53,468 research outputs found
Neutrino masses and mixing in A4 models with three Higgs doublets
We study neutrino masses and mixing in the context of flavor models with A4
symmetry, three scalar doublets in the triplet representation, and three lepton
families. We show that there is no representation assignment that yields a
dimension-five mass operator consistent with experiment. We then consider a
type-I seesaw with three heavy right-handed neutrinos, explaining in detail why
it fails, and showing with a numerical example that agreement with the present
neutrino oscillation data can be recovered with the inclusion of
dimension-three heavy neutrino mass terms that break softly the A4 symmetry.Comment: 10 pages, RevTex, 3 figures. v2: much expanded section on softly
broken A4; refs adde
A Tale of Two Distributions: From Few To Many Vortices In Quasi-Two-Dimensional Bose-Einstein Condensates
Motivated by the recent successes of particle models in capturing the
precession and interactions of vortex structures in quasi-two-dimensional
Bose-Einstein condensates, we revisit the relevant systems of ordinary
differential equations. We consider the number of vortices as a parameter
and explore the prototypical configurations ("ground states") that arise in the
case of few or many vortices. In the case of few vortices, we modify the
classical result of Havelock [Phil. Mag. , 617 (1931)] illustrating
that vortex polygons in the form of a ring are unstable for .
Additionally, we reconcile this modification with the recent identification of
symmetry breaking bifurcations for the cases of . We also briefly
discuss the case of a ring of vortices surrounding a central vortex (so-called
configuration). We finally examine the opposite limit of large and
illustrate how a coarse-graining, continuum approach enables the accurate
identification of the radial distribution of vortices in that limit.Comment: 15 pages, 2 figure
The impact of a wave farm on large scale sediment transport
This study investigates the interactions of waves and tides at a wave farm in the southwest of England, in particular their effects on radiation stress, bottom stress, and consequently on the sediment transport and the coast adjacent to the wave-farm (the Wave Hub). In this study, an integrated complex numerical modelling system is setup at the Wave Hub site and is used to compute the wave and current fields by taking into account the wave-current interaction, as well as the sediment transport. Results show that tidal elevation and tidal currents have a significant effect on the wave height and direction predictions; tidal forcing and wind waves have a significant effect on the bed shear-stress, relevant to sediment transport; waves via radiation stresses have an important effect on the longshore and cross-shore velocity components, particularly during the spring tides. Waves can impact on bottom boundary layer and mixing in the water column. The results highlight the importance of the interactions between waves and tides when modelling coastal morphology with presence of wave energy devices
Two and three electrons in a quantum dot: 1/|J| - expansion
We consider systems of two and three electrons in a two-dimensional parabolic
quantum dot. A magnetic field is applied perpendicularly to the electron plane
of motion. We show that the energy levels corresponding to states with high
angular momentum, J, and a low number of vibrational quanta may be
systematically computed as power series in 1/|J|. These states are relevant in
the high-B limit.Comment: LaTeX, 15 pages,6 postscript figure
Brave Forms of Mentoring Supported by Technology in Teacher Education
Indexación: Web of ScienceQuality education is undoubtedly a global concern, tied closely to preoccupations with economic and social development. Increasingly, the adoption and effective use of current technology tools are being recognized as visible signs of that quality. Scholars are providing increasing evidence of the kinds of empowered teacher identities that will adopt the effective use of technology tools in teaching. Less is being discussed about how technology can support the processes needed to mediate such identities. The context of Teacher Education is a strategic place to begin to initiate such processes. Our aim in this article is twofold: 1) to describe two recent examples of innovative, technology - supported mentoring processes that were conducted in the context of an EFL Teacher Education program in Chile; 2) to revisit the findings of these studies in light of new evidence from participants who have moved on in their careers. This evidence is viewed in the framework of recent scholarship on the responsibilities that Teacher Education plays in their development. The first 16-month study examined the influences of a guided reading program involving e-readers on the identities and literacy skills of pre-service teachers. The second was a student-conceived study. That inquiry sought to determine the influence of upper year students' peer mentoring, made available partly through a social media site (SMS), on the identities and investment in learning of 12 firs-year students in the pedagogy program. The initial evidence from ethnographic tools used in both studies indicated that the participants were struggling with confidence and doubting themselves as knowledgeable, effective future teachers - not predictive of a potential for quality teaching. Positive signs at the end of both studies and more recent reports from participants suggest that the mentoring had longitudinal benefits for some, although not uniformly. The potential of apprenticeship and mentoring in a technology-supported environment requires rethinking Teacher Education mandates if we are to empower emerging teachers to be quality teachers.http://www.ejel.org/issue/download.html?idArticle=48
A Tool for Integer Homology Computation: Lambda-At Model
In this paper, we formalize the notion of lambda-AT-model (where is
a non-null integer) for a given chain complex, which allows the computation of
homological information in the integer domain avoiding using the Smith Normal
Form of the boundary matrices. We present an algorithm for computing such a
model, obtaining Betti numbers, the prime numbers p involved in the invariant
factors of the torsion subgroup of homology, the amount of invariant factors
that are a power of p and a set of representative cycles of generators of
homology mod p, for each p. Moreover, we establish the minimum valid lambda for
such a construction, what cuts down the computational costs related to the
torsion subgroup. The tools described here are useful to determine topological
information of nD structured objects such as simplicial, cubical or simploidal
complexes and are applicable to extract such an information from digital
pictures.Comment: Journal Image and Vision Computing, Volume 27 Issue 7, June, 200
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