1,721,021 research outputs found
Metal-hydride hydrogen compressors for laboratory use
No full textThe development of commercial applications of hydrogen at high pressure (300–700 + bar), for example in fuel cell vehicles and associated filling stations, necessitates the study of hydrogen capacity, and the safety of materials at pressures well above that of standard pressurised cylinders employed in research laboratories. This, in turn, requires laboratory instruments to have some mechanism for hydrogen compression as part of their operation. In this study, the use of metal-hydride compressors for laboratory applications is explored and evaluated. The reduced operating requirements of laboratory instruments, relative to industrial compressors, and the ready availability of laboratory heating and cooling methods, allows the use of relatively simple, single-stage metal-hydride compressors. A simple theoretical derivation enables the determination of the size and amount of hydrogen storage alloy required for a desired pressure, given the experimental volume to be pressurised. Practical requirements, both in terms of the hydrogen storage alloy, and of the pressure vessel, are discussed. Examples of working compressors for both manual operation to 1000 bar, and automated operation to 100 bar, under computer control, are also given.Full Tex
A quantitative review of slurries for hydrogen storage – Slush hydrogen, and metal and chemical hydrides in carrier liquids
No full textMethods of storing hydrogen for energy applications have been widely discussed, both across time and by people from various organisations and backgrounds. Recently, interest in hydrogen storage has developed for space exploration, for both terrestrial and extra-terrestrial applications, and more recently by politicians and business leaders for displacing carbon-intensive fuels. Hydrogen storage options range from solid to gas phases, with several detailed reviews focussing on metal hydrides such as alkali-earth alloys, chemical hydrides such as ammonia, and liquid organic carriers available. An overlooked part of the literature has been hydrogen storage in slurries, where each method of storage has unique advantages, challenges, and stages of research and development. Here, we focus on reviewing the literature on slush hydrogen and slurries of metal and chemical hydrides.No Full Tex
Performance analysis of a Sieverts apparatus for measuring hydrogen uptake
No full textThe most important measurement made on a new hydrogen storage material is the pressure–composition isotherm that captures the storage conditions and the amount of hydrogen stored. The most popular experimental approach for constructing such isotherms is the Sieverts technique, in which the amount of hydrogen absorbed or desorbed by the sample is inferred from measurements of the hydrogen pressure in a stepwise procedure. An in-depth discussion of the factors contributing to good performance is presented, based on a model of the sensitivity of the Sieverts manifold to changes in hydrogen uptake. Quantification of satisfactory performance may be achieved through a Figure of Merit for the apparatus in combination with the sample to be measured. The Figure of Merit is derived for the general case of a Sieverts apparatus in which the constituent volumes are not at the same temperature, and related to the supposed maximum amount of hydrogen taken up by the sample. The analysis confirms that (i) low sample temperature and high sample molar volume pose challenges for authoritative measurements and (ii) tests with a dense sample like LaNi5 do not validate a Sieverts manifold for accurate measurements with high-surface-area adsorbers such as carbons and metal-organic frameworks. The calculation of a Figure of Merit for a proposed experiment provides an indication of the expected accuracy of the results, as well as scope to vary quantities such as the amount of sample in order to improve the Figure of Merit. In addition, a procedure for devising an optimised experiment is proposed, based on the reference and sample volumes of the Sieverts manifold being configurable.No Full Tex
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Extracting adsorbate information from manometric uptake measurements of hydrogen at high pressure and ambient temperature
No full textTo calculate a gas sorption isotherm from measurements made using the manometric (Sieverts) technique requires accurate knowledge of the sample cell void volume, the volume able to be occupied by the free gas. For many combinations of material and morphology, this volume changes as the sample expands or compresses, swells, undergoes chemical change or adsorbs gas. For gas adsorption measurements on porous materials, the volume of the adsorbate is often accepted as the pore volume, and the adsorbate density changes as the material adsorbs. For materials exhibiting IUPAC type I isotherms, including many carbons, the uptake saturates at high pressures and additional information about the volume (adsorption space) and density of the adsorbate can be extracted at high pressure, provided adsorption has finished. For hydrogen, this typically requires cryogenic temperatures at pressures up to 10 MPa. In this work, hydrogen isotherms are conducted at pressures up to 200 MPa, in order to investigate the properties of the adsorbate at ambient temperatures. In addition, the manometric method gas uptake equations for absolute, excess and net isotherms are revisited and extrapolated to high pressure in order to extract information on the adsorbate volume and density, and enable the construction of the absolute isotherm.No Full Tex
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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