1,865 research outputs found

    An Investigation into the Economic Thought of Medieval Arab-Islamic Scholars and Enlightenment Philosophers

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    This student-faculty collaborative research project focused on the contributions to economic thought of two distinct groups: medieval Arab-Islamic scholars and Enlightenment philosophers. The primary goal of the project was to generate two new chapters to supplement the Evolution of Economic Thought text. It looked to answer the research question, “How did the intellectual activity of medieval Arab-Islamic scholars and Enlightenment philosophers reflect and/or contribute to the development of modern economic thought?” The medieval Arab-Islamic chapter produced findings including a centrality of religion to economic life, the importance of specialization for increased efficiency, and an understanding of just price. Ibn Khaldūn, a prominent scholar of the medieval Arab-Islamic era, recognized a need for the division of labor, as individuals lack the capability of providing sufficient goods on their own to subsist. A holistic approach to thinking and an emphasis on rational methodology and objectivity were major contributions from the research on Enlightenment philosophers. Thomas Hobbes’s social contract theory is a philosophical idea that underlies modern economic theory, discussed at length in the Enlightenment chapter. Both chapters will be accessible online and available for instructors to use separately or in conjunction with existing online chapters as precursors to the main, physical text

    Effects of structural confinement and thermal profiles on propagating spin waves, The

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    2018 Spring.Includes bibliographical references.Spintronics is a growing field that relies on the spin degree of freedom in the form of spin currents instead of electronic charge to transmit and process information. There are many advantages to spin-based devices including scalability, a wide range of host materials including insulators, and almost no energy loss due to Joule heating. Spin angular momentum can be transmitted in the form of spin-polarized currents that flow through a metal, pure spin currents, or in the form of spin waves, disturbances in the magnetization state that can propagate and hence can carry energy. If such a spin-based paradigm is to be realized, there are many open questions that must be addressed. Two questions of particular importance are: how can short wavelength spin waves that are needed for information transmission be controllably generated? and once generated, how can these spin waves be modified and controlled? This thesis focusses on answering both of these questions through the investigation of spin waves in two different types of samples, patterned microstructures and thin continuous films, performed using Brillouin light scattering (BLS) spectroscopy. In the first experiment, the possibility of generating short wavelength spin waves by dynamically exciting a non-uniform magnetic state called the antivortex (AV) in a Permalloy microstructure is explored. Frequency scans were performed to identify a spectrum of high-frequency modes of the AV state. These modes were then individually mapped out by pumping at the frequency of the mode and performing spatially-resolved BLS scans. Comparing the experimental results with dispersion curves and micromagnetic simulations reveals that some of most prominent modes involve coupling of the AV dynamics to propagating spin waves in the adjacent nanowires highlighting the fact that the local magnetization state has a significant effect on the spin wave dynamics. Due to the natural way that an antivortex state can be incorporated into a nanowire network, this spin configuration may be useful as a means to generate or control spin waves for applications. In the second study we explore the possibility of modifying the propagation characteristics of both spin waves and spin caustic beams, which could be highly useful in spin-wave-based logic devices, using non-uniform thermal gradients up to 4.5 K/mm. These experiments were performed in a yttrium iron garnet (YIG) thin film - a model system for studying spin waves due to extremely low damping characteristics. An intricate diamond-shaped propagation pattern was observed and explained using the dispersion manifold for the YIG film and considering the range of wavevectors excited by the antenna. Significant modifications to the propagation characteristics such as beam angle, temporal pulse shape, mode profiles, and group velocity were observed as spin waves travelled into heated regions. These results will serve to broaden the understanding of how heat can be used to affect and control spin waves

    Vegetative and Climatic Controls on Holocene Wildfire and Erosion Recorded in Alluvial Fans of the Middle Fork Salmon River, Idaho

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    The Middle Fork Salmon River watershed spans high-elevation mixed-conifer forests to lower-elevation shrub-steppe. In recent decades, runoff from severely burned hillslopes has generated large debris flows in steep tributary drainages. These flows incised alluvial fans along the mainstem river, where charcoal-rich debris-flow and sheetflood deposits preserve a record of latest Pleistocene to Holocene fires and geomorphic response. Through deposit sedimentology and 14C dating of charcoal, we evaluate the processes and timing of fire-related sedimentation and the role of climate and vegetation change. Fire-related deposits compose ~66% of the total measured fan deposit thickness in more densely forested upper basins versus ~33% in shrub-steppe-dominated lower basins. Fires during the middle Holocene (~8000 - 5000 cal yr BP) mostly resulted in sheetflood deposition, similar to modern events in lower basins. Decreased vegetation density during this generally warmer and drier period likely resulted in lower-severity fires and more frequent but smaller fire-related sedimentation events. In contrast, thick fire-related debris-flow deposits of latest Pleistocene-early Holocene (~13,500-8000 cal yr BP) and late Holocene (\u3c 4000 cal yr BP) age are inferred to represent higher-severity fires, though data in the former period are limited. Widespread fires occurred in both upper and lower basins within the Medieval Climatic Anomaly (1050-650 cal yr BP) and the early Little Ice Age ca. 550 cal yr BP. We conclude that a generally cooler late Holocene climate and a shift to denser lodgepole pine forests in upper basins by ~2500 cal yr BP provided fuel for severe fires during episodic droughts

    Multiple Paths Forward: Diversifying Mathematics as a Strategy for College Success (Executive Summary)

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    This executive summary outlines key findings from a report on how colleges are creating math pathways that are aligned with students' programs of study

    The interfascicular matrix enables fascicle sliding and recovery in tendon, and behaves more elastically in energy storing tendons

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    While the predominant function of all tendons is to transfer force from muscle to bone and position the limbs, some tendons additionally function as energy stores, reducing the cost of locomotion. Energy storing tendons experience extremely high strains and need to be able to recoil efficiently for maximum energy storage and return. In the equine forelimb, the energy storing superficial digital flexor tendon (SDFT) has much higher failure strains than the positional common digital extensor tendon (CDET). However, we have previously shown that this is not due to differences in the properties of the SDFT and CDET fascicles (the largest tendon subunits). Instead, there is a greater capacity for interfascicular sliding in the SDFT which facilitates the greater extensions in this particular tendon (Thorpe et al., 2012). In the current study, we exposed fascicles and interfascicular matrix (IFM) from the SDFT and CDET to cyclic loading followed by a test to failure. The results show that IFM mechanical behaviour is not a result of irreversible deformation, but the IFM is able to withstand cyclic loading, and is more elastic in the SDFT than in the CDET. We also assessed the effect of ageing on IFM properties, demonstrating that the IFM is less able to resist repetitive loading as it ages, becoming stiffer with increasing age in the SDFT. These results provide further indications that the IFM is important for efficient function in energy storing tendons, and age-related alterations to the IFM may compromise function and predispose older tendons to injury

    ENSO-driven extreme oscillations in mean sea level destabilise critical shoreline mangroves—An emerging threat

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    Recent ENSO-related, extreme low oscillations in mean sea level, referred to as ‘Taimasa’ in Samoa, have destabilised shoreline mangroves of tropical northern Australia, and possibly elsewhere. In 1982 and 2015, two catastrophic Taimasa each resulted in widespread mass dieback of ~76 km2 of shoreline mangroves along 2,000 km of Australia’s Gulf of Carpentaria. For the 2015 event, we determined that a temporary drop in sea level of ~0.4 metres for up to six months duration caused upper zone shoreline mangroves across the region to die from severe moisture deficit and desiccation. The two dramatic collapse events revealed a previously unrecognised vulnerability of semi-arid tidal wetland habitats to more extreme ENSO influences on sea level. In addition, we also observed a relationship between annual sea level oscillations and mangrove forest productivity where seasonal oscillations in mean sea level were co-incident with regular annual mangrove leaf growth during months of higher sea levels (March-May), and leaf shedding during lower sea levels (September-November). The combination of these periodic fluctuations in sea level defined a mangrove ‘Goldilocks’ zone of seasonal productivity during median-scale oscillations, bracketed by critical threshold events when sea levels became unusually low, or high. On the two occasions reported here when sea levels were extremely low, upper zone mangrove vegetation died en masse in synchrony across northern Australia. Such extreme pulse impacts combined with localised stressors profoundly threaten the longer-term survival of mangrove ecosystems and their benefits, like minimisation of shoreline erosion with rising sea levels. These new insights into such critical influences of climate and sea level on mangrove forests offer further affirmation of the urgency for implementing well-considered mitigation efforts for the protection of shoreline mangroves at risk, especially given predictions of future re-occurrences of extreme events affecting sea levels, combined with on-going pressure of rapidly rising sea levels

    Thrust to weight improvement of JetCat P100-RX turbojet engine

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    The purpose of the presented design is to improve the thrust-to-weight ratio of the JetCat P100-RX small turbojet engine, a project sponsored by the Air Force Research Laboratory. This project is a year-long endeavor ending with a competition at the Wright-Patterson Air Force Base in Dayton, Ohio. The primary challenge is to increase thrust with minimal increase in weight. Several solutions were considered such as nozzle geometry optimization, exit guide vane addition, and material improvement. The final design included the optimized nozzle geometry configured with seven exit guide vanes with leading edges oriented 10-degrees into the exhaust flow. This new nozzle was additively manufactured in titanium to reduce weight and mitigate deformation from high exhaust gas temperatures. An inlet cowling of the original geometry was fabricated from foam to reduce weight. Finally, a new battery was substituted to reduce additional weight. The improved nozzle resulted in a thrust increase of 23%, and the material and battery improvements resulted in a weight reduction of 8%, leading to an overall thrust-to-weight improvement of 32%. The thrust-to-weight ratio was improved from 6.64 to 8.75

    The effects of acute beetroot juice ingestion on upper and lower body muscular power during weightlifting exercise in men

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    Nitrate-rich beetroot juice (BR) supplementation improves movements with high-velocity and high-power muscle contractions which may be due to enhanced blood flow, oxygenation and contractile function in type II muscle fibers. The literature has focused predominantly on the effects of BR supplementation running and cycling performance, but its efficacy in resistance exercise, a modality that relies on type II muscle fibers, has limited data. Furthermore, it is unknown how supplementation strategies impact the physiological and ergogenic effects of BR during exercise. Therefore, the purpose of this study is to assess whether single or multi-day nitrate ingestion will improve performance and muscle oxygenation during resistance exercise. In a double-blind, randomized crossover design, 14 healthy recreationally active men will report to the laboratory for five occasions over a 4-wk period. On the first visit, participants will undergo a 1 repetition-max (1RM) test for back squat and bench press. Subsequently, participants will complete two 4-day experimental trials where they will consume 2 x 70mL doses per day of either nitrate-depleted placebo (PL) or concentrated nitrate-rich BR. On experimental days of each supplementation period (day 1 and 4), subjects will consume 140 mL of their allocated beverage 2.5-h before exercise. On day 2 and 3 of the supplementation period, participants will consume one 70 mL beverage in the morning and one in the evening. On experimental days, participants performed a power protocol, consisting of 2 sets x 2 repetitions of back squats and bench press at 70%1RM followed by repetition-to-failures at 60%1RM. Muscle oxygenation, power and velocity were assessed during exercise using near infrared spectroscopy and a linear transducer, respectively. A subset of data has been collected (n=9) and data collection is ongoing
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