1,720,989 research outputs found
Zn ion diffusion in spinel-type cathode materials for rechargeable batteries: the role of point defects
No full textOxides with spinel structure are attracting increasing attention as potential cathode materials for multivalent ion batteries, such as those based on Mg2+, Ca2+ and Zn2+. Their electrochemical performances generally depend on synthesis conditions, as the intercalation properties of such materials can be highly influenced by the amount and distribution of point defects. In this work we employ atomistic modelling techniques to investigate the trends in the energetics of point defects formation and Zn2+ diffusion in spinel-type ZnCo2O4, in order to shed light on the correlation between structure, defects and intercalation properties. The results of this study indicate that ZnCo2O4 has the potential to be used as cathode material in Zn-ion rechargeable batteries and that synthesis approaches aimed at reducing the degree of spinel inversion and introducing cation under-stoichiometry are expected to improve the intercalation properties of this class of compounds
Na+diffusion mechanism and transition metal substitution in tunnel-type manganese-based oxides for Na-ion rechargeable batteries
No full textNa0.44MnO2 (NMO) with a tunnel-type structure is a reference cathode material for rechargeable Na-ion batteries. In this work, structural, electrochemical and computational investigations are combined to study the properties of this material, particularly with reference to Cu substitution in the structure. For the first time, molecular dynamics (MD) is used to obtain insights into the mechanisms of Na+ diffusion in NMO, highlighting the role of structural modifications and Na distribution. The main results allow the investigation of the implication of high temperature treatments and the effect of Cu substitution on the defect and transport properties of the material with a tunnel-type structure. From an experimental point of view, the substitution promotes an increased stability of the material upon cycling and an improved capacity particularly at higher discharging rates, that stems from the synergistic effects of the composition, morphology and multiple polymorphs of the sample
The attachment of adult women to the Italian labour market in the shadow of COVID-19
Full text linkWe investigate the attachment to the labour market of women in their 30s, who are combining career and family choices, through their reactions to an exogenous, and potentially symmetric shock, such as the COVID-19 pandemic. We find that in Italy a large number of women with small children, living in the North, left permanent (and temporary) employment and became inactive in 2020. Despite the short period of observation after the burst of the pandemic, the identified impacts appear large and persistent, particularly with respect to the men of the same age. We argue that this evidence is ascribable to specific regional socio-cultural factors, which foreshadow a potential long-term detrimental impact on female labour force participation.</p
Lattice effects in cubicLa2Mo2O9: effect of vacuum and correlation with transport properties
No full textThis study aims to investigate correlations between lattice effects and transport properties in cubic La2Mo2O9. High temperature neutron diffraction data, recorded in air and under vacuum, are used to follow the evolution with temperature of selected structural parameters, i.e. bond lengths and angles. Results suggest a possible correlation with the experimentally observed decrease of the
activation energy for oxygen migration at high temperature. The effect on the structural properties of the low oxygen partial pressure used during the measurements in vacuum is negligible and this represents a valuable information in view of possible applications of the material in solid state devices.
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Polymorphism in Na2(Co/Zn)P2O7 and Na2(Co/Fe)P2O7 Pyrophosphates: A Combined Diffraction and 31P NMR Study
No full textPyrophosphates of the general formula A2BP2O7 (A = alkali metal and B = transition metal) find applications in several technological fields, including rechargeable Na-ion batteries. They present a rich polymorphism vs composition, which may strongly influence their functional properties. Therefore, to selectively obtain a specific structure is crucial for applications. Here, we combine structural investigation techniques (solid-state NMR, X-ray and neutron diffraction, and DFT calculations) to investigate the crystal chemistry of the series Na2(M/M’)P2O7 with couples M/M’ = Co/Zn and Co/Fe. For both the series, a phase transition vs composition is observed. A tetragonal to orthorhombic phase transition is found for the Zn/Co series, and an orthorhombic to triclinic phase transition is found for the Co/Fe series. Such changes are interpreted in view of the different electronic structures of the transition metal ion. In addition, with the support of modeling, short- and long-range structural analysis, we show that the coexistence of two polymorphs for a given composition is possible, suggesting that the final structures may be strongly dependent upon the synthesis procedure
Uncertainty and the politics of employment protection
Full text linkThis paper investigates social preferences over employment protection regulation in a general equilibrium model of dynamic labor demand and sheds some light on the comparative dynamics of Eurosclerosis. When firing costs are low, a transition to a rigid labor market is favored by all the employed workers with idiosyncratic productivity below some threshold; when their status quo level is high, preserving a rigid labor market is favored only by the employed with intermediate productivity. A more volatile environment and a lower rate of productivity growth increase the political support for labor market rigidity only in high-rents economies
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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