1,087 research outputs found
Growth, distance to frontier and composition of human capital
We examine the contribution of human capital to economy-wide technological
improvements through the two channels of innovation and imitation.
We develop a theoretical model showing that skilled labor has
a higher growth-enhancing effect closer to the technological frontier under
the reasonable assumption that innovation is a relatively more skill intensive
activity than imitation. Also, we provide evidence in favor of
this prediction using a panel dataset covering 19 OECD countries between
1960 and 2000 and explain why previous empirical research had found no
positive relationship between initial schooling level and subsequent growth
in rich countries. In particular, we show that in OECD economies it is
crucial to isolate the two separate margins of primary/secondary and tertiary
education. Interestingly, the latter type of schooling proves to be a
factor of economic divergence
Enhancing economic cooperation between the EU and the Americas : an economic assessment
Suggests that the EU could gain over 100 billion per annum through liberalisation of the EU-US trade relationship. The gains for the US could be as much as $75 billion per year.The studies also highlight the new challenges to transatlantic trade - in particular, arguing that the EU and US should consider strengthening regulatory dialogue and cooperation, to help prevent 'non-tariff' barriers, such as domestic regulation, becoming an increasing source of trade disputes
Automated supervised classification of variable stars I. Methodology
The fast classification of new variable stars is an important step in making
them available for further research. Selection of science targets from large
databases is much more efficient if they have been classified first. Defining
the classes in terms of physical parameters is also important to get an
unbiased statistical view on the variability mechanisms and the borders of
instability strips. Our goal is twofold: provide an overview of the stellar
variability classes that are presently known, in terms of some relevant stellar
parameters; use the class descriptions obtained as the basis for an automated
`supervised classification' of large databases. Such automated classification
will compare and assign new objects to a set of pre-defined variability
training classes. For every variability class, a literature search was
performed to find as many well-known member stars as possible, or a
considerable subset if too many were present. Next, we searched on-line and
private databases for their light curves in the visible band and performed
period analysis and harmonic fitting. The derived light curve parameters are
used to describe the classes and define the training classifiers. We compared
the performance of different classifiers in terms of percentage of correct
identification, of confusion among classes and of computation time. We describe
how well the classes can be separated using the proposed set of parameters and
how future improvements can be made, based on new large databases such as the
light curves to be assembled by the CoRoT and Kepler space missions.Comment: This paper has been accepted for publication in Astronomy and
Astrophysics (reference AA/2007/7638) Number of pages: 27 Number of figures:
1
Carry-Along Trade.
New empirical and theoretical work has highlighted the importance of multi-product fiĀ
rms in international trade flows. We examine multi-product exporters in the small open economy of Belgium. Linking production and export data at the fiĀ
rm-product level, we discover new and, heretofore, unknown facts about multi-product manufacturing exporters. The large majority of Belgian manufacturing Ā
firms export products that they do not produce. More than three quarters of the exported products and more than one quarter of export value from Belgian manufacturers are in goods that are not produced by the Ā
rm, so-called Carry-Along Trade (CAT). CAT exports are concentrated in the largest and most productive Ā
rms and CAT exports respond diĀ¤erently to variation in Ā
rm productivity and size than do exports of goods that the Ā
rm produces.
Herschel PACS and SPIRE spectroscopy of the Photodissociation Regions associated with S 106 and IRAS 23133+6050
Photodissociation regions (PDRs) contain a large fraction of all of the
interstellar matter in galaxies. Classical examples include the boundaries
between ionized regions and molecular clouds in regions of massive star
formation, marking the point where all of the photons energetic enough to
ionize hydrogen have been absorbed. In this paper we determine the physical
properties of the PDRs associated with the star forming regions IRAS 23133+6050
and S 106 and present them in the context of other Galactic PDRs associated
with massive star forming regions. We employ Herschel PACS and SPIRE
spectroscopic observations to construct a full 55-650 {\mu}m spectrum of each
object from which we measure the PDR cooling lines, other fine- structure
lines, CO lines and the total far-infrared flux. These measurements are then
compared to standard PDR models. Subsequently detailed numerical PDR models are
compared to these predictions, yielding additional insights into the dominant
thermal processes in the PDRs and their structures. We find that the PDRs of
each object are very similar, and can be characterized by a two-phase PDR model
with a very dense, highly UV irradiated phase (n 10^6 cm^(-3), G
10^5) interspersed within a lower density, weaker radiation field phase
(n 10^4 cm^(-3), G 10^4). We employed two different numerical
models to investigate the data, firstly we used RADEX models to fit the peak of
the CO ladder, which in conjunction with the properties derived yielded
a temperature of around 300 K. Subsequent numerical modeling with a full PDR
model revealed that the dense phase has a filling factor of around 0.6 in both
objects. The shape of the CO ladder was consistent with these components
with heating dominated by grain photoelectric heating. An extra excitation
component for the highest J lines (J > 20) is required for S 106.Comment: 20 pages, 10 figures, A&A Accepte
Occurrence of pharmaceuticals in environmental samples: a multi-analyte approach
Pharmaceuticals and their residues in the environment have been recently recognized as one of the emerging research areas in the environmental chemistry and toxicology and caused them to be viewed as a new class of priority substances. It has been reportedthat they are introduced continuously in the environment via household use, effluents from Sewage Treatment Plants (STPs) and animal excreta. Up to date, the potential human, animal and ecological risk associated with the occurrence of these compounds in the environment is not well documented. There is an increased attention due to the fact that they are designed to have specific effects at low doses and to be resistant to Moreover, the science of mixture toxicity is complex and to date quite unknown (Bound et al., 2006; Hernando et al., 2006).Despite the increased research and regulatory interest in the occurrence of pharmaceuticals and their degradation products in STPs effluents and freshwater ecosystems (Hernando et al., 2006), the occurrence, the distribution between the different environmental compartments (i.e. water, sediments, suspended solids and aqueous organisms), the trophic transfer and their potential toxicity is to date far less documented (Emblidge and DeLorenze, 2006).In this sense, this study will present a detection method for the determination of a large group of pharmaceuticals (i.e. antibiotics, beta-agonists, painkillers, tranquilizers, nonsteroidal anti-inflammatory drugs) used both in human and veterinary practice in environmental samples using Liquid Chromatography coupled to multiple Mass Spectrometry
Dusty shells surrounding the carbon variables S Scuti and RT Capricorni
For the Mass-loss of Evolved StarS (MESS) programme, the unprecedented
spatial resolution of the PACS photometer on board the Herschel space
observatory was employed to map the dusty environments of asymptotic giant
branch (AGB) and red supergiant (RSG) stars. Among the morphologically
heterogeneous sample, a small fraction of targets is enclosed by spherically
symmetric detached envelopes. Based on observations in the 70 {\mu}m and 160
{\mu}m wavelength bands, we investigated the surroundings of the two carbon
semiregular variables S Sct and RT Cap, which both show evidence for a history
of highly variable mass-loss. S Sct exhibits a bright, spherically symmetric
detached shell, 138" in diameter and co-spatial with an already known CO
structure. Moreover, weak emission is detected at the outskirts, where the
morphology seems indicative of a mild shaping by interaction of the wind with
the interstellar medium, which is also supported by the stellar space motion.
Two shells are found around RT Cap that were not known so far in either dust
emission or from molecular line observations. The inner shell with a diameter
of 188" shows an almost immaculate spherical symmetry, while the outer ~5'
structure is more irregularly shaped. MoD, a modification of the DUSTY
radiative transfer code, was used to model the detached shells. Dust
temperatures, shell dust masses, and mass-loss rates are derived for both
targets
Spitzer Observations of CO2 Ice Towards Field Stars in the Taurus Molecular Cloud
We present the first Spitzer Infrared Spectrograph observations of the 15.2
micron bending mode of CO2 ice towards field stars behind a quiescent dark
cloud. CO2 ice is detected towards 2 field stars (Elias 16, Elias 3) and a
single protostar (HL Tau) with anabundance of ~15-20% relative to water ice.
CO2 ice is not detected towards the source with lowest extinction in our
sample, Tamura 17 (A_V = 3.9m). A comparison of the Elias 16 spectrum with
laboratory data demonstrates that the majority of CO2 ice is embedded in a
polar H2O-rich ice component, with ~15% of CO2 residing in an apolar H2O-poor
mantle. This is the first detection of apolar CO2 towards a field star. We find
that the CO2 extinction threshold is A_V = 4m +/- 1m, comparable to the
threshold for water ice, but significantly less than the threshold for CO ice,
the likely precursor of CO2. Our results confirm CO2 ice forms in tandem with
H2O ice along quiescent lines of sight. This argues for CO2 ice formation via a
mechanism similar to that responsible for H2O ice formation, viz. simple
catalytic reactions on grain surfaces.Comment: Accepted by Astrophysical Journal Letter
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