Velocity Factor Research Articles

Coiled-up structure with porous material lining for enhanced sound absorption

This paper presents an acoustic metamaterial, coiled-up structure with porous lining (CSPL), which is constructed by adding porous material lining to a coiled-up air channel for the pursuit of broadband and low-frequency sound absorption at subwavelength scales. The porous material is fixed on both sides of the channel wall to enhance the losses of the system, and an air slit is left in the middle of the channel to regulate the impedance matching between the metamaterial and the air. A theoretical model based on double porosity theory and impedance transfer method is established to study the sound absorption performance of the metamaterial, and a finite element (FE) simulation model is constructed to reveal the underlying sound absorption mechanism. To validate these two models, the sound absorption performance of the designed sample is measured in a standing wave tube. The results show that the porous material lining not only enhances the sound energy dissipation, but also reduces the propagation speed of sound wave in the coiled channel, resulting in good low-frequency sound absorption performance of the CSPL. By adjusting the position and length of the porous lining, good sound absorption tunability can be achieved in the considered frequeny range. Moreover, the effect of acoustic properties of the porous material on the sound absorption of the CSPL is revealed and discussed in detail. Finally, several coupled CSPLs are designed to achieve broadband sound absorption in different frequency ranges. This work provides a new approach to design metamaterials for broadband low-frequency sound absorption.

Comparative analysis of thermal damage to laser-irradiated breast tumor based on Fourier conduction and non-Fourier heat conduction models: A numerical study

In recent decades, laser technology has been widely used in surgeries and thermal therapies. To ensure patient safety and enhance therapeutic effectiveness in laser applications, it is crucial to accurately analyze burn injuries during the treatment process. In this study, a bioheat transfer model that includes the effects of metabolic heat generation, capillary blood vessels, and relaxation times of heat flux and temperature gradient was developed to study the non-Fourier heat conduction behavior in 2-D spherical breast tumor during the laser hyperthermia process. By employing different heat conduction models and the Arrhenius burn integration, the temperature distribution and laser-induced thermal damage to tumors were obtained. The progression of burn injury in time and the effect of various parameters on it were investigated. It was observed that the DPL model provides more reliable results in comparison with the CV model in predicting thermal damage to bio-tissue when non-Fourier effects are taken into consideration. The results showed that increasing heat flux phase lag leads to severe thermal damage, earlier onset of empyrosis, and wider and deeper burn injury. However, a greater phase lag of temperature gradient results in lower and superficial thermal damage, milder burn, later onset of empyrosis, and smaller burned area. The effect of laser power density on the onset time of different degrees of burn and their sensitivity to input power were investigated, and the results were represented graphically. Finally, investigation of wave propagation in various tissues revealed that the wave propagation speed is not constant and reduces as time increases.

Ex vivo evaluation of the sensitivity of modified average speed of sound estimation method

The speed of sound (SoS), which is the propagation speed of longitudinal waves, is expected to be effective for the early detection and monitoring of diseases. Several methods that use handheld probes have been proposed to estimate the SoS. In this study, a modified average SoS estimation method, referred to as the improved focusing method, is proposed to increase the accuracy of average SoS estimation. In the proposed method, a plane wave was transmitted, and the center-element position-dependent variations in the SoS estimation were reduced. Ex vivo experiments were conducted using chicken liver to evaluate the applicability and sensitivity of the proposed method to actual tissues. The livers were subjected to continuous temperature changes to induce changes in the SoS. The results suggest that the improved focusing method measures the average SoS accurately as well as small SoS changes of approximately 1.5 m·s−1·°C−1.

Dynamics of Taylor bubble interface in vertical turbulent counter-current flow

Dynamics of the Taylor bubble interface in the vertical counter-current flow was analyzed with video recordings at 100 – 800 frames per second. Taylor bubbles in air-water mixture were studied on time intervals of up to several minutes in stagnant conditions, where buoyancy is dynamically balanced by the inertial bubble drag in the downward turbulent flow. Taylor bubbles of length from 4 to 10 cm were observed in a pipe of 26 mm diameter at Reynolds numbers based on liquid superficial velocity around 6000. Algorithms, developed for analysis of the interface from the video frames were dedicated to the analysis of the cap and the body of the Taylor bubble. The long time averaging of up to 10 min samples do not end up with axisymmetric time-averaged shape of the bubble, but with an asymmetric bullet-train shape, with the thinnest liquid film observed on the belly of the bullet-train shape bubble. The main result of this study is based on high relative sensitivity of our measurements, which was sufficient to track the dynamics of the tiny disturbance waves with a tenth of mm amplitudes traveling along the interface of the Taylor bubble. Cross-correlations of time-dependent interface fluctuations measured at different spatial positions allowed us to measure propagation speeds of the interface waves. When averaged over sufficiently long time intervals of around a minute, the time averaged propagation velocities are shown to be equal to the convective velocity of the interface. Moreover, waves propagating on both sides of the two-dimensional photographs show clear correlation; crest of the wave on one side of the bubble photograph corresponds to the trough of the wave on the other side.

Wave Propagation Speed and Equivalent Impedance of Dielectric-Coated Conductor Representing Lightning Return-Stroke Channel

In electromagnetic models of lightning return stroke, dielectric coating of channel-representing conductor is used to adjust the current wave propagation speed. In this letter, we examine dependences of both the speed and channel equivalent impedance on the electric permittivity and magnetic permeability of such coating. With increasing the permeability, the propagation speed of current wave decreases and the equivalent impedance increases significantly. In contrast, these parameters are not much influenced by the increase of permittivity. The reason for the difference has been explained in terms of the transmission-line theory.

Energy-Efficient Connected Cruise Control With Lean Penetration of Connected Vehicles

This paper focuses on energy-efficient longitudinal controller design for a connected automated truck that travels in mixed traffic consisting of connected and non-connected vehicles. The truck has access to information about connected vehicles beyond line of sight using vehicle-to-everything (V2X) communication. A novel connected cruise control design is proposed which incorporates additional delays into the control law when responding to distant connected vehicles to account for the finite propagation speed of traffic waves. The speeds of non-connected vehicles are modeled as stochastic processes. A fundamental theorem is proven which links the spectral properties of the motion signals to the average energy consumption. Controller synthesis for gain parameters is conducted over downstream traffic data and evaluated over a combination of synthetic and real cycles. It is demonstrated that even with lean penetration of connected vehicles, our controller can bring significant energy savings.

A Stability Result for a Timoshenko System with Infinite History and Distributed Delay Term

This manuscript is mainly focusing on a general stability of solution for one-dimensional Timoshenko system with infinite history and distributed delay term regardless also of the speeds of wave propagation. We prove our result by using the energy method combined with some properties of convex functions.

One-dimensional nonlinear model of generalized thermo-electroelasticity

We investigate a one-dimensional restriction of a nonlinear model of thermo-electroelasticity in extended thermodynamics and in the quasi-electrostatic regime (see Ghaleb et al. in Int J Eng Sci 119:29–39, 2017. https://doi.org/10.1016/j.ijengsci.2017.06.010). An additional dependence of the thermal conductivity and the thermal relaxation time on temperature and heat flux is introduced. The aim of the present work is to assess the effect of some quadratic nonlinear couplings between the mechanical, thermal and electric fields. Such couplings are known to have a crucial effect on the stability of the solutions. It is confirmed that there are two speeds of wave propagation of disturbances, the coupled thermoelastic wave and the heat wave. Formulae are provided for both speeds, showing their explicit dependence on temperature, heat flux and electric field. The purely thermal case is briefly considered. The present results may be useful for the description of a broad range of interactions in large polarizable slabs of electro-thermoelastic materials and for the design of such materials.

Analytical, simulation, and experimental verification of ultrasonic thermometry technique

When an ultrasonic wave travels through a material, such as a rod, the propagation and reflection characteristics are a function of the medium properties. When a material is heated, its mechanical properties, density, and volume change with respect to the medium, and so does the speed of sound. By using ultrasonic waves, the difference in speed can be used to estimate the temperature of a solid material. This technique is known as ultrasonic thermometry. The central hypothesis is that the wave travels slower as the temperature increases. To explain the underlying scientific principles of the technique, we developed analytical methods for estimating the time delays associated with varying temperatures. Time delay curves were developed by repeating the procedure at various temperature values using the corresponding mechanical and thermal properties at those values. That is, young’s modulus, Poisson’s ratio, and the thermal expansion coefficient were considered based on the temperature values. Additionally, this study outlines a numerical study on the temperature dependence of ultrasonic waves propagating through a 304L stainless steel rod using COMSOL software. Numerical results concur with analytically derived estimations, showing a decrease in the wave propagation speed and the wave amplitude as the temperature changes between 20 °C, 100 °C, 300 °C, and 500 °C. The simulated time delays agree well with the analytical calculations, and the displacement–time curve shift occurs due to the mechanical properties and thermal expansion effect. To confirm the accuracy of the technique, additional experiments were conducted on physical samples of 304L stainless steel. However, the frequency was modified to 2.25 MHz to increase spectral resolution given the limited temperature range possible of 25 °C–130 °C. We conclude by indicating that, due to the high accuracy of the analytically derived equations, the equations and technique developed has the potential to be utilized for time delay curves of other metals, in addition to 304L stainless steel.

Numerical modelling of hyperbolic phase change problems: Application to continuous casting

Heat diffusion processes are generally modeled based on Fourier’s law to estimate how the temperature propagates inside a body. This type of modeling leads to a parabolic partial differential equation, which predicts an infinite thermal wave speed of propagation. However, experimental evidence shows that diffusive processes occur with a finite velocity of thermal propagation in many applications. In this paper, we develop a mathematical formulation to predict the finite speed of heat propagation in multidimensional phase change problems. The model generalizes the enthalpy formulation by adding a hyperbolic term. The governing equations are simulated by the finite element method. The proposed model is first verified by comparing numerical and experimental results illustrating the difference between the infinite and finite propagation velocity for heat inside biological tissues. Then, the results of the two and three-dimensional numerical solution of the continuous steel casting process are presented. We will illustrate that the effects of the initial conditions vanish faster when using the parabolic equation, while they persist in the hyperbolic modeling approach. The results demonstrate significant differences in the initial thermal dynamics and at the solid-liquid interface position when adding the hyperbolic term. The changes are more noticeable in the regions of the steel beam where rapid heat loss and, consequently, faster phase change occur.

Quantitative Ultrasound Techniques Used for Peripheral Nerve Assessment.

This review article describes quantitative ultrasound (QUS) techniques and summarizes their strengths and limitations when applied to peripheral nerves. A systematic review was conducted on publications after 1990 in Google Scholar, Scopus, and PubMed databases. The search terms "peripheral nerve", "quantitative ultrasound", and "elastography ultrasound" were used to identify studies related to this investigation. Based on this literature review, QUS investigations performed on peripheral nerves can be categorized into three main groups: (1) B-mode echogenicity measurements, which are affected by a variety of post-processing algorithms applied during image formation and in subsequent B-mode images; (2) ultrasound (US) elastography, which examines tissue stiffness or elasticity through modalities such as strain ultrasonography or shear wave elastography (SWE). With strain ultrasonography, induced tissue strain, caused by internal or external compression stimuli that distort the tissue, is measured by tracking detectable speckles in the B-mode images. In SWE, the propagation speed of shear waves, generated by externally applied mechanical vibrations or internal US "push pulse" stimuli, is measured to estimate tissue elasticity; (3) the characterization of raw backscattered ultrasound radiofrequency (RF) signals, which provide fundamental ultrasonic tissue parameters, such as the acoustic attenuation and backscattered coefficients, that reflect tissue composition and microstructural properties. QUS techniques allow the objective evaluation of peripheral nerves and reduce operator- or system-associated biases that can influence qualitative B-mode imaging. The application of QUS techniques to peripheral nerves, including their strengths and limitations, were described and discussed in this review to enhance clinical translation.

The Riemann problem for a traffic flow model

A traffic flow model describing the formation and dynamics of traffic jams was introduced by Berthelin et al. [“A model for the formation and evolution of traffic jams,” Arch. Ration. Mech. Anal. 187, 185–220 (2008)], which consists of a pressureless gas dynamics system under a maximal constraint on the density and can be derived from the Aw–Rascle model under the constraint condition ρ≤ρ* by letting the traffic pressure vanish. In this paper, we give up this constraint condition and consider the following form: {ρt+(ρu)x=0,(ρu+εp(ρ))t+(ρu2+εup(ρ))x=0,in which p(ρ)=−1ρ. The Riemann problem for the above traffic flow model is constructively solved. The delta shock wave arises in the Riemann solutions, although the system is strictly hyperbolic, its first eigenvalue is genuinely nonlinear, and the second eigenvalue is linearly degenerate. Furthermore, we clarify the generalized Rankine–Hugoniot relations and δ-entropy condition. The position, strength, and propagation speed of the delta shock wave are obtained from the generalized Rankine–Hugoniot conditions. The delta shock may be useful for the description of the serious traffic jam. More importantly, it is proved that the limits of the Riemann solutions of the above traffic flow model are exactly those of the pressureless gas dynamics system with the same Riemann initial data as the traffic pressure vanishes.

Testing gravitational wave propagation with multiband detections

Effective field theories (EFT) of dark energy (DE) — built to parameterise the properties of DE in an agnostic manner — are severely constrained by measurements of the propagation speed of gravitational waves (GW). However, GW frequencies probed by ground-based interferometers lie around the typical strong coupling scale of the EFT, and it is likely that the effective description breaks down before even reaching that scale. We discuss how this leaves the possibility that an appropriate ultraviolet completion of DE scenarios, valid at scales beyond an EFT description, can avoid present constraints on the GW speed. Instead, additional constraints in the lower frequency LISA band would be harder to escape, since the energies involved are orders of magnitude lower. By implementing a method based on GW multiband detections, we show indeed that a single joint observation of a GW150914-like event by LISA and a terrestrial interferometer would allow one to constrain the speed of light and gravitons to match to within 10-15. Multiband GW observations can therefore firmly constrain scenarios based on the EFT of DE, in a robust and unambiguous way.

Prospects of probing dark matter condensates with gravitational waves

The Lambda-Cold Dark Matter model explains cosmological observations most accurately till date. However, it is still plagued with various shortcomings at galactic scales. Models of dark matter such as superfluid dark matter, Bose-Einstein Condensate(BEC) dark matter and fuzzy dark matter have been proposed to overcome some of these drawbacks. In this work, we probe these models using the current constraint on the gravitational wave (GW) propagation speed coming from the binary neutron star GW170817 detection by LIGO-Virgo detector network and use it to study the allowed parameter space for these three models for Advanced LIGO+Virgo, LISA, IPTA and SKA detection frequencies. The speed of GW has been shown to depend upon the refractive index of the medium, which in turn, depends on the dark matter model parameters through the density profile of the galactic halo. We constrain the parameter space for these models using the bounds coming from GW speed measurement and the Milky Way radius bound. Our findings suggest that with Advanced LIGO-Virgo detector sensitivity, the three models considered here remain unconstrained. A meaningful constraint can only be obtained for detection frequencies ≤ 10-9 Hz, which falls in the detection range of radio telescopes such as IPTA and SKA. Considering this best possible case, we find that out of the three condensate models, the fuzzy dark matter model is the most feasible scenario to be falsified/validated in near future.

Influencing mechanisms of gas bubbles on propagation characteristics of leakage acoustic waves in gas-liquid two-phase flow

Propagation speed of acoustic waves in liquid can be significantly degraded when gas bubbles exist. To reveal the influence of gas bubbles on propagation characteristics of leakage acoustic waves in liquid pipelines, numerical simulation is utilized in the present paper. It can be divided into three stages when leakage acoustic waves propagate through a single gas bubble and the influence of each stage on propagation characteristics of acoustic waves is discussed. In gas-liquid two-phase flow, there are two basic mechanisms of gas resistance on wave propagation: elastic resistance effect and drag resistance effect. The results show that the influence of elastic resistance effect on sound speed is much greater than that of drag resistance effect. When propagating through a long gas bubble with the radius of 2 mm and the length of 7 mm, the elastic resistance effect causes a time delay of 0.00038 s while the drag resistance effect only causes a time delay of 0.00002 s. The results of this paper contribute to better understanding of the differences in acoustic wave propagation characteristics between different flow patterns in gas-liquid two-phase flow, and lay a foundation for the utilization of acoustic leakage detection methods in gas-liquid two-phase flow pipelines.

Review on Wearable System for Positioning Ultrasound Scanner

Although ultrasound (US) scan or diagnosis became widely employed in the 20th century, it still plays a crucial part in modern medical diagnostics, serving as a diagnostic tool or a therapy process guide. This review provides information on current wearable technologies and applications used in external ultrasound scanning. It offers thorough explanations that could help build upon any project utilizing wearable external US devices. It touches on several aspects of US scanning and reviews basic medical procedure concepts. The paper starts with a detailed overview of ultrasound principles, including the propagation speed of sound waves, sound wave interactions, image resolution, transducers, and probe positioning. After that, it explores wearable external US mounts and wearable external US transducers applied for sonograph purposes. The subsequent section tackles artificial intelligence methods in wearable US scanners. Finally, future external US scan directions are reported, focusing on hardware and software.

Gravity Effects on the Minimum Explosive Concentrations in 1-D Dust Explosion

ABSTRACT Theoretical predictions of dust-explosion characteristics, such as the minimum explosive concentration (MEC), can help improve the accuracy of quantitative risk assessment. This paper presents a continuum model to simulate one-dimensional dust-cloud combustion. It is found that the dilution of dust by thermal expansion reduces the propagation speed of a combustion wave through a dust cloud. At the same time, the delay in the increase of particle velocity due to relaxation time counteracts the dilution effect. Therefore, neglecting the relaxation time results in the underestimation of propagation speed. In the absence of heat loss, extinction occurs when the adiabatic combustion temperature decreases to the ignition temperature; MEC is independent of particle size in such cases. With the presence of heat loss, on the other hand, extinction occurs at a higher dust concentration; MEC increases with particle size. Accurate evaluation of ignition temperature is key to the quantitative prediction of MEC. A particular focus is given to gravity effects, reflecting recent experimental efforts to obtain fundamental insights into propagation mechanisms without being affected by gravity. In upward propagation, particles fall toward the reaction front, enhancing combustion and increasing the propagation speed. The situation in downward propagation is the opposite, and extinction occurs when the gravity level is beyond a critical value. In upward propagation, MEC can decrease with an increase in particle size, owing to the influence of gravity.

A new general decay for a transmission problem of viscoelastic Timoshenko systems

AbstractIn this paper, we investigate the long‐time behavior for a transmission problem of viscoelastic Timoshenko systems with different speeds of wave propagation. By constructing a new Lyapunov functional and combining the technique of perturbation energy with some precise estimates for multipliers, we establish a general uniform decay estimates for the energy.

Vibrational, thermodynamic and acoustic properties of AgAlS2 crystal

First-principles calculations of vibrational properties of AgAlS2 crystal have been performed for the first time. The phonon dispersion and phonon density of states were calculated. Phonon dispersion curves disclose dynamical stability of the system. The group-theoretical classification of vibrational modes has been done and classification according to selection rules of modes active in infrared and Raman spectra has been performed. Raman and infrared spectra of AgAlS2 were calculated within the DFPT method. The LO-TO splitting of the infrared modes are reported. The effective Born charges for constituent atoms of the crystal were calculated and analyzed. Thermodynamic functions such as enthalpy, entropy, free energy and heat capacity at constant volume are obtained. The propagation velocities of longitudinal and transverse acoustic waves in the crystal were calculated for the (100) and (001) directions. The anisotropy coefficients are calculated and anisotropy of the propagation speed of acoustic waves in AgAlS2 crystal is analyzed.

Observations of Waves and Structures by Frequency–Wavenumber Spectrum in Solar Wind Turbulence

A well-known shortcoming of single-spacecraft spectral analysis is that only the 1D wavenumber spectrum can be observed, assuming the characteristic wave propagation speed is much smaller than the solar wind flow speed. This limitation has motivated an extended debate about whether fluctuations observed in the solar wind are waves or structures. Multispacecraft analysis techniques can be used to calculate the wavevector independent of the observed frequency, thus allowing one to study the frequency–wavenumber spectrum of turbulence directly. The dispersion relation for waves can be identified, which distinguishes them from nonpropagating structures. We use magnetic field data from the four Magnetospheric Multiscale (MMS) spacecraft to measure the frequency–wavenumber spectrum of solar wind turbulence based on the k-filtering and phase differencing techniques. Both techniques have been used successfully in the past for the Earth’s magnetosphere, although applications to solar wind turbulence have been limited. We conclude that the solar wind turbulence intervals observed by MMS show features of nonpropagating structures that are associated with frequencies close to zero in the plasma rest frame. However, there is no clear evidence of propagating Alfvén waves that have a nonzero rest-frame frequency. The lack of waves may be due to instrument noise and spacecraft separation. Our results support the idea of turbulence dominated by quasi-2D structures.