407,683 research outputs found
Background Rejection in Atmospheric Cherenkov Telescopes using Recurrent Convolutional Neural Networks
In this work, we present a new, high performance algorithm for background
rejection in imaging atmospheric Cherenkov telescopes. We build on the already
popular machine-learning techniques used in gamma-ray astronomy by the
application of the latest techniques in machine learning, namely recurrent and
convolutional neural networks, to the background rejection problem. Use of
these machine-learning techniques addresses some of the key challenges
encountered in the currently implemented algorithms and helps to significantly
increase the background rejection performance at all energies.
We apply these machine learning techniques to the H.E.S.S. telescope array,
first testing their performance on simulated data and then applying the
analysis to two well known gamma-ray sources. With real observational data we
find significantly improved performance over the current standard methods, with
a 20-25\% reduction in the background rate when applying the recurrent neural
network analysis. Importantly, we also find that the convolutional neural
network results are strongly dependent on the sky brightness in the source
region which has important implications for the future implementation of this
method in Cherenkov telescope analysis.Comment: 11 pages, 7 figures. To be submitted to The European Physical Journal
A Novel Repetitive Controller Assisted Phase-Locked Loop with Self-Learning Disturbance Rejection Capability for Three-Phase Grids
The synchronization between the power grid and distributed power sources is a crucial issue in the concept of smart grids. For tracking the real-time frequency and phase of three-phase grids, phase-locked loop (PLL) technology is commonly used. Many existing PLLs with enhanced disturbance/harmonic rejection capabilities, either fail to maintain fast response or are not adaptive to grid frequency variations or have high computational complexity. This article, therefore, proposes a low computational burden repetitive controller (RC) assisted PLL (RCA-PLL) that is not only effective on harmonic rejection but also has remarkable steady-state performance while maintaining fast dynamic. Moreover, the proposed PLL is adaptive to variable frequency conditions and can self-learn the harmonics to be canceled. The disturbance/harmonic rejection capabilities together with dynamic and steady-state performances of the RCA-PLL have been highlighted in this article. The proposed approach is also experimentally compared to the synchronous rotation frame PLL (SRF-PLL) and the steady-state linear Kalman filter PLL (SSLKF-PLL), considering the effect of harmonics from the grid-connected converters, unbalances, sensor scaling errors, dc offsets, grid frequency variations, and phase jumps. The computational burden of the RCA-PLL is also minimized, achieving an experimental execution time of only 12 μs
Machine Learning with a Reject Option: A survey
Machine learning models always make a prediction, even when it is likely to
be inaccurate. This behavior should be avoided in many decision support
applications, where mistakes can have severe consequences. Albeit already
studied in 1970, machine learning with rejection recently gained interest. This
machine learning subfield enables machine learning models to abstain from
making a prediction when likely to make a mistake.
This survey aims to provide an overview on machine learning with rejection.
We introduce the conditions leading to two types of rejection, ambiguity and
novelty rejection, which we carefully formalize. Moreover, we review and
categorize strategies to evaluate a model's predictive and rejective quality.
Additionally, we define the existing architectures for models with rejection
and describe the standard techniques for learning such models. Finally, we
provide examples of relevant application domains and show how machine learning
with rejection relates to other machine learning research areas
The Functions and Practices of a Television Network
An Iterative Learning Control disturbance rejection approach is considered and it is shown that iteration variant learning filters can asymptotically give the controlled variable zero error and zero variance. Convergence is achieved with the assumption that the relative model error is less than one. The transient response of the suggested ILC algorithm is also discussed using a simulation example
Building Gene Expression Profile Classifiers with a Simple and Efficient Rejection Option in R
Background: The collection of gene expression profiles from DNA microarrays and their analysis with pattern recognition algorithms is a powerful technology applied to several biological problems. Common pattern recognition systems classify samples assigning them to a set of known classes. However, in a clinical diagnostics setup, novel and unknown classes (new pathologies) may appear and one must be able to reject those samples that do not fit the trained model. The problem of implementing a rejection option in a multi-class classifier has not been widely addressed in the statistical literature. Gene expression profiles represent a critical case study since they suffer from the curse of dimensionality problem that negatively reflects on the reliability of both traditional rejection models and also more recent approaches such as one-class classifiers. Results: This paper presents a set of empirical decision rules that can be used to implement a rejection option in a set of multi-class classifiers widely used for the analysis of gene expression profiles. In particular, we focus on the classifiers implemented in the R Language and Environment for Statistical Computing (R for short in the remaining of this paper). The main contribution of the proposed rules is their simplicity, which enables an easy integration with available data analysis environments. Since in the definition of a rejection model tuning of the involved parameters is often a complex and delicate task, in this paper we exploit an evolutionary strategy to automate this process. This allows the final user to maximize the rejection accuracy with minimum manual intervention. Conclusions: This paper shows how the use of simple decision rules can be used to help the use of complex machine learning algorithms in real experimental setups. The proposed approach is almost completely automated and therefore a good candidate for being integrated in data analysis flows in labs where the machine learning expertise required to tune traditional classifiers might not be availabl
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