1,720,964 research outputs found
Isotopic effect on the aging dynamics of a charged colloidal system
No full textA dynamic light scattering (DLS) investigation of the isotopic H/D substitution on water molecules in aqueous Laponite suspensions is reported for two Laponite weight concentrations (C-w = 1.5% and C-w = 3.0%). Increasing the deuterium percentage results in a slowing down of the dynamics for both concentrations, although the aging behavior of the suspensions is not qualitatively modified by the isotopic substitution. A scaling law for the isotopic effect is found. The relaxation times and the stretching parameters collapse on two distinct master curves, indicating that the two previously found dynamical behaviors of colloidal gels and glasses are preserved. These results may facilitate a large variety of experimental techniques and further theoretical investigations about the role of the solvent in determining the interaction potential
Firing-Induced Microstructural Properties of Quasi-Diamagnetic Carbonate-Based Porous Ceramics: a 1H NMR Relaxation Correlation Study
No full textThis study deals with the application of two-dimensional proton nuclear magnetic resonance relaxometry (2D 1H NMR-R) to the characterization of porous ceramics nearly free of magnetic compounds. Different microstructural properties were obtained by firing a diamagnetic mixture of kaolin, calcium, and magnesium carbonate over a wide range of maximum temperatures (600–1100 °C) and firing times at the maximum temperature (soaking times) (0–10 h). The 2D 1H NMR-R method relies on the correlated measurement of 1H longitudinal (T 1) and transverse (T 2) relaxation times of pore-filling water by which the properties of the interconnected pore space may be investigated. In the absence of significant magnetic susceptibility effect due to para- and ferro-magnetic compounds, the 2D 1H NMR-R maps allow studying the conjoint effects on pore size distribution and inter-pore coupling due to the variations in both time and temperature of firing. The NMR experiments were performed with a low-field 1H NMR sensor, which allows non-destructive and in situ analysis. For ceramic specimens fired at 600 and 700 °C, the fraction of smallest pores increases with firing time at the expenses of those with intermediate size. The pore shrinkage occurring at this stage, and likely associated with the transformation of kaolinite in metakaolinite, is affected in a similar way by soaking time and firing temperature, in line with the concept of equivalent firing temperature. At temperatures from 800 to 1100 °C, the structural modifications involving interconnectivity and average pore size are driven primarily by firing temperature and, secondarily, by soaking time. The 2D 1H NMR-R results are confirmed by more traditional, but destructive, mineralogical, and structural analyses like X-ray powder diffraction, helium pycnometry, mercury intrusion porosimetry, and nitrogen adsorption/desorption method
Firing technique characterization of black-glazed pottery in Praeneste by low resolution 2D NMR relaxometry
No full textFiring technique characterization of black-slipped pottery in Praeneste by low field 2D NMR relaxometry
No full textThis study was aimed at individuating characteristics related to the pottery’s firing technique of Classical
Roman producers, through the low field single-sided NMR relaxometry. The approach is based on
a recent method of analysis, the correlation of the longitudinal and transverse NMR relaxation times of
a liquid probe (in this case distilled water) filling the porous system of ceramics. The analyzed findings
form two homogeneous classes with dating and place of production well established through the
producer trademarks. Pottery findings belong to the black-slipped pottery productions of the Latin
ancient city of Praeneste between third and second century B.C. and have been attributed to two different
”patriziae” production families: gens Samiaria and gens Trebonia. A further fragment with Greek kylix
style, found in the same archaeological area, has also been analyzed, in order to understand if it had been
imported from Greece, or made in Praeneste in imitation of the Greek style
The structure of water near a charged crystalline surface
No full textThe structure of water near a synthetic clay surface, Laponite, is probed experimentally by total neutron scattering,
in both liquid and arrested states. It is shown that the crystalline structure of the Laponite platelets and their
charge distribution determine polarization of the closest water layers, with a local density higher than that of
bulk water. Interestingly these layers show long range order in the plane parallel to the Laponite surface, while
no indication of strong hydrogen bonding between water and Laponite is 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
Effects of Time and Temperature of Firing on Fe-rich Ceramics Studied by Mössbauer Spectroscopy and 2D 1H-NMR Relaxometry
No full textThe combined effect of firing temperature and soaking time on the microstructure of iron-rich
porous ceramics has been studied by 57Fe-Mössbauer spectroscopy and 2D 1H nuclear magnetic
resonance (NMR) relaxometry by using a single-sided probe. The application of the relaxation
correlation method to water-saturated ceramics provides information about the firing-induced
modifications in both porous and magnetic properties by the concurrent measurement of
longitudinal (T1) and transverse (T2) relaxation times, respectively.
The comparison between the characterization of firing-induced rearrangements in the iron-bearing
species provided by Mössbauer and 1H-NMR analyses shows the high sensitivity of the T1-T2 NMR
correlation technique to even subtle modifications in the magnetic behaviour of Fe-bearing species.
Moreover, the single-sided NMR approach has allowed performing depth-resolved measurements at
the millimeter-scale to non-invasively study the microstructural heterogeneities associated with
non-uniform firing effects inside the ceramic material
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
- …
