1,720,974 research outputs found
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
Synthesis of a new class of homochiral amines and novel bio-active tropanes
Get PDFThis thesis describes two main programmes: the synthesis of a new class of homochiral amines and the synthesis of ketone analogues of 3a-esterified tropane alkaloids. In chapter one, a scaled-up synthesis of (5)-a-(diphenylmethyl)pyrrolidine 1 is described. The key hydrogenation step of the oxazolidinone intermediate 2 was extended to the synthesis of the other chiral amines 70, 73, 76, 79 and 82. Hydrogenation of the oxazolidinones proceeded in good yields (71 - 87 %) and was not susceptible to racemisation. Thus, a convenient route from amino acid ester hydrochlorides (S)-valine 65, (S)-phenylalanine 66, (S)-alanine 67, (S)-isoleucine 68 and (S)-leucine 69 allowed a range of novel chiral amines to be prepared. In chapters two and three, a new route to ketone analogues of tropane esters is described. In chapter two, results of an attempt to prepare ketone 110 are outlined. Ketone 110 is an analogue of the tropane alkaloid littorine 101, where the bridging ester O atom is replaced by a CH2 group. The first approach to ketone 110 involved the Wittig reaction of acetylmethylenephosphorane 118 and the Homer-Wadsworth- Emmons reaction of diethylbenzoylmethanephosphonate 122 with tropinone 116. Tropinone 116 was found to be particularly unreactive in both cases. The second approach to ketone 110 involved the coupling reactions of both N-troc-3a- tosyloxymethyltropane 170 and N-troc-3 a-iodomethyltropane 185 with 2-phenylacetyl- 1,3-dithiane 147 and 1,3-ditihiane 142. These were also unreactive and as a result the synthesis of ketone 110 remains unresolved. In chapter three, the synthesis of other ketone analogues of naturally occurring 3 a- esterified tropane alkaloids is described. A six-step route to the ketones was devised and in this route the Grignard reactions of tropan-3 -ylacetaldehyde 227 emerged as the key to the success of the strategy. Three ketone analogues 218, 219 and 220 of tropate esters were successfully prepared. Ketone 220, the analogue of apoatropine 201, was found to be a muscarinic acetylcholine receptor antagonist (EC(_50) 1.9x10(^-7) M) in guinea-pigileum, showing a 500-fold less activity than atropine 202. However the activity is still within the clinical range
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
Some applications and chemistry of (S)-2-(diphenylmethyl)-pyrrolidine
Get PDFThe synthetic utility of (S)-2-(diphenylmethyl)-pyrrolidine (1) and its amide derivative, (S)-2-(diphenylmethyl)-5-oxo-pyrrolidine (2) were examined in two contexts; as chiral auxiliary compounds in asymmetric alkylation reactions and Diels- Alder reactions; as chiral solvating agents (CSAs) for (^1)NMR evaluation of chiral acids and alcohols. In the former case, it was shown that monoalkylation of N-acyl derivatives of (1) and (2) using lithiated bases led to poor diastereoselectivities (1:1 to 1.12:1) and poor yields (28 to 33 %), while alkylation reactions using HMPA proceeded with modest diastereoselectivities (1.49:1 to 4.25:1). The results of the Diels-Alder study remain premature at present. In the latter case, (1) was an excellent chiral solvating agent (CSA) for chiral carboxylic acids, however it was less effective for chiral alcohols. The amide derivative (2) was substantially less effective as a CSA for chiral carboxylic acids and failed completely to resolve chiral alcohols
A reaction-based carbazole-dicyanovinyl conjugated colorimetric and ratiometric fluorescent probe for selective detection of cyanide ions
No full textIn the present work, 4-(9'-hexylcarbazol-3'-yl)benzylidenemalononitrile 5 (probe L) was tested as a colorimetric and ratiometric fluorescent probe in dimethyl sulfoxide (DMSO) medium towards anions, cations and neutral molecules. The sensing properties of probe L were investigated by using UV-Vis absorption and fluorescence spectroscopy techniques. Probe L showed selectivity and sensitivity towards cyanide ions (CN-) in the presence of analytes used. Upon the addition of CN-, intramolecular charge transfer (ICT) band at 425 nm in UV spectrum disappeared. In addition, ICT emission intensity at 593 nm decreased and ligand-centred (LC) emission intensity at 480 nm increased. These findings indicate that nucleophilic conjugate addition of CN- to the dicyanovinyl group of probe L successfully occurs, hence forming a new adduct between probe L and CN-. In this adduct, pi-conjugation was partially blocked, and the ICT transfer was hindered. Adduct formation was proved by Job's plot, H-1 NMR and FT-IR analysis. Probe L showed very low limit of detection (LOD) value of 1.467 nM towards CN-. Probe L was also applied to the CN- detection in real-world water samples by the spike and recovery method. The maximum relative standard deviation (RSD) value was 4.24, indicating this method works successfully. Therefore, probe L could find a potential use in detection of CN- in liquid media.Bursa Uludag University [KUAP (F)-2018/14]; Ataturk University [FBA-2021-8808]This work was supported by Scientific Research Programmes (BAPs) from Bursa Uludag University [KUAP (F)-2018/14] and Ataturk University [Project #: FBA-2021-8808]
A red-orange carbazole-based iridium(III) complex: synthesis, thermal, optical and electrochemical properties and OLED application
Get PDFA novel heteroleptic iridium(III) acetylacetonate (acac) complex, (L-5-CHO)2Ir(acac) (3b), was synthesised from 2-(9’-hexylcarbazole-3’-yl)-5-formylpyridine (L-5-CHO) (1b). The complex 3b was determined to be thermally and electrochemically stable. The photoluminescence properties of the compound were studied, with a dichloromethane solution of 3b giving structureless emission at 662 nm, showing that the formyl group red-shifted the emission by 151 nm compared to the parent complex. Complex 3b was also shown to possess a moderate photoluminescence quantum yield (67%) and a short emission lifetime (τ = 280 ns). Organic light-emitting diodes (OLEDs) were fabricated with a solution-processed emissive layer (EML) consisting of poly(N-vinylcarbazole) (PVK), 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) and iridium complex (3b). The OLEDs containing complex 3b showed red-orange electroluminescence (EL) at 624 nm. The influence of the host materials was studied and the best performance was achieved with both PVK and PBD in the emissive layer, with the resulting OLEDs exhibiting a current efficiency of 0.84 cd/A, a power efficiency of 0.20 lm/W, and an external quantum efficiency (EQE) of 0.66% at a brightness of 2548 cd/m2
Carbazole-based D-π-A molecules: Determining the photophysical properties and comparing ICT effects of π-spacer and acceptor groups
Get PDF4-(9′-Hexylcarbazol-3′-yl)benzaldehyde (Cz-Ph-CHO: 4) and 4-(9′-hexylcarbazol-3′-yl)benzylidenemalononitrile (Cz-Ph-CN: 5) were synthesised with the structure of D-π-A, where carbazole, phenylene and formyl/dicyanovinyl groups act as electron donor (D), pi-spacer (π) and electron acceptor (A) units, respectively. The thermal, electrochemical, optical and intramolecular charge transfer (ICT) properties of compounds 4 and 5 were investigated. Compounds 4 and 5, in particular their ICT behaviour, were also compared with the closely related structure, 2-(9′-hexylcarbazol-3′-yl)-5-pyridinecarbaldehyde (Cz-Py-CHO: 7). For the purpose of tuning chemical structure to obtain targeted properties, electrochemical data and absorption and emission measurements suggest that the dicyanovinyl unit in compound 5 is a better acceptor than formyl in compound 4, and that pyridine in compound 7 is a better π-spacer than benzene in compound 4, in exerting ICT characteristics such as fluorosolvatochromism and Stokes shifts. © 2021 Elsevier B.V
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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