京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第20740号 / 情博第654号 / 新制||情||113(附属図書館) / 京都大学大学院情報学研究科通信情報システム専攻 / (主査)教授 守倉 正博, 教授 大木 英司, 教授 梅野 健 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

Over the last decade, rapid growth of broadband services necessitated research aimed at increasing transmission capacity in fiber-optic communication systems. Wavelength division multiplexing (WDM) technology has been widely used in fiber-optic systems to fully utilize fiber transmission bandwidth. Among optical amplifiers for WDM transmission, semiconductor optical amplifier (SOA) is a promising candidate, thanks to its broad bandwidth, compact size, and low cost. In transmission systems using SOAs, due to their large noise figures, high signal launching powers are required to ensure reasonable optical signal-to-noise ratio of the received signals. Hence the SOAs are operated in the saturation region and the signals will suffer from SOA impairments including self-gain modulation, self-phase modulation, and inter channel crosstalk effects such as cross-gain modulation, cross-phase modulation, and four-wave mixing in WDM. One possibility to circumvent these nonlinear impairments is to use constant-intensity modulation format in the 1310 nm window where dispersion is also negligible. In this dissertation, differential phase-shift keying (DPSK) WDM transmission in the 1310 nm window using SOAs was first considered to increase the capacity of existing telecommunication network. A WDM transmission of 4 x 10 Gbit/s DPSK signals over 540 km standard single mode fiber (SSMF) using cascaded SOAs was demonstrated in a recirculating loop. In order to increase the transmission reach of such WDM systems, those SOA impairments must be compensated. To do so, an accurate model for quantum-dot (QD) SOA must be established. In this dissertation, the QD-SOA was modeled with the assumption of overall charge neutrality. Static gain was calculated. Optical modulation response and nonlinear phase noise were studied semi-analytically based on small-signal analysis. The quantitative studies show that an ultrafast gain recovery time of ~0.1 ps can be achieved when QD-SOAs are under high current injection, which leads to high saturation output power. However more nonlinear phase noise is induced when the QD-SOAs are used in the transmission systems operating at 10 Gbit/s or 40 Gbit/s. Electronic post-compensation for SOA impairments using coherent detection and digital signal processing (DSP) was investigated next in this dissertation. An on-off keying transmission over 100 km SSMF using three SOAs at 1.3 [micrometer] were demonstrated experimentally with direct detection and SOA impairment compensation. The data pattern effect of the signal was compensated effectively. Both optimum launching power and Q-factor were improved by 8 dB. For advanced modulation formats involving phase modulation or in transmission windows with large dispersion, coherent detection must be used and fiber impairments in WDM systems need to be compensated as well. The proposed fiber impairment compensation is based on digital backward propagation. The corresponding DSP implementation was described and the required calculations as well as system latency were derived. Finally joint SOA and fiber impairment compensations were experimentally demonstrated for an amplitude-phase-shift keying transmission.

As implantable medical devices are being used more often to treat medical problems for which pharmaceuticals don’t suffice, it is important to understand their interactions with commonly used medical modalities. The interactions between medical implants and Magnetic Resonance Imaging machines have proven to be a risk for patients with implants. Implanted medical devices with elongated metallic components can create harmful levels of local heating in a Magnetic Resonance Imaging (MRI) environment [1]. The heating of a biological medium under MRI is monitored via the Specific Absorption Rate (SAR). SAR, defined as power absorbed per unit mass (W/kg), can be calculated as , where σ is electrical conductivity of the medium in units of , |E| is the magnitude of the applied electric field in units of , and ρ is the density of the medium in units of . For continuous, uniform power deposition this can be measured experimentally as a rise in temperature over time (∆T/t), where c is the specific heat capacity of the medium in units of. To understand the SAR induced in-vivo, a phantom (Figure 2.10) is used to conduct in-vitro experiments, as it provides a controllable and repeatable experimental setup. In order to experiment in the phantom, an understanding of the background SAR distribution and in turn the exposure field distribution of the phantom is required as per the ASTMF2182-09 standard [2]. In this work, the background SAR distribution of an ASTM standard torso phantom is measured and studied via fiber optic thermometry. The measurements are compared with an electromagnetic model simulated via FDTD, demonstrating agreement between 10-25%. A custom exposure and data collection setup (including oscilloscope, function generator, RF amplifier, directional coupler, and Neoptix Omniflex Fiber Optic Thermometry system) was integrated and automated using NI LabView. The purpose of this thesis is to map the field distribution in a torso phantom under RF exposure from a 64 MHz MRI RF Birdcage, compare the results to an electromagnetic simulation, and finally conclude the accuracy of this method for field measurements in a standard torso phantom. Understanding the capabilities and accuracy of the fiber optic thermometry method will ultimately allow researchers to successfully apply this method to monitor background fields in their respective experimental setups (related to MRI implant heating) and understand its limitations.

This thesis deals with asset management of structures through Building Information Modelling (BIM) and Digital Twins. Background: Current inspection and management processes for civil structures are time-consuming and can even be inaccurate. There is an increasingly high potential to improve these processes through recent advances in technology. Digital Twins offer a common platform to these technologies, so they can interact and be used to their optimal performance. Other industries have significantly advanced in the development of Digital Twins, however, in the construction industry there are still many gaps and room for improvement. Aim and objectives: The main aim of this project was to investigate the status of Digital Twins in the construction industry and propose a methodology for a Digital Twin for asset management of structures. The three immediate objectives sought are (i) Perform a literature review to establish the current practice with digital twins, in both construction and other industries, and what are the gaps for asset management of structures; (ii) Participate in a pilot experimental program that yields data to a potential digital twin prototype; and (iii) Define a methodology for a digital twin for asset management of structures which fills the identified gaps. Methods of investigation: A literature review was performed and served as basis for the development of a methodology for a digital twin. A pilot experimental program was defined and performed, and its results were used for BIM and Finite Element (FE) models. A webapp was also created using Autodesk Forge and Java programming language, andthe BIM model was uploaded into it. Results: The literature review provided insight into the maturity level of digital twins, as well as on bridge inspection, maintenance and monitoring, BIM, facility and asset management, and Bridge Management Systems (BMS). A methodology to achieve a digital twin for asset management was proposed, and the conducted experimental program yielded data results to be used in future research. Conclusion: There has been significant progress in technology to improve structural assessment and analysis, however, their full potential is still under-explored. A digital twin created in a common data environment can provide a platform for these technologies to improve efficiency of current practices. Nonetheless, the construction industry is still significantly behind other industries such as aerospace and automotive.

<p>Fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Thousands of kilometers of optical fiber are used by telecommunications companies to transmit telephone signals, Internet communication, and cable television signals throughout the world. So, working in this area has always been interesting. This thesis analyzes the nonlinearity of fiber-optic systems and proposes a system to mitigate fiber nonlinear e®ects. The topics of this thesis can be categorized into two parts. In the first part of thesis (Chapters 2, 3, and 4), analytical models are developed for fiber-optic nonlinear effects. It is important to have an accurate analytical model so that the impact of a specific system/signal parameter on the performance can be assessed quickly without doing time-consuming Monte-Carlo simulations. In the second part (Chapters 5, and 6), a multi-core/fiber architecture is proposed to reduce the nonlinear effects.</p> <p>In Chapter 2, intrachannel nonlinear impairments are studied and an analytical model for the calculation of power spectral density (PSD) and variance of the non- linear distortion is obtained based on quadrature phase-shift keying (QPSK) signal. For QPSK signals, intrachannel four-wave mixing (IFWM) is the only stochastic non- linear distortion. To develop the analytical model, a first order perturbation theory is used. For a Gaussian pulse shape, a closed form formula is obtained for the PSD of IFWM. For non-Gaussian pulses, it is not possible to find the PSD analytically. However, using stationary phase approximation approach, convolutions become multiplications and a simple analytical expression for the PSD of the nonlinear distortion can be found. The total PSD is obtained by adding the PSD of amplified spontaneous emission (ASE) PSD to that of the nonlinear distortion. Using the total PSD, bit error ratio (BER) can be obtained analytically for a QPSK system. The analytically estimated BER is found to be in good agreement with numerical simulations. Significant computational effort can be saved using the analytical model as compared to numerical simulations, without sacrificing much accuracy.</p> <p>In Chapter 3, the same approach as that in Chapter 2 is used to find an analytical expression for the PSD of the intrachannel nonlinear distortion of a fiber-optic system based on quadrature amplitude modulation (QAM) signal. Unlike the QPSK signal, intrachannel cross-phase modulation (IXPM) is a stochastic process for the QAM signal which leads to the increase of the nonlinear distortion variance. In this chapter, analytical expressions for the PSDs of self-phase modulation (SPM), IXPM, IFWM, and their correlations are obtained for the QAM signal. Simulation results show good agreement between the analytical model and numerical simulation.</p> <p>In Chapter 4, inter-channel nonlinear impairment is studied. This time, a first order perturbation technique is used to develop an analytical model for SPM and cross-phase modulation (XPM) distortions in a wavelength division multiplexing (WDM) system based on QAM. In this case, SPM distortion is deterministic and does not contribute to the nonlinear noise variance. On the other hand, XPM is stochastic and contributes to the noise variance. In this chapter, effects of input launch power, fiber dispersion, system reach, and channel spacing on the nonlinear noise variance are investigated as well.</p> <p>In Chapter 5, a single-channel multi-core/fiber architecture is proposed to reduce intrachannel fiber nonlinear effects. Based on the analytical model obtained in the first part of thesis, the nonlinear distortion variance scales as P³, where P is the fiber input launch power, which suggests that decreasing the fiber input power can reduce the nonlinear distortion significantly. In this system, the input power is divided between multiple cores/fibers by a power splitter at the input of each span and a power combiner adds the output fields of multiple cores/fibers so that one amplifier can be used for each span. In this case, each core/fiber receives less power and hence adds less nonlinear distortion to the signal. In a practical system, individual fiber parameters are not identical; so the optical pulses propagating in the fibers undergo different amounts of phase shifts and timing delays due to the fluctuations of fibers' propagation constants and fibers' inverse group speeds. Optical and electrical equalizers are proposed to compensate for these inter-core/fiber dispersions. In the case of an optical equalizer, adaptive time shifters and phase shifters are adjusted such that the maximum power is obtained at the output of power combiner. Our numerical simulation results show that for unrepeatered systems, the performance (Q factor) is improved by 6.2 dB using 8-core/fiber configuration as compared to single- core fiber system. In addition, for multi-span system, the transmission reach at BER of 2.1*10^-3 is quadrupled in 8-core/fiber configuration.</p> <p>In Chapter 6, a multi-channel multi-core/fiber architecture is proposed to reduce the inter-channel nonlinear distortions. In this architecture, different channels of a WDM system are interleaved between multiple cores/fibers which increases the channel spacing in each core/fiber. Higher channel spacing decreases the inter-channel nonlinear impairments in each core/fiber which leads to system performance improvement. At the end of each span, a multiplexer adds the channels from different cores/fibers so that one amplifier can be used for all of the channels. Unlike the single-channel multi-core/fiber system, the WDM multi-core/fiber system does not require equalizers since different cores/fibers carry channels with different frequencies. Simulation results show that for a 39-span system, the 4-core/fiber system with negligible crosstalk outperforms the single-core system by 2.2 dBQ₂₀. The impact of crosstalk between cores of a multi-core fiber (MCF) on the system performance is studied. The simulation results show that the performance of the multi-core WDM system is less sensitive to the crosstalk effect compared to conventional multi-core systems since the propagating channels in the cores are not correlated in frequency domain.</p> / Doctor of Philosophy (PhD)

This dissertation deals with the solution of three inverse problems in structural mechanics. The first one is load updating for finite element models (FEMs). A least squares fitting is used to identify the load parameters. The basic studies are made for geometrically linear and nonlinear FEMs of beams or frames by using a four-noded curved beam element, which, for a given precision, may significantly solve the ill-posed problem by reducing the overall number of degrees of freedom (DOF) of the system, especially the number of the unknown variables to obtain an overdetermined system. For the basic studies, the unknown applied load within an element is represented by a linear combination of integrated Legendre polynomials, the coefficients of which are the parameters to be extracted using measured displacements or strains. The optimizer L-BFGS-B is used to solve the least squares problem. The second problem is the placement optimization of a distributed sensing fiber optic sensor for a smart bed using Genetic Algorithms (GA), where the sensor performance is maximized. The sensing fiber optic cable is represented by a Non-uniform Rational B-Splines (NURBS) curve, which changes the placement of a set of infinite number of the infinitesimal sensors to the placement of a set of finite number of the control points. The sensor performance is simplified as the integration of the absolute curvature change of the fiber optic cable with respect to a perturbation due to the body movement of a patient. The smart bed is modeled as an elastic mattress core, which supports a fiber optic sensor cable. The initial and deformed geometries of the bed due to the body weight of the patient are calculated using MSC/NASTRAN for a given body pressure. The deformation of the fiber optic cable can be extracted from the deformation of the mattress. The performance of the fiber optic sensor for any given placement is further calculated for any given perturbation. The third application is stiffened panel optimization, including the size and placement optimization for the blade stiffeners, subject to buckling and stress constraints. The present work uses NURBS for the panel and stiffener representation. The mesh for the panel is generated using DistMesh, a triangulation algorithm in MATLAB. A NASTRAN/MATLAB interface is developed to automatically transfer the data between the analysis and optimization processes respectively. The optimization consists of minimizing the weight of the stiffened panel with design variables being the thickness of the plate and height and width of the stiffener as well as the placement of the stiffeners subjected to buckling and stress constraints under in-plane normal/shear and out-plane pressure loading conditions. / Ph. D.

DNA is the substance that encodes the genetic information that cells need to replicate and to produce proteins. The detection of DNA sequences is of great importance in a broad range of areas including genetics, pathology, criminology, pharmacogenetics, public health, food safety, civil defense, and environmental monitoring. However, the established techniques suffer from a number of problems such as the bulky size, high equipment costs, and time-consuming algorithms so that they are limited to research laboratories and cannot be applied for in-vivo situations. In our research, we developed a novel sensing scheme for DNA sequence detection, featuring sequence specificity, cost efficiency, speed, and ease of use. Without the need for labels or indicators, it may be ideal for direct in-cell application. The principle is simple. With capture DNA immobilized onto the probe by layer-by-layer selfassembly, the hybridization of a complementary strand of target DNA increases the optical thickness of the probe. Three kinds of sensors were developed. The optical fiber tip sensor has been demonstrated with good specificity and high sensitivity for target DNA quantities as small as 1.7 ng. To demonstrate the potential of this structure for practical applications, tularemia bacteria were tested. Two other micrometric structures were designed with specific advantages for different applications. The micro-fiber Bragg grating interferometer (Micro-FBGI) has the intrinsic temperature compensation capability. The micro-intrinsic Fabry-Perot interferometer (Micro-IFPI)features simple signal processing due to its simple configuration. Successful DNA immobilization and hybridization have been demonstrated onto the 25μm Micro-IFPI. Both structures have great potential for nanometric protrusion, allowing future in-cell DNA direct detection. In addition, its quick response time leads to the potential for express diagnosis. What's more, the idea of nanoscale probe has a broad impact in scanning near-field optical microscopy (SNOM), intracellular surgery in cell sensing, manipulation, and injection. / Ph. D.

This thesis proposes a novel approach to power electronics system design that is based on the open-architecture distributed digital controller and modular power electronics building blocks (PEBBs). The proposed distributed digital controller partitions the controller in three levels of control authority. The power stage controller, designated as hardware manager, is responsible for low-level hardware oriented tasks; the high level controller, designated as applications manager, performs higher-level application-oriented tasks; and the system level controller handles system control and monitoring functions. Communications between the hardware-oriented controller and the higher-level controller are implemented with the previously proposed 125 Mbits/sec daisy-chained fiber optic communication protocol. Real-time control and status data are communicated by means of communication protocol. The distributed controller on the power converter level makes the system open, flexible and simple to use. Furthermore, this work gives an overview and comparison of current state-of-the-art communication protocols for real-time control applications with emphasis on industrial automation and motion control. All of the studied protocols have been considered as local area networks (LAN) for system-level control in power converter systems. The most promising solution has been chosen for the system level communication protocol. This thesis also provides the details of design and implementation of the distributed controller. The design of both the hardware and software components are explained. A 100 kVA three-phase voltage source inverter (VSI) prototype was built and tested using the distributed controller approach to demonstrate the feasibility of the proposed concept. / Master of Science

Power transformers are one of the most important components in the electrical energy network. Extending transformer life is very economically valuable due to power outage. Therefore the development of instruments to monitor the transformer condition is of great interest. Detection of partial discharges (PDs) in power transformers is an effective diagnostic because it may reveal and quantify an important aging factor and provide information on the condition of the transformer. However, partial discharge diagnostics are still not effectively used for online monitoring of transformers because of the complexity of PD measurements and difficulties of discriminating of PDs and other noise sources. This thesis presents a further study of detection and location of partial discharges in power transformers based on previous work conducted at the Center for Photonics Technology (CPT) at Virginia Tech. The detection and positioning system consists of multiple extrinsic Fabry-Parot interferometric (EFPI) fiber acoustic sensors which can survive the harsh environment of oil-filled transformers. This thesis work is focused on optimal arrangement of multiple sensors to monitor and locate PD activities in a power transformer. This includes the following aspects. First, the sensor design requirements are discussed in order to successfully detect and accurately position the PD sources. In the following sections, Finite Element Method (FEM) is used to model the EFPI sensor fabricated at CPT. Experiments were conducted to measure the angular dependence of the frequency response of the sensor. It is shown that within the range of ±45º incident angles, the sensitivity varies by 3-5dB. Finally, the thesis demonstrates a PD positioning experiment in a 500 gallon water tank (R à H = 74" à 30" cylinder) using a hyperbolic positioning algorithm and time difference of arrival (TDOA). Finally we demonstrated that 100% of the positioning data is bounded by a 22.7à 4.1à 5.3 mm₃ cube, with a sensing range of 810 mm using the leading edge method with FIR filtering. / Master of Science

A partial discharge (PD) is the dissipation of energy caused by the buildup of localized electric field intensity. In high voltage devices such as transformers, this buildup of charge and its release can be symptomatic of problems associated with aging, such as floating components and insulation breakdown. This is why PD detection is used in power systems to monitor the state of health of high voltage transformers. If such problems are not detected and repaired, the strength and frequency of PDs increases and eventually leads to the catastrophic failure of the transformer, which can cause external equipment damage, fires and loss of revenue due to an unscheduled outage. Reliable online PD detection is a critical need for power companies to improve personnel safety and decrease the potential for loss of service. The PD phenomenon is manifested in a variety of physically observable signals including electric and acoustic pulses and is currently detected using a host of exterior measurement techniques. These techniques include electrical lead tapping and piezoelectric transducer (PZT) based acoustic detection. Many modern systems use a combination of these techniques because electrical detection is an older and proven technology and acoustic detection allows for the source to be located when several sensors are mounted to the exterior of the tank. However, if an acoustic sensor could be placed inside the tank, not only would acoustic detection be easier due to the increased signal amplitude and elimination of multipath interference, but positioning could also be performed with more accuracy in a shorter time. This thesis presents a fiber optic acoustic sensing system design that can be used to detect and locate PD sources within a high voltage transformer. The system is based on an optical acoustic (OA) sensor that is capable of surviving the harsh environment of the transformer interior while not compromising the transformer's functionality, which allows for online detection and positioning. This thesis presents the theoretical functionality and experimental validation of a band-limited OA sensor with a usable range of 100-300 kHz, which is consistent with the frequency content of an acoustic pulse caused by a PD event. It also presents a positioning system using the time difference of arrival (TDOA) of the acoustic pulse with respect to four sensors that is capable of reporting the three-dimensional position of a PD to within ±5cm on any axis. / Master of Science