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Originally the word was an abbreviation of, and synonymous to, popular music, but developed around 1954 expressing a specific musical category. The stylistic origins of pop music is folk,jazz,R&B,rock and roll,traditional pop music.The typical instruments are guitar,bass guitar,drum kit and keyboard.The cultural origins go as far back to 1950's in the United States.It is popular worldwide since 1960s.
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
Depth indication: you can tell which metal objects detected are buried in depth;
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