1. These loads are present at infrequent intervals during plant operation. e, g. earthquake, wind, etc. 偶然载荷在装置运行期间内是偶尔出现的载荷，如地震、风载荷等。
2. Rubella is an important childhood disease that was historically widespread but is now very infrequent. 风疹是儿童期疾病中重要一员，在既往很流行，但现在发作很少。
3. Although menus are not used as frequently as toolbar controls, they are still used very often, particularly by new or infrequent users. 尽管菜单使用频率不如工具栏控件高，但它仍然是我们经常要用到的，特别是新手或者生疏用户。
英英解释
adj.
1. not frequent; not occurring regularly or at short intervals
