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<p> This study seeks to extend the work done by Brasell and Beichner on the effect of the Microcomputer-Based Laboratory (MBL) on the quality of instruction in kinematics.</p><p> In this thesis, we investigate the idea that the automatic graphing process involved in a typical kinematics MBL has a black box effect on student understanding. In order to make students focus on the values that create the graph, a group of students first experienced kinematic graphs by drawing by hand before performing the MBL as normal. After testing this treatment with 246 students (141 received treatment, 105 were kept as a control), the results showed that there was a slightly positive but insignificant difference in gains between the two groups (<i>p</i> = 0.362), as measured by Beichner's Test for Understanding Graphs in Kinematics (TUG-K).</p>

Thin film sandwich structures of metal-SiO/B203- metal with the dielectric thickness in the range 400 to 4000 A have been prepared by thermal evaporation in a vacuum of less than 10-5 torr. The metal electrodes used were Cu,, Ag and Al. After the electroforming process the devices showed a voltage-controlled negative resistance (VCNR) and emission of electrons into a vacuum. Devices with Cu electrodes were found to give the most suitable characteristics. The effect of air pressure and temperature on VCNR were studied. The vacuum-electroformed samples exhibited a pressure-voltage memory effect when operated in air at atmospheric pressure and the highimpedance state induced then could be erased by reducing the air pressure and by applying a bias voltage exceeding the threshold voltage, VT. Thermal-voltage memory effects were investigated in devices carrying Cu electrodes and the time-dependent transitions of the high-impedance memory states to a normal low impedance state at low temperatures were measured. The results have been explained employing the filamentary model of Dearnaley, Morgan and Stoneham. The localised defect regions on the surfaces of the samples, produced during the electro-forming process and electrical operation of the device, were investigated by means of a scanning electron microscope. The defects are believed to be mainly due to the formation of conducting filaments across the insulator and to the consequential Joule heating and electrolytic processes occurring along the filaments. A memory switching effect was observed in devices having Ag and Cu electrodes. The samples were formed initially in the atmosphere by the application of a direct voltage in series with a large resistance. The formed sample then could switch between a low conductivity 'off' state and a high-conductivity 'on' state, which has an ohmic characteristic. The observed switching behaviour is explained in terms of a monofilamentary model based on the formation of a metallic filament across the insulator during the forming process of the sample.

Nuclear quadrupole resonance (n.q.r.) spectroscopy is a solid state technique which, when applied to samples containing quadrupolar nuclei, can elucidate fine structural differences and internal electronic distribution. It has-been applied to a variety of inorganic compounds containing the quadrupolar nuclei, chlorine and cobalt, (i.e. (^35) CL and (^59Co)). In order to remove spurious responses on a Robinson type n.q.r. spectrometer, apparatus has been constructed to generate sinusoidal magnetic modulation. Monomeric and chain- structures have been proposed for members of a series of complexes between zinc chloride and ethers. Marked asymmetry in the electric field gradient at chlorine has been reported for tetrachlorides of group IV. Although distortion of the molecules in the solid and disorder in the lattice are likely to produce asymmetry, it is suggested, that pπ-dπ bonding makes a major contribution. Such bonding is postulated for the tetrachlorides above carbon tetrachloride. Zeeman line shape studies on thionyl chloride and tetrachlorophenyl phosphorane have yielded estimates for TT-bonding in the bonds to chlorine. A variable temperature study of the (^59)Co quadrurole resonances of π-cyclopentadienyl cobalt dicarbonyl has revealed the absence of phase changes between 77K and 260K.

The work described in this thesis is directed towards study of the magnetostriction in the Gd-Tb alloy system using resistive strain gauge technique. The experiments were carried out at various ranges of temperatures between 4.5 K and 250 K, and magnetic fields up to 13 Tesla were available. High quality single crystals of Gd(_0.95)Tb(_0.05') Gd(_0.80)Tb(_0.20')Gd(_0.50)Tb(_0.50), and Gd(_0.25)Tb(_0.75) were used to measure the four magnetostriction coefficients λ(^y,2), λ(^a,2)(_2), λ(^a,2)(_1) and λ(^E,2) temperature dependences of the magnetostriction coefficients were fitted with both single-ion mechanism and a theory containing a term representing a two-ion interaction. Only the values of the magnetostric tion coefficients for the samples containing high concentration of Terbium obey the single-ion I5/2 [ £(^-1)(m(_n))]. However, the experimental results were better fitted using the other theory, but in most cases the fit was less close than could have been desired. An anomalous behaviour was observed for the samples containing 5% and 20% of Terbium in the magnetostriction curves along the c-axis, 45 to c-axis, and b-axes in the b-c plane. These anomalies disappeared by raising the field and temperature above 70-K. Another anomaly was observed in the temperature dependence of λ(^a,2)(_2) for the sample containing 20% of Terbium where a very sharp peak was obtained for this coefficient at 60 K. The variation of the coefficients λ(^y),2, λ(^a,2)(_2) with alloy composition were able to be represented using an exponential relation, while a linear relation was found for the coefficient λ(^a,2)(_I). The values of the coefficients extrapolated well to the values of the pure metalsgiven by previous workers. The ratio λ(^e,2)(o) / λ(^y,2)(_o) was found to have anomalously large values compared with that expected for the heavy rare earth metals and increase with increasing Terbium concentration in the alloy.

This study investigates the stresses produced in an embankment dam as a result of excitation due to elastic plane waves. A two dimensional finite element model is used to represent an embankment and its substructure. The model uses a quadrilateral element, formed from triangles with a condensed internal node, which gives a better prediction of stress direction than a constant strain triangle. The equations of motion are assembled with lumped mass and damping matrices, and solved by direct integration using a fourth order Runge-Kutta algorithm. For time-steps in the range of stability this algorithm is shown to be accurate and easy to use. It is shown that the range of stability is considerably reduced with the inclusion of damping, and so damping was not included in the models studied. Tests show that for a finite element grid to model elastic wave propagation it is essential for there to be at least eight elements per wavelength. If this requirement is violated the predicted stresses are seriously affected, and the results of previously published studies must be judged against this condition. The model grid is designed to meet this requirement for the propagation velocity typical of dam materials and the frequencies typical of seismic events. Two models, (a) homogeneous and (b) layered, are excited by P and S waves at several angles. The consequent distortions of static stress distributions are varied, but exhibit conditions that could lead to failure by slumping or by tensional cracking close to the crest. The severity of the stresses was greater in the cases of (a) S-waves, (b) angled waves, (c) layered models. The physical processes producing the stress distributions are examined. It is concluded that the stress distributions are dependent on the angle of incidence and are not capable of explanation in terms of natural modes of vibration only.

Electron spin resonance techniques were used to study the photo-electronic behaviour of defect centres in rutile, using both single crystal and powdered samples. Single crystals of rutile were grown by a plasma torch method. Analysis of the boules by several techniques established that they contained, in general, fewer impurities than crystals grown by the conventional Verneuil method. Some boules were deliberately doped during growth with specific impurities. Control of the oxygen content of the plasma enabled the growth of some boules in a completely stoichiometric state, requiring no subsequent oxidation. Some crystals were doped after growth with various transition metal ions, using either evaporation and diffusion or vacuum capsule diffusion techniques. E.S.R. analysis indicated the presence of several impurity ions, notably iron and nickel, in most samples. Low temperature ultra-violet irradiation caused significant changes to the intensities of most spectra, together with the appearance of several new spectra. Isochronal annealing then revealed the temperatures at which thermally stimulated charge transfers occurred, as reflected in changes to e.s.r. spectra. At least twelve different trapping centres were detected, with thermal ionization temperatures between 30 and 400K. Where possible, the ionization energies were determined by measuring variations in the rate of charge transfer with temperature and many of the values were in good agreement with those reported using other techniques. In most cases it was also possible to determine the polarity of the traps, by studying their interaction with other centres. It is thought that many of the shallow electron traps consist of complexes of intrinsic defects, such as interstitial ions or vacancies. with nearby Aluminium ions. Iron and chromium appear to form hole trapping centres with energy levels near the valence band. Nickel, Manganese and Copper are recombination centres with levels near the centre of the band gap. The same e.s.r. methods were applied to samples of rutile pigments and a computer simulation technique was used to aid analysis and interpretation of powder spectra. All the pigment samples exhibited the same u.v.-activated e.s.r. spectrum. Isochronal annealing suggested that it represented a trapped hole and also inferred the existence of several shallow electron traps.