146 research outputs found
Synthesis and Applications of Dicationic Iodide Materials for Dye-Sensitized Solar Cells
No full textDye-sensitized solar cells (DSSCs) have been receiving growing attentions as a potential alternative to order photovoltaic devices due to their high efficiency and low manufacturing cost. DSSCs are composed of a photosensitizing dye adsorbed on a mesoporous film of nanocrystalline TiO2 as a photoelectrode, an electrolyte containing triiodide/iodide redox couple, and a platinized counter electrode. To improve photovoltaic properties of DSSCs, new dicationic salts based on ionic liquids were synthesized. Quite comparable efficiencies were obtained from electrolytes with new dicationic iodide salts. The best cell performance of 7.96% was obtained with dicationic salt of PBDMIDI
StringTouch: A Non-occlusive 3DoF Haptic Interface Using String Structures for Modulating Finger Sensations
No full textProviding realistic and diverse tactile feedback during interactions with objects in virtual and augmented reality, various studies have explored the use of tangible proxies. However, tangible proxies face limitations due to their fixed physical properties, restricting the expression of various stiffness, weights, and shapes. To address these issues, we propose StringTouch, a device modulating sensations from proxies without obstructing the fingers to preserve finger sensitivity. StringTouch modulates sensations utilizing 0.2mm thin nylon threads tactor to deform fingers with 3DoF. In a user study (n = 12), our string structure showed better performance in distinguishing orientation, roughness, and weight than conditions using a 0.1 mm latex finger cot and was comparable to bare fingers in some of the discriminating tasks. Another experiment (n = 12) verified the device’s capability to modulate orientation, stiffness, and weight perceptions. Finally, in a user study (n = 10) in proxy-based VR scenarios (pouring water, touching a teddy bear, touching a bottle), participants preferred StringTouch over bare finger interactions, with most of them reporting enhanced presence
Blue-colored dyes featuring a diketopyrrolopyrrole spacer for translucent dye-sensitized solar cells
No full textWe report the facile synthesis of blue-colored dyes featuring a diketopyrrolopyrrole (DPP) spacer with dimethylamine and bis(4-dibuotxylphenyl)-phenyl-amine as donor residues (CSD-08 and CSD-09), their spectroscopic, electrochemical and colorific properties, and their application to translucent dye-sensitized solar cells (DSSCs). In the DSSCs fabricated with 5 μm-thick TiO2 photoanodes, CSD-08 and CSD-09 yield power-conversion-efficiencies of 3.43% and 3.62%, respectively, under simulated one sun illumination.
Observability analysis of power distribution systems with distributed energy resources using correlational measurements
No full textThesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 57-59).In this thesis, an observability analysis framework is proposed for power distribution systems. The framework analyzes the sufficiency of the available measurements for monitoring the system. In the areas of the network where sufficient sensors have been deployed, the complex voltage at the nodes may be estimated. The framework also provides a metric that quantifies the accuracy of these voltage estimates. Due to the cost of sensors and the size of distribution systems, it is frequently the case that the available measurements are insufficient for complete observability of the system. In this thesis, the author proposes the use of Correlational Measurements (CMs) for improving distribution system observability by leveraging correlation between loads and between Distributed Energy Resources (DERs). Load correlation due to class-residential, commercial, industrial, etc.- is captured via correlational load measurements, the first type of CM. Injection correlation of DERs-such as wind turbines located in proximity-is captured via correlational DER measurements, the second type of CM. This thesis presents the CM formulation and derives modified node voltage and branch current based state estimators (NVSE and BCSE) accommodating CMs. Additionally, this thesis contains an on-line parameter estimation scheme for CMs that improves the accuracy of state estimates over time. The observability analysis framework with CMs is demonstrated through simulations on the IEEE 123 Node Distribution Test Feeder. It is shown that the introduction of CMs leads to improved observability of the system with only a 0.7% decrease in state estimation accuracy for NVSE and a 0.5% increase in state estimation accuracy for BCSE.by Yohan M. John.S.M.S.M. Massachusetts Institute of Technology, Department of Mechanical Engineerin
My ministry with primary children Central Presbyterian Church Atlanta, Georgia September 1970 - April 1972, 1973
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An Ultra-Low-Cost Soft Error Protection Scheme Based on the Selection of Critical Variables
No full textThe exponentially increasing occurrence of soft errors makes the optimization of reliability, performance, hardware area, and power consumption one of the main concerns in modern embedded processors. Since the design cost of hardware techniques aimed at improving the reliability of microprocessors is quite expensive for resource-constrained embedded systems, software-level fault tolerance mechanisms have been proposed as an attractive solution for soft error threats. However, many software-level redundancy-based schemes are accompanied by considerable performance overhead, which is not acceptable for many embedded applications. In this work, we have introduced an ultra-low-cost soft error protection scheme for embedded applications, which works based on source-code analysis and identifying critical variables. After identification, these vital variables are adequately protected by placing runtime checks at critical points of execution. Our experimental results based on several applications demonstrate that the proposed scheme can mitigate the failure rate by 47% with negligible performance degradation
Survey of Software-Implemented Soft Error Protection
No full textAs soft errors are important design concerns in embedded systems, several schemes have been presented to protect embedded systems against them. Embedded systems can be protected by hardware redundancy; however, hardware-based protections cannot provide flexible protection due to hardware-only protection modifications. Further, they incur significant overheads in terms of area, performance, and power consumption. Therefore, hardware redundancy techniques are not appropriate for resource-constrained embedded systems. On the other hand, software-based protection techniques can be an attractive alternative to protect embedded systems, especially specific-purpose architectures. This manuscript categorizes and compares software-based redundancy techniques for general-purpose and specific-purpose processors, such as VLIW (Very Long Instruction Word) and CGRA (Coarse-Grained Reconfigurable Architectures)
Characterizing System-Level Masking Effects against Soft Errors
No full textFrom early design phases to final release, the reliability of modern embedded systems against soft errors should be carefully considered. Several schemes have been proposed to protect embedded systems against soft errors, but they are neither always functional nor robust, even with expensive overhead in terms of hardware area, performance, and power consumption. Thus, system designers need to estimate reliability quantitatively to apply appropriate protection techniques for resource-constrained embedded systems. Vulnerability modeling based on lifetime analysis is one of the most efficient ways to quantify system reliability against soft errors. However, lifetime analysis can be inaccurate, mainly because it fails to comprehensively capture several system-level masking effects. This study analyzes and characterizes microarchitecture-level and software-level masking effects by developing an automated framework with exhaustive fault injections (i.e., soft errors) based on a cycle-accurate gem5 simulator. We injected faults into a register file because errors in the register file can easily be propagated to other components in a processor. We found that only 5% of injected faults can cause system failures on an average over benchmarks, mainly from the MiBench suite. Further analyses showed that 71% of soft errors are overwritten by write operations before being used, and the CPU does not use 20% of soft errors at all after fault injections. The remainder are also masked by several software-level masking effects, such as dynamically dead instructions, compare and logical instructions that do not change the result, and incorrect control flows that do not affect program outputs
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