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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 âonline informal learningâ 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 âvalueâ 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 âexpertiseâ risk diluting its significance in subtle yet fundamental ways
Fundamental Oscillation Periods of the Interlayer Exchange Coupling beyond the RKKY Approximation
A general method for obtaining the oscillation periods of the interlayer
exchange coupling is presented. It is shown that it is possible for the
coupling to oscillate with additional periods beyond the ones predicted by the
RKKY theory. The relation between the oscillation periods and the spacer Fermi
surface is clarified, showing that non-RKKY periods do not bear a direct
correspondence with the Fermi surface. The interesting case of a FCC(110)
structure is investigated, unmistakably proving the existence and relevance of
non-RKKY oscillations. The general conditions for the occurrence of non-RKKY
oscillations are also presented.Comment: 34 pages, 10 figures ; to appear in J. Phys.: Condens. Mat
Nontopological self-dual Maxwell-Higgs vortices
We study the existence of self-dual nontopological vortices in generalized
Maxwell-Higgs models recently introduced in Ref. \cite{gv}. Our investigation
is explicitly illustrated by choosing a sixth-order self-interaction potential,
which is the simplest one allowing the existence of nontopological structures.
We specify some Maxwell-Higgs models yielding BPS nontopological vortices
having energy proportional to the magnetic flux, , and whose profiles
are numerically achieved. Particularly, we investigate the way the new
solutions approach the boundary values, from which we verify their
nontopological behavior. Finally, we depict the profiles numerically found,
highlighting the main features they present.Comment: 6 pages, 4 figure
Explicit Actions for Electromagnetism with Two Gauge Fields with Only one Electric and one Magnetic Physical Fields
We extend the work of Mello et al. based in Cabbibo and Ferrari concerning
the description of electromagnetism with two gauge fields from a variational
principle, i.e. an action. We provide a systematic independent derivation of
the allowed actions which have only one magnetic and one electric physical
fields and are invariant under the discrete symmetries and . We conclude
that neither the Lagrangian, nor the Hamiltonian, are invariant under the
electromagnetic duality rotations. This agrees with the weak-strong coupling
mixing characteristic of the duality due to the Dirac quantization condition
providing a natural way to differentiate dual theories related by the duality
rotations (the energy is not invariant). Also the standard electromagnetic
duality rotations considered in this work violate both and by inducing
Hopf terms (theta terms) for each sector and a mixed Maxwell term. The
canonical structure of the theory is briefly addressed and the 'magnetic' gauge
sector is interpreted as a ghost sector.Comment: v2: 12 pages; References added, discussion concerning degrees of
freedom corrected; v3: is now used the standard normalization of 1/4 in the
actions; the possibility of theta being a pseudo-scalar implied a title
changing; eq (23) added; signs corrected in equations (39,45-47); references
adde
Flavour symmetries in a renormalizable SO(10) model
In the context of a renormalizable supersymmetric SO(10) Grand Unified
Theory, we consider the fermion mass matrices generated by the Yukawa couplings
to a representation
of scalars. We perform a complete investigation of the possibilities of
imposing flavour symmetries in this scenario; the purpose is to reduce the
number of Yukawa coupling constants in order to identify potentially predictive
models. We have found that there are only 14 inequivalent cases of Yukawa
coupling matrices, out of which 13 cases are generated by symmetries,
with suitable , and one case is generated by a symmetry. A
numerical analysis of the 14 cases reveals that only two of them---dubbed A and
B in the present paper---allow good fits to the experimentally known fermion
masses and mixings.Comment: 36 pages, no figures, revised fits using newer data, added fit for
case A, added references, new appendices concerning the SO(10) scalar
potential and inequalities for the vacuum expectation values, conclusions
unchanged; some minor changes, matches published versio
Scotogenic model for co-bimaximal mixing
We present a scotogenic model, i.e. a one-loop neutrino mass model with dark
right-handed neutrino gauge singlets and one inert dark scalar gauge doublet
, which has symmetries that lead to co-bimaximal mixing, i.e. to an
atmospheric mixing angle and to a -violating phase
, while the mixing angle remains arbitrary.
The symmetries consist of softly broken lepton numbers (), a non-standard symmetry, and three symmetries. We
indicate two possibilities for extending the model to the quark sector. Since
the model has, besides , three scalar gauge doublets, we perform a
thorough discussion of its scalar sector. We demonstrate that it can
accommodate a Standard Model-like scalar with mass , with
all the other charged and neutral scalars having much higher masses.Comment: v2 - 23 pages, 5 figures, minor changes requested by refere
Strain-Modified RKKY Interaction in Carbon Nanotubes
For low-dimensional metallic structures, such as nanotubes, the exchange
coupling between localized magnetic dopants is predicted to decay slowly with
separation. The long-range character of this interaction plays a significant
role in determining the magnetic order of the system. It has previously been
shown that the interaction range depends on the conformation of the magnetic
dopants in both graphene and nanotubes. Here we examine the RKKY interaction in
carbon nanotubes in the presence of uniaxial strain for a range of different
impurity configurations. We show that strain is capable of amplifying or
attenuating the RKKY interaction, significantly increasing certain interaction
ranges, and acting as a switch: effectively turning on or off the interaction.
We argue that uniaxial strain can be employed to significantly manipulate
magnetic interactions in carbon nanotubes, allowing an interplay between
mechanical and magnetic properties in future spintronic devices. We also
examine the dimensional relationship between graphene and nanotubes with
regards to the decay rate of the RKKY interaction.Comment: 7 pages, 6 figures, submitte
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