RESUMO
Wireless sensor networks (WSNs) have gained a positive popularity for structural health monitoring (SHM) applications. The underlying reason for using WSNs is the vast number of devices supporting wireless networks available these days. However, some of these devices are expensive. The main objective of this paper is to develop a cost-effective WSN based on low power consumption and long-range radios, which can perform real-time, real-scale acceleration data analyses. Since a detection system for vibration propagation is proposed in this paper, the synchronized monitoring of acceleration data is necessary. To meet this need, a Pulse Per Second (PPS) synchronization method is proposed with the help of GPS (Global Positioning System) receivers, representing an addition to the synchronization method based on real-time clock (RTC). As a result, RTC+PPS is the term used when referring to this method in this paper. In summary, the experiments presented in this research consist in performing specific and synchronized measurements on a full-scale steel I-beam. Finally, it is possible to perform measurements with a synchronization success of 100% in a total of 30 samples, thereby obtaining the propagation of vibrations in the structure under consideration by implementing the RTS+PPS method.
RESUMO
Nucleic acid-amplification testing (NAT) is not routinely practiced in blood banks from most low-income countries. We did an exploratory comparison of the performance of the standard immunoassay-based screening tests for the hepatitis B (HBV) and C (HCV) viruses with that of NAT, in blood donors. From January 1999 to March 2005, 94,806 blood donors were screened for anti-HCV antibodies and for hepatitis B surface antigen (HBsAg). Also, an exploratory period of molecular screening was carried out on 100 consecutive blood donors to detect HBV DNA and HCV RNA by home-made PCR techniques without sera pooling. In the 75-month period of serologic screening, HBsAg was detected in 219 donors (0.23%; 95% CI, 0.20- 0.26%) and anti-HCV antibodies in 922 (0.97%; 95% CI, 0.90-1.03%). The annual trend for HBsAg prevalence had a decreasing pattern over the years (p<0.001), whereas that for anti-HCV did not (p=0.19). In the molecular screening cohort, HBV DNA was detected in one donor (1%; 95% CI, 0-6%) and HCV RNA in another (1%; 95% CI, 0-6%). All these 100 donors tested negative to HBsAg and anti-HCV. Thus, the prevalence of positive results for HBV and HCV did not differ if considering immunoassays or NAT; nevertheless, these methods did not coincide in detecting HBV or HCV in the molecular screening cohort. In conclusion, NAT can detect cases of HBV and HCV infections that standard immunoassay techniques can not, even in a highly selected population at low risk, like blood donors. Large-scale studies are warranted for NAT to be considered as a systematic method for screening of HBV and HCV in Mexican blood banks.