193 nm激光引发PET表面的化学接枝

将聚对苯二甲酸乙二醇酯[Poly(ethylene terephthalate), PET]材料置于氨气气氛中, 利用激光光子同时激发材料表面及氨气形成自由基, 用激光引发反应并促进氨基在材料表面的接枝. 改性后的测试结果表明, 材料表面粗糙度没有显著变化, 但水接触角的减小表明表面化学结构发生了某种变化. 傅里叶变换红外光谱(FTIR/ATR)图谱在3352和1613 cm-1处出现了新的氨基吸收峰, 证实了表面接枝了氨基. 同时X射线光电子能谱(XPS)也证明了材料表面C—N键的存在, 其C1s结合能为285.5 eV, N1s为398.9 eV. 飞行时间二次离子质谱(Tof-SIMS)也检测到含氨基的分子碎片, 其碎片成像图显示接枝仅发生在激光辐照部位. 实验结果表明, 激光能在生物材料表面进行局部区域的选择性接枝.     

A summation due to Ramanujan revisited

We employ Hardy’s regularly convergent double series to refine an argu- ment of Nanjundiah [7]. In particular, we evaluate some alternating series.     

考虑声誉效应的众包竞赛动态激励机制研究

将声誉效应引入众包竞赛的激励机制可以促使接包方为考虑未来绩效收益而提高当前努力。建立并求解了显性和隐性声誉效应下连续两个任务阶段的动态激励模型,探讨了显性声誉修正系数、隐性声誉系数以及参赛者数量对激励效果的影响,并与无声誉激励机制进行了对比。研究表明,声誉激励机制通过单位绩效激励强度和固定奖励水平两条途径起作用,增大隐性声誉系数有助于提高每个任务阶段的努力程度,显性声誉不确定性则会降低第2任务阶段的努力程度;各种条件下实施声誉激励对第1任务阶段中的努力程度和单位绩效奖励的影响存在不确定性;参赛者数量的增加有助于弱化第1任务阶段中棘轮效应,但也会降低声誉激励机制对努力程度的正向价值,扩大声誉激励机制对单位绩效奖励的负向价值。     

Oscillation theory and numerical solution of fourth-order Sturm--Liouville problems

A shooting method is developed to approximate the eigenvaluesand eigenfunc-tions of a fourth-order Sturm-Liouville problem.The main tool is a miss-distance function M(), which countsthe number of eigenvalues less than A. The method approximatesthe coefficients of the differential equation by piecewise-constantfunctions, which enables an exact solution to be found on eachmesh interval. In order to calculate N() for the approximateproblem, certain oscillation numbers N_L and N_R must be computed.These consist of sums of nullities (or rank deficiencies) of2 x 2 matrices obtained from the solutions of the approximatedifferential equation. Although these solutions can be foundexplicitly, the calculation of N_L and N_R is non-trivial, andis obtained by using certain properties of M().