1,721,424 research outputs found
Enhanced Model for the Analysis of Thermoelectric Effects at Nanoscale: Onsager’s Method and Liu’s Technique in Comparison
No full text: The aim of this paper is twofold. From the practical point of view, an enhanced model for the description of thermoelectric effects at nanoscale is proposed. From the theoretical point of view, instead, in the particular case of the proposed model, the equivalence between two classical techniques for the exploitation of the second law of thermodynamics is shown, i.e., Onsager's method and Liu's technique. An analysis of the heat-wave propagation is performed as well
High-order fluxes in heat transfer with phonons and electrons: Application to wave propagation
No full textWe propose a theoretical model to study heat transfer at the nanoscale by means of high-order thermodynamic fluxes. The model is fully compatible with the model of heat transfer of extended irreversible thermodynamics, represents a generalization of the Guyer-Krumhansl proposal (Guyer & Krumhansl 1966 Phys. Rev. 148) and is able to deal with relaxational and non-local effects. It also accounts for the role played by the different heat carriers (electrons and/or lattice vibrations) and captures different heat-carrier temperatures. The proposed model is hyperbolic and is used to investigate the propagation of thermal waves
Nonlinear heat waves and some analogies with nonlinear optics
No full textThe linear theory of heat waves is generalized to nonlinear situations in a conservation-dissipation formalism in the context of extended thermodynamics. An analogy with the theory of nonlinear electromagnetic waves is pointed out. This analogy emphasizes several physical aspects of the nonlinear theory and allows a parallelism with nonlinear optics, which may be of interest in nonlinear phononics. The proposed nonlinear equation for heat waves is compared with nonlinear transport equations in other fields of non-equilibrium thermodynamics, and it is applied to second-harmonic generation of heat waves in graded materials
Heat-flux dependence of the speed of nonlinear heat waves: Analogies with the Kerr effect in nonlinear optics
No full textWe study the consequences of a nonlinear generalization of the Maxwell–Cattaneo equation on the speed of propagation of nonlinear thermal waves. It turns out that such speed depends on the amplitude of the waves and it is smaller than the speed of linear (small-amplitude) waves. This is analogous to the optical Kerr effect of nonlinear optics. In analogy with the electro-optical Kerr effect, an imposed external heat flux could be used to control the speed of thermal waves in a material layer. As a particular illustration, we consider an externally tunable lens for heat waves propagating in the layer
Nonlocal and nonlinear effects in hyperbolic heat transfer in a two-temperature model
No full textThe correct analysis of heat transport at nanoscale is one of the main reasons of new developments in physics and nonequilibrium thermodynamic theories beyond the classical Fourier law. In this paper, we provide a two-temperature model which allows to describe the different regimes which electrons and phonons can undergo in the heat transfer phenomenon. The physical admissibility of that model is showed in view of second law of thermodynamics. The above model is applied to study the propagation of heat waves in order to point out the special role played by nonlocal and nonlinear effects
An Accurate Equivalent Circuit of High Power/High Frequency Planar Transformers using FEM
No full textThis paper presents an equivalent circuit of high frequency/high power planar transformers obtained using the Finite Element Method. The main transformer parameters: resistances, inductances and capacitances are computed considering different winding arrangements, evaluating and comparing their equivalent circuits and behaviors. In order to validate the proposed procedure that computes the planar transformer electrical parameters, a prototype has been realized. A real application is proposed and the numerical results are compared to the measured ones. The good agreement between them confirms the accuracy of the extracted equivalent circuit of the planar transformer
Wave propagation at nano-scale in coupled transport phenomena: application to thermoelectricity
No full textThe analysis of coupled transport phenomena is one of the most outstanding aspects of non-equilibrium thermodynamics. In this paper the attention is put on thermoelectricity, i.e., the coupling of heat and electricity. We propose a theoretical model which goes beyond the usual relations employed at macro-scale to describe thermoelectric effects. It introduces the non-local effects which should be taken into account in view of the possible applications of thermoelectric effects at nano-scale. The proposed model is here employed to investigate how non-local effects may influence the propagation of waves
Description of the last instar larva of Orthetrum hintzi Schmidt, 1951, and comparison with other African Orthetrum species (Anisoptera: Libellulidae)
No full textThe ultimate instar larva is described and illustrated from specimens collected in the streams nr York, Sierra Leone. It is the smallest of the known Orthetrum larvae, from which it can be separated by the presence of dorsal abdominal spines on S7. The main larval features in 8 African Orthetrum spp. are briefly reviewed
Description of the last instar larva of Agriocnemis F. falcifera Pinhey, 1959 (Zygoptera: Coenagrionidae)
No full textUltimate instar larva of both sexes, from Pietermaritzburg and Durban, South Africa, is for the first time described, illustrated and compared with the African and Asiatic congeners
Larval morphology of three species of the genus Hadrothemis Karsch (Anisoptera : Libellulidae)
No full textThe larval morphology of H. scabrifrons, H. coacta and H. camarensis is described for the first time from specimens collected in East Africa, and a comparison among the species is given
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