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31.
32.
Massive Open Online Course (MOOC) has become a popular way of online
learning used across the world by millions of people. Meanwhile, a vast amount of
information has been collected from the MOOC learners and institutions. Based on the
educational data, a lot of researches have been investigated for the prediction of the
MOOC learner’s final grade. However, there are still two problems in this research field.
The first problem is how to select the most proper features to improve the prediction
accuracy, and the second problem is how to use or modify the data mining algorithms for
a better analysis of the MOOC data. In order to solve these two problems, an improved
random forests method is proposed in this paper. First, a hybrid indicator is defined to
measure the importance of the features, and a rule is further established for the feature
selection; then, a Clustering-Synthetic Minority Over-sampling Technique (SMOTE) is
embedded into the traditional random forests algorithm to solve the class imbalance
problem. In experiment part, we verify the performance of the proposed method by using
the Canvas Network Person-Course (CNPC) dataset. Furthermore, four well-known
prediction methods have been applied for comparison, where the superiority of our
method has been proved. 相似文献
33.
论文以攀西地区白马辉长岩型超低品位钒钛磁铁矿为研究对象,查明了该矿石中化学组分、矿物组成、铁和TiO2的相态。在此基础上进行了多粒级多磁场梯度干式磁选抛尾试验,通过铁和TiO2的相态分析阐述了干式磁选抛尾的合理性;进行了干式磁选精矿阶段磨矿阶段选别试验,二段磁选在-200目占80%细度下获得了TFe 57.78%、TiO2 7.72%、V2O5 0.69%的铁精矿,铁精矿产率为12.93%、铁回收率51.56%,相对磁性铁回收率为98.70%,V2O5回收率78.26%。结果表明该矿石虽然铁品位低,仍具综合回收利用价值。 相似文献
34.
为了验证在某复杂难选铁矿石的选矿工艺中,应用高压辊磨机和立式搅拌磨的优越性,进行了一系列对比试验。结果表明,与颚式破碎机相比,高压辊磨机产品的粉矿率更高,产品的可磨性更好;与球磨机相比,立式搅拌磨机细磨效率更高、效果更好,相同磨矿细度下,立式搅拌磨机磨矿产品的解离度更高,磁选铁精矿品位也更高;高压辊磨+立式搅拌磨在处理复杂难选铁矿石方面具有显著的优势。 相似文献
35.
This work describes the functionalization of a natural and a man-made textile substrate, namely cotton and polyamide 6.6, with inclusion agents, β-cyclodextrins (β-CDs) that are able to release gradually to the user active ingredients. In this study we used aescin (aesculus hippocastanum extract), which is a natural agent with benefits for the treatment of varicose veins.1H NMR and UV–vis data supported the role of β-CDs as an aescin complexing agent, and the covalent nature of the linkage between β-cyclodextrins and the textile substrates, which showed a wash fastness to more than 45 washing cycles. 相似文献
36.
The paper aimed to maximize the fuel burnup performance of plutonium and minor actinides fueled pebble bed high temperature reactor (PBMR-400). The PBMR-400 was designed as a reference core. The neutronic calculations were performed by the code combination MCNP-ORIGEN-MONTEBURNS. In this study, neutronic performances of three different types of nuclear fuels (Reactor Grade Plutonium – RGPu; Weapon Grade Plutonium – WGPu and Minor Actinides – MAs) combined with natural uranium were conducted in a PBMR-400 full core. The neutronic performances were compared with the original uranium fuel designed for this reactor. Neutronic calculations showed that 9.6 wt % enriched uranium has a core effective multiplication factor (keff) of 1.2395. Corresponding to this keff values the natural UO2/RG-PuO2; natural UO2/WG-PuO2 and natural UO2/MAO2 mixture were found 70%/30%, 76%/24% and 63%/37%, respectively. The operation times were computed as ∼2000, ∼2500 and 1400 days whereas, the corresponding burnup values were obtained as ∼163 000, ∼194 000 and ∼116 000 MWD/T, respectively, for end of life keff set equal to 1.08. 相似文献
37.
38.
Sandeep Kumar Singh Venkatesh Teja Banala Girish K. Gupta Ashwni Verma Rahul Shukla Vivek K. Pawar 《Drug development and industrial pharmacy》2015,41(11):1759-1768
The aim of this study was to fabricate docetaxel loaded nanocapsules (DTX-NCs) with a high payload using Layer-by-Layer (LbL) technique by successive coating with alternate layers of oppositely charged polyelectrolytes. Developed nanocapsules (NCs) were characterized in terms of morphology, particle size distribution, zeta potential (ζ-potential), entrapment efficiency and in vitro release. The morphological characteristics of the NCs were assessed using transmission electron microscopy (TEM) that revealed coating of polyelectrolytes around the surface of particles. The developed NCs successfully attained a submicron particle size while the ζ-potential of optimized NCs alternated between (+) 34.64?±?1.5 mV to (?) 33.25?±?2.1 mV with each coating step. The non-hemolytic potential of the NCs indicated the suitability of the developed formulation for intravenous administration. A comparative study indicated that the cytotoxicity of positively charged NCs (F4) was significant higher (p?0.05) rather than negative charged NCs (F3), plain drug (DTX) and marketed preparation (Taxotere®) when evaluated in vitro on MCF-7 cells. Furthermore, cell uptake studies evidenced a higher uptake of positive NCs (≥1.2 fold) in comparison to negative NCs. In conclusion, formulated NCs are an ideal vehicle for passive targeting of drugs to tumor cells that may result in improved efficacy and reduced toxicity of encapsulated drug moiety. 相似文献
39.
《International Journal of Hydrogen Energy》2021,46(79):39536-39547
Free Piston linear Generator (FPLG) engine fueled by compressed natural gas (CNG) has recently gained increased research attention. However, due to the low-velocity burning and poor lean limit of CNG fuel, the FPLG engine combustion stability, performance, and efficiency are still low. Hydrogen has a greater burning velocity with wider flame limits that could extend the lean burn limits and combustion characteristics of CNG. This paper compares pure CNG and 10% hydrogen-enriched CNG at various ignition speeds (0.6 ms, 0.8 m/s, and 1 m/s), injection positions (0 mm, 5 mm, 10 mm and 15 mm), and lambda ratios (0.9, 1.4 and 1.7) on the combustion characteristics, performance, and conversion efficiency are duly discussed. The findings show that the FPLG combustion stability limits increase with the hydrogen addition into the CNG. The CNG in-cylinder pressure increases significantly when the injection position is advanced, whereas the hydrogen addition reduces the influence of the injection position. The heat release rate increases by 15.62% and 23.72% with hydrogen addition, corresponding to the advanced and retarded injection positions. Consequently, the hydrogen addition increases the power RMS to 209.21 W and 232.64 W with an increment of 3.46% and 3.13%, respectively. Conclusively, the hydrogen addition into the CNG evidently shortens the combustion duration while improving the heat release rate, combustion stability, power RMS, Cycle-to-Cycle variation, and conversion efficiency. 相似文献
40.
采用 OM 和 SEM 对 700 MPa 级高强度大梁钢冲压开裂原因进行了分析。结果表明,在高强度大梁钢冲压过程中出现的纵梁穿线孔裂纹主要为连冲工艺不当导致;纵梁端部折弯角部裂纹主要是由于原板坯存在内裂纹和大尺寸 TiN 夹杂物,在冲压过程中外表面受到拉应力产生裂纹,裂纹沿横纵向扩展导致。通过将钛质量分数由 0.10% 降至 0.07%,将氮质量分数控制在不大于 0.004% 的范围内,降低大尺寸TiN析出量。化学成分调整后,力学性能满足供货技术条件要求,对钢板进行冲压验证,端部完好,未见折弯裂纹存在,彻底解决了该缺陷。 相似文献