Flow stress of high density polyethylene and nylon 66 at high rates of strain

Measurement of the flow stress of high density polyethylene (HDPE) and nylon 66 at strain rates of 10³ s^?1 using a split Hopkinson pressure bar technique is discussed. The flow stress at a strain of 10% has been determined for both polymers at 20°C. The intrinsic errors involved in this technique are briefly reviewed. The results indicate that the flow stress of HDPE and nylon 66 were 50MPa and 150MPa, respectively, at strain rates of about 10³s^?1.     

三箱式纺丝技术生产PET/PA6复合纤维

介绍了采用三箱式纺丝技术生产PET/PA6复合纤维的设备及工艺。重点对纺丝箱体、纺丝温度控制进行了详细的讨论。     

FT-IR spectroscopic study of hydrogen bonding in PA6/clay nanocomposites

Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the α-phase, the addition of clay silicate layers favor the formation of the γ-crystalline phase in PA6CN.We focus on the reason why silicate layers favor the formation of γ-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the γ-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding.The silicate layers were indeed found to weaken the hydrogen bonding both in the α- and γ-phases. This was also confirmed by X-ray diffraction studies. The γ-phase is most likely concentrated in regions close to the silicate layers, whereas the α-phase is favored in the bulk matrix.     

强化两相混合的超临界技术制备聚乳酸微粒

针对商品化聚乳酸微球粒径分布较宽难于适用气溶胶给药要求的不足,采用水力空化混合强化超临界流体辅助雾化技术(SAA-HCM)制备聚乳酸(PLA)超细微粒.该技术主要特点是通过在超临界流体和液相进料处引入水力空化混合器,强化两相间的混合.考察SAA-HCM过程混合器压力、温度、沉淀器温度、进料中CO2与液体溶液质量流量比和溶液质量浓度等操作参数对微粒形态和粒径分布的影响,成功制备出球形度较好,粒径分布较窄(1～3μm)的PLA微球.经X射线衍射(XRD)分析和差示扫描量热(DSC)分析显示,与原料PLA相比,微球晶型及热曲线变化不大,但结晶度下降.同时把操作参数与相行为进行关联,探讨了影响颗粒形貌的机理.对比超临界流体辅助雾化法(SAA)的实验结果表明:水力空化的引入能有效强化混合器内的两相传质,混合更好,能制备出适用于气溶胶给药要求的超细微粒.     

基于UDP传输协议的包丢失和失序处理

UDP是互联网上多媒体数据传输采用的主要传输协议。其主要特点是网络开销低但传输不可靠,易产生包丢失或失序。为了对失序数据包进行重排序,应用程序需要预留一个适当的缓冲区以存储期望包到达之前的数据包。该文分析了数据包丢失或失序情况下,缓冲区大小对系统性能的影响,给出了缓冲区大小的一个估计值,并对失序或数据包丢失情况下数据处理的策略进行了讨论。     

万兆以太网物理层编码芯片设计

提出了一种并行处理的编解码方案。采用这种方案．设计了万兆以太网10GBASE-R标准的物理编码子层发送端芯片。芯片由64b／66b编码、扰码和变速箱3部分组成。考虑到测试问题，该芯片内置了伪随机码数据源。这种方案的优点是逻辑简单、速度快。芯片采用TSMC 0.18μmCMOS工艺，用全定制方式实现。芯片引脚分布时参照PLCC48规格。     

Genome-Wide Identification of TaSAUR Gene Family Members in Hexaploid Wheat and Functional Characterization of TaSAUR66-5B in Improving Nitrogen Use Efficiency

Excessive input of nitrogen fertilizer not only causes a great waste of resources but brings about a series of ecological and environmental problems. Although Small Auxin Up-regulated RNAs (SAURs) participate in diverse biological processes, the function of SAURs in the nitrogen starvation response has not been well-studied. Here, we identified 308 TaSAURs in wheat and divided them into 10 subfamilies. The promoter regions of most TaSAURs contain hormone responsive elements, and their expression levels change under the treatment of different hormones, such as IAA, MeJA, and ABA. Interestingly, overexpression of one of the TaSAUR family members, a nitrogen starvation responsive gene, TaSAUR66-5B, can promote the growth of Arabidopsis and wheat roots. In addition, overexpression of TaSAUR66-5B in Arabidopsis up-regulates the expression levels of auxin biosynthesis related genes, suggesting that overexpression TaSAUR66-5B may promote root growth by increasing the biosynthesis of auxin. Furthermore, overexpression of TaSAUR66-5B in wheat can increase the biomass and grain yields of transgenic plants, as well as the nitrogen concentration and accumulation of both shoots and grains, especially under low nitrogen conditions. This study provides important genomic information of the TaSAUR gene family and lays a foundation for elucidating the functions of TaSAURs in improving nitrogen utilization efficiency in wheat.     

Consideration of the BDNF gene in relation to two phenotypes: Hoarding and obesity.

The gene coding for the brain derived neurotrophic factor (BDNF) has emerged as an interesting candidate for multiple brain and brain disorder-related phenomena. The primary aim of the present investigation was to consider the relationship between the BDNF Val66Met variant and two phenotypes: compulsive hoarding as a symptom dimension of obsessive–compulsive disorder (OCD), and body mass index (BMI). We examined the BDNF gene in a large (N = 301) clinical sample of probands with OCD. Participants were classified as hoarding or nonhoarding using a strict, multimeasure grouping approach. Results revealed that the Val/Val genotype was linked with hoarding classification and more severe hoarding behaviors, as well as greater BMI levels. Hoarding status was also associated with greater BMI scores, with individuals in the hoarding group being far more likely to be classified as obese compared with the nonhoarding group. Our findings may provide a distinct avenue through which hoarding and BMI could be linked. These findings are suggestive of a complex gene, body weight, and psychopathology relationship wherein a primitive, survival “thrifty gene” strategy may be conserved and represented in a subgroup of humans manifesting severe hoarding symptoms. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

校园公共广播系统(PAS)设计

以某学院公共广播系统整个设计为实例，较详细地总结了校园公共广播系统设计的依据、步骤、相关计算方法和一些实际中的问题，具有较强的实用意义。     

一种简单RF预失真电路的研究

文章介绍一种基于肖特基二极管的预失真器及其工作原理。预失真器主要由一个肖特基二极管和直流偏置电阻组成,利用二极管的非线性,产生与功放相反的幅度失真与相位失真。通过调节二极管的偏压来调整预失真器的工作状态,使功率放大器在不同输出功率下得到最好的线性度改善。设计实际电路经实验发现,对于应用在C波段的某功率放大器,在不同的输出功率下IMD3的改善不同。在功率放大器1dB增益压缩点处IMD3改善了5dB,而在其他功率点处IMD3最大甚至可以改善20dB。