Neuromagnetic Index of Hemispheric Asymmetry Prognosticating the Outcome of Sudden Hearing Loss

The longitudinal relationship between central plastic changes and clinical presentations of peripheral hearing impairment remains unknown. Previously, we reported a unique plastic pattern of “healthy-side dominance” in acute unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). This study aimed to explore whether such hemispheric asymmetry bears any prognostic relevance to ISSNHL along the disease course. Using magnetoencephalography (MEG), inter-hemispheric differences in peak dipole amplitude and latency of N100m to monaural tones were evaluated in 21 controls and 21 ISSNHL patients at two stages: initial and fixed stage (1 month later). Dynamics/Prognostication of hemispheric asymmetry were assessed by the interplay between hearing level/hearing gain and ipsilateral/contralateral ratio (I/C) of N100m latency and amplitude. Healthy-side dominance of N100m amplitude was observed in ISSNHL initially. The pattern changed with disease process. There is a strong correlation between the hearing level at the fixed stage and initial I/Camplitude on affected-ear stimulation in ISSNHL. The optimal cut-off value with the best prognostication effect for the hearing improvement at the fixed stage was an initial I/Clatency on affected-ear stimulation of 1.34 (between subgroups of complete and partial recovery) and an initial I/Clatency on healthy-ear stimulation of 0.76 (between subgroups of partial and no recovery), respectively. This study suggested that a dynamic process of central auditory plasticity can be induced by peripheral lesions. The hemispheric asymmetry at the initial stage bears an excellent prognostic potential for the treatment outcomes and hearing level at the fixed stage in ISSNHL. Our study demonstrated that such brain signature of central auditory plasticity in terms of both N100m latency and amplitude at defined time can serve as a prognostication predictor for ISSNHL. Further studies are needed to explore the long-term temporal scenario of auditory hemispheric asymmetry and to get better psychoacoustic correlates of pathological hemispheric asymmetry in ISSNHL

Transient energy growth analysis of a thermoacoustic system with distributed mean heat input

Transient growth of flow disturbances has great potential to trigger unwanted thermoacoustic instability. So far transient growth analysis has tended to focus on thermoacoustic systems with acoustically compact heat sources, even though many systems are associated with distributed mean heat input, such as a premixed flame. In this work, transient growth analysis of both choked and open-ended thermoacoustic systems in the presence of a mean flow and a spatially distributed mean heat input is conducted. Unsteady heat release is modeled within the classical time-lag ℵℵ–τ formulation. Both uniform and triangular distributions for the rate of mean heat input are considered. The generation of entropy disturbances with such distributed heat input is studied first. It is shown that the entropy waves generated by the uniform and triangular distributed heat input are increased first and then decreased with increased frequency. This is different from the conventional concentrated heat input, of which the entropy waves produced is frequency-independent. In addition, the entropy eigenmodes are shown to be non-orthogonal. To quantify transient growth of flow disturbances, two energy measures are defined, calculated and compared. One is associated with the conventional acoustical energy. The other is associated with both acoustic and entropy disturbances. It is shown that the maximum transient growth View the MathML sourceGacmax of acoustical energy is in the range of 102–103 in the choked system, while 100 ⩽ View the MathML sourceGacmax ⩽ 101 in the open-ended system. Furthermore, the longer of the uniform distributed heat input, the larger View the MathML sourceGacmax. However, such finding is not observed for the triangular heat input. Further insights are obtained by examining the contribution of eigenmodes in different frequency ranges. It is found that the lower frequency eigenmodes play a dominant role. Finally, the effect of the interaction index ℵℵ on transient growth is examined. It is found that the maximum transient growth of acoustical energy View the MathML sourceGacmax and total energy View the MathML sourceGtotmax are decreased with increased ℵℵ. It is also found that the longer of the uniform distributed heat input, the lower View the MathML sourceGtotmax. These findings are consistent with those obtained in our non-orthogonality and entropy generation analyses

Stability of ultra-thin oxide overgrowths on binary Al–Si alloy substrate

This study presents a thermodynamic formalism to predict the type of ultra-thin oxide overgrowth due to dry, thermal oxidation of bare single-crystalline ⟨AlSi⟩ alloy substrate. The various oxide growth parameters considered in this formulation are Si alloying element content at the alloy/oxide interface, growth temperature, oxide-film thickness (up to 5 nm), and low-index crystallographic surfaces of the alloy substrate. Along with the bulk Gibbs free energies of oxide formation, this developed formalism also considered alloy/oxide interface energies and oxide surface energies. Further for estimating the alloy/oxide interface energies of the crystalline oxide overgrowths, chemical interaction energy and strain energy arising due to the anisotropic growth strain have been taken into account. Similarly, the alloy/oxide interface energies of the amorphous oxides considered contributions arising from chemical interaction, entropy, and enthalpy between the alloy substrate and oxide overgrowth. Overall, the model predicted the stability of amorphous {SiO2} and {Al2O3} at lower and higher oxide-film thicknesses, respectively, followed by phase transformation of amorphous {Al2O3} to γ−⟨Al2O3⟩ on further thickening of the oxide film. Moreover, crystalline ⟨SiO2⟩ was never found to be thermodynamically favorable for the parameters considered in this study. These thermodynamic predictions are found to be in agreement with the experimental findings.by Darshan Ajmera and Emila Pand