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Unsupervised discovery of features, patterns, via variational autoencoders (arxiv.org)
1 point by Anon84 on Jun 24, 2021 | hide | past | pdf | discuss on HN

In plain words: A neural network learns the repeating shapes in microscope images while ignoring where each one sits, so drift and shifts don't blur the picture. Unlike the usual frequency-based analysis, it separated repeating features, their variations, and shifts in real atomic-scale images.

Abstract · Finding simplicity: unsupervised discovery of features, patterns, and order parameters via shift-invariant variational autoencoders

Recent advances in scanning tunneling and transmission electron microscopies (STM and STEM) have allowed routine generation of large volumes of imaging data containing information on the structure and functionality of materials. The experimental data sets contain signatures of long-range phenomena such as physical order parameter fields, polarization and strain gradients in STEM, or standing electronic waves and carrier-mediated exchange interactions in STM, all superimposed onto scanning system distortions and gradual changes of contrast due to drift and/or mis-tilt effects. Correspondingly, while the human eye can readily identify certain patterns in the images such as lattice periodicities, repeating structural elements, or microstructures, their automatic extraction and classification are highly non-trivial and universal pathways to accomplish such analyses are absent. We pose that the most distinctive elements of the patterns observed in STM and (S)TEM images are similarity and (almost-) periodicity, behaviors stemming directly from the parsimony of elementary atomic structures, superimposed on the gradual changes reflective of order parameter distributions. However, the discovery of these elements via global Fourier methods is non-trivial due to variability and lack of ideal discrete translation symmetry. To address this problem, we develop shift-invariant variational autoencoders (shift-VAE) that allow disentangling characteristic repeating features in the images, their variations, and shifts inevitable for random sampling of image space. Shift-VAEs balance the uncertainty in the position of the object of interest with the uncertainty in shape reconstruction. This approach is illustrated for model 1D data, and further extended to synthetic and experimental STM and STEM 2D data.

Maxim Ziatdinov, Chun Yin Wong, Sergei V. Kalinin
arXiv:2106.12472 · cond-mat.dis-nn, cs.LG · submitted Jun 23, 2021
abstract · pdf

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