Joint Power-Trajectory-Scheduling Optimization in A Mobile UAV-Enabled Network via Alternating Iteration

This work focuses on an unmanned aerial vehicle(UAV)-enabled mobile edge computing(MEC) system based on device-to-device(D2D) communication. In this system, the UAV exhibits caching,computing and relaying capabilities to periodically provide specific service to cellular users and D2D receiver nodes in the appointed time slot. Besides, the D2D transmitter can provide additional caching services to D2D receiver to reduce the pressure of the UAV. Note that communication between multi-type nodes is mutually restricted and different links share spectrum resources. To achieve an improved balance between different types of node, we aim to maximize the overall energy efficiency while satisfying the quality-of-service requirements of the cellular nodes.To address this problem, we propose an alternating iteration algorithm to jointly optimize the scheduling strategies of the user, transmitting power of the UAV and D2D-TX nodes, and UAV trajectory. The successive convex approximation, penalty function, and Dinkelbach method are employed to transform the original problem into a group of solvable subproblems and the convergence of the method is proved. Simulation results show that the proposed scheme performs better than other benchmark algorithms, particularly in terms of balancing the tradeoff between minimizing UAV energy consumption and maximizing throughput.     

Process parameters influence on zone refining and thermodynamics analysis of 1,2-diphenylethane

Effective distribution coefficients of 9 impurities in 1,2-diphenylethane have been calculated by directional crystallization under different ambient frozen temperature. The effect of varied zone size, temperature difference between the melt and ambient frozen environment, number of zone on purity of 1,2-diphenylethane have been also investigated during the process of zone refining. The results indicate that the product purity in the intermediate purified region with varied zone size is higher 0.04%-0.2% than that with constant zone size. The product purity increases with temperature difference between the melt and ambient frozen environment. The appropriate temperature difference is adopted 50℃. The product purity in the intermediate region of sample bar with 2 molten zones is higher 0.05%-0.43% than that with 1 molten zone. In addition, the change of enthalpy and entropy between impurities and 1,2-diphenylethane have been determined.     

A Game-Theoretic Perspective on Resource Management for Large-Scale UAV Communication Networks

As a result of rapid development in electronics and communication technology,large-scale unmanned aerial vehicles(UAVs)are harnessed for various promising applications in a coordinated manner.Although it poses numerous advantages,resource management among various domains in large-scale UAV communication networks is the key challenge to be solved urgently.Specifically,due to the inherent requirements and future development trend,distributed resource management is suitable.In this article,we investigate the resource management problem for large-scale UAV communication networks from game-theoretic perspective which are exactly coincident with the distributed and autonomous manner.By exploring the inherent features,the distinctive challenges are discussed.Then,we explore several gametheoretic models that not only combat the challenges but also have broad application prospects.We provide the basics of each game-theoretic model and discuss the potential applications for resource management in large-scale UAV communication networks.Specifically,mean-field game,graphical game,Stackelberg game,coalition game and potential game are included.After that,we propose two innovative case studies to highlight the feasibility of such novel game-theoretic models.Finally,we give some future research directions to shed light on future opportunities and applications.     

Measurement and analysis of the extreme ultraviolet emission band of laser-produced antimony plasmas

The temporal evolution of extreme ultraviolet (EUV) emission spectra of laser-produced antimony (Sb) plasmas has been measured in the 7–16 nm wavelength region using spatio- temporally resolved lase-produced plasma spectroscopy technique. The spectral profiles involve an intense quasi-continuous band with superimposed intense characteristic radiation and are different with the increase of delay time. The spectral structures were also analyzed according to Hartree–Fock calculations with configuration interaction effects and contributed from 4d–4f, 4d–4p, and 4d–5f unresolved transition arrays of Sb⁷⁺ – Sb¹³⁺. A steady-state collisional- radiative model was used to estimate the electron temperature and density range of Sb plasmas. This work would enrich the spectral data of highly-charged ions and provided a possible selection for developing EUV light sources.     

The Self-Assembling Growth of Copper Nanowires for Transparent Electrodes

Long(15-40 μm), thin(diameter of 20 ± 5 nm), and well-dispersed CuNWs Cu nanowires were prepared. The high-resolution TEM and selected area electron diffraction showed that the CuNWs were single-crystalline. To investigate the growth mechanism, we examined the microstructure of these CuNWs at different reaction time. It was found that the CuNWs were actually formed through the self-assembling of Cu nanoparticles along the [110] direction. The transparent electrodes fabricated using the CuNWs achieved a high transparency of 76 % at 31±5 Ω/□.     

Surface wettability and flow properties of non-metallic pipes in laminar flow

In this paper, three liquids flowing in five pipes with the same inner diameter of 14 mm were studied to determine the relationship between the surface wettability and flow properties in laminar flow(Re b 2000). This was motivated by oilfield observations of increased pressure drops in non-metallic pipes compared to those in metal pipes,which was contrary to expectations. A new expression for the frictional coefficient that considers the Reynolds number and contact angle θ in laminar flow for non-metallic pipes was proposed based on the experimental results of single-phase flow using dimension and regression analyses. The solutions of the anomalous phenomenon were proposed from the perspectives of the pipe diameter, contact-angle difference, and the compatibility between flexible composite pipe and JLHW105 oil according to the new formula. The surprising finding was that the surface wettability could control the frictional resistance by the critical contact angle(39.9°) obtained at the same Reynolds number. If 0° b θ≤ 39.9°, the frictional coefficient increased as the contact angle increased. In contrast, if 39.9° b θ b 180°,the frictional coefficient decreased with increasing contact angle. The influences of the pipe diameter and contactangle difference on the pressure drop difference of JLHW105 oil showed an inversely proportional relation. A series of materials and liquids were tested. The selection of pipe material for transporting a given fluid can be based on the contact angle, surface tension, and critical limit of the contact angle obtained. The research results are expected to provide some guidelines for the selection of the appropriate pipe material for a given set of fluids.     

Defensible citadel:History and architectural character of the Lahore Railway Station

This study aims to investigate the defensible character of the Lahore railway station built in response to “the war of independence in 1857,” which greatly impacted the location and design of the building. This study demonstrates the integral role played by the railway station in the development of the new colonial city, which the British wants to be defensive in every aspect. Railways were introduced in Pakistan (India) soon after their inauguration in Britain. Beginning from the mode of transportation, the multifaced contribution of railways toward the urban growth, new architectural style, mode of construction, and technology cannot be recanted. The research is based on the documentation and analysis of the history of Lahore railway station design. First, this study uses primary and secondary data to offer a history of the Lahore railway station from its inception to final execution. Second, it explores the criteria adopted by the British for its site selection to make the station a defensible post. The research finding includes the visual features that enhanced the architectural character of the building. Qualitative methods are used including several other approaches, namely, literature review, archival data collection, analysis of photographs, and study of architectural drawings and old maps, to achieve the objectives.     

PIC simulation of plasma properties in the discharge channel of a pulsed plasma thruster with flared electrodes

Plasma in the discharge channel of a pulsed plasma thruster (PPT) with flared electrodes is simulated by a self-developed two-dimensional code. The fully particle-in-cell method with Monte Carlo collision is employed to model the particle movement and collisions and investigate the plasma properties and acceleration process. Temporal and spatial variations of the electron density distribution and the ion velocity between electrodes are calculated and analyzed in detail. The computational results of the electron number density, which is in the order of 10²³ m⁻³, show good agreements with experimental results of a PPT named ADD SIMP-LEX. The ion velocity distributions along the center line of the channel lead to a comprehensive understanding of ions accelerated by electromagnetic field. The electron distributions of PPT with discharge voltages varying from 1300 to 2000 V are compared. The diffusion of electrons presents strong dependency on discharge voltage and implies higher degree of ionization for higher voltage.     

Efficient polysulfides conversion on Mo2CTxMXene for highperformance lithium–sulfur batteries

The severe shuttle effect and sluggish redox kinetics of polysulfides hinder the application of lithium–sulfur batteries.Herein,delaminated Mo₂CT_x MXene nanosheets are derived by chemical etching approach and further applied as a sulfur host for sulfur spheres(S@Mo₂CT_x).In the MXene encapsulated architecture,the external MXene nanosheets not only immobilize the soluble polysulfides by strong chemical adsorption but also efficiently catalyze the liquid–liquid conversion and liquid–solid nucleation process of lithium polysulfides.In addition,the S@Mo₂CT_x electrode delivered fast charge and lithium-ion transport due to the superior electric conductivity and low lithiumion diffusion energy barrier of MXene nanosheets.As a result,the S@Mo₂CT_x electrode exhibits a high reversible capacity of 918 mAh·g^-1 at 1.0C with good cycling stability and a high areal capacity of 7.0 mAh·cm^-2 with sulfur loading of 7.4 mg·cm^-2 under a lean electrolyte condition.     

Effects of Rapid Cooling Rate on Microstructure Formation and Microhardness of Binary Ti-44Al Alloy

快速冷却速率对Ti-44Al合金组织和显微硬度的影响

陈晓宇^1,2,方虹泽¹,王琪¹,陈瑞润¹,丁宏升¹,苏彦庆¹,郭景杰¹

（1. 哈尔滨工业大学 材料科学与工程学院,哈尔滨 150001;

2. 青岛大学 机电工程学院,山东 青岛 266071）

中文说明：

为细化TiAl合金的显微组织与晶粒,提高其力学性能,采用甩带快速凝固方法在不同冷却速率条件下制备了Ti-44Al（at.%）合金,研究了铸态与快速凝固合金的显微组织和显微硬度。XRD测试结果表明,合金中α2相含量随着冷却速率增加而增加,这是由于高的凝冷却率导致α相直接转变为α2相。随着冷却速率的增加,晶粒形态首先由树枝晶转变为等轴晶和树枝晶混合的组织,而后转变为等轴晶。经快速凝固制备后,合金晶粒尺寸由铸态的200-600 μm降低到快速凝固的18 μm。片层厚度由铸态的4.5 μm降低到快速凝固的1.1 μm。随着冷却速率的增加,α2相含量逐渐增加,γ相含量逐渐减少,并且快速凝固可以降低基体中元素偏析。快速凝固的合金晶粒细化,片层厚度降低,并且α2相含量增加,这导致显微硬度由铸态的247 HV提高到快速凝固的556 HV。

关键词：Ti-44Al合金,显微组织,显微硬度,甩带快速凝固,凝固路径