1,720,995 research outputs found
Physical and chemical aspects of the interaction of molecules with external surface and structural cavities of nanomaterials.
Full text linkThe research work carried out during this PhD project has been aimed to the investigation of molecular surface events relevant for the catalytic formation, in mild conditions, of amide/peptide bonds from non-activated reagents adsorbed on nanomaterials. The formation of C-N bonds is among the topics of high interest in modern research in chemistry, addressing issues ranging from fine to prebiotic chemistry. The implementation of this project required the selection of both catalyst and reactants. As for the nanomaterials, the criteria of choice were simplicity, availability and low cost for possible future applications and, on the other hand, reasonable representativeness of minerals possibly present on the early Earth, and active as catalyst towards adsorbed organic molecules. On this basis the following nanoparticles of silica and titania are selected as well as a zeolite of the ZSM-10 type, with a MOZ framework. This latter material was intended as a porous host for future studies of the high pressure induced oligomerization of amino acids. This part of the work belongs to a very recent project, and then the work carried out in this respect in this PhD thesis is focused on the synthesis of zeolite particles with proper framework features. The choice of reactants was driven, on one hand, on the suitability to be studied in depth by both experimental methods and theoretical modelling, and on the other hand, by the possibility to adsorb them on surfaces of nanomaterials from the vapour phase, i.e. in highly controlled conditions. Thus, the simplest carboxylic acid, HCOOH was selected, as well as two simple primary amines (methylamine and 1-pentanamine). One of the surface reaction investigated was the oligomerization of amino acids on the nanomaterials and for this glycine, alanine, histidine, serine were selected because of the possibility to adsorb them on catalyst via a chemical vapour deposition method. In summary, in Chapter One, the study targeting the elucidation of the mechanism of the amide bond formation between non-activated carboxylic acids and amines at the surface of amorphous silica is reported. The results prepare the ground to address the occurrence of this reaction and of the oligomerization of amino acids (glycine and alanine) at the surface of α-quartz sub-micrometric particles (Chapter Two). The study of the C-N bond formation at the surface of titania nanoparticles is the object of Chapters Three to Five. In particular, Chapter Three is devoted to the investigation the structural requirements of sites expose at the surface of titania nanoparticles in order they can act as catalytic sites towards amino acid oligomerization. In Chapter Four, insights on basic aspects of the interaction of formic acid and methylamine with the 101 anatase titania surface are presented. The possibility to prepare Ser-His dipeptides starting from non-activated amino acids by using titania nanoparticle as catalyst and the possible hydrolytic activity of the obtained peptides is the object of Chapter Five. Finally, in Chapter Six, challenges, successes and problems still to be solved for and effective synthesis of large ZSM-10 particles, required for multitechniques investigations, including single crystal X-ray diffraction
The case of HCOOH on (101) anatase TiO2: where is the acid proton?
No full textLike a pearl in a shell, the formic‐acid proton at the TiO2 anatase(101) surface is concealed from experiments and protected from attacks by bases. This is caused by quantum delocalization at low temperatures and molecule‐to‐surface proton shuttling at room temperature, as reported by E. Fois and co‐workers in their Communication (DOI: 10.1002/anie.201906709). Artwork: Andrea Stangon
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
The case of formic acid on (101) anatase TiO2: where is the acid proton?
Full text linkCarboxylic-acid adsorption on anatase TiO2 is a relevant process in many technological applications. Yet, despite several decades of investigations, the acid-proton localization—either on the molecule or on the surface—is still an open issue. By modeling the adsorption of formic acid on top of anatase(101) surfaces, we highlight the formation of a short strong hydrogen bond. In the 0 K limit, the acid-proton behavior is ruled by quantum delocalization effects in a single potential well, while at ambient conditions, the proton undergoes a rapid classical shuttling in a shallow two-well free-energy profile. This picture, supported by agreement with available experiments, shows that the anatase surface acts like a protecting group for the carboxylic acid functionality. Such a new conceptual insight might help rationalize chemical processes involving carboxylic acids on oxide surfaces
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
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