The ratio of the low frequency to high frequency components in HRV power spectrum(LF/HF) fluctuates with the change in the sleep stages.
HRV频谱中低频和高频成分的比值（LF/HF）随着睡眠深度的变化而波动。
In terms of operation frequency, RFID systems can be divided into four categories: low frequency (LF), high frequency (HF), ultra high frequency (UHF), and microwave.
根据工作频率来分，RFID系统可以分为低频，高频，超高频和微波四个波段。
The present paper gives an analysis of the low frequency (LF) vortex and divergent circulation systems and their interactions in terms of the ECMWF/WMO data (summer of 1984).
利用1984年夏季ECMWF/WMO资料分析了低频涡度系统和低频辐散环流系统，讨论了两者之间的相互作用。
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