Excess low frequency noises in some electronic materials and components
We devised burst noise eliminating equipment and characterized the 1/f and burst noise in some electronic materials, components, electric contacts and bipolar transistors. The burst-eliminated noise spectrum is the 1/f type. The noise intensity is proportional to the square of the current and to the fifth power of the contact resistance. This contact resistance dependence of the noise is analyzed with the constriction resistance of the contact surface material. The measured results are also shown in the amplitude and phase fluctuations in the transistor collector current. They are also of 1/f type and correlate each other. On the other hand, we did not find this correlation in another transistor with burst noise. Hence, the 1/f fluctuation is considered to be due to diffusion or mobility fluctuation and the burst noise is not due to the diffusion process in the solid.
1/f Noise in Metal Contacts and Granular Resistors
To measure the current noise in metal contacts and granular resistors, we arranged a noise measuring system with a switched-capacitor filter. The samples are crossbar contacts and grphite thick-film resistors. All noise spectra are the 1/f type. The noise of crossbar contacts and thick-film resistors increases in proportion to the fifth and third power of the resistance, respectively. A model for the noise of metal contacts and granular resistors is proposed. It is based on the spontaneous fluctuation of temperature of the small Conducting spots between metal surfaces and granular boundaries, respectively. The results of the analysis are qualitatively in agreement with those of measurement.
Effect of Calcium Glycerophosphate on Demineralization in an in vitro Biofilm Model
The aim was to investigate the anti-caries properties of calcium glycerophosphate (CaGP) using an in vitro bacterial flow cell model. Four flow cells, inoculated from a chemostat containing a seven-organism bacterial consortium, were pulsed with sucrose twice daily, to provide an acidic challenge and pH-cycling conditions. Blocks of enamel and dentine were mounted in each flow cell. In a study on the effect of CaGP concentration, CaGP was pulsed into three of the flow cells, at the same time as the sucrose, to give concentrations of 0.10, 0.25 and 0.50%. Water was pulsed into the fourth flow cell with the sucrose. Microradiography revealed a significant dose response of decreasing demineralization as CaGP concentration increased. Reductions at 0.25 and 0.5% were significant when compared to the control. A second study investigated the effect of timing of CaGP pulsing, relative to sucrose, on enamel and dentine demineralization. CaGP (flow cell concentration 0.2%), was pulsed 1 h before, during or 1 h after the sucrose pulse; a water control was employed. In enamel, pulsing CaGP before the sucrose reduced demineralization significantly compared to concurrent pulsing, which in turn gave a significant reduction compared to pulsing after sucrose, which did not reduce demineralization significantly compared to the water control. In dentine, CaGP reduced demineralization significantly only when pulsed before the sucrose. The findings suggest that in vivo, the anti-caries potential of CaGP may be greater if it is applied before a cariogenic challenge.