Signal Propagation Velocity Research Articles

Radiofrequency ice dielectric measurements at Summit Station, Greenland

Abstract We recently reported on the radio-frequency attenuation length of cold polar ice at Summit Station, Greenland, based on bi-static radar measurements of radio-frequency bedrock echo strengths taken during the summer of 2021. Those data also allow studies of (a) the relative contributions of coherent (such as discrete internal conducting layers with sub-centimeter transverse scale) vs incoherent (e.g. bulk volumetric) scattering, (b) the magnitude of internal layer reflection coefficients, (c) limits on signal propagation velocity asymmetries (‘birefringence’) and (d) limits on signal dispersion in-ice over a bandwidth of ~100 MHz. We find that (1) attenuation lengths approach 1 km in our band, (2) after averaging 10 000 echo triggers, reflected signals observable over the thermal floor (to depths of ~1500 m) are consistent with being entirely coherent, (3) internal layer reflectivities are ≈–60 $\to$ –70 dB, (4) birefringent effects for vertically propagating signals are smaller by an order of magnitude relative to South Pole and (5) within our experimental limits, glacial ice is non-dispersive over the frequency band relevant for neutrino detection experiments.

Integration of Experimental Methods for the Correlation of Hardness with the Propagation Velocity of Ultrasonic Signals in Steel: A Proposal for an Undergraduate Material Science Lecture

Integration of Experimental Methods for the Correlation of Hardness with the Propagation Velocity of Ultrasonic Signals in Steel: A Proposal for an Undergraduate Material Science Lecture

MCQsim: A Multicycle Earthquake Simulator

ABSTRACT Multicycle earthquake rupture simulators generate long sequences of earthquakes along predefined fault geometries for statistical analysis of earthquake recurrence and related rupture characteristics. Based on the physical approximations of long-term crustal deformation and the short-term rupture process, they can provide a deeper understanding of the inner workings of the “earthquake machine” as well as inform seismic hazard assessment by filling the observational gap between instrumental seismology and paleoseismology. With MCQsim, we introduce a multi-cycle rupture simulator that (a) can work with complex, nonplanar fault geometries and heterogenous models of fault strength, (b) includes different approximations of long-term stress accumulation, (c) incorporates elastic signal propagation velocity, (d) distinguishes between stable, conditionally stable, and unstable portions of the fault, and (e) includes postseismic relaxation and afterslip. The generated earthquake catalogs allow the identification of parameters that dominate system behavior while also providing probabilities of future ruptures based on their preceding behavior. Here, we focus on the technical aspects of how MCQsim, which is based on elastostatic dislocation theory and the boundary element method, approximates both the seismic cycle and the earthquake’s rupture process. We provide exemplary simulation outputs for verification and validation purposes.

Finite velocity of ECG signal propagation: preliminary theory, results of a pilot experiment and consequences for medical diagnosis

A satisfactory model of the biopotentials propagating through the human body is essential for medical diagnostics, particularly for cardiovascular diseases. In our study, we develop the theory, that the propagation of biopotential of cardiac origin (ECG signal) may be treated as the propagation of low-frequency endogenous electromagnetic wave through the human body. We show that within this approach, the velocity of the ECG signal can be theoretically estimated, like for any other wave and physical medium, from the refraction index of the tissue in an appropriate frequency range. We confirm the theoretical predictions by the comparison with a direct measurement of the ECG signal propagation velocity and obtain mean velocity as low as v=1500 m/s. The results shed new light on our understanding of biopotential propagation through living tissue. This propagation depends on the frequency band of the signal and the transmittance of the tissue. This finding may improve the interpretation of the electric measurements, such as ECG and EEG when the frequency dependence of conductance and the phase shift introduced by the tissue is considered. We have shown, that the ECG propagation modifies the amplitude and phase of signal to a considerable extent. It may also improve the convergence of inverse problem in electrocardiographic imaging.

Precision and Accuracy of Pulse Propagation Velocity Measurement in Power Cables

The partial discharge (PD) measurement is an important method used in determining the condition of medium- and high-voltage cable insulation. Considering the propagation velocity of PD signals in power cables is necessary for determining the location of PD defects. However, the determination of velocity is not straightforward due to propagation-related attenuation and dispersion, which distorts the PD pulse waveform. This introduces a degree of uncertainty into the pulse velocity as well as the PD source locations determined based on that velocity, which is usually considered to be of constant value in PD analysis. This paper investigates the accuracy of the pulse propagation velocity measurement in power cables. Tests were performed on a medium voltage power cable in a laboratory setting using two sets of PD-specific measurement equipment: a high-frequency current transformer (HFCT) and an IEC 60270-compliant conventional measurement system. The propagation velocities and their statistical variability were determined using both devices to assess the uncertainty of the propagation velocity measurement. The results indicate that the measured velocity is slightly higher in the case of the HFCT and that the 50% peak threshold value should be used rather than the peak value of PD sensor response waveforms to increase the precision of velocity measurements.

Analysis and verification of signal propagation as method for temperature monitoring of underground power cables

• Signal propagation velocity can be employed as a measure for the cable temperature. • Conversion of the velocity to temperature is based on the insulation permittivity. • PILC and XLPE insulated power cables show opposite relationship with temperature. • Thermal overloading of XLPE cables can be detected online for cables in service. • The proposed method can be retrofitted to existing power cable connections. Underground power cables are increasingly becoming a bottleneck in the medium-voltage grid due to congestion. Limitations arise from the lack of knowledge on their thermal state. This paper investigates for two commonly applied cable types, PILC and XLPE, how signal propagation velocity can be exploited as means for thermal monitoring. To this end, the transit time of signals sent along a cable is interpreted in terms of the temperature dependency of the cable insulation permittivity. The sensitivity is verified by laboratory and field tests. Shifts in waveforms can be distinguished with a resolution down to 1 °C, but uncertainties in cable parameters hamper a direct conversion of the propagation characteristics to an absolute temperature scale. Instead, changes in waveforms need to be calibrated with respect to a reference signal at a known temperature. Parameter uncertainties then only arise in the relative shift and an accuracy below 5 °C is obtained. The method is demonstrated for a multi-conductor power cable exhibiting distinct signal propagation modes.

Design considerations for diode-based nonlinear transmission lines

Diode-based nonlinear transmission lines (D-NLTL) are a class of pulse shaping networks capable of increasing the discrete spectral content of a pulse at high volumetric power density. However, a systematic design procedure for D-NLTLs is lacking, limiting their prototyping, evaluation, production, and adoption. To produce a D-NLTL design approach, parameters for UHF band (0.3–1 GHz) frequency generation are presented as a function of the input excitation pulse, network topology, and sub-components’ reactive value. Excitation pulse amplitude is found to have a strong effect on center frequency (fc), max frequency (fBragg), peak power (Ppeak), and RF power conversion efficiency (ηRF). In general, when cell inductance is decreased, both fc and signal propagation velocity are increased. The results are then presented as an example to design, build, test, and compare a 40-cell D-NLTL whose measured fc and fBragg are 256 and 446 MHz, respectively. Finally, we used the parameter space study results and empirical validation to present controllable waveform design rules-of-thumb.

An automated method for precise axon reconstruction from recordings of high-density micro-electrode arrays

Objective: Neurons communicate with each other by sending action potentials (APs) through their axons. The velocity of axonal signal propagation describes how fast electrical APs can travel. This velocity can be affected in a human brain by several pathologies, including multiple sclerosis, traumatic brain injury and channelopathies. High-density microelectrode arrays (HD-MEAs) provide unprecedented spatio-temporal resolution to extracellularly record neural electrical activity. The high density of the recording electrodes enables to image the activity of individual neurons down to subcellular resolution, which includes the propagation of axonal signals. However, axon reconstruction, to date, mainly relies on manual approaches to select the electrodes and channels that seemingly record the signals along a specific axon, while an automated approach to track multiple axonal branches in extracellular action-potential recordings is still missing. Approach: In this article, we propose a fully automated approach to reconstruct axons from extracellular electrical-potential landscapes, so-called ‘electrical footprints’ of neurons. After an initial electrode and channel selection, the proposed method first constructs a graph based on the voltage signal amplitudes and latencies. Then, the graph is interrogated to extract possible axonal branches. Finally, the axonal branches are pruned, and axonal action-potential propagation velocities are computed. Main results: We first validate our method using simulated data from detailed reconstructions of neurons, showing that our approach is capable of accurately reconstructing axonal branches. We then apply the reconstruction algorithm to experimental recordings of HD-MEAs and show that it can be used to determine axonal morphologies and signal-propagation velocities at high throughput. Significance: We introduce a fully automated method to reconstruct axonal branches and estimate axonal action-potential propagation velocities using HD-MEA recordings. Our method yields highly reliable and reproducible velocity estimations, which constitute an important electrophysiological feature of neuronal preparations.

Perspectives of temperature assessment based on wave propagation for dynamic rating of medium-voltage power cables

This paper explores the feasibility of wave propagation characteristics as means of probing the temperature of an underground power cable. It utilises the relation between wave velocity and relative permittivity. The permittivity and its temperature dependency are specific for the applied insulation materials. The investigated cable is a three-phase XLPE-insulated mediumvoltage cable with a common earth screen. Combined thermal and electromagnetic analysis is applied to account for the temperature distribution over the cable cross section. The corresponding permittivity distribution is based on the temperature dependency measured for an XLPE sample. Temperature monitoring is achieved by observing the signal transit time along the power cable. The measured variation in signal propagation velocity and attenuation, compared to model predictions, provides an estimate of the cable temperature. It is shown that a sensitivity within 2°C can be achieved for a temperature near the maximum operating value for XLPE insulation.

Дифракция звука на упругой сфероидальной оболочке

Object and purpose of research. This paper obtains solutions and performs estimations of characteristics of sound reflection and scattering by ideal and elastic bodies of various shapes (analytical and non-analytical) near media interface, or underwater sonic channel, or in a planar waveguide with a solid elastic bottom. Materials and methods. The harmonic signals are investigated with the method of normal waves based on the phase velocity of signal propagation, and impulse signals related to the energy transfer are studied using the method of real and imaginary sources and scatterers based on the group velocity of propagation. Main results. The scattered sound field is calculated for ideal spheroids (elongated and compressed) at fluid – ideal medium interface. The spectrum of a scattered impulse signal is calculated for a body placed in a sonic channel. First reflected impulses are found for an ideal spheroid in a planar waveguide with anisotropic bottom. Conclusion. In the studies of diffraction characteristics of bodies at media interfaces it was found that the main contribution to scattered field is given by interference of scattered fields rather than interaction of scatterers (real or imaginary). It is shown that at long distances the spectral characteristics of the channel itself have a prevalent role. When impulse sound signals in the planar waveguide are used, it is necessary to apply the method of real and imaginary sources and scatterers based on the group velocity of sound propagation.

Water Content Monitoring in Water-in-Crude-Oil Emulsions Using an Ultrasonic Multiple-Backscattering Sensor.

This work shows the application of an ultrasonic multiple-scattering sensor for monitoring water-in-petroleum emulsions. The sensor consists of a commercial ultrasonic transducer with an array of cylindrical scatterers placed in the near field. The scatterers are thin metal bars arranged in rows in front of the transducer. The backscattering signals were analyzed by calculating the wave energy and by a cross-correlation between signal segments; they were also used to determine the propagation velocity in the emulsions. The tests performed used emulsions with water volume concentrations from 0% to 50%. The results showed that both the signal energy and propagation velocity strongly depended on the concentration of water in the emulsion. Therefore, the ultrasonic multiple-scattering sensor can be used for on-line and real-time monitoring of the water content in water-in-crude-oil emulsions.

Electrophysiological Characterization of Human Atria: The Understated Role of Temperature.

Ambient temperature has a profound influence on cellular electrophysiology through direct control over the gating mechanisms of different ion channels. In the heart, low temperature is known to favor prolongation of the action potential. However, not much is known about the influence of temperature on other important characterization parameters such as the resting membrane potential (RMP), excitability, morphology and characteristics of the action potential (AP), restitution properties, conduction velocity (CV) of signal propagation, etc. Here we present the first, detailed, systematic in silico study of the electrophysiological characterization of cardiomyocytes from different regions of the normal human atria, based on the effects of ambient temperature (5−50°C). We observe that RMP decreases with increasing temperature. At ~ 48°C, the cells lose their excitability. Our studies show that different parts of the atria react differently to the same changes in temperature. In tissue simulations a drop in temperature correlated positively with a decrease in CV, but the decrease was region-dependent, as expected. In this article we show how this heterogeneous response can provide an explanation for the development of a proarrhythmic substrate during mild hypothermia. We use the above concept to propose a treatment strategy for atrial fibrillation that involves severe hypothermia in specific regions of the heart for a duration of only ~ 200 ms.

Neutron Imaging for Intermetallic Alloy using a Delay Line Current-Biased Kinetic-Inductance Detector

The current-biased kinetic-inductance detector (CB-KID) is a solid-state superconducting neutron detector with high spatial and temporal resolutions, and multi-hit tolerance. We demonstrate high temperature operation of CB-KID at 7.9 K with the delay-line method. High temperature operation reduces imaging pixel size by suppressing signal propagation velocity. High spatial neutron transmission image for a mixed metal alloy consisting of heavy elements Sm and Sn is successfully constructed. We also examine the capability of element discrimination imaging based on the resonance dip analysis.

Estimation of the additive and multiplicative error of the standard algorithm of acoustic emission sources linear location

The paper deals with the results of the standard acoustic emission (AE) source linear location algorithm, which evaluates the location of developing damage in a steel sample under static load test to destruction. The linear location algorithm error is due to many factors: acquisition threshold of the AE signals and the dispersion properties of recorded signals, in particular, the dependence of the AE signal propagation velocity on its amplitude. According to the test results, the additive error in determining the time difference of arrival (TDA) of the AE signals to the transducers array is 52.8 μs and the average multiplicative error level is 0.67.

Mathematical tools and software for the distributed geophone network of Prognoz-ADS geomechanical monitoring system

Introduction. The article considers the problems of the present-day algorithm of acoustic emission events location in Prognoz-ADS geomechanical monitoring system. The ways of solving the flaws in the applied algorithm have been proposed with the account of the specified requirements. Research aim is to propose certain solutions aimed at achieving higher accuracy of seismoacoustic events coordinates calculation; to solve the flat antenna problem and get the opportunity of assessing the efficiency of separate observing network elements; develop the structure of a new location algorithm and calculate its preliminary complexity. Methodology. It is proposed to correct the problems of the existing algorithm by constructing the velocity map of the controlled object and assessing the efficiency of seismoacoustic receivers and data on the observing network sensitivity in various sections of the rock mass. Results. The article provides logical structure of the developed algorithm with complexity O(n). It is proposed to solve the flat antenna problem by using data on seismic receivers complex sensitivity. Certain media of collecting information on the observing network state and signal propagation velocities at the controlled object have been introduced. Summary. The designed algorithm provides for multiple parameters variation, many of them are not taken into account in the existing location method of Prognoz-ADS system. The indicated characteristics selection and the efficient use of the calculating tool’s hardware resources will make it possible to obtain a more accurate and universal location algorithm.

On the Principle of Causality and Superluminal Signal Propagation Velocities

This paper considers the question of superluminal (or negative) group velocities of signals in dispersive media, as well as negative group delay times of signals passing through linear filters. It is shown that information can be transmitted only with the help of jumps in the time dependence of a function or its derivatives and, therefore, the information propagation velocity in any (including dispersive, absorbing, or amplifying) medium exactly coincides with the speed of light in vacuum. As for the group velocity of a wave packet, it is only the propagation velocity of its infinitely differentiable envelope, by means of which the transmission of information, strictly speaking, is impossible. Therefore, in regions with anomalous dispersion, the group velocity can be superluminal or negative without violating the “light limitation” of the theory of relativity or the principle of causality. Examples of situations in which superluminal or negative group velocity occurs are given.

Can Signal Delay be Functional? Including Delay in Evolved Robot Controllers.

Engineers, control theorists, and neuroscientists often view the delay imposed by finite signal propagation velocities as a problem that needs to be compensated for or avoided. In this article, we consider the alternative possibility that in some cases, signal delay can be used functionally, that is, as an essential component of a cognitive system. To investigate this idea, we evolve a minimal robot controller to solve a basic stimulus-distinction task. The controller is constrained so that the solution must utilize a delayed recurrent signal. Different from previous evolutionary robotics studies, our controller is modeled using delay differential equations, which (unlike the ordinary differential equations of conventional continuous-time recurrent neural networks) can accurately capture delays in signal propagation. We analyze the evolved controller and its interaction with its environment using classical dynamical systems techniques. The analysis shows what kinds of invariant sets underlie the various successful and unsuccessful performances of the robot, and what kinds of bifurcations produce these invariant sets. In the second phase of our analysis, we turn our attention to the parameter θ, which describes the amount of signal delay included in the model. We show how the delay destabilizes certain attractors that would exist if there were no delay and creates other stable attractors, resulting in an agent that performs well at the target task.

Transmission of Mechanical Information by Purinergic Signaling

The skeleton constantly interacts and adapts to the physical world. We have previously reported that physiologically relevant mechanical forces lead to small repairable membrane injuries in bone-forming osteoblasts, resulting in release of ATP and stimulation of purinergic (P2) calcium responses in neighboring cells. The goal of this study was to develop a theoretical model describing injury-related ATP and ADP release, their extracellular diffusion and degradation, and purinergic responses in neighboring cells. After validation using experimental data for intracellular free calcium elevations, ATP, and vesicular release after mechanical stimulation of a single osteoblast, the model was scaled to a tissue-level injury to investigate how purinergic signaling communicates information about injuries with varying geometries. We found that total ATP released, peak extracellular ATP concentration, and the ADP-mediated signaling component contributed complementary information regarding the mechanical stimulation event. The total amount of ATP released governed spatial factors, such as the maximal distance from the injury at which purinergic responses were stimulated. The peak ATP concentration reflected the severity of an individual cell injury, allowing to discriminate between minor and severe injuries that released similar amounts of ATP because of differences in injury repair, and determined temporal aspects of the response, such as signal propagation velocity. ADP-mediated signaling became relevant only in larger tissue-level injuries, conveying information about the distance to the injury site and its geometry. Thus, we identified specific features of extracellular ATP and ADP spatiotemporal signals that depend on tissue mechanoresilience and encode the severity, scope, and proximity of the mechanical stimulus.

Traveling-wave fault location algorithms in hybrid multi-terminal networks with a tree-like structure

Traveling-wave methods of the fault location prove their practical efficiency for the power transmission lines (TL) with an arbitrary configuration of any voltage class. This paper formulates algorithms to automate the process of the fault location in the TLs with a tree-like structure. The error of the simplified traveling-wave fault location (TWFL) algorithm based on the average propagation velocity of the transient signals (TS) is analyzed. A tabular algorithm for TWFL, which considers different propagation velocities of the TS in different segments of a hybrid network is proposed. An adaptive TWFL algorithm that considers the registration of the TSs with known places of their occurrence is proposed, to reduce the impact of the inaccuracy of the initial different network segments’ lengths and TS’s propagation velocity determination.

Calcium movement in smooth muscle and evaluation of graded functional intercellular coupling.

Spontaneous activity of vascular smooth muscle is present in small arteries and some venous tissues like the hepatic portal vein. Whereas the ability to generate rhythmic membrane potential changes is expressed in a high number of primary oscillators, the generation of physiological tone and phasic activity requires synchronization of specialized pacemaker activity (Interstitial Cajal-like cells) by intercellular propagation and regeneration of excitation or a strong coupling mechanism of smooth muscle cells. The aim of this study was to deduce oscillator coupling by analyzing the spatiotemporal homogeneity of calcium oscillations within a native tissue preparation. Portal vein tissue was loaded with a calcium-sensitive dye (Fluo-3). By combining confocal microscopy and computation of spatial auto- and cross-correlation of the calcium signals, temporal and spatial coupling between cells was characterized. Spontaneous oscillations of calcium signals were measured at different predefined regions of interest. Cross-correlation analysis of these signals revealed that their damping was very similar in all directions of the investigated z-plane. In single experiments, improved cell-to-cell coupling was seen when noradrenaline (1-10 μM) was added to the bath-solution. With the chosen parameters of frame refresh, the velocity of signal propagation was faster than the maximum detectable velocity, but it could be estimated to exceed 0.1 mm/s. Correlative Network Analysis is a new and very useful tool to determine the functional coupling parameters of quasi-homogenous biological networks and their temporal changes. The action and significance of pharmacological modulators can be well studied on cellular and functional aspects with this newly introduced technique in biological sciences.