PREPARATION AND MORPHOLOGY OF ISOTACTIC POLYPROPYLENE WITH HIGH CONTENT OF β CRYSTALLINE FORM

Isotactic polypropylene (iPP) with high content of ~ crystalline form was prepared by adding a series of new p form nucleators. The spherulites and morphology of//farm iPP (//-iPP) were investigated by wide-angle X-ray diffraction(WAXD), polarizing microscope (PLM), scanning electron microscope (SEM) and small-angle light scattering (SALS). WAXD experimental results indicate that the amount of p form in iPP (K_x) increases with increasing /~ nucleator content from zero to 0.07 wt% or crystallization temperature T_c from 20 to 120℃ and that the highest K_x value is up to 0.95. PLM observations suggest that p spherulites exhibit bright color and that their Maltese Crosses display some concentric banding of a rather spiky, jagged character. Their !amellae are smooth and relaxed layer-plate like structure by SEM and their SALS H_v patterns arc four-petalled.     

Conditional inactivation of Fgf4 reveals complexity of signalling during limb bud development

Development of the vertebrate limb bud depends on reciprocal interactions between the zone of polarizing activity (ZPA) and the apical ectodermal ridge (AER). Sonic hedgehog (SHH) and fibroblast growth factors (FGFs) are key signalling molecules produced in the ZPA and AER, respectively. Experiments in chicks suggested that SHH expression in the ZPA is maintained by FGF4 expression in the AER, and vice versa, providing a molecular mechanism for coordinating the activities of these two signalling centres. This SHH/FGF4 feedback loop model is supported by genetic evidence showing that Fgf4 expression is not maintained in Shh-/- mouse limbs. We report here that Shh expression is maintained and limb formation is normal when Fgf4 is inactivated in mouse limbs, thus contradicting the model. We also found that maintenance of Fgf9 and Fgf17 expression is dependent on Shh, whereas Fgf8 expression is not. We discuss a model in which no individual Fgf expressed in the AER (AER-Fgf) is solely necessary to maintain Shh expression, but, instead, the combined activities of two or more AER-Fgfs function in a positive feedback loop with Shh to control limb development.     

Subduction and collision processes in the Central Andes constrained by converted seismic phases

The Central Andes are the Earth's highest mountain belt formed by ocean-continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S (compressional-to-shear) converted teleseismic waves observed on several temporary networks in the Central Andes to image the deep structure associated with these tectonic processes. We find that the Moho (the Mohorovici? discontinuity--generally thought to separate crust from mantle) ranges from a depth of 75 km under the Altiplano plateau to 50 km beneath the 4-km-high Puna plateau. This relatively thin crust below such a high-elevation region indicates that thinning of the lithospheric mantle may have contributed to the uplift of the Puna plateau. We have also imaged the subducted crust of the Nazca oceanic plate down to 120 km depth, where it becomes invisible to converted teleseismic waves, probably owing to completion of the gabbro-eclogite transformation; this is direct evidence for the presence of kinetically delayed metamorphic reactions in subducting plates. Most of the intermediate-depth seismicity in the subducting plate stops at 120 km depth as well, suggesting a relation with this transformation. We see an intracrustal low-velocity zone, 10-20 km thick, below the entire Altiplano and Puna plateaux, which we interpret as a zone of continuing metamorphism and partial melting that decouples upper-crustal imbrication from lower-crustal thickening.     

利用性诱剂在苹果园控制苹小卷叶蛾的技术研究

文章阐述了利用性诱剂对苹果园控制苹小卷叶蛾的研究及试验方法。     

Functional Materials for Catalytic and Magnetic Applications

1 Introduction Metal, metal oxide and metal compound nanoparticles (NPs) received considerable attention due to their unique properties: catalytic, magnetic, optical, electronic, etc. We believe that for different applications, there are preferable morphologies of NP-stabilizing medium composites. For example, small (1-3 nm) nanoparticles formed in micro/mesoporous hypercrosslinked polystyrene demonstrate excellent catalytic properties in various hydrogenation and oxidation reactions due to high surface...     

工艺条件中温羰基硫水解催化转化率的影响

采用浸渍法制备了氧化铝基羰基硫水解催化剂,考察了温度、空速、氧含量、水蒸汽含量对其上羰基硫水解转化率的影响。实验结果表明:在实验条件下,随着空速、氧含量、水蒸汽含量的提高,羰基硫水解催化转化率下降;但是随着温度的提高,羰基硫水解转化率呈现先上升后下降的趋势。     

磁力驱动离心泵隔离套的设计

介绍了在不同的运行工况下磁力驱动离心泵隔离套的结构设计、材料选择,并给出了隔离套的设计计算公式及加工工艺.     

立体声回波对消的算法性能实验研究及DSP实现的可行性分析

将自适应算法应用于实时立体声回波对消,以提高电话会议的通信质量．探讨了房间冲激响应为上百ms时,实时声回波对消自适应算法的收敛速度和立体声回波对消中的非唯一解问题．实验研究了输入为白噪声或语音信号、学习过程中发送房间冲激响应突变时,立体声回波对消自适应算法的失配和均方误差．比较了该算法的运算复杂度和采用DSP实现所需的指令周期．从DSP实时处理的可行性角度举例说明了选择适当DSP芯片的方法,为工程应用中构建以DSP为核心的声回波对消器提供了参考指标。     

循环级联式的多级PS光学互连网络

提出了一种可实现多级PS光学互连的循环系统,该循环系统主要是在现有的单级PS光学互连实验基础上,由LCD,CCD等光电子器件和计算机构成,这个循环系统可以实现多级PS光学互连和FPS光学互连。     

电子专业课程教学中的结构分析法

所谓结构分析法是指在实施电子类专业课程的教学中,从知识的结构入手,让学生对知识的系统性有个完整的了解。结构分析法应用于教学过程的开始、进行之中及结束。灵活运用结构分析法对提高教学效果有很大的帮助。