NeuDATool：支持GPU硬件加速和计算机集群跨节点并行的开源中子散射数据分析软件

实验势精修是20世纪80年代英国散裂中子源无定型材料组开发的用于分析中子散射实验数据的软件. 实验势精修的目标是根据中子散射数据重建样品的三维原子结构. 在过去的几十年，实验势精修被广泛用于中子散射实验数据分析，为实验用户提供了可靠的分析结果. 但是实验势精修是基于共享内存并行计算(OpenMP)的Fortran程序，不支持计算机服务器集群跨节点并行加速和GPU加速；这限制了它的分析速度. 随着计算机服务器集群的广泛建设和GPU加速技术的普遍使用，有必要重新编写EPSR程序以提高运算速度. 本文使用面向对象的C++语言，开发了一套实现EPSR算法的开源软件包NeuDATool；软件通过MPI和CUDA C实现了计算机集群跨节点并行和GPU加速. 使用液态水和玻璃态二氧化硅的中子散射实验数据对软件进行了测试. 测试显示软件可以正确重建出样品的三维原子结构；并且模拟体系达到10万原子以上时，使用GPU加速可以比串行的CPU算法提高400倍以上的模拟速度. NeuDATool为中子实验用户尤其是对熟悉C++编程并希望定义特殊分析算法的实验科学家提供了一种新的选择.     

Uniform to Accelerated Crystal Twisting Transition in Deuterate Polyethylene/Poly（ethylene-alt-propylene） Blend Films

A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly（ethylene-alt- propylene） （d-PE/PEP） blend films. And the band period is a function of initial d-PE concentration, quench depth and annealing time of phase separation. As Keith and Padden suggested, twisting of lamella is due to the unbalanced stress on its both sides, which can supply a satisfying explanation to banded spherulites formed in homogeneous systems. When it comes to d-PE/PEP blend system, in homogeneous 99% d-PE/PEP （weight fraction of d-PE） blend film, the formation of banded spherulite is observed as a result of uniform twisting of ribbon like d-PE lamellae along the radial direction. With the amorphous PEP piling up, it transfers into accelerated edge-on to fiat-on twisting due to crystallization assisted phase separation. The mechanism can be interpreted as following： d-PE molecules must inter-diffuse to the twisting growth front to continue the secondary nucleation and growth process. Meanwhile, the amorphous PEP molecules are rejected and accumulated at the twisting growth front. Once the d-PE lamella begins to twist because of unbalanced stress on both sides, the accumulated rubber phase at the growth front strengthens the unbalance and accelerates the edge-on to flat-on twisting. The concentration wave propagates further away with constant speed, and leads to concentric ring pattern with periodic nonuniform twisting along the radial direction. Since this is a kinetic effect, the band period can be controlled through initial d-PE concentration, quench depth and annealing time of phase separation. Our result shows that crystallization assisted phase separation can modify lamella growth kinetic pathway, thereby assisting concentric ring pattern formation.     

激光光散射测量荧光/磷光体系溶液结构的原理和方法

通过对商业化激光光散射谱仪改造升级,以4种不同波长的激光785、632.8、532和457 nm作为独立光源,可以根据不同的荧光体系选择不同的入射激光,有效避免荧光、磷光对散射光信号的干扰,从而使激光光散射谱仪能用于荧光/磷光等吸光材料溶液结构的测定.非荧光和荧光聚苯乙烯小球标准样品的测定都验证了改造后仪器测量结果的准确性和精确性.实验结果表明,当荧光体系对入射光有吸收时,动态光散射的相关函数与静态光散射得到的均方回转半径都不能反映荧光样品的真实溶液结构,此时的结果只能作为定性参考,只有选择样品无吸收的入射光波长,符合(准)弹性散射时,所测结果才能反映样品的真实结构.单分子荧光谱仪的对照实验证实了改造光散射谱仪的正确性与必要性.