2,679 research outputs found

    The Hypanis Valles delta: The last highstand of a sea on early Mars?

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    One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars' dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km2). This has an extensive catchment (4.6 x 105 km2) incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (āˆ¼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend āˆ¼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia ā€“ an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perhaps even an ocean that filled the northern plains of Mars

    The radius and mass of the subgiant star bet Hyi from interferometry and asteroseismology

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    We have used the Sydney University Stellar Interferometer (SUSI) to measure the angular diameter of beta Hydri. This star is a nearby G2 subgiant whose mean density was recently measured with high precision using asteroseismology. We determine the radius and effective temperature of the star to be 1.814+/-0.017 R_sun (0.9%) and 5872+/-44 K (0.7%) respectively. By combining this value with the mean density, as estimated from asteroseismology, we make a direct estimate of the stellar mass. We find a value of 1.07+/-0.03 M_sun (2.8%), which agrees with published estimates based on fitting in the H-R diagram, but has much higher precision. These results place valuable constraints on theoretical models of beta Hyi and its oscillation frequencies.Comment: 3 figures, 3 tables, to appear in MNRAS Letter

    Spatial Variation of False Map Turtle (Graptemys pseudogeographica) Bacterial Microbiota in the Lower Missouri River, United States

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    Turtle populations around the world are continually confronted with changing environments that affect their ecology and conservation status. Among freshwater turtles, population dynamics are thought to be mediated by complex yet often cryptic causes. One recent direction of focus in addressing these causes is the turtle-associated microbiota. In turtles, the gut- associated microbiota is of exceptional interest due to its continual association with host species under changing conditions. Diet-based fluctuations and changes in microbial diversity may correspond to varying external environments at both the individual and population level. Environmental responses are of particular interest due to the anthropogenic changes that may underlie them. Pollutants, disruption of climatic patterns, and habitat fragmentation all have the potential to affect turtle-associated microbiota and subsequent population and species conservation. To better understand potential human-induced changes, the diversity of turtle-associated microbiota over local spatial gradients must be better understood. We examined microbial community alpha- and beta-diversity among 30 adult False Map Turtles (Graptemys pseudogeographica) at three sites within the lower Missouri River, United States. Our results indicate significant microbial community centroid differences among sites (beta-diversity), which are likely mediated by various local environmental factors. Such factors will have to be carefully considered in any future attribution of anthropogenic determinants on turtle-associated microbiota as it relates to turtle population dynamics

    The Mission Assessment Post Processor (MAPP): A New Tool for Performance Evaluation of Human Lunar Missions

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    The National Aeronautics and Space Administration s (NASA) Constellation Program paves the way for a series of lunar missions leading to a sustained human presence on the Moon. The proposed mission design includes an Earth Departure Stage (EDS), a Crew Exploration Vehicle (Orion) and a lunar lander (Altair) which support the transfer to and from the lunar surface. This report addresses the design, development and implementation of a new mission scan tool called the Mission Assessment Post Processor (MAPP) and its use to provide insight into the integrated (i.e., EDS, Orion, and Altair based) mission cost as a function of various mission parameters and constraints. The Constellation architecture calls for semiannual launches to the Moon and will support a number of missions, beginning with 7-day sortie missions, culminating in a lunar outpost at a specified location. The operational lifetime of the Constellation Program can cover a period of decades over which the Earth-Moon geometry (particularly, the lunar inclination) will go through a complete cycle (i.e., the lunar nodal cycle lasting 18.6 years). This geometry variation, along with other parameters such as flight time, landing site location, and mission related constraints, affect the outbound (Earth to Moon) and inbound (Moon to Earth) translational performance cost. The mission designer must determine the ability of the vehicles to perform lunar missions as a function of this complex set of interdependent parameters. Trade-offs among these parameters provide essential insights for properly assessing the ability of a mission architecture to meet desired goals and objectives. These trades also aid in determining the overall usable propellant required for supporting nominal and off-nominal missions over the entire operational lifetime of the program, thus they support vehicle sizing

    A two-step learning approach for solving full and almost full cold start problems in dyadic prediction

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    Dyadic prediction methods operate on pairs of objects (dyads), aiming to infer labels for out-of-sample dyads. We consider the full and almost full cold start problem in dyadic prediction, a setting that occurs when both objects in an out-of-sample dyad have not been observed during training, or if one of them has been observed, but very few times. A popular approach for addressing this problem is to train a model that makes predictions based on a pairwise feature representation of the dyads, or, in case of kernel methods, based on a tensor product pairwise kernel. As an alternative to such a kernel approach, we introduce a novel two-step learning algorithm that borrows ideas from the fields of pairwise learning and spectral filtering. We show theoretically that the two-step method is very closely related to the tensor product kernel approach, and experimentally that it yields a slightly better predictive performance. Moreover, unlike existing tensor product kernel methods, the two-step method allows closed-form solutions for training and parameter selection via cross-validation estimates both in the full and almost full cold start settings, making the approach much more efficient and straightforward to implement

    The acceleration of transitions to urban sustainability: a case study of Brighton and Hove

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    Cities raise major challenges and opportunities for achieving sustainability. Much literature on urban sustainability focuses on specific aspects such as planning practices, urban policy or the diffusion of more sustainable technologies or practices. However, attempts at understanding the mechanisms of structural change towards sustainability have resulted in the emergence of an interdisciplinary field of sustainability transitions research. Transitions research has developed a phase model of transitions in which predevelopment, take-off, acceleration and stabilization phases are distinguished. However, the acceleration phase has received limited attention so far. This is a crucial gap as policy makers are keen to accelerate transitions. This paper aims to enhance our understanding of how local actions contribute towards accelerating urban sustainability transitions. It does so by testing an acceleration mechanisms framework through exploring the collective agency of local initiatives in urban sustainability transitions. Drawing on a case study of the city of Brighton & Hove (UK), the paper finds that despite favourable local political conditions, there is a lack of evidence of acceleration apart from in individual domains such as food or mobility. Progress is found to depend on the agency of initiatives to both scale up sustainable practices and embed these practices into local governance arrangements

    Single-photon tunneling

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    Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a thick gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousands photons per second. This result is explained theoretically in terms of "photon blockade", similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. The single-photon tunneling effect may find many applications in the emerging fields of quantum communication and information processing.Comment: 4 pages, 4figure

    Community Education on MTM Services

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    Background: Medication nonadherence, defined as ā€œthe number of doses not taken or taken incorrectly that jeopardizes the patientā€™s therapeutic outcome,ā€ is a major health problem with about 43% of the general population nonadherent to their medications. Medication nonadherence accounts for an estimated 125,000 deaths per year in the US, 33-69% of medication-related hospital readmissions, and an estimated 100to100 to 300 billion in direct and indirect medical costs. Medication therapy management (MTM), defined as ā€œa distinct service or group of services that optimize therapeutic outcomes for individual patients,ā€ has been found to reduce medication nonadherence. However, many individuals eligible for MTM services are not aware of the resource available to them and do not believe the service will be beneficial to them. Objectives: A pre post observational study design will be used to determine the effects of two types of educational interventions on MTM of patientā€™s perceptions of MTM and enrollment in MTM services. Methodology: Participants will be divided into two intervention groups. All participants will complete a pre survey to assess current perceptions of MTM services. One group will attend a community educational event on MTM, and the second group will receive an educational brochure in the mail. All participants will complete a post survey to reassess perceptions of MTM after the educational intervention. In addition, all participants will be tracked to determine future enrollment in an MTM service. Analysis: Descriptive tests and paired t-tests/Wilcoxon Signed Rank tests will be run on data acquired from pre and post surveys. Unpaired t-tests/Mann Whitney and chi-square tests will be run to compare data between intervention groups. Descriptive tests will be run on data acquired from tracking enrollment
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