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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    BT technology journal 17 (1999), S. 155-169 
    ISSN: 1573-1995
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Policy-based management is an approach that has been considered for some years within the distributed systems management research community. The concepts have recently been adopted by standards bodies including the International Telecommunications Union (ITU), Internet Engineering Task Force (IETF), Desktop Management Taskforce (DMTF) and Object Management Group (OMG) and are starting to appear in marketing literature for Internet protocol (IP) network management products. The meaning of the term is not well-defined nor consistently used, but common aspects of policy include that it changes a system' behaviour, that it is defined after system deployment, and that it does not require a full software development life cycle. Technical problems remain which need to be solved before the full ambitions of policy-based management can be achieved. Initial products are likely to address only a sub-set of the full potential and to exist in niche domains.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-07-13
    Description: An electric propulsion thrust stand capable of supporting thrusters with total mass of up to 125 kg and 1 mN to 1 N thrust levels has been developed and tested. The mechanical design features a conventional hanging pendulum arm attached to a balance mechanism that transforms horizontal motion into amplified vertical motion, with accommodation for variable displacement sensitivity. Unlike conventional hanging pendulum thrust stands, the deflection is independent of the length of the pendulum arm, and no reference structure is required at the end of the pendulum. Displacement is measured using a non-contact, optical linear gap displacement transducer. Mechanical oscillations are attenuated using a passive, eddy current damper. An on-board microprocessor-based level control system, which includes a two axis accelerometer and two linear-displacement stepper motors, continuously maintains the level of the balance mechanism - counteracting mechanical %era drift during thruster testing. A thermal control system, which includes heat exchange panels, thermocouples, and a programmable recirculating water chiller, continuously adjusts to varying thermal loads to maintain the balance mechanism temperature, to counteract thermal drifts. An in-situ calibration rig allows for steady state calibration both prior to and during thruster testing. Thrust measurements were carried out on a well-characterized 1 kW Hall thruster; the thrust stand was shown to produce repeatable results consistent with previously published performance data.
    Keywords: Mechanical Engineering
    Type: AIAA Paper 2004-3441 , AIAA/ASME/SAE/ASEE 40th Joint Propulsion Conference; Jul 11, 2004 - Jul 14, 2004; Fort Lauderdale, FL; United States
    Format: application/pdf
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  • 3
    Publication Date: 2019-07-13
    Description: An application of the maximum likelihood state estimator to a space-based power system is presented. The state estimator uses current and voltage measurements to generate estimates of node voltages for an electrical power distribution system for the Space Shuttle. Preliminary results on the effect of noisy measurements on estimated parameters are reported. The software used in generating these results is part of an overall package being developed at Louisiana Tech University. Intended applications of this package include the analysis of power systems and real-time parallel processing on the Space Shuttle.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: Intersociety Energy Conversion Engineering Conference; Aug 12, 1990 - Aug 17, 1990; Reno, NV; United States
    Format: text
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  • 4
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 18 . pp. 320-338.
    Publication Date: 2018-04-05
    Description: We examine the diffusive behavior of the flow field in an eddy-resolving, primitive equation circulation model. Analysis of fluid particle trajectories illustrates the transport mechanisms, which are leading to uniform tracer and potential vorticity distributions in the interior of the subtropical thermocline. In contrast to the assumption of weak mixing in recent analytical theories, the numerical model indicates the alternative of tracer and potential vorticity homogenization on isopycnal surfaces taking place in a nonideal fluid with strong, along-isopycnal eddy mixing. The eastern, ventilated portion of the gyre appears to be sufficiently homogeneous to allow the concept of an eddy diffusivity to apply. A break in a random walk behavior of particle statistics occurs after about 100 days when along-flow dispersion sharply increases, indicative of mean shear effects. During the first months of particle spreading, eddy dispersal and mean advection are of similar magnitude. Eddy kinetic energy is of O(60–80 cm2 s−2) in the model thermocline, comparable to the pool of weak eddy intensity found in the eastern parts of the subtropical oceans. Eddy diffusivity in the model thermocline (Kxx = 8 × 107, Kyy = 3 × 107 cm2 s−1) seems to be higher by a factor of about 3 than oceanic values estimated for these area. Below the thermocline, model diffusivity decreases substantially and becomes much more anisotropic, with particle dispersal preferentially in the zonal direction. The strong nonisotropic behavior, prominent also in all other areas of water eddy intensity, appears as the major discrepancy when compared with the observed behavior of SOFAR floats and surface drifters in the ocean.
    Type: Article , PeerReviewed
    Format: text
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