Synthesis and photo-induced solution properties of new rigid-rod polyimides

A series of new, substituted pyromellitic dianhydrides were synthesized from 1,2,4,5-tetramethylbenzene. New soluble rigid-rod polyimides were obtained from the dianhydrides and 2,2′-bis(trifluoromethyl)-4,4′-biphenyl (PFMB) in phenolic solvents in the presence of isoquinoline as a catalyst. The polyimides are soluble in N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), m-cresol and other solvents, in spite of having no bending in their rigid structures.

UV irradiation changed color of the polyimide solutions and also their viscosity. We observed new absorbance in the 700-nm region and an ESR signal by UV irradiation. The new visible absorbance and the ESR signal are derived from the same origin. They are attributed to the anion radical of the diimide moiety in the polyimide as deduced from the hyper fine structure of the ESR signal. In addition, UV irradiation diminishes the solution viscosity.     

Structural characterization of 1,2-polybutadiene by 13C-n.m.r. spectroscopy: 2. Sequence distribution of 1,2-unit in hydrogenated polybutadienes

The configurational sequences of 1,2-unit in a series of hydrogenated syndiotactic 1,2-polybutadienes were determined in relation to the sequence distribution of 1,2- and 1,4-units on the basis of the ¹³C-n.m.r. signal assignment of the methyl carbons. The observed triad distributions of 1,2- and 1,4-units and configurational distributions of the 1,2-unit are in good agreement with the calculated distributions from transition probabilities. The number average sequence lengths of the 1,2-unit and the 1,2-unit in the racemic addition are 5.7 to 8.0 and 4.1 to 5.4, respectively. From the extrapolation of the plot of the number average sequence length against the crystallinity of the starting 1,2-polybutadienes, the minimum sequence length for crystallization is estimated to be 3.7 for the 1,2-unit in the racemic addition.     

Two-stage stochastic minimum cost consensus models with asymmetric adjustment costs

When dealing with consensus cost problems with asymmetric adjustment costs, the uncertain scenarios with certain probabilities which are becoming a serious problem decision-makers have to face. However, existing optimization-based consensus models have failed to consider uncertain factors that could influence the final consensus and total consensus cost. In order to better deal with these issues, it is necessary to develop practical consensus optimal models. Thus, we establish three two-stage stochastic minimum cost consensus models with asymmetric adjustment costs that may eventually lead the way to better consensus outcomes. The impact of uncertain parameters (such as individual opinions, unit asymmetric adjustment costs, compromise limits, cost-free thresholds) are investigated by modeling three kinds of uncertain consensus models. We solve the proposed two-stage stochastic consensus problem iteratively using the L-shaped algorithm and show the convergence of the algorithm. Furthermore, a case of pollution control negotiations verifies the practicability of the proposed models. Moreover, the comparison of results with the L-shaped algorithm and CPLEX shows that the L-shaped algorithm is more effective in solving time. Some discussions and comparisons on local and global sensitivity analysis of the uncertain parameters are presented to reveal the features of the proposed models. Finally, the relationships between the minimum cost consensus model and minimum cost consensus models with asymmetric adjustment costs and the proposed models are also provided.     

认知任务驱动的fMRI脑功能网络构建方法

针对脑功能网络的构建受到特定大脑图谱对兴趣点描述准确度及覆盖度的限制,提出了基于认知任务信息和神经影像数据的脑功能网络构建方法。首先计算fMRI体素对于认知任务的敏感度,然后在此基础上选取兼顾分布均衡和去中心化的大脑兴趣点,从而构建任务驱动的脑功能网络。实验通过在人脸情绪识别认知任务相关的梭状回构造任务驱动的脑功能网络,其度中心性、聚类系数、全局效率、局部效率这四个复杂网络指标均优于典型大脑图谱梭状回中兴趣点构成的网络。结果表明,计算得到的大脑兴趣点具有更强的整合性,更适合用于表征特定认知任务下的脑功能网络。     

Estimation of access failure probability in D2D underlaid cellular networks

Device-to-Device (D2D) communication can reduce the mobile devices' energy consumption and increase the spectral efficiency in D2D underlaid cellular networks. However, D2D users will interfere with co-channel cellular users, which can lead to cellular communication access failures. There are two reasons for cellular communication access failures: (1)D2D interference and (2)insufficient spectrum resources. To address the absence of research on the performance of cellular services' access in D2D underlaid cellular networks, this paper defines the new services' access failure probability and handoff services' access failure probability to evaluate the effect of both D2D interference and limited resources on cellular communication access. Based on the stochastic geometry and stochastic process, a random network model is presented to estimate the access failure probabilities, which can provide guidelines for network design to ensure cellular services' access. The accuracy of the estimated access failure probability is validated through extensive simulations.     

打车软件混合随机均衡模型时间可靠性研究*

为了探究打车软件出现后对乘客打车行为的影响,揭示是否使用打车软件对乘客候车时间长短的变化规律,基于路网混合随机均衡模型理论,在考虑打车软件对出租车司机搜索行为影响和随机变化的OD对需求条件下,构建基于弹性需求的打车软件随机用户均衡模型;然后结合乘客等车、司机空驶时间和可靠性计算模型,引入连续平均（MSA）算法和随机路径流量分配（Dial）算法进行求解;最后通过算例验证了所建模型和算法的有效性。研究结果表明不同需求弹性下、是否使用打车软件对会乘客候车时间及候车时间可靠性产生明显的差异。     

多维度动态增强核磁共振乳房区域全自动分割

提出了一种基于乳房水平面与乳房矢状面相结合的多维度DCE-MRI乳房图像全自动分割方法。方法分为3部分,即基于乳房水平面的分割,基于乳房矢状面的分割,以及水平面与矢状面相结合的分割方法。首先,基于水平面的分割方法通过阈值确定乳房外边缘,经过梯度算法后,根据乳房与胸大肌分界面的特点设定约束条件,得到分界面的分割曲线。其次,基于乳房矢状面的分割方法使用双边滤波、边缘提取法对图像预处理,分区计算分割曲线。最后,矢状面的分割结果根据图像三维大小按比例映射到水平面上,将两者的分割结果结合,然后根据相邻图像之间的相关性,从而进行优化,输出分割结果。通过对24例DCE-MRI病例测试,与手动分割得到的结果对比,平均重叠率为93．33％,平均差异度为8．14％。     

EMD滤波方法在NMR测井中的应用

核磁共振测井中,回波信号的信噪比对T2谱反演及后续地层解释评价过程有重要影响。基于核磁共振测井信号与噪声的分析,提出了一种采用自适应性较强的经验模态分解（ EMD）算法对核磁共振测井原始数据作消噪处理。结果表明,采用该滤波算法,实验室回波数据信噪比由22 dB提高到46 dB,标准油井回波数据信噪比由11 dB提高到31 dB,反演得到的T2分布更加精确,多次重复测量中孔隙度结果有较高的一致性。     

基于T-S模型的随机双线性系统的稳定问题

主要研究了基于T-S模型的随机双线性系统的稳定性问题。首先,利用并行分布补偿方法设计控制器,确保闭环系统是随机渐近稳定的。其次,基于It^o随机稳定性理论,利用Lyapunov函数方法、不等式变换技巧和Schur补引理,证明了定理所给的稳定条件下的结论是成立的。设计方法的有效性通过一个数值例子来验证。     

基于随机共振原理的低频弱信号检测方法研究

介绍了双稳系统,讨论了产生随机共振的条件以及输出频谱的特性。针对原双稳系统不能检测中低频率信号的问题,利用参数变换原理,推导出了一种新的模型,阐述与分析了该模型的参数变化对输出混合信号的影响。模型相对于经典双稳系统模型降低了对输入的要求。