中性人乳寡糖的分离及结构鉴定

以脱脂、除蛋白后的人乳为原料,联合运用阴离子交换色谱(AEC)、凝胶渗透色谱(GPC)和多孔石墨化碳色谱(PGC)等多种分离纯化技术制备了18种中性人乳寡糖,并采用电喷雾碰撞诱导串联质谱(ESI-CIDMS/MS)技术对其结构进行了鉴定.结果表明,所制备的中性人乳寡糖主要为三至九糖,含有半乳糖(Gal)、葡萄糖(Glc)、N-乙酰葡萄糖胺(GlcNAc)和岩藻糖(Fuc).所有寡糖的还原端均含有乳糖核心(Galβ1-4Glc),非还原端均含有乳糖胺(Galβ1-3/4GlcNAc),并且Fuc以α1-2,α1-3和α1-4连接于主链的Gal,Glc和GlcNAc上.     

KMgF3:Ce3+,Tb3+纳米粒子中Ce3+→Tb3+的发光及能量传递

利用微乳液方法,合成了铈、铽共掺杂的氟镁钾纳米粒子,研究了体系中Ce3+→Tb3+的发光特性以及它们之间的相互作用,结果表明KMgF3:Ce3+Tb3+纳米粒子中存在Ce3+→Tb3+的能量传递过程,即Ce3+可以将吸收的能量直接传递给Tb3+离子,使得Tb3+的绿色发光强度大为增加.     

Beam dynamics and RF design of trapezoidal IH-RFQ with low energy spread

Beam dynamics and RF design have been performed of a new type trapezoidal IH-RFQ operating at 104 MHz for acceleration of 14C+ in the framework of RFQ based 14C AMS facility at Peking University. Low energy spread RFQ beam dynamics design was approached by the method of internal discrete bunching. 14C+ will be accelerated from 40 keV to 500 keV with the length of about 1.1 m. The designed transmission efficiency is better than 95% and the energy spread is as low as 0.6%. Combining the beam dynamics design, a trapezoidal IH-RFQ structure was proposed, which can be cooled more easily and has better mechanical performance than traditional RFQ. Electromagnetic field distribution was simulated by using CST Microwave Studio (MWS). The specific shunt impedance and the quality factor were optimized primarily.     

Discontinuous transition from free flow to synchronized flow induced by short-range interaction between vehicles in a three-phase traffic flow model

In this paper, we incorporate a limitation on the interaction range between neighboring vehicles into the cellular automaton model proposed by Gao and Jiang et al. [K. Gao, R. Jiang, S. X. Hu, B. H. Wang and Q. S. Wu, Phys. Rev. E 76 (2007) 026105], which was established within the framework of Kerner’s three-phase traffic theory and has been shown to be able to reproduce the three-phase traffic flow. This modification eliminates an unrealistic phenomenon found in the previous model, where the velocity-adaptation effect between neighboring vehicles can exist even if those vehicles are infinitely far away from each other. Therefore, in the improved model, we regulate that such interactions can only occur within a finite distance. For simplicity, we suppose a constant value to describe this distance in this paper. As a result, when compared to the previous model, the improved model mainly simulates the following results which are believed to be an improvement. (1) The improved model successfully reproduces the expected discontinuous transition from free flow to synchronized flow and the related “moving synchronized flow pattern”, which are both absent in the original model but have been observed in real traffic. (2) The improved model simulates the correlation functions, time headway distributions and optimal velocity functions which are all more consistent with the empirical data than the previous model and most of the other models published before. (3) Together with the previous two models considering the velocity-difference effect, this model finally accomplishes a significative process of developing traffic flow models from the traditional “fundamental diagram approach” to the three-phase traffic theory. This process should be helpful for us to understand the traffic dynamics and mechanics further and deeper.     

Electroactive shape memory cyanate/polybutadiene epoxy composites filled with carbon black

Electroactive shape memory composites were synthesized using polybutadiene epoxy(PBEP) and bisphenol A type cyanate ester(BACE) filled with different contents of carbon black(CB). Dynamic mechanical analysis(DMA), scanning electron microscopy(SEM), electrical performance and electroactive shape memory behavior were systematically investigated. It is found that the volume resistivity decreased due to excellent electrical conductivity of CB, in turn resulting in good electroactive shape memory properties. The content of CB and applied voltage had significant influence on electroactive shape memory effect of developed BACE/PBEP/CB composites. Shape recovery can be observed within a few seconds with the CB content of 5 wt% and voltage of 60 V. Shape recovery time decreased with increasing content of CB and voltage. The infrared thermometer revealed that the temperature rises above the glass transition temperature faster with the increase of voltage and the decrease of resistance.     

具有非局部时滞的扩散Nicholson苍蝇方程的波前解

研究了具有非局部时滞的扩散Nicholson苍蝇方程,其中时滞由一个定义在所有过去时间和整个一维空间区域上的积分卷积表示.当时滞核是强生成核时,根据线性链式技巧和几何奇异扰动理论,获得了小时滞时波前解的存在性.