Dynamic hierarchical collaborative caching scheme in ultra-dense networks

Pushing popular contents to the edge of the network can meet the growing demand for data traffic, reduce latency and relieve the pressure of the backhaul. However, considering the limited storage space of the base stations, it is impossible to cache all the contents, especially in ultra-dense network ( UDN). Furthermore, the uneven distribution of mobile users results in load imbalance among small base stations (SBSs) in both time and space, which also affects the caching strategy. To overcome these shortcoming, the impact of the changing load imbalance in UDN was investigated, and then a dynamic hierarchical collaborative caching (DHCC) scheme was proposed to optimize latency and caching hit rate. The storage of the SBS is logically divided into the independent caching layer and the collaborative caching layer. The independent caching layer caches the most popular contents for local users爷interest, and the collaborative caching layer caches contents as much as possible for the benefit of content diversity in the region. Different SBSs have respective storage space layer division ratios, according to their real-time traffic load. For SBSs with heavy load, the independent caching layers are allocated with more space. Otherwise, the collaborative caching layers could store more contents with larger space. The simulation results show that, DHCC improved both transmission latency and hit rate compared with existing caching schemes.     

What company characteristics are associated with the adoption of social media?

ABSTRACT

In just one decade, social media have moved from being marginal phenomena to having three billion active monthly users globally in 2017. We use a large representative sample to study which company characteristics are associated with the early adoption of social media. Our findings suggest that digital orientation (outside social media), innovativeness, external collaboration in marketing and sales, and orientation towards consumer markets all increase a company’s probability of adopting social media. In addition, larger and younger companies are more likely to be early movers. Overall, business use of social media has only reached its early maturity; thus, it still has plenty of room to grow.     

复合絮凝剂的研究进展及应用

复合絮凝剂根据成分的不同可分为无机高分子复合絮凝剂、有机复合絮凝剂以及无机-有机复合絮凝剂3类.综述了复合絮凝剂的国内外研究进展,并对各种复合絮凝剂的优缺点及应用领域进行了对比分析,指出无机-有机复合絮凝剂将是今后的研究重点,而工业废物资源化制备复合絮凝剂将是未来的重要生产途径.     

强化污泥厌氧消化的前处理技术研究进展

厌氧消化前采用不同的预处理方法是增强厌氧消化性能的关键,预处理能促进污泥内微生物细胞的分解,加速胞内物质的释放,加快污泥的水解速率.综述了当前研究和应用较多的物理、化学和生物法等污泥预处理技术,如热处理、冻融法、超声波处理法、酸碱法、加盐法、凝聚与絮凝调理、生物酶处理等,分析了各种方法的原理、特点和处理效果.     

市政污水厂出水回用电厂循环水系统工艺研究

采用曝气生物滤池+高效混凝沉淀组合工艺对河北邢台某污水处理厂的二级出水进行了回用中试研究.研究表明:二级出水经组合工艺处理后,CODCr的平均去除率为63.4%-69.2%,浊度的平均去除率为91.8%-95.4%,氨氮的平均去除率为90.5%-95.9%,处理出水可以满足电厂循环冷却水水质要求.     

Synthesis of cobalt nanoparticles to enhance magnetic permeability of metal–polymer composites

Metallic cobalt nanoparticles were synthesized by hydrogen reduction method. Particles were coated in situ with carbon by adding ethene to reaction flow. Particles were characterized by transmission electron microscopy, energy dispersive X-ray emission, X-ray diffraction, X-ray fluorescence and BET method. The observed cobalt particle size distributions in different cobalt batches produced with unvarying reaction parameters was reproducible: The mean diameter of primary cobalt particle varied only 5% from the mean value of 76 nm in different batches. Increased carbon precursor concentration decreased mean diameter of cobalt particles to 17 nm. The produced nanoparticles were used as filler material in 0–3 type metal–polymer composites. Composite samples with varying filler loading were fabricated with mixing extrusion and injection moulding techniques. The magnetic properties of the fabricated composites were measured up to 1 GHz. In order to analyse the particle distribution in composite matrix and its effect on magnetic properties the microstructure was studied.     

Novel Online Diagnostic Analysis for In-Flight Particle Properties in Cold Spraying

In cold spraying, powder particles are accelerated by preheated supersonic gas stream to high velocities and sprayed on a substrate. The particle velocities depend on the equipment design and process parameters, e.g., on the type of the process gas and its pressure and temperature. These, in turn, affect the coating structure and the properties. The particle velocities in cold spraying are high, and the particle temperatures are low, which can, therefore, be a challenge for the diagnostic methods. A novel optical online diagnostic system, HiWatch HR, will open new possibilities for measuring particle in-flight properties in cold spray processes. The system employs an imaging measurement technique called S-PTV (sizing-particle tracking velocimetry), first introduced in this research. This technique enables an accurate particle size measurement also for small diameter particles with a large powder volume. The aim of this study was to evaluate the velocities of metallic particles sprayed with HPCS and LPCS systems and with varying process parameters. The measured in-flight particle properties were further linked to the resulting coating properties. Furthermore, the camera was able to provide information about variations during the spraying, e.g., fluctuating powder feeding, which is important from the process control and quality control point of view.     

加氢裂化尾油综合利用及锦西石化公司尾油利用的探讨

介绍了加氢裂化尾油综合利用的概况,同时根据中国石油锦西石化分公司的实际情况,并借鉴了其他公司生产润滑油基础油和白油的成功经验,提出了该公司加氢裂化尾油综合利用的建议。即利用该公司现有的"老三套"(即酮苯脱蜡、糠醛精制和白土精制)装置以加氢裂化尾油为原料生产润滑油基础油和蜡;用三氧化硫气相磺化法以"老三套"装置生产的脱蜡油为原料生产白油。投产后可为公司带来可观的经济效益。     

基于氧气光谱吸收的被动测距中无云天空背景辐射特性研究

氧气吸收率是利用氧气A 吸收带进行被动测距技术计算的核心,将包含氧气A 吸收带在内的无云天空背景辐射和黑体辐射作为研究对象,利用CART 软件模拟计算了不同观测天顶角、不同时段、不同太阳天顶角的无云天空背景氧气吸收率分布,并与不同观测天顶角、不同距离下的黑体辐射氧气吸收率进行了比较分析,结果表明:当探测距离大于3 km 时,黑体辐射的氧气吸收率大于无云天空背景辐射氧气吸收率,所以根据不同观测条件设置被动测距的氧气吸收率阈值,可提高对目标的探测概率,降低背景辐射对被动测距的影响。