Measurement Of Propagation Velocity Research Articles

AN EXPERIMENTAL STUDY ON FLAME PROPAGATION IN CORNSTARCH DUST CLOUDS

Following the quantitative determination of dust cloud parameters, this study investigates the flame propagation through cornstarch dust clouds in a vertical duct of 780 mm height and 160 × 160 mm square cross section, and gives particular attention to the effect of small scale turbulence and small turbulence intensity on flame characteristics. Dust suspensions in air were produced using an improved apparatus ensuring more uniform distribution and repeatable dust concentrations in the testing duct. The dispersion-induced turbulence was measured by means of a particle image velocimetry (PIV) system, and dust concentrations were estimated by direct weighing method. This quantitative assessment made it possible to correlate observed flame behaviors with the parameters of the dust cloud. Upward propagating dust flames, from both closed/open bottom end to open/closed top end of the duct, were visualized by direct light and shadow photography. From the observation of propagation regimes and the measurements of flame velocity, a critical value of the turbulence intensity can be specified below which laminar flame propagation would be established. This transition condition was determined to be 10 cm/s. Laminar flames propagated with oscillations from the closed bottom end to the open top end of the testing duct, while the turbulent flames accelerated continuously. Both laminar and turbulent flames propagated with steady velocity from the open bottom end to the closed top end of the duct. The measured propagation velocity of laminar flames appeared to be in the range of 0.45–0.56 m/s, and it was consistent with the measurements reported in the literature. In the present experimental study, the influence of dust concentration on flame propagation was also examined, and the flame propagation velocity was found weakly sensitive to the variations in dust concentration. Some information on the flame structure was revealed from the shadow records, showing the typical heterogeneous feature of the dust combustion process.

Ultrasonometric evaluation of bone healing: Experimental study using a model of diaphyseal transverse osteotomy of sheep tibiae

Noninvasive ionizing-radiation-free methods of evaluation, such as ultrasonometry, are desirable in any medical situation. An in vitro ultrasonometric study was undertaken to evaluate the bone healing process of sheep tibiae submitted to a diaphyseal transverse osteotomy at different times after the procedure. Fifteen sheep weighing an average of 37 kg had surgery for a transverse mid-diaphyseal osteotomy of the right tibia; they were divided postoperatively into three groups of five for periods of observation at 30, 45 and 60 days. The intact left tibiae of the 15 animals were used for control. The healing process was monitored with conventional radiographs taken at two-week intervals, and the animals were killed at the end of the period of observation of each group. Both surgical and intact tibiae were removed, their diameters were measured and they were submitted to measurement of underwater ultrasound propagation velocities (USPV) at the osteotomy sites in both the sagittal and frontal planes. The diameters of the surgical tibiae decreased with time in both planes (from 26.9 mm to 22.0 mm and to 20.9 mm in the sagittal plane, and from 29.3 mm to 23.9 mm and to 23 mm in the frontal plane), with significant differences between the periods of observation ( p ≤ 0.018 and p ≤ 0.003 between 30 and 45 days and 30 and 60 days, respectively, for the sagittal plane and p ≤ 0.006 and p ≤ 0.003 between 30 and 45 days and 30 and 60 days, respectively, for the frontal plane) and between surgical and intact tibiae at all time points ( p ≤ 0.0005 for each comparison). USPV increased with time from 2290 m/s to 2399 m/s and to 2382 m/s in the sagittal plane, and from 2376 m/s to 2472 m/s and to 2466 m/s in the frontal plane, accounting for an approximate 5% difference between 30 and 60 days Differences between the surgical and intact tibiae were significant at all time points ( p ≤ 0.0005 for both sagittal and frontal planes) but not between periods for either plane. There was a strong negative correlation between diameter and USPV (Pearson’s correlation coefficient of –0.8998 for the sagittal plane and –0.9192 for the frontal plane). It was concluded that ultrasonometric evaluation of the bone healing process is feasible, yielding precise and reliable results, with a potential for clinical application. (E-mail: chbarbie@fmrp.usp.br)

Characterization of hydrogen concentration in Zircaloy-4 using ultrasonic techniques

The relationship between hydrogen concentration precipitated as hydride particles and ultrasonic parameters, such as velocity and attenuation, was examined in Zircaloy-4 samples for potential applications in the Non-Destructive Test Field. Different amounts of hydrogen (up to 517ppm) were introduced in the samples by gaseous charging. Ultrasonic attenuation measurements were performed with compressive waves at frequencies of 10 and 30MHz, and propagation velocity measurements were performed at 10MHz. Ultrasonic velocity showed an approximately linear increase with hydrogen concentration and it could be used as an assessment parameter when the hydrogen level is high enough. Attenuation versus hydrogen concentration has been fitted by a logarithmic equation at 10MHz. At 30MHz a fluctuating behavior of the attenuation prevented measurement of the hydrogen concentration.

A method for anhysteretic magnetization and magnetostriction measurement of thin ferromagnetic films as a function of applied isotropic stresses

A method for measuring stress-dependent anhysteretic magnetization and magnetostriction in thin-film anisotropic ferromagnetic thin films or wires is described. This method uses a conventional vibrating-sample magnetometer combined with a specially designed loading fixture providing controlled uniaxial stresses on thin films and wires. Stresses are deduced from the characteristic resonant frequency of the sample in the fixture and verified via pulse propagation velocity measurement. Both indirect stress measurements are contactless, relying on remote vibration measurement using a laser Doppler vibrometer. These measurements have been demonstrated for membrane thicknesses down to 50μm and stresses up to 1 GPa, with estimated accuracy better than 0.2%. This method was applied to measure anhysteretic permeability and the magnetization curve of Ni–Fe alloys as functions of stress and temperature. This technique was also shown to be able to measure magnetostriction coefficient as a function of external magnetic field.

Boiling propagation of water on a smooth film heater surface

Boiling propagation of water is investigated experimentally at atmospheric pressure using a small platinum film heater having a surface smoothness of nanometer order. The test water is highly superheated up to approximately 140 K before the inception of boiling on the stepwise powered heater. Boiling is triggered at the prescribed wall superheat before spontaneous inception by generating a boiling bubble at a local section of the heater. The behavior of the propagating bubble is revealed by stroboscopic photography. The propagation takes place at wall superheats larger than approximately 50 K, and the propagation velocity increases significantly with wall superheat up to 24 m/s. The propagating front is followed by prompt collapse of the bubble at the tail, resulting in rapid migration of the boiling region. The measured propagation velocity is compared with the value predicted using an analytical model reported in the literature, and reasonable agreement is shown over the entire range of the wall superheat.

212 圧力流れ場におけるMR流体の流動構造と流動制御特性(2)(OS2-3 機能性流体工学の先端融合化,OS2 機能性流体工学の先端融合化,オーガナイズドセッション)

Experimental analysis on the cluster formation of MR fluid and rheological properties under the magnetic field are carried out. Through the measurement of ultrasonic propagation velocity in MR fluid, the cluster behavior in pressure-driven flow is clarified in detail. Finally, the flow control characteristics of MR fluid in a rectangular channel are evaluated to provide the fundamental data for the design of the advanced MR valve system.

Quantitative ultrasonometry of the phalanges during pregnancy: a longitudinal study

Objective The aim of this study was to determine prospectively the change in results of bone ultrasonometry measurement during pregnancy in healthy German women.Study design Quantitative ultrasonometry (QUS) of the phalanges was performed in 60 healthy, pregnant women. Measurements of amplitude-dependent bone propagation velocity (speed of sound; AdSOS) and the bone transmission time (BTT) were performed during the three trimesters of pregnancy in 60 patients.Results During pregnancy, a significant increase in body weight and body mass index (p ≤ 0.001) were observed. In accordance with bone ultrasonometry, a significant reduction in AdSOS was found in each trimester; AdSOS was significantly lower in the second and third trimesters compared with the first (p ≤ 0.001). The BTT values also decreased significantly in the second and third trimesters compared with the first (p ≤ 0.001). No significant influence was found of possible risk factors such as family risk of osteoporosis, previous pregnancies, age at menarche and prior use of oral contraceptives on QUS measurement results.Conclusions During normal pregnancy, we found a significant reduction of quantitative ultrasonometry variables AdSOS and BTT in healthy pregnant women. This decrease had a large influence on the t score and Z score of QUS in our study and demonstrates therefore a possible clinical relevance. The decrease was independent of osteoporosis-related risk factors and the increase in body weight. More large-scale, prospective studies are needed to increase our knowledge about the mechanism of bone turnover during pregnancy and lactation.

2301 磁場下におけるMR流体の流動構造と流動制御特性(S42-1 複雑流体の流動現象(1),S42 複雑流体の流動現象)

Experimental analysis on the cluster formation of MR fluid and rheological properties under the magnetic field are carried out. Through the measurement of ultrasonic propagation velocity in MR fluid, the cluster behavior in pressure-driven flow is clarified in detail. Finally, the flow control characteristics of MR fluid in a rectangular channel are evaluated to provide the fundamental data for the design of the advanced MR valve system.

Measurement of Velocities Up to 1.1 km/s and Test of a Very Fast Quench Inducing System

Applications such as superconducting pulsed power transformers and fault current limiters require high propagation velocities and numerous quench starting points appearing in a short time interval (typically less than a millisecond). A few years ago, Alstom successfully tested a 500-J superconducting pulsed power transformer . In order to better model its quick transition to the normal state, an appropriate computer code was created. This paper presents this quench program and the experiment developed to validate it. The experimental set-up enabled to measure propagation velocities up to 1.1 km/s, which to our knowledge are the highest ever published. Furthermore, we took the opportunity to test a new magnetic quench inducing system. The latter revealed the possibility of inducing a quench in a few tenths of microseconds with an energy consumption at least ten times lower than a classical quench heater.

Improved Quench Localization and Quench Propagation Velocity Measurements in the LHC Superconducting Dipole Magnets

The series tests performed on the LHC superconducting magnets at cryogenic condition give a unique opportunity to understand the mechanisms responsible for the instabilities causing the so-called training quenches. The first series production tests demonstrated that the weak points in the LHC dipoles are the coil extremities in which the majority of the quenches are located. This evidence triggered the idea of improving the resolution of the measuring system to better characterize the starting region of a quench and the beginning of its propagation. The new quench antennas equipped with sets of small, 4 cm long, and sensitive pick-up coils were designed. The system is described in detail and the first measurement results are presented. It turned out that this tool is also a reliable technique for measuring the quench propagation velocity especially in the particular regions of the superconducting coils like the crossing between the straight section of the magnet and its extremity.

405 ハイタンの火炎伝播速度の測定及び反応速度の推定(エンジンシステム(1))

405 ハイタンの火炎伝播速度の測定及び反応速度の推定(エンジンシステム(1))

Assessment of propagation velocity by contrast echocardiography for standardization of color Doppler propagation velocity measurements

Color Doppler propagation velocity (Vp) (color-Vp) has not yet been standardized, although it should be able to specifically reflect the intraventricular movements of left ventricular (LV) inflow. Because contrast echocardiography can depict a specified flow, we used this modality to standardize measurements of color-Vp of LV inflow. We performed contrast echocardiographic examinations in 100 patients (70 men, 30 women; age 53 +/- 12 years). Four types of color-Vp were measured: by the flow wave front method and by aliasing method using 3 aliasing velocity levels based on the peak velocity of early diastolic flow of transmitral flow. We also determined contrast echocardiographic Vp by M-mode imaging of LV inflow (contrast-Vp). Contrast-Vp and all 4 types of color-Vp could be compared in 86 patients. Contrast-Vp was significantly lower than color-Vp ( P < .01), except for color-Vp measured at the aliasing level 50% > peak velocity of early diastolic flow >/= 40% (color-Vp 40). A close relationship was observed between contrast-Vp and color-Vp 40 ( r = 0.801, P < .0001). Contrast-Vp and color-Vp 40 showed high ability to detect abnormal transmitral flow patterns according to receiver operating characteristics curves (area under curve for contrast-Vp, 0.94; for color-Vp 40, 0.90). Our results should be useful in standardization of color-Vp measurement to specifically reflect propagation of the fluid elements derived from LV inflow, with ability to distinguish LV filling abnormalities.

A wave lab inside a coaxial cable

The study of electromagnetic wave propagation in a coaxial cable can be a powerful approach to the study of waves at an undergraduate level. This study can explore different experimental situations, going from those where the finite velocity of propagation must be considered (distributed or transmission line behaviour), to those where this velocity may be considered infinite (lumped behaviour). We believe that the student observation of the existence of these two regimes can be important for the understanding of wave phenomena in general. In this work we show that this can be achieved using low-cost equipment and a set of quite simple experiments, such as the measurement of wave propagation velocity or the study of standing waves and resonance. The results obtained in a coherent set of selected experiments are discussed.

Conceptual and Experimental Results of the Transverse Normal Zone Propagation in the B0 ATLAS-Barrel Model Coil

The normal zone propagation velocity is an important feature in the design of a superconducting magnet. In the particular case of the ATLAS-Barrel toroid coil protection, it is all the more important as the fast discharge is essentially realized through the toroid windings by exciting quench heaters. The time constant of that fast discharge, and consequently the final magnet temperature, are therefore determined by the heaters activation time constant and the quench propagation kinetics. Taking into account the particular Race-track shape of the ATLAS-Barrel coil, the transverse quench propagation dominates the duration of the fast discharge. In this paper, we present, at first, the experimental measurements of the transverse normal zone propagation velocities made at CERN in 2002 on the B0 model-coil up to a maximal 24 kA operating current. Then, we present a code developed in our laboratory, based upon CAST3M finite-element code, which allows the computation, among others, of the transverse normal zone propagation velocities. We finally compare computation and experimental results and obtain a very satisfactory agreement in a large (15-24kA) operating current range.

Propagation velocity measurement of a magnetic domain wall in a submicron magnetic wire

The propagation velocity of a magnetic domain wall in a magnetic/nonmagnetic/magnetic trilayered wire with submicron width was investigated by utilizing the giant magnetoresistance effect. The magnetic domain wall was nucleated and injected into the magnetic wire by a pulsed local magnetic field (Hloc) applied at an end of the wire. This method using Hloc made it possible to determine the velocity as a function of an external magnetic field (Hext). It was found that the velocity is constant over a distance of 2 mm and that the mobility of the domain wall is constant in the temperature range between 4.2 and 200 K.

Propagation velocity measurement of a magnetic domain wall in a submicron magnetic wire

Abstract The propagation velocity of a magnetic domain wall in a magnetic/nonmagnetic/magnetic trilayered wire with submicron width was investigated by utilizing the giant magnetoresistance effect. The magnetic domain wall was nucleated and injected into the magnetic wire by a pulsed local magnetic field (H loc ) applied at an end of the wire. This method using H loc made it possible to determine the velocity as a function of an external magnetic field (H ext ) . It was found that the velocity is constant over a distance of 2 mm and that the mobility of the domain wall is constant in the temperature range between 4.2 and 200 K.

Doppler echocardiographic evaluation of ventricular function in patients with rheumatoid arthritis.

Cardiac involvement in rheumatoid arthritis (RA) has been reported previously. However, evaluation of ventricular function in this disease by the use of recently proposed Doppler echocardiographic methods has not been reported before. Thus, the aim of this study was to evaluate ventricular function by measurement of myocardial performance index (MPI) and transmitral flow propagation velocity (TFPV). Thirty-two patients with long-standing RA and 32 control subjects (mean ages 52 +/- 11 and 50 +/- 10 years, respectively) participated in this study. Systolic function was assessed by subjective evaluation of wall motion for both ventricles and by fractional shortening for the left ventricle (LV). LV diastolic function was evaluated by standard pulsed-wave Doppler echocardiography, MPI and TFPV. Right ventricular (RV) function was evaluated by MPI. No subject had signs or symptoms of clinically overt heart failure. Systolic function was normal in all subjects. Among the echocardiographic indices of LV diastolic function the peak E velocity, E velocity/A velocity ratio, isovolumetric relaxation time, MPI and TFPV in the RA group were significantly different from those of the controls ( P < 0.05). However, we did not observe a significant difference in RV echocardiographic indices between the two groups. Our results show that there is LV diastolic dysfunction in patients with long-standing RA. The lack of a history of cardiotoxic antirheumatic drug use among our patients suggests that this abnormality is due to RA itself.

Discussion of heater length for normal zone propagation velocity measurement

In order to make a quench test, the MPZ has been chosen as heater length. But the MPZ is very long as a result of the low resistance and high heat conductivity in a superconductor, which is stabilized by pure aluminum. Such a very long heater leads to a high temperature rise in the heater zone and an unstable propagation velocity. In order to achieve a stable propagation velocity, a shorter heater and a longer duration energy injection are necessary. In this paper, the minimum heater power with a long duration time in order to grow the normal zone is described.

Quench propagation and stability of Nb/sub 3/Al superconductors made by rapid heating, quenching, and transformation process

The quench propagation and the stability of external stabilized and internally stabilized RHQT Nb/sub 3/Al superconductors were studied experimentally. The Cu to non-Cu ratio of the externally stabilized conductor and the Ag to non-Ag ratio of the internally stabilized conductor are 0.38 and 0.215, respectively. Measurements were made also with a reference conductor where cladded Cu was removed from the externally stabilized conductor and with another reference conductor where Ag cores of the internally stabilized conductor were replaced by Nb/sub 3/Al. Incorporation of either external or internal stabilizer increases the minimum propagating current. The measured propagation velocities agree with the analytical values. The external stabilization by cladding Cu increases the heater energy required for quench. Either external or internal stabilizer increases the length of normal zone when a certain level of normal voltage appears over the whole sample. It is preferable from the viewpoint of quench protection, because identical Joule heating energy is dissipated in a longer region to reduce the temperature increase at a hot spot.

Propagation velocity measurement: autocorrelation technique applied to the electromyogram.

Muscle fibre conduction velocity is an important measurement in electrophysiology, both in the research laboratory and in clinical practice. It is usually measured by placing electrodes spaced at known distances and estimating the transit time of the action potential. The problem, common to all methods, is the estimation of this time delay. Several measurement procedures, in the time and frequency domains, have been proposed. Time-domain strategies usually require two acquisition channels, whereas some frequency-domain methods can be implemented using a single one. The method described operates in the time domain, making use of the autocorrelation function of the difference signal obtained from two needle electrodes and only one acquisition channel. Experimental results were obtained from the electromyogram of two biceps muscles (two adult male subjects, nine records each) under voluntary contraction, yielding an average of 3.58 m s(-1) (SD=0.04 m s(-1)) and 3.37m s(-1) (SD=0.03 m s(-1)), respectively. Several tests showed that the proposed method works properly with electromyogram records as short as 0.3 s.