Measurement Of Propagation Velocity Research Articles

Influence of voltage and gap distance on the dynamics of the ionization front, plasma dots, produced by nanosecond pulsed discharges at water surface

A streamer discharge is a highly reactive and dynamic non-thermal plasma. It has been used in many applications, including environmental remediation, medicine, and material processing. Although the physics of streamer discharges in gaseous media is well understood, its interaction with a solid and liquid dielectric surfaces remains under investigation, in particular when quantitative data are searched for. In this study, we investigate the influence of voltage amplitude (V a) and interelectrode air gap distance (d) on the pulsed discharge behavior at the surface of distilled water. Time resolved images show the formation and propagation of plasma dots (ionization front of streamers) at water surface. Because of its stochastical nature, a large number of discharge was performed to address the influence of V a and d on the number of plasma dots (N Dots) as well on the charge per dot (Q Dot). As expected, for a given V a, the breakdown voltage is found to increase with d. Moreover, N Dots decreases linearly with d at the rate of ∼1 dot by 200 μm of increase, while the total injected charge decays linearly with a rate of ∼8–9 nC by 200 μm of increase. Based on the measurement of the propagation velocity of the plasma dots and on the estimation of the electric field in the medium, an average mobility of plasma dots of ∼1.5 cm2 Vs−1 is evaluated. From both this value and the instantaneous measured propagation velocity, the temporal evolution of Q Dot and charge number are determined. The observations reported here are of interest for fundamental studies as well as for applications where well-controlled charge transfer to surfaces is crucial.

Thermo-chemo-mechanical characterization, modeling, and analysis of hydration of calcium-sulfoaluminate cement paste

The reaction kinetic of a commercial calcium sulfoaluminate (CSA) cement was characterized by heat flow calorimetry. Distinct behavior is observed whether tartaric acid is added as retarding agent or not. Employing the so-obtained calorimetric data, heat of hydration and chemical affinity of the investigated binder mixture was determined. Furthermore, continuous ultrasonic propagation velocity measurement gave access to the stiffness gain of paste samples. However, the ultrasonic test setup is characterized by a non-constant temperature history (temperature rise and fall). Modeling the temperature history and the history of the degree of hydration with a thermo-chemical analysis scheme, the intrinsic material function of the stiffness evolution of the investigated hydrating CSA paste was obtained. Furthermore, the robustness of the thermo-chemical analysis scheme was demonstrated by the comparison of the measured with the simulated temperature evolution. The versatility of the approach may contribute to a systematic assessment and optimization of the heat/mechanical evolution of CSA binder systems under various geometric, temporal, and thermal boundary condition.

Anisotropic deformability and strength of slate from NW-Spain

Slates are metamorphic rocks characterized by the pervasive occurrence of cleavage or foliation producing a highly anisotropic mechanical behavior characterized by fissility. Deformability and strength of these rocks are therefore dependent on the cleavage plane orientations relative to the principal stresses. In this study, the failure and deformability of these rocks are experimentally investigated by means of a set of standard uniaxial and triaxial compression tests on samples cut with the cleavage forming different angles. Propagation velocity measurements have also been taken in a good number of specimens. Compression tests show that deformability and strength are clearly anisotropic for this rock and that failure through the cleavage plane is observed in the range of dip angles from 15 to 75°. Transversely isotropic elastic parameters are fit based on improved existing approaches. Moreover, the strength of tested samples cut normal and parallel to foliation relevantly differ, something noted qualitatively in the past by some authors in some metamorphic anisotropic rocks. However, this difference has neither been explicitly reported for the case of other foliated sedimentary rocks such as shales, nor formalized in theoretical strength approaches. The triaxial compression experimental data on slates were fit with the Jaeger's plane of weakness (JPW) model. Strength criteria differentiating the strength in directions normal and parallel to foliation are proposed to adapt the JPW model to the observations in slate strength behavior. Other model improvement is proposed, the use of a non-linear strength criterion for the intact rock (Hoek-Brown), which shows to better represent observed strength laboratory results.

Blood pressure wave propagation—a multisensor setup for cerebral autoregulation studies

Objective. Cerebral autoregulation is critically important to maintain proper brain perfusion and supply the brain with oxygenated blood. Non-invasive measures of blood pressure (BP) are critical in assessing cerebral autoregulation. Wave propagation velocity may be a useful technique to estimate BP but the effect of the location of the sensors on the readings has not been thoroughly examined. In this paper, we were interested in studying whether the propagation velocity of a pressure wave in the direction from the heart to the brain may differ compared with propagation from the heart to the periphery, as well as across different physiological tasks and/or health conditions. Using non-invasive sensors simultaneously placed at different locations of the human body allows for the study of how the propagation velocity of the pressure wave, based on pulse transit time (PTT), varies across different directions. Approach. We present a multi-sensor BP wave propagation measurement setup intended for cerebral autoregulation studies. The presented sensor setup consists of three sensors, one placed on each of the neck, chest and finger, allowing simultaneous measurement of changes in BP propagation velocity towards the brain and to the periphery. We show how commonly tested physiological tasks affect the relative changes of PTT and correlations with BP. Main results. We observed that during maximal blow, valsalva and breath hold breathing tasks, the relative changes of PTT were higher when PTT was measured in the direction from the heart to the brain than from the heart to the peripherals. In contrast, during a deep breathing task, the relative change in PTT from the heart to the brain was lower. In addition, we present a short literature review of the PTT methods used in brain research. Significance. These preliminary data suggest that the physiological task and direction of PTT measurement may affect relative PTT changes. The presented three-sensor setup provides an easy and neuroimaging compatible method for cerebral autoregulation studies by allowing measurement of BP wave propagation velocity towards the brain versus towards the periphery.

Effect of heaters on the measurement of normal zone propagation velocity on short YBCO conductors

Based on a fully two-dimensional (2D) electrothermal model, the quench propagation characteristics of short superconducting YBa2Cu3O7-x conductors (AMSC and SuperPower), including the minimum quench energy (MQE), normal zone propagation velocity (NZPV) and hot spot temperature rising rate, are studied by numerical simulations in this paper. It is found that different heater configurations, such as the size of heater and the duration of heat pulse, can result variations of the MQEs and NZPVs. During the quench propagation processes, the NZPV and the normal zone length (LNZ), when viewed as functions of the hot spot temperature Tpeak, i.e., NZPV(Tpeak) and LNZ(Tpeak), are not sensitive to the heater configurations for relatively higher operating temperature from 50 K – 70 K. For both AMSC and SuperPower's YBCO conductor, the simulation results show that the hot spot temperature rising rate dTpeak/dt, as a nearly-linear function of Tpeak, is almost not affected by heater configurations for a given fixed operating temperature in the regime 30 – 70 K. For a fixed operating temperature in the regime 30 – 50 K, the temperature rising rate of SuperPower's conductor can reach 1000 K/s ~ 6000 K/s as Tpeak rising from ~110 K to 300 K, which makes it challenging to experimentally determine the NZPV prior the moment Tpeak reaches the temperature limit 300 K. The relations LNZ(Tpeak) obtained for SuperPower's conductor can provide information for the selection of reference voltage employed to determine the NZPV.

Poloidally resolved measurements of the perpendicular propagation velocity of density fluctuations in ASDEX Upgrade L-mode plasmas

Poloidal asymmetries of the propagation velocity of density fluctuations perpendicular to the magnetic field measured with Doppler reflectometry have been reported in several magnetic confinement plasma devices. Careful analysis of a large variety of different low confinement mode plasma scenarios performed at the ASDEX Upgrade tokamak does not reveal such an asymmetry outside the uncertainties of the evaluation process of the measurement data. The perpendicular velocity is investigated between mid-radius and the plasma edge and follows the poloidal dependence of the E × B drift velocity regardless of the probed turbulence structure size. Compared to measurements of a charge exchange recombination spectroscopy diagnostic this points towards a significantly smaller phase velocity than the E × B drift velocity. The analysis technique is presented in a representative discharge together with a sensitivity study of the impact of density, magneto hydrodynamic equilibrium and diagnostic alignment on the interpretation of the measured Doppler shift using ray tracing and thus on poloidal asymmetries. Three more highly different plasma scenarios with poloidally symmetric velocity profiles are shown.

Assessment of arterial wall stiffness based on the results of pulse wave propagation velocity measurement

Assessment of arterial wall stiffness based on the results of pulse wave propagation velocity measurement

Dynamics of the gas discharge in noble gases sustained by the powerful radiation of 0.67 THz gyrotron

This work was carried out in a frame of the study of the discharge propagation in noble gases in focused beams of the terahertz frequency range radiation. A 40 kW at 670 GHz pulsed gyrotron was used as a source of heating radiation. The propagation velocity of the discharge front in various noble gases (argon, krypton, and a helium–argon mixture) was measured over a wide pressure range (from several atmospheres to several Torr, depending on the type of gas). It is shown that the discharge propagation velocity decreases with increasing gas pressure. Moreover, the velocity decreases with an increase in the atomic mass of the gas from several units of 107 cm/s in the case of a helium–argon mixture to 106–105 cm/s (depending on pressure) in the case of krypton over the entire pressure range. Measurements of the discharge propagation velocity were carried out in several ways: from instant snapshots from the high-speed camera and images of the discharge from a streak-camera. The mechanisms responsible for the propagation of the discharge are currently the subject of further research.

Measurement of splice resistance and normal zone propagation velocity in REBCO tapes for the Superconducting Link of HL-LHC

The Superconducting Link (SC-Link) being developed at CERN in the context of the LHC High-Luminosity upgrade (HL-LHC) will supply the current to superconducting magnets of the HL-LHC Inner Triplets and Matching Sections. The SC-Link consists of MgB2 highcurrent cables, and it includes high temperature superconducting REBCO cables making the electrical transition between the MgB2 and the current leads. Electrical protection of superconducting devices made of REBCO against unexpected quenches is challenging especially when operation is at high current density. Adequate electrical protection of REBCO cables is crucial to insure good performance of the circuit over the lifetime of the machine; protection relies on the detailed knowledge of the quench propagation velocity. In this paper we reviewed the electromagnetic properties of REBCO tapes procured for prototype work. We measured the splice resistance (Rs ) of the REBCO conductors and found a significant variation among the different batches of conductor. The normal zone propagation velocity (NZPV) was reported to be affected by the interfacial resistance which is governing the splice resistance: increasing the interfacial resistance enhances the NZPV. In order to determinate the influence of the internal resistance on the quench behaviour of the tapes, we investigated the normal zone propagation velocity of the epoxy-impregnated tapes at 77 K in self-field and 4.2 K in field up to 7 T in the FRESCA test station. We found that despite the Rs variation observed (up to factor 4), the tapes show similar NZPV at both temperatures. In addition we observed a significant field dependence of the NZPV of the tapes at 4.2 K. The results are compared to numerical simulation and discussed.

Influence of concrete age on the behavior of ultrasonic waves in interfaces (concrete–steel–concrete)

This paper presents the influence of the composite age on the variation of the transmission and reflection coefficients. The composite is the concrete in our case. The studied structure is a multilayer structure composed of two elastic and isotropic layers where each one is characterized by its own physical properties. The problem is simplified in two-dimensional plane waves, and the influence of the attack angle on the acoustic impedances is also examined. Moreover, an experimental study is realized in the formulation of concrete and the measurement of waves propagation velocity. In this work, during the concrete formulation, three different types of concrete were developed: sand concrete, ordinary concrete, and high-performance concrete. The results of simulation and experiments demonstrate that the age of concrete and the internal concrete structure have a direct influence on the evolution of the acoustic parameters as well as the angle of incidence, which has considerably changed the behavior of the transmission and reflection coefficients. This internal structure is directly related to the age of the concrete where its maturity is not reached until after a certain age, which influences the behavior of the waves through the layers of the multilayer structure.

Experimental limit on the validity of Markstein relation

A PIV-based system has been set-up for the simultaneous measurement of the local propagation velocity and the flame stretch of laminar jet premixed flames. The contributions of the flame front curvature and the strain rate of the fresh gas flow to the flame stretch are separately discussed. Laminar jet flames of methane-air lean mixtures have been studied with a secondary flame in a coflow configuration to avoid blow-off. In weakly curved flame tips (low inlet gas velocity), these measurements confirm the prediction of linear velocity-stretch dependence and allow the indirect determination of the Markstein length and planar flame propagation velocity, by extrapolating the experimental results to the zero-stretch condition. In moderately curved flame tips (large inlet gas velocity), experiments show a faster than linear increase of the flame velocity with the stretch. The transition between these two regimes occurs suddenly when a threshold value of the inlet gas velocity is exceeded.

Measurement of Pulse Propagation Velocity, Distensibility and Strain in an Abdominal Aortic Aneurysm Mouse Model

Measurement of Pulse Propagation Velocity, Distensibility and Strain in an Abdominal Aortic Aneurysm Mouse Model

Measurement of Pulse Propagation Velocity, Distensibility and Strain in an Abdominal Aortic Aneurysm Mouse Model.

An abdominal aortic aneurysm (AAA) is defined as a localized dilation of the abdominal aorta that exceeds the maximal intraluminal diameter (MILD) by 1.5 times of its original size. Clinical and experimental studies have shown that small aneurysms may rupture, while a subpopulation of large aneurysms may remain stable. Thus, in addition to the measurement of intraluminal diameter of the aorta, knowledge of structural traits of the vessel wall may provide important information to assess the stability of the AAA. Aortic stiffening has recently emerged as a reliable tool to determine early changes in the vascular wall. Pulse propagation velocity (PPV) along with the distensibility and radial strain are highly useful ultrasound-based methods relevant for assessing aortic stiffness. The primary purpose of this protocol is to provide a comprehensive technique for the use of ultrasound imaging system to acquire images and analyze the structural and functional properties of the aorta as determined by MILD, PPV, distensibility and radial strain.

Acoustic properties of LNM crystal

We report linear acoustic and acousto-optical properties of LiNa5Mo9O30 (LNM) single crystal. This relatively new crystal, known for its complex crystallographic structure, is optically biaxial with high birefringence of 0.2545 at 450.2 nm, and crystals that consist of molybdates are widely used in different applications, from cintillators, double β-decay detectors, “dark matter” sensors to electro optics. The lowest measured propagation velocity of shear wave was 1200 m/s, and for the longitudinal mode it was 4100 m/s, which are a relatively low value for crystalline media. The maximum attenuation of the longitudinal wave at a frequency of 180 MHz was moderate and equal 20 dB/cm·GHz2. The values of the acousto-optic figure of merit for light diffraction on a longitudinal acoustic wave were also determined, the maximum value of the coefficient was 13 c.u., which exceeds the efficiency of the one used in AO devices material α-SiO2. Thus, the set of measured acoustic and elastic-optical properties shows a new promising optically biaxial material for acousto-optics, which needs for further researching.

Accuracy Estimation of Propagation Velocity in Variable Path Ultrasonic Interferometer for Liquids

In this article, we describe the effects and the degree to which they cause error in the measurement of propagation velocity. Various effects include nonlinearity in path measurement, temperature stability and number of maxima or minima consideration. Double-distilled water was used as a sample to estimate various effects. Finally, it has been concluded that the variable frequency approach may be preferred for better accuracy. It has also been observed that the digital frequency selection is more precise than mechanical distance variation.

Behavior of Low-Velocity Detonation in Stoichiometric Mixture of Ammonium Perchlorate and Polymethyl Methacrylate

Low-velocity detonation in mixtures of ammonium perchlorate and fuel additives in high relative density charges is an interesting subject for the scientific research, with potential for practical applications in pulse nozzle and projective setups. However, information about the process is scanty and mainly concerns the measurements of the wave propagation velocities. This paper describes the results of a research aimed at obtaining the data base on properties and behavior of low-velocity detonation (LVD) in pressed charges of the mixture of ammonium perchlorate and 15% polymethyl methacrylate. The firings have been fulfilled at the pulse laboratory projectile setup and the strong steel confinements equipped with the nozzle block or a projectile with the process initiated by a booster produced from RDX or the TNT/RDX 30/70 mixture. The thrust impulse, trajectory of the projectile, pressure, and LVD wave front trajectory have been recorded. According to the measurement results, the muzzle velocity, the pressure at the projectile, and the burning completeness of the mixture have been calculated. In the experiments, the relative charge density has varied from 0.85 to 0.96, the ammonium perchlorate particle size has been from 20 to 200 μm, and the charge length and the projectile mass have varied as well. The experiments were supplemented with numerical simulation. Emphasis was lain on the interaction of a low-velocity detonation wave with end rarefaction waves. The conditions under which the high completeness of chemical conversion of the mixture can be reached with the acceptable level of the maximum pressure (1–1.5 GPa) are considered.

New approach to measurement of the three-dimensional crystallization front propagation velocity in strongly coupled complex plasma

The PK-3 Plus laboratory onboard the International Space Station is used to form complex plasma with a liquidlike particle subsystem in a metastable state and to observe the propagation of crystallization fronts corresponding to the surfaces of crystal domains. We propose the ‘axis’ algorithm of solidlike particles identification, which makes it possible to isolate different domains and their surfaces as well. Determination of the three-dimensional front velocity is based on its definition implying that there exists a small area of the domain surface propagating along some line perpendicularly to it. The velocity measured in this way is an important characteristic of the plasma crystallization kinetics. It proves to be almost independent of time and the direction of front propagation and amounts to ca. 60–80 μm s−1.

Improved ultrasonic interferometer technique for propagation velocity and attenuation measurement in liquids.

Propagation velocity and attenuation are the two basic parameters used for the ultrasonic investigations of liquids. An ultrasonic interferometer is a widely used tool as a cost effective solution for propagation velocity measurement. The ultrasonic attenuation measurements are not possible using the existing interferometers commercially available in the market. Ultrasonic attenuation can be measured using the pulse echo method, which is relatively complex and expensive. Generally, in interferometers, a radio frequency voltage of more than 100 V is used to excite the piezoelectric transducer. In this article, an improved design of the ultrasonic interferometer with low (5 V) rf voltage excitation is discussed. The proposed design has several advantages over existing systems. The low voltage excitation reduces heating of the sample under study. Detection of the received signal is done directly at the transducer. The critical effects of a coaxial cable in rf detection are minimized by dc detection at the transducer node. The impedance response of the transducer is used for the detection of nodes and antinodes for attenuation and velocity measurements. The use of an instrumentation amplifier enables one to amplify the extremely small voltage changes across the transducer due to interference. The developed method has the capability to measure attenuation due to high receiver sensitivity. The technique has been validated for the propagation velocity and attenuation measurement in standard samples of water and other liquids. The results thus obtained have been compared with the literature and the conventional pulse echo technique which shows close agreement.

Experimental Study of Fracture Characterizations of Rocks under Dynamic Tension Test with Image Processing

To investigate the fracture characterizations of rocks under high strain rate tensile failure, a series of dynamic Brazilian tests was conducted using Split Hopkinson pressure bar (SHPB), and a high‐speed digital camera at a frame rate of 50,000 frames per second (FPS) with a resolution of 272 × 512 pixels was adopted to capture the real‐time images and visualize the failure processes. Using the extracted cracks and image processing technique, the relationship between loading condition (impact velocity), crack propagation process (crack velocity, crack fractal characteristic, and crack morphological features), and dynamic mechanical properties (absorbed energy and strain‐stress parameters) was explored and analyzed. The experimental results indicate that (1) impact velocity plays a critical role in both crack propagation process and dynamic mechanical properties, (2) the crack fractal dimension is positively correlated with crack propagation velocity and has a linear relationship with the proposed morphological feature of crack, (3) mean strain rate and max strain of rocks under SHPB loading both decrease with the increase of crack propagation velocity, and (4) the energy absorbed by the rocks increases with increasing impact velocity and has a strong negative correlation with a proposed novel crack descriptor. Experimental studies pertaining to the measurement of crack propagation path and velocity, in particular, some crack feature extraction approaches, present a promising way to reveal the fracture process and failure mechanisms of rock‐like materials.

Effects of water on rock fracture properties: Studies of mode I fracture toughness, crack propagation velocity, and consumed energy in calcite-cemented sandstone

Water-induced strength reduction is one of the most critical causes for rock deformation and failure. Understanding the effects of water on the strength, toughness and deformability of rocks are of a great importance in rock fracture mechanics and design of structures in rock. However, only a few studies have been conducted to understand the effects of water on fracture properties such as fracture toughness, crack propagation velocity, consumed energy, and microstructural damage. Thus, in this study, we focused on the understanding of how microscale damages induced by water saturation affect mesoscale mechanical and fracture properties compared with oven dried specimens along three notch orientations-divider, arrester, and short transverse. The mechanical properties of calcite-cemented sandstone were examined using standard uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests. In addition, fracture properties such as fracture toughness, consumed energy and crack propagation velocity were examined with cracked chevron notched Brazilian disk (CCNBD) tests. Digital Image Correlation (DIC), a non-contact optical measurement technique, was used for both strain and crack propagation velocity measurements along the bedding plane orientations. Finally, environmental scanning electron microscope (ESEM) was employed to investigate the microstructural damages produced in calcite-cemented sandstone specimens before and after CCNBD tests. As results, both mechanical and fracture properties reduced significantly when specimens were saturated. The effects of water on fracture properties (fracture toughness and consumed energy) were predominant in divider specimens when compared with arrester and short transverse specimens. Whereas crack propagation velocity was faster in short transverse and slower in arrester, and intermediate in divider specimens. Based on ESEM data, water in the calcite-cemented sandstone induced microstructural damages (microcracks and voids) and increased the strength disparity between cement/matrix and rock forming mineral grains, which in turn reduced the crack propagation resistance of the rock, leading to lower both consumed energy and fracture toughness (KIC).