9,424 research outputs found
Histogram-Based Flash Channel Estimation
Current generation Flash devices experience significant read-channel
degradation from damage to the oxide layer during program and erase operations.
Information about the read-channel degradation drives advanced signal
processing methods in Flash to mitigate its effect. In this context, channel
estimation must be ongoing since channel degradation evolves over time and as a
function of the number of program/erase (P/E) cycles. This paper proposes a
framework for ongoing model-based channel estimation using limited channel
measurements (reads). This paper uses a channel model characterizing
degradation resulting from retention time and the amount of charge programmed
and erased. For channel histogram measurements, bin selection to achieve
approximately equal-probability bins yields a good approximation to the
original distribution using only ten bins (i.e. nine reads). With the channel
model and binning strategy in place, this paper explores candidate numerical
least squares algorithms and ultimately demonstrates the effectiveness of the
Levenberg-Marquardt algorithm which provides both speed and accuracy.Comment: 6 pages, 8 figures, Submitted to the IEEE International
Communications Conference (ICC) 201
Increasing Flash Memory Lifetime by Dynamic Voltage Allocation for Constant Mutual Information
The read channel in Flash memory systems degrades over time because the
Fowler-Nordheim tunneling used to apply charge to the floating gate eventually
compromises the integrity of the cell because of tunnel oxide degradation.
While degradation is commonly measured in the number of program/erase cycles
experienced by a cell, the degradation is proportional to the number of
electrons forced into the floating gate and later released by the erasing
process. By managing the amount of charge written to the floating gate to
maintain a constant read-channel mutual information, Flash lifetime can be
extended. This paper proposes an overall system approach based on information
theory to extend the lifetime of a flash memory device. Using the instantaneous
storage capacity of a noisy flash memory channel, our approach allocates the
read voltage of flash cell dynamically as it wears out gradually over time. A
practical estimation of the instantaneous capacity is also proposed based on
soft information via multiple reads of the memory cells.Comment: 5 pages. 5 figure
A modified flood severity assessment for enhanced decision support: application to the Boscastle flash flood of 2004
A modified flash flood severity assessment is presented, based on scoring a set of factors according to their potential for generating extreme catchment-scale flooding. Improvements are made to the index through incorporation of parameter uncertainties, managing data absence, and clearer graphical communication. The motive for proposing these changes is to better inform flood managers during the development of a flash flood that may require an emergency response. This modified decision-support system is demonstrated for the Boscastle flood of 2004 and other historical floods in the United Kingdom. For Boscastle, the extreme nature of the flood is underestimated, which is likely to be due to the lack of sophistication in weighting flood parameters. However, the proposed amendments are able to rapidly reflect the reliability of a catchment severity rating, which may further enhance this technique as a decision-support tool alongside radar observations of localized storms
First and subsequent return stroke properties of cloud-to-ground lightning
Lightning properties obtained by a network of magnetic direction finders and by electric field measurements for distances from 50 to 500 km are compared for three summer thunderstorms in Sweden. The data from direct field recordings indicate 31, 17, and 26 pcts. of negative subsequent return strokes with peak current (as inferred from the peak electric field) higher than the first. Electric fields from first strokes are compared with normalized amplitudes registered by the magnetic direction finding system. The efficiency of detection by the magnetic direction finding system is discussed in terms of the percentage of lightning flashes observed by electric field measurements that are not localized. Statistics of the number of strokes per flash and the interstroke time intervals are presented
Electron identification using the TOPAZ detector at TRISTAN
We present an electron-identification method using the time-projection
chamber and the lead-glass calorimeter in the TOPAZ detector system. Using this
method we have achieved good electron identification against hadron backgrounds
over a wide momentum range in the hadronic events produced by both
single-photon exchange and two-photon processes. Pion-rejection factors and
electron efficiencies were 163 and 68.4\% for high- electrons and 137 and
42.7\% for low- electrons in the single-photon-exchange process, and 8600
and 36.0\% for the two-photon process, respectively.Comment: 32 pages, latex format (article), 24 figures, submitted for
publication
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