8,560 research outputs found
Review and critical analysis: Rolling-element bearings for system life and reliability
A ball and cylindrical roller bearing technical specification which incorporates the latest state-of-the-art advancements was prepared for the purpose of improving bearing reliability in U.S. Army aircraft. The current U.S. Army aviation bearing designs and applications, including life analyses, were analyzed. A bearing restoration and refurbishment specification was prepared to improve bearing availability
Results from tests, with van-mounted sensor, of magnetic leader cable for aircraft guidance during roll-out and turnoff
Tests were conducted with a van mounted experimental magnetic leader cable sensor to evaluate its potential for measuring aircraft displacement and heading with respect to the leader cable during roll out and turnoff. Test results show that the system may be usable in measuring displacement but the heading measurement contains errors introduced by distortion of the magnetic field by the metal van or aircraft
LRG-BEASTS III: Ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80
We have performed ground-based transmission spectroscopy of the hot Jupiter
orbiting the cool dwarf WASP-80 using the ACAM instrument on the William
Herschel Telescope (WHT) as part of the LRG-BEASTS programme. This is the third
paper of a ground-based transmission spectroscopy survey of hot Jupiters using
low-resolution grism spectrographs. We observed two transits of the planet and
have constructed transmission spectra spanning a wavelength range of
4640-8840A. Our transmission spectrum is inconsistent with a previously claimed
detection of potassium in WASP-80b's atmosphere, and is instead most consistent
with a haze. We also do not see evidence for sodium absorption at a resolution
of 100A.Comment: 11 pages, 9 figures. Accepted for publication in MNRA
Improved Searches for HI in Three Dwarf Spheroidal Galaxies
Previous searches for HI in our Galaxy's dwarf spheroidal companions have not
been complete enough to settle the question of whether or not these galaxies
have HI, especially in their outer parts. We present VLA observations of three
dwarf spheroidals: Fornax, Leo II, and Draco, all of which have known stellar
velocities. The new data show no HI emission or absorption. Column density
limits in emission are 4--7 x 10^18 atoms/cm^2 in the centers of the galaxies.
The importance of the new observations is that they cover larger areas than
previous searches and they are less plagued by confusion with foreground
(Galactic) HI. The apparent absence of neutral gas in the Fornax dwarf
spheroidal is especially puzzling because recent photometry shows evidence of
stars only 10^8 years old. We discuss whether the VLA observations could have
missed significant amounts of HI.Comment: 20 pages, 7 figures; to appear in the Astronomical Journa
Advanced code-division multiplexers for superconducting detector arrays
Multiplexers based on the modulation of superconducting quantum interference
devices are now regularly used in multi-kilopixel arrays of superconducting
detectors for astrophysics, cosmology, and materials analysis. Over the next
decade, much larger arrays will be needed. These larger arrays require new
modulation techniques and compact multiplexer elements that fit within each
pixel. We present a new in-focal-plane code-division multiplexer that provides
multiplexing elements with the required scalability. This code-division
multiplexer uses compact lithographic modulation elements that simultaneously
multiplex both signal outputs and superconducting transition-edge sensor (TES)
detector bias voltages. It eliminates the shunt resistor used to voltage bias
TES detectors, greatly reduces power dissipation, allows different dc bias
voltages for each TES, and makes all elements sufficiently compact to fit
inside the detector pixel area. These in-focal-plane code-division multiplexers
can be combined with multi-gigahertz readout based on superconducting
microresonators to scale to even larger arrays.Comment: 8 pages, 3 figures, presented at the 14th International Workshop on
Low Temperature Detectors, Heidelberg University, August 1-5, 2011,
proceedings to be published in the Journal of Low Temperature Physic
The Velocity Dispersion Profile of the Remote Dwarf Spheroidal Galaxy Leo I: A Tidal Hit and Run?
(abridged) We present kinematic results for a sample of 387 stars located
near Leo I based on spectra obtained with the MMT's Hectochelle spectrograph
near the MgI/Mgb lines. We estimate the mean velocity error of our sample to be
2.4 km/s, with a systematic error of < 1 km/s. We produce a final sample of 328
Leo I red giant members, from which we measure a mean heliocentric radial
velocity of 282.9 +/- 0.5 km/s, and a mean radial velocity dispersion of 9.2
+/- 0.4 km/s for Leo I. The dispersion profile of Leo I is flat out to beyond
its classical `tidal' radius. We fit the profile to a variety of equilibrium
dynamical models and can strongly rule out models where mass follows light.
Two-component Sersic+NFW models with tangentially anisotropic velocity
distributions fit the dispersion profile well, with isotropic models ruled out
at a 95% confidence level. The mass and V-band mass-to-light ratio of Leo I
estimated from equilibrium models are in the ranges 5-7 x 10^7 M_sun and 9-14
(solar units), respectively, out to 1 kpc from the galaxy center. Leo I members
located outside a `break radius' (about 400 arcsec = 500 pc) exhibit
significant velocity anisotropy, whereas stars interior appear to have
isotropic kinematics. We propose the break radius represents the location of
the tidal radius of Leo I at perigalacticon of a highly elliptical orbit. Our
scenario can account for the complex star formation history of Leo I, the
presence of population segregation within the galaxy, and Leo I's large outward
velocity from the Milky Way. The lack of extended tidal arms in Leo I suggests
the galaxy has experienced only one perigalactic passage with the Milky Way,
implying that Leo I may have been injected into its present orbit by a third
body a few Gyr before perigalacticon.Comment: ApJ accepted, 23 figures, access paper as a pdf file at
http://www.astro.lsa.umich.edu/~mmateo/research.htm
Structure of the Draco Dwarf Spheroidal Galaxy
This article studies the structure of the Draco dwarf spheroidal galaxy with
an emphasis on the question of whether the spatial distribution of its stars
has been affected by the tidal interaction with the Milky Way, using R- and
V-band CCD photometry for eleven fields. The article reports coordinates for
the center, a position angle of the major axis, and the ellipticity. It also
reports the results of searches for asymmetries in the structure of Draco.
These results, and searches for a ``break'' in the radial profile and for the
presence of principal sequences of Draco in a color-magnitude diagram for
regions more than 50 arcmin from the center, yield no evidence that tidal
forces from the Milky Way have affected the structure of Draco.Comment: 25 pages, 11 figures, 3 tables. Accepted for publication in A
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Martian atmospheric O<sub>3</sub> retrieval development for the NOMAD-UVIS spectrometer
The composition of atmospheric trace gases and aerosols is a highly variable and poorly constrained component of the martian atmosphere, and by affecting martian climate and UV surface dose, represents a key parameter in the assessment of suitability for martian habitability. The ExoMars Trace Gas Orbiter (TGO) carries the Open University (OU) designed Ultraviolet and VIsible Spectrometer (UVIS) instrument as part of the Belgian-led Nadir and Occultation for MArs Discovery (NOMAD) spectrometer suite. NOMAD will begin transmitting science observations of martian surface and atmosphere back-scattered UltraViolet (UV) and visible radiation in Spring 2018, which will be processed to derive spatially and temporally averaged atmospheric trace gas and aerosol concentrations, intended to provide a better understanding of martian atmospheric photo-chemistry and dynamics, and will also improve models of martian atmospheric chemistry, climate and habitability. Work presented here illustrates initial development and testing of the OU’s new retrieval algorithm for determining O3 and aerosol concentrations from the UVIS instrument
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