一种基于3因素概率图模型的长尾推荐方法

互联网时代,数据呈爆炸式增长,前所未有的数据量远远超过受众的接收和处理能力,因此,从海量复杂数据中有效获取关键性有用信息成为必须解决的问题.面对信息过载问题,人们迫切需要一种高效的信息过滤系统,“推荐系统”应运而生.在现实的推荐场景中,用户给予项目的评分或者选择项目的频次是一个典型的长尾现象.事实上,长尾现象的深入分析,不仅有助于挖掘用户的个性化偏好,更有助于电商场景中相关利益主体的业绩提升.因此,长尾推荐研究日益受到重视.针对长尾推荐的可解释性问题,提出了基于3因素概率图模型的长尾推荐方法.面对长尾推荐过程中推荐系统、用户对“具有可解释性的长尾项目推荐”的现实需求,着眼于概率图模型在因果关系方面的可解释性优势,立足于“新颖性+准确性”综合考量的方法设计目标,建立了基于用户活跃度、项目非流行度和用户-项目偏好水平的3因素概率图推荐方法.实验比较结果表明,具有可解释性优势的3因素概率图推荐方法在保证一定预测精度的前提下具有更好的新颖性推荐效果.     

Water-gas shift of reformate streams over mono-metallic PGM catalysts

Mono-metallic Pt and Rh catalysts supported on both CeO₂ and TiO₂ were prepared and tested for water-gas shift activity in a Flowrence, high throughput reactor system. The feed composition mimicked a typical fuel processor, steam methane reformer outlet stream. The Pt/CeO₂ catalyst showed the best metal activity of ～3.8 E-07 moles CO converted·gPt^-1 s^-1, at a Pt loading of 0.5 wt%, activity decreasing with increasing metal loading. Furthermore, the Pt/CeO₂ catalyst produced almost no methane while the Rh based catalysts led to substantial methanation.     

石蜡热性能的研究

以柴油作原料,反应温度分别在20℃、40℃、60℃下,通过尿素络合法恒温反应4 h制备石蜡,用气相色谱和差示扫描量热计(DSC)分析所制备的石蜡和市售25#、30#石蜡的正构烷烃组成和相变热并进行比较.通过比较发现,尿素络合石蜡含有多种正构烷烃,而25#、30#石蜡的组分少并集中在两种组分上,且25#、30#石蜡的相变热较高,更符合相变材料的要求.单体正构烷烃虽然满足储能要求,但其价格昂贵,因此可将烷烃组成较多的石蜡通过进一步分离使其正构烷烃组分数减少且集中在一两种组分上,来提高石蜡的相变热从而达到储能的要求.通过使用一种热力学模型预测石蜡的初始结晶点,和实验值对比证明模型能较好地预测石蜡的初始结晶点.因此可以通过调节石蜡的正构烷烃的组成及含量,使用该模型预测其初始结晶点而达到设计储能石蜡的目的.     

Effect of suspension chemistry onto voltage drop: Application to electro-flotation

Electrochemical processes involving particle suspensions are still ill understood. Electro-flotation is process through which particles or ions can be selectively separated. Although the technique has been widely studied, not much is known about the effect of the chemistry of suspended particles on the process performance which constitutes the aim of the present research work.A column-type cell was designed to carry out electro-flotation experiments and standard air flotation experiments. Two minerals, Merensky reef and UG2, were tested.The classic air-flotation operation gave higher recoveries and grade of collected material compared to electro-flotation only when using Merensky reef ore. However, in the case of UG2 ore, the electro-flotation reached similar performance to that of the classic operation. It was found that the electrodes readily interact with the mineral pulp reducing the efficiency to generate bubbles. That efficiency depends significantly on the ore composition. Further electrochemical studies concerning how the voltage is used throughout the process was performed. The conductivity of the pulp formed using UG2 ore increased around 5 times compared to that observed when using Merensky reef ore. Under identical experimental conditions, the froth formed with Merensky reef ore was shallow and precarious compared to the thick and stable froth formed in the case of UG2 ore.     

Investigation of the potential for mineral carbonation of PGM tailings in South Africa

Increasing atmospheric CO₂ concentration is currently of considerable concern in terms of global warming. A possible technology that can contribute to the reduction of CO₂ emissions is its sequestration by mineral carbonation. In this study, tailings from several different platinum mines in South Africa will be mineralogically characterised and their potential for mineral carbonation reviewed. Mg and Ca-rich minerals (plagioclase, olivine, orthopyroxene, clinopyroxene) present in the tailings are good candidates for mineral carbonation, which mimics natural weathering processes in which these minerals react with gaseous CO₂ to form Ca or Mg carbonates. Since the reaction is influenced by particle surface area, the ultra fine grained nature of the PGM tailings provides another reason for the promise of PGM tailings for mineral carbonation. A preliminary ranking of the tailings samples and their efficacy for mineral carbonation has been developed according to whether the samples showed harzburgtic (e.g. Northam Platinum mine), pyroxenetic (e.g. BRPM) or noritic mineral assemblages. This information and understanding will assist in identifying opportunities and guiding the development of engineered facilities for the sequestration of CO₂ by means of mineral carbonation.     

PGM‐Free Cathode Catalysts for PEM Fuel Cells: A Mini‐Review on Stability Challenges

In recent years, significant progress has been achieved in the development of platinum group metal‐free (PGM‐free) oxygen reduction reaction (ORR) catalysts for proton exchange membrane (PEM) fuel cells. At the same time the limited durability of these catalysts remains a great challenge that needs to be addressed. This mini‐review summarizes the recent progress in understanding the main causes of instability of PGM‐free ORR catalysts in acidic environments, focusing on transition metal/nitrogen codoped systems (M‐N‐C catalysts, M: Fe, Co, Mn), particularly MN_x moiety active sites. Of several possible degradation mechanisms, demetalation and carbon oxidation are found to be the most likely reasons for M‐N‐C catalysts/cathodes degradation.     

浅析数字硬盘播出

主要介绍黄五电视台数字硬盘自动播出系统，阐述其特点和优点；讲明系统的主要构我和注意事项；介绍系统设备的配置和选购方法，     

Improving fairness of PGMCC

PGM congestion control (pgmcc), a single‐rate multicast congestion control scheme, is one of the most promising schemes which aim to solve the problem of multicast fairness with TCP. However, by deep investigation, we find that there exist two inappropriate mechanisms in this scheme, which are the fixed slow start threshold (ssthresh) and the mechanism of changing a group representative (acker). Our experiments have revealed the fact that these mechanisms can lead to the unfairness of pgmcc under some network conditions. In this paper, two new mechanisms have been proposed to replace the original ones. One mechanism is to make the sender adapt the value of ssthresh to the network conditions to mimic the action of TCP, and in order to avoid being more aggressive than TCP, the other one is to make the sender reduce the congestion window by half when the acker changes. Our experiment results, parts of which are discussed in this paper, show that the modified pgmcc can achieve better performance than the original one. Copyright © 2005 John Wiley & Sons, Ltd.     

熔炼法从失效汽车尾气催化剂中富集回收铂钯铑

采用火法熔炼技术对失效汽车尾气催化剂中铂族金属的熔炼富集进行了研究。主要考察捕集剂、还原剂、造渣剂等用量对铂钯铑综合回收率的影响。最佳熔炼工艺条件:反应时间4h、捕集剂Fe3O4用量为物料量的20%、还原剂用量9%、CaO用量40%、熔炼温度1 450℃,金属铂钯铑的综合回收率可达到97%以上。熔炼产物PGM-Fe合金的主要成分是单质铁,含量为91%~93%,铂族金属含量在4%~5%。     

炭载铂族金属催化剂中铂、钯、铑、钌的化学分析进展

介绍了国内炭载催化剂中铂、钯、铑、钌化学分析技术的进展,对该类催化剂的制备过程及化学分析特点、试样的前处理、铂族金属含量的测定方法进行了评述,并对未来试样的前处理和提高电感耦合等离子体原子发射光谱法(ICP-AES)测定高量铂族金属的准确度、精密度技术进行了展望。