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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23675号 / 理博第4765号 / 新制||理||1683(附属図書館) / 京都大学大学院理学研究科数学・数理解析専攻 / (主査)教授 坂上 貴之, 教授 泉 正己, 教授 國府 寛司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The turbulent flow through a 90o pipe bend is complex with secondary flow that can affect pressure drop and heat/mass transfer. The mean and unsteady flow is studied using refractive index matched two-dimensional two-component (2D2C) Particle Image Velocimetry in a single 90o bend with Rc/D = 1.5 and at Re = 34800. The measurements were performed in a closed loop using a 1-inch diameter test section that was machined out of acrylic. The flow is imaged in the symmetric plane parallel to the axial flow and at different cross sectional planes including 0.25D and 1D upstream, 10o, 20o, 70o, 80o from the bend inlet and 0.25D and 1D downstream of the bend. The axial flow accelerates on the inner wall at the inlet and then moves towards the outer wall at 40o-50o. A shear layer is formed between high velocity fluid near the outer wall and the slower moving fluid at the inner wall side in the second half of the bend. The axial turbulent kinetic energy ((u^2 ) ̅+(v^2 ) ̅) is found to be high in regions corresponding to high velocity gradient regions: (i) at the outer wall near the inlet that extends up to the outlet, (ii) near the inner wall at 40o-50o, and (iii) at the shear layer formed near the inner wall. In the cross sectional planes, two vortices are formed and have a maximum strength at 80o from the bend inlet. The cross sectional turbulent kinetic energy ((v^2 ) ̅+(w^2 ) ̅) is found to be highest on the inner wall at the 80o plane. The snapshot Proper Orthogonal Decomposition (POD) technique is used to study the unsteady flow structures within the flow. There are long and short flow structures in the upstream pipe which can be related to Very Large Scale and Large Scale Motions. The secondary flow at 20o and further downstream cross sectional planes show evidence of unsteadiness as two vortices oscillate about the symmetry axis with low frequencies of St ~ 0.07, 0.13 and higher frequency at St ~ 0.3-0.6. The low frequency oscillations can be related to Very Large Scale Motions while high frequency oscillations are related to separation of the flow on the inner wall side. Evidence of swirl switching in the high frequency range (St ~ 0.3-0.5) is found at cross sectional plane 1D downstream. / Thesis / Master of Applied Science (MASc)

The detection and localization of important acoustic events in a complex urban environment, such as gunfire and explosions, is critical to providing effective surveillance of military and civilian areas and installations. In a complex environment, obstacles such as terrain or buildings introduce multipath propagations, reflections, and diffractions which make source localization challenging. This dissertation focuses on the problem of source localization in three-dimensional (3D) realistic urban environments. Two different localization techniques are developed to solve this problem: a) Beamforming using a few microphone phased arrays in conjunction with a high fidelity model and b) Fingerprinting using many dispersed microphones in conjunction with a low fidelity model of the environment. For an effective source localization technique using microphone phased arrays, several candidate beamformers are investigated using 2D and corresponding 3D numerical models. Among them, the most promising beamformers are chosen for further investigation using 3D large models. For realistic validation, localization error of the beamformers is analyzed for different levels of uncorrelated noise in the environment. Multiple-array processing is also considered to improve the overall localization performance. The sensitivity of the beamformers to uncertainties that cannot be easily accounted for (e.g. temperature gradient and unmodeled object) is then investigated. It is observed that evaluation in 3D models is critical to assess correctly the potential of the localization technique. The enhanced minimum variance distortionless response (EMVDR) is identified to be the only beamformer that has super-directivity property (i.e. accurate localization capability) and still robust to uncorrelated noise in the environment. It is also demonstrated that the detrimental effect of uncertainties in the modeling of the environment can be alleviated by incoherent multiple arrays. For efficient source localization technique using dispersed microphones in the environment, acoustic fingerprinting in conjunction with a diffused-based energy model is developed as an alternative to the beamforming technique. This approach is much simpler requiring only microphones rather than arrays. Moreover, it does not require an accurate modeling of the acoustic environment. The approach is validated using the 3D large models. The relationship between the localization accuracy and the number of dispersed microphones is investigated. The effect of the accuracy of the model is also addressed. The results show a progressive improvement in the source localization capabilities as the number of microphones increases. Moreover, it is shown that the fingerprints do not need to be very accurate for successful localization if enough microphones are dispersed in the environment. / Ph. D.

Wireless sensor networks and data fusion has received increasing attention in recent years, due to the ever increasing computational power, battery and wireless technology, and proliferation of sensor modalities. Notably, the application of acoustic sensors and arrays of sensors has expanded to encompass surveillance, teleconferencing, and sound source localization in adverse environments. The ability to passively locate and track acoustic sources, be they gunfire, animals, or geological events, is crucial to a wide range of applications. The challenge addressed herein is how to best utilize the massive amount of data collected from spatially distributed sensors. Localization in two acoustic propagation scenarios is addressed: the free-field assumption and the general case. In both cases, it is found that performance is highly dependent on the array-source geometry which in turn drives the design of localization strategies. First, the general surveillance problem including signal detection, classification, data association, localization and tracking is studied. Signal detectors are designed with a focus on robustness and capacity for real time implementation. Specifics of the data association problem relevant to acoustic measurements are addressed. Assuming free-field propagation, a localization algorithm is developed to harness some of the vast potential and robust nature of a sensor networks. In addition, a prototypical sensor network has been constructed to accompany the theoretical development, address real world situations, and demonstrate applicability. Experimental results obtained confirm the practicality of theoretical models, support numerical results, and illustrate the effectiveness of the proposed strategies and the system as a whole. In many situations of interest, obstacles to wave propagation such as terrain or buildings exist that provide unique challenges to localization. These obstacles introduce multiple paths, diffraction, and scattering into the propagation. The second part of this dissertation investigates localization in the general propagation scenario of a multi-wave, semi-reverberant environment characteristic of urban areas. Matched field processing is introduced as a feasible method and found to offer superior performance and flexibility over time reversal techniques. The effects of uncertainty in model parameters are studied in an urban setting. Multiarray processing methods are developed and strategies to mitigate the effects of model mismatch are established. / Ph. D.

In public health, biomedical, epidemiological, and other applications, data collected are often measured with error. When mismeasured data is used in a regression analysis, not accounting for the measurement error can lead to incorrect inference about the relationships between the covariates and the response. We investigate measurement error in the covariates of two types of regression models.  For each we propose a fully Bayesian approach that treats the variable measured with error as a latent variable to be integrated over, and a semi-Bayesian approach which uses a first order Laplace approximation to marginalize the variable measured with error out of the likelihood. The first model is the matched case-control study for analyzing clustered binary outcomes. We develop low-rank thin plate splines for the case where a variable measured with error has an unknown, nonlinear relationship with the response. In addition to the semi- and fully Bayesian approaches, we propose another using expectation-maximization to detect both parametric and nonparametric relationships between the covariates and the binary outcome. We assess the performance of each method via simulation terms of mean squared error and mean bias. We illustrate each method on a perturbed example of 1--4 matched case-control study. The second regression model is the generalized linear model (GLM) with unknown link function. Usually, the link function is chosen by the user based on the distribution of the response variable, often to be the canonical link. However, when covariates are measured with error, incorrect inference as a result of the error can be compounded by incorrect choice of link function. We assess performance via simulation of the semi- and fully Bayesian methods in terms of mean squared error. We illustrate each method on the Framingham Heart Study dataset. The simulation results for both regression models support that the fully Bayesian approach is at least as good as the semi-Bayesian approach for adjusting for measurement error, particularly when the distribution of the variable of measure with error and the distribution of the measurement error are misspecified. / Ph. D.

Research investigating the behavioral and physiological responses of bats to echoes typically includes analysis of acoustic signals from microphones and/or microphone arrays, using time difference of arrival (TDOA) between array elements or the microphones to locate flying bats (azimuth and elevation). This has provided insight into transmission adaptations with respect to target distance, clutter, and interference. Microphones recording transmitted signals and echoes near a stationary bat provide sound pressure as a function of time but no directional information. This dissertation introduces spatial audio techniques to bat biosonar studies as a complementary method to the current TDOA based acoustical study methods. This work proposes a couple of feasible methods based on spatial audio techniques, that both track bats in flight and pinpoint the directions of echoes received by a bat. A spatial audio/soundfield microphone array is introduced to measure sounds in the sonar frequency range (20-80 kHz) of the big brown bat (Eptesicus fuscus). The custom-built ultrasonic tetrahedral soundfield microphone consists of four capacitive microphones that were calibrated to match magnitude and phase responses using a transfer function approach. Ambisonics, a signal processing technique used in three-dimensional (3D) audio applications, is used for the basic processing and reproduction of the signals measured by the soundfield microphone. Ambisonics provides syntheses and decompositions of a signal containing its directional properties, using the relationship between the spherical harmonics and the directional properties. As the first proposed method, a spatial audio decoding technique called HARPEx (High Angular Resolution Planewave Expansion) was used to build a system providing angle and elevation estimates. HARPEx can estimate the direction of arrivals (DOA) for up to two simultaneous sources since it decomposes a signal into two dominant planewaves. Experiments proved that the estimation system based on HARPEx provides accurate DOA estimates of static or moving sources. It also reconstructed a smooth flight-path of a bat by accurately estimating its direction at each snapshot of pulse measurements in time. The performance of the system was also assessed using statistical analyses of simulations. A signal model was built to generate microphone capsule responses to a virtual source emitting an LFM signal (3 ms, two harmonics: 40-22 kHz and 80-44 kHz) at an angle of 30° in the simulations. Medians and RMSEs (root-mean-square error) of 10,000 simulations for each case represent the accuracy and precision of the estimations, respectively. Results show lower d (distance between a capsule and the soundfield microphone center) or/and higher SNR (signal-to-noise ratio) are required to achieve higher estimator performance. The Cramer-Rao lower bounds (CRLB) of the estimator are also computed with various d and SNR conditions. The CRLB which is for TDOA based methods does not cover the effects of different incident angles to the capsules and signal delays between the capsules due to a non-zero d, on the estimation system. This shows the CRLB is not a proper tool to assess the estimator performance. For the second proposed method, the matched-filter technique is used instead of HARPEx to build another estimation system. The signal processing algorithm based on Ambisonics and the matched-filter approach reproduces a measured signal in various directions, and computes matched-filter responses of the reproduced signals in time-series. The matched-filter result points a target(s) by the highest filter response. This is a sonar-like estimation system that provides information of the target (range, direction, and velocity) using sonar fundamentals. Experiments using a loudspeaker (emitter) and an artificial or natural target (either stationary or moving) show the system provides accurate estimates of the target's direction and range. Simulations of imitating a situation where a bat emits a pulse and receives an echo from a target (30°) were also performed. The echo sound level is determined using the sonar equation. The system processed the virtual bat pulse and echo, and accurately estimated the direction, range, and velocity of the target. The simulation results also appear to recommend an echo level over -3 dB for accurate and precise estimations (below 15% RMSE for all parameters). This work proposes two methods to track bats in flight or/and pinpoint the directions of targets using spatial audio techniques. The suggested methods provide accurate estimates of the direction, range, or/and velocity of a bat based on its pulses or of a target based on echoes. This demonstrates these methods can be used as key tools to reconstruct bat biosonar. They would be also an independent tool or a complementary option to TDOA based methods, for bat echolocation studies. The developed methods are believed to be also useful in improving man-made sonar technology. / Doctor of Philosophy / While bats are one of the most intriguing creatures to the general population, they are also a popular subject of study in various disciplines. Their extraordinary ability to navigate and forage irrespective of clutter using echolocation has gotten attention from many scientists and engineers. Research investigating bats typically includes analysis of acoustic signals from microphones and/or microphone arrays. Using time difference of arrival (TDOA) between the array elements or the microphones is probably the most popular method to locate flying bats (azimuth and elevation). Microphone responses to transmitted signals and echoes near a bat provide sound pressure but no directional information. This dissertation proposes a complementary way to the current TDOA methods, that delivers directional information by introducing spatial audio techniques. This work shows a couple of feasible methods based on spatial audio techniques, that can both track bats in flight and pinpoint the directions of echoes received by a bat. An ultrasonic tetrahedral soundfield microphone is introduced as a measurement tool for sounds in the sonar frequency range (20-80 kHz) of the big brown bat (Eptesicus fuscus). Ambisonics, a signal processing technique used in three-dimensional (3D) audio applications, is used for the basic processing of the signals measured by the soundfield microphone. Ambisonics also reproduces a measured signal containing its directional properties. As the first method, a spatial audio decoding technique called HARPEx (High Angular Resolution Planewave Expansion) was used to build a system providing angle and elevation estimates. HARPEx can estimate the direction of arrivals (DOA) for up to two simultaneous sound sources. Experiments proved that the estimation system based on HARPEx provides accurate DOA estimates of static or moving sources. The performance of the system was also assessed using statistical analyses of simulations. Medians and RMSEs (root-mean-square error) of 10,000 simulations for each simulation case represent the accuracy and precision of the estimations, respectively. Results show shorter distance between a capsule and the soundfield microphone center, or/and higher SNR (signal-to-noise ratio) are required to achieve higher performance. For the second method, the matched-filter technique is used to build another estimation system. This is a sonar-like estimation system that provides information of the target (range, direction, and velocity) using matched-filter responses and sonar fundamentals. Experiments using a loudspeaker (emitter) and an artificial or natural target (either stationary or moving) show the system provides accurate estimates of the target's direction and range. Simulations imitating a situation where a bat emits a pulse and receives an echo from a target (30°) were also performed. The system processed the virtual bat pulse and echo, and accurately estimated the direction, range, and velocity of the target. The suggested methods provide accurate estimates of the direction, range, or/and velocity of a bat based on its pulses or of a target based on echoes. This demonstrates these methods can be used as key tools to reconstruct bat biosonar. They would be also an independent tool or a complementary option to TDOA based methods, for bat echolocation studies. The developed methods are also believed to be useful in improving sonar technology.

No / Finite impulse response (FIR) digital filters are extensively used due to their key role in various digital signal processing (DSP) applications. Several attempts have been made to develop hardware realization of FIR filters characterized by implementation complexity, precision and high speed. Field Programmable Gate Array is a reconfigurable realization of FIR filters. Field-programmable gate arrays (FPGAs) are on the verge of revolutionizing digital signal processing. Many front-end digital signal processing (DSP) algorithms, such as FFTs, FIR or IIR filters, are now most often realized by FPGAs. Modern FPGA families provide DSP arithmetic support with fast-carry chains that are used to implement multiply-accumulates (MACs) at high speed, with low overhead and low costs. In this paper, distributed arithmetic (DA) realization of FIR filter as serial and parallel are discussed in terms of hardware cost and resource utilization.

The study of the spatial aspects of multipath in wireless communications environments is an increasingly important addition to the study of the temporal aspects in the search for ways to increase the utilization of the available wireless channel capacity. Traditionally, multipath has been viewed as an encumbrance in wireless communications, two of the major impairments being signal fading and intersymbol interference. However, recently the potential advantages of the diversity offered by multipath rich environments in multiuser communications have been recognised. Space time coding, for example, is a recent technique which relies on a rich scattering environment to create many practically uncorrelated signal transmission channels. Most often, statistical models have been used to describe the multipath environments in such applications. This approach has met with reasonable success but is limited when the statistical nature of a field is not easily determined or is not readily described by a known distribution.¶ Our primary aim in this thesis is to probe further into the nature of multipath environments in order to gain a greater understanding of their characteristics and diversity potential. We highlight the shortcomings of beamforming in a multipath multiuser access environment. We show that the ability of a beamformer to resolve two or more signals in angle directly limits its achievable capacity.¶ We test the probity of multipath as a source of spatial diversity, the limiting case of which is co-located users. We introduce the concept of separability to define the fundamental limits of a receiver to extract the signal of a desired user from interfering users’ signals and noise. We consider the separability performances of the minimum mean square error (MMSE), decorrelating (DEC) and matched filter (MF) detectors as we bring the positions of a desired and an interfering user closer together. We show that both the MMSE and DEC detectors are able to achieve acceptable levels of separability with the users as close as λ/10.¶ In seeking a better understanding of the nature of multipath fields themselves, we take two approaches. In the first we take a path oriented approach. The effects on the variation of the field power of the relative values of parameters such as amplitude and propagation direction are considered for a two path field. The results are applied to a theoretical analysis of the behaviour of linear detectors in multipath fields. This approach is insightful for fields with small numbers of multipaths, but quickly becomes mathematically complex.¶ In a more general approach, we take a field oriented view, seeking to quantify the complexity of arbitrary fields. We find that a multipath field has an intrinsic dimensionality of (πe)R/λ≈8.54R/λ, for a field in a two dimensional circular region, increasing only linearly with the radius R of the region. This result implies that there is no such thing as an arbitrarily complicated multipath field. That is, a field generated by any number of nearfield and farfield, specular and diffuse multipath reflections is no more complicated than a field generated by a limited number of plane waves. As such, there are limits on how rich multipath can be. This result has significant implications including means: i) to determine a parsimonious parameterization for arbitrary multipath fields and ii) of synthesizing arbitrary multipath fields with arbitrarily located nearfield or farfield, spatially discrete or continuous sources. The theoretical results are corroborated by examples of multipath field analysis and synthesis.

在實務上，複選題分析一直處於觀察樣本情形的階段；至於進行檢定以推估母體情形的過程，則幾乎沒有人考慮到。就算曾經試圖想作類似檢定，卻也常常找不到可供參考的文獻或是使用了不適當的分析方法。 本研究的主要目的在於探討各式各樣離散型態相關資料的分析方法，其中亦包含許多複選題的分析方法。幾乎每個方法皆附上範例來說明程式撰寫及分析過程，希望對有此需求的人能有所幫助。 / Problems with multiple responses are usually analyzed by observing only the sample proportions. People don't bother to make any inferences based on the sample information mostly because they do not know how to do it. Even for those who do go beyond the stage of descriptive statistics might not work it out correctly. In the study, we review statistical methods for analyzing dependent proportions, including multiple responses. Almost every method is supplemented with an example which explains the way a related SAS program is written and the way the output is analyzed and explained. We hope that the results presented here will be helpful to those who are engaged in any analysis of multiple responses.