3,172 research outputs found
La Unión Europea y el mundo “en desarrollo”: ¿dónde encaja Centroamérica?
La tormenta del referéndum del Tratado de Libre Comercio entre Estados Unidos y CAFTA-DR hasta hace poco se empieza a calmar, pero desde ya el siguiente gigante en el mundo del comercio global ya está tocando a la puerta de América Central. La Unión Europea y Centroamérica, como región, han iniciado en octubre de 2007 las negociaciones para firmar un Acuerdo de Asociación (AdA). Este AdA probablemente seguirá los pasos de otros acuerdos, tales como los de la UE y Chile, y la UE y México. Pero, ¿cómo encaja este AdA con la estrategia de comercio de la UE?, y ¿cómo sus condicionalidades se comparan con las de otros acuerdos dentro de las estructuras que la UE tiene establecidas, y que le dan a los países en desarrollo acceso a sus mercados? Este artículo se propone realizar un breve análisis del contexto en el cual el AdA es negociado, y lo compara con otras estructuras por medio de las cuales los países en desarrollo obtienen acceso al mercado de la UE, sobresaliendo los Acuerdos de Asociación Económica (EPAs) que los países en desarrollo de África, el Caribe y el Pacífico están negociando con la UE, y el Sistema Generalizado de Preferencia (SGP), el cual ha gobernado hasta ahora las relaciones comerciales entre el Istmo y la UE
Preeclampsia, the Renin-Angiotensin-Aldosterone System and beyond
__Abstract__
The renin-angiotensin-aldosterone system (RAAS) plays an essential role in the regulation of blood pressure and body fluid homeostasis, but also contributes importantly to the pathophysiology of hypertension, renal disease and heart failure. Clinically, the RAAS is of great interest as inhibition at different levels has been proven to be an effective therapy for hypertension, cardiovascular and renal disease.
Angiotensin II mediates its effects via angiotensin II type 1 (AT1) and angiotensin II type 2 (AT2) receptors. AT1-receptors are widely expressed throughout the body and mediate the well-known effects of angiotensin II, including vasoconstriction, sympathetic nervous system activation and sodium and water retention. While experimental studies show that stimulation of the AT2-receptor counteracts these effects by inducing vasorelaxation and natriuresis in healthy animals, our knowledge about AT2-receptor function in humans is limited to a few studies, showing, at most, modest vasodilatory effects upon AT2-receptor stimulation. In contrast to the beneficial effects, recent studies suggest
Two candidate brown dwarf companions around core helium-burning stars
Hot subdwarf stars of spectral type B (sdBs) are evolved, core helium-burning
objects. The formation of those objects is puzzling, because the progenitor
star has to lose almost its entire hydrogen envelope in the red-giant phase.
Binary interactions have been invoked, but single sdBs exist as well. We report
the discovery of two close hot subdwarf binaries with small radial velocity
amplitudes. Follow-up photometry revealed reflection effects originating from
cool irradiated companions, but no eclipses. The lower mass limits for the
companions of CPD-64481 () and PHL\,457
() are significantly below the stellar mass limit. Hence
they could be brown dwarfs unless the inclination is unfavourable. Two very
similar systems have already been reported. The probability that none of them
is a brown dwarf is very small, 0.02%. Hence we provide further evidence that
substellar companions with masses that low are able to eject a common envelope
and form an sdB star. Furthermore, we find that the properties of the observed
sample of hot subdwarfs in reflection effect binaries is consistent with a
scenario where single sdBs can still be formed via common envelope events, but
their low-mass substellar companions do not survive.Comment: accepted to A&
Transferencias condicionadas, regímenes de bienestar e igualdad de género: ¿blancos, negros o grises?
Las transferencias monetarias condicionadas, programas “estrella” de la nueva política latinoamericana, ¿favorecen o atentan contra la igualdad de género? ¿Qué tanto los programas de transferencias condicionadas promueven mayores grados de igualdad como lo argumentan sus defensores? ¿Es posible, por el contrario, constatar que promueven mayores grados de desigualdad entre hombres y mujeres, como lo argumentan sus detractores? ¿Y si no fuera ni una cosa ni lo otro sino una combinación de ambos? Este documento de trabajo presenta un instrumento teórico-empírico novedoso para el estudio de la igualdad de género. Su principal fortaleza es que permite analizar empíricamente dicha (des)igualdad, de manera multidimensional y sistemática, y a partir de diversos tipos de fuentes, tanto cualitativas como cuantitativas. Como segundo aporte al debate regional, el análisis se basa en una combinación de fuentes primarias y secundarias, principalmente cualitativas, relativas a tres países claramente contrastantes en términos de su política social, así como de las relaciones entre política social, mercados laborales y familias: Chile, Costa Rica y El Salvador. Nuestro análisis muestra que, desde el punto de vista de la equidad de género, lejos de blancos o negros, estos programas nos confrontan con una tonalidad de grises. En segundo lugar, una relativa homogeneidad entre programas insertos en regímenes de bienestar altamente diferenciados, indicaría que ésta se debe más a aspectos de diseño de los programas, que de articulación de las políticas sociales con los mercados laborales y las familias. En otras palabras, las limitaciones de los programas para promover mayores grados de igualdad de género, estarían más asociados a aspectos de diseño que a factores estructurales
Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)
Among the competing evolution theories for subdwarf-B (sdB) stars is the
binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary
system consisting of a pulsating sdB star and a late F main-sequence companion
(O'Donoghue et al. 1997), however the period and the orbit semi-major axes have
not been precisely determined. This paper presents orbital characteristics of
the EC 20117-4014 binary system using 20 years of photometric data. Periodic
Observed minus Calculated (O-C) variations were detected in the two highest
amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating
the binary system's precise orbital period (P = 792.3 days) and the
light-travel time amplitude (A = 468.9 s). This binary shows no significant
orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3
as an upper limit). This upper limit of the eccentricity is the lowest
among all wide sdB binaries with known orbital parameters. This analysis
indicated that the sdB is likely to have lost its hydrogen envelope through
stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB
stars. In addition to those results, the underlying pulsation period change
obtained from the photometric data was = 5.4 (0.7)
d d, which shows that the sdB is just before the end of the
core helium-burning phase
Modeling the impact of forecast-based regime switches on macroeconomic time series
Forecasts of key macroeconomic variables may lead to policy changes of governments, central banks and other economic agents. Policy changes in turn lead to structural changes in macroeconomic time series models. To describe this phenomenon we introduce a logistic smooth transition autoregressive model where the regime switches depend on the forecast of the time series of interest. This forecast can either be an exogenous expert forecast or an endogenous forecast generated by the model. Results of an application of the model to US inflation shows that (i) forecasts lead to regime changes and have an impact on the level of inflation; (ii) a relatively large forecast results in actions which in the end lower the inflation rate; (iii) a counterfactual scenario where forecasts during the oil crises in the 1970s are assumed to be correct leads to lower inflation than observed
Period-doubling events in the light curve of R Cygni: evidence for chaotic behaviour
A detailed analysis of the century long visual light curve of the long-period
Mira star R Cygni is presented and discussed. The data were collected from the
publicly available databases of the AFOEV, the BAAVSS and the VSOLJ. The full
light curve consists of 26655 individual points obtained between 1901 and 2001.
The light curve and its periodicity were analysed with help of the O-C diagram,
Fourier analysis and time-frequency analysis. The results demonstrate the
limitations of these linear methods. The next step was to investigate the
possible presence of low-dimensional chaos in the light curve. For this, a
smoothed and noise-filtered signal was created from the averaged data and with
help of time delay embedding, we have tried to reconstruct the attractor of the
system. The main result is that R Cygni shows such period-doubling events that
can be interpreted as caused by a repetitive bifurcation of the chaotic
attractor between a period 2T orbit and chaos. The switch between these two
states occurs in a certain compact region of the phase space, where the light
curve is characterized by ~1500-days long transients. The Lyapunov spectrum was
computed for various embedding parameters confirming the chaotic attractor,
although the exponents suffer from quite high uncertainty because of the
applied approximation. Finally, the light curve is compared with a simple one
zone model generated by a third-order differential equation which exhibits
well-expressed period-doubling bifurcation. The strong resemblance is another
argument for chaotic behaviour. Further studies should address the problem of
global flow reconstruction, including the determination of the accurate
Lyapunov exponents and dimension.Comment: 13 pages, 14 figures, accepted for publication in A&A (some figures
are of reduced quality
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