Error-efficient computing systems

This survey explores the theory and practice of techniques to make computing systems faster or more energy-efficient by allowing them to make controlled errors. In the same way that systems which only use as much energy as necessary are referred to as being energy-efficient, you can think of the class of systems addressed by this survey as being error-efficient: They only prevent as many errors as they need to. The definition of what constitutes an error varies across the parts of a system. And the errors which are acceptable depend on the application at hand. In computing systems, making errors, when behaving correctly would be too expensive, can conserve resources. The resources conserved may be time: By making some errors, systems may be faster. The resource may also be energy: A system may use less power from its batteries or from the electrical grid by only avoiding certain errors while tolerating benign errors that are associated with reduced power consumption. The resource in question may be an even more abstract quantity such as consistency of ordering of the outputs of a system. This survey is for anyone interested in an end-to-end view of one set of techniques that address the theory and practice of making computing systems more efficient by trading errors for improved efficiency

Perceived-Color Approximation Transforms for Programs that Draw

© 1981-2012 IEEE. Human color perception acuity is not uniform across colors. This makes it possible to transform drawing programs to generate outputs whose colors are perceptually equivalent but numerically distinct. One benet of such transformations is lower display power dissipation on organic light-emitting diode (OLED) displays. We introduce Ishihara, a language for 2D drawing that lets programs specify perceptual-color equivalence classes to use in drawing operations enabling compile-time and runtime transformations that trade perceived color accuracy for lower OLED display power dissipation

Efficiency Limits for Value-Deviation-Bounded Approximate Communication

Transferring data between integrated circuits accounts for a growing proportion of system power in wearable and mobile systems. The dynamic component of power dissipated in this data transfer can be reduced by reducing signal transitions. Techniques for reducing signal transitions on communication links have traditionally been targeted at parallel buses and can therefore not be applied when the transfer interfaces are serial buses. In this article, we address the issue of the best-case effectiveness of techniques to reduce signal transitions on serial buses, if these techniques also allow some error in the numeric interpretation of transmitted data. For many embedded applications, exchanging numeric accuracy for power reduction is a worthwhile tradeoff. We present a study of the efficiency of these value-deviation-bounded approximate serial data encoders (VDBS data encoders) and proofs of their properties. The bounds and proofs we present yield new insights into the best possible tradeoffs between dynamic power reduction and approximation error that can be achieved in practice. The insights are important regardless of whether actual practical VDBS data encoders are implemented in software or in hardware

Implementing a technique to improve the accuracy of shuffler assays of waste drums

The accuracy of shuffler assays for fissile materials is generally limited by the accuracy of the calibration standards, but when the matrix in a large drum has a sufficiently high hydrogen density (as exists in paper, for example) the accuracy in the active mode can be adversely affected by a nonuniform distribution of the fissile material within the matrix. This paper reports on a technique to determine the distribution nondestructively using delayed neutron signals generated by the shuffler itself. In assays employing this technique, correction factors are applied to the result of the conventional assay according to the distribution. Maximum inaccuracies in assays with a drum of paper, for example, are reduced by a factor of two or three

Burnup measurements with the Los Alamos fork detector

The fork detector system can determine the burnup of spent-fuel assemblies. It is a transportable instrument that can be mounted permanently in a spent-fuel pond near a loading area for shipping casks, or be attached to the storage pond bridge for measurements on partially raised spent-fuel assemblies. The accuracy of the predicted burnup has been demonstrated to be as good as 2% from measurements on assemblies in the United States and other countries. Instruments have also been developed at other facilities throughout the world using the same or different techniques, but with similar accuracies. 14 refs., 2 figs., 2 tabs

Application of curium measurements for safeguarding at reprocessing plants. Study 1: High-level liquid waste and Study 2: Spent fuel assemblies and leached hulls

In large-scale reprocessing plants for spent fuel assemblies, the quantity of plutonium in the waste streams each year is large enough to be important for nuclear safeguards. The wastes are drums of leached hulls and cylinders of vitrified high-level liquid waste. The plutonium amounts in these wastes cannot be measured directly by a nondestructive assay (NDA) technique because the gamma rays emitted by plutonium are obscured by gamma rays from fission products, and the neutrons from spontaneous fissions are obscured by those from curium. The most practical NDA signal from the waste is the neutron emission from curium. A diversion of waste for its plutonium would also take a detectable amount of curium, so if the amount of curium in a waste stream is reduced, it can be inferred that there is also a reduced amount of plutonium. This report studies the feasibility of tracking the curium through a reprocessing plant with neutron measurements at key locations: spent fuel assemblies prior to shearing, the accountability tank after dissolution, drums of leached hulls after dissolution, and canisters of vitrified high-level waste after separation. Existing pertinent measurement techniques are reviewed, improvements are suggested, and new measurements are proposed. The authors integrate these curium measurements into a safeguards system

Chisel: Reliability- and Accuracy-Aware Optimization of Approximate Computational Kernels

The accuracy of an approximate computation is the distance between the result that the computation produces and the corresponding fully accurate result. The reliability of the computation is the probability that it will produce an acceptably accurate result. Emerging approximate hardware platforms provide approximate operations that, in return for reduced energy consumption and/or increased performance, exhibit reduced reliability and/or accuracy. We present Chisel, a system for reliability- and accuracy-aware optimization of approximate computational kernels that run on approximate hardware platforms. Given a combined reliability and/or accuracy specification, Chisel automatically selects approximate kernel operations to synthesize an approximate computation that minimizes energy consumption while satisfying its reliability and accuracy specification. We evaluate Chisel on five applications from the image processing, scientific computing, and financial analysis domains. The experimental results show that our implemented optimization algorithm enables Chisel to optimize our set of benchmark kernels to obtain energy savings from 8.7% to 19.8% compared to the fully reliable kernel implementations while preserving important reliability guarantees.National Science Foundation (U.S.) (Grant CCF-1036241)National Science Foundation (U.S.) (Grant CCF-1138967)National Science Foundation (U.S.) (Grant IIS-0835652)United States. Dept. of Energy (Grant DE-SC0008923)United States. Defense Advanced Research Projects Agency (Grant FA8650-11-C-7192)United States. Defense Advanced Research Projects Agency (Grant FA8750-12-2-0110)United States. Defense Advanced Research Projects Agency (Grant FA-8750-14-2-0004

Shuffler measurements of previously unverified and unconfirmed inventory items

The two new shufflers at Los Alamos National Laboratory (LANL) have been used on uranium inventory items that could not be previously verified or confirmed because of the lack of a suitable assay instrument. A third shufflers at the Westinghouse Savannah River Site (SRS) is currently measuring yet another inventory. One of the LANL inventories had items with only uranium while the second inventory had many mixtures of uranium and plutonium. The only calibration standards available were uniformly shaped cans of uranium oxide with no significant impurities. The inventory items had a wide variety of compositions, impurities, and geometric forms. Three measurement plans have been used with increasing sophistication as our experience and resources have grown. They are semi-quantitative and quantitative analyses of only the active-mode shufflers data, and quantitative analyses of active- and passive-shuffler data combined with isotopics and enrichments deduced from gamma-ray measurements. Measurement results for the first two approaches for the LANL inventories are given in this paper. Results of the third approach in the SRS case will be reported at a later date after they are completed

Design of a new portable fork detector for research reactor spent fuel

There are many situations in nonproliferation and international safeguards when one needs to verify spent research-reactor fuel. Special inspections, a reactor coming under safeguards for the first time, and failed surveillance are prime examples. Several years ago, Los Alamos developed the FORK detector for the IAEA and EURATOM. This detector, together with the GRAND electronics package, is used routinely by inspectors to verify light-water-reactor spent fuels. Both the FORK detector and the GRAND electronics technologies have been transferred and are now commercially available. Recent incidents in the world indicate that research-reactor fuel is potentially a greater concern for proliferation than light-water-reactor fuels. A device similar to the FORK/GRAND should be developed to verify research-reactor spent fuels because the signals from light-water-reactor spent fuel are quite different than those from research-reactor fuels

The design of the DUPIC spent fuel bundle counter

A neutron coincidence detector had been designed to measure the amount of curium in the fuel bundles and associated process samples used in the direct use of plutonium in Canadian deuterium-uranium (CANDU) fuel cycle. All of the sample categories are highly radioactive from the fission products contained in the pressurized water reactor (PWR) spent fuel feed stock. Substantial shielding is required to protect the He-3 detectors from the intense gamma rays. The Monte Carlo neutron and photon calculational code has been used to design the counter with a uniform response profile along the length of the CANDU-type fuel bundle. Other samples, including cut PWR rods, process powder, waste, and finished rods, can be measured in the system. This report describes the performance characteristics of the counter and support electronics. 3 refs., 23 figs., 6 tabs