Fatigue Strength for Bolts and Nuts Having Slight Pitch Difference Considering Incomplete Threads of Nut

The high strength bolts and nuts are widely used in engineering structures. To investigate the pitch difference on the fatigue strength of bolt, a slight pitch difference is considered between the bolt and nut. Here, the pitch of the nut is α μm larger than the pitch of the bolt. The fatigue experiment is conducted with varying pitch difference. The results show that the fatigue life is extended to about 1.5 times of the one of normal bolt and nut by introducing the suitable pitch difference under the high stress amplitude. According to the detailed observation on the fractured specimens, it is found that the fractured positions and the crack distributions vary depending on the pitch difference. To clarify the improvement mechanism of the fatigue strength, the finite element method is applied to calculate the stress amplitude and mean stress at each bottom of bolt threads. It is found that the finite element analytical model considering the incomplete nut threads is useful for predicting the crack initiation under different pitch difference introduced

Survey of location-centric target tracking with mobile elements in wireless sensor networks

介绍目标跟踪的过程以及移动跟踪的特点;通过区分目标定位为主的方法和目标探测为主的方法,介绍定位为主的移动式目标跟踪方法(称为目标的移动式定位跟踪; )的研究现状;分析和比较不同方法的特点和应用领域,发现现有方法虽然可以提高跟踪质量、降低网络整体能耗,但是还存在一些问题。基于此,总结目标的移动; 式定位跟踪方法在方法类型、网络结构和节点模型等方面可能存在的研究热点,指出其研究和发展趋势。The basic process of target tracking and the properties of tracking; solutions with mobile elements were introduced. By distinguishing; location-centric methods and detection-centric methods, the current; research status of the location-centric target tracking methods were; reviewed. The properties and application fields of different solutions; were analyzed and compared. Although the existing solutions can; significantly improve tracking quality and reduce energy consumption of; the whole network, there are also some problems. Based on these; discoveries, some possible research hotspots of mobile solutions were; summarized in many aspects, such as method types, network architecture,; node model, and so on, indicating the future direction of research and; development.国家自然科学基金资助项目; 国家科技支撑计划项

Artificial local magnetic field inhomogeneity enhances T2 relaxivity

磁性探针作为分子影像技术中的磁共振成像（MRI）造影剂在医学诊断中发挥着重要作用。为满足实际诊断中的准确性和精确性要求，科研工作者们长期致力于发展高性能的MRI造影剂以降低高剂量的使用带来的潜在风险。该文章指出了探针聚集体中局域磁场不均匀性是影响T2弛豫效能的关键因素。该文章首次利用磁场不均匀性因素阐明了单个探针和它们聚集体的MRI造影剂之间的相互关系，将可能成为弥补探针聚集体的造影剂理论的空白，并为发展新型高效的MRI造影剂提供重要参考。 该论文共同第一作者为博士后周子健和博士生田蕊，通讯作者为陈小元教授和聂立铭博士，部分工作得到我校物理学系王瑞方教授和化学化工学院高锦豪教授的支持。【Abstract】Clustering of magnetic nanoparticles (MNPs) is perhaps the most effective, yet intriguing strategy to enhance T2 relaxivity in magnetic resonance imaging (MRI). However, the underlying mechanism is still not fully understood and the attempts to generalize the classic outersphere theory from single particles to clusters have been found to be inadequate. Here we show that clustering of MNPs enhances local field inhomogeneity due to reduced field symmetry, which can be further elevated by artificially involving iron oxide NPs with heterogeneous geometries in terms of size and shape. The r2 values of iron oxide clusters and Landau–Lifshitz–Gilbert simulations confirmed our hypothesis, indicating that solving magnetic field inhomogeneity may become a powerful way to build correlation between magnetization and T2 relaxivity of MNPs, especially magnetic clusters. This study provides a simple yet distinct mechanism to interpret T2 relaxivity of MNPs, which is crucial to the design of high-performance MRI contrast agents.This work was supported by the National Science Foundation of China (81571744 and 81601489), the National Basic Research Program of China (863 Program 2015AA020502), the Fundamental Research Funds for the Central Universities (20720170065), the Science Foundation of Fujian Province (No. 2014Y2004), and by the Intramural Research Program (IRP), National Institute of Biomedical Imaging and Bioengineering (NIBIB), National Institutes of Health (NIH). 研究工作得到了国家自然科学基金委、国家高技术研究发展计划863项目、福建省重大研发平台项目和美国NIH Intramural Research Program的资助