1,721,009 research outputs found
Fumasep FAA-3-PK-130: Exploiting multinuclear solid-state NMR to shed light on undisclosed structural properties
Full text linkFumasep FAA-3-PK-130 is considered the state-of-the-art among the different commercially available Anion Exchange Membranes (AEMs). It is produced by Fumatech GmbH as a cost-effective blend of polyetheretherketone (PEEK) and poly (phenylene oxide) (PPO) characterized by high hydroxyl ions conductivity, high thermal and chemical resistance, and high dimensional stability. Nevertheless, the chemical structure of the anion exchange sites and their contents were unknown so far. In this paper, we report a detailed structural characterization of Fumasep FAA-3-PK-130 to identify the material phase composition, the nature of the conducting moieties and their interactions with the adsorbed water molecules. A complete phase segregation between PPO and PEEK was found on a micrometric scale from 1H spinlattice relaxation times and micro-ATR analysis. Multinuclear (1H, 13C, 19F) Solid-State NMR spectra, combined with nuclear spin relaxation measurements, allowed us to identify the anion exchange moiety with benzyl-ethyldimethylammonium. This is present as functionalizing group of PPO monomers with a functionalization degree of about 40 %. Moreover, the mobility of water absorbed in the membrane was studied by 2H Solid-State NMR on samples hydrated with deuterated water under controlled relative humidity: at low relative moisture, two different types of environments were found for water molecules, compatible with two types of water-ion clusters, one of which contains water molecules with a restricted mobility, limited to C2 jumps, due to strong interactions with ions
Dynamics of Clay-Intercalated Ibuprofen Studied by Solid State Nuclear Magnetic Resonance
No full textIn designing drug delivery systems with improved release properties and bioavailability, the dynamic features of the active pharmaceutical ingredient can be crucial for the final product properties. In this work, we aimed at obtaining the first characterization of the molecular dynamic properties of one of the most common nonsteroidal anti-inflammatory drug, ibuprofen, intercalated in hydrotalcite, an interesting inorganic carrier. By exploiting a variety of solid state NMR techniques, including H-1 and C-13 MAS spectra and T-1 relaxation measurements, performed at variable temperature and carrying out a synergic analysis of all results, it has been possible to ascertain that the mobility of ibuprofen within the carrier is remarkably increased. In particular, strong indications have been obtained that ibuprofen molecules, in addition to internal interconformational dynamics, experience an overall molecular motion. Also considering that ibuprofen is "anchored" to the charged surface of the hydrotalcite layers through its carboxylate moiety, such motion could be a wobbling-in-a-cone. Activation energies and correlation times of all the motions of intercalated ibuprofen have been determined
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
Effect of phosphate additives on the hydration process of magnesium silicate cements: Thermal and spectroscopic characterization
Full text linkThe role of phosphate additives on the hydration process of magnesium silicate cement pastes was investigated through a multi-technique approach. A MgO/SiO2 mixture was hydrated for 28 days either in the absence or in the presence of sodium hexametaphosphate, trimetaphosphate or orthophosphate. Information on the kinetics of the hydration reaction was acquired by monitoring the free water index by means of differential scanning calorimetry, while the hydration products were thoroughly investigated by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and 29Si solid-state nuclear magnetic resonance spectroscopy. The overall results provide new insight into the effect of phosphates on the hydration reaction and on the structure of magnesium silicate hydrate cements. All additives showed a plasticizing effect and promoted the formation of the binding phase magnesium silicate hydrate (M–S–H), without significantly altering its structure. Sodium orthophosphate was found to be by far the best-performing additive, even better than sodium hexametaphosphate, which is commonly used in these cementitious formulations. For the first time, 31P solid-state NMR investigation allowed orthophosphate ion to be identified as the effective species
Solid State NMR Spectroscopy: A multiscale "lens" for understanding complex materials
No full textComplexity is an intrinsic feature typical of the most attractive innovative materials in many different research and application fields, as chemistry, optoelectronics, energy, recycling, medicine. Complexity arises from the coexistence of different chemical components, interfaces and phases, as well as from structural disorder and/ or heterogeneity. Complexity often hinders a detailed characterization of advanced materials, which, on the other hand, is crucial for understanding the functional performances and orienting the design and optimization of innovative materials. Solid State NMR spectroscopy (SSNMR) is an extremely powerful technique, which can effectively bridge this gap. Indeed, it can be applied to substantially every kind of soft and hard material and, by exploiting many nuclear probes and properties, it allows structural and dynamic properties to be characterized on very wide spatial (0.1-100 nm) and frequency (Hz-GHz) scales [1]. In this contribution I will show case studies of advanced materials characterized in the ICCOM-CNR/UNIPI joint lab [2], which, with the acquisition within the year of a last generation SSNMR spectrometer, will be the largest Italian laboratory for the study of materials by SSNMR. Hopefully this contribution will further increase the opportunity for the DSCTM community of taking advantage of this technique.
References:
[1] a. M. Geppi, S. Borsacchi, G. Mollica, C. A. Veracini, Appl. Spectr. Rev. 2009, 44, 1; b. M. Geppi, S. Borsacchi, G. Mollica, Encyclopedia of Magnetic Resonance, Wiley 2008.
[2] (a) F. Martini, M. Tonelli, M. Geppi, F. Ridi, S. Borsacchi, L. Calucci, Cem. Concr. Res. 2017, 102, 60; (b) F. Martini, S. Borsacchi, G. Barcaro, M. Caporali, M. Vanni, M. Serrano-Ruiz, M. Geppi, M. Peruzzini, L. Calucci J. Phys. Chem. Lett. 2019, 10, 5122; (c) E. Carignani, S. Borsacchi, P. Blasi, A. Schoubben, M. Geppi Mol. Pharmaceutics 2019, 16, 2569-2578
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
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