1,720,999 research outputs found
The glass transition in colloidal suspensions of silica nanoparticles in a water-lutidine mixture: A photon correlation study
No full textWe discuss the structural and dynamical properties of a colloidal glass of silica nanoparticles in a water-lutidine mixture probed using photon correlation techniques. We describe the small angle set-up used to perform X-ray photon correlation spectroscopy (XPCS) experiments and the procedure followed to measure the volume fraction of the sample. We describe the structure of the glass using a short range potential model and a theoretical structure factor within the mean spherical approximation. The dynamics finally is characterized by a Gaussian-like intermediate scattering function which is not compatible with the classical picture of an heterogeneous diffusive process
Deviation from the virtual crystal approximation in disordered Au-Cu alloy nanocrystals: EXAFS and GIXRD investigation
No full text
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
Deviation from the virtual crystal approximation in disordered Au-Cu alloy nanocrystals: EXAFS and GIXRD investigation
No full textThe short-range order and the crystalline structure of AuCu and AuAg alloy nanoclusters obtained by sequential ion implantation in silica are investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy and by grazing incidence X-ray diffraction (GIXRD). While in the case of AuAg alloy the nearest neighbor interatomic distances correspond to the lattice parameter, in the case of chemically disordered solid solution AuCu alloy a significant deviation from the virtual crystal approximation is observed: the Au-Au, Cu-Cu and Au-Cu nearest neighbor distances are different, only their average corresponding to the fcc lattice parameter. This result, mainly related to the different atomic radius of the two alloy components, is for the first time reported for nanostructured systems
Temperature dependence of the weak host-guest interactions in the p-tertbutylcalix[4]arene 1 : 1 toluene complex
No full textThe temperature dependence of the CH3...π host-guest interaction in the p-tertbutylcalix[4]arene 1:1 toluene complex has been investigated by comparison of its known molecular structure at room temperature (RT) with that at 220K determined by single crystal X-ray diffraction. The diffraction pattern snowed a phase transition when the temperature was decreased from 298 to 220 K. The structure at 220 K could be solved assuming a twin by pseudo-merohedry with a fourfold twin axis [001] relating two monoclinic components with equal volumes of space group P 112/a a=b= 17.899(2), c=13.827(1) Å, V=4429.8(8) Å3, Z=2, mol. weight 741.06 a.m.u., Dcalc = 1.111 g·cm-3. The structure refinement converged to R1=0.103 and wR2=0.256 for 1655 unique observed data. The complex exists in two different conformations of the hosts which exhibit two different host-guest structural relationships both indicating that the most relevant differences induced by the low temperature are concerning the host-guest interaction mode. Particularly unexpected is the different temperature dependence of the CH3...π interactions between the tert-butyl of the host and the aromatic moiety of the guest with respect to that of the van der Waals interactions. The CH3...π interactions, which stabilizes the complex at RT, strongly decrease as the temperature decreases
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
Relaxation Dynamics, Softness, and Fragility of Microgels with Interpenetrated Polymer Networks
No full textMicrogels are elastic and deformable particles with a hybrid nature between that of polymers and colloids and unconventional behaviors with respect to hard colloids. We investigated the dynamics of a soft microgel made of interpenetrated polymer networks of PNIPAM and PAAc by means of coherent X-ray and light scattering techniques. By varying the particle softness through the PAAc content, we can tune at wish the fragility of IPN microgels. Interestingly, we find the occurrence of a dynamical crossover at a critical weight concentration, which leads to an evolution of the structural relaxation time from a super-Arrhenius to a slower than Arrhenius behavior, a minimum for the shape parameter of intensity autocorrelation function, and the emerging of distinct anomalous mechanisms for particle motion. This complex phenomenology can be described by a Fickian diffusion at very low concentrations, an effective non-Fickian anomalous diffusion at intermediate values, and a ballistic motion well described within the mode coupling theory
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
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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