The absorbance frequencies of the investigated compounds in fifteen solvents are collected in Table 2.
This pattern of change in absorbance with frequency is similar to previous reports from normal-hearing participants, as shown by the comparison to the data of Shahnaz et al. (2013) (dashed line in the top panel).
where A, σ (cm2), L (cm), N (cm-3), and α (cm-1) are the measured absorbance, the frequency-dependent absorption cross-section, path length, analytic particle density, and the attenuation coefficient, respectively, as illustrated in the absorption cell of Figure 1.
The four metrics were (1) low-frequency phase φlow, (2) absorbance at low frequencies Alow, (3) air-leak-resonance frequency falr, and (4) the ratio of compliance volume to physical volume CV/PV.
Low-frequency admittance phase and CV/PV decreased, while low-frequency absorbance and the air-leak resonance frequency increased.
Based on preliminary measurements, four acoustic measures were selected as potential predictors of air leaks: (1) the admittance phase at low frequencies (φlow), (2) the absorbance at low frequencies (Alow), (3) the ratio of compliance volume to physical volume (CV/PV), and (4) resonant frequency of the air leak (falr).
The presence of an air leak can be reliably detected using low-frequency admittance phase or low-frequency absorbance.
Four acoustic metrics were used for predicting the presence of air leaks and for quantifying these leaks: (1) low-frequency admittance phase (averaged over 0.1 0.2 kHz), (2) low-frequency absorbance, (3) the ratio of compliance volume to physical volume (CV/PV), and (4) the air-leak resonance frequency.
Both frequency- (absorbance and refractive index) and time-domain data are presented.
All models featured a strong high-frequency absorbance in the 1675 1680 cm−1 region, with a weaker band around 1640 cm−1, which appears to be distinct from α-helix (∼1650 1658 cm−1), β-sheet (∼1620 1640 cm−1) and turn structures (∼1670 cm−1) (Barth and Zscherp, 2002).
