14,708 research outputs found
The Economic Impact of Migration – Productivity Analysis for Spain and the UK
As a consequence of increased internationalization over the past 20 years labour has become increasingly mobile, and yet the implications for firm and industry performance have been largely ignored. This paper explores the direct economic consequences of immigration on host nations’ productivity performance at a sectoral level. We consider its impact in two very different European countries, Spain and the UK. Whilst the UK has traditionally had a substantial in-flow of migration, for Spain, the phenomenon is much more recent. The paper provides an overview of the role played by immigration on per capita income, highlighting the importance of demographic differences. We then go on to analyze the role of migration on productivity using two different approaches: i) growth accounting methodology and ii) econometric estimation of a production function. Our findings indicate that migration has had very different implications for Spain and the UK, migrants being more productive than natives in the UK but less productive than natives in Spain. This may in part be a function of different immigration policies, particularly related to the skill requirements on entry, but also in part a feature of the host nations’ ability to ‘absorb’ foreign labour.Migration, productivity
The Professor-Tutor of Teaching "Prácticum" Like Professional User of Media
En este artículo presentamos un somero resumen de los resultados más interesantes
obtenidos en una tesis doctoral denominada “Uso de los medios en el Prácticum de
Magisterio”. Estos versan sobre la utilización que hacen de los medios y recursos los
profesores-tutores durante el periodo en el que el estudiante de magisterio esta
realizando las prácticas bajo su asesoría y supervisión.This article shows a brief resume about the more interesting results gotten in a doctoral
thesis titled: “The use of the technological and traditional resources during the teacher
training Practicum”. In this text, we analyse the data obtain about the use of this
resources by the tutor-teachers when they are tutoring student-teachers
Distinguishing the albedo of exoplanets from stellar activity
Light curves show the flux variation from the target star and its orbiting
planets as a function of time. In addition to the transit features created by
the planets, the flux also includes the reflected light component of each
planet, which depends on the planetary albedo. This signal is typically
referred to as phase curve and could be easily identified if there were no
additional noise. As well as instrumental noise, stellar activity, such as
spots, can create a modulation in the data, which may be very difficult to
distinguish from the planetary signal. We analyze the limitations imposed by
the stellar activity on the detection of the planetary albedo, considering the
limitations imposed by the predicted level of instrumental noise and the short
duration of the observations planned in the context of the CHEOPS mission. As
initial condition, we have assumed that each star is characterized by just one
orbiting planet. We built mock light curves that included a realistic stellar
activity pattern, the reflected light component of the planet and an
instrumental noise level, which we have chosen to be at the same level as
predicted for CHEOPS. We then fit these light curves to try to recover the
reflected light component, assuming the activity patterns can be modeled with a
Gaussian process.We estimate that at least one full stellar rotation is
necessary to obtain a reliable detection of the planetary albedo. This result
is independent of the level of noise, but it depends on the limitation of the
Gaussian process to describe the stellar activity when the light curve
time-span is shorter than the stellar rotation. Finally, in presence of typical
CHEOPS gaps in the simulations, we confirm that it is still possible to obtain
a reliable albedo.Comment: Accepted for publication in A&A, 14 pages, 12 figure
Influence of seismic activity on the atmospheric electric field in Lisbon (Portugal) from 1955 to 1991
In the present study, we considered the influence of seismic activity on the atmospheric electric field recorded at Portela meteorological station (Lisbon, Portugal) for the period from 1955 to 1991. To this end, an exploratory method was developed, which involved the selection of events for which the distance from the atmospheric electrical field sensor to the earthquake epicenter is smaller than the preparation radius of the event. This enabled the correlation of the atmospheric electric field variations with a quantity S, defined basically as the ratio of the earthquake preparation radius to the distance between the sensor and the event epicenter. The first results
show promising perspectives, but clearly a more profound study is required, in which a careful analysis of the weather conditions and other variables, like atmospheric radon levels, must be considered
Competition and adaptation in an Internet evolution model
We model the evolution of the Internet at the Autonomous System level as a
process of competition for users and adaptation of bandwidth capability. We
find the exponent of the degree distribution as a simple function of the growth
rates of the number of autonomous systems and the total number of connections
in the Internet, both empirically measurable quantities. This fact place our
model apart from others in which this exponent depends on parameters that need
to be adjusted in a model dependent way. Our approach also accounts for a high
level of clustering as well as degree-degree correlations, both with the same
hierarchical structure present in the real Internet. Further, it also
highlights the interplay between bandwidth, connectivity and traffic of the
network.Comment: Minor content changes and inset of fig.
Correlated enhancement of Hc2 and Jc in carbon nanotube-doped MgB2
The use of MgB2 in superconducting applications still awaits for the
development of a MgB2-based material where both current-carrying performance
and critical magnetic field are optimized simultaneously. We achieved this by
doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in
polycrystalline samples. The optimum nominal DWCNT content for increasing the
critical current density, Jc is in the range 2.5-10%at depending on field and
temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with
extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT
content. The measured Hc2 vs T in all samples are successfully described using
a theoretical model for a two-gap superconductor in the dirty limit first
proposed by Gurevich et al.Comment: 12 pages, 3 figure
Lattice Properties of PbX (X = S, Se, Te): Experimental Studies and ab initio Calculations Including Spin-Orbit Effects
During the past five years the low temperature heat capacity of simple
semiconductors and insulators has received renewed attention. Of particular
interest has been its dependence on isotopic masses and the effect of spin-
orbit coupling in ab initio calculations. Here we concentrate on the lead
chalcogenides PbS, PbSe and PbTe. These materials, with rock salt structure,
have different natural isotopes for both cations and anions, a fact that allows
a systematic experimental and theoretical study of isotopic effects e.g. on the
specific heat. Also, the large spin-orbit splitting of the 6p electrons of Pb
and the 5p of Te allows, using a computer code which includes spin-orbit
interaction, an investigation of the effect of this interaction on the phonon
dispersion relations and the temperature dependence of the specific heat and on
the lattice parameter. It is shown that agreement between measurements and
calculations significantly improves when spin-orbit interaction is included.Comment: 25 pages, 12 Figures, 1 table, submitted to PR
Errors on the inverse problem solution for a noisy spherical gravitational wave antenna
A single spherical antenna is capable of measuring the direction and
polarization of a gravitational wave. It is possible to solve the inverse
problem using only linear algebra even in the presence of noise. The simplicity
of this solution enables one to explore the error on the solution using
standard techniques. In this paper we derive the error on the direction and
polarization measurements of a gravitational wave. We show that the solid angle
error and the uncertainty on the wave amplitude are direction independent. We
also discuss the possibility of determining the polarization amplitudes with
isotropic sensitivity for any given gravitational wave source.Comment: 13 pages, 4 figures, LaTeX2e, IOP style, submitted to CQ
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