published_or_final_version / abstract / Physics / Master / Master of Philosophy

In structural concrete, hooked bars are used to shorten anchorage length when the requirements for straight bar anchorage cannot be provided within the available dimensions of elements. The objective of this study was to provide an overview of hooked bar anchorage. Design examples and structural details are based on Building code requirements for structural concrete (ACI 318-08) and commentary. Examples of standard hooks in exterior beam-column joint and hooked bar anchorage details for reinforced concrete beam-SRC column joints are discussed. The general behavior of anchorage of hooked reinforcing bars is summarized from a review of previous studies. Then, design requirements for the development length of standard hook are discussed and used in an example. An example of the use of hooked bars in reinforced concrete beam-SRC column joint is provided. Four options for short development length are presented and compared: Adding more reinforcement, welding bars, confinement by steel column flanges, and anchorage by plate welded between flanges. / text

In this paper, we present the results of the design and fabrication of a 12 channel nano-membrane-based optical phased array that allows for large angle beam steering operating at wavelength=1.55µm. Our device is fabricated on silicon-on-insulator using standard CMOS process. By implementing unequally spaced waveguide array elements, we can relax the half-wavelength spacing requirement for large angle beam steering, thereby avoiding the optical coupling between adjacent waveguides and reducing the side-lobe-level of the array radiation pattern. 1D beam steering of tranverse-electric polarized single mode light is designed to be achieved thermo-optically through the use of thin film metal phase shifters. / text

Bacterial adhesion is the first step of biofilm formation that plays various roles in the environment and the human body. Examples of undesirable roles of biofilm formation include metal rust, sewage sludge and bacteria-related diseases. Desirable roles are biofiltration and bioremediation.For a decade, Atomic Force Microscopy (AFM) has been the primary tool used to study the adhesion and elastic properties of individual bacteria. In this work we show it is possible to use a Surface Forces Apparatus (SFA) to measure elastic and adhesive properties of small collections of surface bound bacteria. The measurements are conducted with incomplete, patterned bacterial films and we have developed a protocol to image the contact area with AFM after the experiment. Using the SFA, we measured the force profile between a P. Aeruginosa PAO1 film and a bare mica surface. We repeated the measurement in the same contact position for up to ten days to determine the effect of desiccation on the film material properties, and then moved to the new contact area to measure the film thickness and elastic properties. A large shrinkage of the bacterial film thickness was measured during the first few days due to the bacterial film desiccation and rearrangement. The proportion of shrinkage depends on factors such as the bacterial film coverage, roughness, temperature and relative humidity. Thickness compressibility was estimated from the force curves. As a force approximation, the stress at the center of the contact (σ) and the area of the contact were estimated by applying the Hertz model. Since the film is incomplete the calculated area in contact was reduced by a factor estimated from the optical image of the contact zone. Adhesiveness was measured in receding force profiles. Maximum adhesive force was detected in the first day, due to the high capillary force, decreased by the bacterial film desiccation and increased again due to the conditioning film.

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Beams of polarized protons play an important part in the study of the spin dependence of the nuclear force by measuring the analyzing power in nuclear reactions. The source at iThemba LABS produces a beam of polarized protons that is pre-accelerated by an injector cyclotron (SPC2) to a energy of 8 MeV before acceleration by the main separated-sector cyclotron to 200 MeV for physics research. The polarized ion source is one of the two external ion sources of SPC2. Inside the ion source hydrogen molecules are dissociated into atoms in the dissociator and cooled to a temperature of approximately 30 K in the nozzle. The atoms are polarized by a pair of sextupole magnets and the nucleus is polarized by RF transitions between hyperfine levels in hydrogen atoms. The atoms are then ionized by electrons in the ionizer. The source has various sensitive devices, which influence beam intensity and polarization. Nitrogen gas is used to prevent recombination of atoms after dissociation. The amount of nitrogen and the temperature at which it is used plays a very important role in optimizing the beam current. The number of electrons released in the ionizer is influenced by the size and shape of the filament. Optimization of the source will ensure that beams of better quality (a better current and stability) are produced.

This thesis presents a study on the design and analysis of a morphing flap structure integrated with actuation mechanism for potential application to large aircraft. Unlike the conventional rigid flap mounted on the wing trailing edge, the morphing flap is designed as a unitized structural system integrated with three primary components: the upper and lower flexible skins reinforced by stringers, an eccentric beam actuation mechanism (EBAM) with discs fixed on it, and the connection of the discs with the stringers. Based on the EBAM concept proposed by Dr Guo in previous research [1], the current study has been focused on the EBAM design and optimization, kinematic simulation and structural modelling of the morphing flap. Although a lot of efforts have been made to develop the morphing flap in previous research, it is lack of detailed design of the disc-skin linkage and clear view on the mechanism optimization in relation to the shape requirement. The main objective of this research is to meet the morphing shape requirements and calculate the actuation torque for a specified morphing flap. Firstly effort was made to design and optimize the disc shape and locations in the EBAM for the best matching of the specified morphing shape with minimum actuation torque demand. It is found that minimum three discs are required and their locations have little effect on the actuation torque. Secondly attention was focused on designs of the disc and a C-linkage with the stringers. To ensure that the C- linkage works in practice, a twisted stringer flange design was proposed. Thirdly the actuation mechanism was integrated with the stiffened skin to play the role of an active rib in the flap structure. Based on the design, FE modelling and analysis of the morphing flap structure was carried out. The behaviour of the morphing flap under the internal actuation and external aerodynamic load was applied for stress analysis and detailed design of the structures. Finally the kinematics of the integrated morphing flap was simulated by using CATIA to demonstrate the feasibility and the effectiveness of the improved design.

This thesis presents a very efficient hybrid method for analysis and design of optical and passive photonic devices. The main focus is on unbounded wave structures. This class of photonic systems are in general very large in terms of the wavelength of the driving optical sources. The size of the problem space makes the electromagnetic modelling of these structure a very challenging problem. Our approach and main contribution has been to combine or hybridize three methods that together can handle this class of photonic structures as a whole. <br /><br /> The basis of the hybrid method is a novel Gaussian Beam Tracing method GBT. Gaussian Beams (GB) are very suitable elementary functions for tracing and tracking purposes due to their finite extent and the fact that they are good approximations for actual laser beams. The GBT presented in this thesis is based on the principle of phase matching. This method can be used to model the reflection and refraction of Gaussian beams from general curved surfaces as long as the curvature of the surface is relatively small. It can also model wave propagation in free space. The developed GBT is extremely fast as it essentially uses simple algebraic equations to find the parameters of the reflected and refracted beams once the parameters of the incident beam is known. Therefore sections of the systems whose dimensions are large relative to the optical wavelength are simulated by the GBT method. <br /><br /> Fields entering a photonic system may not possess an exact Gaussian profile. For example if an aperture limits the input laser to the system, the field is no longer a GB. In these and other similar cases the field at some aperture plane needs to be expanded into a sum of GBs. Gabor expansion has been used for this purpose. This method allows any form of field distribution on a flat or curved surface to be expanded into a sum of GBs. The resultant GBs are then launched inside the system and tracked by GBT. Calculation of the coefficients of the Gabor series is very fast (1-2 minutes on a typical computer for most applications). <br /><br /> In some cases the dimensions or physical properties of structures do not allow the application of the GBT method. For example if the curvature of a surface is very large (or its radius of curvature is very small) or if the surface contains sharp edges or sub-wavelength dimensions GBT is no longer valid. In these cases we have utilized the Finite Difference Time Domain method (FDTD). FDTD is a rigorous and very accurate full wave electromagnetic solver. The time domain form of Maxwell's equations are discretized and solved. No matrix inversion is needed for this method. If the size of the structure that needs to be analyzed is large relative to the wavelength FDTD can become increasingly time consuming. Nevertheless once a structure is simulated using FDTD for a given input, the output is expanded using Gabor expansion and the resultant beams can then be efficiently propagated through any desired system using GBT. For example if a diffraction grating is illuminated by some source, once the reflection is found using FDTD, it can be propagated very efficiently through any kind of lens or prism (or other optical structures) using GBT. Therefore the overall computational efficiency of the hybrid method is very high compared to other methods.