Institute dEstudis Catalans

Catalonia, Spain

Institute dEstudis Catalans

Catalonia, Spain

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Criado-Sancho M.,Spanish University for Distance Education (UNED) | Jou D.,Autonomous University of Barcelona | Jou D.,Institute DEstudis Catalans
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

We study heat transport in bulk/nanoporous/bulk silicon devices; we show that, despite bulk/nanoporous devices may act as thermal rectifiers, the non-linear aspects of their joint thermal conductance are not strong enough to lead to a negative differential thermal resistance, necessary to allow bulk/nanoporous/bulk Si devices to act as thermal transistors. Furthermore, we explicitly study the effective thermal conductivity of the mentioned devices for several temperatures, geometries, porosities, and pore size. © 2012 Elsevier B.V.


Sellitto A.,University of Basilicata | Alvarez F.X.,University of Barcelona | Jou D.,University of Barcelona | Jou D.,Institute dEstudis Catalans
International Journal of Heat and Mass Transfer | Year: 2012

The aim of this work is to analyze the shape dependence of the effective thermal conductivity of nanowires, based on the model of phonon hydrodynamics. In particular, we consider elliptical and rectangular nanowires, and we compare their respective thermal conductivities with those of circular nanowires and of wide thin plates. © 2012 Elsevier Ltd. All rights reserved.


Alvarez F.X.,Autonomous University of Barcelona | Jou D.,Autonomous University of Barcelona | Jou D.,Institute dEstudis Catalans | Sellitto A.,University of Basilicata
Applied Physics Letters | Year: 2010

Phonon hydrodynamics is used to analyze the influence of porosity and of pore size on reduction in thermal conductivity in porous silicon, with respect to crystalline silicon. The expressions predict that the thermal conductivity is lower for higher porosity and for smaller pore radius, as a consequence of phonon ballistic effects. The theoretical results describe experimental data better than the assumption that they only depend on porosity. © 2010 American Institute of Physics.


Jou D.,University of Barcelona | Jou D.,Institute dEstudis Catalans | Cimmelli V.A.,University of Basilicata | Sellitto A.,University of Basilicata
International Journal of Heat and Mass Transfer | Year: 2012

In the framework of Extended Irreversible Thermodynamics we develop a model for coupled heat conduction by phonons and electrons. Particular emphasis is given to nonlocal effects, which may arise when the mean-free paths of phonons and/or electrons are comparable to the size of the system. As particular cases, we recover two parabolic equations of the Guyer-Krumhansl type which model the concurrent presence of the diffusion of heat superposed to the propagation of heat waves, and two hyperbolic equations of the Maxwell-Cattaneo type. In the latter case, the phase speed of temperature waves is calculated. The size dependence of the Wiedemann-Franz law is briefly analyzed for metallic nanowires. © 2012 Elsevier Ltd. All rights reserved.


Sellitto A.,University of Basilicata | Cimmelli V.A.,University of Basilicata | Jou D.,Autonomous University of Barcelona | Jou D.,Institute dEstudis Catalans
Physica D: Nonlinear Phenomena | Year: 2012

Nonlinear effects may be especially relevant in heat transport at the nanoscale, because small temperature differences divided by minute lengths may yield very high temperature gradients. Here we discuss such effects using a generalized heat-transport equation, whose nonlinear terms are explored in three situations of potential practical interest, namely: length dependence of the thermal conductivity of carbon nanotubes, heat rectification in troncoconical nanowires, and anomalies in the temperature profile in radial heat transport in thin layers or graphene sheets. Their thermodynamic aspects are also discussed. © 2012 Elsevier B.V. All rights reserved.


Cimmelli V.A.,University of Basilicata | Sellitto A.,University of Basilicata | Jou D.,Autonomous University of Barcelona | Jou D.,Institute dEstudis Catalans
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

A dynamical nonequilibrium temperature has been proposed to describe relaxational equations for the heat flux. This temperature provides an alternative description to the Maxwell-Cattaneo equation. In the linear regime and in bulk systems both descriptions are equivalent but this is not so when nonlinear effects are included. Here we explore the influence of nonlinear terms on the phase speed of heat waves in nonequilibrium steady states in both theoretical models and we show that their predictions are different. This could allow to explore which description is more suitable, when experiments on these situations will become available. Furthermore, we have analyzed a nonlinear and nonlocal constitutive equation for the heat flux and we have shown its analogy with the Navier-Stokes equation in the regime of phonon hydrodynamics in nanosystems. This analogy allows one to define a dimensionless number for heat flow, analogous to the Reynolds number, and to predict a critical heat flux where nonlinear effects could become dominant. © 2010 The American Physical Society.


Cimmelli V.A.,University of Basilicata | Sellitto A.,University of Basilicata | Jou D.,Autonomous University of Barcelona | Jou D.,Institute dEstudis Catalans
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

A heat-transport equation incorporating nonlocal and nonlinear contributions of the heat flux is derived in the framework of weakly nonlocal nonequilibrium thermodynamics. The motivation for these terms arises from applications to nanosystems, where strong gradients are found, due to the small distance over which changes in temperature and heat flux take place. This equation generalizes to the nonlinear domain previous equations used in the context of phonon hydrodynamics. Compatibility with second law of thermodynamics is investigated and a comparison with the thermomass model of heat transport is carried out. The analogy between the equations describing the heat flow problem and the hydrodynamic equations is shown and the stability of the heat flow is analyzed in a special case. © 2010 The American Physical Society.


Sellitto A.,University of Basilicata | Cimmelli V.A.,University of Basilicata | Jou D.,Autonomous University of Barcelona | Jou D.,Institute dEstudis Catalans
International Journal of Heat and Mass Transfer | Year: 2013

Nonlocal transport equations for phonon and electron contributions to the heat flux, and for the electron contribution to the electric current, including thermoelectric effects, are proposed. The consequences of the nonlocal contributions on the figure-of-merit in nanowires are examined in two different situations regarding the relative values of the particles' mean-free path and the radius of nanowires. In both cases a dependence of the figure of merit on the transversal radius of the nanowire, as well as on some material coefficients related to the roughness of the walls, is pointed out. It is also shown how the figure-of-merit could be improved by controlling these coefficients. © 2012 Elsevier Ltd. All rights reserved.


Sellitto A.,University of Basilicata | Cimmelli V.A.,University of Basilicata | Jou D.,Autonomous University of Barcelona | Jou D.,Institute dEstudis Catalans
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The form and the role of the entropy flux in the thermodynamic analysis of the transport equations are essentially open questions in nonequilibrium thermodynamics. In particular, nonlocal heat-transport equations at nanoscale may exhibit some peculiar behaviors which seem to violate well-known statements of the second law of thermodynamics. Here we examine one of these behaviors in axial heat transport from the perspective of a generalized entropy flux, i.e., J(s)=q/T+k, and show that such a generalization allows it to be consistent with the second law. In contrast with previous formal analyses, this paper provides an explicit form for the nonclassical part of the entropy flux, that is, k=ℓ2/(λT2)qT·q and links it to a concrete physical phenomenon which is accessible to current experimental possibilities for systems with sufficiently long mean-free path ℓ, whereas for short enough ℓ the classical results are recovered. The derivation of the nonclassical part of the entropy flux is obtained within the frame of extended irreversible thermodynamics from two different perspectives, namely, a 13-field theory with higher-order fluxes and a 4-field theory with higher-order gradients. © 2013 American Physical Society.


Recasens D.,Autonomous University of Barcelona | Recasens D.,Institute dEstudis Catalans
Speech Communication | Year: 2012

Formant frequency data for /l/ in 23 languages/dialects where the consonant may be typically clear or dark show that the two varieties of /l/ are set in contrast mostly in the context of /i/ but also next to /a/, and that a few languages/dialects may exhibit intermediate degrees of darkness in the consonant. F2 for /l/ is higher utterance initially than utterance finally, more so if the lateral is clear than if it is dark; moreover, the initial and final allophones may be characterized as intrinsic (in most languages/dialects) or extrinsic (in several English dialects, Czech and Dutch) depending on whether the position-dependent frequency difference in question is below or above 200/300 Hz. The paper also reports a larger degree of vowel coarticulation for clear /l/ than for dark /l/ and in initial than in final position. These results are interpreted in terms of the production mechanisms involved in the realization of the two /l/ varieties in the different positional and vowel context conditions subjected to investigation. © 2011 Elsevier B.V. All rights reserved.

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