5,979 research outputs found

    Nuclear thermal propulsion test facility requirements and development strategy

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    The Nuclear Thermal Propulsion (NTP) subpanel of the Space Nuclear Propulsion Test Facilities Panel evaluated facility requirements and strategies for nuclear thermal propulsion systems development. High pressure, solid core concepts were considered as the baseline for the evaluation, with low pressure concepts an alternative. The work of the NTP subpanel revealed that a wealth of facilities already exists to support NTP development, and that only a few new facilities must be constructed. Some modifications to existing facilities will be required. Present funding emphasis should be on long-lead-time items for the major new ground test facility complex and on facilities supporting nuclear fuel development, hot hydrogen flow test facilities, and low power critical facilities

    Retention of Low Income Children in Three Dental Studies Investigating Early Childhood Caries

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    Background: To our knowledge no dental studies have looked closely at subject retention, which is crucial to better understand oral health disparities. In this paper, we report retention rates and review and attempt to assess which retention strategies utilized in 3 dental research studies investigating ECC were effective for retaining WIC-enrolled children. The purpose of this paper is to discuss challenges that were encountered when working with these populations, describe characteristics of those not retained, and summarize some recommendations for future dental studies working at WIC sites. Methods: Three dental studies were conducted at WIC clinics in Iowa. Retention strategies focused on maintenance of contact over time, persistence in rescheduling appointments, utilization of incentives, high recruitment, and frequent communication with parents and program staff. Results: Retention rates in the studies ranged from 60 to 75 percent at the final research interventions. Studies were challenged by frequent moves of subjects, missed appointments, disconnected phones, busy schedules of parents, transportation problems, loss of child custody, family illness, and lack of interest. Those not retained in the studies were more likely to be younger, single, and less educated, with a lower household income and a non-Caucasian child. Lower retention was also associated with the presence of carious lesions. Conclusions: Despite many challenges, studies had good retention rates and benefited from the retention strategies. Future dental studies at WIC clinics may also benefit from arranging transportation, obtaining a free, 800 callback number, and offering after-hours appointments for working parents

    NASA/DOE/DOD nuclear propulsion technology planning: Summary of FY 1991 interagency panel results

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    Interagency (NASA/DOE/DOD) technical panels worked in 1991 to evaluate critical nuclear propulsion issues, compare nuclear propulsion concepts for a manned Mars mission on a consistent basis, and to continue planning a technology development project for the Space Exploration Initiative (SEI). Panels were formed to address mission analysis, nuclear facilities, safety policy, nuclear fuels and materials, nuclear electric propulsion technology, and nuclear thermal propulsion technology. A summary of the results and recommendations of the panels is presented

    The transition from amalgam to other restorative materials in the U.S. predoctoral pediatric dentistry clinics

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    Increased concerns about the safety of amalgam restorations in children have resulted in many dental schools emphasizing the teaching of alternative dental materials. This study investigated the current teaching of different dental materials for use in posterior teeth in the United States predoctoral pediatric dentistry programs. In 2011, the authors invited the chairs of the predoctoral pediatric dentistry departments in all accredited dental schools at that time (N = 57) to participate in an internet‐based survey. Descriptive statistics were calculated to describe the frequency of using different restorative materials. Regression models were developed to explore the factors related to the use of dental restorations in predoctoral pediatric clinics. Among the 44 dental schools that responded (77% response rate), 74% used amalgam, and 93% used composite in primary posterior teeth. Glass ionomer was used by 61% of the schools in primary posterior teeth. Placing amalgam in primary posterior teeth was associated with programs that treated more 3–5‐year‐old patients (β = .302, p < .043), whereas the use of glass ionomer was associated with having students serving at off‐site satellite dental clinics (β = .015, p < .012). In general, having departments with chairs who had positive attitudes towards Minimal Invasive Dentistry (MID) used composite (β = .091, p < .0001) and glass ionomer (β = 103, p < .0001) more frequently and were less likely to use amalgam (β = −.077, p < .005) in primary posterior teeth. Although teaching MID concepts in predoctoral pediatric clinics in dental schools is increasing, the use of amalgam in posterior primary and permanent teeth is still widely practiced.This project was funded by NIH/NIDC R T32 Grant DEO 14678‐06

    Who backs up credence claims?: Roles for government as a competent authority in assuring quality attributes

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    The role of government and intergovernmental mechanisms to assure food safety is well established. However, government also has a role in establishing and verifying a range of acceptable production approaches and consequential outcomes relating to credence attributes. The role of government in providing baseline information on the supply side and competent inspection services to verify the effectiveness of control measures at the production and processing levels of the value chain is identified. A meta-accreditation process, whereby government endorses various food safety and quality certification schemes that are coupled with credence attribute assurances is the most cost effective mechanism for government to pursue

    The Most Distant Stars in the Milky Way

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    We report on the discovery of the most distant Milky Way (MW) stars known to date: ULAS J001535.72++015549.6 and ULAS J074417.48++253233.0. These stars were selected as M giant candidates based on their infrared and optical colors and lack of proper motions. We spectroscopically confirmed them as outer halo giants using the MMT/Red Channel spectrograph. Both stars have large estimated distances, with ULAS J001535.72++015549.6 at 274±74274 \pm 74 kpc and ULAS J074417.48++253233.0 at 238 ±\pm 64 kpc, making them the first MW stars discovered beyond 200 kpc. ULAS J001535.72++015549.6 and ULAS J074417.48++253233.0 are both moving away from the Galactic center at 52±1052 \pm 10 km s1^{-1} and 24±1024 \pm 10 km s1^{-1}, respectively. Using their distances and kinematics, we considered possible origins such as: tidal stripping from a dwarf galaxy, ejection from the MW's disk, or membership in an undetected dwarf galaxy. These M giants, along with two inner halo giants that were also confirmed during this campaign, are the first to map largely unexplored regions of our Galaxy's outer halo.Comment: Accepted and in print by ApJL. Seven pages, 2 figure

    Responses From the Field

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    Revealing New Physical Structures in the Supernova Remnant N63A through Chandra Imaging Spectroscopy

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    We present Chandra X-ray observations of the supernova remnant (SNR) N63A in the Large Magellanic Cloud (LMC). N63A, one of the brightest LMC remnants, is embedded in an H II region and probably associated with an OB association. The optical remnant consists of three lobes of emission contained within the approximately three times larger X-ray remnant. Our Chandra data reveal a number of new physical structures in N63A. The most striking of these are the several ``crescent''-shaped structures located beyond the main shell that resemble similar features seen in the Vela SNR. In Vela, these have been interpreted as arising from high speed clumps of supernova ejecta interacting with the ambient medium. Another distinct feature of the remnant is a roughly triangular ``hole'' in the X-ray emission near the location of the optical lobes and the brightest radio emission. X-ray spectral analysis shows that this deficit of emission is a result of absorption by an intervening dense cloud with a mass of ~450 M_sun that is currently being engulfed by the remnant's blast wave. We also find that the rim of the remnant, as well as the crescent-shaped features, have considerably softer X-ray spectra than the interior. Limits on hard X-ray emission rule out a young, energetic pulsar in N63A, but the presence of an older or less active one, powering a wind nebula with a luminosity less than ~4e10^34 erg/s, is allowed.Comment: 18 pages, 5 figures (2 color), accepted for publication in Ap

    AN ANALYSIS OF HOW THE U.S. GOVERNMENT CAN EFFECTIVELY TACKLE SUPPLY CHAIN BARRIERS TO SCALE UP THE LOW COST UNMANNED AERIAL VEHICLE (UAV) SWARMING TECHNOLOGY (LOCUST) PROGRAM

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    The LOCUST program is a scalable system of inexpensive swarming unmanned aerial vehicles to provide disruptive capability in contested environments against anti-area access denial defenses, enabling manned strike operations and localized landing site superiority with reduced cost, risk, and operator launch and workload. Our research and analysis will emphasize the challenges of moving from a U.S. Special Operations Command (USSOCOM) effort to a large program of record. Specific supply chain concerns that will be addressed include: 1) DOD organizational structure; 2) service-specific objectives and currently operating platforms; 3) requirements generation and related procurements to include production and quality challenges; 4) safety and quality assurance standards; 5) lead times, inventory plans, and throughput to include supplier base considerations and consolidations; and 6) latest evolving technologies and continuous improvement principles. Our team will utilize the Define, Measure, Analyze, Improve, Control (DMAIC) evaluative methodology that focuses on data-driven improvement cycles to better optimize process, design and results. Our results and recommendations highlighted multiple strategies that the Office of Naval Research (ONR) must focus on when developing the LOCUST supply chain. These conclusions and findings address both current supply chain development opportunities for the LOCUST program, as well as where the program must focus its efforts in the future.http://archive.org/details/ananalysisofhowt1094563516Civilian, Department of the NavyCivilian, Department of the ArmyCivilian, Department of the ArmyApproved for public release; distribution is unlimited
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