1,721,821 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Superior electrochemical performance of N-doped nanocrystalline FeF3/C with single-step solid-state process
No full textFeF3 is a promising cathodematerial for lithium ion batteries but its poor electronic conductivity makes it non-practical. Here, we significantly improve the electrochemical activity of FeF3 by reducing the strong ionic character of Fe-F with the replacement of some F with N atoms. N-doped nanocrystalline FeF3/C achieves the best electrochemical performance among FeF3 compounds reported to date: similar to 95 mA h g(-1) at 21.1C discharge rate for 250 cycles. The results illustrate that the poor electronic conductivity of metal fluorides can be controlled by doping and this enables FeF3 or metal fluorides to be practically utilized in possible applications including energy conversion and storage.11118sciescopu
Influence of phase transformation pathways on electrochemical properties by using thermally derived solid-solution LiFePO4 nanoparticles
No full textTo understand how a phase transformation pathway affects the electrochemical properties of LiFePO4 nanoparticles (NPs), a sample with the solid-solution phase (SS sample) was prepared by thermal treatment of a sample that contained two phases, LiFePO4 and FePO4, (TP). The SS sample had NPs that experience the solid-solution phase and then may undergo solid-solution phase transformation, and the TP sample had NPs that do not experience and then can undergo typical two-phase transformation. And their electrochemical characteristics were compared under various conditions. The thermodynamic properties of the two samples were evaluated using a galvanostatic intermittent titration technique (GITT) and a potentiostatic intermittent titration technique (PITT), and electrochemical kinetic properties were evaluated by applying current. The two samples had quite similar thermodynamic properties such as OCV and diffusion coefficient, but quite different kinetic properties such as polarization, current decay, voltage flatness and underpotential behavior even though they had a similar particle size and size distribution. The SS sample showed lower polarization, faster current decay at a constant voltage and less-significant underpotential behavior than did the TP sample. Furthermore, during charging/discharging, the voltage profile was a slope for the SS sample but flat for the TP sample even though the OCV of the two samples did not show any significant difference. These facile electrochemical characteristics can be related to nucleation indicating that the SS sample can have less significant nucleation than the TP sample. These different electrochemical properties are caused by different phase transformation pathways rather than the particle size that is the typical cause for those different kinetic properties. The phase transformation pathway of LiFePO4 strongly affects the electrochemical kinetic properties, not the thermodynamic ones. We reveal that undergoing the solid-solution pathway can be kinetically better off leading to a fast electrochemical response.1165sciescopu
Novel and scalable solid-state synthesis of a nanocrystalline FeF3/C composite and its excellent electrochemical performance
No full textA scalable solid-state reaction is presented to synthesize an FeF3 cathode material by using PTFE as a source of both fluorine and carbon. The method yields nanocrystalline FeF3/C showing excellent electrochemical performance even without any conducting additive. This method can be utilized for engineering MFs' properties and developing other fluorine compounds.1156sciescopu
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Understanding abnormal potential behaviors at 1st charge in Li2S cathode material for rechargeable Li-S battery
No full textIn this study, electrochemical behaviors of Li2S such as a large potential barrier at the beginning of the 1st charging process and a continuous increase in potential to similar to 4 V during the rest of this process were understood through X-ray photoelectron spectroscopy measurements and electrochemical evaluations for a full utilization of Li2S. The large potential barrier to the 1st charge in Li2S can be caused by the presence of insulating oxidized products (Li2SO3 or Li2SO4-like structures) on the surface; simple surface etching can remove them and thereby reduce the potential barrier. Even though the potential barrier was substantially reduced, the electrochemical activity of Li2S might not be improved due to the continuous increase in potential. This increase in potential was related to the polarization caused by the Li2S-conversion reaction; the polarization can affect the utilization of Li2S in subsequent cycles. We speculate that the increase in potential is related to the decomposition of oxidized products such as Li2CO3-like or Li2O-like structures on the surface of the Li2S particles. These findings indicate that the full utilization of Li2S can be achieved by controlling their surface characteristics, especially the surface oxidation products.11114sciescopu
Thermally driven metastable solid-solution Li0.5FePO4 in nanosized particles and its phase separation behaviors
No full textNanosized LiFePO4 particles easily show a fast electrochemical response that can be achieved via a non-equilibrium pathway. To understand this intriguing phase transition behavior in nanosized LiFePO4 particles, the metastable solid-solution phase was prepared by thermal treatment with a chemically delithiated nanosized Li0.5FePO4 sample. Thermal treatment makes all the nanosized particles transform easily to the metastable solid-solution phase because of the large thermal energy while an electrochemical reaction does not. The phase separation behavior of the metastable solid-solution sample (Li0.5FePO4) was investigated under various kinetic conditions to understand critical factors affecting the phase separation behavior of nanosized LiFePO4 particles. The main findings in this study are as follows. The first finding is that the depressed phase separation behavior of the metastable phase may originate from the nanoparticle effect, in which the formation of a second phase inside a nanosized particle is not energetically favored because of the large interfacial energy. Therefore, phase separation in nanosized particles occurs between particles rather than inside a particle. If there was no over-potential, such as in the relaxed pellet experiment or in the relaxed electrode experiment in the electrolyte, the metastable phase was quite stable showing no phase separation behavior even though efficient pathways for lithium ions and electrons were well developed. The second finding is that the phase separation behavior of the metastable phase actually depends on the over-potential. Under open circuit voltage (OCV) conditions, the metastable phase started to exhibit a slight structural change during a long relaxation time, about ten days. The slow change of the metastable phase may be due to the low driving force, less than 10 mV, which comes from the energetic difference between the two-phase state and the metastable phase. This indicates that the phase separation behavior may require a large over-potential. When a large over-potential was applied using an external current, phase separation of the metastable phase was achieved, indicating that the phase separation behavior may be related to activation processes. Furthermore, the requirement for a large over-potential indirectly shows that the spinodal decomposition is depressed in nanosized particles. Considering that phase separation in nanosized particles occurs between particles, the surface charge transfer reaction can be a limited reaction for achieving phase separation because it is an activated process and governed by the over-potential. Considering the understanding obtained from the phase separation behavior of the metastable phase, the phase transition behavior of nanosized LiFePO4 particles during charging/discharging can proceed via the metastable phase because there is no spinodal decomposition behavior in nanosized particles and the metastable phase is quite stable.X1123sciescopu
Increase in grain boundary ionic conductivity of Li1.5Al0.5Ge1.5(PO4)3 by adding excess lithium
No full textLi1.5Al0.5Ge1.5(PO4)(3) (LAGP) is a promising solid electrolyte for all-solid-state Li ion batteries. In this work, it was synthesized using solid-state reaction with an excess amount of Li to improve grain boundary ionic conductivity. The additional Li improved grain boundary conductivity even though the relative density decreased. This improvement may originate from a beneficial characteristic of grain boundary induced by the segregation of some of Li to the grain boundary. This segregation was indirectly observed by the change of morphology of particles in samples with excess Li. The segregation of Li may result in a facile Li transport in grain boundaries, as indicated by low activation energy and a high pre-exponential factor of the grain boundary conductivity. Through improving grain boundary conductivity with excess Li, a high total ionic conductivity of 1.9 x 10(-4) S.cm(-1) is achieved at room temperature even with a low relative density of 78%. This porous and high ionic conducting solid electrolyte can be useful in configuring the electrode composite of all-solid-state cells. (C) 2014 Elsevier B.V. All rights reserved.X112522sciescopu
Reactor modeling of magnetically enhanced capacitive RF discharge
No full textMagnetic and collisional effects on capacitive radio frequency (RF) discharges for magnetically enhanced reactive ion etching (RF) are investigated, Using simplified plasma and sheath models, a collisional magnetic-sheath equation that governs the sheath dynamics under a de magnetic field crossed with a sinusoidal RF electric field is obtained, The sheath equation includes global effects of the bulk plasma. Together with the power-balance equation and the particle-conservation equation, the sheath equation is used to extract a circuit model and predict the electrical behavior of MERIE reactors, Numerical results on the plasma density and the power in MERIE reactors agree well with reported experimental results and the circuit model describes the reported discharge properties well.X1115sciescopu
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