Year 12 students' mental models of the nature of light

This article reports on the third year of a three-year longitudinal investigation into six secondary students' understanding of optics at a secondary school level. In the third year of this investigation the students, who by now were in Year 12, underwent a teaching sequence that centred on the teaching and learning of physical optics and quantum ideas. The students' mental models of the nature of light were explored prior to, and following this teaching sequence. The researcher took on the dual roles of teacher and researcher. This paper will outline the findings of the third year of this study and the implications they have for the teaching and learning of optics at secondary school level.

The effect of repeated pulses of light at the same time on period responses of the rat circadian pacemaker.

A consequence of simple velocity-based models is that, in response to light pulses, the circadian period should adjust inversely to phase. In addition, because of the interaction of circadian period and phase response, earlier circadian period changes should modify later circadian period changes. The literature contains few mentions of response curves of circadian period responses following light pulses. Rats were exposed to four pulses of light (60 minutes, 1000 lux) at the same circadian time, a minimum of 26 days apart; we assessed period responses and possible bias in the period-response curve. Modulation of circadian period following light-induced phase responses was examined by assessing the period of running wheel activity onset. Phase and circadian period were not consistently found to share an inverse relationship. Moreover, biases in initial period tended to be increased by the experimental protocol regardless of circadian time of pulse. Rats with a short initial (highvelocity) period had a lengthened period, while rats with a long initial period (low velocity) tended to have a reduce period. However, rats with a long initial period were phase delay biased, not phase advance biased. These results do not support a simple velocity model of the pacemaker.

The prediction of damage condition in regards to damage factor influence of light structures on expansive soils in Victoria, Australia

This paper proposes a neural network model using genetic algorithm for a model for the prediction of the damage condition of existing light structures founded in expansive soils in Victoria, Australia. It also accounts for both individual effects and interactive effects of the damage factors influencing the deterioration of light structures. A Neural Network Model was chosen because it can deal with 'noisy' data while a Genetic Algorithm was chosen because it does not get `trapped' in local optimum like other gradient descent methods. The results obtained were promising and indicate that a Neural Network Model trained using a Genetic Algorithm has the ability to develop an interactive relationship and a Predicted Damage Conditions Model.

Year 12 students' mental models of the nature of light

This paper reports on the third year of a three-year longitudinal investigation into six Year 10 secondary students’ understanding of optics at a secondary school level. During the first two years of the study the students’ understanding of geometrical optics was explored with the adoption of constructivist teaching and learning strategies. The students' understanding of geometrical optics following the Year 11 teaching stage then formed the basis of exploration of their mental models of the nature of light. This exploration occurred before, during and following a Year 12 teaching stage where the students studied physical optics and quantum ideas. Before the Year 12 teaching stage the students had constructed mental models of light that related to their understanding of a ray. Over the Year 12 teaching stage the students’ mental models changed to conceptualizations of a photon. There was evidence in the students’ mental models of a hybridization of the particle and wave scientific models. That is, they conceptualized the photon as having both wave and particle characteristics. The variation in the students’ hybrid models also suggested a variation in the way they conceived of the nature of scientific models.

Amount of mental practice and performance of a simple motor task

The effects of different amounts of mental practice on the performance of a motor skill were studied. Research supports the effectiveness of mental practice on performance; however, little is known about how much practice is needed and whether there is an optimal amount for these practice effects. Participants, 209 students ages 18 to 44 years (M = 20.5, SD = 2.9), completed a pre- and posttest of dart throwing with the nonpreferred hand. In the practice phase, participants completed either 25 (Mental Practice 25), 50 (Mental Practice 50), or 100 (Mental Practice 100) trials of the darts task or 50 trials of a catching task (Catching Task). Performance for all groups improved from pre- to posttest. Improvements for the three mental practice groups were greater than for the Catching Task group; however, there were no differences for the three Mental Practice groups. The findings support the positive effect of mental practice over a control condition and suggest that small amounts of mental practice may be sufficient for performance improvements, at least for a simple motor skill.

The combined effect of light intensity and temperature on the chlorophyll and carotenoid pigments of phytoplankton

Chlorophyll a and other photosynthetic pigments are used as indicators of phytoplankton biomass, composition and physiological state. Extraction and HPLC procedures were developed to analyse for chlorophyll and carotenoid pigments. The effect of the environment on pigment production must be quantified before the pigments can be used to accurately estimate biomass or quantitatively describe phytoplankton composition.

The ranking of factors influencing the behaviour of light structures on expansive soils in Victoria, Australia

In this paper a Neural Network Model was used to develop a ranking of the potential damage influences for light structures on expansive soils in Victoria. These influences include geology, Thornthwaite moisture index, vegetation covers, construction foundation type, construction wall type, geographical region and age of building when first inspected. Approximately 400 cases of damage to light structures in Victoria, Australia were considered in this study. Feedforward Backpropagation was adopted to train the data. The ranking of importance was estimated using connection weight approach and then compared to results calculated from sensitivity analysis. From the analysis, the ranking of importance for potential damage factor was noted.

Predicting amount of saleable products using neural network metamodels of casthouses

This study aims at developing abstract metamodels for approximating highly nonlinear relationships within a metal casting plant. Metal casting product quality nonlinearly depends on many controllable and uncontrollable factors. For improving the productivity of the system, it is vital for operation planners to predict in advance the amount of high quality products. Neural networks metamodels are developed and applied in this study for predicting the amount of saleable products. Training of metamodels is done using the Levenberg-Marquardt and Bayesian learning methods. Statistical measures are calculated for the developed metamodels over a grid of neural network structures. Demonstrated results indicate that Bayesian-based neural network metamodels outperform the Levenberg-Marquardt-based metamodels in terms of both prediction accuracy and robustness to the metamodel complexity. In contrast, the latter metamodels are computationally less expensive and generate the results more quickly.

Measurement of light penetration through a simulated merino fleece

The degree of light penetration along the length of the fibre of a simulated Merino fleece was measured using a fibre optic probe to investigate the relationship between light exposure and photodamage to the wool fibre. The percentage of the total direct sunlight that reached the base of the 100-mm long, simulated, closed Merino fleece was ~1% and the section of the fibre from the root to 60 mm from the root was protected from exposure. The light intensity at the base of the fibre was increased to 2% when the density of the simulated fleece was halved. Wool was scoured and the yellowness and intensity of methylene blue staining was measured to estimate the extent of damage to wool staples.

Modeling of light propagation through biological tissues : a novel approach

An efficient numerical technique for modeling biological tissues using the radiative transfer equation is presented. Time dependence of the transient radiative transfer equation is approximated using Laguerre expansion. Azimuthal angle is discretized using the discrete ordinates method and the resulting set of ordinary differential equations is solved using the Runge-Kutta-Felhberg method.