4,048 research outputs found
Information technology and productivity in developed and developing countries
Previous research has found that information technology (IT) investment is associated with significant productivity gains for developed countries but not for developing countries. Yet developing countries have continued to increase their investment in IT rapidly. Given this apparent disconnect, there is a need for new research to study whether the investment has begun to pay off in greater productivity for developing countries. We analyze new data on IT investment and productivity for 45 countries from 1994 to 2007, and compare the results with earlier research. We find that upper-income developing countries have achieved positive and significant productivity gains from IT investment in the more recent period as they have increased their IT capital stocks and gained experience with the use of IT. We also find that the productivity effects of IT are moderated by country factors, including human resources, openness to foreign investment, and the quality and cost of the telecommunications infrastructure. The academic implication is that the effect of IT on productivity is expanding from the richest countries into a large group of developing countries. The policy implication is that lower-tier developing countries can also expect productivity gains from IT investments, particularly through policies that support IT use, such as greater openness to foreign investment, increased investment in tertiary education, and reduced telecommunications costs. © 2013 M.E. Sharpe, Inc. All rights reserved
Artifacts at 4.5 and 8.0 um in Short Wavelength Spectra from the Infrared Space Observatory
Spectra from the Short Wavelength Spectrometer (SWS) on ISO exhibit artifacts
at 4.5 and 8 um. These artifacts appear in spectra from a recent data release,
OLP 10.0, as spurious broad emission features in the spectra of stars earlier
than ~F0, such as alpha CMa. Comparison of absolutely calibrated spectra of
standard stars to corresponding spectra from the SWS reveals that these
artifacts result from an underestimation of the strength of the CO and SiO
molecular bands in the spectra of sources used as calibrators by the SWS.
Although OLP 10.0 was intended to be the final data release, these findings
have led to an additional release addressing this issue, OLP 10.1, which
corrects the artifacts.Comment: 14 pages, AASTex, including 5 figures. Accepted by ApJ Letter
A Catalog of MIPSGAL Disk and Ring Sources
We present a catalog of 416 extended, resolved, disk- and ring-like objects
as detected in the MIPSGAL 24 micron survey of the Galactic plane. This catalog
is the result of a search in the MIPSGAL image data for generally circularly
symmetric, extended "bubbles" without prior knowledge or expectation of their
physical nature. Most of the objects have no extended counterpart at 8 or 70
micron, with less than 20% detections at each wavelength. For the 54 objects
with central point sources, the sources are nearly always seen in all IRAC
bands. About 70 objects (16%) have been previously identified, with another 35
listed as IRAS sources. Among the identified objects, those with central
sources are mostly listed as emission-line stars, but with other source types
including supernova remnants, luminous blue variables, and planetary nebulae.
The 57 identified objects (of 362) without central sources are nearly all PNe
(~90%).which suggests that a large fraction of the 300+ unidentified objects in
this category are also PNe. These identifications suggest that this is
primarily a catalog of evolved stars. Also included in the catalog are two
filamentary objects that are almost certainly SNRs, and ten unusual compact
extended objects discovered in the search. Two of these show remarkable spiral
structure at both 8 and 24 micron. These are likely background galaxies
previously hidden by the intervening Galactic plane
Carbon-rich dust production in metal-poor galaxies in the Local Group
We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax,
and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the
Spitzer Space Telescope. The spectra show significant quantities of dust around
the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous
comparisons of carbon stars with similar pulsation properties in the Galaxy and
the Magellanic Clouds revealed no evidence that metallicity affected the
production of dust by carbon stars. However, the more metal-poor stars in the
current sample appear to be generating less dust. These data extend two known
trends to lower metallicities. In more metal-poor samples, the SiC dust
emission weakens, while the acetylene absorption strengthens. The bolometric
magnitudes and infrared spectral properties of the carbon stars in Fornax are
consistent with metallicities more similar to carbon stars in the Magellanic
Clouds than in the other dwarf spheroidals in our sample. A study of the carbon
budget in these stars reinforces previous considerations that the dredge-up of
sufficient quantities of carbon from the stellar cores may trigger the final
superwind phase, ending a star's lifetime on the asymptotic giant branch.Comment: ApJ, in press, 21 pages, 12 figures. Replaced Fig 12, corrected two
reference
Complex X-ray Absorption and the Fe Kalpha Profile in NGC 3516
We present data from simultaneous Chandra, XMM-Newton and BeppoSAX
observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and Nov.
We have investigated the nature of the very flat observed X-ray spectrum.
Chandra grating data show the presence of X-ray absorption lines, revealing two
distinct components of the absorbing gas, one which is consistent with our
previous model of the UV/X-ray absorber while the other, which is outflowing at
a velocity of ~1100 km/s has a larger column density and is much more highly
ionized. The broad-band spectral characteristics of the X-ray continuum
observed with XMM during 2001 April, reveal the presence of a third layer of
absorption consisting of a very large column (~2.5 x 10E23 cm^-2) of highly
ionized gas with a covering fraction ~50%. This low covering fraction suggests
that the absorber lies within a few lt-days of the X-ray source and/or is
filamentary in structure. Interestingly, these absorbers are not in thermal
equilibrium with one another. The two new components are too highly ionized to
be radiatively accelerated, which we suggest is evidence for a hydromagnetic
origin for the outflow. Applying our model to the Nov dataset, we can account
for the spectral variability primarily by a drop in the ionization states of
the absorbers, as expected by the change in the continuum flux. When this
complex absorption is accounted for we find the underlying continuum to be
typical of Seyfert 1 galaxies. The spectral curvature attributed to the high
column absorber, in turn, reduces estimates of the flux and extent of any broad
Fe emission line from the accretion disk.Comment: 33 pages, 9 figures, accepted for publication in Ap
On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants
We investigate the occurrence of crystalline silicates in oxygen-rich evolved
stars across a range of metallicities and mass-loss rates. It has been
suggested that the crystalline silicate feature strength increases with
increasing mass-loss rate, implying a correlation between lattice structure and
wind density. To test this, we analyse Spitzer IRS and Infrared Space
Observatory SWS spectra of 217 oxygen-rich asymptotic giant branch stars and 98
red supergiants in the Milky Way, the Large and Small Magellanic Clouds and
Galactic globular clusters. These encompass a range of spectral morphologies
from the spectrally-rich which exhibit a wealth of crystalline and amorphous
silicate features to 'naked' (dust-free) stars. We combine spectroscopic and
photometric observations with the GRAMS grid of radiative transfer models to
derive (dust) mass-loss rates and temperature. We then measure the strength of
the crystalline silicate bands at 23, 28 and 33 microns. We detect crystalline
silicates in stars with dust mass-loss rates which span over 3 dex, down to
rates of ~10^-9 solar masses/year. Detections of crystalline silicates are more
prevalent in higher mass-loss rate objects, though the highest mass-loss rate
objects do not show the 23-micron feature, possibly due to the low temperature
of the forsterite grains or it may indicate that the 23-micron band is going
into absorption due to high column density. Furthermore, we detect a change in
the crystalline silicate mineralogy with metallicity, with enstatite seen
increasingly at low metallicity.Comment: Accepted for publication in MNRAS, 24 pages, 16 figure
Spatially Resolved Outflows in a Seyfert Galaxy at z = 2.39
We present the first spatially resolved analysis of rest-frame optical and UV
imaging and spectroscopy for a lensed galaxy at z = 2.39 hosting a Seyfert
active galactic nucleus (AGN). Proximity to a natural guide star has enabled
high signal-to-noise VLT SINFONI + adaptive optics observations of rest-frame
optical diagnostic emission lines, which exhibit an underlying broad component
with FWHM ~ 700 km/s in both the Balmer and forbidden lines. Measured line
ratios place the outflow robustly in the region of the ionization diagnostic
diagrams associated with AGN. This unique opportunity - combining gravitational
lensing, AO guiding, redshift, and AGN activity - allows for a magnified view
of two main tracers of the physical conditions and structure of the
interstellar medium in a star-forming galaxy hosting a weak AGN at cosmic noon.
By analyzing the spatial extent and morphology of the Ly-alpha and
dust-corrected H-alpha emission, disentangling the effects of star formation
and AGN ionization on each tracer, and comparing the AGN induced mass outflow
rate to the host star formation rate, we find that the AGN does not
significantly impact the star formation within its host galaxy.Comment: 16 pages, 5 figures, accepted for publication in Ap
- …