2,915 research outputs found
Nonlinear trend stationarity of real exchange rates: the case of the Mediterranean countries
The aim of this article is to provide additional evidence on the fulfilment of the Purchasing Power Parity hypothesis in the so-called Mediterranean countries. In order to test for the empirical validity of such hypothesis, we have applied two types of unit root tests. The first group is due to Bierens (1997) who generalizes the alternative hypothesis to nonlinear trend stationariry and, the second is the Leybourne, Newbold and Vougas (1998) approach that uses a nonlinear specification for the intercept and slope in order to detrend the series. The results suggest that the evidence in favour of the Purchasing Power Parity hypothesis increases when we allow for nonlinear alternatives
Bosonic D=11 supergravity from a generalized Chern-Simons action
It is shown that the action of the bosonic sector of D=11 supergravity may be
obtained by means of a suitable scaling of the originally dimensionless fields
of a generalized Chern-Simons action. This follows from the eleven-form
CS-potential of the most general linear combination of closed, gauge invariant
twelve-forms involving the sp(32)-valued two-form curvatures supplemented by a
three-form field. In this construction, the role of the skewsymmetric
four-index auxiliary function needed for the first order formulation of
supergravity is played by the gauge field associated with the five Lorentz
indices generator of the bosonic sp(32) subalgebra of osp(1|32).Comment: Misprints corrected, to appear in NPB plain latex, no figures, 25
page
Surfactant effect in heteroepitaxial growth. The Pb - Co/Cu(111) case
A MonteCarlo simulations study has been performed in order to study the
effect of Pb as surfactant on the initial growth stage of Co/Cu(111). The main
characteristics of Co growing over Cu(111) face, i.e. the decorated double
layer steps, the multiple layer islands and the pools of vacancies, disappear
with the pre-evaporation of a Pb monolayer. Through MC simulations, a full
picture of these complex processes is obtained. Co quickly diffuses through the
Pb monolayer exchanging place with Cu atoms at the substrate. The exchange
process diffusion inhibits the formation of pure Co islands, reducing the
surface stress and then the formation of multilayer islands and the pools of
vacancies. On the other hand, the random exchange also suppress the nucleation
preferential sites generated by Co atoms at Cu steps, responsible of the step
decoration.Comment: 4 pages, latex, 2 figures embedded in the tex
Response of Pinus uncinata Recruitment to Climate Warming and Changes in Grazing Pressure in an Isolated Population of the Iberian System (NE Spain)
Dynamics of magnetic domain wall motion after nucleation: Dependence on the wall energy
The dynamics of magnetic domain wall motion in the FeNi layer of a
FeNi/Al2O3/Co trilayer has been investigated by a combination of x-ray magnetic
circular dichroism, photoelectron emission microscopy, and a stroboscopic
pump-probe technique. The nucleation of domains and subsequent expansion by
domain wall motion in the FeNi layer during nanosecond-long magnetic field
pulses was observed in the viscous regime up to the Walker limit field. We
attribute an observed delay of domain expansion to the influence of the domain
wall energy that acts against the domain expansion and that plays an important
role when domains are small.Comment: Accepted for publication in Physical Review Letter
Influence of topography and Co domain walls on the magnetization reversal of the FeNi layer in FeNi/AlO/Co magnetic tunnel junctions
We have studied the magnetization reversal dynamics of FeNi/AlO/Co
magnetic tunnel junctions deposited on step-bunched Si substrates using
magneto-optical Kerr effect and time-resolved x-ray photoelectron emission
microscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM).
Different reversal mechanisms have been found depending on the substrate miscut
angle. Larger terraces (smaller miscut angles) lead to a higher nucleation
density and stronger domain wall pinning. The width of domain walls with
respect to the size of the terraces seems to play an important role in the
reversal. We used the element selectivity of XMCD-PEEM to reveal the strong
influence of the stray field of domain walls in the hard magnetic layer on the
magnetic switching of the soft magnetic layer.Comment: 8 Pages, 7 Figure
Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin films
We present a detailed study on the magnetic properties, including anisotropy,
reversal fields, and magnetization reversal processes, of well characterized
half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3
(STO) substrates with three different surface orientations, i.e. (001), (110)
and (1-18). The latter shows step edges oriented parallel to the [110]
(in-plane) crystallographic direction. Room temperature high resolution
vectorial Kerr magnetometry measurements have been performed at different
applied magnetic field directions in the whole angular range. In general, the
magnetic properties of the LSMO films can be interpreted with just the uniaxial
term with the anisotropy axis given by the film morphology, whereas the
strength of this anisotropy depends on both structure and film thickness. In
particular, LSMO films grown on nominally flat (110)-oriented STO substrates
presents a well defined uniaxial anisotropy originated from the existence of
elongated in-plane [001]-oriented structures, whereas LSMO films grown on
nominally flat (001)-oriented STO substrates show a weak uniaxial magnetic
anisotropy with the easy axis direction aligned parallel to residual substrate
step edges. Elongated structures are also found for LSMO films grown on vicinal
STO(001) substrates. These films present a well-defined uniaxial magnetic
anisotropy with the easy axis lying along the step edges and its strength
increases with the LSMO thickness. It is remarkable that this step-induced
uniaxial anisotropy has been found for LSMO films up to 120 nm thickness. Our
results are promising for engineering novel half-metallic magnetic devices that
exploit tailored magnetic anisotropy.Comment: 10 pages, 10 figures, 1 tabl
Surfactant induced smooth and symmetric interfaces in Cu/Co multilayers
In this work we studied Ag surfactant induced growth of Cu/Co multilayers.
The Cu/Co multilayers were deposited using Ag surfactant by ion beam sputtering
technique. It was found that Ag surfactant balances the asymmetry between the
surface free energy of Cu and Co. As a result, the Co-on-Cu and Cu-on-Co
interfaces become sharp and symmetric and thereby improve the thermal stability
of the multilayer. On the basis of obtained results, a mechanism leading to
symmetric and stable interfaces in Cu/Co multilayers is discussed.Comment: 7 Pages, 7 Figure
Magnetic relaxation measurements of exchange biased (Pt/Co) multilayers with perpendicular anisotropy
Magnetic relaxation measurements were carried out by magneto-optical Kerr
effect on exchange biased (Pt/Co)5/Pt/FeMn multilayers with perpendicular
anisotropy. In these films the coercivity and the exchange bias field vary with
Pt spacer thickness, and have a maximum for 0.2 nm. Hysteresis loops do not
reveal important differences between the reversal for ascending and descending
fields. Relaxation measurements were fitted using Fatuzzo's model, which
assumes that reversal occurs by domain nucleation and domain wall propagation.
For 2 nm thick Pt spacer (no exchange bias) the reversal is dominated by domain
wall propagation starting from a few nucleation centers. For 0.2 nm Pt spacer
(maximum exchange bias) the reversal is strongly dominated by nucleation, and
no differences between the behaviour of the ascending and descending branches
can be observed. For 0.4 nm Pt spacer (weaker exchange bias) the nucleation
density becomes less important, and the measurements reveal a much stronger
density of nucleation centers in the descending branch.Comment: Europhysical Journal B, in print DOI: 10.1140/epjb/e2005-00053-
Are the determinants of CO2 emissions converging among OECD countries?
This paper studies convergence in CO2emission intensity (CO2 emissions over GDP) among OECD countries over the period 1960-2008 based on its determinants, namely, energy intensity (energy consumption over GDP) and the so-called carbonisation index (CO2 emissions over energy consumption). We apply the Phillips and Sul (2007) methodology, which tests for the existence of convergence clubs. Our results highlight that differences in emission intensity convergence are more determined by differences in convergence of the carbonisation index rather than by differences in the dynamic convergence of energy intensity
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