1,721,010 research outputs found
Multilayer Nanoporous Graphene Membranes for Water Desalination
Get PDFWhile single-layer nanoporous graphene (NPG) has shown promise as a reverse osmosis (RO) desalination membrane, multilayer graphene membranes can be synthesized more economically than the single-layer material. In this work, we build upon the knowledge gained to date toward single-layer graphene to explore how multilayer NPG might serve as a RO membrane in water desalination using classical molecular dynamic simulations. We show that, while multilayer NPG exhibits similarly promising desalination properties to single-layer membranes, their separation performance can be designed by manipulating various configurational variables in the multilayer case. This work establishes an atomic-level understanding of the effects of additional NPG layers, layer separation, and pore alignment on desalination performance, providing useful guidelines for the design of multilayer NPG membranes.National Science Foundation (U.S.) (grant number ACI-1053575)Netherlands Organization for Scientific Research (NWO
Simultaneously Probing Gaseous Diffusion and Adsorption Properties in Porous Materials Using Molecular Dynamics Simulations
No full textAn extended two-phase thermodynamics (2PT) model, denoted
as ext-2PT,
is developed to simultaneously extract both the adsorption and diffusion
properties of adsorbates in porous materials based on molecular dynamics
(MD) simulations. The model describes the chemical potential as a
linear combination of the gas-like and solid-like contribution with
a newly introduced g fraction, aside
from the fluidicity used in the original 2PT method. The ext-2PT method
can be applied to compute the chemical potential of an adsorbed system
as a function of adsorption uptake. An interpolation scheme can then
be employed to determine the equilibrium loading at any given gas-phase
chemical potential values, thus yielding adsorption isotherms. The
diffusion coefficients of adsorbates can, meanwhile, be directly computed
from the density of state (DOS) at zero frequency by the same set
of MD simulations. The applicability of the ext-2PT model is demonstrated
by its accurate predictions on the adsorption and diffusion of methane
in two metal–organic frameworks (MOFs), IRMOF-1 and Cu-BTC,
as well as in zeolite FAU with inaccessible volume. Overall, this
ext-2PT model represents an effective and efficient approach capable
of simultaneously computing adsorption isotherms and diffusion coefficients
by a single set of MD simulations
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Computing Mixture Adsorption in Porous Materials through Flat Histogram Monte Carlo Methods
No full textMixture adsorption properties of
porous materials are
critical
to determine their potential as adsorbents in separation applications.
Toward the discovery of optimal adsorbents, in silico screening studies typically employ the grand canonical Monte Carlo
(GCMC) technique to compute adsorption properties of gas mixtures
in materials of interest at a given condition (i.e., composition,
total pressure, and temperature) or to compute their adsorption properties
for each component, followed by utilizing methods to predict mixture
adsorption isotherms. However, the former approach results in the
need for repeated calculations when different conditions such as compositions
are considered. For the latter, the predictions may involve uncertainties,
sometimes originating from the fitting quality to the pure component
isotherms, and repeated simulations may also be needed for different
temperatures. To this end, this study demonstrates the potential of
flat histogram Monte Carlo methods in addressing the abovementioned
shortfalls. Specifically, the so-called NVT + W method,
first reported by Smit and co-workers, is extended herein to determine
the macrostate probability distribution (MPD) of binary mixtures in
porous materials. The obtained MPD can be reweighted to any conditions,
yielding accurate adsorption isotherms of any desired compositions
and temperatures. This approach, denoted as 2D NVT + W,
is also compared with the widely adopted ideal adsorbed solution theory
(IAST) method, and the former is found to offer more reliable predictions.
Overall, the 2D NVT + W approach represents an efficient
and effective alternative to compute mixture adsorption isotherms
for porous materials, and the obtained MPD can be conveniently reused
by peer researchers. A user-friendly Python code is also provided
along with this article to employ this method
Computing Mixture Adsorption in Porous Materials through Flat Histogram Monte Carlo Methods
No full textMixture adsorption properties of
porous materials are
critical
to determine their potential as adsorbents in separation applications.
Toward the discovery of optimal adsorbents, in silico screening studies typically employ the grand canonical Monte Carlo
(GCMC) technique to compute adsorption properties of gas mixtures
in materials of interest at a given condition (i.e., composition,
total pressure, and temperature) or to compute their adsorption properties
for each component, followed by utilizing methods to predict mixture
adsorption isotherms. However, the former approach results in the
need for repeated calculations when different conditions such as compositions
are considered. For the latter, the predictions may involve uncertainties,
sometimes originating from the fitting quality to the pure component
isotherms, and repeated simulations may also be needed for different
temperatures. To this end, this study demonstrates the potential of
flat histogram Monte Carlo methods in addressing the abovementioned
shortfalls. Specifically, the so-called NVT + W method,
first reported by Smit and co-workers, is extended herein to determine
the macrostate probability distribution (MPD) of binary mixtures in
porous materials. The obtained MPD can be reweighted to any conditions,
yielding accurate adsorption isotherms of any desired compositions
and temperatures. This approach, denoted as 2D NVT + W,
is also compared with the widely adopted ideal adsorbed solution theory
(IAST) method, and the former is found to offer more reliable predictions.
Overall, the 2D NVT + W approach represents an efficient
and effective alternative to compute mixture adsorption isotherms
for porous materials, and the obtained MPD can be conveniently reused
by peer researchers. A user-friendly Python code is also provided
along with this article to employ this method
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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