http://hdl.handle.net/10256/1544 2013-05-25T22:25:23Z 2013-05-25T22:25:23Z Pradell, Trinitat Climent-Font, A. Molera, J. Zucchiatti, A. Ynsa, M.D. Roura Grabulosa, Pere Crespo, D. http://hdl.handle.net/10256/7840 2013-05-14T00:00:40Z 2007-01-01T00:00:00Z

Metallic and nonmetallic shine in luster: An elastic ion backscattering study Pradell, Trinitat; Climent-Font, A.; Molera, J.; Zucchiatti, A.; Ynsa, M.D.; Roura Grabulosa, Pere; Crespo, D. Luster is a metal glass nanocomposite layer first produced in the Middle East in early Islamic times ( 9th AD) made of metal copper or silver nanoparticles embedded in a silica-based glassy matrix. These nanoparticles are produced by ion exchange between Cu+ and Ag+ and alkaline ions from the glassy matrix and further growth in a reducing atmosphere. The most striking property of luster is its capability of reflecting light like a continuous metal layer and it was unexpectedly found to be linked to one single production parameter: the presence of lead in the glassy matrix composition. The purpose of this article is to describe the characteristics and differences of the nanoparticle layers developed on lead rich and lead free glasses. Copper luster layers obtained using the ancient recipes and methods are analyzed by means of elastic ion backscattering spectroscopy associated with other analytical techniques. The depth profile of the different elements is determined, showing that the luster layer formed in lead rich glasses is 5–6 times thinner and 3–4 times Cu richer. Therefore, the metal nanoparticles are more densely packed in the layer and this fact is related to its higher reflectivity. It is shown that lead influences the structure of the metal nanoparticle layer through the change of the precipitation kinetics

2007-01-01T00:00:00Z Méndez López, Vicenç http://hdl.handle.net/10256/7839 2013-05-14T00:00:39Z 1998-01-01T00:00:00Z

Variational principles for nonlinear dynamical systems Méndez López, Vicenç A variational method for Hamiltonian systems is analyzed. Two different variational characterization for the frequency of nonlinear oscillations is also supplied for non-Hamiltonian systems

1998-01-01T00:00:00Z Fort, Joaquim Llebot, Josep Enric http://hdl.handle.net/10256/7838 2013-05-14T00:00:36Z 1998-01-01T00:00:00Z

Information-theoretical derivation of an extended thermodynamical description of radiative systems Fort, Joaquim; Llebot, Josep Enric A radiative equation of the Cattaneo–Vernotte type is derived from information theory and the radiative transfer equation. The equation thus derived is a radiative analog of the equation that is used for the description of hyperbolic heat conduction. It is shown, without recourse to any phenomenological assumption, that radiative transfer may be included in a natural way in the framework of extended irreversible thermodynamics

1998-01-01T00:00:00Z Rius, J. Figueras, M. Herrero, R. Farjas Silva, Jordi Pi i Vila, Francesc Orriols Tubella, Gaspar http://hdl.handle.net/10256/7834 2013-05-14T00:00:38Z 2000-01-01T00:00:00Z

N-dimensional dynamical systems exploiting instabilities in full Rius, J.; Figueras, M.; Herrero, R.; Farjas Silva, Jordi; Pi i Vila, Francesc; Orriols Tubella, Gaspar We report experimental and numerical results showing how certain N-dimensional dynamical systems are able to exhibit complex time evolutions based on the nonlinear combination of N-1 oscillation modes. The experiments have been done with a family of thermo-optical systems of effective dynamical dimension varying from 1 to 6. The corresponding mathematical model is an N-dimensional vector field based on a scalar-valued nonlinear function of a single variable that is a linear combination of all the dynamic variables. We show how the complex evolutions appear associated with the occurrence of successive Hopf bifurcations in a saddle-node pair of fixed points up to exhaust their instability capabilities in N dimensions. For this reason the observed phenomenon is denoted as the full instability behavior of the dynamical system. The process through which the attractor responsible for the observed time evolution is formed may be rather complex and difficult to characterize. Nevertheless, the well-organized structure of the time signals suggests some generic mechanism of nonlinear mode mixing that we associate with the cluster of invariant sets emerging from the pair of fixed points and with the influence of the neighboring saddle sets on the flow nearby the attractor. The generation of invariant tori is likely during the full instability development and the global process may be considered as a generalized Landau scenario for the emergence of irregular and complex behavior through the nonlinear superposition of oscillatory motions

2000-01-01T00:00:00Z Colomer, Jordi Serra Putellas, Teresa Casamitjana, Xavier http://hdl.handle.net/10256/7820 2013-05-09T00:00:41Z 2004-01-01T00:00:00Z

L' embassament de Boadella Colomer, Jordi; Serra Putellas, Teresa; Casamitjana, Xavier Article que descriu el règim hidrològic, les característiques fisicoquímiques de l'aigua i les partícules en suspensió a l' aigua de l' embassament de Boadella (Alt Empordà)

2004-01-01T00:00:00Z Fort, Joaquim Pujol i Sagaró, Toni Cavalli-Sforza, Luca http://hdl.handle.net/10256/7774 2013-05-04T00:00:46Z 2004-01-01T00:00:00Z

Palaeolithic Populations and Waves of Advance Fort, Joaquim; Pujol i Sagaró, Toni; Cavalli-Sforza, Luca The wave-of-advance model has been previously applied to Neolithic human range expansions, yielding good agreement to the speeds inferred from archaeological data. Here, we apply it for the first time to Palaeolithic human expansions by using reproduction and mobility parameters appropriate to hunter-gatherers (instead of the corresponding values for preindustrial farmers). The order of magnitude of the predicted speed is in agreement with that implied by the AMS radiocarbon dating of the lateglacial human recolonization of northern Europe (14.2–12.5 kyr BP). We argue that this makes it implausible for climate change to have limited the speed of the recolonization front. It is pointed out that a similar value for the speed can be tentatively inferred from the archaeological data on the expansion of modern humans into the Levant and Europe (42–36 kyr BP)

2004-01-01T00:00:00Z Pujol i Sagaró, Toni Llebot, Josep Enric http://hdl.handle.net/10256/7721 2013-04-13T00:00:41Z 2000-01-01T00:00:00Z

Extremal climatic states simulated by a 2-dimensional model Part II: Different climatic scenarios Pujol i Sagaró, Toni; Llebot, Josep Enric Different climatic simulations have been obtained by using a 2-Dim horizontal energy balancemodel (EBM), which has been constrained to satisfy several extremal principles on dissipationand convection. Moreover, 2 different versions of the model with fixed and variable cloud-coverhave been used. The assumption of an extremal type of behaviour for the climatic system canacquire additional support depending on the similarities found with measured data for pastconditions as well as with usual projections for possible future scenarios

2000-01-01T00:00:00Z Pujol i Sagaró, Toni Llebot, Josep Enric http://hdl.handle.net/10256/7720 2013-04-13T00:00:41Z 2000-01-01T00:00:00Z

Extremal climatic states simulated by a 2-dimensional model Part I: Sensitivity of the model and present state Pujol i Sagaró, Toni; Llebot, Josep Enric The criterion, based on the thermodynamics theory, that the climatic system tends to extremizesome function has suggested several studies. In particular, special attention has been devoted to the possibility that the climate reaches an extremal rate of planetary entropy production.Due to both radiative and material effects contribute to total planetary entropy production,climatic simulations obtained at the extremal rates of total, radiative or material entropy production appear to be of interest in order to elucidate which of the three extremal assumptions behaves more similar to current data. In the present paper, these results have been obtainedby applying a 2-dimensional (2-Dim) horizontal energy balance box-model, with a few independent variables (surface temperature, cloud-cover and material heat fluxes). In addition, climatic simulations for current conditions by assuming a fixed cloud-cover have been obtained. Finally,sensitivity analyses for both variable and fixed cloud models have been carried out

2000-01-01T00:00:00Z Pujol i Sagaró, Toni North, Gerald R. http://hdl.handle.net/10256/7719 2013-04-13T00:00:39Z 2003-01-01T00:00:00Z

Analytical investigation of the atmospheric radiation limits in semigray atmospheres in radiative equilibrium Pujol i Sagaró, Toni; North, Gerald R. We model the wavelength-dependent absorption of atmospheric gases by assuming constant mass absorption coefficients in finite-width spectral bands. Such a semigray atmosphere is analytically solved by a discrete ordinate method. The general solution is analyzed for a water vapor saturated atmosphere that also contains a carbon dioxide-like absorbing gas in the infrared. A multiple stable equilibrium with a relative upper limit in the outgoing long-wave radiation is found. Differing from previous radiative–convective models, we find that the amount of carbon dioxide strongly modifies the value of this relative upper limit. This result is also obtained in a gray (i.e., equal absorption of radiation at all infrared wavelengths) water vapor saturated atmosphere. The destabilizing effect of carbon dioxide implies that massive carbon dioxide atmospheres are more likely to reach a runaway greenhouse state than thin carbon dioxide ones

2003-01-01T00:00:00Z Pujol i Sagaró, Toni Fort, Joaquim http://hdl.handle.net/10256/7718 2013-04-13T00:00:40Z 2002-01-01T00:00:00Z

States of maximum entropy production in a onedimensional vertical model with convective adjustment Pujol i Sagaró, Toni; Fort, Joaquim We investigate the hypothesis that the atmosphere is constrained to maximize its entropy production by using a one-dimensional (1-D) vertical model. We prescribe the lapse rate in the convective layer as that of the standard troposphere. The assumption that convection sustains a critical lapse rate was absent in previous studies, which focused on the vertical distribution of climatic variables, since such a convective adjustment reduces the degrees of freedom of the system and may prevent the application of the maximum entropy production (MEP) principle. This is not the case in the radiative–convective model (RCM) developed here, since we accept a discontinuity of temperatures at the surface similar to that adopted in many RCMs. For current conditions, the MEP state gives a difference between the ground temperature and the air temperature at the surface ≈10 K. In comparison, conventional RCMs obtain a discontinuity ≈2 K only. However, the surface boundary layer velocity in the MEP state appears reasonable (≈3 m s-¹). Moreover, although the convective flux at the surface in MEP states is almost uniform in optically thick atmospheres, it reaches a maximum value for an optical thickness similar to current conditions. This additional result may support the maximum convection hypothesis suggested by Paltridge (1978)

2002-01-01T00:00:00Z