Small Displacement Amplitudes Research Articles

Passive viscoelastic work of isolated rat, Rattus norvegicus, diaphragm muscle.

1. The passive elastic and viscous properties of isolated rat diaphragm muscle were studied, under various strains and strain rates similar to those in the animal, to measure their effects on the storage and release of mechanical potential energy. 2. Increasing the muscle length or amplitude of the displacement increased energy loss per stretch/shorten cycle, and increased the relative recovery of potential energy from the stretch during subsequent shortening. 3. Increasing strain rates increased energy loss per cycle and decreased the relative recovery of energy put into the stretch. 4. These effects were due to increased viscous resistance and increased elastic tension with increased length, and increased viscous resistance with increased strain rates. 5. The effects of increasing strain rate alone (1-4 Hz) were small relative to the effects of a 10% increase in muscle length or the amplitude of the length cycle. 6. Diaphragm muscle movements involving low velocity, small amplitude displacements at long muscle lengths are most effective at conserving net passive mechanical energy, while short muscle lengths minimize gross energy loss.

Comparison of two ultrasonic units in shaping simulated curved canals

The effects of ultrasonic instrumentation on the preparation shape of curved simulated canals were investigated. Measurements of the displacement amplitudes of the files were made to examine the possible relationship between displacement amplitude and the cutting ability of the file. Twenty-five simulated canals in clear resin blocks were instrumented using a Cavi-Endo unit at a power setting of 1 with differing times of instrumentation and with water as irrigant. Another group of 25 canals received similar treatment but were instrumented with an Enac unit at a power setting of 1. The canal shape and the incidence of elbow formation were evaluated using various measurements taken from photographic prints of the canals. All canals exhibited unequal removal along the canal with more removal occurring coronally. The Enac group exhibited a higher incidence of elbows which occurred further apically than those in the Cavi-Endo group. There was no significant difference between groups in the amount of apical canal enlargement. Coronally, the Enac appeared to cut significantly better. The Enac also caused significantly greater apical deviation and change in width. In both units more elbows were formed following instrumentation, with less flexible files having smaller displacement amplitudes.

Measurement of subatomic displacements for Mossbauer spectroscopy

A SQUID-based sensor capable of measuring displacements with a resolution of 8 fm/ square root Hz in the frequency band from DC to 10 kHz was constructed. Calibration of the sensor was performed with the aid of 67Zn-Mossbauer spectroscopy. The sensor was used to determine the linearity and hysteresis of a piezoelectric PZT-4 transducer at very small displacement amplitudes. The performance of the transducer at a temperature of 4.2K was found adequate for a high-precision Mossbauer velocity drive.

Modes of natural vibration for magnetic domains

We analyze wall-vibration modes for the case of plane parallel stripe domains in a uniaxial film whose easy axis is normal to the film plane, using Landau-Lifshitz equations carried to the limit of vanishing wall thickness. We take into account long-range dipole interactions and wall-moment twist due to stray fields from magnetic charges on the film surfaces. The small-amplitude wall displacement q( k, z) depends on the position coordinate z normal to the film plane, and on a two dimensional wave vector k parallel to the film plane. Numerically computed natural frequencies v n ( k) depend on the number of nodes n(=0, 1, 2 …) in the dependence of q on z. Surface and bulk modes are distinguished by the z-dependence of computed eigenmodes q n ( k, z). The spectrum of computed natural frequencies compares favorably with available experimental data.

Identification of the stretch reflex using pseudorandom excitation: electromyographic response to displacement of the human forearm.

System identification techniques are applied to the human stretch reflex by crosscorrelating a random displacement of the forearm with a surface electromyographic signal obtained from biceps muscle. Since the random forcing function is too fast to be tracked by the subject, the resulting responses reflect components of the limb control system which are automatic. Clear responses are obtained for small displacement amplitudes, typically 0·5 mm at the wrist, with a test duration of about 1 minute. The results, which are highly reproducible, are compared with simulations based upon a linear model of the stretch reflex.

Unsteady Thin Airfoil Theory for Transonic Flows with Embedded Shocks

A simple modification of classical unsteady thin airfoil theory is presented which accounts for the presence and induced motion of the embedded partial chord shock waves which appear at supercritical transonic Mach numbers. The basic model is found to be divergent at zero frequency because of an unbounded growth of the shock excursion amplitude. This behavior is eliminated by introducing a term associated with the mean flow Mach number gradient near the shock. Numerical results are given for the loads induced by an oscillating flap. LASSICAL unsteady thin airfoil theory fails for low frequencies at the subsonic freestream Mach number at which local supersonic flow first occurs. The main cause of this sudden failure is the formation of a shock wave, which shields the forward region of the airfoil from aft generated disturbances. In the present study,l a simple modification of classical thin airfoil theory is given which accounts for the presence and induced motion of such shocks. Predicted airloads are shown to be in favorable agreement with both experimental observations and finite difference calculations. We assume that the unsteady flow is generated by in- finitesimal harmonic oscillations of an airfoil which is suf- ficiently thin and at sufficiently small mean angles of attack that the transonic small disturbance approximation is valid. The unsteady problem can then be linearized about the steady flow, taking due account of the (small amplitude) displacement of any embedded shocks. The linearized un- steady problem has been formulated for an arbitrary three dimensional planar lifting surface in an earlier paper.2 The linearized equations of motion depend through various coefficients on the steady local Mach number M0 (jc), which in general varies in some complicated way throughout the flowfield. Unless the functional form of M0 is very simple, the boundary value problem for the unsteady flow field must be solved by purely numerical techniques. This has been attempted using finite difference methods by Weatherill et al.3 and Traci et al. 4 However, neither of these studies properly accounted for the between the embedded shocks and the unsteady disturbance field. (Of course, this issue does not arise in nonlinear formulations of the unsteady problem, in which the interaction is implicit; flow with oscillating shocks has been successfully computed from the nonlinear small disturbance equation by, for example, Ballhaus and Goor jian.5) An alternative to direct numerical methods is to ap- proximate the steady Mach number distribution M0(x) in such a way that analytical or semianalytica l methods can be applied. Classical theory, where M0 is set equal to the freestream Mach number M^, is, of course, one example. The

Acoustic Emission as an Indication of Stability Decrease in Fracture Zones of Avalanches

AbstractMeasurements of the event rate of natural, small-amplitude displacement accelerations in potential fracture zones of avalanches prove to be good indications for decrease of stability.

Acoustic Emission as an Indication of Stability Decrease in Fracture Zones of Avalanches

AbstractMeasurements of the event rate of natural, small-amplitude displacement accelerations in potential fracture zones of avalanches prove to be good indications for decrease of stability.

Visualization of heaving aerofoil wakes including the effect of a jet flap

Theoretical solutions exist for the flow about aerofoils in various modes of unsteady motion. This is also true for aerofoils whose lift is augmented by a jet flap. A common feature of these theories is the assumption of small amplitude displacements from the mean path and the generation of a continuous vortex sheet wake. However, in practice when the motion is oscillatory and of finite amplitude, an alternating trail of individual vortices is often found. The present visual investigation includes the measurement of some vortex street parameters associated with heaving aerofoils. The results are compared with those of conventional thin aerofoil theory in order to assess the significance of this departure from the conventional small displacement flow model.