649 research outputs found
Trade costs, 1870â2000
What has driven trade booms and trade busts in the past century and a half? Was it changes in global output or in the costs of international trade? To address this question, we derive a micro-founded measure of aggregate bilateral
trade costs based on a standard model of trade in differentiated goods. These trade costs gauge the difference between observed bilateral trade and frictionless trade in terms of an implied markup on retail prices of foreign goods. Thus, we are able to estimate the combined magnitude of tariffs, transportation costs, and all other macroeconomic frictions that impede international
trade but that are inherently difficult to observe. We use this measure to examine the growth of global trade between 1870 and 1913, its retreat from 1921 to 1939, and its subsequent rise from 1950 to 2000. We find that trade cost
declines explain roughly 55 percent of the preâWorld War I trade boom and 33 percent of the postâWorld War II trade boom, while a precipitous rise in trade costs explains the entire interwar trade bust
Spectroscopy of Giant Stars in the Pyxis Globular Cluster
The Pyxis globular cluster is a recently discovered globular cluster that
lies in the outer halo (R_{gc} ~ 40 kpc) of the Milky Way. Pyxis lies along one
of the proposed orbital planes of the Large Magellanic Cloud (LMC), and it has
been proposed to be a detached LMC globular cluster captured by the Milky Way.
We present the first measurement of the radial velocity of the Pyxis globular
cluster based on spectra of six Pyxis giant stars. The mean heliocentric radial
velocity is ~ 36 km/sec, and the corresponding velocity of Pyxis with respect
to a stationary observer at the position of the Sun is ~ -191 km/sec. This
radial velocity is a large enough fraction of the cluster's expected total
space velocity, assuming that it is bound to the Milky Way, that it allows
strict limits to be placed on the range of permissible transverse velocities
that Pyxis could have in the case that it still shares or nearly shares an
orbital pole with the LMC. We can rule out that Pyxis is on a near circular
orbit if it is Magellanic debris, but we cannot rule out an eccentric orbit
associated with the LMC. We have calculated the range of allowed proper motions
for the Pyxis globular cluster that result in the cluster having an orbital
pole within 15 degrees of the present orbital pole of the LMC and that are
consistent with our measured radial velocity, but verification of the tidal
capture hypothesis must await proper motion measurement from the Space
Interferometry Mission or HST. A spectroscopic metallicity estimate of [Fe/H] =
-1.4 +/- 0.1 is determined for Pyxis from several spectra of its brightest
giant; this is consistent with photometric determinations of the cluster
metallicity from isochrone fitting.Comment: 22 pages, 5 figures, aaspp4 style, accepted for publication in
October, 2000 issue of the PAS
The Midlands LGBT Needs Assessment Community Report
Health disparities research seeks to understand specific health-related needs and outcomes for groups of people, particularly minority groups. In 2011, the Institutes of Medicine (IOM) released a report commissioned by the National Institutes of Health entitled The Health of Lesbian, Gay, Bisexual, and Transgender (LGBT) People: Building a Foundation for Understanding. For the first time, research on the health and well-being of LGBT persons has been prioritized by research funders at the highest levels
Sustained metabolic benefits of ÎTRTXâAc1, a tarantula venomâderived peptide, when administered together with exenatide in highâfat fed mice
Primordial helium recombination III: Thomson scattering, isotope shifts, and cumulative results
Upcoming precision measurements of the temperature anisotropy of the cosmic
microwave background (CMB) at high multipoles will need to be complemented by a
more complete understanding of recombination, which determines the damping of
anisotropies on these scales. This is the third in a series of papers
describing an accurate theory of HeI and HeII recombination. Here we describe
the effect of Thomson scattering, the He isotope shift, the contribution of
rare decays, collisional processes, and peculiar motion. These effects are
found to be negligible: Thomson and He scattering modify the free electron
fraction at the level of several . The uncertainty in the
rate is significant, and for conservative estimates gives
uncertainties in of order . We describe several convergence
tests for the atomic level code and its inputs, derive an overall
error budget, and relate shifts in to the changes in , which
are at the level of 0.5% at . Finally, we summarize the main
corrections developed thus far. The remaining uncertainty from known effects is
in .Comment: 19 pages, 15 figures, to be submitted to PR
Exploring Halo Substructure with Giant Stars. VI. Extended Distributions of Giant Stars Around the Carina Dwarf Spheroidal Galaxy -- How Reliable Are They?
The question of the existence of active tidal disruption around various dSph
galaxies remains controversial. That debate often centers on the nature (bound
vs. unbound) of extended populations of stars. However, the more fundamental
issue of the very existence of the extended populations is still contentious.
We present an evaluation of the debate centering on one particular dSph,
Carina, for which claims both for and against the existence of stars beyond the
King radius have been made. Our review includes an examination of all previous
studies bearing on the Carina radial profile and shows that the survey method
which achieves the highest detected dSph signal-to-background in the outer
parts of the galaxy is the Washington M, T2 + DDO51 (MTD) filter approach from
Paper II in this series. We then address statistical methods used to evaluate
the reliability of MTD surveys in the presence of photometric errors and for
which a new, a posteriori statistical analysis methodology is provided.
Finally, these statistical methods are tested by new spectroscopy of stars in
the MTD-selected Carina candidate sample. Of 74 candidate giants with follow-up
spectroscopy, the MTD technique identified 61 new Carina members, including 8
stars outside the King radius. From a sample of 29 stars not initially
identified as candidate Carina giants but that lie just outside of our
selection criteria, 12 have radial velocities consistent with membership,
including 5 extratidal stars. Carina is shown to have an extended population of
giant stars extending to a major axis radius of 40' (1.44x the nominal King
radius).Comment: 56 pages, 10 figures. Submitted to the Astronomical Journal, 2004 Sep
2
The Arecibo Legacy Fast ALFA Survey: X. The HI Mass Function and Omega_HI From the 40% ALFALFA Survey
The Arecibo Legacy Fast ALFA (ALFALFA) survey has completed source extraction
for 40% of its total sky area, resulting in the largest sample of HI-selected
galaxies to date. We measure the HI mass function from a sample of 10,119
galaxies with 6.2 < log (M_HI/M_Sun) < 11.0 and with well-described mass errors
that accurately reflect our knowledge of low-mass systems. We characterize the
survey sensitivity and its dependence on profile velocity width, the effect of
large-scale structure, and the impact of radio frequency interference in order
to calculate the HIMF with both the 1/Vmax and 2DSWML methods. We also assess a
flux-limited sample to test the robustness of the methods applied to the full
sample. These measurements are in excellent agreement with one another; the
derived Schechter function parameters are phi* = 4.8 (+/- 0.3) * 10^-3, log
(M*/M_Sun) + 2 log(h_70) = 9.96 (+/- 0.2), and alpha = -1.33 (+/- 0.02). We
find Omega_HI = 4.3 (+/- 0.3) * 10^-4, 16% larger than the 2005 HIPASS result,
and our Schechter function fit extrapolated to log (M_HI/M_Sun) = 11.0 predicts
an order of magnitude more galaxies than HIPASS. The larger values of Omega_HI
and of M* imply an upward adjustment for estimates of the detection rate of
future large-scale HI line surveys with, e.g., the Square Kilometer Array. A
comparison with simulated galaxies from the Millennium Run and a treatment of
photoheating as a method of baryon removal from HI-selected halos indicates
that the disagreement between dark matter mass functions and baryonic mass
functions may soon be resolved.Comment: 21 pages, 13 figures, submitted to Ap
Exploring Halo Substructure with Giant Stars IV: The Extended Structure of the Ursa Minor Dwarf Spheroidal
We present a large area photometric survey of the Ursa Minor dSph. We
identify UMi giant star candidates extending to ~3 deg from the center of the
dSph. Comparison to previous catalogues of stars within the tidal radius of UMi
suggests that our photometric luminosity classification is 100% accurate. Over
a large fraction of the survey area, blue horizontal branch stars associated
with UMi can also be identified. The spatial distribution of both the UMi giant
stars and the BHB stars are remarkably similar, and a large fraction of both
samples of stars are found outside the tidal radius of UMi. An isodensity
contour map of the stars within the tidal radius of UMi reveals two
morphological peculiarities: (1) The highest density of dSph stars is offset
from the center of symmetry of the outer isodensity contours. (2) The overall
shape of the outer contours appear S-shaped. We find that previously determined
King profiles with ~50' tidal radii do not fit well the distribution of our UMi
stars. A King profile with a larger tidal radius produces a reasonable fit,
however a power law with index -3 provides a better fit for radii > 20'. The
existence of UMi stars at large distances from the core of the galaxy, the
peculiar morphology of the dSph within its tidal radius, and the shape of its
surface density profile all suggest that UMi is evolving significantly due to
the tidal influence of the Milky Way. However, the photometric data on UMi
stars alone does not allow us to determine if the candidate extratidal stars
are now unbound or if they remain bound to the dSph within an extended dark
matter halo. (Abridged)Comment: accepted by AJ, 32 pages, 15 figures, emulateapj5 styl
An experimental characterization of thermophysical properties of a porous ceramic shell used in the investment casting process
This study presents the results of an investigation that characterises the thermophysical properties of an investment casting mould, comprising of a Zirconium dioxide/Cobalt aluminate prime slurry and a fused Silica/fibre reinforced backup slurry. Growing prevalence of successful computer simulations within the foundry industry enables defects that emerge during the casting process to become increasingly predictable, providing cost-effective alternatives to trial castings. The viability of these simulations as predictors is heavily dependent upon the facilitation of accurate material property data, as attained through this investigation. Differential scanning calorimetry (DSC) and laser flash analysis (LFA) were utilized to determine the specific heat capacity and thermal diffusivity, respectively. These values, in combination with the material density and linear coefficient of thermal expansion, have been used to determine the thermal conductivity of the mould. With the aim of verifying these parameters, initial studies in Flow-3DÂź simulation software have been performed to determine the constraints needed to reduce variability in simulation parameters. Due to the diversity of casting moulds used throughout the industry, ensuring the material database is kept as comprehensively populated as possible is a crucial undertaking
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