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( 4 ) whereV is the probe potential with respect to the potential of plasma V = 0 , \ sqrt is the lowest electron velocity value at which the electron still could reach the probe surface charged to the potential V , \ zeta is the upper limit of the angle \ vartheta at which the electron having initial velocity v can still reach the probe surface with a zero-value of its velocity at this surface .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities:  
Answer:
 None