Homogenization modeling of domain switching in ferroelectric materials

We presented a multiscale nonlinear finite element simulation to analyze domain switching behaviors in ferroelectric materials. We utilized an incremental form of fundamental constitutive law to consider changes in the material properties caused by domain switching. A multiscale nonlinear problem was formulated by employing the asymptotic homogenization theory based on the perturbation method and implemented using finite element analysis. The developed simulation was applied to barium titanate with a Perovskite-type tetragonal crystal structure. The 90° and 180° domain switching behaviors of a single crystal were computed for verification. The nonlinear behaviors of a bulk polycrystal with virtual microstructure were analyzed as a case study. The variation of the crystal orientation distribution in the polycrystalline microstructure was analyzed to reveal its influence on macroscopic hysteresis and butterfly curves.     

A Geometrically Consistent Viscous Fluid Solver with Two‐Way Fluid‐Solid Coupling

We present a grid‐based fluid solver for simulating viscous materials and their interactions with solid objects. Our method formulates the implicit viscosity integration as a minimization problem with consistently estimated volume fractions to account for the sub‐grid details of free surfaces and solid boundaries. To handle the interplay between fluids and solid objects with viscosity forces, we also formulate the two‐way fluid‐solid coupling as a unified minimization problem based on the variational principle, which naturally enforces the boundary conditions. Our formulation leads to a symmetric positive definite linear system with a sparse matrix regardless of the monolithically coupled solid objects. Additionally, we present a position‐correction method using density constraints to enforce the uniform distributions of fluid particles and thus prevent the loss of fluid volumes. We demonstrate the effectiveness of our method in a wide range of viscous fluid scenarios.     

Simultaneous band reduction of two symmetric matrices

In this paper, we consider simultaneous band reduction of two dense symmetric matrices by congruent transformations. The ideas of simultaneous tridiagonalization are generalized to propose an efficient algorithm for the simultaneous band reduction. In contrast to the algorithms of simultaneous tridiagonalization which are mainly based on matrix–vector operations, the proposed algorithm of simultaneous band reduction has the advantage that matrix–matrix operations can be fully used to achieve better performance on modern computer architecture. Numerical results are presented to illustrate the effectiveness of our proposed algorithm.     

An Efficient Hybrid Incompressible SPH Solver with Interface Handling for Boundary Conditions

We propose a hybrid smoothed particle hydrodynamics solver for efficientlysimulating incompressible fluids using an interface handling method for boundary conditions in the pressure Poisson equation. We blend particle density computed with one smooth and one spiky kernel to improve the robustness against both fluid–fluid and fluid–solid collisions. To further improve the robustness and efficiency, we present a new interface handling method consisting of two components: free surface handling for Dirichlet boundary conditions and solid boundary handling for Neumann boundary conditions. Our free surface handling appropriately determines particles for Dirichlet boundary conditions using Jacobi‐based pressure prediction while our solid boundary handling introduces a new term to ensure the solvability of the linear system. We demonstrate that our method outperforms the state‐of‐the‐art particle‐based fluid solvers.     

Simple Method to Obtain Large‐Size Single‐Crystalline Oxide Sheets

Synthetic techniques to prepare large‐size, flexible, and high‐quality single‐crystalline sheets of transition metal oxides are crucial to developing low‐energy consumption devices. One promising way is a lift‐off and transfer technique using a heterostructure of polymer supporting oxide and Sr₃Al₂O₆ (SAO) layers grown on a single‐crystalline substrate. By removing the water‐soluble SAO and the supporting layers, the oxide sheet is obtained. Although some ferroelectric flexible sheets are prepared by this method, a simpler method for obtaining large‐size sheets is required. Herein, a lift‐off and transfer method is proposed without a supporting layer. With this simple method, single‐crystalline SrRuO₃ and BaTiO₃ flexible sheets with a lateral size of a few millimeters are successfully prepared. The SrRuO₃ sheet exhibits high crystallinity and conductivity. Meanwhile, the ferroelectricity of the BaTiO₃ sheet is successfully observed via polarization hysteresis loop measurements. In addition to the simplicity, this method has low costs and the substrate is reusable. Accordingly, the proposed method could enhance the development of various kinds of large‐size functional oxide sheets.     

A Community Structure‐Based Approach for Network Immunization

We propose a community structure‐based approach that does not require community labels of nodes, for network immunization. Social networks have been widely used as daily communication infrastructures these days. However, fast spreading of information over networks may have downsides such as computer viruses or epidemics of diseases. Because contamination is propagated among subgraphs (communities) along links in a network, use of community structure of the network would be effective for network immunization. However, despite various research efforts, it is still difficult to identify ground‐truth community labels of nodes in a network. Because communities are often interwoven through intermediate nodes, we propose to identify such nodes based on the community structure of a network without requiring community labels. By regarding the community structure in terms of nodes, we construct a vector representation of nodes based on a quality measure of communities. The distribution of the constructed vectors is used for immunizing intermediate nodes among communities, through the hybrid use of the norm and the relation in the vector representation. Experiments are conducted over both synthetic and real‐world networks, and our approach is compared with other network centrality‐based approaches. The results are encouraging and indicate that it is worth pursuing this path.     

Separation and recovery of rare earths via a dry chemical vapour transport based on halide gaseous complexes

The progress in the field of mutual separation of rare earths from the rare earth ores and their recovery from rare earth containing industrial waste by the dry chemical vapour transport (CVT) process mediated by the corresponding gaseous rare earth complexes with aluminum or alkali chlorides, RAI_nCl_3+3n or KRCl₄, is reviewed and discussed on the basis of their thermodynamic characteristics. The experimental results for the mutual separation and recovery of rare earth elements show the potential of this simple dry CVT process to substitute the conventional energy consuming complicated wet methods used at present for the costly preparation of the rare earths.     

Structure-property relations in crack-resistant alkaline-earth aluminoborosilicate glasses studied by solid state NMR

The effect of the average ionic potential ξ = Ze/r of the network modifier cations on crack initiation resistance (CR) and Young's modulus E has been measured for a series of alkaline-earth aluminoborosilicate glasses with the compositions 60SiO₂–10Al₂O₃–10B₂O₃–(20−x)M₍₂₎O–xM’O (0 ≤ x ≤ 20; M, M’ = Mg, Ca, Sr, Ba, Na). Systematic trends indicating an increase of CR with increasing ionic potential, ξ, have been correlated with structural properties deduced from the NMR interaction parameters in ²⁹Si, ²⁷Al, ²³Na, and ¹¹B solid state NMR. ²⁷Al NMR spectra indicate that the aluminum atoms in these glasses are essentially all four-coordinated, however, the average quadrupolar coupling constant <C_Q> extracted from lineshape analysis increases linearly with increasing average ion potential computed from the cation composition. A similar linear correlation is observed for the average ²⁹Si chemical shift, whereas the fraction of four-coordinate boron decreases linearly with increasing ξ. Altogether the results indicate that in pure alkaline-earth boroaluminosilicate glasses the crack resistance/E-modulus trade-off can be tailored by the alkaline-earth oxide inventory. In contrast, the situation looks more complicated in glasses containing both Na₂O and the alkaline-earth oxides MgO, CaO, SrO, and BaO. For 60SiO₂–10Al₂O₃–10B₂O₃–10MgO–10Na₂O glass, the NMR parameters, interpreted in the context of their correlations with ionic potentials, are consistent with a partial network former role of the MgO component, enhancing crack resistance. Altogether the presence of MgO in aluminoborosilicate glasses helps overcome the trade-off issue between high crack resistance and high elasticity modulus present in borosilicate glasses, thereby offering additional opportunities for the design of glasses that are both very rigid and very crack resistant.     

Analysis and design of impulse signal generator based on current-mode excitation and transmission line resonator

Hierarchical temporal memory (HTM) is a neuromorphic algorithm that emulates sparsity, hierarchy and modularity resembling the working principles of neocortex. Feature encoding is an important step to create sparse binary patterns. This sparsity is introduced by the binary weights and random weight assignment in the initialization stage of the HTM. We propose the alternative deterministic method for the HTM initialization stage, which connects the HTM weights to the input data and preserves natural sparsity of the input information. Further, we introduce the hardware implementation of the deterministic approach and compare it to the traditional HTM and existing hardware implementation. We test the proposed approach on the face recognition problem and show that it outperforms the conventional HTM approach.