Our lives are dominated by a complex visual world, and spatially selective attention allows us to process only the most relevant information. Previous evidence suggests that if possible locations of stimulus presentation are delineated, attention affects processing in a spatially graded manner. This gradient is seen in both behavioral measures and in visual evoked potentials (VEPs). Stimuli presented close to cued regions elicit faster responses and larger VEPs than those presented farther away. However, both position in the visual field and allocation of attention may contribute to the observed gradients. These relative contributions can be distinguished by comparing responses on physically identical trials when attention is directed to locations at various distances from the stimuli. In the current study, participants attended to one of 12 squares arranged in a circle around fixation. Letters appeared individually, each in one of the squares; 80% were O’s (standards) and 20% were X’s (deviants). Participants were instructed to press a button when an X appeared at the attended location. The largest amplitude N1s (150-200 ms) were observed when participants attended to the location where a standard was presented. VEPs elicited by standards showed evidence of asymmetric attentional gradients. Specifically, the gradient of facilitation spread down more than up. Results also showed that attention had differential effects on the stages of processing indexed at specific time windows. These results confirm that attention can be applied to visual processing in a spatial gradient, reveal its asymmetric distribution, and elaborate on the timing of its selectivity.

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Additively manufactured parts produced using selective laser melting (SLM) are prone to defects created during the build process due to part shrinkage while cooling. Currently defects are found only after the part is removed from the printer. To determine whether cracks can be detected before a print is completed, this project developed print parameters to print a test coupon with inherent defects – warpage and cracking. Data recorded during the build was then characterized to determine when the defects occurred. The test coupon was printed using two sets of print parameters developed to control the severity of warpage and cracking. The builds were monitored using an accelerometer recording at 12500 samples per second, an iphone recording audio at 48000 samples a second, and a camera taking a photo every build layer. Data was analyzed using image comparison, signal amplitude, Fourier Transform, and Wavelet Decomposition. The developed print parameters reduced warpage in the part by better distributing heat throughout the build envelope. Reducing warpage enabled the lower portion of the part to be printed intact, preserving it to experience cracking later in the build. From physical evidence on the part as well as time stamps from the machine script, several high energy impulse events in the accelerometer data were determined to be when cracking occurred in the build. This project’s preliminary investigation of accelerometers to detect defects in selective laser melting will be used in future work to create machine learning algorithms that would control the machine in real time and address defects as they arise.

Frequency selective surfaces (FSS) were originally developed for electromagnetic filtering applications at microwave frequencies. Electron-beam lithography has enabled the extension of FSS to infrared frequencies; however, these techniques create sample sizes that are seldom appropriate for real world applications due to the size and rigidity of the substrate. A new method of fabricating large area conformal infrared FSS is introduced, which involves releasing miniature FSS arrays from a substrate for implementation in a coating. A selective etching process is proposed and executed to create FSS particles from crossed-dipole and square-loop FSS arrays. When the fill-factor of the particles in the measurement area is accounted for, the spectral properties of the FSS flakes are similar to the full array from which they were created. As a step toward scalability of the process, a square-patch design is presented and formed into FSS flakes with geometry within the capability of ultraviolet optical lithography. Square-loop infrared FSS designs are investigated both in quasi-infinite arrays and in truncated sub-arrays. First, scattering-scanning near-field optical microscopy (s-SNOM) is introduced as a characterization method for square-loop arrays, and the near-field amplitude and phase results are discussed in terms of the resonant behavior observed in far-field measurements. Since the creation of FSS particles toward a large area coating inherently truncates the arrays, array truncation effects are investigated for square-loop arrays both in the near- and far-field. As an extension of the truncation study, small geometric changes in the design of square-loop arrays are introduced as a method to tune the resonant far-field wavelength back to that of the quasi-infinite arrays.

Meanderline structures are widely used as engineered birefringent materials for waveplates and retarders at radiofrequencies, and have been previously demonstrated at frequencies up to 90 GHz in the millimeter-wave band. In this dissertation, we present results related to the modeling, fabrication, and experimental characterization of meanderlines across the range from 30 to 100 THz, in the long-wave and mid-wave infrared bands. Specific issues addressed in these new designs include spectral dispersion and angular dependence of the retardance, as well as axial ratio and throughput. The impact resulting from the infrared properties of the metals and dielectrics is explicitly included throughout. Several novel applications are identified, including integrated circular polarizers, reflective waveplates, and large-area polarization tags.

Selective laser melting is a promising metallic additive manufacturing process with many potential applications in a variety of industries. Through a gracious donation made by Lawrence Livermore National Laboratory, California Polytechnic State University received and installed an SLM 125 HL selective laser melting machine in February 2017. As part of the initial setup effort, a preliminary machine verification study was conducted to evaluate the general print quality of the machine with default parameter settings. Coincidentally, the as-printed microstructure of SLM components was evaluated through nil strength fracture surface examination, an alternative to conventional polish-and-etch metallography. A diverse set of components were printed on the SLM 125 HL to determine the procedural best practices and inherent constraints. Additionally, the mode and mechanism of failure for a defective Lawrence Livermore National Laboratory component fabricated at their facility was investigated. From these studies, extensive documentation in the form of standard operating procedures, guidelines, templates, and summary reports was generated with the intent of facilitating future selective laser melting research at Cal Poly and strengthening the learning of students interfacing with the novel technology.

Studies have shown that facial sexual dimorphism, ranging on a continuum from very feminine to very masculine, affects observers’ ratings of dominance and threat. These studies, however, have used forced-choice paradigms, in which a pair of faces that have been manipulated to appear more masculine (masculinized) and feminine (feminized) are presented side by side. They are susceptible to demand characteristics, situational aspects of the experiment which produce the desired outcome, because participants may be able to draw the conclusion that faces which appear more masculine should be rated as more dominant. In this dissertation, I evaluated whether facial sexual dimorphism affects observers' threat perceptions in a way that minimizes the confounds caused by demand characteristics. In Experiment 1 and Experiment 2, I presented observers with masculinized and feminized faces individually, rather than in pairs, and for an extremely brief duration (Experiment 1). I predicted that observers would assign higher dominance (Experiment 1) and threat ratings (Experiment 2) to masculinized faces. Observers assigned higher dominance (Experiment 1) and threat (Experiment 2) ratings to masculinized faces, even when they were presented individually, and for as little as 100 milliseconds (ms) (Experiment 1). This would suggest that they can appraise differences in facial sexual dimorphism following very brief exposure. I proceeded to evaluate the effects of facial sexual dimorphism on men’s selective attention, while reducing the effects of demand characteristics, by testing for an attentional bias towards task-irrelevant masculinized men’s faces. In Experiment 3, forty-five men completed a Posner Cueing Paradigm in which they classified shapes, presented either right or left of center screen after a masculinized or feminized man’s face was presented in either the same or opposite location. Participants were faster to classify the shape following the presentation of a masculine face; however, they were not faster when a masculine face cued target position. In Experiment 4, forty-four men completed a Flanker Task in which they judged letter orientation (i.e., upright or upside-down), while ignoring flanking faces. Participants’ RT was not affected by Morph Type (i.e., whether the face was masculinized, feminized or unmodified). In Experiment 5, forty-one men completed a Dot Probe Task. They were presented with two facial photographs of different Morph Types to the left and right of center screen. This was followed by the presentation of a target shape, in the location of one of the faces. Participants’ objective was to classify shape orientation. Facial sexual dimorphism did not affect participants' classification speed. In Experiment 6, I primed participants with images meant to induce fear or arousal before each trial of a Dot Probe Task. Following the presentation of a fear inducing picture, participants RT to classify shapes when a masculinized face cued target position did not differ from when a feminized face cued target position. The two different presentation times did not create different patterns of results, indicating that masculinized faces did not induce either a cueing or inhibitory affect. Overall, my results do not support my hypothesis that men selectively attend to masculinized faces when they are presented as irrelevant information. I conclude by discussing future directions for evaluating the effects that facial sexual dimorphism has on observers’ interpersonal perceptions of threat and dominance, while controlling for the effects of demand characteristics.

The potential of increasing disease problems through the use of recycled irrigation water in horticultural operations is a serious concern, yet basic research on waterborne plant pathogens in Virginia is lacking. In this work seasonal fluctuations and locations of Pythiaceae in a recycled water irrigation system at a container nursery were determined. <i>Pythium</i> spp. were recovered more frequently and in greater numbers than <i>Phytophthora</i> spp. Species of <i>Phytophthora</i> recovered in filtering assays were identified as <i>P. capsici, P. citricola, P. citrophthora, P. cryptogea, P. drechsleri,</i> and <i>P. nicotianae. P. cryptogea</i> and <i>P. drechsleri</i> were the only <i>Phytophthora</i> spp. recovered from baits placed on the surface of the irrigation reservoir, whereas a greater diversity of species was recovered from baits placed at depths. Hymexazol-amended medium was found to have limitations in recovery of <i>Phytophthora</i> spp. In pathogenicity tests, <i>P. cactorum, P. capsici, P. citrophthora,</i> and <i>P. nicotianae</i> caused significant mortality of <i>Salvia officinalis</i> and <i>P. cactorum</i> showed limited pathogenicity on <i>Gerbera jamesonii</i>. Asymptomatic (aboveground) plants were found to harbor inoculum long after <i>Phytophthora</i>-inoculation. Fresh weight analyses of roots and shoots of asymptomatic plants demonstrated that <i>Phytophthora</i> inoculation may either reduce or stimulate plant shoot growth, but little effect is apparent on roots. Irrigation with naturally infested irrigation water reduced plant growth. This research provides data for prioritizing development of detection technology and management practices for plant pathogens in irrigation water. The results may also lead to improvements in conventional water assay protocols for plant pathogens. / Master of Science

In the lowlands of Southeast Asia, the island of Borneo faces rates of primary forest degradation and deforestation exceeding tropical forests across the globe. For critically endangered Bornean orangutans (Pongo pygmaeus wurmbii), habitat loss greatly threatens the long-term stability of remaining populations. With rates of forest loss and fragmentation on the rise, it is critical we explore the role of anthropogenically-modified landscapes in conserving wild orangutans. Here I investigate orangutan habitat quality within Gunung Palung National Park (GPNP), in Borneo, Indonesia, focusing on the conservation value of a secondary forest with a history of logging. Orangutans in GPNP flexibly inhabit a range of habitats within the primary forest, suggesting the nearby secondary forest could provide population support if sufficient resources are available. Monthly phenology and focal follow data were utilized to assess feeding behavior in relation to food availability. While overall fruit availability was consistently higher in the primary forest, the abundance and fruiting frequency of preferred foods were significantly greater in the secondary forest. The fruiting pattern of preferred resources also significantly predicted orangutan presence. These findings suggest post-disturbance landscapes, if safeguarded and able to become secondary forest, could be vital areas of refuge for Bornean orangutans across an ever-changing landscape.

This research studied Ho166/PLLA microspheres, a promising treatment for tumours in the liver. The Ho166 is generated through a neutron capture reaction during irradiation in a nuclear reactor. Previous work has found that neutron-irradiation in-core causes damage to microspheres and causes additional degradation to progress once suspended in media. The cause of this damage was not well understood and is the focus of this research. This research studied factors present in-core such as heat, gamma radiation, and impacts of lead shielding, for their impact on microsphere quality. Additionally, this research looked at the potential of reactive oxygen species causing damage once microspheres are suspended in liquid. Thresholds for damage were identified to correlate with the glass transition temperature of poly- l-lactic acid. Exposure to gamma radiation induces heating, as well as structural changes to the polymer which shifts the temperature where the glass transition occurs. Damage formed from gamma radiation, independent of other variables, was seen at extreme accumulated doses. Notably, exposure to gamma radiation and heat did not cause a progression of damage over time. Samples exposed only to these factors remained stable in solution for extended periods. A theory was proposed that reactive oxygen species formed by the interaction of ionizing radiation with the suspending media may be causing the progression of damage over time. This factor would only be present for microspheres having undergone neutron capture reactions, forming radioactive holmium. Testing confirmed a potential impact of radiation interactions with the suspending media contributing to damage progression. Several thicknesses of lead shielding surrounding the sample chamber were tested in-core. There were significant impacts on temperature, neutron flux, and microsphere quality. / Thesis / Master of Science (MSc) / This research studied Ho166/PLLA microspheres, a promising treatment for tumours in the liver. The preparation of this treatment includes microspheres being neutron irradiated in the core of a nuclear reactor. Irradiation in-core leads to damage of microspheres. This research studied factors present in-core such as heat, gamma radiation, and thickness of lead shielding, for their impact on microsphere quality. Additionally, this research looked at the potential of reactive oxygen species causing damage once microspheres are suspended in liquid. Thresholds for damage were identified for temperature and gamma radiation exposure. Radiation interactions in liquid suggest possible damaging effects over time. Finally changing the thickness of lead shielding in core had significant impact on temperature, neutron flux, and microsphere quality.