No abstract

Several studies have been published on noncontact heartbeat detection recently. Particularly, a few studies have found that radar for noncontact detection is effective for long-term monitoring. As the novel coronavirus continues to spread worldwide, the use of radar is expected to prevent the contamination of equipment by the virus and enable heartbeat detection from a safe distance. To monitor heartbeat fluctuation, heartbeat signals must be detected over a short period; however, conventional methods require approximately 5 s for detection in the stationary state of the human body. This study developed a method for detecting heartbeat in approximately 2.5 s based on nonharmonic analysis (NHA) to suppress sidelobes. The method has nearly no data length limitations in terms of frequency resolution. To validate the method, heartbeat detection is performed in a stationary state with reduced noise and a driving simulation environment with high noise. Frequency analysis of the received signals enabled the detection of heartbeat harmonics, suggesting the possibility of detecting the fundamental heartbeat frequency from its harmonics. To test this aspect, the detectability of heartbeat harmonics is determined under the stationary and driving simulation conditions from a comparison of the conventional short-time Fourier transform, continuous wavelet transforms, and the proposed NHA method.INDEX TERMS Continuous wave Doppler radar (CW Doppler radar), driving simulation, harmonic, heartbeat, non-harmonic analysis (NHA).

The heat of reactions in supercritical water is difficult to measure. Our group fabricated a new reactor to enable the measurement of this heat with extremely high accuracy. The system consisted of a single, insulated tube reactor. The reaction heat was determined by the temperature change of the flow caused by the heat. We found, however, that the heat loss of the reactor compromised the measurements accuracy. Though small, this factor was impossible to completely remove, especially when the reaction was fast or the flow was slow. To compensate, we measured the heat loss and used the measured value to correct our calculation of the reaction heat. The direct measurements of the reaction heat agreed well with the calculated values, with relative error of only around 5% up to reaction heats as large as 100 kJ/kg-water.

No abstract