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Hollow ZnV(2)O(4) microspheres with a clewlike feature were synthesized by reacting zinc nitrate hexahydrate and ammonium metavanadate in benzyl alcohol at 180 degrees C for the first time. GC-MS analysis revealed that the organic reactions that occurred in this study were rather different from those in benzyl alcohol based nonaqueous sol-gel systems with metal alkoxides, acetylacetonates, and acetates as the precursors. Time-dependent experiments revealed that the growth mechanism of the clewlike ZnV(2)O(4) hollow microspheres might involve a unique multistep pathway. First, the generation and self-assembly of ZnO nanosheets into metastable hierarchical microspheres as well as the generation of VO(2) particles took place quickly. Then, clewlike ZnV(2)O(4) hollow spheres were gradually produced by means of a repeating reaction-dissolution (RD) process. In this process, the outside ZnO nanosheets of hierarchical microspheres would first react with neighboring vanadium ions and benzyl alcohol and also serve as the secondary nucleation sites for the subsequently formed ZnV(2)O(4) nanocrystals. With the reaction proceeding, the interior ZnO would dissolve and then spontaneously diffuse outwards to nucleate as ZnO nanocrystals on the preformed ZnV(2)O(4) nanowires. These renascent ZnO nanocrystals would further react with VO(2) and benzyl alcohol, ultimately resulting in the final formation of a hollow spatial structure. The lithium storage ability of clewlike ZnV(2)O(4) hollow microspheres was studied. When cycled at 50 mA g(-1) in the voltage range of 0.01-3 V, this peculiarly structured ZnV(2)O(4) electrode delivered an initial reversible capacity of 548 mAh g(-1) and exhibited almost stable cycling performance to maintain a capacity of 524 mAh g(-1) over 50 cycles. This attractive lithium storage performance suggests that the resulting clewlike ZnV(2)O(4) hollow spheres are promising for lithium-ion batteries.

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In this paper, we focus on a typical cooperative communication system with one pair of source and destination, where a unmanned aerial vehicle (UAV) flying from a start location to an end location serves as a mobile relay. To efficiently utilize energy in ambient environment, the UAV's transmission capability is powered exclusively by radio signal transmitted from the source via the power-splitting mechanism. In such a cooperative communication system, we study the end-to-end cooperative throughput maximization problem by optimizing the UAV's power profile, power-splitting ratio profile and trajectory for both amplify-and-forward (AF) and decode-and-forward (DF) protocols. The problem is decomposed into two subproblems: profile optimization given trajectory and trajectory optimization given profile. The former one is solved via the dual decomposition with in-depth analysis and the latter one is solved via successive convex optimization, by which a lower bound is iteratively maximized. Then the end-to-end cooperative throughput maximization problem is solved by alternately solving the two subproblems.The numerical results show that with the proposed optimal solution, choice for the UAV's power profile and power-splitting ratio profile is more long-sighted than the greedy strategy from our previous work and the successive optimization is able to converge in a few rounds of iteration. Moreover, as for the end-to-end cooperative throughput, the proposed optimal solution outperforms both static and greedy strategies, especially for the AF protocol. Index TermsCooperative communications, UAV-assisted communications, wireless power and information transfer. I. INTRODUCTIONIn recent years, wireless communications aided by unmanned aerial vehicles (UAV, also known as drones) have received significant attention from academia, industry as well as government [1]. 2 Compared to terrestrial infrastructures in conventional wireless communications, UAVs that serve as aerial transceivers have remarkable advantages in terms of low cost, miniaturized size, high mobility and deployment flexibility such that UAV-assisted wireless communication systems have been extensively applied in a number of applications such as military operations and scientific missions.UAV-aided ubiquitous coverage and UAV-aided information dissemination are two major applications of UAV-assisted communications [2]. In the former one, UAVs are deployed to assist existing communication infrastructures in order to provide seamless coverage within an area. Two typical scenarios are rapid service recovery (e.g., when infrastructures are damaged due to natural disasters [3]) and base station offloading in extremely crowded areas, which is also one of the five key scenarios that need to be effectively addressed in the fifth generation (5G) wireless communication systems [4]. In the latter one, UAVs are deployed to disseminate (collect) delay-tolerant information to (from) a large number of wireless devices. A typical example is information collection in smart agricu...

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To save drying time and increase productivity, a novel idea was proposed for freeze‐drying of liquid materials by creating an initially unsaturated frozen structure. An experimental investigation was carried out aiming at verifying the idea using a multifunctional freeze‐drying apparatus. Mannitol was selected as the primary solute in aqueous solution. Liquid nitrogen ice‐cream making method was used to prepare the frozen materials with different initial porosities. Results show that freeze‐drying can be significantly enhanced with the initially unsaturated frozen material, and substantial drying time can be saved compared with conventional freeze‐drying of the initially saturated one. Drying time was found to decrease with the decrease in the initial saturation. The drying time for the initially unsaturated frozen sample (S0 = 0.28 or 0.69 of initial porosity) can be at best 32% shorter than that required for the saturated one (S0 = 1.00 or zero porosity). This unique technique is easy to implement and improves the freeze‐drying performance of liquid materials. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2048–2057, 2015

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