Synthesis of high molecular weight poly(L‐lactic acid) via melt/solid polycondensation: Intensification of dehydration and oligomerization during melt polycondensation

Melt/solid state polycondensation (MP/SSP) is a cost‐effective route for synthesis of high molecular weight poly(L ‐lactic acid) (PLLA). However, the reaction rates in its four stages need to be enhanced greatly and the reaction times to be shortened largely before the MP/SSP technology can be industrialized. In this study, a new catalyst addition policy, i.e., adding TSA at the dehydration stage and SnCl₂·2H₂O at the MP stage, and more appropriate temperature and pressure programs were presented and applied in the MP process of LLA. The presence of TSA from dehydration appeared very effective for speeding up the dehydration and oligomerization stages as well as depressing racemization in the whole MP process. The polymerization degree (X_n) of oligomer was clearly increased, and the reaction time was shortened to a great extent. Direct using reduced pressure was also very helpful for intensifying the dehydration stage, only leading to LLA loss as little as 2%. A PLLA with M_w of 44,000 and optical purity of 96.8% suitable for subsequent SSP was produced after dehydration for 2 h, oligomerization for 2 h and MP for 4 h under appropriate conditions. And an interesting strong dependence of the M_w of final PLLA product on the X_n of the oligomer was observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Optimal pricing and trade-in policies in a dual-channel supply chain when considering market segmentation

Many companies are implementing trade-in programmes through multiple channels. This may ultimately lead to fiercer channel conflict and competition. Few studies have explored firms’ optimal trade-in policies in such an environment. To fill the gap, we build a theoretical model that captures the features of a dual-channel situation in which a manufacturer implements a trade-in programme through retail and direct channels simultaneously. Compared with the case in which there is no trade-in rebate, the results show that a trade-in programme can intensify or mitigate the double marginalisation effect if the retailer can initially decide the trade-in rebate in the retail channel. This significantly relies on market segmentation. However, when the retailer cannot decide the trade-in rebate in the retail channel, the trade-in programme aggravates the double marginalisation effect. Second, the trade-in rebate offered by the retailer may be higher than the subsidy offered by the manufacturer, as long as the retailer can autonomously decide the trade-in rebate in the retail channel. Furthermore, we find that both the manufacturer and retailer prefer to obtain the right to autonomously decide the trade-in rebate in the retail channel, but the supply chain prefers that the manufacturer do it. Some numerical examples are provided to further explain these outcomes.     

基于属性加密的广域信息管理的授权方法

为了解决广域信息管理(system wide information management,SWIM)信息安全问题,根据SWIM面向服务的系统架构(service-oriented architecture,SOA)的特点,设计SWIM的访问策略,提出了一种基于属性密码(attribute-based encryption,ABE)的授权方法.该方法根据SWIM访问结构中分布性、异构性和动态性的特点,采用密文访问策略(cipher policy-attribute based encryption,CP-ABE)实现.在模拟环境中对该方法进行仿真实验和安全性分析,实验结果表明:该方法支持SWIM航空用户细粒度的授权,降低了SWIM授权管理的复杂度,提高了SWIM系统的安全性.     

一种利用运动补偿的改进JPDA-UKF算法

在恒虚警条件下,针对传统的航海雷达模拟器目标跟踪采用的基于不敏卡尔曼滤波的联合概率数据互联算法( JPDA-UKF)发散、复杂度高和实时性差的问题,提出了一种利用运动补偿的笛卡尔坐标下改进的JPDA-UKF滤波方法。该算法引入相邻周期回波间运动补偿提取的目标量测可信度矩阵,限制进入跟踪门相交区域中的虚假量测数量,并将软跟踪门技术应用于滑窗逻辑法实现航迹管理。仿真结果表明,所提方法径向速度误差比传统的JPDA-UKF算法与自适应的α-β滤波算法分别降低10%和20%,目标获得稳定航迹后径向速度归一化均方根误差( RMSE)比上述两种方法分别具有约10 dB和15 dB的性能优势,算法的复杂度符合真实雷达的边扫描边跟踪的实时处理。     

网络技术在气象灾害预警系统的应用

阐述了网络技术在晋城市气象灾害预警公共服务系统中的运用,详细介绍了该系统的总体结构和关键技术,并提出了相应的安全防范措施。     

A Universal Strategy to Utilize Polymeric Semiconductors for Perovskite Solar Cells with Enhanced Efficiency and Longevity

In this contribution, a facile and universal method is successfully reported to fabricate perovskite solar cells (PSCs) with enhanced efficiency and stability. Through dissolving functional conjugated polymers in antisolvent chlorobenzene to treat the spinning CH₃NH₃PbI₃ perovskite film, the resultant devices exhibit significantly enhanced efficiency and longevity simultaneously. In‐depth characterizations demonstrate that thin polymer layer well covers the top surface of perovskite film, resulting in certain surface passivation and morphology modification. More importantly, it is shown that through rational chemical modification, namely molecular fluorination, the air stability and photostability of the perovskite solar cells are remarkably enhanced. Considering the vast selection of conjugated polymer materials and easy functional design, promising new results are expected in further enhancement of device performance. It is believed that the findings provide exciting insights into the role of conjugated polymer in improving the current perovskite‐based solar cells.     

北京一地基微波辐射计的观测数据一致性分析和订正实验

基于辐射传输理论,以地基微波辐射计亮温数据质量控制研究为目的,以北京一台多通道微波辐射计为例,对其2010和2011年每天8:00和20:00(BT)的“晴空”观测亮温数据进行了分析,并利用独立来源的大气层结资料通过辐射传输方程进行亮温模拟计算,检验了亮温数据的“晴空”观测和数值模拟结果之间的一致性,发现了因“定标”和“搬迁”引起的数据不连续和不一致问题,考虑到“定标”使观测和数值模拟结果之间的一致性优于定标之前而“搬迁”改变的是地基微波辐射计的工作环境,通过对观测数据进行分段拟合订正,改善了观测数据的连续性和一致性。该研究对基于辐射传输理论的观测数据质量控制和提高观测资料的可利用性有参考价值。     

员工脱岗与企业安全检查的演化博弈研究

矿工与煤矿企业之间的策略依存性符合博弈论的基本特征。为降低矿工脱岗的极大似然估计值,首先基于演化博弈理论建立矿工与煤矿企业的博弈模型,然后分析结果表明矿工与煤矿企业的策略相互影响且受脱岗外部损失K、脱岗处罚H、检查脱岗成本F等等诸多因素影响。最后结合某集团煤矿脱岗实例验证结论并给出降低矿工脱岗概率的建议。     

城市轨道交通列车快慢车模式运行图自动生成与CAD实现

根据人工手动绘制快慢车运行图的思路,提出将快车与慢车不同比例模块化的思路,保证不同时段行车对数满足要求的情况下,在不同模块之间添加过渡和调整以满足列车正常出入库,使自动生成的运行图最大限度地符合设计者的需求,能够在快慢车特定对数比例下完成不同线路的不同全日行车计划的绘制。而且能将运行图的数据用CAD脚本命令的格式导出,在CAD软件中实现运行图的自动铺画。最后以成都地铁18号线为例实现了快慢车模式下全日运行图的自动生成,验证了该方法的可行性。     

High‐Performance Red,Green, and Blue Electroluminescent Devices Based on Blue Emitters with Small Singlet–Triplet Splitting and Ambipolar Transport Property

Two coordination complex emitters as well as host materials Be(PPI)₂ and Zn(PPI)₂ (PPI = 2‐(1‐phenyl‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl)phenol) are designed, synthesized, and characterized. The incorporation of the metal atom leads to a twisted conformation and rigid molecular structure, which improve the thermal stability of Be(PPI)₂ and Zn(PPI)₂ with high T_d and T_g at around 475 and 217 °C, respectively. The introduction of the electron‐donating phenol group results in the emission color shifting to the deep‐blue region and the emission maximum appears at around 429 nm. This molecular design strategy ensures that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) HOMO and LUMO of Be(PPI)₂ and Zn(PPI)₂ localize on the different moieties of the molecules. Therefore, the two complexes have an ambipolar transport property and a small singlet–triplet splitting of 0.35 eV for Be(PPI)₂ and 0.21 eV for Zn(PPI)₂. An undoped deep‐blue fluorescent organic light‐emitting device (OLED) that uses Be(PPI)₂ as emitter exhibits a maximum power efficiency of 2.5 lm W^?1 with the CIE coordinates of (0.15, 0.09), which are very close to the National Television Standards Committee (NTSC) blue standard (CIE: 0.14, 0.08). Green and red phosphorescent OLEDs (PhOLEDs) that use Be(PPI)₂ and Zn(PPI)₂ as host materials show high performance. Highest power efficiencies of 67.5 lm W^?1 for green PhOLEDs and 21.7 lm W^?1 for red PhOLEDs are achieved. In addition, the Be(PPI)₂‐based devices show low‐efficiency roll‐off behavior, which is attributed to the more balanced carrier‐transport property of Be(PPI)₂.