1,721,000 research outputs found
Promising isotope effect in Pd77Ag23 for hydrogen separation
Full text linkPd–Ag alloys are largely used as hydrogen separation membranes and, as a consequence, the Pd–Ag–H system has been intensively studied. On the contrary, fewer information is available for the Pd–Ag–D system; thus, the aim of this work is to improve the knowledge of the isotope effect on the commercial Pd77 Ag23 alloy, especially for temperature above 200◦ C. In particular, deuterium absorption measurements are carried out in the Pd77 Ag23 alloy in the temperature range between 79 and 400◦ C and in the pressure range between 10−2 and 16 bar. In this exploited pressure (p) and composition (c) range, above 300◦ C the pc isotherms display the typical shape of materials where only a solid solution of deuterium is present while at lower temperatures these curves seem to be better described by the coexistence of a solid solution and a deuteride in a large composition range. The obtained results are compared and discussed with the ones previously measured with the lightest hydrogen isotope. Such a comparison shows that the Pd77 Ag23 alloy exhibits a clear inverse isotope effect, as the equilibrium pressure of the Pd–Ag–D system is higher than in Pd–Ag–H by a factor of ≈2 and the solubility of deuterium is about one half of that of hydrogen. In addition, the absorption measurements were used to assess the deuteration enthalpy that below 300◦ C is ∆Hdeut = 31.9 ± 0.3 kJ/mol, while for temperatures higher than 300◦ C, ∆Hdeut increases to 43 ± 1 kJ/mol. Additionally, in this case a comparison with the lighter isotope is given and both deuteration enthalpy values result lower than those reported for hydrogenation. The results described in this paper are of practical interest for applications operating above 200◦ C, such as membranes or packing column, in which Pd77 Ag23 has to interact with a gas stream containing both hydrogen isotopes
Influence of the alkyl chain length on the low temperature phase transitions of imidazolium based ionic liquids
No full textThe effects induced by alkyl chain length on the thermal phase behavior for a series of imidazolium based ionic liquids (ILs) containing the anion bis(trifluoromethanesulfonyl)imide (TFSI) were investigated by infrared spectroscopy combined with density functional theory (DFT) calculations. In agreement with previous results on pyrrolidinium and ammonium based ionic liquids sharing the TFSI anion, our study shows that with increasing the length of the alky chain only the less stable cis-TFSI is retained in the solid state, while for shorter chain the trans-TFSI predominates in the crystalline phase. Also, we examined the remarkable effect on the packing efficiency due to the addition of 2-hydroxyethyl group on the imidazolium cation ring, reporting that the absence of crystallization is observed in correspondence with the presence of both the conformers of TFSI in the whole temperature range (150–325 K). Moreover, a detailed study of 1-ethyl-2,3-dimethylimidazolium-TFSI (EDMIM-TFSI) reveals the existence of cation rotational isomerism. In the liquid phase both planar (P) and non-planar (Np) conformers are present in the equilibrium, while a conformational change for the CNCC dihedral angle of the EDMIM cation leads to stabilize the formation of the more stable non-planar geometry in the crystalline phase
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
Hopping and clustering of oxygen vacancies in BaTiO3− and the influence of the off-centred Ti atoms
No full textThe diffusion and aggregation of oxygen vacancies (VO) in perovskites are still poorly understood, even though they are involved in a wide range of applications and phenomena, from solid-state electrolytes for fuel cells to ferroelectric fatigue. In strontium titanate it has been possible, by measuring the complex elastic modulus, to identify peaks in the elastic energy loss versus temperature due to hopping of isolated and paired VO and evaluate all the relevant kinetic and thermodynamic parameters. We present similar experiments in barium titanate, where the ferroelectric transition at TC = 400 K partially hides the anelastic relaxation processes due to VO. The introduction of VO, however, depresses TC, and it has been possible to lower it enough to reveal all the relaxation processes due to free and clustered VO. The resulting anelastic spectra are similar to those of SrTiO3−δ but there are also important differences. In BaTiO3−δ the anisotropy of the elastic dipole of the isolated VO is about three times larger, the anelastic relaxation peaks markedly shift to lower temperature with doping, the activation energy for the diffusion of the isolated VO is 0.72 eV, larger than 0.60 eV in SrTiO3, while that for the pair reorientation is smaller, 0.86 eV compared to 0.97 eV. All these observations are explained by taking into account that, unlike in SrTiO3, Ti is dynamically disordered over eight off-centre positions. A strong indication in this sense comes from the temperature dependence of Young’s modulus, with anharmonic stiffening perfectly linear in temperature down to 200 K in SrTiO3, and with anomalous softening already below 750 K in BaTiO3
H tunneling and trapping in Y by anelastic relaxation measurements
No full textWe present the first evidence by acoustic measurements of H tunneling and trapping by 0 atoms in a
rare-earth-hydride system. The YO00027HOO]6 alloy presents three new elastic-energy-loss peaks most
likely due to H trapped by 0 between 1.4 and 330 K. The peak at the lowest temperature is due to tunneling
of the trapped H; its relaxation rate strongly depends on temperature, indicating a dominant contribution
of multiphonon processes already at a few kelvin. The other two peaks, with activation energies
of 0.14 and 0.22 eV, can be attributed to jumps of H in the distorted environment of the 0 atom
Molecular assembling in mixtures of hydrophilic 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid and water
Full text linkThe infrared absorbance spectrum of the ionic liquid 1-butyl-1-methylpyrrolidinium dicyanamide, mixed with water at two different concentrations, was measured between 160 and 300 K in the mid infrared range. Both mixtures do not crystallize on cooling; however, remarkably, the one with an ionic liquid (IL):water composition of 1:3 displays a cold crystallization process on heating in a restricted temperature range between 240 and 250 K. A portion of the water participates to the cold crystallization. On the contrary, with an IL:water composition of 1:6.6 no crystallization takes place. Upon water addition the vibration frequencies of the anion and of some lines of the cation are blue shifted, while the absorption lines of water are red shifted. These facts are interpreted as the evidence of the occurrence of the hydrogen bonding of water, as the hydrogen bonding acceptor with respect to the anion (anion···O-H bonds develop) and as hydrogen donor for the cation (C-H···O bonds can form). Microscopic inhomogeneities in the samples and their evolution with temperature are discussed
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