Circular polarization is valuable for many electromagnetic radiation applications such as wireless and satellite communication, radars, RFID, global positioning systems, etc. Many efforts have been made to manipulate and control polarization by using linear-to-linear or linear-to-circular transmission or reflection polarization converters. Most of the existing linear-to-circular single-layer polarizers have been found to be narrowband. Some attempts have been made to improve the bandwidth of these polarizers including using multiple layered structures at the expense of a bulkier device. There was, however, still a requirement for thin single-layer linear-to-circular polarizers with enhanced bandwidth. The purpose of this research was to design two thin single-layer linear-to-circular polarizers, one for transmission and the other for reflection, with enhanced bandwidth. A thin single-layer linear-to-circular transmission polarizer with a 3 dB axial ratio bandwidth of 34% is presented. The bandwidth of this polarizer is significantly better than that of previously published polarizers of the same type. The unit cell of the polarizer consists of an I-shaped strip and a perpendicular linear strip printed on the one side of a thin dielectric substrate and two additional capacitive coupling strips printed on the other side of the substrate. Experimental results were found to agree well with the simulated results. A thin single-layer reflective linear-to-circular polarizer with a 3 dB axial ratio bandwidth of 57% is also presented. The unit cell of the polarizer consists of an I-shaped strip and a perpendicular linear strip printed on the one side of a substrate and a ground plane on the other side of the substrate. Experimental results for this polarizer were also found to agree well with the simulated results. / Dissertation (MEng)--University of Pretoria, 2018. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

Despite the many advancements to forensic DNA analysis adopted by crime laboratories across the country, the most common method for the differential extraction of sexual assault samples has remained relatively unchanged since forensic deoxyribonucleic acid (DNA) typing was discovered in 1985. As the quantity and quality of extracted DNA has significant implications on the success of subsequent analysis methods, the development and optimization of effective extraction procedures is vital to progressing the field of forensic DNA analysis. The graduate students and faculty at the Boston University School of Medicine have been developing a differential extraction process that utilizes a multi-enzymatic approach to preferentially lyse and wash the cell types within temperature controlled environments. The overall procedure is less labor-intensive and time-consuming than the conventional method. Through the extraction process, the inhibitory nature of each enzyme on the amplification process is avoided, circumventing the need for an additional purification step. A single centrifugation step is required in order to pellet the sperm while the cumbersome wash steps are replaced with selective digestion in order to remove the residual epithelial cell DNA from the sperm fraction. The three enzyme used (EA1, Benzonase®, and Acrosolv) operate optimally at distinct temperatures which allows for controlled and sequential activation to achieve desired lysis and digestion outcomes. The enzymatic reactions are conducted within a DNA extraction lab thermal cycler to obtain rapid and accurate temperature changes. This novel temperature controlled differential extraction protocol has been developed and optimized for extraction of primarily liquid mixed samples in 0.2 milliliter (mL) tubes. The epithelial cell lysis and sperm cell lysis stages of the extraction contained a final reaction volume of 100 microliters (µL). Slight modifications to this 100 direct-lysis differential extraction method resulted in a similarly efficient method with a high male DNA yield (74-100%) and minimal female carryover among varying ratios of epithelial cells to sperm cells. This sensitive technique provided nearly complete profiles (14/16 loci) of the male contributor in mixed samples containing ~15,200 female epithelial cells and ~500 sperm, with complete profiles observed in mixed samples containing ~1000 sperm. This modified extraction protocol better accommodates sample sizes that may be encountered in forensic casework testing while providing a more concentrated sperm fraction, possibly eliminating the need for an additional concentration step in some dilute samples. The ease of implementation and the rapid processing time of 2-3 hours make it a great candidate for use in forensic DNA laboratories and may help alleviate backlogs of sexual assault kit. However, further work is needed to alter the composition of the sperm lysis buffer to make it compatible with currently used amplification kits. Until such time, caution must be taken in the kit selection used for amplification of extracts produced with this method. This study also demonstrated a sensitivity of the GlobalFiler® PCR Amplification Kit to inhibition by the buffers used in this extraction protocol, particularly the Orange+ Buffer. This inhibition has dramatic effects on the profile quality of the amplified sperm fractions, with extensive allelic drop-out observed even when the Orange+ Buffer concentration was scaled from 1.0X to 0.2X. Amplification using the AmpFℓSTR® Identifiler® Plus PCR Amplification Kit showed marginal recovery in the profile quality. Other expanded-loci STR amplification kits may also demonstrate resistance to this inhibition.

Les travaux de recherche présentés dans ce manuscrit ont pour but de concevoir, simuler, fabriquer et caractériser un convertisseur modal à base de canne microstructurée air-silice (CMAS). Cette fonction représente un élément clé pour les multiplexeurs modaux et les compensateurs de dispersion chromatique. Le composant proposé est basé sur une CMAS effilée dite « taper » qui constitue une transition entre les deux fibres différentes. La conversion se fait à travers l’excitation d’un mode particulier dans une fibre multimode à partir d’une fibre standard. Dans les structures à diamètre évolutif, la compréhension des différentes théories régissant le couplage entre les différents modes est nécessaire. Une étude approfondie est réalisée pour analyser le phénomène de couplage et étudier le critère d’adiabaticité. Ce composant est élaboré autour d’une technologie de fabrication existante à XLIM qui se base sur la technique fusion-étirage. Enfin, nous validons numériquement et expérimentalement ce principe. Nous réussissons à exciter le mode fondamental et d’autres modes d’ordre supérieur dans une fibre multimode. / These research works presented in this manuscript aim at designing, simulate, manufacture and characterizing the modal converter based microstructured air-silica cane. This function represents a key element for modal multiplexers and chromatic dispersion compensators. The proposed component is based on a tapered microstructured air-silica cane « taper » which constitutes a transition between the two different fibers. The conversion is done through the excitation of a particular mode in a multimode or few mode fibers from a standard fiber. In the tapered structures, the understanding of the different theories involving the coupling between the different modes was yet necessary. A thorough study is carried to analyze the phenomenon of coupling and study the adiabatic criterion. This component is developed around an existing manufacturing technology at XLIM which based in the technique « stack and draw». Finally, we validate numerically and experimentally that principle. We succeed to excite the fundamental mode and higher order modes in a multimode fiber.

Children must learn not to trust everyone to avoid being taken advantage of. In the current study, 5- and 7-year-old children were paired with a partner whose incentives were either congruent (cooperative condition) or conflicting (competitive condition) with theirs. Children of both ages were more likely to mistrust information spontaneously provided by the competitive than the cooperative partner, showing a capacity for detecting contextual effects on incentives. However, a high proportion of children, even at age 7, initially trusted the competitive partner. After being misled once, almost all children mistrusted the partner on a second trial irrespective of the partner’s incentives. These results demonstrate that while even school age children are mostly trusting, they are only beginning to spontaneously consider other’s incentives when interpreting the truthfulness of their utterances. However, after receiving false information only once they immediately switch to an untrusting attitude.

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The durability of two solar-selective aluminium titanium oxynitride multilayer coatings was studied under conditions simulating realistic operation of central receiver power plants. The coatings were deposited by cathodic vacuum arc applying an optimized design concept for complete solar-selective coating (SSC) stacks. Compositional, structural and optical characterization of initial and final stacks was performed by scanning electron microscopy, elastic recoil detection, UV-Vis-NIR-IR spectrophotometry and X-Ray diffraction. The design concept of the solar selective coatings was validated by an excellent agreement between simulated and initial experimental stacking order, composition and optical properties. Both SSC stacks were stable in single stage tests of 12 hours at 650°C. At 800°C, they underwent a structural transformation by full oxidation and they lost their solar selectivity. During cyclic durability tests, multilayer 1, comprised of TiN, Al0.64Ti0.36N and an Al1.37Ti0.54O top layer, fulfilled the performance criterion (PC) ≤ 5% for 300 symmetric, 3 hours long cycles at 600°C in air. Multilayer 2, which was constituted of four AlyTi1-y(OxN1-x) layers, met the performance criterion for 250 cycles (750 hours), but was more sensitive to these harsh conditions. With regard to the degradation mechanisms, the coarser microstructure of multilayer 1 is more resistant against oxidation than multilayer 2 with its graded oxygen content. These results confirm that the designed SSCs based on AlyTi1-y(OxN1-x) materials withstand breakdown at 600ºC in air. Therefore, they can be an exciting candidate material for concentrated solar power applications at high temperature.

The transparent conductive oxide (TCO) SnO2:Ta is developed as a selectively solar-transmitting coating for concentrated solar power (CSP) absorbers. Upon covering with an antireflective layer, a calculated absorptivity of 95% and an emissivity of 30% are achieved for the model configuration of SnO2:Ta on top of a perfect black body (BB). High-temperature stability of the developed TCO up to 1073 K is shown in situ by spectroscopic ellipsometry and Rutherford backscattering spectrometry. The universality of the concept is demonstrated by transforming silicon and glassy carbon from non-selective into solar-selective absorbers by depositing the TCO on top of them. Finally, the energy conversion efficiencies of SnO2:Ta on top of a BB and an ideal non-selective BB absorber are extensively compared as a function of solar concentration factor C and absorber temperature TH. Equal CSP efficiencies can be achieved by the TCO on BB configuration with approximately 50% lower solar concentration. This improvement could be used to reduce the number of mirrors in a solar plant, and thus, the levelized costs of electricity for CSP technology.

The design of efficient and stable solar selective coatings for Concentrating Solar Power (CSP) central receivers requires a comprehensive knowledge about the incorporated materials. In this work solar selective coatings were grown by filtered cathodic vacuum arc (FCVA) deposition. The complete stacks consist of an infrared reflection layer, an absorber layer of C:ZrC nanocomposites and an antireflection layer. The Carbon-transition metal nanocomposites were studied as absorber materials because they show appropriate optical properties, i.e. high absorption in the solar region and low thermal emittance. Furthermore metal carbides are thermally and mechanically stabile in air at high temperatures. In order to optimize the absorber layer, the metal content was controlled by adjusting the pulse ratio between the two arc sources. The elemental composition of the absorber layers was determined by Ion Beam Analysis. X-Ray diffraction (XRD) measurements show the formation of metal carbides when the metal content is high enough. The optical properties of the deposited coatings were characterized by spectroscopic ellipsometry (SE). The reflectance spectra of the complete selective coating were simulated with the optical software CODE. Bruggeman effective medium approximation (EMA) was employed to average the dielectric functions of the two components which compose the nanocomposite in the absorber layer. Good agreement was found between simulated and measured reflectance spectra of the solar selective multilayer.

Using low energy devices to communicate over the air presents many challenges to reach security as resources in the world of Internet Of Things (IoT) are limited. Any extra overhead of computing or radio transmissions that extra security might add affects cost of both increased computing time and energy consumption which are all scarce resources in IoT. This thesis details the current state of security mechanisms built into the commercially available protocol stacks Zigbee, Z-wave, and Bluetooth Low Energy, and collects implemented and proposed solutions to common ways of attacking systems built on these protocol stacks. Attacks evaluated are denial of service/sleep, man-in-the-middle, replay, eavesdropping, and in mesh networks, sinkhole, black hole, selective forwarding, sybil, wormhole, and hello flood. An intrusion detection system is proposed to detect sinkhole, selective forwarding, and sybil attacks in the routing protocol present in the communication stack Rime implemented in the operating system Contiki. The Sinkhole and Selective forwarding mitigation works close to perfection in larger lossless networks but suffers an increase in false positives in lossy environments. The Sybil Detection is based on Received Signal Strength and strengthens the blacklist used in the sinkhole and selective forwarding detection, as a node changing its ID to avoid the blacklist will be detected as in the same geographical position as the blacklisted node.

3D printing, also known as additive manufacturing (AM), has got rapidly developed since 1987. Compared with conventional manufacturing methods, 3D printing provides some advantages such as increasing material utilization and less waste of material. Maraging steel provides good strength and toughness without losing ductility, which has been used for the 3D printing technique. Selective laser melting (SLM) is one of the 3D printing methods, which is mostly used for metal and alloy powder. In this thesis, selective laser melting will be used for maraging steel. 3D printing maraging steel is a new material, the research about the properties of 3D printing maraging steel is still ongoing. Corrosion resistance is one of the most important properties of maraging steel due to the high cost of corrosion. So this thesis will focus on the corrosion behavior of 3D printing maraging steel. The purpose of this thesis was to find the best heat treatment condition for high corrosion resistance and to find the relationship between microstructure and corrosion behavior of maraging steel. In this thesis, several kinds of maraging steel samples with different heat treatment conditions were used. SLM, SLM austenized&quenched, SLM aged, conventional austenized&quenched, and conventional aged. Besides, two kinds of solutions were produced, NaOH (pH=11.5) and Na2SO4 (pH=6.5). To observe the microstructure, an optical microscope was used. The grain size is different between SLM and conventional samples, and also different between the samples with different heat treatment conditions. The potentiodynamic polarization method was used to measuring the corrosion behavior. SLM samples have much lower current density, and the passivation potential and the corrosion rate are similar compared with conventional samples. But due to the lack of further experiments, the relationship between corrosion behavior could be affected by the combined effect of several factors.