你说的是什么原理？
当然是利用热胀冷缩的原理啦。[{'character': '当', 'pinyin': 'dang1', 'highest pitch': 11.65, 'lowest pitch': 10.41, 'duration': 0.16, 'prosody hierarchy': 'null'}, {'character': '然', 'pinyin': 'ran2', 'highest pitch': 11.51, 'lowest pitch': 8.96, 'duration': 0.16, 'prosody hierarchy': '#1'}, {'character': '是', 'pinyin': 'shiii4', 'highest pitch': 9.51, 'lowest pitch': 8.92, 'duration': 0.14, 'prosody hierarchy': '#1'}, {'character': '利', 'pinyin': 'li4', 'highest pitch': 9.07, 'lowest pitch': 8.04, 'duration': 0.18, 'prosody hierarchy': 'null'}, {'character': '用', 'pinyin': 'iong4', 'highest pitch': 8.33, 'lowest pitch': 7.4, 'duration': 0.19, 'prosody hierarchy': '#1'}, {'character': '热', 'pinyin': 're4', 'highest pitch': 10.52, 'lowest pitch': 8.3, 'duration': 0.17, 'prosody hierarchy': 'null'}, {'character': '胀', 'pinyin': 'zhang4', 'highest pitch': 9.86, 'lowest pitch': 8.33, 'duration': 0.2, 'prosody hierarchy': '#1'}, {'character': '冷', 'pinyin': 'leng3', 'highest pitch': 8.33, 'lowest pitch': 4.91, 'duration': 0.17, 'prosody hierarchy': 'null'}, {'character': '缩', 'pinyin': 'suo1', 'highest pitch': 10.47, 'lowest pitch': 5.13, 'duration': 0.17, 'prosody hierarchy': 'null'}, {'character': '的', 'pinyin': 'de5', 'highest pitch': 10.95, 'lowest pitch': 8.28, 'duration': 0.15, 'prosody hierarchy': '#1'}, {'character': '原', 'pinyin': 'van2', 'highest pitch': 8.28, 'lowest pitch': 6.64, 'duration': 0.16, 'prosody hierarchy': 'null'}, {'character': '理', 'pinyin': 'li3', 'highest pitch': 7.51, 'lowest pitch': 5.93, 'duration': 0.17, 'prosody hierarchy': 'null'}, {'character': '啦', 'pinyin': 'la5', 'highest pitch': 7.25, 'lowest pitch': 5.92, 'duration': 0.3, 'prosody hierarchy': '#4'}]