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As shown in 3 on topology optimization , various unit cells with maximal bulk modulus , maximal shear modulus , prescribed stiffness ratios in three directions , and functionally graded structures can be obtained through the BESO method .
 material: As; engineering feature: topology optimization; concept or principle: unit cells; machanical property: bulk modulus; machanical property: shear modulus; machanical property: stiffness; engineering feature: functionally graded structures; material: be; concept or principle: BESO method
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:
 material: As; engineering feature: topology optimization; concept or principle: unit cells; machanical property: bulk modulus; machanical property: shear modulus; machanical property: stiffness; engineering feature: functionally graded structures; material: be; concept or principle: BESO method