RAFM钢TIG焊和电子束焊疲劳性能实验和分析模拟

利用ANSYS 对低活化铁素体马氏体(RAFM)钢进行非熔化极气体保护焊(TIG 焊)与电子束焊的抗疲劳模拟分析，再利用SDS200 电液伺服疲劳试验机对TIG 焊和电子束焊的两种RAFM 钢试件进行实验。通过施加相同梯度负荷对TIG 焊和电子束焊试件进行焊缝的疲劳性能实验。与实验结果对比分析，结果显示电子束焊优于 TIG 焊，但在一定负载下可以用TIG 焊代替电子束焊。     

Characterization of moisture mobility and diffusion in fresh tobacco leaves during drying by the TG–NMR analysis

This paper presents the stabilization effects of inorganic filler, cerium-doped lead zirconate titanate on high-density polyethylene. The filler was loaded in two concentrations (1 and 3 wt%). The dopant contents in PbZrO₃ were 0, 0.05, 0.075, 0.1 and 0.125 mol%. The degradation of hybrid samples was accomplished by γ-irradiation at various doses up to 200 kGy. The isothermal and nonisothermal chemiluminescence (CL) and thermal analysis (TG-DSC) were applied for the thermal stability characterization of modified HDPE samples. The mechanistic considerations and radiochemical consequences caused by the variation of filler concentration and doping level are discussed. The results demonstrate that the filler acts efficiently as stabilizer at low concentration of additive when the lower filler amount is present. The start of degradation precedes melting by four processes through which the chain scission and radical oxidation represent the essential degradation stage. The filler concentration influences the degradation due to the intimate interaction between solid-state defects and free radicals. The polymer protection against oxidation is based on the scavenging of radicals by the doping elements, that is, they trap and block radicals delaying material aging. The present results open a new perspective in the quality amelioration of organic products toward high durability.

     

基于毛竹叶片理化参数的刚竹毒蛾危害检测研究

虫害检测算法研究是开展虫害快速、准确监测，制定精准森防检疫措施的重要基础。以毛竹叶片为研究尺度，基于刚竹毒蛾危害下的寄主外部形态与内部生理现象总结，选择并实测叶损量LL、相对叶绿素含量RCC、相对含水量RWC、原始光谱的733.66~898.56 nm值(ρ_{733.66~898.56})、一阶微分光谱的562.95~585.25 nm值(ρ′_{562.95~585.25})与706.18~725.41 nm值(ρ′_{706.18~725.41})等理化参数，随机划分实验组(63组)和验证组(37组)并设计5次重复实验；分别运用Fisher判别分析、BP神经网络、随机森林等三种方法建立刚竹毒蛾危害等级的检测模型，从检测精度、Kappa系数及R2等指标对模型的检测效果予以分析和比较。结果显示，Fisher判别分析、BP神经网络、随机森林的检测精度分别为69.19%，65.41%，83.78%，Kappa系数分别为0.576 9，0.532 4和0.778 8，R2分别为0.722 2，0.582 6和0.870 9，总体而言，三种方法均具备刚竹毒蛾危害的检测能力，随机森林的检测效果最优，Fisher判别分析次之，再次为BP神经网络；从分等级来看，随机森林的检测精度亦优于Fisher判别分析与BP神经网络，但3种方法对中度危害等级的检测精度均有所不足。该成果可为刚竹毒蛾危害及其他病虫害检测算法的选择提供参考，并为进一步建立冠层、遥感影像像元等尺度的虫害检测模型奠定基础。     

Selective Excitation of Band Extrema in Valley Photonic Crystals

Flexible control of building blocks of photonic crystals enables achieving desirable band structures. Exploration of photonic band extrema has brought many fantastic features to design artificial optical materials, such as Brillouin‐zone‐corner extrema for valley photonic materials and zone‐center extremum for zero‐index metamaterials. However, two such kinds of extrema are always found independently in different photonic crystals. In this work, a kind of valley photonic crystals possessing both zone‐center and zone‐corner band extrema almost at the same frequency is proposed. Inspired by antennas theory, a three‐antenna array (TAA) source is devoted to individually manipulate each extremum. The correlation coefficient is given to determine the coupling efficiency between the TAA source and extrema eigenmodes. By using a source with a high correlation coefficient, these extrema bulk states are selectively excited consistent with their eigenfields. Furthermore, three control cases are shown that multiple extrema points are simultaneously excited, in order to confirm the validity of the correlation coefficient. Finally, a potential application of a beam‐steering device is proposed through selective excitation of ternary extrema. This work develops binary valley states into ternary mix states, rendering more degrees of freedom for on‐chip optical information transport, particularly for beam steering and mode division multiplexing.     

Crystal structures of silicon-rich lithium silicides at high pressure

Silicon (Si) is one of the most essential elements, as it is indispensable for modern electronic technology. The standard Si structure at ambient conditions is the cubic diamond structure, and it has an indirect band gap, which prevents it from being considered as a next-generation platform for semiconductor technologies. Therefore, the search for new allotropes of silicon has attracted great attention. Herein, first principles swarm-intelligence structure searches coupled with density-functional theory were performed to explore the stable high-pressure phases of silicon-rich lithium containing compounds, LiSi_x ($x=4\text{–}8$). The LiSi₄ stoichiometry was predicted to be stable, and it was found to assume one of the following space groups, P4/mnc, Cmmm, and C2/m within the pressure range of 0 to 50 GPa. By removing the Li atoms from these compounds, three silicon allotropes were obtained that were metastable at ambient pressures. Our work illustrates how novel silicon allotropes can be predicted using the CALYPSO method.     

Size effect of lead-free halide double perovskite on luminescence property

Lead-free halide double perovskites have gathered wide scientific interest since they are environmentally friendly and stable.However,compared to the lead perovskites,their optoelectronic properties are compromised.Herein we report a series of bulk lead-free mixed Bi-In halide double perovskites:Cs_2AgBi_(1-x)In_xCl_6(0x1).The Cs_2AgBi_(0.125)In_(0.875)Cl_6breaks the parity-forbidden transition and retains direct band gap structure,having warm-white light emission,with photoluminescence quantum efficiency(PLQE)of 70.3%,much higher than the PLQE of reported lead perovskite materials.Its exciton self-trapping dynamics is investigated.Meanwhile,the Cs_2AgBi_(0.125)In_(0.875)Cl_6nanocrystals and Cs_2AgBi_(0.125)In_(0.875)Cl_6microcrystals can be synthesized by modified hot injection and rapid cooling crystallization,respectively.The size effect of Cs_2AgBi_(0.125)In_(0.875)Cl_6is studied on the photoluminescence(PL)property.Additionally,the bulk material exhibits excellent stability on exposure to light,humidity and air for more than 3 months.It is a promising candidate as highly efficient warm white-light emitting material for road lighting.     

熔盐环境下热障涂层新材料Mg2SiO4的高温腐蚀研究

采用高温固相反应法合成了Mg2 SiO4陶瓷粉末,冷压成型后烧结成陶瓷块材.盐涂法制备V2 O5涂覆的样品,利用马弗炉在950℃空气气氛下保温不同时间.对热腐蚀后的样品进行表面形貌、截面特征的表征,并对Mg2 SiO4的高温熔盐腐蚀机制进行分析研究.结果表明:熔融的V2 O5对Mg2 SiO4陶瓷试样产生两种形式的腐蚀降解作用,即溶解-沉淀机制形成腐蚀产物Mg2 V2 O7和SiO2以及沿晶界腐蚀为主的渗透腐蚀作用.     

EAST上由垂直不稳定性引发破裂的分析与预测

从EAST 装置2016 年的放电实验中，选取了119 次等离子体破裂放电数据，分析诱发等离子体破裂的原因，发现约60%的破裂是由垂直不稳定性直接引起的，其破裂后将会产生更大的晕电流，从而产生更大的电磁应力损坏装置。对由垂直不稳定性引起的破裂(简称为VID)(72 次放电)进行了研究，建立了分别基于单变量(垂直位移)和两维变量(垂直位移、垂直位移增长率)的预测模型用于对VID 破裂的预测。离线测试表明，基于两维变量的预测模型可以在破裂发生前20ms 给出破裂预警信号，预测成功率达93%。     

基于回波平移序列的快速三维磁共振温度成像方法

高强度聚焦超声（HIFU）是一种无创的热消融疗法，为保证其安全性和有效性，需要一种精度高、速度快的测温方法在其治疗过程中对温度进行监控.基于质子共振频率位移（PRFS）的磁共振温度成像（MRT）对温度具有较高的灵敏度，且与温度具有良好的线性关系，因此常被用于引导HIFU治疗.然而在实际应用中，HIFU治疗的最大隐患在于可能造成表皮灼伤，并且灼伤区域可能与焦点区域相隔较远.因此MRT的监控范围十分重要.本文基于三维回波平移成像序列，结合可控混叠的空间并行成像技术，实现了时间分辨率为3 s的快速三维温度成像.为了验证该方法的精度，本文首先设计了仿体降温实验，利用光纤温度计验证回波平移序列测温的准确度和精确度.然后在室温条件下扫描离体猪肉组织，对比加速前后的MRT的测温精确度.在HIFU加热条件下扫描离体猪肉组织，对比加速前后的MRT的测温准确度.结果显示，本文提出的方法可以在3 s内完成三维温度精准测量，对于HIFU治疗的安全监控具有重要意义.