1,116 research outputs found
The IceCube Neutrino Observatory I: Point Source Searches
Searches for point sources of astrophysical neutrinos and related
measurements: Searches for steady and time-variable sources; Follow-up
programs; AGNs; GRBs; Moon shadow; Submitted papers to the 32nd International
Cosmic Ray Conference, Beijing 2011.Comment: Papers submitted by the IceCube Collaboration to the 32nd
International Cosmic Ray Conference, Beijing 2011; part
The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs
Using the largest high-resolution spectroscopic sample to date of young, very
low mass stars (VLMS) and brown dwarfs (BDs), we investigate disk accretion in
objects ranging from just above the hydrogen-burning limit all the way to
nearly planetary masses. Our 82 targets span spectral types from M5 to M9.5, or
masses from 0.15 Msun down to ~15 Jupiters. They are confirmed members of the
rho Oph, Taurus, Cha I, IC 348, R CrA, Upper Sco and TW Hydrae regions, with
ages = M6.5). We
find that: (1) classical T Tauri-like disk-accretion persists in the BD domain
down to nearly the deuterium-burning limit; (2) in addition to H-alpha,
permitted emission lines of CaII, OI and HeI are also good accretion
indicators, as in CTTs; (3) the CaII 8662A flux is an excellent quantitative
measure of the accretion rate (Mdot) in VLMS and BDs(as in CTTs); (4) Mdot
diminishes as M^2 -- our measurements support previous findings of this
correlation, and extend it to the entire range of sub-stellar masses; (5) the
accretor fraction among VLMS and BDs decreases substantially with age, as in
higher-mass stars; (6) at any given age, the VLMS and BD accretor fraction is
comparable to that in higher-mass stars; and (7) a number of sources with IR
disk excesses do not evince measurable accretion, with the incidence of such a
mismatch increasing with age: this implies that disks in the low mass regime
can persist beyond the main accretion phase, and parallels the transition from
the classical to post-T Tauri stage in more massive stars. These strong
similarities at young ages, between higher-mass stars and low-mass bodies close
to and below the hydrogen-burning limit, are consistent with a common formation
mechanism in the two mass regimes. (abridged)Comment: 64 pages, 7 figures. ApJ accepte
Space shuttle low cost/risk avionics study
All work breakdown structure elements containing any avionics related effort were examined for pricing the life cycle costs. The analytical, testing, and integration efforts are included for the basic onboard avionics and electrical power systems. The design and procurement of special test equipment and maintenance and repair equipment are considered. Program management associated with these efforts is described. Flight test spares and labor and materials associated with the operations and maintenance of the avionics systems throughout the horizontal flight test are examined. It was determined that cost savings can be achieved by using existing hardware, maximizing orbiter-booster commonality, specifying new equipments to MIL quality standards, basing redundancy on cost effective analysis, minimizing software complexity and reducing cross strapping and computer-managed functions, utilizing compilers and floating point computers, and evolving the design as dictated by the horizontal flight test schedules
SIRU development. Volume 1: System development
A complete description of the development and initial evaluation of the Strapdown Inertial Reference Unit (SIRU) system is reported. System development documents the system mechanization with the analytic formulation for fault detection and isolation processing structure; the hardware redundancy design and the individual modularity features; the computational structure and facilities; and the initial subsystem evaluation results
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