QoE-Driven Video Transmission: Energy-Efficient Multi-UAV Network Optimization

This paper is concerned with the issue of improving video subscribers' quality of experience (QoE) by deploying a multi-unmanned aerial vehicle (UAV) network. Different from existing works, we characterize subscribers' QoE by video bitrates, latency, and frame freezing and propose to improve their QoE by energy-efficiently and dynamically optimizing the multi-UAV network in terms of serving UAV selection, UAV trajectory, and UAV transmit power. The dynamic multi-UAV network optimization problem is formulated as a challenging sequential-decision problem with the goal of maximizing subscribers' QoE while minimizing the total network power consumption, subject to some physical resource constraints. We propose a novel network optimization algorithm to solve this challenging problem, in which a Lyapunov technique is first explored to decompose the sequential-decision problem into several repeatedly optimized sub-problems to avoid the curse of dimensionality. To solve the sub-problems, iterative and approximate optimization mechanisms with provable performance guarantees are then developed. Finally, we design extensive simulations to verify the effectiveness of the proposed algorithm. Simulation results show that the proposed algorithm can effectively improve the QoE of subscribers and is 66.75\% more energy-efficient than benchmarks

Bio-inspired titanium dioxide materials with special wettability and their applications

Titanium dioxide (TiO2) is one of the most widely used nanomaterials in our daily life. In 1972, Fujishima and Honda reported the photo electrolysis of water into H2 and O2 utilizing an electrochemical cell in which the TiO2 single-crystal electrode is connected with a Pt electrode. This is analogus with the natural photosynthesis that produces oxygen through oxidizing water and reducing carbon dioxide using sunlight, where solar energy is converted into chemical energy. Since that time, photocatalysis has received considerable attention owing to its important applications in the conversion of light energy into useful chemical energy. In 1997, Fujishima et al. first reported the photogeneration of a superamphiphilic (both superhydrophilic and superoleophilic, where the contact angle of water and oil on a surface is almost 0°, respectively) TiO2 surface under UV light irradiation, showing self-cleaning and antifogging characteristics. This breakthrough work expanded the research field of TiO2 materials and marked the beginning of a new era in TiO2-based self-cleaning materials. Since then, an important effort has been focused on the understanding of the fundamental mechanism of this novel function and on the development of selfcleaning materials for a wide range of applications in energy, environmental, and industrial fields, resulting in the generation of new markets. Although photocatalysis and photoinduced superhydrophilicity can take place simultaneously on the same TiO2 surface, they are intrinsically different processes. In recent years, environmental pollution and damage on a global scale have emerged as a serious issue. The viable environmental cleanup has attracted a great deal of attention to achieve important breakthroughs in the design of advanced materials and in the development of new technology. Now, a variety of TiO2-based materials have been commercialized arising from their unique photoinduced properties. Furthermore, these commercial products demonstrate their importance in the environmental cleanup

A combined interfacial and in-situ polymerization strategy to construct well-defined core-shell epoxy-containing SiO2-based microcapsules with high encapsulation loading, super thermal stability and nonpolar solvent tolerance

SiO2-based microcapsules containing hydrophobic molecules exhibited potential applications such as extrinsic self-healing, drug delivery, due to outstanding thermal and chemical stability of SiO2. However, to construct SiO2-based microcapsules with both high encapsulation loading and long-term structural stability is still a troublesome issue, limiting their further utilization. We herein design a single-batch route, a combined interfacial and in-situ polymerization strategy, to fabricate epoxy-containing SiO2-based microcapsules with both high encapsulation loading and long-term structural stability. The final SiO2-based microcapsules preserve high encapsulation loading of 85.7 wt% by controlling exclusively hydrolysis and condensed polymerization at oil/water interface in the initial interfacial polymerization step. In the subsequent in-situ polymerization step, the initial SiO2-based microcapsules as seeds could efficiently harvest SiO2 precursors and primary SiO2 particles to finely tune the SiO2 wall thickness, thereby enhancing long-term structural stability of the final SiO2-based microcapsules including high thermal stability with almost no any weight loss until 250°C, and strong tolerance against nonpolar solvents such as CCl4 with almost unchanged core-shell structure and unchanged core weight after immersing into strong solvents for up to 5 days. These SiO2-based microcapsules are extremely suited for processing them into anticorrosive coating in the presence of nonpolar solvents for self-healing application

Ag-Conjugated Graphene Quantum Dots with Blue Light-Enhanced Singlet Oxygen Generation for Ternary-Mode Highly-Efficient Antimicrobial Therapy

The increasing prevalence of antibiotic resistance highlights the need for new antibacterial drugs and, in particular, the development of alternative approaches such as photodynamic therapy (PDT) and photothermal therapy (PTT) to manage this growing issue. In the present study, a broad-spectrum antibacterial system was produced in which Ag nanoparticle-conjugated graphene quantum dots (GQD-AgNP) were utilised as a blue light-enhanced nanotherapeutic for efficient ternary-mode antimicrobial therapy. The successful conjugation of AgNPs onto the surface of GQDs can significantly improve the production of reactive oxygen species in light-activatable GQDs and the transformation of light energy to hyperthermia with high efficiency. There was a remarkable increase in the sample temperature of nearly 40 °C via photoexcitation after only 10 min of 450 nm laser exposure (14.2 mW cm-2). The hybrids exhibited much more efficient bactericidal capability against both Gram-negative and Gram-positive bacteria compared with GQDs alone, using 450 nm light irradiation. This is likely a consequence of their enhanced PDT, concomitant PTT, and the synergistic function of AgNPs. The antibacterial mechanism of the new-style nanocomposites was found to irreversibly destroy the bacterial membrane structure, leading to the leaking out of the cytoplasmic contents and the death of the bacteria. At low doses, the biocompatible GQD-AgNP hybrids promoted healing in bacteria-infected rat wounds, with negligible adverse impact to the normal tissue, indicating a promising future for combined photodynamic and photothermal antibacterial applications in clinical medicine

Single-site pyrrolic-nitrogen-doped sp 2-hybridized carbon materials and their pseudocapacitance

A mixture of nitrogen species in carbon materials typically hinders the precise identification of electrochemically active nitrogen configurations for specific reactions. Here the authors show single-site pyrrolic-nitrogen-doped sp 2-hybridized carbon materials and their pseudocapacitive properties

UV-Triggered Self-Healing of a Single Robust SiO₂ Microcapsule Based on Cationic Polymerization for Potential Application in Aerospace Coatings

UV-triggered self-healing of single microcapsules has been a good candidate to enhance the life of polymer-based aerospace coatings because of its rapid healing process and healing chemistry based on an accurate stoichiometric ratio. However, free radical photoinitiators used in single microcapsules commonly suffer from possible deactivation due to the presence of oxygen in the space environment. Moreover, entrapment of polymeric microcapsules into coatings often involves elevated temperature or a strong solvent, probably leading to swelling or degradation of polymer shell, and ultimately the loss of active healing species into the host matrix. We herein describe the first single robust SiO₂ microcapsule self-healing system based on UV-triggered cationic polymerization for potential application in aerospace coatings. On the basis of the similarity of solubility parameters of the active healing species and the SiO₂ precursor, the epoxy resin and cationic photoinitiator are successfully encapsulated into a single SiO₂ microcapsule via a combined interfacial/in situ polymerization. The single SiO₂ microcapsule shows solvent resistance and thermal stability, especially a strong resistance for thermal cycling in a simulated space environment. In addition, the up to 89% curing efficiency of the epoxy resin in 30 min, and the obvious filling of scratches in the epoxy matrix demonstrate the excellent UV-induced healing performance of SiO₂ microcapsules, attributed to a high load of healing species within the capsule (up to 87 wt %) and healing chemistry based on an accurate stoichiometric ratio of the photoinitiator and epoxy resin at 9/100. More importantly, healing chemistry based on a UV-triggered cationic polymerization mechanism is not sensitive to oxygen, extremely facilitating future embedment of this single SiO₂ microcapsule in spacecraft coatings to achieve self-healing in a space environment with abundant UV radiation and oxygen

Role of layered structure in ductility improvement of layered Ti-Al metal composite

Layered Ti-Al metal composite (LMC) was designed and fabricated by hot-rolling and annealing of pure Ti and Al sheets. The as-prepared composite exhibits high tensile ductility, being superior to any individual Ti or Al sheets. The stress/strain evolution and fracture behavior of the LMC were analyzed by in-situ observations during the tensile deformation. Three deformation stages of LMC were clearly observed by neutron diffraction: elastic stage, elastic-plastic stage and plastic stage. It is found that stress partitioning at the elastic-plastic deformation stage improves the strain balance of LMC, but leads to an internal stress accumulated at the interface. Additionally, a strain-transfer from Ti to adjacent Al layers relieves the strain localization of Ti layers in LMC, which improves the ductility of Ti. Both stress partitioning and strain localization of Ti layers facilitate the nucleation of cracks at a low macro strain. However, the crack propagation is constrained by layered structure. In terms of the Al layers, the constrained micro-cracks relieve the stress concentration in Al layer and improve the ductility of Al layers, so that cracking indirectly affects the plastic deformation behavior of LMC, then improving its entire ductility. This work provides a new structural strategy towards simultaneously improving strength and ductility to develop high performance LMC by structural design