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At least 1,765 records · Page 98Linked to original sources
PubMed2001

A model of echolocation of multiple targets in 3D space from a single emission.

Bats, using frequency-modulated echolocation sounds, can capture a moving target in real 3D space. The process by which they are able to accomplish this, however, is not completely understood. This work offers and analyzes a model for description of one mechanism that may play a role in the echolocation process of real bats. This mechanism allows for the localization of targets in 3D space from the echoes produced by a single emission. It is impossible to locate multiple targets in 3D space by using only the delay time between an emission and the resulting echoes received at two points (i.e., two ears). To locate multiple targets in 3D space requires directional information for each target. The frequency of the spectral notch, which is the frequency corresponding to the minimum of the external ear's transfer function, provides a crucial cue for directional localization. The spectrum of the echoes from nearly equidistant targets includes spectral components of both the interference between the echoes and the interference resulting from the physical process of reception at the external ear. Thus, in order to extract the spectral component associated with the external ear, this component must first be distinguished from the spectral components associated with the interference of echoes from nearly equidistant targets. In the model presented, a computation that consists of the deconvolution of the spectrum is used to extract the external-ear-dependent component in the time domain. This model describes one mechanism that can be used to locate multiple targets in 3D space.

Animals↗
PubMed2002

The optimal stack spacing for thermoacoustic refrigeration.

The characteristic pore dimension in the stack is an important parameter in the design of thermoacoustic refrigerators. A quantitative experimental investigation into the effect of the pore dimensions on the performance of thermoacoustic devices is reported. Parallel-plate stacks with a plate spacing varying between 0.15 and 0.7 mm are manufactured and measured. The performance measurements show that a plate spacing in the stack of 0.25 mm (2.5 deltak) is optimum for the cooling power. A spacing of 0.4 mm (4 deltak) leads to the lowest temperature. The optimum spacing for the performance is about 0.3 mm (3 deltak). It is concluded that a plate spacing in the stack of about three times the penetration depth should be optimal (3 deltak) for thermoacoustic refrigeration.

Journal Article↗
PubMed2005

Acoustics of the human middle-ear air space.

The impedance of the middle-ear air space was measured on three human cadaver ears with complete mastoid air-cell systems. Below 500 Hz, the impedance is approximately compliance-like, and at higher frequencies (500-6000 Hz) the impedance magnitude has several (five to nine) extrema. Mechanisms for these extrema are identified and described through circuit models of the middle-ear air space. The measurements demonstrate that the middle-ear air space impedance can affect the middle-ear impedance at the tympanic membrane by as much as 10 dB at frequencies greater than 1000 Hz. Thus, variations in the middle-ear air space impedance that result from variations in anatomy of the middle-ear air space can contribute to inter-ear variations in both impedance measurements and otoacoustic emissions, when measured at the tympanic membrane.

Acoustic Stimulation↗
PubMed2006

The effect of intertalker speech rate variation on acoustic vowel space.

The present study aimed to examine the size of the acoustic vowel space in talkers who had previously been identified as having slow and fast habitual speaking rates [Tsao, Y.-C. and Weismer, G. (1997) J. Speech Lang. Hear. Res. 40, 858-866]. Within talkers, it is fairly well known that faster speaking rates result in a compression of the vowel space relative to that measured for slower rates, so the current study was completed to determine if the same differences in the size of the vowel space occur across talkers who differ significantly in their habitual speaking rates. Results indicated that there was no difference in the average size of the vowel space for slow vs fast talkers, and no relationship across talkers between vowel duration and formant frequencies. One difference between the slow and fast talkers was in intertalker variability of the vowel spaces, which was clearly greater for the slow talkers, for both speaker sexes. Results are discussed relative to theories of speech production and vowel normalization in speech perception.

Adolescent↗
PubMed1989

Perceptual differences between vowels located in a limited phonetic space.

The perception of subphonemic differences between vowels was investigated using multidimensional scaling techniques. Three experiments were conducted with natural-sounding synthetic stimuli generated by linear predictive coding (LPC) formant synthesizers. In the first experiment, vowel sets near the pairs (i-I), (epsilon-ae), or (u-U) were synthesized containing 11 vowels each. Listeners judged the dissimilarities between all pairs of vowels within a set several times. These perceptual differences were mapped into distances between the vowels in an n-dimensional space using two-way multidimensional scaling. Results for each vowel set showed that the physical stimulus space, which was specified by the two parameters F1 and F2, was always mapped into a two-dimensional perceptual space. The best metric for modeling the perceptual distances was the Euclidean distance between F1 and F2 in barks. The second experiment investigated the perception of the same vowels from the first experiment, but embedded in a consonantal context. Following the same procedures as experiment 1, listeners' perception of the (bv) dissimilarities was not different from their perception of the isolated vowel dissimilarities. The third experiment investigated dissimilarity judgments for the three vowels (ae-alpha-lambda) located symmetrically in the F1 X F2 vowel space. While the perceptual space was again two dimensional, the influence of phonetic identity on vowel difference judgments was observed. Implications for determining metrics for subphonemic vowel differences using multidimensional scaling are discussed.

Adult↗
PubMed1994

Mean-scatterer spacing estimates with spectral correlation.

An ultrasonic backscattered signal from material comprised of quasiperiodic scatterers exhibit redundancy over both its phase and magnitude spectra. This paper addresses the problem of estimating mean-scatterer spacing from the backscattered ultrasound signal using spectral redundancy characterized by the spectral autocorrelation (SAC) function. Mean-scatterer spacing estimates are compared for techniques that use the cepstrum and the SAC function. A -scan models consist of a collection of regular scatterers with Gamma distributed spacings embedded in diffuse scatterers with uniform distributed spacings. The model accounts for attenuation by convolving the frequency dependent scattering centers with a time-varying system response. Simulation results indicate that SAC-based estimates converge more reliably over smaller amounts of data than cepstrum-based estimates. A major reason for the performance advantage is the use of phase information by the SAC function, while the cepstrum uses a phaseless power spectral density that is directly affected by the system response and the presence of diffuse scattering (speckle). An example of estimating the mean-scatterer spacing in liver tissue also is presented.

Culture Techniques↗
PubMed2006

Lumbar disc degeneration: association between osteophytes, end-plate sclerosis and disc space narrowing.

BACKGROUND: Lumbar disc degeneration is characterised radiologically by the presence of osteophytes, end-plate sclerosis and disc space narrowing. AIM: To determine the strength of the association between increasing severity of combinations of these features in a population sample of men and women. METHODS: Men and women aged >or=50 years were recruited from a primary care-based community health index in Aberdeen, UK. Participants had lateral spinal radiographs performed according to a standard protocol. The intervertebral disc spaces (L1/2-L4/5) were evaluated for the presence of anterior osteophytes, end-plate sclerosis and disc space narrowing using a graded semiquantitative score (grade 0-3). Log linear modelling was used to determine the associations (pairwise) between increasing severity of these features, with the results expressed as beta coefficients and 95% confidence intervals (CIs). RESULTS: There were 286 men (mean age 65.3 years) and 299 women (mean age 65.2 years) with spinal radiographs, yielding a total of 2340 assessable lumbar vertebral levels. In all, 73% of vertebral levels had evidence of osteophytes, 26% of sclerosis and 37% of disc space narrowing. Increasing severity of osteophyte grade was associated with an increasing severity both of sclerosis and of disc space narrowing, whereas the severity of sclerosis was associated with the severity of narrowing. This was true at all vertebral levels. The strongest association, however, was between osteophytes and sclerosis (beta coefficient = 2.7, 95% CI 2.4 to 3.1). For sclerosis and narrowing the beta coefficient was 1.9 (95% CI 1.7 to 2.1), whereas for osteophytes and narrowing the beta coefficient was much weaker at 1.2 (95% CI 1.1 to 1.3). There was no important influence of vertebral level on any of these associations. CONCLUSION: The association between increasing severity of osteophytes and end-plate sclerosis is stronger than for other combinations of radiographic features of lumbar disc degeneration.

Aged↗
PubMed1999

Are radiological joint space widths of normal hips asymmetrical?

BACKGROUND: To be certain that the joint space width is abnormal in the case of hip joint pain when compared with the contralateral hip requires knowledge of physiological dissymmetry. AIM OF THE STUDY: To assess interindividual variability and dissymmetry in pelvic radiological joint space width. METHODS: Pelvic radiographs of subjects without hip joint disease. Measurement with a 0.1 mm graduated magnifying glass and 0.5 mm graduated flat ruler at the hip superointermediate site (vertical going through the femoral head centre). After randomisation of the side to measure, analysis of nine groups of 19 plain films by one investigator blind for the result of the contralateral side. RESULTS: The difference between the left and right hip was plotted against the corresponding mean for all 171 normal subjects. This shows the frequency and the limits of the asymmetry at each measurement site. The asymmetry is independent of interindividual variability of the joint space width and greater than the measurement error in most subjects. CONCLUSION: This study confirms the interindividual variability of hip joint space width, shows the frequency of hip joint space asymmetry and defines its limit.

Female↗
PubMed2003

Noise levels within the ear and post-nasal space in neonates in intensive care.

BACKGROUND: Noise exposure in neonatal units has long been suspected of being a cause of hearing loss associated with such units. The noise intensity to which the neonate is exposed varies with the type of ventilatory support used. Also, the post-nasal space is an enclosed cavity that is close to the inner ear and an area of turbulent and hence potentially noisy airflow. AIM: To determine noise intensities within the ear and post-nasal space in neonates on different modes of ventilatory support using probe microphones, measures previously not undertaken. METHODS: A portable instrument with a probe microphone was used for the measurements. Three groups of infants were included: (a) those receiving no respiratory support (NS); (b) those receiving conventional ventilation (CV); (c) those receiving continuous positive airways pressure (CPAP) support. RESULTS: The mean in-the-ear noise intensities (at 1 kHz) were 41.7 dB SPL (NS), 39.5 dB SPL (CV), and 55.1 dB SPL (CPAP). The noise intensities in the post-nasal space in those receiving CPAP support were higher than in the other groups, reached mean levels of up to 102 dB SPL at some frequencies, and increased with increasing flow rates. CONCLUSIONS: The most important finding is the high noise intensities in the post-nasal space of those receiving CPAP support. Given the proximity of the post-nasal space to the inner ear, enough noise could be transmitted, especially in infants receiving the higher flow rates, to cause cochlear damage and hence hearing loss. It would therefore be wise, wherever possible, to avoid using the higher flow rates.

Cochlea↗
PubMed1990

Morning serum cortisol concentrations after 2 mg inhaled beclomethasone dipropionate in normal subjects: effect of a 750 ml spacing device.

Large spacing devices have been shown to provide more selective delivery of an inhaled steroid to the lung but the effect on the hypothalamo-pituitary-adrenal suppression associated with high dose inhaled corticosteroids has been little studied. The effect of a large spacing device (Volumatic; 750 ml) on suppression of 0900 h cortisol after 2 mg inhaled beclomethasone dipropionate was therefore investigated in normal, healthy volunteers. Twenty four subjects (12 male, 12 female) took part in a randomised, double blind, placebo controlled cross over study in which a single dose of 2 mg beclomethasone dipropionate was taken at 2300 h on two occasions seven days apart, once from a metered dose inhaler alone and once from a metered dose inhaler attached to a 750 ml spacing device. The 0900 h serum cortisol concentration was the same on the morning before each administration (468 nmol/l, 95% confidence interval (CI) 390-561 nmol/l, day 1 v 479 nmol/l, 95% CI 463-494 nmol/l, day 8). The 0900 h serum cortisol concentration the following morning, however, was lower when 2 mg beclomethasone dipropionate was given by metered dose inhaler alone (182 (95% CI 128-264) nmol/l) than when it was given by a spacing device (363 (95% CI 281-475) nmol/l). These results suggest that a large spacing device attached to a metered dose inhaler may decrease the risk of hypothalamo-pituitary-adrenal suppression by high dose inhaled steroid treatment.

Administration, Inhalation↗
PubMed1980

The effects of reducing manger space on dairy cow behaviour and production.

The manger space for a group of 30 cows was reduced from 105 cm to 15 cm per cow during a period of six weeks. Before each reduction in manger space the cows were observed for 24 hours and their activity and aggressive behaviour recorded. The activity of individual cows varied little but there was wide variation among cows. The reduction in manger space did not change the mean number of visits by cows to the manger, the total time spent feeding, the amount of aggressive behaviour, the milk yield or the general activity of the cows in comparison with a control group allowed 105 cm of manger space per cow for the whole period. There was a reduction in the total time spent feeding by cows which were clinically ill and a change in the number of visits made to the manger by cows in oestrus. A reduction in the allocation of manger space would make it possible either to build smaller, cheaper housing or to convert existing buildings to accommodate more cows. It would also make it possible to use automated systems to record the feed intake and number of visits to the manger of individual cows and would help to detect cows which were sick or in oestrus.

Aggression↗
PubMed1986

Intraperitoneal paravesical spaces: CT delineation with US correlation.

The urinary bladder, obliterated umbilical arteries, and inferior epigastric vessels located within the extraperitoneal space of the anterior abdominal wall indent the anterior parietal peritoneum, forming intraperitoneal paravesical fossae. These are the supravesical space and the medial and lateral inguinal fossae. More posteriorly, the peritoneum covering the bladder is reflected onto the rectum to form the rectovesical space, which is divided by the uterus into an anterior vesicouterine recess and a posterior rectouterine pouch, or cul-de-sac. The cul-de-sac is continuous with the pararectal and ovarian fossae and is bounded posterolaterally by the rectouterine (sacrogenital) folds. These peritoneal compartments form a large potential space for the accumulation of ascites and are separated from the equally large extraperitoneal paravesical spaces by only a thin layer of peritoneum or peritoneum and umbilicovesical fascia. The computed tomographic scans of 100 patients with ascites were reviewed, with particular attention to the differentiation between intraperitoneal and extraperitoneal paravesical collections. The scans of intraperitoneal collections were found to have certain characteristic appearances, including inferior displacement of the distended urinary bladder, visualization of the umbilical folds, and preservation of the preperitoneal fat.

Ascites↗
PubMed1993

Effects of arginine vasopressin and atriopeptin on glial cell volume measured as 3-MG space.

This study evaluates the hypothesis that arginine vasopressin (AVP) and atriopeptin, peptide hormones synthesized and released within the brain, are regulators of brain cell volume using cultured astroglial cells derived from newborn rats. Cell water content, regarded as volume, was measured in defined, serum-free medium as the 3-O-methylglucose (3-MG) space. Initial experiments established conditions such that glucose, which competes with 3-MG for the glucose carrier, would not interfere with the measurement of the 3-MG space. AVP increased the 3-MG space of glial cells by an average of 25% between 30 and 120 min of exposure, whereas atriopeptin decreased it by 32%. The 3-MG space remained close to normal after coadministration of both peptides. The AVP-dependent increase in 3-MG space was blocked both by the V1 antagonist d(CH2)5Tyr(Me)AVP (Manning compound) and by the cotransport inhibitor, bumetanide. Results are consistent with a role for AVP and atriopeptin in the homeostasis of atroglial cell volume.

3-O-Methylglucose↗
PubMed2001

In vivo fluorescence measurement of Na(+) concentration in the pericryptal space of mouse descending colon.

A method involving surgical exposure of the colonic mucosa, fluorescent dye addition, and confocal microscopy has been developed for monitoring colonic crypt function in vivo in mice. Na(+) concentration in the extracellular pericryptal space of descending colon was measured using a low-affinity Na(+)-sensitive fluorescent indicator consisting of an Na(+)-sensitive chromophore (sodium red) and an Na(+)-insensitive chromophore (Bodipy-fl) immobilized on 200-nm-diameter polystyrene beads. The Na(+) indicator beads accumulated in the pericryptal spaces surrounding the colonic crypts after a 1-h exposure of the colonic luminal surface to the bead suspension. Na(+) concentration ([Na(+)]) in the pericryptal space was 491 +/- 62 mM (n = 4). After a 70-min exposure to amiloride (0.25 mM), pericryptal [Na(+)] was reduced to 152 +/- 21 mM. Blockage of the crypt lumen with mineral oil droplets reduced pericryptal [Na(+)] to 204 +/- 44 mM. Exposure of the colonic mucosa to FITC-dextran (4.5 kDa) led to rapid accumulation of the dye into the crypt lumen with a half time of 19.8 +/- 1.0 s, which was increased to 77.9 +/- 6.0 s after amiloride treatment. These results establish an in vivo fluorescence method to measure colonic crypt function and provide direct evidence for accumulation of a hypertonic absorbate in the pericryptal space of descending colon. The pericryptal space represents the first example of a hypertonic extracellular compartment in mammals that is not created by a countercurrent amplification mechanism.

Amiloride↗
PubMed2001

Space-time pressure structure of pharyngo-esophageal segment during swallowing.

We applied high-resolution manometry with spatiotemporal data interpolation and simultaneous videofluoroscopy to normal pharyngeal swallows to correlate specific features in the space-time intraluminal pressure structure with physiological events and normal deglutitive transsphincteric bolus flow to define normal biomechanical properties of the pharyngo-esophageal (PE) segment. Pressures were recorded by microperfused catheter, and the two-dimensional space-time data sets were plotted as isocontours. On these were superimposed bolus trajectories, anatomic segment movements, and hyo-laryngeal trajectories from concurrent videofluoroscopy. Correlation of the highly reproducible space-time-pressure structure with radiographic images confirmed that primary deglutitive PE segment functions (pressure profile, laryngeal elevation, axial sphincter motion, timing of relaxation, contraction) are accurately discernible from single isocontour pressure visualization. Pressure during bolus flow was highly dependent on axial location within PE segment and time instant. The intrabolus pressure domain, corresponding to the space-time region between bolus head and tail trajectories, demonstrated significant bolus volume dependence. High-resolution manometry accurately, comprehensively, and highly reproducibly depicts the PE segment space-time-pressure structure and specific physiological events related to upper esophageal sphincter opening and transsphincteric flow during normal swallowing. Intrabolus pressure variations are highly dependent on position within the PE segment and time.

Adult↗
PubMed1987

Effect of pressure and intimal damage on 131I-albumin and [14C]sucrose spaces in aorta.

To measure the distribution volume for sucrose and albumin in the media of the rabbit thoracic aorta, we studied the uptake of tracers in vitro. In most cases the tracers were applied to both luminal and adventitial surfaces at the same concentration. When transmural convection was prevented by pressurization of the arteries with air, there was a decrease in sucrose space (19% at 70 mmHg and 28% at 180 mmHg) and in albumin space (60% at 70 mmHg and 66% at 180 mmHg), compared with the respective spaces in relaxed arteries (0.42 for sucrose and 0.08 for albumin). Much smaller changes were found when intact vessels were pressurized with liquid (insignificant for sucrose, decreases of 24% at 70 mmHg and 14% at 180 mmHg for albumin). Removal of the endothelium, which increases transmural fluid flux, increased the space for sucrose (not significantly at 70 mmHg and 17% at 180 mmHg) and particularly for albumin (100% at 70 mmHg and 250% at 180 mmHg). We conclude that the interstitial volume and consequently the protein space within the media can be modified both by distending stresses applied to the vessel and by transmural fluid flux.

Albumins↗
PubMed1988

Reabsorption kinetics of albumin from pleural space of dogs.

The reabsorption of albumin from the pleural space was measured in eight dogs receiving 0.5 ml intrapleural injection of 131I-labeled albumin and a simultaneous intravenous injection of 125I-labeled albumin. Plasma curves for both tracers were obtained over 24 h. The 125I-albumin curve served as input function of albumin for interstitial spaces, including pleura, whereas the 131I-albumin curve represented the output function from pleural space. The frequency function of albumin transit times from pleural space to plasma was obtained by deconvolution of input-output plasma curves. Plasma recovery of 131I-albumin was complete by 24 h, and the mean transit time from pleura to plasma averaged 7.95 +/- 1.57 (SD) h. Albumin reabsorption occurred mainly via lymphatics as indicated by experiments in 16 additional dogs in which their right lymph ducts or thoracic ducts were ligated before intrapleural injection. A pleural lymph flow of 0.020 +/- 0.003 (SD) ml.kg-1.h-1 was estimated, which is balanced by a comparable filtration of fluid into the pleural space. This suggests that, under physiological conditions, the subpleural lymphatics represent an important control mechanism of pleural liquid pressure.

Absorption↗
PubMed1976

Effect of epinephrine on vascular space of gills and head of rainbow trout.

The filling of the gills and head vascular space of a teleost fish was measured in vitro by perfusing an isolated head of a trout with a Ringer solution containing 131I-labeled human serum albumin. The presence of epinephrine in the Ringer solution significantly increased afferent (ventral aortic) flow rate and efferent (dorsal aorta) flow rate, whereas branchial venous system circulation was reduced. When perfused with an epinephrine-free Ringer, the branchial vascular space appears 5-6 times greater than the head vascular space (per 100 g of tissue). Epinephrine, 10(-5) M, in the Ringer solution significantly decreased the branchial vascular space without modifying that of the head. The increase in perfusion rate and decrease in branchial vascular space due to the epinephrine can only be interpreted by taking into account a branchial nonlamellar compartment of a considerable volume.

Animals↗