Propagation Phenomena Research Articles

The iron and nickel spectra measured with CALET on the international space station

Recent direct measurements of the energy spectra of the charged cosmic ray have revealed unexpected spectral features, most notably the onset of a progressive hardening at few hundreds of GeV/n not only of proton and He spectra but also observable for heavier nuclei. Thus, the study of the spectra behavior of heavy elements may shed light on understanding propagation and acceleration phenomena in our Galaxy. In particular, Fe and Ni provide favorable conditions for observations thanks to the low background contamination from spallation of higher mass elements they are affected by. The CALorimetric Electron Telescope, CALET, has been measuring high-energy cosmic rays on the International Space Station since October 2015. The instrument consists of two layers of segmented plastic scintillators, a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter and a 27 radiation length thick PWO calorimeter. It identifies the charge of individual elements up to Ni and beyond and it measures the energy of cosmic-ray nuclei providing a direct measurement of their spectra. In this contribution, the iron and nickel spectra, resulted after 5 years of data acquisition, are presented in the energy range between 10 and 2000 GeV/n and between 8.8 and 240 GeV/n, respectively. The analysis procedure and the assessment of systematic errors are detailed, in addition to the ratio between the two fluxes. Both spectra show similar shape and energy dependence.

A Line of Sight/Non Line of Sight Recognition Method Based on the Dynamic Multi-Level Optimization of Comprehensive Features.

With the advent of the 5G era, high-precision localization based on mobile communication networks has become a research hotspot, playing an important role in indoor emergency rescue in shopping malls, smart factory management and tracking, as well as precision marketing. However, in complex environments, non-line-of-sight (NLOS) propagation reduces the measurement accuracy of 5G signals, causing large deviations in position solving. In order to obtain high-precision position information, it is necessary to recognize the propagation state of the signal before distance measurement or angle measurement. In this paper, we propose a dynamic multi-level optimization of comprehensive features (DMOCF) network model for line-of-sight (LOS)/NLOS identification. The DMOCF model improves the expression ability of the deep model by adding a res2 module to the time delay neural network (TDNN), so that fine-grained feature information such as weak reflections or noise in the signal can be deeply understood by the model, enabling the network to realize layer-level feature processing by adding Squeeze and Excitation (SE) blocks with adaptive weight adjustment for each layer. A mamba module with position coding is added to each layer to capture the local patterns of wireless signals under complex propagation phenomena by extracting local features, enabling the model to understand the evolution of signals over time in a deeper way. In addition, this paper proposes an improved sand cat search algorithm for network parameter search, which improves search efficiency and search accuracy. Overall, this new network architecture combines the capabilities of local feature extraction, global feature preservation, and time series modeling, resulting in superior performance in the 5G channel impulse response (CIR) signal classification task, improving the accuracy of the model and accurately identifying the key characteristics of multipath signal propagation. Experimental results show that the NLOS/LOS recognition method proposed in this paper has higher accuracy than other deep learning methods.

Wave transformation in transmission lines with rapid connection and disconnection of reactive elements

Rapid switching of transmission line parameters has emerged as a way to manipulate signals and as a testbed for various electromagnetic processes in time-varying media, including metamaterials. In general, the switching results in wave reflection and transmission similar to that for a spatial interface but at new frequencies. Here, various realizations of parameter switching are studied: connection and disconnection of reactive elements (capacitors and inductors) in series and in parallel. The temporal boundary conditions for the current and voltage distributions are derived rigorously based on the telegrapher’s equations that explicitly model additional elements, instead of taking the equivalent values. It is shown that the temporal boundary conditions depend not only on the parameter values before and after switching but on its specific realization. Connecting or disconnecting reactive elements always involves energy losses. When new elements are added, two types of losses are identified. The first type is related to the creation of static magnetic and electric fields in the elements after switching. The second type is related to a very rapid energy dissipation during switching even for a vanishingly small resistivity in the line. When elements are removed, their energy is also removed from the waves. The effects of finite switching times are discussed. This study defines some serious constraints in using switchable transmission lines for the realization of photonic time crystals and efficient wave manipulation without externally added energy. The results are also applicable to wave propagation phenomena in other media with time-varying parameters.

APPLICATION OF CABARET AND WENO SCHEMES FOR SOLVING THE NONLINEAR TRANSPORT EQUATION IN THE MODELING OF SOUND WAVE PROPAGATION IN THE ATMOSPHERE

The most convenient model for describing the phenomenon of shock wave propagation in the atmosphere is the extended Burgers equation. This work investigates the influence of the numerical scheme on the results of solving the equation, which accounts for the nonlinear nature of shock wave propagation in the atmosphere. This equation is a key component of the extended Burgers equation and defines the transformation of the perturbed pressure profile during its propagation. Two numerical schemes were applied for the solution: CABARET and WENO, which are quasi-monotonic finite difference schemes that allow for solutions without significant numerical oscillations. An analysis of the applicability of these schemes for solving the considered problem was conducted.

Modeling and Analysis of Dispersive Propagation of Structural Waves for Vibro-Localization.

The dispersion of structural waves, where wave speed varies with frequency, introduces significant challenges in accurately localizing occupants in a building based on vibrations caused by their movements. This study presents a novel multi-sensor vibro-localization technique that accounts for dispersion effects, enhancing the accuracy and robustness of occupant localization. The proposed method utilizes a model-based approach to parameterize key propagation phenomena, including wave dispersion and attenuation, which are fitted to observed waveforms. The localization is achieved by maximizing the joint likelihood of the occupant's location based on sensor measurements. The effectiveness of the proposed technique is validated using two experimental datasets: one from a controlled environment involving an aluminum plate and the other from a building-scale experiment conducted at Goodwin Hall, Virginia Tech. Results for the proposed algorithm demonstrates a significant improvement in localization accuracy compared to benchmark algorithms. Specifically, in the aluminum plate experiments, the proposed technique reduced the average localization precision from 7.77 cm to 1.97 cm, representing a ∼74% improvement. Similarly, in the Goodwin Hall experiments, the average localization error decreased from 0.67 m to 0.3 m, with a ∼55% enhancement in accuracy. These findings indicate that the proposed approach outperforms existing methods in accurately determining occupant locations, even in the presence of dispersive wave propagation.

A novel flexible infinite element for transient acoustic simulations

This article addresses the efficient solution of exterior acoustic transient problems using the Finite Element Method (FEM) in combination with infinite elements. Infinite elements are a popular technique to enforce non-reflecting boundary conditions. The Astley–Leis formulation presents several advantages in terms of ease of implementation, and results in frequency-independent system matrices, that can be used for transient simulations of wave propagation phenomena. However, for time-domain simulations, the geometrical flexibility of Astley–Leis infinite elements is limited by time-stability requirements. In this article, we present a novel infinite element formulation, called flexible infinite element, for which the accuracy does not depend on the positioning of the virtual sources. From a software implementation perspective, the element proposed can be seen as a specialized FEM element and can be easily integrated into a high-order FEM code. The effectiveness of the flexible formulation is demonstrated with frequency and time-domain examples; for both cases, we show how the flexible infinite elements can be attached to arbitrarily-shaped convex FE boundaries. In particular, we show how the proposed technique can be used in combination with existing model order reduction strategies to run fast and accurate transient simulations.

Heat propagation phenomenon of compressed natural gas /air premixed laminar flame impinging on a flat surface

In this paper the heat transfer characteristics have been determined theoretically using heat propagation phenomena of compressed natural gas (CNG)/air premixed laminar flames impinging on flat surfaces. Effects of varied equivalence ratios (Ф), Reynolds numbers (Re), separation distances (H/d) and burner diameters (d) on stagnation point heat flux have been investigated. The simulation findings were validated with the available experimental data. The flat plate with the maximum heat flux at the stagnation position is located close to the margin of the innermost premixed reaction zone (i.e., at H/d, Re and d are 5, 1000, 8 mm). The flow of heat steadily decreases in axial direction as the separating distance from the inner reaction zone's tip increases. Greater separation lengths at the stagnation region cause a subsequent increase in heat flux. The objective of this investigation is to get an idea about the impact of existence of the plate on the flame and temperature distribution and to get clarity about the reason behind higher amount of heat flux owing to tip of the innermost reaction area at stagnation region.

Complete dynamic model of a Slinky based on torsion springs

In this paper a dynamic torsion spring model is extended to be applicable to Slinky's with a wide range of possible initial configurations. In the extended model the coil-on-coil impact is modelled by conserving momentum and modelling the impact as an inelastic impact with a zero coefficient of restitution. The extended model is applied to a plastic Slinky and a steel Slinky. The extended model is demonstrated to have the qualitatively correct dynamic behavior. The extended torsion spring model is now in a form to be applied to a wide range of Slinky behavior such as pseudo-levitation, wave propagation phenomena and stair walking.

Two scientific perspectives on nerve signal propagation: how incompatible approaches jointly promote progress in explanatory understanding

We present a case study of two scientific perspectives on the phenomenon of nerve signal propagation, a bio-electric and a thermodynamic perspective, and compare this case with two accounts of scientific perspectivism: those of Michela Massimi and Juha Saatsi, respectively. We demonstrate that the interaction between the bio-electric perspective and the thermodynamic perspective can be captured in Saatsi’s terms of progress in explanatory understanding. Using insights from our case study, we argue that both the epistemic and pragmatic dimensions of scientific understanding are important for increasing explanatory understanding of phenomena. The epistemic dimension of understanding is important for increasing the number of actually answered what-if-things-had-been-different questions about a phenomenon, the pragmatic dimension for pointing out the potentially answerable what-if questions that have been overlooked or purposefully neglected thus far. Exposing the limitations of the acquired understanding within a particular perspective can be achieved by criticizing the assumptions that have been adopted to make models of the perspective intelligible, but that are considered problematic from a rival perspective.

Helmholtz FEM solutions are locally quasi-optimal modulo low frequencies

For h-FEM discretisations of the Helmholtz equation with wavenumber k, we obtain k-explicit analogues of the classic local FEM error bounds of Nitsche and Schatz (Math. Comput. 28(128), 937–958 1974), Wahlbin (1991, §9), Demlow et al.(Math. Comput. 80(273), 1–9 2011), showing that these bounds hold with constants independent of k, provided one works in Sobolev norms weighted with k in the natural way. We prove two main results: (i) a bound on the local H1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H^1$$\\end{document} error by the best approximation error plus the L2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$L^2$$\\end{document} error, both on a slightly larger set, and (ii) the bound in (i) but now with the L2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$L^2$$\\end{document} error replaced by the error in a negative Sobolev norm. The result (i) is valid for shape-regular triangulations, and is the k-explicit analogue of the main result of Demlow et al. (Math. Comput. 80(273), 1–9 2011). The result (ii) is valid when the mesh is locally quasi-uniform on the scale of the wavelength (i.e., on the scale of k-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k^{-1}$$\\end{document}) and is the k-explicit analogue of the results of Nitsche and Schatz (Math. Comput. 28(128), 937–958 1974), Wahlbin (1991, §9). Since our Sobolev spaces are weighted with k in the natural way, the result (ii) indicates that the Helmholtz FEM solution is locally quasi-optimal modulo low frequencies (i.e., frequencies ≲k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lesssim k$$\\end{document}). Numerical experiments confirm this property, and also highlight interesting propagation phenomena in the Helmholtz FEM error.

Micro-damage instability mechanisms in composite materials: Cracking coalescence versus fibre ductility and slippage

The load-displacement softening response of quasi-brittle solids exhibits an unstable structural behavior, which is characterised by a negative slope in the post-peak regime. In severely brittle situations, the post-peak behaviour can show a virtual positive slope, the fracture propagation occurring unexpectedly with a catastrophic loss in the load-carrying capacity. In this case, if the displacement controls the loading process, the curve exhibits a discontinuity and the representative point drops to the lower branch with a negative slope. On the other hand, in order to obtain a stable crack growth, a decrease both in load and in displacement is required. In the last forty years, in-depth study of the so-called snap-back instability was conducted in relation to crack propagation phenomena in quasi-brittle materials. In the present work, the structural response of two brittle-matrix specimens is analysed: the first contains a distribution of collinear micro-cracks, whereas the second presents multiple parallel reinforcing fibres embedded in the matrix. In both cases, it is shown that the structural response presents a discrete number of snap-back instabilities with related peaks and valleys, the crack propagation occurring alternately within the matrix and through the heterogeneities. Thus, the strong analogy between weakened and strengthened zones consists in a multiple snap-back mechanical response, where descending branches of propagating cracks alternate with ascending (linear) branches of arrested cracks.

Investigation on the transmission of Love waves due to an impulsive line source in a heterogeneous double porous rock structure

The region around the reservoir sometimes encounters the seismic response of ground. The phenomena of Love waves propagation also caused by seismic activity which can further significantly influenced by an impulsive line source present in the rock structures of ground. The current study elucidates the propagation behavior of Love waves induced by an impulsive line source within the anisotropic layered heterogeneous double porous rock structures commonly found in proximity to the reservoir areas. The expression of the dispersion relation for the Love waves propagation due to an impulsive line source has been derived by using the Fourier transformation and Green’s function technique. The above-mentioned rock composite structure is consisted of two different portions: upper transversely isotropic double porous (TIDP) layer medium and lower heterogeneous isotropic double porous half-space (IDP) medium. In the aforesaid half-space medium, both types of heterogeneities viz. linear and quadratic have been considered. The impacts of heterogeneity parameters associated with the lower heterogeneous IDP half-space, porosity parameter (corresponds to both upper TIDP layer and lower IDP half-space) and anisotropic parameter of TIDP layer on Love waves phase velocity have also been studied. Some special outlines have also been depicted graphically.

New periodic solutions and solitary wave solutions for the time-fractional differential equations

In this paper, we obtain many different types of exact solutions to the time-fractional Klein–Gordon equation and the time-fractional generalized Hirota-Satsuma coupled KdV system by using the modified rational function approach. Some new solutions such as the kink-periodic solution, the anti-kink-periodic solution and the concave-convex-periodic solution are constructed. Furthermore, the kink and the singular kink waves, the bell shaped soliton and the singular soliton solutions of the two equations also are found. Some numerical simulations are presented, these works can effectively reflect the propagation phenomena of time-fractional nonlinear systems, and also enable us to understand time-fractional nonlinear physical phenomena more clearly.

Propagation dynamics of a three-species predator–prey model with non-local dispersal in a shifting habitat

This paper is concerned with the propagation phenomenon of a non-local dispersal predator–prey system involving two preys and one predator in a shifting habitat. Assuming that the growth rate of each prey is moving to the right at a speed of [Formula: see text] and the habitat is suitable for each prey to survive before the shifting edge, while the habitat behind the boundary is not suitable for survival. For any given speed of the shifting habitat edge, we establish four types of forced extinction waves, which describe the conversion from the state of a saturated aboriginal prey with a pair of invading alien predator–prey, two aboriginal co-existent preys with an invading alien predator, a pair of aboriginal co-existent predator–prey and an invading alien prey, and the co-existence of three species to the extinction state, respectively. Meanwhile, we show the non-existence of some forced waves.

Modeling of a moving point source in inhomogeneous and turbulent media - Application to aircraft noise

Engineering solutions for the modeling of aircraft noise often rely on simplified approaches that consider quasi-static sources and homogenous propagation conditions. These hypothesis may lead to significant inaccuracies on sound pressure level predictions in certain configurations, especially for source traveling at high mach number and at several hundred meters from the receiver. In order to overcome these limitations, an efficient numerical model based on the coupling of a heuristic formulation and a ray-tracing model is proposed. The modeling takes into account source motion effect (Doppler effect and convective amplification), as well as the sound propagation phenomena in inhomogeneous media (waves refraction and scattering by atmospheric turbulence). Several case study related to aircraft noise are presented, for which wind and temperature profiles correspond to experimental measurements. The influence of atmospheric turbulence for such configuration is finally discussed. This work is part of the program MAMBO (Advanced methods for engine and aicraft noise modelling" coordinated by Airbus SAS and supported by the Direction Générale de l'Aviation Civile (DGAC).

Performance of an oscillating water column wave energy converter device under random ocean waves and ocean currents

The present study investigates the hydrodynamic performance of an onshore oscillating water column (OWC) device placed over an undulated bottom topography by analyzing its hydrodynamic efficiency under the action of combined wave–current interaction. The classical small-amplitude water wave theory is used to model the physical problem. The constant boundary element method is employed to solve the boundary value problem. Significant attention is devoted to describing the hydrodynamic parameters associated with the OWC device by considering the mutual combination of the random waves and ocean currents in the wave propagation phenomena. To examine the complex dynamics of the combined irregular wave current phenomena, the Det Norske Veritas spectrum accompanied by a suitable sea state has been considered for the present study. Considering the existence of opposing and following currents in wave propagation, a comprehensive analysis is conducted on the interactions of regular and irregular water waves with the OWC device. The simulated results demonstrate that the presence of ocean currents in the wave propagation phenomenon strongly influences the resonating patterns of the efficiency and force curves. Additionally, the Doppler shift in the apparent frequency caused by the following currents in the random wave–current interaction significantly improves the device's efficiency for an appropriate structural design.

Research on the characteristics of information propagation dynamic on the weighted multiplex Weibo networks

In order to simulate the forwarding situation of different categories of Weibo and discover interesting propagation phenomena in different layers of Weibo networks, this paper proposes the retweeting weighted multiplex networks and propagation model coupled with multi-class Weibo. Firstly, the weighted multiplex social network is constructed through the processing of Weibo network data. Secondly, a new information propagation model is established by using the weight and interlayer information of the Weibo multiplex network combined with the coupling factors in the propagation. Finally, the information propagation simulated by the propagation model is compared with the real data, so as to summarize different information propagation phenomena in multiplex social multiplex network. At the same time, by comparing the structure of the forwarding weighted multiplex network constructed by the short time data and the long time data, we find the self-similarity of the forwarding weighted multiplex network, which proves the generalization of the experiment. Through the above research, the mystery of the Weibo social network has been deeply explored, and a new perspective has been opened up for the exploration of social media information propagation.

Mechanical behaviour and instability mechanism of sandstones with impact tendency under different loading paths

ABSTRACT To reveal the instability and failure mechanism of pillars with impact tendency, the Brazilian test, uniaxial compressive test, cyclic loading and unloading (CLU) tests were performed on sandstones which had impact tendency. The stress drop phenomenon was obvious in the fracture stage during the Brazilian test. The main tensile crack with penetration type appeared. Under the CLU condition, the CLU had a significant effect in enhancing the mechanical character of rocks. Under the combined loading, the character stress of rocks tested with the CLU was greater than the uniaxial loading. Moreover, the greater the first cyclic threshold, the greater the character stress of rocks. Under the uniaxial loading, the failed samples showed tensile fractures. The damage location of the samples was closely related to the Poisson effect and the ending face effect. With the electron microscope which had the same magnification, the crack deterioration degree of samples under the uniaxial loading was greater than the CLU condition. Moreover, with the first cycle threshold increasing, the surface roughness of rocks gradually decreased. The quantity of secondary micro cracks gradually decreased. The propagation and penetration phenomenon gradually disappeared. The micro structure and loading properties of rocks were affected by the bonding force and structural characters between the internal structure and matrix. Based on the micro-seismic signal of the damaging threshold, the seismic source damage location can be located. Moreover, the pillar-typed burst area can be forewarned. This research benefits predicting the pillar-typed burst disaster.

Symmetry and structure in the “Generalized Plasma Focus problem”

The “Generalized Plasma Focus problem” refers to a generic class of plasma propagation phenomena that share many features of a dense plasma focus device. Its recent theoretical development has been shown to predict some features of the pinch phase in PF-1000 and POSEIDON. The theory attempts to decompose the plasma propagation problem into two weakly interdependent subproblems. This is achieved by expressing every physical variable of an applicable continuum model of the plasma as the product of a scaling parameter, which contains device-related information and represents its numerical magnitude, and a scaled variable that is devoid of device-related information, is of order unity, and represents the spatiotemporal structure of that variable. The first subproblem seeks a traveling surface of revolution whose local normal velocity equals the scaling parameter for velocity and is aligned with the magnetic force density. Spatiotemporal distributions of all the scaled variables must move along with this reference surface by definition. This paper explores the resulting scaling theory and its symmetry properties. A new coordinate transformation results in a formula for the spatiotemporal distribution of the magnetic field of the curved and non-steady plasma sheath. New insights into the snowplow effect are obtained. A current sheath with a rear boundary exists only when the current is decreasing and only when the current carrying plasma is less dense than the fill gas. The current sheath thickness is the same for small and large devices. The geomagnetic flux compression problem has an exact solution.

Exploring tau protein and amyloid-beta propagation: A sensitivity analysis of mathematical models based on biological data

Alzheimer’s disease is the most common dementia worldwide. Its pathological development is well known to be connected with the accumulation of two toxic proteins: tau protein and amyloid-β. Mathematical models and numerical simulations can predict the spreading patterns of misfolded proteins in this context. However, the calibration of the model parameters plays a crucial role in the final solution. In this work, we perform a sensitivity analysis of heterodimer and Fisher–Kolmogorov models to evaluate the impact of the equilibrium values of protein concentration on the solution patterns. We adopt advanced numerical methods such as the IMEX-DG method to accurately describe the propagating fronts in the propagation phenomena in a polygonal mesh of sagittal patient-specific brain geometry derived from magnetic resonance images. We calibrate the model parameters using biological measurements in the brain cortex for the tau protein and the amyloid-β in Alzheimer’s patients and controls. Finally, using the sensitivity analysis results, we discuss the applicability of both models in the correct simulation of the spreading of the two proteins.Statement of significance: Alzheimer’s disease is related to the accumulation of tau protein and amyloid-β. Mathematical models to predict the spreading patterns require accurate parameter calibration. In this work, we perform a sensitivity analysis of heterodimer and Fisher–Kolmogorov models to evaluate the impact of the equilibrium values of protein concentration on the solution patterns obtained with advanced numerical simulations on patient-specific brain geometry derived from magnetic resonance images. By using biological measurements in the brain cortex for the proteins in Alzheimer’s patients and controls, we use sensitivity analysis to discuss the applicability of models in simulating protein spreading.