Horizontal Axis Of Rotation Research Articles

SPECT breast imaging combining horizontal and vertical axes of rotation

Vertical-axis-of-rotation (VAOR) geometries, in which a gamma camera orbits a pendulous breast of a prone patient, have been proposed for SPECT breast imaging. Dedicated VAOR systems would be advantageous since they allow for minimal radius of rotation around the breast, which improves resolution-sensitivity tradeoffs, and there is less attenuation and scatter between the breast and the camera. However, the torso may not be viewed at enough angles to estimate contamination from torso activity. Also, VAOR geometries may involve camera tilt to scan for tumors near the chest wall. These tilted VAOR projections may be insufficient to establish even breast activity alone. Thus, we investigated the utility of designing VAOR systems to function inside some general-purpose horizontal-axis-of-rotation (HAOR) scanners, with the HAOR scanner orbiting a 192/spl deg/ angular range posteriorly, alleviating the insufficient-data problems. We simulated the expected projection data from six various-sized lesions with different activity concentrations in the breast and axilla, additionally considering the contribution from background activity from the torso. The data were then statistically reconstructed considering 360/spl deg/ HAOR, VAOR plus small additional arcs and combined HAOR-VAOR orbits, and the results were compared with the known activity concentration distribution. Substantial improvement in the noise versus bias was observed in the breast and axilla, an important and otherwise difficult region to image.

Steady natural convection in a cylindrical cavity

We present a numerical and experimental study of steady natural convection in a small aspect ratio cylindrical cavity with circular cross section. The main objective of the present communication is to highlight some difficulties encountered when a comparison of theoretical and experimental velocity results is attempted. We keep the aspect ratio (radius/height), the Prandtl number and the Rayleigh number fixed to 0.28, 6 and 2.25 × 10 6 respectively and make observations in a vertical plane that contains the axis of symmetry of the cylinder with a particle image velocimetry (PIV) technique. The main structure present in the flow is a single non-axisymmetric cell with a horizontal rotation axis. Due to the symmetry of the geometry of the cavity and of the heating and cooling systems, the orientation of the convective structure is undefined by the boundaries. In order to make a theoretical-experimental comparison, it is necessary to make a full description of the three dimensional velocity field to find the plane that corresponds to the one observed in the experiment.

Horizontal vestibuloocular reflex (VOR) head velocity estimation in Purkinje cell degeneration (pcd/pcd) mutant mice.

The horizontal vestibuloocular reflex (VOR) of Purkinje cell degeneration (pcd/pcd) mutant mice, which lack a functional cerebellar cortex, was compared in darkness to that of wild-type animals during constant velocity yaw rotations about an earth-horizontal axis and during sinusoidal yaw rotations about an earth-vertical axis. Both wild-type and pcd/pcd mice showed a compensatory average VOR eye velocity, or bias, during constant velocity horizontal axis rotations, evidence of central neural processing of otolith afferent signals to create a signal proportional to head angular velocity. Eye velocity bias was greater in pcd/pcd mice than in wild-type mice at a low rotational velocity (32 degrees/s), but less at higher velocities (128 and 200 degrees/s). Lesion of the medial nodulus severely attenuated eye velocity bias in two wild-type mice, without attenuating VOR during sinusoidal vertical axis yaw rotations at 0.2 Hz. These results show that while head velocity estimation in mice, as in primates, depends on the cerebellum, pcd/pcd mutant mice develop velocity estimation without a functional cerebellar cortex. We conclude that neural circuits that exclude cerebellar cortex are capable of the signal processing necessary for head angular velocity estimation, but that these circuits are insufficient for normal estimation at high velocities.

X-ray fluorescence micro-tomography of an individual fluid inclusion using a third generation synchrotron light source

The aim of this study was to establish the feasibility of obtaining 3D elemental images of fluid inclusions, which consist of multiphase and irregular objects trapped in a host mineral. These experiments are based on the fluorescence micro-tomography technique, which combines X-ray fluorescence measurements and 2D tomographic reconstruction algorithms. For this purpose, multiphase aqueous fluid inclusions were synthesized in fractured quartz crystal within gold capsule at high temperature and pressure. A single fluid inclusion was isolated in a tiny quartz parallelepiped, polished on all its faces. On the basis of the parallel collection technique, the sample was successively scanned vertically over a few hundred micrometers, in steps of 3 μm and with an acquisition time of 1 s/point, and rotated by an angle of 2°. The 2D projection images, which consist in relative elemental concentration regions, provide the size and the location of the fluid inclusion as well as the elemental location and combination. By iterating the procedure along the horizontal rotation axis, full 3D elemental images can be obtained.

Canal-otolith interactions after off-vertical axis rotations I. Spatial reorientation of horizontal vestibuloocular reflex.

We examined the three-dimensional (3-D) spatial orientation of postrotatory eye velocity after horizontal off-vertical axis rotations by varying the final body orientation with respect to gravity. Three rhesus monkeys were oriented in one of two positions before the onset of rotation: pitched 24 degrees nose-up or 90 degrees nose-up (supine) relative to the earth-horizontal plane and rotated at +/-60 degrees /s around the body-longitudinal axis. After 10 turns, the animals were stopped in 1 of 12 final positions separated by 30 degrees. An empirical analysis of the postrotatory responses showed that the resultant response plane remained space-invariant, i.e., accurately represented the actual head tilt plane at rotation stop. The alignment of the response vector with the spatial vertical was less complete. A complementary analysis, based on a 3-D model that implemented the spatial transformation and dynamic interaction of otolith and lateral semicircular canal signals, confirmed the empirical description of the spatial response. In addition, it allowed an estimation of the low-pass filter time constants in central otolith and semicircular canal pathways as well as the weighting ratio between direct and inertially transformed canal signals in the output. Our results support the hypothesis that the central vestibular system represents head velocity in gravity-centered coordinates by sensory integration of otolith and semicircular canal signals.

Effects of granular additives on transition boundaries between flow states of rimming flows

An experimental study of the rimming flow established inside a partially fluid-filled cylinder rotating around a horizontal axis of rotation is described. For the first time effects of granular additives on transition boundaries between flow states adopted by the fluid for different experimental conditions are studied. For the granule-free fluid and low filling levels we confirm results of previous authors showing that the ratio of viscous stresses and gravitational force remains constant along the transition boundaries considered. For higher filling levels our new data indicate, however, that the gravitational force becomes increasingly more important. For the solid–liquid two-phase flow our data reveal that even small amounts of granular additives can have a significant effect on a suitable parameter defined to characterize the transition boundaries. Granular additives can lead to the stabilization of states and to the extension of the parameter range over which certain states can be observed. It is shown that the origin of the observed effects appears to be associated with an increased bulk density of the solid–liquid flow. For high granule concentrations a pattern of equally-spaced circumferential granular bands is observed to form on the inner cylinder wall. It is speculated that these bands form as a consequence of the mechanism which has been referred to as shear-induced migration/diffusion in the literature in the past. It appears that the granule-band pattern has not been observed previously for the flow investigated here.

Effects of Static Orientation upon Human Optokinetic Afternystagmus

?Normal? human subjects were placed in a series of 5 static orientations with respect to gravity and were asked to view an optokinetic display moving at a constant angular velocity. The axis of rotation coincided with the subject's rostro-caudal axis and produced horizontal optokinetic nystagmus and afternystagmus. Wall (1) previously reported that these optokinetic afternystagmus responses were not well characterized by parametric fits to slow component velocity. The response for nose-up, however, was larger than for nose-down. This suggested that the horizontal eye movements measured during optokinetic stimulation might include an induced linear VOR component as presented in the body of this paper. To investigate this hypothesis, another analysis of these data has been made using cumulative slow component eye position. Some subjects' responses had reversals in afternystagmus direction. These reversals were ?filled in? by a zero slow component velocity. This method of analysis gives a much more consistent result across subjects and shows that, on average, responses from the nose-down horizontal (prone) orientation are greatly reduced (p<0.05) compared to other horizontal and vertical orientations. Average responses are compared to responses predicted by a model previously used to predict successfully the responses to post-rotatory nystagmus after earth horizontal axis rotation. Ten of 11 subjects had larger responses in their supine than their prone orientation. Application of horizontal axis optokinetic afternystagmus for clinical otolith function testing, and implications for altered gravity experiments are discussed.

Yaw Sensory Rearrangement Alters Pitch Vestibulo-Ocular Reflex Responses

Ten male subjects underwent two types of adaptation paradigm designed either to enhance or to attenuate the gain of the canal-ocular reflex (COR), before undergoing otolith-ocular reflex (OOR) testing with constant velocity, earth horizontal axis and pitch rotation. The adaptation paradigm paired a 0.2 Hz sinusoidal rotation about an earth vertical axis with a 0.2 Hz optokinetic stimulus that was deliberately mismatched in peak velocity or phase and was designed to produce short-term changes in the COR. Preadaptation and postadaptation OOR tests occurred at a constant velocity of 60%sec in the dark and produced a modulation component of the slow phase velocity with a frequency of 0.16 Hz due to otolithic stimulation by the sinusoidally changing gravity vector. Of the seven subjects who showed enhancement of the COR gain, six also showed enhancement of the OOR modulation component. Of the seven subjects who showed attenuation of the COR gain, five also showed attenuation of the OOR modulation component. The probability that these two cross-axis adaptation effects would occur by chance is less than 0.02. This suggests that visual-vestibular conditioning of the yaw axis COR also induced changes in the pitch axis OOR. We thus postulate that the central nervous system pathways that process horizontal canal yaw stimuli have elements in common with those processing otolithic stimuli about the pitch axis.

Plasticity of Responses to Off-Vertical Axis Rotation

Koizuka I, Furman JM, Mendoza JC. Plasticity of responses to off-vertical axis rotation. Acta Otolaryngol (Stockh) 1997; 117: 321-324.This study assessed whether a change in the magnitude of the angular vestibulo-ocular reflex (VOR) influences the magnitude of the linear VOR, thereby suggesting a common gain element for these reflexes. The responses to linear acceleration using yaw off-vertical axis rotation (OVAR) at 30o tilt were recorded before and after an adaptation protocol designed to increase the angular VOR gain. Subjects included eight asymptomatic healthy young individuals. Eye movements, recorded with electro-oculography, were analyzed to yield gain of the horizontal angular VOR and the magnitude of the modulation and bias components of the response to OVAR. Results indicated that there was no consistent influence of angular VOR gain on the eye movement response to OVAR. Since previous studies have shown that responses to earth horizontal axis rotation are influenced consistently by angular VOR gain, our study suggests that high intensity otolithic stimulation is required to observe changes in the linear VOR following modification of the angular VOR.

Anthropometric analysis of the female Latino nose. Revised aesthetic concepts and their surgical implications.

To determine whether the present aesthetic concepts set forth for rhinoplasty in white patients can be applied to the ethnic variations seen in Latino women and, if not, to develop a reproducible means of analysis to serve as a guide for surgical correction. Cohort analytic study; criterion standard analysis of nasal aesthetics. Ninety-seven Latino women and 40 white women. Patients were separated according to geographic area of origin, either the Caribbean, Central America, or South America. Anthropometric measurements were obtained and nasal indexes were calculated. Results were compared with previously reported data for African Americans and whites. All patients underwent complete nasal photographic analysis. Caribbean subjects showed the greatest divergences from whites and resembled African-American anthropometric norms, whereas Central and South American subjects more closely resembled white norms. Two new aesthetic concepts were developed, the dorsal nasal breakpoint and the horizontal nasal axis, which have implications for aesthetic rhinoplasty. The breakpoint is a pivotal point along the nasal dorsum, structurally determined, which was found at different locations in all the groups studied. Caribbean subjects had breakpoints approximately halfway down the dorsum. Central and South Americans had breakpoints about two thirds of the way down the dorsum, and whites had breakpoints three fourths of the way down the dorsum. The horizontal rotation axis is present along a plane that connects the top of the ala with the tip. Rotation of the tip about this axis affects both the characteristics of the dorsal breakpoint and the final appearance of the nose. In general, Latino noses can be anthropometrically categorized as mesorrhine. When the geographically derived groups were examined individually, the Latino nose ranged from subplatyrrhine to paraleptorrhine. Surgical correction should be individualized, as each group requires correction of different nasal features. The dorsal breakpoint and the horizontal axis plane can act as nasal profile guides for surgical modifications that would achieve the current concept of the aesthetic nose.

Late Cenozoic tectonics and paleomagnetism of North Cauca Basin intrusions, Colombian Andes: Dual rotation modes

Further paleomagnetic results are reported from 18 sites in Late Tertiary hypabyssal igneous rocks adjacent to the Romeral fault system which forms the eastern boundary of the North Cauca Basin. The paleomagnetic directions in these massive igneous intrusions are distributed in vertical planes parallel to the adjacent Romeral suture zone. Two modes of rotation, involving non-coherent rotations about horizontal rotation axes and coherent rotations about vertical rotation axes, can explain the observed remanence patterns. The paleovectors have been rotated variably (non-coherently), both upwards and downwards, through up to nearly 90°, about horizontal axes which are perpendicular to the prevailing structural trend. These horizontal axis rotations are believed to be associated with shear gradients operating on rough projections or “asperities” on otherwise approximately lenticular bodies. These give rise to torques which cause variable horizontal axis rotation along splay faults of the Romeral and adjacent systems. In addition, the north segment of the zone of intrusions has been rotated coherently, i.e. through uniform angles, of about 30° counterclockwise, about vertical axes relative to the southern zone. The change in declination trend corresponds to a major change in trend of the Romeral suture zone. The vertical-axis rotations are believed to represent regional-scale kinking of vertical lenti-laminar fault panels of crust accreted to the paleocontinental margin along the Romeral suture. It is hypothesized that oblique transpression has pressed the zone of intrusions into the Caldas Re-entrant in the paleocontinental margin.

A review of palaeomagnetic research in the Troodos ophiolite, Cyprus

Abstract A summary of the most significant results of palaeomagnetic research within the well-known Troodos ophiolite of Cyprus is presented. The studies are broadly divided into those relating to microplate rotation and those which shed light on processes operating during crustal genesis. Early recognition that the Troodos Complex as a whole experienced a 90° anticlockwise rotation generated several attempts to constrain the precise timing of rotation. A series of palaeomagnetic data obtained within the in situ Late Cretaceous to Recent sedimentary cover of the ophiolite demonstrate that rotation began in the Campanian, soon after Turonian crustal genesis, and was complete by the Early Eocene. Rotation occurred at an approximately constant rate of c. 2° Ma −1 . The most popular rotation mechanism is one involving a combination of oblique subduction to the south of Cyprus and collision of the trench with the Arabian continental margin to the east. A Troodos microplate became detached and rotated in response to the resultant anticlockwise torque exerted upon the supra-subduction zone crust. Detailed palaeomagnetic and structural studies have also revealed details of the Troodos spreading configuration, and specifically the relationships of horizontal and vertical axis rotations to ridge-parallel faulting and transform tectonism. Extension was achieved through a combination of magmatic accretion and amagmatic stretching, the latter producing significant rotations about ridge-parallel, sub-horizontal axes. Dykes and extrusives adjacent to the fossil Southern Troodos transform zone have been rotated clockwise in response to dextral shear along the transform, producing deviations away from the predominant N-S dyke trend within the Sheeted Dyke Complex of the ophiolite. The intersection of the transform with the principal Troodos spreading axis along the Solea graben has been identified, and transform-related rotations are now suggested to have occurred mainly in the active corner of the intersection. On-going palaeomagnetic research is now focused on the relationship between the Troodos Complex and the other major tectonostratigraphic terranes of Cyprus.

Vestibular Function Test Anomalies in Patients with Chronic Fatigue Syndrome

Chronic fatigue syndrome (CFS) is distinguished by the new onset of debilitating fatigue that lasts at least 6 months, concomitant with other symptoms to be described later. Many CFS patients complain of disequilibrium, yet the exact type of the balance dysfunction and its function and its location (peripheral vs. central) have not been described. Herein we report results of vestibular function testing performed on 11 CFS patients. These results revealed no predominant pattern of abnormalities. Patients typically performed below average in dynamic posturography testing, with a significant number of falls in the tests requiring subjects to depend heavily on the vestibular system. One patient had abnormal caloric testing, while 3 had abnormally low earth vertical axis rotation (EVA) gains at the higher frequencies tested. As a group, the average gain of EVA was significantly lower than normals in the 0.1 - 1.0 Hz range (p < 0.05). In earth horizontal axis rotation, the CFS group had a higher than normal bias value for the optokinetic (OKN) and eyes open in the dark conditions (p < 0.05), but had normal scores during visual vestibular reflex testing. Five of the 11 subjects had an abnormal OKN bias build up over the course of the run, equal to or actually exceeding the 60 degrees/s target velocity by as much as 14 degrees/s. Altogether, these results are more suggestive of central nervous system deficits than of peripheral vestibular disfunction.

Effect of target velocity upon horizontal axis otolith-visual interactions.

Visual-vestibular interactions were assessed for eleven human subjects during earth-horizontal axis rotation. The apparatus consisted of a rotating chair and an independently controlled rotating optokinetic surround. Subjects underwent ten different test runs where vestibular and optokinetic stimuli were given independently and in combination. The resultant nystagmus slow component velocity was analyzed. When vestibular stimuli were given, the typical slow component velocity response consisted of an exponential decay to a non-zero baseline value (bias component). Superimposed on this was a cyclic modulation of the slow component velocity whose period was equal to the time required for one complete revolution. Our data indicate that the addition of visual input to otolith input does not affect the slow component velocity modulation component during earth horizontal axis rotation. The average bias component during otolith stimulation alone was much lower than the stimulus velocity. The bias component during optokinetic stimulation produce velocity dependent saturation. Thus, neither input alone was adequate to produce a bias component that matched the higher stimulus velocities. In contrast, the average bias component during otolith-visual interaction runs produced responses that were nearly equal to the relative target velocity. This occurred despite large individual variability of the otolith alone and optokinetic response alone. Thus, the brain compensates to match the target velocity when otolith and visual stimuli are presented together.

Plasticity of the Human Otolith-ocular Reflex

The eye movement response to earth vertical axis rotation in the dark, a semicircular canal stimulus, can be altered by prior exposure to combined visual-vestibular stimuli. Such plasticity of the vestibulo-ocular reflex has not been described for earth horizontal axis rotation, a dynamic otolith stimulus. Twenty normal human subjects underwent one of two types of adaptation paradigms designed either to attenuate or enhance the gain of the semicircular canal-ocular reflex prior to undergoing otolith-ocular reflex testing with horizontal axis rotation. The adaptation paradigm paired a 0.2 Hz sinusoidal rotation about a vertical axis with a 0.2 Hz optokinetic stripe pattern that was deliberately mismatched in peak velocity. Pre- and post-adaptation horizontal axis rotations were at 60 degrees/s in the dark and produced a modulation in the slow component velocity of nystagmus having a frequency of 0.17 Hz due to putative stimulation of the otolith organs. Results showed that the magnitude of this modulation component response was altered in a manner similar to the alteration in semicircular canal-ocular responses. These results suggest that physiologic alteration of the vestibulo-ocular reflex using deliberately mismatched visual and semicircular canal stimuli induces changes in both canal-ocular and otolith-ocular responses. We postulate, therefore, that central nervous system pathways responsible for controlling the gains of canal-ocular and otolith-ocular reflexes are shared.

Test for Otolith Organs with Barbecue Rotation

In the sitting position, vertical axis head rotation stimulates only the horizontal canal. In the supine position, horizontal axis rotation, so-called barbecue rotation, is a stimulus to both the horizontal canal and otolith organs. We compared dynamic otolith response to these two types of harmonic rotations in 15 normal subjects. The subjects' heads were rotated, passively with eyes open but covered, at the following frequencies: 0.17, 0.33, 0.50, 0.67 and 1.00 Hz. Head movement and eye movement were recorded by scleral search coil technique. Compensatory eye movements were present on each record. Vestibulo-ocular reflex (VOR) gain was calculated using peak-to-peak velocity of the eye and head. At all frequencies the VOR gain of horizontal axis rotation was larger than that of vertical axis rotation. This difference was maximal at the lowest frequency, 0.17 Hz, suggesting that dynamic otolith stimulus improves VOR at low frequencies.

Fish-protecting functions of water treatment machines in water supply systems of thermal and nuclear power plants

1. More than a decade of operation of water-cleaning machines with a conical net has demonstrated their good technical and economic characteristics as regards failure-free operation and water-cleaning performance. 2. After a simple modification, the existing water-cleaning machines with a vertical axis of cone rotation can perform a fish-protecting function. 3. For larger water consumers (such as water supply systems of thermal and nuclear power plants) machines with a horizontal cone rotation axis are recommended (so-called directflow water-cleaning machines). With some modernization of the flowthrough component, water offtake facilities can ensure bypass and survival of over 90% of young fish without building any expensive fish guard structures. 4. Instead of fish guard facilities planned to be built at operating thermal and nuclear power plants, one should consider the possibility of removing the existing water-cleaning machines with flat nets and installing machines with conical nets.

Spatial properties of second-order vestibulo-ocular relay neurons in the alert cat

Second-order vestibular nucleus neurons which were antidromically activated from the region of the oculomotor nucleus (second-order vestibuloocular relay neurons) were studied in alert cats during whole-body rotations in many horizontal and vertical planes. Sinusoidal rotation elicited sinusoidal modulation of firing rates except during rotation in a clearly defined null plane. Response gain (spike/s/deg/s) varied as a cosine function of the orientation of the cat with respect to a horizontal rotation axis, and phases were near that of head velocity, suggesting linear summation of canal inputs. A maximum activation direction (MAD) was calculated for each cell to represent the axis of rotation in three-dimensional space for which the cell responded maximally. Second-order vestibuloocular neurons divided into 3 non-overlapping populations of MADs, indicating primary canal input from either anterior, posterior or horizontal semicircular canal (AC, PC, HC cells). 80/84 neurons received primary canal input from ipsilateral vertical canals. Of these, at least 6 received input from more than one vertical canal, suggested by MAD azimuths which were sufficiently misaligned with their primary canal. In addition, 21/80 received convergent input from a horizontal canal, with about equal number of type I and type II yaw responses. 4/84 neurons were HC cells; all of them received convergent input from at least one vertical canal. Activity of many vertical second-order vestibuloocular neurons was also related to vertical and/or horizontal eye position. All AC and PC cells that had vertical eye position sensitivity had upward and downward on-directions, respectively. A number of PC cells had MADs centered around the MAD of the superior oblique muscle, and 2/3 AC cells recorded in the superior vestibular nucleus had MADs near that of the inferior oblique. Thus, signals with spatial properties appropriate to activate oblique eye muscles are present at the second-order vestibular neuron level. In contrast, none of the second-order vestibuloocular neurons had MADs near those of the superior or inferior rectus muscles. Signals appropriate to activate these eye muscles might be produced by combining signals from ipsilateral and contralateral AC neurons (for superior rectus) or PC neurons (for inferior rectus). Alternatively, less direct pathways such as those involving third or higher order vestibular or interstitial nucleus of Cajal neurons might play a crucial role in the spatial transformations between semicircular canals and vertical rectus eye muscles.

An X-ray diffractometer for studying the effect of external fields on the structure and electron distribution of single crystals

A new four-circle X-ray diffractometer (RMD) for single crystals is described that has only one (horizontal) axis of specimen rotation and a movable X-ray tube and detector. The diffractometer is characterized by the equatorial geometry. The equatorial plane rotates about the χ axis lying in this plane whereas the φ axis is fixed. This permits the use of various external (electromagnetic, magnetic etc.) fields applied to specimens along the φ axis. The angles between this direction and all the other crystallographic directions in the specimen remain constant in the course of intensity measurements. The designed RMD diffractometer allows the study of structural changes and electron distribution variations in a crystal subjected to external actions. The geometry and the design of the goniometer are considered in detail. Experiments carried out on the RMD diffractometer have demonstrated its efficiency for precision X-ray structure analysis.

Dynamic otolith stimulation improves the low frequency horizontal vestibulo-ocular reflex.

The horizontal vestibulo-ocular reflex was measured electro-oculographically in four cats during sinusoidal rotations in the dark at frequencies from 0.01 Hz to 1.0 Hz in five body orientations. Vertical axis rotations in the prone and supine positions were used to stimulate horizontal canals only. Horizontal axis rotations, with the cat on the left or right side or nose down (pitched 90 degrees from prone) were used to stimulate horizontal canal plus otolith organs. At frequencies below 0.05 Hz the horizontal vestibulo-ocular reflex produced by horizontal canal plus otolith stimulation showed a more accurately compensatory response than the horizontal vestibulo-ocular reflex produced by horizontal canal stimulation alone. Canal plus otolith horizontal vestibulo-ocular reflex gain and phase remained relatively constant across all frequencies, while the horizontal vestibulo-ocular reflex gain and phase from orientations involving canal stimulation alone changed dramatically as rotation frequency decreased. In addition, the reflex in the supine position showed gain decreases and phase advances at higher frequencies than in the prone position.