Additively manufactured respirators: quantifying particle transmission and identifying system-level challenges for improving filtration efficiency

The COVID-19 pandemic has disrupted the supply chain for personal protective equipment (PPE) for medical professionals, including N95-type respiratory protective masks. To address this shortage, many have looked to the agility and accessibility of additive manufacturing (AM) systems to provide a democratized, decentralized solution to producing respirators with equivalent protection for last-resort measures. However, there are concerns about the viability and safety in deploying this localized download, print, and wear strategy due to a lack of commensurate quality assurance processes. Many open-source respirator designs for AM indicate that they do not provide N95-equivalent protection (filtering 95% of SARS-CoV-2 particles) because they have either not passed aerosol generation tests or not been tested. Few studies have quantified particle transmission through respirator designs outside of the filter medium. This is concerning because several polymer-based AM processes produce porous parts, and inherent process variation between printers and materials also threaten the integrity of tolerances and seals within the printed respirator assembly. No study has isolated these failure mechanisms specifically for respirators. The goal of this paper is to measure particle transmission through printed respirators of different designs, materials, and AM processes. The authors compare the performance of printed respirators to N95 respirators and cloth masks. Respirators in this study printed using desktop- and industrial-scale fused filament fabrication processes and industrial-scale powder bed fusion processes were not sufficiently reliable for widespread distribution and local production of N95-type respiratory protection. Even while assuming a perfect seal between the respirator and the user’s face, although a few respirators provided >90% efficiency at the 100−300 nm particle range, almost all printed respirators provided <60% filtration efficiency. Post-processing procedures including cleaning, sealing surfaces, and reinforcing the filter cap seal generally improved performance, but the printed respirators showed similar performance to various cloth masks. The authors further explore the process-driven aspects leading to low filtration efficiency. Although the design/printer/material combination dictates the AM respirator performance, the identified failure modes originate from system-level constraints and are therefore generalizable across multiple AM processes. Quantifying the limitations of AM in producing N95-type respiratory protective masks advances understanding of AM systems toward the development of better part and machine designs to meet the needs of reliable, functional, end-use parts.     

Effects of Sm-doping on microstructure,magnetic and microwave absorption properties of BiFeO_3

In this paper,polycrystalline samples of Bi_(1-x)Sm_xFeO~3(x=0,0.05,0.1,0.15) were successfully synthesized by sol-gel method.The effects of Sm concentration on the crystal structure,morphology,chemical states,magnetic properties and microwave absorption performance were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),a vibrating sample magnetometer(VSM) and a Vector network analyzer(VNA),respectively.The results show that the rare earth Sm doping causes the crystal structure to change.When x≤0.1,Bi_(1-x)Sm_xFeO_3 is the distorted rhombohedral structure with space group R3 c.With the increase of Sm doping amount to x=0.15,the phase structure of Bi_(1-x)Sm_xFeO_3 changes from rhombohedral structure to cubic structure with the space group Pm3 m.The particle size decreases with the increase of the Sm doping amount.The analysis results show that Sm doping can effectively reduce the oxygen vacancies and significantly improve its magnetic properties.The results exhibit that moderately doped rare earth Sm element can effectively improve microwave absorption properties of Bi_(1-x)Sm_xFeO_3 powders.When Sm doping amount of x is 0.1,the Bi_(0.9)Sm_(0.1) FeO_3 compound has good microwave absorption performance,and the minimum reflection loss value of Bi_(0.9)Sm_(0.1)FeO_3 powder reaches about-32.9 dB at11.7 GHz,and its effective absorption bandwidth(RL -10 dB) is 2.6 GHz with the optimal matching thickness of 2.0 mm.     

基于密集神经网络的灰度图像着色算法

针对在灰度图像着色领域中，传统算法信息提取率不高、着色效果不理想的问题，提出了基于密集神经网络的灰度图像着色算法，以实现改善着色效果，让人眼更好地观察图片信息的目的。利用密集神经网络的信息提取高效性，构建并训练了一个端到端的深度学习模型，对图像中的各类信息及特征进行提取。训练网络时与原图像进行对比，以逐渐减小网络输出结果的信息、分类等各类型的损失。训练完成后，只需向网络输入一张灰度图片，即可生成一张颜色饱满、鲜明逼真的彩色图片。实验结果表明，引入密集网络后，可有效改善着色过程中的漏色、细节信息损失、对比度低等问题，所提算法着色效果较基于VGG网络及U-Net、双流网络结构、残差网络（ResNet）等性能优异的先进着色算法而言取得了显著的改进。     

基于声发射和高斯混合模型的灰岩破裂特征识别研究

通过单轴压缩条件下灰岩破裂过程的声发射试验研究,利用高斯混合模型(GMM)对加载过程声发射信号波形特征进行深入分析,探索性识别灰岩破裂失稳过程的裂纹模式及其前兆特征。分析结果表明,灰岩在单轴加载过程中先后主要存在张拉和剪切两种破裂模式。其中,张拉破裂的声发射信号波形特征在AF-RA坐标空间呈现低A_F值、高R_A值分布;剪切破裂的声发射信号波形特征在AF-RA坐标空间呈现低R_A值、高A_F值,且随着应力的增加分布中心向A_F轴靠拢。GMM分析结果揭示了灰岩在整个应力加载过程中以张拉裂纹为主,在加载前中期几乎全为张拉裂纹,临近破坏阶段过渡到剪切破坏为主。剪切裂纹所占比例的最大值出现在(0.8～0.9)σ_c阶段,也是AF-RA坐标轴分布呈现最大A_F值时。研究结果可为预测早期灰岩破裂失稳提供参考,同时为深入研究识别岩石破裂失稳前兆信号特征提供了一种分析方法。     

阳泉矿区煤样不同应力状态下声发射特性分析

为探索原煤煤样的力学性能和不同应力状态下的声发射活动特性,对阳泉矿区新景矿、平舒矿主采煤层的煤样进行了单轴、三轴压缩和巴西劈裂的声发射试验,分析了2种煤样力学性能及不同加载过程的声发射活动规律。证明通过监测声发射(微震)活动分析煤样或煤岩体内部破坏状态是一种方便有效的手段。     

往复式活塞压缩机中间喷液制冷系统的(火用)分析

通过对往复式活塞压缩机进行改造，在单级活塞压缩系统的基础上搭建了一种中间喷液冷却的准两级压缩系统并在蒸发温度为-20 ℃的工况下进行实验测量，根据实验数据对单级活塞压缩系统和新型中间喷液冷却活塞压缩系统的COP、〖HT5”，7”〗火〖KG-*3〗用〖HT5”〗损失和〖HT5”，7”〗火〖KG-*3〗用〖HT5”〗效率进行计算。结果表明：加入中间喷液冷却系统后，系统的COP由1.27提升至1.36，单位制冷量由155.1 kJ/kg提升至176.7 kJ/kg；单级活塞压缩系统〖HT5”，7”〗火〖KG-*3〗用〖HT5”〗损失较大的部分是压缩机和膨胀阀，分别占压缩机输入〖HT5”，7”〗火〖KG-*3〗用〖HT5”〗的16.2%和14.8%，加入中间喷液冷却系统后压缩机部分的〖HT5”，7”〗火〖KG-*3〗用〖HT5”〗损失明显降低，仅占压缩机输入〖HT5”，7”〗火〖KG-*3〗用〖HT5”〗的3.6%，冷凝器及膨胀阀的〖HT5”，7”〗火〖KG-*3〗用〖HT5”〗损比也有所下降。     

High-resolution FIB-TEM-STEM structural characterization of grain boundaries in the high dielectric constant perovskite CaCu3Ti4O12

In this work, the grain boundaries composition of the polycrystalline CaCu₃Ti₄O₁₂ (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu₂O and the metastable phase Cu₃TiO_4.     

Functional organisation of the endomembrane network in the digestive gland of the Venus flytrap: revisiting an old story with a new microscopy toolbox

Up-to-date imaging approaches were used to address the spatiotemporal organisation of the endomembrane system in secretory cells of Dionaea muscipula. Different ‘slice and view’ methodologies were performed on resin-embedded samples to finally achieve a 3D reconstruction of the cell architecture, using ultrastructural tomography, array tomography, serial block face-scanning electron microscopy (SBF-SEM), correlation, and volume rendering at the light microscopy level. Observations of cryo-fixed samples by high-pressure freezing revealed changes of the endomembrane system that occur after trap activation and prey digestion. They provide evidence for an original strategy that adapts the secretory machinery to a specific and unique case of stimulated exocytosis in plant cells. A first secretion peak is part of a rapid response to deliver digestive fluids to the cell surface, which delivers the needed stock of digestive materials ‘on site’. The second peak of activity could then be associated with the reconstruction of the Golgi apparatus (GA), endoplasmic reticulum (ER) and vacuolar machinery, in order to prepare for a subsequent round of prey capture. Tubular continuum between ER and Golgi stacks observed on ZIO-impregnated tissues may correspond to an efficient transfer mechanism for lipids and/or proteins, especially for use in rapidly resetting the molecular GA machinery. The occurrence of one vacuolar continuum may permit continuous adjustment of cell homeostasy. The subcellular features of the secretory cells of Dionaea muscipula outline key innovations in the organisation of plant cell compartmentalisation that are used to cope with specific cell needs such as the full use of the GA as a protein factory, and the ability to create protein reservoirs in the periplasmic space. Shape-derived forces of the pleiomorphic vacuole may act as signals to accompany the sorting and entering flows of the cell.     

基于等切共轭的弧齿锥齿轮差曲面建立与解析

对弧齿锥齿轮提出了一种新的共轭求解方法，来更方便地求解共轭小轮的齿面方程，在此基础上进行了齿面接触分析。在分析过程中提出了一种新的ease-off差曲面计算方法，即用对应点的转角误差替代直线误差进行差曲面求解，使得传动误差解析、齿面修形量的确定更为直观和准确。提取了ease-off曲面上的差曲线，以方便地确定出接触路径和边缘接触点。根据全程差曲线得到了齿面接触印痕分布情况。