1,721,066 research outputs found
Validation of Hydrogenography for the search of promising hydrogen storage materials
No full textHydrogenography is a combinatorial optical thin film technique to study the thermodynamic properties of metal hydride storage materials. It allows to study thousands of compositions simultaneously with exactly the same experimental conditions. Hydrogenography can pin point the most interesting regions/compositions in binary, ternary, quaternary etc. M-H phase diagrams. This valuable information can then be used in bulk experiments to measure other parameters such as the hydrogen volumetric density. The main advantage of Hydrogenography comes from the possibility to create thin film compositional gradients, allowing for fast and efficient screening. The main drawback of this approach is the presence of the rigid substrate, used to support the metal thin films. During (de-)hydrogenation reaction the substrate exerts a force, due to the clamping, leading to a modification of the thermodynamics properties as measured by Hydrogenography. Therefore, before drawing conclusions on the corresponding bulk materials, the Hydrogenography experiment should be properly analyzed. First, it is important to verify whether the film remains clamped to the substrate or has a tendency to delaminate. Delaminated or buckled films, as in the case of Pd, exhibit thermodynamic properties similar to bulk materials; in this case no correction to the enthalpies or entropies should be applied, i.e. Hfilm?Hbulk, Sfilm?Sbulk. Similar conclusion holds for other metal hydride systems, if the film under investigation is protected from the interaction (alloying) with the capping layer (Pd, Ni) by means of a buffer layer. Otherwise, a larger influence of the substrate on the thermodynamics is expected. Second, one needs to be aware of an expanded hysteresis and, consequently, affected thermodynamic parameters when the film remains in full contact with the substrate. The enthalpy of formation- which is always modified by a bulk hysteresis term- obtains an additional component due to the clamping by the substrate (Hfilm?Hbulk+Hclamping). The proper way to estimate the thermodynamics of the bulk from the thermodynamics of the clamped film, is then to perform a stress-strain analysis at several temperatures. The stress-strain model, developed in this thesis, is able to quantitatively predict the clamping effect. It postulates that the increase of the hysteresis in thin films is taking place due to severe ‘reversible’ plastic deformations. Bulk metal hydrides disproportionate into small grains, when the hydrogenation stresses become higher than the Yield stress, thus releasing most of the stresses. This behavior is not possible in films due to presence of the substrate. The outcome of the stress-strain analysis is Ghyst parameter, which represents an additional mechanical work, performed by the film during the (de-)hydrogenation cycle due to the expansion constraints. This mechanical work increases when increasing the ‘complexity’ of the hydrogen storage system. For the metal hydrides studied in this thesis it ranges from 1.69 kJ/mol H for PdH0.6, 2.93 kJ/mol H for MgH2, 3.52 kJ/mol H for Mg2NiH4 to 4.25 kJ/mol H for YH3. Ghyst can be used to recalculate back the equilibrium pressures of the free-standing film (film without a substrate). From the linear fit to the new pressure values the enthalpy and entropy of the corresponding bulk materials can be evaluated. This approach, however, is only valid for metal hydrides with no structure transformation (Pd case) or for metal hydrides which become amorphous on subsequent (de-)hydrogenation, such as MgH2. When the material cycles between preferentially oriented crystalline metal and metal hydride states, as in the case of YH3 and Mg2NiH4, the equilibrium pressures become affected by an additional parameter, Gstr. It represents the energy involved in the structure transformation and should be added to Ghyst in order to fully describe the hysteresis behavior in these films. The Gstr equals to 5.2 kJ/(mol H) and 4.5 kJ/(mol H) for YH3 and Mg2NiH4, respectively, which is a quite substantial amount of energy which cannot be disregarded. Thus, any other metal hydride system, possessing a structure transformation and remaining crystalline on cycling, will require this parameter, which can be measured via calorimetry or calculated via first principles methods. An alternative approach to correct for the clamping effect is to subtract the energetic value of the clamping effect, Hclamping (the change in enthalpy due to clamping in kJ/mol H), from the measured thin film enthalpy: Hbulk ? Hfilm -Hclamping. This, however, requires knowledge of the Hclamping in advance, which, again, can be estimated from the stress-strain analysis. The problem with this approach is that the entropy cannot be recalculated in this way. Hydrogenography allows for comparison of thousands of compositions under exactly the same conditions. As a result, by measuring the Mg-Ti-Al-H system we identified an enthalpy-entropy compensation effect. Whenever we saw an increase of the enthalpy, simultaneously the entropy values were increasing (both in absolute sense). As a result, the equilibrium pressures remain almost the same. We can exclude trivial reasons related to the conditions of measurement, presence of the substrate etc. The origin of this effect remains unclear and requires further study. It shows, however, that the analysis of absorption/desorption equilibrium pressure at the relevant temperature is required in addition to the estimated thermodynamic parameters in order to evaluate different metal hydrides as hydrogen storage systems.DelftChemTechApplied Science
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
- …
