Auto-parametric resonance of a continuous-beam-bridge model under two-point periodic excitation:an experimental investigation and stability analysis

The auto-parametric resonance of a continuous-beam bridge model subjected to a two-point periodic excitation is experimentally and numerically investigated in this study.An auto-parametric resonance experiment of the test model is conducted to observe and measure the auto-parametric resonance of a continuous beam under a two-point excitation on columns.The parametric vibration equation is established for the test model using the finite-element method.The auto-parametric resonance stability of the structure is analyzed by using Newmark's method and the energy-growth exponent method.The effects of the phase difference of the two-point excitation on the stability boundaries of auto-parametric resonance are studied for the test model.Compared with the experiment,the numerical instability predictions of auto-parametric resonance are consistent with the test phenomena,and the numerical stability boundaries of auto-parametric resonance agree with the experimental ones.For a continuous beam bridge,when the ratio of multipoint excitation frequency(applied to the columns)to natural frequency of the continuous girder is approximately equal to 2,the continuous beam may undergo a strong auto-parametric resonance.Combined with the present experiment and analysis,a hypothesis of Volgograd Bridge's serpentine vibration is discussed.

Effect of the mixing of s-wave and chiral p-wave pairings on electrical shot noise properties of normal metal/superconductor tunnel junctions

We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime. In the chiral triplet p-wave pairing dominated regime, the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region. In the singlet s-wave pairing dominated regime, the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.

SURFACE CHARACTERISTICS OF 10Ni3MnCuAl STEEL BY SHOT PEENING

The surface of grinding 10Ni3MnCuAl steel is processed by the shot peening with different intensities. After shot peening, the metallographic structure of 10Ni3MnCuAl steel and the micro-structure on the surface layer are analyzed. The micro-hardness in the shot peening affected layer and the residual pressure stress are surveyed. The changes of surface quality, such as micro-hardness, metallographic structure and residual stress caused by shot peening are investigated. The result shows that shot peening can significantly improve surface quality and fatigue life of 10Ni3MnCuAl steel. The over peening effect is produced when the shot peening intensity is high, and it leads to the decrease of the fatigue life. When the optimal arc high value of shot peening is 0. 40 mm in experiments, the best surface quality is obtained and the depth of the residual stress in the precipitation-hardening layer reaches 450μm.

一种自动门限选取的视频Shot分割方法

文中首先针对镜头Ｓｈｏｔ分割在基于内容的视频检索中的重要性，介绍了现在普遍采用的镜头分割新方法，同时针对这些方法的不足，提出了一种基于自动门限选取的镜头分割及分类方法，该方法能同时检测视频中的突变（ｂｒｅａｋ）、缓变（ｇｒａｄｕａｌ）等镜头变换和视频中的闪光灯以及运动区域．通过实际测试。

Effect of wet shot peening on Ti-6Al-4V alloy treated by ceramic beads

Ti-6Al-4V alloy was processed by wet shot peening with ceramic beads. The effects of the shot peened intensity on the microstructure, surface morphology, and residual stress were investigated. A tensile-tensile fatigue test was performed and the fracture mechanism was proposed. The results demonstrate that the surface roughness after wet shot peening is obviously lower than that after dry shot peening. With the increase of the shot peened intensity, the depth of the residual stress layer increases to 250 ktrn, and the maximum stress in this layer increases to -895 MPa. The fatigue strength also increases by 12.4% because of the wet shot peening treatment. The dislocation density of the surface layer is significantly enhanced after the wet shot peening with ceramic beads. The microstructure of the surface layer is obviously refined into ultra-fine grains.

Vacuum assisted high-pressure die casting of AZ91D magnesium alloy at different slow shot speeds

The effects of vacuum assistance on the microstructure and mechanical properties of high-pressure die cast AZ91 D alloy at different slow shot speeds were evaluated. Plate-shaped castings of AZ91 D alloy were carried out on a TOYO BD-350V5 cold chamber die casting machine incorporated with a self-improved TOYO vacuum system. It was found that the vacuum pressure in the die cavity at the beginning of mold filling increases with the increase of slow shot speed, following a cubic polynomial curve, resulting in a decline in the porosity-reduction ability of vacuum assistance with the increase of slow shot speed. The externally solidified crystal（ESC） contents in conventional and vacuum die castings behave similar against the slow shot speed. The tensile properties of vacuum die castings were strongly influenced by the ESC content at relative low slow shot speeds. With the increase of slow shot speed, the influence of the gas porosity level in vacuum die castings would get prominent.

Effect of multi-step slow shot speed on microstructure of vacuum die cast AZ91D magnesium alloy

Two multi-step （two-step and three-step） slow shot speeds were used in the vacuum die casting process of AZ91D magnesium alloy. The vacuum pressure variation in the die cavity before mold filling was monitored by using a pressure sensor. The microstructures of the produced castings were analyzed with optical microscope and image analysis software. The experimental results demonstrate that, the vacuum pressure in the die cavity at the beginning of mold filling is significantly reduced by using three-step slow shot speed, resulting in a low gas porosity level in the produced castings. At an appropriate multi-step slow shot speed, the dwell time of the liquid metal in the shot sleeve before mold filling can be reduced and the flow of the liquid metal in the shot sleeve at the later stage of the slow shot process can be restrained, which cause a low externally solidified crystal content in the produced castings.

SHOTS模拟系统初体验

伴随着计算机技术的不断进步,与以往实物教学培训有着根本不同的模拟器培训已经在很多行业中得到了运用,致力于模拟器开发的法国Sinapse公司也开发出了适用于印刷的模拟器系统,但该模拟系统在国内的印刷行业还没有得到推广。

SHOTS系统在印刷专业教学中的应用探索

结合印刷技术专业实训操作过程中排除印刷故障耗时长、成本高及操作难度大的现状进行了深入的研究剖析,探索了应用SHOTS系统实现与传统印刷机同步模拟排除印刷故障的方式重构实训环节的总体框架,尝试和创新符合学校实际情况的实训教学模式。以真正实现“做中学、学中做”,将印刷理论与实际操作结合在一起,使学生对印刷机的操作更熟练,从而达到在提高教学效率和教学质量的同时又节约资源的目的。

SHOTS模拟培训的优势及其前景

随着计算机技术的不断进步,模拟器培训已经在各行各业中得到广泛的普及,从飞机操作到各种大型机械的培训,模拟器培训获得普遍好评。

基于B-SHOT特征和3D-NDT的点云自动配准

提出一种结合B-SHOT特征的3 D-NDT点云自动配准方法。首先分别提取两个点集的B-SHOT特征点,并且估算这些特征点的B-SHOT特征描述子,然后通过双向汉明距离估计两个点集之间的三维特征匹配点对,并利用随机采样一致性算法估计两个点集的初值转换参数,最后使用3D-NDT算法完成精确配准。实验结果表明,算法能快速精确的进行两个点云集之间的自动配准。

一种基于ISS-SHOT特征的点云配准算法

针对点云配准过程中易产生错误对应点、收敛速度慢、配准时间长等问题,提出了一种基于内部形态描述子(ISS)及方向直方图描述子(SHOT)特征的点云配准算法。运用体素格网法下采样后,采用ISS算法提取特征点,并用SHOT对特征点进行描述,利用余弦相似度匹配对应点对,再采用RANSAC算法剔除错误对应点对,使得两片点云获得良好的初始位姿,最后采用点到平面的ICP算法进行精确配准。试验结果表明,与传统ICP算法及基于ISS的SAC-IA+ICP算法相比,本文算法配准精度及配准效率更高,对数据量大、重叠率较低点云具有很好的稳健性。

Correction of buckling distortion by ultrasonic shot peening treatment for 5A06 aluminum alloy welded structure

Ultrasonic shot peening treatment （USPT） was proposed to correct welding buckling distortion. The residual stress distribution along the depth direction of the peened zone was measured by an X-ray diffractometer. The microstructure of the treated specimens was investigated by scanning electron microscopy （SEM）. The Vickers microhardness was measured in different areas of welded joint before USPT and along the depth direction of the weld after USPT. The experimental results indicated that the welding buckling distortion of 5A06 aluminum alloy butt joint can be essentially corrected by USPT; the average correction rate reached 90.8% in this study. Furthermore, USPT enhanced specimens by work hardening. The microstructure of the peened zone was improved; moreover, the distribution of the precipitates and grains presented an apparent orientation.

第59届国际技术史学会(SHOT)年会综述

2016年6月22日-26日,国际技术史学会（Society for the History of Technology,SHOT）第59届年会在新加坡国立大学举行。法国哲学家和科学社会学家拉图尔（Bruno Latour）、美国技术史家露丝·史瓦兹·柯望（Ruth Schwartz Cowan）和英国爱丁堡大学社会人类学教授、本届SHOT主席白馥兰（Francesca Bray）女士,分别做了主旨报告。

基于SHOT、PPF特征的遮挡目标识别研究

针对机器人无序工件分拣过程中在遮挡情况下不同外形工件识别率差异较大的问题,对全局特征描述子和局部特征描述子的描述及投票过程进行详细地分析,分别选取其中实时性较好的PPF(Point Pair Feature)和SHOT(Signature of Histograms of OrienTations)描述子在不同程度遮挡情况下使用不同外形工件进行识别实验,有针对性地对机器人无序分拣中不同外形工件适用的算法进行实验对比和总结,使在不同外形工件上的识别率达到最大化,实验结果表明:PPF全局描述子对工件点云模型的外形特征和遮挡较为敏感,特征不明显工件的识别率为0%,对于外形特征明显、无遮挡的点云模型工件识别速度较快(1 s内)且准确率较高,SHOT局部描述子对遮挡的鲁棒性较强,并且对外形特征不明显工件有一定的识别能力,特征明显与特征不明显工件的识别率均保持在90%以上。

技术史学会(SHOT)年会信息统计分析及启示:2000~2019年

以技术史学会(SHOT)2000~2019年年会日程信息为主要数据源,对会议基本信息进行梳理统计,包括对学者、所属机构和国家、担任重要角色次数进行排序,运用共现方法和聚类分析展示参会者及其所在机构和国家组成的网络,对标题进行词频和时段统计,以及通过对比方式量化显示中国大陆学者和学术机构在年会中的参与情况。统计结果显示了技术史学会年会逐渐增加的规模、年会网络中日趋紧密的学者社区及参会机构存在历时性变化、各国参与程度分组后逐渐递减、会议重视现当代议题等特点,为中国技术史学界的未来发展提供借鉴意义。

基于SHOT特征描述子的自动提取球形标靶方法研究

针对复杂场景下的三维激光点云球形标靶精确自动化提取问题,提出了一种基于SHOT特征的自动精确提取球形标靶的方法。该方法设计了粗提取和精提取处理过程,粗提取过程首先采用SHOT特征描述子提取场景内全部的球形标靶点云;其次,利用欧氏聚类分割球形标靶点云,并采用最小二乘方法计算球形标靶的粗略参数。精提取过程依据迭代最小二乘方法和法向滤波剔除非球面点,得到球形标靶点云和精确的球形标靶参数。设计了含有4个球形标靶的实验场景,使用德国Z+F Image 5016扫描仪进行场景数据采集,自动提取得到实验场景中的球形标靶点云和球形标靶参数。结果表明,在10 m范围内,该方法自动提取的球形标靶半径中误差为0.25~0.33 mm,较人工提取球形标靶点云的半径中误差减小0.02~0.06 mm,较基于微分方法减少0.01~0.09 mm;该方法能够得到较高的球形标靶定位精度和稳健地去除场景点云中的噪声,可在30 s内完成百万级点云球形标靶的自动提取任务。

Numerical Calculation and Experimental Research on Residual Stresses in Precipitation-hardening Layer of NAK80 Steel for Shot Peening

Shot peening can improve fatigue strength of materials by creating compressive residual stress field in their surface layers,and offers a protection against crack initiation and propagation,corrosion,etc.And fatigue fracture and stress corrosion cracking of NAK80 steel parts are improved effectively.Currently there lacks in-depth research in which the beneficial effect of the residual stress may be offset by the surface damage associated with shot peening,especially in terms of the research on the effective control of shot peening intensity.In order to obtain the surface residual stress field of NAK80 steel after shot peening,the samples are shot peened by pneumatic shot peening machine with different rules.The residual stress in the precipitation-hardening layer of NAK80 steel is measured before and after a shot peening treatment by X-ray diffraction method.In order to obtain true residual stress field,integral compensation method is used to correct results.By setting up analytical model of the residual stress in the process of shot peening,the surface residual stress is calculated after shot peening,and mentioning the reason of errors occurred between calculated and experimental residual stresses,which is mainly caused by the measurement error of the shoot arc height.At the same time,micro hardness,microstructure and roughness in the precipitation-hardening layer of NAK80 steel before and after shot peening were measured and surveyed in order to obtain the relation between shot peening strength and surface quality in the precipitation-hardening layer.The results show that the surface quality of NAK80 steel is significantly improved by shot peening process.The over peening effect is produced when the shot peening intensity is too high,it is disadvantageous to improve sample＇s surface integrity,and leading to reduce the fatigue life.When arc high value of optimal shot peening is 0.40 mm,the surface quality is the best,and the depth of residual stress in the precipitation-hardening layer reaches to about 450 μm.Numerical calculation is very useful to define the process parameters when a specific residual stress profile is intended,either to quantify the benefits on a specific property like fatigue life or to help on modeling a forming process like shot peen forming.In particular,the proposed parameter optimization in the progress of shot peening and effective control of the surface texture provide new rules for the quantitative evaluations of shot peening surface modification of NAK80 steel.

基于one-shot学习的小样本植物病害识别

针对植物病害小样本问题提出一种基于one-shot学习的植物病害识别方法。以公开数据集PlantVillage中8类样本数量较少的植物病害图像作为识别对象,使用焦点损失函数(focal loss,FL)训练基于关系网络的植物病害分类器。训练过程中,调整FL超参数使模型聚焦于困难样本,从而提高植物病害识别精确率。结果表明:该方法在5-way、1-shot任务中识别精确率达到89.90%,相比原始关系网络模型精确率提高了4.69个百分点。同时,与匹配网络和迁移学习相比,改进后的方法在实验数据集上识别精确率分别提高了25.02个百分点和41.90个百分点。

Simulation on Residual Stress of Shot Peening Based on a Symmetrical Cell Model

The symmetrical cell model is widely used to study the residual stress induced by shot peening. However, the correlation between the predicted residual stresses and the shot peening coverage, which is a big challenge for the researchers of the symmetrical cell model, is still not established. Based on the dynamic stresses and the residual stresses outputted from the symmetrical cell model, the residual stresses corresponding to full coverage are evalu- ated by normal distribution analysis. The predicted nodal dynamic stresses with respect to four corner points indicate that the equi-biaxial stress state exists only for the first shot impact. Along with the increase of shot number, the interactions of multiple shot impacts make the fluctuation of the nodal dynamic stresses about an almost identical value more and more obvious. The mean values and standard deviations of the residual stresses gradually tend to be stable with the increase of the number of shot peening series. The mean values at each corner point are almost the same after the third peening series, which means that an equi-biaxial stress state corresponding to the full coverage of shot peening is achieved. Therefore, the mean values of the nodal residual stresses with respect to a specific transverse cross-section below the peened surface can be used to correlate the measured data by X-ray. The predicted residual stress profile agrees with the experimental results very well under 200% peening coverage. An effective correlation method is proposed for the nodal residual stresses predicted by the symmetrical cell model and the shot peening coverage.