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Featured submissions


November 2022

October 2022


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  • Snowtography quantifies effects of forest cover on net water input to soil at sites with ephemeral or stable seasonal snowpack in Arizona, USA

    Dwivedi, Ravindra; Biederman, Joel A.; Broxton, Patrick D.; Lee, Kangsan; van Leeuwen, Willem J. D.; School of Natural Resources and the Environment, The University of Arizona; School of Geography, Development and Environment, The University of Arizona (Wiley, 2022-11-08)
    Forested, snow-dominated watersheds provide a range of ecosystem services including water supply, carbon sequestration, habitat and recreation. While hydrologic partitioning has been well-studied in watersheds with stable seasonal snowpack, less is known about watersheds with ephemeral snowpack. Furthermore, drought-related disturbances and/or management practices are altering vegetation cover in many forests, with unknown and potentially different, consequences for stable seasonal versus ephemeral snowpacks. This study quantifies net water input (NWI) to soil for two sites with contrasting stable seasonal and ephemeral snowpacks, respectively, for three water years in Arizona, USA. Observations include a network of automated cameras and graduated snow stakes (snowtography) deployed across gradients of forest structure, airborne lidar maps of topography and forests and SNOTEL station records. Given the importance of mixed-phase precipitation in ephemeral snowpack watersheds, an algorithm is developed to distinguish among snowfall and rainfall that does/does not contribute to snowpack mass. Finally, existing canopy interception and snowpack models are used to estimate how NWI varies with canopy cover. At the ephemeral snowpack site, increasing canopy cover reduces NWI amount and advances its seasonal timing less strongly than at the stable seasonal snowpack site. Interestingly, canopy reduces NWI duration at the ephemeral site but prolongs it at the stable seasonal snowpack site. These effects are more important in a cool/wet and average year than a warm/dry year. Understanding differences between canopy impacts on amount, timing and duration of NWI for areas with ephemeral versus stable seasonal snowpack is increasingly important as the number of watersheds with ephemeral snowpack grows.
  • Advancements in Light Field-based Laparoscopes

    Hua, Hong; Kwan, Elliott; Liang, Rongguang; Sawyer, Travis W. (The University of Arizona., 2022)
    In the 20th century, rigid laparoscopes revolutionized surgery such that minimally invasive procedures are now the norm. However, these systems only provide surgeons with a two-dimensional (2D) view of the operative field and are subject to two major optical limitations: (1) the absence of binocular vision results in restricted depth perception and (2) the field of view (FOV) is restricted to the local operating region to ensure high image spatial resolution. Performing surgery through a monitor without depth perception is challenging and requires extensive training. Meanwhile, surgical accidents that occur outside of the limited FOV and have gone unnoticed may cause unnecessary trauma to the patient. In this dissertation, two novel optical designs were developed to address the two limitations and further advance this technology. The conceptualization, lens design, prototyping, calibration, and processed results are discussed for both designs. The first design is a programmable aperture light field laparoscope. It was used to investigate and explore the requirements of three-dimensional depth information extraction in a monocular form factor. Compared to state-of-the-art dual objective stereoscopic laparoscopes, this form factor preserves more design volume for transmitting more of the object scene’s light field. A programmable aperture is used to preserve the laparoscope’s conventional high resolution 2D imaging and upon demand, capture the light field. The light field information enables this system to view the object scene from different viewing angles, digitally refocus, and generate depth maps for surgical guidance in post processing. A second-generation design called a tri-aperture monocular laparoscope was then developed to address the depth perception and FOV limitations simultaneously. This system uses two displaced apertures and a custom prism to capture the stereoscopic views simultaneously, which can then be processed to generate absolute depth maps. Meanwhile, a wide FOV for situational awareness is captured via a central third aperture. It provides 2D vision over an area 2x as large as that of the stereoscopic views. Such a system may pave the way towards restoring the binocular and large, foveated FOV qualities of human vision within the minimally invasive surgical setting.
  • The Rise and Fall of Lunar Topography

    Byrne, Shane; O'Brien, Patrick; Pelletier, Jon; McEwen, Alfred; Zega, Tom; Bray, Veronica (The University of Arizona., 2022)
    Landscape evolution on the Moon is driven by a relatively small number of physical mechanisms, making it an ideal laboratory for studying how the surfaces of airless planetary bodies change over time. By investigating the processes that shape topography, predominantly impact cratering, we can better interpret the present-day lunar surface. Decades of remote sensing observations have vastly improved our understanding of lunar topography and constrained the present-day crater formation rate. Coupled with high-resolution remote sensing datasets, numerical models offer a powerful tool for investigating the drivers of lunar geomorphology. In this thesis, I study the evolution of small-scale topography on the Moon across three main areas of focus. I first develop a general-purpose landscape evolution model for airless bodies that is calibrated by tuning the rate of diffusive degradation to match topographic roughness statistics on the maria. Using this model, I simulate the horizontal and vertical mixing of lunar regolith to constrain the timescales of surface exposure during which soil grains are exposed to space weathering effects. Over 3.5 Gyr of surface evolution, grains spend relatively little time at the uppermost surface due to rapid gardening by small impacts, with 98% of regolith tracer particles spending less than 20 Myr within a millimeter of the surface. By mapping the distribution of regolith exposure ages onto existing soil maturity measurements, I find that regolith grains reach a state of chemical maturity after 7-19 Myr of cumulative surface exposure. The same processes that excavate, transport, and bury regolith are also responsible for the erosion of lunar surface features and are therefore crucial for interpreting their ages. I next model the degradation of kilometer-scale craters and quantify the rate of topographic diffusion from small impacts to assess whether micrometeorite gardening has been the dominant erosional mechanism on the lunar surface over the last few billion years. Under commonly used lunar crater production functions, the erosion rate from small impacts is approximately 200 times lower than the value inferred from elevation profiles of degraded kilometer-scale craters on the maria. However, the abundance of fresh craters detected over the last decade is consistent with small impacts dominating the erosion of these features, but only if that abundance continues down to the sub-millimeter scale. My results also demonstrate that, regardless of the magnitude of diffusivity, mass transport from small impacts is fundamentally a nonlinear diffusion process and so are a revision to canonical lunar erosion models. Finally, the landforms resulting from impact processes, i.e., craters, can serve as reservoirs for thermally unstable species that record the delivery of volatiles to the inner solar system. Because of the Moon's low obliquity, small topographic depressions on the floors of large circumpolar craters can be doubly shadowed, shielded from both direct solar illumination and scattered light from nearby sunlit terrain. These locations are among the coldest in the solar system and could hold clues to the origins of the Moon's most volatile deposits. With illumination models applied to high-resolution digital terrain models, I derive the first map of double shadows at the lunar poles. At 30 m/pxl resolution, the total doubly shadowed surface area is 1.47 km$^2$ in the north and 5.37 km$^2$ in the south (~0.04% of singly shadowed area poleward of 85$^{\circ}$ latitude). The largest double shadows, nearly 600 meters across, could potentially be resolved with orbital temperature and reflectance measurements and are high-priority targets for future in situ exploration.
  • "We're All Doing the Best that we Can": A Hermeneutic Phenomenological Study of Novice Principal's Sense-Making of the Transition into the Role of a Principal in the Age of COVID-19

    Bosworth, Kris; Thompson, Kent Alan; Brunderman, Lynnette; Demps, Dawn; Ylimaki, Rose (The University of Arizona., 2022)
    Novice public-school principals face tremendous external pressures (e.g., high-stakes accountability, market forces, legitimization) and internal pressures (e.g., identity (re)construction, identity verification, authenticity) in the enactment of their role as a novice principal. These pressures converge in the dissonance of competing values, exacerbated by shifting roles and identities from teacher to leader. This qualitative hermeneutic phenomenological study on the lived experiences of five novice principals in southern Arizona investigates the meaning-making and sense-making processes of navigating the transition into the principalship at the tension points of neoliberal accountability regimes and social justice values. Informed by frameworks of hermeneutical phenomenology, sociological identity theory, neoliberalism, and social justice leadership, this study uses a hermeneutic phenomenological research design with methodological procedures modeled on interpretive phenomenological analysis, IPA. Additionally, a hermeneutic circle is woven throughout, charting a path of my journey and work as a researcher and participant. The five study participants, representing a variety of identities, personal histories, and lived experiences, provided experiences, values, and motivations that led to several key findings: Novice principals are largely motivated by their personal values of supporting those around them, specifically the importance of student-centered leadership and practice. Novice principals in this study held values that reflected current neoliberal accountability frameworks of monolithic student achievement over social justice leadership values. Novice principal motives, judgments, and experiences shed light on inadequacies of principal preparation programs and district mentoring efforts, which are exacerbated by neoliberal policy and practices.
  • Improving Skin Protection Behaviors in People With Skin Cancer

    Prettyman, Allen; Shaw, Patricia Ann; Kiser, Lisa H.; Autry, Tiffany K. (The University of Arizona., 2022)
    Purpose: This project aims to identify knowledge gaps in skin cancer and skin protection to determine if an educational program focused on skin cancer prevention will result in a greater understanding of skin cancer and adopting new behaviors to prevent skin cancer. Background: The number of skin cancer diagnoses increases significantly every year. The cost of treating skin cancers places a tremendous burden on healthcare costs. Exposure to ultraviolet rays is a known cause of skin cancer. The perception and knowledge of skin cancer vary significantly among patients diagnosed with skin cancer. A knowledge deficit about skin cancer and skin cancer prevention practices can diminish sun protection practices. Method: A 12-question Likert scale pre-questionnaire was administered to measure patient knowledge of skin cancer, risk factors, and skin cancer prevention. The same pre-questionnaire was distributed to a family member/friend. A 15-minute educational PowerPoint with voice-over was then presented. Following the PowerPoint, an open forum of questions/answers was conducted. The same 12-question Likert scale post-questionnaire was administered again to the patient and family member/friend. The Likert scale was utilized because it provides information about patient thoughts and feelings about the topic and can offer insight into patient perceptions. The results of the composite scores of the questionnaire were analyzed. Results: 16 participants, 10 patients, and six family members/friends participated in the session. There was a higher composite score in the patient group following the educational session, except for one question determined to be confounding. Likewise, the overall combined score of the family member/friends increased after the educational session. Conclusion: The educational session was successful, given the increase in scores following the session. It was clear from the scores that knowledge of skin cancer and skin protection measures is understood. What is not clear is if the increased knowledge will ultimately result in the adoption of skin protection behaviors. In future quality improvement (QI) projects on this topic, a follow-up questionnaire could be administered to directly measure the practice of skin protection behaviors of the participants.

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