Function Decomposition Network

Author(s):  
Yevgeniy Bodyanskiy ◽  
Sergiy Popov ◽  
Mykola Titov
2019 ◽  
Vol 150 (5) ◽  
pp. 2216-2254
Author(s):  
Yingwei Li

AbstractUsing pointwise semigroup techniques, we establish sharp rates of decay in space and time of a perturbed reaction diffusion front to its time-asymptotic limit. This recovers results of Sattinger, Henry and others of time-exponential convergence in weighted Lp and Sobolev norms, while capturing the new feature of spatial diffusion at Gaussian rate. Novel features of the argument are a pointwise Green function decomposition reconciling spectral decomposition and short-time Nash-Aronson estimates and an instantaneous tracking scheme similar to that used in the study of stability of viscous shock waves.


2020 ◽  
Vol 13 (3) ◽  
pp. 1609-1622 ◽  
Author(s):  
Alexander Barth ◽  
Aida Alvera-Azcárate ◽  
Matjaz Licer ◽  
Jean-Marie Beckers

Abstract. A method to reconstruct missing data in sea surface temperature data using a neural network is presented. Satellite observations working in the optical and infrared bands are affected by clouds, which obscure part of the ocean underneath. In this paper, a neural network with the structure of a convolutional auto-encoder is developed to reconstruct the missing data based on the available cloud-free pixels in satellite images. Contrary to standard image reconstruction with neural networks, this application requires a method to handle missing data (or data with variable accuracy) in the training phase. The present work shows a consistent approach which uses the satellite data and its expected error variance as input and provides the reconstructed field along with its expected error variance as output. The neural network is trained by maximizing the likelihood of the observed value. The approach, called DINCAE (Data INterpolating Convolutional Auto-Encoder), is applied to a 25-year time series of Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature data and compared to DINEOF (Data INterpolating Empirical Orthogonal Functions), a commonly used method to reconstruct missing data based on an EOF (empirical orthogonal function) decomposition. The reconstruction error of both approaches is computed using cross-validation and in situ observations from the World Ocean Database. DINCAE results have lower error while showing higher variability than the DINEOF reconstruction.


2018 ◽  
Author(s):  
Marten Blaauw ◽  
Nedjeljka Žagar

Abstract. The paper presents the seasonal variability of Kelvin waves (KWs) in 2007–2013 ECMWF analyses on 91 model levels. The waves are filtered using the normal-mode function decomposition which simultaneously analyses wind and mass field based on their relationships from linear wave theory. Both spectral as well as spatiotemporal features of the KWs are examined in terms of their seasonal variability in comparison with background wind and stability. Furthermore, a differentiation is made using spectral bandpass filtering between the slow horizontal barotropic KW response and the fast vertical projection response observed as vertically-propagating KWs. Results show a clear seasonal cycle in KW activity which is predominantly at the largest zonal scales (wavenumber 1–2) where up to 50 % more energy is observed during the solstice seasons in comparison with spring and autumn. The spatiotemporal structure of the KW reveals the slow response as a robust Gill-type structure with its position determined by the location of the dominant convective outflow winds throughout the seasons. Its maximum strength occurs during northern summer when easterlies in the Eastern Hemisphere are strongest. The fast response in the form of free traveling KWs occur throughout the year with seasonal variability mostly found in the wave amplitudes being dependent on background easterly winds.


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