4,491 research outputs found
Flight research capabilities of the NASA/Army rotor systems research aircraft
A description is given of the capabilities and limitations of the Rotor Systems Research Aircraft (RSRA) that was demonstrated during the development contract, and assesses the expected research capabilities of the RSRA on delivery to the government
Three field tests of a gas filter correlation radiometer
Test flights to remotely measure nonurban carbon monoxide (CO) concentrations by gas filter correlation radiometry are discussed. The inferred CO concentrations obtained through use of the Gas Filter Correlation Radiometer (GFCR) agreed with independent measurements obtained by gas chromatography air sample bottle analysis to within 20 percent. The equipment flown on board the aircraft, the flight test procedure, the gas chromatograph direct air sampling procedure, and the GFCR data analysis procedure are reported
Discounting in Games across Time Scales
We introduce two-level discounted games played by two players on a
perfect-information stochastic game graph. The upper level game is a discounted
game and the lower level game is an undiscounted reachability game. Two-level
games model hierarchical and sequential decision making under uncertainty
across different time scales. We show the existence of pure memoryless optimal
strategies for both players and an ordered field property for such games. We
show that if there is only one player (Markov decision processes), then the
values can be computed in polynomial time. It follows that whether the value of
a player is equal to a given rational constant in two-level discounted games
can be decided in NP intersected coNP. We also give an alternate strategy
improvement algorithm to compute the value
Radio continuum and far-infrared emission from the galaxies in the Eridanus group
The Eridanus galaxies follow the well-known radio-FIR correlation. Majority
(70%) of these galaxies have their star formation rates below that of the Milky
Way. The galaxies having a significant excess of radio emission are identified
as low luminosity AGNs based on their radio morphologies obtained from the GMRT
observations. There are no powerful AGNs (L{20cm} > 10^{23} W Hz^{-1}) in the
group. The two most far-infrared and radio luminous galaxies in the group have
optical and HI morphologies suggestive of recent tidal interactions. The
Eridanus group also has two far-infrared luminous but radio-deficient galaxies.
It is believed that these galaxies are observed within a few Myr of the onset
of an intense star formation episode after being quiescent for at least a 100
Myr. The upper end of the radio luminosity distribution of the Eridanus
galaxies (L_{20cm} ~ 10^{22} W Hz^{-1}) is consistent with that of the field
galaxies, other groups, and late-type galaxies in nearby clusters.Comment: 16 pages; Accepted for publication in Journal of Astroph. & Astron.
March, 200
Probing Fine-Scale Ionospheric Structure with the Very Large Array Radio Telescope
High resolution (~1 arcminute) astronomical imaging at low frequency (below
150 MHz) has only recently become practical with the development of new
calibration algorithms for removing ionospheric distortions. In addition to
opening a new window in observational astronomy, the process of calibrating the
ionospheric distortions also probes ionospheric structure in an unprecedented
way. Here we explore one aspect of this new type of ionospheric measurement,
the differential refraction of celestial source pairs as a function of their
angular separation. This measurement probes variations in the spatial gradient
of the line-of-sight total electron content (TEC) to 0.001 TECU/km accuracy
over spatial scales of under 10 km to over 100 km. We use data from the VLA
Low-frequency Sky Survey (VLSS; Cohen et al. 2007, AJ 134, 1245), a nearly
complete 74 MHz survey of the entire sky visible to the Very Large Array (VLA)
telescope in Socorro, New Mexico. These data comprise over 500 hours of
observations, all calibrated in a standard way. While ionospheric spatial
structure varies greatly from one observation to the next, when analyzed over
hundreds of hours, statistical patterns become apparent. We present a detailed
characterization of how the median differential refraction depends on source
pair separation, elevation and time of day. We find that elevation effects are
large, but geometrically predictable and can be "removed" analytically using a
"thin-shell" model of the ionosphere. We find significantly greater ionospheric
spatial variations during the day than at night. These diurnal variations
appear to affect the larger angular scales to a greater degree indicating that
they come from disturbances on relatively larger spatial scales (100s of km,
rather than 10s of km).Comment: Accepted for publication by The Astronomical Journa
Multipole decomposition of LDA+ energy and its application to actinides compounds
A general reformulation of the exchange energy of -shell is applied in
the analysis of the magnetic structure of various actinides compounds in the
framework of LDA+U method. The calculations are performed in an efficient
scheme with essentially only one free parameter, the screening length. The
results are analysed in terms of different polarisation channels, due to
different multipoles. Generally it is found that the spin-orbital polarisation
is dominating. This can be viewed as a strong enhancement of the spin-orbit
coupling in these systems. This leads to a drastic decrease in spin
polarisation, in accordance with experiments. The calculations are able to
correctly differentiate magnetic and non-magnetic Pu system. Finally, in all
magnetic systems a new multipolar order is observed, whose polarisation energy
is often larger in magnitude than that of spin polarisation.Comment: Fixed some references and picture
A Semi-automatic Search for Giant Radio Galaxy Candidates and their Radio-Optical Follow-up
We present results of a search for giant radio galaxies (GRGs) with a
projected largest linear size in excess of 1 Mpc. We designed a computational
algorithm to identify contiguous emission regions, large and elongated enough
to serve as GRG candidates, and applied it to the entire 1.4-GHz NRAO VLA Sky
survey (NVSS). In a subsequent visual inspection of 1000 such regions we
discovered 15 new GRGs, as well as many other candidate GRGs, some of them
previously reported, for which no redshift was known. Our follow-up
spectroscopy of 25 of the brighter hosts using two 2.1-m telescopes in Mexico,
and four fainter hosts with the 10.4-m Gran Telescopio Canarias (GTC), yielded
another 24 GRGs. We also obtained higher-resolution radio images with the Karl
G. Jansky Very Large Array for GRG candidates with inconclusive radio
structures in NVSS.Comment: 4 pages, 1 figure, to appear in the proceedings of The Universe of
Digital Sky Surveys, Naples, Italy, Nov 25-28, 2014; Astrophysics and Space
Science, eds. N.R. Napolitano et a
Maintaining pre-school children's health and wellbeing in the UK: A qualitative study of the views of migrant parents
© The Author 2016. Published by Oxford University Press on behalf of Faculty of Public Health. Background There is evidence that key health behaviours of people who migrate deteriorate over time, which has a consequent impact upon the health of dependent children. As health in the early years sets the course for lifelong health, it is important to explore parents' views on maintaining children's health following migration. Methods Five focus groups were held with parents of preschool children who had migrated to the UK within the last 10 years (n = 28). Parents originated from Romania, Poland, Somalia and Pakistan, with one group of Roma Gypsy parents. Data collection took place in January to March 2015. Results All groups, apart from the Roma, perceived barriers to maintaining optimal health and well-being for their preschool children following migration to the UK. Eastern European parents experienced difficulties in ensuring family financial security, while parents from more established communities focused on barriers to children's exercise, play and nutrition. Conclusions This study highlights aspects of public health where migrants and their children can experience adverse effects in the UK. These findings have implications for policymakers, commissioners and providers of health services who aim to promote good health among preschool children
The KCAL VERA 22 GHz calibrator survey
We observed at 22 GHz with the VLBI array VERA a sample of 1536 sources with
correlated flux densities brighter than 200 mJy at 8 GHz. One half of target
sources has been detected. The detection limit was around 200 mJy. We derived
the correlated flux densities of 877 detected sources in three ranges of
projected baseline lengths. The objective of these observations was to
determine the suitability of given sources as phase calibrators for dual-beam
and phase-referencing observations at high frequencies. Preliminary results
indicate that the number of compact extragalactic sources at 22 GHz brighter
than a given correlated flux density level is twice less than at 8 GHz.Comment: Accepted for publication by the Astronomical Journal. 6 pages, 3
figures, 3 table. The machine readable catalogue file, kcal_cat.txt can be
extracted from the source of this submissio
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