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Spark (mathematics)

About: Spark (mathematics) is a research topic. Over the lifetime, 7304 publications have been published within this topic receiving 63322 citations.


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Book ChapterDOI
14 Jun 2017
TL;DR: Different scalable methods to predict time series of very long length such as time series with a high sampling frequency and the Apache Spark framework for distributed computing is proposed in order to achieve the scalability of the methods.
Abstract: This paper presents different scalable methods to predict time series of very long length such as time series with a high sampling frequency The Apache Spark framework for distributed computing is proposed in order to achieve the scalability of the methods Namely, the existing MLlib machine learning library from Spark has been used Since MLlib does not support multivariate regression, the forecasting problem has been split into h forecasting subproblems, where h is the number of future values to predict Then, representative forecasting methods of different nature have been chosen such as models based on trees, two ensembles techniques (gradient-boosted trees and random forests), and a linear regression as a reference method Finally, the methodology has been tested on a real-world dataset from the Spanish electricity load data with a ten-minute frequency

19 citations

Journal ArticleDOI
TL;DR: This work proposes a non-iterative algorithm called parallel two-phase mic-mac hot topic detection (TMHTD), and implements it in the Apache Spark environment, and indicates that the accuracy and performance of the TMHTD algorithm are significant improvements over previous methods.

19 citations

Proceedings ArticleDOI
TL;DR: Cheng et al. as mentioned in this paper used head space gas chromatography to measure solubilities, and Nuclear Magnetic Resonance (NMR) was used to establish diffusion rates for the fuel components and lubricants.
Abstract: One mechanism by which some fuel may escape the main combustion process in spark-ignition engines and be exhausted as unburned hydrocarbons is by absorption in the lubricating oil on the cylinder liner. The importance of this mechanism is, however, uncertain. Modeling studies suggest that the process can take place within an engine cycle, and that the amount of fuel absorbed in the oil layer is significant. Investigations in combustion bombs, and engines operated without lubricant indicate that this contribution is substantial. However, several researchers have reported no significant effect, when using combinations of fuels and oils with very different solubility characteristics. This study comprise the results from several experiments and modeling efforts. A ten component synthetic fuel, and different lubricants formulated to study the effect of base stock and viscosity were tested. The predicted variation in oil layer thickness caused by viscosity differences, were of the order of 20-40%. Steady state engine tests were carried out at three different coolant temperatures using a single cylinder engine with the combustion chamber of a production engine. A piston with reduced ring-pack crevices, and a cylinder head gasket designed to line up flush with the liner, were used to minimize the combustion chamber crevice volumes, and thus focus on HC derived from the oil layer mechanism. In addition to total HC, speciated engine-out emissions were recorded for the cold operating condition. Critical unknown physical parameters for the fuel components and lubricants were experimentally determined. Head space gas chromatography was used to measure solubilities, and Nuclear Magnetic Resonance was used to establish diffusion rates. Numerical modeling was employed to estimate the oil layer thickness, and the absorption rates for the individual fuel components. The estimated differences in absorption rate or \"source strength\" for the different lubricants, as caused primarily by different oil layer thickness, and fuel-oil solubility were of the order of 20%. The speciated emissions showed some sensitivity to oil layer thickness at low load and speed, with thicker oil layers producing more of the heavy, i.e. more soluble, fuel components. At higher loads and speeds speciated emissions showed very little to none sensitivity to oil layer thickness. For total engine-out HC, i.e. fuel and non-fuel HC, no significant effect of oil layer thickness, or calculated source strength, was observed at any of the operating conditions, contrary to what would be expected if fuel-oil absorption was contributing significantly to engine-out HC. Thus these results do not support oil layer mechanism as a significant source of unburnt hydrocarbons in the tested engine. Thesis Supervisor: Wai K. Cheng Title: Professor of Mechanical Engineering

19 citations

Journal ArticleDOI
01 Jan 2001
TL;DR: Enhanced accuracy of spark ignition modeling might help to better compute the early flame propagation and its influence on the cyclic variability of engines, potentially leading to design of new spark plugs.
Abstract: The amount of spark energy deposited into the combustion chamber is key to an optimum ignition as one can end up with misfires when this energy is low or with other undesired effects on engine performance and byproducts when it is high. Experimentally, up to now, no one has been able to correlate the combustion outcome accurately to the spark parameters in a controllable way. Theoretical investigation and computer modeling is leading to a better understanding of how spark flames propagate. A new computational approach to ignition dynamics is presented here for spark-ignited (SI) engine combustion simulations. Our computational model, using the MPI communication library, attempts to solve temporal and spatial equations of the electromagnetic (EM) equations in conjunction with the well-known Navier-Stokes equations of the standard KIVA-3 engine code. The interaction between the gas and the flame (plasma) kernel in the spark region is computed through the momentum and energy exchange between these two fields. Preliminary results show a distinct spatial distribution of physical quantities at the flame front and within the inflammation zone. A slight change in the spark discharge current has significant impact on the combustion and emissions. Enhanced accuracy of spark ignition modeling might help us better compute the early flame propagation and its influence on the cyclic variability of engines, potentially leading to design of new spark plugs.

19 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental analysis of a multiple spark ignition system was carried out with conventional and optical non-intrusive methods, which is capable of multiple discharges with reduced dwell time.

19 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202210
2021429
2020525
2019661
2018758
2017683