Visualizing and understanding graph convolutional network

Multimedia Tools and Applications - The graph convolutional network (GCN), which can handle graph-structured data, is enjoying great interest in recent years. However, while GCN achieved remarkable...     

SDN南向通道的安全性研究

软件定义网络(SDN)技术分离了网络的控制平面和数据平面,有效地解决了网络安全管理和控制问题,然而SDN自身安全性也尚有诸多问题需要解决.本文在分析SDN架构及其安全性的基础上,针对南向通道安全进行了研究,并基于OTR协议给出了一种安全解决方法.该方法具有前向安全性、安全认证等特性,对于SDN环境中的安全身份认证、密钥安全保存以及SDN组件隐蔽保护等问题提供了较好的解决方案.     

煤粉源集合体对水力压裂效果的影响

煤粉颗粒在压裂液中发生"造浆"及"聚集"作用是影响煤层气藏水力压裂效果的关键.构造煤粉源集合体对压裂效果影响显著,研究结果表明:原位状态下,煤粉以构造煤粉源和原生裂缝煤粉源集合体两种形式赋存.前者体积在20~30m3之间,呈顺层和断层两种产状,其明显受煤储层小微构造的控制;后者规模很小,主要分布在内生裂隙缝间,其受煤变质程度和煤岩类型影响.煤层气完井期间,井筒附近构造煤坍塌扩径,构造煤粉源卸压膨胀,煤粉颗粒启动难度降低;压裂期间,在压裂液动压、紊流搅动作用下,煤粉颗粒均匀混合在流体中形成浆体;排采期间,回排的压裂液中煤粉含量较高,导致气井近井部位压裂裂缝及炮眼较早地堵塞,气井减产.而原生裂缝内煤粉在压裂液中通过颗粒疏水相互作用发生聚集,在压裂裂缝内形成堵塞,但堵塞程度较轻.稳定压裂液注入排量、减小流速,利用煤储层小微构造解剖技术预测构造煤粉源集合体发育部位能够降低近井部位堵塞的风险,改善水力压裂效果.     

Numerical Simulation of Energy Saving Potential in Dispersing Process of Blasted Smoke in Mines

The dispersing process of the blasted smoke in underground mines by ventilation is very important for the safety of personnel, and its energy consumption is also worthy of concern. In this study, the impact of supply air flow rate on the decay process of harmful gases and fan energy, and the role of harmful gases buried by blasted pile in the smoke dispersing process is analyzed with three-dimensional numerical simulation. According to the results, air flow facilitates quick smoke dispersion and the gas emits from the blasted pile is only significant at the beginning of ventilation. It is thus recommended that large amount of air supply is taken to disperse the smoke quickly until the concentration of harmful gases reaches relevant standards, and reduce the amount of air in the remain time with frequency conversion technology to save energy. In the given study, 12 m/s air flow rate is taken for dispersing smoke and 3 m/s air flow rate is taken for the waiting time. The energy consumption for ventilation is reduced by about 50％. In addition, due to the gases in the blasted pile remains very high concentration after the dispersing process, it is recommended to keep suitable amount of ventilation in the consequent process.     

Grid-Based Path Planner Using Multivariant Optimization Algorithm

To solve the shortest path planning problems on grid-based map efficiently, a novel heuristic path planning approach based on an intelligent swarm optimization method called Multivariant Optimization Algorithm (MOA) and a modified indirect encoding scheme are proposed. In MOA, the solution space is iteratively searched through global exploration and local exploitation by intelligent searching individuals, who are named as atoms. MOA is employed to locate the shortest path through iterations of global path planning and local path refinements in the proposed path planning approach. In each iteration, a group of global atoms are employed to perform the global path planning aiming at finding some candidate paths rapidly and then a group of local atoms are allotted to each candidate path for refinement. Further, the traditional indirect encoding scheme is modified to reduce the possibility of constructing an infeasible path from an array. Comparative experiments against two other frequently use intelligent optimization approaches: Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) are conducted on benchmark test problems of varying complexity to evaluate the performance of MOA. The results demonstrate that MOA outperforms GA and PSO in terms of optimality indicated by the length of the located path.     

LS—SVM算法在光伏短期功率预测中的应用

以光伏阵列为研究对象,分析了辐照强度、温度以及日类型对光伏阵列出力的影响。建立了光伏短期功率预测最小二乘支持向量机LS-SVM模型。依据实验数据对模型进行了验证计算．并与BP神经网络模型做了比较,其中LS-SVM模型最大相对误差值为10．54％,平均绝对百分比误差（MAPE）为8．18％,绝对误差平方和平均值的均方根（RMSE）为0．4884,表明模型预测值离散化程度较小,所有预测点均与实际值非常接近,模型具有较好的拟合效果和泛化能力．可以有效地预测短期光伏发电功率。     

High lumen density of Al2O3-LuAG: Ce composite ceramic for high-brightness display

Thermally robust and highly efficient green-emitting luminescent ceramics are gradually attracting great attention as promising phosphors using in high-brightness laser phosphor display to reduce serious speckle noise as well as high cost. However, lumen density is still seriously restricting their potential applications especially under high-power density laser due to insufficient absorption of blue laser and significant thermal quenching. Here, we report an Al₂O₃-LuAG: Ce composite ceramic phosphor (CCP) for high-brightness laser phosphor display. Owing to good optical properties and high thermal conductivity of Al₂O₃, the Al₂O₃-LuAG: Ce CCP shows high photoluminescence quantum yield (79.6%), low thermal quenching (only 3.2% loss in luminescence at 200°C), and high thermal conductivity (18.9 W·m⁻¹·K⁻¹). Moreover, the Al₂O₃, as scattering centers, enhances the Rayleigh–Mie scattering of the blue laser, and hence the absorption of the Al₂O₃-LuAG: Ce CCP exhibits a remarkable improvement (~2.3 times) at 450 nm. Finally, with optimized thickness (0.3 mm) of Al₂O₃-LuAG: Ce CCP, an excellent luminous efficiency (216 lm·W⁻¹) and outstanding lumen density (6129 lm·mm⁻²) of the green-emitting light source was obtained by driving under a high-power density (28.33 W·mm⁻²) blue laser. All of those validate the suitability of the Al₂O₃-LuAG: Ce CCP for high-brightness display.     

Degradability and biocompatibility of bioglass/poly(amino acid) composites with different surface bioactivity as bone repair materials

Bioglass (BG) possesses excellent bioactivity and has been widely used in the manufacture of biomaterials. In this study, a composite with different surface bioactivity was fabricated via in situ melting polymerization by incorporating BG and poly(amino acid) (PAA) at a suitable ratio. The structure of the composite was characterized by Fourier transform infrared spectroscopy and XRD. The compressive strength of the BG/PAA composites was 139 MPa (BG:PAA = 30:70). The BG/PAA composites were degradable, and higher BG in composite showed higher weight loss after 4 weeks of incubation in simulated body fluid. In addition, the BG/PAA composite maintained adequate residual compressive strength during the degradation period. The SEM results showed the differences in surface bioactivities of the composites directly, and 30BG/PAA composite showed thicker apatite layer and higher Ca/p than 15BG/PAA. in vitro MG-63 cell culture experiments showed that the composite was noncytotoxic and thus allows cells to adhere, proliferate, and differentiate. This indicates that the composite has good biocompatibility. The implantations in the bone defects of rabbits for 4 and 12 weeks were studied. The composites had good biocompatibility and were capable of guiding new bone formation without causing any inflammation. The composite may be successfully used in the development of bone implants.     

Preparation of treelike and rodlike carboxymethylated nanocellulose and their effect on carboxymethyl cellulose films

In this work, carboxymethyl cellulose (CMC) with low substitution degree, followed by different posttreatments, was applied to prepare treelike CMC nanofibrils (CMCNFs) and rodlike CMC nanocrystals (CMCNCs), and their performance in CMC composite film was evaluated simultaneously. From transmission electron microscopy results, it was found that the treelike CMCNCFs exhibited a lager aspect ratio compared to the rodlike CMCNCs. As for reinforcing CMC film, 4 wt% was the best adding amount, at this time, the tensile strength of CMC/CMCNFs and CMC/CMCNCs composite films was increased by 72.1% and 47.3%, respectively. Moreover, adding these nanofillers to CMC also could enhance the thermal stability of composite films slightly, while the transmittance of composite films was reduced at the same time. In addition, CMC/CMCNFs film was designed as a packaging box to determine its performance. Therefore, this study could reveal the differences of properties for composites with different types of nanocellulose and provide a foundation for further application of nanocellulose.     

Removal behavior and mechanism of silver from low concentration wastewater using cellulose aerogel modified by thiosemicarbazide

Due to the low concentration of silver in water, most of the cellulose adsorbents exhibited low removal efficiency, which greatly limited their practical applications. Herein, a cellulose aerogel modified by thiosemicarbamide (CAT) was fabricated for reducing and adsorbing silver ions from low concentration wastewater. The characterization results concluded that CAT owned a three-dimensional spongy structure with many circular microspheres and a better specific surface area (19.37 m² g⁻¹), as well as the functional groups of ─C═N⁺─H and ─(C═S)─N. The static batch adsorption experiments demonstrated that CAT could reached the maximum removal percentage of 94.94% and adsorption capacity of 42.12 mg g⁻¹ under the initial concentration of Ag(I) was 15 mg L⁻¹ and the pH value was 7. Meanwhile, the adsorption of Ag(I) on CAT was second-order reaction, and the Langmuir model could better fit the adsorption process. In addition, CAT exhibited wide pH values (1–9) adaptability and excellent adsorption performance for silver through electrostatic interaction, chelation, and reduction. This study probably provides a new method as well as important experimental data and theoretical reference for the removal of silver ions and other metals.