1,721,022 research outputs found
Linear and nonlinear transient evoked otoacoustic emissions in humans exposed to noise
No full textTransient evoked otoacoustic emissions (TEOAEs) have been analyzed in a population of 134 ears, divided into three classes: (1) nonexposed ears in bilaterally normal hearing subjects, (2) audiometrically normal ears of subjects exposed to noise and affected by unilateral high-frequency (f>3 kHz) hearing loss in the contralateral ear, and (3) the contralateral impaired ears of the exposed subjects. The statistical distributions of global and spectral signal-to-noise ratio (SNR) were analyzed. TEOAEs were recorded both in the linear and nonlinear acquisition mode to evaluate the effectiveness of two standard averaging techniques with respect to their sensitivity to the early effects of noise exposure. Good discrimination between nonexposed and exposed ears was obtained using either the linear or the nonlinear mode. Despite its intrinsically higher SNR, the linear mode is not more sensitive than the nonlinear mode for this purpose because it is not possible to find a window for effectively cancelling the linear artifact while keeping a suitable sensitivity to the short-latency high-frequency aspect of the response. Moreover, with respect to another measurable parameter, the TEOAE latency, good discrimination is obtained only by using the nonlinear mode because, again, the linear artifact masks the high-frequency TEOAE response. © 2002 Elsevier Science B.V. All rights reserved
Otoacoustic emissions and early detection of noise induced hearing loss
No full textThe idea that otoacoustic emissions (OAEs) can be used to perform an early detection of hearing loss is strongly supported by both theoretical considerations and experimental evidence. It is well-known that the amplitude of the transient evoked OAE (TEOAEs) is dominated by the contribution of the spectral components for which the cochlear amplifier is most effective (spontaneous or long-lasting OAEs). It is also well-known that the outer hair cells (OHCs) are the first part of the auditory system to be damaged by noise. Thus it is quite obvious to predict that mild cochlear damage due to the early effects of noise exposure could be detected by using OAE measurements. Hall and Lutman (1999) have shown that OAEs are indeed more sensitive than standard audiometry in a range of mild hearing loss, by taking into account the sensitivity and test-retest fluctuations of both techniques. Lucertini et al. (2002) have shown that TEOAE parameters can effectively discriminate not only between populations of normal and impaired subjects, but also between exposed and nonexposed to noise. Moleti et al. (2002) have further demonstrated that both linear and nonlinear TEOAEs can effectively be used for this task
Spontaneous otoacoustic emissions and relaxation dynamics of long decay time OAEs in audiometrically normal and impaired subjects
No full textThe relationship between hearing loss, detected by measuring the audiometric threshold shift, and the presence of long-lasting otoacoustic emissions, has been studied in a population of 66 adult males, by analyzing the cochlear response in the 80 ms following the subministration of a click stimulus. Most long-lasting OAEs are also recognizable as Synchronized Spontaneous OAEs (SSOAEs). The OAE characteristic decay times were evaluated according to the model by Sisto and Moleti [J. Acoust. Sec. Am. 106, 1893 (1999)]. The starting hypothesis, confirmed by the results, is that long decay time and large equilibrium amplitude are both manifestations of the effectiveness of the active feedback mechanism. The prevalence and frequency distribution of long-lasting OAEs, and of their SSOAE subset, have been separately analyzed for normal and impaired ears. No long-lasting OAE was found within the hearing loss frequency range, but several were found in impaired ears outside the hearing loss range, both at lower and higher frequencies. This result suggests that the correlation between the presence of long-lasting OAEs and good cochlear functionality be local in the frequency domain. The monitor of the OAE decay time is proposed as a new possible method for early detecting hearing loss in populations exposed to noise. (C) 2001 Acoustical Society of America
Experimental evidence for the basal generation place of the short-latency transient-evoked otoacoustic emissions
No full textTime-frequency analysis of the transient-evoked otoacoustic emission response was performed on a population of subjects affected by sensory-neural hearing loss characterized by a sharp audiometric profile, caused by firearm noise exposure (42 ears), and on a control population of normal-hearing subjects (84 ears). Time-frequency filtering permitted a careful evaluation of the relation between the audiometric profile and the spectral shape of the long- and short-latency otoacoustic components. Both filtered spectra closely follow the shape of the audiometric profile, with a frequency shift between them. The typical frequency shift was evaluated by averaging the otoacoustic spectra and the audiograms among groups of ears with the same cutoff frequency. Assuming that the otoacoustic emission source function depends on the local effectiveness of the cochlear amplifier, this experimental evidence suggests that the short-latency response is generated at a cochlear place displaced towards the base by about 0.5-1 mm with respect to the generation place of the long-latency component. The analysis of the control group demonstrates that, below 4 kHz, the observed effect is not dependent on the data acquisition and analysis procedure. These results confirm previous theoretical estimates and independent experimental evidence based on the measured latency difference between the two component
Workload Balancing and Part Transfer Minimization in Flexible Manufacturing Systems
No full textProblems related to the flow management of a flexible manufacturing system (FMS) are here formulated in terms of combinatorial optimization. We consider a system consisting of several multitool automated machines, each one equipped with a possibly different tool set and linked to each other by a transportation system for part moving. The system operates with a given production mix.
The focused flow-management problem is that of finding the part routings allowing for an optimal machine workload balancing. The problem is formulated in terms of a particular capacity assignment problem.
With the proposed approach, a balanced solution can be achieved by routing parts on a limited number of different paths. Such a balancing routing can be found in polynomial time. We also give polynomial-time and-space algorithms for choosing, among all workload-balancing routings, the ones that minimize the global amount of part transfer among all machines
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