Efficient Task Replication for Fast Response Times in Parallel Computation

One typical use case of large-scale distributed computing in data centers is to decompose a computation job into many independent tasks and run them in parallel on different machines, sometimes known as the "embarrassingly parallel" computation. For this type of computation, one challenge is that the time to execute a task for each machine is inherently variable, and the overall response time is constrained by the execution time of the slowest machine. To address this issue, system designers introduce task replication, which sends the same task to multiple machines, and obtains result from the machine that finishes first. While task replication reduces response time, it usually increases resource usage. In this work, we propose a theoretical framework to analyze the trade-off between response time and resource usage. We show that, while in general, there is a tension between response time and resource usage, there exist scenarios where replicating tasks judiciously reduces completion time and resource usage simultaneously. Given the execution time distribution for machines, we investigate the conditions for a scheduling policy to achieve optimal performance trade-off, and propose efficient algorithms to search for optimal or near-optimal scheduling policies. Our analysis gives insights on when and why replication helps, which can be used to guide scheduler design in large-scale distributed computing systems.Comment: Extended version of the 2-page paper accepted to ACM SIGMETRICS 201

Defect tolerance: fundamental limits and examples

This paper addresses the problem of adding redundancy to a collection of physical objects so that the overall system is more robust to failures. In contrast to its information counterpart, which can exploit parity to protect multiple information symbols from a single erasure, physical redundancy can only be realized through duplication and substitution of objects. We propose a bipartite graph model for designing defect-tolerant systems, in which the defective objects are replaced by the judiciously connected redundant objects. The fundamental limits of this model are characterized under various asymptotic settings and both asymptotic and finite-size systems that approach these limits are constructed. Among other results, we show that the simple modular redundancy is in general suboptimal. As we develop, this combinatorial problem of defect tolerant system design has a natural interpretation as one of graph coloring, and the analysis is significantly different from that traditionally used in information redundancy for error-control codes.©201

Crianças viadas e o deslugar do gênero na escola: notas para um feminismo cor de ar

No presente texto, problematizarei a potência do que chamarei de deslugar do gênero na escola: o gênero como matéria de uma diferença radical que pode, talvez, nos permitir vislumbrar, no campo da educação, um caminho para a construção de resistências mais plurais diante da onto-epistemologia liberal das políticas identitárias contemporâneas. Mais centralmente, e recorrendo às memórias escolares de crianças viadas, desejo mostrar a potência dos corpos abjetos para pensarmos a criação de pontos de conexão que, distante da lógica binária das identidades, nos permitem sugerir uma política interseccional pós-identitária de um feminismo cor de ar

Dark-ages Reionization and Galaxy Formation Simulation -- XIX: Predictions of infrared excess and cosmic star formation rate density from UV observations

We present a new analysis of high-redshift UV observations using a semi-analytic galaxy formation model, and provide self-consistent predictions of the infrared excess (IRX) -- $\beta$ relations and cosmic star formation rate density. We combine the Charlot & Fall dust attenuation model with the Meraxes semi-analytic model, and explore three different parametrisations for the dust optical depths, linked to star formation rate, dust-to-gas ratio and gas column density respectively. A Bayesian approach is employed to statistically calibrate model free parameters including star formation efficiency, mass loading factor, dust optical depths and reddening slope directly against UV luminosity functions and colour-magnitude relations at z ~ 4-7. The best-fit models show excellent agreement with the observations. We calculate IRX using energy balance arguments, and find that the large intrinsic scatter in the IRX -$\beta$ plane is driven by the specific star formation rate. Additionally, the difference among the three dust models suggests a factor of two systematic uncertainty in the dust-corrected star formation rate when using the Meurer IRX - $\beta$ relation at z > 4.Comment: 15 pages, 10 figure. Accepted for publication in MNRA

Lossy compression of permutations

We investigate the lossy compression of permutations by analyzing the trade-off between the size of a source code and the distortion with respect to Kendall tau distance, Spearman's footrule, Chebyshev distance and ℓ[subscript 1] distance of inversion vectors. We show that given two permutations, Kendall tau distance upper bounds the ℓ[subscript 1] distance of inversion vectors and a scaled version of Kendall tau distance lower bounds the ℓ[subscript 1] distance of inversion vectors with high probability, which indicates an equivalence of the source code designs under these two distortion measures. Similar equivalence is established for all the above distortion measures, every one of which has different operational significance and applications in ranking and sorting. These findings show that an optimal coding scheme for one distortion measure is effectively optimal for other distortion measures above.United States. Air Force Office of Scientific Research (Grant FA9550-11-1-0183)National Science Foundation (U.S.) (Grant CCF-1017772

Effects of Seed Treatments and a Soil-applied Nematicide on Corn Yields and Nematode Population Densities

Plant-parasitic nematodes are microscopic worms that feed on plants. Almost every nematode that feeds on corn is capable of feeding on many other plants. These nematode parasites are thought to be native to most Iowa soils and to have fed upon native plants before corn was grown as a cultivated crop. Population densities (numbers) of most species of plant-parasitic nematodes that feed on corn have to increase to damaging levels (called damage thresholds) before yield loss occurs. Products that are currently available to manage plant-parasitic nematodes on corn in the state include the soil-applied insecticide/nematicide Counter® and two relatively new protectant seed treatments, Avicta® and Votivo®. Counter® is a contact and systematic nematicide with the active ingredient terbufos. Avicta® is a contact nematicide (active ingredient abamectin) that moves on the surface of the root, and Votivo® is a special strain of the natural soil bacterium Bacillus firmus that grows on the root. Counter® is available from AMVAC, Avicta® from Syngenta Seedcare, and Votivo® from Bayer CropScience. The objective of this experiment was to assess and compare the nematode population densities and yields of corn growing in plots with and without the seed-treatment nematode protectants and the soil-applied nematicide Counter®

A simple class of efficient compression schemes supporting local access and editing

In this paper, we study the problem of compressing a collection of sequences of variable length that allows us to efficiently add, read, or edit an arbitrary sequence without decompressing the whole data. This problem has important applications in data servers, file-editing systems, and bioinformatics. We propose a novel and practical compression scheme, which shows that, by paying a small price in storage space (3% extra storage space in our examples), we can retrieve or edit a sequence (a few hundred bits) by accessing compressed bits close to the entropy of the sequence.United States. Air Force Office of Scientific Research (Grant FA9550-11-1-0183)National Science Foundation (U.S.) (Grant CCF-1017772

Efficiency of low versus high airline pressure in stunning cattle with a pneumatically powered penetrating captive bolt gun

The efficiency of stunning cattle was assessed in 443 animals (304 pure Zebu and 139 crossbred cattle), being mainly mature bulls and cows. Cattle were stunned using a Jarvis pneumatically powered penetrating captive bolt gun operating with low (160–175 psi, N = 82) and high (190 psi, N = 363) airline pressure, which was within the manufactures specifications. Signs of brain function and the position of the shots on the heads were recorded after stunning. Velocity of the captive bolt and its physical parameters were calculated. Cattle shot with low pressures showed more rhythmic respiration (27 vs. 8%, P < 0.001), less tongue protrusion (4 vs. 12%, P = 0.03) and less masseter relaxation (22 vs. 48%, P < 0.001). There was an increased frequency of shots in the ideal position when cattle were shot with the low compared to high airline pressures (15.3 vs. 3.1%). Bolt velocity and its physical parameters were significantly (P < 0.01) higher when using high pressure. Airline pressures below 190 psi are inappropriate when shooting adult Zebu beef cattle with pneumatically powered penetrating captive bolt guns

Effects of Seed Treatments and a Soil-applied Nematicide on Corn Yields and Nematode Population Densities

Plant-parasitic nematodes are microscopic worms that feed on plants. Almost every nematode that feeds on corn is capable of feeding on many other plants. These nematode parasites are thought to be native to most Iowa soils and to have fed upon native plants before corn was grown as a cultivated crop. Population densities (numbers) of most species of plant-parasitic nematodes that feed on corn have to increase to damaging levels (called damage thresholds) before yield loss occurs