65,325 research outputs found
Faceted anomalous scaling in the epitaxial growth of semiconductor films
We apply the generic dynamical scaling theory (GDST) to the surfaces of CdTe
polycrystalline films grown in glass substrates. The analysed data were
obtained with a stylus profiler with an estimated resolution lateral resolution
of m. Both real two-point correlation function and power spectrum
analyses were done. We found that the GDST applied to the surface power spectra
foresees faceted morphology in contrast with the self-affine surface indicated
by the local roughness exponent found via the height-height correlation
function. This inconsistency is explained in terms of convolution effects
resulting from the finite size of the probe tip used to scan the surfaces. High
resolution AFM images corroborates the predictions of GDST.Comment: to appear in Europhysics Letter
Exchange coupling between magnetic layers across non-magnetic superlattices
The oscillation periods of the interlayer exchange coupling are investigated
when two magnetic layers are separated by a metallic superlattice of two
distinct non-magnetic materials. In spite of the conventional behaviour of the
coupling as a function of the spacer thickness, new periods arise when the
coupling is looked upon as a function of the number of cells of the
superlattice. The new periodicity results from the deformation of the
corresponding Fermi surface, which is explicitly related to a few controllable
parameters, allowing the oscillation periods to be tuned.Comment: 13 pages; 5 figures; To appear in J. Phys.: Cond. Matte
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Open educational resources and teaching in the 21st century: questions concerning authority
As a source of materials for education the Web is, to a large extent, shifting ground. Open Educational Resources (OER) provided by Higher Education Institutions constitute, at least in principle, a reliable category of Web-based resources given their association with traditional forms of expert authority. Nevertheless, OER embody different aspects of academic thinking and practice, competing, in an unlevelled field, with other sources that may provide a much more immediate appeal in that they afford quick and easy consumption of information delivered in a piecemeal, often uncritical, fashion.
This paper draws upon a piece of research in the area of ‘online informal learning’ to illustrate issues arising from the availability of open content and, in particular, OER. This research suggests a number of aspects related to the impact of open content on assumed boundaries between teacher/learner, formal/informal learning, training/education, content/presentation and, crucially, in how the blurring of these boundaries may have an impact on the location of ‘value’ within views of education in which marketing and business discourses predominate. The paper argues that, despite the need for critical debate on issues regarding validation, current arguments focusing on ‘expertise’ risk diluting its significance in subtle yet fundamental ways
Capturing asymmetry in real exchange rate with quantile autoregression
Quantile autoregression is used to explore asymmetries in the adjustment process of pair wise real exchange rate between the Italian lire, French franc, Deutsch mark, and the British pound. Based on the best specification for each quantile we construct predicted conditional density functions which guided us to identify two sources of asymmetry: 1) dispersion depends on the conditioned value of the real exchange rate, i.e., “conditional” heterokedasticity; 2) the probability of increases and falls also changes according to the conditioned value, i.e., there is higher probability for the real exchange rate to appreciate (depreciate) given the currency is depreciated (appreciated).We only verified strong heterokedasticity in relations among the lire, franc, and mark, which was resolved by estimating quadratic autoregressive model for some quantiles. Relations involving the pound presented stable but higher dispersion indicating larger probability of wider oscillation.exchange rate; quantile autoregression; unit root; asymmetry
The Ellis semigroup of a nonautonomous discrete dynamical system
We introduce the {\it Ellis semigroup} of a nonautonomous discrete dynamical
system when is a metric compact space. The underlying
set of this semigroup is the pointwise closure of \{f\sp{n}_1 \, |\, n\in
\mathbb{N}\} in the space X\sp{X}.
By using the convergence of a sequence of points with respect to an
ultrafilter it is possible to give a precise description of the semigroup and
its operation. This notion extends the classical Ellis semigroup of a discrete
dynamical system. We show several properties that connect this semigroup and
the topological properties of the nonautonomous discrete dynamical system
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