再谈“负温状态的稳定性”——答王家庆同志

重申了关于负温状态稳定性的观点，认为关于负温状态稳定性的讨论是必要的，稳定性条件的推导是合理的。     

Synthesis and properties of novel poly(p-phenylenevinylene) copolymers for near-infrared emitting diodes

A series of novel near-infrared (NIR) electroluminescence (EL) copolymers based on a host poly(p-phenylenevinylene) (PPV) derivative of poly(2-methoxy-5-octyloxy-p-phenylenevinylene) (PMOPV) with different content of narrow band-gap (NBG) unit 4,7-bis(2-thienyl)-2,1,3-benzothiadiazolevinylene (DBTV) or 4,7-bis(2-thienyl)-2,1,3-benzoselenadiazolevinylene (TBSV) was prepared by Stille coupling reaction. All the copolymers are soluble in common organic solvents, most of which emit NIR light accompanied by gradually red-shifting with increasing the content of the NBG units. The peak EL emission of the copolymers with around 30% TBSV content is at about 800 nm.     

Visualization of mouse spinal cord intramedullary arteries using phase‐ and attenuation‐contrast tomographic imaging

Many spinal cord circulatory disorders present the substantial involvement of small vessel lesions. The central sulcus arteries supply nutrition to a large part of the spinal cord, and, if not detected early, lesions in the spinal cord will cause irreversible damage to the function of this organ. Thus, early detection of these small vessel lesions could potentially facilitate the effective diagnosis and treatment of these diseases. However, the detection of such small vessels is beyond the capability of current imaging techniques. In this study, an imaging method is proposed and the potential of phase‐contrast imaging (PCI)‐ and attenuation‐contrast imaging (ACI)‐based synchrotron radiation for high‐resolution tomography of intramedullary arteries in mouse spinal cord is validated. The three‐dimensional vessel morphology, particularly that of the central sulcus arteries (CSA), detected with these two imaging models was quantitatively analyzed and compared. It was determined that both PCI‐ and ACI‐based synchrotron radiation can be used to visualize the physiological arrangement of the entire intramedullary artery network in the mouse spinal cord in both two dimensions and three dimensions at a high‐resolution scale. Additionally, the two‐dimensional and three‐dimensional vessel morphometric parameter measurements obtained with PCI are similar to the ACI data. Furthermore, PCI allows efficient and direct discrimination of the same branch level of the CSA without contrast agent injection and is expected to provide reliable biological information regarding the intramedullary artery. Compared with ACI, PCI might be a novel imaging method that offers a powerful imaging platform for evaluating pathological changes in small vessels and may also allow better clarification of their role in neurovascular disorders.     

凸约束非光滑方程组一个新的谱梯度投影算法

基于寻找分离超平面的三种经典线搜索技术,本文提出了一种自适应线搜索技术.结合谱梯度投影法,提出了凸约束非光滑单调方程组的一个谱梯度投影算法.该算法不需要计算和存储任何矩阵,因而适合求解大规模非光滑的非线性单调方程组.在较弱的条件下,证明了方法的全局收敛性,并分析了算法的收敛率.数值试验结果表明算法是有效的和鲁棒的.     

基于神经网络的机械零部件可靠性稳健设计

将可靠性优化设计理论、可靠性灵敏度技术和可靠性稳健设计方法相结合,利用神经网络的非线性映射功能,模拟得到随机设计变量与机械零部件结构响应之间的关系,以训练好的神经网络模型为基础,结合随机摄动技术,进行结构可靠性稳健设计.从而解决了工程实际中很难给出极限状态函数的显性表达式问题,并有效地克服了目前随机有限元法和响应面法存在的缺陷.     

基于径向基函数的无单元法求解力学问题误差分析

径向基函数形状参数的选择在无单元法数值计算中一直是一个热门的问题,现在已总结出许多确定形状参数的经验公式. 但还没有相关研究表明这些形状参数是如何随着影响域尺寸而变化的. 本文研究了MQ(multi-quadrics) 径向基函数中形状参数对无单元法计算误差的影响. 首先,从理论上分析了形函数导数随着形状参数值的变化趋势,和以计算点为中心节点对称布置与不对称布置的形函数导数的变化规律;然后分析了影响域尺寸对误差的影响,得到了在不同影响域尺寸下,误差随形状参数值变化的规律;在此基础上,给出了影响域范围值.     

The 3D characteristics of post‐traumatic syringomyelia in a rat model: a propagation‐based synchrotron radiation microtomography study

Many published literature sources have described the histopathological characteristics of post‐traumatic syringomyelia (PTS). However, three‐dimensional (3D) visualization studies of PTS have been limited due to the lack of reliable 3D imaging techniques. In this study, the imaging efficiency of propagation‐based synchrotron radiation microtomography (PB‐SRµCT) was determined to detect the 3D morphology of the cavity and surrounding microvasculature network in a rat model of PTS. The rat model of PTS was established using the infinite horizon impactor to produce spinal cord injury (SCI), followed by a subarachnoid injection of kaolin to produce arachnoiditis. PB‐SRµCT imaging and histological examination, as well as fluorescence staining, were conducted on the animals at the tenth week after SCI. The 3D morphology of the cystic cavity was vividly visualized using PB‐SRµCT imaging. The quantitative parameters analyzed by PB‐SRµCT, including the lesion and spared spinal cord tissue area, the minimum and maximum diameters in the cystic cavity, and cavity volume, were largely consistent with the results of the histological assessment. Moreover, the 3D morphology of the cavity and surrounding angioarchitecture could be simultaneously detected on the PB‐SRµCT images. This study demonstrated that high‐resolution PB‐SRµCT could be used for the 3D visualization of trauma‐induced spinal cord cavities and provides valuable quantitative data for cavity characterization. PB‐SRµCT could be used as a reliable imaging technique and offers a novel platform for tracking cavity formation and morphological changes in an experimental animal model of PTS.     

基于降维积分的结构系统可靠性分析研究

复杂结构系统一般具有多个失效模式. 传统系统可靠性分析模型是在假设各失效模式相互独立的条件下建立的. 而在工程实际问题中,由于结构系统的组成单元之间紧密联系,系统的失效模式大多是相互耦合的. 简单地在失效模式相互独立的假设条件下进行系统可靠性分析与评价常常会导致过大的误差,甚至得出错误的结论. 提出一种相关失效模式结构系统可靠性分析方法. 利用降维法和Gauss-Hermite数值积分技术计算随机参数结构系统极限状态函数的统计矩,采用极限状态函数的前四阶累积量拟合其累积量生成函数,通过鞍点逼近方法拟合结构系统极限状态函数的概率密度函数和累积分布函数,进而获取结构系统的可靠度(或失效概率).数值算例表明该方法具有较高的计算精度和效率,通用性强.     

An Extremely Narrow‐Band‐Gap Conjugated Polymer with Heterocyclic Backbone and its Use in Optoelectronic Devices

Summary: A novel narrow‐band‐gap conjugated polymer with heterocyclic backbone, poly[4,7‐bis(4‐decanyl‐2‐thienyl)‐2′,1′,3^′‐benzothiadiazole‐thiophene‐2,5‐] (PDDBT, E_g = 1.38 eV) was synthesized by a Stille coupling reaction. Prototype bulk heterojunction photovoltaic cells from PDDBT and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) with a ITO/PEDOT:PSS/PDDBT:PCBM(1:3)/Ba/Al device architecture showed power conversion efficiencies up to 0.13% under AM1.5 solar simulator (100 mW · cm⁻²) with an open‐circuit voltage V_oc of 0.65 V, a short‐circuit current density J_sc of 0.6 mA · cm⁻², and a photocurrent response up to 880 nm. The electroluminescent device from PDDBT showed a near‐infrared light emission peak at around 830 nm with maximal external quantum efficiency of 0.08% and a turn‐on voltage at 3.5 V.

Normalized PL and EL spectra of PDDBT and photosensitivity of PVCs based on PDDBT/PCBM (1:3) blend. The scheme shows the chemical structure of PDDBT.