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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
When a driver is texting, her or his full focus and attention are dedicated to the phone. This attention is diverted while traffic, pedestrians and objects carry on and move past the automobile on the road. Research has proven that texting will not simply take the driver?s attention when they're engaged in the act, and also seriously impairs power they have to manage their vehicle for a number of seconds afterward while their attention must be refocused back on the road. Time lost during texting when readjusting to driving can cause serious accidents, injuries and death.
It is also known as welding long rail line, which is a kind of line that welded normal rails without rail seam. The welding rail is not less than 200 meters long, and the actual application is usually 800~1000 meters or more. The long track is laid in the specified temperature range and fixed on the pillow. The long rail ends with a rail joint, while the middle part cannot scale up and down with the temperature. Therefore, there will be a great temperature pressure in the middle of the rail during the summer, which will produce a great temperature tension in winter. The greatest pressure on the rail and tension according to the years of rail laying and the highest temperature and minimum temperature calculation, rail tracks the maximum pressure should not cause to drum up by maximum tension should not cause rail fracture
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