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[en] External matching networks are crucial and necessary for operating capacitively coupled plasmas in order to maximize the absorbed power. Experiments show that external circuits in general heavily interact with the plasma in a nonlinear way. This interaction has to be taken into account in order to be able to design suitable networks, e.g., for plasma processing systems. For a complete understanding of the underlying physics of this coupling, a nonlinear simulation approach which considers both the plasma and the circuit dynamics can provide useful insights. In this work, the coupling of an equivalent circuit plasma model and an external electric circuit composed of lumped elements is discussed. The plasma model itself is self-consistent in the sense that the plasma density and the electron temperature is calculated from the absorbed power based on a global plasma chemistry model. The approach encompasses all elements present in plasma systems, i.e., the discharge itself, the matching network, the power generator as well as stray loss elements. While the main result of this work is the conceptual approach itself, at the example of a single-frequency capacitively coupled discharge its applicability is demonstrated. It is shown that it provides an effective and efficient way to analyze and understand the nonlinear dynamics of plasma systems including the external circuit and, furthermore, may be applied to synthesize optimal matching networks. (paper)
[en] The Brazilian–German project EcoRespira-Amazon currently conducts a study of soil respiration and soil chemistry in the Brazilian Amazon basin that comparatively examines forested land with post-forest land cover. The Amazon region, long recognized as a key component of the global carbon cycle and a tipping point in the global climate system, covers an area of 7 million km2; this study provides representative regional data that will help to fill existing knowledge gaps and to verify (or falsify) current assumptions on the role of humid tropical forest regions in the climate system.
[en] In this paper, CoxNi(1−x)(OH)2 with various molar ratios of Ni/Co is synthesized through chemical treatment. Effects of Ni/Co molar ratios on microstructure and property of CoxNi(1−x)(OH)2 are explored. It is found that electrochemical property of the Co–Ni hydroxides could be optimized for a Ni/Co molar ratio of 1. The obtained Co0.5Ni0.5(OH)2 exhibits the most hollow out structure and preferable electrochemical performance as electrode material in hybrid supercapacitor. The interconnected and porous architecture built by thin nanosheets of Co0.5Ni0.5(OH)2 facilitates ion diffusion and electron transportation. The experiment results further show that the property decay during charging/discharging may be caused by the collapse of structure.
[en] The work reported in this thesis was conducted around two main themes: The first one is the plasma diagnosis: as the optimization of the analytical use of fluorescence and emission requires knowledge of the mechanisms responsible for the population of the different atomic or ionic levels, it is proposed to make the diagnosis of such a plasma created on a solid target. The temporal behavior of the plasma is studied from the temporal evolution of the emission and fluorescence signals. Two types of fluorescence are compared: direct line non-resonant fluorescence and cascade fluorescence. The evolution of the characteristics of the plasma according to the nature and the pressure of the surrounding atmosphere is also studied. The second theme is the analytical study through the evaluation of the performance of two spectroscopic techniques of emission and fluorescence for the analysis of solid samples from a plasma produced by a nitrogen laser at atmospheric pressure. From the results and observations made in the diagnostic part, the analytical conditions and in particular the temporal position at which it is advisable to be placed in the plasma are optimized. The limits of detection are evaluated for copper in aluminum matrices. The performances obtained by the two detection techniques are compared. This document is in three parts: the first part presents a description of the laser-material interaction based on a bibliographic synthesis. The second part presents the principles and parameters which govern the analytical exploitation by emission and fluorescence spectrometry of plasmas produced by laser. The third part gives and interprets the results obtained for the plasma diagnosis and for analytical studies. A preliminary study of a plasma produced by an excimer laser is presented at the end of this work. The results obtained are compared with those obtained on a plasma produced by a nitrogen laser.
[fr]Notre travail a pour but de caracteriser un plasma cree par un laser a azote a pression atmospherique sur des echantillons solides. Une vapeur atomique exploitable par spectrometrie d'emission et de fluorescence est ainsi produite. Une premiere etude realisee au laboratoire a montre que la technique d'ionisation resonnante n'est pas bien adaptee pour le diagnostic et l'analyse de tels plasmas mais que la fluorescence represente une voie plus interessante. C'est donc dans cet axe de recherche que nous nous sommes orientes. Les travaux rapportes dans cette these ont ete conduits autour des deux grands themes suivants: 1. Le diagnostic du plasma - L'optimisation de l'exploitation analytique de la fluorescence et de l'emission necessite la connaissance des mecanismes responsables de la population des differents niveaux atomiques ou ioniques. En effet ce sont, entre autre, ces populations qui orientent le choix des raies analytiquement exploitables. Jusqu'a present aucune etude systematique de ce type n'a ete faite sur des plasmas produits par laser a pression atmospherique. Nous nous proposons donc de faire le diagnostic d'un tel plasma cree sur une cible solide. Le comportement temporel du plasma est etudie a partir de l'evolution temporelle des signaux d'emission et de fluorescence. Deux types de fluorescence sont compares: la fluorescence non-resonnante de raie directe et la fluorescence de cascade. L'evolution des caracteristiques du plasma en fonction de la nature et de la pression de l'atmosphere environnante est egalement etudiee. 2. L'etude analytique - Le but de cette etude est d'evaluer les performances des deux techniques spectroscopiques d'emission et de fluorescence pour l'analyse d'echantillons solides a partir d'un plasma produit par un laser a azote a pression atmospherique. A partir des resultats et des observations faites dans la partie diagnostic, les conditions analytiques et en particulier la position temporelle a laquelle il convient de se placer dans le plasma sont optimisees. Les limites de detection sont evaluees pour le cuivre dans des matrices d'aluminium. Les performances obtenues par les deux techniques de detection sont comparees. Ce document se decompose en trois parties: La premiere partie presente une description de l'interaction laser-matiere fondee sur une synthese bibliographique. La deuxieme partie presente les principes et les parametres qui regissent l'exploitation analytique par spectrometrie d'emission et de fluorescence des plasmas produits par laser. Dans la troisieme partie, nous donnons et interpretons les resultats obtenus pour le diagnostic du plasma et pour les etudes analytiques. Une etude preliminaire d'un plasma produit par laser a excimeres est presentee a la fin de ce travail. Les resultats obtenus sont compares a ceux obtenus sur un plasma produit par un laser a azote. (auteur)
[en] The behavior of an electrochemical integrator based on a solid electrolyte is studied in the galvanoharmonic charging mode. The possibility of applying simpler and more graphic calculation techniques and separating the impedance of electrochemical systems into active and reactive components is shown. The plotting of the dependences of the active and reactive impedance components on the ac frequency is used to determine the parameters of the studied equivalent electric cuircuits.
[en] In this work, the combined effects of heat treatment and Sb addition on the discharge performance of Al-Sb alloys as anode for Al-air batteries have been evaluated experimentally. The results indicate that heat treatment decreases the electrochemical and discharge activities of Al-Sb alloys. Heat-treated Al-Sb alloys at 550 °C for 3 h show an improved anode performance. The Al-0.02Sb alloy exhibits a high discharge capacity and anodic efficiency of 2758 Ah kg−1 and 92.6%, respectively. Further prolonging the heat treatment time results in a decrease in anode performance. Microstructure characterization indicates that such negative effect is due to the higher-temperature and prolonged heat treatment to bring out significant grain growth and coarsening of Al-Sb precipitates. The corresponding corrosion behaviors are also discussed in detail.
[en] Flexible and efficient fiber-shaped supercapacitors are being widely studied due to their enormous potential applications in portable electronics. Mesoporous CuCo2S4 nanosheets were prepared firstly on Ni wires (NW) with hydrothermal route and two same NW@CuCo2S4 electrodes were used to assemble a fiber-shaped all-solid-state symmetric supercapacitor. Electrochemical investigation demonstrated that as-fabricated device displayed good performances with high specific capacitance of 35.83 mF cm−2 at 1 mA cm−2 and high energy density of 7.2 µWh cm−2 at power density of 599.9 µW cm−2. In addition, the flexibility of the fiber-shaped supercapacitor was good and two devices in series can light up a red LED for more than 15 s. These results indicating its excellent comprehensive performance, which can meet the demand of practical applications in portable electronic devices.
[en] AZ61 and AZ61-0.5La (wt.%) alloys are prepared by the conventional casting method and then, AZ61 and AZ61-0.5La alloy sheets are obtained with multi-pass hot rolling. Microstructures and electrochemical properties of four alloys are investigated, and discharge properties are tested by an assembled Mg-air battery using alloy anode sheets with a dimension of 70 × 100 × 2.5 mm. Results show that Al11La3 phases are formed in as-cast AZ61-0.5La alloy and promote the grain refinement and the formation of uniform microstructure in as-rolled AZ61-0.5La alloy. As-rolled AZ61-0.5La alloy exhibits a weak self-corrosion tendency but a strong discharge activity. After discharge test for 5 h, the Mg-air battery based on the as-rolled AZ61-0.5La sheet can provide the maximum power output of 1.625 W, and as-rolled AZ61-0.5La anode can supply the maximum energy density of 1417 mWhg−1. In addition, the relationship between microstructures and discharge properties is sufficiently described and discussed in this paper.
[en] Supercapacitor devices have attained great importance in energy storage due to its superior power densities compared to batteries. However, they still suffer from lower energy densities than rechargeable batteries. In this talk, I will discuss about our recent work on various metal oxide based nanostructured materials such as nanofibers, layered double hydroxide (LDH) etc. for supercapacitor applications. A facile, cost effective, and potentially scalable electrospinning technique was used to synthesize nanofibers.The effect of doping was investigated on supercapacitor device performance through detailed electrochemical and morphological characterization. Further, LDH nanosheets were synthesized via hydrothermal method.The characterization techniques such as cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy were used to study electrochemical properties of the developed LDH materials. Further, LDH nanosheets were grown on carbon cloth (CC)and were used as electrode material for flexible supercapacitor applications.Full solid-state hybrid supercapacitor device was fabricated. The electrochemical performance of the solid-state flexible supercapacitors showed a negligible change against bending and twisting of the devices. The performance of LDH@CC indicates the great potential of the material for future flexible energy storage devices. (author)