Time Phase Difference Research Articles

On the Development of Real-Time Structural Health Monitoring Methods. 1st Report. Measurement of Frequency Response Functions under Steady Operational Condition.

Various methods for detecting damages in structures are already proposed. Some of them use dynamical response of structure, FRFs, mode shapes, natural frequencies and so on. In almost of these techniques dynamical response is obtained from vibration testing of structures out of operation or the existence of measured dynamical response is assumed. However, in operation real-time methods for detecting damages are desired. In this paper, we propose a method for measuring FRFs under steady operational condition and perform two fundamental experiments as the first report of our researches on the development of real-time structural health monitoring. The fundamental concept of the method is measuring noise caused by steady operation at first, and then subtracting the noise from response to testing forces, Note here that the phase of measured noise and that of included in response are different. Simply subtraction is inexact. In the proposed method, we mesure two time series data of noise and obtain the relation between time difference and phase difference. Then we predict noise included in response by using this relation and subtract predicted noise from response.

Nonperturbative modal tomography inversion. Part II. Numerical simulation

In a previous paper [Jones et al., J. Acoust. Soc. Am. 94, 2296–2302 (1993)], it has been shown that implementation of nonperturbative modal ocean acoustic tomography based on the Abel transform requires only to determine an integer Nm0 (equal to the number of convergence zones between the source and receiver) from modal travel time and modal phase difference measurements. This integer Nm0 can be estimated by using climatological data or by using a ‘‘dual point’’ measurement scheme for a range‐independent case as proposed in this paper. Numerical simulations of inversions both for a range‐independent (RI) case and a range‐dependent (RD) case are presented. Finally, the error of the Abel transform inversion is discussed.

On the possibility of superconducting phase coherence through time barriers

The possibility of the occurrence of weak coupling between the superconducting order parameters in a single superconductor before and after an ultrashot quenching of superconductivity, is analyzed. The time barrier corresponding to such a quenching of the order parameter has to be shorter than, or comparable with, the characteristic “coherence time”τ≈ħ/Δ. Such an effect is somewhat analogous to a Josephson effect in which phase difference is now considered in the time domain rather than in space. A qualitative derivation of the constitutive relation for such a weak time correlation is obtained which gives, by the duality condition, a dependence of the supercharge on the time phase difference. The role of high-T c superconductors in the detection of this coherent transient response appears to be quite relevant.

Light forces in two crossed standing waves with controlled time-phase difference.

We have experimentally studied the interaction of a collimated thermal rubidium beam with a two-dimensional intense standing wave generated in the intersection area of the ${\mathrm{TEM}}_{00}$ modes of two mutually orthogonal linear optical resonators. The relative time-phase difference of the two resonator modes was controlled. We observe transverse confinement of the atoms in the node or antinode structure of the standing wave and a deflection of the atoms after their passage through the light field. In both cases the time-phase difference can be identified as an important parameter for the kinematics of the interaction process between atoms and standing waves. Our experimental data are in qualitative agreement with the results of a Monte Carlo simulation based on a two-level atom.

Neural mechanisms of directional hearing in the pigeon

The directional sensitivity of single auditory neurons in the midbrain (Nucleus mesencephalicus lateralis pars dorsalis) of the pigeon (Columba livia) was studied, using acoustic free-field stimulation (usually pure tones) in the frontal hemifield. Of a total of 337 units, 84.6% showed statistically significant changes of their responses as a function of sound azimuth. Of these, most units respond maximally to sounds in a particular azimuthal range, each has its "best area". These neurons were classified into four classes according to the properties of their best areas: (1) contralateral neurons (53.4%); (2) ipsilateral neurons (6.2%); (3) frontal neurons (18.1%); and (4) complex neurons (3.3%). The first two showed only one border of the best area within the frontal hemifield, with an increase of response strength towards the contralateral and the ipsilateral side, respectively; with frontal neurons, the best area was bounded towards both sides within the frontal hemifield, whereas the complex neurons had two or more separated best areas or extensive frontal inhibitory areas. In the remaining units (3.6%), termed weakly directional neurons, changes of their discharge rate depending on sound azimuth were statistically significant, but too poor to determine any best areas. There was a significant under-representation of best frequencies in the mid-frequency range (1-2 kHz) with a minimum in the relative number of MLD neurons recorded from at 2 kHz. However, the directional sensitivity of the neurons quantified by analysing different parameters of the directional diagrams (dynamic range, roll-off steepness, best area width) was undiminished in the mid-frequency range. In several experiments, in addition to the neurons' directional sensitivity in free-field sound, their sensitivity to interaural ongoing time (phase) differences (OTDs) and interaural intensity differences (IIDs) were also tested, using dichotic stimulation (pure tones) by headphones. Directional sensitive neurons tuned to low frequencies (best frequency less than 2 kHz) were either sensitive exclusively to OTDs or to both OTDs and IIDs; the ranges of best OTDs were correlated significantly with the azimuthal position of the best area. "High frequency" units (best frequency greater than 2 kHz) were sensitive to IIDs but not to OTDs.(ABSTRACT TRUNCATED AT 400 WORDS)

An optically linked electric and magnetic field sensor for Poynting vector measurements in the near fields of radiating sources

A unique, single-element antenna measurement scheme that can simultaneously measure the electric, magnetic, and time-dependent Poynting vectors of electromagnetic (EM) fields is described. The electric and magnetic responses of the antenna sensor are separated by a O degrees /180 degrees hybrid junction. The resulting two RF voltages, along with relative phase and frequency information, are transmitted to a remotely located vector analyzer by a pair of well-matched fiber optic downlinks. The remote receiver measures and displays the electric dipole response, the magnetic loop response, and the time phase difference between the two. This information is sufficient to determine the time-dependent Poynting vector. Both a theoretical analysis and a discussion of experimental measurements performed, which describe the capabilities and performance of a working prototype of the antenna measurement scheme, are presented. The results demonstrate that a three-axis (isotropic) version of this system could be used to measure the near fields of EM sources, as well as to completely describe the resultant flow of energy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Early cardiovascular changes with ibopamine: evidence for a biphasic haemodynamic action.

1. The haemodynamic effects of ibopamine, an oral dopamine derivative, were studied in eight patients with left ventricular dysfunction using invasive catheterisation techniques. 2. An early rise was seen in the mean right atrial pressure (P less than 0.05), the mean capillary wedge pressure (P less than 0.01) and the mean pulmonary arterial pressure (P less than 0.001) which occurred at 15 min and persisted for 30 min. 3. A second, later, positive chronotropic effect was seen as an increase in the heart rate (P less than 0.05) at 45 min with an increased cardiac output (P less than 0.05) persisting above baseline values at 1 h, but with no change in stroke volume. 4. These results support a biphasic mode of action for ibopamine which may be explained by a time phase difference in alpha- and beta-adrenoceptor stimulatory effects.

A NEW APPROACH TO PERFORMANCE ANALYSIS OF CHOPPER CONTROLLED D.C. MOTOR DRIVE

ABSTRACT An analytical method for performance analysis of a d.c. separately excited motor fed from a chopper is presented. The motor input voltage is represented as a series of step-voltages with a time phase difference. The system equations are solved to obtain closed-form solutions for motor current and speed, for transient as well as steady state conditions. The method presented is superior to existing methods in that the solution is in closed-form, and does not make recourse to recursive numerical techniques. The solutions for steady state condition corresponding to any set of operating conditions (voltage, chopper duty factor, load torque) can be directly obtained. The computational effort and time needed is therefore extremely small as compared to other methods.

Metachronal rhythms and gill movements of the nymph of caenis horaria (Ephemeroptera) in relation to water flow

The gills of some Ephemerid nymphs are always motionless, e. g ., many Bætine forms of English streams. In many others, however, the gills move rapidly in metachronal rhythm, by virtue of which currents are created in the water. These currents are peculiar to the species and probably have an adaptational significance. In many forms already under investigation, e. g ., Cholen dipterum. Siphlurus sp. Ecdyonurus venosus, Ephemerella sp. Leptophlebia marginata and Ephemera vulgata , a common feature is noticeable. This is that in their rhythmical movements both members of each pair of gills beat together, i. e ., and their movements are co-phasedly synchronized. Since, therefore, the effect of the gills on one side of the body is exactly duplicated on the other, whatever may be the precise mechanism for the production of currents, the latter are symmetrical with the longitudinal axis of the body (Eastham, 1932). An intersting exception in the nymph of Caenis horaria . In this animal the currents pass over the body from one side to the other. The gills beat in metachronal rhythm down each side of the body, but though the rhythms are synchronous there is a time phase difference between them. In other words, members of a pair are not co-phasedly synchronized in movement. We have thus in Caenis horaria a bi-laterally symmetrical animal producing movements in the surrounding medium which are not of the nature of an axial flow. It is with this phenomenon that this paper deals.