Absolute Velocity Measurements Research Articles

Anomalous elastic response of HoBa 2− xHo xCu 3O 7− δ ceramic superconductors

Anomalous elastic response has been observed in superconducting HoBa 2− x Ho x Cu 3O 7− δ ( x=0 and 0.15) from temperature dependent ultrasonic velocity measurements between 80 and 270 K. Longitudinal velocity of superconducting HoBa 2Cu 3O 7− δ ( T c zero ∼89 K) showed an anomaly around 230 K indicating a pronounced lattice stiffening. Superconducting HoBa 1.85Ho 0.15Cu 3O 7− δ ( T c zero ∼70 K) also showed a similar longitudinal velocity anomaly around the same temperature. No anomaly was observed for oxygen-reduced non-superconducting HoBa 2Cu 3O 7− δ . Temperature dependent shear velocity profiles and absolute velocity measurements at 80 K are also reported and the influence of oxygen content on elastic properties is discussed.

Measurement of Azimuthal Flow Velocity Using Laser-Induced Fluorescence Spectroscopy in a HYPER-I Plasma

A laser-induced fluorescence (LIF) spectroscopy has been applied to an electron cyclotron resonance plasma. The absolute azimuthal flow velocity has been determined by the Doppler-shifted LIF spectrum and compared with that measured with a directional Langmuir probe (DLP) and the E × B drift velocity, respectively. The velocity profiles obtained with the three different methods show good agreement. The validity of LIF spectroscopy as a tool of local and absolute flow velocity measurement has been confirmed.

Measurements of Ion Temperature and Flow Velocity in Divertor Simulator MAP-II from Hydrogenic Helium Line Emission

Ion temperature and flow velocity in the MAP-II divertor simulator plasmas were measured using a high-resolution spectrometer combined with image expander optics which can also correct the astigmatism in spherical mirrors. The fine structure of the hydrogenic helium line was taken into consideration in the fitting procedures. This enables the comparison of the absolute flow velocity measurements between spectroscopy and the Mach probe.

Simultaneous measurement of absolute OH concentration, temperature and flow velocity in a flame by photothermal deflection spectroscopy

We demonstrate the use of photothermal deflection spectroscopy for a simultaneous measurement of absolute minority-species concentration, temperature and flow velocity in a flame from the analysis of a single data trace. The ability to make absolute concentration measurements, as well as the ability to measure three important combustion parameters simultaneously, may make this technique quite useful in many circumstances.

A Mean Synoptic View of the Subantarctic Front South of Australia

Abstract A mean synoptic view of the subantarctic front (SAF) is obtained from current meter and hydrographic data by averaging absolute and baroclinic velocity measurements in bins defined by a cross-stream coordinate that moves with the current. The cross-stream coordinate is derived from current meter measurements of vertical shear of the horizontal velocity and is expressed in terms of specific volume anomaly at 780 dbar (δ780). By averaging absolute and baroclinic velocity measurements in stream coordinates, the spatial smoothing that results from Eulerian averaging of measurements of a meandering current is avoided. The mean SAF velocity profile is composed of one central peak and several smaller peaks. In the central peak, the 2-yr mean absolute velocity from current meters reaches 52 cm s−1 at 420 dbar; the mean baroclinic velocity from six CTD sections reaches 34 cm s−1. The SAF flow is coherent at all levels, reaches the seafloor, and is at least 220 km wide. The cross-stream structure of barocl...

2306 鉄道における車両絶対速度計の研究 : サーボ型加速度センサ信号をディジタル積分して求める方法

The Brake Demand Operating device can not measure the absolute vehicle velocity due to wheel slide or lock. Therefore I studied a measurement to use a servo type acceleration sensor, and apply digital integral to the signals obtained with the microprocessor. In the brake system, the interaction is performed on a print circuit board, such as the Brake Demand Operating device. I perform experiments by using test vehicles on test line in the Railway Technical Research Institute and on a service line in JR. This paper reports the knowledge of the measurement of absolute velocity of railway vehicles obtained from those experiments.

Structure of the North Atlantic current in stream-coordinates and the circulation in the Newfoundland basin

Accurate knowledge of the absolute North Atlantic Current (NAC) transport has been limited in the past by the difficulty of obtaining absolute velocity measurements. For this study, historical hydrography was combined with time series of round trip travel time from inverted echo sounders, bottom pressure sensor measurements, and measured velocities from deep current meters, via a “Gravest Empirical Mode” technique, to yield time series of temperature and absolute velocity sections. These sections were used to determine the mean NAC stream-coordinates structure of temperature and absolute velocity for the period from August 1993 to February 1995. This structure is narrower and stronger than the corresponding Eulerian average, with peak speeds greater than 80 cm s −1 and bottom velocities exceeding 10 cm s −1 . The calculated mean NAC transport was 131±14 (×10 6 m 3 s −1 ); temporal variations resulted in a 41×10 6 m 3 s −1 standard deviation. The stream-coordinates estimate of mean absolute transport was found to be about 10% smaller than the corresponding Eulerian mean transport of 146×10 6 m 3 s −1 as a result of partially summing the north and south transports within the Mann Eddy, a large semi-permanent anticyclonic eddy normally located just offshore of the NAC. Most transport sections across the NAC in this region include the northward transport of the inshore side of the Mann Eddy because it is difficult to discriminate between the two flows. Historical estimates place the Mann Eddy absolute transport around 50–60×10 6 m 3 s −1 ; thus, the transport crossing this transect that can be identified with the NAC is about 90×10 6 m 3 s −1 . The barotropic component of the transport (defined as the bottom velocity multiplied by the water depth) is found to contribute at least 30% of the total absolute transport, depending on the choice of baroclinic reference level. Because a time series of transport measurements was made in this study, the accuracy of the mean transport estimate is better than previous estimates, which have all been based on snapshot measurements. From a combination of these measurements with other published measurements, a scheme for the overall circulation and transport in the Newfoundland Basin is suggested.

Temporal evolution of the deep western boundary current where it enters the sub-tropical domain

Four repeat hydrographic sections across the Deep Western Boundary Current (DWBC) at 55°W, occupied between 1983–1995, are used to investigate the inter-annual variability of the deep flow. The sections include measurement of tracers (oxygen, CFCs) and absolute geostrophic velocity. All properties are interpolated onto a regular grid, both in depth space and density space. The analysis focuses on two of the water masses of the DWBC: the Denmark Strait overflow water (DSOW) and classical Labrador Sea water (CLSW), both of which are clearly revealed in the property sections. The mean volume flux of water denser than σθ=27.8kg/m3 is 13.3(±4.2)Sv, comparable to that measured south of Greenland in the DWBC, suggesting that this is an accurate measure of the deep throughput into the sub-tropical North Atlantic. The largest property variability over the 12yr period occurs in the CLSW, which in the 1990s became markedly colder, fresher, more weakly stratified, and higher in oxygen and CFCs – all indicative of new ventilation. By contrast, over this same period the deeper DSOW became less well-ventilated. Such opposite behavior of the two water masses is consistent with the large-scale atmospheric forcing in the North Atlantic. The deep absolute velocities were decomposed into a barotropic (CLSW) and baroclinic (DSOW) contribution. The DSOW flow intensified with the appearance of the new CLSW in 1991. An attempt is made to explain this, but it remains unclear to what extent the change could be due to local versus remote forcing.

The mean and variability of ocean circulation past northern New Zealand: Determining the representativeness of hydrographic climatologies

Eastward flow in the Tasman Sea, from the separated East Australia Current, reattaches to the shelf break near North Cape, New Zealand, and then continues alongshore to the southeast as the East Auckland Current. A series of three permanent warm core eddies occurs along the offshore side. The mean transport of the East Auckland Current is about 9 Sv, with an additional 10 Sv or more of circulation in the eddies. An extensive hydrographic data set, archived broad scale expendable bathythermograph (XBT) data, two repeating high‐resolution XBT transects, neutrally buoyant float trajectories, and TOPEX altimetric data are used to estimate the temperature and absolute flow fields and to characterize variability. The aim is to examine the usefulness of time series information and absolute velocity measurements in the interpretation of hydrographic snapshots and climatologies, as well as to describe a region having intrinsic oceanographic interest and complexity. Issues of representativeness of the hydrographic data, of the magnitude and scales of the underlying variability, of the existence of permanent fine‐scale features, and of the appropriateness of deep reference levels are addressed directly. The relatively well sampled hydrographic climatology is shown to contain the equivalent of as many as 10 independent realizations. Temperature errors, relative to the true mean, are typically a few tenths of a degree. Significant seasonal bias is identified in the surface layer, and interannual bias is seen in the position of an eddy near North Cape. The dynamic height field at 1000 dbar relative to 2000 dbar is similar to estimates based on float trajectories and the assumption of geostrophic dynamics. This study underlines the value of time series data in the interpretation of a hydrographic climatology, in quantifying the errors in the estimated mean field as well as determining the magnitude and nature of variability. It also highlights the fact that the mean circulation of the oceans contains significant mesoscale structure, unnoticed in coarsely smoothed climatologies.

Mesure en mode autodyne de vitesses et de distances absolues à l'aide d'un microlaser Nd:YAG-LiTaO3balayé en fréquence

In this paper, a theoretical analysis of a sensor which uses a self-mixing interference effect inside a microchip laser is reported. Experimentally, the FMCW approach has been implemented by using both a Nd:YAG microchip laser emitting at and an intracavity crystal. By using the Pockel effect a total 10 GHz shift of the optical wave has been obtained by applying a transverse electrical field inside the crystal. We demonstrated that the dynamics of the microchip laser can be used to perform highly sensitive preamplified detection for absolute distance and velocity measurements from 1 to and from 0.1 to , respectively.

Absolute concentration, temperature, and velocity measurements in a diamond depositing dc-arcjet reactor

Spatial distributions of the absolute concentration of H, CH, C 2 , and C 3 reactive intermediate species have been measured by laser-induced fluorescence (LIF) in the freestream plume of a dc-arcjet. Diamond film grows from this reactive mixture on a water-cooled molybdenum substrate in a 25 Torr reactor. The temperature of the gas jet is determined from LIF measurements of the rotational distribution of CH radicals in the plume. The directed velocity of the gas plume is derived from the Doppler shift of LIF. The fraction of the feedstock hydrogen dissociated is obtained from calorimetry. The atomic hydrogen concentration and gas temperature are used to constrain a model of the gas phase chemistry in the reactive plume. Concentration measurements of CH, C 2 , and C 3 provide a stringent test for the model of the diamond precursor chemistry.

Application of interhemispheric index for transcranial Doppler sonography velocity measurements and evaluation of recording time.

To validate the reliability of transcranial Doppler sonography velocity measurements in clinical settings, assessment of the reproducibility of repeated bilateral simultaneous measurements and the optimal recording time is needed. Our hypothesis was that interhemispheric indices would prove more valid than the absolute velocity measurements usually applied. The potential interference between ultrasound beams in bilateral samplings also needs evaluation. Thirty healthy volunteers were studied at rest within hours or with a 2-month interval between measurements. Absolute blood flow velocities and side-to-side indices between velocities obtained in the middle cerebral arteries were measured over a 30-second period by two independent examiners. The correlation coefficient (r) and the coefficients of variation of the difference between either absolute velocities (CV) or indices (CVi) were calculated. The beat-to-beat variation of the diastolic, systolic, and mean velocities was also recorded. For evaluation of ultrasound beam interference, measurements were performed with and without one probe unplugged. In the interobserver study in which measurements were repeated within hours, r = .92, CV = 8.8%, and CVi = 4.1%. In the intraobserver study in which measurements were repeated with a 2-month interval, r = .8, CV = 13.0%, and CVi = 7.3%. A recording time of 30 seconds reduced CVi to 2.6%, whereas for absolute velocities 5-second recordings produced an acceptable variation. There was no significant interference between bilaterally placed probes. The introduction of interhemispheric indices improve interobserver and intraobserver reproducibility by approximately 50%. We recommend use of the index in clinical settings in which unilateral velocity changes are expected. For measurement of an interhemispheric index, a recording time of 30 seconds is recommended, whereas 5-second measurement periods yield a sufficient estimate of absolute velocities.

A Deep-Towed ADCP-CTD Instrument Package Developed for Abyssal Overflow Measurements in the Northeastern Caribbean Sea

Abstract A deep-towed instrument package has been developed to study the velocity and tracer signature of abyssal overflows in the northeastern Caribbean. Primary package components include a conductivity-temperature-depth (CTD) instrument and an acoustic Doppler current profiler (ADCP), allowing for simultaneous measurement of density, watermass tracers, and absolute velocity. A description of package construction and operation is supplemented by examples from a set of 17 deployments during two oceanographic cruises in January 1991 and March 1992. A new method for determining the three-dimensional position of the instrument package is described, based on the ability of the ADCP to acquire reference velocities corresponding to its motion over the seafloor. Factors affecting ADCP data quality are discussed, particularly those stemming from the low-scatterer environment at abyssal depths and the impact of large vertical accelerations due to surface wave-induced ship heave.

Ultrasonic measurement of the elastic constants of LiKSO 4 between 300 and 370 K

All five independent elastic constants of LiKSO 4 have been determined from absolute velocity measurements on single crystal samples using ultrasonic pulse echo overlap technique. The constant C 13 is reported for the first time. Measurement of the temperature variation of elastic constants between 300 and 370 K indicates no anomaly near 333 K, ruling out a phase transition occurring in the sample at this temperature reported in an earlier Brillouin scattering work.

Free-Radical Kinetics at High Pressure: A Mathematical Analysis of the Flow Reactor

Highly accurate reaction rate constants may be extracted from data obtained in well-developed (laminar or turbulent) diffusive flow over a wide range of experimental conditions. In many cases, data obtained in the core of such a flow may be treated as if the flow were one dimensional, leaving only a small correction for radial diffusion. This correction factor is derived analytically and presented in terms of easily observed quantities. The correction is robust; experimental and theoretical evidence is presented showing that it is insensitive to assumed axial symmetry and remains small so long as the interaction between the core and wall of a flowtube falls within well-defined bounds. The major limitations to accuracy in our high-pressure flow kinetics system (HPFS) are discussed in conjunction with observations of bimolecular reaction rate constants made over a very wide range of experimental conditions for the reactions OH + ethane → products and OH + cyclohexane → products. In the current experiment, accuracy for hydroxyl radical reactions is limited to roughly 12% for pressures of nitrogen ranging from 2 to 600 Torr. The accuracy in the measured ratio of two hydroxyl radical reaction rate constants is roughly 6%. Accuracy is currently limited primarily by absolute velocity measurements and by radical detection sensitivity. Strategies for further improving the accuracy of the high-pressure flow (HPF) technique are discussed.

High-temperature pulsed photoacoustic studies of surface waves on solids

A noncontact laser system has been designed that employs a pulsed photoacoustic source and an interferometric detector for the measurement of absolute velocity of surface waves. This can be achieved accurately at high temperatures without the need for thermal expansion corrections. Studies have been carried out on polycrystalline aluminum and single-crystal silicon and results have been presented for both at temperatures up to 800 °C. The angular dependence of surface wave velocities for propagation in the (001) plane of silicon has also been investigated, and has confirmed the system’s 0.5% room temperature accuracy.

Determination of texture coefficients in hexagonal polycrystalline aggregates with orthorhombic symmetry using ultrasounds

A method to characterize the texture of hexagonal polycrystalline aggregates with orthorhombic macroscopic symmetry is presented. Previous methods are extended to the analysis of waves propagating on three principal planes of the material. Five coefficients of the crystallographic orientation distribution function, W200, W220, W400, W420, and W440, are determined from angular variations of the phase velocity of the five ultrasonic modes considered: Bulk longitudinal waves, shear waves with in-plane and plane-normal polarizations, Rayleigh surface waves, and the fundamental symmetric plate mode (in the long-wavelength limit). Analytical expressions for the texture coefficients are found for an arbitrary number of principal planes. Measurements are reported for a Zr–2.5% wt Nb pressure tube, an alloy used in CANDU nuclear reactors. The angular variations of the phase velocity of leaky Rayleigh waves and leaky surface skimming compressional waves are measured with a line-focus acoustic microscope. Although these waves are not exactly those treated in the theory, they are closely related to pure Rayleigh waves and bulk longitudinal waves. The determined texture coefficients are sensitive to the input physical parameters when certain combinations of planes and acoustic waves requiring absolute velocity measurements are used. However, the coefficients are less sensitive to the input parameters when combinations requiring only relative velocity measurements are used. Results derived from relative measurements agreed with neutron scattering measurements.

Doppler sonographic measurement of phasic renal artery blood flow velocity in patients with chronic glomerulonephritis.

The phasic arterial blood flow velocity at the renal hilus was measured by Doppler sonography in 25 healthy subjects and 78 patients with chronic glomerulonephritis. Doppler velocity waveform was analyzed to give peak systolic velocity (S), end-diastolic velocity (D), resistive index (RI), and pulsatility index (PI). Creatinine clearance correlated with S (r = 0.76), D (r = 0.80), RI (r = -0.74), and PI (r = -0.85). Color Doppler sonography facilitated the detection of blood flow and permitted the measurement of absolute blood flow velocity, which previously had been difficult to determine. These results suggest that renal arterial blood flow as detected by Doppler ultrasonography may be useful for noninvasive, direct, rapid, and simple evaluation of renal function, although various modifying factors also need to be considered.

Doppler ultrasound and the neonatal cerebral circulation: methodology and pitfalls.

Doppler ultrasound is a popular technique for investigating the haemodynamics of the neonatal cerebral circulation. Different types of instrumentation are available of which a duplex scanner is a suitable choice for spot measurements, whilst a simple continuous wave directional Doppler may be better for long-term monitoring purposes. Doppler signals may be obtained from many arterial and venous sites within the neonatal brain, but most measurements are made from the anterior or middle cerebral arteries. It is usual to process the Doppler signal to obtain an envelope waveform which may represent either mean velocity or maximum velocity, although the latter has some distinct advantages. The zero-crossing detector used for early studies is unsuitable for use with Doppler signals. Changes in the shape of the velocity waveform may be quantified using different methods, of which the so-called resistance index is the most popular. It is also possible to make absolute velocity measurements, although these cannot be converted to flow because it is not possible to measure the diameter of neonatal cerebral vessels. There is considerable controversy as to whether the diameter of the vessels at the sites of ultrasound insonation can be affected by factors such as blood pressure and arterial gases, but it is unlikely that any such changes could invalidate the basic findings of Doppler studies. With care and attention to detail, Doppler ultrasound provides a valuable window on the neonatal cerebral circulation.

Errors in Doppler catheter absolute velocity measurements: The effect of inhomogeneous beam power distribution

Errors in Doppler catheter absolute velocity measurements: The effect of inhomogeneous beam power distribution