ABSTRACT
Cr (VI) is indispensable in industrial manufacturing, and its extensive use leads to severe heavy-metal pollution in the water environment around people, posing a great danger to physical health and living environment of multitudinous organisms. Expanded graphite (EG) is considered as a typical material for adsorption, while nanoscale zero-valent iron (nZVI) can be applied to degrade and sedimentate various organic or inorganic pollutants. In this study, a simultaneous collaboration of EG and nZVI is carried out, with the investigation on the influence of different test conditions for adsorption performances. These findings demonstrate that nZVI@EG manifests favourable adsorptive performance on the removal of hexavalent chromium efficiently. nZVI, acting as an electron donor, is supposed to reduce Cr (VI) to Cr (III), turning itself into iron oxide or hydroxide. The whole process is an exothermic reaction, accompanying chemical reduction and physical adsorption. And Cr (III) is fastened on the appearance by deposition of chromium hydroxide or ferrochromium complex precipitation, which greatly reduces the total chromium content in the aqueous solution. Herein, as a new composite adsorbent, nZVI@EG shows promising prospects of practical applications in water contamination and environmental remediation.
ABSTRACT
This paper presents the design and testing of a wireless sensor system developed using a Microchip PICDEM developer kit to acquire and monitor human heart sounds for phonocardiography applications. This system can serve as a cost-effective option to the recent developments in wireless phonocardiography sensors that have primarily focused on Bluetooth technology. This wireless sensor system has been designed and developed in-house using off-the-shelf components and open source software for remote and mobile applications. The small form factor (3.75 cm × 5 cm × 1 cm), high throughput (6,000 Hz data streaming rate), and low cost ($13 per unit for a 1,000 unit batch) of this wireless sensor system make it particularly attractive for phonocardiography and other sensing applications. The experimental results of sensor signal analysis using several signal characterization techniques suggest that this wireless sensor system can capture both fundamental heart sounds (S1 and S2), and is also capable of capturing abnormal heart sounds (S3 and S4) and heart murmurs without aliasing. The results of a denoising application using Wavelet Transform show that the undesirable noises of sensor signals in the surrounding environment can be reduced dramatically. The exercising experiment results also show that this proposed wireless PCG system can capture heart sounds over different heart conditions simulated by varying heart rates of six subjects over a range of 60-180 Hz through exercise testing.
