1,204 research outputs found
Summertime partitioning and budget of NOycompounds in the troposphere over Alaska and Canada: ABLE 3B
As part of NASA's Arctic Boundary Layer Expedition 3A and 3B field measurement programs, measurements of NO(x) HNO31, PAN, PPN, and NOy were made in the middle to lower troposphere over Alaska and Canada during the summers of 1988 and 1990. These measurements are used to assess the degree of closure within the reactive odd nitrogen (NxOy) budget through the comparison of the values of NOy measured with a catalytic convertor to the sum of individually measured NOy(i) compounds (i.e., Sigma NOy(i) = NOx + HNO3 + PAN + PPN). Significant differences were observed between the various study regions. In the lower 6 km of the troposphere over Alaska and the Hudson Bay lowlands of Canada a significant traction of the NOy budget (30 to 60 per cent) could not be accounted for by the measured Sigma NOy(i). This deficit in the NOy budget is about 100 to 200 parts per trillion by volume (pptv) in the lower troposphere (0.15 to 3 km) and about 200 to 400 pptv in the middle free troposphere (3 to 6.2 km). Conversely, the NOy budget in the northern Labrador and Quebec regions or Canada is almost totally accounted for within the combined measurement uncertainties of NOy and the various NOy(i) compounds. A substantial portion of the NOx budget's 'missing compounds' appears to be coupled to the photochemical and/or dynamical parameters influencing the tropospheric oxidative potential over these regions. A combination of factors are suggested as the causes for the variability observed in the NOy budget. In addition, the apparent stability of compounds represented by the NOy budget deficit in the lower-attitude range questions the ability of these compounds to participate as reversible reservoirs for "active" odd nitrogen and suggest that some portion of the NOy budget may consist of relatively unreactive nitrogencontaining compounds. Bei der Rationalisierung von Kommissioniersystemen besteht bei vielen Unternehmen noch Nachholbedarf. Dies ergab eine Umfrage des Fraunhofer-Instituts für Materialfluss und Logistik in Dortmund bei ca. 800 Unternehmen. Keins der Unternehmen setzt Kommissionierautomaten ein, die Voraussetzungen für durchgehende Automatisierung fehlen
A Distributed Multilevel Force-directed Algorithm
The wide availability of powerful and inexpensive cloud computing services
naturally motivates the study of distributed graph layout algorithms, able to
scale to very large graphs. Nowadays, to process Big Data, companies are
increasingly relying on PaaS infrastructures rather than buying and maintaining
complex and expensive hardware. So far, only a few examples of basic
force-directed algorithms that work in a distributed environment have been
described. Instead, the design of a distributed multilevel force-directed
algorithm is a much more challenging task, not yet addressed. We present the
first multilevel force-directed algorithm based on a distributed vertex-centric
paradigm, and its implementation on Giraph, a popular platform for distributed
graph algorithms. Experiments show the effectiveness and the scalability of the
approach. Using an inexpensive cloud computing service of Amazon, we draw
graphs with ten million edges in about 60 minutes.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Partitioner Selection with EASE to Optimize Distributed Graph Processing
For distributed graph processing on massive graphs, a graph is partitioned
into multiple equally-sized parts which are distributed among machines in a
compute cluster. In the last decade, many partitioning algorithms have been
developed which differ from each other with respect to the partitioning
quality, the run-time of the partitioning and the type of graph for which they
work best. The plethora of graph partitioning algorithms makes it a challenging
task to select a partitioner for a given scenario. Different studies exist that
provide qualitative insights into the characteristics of graph partitioning
algorithms that support a selection. However, in order to enable automatic
selection, a quantitative prediction of the partitioning quality, the
partitioning run-time and the run-time of subsequent graph processing jobs is
needed. In this paper, we propose a machine learning-based approach to provide
such a quantitative prediction for different types of edge partitioning
algorithms and graph processing workloads. We show that training based on
generated graphs achieves high accuracy, which can be further improved when
using real-world data. Based on the predictions, the automatic selection
reduces the end-to-end run-time on average by 11.1% compared to a random
selection, by 17.4% compared to selecting the partitioner that yields the
lowest cut size, and by 29.1% compared to the worst strategy, respectively.
Furthermore, in 35.7% of the cases, the best strategy was selected.Comment: To appear at IEEE International Conference on Data Engineering (ICDE
2023
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