1,720,962 research outputs found
Interface Enthalpy-Entropy Competition in Nanoscale Metal Hydrides
Full text linkWe analyzed the effect of the interfacial free energy on the thermodynamics of hydrogen sorption in nano-scaled materials. When the enthalpy and entropy terms are the same for all interfaces, as in an isotropic bi-phasic system, one obtains a compensation temperature, which does not depend on the system size nor on the relative phase abundance. The situation is different and more complex in a system with three or more phases, where the interfaces have different enthalpy and entropy. We also consider the possible effect of elastic strains on the stability of the hydride phase and on hysteresis. We compare a simple model with experimental data obtained on two different systems: (1) bi-phasic nanocomposites where ultrafine TiH2 crystallite are dispersed within a Mg nanoparticle and (2) Mg nanodots encapsulated by different phases
Hydrogen Desorption below 150 °c in MgH2-TiH2 Composite Nanoparticles: Equilibrium and Kinetic Properties
Full text linkReversible hydrogen sorption coupled with the MgH2 <-> Mg phase transformation was achieved in the remarkably low 340-425 K temperature range using MgH2-TiH2 composite nanoparticles obtained by reactive gas-phase condensation of Mg Ti vapors under He/H-2 atmosphere. The equilibrium pressures determined by in situ measurements at low temperature were slightly above those predicted using enthalpy Delta H and entropy Delta S of bulk magnesium. A single van't Hoff fit over a range extended up to 550 K yields the thermodynamic parameters Delta H = 68.1 0.9 kJ/molH(2) and Delta S = 119 2 J/(Kmo1H2) for hydride decomposition. A desorption rate of 0.18 wt % H-2/min was measured at T = 423 K and p(H-2) approximate to 1 mbar, i.e., close to equilibrium, without using a Pd catalysts. The nanoparticles displayed a small absorption desorption pressure hysteresis even at low temperatures. We critically discuss the influence exerted by nanostructural features such as interface free energy, elastic clamping, and phase mixing at the single nanopartide level on equilibrium and kinetic properties of hydrogen sorption
The Cuban Cure: Culture and identity in global science
No full textThe thesis explores the paradigms that inform the design of the New Headquarters for the Cuban Pharmaceutical Industry
Structure and magnetic properties of Fe-Co alloy nanoparticles synthesized by pulsed-laser inert gas condensation
Full text linkFe-Co alloy nanoparticles of different compositions (Fe content of 76, 51, and 30 at%), along with pure Fe and Co
nanoparticles, were prepared by pulsed-laser inert gas condensation, consisting in laser ablation of Fe-Co alloy
targets under helium atmosphere. From the morphological point of view, the obtained nanoparticles have nearly
spherical shape, follow a lognormal size distribution and exhibit little aggregation. X-ray diffraction and highresolution
electron microscopy coupled with electron energy loss spectroscopy show that the Fe-Co nanoparticles
are single crystals with body-centered cubic structure. Furthermore, in the majority of nanoparticles the
composition is highly uniform across the whole diameter and there is little variation in composition from one
nanoparticle to another. Exposure to non-inert atmosphere leads to the formation of a core@shell metal@oxide
morphology characterized by a spinel oxide shell of 2–3 nm around the metallic alloy core. All samples display a
ferromagnetic behavior, characterized by a hysteretic magnetization loop. The saturation magnetization attains
a maximum value of 2.43 Bohr magnetons per atom for Fe content of 76 at%, in agreement with the Slater-
Pauling curve for alloys of 3d elements. Instead, the coercive field, ranging from 29 to 60 kA m−1, is much larger
than the reported values for polycrystalline bulk Fe-Co compounds and monotonically increases from pure Fe to
pure Co. These results demonstrate that pulsed-laser inert gas condensation allows to prepare high-quality
nanoalloys with tailorable magnetic properties, overcoming the limitations of thermal evaporation methods with
respect to compositional control
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
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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