1,720,994 research outputs found
The three-dimensional hydrogen-bonded structures in the ammonium and sodium salt hydrates of 4-aminophenylarsonic acid
No full textThe structures of two hydrated salts of 4-aminophenylarsonic acid (p-arsanilic acid), namely ammonium 4-aminophenylarsonate monohydrate, NH4(+)·C6H7AsNO3(-)·H2O, (I), and the one-dimensional coordination polymer catena-poly[[(4-aminophenylarsonato-κO)diaquasodium]-μ-aqua], [Na(C6H7AsNO3)(H2O)3]n, (II), have been determined. In the structure of the ammonium salt, (I), the ammonium cations, arsonate anions and water molecules interact through inter-species N-H...O and arsonate and water O-H...O hydrogen bonds, giving the common two-dimensional layers lying parallel to (010). These layers are extended into three dimensions through bridging hydrogen-bonding interactions involving the para-amine group acting both as a donor and an acceptor. In the structure of the sodium salt, (II), the Na(+) cation is coordinated by five O-atom donors, one from a single monodentate arsonate ligand, two from monodentate water molecules and two from bridging water molecules, giving a very distorted square-pyramidal coordination environment. The water bridges generate one-dimensional chains extending along c and extensive interchain O-H...O and N-H...O hydrogen-bonding interactions link these chains, giving an overall three-dimensional structure. The two structures reported here are the first reported examples of salts of p-arsanilic acid
Potential forensic markers from synthetic pathways to 1-phenyl-2-propanone from uncontrolled and controlled substances
No full text2-Phenylpropionaldehyde (a controlled substance; known as hydratropic aldehyde) was converted to 1-phenyl-2-propanone, using acid sources, with both a very high acidity and low oxidising strength. Key side products, acetophenone and 1,4-dimethyl-2-phenylnaphthalene, were identified as potential marker compounds. These results allowed 2-phenylpropionaldehyde to be identified as a pre-precursor to methamphetamine. Application of a previously reported rearrangement of hydratropic aldehyde, and formation of semicarbazone derivatives, established that acetophenone had been erroneously reported in the older literature as 1-phenyl-2-propanone. Density functional theory calculations at the B3LYP/6-31G(d,p) and ωB97X-D/6–31++G(d,p) level of theory indicated that a proposed superelectrophile rearrangement mechanism of 2-phenylpropionaldehyde to 1-phenyl-2-propanone (involving double protonation of the 2-phenylpropionaldehyde) was more energetically favourable than an analogous mechanism involving singly protonated species, rationalising the requirement for very high acidities to achieve the rearrangement. Ethyl methylphenylglycidate (an uncontrolled substance) was identified as a potential pre-precursor to methamphetamine through conversion to 2-phenylpropionaldehyde and its subsequent rearrangement to 1-phenyl-2-propanone and key side product acetophenone. Notably, the key side products acetophenone and 1,4-dimethyl-2-phenylnaphthalene should serve as forensic markers for profiling and may indicate the 2-phenylpropionaldehyde and ethyl methylphenylglycidate rearrangement pathways when screening seized clandestine samples of 1-phenyl-2-propanone and methamphetamine.No Full Tex
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
Forensic implications of novel synthesis of cathinone derivatives by Neber and modified Neber rearrangements
No full textCathinone and its synthetic analogues are known compounds of clandestine interest. Investigation into novel pathways for synthesising cathinone derivatives has potential for forensic analysis and tracking. The known Neber rearrangement of commercially available phenylpropanones that were evaluated yielded amides described herein and was not viable for clandestine synthesis of cathinone derivatives. Whereas the known modified Neber rearrangement of phenylpropanones that were evaluated via stable aziridine salts and subsequent treatment with acid, gave cathinone derivatives described herein in poor to low yields (2–17%). Assessment of the reagents, equipment, and procedures required for the modified Neber rearrangement was considered as only viable for more advanced clandestine operations. An improved understanding of the potential by-product formation from the modified Neber rearrangement was determined by density functional theory (DFT) of hydrazone to azirine to aziridine intermediates and attempted dynamic NMR spectroscopy of a hydrazone described herein. The substantially lower energy of the azirine step compared to the starting hydrazonium salt step of the reaction mechanism implied that the azirine structure was a short-lived intermediate, and unable to be experimentally determined. New mass-spectral fragmentation data of compounds described herein was reported, where differentiation was observed for some individual compounds at the GC-EIMS fragmentation pattern level. From this study, individual mass-spectrometry fragmentation of key compounds evaluated from the modified Neber rearrangement of commercially available phenylpropanones indicates potential for forensic profiling analysis applications.Full Tex
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
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