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  1. Ye, Qiang (Ed.)
    An inexact rational Krylov subspace method is studied to solve large-scale nonsymmetric eigenvalue problems. Each iteration (outer step) of the rational Krylov subspace method requires solution to a shifted linear system to enlarge the subspace, performed by an iterative linear solver for large-scale problems. Errors are introduced at each outer step if these linear systems are solved approx- imately by iterative methods (inner step), and they accumulate in the rational Krylov subspace. In this article, we derive an upper bound on the errors intro- duced at each outer step to maintain the same convergence as exact rational Krylov subspace methodmore »for approximating an invariant subspace. Since this bound is inversely proportional to the current eigenresidual norm of the target invariant subspace, the tolerance of iterative linear solves at each outer step can be relaxed with the outer iteration progress. A restarted variant of the inexact rational Krylov subspace method is also proposed. Numerical experiments show the effectiveness of relaxing the inner tolerance to save computational cost.« less
    Free, publicly-accessible full text available March 8, 2023
  2. Free, publicly-accessible full text available June 10, 2023
  3. Azaindoles and azaindolines are important core structures in pharmaceuticals and natural products, which have found wide applications in the field of medicinal chemistry. In this study, we developed a novel one-pot method for selectively synthesizing 7-azaindoles and 7-azaindolines, which can be generated by reactions between the readily available 2-fluoro-3-methylpyridine and arylaldehydes. The chemoselectivity is counterion dependent, with LiN(SiMe 3 ) 2 generating 7-azaindolines and KN(SiMe 3 ) 2 furnishing 7-azaindoles. A range of substituents can be introduced under these conditions, providing handles for further elaboration and functionalization.
    Free, publicly-accessible full text available May 3, 2023
  4. Free, publicly-accessible full text available October 2, 2022
  5. null (Ed.)
  6. Abstract Ferroelectric topological objects provide a fertile ground for exploring emerging physical properties that could potentially be utilized in future nanoelectronic devices. Here, we demonstrate quasi-one-dimensional metallic high conduction channels associated with the topological cores of quadrant vortex domain and center domain (monopole-like) states confined in high quality BiFeO 3 nanoislands, abbreviated as the vortex core and the center core. We unveil via the phase-field simulation that the superfine metallic conduction channels along the center cores arise from the screening charge carriers confined at the core region, whereas the high conductance of vortex cores results from a field-induced twisted state.more »These conducting channels can be reversibly created and deleted by manipulating the two topological states via electric field, leading to an apparent electroresistance effect with an on/off ratio higher than 10 3 . These results open up the possibility of utilizing these functional one-dimensional topological objects in high-density nanoelectronic devices, e.g. nonvolatile memory.« less
    Free, publicly-accessible full text available December 1, 2022
  7. Thin-film electrostatic engineering is used to uncover a hidden antiferroelectric phase.
    Free, publicly-accessible full text available February 4, 2023