91,462 research outputs found
Low frequency vibration isolation technology for microgravity space experiments
The dynamic acceleration environment observed on Space Shuttle flights to date and predicted for the Space Station has complicated the analysis of prior microgravity experiments and prompted concern for the viability of proposed space experiments requiring long-term, low-g environments. Isolation systems capable of providing significant improvements in this environment exist, but have not been demonstrated in flight configurations. This paper presents a summary of the theoretical evaluation for two one degree-of-freedom (DOF) active magnetic isolators and their predicted response to both direct and base excitations, that can be used to isolate acceleration sensitive microgravity space experiments
Magnetic bearings with zero bias
A magnetic bearing operating without a bias field has supported a shaft rotating at speeds up to 12,000 rpm with the usual four power supplies and with only two. A magnetic bearing is commonly operated with a bias current equal to half of the maximum current allowable in its coils. This linearizes the relation between net force and control current and improves the force slewing rate and hence the band width. The steady bias current dissipates power, even when no force is required from the bearing. The power wasted is equal to two-thirds of the power at maximum force output. Examined here is the zero bias idea. The advantages and disadvantages are noted
Nonintrusive inertial vibration isolation technology for microgravity space experiments
The dynamic acceleration environment observed on Space Shuttle flights to date and predicted for the Space Station has complicated the analysis of prior microgravity experiments and prompted concern for the viability of proposed space experiments requiring long-term, microgravity environments. Isolation systems capable of providing significant improvements to this environment exist, but at present have not been demonstrated in flight configurations. A summary of the theoretical evaluation for two one degree-of-freedom (DOF) active magnetic isolators and their predicted response to both direct and base excitations is presented. These isolators can be used independently or in concert to isolate acceleration-sensitive microgravity space experiments, dependent on the isolation capability required for specific experimenter needs
Limits on new long range nuclear spin-dependent forces set with a K-3He co-magnetometer
A magnetometer using spin-polarized K and He atoms occupying the same
volume is used to search for anomalous nuclear spin-dependent forces generated
by a separate He spin source. We measure changes in the He spin
precession frequency with a resolution of 18 pHz and constrain anomalous spin
forces between neutrons to be less than of their magnetic or
less than of their gravitational interactions on a length
scale of 50 cm. We present new limits on neutron coupling to light pseudoscalar
and vector particles, including torsion, and constraints on recently proposed
models involving unparticles and spontaneous breaking of Lorentz symmetry.Comment: 4 pages, 4 figures, latest version as appeared in PR
Extension and application of a sequential estimator
Improved sequential estimation technique for nonlinear time varying system
Mollusca of the Illinois River, Arkansas
The Illinois River is in the Ozark region of northwestern Arkansas and eastern Oklahoma. A survey of the Illinois River in Arkansas produced nine species and one morphological subspecies of gastropods, three species of sphaeriid clams, and 23 species of unionid mussels. Museum records resulted in another two species and an ecophenotype of the Unionidae. This represents the first published survey of molluscan species from the Illinois River in Arkansas
Temporal and Spatial Turbulent Spectra of MHD Plasma and an Observation of Variance Anisotropy
The nature of MHD turbulence is analyzed through both temporal and spatial
magnetic fluctuation spectra. A magnetically turbulent plasma is produced in
the MHD wind-tunnel configuration of the Swarthmore Spheromak Experiment (SSX).
The power of magnetic fluctuations is projected into directions perpendicular
and parallel to a local mean field; the ratio of these quantities shows the
presence of variance anisotropy which varies as a function of frequency.
Comparison amongst magnetic, velocity, and density spectra are also made,
demonstrating that the energy of the turbulence observed is primarily seeded by
magnetic fields created during plasma production. Direct spatial spectra are
constructed using multi-channel diagnostics and are used to compare to
frequency spectra converted to spatial scales using the Taylor Hypothesis.
Evidence for the observation of dissipation due to ion inertial length scale
physics is also discussed as well as the role laboratory experiment can play in
understanding turbulence typically studied in space settings such as the solar
wind. Finally, all turbulence results are shown to compare fairly well to a
Hall-MHD simulation of the experiment.Comment: 17 pages, 17 figures, Submitted to Astrophysical Journa
Texas Natural Resources Inventory and Monitoring System (TNRIMS), Applications System Verification and Transfer (ASVT), Remote Sensing Information Subsystem (RSIS): Acceptance test procedures
There are no author-identified significant results in this report
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