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In order to gain a better understanding of the physics of keV cluster bombardment of surfaces and nanoparticles ( NPs ) , the effects of the atomic masses of the projectile and of the target on the energy deposition and induced sputtering have been studied by means of molecular dynamics simulations .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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