Nanobridged rhombic antennas supporting both dipolar and high-order plasmonic modes with spatially superimposed hotspots in the mid-infrared

Mid-infrared antennas (MIRAs) support highly-efficient optical resonance in the infrared, enabling multiple applications, such as surface-enhanced infrared abso...     

深浅特征融合的实时单目标行人跟踪

单目标行人跟踪是计算机视觉目标跟踪领域最基础、也是研究最广泛的任务之一,而目前大多数使用的相关滤波类算法和深度学习类算法则分别在跟踪精度和跟踪实时性上存在不足.针对上述问题,本文提出一种将目标图像的深浅特征融合的实时单目标行人跟踪方法.算法利用卡尔曼滤波器预测目标位置,通过计算四分颜色直方图提取目标的浅层颜色特征,并获得预测相似性以判定预测的可靠性.使用YOLOv4模型作为检测器,提取目标深度特征并分别计算运动信息和外观信息的距离度量,同时提取浅层颜色特征计算得到相似距离度量,通过特征距离度量的加权融合对检测目标进行匹配与更新.最后,利用提出的轨迹更新策略协调预测和检测的调用关系,达到准确性与实时性的平衡.算法在OTB100和LaSOT数据集上进行了测试实验,结果表明:所提算法的跟踪准确率分别达到0.581和0.453,在GPU上分别能达到33.64 FPS和35.32 FPS的跟踪速度,满足实时跟踪的要求.     

Effect of nickel content of 9Cr-1MoVNb and 12Cr-1MoVW steels on the aging and irradiation response of impact properties

Irradiating nickel-containing alloys in a mixed-spectrum reactor can simulate both transmutation helium and displacement damage expected in a fusion reactor first wall. Impact properties of 9Cr-1MoVNb and 12Cr-1MoVW steels doped with nickel were determined in the as-heat-treated, thermally aged, and irradiated conditions to determine if nickeldoping affects the behavior. The irradiation was carried out in a fast-spectrum reactor which produces only an insignificant amount of helium during irradiation, thereby evaluating the effect of nickel alone. Only limited property changes resulted from thermal aging or irradiation to 12 dpa at 450 to 550°C. Irradiation of the 12Cr-1MoVW steel at 390°C produced severe degradation of impact properties. Nickel additions affected the unirradiated material properties, but subsequent radiationinduced changes were similar. The results indicate that nickel doping and subsequent irradiation in a mixed spectrum reactor is a viable method for simulating irradiation effects in a fusion reactor first wall.     

Simulation and risk assessment of hydrogen leakage in hydrogen production container

In this paper, the hydrogen leakage and diffusion characteristics analysis and risk assessment are carried out on the container where a 2 Nm³/h alkaline hydrogen production device is located. Firstly, the transient and steady process of hydrogen leakage from hydrogen production container is analyzed. Secondly, the dynamic balance of combustible hydrogen cloud is analyzed, the concept of critical ventilation flow is put forward. It was found that in order to reduce the flammable volume by 85%, the installed ventilation can only cover the leakage flow of 1.0 Nm³/min. Finally, TNT equivalent method is used to evaluate the hazard degree of hydrogen leakage. It is found that the existed hydrogen production container ventilation device can only exhaust the hydrogen-air cloud with small flow leakage, while the accumulation of gas cloud still exists in large flow leakage. Under the critical ventilation flow, the minor injury radius can be reduced from 4.8 m to 2.78 m. The effect of critical ventilation flow was verified.     

基于UG的采煤机防爆盖板三维标注及数控工艺研究

随着三维CAD技术的发展,产品制造信息在三维模型和二维图纸之间的反复传递,严重影响了产品制造信息的正确、快速传递。基于三维产品制造信息技术,以采煤机防爆盖板为例,在UG NX10.0中建立了防爆盖板的三维模型并进行了三维标注,设计了加工工艺路线,规划了数控加工刀具轨迹,进行了加工仿真,验证了数控加工的正确性,在此基础上完成了采煤机防爆盖板的三维工艺式设计。该研究对基于模型定义的数字化设计与制造研究,实现制造业信息化具有重要意义。     

Influences of processing conditions on mechanical properties of recycled epoxy-anhydride vitrimers

The chemically crosslinked network structures make epoxies, the most common thermosets, unable or hard to be recycled, causing environmental problems and economic losses. Epoxy-based vitrimers, polymer networks deriving from epoxy resins, can be thermally malleable according to bond exchange reactions (BERs), opening the door to recycle epoxy thermosets. Here a series of experiments were carried out to study the effects of processing conditions (such as particle size distributions, temperature, time, and pressure) on recycling of an epoxy-anhydride vitrimer. Polymer powders from the epoxy-anhydride vitrimer with different size distributions were prepared and characterized, and the influence of particle size on the mechanical performance of recycled epoxy-anhydride vitrimers was investigated by dynamic mechanical analysis and uniaxial tensile test. Experimental results demonstrated that finer polymer powders can increase the contacting surfaces of recycled materials and thus result in high quality of recycled materials. In addition, the influences of other treating parameters, such as temperature, time, and pressure, were also discussed in this study. Adjusting these treating parameters can help the design of an optimized reprocessing procedure to meet practical engineering applications.     

A modified two-dimensional numerical method for prediction of outer wall temperature distribution of rectangular micro-combustors

Two-dimensional (2D) numerical models are frequently adopted to investigate combustion and thermal performances in rectangular micro-channels for micro-thermophotovoltaic and thermoelectric devices. However, large error may exist by applying a simple 2D model. In the present work, the outer wall temperature distributions predicted by 3D model and simple 2D model were compared. The results showed that the maximum relative error of the simple 2D model depends significantly on the aspect ratio (α) of the micro-channel. To be specific, the maximum relative error was >30% for α = 1 and > 10% for 2≤α ≤ 4. However, it was <5% for α ≥ 9. A new 2D model was proposed to modify the underestimated heat loss ratio. The new computational results demonstrated that the maximum relative error of α = 1 decreased to 8.07% and for micro-channels with α ≥ 2, all the maximum relative errors are <5%. In summary, the modified 2D numerical model can achieve a satisfactory prediction with low computation cost.     

A fiber fracture model for metal matrix composite monotape consolidation

The consolidation of plasma sprayed monotapes is emerging as a promising route for producing metal and intermetallic matrix composites reinforced with continuous ceramic fibers. Significant fiber fracture has been reported to accompany the consolidation of some fiber/matrix systems, particularly those with creep resistant matrices. Groves et al. [Acta metall. mater.42, 2089 (1994)] determined the predominant mechanism to be bending at monotape surface asperities and showed a strong dependence of damage upon process conditions. Here, a previous model for the densification of monotapes [Elzey and Wadley, Acta metall. mater.41, 2297 (1993)] has been used with a stochastic model of the fiber failure process to predict the evolution of fiber fracture during either hot isostatic or vacuum hot pressing. Using surface profilometer measured roughness data for the monotapes and handbook values for the mechanical properties of different matrices and fibers, this new model is used to elucidate the damage dependence on process conditions, monotape surface roughness, and the mechanical properties both of the fiber and matrix. The model is used to investigate the “processibility” of several currently important matrix and fiber systems and to identify the factors governing this. An example is also given of its use for the simulation of a representative consolidation process cycle. This approach to the analysis of a complex, nonlinear, time-varying process has resulted in a clear understanding of the causal relationships between damage and the many process, material and geometric variables of the problem and identified new strategies for its elimination.     

车桥耦合系统固有频率的研究

建立了用来计算车桥耦合系统各阶固有频率的特征值方法理论,研究了系统的各阶固有频率随车辆在桥梁上相对位置和车辆与桥梁相对刚度的变化规律,以及系统基频随车速和加速度的变化规律.数值算例结果表明,车桥耦合系统的各阶固有频率不仅与相对位置有关,而且与相对刚度有关,并且呈现一定的规律性,车速和加速度对耦合系统的基频也有一点程度的影响,若用桥梁的固有频率取代耦合系统的固有频率将会产生较大误差.