Values Of Phase Velocity Research Articles

Rigorous Analysis of Numerical Phase and Group Velocity Bounds in Yee's FDTD Grid

We present a systematic derivation of the extreme values of phase and group velocity in Yee's finite difference time domain (FDTD) lattice with unequal aspect ratios. Using a Lagrange multiplier based approach; we derive necessary conditions that propagation vector components need to satisfy to attain extreme values in phase and group velocity. Knowledge of these extreme values is useful in designing low numerical dispersion FDTD schemes and also seeding numerical inversion routines of FDTD dispersion relations.

Simulation on laser-induced surface acoustic wave on isotropic cylinders by finite element method

Based on the thermoelastic theory, a finite element model is developed to simulate the process of laser inducing ultrasonic field in isotropic cylinders, which can take the temperature dependence of thermal parameters into account. Using the finite element model, we have simulated the ultrasonic fields induced by a pulse laser line source impacting on the generatrix of aluminum cylinders with different diameters. And the intact waveforms of surface acoustic wave (SAW including cylindrical Rayleigh and Whispering gallery (WG) modes) are presented, which are in very good agreement with the calculated and experimental waveforms in other literatures. Furthermore, the dispersion properties of cylindrical Rayleigh waves are analyzed by the method of phase spectral analysis, and the results show that with the increasing frequency, the phase velocity of cylindrical Rayleigh wave rapidly increases to the maximum value, and then gradually decreases to that of plane Rayleigh wave. With the diameter of cylinder decreasing, the maximum value of phase velocity and the corresponding frequency increase.

Gradients and phase velocities of ULF geomagnetic disturbances used to determine the source of an impending strong earthquake

Results of studying the behavior of the vectors of gradients and phase velocities of ULF geomagnetic disturbances (F 5), the values of gradients and phase velocities start anomalously changing, and directions toward sources of impending strong earthquakes appear in the distribution of gradient vector directions. Directions from sources of impending earthquakes appear in the distribution of phase velocity vector directions. It is proposed to use gradients and phase velocities of ULF and ELF geomagnetic disturbances as one of the factors in a short-term prediction of strong earthquakes.

Use of surface waves and seismic refraction for the inspection of circular concrete structures

In this paper, the propagation of both longitudinal and surface waves will be investigated within the scope of seismic measurements recorded along the circumference of concave structures. The underlying objective herein is to recover, in a non-destructive manner, the mechanical material properties from seismic refraction as well as multiple-channel analysis of surface wave measurements. This experimental set-up along the circumference is currently employed in the case of circular concrete tunnels or shafts when sensors cannot be installed along the structural baseline. The influence of curvature on longitudinal wave propagation will first be quantified by means of a simple analytical model. If curvature is neglected, the thickness of a damaged concrete cover will be overestimated, whereas its longitudinal wave propagation velocity will be underestimated. For surface waves, it will be shown that the influence of curvature exerts a major impact on phase velocity, which cannot be incorporated into the classical multiple-channel analysis of the surface wave forward problem. Consequently, we have developed a numerical model dedicated to such geometries that relies upon complex values of the surface wave phase velocity. The first part of this article is dedicated to the description of the mathematical derivation of the propagation of surfaces wave in a curved medium. This numerical model is then compared with experimental data recorded on a reduced-scale concrete tunnel of metric size. The agreement between experimental and numerical results, as well as seismic refraction and the multiple-channel analysis of surface wave complementarity, form the basis of an in situ, non-destructive testing technique.

Determination of hearth position of a forthcoming strong EQ using gradients and phase velocities of ULF geomagnetic disturbances

Behavior of gradient and phase velocity vectors of ULF ( F < 1 Hz) geomagnetic disturbances was investigated for two earthquake (EQ) events in Japan in 2000 ( M > 6) and 2003 ( M = 5.8) years. The gradient and phase velocity vectors were determined using the data of three high-sensitive three-component magnetic stations situated at a distance ∼5 km from each other (magnetic gradientometer). Two gradientometers were installed southeast and southwest of Tokyo at a distance ∼150 km from each other. It was found that the gradient and phase velocity values had anomaly changes 3–4 months before the strong EQs. New directions of the gradient vectors took place in the same period – the directions just to the forthcoming EQ epicenter. The directions from the forthcoming EQ epicenter arouse for the phase velocity vectors. We propose to use the gradient and phase velocity vectors of the ULF geomagnetic disturbances as important factors of the short-term prediction of strong earthquakes.

Analyzing and Filtering Surface-Wave Energy By Muting Shot Gathers

Accurate estimation of the fundamental-mode dispersion curve is the most critical processing step of many shallow surface-wave methods. Use of multichannel analysis of surface waves (MASW), has proven very effective in separating different dispersive events that share the same seismic-frequency range. Yet, under certain circumstances, even when using such a data-redundant method, it may not be possible to separate the fundamental mode of the surface waves from higher modes. Dominant higher surface-wave modes, together with body- and guided waves, can impede the estimation of the fundamental mode. This is especially true when relatively short spread lengths are required for the survey for reasons such as higher lateral-resolution demands or presence of noise at the far offsets. A simple multichannel processing technique that mutes the interfering seismic waves in the shot records (offset-time [Formula: see text] domain) can be used to analyze and filter noisy surface-wave modes and thus significantly improve the range and resolution of multimodal dispersion curves in the phase-velocity-frequency domain. This is demonstrated on both synthetic and real shot gathers. One shortcoming of the muting method is the estimation of artificially high phase-velocity values at low frequencies. This artifact can be countered by employing dispersion-curve estimation in the same low-frequency range using the unmuted shot records. The proposed muting technique can be beneficial not only for the evaluation of the fundamental mode of the Rayleigh wave, but also for other types of dispersive seismic energy, such as higher Rayleigh-wave modes, Lamb, guided, and Love waves.

Piecewise continuous distribution function method in the theory of wave disturbances of inhomogeneous gas

The system of hydrodynamic-type equations for a stratified gas in gravity field is derived from BGK equation by method of piecewise continuous distribution function. The obtained system of the equations generalizes the Navier–Stokes one at arbitrary Knudsen numbers. The problem of a wave disturbance propagation in a rarefied gas is explored. The verification of the model is made for a limiting case of a homogeneous medium. The phase velocity and attenuation coefficient values are in an agreement with former fluid mechanics theories; the attenuation behavior reproduces experiment and kinetics-based results at more wide range of the Knudsen numbers.

A validity study of phase velocity measurements in spinal cord injury

We measured a cross-section of able-bodied (AB) men (n = 175) and men with chronic spinal cord injury (SCI) (n = 33) residing in the community, 14 to 65 years old, to identify associations between dietary factors, physical activity, health status, and mechanical properties of long bones assessed by phase velocity measurement of flexural waves in the tibia during the second to seventh decades. This study (1) evaluated the influence of different types of osteoporosis risk factors on measured phase velocity of tibia bone as measured by Bone Stiffness Measurement Device (BSMD)-Swing in AB men and in men with long-standing SCI and (2) estimated the construct validity of phase velocity measurements by assessing the discriminatory capability of the BSMD-Swing. Linear regression analysis suggests a direct relationship between health status, tibia length, age, and phase velocity (R(2) = 23%). An analysis of variance results in significant differences in phase velocity values between AB controls and individuals with SCI with and without pathologic fracture history. Phase velocity measurements in the tibia shaft provide useful information about bone status in populations at risk for low-trauma fractures and seems well suited for assessing tibia bone status in SCI.

Variations of phase velocity and gradient values of ULF geomagnetic disturbances connected with the Izu strong earthquakes

Abstract. Results of study of anomaly behavior of amplitudes, phase velocities and gradients of ULF electromagnetic disturbances (F = 0.002 – 0.5 Hz) before and during a seismic active period are presented. Investigations were carried out in Japan (Izu and Chiba peninsulas) by two groups of magnetic stations spaced apart at a distance ~ 140 km. Every group (magnetic gradientometer) consists of three 3-component high sensitive magnetic stations arranged in a triangle and spaced apart at distance 4–7 km. Kakioka magnetic station (&gt;200 km to the North from Izu) was used as a reference point. Available data (only night-time intervals 00:00–07:00 LT) were preliminary filtrated by narrow pass-band filters (16 frequency bands – periods T = 2–512 s). The amplitude, gradient and phase velocity values and probabilities of directions of gradient and phase velocity vectors were constructed for the every frequency band. Apparent resistivities of the Earth’s crust in the every frequency band were calculated using the phase velocity values. It was found that Z component amplitudes of the ULF magnetic disturbances increased at Izu peninsula 2–4 weeks before the seismic active period and 2–4 days before the strongest seismic shocks (M &gt; 6). Ratio of Z component amplitudes of Kamo (Izu) and Kakioka data (Zk/Zkk) increased during 2–4 weeks before the seismic activity start (27 June 2000) and reached a maximum just before a moment of the strongest seismic shock (EQ with M = 6.4). The gradient and the phase velocity values had an anomaly behavior during the same 2–4 weeks before the start of seismic active period. The gradient vectors of the total horizontal component of the ULF magnetic pulsations were probably directed to the regions with increased conductivity. New additional direction of the gradient vectors appeared 2–3 weeks before the seismic activity start – the direction to the seismic active area which appeared due to a magma rising.

Air caloric computer system application in monitoring vestibular function changes after cochlear implantation

Introduction: The computer-based ENG system's analytical routine refinements are available only in research laboratories. The computer-based system contains a stimulator for saccadic eye-movement and an air caloric stimulator interconnected to the registration program and analysis software. Several authors have reported the preoperative and postoperative vestibular functions in cochlear implant patients. The safe examination of the operated ear and comparison of the preoperative and postoperative average slow phase velocities of the caloric nystagmus is possible using the air caloric computer system. Methods: The authors have used a computer-based ENG system with caloric air stimulation, which is very useful for examination of the operated ear. The vestibular system of patients with total deafness was examined before and after the cochlear implantation. The results of 60 vestibular examinations of 64 patients are reported. Results: The vestibular function in the operated ear was found unchanged in 20 patients. In 14 patients the vestibular function was worse. In 16 patients the postoperative vestibular responsiveness improved. The detailed data analysis of 10 patients in whom preoperative and postoperative vestibular examination was similar was performed by the authors. The preoperative and postoperative average slow phase velocity values and the relative canal paresis was observed. The values demonstrated that the caloric responsiveness of the operated ear improved in few cases. Conclusions: The computer-based air caloric system is a useful and safe method in evaluation of the vestibular system changes after ear surgery. The reason of the improvement of vestibular responsiveness is not clear. The results need further investigation to solve the problem of vestibular responsiveness improvement after cochlear implantation. (Otolaryngol Head Neck Surg 2001;125:631-4.)

Mobile phase viscosity and velocity dependence on protein retention using nonequilibrium chromatographic techniques.

Nonequilibrium chromatography (NEC) is an alternative chromatographic procedure for the separation of macromolecules. The retardation of a protein series is studied using a phosphate buffer as a mobile phase with various concentrations of glycerol fraction (used as a viscosity modifier) at different mobile phase velocities and a C1 column with a very low packing particle diameter as a stationary phase. It is shown that the two factors (viscosity and velocity) of the mobile phase constituted important parameters in the retention mechanism of the proteins in NEC. The retardation velocity domain is divided into two regions. For low velocity regions, the protein retention decreased with a mobile phase velocity increase. This retention is enhanced above a critical value of the mobile phase velocity. The transition between the two well-known NEC methods, slalom chromatography and hydrodynamic chromatography, is clearly visualized for the first time for the protein retention of particular values of the mobile phase velocity.

COMMENTS ON VAN DEEMTER PLOT IN HIGH SPEED COUNTERCURRENT CHROMATOGRAPHY

An inaccuracy in the computation of the linear mobile phase velocity rendered the whole content of a recently published article, Q.Z. Du, P.D. Wu, Y, Ito, J. Liq. Chromatogr. & Rel. Technol., 23(19), 2929 (2000), erroneous. Since the stationary phase volume was given, the correct mobile phase velocity values were computed and the new values for the Van Deemter plots of three compounds are listed. It is concluded that the 1.5 mL/min flow rate, corresponding to the minimum of the Van Deemter plots, or the maximum efficiency, does not justify calling the technique High Speed CCC since three hours are needed to develop the chromatogram.

部分的末梢前庭障害モデルの前庭機能評価法

In this study we used the trapezoid rotation test to evaluate vestibular function in normal guinea pigs or guinea pigs with peripheral vestibular disorder. Post-rotatory nystagmus (PRN) was recorded on videotape under dark conditions with an infrared charge-coupled device camera. The analysis was performed using the pubic domain NIH Image program, and the horizontal and vertical components were calculated automatically. The mean value of maximum slow phase velocity (MSPV) in the normal guinea pigs and guinea pigs with vestibular disorder was 37.288±9.423 degree/sec and 9.786±2.758 degree/sec respectively. There was a significant correlation between the PRN number and MSPV.We consider that this system makes it possible to evaluate vestibular function in animal models easily and inexpensively.

Velocity Dispersion and Amplitude Attenuation of Rayleigh Waves Across the Philippine Sea

The fundamental-mode interstation group and phase velocities and attenuation coefficients of Rayleigh waves along four paths across the Philippine Sea are determined to have periods of between 20 and 110 seconds by the two-station method. The values of group and phase velocities are quite consistent with the results of previous studies using the single-station method. Group and phase velocities vary significantly with different wave-paths at periods of less than 50 seconds, but for longer periods, the phase velocities are quite close. The inversion results show that the thickness of the lithosphere is about 60 km in the Philippine Sea, except in the area of the eastern volcanic islands where a slightly thinner lithosphere (about 50 km) is deduced. The attenuation coefficients observed in the Philippine Sea are higher than the values obtained in the Pacific. This result simply reflects that the Philippine Sea plate is younger than that of the Pacific. Lateral variation in attenuation coefficient is not as clear as it is in velocity because of its large variance. However, the vertical distribution of Qβ-1 is quite similar to that for the shear velocity model.

Investigation on recent quartz-like materials for SAW applications

Recent progress in growing and characterizing quartz-like materials of the trigonal system class 32 has been reported by several groups. The promising perspective for bulk acoustic wave frequency control applications indicates the potentiality of employing these materials for SAW applications as well. This paper reports results of investigations focused on SAW orientations of langasite (LGS), gallium phosphate (GaPO(4)), and langanite (LGN), both singly and doubly rotated cuts. Among the characteristics explored, major attention is paid to the temperature coefficient of delay (TCD), the electromechanical coupling coefficient (K(2)), and the power flow angle (PFA). Contour graphs are plotted based on our calculated results and show the regions in space in which low TCD and high K(2 ) can be obtained; they also exhibit the associated PFA and phase velocity characteristics. The influence of different sets of material constants is addressed. The spatial investigation performed shows that there are promising orientation regions in these materials at which zero or reduced TCD (<10 ppm/ degrees C) and PFA are obtained. Additional attractive characteristics for SAW applications have been observed: values of K(2) a few times higher than the K(2) of quartz ST-X, thus finding applications in larger bandwidth devices; variation of the TCD with respect to temperature, which is comparable to the variation found for quartz ST-X and less than that for zero TCD Li (2)B(4)O(7) cuts like 45 degrees X-Z and (0 degrees 78 degrees 90 degrees ); and phase velocity values circa 13 to 26% smaller than the phase velocity of quartz ST-X thus allowing a reduction in size for intermediate frequency device applications.

Further examples of seasonal variations of ELF radio propagation parameters

In this paper we use experimentally determined values of effective attenuation rate, excitation factor, and relative phase velocity, along with the theoretical expressions derived by C. and P. Greifinger, to establish the seasonal variation of representative ionospheric conductivity parameters. These parameters include the reflection heights h0 and h1 (or hE), inverse scale height β, and reference height H. The basis for this analysis is provided by the 1990–1992 76‐Hz field strength measurements taken at four land‐based ELF monitoring sites established by the U.S. Navy. The source for these measurements was the U.S. Navy's dual‐antenna transmitting system (WTF/MTF). The main conclusion of this paper is that the summertime and January nighttime attenuation rates are substantially lower than during other times of the year. This nighttime attenuation rate decrease appears to be mainly due to an increase in the inverse scale height β, rather than to an increase in the reflection heights h0 and hE.

Instrumentation avancée en écoulement diphasique : rêve ou réalité ?

The design and optimisation of industrial equipment could be made easier if validated computer multiphase flow software would exist. Two-phase flow model development is indeed stalled due to the lack of appropriate measuring techniques. Among the most necessary ones there are the local instantaneous diagnostic tools, obviously because computer software is based on average equations which require appropriate closure. The validation of these closure relations requires at least the experimental knowledge of the values of the local phase velocity, the interfacial area and phase fractions as well as some estimate of the velocity fluctuations. This paper reports recent progress in this field which have been presented at the last OECD-sponsored meeting on two-phase flow instrumentation held in March 1997 at Santa Barbara, CA (USA).

Horizontal parameters of the internal gravity waves registered over Yakutia

Results of the investigation of the horizontal parameters of internal gravity waves with period >3 hours propagating at the mesopause region are presented. Wave disturbance registrations were carried out at station Maimaga (63°N, 129.5°E) by their influence on the intensity of the nightglow emission OH(7,3). Data obtained at bright moonless nights in winter 1982–1988 were used. Analysis of the 66 selected cases showed that the number of westward waves was greater than eastward ones, the mean value of eastward phase velocity exceeded the westward velocity mean value. It is shown that such horizontal phase velocity behavior can be the effect of the background wind filtration. A distribution of the averaged wave periods depends on the direction of propagation. Suggestions which could explain this effect are listed.

Radiation of slow electromagnetic waves in an isotropic medium with spatial dispersion

This paper discusses the distinctive features of radiation of electromagnetic waves with anomalously large values of the wave vector and small phase velocity that exist near narrow absorption lines. The distribution of radiated energy with respect to angle and frequency is calculated for Cerenkov radiation and bremsstrahlung of the slow waves. It is shown that the angular distribution of the slow-wave bremsstrahlung exhibits a characteristic maximum in the direction perpendicular to the plane of motion of the particles.

The influence of porosity and pore size on the ultrasonic properties of bone investigated using a phantom material.

Ultrasonic propagation in bone has been investigated using the Leeds Ultrasonic Bone Phantom Material. Phantoms were produced with different porosities in the range of 45-83% and pore sizes of 1.3 and 0.6 mm. The phase velocity at 600 kHz was found to follow a second-order polynomial as a function of porosity. Phase velocity values between 1545 and 2211 m s-1 were measured and found to be largely independent of pore size for a given porosity. The slope of the phase velocity as a function of frequency (dispersion) decreases with increasing porosity. The values obtained from samples having different pore sizes were also similar. The attenuation coefficient and normalized broadband ultrasonic attenuation (nBUA) reached a maximum at about 50%. The normalized attenuation ranged from 6 to 25 dB cm-1 over the porosity range available and consistently showed higher values for the larger pore size. Similarly, the nBUA values were found to be between 14 and 53 dB MHz-1 cm-1, with the values for the larger pore size being roughly 10 dB MHz-1 cm-1 greater than those for the smaller pore size. These findings demonstrate that the Leeds phantom can be used to investigate the effect of structural changes in bone and to aid the understanding of quantitative ultrasound. The results support the assumption that the velocity in trabecular bone is not dependent on pore size but is influenced by the mechanical properties of the bone's constituents and the overall framework, whereas the attenuation and BUA are also influenced by structure.