Torsional Velocities Research Articles

Concussed patients with visually induced dizziness exhibit increased ocular torsion and vertical vergence during optokinetic gaze-stabilization

Visually Induced Dizziness (VID) is a common post-concussion sequalae that remains poorly understood and difficult to quantify. The present study aims to identify biomarkers for VID in the form of gaze-stabilizing eye movements. Nine patients with post-commotio VID and nine age-matched healthy controls were recruited by physiotherapists at a local neurorehabilitation centre. Torsional and vergence eye movements were recorded while participants viewed a series of optokinetic rotations where the central- and peripheral regions moved coherently, incoherently, or semi-randomly. Results showed that vergence and torsional velocities were increased in VID patients, reflecting increased oculomotor gain to visual motion, and that responses correlated with symptom severity. Coherent stimulation produced fastest torsional slow-phases across all participants; when faced with confliction directional information, eye movements tended to follow the direction of the central visual field, albeit at slower velocities than during coherent motion, meaning that while torsion was sensitive to visual content of the entire visual field it expressed directional preference to the central stimulation. In conclusion, post-commotio VID was associated with faster slow-phases during optokinetic gaze-stabilization, with both vergence and torsion being correlated to symptom intensity. As torsional tracking remains inaccessible using commercial eye-trackers, vertical vergence may prove particularly accessible for clinical utility.

Intensified visual clutter induces increased sympathetic signalling, poorer postural control, and faster torsional eye movements during visual rotation

Many dizzy patients express a hypersensitivity to visual motion and clutter. This study aims to investigate how exposure to rotating visual clutter affects ocular torsion, vertical skewing, body-sway, the autonomic pupillary response, and the subjective feeling of discomfort to the stimulation. Sixteen healthy subjects were exposed to 20 seconds rotational visual stimulation (72 deg/s; 50 deg visual field). Visual stimuli were comprised of black lines on a white background, presented at low and high intensity levels of visual clutter, holding 19 lines and 38 lines respectively. Ocular torsion and vertical skewing were recorded using the Chronos Eye Tracker, which also measured pupil size as a reflection of the autonomic response. Postural control was evaluated by measuring body-sway area on the Wii Balance Board. Values were compared to data retrieved 20 seconds before and after the optokinetic stimulation, as subjects viewed the stationary visual scene. The high intensity stimulus resulted in significantly higher torsional velocities. Subjects who were exposed to low intensity first exhibited higher velocities for both intensities. Both pupil size and body sway increased for the higher intensity to both the moving and stationary visual scene, and were positively correlated to torsional velocity. In conclusion, exposure to visual clutter was reflected in the eye movement response, changes in postural control, and the autonomic response. This response may hold clinical utility when assessing patients suffering from visual motion hypersensitivity, while also providing some context as to why some healthy people feel discomfort in visually cluttered surroundings.

A model for the study of the optical transmission dynamics of liquid crystals dispersions under the influence of an electric field

In this paper, mathematical models are developed to correlate the time-resolved optical transmission experiments of liquid crystals dispersion devices under the influence of an electric field. The dispersion of liquid crystal in the confining matrices is supposed to be composed of identical spherical microdroplets containing the nematic liquid crystal phase. It is proposed that the confining surface induces the formation of a gradient of the torsional molecular velocities (switching velocities) in the response to an electric field or relaxation by the removal of an electric field, along the radius of the liquid crystal microdroplets. A method is proposed to determine the probability density function of the switching velocities. Applying the Laplace transform, the time-dependent functions for the optical transmission behavior of the liquid crystal dispersions are obtained. The model was applied to the study of the dynamics of glass dispersed liquid crystals devices, showing good correlation with the experimental data.

Semicircular canal contributions to the three-dimensional vestibuloocular reflex: a model-based approach.

1. We studied the contribution of the individual semicircular canals to the generation of horizontal and torsional eye movements in cynomolgus monkeys. Eye movements were elicited by sinusoidal rotation about a vertical (gravitational) axis at 0.2 Hz with the animals tilted in various attitudes of static forward or backward pitch. The gains of the horizontal and torsional components of the vestibuloocular reflex (VOR) were measured for each tilt position. The gains as a function of tilt position were fit with sinusoidal functions, and spatial gains and phases were determined. After control responses were recorded, the semicircular canals were plugged, animals were allowed to adapt, and the test procedure was repeated. Animals were prepared with only the anterior and posterior canals intact [vertical canal (VC) animals], with only the lateral canals intact [lateral canal (LC) animal], and with only one anterior and the contralateral posterior canals intact [right anterior and left posterior canal (RALP) animals; left anterior and right posterior canal (LARP) animals]. 2. In normal animals, the gain of the horizontal (yaw axis) velocity of the compensatory eye movements decreased as they were pitched forward or backward, and a torsional velocity appeared, reversing phase at the peak of the horizontal gain. After the anterior and posterior canals were plugged (LC animal), the horizontal component was reduced when the animal was tilted backward; the gain was zero with about -60 degrees of backward tilt. The spatial phase of the torsional component had the same characteristics. This is consistent with the fact that both responses were produced by the lateral canals, which from our results are tilted between 28 and 39 degrees above the horizontal stereotaxic plane. 3. After both lateral canals were plugged (VC animals), horizontal velocity was reduced in the upright position but increased as the animals were pitched backward relative to the axis of rotation. Torsional velocities, which were zero in the upright position in the normal animal, were now 180 degrees out of phase with the horizontal velocity. The peak values of the horizontal and torsional components were significantly shifted from the normal data and were closely aligned with each other, reaching peak values at approximately -56 degrees pitched back (-53 degrees horizontal, -58 degrees torsional). The same was true for the LARP and RALP animals; the peak values were at -59 degrees pitched back (-55 degrees horizontal, -62 degrees torsional). Likewise, in the LC animal the peak yaw and roll gains occurred at about the same angle of forward tilt, 35 degrees (30 degrees horizontal, 39 degrees torsional). Thus, in each case, the canal plugging had transformed the VOR from a compensatory to a direction-fixed response with regard to the head. Therefore there was no adaptation of the response planes of the individual canals after plugging. 4. The data were compared with eye velocity predictions of a model based on the geometric organization of the canals and their relation to a head coordinate frame. The model used the normal to the canal planes to form a nonorthogonal coordinate basis for representing eye velocity. An analysis of variance was used to define the goodness of fit of model predictions to the data. Model predictions and experimental data agreed closely for both normal animals and for the animals with canal lesions. Moreover, if horizontal and roll components from the LC and VC animals were combined, the summation overlay the response of the normal monkeys and the predictions of the model. In addition, a combination of the RALP and LARP animals predicted the response of the lateral-canal-plugged (VC) animals. 5. When operated animals were tested in light, the gains, peak values, and spatial phases of horizontal and roll eye velocity returned to the preoperative values, regardless of the type of surgery performed. This indicates that vision compensated for the lack o

Torsional wave propagation in an orthotropic magneto-elastic hollow circular cylinder

The aim of this work is to present numerical data on the velocities of torsional vibrations of a perfectly conducting orthotropic hollow circular cylinder in the presence of an axail magnetic field. The extremes of the geometry are investigated. The values of the characteristic numbers governing the velocities of the first five models for various geometries of the circular cylinder are numerically computed. The phase velocities of the disturbances for the different wave numbers corresponding to the first five modes are calculated. It is found that torsional wave phase velocities increase with decreasing wall thickness of the hollow circular cylinder for all modes and increase with the higher modes of motion.

Torsional wave propagation in an orthotropic magneto-elastic hollow circular cylinder

The aim of this work is to present numerical data on the velocities of torsional vibrations of a perfectly conducting orthotropic hollow circular cylinder in the presence of an axail magnetic field. The extremes of the geometry are investigated. The values of the characteristic numbers governing the velocities of the first five models for various geometries of the circular cylinder are numerically computed. The phase velocities of the disturbances for the different wave numbers corresponding to the first five modes are calculated. It is found that torsional wave phase velocities increase with decreasing wall thickness of the hollow circular cylinder for all modes and increase with the higher modes of motion.

Acoustic velocities and energy losses in granular aggregates

Extensional and torsional velocities in granular aggregates were found to increase with confining pressure, while the associated fractional energy losses per cycle 2πQ−1 decreased. Velocities of elastically deforming aggregates varied as the 1/3 power of pressure for aggregates of clean spherical particles, as the 1/3.5–1/5 power for lubricated spherical particles, and as the 1/4–1/6 power for clean and lubricated angular particles. Lubrication raised the velocities, at a given pressure, of the spherical particle aggregates but not of the angular particle aggregates. These results can be interpreted in terms of contact theory modified to include the changing number of interparticle contacts with pressure and lubrication. Also interpretable within the framework of contact theory is the observed decrease of velocity with decreasing spherical grain size and with increasing angularity. The velocity behavior in aggregates of plastically deforming particles, including the observation that the velocity becomes almost pressure independent above a certain pressure, can also be explained in terms of a modified contact theory. Values of Q−1 for all aggregates were independent of vibration frequency (1–20 kHz) and essentially independent of vibration amplitude over the range studied. Lubrication generally increased relative energy losses, sometimes by a factor of 10. The energy dissipation at low pressures, which is thought to be related to lightly made contacts, is not adequately described by any present theory. The measured extensional velocities of clean aggregates at pressures of about 1 bar ranged from about 0.3 to 0.6 km/sec, and the associated values of Q−1 ranged from about 4 × 10−3 to 2 × 10−2. Extrapolations of these values to appropriate lunar conditions compare favorably with the velocities and the Q−1 values reported in a study of man-made impacts on the moon.

Effect of temperature on ultrasonic velocities in some Indian rocks

The variations of both longitudinal and torsional velocities in the temperature range 3° to 110° C. have been determined in a few Indian rock specimens. It is observed that the variation is linear and the velocities decrease markedly with increase of temperature. The velocities go back again to the original values as the specimens cool provided the maximum temperature at which the measurements are taken does not exceed 110° C. and the specimens are allowed to cool for a sufficiently long time. The temperature gradient of longitudinal velocities is generally higher than that of the torsional velocities. It is possible that the high frequency method employed in this investigation is such that it is insensitive to small structural changes, if any, that occur in the rock when it is heated at ordinary pressures to 110° C.

Seismic studies on Fletcher's Ice Island, T‐3

Seismic studies were made on Fletcher's Ice Island in the Arctic Ocean fertng June and July, 1952, to determine the thickness and elastic characteristics of this ice body. Two types of seismic profiles were made, one using explosives detonated at or near the surface, and one using mechanical impacts. Compressional and torsional velocities were obtained, as well as good flexural waves at the longer distances. A single shot was fired at the surface at a distance of 5 ½ miles for the generation of an air‐ice coupled wave. In addition to these standard types, a constant frequency multi‐reflected SV wave showed unusually large amplitudes at the long distances. The ice thickness was obtained independently by seismic energy reflected from the ocean bottom. The arrival times through the island were compared with arrival times to the surrounding ice pack at sea level. The thicknesses obtained by these various types of measurement are quite consistent, giving from 160 to 170 ft, corresponding to an average density of about 0.91 gms/cm3, as deduced from the elevations. This value of density was also obtained by direct measurements in the upper 50 ft of ice.

Measurement of ultrasonic velocities in some Indian rocks

The phenomenon of total internal reflection has been employed in developing a technique for measuring the ultrasonic velocities in solids using pulsed ultrasonic beams. The ease and accuracy with which the critical angles can be measured make this method superior to other methods in some respects. Besides the longitudinal velocities, torsional velocities have also been measured in a number of Indian rocks for the first time. It is essential to use fairly large sized samples in this method. An earlier observation indicating a dependence of sound transmission on granular texture of the rocks has been confirmed qualitatively in this investigation as well.