M.Phil. (Optometry) / An investigation of the nature of variability or variation of refractive behaviour (in a sample of universi ty students studying optometry) is described. Measurements of refractive behaviour were obtained by means of autorefraction. This study was based upon multivariate methods of statistical analysis which have only recently become available in optometric science. Variation is examined using both quali tative and quanti tative methods including stereo-pair scatter plots, confidence and distribution ellipsoids, trajectories of change of dioptric power, meridional profiles, testing of hypotheses on means and variance-covariance, and graphs which represent the type of uniform variation in a 2-dimensional plane known as the i)-plane. These methods are of great assistance in developing an understanding of the nature of the variation shown, as well as, in developing an awareness of the distribution or spread of the population from which the sample was drawn. Analyses of variability of refractive behaviour on both an artificial, or test eye, and on several individual human eyes are also described. The significance of some important aspects of variabili ty of refractive behaviour involving normality and departures therefrom (such as results from outliers) are discussed and illustrated by means of examples. Distributions were found in which more than one mode was present (polymodal or multimodal behaviour). Distributions were also observed to vary from having an almost spherical spread of measurements (of refractive behaviour) to having a spindle or rod-like spread of measurements instead...

No description available.

No description available.

No description available.

The turbidimetric method for the determination of lead ion developed in this work is not intended as a replacement for standard analytical procedures, but is presented solely as a laboratory exercise for courses in elementary instructional analysis.

No description available.

As Organic solar cells (OSCs) become a promising complementary to traditional inorganic solar cells, studying the optical properties of OSCs plays a critical role to understand and improve the performance of organic solar cells. Studying optical properties is essential because it can help to understand how light interacts with the materials used in organic solar cells, which can help to improve the efficiency of organic solar cells. In this work, the optical properties of the organic photovoltaic system PM6:Y6 prepared from two different solvents, namely, chloroform and o-xylene, were investigated. The optical constants, specifically the refractive index and absorption coefficient of thin films of these materials, and the effects of thermal annealing on the optical properties were studied. The optical properties of isotropic and anisotropic organic materials were also compared, and the obtained optical constants were used to simulate the optical properties of the devices using the transfer matrix approach. The results suggest that more accurate measurements and analysis of the optical constants help to achieve more accurate simulations. This, in turn, provides more information about how the molecular orientation affects the optical properties of OSCs. However, it is important to note that the optical properties of PM6:Y6 blends that were studied are limited to those obtained under the conditions used to prepare the films. In fact, changes in the thickness or concentrations of solutions will need to be considered as well. Lastly, the glass transition temperature was determined using the change in the ellipsometric data (Ψ). This helps to select and test different thermal annealing temperatures for the material system, which could improve the efficiency of the respective solar cells.

The use of DC arc optical emission spectroscopy (OES) for quantitative analysis of thin films deposited on graphite electrodes was investigated as a process control tool. Three binary systems were evaluated: nickel-chromium, phosphorous-silicon, and silicon-aluminum. Sampling by direct deposition onto graphite electrodes placed in the deposition chamber with product runs proved to be a rapid, representative, and non-disruptive technique. Standard electrodes were prepared for each system either by evaporation of solutions of known concentration onto the tips of electrodes or by weighing out powdered standards of the appropriate concentrations. Standard curves were then prepared by burning multiple sets of standard electrodes in a DC arc of 15 amperes and obtaining intensity rations of selected analytical line pairs. Comparison of the OES technique with atomic absorption, electron microprobe, or gravimetric analysis of samples from the same deposition showed absolute agreement to within ±3% for the nickel-chromium system, ±0.3% for the phosphorous-silicon system, and ±0.2% for the silicon-aluminum system. Maximum relative percent error for the techniques were 5%, 10%, and 12.5% respectively.

No description available.

Studies have been done to determine rare-earth elements’ optical and luminescent properties using wide bandgap nitride semiconductors as suitable hosts. Research done here will contribute to the information needed to further study rare-earth elements and their unique properties. Thin films of rare-earth elements erbium, terbium, ytterbium, and both erbium and ytterbium doped into AlN are studied by laser excitation. A 532 nm Nd: YAG green laser and 783nm crystal infrared laser are used for excitation in conjunction with a spectrometer to measure photoluminescence. With the 532 nm laser, AlN: Er emits peaks at 554 nm, 561 nm, and 1552 nm, AlN: Tb emits peaks at 549 nm and 562 nm, AlN: Yb emits peaks at 966 nm, and co-doped AlN: ErYb contains peaks including both AlN: Er and AlN: Yb. Energy transfer occurred from Er to Yb resulting in an increased magnitude and peak shift. The 783 nm laser gave peaks at 1563nm for AlN: Er, 1508 nm and 1533 nm for AlN: Tb, and 1567nm for AlN: ErYb. No detectable peaks were given for AlN: Yb. A peak shift was detected in comparison of AlN: Er and AlN: ErYb. A magnetic field of 1000 G was applied to AlN: ErYb resulting in an increase in intensity of the major peak at 561nm with a splitting, creating a secondary peak at 564.5 nm. Biomedical applications can be used from the high penetration ability of lower wavelength lasers and the use of a magnetic field, which is not harmful to the human body. Enhanced green emission in erbium can be useful in future optical, photonic, and electrical devices. / Department of Physics and Astronomy