11,934 research outputs found
Low-pressure, chemical vapor deposition polysilicon
The low-pressure chemical vapor deposition (LPCVD) of polycrystalline silicon was investigted. The physical system was described, as was the controlling process parameters and requirements for producing films for use as an integral portion of the solar cell contact system
Tracing Quasar Narrow-Line Regions Across Redshift: A Library of High S/N Optical Spectra
In a single optical spectrum, the quasar narrow-line region (NLR) reveals low
density, photoionized gas in the host galaxy interstellar medium, while the
immediate vicinity of the central engine generates the accretion disk continuum
and broad emission lines. To isolate these two components, we construct a
library of high S/N optical composite spectra created from the Sloan Digital
Sky Survey (SDSS-DR7). We divide the sample into bins of continuum luminosity
and Hbeta FWHM that are used to construct median composites at different
redshift steps up to 0.75. We measure the luminosities of the narrow-emission
lines [NeV]3427, [NeIII]3870, [OIII]5007, and [OII]3728 with ionization
potentials (IPs) of 97, 40, 35, and 13.6 eV respectively. The high IP lines'
luminosities show no evidence of increase with redshift consistent with no
evolution in the AGN SED or the host galaxy ISM illuminated by the continuum.
In contrast, we find that the [OII] line becomes stronger at higher redshifts,
and we interpret this as a consequence of enhanced star formation contributing
to the [OII] emission in host galaxies at higher redshifts. The SFRs estimated
from the [OII] luminosities show a flatter increase with z than non-AGN
galaxies given our assumed AGN contribution to the [OII] luminosity. Finally,
we confirm an inverse correlation between the strength of the FeII4570 complex
and both the [OIII] EW (though not the luminosity) and the width of the Hbeta
line as known from the eigenvector 1 correlations.Comment: 17 pages, colour figures, accepted for publication in MNRA
Accurate near-field calculation in the rigorous coupled-wave analysis method
The rigorous coupled-wave analysis (RCWA) is one of the most successful and
widely used methods for modeling periodic optical structures. It yields fast
convergence of the electromagnetic far-field and has been adapted to model
various optical devices and wave configurations. In this article, we
investigate the accuracy with which the electromagnetic near-field can be
calculated by using RCWA and explain the observed slow convergence and
numerical artifacts from which it suffers, namely unphysical oscillations at
material boundaries due to the Gibb's phenomenon. In order to alleviate these
shortcomings, we also introduce a mathematical formulation for accurate
near-field calculation in RCWA, for one- and two-dimensional straight and
slanted diffraction gratings. This accurate near-field computational approach
is tested and evaluated for several representative test-structures and
configurations in order to illustrate the advantages provided by the proposed
modified formulation of the RCWA.Comment: 13 pages, 12 figure
X-ray Spectroscopy of QSOs with Broad Ultraviolet Absorption Lines
For the population of QSOs with broad ultraviolet absorption lines, we are
just beginning to accumulate X-ray observations with enough counts for spectral
analysis at CCD resolution. From a sample of eight QSOs [including four Broad
Absorption Line (BAL) QSOs and three mini-BAL QSOs] with ASCA or Chandra
spectra with more than 200 counts, general patterns are emerging. Their
power-law X-ray continua are typical of normal QSOs with Gamma~2.0, and the
signatures of a significant column density [N_H~(0.1-4)x10^{23} cm^{-2}] of
intrinsic, absorbing gas are clear. Correcting the X-ray spectra for intrinsic
absorption recovers a normal ultraviolet-to-X-ray flux ratio, indicating that
the spectral energy distributions of this population are not inherently
anomalous. In addition, a large fraction of our sample shows significant
evidence for complexity in the absorption. The subset of BAL QSOs with broad
MgII absorption apparently suffers from Compton-thick absorption completely
obscuring the direct continuum in the 2-10 keV X-ray band, complicating any
measurement of their intrinsic X-ray spectral shapes.Comment: 9 pages, 6 figures, uses AASTeX. Accepted to the Astrophysical
Journa
The Exceptionally Soft X-ray Spectrum of the Low-mass Starburst Galaxy NGC 1705
NGC 1705 is one of the optically brightest and best studied dwarf galaxies.
It appears to be in the late stage of a major starburst and contains a young
super star cluster. Type II supernovae are therefore likely to have been a
major effect in the recent evolution of this galaxy and are likely to have
produced a superbubble whose affects on the low-density ambient interstellar
medium can be ideally studied. ROSAT PSPC observations of this galaxy reveal
two striking blobs of X-ray emission embedded in \Ha loops which can be
interpreted as both sides of the upper plumes of the same superbubble. These
sources are a surprise. They are much softer than those observed from other
starburst dwarf galaxies, and are so soft that they should have been blocked if
the observed Galactic HI column density were uniformly distributed across NGC
1705 or if the sources were embedded in the HI disk of NGC 1705. In addition,
the total X-ray luminosity in the ROSAT energy band of 1.2x10^{38} erg s^{-1}
is low in comparison to similar objects. We discuss possible models for the two
X-ray peaks in NGC 1705 and find that the sources most likely originate from
relatively cool gas of one single superbubble in NGC 1705. The implications of
the exceptional softness of these sources are addressed in terms of intrinsic
properties of NGC 1705 and the nature of the foreground Galactic absorption.Comment: 7 pages, 2 ps-figures, LATEX-file; accepted for publication in
ApJ.Letter
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