Normal voice is characterized by periodic oscillations of the vocal folds. On the other hand, disordered voice dynamics (e.g., subharmonic and aperiodic oscillations) are often associated with voice pathologies and dysphonia. Unfortunately, not all investigations may be conducted on human subjects; hence animal laryngeal studies have been performed for many years to better understand human phonation. The rabbit larynx has been shown to be a potential model of the human larynx. Despite this fact, only a few studies regarding the phonatory parameters of rabbit larynges have been performed. Further, to the best of our knowledge, no ex vivo study has systematically investigated phonatory parameters from high-speed, audio and subglottal pressure data with irregular oscillations. To remedy this, the present study analyzes experiments with sustained phonation in 11 ex vivo rabbit larynges for 51 conditions of disordered vocal fold dynamics. (1) The results of this study support previous findings on non-disordered data, that the stronger the glottal closure insufficiency is during phonation, the worse the phonatory characteristics are; (2) aperiodic oscillations showed worse phonatory results than subharmonic oscillations; (3) in the presence of both types of irregular vibrations, the voice quality (i.e., cepstral peak prominence) of the audio and subglottal signal greatly deteriorated compared to normal/periodic vibrations. In summary, our results suggest that the presence of both types of irregular vibration have a major impact on voice quality and should be considered along with glottal closure measures in medical diagnosis and treatment.
In previous work, quantitative measurement of the medial surface dynamics of the vocal folds was reported using a hemilarynx methodology. The technique was applied to excised larynges from both humans and canines, as well as to in vivo canine larynges. In the present investigation, a vocal tract was attached to the excised hemilarynx preparation, and systematic changes were made in vocal tract shape to study its influence on the medial surface dynamics. In particular, the width of the epilarynx was varied across experiments. Previously, in a similar experiment, phonation threshold pressure was investigated as a function of epilarynx width. It has also been shown that epilarynx width has an influence on glottal volume velocity and the acoustic output [I. R. Titze and B. H. Story, J. Acoust. Soc. Am. 101, 2234–2243]. However, the direct influence of the epilarynx width on vocal fold vibration has never been quantified. The present investigation considered the impact of epilarynx width on the medial surface dynamics, including the underlying empirical eigenfunctions which make up the vibration patterns. Further, quantitative measures such as displacement and velocity were reported and compared. [Work supported by NIH/NIDCD Grant No. R01 DC03072.]
This study presents a linear stability analysis of a two-dimensional aeroelastic model of phonation, which incorporates the interaction between the glottal flow and the vocal folds. The model consists of a wall constriction (shaped by the medial surface of vocal the folds), which is situated in a rigid pipe with an applied potential flow. The vocal-fold constriction is modeled as a plane-strain linear elastic layer. An eigenvalue problem is formulated and the eigenvalues of the coupled system and the eigenshape of the vocal fold surface are calculated. Both linear divergence and flutter instabilities are possible. Phonation onset frequency and pressure are investigated as a function of glottal channel width, vocal fold geometry, and vocal fold material properties. Based on aeroelasticity theory, this model allows the prediction of the effects of changing geometric and viscoelastic properties of the vocal folds on phonation onset.
This paper presents two calculations of the free-neutron lifetime. The calculations reflect two distinct physical viewpoints, and both are in exact agreement with each other, and within reported significant figures, in exact agreement with the NIST Beam Experiment measurement of the neutron lifetime (887.7 (+/- 3.1) seconds (615.3 second half-life)). Both calculations are a priori requiring no arbitrary parameters. CODATA 2018 values used for physical constants. Currently the 'beam' method and the 'magnetic bottle/trap' method are the two primary experiments for determining neutron lifetime. Given the error bands, the results of the experiments are not in agreement. It is considered a significant objective to bring the measurements into agreement or provide a theoretical explanation of why they are different. This paper presents results of two calculations based on different physical origins.The half-life result of both calculations are in exact agreement with the 'beam' experiment.
Isomorphic substitution of Rh at varying levels on the B site of lanthanum zirconate pyrochlore (La2Zr2O7; designated LZ) resulted in the formation of thermally stable catalysts suitable for fuel reforming reactions operating at 900 °C. Three specific catalysts are reported here: (a) unsubstituted lanthanum zirconate (LZ), (b) LZ with 2 wt% substituted Rh (L2RhZ), and (c) LZ with 5 wt% substituted Rh (L5RhZ). These catalysts were characterized by XRD, XPS, and H2-TPR. XRD of the fresh, calcined catalysts showed the formation of the pyrochlore phase (La2Zr2O7) in all three materials. In L5RhZ, the relatively high level of Rh substitution led to the formation of LaRhO3 perovskite phase which was not observed in the L2RhZ and LZ pyrochlores. TPR results show that the L5RhZ consumed 1.57 mg H2/gcat, which is much greater than the 0.508 H2/gcat and 0.155 mg H2/gcat for L2RhZ and LZ, respectively, suggesting that the reducibility of the pyrochlore structure increases with increasing Rh-substitution. DRM was studied on these three catalysts at three different temperatures of 550, 575, and 600 °C. The results showed that CH4 and CO2 conversion was significantly greater for L5RhZ compared to L2RhZ and no activity was observed for LZ, suggesting that the surface Rh sites are required for the DRM reaction. Temperature programmed surface reaction showed that L5RhZ had light-off temperature 80 °C lower than L2RhZ. The spent catalysts after runs at each temperature were characterized by temperature programmed oxidation (TPO) followed by temperature programmed reduction and XRD. The TPO results showed that the amount of carbon formed over L5RhZ is almost half of that formed on L2RhZ.
With the Falck fluorescent histochemical method for catecholamines, the development of sympathetic nerve fibers in the brown fat of the rat was studied. At birth a low level of catecholamine fluorescence was found in preterminal axon bundles, which have been called here sheathed axons. The fluorescence in these bundles reached a maximum at about 5 days of age. Parenchymal nerve catecholamine fluorescence was discernible at 2 to 3 days of age. These nerves progressively got brighter until adult levels had been reached at about 10–15 days. The sympathetic nerve fiber network seen on arterial blood vessels in the adult was not seen in the young rat until 8–10 days of age. These blood vessel nerves reached maturity at about 15–21 days. The parenchymal nerve innervation was shown to originate in the sympathetic chain. The sympathetic chain gave off sheathed axon bundles which reach the parenchyma by passing along septa or beside blood vessels.
Physical mechanisms of regular and irregular vocal fold vibration were first studied using a computational model of vocal fold vibration. Later physical mechanisms of vocal fold vibration were studied in laboratory hemilarynx studies, where the medial surface of the vocal folds were imaged. While the method was also extended to clinical studies of vocal vibration, the method exhibited significantly less interpretive power in the clinical applications in which the superior surface of the vocal folds was imaged in 2D. Our hypothesis is that the interpretive power of the method of empirical eigenfunctions in studying the superior surface dynamics of the vocal folds will be significantly increased if one performs 3D imaging of the dynamics versus the standard 2D imaging. To test this hypothesis, the method of empirical eigenfunctions was employed on the same finite element model used in previous computational experiments. Our results confirm the hypothesis that the interpretive power of the method of empirical eigenfunctions was significantly increased in studying the superior surface dynamics of the vocal folds when 3D imaging was employed.
