1,721,170 research outputs found
The alkyne-cluster interaction: structural, theoretical and mechanistic studies on the M2M'(CO)9(.mu.3-.eta.2-alkyne) complex (M = Fe; M' = Fe and Ru)
No full textOximation of acetyl(hydroxyimino)acetone: nuclear magnetic resonance spectroscopic, chemical, and X-ray crystallographic studies of the reaction products
No full textFrom molecular crystals to salt co-crystals of barbituric acid via the carbonate ion and an improvement of the solid state properties
No full textCo-crystals formed by neutral barbituric acid (HBA) molecules and alkaline barbiturate salts have been prepared by solvent-free mechanochemical treatment of solid HBA and alkaline carbonates or bicarbonates. During the reaction the carbonate salts release CO2 and H2O, affording the corresponding barbiturate salts which then co-crystallize with the neutral molecule. These "salt co-crystals" have the general formula M x+(BA-)x·HBA·nH 2O with (M = Na and K). The compounds can be obtained in a single step, by directly grinding HBA with M2CO3 (4:1 ratio) or MHCO3 (2:1 ratio), or, alternatively, in two steps: the preparation of the BA salt followed by a further grinding process or crystallization of the resulting salts with a stoichiometric amount of neutral HBA. All compounds have been characterized by means of single-crystal and powder XRD, solid-state NMR (1H MAS, 13C and 15N CPMAS), vibrational spectroscopies and thermal methods (DSC and TGA). A series of BA- salts (either hydrated or anhydrous) of formula Mx +(BA-)x·nH2O (M = Na, K, Mg and Ca) have also been prepared and reported for comparison
Molecular Salts of Anesthetic Lidocaine with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study
No full textFour lidocaine molecular salts of dicarboxylic acids (oxalic, fumaric, malonic, and succinic) were synthesized and characterized by a combined use of X-ray power and single-crystal diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and solid-state NMR (H-1 MAS and CRAMPS, and C-13 and N-15 CPMAS); all molecular salts show a dramatic increase in their melting point with respect to both lidocaine and lidocaine hydrochloride, and a higher dissolution rate and thermodynamic solubility in physiological solution with respect to the free base
Precessional Motion in Crystalline Solid Solutions of Ionic Rotors
No full textThe order–disorder phase transition associated with the uprise of reorientational motion in (DABCOH2)2+, in the supramolecular salts of general formula [1·(DABCOH2)]X2 (where 1=12-crown-4, DABCO=1,4- iazabicyclo[2.2.2]octane, and X=Cl- or Br-), has been investigated by variable temperature X-ray diffraction on single crystals and powder samples, as well as by DSC and solid-state NMR spectroscopy (SSNMR). The two compounds undergo a reversible phase change at 292 and 290 K, respectively. The two crystalline materials form solid solutions [1·(DABCOH2)]Cl2xBr2(1-x) in the whole composition range (0 < x<1), with a decrease
in the temperature of transition to a minimum of ca 280 K, corresponding to x=0.5. Activation energy values for the dynamic processes, evaluated by variable-temperature 13C magic-angle spinning (MAS) SSNMR and line-shape analysis are ca. 50 kJmol-1 in all cases. Combined diffraction and spectroscopic evidence has allowed the detection of a novel dynamic process for the (DABCOH2)2+ dications, based on a room temperature precessional motion that is frozen out below the disorder–order transition; to the best of the authors’ knowledge this phenomenon has never been observed before
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
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