13,119 research outputs found
Scene simulation for passive IR systems
The development of large mosaic detector arrays will allow for the construction of staring long wave infrared (LWIR) sensors which can observe large fields of view instantaneously and continuously. In order to evaluate and exercise these new systems, it will be necessary to provide simulated scenes of many moving targets against an infrared clutter background. Researchers are currently developing a projector/screen system. This system is comprised of a mechanical scanner, a diffuse screen, and a miniature blackbody. A prototype of the mechanical scanner, which is comprised of four independently driven scanners, has been designed, fabricated, and evaluated under room and cryogenic vacuum conditions. A large diffuse screen has been constructed and tested for structural integrity under cryogenic/vacuum thermal cycling. Construction techniques have been developed for the fabrication of miniature high-temperature blackbody sources. Finally, a concept has been developed to use this miniature blackbody to produce a spectrally tailorable source
Geometric, aerodynamic, and kinematic characteristics of two twin keel parawings during deployment
Flight test data on geometric, aerodynamic, and kinematic characteristics of two twin keel parawings during deploymen
The impact of the warm outflow in the young (GPS) radio source & ULIRG PKS 1345+12 (4C 12.50)
(Abridged) We present new deep VLT/FORS optical spectra with intermediate
resolution and large wavelength coverage of the GPS radio source and ULIRG
PKS1345+12 (4C12.50; z=0.122), taken with the aim of investigating the impact
of the nuclear activity on the circumnuclear ISM. PKS1345+12 is a powerful
quasar and is also the best studied case of an emission line outflow in a
ULIRG. Using the density sensitive transauroral emission lines [S II]4068,4076
and [O II]7318,7319,7330,7331, we pilot a new technique to accurately model the
electron density for cases in which it is not possible to use the traditional
diagnostic [S II]6716/6731, namely sources with highly broadened complex
emission line profiles and/or high (Ne > 10^4 cm^-3) electron densities. We
measure electron densities of Ne=2.94x10^3 cm^-3, Ne=1.47x10^4 cm^-3 and
Ne=3.16x10^5 cm^-3 for the regions emitting the narrow, broad and very broad
components respectively. We calculate a total mass outflow rate of 8 M_sun
yr^-1. We estimate the total mass in the warm gas outflow is 8x10^5 M_sun. The
total kinetic power in the warm outflow is 3.4x10^42 erg s^-1. We find that
only a small fraction (0.13% of Lbol) of the available accretion power is
driving the warm outflow, significantly less than currently required by the
majority of quasar feedback models (~5-10\% of Lbol), but similar to recent
findings by Hopkins et al. (2010) for a two-stage feedback model. The models
also predict that AGN outflows will eventually remove the gas from the bulge of
the host galaxy. The visible warm outflow in PKS1345+12 is not currently
capable of doing so. However, it is entirely possible that much of the outflow
is either obscured by a dense and dusty natal cocoon and/or in cooler or hotter
phases of the ISM. This result is important not just for studies of young
(GPS/CSS) radio sources, but for AGN in general.Comment: Accepted for publication in MNRAS. 11 pages, 4 figure
Gas outflows in radio galaxies
We present a summary of our recent results on gas outflows in radio galaxies.
Fast outflows (up to 2000 km/s) have been detected both in ionized and neutral
gas. The latter is particularly surprising as it shows that, despite the
extremely energetic phenomena occurring near an AGN, some of the outflowing gas
remains, or becomes again, neutral. These results are giving new and important
insights on the physical conditions of the gaseous medium around an AGN.Comment: To appear in the proceedings of the IAU Symposium #217, Recycling
Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E.
Brinks, 6 pages. The full paper with high resolution images can be downloaded
from http://www.astron.nl/~morganti/Papers/outflows.ps.g
Unique Access to u-Channel Physics: Exclusive Backward-Angle Omega Meson Electroproduction
Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep→e′pω, at central Q² values of 1.60, 2.45 GeV², at W=2.21 GeV. The results of our pioneering −u≈−u_(min) study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L/T/LT/TT separations in this never explored kinematic territory. At Q²=2.45 GeV², the observed dominance of σ_T over σ_L, is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics
Impact of ¹⁶O(e,e′α)¹²C measurements on the ¹²C(α,γ)¹⁶O astrophysical reaction rate
The ¹²C(α,γ)¹⁶O reaction, an important component of stellar helium burning, has a key role in nuclear astrophysics. It has direct impact on the evolution and final state of massive stars and also influences the elemental abundances resulting from nucleosynthesis in such stars. Providing a reliable estimate for the energy dependence of this reaction at stellar helium burning temperatures has been a longstanding and important goal. In this work, we study the role of potential new measurements of the ¹⁶O(e,e′α)¹²C reaction in reducing the overall uncertainty. A multilevel R-matrix analysis is used to make extrapolations of the astrophysical S factor for the ¹²C(α,γ)¹⁶O reaction to the stellar energy of 300 keV. The statistical precision of the S-factor extrapolation is determined by performing multiple fits to existing E1 and E2 ground state capture data, including the impact of possible future measurements of the ¹⁶O(e,e′α)¹²C reaction. In particular, we consider a proposed MIT experiment that would make use of a high-intensity low-energy electron beam that impinges on a windowless oxygen gas target as a means to determine the total E1 and E2 cross sections for this reaction
Equivalence-based Security for Querying Encrypted Databases: Theory and Application to Privacy Policy Audits
Motivated by the problem of simultaneously preserving confidentiality and
usability of data outsourced to third-party clouds, we present two different
database encryption schemes that largely hide data but reveal enough
information to support a wide-range of relational queries. We provide a
security definition for database encryption that captures confidentiality based
on a notion of equivalence of databases from the adversary's perspective. As a
specific application, we adapt an existing algorithm for finding violations of
privacy policies to run on logs encrypted under our schemes and observe low to
moderate overheads.Comment: CCS 2015 paper technical report, in progres
Unique Access to u-Channel Physics: Exclusive Backward-Angle Omega Meson Electroproduction
Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep→e′pω, at central Q² values of 1.60, 2.45 GeV², at W=2.21 GeV. The results of our pioneering −u≈−u_(min) study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L/T/LT/TT separations in this never explored kinematic territory. At Q²=2.45 GeV², the observed dominance of σ_T over σ_L, is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics
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