The Experts below are selected from a list of 441546 Experts worldwide ranked by ideXlab platform
Brian C J Moore - One of the best experts on this subject based on the ideXlab platform.
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effect of age test Frequency and level on thresholds for the ten hl test for people with normal hearing
International Journal of Audiology, 2020Co-Authors: Brian C J MooreAbstract:Objective: The objective was to assess the effect of age on thresholds for the TEN(HL) test for diagnosing dead regions in the cochlea, as a function of Signal Frequency and TEN(HL) level.Design: T...
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reference thresholds for the ten hl test for people with normal hearing
International Journal of Audiology, 2017Co-Authors: Andreas S Hansen, Oyvind Raen, Brian C J MooreAbstract:Objective: To estimate normative values and repeatability of thresholds for the TEN(HL) test for diagnosing dead regions in the cochlea, as a function of Signal Frequency, TEN(HL) level, age and ge...
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effects of masker component phase on the forward masking produced by complex tones in normally hearing and hearing impaired subjects
Hearing Research, 2004Co-Authors: Brian C J Moore, Thomas H Stainsby, Esme TarasewiczAbstract:For normally hearing subjects, harmonic complex tones that give "peaky" waveforms on the basilar membrane (Schroeder-positive phase, sine phase or cosine phase) lead to less forward masking than complex tones that give less peaky waveforms (Schroeder-negative phase or random phase), but have the same power spectrum. This difference has been attributed mainly to the combined effects of peripheral compression and suppression, both of which depend on the operation of the active mechanism in the cochlea. If this explanation is correct, the phase effect should be reduced or absent for subjects with moderate cochlear hearing loss. We measured growth-of-masking functions for forward maskers containing the first 40 harmonics of a 100-Hz fundamental, with components added either in cosine phase or random phase, using both normally hearing subjects and subjects with moderate cochlear hearing loss. The Signal Frequency was 1 or 2 kHz. For the normally hearing subjects, the mean slopes of the growth-of-masking functions at 1 and 2 kHz, respectively, were 0.53 and 0.44 for the random-phase masker and 0.31 and 0.26 for the cosine-phase masker. For high masker levels, the former produced considerably more masking than the latter. The phase effect was smaller for the hearing-impaired than for the normally hearing subjects, which is consistent with the idea that it is partly caused by peripheral compression and suppression. However, three of the five hearing-impaired subjects showed a significant effect of masker phase for at least one Signal Frequency. In one case, this occurred when the hearing loss at the Signal Frequency was 65 dB. The slopes of the growth-of-masking functions were consistently less than one for the hearing-impaired subjects. Further testing suggested that the efferent system was not involved in producing the phase effect.
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a test for the diagnosis of dead regions in the cochlea
British Journal of Audiology, 2000Co-Authors: Brian C J Moore, Brian R Glasberg, Deborah Vickers, Martina Huss, Joseph I AlcantaraAbstract:Hearing impairment may sometimes be associated with complete loss of inner hair cells (IHCs) over a certain region of the basilar membrane. We call this a 'dead region'. Amplification (using a hearing aid) over a Frequency range corresponding to a dead region may not be beneficial and may even impair speech intelligibility. However, diagnosis of dead regions is not easily done from the audiogram. This paper reports the design and evaluation of a method for detecting and delimiting dead regions. A noise, called 'threshold equalizing noise' (TEN), was spectrally shaped so that, for normally hearing subjects, it would give equal masked thresholds for pure tone Signals at all frequencies within the range 250-10,000 Hz. Its level is specified as the level in a one-ERB (132 Hz) wide band centred at 1000 Hz. Measurements obtained from 22 normal-hearing subjects and TEN levels of 30, 50 and 70 dB/ERB confirmed that the Signal level at masked threshold was approximately equal to the noise level/ERB and was almost independent of Signal Frequency. Masked thresholds were measured for 20 ears of 14 subjects with sensorineural hearing loss, using TEN levels of 30, 50 and 70 dB/ERB. Psychophysical tuning curves (PTCs) were measured for the same subjects. When there are surviving IHCs corresponding to a Frequency region with elevated absolute thresholds, a Signal in that Frequency region is detected via IHCs with characteristic frequencies (CFs) close to that region. In such a case, threshold in the TEN is close to that for normal-hearing listeners, provided that the noise intensity is sufficient to produce significant masking. Also, the tip of the PTC lies close to the Signal Frequency. When a dead region is present, the Signal is detected via IHCs with CFs different from that of the Signal Frequency. In such a case, threshold in the TEN is markedly higher than normal, and the tip of the PTC is shifted away from the Signal Frequency. Generally, there was a very good correspondence between the results obtained using the TEN and the PTCs. We conclude that the measurement of masked thresholds in TEN provides a quick and simple method for the diagnosis of dead regions.
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relationship between loudness perception and peripheral compression in subjects with unilateral cochlear hearing loss
Journal of the Acoustical Society of America, 1999Co-Authors: Brian C J Moore, Christopher J Plack, Deborah Vickers, Andrew J OxenhamAbstract:Loss of compression on the basilar membrane (BM) associated with outer hair cell damage (OHC) is thought to be the main factor underlying loudness recruitment in people with cochlear heating loss. To assess this idea, subjects with unilateral cochlear hearing loss were tested. Recruitment was measured by obtaining loudness matches between tones presented alternately to the two ears. Compression was estimated from the slopes of growth‐of‐masking functions in forward masking. The ratio of slopes for a masker centered well below the Signal Frequency and a masker centered at the Signal Frequency gives a measure of BM compression at the place corresponding to the Signal Frequency [A. J. Oxenham and C. J. Plack, J. Acoust. Soc. Am. 101, 3666–3675 (1997)]. The measures of loudness recruitment were used to derive a parameter HLOHC, the amount of the hearing loss attributable to OHC damage [B. C. J. Moore and B. R. Glasberg, Auditory Neurosci. 3, 289–311 (1997)]. The value of HLOHC is directly related to the amoun...
R Tomasiūnas - One of the best experts on this subject based on the ideXlab platform.
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differential carrier lifetime in ingan based light emitting diodes obtained by small Signal Frequency domain measurements
Journal of Applied Physics, 2017Co-Authors: I Reklaitis, Felix Nippert, R Kudžma, T Malinauskas, Sergey Yu Karpov, Ines Pietzonka, Hansjuergen Lugauer, Martin Strassburg, Pranciskus Vitta, R TomasiūnasAbstract:Recently, a novel method for evaluation of recombination coefficients corresponding to Shockley-Read-Hall, radiative, and Auger recombination channels has been proposed, which combines measurements of the light emitting diode (LED) external quantum efficiency under continuous wave operation with the determination of non-equilibrium carrier differential life time (DLT) by small-Signal time-resolved photoluminescence [Nippert et al., Jpn. J. Appl. Phys., Part 1 55, 05FJ01 (2016)]. In this work, we suggest an alternative technique, small-Signal Frequency-domain lifetime measurements, which is implemented more easily and capable of operating in a wider range of LED operating currents. The DLTs measured by both techniques are shown to agree well with each other, but saturate at low currents, contrary to the trend predicted by the well-known ABC-model. We discuss possible reasons for this deviation, as well as advantages and limitations of the measurement techniques.
Wei-hua Chieng - One of the best experts on this subject based on the ideXlab platform.
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Estimation of single-tone Signal Frequency with special reference to a Frequency-modulated continuous wave system
Measurement Science and Technology, 2012Co-Authors: Chih-fang Huang, Hsiang Pin Lu, Wei-hua ChiengAbstract:Estimating the Frequency of a single-tone Signal is a common problem in radar applications, such as Frequency-modulated continuous wave radar. This study presents a Frequency estimation algorithm called the gradient search method using the derivative of discrete Fourier transform on the received Signal samples. The analytical boundaries of the proposed method for different Signal-to-noise ratios under the two conditions, with the rectangular window and with the Hann window, are derived. This study also compares the most appropriate algorithms available in the literature, including chirp-Z transform and other advanced methods. Simulation and experimental results show that the proposed algorithm provides superior performance to previous methods.
Vladimir V Lukin - One of the best experts on this subject based on the ideXlab platform.
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fast communication estimation of single tone Signal Frequency by using the l dft
Signal Processing, 2007Co-Authors: Igor Djurovic, Vladimir V LukinAbstract:Frequency estimation of complex sinusoidal Signal parameters for mixed Gaussian and impulse noise environment is considered. We assume that the sinusoid has constant amplitude. The first stage in the proposed algorithm is calculation of the L-DFT forms for various parameters. Then, an optimal value of the L-DFT parameter is estimated as a value minimizing the L-DFT energy. Position of the L-DFT maximum calculated for the optimal parameter is used as a coarse Frequency estimate. Fine estimation is performed by a recently proposed iterative procedure. Numerical analysis confirms accuracy of the proposed technique.
Dmitriy A Yablonskiy - One of the best experts on this subject based on the ideXlab platform.
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magnetic susceptibility induced white matter mr Signal Frequency shifts experimental comparison between lorentzian sphere and generalized lorentzian approaches
Magnetic Resonance in Medicine, 2014Co-Authors: Jie Luo, Dmitriy A YablonskiyAbstract:Purpose The nature of the remarkable phase contrast in high-field gradient echo MRI studies of human brain is a subject of intense debates. The generalized Lorentzian approach (He and Yablonskiy, Proc Natl Acad Sci USA 2009;106:13558–13563) provides an explanation for the anisotropy of phase contrast, the near absence of phase contrast between white matter and cerebrospinal fluid, and changes of phase contrast in multiple sclerosis. In this study, we experimentally validate the generalized Lorentzian approach. Theory and Methods The Generalized Lorentzian Approach suggests that the local contribution to Frequency shifts in white matter does not depend on the average tissue magnetic susceptibility (as suggested by Lorentzian sphere approximation), but on the distribution and symmetry of magnetic susceptibility inclusions at the cellular level. We use ex vivo rat optic nerve as a model system of highly organized cellular structure containing longitudinally arranged myelin and neurofilaments. The nerve's cylindrical shape allowed accurate measurement of its magnetic susceptibility and local Frequency shifts. Results We found that the volume magnetic susceptibility difference between nerve and water is −0.116 ppm, and the magnetic susceptibilities of longitudinal components are −0.043 ppm in fresh nerve, and −0.020 ppm in fixed nerve. Conclusion The Frequency shift observed in the optic nerve as a representative of white matter is consistent with generalized Lorentzian approach but inconsistent with Lorentzian sphere approximation. Magn Reson Med 71:1251–1263, 2014. © 2013 Wiley Periodicals, Inc.
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biophysical mechanisms of mri Signal Frequency contrast in multiple sclerosis
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Dmitriy A Yablonskiy, Jie Luo, Alexander L Sukstanskii, Aditi Iyer, Anne H CrossAbstract:Phase images obtained with gradient echo MRI provide image contrast distinct from T1- and T2-weighted images. It is commonly assumed that the local contribution to MRI Signal phase directly relates to local bulk tissue magnetic susceptibility. Here, we use Maxwell’s equations and Monte Carlo simulations to provide theoretical background to the hypothesis that the local contribution to MRI Signal phase does not depend on tissue bulk magnetic susceptibility but tissue magnetic architecture—distribution of magnetic susceptibility inclusions (lipids, proteins, iron, etc.) at the cellular and subcellular levels. Specifically, we show that the regular longitudinal structures forming cylindrical axons (myelin sheaths and neurofilaments) can be locally invisible in phase images. Contrary to an expectation that the phase contrast in multiple sclerosis lesions should always increase in degree along with worsening of lesion severity (which happens for all known MR magnitude-based contrast mechanisms), we show that phase contrast can actually disappear with extreme tissue destruction. We also show that the phase contrast in multiple sclerosis lesions could be altered without loss of nervous system tissue, which happens in mild injury to the myelin sheaths or axonal neurofilaments. Moreover, we predict that the sign of phase contrast in multiple sclerosis lesions indicates the predominant type of tissue injury—myelin damage (positive sign) vs. axonal neurofilament damage (negative sign). Therefore, our theoretical and experimental results shed light on understanding the relationship between gradient echo MRI Signal phase and multiple sclerosis pathology.
