The Adaptive Priority Queue with Elimination and Combining

Priority queues are fundamental abstract data structures, often used to manage limited resources in parallel programming. Several proposed parallel priority queue implementations are based on skiplists, harnessing the potential for parallelism of the add() operations. In addition, methods such as Flat Combining have been proposed to reduce contention by batching together multiple operations to be executed by a single thread. While this technique can decrease lock-switching overhead and the number of pointer changes required by the removeMin() operations in the priority queue, it can also create a sequential bottleneck and limit parallelism, especially for non-conflicting add() operations. In this paper, we describe a novel priority queue design, harnessing the scalability of parallel insertions in conjunction with the efficiency of batched removals. Moreover, we present a new elimination algorithm suitable for a priority queue, which further increases concurrency on balanced workloads with similar numbers of add() and removeMin() operations. We implement and evaluate our design using a variety of techniques including locking, atomic operations, hardware transactional memory, as well as employing adaptive heuristics given the workload.Comment: Accepted at DISC'14 - this is the full version with appendices, including more algorithm

Diversity indices applied in desert grassland communities of Otero Mesa, New Mexico

To describe plant community (alpha) diversity on rangelands, managers are confronted with a variety of commonly used indices. The choice, performance, and interpretations of these indices are often not clear. Biodiversity indices were computed for a variety of plant communities in a desert grassland of southern New Mexico. Data consisted of reported importance values, range transect data for both grazed and ungrazed pastures, and search-and-find data specifically addressed to plant community diversity. Occurrence of threatened and endangered plants was considered by a weighting procedure. Performance of each diversity index was evaluated by ranking plant communities from low to high and comparing the rankings yielded by the various indices. Data based upon importance or dominance that omit plant species of lesser importance or dominance should not be the basis of comparisons for alpha diversity. Communities described by range transect data ranked differently depending upon the index used. The most practical measure of plant species diversity may be the number of species found by search-and-find procedures

The Effects of Load Carriage on the Ground Reaction Force Loading Rates and Physiological Responses of Soldiers

Please view abstract in the attached PDF file

On the Importance of Registers for Computability

All consensus hierarchies in the literature assume that we have, in addition to copies of a given object, an unbounded number of registers. But why do we really need these registers? This paper considers what would happen if one attempts to solve consensus using various objects but without any registers. We show that under a reasonable assumption, objects like queues and stacks cannot emulate the missing registers. We also show that, perhaps surprisingly, initialization, shown to have no computational consequences when registers are readily available, is crucial in determining the synchronization power of objects when no registers are allowed. Finally, we show that without registers, the number of available objects affects the level of consensus that can be solved. Our work thus raises the question of whether consensus hierarchies which assume an unbounded number of registers truly capture synchronization power, and begins a line of research aimed at better understanding the interaction between read-write memory and the powerful synchronization operations available on modern architectures.Comment: 12 pages, 0 figure

Native and non-native sources of carbohydrate correlate with abundance of an invasive ant

Invasive species threaten many ecological communities and predicting which communities and sites are invasible remains a key goal of invasion ecology. Although invasive ants often reach high abundances in association with plant-based carbohydrate resources, the source and provenance of these resources are rarely investigated. We characterized carbohydrate resources across ten sites with a range of yellow crazy ant abundance in Arnhem Land, Australia and New Caledonia to determine whether yellow crazy ant (Anoplolepis gracilipes) abundance and trophic position correlate with carbohydrate availability, as well as the relative importance of native and non-native sources of carbohydrates to ant diet. In both locations, measures of yellow crazy ant abundance strongly positively correlated with carbohydrate availability, particularly honeydew production, the number of tended hemipterans, and the number of plants with tended hemipterans. In Arnhem Land, 99.6% of honeydew came from native species, whereas in New Caledonia, only 0.2% of honeydew was produced by a native hemipteran. More honeydew was available in Australia due to three common large-bodied species of Auchenorrhyncha honeydew producers (treehoppers and leafhoppers). Yellow crazy ant trophic position declined with increasing yellow crazy ant abundance indicating that in greater densities the ants are obtaining more of their diet from plant-derived resources, including honeydew and extrafloral nectar. The relationships between yellow crazy ant abundance and carbohydrate availability could not be explained by any of the key environmental variables we measured at our study sites. Our results demonstrate that the positive correlation between yellow crazy ant abundance and honeydew production is not contingent upon the provenance of the hemipterans. Native sources of carbohydrate may play an underappreciated role in greatly increasing community invasibility by ants

Chinese medicine in the West 2009

In January 1985 The Journal of Chinese Medicine published an edited transcript of a discussion called ‘Acupuncture in the West’ between Peter Deadman, Ted Kaptchuk, Giovanni Maciocia and Felicity Moir. It was a particularly popular article and to celebrate the 30th anniversary of the JCM we decided to convene another discussion, in London in March 2009. Present this time were Peter Deadman (PD), Hugh MacPherson (HM), Daniel Maxwell (DM), Felicity Moir (FM) and Volker Scheid (VS). All are past or present practitioners of acupuncture and/or herbal medicine