Computer architecture for efficient algorithmic executions in real-time systems: New technology for avionics systems and advanced space vehicles

Improvements and advances in the development of computer architecture now provide innovative technology for the recasting of traditional sequential solutions into high-performance, low-cost, parallel system to increase system performance. Research conducted in development of specialized computer architecture for the algorithmic execution of an avionics system, guidance and control problem in real time is described. A comprehensive treatment of both the hardware and software structures of a customized computer which performs real-time computation of guidance commands with updated estimates of target motion and time-to-go is presented. An optimal, real-time allocation algorithm was developed which maps the algorithmic tasks onto the processing elements. This allocation is based on the critical path analysis. The final stage is the design and development of the hardware structures suitable for the efficient execution of the allocated task graph. The processing element is designed for rapid execution of the allocated tasks. Fault tolerance is a key feature of the overall architecture. Parallel numerical integration techniques, tasks definitions, and allocation algorithms are discussed. The parallel implementation is analytically verified and the experimental results are presented. The design of the data-driven computer architecture, customized for the execution of the particular algorithm, is discussed

Numerical Computations for Estuarine Flood Plains

Construction on estuarine flood plains can contribute significantly to flooding problems during times of large river inflow. A two dimensional depth averaged finite difference model is presented which allows for improved environmental impact assessment of construction on estuarine flood plains. The model is applied to the delta region above Mobile Bay, Alabama where a railroad crosses the flood plains. The railroad is built on a fill with trestles at established channels. The model is used to evaluate the effect which the railroad has on known flooding problems in the delta region. Partial calibration and verification of the numerical model is accomplished with available prototype data from previous flood events. The numerical model demonstrates that while a great amount of water may be stored on flood plains, conditions are not generally conducive for large flow rates. Most of the flood still moves along major established channels. Construction on flood plains may exert a significant influence on flood stage elevations in certain regions with other regions experiencing a very minor effect. In particular, construction in the interior of the flood plains may produce large effects in the interior with only minor effects propagating to the boundaries

Atmospheric Escape From Three Terrestrial Planets in the L 98-59 System

A critically important process affecting the climate evolution and potential habitability of an exoplanet is atmospheric escape, in which high-energy radiation from a star drives the escape of hydrogen atoms and other light elements from a planet's atmosphere. L 98-59 is a benchmark system for studying such atmospheric processes, with three transiting terrestrial-size planets receiving Venus-like instellations (4-25 S$_\oplus$) from their M3 host star. We use the VPLanet model to simulate the evolution of the L 98-59 system and the atmospheric escape of its inner three small planets, given different assumed initial water quantities. We find that, regardless of their initial water content, all three planets accumulate significant quantities of oxygen due to efficient water photolysis and hydrogen loss. All three planets also receive enough XUV flux to drive rapid water loss, which considerably affects their developing climates and atmospheres. Even in scenarios of low initial water content, our results suggest that the James Webb Space Telescope (JWST) will be sensitive to observations of retained oxygen on the L 98-59 planets in its future scheduled observations, with planets b and c being the most likely targets to possess an extended atmosphere. Our results constrain the atmospheric evolution of these small rocky planets, and they provide context for current and future observations of the L 98-59 system to generalize our understanding of multi-terrestrial planet systems.Comment: 17 pages, 7 figures, accepted for publication in the Astrophysical Journa

Contaminant Release from Storm Water Culvert Rehabilitation Technologies: Understanding Implications to the Environment and Long-Term Material Integrity

Millions of miles of existing U.S. storm water culverts are critical for roadway safety but much of this infrastructure requires repair. State departments of transportation (DOT) are increasingly choosing to rehabilitate culverts with spray-on and cured-in-place pipe (CIPP) lining processes. These culvert lining practices involve the manufacture of a new plastic liner inside a damaged culvert. DOTs are selecting these outdoor plastic manufacturing methods partly to avoid open-trench excavation, which can cause traffic disruption and work zone traffic safety issues. This study was conducted to better understand current knowledge about culvert lining caused environmental contamination, final product quality, and recommend improved construction specifications, project oversight, and testing requirements to limit undesirable consequences. Literature reviews, a survey of construction specifications and special provisions for 32 transportation agencies, as well as field- and bench-scale testing for CIPP projects in California, New York, and Virginia, were completed. During this project, the safety of workers, transportation agency employees, and the general public at lining installation sites, was raised as a concern by state and federal agencies. Due to previously unreported hazards which were encountered at multiple CIPP field sites, the provision of worksite safety recommendations for DOTs was added to this study. Recommendations are provided for spray-on lining and CIPP lining culvert repair projects that can (1) limit environmental contamination, (2) improve worksite safety, and (3) aid DOTs in better understanding the quality of their new liners

The National Fire and Fire Surrogate Study: Effects of Fuel Reduction Methods on Forest Vegetation Structure and Fuels

Changes in vegetation and fuels were evaluated from measurements taken before and after fuel reduction treatments (prescribed. re, mechanical treatments, and the combination of the two) at 12 Fire and Fire Surrogate (FFS) sites located in forests with a surface. re regime across the conterminous United States. To test the relative effectiveness of fuel reduction treatments and their effect on ecological parameters we used an information-theoretic approach on a suite of 12 variables representing the overstory (basal area and live tree, sapling, and snag density), the understory (seedling density, shrub cover, and native and alien herbaceous species richness), and the most relevant fuel parameters for wild. re damage (height to live crown, total fuel bed mass, forest floor mass, and woody fuel mass). In the short term (one year after treatment), mechanical treatments were more effective at reducing overstory tree density and basal area and at increasing quadratic mean tree diameter. Prescribed. re treatments were more effective at creating snags, killing seedlings, elevating height to live crown, and reducing surface woody fuels. Overall, the response to fuel reduction treatments of the ecological variables presented in this paper was generally maximized by the combined mechanical plus burning treatment. If the management goal is to quickly produce stands with fewer and larger diameter trees, less surface fuel mass, and greater herbaceous species richness, the combined treatment gave the most desirable results. However, because mechanical plus burning treatments also favored alien species invasion at some sites, monitoring and control need to be part of the prescription when using this treatment

On-chip picosecond pulse detection and generation using graphene photoconductive switches

We report on the use of graphene for room temperature on-chip detection and generation of pulsed terahertz (THz) frequency radiation, exploiting the fast carrier dynamics of light-generated hot carriers, and compare our results with conventional low-temperature-grown gallium arsenide (LT-GaAs) photoconductive (PC) switches. Coupling of picosecond-duration pulses from a biased graphene PC switch into Goubau line waveguides is also demonstrated. A Drude transport model based on the transient photoconductance of graphene is used to describe the mechanism for both detection and generation of THz radiation

A planet within the debris disk around the pre-main-sequence star AU Microscopii

AU Microscopii (AU Mic) is the second closest pre main sequence star, at a distance of 9.79 parsecs and with an age of 22 million years. AU Mic possesses a relatively rare and spatially resolved3 edge-on debris disk extending from about 35 to 210 astronomical units from the star, and with clumps exhibiting non-Keplerian motion. Detection of newly formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic activity on the star. Here we report observations of a planet transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of 8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4 Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3 sigma confidence. Our observations of a planet co-existing with a debris disk offer the opportunity to test the predictions of current models of planet formation and evolution.Comment: Nature, published June 24th [author spelling name fix