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Alexander Bogdanov

Publications and source records attributed to Alexander Bogdanov.

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Aligning Distributionally Robust Optimization with Practical Deep Learning Needs

While traditional Deep Learning (DL) optimization methods treat all training samples equally, Distributionally Robust Optimization (DRO) adaptively assigns importance weights to different samples. However, a significant gap exists between DRO and current DL practices. Modern DL optimizers require adaptivity and the ability to handle stochastic gradients, as these methods demonstrate superior performance. Additionally, for practical applications, a method should allow weight assignment not only to individual samples, but also to groups of objects (for example, all samples of the same class). This paper aims to bridge this gap by introducing ALSO $\unicode{x2013}$ Adaptive Loss Scaling Optimizer $\unicode{x2013}$ an adaptive algorithm for a modified DRO objective that can handle weight assignment to sample groups. We prove the convergence of our proposed algorithm for non-convex objectives, which is the typical case for DL models. Empirical evaluation across diverse Deep Learning tasks, from Tabular DL to Split Learning tasks, demonstrates that ALSO outperforms both traditional optimizers and existing DRO methods.

cs.LG

Ultrafast core-to-core luminescence in BaF$_2$-LaF$_3$ single crystals

This study investigates the mechanisms underlying ultrafast cross-luminescence observed in BaF$_2$ crystals doped with LaF$_3$. We identified an ultrafast luminescent component with a decay time of approximately 150 ps, which emerges under excitation energies exceeding 24 eV as a novel radiative recombination process between electrons in the 5p core band of Ba2+ and holes in the 5p core band of La$^{3+}$. Ab initio calculations support this hypothesis, showing that the energy levels of the core bands facilitate such transitions. The findings indicate that BaF$_2$-LaF$_3$ scintillators hold significant promise for applications in time-of-flight tomography.

cond-mat.mtrl-sci