Nonlinear effects in 3rd and 4th-order moments of transport-hydrodynamical models in semiconductors within Extended Thermodynamics

In this paper, we treat the closure relations of hydrodynamical models in order to study electron transport in semiconductors. We adopt the Extended Thermodynamics theory in order to derive hydrodynamical equations for carrier transport and we try to close the system, i.e. to find constitutive equations for the third and fourth-order moments, by means of a generalized nonequilibrium distribution function.In this paper, we treat the closure relations of hydrodynamical models in order to study electron transport in semiconductors. We adopt the Extended Thermodynamics theory in order to derive hydrodynamical equations for carrier transport and we try to close the system, i.e. to find constitutive equations for the third and fourth-order moments, by means of a generalized nonequilibrium distribution function

Caractérisation et modélisation des polymères électro-actifs (Application à la récupération d'énergie)

Le concept de la récupération d'énergie se rapporte généralement au processus d'utilisation de l'énergie ambiante, qui est converti, principalement (mais pas exclusivement) en énergie électrique pour faire fonctionner des dispositifs électroniques petites et autonomes. Les tendances récentes à la fois dans l'industrie et au domaine de la recherche ont mis l'accent sur les polymères électro-actifs pour la conversion d'énergie électromécanique. Cet intérêt s'explique par de nombreux avantages tels que la productivité élevée, la grande flexibilité, et la facilité de traitement. Le but de ce travail de recherche est d explorer la potentialité des polymères électro-actifs pour une application de récupération d énergie mécanique ambiante. Dans la première partie, une synthèse des composites à base de polyuréthane (PU) et de P(VDF-TrFE-CFE) a été réalisée, suivie d une caractérisation électrique et mécanique de ces polymères et composites afin d évaluer leurs paramètres intrinsèques. La seconde partie de ce travail de thèse concerne la caractérisation électromécanique de ces polymères. Un modèle analytique électromécanique est mise en place afin de déterminer finement le comportement physique des polymères électrostrictifs ainsi que les variations de leurs paramètres intrinsèques. Ce modèle analytique est validé par une série de tests à travers un banc d essai. La dernière partie de ce travail consiste à évaluer les performances électromécaniques des polymères électrostrictifs pour la récupération d énergie mécanique. Deux nouvelles techniques sont testées afin de maximiser la densité d énergie récupérée. Ainsi qu une comparaison avec les méthodes classiques a été réalisée. Un excellent potentiel de ces techniques pour la récupération d'énergie a été démontré. Le deuxième point porte sur l étude de l efficacité de la conversion électromécanique pour la récupération d énergie mécanique en utilisant l'analyse spectrale FFT. Il a été montré que cette méthode permet de prévoir le rendement énergétique de nos polymères en accord avec les prédictions théoriques. Le dernier point se focalise sur l amélioration de cette efficacité de conversion électromécanique en utilisant des électrets de polypropylène cellulaire, afin d assurer un meilleur rendement énergétique.The concept of energy harvesting generally relates to the process of using ambient energy, which is converted, primarily (but not exclusively) into electrical energy in order to power small and autonomous electronic devices. Recent trends in both industrial and research fields have focused on electro-active polymers for electromechanical energy conversion. This interest is explained by many advantages such as high productivity, high flexibility, and processability. The purpose of this research work is to explore the potential of electro-active polymers for application of mechanical energy harvesting. At first, a synthesis of the composite based on polyurethane (PU) and P (VDF-TrFE-CFE) was performed, followed by electrical and mechanical characterization of these polymers and composites in order to evaluate their intrinsic parameters. The second part of this thesis concerns electromechanical characterization of these polymers. An electromechanical analytic modeling is detailed in order to determine the physical behavior of electrostrictive polymers and the variations of intrinsic parameters. This modeling is validated by a series of tests using a test bench. The last part of this work consists to evaluate the electromechanical performance of electrostrictive polymers for the mechanical energy harvesting. Two new techniques are tested in order to maximize the density of energy recovered. As well as a comparison against those classic has been performed. Excellent potential of these techniques for energy harvesting has been demonstrated. The second point is about the study of the electromechanical conversion efficiency for scavenging mechanical energy using spectral analysis FFT. It was shown that this method allows predicting the energy efficiency of our polymers, in accordance with the results predicted by the model. The last point focuses on improving the efficiency of electromechanical conversion by using cellular polypropylene electrets to ensure better energy efficiency.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Wave Energy Harvesting System Using Piezocomposite Materials

Marine energies are a strategic channel for renewable energies to diversify and complement the global energy mix. From this perspective, several researches have seen the light in order to allow the maximum exploitation possible of the energy estimated at 80,000 TWh/year, presenting multiple vacant possibilities concerning energy not yet exploited on a large scale. The purpose of this paper is the use of ocean vibratory energy coupling with a smart composite material in order to harvest the maximum power. This study will be devoted to the design, modeling, and simulation of a floating harvester energy system that combines the mechanical strength and flexibility of polymer with the high piezo and pyroelectric activities of ceramic. The harvester system is composed of a mass-spring system used to transfer wave movements to mechanical vibrations, and two piezoelectric lever devices will be used to amplify and convert the harvested mechanical vibration into electrical power. With this flexible device, the maximum power harvested is 56.45 μW/mm², using PU/PZT composite with the optimal resistance of 108 MΩ. Considering these results, this system can be used in very different ways in marine applications

Flexible Smart Textile Coated by PVDF/Graphene Oxide With Excellent Energy Harvesting Toward a Novel Class of Self-Powered Sensors: Fabrication, Characterization and Measurements

Because of some of their diverse benefits, intelligent textiles have attracted a great deal of interest among specialists over the past decade. This paper describes a novel approach to the manufacture of intelligent piezoelectric polymer-based textiles with enhanced piezoelectric responses for applications that extract biomechanical energy. Here we report a highly scalable and ultrafast production of smart textile piezoelectric containing graphene oxide nanosheets (GONS) dispersed in polyvinylidene fluoride (PVDF). In this work, Cotton textiles (CT) were functionalized and by graphene oxide (GO), using PVDF as a binder to obtain a CT-PVDF-GO material. Tetraethyl orthosilicate (TEOS) was further grafted as a coating layer to improve the surface compatibility, resulting in the CT-PVDF-GO-TEOS composite. The research results show that the addition of GONS significantly improves PVDF's overall crystallization rate on CT. More specifically, the piezoelectric β-phase content (100 % higher F[β]) and crystallinity degree on the piezoelectric properties of composite cotton fiber has been improved effectively. Consequently, this fabricated piezo-smart textile has a glorious piezoelectricity even with comparatively low coating content of PVDF-GONS-TEOS. Based on it, the as-fabricated piezoelectric textile device has resulted in the output voltage of up to 13 mV for a given frequency (fm = 8 Hz) at fixed strain amplitude value (0.5 %). It is believed that this research may further reveal the field of energy harvesting for possible applications in the future.. In addition, the set of experimental results that illustrate the smart textile was carried out and discussed, and how it can be used as a wearable device source for this smart textile. Finally, the approach described in this study can also be used to construct other desirable designs, for a wearable low-consumption sensor, etc

Modélisation de vésicules en géométrie étendue et dans des systèmes micro-fluidiques

La déformation et le comportement dynamique d'une vésicule sous l'action d'un écoulement externe appliqué (cisaillement simple et Poiseuille) est étudié dans la limite de faibles nombres de Reynolds. Les cas de géométries non-confmée et confinée sont considérés. On fait usage de plusieurs méthodes: (i) un calcul analytique tridimensionnelle (théorie de faible déformation) (ii) des simulations bidimensionelle (méthodes de Boltzmann sur réseau et intégrale de frontière) dans le but de résoudre les équations hydrodynamiques correspondantes et de suivre explicitement la dynamique de la vésicule. La théorie analytique de faible déformation est utilisée pour construire le diagramme de phase résumant tous les régimes dynamiques connus pour une vésicule (chenille de char, bascule et vacillation-respiration) sous un écoulement de cisaillement. L'impacte de la variation des paramètres, contrôlant la dynamique, sur l'évolution de différentes quantités caractérisant chaque régime dynamique d'une vésicule est présenté.On utilise également la méthode de Boltzmann sur réseau afin de simuler la dynamique d'une vésicule dans une géométrie confinée (e.g. un micro-canal). Comme cas test, les formes d'équilibre d'une vésicule et son mouvement de chenille de char sous cisaillement ont été analysés. L'effet du confinement sur la dynamique de la vésicule a été examiné. La migration latérale d'une vésicule placée dans un écoulement de Poiseuille non-confiné et semi-confiné est traité en utilisant des simulations basées sur la méthode d'intégrale de frontière. Pour le cas de la géométrie non-confinée, on a trouvé que le caractère non linéaire de l'écoulement de Poiseuille combiné à la déformabilité de la vésicule, induit une migration latérale des vésicules vers le centre de l'écoulement. La présence d'une paroi délimitant le fluide externe induit également une force de portance. On a analysé la compétition entre la force de portance due à la paroi et celle du la courbure de l'écoulement de Poiseuille. Une loi donnant la vitesse de migration latérale (en fonction des paramètres caractérisant la vésicule et l'écoulement) est proposée et est en accord avec les résultats expérimentaux.Dynamical behavior and deformation of a single neutrally buoyant suspended vesicle (a closed phospholipid membrane), as a response to external applied flows (simple shear and Poiseuille flows), is studied in the limit of small Reynolds numbers. Unbounded and confined geometries are both considered here. For this purpose we use three dimensional analytical calculation (small deformation theory) as weIl as two-dimensional simulations (lattice Boltzmann and boundary integral methods) to solve the corresponding hydrodynamical equations and to track explicitly the vesicle dynamics.The small deformation theory is used to draw the phase-diagram summarizing the known vesicle dynamical regimes (tank-treading, tumbling and vacillating-breathing), under shear flow. Impact of varying controlling parameters on the evolution of various quantities characterizing each vesicle dynamical regime is reported.We present also how we adapted the lattice Boltzmann method to simulate dynamics of vesicles in confined geometries (e.g. a micro-channel). As benchmarkings, the vesicle equilibrium shapes in a fluid at rest are recovered together with dynamical behavior of a vesicle under simple shear flow - tank-treading -. The effect of confmement on the vesicle dynamics is investigated. Lateral migration of a vesicle placed in unbounded and semi-bounded Poiseuille flow is investigated using the boundary integral method simulations. ln the unbounded geometry we fmd that the nonlinear character of the Poiseuille flow, together with the vesicle deformability, causes a lateral migration of the vesicles towards the flow centerline. ln the presence of a bounding wall an additionallift force appears. ln this situation we investigate the interplay between the wall- and the Poiseuille flow curvature- induced lift forces. A similarity law for the lateral migration velocity (as a function of relevant structural and flow parameters) that is consistent with experimental results is proposed.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Dynamics Of Cu Monomer, Dimer And Trimer On Ag (110) (1 × 2) Missing-Row Reconstructed Surface

The authors aimed to investigate the diffusion of Cu monomer, dimer and trimer on Ag (110) (1×2) missing-row surface. This problem is addressed through molecular dynamic simulation based on semi-empirical many-body potential, derived from the embedded atom method. Within this approach, we have identified and calculated the activation energy of each microscopic mechanism. Thus, for Cu monomer, the diffusion process occurs essentially by simple hopping between nearest-neighbor sites. While for the Cu dimer, three processes have been identified such as dissociation-reassociation (DR), concerted jump (CJ) and leapfrog mechanisms (LF) with a slight predominance of DR process and a dual competition between CJ and LF processes. But, in the case of small one-dimensional cluster such as trimer on (110)(1×2) missing-row reconstructed surface, the main diffusion mechanism is the LF process. These results shed light on the diffusion processes on missing-row reconstructed surfaces, especially for heterogeneous systems. © 2013 John Wiley & Sons, Ltd

Flexible thermoelectric device to harvest waste heat from the laptop

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Energy barriers of single-adatoms diffusion on unreconstructed and reconstructed (110) surfaces

The present paper is aimed mainly to investigate theoretically the diffusion of Ag, Cu, Au and Pt adatoms on the (1 × 1) unreconstructed geometry for Ag, Cu and Pt (110), and reconstructed geometries ((1 × 2), (1 × 3) and (1 × 4)) for Pt and Au (110) surfaces. We consider the single adatom diffusion when additional atoms are deposited in adjacent row. For this study, we have used the molecular statics simulations combined with the embedded atom method. For several systems, we have calculated the activation barriers for hopping mechanism. For the diffusion on the unreconstructed surfaces, the trends for the activation barriers are the same for all considered systems except for Cu/Ag (110) system, where the activation barrier do not change. Further, our results indicate that additional atoms lead to a small decreasing of activation barriers for diffusion on reconstructed surfaces for some systems, while for other systems; the activation barrier remains practically unchanged