Investigation of seasonal variations of Beijing pavement condition data using unevenly spaced dynamic panel data model

Beijing municipal highway administration started to collect pavement condition data on its major expressways since 2006. It is advised in the Chinese practice standard that data collection shall be conducted on annual basis. However, pavement data are usually collected at different seasons of the year, which may cause significant seasonal variations in the observed condition. Moreover, for some reasons, data are missing for some of the pavement sections at certain years, which could bring up difficulties in performance model estimation and inference. These concerns have been simply neglected in past practice. This study proposed an unevenly spaced dynamic panel data model to investigate the seasonal patterns of a performance indicator called Ride Quality Index (RQI). A quasi-differencing approach was adopted for the estimation. Data collected from the 5th Ring Road of Beijing were used in the case study. It was found that RQI data collected during the fall season are expected to be lower than that collected during the spring or summer seasons. Findings from this research would be helpful to pavement engineers in using unevenly spaced pavement condition data for future condition estimation.     

《钢结构设计规范》(GB 50017-2003)应用中的几个问题

《钢结构设计规范》(GB 50017-2003)施行两年以来,在应用过程中提出了一些问题。就所接触到的问题陈述了个人的见解。问题包括:T形截面的梁端加劲肋的稳定计算、箱形截面轴心压杆的壁板宽厚比限值和超过限值时的有效宽度、框架二阶分析所涉及的重力荷载和柱压力、对接焊缝的强度设计值。     

宽腹板工形截面偏压杆的M-P-Φ曲线

腹板失稳并不预示着工形截面偏压杆丧失承载能力。由此,本文考虑腹板初始凸曲和残余应力,利用腹板屈后强度,计算了宽腹板工形截面杆的M-P-Φ关系,以便进一步计算其压溃荷载。计算结果表明:腹板有凸曲截面的M-P-Φ曲线和一般的M-P-Φ曲线有本质的不同,明显地反映出腹板凸曲变形的影响。     

Visible light driven photodynamic anticancer activity of graphene oxide/TiO2 hybrid

Graphene oxide/TiO₂ hybrid (GOT) was prepared by using Ti(OC₄H₉)₄ and graphene oxide (GO) as reactants. Superior adsorption and photocatalysis performance under visible radiation were achieved in the presence of the GOT rather than in unmodified TiO₂. GO that no toxicity in vitro acted as electron sink in GOT efficiently enhance the photodynamic activities. Consistent with photocatalytic performance of TiO₂, GOT generated reactive oxygen species after visible light irradiation both in cell free condition and in vitro. No dark cytotoxicity was observed using 0–100 μg/mL GOT during long incubation time. In parallel, following exposure of cells to GOT and irradiation, a marked decrease in mitochondrial membrane potential, cell viability, activities of superoxide dismutase, catalase and glutathione peroxidase, as well as increased malondialdehyde production were observed. Moreover, GOT caused significant elevation in caspase-3 activity, and induced apoptotic death. The results indicated that GOT had excellent photodynamic anticancer activity without dark cytotoxicity.     

掺钕钒酸钇激光晶体的研制和开发

掺钕钒酸钇激光晶体是一种优秀LD泵浦的激光晶体材料,是当前中、小功率全固态激光器的首选材料,它广泛应用于激光通讯、激光测距、激光印刷、卫星测量、导航等各个领域。首先回顾了LD泵浦的激光晶体材料的发展过程及其对激光晶体的要求,系统介绍了掺钕钒酸钇激光晶体的特性。同时比较详细介绍了大尺寸、高质量掺钕钒酸钇激光晶体生长技术及其应用。目前产品已销往美、英、日等21个国家和地区,成为我国唯一能够大量进入国际市场的激光晶体产品,极大地推动了我国激光晶体行业的发展,扩大了我国晶体行业在国际上的影响力。     

基于软件层次化模型的软件测试数据生成

针对基于Markov链模型的软件测试技术在测试数据生成时不考虑软件的结构信息,生成的测试数据集对代码路径的覆盖能力以及缺陷检测能力都较低的问题,将统计测试与基于Markov链模型的测试相结合,提出了一种新的软件测试模型——软件层次化模型。该模型涵盖了软件与外部环境之间的交互,同时描述了软件内部结构信息。还给出了该模型测试数据集的生成算法：首先生成符合使用情况的测试序列,然后为测试序列生成覆盖软件内部结构的输入数据。通过针对示例软件的实验结果表明,与基于Markov链模型的测试方法对比,基于软件层次化模型的测试在满足软件测试充分性要求的同时,提高了测试数据集的代码路径覆盖能力和缺陷检测能力。     

QuEChERS-超高效液相色谱-串联质谱法快速测定饮料中13 种饱和内酯类合成香料

建立超高效液相色谱-串联质谱法快速测定饮料中13 种饱和内酯类合成香料的方法。采用QuEChERS前处理法,以乙腈提取,N-丙基乙二胺填料吸附剂直接净化,电喷雾离子源、多反应监测正离子模式扫描,外标法定量。13 种饱和内酯在0.025～0.50 μg/mL范围内质量浓度与峰面积呈良好的线性关系,仪器检出限为0.025 μg/mL,方法的检出限为0.10 mg/kg,定量限为0.40 mg/kg,添加量为0.10、0.20、0.40 mg/kg时13 种饱和内酯的平均回收率范围分别为88.5%～103%,相对标准偏差为3.8%～11%（n=10）。本方法可用于饮料中饱和内酯类化合物的快速定性、定量检测。     

High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

The hypoeutectic composite material composed of BCC phase and in situ precipitated Ti₅Si₃ was prepared by adding Si into MoNbTaTiV high-entropy alloy. The obvious oriented in situ Ti₅Si₃ phase formed eutectic phase with BCC phase in the inter-dendritic area, which leads to excellent properties of the composite. The alloy exhibits ultra-high yield stress of 718 MPa at 1200 °C and obvious compression plasticity. After reaching the maximum strength, dynamic recovery (DRV) and dynamic recrystallization (DRX) caused soften phenomena. The DRX mechanism of the dual-phase eutectic structure is analyzed by electron backscatter diffraction. The DRX of the BCC phase conforms to the discontinuous DRX and continuous DRX mechanisms, while the Ti₅Si₃ phase has a geometric DRX mechanism in addition to the above two mechanisms. The high performance of this composite has enough potential high-temperature applications such as nuclear and aero engine.     

Micromechanics modeling of plastic yielding in a solid containing mode III cohesive cracks

A new micromechanics damage model is proposed by averaging distributed microcracks with cohesive zones in a two dimensional representative volume element. The cohesive microcracks are mode-III Dugdale-Bilby-Cottrell-Swinden (Dugdale-BCS) crack. The damage model may be used to construct plasticity potentials that take into account the presence of such microcracks.