1,720,985 research outputs found
MAS NMR characterization of syndiotactic polypropylene: crystal structure and amorphous phase conformation
No full textStretching polymer chains: conformational behaviour of syndiotactic polypropylene in metastable and stable phases
No full textCage-Like Local Structure of Ionic Liquids Revealed by a 129Xe Chemical Shift
No full textThe chemical shift of xenon (at natural abundance) dissolved in a
variety of 1-butyl-3-methylimidazolium-based ionic liquids (ILs) has been measured
with 129Xe NMR spectroscopy. The large chemical shift differences observed are
mainly related to the type of anion; the strongest deshielding effect is observed ILs with
I−, Br−
, and Cl−
anions, and the strongest shielding is found for the
bis(trifluoromethanesulfonyl)imide ([Tf2N]−)-based IL. The measured 129Xe chemical
shift variations correlate well with the IL structure organization imposed by the anions
and with the size of the empty voids due to charge alternation patterns. Descriptors
taken from literature data on X-ray and neutron scattering, as well as single-crystal
structures where available, support this interpretation. The proposed methodology
adds a new investigating tool to the elucidation of the short-range order in ILs. The
observed chemical shift trend provides information about how these solvents are
organized
Funzionalizzazione di nanocellulosa per migliorare la reazione di grafting in situ del copolimero poli(lattide-co-caprolattone)
No full textLow temperature crystallization of ethylene-butene chain segments confined in rigid lamellar geometry
No full textA method based on time domain nuclear magnetic resonance for the forensic differentiation of latex gloves
No full textLatex gloves are employed by felons who want to avoid shedding fingermarks or biological traces, and are sometimes discarded on the crime scene or nearby. Comparison between the gloves found at the crime scene and those seized in the suspect's premises can provide useful information to investigators. This paper proposes the use of 1H time domain nuclear magnetic resonance (TD-NMR) as a method for performing such a comparison. Two parameters can be quantified by this technique: the proton weight fraction, which is correlated to the chemical nature and formulation of the material, and the relaxation time T2, which is a measure of polymer chain dynamics. Both these features can be ultimately associated to differences in raw materials, formulation and processing of the gloves, thereby offering a means to discriminate items which are indistinguishable by visual examination. TD-NMR, without sample preparation and preserving the integrity of the specimen, allows differentiating 88% of the possible pairs of samples in a population of 20 latex gloves. TD-NMR data are complementary to those coming from thermal analysis
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
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