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In recent work using topology optimization techniques , an optimized light-weight structure for an airplane wing was demonstrated through simulation and optimization , with the obtained structure having a strong resemblance to the structure of bird wing bones , i.e. , a solid shell and connecting rods at angles inside the hollow structure .
 engineering feature: topology optimization; machanical property: light-weight; application: airplane wing; enabling technology: simulation; concept or principle: optimization; concept or principle: structure; concept or principle: structure; machine or equipment: shell; concept or principle: structure
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:
 engineering feature: topology optimization; machanical property: light-weight; application: airplane wing; enabling technology: simulation; concept or principle: optimization; concept or principle: structure; concept or principle: structure; machine or equipment: shell; concept or principle: structure