636 research outputs found
Adirondack Landslides: History, Exposures, and Climbing
Rock, soil, and vegetation avalanche down the slopes of the Adirondack Mountains, especially the High Peaks, on a regular basis. These landslides occur most often in response to heavy rainfall events and saturated conditions. The first guides and explorers used slides as the path of least resistance en route to various summits. Some slides have received considerable interest because of their recreational potential, location and accessibility, recent activity, or the well exposed geological features they contain. Tropical Storm Irene struck the region on August 28, 2011. It wreaked havoc on local communities, as well as, many areas of the backcountry. The deluge triggered over forty significant slides and countless minor ones, some of which are easily accessible. It thus opened up slide climbing to a wider audience and provided exceptional bedrock exposures for geoscientists interested in the Adirondack Region. The text below incorporates a short history of the slides and a sample of the more interesting Irene-related slides
Igneous Rock Associations 18. Transition Metals in Oceanic Island Basalt: Relationships with the Mantle Components
Incompatible elements and isotopic ratios identify three end-member mantle components in oceanic island basalt (OIB); EM1, EM2, and HIMU. We estimate compatible to mildly incompatible transition metal abundance trends (Ni, Co, Fe, Cu, Cr, V, Mn, Sc, and Zn) in âprimitiveâ basalt suites (Mg# = Mg/(Mg + 0.9*Fe) atomic = 0.72) from 12 end-member oceanic islands by regressing metals against Fe/Mg ratios in sample suites, and solving for concentrations at Mg/Fe = 1 (Mg# = 0.72). Using the transition metal estimates, exploratory statistics reveal that islands âgroupâ based on mantle component type even when La/Yb ratios are used to compensate metal concentrations for percentage melting. Higher chalcophile Zn (and Pb, earlier work) in EM1 and EM2 compared to HIMU, and higher Cr (3+) and Sc in HIMU relative to EM1, support views that HIMU represents subduction-processed ocean floor basalt. Incompatible elements, ratios and isotopes indicate that EM1 is Archean, EM2 is Proterozoic or younger, and both are related to sediment subduction. As found with incompatible elements, EM1 and EM2 show similar âcompatibleâ element concentrations, but lower (multi-valence) Cr, Fe and Mn in EM1 could indirectly reflect increasing oxidation of subducted sediment between the Archean and Proterozoic. Alternatively, changes in subduction processes that yielded peak continental formation in the Neoarchean, and craton-suturing in the Paleoproterozoic may account for EM1âEM2 differences. EM1 shows similar or lower Cr, Ni and Co compared to HIMU and EM2 suggesting that economic viability of layered intrusions, which have extreme EM1-like signatures, is unrelated to high metals in EM1 mantle sources, but that high % melting appears important. Because core-concentrated transition metals correlate with mantle component type, lithospheric recycling apparently controls their concentrations in OIB and core-mantle interaction may be unimportant.RĂSUMĂLes Ă©lĂ©ments incompatibles et les rapports isotopiques permettent de dĂ©limiter trois termes extrĂȘmes de composants mantĂ©liques dans des basaltes insulaires ocĂ©aniques (OIB), soit EM1, EM2, et HIMU. Nous estimons les tendances dâabondance de mĂ©taux de transition (Ni, Co, Fe, Cu, Cr, V, Mn, Sc, and Zn) compatibles Ă modĂ©rĂ©ment incompatibles dans des suites de basaltes « primitifs » (Mg# = Mg/(Mg + 0,9*Fe) rayon atomique = 0,72) sur 12 termes extrĂȘmes de matĂ©riaux insulaires ocĂ©aniques, par rĂ©gression des concentrations des mĂ©taux sur les rapports Fe/Mg dans des Ă©chantillons des suites, la dĂ©termination Ă©tant dĂ©finie au rapport Mg/Fe = 1 (Mg# = 0,72). Lâutilisation dâune approche statistique exploratoire sur les estimations de mĂ©taux de transition montre que la composition des Ăźles se « regroupent » en fonction du type de composition du manteau, cela mĂȘme lorsque les ratios La/Yb sont utilisĂ©s pour compenser les concentrations de mĂ©taux pour dĂ©terminer le pourcentuel de fusion. Le caractĂšre plus chalcophile du Zn (et Pb, travail antĂ©rieur) dans EM1 et EM2 comparĂ© Ă HIMU, et la plus grande teneur en Cr (3+) et Sc dans HIMU par rapport Ă EM1, accrĂ©ditent lâidĂ©e que HIMU reprĂ©sente le basalte de subduction des fonds ocĂ©aniques. Les Ă©lĂ©ments incompatibles, les ratios et les isotopes montrent que EM1 est archĂ©en, que EM2 est protĂ©rozoĂŻque ou plus jeune, et que les deux sont liĂ©s Ă la subduction sĂ©dimentaire. Comme constatĂ© pour les Ă©lĂ©ments incompatibles, EMI et EM2 affichent une compatibilitĂ© similaire des concentrations en Ă©lĂ©ments « compatibles », toutefois une concentration infĂ©rieure en Cr (multivalent), Fe et Mn dans EM1 pourrait reflĂ©ter indirectement une oxydation croissante des sĂ©diments subduits entre lâArchĂ©en et le ProtĂ©rozoĂŻque. Par ailleurs, les changements dans les mĂ©canismes de subduction qui ont menĂ© Ă un maximum de formation continentale au NĂ©oarchĂ©en et Ă des Ă©pisodes de sutures cratoniques au PalĂ©oprotĂ©rozoĂŻque, peuvent expliquer les diffĂ©rences entre EM1 et EM2. La teneur similaire ou infĂ©rieure en Cr, Ni et Co de EM1 par rapport Ă HIMU et EM2 permet de croire que la viabilitĂ© Ă©conomique des intrusions stratifiĂ©es â lesquelles montrent des signatures extrĂȘmes EM1 â est sans rapport avec les sources mantĂ©liques Ă fortes teneurs en mĂ©taux, mais que le fort pourcentuel de fusion qui importerait. Parce que la concentration du noyau en mĂ©taux de transition correspond avec le type de composant du manteau, câest le recyclage lithosphĂ©rique qui contrĂŽle apparemment leurs concentrations dans l'OIB, et l'interaction noyau-manteau pourrait ĂȘtre sans importance
A Comparison of Inverse Simulation-Based Fault Detection in a Simple Robotic Rover with a Traditional Model-Based Method
Robotic rovers which are designed to work in extra-terrestrial environments present a unique challenge in terms of the reliability and availability of systems throughout the mission. Should some fault occur, with the nearest human potentially millions of kilometres away, detection and identification of the fault must be performed solely by the robot and its subsystems. Faults in the system sensors are relatively straightforward to detect, through the residuals produced by comparison of the system output with that of a simple model. However, faults in the input, that is, the actuators of the system, are harder to detect. A step change in the input signal, caused potentially by the loss of an actuator, can propagate through the system, resulting in complex residuals in multiple outputs. These residuals can be difficult to isolate or distinguish from residuals caused by environmental disturbances. While a more complex fault detection method or additional sensors could be used to solve these issues, an alternative is presented here. Using inverse simulation (InvSim), the inputs and outputs of the mathematical model of the rover system are reversed. Thus, for a desired trajectory, the corresponding actuator inputs are obtained. A step fault near the input then manifests itself as a step change in the residual between the system inputs and the input trajectory obtained through inverse simulation. This approach avoids the need for additional hardware on a mass- and power-critical system such as the rover. The InvSim fault detection method is applied to a simple four-wheeled rover in simulation. Additive system faults and an external disturbance force and are applied to the vehicle in turn, such that the dynamic response and sensor output of the rover are impacted. Basic model-based fault detection is then employed to provide output residuals which may be analysed to provide information on the fault/disturbance. InvSim-based fault detection is then employed, similarly providing \textit{input} residuals which provide further information on the fault/disturbance. The input residuals are shown to provide clearer information on the location and magnitude of an input fault than the output residuals. Additionally, they can allow faults to be more clearly discriminated from environmental disturbances
Investigating the role of model-based reasoning while troubleshooting an electric circuit
We explore the overlap of two nationally-recognized learning outcomes for
physics lab courses, namely, the ability to model experimental systems and the
ability to troubleshoot a malfunctioning apparatus. Modeling and
troubleshooting are both nonlinear, recursive processes that involve using
models to inform revisions to an apparatus. To probe the overlap of modeling
and troubleshooting, we collected audiovisual data from think-aloud activities
in which eight pairs of students from two institutions attempted to diagnose
and repair a malfunctioning electrical circuit. We characterize the cognitive
tasks and model-based reasoning that students employed during this activity. In
doing so, we demonstrate that troubleshooting engages students in the core
scientific practice of modeling.Comment: 20 pages, 6 figures, 4 tables; Submitted to Physical Review PE
Inverse Simulation as a Tool for Fault Detection and Isolation in Planetary Rovers
With manned expeditions to planetary bodies beyond our own and the Moon currently intractable, the onus falls upon robotic systems to explore and analyse extraterrestrial environments such as Mars. These systems typically take the form of wheeled rovers, designed to navigate the difficult terrain of other worlds. Rovers have been used in this role since Lunokhod 1 landed on the Moon in 1970. While early rovers were remote controlled, communication latency with bodies beyond the Moon and the desire to improve mission effectiveness have resulted in increasing autonomy in planetary rovers. With an increase in autonomy, however, comes an increase in complexity. This can have a negative impact on the reliability of the rover system. With a fault-free system an unlikely prospect and human assistance millions of miles away, the rover must have a robust fault detection, isolation and recovery (FDIR) system. The need for comprehensive FDIR is demonstrated by the recent Chinese lunar rover, Yutu (or âJade Rabbitâ). Yutu was rendered immobile 42 days after landing and remained so for the duration of its operational life: 31 months. While its lifespan far exceeded its expected value, Yutu's inability to move severely impaired its ability to perform its mission. This clearly highlights the need for robust FDIR. A common approach to FDIR is through the generation and analysis of residuals. Output residuals may be obtained by comparing the outputs of the system with predictions of those outputs, obtained from a mathematical model of the system which is supplied with the system inputs. Output residuals allow simple detection and isolation of faults at the output of the system. Faults in earlier stages of the system, however, propagate through the system dynamics and can disperse amongst several of the outputs. This problem is exemplified by faults at the input, which can potentially excite every system state and thus manifest in every output residual. Methods exist for decoupling and analysing output residuals such that input faults may be isolated, however, these methods are complex and require comprehensive development and testing. A conceptually simpler approach is presented in this paper. Inverse simulation (InvSim) is a numerical method by which the inputs of a system are obtained for a desired output. It does so by using a Newton-Raphson algorithm to solve a non-linear model of the system for the input. When supplied with the outputs of a fault-afflicted system, InvSim produces the input required to drive a fault-free system to this output. The fault therefore manifests itself in this generated input signal. The InvSim-generated input may then be compared to the true system input to generate input residuals. Just as a fault at an output manifests itself in the residual for that output alone, a fault at an input similarly manifests itself only in the residual for that input. InvSim may also be used to generate residuals at other locations in the system, by considering distinct subsystems with their own inputs and outputs. This ability is tested comprehensively in this paper. Faults are applied to a simulated rover at a variety of locations within the system structure and residuals generated using both InvSim and conventional forward simulation. Residuals generated using InvSim are shown to facilitate detection and isolation of faults in several locations using simple analyses. By contrast, forward simulation requires the use of complex analytical methods such as structured residuals or adaptive thresholds
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