660 research outputs found
Approximation with Error Bounds in Spark
We introduce a sampling framework to support approximate computing with
estimated error bounds in Spark. Our framework allows sampling to be performed
at the beginning of a sequence of multiple transformations ending in an
aggregation operation. The framework constructs a data provenance tree as the
computation proceeds, then combines the tree with multi-stage sampling and
population estimation theories to compute error bounds for the aggregation.
When information about output keys are available early, the framework can also
use adaptive stratified reservoir sampling to avoid (or reduce) key losses in
the final output and to achieve more consistent error bounds across popular and
rare keys. Finally, the framework includes an algorithm to dynamically choose
sampling rates to meet user specified constraints on the CDF of error bounds in
the outputs. We have implemented a prototype of our framework called
ApproxSpark, and used it to implement five approximate applications from
different domains. Evaluation results show that ApproxSpark can (a)
significantly reduce execution time if users can tolerate small amounts of
uncertainties and, in many cases, loss of rare keys, and (b) automatically find
sampling rates to meet user specified constraints on error bounds. We also
explore and discuss extensively trade-offs between sampling rates, execution
time, accuracy and key loss
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EDDE : a framework to explore, design, develop and evaluate technology-enhanced instruction for construction
textTechnology-enhanced instruction has a great potential to support the learning process. However, the engaging power of technology can become a distracting factor if it is not deployed properly. Unfortunately, the current literature in instructional design and user interface design is broad and not easily accessible by construction faculty. This dissertation presents a framework to guide the development of technology-assisted instruction for the classroom. The framework developed is called EDDE which stands for four conceptual steps involved in the creation of a technology-supported teaching tool: Explore, Design, Develop, and Evaluate. EDDE contains a novel synthesis of the literature in instructional design and user interface design as well as survey data of student subject matter knowledge and information technology background. A computerized tool called EDDEaid makes accessible the large store of knowledge supporting EDDE. Assessment of EDDEaid is presented with evaluation results from nine university faculty that teach construction subjects as well as through critique of and changes to an existing interactive learning tool. EDDE and EDDEaid are found to contribute to the body of knowledge regarding the deployment of technology-enhanced instruction and provide support to construction faculty developing learning tools.Civil, Architectural, and Environmental Engineerin
Retrieval of interatomic separations of molecules from laser-induced high-order harmonic spectra
We illustrate an iterative method for retrieving the internuclear separations
of N, O and CO molecules using the high-order harmonics generated
from these molecules by intense infrared laser pulses. We show that accurate
results can be retrieved with a small set of harmonics and with one or few
alignment angles of the molecules. For linear molecules the internuclear
separations can also be retrieved from harmonics generated using isotropically
distributed molecules. By extracting the transition dipole moment from the
high-order harmonic spectra, we further demonstrated that it is preferable to
retrieve the interatomic separation iteratively by fitting the extracted dipole
moment. Our results show that time-resolved chemical imaging of molecules using
infrared laser pulses with femtosecond temporal resolutions is possible.Comment: 14 pages, 9 figure
Stability of bedforms in laminar flows with free surface: from bars to ripples
International audienceThe present paper is devoted to the formation of sand patterns by laminar flows. It focuses on the rhomboid beach pattern, formed during the backswash. A recent bedload transport model, based on a moving-grains balance, is generalized in three dimensions for viscous flows. The water flow is modelled by the full incompressible Navier–Stokes equations with a free surface. A linear stability analysis then shows the simultaneous existence of two distinct instabilities, namely ripples and bars. The comparison of the bar instability characteristics with laboratory rhomboid patterns indicates that the latter could result from the nonlinear evolution of unstable bars. This result, together with the sensibility of the stability analysis with respect to the parameters of the transport law, suggests that the rhomboid pattern could help improving sediment transport models, so critical to geomorphologists
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