Melting Behavior of PET After Solid State Polycondensation

Dual endotherms during differenUal scanning calorimetric (DSC) measurement occur when dried PET pellets are pretreated with solld state polyeondensation (SSP) at 215-230℃ for appropriate holding, times. The two endothermic fusion peaks arise from melting and recrystallization, taking place during scanning in the calorimeter,of imperfect crystals initial present in sample. The lower temperature peak appears higher than the SSP reaction temperature for 5-20℃ accordingly and linear relaflonship with SSP reaction temperature, logarithmic linear relationship vs. SSP reaction time, while the position of higher temperature peak nearly does not change. The higher the SSP reaction temperature, the larger the total area of the endotherms, namely, the higher crystallinity. For 4 reaction temperatures the crystallinity show logarithmic linear relationship vs, SSP reaction time.     

基于微扰法的快速声速剖面反演

传统的基于声传播时间的声速剖面反演需要多次搜索不同声速剖面条件下的特征声线,降低了声速剖面反演的速度.通过一个简单的近似,微扰法将实际声传播时间表示为背景声速下的声传播时间与扰动项之和,从而使得声速剖面反演由原来的非线性优化问题转化为线性方程组的求解形式.实验数据处理结果表明,与传统方法相比,虽然微扰法反演的精度下降了近50%,但是计算时间由10 h减少到了3 s,从而实现声速剖面海上实时监测.