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The rapid development of air filters is closely related to the development of military industry and electronic industry. In the first world war, the use of various chemical agents, asbestos fibre filter paper as the smoke filter layer of military gas masks came into being. The glass fiber filter medium is used in air filtration to obtain a patent in the United States in October 1940. In the 1950s, the United States studied the production process of glass fiber filter paper, and the air filter was improved and developed. In the 1960s, HEPA filters came out; In the 1970s, the filter paper of fine glass fiber was used as the HEPA filter of filter medium, and the filtration efficiency of particle size of 013 micron particle diameter was 99.9998%. Since the eighty s, with the emergence of new test method, use evaluation to improve and to improve the filtering performance requirements, found the HEPA filter there is a serious problem, and he had a higher ULPA filter performance. Countries are still working on it and expect more advanced air filters soon
"Okay, I'll go." I took the potions of the three patients in bed of six, seven and eight, and hurried to the ward in front of the family. Put the potions one by one on the bed number and name, keep the infusion smooth, and then explain to the patient's family. "Six bed zhang big ye, you last night diarrhea, now dozen of medicine mixed with potassium chloride solution, drop number control at 30 droplet each minute, you can't go to disorderly to adjust the number of droplet yourself. If you play fast, you will not only feel the pain in the needle, but you will also be killed. Please feel free to tell us any
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