邻位取代基对芳基杂环磷酸盐成核有效性的影响

以2,4-二叔丁基苯酚为原料分别合成2,2'-亚甲基双(4,6-二叔丁基苯基)磷酸钠(NA-1)和2,2'-亚甲基双(4-叔丁基苯基)磷酸钠(NA-2),并将其应用于等规聚丙烯(i PP),研究该类芳基杂环磷酸盐成核剂邻位取代基对其成核有效性的影响.通过红外吸收光谱(FTIR)、核磁共振谱(NMR)、X-Ray多晶粉末衍射(XRD)、扫描电镜分析(SEM)和热分析对其化学结构、凝聚态结构、颗粒形貌和物性特征进行了表征,确定了NA-1和NA-2的分子结构和凝聚态颗粒的结构、形貌和物性特征.利用偏光显微观察(POM)、扫描电镜(SEM)断口分析、示差式扫描量热分析(DSC)和雾度测试分析对其与i PP的复合材料的晶粒结构、结晶行为及宏观光学性能进行测试表征.结果表明,添加量0.2%时,邻位叔丁基(NA-1)的存在可使复合材料球晶尺度更加细密,结晶温度比无邻位叔丁基(NA-2)增加5.1 K,等温结晶速率提高至0.56 w/g是NA-2的7倍,半结晶时间由NA-2的11.55 min下降至2.36 min,邻位叔丁基存在对材料透光率和雾度值的影响分别达到4.3%,7.4%.SEM断口分析表明二者在i PP基体中分散均匀,平均粒径相近分别为0.79μm和0.82μm,粒径分布曲线相近,二者分散分布的差异性不显著.     

基于预测有效度的非负变权组合预测模型研究

本以预测方法有效度为准则,分别在样本区间、预测区间及总区间上建立了非负变权的组合预测模型,并给出其线性规划的解法,该模型具有较二次规划计算简便的特点,而且目标函数具有可比性,能反映不同指标序列预测方法有效性,同时变权能适应外界环境的变化。     

高等数学多媒体课堂教学浅议

从使用多媒体讲授高等数学的经验出发,分析高等数学教学中应用多媒体教学手段的优势,同时给出在多媒体教学条件下进一步提高教学效果的几点建议,指出教师必须用现代化的教学思想为指导,综合运用各种教学手段提高高等数学教学效果,适应现代化教学的发展.     

非参数假设检验在证券投资分析中的应用

通过引入一种新的估计方法——非参数假设检验方法,以达到对证券投资咨询机构对证券市场大盘走势预测准确度的估计.通过对估计结果的分析得出结论,有99%的把握认为,中国证券市场投资咨询机构所提供的对大盘涨跌的预测,每次有一半家数正确的概率没有达到45%,因而投资者应慎重对待投资咨询机构的大盘预测.     

致密微孔壁绝热冷却效果研究

本文采用经热电偶标定的红外热像表面温度测量技术,实验研究了吹风比M(M=0．30-1．59)对致密微孔壁热侧壁面上绝热冷却效果ηaw的影响,并与数值模拟结果进行了比较。实验与数值模拟的结果都表明:与常规气膜冷却在M≥1．0时ηaw随着M增大而减小的现象不同,致密微孔壁的ηaw随着M增大逐渐增加的,但随着M的增大,ηaw增加的幅度越来越小。在相同的吹风比M下,致密微孔壁的绝热冷却效果ηaw明显高于常规气膜冷却的ηaw。     

A joint measurement of efficiency and effectiveness for non-storable commodities: Integrated data envelopment analysis approaches

Efficiency and effectiveness for non-storable commodities represent two distinct dimensions and a joint measurement of both is necessary to fully capture the overall performance. This paper proposes two novel integrated data envelopment analysis (IDEA) approaches, the integrated Charnes, Cooper and Rhodes (ICCR) and integrated Banker, Charnes and Cooper (IBCC) models, to jointly analyze the overall performance of non-storable commodities under constant and variable returns to scale technologies. The core logic of the proposed models is simultaneously determining the virtual multipliers associated with inputs, outputs, and consumption by additive specifications for technical efficiency and service effectiveness terms with equal weights. We show that both ICCR and IBCC models possess the essential properties of rationality, uniqueness, and benchmarking power. A case analysis also demonstrates that the proposed novel IDEA approaches have higher benchmarking power than the conventional separate DEA approaches. More generalized specifications of IDEA models with unequal weights are also elaborated.     

大学生就业扶持政策的有效性分析及改进:基于DEA方法的实证分析

鉴于数据包络分析(DEA)方法在评价多输入、多输出系统相对有效性方面所具有的优越性,基于DEA方法构建了C2R模型及相应投影分析模型和评价指标体系,对1999-2008年中国所实行的大学生就业扶持政策的有效性进行了评价分析,实证分析结果表明1999-2002年的大学生就业扶持政策在促进和解决大学生就业方面的效果显著,而2003年以后的大学生就业扶持政策在解决大学生就业问题上存在明显的效率损失,且政策效果逐年下降.为了提高大学生就业扶持政策的实施效果,就业扶持政策在未来的改进重点应着力从财政补贴、高等教育经费投入和贷款补助等政策内容入手,并提高政策的执行力度.     

A numerical study of rotation effects on jets effusing from inclined holes into a cross-flow

In this work, the complexity of the flow field arising from the impact of the interaction of coolant jets with a hot cross-flow under rotation conditions was numerically simulated using large eddy simulation with artificial inflow boundary condition. The finite-volume method and the unsteady PISO (Pressure Implicit with Splitting of Operators) algorithm were applied on a non-uniform staggered grid. The simulations were performed for four different values of rotation number (Ro) of 0.0, 0.03021, 0.06042, and 0.12084, a jet Reynolds number of 4700, based on the hole width and the jet exit velocity. The air jet was injected at 30° and 90° in the streamwise direction with a density ratio of 1.04 and a velocity ratio of 0.5. The flow fields of the present study were compared with experimental data in order to validate the reliability of the LES technique. It was shown that the rotation has a strong impact on the jet trajectory behaviour and the film cooling effectiveness. The film trajectory always inclines centrifugally. Under rotating conditions, the film trajectory departs from the centreline to the left boundary. The deflection becomes greater as Ro increases. Furthermore, it was also found that the injection angle has a strong impact on separation and reattachment behaviour as well as the strength of the penetration into the cross-flow. As it increases, the distribution of the film cooling downstream the jet exit is more non-uniform and the film cooling effectiveness level slightly decreases.     

Surface activity of commercial food grade modified starches

An attempt to quantitative evaluation of the functionality of food grade chemically modified starches in the emulsion systems by estimation of their surface activity as well as the capability of thickening food products was the main purpose of this present work. It was stated that chemically modified starches reveal higher surface activity at air/water and toluene/water interfaces in comparison to the native starch. The increase of the degree of substitution of polar carboxyl groups as well as rather non-polar acetyl ones results in an enhance of surface activity. Starch sodium octenylsuccinate stands out from other investigated starches, in its excellent capability of lowering surface and interfacial tension. Cross-linked starches reveal excellent stabilisation activity at a pH range of 5.5–7.0 but their surface activity is lower than those of other modified starches. Acetylated starch as well as starch sodium octenylsuccinate reveal satisfactory thickening capability up to pH 4.5 and moreover their surface activity (especially of E 1450) allows us to recommend them as functional constituents of food emulsions. Low thickening capability of oxidised starches rather excluded these derivatives from the group of potential functional additives for food emulsions.     

Viscoelastic Properties and Thermal Stability of Nanohydroxyapatite Reinforced Poly-Lactic Acid for Load Bearing Applications

We studied the reinforcing effects of treated and untreated nanohydroxyapatite (NHA) on poly-lactic acid (PLA). The NHA surface was treated with three different types of chemicals; 3-aminopropyl triethoxysilane (APTES), sodium n-dodecyl sulfate (SDS) and polyethylenimine (PEI). The nanocomposite samples were prepared using melt mixing techniques by blending 5 wt% untreated NHA and 5 wt% surface-treated NHA (mNHA). Based on the FESEM images, the interfacial adhesion between the mNHA filler and PLA matrix was improved upon surface treatment in the order of mNHA (APTES) > mNHA (SDS) > mNHA (PEI). As a result, the PLA-5wt%mNHA (APTES) nanocomposite showed increased viscoelastic properties such as storage modulus, damping parameter, and creep permanent deformation compared to pure PLA. Similarly, PLA-5wt%mNHA (APTES) thermal properties improved, attaining higher Tc and Tm than pure PLA, reflecting the enhanced nucleating effect of the mNHA (APTES) filler.