基于超声导波SC-DTW的金属板微损检测方法

针对金属板材的质量控制与服役性能评估问题,在对金属板材微损伤进行超声导波检测的基础上,结合形状上下文(shape context,SC)与动态时间规整方法对其损伤劣化程度进行量化评估.该方法以无损Lamb波信号为基准,采用动态时间规划(dynamic time warping,DWT)算法对损伤信号进行相似匹配分析对比,确定基准信号与损伤信号的最佳匹配路径.引入SC的轮廓识别方法对Lamb波的局部波形信息进行统计分析,以波形形状距离代替传统欧氏距离匹配方法,解决DTW相似匹配中的病态对齐问题.最后,将无损Lamb波与损伤Lamb波信号间SC-DTW匹配距离作为损伤程度的量化指标,采用随机闭合裂纹的有限元仿真模型和铝板弯折实验对所提出方法进行验证,结果表明,基于Lamb波SC-DTW的损伤量化指数对铝板早期裂纹具有较高的敏感性和较好的量化表征能力.该方法无需对波包进行识别,也不必进行复杂的特征提取,具有简单高效和抗噪声能力强等优点,在金属板服役性能评估与质量控制中有较好的实用性和推广价值.     

Novel Bi4O5Br2/MnxZn1-xFe2O4 magnetic composite with an enhanced photodegradation activity and excellent recyclability

Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ nanocomposites with impressive photocatalytic and recyclability properties were synthesised using a microemulsion method. In addition to the photocatalytic effect, the crystal structure and morphology, photoelectrochemical characteristics, magnetic effect and photocatalytic mechanism of Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ were also investigated. As the best sample, the removal rate of the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ photocatalyst with 7.5 wt% Mn_xZn_1-xFe₂O₄ to rhodamine B (RhB) reached up to 99.4% within 60 min. The enhanced photocatalyst activity was mainly attributed to the type-II heterojunction formed between Bi₄O₅Br₂ and Mn_xZn_1-xFe₂O₄, which not only optimised the energy band structure, but also led to the building of an interior electromagnetic field within the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ heterojunction. Meanwhile, the constantly producing and migrating h⁺ and ·O₂^? were the main active components. In particular, the results of the saturation magnetization tests and magnetic recovery experiments revealed that the magnetic composite photocatalyst can be recovered effectively. The results of the removal rate of RhB remaining at 85.2% after five uses reflected the advantages of the stability of the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ photocatalyst. In brief, this paper presented an original idea to develop a novel composite magnetic photocatalyst and research the enhancement mechanism of photocatalysis.     

Effect of ball-milling parameters on the rheological properties of mold powder slurry

In this study, mold powder slurries with high solid loading and low viscosity were prepared during the ball-milling process for improving the homogeneity and mechanical properties of granules after spray-drying. The effect of ball-milling parameters, such as solid loading, binder/dispersant content, and ball-milling time, on the flowability, dispersibility, stability, and rheological behavior of mold powder slurries was systematically investigated by rheology observation and sedimentation tests. As these parameters varied, the slurry exhibited the shear-thinning behavior of a non-Newtonian fluid with a shear rate range of 0–50 s^?1, which was adequately described by the Herschel-Bulkley model. The optimal parameters that optimized the flowability, dispersibility, and stability of the slurry, along with its rheological behavior, were chosen as follows: solid loading, 60 wt%; modified sodium carboxymethyl cellulose binder content, 1.0 wt%; sodium tripolyphosphate dispersant content, 0.5 wt%; ball-milling time, 60 min.     

A Dynamic Programming Framework for Large-Scale Online Clustering on Graphs

Neural Processing Letters - As a fundamental technique for data analysis, graph clustering grouping graph data into clusters has attracted great attentions in recent years. In this paper, we...     

Computing approximate blocking probabilities for transparent waveband switching based WDM networks using hierarchical cross-connects

An analytical model is presented to study the dynamics of wavelength division multiplexing (WDM) networks with waveband switching (WBS). The reduced load approximation method is considered to compute approximated network blocking probabilities in WBS-based WDM networks. The analytical model considers the link blocking probability due to insufficient link capacity and an impact of the waveband granularity (G). The analytical model also considers the node blocking probability due to unavailability of a switch port at the wavelength cross connect (WXC) layer of an Hierarchical cross connect (HXC) switch node. The set of nonlinear equations is obtained with the link independence assumption and solved using repeated substitutions. The accuracy of the analytical model is examined by comparing with simulation results considering the random-fit algorithm for waveband and wavelength assignments in different network scenarios. Lightpaths are routed between source and destination (s-d) HXC switch nodes using shortest path first (SPF) routing. An impact of the switch parameter to limit the input and the output WXC switch ports of an HXC switching node is also being investigated using the analytical model as well as through simulation results.     

Convolutional neural network with adaptive inferential framework for skeleton-based action recognition

In the task of skeleton-based action recognition, CNN-based methods represent the skeleton data as a pseudo image for processing. However, it still remains as a critical issue of how to construct the pseudo image to model the spatial dependencies of the skeletal data. To address this issue, we propose a novel convolutional neural network with adaptive inferential framework (AIF-CNN) to exploit the dependencies among the skeleton joints. We particularly investigate several initialization strategies to make the AIF effective with each strategy introducing the different prior knowledge. Extensive experiments on the dataset of NTU RGB+D and Kinetics-Skeleton demonstrate that the performance is improved significantly by integrating the different prior information. The source code is available at: https://github.com/hhe-distance/AIF-CNN.     

Low Li ion diffusion barrier on low-crystalline FeOOH nanosheets and high performance of energy storage

Nano Research - To obtain symmetric supercapacitors (SCs) with high energy density, it is critical to fabricate an electrode with wide potential window and excellent capacitive performance. Herein,...     

时效工艺对纳米结构2297铝锂合金力学性能与微观组织的影响

采用535 ℃×2 h固溶制度,将热锻态2297铝锂合金固溶水淬后冷轧,冷轧压下量为95%,然后将轧制样品在不同温度(120~190 ℃)和时间(0~80 h)范围内进行时效处理。采用拉伸、扫描电镜(SEM)和透射电镜(TEM)等测试方法,分析时效温度和时间对铝锂合金组织与性能的影响。结果表明:时效前的大塑性变形能获得纳米结构组织,能促进T₁相均匀细小地析出,缩短合金达到峰时效的时间,最终成功制备了高强高塑性铝锂合金。在120~140 ℃温区内时效时,时效温度越高,达到峰时效的时间越短、强度越高。140 ℃达到峰时效时间缩短为40 h,此时合金的抗拉强度、屈服强度和伸长率分别为525 MPa、478 MPa和7.7%,主要强化相为细小的T₁相。在170~190 ℃温区内时效时,时效温度越高,达到峰时效的时间越短,但抗拉强度与屈服强度迅速下降。170 ℃时效8 h达到峰时效状态,此时合金的抗拉强度、屈服强度和伸长率分别是503 MPa、462 MPa和5.0%,主要强化相仍为T₁相,但已经明显粗化。     

A narrow-frame antenna for WWAN/LTE/WiMAX/WLAN mobile phones

In this paper, we present a novel narrow-frame antenna with a size of 75 × 8 × 5.8 mm³ for 5.7 in. mobile phones. The antenna mainly consists of a monopole with four branches that are coupled to a two-branch grounded strip. Our antenna is able to cover more bands than other narrow-frame antennas by excitation of several resonant modes. The improved range of the antenna covers the following eleven bands: LTE700, GSM850, GSM900, DCS, PCS, UMTS, LTE2300, LTE2500, LTE3400 (3400–3800 MHz)/WiMAX3.5 GHz (3400–3650 MHz), WLAN5.2 GHz (5150–5350 MHz) and WLAN5.8 GHz (5725–5875 MHz). Another advantage of the proposed antenna is that it does not need any lumped element to match the antenna. The working principles of the proposed antenna are thoroughly studied. A prototype of the proposed antenna is fabricated and measured, with the results in good agreement with the simulation results.