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Multiple equilibria describe the complete adsorption isotherms of nonporous, microporous, and mesoporous adsorbents
Full text linkThe adsorption of simple gases begins with the formation of a monolayer on the pristine surface, not always followed by the formation of a second or more monolayers. Subsequently, cluster formation or cavity filling occurs, depending on the properties of the surface. The characteristically different shape of the isotherms related to these processes allows to clearly differentiate them. We analyzed argon and N2 adsorption isotherms quantitatively over the entire relative pressure range for adsorbents bearing different properties: the nonporous Stöber-type particles, the microporous zeolite L (ZL) and zeolite L filled with indigo (Indigo-ZL), and three mesoporous silica adsorbents of different pore size. The formal equilibria involved in cluster formation and in cavity filling have been derived and successfully applied to quantitatively describe the isotherms of the adsorbents. No indication regarding formation of a second monolayer on top of the first one was observed for the Stöber-type particles. Instead, cluster generation, which minimizes surface tension, starts early. The behavior of microporous ZL and of Indigo-ZL is different. A second monolayer sets up and cluster formation starts with some delay. The enthalpy of cluster formation is, however, practically identical with that seen for the Stöber-type particles. The difference between the experimental and the calculated inflection points is very small. The shapes of the isotherms seen for the mesoporous adsorbents differ significantly from those seen for the nonporous and for the microporous adsorbents. The quantitative analysis of the data proves that formation of a second monolayer is followed by filling of cavities which ends as soon as all cavity sites are filled. The sum of the individual fractional contributions, namely the monolayer formation ΘmL, the appearance of a second monolayer Θ2L on top of the first one, and the cavity filling, yields a calculated adsorption isotherm Θcalc which describes the experimental data Θexp well. The experimental and the calculated first inflection points are in excellent agreement, which is also the case for the second inflection points. The value of the cavity filling enthalpy is roughly 10% larger than that for the cluster formation seen in the nonporous and the microporous adsorbents. The volume for cavity filling is significantly smaller than the monolayer volume for the mesoporous adsorbent with a pore diameter of 2.7 nm, while it is the same or larger for pore diameters of 4.1 nm and 4.4 nm, respectively. We conclude that understanding the adsorption isotherms as signature of several sequential chemical equilibrium steps provides additional information data for clusters, cavities, and position of the inflection points, not accessible by means of the conventional models. The theory reported herein covers type I, II, IV and to some extent also type VI isotherms
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
Entropy in multiple equilibria : argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous materials
Full text linkAnalysis of multiple equilibria of compounds with different coordination sites is extended to the description of adsorption isotherms with focus on the low relative pressure range. The entropy evolution is described using the particle distribution theory which also holds for adsorbents consisting of materials bearing more than one type of sites and applies for the condition that the adsorptive-adsorbent binding strength is larger than the adsorptive- adsorbate binding strength, so that monolayer coverage is favored. This allows to accurately determine the adsorption enthalpy. No assumption concerning the growth mechanism and specifics regarding the structure of the surface is needed. We find on a rigorous basis that this leads to Langmuir’s equation for each site inde-pendently, that the total fractional amount of bound adsorptive can be described as a linear combination of individual Langmuir isotherms, and that such a linear combination has never the shape of the original Langmuir isotherms. The results are successfully applied to argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous adsorbents which allows comparing systems for which the properties of the active surface span a large range. We observe that all experimental data can accurately be described by means of a linear combination of two Langmuir isotherms in the low relative pressure range up to a coverage of 60%–95%. This means that the shape of all adsorption isotherms is essentially determined by the entropy decrease with increasing coverage. The two site interactions involved exhibit substantially different adsorption enthalpies. Interestingly the Ar enthalpy of adsorption ΔadsH∅1 of the sites 1 for the St¨ober-type silica and of the three investigated MCM-41 adsorbents (with pore size of 2.7 nm, 4.1 nm, and 4.4 nm) are similar, namely 11 kJ/mol. The situation is analogous for the enthalpy of adsorption ΔadsH∅2 for the sites 2, which amounts to 8 kJ/mol. A significantly larger enthalpy of adsorption ΔadsH∅1 for the sites 1, namely 14.3 kJ/mol, and ΔadsH2∅ = 11.7 kJ/mol for the sites 2 is measured for potassium zeolite L thus reflecting the more polar nature of this adsorbent. The measured specific surface area for these samples ranges from 14 m2/g for the St¨ober-type silica up to 1100 m2/g for the MCM-41(4.1 nm) adsorbent. The information provided by the lc2-L (linear combination of 2 Langmuir functions) analysis allows calculating the evolution of the coverage of site 1 and of site 2 as a function of increasing pressure. The inflection points of the isotherms, which mark the point where the curvature changes sign, were determined by numerically evaluating the second derivatives which vanish at this point and are compared with values obtained using BET analysis
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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