摘要 ：

焊接区的视觉图像含有丰富的熔池成形和焊缝成形信息，然而，由于焊接区的状态复杂、干扰因素众多，图像处理算法设计非常困难，很难实现工程化应用。利用深度学习技术中的卷积神经网络（VGG网络）实现了薄板TIG焊的熔透状态的检测。首先采用VGG网络构建了从熔池反面视觉图像判断熔透状态的模型，实现了未熔透、熔透和烧穿的可靠识别，准确率可达97.2%；在此基础上，又采用SSD网络构建了熔透状态下熔宽的检测模型，实现了反面熔宽的准确测量。此外，采用数据增强的方法模拟了不同的检测条件，使模型的适应性达到了工程化水平。同时构建了从正面熔池预测反面熔透的网络模型，解决无法直接从反面判断的情况，模型的预测准确率为96...

关键词 ：

卷积神经网络 熔池检测 数据增强 SSD网络

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利用超声辅助瞬态液相连接（超声-TLP）对Cu/Sn/Cu三明治结构进行钎焊试验，超声波的频率和功率分别为600 W、20 k Hz，焊接时加热温度为280℃，施加压力为0.06 MPa。在施加超声20 s后获得了全Cu_3Sn焊点，相比于传统TLP钎焊，大幅度提高了焊接效率；钎焊过程中，Cu_3Sn呈锯齿状，焊缝中Cu_6Sn_5为棒状或条状，最终转变成全Cu_3Sn焊点，且Cu_3Sn晶粒呈现出等轴晶形态。通过超声-TLP制备的全金属间化合物（IMC）焊点具有均匀的力学性能，其中Cu_3Sn相的杨氏模量和硬度分别为129.183、4.861GPa,Cu_6Sn_5相的杨氏模量和硬度分别为1...

关键词 ：

全Cu_3Sn焊点 剪切强度 超声-TLP 金属间化合物

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The crystal structures, stability, mechanical behaviors, thermodynamic properties and electronic structures of Al2Si2La and Al2Si2Pr compounds have been investigated by means of first-principles calculations. It is revealed from formation enthalpies that Al2Si2La exhibit much more thermodynamically stability. According to the results of elastic constants, Al2Si2Pr has stronger incompressibility, stronger shape deformation resistance and higher stiffness. It can be concluded from Debye temperature and minimum thermal conductivity that Al2Si2Pr and Al2Si2La exhibit nearly the same thermal conductivity. Electronic structures results demonstrate that the Al-Si bonds in Al2Si2La and Al2Si2Pr are attributed to the hybridization of Al 3s state, Al 3p state and Si 3p state, while RE-Si bonds are the contribution of Si 3p state and La 5d or Pr 4f state in Al2Si2La and Al2Si2Pr, respectively.

关键词 ：

Electronic structure Debye temperature Thermodynamic First-principles calculations Formation enthalpy Mechanical property

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The concentration of cell-free fetal DNA fragments should be detected before noninvasive prenatal testing (NIPT). The fetal DNA molecules have significant clinical potential in determining the overall performance of NIPT and clinical interpretation. It is important to measure fetal DNA fraction before NIPT. However, there is still little research on how to calculate the concentration of female fetuses. Two estimation approaches were proposed to calculate fetal DNA fraction, including the fragments size-based approach, aneuploid-based approach, which are all approaches based on chromosome segments. Based on high-throughput sequencing data, two approaches to calculate the DNA fraction of male fetuses were tested and obtained the experiment values, which were close to the actual values. The correlation coefficient of fragments size-based approach was 0.9243 (P < 0.0001) and the aneuploid-based approach reached 0.9339 (P < 0.0001). We calculated the concentration of female fetuses and obtained remarkable experimental results. We came up with two approaches for calculating the fetal DNA fraction of female fetuses. It provides an important theoretical basis for the detection of female fetal concentration in future clinical diagnosis.

关键词 ：

Female fetus Fetal DNA fraction Cell-free fetal DNA Noninvasive prenatal testing

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Nano-zero-valent iron (nZVI), as a typical nano-material, has been recently used in wastewater treatment and combination with bioreactors. Using nZVI coupled denitrification system research the effect and influence of nZVI enhanced denitrification sludge on the degradation of toxic compounds and system performance. The nZVI coupled denitrification system showed better resistance to 2,6-DCP impact, and the concentrations of effluent NO2- and NO3- were below 2.0 mg/L. At the same time, the addition of nZVI enabled the denitrification system to quickly adapt to the toxic environment of 2,6-DCP within 15 days, and the degradation efficiency of 2,6-DCP reached 99.9%. The released SMP reduced after nZVI coupled with denitrification sludge in 2,6-DCP environment, which could improve the effluent water quality. Nuclear magnetic resonance spectroscopy showed that the addition of nZVI would change the structure of EPS in denitrification sludge. After 90 days of operation, the dominant bacteria in the denitrifying sludge have undergone great changes. Moreover, Thauera was responsible as the dominant bacteria for degrading 2,6-DCP in the denitrification system. The increased in the proportion of functional bacteria with nitrate_reduction, nitrogen_respiration, nitrate_respiration and nitrite_respiration in the presence of NZVI further reveals the mechanism of enhanced denitrification.

关键词 ：

2,6-dichlorophenol Denitrification Microbial structure Molecular weight Nano-zero-valent iron

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In China, rapid and continuing infrastructure growth will significantly affect the feasibility of achieving CO2 emission reduction targets. It is uncertain whether the current infrastructure designs are consistent with the national emission targets of China, consequently posing a threat to the national commitment to reaching carbon neutrality. To illustrate the gap in achieving the emission targets with respect to bridges, we present carbon intensity reduction targets relevant to bridges by 2040. By exploring three policy-economic scenarios that combine with CO2 emission reduction policy scenarios of the International Energy Agency and shared socioeconomic pathways, we assess the adaptability of the bridge designs to short-, medium- and long-term carbon intensity targets. We propose a new sustainability design approach based on a bridge big data set that integrates reliability, environmental impacts, and cost. We show that, under the current policy-economic scenario, more than 50% of code-based bridges would meet the five-year CO2 emission target, whereas only one in ten thousand could meet the ten-year target under the new policy-economic scenario. Under the sustainable development policy-economic scenario, none of the bridge designs would meet the carbon reduction targets over the next 20 years. Our findings highlight that the bridges in China need to be duly considered in setting CO2 reduction targets, and in the national move toward zero carbon, careful consideration should be given to implementing our proposed bridge sustainability design.

关键词 ：

Big data method Bridge sustainability CO2 emission target Policy scenario Reduction gap assessment Sustainability design

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The oil-based Nd-Fe-B sludge waste was directly recycled to single-phase Nd2Fe14B powders via the combination of purification and modified Ca-reduction reaction method. The impurities and organics in the purified Nd-Fe-B sludge waste were greatly reduced, reducing calcium consumption in the subsequent reduction and diffusion (RD) process, thereby reducing the cost. By further optimizing the Ca-reduction diffusion parameters, especially the mass ratio of CaCl2 and KCl, where the liquid CaCl2, along with the gaseous KCl provide conditions for sufficient and uniform Ca-reduction reaction, high-property Nd-Fe-B magnetic powders with good dispersion, uniform particle sizes, and excellent orientation, were successfully obtained. Using the mixed diffusion medium of CaCl2 and KCl with a mass ratio of 1:1, the room-temperature magnetization of the recycled Nd-Fe-B powders was increased to 157 emu/g at 3 T-magnetic field, which was about 28 % higher than that of the original sludge. The contents of carbon, hydrogen, and oxygen in the recycled magnetic powders were significantly reduced from 6.8, 1.8, and 5.9 wt% to 0.1, 0.19, and 0.56 wt%, respectively. In addition, the uniform grain size with X-50 = 3.6 mu m and good distribution greatly improved the orientation, which can be beneficial to the preparation of the bonded or sintered Nd-Fe-B based magnets. The reasons that CaCl2-KCl mixed diffusion medium can lead to well-dispersed, uniform recycled powder with high magnetization arise from a combination of factors for improving the liquid phase reaction environment and the gaseous KCl to prevent agglomeration and inhibit particles merging or growth.

关键词 ：

Ca-reduction reaction Nd-Fe-B sludge waste Purification Recycling

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Recently, with the deterioration of the environment, increasing companies choose horizontal cooperation to achieve the goal of reducing environmental pollution and cost in the urban distribution industry. However, companies worry that the business information is leaked in the process of horizontal cooperation. This kind of mistrust often leads to the failure of horizontal cooperation. The emergence of blockchain technology has become a great means to resolve trust problem between partners, which ensures data sharing and trust through peer-to-peer, consensus mechanism and encryption technology. In response, this study proposes architecture of blockchain-based urban distribution system for horizontal cooperation that analyzes the components and layers of the urban distribution. Meanwhile, a smart contract, the innovative applications of blockchain, is designed to match the resource of supply and demand to design the distribution routes in the urban distribution system. To achieve the above goal, an open vehicle routing model of urban distribution taking into account environmental pollution factors is developed as the mathematical logic of smart contract, which aims at the lowest total cost including fixed, fuel, penalty, carbon emission and pollutant emission costs. Furthermore, the genetic algorithm is developed to support the implementation of smart contract, and the effectiveness of the smart contract is verified through a real case. This study narrows the knowledge gap in applying blockchain technology to urban distribution, and has brought contributions to the fields of blockchain and urban distribution. Finally, the limitation and future research direction are discussed.

关键词 ：

Blockchain Horizontal cooperation Smart contract Urban distribution Vehicle routing

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A large-scale 3D combined geomechanical model test is conducted in this study to investigate the mechanical characteristics for linings of asymmetrically closely-spaced twin-tunnels constructed in sandy ground. A series of experimental results (i.e., excavation and overloading) effectively reveal the mechanical features of the linings and the stress release and displacement characteristics of the sandy ground for asymmetrical twin-tunnels during the excavation and overloading under the condition of great buried depth (vertical stress) and high stress coefficient (the ratio of lateral to vertical stress). Afterward, numerical analyses are conducted by a finite difference program FLAC3D to verify experimental results. The influences of construction sequence, stress coefficient, clear distance and lining stiffness on mechanical behaviors of linings and stratum are discussed in some details. The experimental results show that during the excavation of the asymmetrically closely-spaced twin-tunnels, the linings are in a state of compression. The lining of the smaller diameter tunnel which excavated later is susceptible to bias pressure. The bending moment located on the lateral side of the larger diameter tunnel close to the smaller diameter tunnel decrease when the smaller diameter tunnel is excavated. The change of stress release direction in the middle soil pillar is the main reason that results in the change of stress state in linings. The overloading process only causes the bending moments increasing continuously, but not affect the basic distribution patterns in linings. Numerical results indicate that if the smaller diameter tunnel is excavated first, the continuous tunneling of the larger diameter tunnel will cause sharp changes in lining moment of smaller diameter tunnel, but it will not cause serious adverse effects on the existing tunnel lining (larger diameter tunnel) if the larger diameter tunnel is excavated first.

关键词 ：

Asymmetrically closely-spaced twin-tunnels Geomechanical model test Linings Middle soil pillar Numerical simulation

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Pedestal looseness and supporting stiffness nonlinearities usually occur in rotating machines. To enhance the robustness and accurately forecast the nonlinear behaviors of rotor systems, these two kinds of common nonlinearities should be considered so that to meet the requirements of the dynamical design of a multi-disk rotor system. In this paper, the rotor system model with cubic supporting stiffness and looseness fault is established by the Lagrange method. The harmonic balance (HB) and Runge-Kutta (RK) methods are used to solve the dynamic response of the double disk rotor system, and the accuracy of the HB method is justified in comparison to the RK method. The bifurcation diagram, time history, frequency spectrum, phase portrait and Poincare map are provided to discuss the individual and coupling effects of these two nonlinearities on the transient and steady-state response. The obtained experimental results indicate that the proposed model can capture the main nonlinear behaviors of looseness fault and nonlinear supporting stiffness, verifying the accuracy of theoretical and numerical results.

关键词 ：

Dynamic behaviors Geometric nonlinearity Looseness fault Rotor system

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