Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

Unexpected, yet useful functionalities emerge when two or more materials merge coherently. Artificial oxide superlattices realize atomic and crystal structures that are not available in nature, thus providing controllable correlated quantum phenomena. This review focuses on 4d and 5d perovskite oxide superlattices, in which the spin–orbit coupling plays a significant role compared with conventional 3d oxide superlattices. Modulations in crystal structures with octahedral distortion, phonon engineering, electronic structures, spin orderings, and dimensionality control are discussed for 4d oxide superlattices. Atomic and magnetic structures, J_eff = 1/2 pseudospin and charge fluctuations, and the integration of topology and correlation are discussed for 5d oxide superlattices. This review provides insights into how correlated quantum phenomena arise from the deliberate design of superlattice structures that give birth to novel functionalities.     

Short packet communication in underlay cognitive network assisted by an intelligent reflecting surface

We propose short packet communication in an underlay cognitive radio network assisted by an intelligent reflecting surface (IRS) composed of multiple reconfigurable reflectors. This scheme, called the IRS protocol, operates in only one time slot (TS) using the IRS. The IRS adjusts its phases to give zero received cumulative phase at the secondary destination, thereby enhancing the end-to-end signal-to-noise ratio. The transmitting power of the secondary source is optimized to simultaneously satisfy the multi-interference constraints, hardware limitations, and performance improvement. Simulation and analysis results of the average block error rates (BLERs) show that the performance can be enhanced by installing more reconfigurable reflectors, increasing the blocklength, lowering the number of required primary receivers, or sending fewer information bits. Moreover, the proposed IRS protocol always outperforms underlay relaying protocols using two TSs for data transmission, and achieves the best average BLER at identical transmission distances between the secondary source and secondary destination. The theoretical analyses are confirmed by Monte Carlo simulations.     

Rational Design and Synthesis of Extremely Efficient Macroporous CoSe2–CNT Composite Microspheres for Hydrogen Evolution Reaction

Uniquely structured CoSe₂–carbon nanotube (CNT) composite microspheres with optimized morphology for the hydrogen‐evolution reaction (HER) are prepared by spray pyrolysis and subsequent selenization. The ultrafine CoSe₂ nanocrystals uniformly decorate the entire macroporous CNT backbone in CoSe₂–CNT composite microspheres. The macroporous CNT backbone strongly improves the electrocatalytic activity of CoSe₂ by improving the electrical conductivity and minimizing the growth of CoSe₂ nanocrystals during the synthesis process. In addition, the macroporous structure resulting from the CNT backbone improves the electrocatalytic activity of the CoSe₂–CNT microspheres by increasing the removal rate of generated H₂ and minimizing the polarization of the electrode during HER. The CoSe₂–CNT composite microspheres demonstrate excellent catalytic activity for HER in an acidic medium (10 mA cm^?2 at an overpotential of ≈174 mV). The bare CoSe₂ powders exhibit moderate HER activity, with an overpotential of 226 mV at 10 mA cm^?2. The Tafel slopes for the CoSe₂–CNT composite and bare CoSe₂ powders are 37.8 and 58.9 mV dec^?1, respectively. The CoSe₂–CNT composite microspheres have a slightly larger Tafel slope than that of commercial carbon‐supported platinum nanoparticles, which is 30.2 mV dec^–1.     

Designing Metallic and Insulating Nanocrystal Heterostructures to Fabricate Highly Sensitive and Solution Processed Strain Gauges for Wearable Sensors

All‐solution processed, high‐performance wearable strain sensors are demonstrated using heterostructure nanocrystal (NC) solids. By incorporating insulating artificial atoms of CdSe quantum dot NCs into metallic artificial atoms of Au NC thin film matrix, metal–insulator heterostructures are designed. This hybrid structure results in a shift close to the percolation threshold, modifying the charge transport mechanism and enhancing sensitivity in accordance with the site percolation theory. The number of electrical pathways is also manipulated by creating nanocracks to further increase its sensitivity, inspired from the bond percolation theory. The combination of the two strategies achieves gauge factor up to 5045, the highest sensitivity recorded among NC‐based strain gauges. These strain sensors show high reliability, durability, frequency stability, and negligible hysteresis. The fundamental charge transport behavior of these NC solids is investigated and the combined site and bond percolation theory is developed to illuminate the origin of their enhanced sensitivity. Finally, all NC‐based and solution‐processed strain gauge sensor arrays are fabricated, which effectively measure the motion of each finger joint, the pulse of heart rate, and the movement of vocal cords of human. This work provides a pathway for designing low‐cost and high‐performance electronic skin or wearable devices.     

Some peculiarities of electric discharge between a solid electrode and technical water

We present the results of experimental study of the electric discharge between metal electrodes of various geometry and technical water within the pressure range of 8 × 10³–10⁵ Pa at the saw-tooth voltage generator frequency, f = 40 MHz, and the interelectrode distance, l = 3–30 mm. We consider transfer of the streamer discharge into spark one depending on the geometry of the metal electrode and its material. We investigate the electrical characteristics of the discharge between the plate electrode and the technical water within a wide pressure range. The essential influence of the streamer discharge type on the ozone release within the investigated parameters range is discovered.     

Error estimation for the automated multi‐level substructuring method

In this study, we propose an effective method to estimate the reliability of finite element models reduced by the automated multi‐level substructuring (AMLS) method. The proposed error estimation method can accurately predict relative eigenvalue errors in reduced finite element models. A new, enhanced transformation matrix for the AMLS method is derived from the original transformation matrix by properly considering the contribution of residual substructural modes. The enhanced transformation matrix is an important prerequisite to develop the error estimation method. Adopting the basic concept of the error estimation method recently developed for the Craig–Bampton method, an error estimation method is developed for the AMLS method. Through various numerical examples, we demonstrate the accuracy of the proposed error estimation method and explore its computational efficiency. Copyright © 2015 John Wiley & Sons, Ltd.