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1.
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. 相似文献
2.
本文描述在Unix环境下开发的通用绘图软件NuSlide中的图形用户界面的设计思想和实际方法。其特点是基子面向对象的技术,提供多窗口、菜单驱动、选择面板、键盘输入等多种才法。该图形用户界面具有灵活性、可扩充性和易使用性。 相似文献
3.
主要研究了CDMA蜂窝通信系统的工作原理,且以基于IS-95标准的前向链路为主。利用MATLAB软件建立了前向链路中各器件的模块,实现了CDMA基带信号发生器,并在时域及频内进行了测量。 相似文献
4.
使用自粘性防水卷材对带钢副框的铝合金门窗窗边进行粘接,以防止雨水通过副框与墙体之间的缝隙渗漏到室内,重点介绍了详细的施工措施。 相似文献
5.
An approximate method is presented for predicting the effect of a louvered blind on the centre‐glass thermal performance of a fenestration. The method combines a one‐dimensional heat transfer model with data from a numerical simulation of the window and blind. Sample results for a blind mounted on the indoor surface of a window show the effect of blind slat angle on heat transmission. Both summer and winter conditions are considered. The results show that a louvered blind can improve the U‐value of a standard double‐glazed window by up to 37%. Also, the radiation heat exchange with the room can be dramatically reduced (by up to 60%), which will improve the level of occupant comfort. However, there was found to be a trade‐off between U‐value and occupant comfort; placing the blind closer to the window improves the U‐value, but increases the radiation heat exchange with the room. The predictions from the present simplified method compare well with results from a full two‐dimensional computational fluid dynamics solution of the conjugate blind/window interaction. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
6.
The complete verification of the timing properties of a large critical system cannot be undertaken in a single step or with
a single method. In this paper we present a process that links together a number of techniques and approaches that cover all
stages of development from requirements analysis to code testing. The key elements of the process are: a constrained form
of timed automata that uses delay and deadline to define temporal behaviour, notions of rely and guarantee to cover temporal dependencies, model checking for design verification, SPARK and Ravenscar restrictions for programming,
and scheduling and response time analysis for asserting implementation compliance. Extended examples of the use of the process
are given. 相似文献
7.
李红宇 《数字社区&智能家居》2007,(17)
介绍了在VC .net的运行环境下运用拆分窗口功能实现界面切换的步骤及具体实现方法,并给出了关键的实现函数与事例. 相似文献
8.
徐云生 《昆明理工大学学报(自然科学版)》1996,21(6):21-25
基于太阳辐射的光变特性和多层薄膜材料的变色效应,分析了新型太阳能节能窗对热候,冷候和温候空调的工作原理,重点讨论了可实现外加参量的动态调节透光性的薄膜材料的性能。 相似文献
9.
研究了在250℃、不同挤压比下挤压变形对Mg95 Zn4.3 Y0.7合金组织及性能的影响。结果表明,Mg95 Zn4.3 Y0.7经过挤压变形后,合金中晶界处的共晶相破碎,弥散分布至晶粒内部,并且晶粒显著细化。同时,随着挤压比的增大,晶粒细化程度增加,合金的力学性能单调增加。当挤压比为16时,合金晶粒尺寸为5-8μm,抗拉强度为288.9MPa,显微硬度HV值为117.8。 相似文献
10.