1,720,975 research outputs found
NON-LINEAR INDUCTOR CONTRIBUTION TO HARMONIC SPECTRUM IN POWER CONVERTERS
Full text linkThe paper investigates the harmonic content in DC/DC power converters where the inductor is operated in the non-linear region. This operation is often exploited to use lighter and cheaper inductors; as a drawback, an increasing number of harmonics is noticeable. A theoretical analysis is proposed. It is based on a polynomial model of the inductor used in a boost converter. Results are given by the spectra of the output voltage performed on a circuit prototype
Thermal Stability of a DC/DC Converter with Inductor in Partial Saturation
Full text linkInductors operated in quasi saturation in DC/DC converters allow reduction of the core size and realization costs; on the other hand, they imply an increase of dissipated power that can jeopardize the thermal stability of the converter. In this paper, this issue is studied by a mathematical model able to represent both the inductor non-linearity and its temperature dependence. The main losses, such as ohmic, skin effect and magnetic, are taken into account in the model. The inductor is characterized by a polynomial curve whose parameters are a function of the temperature. Finally, the whole converter is modeled and simulation results, obtained on a boost converter, are compared with experimental measurements showing that the thermal behavior is reproduced in detail
Metallization of Si heterojunction solar cell by Cu electroplating
No full textIn response to recent climate change, many renewable energy solutions have acquired great importance; in fact, the need of sustainable development is increasing and the use of renewable energy, such as solar energy, can be applied to many industrial and consumer applications. Photovoltaic systems, which are made up of solar cells, are used for electrical vehicle charging stations and to supply remote areas not connected to the power distribution network; moreover, solar energy is widely used as a primary or secondary source of domestic electric power. In this scenario, the increasing in efficiency, and the cost reduction of solar cells, becomes a priority in the diffusion of PV systems for energy supply.
One of the most recent and promising technology in the field of solar cells is the silicon based HJT (heterojunction technology); in this type of cells, a monocrystalline Si layer is covered by two thin films of hydrogenated amorphous silicon (a-Si:H) on both side; the inner passivate the surface, allowing very large carrier lifetimes as well as record efficiency over 25% [1]; the other a-Si layers, instead, are doped to create the p-n device structure (Fig. 1).
Since the lateral conductivity of the doped amorphous silicon films is quite low, a transparent conductive oxide film (TCO) is used to enhance the lateral current flow to the contacts; this layer, made by sputtering of indium-tin oxide (ITO), acts also as an anti reflection material.
Last step in the technological process involves the contact realization, which is generally made up by silver paste; the metallization is the second most expensive process of the solar cell manufacture and affects the performance of the solar cell [2].
A limitation of silicon heterojunction solar cells is the requirement of a low-temperature process after the a-Si:H layer deposition; otherwise a degradation of the passivation properties of the material would occur. This constraint imposes the use, in the metallization process, of low temperature cured Ag pastes. The use of this material limits the performance of the cell, as the conductivity of silver pastes is minor than bulk Ag [3].
To overcome this problem and to reduce the cost of the cell, authors intend to create, as a proof of concept, a set of samples where silver contacts are replaced with a low-cost material i.e. copper, which presents a conductivity comparable to bulk Ag (Tab. 1).
These samples, consisting of an ITO film on a glass substrate, emulate the top section of the HJT solar cell. The metallization is drawn on the ITO film using photoresist as a negative mask; afterwards, a thick copper layer is grown up on the uncovered areas using an electroplating process (Fig. 2). The track of the metallization reproduces a common used pattern in solar cells which is called H-grid (Fig. 3).
The result expected is an improvement of the quality of the metallization in term of contact resistance respect printing process paste based Ag
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
Coalescence of ZnO nanorods grown by chemical bath deposition
No full textIn this work, a way to grow isolated and coalesced ZnO nanorods on p-GaN/sapphire
structure is presented. Chemical bath deposition [1],[2] was used to grow ZnO nanorods of
device-quality on a p-GaN/n-GaN/sapphire template, simply controlling the duration time of
the growth process and the concentration of the nutrient solution in the bath. Several p-GaN
templates were soaked in a nutrient solution, prepared with different concentration of zinc
nitrate hexahydrate (Sigma-Aldrich, reagent grade 98%) and hexamethylenetetramine (Alfa
Aesar, ACS 99%) in deionized water, while being heated at a temperature of 80 °C for a
period varying from 8 to 25 hours; then, the samples were left in the solution to cool down
naturally to room temperature. Increasing the duration of the process leads to compact and sound layers (instead of separated
nanorods), as well as the concentration of the solution. Fig. 1 shows the top-view fieldemission
scanning electron microscopy (FE-SEM) images of the samples, obtained for
different growth time and 70 mM concentration. The first sample (grown for 8 h) exhibits a
typical nanorod layout (Fig. 1.a). The nanorods are oriented along the (0001) direction of the
substrate. After 15 h, most of the rods coalesce into a unique layer but the uniformity of the
latter is broken by several “empty” areas where ZnO does not seem to be grown (Fig. 1.b).
After 25 h, the ZnO appears as a sound compact layer with some defects on the surface (Fig.
1.c). In general, an increase of the concentration results in a better coalescence of the rods but too
high concentrations stop the growth process. ZnO layer grown for 25 h in 100 mMconcentrated
solution (Fig. 2.a) appears to be more compact than in the case of 70 mM
concentration. The improved coalescence should be due to the increase of the nanorods
diameter with the concentration, as reported in [3]. Concerning the 500 mM sample (Fig. 2.b),
surprisingly only several nanoflowers and nanopillars appear to be deposited on the surface;
in particular, the latter are not aligned along the (0001) sapphire plane but just placed on the
surface with random orientations. Probably the kinetics of the chemical reactions is hindered
by the oversaturation of the solution
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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