20,786 research outputs found
Reversible current control apparatus Patent
Reversible current directing circuitry for reversible motor contro
Spacecraft high-voltage power supply construction
The design techniques, circuit components, fabrication techniques, and past experience used in successful high-voltage power supplies for spacecraft flight systems are described. A discussion of the basic physics of electrical discharges in gases is included and a design rationale for the prevention of electrical discharges is provided. Also included are typical examples of proven spacecraft high-voltage power supplies with typical specifications for design, fabrication, and testing
Statistical Filtering of Space Navigation Measurements
Statistical filtering of space navigation measurement
Optimization of midcourse velocity corrections
Optimum time to apply single midcourse velocity correction and optimum schedule for corrections in variable time-of-arrival guidance - geometrical mode
Tests of non-standard electroweak couplings of right-handed quarks
The standard model can be interpreted as the leading order of a Low-Energy
Effective Theory (LEET) invariant under a higher non linearly realized symmetry
equipped with a systematic power
counting. Within the minimal version of this ``not quite decoupling'' LEET, the
dominant non-standard effect appears at next-to-leading order (NLO) and is a
modification of the couplings of fermions to W and Z. In particular, the
coupling of right-handed quarks to Z is modified and a direct coupling of
right-handed quarks to W emerges. Charged right-handed lepton currents are
forbidden by an additional discrete symmetry in the lepton sector originally
designed to suppress Dirac neutrino masses. A complete NLO analysis of
experimental constraints on these modified couplings is presented. Concerning
couplings of light quarks, the interface of the electroweak tests with QCD
aspects is discussed in detail.Comment: 56 pages, 14 figures, v2: references added, minor modifications in
the text, accepted for publication in JHE
Photon breeding mechanism in relativistic jets: astrophysical implications
Photon breeding in relativistic jets involves multiplication of high-energy
photons propagating from the jet to the external environment and back with the
conversion into electron-positron pairs. The exponential growth of the energy
density of these photons is a super-critical process powered by the bulk energy
of the jet. The efficient deceleration of the jet outer layers creates a
structured jet morphology with the fast spine and slow sheath. In initially
fast and high-power jets even the spine can be decelerated efficiently leading
to very high radiative efficiencies of conversion of the jet bulk energy into
radiation. The decelerating, structured jets have angular distribution of
radiation significantly broader than that predicted by a simple blob model with
a constant Lorentz factor. This reconciles the discrepancy between the high
Doppler factors determined by the fits to the spectra of TeV blazars and the
low apparent velocities observed at VLBI scales as well as the low jet Lorentz
factors required by the observed statistics and luminosity ratio of
Fanaroff-Riley I radio galaxies and BL Lac objects. Photon breeding produces a
population of high-energy leptons in agreement with the constraints on the
electron injection function required by spectral fits of the TeV blazars.
Relativistic pairs created outside the jet and emitting gamma-rays by inverse
Compton process might explain the relatively high level of the TeV emission
from the misaligned jet in the radio galaxies. The mechanism reproduces basic
spectral features observed in blazars including the blazar sequence (shift of
the spectral peaks towards lower energies with increasing luminosity). The
mechanism is very robust and can operate in various environments characterised
by the high photon density.Comment: 6 pages, 3 figures, to appear in the proceedings of the HEPRO
conference, September 24-28, 2007, Dublin, Irelan
The Angular Clustering of WISE-Selected AGN: Different Haloes for Obscured and Unobscured AGN
We calculate the angular correlation function for a sample of 170,000 AGN
extracted from the Wide-field Infrared Survey Explorer (WISE) catalog, selected
to have red mid-IR colors (W1 - W2 > 0.8) and 4.6 micron flux densities
brighter than 0.14 mJy). The sample is expected to be >90% reliable at
identifying AGN, and to have a mean redshift of z=1.1. In total, the angular
clustering of WISE-AGN is roughly similar to that of optical AGN. We
cross-match these objects with the photometric SDSS catalog and distinguish
obscured sources with (r - W2) > 6 from bluer, unobscured AGN. Obscured sources
present a higher clustering signal than unobscured sources. Since the host
galaxy morphologies of obscured AGN are not typical red sequence elliptical
galaxies and show disks in many cases, it is unlikely that the increased
clustering strength of the obscured population is driven by a host galaxy
segregation bias. By using relatively complete redshift distributions from the
COSMOS survey, we find obscured sources at mean redshift z=0.9 have a bias of b
= 2.9 \pm 0.6 and are hosted in dark matter halos with a typical mass of
log(M/M_odot)~13.5. In contrast, unobscured AGN at z~1.1 have a bias of b = 1.6
\pm 0.6 and inhabit halos of log(M/M_odot)~12.4. These findings suggest that
obscured AGN inhabit denser environments than unobscured AGN, and are difficult
to reconcile with the simplest AGN unification models, where obscuration is
driven solely by orientation.Comment: Accepted for publication in ApJ. 13 pages, 15 figure
A preliminary quarantine analysis of a possible Mariner Venus 1972 mission
Spacecraft contamination preliminary quarantine analysis for possible 1972 Mariner Venus prob
Rural Community Participation, Social Networks, and Broadband Use: Examples from Localized and National Survey Data
Although attention has been given to how broadband access is related to economic development in rural areas, scant consideration has been given to how it may be associated with voluntary participation. This issue is important in that numerous studies have shown how much more vital community participation is in rural areas as compared to suburban and urban places. Drawing on three diverse data sets, we examine the influence of broadband access on community participation. In addition, we explore whether broadband access exerts its influence through, in conjunction with, or independent of social networks. The results suggest that broadband access and social network size have independent effects on volunteering in rural places.rural sociology, social networks, broadband, digital inequality, volunteerism, Community/Rural/Urban Development, Research and Development/Tech Change/Emerging Technologies,
Juncture stress fields in multicellular shell structures. Volume III - Stresses and deformations on fixed-edge segmental conical shells Final report
Equations for thin elastic conical shells and digital program for analysis of stress and deformation on fixed edge segmental conical shells - solution by finite difference techniqu
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