Continuous Monitoring of the Photochemical Loss for in-vivo Plants Using an Open-Ended Photothermal Cell

Abstract An automated photothermal system has been developed to measure the photochemical loss of in vivo plant leaves. In this paper we p resent results obtained with a programmed system calibrated to measure the hourly photochemical loss during a period of one week (168 hours). To show the usefulness of our technique, we compare the results obtained for a plant maintained inside a receptacle containing a single solution of water and nutrients with the results obtained for another plant that was immersed in the same solution plus polyethylene-glycol to see the effect of water stress on the photochemical loss measurement. Our results indicate that the present technique permits a study of the response of in vivo plants submitted to different water stress conditions

Microcontrolled pyro-electric instrument for measuring X-ray intensity in mammography

A novel instrument for measurement of X-ray intensity from mammography consists of a sensitive pyro-electric detector, a high-sensitivity, low-noise current-to-voltage converter, a microcontroller and a digital display. The heart of this device, and what makes it unique is the pyro-electric detector, which measures radiation by converting heat from absorbed incident X-rays into an electric current. This current is then converted to a voltage and digitised. The detector consists of a ferro-electric crystal; two types were tested; lithium tantalate and lithium niobate. X-ray measurement in mammography is challenging because of its relatively low photon energy range, from 11 keV to 15 keV equivalent mean energy, corresponding to a peak tube potential from 22 to 36 kV. Consequently, energy fluence rate or intensity is low compared with that of common diagnostic X-ray. The instrument is capable of measuring intensities as low as 0.25 mWm -2 with precision greater than 99%. Not only was the instrument capable of performing in the clinical environment, with high background electromagnetic interference and vibration, but its performance was not degraded after being subjected to 140 roentgen (3.6 × 10 -2 C kg -2 air) as measured by piezo-electric (d 33) or pyro-electric coefficients. © IFMBE 2005