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In January 2011 , research by the American Astronomical Society discovered antimatter ( positrons ) originating above thunderstorm clouds ; positrons are produced in gamma-ray flashes created by electrons accelerated by strong electric fields in the clouds .
 American Astronomical Society
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 American Astronomical Society