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No description available.

Soft materials have a wide range of applications, which include the production of masks for nano–lithography, the separation of membranes with nano–pores, and the preparation of nano–size structures for electronic devices. Self–organization in soft matter is a primary mechanism for the formation of structure. Block copolymers are long chain molecules composed of several different polymer blocks covalently bonded into a single macromolecule, which belong to an important class of soft materials which can self–assemble into different nano–structures due to their natural ability to microphase separate. Experimental and theoretical studies of block copolymers are quite challenging and, without computer simulations, it is difficult and problematic to analyse modern experiments. The Cell Dynamics Simulation (CDS) technique is a fast and accurate computational technique, which has been used to investigate block copolymers. The stability has been analysed by making use of different discrete Laplacian operators using well–chosen time steps in CDS. This analysis offers stability conditions for phase–field, based on the Cahn–Hilliard Cook (CHC) equations of which CDS is the finite difference approximation. To overcome grid related artefacts (discretization errors) in the computational grid, the study has been done for employing an isotropic Laplacian operator in the CDS framework. Several 2D and 3D discrete Laplacians have been quantitatively compared for their isotropy. The novel 2D 9–point BV(D2Q9) isotropic stencil operators have been derived from the B.A.C. van Vlimmeren method and their isotropy measure has been determined optimally better than other exiting 2D 9–point discrete Laplacian operators. Overall, the stencils in 9–point family Laplacians in 2D and the 19–point stencil operators in 3D have been found to be optimal in terms of isotropy and time step stability. Considerable implementation of Laplacians with good isotropy has played an important role in achieving a proper structure factor in modelling methods of block copolymers. The novel models have been developed by implementing CDS via more stable implicit methods, including backward Euler, Crank–Nicolson (CN) and Alternating Direction Implicit (ADI) methods. The CN scheme were implemented for both one order and two order parameter systems in CDS and successful results were obtained compared to forward Euler method. Due to the implementation of implicit methods, the CDS has achieved second–order accuracy both in time and space and it has become stronger, robust and more stable technique for simulation of the phase–separation phenomena in soft materials.

A general system for controlling an unknown process by adjusting compensation networks is discussed. The control operation is divided into two parts, that of identification of the unknown process dynamics and that of adaption by adjusting the compensation networks. Both operations are carried out by the method of steepest descent, using a suitable error signal as a performance function. A general method of investigation is considered, which is applicable to all systems of this type. The systems are classified as Type I and Type II; it is shown that a Type I system is stable for all input signals and initial conditions. The systems which are not of Type I are designated as Type II and it is shown that the behaviour of Type II systems can be approximated by that of a Type I system in the neighbourhood of the optimum point of operation. These results are applied to investigating the behaviour of a number of controllers and identification systems. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

[No abstract available] / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Charge-transfer complexes of the aromatic hydrocarbon-trinitrobenzene type are stabilized principally by interaction between a dative- and a "no-bond" state: φN= a ψ₀ (DA) + b ψ₁ (D⁺A¯) . The resulting complexes usually possess a colour which is associated with an electronic transition between the ground state φN and a predominantly dative excited state; the transition therefore corresponds to the partial transfer of an electron from the donor (D- usually the hydrocarbon) to the acceptor (A). Most of the previous spectroscopic work on CT complexes has been concerned with solutions of the complexes; no detailed investigation of a crystalline complex has been made. The somewhat random nature of CT interaction in solution tends to limit the amount of information we can gain from such studies, and this has prompted the present work on solid complexes. With a system of definite composition and structure, both the spectroscopic examination and theoretical treatment can be carried out at a more quantitative level. The results of a detailed spectroscopic study of the crystalline anthracene-trinitrobenzene complex are presented. It is shown that 1) The CT transition moment is strongly polarized parallel to the c-axis of the crystal (approximately perpendicular to the molecular planes), with a polarization ratio greater than that predicted by the simple oriented gas model. 2) A portion of the intensity of the CT state is derived from mixing with the more intense ¹La state of anthracene, confirming the prediction of J. Murrell. 3) The crystal emission spectrum consists almost entirely of CT fluorescence with vibrational structure similar to that of the absorption. The entire spectrum is blue-shifted with respect to that of the rigid-glass solution; as in solution, there is a very wide gap between the absorption and fluorescence origins. 4) The emission intensity is strongly temperature dependent; a portion of this dependence is reversible, while the remainder is apparently connected with the creation of crystal defects on cooling, and cannot be reversed. It is suggested that the CT state is highly delocalized in the crystal, and that the transition dipole moment connecting the ground- and CT states must be polarized along the c-axis of the crystal, rather than between the centers of the individual donor-acceptor pairs. A number of TNB complexes of other hydrocarbons were studied, although in much less detail. Their spectroscopic properties appear to be similar to those of anthracene-TNB. Polarized phosphorescence- and triplet-triplet absorption spectra of several aromatic hydrocarbons dissolved in crystalline benzophenone are given. This is the first reported observation of triplet-triplet absorption in crystals, and it is shown that it is polarized mainly in the planes of the molecules investigated. / Science, Faculty of / Chemistry, Department of / Graduate

[No abstract submitted] / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The solubility of calcium carbonate in calcareous soils was studied with a view of testing the validity of the application of equations based on calcite solubility in calcareous soils. For this purpose the solubility of calcium carbonate in calcareous soils was examined under a variety of experimental conditions. Calcareous soils equilibrated in water at constant partial pressure of carbon dioxide showed a state of supersaturation with respect to calcite. The values for pH-½pCa for each soil were constant, but varied from one soil to another. Varying the soil-water ratio over a range of 1:2 to 1:10 did not affect the constancy of pH-½pCa values in the soils studied. The addition of CaCl₂ varying in concentration from 0.0025 to 0.01 mole/l. did not affect the constancy of values for pH-½pCa. When dissolution of part of the calcareous materials present was effected by the addition of increments of a H-Resin or dilute HCl acid, the values for pH-½pCa did not remain constant. The reactions between orthophosphate solutions and calcareous soils varying in calcium content was examined. It was found that in all cases the initial rate of phosphorus fixation was rapid with about 98% of the phosphate added being fixed within 2 days. The calcium carbonate exerted its normal effect on the solution equilibrium regardless of the mechanism of the reaction between solid calcium carbonate and dilute solutions of KH₂PO₄. The application of solubility criteria revealed a state of supersaturation with respect to dicalcium phosphate. A study was made to determine whether the proton transfer mechanism associated with hydrated aluminum ions was responsible for the constancy of the values for pH-½pCa in soils. The constancy of ion ratios was studied in cation exchange resin suspensions. It was found that the values for pH-½pCa were constant in resins saturated with calcium and hydrogen over a range of calcium saturation from 21% to 85%. At 95% calcium saturation, constancy of pH-½pCa was not observed. In a calcium-aluminum resin saturated 47% with aluminum, the values for pH-½pCa were found to be relatively constant with a maximum difference of 0.08. / Land and Food Systems, Faculty of / Graduate

Photographic and Photoelectric measurements were made on the shock excited spectra of Argon and Helium. The plasma temperature and electron density in the region behind the shock wave were calculated from the spectroscopic measurements. These quantities were compared with the values obtained from the Rankine Hugoniot shock theory including the effect of ionization. Considerable disagreement was found between experimental results and theoretical predictions. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The pure rotational spectrum of difluorochloromethane, Freon 22, has been obtained in the K-band microwave region with a Stark modulation spectroscope. Over two hundred spectrum lines, of which the majority are grouped into doublets or quadruplets, have been found. Fifteen doublets and one quadruplet correspond in frequency with previous determinations but the majority of the lines and structures have not previously been recorded. In addition, a definite sestet of lines and two definite triplets have been noted. The grouping into multiplets has been made possible by similarities in the line shape, in the Stark modulation response, and in the effects of chilling the Stark cell with dry ice. The latter effect has been the most important factor in identifying several transitions involving low values of J, the total angular momentum quantum number. The sestet and two quadruplets have been found to be the result of the interaction of the Cl³⁵ quadrupole moment with the electrostatic potential at the site of the nucleus. The sestet represents six of the possible eight lines for a transition from a J=1 rotational level to a J=2 level. The quadruplets represent two transitions involving only J=3 rotational levels. From these three structures have been obtained the complete solution for the spectrum of the molecule containing CI³⁵ and the values of the components of the quadrupole coupling constant for the CI³⁵ nucleus along the principal axes of the angular momentum ellipsoid. In all, eight multiplets have been correctly identified for the molecule containing Cl³⁵ and the two theories of the rotational levels and of the hyperfine structure for an asymmetric top molecule have been verified. From the rotational constants for the molecule containing CI³⁵ the values for the molecule containing CI³⁷ can be closely estimated and the rotational spectrum for the latter case has accordingly been predicted with considerable accuracy. By means of the predicted values, five multiplets and one single line have been identified for the molecule containing CI³⁷ and the theories for the rotational levels and for the hyperfine splittings can be rechecked. From the spectra for the two molecules, five independent rotational constants have been obtained with a precision that compares favourably with the precision of other experimenters in the field of microwave spectroscopy. With these five constants and an approximation to the carbon-hydrogen bond length, the structure of the molecule has been calculated with an accuracy much better than that obtained from electron diffraction measurements. The quadrupole coupling constant for CI³⁵ in Freon 22 has been found to be -71.6 ± 0.5 Mc/s, a value which is about 1 Mc/s larger than the value for the molecule in the solid state. The difference between the components of the quadrupole coupling tensor along two axes perpendicular to the carbon-chlorine bond has been found to be rather small in comparison with the value suggested by bond theory. Some comments are offered on the nature of the chemical bond in the light of these electric quadrupole moments for CI³⁵ and the bond lengths for the carbon-chlorine and carbon-fluorine bonds which have been calculated to be 1.7576 ± .0093 Å and 1.3405 ± .0058 Å respectively for Freon 22. / Science, Faculty of / Physics and Astronomy, Department of / Graduate