A Cross-Cultural Study of Young Children's Mapping Abilities

The mapping abilities of four-year-old children in York, England, Durban, South Africa, Tehran, Iran, Mexico City, Mexico and Evanston, Illinois, USA were investigated, using a methodology involving air-photo identification and simulated navigation on an air photo. The results show that essential mapping abilities (perspective and scale transformations) are well developed by the age of four in these cultures, and provide some evidence in support of the hypothesis that mapping abilities emerge without training in very young children of all cultures.     

Thermally assisted OSL: A potent tool for improvement in minimum detectable dose and extension of dose range of Al2O3:C

The influence of electron-phonon interaction on the shape of the optically stimulated luminescence decay curve of Al₂O₃:C has been studied using thermally assisted optically stimulated luminescence (TA-OSL). The minimum detectable dose (MDD) of a phosphor depends on the standard deviation of the background signal which affects the signal-to-noise ratio. The standard deviation of the background signal reduces at lower stimulation light intensity while the readout time increases. Further, measurement at higher temperature enhances the OSL signal with faster decay due to the temperature dependence of photo-ionization cross-section. To achieve the same decay constant and more signal, the temperature of measurement was raised. As a result of lowering the stimulation in-tensity at higher temperature (85°C) the overall MDD of α-Al₂O₃:C was found to improve by 1.8 times. For extension of dose linearity in higher range, deeper traps were studied by simultaneous application of CW-OSL and thermal stimulation up to 400°C, using a linear heating rate of 4K/s. By using this method, two well defined peaks at 121°C and 232°C were observed. These TA-OSL peaks have been correlated with two deeper defects which can be thermally bleached at 650°C and 900°C respectively. These deeper defects are stable up to 500°C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or heat. The dose vs. TA-OSL response from deep traps of α-Al₂O₃:C was found to be linear up to 10 kGy, thus extending its application for high dose dosimetry.