激光尘埃粒子计数器微型光学传感器的研究

研制成功便携式激光尘埃粒子计数器的核心部件——微型光学传感器。该传感器采用直角散射光收集形式。以高功率半导体激光器作为光源，同时采用高性能的PIN型光电二极管作为光电探测器。散射光收集系统为单一大数值孔径的球面反射镜，其对粒子散射光的收集角范围从20°到160°。粒子散射光信号是脉冲信号，其频谱成份主要在高频段，所以在PIN型光电二极管后用一个带通式前置放大器来消除外界的低频噪声．根据米氏散射理论计算了该光学传感器的光散射响应特性，并用聚苯乙烯标准粒子实测了该光学传感器的性能。结果表明，该系统具有高的信噪

Enhanced crystallization of the gamma-form of propylene-ethylene copolymer in its miscible blends with propylene homopolymer

BACKGROUND: How to promote the formation of the gamma-form in a certain propylene-ethylene copolymer (PPR) under atmospheric conditions is significant for theoretical considerations and practical applications. Taking the epitaxial relationship between the alpha-form and gamma-form into account, it is expected that incorporation of some extrinsic alpha-crystals, developed by propylene homopolymer (PPH), can enhance the crystallization of the gamma-form of the PPR component in PPR/PPH blends.RESULTS: The PPH component in the blends first crystallizes from the melt, and its melting point and crystal growth rate decrease with increasing PPR fraction. On the other hand, first-formed alpha-crystals of the PPH component can induce the lateral growth of PPR chains on themselves, indicated by sheaf-like crystal morphology and positive birefringence, which is in turn responsible for enhanced crystallization of the gamma-form of the PPR component.