Correlation between Spin Polarization and Magnetic Moment in Ferromagnetic Alloys

The correlation between the magnetic moment in ferromagnetic alloys and the tunneling spin polarization in ferromagnet-insulator-superconductor tunneling experiments has been a mystery. The measured spin polarization for Fe, Co, Ni, and various Ni alloys is positive and roughly proportional to their magnetic moments, which can not be explained by considering the net density of states. Using a tight-binding coherent potential approximation (CPA) model, we show that while the polarization of the net density of states is not correlated with the magnetic moment, the polarization of the density of states of {\it s} electrons is correlated with the magnetic moment in the same manner as observed by the tunneling experiments. We also discuss the spin polarization measurements by Andreev reflection experiments, some of which obtained different results from the tunneling experiments and our calculations.Comment: 8 RevTEX pages, 9 figures in ep

Attention, Please! Adversarial Defense via Attention Rectification and Preservation

This study provides a new understanding of the adversarial attack problem by examining the correlation between adversarial attack and visual attention change. In particular, we observed that: (1) images with incomplete attention regions are more vulnerable to adversarial attacks; and (2) successful adversarial attacks lead to deviated and scattered attention map. Accordingly, an attention-based adversarial defense framework is designed to simultaneously rectify the attention map for prediction and preserve the attention area between adversarial and original images. The problem of adding iteratively attacked samples is also discussed in the context of visual attention change. We hope the attention-related data analysis and defense solution in this study will shed some light on the mechanism behind the adversarial attack and also facilitate future adversarial defense/attack model design

Variational sparse inverse Cholesky approximation for latent Gaussian processes via double Kullback-Leibler minimization

To achieve scalable and accurate inference for latent Gaussian processes, we propose a variational approximation based on a family of Gaussian distributions whose covariance matrices have sparse inverse Cholesky (SIC) factors. We combine this variational approximation of the posterior with a similar and efficient SIC-restricted Kullback-Leibler-optimal approximation of the prior. We then focus on a particular SIC ordering and nearest-neighbor-based sparsity pattern resulting in highly accurate prior and posterior approximations. For this setting, our variational approximation can be computed via stochastic gradient descent in polylogarithmic time per iteration. We provide numerical comparisons showing that the proposed double-Kullback-Leibler-optimal Gaussian-process approximation (DKLGP) can sometimes be vastly more accurate for stationary kernels than alternative approaches such as inducing-point and mean-field approximations at similar computational complexity.Comment: Accepted at the 2023 International Conference on Machine Learning (ICML). 18 pages with references and appendices, 14 figure

Vremenski razlučeni fotoluminescentni spektri legure (AlxGa1−x)0.51In0.49P (x = 0.29)

Measurements of time-resolved photoluminescence (TRPL) spectra were made in a study of the optical properties of partially ordered quaternary (AlxGa1-x)0.51In0.49P (x=0.29) alloy. Both excitation-wavelength dependence of lifetime and excitation-intensity dependence of lifetime show a wide distribution of carriers. In TRPL spectra measured at 300 K, a blue-shift of photoluminescence (PL) peaks in (AlxGa1-x)0.51In0.49P is observed. The phenomenon is in agreement with the Z-shaped temperature dependence of the PL peak. Possible origins of the blue-shift and Z-shaped behaviour of PL peak are presented.Načinili smo vremenski-razlučena (VR) mjerenja fotoluminescentnih (FL) spektara radi istraživanja optičkih svojstava djelomično sređene četverokomponentne legure (AlxGa1−x)0.51In0.49P (x = 0.29). Obje ovisnosti vremena života, uzbuda – valna duljina i uzbuda – intenzitet pokazuju široku raspodjelu nositelja. VR FL spektri (AlxGa1−x)0.51In0.49P na 300 K pokazuju plavi pomak fotoluminescentnih linija. Ta je pojava u skladu s temperaturnom ovisnošću FL vrha u vidu slova Z. Raspravljaju se mogući uzroci plavog pomaka i Z-ovisnosti FL vrha