基于NOMA的5G超密网计算迁移与资源分配策略

针对5G超密网中移动设备计算能力不足、频谱资源有限的问题,提出了一种基于非正交多址接入（NOMA）的计算迁移与带宽分配策略。首先,对系统模型进行了分析,并在此基础上以最小化设备计算代价为目标对所研究的问题进行形式化定义;然后,将该问题分解成设备的计算迁移、系统的带宽分配和设备的分组匹配三个子问题,并利用模拟退火、内点法和贪心算法对这三个子问题进行求解;最后,通过联合优化算法对上述子问题进行交替性迭代求解,最终获得最优计算迁移和资源分配策略。仿真结果表明,所提出的联合优化策略不但优于传统的正交多址接入（OMA）方式,而且能获得比平均分配带宽的NOMA技术更低的设备计算代价。     

矩形窗正交时频空检测算法

针对正交时频空(Orthogonal Time Frequency Space, OTFS)调制系统采用矩形窗函数时,信道矩阵结构复杂导致的鲁棒性差的问题,提出了一种基于时域处理和酉近似消息传递的检测算法。该算法首先添加循环前缀,将时域信道转换为分块对角矩阵;然后应用酉变换和近似消息传递建立迭代检测算法。仿真结果表明,所提检测算法能够在不增加复杂度的条件下有效提升检测精度和鲁棒性,特别是存在信道编码的条件下表现出2 dB的性能增益,使得该算法更适用于杂散多径、高速移动等环境,具有较高的应用价值。     

大数据相似性连接查询技术研究进展

为了深入理解和全面把握大数据相似性连接查询技术的研究进展，更好地促进其在图片聚类、实体解析、相似文档检测、相似轨迹检索等领域的广泛应用，对大数据相似性连接查询技术相关研究工作进行了深入调研和分析。首先对相似性连接查询的基本概念进行了介绍，然后分别对集合、向量、空间数据、概率数据、字符串等不同类型大数据的相似性连接查询相关研究工作进行了深入研究，对其优缺点进行了分析和总结。最后，指出了大数据相似性连接查询面临的若干挑战性问题及未来的研究重点。     

Electrospun porous carbon nanofibers derived from bio-based phenolic resins as free-standing electrodes for high-performance supercapacitors

Phenolic resins were employed to prepare electrospun porous carbon nanofibers with a high specific surface area as free-standing electrodes for high-performance supercapacitors. However, the sustainable development of conventional phenolic resin has been challenged by petroleum-based phenol and formaldehyde. Lignin with abundant phenolic hydroxyl groups is the main non-petroleum resource that can provide renewable aromatic compounds. Hence, lignin, phenol, and furfural were used to synthesize bio-based phenolic resins, and the activated carbon nanofibers were obtained by electrospinning and one-step carbonization activation. Fourier transform infrared and differential scanning calorimetry were used to characterize the structural and thermal properties. The results reveal that the apparent activation energy of the curing reaction is 89.21 kJ·mol^–1 and the reaction order is 0.78. The activated carbon nanofibers show a uniform diameter, specific surface area up to 1100 m²·g^–1, and total pore volume of 0.62 cm³·g^–1. The electrode demonstrates a specific capacitance of 238 F·g^–1 (0.1 A·g^–1) and good rate capability. The symmetric supercapacitor yields a high energy density of 26.39 W·h·kg^–1 at 100 W·kg^–1 and an excellent capacitance retention of 98% after 10000 cycles. These results confirm that the activated carbon nanofiber from bio-based phenolic resins can be applied as electrode material for high-performance supercapacitors.     

Controlled synthesis of W–Co3S4@Co3O4 as an environmentally friendly and low cost electrocatalyst for overall water splitting

Electrochemistry splitting of water is considered to be one of the most fascinating methods to replace traditional chemical fuels. Here, we design a new method to exploit W–Co₃S₄@Co₃O₄ heterostructures. The W–Co₃S₄@Co₃O₄ material was first prepared and grown in situ on nickel foam by a typical hydrothermal and calcination approach. Based on the principle of electronic regulation, the synergistic effect of W and Co metal ions can increase the charge transfer of the electrode, thus significantly prompting the catalytic activity of the electrode. The W–Co₃S₄@Co₃O₄ material present superior catalytic performance for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and the overpotential at 10 mA cm⁻² is 260 mV and 140 mV, respectively. Notably, W–Co₃S₄@Co₃O₄ catalyst showed excellent water splitting performance under alkaline conditions (cell voltage of 1.63V @10 mA cm⁻²). Density functional theory calculation shows that the existence of the Co₃O₄ material accelerates the rate of hydrogen production reaction, and the existence of the W–Co₃S₄ material promotes the conductivity of the W–Co₃S₄@Co₃O₄ electrode. The synergistic effect of W–Co₃S₄ and Co₃O₄ materials is beneficial to the improvement of the catalytic activity of the electrode. This study provides a novel view for the development of electrodes synthesis and a novel paradigm for the development of robust, better and relatively non-toxic bifunctional catalysts.     

Kinetically stabilized hydrogen storage materials

Kinetically stabilized hydrides are characterized by a low reaction enthalpy and a decomposition reaction that is thermodynamically favorable under ambient conditions. The rapid, low temperature hydrogen evolution rates offer much promise for mobile proton exchange membrane fuel cell applications. However, a critical challenge exists to develop new methods to regenerate or recycle the hydride directly from the reactants and hydrogen gas.     

The role of oxygen vacancies in the CO2 methanation employing Ni/ZrO2 doped with Ca

The Ni/ZrO₂ catalyst doped with Ca and Ni/ZrO₂ were employed in the CO₂ methanation, a reaction which will possibly be used for storing intermittent energy in the future. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS, reduction in situ), X-ray diffraction (XRD, reduction in situ and Rietveld refinement), electron paramagnetic resonance (EPR), temperature-programmed surface reaction, cyclohexane dehydrogenation model reaction, temperature-programmed desorption of CO₂ and chemical analysis. The catalytic behavior of these catalysts in the CO₂ methanation was analyzed employing a conventional catalytic test. Adding Ca to Ni/ZrO₂, the metallic surface area did not change whereas the CO₂ consumption rate almost tripled. The XRD, XPS and EPR analyses showed that Ca⁺² but also some Ni²⁺ are on the ZrO₂ surface lattice of the Ni/CaZrO₂ catalyst. These cations form pairs which are composed of oxygen vacancies and coordinatively unsaturated sites (cus). By increasing the number of these pairs, the CO₂ methanation rate increases. Moreover, the number of active sites of the CO₂ methanation rate limiting step (CO and/or formate species decomposition, rls) is enhanced as well, showing that the rls occurs on the vacancies-cus sites pairs.     

Improved lithium manganese oxide spinel/graphite Li-ion cells for high-power applications

The degradation mechanism of lithium manganese oxide spinel/graphite Li-ion cells using LiPF₆-based electrolyte was investigated by a Mn-dissolution approach during high-temperature storage, and by ac impedance measurement using a reference electrode-equipped cell. Through these studies, we confirmed that Mn ions were dissolved from the spinel cathode in the electrolyte and were subsequently reduced on the lithiated graphite electrode surface, due to the chemical activity of the lithiated graphite, and caused a huge increase in the charge-transfer impedance at the graphite/electrolyte interface, which consequently deteriorated cell performance. To overcome the significant degradation of the spinel/graphite Li-ion cells, we investigated a new electrolyte system using lithium bisoxalatoborate (LiBoB, LiB(C₂O₄)₂) salt not having fluorine species in its chemical structure. Superior cycling performance at elevated temperature was observed with the spinel/graphite cells using LiBoB-based electrolyte, which is attributed to the inert chemical structure of LiBoB that does not generate HF. Mn-ion leaching experiments showed that almost no Mn ions were dissolved from the spinel powder after 55 °C storage for 4 weeks. Through optimization of organic solvents for the LiBoB salt, we developed an advanced Li-ion cell chemistry that used lithium manganese oxide spinel, 0.7 M LiBoB/EC:PC:DMC (1:1:3), and graphite as the cathode, electrolyte, and anode, respectively. This cell provides excellent power characteristics, good calendar life, and improved thermal safety for hybrid electric vehicle applications.     

Two-level pattern recognition in a class of knowledge-based systems

In the paper, the problem of pattern recognition in a two-level expert system with the logical knowledge representation is investigated. In the first part, formulation and solution algorithm of this problem are presented. To solve the pattern recognition problem, a logic-algebraic method is used. In the second part, it is shown how the method of learning may be applied to the pattern recognition system with unknown parameters in knowledge representation. The concepts considered here are illustrated by a simple numerical example.     

Light-modulated ferromagnetism of strained NiFe2O4 nanocrystals

Light provides a potential approach to modulate magnetism due to the low energy consumption, which could be used for the development of optical-magnetic coupling devices, data storage technology and quantum computation technology. In this work, NiFe₂O₄ nanocrystals with inverse spinel structure confined in non-magnetic Al₂O₃ film are synthesized. Based on theoretical calculation and experimental validation, it is revealed that the NiFe₂O₄ nanocrystals experience compressive strain from Al₂O₃ film. The compressive strain can be partially relaxed, leading to the formation of disorder layers at the surfaces of strained NiFe₂O₄ nanocrystals, which provide an ideal platform to modulate magnetism optically. A remarkable light-modulated ferromagnetism in the strained NiFe₂O₄ nanocrystals is observed. This work demonstrates a novel approach to optically engineer the ferromagnetic properties for applications in next generation of magnetic nano-devices.