Numerical study of flow distribution uniformity for the optimization of gradient porosity configuration of porous copper fiber sintered felt for hydrogen production through methanol steam reforming micro-reactor

A macroscopic numerical method is proposed to study the flow distribution uniformity of a novel porous copper fiber sintered felt (PCFSF), which has gradient porosities and was developed as the methanol steam reforming micro-reactor catalyst support for hydrogen production for fuel cell applications. The macroscopic porous media developed by the ANSYS/FLUENT software is used to represent the PCFSF. Our results indicate that the gradient porosity can reshape the flow distribution of PCFSFs greatly, thus producing significant influence on their performance. It is further revealed that, for a PCFSF with a determined gradient porosity configuration but different reactant feed directions, the velocity uniformity can be used as a quantitative criterion to evaluate the performance of hydrogen production. Furthermore, new gradient PCFSFs are produced according to the flow distribution of original gradient PCFSFs. The preliminary experimental results of the new gradient PCFSFs of 0.8-0.9-0.7 and 0.7-0.9-0.8 exhibit better methanol conversion and H₂ flow rate. This indicates that the numerical method can be used for the optimization of PCFSFs' gradient porosity configuration, which consists of the shape and position of the interfaces between different porosity portions, the number of interfaces and the porosity distribution in different portions.     

喷射成形—热等静压9V高钒钢的组织与性能研究

采用喷射成形工艺制备9V高钒钢。分别对试样进行热等静压处理和热处理,研究了HIP前后孔隙率和组织的变化,以及热处理后硬度的变化。研究结果表明喷射成形高钒钢在沉积态的组织孔隙率为0.28%,经热等静压技术处理后孔隙率为0.06%。喷射成形高钒钢在沉积态的组织为铁素体和碳化钒,碳化钒主要呈团球状和块状,其中块状碳化钒主要弥散分布于基体晶粒的晶界处,球状碳化物大部分弥散分布于基体晶粒内部,碳化物的平均粒径为1μm,最大尺寸小于2μm。经热处理后硬度高达63.1HRC,随回火次数增加,硬度逐渐降低。     

Nonsolvent-induced phase separation-derived TiO_2 nanotube arrays/porous Ti electrode as high-energy-density anode for lithium-ion batteries

TiO_2 nanotube arrays,growing on three-dimensional(3 D) porous Ti membrane,were synthesized using a facile nonsolvent-induced phase separation and anodization process.The length of those three-dimensional nanotube arrays could be tuned by prolonging the anodizing time.When the anodizing time is 8 h,the three-dimensional TiO_2 nanotube arrays/porous Ti electrode exhibits well cycling stability and ultra-high specific capacity,which is used in lithium-ion batteries,attributed to the high utilization rate of the substrate and the high growth intensity of the active materials.Three-dimensional TiO_2 nano tube arrays/porous Ti electrode,at 100 μA·cm~(-2) with 8 h anodizing time,shows a typical discharge plateau at 1.78 V and exhibits the specific capacity with 2126.7 μAh·cm~(-2),The novel nanotube arrays@3 D porous architecture effectively shortens the electron/ion transmission path,which could pave way for optimizing the design of highperformance anode materials for next-generation energy storage system.     

大规模流媒体应用中关键技术的研究

支持大规模用户在线使用的流媒体应用是Internet中极富潜力的一项"重磅级应用",但由于Internet缺乏服务质量(QoS)与相应的安全保障,并且网络和终端系统又存在着较大的异构性,这使得在Internet上构建支持大规模用户的在线流媒体应用面临很多的挑战.该文从支持该应用的流媒体编码技术和网络技术两个角度出发,针对其面临的挑战,深入、全面地综述了编码技术与网络技术的发展与现状.提出了一个新的流媒体应用体系结构,以同时解决大规模流媒体应用中的性能瓶颈、异构性、安全传输以及服务质量等问题,并指出了大规模流媒体应用中关键技术的研究方向.     

针对执行器非光滑反向间隙-饱和的柔性立管边界控制

研究了针对执行器非光滑反向间隙-饱和约束特性的深海柔性立管系统振动控制和全局稳定问题.为了实现控制效果和品质,引入辅助系统和函数设计边界控制策略,以抑制立管系统振动并消除混合的反向间隙-饱和输入非线性影响.采用严格的分析且无需求助于模型降阶,所研发的控制器确保闭环系统在Lyapunov意义下的一致有界稳定性.通过选取恰当的设计参数,仿真结果验证了所设计控制器的控制性能.能.     

Preparation of sheath–core bicomponent composite ion-exchange fibers and their properties

Based on sheath–core bicomponent composite ion-exchange fibers with modified polystyrene and modified polypropylene, composite fibers were further crosslinked and sulfonated with chlorosulfonic acid to produce strongly acidic cation-exchange fibers. The optimal technology of the obtained fibers was examined, and the structures of the fibers were investigated with Fourier transform infrared spectrophotometry, differential scanning calorimetry, and so forth. The properties were measured with chemical titration, filament strength instrumentation, scanning electron microscopy, and so forth. The results showed that cation-exchange fibers with better mechanical properties and a higher exchange capacity were obtained, and they had higher practicability. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

An Improved Markov Model for IEEE 802.15.4 Slotted CSMA/CA Mechanism

IEEE 802.15.4 protocol is proposed to meet the low latency and energy consumption needs in low-rate wireless applications,however,few analytical models are tractable enough for comprehensive evaluation of the protocol.To evaluate the IEEE 802.15.4 slotted CSMA/CA channel access mechanism in this paper,we propose a practical and accurate discrete Markov chain model,which can dynamically represent different network loads.By computing the steady-state distribution probability of the Markov chain,we obtain a...     

优化气相色谱法测定食品中的甜蜜素

目的优化气相色谱法测定食品中甜蜜素的方法。方法选用氢火焰离子化检测器和U型玻璃填充柱,对衍生化条件(亚硝酸钠用量、硫酸用量、衍生温度、衍生时间)进行优化,结果得到最适衍生化条件为:亚硝酸钠用量:2.5 mL;硫酸用量:2.5 mL;冰浴中衍生35 min。最佳条件下得到的检出限20 mg/kg。甜蜜素的加标回收率在96.8%~105.8%之间,甜蜜素相对标准偏差在2.5%~3.2%之间。结论该方法具有快速准确、回收率高、检出限低等优势,可以满足食品中甜蜜素的分析测定要求,为实践生产中食品甜蜜素的检测和食品质量安全的控制起到指导作用。     

中国沙棘雄花花被和花粉蛋白质营养评价

目的 分析中国沙棘雄花花被及花粉蛋白质含量和氨基酸组成及其营养均衡性。方法 采用凯氏定氮法和柱后衍生阳离子交换色谱方法分析中国沙棘雄花花被及花粉中蛋白质和氨基酸的含量,并结合国际上通用的营养价值评价方法对其蛋白质含量、化学评分(chemical sore, CS)、氨基酸评分(aminoacid score, AAS)、必需氨基酸指数(essential amino acid index, EAAI)、氨基酸比值系数分(score of ratio coefficient of amino acid,SRCAA)、生物价(biological value, BV)和营养指数(nutritional index, NI)等进行综合评价。结果 中国沙棘雄花花被及花粉蛋白质含量分别为16.07%、20.45%;中国沙棘雄花花被及花粉中氨基酸含量无显著差异, 17种氨基酸总含量分别为13.59 g/100 g、17.06 g/100 g;蛋白质营养评价表明,中国沙棘雄花花被及花粉中总必需氨基酸分别为31.14g/100g、33.10g/100g,接近于联合国粮农组织与世界卫生组织(Foodan...     

Effects of carbon on electrochemical performance of red phosphorus(P) and carbon composite as anode for sodium ion batteries

Red phosphorus/graphite(P/G) and red phosphorus/carbon nanotube(P/CNT) composites were prepared by ball milling red phosphorus with CNTs and graphite, respectively. The electrochemical results show superior electrochemical performances of the P/G and P/CNT composites compared with that of the reference sample milled with Super-P carbon. After 70 cycles, the P/G and P/CNT composites remained771.6 and 431.7 mA h g^-1, with 68 % and 50 % capacity retention, respectively. With increasing the milling time(20 h), CNTs were cut into short pieces and then broken into carbon rings and sheets which were well mixed with red phosphorus. The morphology of the P/CNT composite can buffer the large volume changes from alloying and de-alloying during cycling, resulting in the enhanced cycling stability.