717 research outputs found
Mini-BRU/BIPS foil bearing development
The analysis revealed the failure agent to be a combination of poor teflon coating adhesion, a decrease in bearing sway space and, possibly, lack of flushing flow through the bearing. A change in Teflon coating vendors provided substantially improved coating quality and surface finish. The sway space was increased and the cooling bleed flow was adjusted to flush the bearing. These changes were included in a test conducted in the WHL from 6 April to 22 May 1978 which resulted in the completion of 1006.9 hours of operation at temperature and load. Post-test inspection revealed the bearings to be in excellent condition and capable of completing a much longer test
Analysis, design, fabrication and testing of the mini-Brayton rotating unit (Mini-BRU). Volume 1: Text and tables
A 500 to 2100 watt power output Mini-Brayton Rotating Unit (Mini-BRU)was analyzed, designed, fabricated and tested. Performance and test data for the various components is included. Components tested include the 2.12 in. diameter compressor, the 2.86 in. diameter turbine, the Rice alternator and the cantilevered foil-type journal and thrust bearings. Also included are results on the fabrication of a C-103 turbine plenum/nozzle assembly and on offgassing of the organic materials in the alternator stator
Analysis, design, fabrication and testing of the Mini-Brayton rotating unit (MINI-BRU). Volume 2: Figures and drawings
This volume contains the figures and drawings reference in Volume 1
The Case for a 700+ GeV WIMP: Cosmic Ray Spectra from PAMELA, Fermi and ATIC
Multiple lines of evidence indicate an anomalous injection of high-energy e+-
in the Galactic halo. The recent fraction spectrum from the Payload for
Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) shows a
sharp rise up to 100 GeV. The Fermi Gamma-ray Space Telescope has found a
significant hardening of the e+e- cosmic ray spectrum above 100 GeV, with a
break, confirmed by HESS at around 1 TeV. The Advanced Thin Ionization
Calorimeter (ATIC) has also detected detected a similar excess, falling back to
the expected spectrum at 1 TeV and above. Excess microwaves towards the
galactic center in the WMAP data are consistent with hard synchrotron radiation
from a population of 10-100 GeV e+- (the WMAP ``Haze''). We argue that dark
matter annihilations can provide a consistent explanation of all of these data,
focusing on dominantly leptonic modes, either directly or through a new light
boson. Normalizing the signal to the highest energy evidence (Fermi and HESS),
we find that similar cross sections provide good fits to PAMELA and the Haze,
and that both the required cross section and annihilation modes are achievable
in models with Sommerfeld-enhanced annihilation. These models naturally predict
significant production of gamma rays in the galactic center via a variety of
mechanisms. Most notably, there is a robust inverse-Compton scattered (ICS)
gamma-ray signal arising from the energetic electrons and positrons, detectable
at Fermi/GLAST energies, which should provide smoking gun evidence for this
production.Comment: 28 pages; v2 plots corrected, references added; v3 included Fermi
electron data at reviewer request, references adde
Magnetic topologies of cool stars
Stellar magnetic fields can be investigated using several, very complementary
approaches. While conventional spectroscopy is capable of estimating the
average magnetic strength of potentially complex field configurations thanks to
its low sensitivity to the vector properties of the field, spectropolarimetry
can be used to map the medium- and large-scale structure of magnetic
topologies. In particular, the latter approach allows one to retrieve
information about the poloidal and toroidal components of the large-scale
dynamo fields in low-mass stars, and thus to investigate the physical processes
that produce them. Similarly, this technique can be used to explore how
magnetic fields couple young stars to their massive accretion disc and thus to
estimate how much mass and angular momentum are transfered to the newly-born
low-mass star. We present here the latest results in this field obtained with
spectropolarimetry, with special emphasis on the surprising discoveries
obtained on very-low mass fully-convective stars and classical T Tauri stars
thanks to the ESPaDOnS spectropolarimeter recently installed on the 3.6m
Canada-France-Hawaii Telescope.Comment: 10p invited review paper, 3 figures, to be published in the
proceedings of the 14th Cambridge Workshop on Cool Stars, Stellar Systems,
and the Sun, November 6-10, 2006, ed. G. van Belle (ASP Conf Ser
Magnetic field generation in fully convective rotating spheres
Magnetohydrodynamic simulations of fully convective, rotating spheres with
volume heating near the center and cooling at the surface are presented. The
dynamo-generated magnetic field saturates at equipartition field strength near
the surface. In the interior, the field is dominated by small-scale structures,
but outside the sphere by the global scale. Azimuthal averages of the field
reveal a large-scale field of smaller amplitude also inside the star. The
internal angular velocity shows some tendency to be constant along cylinders
and is ``anti-solar'' (fastest at the poles and slowest at the equator).Comment: 12 pages, 11 figures, 2 tables, to appear in the 10 Feb issue of Ap
Integral equations in MHD: theory and application
The induction equation of kinematic magnetohydrodynamics is mathematically
equivalent to a system of integral equations for the magnetic field in the bulk
of the fluid and for the electric potential at its boundary. We summarize the
recent developments concerning the numerical implementation of this scheme and
its applications to various forward and inverse problems in dynamo theory and
applied MHD.Comment: 17 pages, 4 figure
Intensity-Modulated Continuous-Wave Lidar at 1.57 Micrometer for Atmospheric CO2 Measurements
Understanding the earth's carbon cycle is essential for diagnosing current and predicting future climates, which requires precise global measurements of atmospheric CO2 through space missions. The Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) space mission will provide accurate global atmospheric CO2 measurements to meet carbon science requirements. The joint team of NASA Langley Research Center and ITT Exelis, Inc proposes to use the intensity-modulated, continuous-wave (IM-CW) lidar approach for the ASCENDS mission. Prototype instruments have been developed and used to demonstrate the power, signal-to-noise ratio, precision and accuracy, spectral purity, and stability of the measurement and the instrument needed for atmospheric CO2 observations from space. The ranging capability from laser platform to ground surfaces or intermediate backscatter layers is achieved by transmitted range-encoded IM laser signals. Based on the prototype instruments and current lidar technologies, space lidar systems and their CO2 column measurements are analyzed. These studies exhibit a great potential of using IM-CW lidar system for the active space CO2 mission ASCENDS
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