2394Kuhl, U., Izrailev, F. M., Krokhin, A. A., & Stöckmann, H.-J. (2000). Experimental observation of the mobility edge in a waveguide with correlated disorder. Applied Physics Letters, 77(5), 633-635. doi:10.1063/1.127068Torquato, S. (2002). Random Heterogeneous Materials. Interdisciplinary Applied Mathematics. doi:10.1007/978-1-4757-6355-3Uche, O. U., Stillinger, F. H., & Torquato, S. (2004). Constraints on collective density variables: Two dimensions. Physical Review E, 70(4). doi:10.1103/physreve.70.046122Kuhl, U., Izrailev, F. 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C., … Steinhardt, P. J. (2013). Isotropic band gaps and freeform waveguides observed in hyperuniform disordered photonic solids. Proceedings of the National Academy of Sciences, 110(40), 15886-15891. doi:10.1073/pnas.1307879110Man, W., Florescu, M., Matsuyama, K., Yadak, P., Nahal, G., Hashemizad, S., … Chaikin, P. (2013). Photonic band gap in isotropic hyperuniform disordered solids with low dielectric contrast. Optics Express, 21(17), 19972. doi:10.1364/oe.21.019972Torquato, S. (2016). Hyperuniformity and its generalizations. Physical Review E, 94(2). doi:10.1103/physreve.94.022122Torquato, S., Zhang, G., & Stillinger, F. H. (2015). Ensemble Theory for Stealthy Hyperuniform Disordered Ground States. Physical Review X, 5(2). doi:10.1103/physrevx.5.021020Leseur, O., Pierrat, R., & Carminati, R. (2016). High-density hyperuniform materials can be transparent. Optica, 3(7), 763. doi:10.1364/optica.3.000763Gkantzounis, G., Amoah, T., & Florescu, M. (2017). 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Screened thermonuclear reactions and predictive stellar evolution of detached double-lined eclipsing binaries

The low energy fusion cross sections of charged-particle nuclear reactions (and the respective reaction rates) in stellar plasmas are enhanced due to plasma screening effects. We study the impact of those effects on predictive stellar evolution simulations for detached double-lined eclipsing binaries. We follow the evolution of binary systems (pre-main sequence or main sequence stars) with precisely determined radii and masses from 1.1Mo to 23Mo (from their birth until their present state). The results indicate that all the discrepancies between the screened and unscreened models (in terms of luminosity, stellar radius, and effective temperature) are within the observational uncertainties. Moreover, no nucleosynthetic or compositional variation was found due to screening corrections. Therefore all thermonuclear screening effects on the charged-particle nuclear reactions that occur in the binary stars considered in this work (from their birth until their present state) can be totally disregarded. In other words, all relevant charged-particle nuclear reactions can be safely assumed to take place in a vacuum, thus simplifying and accelerating the simulation processes.Comment: 5 RevTex pages,no figures. Accepted for publication in Phys.Rev.

Dark solitons in cigar-shaped Bose-Einstein condensates in double-well potentials

We study the statics and dynamics of dark solitons in a cigar-shaped Bose-Einstein condensate confined in a double-well potential. Using a mean-field model with a non-cubic nonlinearity, appropriate to describe the dimensionality crossover regime from one to three dimensional, we obtain branches of solutions in the form of single- and multiple-dark soliton states, and study their bifurcations and stability. It is demonstrated that there exist dark soliton states which do not have a linear counterpart and we highlight the role of anomalous modes in the excitation spectra. Particularly, we show that anomalous mode eigenfrequencies are closely connected to the characteristic soliton frequencies as found from the solitons' equations of motion, and how anomalous modes are related to the emergence of instabilities. We also analyze in detail the role of the height of the barrier in the double well setting, which may lead to instabilities or decouple multiple dark soliton states.Comment: 35 pages, 12 figure