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In this paper, the averages annual radon concentrations in buildings placed in a karst area are analyzed in order to understand which factors may affect the occurrence of high levels of radon indoor. Statistical analysis on the radon dataset is performed using analytical factors described by two or three levels according to the characteristic of the measured buildings. The factors that determine higher radon levels in terms of arithmetic mean (AM) at ground floor (GF) are mainly the presence of sedimentary calcareous rock (SCR) in walls and the direct attack or crawl space as type of foundation. At first floors (FF), the presence of walls of only SCR showed radon levels higher (in terms of AM) than the one found for walls of mixed typology. These outcomes suggest that in karstic area buildings with SCR as the main construction material and direct attack or crawl space as the type of foundation, can be considered as radon-prone buildings. Moreover, this study confirms the need to measure radon levels not only at below ground floor and at GF, but also at FF and above for buildings in karst areas with construction materials including SCR blocks. [ABSTRACT FROM AUTHOR]

BACKGROUND: The evaluation of how air rarefaction can affect a loudspeaker performance at altitude implies the need for characterization of earphones during hypobaric conditions. The aim of this study was phonometric analysis at different altitudes of the acoustic output of a widely used earphone model, along with its consequences on audiological investigations conducted under such environmental conditions. METHODS: The transfer function of a TDH-39P earphone was analyzed with an artificial ear under nine different altitude levels, from sea level up to 35,000 ft, inside a hypobaric chamber. A specific phonometric system not sensitive to environmental pressure changes was used. Other potentially confounding factors, such as environmental temperature and humidity, were continuously monitored. RESULTS: No relevant temperature or humidity changes were detected. The sound pressure level generated by the earphone under hypobaric conditions was found considerably affected by air density changes. These data produced a correction table aiming at recalibrating the earphone's output at each audiometric octave test frequency within the 250-8000 Hz range. Quite different characteristics of response were observed at different audiometric frequencies. Such findings were particularly evident for altitudes exceeding 12,000 ft. DISCUSSION: The development of a frequency-selective and altitude-related correction factor for acoustic stimuli is an essential aspect when hearing threshold measurements in hypobaric environments are performed. [ABSTRACT FROM AUTHOR]

In this study, a systematic analysis of the dependence on stimulus level and primary frequency ratio r of the different components of human distortion product otoacoustic emissions has been performed, to check the validity of theoretical models of their generation, as regards the localization of the sources and the relative weight of distortion and reflection generation mechanisms. 2f1 - f2 and 2f2 - f1 distortion product otoacoustic emissions of 12 normal hearing ears from six human subjects have been measured at four different levels, in the range [35, 65] dB sound pressure level, at eight different ratios, in the range [1.1, 1.45]. Time-frequency filtering was used to separate distortion and reflection components. Numerical simulations have also been performed using an active nonlinear cochlear model. Both in the experiment and in the simulations, the behavior of the 2f1 - f2 distortion and reflection components was in agreement with previous measurements and with the predictions of the two-source model. The 2f2 - f1 response showed a rotating-phase component only, whose behavior was in general agreement with that predicted for a component generated and reflected within a region basal to the characteristic place of frequency 2f2 - f1, although alternative interpretations, which are also discussed, cannot be ruled out. [ABSTRACT FROM AUTHOR]

Time-domain numerical solutions of a nonlinear active cochlear model forced by click stimuli are analyzed with a time-frequency wavelet technique to identify the components of the otoacoustic response associated with different generation mechanisms/places. Previous experimental studies have shown evidence for the presence of at least two components in the transient otoacoustic response: A long-latency response, growing compressively with increasing stimulus level, and a shorter-latency response, characterized by faster growth. The possible mechanisms for the generation of the two components are discussed using the results of the numerical simulations. The model is a one-dimensional (1-D) transmission line model with nonlinear and nonlocal active terms representing the anti-damping action of the 'cochlear amplifier.' The dependence on the stimulus level of latency and level was measured for the different components of the response. The generation mechanisms/places of the different components were identified by varying the stimulus level and by turning off the cochlear roughness in well-defined cochlear regions. The results suggest that reflections from roughness coming from basal regions of the cochlea may give a relevant contribution to the early otoacoustic response, whereas nonlinear mechanisms seem to produce a much smaller additional contribution. [ABSTRACT FROM AUTHOR]

This study focuses on the theoretical prediction and experimental evaluation of the latency of transient-evoked otoacoustic emissions. Response components with different delay have been identified in several studies. The main generator of the transient response is assumed to be coherent reflection from cochlear roughness near the resonant place. Additional components of different latency can be generated by different mechanisms. Experimental data are re-analyzed in this study to evaluate the dependence of the latency on stimulus level, for each component of the response, showing that previous estimates of the otoacoustic emission latency were affected by systematic errors. The latency of the emission from each generator changes very little with stimulus level, whereas their different growth rate causes sharp changes of the single-valued latency, estimated as the time of the absolute maximum of the bandpass filtered response. Results of passive linear models, in which gain and bandwidth of the cochlear amplifier are strictly related, are incompatible with the observations. Although active linear models including delayed stiffness terms do predict much slower dependence of latency on the stimulus level, a suitable nonlinear model should be designed, capable of decoupling more effectively the dependence on stimulus level of amplitude and phase of the otoacoustic response. [ABSTRACT FROM AUTHOR]

This study explores the phenomenology of distortion products in nonlinear cochlear models, predicting their amplitude and phase along the basilar membrane. The existence of a backward-traveling wave at the distortion-product frequency, which has been recently questioned by experiments measuring the phase of basilar-membrane vibration, is discussed. The effect of different modeling choices is analyzed, including feed-forward asymmetry, micromechanical roughness, and breaking of scaling symmetry. The experimentally observed negative slope of basilar-membrane phase is predicted by numerical simulations of nonlinear cochlear models under a wide range of parameters and modeling choices. In active models, positive phase slopes are predicted by the quasi-linear analytical computations and by the fully nonlinear numerical simulations only if the distortion-product sources are localized apical to the observation point and if the stapes reflectivity is unrealistically small. The results of this study predict a negative phase slope whenever the source is distributed over a reasonably wide cochlear region and/or a reasonably high stapes reflectivity is assumed. Therefore, the above-mentioned experiments do not contradict 'classical' models of cochlear mechanics and of distortion-product generation. [ABSTRACT FROM AUTHOR]

The state-space formalism [Elliott S. J., et al. (2007). J. Acoust. Soc. Am. 122, 2759–2771] allows one to discretize cochlear models in a straightforward matrix form and to modify the main physical properties of the cochlear model by changing the position and functional form of a few matrix elements. Feed-forward and feed-backward properties can be obtained by simply introducing off-diagonal terms in the matrixes expressing the coupling between the dynamical variables and the additional active pressure on the basilar membrane. Some theoretical issues related to different cochlear modeling choices, their implementation in a state-space scheme, and their physical consequences on the cochlear phenomenology, as predicted by numerical simulations, are discussed. Different schematizations of the active term describing the behavior of the outer hair cell’s feedback mechanism, including nonlinear and nonlocal dependences on either pressure or basilar membrane displacement, are also discussed, showing their effect on some measurable cochlear properties. [ABSTRACT FROM AUTHOR]

In the framework of a collaboration between INAIL and University of Salento, an indoor radon survey in 54 buildings belonging to the UniSalento University (Southeast Italy) was carried out. The monitored buildings differ by type, construction period, materials, etc., and are located in an area with a morphology characterized mainly by marls, calcareous marls, and calcarenites (karst area). The sample of the survey includes 963 rooms at different floors: it consists in rooms mainly located at ground floor (67%), first floor (12%), and below ground (12%). SSNTD passive dosimeters measured the average radon activity concentration for two consecutive semesters (spring/summer and autumn/winter) from which annual radon averages were estimated for each room. The spatial variability within buildings was investigated in terms of variation between floors and among rooms at the same floor. Data analysis provides evidence that the distributions (in terms of arithmetic mean, standard deviation, median, and geometric mean) of indoor radon annual averages at ground floor and at first floor within building are very similar. This highlights that the karstic characteristics of soil and building materials affect radon levels not only below ground and at ground floor, but also at first floor. Moreover, to evaluate the spatial variability of radon among buildings or floors, the analysis of the distribution of coefficient of variation (CV) was carried out: the results show a low spatial variability with median and average values of CVs ≤ 30% both for the whole building and at different floor levels. [ABSTRACT FROM AUTHOR]