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Results demonstrate the effects of different material gradient patterns and different material transition lengths on the fatigue life of multi-material specimens .
 concept or principle: material gradient; material: material; machanical property: fatigue life; concept or principle: multi-material
Given options, please tell me the categories of all the listed entity words.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} 
 Entities: material gradient, material, fatigue life, multi-material 
Answer:
 concept or principle: material gradient; material: material; machanical property: fatigue life; concept or principle: multi-material