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Despite broad research interest in this field , it has remained challenging to measure warpage in general as well as RS distributions in situ , which has obfuscated the mechanisms of stress formation during the printing process .
 research, warpage, as, as, distributions, stress, printing process
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 research, warpage, as, as, distributions, stress, printing process