In this tutorial paper, a comprehensive survey is given on several major systematic approaches in dealing with delay-aware control problems, namely the equivalent rate constraint approach, the Lyapunov stability drift approach and the approximate Markov Decision Process (MDP) approach using stochastic learning. These approaches essentially embrace most of the existing literature regarding delay-aware resource control in wireless systems. They have their relative pros and cons in terms of performance, complexity and implementation issues. For each of the approaches, the problem setup, the general solution and the design methodology are discussed. Applications of these approaches to delay-aware resource allocation are illustrated with examples in single-hop wireless networks. Furthermore, recent results regarding delay-aware multi-hop routing designs in general multi-hop networks are elaborated.Finally, the delay performance of the various approaches are compared through simulations using an example of the uplink OFDMA systems. Index TermsDelay-aware resource control, large deviation theory, Lyapunov stability, Markov decision process, stochastic learning.

As human society enters the big data era, huge data storage and energy‐efficient data processing are in great demand. The resistive switching device is an emerging device with both inherent memory and computation capabilities. It may bring disruptive influences to modern information technology from bottom up. After decades of study of the materials, mechanisms, and devices, the maturity of the resistive switching device in various applications, for example, nonvolatile memory, artificial neural networks, and information security, could be foreseen. Herein, the recent progress of the resistive switching device from the aspects of materials, devices, and applications is reviewed. First, the resistive switching device, including mechanisms and materials, is briefly discussed. Performance improvement methods with respect to individual device properties are systematically illustrated. Second, characterization technologies for understanding the mechanism and guidance of device design are classified and discussed in depth. Third, various applications based on resistive switching devices are summarized. The review ends with a brief conclusion concerning the challenges from mechanism to algorithm level and the future outlook.

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Zero-dimensional boron structures have always been the focus of theoretical research owing to their abundant phase structures and special properties. Boron clusters have been reported extensively by combining structure searching theories and photoelectron spectroscopy (PES) experiments; however, crystalline boron quantum dots (BQDs) have rarely been reported. Here, we report the preparation of large-scale and uniform crystalline semiconductor BQDs from the expanded bulk boron powders via a facile and efficient probe ultrasonic approach in the acetonitrile solution. The obtained BQDs have 2.46 nm average lateral size and 2.81 nm thickness. Optical measurements demonstrate that a strong quantum confinement effect occurs in the BQDs, implying the increase of the band gap from 1.80 eV for the corresponding bulk to 2.46 eV for the BQDs. By injecting the BQDs into poly­(vinylpyrrolidone) as an active layer, a BQD-based memory device is fabricated that shows a rewriteable nonvolatile memory effect with a low transition voltage of down to 0.5 V and a high on/off switching ratio of 103 as well as a good stability.

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This paper studies simultaneous wireless information and power transfer (SWIPT) systems in two-way relaying (TWR) channels. Here, two source nodes receive information and energy simultaneously via power splitting (PS) from the signals sent by a multi-antenna relay node. Our objective is to maximize the weighted sum of the harvested energy at two source nodes subject to quality of service (QoS) constraints and the relay power constraints. Three well-known and practical two-way relay strategies are considered, i.e., amplify-andforward (AF), bit level XOR based decode-and-forward (DF-XOR) and symbol level superposition coding based DF (DF-SUP). For each relaying strategy, we formulate the joint energy transmit beamforming and PS ratios optimization as a nonconvex quadratically constrained problem. To find a closed-form solution of the formulated problem, we decouple the primal problem into two subproblems. In the first problem, we intend to optimize beamforming vector for a given PS ratio. In the second subproblem, we optimize the PS ratio with a given beamforming vector. It is worth noting that although the corresponding subproblem are nonconvex, the optimal solution of each subproblem can still be found by using certain techniques. We provide numerical results that demonstrate the advantage of adapting the different relaying strategies and weighted factors to harvest energy in two-way relaying channel.Index Terms-Beamforming, energy harvesting, simultaneous wireless information and power transfer (SWIPT), two-way relaying (TWR), power splitting (PS).

Two-dimensional boron sheets with a quasicubic structure have been synthesized on a Ni foil substrate by chemical vapor deposition, and possess a direct bandgap of around 2.4 eV.

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