182,012 research outputs found
The Automatic Identification and Tracking of Coronal Flux Ropes -- Part I: Footpoints and Fluxes
Investigating the early-stage evolution of an erupting flux rope from the Sun
is important to understand the mechanisms of how it looses its stability and
its space weather impacts. Our aim is to develop an efficient scheme for
tracking the early dynamics of erupting solar flux ropes and use the algorithm
to analyse its early-stage properties. The algorithm is tested on a data-driven
simulation of an eruption that took place in active region AR12473. We
investigate the modelled flux rope's footpoint movement and magnetic flux
evolution and compare with observational data from the Solar Dynamics
Observatory's Atmospheric Imaging Assembly in the 211 \unicode{x212B} and
1600 \unicode{x212B} channels. To carry out our analysis, we use the
time-dependent data-driven magnetofrictional model (TMFM). We also perform
another modelling run, where we stop the driving of the TMFM midway through the
flux rope's rise through the simulation domain and evolve it instead with a
zero-beta magnetohydrodynamic (MHD) approach. The developed algorithm
successfully extracts a flux rope and its ascend through the simulation domain.
We find that the movement of the modelled flux rope footpoints showcases
similar trends in both TMFM and relaxation MHD run: they recede from their
respective central location as the eruption progresses and the positive
polarity footpoint region exhibits a more dynamic behaviour. The ultraviolet
brightenings and extreme ultraviolet dimmings agree well with the models in
terms of their dynamics. According to our modelling results, the toroidal
magnetic flux in the flux rope first rises and then decreases. In our
observational analysis, we capture the descending phase of toroidal flux. In
conclusion, the extraction algorithm enables us to effectively study the flux
rope's early dynamics and derive some of its key properties such as footpoint
movement and toroidal magnetic flux.Comment: Accepted for publication in Astronomy & Astrophysic
Partial mixture model for tight clustering of gene expression time-course
Background: Tight clustering arose recently from a desire to obtain tighter and potentially more informative clusters in gene expression studies. Scattered genes with relatively loose correlations should be excluded from the clusters. However, in the literature there is little work dedicated to
this area of research. On the other hand, there has been extensive use of maximum likelihood techniques for model parameter estimation. By contrast, the minimum distance estimator has been largely ignored.
Results: In this paper we show the inherent robustness of the minimum distance estimator that makes it a powerful tool for parameter estimation in model-based time-course clustering. To apply minimum distance estimation, a partial mixture model that can naturally incorporate replicate
information and allow scattered genes is formulated. We provide experimental results of simulated data fitting, where the minimum distance estimator demonstrates superior performance to the maximum likelihood estimator. Both biological and statistical validations are conducted on a
simulated dataset and two real gene expression datasets. Our proposed partial regression clustering algorithm scores top in Gene Ontology driven evaluation, in comparison with four other popular clustering algorithms.
Conclusion: For the first time partial mixture model is successfully extended to time-course data analysis. The robustness of our partial regression clustering algorithm proves the suitability of the ombination of both partial mixture model and minimum distance estimator in this field. We show that tight clustering not only is capable to generate more profound understanding of the dataset
under study well in accordance to established biological knowledge, but also presents interesting new hypotheses during interpretation of clustering results. In particular, we provide biological evidences that scattered genes can be relevant and are interesting subjects for study, in contrast to prevailing opinion
Carbon capture from natural gas combined cycle power plants: Solvent performance comparison at an industrial scale
Natural gas is an important source of energy. This article addresses the problem of integrating an existing natural gas combined cycle (NGCC) power plant with a carbon capture process using various solvents. The power plant and capture process have mutual interactions in terms of the flue gas flow rate and composition vs. the extracted steam required for solvent regeneration. Therefore, evaluating solvent performance at a single (nominal) operating point is not indicative and solvent performance should be considered subject to the overall process operability and over a wide range of operating conditions. In the present research, a novel optimization framework was developed in which design and operation of the capture process are optimized simultaneously and their interactions with the upstream power plant are fully captured. The developed framework was applied for solvent comparison which demonstrated that GCCmax, a newly developed solvent, features superior performances compared to the monoethanolamine baseline solvent
A unified wavelet-based modelling framework for non-linear system identification: the WANARX model structure
A new unified modelling framework based on the superposition of additive submodels, functional components, and
wavelet decompositions is proposed for non-linear system identification. A non-linear model, which is often represented
using a multivariate non-linear function, is initially decomposed into a number of functional components via the wellknown
analysis of variance (ANOVA) expression, which can be viewed as a special form of the NARX (non-linear
autoregressive with exogenous inputs) model for representing dynamic input–output systems. By expanding each functional
component using wavelet decompositions including the regular lattice frame decomposition, wavelet series and
multiresolution wavelet decompositions, the multivariate non-linear model can then be converted into a linear-in-theparameters
problem, which can be solved using least-squares type methods. An efficient model structure determination
approach based upon a forward orthogonal least squares (OLS) algorithm, which involves a stepwise orthogonalization
of the regressors and a forward selection of the relevant model terms based on the error reduction ratio (ERR), is
employed to solve the linear-in-the-parameters problem in the present study. The new modelling structure is referred to
as a wavelet-based ANOVA decomposition of the NARX model or simply WANARX model, and can be applied to
represent high-order and high dimensional non-linear systems
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