A Study on Improving Characteristics of AlGaNGaN HEMTs by Reducing Self-Heating Effect

학위논문(석사) --서울대학교 대학원 :전기. 컴퓨터공학부,2010.2.Maste

Correlations between Acoustic Properties and Bone Density in Bovine Cacellous Bone

Correlations between acoustic properties and bone density are investigated in bovine cancellous bone. Speed of sound (SOS), broadband ultrasonic attenuation (BUA), and broadband ultrasonic reflection (BUR) are measured in ten defatted bovine cancellous bone specimens in vitro. SOS shows a significant correlation with apparent density. A comparable correlation is observed between BUA and apparent density. BUR is rather highly correlated with apparent density. The linear combinations of all three ultrasonic parameters in a multiple regression model lead to a significant improvement in predicting apparent density. These results suggest that BUR can be useful as an alternative diagnostic parameter of osteoporosis.2

자이로 지원 블러 커널 생성을 위한 마이크로볼로미터 메커니즘 해석 및 그 응용

학위논문(박사) - 한국과학기술원 : 전기및전자공학부, 2024.2,[vi, 97 p. :]Various types of motion blur are frequently observed in the images captured by sensors based on thermal and photon detectors. The difference in mechanisms between thermal and photon detectors directly results in different patterns of motion blur. Motivated by this observation, we propose a novel method to synthesize blurry images from sharp images by analyzing the mechanisms of the thermal detector. Further, we propose a novel blur kernel rendering method, which combines our proposed motion blur model with the inertial sensor in the thermal image domain. The accuracy of the blur kernel rendering method is evaluated by the task of thermal image deblurring. We construct a synthetic blurry image dataset based on acquired thermal images using an infrared camera for evaluation. This dataset is the first blurry thermal image dataset with ground-truth images in the thermal image domain. Qualitative and quantitative experiments are extensively carried out on our dataset, which shows that our proposed method outperforms state-of-the-art methods. Furthermore, we applied the gyro-aided blur kernel rendering method to the object tracking. We propose a novel gyro-based tracking assistant designed to excel in aerial environments, where the use of drones equipped with infrared cameras is expanding rapidly. Our proposed method comprises two sub-modules. First, the search region prediction module independently estimates the search region position for the current frame using only gyroscope sensor data. The prediction module estimates the displacement of the search area location between adjacent frames due to camera motion using the homography transform. Second, the search region deblurring module renders a blur kernel using only gyroscope sensor data. The deblurring module introduces an approach that models an infrared sensor mechanism and merges this model with the homography transform to synthesize the blur kernel. The rendered blur kernel is used to deblur the search region with a deconvolution algorithm. To quantitatively evaluate our proposed method, we constructed a dataset ourselves. We collected and synchronized gyroscope sensor data and infrared images in a configuration similar to a drone environment. Our dataset comprises 15 sequences and two classes, with camera motion effects encompassing six distinct steps. Our experiments were structured into two main categories. First, we analyzed the degradation in tracking performance caused by camera motion. This analysis revealed that displacement has a more significant impact on tracking performance than motion blur. Second, we evaluated the effectiveness of our gyro-based tracking assistant. Through extensive quantitative experiments, we demonstrated that our integrated tracker outperforms the use of state-of-the-art trackers alone.한국과학기술원 :전기및전자공학부

Correlations Among Speed of Sound, Broadband Ultrasonic Attenuation, Broadband Ultrasonic Reflection, and Bone Density in Bovine Cancellous Bone

Correlations between acoustic properties and bone density have been investigated in bovine cancellous bone. Speed of sound (SOS), broadband ultrasonic attenuation (BUA), and broadband ultrasonic reflection (BUR) were measured in 10 defatted bovine cancellous bone specimens in vitro. SOS showed a significant correlation with the apparent density of the bone. A comparable correlation was observed between BUA and the apparent density. BUR was rather highly correlated with the apparent density. It was shown that BUR had a weak correlation with BUA and a significant correlation with SOS. This indicates that the parameter BUR can provide important information that may not be contained in BUA and SOS and, therefore, can be useful as an alternative diagnostic parameter of osteoporosis. As expected, a linear combination of all three ultrasonic parameters in a multiple regression model resulted in a significant improvement in predicting the apparent bone density.22Nkc

Generation of subharmonic and difference frequency acoustic waves in a water-saturated sandy sediment

Generation of subharmonic and difference frequency acoustic waves in a water-saturated sandy sediment was investigated. Subharmonic frequency acoustic wave was observed to be generated due to the nonlinearity of water-saturated sandy sediment when the fundamental frequency acoustic wave exceeded a certain threshold pressure amplitude. Pressure spectrum level of the subharmonic frequency acoustic wave linearly increased as the driving acoustic pressure amplitude increased. The pressure level was 10 dB higher than the background noise level. Generation of the difference frequency acoustic wave was also observed by the collinear acoustic waves with two different fundamental frequencies. The pressure level of the difference frequency acoustic wave was 5 dB higher than the background noise level. It seems very useful to evaluate the nonlinear parameter of water-saturated sandy sediment without disturbing the sediment. Such nonlinear acoustic responses of water-saturated sandy sediment can be utilized for the diagnosis of marine gassy sandy sediment.1

Comparative Study of Acoustic Iterative Inverse Method for Bubble Sizing in Water

Comparative study was carried out for an acoustic iterative inverse method to estimate bubble size distributions in water was carried out. Conventional bubble sizing methods consider only sound attenuation for sizing. Choi and Yoon[IEEE, 26(1), 125-130 (2001)] reported an acoustic iterative inverse method, which extracts the sound speed component from the measured sound attenuation. It can more accurately estimate the bubble size distributions in water than the conventional methods. The estimation results of acoustic iterative inverse method were compared with other experimental data. The experimental data show good agreement with the estimation from the acoustic iterative inverse method. This iterative technique can be utilized for bubble sizing in the ocean.1

Estimation of bubble density with subharmonic acoustic wave in bubbly water

Bubble density was estimated with a subharmonic acoustic wave generatedin bubbly water. The subharmonic acoustic wave can be easilygenerated due to the nonlinearity of bubbly water if the frequency ofprimary acoustic wave is double of the bubble resonance frequency andthe driving acoustic pressure amplitude exceeds a certain threshold value.The frequency of primary acoustic wave was varied from 200 kHz to 500kHz while the bubble resonance radius at subharmonic frequency wasfrom 12 um to 28 um. The pressure level of the subharmonic acousticwave linearly increased as the driving acoustic pressure amplitude increased.With the subharmonic pressure level, the bubble density was estimatedfrom nonlinear bubble oscillation equation Yu. A. Ilinskii and E. A. Zabolotskaya, J. Acoust. Soc. Am. 92, 2837–2841 1992 . The estimatedbubble densities were also compared with those from a linear conventionalacoustic bubble sizing method. Bubble sizing with subharmonicacoustic wave seems to be easily utilized for the diagnosis of sandy sedimentwith bubbles.1

Acoustic Characteristics of Subharmonics Generated from Water-Saturated Sandy Sediment

Nonlinear acoustic characteristics of sediments are veryimportant to understand nonlinear phenomena of marine gassysediments. Acoustic characteristics of subharmonics generatedfrom water-saturated sandy sediment were investigated. Whena harmonic sound wave with high-amplitude was incident onthe water-saturated sandy sediment, subharmonic componentsof incident wave were generated due to nonlinearity of water-saturatedsandy sediment. The level of generated firstsubharmonic sound wave was about 23 dB greater than thebackground noise level at fundamental frequency withmaximum incident pressure. The level of subharmonic soundwaves was dependent on the amplitude of the harmonics aswell as of the fundamental.2

Nonlinear Scattering of Difference Frequency Acoustic Wave in Water-Saturated Sandy Sediment

Nonlinear scattering of difference frequency acoustic wave in a water-saturated sandy sediment was investigated. Difference frequency acoustic wave was observed to be scattered due to the nonlinearity of water-saturated sandy sediment when the collinear acoustic waves with two different fundamental frequencies are incident on the sediment. The pressure level of the difference frequency acoustic wave was 6 dB higher than the background noise level. It seems very useful to evaluate the nonlinear parameter of water-saturated sandy sediment without disturbing the sediment. Such nonlinear acoustic response of water-saturated sandy sediment can be used as background acoustic data for estimating the gas void fraction in marine gassy sandy sediment.2