Signal Propagation Speed Research Articles

Time-Dependent Retarded Microwave Electromagnetic Motors

In a previous work, we showed that Newton’s third law does not strictly hold in a system with remote elements due the finite speed of signal propagation, and thus force imbalance occurs at the system’s center of mass. As the said system is affected by a total force for a finite time interval, mechanical energy and momentum are gained by the system. In early works, we assumed that the bodies were macroscopically charge-neutral. Later, we removed this restriction, thus analyzing the consequences of a possible electrically charged relativistic motor. In the first published paper on this subject, we studied this phenomenon in general but gave only an example of a system reaching a stationary state. In this paper, we shall analyze a charged retarded electromagnetic motor in a more general time-dependent setting, giving specific examples in which the system never reaches a stationary state yet produces steady linear momentum nonetheless. We show that the device is more efficient in the microwave (or higher) frequencies.

Dynamical Tests of a Deep Learning Weather Prediction Model

Abstract Global deep learning weather prediction models have recently been shown to produce forecasts that rival those from physics-based models run at operational centers. It is unclear whether these models have encoded atmospheric dynamics or simply pattern matching that produces the smallest forecast error. Answering this question is crucial to establishing the utility of these models as tools for basic science. Here, we subject one such model, Pangu-Weather, to a set of four classical dynamical experiments that do not resemble the model training data. Localized perturbations to the model output and the initial conditions are added to steady time-averaged conditions, to assess the propagation speed and structural evolution of signals away from the local source. Perturbing the model physics by adding a steady tropical heat source results in a classical Matsuno–Gill response near the heating and planetary waves that radiate into the extratropics. A localized disturbance on the winter-averaged North Pacific jet stream produces realistic extratropical cyclones and fronts, including the spontaneous emergence of polar lows. Perturbing the 500-hPa height field alone yields adjustment from a state of rest to one of wind–pressure balance over ∼6 h. Localized subtropical low pressure systems produce Atlantic hurricanes, provided the initial amplitude exceeds about 4 hPa, and setting the initial humidity to zero eliminates hurricane development. We conclude that the model encodes realistic physics in all experiments and suggest that it can be used as a tool for rapidly testing a wide range of hypotheses.

A Co-Localization Algorithm for Underwater Moving Targets with an Unknown Constant Signal Propagation Speed and Platform Errors.

Underwater mobile acoustic source target localization encounters several challenges, including the unknown propagation speed of the source signal, uncertainty in the observation platform's position and velocity (i.e., platform systematic errors), and economic costs. This paper proposes a new two-step closed-form localization algorithm that jointly estimates the angle of arrival (AOA), time difference of arrival (TDOA), and frequency difference of arrival (FDOA) to address these challenges. The algorithm initially introduces auxiliary variables to construct pseudo-linear equations to obtain the initial solution. It then exploits the relationship between the unknown and auxiliary variables to derive the exact solution comprising solely the unknown variables. Both theoretical analyses and simulation experiments demonstrate that the proposed method accurately estimates the position, velocity, and speed of the sound source even with an unknown sound speed and platform systematic errors. It achieves asymptotic optimality within a reasonable error range to approach the Cramér-Rao lower bound (CRLB). Furthermore, the algorithm exhibits low complexity, reduces the number of required localization platforms, and decreases the economic costs. Additionally, the simulation experiments validate the effectiveness of the proposed localization method across various scenarios, outperforming other comparative algorithms.

Unified Near-Field and Far-Field TDOA Source Localization Without the Knowledge of Signal Propagation Speed

Unified Near-Field and Far-Field TDOA Source Localization Without the Knowledge of Signal Propagation Speed

Dynamical analysis of the FitzHugh–Nagumo model with memristive synapse

Understanding the transition mechanism between different activity patterns in realistic neuron models brings forward fundamental challenges for the dynamical systems theory. The knowledge about the mechanisms can present precious predictions and intuitions for determining fundamental principles of neuron functioning. This paper aims to present a dynamic analysis of the FitzHugh–Nagumo neuron model with a memristive synapse. In this article, the effects of memristive synapse's conductance gain, applied current, and the speed of electrical signal propagation along axons and dendrites on the system's behavior and the neuron's membrane potential are investigated. Analyzes are performed by investigating bifurcation and Lyapunov exponent diagrams versus various model parameters. The physiological role of some parameters and the effect of parameter changes on the model behaviors are discussed. The results demonstrate that when no current is applied to the system, the maximum value of membrane potential is larger, and also, a lower memristive synapse conductance gain leads to a larger maximum value of membrane potential. So, it can be concluded that the neuron in an amplitude death state may be triggered and start firing by decreasing the conductance gain or not applying current.

О покрытии поверхности цилиндра и конуса равными шарами

The article concerns the problem of covering the lateral surface of a right circular cylinder or a cone with equal balls. The surface is required to belong to their union, and the balls’ radius is minimal. The centers of the balls must lie on the covered surface. The problem is relevant for mathematics and for applications since it arises in security and communications. We develop heuristic algorithms for covering construction based on a geodesic Voronoi diagram. The construction of a covering is a non-trivial task since the line of intersection of a cylinder or a cone with a sphere is a closed curve of the fourth order. To compare the numerical results with the known ones, we unroll the surface of revolution onto a plane. Another feature is that, we use both Euclidean distance and a special non-Euclidean metric, which can describe the speed of signal propagation in a heterogeneous medium. We also perform a numerical experiment and discuss its results. Meanwhile, it is shown that with a small number of circles covering a planification of the cylindrical surface, their radius is significantly less than for a similar rectangle.

Prospects for the use of Gaussian quadrature to determine the mean integral refractive index of air by its local values measured at two points of the trace

The Earth’s atmosphere has a significant impact on the results of laser range measurements on near-earth traces. This influence is caused by the dependence of the laser signal propagation speed on the refractive index of the air, which varies along the measured trace. Correct accounting of this influence is important for the implementation of metrological traceability of linear measurements from a length measurement standard to distance measurements in large-scale construction, geodesy, geodynamics, navigation, etc. To ensure the required accuracy of such measurements, their results shall be corrected by introducing a correction for the mean refractive index of air along the signal trajectory.
 The simplest and most commonly used method for determining this correction is based on the representation of the integral of the refractive index by the quadrature trapezoidal formula in its simplest form, which requires the determination of only two local values of the refractive index at the endpoints of the trace. The accuracy of this method is often insufficient. In this regard, this paper presents the results of the research that will further substantiate a more accurate model for determining the correction under discussion based on two local refractive index values. The proposed model is based on the use of Gaussian quadrature, for which local values are determined not at the end points of the trace, but within the integration interval.

Trajectory Optimization for Target Localization Using Time Delays and Doppler Shifts in Bistatic Sonar-Based Internet of Underwater Things

Efficient target localization is critical to many marine applications in the Internet of Underwater Things (IoUT). Doppler effect becomes more predominant in the underwater environment when the relative speed of the moving object, i.e., the observer, to the signal propagation speed in water is much larger than that in the air. This along with the observer-target geometry will bring in a notable impact on the localization performance. In this paper, we derive the Cram´er–Rao lower bound (CRLB) and formulate the A-optimality criterion-based observer trajectory optimization problem to improve the localization performance based on time delay and Doppler shift measurements. We show that in the worst-case scenario, there will be a conflict between the non-accessible zone constraint and the observer dynamics constraint, which will lead to an erroneous result. To address this problem, we propose a warning zone-based augmented Lagrange multiplier method (ALMM) where the non-accessible zone constraint is relaxed to resolve the conflict and ensure the non-accessible requirement of the targeted zone is maintained. Performance evaluations are conducted through extensive simulations for different scenarios, and the results are compared to other methods with or without trajectory optimization. We demonstrate that trajectory optimization using time delays and Doppler shifts can greatly improve the target localization accuracy in underwater networks.

Research on the detection of the hole in wood based on acoustic emission frequency sweeping

In order to detect the hole defect in the wood, the intrinsic frequency of wood is investigated by frequency sweeping and combining with pencil-lead break (PLB) tests to examine the influence of the hole defect on the intrinsic frequency to obtain the significant change index for non-destructive detection of the holes. Initially, the sweeping frequency test is conducted in the range of 10–180 kHz on two different sizes of Zelkova schneideriana and Pinus sylvestris var. mongholica specimens, followed by the signal's frequency domain analysis to determine the natural frequency and its range. Then, holes with diameters of 5, 10, and 20 mm are drilled on the Zelkova schneideriana specimens to explore the impact of hole diameter on the natural frequency using PLB and frequency sweeping. Finally, 1, 3, and 5 holes of 8 mm are drilled to investigate the influence of hole number on natural frequency. The results showed that the natural frequency of wood falls within two frequency ranges of 30–50 kHz and 150–180 kHz. In addition, the hole hinders the AE signal's propagation. The energy decay rate in the two natural frequency ranges increases as the diameter and number of holes rise. In addition to the traditional method for calculating signal propagation speeds, this study proposes effective measures for detecting holes in wood.

Source Localization by Frequency Measurements in Unknown Signal Propagation Speed Environments

Signal propagation speed may not be available in practical localization scenarios. This paper addresses both the moving and stationary source localization problems by using frequency measurements when the signal propagation speed is unavailable. The task is fulfilled by exploiting the Doppler frequency shift coming from the relative motion between the source and a network of mobile sensors. Owing to the complicated nonlinear measurement model and the absence of the knowledge about signal propagation speed, it is difficult to conduct localization. To address this problem, we first transform the measurement model to a tractable form, from which to formulate a constrained weighted least squares (CWLS) problem. Afterwards, we propose two methods to solve the non-convex CWLS problem. The first method relaxes the CWLS problem into a semidefinite programming (SDP) problem by applying semidefinite relaxation (SDR). The second method adopts the alternating estimation procedure by utilizing the prior information about the nominal value of the signal propagation speed. Two subproblems are formulated and solved in an alternate manner, one in estimating the source position and velocity by applying SDR and the other the signal propagation speed by an explicit expression. Furthermore, we conduct the mean square error (MSE) analysis to show that the CWLS solution is able to reach the Cramér-Rao lower bound (CRLB) performance. Simulation results validate the expected performance of the proposed methods.

Time delay induced by plasma in strong lens systems

ABSTRACT If the gravitational lens is surrounded by non-homogeneous plasma, in addition to the vacuum gravitational deflection, chromatic refraction occurs. Also, the speed of signal propagation decreases compared to a vacuum. In this article, we investigate analytically the time delay in the case of gravitational lensing in plasma, focusing on strong lens systems. We take into account the following contributions: geometric delay due to trajectory bending in the presence of both gravity and plasma; potential delay of the ray in the gravitational field of the lens; dispersion delay in the plasma due to decrease in the speed of light signal in the medium. We consider the singular isothermal sphere as a model of a gravitational lens and the arbitrary spherically symmetric distribution of surrounding plasma. For this scenario, plasma corrections for the time delay between two images are found in a compact analytical form convenient for estimates.

Source Localization Using TDOA Measurements From Underwater Acoustic Sensor Networks

In this letter, we investigate the problem of TDOA localization with unknown signal propagation speed in underwater acoustic sensor networks (UASNs). Although the state-of-the-art semidefinite programming (SDP)-based algorithm has good accuracy, its computational complexity is huge. We develop a two-step algorithm to estimate the source position and signal propagation speed. It not only has better accuracy than the SDP-based algorithm but also has much less computational complexity. The first step of the proposed algorithm is a least squares (LS) estimator, and the second step of the proposed algorithm is a fixed point iteration (FPI) estimator. Numerical simulations validate that the proposed algorithm is superior to the SDP algorithm and reaches the Cramér-Rao lower bounds (CRLB).

USE OF GPR TECHNOLOGIES IN THE ROAD PAVEMENT SURVEY

The article contains information on the study of the possibilities of introducing GPR technologies into the practice of road surveying. The prospects for the development of this scientific direction are also analyzed. The tasks that can be solved with the use of ground-penetrating radar equipment during the non - rigid pavement. The main reasons preventing a more dynamic implementation of ground-penetrating radar technologies in the construction industry are considered in detail. The main reasons are: the difficulty of interpreting GPR data, the lack of an instrument base, the lack of a single complex of equipment and mathematical support for non - rigid pavement, which allows for guaranteed high-precision interpretation of the results of GPR surveys of non - rigid pavement and ground surfaces, and the absence of a regulatory framework that regulates the survey of highways with the use of ground-penetrating radars. Modeling of signal propagation in an environment with known electrophysical characteristics allows to determine the shape and amplitude of a complete signal, giving the possibility of correct interpretation of radargrams in order to determine the speed of signal propagation in the studied structures, electrophysical characteristics of structural materials of layers of non - rigid pavement, the interface of environments. To carry out experimental studies aimed at the development of methods of thickness measurement and defectoscopy of structural layers of non - rigid pavement, specialists of the Kharkiv national automobile and highway university use a set of geolocation equipment that uses ultra-broadband signals. A set of georadar equipment is used both for conducting experimental laboratory research of road clothing and for field surveys for the purpose of developing a road monitoring system using radar methods. For the verification and practical use of the proposed scheme for determining the time delay of signals, which allows to calculate the thickness of the structure under study, appropriate software was developed. A series of laboratory experiments were conducted using this software product. As shown by the experimental laboratory studies, the method allows to restore the thickness of the layer under investigation with a fairly high accuracy. Keywords: GPR diagnostics, highway, non - rigid pavement, ground surface, reliability, operational condition, research, electrophysical properties.

Nonlinear acoustic propagation in low-density media

Nonlinear acoustic propagation in the atmosphere is usually modeled using an augmented Burgers equation accounting for atmospheric absorption and weak nonlinearity. However, the weak-nonlinearity assumption may not apply to acoustic signals propagating from the lower atmosphere that are subsequently refracted downward from the upper atmosphere (e.g., stratosphere and thermosphere) due to the decreasing air density with increasing altitude [Lonzaga, et al., Geophys. J. Int. 200(3), 1347–1361]. Consequently, this paper discusses the effects of a strong nonlinearity that lead to an amplitude-dependent increase in signal propagation speed. This propagation speed is obtained using a perturbation expansion where the leading-order term is simply the small-amplitude sound speed while the first-order term is the existing expression that gives rise to waveform steepening and stretching. Furthermore, the second-order term is proportional to the spectral density of the acoustic signal and is inversely proportional to the local density of the medium. Consequently, for an impulsive signal such as a sonic boom or an infrasound, the second-order effect causes a dispersion of the signal similar to the observed dispersion of acoustic signals from supersonic Concorde as well as from large explosions. This paper also discusses the extension of these results in general low-density propagation media.

Temperature response in skin tissue during hyperthermia based on three-phase-lag bioheat model using RBF meshfree method

Various non-Fourier heat conduction models have been proposed to overcome the paradox of the infinite propagation speed of heat signals in Fourier’s law. The three-phase-lag (TPL) heat model is a non-Fourier model based on the linearized theory of coupled thermoelasticity that combines heat flux, temperature gradient, and thermal displacement gradient. The present paper proposes a novel method with meshfree and spectral nature to solve the two-dimensional three-phase lag (TPL) bioheat model for tissue heating during hyperthermia. In the space domain, radial basis functions (RBFs) and, in the time direction, shifted Chebyshev polynomials are employed to solve the model. The use of Chebyshev polynomials in the time direction enables one to get the solution in the whole time domain simultaneously with fewer nodes. Further, there is no need for background meshes in space due to the meshless nature of RBFs, and the proposed method is equally applicable to irregular domains. The proposed method is validated with the existing semi-analytical solution of the TPL model in one spatial dimension and found to be in good agreement. The temperature profile and the impact of various parameters, such as phase lag times, blood perfusion rate, and heat source parameters on heat transfer in tissue, have also been discussed.

An expedition to the islands of stability in the first-order causal hydrodynamics

The recently proposed connection between the Lorentz invariance of stability and the speed of signal propagation has been tested for a first-order relativistic dissipative hydrodynamic theory. The fact that the stability situation in different reference frames agrees with each other only as long as the signal propagation respects causality, has been explicitly established for the theory, which is microscopically derived from the covariant kinetic equation in general hydrodynamic frames with arbitrary momentum-dependent interactions.

Research on WLAN scenario optimisation policy based on IoT smart campus

In this paper, we analysed the development history of IoT wireless technology, and further analysed the need for dedicated low power wide area technology in IoT systems. Because of the internet of things (IoT), which connects various network-embedded devices to the internet, this paper studies the problems in WLAN of college students' dormitory, as well as introducing and analysing the optimal way of the short-distance WLAN technology in IoT. After reviewing the methods to optimise WLAN optimisation, WLAN scenarios for the student dormitory are studied in depth and the optimisation scheme of wireless local area networks based on IoT short-range technology is proposed. Targeted network optimisation strategies are elaborated. Comparisons revealed that the optimisation resulted in significant improvement in terms of signal strength, latency, packet loss, throughput, propagation speed, and roaming success rate. The network became more stable, with better performance and user experience. In addition, the new network solved many previous issues and achieved the desired results.

Research and Simulation of Negative Group Delay and Superluminal Propagation

Abstract In recent years, negative group delay circuits have attracted much attention due to their propagation characteristics and wide application prospects. In the history of human exploration, the exploration of the speed of light has never stopped. The theory of relativity points out that the speed of light in vacuum is the limit speed of signal propagation. However, it is found through research that phase velocity and group velocity appear faster than the speed of light, which does not violate the causal relationship. This paper first introduces the related concepts of negative group delay and superluminal phenomenon, the second focuses on the principle of negative group delay and superluminal phenomenon in-depth analysis and research, finally using the principle of Multisim software, the bandwidth of two different job, different structure of circuit design, the virtual simulation experiment to negative group delay phenomenon and measurement data. It is of great significance to explore the field of faster-than-light and negative group delay in today's rapidly developing information age, and it can try to meet the high requirements for signal transmission. In the future, the interdisciplinary research direction of this research topic also has great development space.

Special solutions to the space fractional diffusion problem

We derive a fundamental solution {{mathscr {E}}} to a space-fractional diffusion problem on the half-line. The equation involves the Caputo derivative. We establish properties of {{mathscr {E}}} as well as formulas for solutions to the Dirichlet and fixed slope problems in terms of convolution of {{mathscr {E}}} with data. We also study integrability of derivatives of solutions given in this way. We present conditions, which are sufficient for uniqueness of solutions. Finally, we show the infinite speed of signal propagation.

Underwater passive manoeuvring target tracking with isogradient sound speed profile

Compared with the traditional tracking problem, the underwater 3-D passive manoeuvring target tracking faces the following challenging problems: (1) Since the signal propagation delay is varying and unknown, the relationship between the two adjacent target states is hard to describe; (2) limited by the underwater environment, it is more difficult to establish a target manoeuvring motion model; (3) the propagation speed of the underwater acoustic signal varies with the depth, and the propagation path will be curved instead of straight. Various parameters including signal propagation delay, target pitch angle and receiving frequency measured by the observer cannot be calculated as usual. In this paper, we improved a 3-D constant turn (3D-CT) model to match the underwater target motion. For the problems (1) and (3), this paper proposes a novel interacting multiple model underwater Gauss-Helmert unscented Kalman filter (IMM-UGHUKF) with isogradient sound velocity profile, which analytically describes the relationship between the state to be estimated and the passive measurement. This method augments the unknown signal emission time into the state with implicit equations, and transits the state by the Gauss–Helmert model. Simulation tests have been carried out, and the results show that IMM-UGHUKF can significantly reduce the estimation error compared with other approaches.