1,721,010 research outputs found
Magnetic and relaxometric properties of novel classes of superparamagnetic MRI contrast agents
No full textLi-7 Nuclear Magnetic Resonance in the Hexairon(III) Antiferromagnetic Molecular Ring Fe6:Li
No full textThe mol. nanomagnet [LiFe6(OCH3)12(dbm)6]BPh4·5CH2Cl2 (Fe6:Li in short) is formed by six Fe(III) s = 5/2 spins arranged in an almost coplanar ring with antiferromagnetic (AFM) nearest-neighbor coupling const. J/kB∼20 K. The authors report 7Li NMR spectra and nuclear spin-lattice relaxation rate (NSLR) measurements as a function of temp. from 1.5 to 50 K with applied field H = 1.5 T. No evidence of quadrupole effects was found on the 7Li NMR spectrum within the linewidth resoln. (∼25 kHz) ruling against a mol. distortion. The 7Li NSLR is compared with the 1H NSLR results in Fe6:Li and in other AFM rings
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
Easily available, low cost 19F MRI agents: Poly(ethylene-glycol)-functionalized fluorinated ethers
No full textA simple derivatisation of commercially available poly(ethylene-glycols) of different molecular weight followed by the reaction with the selected fluorinated organic molecule, perfluoro-tertbutanol, allowed an easy synthesis of several novel polymers of different fluorine content. The properties of the new materials as MRI agents were preliminarily investigated. In all cases a single 19F signal at NMR in deuterated chloroform and D2O was registered; for a few fluorinated polymeric candidates a good solubility in water was observed and MR imaging of the fluorinated polymer successfully provided images. Most interesting results were obtained with the sample of 1436 MW (24% fluorine content) that not only gave a spectrum with a single resonance line, but, most importantly, was tolerated in low doses when in vivo experiments on animals (mice) were conducted
In vivo imaging of glia activation using 1H-magnetic resonance spectroscopy to detect putative biomarkers of tissue epileptogenicity
No full textPurpose: Long-lasting activation of glia occurs in brain
during epileptogenesis, which develops after various central
nervous system (CNS) injuries. Glia is the cell source
of the biosynthesis and release of molecules that play a
role in seizure recurrence and may contribute to epileptogenesis,
thus representing a putative biomarker of epilepsy
development and severity. In this study, we set up an
in vivo longitudinal study using 1H-magnetic resonance
spectroscopy (MRS) to measure metabolite content in
the rat hippocampus that could reflect the extent and the
duration of glia activation. Our aim was to explore if glia
activation during epileptogenesis, or in the chronic epileptic
phase, can be used as a biomarker of tissue epileptogenicity
(i.e., a measure of epilepsy severity).
Methods: 1H-MRS measurements were done in the adult
rat hippocampus every 24 h for 7 days after status epilepticus
(SE) and in chronic epileptic rats, using a 7 T Bruker
Biospec MRI (magnetic resonance imaging)/MRS scanner.
We studied changes in metabolite levels that reflect astrocytes
(myo-inositol, mIns; glutathione, GSH), microglia/
macrophage activation and the associated neuronal cell
injury/dysfunction (lactate, Lac; N-acetyl-aspartate, NAA).
1H-MRS results were validated by post hoc immunohistochemistry
using cell-specific markers. Data analysis was
done to determine whether correlations exist between
the metabolite changes and spontaneous seizure frequency
or the extent of neuronal cell loss. Key Findings: The analysis of 1H-MRS spectra showed a
progressive increase in mIns and GSH levels after SE,
which was maintained in epileptic rats. Lac signal transiently
increased during epileptogenesis being undetectable
in chronic epileptic tissue. NAA levels were
chronically reduced from day 2 post-SE. Immunohistochemistry
confirmed the activation of microglia and astrocytes
and the progressive neuronal cell loss. GSH levels
during epileptogenesis showed a negative correlation with
the frequency of spontaneous seizures, whereas S100b levels
in epileptic tissue were positively correlated with this
outcome measure. A negative correlation was also found
between GSH or mIns levels during epileptogenesis and
the extent of neurodegeneration in hippocampus of epileptic
rats.
Significance: 1H-MRS is a valuable in vivo technique for
determining the extent and temporal profile of glia activation
after an epileptogenic injury. S100b levels measured in
the epileptic tissue may represent a biomarker of seizure
frequency, whereas GSH levels during epileptogenesis
could serve as a predictive marker of seizure frequency.
Both mIns and GSH levels measured before the onset of
spontaneous seizures predict the extent of neuronal cell
loss in epileptic tissue. These findings highlight the potential
of serial 1H-MRS analysis for searching epilepsy biomarkers
for prognostic, diagnostic, or therapeutic purposes
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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