7,129 research outputs found

    Far Field Monitoring of Rogue Nuclear Activity with an Array of Large anti-neutrino Detectors

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    The result of a study on the use of an array of large anti-neutrino detectors for the purpose of monitoring rogue nuclear activity is presented. Targeted regional monitoring of a nation bordering large bodies of water with no pre-existing legal nuclear activity may be possible at a cost of about several billion dollars, assuming several as-yet-untested schemes pan out in the next two decades. These are: (1) the enabling of a water-based detector to detect reactor anti-neutrinos by doping with GdCl3_3; (2) the deployment of a KamLAND-like detector in a deep-sea environment; and (3) the scaling of a Super-Kamiokande-like detector to a size of one or more megatons. The first may well prove feasible, and should be tested by phase-III Super-Kamiokande in the next few years. The second is more of a challenge, but may well be tested by the Hanohano collaboration in the coming decade. The third is perhaps the least certain, with no schedule for construction of any such device in the foreseeable future. In addition to the regional monitoring scheme, several global, untargeted monitoring schemes were considered. All schemes were found to fail benchmark sensitivity levels by a wide margin, and to cost at least several trillion dollars.Comment: 17 pages, 8 figures, proceedings for Neutrino Sciences 2005, submitted to Earth, Moon, and Planet

    Thermomagnetic analysis of meteorites. 3: C3 and C4 chondrites

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    Thermomagnetic analysis on all of the C3 and C4 chondrites, conducted under conditions of controlled oxygen fugacity, indicates the presence of a thermally unstable component in at least 5 of the C3 chondrites which upon heating results in magnetite production. This unstable component is most likely troilite (FeS). The presence of the unstable substance may affect the estimation of paleointensities in meteorites which contain it. Our results indicate that Grosnaja, Ornans, Kainsaz, Felix, and Warrenton are likely to be less complicated for paleointensity determinations than the other C3 chondrites. Both C4 chondrites should lead to reliable results

    Thermomagnetic analysis of meteorites, 2: C2 chondrites

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    Samples of all eighteen of the known C2 chondrites were analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low(generally 1%) and the J sub s-T curves are irreversible. The heating curves show variable and erratic behavior, whereas the cooling curves appear to be that of Fe3O4. The saturation moment after cooling is greater (up to 10 times larger) than it is initially. This behavior is interpreted to be the result of the production of magnetite from a thermally unstable phase--apparently FeS. Four of the remaining 7 C2 chondrites contain Fe3O4 as the only significant magnetic phase: initial magnetite contents range from 4 to 13 percent. The remaining three C2 chondrites contain iron or nickel-iron in addition to Fe3O4. These seven C2 chondrites show little evidence of the breakdown of a thermally unstable phase

    Robotic control of the seven-degree-of-freedom NASA laboratory telerobotic manipulator

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    A computationally efficient robotic control scheme for the NASA Laboratory Telerobotic Manipulator (LTM) is presented. This scheme utilizes the redundancy of the seven-degree-of-freedom LTM to avoid joint limits and singularities. An analysis to determine singular configurations is presented. Performance criteria are determined based on the joint limits and singularity analysis. The control scheme is developed in the framework of resolved rate control using the gradient projection method, and it does not require the generalized inverse of the Jacobian. An efficient formulation for determining the joint velocities of the LTM is obtained. This control scheme is well suited for real-time implementation, which is essential if the end-effector trajectory is continuously modified based on sensory feedback. Implementation of this scheme on a Motorola 68020 VME bus-based controller of the LTM is in progress. Simulation results demonstrating the redundancy utilization in the robotic mode are presented

    Brain dehydration and neurologic deterioration after rapid correction of hyponatremia

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    Brain dehydration and neurologic deterioration after rapid correction of hyponatremia. We made rats severely hyponatremia varying the rate of onset and duration of the disturbance, and then compared rapid correction to slow correction. An acute fall in the plasma Na to 106 mEq/liter within seven hours caused seizures and coma, but these findings resolved and survival was 100%after either rapid or slow correction. A more gradual fall in plasma Na to 95 mEq/liter in three days caused neither seizures nor coma. Measurements of brain water and electrolytes showed that adaptive losses of brain Na and K (maximally depleted within seven hours) and slower losses of non-electrolyte solutes progressively reduced brain edema. After three days of hyponatremia, rapid correction to 119 mEq/liter with 1m NaCl or to 129 mEq/liter by withdrawing DDAVP caused brain dehydration because lost brain K and non-electrolyte solutes were recovered slowly. This treatment was followed by a delayed onset of severe neurologic findings, demyelinating brain lesions and a mortality rate of over 40%. Slow correction (0.3 mEq/liter/hr) avoided these complications and permitted 100%survival. We conclude that the rat adapts quickly to hyponatremia and can survive with extremely low plasma sodium concentrations for prolonged periods. Although rapid correction is well tolerated when hyponatremia is of brief duration, it may cause brain damage in animals that have had time to more fully adapt to the disturbance

    The laboratory telerobotic manipulator program

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    New opportunities for the application of telerobotic systems to enhance human intelligence and dexterity in the hazardous environment of space are presented by the NASA Space Station Program. Because of the need for significant increases in extravehicular activity and the potential increase in hazards associated with space programs, emphasis is being heightened on telerobotic systems research and development. The Laboratory Telerobotic Manipulator (LTM) program is performed to develop and demonstrate ground-based telerobotic manipulator system hardware for research and demonstrations aimed at future NASA applications. The LTM incorporates traction drives, modularity, redundant kinematics, and state-of-the-art hierarchical control techniques to form a basis for merging the diverse technological domains of robust, high-dexterity teleoperations and autonomous robotic operation into common hardware to further NASA's research
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