Signal Propagation Velocity Research Articles

Probing the nature of the contact between fine particles by using ultrasound propagation

The propagation velocity ( v s ) of an ultrasonic signal through a granular material depends on the type of interparticle contact. For noncohesive glass beads, a power law behavior v s ∝ σ c 1 / 6 for consolidation stresses applied ( σ c ) above 1 MPa has been measured in previous work. This equation is compatible with Hertz's interaction law between elastic solids. In the present work, we have tested the propagation velocity of ultrasound signals through a sample of fine powder. The tensile strength and compactivity of the powder were previously measured by means of the Seville powder tester (SPT), indicating plastic deformation of the surface asperities in contact for small to moderate consolidation stresses. However, the measurements of ultrasound propagation at high consolidations presented here are compatible with Hertz's law. This finding suggests that for high consolidation stresses, surface asperities are flattened, and it is therefore the elastic deformation of the bulk of the particles that determines the transmission of ultrasonic pulses.

Distributed parametric effect in long lines and its applications

The article considers a parametric effect which takes place when the velocity of signal propagation in a long line changes. We found the analytical solution describing the form of the transformed signal for a line with losses, when line parameters change symmetrically. We also considered lines without losses, with asymmetrical change of parameters. Our theoretical results comply with experimental data. In certain conditions, such a line can be used as an amplifier. The parametric effect in optics is described by Maxwell's equations, while in case of a long line, the analysis is based on telegrapher's equations. However, it turns out that in the end, both in optics and electronics, the parametric effect is described by wave equations that are mathematically similar. This is because fundamentally, when the parameters of the propagating medium change, the parametric effect is physically based on energy interchange between the controlling (pump) signal and the transformed one. So, the obtained results can be used for analysis of parametric effects in optics and electronics.

High Frequency Signal Propagation in Solid Dielectric Tape Shielded Power Cables

High frequency signal propagation in shielded power cable is important to many cable diagnostic techniques including time domain reflectometry, partial discharge location, etc. The signal propagation characteristics, including electromagnetic propagation velocity, cable characteristic impedance, and attenuation are well studied in power cables with concentric neutral wires or solid metallic shield. However, high frequency signal propagation in tape shielded cable is more complicated as conduction at the tape laps tends to decrease with cable aging, which forces more of shield current to spiral down the tape shield. The cable inductance increases with the fraction of the shield current in circumferential direction, which affects all the signal propagation characteristics. High frequency signal propagation characteristics of tape shielded power cable were studied using a custom manufactured 15 kV cable sample which has a PET tape intercalated with the copper tape shield to eliminate conduction at the overlap, which simulates the effects of corrosion in aged tape shielded cables. The inductance of the cable sample was computed as a function of fraction of shield current following a spiraling path along the cable, as were the signal propagation velocity, and the cable characteristic impedance, all of which are in reasonable agreements with measurements. Calculations and measurements of high frequency attenuation indicate that large eddy current and “transformer effect” losses in the ground shield semicon dominate once a substantial fraction of shield current spirals down the tape.

Frequency dispersion of losses during acoustic sounding of water in Lake Baikal

The processes of horizontal and vertical water exchange play the most important role in the ecosys� tem of Lake Baikal providing the transport of organic and inorganic matter including oxygen in the entire volume of water up to the limiting depths. The investi� gation of the main processes of water transport in Lake Baikal based on the traditional methods of episodic profiling from research ships does not supply sufficient information about many inhomogeneous and nonsta� tionary processes. The difficulties are also related to the insufficient sensitivity of the existing instruments for measuring the vertical motion of water whose velocity usually does not exceed a few fractions of a millimeter per second. An infrastructure was created within the project of the Baikal neutrino telescope (1), and new technolo� gies were developed that make it possible to set up sys� tems of longterm multiparameter monitoring of dif� ferent processes in the lake including precise acoustic measurements. The initial goal of the investigations presented in this paper was to develop the methods of acoustic tomography (2) as a tool for investigation of the hydrophysical processes in Lake Baikal. It is possi� ble to study multiscale processes using acoustic path� ways with a length from tens of meters to tens of kilo� meters. The preliminary results of acoustic sounding in the water under ice over basic lengths on the order of hun� dreds of meters based on pulse signals were published in (3, 4). The key idea of the method is to measure the intrapulse phase distortions, which allows us not only to increase the sensitivity (as during typical phase measurements) but also to take into account the dis� persion distortions of the signals related to the depen� dence of attenuation on frequency. The amplitude, delay, and phase of the pulse signal and also the addi� tional phase modulation that results from the fre� quency dependence of attenuation in the signal band were recorded in the experiments. This dependence is manifested in the slope of the amplitudefrequency characteristic of the channel. In this case, the spec� trum of the amplitudemodulated pulse no longer remains symmetric with respect to the carrier fre� quency, which is manifested as additional intrapulse phase modulation. We note that this effect for the pulse narrow band signals is the effect of the first order of magnitude with respect to the bandwidth, while the usual dispersion (the dependence of the signal propa� gation velocity on frequency) leads to the effects of the second order with respect to the bandwidth. The appearance of additional phase modulation is not manifested on the envelope curve of the received sig� nal, but an additional quadrature component propor� tional to the derivative of the inphase component whose amplitude is proportional to the slope of the amplitudefrequency characteristic appears during detection by a synchronous phase detector.

On-chip constructive cell-Network study (I): Contribution of cardiac fibroblasts to cardiomyocyte beating synchronization and community effect

BackgroundsTo clarify the role of cardiac fibroblasts in beating synchronization, we have made simple lined-up cardiomyocyte-fibroblast network model in an on-chip single-cell-based cultivation system.ResultsThe synchronization phenomenon of two cardiomyocyte networks connected by fibroblasts showed (1) propagation velocity of electrophysiological signals decreased a magnitude depending on the increasing number of fibroblasts, not the lengths of fibroblasts; (2) fluctuation of interbeat intervals of the synchronized two cardiomyocyte network connected by fibroblasts did not always decreased, and was opposite from homogeneous cardiomyocyte networks; and (3) the synchronized cardiomyocytes connected by fibroblasts sometimes loses their synchronized condition and recovered to synchronized condition, in which the length of asynchronized period was shorter less than 30 beats and was independent to their cultivation time, whereas the length of synchronized period increased according to cultivation time.ConclusionsThe results indicated that fibroblasts can connect cardiomyocytes electrically but do not significantly enhance and contribute to beating interval stability and synchronization. This might also mean that an increase in the number of fibroblasts in heart tissue reduces the cardiomyocyte 'community effect', which enhances synchronization and stability of their beating rhythms.

Introducing DuPont™ GreenTape™ 9K5 Low Dielectric Constant, Low Temperature Co-Fired Ceramic (LTCC) Tape System

Low Temperature Co-fired Ceramic (LTCC) material systems have been successfully used in microwave and millimeter wave systems for several years. LTCC has very low dielectric loss, high reliability due to inherent hermeticity; high interconnect density, multilayer processing capability leading to true 3D packaging, and better cost-performance balance. While the medium range dielectric constants (7.00 – 8.00) offered by current tape systems have advantages, it is generally difficult to realize high speed systems and efficient antennas on LTCC, especially at millimeter wave frequencies. The difficulty arises from the reduced signal propagation velocity in high-speed applications, and lower radiation efficiency for antennas, both due to higher dielectric constant. To enable and extend applications of LTCC technology to these subsystems, DuPont has developed a new low dielectric constant LTCC system – DuPont™ GreenTape™ 9K5 - which has a dielectric constant of 5.80 (at 10 GHz) that is compatible with the commercial DuPont™ GreenTape™ 9K7 LTCC System. This is achieved without compromising excellent microwave loss properties of the 9KX GreenTape™ platform. These materials systems enable high-speed, high reliability applications while also realizing efficient antennas on LTCC. This paper presents initial characterization of the new DuPont™ GreenTape™ 9K5 LTCC system consisting of low K dielectric tape, gold and silver conductors to evaluate the effects of chemistry, processing conditions, processing latitude, microstructure, and microwave performance. Test coupons with various transmission and resonating structures are designed, fabricated, and tested for the evaluation of transmission losses and dielectric properties. Stability of the material system over multiple re-fire steps is also examined

458: Propagation velocity of electrical signals of the uterus is significantly higher in patients during labor at term and preterm compared to non-labor states

Action potentials propagated through the uterus are responsible for contractions. It has been shown in-vitro that propagation increases prior to labor due to increased coupling between cells. The objective of this study was to examine the propagation velocity of electrical activity in labor and non-labor patients at term and preterm using trans-abdominal uterine electromyography (EMG), and to determine whether there is a preferred propagation directionality, which would suggest a pacemaker in the uterus.

Settling velocity spectra and the ballast ratio hypothesis

Abstract Recently it has been observed that a strong quantitative relationship exists between asymptotic fluxes of particulate organic carbon (POC) to the deep ocean and asymptotic fluxes of “ballast” minerals (opal; calcium carbonate; dust). It has further been suggested that this relationship might provide a mechanistic basis for improved representations of remineralization in ocean carbon models. Since the depth scale of remineralization z* is the ratio k/v of a remineralization rate k and a settling velocity (SV) v, a mechanistic understanding of settling velocities will be crucial in developing such models. Historically, there have been two approaches to estimating the speed with which POC is transported to the deep ocean. First, settling speeds of single particles have been observed directly in both field and laboratory settings; estimates of fecal pellet sinking velocities tend to be higher and more variable than those of aggregates. Second, estimates have been made of the velocity at which temporal patterns in flux propagate between pairs of sediment traps separated in depth (the “benchmark approach”); recent studies have shown these results to be variable and to depend on mineral ballasting. Here we present SV estimates using a relatively new technology: indented rotating sphere (IRS) sediment traps run in settling velocity (SV) mode. In this approach, particles are separated into SV classes during settling to collection cups. In MedFlux, SV data were collected concurrently with time-series (TS) data; the latter were used to construct benchmark estimates for comparison to the SV estimates. From the SV data, the range of modal settling velocities (sinking velocities having the largest time-averaged mass flux densities on a logarithmic scale of SV) in the fast-sinking fraction was estimated to be 287–503 m/d; the average of these modal values is 353 m/d, with standard deviation 76 m/d. In contrast, mean settling velocities of the fast-sinking fraction depend on the range of settling velocity classes included in the estimate. If only SV classes settling at >50 m/d are included, the range of SVs at MedFlux was 214–298 m/d, with average mean value 242 m/d and standard deviation 31 m/d. These mean-velocity results are in excellent agreement with benchmark estimates of signal propagation velocities at Medflux (220±65 m/d); they are also well within the range of other recent benchmark studies. The agreement between the benchmark estimates and mean settling velocity estimates at MedFlux, but not with modal velocities, argues that the benchmark method estimates mean settling velocities.

Signal propagation in time-dependent spin transport

This paper analyzes theoretically the signal propagation in spin transport by modulating the current passing through magnetic multilayers. Using a macroscopic description of spin transport based on the dynamical Boltzmann equation, we show that time-dependent spin transport possesses a wavelike character that leads to modifications of pure spin-diffusion dynamics. In particular, the wavelike characteristics allow one to extract a finite spin signal-propagation velocity.

Interaction of acoustic and biological waves in muscular tissue

In studying biological tissues from the viewpoint of diagnosis of their structure and function, the wave processes revealing the active properties of tissues (muscles, nerves, brain, etc.) are of special interest. Muscular tissue is penetrated not only by a branched network of blood vessels with smooth muscles, but also by a branched network of nerve fibers. In these tissues, the waves of acoustomechanic (deformation) and electric (action potential, ion concentrations) nature with propagation velocities of close values (1‐100 m/s) can travel and interact [1‐3]. In this case, the “relativistic” effects connected with the finiteness (limitation) of the propagation velocity of information-carrying excitation signals in nerve fibers and tissues are possible [4]. In addition to mechanochemical processes, electrical processes proceed in muscular tissue, which are connected with the tissue excitation. Typically, an electric wave initiates a mechanical contraction of a muscle. Some facts testify to the interaction between these wave processes (muscular twitching, cramp, overstress, etc.) [5]. Muscle contraction can be initiated by a mechanical action [2], change in temperature, and other factors (including acoustic irradiation) [6]. It is also known that the deformation of tissue can change its electrical properties and, consequently, the conditions of the propagation of the excitation potential [7, 8]. In a number of papers, a fragmentary attempt to describe mathematically the muscle contraction under the action of the excitation potential and their interrelation was made [2, 7, 8]. However, no complete mathematical description of the interaction between electric and acoustic waves in the course of their propagation in a muscle can yet be found in the literature.

Buried Cylinders Geometric Parameters Measurement by Means of GPR

Interactive technique that measures geometric parameters of buried cylinders in a homogeneous medium with unknown velocity of signal propagation is developed. After 3D GPR data processing, the velocity of signal propagation is estimated; radius, length and position of the cylinder are measured. Experimental data obtained by GPR “Defectoscope” are given.

Source Localization With Isotropic Arrays

We consider the effect of unknown signal propagation velocity on direction-of-arrival (DOA) estimation performance using an array of sensors. For general arrays, the DOA estimation variance, as measured by the Crame/spl acute/r-Rao bound (CRB), degrades when the propagation velocity is unknown. In this letter, we show that for both two- and three-dimensional arrays, the CRB on the DOA angle is independent of whether or not the propagation velocity is known if and only if the sensor locations satisfy the isotropy conditions given in earlier work. The results hold for both narrowband and wideband signals.

INVESTIGATION OF BOILING OF REFRIGERATING MEDIUM UNDER CONDITIONS OF IMPULSE DISTURBANCES

This article describes investigations of bubbly boiling in flow of a refrigerating medium under conditions of impulse disturbances occurring in refrigeration engineering systems. The development and decay of boiling is induced by impulsively changing parameters, such as pressure and mass flux density, of the two-phase system in a tubular channel. It is confirmed that the two-phase systems exhibit wave properties and the induced disturbances propagate with a finite velocity. Correlations are elaborated to evaluate the propagation velocity of disturbance signals during the development and decay of boiling in a coil tube. Investigations are conducted by feeding under pressure a heat exchanger with an environment-friendly refrigerant R404A.

Investigation of the effective space-time of the vacuum nonlinear electrodynamics in a magnetic dipole field

The metric tensor of the effective pseudo-Riemannian space–time for an electromagnetic wave propagating in the magnetic dipole field and the gravitational field of a neutron star is obtained within a parameterized post-Maxwellian vacuum electrodynamics. The angles of the nonlinear electrodynamic and gravitational ray bending for electromagnetic waves propagating in the magnetic equatorial plane of the star are calculated based on an analysis of isotropic geodesics of this space. We show that for all nonlinear theories whose post-Maxwellian parameters do not coincide, the velocity of the electromagnetic signal propagation in external fields and the rays along which these signals propagate depend on the polarization of the electromagnetic waves. The difference of the source-to-detector propagation time of these signals for two principal polarization states is calculated.

Distributed multichannel acoustic-emission system equipped with microprocessors for strength testing of long objects

The paper analyzes the structure of a distributed multichannel microprocessor acoustic-emission (AE) facility for diagnosing metallic tested objects of large lengths. Each unit of the distributed AE facility is housed in a small case and equipped with a built-in simulator of an AE signal, which enables one to tune up in the automatic mode acoustic emission transducers and measure the propagation velocity of acoustic signals. The measuring channels are connected to a computer using the Ethernet technique. The paper describes a technique for estimating remaining service lives taking as examples samples of aircraft materials and compares calculations to experimental data.

The GPS Radio Occultation Technique

Radio occultation observations represent a planetary-scale optics experiment in which the atmosphere acts as a lens and alters the propagation velocity and paths of microwave signals passing through it. In this paper we review the process of inverting the radio occultation observations acquired using the Global Positioning System (GPS) in order to derive atmospheric quantities of interest including temperature, geopotential and water vapor. Beginning with geometric optics, we derive the Abel integral used to transform the observations into profiles of refractivity. In the process, we characterize why the Abel transform works so well as a first approximation for deriving atmospheric profiles. We discuss the resolution of the observations and the improvements that can be achieved via the backpropagation concept where the receiver’s position is effectively moved closer to the limb of the Earth in post-processing. We discuss several factors that complicate the observations in the Earth’s troposphere including critical refraction and atmospheric multipath. Critical refraction refers to the situation where the bending becomes so great that the occulted signal disappears whereas atmospheric multipath refers to the situation where multiple signal paths connect the transmitter and receiver. We describe the derivation of temperature, pressure and water vapor from the observations including the optimal combining of the occultation observations with weather and climate analyses. We describe some key issues in deriving profiles from real data including the correction of clock errors and ionospheric effects, and the estimation of the resolution and atmospheric Doppler in a self-consistent manner. We conclude by summarizing the expected and achieved accuracy and resolution.

Dynamic Excitations of Fractional Quantum Hall Edge Channels

We investigate the electrodynamic properties of charged edge excitations in the fractional quantum Hall regime by means of time-resolved magnetotransport. In samples with a smooth edge potential and an additional screening electrode, the propagation velocity of high frequency signals is related to the width of fractional edge channels. While the observed edge magnetoplasmons around filling factor 1y3 hint at a similar electronic edge structure as around filling factor 1, characteristic deviations appear for other fractions, especially around n ­ 2y3. [S0031-9007(97)04426-8]

Analysis of Optical Density Wave Propagation and Cell Movement during Mound Formation inDictyostelium discoideum

Aggregation fields ofDictyosteliumamoebae are organized by propagating concentric or spiral waves of cAMP. These waves coordinate cell movement directed toward the aggregation center. We now systematically investigated dark-field wave propagation and chemotactic cell movement during late aggregation and mound formation. The period and the signal propagation velocity decreased continuously during aggregation leading to a 15-fold decrease of the chemical wavelength. By analyzing the behavior of single GFP-labeled cells in aggregates and mounds we measured cell movement velocity, changes in cell shape, periodicity of cell movement, and cell trajectories. In early mounds of strain AX-3 dark-field waves propagated frequently as multiarmed (high-frequency) spirals. During the high-frequency waves observed in the early mound stage, cell movement speed is low and cell movement rather undirected. During tip formation the wave period decreased again and the cells started to rotate in the mound at unusually high average speeds of 40 μm/min. The rotation was almost monotonic with no clear periodicity. Since at this time the majority of the cells had already differentiated into prespore cells, this implies that prespore cells moved faster than aggregation stage cells. At 12 hr of development cell movement velocity dropped again and became highly periodic. These measurements show that the relay system is characterized by a specific temporal evolution, which is closely correlated with cellular differentiation. The remarkable changes in cell movement speed and period indicate a qualitative change in signal and movement parameters which might well be caused by the observed switch from high- to low-affinity cAMP receptors during mound formation. This switch might be required to copy with the increase in cell density and most likely plays a crucial role in the process of cell sorting.

Wave model for longitudinal dispersion: Development of the model

AbstractA new 1‐D model for longitudinal dispersion is proposed as an alternative to the Fickian‐type dispersed plug‐flow model. Accounting for significant features of longitudinal mixing gives rise to a quasilinear hyperbolic system of two first‐order equations for the average concentration. The model equations are obtained based on minor extensions of the heuristic equilibrium analysis of Taylor. A qualitative, more general derivation of the equations is given on the basis of the simple generalization of Fick's law, taking into account the finite velocity of fluid elements. For linear problems the mean concentration and the dispersion flux obey a hyperbolic equation of the second order. The proposed hyperbolic model contains three parameters that depend only on the flow conditinos, the physical properties of the fluid, and the gemetry of the system. It effectively resolves the well‐known problem of boundary conditions that, for unidirectional flow, are formulated now only at the reactor inlet. The new model eliminates the conceptual shortcomings inherent to the Fickian dispersed plug‐flow model: it predicts a finite velocity of signal propagation and does not involve backmixing in the case of unidirectional flow.

Ground probing radar applications in site investigation : Fenning, P J; Jack, A G; Veness, J K Non-destructive Testing in Civil Engineering, Liverpool (United Kingdom), 14–16 Apr 1993. Vol. 2, pp 113–140. Edited by J H Bungey. The British Institute of NDT (1993)

Although early experiments in the application of Ground Probing Radar to site investigation occurred in the early part of this century, it is only in the last ten years that this geophysical method has been used as a routine site investigation technique. All too often this technique has been misapplied and has led to disappointing results, often of little use to the Geotechnical Engineer. The reasons for this are examined and it is suggested that the introduction of Ground Probing Radar systems which are based on proven seismic reflection methodology will overcome some of the misapplications of the past. Reference is made to the requirement for radar signal propagation velocity determination to be made on site and the pre-survey requirement of assessing theoretical ground radar applicability before commencing a radar survey. Examples of case histories are given. (A) For the covering abstract see IRRD 861706.