Strong, thorough, and efficient memory protection against existing and emerging DRAM errors

Memory protection is necessary to ensure the correctness of data in the presence of unavoidable faults. As such, large-scale systems typically employ Error Correcting Codes (ECC) to trade off redundant storage and bandwidth for increased reliability. Single Device Data Correction (SDDC) ECC mechanisms are required to meet the reliability demands of servers and large-scale systems by tolerating even severe faults that disable an entire memory chip. In the future, however, stronger memory protection will be required due to increasing levels of system integration, shrinking process technology, and growing transfer rates. The energy-efficiency of memory protection is also important as DRAM already consumes a significant fraction of system energy budget. This dissertation develops a novel set of ECC schemes to provide strong, safe, flexible, and thorough protection against existing and emerging types of DRAM errors. This research also reduces energy consumption of such protection while only marginally impacting performance. First, this dissertation develops Bamboo ECC, a technique with strongerthan-SDDC correction and very safe detection capabilities (≥ 99.999994% of data errors with any severity are detected). Bamboo ECC changes ECC layout based on frequent DRAM error patterns, and can correct concurrent errors from multiple devices and all but eliminates the risk of silent data corruption. Also, Bamboo ECC provides flexible configurations to enable more adaptive graceful downgrade schemes in which the system continues to operate correctly after even severe chip faults, albeit at a reduced capacity to protect against future faults. These strength, safety, and flexibility advantages translate to a significantly more reliable memory sub-system for future exascale computing. Then, this dissertation focuses on emerging error types from scaling process technology and increasing data bandwidth. As DRAM process technology scales down to below 10nm, DRAM cells are becoming more vulnerable to errors from an imperfect manufacturing process. At the same time, DRAM signal transfers are getting more susceptible to timing and electrical noises as DRAM interfaces keep increasing signal transfer rates and decreasing I/O voltage levels. With individual DRAM chips getting more vulnerable to errors, industry and academia have proposed mechanisms to tolerate these emerging types of errors; yet they are inefficient because they rely on multiple levels of redundancy in the case of cell errors and ad-hoc schemes with suboptimal protection coverage for transmission errors. Active Guardband ECC and All-Inclusive ECC make systematic use of ECC and existing mechanisms to provide thorough end-to-end protection without requiring redundancy beyond what is common today. Finally, this dissertation targets the energy efficiency of memory protection. Frugal ECC combines ECC with fine-grained compression to provide versatile and energy-efficient protection. Frugal ECC compresses main memory at cache-block granularity, using any left over space to store ECC information. Frugal ECC allows more energy-efficient memory configurations while maintaining SDDC protection. Its tailored compression scheme minimizes insufficiently compressed blocks and results in acceptable performance overhead. The strong, thorough, and efficient protection described by this dissertation may allow for more aggressive design of future computing systems with larger integration, finer process technology, higher transfer rates, and better energy efficiencyElectrical and Computer Engineerin

Sustainable development of refrigerator systems using replacement environmentally acceptable refrigerants

Environmental considerations have led to the phase out of chlorofluorocarbon (CFC) refrigerants from the domestic refrigeration industry. One intriguing aspect is that the chlorine in CFCs is a good lubricating agent and any deterioration of system performance may adversely influence other environmental considerations. Based on the above, the aim of this research is to address the sustainable development of domestic refrigeration systems using the replacement refrigerant HFC-134a. The work focuses on the emissions that may arise if the electrical consumption of the product deteriorates or its durability is curtailed. Tribological characteristics on compressor components influence both of these product attributes and therefore a thorough system analysis was carried out. An in-house built experimental test rig, which monitored slight variations in the electrical power drawn by a reciprocating hermetic compressor, was used under different experimental conditions. Furthermore, a detailed life cycle assessment on a domestic refrigerator was performed to help quantify the ensuing environmental burdens. In this way, a relation between tribological characteristics, power consumption and environmental impact was studied. Results have shown that the CFC substitute will increase friction and wear characteristics on the aluminium alloy connecting rod and the steel gudgeon pin. These characteristics led to an increase in the electrical energy consumption of the compressor such that the indirect global warming implications are set to rise with HFC-134a. If the sustainable development of this product is to be ascertained then a change in refrigerants alone will not suffice. New design considerations, primarily aimed at servicing and extending the life of the hermetic compressor itself, are considered. This work helps stimulate new ideas to address environmental issues influenced by traditional engineering disciplines. For this reason additional future research work, which will help determine these implications further, is outlined

Aeronautical engineering: A continuing bibliography with indexes (supplement 234)

This bibliography lists 539 reports, articles, and other documents introduced into the NASA scientific and technical information system in December, 1988. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Detection, Diagnosis and Prognosis: Contribution to the energy challenge: Proceedings of the Meeting of the Mechanical Failures Prevention Group

The contribution of failure detection, diagnosis and prognosis to the energy challenge is discussed. Areas of special emphasis included energy management, techniques for failure detection in energy related systems, improved prognostic techniques for energy related systems and opportunities for detection, diagnosis and prognosis in the energy field

Prognostic Health Assessment of an Automotive Proton Exchange Membrane Fuel Cell System

Proton exchange membrane fuel cells are a promising technology for the automotive industry. However, it is necessary to develop effective diagnostic tools to improve system reliability and operational life to be competitive in the automotive market. Early detection and diagnosis of fuel cell faults may lead to increased system reliability and performance. An efficient on-line diagnosis system may prevent irreparable damage due to poor control and system fatigue. Current attempts to monitor fuel cell stack health are limited to specialized tests that require numerous parameters. An increased effort exists to minimize parameter input and maximize diagnostic robustness. Most methods use complex models or black-box methods to determine a singular fault mode. Limited research exists with pre-processing or statistical methods. This research examines the effectiveness of a Na¨ıve Bayes classifier on determining multiple states of health; such as healthy, dry, degraded catalyst, and inert gas build-up. Independent component analysis and principal component analysis are investigated for pre-processing. An automotive style fuel cell model is developed to generate data for these purposes. Since automotive applications have limited computational power, a system that minimizes the number of inputs and computational complexity is preferred

Non-intrusive fault detection in reciprocating compressors

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 128-130).This thesis presents a set of techniques for non-intrusive sensing and fault detection in reciprocating compressors driven by induction motors. The procedures developed here are "non-intrusive" because they rely only on electrical measurements to reconstruct the mechanical signals internal to the compressor. This allows for easy and non-intrusive determination of many fault sensitive signals that usually require complicated, expensive, and time consuming operations to measure. A sample of the signals produced by the procedures of this thesis are estimates of the cylinder suction and discharge pressures and a composite torque signal containing the effects of the mechanical loads within the compressor. This load torque signal is especially sensitive to faults, and a demonstration of the effect on and detection of compressor valve faults from the load torque signal is given. One of the key steps in the algorithm presented here is a procedure to "invert" the induction motor dynamic model equations to allow direct calculation of motor shaft speed and torque from stator current and voltage measurements. For this procedure a non-intrusive method to estimate motor model parameters from an in-situ induction motor driving a periodic load was developed.by Christopher James Schantz.S.M

Gas Turbine Blade Failures - Causes, Avoidance, And Troubleshooting.

Tutorialpg. 129-180With blading problems accounting for as many as 42 percent of the failures in gas turbines (Allianz, 1 978) and with its severe effect on plant availability, there is a pressing need for a unified treatment of the causes, failure modes, and troubleshooting to assist plant engineers in tackling blade failure problems. This paper provides a comprehensive practical treatment of the subject, taking into account the complex nature of blading problems, influence of the operating environment, design factors, and maintenance practices. Blade failure modes such as fatigue, environmental attack, creep, erosion, and embrittlement are addressed along with a synopsis of design tools to review blade reliability. Peripheral issues affecting blade integrity such as fuel and blade quality control are addressed. A blade failure troubleshooting chart is furnished to assist users in diagnosing common failure modes. The object of this paper is to show, in the context of blading problems, the interrelationship between design, operation, maintenance, and the operational envelope. Several case studies are presented dealing with a variety of failure modes. The treatment focuses on practical troubleshooting of blading problems augmented, in some cases, by the use of analytical tools. APPENDIX A provides applicable tools, rules of thumb, and formulae that can be used by gas turbine users for design review and troubleshooting