A method for comparing quality of bank notes in circulation based on both a subjective visual sorting technique and on quantitative wear evaluations is described and applied to circulated Canadian bank notes. The sample notes, which were part of a $5 circulation trial, issued over a 4 to 6 week period, had been in circulation for roughly 6 months. Notes were first sorted visually into four defined substrate categories (No Edge Wear, Corner Folds, Minimal Edge Wear and Edge Wear) and four surface wear categories (None, Low, Medium and High). Samples of each category were tested at Crane and Co. using a range of physical and optical techniques: air resistance, air
permeability, stiffness deflection, double folds, gray scale, brightness, perimeter length, and top/bottom mean and maximum deviations. The visual sort showed that neither soiling nor ink loss are the major wear problems for bank notes in Canada. However, the substrate does become tattered and worn. The mechanical and optical wear tests show that most of the parameters change logically as the soil level increases. The changes for other parameters are less clear as a function of wear categories, but are relatively consistent in distinguishing between the No Edge Wear and Edge Wear. Impact of wear on the effectiveness of security features will also be described.
Experimental measurements of threshold current density as a function of temperature have been analyzed in terms of the characteristic temperature, T0, and temperature gradient (Delta) TJth equals (delta) Jth/(delta) T, for a number of semiconductor laser device structures. These include AlInGaAs/InP, InGaAsP/InP, and AlGaAs/GaAs. A theoretical model is used to investigate the possible loss mechanisms in laser diodes that cause the superlinear increase of threshold current with temperature. The characteristic temperature T0 is found to vary with temperature and device length, thus making it somewhat misleading when quoted without qualification. A different approach based on plotting ln((Delta) TJth) vs. ln(Jth) shows a linear relationship that is dependent on device structure only, allowing the use of a new figure of merit for the temperature performance of semiconductor lasers.