Propagation Speed Research Articles

Analysis of the Dynamic Behavior of Multi-Layered Soil Grounds

The ground consists of many layers of soil with different properties. The propagation speed and path of seismic waves are affected by different soil layers. It is necessary to understand that layered soil exhibits different dynamic behaviors and responses under the action of seismic waves. This study utilized weathered soil and silica sand as materials to create multi-layered soil conditions with varying degrees of compaction. By conducting a 1 g shaking-table test on multi-layered soil, the interactions and influences between different soil layers under different earthquake conditions were observed. The approach of our numerical analysis aimed to complement the experimental results and provide an in-depth understanding of the dynamic behavior of multi-layered soil surfaces during seismic events. The acceleration results achieved with the ABAQUS and DEEPSOIL models for multi-layered soil were in good agreement with the experimental results. By comparing the stress–strain curves, the deformation mechanisms under different constitutive models in the numerical analysis were studied. The results of this study show that the amplification effect of seismic waves is related to the number of soil layers and the degree of compaction of the soil layers. This indicates that multi-layered soil ground and the behavior of the soil layers play an important role in the propagation and impact of seismic waves, and this amplification effect is of great significance in the design of actual seismic disaster risk assessments.

Research on features and localization of AE signals from the mechanical body of industrial robots based on WD-EMD

Abstract In order to reveal the propagation characteristics of acoustic emission (AE) signals in the body of industrial machinery, the characteristic frequencies and wave speeds of AE signals propagated on the interior and exterior surfaces (IS and ES) of the body were extracted. Subsequently, an algorithm utilizing characteristic frequency and time difference of arrival (TDOA) is proposed for the identification and localization of AE sources. Initially, an AE source is induced on the IS and ES of the body using the pencil-lead break method in accordance to ASTM standards, and the AE signal is captured by two piezoelectric sensors at a sampling frequency of 3 MHz. Then, to avoid the limitations of wavelet decomposition using self-selected wavelet scale and the problem that a single indicator cannot properly evaluate the correlation between independent mode functions (IMFs) with the original signal, this paper will conduct 4-layer wavelet decomposition of the original signal according to the response frequency range of the sensor, and select the wavelet details within the stable range of the response frequency of the sensor for preliminary reconstruction,and then the empirical mode decomposition (EMD) method is used to decompose the de-noised AE signal into 7 IMFs, and the AE waveform is reconstructed by the combined information of correlation coefficient and variance accounted for. Secondly, the reconstruction method combined with EMD analysis and a single index is compared with the proposed method in this paper to verify the reliability of the proposed method. In addition, the frequency domain characteristics of AE signal propagation process on the IS and ES of the body are extracted. Finally, based on the TDOA principle, the propagation speed of AE signal on the IS and ES of the body is calculated. Based on the geometric relationship between the AE source and two sensors, an algorithm for the location of the AE source is proposed. The results show that the proposed signal reconstruction method can effectively extract the features of AE signals, and the average positioning accuracy of the localization algorithm based on characteristic frequency and TDOA reaches 0.86%.

Application of Deep Learning in Social Network Public Opinion Sentiment

With the rapid development of social network platform, in order to purify the network environment, prevent the abuse of public opinion information, and control public opinion in a very short time, this paper proposes the application research of deep learning in social network public opinion sentiment recognition and analysis. Through the construction of social network model and social network knowledge map and the analysis of key technology, a network public opinion algorithm based on deep learning is proposed, and a competitive public opinion information communication model in online social networks is constructed, and then a simulation experiment is conducted on the improved model of the constructed social networks. The result shows that in public opinion management and control, for users with larger node degree, this technology can effectively understand and obtain public opinion information in a very short time with faster and wider information propagation speed, so as to realize the effective control of public opinion information and the processing of massive information.

Black holes, multiple propagation speeds, and energy extraction

Black holes, multiple propagation speeds, and energy extraction

An explicit primitive conservative solver for the Euler equations with arbitrary equation of state

This work presents a procedure to solve the Euler equations by explicitly updating, in a conservative manner, a generic thermodynamic variable such as temperature, pressure or entropy instead of the total energy. The presented procedure is valid for any equation of state and spatial discretization. When using complex equations of state such as Span–Wagner, choosing the temperature as the generic thermodynamic variable yields great reductions in the computational costs associated to thermodynamic evaluations. Results computed with a state of the art thermodynamic model are presented, and computational times are analyzed. Particular attention is dedicated to the conservation of total energy, the propagation speed of shock waves and jump conditions. The procedure is thoroughly tested using the Span–Wagner equation of state through the CoolProp thermodynamic library and the Van der Waals equation of state, both in the ideal and non-ideal compressible fluid-dynamics regimes, by comparing it to the standard total energy update and analytical solutions where available.

In situ TEM nanomechanical study on enhanced toughness of graphene-nanoparticle nanocomposite

Although theoretical studies and experimental research have shown outstanding mechanical properties of graphene, its brittleness and low toughness restrict its widespread industrial use. Here, we conducted a study to examine the impact of encapsulated Ag nanoparticles on the mechanical properties of graphene through in situ nanomechanical testing in an aberration-corrected transmission electron microscope (TEM). The presence of Ag nanoparticles was found to decrease crack propagation speed, enabling the TEM observation of crack deflection around the nanoparticles at nanoscale, as well as real-time measurement of the concomitant increase in stress. Using our nanomechanical testing data, we were able to quantitatively estimate the stress intensity factor, which serves as a measurement of fracture toughness for graphene, and then compared our results with previously reported values. We further discuss the role of nanoparticles in the propagation of cracks and their potential to enhance the toughness of materials. These findings have practical implications for the development of high-performance graphene composite materials.

Endothelial calcium dynamics elicited by ATP release from red blood cells

Red blood cells (RBCs) exhibit an interesting response to hydrodynamic flow, releasing adenosine triphosphate (ATP). Subsequently, these liberated ATP molecules initiate a crucial interaction with endothelial cells (ECs), thereby setting off a cascade involving the release of calcium ions (Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document}). Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document} exerts control over a plethora of cellular functions, and acts as a mediator for dilation and contraction of blood vessel walls. This study focuses on the relationship between RBC dynamics and Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document} dynamics, based on numerical simulations under Poiseuille flow within a linear two-dimensional channel. It is found that the concentration of ATP depends upon a variety of factors, including RBC density, channel width, and the vigor of the flow. The results of our investigation reveals several features. Firstly, the peak amplitude of Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document} per EC escalates in direct proportion to the augmentation of RBC concentration. Secondly, increasing the flow strength induces a reduction in the time taken to reach the peak of Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document} concentration, under the condition of a constant channel width. Additionally, when flow strength remains constant, an increase in channel width corresponds to an elevation in calcium peak amplitude, coupled with a decrease in peak time. This implies that Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document} signals should transition from relatively unconstrained channels to more confined pathways within real vascular networks. This notion gains support from our examination of calcium propagation in a linear channel. In this scenario, the localized Ca2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2+}$$\\end{document} release initiates a propagating wave that gradually encompasses the entire channel. Notably, our computed propagation speed agrees with observations.

Surfing Acceleration of Radiation Belt Relativistic Electrons Induced by the Propagation of Interplanetary Shock

AbstractInterplanetary shocks (IPS) can initiate prompt acceleration of relativistic electrons in the Earth's radiation belt, which is related to the generation and propagation of impulsive electric field (IEF). We investigate the effect of IEF on accelerating radiation belt electrons in the 6 September 2017 IPS event. A “surfing” effect of electrons with respect to the electric field, referring to electrons that drift together with the tailward‐propagating IEF in the duskside, is investigated in this study. Our results show that the maximum increase of electron differential flux is at 3.4 MeV by a factor of 2.2, corresponding to a drift velocity of 531 km/s, which is more consistent with the IPS propagating speed of 621 km/s rather than the fast‐mode speed of 1,074 km/s. We suggest that the effect of IPS propagation is important for radiation belt dynamics, and we highlight the potential importance of the parameter of IPS propagation speed.

Flame propagation dynamic characteristics and mechanisms of methane–syngas–air mixtures in a semi-enclosed duct

The composition of syngas is complex, often leading to the generation of methane, which impacts the explosive characteristics of syngas. The analysis focused on the kinetic characteristics and mechanisms of flame propagation in methane–syngas–air mixtures in a semi-enclosed duct under various equivalence ratios (φ = 0.8–1.4) and methane volume ratios (R = 0 %–70 %) under ambient temperature and pressure. The results indicated that the flame speed and pressure propagation of methane–syngas–air mixtures could be divided into three stages: a stable stage, an oscillatory increase stage, and an oscillatory decrease stage. In the stable stage, as the methane proportion in the premixed gas increased, the oscillations in the flame and pressure decreased. Turbulent flow of the mixed gas was observed due to restrictions and obstructions within the duct. This led to an increase in the peak pressure and flame speed of the mixed gas, thereby resulting in an oscillatory increase stage. Distorted tulip-shaped flames were also formed in the semi-enclosed duct. The flame of the pure syngas/air mixture exhibited a hemispherical shape and a finger-shaped and slope-shaped propagation structure. When 30 %, 50 %, or 70 % of the methane in the methane–syngas–air mixtures was added, the flame exhibited a propagation structure characterized by a hemispherical shape, finger shape, slope shape, flat shape, tulip shape, or distorted tulip shape. The flame front evolved with time from a linear growth stage to a nonlinear growth stage. The flame front speed of the methane–syngas–air mixtures was closely related to the pressure and flame structure. With the increase in the methane proportion in the methane–syngas–air mixtures, the concentration of key radicals and the rate of OH* generation and consumption gradually decreased. Sensitivity analysis revealed that with increasing methane proportion in the premixed gas, the most important reaction dominating OH* consumption changed from R15 (H + O2(+M) <=> HO2(+M)) to R138 (CH4 + OH <=> CH3 + H2O) and then to R112 (2CH3(+M) <=> C2H6(+M)); moreover, the most important reaction dominating OH* generation remained R1 (H + O2 <=> O + OH). The addition of methane interrupted the hydrogen–oxygen chain reaction of the methane–syngas–air explosion process.

The determination of some sizes and physical characteristics of metals by ultrasound

Recently, ultrasound has found extensive applications in various areas such as industry, medicine, and agriculture. This paper introduces a method of determining the thickness, speed of propagation of ultrasound in metal, and the modulus of elasticity for selected metals by ultrasound. The determination of these properties was done with the NDT USM25 ultrasonic flaw detector by Krautkramer. For this purpose, straight beam contact transducer and angle beam transducers (60o) were used. The presented method offers a practical and reliable way of measuring thickness and other properties of metal and metal alloys.

Ignition energy, explosion flame propagation, and particle movement process of coal dust cloud in vertical Hartmann tube

To discuss the ignition energy, explosion flame propagation, and particle movement process of coal dust in vertical glass tube, experimental analysis and numerical simulation methods are used to carry out research. The experimental research results show that the optimal ignition delay time is 1 s, under this condition, the dust cloud near the ignition electrode has the highest turbulence, making it easier to ignite. When the dust cloud mass concentration is 2500 g/m3, the ignition energy is the smallest, resulting in the highest risk of explosion. The simulation results show that the propagation speed of flame is 4 m/s, due to the small amount of suspended dust used, the intensity of the explosion is not significant. The further away from the explosion source, the more energy is lost, the lower the temperature of the flame. Within 30∼50 ms after the ignition, the temperature near the explosion source rapidly increases, from 900 K to 1300 K. During the period of 0.2–0.5 s after dust injection, most particles move upwards along the tube. At 1 s after the dust injection, most particles move downwards and gather near the ignition electrode, forming a suspended dust cloud that is easily ignited, which is consistent with the optimal ignition delay time of 1 s obtained from the experiment.

The Structure Characteristics of Laminar Premixed Flames of Gasoline-like Fuel Under CI Engine-Relevant Conditions.

Gasoline compression ignition characterized by partially premixed and long ignition delays typically features complex flame structures such as deflagration or spontaneous ignition fronts. In this study, the flame structure and propagation characteristics of PRF90/air mixtures under compression ignition engine-relevant conditions are investigated numerically. Similar to other types of fuels, under such conditions, the propagation speed of PRF90 laminar premixed flames depends not only on the unburnt mixture properties but also on the residence time, and the transition of the flame regime depends only on the residence time. Nevertheless, due to the temperature-dependent autoignition chemistry of PRF90, flames with excessively high unburnt temperatures show different combustion behaviors after the transition from deflagration to autoignition-assisted flames. Sensitivity analysis showed that, the dominant chain branching reactions in the deflagration mode are H + O2 = OH + O and CO + OH = CO2 + H, and that in the autoignition-assisted flames with lower unburnt temperature are H2O2(+M) = 2OH(+M) and IC8H18 + HO2 = AC8H17 + H2O2, while for higher unburnt temperatures, the reactions C3H5 + HO2 = C2H3 + CH2O + OH and IC8H18 = IC4H9 + TC4H9 are more important than the fuel low-temperature oxidation reactions. In addition, a criterion based on chemical explosive mode analysis is used to analyze the local combustion mode. The results show that the difference in diffusion/chemical structure at the crossover progress variables C 0 and crossover temperature allows both C 0 and to be used as a flame location for distinguishing propagation modes in premixed flame. However, the effects of the equivalence ratio on C 0 are different from that on , which means that the selection of C 0 and may lead to different discriminant results for stratified mixtures. Comparing the applicability of C 0-based and -based locations in three-dimensional gasoline compression ignition flame, it is found that the flame location based on the value of C 0 at ϕ = 1.0 can more completely reflect the flame development characteristics in stratified premixed combustion.

Unified lattice Boltzmann framework for coupled non-Fourier conduction and thermal radiation based on the C-V model

This research enhances our previously established unified lattice Boltzmann (LB) framework, initially developed for classical Fourier heat conduction and radiation coupling, to now adeptly handle non-Fourier heat conduction and thermal radiation transfer at the micro and nanoscale. It effectively manages the disparities in propagation speeds and complex transient boundary conditions. Validation against one-dimensional benchmarks confirms its accuracy and reliability. The study also examines the influence of critical parameters like the radiative heat transfer parameter Nc, scattering albedo, and optical thickness on thermal dynamics. Significantly, it provides a quantitative error analysis of the steady-state radiation assumption in coupled problems, revealing its limitations under various conditions. This enhanced framework represents a solid improvement in micro and nanoscale multiphysics simulations using the lattice Boltzmann method, ensuring a balance between computational precision and efficiency. It contributes to the development of more refined thermal management strategies in diverse industrial and scientific applications.

The internal ballistics of a spring gun

We consider the features of pellet motion under the elastic force acting from a decompressing spring of a finite mass. The muzzle speed of the pellet decreases as the ratio between spring and pellet mass increases. In the general case, the pellet loses contact with the spring as it is stretched. This effect occurs due to the fact that the peak of elastic displacement wave, propagating from the fixed end, reaches the opposite end of the spring. With a large relative mass of the pellet, it accelerates along a quarter of the sinusoid. At the limit of a very small pellet mass, it moves nearly all the time along with the end of the spring at an almost constant speed, approximately equal to the speed of sound propagation in the spring. In this case, after the initial compression, the pellet passes the equilibrium position, and comes off after moving a similar distance beyond the equilibrium.

Hybrid Method of Uncertainty Propagation for Near-Earth Conjunction Analysis

In this research, several existing semi-analytical dynamics and uncertainty propagation techniques are combined with conjunction models to achieve fast and accurate probability of collision results. Initial Gaussian uncertainty associated with two objects is split into smaller Gaussian distributions using Gaussian mixture models to achieve mixture components that will maintain linearity over longer propagation times. These mixture components are propagated forward using second-order state transition tensors that can capture the nonlinearity in the propagation accurately by taking into account the desired dynamics. The dynamic solution and these tensors are computed using the Deprit–Lie averaging approach, including transformations between mean and osculating states, which accounts for perturbations due to solar radiation pressure and J2. This simplified dynamic system allows fast and accurate propagation by combining the speed of propagation with averaged dynamics and the accuracy of short-period variation addition. Combined, these mathematical tools are used to propagate the object’s uncertainties forward. The final distributions are compared using analytical conjunction methods to compute the probability of collision, which is then compared to the Monte Carlo result to confirm the method’s validity.

Investigation of risk propagation and control in emergency response logistics networks: A cellular automata based approach

Emergency logistics is crucial for responding to natural disasters and public health emergencies. In emergency logistics systems, risk propagation must be effectively controlled and mitigated, and otherwise it may lead to serious consequences. This study, for the first time, investigates the risk propagation of emergency logistics networks and their protection strategies from a dynamic perspective using the method of cellular automata. The purpose is to reveal the risk propagation mechanism of emergency logistics networks and its influencing factors, which provides a basis for improving the risk resistance of emergency logistics networks. Specifically, this paper constructs an emergency logistics network based on the weighted scale-free algorithm and establishes a risk propagation model by using metric automata. Also, this paper carries out a comprehensive numerical investigation on risk propagation in the emergency logistics network by adjusting the model parameters and adopting different protection strategies. The results of this research indicate that (1) the speed and range of risk propagation are not sensitive to the network size, while the reduction of the network size leads to an increase in the volatility and a decrease in the stability of the propagation; (2) the state characteristics of the network nodes are more important than the structural characteristics of the network for controlling the risk of node vulnerability; (3) increasing the level of risk recovery is more effective than reducing risk infection in controlling the scope of risk propagation throughout the network; (4) finally, the targeted protection strategy is more effective than the random protection strategy. The findings are potentially impactful in that they reveal the nature of risk propagation in emergency logistics networks, further expand methodological research of risk propagation, and provide a solid foundation for effective risk management and control.

Generation of Bright–Dark Pulse Pairs in the Er-Doped Mode-Locked Fiber Laser Based on Doped Fiber Saturable Absorber

This study reports new types of passive mode-locked Er-doped fiber laser (EDFL) based on a segment of doped fiber saturable absorber (DFSA) with Tm/Ho-doped fiber (THDF), Yb-doped fiber (YDF), and Er-doped fiber (EDF). By employing THDF-SA, a bright pulse sequence with a fundamental repetition rate of 17.86 MHz was obtained. In addition, various mode-locked output states, including dark pulses, dark–bright pulse pairs, bright–dark pulse pairs, and second-harmonic pulses, were obtained through polarization modulation and gain modulation, and the orthogonality of dark–bright pulses in both polarization directions was verified. Furthermore, using EDF-SA and YDF-SA, dark pulses and dark–bright pulses were obtained. A comparison of the three experiments revealed that THDF-SA effectively reduces the mode-locked threshold and improves the average output power. Compared with bright pulses, dark pulses offer several advantages such as resisting noise, increasing propagation speed, and suppressing nonlinear scattering (such as pulse-intrinsic Raman scattering); thus, the EDFL can find broad application in long-distance transmission, precision measurement, and other fields.

Study of energy transfer and stress wave propagation during SPT through energy measurement and PIV

The blow counts in standard penetration tests (SPT) require suitable corrections to account for energy losses. Over 4,000 energy measurement data collected from four test sites across Hong Kong have been collected and analysed in this study. On average for all instrumented hammer blows, approximately 62% of the theoretical hammer potential energy is transferred to the drill rod assembly. Using high-speed camera imagery and particle image velocimetry (PIV), the detailed mechanism of stress wave propagation has been visualised and assessed. This has revealed new details and allowed nuances in the results of routine energy measurements to be interpreted in new light. It has been confirmed that the initial compressive wave is reflected as a tensile wave for low end-restraint at the SPT sampler and as a second compressive wave for high end-restraint. The commonly observed discrepancy between the theoretical and measured speeds of wave propagation is highlighted and explored. Energy loss arises from friction during free-fall of the hammer, at the anvil, and from other sources such as the horizontal motion of the hammer-anvil system. The proportion of each major source of energy loss is quantified.

Data-driven modeling of equatorial atmospheric waves: The role of moisture and nonlinearity on global-scale instabilities and propagation speeds.

The equatorial region of the Earth's atmosphere serves as both a significant locus for phenomena, including the Madden-Julian Oscillation (MJO), and a source of formidable complexity. This complexity arises from the intricate interplay between nonlinearity and thermodynamic processes, particularly those involving moisture. In this study, we employ a normal mode decomposition of atmospheric reanalysis ERA-5 datasets to investigate the influence of nonlinearity and moisture on amplitude growth, propagation speed, and mode coupling associated with equatorially trapped waves. We focus our analysis on global-scale baroclinic Kelvin and Rossby waves, recognized as crucial components contributing to the variability of the MJO. We examine the dependence of wave amplitudes on the background moisture field in the equatorial region, as measured by total column water vapor. Our analysis demonstrates the crucial role of moisture in exciting these waves. We further investigate the dependence of the propagation speed of the waves on their amplitudes and the background moisture field. Our analysis reveals a robust correlation between the phase speed of the normal modes and their corresponding amplitude, whereas a weaker correlation is found between the eigenmodes' phase speed and the moisture field. Hence, our findings suggest that moisture plays a role in exciting the global-scale Rossby-Kelvin structure of the MJO. In this context, the propagation speed of the eigenmodes is mainly influenced by their amplitudes, underscoring the significant role of nonlinearity in wave propagation.

Internal solitary wave in the Lombok Strait: Satellite-observed spatiotemporal characteristics and their propagations modulated by the Indonesian Throughflow

The Lombok Strait shows active large-amplitude internal solitary waves (ISWs) and is also a primary gateway for the Indonesian Throughflow (ITF), which is a critical ocean current affecting the ocean ecosystem. This study collected 858 satellite images from 2018 to 2022, and ISW wave crests were extracted. Analysis shows that ISW 5-year cumulative occurrences reached the highest/ lowest of 136/28 days, with a 29 %/6 % frequency in October/ June. Satellite and reanalysis data revealed that ISW occurrence and propagation speed correlate to ITF variations. Enhanced southward ITF corresponds to less ISW occurrence and decreased/increased northward/southward ISW propagation speed. To understand how ITF modulates ISWs, three-dimensional MITgcm simulations were employed. Results show that when southward ITF decreases, ISWs tend to generate earlier/later, thus leading to a longer/shorter propagation distance for ISWs in the north/ south direction, revealing a suppressive effect on northward ISW generation.