1,721,053 research outputs found
In-Depth Induction Heating of Large Steel Slabs by Means of a DC Saturating Field Produced by Superconducting Coils
No full textThe feasibility of an innovative in-depth AC induction heating method for large steel slabs is investigated. Aside from the AC field, which induces the heating currents, a large DC magnetic field is also applied, which brings the material to saturation. Due to saturation, permeability is reduced by orders of magnitude and the penetration depth is drastically increased, thus enabling much faster and more uniform heating. In order to produce the field needed for the saturation of common steel workpieces, lossless DC superconducting magnets need to be employed. A possible layout of an AC induction heater employing magnetic saturation (saturated AC induction heater) is discussed. The conceptual design of the superconducting magnet needed is carried out based on present state-of-the-art superconducting materials. The performance of the saturated AC induction heater is numerically investigated and compared with the case without magnetic saturation
Design and performance of a 1 MW-5 s high temperature superconductor magnetic energy storage system
No full textThe feasibility of a 1 MW-5 s superconducting magnetic energy storage (SMES) system based on state-of-the-art high-temperature superconductor (HTS) materials is investigated in detail. Both YBCO coated conductors and MgB2 are considered. A procedure for the electromagnetic design of the coil is introduced and the final layout is arrived at and compared for the two materials. The choice of the inductance of the coil is carried out as part of the design procedure. Both low-field (3 T) and high-field (8 T) designs are considered for the YBCO. AC losses during a complete charge/discharge cycle at full power are estimated and the cooling power needed for continuous operation is derived. The power conditioning system and control algorithms needed to carry out various operations are discussed in detail. Performances of the SMES system during voltage sag compensation, load leveling and power factor correction are investigated by means
of numerical simulation
AC induction heating of ferromagnetic slabs saturated with a DC field
No full textPurpose -This study aims to investigate the feasibility of saturated AC heating of magnetic metals. In AC heating of magnetic steel below the Curie temperature, because of the high magnetic permeability, the penetration depth is in the order of 1-6mmat 50 Hz. Surface heating is then obtained, in practice, if large slabs are processed. The necessity to provide the required surface-To-core temperature uniformity (about 25°C) at the end of the heating process, avoiding excessive thermal stresses which can lead to cracks, thus implies a long heating time. Design/methodology/approach -The penetration depth can be increased if the material is brought to saturation by applying an external DC magnetic field, and a faster in-depth heating can be obtained. The DC saturating field can be produced with no losses over large volumes by means of superconducting (SC) coils. Findings -The feasibility of in-depth induction heating of a 200 1,000 5,000 mm magnetic steel slab with an applied 2 T DC saturating field is numerically investigated. The results show that the use of a DC saturating field leads to shorter processes which fulfil the heating objectives. Practical implications -A DC saturating field cannot be produced by means of copper coils because of the large amount of material and the unaffordable power required. However, this field can effectively be produced by means of SC magnets based on state-of-The-Art materials. Originality/value - Superconductivity may be the enabling technology for fast and efficient induction heating of magnetic steel slabs if the increase in productivity can balance the additional costs due to the SC magnet
Temperature distribution in aluminium billets heated by rotation in static magnetic field produced by superconducting magnets
No full textPurpose of this paper: To investigate the feasibility of a novel scheme of high-efficiency induction heater for non-magnetic metal billets which use superconducting coils.
Design/methodology/approach: The idea is to force the billet to rotate in a static magnetic field produced by a DC superconducting magnet. Since a static superconducting magnet has no losses, the efficiency of the system is the efficiency of the motor used. In order to evaluate the temperature distribution arising from the field profile produced by a given SC coil configuration, a numerical model, based on an equivalent electric network with temperature-dependent parameters, is developed.
Findings: A substantial independence of the shape of the temperature profile on the angular velocity and the value of the uniform magnetic field applied, is observed. A strong temperature gradient is observed in the radial direction in the proximity of the penetration front and in the axial direction at the top and the bottom surface of the billet. Small temperature gradient was observed in the central part of the billet.
Research limitations/implications: The reported temperature profile is inadequate for an actual extrusion process which is desired to happen at a constant temperature. The appropriate profile along the billet length can be achieved by a suitable axial shaping of the magnetic field, through the optimization of the coil layout, whereas the undesired radial gradient can be reduced by interspacing the rotation with temperature smoothing intervals.
Practical implications: The investigation of the profile of applied magnetic field and the heating procedure which allow to achieve the distribution of temperature suitable for the extrusion process can be carried out by using the present model.
What is original/value of paper: A high-efficiency induction heater for non-magnetic metal billets using superconducting coils in a novel scheme is investigated
A Solid Nitrogen Cooled Linear Levitating System Based on MgB2 Bulks
No full textAn innovative linear levitating system based on MgB2 bulks produced by the Reactive Liquid Infiltration (RLI) method is designed and built. Details of the system are presented. The levitation performance is also evaluated by means of previous experimental data.
The linear levitating system consists of four MgB2 arc-shaped tiles lodged inside a double shells dewar sliding on a guide made of Nd-Fe-B permanent magnets. The magnets on the guide are properly arranged in a flux shaper configuration in order to pro-duce the maximum stiffness. Each MgB2 bulk have curvature radius of 165 mm (arc length 200 mm), thickness 10 mm and width 70 mm The system is cooled by means of a Solid Nitrogen heat sink. Helium gas supply to a heat exchanger is used in order to cool down the MgB2 slabs and the nitrogen at a temperature in the range 20-30 K. When the flow of helium gas is interrupted the temperature of the solid nitrogen remains below 39 K for half an hour. During this time interval levitation measurements can be performed. Experimental verification of the cooling concept has been carried out successfully
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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