144,335 research outputs found
Circumferential pressure distributions in a model labyrinth seal
A research program to isolate and study leakage flow through labyrinth glands was initiated. Circumferential pressure distributions were measured in the labyrinth glands with geometry appropriate to the high pressure labyrinths in large steam turbines. Knowledge of this pressure distribution is essential as it is this unequal pressure field that results in the destabilizing force. Parameters that are likely to affect the pressure distributions are incorporated into the test rig. Some preliminary pressure profiles are presented
TMS communications software. Volume 1: Computer interfaces
A prototype bus communications system, which is being used to support the Trend Monitoring System (TMS) as well as for evaluation of the bus concept is considered. Hardware and software interfaces to the MODCOMP and NOVA minicomputers are included. The system software required to drive the interfaces in each TMS computer is described. Documentation of other software for bus statistics monitoring and for transferring files across the bus is also included
Diagnostic procedures for Trend Monitoring System (TMS) communications
A prototype coaxial cable bus communications sytem was developed to support the trend monitoring system (TMS). Troubleshooting procedures are described at the system level. The procedures can be used by repair personnel to isolate a fault in the TMS and to restore the system to operation by swapping out failed components
Impact of Rotation on the Evolution of Low-Mass Stars
High precision photometry and spectroscopy of low-mass stars reveal a variety
of properties standard stellar evolution cannot predict. Rotation, an essential
ingredient of stellar evolution, is a step towards resolving the discrepancy
between model predictions and observations. The first rotating stellar model,
continuously tracing a low-mass star from the pre-main sequence onto the
horizontal branch, is presented. The predicted luminosity functions of stars of
globular clusters and surface rotation velocities on the horizontal branch are
discussed.Comment: 5 pages, 4 figures. Oral contrubution. Proceedings of the workshop
"XXI Century challenges for stellar evolution", held in Cefalu' (Sicily,
Italy), August 29 - September 2, 2007; S. Cassisi and M. Salaris Eds. To be
published in Mem. SAIt Vol. 79 No.
Nitrogen superfractionation in dense cloud cores
We report new calculations of interstellar 15N fractionation. Previously, we
have shown that large enhancements of 15N/14N can occur in cold, dense gas
where CO is frozen out, but that the existence of an NH + N channel in the
dissociative recombination of N2H+ severely curtails the fractionation. In the
light of recent experimental evidence that this channel is in fact negligible,
we have reassessed the 15N chemistry in dense cloud cores. We consider the
effects of temperatures below 10 K, and of the presence of large amounts of
atomic nitrogen. We also show how the temporal evolution of gas-phase isotope
ratios is preserved as spatial heterogeneity in ammonia ice mantles, as
monolayers deposited at different times have different isotopic compositions.
We demonstrate that the upper layers of this ice may have 15N/14N ratios an
order of magnitude larger than the underlying elemental value. Converting our
ratios to delta-values, we obtain delta(15N) > 3,000 per mil in the uppermost
layer, with values as high as 10,000 per mil in some models. We suggest that
this material is the precursor to the 15N `hotspots' recently discovered in
meteorites and IDPsComment: accepted by MNRA
Experimental investigation of lateral forces induced by flow through model labyrinth glands
The lateral forces induced by flow through model labyrinth glands were investigated. Circumferential pressure distributions, lateral forces and stiffness coefficients data obtained are discussed. The force system is represented as a negative spring and a tangential force orthogonal to eccentricity. The magnitude of these forces are dependent on eccentricity, entry swirl, rotor peripheral velocity and seal size. A pressure equalization chamber at midgland tests should in significantly reduced forces and stiffness coefficients
Single- and dual-carrier microwave noise abatement in the deep space network
The NASA/JPL Deep Space Network (DSN) microwave ground antenna systems are presented which simultaneously uplink very high power S-band signals while receiving very low level S- and X-band downlinks. Tertiary mechanisms associated with elements give rise to self-interference in the forms of broadband noise burst and coherent intermodulation products. A long-term program to reduce or eliminate both forms of interference is described in detail. Two DSN antennas were subjected to extensive interference testing and practical cleanup program; the initial performance, modification details, and final performance achieved at several planned stages are discussed. Test equipment and field procedures found useful in locating interference sources are discussed. Practices deemed necessary for interference-free operations in the DSN are described. Much of the specific information given is expected to be easily generalized for application in a variety of similar installations. Recommendations for future investigations and individual element design are given
Phase Structure of 2-Flavor Quark Matter: Heterogeneous Superconductors
We analyze the free energy of charge and color neutral 2-flavor quark matter
within the BCS approximation. We consider both the homogeneous gapless
superconducting phase and the heterogeneous mixed phase where normal and BCS
superconducting phases coexist. We calculate the surface tension between normal
and superconducting phases and use it to compare the free energies of the
gapless and mixed phases. Our calculation, which retains only the leading order
gradient contribution to the free energy, indicates that the mixed phase is
energetically favored over an interesting range of densities of relevance to 2
flavor quark matter in neutron stars.Comment: 11 pages, 4 figures. Major Revisions. Includes a detailed discussion
of the kinetic terms of the effective theory, instabilities of the gapless
phase and the charge neutral phase diagra
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
Absolute continuity and spectral concentration for slowly decaying potentials
We consider the spectral function for the
Sturm-Liouville equation on with the
boundary condition and where has slow decay
as . We develop our previous methods of locating spectral
concentration for with rapid exponential decay (JCAM 81 (1997) 333-348) to
deal with the new theoretical and computational complexities which arise for
slow decay
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