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1. A Look-Up Table-Based Ray Integration Framework for 2-D/3-D Forward and Back Projection in X-Ray CT

   https://doi.org/DOI: 10.1109/TMI.2017.2741781  

   Ha, Songsoo and (August 2017, IEEE transactions on medical imaging)

   Iterative algorithms have become increasingly popular in Computed Tomography (CT) image reconstruction since they better deal with the adverse image artifacts arising from low radiation dose image acquisition. But iterative methods remain computationally expensive. The main cost emerges in the projection and backprojection operations where accurate CT system modeling can greatly improve the quality of the reconstructed image. We present a framework that improves upon one particular aspect - the accurate projection of the image basis functions. It differs from current methods in that it substitutes the high computational complexity associated with accurate voxel projection by a small number of memory operations. Coefficients are computed in advance and stored in look-up tables parameterized by the CT system's projection geometry. The look-up tables only require a few kilobytes of storage and can be efficiently accelerated on the GPU. We demonstrate our framework with both numerical and clinical experiments and compare its performance with the current state of the art scheme - the separable footprint method. 

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2. Hybrid Organic–Inorganic Halide Derivatives of the 2H Hexagonal Perovskite Structure

   https://doi.org/10.1021/acs.chemmater.2c00688  

   Holzapfel, Noah P.; Milder, Alexander; Woodward, Patrick M. (September 2022, Chemistry of Materials)

   Four quaternary hybrid halide perovskites have been synthesized in hydrohalic acid solutions under hydrothermal conditions. The structures of (CH3NH3)2AgRhX6 and (CH3NH3)2NaRhX6, (X = Cl–, Br–) consist of infinite one-dimensional chains of face-sharing metal-halide octahedra. The structure is closely related to the 2H hexagonal perovskite structure, but the space group symmetry is lowered from hexagonal P63/mmc to trigonal P3 ̅m1 by site ordering of the Rh3+ and Ag+/Na+ cations. All compositions demonstrate broad-spectrum visible light absorption with optical transitions arising from rhodium d-to-d transitions and halide-to-rhodium charge transfer transitions. The bromides show a 0.2 eV red shift in the optical transitions compared to the analogous chlorides. Crystal field splitting energies were found to be 2.6 eV and 2.4 eV for the chloride and bromide compositions, respectively. Band structure calculations for all compositions give rather flat valence and conduction bands, suggesting a zero-dimensional electronic structure. The valence bands are made up of crystal orbitals that are almost exclusively Rh 4d–Cl 3p (Br 4p) π* in character, while the conduction bands have Rh 4d–Cl 3p (Br 4p) σ* character. 

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3. Annealing Induced Structural Phase Change of Hexagonal‐LuFeO3 Thin Films

   R. C. Rai, D. Mckenna (April 2018, Ceramic Transactions Series)

   This chapter presents structural, optical, and magnetic properties of multiferroic LuFeO3 thin films, deposited on single crystal sapphire and YSZ substrates by an RF magnetron sputtering system. Growth temperature and annealing are found to be critical to stabilize hexagonal LuFeO3 thin films. Radio‐Frequency (RF) Magnetron Sputtering is relatively cost effective and one of the most commonly used methods for the deposition of oxides. An RF Magnetron Sputtering offers flexibility in terms of controlling the growth conditions, maintaining the stoichiometry, and a higher deposition rate. When the lattice strain is released due to annealing, the thin film can form bigger granular structures, as observed in the AFM image, by the nucleation process. The inset shows an example of the energy band edge fitting with the direct energy band gap model. 

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4. Magnetic properties and spin reorientation of hexagonal HoFeO3 thin films

   https://doi.org/https://doi.org/10.1016/j.tsf.2021.138596  

   R.C. Rai, C. Horvatits (April 2021, Thin solid films)

   null (Ed.)

   We present structural, magnetic, and optical properties of hexagonal HoFeO3/Al2O3 thin films deposited by Magnetron Sputtering. The x-ray diffraction patterns of HoFeO3 thin films show the c-planes of a hexagonal structure. The magnetization data display an antiferromagnetic transition temperature, TN∼120 ± 5 K and the magnetization-field hysteresis loops were measured below 100 K, confirming a weak ferromagnetism arising from a spin canting of the Fe3+ moments. The magnetization data also show an anomaly around ∼40 K due to a spin-reorientation transition caused by the Ho3+- Fe3+ interactions. We observed comparable magnetization along the ab plane and c axis although the spin canting of Fe3+ sites has a preferential component along the c axis, suggesting that the Ho3+- Fe3+ interactions dominate in the low temperature magnetic structures of hexagonal-HoFeO3. The observed electronic excitations at ∼2.29, 2.87, 3.82, 4.79, and 6.53 eV have been assigned to the Fe3+ d to d on-site as well as O 2p to Fe 3d, Ho 6s, and 5d charge-transfer excitations, respectively. The room temperature energy band gap of the hexagonal-HoFeO3 thin film was measured to be ∼1.99 ± 0.04 eV. 

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5. Regularized and smooth double core tensor factorization for heterogeneous data

   Tarzanagh, Davoud Ataee; Michalidis, George (January 2022, Journal of machine learning research)

   We introduce a general tensor model suitable for data analytic tasks for heterogeneous datasets, wherein there are joint low-rank structures within groups of observations, but also discriminative structures across different groups. To capture such complex structures, a double core tensor (DCOT) factorization model is introduced together with a family of smoothing loss functions. By leveraging the proposed smoothing function, the model accurately estimates the model factors, even in the presence of missing entries. A linearized ADMM method is employed to solve regularized versions of DCOT factorizations, that avoid large tensor operations and large memory storage requirements. Further, we establish theoretically its global convergence, together with consistency of the estimates of the model parameters. The effectiveness of the DCOT model is illustrated on several realworld examples including image completion, recommender systems, subspace clustering, and detecting modules in heterogeneous Omics multi-modal data, since it provides more insightful decompositions than conventional tensor methods. 

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