1,721,004 research outputs found
Spray synthesis of monodisperse sub-micron spherical silica particles
No full textA novel spray approach has been developed for the synthesis of controlled size oxide microparticles and the technique is illustrated by the preparation of ca. 250 nm silica particles. Stöber-type spherical silica of uniform particle size is formed by spraying a tetraethoxysilane precursor solution onto the surface of a stirred ammoniacal hydrolysis medium. Particle size characteristics are determined through selection of reaction conditions, with solvent, temperature, reagent concentrations and mixing contributing to the particle size and dispersity. The silica products have been characterized by particle size distribution measurements, electron microscopy and nitrogen adsorption studies. The mechanism of particle formation under differing experimental conditions is discussed.<br/
Analysis of single polymer beads for solid phase combinatorial synthesis: the determination of reactive thiol and within batch polydispersity of bead loadings
No full textPolymer beads are the starting point of many synthetic protocols, and in a number of combinatorial syntheses such studies are based on single beads. It has therefore become important that individual beads carry the same functional group activity and quality control of populations of beads requires a knowledge of the distribution of activity between the individual beads. A procedure was developed for the measurement of the thiol loading of single copolymer beads which is based on the bleaching of Michler's hydrol [4,4'-bis(dimethylamino)diphenylcarbinol (BDC-OH)]. Flow injection colorimetry permits the small volumes of solution generated from single beads to be measured with rapid turnover and with a reproducibility of ca. 2%. The solution detection limit of 0.17 mM corresponds to a bead thiol concentration of 0.33 mmol g(-1). The procedure and the variability of a bead population were demonstrated using modified styrene-divinylbenzene copolymer beads. The apparatus allowed fast, simple and accurate determinations to be carried out on the individual polymer beads. Within a single batch of thiol-modified styrene-divinylbenzene beads thiol loadings ranged from mol per bead. Polydispersity may therefore significantly influence screening decisions based on single bead syntheses
Spectrofluorimetric determination of surface-bound thiol groups and its application to the analysis of thiol-modified silicas
No full textA sensitive spectofluorimetric method has been developed for the quantitative measurement of surface-bound thiol groups. The procedure is based on the quantitative esterification of the thiol group with Rhodamine B and its subsequent release from the solid by base hydrolysis for spectrofluorimetric determination. Application of the method to the analysis of thiol-modified nanoparticulate silicas yielded results that compared favourably against alternative approaches based on measurements of mercury capacity and iodometric titration of the thiol groups. Non-specific Rhodamine uptake, assessed using unmodified silica and C-18-modified silica, did not significantly influence the analytical results. When applied to a typical 50 mg sample, the detection limit of the procedure was 1 nmole SH g(-1) silica
Measurement of the FMOC loading of protected amine-functionalised polymer beads
No full textThis paper presents in HPLC based procedure that has been developed for the determination of the 9-fluorenylmethoxycarbonyl (FMOC) content of protected amine-functionalised polymer beads. FMOC reagents are frequently employed both in the protection of amines and in their determination. The procedure utilises the stoichiometric base cleavage of dibenzofulvene from the protected amine using 1,8-diazabicyclo undec-7-ene. This stearically hindered base prevents the adduct formation that occurs with alternative base systems and measurement performance is enhanced by the incorporation of anthracene into the system as a non-reactive internal standard. HPLC separation of the reaction products permits the measurement of FMOC in the presence of additional chromophores that might otherwise impede direct measurement by UV-vis spectrophotometry. The procedure has been evaluated for the measurement of the FMOC content of protected amine-modified polymer beads employed in combinatorial solid phase synthesis
Tritium accumulation in salt marsh sediments from the Severn Estuary, UK (abstract of poster presented at AGU 2004 Joint Assembly, 17-21 May 2004, Montreal, Canada)
No full textSpatial and temporal variation of tritium activities in coastal marine sediments of the Severn Estuary (abstract of paper presented at 12th Annual V.M. Goldschmidt Conference, Davos, Switzerland, August 18-23, 2002)
No full textFactors influencing operational efficiency of an electrostatic solvent extraction system
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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
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
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