490 research outputs found
Electrical Stimulation of the Auditory System
In many healthcare systems electrical stimulation of the human auditory system, using cochlear implants, is a common treatment for severe to profound deafness. This chapter will describe how electrical stimulation manages to compensate for sensory-neural hearing loss by bypassing the damaged cochlea. The challenges involved in the design and application of cochlear implants will be outlined, including the programming of clinical systems to suit the needs of implanted patients. Today’s variety of patient will be reviewed: unilaterally and bilaterally implanted, bimodal users of a cochlear implant as well as a contralateral hearing aid, CROS device users having either asymmetrical hearing loss or single-sided deafness. Alternative devices such as auditory brainstem implants will be described, and additionally the more experimental auditory mid-brain implants and intraneural stimulation approaches. Research that is likely to bring medium term benefits to the clinical application of cochlear implants will also be described
A Search for Nitrogen Enriched Quasars in the Sloan Digital Sky Survey Early Data Release
A search for nitrogen-rich quasars in the Sloan Digital Sky Survey Early Data
Release (SDSS EDR) catalog has yielded 16 candidates, including five with very
prominent emission, but no cases with nitrogen emission as strong as in
Q0353-383. The quasar Q0353-383 has long been known to have extremely strong
nitrogen intercombination lines at lambda 1486 and lambda 1750 Angstroms,
implying an anomalously high nitrogen abundance of about 15 times solar. It is
still the only one of its kind known. A preliminary search through the EDR
using the observed property of the weak C IV emission seen in Q0353-383
resulted in a sample of 23 objects with unusual emission or absorption-line
properties, including one very luminous redshift 2.5 star-forming galaxy. We
present descriptions, preliminary emission-line measurements, and spectra for
all the objects discussed here.Comment: 20 pages, 5 figures, submitted to AJ; final refereed versio
The BTC40 Survey for Quasars at 4.8 < z < 6
The BTC40 Survey for high-redshift quasars is a multicolor search using
images obtained with the Big Throughput Camera (BTC) on the CTIO 4-m telescope
in V, I, and z filters to search for quasars at redshifts of 4.8 < z < 6. The
survey covers 40 sq. deg. in B, V, & I and 36 sq. deg. in z. Limiting
magnitudes (3 sigma) reach to V = 24.6, I = 22.9 and z = 22.9. We used the
(V-I) vs. (I-z) two-color diagram to select high-redshift quasar candidates
from the objects classified as point sources in the imaging data. Follow-up
spectroscopy with the AAT and CTIO 4-m telescopes of candidates having I < 21.5
has yielded two quasars with redshifts of z = 4.6 and z = 4.8 as well as four
emission line galaxies with z = 0.6. Fainter candidates have been identified
down to I = 22 for future spectroscopy on 8-m class telescopes.Comment: 27 pages, 8 figures; Accepted for publication in the Astronomical
Journa
Quasar Candidates in the Hubble Deep Field
We focus on the search for unresolved faint quasars and AGN in the crude
combine images using a multicolor imaging analysis that has proven very
successful in recent years. Quasar selection was carried out both in multicolor
space and in "profile space," defined as the multi-parameter space formed by
the radial profiles of the objects in the different images. By combining the
dither frames available for each filter, we were able to obtain well-sampled
radial profiles of the objects and measure their deviation from that of a
stellar source. We also generated synthetic quasar spectra in the range 1.0 < z
< 5.5 and computed expected quasar colors. We determined that the data are 90%
complete for point sources at 26.2, 28.0, 27.8, 26.8 in the F300W, F450W, F606W
and F814W filters, respectively. We find 41 compact objects in the HDF: 8
pointlike objects with colors consistent with quasars or stars, 18 stars, and
15 slightly resolved objects, 12 of which have colors consistent with quasars
or stars. We estimate the upper limit of unresolved and slightly resolved
quasars/AGNs with V < 27.0 and z < 3.5 to be 20 objects (16,200 per deg^2). We
find good agreement among authors on the number of stars and the lack of quasar
candidates with z > 3.5. We find more quasar candidates than previous work
because of our more extensive modeling and use of all of the available color
information. (abridged)Comment: We have clarified our discussion and conclusions, added some
references and removed the appendix, which is now available from the first
author. 37 pages including 10 embedded postscript figures and 6 tables. To
appear in the Feb. 99 issue of A
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