The aim of this thesis work is to design and manufacture a Dissimilar Channel Angular Pressing (DCAP) system for severe plastic deformation of aluminum alloy sheets in order to obtain ultra-fine grained structure. First, a DCAP system was designed by Finite Element Analysis and constructed after various optimization trials. Next, 6061-T0 aluminum alloy plates were severely deformed by various DCAP passes through the system. The samples were characterized by metallography, X-ray diffraction, tension and hardness tests. It has been observed that the yield strength was improved about 100 % after 2 DCAP passes, and 45 nm sub-grain size was obtained.

In this thesis work construction of the angular acceleration signal of a 2-DOF gimbal platform and use of this signal for improving the stabilization performance is aimed. This topic can be divided into two subtopics, first being the construction of angular acceleration and the second being the use of this information in a way to improve system performance. Both problems should be tackled in order to get satisfactory results. The most important output of this work is defined as the demonstration of the improvements obtained both theoretically and on experimental setup. Although the system to be studied is a two axis gimbal platform, the results obtained can be applied to other servo control problems. It is possible to define different performance criteria for a servo control problem and different techniques will be addressed with different control objectives. For this thesis work, the performance criterion is defined as the stabilization performance of the platform. As a result, disturbance rejection characteristics of the controller emerges as the main topic and methods for rejecting these disturbances such as the friction torques and externally applied moments are focused on throughout the studies. As expected, remarkable improvement is achieved as a result of the use of acceleration feedback.

No description available.

Micromirror scanners are the most significant of the micro-optical actuator elements with applications in portable digital displays, automotive head-up displays, barcode scanners, optical switches and scanning optical devices in the health care arena for external scanning diagnostics and in vivo scanning diagnostics. Recent development in microscanning technology has seen a shift from conventional electrostatic actuation to electromagnetic actuation mechanisms with major advantages in the ability to produce large scan angles with low voltages, remote actuation, the absence of the pull-in failure mode and the acceptable electrical safety compared to their electrostatic counterparts. Although attempts have been made to employ silicon substrate based MEMS deposition techniques for magnetic materials, the quality and performance of the magnets are poor compared to commercial magnets. In this project, we have developed novel low-cost single and dual-axis polymer hard magnetic micromirror scanners with large scan angles and low power consumption by employing the hybrid fabrication technique of squeegee coating to combine the flexibility of polydimethylsiloxane (PDMS) and the superior magnetic performance of fine particle isotropic NdFeB micropowders. PCB coils produce the Lorentz force required to actuate the mirror for scanning applications. The problem of high surface roughness, low radius of curvature and the magnetic field interaction between the gimbal frame and the mirror have been solved by a part PDMS-part composite fabrication process. Optimum magnetic, electrical and time dependent parameters have been characterized for the high performance operating conditions of the micromirror scanner. The experimental results have been demonstrated to verify the large scan angle actuation of the micromirror scanners at low power consumption.

No description available.

Austenitic stainless steels are commonly used in nuclear reactors and have been considered as potential structural materials in fusion reactors due to their excellent corrosion resistance, good creep and fatigue resistance at elevated temperatures, but their relatively low yield strength and poor radiation tolerance hinder their applications in high dose radiation environments. High angle grain boundaries have long been postulated as sinks for radiation-induced defects, such as bubbles, voids, and dislocation loops. Here we provide experimental evidence that high angle grain boundaries can effectively remove radiation-induced defects. The equal channel angular pressing (ECAP) technique was used to produce ultrafine grained Fe-Cr-Ni alloy. Mechanical properties of the alloy were studied at elevated temperature by tensile tests and in situ neutron scattering measurements. Enhanced dynamic recovery process at elevated temperature due to dislocation climb lowers the strain hardening rate and ductility of ultrafine grained Fe-Cr-Ni alloy. Thermal stability of the ultrafine grained Fe-Cr-Ni alloy was examined by ex situ annealing and in situ heating within a transmission electron microscope. Abnormal grain growth at 827 K (600°C) is attributed to deformation-induced martensite, located at the triple junctions of grains. Helium ion irradiation studies on Fe-Cr-Ni alloy show that the density of He bubbles, dislocation loops, as well as irradiation hardening are reduced by grain refinement. In addition, we provide direct evidence, via in situ Kr ion irradiation within a transmission electron microscope, that high angle grain boundaries in nanocrystalline Ni can effectively absorb irradiation-induced dislocation loops and segments. The density and size of dislocation loops in irradiated nanocrystalline Ni were merely half of those in irradiated coarse grained Ni. The results imply that irradiation tolerance in bulk metals can be effectively enhanced by microstructure refinement.

The user of an image database often wishes to retrieve all images similar to the one (s)he already has. In this thesis, shape analysis methods for retrieving shape are investigated. Shape analysis methods can be classified in two groups as contour-based and region-based according to the shape information used. In such a classification, curvature scale space (CSS) representation and angular radial transform (ART) are promising methods for shape similarity retrieval respectively. The CSS representation operates by decomposing the shape contour into convex and concave sections. CSS descriptor is extracted by using the curvature zero-crossings behaviour of the shape boundary while smoothing the boundary with Gaussian filter. The ART descriptor decomposes the shape region into a number of orthogonal 2-D basis functions defined on a unit disk. ART descriptor is extracted using the magnitudes of ART coefficients. These methods are implemented for similarity comparison of binary images and the retrieval performances of descriptors for changing number of sampling points of boundary and order of ART coefficients are investigated. The experiments are done using 1000 images from MPEG7 Core Experiments Shape-1. Results show that for different classes of shape, different descriptors are more successful. When the choice of approach depends on the properties of the query shape, similarity retrieval performance increases.

TiNiPd high-temperature shape memory alloys (HTSMAs) have attracted considerable attention as potential solid-state actuators capable of operating at temperatures up to 500 °C, exhibiting excellent corrosion resistance, adequate ductility levels and significant strain recovery under both constrained and unconstrained thermomechanical conditions. During operation, these actuators may be subjected to multiple cycles and from an application point of view, the functional stability, i.e. conservation of original actuator dimensions and transformation temperatures during repeated employment, is of considerable importance. This study addresses the issue of functional stability in a model HTSMA, Ti50.5Ni24.5Pd25, for its use as a compact solid-state actuator. Since the primary reason for functional instability is the creation of lattice defects (dislocations, vacancies, etc.) during repeated transformation cycles, several methods were successfully undertaken to improve the functional stability through inhibiting the generation of these defects. Solid-solution strengthening through Sc microalloying and thermomechanical treatments via severe plastic deformation were the two approaches used to strengthen the HTSMA against defect generation. Thermal cycling the HTSMA under stress was the third method to voluntarily introduce defects into the microstructure such that further defect generation during application would be impeded. Overall, severe plastic deformation was found to be more efficient than other strengthening methods in improving the functional stability of TiNiPd HTSMA, yet it brought about disadvantages such as reduction in transformation strain and transformation temperatures. While functional instability is due to the creation of lattice defects, the generation of these defects is mainly controlled by the crystallographic incompatibility between martensitically transforming phases and the strength levels for plastic deformation. It was shown that TiNiPd HTSMAs, which exhibited martensitic transformation from a cubic (B2) to orthorhombic (B19) symmetry, illustrated better compatibility and thus better functional stability levels compared to TiNi SMAs, which had a B2 to monoclinic (B19’) transition. Although crystallographic incompatibility seems to be the governing factor for the functional stability of the TiNiPd HTSMA, the strength differential between the onset of plastic deformation and local constraint due to the martensitic transformation was also found to be an influential factor determining the overall stable behavior. Functional stability was also investigated for the two-way shape memory effect (TWSME) in TiNiPd HTSMAs. Better strength and compatibility levels compared to TiNi SMAs were also reflected in the TWSME characteristics in the form of enhanced stability under stress-free thermal cycling. The stability during constrained thermal cycling was not as good and TWSME degraded rapidly while doing work against an opposing stress. Nevertheless, work output levels were much higher as compared to those obtained from conventional TiNi and Cu-based SMAs.

This master thesis investigates how certain components error margin may affect the accuracy of a IFF monopulse receiver. The IFF monopulse receiver measures the angle of arrival of the incident signal by comparing sum and difference signals created in the receiver. The components of interest are phase shifters and attenuators, where both can give individual and different errors depending on the antenna steering angle. The project is conducted at Saab Aeronautics, based on a receiver in development for the Gripen E aircraft. The results of the thesis generated results showing that the angular accuracy decreases with the increase of steering angle. The angular deviation can for some cases be seen as sufficiently small for the receiver to work properly in the ideal case.

Polarised synchrotron emission from the Milky Way is of interest for its role as a foreground to the polarised CMB and as a probe of the interstellar medium. The Galactic ALFA Continuum Transit Survey (GALFACTS) and the Global Magneto-Ionic Medium Survey (GMIMS) are two ongoing surveys of the diffuse polarised emission around 1.4 GHz, with wide bandwidths and high frequency-resolution. In this thesis, I use early data from GALFACTS to investigate the behaviour of polarised, diffuse Galactic synchrotron emission. I also analyse GMIMS total intensity data. I derive a rotation measure (RM) map of the GALFACTS sky using a combination of RM-synthesis and linear angle fitting, commenting on the structure of the maps in general and on specific regions in particular. Overall I find that the maps are rich in features, and probe the RM structure of the extended Galactic emission with reasonable accuracy. I also derive the Angular Power Spectrum (APS) of the polarised emission for thirty-one 15 by 15 degree subregions across the GALFACTS data. I compute the E- and B-modes (E+B) and the scalar APS of the polarised emission (PI). I parametrise the APS by fitting a power law to the data. Comparing the E+B APS to the PI APS shows that E+B is consistently steeper across the sky. The APS data is also used to estimate the level of foreground contamination of the CMB B-mode by the synchrotron emission. I find that the slope of the APS averaged over high-latitude, low-emission subregions agrees exactly with that of the Planck 30 GHz polarised emission, thus setting an upper limit to the synchrotron contamination of CMB B-modes. Finally, I evaluate the spurious, systematic, temperature zero-level offset and associated uncertainty in preliminary GMIMS total intensity maps, finding a lower limit of ±0.26 K. I also make spectral index maps made using the GMIMS data and the Haslam et al. (1982) 408 MHz map, improving upon previous spectral index maps in the literature.