Sun-I. Kim

Effects of bridging groups on electronic structures of conjugated cyclic polymers

Summary form only given. Theoretical investigation was performed to elucidate effects of the bridging groups on the band gaps of conjugated cyclic polymers. In addition to poly(para-phenylene) and heterocyclic polymers such as polythiophene, polypyrrole, and polyfuran, the polymers concerned in this study include the conjugated cyclic polymers which contain bridging groups of an XY/sub 2/ form (CH/sub 2/, CF/sub 2/, SiH/sub 2/ and SiF/sub 2/) or an X=Y form (C=CH/sub 2/, C=O and C=S). Geometrical structures of the polymers were optimized through semiempirical band calculations with AM1 Hamiltonians. A modified extended Huckel method was employed to obtain electronic structures of the polymers. Effects of the bridging groups on band gaps of the polymers were analyzed in terms of geometrical relaxations and electronic perturbations.

Objective Evaluation of Beamforming Techniques for Hearing Devices with Two-channel Microphone

Hearing devices like cochlear implant, vibrant soundbridge, etc. try to offer better sound for people. In hearing devices, several beamformers including conventional directional microphone are applicable to noise reduction. Each beamformer has different directional response and it could change sound intelligibility or quality for listeners. Therefore, we investigated the performance of three beamformers, which are first and second order directional microphone, and broadband beamformer(BBF) with a computer simulation assuming hearing device microphone configuration. We also calculated objective measurements which have been used to evaluate speech enhancement algorithms. In the simulation, a single speech and a single babble noisewere propagated from the front and azimuth degrees respectively. Microphones were configured in an end-fire array and the spacing was varied in comparison. With 3 cm spacing, BBF had about 3 dB higher enhanced SNR than that of directional microphones. However, enhancement of segmental SNR and frequency weighted segmental SNR were similar between the first order directional microphone and broadband beamformer. In addition when steady state noise was used, broadband beamformer showed the increased performance and had the highest enhanced SNR, and segmental SNR.

A Study on the Performance of Companding Algorithms for Digital Hearing Aid Users

Companding algorithms have been used to enhance speech recognition in noise for cochlea implant users. The efficiency of using companding for digital hearing aid users is not yet validated. The purpose of this study is to evaluate the performance of the companding for digital hearing aid users in the various hearing loss cases. Using HeLPS, a hearing loss simulator, two different sensorinerual hearing loss conditions were simulated; mild gently sloping hearing loss(HL1) and moderate to steeply sloping hearing loss(HL2). In addition, a non-linear compression was simulated to compensate for hearing loss using national acoustic laboratories-non-linear version 1(NAL-NL1) in HeLPS. In companding, the following four different companding strategies were used changing Q values(q1, q2) of pre-filter(F filter) and post filter(G filter). Firstly, five IEEE sentences which were presented with speech-shaped noise at different SNRs(0, 5, 10, 15 dB) were processed by the companding. Secondly, the processed signals were applied to HeLPS. For comparison, signals which were not processed by companding were also applied to HeLPS. For the processed signals, log-likelihood ratio(LLR) and cepstral distance(CEP) were measured for evaluation of speech quality. Also, fourteen normal hearing listeners performed speech reception threshold(SRT) test for evaluation of speech intelligibility. As a result of this study, the processed signals with the companding and NAL-NL1 have performed better than that with only NAL-NL1 in the sensorineural hearing loss conditions. Moreover, the higher ratio of Q values showed better scores in LLR and CEP. In the SRT test, the processed signals with companding(SRT