Towards an Ashtekar formalism in eight dimensions

We investigate the possibility of extending the Ashtekar theory to eight dimensions. Our approach relies on two notions: the octonionic structure and the MacDowell-Mansouri formalism generalized to a spacetime of signature 1+7. The key mathematical tool for our construction is the self-dual (antiself-dual) four-rank fully antisymmetric octonionic tensor. Our results may be of particular interest in connection with a possible formulation of M-theory via matroid theory.Comment: 15 pages, Latex, minor changes, to appear in Class. Quantum Gra

Exercises using a touchscreen tablet application improved functional ability more than an exercise program prescribed on paper in people after surgical carpal tunnel release: a randomised trial

Question: In people who have undergone surgical carpal tunnel release, do sensorimotor-based exercises performed on the touchscreen of a tablet device improve outcomes more than a conventional home exercise program prescribed on paper? Design: Randomised, parallel-group trial with concealed allocation, assessor blinding, and intention-to-treat analysis. Participants: Fifty participants within 10 days of surgical carpal tunnel release. Intervention: Each participant was prescribed a 4-week home exercise program. Participants in the experimental group received the ReHand tablet application, which administered and monitored exercises via the touchscreen. The control group was prescribed a home exercise program on paper, as is usual practice in the public hospital system. Outcome measures: The primary outcome was functional ability of the hand, reported using the shortened form of the Disabilities of the Arm, Shoulder and Hand (QuickDASH) questionnaire. Secondary outcomes were grip strength, pain intensity measured on a 10-cm visual analogue scale, and dexterity measured with the Nine-Hole Peg Test. Outcomes were measured by a blinded assessor at baseline and at the end of the 4-week intervention period. Results: At Week 4, functional ability improved significantly more in the experimental group than the control group (MD –21, 95% CI –33 to –9) on the QuickDASH score (0 to 100). Although the mean estimates of effect on the secondary outcome also all favoured the experimental group, none reached statistical significance: grip strength (MD 5.6 kg, 95% CI –0.5 to 11.7), pain (MD –1.4 cm, 95% CI –2.9 to 0.1), and dexterity (MD –1.3 seconds, 95% CI –3.7 to 1.1). Conclusion: Use of the ReHand tablet application for early rehabilitation after carpal tunnel release is more effective in the recovery of functional ability than a conventional home exercise program. It remains unclear whether there are any benefits in grip strength, pain or dexterity. Trial registration: ACTRN12618001887268

Self-dual gravity and self-dual Yang-Mills in the context of Macdowell-Mansouri formalism

In this work we propose an action which unifies self-dual gravity and self-dual Yang-Mills in the context of the Macdowell-Mansouri formalism. We claim that such an action may be used to find the S-dual action for both self-dual gravity and self-dual Yang-Mills.Comment: 8 pages, Revtex, no figures, submitted to Phys. Rev.

Hamiltonian Noether theorem for gauge systems and two time physics

The Noether theorem for Hamiltonian constrained systems is revisited. In particular, our review presents a novel method to show that the gauge transformations are generated by the conserved quantities associated with the first class constraints. We apply our results to the relativistic point particle, to the Friedberg et al. model and, with special emphasis, to two time physics.Comment: 20 pages, Latex, references added, the "massless" sense of (87) is clarifie

Impact of land cover change on ecosystem service supply in mountain systems: a case study in the Cantabrian Mountains (NW of Spain)

P. 529–542Land abandonment and the loss of traditional farming practices are thought to control land cover dynamics, and hence the ecosystem service supply in traditionally managed mountain landscapes. We evaluate the impact of land cover changes in Cantabrian Mountains (NW Spain), over 1990–2012, on the potential supply capacity of ecosystem services (regulating, provisioning, and cultural) at both regional and local scales. We also analyze trends in the use of ecosystem services at the local scale. Land cover changes were estimated from CORINE Land Cover database. Patterns of potential ecosystem service supply were assessed by applying an ecosystem service supply capacity matrix and trends in their actual use by using field data. Main trajectories of land cover change encompassed woody vegetation spread in semi-natural open systems and agricultural expansion in the most suitable areas. The capacity of landscape to provide ecosystem services improved during 1990–2012 at both scales. We detected trade-offs between the potential supply of ecosystem services associated to natural systems and those linked to traditional land uses, at both regional and local scales. Changes in the potential supply of ecosystem services matched trends in ecosystem service use. This study could help develop future scenarios to address upcoming challenges in ecosystem service supplyS

Intensity Distribution of Modes in Surface Corrugated Waveguides

Exact calculations of transmission and reflection coefficients in surface randomly corrugated optical waveguides are presented. As the length of the corrugated part of the waveguide increases, there is a strong preference to forward coupling through the lowest mode. An oscillating behavior of the enhanced backscattering as a function of the wavelength is predicted. Although the transport is strongly non isotropic, the analysis of the probability distributions of the transmitted waves confirms in this configuration distributions predicted by Random Matrix Theory for volume disorder

Gravitational Duality in MacDowell-Mansouri Gauge Theory

Strong-weak duality invariance can only be defined for particular sectors of supersymmetric Yang-Mills theories. Nevertheless, for full non-Abelian non-supersymmetric theories, dual theories with inverted couplings, have been found. We show that an analogous procedure allows to find the dual action to the gauge theory of gravity constructed by the MacDowell-Mansouri model plus the superposition of a $\Theta$ term.Comment: 9 pages, LaTeX, no figure

Resonant radiation pressure on neutral particles in a waveguide

A theoretical analysis of electromagnetic forces on neutral particles in an hollow waveguide is presented. We show that the effective scattering cross section of a very small (Rayleigh) particle can be strongly modified inside a waveguide. The coupling of the scattered dipolar field with the waveguide modes induce a resonant enhanced backscattering state of the scatterer-guide system close to the onset of new modes. The particle effective cross section can then be as large as the wavelength even far from any transition resonance. As we will show, a small particle can be strongly accelerated along the guide axis while being highly confined in a narrow zone of the cross section of the guide.Comment: RevTeX,4 pages,3 PS figure

Priming human adipose-derived mesenchymal stem cells for corneal surface regeneration.

Limbal stem cells (LSC) maintain the transparency of the corneal epithelium. Chemical burns lead the loss of LSC inducing an up-regulation of pro-inflammatory and pro-angiogenic factors, triggering corneal neovascularization and blindness. Adipose tissue-derived mesenchymal stem cells (AT-MSC) have shown promise in animal models to treat LSC deficiency (LSCD), but there are not studies showing their efficacy when primed with different media before transplantation. We cultured AT-MSC with standard medium and media used to culture LSC for clinical application. We demonstrated that different media changed the AT-MSC paracrine secretion showing different paracrine effector functions in an in vivo model of chemical burn and in response to a novel in vitro model of corneal inflammation by alkali induction. Treatment of LSCD with AT-MSC changed the angiogenic and inflammatory cytokine profile of mice corneas. AT-MSC cultured with the medium that improved their cytokine secretion, enhanced the anti-angiogenic and anti-inflammatory profile of the treated corneas. Those corneas also presented better outcome in terms of corneal transparency, neovascularization and histologic reconstruction. Priming human AT-MSC with LSC specific medium can potentiate their ability to improve corneal wound healing, decrease neovascularization and inflammation modulating paracrine effector functions in an in vivo optimized rat model of LSCD

Remarks on 2+1 Self-dual Chern-Simons Gravity

We study 2+1 Chern-Simons gravity at the classical action level. In particular we rederive the linear combinations of the ``standard'' and ``exotic'' Einstein actions, from the (anti) self-duality of the ``internal'' Lorentzian indices. The relation to a genuine four-dimensional (anti)self-dual topological theory greatly facilitates the analysis and its relation to hyperbolic three-dimensional geometry. Finally a non-abelian vector field ``dual'' action is also obtained.Comment: 16+1 pages, LaTeX file, no figures, clarifications and comments added, typos corrected and one reference adde