otoacoustic emissions from normal hearing and hearing impaired subjects distortion product responses distortion product otoacoustic emissions dpoae were measured in normal hearing and hearing impaired human subjects analyses based on decision theory were used to evaluate dpoae test performance specifically relative operating characteristic roc curves were constructed and the areas under these curves were used to estimate the extent to which normal and impaired ears could be correctly identified by these measures dpoae amplitude and dpoae noise measurements were able to distinguish between normal and impaired subjects at 4000 8000 and to a lesser extent at 2000 hz the ability of these measures to distinguish between groups decreased however as frequency and audiometric criterion used to separate normal and hearing impaired ears decreased at 500 hz performance was no better than chance regardless of the audiometric criterion for normal hearing cumulative distributions of misses hearing impaired ears incorrectly identified as normal hearing and false alarms normal hearing ears identified as hearing impaired were constructed and used to evaluate test performance for a range of hit rates i e the percentage of correctly identified hearing impaired ears depending on the desired hit rate criterion values of 5 to 12 db spl for dpoae amplitudes and 8 to 15 db for dpoae noise accurately distinguished normal hearing ears from those with thresholds greater than 20 db hl for the two frequencies at which performance was best 4000 and 8000 hz it would appear that dpoae measurements can be used to accurately identify the presence of high frequency hearing loss but are not accurate predictors of hearing status at lower frequencies at least for the conditions of the present measurements

measuring distortion product otoacoustic emissions using continuously sweeping primaries distortion product otoacoustic emission dpoae level from normal hearing individuals can vary by as much as 30db with small frequency changes a phenomenon known as dpoae fine structure this fine structure is hypothesized to stem from the interaction of components from two different regions of the cochlea the nonlinear generator region and the reflection component from the dp region an efficient procedure to separate these two components would improve the clinical and research utility of dpoae by permitting separate evaluation of different cochlea regions in this paper two procedures for evaluating dpoae fine structure are compared dpoae generated by fixed frequency primaries versus continuously sweeping primaries the sweep dpoae data are analyzed with a least squares fit filter sweep rates of greater than 8s per octave permit rapid evaluation of the cochlear fine structure a higher sweep rate of 2s per octave provided dpoae without fine structure under these conditions the longer latency reflection component falls outside the range of the filter consequently dpoae obtained with sweeping tones can be used either to get more rapid estimates of dpoae fine structure or to obtain estimates of dpoae from the generator region uncontaminated by energy from the reflection region

supercritical speed stability of the trivial equilibrium of an axially moving string on an elastic foundation the stability of an axially moving string supported by a discrete or distributed elastic foundation is examined analytically particular attention is directed at the distribution of the critical speeds and identifying the divergence instability of the trivial equilibrium the elastically supported string shows unique stability behavior that is considerably different from unsupported axially moving string in particular any elastic foundation discrete or distributed leads to multiple critical speeds and a single region of divergence instability above the first critical speed whereas the unsupported string has one critical speed and is stable at all supercritical speeds additionally the elastically supported string critical speeds are bounded above and the maximum critical speed is the upper bound of the divergent speed region the analysis draws on the self adjoint eigenvalue problem for the critical speeds and a perturbation analysis about the critical speeds neither numerical solution nor spatial discretization which can produce substantially incorrect results are required the system falls in the class of dispersive gyroscopic continua and its behavior provides a useful comparison for general gyroscopic systems the analytical findings also serve as a benchmark for approximate methods applied to gyroscopic continua

asymmetrical pulse shaped qpsk modulation systems to enable differential detection of coincident hard limited and reduced sidelobe qpsk type of signals we introduce asymmetrical pulse shapes this asymmetry in the i and q baseband channels leads to coincident unstaggered qpsk system applications we consider the bit error probability performance of these modulation schemes on a hardlimited channel in the presence of uplink and downlink additive gaussian noise it is found that the unstaggered qpsk modulation with the asymmetrical pulse has better bit error probability performance than qpsk and staggered qorc

spectral analysis for the transverse vibration of an axially moving timoshenko beam the use of frequency dependent spectral element matrix or exact dynamic stiffness matrix in structural dynamics is known to provide very accurate solutions while reducing the number of degrees of freedom to resolve the computational and cost problems thus in the present paper the spectral element model is formulated for the axially moving timoshenko beam under a uniform axial tension the high accuracy of the present spectral element is then verified by comparing its solutions with the conventional finite element solutions and exact analytical solutions the effects of the axial velocity and axial tension on the vibration characteristics the dispersion relation and the stability of a moving timoshenko beam are analytically and numerically investigated

non linear parametric vibration and stability of axially moving visco elastic rayleigh beams abstract an axially moving visco elastic rayleigh beam with cubic non linearity is considered and the governing partial differential equation of motion for large amplitude vibration is derived through geometrical constitutive and dynamical relations by directly applying the method of multiple scales to the governing equations of motion and considering the solvability condition the linear and non linear frequencies and mode shapes of the system are analytically formulated in the presence of damping terms it can be seen that the amplitude is exponentially time dependent and as a result the non linear natural frequencies of the system will be time dependent for the resonance case through considering the solvability condition and routh hurwitz criterion the stability conditions are developed analytically eventually the effects of system parameters on the vibrational behavior stability and bifurcation points of the system are investigated through parametric studies

distortion product otoacoustic emissions cochlear source contributions and clinical test performance it has been proposed that the clinical accuracy of distortion product otoacoustic emissions dpoaes is affected by the interaction of distortion and reflection sources contributing to the response this study evaluated changes in dichotomous decision test performance and threshold prediction accuracy when dpoae source contribution was controlled data were obtained from 205 normal and impaired ears with l2 ranging from 0 to 80db spl and f2 2 and 4khz data were collected for control conditions no suppressor f3 and with f3 presented at three levels that previously had been shown to reduce the reflection source contribution the results indicated that controlling source contribution with a suppressor did not improve diagnostic accuracy as reflected by relative operating characteristic curve area and frequently resulted in poorer test performance compared to control conditions likewise correlations between dpoae and behavioral thresholds were not strengthened when using the suppressors to control sou

infinite mode analysis and truncation to resonant modes of axially accelerated beam vibrations abstract the transverse vibrations of simply supported axially moving euler bernoulli beams are investigated the beam has a time varying axial velocity with viscous damping traveling beam eigenfunctions with infinite number of modes are considered approximate analytical solutions are sought using the method of multiple scales a perturbation technique a detailed analysis of the resonances in which upto four modes of vibration involved are performed stability analysis is treated for each type of resonance approximate stability borders are given for the resonances involving only two modes for higher number of modes involved in a resonance sample numerical examples are presented for stabilities

cochlear nonlinearity in normal hearing subjects as inferred psychophysically and from distortion product otoacoustic emissions the aim was to investigate the correlation between estimates of compression ratio compression threshold and cochlear gain for normal hearing subjects inferred from temporal masking curves tmc and distortion product otoacoustic emission dpoaes input output i o curves special care was given to reduce the influence of dpoae fine structure on the i o curves data were collected for 10 subjects and for cochlear places with characteristic frequencies cfs of 0 5 1 2 and 4 khz except at 4 khz little correlation was found between ratio estimates obtained with the two methods one reason is that the dpoae i o curves show plateaus or dips which result in unexpectedly high compression estimates moderately high correlation was found between the compression threshold estimates obtained with the two methods although dpoae based values were systematically lower than those based on the tmcs both methods confirmed that compression ratio and threshold are approximately constant across the cf range considered cochlear gain could be estimated from tmcs only and it was found to increase slightly with increasing cf it is discussed that dpoae i o curves may be inappropriate to infer precise individual nonlinear cochlear characteristics in normal hearing listeners particularly at low cfs work supported by imserso 131 06 profit cit 390000 2005 4 mec bfu 2006 07536 and the oticon foundation

transverse vibration of an axially accelerating string abstract the transverse vibration of an axially accelerating string is investigated the equation of motion is developed using hamilton s principle the resulting partial differential equations are discretized using galerkin s method assuming the axial velocity to be periodic a stability analysis is performed using floquet theory one two three four six and eight term series approximations are considered in the galerkin s method the one term approximation leads to a mathieu equation the solution of which is well known the numerical results for one term are compared with the analytical solution for the mathieu equation and they are in full agreement the two term approximation leads to gyroscopically coupled equations and the solutions differ significantly from that of the one term approximation whereas the three term approximation solutions look similar to the one term approximation solutions the analysis is carried out for higher order even approximations and the solutions are in qualitative agreement the two and four term approximation solutions are compared with the analytical results from hsu s method and are in reasonable agreement the results show that instabilities occur at much higher amplitudes and frequencies of the periodic axial velocity than that of typical devices such as tape machines and band saws

transition behaviour from string to beam for an axially accelerating material an approximate analytical expression for the natural frequency is given for the problem for velocity profiles harmonically varying about a mean velocity stability borders are determined analytically for fluctuation frequency versus amplitudes beam effects cause the stability boundaries to shift to higher frequency values

sources of distortion product otoacoustic emissions revealed by suppression experiments and inverse fast fourier transforms in normal ears primary and secondary sources combine to produce the 2f1 f2 distortion product otoacoustic emission dpoae measured in the ear canals of humans dpoaes were obtained in nine normal hearing subjects using a fixed f2 paradigm in which f1 was varied the f2 was 2 or 4 khz and absolute and relative primary levels were varied data were obtained with and without a third tone f3 placed 15 6 hz below 2f1 f2 the level of f3 was varied in order to suppress the stimulus frequency otoacoustic emission sfoae coming from the 2f1 f2 place these data were converted from the complex frequency domain into an equivalent time representation using an inverse fast fourier transform ifft iffts of unsuppressed dpoae data were characterized by two or more peaks relative amplitudes of these peaks depended on overall primary level and on primary level differences the suppressor eliminated later peaks but early peaks remained relatively unaltered results are interpreted to mean that the dpoae measured in humans includes components from the f2 place intermodulation distortion and dp place in the form of a sfoae these findings build on previous work by providing evidence that multiple peaks in the ifft are due to a secondary source at the dp place

the effect of stimulus frequency ratio on distortion product otoacoustic emission components a detailed measurement of distortion product otoacoustic emission dpoae fine structure was used to extract estimates of the two major components believed to contribute to the overall dpoae level in the ear canal a fixed ratio paradigm was used to record dpoae fine structure from three normal hearing ears over a range of 400 hz for 12 different stimulus frequency ratios between 1 053 and 1 36 and stimulus levels between 45 and 75 db spl inverse fourier transforms of the amplitude and phase data were filtered to extract the early component from the generator region of maximum stimulus overlap and the later component reflected from the characteristic frequency region of the dpoae after filtering the data were returned to the frequency domain to evaluate the impact of the stimulus frequency ratio and stimulus level on the relative levels of the components although there were significant differences between data from different ears some consistent patterns could be detected the component from the overlap region of the stimulus tones exhibits a bandpass shape with the maximum occurring at a ratio of 1 2 the mean data from the dpoae characteristic frequency region also exhibits a bandpass shape but is less sharply tuned and exhibits greater variety across ears and stimulus levels the component from the dpoae characteristic frequency region is dominant at ratios narrower than approximately 1 1 the transition varies between ears the relative levels of the two components are highly variable at ratios greater than 1 3 and highly dependent on the stimulus level the reflection component is larger at all ratios at the lowest stimulus level tested 45 45 db spl we discuss the factors shaping dpoae component behavior and some cursory implications for the choice of stimulus parameters to be used in clinical protocols

interrelations among distortion product phase gradient delays their connection to scaling symmetry and its breaking distortion product otoacoustic emission dpoae phase versus frequency functions and corresponding phase gradient delays have received considerable attention because of their potential for providing information about mechanisms of emission generation cochlear wave latencies and characteristics of cochlear tuning the three measurement paradigms in common use fixed f1 fixed f2 and fixed f2 f1 yield significantly different delays suggesting that they depend on qualitatively different aspects of cochlear mechanics in this paper theory and experiment are combined to demonstrate that simple phenomenological arguments which make no detailed mechanistic assumptions concerning the underlying cochlear mechanics predict relationships among the delays that are in good quantitative agreement with experimental data obtained in guinea pigs to understand deviations between the simple theory and experiment a general equation is found that relates the three delays for any deterministic model of dpoae generation both model independent and exact the general relation provides a powerful consistency check on the measurements and a useful tool for organizing and understanding the structure in dpoae phase data e g for interpreting the relative magnitudes and intensity dependencies of the three delays analysis of the general relation demonstrates that the success of the simple phenomenological approach can be understood as a consequence of the mechanisms of emission generation and the approximate local scaling symmetry of cochlear mechanics the general relation is used to quantify deviations from scaling manifest in the measured phase gradient delays the results indicate that deviations from scaling are typically small and that both linear and nonlinear mechanisms contribute significantly to these deviations intensity dependent mechanisms contributing to deviations from scaling include cochlear reflection and wave interference effects associated with the mixing of distortion and reflection source emissions as in dpoae fine structure finally the ratio of the fixed f1 and fixed f2 phase gradient delays is shown to follow from the choice of experimental paradigm and in the scaling limit contains no information about cochlear physiology whatsoever these results cast considerable doubt on the theoretical basis of recent attempts to use relative dpoae phase gradient delays to estimate the bandwidths of peripheral auditory filters

evidence for the distortion product frequency place as a source of distortion product otoacoustic emission dpoae fine structure in humans ii fine structure for different shapes of cochlear hearing loss distortion product otoacoustic emissions dpoae were recorded from eight human subjects with mild to moderate cochlear hearing loss using a frequency spacing of 48 primary pairs per octave and at a level l1 l2 60 dbspl and with a fixed ratio f2 f1 subjects with different shapes of hearing thresholds were selected they included subjects with near normal hearing within only a limited frequency range subjects with a notch in the audiogram and subjects with a mild to moderate high frequency loss if the primaries were located in a region of normal or near normal hearing but dp frequencies were located in a region of raised thresholds the distortion product 2 f1 f2 was still observable but the dp fine structure disappeared if the dp frequencies fell into a region of normal thresholds fine structure was preserved as long as dpoae were generated even in cases of mild hearing loss in the region of the primaries these experimental results give further strong evidence that in addition to the initial s

sources of dpoaes revealed by suppression experiments inverse fast fourier transforms and sfoaes in impaired ears dpoae sources are modeled by intermodulation distortion generated near the f2 place and a reflection of this distortion near the dp place in a previous paper inverse fast fourier transforms iffts of dpoae filter functions in normal ears were consistent with this model konrad martin et al j acoust soc am 109 2862 2879 2001 in the present article similar measurements were made in ears with specific hearing loss configurations it was hypothesized that hearing loss at f2 or dp frequencies would influence the relative contributions to the dpoae from the corresponding basilar membrane places and would affect the relative magnitudes of sfoaes at frequencies equal to f2 and fdp dpoaes were measured with f2 4 khz f1 varied and a suppressor near fdp l2 was 25 55 db spl l1 l2 10 db sfoaes were measured at f2 and at 2 7 khz the average fdp produced by the f1 sweep for stimulus levels of 20 60 db spl sfoae results supported predictions of the pattern of amplitude differences between sfoaes

bandwidth efficient quadrature overlapped squared raised cosine modulation this correspondence describes staggered quadrature overlapped squared raised cosine qosrc modulation the power spectrum of qosrc attains good spectral characteristics over a bandpass hardlimited channel compared to quadrature overlapped raised cosine qorc modulation because of less fluctuation of the signal envelope it is found that qosrc has better bit error probability performance than qorc

fine structure of hearing threshold and loudness perception hearing thresholds measured with high frequency resolution show a quasiperiodic change in level called threshold fine structure or microstructure the effect of this fine structure on loudness perception over a range of stimulus levels was investigated in 12 subjects three different approaches were used individual hearing thresholds and equal loudness contours were measured in eight subjects using loudness matching paradigms in addition the loudness growth of sinusoids was observed at frequencies associated with individual minima or maxima in the hearing threshold from five subjects using a loudness matching paradigm at low levels loudness growth depended on the position of the test or reference tone frequency within the threshold fine structure the slope of loudness growth differs by 0 2 db db when an identical test tone is compared with two different reference tones i e a difference in loudness growth of 2 db per 10 db change in stimulus finally loudness growth was measured for the same f

distortion product otoacoustic emission fine structure analysis of 50 normal hearing humans when distortion product otoacoustic emissions dpoaes are measured with a high frequency resolution the dpoae shows quasi periodic variations across frequency called dpoae fine structure in this study the dpoae fine structure is determined for 50 normal hearing humans using fixed primary levels of l1 l2 65 45db an algorithm is developed which characterizes the fine structure ripples in terms of three parameters ripple spacing ripple height and ripple prevalence the characteristic patterns of fine structure can be found in the dpoae of all subjects though the dpoae fine structure characteristics are individual and vary from subject to subject on average the ripple spacing decreases with increasing frequency from 18 oct at 1khz to 332 oct at 5khz the ripple prevalence is two to three ripples per 13 oct and ripple heights of up to 32db could be detected the 50 normal hearing subjects were divided into two groups the subjects of group a having slightly better hearing levels than subjects of gr

new modulation techniques for low cost power and bandwidth efficient satellite earth stations new power and bandwidth efficient modulation techniques named intersymbol interference and jitter free ijf qpsk and ijf oqpsk are presented the properties of the ijf qpsk and ijf oqpsk signals in linear and nonlinear earth station satellite systems are studied a finite state markov chain model is used to calculate power spectra of hard limited ijf qpsk and ijf oqpsk the model provides insights into the spectral spreading action of the ideal hard limiter on the ijf qpsk and ijf oqpsk signals experimental simulation and theoretical results are in good agreement the results indicate that the ijf oqpsk modulated signal exhibits much less spectrum spreading than qpsk oqpsk and msk the error probability p e performance of ijf qpsk and ijfoqpsk in an additive white gaussian noise and adjacent channel interference environment is evaluated the results show that the p e performance of the ijf oqpsk is superior to that of qpsk oqpsk and msk in narrow band nonlinear channels