1,721,110 research outputs found
Comment on “High-accuracy estimation of ‘slow’ molecular diffusion rates in zeolite nanopores, based on free energy calculations at an ultrahigh temperature”
No full textIn a recent article, Nagumo et al. proposed a method to obtain slow diffusivity, D, at low temperatures of guest molecules in zeolites, where the usual molecular dynamics method is unable to give accurate results. There are several computational methods already in the literature that attempt to estimate slow diffusivities. Although the method proposed by Nagumo et al. is a timely addition to the available computational techniques, certain aspects discussed in their article need to be carefully examined
Existence of a Size-Dependent Diffusivity Maximum for Uncharged Solutes in Water and Its Implications
No full textRecent studies suggest that there exists a size-dependent diffusivity maximum in binary mixtures interacting via Lennard-Jones potential when the size of one of the two components is varied (Ghorai, P. K.; Yashonath, S. J. Phys. Chem., 2005, 109, 5824). We discuss in the present paper the importance of the existence of a size-dependent maximum for an uncharged solute in liquid or amorphous solid water and its relation to the ionic conductivity maximum in water. We report molecular dynamics investigations into the size dependence of the self-diffusivity, D, of the uncharged solutes in water at low temperatures ( 30 K) with immobile as well as mobile water. We find that a maximum in self-diffusivity exists as a function of the size of solute diffusing within water at low temperatures but not at high temperatures. This is due to the relatively weak interactions between the solute and the water compared to the kinetic energy at room temperature. Previously, we have shown that a similar maximum exists for guests sorbed in zeolites and is known as the levitation effect ( LE). Thus, it appears that the existence of a size-dependent maximum is universal and extends from zeolites to simple liquids to solvents of polyatomic species. We examine the implications of this for the size-dependent maximum in ionic conductivity in polar solvents known for over a hundred years. These results support the view that the size-dependent maximum seen for ions in water has its origin in the LE ( see Ghorai, P. Kr.; Yashonath, S.; Lynden-Bell, R. M. J. Phys. Chem. 2005, 109, 8120)
Dependence of self-diffusivity on the bond length of homonuclear a diatomic molecule in Na Y zeolite
No full textA molecular dynamics and molecular level explanation of pressure dependence of ionic conductivity of potassium chloride in water
No full textA comparative mlecular dynalics study of diffusion of n-decane and 3-methyl pentane in Y zeolite
No full textA comparative molecular dynamics study of diffusion of n-decane and 3-methyl pentane in Y zeolite
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Diffusion Anomaly as a Function of Molecular Length of Linear Molecules: Levitation Effect
No full textPrevious work on monatomic spherical sorbates has shown the existence of an anomalous peak in self-diffusivity (D) when plotted as a function of size of the diffusant. Molecular dynamics studies on linear molecules of different lengths l in zeolite NaY at 140 and 200 K are reported. It is seen that there is a peak in D as a function of l, suggesting that the levitation effect exists for linear molecules, the simplest member of polyatomics. This is confirmed by the lowering of the activation energy for the molecule whose length l exhibits highest D. Related quantities of interest such as the guest-host interaction energy and preexponential factor are discussed
Variations on the Author
Get PDF“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
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