玄武岩催化甲烷裂解制 C2 烃

以天然玄武岩为甲烷裂解催化剂,通过XRF、XRD、SEM及XPS对催化剂组成、结构、表面活性物种进行了研究。利用固定床反应装置考察了不同反应温度、空速条件下玄武岩催化甲烷裂解制C_2烃的效果。结果表明,在气体空速为4 L·h-1条件下,当反应温度为1 225 K时,甲烷的转化率为7.66%,C_2烃的选择性为33.64%;当反应温度升至1 325 K时,甲烷的转化率可达17.13%,同时C_2烃的选择性为27.21%。相同温度下,气体空速越大,乙烷的选择性越高,乙炔的选择性越低。催化剂活性因表面积炭的产生而降低,积炭类型为芳烃积炭。     

A sorbent of expanded rice husk powder for removal of uranyl ion from aqueous solution

A novel sorbent for the removal of uranyl ion was prepared by expanded rice husk powder. Batch adsorption experiments were performed on factors of p H,temperature, initial uranyl ion concentration, adsorbent dosage and contact time to evaluate the adsorption capacity. The results show that the saturation adsorption capacity is 5.7 mgág~(-1) using expanded rice husk powder treating uranyl ion aqueous solution(80 mgáL~(-1)) for 24 h at 25 °C with initial pH3. Adsorption process could be well described by Langmuir isotherm model. The adsorption kinetic data are fitted well with pseudo-second-order model. The results obtained show that expanded rice husk adsorbent is a promising adsorbent for the removal of uranium from aqueous solutions.     

Blind 2-D Angles of Arrival Estimation for Distributed Signals Using L-Shaped Arrays

Most existing two dimensional（2-D）angles of arrival（AOAs）estimation methods are based on the assumption that the signal sources are point sources.However,in mobile communications,local scattering in the vicinity of the mobile results in angular spreading as seen from a base station antenna array.In this paper,we consider the problem of estimating the 2-D AOAs of spatially distributed sources.First we perform blind estimation of the steering vectors by exploiting joint diagonalization,then the 2-D AOAs are obtained through two fast Fourier transforming of the estimated steering vectors.Simulations are carried out to illustrate the performance of the method.     

Fe3O4/TiO2核壳结构胶体光子晶体的光学传输特性分析

通过时域有限差分方法(FDTD)计算了核壳结构胶体光子晶体的光学传输特性.这一核壳结构是由低介电的Fe3O4核与高介电的TiO2壳构成的.计算结果表明,阻带的行为受到材料介电常数和核壳比的调控.随着材料介电常数的增加,阻带不断红移,并且带宽不断增大.当核壳结构的整体尺寸一定时,随着核直径的增大,阻带不断蓝移,并且在核壳结构直径与核直径之比为150 nm:130 nm时,带宽最大,达到33.4％;当核尺寸一定时,随着核壳结构整体尺寸的增大,阻带红移.在Fe3O4@TiO2核壳结构中,能够出现阻带的TiO2壳层的最小厚度是3 nm.     

带通配符和One-Off条件的序列模式挖掘

很多应用领域产生大量的序列数据。如何从这些序列数据中挖掘具有重要价值的模式,已成为序列模式挖掘研究的主要任务。研究这样一个问题：给定序列S、支持度阈值和间隔约束,从序列S中挖掘所有出现次数不小于给定支持度阈值的频繁序列模式,并且要求模式中任意两个相邻元素在序列中的出现位置满足用户定义的间隔约束。设计了一种有效的带有通配符的模式挖掘算法One-Off Mining,模式在序列中的出现满足One-Off条件,即模式的任意两次出现都不共享序列中同一位置的字符。在生物DNA序列上的实验结果表明,One-Off Mining比相关的序列模式挖掘算法具有更好的时间性能和完备性。     

Effect of spatial confinement on the development of β phase of polypropylene

The focus of this study was the effect of spatial confinement on the development of nucleating agent-induced β phase polypropylene (PP) in the dynamically vulcanized thermoplastic elastomers (TPVs) based on dynamically vulcanized PP/ethylene-propylene-diene rubber (EPDM) blend. The melting behaviors, crystalline structures and the morphologies of the blends were studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). The results indicate that the EPDM phase undergoes a series of changes from the dispersed phase to a continuous one, and again to the dispersed phase with increased content of curing agent, and the PP component always shows itself in a continuous phase. In this process, with the content of the nucleating agent unchanged, the content of β phase PP in the blends initially increases a little and then decreases with increasing PF (Phenolic resin) content. We believe spatial confinement provides a good explanation for the development of β phase PP.     

纯玉米粉条加工用辅助剂

粉条,是我国人民所喜好的家常食品之一。粉条的加工历来以豆类、薯类淀粉为原料。过     

Web挖掘中发现用户访问模式算法的改进与分析

Web日志挖掘的一个主要任务是获得用户的浏览模式,这对Web站点的改进和为用户提供个性化服务提供了有价值的潜在信息.本文提出了一种改进算法--RD_Close.该算法对数据挖掘中的Close方法进行了改进,并引入了RD_Apriori方法中缩减数据库的思想.这种改进算法能有效发现用户频繁访问模式.最后,用实际数据对算法性能进行了充分验证和深入分析.     

模式特征对带有通配符和长度约束的模式匹配问题的影响

带有通配符的模式匹配问题(PMWL)模式定义的灵活性给用户提供方便,却也造成求解上的困难。目前没有任何多项式算法能得到该问题的完备解,同时也缺少足够的完备性分析。文中认为模式特征是影响PMWL完备性的关键因素,并提出模式重复度的概念,记为rep。证明在rep=0的限定条件下PMWL的完备性,同时分析rep>0时PMWL不完备的原因。实验以近似比为指标,说明rep对PMWL完备性的影响。     

一步法合成磷掺杂石墨相氮化碳及其光催化性能

以尿素(CO(NH₂)₂)和磷酸氢二铵((NH₄)₂HPO₄)作为原料, 通过热聚合法制备了磷(P)掺杂石墨相氮化碳(g-C₃N₄)材料(P-CN)。通过X射线衍射、红外光谱、X射线光电子谱、扫描电子显微镜、透射电子显微镜、紫外可见漫反射光谱和N₂吸附-脱附对样品进行了表面形貌及结构表征, 通过对罗丹明B(RhB)的降解实验, 研究了样品的可见光催化性能, 对其催化机理进行了分析。结果表明, 合成过程中磷原子的掺杂会取代g-C₃N₄中的C原子, 从而改变g-C₃N₄的表面形貌和电子结构。在可见光条件下, P-CN材料表现出优异的光催化性能, 其对RhB的降解速率明显优于纯氮化碳。其中3%P-CN样品催化活性最高, 反应30 min时, RhB降解率达到96.8%。分析认为, P原子对g-C₃N₄中的C原子的取代使P-CN样品表面处于富电子状态, 并导致P-CN样品导带位置升高, 光电子还原性增强。这些电子与水中的溶解氧形成超氧自由基(·O₂^-), 从而使得光催化性能显著提高。