751 research outputs found
Energy Efficient Engine combustor test hardware detailed design report
The Energy Efficient Engine (E3) Combustor Development effort was conducted as part of the overall NASA/GE E3 Program. This effort included the selection of an advanced double-annular combustion system design. The primary intent was to evolve a design which meets the stringent emissions and life goals of the E3 as well as all of the usual performance requirements of combustion systems for modern turbofan engines. Numerous detailed design studies were conducted to define the features of the combustion system design. Development test hardware was fabricated, and an extensive testing effort was undertaken to evaluate the combustion system subcomponents in order to verify and refine the design. Technology derived from this development effort will be incorporated into the engine combustion system hardware design. This advanced engine combustion system will then be evaluated in component testing to verify the design intent. What is evolving from this development effort is an advanced combustion system capable of satisfying all of the combustion system design objectives and requirements of the E3. Fuel nozzle, diffuser, starting, and emissions design studies are discussed
Energy Efficient Engine (E3) combustion system component technology performance report
The Energy Efficient Engine (E3) combustor effort was conducted as part of the overall NASA/GE E3 Program. This effort included the selection of an advanced double-annular combustion system design. The primary intent of this effort was to evolve a design that meets the stringent emissions and life goals of the E3, as well as all of the usual performance requirements of combustion systems for modern turbofan engines. Numerous detailed design studies were conducted to define the features of the combustion system design. Development test hardware was fabricated, and an extensive testing effort was undertaken to evaluate the combustion system subcomponents in order to verify and refine the design. Technology derived from this effort was incorporated into the engine combustion hardware design. The advanced engine combustion system was then evaluated in component testing to verify the design intent. What evolved from this effort was an advanced combustion system capable of satisfying all of the combustion system design objectives and requirements of the E3
KECK HIRES Spectroscopy of APM 08279+5255
With an optical R-band magnitude of 15.2, the recently discovered z=3.911 BAL
quasar APM 08279+5255 is an exceptionally bright high redshift source. Its
brightness has allowed us to acquire a high signal-to-noise ratio (~100), high
resolution (~6 km/s) spectrum using the HIRES echelle spectrograph on the 10-m
Keck I telescope. Given the quality of the data, these observations provide an
unprecedented view of associated and intervening absorption systems. Here we
announce the availability of this spectrum to the general astronomical
community and present a brief analysis of some of its main features.Comment: 21 pages including 5 figures. Accepted for publication by PAS
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as
the basis for constructing a new radio-selected sample of optically bright
quasars. This is the first radio-selected sample that is competitive in size
with current optically selected quasar surveys. Using only two basic criteria,
radio-optical positional coincidence and optical morphology, quasars and BL
Lacs can be identified with 60% selection efficiency; the efficiency increases
to 70% for objects fainter than magnitude 17. We show that a more sophisticated
selection scheme can predict with better than 85% reliability which candidates
will turn out to be quasars.
This paper presents the second installment of the FIRST Bright Quasar Survey
with a catalog of 636 quasars distributed over 2682 square degrees. The quasar
sample is characterized and all spectra are displayed. The FBQS detects both
radio-loud and radio-quiet quasars out to a redshift z>3. We find a large
population of objects of intermediate radio-loudness; there is no evidence in
our sample for a bimodal distribution of radio characteristics. The sample
includes ~29 broad absorption line quasars, both high and low ionization, and a
number of new objects with remarkable optical spectra.Comment: 41 pages plus 39 gifs which contain all quasar spectra. Accepted for
publication in the Astrophysical Journal Supplement Serie
Red and Blue Shifted Broad Lines in Luminous Quasars
We have observed a sample of 22 luminous quasars, in the range 2.0<z<2.5, at
1.6 microns with the near-infrared (NIR) spectrograph FSPEC on the Multiple
Mirror Telescope. Our sample contains 13 radio-loud and 9 radio-quiet objects.
We have measured the systemic redshifts z_(sys) directly from the strong [O
III]5007 line emitted from the narrow-line-region. From the same spectra, we
have found that the non-resonance broad H lines have a systematic mean
redward shift of 520+/-80 km/s with respect to systemic. Such a shift was not
found in our identical analysis of the low-redshift sample of Boroson & Green.
The amplitude of this redshift is comparable to half the expected gravitational
redshift and transverse Doppler effects, and is consistent with a correlation
between redshift differences and quasar luminosity. From data in the
literature, we confirm that the high-ionization rest-frame ultraviolet broad
lines are blueshifted ~550-1050 km/s from systemic, and that these velocity
shifts systematically increase with ionization potential. Our results allow us
to quantify the known bias in estimating the ionizing flux from the
inter-galactic-medium J_(IGM) via the Proximity Effect. Using redshift
measurements commonly determined from strong broad line species, like Ly\alpha
or CIV1549, results in an over-estimation of J_(IGM) by factors of ~1.9-2.3.
Similarly, corresponding lower limits on the density of baryon Omega_b will be
over-estimated by factors of ~1.4-1.5. However, the low-ionization MgII2798
broad line is within ~50 km/s of systemic, and thus would be the line of choice
for determining the true redshift of 1.0<z<2.2 quasars without NIR
spectroscopy, and z>3.1 objects using NIR spectroscopy.Comment: 12 pages, Latex, 2 figures, 2 tables, Accepted for publication in ApJ
Letter
What Determines the Depth of BALs? Keck HIRES Observations of BALQSO 1603+300
We find that the depth and shape of the broad absorption lines (BALs) in
BALQSO 1603+3002 are determined largely by the fraction of the emitting source
which is covered by the BAL flow. In addition, the observed depth of the BALs
is poorly correlated with their real optical depth. The implication of this
result is that abundance studies based on direct extraction of column densities
from the depth of the absorption troughs are unreliable. Our conclusion is
based on analysis of unblended absorption features of two lines from the same
ion (in this case the Si IV doublet), which allows unambiguous separation of
covering factor and optical depth effects. The complex morphology of the
covering factor as a function of velocity suggests that the BALs are produced
by several physically separated outflows. The covering factor is ion dependent
in both depth and velocity width. We also find evidence that in BALQSO
1603+3002 the flow does not cover the broad emission line region.Comment: 13 pages, 2 figures, accepted for publication in Ap
A spectroscopic study of component C and the extended emission around I Zw 18
Long-slit Keck II, 4m Kitt Peak, and 4.5m MMT spectrophotometric data are
used to investigate the stellar population and the evolutionary status of I Zw
18C, the faint C component of the nearby blue compact dwarf galaxy I Zw 18.
Hydrogen H and H emission lines are detected in the spectra of I
Zw 18C, implying that ionizing massive stars are present. High signal-to-noise
Keck II spectra of different regions in I Zw 18C reveal H, H
and higher order hydrogen lines in absorption. Several techniques are used to
constrain the age of the stellar population in I Zw 18C. Ages derived from two
different methods, one based on the equivalent widths of the H,
H emission lines and the other on H, H absorption lines
are consistent with a 15 Myr instantaneous burst model. We find that a small
extinction in the range = 0.20 -- 0.65 mag is needed to fit the observed
spectral energy distribution of I Zw 18C with that model. In the case of
constant star formation, all observed properties are consistent with stars
forming continuously between ~ 10 Myr and < 100 Myr ago. We use all available
observational constraints for I Zw 18C, including those obtained from Hubble
Space Telescope color-magnitude diagrams, to argue that the distance to I Zw 18
should be as high as ~ 15 Mpc. The deep spectra also reveal extended ionized
gas emission around I Zw 18. H emission is detected as far as 30" from
it. To a B surface brightness limit of ~ 27 mag arcsec we find no
observational evidence for extended stellar emission in the outermost regions,
at distances > 15" from I Zw 18.Comment: 38 pages, 11 Postscript figures, accepted for publication in the
Astrophysical Journa
Hard X-ray emitting Active Galactic Nuclei selected by the Chandra Multi-wavelength Project
We present X-ray and optical analysis of 188 AGN identified from 497 hard
X-ray (f (2.0-8.0 keV) > 2.7x10^-15 erg cm^-2 s^-1) sources in 20 Chandra
fields (1.5 deg^2) forming part of the Chandra Multi-wavelength Project. These
medium depth X-ray observations enable us to detect a representative subset of
those sources responsible for the bulk of the 2-8 keV Cosmic X-ray Background.
Brighter than our optical spectroscopic limit, we achieve a reasonable degree
of completeness (77% of X-ray sources with counter-parts r'< 22.5 have been
classified): broad emission line AGN (62%), narrow emission line galaxies
(24%), absorption line galaxies (7%), stars (5%) or clusters (2%). We find that
most X-ray unabsorbed AGN (NH<10^22 cm^-2) have optical properties
characterized by broad emission lines and blue colors, similiar to
optically-selected quasars from the Sloan Digital Sky Survey but with a slighly
broader color distribution. However, we also find a significant population of
redder (g'-i'>1.0) AGN with broad optical emission lines. Most of the X-ray
absorbed AGN (10^22<NH<10^24 cm^-2) are associated with narrow emission line
galaxies, with red optical colors characteristically dominated by luminous,
early type galaxy hosts rather than from dust reddening of an AGN. We also find
a number of atypical AGN; for instance, several luminous AGN show both strong
X-ray absorption (NH>10^22 cm^-2) and broad emission lines. Overall, we find
that 81% of X-ray selected AGN can be easily interpreted in the context of
current AGN unification models. Most of the deviations seem to be due to an
optical contribution from the host galaxies of the low luminosity AGN.Comment: 26 pages; 13 figures (7 color); accepted for publication in the
Astrophysical Journa
Production of tongue twisters by speakers with partial glossectomy
Bressmann T, Foltz A, Zimmermann J, Irish JC. Production of tongue twisters by speakers with partial glossectomy. Clinical Linguistics & Phonetics. 2014;28(12):951-964.A partial glossectomy can affect speech production. The goal of this study was to investigate the effect of the presence of a tumour as well as the glossectomy surgery on the patients' production of tongue twisters with the sounds [t] and [k]. Fifteen patients with tongue cancer and 10 healthy controls took part in the study. The outcome measures were the patients' speech acceptability, rate of errors, the time needed to produce the tongue twisters, pause duration between item repetitions and the tongue shape during the production of the consonants [t] and [k] before and after surgery. The patients' speech acceptability deteriorated after the surgery. Compared to controls, the patients' productions of the tongue twisters were slower but not more errorful. Following the surgery, their speed of production did not change, but the rate of errors was higher. Pause duration between items was longer in the patients than in the controls but did not increase from before to after surgery. Analysis of the patients' tongue shapes for the productions of [t] and [k] indicated a higher elevation following the surgery for the patients with flap reconstructions. The results demonstrated that the surgical resection of the tongue changed the error rate but not the speed of production for the patient. The differences in pause duration also indicate that the tumour and the surgical resection of the tongue may impact the phonological planning of the tongue twister
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