On a pair of difference equations for the 4F3_4F_3 type orthogonal polynomials and related exactly-solvable quantum systems

We introduce a pair of novel difference equations, whose solutions are expressed in terms of Racah or Wilson polynomials depending on the nature of the finite-difference step. A number of special cases and limit relations are also examined, which allow to introduce similar difference equations for the orthogonal polynomials of the $_3 F_2$ and $_2 F_1$ types. It is shown that the introduced equations allow to construct new models of exactly-solvable quantum dynamical systems, such as spin chains with a nearest-neighbour interaction and fermionic quantum oscillator models.Comment: 8 pages, to be published in Springer Proceedings in Mathematics & Statistic

Dynamical measure and field theory models free of the cosmological constant problem

Summary of abstract Field theory models including gauge theories with SSB are presented where the energy density of the true vacuum state (TVS) is zero without fine tuning. The above models are constructed in the gravitational theory where a measure of integration \Phi in the action is not necessarily \sqrt{-g} but it is determined dynamically through additional degrees of freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in terms of the matter degrees of freedom due to the existence of a constraint. We study a few explicit field theory models where it is possible to combine the solution of the cosmological constant problem with: 1) possibility for inflationary scenario for the early universe; 2) spontaneously broken gauge unified theories (including fermions). The models are free from the well known problem of the usual scalar-tensor theories in what is concerned with the classical GR tests. The only difference of the field equations in the Einstein frame from the canonical equations of the selfconsistent system of Einstein's gravity and matter fields, is the appearance of the effective scalar field potential which vanishes in TVS without fine tuning.Comment: Extended version of the contribution to the fourth Alexander Friedmann International Seminar on Gravitation and Cosmology; accepted for publication in Phys. Rev. D; 31 page

Superextendons with a modified measure

For superstrings, the consequences of replacing the measure of integration $\sqrt{-\gamma}d^2 x$ in the Polyakov's action by $\Phi d^2 x$ where $\Phi$ is a density built out of degrees of freedom independent of the metric $\gamma_{ab}$ defined in the string are studied. As in Siegel reformulation of the Green Schwarz formalism the Wess-Zumino term is the square of supersymmetric currents. As opposed to the Siegel case, the compensating fields needed for this do not enter into the action just as in a total derivative. They instead play a crucial role to make up a consistent dynamics. The string tension appears as an integration constant of the equations of motion. The generalization to higher dimensional extended objects is also studied using in this case the Bergshoeff and Sezgin formalism with the associated additional fields, which again are dynamically relevant unlike the standard formulation. Also unlike the standard formulation, there is no need of a cosmological term on the world brane.Comment: typos corrected, references adde

The chemistry of La on the Si(001) surface

This paper reports state-of-the-art electronic structure calculations of La adsorption on the Si(001) surface. We predict La chains in the low coverage limit, which condense in a stable phase at a coverage of 1/5 monolayer. At 1/3 monolayer we predict a chemically rather inert, stable phase. La changes its oxidation state from La(3+) at lower coverages to La(2+) at coverages beyond 1/3 monolayer. In the latter oxidation state, one electron resides in a state with a considerable contribution from La-d and f states.Comment: 10 pages, 13 figures, 3 table

The Rashba Hamiltonian and electron transport

The Rashba Hamiltonian describes the splitting of the conduction band as a result of spin-orbit coupling in the presence of an external field and is commonly used to model the electronic structure of confined narrow-gap semiconductors. Due to the mixing of spin states some care has to be exercised in the calculation of transport properties. We derive the velocity operator for the Rashba-split conduction band and demonstrate that the transmission of an interface between a ferromagnet and a Rashba-split semiconductor does not depend on the magnetization direction, in contrast with previous assertions in the literature.Comment: one tex file, two figures; paper to appear in this form in PRB (RC

Continuity theorems for the M/M/1/nM/M/1/n queueing system

In this paper continuity theorems are established for the number of losses during a busy period of the $M/M/1/n$ queue. We consider an $M/GI/1/n$ queueing system where the service time probability distribution, slightly different in a certain sense from the exponential distribution, is approximated by that exponential distribution. Continuity theorems are obtained in the form of one or two-sided stochastic inequalities. The paper shows how the bounds of these inequalities are changed if further assumptions, associated with specific properties of the service time distribution (precisely described in the paper), are made. Specifically, some parametric families of service time distributions are discussed, and the paper establishes uniform estimates (given for all possible values of the parameter) and local estimates (where the parameter is fixed and takes only the given value). The analysis of the paper is based on the level crossing approach and some characterization properties of the exponential distribution.Comment: Final revision; will be published as i

The Particle Spectrum of Heterotic Compactifications

Techniques are presented for computing the cohomology of stable, holomorphic vector bundles over elliptically fibered Calabi-Yau threefolds. These cohomology groups explicitly determine the spectrum of the low energy, four-dimensional theory. Generic points in vector bundle moduli space manifest an identical spectrum. However, it is shown that on subsets of moduli space of co-dimension one or higher, the spectrum can abruptly jump to many different values. Both analytic and numerical data illustrating this phenomenon are presented. This result opens the possibility of tunneling or phase transitions between different particle spectra in the same heterotic compactification. In the course of this discussion, a classification of SU(5) GUT theories within a specific context is presented.Comment: 77 pages, 3 figure

Physical activity, mindfulness meditation, or heart rate variability biofeedback for stress reduction: a randomized controlled trial

In contemporary western societies stress is highly prevalent, therefore the need for stress-reducing methods is great. This randomized controlled trial compared the efficacy of self-help physical activity (PA), mindfulness meditation (MM), and heart rate variability biofeedback (HRV-BF) in reducing stress and its related symptoms. We randomly allocated 126 participants to PA, MM, or HRV-BF upon enrollment, of whom 76 agreed to participate. The interventions consisted of psycho-education and an introduction to the specific intervention techniques and 5 weeks of daily exercises at home. The PA exercises consisted of a vigorous-intensity activity of free choice. The MM exercises consisted of guided mindfulness meditation. The HRV-BF exercises consisted of slow breathing with a heart rate variability biofeedback device. Participants received daily reminders for their exercises and were contacted weekly to monitor their progress. They completed questionnaires prior to, directly after, and 6 weeks after the intervention. Results indicated an overall beneficial effect consisting of reduced stress, anxiety and depressive symptoms, and improved psychological well-being and sleep quality. No significant between-intervention effect was found, suggesting that PA, MM, and HRV-BF are equally effective in reducing stress and its related symptoms. These self-help interventions provide easily accessible help for people with stress complaints

KINDERTIVITY: Using Interactive Surfaces to Foster Creativity in Pre-kindergarten Children

© Owner/Author 2015. This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in {Interacción '15 Proceedings of the XVI International Conference on Human Computer Interactionhttp://dx.doi.org/10.1145/10.1145/2829875.2829881Taking into account the existent educative and pedagogical techniques, which have proved its effectiveness to foster the innovation and creativity, this thesis poses to develop, experiment and evaluate a new technological framework based on interactive surfaces to be applied in the context of preschool education. The goal is to facilitate the three factors required for creative learning: knowledge, creative thinking and motivation but taking into account the cognitive and interaction limitations of these very young users.Work supported by the MINECO (grants TIN2010-20488 and TIN2014-60077-R) and from GVA (ACIF/2015/075).Nácher-Soler, VE.; Jaén Martínez, FJ. (2015). KINDERTIVITY: Using Interactive Surfaces to Foster Creativity in Pre-kindergarten Children. ACM. https://doi.org/10.1145/2829875.2829881SBuxton, B. Multi-touch systems that I have known and loved. 2013. http://billbuxton.com/multitouchOverview.html.Catala, A., Jaen, J., van Dijk, B., and Jordà, S. Exploring tabletops as an effective tool to foster creativity traits. In Proc. of TEI'12, pp. 143--150.Comisión Europea. Conclusiones del Consejo de 12 de mayo de 2009 sobre un marco estratégico para la cooperación europea en el ámbito de la educación y la formación («ET 2020»). 2009.Common Sense Media. Zero to Eight: Childrens Media Use in America 2013. 2013.Cropley, A.J. Creativity in Education and Learning: A Guide for Teachers and Educators. Kogan Page, (2001).Damon, W., Lerner, R.M., Kuhn, D., and Siegler, R.S., eds. Handbook of Child Psychology, Volume 2, Cognition, Perception, and Language. Wiley, 2006.Fleck, R., Rogers, Y., Yuill, N., et al. Actions speak loudly with words. Proc. of ITS'09, pp. 189--196.Helmes, J., Cao, X., Lindley, S.E., and Sellen, A. Developing the story. Proc. of ITS'09, pp. 49--52.Hourcade, J.P. Interaction Design and Children. Foundations and Trends® in Human-Computer Interaction 1, 4 (2007), 277--392.Johnson, L., Adams, S., and Cummins, M. The NMC Horizon Report: 2012 K-12. The New Media Consortium, Austin, Texas, 2012.Khandelwal, M. and Mazalek, A. Teaching table: a tangible mentor for pre-k math education. Proc. of TEI'07, 191--194.Mansor, E.I., De Angeli, A., and De Bruijn, O. Little fingers on the tabletop: A usability evaluation in the kindergarten. Proc. of TABLETOP'08, 93--96.Nacher, V., Jaen, J., & Catala, A. (2014). Exploring Visual Cues for Intuitive Communicability of Touch Gestures to Pre-kindergarten Children. Proc. of ITS'14, 159--162.Nacher, V., Jaen, J., Navarro, E., Catala, A., and González, P. Multi-touch gestures for pre-kindergarten children. International Journal of Human-Computer Studies 73 (2015), 37--51.Nacher, V., Jaen, J., Catala, A., Navarro, E., and Gonzalez, P. Improving Pre-Kindergarten Touch Performance. Proc. of ITS '14, 163--166..Rick, J., Francois, P., Fields, B., Fleck, R., Yuill, N., and Carr, A. Lo-fi prototyping to design interactive-tabletop applications for children. Proc. of IDC'10, pp. 138--146.Rick, J. and Rogers, Y. From DigiQuilt to DigiTile: Adapting educational technology to a multi-touch table. Proc. of TABLETOP'08, pp. 73--80.Sluis, R.J.W., Weevers, I., van Schijndel, C.H.G.J., Kolos-Mazuryk, L., Fitrianie, S., and Martens, J.B.O.S. Read-It: Five-to-seven-year-old children learn to read in a tabletop environment. Proc. of IDC'04, pp. 73--80.Smith, S.P., Burd, E., and Rick, J. Developing, evaluating and deploying multi-touch systems. International Journal of Human-Computer Studies 70, 10 (2012), 653--656

Effects of dimensionality and anisotropy on the Holstein polaron

We apply weak-coupling perturbation theory and strong-coupling perturbation theory to the Holstein molecular crystal model in order to elucidate the effects of anisotropy on polaron properties in D dimensions. The ground state energy is considered as a primary criterion through which to study the effects of anisotropy on the self-trapping transition, the self-trapping line associated with this transition, and the adiabatic critical point. The effects of dimensionality and anisotropy on electron-phonon correlations and polaronic mass enhancement are studied, with particular attention given to the polaron radius and the characteristics of quasi-1D and quasi-2D structures. Perturbative results are confirmed by selected comparisons with variational calculations and quantum Monte Carlo data