1,327 research outputs found
Functional form for United States-México trade equations
The literature concerning bilateral trade flows between Mexico and the United States is comparatively small. With the growing importance of international commerce between these economies, potential trade flow responses to changes in relative prices and income performance deserves more attention. This paper attempts to partially fill this gap in the literature by estimating bilateral trade flow equations that decompose relative import and relative export prices into foreign prices, domestic prices, and the exchange rate.
Intra-industry trade in Latin America and the Caribbean
An increasingly important component of total world trade is intra-industry trade (IIT). The large volume of literature on IIT is reflective of this importance. However, this extensive literature has focused almost completely on explaining the causes of IIT. This focus has left a puzzling gap in the literature. Specifically, it is almost impossible to determine the level of IIT for a particular country or region. Further, there is almost no information on the level of IIT at the industry level either globally or for a region or country. In this paper we provide estimates of IIT for the world and for the countries of the Western Hemisphere. Further, we provide estimates of IIT for ten different SITC product categories on the same basis. The findings of the paper indicate that in most industries, IIT in Latin America is substantially lower overall than the world average. There are, however, substantial variations observed both by country and by industry. Because the results are the first available for the region as a whole, they should allow researchers to get a better picture of the extent of IIT in Latin America and the Caribbean by country and by industry.Intra-industry trade; Latin America
Structure and clumping in the fast wind of NGC6543
Far-UV spectroscopy from the FUSE satellite is analysed to uniquely probe
spatial structure and clumping in the fast wind of the central star of the
H-rich planetary nebula NGC6543 (HD164963). Time-series data of the unsaturated
PV 1118, 1128 resonance line P Cygni profiles provide a very sensitive
diagnostic of variable wind conditions in the outflow. We report on the
discovery of episodic and recurrent optical depth enhancements in the PV
absorption troughs, with some evidence for a 0.17-day modulation time-scale.
SEI line-synthesis modelling is used to derive physical properties, including
the optical depth evolution of individual `events'. The characteristics of
these features are essentially identical to the `discrete absorption
components' (DACs) commonly seen in the UV lines of massive OB stars. We have
also employed the unified model atmosphere code CMFGEN to explore spectroscopic
signatures of clumping, and report in particular on the clear sensitivity of
the PV lines to the clump volume filling factor. The results presented here
have implications for the downward revision of mass-loss rates in PN central
stars. We conclude that the temporal structures seen in the PV lines of NGC6543
likely have a physical origin that is similar to that operating in massive,
luminous stars, and may be related to near-surface perturbations caused by
stellar pulsation and/or magnetic fields.Comment: 11 pages, 11 figures. Accepted for publication in MNRA
Borderplex Long-Term Economic Trends to 2026
Long-term prospects for the El Paso - Ciudad Juárez borderplex economy call for steady growth. On the north side of the border, the population of El Paso is projected to reach 965 thousand by 2026, the last year of the forecast period. Real gross metropolitan product, the broadest measure of local economic activity, is expected to increase by more than 85 percent over the course of the next two decades to more than 20.7 billion by the end of the simulation period. Given this projected state of affairs, the UTEP Borderplex Econometric Model forecasts housing starts to average more than 5 thousand units per year through 2026. Substantially higher single-family home prices result under these circumstances. Demographic expansion and business growth jointly lead to greater demand for water in El Paso. As shown in Table 1, total consumption will approximate 45.8 billion gallons per year by the end of the forecast period.Border Economies; Econometric Forecasting Analysis
Infrastructure Tolls in Texas: Evidence from the Borderplex
Do changes in toll rates affect pedestrian, car, and truck traffic across the bridges between El Paso and Ciudad Juarez, Mexico? As more and more attention is paid to the use of tolls as funding mechanisms for new road and infrastructure construction in Texas, the answer to this question has policy implications not only for local and state lawmakers, but also for firms importing and exporting goods between Texas and Mexico. This article uses bridge traffic data from the Borderplex to examine the relative impact of tolls and concludes that local policymakers have more leeway than they thought in raising funds to make infrastructure improvements.Tolls; International Bridges; Border Economics
Modeling Ultraviolet Wind Line Variability in Massive Hot Stars
We model the detailed time-evolution of Discrete Absorption Components (DACs)
observed in P Cygni profiles of the Si IV lam1400 resonance doublet lines of
the fast-rotating supergiant HD 64760 (B0.5 Ib). We adopt the common assumption
that the DACs are caused by Co-rotating Interaction Regions (CIRs) in the
stellar wind. We perform 3D radiative transfer calculations with hydrodynamic
models of the stellar wind that incorporate these large-scale density- and
velocity-structures. We develop the 3D transfer code Wind3D to investigate the
physical properties of CIRs with detailed fits to the DAC shape and morphology.
The CIRs are caused by irregularities on the stellar surface that change the
radiative force in the stellar wind. In our hydrodynamic model we approximate
these irregularities by circular symmetric spots on the stellar surface. We use
the Zeus3D code to model the stellar wind and the CIRs, limited to the
equatorial plane. We constrain the properties of large-scale wind structures
with detailed fits to DACs observed in HD 64760. A model with two spots of
unequal brightness and size on opposite sides of the equator, with opening
angles of 20 +/- 5 degr and 30 +/- 5 degr diameter, and that are 20 +/- 5 % and
8 +/- 5 % brighter than the stellar surface, respectively, provides the best
fit to the observed DACs. The recurrence time of the DACs compared to the
estimated rotational period corresponds to spot velocities that are 5 times
slower than the rotational velocity. The mass-loss rate of the structured wind
model for HD 64760 does not exceed the rate of the spherically symmetric smooth
wind model by more than 1 %. The fact that DACs are observed in a large number
of hot stars constrains the clumping that can be present in their winds, as
substantial amounts of clumping would tend to destroy the CIRs.Comment: 58 pages, 16 figures, 1 animation. Accepted for publication in The
Astrophysical Journal, Main Journal. More information and animations are
available at http://alobel.freeshell.org/hotstars.htm
CIR Modulation of the X-ray Flux from the O7.5 III(n)((f)) Star xi Persei?
We analyze a 162 ks HETG Chandra observation of the O7.5 III(n)((f)) star xi
Per, together with contemporaneous H alpha observations. The X-ray spectrum of
this star is similar to other single O stars, and not pathological in any way.
Its UV wind lines are known to display cyclical time variability, with a period
of 2.086 days, which is thought to be associated with co-rotating interaction
regions (CIRs). We examine the Chandra and H alpha data for variability on this
time scale. We find that the X-rays vary by about 15% over the course of the
observations and that this variability is out of phase with variable absorption
on the blue wing of the H alpha profiles (assumed to be a surrogate for the UV
absorption associated with CIRs). While not conclusive, both sets of data are
consistent with models where the CIRs are either a source of X-rays or modulate
them.Comment: Accepted by MNRAS. 9 pages, 9 figure
The Influence of Stellar Wind Variability on Measurements of Interstellar O VI Along Sightlines to Early-Type Stars
A primary goal of the FUSE mission is to understand the origin of the O VI
ion in the interstellar medium of the Galaxy and the Magellanic Clouds. Along
sightlines to OB-type stars, these interstellar components are usually blended
with O VI stellar wind profiles, which frequently vary in shape. In order to
assess the effects of this time-dependent blending on measurements of the
interstellar O VI lines, we have undertaken a mini-survey of repeated
observations toward OB-type stars in the Galaxy and the Large Magellanic Cloud.
These sparse time series, which consist of 2-3 observations separated by
intervals ranging from a few days to several months, show that wind variability
occurs commonly in O VI (about 60% of a sample of 50 stars), as indeed it does
in other resonance lines. However, in the interstellar O VI 1032
region, the O VI 1038 wind varies only in 30% of the cases. By
examining cases exhibiting large amplitude variations, we conclude that
stellar-wind variability {\em generally} introduces negligible uncertainty for
single interstellar O VI components along Galactic lines of sight, but can
result in substantial errors in measurements of broader components or blends of
components like those typically observed toward stars in the Large Magellanic
Cloud. Due to possible contamination by discrete absorption components in the
stellar O VI line, stars with terminal velocities greater than or equal to the
doublet separation (1654 km/s) should be treated with care.Comment: Accepted for publication in the Astrophysical Journal Lette
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High-Flow Vascular Malformations in Children.
Children can have a variety of intracranial vascular anomalies ranging from small and incidental with no clinical consequences to complex lesions that can cause substantial neurologic deficits, heart failure, or profoundly affect development. In contrast to high-flow lesions with direct arterial-to-venous shunts, low-flow lesions such as cavernous malformations are associated with a lower likelihood of substantial hemorrhage, and a more benign course. Management of vascular anomalies in children has to incorporate an understanding of how treatment strategies may affect the normal development of the central nervous system. In this review, we discuss the etiologies, epidemiology, natural history, and genetic risk factors of three high-flow vascular malformations seen in children: brain arteriovenous malformations, intracranial dural arteriovenous fistulas, and vein of Galen malformations
The Discordance of Mass-Loss Estimates for Galactic O-Type Stars
We have determined accurate values of the product of the mass-loss rate and
the ion fraction of P^{4+}, Mdot q(P^{4+}), for a sample of 40 Galactic O-type
stars by fitting stellar-wind profiles to observations of the P V resonance
doublet obtained with FUSE, ORFEUS/BEFS, and Copernicus. When P^{4+} is the
dominant ion in the wind, Mdot q(P^{4+}) approximates the mass-loss rate to
within a factor of 2. Theory predicts that P^{4+} is the dominant ion in the
winds of O7-O9.7 stars, though an empirical estimator suggests that the range
from O4-O7 may be more appropriate. However, we find that the mass-loss rates
obtained from P V wind profiles are systematically smaller than those obtained
from fits to Halpha emission profiles or radio free-free emission by median
factors of about 130 (if P^{4+} is dominant between O7 and O9.7) or about 20
(if P^{4+} is dominant between O4 and O7). These discordant measurements can be
reconciled if the winds of O stars in the relevant temperature range are
strongly clumped on small spatial scales. We use a simplified two-component
model to investigate the volume filling factors of the denser regions. This
clumping implies that mass-loss rates determined from "density squared"
diagnostics have been systematically over-estimated by factors of 10 or more,
at least for a subset of O stars. Reductions in the mass-loss rates of this
size have important implications for the evolution of massive stars and
quantitative estimates of the feedback that hot-star winds provide to their
interstellar environments.Comment: 26 pages, 4 figures; accepted for publication in Ap
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