Mostrando recursos 121 - 140 de 106,577

  1. Modelling of plasmodic and graphene nanodevices. Modelización de nanodispositivos plasmódicos y de grafeno.

    Munárriz Arrieta, Javier

  2. Reflectividad en estructuras compuesto-metal. Permitividad eléctrica y permeabilidad magnética efectivas de compuestos

    Flores Vidal, María de la Sierra

  3. Pion gas viscosity at low temperature and density

    Dobado González, Antonio; Santalla Arribas, Silvia Noemí
    By using chiral perturbation theory and the Uehling-Uhlenbeck equation we compute the viscosity of a pion gas, in the low temperature and low density regime, in terms of the temperature and the pion fugacity. The viscosity turns out to be proportional to the square root of the temperature over the pion mass. Next to leading corrections are proportional to the temperature over the pion mass to 3/2.

  4. Self-interactions of the lightest minimal supersymmetric standard model Higgs boson in the large pseudoscalar-mass limit

    Dobado González, Antonio; Herrero, M. J.; Hollik, W.; Peñaranda , Siannah
    We investigate the decoupling properties of the Higgs-sector-induced one-loop corrections in the lightest Higgs-boson self-couplings, in the framework of the minimal supersymmetric standard model (MSSM). The renormalized n-point vertex functions with external Higgs particles in the MSSM and in the SM are derived to the one-loop level and compared in the M(A)(0)much greater thanM(Z) limit. The computation has been done in a general R-xi gauge and the on-shell renormalization scheme is chosen. By a comparison of the renormalized lightest Higgs-boson h(0) vertex functions with respect to the corresponding SM ones, we find that the differences between the predictions of both...

  5. Is the CMB cold spot a gate to extra dimensions?

    Ruiz Cembranos , José Alberto; Cruz Dombriz, Álvaro de la; Dobado González, Antonio; López Maroto, Antonio
    One of the most striking features found in the cosmic microwave background data is the presence of an anomalous cold spot (CS) in the temperature maps made by the Wilkinson Microwave Anisotropy Probe (WMAP). This CS has been interpreted as the result of the presence of a collapsing texture, perhaps coming from some early universe grand unified theory (GUT) phase transition. In this work we propose an alternative explanation based on a completely different kind of texture which appears in a natural way in a broad class of brane-world models. This type of texture, known as a brane-skyrmion, can be...

  6. Thermal rho and sigma mesons from chiral symmetry and unitarity

    Dobado González, Antonio; Gómez Nicola, Ángel; Llanes Estrada, Felipe J.; Peláez Sagredo, José Ramón
    We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pipi scattering amplitude in chiral perturbation theory at Tnot equal0 is unitarized via the inverse amplitude method. Our results predict a clear increase with T of both the rho and sigma widths. The masses decrease slightly for high T, while the rhopipi coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration.

  7. Phenomenological implications of brane world scenarios with low tension

    Ruiz Cembranos, José Alberto; Dobado González, Antonio; López Maroto, Antonio
    The recent proposal of theories with compactified large extra dimensions is reviewed. We pay especial attention to brane world models with low tension where the only relevant degrees of freedom at low energies are the Standard Model (SM) particles and the branons, which are transversal brane oscillations. By using an effective Lagrangian, we study some phenomenological consequences of these scenarios in a model independent way.

  8. XANES and EXAFS study of the local order in nanocrystalline yttria-stabilized zirconia

    Durá, O. J.; Boada, R.; López de la Torre, M.A.; Aquilanti, G.; Rivera Calzada, Alberto Carlos; León Yebra, Carlos; Chaboy, J.
    The local order around Zr and Y atoms of nanocrystalline yttria-stabilized zirconia (YSZ) powders with different grain sizes has been investigated by x-ray absorption spectroscopies. The samples were prepared by means of mechanical alloying with or without subsequent sintering treatment and also by milling commercial YSZ. Our study is motivated by the interest in the electrical properties of grain boundaries and the controversy about the level of disorder in the intergrain regions in nanocrystalline YSZ. The x-ray absorption near edge structure (XANES) analysis indicates that the local order of all the sintered samples is independent of the grain size. This is confirmed by the analysis...

  9. Disorder-controlled superconductivity at YBa2Cu3O7/SrTiO3 interfaces

    Garcia Barriocanal, Javier; Perez Muñoz, A.M.; Sefrioui, Zouhair; Arias, D.; Varela del Arco, María; León Yebra, Carlos; Pennycook, S.J.; Santamaria Sánchez-Barriga, Jacobo
    We examine the effect of interface disorder in suppressing superconductivity in coherently grown ultrathin YBa2Cu3O7 (YBCO) layers on SrTiO3 (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO2 and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intracell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO2 planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers.

  10. Turbulent shear flow over active and passive porous surfaces

    Jiménez, J.; Uhlmann, Markus; Pinelli, Alfredo; Kawahara, Genta
    The behaviour of turbulent shear flow over a mass-neutral permeable wall is studied numerically. The transpiration is assumed to be proportional to the local pressure fluctuations. It is first shown that the friction coefficient increases by up to 40% over passively porous walls, even for relatively small porosities. This is associated with the presence of large spanwise rollers, originating from a linear instability which is related both to the Kelvin–Helmholtz instability of shear layers, and to the neutral inviscid shear waves of the mean turbulent profile. It is shown that the rollers can be forced by patterned active transpiration through...

  11. Thermophoretic sampling of combustion particles from a fluidized bed combustor

    Sanz, D.; Muñoz, R.; Armesto, L.; Hontañón, E.; Pinelli, Alfredo; Espigares, M. M.

  12. Toward direct numerical simulation of reacting fluidized beds

    Uhlmann, Markus; Pinelli, Alfredo; García Ybarra, P. L.
    Nowadays, the most used techniques to design dense gas-solid flow reactors rely upon numerical predictions obtained from hydrodynamic models, usually derived through some averaging processes of the complete conservation equations. The averaging process leads to unknown correlation terms that need further modeling for the final closure of the equations. Many of these terms represent complex interactions between phases and are usually modeled through semi-empirical relations. Direct Numerical Simulation (DNS) of idealized situations can help in grasping the basic mechanisms governing these systems, therefore fostering the development of improved models.

  13. Interaction of multiple flapping filaments for cylinder wake modification using the Lattice Boltzmann Method

    Revell, A.; Favier, J.; Pinelli, Alfredo
    This paper introduces the recent work undertaken on the development of a code based on the combination of the Lattice Boltzmann Method (LBM) with a recent version of the Immersed Boundary Method (IBM). The code is first validated against existing results, before being applied to investigate the different modes of flapping behaviour for single and multiple filaments at various separation distances. The work proceeds to investigate the cylinder wake modification for moderate Reynolds number when groups of said filaments are attached to the ley-side of a circular cylinder.

  14. Large Eddy simulation of turbulence on an alliant FX computer

    Benocci, C.; Pinelli, Alfredo; Abba, A.

  15. A two dimensional Chebyshev collocated multi-domain algorithm for the incompressible Navier-Stokes equations

    Pinelli, Alfredo; Vacca, A.

  16. Preconditioned parallel algorithms and spectral solutions for the incompressible Navier-Stokes equations

    Pinelli, Alfredo

  17. A new multi-domain algorithm for the spectral solution of the incompressible Navier-Stokes equations

    Pinelli, Alfredo; Vacca, A.

  18. A parallel spectral multi-domain solver suitable for DNS and LES numerical simulation of incompressible flows

    Pinelli, Alfredo; Vacca, A.

  19. The autonomous near-wall turbulent cycle

    Jiménez, J.; Pinelli, Alfredo
    The regeneration cycle of near-wall turbulence is investigated by numerical experiments in which different possibly-important effects are selectively removed either from the equations of motions or from the boundary conditions. A candidate is considered important to the cycle if its removal results in substantial damping or decay of the turbulence intensity. Other effects, although probably present, are considered secondary. It is shown in this way that neither the presence of a turbulent core nor the generation of secondary vorticity at the wall are important in the generation of turbulence, while the presence of low-velocity streaks is crucial. Damping the streaks,...

  20. The autonomous near-wall turbulent region

    Jiménez, J.; Pinelli, Alfredo
    The near-wall region is the only place in zero-pressure-gradient boundary layer where the production of turbulent energy exceeds dissipation. The excess energy helps maintain turbulence in the core region, where the opposite is true. It is shown that it is possible to maintain turbulence in the region below y^+≈ 60 without any input from the outer flow. In the numerical experiment all the fluctuations in a plane channel are artificially damped by increasing viscosity with height, and the outer flow is laminar above that level. The near-wall region nevertheless survives indefinitely, suggesting that wall turbulence can be studied in terms...

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