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Ultra-Fine Pointing for Nanosatellite Telescopes with Actuated BoomsThe smallsat revolution has impacted the architecture of most modern satellites with the notable exception of fine-pointing space telescopes. Conventional attitude control hardware scales poorly as the spacecraft gets smaller, resulting in significant mass and performance penalties for nanosatellites with strict pointing requirements. This paper presents a novel attitude actuation and planning strategy that utilizes actuated booms with tip masses and magnetorquers for three-axis pointing and momentum desaturation. The speed of the booms is an appropriate match for the slowly varying environmental disturbance torques encountered in low-Earth orbit. As a result, these booms do not create the high-frequency jitter that reaction wheels do, lessening the need for complex second-stage correction hardware in the payload. An optimization-based motion planner is able to reason about the orbital ephemeris to ensure the booms never exceed their actuation limits, and a Linear Quadratic Gaussian controller is able to maintain fine-pointing during times of payload operation.
Precipitation stable isotope composition, moisture sources, and controlling factors in Xi'an, Northwest ChinaSeasonal and interannual variations in precipitation stable isotopes are crucial for clarifying complex moisture sources at the inland margins of the summer monsoon such as Northwest China. Stable hydrogen and oxygen isotope data (δD, δ18O) of totally 317 event-based precipitation samples from 2016 to 2020 in Xi'an show a consistent annual cycle in which, maximum δD and δ18O values occur in the pre-monsoon season (April–June), and minimum in the late monsoon to post-monsoon (November–March) seasons. Values of d-excess are lowest in the monsoon season. The local meteoric water line is δD = 7.5δ18O + 9.7. Precipitation δ18O in monthly time scale correlates weakly with relative humidity in the monsoon season, and with precipitation amount in the pre-monsoon season. Maps of potential water sources and wind fields, considered with monsoon intensity indices and the isotope data, are consistent with moisture sources as follows: during the monsoon, moisture advected by air flow mainly from the Bay of Bengal or recycled from land surfaces along this path; during the pre-monsoon, moisture advected in westerly circulation passing north of the Tibetan Plateau; and during the post-monsoon, recycled monsoon moisture advected from the south or southwest of Xi'an, and influenced by the intensity of the preceding South Asian Summer Monsoon (SASM). Moisture recycled from land surfaces is important in all seasons. The SASM index controlled the variation of mean seasonal δ18O, but not precipitation amount in the monsoon season. The westerly index (WI) controlled the precipitation amount in the pre-monsoon season and mean seasonal δ18O in the post-monsoon season. Seasonal change in moisture sources is the main reason of the seasonal variation of mean precipitation δ18O.
Towards Developing Metrics to Evaluate Digital EngineeringModel-based systems engineering (MBSE) is an increasingly accepted practice in the Systems Engineering (SE) community, however, little has been done to empirically show that MBSE provides value. Furthermore, as the industry continues in the direction of digital transformation, MBSE will become a critical component of the larger Digital Engineering (DE) approach. This paper presents a measurement framework for selecting and developing appropriate metrics to assess the value/benefits of MBSE and subsequently DE. Utilizing expected benefits identified in a review of MBSE literature, a causal map was hypothesized to show how expected benefits (potential metrics) influence and relate to each other. This was done in order to systematically determine which benefits would be the most impactful to measure. The hypothesized causal model was presented for feedback to subject-matter experts from a working group developing the first DE measurement framework. This group is a joint effort with industry, academia, and the USA government to develop DE metric standards. Once the causal map was finalized, a case study was used to partially validate the causal model. Based on the causal map and subsequent analysis, we can recommend the first metrics to be employed for DE/MBSE based on the most influential nodes of the causal model. The potential metric candidates include: system quality, defects, time, rework, ease of making changes, system understanding, Effort, accessibility of information, collaboration, project methods/processes, and use of DE/MBSE tools. We believe a concerted effort across the industry to focus on measuring these variables is the most effective way to establish proof of the value of MBSE and DE.
Integrating resilience attributes into local disaster management plans in Metro Manila: Strengths, weaknesses, and gapsIntegrating resilience attributes into local plans is considered an important step in enhancing disaster risk reduction. However, the extent to which resilience is captured in local disaster management plans remains underexplored. This paper utilizes content analysis to examine the integration of the United Nations Office for Disaster Risk Reduction's (UNDRR) resilience attributes across 11 cities in Metro Manila. Results show strong integration in governance and risk identification while gaps exist in ecosystem protection, city-to-city learning, and disaster victims' participation in recovery planning. The paper recommends introducing metropolitan-level platforms for inter-city learning, turning local authorities' attention towards nature-based solutions, and including disaster victims in the recovery planning process.
Fire risk communication in the urban informal sector: Evidence from traditional marketplaces in Accra, GhanaUrban marketplace fires in Ghana are chronic, devasting in economic losses and disproportionately impacting informal sector workers. Yet, the scholarly works on urban disasters have focused on hydrometeorological and other man-made disasters to the neglect of marketplace fires, particularly the challenges in risk communication between emergency management agencies and urban marketplace workers. In seeking to extend the emerging but scant work on urban marketplace fires in Ghana, this paper analysed fire risk communication to understand how socio-cultural factors influence the perceptions and protective behavioral strategies of traders in two traditional urban marketplaces of Accra. In-depth interviews with both public agencies and traders showed that traders’ social networks and interactions are important sources and channels for fire risk communication, albeit unharnessed by formal emergency management agencies. It also revealed how cultural elements such as religious beliefs about fire risks affect proactiveness in fire risk preparedness and response. To ensure effective risk communication about marketplace fires, this paper calls attention to and mainstreaming of socio-cultural aspects of everyday life in marketplaces into disaster risk planning and management.