Sharp Decrease In Amplitude Research Articles

Experimental investigation of flow-induced vibration of a rotating circular cylinder

While flow-induced vibration of bluff bodies has been extensively studied over the last half-century, only limited attention has been given to flow-induced vibration of elastically mounted rotating cylinders. Since recent low-Reynolds-number numerical work suggests that rotation can enhance or suppress the natural oscillatory response, the former could find applications in energy harvesting and the latter in vibration control. The present experimental investigation characterises the dynamic response and wake structure of a rotating circular cylinder undergoing vortex-induced vibration at a low mass ratio ($m^{\ast }=5.78$) over the reduced velocity range leading to strong oscillations. The experiments were conducted in a free-surface water channel with the cylinder vertically mounted and attached to a motor that provided constant rotation. Springs and an air-bearing system allow the cylinder to undertake low-damped transverse oscillations. Under cylinder rotation, the normalised frequency response was found to be comparable to that of a freely vibrating non-rotating cylinder. At reduced velocities consistent with the upper branch of a non-rotating transversely oscillating cylinder, the maximum oscillation amplitude increased with non-dimensional rotation rate up to $\unicode[STIX]{x1D6FC}\approx 2$. Beyond this, there was a sharp decrease in amplitude. Notably, this critical value corresponds approximately to the rotation rate at which vortex shedding ceases for a non-oscillating rotating cylinder. Remarkably, at $\unicode[STIX]{x1D6FC}=2$ there was approximately an 80 % increase in the peak amplitude response compared to that of a non-rotating cylinder. The observed amplitude response measured over the Reynolds-number range of ($1100\lesssim Re\lesssim 6300$) is significantly different from numerical predictions and other experimental results recorded at significantly lower Reynolds numbers.

Monitoring of cerebrospinal dynamics using continuous analysis of intracranial pressure and cerebral perfusion pressure in head injury.

Cerebrospinal dynamics has been investigated by statistical analysis of results of computerised monitoring of 80 head injured patients admitted to the Intensive Care Unit at Pinderfields General Hospital. One minute average values of intracranial pressure (ICP), systemic arterial pressure (ABP), cerebral perfusion pressure (CPP), amplitude of the fundamental component of the intracranial pressure pulse wave and the short-term moving correlation coefficient between that amplitude and mean ICP (RAP) were recorded. It was found that reduction of CPP down to 40 mmHg was more often caused by decrease in ABP than increase in ICP. Further falls in CPP below 40 mmHg were caused by substantial increases in ICP above 25 mmHg. The relationship between the ICP pulse wave amplitude and CPP showed a significant gradual increase in amplitude with CPP decreasing from 75 to 30 mmHg. For CPP below 30 mmHg there is a sharp decrease in amplitude followed by a change in the coefficient RAP from positive to negative values. This was interpreted as a sign of critical disturbance in cerebral circulation.

IP RESPONSE FOR A 2D HORIZONTAL CYLINDER1

AbstractThe induced polarization response for a 2D horizontal cylinder embedded in a half‐space is calculated for a uniform electric source. Response curves, in the form of apparent charge‐ability taking into account the effect of the air‐earth interface, exhibit a sharp decrease in amplitude with an increase in depth of burial of the target. The resistivity contrast between the cylinder and the host plays a dominant role in determining the IP response, i.e. the amplitude decreases considerably with the increase in resistivity contrast. The decrease is due to the defocusing effect caused by the resistive cylinder. The current lines tend to deviate away from the cylindrical target. In the case of a highly conducting cylinder, apparent defocusing takes place as current lines are confined to the surface of the conducting cylinder. An increase in chargeability contrast is reflected as a steady rise in the response. The peak response at the centre is reduced by about half the magnitude when the air–earth interface is not considered. The variation of response along the profile, though noticeable, is not as high as that obtained at the centre.

Effect of elimination of visual afferentation on electrical activity of various brain structures

Changes in spontaneous brain electrical activity were studied in experiments on rabbits totally blinded by enucleation befor acquiring vision, and on rabbits with direct vision excluded. Total exclusion of vision causes a sharp decrease in amplitude of electrical potentials in the cortex and subcortex. Depression of activity is greatest in the visual cortex and adjacent regions. Deprivation of direct vision also leads to definite changes in the EEG. The most marked changes are produced by restoration of normal vision. The possible mechanisms of the manifestation of depression in the brain electrical activity of animals with blocked visual function are discussed.

Changes in absorption of ultrasonic energy travelling through rock specimens stressed to fracture

The variation in amplitude of ultrasonic energy travelling through uniaxially compressed specimens of some crystalline rocks was studied. The amplitude of energy generally increased up to about half the fracture stress and then started decreasing, especially beyond 3 4 of the fracture stress, resulting in the total disappearence of the pulse at the instant of total failure. In some cases, the amplitude remained constant before it started decreasing at high stress level. Similar changes in the amplitude were observed even in the case of confined microfracturization tests. The sharp decrease in amplitude in the high stress region has been found to correspond closely to the accumulated energy of seismo-acoustic emissions. The anomalous behaviour exhibited by schist rock specimens has been explained in terms of a hypothesis, postulated here, about the mechanism of rock-faulting in homogeneous rock specimens. Experimental results reported in this paper suggest that the studies on the amplitude changes, in time, of seismic energy travelling in between prefixed points in a tectonically active region may prove to be useful in finding out stress build-up or stress-drop prior to an earthquake.

Evoked potentials of acoustic nuclei and character of hearing inRana temporaria

1. The chief parameters of evoked potentials recorded in response to acoustic stimulation (clicks, tones) in the acoustic nuclei of the medulla (dorsal cochlear nucleus, olivary nucleus) inRana temporaria are described. 2. The maxima of frequency sensitivity of medullary evoked potentials lie in the region 0.4–1.4 kHz. The frequency curves exhibit variability and dependence on stimulus intensity. 3. Extirpation of the columella and tympanic membrane changes the frequency curve, and the amplitude of responses to clicks and tones falls. It may be assumed that columellar transmission of sound in frogs is not the only channel of sound conduction. 4. Recovery cycles obtained during the action of paired clicks have a mean duration of 30 msec for medullary potentials. 5. An increase in duration of the front of tonal stimuli from 0 to 3 msec leads to a sharp decrease in amplitude of the medullary responses. With a further increase in duration of the fronts, the response amplitude shows a smaller change. It is also dependent on stimulus frequency.

Head waves from a linear transition layer in a liquid

An approximate harmonic solution has been derived for head waves from a linear velocity transition layer in a liquid medium of uniform density. When the frequency of wave motion is much higher than the spatial gradient of velocity in the transition layer, the velocity potential decreases with increasing frequency in proportion to the minus two-thirds power of the frequency. In the frequency range approximately equal to the velocity gradient, the velocity potential is nearly constant for some frequency ranges and has a relatively sharp decrease in amplitude at the high-frequency end. This phenomenon is similar to that observed previously in plastic models.

Atmospheric phenomena noted in simultaneous observations of 1958 δ2 (Sputnik III)

Amplitude and doppler records of the 20 Mc/s transmissions of 1958 δ2 (Sputnik III) were simultaneously made at six radio observatories in Europe. Several distinct phenomena were noted. A sharp decrease in amplitude, which lasted from 1 2 −1 1 2 min and was followed by an abrupt return of the signal, occurred at the same time at all stations. This phenomenon has been termed “dropout”, although indications of low-level signals were usually present, and is explained as a sudden decrease in transmitter power of the satellite perhaps when the satellite passed through a region of high electron flux. Another type of decrease in the signal was attributed to highly localized absorbing or scattering regions. A third phenomenon, recorded by techniques of simultaneous measurements, was observed in the concurrence of scintillating signals at some stations and Faraday fading at others. The overlap of the propagation path to each station recording the scintillations defines a vertical slab of ionospheric region responsible for the scintillations. The region is about 400–600 km in the horizontal plane but includes small scale irregularities of less than 1 km.