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Search Results: 1 - 10 of 542300 matches for " M. C. Verges "
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A note on the 3D Brans-Dicke theory
T. G. do Prado,V. S. Mendes,M. C. Verges
Physics , 2010,
Abstract: Since the evidence for an accelerated universe and the gap of 70% in the total energy, collected by WMAP, search for alternatives for the general relativity is an important issue, for this theory is not suited for these new phenomena. A particular alternative is the Brans-Dicke theory which has being allowing inspiring results, for example, concerning k-essence type fields in 4 dimensions. However, this theory is almost unexplored in the context of the dimensional reduction of the theory in 3 dimensions. In this work, we address some problems in this dimensional reduction, namely, evaluation of the deceleration parameter of the universe described by the 3 dimensional Brans-Dicke with and without matter. In both cases, we see that it is not possible to consider the theory as a model of k-essence descrybing the dark energy, but it can be considered as descrybing the dark matter.
The one-particle Green's function of one.dimensional insulating materials
M. C. Refolio,J. M. Lopez Sancho,J. Rubio,J. A. Verges
Physics , 2004,
Abstract: The single particle spectral-weight function (SWF) of the ionic Hubbard model at half filling is calculated in the cluster perturbation theory approximation. An abrupt change of regime in the low-energy region, near the chemical potential, is found at a critical value, $U_{c}$, of the coupling constant (Hubbard $U$). The SWF at the Fermi points $k_{F}$=$\pm{\pi}/2$ jumps, as $U$ increases, from a two-peak structure, the gap edges, to a four-peak structure accompanied by a (non-vanishing) minimum of the charge-gap. The two inner peaks of this structure show very small dispersion (flat bands) away from the Fermi points, whereas the outer peaks mark the edges of the Hubbard bands. No other signatures of abrupt change are detected in the SWF. The two regimes are physically realized in the angle-resolved photoelectron spectra of $(TaSe_{4})_{2}I$, and the blue-bronze $K_{0.3}MoO_{3}$, respectively.
Comparaison de méthode: A propos de l'article 'Apport des modèles graphiques gaussiens en analyse de similitude'
Verges, Pierre,Flament, C.
Papers on Social Representations , 1997,
Abstract:
Confinement of hydrodynamic modes on a free surface and their quantum analogs
M. Torres,J. P. Adrados,P. Cobo,A. Fernandez,C. Guerrero,G. Chiappe,E. Louis,J. A. Miralles,J. A. Verges,J. L. Aragon
Physics , 2005,
Abstract: A subtle procedure to confine hydrodynamic modes on the free surface of a fluid is presented here. The experiment consists of a square vessel with an immersed square central well vibrating vertically so that the surface waves generated by the meniscus at the vessel boundary interfere with the bound states of the well. This is a classical analogy of a quantum well where some fundamental phenomena, such as bonding of states and interference between free waves and bound states, can be visualized and controlled. The above mentioned interference leads to a novel hydrodynamic transition from quasiperiodic to periodic patterns. Tight binding numerical calculations are performed here to show that our results could be transferred to design quantum confinements exhibiting electronic quasiperiodic surface states and their rational approximants for the first time.
A Extended Cosmological Cardy-Verlinde Formula
Thiago G. Prado,Marcos C. Verges
Physics , 2010,
Abstract: E. Verlinde obtained a generalized formula for the entropy of a conformal field theory. For this we consider a (n+1) dimensional closed radiation dominated FLWR in the context of the holographic principle. In this work we construct a extension of the Cardy-Verlinde formula to positive cosmological constant spaces (dS spaces) with arbitrary topology
Magnetic Nanoparticles for Power Absorption: optimizing size, shape and magnetic properties
M. A. Gonzalez-Fernandez,T. Torres,M. Andres-Verges,R. Costo,P. de la Presa,C. J. Serna,M. P. Morales,C. Marquina,M. R. Ibarra,G. F. Goya
Physics , 2009, DOI: 10.1016/j.jssc.2009.07.047
Abstract: We present a study on the magnetic properties of naked and silica-coated Fe3O4 nanoparticles with sizes between 5 and 110 nm. Their efficiency as heating agents was assessed through specific power absorption (SPA) measurements as a function of particle size and shape. The results show a strong dependence of the SPA with the particle size, with a maximum around 30 nm, as expected for a Neel relaxation mechanism in single-domain particles. The SiO2 shell thickness was found to play an important role in the SPA mechanism by hindering the heat outflow, thus decreasing the heating efficiency. It is concluded that a compromise between good heating efficiency and surface functionality for biomedical purposes can be attained by making the SiO2 functional coating as thin as possible.
Metástasis cutánea de carcinoma de células renales
García Torrelles,M.; Beltrán Armada,J.R.; Verges Prosper,A.; Santolaya García,J.I.; Espinosa Ruiz,J.J.; Tarín Planes,M.; Sanjuán de Laorden,C.;
Actas Urológicas Espa？olas , 2007, DOI: 10.4321/S0210-48062007000500018
Abstract: renal cell carcinoma has an unknown evolution. we report a case of a man with a skin metastases from renal cell carcinoma and an unfortunate result, five years after its radical surgical treatment. we review the literature and emphasize the need of a long and exhaustive surveillance in these patients.
Classical trajectories in quantum transport at the band center of bipartite lattices with or without vacancies
G. Chiappe,E. Louis,M. J. Sanchez,J. A. Verges
Physics , 2003, DOI: 10.1103/PhysRevB.69.201405
Abstract: Here we report on several anomalies in quantum transport at the band center of a bipartite lattice with vacancies that are surely due to its chiral symmetry, namely: no weak localization effect shows up, and, when leads have a single channel the transmission is either one or zero. We propose that these are a consequence of both the chiral symmetry and the large number of states at the band center. The probability amplitude associated to the eigenstate that gives unit transmission ressembles a classical trajectory both with or without vacancies. The large number of states allows to build up trajectories that elude the blocking vacancies explaining the absence of weak localization.
Mean Free Path and Energy Fluctuations in Quantum Chaotic Billiards
E. Louis,E. Cuevas,J. A. Verges,M. Ortuno
Physics , 1997, DOI: 10.1103/PhysRevB.56.2120
Abstract: The elastic mean free path of carriers in a recently introduced model of quantum chaotic billiards in two and three dimensions is calculated. The model incorporates surface roughness at a microscopic scale by randomly choosing the atomic levels at the surface sites between -W/2 and W/2. Surface roughness yields a mean free path l that decreases as L/W^2 as W increases, L being the linear size of the system. But this diminution ceases when the surface layer begins to decouple from the bulk for large enough values of W, leaving more or less unperturbed states on the bulk. Consequently, the mean free path shows a minimum of about L/2 for W of the order of the band width. Energy fluctuations reflect the behavior of the mean free path. At small energy scales, strong level correlations manifest themselves by small values of the number of levels variance Sigma^2(E) that are close to Random Matrix Theory (RMT) in all cases. At larger energy scales, fluctuations are below the logarithmic behavior of RMT for l > L, and above RMT value when l < L.
Réaction à l'article de J.-M. Ramos
Verges, Pierre
Papers on Social Representations , 1994,
Abstract:
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