Median Vertical Plane Research Articles

Experimental study of a natural convection flow in a cubic enclosure with a partially heated inner block

In many industrial contexts, buoyancy driven flows are the only cooling strategy in case of breakdown of the forced convection cooling system. In order to study those flows in a simplified configuration, a buoyancy-driven flow is generated inside a cubic enclosure by a partially heated block (Ra = 1.4 × 109). The flow is studied experimentally in the vertical median plane, in the part of the enclosure where the flow is generated i.e. close to the heated side of the block. Velocity fields, mean profiles and RMS statistics are analyzed. The results show the presence of boundary layer flows with a central zone nearly at rest and stratified. RMS velocities are intensified with elevation.

Crosspoint Localization of Spiral and Girth Welds of Spiral Steel Pipelines

Crosspoint of spiral and girth welds of spiral steel pipelines transporting high-pressure oil and gas is easy to crack due to welding defects and corrosion, so routine excavation and careful inspection are required. In order to reduce the workload and cost of excavation, it is necessary to determine the crosspoint's angular position on the girth weld. This article proposes a low-cost and high-efficiency method for locating the spiral-girth weld crosspoint based on the inner Spherical Detector (SD). Theoretical analysis and experiments demonstrate that the magnetometer with a smaller lift-off could detect more noticeable magnetic valley of the spiral welds at the pipe bottom, so a smaller SD should be used; the spiral direction can be determined by the phase difference of the dual-channel magnetic signals, when dual magnetometers are symmetrically fixed about the median vertical plane on the rotation axis of the SD. When the girth weld, at least one spiral weld and the spiral direction are detected and determined, the crosspoint's angular position can be calculated. The maximum localization error of the crosspoint is less than 30° and the average error is less than 20°, that is, no more than one hour's angle, whose accuracy is sufficient for excavation and maintenance in the field, because it will reduce the amount of excavation by nearly half.

Acoustic basis of directional acuity in laboratory mice.

The acoustic basis of auditory spatial acuity was investigated in CBA/129 mice by relating patterns of behavioral errors to directional features of the head-related transfer function (HRTF). Behavioral performance was assessed by training the mice to lick a water spout during sound presentations from a "safe" location and to suppress the response during presentations from "warning" locations. Minimum audible angles (MAAs) were determined by delivering the safe and warning sounds from different locations in the inter-aural horizontal and median vertical planes. HRTFs were measured at the same locations by implanting a miniature microphone and recording the gain of sound energy near the ear drum relative to free field. Mice produced an average MAA of 31° when sound sources were located in the horizontal plane. Acoustic measures indicated that binaural inter-aural level differences (ILDs) and monaural spectral features of the HRTF change systematically with horizontal location and therefore may have contributed to the accuracy of behavioral performance. Subsequent manipulations of the auditory stimuli and the directional properties of the ear produced errors that suggest the mice primarily relied on ILD cues when discriminating changes in azimuth. The MAA increased beyond 80° when the importance of ILD cues was minimized by testing in the median vertical plane. Although acoustic measures demonstrated a less robust effect of vertical location on spectral features of the HRTF, this poor performance provides further evidence for the insensitivity to spectral cues that was noted during behavioral testing in the horizontal plane.

Vertical auditory acuity of the bottlenose dolphin

The accuracy in locating underwater sounds in the vertical median plane was determined for the Black Sea bottlenose dolphin Tursiops truncatus trained by operant conditioning with food reinforcement. The minimal perceived angles for 1-s tone signals were 2.5° at 5 or 20 kHz and 2.0° at 120 kHz; for 1-s trains of clicks centered at 120 kHz the acuity was still better, ∼1.5°. Dolphins may locate different sounds using different yet equally efficient mechanisms, and they are the best in analyzing the acoustic space among marine mammals studied.

Directional hearing in sharks and other fishes

Art Myrberg and his co‐workers were among the first biologists to obtain clear evidence that predatory sharks are able to locate sound sources at long distances. Previous experiments had shown that elasmobranches were relatively insensitive to sounds, and it had been suggested that fish were incapable of determining the direction of a sound source in the far field. It was subsequently shown that fish could discriminate between sounds from spatially separated sources in the horizontal and median vertical planes. They could even distinguish between identical sound sources at differing distances. It has been suggested that fish determine direction using particle motion detectors, the otolith organs of the inner ear. An array of vector detectors is capable of detecting the axis of propagation, but as they are inherently bidirectional there remains a problem in detecting the actual direction of the source. This paper considers the proposal that the ambiguities are resolved by phase comparison between the vector detectors and other detectors responding to the sound pressure incident upon the gas‐filled swimbladde.

Detection of advected, reacting redox fronts from self-potential measurements

We report on an experiment aimed at testing the use of self-potential measurements to monitor the motion and mixing of redox reactants advected through a well-controlled, laboratory-scale, artificial aquifer system. A rectangular, plastic tank was filled up with water-saturated sand and an array of unpolarizable electrodes was installed in the sand body. A nearly uniform, steady-state flow was established by tilting the tank and controlling the water level in reservoirs at both ends. Then, we simultaneously injected a known quantity of KMnO 4 and FeCl 2, respectively, into two separate compartments forming the upstream reservoir. We thus generated two abrupt fronts, one oxidizing and the other reducing, which subsequently travelled in parallel by advection through the sand body. The KMnO 4 and FeCl 2 solutions were in contact and reacted with each other in a region located along the median vertical plane parallel to the flow direction. During flow, the electrical potential differences between each electrode and a reference located in the downstream reservoir were recorded. In the unreacted FeCl 2 region the electric potential showed sudden variations successively occurring at increasing distances in the flow direction, associated with the passage of the FeCl 2 front. These signals essentially corresponded to the junction potential produced by the difference in ionic mobility of Fe 2+ and Cl −. In the unreacted KMnO 4 region sharp signals, but with much smaller amplitudes, were also observed. Near the vertical median plane on the FeCl 2 side, we observed a second front associated with the spreading of the reaction zone. The shape and evolution of the reaction zone was largely controlled by the precipitation of Fe(OH) 3.

Spatial Sensitivity in the Dorsal Zone (Area DZ) of Cat Auditory Cortex

We compared the spatial sensitivity of neural responses in three areas of cat auditory cortex: primary auditory cortex (A1), the posterior auditory field (PAF), and the dorsal zone (DZ). Stimuli were 80-ms pure tones or broadband noise bursts varying in free-field azimuth (in the horizontal plane) or elevation (in the vertical median plane), presented at levels 20-40 dB above units' thresholds. We recorded extracellular spike activity simultaneously from 16 to 32 sites in one or two areas of alpha-chloralose-anesthetized cats. We examined the dependence of spike counts and response latencies on stimulus location as well as the information transmission by neural spike patterns. Compared with units in A1, DZ units exhibited more complex frequency tuning, longer-latency responses, increased prevalence and degree of nonmonotonic rate-level functions, and weaker responses to noise than to tonal stimulation. DZ responses also showed sharper tuning for stimulus azimuth, stronger azimuthal modulation of first-spike latency, and enhanced spatial information transmission by spike patterns, compared with A1. Each of these findings was similar to differences observed between PAF and A1. Compared with PAF, DZ responses were of shorter overall latency, and more DZ units preferred stimulation from ipsilateral azimuths, but the majority of analyses suggest strong similarity between PAF and DZ responses. These results suggest that DZ and A1 are physiologically distinct cortical fields and that fields like PAF and DZ might constitute a "belt" region of auditory cortex exhibiting enhanced spatial sensitivity and temporal coding of stimulus features.

Velocity discrimination of auditory image moving in vertical plane

This research investigated the ability of humans to discriminate changes in velocity of apparent movement of a sound source (as defined by the time required for the sound to traverse a 180 deg arc) in the median vertical plane. Apparent auditory movement was created by successive switching of the loudspeakers situated over the arc. The broadband noise with band width of 0.25–4 kHz (low-pass noise – LP) and of 4–12.5 kHz (high-pass noise – HP) was employed as stimuli. Discrimination thresholds were calculated for reference velocities of 58 and 115 deg/s under four stimuli types: movement of stepped movement of noise for low-pass noise and for high-pass noise and continuous motion for low-pass noise and for high-pass noise. The result showed that discrimination of the velocity depended on the signal frequency spectrum. The differential thresholds for the signals with low pass noise were significantly higher than those for signals with high pass noise ( F(1;78) ≫ 3.96, p < 0.05). Magnitude of the absolute thresholds was the highest when the velocity was 115 deg/s for each of four types. It is interesting to note that the thresholds magnitude depended on the type of signal motion, that is on whether it was continuous or stepped.

Experimental and numerical investigation of turbulent natural convection in a large air-filled cavity

We investigate experimentally and numerically the turbulent natural convection flow that develops in a differentially heated cavity of height H=1 m, width W= H and depth D=0.32 H, submitted to a temperature difference between the active vertical walls equal to 15 K resulting in a characteristic Rayleigh number equal to 1.5 × 10 9. In the experiment temperature is measured by 25 μm micro-thermocouples and velocity by a Laser Doppler Anemometer. Both 2D and 3D LES and 3D DNS are performed. DNS uses a Chebyshev spectral method and LES a finite volume method with a local subgrid diffusivity model. Numerical simulations are performed for both adiabatic conditions and experimentally measured temperature on the horizontal walls. Time-averaged quantities and turbulent statistics in the median vertical plane are presented and compared.

A Model Describing Bending in Flagella

In Part I of this paper, we present a modelto account for the force generationproducing bending, and the formation of awaveform in sperm flagella. The model isbased on the observation that dimers, andhence microtubules, possess dipole moments.The electric field these dipoles produce isthe source for storing mechanical work indynein arms. The mechanical work is thenreleased and act on the doublets to producea distally directed force with the resultthat bending occurs. The model described isconsistent with experimental observationsreported in the literature. The flexuralrigidity of a dynein arm is alsocalculated. In Part II of this paper, theconsequences of the bending mechanism arediscussed. It is shown that the sum offorces from dynein arms acting distallyalong doublet microtubules in a flagellumis essentially zero when all dyneins areattached thus resulting in the rigor state.The waveform in a flagellum occurs if oneof the sets of bending moments is zero,that is, a row of dyneins are detached oversome distance along the flagellum. Thedirection of the bend in the waveform isdetermined by which set of dynein arms aredetached with respect to the verticalmedian plane of the flagellum. Thepropagation of a bending wave is the resultof a moving region in which alternate sidesfrom the vertical median plane haveinactive dynein arms. The processes bywhich this moving region occurs and therelationship of the above results to thepropulsion of the flagellum are notconsidered.

Sound localization cues of binaural hearing

The ability to localize sound sources in space is of considerable importance to the human safety- and survival-system. Consequently the current scientific interest in improving the safety-standard i. e. in air-traffic control has provided a new momentum for investigating spatial hearing. This review deals with the nature and the relative salience of the localization cues. Localization refers to judgements of the direction and distance of a sound source but here we will deal with direction only. We begin with a short introduction into the so-called Duplex theory which dates back to John William Strutt (later Lord Rayleigh). The idea is that sound localization is based on interaural time differences (ITD) at low frequencies and interaural level differences (ILD) at high frequencies. If the head remains stationary neither a given ITD nor an ILD can sufficiently define the position of a sound source in space. On such a theoretical basis cones of confusion which open outward from each ear can be predicted ambiguously projecting any source on the surface of such a cone onto an interaural axis. Our restricted ability at localizing sound sources in the vertical median plane is another example of possible ambiguity. At the end of the 19th century scientists already realized that occlusion of the pinnae cavities decreases localization competence. As a result of later achievements in physics and signal-theory it became more obvious that the pinnae may provide an additional cue for spatial hearing and that the outer ear together with the head and the upper torso form a sophisticated direction-dependent filter. The action of such a filter is mathematically described by the so-called Anatomical Transfer Function (ATF). The spectral patterning of the sound produced by the pinnae and the head is most effective when the source has spectral energy over a wide range and contains frequencies above 6 kHz, that is it contains wavelengths short enough to interact with the anatomical characteristics of the outer ears. Scientific findings further suggest that spectral patterns like peaks and notches may also be exploited monaurally, albeit an a priori-knowledge at the central-auditive level concerning the corresponding transfer functions and relevant real-world sounds is required. Binaural spectral cues are more likely to play a major role in localization. They are derived from another transfer function, the so-called Interaural Transfer Function (ITF), being the ratio of the ATFs at the two ears. The contributions of all these cues may sometimes not be enough to prevent the listener from opting for the wrong direction. But things can be eased by allowing head-movements: More than 60 years ago science reasoned that small head movements could provide the information necessary to resolve most of the ambiguities. Recent studies have proved that these findings have been accurate all along.

A comparison of the contrast effects in sound localization in the horizontal and vertical planes.

The effect of a background sound on the auditory localization of a single sound source was examined. Nine loudspeakers were arranged crosswise in the horizontal and the median vertical plane. They ranged from -20 degrees to +20 degrees, with the center loudspeaker at 0 degree azimuth and elevation. Using vertical and horizontal centimeter scales, listeners verbally estimated the position of a 500-ms broadband noise stimulus being presented at the same time as a 2 s background sound, emitted by one of the four outer loudspeakers. When the background sound consisted of continuous broadband noise, listeners consistently shifted the apparent target positions away from the background sound locations. This auditory contrast effect, which is consistent with earlier findings, equally occurred in both planes. But when the background sound was changed to a pulse train of noise bursts, the contrast effect decreased in the horizontal plane and increased in the vertical plane. This discrepancy might be due to general differences in the processing of interaural and spectral localization information.

Spatial sensitivity in field PAF of cat auditory cortex.

We compared the spatial tuning properties of neurons in two fields [primary auditory cortex (A1) and posterior auditory field (PAF)] of cat auditory cortex. Broadband noise bursts of 80-ms duration were presented from loudspeakers throughout 360 degrees in the horizontal plane (azimuth) or 260 degrees in the vertical median plane (elevation). Sound levels varied from 20 to 40 dB above units' thresholds. We recorded neural spike activity simultaneously from 16 sites in field PAF and/or A1 of alpha-chloralose-anesthetized cats. We assessed spatial sensitivity by examining the dependence of spike count and response latency on stimulus location. In addition, we used an artificial neural network (ANN) to assess the information about stimulus location carried by spike patterns of single units and of ensembles of 2-32 units. The results indicate increased spatial sensitivity, more uniform distributions of preferred locations, and greater tolerance to changes in stimulus intensity among PAF units relative to A1 units. Compared to A1 units, PAF units responded at significantly longer latencies, and latencies varied more strongly with stimulus location. ANN analysis revealed significantly greater information transmission by spike patterns of PAF than A1 units, primarily reflecting the information transmitted by latency variation in PAF. Finally, information rates grew more rapidly with the number of units included in neural ensembles for PAF than A1. The latter finding suggests more accurate population coding of space in PAF, made possible by a more diverse population of neural response types.

The effect of eye position and background noise on vertical sound localization

The influence of the eye position in combination with a simultaneously presented background (frame) sound on the auditory localization of a single (target) sound source was investigated in the median vertical plane (MVP). Five loudspeakers ranged from −20° to +20° with the center speaker at 0° elevation. Listeners verbally estimated the position of a 500-ms noise stimulus, which was presented while they were fixating visual targets in various elevations. The perceived sound elevation appeared to be shifted 8.6° on average towards the direction of eccentric gaze. When the target was temporarily embedded in a 2-s frame sound (emitted by one of the two outer loudspeakers) and the gaze was fixated at a straight-ahead position, the listeners consistently shifted the apparent target positions about 4° away from the frame locations. This auditory contrast effect, which is consistent with earlier findings, remained even if the gaze direction deviated from straight ahead. It is concluded that the auditory contrast effect exists independently from the eye position effect and that the two effects act separately on auditory sound localization.

Under-balcony acoustics in concert halls: Vertical energy loss at the listener and acceptable view angles deduced from its effects

Recent investigations into acoustics in under-balcony spaces have found that balcony overhangs reduce the early energy from above as well as the late energy from the main space, and hence cause an acoustic defect in the vertical. Based upon these findings, this research analyzes energy loss under the balcony, when sound energy comes from above through a vertical median plane. Fundamentally, it aims to find acoustically acceptable view angles (Θ) against the balcony opening height (H). Scale-model experiments in an anechoic room were done to obtain the amount of energy reduction (or reduction coefficient) by balcony overhangs as a function of incidence angle. Next, psychoacoustical experiments associated with listener envelopment were conducted under synthetic sound fields with constant lateral energy but with variable vertical energy to determine the appropriate Θ. These experiments, which combined with data from the scale-model experiments, cover paired comparison tests under two sets: with balcony and without balcony conditions. Results of the scale-model experiments show that sound energy decreases greatly within certain incidence angles near the balcony and at lower frequency bands. The minimum vertical angle of view is inferred to be 30–40 deg from psychoacoustical experiments. Overhang depth (D), D/H ratio, and their relationship are also discussed.

Cortical Mechanisms for Auditory Spatial Illusions

Frequency transformation by the external ears provides the spectral cues for localization of broadband sounds in the vertical plane. When human subjects listen to spectrally-impoverished narrowband sounds presented in a free field, the perceived locations vary with the centre frequency and are largely independent of the actual source locations. The present study explored the substrate of spatial illusion by examining the responses of cortical neurons to narrowband stimuli. Single-unit responses were recorded in area A2 of anaesthetized cats. Broadband noise bursts were presented at 14 locations in the vertical median plane, from 60° below the front horizon, up and over the head, to 20° below the rear horizon. Narrowband (1/6-oct) noise bursts were presented at +80° elevation. An artificial neural network was trained to recognize the spike patterns elicited by broadband noise and, thereby, to register the spike patterns with sound-source elevation. When the trained network was presented with neural responses elicited by narrowband noise, the elevation estimated by the neural network varied with the centre frequency of the narrowband stimuli. Consistent with psychophysical results in human, the locations associated with a given centre frequency could be predicted by comparing the stimulus spectrum with the directional transfer functions of the cat's external ear. The results support the hypothesis that full spike patterns (including spike counts and spike timing) of cortical neurons code information about sound location and that the auditory cortical neurons play a pivotal role in localization behaviour.

Receptive fields and binaural interactions for virtual-space stimuli in the cat inferior colliculus.

Sound localization depends on multiple acoustic cues such as interaural differences in time (ITD) and level (ILD) and spectral features introduced by the pinnae. Although many neurons in the inferior colliculus (IC) are sensitive to the direction of sound sources in free field, the acoustic cues underlying this sensitivity are unknown. To approach this question, we recorded the responses of IC cells in anesthetized cats to virtual space (VS) stimuli synthesized by filtering noise through head-related transfer functions measured in one cat. These stimuli not only possess natural combinations of ITD, ILD, and spectral cues as in free field but also allow precise control over each cue. VS receptive fields were measured in the horizontal and median vertical planes. The vast majority of cells were sensitive to the azimuth of VS stimuli in the horizontal plane for low to moderate stimulus levels. Two-thirds showed a "contra-preference" receptive field, with a vigorous response on the contralateral side of an edge azimuth. The other third of receptive fields were tuned around a best azimuth. Although edge azimuths of contra-preference cells had a broad distribution, best azimuths of tuned cells were near the midline. About half the cells tested were sensitive to the elevation of VS stimuli along the median sagittal plane by showing either a peak or a trough at a particular elevation. In general receptive fields for VS stimuli were similar to those found in free-field studies of IC neurons, suggesting that VS stimulation provided the essential cues for sound localization. Binaural interactions for VS stimuli were studied by comparing responses to binaural stimulation with responses to monaural stimulation of the contralateral ear. A majority of cells showed either purely inhibitory (BI) or mixed facilitatory/inhibitory (BF&I) interactions. Others showed purely facilitatory (BF) or no interactions (monaural). Binaural interactions were correlated with azimuth sensitivity: most contra-preference cells had either BI or BF&I interactions, whereas tuned cells were usually BF. These correlations demonstrate the importance of binaural interactions for azimuth sensitivity. Nevertheless most monaural cells were azimuth-sensitive, suggesting that monaural cues also play a role. These results suggest that the azimuth of a high-frequency sound source is coded primarily by edges in azimuth receptive fields of a population of ILD-sensitive cells.

Minimum audible movement angle in vertical, horizontal, and oblique planes: Effects of velocity and frequency content

Minimum audible movement angles (MAMAs) were measured employing a pseudo-virtual method of stimulus presentation. All stimuli were digitally recorded through KEMAR’s two ears while he was positioned in an anechoic chamber with moving loudspeakers presenting sounds in one of seven planes: frontal horizontal, lateral horizontal, median sagittal, lateral vertical, or one of three different oblique planes. These recorded binaural stimuli were subsequently played through insert earphones to subjects seated in a darkened sound-insulated room. Subjects had to say on each trial whether a single moving sound moved ‘‘left’’ or ‘‘right’’ (‘‘up’’ or ‘‘down;’’ ‘‘front’’ or ‘‘back’’). With velocity held constant during a run (from 0 to 180°/s), stimulus duration was varied adaptively to track the MAMA threshold. Stimuli were Gaussian noise bursts that were either wideband, 4-kHz low-passed, or 4-kHz high-passed. Results will be discussed in terms of human sensitivity at low and high frequencies to dynamic information provided primarily by (1) changing interaural difference cues (frontal horizontal plane); (2) changing spectral cues (median vertical plane); and (3) combinations of changing interaural and spectral cues. [Work supported by NIDCD.]

The effect of head rotations on vertical plane sound localization.

Current understanding gives predominant weight to stationary cues for auditory localization. Two experiments were conducted to investigate the possible existence of a dynamic cue. The first experiment involved localization of concealed sources in the upper median vertical plane (MVP) and showed, as expected, that elevation was not detectable with motionless listening when high-frequency energy was absent or when normal pinna function was distorted. Elevation under such conditions did become detectable with horizontal head rotations, provided low-frequency energy was present in the signal. This indicates that the basis of the dynamic cue is variation in the rate of transformation of low-frequency interaural time/phase differences. The second experiment involved localization of sources arrayed throughout upper and lower regions of the MVP and in the left lateral vertical plane (LVP); it showed that upper hemisphere sources can be distinguished somewhat from those in the lower hemisphere, even in motionless listening conditions, but more so with rotation. The greatest benefit for localization from rotation of the head appears to be gained for sources positioned in the front MVP.

On the mechanics of the arrow: Archer's Paradox

In ancient bows the grip of the bow was in the way of the arrow. The arrow needed to get round the bow while being accelerated; this phenomenon is called the ‘Archer's Paradox’. In the forties it was observed experimentally with high-speed cameras that the arrow vibrates in a horizontal plane perpendicular to the vertical median plane of the bow. These movements are started and controlled by the movements of the two points of contact with the bow, viz. the middle of the string in contact with the rear end of the arrow and the grip where the arrow slides along the bow. The latter contact imposes a moving-boundary condition. The numerically obtained results are satisfactorily in agreement with experimental data. The model can be used to estimate the drawing force of ancient bows of which only the contemporary arrows are available and also for the design of new archery equipment.