126 research outputs found
RowHammer: Reliability Analysis and Security Implications
As process technology scales down to smaller dimensions, DRAM chips become
more vulnerable to disturbance, a phenomenon in which different DRAM cells
interfere with each other's operation. For the first time in academic
literature, our ISCA paper exposes the existence of disturbance errors in
commodity DRAM chips that are sold and used today. We show that repeatedly
reading from the same address could corrupt data in nearby addresses. More
specifically: When a DRAM row is opened (i.e., activated) and closed (i.e.,
precharged) repeatedly (i.e., hammered), it can induce disturbance errors in
adjacent DRAM rows. This failure mode is popularly called RowHammer. We tested
129 DRAM modules manufactured within the past six years (2008-2014) and found
110 of them to exhibit RowHammer disturbance errors, the earliest of which
dates back to 2010. In particular, all modules from the past two years
(2012-2013) were vulnerable, which implies that the errors are a recent
phenomenon affecting more advanced generations of process technology.
Importantly, disturbance errors pose an easily-exploitable security threat
since they are a breach of memory protection, wherein accesses to one page
(mapped to one row) modifies the data stored in another page (mapped to an
adjacent row).Comment: This is the summary of the paper titled "Flipping Bits in Memory
Without Accessing Them: An Experimental Study of DRAM Disturbance Errors"
which appeared in ISCA in June 201
Improving DRAM Performance by Parallelizing Refreshes with Accesses
Modern DRAM cells are periodically refreshed to prevent data loss due to
leakage. Commodity DDR DRAM refreshes cells at the rank level. This degrades
performance significantly because it prevents an entire rank from serving
memory requests while being refreshed. DRAM designed for mobile platforms,
LPDDR DRAM, supports an enhanced mode, called per-bank refresh, that refreshes
cells at the bank level. This enables a bank to be accessed while another in
the same rank is being refreshed, alleviating part of the negative performance
impact of refreshes. However, there are two shortcomings of per-bank refresh.
First, the per-bank refresh scheduling scheme does not exploit the full
potential of overlapping refreshes with accesses across banks because it
restricts the banks to be refreshed in a sequential round-robin order. Second,
accesses to a bank that is being refreshed have to wait.
To mitigate the negative performance impact of DRAM refresh, we propose two
complementary mechanisms, DARP (Dynamic Access Refresh Parallelization) and
SARP (Subarray Access Refresh Parallelization). The goal is to address the
drawbacks of per-bank refresh by building more efficient techniques to
parallelize refreshes and accesses within DRAM. First, instead of issuing
per-bank refreshes in a round-robin order, DARP issues per-bank refreshes to
idle banks in an out-of-order manner. Furthermore, DARP schedules refreshes
during intervals when a batch of writes are draining to DRAM. Second, SARP
exploits the existence of mostly-independent subarrays within a bank. With
minor modifications to DRAM organization, it allows a bank to serve memory
accesses to an idle subarray while another subarray is being refreshed.
Extensive evaluations show that our mechanisms improve system performance and
energy efficiency compared to state-of-the-art refresh policies and the benefit
increases as DRAM density increases.Comment: The original paper published in the International Symposium on
High-Performance Computer Architecture (HPCA) contains an error. The arxiv
version has an erratum that describes the error and the fix for i
Impact of Dietary Fat Source on Beef Display Life
This study was conducted to evaluate the effects of dietary fat source with modified distillers grains plus solubles (MDGS) on beef display life. Steers were fed either a corn control, full-fat MDGS, de-oiled MDGS, or de-oiled MDGS plus corn oil diet. Strip loins were aged for 2, 9, 16 and 23 days and placed under retail conditions for 7 days. Results suggest that feeding MDGS to cattle increases polyunsaturated fatty acid content of beef and has the potential to reduce beef color and lipid stability in comparison to corn diets. These data indicate that feeding MDGS to cattle may decrease beef display life. Addition of corn oil to de-oiled MDGS decreased redness and increased discoloration and lipid oxidation in comparison to corn control diets
The Efficacy of Error Mitigation Techniques for DRAM Retention Failures: A Comparative Experimental Study
As DRAM cells continue to shrink, they become more susceptible to retention failures. DRAM cells that permanently exhibit short retention times are fairly easy to identify and repair through the use of memory tests and row and column redundancy. However, the retention time of many cells may vary over time due to a property called Variable Retention Time (VRT). Since these cells intermittently transition between failing and non-failing states, they are particularly difficult to identify through memory tests alone. In addition, the high temperature packaging process may aggravate this problem as the susceptibility of cells to VRT increases after the assembly of DRAM chips. A promising alternative to manufacturetime testing is to detect and mitigate retention failures after the system has become operational. Such a system would require mechanisms to detect and mitigate retention failures in the field, but woul
The Relationship between Marbling, Superoxide Dismutase, and Beef Tenderness
This study was conducted to evaluate the relationships between animal oxidative status (as indicated by superoxide dismutase [SOD] activity) to marbling and beef tenderness. Prime and Select-grade strip loins were selected and aged for 2, 7, 14, 21, and 28 days for Warner Bratzler shear force, Troponin-T, and SOD activity. Results showed that meat exhibiting higher levels of marbling had lower shear force values and thus were more tender. Low-marbled samples tended to have a greater tenderness response to aging. The effect of oxidative stress, however, was not evident in this study as SOD values were similar. Although the effects of oxidative stress on beef tenderness are still unclear, results from this study provide a conceptual foundation for a new research perspective on meat tenderness
FHEmem: A Processing In-Memory Accelerator for Fully Homomorphic Encryption
Fully Homomorphic Encryption (FHE) is a technique that allows arbitrary
computations to be performed on encrypted data without the need for decryption,
making it ideal for securing many emerging applications. However, FHE
computation is significantly slower than computation on plain data due to the
increase in data size after encryption. Processing In-Memory (PIM) is a
promising technology that can accelerate data-intensive workloads with
extensive parallelism. However, FHE is challenging for PIM acceleration due to
the long-bitwidth multiplications and complex data movements involved. We
propose a PIM-based FHE accelerator, FHEmem, which exploits a novel processing
in-memory architecture to achieve high-throughput and efficient acceleration
for FHE. We propose an optimized end-to-end processing flow, from low-level
hardware processing to high-level application mapping, that fully exploits the
high throughput of FHEmem hardware. Our evaluation shows FHEmem achieves
significant speedup and efficiency improvement over state-of-the-art FHE
accelerators
The regulation of equatorial Pacific new production and pCO 2 by silicate-limited diatoms
a b s t r a c t Modeling and data from the JGOFS EqPac program suggested that the eastern equatorial Pacific upwelling ecosystem includes a quasi-chemostat culture system dominated by diatoms and limited by Si(OH) 4 due to a low ratio of Si(OH) 4 to NO 3 in the upwelling source water, the Equatorial Undercurrent. Diatoms were hypothesized to be the major users of NO 3 in this system and the amount assimilated limited by the low amount of Si(OH) 4 available. As a consequence NO 3 is left in the surface waters along with unused CO 2 . Two cruises to the eastern equatorial Pacific (EB04 and EB05) were made to test the existing hypothesis of Si(OH) 4 limitation, and study the roles of source concentrations of Si(OH) 4 and Fe, and nutrient uptake kinetics for comparison with model predictions. Fractionated nitrogen uptake measurements showed that diatoms at times take up the major portion of the NO 3 . Picoplankton and some phytoplankton in the 4 5-mm size group carried out primarily regenerated production, i.e. NH 4 uptake in a grazing dominated system. Equatorial diatoms followed uptake kinetics for Si(OH) 4 and NO 3 uptake as observed in laboratory investigations of diatoms under Si(OH) 4 and Fe limitations. Si(OH) 4 uptake responded to additions of Si(OH) 4 on a time scale of hours in uptake kinetic experiments while NO 3 uptake was unaffected by added NO 3 . The uptake of Si(OH) 4 varied in a narrow range on a Michaelis-Menten hyperbola of Si(OH) 4 uptake vs. Si(OH) 4 concentration, with a maximal Si(OH) 4 uptake rate, V 0 maxSi set to a relatively low value by some factor(s) other than Fe on a longer time scale, i.e., days in shipboard enclosures. Simply enclosing water collected from the mid euphotic zone and incubating for some days on deck at 50% surface irradiance increased
Fresh Beef Quality from Cattle Fed Field Peas During Pasture and Finishing Phases of Production
This study evaluated the use of field peas during two phases of production on fresh beef quality. Cattle (n = 232) were assigned to one of six dietary treatments in a 3x2 factorial design consisting of 3 pasture and 2 finishing supplementations. The pasture phase consisted of 1) no supplement, 2) field peas at 0.5% body weight (BW), or 3) dry-rolled corn supplement at 0.5% BW. The finishing phase consisted of 1) no field peas or 2) field peas at 20% dry-matter basis. Strip loin samples, aged 14 d, were subjected to retail display (RD) for an additional 7 d. Tenderness via Warner-Bratzler shear force (WBSF) and Slice Shear force (SSF), objective (L*, a*, and b*) and subjective color, lipid oxidation (TBARS) and fatty acid composition were evaluated. Dietary treatment had no effect on tenderness. Steak discoloration was low (< 3%). All objective color measurements displayed interactions between pasture and finishing diets (L*, P = 0.0035; a*, P = 0.0189; b*, P < 0.0001) yet no consistent patterns among treatments could be identified. Extended aging periods would be required to visually influence consumer color perception. Beef finished with field peas had slightly greater lipid oxidation than samples from cattle not receiving field peas during finishing (1.56 vs. 1.44 mg malonaldehyde/kg tissue, respectively; P = 0.0541). There was a significant interaction between pasture and finishing treatments for C15:1 (P = 0.0331). Feeding field peas during the pasture phase increased C 18:2 (P = 0.0381) relative to cattle supplemented with corn; cattle without supplement in the pasture phase had intermediate amounts of C18:2. Total saturated, unsaturated, monounsaturated, and polyunsaturated fatty acids (P > 0.05) were unaffected by dietary treatments. Field peas may be used for cattle with minimal negative impact on fresh meat quality
ReQON: a Bioconductor package for recalibrating quality scores from next-generation sequencing data
AbstractBackgroundNext-generation sequencing technologies have become important tools for genome-wide studies. However, the quality scores that are assigned to each base have been shown to be inaccurate. If the quality scores are used in downstream analyses, these inaccuracies can have a significant impact on the results.ResultsHere we present ReQON, a tool that recalibrates the base quality scores from an input BAM file of aligned sequencing data using logistic regression. ReQON also generates diagnostic plots showing the effectiveness of the recalibration. We show that ReQON produces quality scores that are both more accurate, in the sense that they more closely correspond to the probability of a sequencing error, and do a better job of discriminating between sequencing errors and non-errors than the original quality scores. We also compare ReQON to other available recalibration tools and show that ReQON is less biased and performs favorably in terms of quality score accuracy.ConclusionReQON is an open source software package, written in R and available through Bioconductor, for recalibrating base quality scores for next-generation sequencing data. ReQON produces a new BAM file with more accurate quality scores, which can improve the results of downstream analysis, and produces several diagnostic plots showing the effectiveness of the recalibration
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