RESUMEN
The traditional measurement method can't achieve real-time monitoring of soil moisture content (SMC) within a two-dimensional area. To solve the above problems, we propose a rapid SMC monitoring method for two-dimensional area based on distributed acoustic sensing (DAS). DAS demodulates the backward Rayleigh scattering signal containing seismic wave sound velocity information from the active seismic source. The folding ruler approximation is employed to calculate the sound velocity of the soil, which is then inverted to determine the soil moisture content. The experiment measured the soil within a two-dimensional area formed by the seismic source and the acoustic sensing optical cable. The sensing optical cable and the active seismic source are organized into a two-dimensional area and the measurement range is 3 × 10 m with 33 points. The SMC ranges from 15% to 40%. The experiment shows that the absolute error between the measured values obtained by DAS and the water cut meter is 7%. This experiment verifies the feasibility of using the Rayleigh scattering properties to invert SMC and provides a new method for real-time monitoring of SMC in a large area.
RESUMEN
BACKGROUND: The epidemiologies of hepatitis C virus (HCV) and hepatitis B virus (HBV) infections in specific populations in certain areas of China are poorly understood. A pilot survey of HCV/HBV infections was carried out in villages in Kuancheng County, Heben Province, where injection of sodium benzoate or amphetamines using shared needles has been a common practice. The aims of this study were to analyze the endemicity and characterize HCV/HBV infections in this population. METHODS: Data on demographic characteristics and drug abuse were collected from individuals who signed informed consent forms. Serum HCV antibody (anti-HCV), hepatitis B surface antigen (HBsAg), and hepatitis B core antibody (anti-HBc) were measured in all participants. HCV RNA was measured in samples positive for anti-HCV using real-time polymerase chain reaction. RESULTS: Among 852 participants from 11 villages, 49.9% had used sodium benzoate or amphetamine at least once, by intravenous injection. The overall prevalence of anti-HCV, HCV RNA, anti-HBc, HBsAg, and HCV/HBV co-infection was 37.1%, 26.6%, 67.7%, 10.7%, and 30.0%, respectively. Two-hundred-twenty-three of 227 (98.2%) participants positive for HCV RNA were aged >40 years. Co-infection was related to sex, age, number of injections, and time from first injection. The rate of spontaneous HCV RNA clearance was 28.2% (89/316), and was related to the number of injections, time from first injection, and HBsAg positivity. However, HBsAg was related to the anti-HBc signal/cut-off ratio rather than to the above parameters. Trend tests demonstrated that the prevalence of anti-HCV, HCV RNA, and anti-HBc was related to the number of injections (P < 0.001), while HBsAg prevalence was not (P = 0.347). CONCLUSIONS: The prevalence of HCV and HBV infection is likely to be high among individuals older than 40 years in areas of needle sharing, and one-time screening for HCV infection should be offered to these populations.
