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The study reports some process challenges that need to be overcome , for instance , the thermally induced stresses , caused by the deposition of the new cold powder layers on top of the preheated ceramic , and the surface roughness values .
 concept or principle: process; material: be; concept or principle: deposition; material: cold powder layers; material: ceramic; machanical property: surface roughness
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: 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:
 concept or principle: process; material: be; concept or principle: deposition; material: cold powder layers; material: ceramic; machanical property: surface roughness