Stress wave propagation in adhesively bonded functionally graded cylinders: an improved model

This study presents an improved mathematical model to analyse the stress wave propagation in adhesively bonded functionally graded (FG) circular cylinders (butt joint) under an axial impulsive load. The volume fractions of the material constituents in the upper and lower cylinders were functionally tailored through the thickness of each cylinder using a power-law. The effective material properties of both cylinders, which are made of aluminum (Al) and silicon carbide (SiC), at any point were predicted by using the Mori–Tanaka homogenization scheme. In this improved model, the governing equations of the wave propagation include the spatial derivatives of local mechanical properties and were discretized by means of the finite difference method. The influence of these spatial derivatives and the compositional gradient exponent on the displacement and stress distributions of the joint was investigated. The material composition variations of both cylinders affected the displacement and stress fields whereas the compositional gradient exponent had a minor effect. The stress concentrations were alleviated in time, the displacement and stress distributions/variations around/along the upper and lower cylinder-adhesive interfaces were significantly affected by the adhesive layer. The spatial derivatives also affected the temporal histories of the displacement and stress components evaluated at the selected critical points of the upper cylinder, adhesive layer and lower cylinder. The consideration of the spatial local material derivatives provided a more accurate mathematical model of wave propagations through the graded layered structures.     

Surface treatment of titanium dioxide nanopowder using rotary electrode dielectric barrier discharge reactor

Titanium dioxide (TiO2) nanopowder (P-25;Degussa AG) was treated using dielectric barrier discharge (DBD) in a rotary electrode DBD (RE-DBD) reactor.Its electrical and optical characteristics were investigated during RE-DBD generation.The treated TiO2 nanopowder properties and structures were analyzed using x-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR).After RE-DBD treatment,XRD measurements indicated that the anatase peak theta positions shifted from 25.3° to 25.1°,which can be attributed to the substitution of new functional groups in the TiO2 lattice.The FTIR results show that hydroxyl groups (OH) at 3400 cm-1 increased considerably.The mechanism used to modify the TiO2 nanopowder surface by air DBD treatment was confirmed from optical emission spectrum measurements.Reactive species,such as OH radical,ozone and atomic oxygen can play key roles in hydroxyl formation on the TiO2 nanopowder surface.     

多模态影像学检查在诊断早期强直性脊柱炎骶髂关节疾病中的效果

目的:探究在早期强直性脊柱炎骶髂关节疾病诊断中不同放射影像学检查方法的应用效果。方法:抽取2018年5月-2020年1月本院收治的早期强直性脊柱炎骶髂关节疾病患者65例作为研究对象,所有患者均开展X线、CT、MRI影像学检查,对比三种不同影像学检查方法的检出率、影像学特征。结果:X线、CT、MRI检出率分别为38.46%(25/65)、60.00%(39/65)、76.92%(50/65),检出率相比,MRI、CT明显高于X线,P<0.05;X线、CT、MRI影像学特征,发现关节间隙出现不同的异常,如关节面出现侵蚀、骨质囊变现象,关节面下骨质出现硬化与关节软骨出现肿胀,其中MRI、CT检查,阳性率高于X线,P<0.05。而对于软组织肿胀、骨髓水肿、滑膜炎症、关节滑膜增厚等现象,只能通过MRI检查才能诊断。结论:在早期强直性脊柱炎骶髂关节疾病诊断中,X线、CT、MRI影像学检查均具有一定的指导意义,而MRI不仅可以提高检出率,还能准确反映微小病灶及其软组织病变,对于早期发现骶髂关节炎值得推荐。     

Inconel 690传热管GTAW对接焊接头组织及力学性能研究

对Inconel 690传热管材进行钨极气体保护焊(GTAW)对接焊,采用拉伸试验机、压扁试验机和光学显微镜测试和分析传热管焊接接头,同时利用ANSYS软件开展焊接接头在设计工况失压时的一次应力强度校核。研究结果表明:焊缝中心为树枝胞状晶,熔合线附近为粗大柱状晶。室温时接头的平均抗拉强度为619 MPa,平均屈服强度为292 MPa,350℃时接头平均抗拉强度为475 MPa,平均屈服强度为206 MPa,拉伸接头断裂从熔合区开始贯穿整个焊缝组织,呈塑性断裂。压扁试验和反向压扁试验结果表明管接头完好。通过ANSYS分析可知,设计工况下传热管接头350℃许用应力强度150 MPa限值可满足其一次应力强度要求,且裕量较大。     

An automated patient monitoring using discrete‐time wireless sensor networks

In recent years, Internet of Things (IoT) devices are used for remote health monitoring. For remotely monitoring a patient, only the health information at different time points are not sufficient; predicted values of biomarkers (for some future time points) are also important. In this article, we propose a powerful statistical model for an efficient dynamic patient monitoring using wireless sensor nodes through Bayesian Learning (BL). We consider the setting where a set of correlated biomarkers are measured from a patient through wireless sensors, but the sensors only report the ordinal outcomes (say, good, fair, high, or very high) to the sink based on some prefixed thresholds. The challenge is to use the ordinal outcomes for monitoring and predicting the health status of the patient under consideration. We propose a linear mixed model where interbiomarker correlations and intrabiomarker dependence are modeled simultaneously. The estimated and the predicted values of the biomarkers are transferred over the internet so that health care providers and the family members of the patient can remotely monitor the patient. Extensive simulation studies are performed to assess practical usefulness of our proposed joint model, and the performance of the proposed joint model is compared to that of some other traditional models used in the literature.     

Interfacial failure analysis of functionally graded adhesively bonded double supported tee joint of laminated FRP composite plates

This paper deals with three-dimensional non-linear finite element analyses to assess the structural behavior of adhesively-bonded double supported tee joint of laminated FRP composites having embedded interfacial failures. The onset of interfacial failures is predicted by using Tsai–Wu coupled stress failure criterion with pre-determined stress values. The concept of fracture mechanics principle is utilized to study the sustainability of the tee joint having interfacial failures pre-existed at the critical locations. Individual modes of the strain energy release rates (SERR) G_I, G_II and G_III, are considered as the damage growth parameters and, are evaluated using the Modified crack closure integral (MCCI) technique based on the concept of linear elastic fracture mechanics (LEFM). Based on the stress analyses, it has been observed that the interfacial failures in tee joint structure trigger at the interface of base plate and adhesive layer from both ends of base plate. Depending on the SERR magnitudes, it has been noticed that the interfacial failure propagates under mixed mode condition. Therefore total SERR (G_T) is considered as the governing parameter for damage propagation. Furthermore, efforts have been made to retard damage propagation rate by employing functionally graded adhesive (FGA) instead of monolithic adhesive material. Series of numerical simulations have been performed for varied interfacial failure length in functionally graded adhesively bonded double supported tee joint structure in order to achieve the significant effect of FGA with various modulus ratios on SERR. Material gradation of adhesive indicates significant SERR reduction at the incipient stage of failure which necessitates the use of functionally graded adhesive for the tee joint and prolong the service life of the structure.     

回转窑煅烧段烟气最高温度的间接测量

通过对球团回转窑内的热平衡分析,得到回转窑稳定工作时,煅烧段烟气最高温度与窑尾烟气温度之间的理论关系式。该公式表明回转窑在稳定工作时,窑尾烟气温度与煅烧段烟气最高温度存在线性关系。通过三维建模,运用有限元技术对窑尾烟气温度与煅烧段烟气最高温度进行了数值模拟。研究结果可为回转窑煅烧段温度在线监测和自动化调节火焰温度提供理论指导。     

转底炉处理赤泥工艺技术

为了综合利用氧化铝冶炼产生的赤泥，探索在转底炉中直接还原赤泥、磨矿磁选获得高品位直接还原铁。通过实验室试验摸索了转底炉还原工艺参数，并在转底炉工业试验线进行了工业试验。实验室结果表明，赤泥还原后的直接还原铁(DRI)金属化率可达88.6%，磁选后的铁品位可达82.1%，磁选后的铁回收率可达88.9%。工业试验中，转底炉还原后，产品金属化率平均为69.2%，将还原后的DRI磁选获得高品位的DRI产品，磁选后DRI的铁品位为72.8%，磁选后铁回收率达到了85.2%,初步打通了在转底炉中还原赤泥、磁选的工艺路径。     

非径向管板焊接接头的超声检测

对AP1000压水堆核电站安全壳贯穿件的非径向管板焊接接头结构特点进行了介绍,并分析其超声检测工艺的重点和难点。通过建立统一的缺陷定位坐标系并结合被检构件的几何特点进行综合分析,推导得出了h值(缺陷回波最高点距套管外壁的距离)的计算方法。为超声检测对这类焊接接头缺陷的准确识别和定位提供了行之有效的方法,为解决这类焊接接头的超声检测技术受限区提供了行之有效的措施。     

基于深度学习的人体姿态估计方法综述

基于深度学习的人体姿态估计方法旨在通过构建合适的神经网络，直接从二维的图像特征中回归出人体姿态信息。主要按照2D人体姿态估计到3D人体姿态估计的顺序，并从单人检测与多人检测、稀疏的关节点检测与密集的模型构建等方面，对近年来基于深度学习的人体姿态估计方法进行系统介绍，从而初步了解如何通过深度学习的方法得到人体姿态的各个要素，包括肢体部件的相对朝向和比例尺度、骨骼关节点的位置坐标和连接关系，甚至更为复杂的人体蒙皮模型信息。最后,对当前研究面临的挑战以及未来的热点动向进行概述，清晰地呈现出该领域的发展脉络。