1,720,973 research outputs found
Dilation and intercalation of gases within carbon nanostructures
No full textWe present, a study of the mutual effects of the interactions between an adsorbed gas and an adsorbing porous environment when the possible expansion of the pore is considered. In particular, we have studied the dilation, of a carbon nanotube bundle when quantum gases are absorbed within the interstitial channels and also the possibility of gas (H(2) and (4)He) intercalation between two graphene planes when the distance between them is allowed to change. We find that the dilation of the bundle increases significantly the binding energy of adsorption while intercalation between two graphene sheets is energetically unfavorable for both gases
Physics of solvation
No full textCalculations are presented of the energetics of an impurity (atom or ion) interacting with a fluid. Two possible configurations are considered: a surface state and a solvated state. For two distinct model problems which we consider (any classical fluid and superfluid helium) we find a common behaviour: the value of a dimensionless parameter lambda determines the relative stability of the surface and solvated states. For lambda greater (less) than 1.9, the sovated (surface) stare is favored, A more realistic estimate for a classical fluid is lambda similar to 1. Predictions are made of a universal solvation behaviour derived from the law of corresponding states. Results are presented for the solvated fraction as a function of cluster radius and temperature. Quantum corrections and the kinetics of solvation are discussed briefly
Anomalous low temperature specific heat of He-3 inside nanotube bundles
No full textHelium atoms and hydrogen molecules can be strongly bound inside interstitial channels within bundles of carbon nanotubes. An exploration of the low energy and low temperature properties of He-3 atoms is presented here. Recent study of the analogous He-4 system has shown that the effect of heterogeneity is to yield a density of states N(E) that is qualitatively different from the one-dimensional (1D) form of N(E) that would occur for an ideal set of identical channels. In particular, the functional form of N(E) is that of a 4D gas near the very lowest energies and a 2D gas at somewhat higher energies. Similar behavior is found here for He-3. The resulting thermodynamic behavior of this fermi system is computed, yielding an anomalous form of the heat capacity and its dependence on coverage
Bose-Einstein Condensation of Helium and Hydrogen inside Bundles of Carbon Nanotubes
No full textHelium atoms or hydrogen molecules are believed to be strongly bound within the interstitial channels (between three carbon nanotubes) within a bundle of many nanotubes. The effects on adsorption of a nonuniform distribution of tubes are evaluated. The energy of a single-particle state is the sum of a discrete transverse energy E-t (that depends on the radii of neighboring tubes) and a quasicontinuous energy E-z of relatively free motion parallel to the axis of the tubes. At low temperature, the particles occupy the lowest-energy states, the focus of this study. The transverse energy attains a global minimum value (E-t=E-min) for radii near R-min=9.95 Angstrom for H-2 and 8.48 Angstrom for He-4. The density of states N(E) near the lowest energy is found to vary linearly above this threshold value, i.e., N(E) is proportional to (E-E-min). As a result, there occurs a Bose-Einstein condensation of the molecules into the channel with the lowest transverse energy. The transition is characterized approximately as that of a four-dimensional gas, neglecting the interactions between the adsorbed particles. The phenomenon is observable, in principle, from a singular heat capacity. The existence of this transition depends on the sample having a relatively broad distribution of radii values that include some near R-min
STRUCTURE OF ALKALI DIMERS AT THE SURFACE OF LIQUID-HELIUM
No full textCalculations are presented of the equilibrium configuration (''dimple'') of a Na-2 or Li-2 molecule absorbed on the surface of liquid He-3 or liquid He-4. The computed dimer binding energies are somewhat greater than those of the monomers. The lowest energy occurs when the molecule lies flat, but the energy in the erect orientation is only similar to 1 K higher (implying relatively free rotation). The center of mass lies similar to 4 Angstrom above the liquid surface and the dimple has a depth similar to 3 Angstrom. An exceptional case is Li-2 on liquid He-3, for which the surface state is unstable relative to solvation in the bulk
Evidence concerning drying behavior of Ne near a Cs surface
No full textUsing density functional and Monte Carlo methods, we have studied the properties of Ne adsorbed on a Cs surface, focusing on the region at and near saturated vapor pressure (SVP). In the case of Ne/Rb, the experimental data of Hess, Sabatini, and Chan are consistent with the calculations based on an ab initio fluid-substrate potential, while in the Ne/Cs case there is indication that the potential is similar to9% too deep. In that case, the calculations yield partial drying behavior consistent with the experimental finding of depressed fluid density near the surface, above SVP. However, we find no evidence of a drying transition, a result consistent with the mean-field calculation of Ebner and Saam
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
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