1,721,078 research outputs found
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
High accuracy OrMoSil (Polyvinylidene Fluoride)-supported colorimetric sensor: Novel approach for the calculation of the pH prediction error
No full textpH colorimetric sensors with prediction error comparable to the potentiometric measurements in the working range of the indicator employed, were prepared. Bromothymol Blue (BB), Tetrabromophenol Blue (TBB), Cresol Red (CR) and Brilliant Yellow (BY) in PVDF (Polyvinylidene Fluoride)-supported OrMoSil (organically modified silicate) matrix, were used. Sensor preparation was reproducible. Signal was based on a suitably modified Hue coordinate from HSV (Hue, Saturation, Value) color space, H. Although H profile was not influenced by the indicator concentrations, the prediction error depended on the product of saturation and luminance, Δ. By using H, the response of every spot was less affected by shape and optical inhomogeneity. The H calibration held for all the spots of the same lot and remained identical in time giving an advantage with respect to a glass electrode requiring calibration before each set of measurements. The prediction errors both in solution and in the OrMoSil matrix were similar: for BB, spHjavax.xml.bind.JAXBElement@315a8962 = 0.03 in both environments; for TBB, spHjavax.xml.bind.JAXBElement@4f058030 = 0.02 in the sensing spot and 0.05 in solution; for CR, spHjavax.xml.bind.JAXBElement@4ee5bdc0 = 0.11 in the sensing spot and 0.04 in solution; for BY, spHjavax.xml.bind.JAXBElement@36932dcd = 0.17 in the sensing spot and 0.07 in solution. Indeed, H values of TBB and BB increased their variances near the inflection point where Δ has the minimum value (heteroscedastic behavior)
Analisi Energetica LCA di un Collettore Solare Sotto-Vuoto
No full textNel panorama delle tecnologie alimentate da fonti rinnovabili, i sistemi che sfruttano la fonte solare rappresentano probabilmente le tecnologie oggi più affidabili. Gli stessi impianti sono peraltro soggetti ad una continua evoluzione tecnologica con rapidi tempi di recepimento da parte dell’industria.
Questo articolo rappresenta una analisi sul ciclo di vita (LCA, Life Cycle Assessment) di un impianto solare termico a collettore sottovuoto, a circolazione naturale, utilizzato per la produzione di acqua calda sanitaria e per il riscaldamento. L’analisi svolta ha permesso di valutare in termini energetici, ambientali ed economici la convenienza di un siffatto impianto solare termico con riferimento ad un edificio monofamiliare.
Le analisi energetiche sono state elaborate, simulando l’esercizio dell’impianto in tre diverse località italiane (Palermo, Roma e Bologna)
Kinetic response of pH colorimetric sensors: Role of the cationic surfactant concentration and amount and type of solvent used in the preparation of the sensing spot
No full textA pH colorimetric sensor array (CSA) with a kinetic response comparable to those of the pH-meter was prepared. The signal comes from the Hue coordinate (H) and RGB profiles of some pH indicators such as Bromothymol Blue (BB) and Nitrazine Yellow (NY) in polyvinylidene fluoride (PVDF)-supported organically modified silicate (OrMoSil) spots. The t95 is of the order of 50–150 s for RGB coordinates but is lowered of one order of magnitude employing the H coordinate as the detection signal. The addition of the Hexadecyltrimethylammonium p-toluenesulfonate (CTApTs) additive in the interval 0.10 0.19 gCTApTs/gprecursors, the transition from the basic to the acid form was hindered by the cationic interface due to the surfactant. The CTApTs concentrations, leading to a t95 lower than one minute, were in the interval 0.10 < R < 0.37 gCTApTs/gprecursors for NY and 0.10 < R < 0.28 gCTApTs/gprecursors for BB, comparable to the response time of the potentiometric measurements. Indeed, the kinetic profiles did not change with the amount and type of solvent
Influence of surfactant chain length, counterion and OrMoSil precursors on reversibility and working interval of pH colorimetric sensors
No full textAn in-depth study was conducted to determine the influence of some important parameters to produce a pH colorimetric sensor characterized by long-term stability, lack of leaching, high reversibility, repeatability and extended working range. Bromothymol Blue (BB) was used as pH sensitive molecule. Its performance was monitored while tailoring the concentration of some added cationic surfactants, together with the organic fraction of the sol-gel composition to avoid leaching phenomena, low homogeneity and to increase reversibility. Five cationic surfactants with different linear alkyl chain length (from C8 to C18) were added to a sol-gel containing BB. The C16 was chosen as optimal. The effect of the surfactant counterion was also investigated. The C16 surfactant had a pH working interval of 3 pH unit by using chloride, 1.5 with bromide and 1 pH unit with p-toluenesulfonate as counterions, respectively. Chloride was characterized by a larger inhomogeneity while p-toluenesulfonate gave homogeneity and high repeatability. The hexadecyltrimethylammonium p-toluenesulfonate was therefore chosen as the best surfactant. Leaching in alkaline medium was avoided by using the dodecyl moiety among three organic groups linked to the OrMoSil matrix (dodecyl, phenyl and methyl). Colorimetric sensor arrays made with these specifications remained stable and reversible for months
Determination of the relevant equilibrium constants working in pH Colorimetric Sensor Arrays (CSAs)
No full textThe rationalization of the behavior of pH Colorimetric Sensor Arrays, based on Bromophenol Blue embedded in tetraethyl orthosilicates-based matrices, was accomplished by calculating the thermodynamic constants of the reactions involved. The constants were determined in four matrices upon variation of the concentration of surfactant, indicator, and anionic species present in buffers and samples. Based on the values found, it was demonstrated that the variation of the surfactant concentration widened the working interval up to 1.80 and 5.30 pH units in the solution and one of the tested polymers, respectively. The competitive reaction between anionic species and cationic head-groups of the surfactant shifted the position of the calibration profile up to 1.50 pH units in solution. For the CSA, the shift was 0.35 pH units for a large concentration of surfactant (0.1 M) and negligible at low concentrations (<0.01 M). The proposed mechanism allowed for a very good curve fitting in all conditions
Reversible and high accuracy pH colorimetric sensor array based on a single acid-base indicator working in a wide pH interval
No full textA pH colorimetric sensor array (CSA) with fast response time (<1 min) using only one acid-base indicator, Bromothymol Blue (BB), was prepared and characterized by modulating the amount, C, of the surfactant Hexadecyltrimethylammonium p-toluenesulfonate between 0 and 0.3725 gCTApTs/gprecursor with a constant amount of the OrMoSil precursors. The effect of the C increase is a continuous acidic shift of the calibration position, i.e. a huge variation of the pKa value of BB in the pH range 5.80-13.50. The precision error decreased with increasing C from 0.096 pH units (lower C values) to 0.023 pH units (larger C values). This result led to the development of a model to determine the number of spots with suitable C values required for having a similar value of precision in the entire working interval of the CSA. By selecting only 4 spots the precision error is < 0.100 pH units in the pH range 5.80–13.50. With 256 spots (diameter of each spot ≈ 3 mm), the model predicted an error almost constant (≈0.010) in the entire pH range
- …
