Improving Sparse Representation-Based Classification Using Local Principal Component Analysis

Sparse representation-based classification (SRC), proposed by Wright et al., seeks the sparsest decomposition of a test sample over the dictionary of training samples, with classification to the most-contributing class. Because it assumes test samples can be written as linear combinations of their same-class training samples, the success of SRC depends on the size and representativeness of the training set. Our proposed classification algorithm enlarges the training set by using local principal component analysis to approximate the basis vectors of the tangent hyperplane of the class manifold at each training sample. The dictionary in SRC is replaced by a local dictionary that adapts to the test sample and includes training samples and their corresponding tangent basis vectors. We use a synthetic data set and three face databases to demonstrate that this method can achieve higher classification accuracy than SRC in cases of sparse sampling, nonlinear class manifolds, and stringent dimension reduction.Comment: Published in "Computational Intelligence for Pattern Recognition," editors Shyi-Ming Chen and Witold Pedrycz. The original publication is available at http://www.springerlink.co

Orbital redistribution in molecular nanostructures mediated by metal-organic bonds

Dicyanovinyl-quinquethiophene (DCV5T-Me) is a prototype conjugated oligomer for highly efficient organic solar cells. This class of oligothiophenes are built up by an electron-rich donor (D) backbone and terminal electron-deficient acceptor (A) moieties. Here, we investigated its structural and electronic properties when it is adsorbed on a Au(111) surface using low temperature scanning tunneling microscopy/spectroscopy (STM/STS) and atomic force microscopy (AFM). We find that DCV5T-Me self-assembles in extended chains, stabilized by intercalated Au atoms. The effect of metal-ligand hybridization with Au adatoms causes an energetic downshift of the DCV5T-Me lowest unoccupied molecular orbital (LUMO) with respect to the uncoordinated molecules on the surface. The asymmetric coordination of a gold atom to only one molecular end group leads to an asymmetric localization of the LUMO and LUMO+1 states at opposite sides. Using model density functional theory (DFT) calculations, we explain such orbital reshaping as a consequence of linear combinations of the original LUMO and LUMO+1 orbitals, mixed by the attachment of a bridging Au adatom. Our study shows that the alignment of molecular orbitals and their distribution within individual molecules can be modified by contacting them to metal atoms in specific sites

Correlating the electronic structure of perovskite La1−Sr CoO3 with activity for the oxygen evolution reaction: The critical role of Co 3d hole state

Perovskite LaCoO3 is being increasingly explored as an effective low-cost electrocatalyst for the oxygen evolution reaction (OER). Sr doping in LaCoO3 (La1xSrxCoO3) has been found to substantially increase its catalytic activity. In this work, we report a detailed study on the evolution of the electronic structure of La1xSrxCoO3 with 0 x 1 and its correlation with electrocatalytic activity for the OER. A combination of X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) was used to unravel the electronic density of states (DOS) near the Fermi level (EF), which provide insights into the key electronic structure features for the enhanced OER catalytic activity. Detailed analysis on the Co L-edge XAS suggest that LaCoO3 has a low spin state with t2g 6 eg 0 configuration at room temperature. This implies that the high OER catalytic activity of LaCoO3 should not be rationalized by the occupancy of eg = 1 descriptor. Substituting Sr2+ for La3+ in LaCoO3 induces Co4+ oxidation states and effectively dopes hole states into the top of valence band. A semiconductor-to-metal transition is observed for 0.2, due to the holeinduced electronic DOS at the EF and increased hybridization between Co 3d and O 2p. Such an electronic modulation enhances the surface adsorption of the *OH intermediate and reduces the energy barrier for interfacial charge transfer, thus improving the OER catalytic activity in La1xSrxCoO3. In addition, we found that the La1xSrxCoO3 surface undergoes amorphization after certain period of OER measurement, leading to a partial deactivation of the electrocatalyst. High Sr doping levels accelerated the amorphization process.K.H.L. Zhang is grateful for funding support by the National Natural Science Foundation of China (Grant No. 21872116). J.C. gratefully acknowledges the financial support by the National Natural Science Foundation of China (Grant No. 21621091 and 21373166). Freddy E. Oropeza and Victor A. de la Peña O'Shea are grateful for the funding supported by the Spanish AEI (NyMPhA PID2019-106315RB-I00). Victor A. de la Peña O'Shea also wishes to thank ''Comunidad de Madrid" and European Structural Funds for their financial support to FotoArt-CM project (S2018/NMT-4367) and the Fundación Ramón Areces. C. M. Tian gratefully acknowledges financial support by the China Scholarship Council (CSC). K.H.L. Zhang and Jan P. Hofmann also ackonwledge the Sino-German Mobility Program (Grant No. M-0377). Preliminar spectroscopic measurements were performed at the CLAESS beamline at the ALBA synchrotron

Stable iridium dinuclear heterogeneous catalysts supported on metal-oxide substrate for solar water oxidation.

Atomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single-atom catalysts (SACs) and nanoparticles (NPs). While SACs and NPs have been extensively reported, catalysts featuring a few atoms with well-defined structures are poorly studied. The difficulty in synthesizing such structures has been a critical challenge. Here we report a facile photochemical method that produces catalytic centers consisting of two Ir metal cations, bridged by O and stably bound to a support. Direct evidence unambiguously supporting the dinuclear nature of the catalysts anchored on α-Fe2O3 is obtained by aberration-corrected scanning transmission electron microscopy (AC-STEM). Experimental and computational results further reveal that the threefold hollow binding sites on the OH-terminated surface of α-Fe2O3 anchor the catalysts to provide outstanding stability against detachment or aggregation. The resulting catalysts exhibit high activities toward H2O photooxidation