5,635 research outputs found

    Atomic clouds as distributed sources for the plasma torus

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    Implications of recent developments for the neutral particle environment of Jupiter are considered. The first detection is reported of very hot S+ ions with gyrospeeds comparable to the corotations speed, a phenomenon which results from a neutral sulfur cloud. Evidence supports the hypothesis that extensive neutral clouds of oxygen and sulfur exist and are important sources of ions and energy for the Io torus

    Gradients and anisotropies of high energy cosmic rays in the outer heliosphere

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    Previous studies at lower energies have shown that the cosmic ray density gradients vary in space and time, and many authors currently are suggesting that the radial gradient associated with solar cycle modulation is supported largely by narrow barriers which encircle the Sun and propagate outward with the solar wind. If so, the anisotropy is a desirable way to detect spatial gradients, because it can be associated with the local solar wind and magnetic field conditions. With this in mind, the anisotropy measurements made by the UCSD Cerenkov detectors on Pioneers 10 and 11 are studied. It is shown that the local anisotropy varies greatly, but that the long term average is consistent with the global radial gradient measured between two spacecraft over a baseline of many AU

    Gradients and anisotropies of high energy cosmic rays in the outer heliosphere

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    Two cosmic rays which pass through the same point going in opposite directions will, in the absence of scattering and inhomogeneities in the magnetic field, trace helices about adjacent flux tubes, whose centerlines are separated by one gyrodiameter. A directional anisotropy at the point suggests a difference in the number of cosmic rays loading the two flux tubes; that is, a density gradient over the baseline of a gyrodiameter. Previous studies at lower energies have shown that the cosmic ray density gradients vary in time and space. It is suggested that the radial gradient associated with solar cycle modulation is supported largely by narrow barriers which encircle the sun and propagate outward with the solar wind. If so, the anisotropy is a desirable way to detect spatial gradients, because it can be associated with the local solar wind and magnetic field conditions. Anisotropic measurements made by Cerenkov detectors on Pioneers 10 and 11 were studied. It was found that local anisotropy varies greatly, but that the long term average is consistent with the global radial gradient measured between two spacecraft over a baseline of many AU

    Non-thermal Origin of the EUV and Soft X-rays from the Coma Cluster - Cosmic Rays in Equipartition with the Thermal Medium

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    The role of cosmic rays (CR) in the formation and evolution of clusters of galaxies has been much debated. It may well be related to other fundamental questions, such as the mechanism which heats and virializes the intracluster medium (ICM), and the frequency at which the ICM is shocked. There is now compelling evidence both from the cluster soft excess (CSE) and the `hard-tail' emissions at energies above 10 keV, that many clusters are luminous sources of inverse-Compton (IC) emission. This is the first direct measurement of cluster CR: the technique is free from our uncertainties in the ICM magnetic field, and is not limited to the small subset of clusters which exhibit radio halos. The CSE emitting electrons fall within a crucial decade of energy where they have the least spectral evolution, and where most of the CR pressure resides. However their survival times do not date them back to the relic CR population. By using the CSE data of the Coma cluster, we demonstrate that the CR are energetically as important as the thermal ICM: the two components are in pressure equiparition. Thus, contrary to previous expectations, CR are a dominant component of the ICM, and their origin and effects should be explored. The best-fit CR spectral index is in agreement with the Galactic value.Comment: ApJ accepted; 10 pages LaTeX; 2 figures and 1 table in PostScrip

    Densities and abundances of hot cometary ions in the coma of P/Halley

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    On its flight by P/Halley, the Giotto spacecraft carried a High Energy Range Spectrometer (HERS) for measuring the properties of cometary ions picked up by the solar wind in the nearly collisionless regions of the coma. Preliminary estimates of the ion densities observed by HERS were reevaluated and extended; density profiles along the Giotto trajectory are presented for 13 values of ion mass/charge. Comparison with the physical-chemical model of the interaction of sunlight and the solar wind with the comet by other researchers reveals that, with the exception of protons and H2(+), all ion densities were at least an order of magnitude higher than predicted. The high ion densities cannot be explained on the basis of compression of the plasma, but require additional or stronger ionization mechanisms. Ratios of the densities of different ion species reveal an overabundance of carbonaceous material and an underabundance of H2(+) compared to the predictions of the Schmidt. While the densities of solar wind ions (H(+) and He(++)) changed sharply across a magnetic discontinuity located 1.35(10)(exp 5) km from the comet, this feature, which has been called both the 'cometopause' and the 'magnetic pileup boundary' was barely distinguishable in the density profiles of hot cometary ions. This result is consistent with the interpretation that the magnetic pileup boundary detected by Giotto was caused by a discontinuity in the solar wind and is not an intrinsic feature of the interaction of the solar wind with an active comet

    Optimisation problems and resolution methods in satellite scheduling and space-craft operation: a survey

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    The fast development in the production of small, low-cost satellites is propelling an important increase in satellite mission planning and operations projects. Central to satellite mission planning is the resolution of scheduling problem for an optimised allocation of user requests for efficient communication between operations teams at the ground and spacecraft systems. The aim of this paper is to survey the state of the art in the satellite scheduling problem, analyse its mathematical formulations, examine its multi-objective nature and resolution through meta-heuristics methods. Finally, we consider some optimisation problems arising in spacecraft design, operation and satellite deployment systemsPeer ReviewedPostprint (author's final draft

    On a Unified Definition of the Service System: What is its Identity?

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    In this paper, a unified definition of the service system is proposed. The motivation of this research effort is based on our observation that there are diverse definitions or descriptions of the service system in the literature and they have not provided an identity of the service system. Our goal to define the service system is thus to establish its identity. The most salient feature in our definition is the introduction of three subsystems in a service system: infrastructure, substance, and management. The substance flows over the infrastructure under the constraints of management. A service is established at the moment when the substance interacts with the human to cause a change in the human's status or state under a protocol, which further meets the human's request and need. With this new definition, a service system can be distinguished from other systems, such as manufacturing system, agricultural system, and product system. The new definition will be useful to classification of various service systems and various theories for service systems, which is the key to knowledge management for service systems and to optimization of design and management of service systems. © 2014 IEEE.published_or_final_versio
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