Morphology and structure of poly(p-phenylene terephthalamide) crystallized from dilute organic solution

The high-temperature crystallization of poly(p-phenylene terephthalamide) (PPTA) from dilute organic solutions was achieved through the introduction of a non-solvent, or precipitating agent, at the desired crystallization temperature. The morphology and crystal structure were examined for crystals produced from PPTA polymer with two different molecular weights (M_w = 46000 and 3430 g mol⁻¹), using transmission electron microscopy. For the high-molecular-weight polymer, ribbon-like crystals were produced, while the low-molecular-weight polymer yielded small needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weight polymer, the molecular axes were parallel to the ribbon axes in a chain-extended type structure. A hypothesis for the orientation of the low-molecular-weight PPTA in the small platelets, is also given.     

A comparison of leaf-spring with aircushion trailer suspensions in the transport environment

Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies.     

硼酸铝钕(NAB)晶体光学均匀性的测量

NAB晶体是一种综合性能较好的新型激光工作物质,有希望做成高效的小型固体激光器。本文介绍一种测量这种晶体光学均匀性的方法。 一般都采用在干涉仪上观测干涉图样来判定激光棒的光学均匀性。NAB晶体的吸收光谱曲线显示出其在可见光光谱区内有多个吸收峰。我们注意到:通常用做激光干涉仪光源的He-Ne激光器发射的632.8nm谱线正位于NAB晶体的一个吸收峰,并用输出约为45mW     

Influence of the counter-ion on the effective charge of polyacrylic acid in dilute condition

Osmotic pressure measurements were satisfactorily used to compute the effective charge of poly(acrylic) acid (PAA) at different pHs and with different monovalent and divalent counterions. This experimental method is sensitive to the osmotically active species (polymer and counterions). After correction for the polymer contribution to the total osmotic pressure (solvency and excluded volume), the remaining pressure can be attributed to the polyelectrolyte counterions and processed with Donnan and equation of state in order to compute the effective charge number per polymeric chain (Z^eff). The behavior of Z^eff against the chain concentration and pH was investigated after neutralization of PAA with LiOH, NaOH, and TMAOH. The results clearly indicate that the nature of the monovalent counterion has no effect on Z^eff leading to the conclusion that the interaction between monovalent counterions and the acrylate functionality is purely electrostatic in agreement with conductimetric and potentiometric results reported in the literature. The behavior of Z^eff against the degree of ionization of the polymer and its concentration is also in good agreement with the theoretical expectations of the theory of ionic condensation. Osmotic measurements were also used in order to understand the influence of divalent cations (Mg²⁺, Ca²⁺, Ba²⁺) on Z^eff of the sodium salt of PAA at pH 9 and at different divalent/acrylate molar ratio. All the divalent cations depress Z^eff each of one at different degrees, confirming a specific divalent/polymer interaction. The energy of hydration of cations can explain most of the observed results with divalents.     

光泵腔式NH3分子亚毫米波激光的调谐特性研究

通过求解量子系统的密度矩阵方程，计算了不同管长和不同输入输出功率反射系数的光泵腔式激光器对281um和90.4um的亚毫米波信号的调谐特性，给出了其调谐特性随信号波长λ，激光管长l和功率反射系数R的变化关系。     

DS18B20在大功率激光二极管恒温制冷系统中的应用

本文介绍了利用数字式温度传感器 ＤＳ１８Ｂ２０构造大功率激光二极管恒温制冷系统的方法．该系统利用ＤＳ１８Ｂ２０作为温度传感元件，单片机作为核心控制部件控制半导体制冷器对大功率激光二极管进行制冷和制热．该系统具有体积小、外围电路简单、温控精度高等特点，温控精度可达±０．１℃．     

激光扫描共焦荧光显微镜的电子控制系统研究

介绍了激光扫描共焦荧光显微镜的电子控制系统，为了提高激光扫描器的定位精度，在系统中提出采用基于闭环象素时钟发生器的检流计振镜所固有的扫描非线性失真补偿方案，减少输出图象的枕形畸变，实现行扫描空间位置的均匀性。在以细分梯形波电流驱动反应式步进电机情况下，根据实测θｉ曲线，用反插法求得与步进电机运行非均匀性相补偿的相电流波，从而获得在小电流情况下高角度均匀的步进电机细分运行特性。     

利用锁模光纤激光器做时钟提取器的OTDM通信系统

简短评述了大容量和超大容量光通信系统的ＷＤＭ和ＯＴＤＭ技术，提出了一个在ＯＴＤＭ通信系统中用锁模光纤激光器做时钟提取器的新方法，给出了一个利用设置波分预标时钟脉冲方案构成的新的全光型ＯＴＤＭ通信实验系统结构。