According to classical linearized resistive magnetohydrodynamics theory, pressuredriven modes are unstable in the reversed-field pinch (RFP) due to unfavorable magnetic field line curvature. The result is based on the assumption of an adiabatic energy equation where anisotropic thermal conduction effects are ignored as compared to convection and compression. In this thesis the effects of heat conduction in the energy equation have been studied. We have examined these effects on the linear stability of pressure-driven resistive modes using boundary value theory (Δ´ ) and a novel initial-value full resistive MHD code employing the Generalized Weighted Residual Method (GWRM). In the Δ´ method, a shooting technique is employed by integrating from the resistive layer to boundaries. The GWRM method, on the other hand, is a time-spectral Galerkin method in which the fully linearized MHD equations are solved. For detailed computations, efficiency requires the temporal and spatial domains to be divided into subdomains. For this purpose, a number of challenging test cases including linearized ideal MHD equations are treated. Numerical and analytical investigations of equilibria reveal that thermal conduction effects are not stabilizing for reactor relevant values of Lundquist number, S0, and normalized pressure, βθ, for tearing-stable plasmas. These studies show that growth rate scales as  γ~_ S0−1/5 , which is weaker than for the adiabatic case, γ~_ S0−1/3. A numerical study of optimized confinement for an advanced RFP scenario including ohmic heating and heat conduction, is also part of this thesis. The fully nonlinear resistive MHD code DEBSP has been employed. We have identified, using both Δ´ and GWRM methods, that the observed crash of the high confinement is caused by resistive, pressure-driven modes. / <p>QC 20130503</p>

<p>A wide range of unstable current driven MHD modes is present in the re- versed τeld pinch (RFP) conτguration. An ideally conducting wall facing the plasma can stabilize the ideal MHD modes. In the presence of a resistive wall characterized by the wall time τw, fast mode rotation with the frequency exceeding the inverse wall time gives stabilization for resistive MHD modes. The ideal MHD modes in the RFP are non-rotating modes and can not be stabilized by the resistive wall. Instead they are converted into resistive wall modes (RWM) growing with a growth rate proportional to the inverse of the wall time τw. EXTRAP T2R is an RFP device equipped with a thin resistive wall having the wall time shorter than the plasma pulse duration τw < τp. This feature allows the study of non-resonant non-rotating resistive wall modes. Resistive wall modes dynamics has been studied in EXTRAP T2R . RWM growth rates has been measured and compared with linear MHD stability calculations. Quantitative agreement is observed. In the case τw < τp the RWM can cause discharge degradation and should be stabilized. Active feedback is the way to stabilize the RWM in the RFP. An intelligent shell scheme is one possible feedback scenario. An active feed- back system including a set of sensors and discrete active coils is installed in EXTRAP T2R. The intelligent shell tries to keep the magnetic flux zero at the positions of the sensor. The analog PID controller for the intelligent shell feedback scheme has been studied. A model of the active control system was developed and comparison with the experimental results showed good agree- ment. Encouraging experimental results on the active feedback stabilization of multiple RWMs in the RFP plasmas were obtained.</p>

Le siècle dernier a vu le développement de la physique des particules, avec la fondation du célèbre modèle Standard de la physique des particules. Plus spécifiquement, durant les 70 dernières années de nombreuses particules ont été détecté et étudié. Parallèlement à ces découvertes, les moyens expérimentaux et les détecteurs ont grandement évolué. de la simple chambre à bulles de l'expérience Gargamel, qui a posé la première brique expérimentale du modèle standard, aux détecteurs complexes d'aujourd'hui tel que le LHC. Durant le développement de nouveaux détecteurs, nous pouvons distinguer deux grandes catégories: les détecteurs dits Solid State et les détecteurs gazeux. La première englobe les détecteurs tels que les Cherenkov ou les scintilateurs tandis que les derniers utilisent un gaz comme moyen de détection.Les détecteurs gazeux ont aussi grandement évolué durant le siècle dernier, des tubes Geiger-Muller au chambres à étincelles ou Pestov, qui peuvent faire face aux taux de détections toujours grandissant des accélérateurs de particules. The Parallel Plate Avalanche Chamber est un détecteur gazeux similaire mais fonctionne en mode avalanche, où les signaux électriques sont produits par une multiplication contrôlée des électrons dans le gaz. Les autres détecteurs susmentionnées fonctionnent eux en mode étincelle, où le signal détectée est produit par une décharge électrique dans le gaz.Le mode avalanche permets un taux de détection encore supérieur mais au prix de signaux électriques beaucoup plus faibles. Au début des années 80 un nouveau type de détecteur gazeux commence à se développer, les Resistive Plate Chambers. Ce détecteur présente la particularité de pouvoir fonctionner en mode étincelle ou avalanche, selon le design. Utilisé en mode avalanche, ils présentent un taux de détection particulièrement intéressant au prix de signaux électriques faibles, nécessitant un circuit d'amplification dédié. De nos jours les Resistive Plate Chambers sont très largement utilisés dans de nombreuses expériences de physique des particules, notamment pour leurs performances intéressantes et leur prix contenu. Malgré leur usage répandu, les Resistive Plate Chambers n'ont pas été beaucoup étudié d'un point de vue modélisation et simulation. La simulation d'un détecteur est un outil essentiel pour leur développement et leur fabrication, permettant de tester un design et calculer les performances que l'on est en droit d'attendre. Dans les travaux présentés dans ce document nous nous sommes intéressés à la description des différents phénomènes physiques se produisant durant une avalanche électronique au sein d'un Resistive Plate Chambers fonctionnant en mode avalanche, dans le but de les modéliser et simuler. Nous décrivons un modèle détaillé pour le processus d'ionisation, qui est l'évènement fondamental pour tout détecteur gazeux. Nous décrivons aussi un modèle mis au point par Riegler-Lippmann-Veenhof pour le développement d'avalanche électronique. Une simulation C++ a été produite dans le contexte de cette étude et quelques résultats sont présentés. / The 20th century saw the development of particle physics research field, with the fundationof the famous Standard Model of particle physics. More specifically during the past 70 years numerous particles have been detected and studied. Alongside those discoveries, the experimental means and detectors has greatly evolved. From the simple Gargamel bubble chamber, which lay the first brick to the Standard Model theory, to the nowadays complex detectors such as the LHC. In the development of newer particles detector, one can distinguish two big categories:the solid state detectors et the gaseous detectors. The former encompass detectors suchas Cherenkov and scintillator counters while the later make use of gases as detection medium. The gaseous detectors have also greatly evolved during the past century from theGeiger-Muller tube to the spark or Pestov chambers, which can cope with the increasing detection rate of particles accelerator. The Parallel Plate Avalanche Chamber is a similar gaseous detector but operates in avalanche mode, where the detected signal is producedby a controlled multiplication of electrons in the gas. The aforementioned detectors were operated in spark mode, where the detection is made through a spark discharge in the gas.The avalanche mode allows even greater detection rates at the expense of signal amplitude. In early 80s a new gaseous detector design began to emerge: the Resistive Plate Chambers.This detector has the particularity to operates in spark or avalanche mode depending on its design. Operated in avalanche mode, they present an impressing detection rates at the expense of very small electric signals, requiring dedicated amplification circuitries. Nowadays the Resistive Plate Chambers are widely used in numerous experiments worldwide,because of their interesting performances and relatively small price. Despite their widespread usage, the Resistive Plate Chambers have not been extensively studied from a simulation and modelisation point of view. Simulation of a detectoris an essential tool for its development and construction, as it allows to test a design and predict the performances one may get. In this work we focused on the description of the physics phenomenons occuring during an electronic avalanche inside a Resistive Plate Chambers operated in avalanche mode, in order to properly modelise and simulate them. We review a detailed model of the ionisation process, which is the fundamental event in any gaseous particle detector, alongside theRiegler-Lippmann-Veenhof model for the electronic avalanche. A C++ simulation has been produced in the context of this work and some results are presented.

A wide range of unstable current driven MHD modes is present in the re- versed τeld pinch (RFP) conτguration. An ideally conducting wall facing the plasma can stabilize the ideal MHD modes. In the presence of a resistive wall characterized by the wall time τw, fast mode rotation with the frequency exceeding the inverse wall time gives stabilization for resistive MHD modes. The ideal MHD modes in the RFP are non-rotating modes and can not be stabilized by the resistive wall. Instead they are converted into resistive wall modes (RWM) growing with a growth rate proportional to the inverse of the wall time τw. EXTRAP T2R is an RFP device equipped with a thin resistive wall having the wall time shorter than the plasma pulse duration τw &lt; τp. This feature allows the study of non-resonant non-rotating resistive wall modes. Resistive wall modes dynamics has been studied in EXTRAP T2R . RWM growth rates has been measured and compared with linear MHD stability calculations. Quantitative agreement is observed. In the case τw &lt; τp the RWM can cause discharge degradation and should be stabilized. Active feedback is the way to stabilize the RWM in the RFP. An intelligent shell scheme is one possible feedback scenario. An active feed- back system including a set of sensors and discrete active coils is installed in EXTRAP T2R. The intelligent shell tries to keep the magnetic flux zero at the positions of the sensor. The analog PID controller for the intelligent shell feedback scheme has been studied. A model of the active control system was developed and comparison with the experimental results showed good agree- ment. Encouraging experimental results on the active feedback stabilization of multiple RWMs in the RFP plasmas were obtained.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18285号 / 工博第3877号 / 新制||工||1595(附属図書館) / 31143 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 藤田 静雄, 准教授 掛谷 一弘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

As the semiconductor industry grapples with escalating scaling challenges associated with the floating gate MOSFET, alternative memory technologies like Resistive Random Access Memory (ReRAM) are gaining prominence in the scientific community. Boasting a straightforward device structure, ease of fabrication, and compatibility with CMOS (Complementary Metal-oxide Semiconductor) Back-end of Line (BEOL), ReRAM stands as a leading candi- date for the next generation of non-volatile memory (NVM). ReRAM devices feature nanoionics-based filamentary switching, outperforming flash memory in terms of power consumption, scalability, retention, ON/OFF ratio, and endurance. Furthermore, integrating ReRAMs within the CMOS BEOL/low-k Cu interconnect system not only reduces latency between the connectivity constraints of logic and memory modules but also minimizes the chip footprint. However, investigations have revealed a significant concern surrounding ReRAMs—specifically, their electro-thermal reliability. This research provides evidence highlighting the critical influence of material properties, deposition effects, and thermal transport on the device's performance and reliability. Various material systems have undergone in this work scrutiny to comprehend the impact of intrinsic material properties such as thermal conductivity, specific heat capacity, thermal diffusivity, and deposition effects like surface roughness on the electroforming voltages of ReRAM devices. The reference device structure considered in this work is Cu/TaOx/Pt, which has been compared with alternative configurations involving metals like Ru and Co as potential substitutes for Pt. Additionally, a new vehicle has been introduced to quantify cell degradation resulting from thermal cross-talk in crossbar Resistive Random Access Memory (ReRAM) arrays. Furthermore, a novel methodology has been presented to predict cell degradation due to remote heating, taking into account the cell's location, the material properties of the device, and geometry of its electrodes. The experimental results presented in this study showcase filament rupture caused by remote heating, along with spontaneous filament restoration ensuing from the subsequent cooling of the ReRAM cell. / Doctor of Philosophy / As the demand for compact, high-speed logic-memory modules continues to surge, the diminishing silicon real estate in our gadgets poses a challenge in extending Moore's law to meet the scaling needs of the semiconductor device industry. To tackle this challenge, emerging memory technologies like Resistive Random Access Memory (ReRAM) are positioned as promising successors to flash memory. ReRAM devices offer distinct advantages over flash memory, showcasing superior power consumption, scalability, long retention, a high ON/OFF ratio, and good endurance. Their compatibility with current CMOS (Complementary Metal-oxide Semiconductor) technology facilitates seamless integration. However, a significant concern associated with ReRAMs is their electro-thermal reliability. This research delves into how material properties comprising a ReRAM device and fabrication factors, such as the surface roughness of the material, can impact the electrical and thermal reliability of a ReRAM cell. In this context, a novel methodology has been introduced to predict cell degradation within ReRAM crossbar arrays induced by thermal cross-talk, considering material properties and the geometry of the device. The new methodology has been thoroughly verified on manufactured ReRAM arrays with various composite electrodes. The study also presents experimental results demonstrating the rupture of cell filaments due to remote heating, along with instances of spontaneous filament restoration due to subsequent cooling.

Non-volatile memories (NVM) including flash memories and resistive memories have attracted significant interest as data storage media. Flash memories are widely employed in mobile devices and solid-state drives (SSD). Resistive memories are promising as storage class memory and embedded memory applications. Data reliability is the fundamental requirement of NVM as data storage media. However, modern nano-scale NVM suffers from challenges of inter-cell interference (ICI), charge leakage, and write endurance, which threaten the reliability of stored data. In order to cope with these adverse effects, advanced coding techniques including soft decision decoding have been investigated actively. However, current coding techniques do not capture the physical properties of NVM well, so the improvement of data reliability is limited. Although soft decision decoding improves the data reliability by using soft decision values, it degrades read speed performance due to multiple read operations needed to obtain soft decision values. In this dissertation, we explore coding schemes that use side information corresponding to the physical phenomena to improve the data reliability significantly. The side information is obtained before writing data into memory and incorporated during the encoding stage. Hence, the proposed coding schemes maintain the read speed whereas the write speed performance would be degraded. It is a big advantage from the perspective of speed performance since the read speed is more critical than the write speed in many memory applications. First, this dissertation investigates the coding techniques for memory with stuckat defects. The idea of coding techniques for memory with stuck-at defects is employed to handle critical problems of flash memories and resistive memories. For 2D planar flash memories, we propose a coding scheme that combats the ICI, which is a primary challenge of 2D planar flash memories. Also, we propose a coding scheme that reduces the effect of fast detrapping, a degradation factor in 3D vertical flash memories. Finally, we investigate the coding techniques that improve write endurance and power consumption of resistive memories.

PURPOSE: Doppler renal resistive index (RRI) has emerged in the last decade as a useful prognostic indicator for transient (fluid responsive) and persistent acute kidney injury (AKI). The determinants of RRI are largely systemic and recent studies confirm that RRI measurement could also be a useful early marker for sub-clinical AKI and post procedural AKI risk. This study aimed to determine the feasibility of RRI measurement in an Emergency Department (ED) resuscitation room setting using a point­of­care ultrasound system. METHODS: In this prospective single centre study, RRI measurement was attempted in 20 non-consecutive patients (meeting the inclusion criteria) by a single expert sonographer. RRI measurements were evaluated against context specific feasibility criteria and target outcomes. RESULTS: 20 patients (11 male, 9 female) were recruited to the study. Age of patients ranged from 33 years to 91 years (mean 62.3 years). Adequate visualisation of both kidneys was achieved in 60% of patients (n=12). In patients where it was not possible to achieve adequate views of both kidneys (n=8), limiting technical factors were shortness of breath (SOB) (n=6), high BMI (n=2). At least one measurement of RRI was achieved in 70% of patients (n=14). However, in 9 of these patients (64.3%) the Doppler spectral traces achieved were substandard and did not meet the measurement criteria for RRI as specified in the study protocol. In 30% of patients (n=6) no usable spectral trace was achieved and it was not possible to measure RRI. SOB was noted as a technical difficulty in 60% of patients (n=12) including three for whom RRI measurements were achieved. In 9 patients (45%) SOB was recorded as the primary reason for failure to acquire a usable Doppler trace. All criteria for RRI measurements were met in only 3 patients (15%). CONCLUSION: Measurement of RRI was not feasible in patients requiring resuscitation room care using a current point of care ultrasound system. If RRI is to play a useful role in this high priority patient group, adaptation of the available technology is required to mitigate the problem of image blur due to patient breathing movement.

abstract: The Resistive Random Access Memory (ReRAM) is an emerging non-volatile memory technology because of its attractive attributes, including excellent scalability (< 10 nm), low programming voltage (< 3 V), fast switching speed (< 10 ns), high OFF/ON ratio (> 10), good endurance (up to 1012 cycles) and great compatibility with silicon CMOS technology [1]. However, ReRAM suffers from larger write latency, energy and reliability issue compared to Dynamic Random Access Memory (DRAM). To improve the energy-efficiency, latency efficiency and reliability of ReRAM storage systems, a low cost cross-layer approach that spans device, circuit, architecture and system levels is proposed. For 1T1R 2D ReRAM system, the effect of both retention and endurance errors on ReRAM reliability is considered. Proposed approach is to design circuit-level and architecture-level techniques to reduce raw Bit Error Rate significantly and then employ low cost Error Control Coding to achieve the desired lifetime. For 1S1R 2D ReRAM system, a cross-point array with “multi-bit per access” per subarray is designed for high energy-efficiency and good reliability. The errors due to cell-level as well as array-level variations are analyzed and a low cost scheme to maintain reliability and latency with low energy consumption is proposed. For 1S1R 3D ReRAM system, access schemes which activate multiple subarrays with multiple layers in a subarray are used to achieve high energy efficiency through activating fewer subarray, and good reliability is achieved through innovative data organization. Finally, a novel ReRAM-based accelerator design is proposed to support multiple Convolutional Neural Networks (CNN) topologies including VGGNet, AlexNet and ResNet. The multi-tiled architecture consists of 9 processing elements per tile, where each tile implements the dot product operation using ReRAM as computation unit. The processing elements operate in a systolic fashion, thereby maximizing input feature map reuse and minimizing interconnection cost. The system-level evaluation on several network benchmarks show that the proposed architecture can improve computation efficiency and energy efficiency compared to a state-of-the-art ReRAM-based accelerator. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019

Image smoothing and segmentation algorithms are frequently formulatedsas optimization problems. Linear and nonlinear (reciprocal) resistivesnetworks have solutions characterized by an extremum principle. Thus,sappropriately designed networks can automatically solve certainssmoothing and segmentation problems in robot vision. This papersconsiders switched linear resistive networks and nonlinear resistivesnetworks for such tasks. The latter network type is derived from thesformer via an intermediate stochastic formulation, and a new resultsrelating the solution sets of the two is given for the "zerostermperature'' limit. We then present simulation studies of severalscontinuation methods that can be gracefully implemented in analog VLSIsand that seem to give "good'' results for these non-convexsoptimization problems.