Non-Linear Affine Embedding of the Dirac Field from the Multiplicity-Free SL(4,R) Unirreps

The correspondence between the linear multiplicity-free unirreps of SL(4, R) studied by Ne'eman and {\~{S}}ija{\~{c}}ki and the non-linear realizations of the affine group is worked out. The results obtained clarify the inclusion of spinorial fields in a non-linear affine gauge theory of gravitation.Comment: 13 pages, plain TeX, macros include

Factores que favorecen el aprendizaje de la estadística con proyectos

El presente estudio tiene como objetivo describir la percepción que tienen los alumnos sobre el aprendizaje de la estadística con proyectos e identificar los factores que favorecen su aprendizaje. La investigación se fundamenta en la Reforma Integral de Educación Media Superior (RIEMS en México), la cual se implementó desde 2011 a través de un enfoque por competencias

Gravitational contribution to fermion masses

In the context of a nonlinear gauge theory of the Poincar\'e group, we show that covariant derivatives of Dirac fields include a coupling to the translational connections, manifesting itself in the matter action as a universal background mass contribution to fermions.Comment: revtex4, 9 pages, no figures, to be published in Eur.Phys.J.C, 200

Modeling Star counts in the Monoceros stream and the Galactic anti-centre

There is a continued debate as to the form of the outer disc of the Milky Way galaxy, which has important implications for its formation. Stars are known to exist at a galacto-centric distance of at least 20 kpc. However, there is much debate as to whether these stars can be explained as being part of the disc or whether another extra galactic structure, the so called Monoceros ring/stream, is required. To examine the outer disc of the Galaxy toward the anti-centre to determine whether the star counts can be explained by the thin and thick discs alone. Using Sloan star counts and extracting the late F and early G dwarfs it is possible to directly determine the density of stars out to a galacto-centric distance of about 25 kpc. These are then compared with a simple flared disc model. A flared disc model is shown to reproduce the counts along the line of sights examined, if the thick disc does not have a sharp cut off. The flare starts at a Galacto-centric radius of 16 kpc and has a scale length of 4.5+/-1.5 kpc. Whilst the interpretation of the counts in terms of a ring/stream cannot be definitely discounted, it does not appear to be necessary, at least along the lines of sight examined towards the anti centre.Comment: 11 pages, 4 figures, accepted to be published in A&

Efficacy of Bracing on Thoracic Kyphotic Angle and Functionality in Women with Osteoporosis: A Systematic Review

[Abstract] Background and purpose: Osteoporotic hyperkyphosis is associated with adverse outcomes, such as fatigue, back pain, or reduced back extensor strength, with a negative impact on functionality and quality of life. The purpose of this review is to assess the effectiveness of spinal orthosis on these adverse effects. Methods: A systematic review following the PRISMA guidelines was performed. Inclusion criteria were (1) women with osteoporosis; (2) randomized controlled trials only; and (3) type of intervention: spinal bracing. Exclusion criteria were (1) article not written in English; (2) full-text not available; and (3) no kyphosis assessment. Quality-of-life variables such as back pain, functional variables such as back extensor strength, and osteoporotic-related variables such as lumbar spine bone mineral density were extracted and recorded before and after the intervention. The characteristics of the intervention programs were also extracted and recorded. The characteristics of studies, interventions, and participants are summarized in a table. Then, the revised Cochrane risk-of-bias tool for randomized trials (RoB 2) was used to assess the quality of the studies. Results and Discussion: Four randomized controlled trials with a low risk of bias were included (n = 326 women with osteoporosis, aged 51–93 years). Interventions consisting of wearing a dynamic hyperextension orthosis for at least two hours per day for six months improved functionality, mobility, back extensor strength, respiratory function, and reduced the thoracic kyphosis angle. Conclusions: Spinal orthosis, especially dynamic hyperextension braces, seems effective in improving the adverse outcomes of osteoporotic hyperkyphosis. It does not seem necessary to wear the orthosis during all daily activities

Reaffirming the connection between the Galactic stellar warp and the Canis Major overdensity

We perform a critical re-analysis and discussion of recent results presented in the literature which interpret the CMa overdensity as the signature of an accreting dwarf galaxy or a new substructure within the Galaxy. Several issues are addressed. We show that arguments against the ``warp'' interpretation are based on an erroneous perception of the Milky Way. There is nothing anomalous with colour--magnitude diagrams on opposite sides of the average warp mid-plane being different. We witnessed the rise and fall of the blue plume population, first attributed to young stars in a disrupting dwarf galaxy and now discarded as a normal disc population. Similarly, there is nothing anomalous in the outer thin+thick disc metallicities being low (-1<[Fe/H]<-0.5), and spiral arms (as part of the thin disc) should, and do, warp. Most importantly, we show unambiguously that, contrary to previous claims, the warp produces a stellar overdensity that is distance-compatible with that observed in CMa.The CMa over-density remains fully accounted for in a first order approach by Galactic models without new substructures. Given the intrinsic uncertainties (concerning the properties of the warp, flare and disc cutoff, the role of extinction and degeneracy), minor deviations with respect to these models are not enough to support the hypothesis of an accreted dwarf galaxy or new substructure within the Milky Way disc.Comment: A&A Letter, accepted, 4 pages, 3 figure

The role of translational invariance in non linear gauge theories of gravity

The internal structure of the tetrads in a Poincar\'e non linear gauge theory of gravity is considered. Minkowskian coordinates becomes dynamical degrees of freedom playing the role of Goldstone bosons of the translations. A critical length allowing a covariant expansion similar to the weak field approach is deduced, the zeroth order metric being maximally symmetric (Minkowskian in some cases).Comment: 17 pages, LaTe