Understanding and Mimicking the Fly's Directional Hearing: Modeling, Sensor Development, and Experimental Studies

Microphone arrays have been widely used in sound source localization for many applications. In order to locate the sound in a discernible manner, the separation between microphones needs to be greater than a critical distance, which poses a fundamental constraint for the miniaturization of directional microphones. In nature, animal hearing organs are also governed by the size constraint; the smaller the organ size, the smaller the available directional cues for directional hearing. However, with an auditory organ separation of only 520 µm, the fly Ormia ochracea is found to exhibit remarkable ability to pinpoint its host cricket at 5 kHz. The key to this fly's phenomenal directional hearing ability is believed to be the mechanical coupling between the eardrums. This innovative solution can inspire one to find alternative approaches to tackle the challenge of developing miniature directional microphones. The overall goal of this dissertation work is to unravel the underlying physics of the fly ear hearing mechanisms, and to apply this understanding to develop and study novel bio-inspired miniature directional microphones. First, through mechanics and optimization analysis, a fundamental biological conclusion is reached: the fly ear can be viewed as a nature-designed optimal structure that is endowed with the dual optimality characteristic of maximum average directional sensitivity and minimum nonlinearity, at its working frequency of 5 kHz. It is shown that this dual optimality characteristic is only achievable when the right mechanical coupling between the eardrums is used (i.e., proper contributions from both rocking and bending modes are used). More importantly, it is further revealed that the dual optimality characteristic of the fly ear is replicable in a synthetic device, whose structural parameters can be tailored to work at any chosen frequency. Next, a novel bio-inspired directional microphone with mechanically coupled diaphragms is designed to capture the essential dynamics of the fly ear. To study the performance of this design, a novel continuum mechanics model is developed, which features two coupling modules, one for the mechanical coupling of the two diaphragms through a beam and the other for each diaphragm coupled through an air gap. Parametric studies are carried out to explore how the key normalized parameters affect the performance of this directional microphone. Finally, this mechanics model is used to guide the development of a large-scale microphone and a fly-ear sized microphone, both of which are experimentally studied by using a low-coherence fiber optic interferometric detection system. With the large-scale sensor, the importance of using proper contribution from both rocking and bending modes is validated. The fly-ear sized sensor is demonstrated to achieve the dual optimality characteristic at 8 kHz with a ten-fold amplification in the directional sensitivity, which is equivalent to that obtainable from a conventional microphone pair that is ten times larger in size. To best use this sensor for sound source localization, a robotic platform with a control scheme inspired by the fly's localization/lateralization scheme is developed, with which a localization accuracy of better than ±2 degrees (the same as the fly ear) is demonstrated in an indoor lab environment. This dissertation work provides a quantitative and mechanistic explanation for the fly's sound localization ability for the first time, and it provides a framework for the development of fly-ear inspired acoustic sensors that will impact many fronts

Functional studies on the extrinsic proteins of Photosystem II

The function of the PsbO and the PsbR protein in Arabidopsis thaliana were studied. The Arabidopsis mutant psbo1 contains a point mutation in the psbO-1 gene leading to defective expression of the PsbO-1 protein. Functional studies demonstrated both the reducing-side and oxidizing-side of Photosystem II are significantly altered. Using the psbo1 mutant plant as a transgenic host, two plant lines were produced, which contained an N-terminally His6-tagged PsbO-1 protein. Photosystem II closure kinetics demonstrated that the defective double reduction of QB and the delayed exchange of QBH2 with the plastoquinone pool in the psbo1 mutant were effectively restored to the wild type levels by the His6-tagged PsbO-1 protein. Flash fluorescence induction analysis indicated that a higher level of the modified PsbO-1 protein was required to increase the ratio of PS IIα to PS IIβ reaction centers to wild type levels. Fluorescence decay kinetics in the absence of DCMU indicated that the His6-tagged PsbO-1 protein restored deficient reducing-side electron transfer, while in the presence of DCMU, charge recombination between QA- and the S2 state of OEC occurred at near wild type rates. Our results indicated that high expression of the His6-tagged PsbO-1 protein efficiently complemented all of the photochemical defects observed in the psbo1 mutant. Additionally, this study established a new method to isolate PS II core complex in higher plants which can be used for biochemical and biophysical analysis. The psbR mutant was screened and characterized. The D2 protein of the Photosystem II complex is reduced in this mutant. Immunological analysis indicated that less than 50% of the PsbP protein is bound to the PS II when compared to wild type. A similar pattern is observed for the PsbQ protein. Impaired electron transport on the reducing side of the photosystem may result from the reduced level of the D2, PsbP and PsbQ components. The transgenic studies demonstrated that most of the defective phenotype of the can be complemented with a C-terminally His6-tagged PsbR protein in the PsbRICH transgenic plant. This is the first report that C-terminus of the PsbR protein is not involved in most photochemical processes in higher plants

Core percolation on complex networks

As a fundamental structural transition in complex networks, core percolation is related to a wide range of important problems. Yet, previous theoretical studies of core percolation have been focusing on the classical Erd\H{o}s-R\'enyi random networks with Poisson degree distribution, which are quite unlike many real-world networks with scale-free or fat-tailed degree distributions. Here we show that core percolation can be analytically studied for complex networks with arbitrary degree distributions. We derive the condition for core percolation and find that purely scale-free networks have no core for any degree exponents. We show that for undirected networks if core percolation occurs then it is always continuous while for directed networks it becomes discontinuous when the in- and out-degree distributions are different. We also apply our theory to real-world directed networks and find, surprisingly, that they often have much larger core sizes as compared to random models. These findings would help us better understand the interesting interplay between the structural and dynamical properties of complex networks.Comment: 17 pages, 6 figure