52,970 research outputs found
A Color-Magnitude Diagram for a Globular Cluster In the Giant Elliptical Galaxy NGC 5128
The Hubble Space Telescope has been used to obtain WFPC2 (V,I) photometry for
a large sample of stars in the outer halo of the giant elliptical NGC 5128 (d =
4 Mpc). The globular cluster N5128-C44, at the center of the Planetary Camera
field, is well enough resolved to permit the construction of a color-magnitude
diagram (CMD) for it which covers the brightest two magnitudes of the giant
branch. The CMD is consistent with that of a normal old, moderately
low-metallicity ([Fe/H] = -1.30 globular cluster, distinctly more metal-poor
than most of the field halo stars at the same projected location (which average
[Fe/H] ~ -0.5). This is the most distant globular cluster in which direct
color-magnitude photometry has been achieved to date, and the first one
belonging to a giant E galaxy.Comment: 12 pages, LaTeX, including 5 postscript figures; submitted to
Astronomical Journa
Phase 2 and 3 wind tunnel tests of the J-97 powered, external augmentor V/STOL model
Static and forward speed tests were made in a 40 multiplied by 80 foot wind tunnel of a large-scale, ejector-powered V/STOL aircraft model. Modifications were made to the model following earlier tests primarily to improve longitudinal acceleration capability during transition from hovering to wingborne flight. A rearward deflection of the fuselage augmentor thrust vector was shown to be beneficial in this regard. Other augmentor modifications were tested, notably the removal of both endplates, which improved acceleration performance at the higher transition speeds. The model tests again demonstrated minimal interference of the fuselage augmentor on aerodynamic lift. A flapped canard surface also showed negligible influence on the performance of the wing and of the fuselage augmentor
Dusty plasma cavities: probe-induced and natural
A comprehensive exploration of regional dust evacuation in complex plasma
crystals is presented. Voids created in 3D crystals on the International Space
Station have provided a rich foundation for experiments, but cavities in dust
crystals formed in ground-based experiments have not received as much
attention. Inside a modified GEC RF cell, a powered vertical probe was used to
clear the central area of a dust crystal, producing a cavity with high
cylindrical symmetry. Cavities generated by three mechanisms are examined.
First, repulsion of micrometer-sized particles by a negatively charged probe is
investigated. A model of this effect developed for a DC plasma is modified and
applied to explain new experimental data in RF plasma. Second, the formation of
natural cavities is surveyed; a radial ion drag proposed to occur due to a
curved sheath is considered in conjunction with thermophoresis and a flattened
confinement potential above the center of the electrode. Finally, cavity
formation unexpectedly occurs upon increasing the probe potential above the
plasma floating potential. The cavities produced by these methods appear
similar, but each are shown to be facilitated by fundamentally different
processes.Comment: 10 pages, 12 figure
Effects of digital altimetry on pilot workload
A series of VOR-DME instrument landing approaches was flown in the DC-9 full-workload simulator to compare pilot performance, scan behavior, and workload when using a computer-drum-pointer altimeter (CDPA) and a digital altimeter (DA). Six pilots executed two sets of instrument landing approaches, with a CDPA on one set and a DA on the other set. Pilot scanning parameters, flight performance, and subjective opinion data were evaluated. It is found that the processes of gathering information from the CDPA and the DA are different. The DA requires a higher mental workload than the CDPA for a VOR-DME type landing approach. Mental processing of altitude information after transitioning back to the attitude indicator is more evident with the DA than with the CDPA
HST Photometry for the Halo Stars in the Leo Elliptical NGC 3377
We have used the ACS camera on HST to obtain (V,I) photometry for 57,000
red-giant stars in the halo of the Leo elliptical NGC 3377. We use this sample
of stars to derive the metallicity distribution function (MDF) for its halo
field stars, and comment on its chemical evolution history compared with both
larger and smaller E galaxies. Our ACS/WFC field spans a radial range extending
from 4 to 18 kpc projected distance from the center of NGC 3377 and thus covers
a significant portion of this galaxy's halo. We find that the MDF is broad,
reaching a peak at [m/H] ~ -0.6. It may, in addition, have relatively few
stars more metal-rich than [m/H] = -0.3$, although interpretation of the
high-metallicity end of the MDF is limited by photometric completeness that
affects the detection of the reddest, most metal-rich stars. NGC 3377 appears
to have an enrichment history intermediate between those of normal dwarf
ellipticals and the much larger giants. As yet, we find no clear evidence that
the halo of NGC 3377 contains a significant population of ``young'' (< 3 Gy)
stars.Comment: 40 pages, 17 figure
Transport on randomly evolving trees
The time process of transport on randomly evolving trees is investigated. By
introducing the notions of living and dead nodes a model of random tree
evolution is constructed which describes the spreading in time of objects
corresponding to nodes. By using the method of the age-dependent branching
processes we derive the joint distribution function of the number of living and
dead nodes, and determine the correlation between these node numbers as a
function of time. Also analyzed are the stochastic properties of the end-nodes;
and the correlation between the numbers of living and dead end-nodes is shown
to change its character suddenly at the very beginning of the evolution
process. The survival probability of random trees is investigated and
expressions are derived for this probability.Comment: 16 pages, 8 figures, published in Phys. Rev. E 72, 051101 (2005
Analytical techniques of pilot scanning behavior and their application
The state of the art of oculometric data analysis techniques and their applications in certain research areas such as pilot workload, information transfer provided by various display formats, crew role in automated systems, and pilot training are documented. These analytical techniques produce the following data: real-time viewing of the pilot's scanning behavior, average dwell times, dwell percentages, instrument transition paths, dwell histograms, and entropy rate measures. These types of data are discussed, and overviews of the experimental setup, data analysis techniques, and software are presented. A glossary of terms frequently used in pilot scanning behavior and a bibliography of reports on related research sponsored by NASA Langley Research Center are also presented
Efficient Irrigation for Water Conservation in the Rio Grande Basin
The Rio Grande Basin Initiative began in 2001 aimed at improving irrigation and water use efficiencies, and meeting present and future water demands throughout the Basin in Texas and New Mexico
Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 2: Advanced energy conversion systems. Part 3: Direct energy conversion cycles
For abstract, see N76-23680
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