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In contrast to the standard objective function , a local rather than a global volume constraint was employed in both studies , meaning the density of the neighbouring elements was limited in a predefined radius , controlling the porosity locally .
 concept or principle: standard; process parameter: volume constraint; machanical property: density; material: elements; machanical property: porosity
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: standard; process parameter: volume constraint; machanical property: density; material: elements; machanical property: porosity