1,721,003 research outputs found
Electromagnetic Losses Minimization in High-Speed Flywheel Energy Storage Systems
Full text linkThis paper deals with electromagnetic loss analysis and minimization in an integrated Flywheel Energy Storage System (FESS). The FESS consists of a large-airgap Surface-Mounted Permanent Magnet Synchronous Machine (SPM), whose inner rotor integrates a carbon-fiber flywheel, leading to a compact and efficient FESS. Electromagnetic losses minimization is achieved through an accurate SPM modelling, which accounts for both Joule and core losses, as well as for flux-weakening operation. Consequently, SPM maximum efficiency is obtained by injecting a proper demagnetization current component at each operating condition, which guarantee the optimal trade-off among the different losses’ contributions. The effectiveness of the proposed approach is validated through numerical simulations
Magnetic Energy Landscape of a Dymolybdenum Tetraacetate on a Bulk Insulator Surface
No full textThe magnetic states and the magnetic anisotropy barrier of a transition metal molecular complex, dimolybdenum tetraacetate, are investigated via density functional theory (DFT). Calculations are performed in the gas phase and on a calcite (10.4) bulk insulating surface, using the Generalized-Gradient Approximation (GGA)-PBE and the Hubbard-corrected DFT + U and DFT + U + V functionals. The molecular complex (denoted MoMo) contains two central metallic molybdenum atoms, embedded in a square cage of acetate groups. Recently, MoMo was observed to form locally regular networks of immobile molecules on calcite (10.4), at room conditions. As this is the first example of a metal-coordinated molecule strongly anchored to an insulator surface at room temperature, we explore here its magnetic properties with the aim to understand whether the system could be assigned features of a single molecule magnet (SMM) and could represent the basis to realize stable magnetic networks on insulators. After an introductory review on SMMs, we show that, while the uncorrected GGA-PBE functional stabilizes MoMo in a nonmagnetic state, the DFT + U and DFT + U + V approaches stabilize an antiferromagnetic ground state and several meta-stable ferromagnetic and ferrimagnetic states. Importantly, the energy landscape of magnetic states remains almost unaltered on the insulating surface. Finally, via a noncollinear magnetic formalism and a newly introduced algorithm, we calculate the magnetic anisotropy barrier, whose value indicates the stability of the molecule's magnetic moment
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
Design of a Battery Pack for the Power System of an All-Electric Aircraft by Cell Characterization
No full textThe battery characterization and modelling of
a Lithium-ion battery aimed at supporting the design of the
energy storage system of an All-Electric Aircraft (AEA) is
presented. Specifically, the developed model is employed to
evaluate the energy and power performance of a battery
pack designed for the AEA concept X- 57 Maxwell Mod.II.
The preliminary battery pack sizing is performed referring
to a project-flight mission-oriented to air city taxing. The
evaluation of the design targets satisfaction has been ver
ified through a simulation study based on the proposed
battery modelling. The comparison between the simulation
and preliminary results confirms the need of employing a
battery dynamic model for designing AEA’s battery pack
that satisfies all targets imposed
Design of a Battery Pack for the Power System of an All-Electric Aircraft by Cell Characterization
No full textThe battery characterization and modelling of a Lithium-ion battery aimed at supporting the design of the energy storage system of an All-Electric Aircraft (AEA) is presented. Specifically, the developed model is employed to evaluate the energy and power performance of a battery pack designed for the AEA concept X- 57 Maxwell Mod.II. The preliminary battery pack sizing is performed referring to a project-flight mission-oriented to air city taxing. The evaluation of the design targets satisfaction has been verified through a simulation study based on the proposed battery modelling. The comparison between the simulation and preliminary results confirms the need of employing a battery dynamic model for designing AEA's battery pack that satisfies all targets imposed
Magnetic properties of Cr8 and V8 molecular rings from ab initio calculations
No full textMolecular nanomagnets are systems with a vast phenomenology and are very promising for a variety of technological applications, most notably spintronics and quantum information. Their low-energy spectrum and magnetic properties can be modeled using effective spin Hamiltonians, once the exchange coupling parameters between the localized magnetic moments are determined. In this work we employ density functional theory (DFT) to compute the exchange parameters between the atomic spins for two representative ring-shaped molecules containing eight transition-metal magnetic ions: Cr8 and V8. Considering a set of properly chosen spin configurations and mapping their DFT energies on the corresponding expressions from a Heisenberg Hamiltonian, we compute the exchange couplings between magnetic ions which are first, second, and further neighbors on the rings. In spite of their chemical and structural similarities the two systems exhibit very different ground states: antiferromagnetic for Cr8, ferromagnetic for V8, which also features non-negligible couplings between second nearest neighbors. A rationalization of these results is proposed based on the filling of the magnetic centers' d states
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
Fine-Tuning the Electrostatic Properties of an Alkali-Linked Organic Adlayer on a Metal Substrate
Full text linkThe performance of modern organic electronic devices is often determined by the electronic level alignment at a metal–organic interface. This property can be controlled by introducing an interfacial electrostatic dipole via the insertion of a stable interlayer between the metallic and the organic phases. Here, we use density functional theory to investigate the electrostatic properties of an assembled structure formed by alkali metals coadsorbed with 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules on a Ag(100) substrate. We find that the interfacial dipole buildup is regulated by the interplay of adsorption energetics, steric constraints and charge transfer effects, so that choosing chemical substitutions within TCNQ and different alkali metals provides a rich playground to control the systems’ electrostatics and in particular fine-tune its work-function shift
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