1,911 research outputs found
Large scale evaluation of importance maps in automatic speech recognition
In this paper, we propose a metric that we call the structured saliency
benchmark (SSBM) to evaluate importance maps computed for automatic speech
recognizers on individual utterances. These maps indicate time-frequency points
of the utterance that are most important for correct recognition of a target
word. Our evaluation technique is not only suitable for standard classification
tasks, but is also appropriate for structured prediction tasks like
sequence-to-sequence models. Additionally, we use this approach to perform a
large scale comparison of the importance maps created by our previously
introduced technique using "bubble noise" to identify important points through
correlation with a baseline approach based on smoothed speech energy and forced
alignment. Our results show that the bubble analysis approach is better at
identifying important speech regions than this baseline on 100 sentences from
the AMI corpus.Comment: submitted to INTERSPEECH 202
MMT observations of new extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey
We present 6.5-meter MMT spectrophotometry of 20 H II regions in 13 extremely
metal-poor emission-line galaxies selected from the Data Release 5 of the Sloan
Digital Sky Survey to have [O III] 4959/Hbeta < 1 and [N II] 6583/Hbeta < 0.05.
The electron temperature-sensitive emission line [O III] 4363 is detected in 13
H II regions allowing a direct abundance determination. The oxygen abundance in
the remaining H II regions is derived using a semi-empirical method. The oxygen
abundance of the galaxies in our sample ranges from 12+logO/H ~ 7.1 to ~ 7.8,
with 10 H II regions having an oxygen abundance lower than 7.5. The lowest
oxygen abundances, 12+logO/H = 7.14+/-0.03 and 7.13+/-0.07, are found in two H
II regions of the blue compact dwarf galaxy SDSSJ0956+2849=DDO 68, making it
the second most-metal deficient emission-line galaxy known, after SBS
0335-052W.Comment: 28 pages, 3 figures. Accepted for publication in the Astrophysical
Journa
SBS 0335-052W: The Lowest-Metallicity Star-Forming Galaxy Known
We present 4-meter Kitt Peak telescope and 6.5-meter MMT spectrophotometry of
the extremely low-metallicity galaxy SBS 0335-052W, the western companion of
the blue compact dwarf galaxy SBS 0335-052E. These observations have been
combined with published 10-meter Keck data to derive for the brightest region
of SBS 0335-052W an oxygen abundance 12+logO/H=7.12+/-0.03. This makes SBS
0335-052W the lowest metallicity star-forming galaxy known in the local
universe. Using a Monte Carlo technique, we fit the spectral energy
distribution of SBS 0335-052W to derive the age of the oldest stars
contributing to its optical light. We find that star formation in SBS 0335-052W
began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical
Journa
The Spitzer View of Low-Metallicity Star Formation: II. Mrk 996, a Blue Compact Dwarf Galaxy with an Extremely Dense Nucleus
(abridged) We present new Spitzer, UKIRT and MMT observations of the blue
compact dwarf galaxy (BCD) Mrk 996, with an oxygen abundance of
12+log(O/H)=8.0. This galaxy has the peculiarity of possessing an
extraordinarily dense nuclear star-forming region, with a central density of
~10^6 cm^{-3}. The nuclear region of Mrk 996 is characterized by several
unusual properties: a very red color J-K = 1.8, broad and narrow emission-line
components, and ionizing radiation as hard as 54.9 eV, as implied by the
presence of the OIV 25.89 micron line. The nucleus is located within an
exponential disk with colors consistent with a single stellar population of age
>1 Gyr. The infrared morphology of Mrk 996 changes with wavelength. The IRS
spectrum shows strong narrow Polycyclic Aromatic Hydrocarbon (PAH) emission,
with narrow line widths and equivalent widths that are high for the metallicity
of Mrk 996. Gaseous nebular fine-structure lines are also seen. A CLOUDY model
requires that they originate in two distinct HII regions: a very dense HII
region of radius ~580 pc with densities declining from ~10^6 at the center to a
few hundreds cm^{-3} at the outer radius, where most of the optical lines
arise; and a HII region with a density of ~300 cm^{-3} that is hidden in the
optical but seen in the MIR. We suggest that the infrared lines arise mainly in
the optically obscured HII region while they are strongly suppressed by
collisional deexcitation in the optically visible one. The hard ionizing
radiation needed to account for the OIV 25.89 micron line is most likely due to
fast radiative shocks propagating in an interstellar medium. A hidden
population of Wolf-Rayet stars of type WNE-w or a hidden AGN as sources of hard
ionizing radiation are less likely possibilities.Comment: 48 pages, 13 figures, accepted for publication in the Astrophysical
Journa
Chandra Observations of the Three Most Metal-Deficient Blue Compact Dwarf Galaxies known in the Local Universe, SBS 0335-052, SBS 0335-052W, and I Zw 18
We present an X-ray study of the three most metal-deficient blue compact
dwarf (BCD) galaxies known in the local Universe, based on deep Chandra
observations of SBS 0335-052 (0.025 solar abundance), SBS 0335-052W (0.02 solar
abundance) and I Zw 18 (0.02 solar abundance). All three are detected, with
more than 90% of their X-ray emission arising from point-like sources. The
0.5-10.0 keV luminosities of these point sources are in the range
(1.3-8.5)x1e39 erg/s. We interpret them to be single or a collection of
high-mass X-ray binaries, the luminosities of which may have been enhanced by
the low metallicity of the gas. There are hints of faint extended diffuse X-ray
emission in both SBS 0335-052 and I Zw 18, probably associated with the
superbubbles visible in both BCDs. The spectrum of I Zw 18 shows a OVIII
hydrogen-like emission line. The best spectral fit gives an O overabundance of
the gas in the X-ray point source by a factor of ~7 with respect to the Sun, or
a factor of ~350 with respect to the O abundance determined for the HII region.Comment: emulateapj.cls used, 7 pages, 7 figures + 1 table, accepted for
publication in Ap
Deep Hubble Space Telescope/ACS Observations of I Zw 18: a Young Galaxy in Formation
We present V and I photometry of the resolved stars in the most
metal-deficient blue compact dwarf galaxy known, I Zw 18 (Zsun/50), using
Hubble Space Telescope/Advanced Camera for Surveys (ACS) images, the deepest
ones ever obtained for this galaxy. The resulting I vs. V-I color-magnitude
diagram (CMD) reaches limiting magnitudes V=I=29 mag. It reveals a young
stellar population of blue main-sequence (MS) stars (age <30 Myr) and blue and
red supergiants (10 Myr<age<100 Myr), but also an older evolved population of
asymptotic giant branch (AGB) stars (100 Myr<age<500 Myr). We derive a distance
to I Zw 18 in the range 12.6 Mpc - 15 Mpc from the brightness of its AGB stars,
with preferred values in the higher range. The red giant branch (RGB) stars are
conspicuous by their absence, although, for a distance of I Zw 18 <15 Mpc, our
imaging data go ~ 1-2 mag below the tip of the RGB. Thus, the most evolved
stars in the galaxy are not older than 500 Myr and I Zw 18 is a bona fide young
galaxy. Several star formation episodes can be inferred from the CMDs of the
main body and the C component. There have been respectively three and two
episodes in these two parts, separated by periods of ~ 100-200 Myr. In the main
body, the younger MS and massive post-MS stars are distributed over a larger
area than the older AGB stars, suggesting that I Zw 18 is still forming from
the inside out. In the C component, different star formation episodes are
spatially distinct, with stellar population ages decreasing from the northwest
to the southeast, also suggesting the ongoing build-up of a young galaxy.Comment: 29 pages, 13 Postscript figures, accepted for publication in the
Astrophysical Journa
Methodologies for predicting natural frequency variation of a suspension bridge
Journal ArticleThis is the accepted version of an article published in Engineering Structures, 80 (1) pp. 211–221. The Version of Record is available online at http://dx.doi.org/10.1016/j.engstruct.2014.09.001.In vibration-based structural health monitoring, changes in the natural frequency of a structure are used to identify changes in the structural conditions due to damage and deterioration. However, natural frequency values also vary with changes in environmental factors such as temperature and wind. Therefore, it is important to differentiate between the effects due to environmental variations and those resulting from structural damage. In this paper, this task is accomplished by predicting the natural frequency of a structure using measurements of environmental conditions. Five methodologies - multiple linear regression, artificial neural networks, support vector regression, regression tree and random forest - are implemented to predict the natural frequencies of the Tamar Suspension Bridge (UK) using measurements taken from 3 years of continuous monitoring. The effects of environmental factors and traffic loading on natural frequencies are also evaluated by measuring the relative importance of input variables in regression analysis. Results show that support vector regression and random forest are the most suitable methods for predicting variations in natural frequencies. In addition, traffic loading and temperature are found to be two important parameters that need to be measured. Results show potential for application to continuously monitored structures that have complex relationships between natural frequencies and parameters such as loading and environmental factors
HST observations of the blue compact dwarf SBS 0335-052: a probable young galaxy
We present HST WFPC2 V and I images and GHRS UV spectrophotometry of the
spectral regions around Ly and OI 1302 of the extremely metal-deficient
(Z~Zsun/41) blue compact dwarf (BCD) galaxy SBS 0335-052. All the star
formation in the BCD occurs in six super-star clusters (SSC) with ages =< 3-4
Myr. Dust is clearly present and mixed spatially with the SSCs. There is a
supershell of radius ~380 pc, delineating a large supernova cavity. The
instantaneous star formation rate is ~0.4 Msun yr^-1. Strong narrow Ly
emission is not observed. Rather there is low intensity broad (FWZI = 20 A)
Ly emission superposed on even broader Ly absorption by the HI
envelope. This broad low-intensity emission is probably caused by resonant
scattering of Ly photons. The BCD appears to be a young galaxy,
undergoing its very first burst of star formation. This conclusion is based on
the following evidence: 1) the underlying extended low-surface-brightness
component is very irregular and filamentary, suggesting that a significant part
of the emission comes from ionized gas; 2) it has very blue colors (-0.34 =<
(V-I) =< 0.16), consistent with gaseous emission colors; 3) the OI 1302
line is not detected in absorption in the GHRS spectrum, setting an upper limit
for N(O)/N(H) in the HI envelope of the BCD of more than 3000 times smaller
than the value in Orion.Comment: 20 pages and 6 Postscript figures. Submitted to Astrophysical Journa
Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory
We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane
wave supercell calculations in wurtzite aluminum nitride in order to
characterize the geometry, formation energies, transition levels and hyperfine
tensors of the nitrogen split interstitial defect. The calculated hyperfine
tensors may provide useful fingerprint of this defect for electron paramagnetic
resonance measurement.Comment: 5 pages, 3 figure
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